NAS-NS-3060.txt

 

NAS-NS-3060

NUCLEAR SCIENCE SERIES

National Academy of Sciences-National Research Council

Published by
Technical Information Center, Office of Information Services
UNITED STATES ATOMIC ENERGY COMMISSION
COMMITTEE ON NUCLEAR SCIENCE

D. A. Bromiey, Chairman, Yals University

C. K. Reed, Executive Secretary, National Acacemy of Sciences
Victor P. Bend, Brookhaven National Laboratory

Gregory R. Choppin, Floride State University

Herman Feshbach, Mamachusetts Institute of Technology
Russell L. Heath, Aesrojet Nuciear Co., inc.

Bernd Kahn, National Environimental Ressarch Center, EPA
Jossph Wenaser, Brookhsven National Lashoritory

Sheldon Woltf, University of California Medical Center

Members-at-Large

John R, Huirengs, Univentity of Rochaster
G. C. Phillips, Rice University
Alexander Zucker, Osk Ridgs Nationa! Laboratory

Liaison Members

John McElhinney, Navsl Ressarch Laborstory
William S, Rodney, Nationsl Science Foundation
George Rogoms, U. S. Atomic Energy Comm:siion

Subcommittee on Radiochemistry

Gragory R. Choppin, Chairman, Flovida State University
Raymond Davis, Jr., Brockhaven National Lalworatory
Glon E. Gordon, University of Maryland

Rolfe Herber, Rutgers University

John A. Miskel, Lawrence Radiation Laboratcry

G. D. O’'Keiley, Osic Ridge National Laborstory

Richerd W, Perking, Pacitic Northwast Laborstory
Andraw F. Stehney, Argonne Nations! Laboritory

Kurt Wolfsherg, Los Alamos Scientific Laboritory
NAS-NS-3060
AEC Dstribution Category UC -4

pr—rrmsmemees st N Q) T 4 € i -
This repoel was prepared a8 an sccount of work ’
sponsored by the United States Government. Nether ,’
the United States nor tha United 3tales Atomic Energy |
Commission. nor any of their employesss, not sny of |
theif con*ractors, 3UBCORTIACION., of lhell ¢mMployses, f
makes a y wartanty, express or implied, or assumes sny |
legal liab 'ty v responsibiity for the accuracy. com- [
platenass o usfulness of any iaformation, sppafsius, ;
product of p.ocess duclowd. o reprewnts that its we |
would not infr.ngs privately owned rights. |

e i —emb it s, = il

 

 

— e Aottt =t e

 

 

RADIOCHEMISTRY OF NEPTUNIUM
by

G. A. Burney
and
R. M. Harbour

Savannah River Laboratcry
E. I. du Pont de Nemours § Co.
Aiken, South Carolina 9801

Prepared for Subcommittee on Radiochemistry
National Academy of Sciences - National Research Council

Issuance Date: December 1874

Published by
Technical Information Center, Office of information Services
UNITED STATES ATOMIC ENERGY COMMISSION
This paper was prepared in connection with work under Contract
No. AT(07-2)-1 with the U. S. Atomic Energy Commission. By
acceptance of this paper, the publisherr and/or recipient
acknowledges the U. S. Government's rijht to retain a non-
exclusive, royalty-free license in and to any copyright cover-
ing this paper, along with the right to reproduce and to
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Prce $300. whah i the muvemum order pue for edhee one
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wews Addionst indrrdiudl copeey vl be 90id n ncrements of
thuee for §3 00 Avaslabrle trom

Natwonat Technxsl Informption Sevwice
U S Depertmeru of Comenpece
Sot ingldd. Vagerny 22181

Posted on she Unaied Tostes of A e

 

VEALC Yeshmugsy! bnigemmgtean Contew . Onh W uligs, Tommer s
"
Foreword

The Subcommitiee on Radiochemistry 1s one of a number of jubcommutiees working under the
Committee on Nuclear Scence within the National Academy of Sciences-——Nanional Research
Council. its members represent government, industrial, and university laboratornies in the areas
of nuciear chemistry and analytical chemistiy.

The Subcommittee has concerned itself with those area: of nuclear science which involve
the chemust, such as the collection and distnbution o radiochemical procedures, the
radiwochemical purity of reagents, the piace o! radiochenistry in college and university
programs, and radiochemistry in environmental science.

This series of monographs has grown out of the need for compilations of radiochemical
mnformation, procedures, and techniques. The Subcommittee has endeavored to present a series
that will be of maximum use to the working scientist. Each monograph presents pertinent
information required for radiochemical work with an indivafual element or with a specialized
technue,

Experts in the particular radiochemical technique have written the monographs. The
Atomic Energy Commission has sponsored the printing of the series.

The Subcommittee is confident these publications will te useful not only to radiochemists
but aiso to research workers in other fields such as physics, b-ocliemistry, or medicine who wish
10 use radiochemical techniques to soive specific problems.

Gregory R, Choppin, Chairman
Subcommitiee on Radiochemistry
II1.

II1.

IV.

VI.

VII.

VIII.

CONTENTS

General Review of the Inorganic and Analytical
Chemistry of Neptunium . . . . . . .

General Review of the Radiochemistry of
Neptunium . . . . . . . . . . . . . ..

Discovery and Occurrence of Neptunium
Isotopes and Nuclear Properties of Neptunium .

Chemistry of Neptunium . . . . . . .

A. Metallic Neptunium .

A.1 Preparation . e e e s e
A.2 Physical Properties . . . . . . .
A.3 Chemical Properties . . . .
Alloys and Intermetallic Colpoxnds .
Compounds of Neptunium . . ..
Neptunium Ions in Solution .

D.1 Oxidation States .
Oxidation-Reduction Reactlons .
Disproportionatior of Neptunium .
Radiolysis of Nepiunium S>lutions .
Hydrolysis of Neptunium . ., .
Complex Ion Formation .

o0 w

FPUUU
LN

Preparation of Neptunium Samples for Analys:s
A. Neptunium Metal and Alloys . .
B. Neptunium Compounds . . . . .

C. Biological and Environmental Salples v e s

Separation Methods .

A. Coprecipitation and PrecipitatLon. - e v e
B. Solvent Extraction . . . . . . . c e e
C. Ion Exchange . . . . . . . ..
D. Chromatography . . . . . . . . .
E. Other Methods .

Analytical Methods , . .
A. Source Preparation and Radione.ric Hethods .
B. Spectrophotometry . . . . e e
C. Controlled Potential Coulo-etrr e e
D. Polarography . .
E. Titration

Page

12
12
12
12
14
14
16
20

2
d-

24
24
29
31
33

39
39
39
40

41
41
54

104
107

109
109
114
119

. 121
- 123
IX.

CONTENTS (CONTINUED)

F. Emission Spectrometry .
G. Gravimetric Methods .
H. Spot Tests
I. Mass Spectrouetry . .
J. X-Ray Fluworescence Spectronetry .
K. Neutron Activation . . .
L. Other Methods .
Radiocactive Safety Considerations . . . . . . . .
Collection of Procedures
A. Introduction . .
B. Listing of Contents . . . .
Procedure 1. Separation of Np by TTA
Extraction .
Procedure 2. Separation of Np by TTA
Extraction .
Procedure 3. Determination of “’Np in
Samples Containing U, Pu, and
Fission Products ..
Procedure 4. Determination of Np . . .
Procedure 5. Determination of Small Aununts
of Np in Fu Metal .

Procedure 6. Determination of Np in Sauples
Containing Fission Products, U,
and Other Actinides .
Procedure 7. Detzmination of Np in Sanples
of U and Fission Products .
Procedure 8. Extraction Chronmtographic
Separation of ***Np from
Fission and Activation Pro-
ducts in the Determination of
Micro and Sub-microgram
Quantities of U . boe e
Procedure 9. Separation of U, Np, Pu, and
Am by Reversed Phase Partition
Chromatogr:aphy .o
Procedure 10. An Analytical Method for
Using Anion Exchange
Procedure 1i. Separation of U, Np, and Pu
Using Anion Exchange
Procedure 12. Separation of Ir, Np, and Nb
Using Anion Exchange

2 ”Np

132
134
134
134
138
141
145
150

185

158

161

163

165
167
169

171
References .

CONTENTS (CONTINUED)

Procedure
Procedure

Procedure

Procedure

Procedure

Procedure
Procedure

Procedure
Procedure
Procedure

Procedure

Procedure

Procedure

13.
14.

15.

16.

17.

18.
19.

20.
21,
22.

23.

24,

25.

Separation ¢. Np and Pu

by Anion ¥ .change . .
Separation of Np and Pu

by Cation Exchange . .
Separation and Radiochcsinal
Determination of U and
Transuranium Elements Using
Barium Sulfate

The Low-Level Radio*heulcml
Determination of 2*’Np in
Environmental Sampl:es .
Radiochemical Procedure for
the Separation of Trace
Amounts of 2*’Np from Reactor
Effluent Water .
Determination of Np in Urine
Determination of 7
Ray Spectrometry . . . . .
Spectrophotometric Uetermx-
nation of Np . . . .
Microvolumetric Commlexonetrxc
Method for Np with EDTA .
Photometric Determination of
Np as the Peroxide Complex
Separation of Np for
Spectrographic Analysis of
Impurities . . . .
Photometric Determlnatxon of
Np as the Xylenol Orange
Complex . .
Analysis for Np by Cantrolled
Potential Coulometry

-4 -

"Np by Gamma

173

175

176

179

184
186

189
193
197

199

209
RADIOCHEMI!STRY OF HEPTUNIUM*

by

G. A. Burney
and
R. M. Harbour

Savannah River Laboratory
E. I. du Pont de Nemours § Co.
Aiken, South Carolina 29801

I. GENERAL REVIEW OF THE INORGANIC FND ANALYTICAL CHEMISTRY OF

-

NEPTUNIUM

J. J. Katz and G. T. Seaborg, The Chemistry of the
Actinide Elements, Chap. V1, p 204-236, John Wiley and
Sons, Inc., New York (1957).

C. F. Metz and G. R. Waterbusy, '"The Transuranium
Actinide Elements," in I. M. Kolthoff and P. J. Elving
(Ed.), Treatise on Analytical Chemistry of the Elements,
Volume 3, Uranium and the Actinides, p 194-397, John
Wiley and Sons, Inc., New York (1962).

"Neptunium," in P, Pascal (Ec¢.), Nowveau Traiile de
Chimie Minerale, Vol. XV, Trcnsuraniens, p 237-324,
Masson et Cie, Paris (1962).

"tleptunium,' in P. Pascal (Ec¢.), Nouveau Traite de
Chimie Minerale, Vol. XV, Trcnsuraniens (Supplement),
p 1-94, Masson et Cie, Paris (1962).

B. B. Cunningham and J. C. Hindman, "The Chemistry of
Neptunium,' in G. T. Seaborg and J. J. Katz (Ed.), The
Actinide Elements, p 456-483, Vol. 14A, Chap. 12, McGraw-
Hill Book Co., New York (1954).

 

*The 1nformation contained in this article was developed during
the course of work under Contract AT(07-2)-1 with the U, S.
Atomic Energy Commission.
6.

10.

11.

1z,

13.

14,

15.

J. C. Hindman, L. B. Magnusson, and T. J. LaChapelle,
"Chemistry of Neptunium. The Oxidation States of
Nuptunium in Aqueous Solution," in C. T. Seaborg, J. J.
Katz, and W. M. Manning (Ed.), The Iransuranium Elements,
p 1032-1038, Vol. 14B, McGraw-Hill Fook Co., New York
(1949).

J. C. Hindman, L. B. Magnusson, and T. J. LaChapelle,
"Chemistry of Neptunium. Absorption Spectrum Studies

of Aqueous Ions of Neptunium," in G. T. Seaborg, J. J.
Katz, and W. M. Manning (Ed.), The 'ransuranium Elements,
p 1039-1049, McGraw-Hill Book Co., New York (1949).

L. B. Magnusson, J. C. Hindman, and T. J. LaChapelle,
“"Chemistry of Neptunium. First Preparation and Solubili-
ties of Some Neptunium Compounds in Aqueous Solutions,'
in G. T. Seaborg, J. J. Katz, and W. M. Manning (Ed.),
The Transuranium Elements, p 1097-1110, McGraw-Hill Book
Co., New York (1949).

S. Fried and N. R. Davidson, '"The Basic Dry Chemistry of
Neptunium,™ in G. T. Seaborg, J. J. Katz, and W. M.
Manning (Ed.), The Transuranium Elenents, p 1072-1096,
McGraw-Hill Book Co., New York (19493).

C. Keller, The Chemiatry of the Transuranium Elemaenta,
p 253-332, Verlag Chemie, Germany (1971).

G. A. Burney, E. K. Dukes, and H. J. Groh, "Analytical
Chemistry of Neptunium,"™ in D. C. Stewart and H. A. Elion
(Ed.), Progrees in Nuclear Energy, Series IX, Analytical
Chemiatry, Vol. 6, p 181-211, Pergsmon Press, New York
(1966) .

J. Korkisch, Moderm Methods for the Separation of Rarer
Metal Ions, p 28-196, Pergamon Pre:«s, New York (1969).

J. Ulstrup, '"Methods of Separating the Actinide Elements,”™
At. Energy Rev. 4(4), 35 (1966).

A. J. Moses, The Analytical Chemis:ry of the Actinide
Elements, MacMillan Co., New York [1963).

A. D. Gel'man, A. G. Moskvin, L. M. Zaitssv, and M, P.
Mefod'eva, "Complex Compounds of Transuranides,” Israel
Prozram for Scientific Translations (1967), translated
by J. Schmorak.
16. P. N. Palei, "Analytical Chemistry of the Actinides,"
translated by S. Botcharsky, AERE-LIB/TRANS-787., [See
also J. Anal. Chem. USSR 12, 663 (1957)].

17. Gmeling Handbuch der Anorgar iachen Chemie, Volume g,
Transurane, Part C (1972).

18. Gmelins Handbuch der Anorgarischen Chemie, Volume 8,
Trangsurane, Parts A, B, and D (1973).

19. V. A. Mikhailov and Uy. P. Movikov, '""Advances in the
Analytical Chemistry of Neptunium (A Review)," J. Anal.
Chem. USSR 25, 1538 (1970).

20. V. A. Mikhailov, Analyticai Chemisiru of Neptunium,
John Wiley & Sons, New York (1973).

21. B. B. Cunningham, "Chemistry of the Actiaide Elements,"
in Amnual Rev. Nuel. Sci. 14, 323 (1964),

22. K. ¥W. Bagnell, The Actinide Elements, Elsevier Publishing
Co., London (1972).

II. GENERAL REVIEW OF THE RADIOCHEMISTRY OF NEPTUNIUM

E. K. Hyde, "Radiochemical Separations of the Actinide
Elements,” in G. T. Seaborg and J. J. Katz (Ed.), The Actinide
Elaments, Chapter 15, National Nuclear Energy Series, Div. IV,
Vol. 14A, McGraw-Hill Book Co., MNew York (1954).

E. K. Hyde, "Radiochemical Separstions Methods for the Actinide
Elements," Intermational Confererece on the Peaceful Uses of
Atomic Emergy, 2nd Gemeva, 7, 281 (1955).

M. Page "Separation and Purification of Neptunium," in
Transuraniens, p 249-272, Masson et Cie, Paris (1962),
ITI. DISCOVERY AND OCCURRENCE OF NEPTUNIUM
Neptunium was discovered in 1940 by McMillan and Abelson.!
They bombarded a thin uranium foil with low-energy neutrons
and showed that the 2.3-day activity tha: was formed was an

isotope of element 93 produced by the nu:lear r2actions:
2320 (n,y) 233U x> itNp -
It was shown in 1941 that the decay product of 23°Np was 2%9pu.2

239Np is produced in large quantities as the intermediate
in the nuclear reactor production of 23%-y, but because of its

short half-life it is used only as a tra:er.

Wahl and Seaborg® discovered the long-lived isotope 2*7Np

in 1942. It was produced by the nuclear reactions:

30 (n2n) P30 geg 33N

The first weighable quantity of 2?7Np (v45 ug of NpOz) was

isolated by Magnusson and .aChapelle in 1944." These workers

were the first to measure the specific a:tivity of 2?’Np.

As a result of these reactions, Np is produced in
relatively large quantities in nuclear rzactors fueled with
natural U. When fuels entiched in 23%0 and 235U are used in

nuclear reactors, the following reactions are increasingly

important.

233U (n,yv) 2330 (n,y) v T‘g';"f 23inNp
Since about 1957, the U. S. Atomic Energy Commission has
recovered and purified bhyproduct Np in its production facilities.
237Np is used as target for the production of 22%pu, an isotope
in demand for fueling radioisotopic power sources. ’

233Np (n,v) 23%Np -2-_-%-&0 238,

The half-life of 2?’Np is very short compared to the age
of the earth. Therefore, it is found only in trace quantities
in U minerals where it is formed cont:nuouslv by neutron
reactions described previously.® It vas found that the abundance
of 23”Np in a sample of Katanga pitchtlende was 2.16 x 10”'2 atoms
per atom of 2%, while that of 2%Pu was 3.10 x 10°'? atoms per

atom of 23%.7

IV. [1SOTOPES AND NUCLEAR PROPERTIES OF NEPTUNIUM
The known isotopes and celected ruclear properties of
Np are listed in Table 1. The radioaralytical chemist works
mostly with long-lived %?"Np and short-lived 2?°Np and 23°Np.
The decay schemes of these most important isotopes of Np are

presented in Figure 1.

Thermal neutron cross sections and resonance integrals

for Np isotopes are shown in Table 2.
Mass

Nember Half-1ife

n"
7]

25
133

238"
257

240"

240
11

a sf e
a w
EC =

4.6 nin

50 min

15 min
35 min
4.40 day

386.1 day

22 hr

>5000 yr
2.14 x 10° yr

2.12 day

2,35 day

7.5 min

67 min
16 mla

ISOTOPES OF MEPTURIUN®:®

Specific
A=tiviey

1.031 xapt*
4.5 x 10"

3.945 1 10"

3.514 2 10"

1.3 x 10'*
$.117 x 10'*
2.815 x 10"

5.114 x 10"

3.397 z 10"

1.564 a2 10"

5.744 x 10"

5.160 2 10!

2.595 = 10"
1.0a2 x 10'*

spoatansous fissiom
alpha decay
slectroa caspture decay
f~ = ssgatrom decay

TABLE 1

ode of®

Mecyy

sf
a(>0.5)
BC(<0.5)
BC{0.97)
a(0.03)
EC(n0.99)

a("0.01)
EC

ec
a(? 2 107%)
EC
a(<10” ")
£’
a(~10" 1)

EC(0.48)
A°(0.52)

a

1

sf (5 n 10°'Y)

L
af(<® x 10°'")

- 10 -

Lecay

Enmrgy (We¥V)

. - 6.66

a " 6.0

a = 6.28

E, = 5.53

E’., = 0.8

. " 5.095(4%)
5.015(831)
4.925(12%)
4.064(1Y)

g- " 0-518(601)
0.36(408)

- 4.786(42%)
4.760(01)
4. 764 (SV)
4.661(5.5%)
4.634(6%)

g- " 1.25(4a5%)
0.26(54\)

EY = 1.027(231)
0.945(261)

a- " 0.713(™)
0.437(aab)
0.393(13%)
0.332(204)

E’V « 0.278[130)
0.220012%)
0.106(214)

g - 2.18(52%)
1.60(31%)

g~ - 0.89(100%)

El' = 1.3

Methods of
Preperation

:".i - ll".
I'Iu(’.sn)

1% (p,4n)

13%)(a,50)
138%(d,9m)
13%y(d, 5n)
V%4, )
3% (d, 4n)
1¥%(4, 3n)
"’I.l[d,ln)

M%y(4, )

'“U{d,n)
'.’“[I,h)
"'U[d,‘n)
"% in,m)
"y(e, v’
T3y (s--decay)

I an(x-decay)
21 T"P [. ..',)

13 .“[d . h)
"’U(G.'P)

" %(n,T)
1% (B-decay)

218 (d-fl)
" pa(a-decay)
’..U(B-fl.flyl

'I.uru'p]
'..u(ulpl
237y, 52

 

   
   
   
 
 
  
  

(0.02°4) (52

/ .
11/

(0.5%) 459
(60%) 4636 .
N6"%) 4592 L7786 (L2%)

 

 

 

 

 

 

 

(22%) 4708 4803 (15%)
Sein  Emergy .
ond [heVi 4815 (12%)
parity 4o 4865 (1]
28
52} 3G ———
Q2e) 2
192
166
%2
o2 108
e |
/D) 86 et
§2- 69—
we- 57
w2 8

 

 

 

 

Energy
(navi

556 2
=S
- 8083
- L9122
T
o~ 18

noy
85
t817s
”»sn

7y
765

 

2%

Pu

Enargy

Spin
and
fardy
3o

rg

)fia

Spin ond
patity

7 1B
L7 ]
WH-
$f2l-:
mia

N
Uk
W2«

Vo
Vi

Figure 1. Decay Schemes of the Most Imgartant Neptunium

Isotopes, 2*’Np, 23®Np, and 2?3Np.B*!°
TABLE 2
CRUSS SECTIONS AND RESONANCE INTEGRALSY FOR NEPTUNIN. 1SOTOPES®

 

 

 

Neuwtron Capture Fis:ion
Mass Number c(n,n lp.n I¢ i E_{ 2&9_,_2__!3}_
234 900
235 1a8d
236 2,800
237 185 600 0.02 0 0.0013°
1,424
238 1,600 600 2,070 800
23¢ 35¢ (to **"™wp) s

25¢ (ro 2"'Np)

 

Cross-sections expressed in barms, 10~ “cal.

J. #. Landrum, R. J. Nagle, M. Lininer, UCRL-S1263 (1972).
For neutrons with the fission spectrum.

For 3 MeV neutrons.

For "reactor neutrons',

2

Y ke TR

V. CHEMISTRY OF NEPTUNIUM
A. METALLIC NEPTUNIUM
A.1 Preparation
Np metal was first prepared by Fried and Davidson in 1948
by the reduction of S0 ug of NpF, with Ba vapor at 1200°C.'!
A similar method was used by Westrum and Eyring.'? Reduction
of NpF. by excess Ca metal with iodine as a booster'? !? was

used to produce multigram quantities of Np metal,

A.2 Physical Properties

Pure Np is a silvery ductile metal with a melting point of
637°C. The metal undergoes three allotropic modifications below
the melting point. The physical properties ure summarized in

Table 3.

- 312 -
L.

TABLE 3
PHYSICAL PROPERTIES OF NEPTUNIUM METAL3®+17:1¢

Appearance: Silvery white (slowly c¢cated with oxide in dry
air at room temperature)

Melting Point: 637°C
Boiling Point: 4175°C (extrapolated frcm vapor PIgssure

measurements of liquid Np' ')
Heat of Vaporization: AH 1800°K = 94.3 kcal/(g-atom)
Properties of Various
Allotropic Modifications: & 8 v
Transition temperature
to next higher phase, °C 280 577 637
Density, g/ca’ (at T°C) 20.48  19.40 18.04
Crystal Structure Orthor- Totragonal Cubic

hoabic

Stephens?'! determined the pressure-temperature relationship

for Np. The specific heat (Cp) of Np is high. The Dulong and

Petit value of 3R is reached at 140°K and 7.093 cal/(mol-°"K) st

27°C.?' The high specific heat can be entircly accounted for by

the very high electronic contributions. No magnetic ordering

in a-Xp occurs down to 1.7°K.°?

- 18 -
A.3 Chemical Properties

Np is a reactive metal. The potential for the couple
Np » Np” + 3¢ is 1.83 volts. Metallic Np is slowly covered
with a thin oxide layer when exposed to dry air at sbout 20°C,
and rapid oxidation to NpO; occurs at higher temperatures
especially in moist air. Hydrogen, halogens, phosphorus, and
sulfur react with Np metzl at elevated tempuratures. Hydrogen

rescts to form the hydride at relatively low temperatures.

Np forms intermetallic compounds of intermediate solid

solutions with U, Pu, Be, Al, B, Cd, Ir, Pd, and Rh.

Np dissolves readily in HCl at room temperature and H250,
at elevated temperature. The behavior of Np toward various

solutions is given in Table 4.

8. ALLOYS AND INTERMETALLIC COMPOUNDS
Complete phase diagrams are reported for Np-Pu and Np-U.?3728

Complete miscibility has been reported betveen y-Np and y-U and
between y-Np and L-Pu. Np is a unique elenent because of its

extremely high solubility in both a-Pu and 8-Pu,

The intermetallic compounds of Np with Al and Be (NpAl,,
NpAl:, NpAl,, and NpBe;;) are prepared directly by reducing NpFi
with an excess of metallic Al or Be. The borides (NpB;, NpBw,
NpBs, and NpB,;) and the intermetallic corpounds NpCdg and

NpCd:2 are obtained directly from the elcments.2?”2%  Several

- 14 -
TABLE 4

BEHAVIOR OF Np METAL IN VARIOU:; SOLUTIONS'?®

 

 

Observations
Solution Concentration (M) Initial After 4 days
H,0 Very slowly atta:ked
He1? 1.5 Immediate vigoroas Completely dissolved
reaction
6 131 "
12 1y tE
HNO 4 2 No visible reaction Some turbidity,
hydrated oxide
8 " e
15.7 " No resction-
clear solvent
H250.,% 2.25 Slow reaction No reaction-
clegr solvent
9 1" "
18 No noticesble resction v
(H,000H% 2 Slight initial reaction-  Soms turbidity
ceased hydrated oxide
a " ”
16 No visible reaction No resction-
clear solution
HC10, Conc. Rapid dissoluticn "
vhen hested
HyPOs Conc. Rapid dissoluticn
when heated
HSO yNH Rapid dissoluticm "
when heatad
Conc. HNGy - Dissolution whey refluxod "
trace HF

2. At ambient temperature,

- 18 -
compounds with noble metals, such as NpPt; and NpPts, have
been prepared by hydrogen reduction of NpO: at 1300°C in the

0

presence of platinum.?® Alsc, Erdmann’! used the same method

10 prepare several other compcunds, Nplr,, NpPdi, and NpRhj.

(.. COMPOUNDS OF NEPTUNIUM

Compounds of Np for the III, IV, V, VI, and VII oxidation
states have been prepared. The solubilities anc compositions
of some of the compounds have not been verified because they
were initially determined with small amounts of Np shortly
after discovery and therefore may be semi-quant:.tative. Where
studies have been made with larger amounts of neptunium, i.e.,

oxalates and peroxides, more quantitive data is available.

Numercus Np compounds, such as nitrates, chlorides, and
possibly thiocyanates, are readily soluble in s>lvating organic
solvernits such as diethyl ether, hexone, TBP, ani other acid-

containing solvents saturated with water.

Investigation of compounds containing trivalent neptuniuwas
has been limited because of the instability of Np(Ill) in
aqueous solution in the presence of atmospheric oxygen. Np(III)
is produced under hydmgen {on a platinum catalyst), by electro-
chemical reduction and with rongalite, NaHSO:.(H;0‘2H,0., Mefod’eva
¢t al.’? have prepared several Np(ll1l) compouncis from solution with

protection from oxygen. All the reagent solutions and water were

- 16 -
purged with pure argon. The precipitation and subsequent
operations (centrifugation and washing) were conducted with a
layer of benzene over the solution. The solids were washed with
acetone or ether and dried in a strear of argon. Np(III) oxalate
was prepared, but it was appreciably oxidized in a few hours.

The solid was brown and was in the fo:rm of tetragonal prisms.
Np(III) phenylarsonate is rose-lilac colored with the composition
Np2 (CeHsAsO3) 3°nH20 when well dried; the compound is stable for
a long period at room temperature. Np(III) salicylate and grayish-
lilac Np(IIl} fluoride were also precipitated under controlled
conditions. Two complex double sulfates of Np(III), KsNp(S04)s
and NaNp(SO.)2°-nH20, were precipitated. In the dry form, these
salts were stable to oxidation during prolonged storage even at

increased temperature,

Only one solid compound of Np(VII), Co(MH3)¢NpOs-3H20, has

been reported.’?

Compounds of Np(IV), (V), and (VI) are shown in Tables 5
and 6. Table 5 includes compounds produced in aqueous
solution, and Table 6 includes compounis produced by other

motliods.

-17 -
TABLE 5

NEPTUNIUM COMPOUNDS PRECIPITATED FROM AQUEDU!: SOLUTION

 

Composition
Compound Color __of Solution
NpO; (OH) x~aq Black NaOH - NaNO,
pHS5 9
Np(IV) hydroxide Srown green 1M NaDH -~
IM NaNO,
Np(V) hydroxide Green IM NaQH -
dilute
ammonia
{NH4 ) 2NpP209 Brown 1M N4, OH -
0.5M (NH,);50.
Np(IV) peroxide Purple 2.5M HND, -
6.5M Hy0,
NpF,+XH,0 Grayish 0.3 HCY -
Iilac 0.3M HF
(srgon atm)
NpF .+ *XH;0 Green 1M HNO, -
IM HF
NHNpF -+ Green IM HF -
0.01M NH.F
KNpaFe Gresn dM HF - 1N KF
LaaNpF 3 XH0
Np(IV) iodate Tan Srown IM HC1 -
0.1M K10,
Np(111) oxalate Brown
Npl(C204);°6H0 Grean 0.14 H;C;0., -
M IND,
NpO:C;0.H*7H,0 Green
NpO2C 04 3,0 Grey green
L"“;Cfl. Tan H,D
KgNpO2 (C0y) Greenish blue H,0 -
0.M K00,
CaNp0; (CO») )y Greenish bluse H,0
ENpO, (CaH 03 )« Green 0.°M 4,380, -
0.0™ NaNO, .
M NaC;1,0;
Np(HPO, ) 2=XI;0 Green IM HC1 - 0.5
HyPO,
KaNp (50. 1, Bluish lilac 0.3 HC1 - sat
K250 - 0.2V N;50.
NaXp(S0.) ;*nmi20 Blue 0.3M HC]1 - st
K50, - 0.2 H,;S0,
Np(CgligAs0,y); Green 0.1M CHsAsOH; -
0.5M HND,
NpO2CeHy AsO 0.D8M CyllsAnDH; -
0.5M HNOD,
[ Q) 2 (CoHla@fy) N2t 6 to BM \ND,
NpiND,y ),

So.ubility(mg Np/1)

Dissolves in elithar
acid or base

Stod

17
e
120
28

1:

13
11

13
100

Refsronce

33

2

37

n
»

32
40

41
42
43

32

32
TABLE 6
OTHER NEPTUNIUM COMPQUNDS

 

Compound Color Lattice Symmetry Reference
Npil; Cubic 47
NpH, Hexagonal 47
NpO, Green Cubic 48,49
Np20s Dark brown Monoclinic 49a
Np10Os Dark brown Orthorhombic 50,51
NpOjy+H,0 Red brown Orthorhombic 47

A large wmber of termary and polynary oxides of Np(VII),
Np(VI), Np(V), and Np(IV) with glkali metals and alkaline
earth matale are knoum. Also, sindilar compournds are reported
with thgzrare earths, other actinides, and alements in Groups
4 to 7.

NpN Black Cubic 53
NpF Purple LaF, 54
NpF, Green 55
NpFe Orange Orthorhombic 52,56

A large number of fluoro ocompourde of alicali or alkagline earth
metals with Np(IV) and fluoride -have baem reported; a few such

compounda with Mp(V) and Np(VI) aleo are reported.®?
NpO:F Green Tetrajonal s7
NpOF Green Rhombohedral 58
NpO,F 2 Pink 57
NpCl, Green 11
NpCl. Orange brown 11,58
NpOC); Orange 59
NpBr) Green 60
NpBr. Dark red 61
Npl, Brown 62
NpS Cubic 63,64
NpaSs (4 di fferent 63,64
structures)

NpsSs Orthorhombic 63,64
Np2Ss Tetrngonal 63,64
NpS) Mono:linic 63,64

- 19 -
D. NEPTUNIUM IONS IN SOLUTION
D.1. Oxidation States

Neptunium exists in the (II1I), (IV), (V), (VI), and (VI1I)
oxidation states in aqueous solutions. The heat of formation,
the entropy of the individual ionic species, and simple methods
of preparation are listed in Table 7. The first four of these
oxidation states exist as hydrated ions in the absence of
complexing agents. Np(VII) is stable only ir alkaline solutions;

reduction to Np(Vi) occurs in acid solutions.

