(IV) Couple in Various Media - ACS Publications

21

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch021

A Contribution to the Study of the Oxidation Potential of the Berkelium (III)-(IV) Couple in Various Media C. MUSIKAS and R. BERGER Department de Chimie, Services de Chimie des Combustibles Irradies, Section d'Etudes Chimiques et Radioactives, Commisariat a l'Energie Atomique, Centre d'Etudes Nucléaires, Fontenay aux Roses, France

Indirect determinations of the formal oxidation potential of Bk(IV)—Bk(III) couple in sulfuric and nitric acids have been made by tracer measurement. From the Bk(IV)/Bk(III) ratios and the corresponding Ce(IV)/Ce(III) ratios at equilibrium conditions one can calculate the oxidation potential of the Bk(IV)-Bk(III) couple. The Bk(IV)/Bk(III) ratio can be determined by extracting Bk(IV) by an appropriate organic solvent. The formal oxidation potentials of the Bk(IV)Bk(III) couple in 1N and 0.5N sulfuric acid were found to be 1.42 and 1.44 volts using trilaurylmethylammonium sulfate in carbon tetrachloride as a solvent. In 6N nitric acid the oxidation potential of the couple was found to be 1.56 volts by using 0.18M tributylphosphate. Whereas, in 1N to 2N nitric acid berkelium was not oxidized by cerium(IV).

/ ~ \ x i d a t i o n of b e r k e l i u m to t h e tetravalent state w a s d e m o n s t r a t e d i n 1950 b y T h o m p s o n , C u n n i n g h a m , a n d S e a b o r g

(7).

Using

eerie

i o d a t e as a t e t r a v a l e n t species c a r r i e r f o r tracer experiments, t h e y f o u n d that i n 8N H N 0

3

m e d i u m t h e f o r m a l o x i d a t i o n potentials of t h e C e ( I V ) -

C e ( I I I ) a n d t h e B k ( I V ) - B k ( I I I ) couples w e r e n e a r l y t h e same. I n t h e same y e a r Jones a n d C u n n i n g h a m c o n t i n u e d these e x p e r i ments (2)

a n d f o u n d t h a t the c e r i u m a n d t h e b e r k e l i u m a d s o r p t i o n o n

z i r c o n i u m p h e n y l a r s o n a t e c a r r i e r w e r e s i m i l a r regardless of t h e o x i d i z i n g agent ( b i c h r o m a t e , c h l o r a t e , h y p o c h l o r i t e , or b r o m a t e ) , or t h e m e d i u m ( I N n i t r i c a c i d , 1 M l i t h i u m p e r e h l o r a t e - p e r e h l o r i c a c i d at h y d r o g e n i o n 296

Fields and Moeller; Lanthanide/Actinide Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

21.

MusiKAs

A N D

Oxidation

B E R G E R

concentrations f r o m 0 . 1 N to I N ) .

297

Potential

F r o m these experiments t h e y

con-

c l u d e d t h a t the o x i d a t i o n p o t e n t i a l of the B k ( I V ) - B k ( I I I ) c o u p l e d i d not differ b y m o r e t h a n 60 m v . f r o m that of the C e ( I V ) - C e ( I I I )

couple.

I n o r d e r to c o m p l e t e these experiments w e u n d e r t o o k tracer l e v e l measurements of the f o r m a l o x i d a t i o n p o t e n t i a l of the B k ( I V ) - B k ( I I I ) c o u p l e i n n i t r i c a c i d a n d s u l f u r i c a c i d solutions, u s i n g the

Ce(IV)-

C e ( I I I ) c o u p l e as a m e d i a t o r . T h e tetravalent species w e r e extracted b y Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch021

o r g a n i c solvents. A s i m i l a r m e t h o d was u s e d b y M a t s u u r a a n d H a i s s i n s k y i n 1958

(4)

a n d b y H a i s s i n s k y a n d P l u c h e t i n 1962 ( I ) for d e t e r m i n i n g the f o r m a l o x i d a t i o n potentials of

the P o ( V I ) - P o ( I V )

a n d the

Pa(V)-Pa(IV)

couples r e s p e c t i v e l y . W e took a d v a n t a g e of the p r o p e r t y of different solvents to extract selectively the tetravalent a c t i n i d e a n d l a n t h a n i d e elements. t h e m are sufficiently stable i n the presence of o x i d i z i n g agents. the o r g a n o n i t r o g e n a n d o r g a n o p h o s p h o r u s

Some

of

Among

compounds we used were t r i -

l a u r y l m e t h y l a m m o n i u m ( T L M A ) salts a n d t r i b u t y l p h o s p h a t e ( T B P ) i n carbon tetrachloride.

