Solubilities of Pu(III), Am(III), and Cm(III) oxalates

INORG.

NUCL.

CHEM. LETTERS

Vat. 3,

pp.

79-85, 1 9 6 7 .

Pergamon

PreJs

Ltd.

Printed

Great Britain.

In

SOLUBILITIES OF Pu(lll), Am(lll), AND Cm(lll) OXALATES G. A. Burney

and J. A. Porter

Savannah River Laboratory E. I. du Pont de Nemours and Co. Aiken, South Carolina 29801 (Recelved ! Decembe, I~6}

This paper reports Am(lll), These

and Cm(lll)

oxalates

plutonium, Cm(lll)

measurements

oxalates

are useful

americium,

are known

in nitric

to form quite

study of solubilities

in nitric

reported

Several

have been

reported

V. N. K o s y a k o v (5) solubility However, Cm(lll)

insoluble

no m e a s u r e m e n t s

have

oxalates,

acid--oxalic

acid

solutions.

studies

of

Am(lll),

and

no systematic solutions

has been

of limited

scope

and G. N. Yakovlev

that a precipitate

of 18 mg per liter was formed

acid

Pu(lll),

oxalate, (~-4)

reported

of Pu(lll),

and purification

Although

solubility

for Pu(lll) have

acid--oxalic

in the separation

and curium.

previously.

of the solubilities

of Am(lll)

and

with a

in O. IM HNO3--O. IM H2C~© 4.

been reported

for the solubility

of

oxalate.

EXPERIMENTAL Reagents A stock solving

sample

a specimen

Plutonlum(lll)

of pure ~39Pu(lll) of pure

oxalate

tion by the addition tation,

precipitate drying Pu(lll)

solution

the Pu(lll)

state.

was washed

by a s p i r a t i o n oxalate

Americium

metal

was precipitated

of IM H~C204.

the p l u t o n i u m

stabilize

plutonium

oxalate

decahydrate and curium

from

solution volume

temperature,

79

acid

was filtered,

and

of O. IM H~C304. the bright

solu-

to the precipi-

to O.05M ascorbic

was a f r e e - f l o w i n g

separated

prior

by dis-

acid.

the sulfamic

Immediately

with a small

at room

in sulfamic

was adjusted The

was prepared

acid the

After

blue-green,

powder.

from n e u t r o n - i r r a d i a t e d

~3~Pu

to

80

SOLUBILITIES

OF Pu(lll), Am(ill), AND Cm(lll) OXALATES

Yol. 3, No. 3

were used to prepare stock solutions of their purified nitrates. The separation program,

scheme was developed as part of a large production

which has been described

irradiated

elsewhere. (e)

plutonium was dissolved;

with trlbutyl phosphate; flssion-product

precipitation

the residual plutonium extracted

solution.

with tertiary amine from concentrated Americium was separated from curium by

of K3AmOs(COm) ~ in KsCOe;

element were precipitated

and calcined

dissolved

acid;

in hydrochloric

purified by anion exchange, hydroxide.

the

and the a m e r i c i u m and curium separated from

lanthanides

lithium chloride

In brief,

then the oxalates of each to the oxide.

The oxide was

the americium and curium were

and then precipitated

with ammonium

The americium and curium hydroxides were dissolved

nitric acid.

The a m e r i c i u m was essentially pure ~43Am;

was a p p r o x i m a t e l y

95% 2"4Cm.

The americium

a~pha spectrometry. spectrometric

the curium

stock contained

tha~ two parts of curium per thousand of americium,

in

less

as determined

by

The americium was shown to be trivalent by

analysls. C'7)

two parts of americium

The curium stock contained

per thousand of curium,

extraction and gamma countlng (e) of the a known period of in-growth. •firmed that no other cationic solutions in greater

Emission

SaONp

less than

as determined

by

daughter of S4SAm after

spectrographic

analyses con-

impurities were present in the stock

than one part per thousand of actinide.

All other reagents were prepared from reagent-grade

chemicals.

Pr~edures To determine Cm(III) oxalate,

the equilibrium

solubilities

an aliquot of purified Am(III)

o£ Am(III) or Cm(III)

oxalate or stock

solution was added to a solution of nitric and oxalic acids in the desired concentrations, nation,

in a polyethylene

bottle.

In each determi-

enough americium or curium was added to ensure an excess of

the solid actinide oxalate at equilibrium. placed on a mechanical

shaker and agitated at 23°C.

~n aliquot of the sample was withdrawn was filtered,

The plastic bottle was

and the c o n c e n t r a t i o n

supernate was determined

for analysis.

At intervals, This aliquot

of americium or curium in the

using the methods described

in the pre-

Voh 3, No. 3

SOLUBILITIES OF Pu(lll), Am(ill), AND Cm(lll) OXALATES

ceding section.

The c o n c e n t r a t i o n

tion with standard

ganate.

of acid was determined

sodium hydroxide,

oxalate was determined

by titration with standard potassium perman-

required

Pu(III) oxalate differed oxalates.

included

acid,

solubility of

oxalate decahydrate

acid solutions.

were performed at 2i°C.

absence of ascorbic erroneous

the equilibrium

An excess of solid Pu(III)

in the solutions

equilib-

somewhat from that for the Am(III) and

was added to the nitric acid--oxalic equilibrations

the system reached

less than sixteen hours.