The singly charged, hydrated neptunyl ion, [NpOz(H20)51+,
is the most probable oxidation state in solution. Because Np02+
hydrolyzes only at pH >7, disproportionates 3nly at high acid
concentrations, and forms no polynuclear complexes, it is stable
compared to the other pentavalent actinides. The standard
potentials and formal electrode potentials in IM HC10, of pairs

of neptunium ions are shown in Table 8.

The formal oxidation potentials for Np couples in various
IM solutions are given in Table 9, with the hydrogen electrode
in the stated medium as the reference. The change in the
potentials in 1.0M HSO. as compared to 1M solutions of HC10,,
HC1, and HNO3 indicates strong complex formation cof Np“* with

sulfate ions.

~ 20 ~
TABLE 7

MEPTUNIUM TONS IM AQUEOUS SOLUTIIM®**!

Heat of Formation

 

AHye ek
Oaidation State Ionic Form Color (kcal/mol)
.3 Np(H,0) {* Blus violet -127
. Np(Hg0)3* Yellow green -132.5
*5 NpO;(H;0);  Gresn -231
*6 NpO, (HyM)2* Pink or red -208
'™ o
+7 m! Green
a. J. C. Hiochey, J. . Cobble. Imorg. Cham. 4, 992 (1970).

R. Brandr, J. W, Cobble.

J.
C. Brown in HClO..

Incrg
J. C. Sullivan and A. J. Zielen.

. Chaw. 2, 912 (1970).
Inorg.

- 21

Mual.

cal

Simple Mathous of Preparscion

 

Entropy
Hree®K
~atom-"K)]

3.5 D
2)

-8 1)
2)
3)

- o:-.z'J 1)

)
B

1)
1)

—

)]

Np(>T11] « Hy/Pr
Electrolytic reduction

Np'T O
Np(V) + 502
Np(v) ¢ I-(5M HC1)

Np** « NGy (heat)

Np(¥1) +« stoichiouetric I°
Np(V1) +« NH,0H

Np{<¥1) - HC1O0, (evaporate)
Hp£¢\'l) « Ag(IL}0 (or BrO;,
Ca ")

Nissolutlon of chermally prepared
LIyNpO¢ In dllute alkalis

NP(V[) « otone [or Xel,,K;Sp0,,
periodate) in 0.5 to 3.5 MDH

Chen'. Latters I, 927 (1969).
TABLE 8

STANDARD AND FORMAL REDOX POTENTIALS OF PAIRS OF NEPTUNIUM IONS**

 

Standaid Formal Poten-
Potenticls tials in 1M
Electrode Process (volts) HC10, (voits)

Np = Np** + 3e- -1.856 -1.83
2Np + 3H,0 = Npy0y + 6H* + Se- -1.420 -
Np20y + Ha0 = 2NpO, + 2H* + 2e- -0.96 -
Np;03 + SH,0 = 2Np(OH), + 21I* 2e- -0.921 -
Np?* = Np** 4 e- -0.152 0.1S5
Np'* + 2H,0 = NpO, + 4H* + e- 0.337 -
Np'* + 4H20 = Np(OH,) + 4H* + e- 0.391 -
Np’* + 2H20 = NpO} + 4H* + 2e- 0.451 0.447
Np(OH), = NpO3 + 2H,0 + e- 0.530 -
NpO; = NpO3 + e- 0.564 -
Np“* + 2H,0 = NpO3 « 4H" + e- 0.749 0.739
NpO2 = NpO3* + e- 1.149 1.137
2Np{OH)% = Np3Os ¢ 2H,0 + 2H* + 2e- 1.219 -
2NpOz + Ha0 = NpaOs + 2H* + 2e- 1.283 -
Np20s + H,O0 = 2NpO,3 + 2H* 2e- 1.310 -
NpO; ¢ H,0 = NpOy ¢+ 2H' + e- 1.9¢8 -
Np'* + 2H,0 a NpO3* + 4H* + 3e- - 0.677
Np*® ¢ 2H0 = NpO3* + aH" + 2e- - 0.938

- 22 -
TABLE 9
REDOX POTENTIALS OF NEPTUNIUM (IN VOLTS AT 25°C) ?*¢¢°°°

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1.0M HC10,
-0.477

-1.137(¢-1.236)% | - 0.739 -0.155 | +1.83

NpO3* NpO$ e Np* b Np¥ e Np
| -0.938 ]
-0.677
1.0M HC1
-0.437
~o-1ass | -0.737 -0.137 | 1.87
NpO3* NpOf —— — Np** Np3: Np
| -0.936 ]
-0.670

1.0M stfl'n

-1.084 -0.99 +0.1
Nlfl%t—_—.——.— Nw; pri‘ _-NPS"'

| ~1.04

1.02M HNO,

-1.138
Npo3* Np03
1.0M NaOH

-0.48 -0.39 +1.76 +2.25
NpOz (OH) 2 ——-———-—-NwQOH e e Np (U*{) I e rerinee Np fOH) 5 --————-Np
(-0.43)
0.582 5

Np(VII) ———— Np(VI)

 

a. Standard potential®
b. According to the half-reaction NpOi~ + e~ + H,0 = Np02~ + 20H"%9 the

dependance of E; on the OH™ concentration is expressaed by7°:
Eo = 0.600 + 0.059 ¢ log [OH-]""

- 23 -
The current-voltage curves for oxidation-reduction

reactions of Np in aqueous solutions are shiown in Figure 2,

D.2. Oxidation-Reduction Reactions

Table 10 lists reagents and conditions; necessary to change
oxidation states for Np ions. For cases wiere only one electron
is t-ansferred, e.g., Np' /Np*" and Np0,*/Np022", the establish-
went of redox equilibrium is rapid. Redox reactions that involve
forming or rupturing of the neptunium-oxygen bond, e.g.,

Np“*/Npoz’ and Np“*/NpOzz*. have a slower reaction rate.

Rate constants (k) and half-conversicn periods of the
redox reactions in IM acid solutions at 25°C are given in

Table 11.

D.3. Disproportionation of Neptunium

Only the Np(V) oxidation state underjoes appreciable
disproportionation. The reaction 2Np02+ + 40" -'Np"+ + Np022+
+ 2H20 shows that disproportionation of Np(V) is favored by
high acid concentrations. Because Np"+ and NpOaz* form more
stable complexes than the NpOg‘ ion, the disproportionation of
Np(V) is promoted by the addition of complexing agents. The
equilibrium constants, K, for various acid solutions are listed

in Table 12 where

Np (1V VI
Np(V)

- 24 -
 

LR L T T 1 r 1 1 v v °r T 1

Np{IV)«=— Np(V)

   
 
  

100 ¢

Np{V)—e= Np(VI} —
No{ M)=a—Npl1v) o MOV F==—RptVI) ~o—0

q Np{IV) —e= Np(V)
x ——

   

(01) —e=Np(1V)

  

Current, mA
o8 5388388

 

 

-0.2 -0A4 -08 -0.8 -0 1.2 -1A4 -1.6 -1.8 -2.0
Volts

Figure 2. Current-Voltage Curve for Redux Reactions of Neptunium."

- 25 -
i
KW © Apitet}
) ~ Npir)

W - Npor)

o3 = apIn)

Wpivr) - i)
Wpdye) -~ Ppn

Nplvt) = Vil

Npdd} - Wpivl)

wp(vl) - WpVIL}

Np(VEt) = Wp(vis

s0f

feriadate

WOC1, MOBy

"0,

L R,

-y

0.0m W,
-

» W
L

«

A,

B,

s mselrmt
-

"

" e,
& m,

[ .1

el

b U
1.5 8 18" set,
X

.50 MW
2.8 n"\ e,
.73 = ol

b, A0,
., )
"o

W, )
D,
$ s 9wy
L e 10 e g,

2.8 ¢ 10N Yy
e

Iha MY
0.1% 8,5,0,

(B N

2.5 2 18 N
O.IW

1.5 % 40 "W %p
o

.5 a [0 ™™ %
2w 18 ' W
" s

s i "wy
S ow 1o 'wowDt
O 1Y TOW

D% te W R

- 26 -

sl saus BasBea

4% 3ILSIJITINT 2UE

3

3

s s

"

53

20

Yyry
2

M T

Yary
fost
Tosy
LY 1Y)
Yeory
Tost

A renversion ia W e

?ase

1fa

Y2

Yprs

Yy

% e
e Y Y

fant

S T

=1} atn
A .-

o maw

20 e

I mas

M ms
-‘z-

" :
m-fl'-’:'
" l'“l“
o“--"nr

™ . '
el = W x 8
".'h. ’.“"*v
.Q"--"-.‘u-
» ¢ ¥ l* ‘

- 5 v Wy 3.i e T
. n Wiy ~ Wb

=5 .
m"s-r-m

= !
:”".c

 

 

spp™iive it

sty gt

VP et

Psil Aol Tl o« a Byt eyt

'fi E TER, Ut o ¢

‘v
"ty
st in ey

popsd™ |1, b b
L IRV =

T

s pnptf ) pom |
LIt - b T Y

gt i
W] I (1) M W CUMEOTEN ICASIN W %€ St MUNITOM TR e AED MamA &5 Mgt T

MMM

o s,

=20, :
_,yE,

-, %
-t $ 4
¥, 3
e, = WMy,

w3k, v

WRE, x WA, ;.3

e, ¥
s, i
" ek, i
-y ¥
s, »
-, e
.,

5P ek, 3
gg ® ¥
$. 00 0T 90, v 2

T W TR D e b S S it

} 3

v ¥

HE A
!l

By ¥ 5% & 3
B, o+ F b
i"?}"

Sy £ B %, b o

€00 2% &, vy
"
‘*:‘-‘v"vl'l,

“*’-’.‘L'?‘;‘,
% ¢t 37 3

By t # &) 8 iy
tit;i

e 5
B ¢+ 2

e & %
‘;i‘,‘.

" * i
¥ ¢ 5 #

vk epF’

8, 58 ks syt
‘;"l’. rw,‘

¥ Mflj*‘

Ll ol

-
»

et
i3

. -
;b B

t e 50

’l
‘i

t .
om

' s

]

et

5

Wierplemh biavgy

AR IBEYS

»
.
*

¥

e 4
ez
v 4
e

e
bl - Ay
> W
TABLE 12

EQUILIBRIUM COMSTANTS FOR DISPROIPORTIONATION
OF Mp(V) IN VARIOUS ACID SOLUTIONS AT 25°C 3

 

 

Solution ?
IN HC10, 4 x 107
S.34M HCIO0, 0.127
8.67M HCIO, 200
IM H,S0, 2.4 x 1072
1.86M H;S0, .16
a. K » v vi

* 2

(Np(V))

. 28 -
The reverse reaction

vt

Np** « Np022* + 2H0-ws2Np);* + 4n"®

takes place rapidly in weakly acid solutions. The rate

constant in IM HC10, is 2.69 (M.min) !.?*

D.4. Radiolysis of Neptunium Soluticns

The radiolysis of Np(VI) by self-radiation of ?*’Np
causes reduction to Np(V} with & rate constant of
(3.1 $0.2) x 10°® sec” ! (0.5 to 1.7M HC10,) and a radiolytic
reduction yield (G) of 6.4 ions/100 ev.””" 7" Compared to
other hexavalent actinides, Np(VI) has a much lower rate of

radiolytic reduction.

For the *°Co irradiation of 0.1M Np(VI) in 1.1M HCIO.,
G = 3.4. The radiolytic yields for rudiolysis of Np solutions
(saturated with atmospheric oxygen) exposed to a ~ | MeV

9231 3re shown in Table 13, Np(V) has a compara-

electron beanm’
tively high stability to radiolysis. Np(IV) is oxidized to
Np(V).

When 2%°Np is prepared by neutron irradiation of

uranyl salts, 80 to 90% of Np is in the tetravalent state.'?

- 29 -
TABLE 13

RADIOLYSIS OF NEPTUNIUN SOLUTIONS [N AN
ACCELERATED 1-MeV ELECTRON

 

 

 

 

Radiolytic
Acid Con- Yield G
centration {ramber of lons
ion Acid ) per 100 eV)
NpO$* ~ NpD,* HC10, 0.018 4.45
0.80 $.76
0.126 $.7
0.? 6.7
1.§ 4.7
3.4 1.9
HNO, 0.08 8.2
H2S0, 0.86 3.0
Np** < NpO,* H250, 0.8 2.1
0.5. Hydrolysis of Neptunium

The hydrolysis of a metal ion is a special case of complex
formation with OH™ ijon. Hydrolysis consists of the transfer
of a proton from a coordinated water molecule to a water molecule

in the outer sphere, ¢.3.,

Np(H20)4"" + H O = [Np(OH) (H;0)7]*" + Hy0"

with K, - mgw“u,ohl” (Hy0]"
[Np(H20) 4]

The most recent and extensive hydrolytic studies of Np
were made by A. 1. Moskvin.®?! Hydrolys.s constants, K, are
listed in Table 14 for Np(1V), (V), and (VI).* The tendency
for Np ions in dilute acid solutions to undergo hydrolysis
increases with increasing ionic potential (d) where d = Z/r,
Z is the ionic charge, and r is the ionic radius. Thus, the
tendency to undergo hydrolysis increases in the order:

’+ wt

NpO2* <Np022* <Np02!* <Np* «Np*”.
Successive hydrolysis reactions in Pu(IV) solutions result
in the formation of colloidal aggregates. The polymer pre-

sunably forms irreversibly with oxygen or hydroxyl bridges.®®

 

*The stability constant K; of the Np hydroxo complexes may be
calculated from K; = f%;——- where K, is the ionic product of

water, 107",

- 31 -
TABLE 14

FIRST HYDROLYSIS CONSTANTS AND
SOLUBILITY PRODUCTS FOR NEPTUNIUM IONS

 

 

 

 

_lon Hydroxide Ksp Hydrolysis Product xH Reference
Np** Np (OH) 6 x 10°5 83
(NpOH) ** 5 x 1077 84
% x 107° 34
NpO2*  NpOa (OH) 9.5 x 10719 NpO20H 8.3 x 10”!! 86
1.3 x 10°° 85
8 x 10~1¢ 10°1° 34
NpO3*  NpO2(OH), 2 x 1077} [NpO2 (OH) }* 4.3 x 10°" 83

- 32 -
Moskvin®? reports evidence for formition of polymer forms of

Np(IV) in aqueous solution at [H'] <0.3M.

D.6. Complex Ion Formation

The formation of complex specios by the actinides in
different oxidation states with a variety of ligands offers
potential for separating the actinicdes from each other and
from other cations. Complex formation and hydrolysis are
competing reactions. The mechanism of complex ion formation
can be represented as successive reuactions between water
molecules from the inner sphere of the hydrated cation and

anions, A, e.g.,

Np(H20)4"" + A = NpA(H20)7'" + Hz0
The ability of an ion to form complexes is dependent on the
magnitude of the ionic potential. The relative tendency of

Np ions to form complexes is usually:

+

Np**" >Np®® »>Np023* »Np022* 5NpO.

Neptuwnium (I1I)
Np(III) exists in aqueous solutions as Np(H20)e’*.
The chloride and bromide complexes cf Np(III) have been studied
spectroscopically in concentrated LiCl and LiBr solutions

(see Table 15).

- 33 -
TADLE 18
COWPLEINS OF NEPTUNIWN IR AQUEOUS SOL JTION'*®

cmim Lissme Moched” £°c} Madmm Speciey _ 'c.l-:::::_b Refereace
npt Quleride spec 3 Cemc LiC1 wpC1** f - 2.42 “
"l.’ b -40
Brexide pex n Camc Libw fphe* # - 48 »
Rpber, * hy - 6.54
p"* Qularids disea 20 1.00 MC10, w1 ** B, - 0,04 ”
w1 By -0.24
mpCiy* By -0.4
-t n 1.0M NC10, 8, -0.3 20
dlaem » 2.0 ACI0, 8, +0.04 "
By ~-0.1&
dista ;-] 4.0 HC10, . AL - 5.10 Pl
B, - 0.10
Flueride fex 20 4.0M HC10, NpP'* B, 402 02
npFi* Ba + 7.57
WpF,* By - 8.9
NpP, By 211
Ritrste dista 0 1.0M HC10, NpfwD,) "t B, +0.M4 B9
wp (0, §* By * 0.08
Np(NO,),* By -0.120
-t s 1.0M HC10. B, + 0.38 20
dista 0 2.0M KCIO, B, +0.34 )
dirtn 23 4. KCIO, g, -0.15 Y|
Ba - 0.7
Hydronide pet 0.1 to ™ K10, npOH'* By ~I1.7 %
» SulfsLe dista B 2.0M HC10, [Np(so 1 Br + 2.43 93
Np(SD.) 2 B; + 147
-f s 3.04 NaClO« By + 2.49 9
By ¢ .57
tex 2 4.0W NCIO, g, +2.70 92
By + 4,26
Oxalsts sol 5 - [Np(CA0e) %" 8, -« 8.5} 95
Mp(CyOu) s 6:r -I17.8%
INp(Ca0a) 01" By +23.96
[Np(CsON )4 )" A +27.4D
sol b 1.0M KC1O, 8y =~ 7.40 %%
By *1%.82
8y =19. 48
dista » 1.0M HC10, B, +~0.19
8, sl14.42
fermats pac - 0.1 to 0.3 NgOOCH  "Wp(HO0),]" By » 2.7 u
Acetate len, ouf - 0. D4 e, cl [Np(AC)]?* 8 - Lol 27
(AC7) [Np(AC),)?* B + 478
[Mpeacy,)* B: +7.49
Mp(AL). Be » 0.87
[Np(AC)s]" & 1.9
(Mp(AC)4)*” Ay 4.7
[eprAC)s)*” Br 174
{ep{AC)a]*- Be 20,2

a. dists, distriimiies sessyyeusats: iea, \om exchange: spec, spactrophotwme'ry; emf, eloctromotive force. redon, eaf
with redox slectrode; pH, pH methed.

b. Stabtlity comstasts ars givem as logarithre to base 10 of the equilibrium : emstants.
Per the resctiom of s cation N with Higmeds L, the canstamt X ond § mre d¢ fingd a3

l.-l.-fih—-l.-%l.-%m.

Therefore B = K Lg, By = [,E,K,, ®c.
 

 

Table 15. Cortinued
Log of b
Tamperaturs Equillbrium
Cation __ Liggd = ethod” ("c) Mod | um Spec Les Constant RAsfsrence
Np** 8-k dists <5 0_1M NH,C10. Np(OX), E. +4%.20 98
wminolimate
ox-)
5,7-Dichloro- dintn 2% 0.1IM NHLC10 Np(DCD ' & B. +46.0% 98
i-hypdroxy-
quisolinats
o)
Ethylens- dismn 21 0.5M (HCL) Hp (EMTA) 8, +26.% 9
dismine-
tetrascetate
(EDTA)" "
Thenoyl - distn 21 0. 1N HNO, Np(TTA , A0+ 5,18 100
triflvore
acetcoate
(oTeA)t”
tiethylene- lex IN HC104 Rp(DTPA) g - 29.79 101
trimmine-
peataacatite
(DTPA) *~
NpO,* Chloride fex 2L 1.0M HC1 NpaC. 8; -0 102
distn 2L 4. 0M HCI10, A, - 2.82 91
[NpOsCEs]” By - 1.5%
Nitrats lax 2.0W MC10. NpD, N, B, - 0.1% 102
distn 25 4.0M HC10. B, - 1.6 91
[NpO3 N0y 417 g, - 1.4
Hydroxide mf Lo M 1ND, NpD,OH B, = 5.1 74
spac By » a 86
Suifite iex [NpO; 'S0 A, » 2.13 103
[NpO '50503 " 8, + 1,00
Sicarbonate iex NpD, (187004} By, + 2.4} 103
Tnalete Llex 0.05M NH.CIO. [¥po, 'C304) ] B, - 4.0 194
g, + 7.3%
Acetats pec NpO; (1L} A, = 1.3% 105
[AC)™ [NpO, 'AC}, 1" fA; + 1.80
spec 1.5M NHLCID, #, + 1.08
B, =« !1.5%
8-hydroxy- spec 7 0.1M Mi.ClO, NpO; (O1) A, + 8.32 106
quimolinate
(ox) " [NpOy ‘OX) 1aq]” A, +11.50
Glycolate spec 2% 0. 1M NH.CIO Np, (GLYC) 9y «1.51 107
(GLYC) "~
Lactate spec 25 0. LM NHWC10W NpO, (LACT) By =~ i.75 107
(LACT) " jex
0.2M MHLC10. [NpOy  LACTY,;)" #, - 2.20 10%
da. distn, distribution ssasuressnts; iex, lon exchangs; spéc, ipect -ophotoleiry; effl, electrfomotive force: redox, enf

with redoxy eloctrode:. pH, pH sethod.
5. Stability constants ure given as logarithm to base 10 of the equ librium comstants.
For the resction of a cation M with ligands L, the constant K az! A are defined ax:

l,-h-#flrl.-%h-%-u.

Thersfore By = KL, By = K;L;Ky, etc.

. A H*
wpf”

e,

3. divga, J1ut/ibntljcs SPSEIGERrLs . (¢,
s1th reder clociraje: pR, p agthed

—hnd
a-hpdroxy -
| sabmtyrate
(W19}~

Tlnru.-
(TaRY) "'

Citrate
cmy ™

Acetyl
acotommte
[AR)
Thaaslytira
flusress ol anst e
(TTA) "
Digthylisus .
trimmee.
pont aacet sl e
(oTPa;t”
nitrile-
Triacetpls
oy’
fehyloes -
digmine .
totrascetate
Ayt
hiorids

Sitrate
¥luor i de
wilate
Juglate

Melote

wifsta

upehns”

L

"pec

wper

distm

dists

1

Toblg 14.

Tamporutwrs
)

%

%

Cont | nued

gl-

0 2 % MLCLO,

G 1IN MLClO0.

0.1 MLCID.

0. 1N WLULIO,

o 1IN WMLClo,

0 4N WALC10.
-l NCI0,

o MM NCL,
- N0,

1 W Kio.

1 Om wio.

t 4m w1,

1.7 saClO.

—Sweiey
Tipd; MHIBA)
[Mg0, MIBA),]"
(Mgl MIBA) |-
NgO, (HTART)
{¥p0, (YART) ]~
(w0, (TamT)"
(g0, (YART), )"
(Wpo, CITR) |-
{mgo, (CTTR) )"
Mgl (AR)

| WOy (AR)y]"

g0, CITA)
[, (YA, ]

(MgG , (DTPa} ]~

(0, OITR) |-
(mp0, (orray |~

g0, EWTR) |7

sgn, (e9TA) )"

1Ny L1
[ 21)°
[mlf'l]l.

[%pa,f)*

L T

Mg, %0,
lul(”-lll"-
Wl g0
{Wp0,(Ce0a),]""
(W, (C)]"
Wpo, (ALY,
{Wpc,(aC),)"

[Tyt 901"
(9t ,(90.),}"

P otabi ity coaniants are gives as logarithe vo base 10 of the squilibriun coly 'ats.
Yor the resciion nof o calioh W with ligands L, Thy cowstant & and # ore defind as:

M solare A, 0,8y,

. - Efl-h-. 8 -m. oc.

By =« B8,y wir.

Lag
i

B,

iy
.,
s}
L

- 2.17
« 3.07
= 3.33

-« 3 32

« 347
« &§.08
- 7.00

-« 1.0
« §.40

. 5.08
« 7.1

- 0.8
- 0.13%
- D.9R
-~ 0.68
= 308
» 8.27
s 1.90
v« .7
- 6.0

- 408
«2.1a
. 4,00
« 6.0
» 2.1
- 4.23
.« 8.0

« 1.9
-« §. 24

et

nn

111

il

L5

n

s
1
L1a
”
L5
1ls

a2

u?

Lie

ok enchaige: spic. spictiraphotaintiry: ol , eleciraisd ive forve. redcs, eaf
Neptunium (IV)

Np(IV), which exists as Np(Hz0)s"* in aqueous solution, forms
strong complexes with most anions. Analogous to U and Pu, Np(IV)
forms negatively charged chloro and nitrate complexes in concen-
trated HCl and HNOy; these complexes are sorbed on anion ex-
changers. Np(C204)2 is soluble in dilute (NH&)200y solution in-
dicating that the carbonate complexes, which have not been
studied in detail, are more stable than the oxalate complexes.'
Definitive studies of the nature arnd composition of peroxide
complexes in solution have not beern made. A purple-gray Np(lV)
peroxide precipitate is formed by uddition of H20;to a solution
of Np(IV) in nitric acid.

From the stability constants .isted in Table 15, the
following series of ligands were arranged according to in-

creasing strength of the complexes formed by addition of the

first ligand to Np*':

C10,~ <Cl~ <NO3 <S042~ W H3C00"
<F~ <C,0,1" <OH™ <EDTA™ <DTPA%™ <OX~

Neptuniws: (V)
Np(V), present in aqueous solution as singly charged
neptunyl ion, Npoz(Hzo);’, is & poor complexing agent because
of its large size and low charge. The neptunyl complexes,

which are comparable in stability to Mg?', ca?’, and 2n?’

- 37 -
complexes,“’ are much more stable than pentavalent uranium,
piutonium, and americium complexes.

Studies of cationic complexes of Np(V. with U022*,
Cr**, Fe?*, Th**, and other cations in HCi0 , solutions have
been made. ®

From the stability constants listed in Table 15, the
following series of ligands were arranged according to in-
creasing strength of the complexes formed Hy the addition of

the first ligand to NpOz*:

Ci0, <Cl1  <NO; <AC <NTA <SO3? “{IBA~
NTART2™  HCO3~ <TTA™ <CITRY™ €042 HAA

<DH™ <DTPA3 ™ <EDTA‘”

Neptuniwm (VI)
Np(VI) exists in aqueous solution as NpO,(H20)¢?”. From
the stability constants listed in Table 15, the following series
of ligands were .rr.ged according to increasing strength of

the complexes formed by the addition of the first ligand to

Npn22*:

C10," <NO+~ <C1~ <S0," <CH3CO0~ <F~ <Ca04

Neptunium(VI.'}
Very few studies of N (VII) complexe: have been made.
Sulfate compiexes of the Npoz” ion in acid solution show that

NpOz’* has a higher tendency towards complex formation with

- 38 -
sulfate ions than the neptunyl NpO;2+ ion., This is reasonable

because the charge of the NpOz"’ group increases from hexavalent

to heptavalent neptunium.

¥1. PREPARATION OF NEPTUNIUM SAMPLES FOR ANALYSIS
A. NEPTUNIUM METAL AND ALLOYS
Neptunium metal dissolves in HCl, other halogen acids, and
sulfamic acid but not in HNO, or concentrated H;S0.,. Hot dilute
H2S0, attacks Np slowly. Np is dissolved slowly in hot concen-

trated nitric acid containing fluoride.

Np-Al alloys are soluble in 6 to 10M HNOs containing "0.05M
Hg(NOy}2 and ~0.02M KF; they are also scluble in HC1 and HC1O.,.
An alternative method is to selectively cissolve the Al in a
solution of NaOH-NaNOj; the Np and other actinide elements
are separated by filtration or centrifugation and are soluble in

boiling HNO,-HF or HCI.

B. NEPTUNIUM COMPOUNDS

NpO2 prepared by ignition of the oxalate at 400 to 600°C is
soluble in hot 10M HNOs;. When ignition is done at higher tempera-
tures, refluxing in strong nitric acid for a long period, even with
the addition of HF, is required. Fusion with potassium bisulfate
and dissolution of the melt in dilute acid is useful for dissolving
NpO2 fired at very high temperatures. bMNp fluorides are readily

soluble in nitric acid solutions containing aluminum or borate ions.

- 30 -
NpO:-Al targets are soluble in hot strong nitric acid solu-

tions containing mercuric and fluoride ions.

C. BIOLOGICAL AND ENVIRONMENTAL SAMPLES

Np in these samples ranges from readily soluble metabolized
neptunium in excreted samples to extrem:ly refractory fallout
samples. Most procedures for dissolving fallout or other environ-
mental samples involve treatment with HF or a basic fusion step
which renders Np soluble in acids. There has been little
investigation of Np in these types of samples; however, numerous
determinations of plutonium in tissw. bcne, feces, urine, vegeta-
tion, soil, and water have been reported and the same methods of
dissolution would probably be applicable for Np; Nielsen and
Beasley'!? have susmarized many of these methods. Dissolution
of biological samples and vegetation is generally accomplished by
nultiple wet ashing or a combination of wet and dry ashing. In
wet ashing, strong oxidizing agents such as perchloric acid and
nitric acid are used (individually or in combination), or sul-
furic acid and hydrogen peroxide. In some cases the sample is
tused with sodium or potassium carbonate, and the melt is dissolved

in water or dilute acid.!?°

- 40 -
VII. SEPARATION METHODS

A. COPRECIPITATION AND PRECIPITATION

Coprecipitation is the "classic" method for ssparating
tracer quantities in radiochemical analyses. Hecause Np in
aqueous solution is easily converted to Jifferemt oxidation
states that exhibit markedly different behavior in coprecipitation,
separation from other elements can be attained. However, ion
exchange, extraction chromatography, and solvent extraction
separation are used almost exclusively because more complete

separation is attained more rapidly.

Precipitation of neptunium oxalat: :s regularly used in
large-scale processing of neptunium zs an intermediate to
neptunium oxide. Precipitation of other Np compounds is very

iimited.

The coprecipitation behavior of the different oxidation

states of Np is shown in Table 16.

Lanthamom Fluoride. The first separation of a pure Np
compound described by Magnusson and LaC!htpello'h used LaF,
coprecipitation. Np(IV), Pu(IIl), and Pu(IV) are carried almost
quantitatively by lanthanum fluoride from mineral acids. U decon-
tamination is best from H2S0, because of the strong uranyl sulfate
complexes. Np is reduced to the tetravalent state and precipitated

by adding fluoride and lanthanum ions. I[nsoluble fluorides

- 41 -
TABLE 16
COPRECIPITATION BEWAVIOR OF TRACE AMOUNTS

 

OF NEPTUNIUM
Carrier Cowpound Np(IV) Np(V) Np{V])
Lanthanum Fluoride ca C NC
Zirconium Phosphate c NC NC
Thorium Oxalate C
Lanthamm Oxalate Nc?
Thorium Iodate C NC
Zirconium Phenylarsonate c Poor NC
Zirconium Benzenesulfinate c NC NC
Sodium Uranyl Acetate NC Poor C
Thorium Peroxide C
Bismuth Phosphate c NC NC
Barium Sulfate C NC NC
Potassium Lanthanum Sulfate C NC NC
Potassium Uranyl Carbonate NC C C
Hydroxides C C C

 

a. C indicates co-precipitation nearly complete
under proper condition.

b. NC indicates co-precipitation less han a few
percent under proper conditions.

- 42 -
including the rare earths and Th also precipitate. Hold-back
carriers are added to decrease the precipitation of Zr and alka-
line earths. The fluoride precipitate is converted either to
acid-soluble sulfates by evaporating unti. fumes of H2S50, appear,
or to hydroxides by metathesis with alkali hydroxide. Oxidation
at room temperature with bromate yields ff.uoride-scluble Np(VI),
but other actinides and lanthanides are not oxidized and, hence,
are precipitated in a subsequent LaFy precipitation step. After
removal of solids, Np is reduced to the tetravalent state and
again coprecipitated with LaFsy. Pa is coprecipitated with manganese
dioxide preceding the LaFi precipitation us required.'?' LaF,
precipitation has been used to separate Np(IV) and Np(V)} from

Np(VI).!'??