Principle of the Method T h e f o r m a l o x i d a t i o n p o t e n t i a l of the B k ( I V ) - B k ( I I I ) c o u p l e c a n b e deduced

f r o m N e r n s t s l a w i f the d i s t r i b u t i o n e q u i l i b r i a b e t w e e n

aqueous phase a n d the n o n m i s c i b l e o r g a n i c phase is r e a c h e d .

the

This can

be w r i t t e n as: E

i

EU

_ -

F f

Ef

ce

+ M [Ce(IV)] + - p - log [

C

e

(

m

)

L

a

X

[Bk(III)]. (IV)]

[ B k

e

m ( 1 )

i n w h i c h the concentrations are aqueous concentrations after extraction. T h e different terms of E q u a t i o n 1 w e r e o b t a i n e d as f o l l o w s — E f , f o r m a l p o t e n t i a l of the C e ( I V ) - C e ( I I I ) c o u p l e i n the m e d i u m , w a s taken from publications; [ C e ( I V ) ] and [ C e ( I V ) ] have been measured b y direct absorption spectrophotometry; [ C e ( I I I ) ] was c a l c u l a t e d b y difference b e t w e e n t o t a l c e r i u m , t i t r a t e d b y p o t e n t i o m e t r y , a n d t e t r a v a l e n t c e r i u m ; [ B k ( I V ) ] was c a l c u l a t e d f r o m the solvent b e t a c o u n t i n g , a l l o w i n g for the m e a s u r e d d i s t r i b u t i o n coefficient of B k ( I V ) ; [ B k ( I I I ) ] was d e t e r m i n e d b y s u b t r a c t i n g the [ B k ( I V ) ] v a l u e f r o m the aqueous c o u n t i n g ; i n a l l cases [ C e ( I I I ) ] a n d [ B k ( I I I ) ] w e r e f o u n d to b e negligible. Ce

a

0

f f

a

a

a

0

0

T o t a l oxidation a n d extraction e q u i l i b r i u m were verified b y p l o t t i n g : [Bk(IV)]

w

[Ce ( I V ) ] q

a

- W i n n : ° i^mm: a n d c h e c k i n g to see that the slope of the straight l i n e w a s close to 1. l

o

g

m

l o g l


298

LANTHANIDE /ACTINIDE

CHEMISTRY

Preliminary Experiments T o d e t e r m i n e t h e aqueous a n d o r g a n i c concentrations of t h e tetrav a l e n t c e r i u m a n d b e r k e l i u m w i t h sufficient a c c u r a c y , i t w a s necessary % initial. Cerium (IV)


100 0.05 M TLMA sulfate . C C U 90 H

A

80

0.1 M

704

60

0,08M

50

TLA

1h

Figure 1.

Reduction

TLMA-HNOs.CCU

sulfate.CCU

• Time hours 3h

2h

rate of cerium(IV)

in various organic solvents

% initial Cerium (IV)

1N H2S04

100 1N

H 2 S O 4 - I N HNOs

1N HCUK

8 Time hours

Figure 2.

Reduction

rate of cerium(IV)

in various aqueous media


21.


Optical

MusrxAs

Oxidation

Potential

299

density

Figure 3.

Optical

A N D B E R G E R

A:1N

H z S O J » non electrolysed

Β · 1N

Ht SOùt

electrolysed

(used

for

dilutions)

Effect of the electrolytic oxidation of sulfuric acid on Beers lines at 380 mμ for cerium(IV)

density

straight

A : 1N HeSOt aqueous Β : 0.18 M T B P - CCI 4

A

C:

Figure 4.

0.05M

TLMA sulfate. C C U .