The procedure used to determine

Cm(III)

by titra-

and the c o n c e n t r a t i o n of

Analyses were continued until

rium, which usually

81

to stabilize

Also,

the

O.05M ascorbic acid was also the Pu(III)

the oxidation of Pu(III)

state;

in the

to Pu~(IV) caused

results.

RESULTS AND DISCUSSION Plutonium(Ill) Oxalate The solubility of Pu(Ill) 0.285M H~C204

and 0.5 to 3.1M HNO 3.

show that increasing creases

Increasing

the solubility

where soluble oxalato

in 0.095 to

The solubility data in Figure

the concentration

the solubility.

decreases

oxalate was measured

of nitric acid greatly in-

the oxalic acid concentration

except at low nitric acid concentration,

complexes

are formed.

Americium(Ill) Oxalate Tan-brown Am(III) species precipitated The solubility

oxalate heptahydrate from aqueous

of Am(III)

increases

centration, formed. tions.

decreases

in 0.025 to

The solubility data in Figure 2

the concentration

the solubility.

solubility

solution.

oxalate was measured

0. SM H2C~O 4 and 0. i to 4M HN0~. show that increasing

is the reported (9)

of nitric acid greatly

In 0. I and 0.25M HN03

initially with increases

solutions,

the

in oxalic acid con-

and then increases as soluble oxalato complexes

are

This effect is not noted at higher nitric acid concentraThe solubility of Am(III)

Pu(III) oxalate.

oxalate

is similar to that of

i

82

SOLUBILITIES

OF Pu(III), Am(Ill),

AND Cm(lll) OXALATES

Vol. S, No. 3

I000 '

'

I

'

'

'

'

'

'

'

'

HN03, M 3.l

._=

2.6

#-,oo 2.0

E _o

1.5

o

g.

1.0

~0 ,ID

~

0.5

0

1.0

I

I

( ,

0.I

,

r

J

I

i.O

H2Cz04, M

FIG. I SOLUBILITYOF Pu(lll) OXALATE IOOC

p

=

= slllr

I

I

I

I p+rrl

•

1

r

[

1

I

Ilr

4.0

Ha~3,M

~ IOC ,
E

o o

~

~0

E

0.25 0.10 ~

1.0

Temperc~ture: 23"C 0.1

I

0.01

I

I IIIllJ

t

l

J IllJJJ

0.1

I

i

I I I

H2C204, M FIG. 2

SOLUBILITY

OF A m ( i l l )

I

I0

1.0 OXALATE

Vol. 3, Nc~. 3

SOLUBILITIES

OF Pu(III), Am(Ill), AND era(Ill) OXALATES

83

Depletion of oxalate ion or hydrogen ion by alpha radiolysls was not a problem when ~'aAm was used for the solubility determinations.

After the first 4 to 12 hours in some three-day equilibra-

tions,

there were no detectable variation~ in solution composition

or changes in solubility. Curium(Ill) Oxalate

The solubility of Cm(III) oxalate was measured in 0.025 to 0.5M H~C204

and 0.1 to 4M HN0 a.

The solubility data in Figure 3

are similar to those in Figure 2; however,

curium oxalate is

slightly less soluble than americium oxalate at a given solution composition.

IO00 '

' ''''"I

'

' ' '''"I

'

' ' ''"~

.= ioo

HNi~, M

E

O ¢P

E

o o

I0

-g U

0 50 ¢1 "6 (/)

0.25 O]O

1,0

Temperoture:

010.01

I

I

I

I

I lllll

i

I

I I I I i I

0.1

1.0

J

2YC I

l

I I I II

I0

H2C204, M

FIG. 3 SOLUBILITY OF Cm(lll) OXALATE The radiolytic destruction of oxalate ion is rapid enough in solutions of ~''Cm that this effect must be considered in attempting to determine equilibrium solubilities.

The solubilities reported in

84

SOLUBILITIES OF Pu(III), Am(Ill), AND Cm(lll) OXALATES

Yol. 3, No. 3

Figure 3 that are less than i0 mg of S4*Cm per liter are considered to be as accurate as those reported for americium oxalate, the changes in oxalate concentration

because

that resulted from radiolytic

destruction of oxalate ion were less than the limits of accuracy of the analytical determination

(~3%).

At concentrations

of approxi-

mately 50 mg of S4*Cm per liter and less than O. IM oxalate, uncertainty in the data caused by radlolysis 5%.

At solubilities

the

effects is approximately

greater than 500 mg of ~4*Cm per liter in solu-

tions containing less than 0. SM oxalate, depletion of oxalate is relatively rapid,

the rate of radlolytlc and the data in this re-

gion of Figure 3 should be considered only approximate. The light green Cm(II~ oxalate decomposes

very rapidly even at

room temperature when removed from the oxalic a c i d ~ n i t r l c supernatant

solution.

a carbonate

species within a few hours after filtration,

by rapid dissolution Thermogravlmetric

It is apparently converted radiolytically

analysis

showed decomposition

radiolytic degradation occurring

as evidenced

500°C in air.

to be less well de-

probably because of the

simultaneously with thermal decom-

The oxalate is converted

approximately

to

in dilute acid with the evolution of gas.

fined than that for Am(III) oxalate,

position.

acid

to black curium dioxide at

Vol. 3, No. 3

SOLUBILITIES

OF Pu(lll), Am(Ill), AMO Cm(lll) OXALATES

85

ACKNOWLEDGMENT The information contained

in this article was developed during

the course of work under Contract AT(07-2)-I with the U. S. Atomic Energy Commission.

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1.

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