Zirconium Phosphate. Tetravalent ions of Np, Pu, Ce, Th,
and other elements are coprecipitated with zirconium phosphate.
A variation of this method by Magnusson, ~hompson, and Seaborg!?!
is based on oxidation-reduction cycles. iAfter zirconium ion and
NaBiO; are added, the solution is heated 0o oxidize Np and Pu to
the hexavalent state. H3PO, is added to carry tetravalent ions.
The supernatant solution is treated with e¢xcess hydrazine to
destroy bismuthate and then with ferrous :ion to yield Np(IV) and
Pu(1il;; Np 1is carried with zirconium phosphate, but Pu(III) and
U(VI) are not carried. The zirconium phosphate is dissolved in

HNOsy - HF, and Np is separated from Zr by coprecipitation with LaFy.

- 43 -
Barium Sulfate. Ce, Ba, La, and Np(IV) in quantities from
carrier-free trace levels to | mg are coprecipitated >99.7% by
barium sulfate from strong sulfuric acid solutions containing
potassium salts and hydrogen peroxide. This causes a separation
from most other elements. Np was separated by dissolution of
the barium sulfate and reprecipitation fros concentrated sulfuric
acid containing chromic acid; Np(IV¥} was nct carried with the Ce,
Ba, and La. The Np in the supernatant was reduced to Np(IV} with
hydrogen peroxide and again coprecipitated with barium sulfate.
After the precipitate was filtered, ??’Np vas determined by gamma
comting of the filter.'?’ The method has been further modified'?"
and also applied to a wide variety of environmental and biological

samples'?® (Procedure 15, p176).

Hydroxides. Insoluble hydroxides coprecipitate all oxidation
states of Np except Np(VII).*3:,127-12% Ganerally, the trivalent
and tetravalent states are carried most effectively. The choice
of reagent for precipitation depends on the composition of the
solution. Strong bases are used when the solution contains cations
that are amphoteric (Al, Pb, Zn) or when the solution contains
organic complexing ligands. When the solution contains cations
that form ammine complexes or are insoluble in strong base (Cu,

Co, Ni, Ca, Mg), ammonia is used as precipitant.

- 44 -
Other Inorganie Coprecipitants. Np(IV) is coprecipitated
with bismuth phosphate and the double sulfate of lanthanum and
potassium. Coprecipitation with lanthanum potassium double sele-
nate gives results siniiar to those described for the double

sulfate but does not have any advantages.!®®

The pentavalent cations of the transuranium elements are

coprecipitated with potassium uranyl tricarbonate.®'’!

Dupetit and Aten'’? described the coprecipitation of tetrava-
lent actinides with thorium peroxide and uranium peroxide.
Neptunium is completely carried by thorium peroxide, but results
were poor with uranium peroxide. This was attributed to the

presence of Np(V).

Other less common carriers for Np(IV) include thorium and

lanthanum oxalates and zirconium, thorium, and ceric iodates.

Other Organic Coprecipitantg. Zirconium phenylarsonate and
zirconium benzenesulfinate are specific for coprecipitation of
the tetravalent ions from solution. The t::ansuranium elements
are separated from other cations and from cach other by a series
of oxidation-reduction steps similar to those outlined for

zirconium phosphate. '?*’

Kuznetsov and Akimova'?" have proposed a number of organic
reagents for concentrating the tetravalent cations of the trans-
uranium elements from very dilute solutions. Np(IV) and Pu(lV)

form hexanitrato species in nitric acid-nitrate salt solutions,

- 45 -
and these cations are coprecipitated with the nitrate precipitates
of heavy organic cations. Of the reagents studied, butylrhodamine
was the most effective organic cation. In concentrated nitrate
solutions, U(IV), TR(IV), and Ce(IV) coprecipitate with Np(IV)

and Pu(IV). Other coprecipitation was with quaternary ammonium
bases, dimethyl dibenzyl ammonium, and benzylquinolium compounds.
Excellent separation from rare earths, iron, chromium, manganese,

and copper was attained.'??

With many organic reagents containing sulfonic groups,
tetravalent elements form soluble cyclic salts that are coprecipi-
tated with precipitates formed by the cation of a ba. 'c dye
(arsenazo) and the cyclic organic reagent. Compared to the organic
nitrates above, the precipitation is more complete but less

sejective. t 3¢

Np(VI) is carried with sodium uranylacctate.

Precipitation. Precipitation of macro quantities of Np is
seldom used as an analytical or radiochemical method. If other
cations that form insoluble compounds are present, these must
be separated first. When the solution is relatively free from
other ions, a method such as alpha counting is usually more rapid
and offers less health hazard. A number of Np compounds have
low solubilities in aqueous solution; however, indefinite
stoichiometry or necessity for calcination to the oxide limits

the usefulness of direct gravimetric determination.

- 46 -
Hydrozxides. No information is available on Np(III) "hydroxide,"
probably because it is rapidly oxidized even in an inert atmosphere.
Np(IV) is precipitated from mineral acid solutions by sodium,
potassium, and ammonium hydroxides as the¢ hydrated hydroxide or
hydrous oxide. The brown-green gelatinous solid is difficult to
filter; it is easily redissolved in mine:al acids. No formal
solubility studies are reported, but the solubility in 1M NaNO; -

IM NaOH is <1 mg/l.

Np(V) "hydroxide'" is green. The solubility in dilute ammonium
solution is 0.18 g/1; in 1M NaOH, 0.017 g¢/1; and in 2.2M NaOH,
0.014 g/1.%> There was speculation in the early  iterature’®
that Np(V) might precipitate as NH4NpO3;*:H;0 or an analogous
sodium compound as well as NpO;(OH)*H;0; however, the exact nature
of the precipitate has not been confirmed. Np(VI) is precipitated
as dark brown (NHs)2Np207°H;0 with exces: ammonia from mineral
acid solution; the solubility is given as 25 mg Np/l.35 When
sodium hydroxide is the precipitant, a bi;rown compound with reported
composition NazNp207*xH;0 is precipitated. Studies on the variable
composition of the uranates leave some question as to the composi-

tion of the neptunates given above.'?’

Fluorides. Grayish-lilac colored Np(IIl) fluoride is pre-
cipitated by adding a dilute HCl solution of Np(III) containing
Rongalite to a solution of ammonium fluo:ride or hydrofluoric acid
in dilute hydrochloric acid while sparging with argon. The dry

compound was quite stable to oxidation.'* Np(IV)} fluoride hydrate

- 47 -
is precipitated when hydrofluoric acid is added to an acid solution

of Np(IV).

Ammonium Np(IV) pentafluoride precipitates as a bright-green
granular solid when hydrofluoric acid is added to a solution of
Np(IV) containing NH," ions. A similar precipitation in the pre-
sence of potassium ions yields a bright-green precipitate that
X-ray diffraction indicates is KNp2Fs. Tie supernatant IM HF -
0.01M NH., from precipitation of the ammonium salt contained 1.1
mg Np/l two hours after precipitation; th2 solubility of the
potassium salt was 1.7 mg Np/1 after 16 hours in 0.5M H.,SO, -

0.5M K,50, - 2M HF.?®

A double fluoride precipitate of La and Np with an approximate
composition LaNpF;o*xH;0 is obtained by adding hydrofluoric acid
to an acid solution o equivalent amounts of La®" and Np“*. The

solubility of the salt in water was 4 mg/;.3g

Rubidium neptunyl(V) fluoride was prepared by injecting a
chilled ~C. 1M HNO; solution of NpOz+ into a chilled solution of
"12M RbF at 0°C. The gray-green precipitate was washed with small

amounts of water, methanol, and acetone fullowed by air drying.HB

Oxalates. Brown Npz(C204)3°nH20 (n ~11) is precipitated by
adding oxalic acid containing Rongalite irto a dilute acid solution
of Np(1I1l) also containing Rongalite. The compound is appreciably

. . . A %
oxidized within a few hours. 2

- 48 -
After valence adjustment to Np(IV) with ascorbic acid,"®
bright-green Np(C204)2°6H20 is precipitated from solutions
originally containing 5 to 50 g of Np(IV), (V), or (VI) in 1 to
4M HNO3y by the addition of oxalic acid. Tie solubility varies as
a function of the concentration of nitric acid and oxalic acid
(Figure 3). At oxalic acid concentrations ncar 0.1M, the solu-
bility varies between 6 and 10 mg/l as the nitric acid concentra-
tion is varied between 1 and 4M. The solutility is very dependent
on maintaining all the neptunium in the tetravalent state,

Significant separation from a number of cations is attained.

The salt (NHy)«[Np(C204)4]® (NHy)2C204°xH20 has bec.. isolated.???
The soluble aqueous complex was cooled to 0°C to remove excess
ammonium oxalate. Ethyl alcohol addition produced an oily, dark-

green liquid that yielded dark-green crysta.s when treated with

96% ethanol.

Green neptunyl (V) oxalate (Np0,C,04H*2H20) is precipitated
when a solution of Np(V) in 1M HCl is treated with a 10% solution

of oxalic acid in tert-butanol. !

Neptunyl(VI) oxalate (Np02C;0,°3H20), a grayish-green
crystalline solid, is precipitated from 2M HNO3; - 0.05M KBrO,
containing 20 to 40 g Np/l1 by adding oxalic 3cid until the solution
is "0.3M H2C204."? The solubility in 0.5M HNO3 - 0.023M H,C,0.
increased from 0.5 to V1.5 g Np/l1 over the :emperature range 0 ;o

20°C. In IM HNOjy at 14°C, the solubility varied from “3.8 to

- 49 -
Solubiiity of Np Oxalate, mg/¢

 

 

 

 

100 - Temperoture: 23°C ' '| HNO, Con:eniration, M"fi
o /’ 0.37 ]
- -4
A oas
& .64
10— - g
- _-2.83 ]
- 376 _|
x i 1. 1111 ll l i i J _J . i.Ll
0.0 0.} 1.0
Oxalic Acid, M
Figure 3. Solubility of Np(IV) Oxalate

- 50 -
“0.75 g Np/l as the oxalic acid concentration varied from 0.002M

-

to 0. 15M.

Peroxide. Np(IV) peroxide is precipitated from solutions
containing Np(IV), (V), or (VI) in >3M HNO; by the addition of
hydrogen peroxide.'"® The higher valence states are rapidly
reduced to Np(IV), and gray-purple neptunium peroxide precipitates.
The precipitation does not progress through the highly colored,
soluble peroxy complexes that are characteristic of plutonium
peroxide. Two crystalline forms were prepared depending on the
acidity of the precipitation solution. The solubility is reported
as a function of the concentrations of nitric acid and hydrogen
peroxide. A minimum solubility of “10™“M neptunium occurred in
solutions 1.5 to 2.5M HNOj; and 4.5M H:02. T7The solubilities were

not readily reproducible at nitric ac.d concentrations of <2.5M.

Iodates. Precipitation of Np(IIl) iodate has not been
reported. Np(IV) iodate, a tan-brown solid, is precipitated when
HIO3 or KIOs is added to a dilute mineral acid solution. The
solubility in IM HCI - 0.1M HIO3 is 0.8 g/1; in 1M HCl1 - 0.1M KIO,,
0.08 g/1.°% These solubilities appear to be high, possibly because

some Np was in higher oxidation states.

Acetate. Rose-colored NaNpO; (C2H30:)3 is precipitated when
a sodium acetate - sodium nitrate solution is added to a dilute
sulfuric acid solution that has been heated to 90°C in the pres-

ence of potassium bromate to give NpO22*. The solubility is

0,1 g/1 in 0.5M H2S04 - 0.07M NaNOs - 2M NaCzH;0,.°*%

- 51 -
Carbonates. No simple carbonates of Ny (III) and Np(1V) are
reporied. A light-colored precipitate of Np (V), KNpO2COs, is
precipitated by addition of solid alkali carbonate (to about pH 7)
to a solution of Np(V) made by reduction of Np(VI) with iodide

ion."?

Phosphate. A green gelatinous precipitate, Np(HPO,):*xH.0,
is formed when phosphoric acid is added to Mp(IV) in hydrochloric
or nitric acid. The solubility in IM HCl - 0.5M HsPO, is 56

mg/l, and the solubility in IM HNO; - 1M H;P0, is V134 mg/1."°

Sulfates. Mefod'eva and Gel'man?? report precipitation of
Np(III) as the complex sulfates KsNp(S04)4 iand NaNp(SOs)2+nH20.
Np(III) is produced in dilute hydrochloric and sparged with argon
at ~50°C using Rongalite reductant. In the dry form, the complex
sulfates are stable to oxidation even at increased temperature.®?
Np(IV) is crystallized from hot concentrated sulfuric acid as a
bright-green compound, presurably Np(SO4)2°*:tH20. The solubility
is 16 g Np/1. Sulfuric acid solutions of lip(V) and Np(VI) have
becn reported, but no data are given on solubility.?® Although
not reported, it is expected that Np(IV) commpounds analogous to

Pu(IV) compounds could be precipitated from a solution containing

sulfate salts, alkali metal ions, and Np(IV).

Other Compounds. Several Np(IV) chloride complex salts have
been prepared. Yellow Cs:NpCl; was precipi:ated by mixing solutions

of Np(1V) and CsCl in 2 to 1IM HCl and saturating the resulting

- 52 -
solution with hydrogen chloride. The solubility in “10M HCl is
<0.0IM and increases to v1.4M in VIM HC1.'"! A similar compound,
[(C2Hs)«N]2NpCle, was precipitated by adding tetraethylammonium
chloride in 12M HC1 to Np(IV) in 8 to 12M HCL.'*? Several other
complex salts of Np(V) and Np(VI) have been reported. Yellow
[(CzHs)uN]2Np02Cl, was precipitated by the same procedure used

for the Np(IV) salt,'*? and Cs;NpOCls (bright yellow), (PhyAs) NpOCls
(bright yellow), Cs3NpOCl, (turquoise), and Cs;Np02Cl, (dark yellow)

were made by variations of the same pracedure.*®

The phenylarsonate and salicylate of Np(IIl) have been

reported. > They are quite stable at ambient temperature when

dry.

- 53 -
B. SOLVENT EXTRACTION

Solvent extraction of Np from aqueous solution into immiscible
organic solvents is probably used most often for separation because
of its rapidity, simplicity, and reliability. Solvent extraction
of Np is usually made from nitrate systems. Generally the effi-
c.ency and specificity are decreased from chloride systems; other
systems, such as fluoride, sulfate, and phosphate, form complex ions

with neptunium, and extraction is inhibited.

There are examples of both ion association extraction and
chelate extraction among the solvent extrac:ion systems for Np,'*“»1%%
In chelate systems, compounds such as TTA, cupferron, acetylacetone,
and 8-hydroxyquinoline replace coordinated vater from neptunium
ions and form neutral, almost covalent, cheilate compounds that are
soluble in such organic compounds as hydrocirbons. In ion associa-
tion systems, several mechanisms are possible by which uncharged,
extractable compounds are formed by electrostatic attraction
between oppositely charged ions. In one ion association system,
an oxygen-containing organic compound such as ether is coordinated
to Np(IV), and the complex cation is associated with nitrate ions
to give an uncharged extractable species. Ion association solvents
commonly used for Np extraction include TBP, hexone, diethylether,
isocamyl alcohol, pentaether, and dibutyl carbinol. For solvents
such as hexone and diethylether, which forz coordination complexes

with actinide nitrates, the order of extractability of the various

- 54 -
oxidation states is usually (VI) > (IV) > (III1) and (V), with the
last two states generally considered to be nonextractable. The
(IV) oxidation state is poorly extracted Ly diethylether but is
extracted into hexone and dibutyl carbinol. For TBP and chelating
agents, which form coordination complexes with the metal nitrates,
the stable oxidation state giving the strongest complex is usually
extracted most efficiently. The tendencies of the actinides to
form complexes is (IV) > (VI) > (III) and (V). Thus, TBP, TTA,
and other complexing agents usually extract the (IV) state most
effectively. An exception (Table 17) is lip(IV)-TBP; however, these
exceptions may be the result of the instability of the oxidation

state in the aquebus solution.

Groh and Schlea!“® and Schulz and Benedict® have reviewed

production-scale neptunium processes, including solvent extraction.

Chelate Syetems. A large number of 5>i-functional reagents
that form strong coordination complexes wvith metal ions have
been investigated, These complexes are more soluble in nonpolar
organic solvents, such as benzene or CCl,, than in the aqueous
phase. Of these compounds, the fluorinated 8-diketone, 2-
thenoyltrifluoroacetone (TTA) has been most widely used for extrac-
tion of Np in radiochemical and analytical applications.!'*7.1%%®
Many variations include TTA extraction as a part of the total

separation scheue before the analysis of Np or the determination

of its oxidation states,127,132,149,150

- §5 -
orsands These
198 TBP-kerosene

0.5M TTA-xylene
Diethyl ether

Hexone

TABLE 17

VYARIATION OF EXTRACTION COEFFICIENTS WITH OXILATION STATE

 

Aqueous Phase Np(IT1) MNp(IV) _Np(¥)  Np(VI) _Pu(III) Pu{iv) _Pu(¥l) Am(I11} Am(VI)
PYRTEN 3.0 0.13  11.0 0.014 1.5 2.% 0.08

IM HNO» 10°* to* 10" 107? 10t 1ot 0.004 107

oM HNO» 0.1 0.3 4.6 P

1M HNO;-sat 1.2

NEi ND

0.5M4 HNO3-11.1N 0.14 1.7 9.8

NHoNDy

6 1O, 0.3 1.7 3.5 >100

- 56 =
Some data for the extraction of Np and other cations into
0.5M TTA in xylene for a range of nitric acid concentrations are

given in Table 18.

Shepard and Meinke have compil:d a useful set of TTA extrac-
tion curves showing extraction as a function of pH for a number
of elements.!%? The data show that by judicious pH control, TTA
extraction is useful to separate neptunium from many other

elements.

Basically, the TTA method depends on quantitative reduction
of Np to the highly extractable tetravalent state while inter-
fering ions are stabilized in inextractable oxidation states.
(Procedures 1 and 2, p 138 and 141). Neptunium in 1M HNOy or 1M
HCl is rapidly and completely reduced with ferrous sulfamate,
hydroxylamine hydrochloride-potassiim iodide, or hydroxylamine
hydrochloride-ferrous chloride. Np(IV) is extracted into the TTA,
and Pu(I1I) and U(VI) remain in the aqueous phase. If no inter-
fering cations are present, the extract can be evaporated
directly for counting. The efficiency of separation from other
alpha emitters 1s verified by alpha pulse height analysis.
Fe(I11), Zr(1V), and Pa(V) are strongly extracted from 1M HNO,,
but separation is attained by stripping the Np(IV) from the
TTA-xylene into 8M HNO;. Trivalent actinides and lanthanides
do not interfere. Sulfate, phosphate, oxalate, and chloride,
if present in the aqueous phase, ar: complexed with Al’* before
extraction to prevent interference.

- 57 -
TABLE 18
149
EXTRACTION COEFFICIENTS FOR VARIOUS IONS INTO 0.5M TTA-XYLENE

Extraction Coefticient

 

__Ion_ HNOs (M) at 25°C
Np(I1I) 1.0 <3 x 107"
Np (IV) 1.0 1 x 10"
8.0 <1 x 10-2
Np (V) 0.8 <5 x 107"
Np (VI) 0.8 <1 x 107}
Pu(IIl) 1.0 1 x10°°
Pu(IV) 1.0 1 x 10"
8.0 <1 x 10 2
Pu (V) 1.0 <1 x 107"
Pu(VI) 1.0 4 x107°
UvI) 1.0 3 x 103
Fe(Il) 1.0 <1 x 107°?
Fe(III) 1.0 375
Ce(lII) 1.0 1 x 10°°
Ce(1V) 1.0 1 x 10?
Zr (IV) 1.0 1 x 107
8.0 250
Am(III) 1.0 1 x Lo~?
Al(III) 1.0 1 x 10720
Na 1.0 1 x 10729
Nb (V) 1.0 4 x 107}
Th (1V) 1.0 3.)

- 58 -
The relative standard deviation for :he analysis is 12%,
The nominal decontamination attained from plutorium is 10? to
104.1512152 gome data on the extraction of Np from sulfate and
perchlorate systems with TTA have been given by Sullivan and

Hindman, ?3

TTA extraction preceded by a LaFy coprecipitation cycle has
also been described.!5'"!*® Np has been separated from numerous
special materials where a combination of methods including TTA
extraction was used. Holcomb'37 has described a method for
separating 17 gamma-emitting radionuclides, including 23%Np, from
heavy water moderator by TTA solvent extiaction and anion exchange.
The individual nuclides were determined ty gamma counting and

gamma spectrometry.

8-Hydroxyquinoline forms the following chelates with Np:
Np(CoHgNO) ¢ with Np(IV) and H[NpOa{(CeHgNO),] with Np(V). Extrac-
tion of a number of elements as a function of pH into 0.1M
8-hydroxyquinoline in CHCl; is shown in l‘igure 4. The trivalent
actinides extract only at pH 4-6, and at this pH appreciable

hydrolysis of the metal cation occurs. *’

Np(IV) cupferron is
extracted almost quantitatively into chloroform from 1M HC1 and

is back extracted in BM HCl,'S®®

Separation with acetylacetonate has been reported for U and

Pu and probably has application for Np.

- 59 -
FIGURE 4.

 

T

 

e

' Patvi| INotv)  Cmim ActmD ramf \Paiv)

5

2 s0f- ]
! Am{IIl)

 

 

 

 

 

 

 

 

). "7

0 2 4 6 8 10 12 4
pH

|
-

 

Percentage Extraction of Tracer Quantities of Ac(iIl), Am{III),
Cm(111), CF(IILX), Np(IV), and Pa(V) with 0.1M 8.Hydroxyquinoline
/CHC1, and of Ra({II) with 1.0M 8-Hydroxyquinoline/CHCly [u = 0.1M
(Na, NH,, H)C10,, 25°C]. [C. Keller and M. Mosdzelenski, Radiochim.
Aota. 7, 185(1967) Supplemented].

- 60 =
Extraction of plutonium dibenzoylmethane or salicylate has been
reported.159'15° Neptunium dibenzoylmethane is unstable in aqueous
solution, so Pu and U, which form extractable complexes, can be

separated. 33,181

Chmutova et al. extracted Pu(IV) from 3M HNCiy with a chloroform
sclution of N-benzoylphenylhydroxylamine; H0,2%, Am(III), (V),

162

and fission products (except Zr and Nb) do not extract.

Np(IV) is strongly extracted from 1 to 4M HNO; and 1 to
6M HC1 with 4-benzoyl-3-methyl-1l-phenyl-pyrazolin-5-one; under the
same conditions, Np(V) and (VI) are not extracted.!®’ Np is ex-
tracted at pH 9 to 10 with l-nitroso-2-napthol in n-butanol and

isopentancol and is separated from U and Pu.'®"

Ion Association Systems. The TBP-HNOs system is a useful
system for large-scale processing but is not widely used
for quantitative analytical separation., TB’> forms an organic-
soluble coordination complex with the metal nitrate, generally of
the type M(NOs3),*2TBP.'®> Increasing the nitrate concentration by
adding nitrate salts of Al or Ca favors ext::action. Other factors
that affect the extraction include complexing ions, reagent purity,
free TBP concentration, temperature, and mi>ing time. A summary
of the early work with TBP has been given by Geary.'®® The
physical and chemical properties of TBP as an extracting agent
have been summarized by McKay and Healy.!®’ Other discussions of

the use of TBP are in References 168-170. Extraction coefficients

- 61 -
for many elements for a variety of aqueous solutions and TBP
concentrations have been reported by Schneider and Harmon;l“'

data are shown in Table 19.

Np(VI) is almost completely separated from Al(III), Am(III),
Cr(III), Fe(Il), Fe(III), Na(I), Zn(I1), and many other cations
in one stage of TBP extraction. Separation of Np from Pu and U
involves either oxidation of Np to the (VI) state for extraction
and subsequent stripping of Np(V), or stabilization of inextract-

able Np(V) followed by extraction of Pu and U.

The following sequence of extractability has been found for
the various oxidation states of the actinides: M(IV) > M(VI) >>
M(III) > M(V). For the tetravalent actinides the sequence is
Pu(IV) > Np(1V) > U(1IV) > Th(IV), while among the hexavalent
actinides the extractability decreases with increasing atomic

number: U(VI) > Np(VI) > Pu(VI)'®® (Figures 5 ard 6).

The tetravalent and hexavalent actinides ar: extracted from
HCl solutions with similar relative distribution coefficients as
from nitric acid but exhibit no maxima. Lower d:.stribution coef-
ficients are observed for extraction from perchloric acid solutions
because of weak complexing by the perchlorate ion. Strong complexing
agents, such as, S042~, P0,?", and F-, reduce the extractability of
all actinides appreciably; however, cations such as Al that form
quite stable complexes with these anions partially negate the

deletericus effect on actinide extraction. Distribution

- 62 -
Ton
Am(III)
Al
Ca
Co(1I)
Cr(IIl)
Cu(II)
Fe(II)
Fe(III)
Mg
Na
Ni(II)
Np(1V)
Np(VI)
Th
Pa
Zn
Ru
Zr
Nb
Rare earths
Pu(IIIl)
Pu(1V)
Pu(VI)
u(Iv)
uqvI)
HNO»

 

TABLE 19
EXTRACTION COEFFICIENT DATA FOR TBP!*®

Extraction
Coefficient

Solution _TEP_(%) At 25°C
4.0M HNOj 30 0.013
4.7M 15 0.0003
4.7M 15 0.0003
2.14M Co(NO,) , 60 0.002
3.0M HNO> 100 0.0001
3.0M 100 0.0004
4.7M 15 0.005
2.0M 12.5 0.003
4.7 15 0.0003
2.0M 12.5 0.003
3.0M 100 0.00006
4.0M 30 3.0
4.0M 30 12.0
4.0M 30 2.8
4.0M 50 2.8
2.0M Zn(NO3)2 12.5 0.0001
2.0M HNO3 30 0.15
2.0M 30 0.09
2.0M 30 0.03
2.0M 30 0.02
5.0M 20 0.012
5.0M 20 16.6
5.0M 20 2.7
4.0M 25 10
4.0M 25 23

2.0M 30 0.26

- 63 -
 

Cistribution Coefficiens

 

 

 

0‘! 1 l
0 S 0 13
HNOy, mole /.t

Figure 5. Distribution Coefficients for tre Extraction
of Tetravaient Actinides by 19 vol % _
TBP-Kerosene from Nitric Acid Solutfon.'*?
 

L4 1 1ilzd

c
7

Distribution Coefficient
»
(( (

10

31 0 aud

L a2 1taiul

 

 

-t | L
° o ) Ky s
HNOy, mol /2

Figure 6. Distribution Coefficients for the Extraction
of Hexavalent Actinides by 19 vol % .
TBP-Kerosene from Nitric Acid Solutifon.’®®

- 65 -
coefficients for Np(V) and trivalent actinides are appreciably

lower'’! than for tetravalent and hexavalent actinides.

For NpOy":
NpO2" gy ¢ N0 oy ¢ TBP o = [NpO2 (NOS)*TBP]

For analytical applications with small volumes, equilibrium is

attained in less than five minutes with good mixing.

The extraction properties of many >ther organophosphorus
compounds have been studied; however, f@w separation methods for
Np have been defined. Higgins et al, working with the butyl series
found the order to be phosphate ((RO)3P0) < phosphonate (R(R0)2P0O)

< phosphinate (R2(RO)PO) < phosphine ox:.de (RyP0O). 172

The distribution coefficients for the extraction of some
tetravalent and hexavalent actinides with various trialkyl

phosphates are given in Table 20.

Burger!’*+17% and Petrov et aqZ!’%® found that electronegative
substituents in the alkyl chain, such as, chloride and phenyl,
strongly depressed the extraction. Siddall’? found that increasing
the length of the alkyl chain in the phosphate series made little
difference for up to eight carbon atoms for tetravalent and
hexavalent actinides., The effect of branching the alkyl chain is
to increase the extraction of U, Np, and Pu, but to strongly depress
extraction of Th, The extraction mechanism of these compounds is

generally the same as that for TBP, but the solvation number is not

- 66 -
TABLE 20
DISTRIBUTION COEFFICIENTS FOR THE EXTRACTION OF TETRAVALENT
AND HEXAVALENT ACTINIDES WITH 1.9M TRIALtYL PHOSPHATE/
n-DODECANE FROM 2M HNO, AT 30°C’*

Distribution Coefficients?

 

 

 

 

Extractant Th  Np(IV)? Pu(IV)®  JOVI)  Np(VD)Y  Pu(vI)
Tri-n-butyl phosphate 2.9 3.2 16.1 26 15.6 3.5
Triisobuty! phosphate 2.4 2.7 11.8 22 15.9 3.4
Tri-n-amyl phosphate 2.9 4,2 15.6 32 19.3 4.1
Triisoamyl phosphate 4.2 4,7 17.8 34 18.9 4.4
Tri-n-hexyl phosphate 3.0 3.6 15.6 38 20.0 4.5
Tri-n-octyl phosphate 2.4 3.4 15.3 33 15.7 3.9
Tri-(2-ethylhexyl)

phosphate 2.5 4.3 25 58 23 5.7
Tri-(2-butyl}

phosphate 0.45 4. 28 42 20 4.6
Tri-(3-amyl) phosphate 0,22 3. 18.1 49 22 5.0
Tri- (3-methyl-2-butyl)

phosphate 0.18 3.0 24 47 25 5.4
Tri-(4-methyl-2-amyl)

phosphate 0.047 3.5 22 38 24 4.9

 

a. For tracer amounts of the given elements.

b. The aqueous phase contains 0.01M Fe(NHz2S0y)2.

¢. The aqueous phase contains 0.0lM NaNO,.

d. The aqueous phase contains 0.0IM (NH,),Ce(NO,),.

- 67 -
necessarily the same for all elements.'’?

A method with mono{2-ethylhexyl]orthophosphoric acid in
contact with 12M HC1 + 0.1M hydroquinone has been effective for
separating Np(IV) from U(VI), Pu(III), Am(I[I), Cm(I1I}), and
trivalent rare earths. The K value for Np([V) is ~103, and for
the other cations,™107!; thus, separation is attained by a single
contact followed by multiple scrubbing of the organic phase.!’’
K. Kimura'’® has determined the acid dependency of the distribu-
tion coefficients for many elements extracted by 50 vol%
bis(2-ethylhexyl)orthophosphoric acid (HDEHP  from HC1l solutions

(Figure 7). These data offer the basis for separating Np from

many cations,

The distribution coefficients of Am(IIl), Pu(IV), Np(V), and
U(VI) in HDEHP from HNOj; are given in Figure 8.'7% The dis-
continuity in the Np(V) curve at high acid concentrations is
prcbably due to disproportionation of Np(V) into Np(IV) and Np(VI),

both of which are more extractable than Np(V].

Np(V) in dilute nitric acid has been separated from U(VI),
Pu(1V), and Th(IV) by HDEHP extraction; however, there was evidence
that a few percent of the Np(V) was reduced to Np(lV) and not

80  Kosyakav et all’? used

separated by a single extraction.!
HDEHP to purify Am(III) from other actinides in higher valence
states and to accomplish their mutual separa:ion. Am(IIl), Pu, and U

were extracted from 0.01IM HNO; after stabill:ation of Np in the

- 68 -
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

S rFedl
L * »t
"\'f" 1
- ‘1' fll
kl_LLL‘L ]
el wdl Rl L Agdl cdld ndb  Sall e Sb Tell 14
b 1t 1 j MNEL» -p\.: jr"s hjr e» 4
ik I N Y-
r 4 L E - 4 <4 -4 r
bt = dE N M T e
L Redf O8]l Ir '“‘R]L"KJ. - ”] "h.»Tfij»'E L At
T =1 [ | o {leaml\m ][ \T11] L
"‘l" J:—\ja.‘-‘Jjfl/t\4r(”n-p\j, p 4
) 1t 4 4 L . [ b p
Aok i A 2 x .2 & el oo d i &oa *klnngfig.‘.‘||.|h_. 14 L

 

 

 

 

 

 

 

 

~ DFP values hasing on Duts of [MF Peppard et at
- CAB Dataor CA Blake et a.

=Tl Dataof T Ishimori.

“*EN  Dataof £ Nehamuri

 

S Scrubbing

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[ . ) T v e -y L v T ey -y
}‘.‘ C. - fiq- mi P--i- &1 E.{ 3 m u
t'\ } 4 el - P
\ 1F 4 4k 4+ < - - 4
] 9 b F 4} 't b 4
F - o 4 -+
Lan 2 Bl 11 g bl 41;.1 i, ] i
N - v T ey -
ch{ - Pei\ A=l C={t O )
b 1k { .
b 45 4% - ]- 1 }
4t s ey {4 {t ] 3 it { 00101 1 10
41 4} 4 L 4t »
i, s Fuy Aredhin i A . 4 Lotk il

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 7. Extraction of Elements frcm HC1 Solution by 50% HDEHP
in Toluene as a Function cf Acid Concentration.!?®

- 69 -
 

 

 

 

 

Log [HNOs]

Figure 8. Extraction of Various Actinides into 0.5M HDEHP
(isooctane diluent) from HNO; Solutions.179

- 70 -~
pentavalent state with sodium nitrite. HNp(V) was then oxidized
to Np(VI) and extracted with HDEHP. Np(Y'I) was reduced to Np(V)
and recovered from the organic phase by vashing with 0.1M HNOs.
Am was back-extracted from the HDEHP with 3M HNO; and Pu was
reduced to Pu(III) and recovered by back extraction with 3M HNOs-

U(VI) was recovered by back extraction w.th IM (NH,)2 CO,.

Chudinov and Yakovlsv' ~° extracted !J and Fu from Np(V) with
HDEHP as a preliminery step in the colorimetric determination of

Np(IV) with Arsenazo(III).

Peppard et al!?’,1®! studied the ex:raction of several actinides
by mono-2-ethylhexylphosphoric acid (HM:HP) from HCl solutions
(Figure 9). The distribution coefficien: for Np(IV) in 12M HC1
was v10?, 10" times larger than the non-:etravalent species studied.
Gindler et al.!®? used this method to purify 2®Pu for fission
counting. The Np(IV) can be returned to the aqueous phase by
addition of TBP to the organic phase, re;ulting in a great

reduction in the distribution coefficien:.

Kosyakov et al.!’? determined the distribution coefficients
of Am(III), Np(V), Pu(IV), and U(VI) in H,MEHP from nitric acid
(Figure 10). They are generally higher for the same aqueous

conditions than those for HDEHP.

White and Ross'®? have written a general review of the

extractive properties of tri-n-octylphosphine oxide (TOPQ).

- 71 -
 

 

 

 

 

HCI, M

Figure 9. Extraction of some Actinide Cations into 0.48M
H,MEHP in Toluene as a Function of HC1 Concentration.!”’

- 72 -
 

 

 

 

6
° I T T T
S.OT—\\- PullY) —_
———
4.0 — e
Np(X)
3.0 s— —
o u(xn
g 2.0 — -
wd
'.»0 P el
N\
sl
0 Am(I) —
-'.O . \ g
2.0 l 1 | 1
~-1.0 -0.% 0 0.5 1.0
t.og [HNO,]

Figure 10. Extraction of Various Actinides irto 0.2M
H,MEHP (Isooctane diluent) From HNOs; Solutions.!’?

« 73 .
Extraction data for Np and other actinides into TOPO have been

summarized by Weaver and Horner.!'®"

Extraction with methyl isobutyl ketone (hexone) is based on
the solvent power of hexone for the covalent nitrates of the (VI)
oxidation states. Hexone was used for large-scale prccessing of
irradiated nuclear fuels (''redox" process) but has been supplanted
by other solvents both in plant and laboratory applications. A two-
cycle extraction system for the separation of neptunium from
uranium-fission product mixtures has been given by Maeck.'®’
Hexone extraction of Np(VI) from acid-deficient ALI(NO,),; was
followed by TTA extraction. Excellent separation from U, Pu, Ru,
and Zr was attained. Also, Np has been separated from Pu and La.
Np(VI) and Pu(VI) were produced by oxidition with KBrdi; both
were extracted into hexone from an A1{NJi); solution. Back
extraction with an aqueous sodium nitrite soluticn yielded Np(V)
and Pu(IIl), neither of which is soluble in hexone. The hydroxides
were precipitated and dissolved in nitric acid, and ferrous
sulfamate war added to give Np(IV) and Pu(III). Np was extracted
into a solution of tributylamine in hejone, leaving the Pu in the

aqueous phase.’??

Extraction coefficients for ions :nto hexone from several

different aqueous compositions are shown in Table 21.

Diethylether quantitatively extra:ts hexavalent Np, Pu, and

Am from salted solutions containing a strong oxidant (Table 22).'%S

- 74 -
TABLE 21
EXTRACTION COEFFICIENTS OF VARIOUS SOLUTES INTO HEXONE AT 25°C!*?

 

Extraction
Solute” Salting Agent (M) NGy~ (M) HNOy (M)  Coefficient
Na* A1(NOs)s 1.3 4.0 0.1 0.02
AlY 1.3 3.9 0.0 <0.0001
Cr 03~ 2.0 6.1 1.7 pH 0.011
crt 2.0 6.1 0.1 0.0003
yt* 1.3 4.4 0.5 2.1
Am®* 1.95 6.35 0.5 0.0018
tip** 1.3 1.4 0.5 1.5
Np3*t 1.5 5.0 0.5 <0.001
Np** 0.7 2.6 0.5 1.7
HNO s 1.0 5.4 0.4 0.82
NOs~ 1.5 4.5 0.0 1.1
Cs* 1.0 3.5 0.5 0.009
Zr-Nb 1.0 .25 0.25 0.01
Ru 1.0 1 0.10 0.10
e 1.3 da.1 0.20 0.12
F.p.b 1.4 ‘.6 0.4 0.10
Fe** NH,NO 8 £.2 0.2 0.004
Fe* 8 §.2 0.2 0.0005
Pu'’ 11.1 11.6 0.5 1.7
Put* 11.1 11.6 0.5 9.8
put” 11.1 11.6 0.5 0.14
put”’ A1(NO,s ), 2.0 6.3 0.3 50.0
us* Al (NO3)3 0.5 1.8 0.3 0.1
1.0 3.3 0.3 2.0
2.0 6.3 0.3 30.0
NH NO, 4.3 4.6 0.3 0.18
8.7 9.0 0.3 2.0
11.0 il 3 0.3 14.0

 

a. Concentration of all solutes is 2 g/:
b. Gamms-emitting fission products after 144-day cooling period.

- 75 -
TABLE 22
EXTRACTION OF NEPTUNIUM, PLUTONIUM, AND AMERICIUM INTC VARIOUS SOLVENTS

% Extracted

 

 

 

 

Solvent Aqueous Phase Np (IV)E Rp (V) Mp (VD) Pu (I1I1) Pu (VI}  Am_(VI)
Ethyl ether iIM HNOjy; sat NH NO, a 100
6M HNOy 9 17 32 70
9M HNO, 17 65 12 89
Dibutyl G HNO, 17 23 il 8
carbinol 7 co M HNO, 23 48 49 35
DBBP,S 30% 4M HNO, 91
7™M HNO, 15
0BE,d 85% 2.4M Ca(NOy)2; 0.6M HNO, 11
5.4M Ca(NO3s)z; 0.0SM HNO, 0.3 41

 

a. High efficiency; no value given.
b. Np(IV) unstable in HNOy.

¢. Dibutyl-butyl phosphonate, DBBP.
d. Dibutyl ether. DBE, +ith 15% CCls.

- 76 -
Other elements that extract strongly are Ze(IV), Au(1Il), and
Sc(IIl); P, Cr(V1), As(V), Hg(II), TI1(I1Il), Th(IV), and Bi(III)
are partially extracted. After back-extriction with dilute acid,
ferrous ion and urea or hydrazine are added to reduce Np(VI) to
Np(V); NH(NOy is added for salting. A second extraction with

diethylether further separates Np(IV) from U(VI).127.18¢

Distribution data for several of the actinides, including
neptunium,as a function of nitric acid concentration into dibutyl

carbitol are reported.’®’,18%®

Arine extractants, including long-chain alkyl or aryl primary,
secondary, and tertiary amines, and quaternary amine salts react
with acids to form an ion-association complex which is soluble in
the organic phase. The mechanism is illustrated with a tertiary

amine:

* + A” » RyNHY -

RaNorg) * M (aq) * A (aq) A (org)

A~ may be either a simple anion or the an:on of a complex metal
acid. The complex may undergo a further reaction with another

anion in a manner analogous to anion exchinge.

+* -
*RaNH == B org) * * (aq)

RaNH === A org) * B (aq)

The higher amines are excellent extractants for Np(IV), Pu(IV),
and U, The advantage of amines over orgarnophosphorus compounds is
the greater stability to radiation and hydrolysis in radioactive

solutions. The amines are usually dissolved in an organic

- 77 -
solvent (xylene, benzene, or chloroform). Tco achieve rapid phase
separation and to prevent formation of a third phase during
extraction,a small amount (3 to S vol¥) of a long chain aliphatic
alcohol is added to the organic phase. The relative extractroility
of Np in nitrate solution is Np(IV) > Np(VI) > Np(V), although the
selectivity depends on the structure of the umine and the composi-
tion of the aqueous phase. The extractive power of the amines in
nitrate and chloride solutions varies in the order quarternary
ammonium > tertiary > secondary > pri-ary"’; from H,SO0, solutions,
the sequence is reversed. The distribution coefficient of tetra-
valent and hexavalent actinides from HCl and HNJ, acid solutions

decreases in the sequence Pu > Np > U > Ps > Th.

Keder et al.'®® have reported distribution coefficients for
several actinide elements (more than one oxiijation state) from

nitric acid solutions with tri-n-octylamine (TOA) diluted with

xylene (Figures i, 12, and 13).

The tetravalent ions show a second power deperdence on the
amine concentration, indicating that the extracted complex involves
two amine molecules. Extraction of Np(IV) md Np(VI) with
trilaurylamine (TLA) from nitric acid is reported.'*!.!*? @

review of liquid-liquid extraction with high molecular weight

amines has been publi:ned, '?’?

Np(IV) has been separatea from U(VI), Pu(III), Am(Ill), and

fission products by extraction of Np(IV) into tri-iso-octylamine

- 78 -
 

 

 

 

 

 

ot i L1114
O 2 4 & & 10 12 M

Agqueows HNO,, M

Figure 11. The Extraction of the Quadravalent Actinide
Nitrates by 10 vol % TOA {n Xylene.'®?

- 79 -
 

0

0 .0

 

 

 

 

 

L+ -+ 1 111 ]
O 2 &4 6 8 W0 12 14

Aquecwus HNO,; M

Figure 12. The Extraction of the Hexavalent Actinide
Nitrates by 10 vol £ TOA in Xylene.'®*
 

 

 

 

 

 

 

 

i
B
‘ —
0! =
-— A
-3

D 0 —?_
3
and
ra
|°“" / ":_.."
-

10" J ] 1
o 2 4 S 8 10 12 14

Agueous HNQO,, M

Figure 13. The Ext-action of Pentavalent and Trivalent
Actinide Kitrates by 10 vol % TOA in xylene.'®®

- 81 -
(TIOA) in xylene from aqueous 5M nitric acid solution containing
ferrous sulfamate. For further separation, the neptunium-bearing
organic solution was scrubbed with 5M HNO, containing ferrous
sulfamate. Final purification of lp was achieved with a TTA
extraction.!?*»!%% 23N, hag been separated from 2*’Am by
extraction with TIOA.'®* Np(IV) was extracted i > 20) from 0.1
to 10M HNOy with 0.1M tetraheptyl ammonium nitrate in xylene.

The K was >2000 in IM HNO;.''” pistribution data for a large
number of clements in quaternary smmonium compounds from various
solutions have been determined, and a proceclure for separating

Np and Pu with thix system has been reportexl.'®®

Keder'®® has reported the distribution coefficients from

tetra - and hexavalent Np, Pu, and U from HC] solutions into TOA

(Figures |4 and 15). Pu(lV) is much more extractable than Np(1V)
and U(IV) under the same conditions, and the hexavalent actinides

are more extractable than the tetravalent in this system.

Np(IV) and Pu(IV) were strongly extracted from sul furic
acid by the primary amine "Primene” JM-T in xylene. In general,
the order of extraction of Np(IV) and Pu(IV) from sulfate solution
was primary >> secondzry > tertiary amine.’®® Many more proce-
dures for acine extraction have been reported for U and Pu, and

these methods also offer potential for Np separation.*t.'??,79!

Mixred Extraotoite (diluents;. The term synergism is used
to denote enhanced (or depressed) extraction of metals by mixed

extractants (diluents) as compared to extraction by each extractant

 

* Registered tradename of Rohm and liaas Co.
- 82 -
 

 

 

“
A 10 /
1.0 ' 0"
10~ 0~?
Efium
® lip () .
-2 0~
10 ¢ ()
0o 2 4 3 o 0
HCI. N

Figure 14. Extraction o U(IV) and Np(IV)
’ by 10X TOA and Pu(IV) b ’1‘.01
TOA from HC! Solutions.

- 8% -
 

 

 

 

 

 

 

 

 

i
*E
10 -
~ -
- -
o el
D 'oo P -
- 3
o -
puone —g
w! E- —
aud unf
0 2 4 8 S 10
HCi, W

Figure 15. Extraction of Hexavalent U, Np, and
Pu from HC1 Solution with 1.0X TOA
in Xylene.!??
(diluent) taken separately. The rang» of phenomena described
under the term synergism is diverse, :omplex, and not completely
understood. A review of this subject is given by Marcus,'’?®
Although the subject has received considerable attention, only

a few examples are reported for Np. Lebedev et al.?°? have
reported a procedure to determine ?“’Am through its daughter
product *Np in solutions containing large quantities of curium
and fission products. 0.1M ]l-phenyl-3-methyl-4-benzoyl-pyrazolon-5
(PMBP) and 0.25M tributylphosphate (T3P) in benzene were used to
separate Np(IV® from Zr, Nb, Cs, Ce, \m and Cm in 0.5M HNO, and

IM H4PO,. More than 99% of the Np was extricted with <0.1% of

other elements. The 2“’Am was determined by measurement of the

gamma activity of the extracted ?Np.

Taube?®? has discussed the influsnce of polarity in two-
component diluent mixtures of chloroform, benzene and carbon
tetrachloride on the extraction of Np(IV) and Np(VI) complexes with
several phosphate and amine extractants. The results are inter-
preted in terms of the size of the complex species, the diluent
structure, dipole interaction between complex and diluent, and
other factors. Figures 16 and 17 show tne effects of variation
of diluent mixtures on the dis*ribution of Np{IV) and (VI) into

TBP and tetrabutylammonium nitrate from nitric acid.

- 85 -
@*———LHC1 3 /CeHp—m
| T T T

 

Qo

¥ "l!‘l'

Distribution Coefficient

 

 

 

 

0.2 Od‘ 0.6 0.8 1.0
Mole Froctions of Diluens

Figure 16. Neptunium Extraction with TBP frrom
5M HNO; into Diluent Mixtures.?’?
 

o
I
-

"

Distribution Coefficient

o
-

 

 

 

 

0 0.2 04 0.6 08 1.0
Moie Froctions of Dilvents

Figure 17, Distribution Coefficients for Np(Iv)
Extraction with 10-2M Tetratwutyl-
Ammonfum Nitrate from 3M HN(, Using
Mixtures of Different Diluents,2°?

- A7 -
C. ION EXCHANGE

Many variations of ion exchange are used for separating
Np from other ions. Np ions in dilute mineral acids with no strong
complexing ions are sorbed by strongly acidic cation exchange
resins, such as sulfonated polystyrene. In general, the ability
of cations to be sorbed on cation exchargers increases with
increasing charge and decreasing hydrated radius., Thus, the order
of sorbability on cation exchangers for Np is Np(IV) > Np(III) >
Npoz2+ > Np03. All Np species are sorted at low acid concentra-
tions and eluted with high voncentraticrs of mineral acids;
elution of NpOZ proceeds first and Np(IV) s last. Some anions
form neutral or anionic complexes with c¢ifferent oxidation states
of Np, so that Np may be eluted by this mechanism. Both Np(V) and
Np(VI) are slowly reduced to Np(IV) by common organic base resins.
For this reason and because cation exchange of Np(IV) cffers
limited selectivity in the separation from other multivalent
cations, this method has not been used widely for analytical

applications.

Anion exchange is one of the techniques most used for
separation of Np in analytical and process applications. The
method is simple to perform and yields excellent separation from

many other elements, including most of the fission products.

lon exchange has been the subject ¢f many reviews., The

books of Helfferich,?°" Samuelson,?°® Anphlett,?’® and Rieman anc
Walton?®? are good references to the theury and applications of
ion exchangers. Other reviews of ion exchange include Massart,2°°®
10

h,299,211

Korkisc and Faris and Buchanan.

Anion Exchange. Np(1V) forms anionic nitrate and chloride
complexes that are strongly sorbed by anion resins; the anionic
species provide separation from the cations of many other elements.
The hexavalent state of the actinides al:io form strongly sorbed
anionic chloride complexes. Greater sep:iration of Np is attained
from most other elements in the nitrate system than in the chloride
system. The distribution coefficients o many elements over a
wide range of nitric acid and nitrate concentrations have been

reported. Data are given in Figure 13,

In a typical anion exchange cycle, a sample containing Np
is adjusted to 7 to 8M HNOy for optimum sorption of Np(NO3)e?~
ions, and 0.01 to 0.05M ferrous sulfamat: is added to ensure that
all Np(V) and Np(VI) is reduced to Np(IV). The solution is heated
to 55°C for 30 minutes or treated with sufficient sodium nitrite
to react all the sulfamate and oxidize excess Fe(II) to Fe(III);
this treatment is necessary to prevent excessive gassing in the
resin bed. The resin is washed with strong nitric acid to remove
Zr, Ru, Pa, Fe, Al, rare earths, U, transplutonium elements, and
most other cationic contaminants. Th(IV) and Pu(1V) are not
separated; however, washing with 5 to 15 bed volumes of S to

6M HNOy-0.05M ferrous sulfamate-0.05M hydrazine reduces Pu(IV) to
_OG-

  
 

  

N0 ADE. - WO ADDORPTION FROM Oi-H R 1Oy
B ADD. - SLIONT ADGORTFTiON

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 18. Sorption of the Elements from Nitric Aciczl §olut1’ons
by Strongly Basic Anion Exchange Resins.?!
Pu(IIl), which is removed from the column. Washing with 84

HC1 removes Th. The Np is eluted with 0,.3M HNO;. Cross-linking
and particle size of the resin greatly influences the separation
from other cations as well as elution of the Np. !32»213-215
Macroporous anion resin is superior to gel-type anion resin for
separation of Pu from Np.2!®*3 A number of similar procedures with
variations in acid concentration and substitution of semicarbazide
or aminoguanidine for hydrazine have been reported.

The separation of tracer amounts of Np(VI), Th(IV), Am(III),
and Pu’IV) in nitric acid by anion exchinge has been reported.2!®
The feed was ad:iusted to 7.2M HNO;-0.054 NaNO; at 50°C to yield
Np(VI) and Pu(IV). After sorption on "Jowex" 1-X4 resin, the
column was washed with 7.2M HNO,; to elute Am(III} and Np022+,
then with 4M HNO3 to elute Th(IV), and finally with 0.35M HNO,
to elute Pu(IV). Other work with macro quantities of these
cations has shown incomplete separation of Np probably because
of some reduction to Np(IV). Also, Th(I[V) and Pu(IV) were not
completely separated. The separation o Np from fission products
in 7.SM HNOy using ascorbic acid reductant is reported by

Ichikawa.2?!?

Radiochemically pure Np has been p:repared for production of
high purity metal with one nitrate anion exchange cycle and two

chloride anion exchange cycles successively.?!'®

The distribution coefficients of miuny elements over a wide

range of hydrochloric acid concentrations have been reported.

- 9] -
These data are used to design separation systems for chloride anion
exchange (Figure 19).’2"21’ Np, Th, and Pu are separated by
chloride anion excharige by sorbing the anionic chloro-complexes

of Np(IV) and Pu(IV) in 8 to ]J2M HCl. Pu(IIl) is eluted with

NHyI in 8M HC1, NH20H-NH,I in 12M HCl or Fecl, in 8M HCl; Th is

156,429 pictribution

not retained; and Np is eluted with 0.3M HCL.
data for 65 elements on "Dowex" 1-X8 from 2 to 17.4M acetic acid
in water have been reported??! (Figure 20), Examples of several
separations including U and Np are given. Distritution data for
60 elements on cation exchange resin from 1 to 17.4M acetic acid

in water have also been reported.22? With Np(VI) in 7.9M HC,H;0,,

equilibrium was not reached even after 40 hours of mixing.

A method to separate and determine Np, Pu, U, Zr, Nb, and Mo
in mixed fission products by anion exchange with HC1-HF solutions

d.??? Trace quantities of Np have been separated

has been develope
from macro amounts of Zr and trace amounts of Nb by elution with
HC1-HF solutions.?2" Also, HC1 and HF solutions have been used
to separate U, Pu, and Np from each other ard from alkali metals,
alkaline earths, rare earths, trivalent actinides, Al, Sc, Ac,
Th, Y, and N1 (Figure 21).%%2% (Controlled elution with a series
of solvent mixtures was used to separate Np, Pu, Zr, Nb, Mo, Te¢,

Te, and U from fission products.?2¢

The chloro complexes were
sorbed on anion resin and sequential washes with 12M HC1-NH,OH-NH,I (Pu),
10M HC1-Aq H:02 (Np), 9M HCi-Aq H;0, (Np and Zr), 9M HCl-ethanol

(1:i, 2r), 6M HCl-ethanol (1:1, Nb), ethanol-1M HCl1(4:1, Te)},

 

* Registered Trademark of Dow Chemical Co.
- 92 -
»26-

 

[l

" ods. - MO ADSORPTION Q¢ c A HCLeR

i, ods. - SLIGHT ADSORPTION N 12 & HC!
{0350g1)

sir.ods. - STRONG ADSORPTION O, » ¢

 

 

 

LOS OISR, COLFT., D,

 

 

 

 

Figure 19. Sorption of the Elements from Hydrochloric Acid
Selutions by Strongly Basic Anion Exchange Resins, ?!®
 

 

 

 

 

W

14

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

l'.’.r-lltl

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_M 4 A i
r R AFYd ER
2 .+It.__ ——— 3 - [L W.H..hd NqAIL -
. —— . — L - et
ety B i) 1=
v v " - = - ™
< # faads ] e 44 LD
- m.irdmn ..mm- hf fl.lrla\rdl._r “H .
5 ® Eoo i By Fet
m : «B J .r;\blllh- v : . "y 41 Y
] M*TL r“o —— E“-. TH. lfi +
-« o r’L‘.a.!T.rn “:-!I»PIOII@IL aE. “
i — Al
— H.O..L.L i e 5 —= T S . i
5 ~ddli .4 o - ..l\.‘“’&| - IdNEL E
¥
N |4..4.|+I¢_|1 *I.l.dl w IFIII.TL. | w.. e
| . IIFHH...L | I » JJwI.Tfl[ T*.l’tfl..llnsl lrl.mn...l.wL I.._ 4
b —— gl ey - g + -
bt et fiw.nla.nupl 21 -t
l|.l.”||fl|L A i o e ~ bj 1 m — w 1T

 

 

 

Sorption of the Elements from Acetic Acid Solutions by an Anion-Exchange Resin22}

Figure 20.
Figure 21.

 

5 T T 1 1

Igg HC!
4% om HeI-0.09M NH,) ~

< 50° &M HCI-0.1M HF

O ( - SN NCIUIM WY

B tined 0.5M HC - 1M HF
- tle- N . o e
§ 3 merns N [50° —
g v

O

! ;z b ’b -
:

o«

 

 

 

 

 

 

 

 

 

4
\
ofi—i‘g‘“fij 10 i ”t;_—-]

Eivent Volume, column volumis
Uranium-Neptunium-Plutonium Separation by Anion

Exchange ("Dowex" 1-X10, <400 Mesh, 0.25 cm?
x 3 cm Column) 223

- 9% -
othanol-6M HC1(4:1, Mo), O.IN HCI(W1), and 4M HNO, (Tc).

Other literature has included a study of the elution charac-
teristics of Np, Pu, U, Pa, and 2r in HC1, INO,, and H,SO. systems
with "Dowex''-2 an’on resin. Fquilibrium data were given for cach
acid from 0.1V to concentrated, and possible separations based on
equilibrium daza were summarized.??’ Fquilibrium data were given
for a number of elements including Np in 0.1 to 30N H,PO. with
“Dowex'-2 resin. Separation of Np from Cs and Te was attained,

but data were erratic.??®

Np has hcen separated from Pa by elution with 12M HC1-0.5M IIF
with Pa eluting first.”'" Separation has also been achieved by
clution with SN HCl from anion resin, in which case Np eclutes

firse. ???

Np(IV) has heon sorbed quantitatively on "“Dowex’-1 from 0.IM

Na;00, and eluted with NH,C1 or dilute HC1.???

Np(VII) forms stable alkaline solutions as the 5p0s'- ion.
Novikov 22 al.?'! studied the anion exchange hehavior of this
soluble complex as a possible basis for separation from other
clements. The sorption was irreversible for all experiments; this

was attributed to the reduction of the Np(\Vll) by the resin.
An anion exchange method using the nitrate system has been
reported for removal of Np before spectrochemical determination

of cationic impurities?’? (Procedure 23, p 200).

In several reported instances, anion exchanje resin exploded
or ignited after use in nitric acid or strong ni:rate solutions.???
These accidents are thought to be due to nitration of the skeleton
of the exchange resin, leading to the spontaneous reaction in the
presence of heat. Anion exchange resin in the nitrate form
should not be stored in the dry state, and temperature should be
carefully controlled at <60°C when used in stronj nitric acid.

The nitric acid concentration should be <8.5M, and flow to the

column shculd not be interrupted, particularly wihen high levels

of radioactivity are in the column.

Cation Exchange. Sulfonic acid type resins have had limited
applications for Np separations because both Np(VI) and Np(V) are
reduced slowly by the resin.’'" Several separations have been
reported for the pentavalent state of Np. Y. A, Zolotov and
D. Nishanov??® reported the separation of Np from U, Pu, and
fissior products by elution of Np(V) ahead of U(VI) with 1M HNO,
from a cation resin in the hydrogen form. Np was initially oxi-
dited to the hexavalent state with bromate. Separation of Np
depended on reduction to Np(V) by the resin. Also, cation
exchange Las been used for partial separation of Np from Pu(IV),

Th(IV), and Zr(1V). Np was oxidized to Np(V) in dilute nitric

- 97 .
acid before sorption on the resin, but a few percent of the Np(V)
was reduced to Np(IV) by the '"Dowex"-50W re«in and was not

separated from the other cations,?3?®

The distribution coefficients for many of the elements were
determined in 0.1 to 12M HBr with ''Dowex"-5C resin. Conditions
for separation of U(VI) and Np(IV) and separation of Np(IV) and
Pu(III) were given (Figures 22 and 23). Mary other separation
methods for Np could be devised from the distribution data

(Figure 24).%%7

Np and Pu have been separated by elution from cation resin
with HF after reduction to Np(IV) and Pu(IIl) with S0,.%2%® Np(IV)
was eluted first with 0.02M HF?}?, and then Pu(IIIl) was eluted
with 0.5M HF. Also, Np was separated from Pu by cation exchange

with HBr followed by TTA extraction.2?“?

Pressurized elution development chromatography on cation resin
at 70 to 90°C with a-hydroxyisobutyric acid has been very useful
for separation of trivalent actiride elements both in the labora-

! Although no specific

tory and with macroscopic quantities,?"
separations of this type for Np are reported, the method is useful

for highly radioactive solutions.

Distribution data for many of the elements on "Dowex'.50 resin
over a range of hydrochloric acid concentrations and also over a
range of perchloric acid concentrations have been reported (Figures

25 and 26).%%°

- 98 -
 

A
-
-
.
—‘I
-4

 

-~ ug— Sample
L.
L 9M HBr
2 \Np(w)
utvi} r

|
]

Concentration (arbitrary units)

 

 

 

 

 

o 4 O 1 &o___ J‘_ @j

O 2 4 6 8 10
Column Volumes

 

Figure 22. Separation of U(VI) and Np(IV) by Cation Lxchange
("Dowex* 50-X4 0.2 cm® x 2 om Column, 25°)2

 

 

 

 

 

 

3 T T 1
-
€
2 _9M HBr - 0.2M HF
:‘ e ettt ...J
£
3 Pu(OI} Np{IV)
2
f!_ I+ —
:
v
o e B e
0 4 8 12 [

Column Volumes

Figure 23. Separation of Pu(lll) and Np(IV) by Cation Exgl;gnge
("Dowex" 50-X4, 0.28 cm? x 3 ¢m Column, 60°)

- 99 .
- 001 -

 

Figure 24.

 

 

 

 

 

 

= R
&Ko ot o0 Lx}
toghsll |l 2o« @ NAR R Ll \B+ a0

He
ah Kot

Rt
e ptl) i3 ol o W8

 

Elements from HBr Solutions by a Cation Exchange

Sorption of the

Resin.2??
101

 

     
  
   
  

   
 

 
 
   
 

 

 

 
  
   

        
 
     
   
 
      
  

 

 

 

  

 

 

 

    

 

 

(Y =71 4
g'L-. -4 E)' ] -
1 b b -3} P NO,
113 ELEMENT ao #
b e I %2 i - prewen 0reee
“TT""'{ t:h-_-hfl =
- oy .V—’ P
'.hy - »!‘u +—| &
Padl b 3 PO,
- ét l 4 —i—- — - P
\h‘- ‘e asane

 

 

 

s ot el
v

[

;

pood
BT
e
T
e
]

-
i
»" '..,u..\ '!’ '
-y ]
=<
B__?.__.,___,..‘ -
T
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Ry, P
‘ A yIr hu 4 m n 1

       
   

      
   

g«l
Qlwd

8t

Sy

8,
QIiey

4(!
Clemed

& ot
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o

 

 

 

 

 

 

 

 

 

 

    
  
 
   

        

   

  

 

      

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

rer man nr i
- —— —_——— — 11—

i 4 8,4t 8,41 &« L OB st
\ T . dewwew |lotcwin]|ozmn 0. beapend ;A Abeamag
r;iA L‘ o1 a1, ‘_IAIL al s Al 2 2 3 a1 4 R4
el L

T
e a ey

P
_1r_1

ity

 

Figure 25, Sorption of the Elemen}g from HC] Solutions by a
Cation Exchange Resin.
- 201 -

     

"

 

v Y

P
- ELEmEnT -

 
 

o,

   

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N ANQ p
OXiDATHON
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- i l 4

0O 4 & 7
MOLARITY HCK,

 

 

LOG OISTR, COEFF
~

   

o

 

 
   
   
 
 

v

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

800 400
eh e

 
    
 

Figure 26, Sorption of the Elements from HC10,

Solutions by a Catfon Exchange Resin.??®
Inonganioc Ion Exchangera. Inorganic exchangers have been
largely superseded by synthetic resins principally because of
higher capacities and more useful physical characteristics of
the synthetic resins. However, inorganic exchangers have the
advantage of greater resistance to radiation damage. The distri-
bution coefficients of 60 cations, including Np, on hydrous
zirconium oxide, zirconium phosphate, zirconium tungstate, and
zirconium molybdate have been measured.?“? Shafiev et ai.?"?
have studied the separation of Np, Pu, and Pm on zirconium
phosphate. Np(V) is not retained while trivalent elements are
readily eluted with IM HNO);. Pu(IV) is eluted with 0.5M HNO,
containing reducing agents such as ferrcus sulfamate or hydro-
quinone. Zirconium phosphate does not change the oxidation state
of Np{V). The sorption of Np, Th, and U from HNO,, H-S0., and
HF solutions on ammonium molybdophosphate (AMP) columns has been
determined.?*"*2*5 The sequence of sorption is Np(IV) > Th(IV) >>
U(VI) >> Np(VI) > Np(V). These same workers demonstrated the
separation of Th, U, and Np using columns loaded with AMP,6?%%
Tsuboya et al.2'” demonstrated conditions in a HNOy system for
separating Np(IV) and U(VI) with a tung:tic acid exchanger; Np(IV)

is much more strongly retained than U(V) from 0.5 to 2N HNO,.

- 103 -
D. CHROMATOGRAPHY

Extraction Chromatography. Extrac:ion chromatography has
been applied to the separation of Np, Pu, Am, and U with 100%
TBP sorbed on diatomaceous silica. The diatomaceous silica was
initially exposed to dimethylsilane vapor, then treated with TBP,

and used as the stationary phase. Nitric acid, with and without

ing 9

reducing agents, was used as the mobile »hase. Other workers?"
used this system for a similar separation of Np and found that
modifications were required to prevent reduction of Np{VI) to
Np(V) and to improve separation from some fission products.
Eschrich?3® used the same system to determine the oxidation states
of Np by eluting with 0.5 to 2M HNO;. The order of elution was
Np(V), Np(1V), and Np(VI). It is probablz that some reduction of

Np(VI) occurred.

239Np was separated from fission procucts and U on a column
of TTA sorbed on glass powder.?®! The chromatsgraphic method gave
much more effective separation than batch extraction; recovery was
adequate so that isotopic dilution was not necessary. However,
two column separations were necessary to s:zparate Np frrm .r.
Wehner et al. 252 have also reported separition cf *3’Np from
fission and activation products on Poropak-Q impregnated with

TTA~0-xylene.

Some workers have used "Kel-F"* or '"Teflon"** powders coated

with an organic extractant as the stationary phase for extraction

 

* Registered tradename of M. W. Kellogg Co.
**Registered tradename of Du Pont.

- 104 -
chromatography separations. ''Kel-F'" powder :oated with trilaurylamine
nitrate has been used to separate Np from U, Pu, and fission

products. The feed was adjusted to 2M HNO; - 0.1M Fe(SO3NH;), and
passed through the bed. After the column wa:; washed with IM HNO,
containing Fe(SO3NH2)2, thc Np was eluted with H2S0, - HNO,.

The method is very selective for Np(IV) and has yielded chemically
pure ?2?°Np when the weight ratio of U to Np was >10!% in the feed?5?
The separation requires one to two days. A similar method was

developed for the coseparation of Np and Pu from U.%%"

Paper Chromatography. Paper chromatography Rf values for
elements Ac through Am in many mixtures of either HNQ3; or HCl
with methanol, ethanol, and butanol have been determined by
Keller.2%® It was necessary to reduce Np(VI) to Np(V) or (IV)
before starting the separation because Np(VI) is slowly reduced
in the column rcsulting in poor separation of the bands.
Neptunium(IV) was separated from Th(IV) with 12M HCl-butanol and
>8M HNO3-butanol mixtures. Also, good separation of Np(IV) from
U(VI) was attained with >1M HCl-butanol; Np(V) was separated

from U(VI) with 2M HCl-ethanol as developer.

Clanet?®® measured the R¢ values for elements with atomic
numbers 90 through 96 in mixtures of mineral acids with alcohols

and discussed analytical applications,

Rg values for Np(1V), (V), and (VI) have been reported for

paper treated with TOA using 0.5M HNO; developer solutions

- 105 -
- ae Al i ke AN fatcas

containing LiNOy, NH4NO,, or A1(NOj3)3;. The valuzs are well
separated for the different oxidation states of Np and for the

different actinides, 2%’

Rg values were also obtained for paper
treated with solutions of tetrabutylhypophosphate in acetone-
water (20:1) using developer solutions of nitric and perchloric

acid.?5?

Twelve fission and neutron capture isotopes including 23°Np,
have been separated from irradiated uranium with aquecus hydro-
filuoric and methylethyl ketone-hydrofluoric acid mixtures as

developers.?5?

Thin Layer Chromatography. Rapid separation of different
valence states of Np from each other and from cther actinide
elements by thin layer chromatography on "Teflcn"-40 powder
saturated with 0.IM tetrabutylhypophosphate solution has been

demonstrated.?%®

a8 Chromatography. Effective separation of the transuranium
elements by gas chromatography of their chloriies has been
demonstrated.?®® The volatile chloride complexes were synthesized
at A500°C by adding Al,Clg vapors into the carrier gas. The
experiments were carried out in glass capillary coluans maintained
at 250°C with less than one microgram of each actinide. Cm, Am,
and Pu were eluted in order of decreasing atonic number in about
the same position as lighter lanthanide elements in a similar

experiment. The retention times of Np, U, and Pa are much

- 106 -
shorter; it is postulated that the tetrachlorides of these elements
are produced. The chromctogram is measured by collecting fractions
of Al;Cle condensate at the exit of the column. The actinide
hydroxides are carried with La from strongly basic sclution and
separated from Al. Then the actinide is deposited, and the alpha
spectrum is measured with a surface barrier detector and multi-

channel pulse height analyzer,

E. OTHER METHODS

Volatilization. Separation of more-volatile Np{IV) chloride
from Pu{lIII) chloride and other less voletile chlorides has been
reported.?%!+2%2 The actinide chlorides were prepared by passing
carbon tetrachloride vapor at 650°C over mixtures of plutonium-
neptunium oxides or oxalates. The nepturium chloride sublimate
was collected with a separation factor of "3 x 10° for Np initially
containing 4% Pu; the yield was 96%. Tle method is useful for
obtaining quite pure Np where a quantitative separation is not

required.

NpFe is quite volatile, intermediate between UFg &and PuFg.
Separation was attained from UF¢ by co-scrption of the hexafluo-
rides on NaF. Then the NpF¢*NaF complex was reduced, and the UFg

desorbed. After refluorination, the NpF¢ was desorbed,?®?

Electrophoresis. Clanet?®® has developed an electrophoretic
nethod on cellulose acetate membranes to separate the charged

species formed by elements with atomic numbers 50 to 86 in 1 to

- 107 -
12M HC1 and HNO;. Mobility curves have beer obtained for the acid
concentration range for both acids. A large number of potential
separations of these elements and the solution conditions are
tabulated, Some of the separations of Np irclude Np(IV) or (V)
from U(VI); Np(IV) from Pu(IV) or (VI); Np(1V), (V), or (VI) from

Am(ZiI) and Cm(III); and separation of the c¢xidation states of Np.

Electrodepcaittion. Although electrodeposition has been used
to prepare mounts for radiometric measurement, electrolysis has
not been used as a separation method. There has been one report
that U, Pu, and Np were separated by electrolysis from HNO, by
varying the pH. Optimum conditions were stuted as current density
750 to 1000 mA/cm? with a plating time of 2 to 3 hours and solution
volume of 20 to 30 ml. Np is completely deposited at pH > 9, and
Pu and U are completely deposited at pH <6 und pH <3, respectively.?®*
Other workers using different media for electrolysis have been
unsuccessful in separating Np from other ac:inides. Although

partial separation from a number of common cations has been attained,

no useful separation method has been reported.

Miscellatecus. An analytical schewme has beern described which
yields sequential separation of the elements including Np remaining
after neutron exposure of 1 mg of a fissile dlement.”** The
products were separated and isolated for determination of isotopic
abundance by mass spectrometry using solvent extraction, ion

exchange, extraction chromatography, and precipitation methods,

- 108 -
VIII. ANALYTICAL METHODS

A. SOURCE PREPARATION AND RADIOMETRIC METHODS

Counting. Because counting methods are more se.sitive than
chemical or spectrochemical methods, they are the primary methods
for identifying and quantitatively determining Np. The two most
common Np isotopes are 2'’Np and *?’Np. ?*7vyp is usually determined
by alpha counting its two major alpha transitions at 4.781 and 4.762
MeV. If ?'"Np has decayed for a period of about 6 months or longer,
it can be determined by gamma ray spectroscopy of its 2''pa
daughter. If ?3’Np is separated from 2''Pa which has an B86.6-keV
gamma ray, the 2Y'Np 86.6-keV gamma ray can be counted directly.
239Np is determined by gamma counting its gaima transitions at
228 and 278 kev.'®

The gross alpha activity of 2'’Np can be determined with a
proportional counter or plastic scintillation counter. If other
alpha-emitting nuclides are present, an alphu pulse height
analysis with a surface barrier detector allcws a determination of
the percentage of the total alpha counts attributable to 2*7Np,

Liquid scintillation counting can be us«d to determine gross
alpha activity with almost 100\ efficiency ard in wmany cases can
be used to determine *’’Np in the presence of other alpha-emitting

nuclides. The energy resolution in liquid scintillation is 600 KeV
as compared to IS5 KeV for surface barrier detectors.

Gamma-ray spectrometry with either a Mal scintillation
detector or a Ge(Li) detector may be used o determine ?*?Np.
For 2’*Np gamma rays (228, 278 KeV), the energy resolution of a
typical coaxial Ge(Li) detector (about 1.0 KeV) is much better
than for Nal (about 20 KeV). The efficien:y of such Ge(lLi)
detectors relative to a 3 x 3 in. Nal dete:tor is 3 to 15% for the
1.23-MeV gamma ray. Ge(Li) low-energy photon detectors (LEP)
have an energy resolution of 0.5 KeV with lower efficiency.

An a-y coincidence method for determinating **’Np was

* The resolving time of

developed which increased selectivity.?®
the coincidence system was taken as 8 x 1(~% sec.
A radioactivation method was developed to increase the

> The activation product is

sensitivity for determining *3’Np.?®
short-lived ?°’Np which is determined by counting its 1.0 MeV

gamma ray. To obtain maximum sensitivity the Np should be purified
before and after neutron irradiation.

A summary of the sensitivity and sel:ctivity of radiometric
and radioactivation methods for determiniig Np is presented in
Table 23, In summary, alpha counting is the most convenient method
for 2*’Np, and gamma spectrometric methods are preferred for 23®Np
and ?*°Np. Because of the continuing advancements in nuclear
radiation detection systems, the sensitivity, precision, and

accuracy of the radiometric methods discussed above could be

- 110 -
SERSITIVITY AND fllflmn oF

TALE 13

MADISNITRIC S0 AABIOACTIVATION RETHODS
CETCRNTRAIVE REPTURIUN®®S®

Perainsibles tmowmr

 

 

is Yorms of
Seasitivily of Interforing ——
Isstape athed Nt had El omamt » p
weight Activity
<Ll
"y a-Commting 0.05 to 0.1 g 3y 510" o.m2
Meipg 1310 o002
ll‘” - gL
v 20 0.02
e -- R N
srb s0 -
"y a-Spec - 0.1 t0 0.5 ug 1ntpy 0.2 1
tremetry nipg 4xtp? m
lll~ — Ill‘
v S0 0.05
Fr -s 1t
sl 30 -
"y v-Spec- 0.01 to 0.1 ng Ny, 10 1t
trometry ninpy - 0.02
N irm 5x 10" 5L
l...ll.c. - fi-l
u 100 1
r -- 1
sl 10° -
17 a.v-Coln- 0.) te 0.5 ug 1ty 20 1010
cldouce iy 5210 50
(90 keV) " -- io' to 210"
P .- 0! te 10*
51 $0
gy S-Commting 10° uCi P -- 0.1
gy 1y, o 0.
1] (0.1 te 1)
51 (0.1 to 1)
" 7-Spac- 107" te iy -- 10
trametry 10°° oci e - 100
(100 kav) 1nbeltte, e.:
u 100 1
r -- 3
51 100
Py v-Spac- 10°° te ey, (>1) 1c*
trammtry lo-' aCl ll'~ (’l) ,Iol
(1000 LeV) v (»100) »19'
" - g.1
'
e e -- 2.1
l!l-
» - |
st 189)
"y Radioactl- 107" ug [wjgh L 1 10’ e 10°
wmtion by fimm of ) disy 1
y-mpec- o/ (ca’-s0e) ] ey 308 _
tram of
1np) Ochar >100 .
ol eumed s
rnr nyewl

 

FP - Fissiea Product
11 - Stebier isstopes

Durstisa
of
Amalyuin

10 ts &0

&0 to 200

17 to &0

5 to &0

14 10 180
improved with available advanced instrumentation,

Scurce Preparation. Direct evaporation is the simplest
method for preparing sample aliquots for counting. The
disadvantage for alpha pulse height analysis is the thickness
of the deposit, which results in self absorption of the alpha
particles. If a surfactant such as tetraethyleneglycol
(S0 ug/cnz) is added to the aqueous solution, t:he Np solution is
evaporated from a film rather than a drop resuiting in a more

267+26% The surfactant po.ymerizes on heating

homogeneous deposit.
and burns up when ignited. The diluted sample is transferred to

& suitable counting plate, e.g. stainless stee] disk, and slowly
evaporated to dryness to prevent spattering. The direct mount is
flamed to dull red heat, cooled, and coated with a thin layer of
collodion solution, and the Np is counted.

Electrodeposition has been widely used to prepare high-quality
sample mounts for precise alpha counting. The procedure is extremely
useful when samples contain a mixture of alpha emitters that need
to be resolved. Electrodeposition results in excellent sample
mounts from organic solutions that evaporate very slowly or leave
large amounts of residue and from aqueous solutions that contain
large amounts of dissolved solids.

Np and other actinides can be deposited from a variety of

electrolytes and under several conditions. Graves?®? described

- 112 -
a semiquantitative method for depositing 237Np from Li onto Pt.
Ko?7? reported a method for quantitative deposition of Np from
0.2M HC10, - 0.15M NH4COOH, and Mitchell?’! used NH,CI - HCl to
obtain a yield of 94%. Some systems used by other workers?’2 27"
are formic acid-ammonium formate, ammonium coxalate, ammonium
acetate, ethanol, isopropanol, and NH,C1l witl uranium carrier.
Donnan and Dukes?’°® developed one of the fastest procedures
for quantitative depositions by combining Mitchell's method with
uranium carrier addition. 23°U is added as a carrier in three
increments to the NH,Cl electrolyte to ensure quantitative vield;
only 20 minutes deposition time is required. An average recovery
of 99.8% with a relative standard deviation of #0.2% (n = 10) was
obtained with Pu. Similar results were obtained with Np.
Resolution of 20 keV is achieved consistently with electro-
deposited mounts and a silicon surface-barrier detector.

® reviewed electrodeposition procedures

Parker and Colonomos?®’
and described two new methods. One is a co-deposition method for
alpha-spectrometry, and the other for preparation of carrier-free
layers as fission detectors. In the co-depcsition method with
uranium carrier, ??’Np was deposited quantitatively in 10 min at
1700 V with stainless steel as the cathode.

In other recent work, Np was deposited quantitatively from

ammonium oxalate or ammonium acetate solution or mixed ammonium

- 113 -
277-280  A)cohol is an

oxalate-ammonium chloride electrolyte.
excellent plating medium for aqueous and organic samples. Methods
have been reported for ethanol, isopropanol, and alcohcl saturated
with ammonium chloride.2®'~2%% peposition from sulfuric, hydrochloric,
perchloric, and oxalic acid has been reported by Palei.?®*
The effect of variables on the quantitative de¢position on Np and
other actinide elements has been reported by other authors.?®%5'286¢
Other methods which have a lower efficiency but yield sources
with excellent resolution include vacuum sublimation and electro-
spraying.2%%°29! poth electrodeposition and ¢lectrospraying have
several disadvantages. These methods take a longer time than
evaporation and require special equipment including a specially
designed electrolytic cell for electrodeposition, high voltage
equipment, and special capillary with a needle electrode for

electrostatic spraying.?%®

B. SPECTROPHOTOMETRY

Although different oxidation states of Np have sharp absorption
bands, spectrophotometric analysis has had limited use because
radiometric procedures are more sensitive. Further, alpha contain-
ment is required for the spectrophotometer, anu operation within
a glove box is tedious. Generally, procedures used for other
actinides can be applied to the determination. Np is adjusted to
a single oxidation state, and the concentration is calculated

from the molar extinction coefficient and the absorption of the

- 114 -
sclution at the proper wavelength. When more than one oxidation
state is present, appropriate equations may be fcrmulated for the

concentration of each component,???2

Absorption Bande. Important absorption bands and molar
extinction coefficients of the different oxidation states are
listed in Table 24. Most of the sharp bands can be used for
qualitative or quantitative work even though they only obey
Beer's Law over a limited concentration range. The best band to
use for analysis of Np(IIll) is at 786 my tecause this band obeys
Beer's Law. The strongest bands for Np(IV) (960 mu, 723 mu)
do not obey Beer's Law, but they can be used with appropriate
calibration and constant slit width. The strongest band for
Np(V) (at 980 mu in 1M HNO,) does obey Becr's Law;2?® a high-
resolution monochromator (e.g., a double-grating monochromator)
should be used. Cauchatier' and coworker:;2°® have developed a
method for determining Np in irradiated nuclear fuels by measuring
the Np(V) band in IM HNO3. The pentavaleat state is produced by
adding hydrazine to a Np(V)-Np(VI) mixture obtained after
evaporation of the nitric acid solution. Correction for Pu(VI)
is necessary. The most useful band for Np(VI) is at 1.23 um;
Colvin developed a method using this band for measurements in
nitrate solution.??? In this method, Np is oxidized to the
hexavalent state with sodium dichromate, and then the acidity is

adjusted to 1 to 2M, The absorbance is measured at 1.23 um

- 118 -
TABLE 24
[MPORTANT ABSORPTION PEAKS OF NEPTUNIUMZ®?-297
Absorption Band (my)  Molar Extinction Coefficient

 

Np (111) 5524 44.5
607724 25.8
661%:4 30.5
7862+ 44 (50 to 60°C)
849 25
9910 27
1363 39
Np(1V) 500° n15
50494 22.9
590.59»9 16.1
600° n 7.5
715004 n 3.7
723b 127
74374 43.0
8oo® 21
g25%:9 245
960P 162
975° n32
Np (V) 4284 1.1
617029 22
v617°29 18
980” 395
990° n]180
Np (V1) 4767 6.4
5572 6.8
1223554 a5
1230%+9 a3
Np(VII) 412° 1370 +40
618¢ 382 +10
a. 1M HC10, .
b, 2M HC10w.
c. 1M HNO».

d. Obeys Beer's Law.
€. KOH Solution.

- 116 -
against a reference HNOs solution that i:; the same HNJ3; concentration
as the sample. The method has a relative standard deviation of
*0.5% at 3 g/. A number of ions, including Pu, do not interfere
when present in amounts ten times that o:® the Np. A study on heavy
water solutions of neptunium salts in wh:ch numerous well-defined
bands were found in the region 1.2 to 1.8 um is reported by
waggener.3?°

Color Complexes. Spectrophotometri: methods for Np lack
sensitivity. Furthermore, the position of the band extinction
coefficients are affected by some anions and by the Np concen-
tration. These disadvantages are partially overcome when color
complexcs that have very high molar extinction coefficients are
used, A method with arsenazo III [1, 8-dihydrcxynapthalene-3,
6-disulfonic acid-2, 7-bis(azo-1) benzene -2-arsonic acid] is
reported. %1393 The intensity of the s:able green complex
of Np(IV) and arsenazo III is measured a: 665 mu. The color
forms instantaneously, and its intensity is constant over
the concentration range 4 to 6M HNO3;. The molar extinction
coefficient at 665 mu is ~10°. Chudinov and Yakovlev separated
U(Iv), Pu(lv), and Th(IV), which form colored complexes, from
Np02+ by extraction with di-2-ethylhexylphosphoric acid (HDEHP) in
carbon tetrachloride. After extraction, Np is reduced to Np(IV),
and arsenazo III is added. The lower linit of detection is

0.04 ug/ml, and the relative accuracy is between 1 and 7%.

- 117 -
Bryan and Waterbury?®?

separated Np from U and Pu by extrac-
tion with tri(iso-octyl)amine (TIOA) before determining the
arsenazo III complex. They found that of 45 ¢lements teste,
only Pd, Th, U, Pu, and Zr interfered. The reclative standard
deviation was between 7.2 and 1.1% in 200-mg samples of 8.5 tn
330 ppm of Np. (Procedure 20, p192.) Novikor et al. have
studied the color complex of Np(IV) with Arsenazo M.*%“ At

664 my the molar extinction coefficient is 1.18 % 10% in 7M HCl

and 9.5 x 10" in 0.SM HC1.

Thorin was used by scveral workers to analyze Np.’'%%*306

The absorbance is measured at 540 mu against a reference solution
not containing Np. The molar extinction coefficient measured
with a Beckman DU spectrophotometer is 14,500. The precision of
the method at the 95% confidence limits is *2.1% for 0.63 ug of
Np/ml. Chudinov and Yakovlev used extraction to separate Np from
U and Fu interferences. The thorin method has also been automated®®’
with the Technicon AutoAnalyzer, and the precision has been
improved.

Np reacts in weakly acidic solution (pHv2) with xylencl
orange to form a colored complex with an abscrbance maximum at
550 mu and molar extinction coefficient of 5.5 x 10“.%%% Xylenol
orange is three times more sensitive than thorin but only one-half

as sensitive as arsenazo I[{Il as a reagent for Np(IV). The greatest

- 118 -
advantage of xylenol orange is that uranyl ions do not interfere.
Fe(III), 2Zr, Th, and Bi interfere.

Np(IV) forms a color complex with quercetin that is stable
in the pH range 3 to 7 and obeys Beer's Law over a concentration
range 0.4 to 4.0 ug/ml. The molar extinction coefficient is
2,3 x 10* at 425 mu. This method requires an extensive purification
to remove cations and traces of organic impurities.’°’

The color complex of Np(V) and arsenizo IIl exists over a
narrow pH range and was studied by Chudinov ind Yakovlev.3'? A
method with the green-colored complex of Np(V) and chlorophosphonazo

' Chemical separation

IIT was also Jeveloped by these workers.®:
or masking agents are required for a nurber of elements. Chudinov
has studied spectrophotometrically the interaction of 12 organic
dyes of different types with Np02+.3’2 He concluded that the most
promising reagents for pentavalent neptunium are 1-(2-pyridylazo)

resorcinol (PAR), arsenazo Ill, and chlorophosphonazo III. With PAR,

the molar extinction coefficient is 4.3 x 10" at 510 mu.

C. CONTROLLED POTENTIAL COULOMETRY

Determination of Neptuniwm Conzentration. Alpha counting is
generally superior to coulometry for determining less than a few
micrograms of Np; however, controlled poteiitial coulometry is an
accurate and precise method for determininj; Np above the 10-ug
level.?!'? The electrolysis cell contains a platinum electrode at

which the Np(V/VI) couple is titrated in 0.5M H2S0,. First,

- 119 -
the Np is oxidized to Np(VI) with Ce(IV), the Np(VI) and Ce(IV)
are electrolytically reduced to Np(V) and Ce(IIl), and then Np(V)
is coulometrically oxidized to Np(VI). The integrated current

in the last step is used tc calculate the concerntration of Np.
The standard deviation ranged from 6% for 7 ug to 0.05% for about
i mg of Np. As little as 2 ug was detectad. Elements which
significantly interfere are Au, Pt, Hg, Tl, and Cl1 ; Pu and Pd
cause only slight interference., Stromatt's method was used
successfully with a gold electrode instead of a platinum electrode
to eliminate the Pt/Pt(OH)2 reaction repo:-ted by'Fulda*"“

Fulda obtained a precision of *0.6% for 6 mg of Np. In another
application of Stromatt's method, the precision was 0.1% (n = 8)
for 9 mg of Np. Also, Buckingham®!® demonstrated a ccefficient
of variation for the coulometric method of *0.8% for neptunium
oxide and *1.1% (n = 11) for neptunium nitrate solutions.

Delvin and Duncan’'® used the same method in the presence of

7 used

nitrate with H;50, electrolyte. Plock and Polkinghornegl
coulometry to analyze solutions of dissolved alloys for both U and
Np without prior chemical separation. Propst?!® has reported a

coulomteric method for Np using a conducting glass electrode in a

thin-layer electrochemical cell. Organic contaminants interfered

and were removed by bisulfate fusion before coulometry.

- 120 -
Determination of Oxidation States. This method applies to
the (IV), (V), and (VI) states and was reportel by Stromatt.>!?
The analysis depends on the fact that Np(IV) is not cxidized, nor
is Np(V) reduced at a significant rate at a plitinum electrode in
IM H S0, electrolyte. The procedure is: (1) 1 potential is applied
at the controlled potential electrode to reduc2 Np(VI) to Np(V);
(2) Np(V) is electrolytically oxidized to Np(VI); (3) Ce(IV) is
added to oxidize Np(IV) to Np(VI); (4) excess Ze(IV) and Np(VI)
are electrolytically reduced to Ce(IlI) and Np(V); and (5) Np(V)
is electrolytically oxidized to Np(VI). Np(VI) is determined in
the first step. The difference between the integrated currents
for the first and second titrations corresponds to Np(V), and
the difference between the integrated currents for Step S and
Step 2 corresponds to Np(IV).

Determination of Oxidation-Reduction Poteiatial. The potential
for the Np(V)/(VI) couple was measured in sulfaric, perchloric, and

2 The potential in HCl

nitric acids with a platinum electrode.’
was not obtained because of reduction of Np(VI) by chloride.
The inability of the method to measure irreversible couples,

such as Np(IV)/(V), is a serious limitation. The potential for

the Np(III)/(IV) couple was obtained with a mercury electrode.

D. POLAROGRAPHY
Alternating current polarography with square-wave or pulse

polarographs has been applied to determine small concentrations

- 121 -
of Np. Slee and others’’* have reported an analytical method
with square-wave polarography to determine Np la Pu after pre-
liminary separation from Pu by TTA extraction. Np is back-
cxtracted from the TTA into 10M HNO,. After several evapora-
tions with nitric acid and wet ashing with mixed nitric

and perchloric acid (to oxidize organic material)}, the final per-
chlorate residue is taken up in | ml of HC1. I wmi of SM hydroxyl-
amine hydrochloride is added, and the solution is evaporated to
reduce the volume to 0.5 xl. Then, 0.5 ]l of IM EDTA is added;
the solution is adjusted to pH 5.5 to 6.5 with several drops of
ammonia and diluted to S ml. Exactly 2 =]l of the dilution are
transferred to a polarographic cell and sparged with nitrogen.
The Np peak is recorded at about -0.8V against the mercury pool
electrode on the square-wave polarograph. Theri an accurately
measured aliquot of a standard Np solution prepared in EDTA is
added to the cell, and the Np concentration in the original
solution is calculated from the increase in pesk height.
Interference from the oxidation of chloride ions is decreased

by adding EDTA to shift the half-wave potential of the Np peak.
The potential for the reduction of the EDTA complex is about

700 mV more negative than for the reduction of neptunium ions;
therefore, the peak is shifted well away from the anodic oxidation
of chloride ions and is well defined. The authors report

precision of *2% and *10% for concentration ranges of 500 and

25 ppm, respectively.
Cauchetier ¢t al.?*® reported a method which mskes use of
the Np(IV)-Np(i11) couple for determining Np in solutions of
irradiated nuclear fuels and ?’'Np targets. Np is reduced
electrolytically to Np(1V), and the polarogram is taken. An
aliquot of standard Np is added to the cell, and the procedure is
repeated. The method was used to analyie solutions with a Np
content >20 mg/L containing Pu, U, Fa, Ni, Cr, and fission
products, with a precision of 2\,

Polarography and other methods were used to compare the
chemistry of U, Np, and Pu by Kraus, ¢t al.’?! Jenkins used a
manua)l polarograph to study the nature and stability of EDTA
complexes with Np(II1) and Np(IV).’2? Np(II1) and (IV) were
studied in chloride and perchlorate media by Hindman and
Kritchevsky.®??

Np was included in a review of electrochamistry of the

&

actinides by Milner.'?" The sulfate complexes of Np(1V) were

studied polarographically by Musikas.®?’

E. TITRATION

Potentiometric. 10- to 100-mg quantities ¢f Np were determined
by redox titration.’?® Cc(IV) is used to tityate Np(V) to Np(VI),
and iron(Il) perchlorate was used to titrate Mp(VI) to Np(V). The
methods can be used successively on the same sliquot of sample
if HNOy is present (to give the required ceric oxidation potential)

and chloride ion is absent (it would be oxidi:ied to chlorine).

- 123 -
Stoppered weight burets were used for adding reagents, and a
platinum-calomel system was used to detect the end points. Relative
standard deviations for a single determination were 0.15% for
ferrous titers and 0.59% for ceric titers.

Complexomstrio Titration. Np(IV) is titrated with a solution
of EDTA at pH 1.3 to 2.0 with xylenol orangu as iniicator. The
reaction of Np(IV) with EDTA is stoichiometric and the color
changes from bright rose to light yellow at equal molar concentrations.
The error for determining 1 to 4 mg of Np i3 1 to 2%, Np(IV) is
produced in 0.01 to 0.05M HC1 with hydroxylamine reductant. Fe’®,
Zr'*, Pu", Th“’. and ascorbic acid interfere. Reasonably large
amounts of alkali, alkaline-earth, rare earth elements, Zn’*,
cd?*, co?*, Cr'*, Mn?*, Ni?*, and UO,2" do not interfere.’2®

Chronopotentiometric. There has been little analytical
chemistry done in molten salts, and so “ar the only useful results
have been obtained from electroanalytical methods. Np(IV) was
determined quantitatively in molten LiC1-K(1 eutectic at 400 to

500°C with an accuracy of +4%. %27

F. EMISSION SPECTROMETRY

Np has a line-rich emission spectra with the more-sensitive
lines at 4154.5, 4098.8, 3999.5, and 3829 X.%29732% Qther methods
are more useful for quantitative determina:ion of Np than the
spectrochemical method, which is generally used only for analyses
of impurity elements. To prevent interference by the numerous
spectral lines of Np, a chemical separation is usually made, or the

carrier distillation method with gallium sesquioxide is used.
- 124 -
A quantitative method for determinatior of impurities in Np

232

is reported by Wheat (Procedure 23, page 200). The method is

7% The neptunium

a modification of one reported by Ko for Pu.
oxide is dissolved in HNOs, reduced to the tetravalent state

with hydrazine and sulfamic acid, and then sorbed on anion

exchange resin. Two cycles of anion exchange are used to separate

Np. The second effluent is evaporated to dryness to decompose
hydrazine. The residue is made water soluble with aqua regia,
‘evaporated to dryness, and dissolved in 6M HCl containing Co as

the internal standard for the spectrographic anaiysis. The coefficient
of variation for a single determination of a number of common metal

ion impurities ranges from 9 to 24%. For a 50-mg sample, the

minimum concentration of impurities that car be analyzed is 0.5

to 10 ppm.

G. GRAVIMETRIC METHODS

Precipitation of Np for yravimetric determination is not a
useful method. 1If other ions which form insoluble salts are
present, these must be separated first. When the solution is
relatively free from other ions, alpha counting or some other
method is usually more rapid and offers less health hazard. A
number of Np compounds have low solubilities in aqueous solution;
however, indefinite stoichiometry or necessity for calcination
to the oxide limits the usefulness of direct gravimetric
determination. Often the small quantity or low concentration of

neptunium precludes the use of gravimetry.

- 125 -
Hydroxide. Np(IV) is completely precipitatod from mineral
acid solution by Na, K, or NH,OH as the hydrated hydroxide or
hydrous oxide. The brown-green gelatinous solid that forms is
difficult to filter but is easily redissclved in acids. The
solubility in IM NaNO, - IM NaOH is <0.,1 sg/t. Np(V) "hydroxide’
1% green; it is somewhat more soluble in a2 sodium nitrate-sodium
hydroxide solution. Np(VI) is precipitated as dark brown
(NH4) 2Np209+H20 with excess NH,OH from minersl acid solution.®?

Fluorides., Np(IV) is precipitated f:rom mineral acid solution
as green hydrated NpF, by adding excess H°. The compound dissolves
readily in reagents which complex fluorid: ion, such as Al’* or
boric acid. When K or NH.F 1is used as tho precipitant, the green
double salt KNp,Fy or NH NpFs is produced.

Peroxides. Purple Np(IV) peroxide is precipitated when a
large excess of H,0, is added to a strongly acidic solution of
Np(IV}, Np(V), or Np(Vl), because peroxide rapidly reduces
Np to the tetravalent state. Reduction is much slower in dilute
mineral acid. Np(IV) peroxide always incorporates some of the
anion into the crystal and may have different crystalline forms
depending on the acid contentration of the supernatant. Np is
separated from many cations by precipitation of neptunium
peroxide. '®

Oralates. Green Np(IV) oxalate hexiahydrate is precipitated
from dilute acid solution with oxalic acid. Because quantitative

precipitation is not attained for Np(V) >r Np(VI), a reducing

- 126 -
agent, such as ascorbic acid, is used to ensure complete reduction
to Np(IV). A granular, easily-filtered precipitate is produced
under controlled conditions.“® (NHy)WNp(C204)« and NpO2HC20,
have also been precipitated from Np(1V) and Np(Y) solution.

Todate. Light tan Np(IV) iodate is precipitated from dilute
mineral acid by adding excess potassium iodate.’'®

Carbonatae. The double carbonate of Np(V), KNpO,CO,, is
produced by adding potassium bicarbonate to a dilute acid solution
of Np(V), until the resulting solution is 0.IM in bicarbonate.
The solution is heated at 90°C for 3 to 4 hours to produce the
light tan double salt."’®

Acatate. Sodium neptunium(VI) dioxytriacetate,
NaNpO; (C2Hy02) s, 1s pink by transmitted light and pale green by
reflected light. Np is oxidized in dilute acid with KBrO; at
$0°C to Np022*. Sodium neptunylacetate is precipitated by adding
an equal volume of 4M NaNOy - 4M NaC,Hs0; solution.3®

Phosphate. Np(IV) di(monohydrogenphisphate) hydrate
[Np(HPO,) ;- XH,0], a pale-green gel, is precipitated by adding

phosphoric acid to a dilute acid solution of Np(IV).>®

H. SPOT TESTS
Spot tests for determining oxidation states of Np and Pu
were obtained for 36 organic and inorgani: reagents commonly used

in paper chromatography.??! The tests we:e made on Whatman No. 1

- 127 -
paper which was treated with 2M HC1 in descenling chromatography
for 12 hours to remove traces of Fe, Mg, and Ca, The paper was
treated with two successive 24-hour washings by migration with
twice-distilled water. Because of hazards of these alpha emitters
and the high sensitivity of radioactive measurement K very
sensitive spot tests with an identification limit of less than

1 ug of actinide were selected. Observations were pade in white
and ultravioclet light for both acidic and basic media with each
reagent. First the acidic media was allowed to dry; then ammonia
was added and evaporated. A standard scale ¢f colors was used
for comparison. In most cases, a color reaction was obtained
with less than 1 ug of actinide, but the colur was the same for
all oxidation states of both Np and Pu.

Diphenylcarbazide gives a color reaction with Np(VI) but not
Np(V); however, Pu(VI) gives the same color :reaction. In acid
solution, sodium alizarinsulfonate or arsenazo give a color with
Pu(IV) and Pu(VI), but no color with Np(V) and Np(VI). Four of
the reagents, chromazural-S, arsenazo, 4,2-pyridyl-azo-resorcinol,
and pyrocatechol, give fluorescent spots under ultravioclet light
with all oxidation states of Pu and Np; kojic acid fluoresces
only with Pu(III).

The oxidation states of Np and Pu were characterized from

color reactions on chromatograms and electrcpherograms.?®®

- 128 -
The tetravalent states give characteristic colors with alizarin,
arsenazo-I, and thorin-I; however, diphenylcarbaiide was used for

the hexavalent state.

I. MASS SPECTROMETRY

f ?*’Np were determined with a mass

Subnanogram quantities o
spectrometer by Landrum, et al.’''? The instrument was a double-
focusing, 60-degree sector type, with a 12-inch radius. The
source chamber contained a tantalum filament (from whick the
sample was volatilized) and a rhenium filsment (on which gaseous
species were ionized). After mass analysis, the ionized Np atoms
were collected in a Faraday cup. The method uses isotopic
dilution with 235Np or preferably 2%®™Np. This method is much more
rapid than neutron activation, and the sensitivity is at least ten
times greerer. The standard deviation for 0.1 to 0.5 nanogram
of Np was 1 to 2%. Isotope dilution with 27?Np has also been
applied to determine ?3’Np, 3?3

Spark source mass spectrometry is useful for less quantitative
measurements of many elements including Np; however, it is most
often used for determining cationic impurities in Np and other

actinides.?3"

J. X-RAY FLUORESCENCE SPECTROMETRY
The ease of production and simplicity of the X-ray spectra

produced for elements of high atomic numter allow mixtures of

- 129 -
actinides to be analyzed by X-ray fluorescenc: spectrometry with
considerable precision and accuracy. Either s3o0lid cr liquid
samples can be analyzed by the internal standard technique.
Mixtures of U, Np, and Pu were analy.ced at razios as high as
1:1:1; results were comparable to standard counting. U, Np, and
Pu in any combination of two elements were analyzed at ratics

as high as 1:8 without seriously affecting ac:uracy. However, at
ratios of 1:10, low results of 5 to 7% were n>tained for the
element present at lower concentration. The principal L series
X-ray emission lines of elements with atomic numbers 92 through
96 are given by Kofoed.33® Novikov et al.?%® used X-ray
fluorescence to determine microgram amounts of Np in pure
solutions or in solutions containing Pu. The sensitivity was
0.2 to 0.3 ug of Np. The relative standard error in determining
1 ug Np was 5%, and the analysis, including sample preparation,
required 30 to 40 minutes. The Ka) and Ka, X-ray energies for

Np, Pu, and Am were measured by Nelson, et al.?3’

K. NEUTRON ACTIVATION

Neutron activation was used to determine subnanogram quantities
of 2?7Np.??? The unknown sample was irradiated with another Np
sample of known Np content and comparable weight in the same

average time-integrated neutron flux. After irradiation,

- 130 -
the 2?®Np was determined by gamma spec:rometry. Conventional
radiochemical separation methods were used. Isotopic dilution
with mass quantities of 237Np served t» determine chemical

recovery.

L. OTHER METHODS

Gamma counting 239Np, the decay product of 2%3am, has been
used to determine 2"%Am in solutions containing large amounts of
Cm. The ratio of the equilibrium amount of “3**Np to the amount
of **3Am was determined by separating (by TTA extraction) and
analyzing (gamma counting) 239Np trom samples in which **3am and
zasz were known to be in secular equilibrium. The method was
compared to determining °“’Am by the isotope dilution-mass spectro-
metric method. The precision of the mz2thod was 7% at the 95% con-
fidence limits (n = 16) for sample alijuots that contained 0.1 to
5 ug of °“?Am.?® A similar approach sas reported by Lebedev et al.?°?

233pa, the daughter of 2°’Np decay, has more-abundant gamma
rays, which are easier to measure than 237Np. Cofield??® used
this as a basis for determining ?3’Np-2?%Pa in human lungs by
in vivo gamma spectrometry with a large Nal scintillation detector
in a low-background counting chamber.

The neutron capture cross section of 2%%U was measured by
analysis of 23%Np produced [2*%U(n,y)?%% & 239%p] . The procedure
uses isotope dilution with 237Np to determine chemical yield,

TTA extraction for separation of Np ard U, electrodeposition for

- 131 -
Np source preparation, and gamma counting’“’ fo: analyses.
Characteristic isomer shift ranges have besn measured
fcr several valence states of Np using MUssbauer resonance
of the 5$9.54-keV gamma ray of ??'Np. They exteard from about
-6.8 cm/sec to +5 cm/sec for the individual oxidation scates
of +7 to +3 and are clearly defined.?“'’?“? The isomer shift
charact.ristic of each oxidation state is useful for study of
bonding in Np compounds. Dunlop and Kalvius have also made

. . . . L1a
significant contributions,*!

IX. RADIOACTIVE SAFETY CONSIDERATIONS
The Np isotopes emit high-energy alpha particles, medium-
encrgy beta particles, and low-energy gamma ravs. The tendency
of Np tu concentrate in the bones with a biological half-life
of 7.5 x 10* vears makes ingestion the primary hazard to personnel.
Studies of the distribution of ?’’Np in animal tissue showed

131

60 to 80% of the Np was Jeposited in the bone-. Studies have

also heen made of the inhalation, pulmonary absorption, gastro-
intestinal absorption, and short-term retention of ?*’Np in rats,?"?
Because 2?7Np (T, = 2.14 x 10°y) is the only isotope of Np which

is available in weighable amounts, it presents the only serious
hazard. The radiati-n hazard is small due to the low specific
activity of ?’Np and the low energy of its gamma radiation. Table
25 lists body burdens and maximum permissible concentrations of

Iy

2375%p and ?'*N\p for continuous occupational erposure. In

- 132 -
handling large quantities of ?*’Np, standard gloved-boxes maintained
at a negative air pressure with respect to the laboratory air’“®
should be considered for containment.

Criticality is no problem for ?*’Np because the bare critical

mass for a sphere of density 20.45 g/m’ is 68.6 kg.'"®

TABLE 25
HEALTH HAZARD DATA FOR NEPTUNIUM [SOTOPES®**

Maximum Permissible
Concentration for
Max Permissible 40-hr Week (uCi/cc)

 

 

 

Isotope Organ Body Burden (uCi:' Water Air

2379p (sol.) Bone 0.06 9 x 10°% 4 x 10712
Kidney 0.1 2 x 107 7 x10°!2

Total Body 0.5 4 x 107 2 x 107!

Liver 0.5 6 x 107% 2 x 107!

GI(LLI) 9 x 107% 2 x 1077

(insol.) Lung 1071°

GI (LLI) 9 x 107" 2 x 1077

23%p (sol.) GI(LLI) 4 x 1077 8§ x 1077
Bone 30 100 4 x 107

Kidney 40 200 7 x 10°¢

Total Body 70 300 1073

Liver 100 500 2 x 1073

(insol.)  GI(LLI) 4 x10°* 7 x 107
Lung 2 x107°

- 133 -
X. COLLECTION OF PROCEDURES

A. INTRODUCTION
The procedures are divided into three categories:

® Procedures for extraction, extraction ch:omatography, iion
exchange, and carrier precipitation or some combination of
these nathods with highly radioactive samples. Most of these
methods utilize alpha counting (alpha pulse height analysis),
gamma spectroscopy, or possibly isotopic dilution. The
method of determination is not detailed for all procedures.

e Procedures used for environmental and biological samples.

e Miscellaneous procedures for quantitative determination,
including absorption spectrometry of color complexes,
coulometry, and gamma spectrometry.

B. LISTING OF CONTENTS
Procedure  Author Title cr Method Page
1 Moore!"® Separation ¢f Np by TTA
Extraction 138
2 Dorsett!®! Separation of Np by TTA
Extraction 141
3 Smith?*’ Determination of Z3INp in
Samples Countaining U, Pu
and Fission Products 145
4 Landrum?®“® Determination of Np 150
5 Slee et al,’?° Determination of Small

Amounts of Np in Fu Metal 155

- 134 -
Procedure

6

10

11

12

13

14

15

Author

Schneider?!?"*

Maeck et q/.!®"

Wehner et al.?2°?

Eschrich?"®

Roberts?!"

Nelson et ai.22°

Holloway et al.®?“

Jackson et al.3“?

Zagrai et al.?3?

Si11l23,12“,125

Title or Method

Determination of Np in
Samples Containing
Fission Products, U and

Other Actinides

Determination of Np in
Samples of U and Fission

Products

Extraction Chromatographic
Separation of ?’?Np from
Fission and Activation
Products in the Determi-
nation of Micro and
Submicregram Quantities

of U

Separaticn of U, Np, Pu,

and Am by Reversed Phase
Partitior Chromatography

An Analytical Method for
237Np Using Anion Exchange

Separaticn of U, Np, and

Pu Using Anion Exchange

Separaticn of Zr, Np, snd

Nb Using Anion Exchange

Separation of Np and Pu
by Anion Exchange

Separation of Np and Pu
by Catiorn Exchange

Separation and Radiochemical
Determination of U and
Transuranium Elements

Using Barium Sulfate

- 135 -

Page

158

161

163

165

167

169

171

173

175

176
Procedure

Type
16

17

18

Type
19

21

22

23

24

II

III

Author

Taylor?®?

Perkins! 33

Butler’®!

Granade?s?

Bryan et al.}'%?

Sairnov-

Averin et al.’?®

Novikov et al.?'*?

Wheat?3?2

Ermoloev et aql.3°%*

Title or Method

The Low-Level Radiochemical
Determination of 2*’Np in
Environmertal Samples

Radiochemical Procedure for
the Separ:ition of Trace
Amounts of 2¥Np from
Reactor Eiifluent Water

Determina:ion of Np in

Urine

Determination of 2¥'Np

by Gamma Ray Spectrometry

Spectrophotometric
Determination of

Np

Microvolumetric Complexo-
metric Mathod for Np with
EDTA

Photometi'ic Determination
of Np as the Peroxide
Complex

Separation of Mp for
Spectrographic Analysis
of Impurities

Photometric Determination
of Np as the Xylenol
Orange (omplex

- 136 -

Pfl‘fi

179

184

186

189

193

197

199

201

204
Procedure

25

Author

Stromatt?!?

Title or Method

Analysis for Np by
Controlled Potential
Coulcmetry

- 137 -

206
Procedure 1. Separation of Np by TTA Extraction
F. L. Moore!“®

Outline of Method

Np is separated from fission products, U, Pu, transplutonium
elements, and nonradioactive elements by extraction into
thenoyltrifluoroacetone (TTA). After separation, an aliquot 1is
suitably prepared for either alpha counting of ?3?’Np or gamma

counting of *"Np.

Reagents (C.F. Chemicals)
e HCl, IM
® HNO,, 10M

e Hydroxylamine hydrochloride (NH,OH+*HCl1l) solution, 5SM,
Dissolve 69.5 g of reagent in 200 ml of distilled water

and warm if necessary for dissolution.

e FeCl , v2M. Dissolve 40 g of reagent-grade FeCl;<*4H;0
tetrahydrate in 100 ml of 0.2M HCl. Store in a dark
glass stoppered bottile,

® 2-Thenoyltrifluoroacetone-xvlene solution, “0,5M,
Dissolve 111 g of compound in one liter of reagent-

grade xylene.

Equipment
e Extraction vessel with mixing device
e Hot plate
e Micropipets
e Stainless steel counting plates
e Counting plate heater

® Meeker burner

- 138 -
® Asbestos board
e Sample carrier

® Alpha proportional counter (or gamma counter)

Pretreatment

If interferences may be present in salution with the Np
tracer, Np is adjusted to Np(IV) and carried on 1 mg of La pre-
cipitated as the hydroxide. The hydroxide precipitates are
dissolved in IM HNOs, and LaFs is precipitated to carry Np(1V).
The fluoride precipitates are dissolved in a few drops of 2M Al1(NOs)s
and dilute HC1. While the extraction of Np(IV) from HNC, is
usually very effective, HCl should be used whenever possible
because there is a greater tendency to form extractable Fe(III)

ion in the HNOj3; system.

It is desirable to measure the chemical yield if much
chemistry is employed. A 2?7Np spike is vseful for determining

239yp recovery; 2¥°Np may be used for determining 2’’Np yield.

Procedure

1. Pipet a suitable aliquot of the sumple intc a separatory

funnel or other extraction vessel.

2. Adjust the solution to 1M HC1 - 1M NH,OHeHC1 - 0.25M Fe(Cl,.
KI may be used as a reductant in place of FeCl,.

3. Mix the solution for 5 min at amb: ent temperature.
4, Add an equal volume of 0.5M TTA and mix for 10 min.

5. Allow the phases to separate; then remove the aqueous
phase and discard it.

- 139 -
~4

Nash the organic phase by mixing with an equal volume of
IM HC]1 for 3 min. Allow the phases to sepa-ate and

discard the aqueous wash.

Strip the Np from the organic phase by mixing with an
equal volume of 10M HNOy for 2 min. (If the aqueous

strip is too high in gamma activity for alpha measurement,
the last traces of radioactive Zr and Pa may be removed
by a 5 min re-extraction of the 10M HNO, strip solution

with an equal volume of TTA.

Ordinarily, the small amount of Fe in the TTA causes
negligible self absorption in counting, and the TTA
extract is mounted directly on the counting plate. If
Fe is a problem, excellent separation is attained by
stripping the Np into 10M HNO,.

A suitable aliquot of the TTA extrict or the 10M HNO;

strip is prepared by conventional nethods for either

237

alpha counting for *’’Np or gamma :ounting for “’°Np.

- 140 -
Procedure 2. Separation of N? by TTA Extraction
R. S. Dorsett!?®

Outline of Method

Np is determined in the presence of Pu, U, fission products,
and other alpha-emitting nuclides by extraction into thenoyltrifluoro-
acetone (TTA) followed by alpha counting of the TTA. The analysis
consists of three parts: (1) the pre-extriction step in which
acid and oxidation state are adjusted, (2) the extraction in
which Np is quantitatively extracted into 1TA, and (3) the mounting
and alpha counting of the TTA extract. When additional purifi-
cation is required, the Np is stripped fron the TTA, acid and
oxidation state are adjusted, and a second extraction is done.
The precision of the method is dependent on the type and quantities
of interferences. The interferences caused by sulfate, phosphate,
fluoride, and oxalate ions are eliminated by addition of Al1(NO;3),
which complexes these ions. A coefficient of variation of 2% is

obtained with relatively pure solutions.

Reagenta

¢ Hydroxylamine hydrochloride (NH,0OH*HCl1), 1M, is prepared
by dissolving 69.5 g of C.P. grade compound and diluting

to one liter.

e (NaNO:), 1M, is prepared by dissolving 69 g of C.P. grade

comgcund and diluting to one liter,

e 2-Thenoyltrifluoroacetone-xylene, 0.5M, is prepared by
dissolving 111 g of the compound in one liter with

C. P. xylene.

- 141 -
¢ Ferrous sulfamate {Fe(NHS0,4)2]), 2M, is prepared by dis-
solving iron powder in an excess of sulfamic acid with
minimum heating. The solution |s filtered after dis-
solution.

® Aluminum nitrate [Al1(NOjy):], 2M, is prepared by dis-
solving 750 g of C.P., grade compound and diluting to
one liter,

e (HNO3) nitric acid solutions are prepared as required
from C.P. grade stock.

e Collodion solution, 0.5 mg/ml, is prepared by dissolving
S00 mg of collodion in one liter of 1-to-1 ethyl alcohol-
ethyl ether.

Equipment

e Centrifuge cones (with caps)

e Vortex mixer

® Micropipets

®» Stainless steel counting plates

e Counting plate heater

® Meeker burner

® Asbestos board

e Sample carrier

® Alpha proportional counter

e Alpha pulse height analyser

Pretreatment

Fluoride method. When it is not known what impurities are

present in the solution, Np(Pu) can be carrier precipitated with

La(OH) .

The hydroxide is dissolved in HNOy, and La is

- 142 -
reprecipitated as the fluoride. The fluoride precipitate con-
taining the actinides and lanthanides is dissolved in Al(NOs)i

and dilute HNOj;, and this solution is extra:ted with TTA.

Np in Tributylphosphate (TBP). 1f Np :s present in TBP or
other organic extractants, it is stripped w:th dilute HNO, ("0, 1M)

and then analyzed by the procedure.

Separation of Np and U. Acid control is very important for
this separation. In the analysis of low-level Np solutions that
contain large quantities of U, the prcblem is complicated because
237Np and 2°“U have the same alpha energies. Also, the specific
activity of 2%*U is 10 times greater than 2?’Np. An accurate
analysis is assured by (1) close control of :he extraction acidity,
(1 +0.1M}, (2) a double extraction cycle, and (3) in extreme cases,
a fluorophotometric determination of U conternt of the final TTA

extract.

Proaedure

1. Pipet 10® to 10" dis/min alpha of ?*'Np into a 15-ml
centrifuge cone.

e

Add sufficient water or HNO; so that at the end of Step 3
the acid is 1M. Mix.

3. Add 1 ml of 2M Fe(NH2S03)2 solution., Mix and let the

solution stand for 5 min.

4. Add 3 ml of 0.5M TTA in xylene, and mix for 5 min in a

vortex mixer.

S. Allow the phases to separate; then renmove the aqueous
phase and discard it. Add 4 ml of IM HNO, to the organic
phase, and mix for 2 min in the vorte) mixer.

- 143 -
10.

11.

12,

If the alpha activity due to Pu and U is <10? dis/min,
proceed to Step 9. If the alpha activity is >103,
proceed to Step 7.

Remove the aqueous phase from St2p 5 and discard it.
Add 1 ml of 8M HNO; to the organic phase, and mix for
5 min in the vortex mixer.

Discard the organic phase. Repeit-Steps 2 through 5.

Turn on the counting plate heater, heat to 175° to 190°C,
ad place a clean stainless steel counting plate on the
heater.

Pipet an aliquot from the organi: phase that contains

~10? dis/min Np, and add it dropwise to the plate. Rinse

the pipet twice with xylene, and add both rinses to the

plate. Heat the plate until dry.

Heat the plate over a Meeker burier flame until the plate
is a dull red color. Place the »’late on an asbestos

board to cool.

When the plate is cool, add 1 drap of coilodion to cover
the surface. Allow the plate to dry several minutes

before counting.

- 144 -
Procedure 3. Determinatfon of 2?°Np in Sanples Containing
U, Pu, and Fission Products

H. L. Smith®"7
Introduction
The procedure for determining ??°Np arfords excellent decon-
tamination from milligram quantities of U, the fissi m products
obtained from 10!? fissions, and Pu. The decontamination factor

for Pu is about 10"“.

An initial fuming with H,SO, is required to ensure exchange
between the 23’Np tracer employed and 2?°Np, and also to complex
U(VI). If the sample is a dissolved U foil, HNOj; must be added
before the fuming step to convert U to the VI oxidation state.
Np(IV) and (V) are carried by LaFi precipitations in the presence
of Zr and Sr holdback carriers. The preciritations provide
decontamination from the activities of Zr and Sr a: well as from
U. LaF3 scavenging with Np in the VI oxidation state decontaminates

from the lanthanides and partially from Pu.

The chemical yield is about 50%, and eight samples can be

analyzed in one day.

Reagents

@ La carrier: 5 mg La/ml, added as La(NO;),.
6H>0 in H,0

® Sr carrier: 10 mg Sr/ml, added as Sr(NOi)..
4H,0 in H,0

@ 2r carrier: 10 mg Zr/ml, added as ZrOCl; in H,0

e 2?'Np standard solution: 5,000 t> 10,000 courts/(min-ml)
in 2 to 4M HC1 or HNO,

- 145 -
e HCl: O0.1M; 2M; concentrated

® H2S50,: concentrated

e HNO,y: concentrated

e HyBO,;: saturated solution

@ HF: 1:1 H,0 and concentrated HF

e HI-HCl: 1 ml 47% HI + 9 ml concentrated HCl

® HF-HNO;: equal parts by volume of 2M solutions
® NHOH*HCl: 5SM (or saturated)

e KMnO,: 10% solution

e MNH,OH: concentrated

e 'Dowex'" 1-X10 anion exchange resin:
100 to 200 or 200 to 4N0 mesh, slurry in H,O*

Procedure

Step 1. Pipet 1 ml of ??’Np standard into a clean 125-ml
erlenmeyer flask, and then pipet in the sample. Wash down the
sides of the flask with a little H;0, add 1( drops of concentrated
H2S04,** and evaporate nearly to dryness on a hot plate. (No harm

is done if the solution is permitted to evajorate to hard dryness.)

Step 2. Dissolve the residue by boilirg briefly in & minimum

of 2M HCl. Transfer the solution to a clear. 40-ml Pyrex centrifuge

* The resin is supplied by thc Bio-Rad Laboratories, Richmond,
Calif., who purify and grade the resins nianufactured by the
Dow Chemical Co.

** If the sample has been obtained from more than the equivalent
of 50 mg of soil, do not add any H,S0, since CaSO, will pre-
cipitate and carry Np to some extent.

- 146 -
tube; wash the fla... once wit H;0, and transfer the washings to
the tube, The volume of solution shou.d be 5 to 10 ml. (Ignore

any small residue.)

Step 3. Add 5 drops of La carrier and 3 drops of Zr hold-
back carrier. Add 2 drops of NH,OH*HC] for each ml of solution,
stir, and let stand for a few minutes. Add HF dropwise until the
yellow color of the solution disappear: and the solutio. becomes
cloudy (LaF3). Centrifuge. Remove anc¢ discard the supernate.

Wash the precipitate with 1 to 5 ml of HF-HNOj;.

Step 4. Dissolve the precipitate by slurrying with 3 drops
of saturated HiBO3; and adding 3 drops of concentrated HCl. (Ignore
any small residue.) Add 3 ml of 2M HCl and precipitate La(OH),
by adding about 1 ml of concentrated NH,OH. Centrifuge, and
discard the supernate. Wash the precipitate by boiling it briefly

with several milliliters of H,0. Centrifuge and discard the

supernate.

Step 5. Dissolve the precipitate in about 5 ml of 2M HC1.
Reprecipitate LaF; by adding 10 drops of HF; centrifuge, and
discard the supernate. Wash the precipitate with 1 ml of HF-HNO,.
If the precipitate volume is greater thin 0.2 ml, repeat the
hydroxide and fluoride precipitations until the volume of LaF,

precipitate docs not exceed 0.2 ml.

- 147 -
Step 6. Dissolve the fluoride precipitate in 1 drop each ..f
saturated H3BO; and concentrated HNO,y. Add 10 drops of KMnO,,
and allow to stand for 5 min. Add 2 drops of HF, and allow the
solution to stand for a few mirutes. Centrifuge, and transfer
the supernate to a clean centrifuge tube, Wash the precipitate
with 1 m]l of HF-HNOj3, centrifuge, and add the supernate to the

previous one. Discard the precipitate.

Step 7. Add 2 drops of La carrier to the sclution, stir.
centrifuge, and transfer the supernate to i clean centrifuge
tube. Wash the precipitate with ] ml of HIF'-HNO,, add the

washings to the previous supernate, and di:scard the precipitate.

Step §. Add 5 drops of NH,OH¢HC1 and 2 drops of ZIr carrier,
and let stand for a few minutes. Add 2 drops of La carrier, stir
well, centrifuge, and discard the supernate. Wash the prec pitate

with 1 ml of HF-HNO,, centrifuge, and disczrd the supernsatc.
Step 9. Repeat Steps 6 and 7.

Stepr 10. Add 5 drops of NH,OH*HCl ard 2 drops ot S hold-
back carrier, and let stand for a few minuttes. Add 2 drops of
La carrier, stir well, centrifuge, and discard the supernate.

Wash the precipitate with 1 ml of HF-HNOj;, centrifuge, and discard

the supernate,

- 148 -
Step 11. Dissolve the precipitate with 1 drop of saturated
H3BOy and 10 drops of concentrated HCL. Pass the soluticn through
a ""Dowex" 1-X10 anion exchange column, 3 c¢n x 3 mm, and wash the
column with 1 ml of concentrated HCl. The Np, now in the IV
oxidation state, is sorbed on the column. If necessary, remove
Pu from the column with HI-HCi.* Add approximately 1 ml of
0.1M HC1 to the reservoir of the column. §iscard the first 2 drops
that come off the column, and then collect approximately 0.25 ml
in a clean, dry centrifuge tube. Use no air pressure when eluting
the Np. Pick up the solution in a transfer pipet and evaporate
by stippling on a 2.5 cm Pt plate. If possible keep the deposit
within a 1.3 cm circle. Flame the sample to dull red in a
burner, mount with double-sided Scotch tape in the center of an

Al plate, and o- and B-count on 3 successive days,*~

* The procedure should remove 95% of the Pu initially present in
the sample. If, at this point, there remains enough Pu to
interfere with the determination of the Np yield, that is,
more than 1% of the Np tracer, Pu may be removed more efficiently
in the following way: Allow 1 ml of HI-HCl solution to drip
through the column with no added pressure. Wash the column
with several ml of concentrated HC1l, and discard the effluent,
which contains Pu in the III oxidation state, and proceed with
the rest of Step 11. One elution step such as the one just
described removes 99.5% of the Pu.

** Alpha-counting: The sample is counted in a 7.5 cm i.d. methane-
flow proportional counter with a loop ¢node, operated in the
a-plateau region. Beta counting: The sample is placed on the
third shelf of a methane-flow proporticnal counter with a
window thickness of 4.8 mg/cm?’. An absorber (about 5 mg Al/cm?),
placed on the first shelf, stops soft tetas and alphas. The
individual counts are corrected to t,, using a half-life of
56.6 hr, and are then averaged.

 

- 149 -
Procedure 4. Determination of Np

J. Landrum?“®

Outline of Method

After the sample is dissolved, the vo.ume is reduced by

evaporation. Np and other hydroxides are precipitated with 50%

NaOH to separate Al. The precipitate is di.ssolved in concentrated

H71, and Np is separated from many impuriti.es by chloride anion

exchange.

Further separation is attained by performing in order:

TTA extraction, cupferron extraction, and chloride anion exchange.

The plate for counting is prepared by electrolysis.

Reagents
e 50% NaOH
e La carrier, 5 mg La/ml (as La(NO;)3*6H,0 in H,0)
e Concentrated HCI1
® 55% HI solution
® HCl pas
@ Bio-Rad AG 1 x 8, 50 to 100 mesh resin
e 10M HC1 - 0.S5M HI
e 5M HC1
e IM HC1
® 0.4M Thenoyltrifluoroacetone (TTA) in xylene
e 6% Cupferron
e CHCl,
e Saturated NH,Cl solution
e Concentrated NH,OH

- 150 -
Procedure

1.

To the sample add about 3 x 10° alpha counts/min ?°®’Np stan-
dardized tracer. Add "2 mg of La’* carrier and 2 ml $5% HI

(no inhibitor), and boil the sclution until the volume has been
reduced to about 10 ml. Transfer to a 40-ml cone. Add suffi-
cient 50% NaOH to dissolve any Al that may be present. Heat

in a water bath, centrifuge, and discard the supernatant

liquid.

Wash the precipitate with 10 ml of 10M NaOH. Again heat,
centrifuge, and decant. Wash the precipitate thoroughly
with 30 ml of H0 (to remove most of the Na* salts),

centrifuge, and decant.

Dissolve the precipitate in 10 ml of concentrated HCIl.
Add 2 drops of 55% HI (no inhititor).

Cool and saturate the solution with HCl gas. (If white
salts precipitate, centrifuge them and decant.) Pass

the solution through a "Dowex" 1-X8, 50 to 100 mesh
column, 6 mm I.D. by 11 cm, pretreated with concentrated
HCl - 0.5M HI. Discard the effluent. If 23%Pu is to

be measured, save the effluent and note the time of Np-Pu

separation.

Wash the column with 15 ml of 10M HC1 - 0.5M HI, and
collect the wash with the effluent.

Elute the Np with three 5-ml portions of SM HCl, and
allow a minute or so between elutions. Collect the

eluate in a 125-ml Erlenmeyer flask.

Add 2 drops HI, and boil to neer dryness. Transfer to
a 40-ml cone with 1M HCl. Add IM HCl to make approximately
15 ml.

- 151 -
10.

11.

12.

13.

Add 10 ml1 of 0.4M TTA in benzene, toluene, or xylene,
and equilibrate for 30 min. Soparate the layers by
centrifuging, and transfer the organic layer into a
clean 40-ml cone. Repeat the oxtraction with 5 ml of
0.4M TTA for 10 min. Combine t:he organic fractions.

Discard the aqueous fraction,

Wash the organic with 5 ml of IM HC1l for 2 min. Centri-

fuge, and discard the aqueous.

Back-extract the Np by equilibrating the TTA with 2 ml
of SM HCl for 10 min. Separate the layers as before,
and transfer the aqueous to a clean cone. Repeat the
extraction with 1 ml of 9M HC1 for S min. Combine the

aqueous phases.

To the combined aqueous phases, add 2 drops of 6%
cupferron and 5 ml of CHCl;. Ejuilibiate for 30 sec.
Discard the CHCl; (lower layer). Add 5 ml of CHCl; and
repeat the extraction. Again discard the CHCl3. This

step is designed to remove trou>lesome Nb activity.

Transfer the solution to a 125-inl Erlenmeyer flask, add 1 ml
concentrated HNO,;, and boil to near dryness. Add S ml of 9M
HCl1 and 1 ml of concentrated fo:rmic acid. (CAUTION: The
reaction between HNO; and formi: acid may be violent if too
much HNOs is present.) Warm the solution until the HNOj3 has
been destroyed. This step oxid:zes U(VI) and reduces
Np(1IV).

Add 5 ml of fresh concentrated HC1l (final HCl concentration
should be >10M, use HC1 gas if necessary). Pass the
solution through a '"Dowex" 1-X8, 50 to 100 mesh, 6-mm

I.D. x 5 cm column, pretreated with 10M HCl. Wash the
column with 5 ml of 10M HCl, Discard the effluent and

wash,

- 152 -
14, Elute the Np as in Step 6, but with 10 ml of 5M HCI.
Collect in a 125-ml Erlenmeyer flask.

15. Repeat Steps 7, 8, 9, and 10. (TTA extraction)

16. Examine on a Nal detector for gammi contemination. If

the sample is radiochemically pure, plate the sample.

Electroplating

Boil the solution from Step 10 to near dryness. Add 1 ml of
saturated NH,Cl and one drop of methyl red indicator, and adjust
acidity with NH,OH and 1M HCl so that one drop of IM HCl turns the
solution red. (Volume should be 3 to 4 ml.)] Transfer the solution
to an electroplating cell fitted with a Pt wire anode and a 1-in.-
diameter Pt disc cathode. Pass approximately 1.5 amps through

the cell for 15 min.

Add 1 ml of concentrated NH,OH to the cell while electrolysis
is in progress. Continue plating for another 15 to 30 sec. Remove
the solution from the cell, and check it for activity in a well
counter. If appreciable activity is present, repeat the plating

procedure without the addition of NH4Cl.

Dismantie the cell, flame the Pt disc to a dull red, and
alpha count for chemical yield. Gamma and beta count for 2?°Np

and 2?%Np.

Notes

1. Using this procedure, Np is separated from solutions whose
contents underwent 10!° fissions (one week previous) and
up to one gram of dissolved soil. CGamma-ray spectroscopy

showed no activities other than 2?Mp and 2*°Np,

- 153 —
2. 10 to 12 hours is required for six samples.

3. The yield for this procedure is 30 to 60%.

- 154 -
ocedure 5. Determination of Small Amounts of Np in Pu Metal

L. J. Slee, G. Philllps &nd E. N. Jenklns32?®

Outline of Method

Pu metal is dissolved in HC1l. The Np (10 to 2000 ppm) is

parated from Pu by TTA extraction and determined with a square-

ve polarograph.

Reagents

Distilled water
HNOs, analytical-reagent grade
Hydroxyamine hydrochloride (NF2OH-HCl) solution, SM

TTA solution, 0.5M in xylene: Dissolve 28 g of 2-
thenoyltrifluoroacetone (TTA) in 200 ml of pure xylene,
filter, and dilute with xylene to 250 ml.

Ferrous chloride (FeCl,)

EDTA solution: Dissolve 37 g o2f discodium ethylenediamine-
tetraacetate (EDTA) in distilled water, adjust to pH 7

with ammonia solution, and dilute to 100 ml.

Procedure

1. Weigh 300 mg of Pu metal accurstely.

2, Add S ml of distilled water and then slowly add 0.5 ml of
10M HCl. When the reaction subsides, add 1 ml of 10M HCl
and 2 ml1 of 5M NH;OH*HCl1 and warm the solution.

3. Dilute to 10 ml with distilled water, add 250 mg of FeCl,,
allow 5 min for oxidation state adjustnent.

4. Transfer quantitatively to an extraction vessel, and add

S ml of 0.5M TTA. Stir for 10 minutes, allow the phases
to separate, and remove the organic phase.

- 155 -
10,

11.

12.

13.

1‘30

15.

16.

17.

18.

Repeat the extraction with 5 ml of 0,5M TTA,

Combine the organic phases in the extraction vessel, add
1 ml of IM HCl, and stir for 1 min (to remove entrained
Pu. Remove the aqueous phase.

Add 5 ml of 10M HNO,, and stir for 10 min to strip the
Np.

Remove the aqueous phase into a clear vessel, and repeat

Steps 7 and 8.

Evaporate the 10M HNO3; to ~3 ml and then add 5 ml of

analytical-grade concentrated HNOj,

Evaporate to 1 ml, and repeat evaporation with two more

5-ml portions of concentrated HNO,.

Add 3 ml of analytical-grade perchloric acid (606%) and
more concentrated HNO3 and evaporate to complete wet

oxidation of organic matter.
Heat until solid perchlorates remain but do not bake.

Dissolve the residue in 1 ml of warm 6M HCl and 1 ml of

water,
Add 2 ml of 5M NH,OH*HCl and evaporate slowly to “}.5 ml.

Add 0.5 ml of 1M EDTA and 4 to 7 drops of ammonia to
adjust pH to 5.5 to 6.5.

vilute to 5.0 ml, and mix thoroughly. Transfer 2.00 ml
to a polarograph cell, and de-aerate with N, (pre-saturated

with water) for 3 min,

Record the Np peak at about -0.8 V apainst the mercury-

pool anode on the square wave polarojyraph.

Add 0.2 ml of a standard Np solution prepared in EDTA
so that the original peak height is upproximately doubled.
Deduce the Np concentration of the or-iginal solution from

- 156 -
the increase in peak height. Interference from the
oxidation of chloride ions is decreased by adding EDTA
to shift the half-wave potential of the Np peak.

The precision is *2 and #10% for concentrations of

500 and 25 ppm, respectively.

~ 157 -
Procedure 6. Determination of Np in Sample Containing Fission
Products, U, and Other Actinides

A. Schneider!®®

Introduction

This procedure describes an analytical solvent extraction
method for separating Np from Pu, Am, Cm, U, Th, and fission
products using tri-iso-octylamine (TIOA) and thenoyltrifluoroacetone
(TTA). Np is separated from Pu, Am, Cm, and fission products by
extraction of Np(IV) into the amine from HNO,; containing a
reducing agent. Further purification is obtained by stripping
Np from the amine with dilute HCl anil then extracting the Np

into TTA,

Reagents
e 5M HNO,
® 3M [Ferrous Sulfamate], Fe(NH2S0:):
® 5.5M [hydrazine], N:H,
® 10 Vol% tri-isooctylamine (TIOA) in xylene
e IM HCl1
® 5M [hydroxylamine hydrochloride] (NH20H=HC1)

@ 0.5M TTA in xylene

Procedure

1., To a 5-ml extraction vial add 1.5 ml of S5M HNO; and a
glass-covered magnetic stirring bar.

2. Pipet the sample (not to exceed 200 uR) into the HNO,

and stir.

- 158 -
Add 3 drops 2M Fe(NH;S03); aad 1 drop of 5,5M NaHs.
Stir and allow to stand for 5 min at room temperature.

Add 1.0 ml of 10% TIOA in xylene and stir for 3 min to
produce an emulsion. Allow he phases to separste.
Separate the phases, and discard the aqueous.

Transfer the organic phase fiom the original vial to a
clean vial containing 1.5 ml of SM HNO,, 3 drops of
Fe(NH2S03)2, and 1 drop of N;H,. Stir for two minutes,
allow the phases to separate, and discard the aqueous

phase.

Transfer exactly 0.75 ml of the organic phase to a clean
vial containing 2.5 ml of IM HCl and 1.5 ml of xylene.
Rinse the 0.75-ml pipet in tle xylene phase of the new
vial. Stir for 3 min and allow the phases to separate.

Discard the organic phase.

Transfer exactly 2.0 ml of the aqueous HC1l phase to a
clean vial. Add 3 drops of 5M NH;OH*HCl and 3 drops of
2M Fe(NH2S03)2. Stir and heat at 65°C for 3 min. Remove
from the bath, and let stand for 3 min.

Add 1.0 ml of 0.5M TTA in xylene. Stir for 4 min to give
a complete emulsion. Allow the phases to zeparate. The
organic phase contains the purified Np. This phase is

mounted for alpha counting for measurament of 2%7Np.

Notes

1.

The presence of fluoride, sulfate, uxalate, and phosphate
lower the extraction coefficiznt of Np(IV) into TIOA;
Chloride ion does not interfere. 7The deleterious effect
of these anions is circumvent:d by reducing the sample
size or by adding Al ion.

- 159 -
ta

For U-tree samples, the combined system yields 96 *2%
recovery. For U-bearing samples, the recoveries are
dependent on the amount of U taken., 7The extraction
conditions are reproducible, and for control analyses
the recovery factnrs are included in the calculations.

In routine use, the combined extraction system achieves
a separation from common fission products (Ce, Ru, Nb,
Zr, Cs and St) of about 1 x 10° and a Pu separation

factor of S to 50 x 10°,

Control of the method for samples of unknown composition
is maintained by spiking a portion of the sample solution
with 2?’Np or ??’Np and evaluating the recovery of the
spike. An alpha pulse height analysis may be necessary

if large amounts of Pu are initially present in the sample.

- 160 -
Procedure 7. Determination of Np in Samples of U and Fission
Products

W. J. Maeck

; G. L. Booman, M. C. Elliott, and
J. E. Rein'®®

Introduction

This procedure describes a method for sezparation and
determination of Np in solutions of U and fission products using
methyl isobutyl ketone and thenoyltrifluoroa:etone (TTA) extractants.
Np is oxidized to the hexavalent state and quantitatively extracted
as a nitrate complex into methyl isobutyl ke:one from an acid-
deficient AI1(NOs)s solution containing tetrapropylammonium nitrate.
Np is stripped from the ketone with 1M HCl containing reductants
and then quantitatively extracted into TTA-xrlene to complete the

separation.

Reagentsa

@ Al(NOy}; salting solution: Dissolve 1050 g of
A1 {NOjy) 3*9H20, add 135 ml of concentrated NH,OH with
mixing, and cool to 50°C. Add S0 mi of 104

tetrapropylammonium hydroxide reagent, and stir the
solution until all solid is dissolved. Dilute the
solution to one liter with water.

¢ Reducing-strip solution: IM HI - (.5M NH,OH<HCl and
0.25M FeCl; solution.

e 0.25M KMnO,
® Methyl isocbutyl ketone
¢ 0.5M TTA in xylene

e Ethylenediamine

- 161 -
Procedure

l\'

Add 6 ml of Al1(NOy), salting solution to a tube containing
0.1 ml of 0.25M KMnO,. Then p.pet 1 ml or less of the
sample into the tube and mix.

Add 3 ml of methyl isobutyl ketone, and mix for 3 minutes,
Centrifuge to separate the phases,

Remove 2 ml of the organic phase, and transfer to another
tube containing 4 ml of the reducing strip solution. Mix

for 10 min and allow the phase; to separate.

Transfer 3 ml1 of the aqueous phase to a 30-ml separatory
funnel; add 3 ml of 0.5M TTA, and stir vigorously for

10 min,

Let the phases separate, and discard the aqueous phase,
Add 3 ml of reducing-strip solition, and scrub for 5

minutes,

Remove an aliquot of the organic phase, and dry it on a
counting plate under a heat lamp. Cover the residue with
2 to 3 drops of ethylenediamine, evaporate to dryness,

ignite, and count.

Notes

1.

2
®

Extraction from acid-deficient A1(NO,)s with methy!l
isobutyl ketone yields very good sepiaration from Zr, and
extraction with TTA gives good separation from Pu and U.
The extraction of U and Pu is <0.,1 and 0.01%, respectively,
Ru and Zr, the only 80-day cooled fission products that
follow Np, are separated by >10%.

An alpha scintillation counter is used for gross counting,
and a Frisch-grid chamber, 256-channel analyzer system is
used for pulse height analysis.

- 162 -
Procedure 8. Extraction Chromatographic Separatior of 2°°Np
From Fission and Activation Products in the
D:tfirmination of Micro and Subinicrogram Quantities
o

H. Wehner, S. Al-Murab, and M, Stoeppler?3?
Introduotion
This procedure describes extraction chromatographic separa-
tion of 2*°Np from fission and activation products after neutron
irradiation. The system is Poropak-Q resin impregnated with
TTA-xylene. It is suggested that radioactive samples are more
easily analyzed with extraction chromatography than with TTA

extraction.

Raeagents
® Poropak-Q resin, 100 to 120 mesh
® 0.4M TTA in xylene (=mall amount of n-pentane added)
e 2M HCl1
e IM FeCl:
e 3M NH,OH<HC1

e 10M HNO;

Proceadure

1. Dissolve sample in 2M HCl or convert to chloride with
HC1.

2. Add 3 ml of freshly prepared IM Fe(l, and 4 ml of 3M
NH20H*HC1 mix, and let stand for 1% min.

3. Transfer the adjusted solution to & column (5 cm long and
0.6 cm I.D.) of Poropak Q impregrated with TTA-xylene
at V1 ml/(cm?-min).

- 163 -
When the feed has passed through the column, wash with
2 ml of IM HC1 and then a few drops of distilled water,
Discard the effluents,

5. Pass 5 ml of 10M HNO; through the column to strip the Np.

6. Count the HNO, solution containing the ?*°Np immediately
after separation with a 3 x 3 in. NaI(TL} detector con-
nected to a 512-channel pulse-he:ght analyzer and evaluate
the 0.106-MeV photopeak.

Notes

1. The method was suggested for determining low concentra-

tions of U by irradiating a standard sample of known U
content at the same time as the unknown and then deter-
mining the ??°Np content of both samples. A sensitivity
of 1 ug of U was determined for a ~1 hour irradiation,
at a thermal neutron flux of 2 x 10!? n/cm?-sec with a
cooling period of 20 hours. With a longer irradiation,

a detection limit of 0.5 ug is suggested.

- 164 -
Procedure 9. Separation of U, Np, Pu, and Am by Reversed
Phase Partition Chromatography

H. Eschrich?*®
Introduction
This procedure describes extraction chromatographic separa-
tion of U, Np, Pu, and Am. The system is Hyflo Super-Cel
(diatomaceous silica) impregnated with tributyl phosphate (TBP)

and aqueous HNOjy solutions of the actinides.

Reagents and Materials

e Hyflo Super-Cel

e Purified tributyl phosphate (TEF)

e HNO;

e Sodium dichromate solution (Na2Cr:07)
® Dichloro-dimethylsilane

e Glass column

Procedure

1. Add NaCr207 to 1 to 2M HNOs containing the actinides,
and heat at 75°C for five hours t> yield hexavalent U,

Np, and Pu.

2. Wash the packed column with ~10 ¢>lumn volumes of ~VvIM HNO,
at relatively high flow and pressure to remove any air
and nonsorbed TBP.

3. Add the sample volume (not greater than 1/10 of the total
column volume and containing a macimum cf 1 mg TBP-
extractable species per 100 mg of silaned Hyflo Super-Cel)
at a flow of 0.4 to 0.8 ml/(min-cn?).

- 165 -
4. Wash the column with 1.7M HNO, to remove (in order)
Am(IIT), Cr(VI), and Pu(VI).

S. After Pu(VI) elution, switch to 1.7M HNOy - 0.1M N;H.
wash., (Np is reduced to Np(V) and elutes immediately,

and U(VI) is removed.)

Note

If U, Np, and Pu are present, no oxidation step is required.
The feed is adjusted 0.7M HNO, - 0.02M Fe(SO3NH2), to yield Pu(III),
Np(IV), and U(VI), and the same composition wash solution is used.

The order of elution is Pu(IIl), Np(IV), and U(VI).

- 166 -
Procedure 10, An Analytical Method for 2*7lp Usiny Anfon Exchange
F. P. Roberts2?!"

Outline of Method

This method separates Np from Pu, U, An, Cm, and fission
products by anion exchanpge in HNO; solutions to permit ?*"Np
estimation by gamma spectrometry. The sample is spiked with 23'Np
tracer to permit yield corrections and loaded onto a small column
of "Dowex" 1-X4 (100 to 200 mesh) resin from 8M HNOjs containing
Fe (NH2SO3)2 and semicarbazide. After washing with 30 to 40 column
volumes of 4.5M HNOy containing Fe(NH2SOs); and semicarbazide, the
Np is eluted with dilute HNOy containing 0,005M Ce(SOs)2. Np
recovery is “95% with a Pu decontamination factor of 5 x 10°.
Decontamination factors from U, Am, Cm, and gross fission products
are all >10*. Uranium at concentrations up to 180 g/% in the feed
does not interfere. The Pu decontamination factor can be increased
10 to 100 by following the HNO3; wash with L2M HCl - 0.IM NH.I.
Np is then eluted with 6.5M HCl - 0.004M HF. The method is appli-

cable to samples containing high salt concentrations.

Reagenta (C.P. Chemicals)
e Concentrated HNOj,
e "2M Fe(SO3NH:)2
¢ Semicarbazide

® zasz tracer

Materials
e 'Dowex" 1-X4, 100-200 mesh

e Glass colum, 0.3 cm x 7 cm with 10-m]l reservoir

~ 167 -
e Counting equipment

Proocedure

1. Adjust an aliquot of sample to w8V HNO, with concentrated
HNO 4,

2. Add an equal volii.e of 8M HNOy - 0.02 Fe(NH;S03), - 0.2M
semicarbazide and mix.

3. Add ?’’Np tracer (“10° dis/min).

4. Pass the adjusted sample through the column at 3 to 6
drops/min.

5. Rinse the reservoir several times with a few drcps of.
8M HNO,, pass through the column, and discard.

6., Pass 15 to 20 ml of 4.5M HNO; - 0. IM semicarbazide - 0.01M
Fe(NH2503) 2 through the column at J§ to 6 drops per minute
{(Pu fraction).

7. Pass 2 m]l of 8M HNO3 rinse through the column.

8. Elute the Np with 2 ml of 0.005M Ce(SO4)2 in 0.25M HNO,.
Catch the eluate in a 2-ml volumetric flask.

9. Mount an aliquct of the Np product on a Pt disc for alpha
counting and alpha energy analysis. (The yield is
determined by comparative counting of the 0.23 MeV 23°Np
gamma from the disc with that of a standard °?°Np disc.)

- 168 -
Procedure 11. Separation of U, Np, and Pu Using Anion Exchange
F. Nelson, D. C. Michelson, and J. H. Holloway*??

Cutline of Method

This method utilizes anion exchange .n HC1 for separating
U, Np, and Pu from '"1~n-adsorbable" elensents which include alkali
metals, alkaline earths, trivs!=i1t actiiides, rare earths, and a

number of other elements such as Al, Sc, Y, Ac, Th, and Ni.

Sorption of the uranides by anion =xchangers from HCI
solutions can occur in either the +4 or +6 oxidation states but
not in the +3 or +5 states. In this pracedure, U is sorbed as
+6, while Np and Pu are sorbed in the +! oxidation state. Pu is
selectively reduced to Pu(III) and elut:d, while U®* and Np**
remain sorbed. The latter are then eluted in separate portions

with HCl - HF mixtures.

Reagents (C.P. Chemicals)
® 9M HC1
® 9M HC1l - 0.05M NH,I
e 4M HC1 - 0.1M HF

e O0.5M HC1 - IM HF

Materials
e '"Dowex" 1-X10, -400 mesh anion resin

e Column, 0.6 cm I.D. and 12 cm in length, with heating

device.

e Resin bed, 0.28 cm? x 3 cm long.

® Plastic test tubes

- 169 -
® "Teflon" evaporating dishes

@ Plastic transfer pipettes

Procedure
1. Evaporate sample to near drynmess.

2. Add 1 ml of 9M HC: - 0.O0SM HNO3 and heat for 5 min. Do
not boil.

3. Heat column to 50° and maintain throughout elution.

4, Pretreat resin bed with 3 column volumes of 9M HC1.

Use air pressure to obtain flow of G.& cm®/min.
S. Pass sample through resin bed a: 0.8 cm/min.
6. Wash bed with 4 column volumes of 9M HCI.

7. Wash bed with 8 coiumn volumes of 9M HC1 - 0.05M NHuI
fPu fraction).

8. Wash bed with 4 coiumn volumes of 4M HC1 - {O,1M HF
(Np fraction).

9, Wash bed with 3 column volumes c¢f 0G.5M HC1 - IM HF

(U fraction).
10. Regenerate the column with 3 column volumes of SM HCI.

The total time for the column operation is about 80 min.

- 170 -
Procedure 12. Separation of Zr, Np, and Nb Using Anion Exchange

J. H. Holloway and F. Nelson?2"

Qutline of Method

This procedure is used to separate trace amounts of Np and

Nb from micro-amounts of Zr. It makes use of ¢he fact that Zr(IV)

in HCl - HF media at high HCl concentrations is essentially non-

sorbable by anion exchange resin under conditions where Np(VI) and

Nb(V) are strongly sorbed.

Keagents
¢ OM HC: - IM HF - Cl;
¢ ©OM HC1 - IM HF
¢ O.5M HC1 - 1.0M HF
e 4M HNOj3; - 1M HC1 - 0.2M HF
Matertale
e '"Dowex' 1-X10, -400 mesh anior resin
¢ Column, 0.9 cm I.D. x 12 cm ir length containing 2 ml of
resin
e '"Teflon" evaporating dishes
¢ Plastic transfer pipettes
e Plastic test tubes
® Chlorine gas
Prceedure
1. Dissolve the sample, and evaporate it to near drymness.
2, Add 1 ml of 6M HCI - 1M HF - Cl,, and warm.
3. Transfer the sample to a plastic tube and bubble Cl: gas

through it for ~3 min.

- 171 -
4. Chlorinate the resin, and add it to the column.

5. Wash the bed with 2 column volumes {4 ml) of 6M HC1l -
IM HF - Cl,. Then pass the sample through the bed.
(Control the flow with air pressure at 0.8 cm/min.

When the sample has passed, wash with arn additional
3.5 column volumes of 6M HC1 - IM HF - Cl; (Zr fraction).

6. Wash with 3 column volumes of 0.5M HCl - IM HF to elute
Np.

7. Wash with 3 colummn volumes of 4M FENOs - IM HCl - 0.2M HF
to elute Nb.

8. Regenerate with 3 column volumes of 6M HC1 - IM HF - Cl,.

The total time for the column operation is 'v30 mir.,
Procedure 13. Separation of Np and Pu by Anion Exchange
N. Jackson and J, F. Short3"?

Outline of Method

This procedure describes separation of macro amounts of Pu
and Np. It is based on the fact that Pu(IIl) is not sorbed on
anion exchange resin, while Np(IV) is strongly sorbed at high
HC1 concentrations. The valence adjustment is don2 before sorp-
tion on the column by dissolving the hydroxides in a concentrated
HC1 solution that has been saturated with NH4I. The Np is removed
from the column with 2 M HCl. The separation is quantitative and

complete,

Procedure

The purification of 2.3 g of Np?37 from approximately 50 mg
of Pu??? was then undertaken. The Np and Pu were precipitated as
hydroxides, centrifuged, and dissolved in 210 ml of concentrated
HC1 saturated with NH,I. The solution was allowed to s*and for
30 min and poured onto a Deacidite FF*anion column 20 cm long and
2.5 cm diameter, while a flow rate of 1 ml/nin was maintained.
The first 200 ml of effluent were pale blue [Pu(IIl)]. The column
was then washed with 100 ml of concentrated HCl, and wash was
collected separately. No activity was found in a drop collected

at the end of the washing.

The Np was eluted with 2M HC1l. It was possible to follow the
dark green band of the Np down the column, and the first 4C ml of

eluate was included with the concentrated HCl wash. All the Np

*Deacidite is supplied by Permutit Co. Ltd., England.

- 173 -
was collected in the next 50 ml of eluate. No activity was found
in any eluate after this stage. Some f-y a:tivity was detected
on the glass wool at the top of the resin column and was assumed

to be ??'pa, the daughter of Np2'7,

- 174 -
Procedure 14. 5Separation of Np and Pu by Cation Exchange
V. D. Zagrai and L. {. Se!'chenkov?’?

Cutline of Method

Np(IV) and Pu(liI) are adsorbed on the cation resin MUl or
KU2 from 0.25M HCl solution after reduction with SO, at boiling
water temperatures. Np is eluted with 0.02M HF, and Pu stripped

with 0.5M HF.

Procedure

1. To 6 to 8 m1 © 2,25N HC1 containing ug awounts of Np
and Pu, add a >ut half of the resir in the hydrogen form
required to fill the plerigluss column (1 mm diameter x
90 mm high) and 1 to 2 m! of water.

2. Pass SO, gas through the solution vigorously for 15 to
20 min, while the solutions heating on 2z boiling water bath,

3. Allow the solution to cool to room temperature, and
transfer the resin to the column with a pipette. Plug
the top of the column with cotton, and pass the remaining

solution through the column.

4. Wash the resin with i0 m) of 0.25 ¥ HCl, followed by 10
ml of H20.

S. Elute the Np into a Pt disk or a "Teflon" beaker with
40 to 60 ml of 0.02M HF.

6. Elute the Pu with 4 to S mi of 0.5 HF.

- 175 -
Procedure 15. Separation and Radfochemical Determination of
lsl 4]|lf1d the Transuranium Elemerts Using Barium
ulfate

C. W. si'l!!l,llb'lls

Introduotion

Large trivalent and tetravalent ions are precipitated with
BaS0, while monovalent and divalent cations sre not precipitated.
This procedure outlines the separation of U and transuranium
elements both from other elements and from each other. The
oxygenated cations of the hexavalent state are too large to fit
into the BaSO, lattice and are not carried. The BuSO, precipitate
can be alpha counted directly with 92% counting efficiency, or

the radionuclides can be electrodeposited for alpha spectrometry.

Reagents and Equipment
o Concentrated H;SO.
o (.P, K3SO.
e Concentrated HNO,
e Concentrated porchloric acid (HC10.)
e C.P. KNO,

C.P. potassium dichromate (KCr;0y]
® 30V hydrogen peroxide (H;0;)

Erlenmeyer flask

¢ Centrifuge and special tubes
o Counting supplies and equirment

-~ 176 -
Procedure

S.

6,

10.

Add 3 g of anhydrous K;SO, 2 ml of concentrated H;SO.,

6 drops each of concentrated HNOj and HC10,, and 2.00 ml
of 0.45% solution of BaCl,*2H;0 (5 ng of Ea) to the
solution containing the elements to be precipitated in

a 250-m] Erlenmeyer flask and evaporate until fumes of
H2S0, appear. (If there is any question about removal

of organic matter, add HNO, and/or HCiO, and re-svaporate.

Heat the solution over a blast burner with swirling until
the excess H2S0, and HC)O, are volatilized and a clear

pyrosulfate melt is obtained.

Cool the melt, add 2 al of concentrated H;SO,, and heat
to boiling or until the pyrosulfate melt is dissolved.
Do not volatilize much H,;S0,..

Cool and add ~10 mg of solid K;Cr;0,, and mix to ensure
complete cxidation of Np. Do not heat because Pu will
be oxidized and the excess dichromate will be theraally

decomposed.

Cool to "40°C and add ~20 m1 of water; boil for 1 minute,
Cool, centrifuge, and wash the prccipitate: the Np and

U are in the supernate.

Add 0.5 ml of 30V H;0; and 2.00 m] of 0.45% BaCl; to the
supernate, and evaporate until fumes of H;5%0. appear to
reduce any Pu that may have followed the Np.

Heat the H,S0. to hoiling, cool for } minutes, and add
V0 g of Kj<lri0r to reoxidize the Np.

Add 20 ml of water and boil for 1 minute; cool, centrifuge,
and combine the supernate with that ‘rom Step 6.

Add 0.5 ml of 30% H;0; to reduce Np 0 the quadrivalent
state, and evaporate to 25 ml.

- 177 -.
11,

Cool and add BaCl,; then boil, centrifuje, wash, and mount
the BzSO, which contains the ?*’Np. The U remains quantita-

tively in the supernate.

Notes

1. Several other shorter procedures fo:r Np are given when

Np is to be separated from one or tiwo other cations,

2. Details are given in the reference article for depositing
the precipitate on a stainless stee! disc that fits into
a specially designed centrifuge holder and also into a
specially designed counting holder. An slternative pro-
cedure uses electrodeposition of the radionuclides for

alpha spectrometry.

- 178-
Procedure 16. The Low-Level Radiochemical Determination of 237Np
In Environmental Samples

R. W. Taylor?30
Introduction
Np, along with Pu and U, is removed frem 8M HC1l by anion
exchange to triisooctylamine (TIOA). Each element can be indi-
vidually removed from the TIOA. Pu is stripped first with 8M
HC1 - 0.05M NHyI. Np 1s removed next with 4M HC1 - 0.05M HF,

and U is removed last with 0.5M HNO,.

Most environmental sampies contain large quantities of Fe
that will extract with the actinide elements into TIOA. Much of
the Fe will be stripped from the TIOA alcng with Np, but it is
easily removed from 8 M HCl vy isopropyl ether. If the sample
is known to contain no Fe, the ether extraction step may be

omitted.

Final decontamination of Np is accomplished by solid ion
exchange. Np is finally electrodepositec for radioassay by alpha

pulse height analysis.

When the sample contains large quantities of U, some of it
may follow the Np and be electrodepositeci on the plate. ?°‘U and
237Ny Nave the same alpha energy (4.75 MeV) and cannot be distin-
guished from one another. The Np can be converted to **Pu by
neutron irradiation for verification of ‘’’Np. Also, when the Np
activity is very low, conversion to 230, will decrease the counting
time. Two-hour irradiations at a flux of 1 x 10’} n/(cm?-sec)

result in a 2?%Pu activity level about 7 to 10 times greater thsn

- 179 -
the original activity due to Np.

Reagente

e HNO,, 16M, 1M

e HC1, 12M, 8M

& HzOz s 30%

¢ NH,OH, 1.5M

\

o KOH, 12M

e 8M HCl - 0.05M NH4,I: This reigent must be prepared fresh
just prior to use. Discard aily unusel reagent at the
end of the day.

e 10% TIOA (triisooctylaminc): 10% volume/volume TIOA in
xylene. Clean the reagent by shaking in a separatory
funnel with half its volume of 0.5M HNO;. Repeat the
HNO3 wash, and wash finally with distiiled water. Store
the cleaned TIOA in a glass flask.

® 4M HC1 - 0.05M HF

® Isopropyl ether

® '"Dowex" 2-X8 anion exchange resin, 200 to 400 mesh

Procedure

1. Adjust the sample to be analyzed to M HC1. Soluble
samples may be dissolved direc:ly; insoluble materials
may be leached with hot M HCl; aquecus samples may be
evaporated to near dryness and brought up in 8M HCI.
The sample should be adjusted 0 a convenient volume of
from 200 to 400 m!.

2. Add 5 mi of 30% H;0; to the sample and heat at about

80°C until effervescence ceases. Cocl the sample to about

room temperature.

- 180 -
Transfer the sample to a 500-ml separatory funnel. Add

an amount of 10% TIOA equal to one-fourth the amount of

the original sample. Shake the funnel for one minute.

Allow the phases to separate, and drain the bottom (aqueous)

phase. Retain for other analyses,

Add 10 to 20 ml 8M HCl1 (according to volume of original
sample) and shake one minute. Allow phases to separate,

drain, and discard the aqueous.

To strip Pu from the TIOA, add to the separatory funnel
an amount of 8M HCl1 - 0.0°M NHyl equal to one-half the
volume of TIOA. Shake one minute and then allow phases
to separate. Drain the aqueous and retain for Pu

analysis. Repeat the Pu strip with a fresh portion of
8M HC1 - 0.05M Nryi. Combine the two strips, and save

for Pu analysis.

To remove Np from the TIOA, add to the separatsry funnel
an amount of 4M HCl - 0.05M HF =»qual to one-nalf the
volume of TIOA and shake for on® minute. Allow the
phases to separate, and drain the aqieous which contains
Np. Repeat the strip with a fresh portion of &1 HC1 -
0.05M HF, and combine the two s:rips. U can now be
stripped from the TIOA with 0.5 HNOy.)

Add an equal amount of 12M HC1 o the combined strips,
and transfer to a clean separatory furnel. Add 25 ml
isopropyl ether and shake one m:inute. (CAUTION: Vent
the separatory funnel frequently while shaking.) Drain
the aqueous, and retain. Discard the ether in accordance
with safety regulations. Repeal the ether extraction
with a fresh portion of ether.

Evaporate the aqueous phase fron Step 7 to dryness. Place
in a muffle furnace at 400°C for at least 4 hours. Wet
oxidize the sample two or three times with 3 or 4 mi

- 181 -
10,

11.

12.

13.

16M HNOy and 30% H202. Add 2 or 3 nl 12M HC1 and
evaporate to dryness. Repeat the 12M HC1 evaporation.

Dissolve the sample in 10 ml of 8M HCl and pass through
a "Dowex" 2-X8, 200 to 400 mesh, anion exchange column.
The resin bed should be 50 mm long and 6 mm in diameter;
it must be pre-conditioned with S5 ml of 8M HC1l. After
the sample passes through the column, pass an additional
S ml of 8M HCl through it. Elute the Np from the column
with 10 m1 of 0.1M HC1l. Evaporate to dryness.

Add 2 ml of 16M HNOs to the sample, and evaporate to
dryness. Repeat the HNOj evaporation. Add 2 ml 1M HNO,
to the sample, and heat gently to ensure dissolution,
Cool, and transfer the sample to an electrodeposition
cell. Rinse the beaker twice with 2 ml of distilled
water, and transfer the rinse to the cell. Add 2 ml of
1.5M NH,OH to the cell, and add distilled water until
the cell is full.

Electrodeposit the sample at 10 V and about 200 mamp for
three hours. Maintain the pH of the solution between

1 and 3 during electrodeposition. A= the end of the
electrodeposition period, add 1 =l of 12M KOH and plate
for 1 min., Empty the cell, rinse with distilled water
and remove the plate. Dry the plate and flame it.

Count the plate by alpha pulse height analysis. If
there is no U present and if there is sufficient 2'Np
present, radinassay can be accomplished directly. In
the presence of U or when there is very little ?°™Vp
present, increased sensitivity can be achieved by con-
version of 2?’Np to 2?"Pu by neutron irradiation. The
absence of 2'%Pu is verified by the initial count.

Irradiate the Np sample for approximstely two hours at
a flux of 1 x 10'? n/(cm?-sec). Allww the plate to

- 182 -
cool long enough to permit decay of induced Pt activities
and to allow 2®Np to de:zay to 2'%Pu. Recount the plate
by alpha pulse height analysis. Correct the amount of
23%y now present by any originally present on the plate,
if necessary. Calculate the amount of Np present before
irradiation from the activation formula.

- 183 -
Procedure 17. Radiochemical Procedure for tie Separation of

Trace Amounts of 23*Np from Reactor Effluent
Water

R. W. Perking?5s3

Introduction

This procedure accommodates a relatively large volume of

reactor effluent water, and emphasis is placad on speed of

separation and high radiochemical purity ratier than high yield.

Procecdure

1.

10.

i1.

Add 20 mg of La carrier and 5 ml of concentrated HCl to
one gallon of reactor effluent water, and evaporate to
S50 ml.

Cool the solution, dissolve 0.25 g >f Fe(NH2503),, and

let stand for S min.

Transfer to a 100-ml plastic tube, 3add 5 ml of concentrated

HF, stir, and let stand 5 min.
Centrifuge, and discard the liquid phase.

Dissolve the precipitate in 20 vo 50 ml of IM HC1, and
dilute to 75 ml with IM HCI.

Add 5 ml of concentrated HF, stir, and ler stand for

5 min,
Centrifuge and discard the liquid phase.
Repeat Steps 5 through 7.

Transfer the precipitate to a 50-ml beaker containing
3 ml of concentrated HC10.,, and evaporate to dryness.

Dissolve the residue in 20 ml of 1M HCl1 by boiling. Cool
the solution and dissolve 0,25 g of Fe(NH,;S0s),.

Transfer the solution to a 125-ml separatory funnel and
mix., Add 20 ml of TTA in benzene, and extract for 10 min.
Discard the aqueous phase.

- 184 -
12,

13.

14.

15.

16.

Note

Wash the organic phase with three 20-ml portions of
IM HC1 for 5 min each. Discard the aqueous solutions.

Back-extract the 2%?Np with 10 ml of BM HNO; for 10 min.
Place the aqueous in a 50-ml beaker containing 3 ml of
concentrated HC10,, and evaporate to dryness under a

JAeat lamp,

Cool the beaker, add 5 ml of 8M HNO;, and heat to
boiling.

Dilute the solution to a measured volume and analyze by

gamma counting.

The analysis requires 6 hours, and tle yield is >90%,

- 185 -
Procedure 18. Determination of Np in Urine
F. E. Butler?’’

Outline of Method

Urine is wet ashed with HNO,; and H;02 to destroy organic
matter. The salts are dissolved in 8M HCl and extracted with
TIOA (tri-isooctylamine). The Np is then back extracted, and
the alpha activity is determined by direct planchetting and

counting on low background solid-state counters.

A variation of the procedure provides for sequential deter-
mination of actinides in biological and environmental samples.
Pu, Np, and U are extracted from 8M HCl to TIOA. The residual
8 HCl containing Th, Am, Cm, Bk, Cf, and Es are extracted from
i2M HNO3 to DDCP (dibutyl N, N-diethylcarbamyl phosphonate}. The
actinides of interest are back-extracted sequentially for quanta-

tive determinations.

Preparation of Sample

Urine collected in polethylene bottles is transferred to an
Erlenmeyer flask with concentrated HNO; (20) ml of acid per liter).
Acid is added to the urine in the polyethylone bottle to remove
the Np, which may be adsorbed on the walls of the container. The
acidified sample is evaporated to dryness, and the residue is wet
ashed with HNOj and H;0,. Nitrates are met:uthesized to cnlorides

by evaporation to prevent interference with Pu (1iI) removal.

- 186 -
Reagents and Equipment
The liquid anion exchanger, TIOA (Bram Chemical Cc.) is
diluted to 10 vol % with Xxylene and washed with half its volume

of 0.1M HC1 before use.

The alpha-detection equipment are 2l solid-state counters.
The counters are equipped with detectors *hat have an active area
of 350 mm? and ure capable of accepting l-in. stainless steel

planchets.

All other reagents used in the procecure are prepared from

analytical grade chemicals.

Froccdure

1. Wet ash urine with HNO3; and H,0,; then add 19 ml of 8M HCI
to the white salts twice and evaporate the solution to dryness

each time.

Z. Dissolve the salts in freshly prepared 8M HC! - 0.05M NH4I
(50 ml of acid/250 ml of urine in sample), and heat to com-

plete solution.

3. Transfer a 50-ml aliquot of the solution witk 25 ml TIOA-xylene
into a separatory funnel and shake for 1l min. (For urine samples
of 250 ml or less, rinse the flask twice with 10 ml of 8M HC1,

and add the rinses to the funnel.)

4. Drain and store the aqueous (lower) layer for Pu, Th, Am, Cm,

and Cf analysis.

5. Rinse the organic phase with 25 ml of &M HCl - 0.05M NH.I at
80°C and shake for 1 min. Discard the rinse solution or com-

bine with solution stored for other actinide analysis.

- 187 -~
10.

Add 25 ml of 4M HC1 - 0.02M HF to the funnel and shake
vigorously for 10 sec. Drain the Np strip to a i00-ml breaker.
Repeat a second time and combine the two 25-ml solutions.
Discard the organic phase or strip with 0.IM HC]l for uranium
analysis.

Cvaporate the Np strip to dryness. Wet ash with HNO, and H;0;.
Rinse sides of breaker with 4M HNO3; and evaporate solution to
dryness.

Add 1 ml 4M IINO; and transfer solution to stainless steel

planchets and evaporate to dryness under an infrared lamp.

Complete transfer with 3 rinses of 4M HNO;.

Flame the dried planchet tc dull red, cool, and count on low-

level solid state alpha counters.

Calculation:

Np activity on planchet is determined as follows:

total count - Bkfll_
(t)(counter cff.)

dis/(min-planchet)

where: Bkgd. = counter background (3 to 10 counts/Z24 hr)
t = counting time in minutes
counter eff = counter efficiency as a fraction

{normally 0. 30)

The sensitivity of this analysis is 0.02 * 0.01 dis/ min-sample).

The recovery efficiency is determined by adding a known amount

of Np standard to an aliquot of urine sample and following the

same procedure for analysis.

- 188 -
Procedur2 19. Determination of 237Np by Gamma Ray Spectrometry
W. 0. Granade??

Introduction

A gamma spectrometric method was develored that allows for
the rapid determination of Np in process solttions containing
fission products. The method is unaffected Ly highly salted,

217

corrosive, or organic media. Np is determined by gamma

spectrometry using a thin lithium-drifted germanium [Ge(Li)] semi-

conductor detector to resolve the 86.6-keV 2?’Np gamma ray.

Apparatus

The detector system consists of an Ortec model 3113-10200,
low-energy photon detector with cooled FET przamp and a resolution
of 900-keV full width at half maximum (FWHM) at 86.6-keV. A
4096-channel pulse height analy:zer is used for the sccumulation
and storage of the gamma sjpectra. The data are read onto magnetic
tape or printed out directly from a high-spee digital printer.
Datz reduction is performed using an IBM 360 .:system and FORTRAN

programs developed to calculate nuclide abundanccs from multi-

channel gamma ray spectra.®

Procedure

Calibration. ?%*Pa, the daughter of 2?™Mp, has a 0.017
abundant gamma ray at B6.6-keV that interfere: with the mcasure-
ment of the 2?’Np gamma ray of the same erergy. 227Pa also has
4 0.34 abundant gamma ray at 311.9-keV that ir not associated with

a 2?’Np gamma ray. In order to determine the 2??Pa :ontribution

- 189 -
to the 86.6-keV 2?7Np photopeak, a pure stancard solution of

233pa is required. 2?%Pa is purified by passing an equilibrium
solution of 23’Pm-anp throveh a diatomaceors earth column which
sorbs *3%a. The 2%¥%a is eluted, and the 2°'Np contaminant level
is determined by alpha counting (??°Pa does not decay by alpha
emission). Aliquots of *'?Pa are pipetted into a standard gamma
counting geometry. A series of counts of the 2?3Pa are made to
determine the ratio of gamma counts at the 86.6-keV peak to counts
at the 311.9-keV peak. The ratio is used to calculate the 2?%pa

contribution to the total counts detected at the 86.6-keV peak.

The efficiency of the Ge(Li) detector for 86.6-keV gamma
rays is determined by calibration with known gamma standards

between 43.5 and 511.6-keV.

Araiyeis

The standards and sample are counted in a holder which ensures
a reproducible geometry at 2 cm. The deadtime correction (always
<20%) was found to be accurate to <1%. The gain setting of the
amplifier is adjusted to provide a peak width of 7 to 10 channels
(FWiiM) to allow reliable integration of the photopeak area. For
a Gaussian distribution, 99% of a peak area is contained in 2.1 x
FwliM. Therefore a peak area of 24 channels is used with a gain

setting giving 10 channels FWHM.

The net counts per minute of ?*’Np is calculated by subtractin
p P Y g

the Compton background and the 2?%pa contribution from the 86.6-keV

- 190 -
total photopeak area. The contribution of underlying Compton
background is assumed to be linear over the peak arca. An
average of the counts from 4 channels on each side of the peak

is used to determine the background correction. For an analyvsis
above the determination limit (the relative standard deviation is
less than 10% of the measured value), the peak area minus the

background should be greater than?:

o[- 2ae]

12.

The absolute disintegration per minute value of *’'N\p is
obtained by dividing the net counts per minute hy the product of
the gamma ray abundance (photon/disintegration) and the detector

efficiency at 86.6-keV.

A comparison of 2'’Np results obtaincd by gamma spectrometry
and TTA extraction® agreed within 3%. An aliquet of 1.06 x 103
alpha dis/(min-ml) z"Np standard solution was e¢xtracted using
TTA. A standard geometry sample was made from the TTA [orpanic)
phase and one from the aqucous phase. The resulting gamma count-
ing showed that 97% of the ??'Np had been extracted into the TTA
phase. Close agreement between the two mithods demonstrated the
reliability of the gamma pulse height analysis. Samples can be
counted in organic media with no adverse offects. A lower limit
of detection of 1 x 10° d/m/ml at a conficdence level of 95% was
determined from a series of counts using : diluted standard ?°7Np

solution.

- 191 -
Refarence
1. R. V. Slates. GELI 2 and SPAV 2, Fortro: Programs to

Caleulate liuclide rAdundances from Huitiarnel Garwma Ray
Spactra. USAEC Report DP-1275 (1971).

s
a

M. A. Kakat and E. K. Dukes, /. Szdioaniilve. Cier. <, 109
(1970).

3. F. Rider. Seciaciod Anciytival ¥etnodr Jor Furex Frococss
tontreic.  USAEC Report KAPL-890 (1953).

wr
-

- 192 -
Procedure 20, Spectrophotometric Determination of Np
R. G. Bryan and G. R. Waterbury®??

Outline of Method

Np is measured spectrophotometricallyr as the arsenazo III
complex after separation from Pu and impurity elements by liquid-
liquid extraction. U is removed first by extraction from 4M HCl
into triisooctyl amine (TIOA)}-carbon tetriachloride, while Np(IV)
and Pu(I1l) are stabilized in their nonexiractable oxidation
states by Fe(ll) and ascorbic acid. Then Np(IV) is extracted
from 84 HCl1 into TIOA and back-extracted into 0.1M HC1l. The
Np-arsenazo IIl complex is formed in 6.1M HCl, and the absorbance

is measured at a wavelength of 665 nm.

Heagente

® Arsenazo IIl, 0.2% [i,8-dihydroxynapthalene -3, 6-disulfonic
acid-2, 7-bis {azo-2)-phenylarsonic acid]. Dissolve 1 g
of arsenazo Il in 500 ml of water containing two KOH pellets.

® Ascorbic acid, 5%. Dissolve 6 grams of ascorbic acid in
120 m]1 of 8M HC1.

¢ Carbon tetrachloride, (CCl,) reagent grade.

e HCl, 12M, reagent grade.

e HCl, 8M, 4M, and 0.1,

& Np stock solution. Dissolve high purity Np metal in 12M KCl.
® Phosphoric acid, (1,P0,) 15.9M, reragent grade.

® KOH, pellets, reagent grade.

- 193 -
® Reducing solution, 5% ascorbic acid and 0.5% Fe(II)
ion in 4M HCl. Dissolve 2.5 gy of ascorbic acid and

1.75 g of Fe(NH2S03)2 in 50 ml of 4M NCI.

@ Tri(iso-octyl)amine-xylene (TIOA in xylene), 5%.
Dissolve 31 ml of TIOA in 500 ml of reagent-grade xylene.

e Tri(iso-octyl)amine-carbon tetrachloride (TIOA-CCl,),
S%. Dissolve 31 ml of TIOA ir 500 ml of CCl,.

Equipment

¢ Extractors (see figure in Reference 302).
e Laboratory glassware (beakers, pipets, syringes, and

volumetric flasks).

e Spectrophotometer, Beckman model DU or equivalent, with

matched fused-silica cells having l-cm light paths.

Pretreatment
The sample of metal or alloy is inspected, and extraneous

material is removed. Cutting oil is removed by washing with methyl
chloroform. For each Pu metal sample, take two accurately weighed
portions, each not greater than 200 mg and containing less than

60 ug of Np. Make duplicate determinations on each sample, on a
solution containing a known quantity of WNp, and on the reagent

blank solution.

- 194 -
Procedure

1.

10.

Place each accuratcly weighed sample in a glass extractor
and add 1.5 ml of 12M HCl. When the sample has dissolved,

add 1 ml of the reducing solution and 2.5 ml of water.

Prepare reagent blank solutions by adding 1 ml of reduc-

ing solution and 4 ml of 4M HCl to each of two extractors.

Prepare known Np solutions by adding an aliquot of

standard Np solution that contains an amount of Np
approximately equal to that expected in the sample and

1 ml of reducing solution to each of two extractors. Dilute

the solutions to 5 ml with 4M HCI.

Add 5 ml of TIOA-CCl, to ecach of the solutions prepared
in previous steps, mix the phases for 2 min, and then

allow the phases to separate for 1 min.
Separate the TIOA-CCl., layer and discard.
Repeat Steps 4 and 5.

Add S ml of 12M HCl and 10 ml of TIOA-xylene to each
extractor, mix the phases for 5 min and allow the phases
to separate for 1 min. Remove the aqueous phase con-

taining the Pu.

Wash the inside of the extractor with 5% ascorbic
acid-81 HCl, mix the phases for 2 min, and allow the

phases to separate for 1 min. Remove the aquecous phase.

WNash the inside of the extractor with B8M lHCl. Mix the
phases for 2 min, and allow to separate for 1 min.

Remove the aqueous phase.

Add 4 ml of 0.1M HC] to each extractor. Mix the phases

for 3 min, and allow to separate for 1 min.

- 195 -
11.

13.

14.

15,

Remove the aqueous phase into a 25-ml volumetric flask

containing 0.6 ml of H3PO,, 1 ml of 5% ascorbic acid-

8 HC1l, and 12.7 m]l of 12M HCI.

Repeat Steps 10 and 11,

Add 2.5 ml of 0.2% Arsenaz> III solution to the volumetric
flask, and dilute to 25 ml with water. Stopper and mix

the contents of the f'ask,

Measure the absorbance of the solution in cells having

l-cm light paths at a wavelength of 665 nm.

Np, ppm =
Ab =
Ak
As =
Wk =

(As-Ab) (Wk, ug of Np)
(Ak-Ab) (sample wt in grams)

absorbance of blank
absorbance of known Np solution
absorbance of unknown sample

ug of Np in known N solution

Relative standard deviations range between 7.2 and 1.1% in

measuring 8.5 to 330 ppm of Np in 200 mg samples. Of 45 elements

tested only Pd, Th, U, and Zr cause serious interference, but

only if present in concentrations greater than 0.8%. However,

initial extraction from 4M HCl into TIOA removes some U, and Th

is not significantly extracted from HC. solution. Also, H,4PO,

complexes up to | mg of Zr without affecting the analysis., HF

and HNO; cause low results unless removed by volatilization. The

method tolerates the intense radioactivity from quantities of

2)8py as large as 100 mg.

- 196 -
Procedure 21. Microvolumetric Complexonetric Method for Np

with EDTA

A. P. Smirnov-Averin, G. S. Kovalenko,
N. P. Ermoloev, and N. N. Krot'?®

Outline of Method

Np(IV) 1is titrated with a solution of EDTA at pH 1.3 to 2.0

with xylenol orange as indicator. The ireaction of Np(IV) with

EDTA is stoichiometric, and the color changes from bright rose

to light

yellow at equal molar concentriations. The determination

takes approximately two hours; the erro: is *(0.03 mg.

Reagents and Equipment

HC]l, reagent grade

Test solution, 10 mg Mn?® and 50 mg NH,OH<HC1 per ml
30% KOH

10% NaCl in 4M HC1

0.1% xylenol orange

Centrifuge tubes

Micro or semimicroburet

Procedure

1.

o
*

Add 1 to 4 ml of Np solution and 2 ml of test solution
containing 10 mg Mn?* and 50 mg of Nii,OH*HCl per ml into

a centrifuge tube.

Dilute to 6 to 8 ml, and heat to 60°C; add 30% KOH with
mixing until the pH >10.

Centrifuge the precipitate, and discard the solution.

Add 10% NaCl in 4M HCl1 dropwise until the precipitate is
dissolved.

- 197 -
5. Add 1 to 1.5 ml of 4M HC! containing 50 mg of NI20H*HCl
per ml, and heat the solution for 20 min on a boiling
water bath.

6. Cool the solution, dilute to ~1J0 ml with water, and add
1 to 2 drops of 0.1% xylenol orange.

7. Titrate with 2 x 1073M EDTA fronr a microburet until the
cclor changes from rose to brigit yellow.

Notes

1. HCl solutions are preferred in >rder to reduce all the
Np to the tetravalent state with NH0H*HCl. Ascorbic
acid is not suitable, since its decomposition products
interfere with the titration.

2. Doubly charged readily hydrolyzable ions (Mn**, Ni2*,
U022%), which do not interfere with the titration, are
used as carriers.

3. Np can be determined with an error of $0.03 mg in the

presence of large amounts of alkali, alkaline earth, and
rare carths elements, Mn2*, Zn2?*, cd?*, Pb?*, Cr?* (up

to 20 mg), Ni?*, Co?* and U022*. Anions which are
scparated by strong base precipitation include NO;~,
Q1,000™, SO04?™, C2042", Cr,0,2", and EDTA*". Pu is reduced
to Pu(III) and does not interfere up to 2 mg. Zr**, Th**,

and Fe®® interfere because they are cotitrated with Np(1V).

- 198 -
Procedure 22. Photometric Determination of Hp as the Peroxide
Complex

Yu. P, Novikov, S. A. lvanova, E. V. Bezrogova,
and A. A. Nemodruk???

Outline of Method

Np(V) forms an intensely colored complex in alkaline solutions
(pH >8). The ratio of Np(V) to H0; in the complex is 1:1; the
molar absorptivities of the complex at 430 and 370 nm are 5010 2210

and 7950 £350, respectively. The method is highly selective for Np.

Peagents and Eq': . ent
e NaOH, CP gradc
® "202, CP grade

e Spectrophotometer and cells.

Procedure

1. Add the dilute acid (HNO,;, HCl1l, or hHClQ,) solution,
2.5 ml containing 5 to 50 ug of Np into a test tube.

N

Adjust to Np(V) by adding 0.1 ml of 30% H,0,, and keep

in a boiling water bath for 10 min.
3. Cool the solution, and add 0.1 ml of 0.5M H,0,.

4. Neutralize to pH 1 to 3 with Na0l, and add an extra 1 ml
of 4M NaOH.

5. Dilute to exactly 4 m}l with water, and mix thcrcughly.

6. Measure the absorbance in a 1 cm cell at 430 or 370 nm

realtive to a blank.

7. Determine the Np content using a calibration curve.

-~ 199 -
Notes

1.

Np(V), but not Np(IV) or Nu(VI), gives a color reaction
with H-0,.

The stability of the colored Np(V) peroxide complex
increases as the pH is increased. In 0.IM NaCOH solution,

the absorbance remrins unchanged for two hours.

Increasing the H,0; concentratiol to >7 x 107°M does not
change the ahsorbance. At higher H202 concentrations,

the time for constant absorbance increases.

When the solution contains U, 7 to 10 mg of (NHs4)2HPO,
is added before the NaOH. Great2r amounts of the phosphate
reduce absorbance of the Np(V) complex.

Fluoride reduces the absorbance of the Np(V) peroxide
complex. Tartrate, carbonate, and sulfate ions to 0.1M
have no effect. When iron is present, Fe(OH).; precipitates
and is removed by centrifugation. Up to 300-fold amounts
of Fe do not interfere. Four-fold amounts of Pu do not

interfere.

- 200 -
Procedure 23. Separation of Np for Spectrographic Analysis of
Impurities

J. A, Wheat???

Outiine of Method

Np compounds are dissolved in concentratec¢ HNOj, and the
solution is heated to dryness. The residue is dissolved in
dilute HNO3, and Np oxidation state adjustment is made with NzH.
and sulfamic acid. The hexanitrato anionic complex of Np(IV) is
sorbed on strong base anion resin; the cationic impurities are
not sorbed by the resin. The cycle is rzpeated, and the effluents
are evaporated and baked at 400°C. The residue is dissolved in
6M HCl, and the cationic impurities are determined by emission

spectroscopy.

Reagents and Equipment

® Double-distilled HNO;

e "Dowex" 1-4 100 mesh

e Hydrazine (N2Ha)

@ Sulfamic acid

e Cobalt solution

® Small glass column

® Spectrograph
Procedure

1. Dissolve 50 mg of sample in concentrated HNO,, and

evaporate to dryness.

2. Dissolve solid residue in 2 ml of 0.35M HNO, and add one-
fourth ml of 11M aqueous solut.on of N,li,. Wait at
least 30 min for valance adj'::ment.

- 201 -
3. Add one-half ml of 3M sulfamic acid and 2.5 ml of 16M

HNO,, and mix the solution.

4. Pass the adjusted solution thraugh a 3 ml bed of !JU-mesh
"Dowex" 1-X4 resin at <3 ml/(min-cm?®), and collect the

effluent.

5. Wash the resin with 10 ml of BM HNO;, and combine the
effluent with that from Step 2.

6. Elute Np from the resin with 0.35M HNO;, and condition
the column with 8M HNO; for rease.

7. Evaporate the sorption and was: effluents tc dryness,
and repeat Steps 2 through 6. (99.96% of the Np was

removed with two cycles of aniin exchange).

8. Evaporate the sorption and wasi effluents from Step 7
to dryness and bake at 400°C t> expel hydrazine.

9. Dissolve the residue in 1 ml of aqua repgia, and evaporate

to dryness.

10. Dissolved the last residue in | ml of GM HCl containing
100 ug of Co, which serves as in internal standard.

11. Evaporate two hundred uf of th:2 solution to dryness on
top of a 1/4-inch-diameter flat-top electrode.

12. Excite the sample for 30 sec bs a 10-amp dc arc using a
large Littrow spectrograph in the 2500 to 3500 A
wavelength region. The slit width is 10 ym, and a two-
step neutral filter 100%/35% is inserted in the slit.

SA-2 emulsion is used.
Because of the relatively large volume of reagents used,
a reagent blank should be carried throuzh the procedure. Doubly

distilled HNO3; was used.

- 202 -
Recovery was 88 to 106% for all elements except Ni which was

65%.

The coefficient of variation for a single determination of
the several elements varies from 9 to 24% with an average of
17%. The precision is affected by large volumes of reagents and
incomplete removal of cationic impurities from the resin column.
The method was applied to determination of Fe, Cr, Ni, Mn, Cu,

Al, and Mg.

- 203 -
Procedure 24. Photometric Determination of Np as the
Xylenol Orange Complex

N. P. Ermoloev, G. 5. Kovalenko, N. N. Krot,
and V. J. Blokhin3%®

Outline of Metnod

Np(IV) reacts in weakly acidic solution {pH “2) with xylenol
orange to form a color complex with an absorbance maximum at 550
nm and molar extinction coefficient of 5.5 x L0°. Xylenol orange
15 three times more sensitive than thorin but only one-half as
sensitive as Arsenazo I11 as a reagent for Np{IV). The greatcst
advantage of xylenol orange compared to thorin and Arsena:zo III

is the relatively minor interference of U.

Reagents and Equipment

e HCI
e 30% KOH
@ Test solution, 10 mg Mn?* and 50 mp of Ni;0t=1C] per ml
® 100 mg NI;0H*HC] per ml in 7N {IC]
® M NH, Ol
® 0.05% xylenol orange
e pli meter
® Spectrophotometer
® Centrifuge tubes
Frooedure

L. Add sclution containing S to 0 ug of NXp to a centrifuge
tube, and dilute to § to 8 ml; then add 30% KOM until
pil >10.

fe

Add | @l of test solution contnining 10 mg of n®® and
50 mp of NN;ON-ICLl int: the contrifupe tube.

- 204 -
Mix and centrifuge the precipita:e. Discard the liquid;
then dissolve the precipitate in 2 ml ¢f M HCl contain-
ing 100 mg NH20t<HC1 per ml.

Heat the solution to almost boiling on a water bath for

25 min to obtain Np(IV).

Dilute to 15 ml with water, add exactly 1 ml of 0.05%
xylenol orange, and adjust to pH 2.0 to 2.2 with 21 NH,OH.

Transfer the solution quantitatively to a 25 ml volumetric

flask, and dilute to volume with water.

Mix and measure the optical density of the solution on an
FE'K-M Instrument fitted with a preen filter and using
cells with a path of 5 cm at 550 nm. The reference
solution is the same pli and rcagent composition as the

Np solution.

doten

The Np concentration is determincd from a standard

calibration curve.

The determination requires -3 hours, and the crror usually
is <2lug.

Np can he determined by the above method in HCl, INO,,
ICz00,0;, and NSO, solutions and also (& solutions
contalning other anions that are removed by the strong
base precipitation; fluoride and phosphate interfere.

Alkali, alkaline-carth, rare carths, and n®*, cd?®, wn?°,
Xi?®, and Cr'® can be tolerated at 100 times the wcight
of Np. liexavalent U up to 10 mg does not interfere.
fu(lll) up to 200 ug doos not interfere unless storcd for
a period of time which results in oxidation to Pu(IV).
Fel®, 2r*'. Th*®, and 84'° jons form intensely colored
species that interferc unlcss seoparated.

- zu -
Procedure 25. Analysis for Np by Controllied Potential Coulometry
R. W. Stromatt*!?

Introduction

Controlled potential coulometry is uteful for detecting as
little as 2 ug of Np, and 7 ug can be determined with 6% standard
deviation. The general procedure is to first oxidize all the Np
to Np(VI) with Ce(IV), then the Np(VI) and excess Ce(IV) are
electrolytically reduced to Np(V) and Ce(111). Finally the Np(V)

is coulometrically oxidized to Np{VI) to determine the concentration

of Np.

Reagents and Equipment

1M H3SOs

Mercury metal

Mercuric sulfate

Pure helium gas

Sodium silicate solution

Controlled potential coulcmeter

Titration cell (working electrode Pt gauze, isolated
electrode Pt wire and saturated calomel

reference)

Procedure

1. Add the Np sample and the titration medium into the cell,
and adjust the hydrogen ion and sulfate ion concentrations
to vIN. (The hydrogen ion concer.tration is not critical
between 0.4 to 2N but the electrvde potential of the
Np(V/V1) couple is affected by the sulfate concentration).

2. Add Ce(lV) solution untii there is an excess as evidenced

by a persistent color.

- 206 -
De-aerate the solution with He for 5 min. (If during
this time the excess Ce(lV) has reacted, add additional

ce(IV)].

Apply the potential to reduce the \wp(VI) and excess
Ce(IV) to Np(V) and Ce(111) until the current becomes

constant.

Apply the potential to oxidize the Np(V) to Np(VI).

The oxidation is continued until a constant current is
obtained. Make several recadings of the integrated
current, and extrapolate the integrated current curve to

zero time.

Prepare a blank solution containing the same amount of

Ce(IV), and after 5 min of de-aeration perform reduction
and oxidation titrations at the same potentials as used
for the Np titration. After conrstant current is reached
for oxidation, read the integratec currcnt several times

and extrapolate to zero time.

Subtract the zero-time integrated current of the blunk

from that for the Np titration, ard calculste the amount

of Np based on the instrument calibration. (lor highest
accuracy, the Np lost in the de-acration and (rom migration

in the cell are taken into account.)

Notes

1.

The Np(V)/(VI) couple can be titrated gquantitatively and
reversibly in HNO,, 1iC10., and lI;50,; however, more
reproducible results arc obtained with 11;50,. Also, the
potentials of the Pu(Ill)/(1V) and Np(V)/({VI) counles are
separated better in 113S0..

- 207 -
Ce(IV) ion is used for oxidation because oxidation of
Np is rapid and quantitative, and Pu(IV) is not oxidized

significantly in H;S0,.

Coulometric titrations in solutions containing organic

contaminants are often slow and yield low values.

The concentration of Np in the different oxidation
states can be made using the Pt electrode cell. The
Np(V)/ (V1) couple can be titrated without interference
from oxidation of Np(IV).

Np(VI) is determined by coulometric reduction to Np(V).
The Np(V) is then oxidized coulcmetrically, and the
difference between these two titrations is the Np(V)
initially present. The total Np concentration is deter-
mined as previously discussed, and Np(IV) is calculated
from the difference between the concentrations of Np(V)

plus Np(VI) and the total Np.

Propst®'® has reported a coulometric method for Np
utilizing a conducting glass ele:ctrode in a thin-layer
electrochemical cell. Organic contaminants interfered

and were removed by a bisulfate fusion procedure.

- 208 -
1.

2.

10.

il.

12.

13.

14.

15.

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- 209 -
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31.

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- 210 -
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