Absorption of cerium(IV) at 380 m μ in various media

to find a solvent i n w h i c h the d i s t r i b u t i o n coefficients of these t w o tetra v a l e n t species b e t w e e n the solvent a n d the chosen aqueous m e d i u m w a s i n the r a n g e 0.1 to 10. I n a d d i t i o n the o x i d a t i o n rate of the solvent b y the t e t r a v a l e n t elements s h o u l d be sufficiently l o w . F o r s u l f u r i c a c i d solutions, t r i l a u r y l m e t h y l a m m o n i u m sulfate i n c a r b o n t e t r a c h l o r i d e w a s p r e f e r r e d to t r i l a u r y l a m i n e sulfate because i t is less sensitive to o x i d a t i o n b y c e r i u m ( I V ) ( F i g u r e 1 ). I n the case of n i t r i c a c i d , t r i b u t y l p h o s p h a t e


300

LANTHANIDE /ACTINIDE

CHEMISTRY

i n c a r b o n t e t r a c h l o r i d e gives h i g h e r d i s t r i b u t i o n coefficients for b e r k e l i u m t h a n t r i l a u r y l m e t h y l a m m o n i u m n i t r a t e i n the same d i l u e n t . B e c a u s e the r e d u c t i o n rate of c e r i u m ( I V )

i n these solvents is not

n e g l i g i b l e , i t is necessary to take samples for b e t a c o u n t i n g a n d spectrophotometry? analysis at the same t i m e . T h e c o n c e n t r a t i o n of c e r i u m ( I V ) w a s d e t e r m i n e d b y d i r e c t a b s o r p t i o n s p e c t r o p h o t o m e t r y at 380 m/x, b o t h i n aqueous a n d i n o r g a n i c solutions. T h i s w a v e l e n g t h was chosen i n o r d e r


to a v o i d a n y i n t e r f e r e n c e b y the reagents. I n s u l f u r i c a c i d , t e t r a v a l e n t c e r i u m is m o r e stable t h a n i n the other a q u e o u s solutions ( F i g u r e 2 ) .

F o r this reason I N H S 0 2

the m e d i u m for s p e c t r o p h o t o m e t r i c measurements.

4

was chosen as

N e v e r t h e l e s s i t was

necessary to o x i d i z e e l e c t r o l y t i c a l l y a l l the reagents b e f o r e the spectrop h o t o m e t r i c measurements.

T h i s is i l l u s t r a t e d b y F i g u r e 3 i n w h i c h the

o p t i c a l densities vs. the c e r i u m ( I V ) concentrations are p l o t t e d . T h e v e r i f i c a t i o n of L a m b e r Beer's l a w is s h o w n i n F i g u r e 4.

Organic

solutions of c e r i u m w e r e p r e p a r e d b y e x t r a c t i n g c e r i u m ( I V ) f r o m t i t r a t e d a q u e o u s solutions a n d s t a n d a r d i z e d b y b e t a c o u n t i n g of

1 4 1

C e tracer.

S t a n d a r d i z a t i o n curves w e r e p l o t t e d f r o m three values for f u r t h e r spect r o p h o t o m e t r i c d e t e r m i n a t i o n s of c e r i u m ( I V ) . T h e b e r k e l i u m ( I V ) e x t r a c t i o n coefficients h a v e b e e n d e t e r m i n e d b y s t r i p p i n g solvents p r e v i o u s l y l o a d e d w i t h t e t r a v a l e n t c e r i u m a n d b e r k e l i u m i n the presence of s o d i u m b i s m u t h a t e .

Sodium bismuthate

has

b e e n f o u n d to be a n efficient o x i d i z i n g agent for t r i v a l e n t c e r i u m . B e c a u s e of its s m a l l s o l u b i l i t y i t does not affect the d i s t r i b u t i o n coefficients

of

tetravalent cerium.

by

These two properties have been demonstrated

c o m p a r i n g the d i s t r i b u t i o n coefficients of c e r i u m ( I V ) m e a s u r e d b y spect r o p h o t o m e t r y w i t h those of c e r i u m o x i d i z e d b y s o d i u m b i s m u t h a t e a n d m e a s u r e d b y b e t a c o u n t i n g of the

1 4 3

c e r i u m isotope tracer. T h e d a t a are

s u m m a r i z e d i n T a b l e I a n d i n d i c a t e no r e a l difference i n the d i s t r i b u t i o n coefficients

of c e r i u m o b t a i n e d b y these t w o m e t h o d s

when using tri-

l a u r y l m e t h y l a m m o n i u m s a l t s - c a r b o n t e t r a c h l o r i d e as solvent. Table I.

Effect of Sodium Bismuthate on the Distribution Coefficients of Cerium (IV) E° a

Organic 0.05M TLMA-Sulfate

Spectrophotometric Determination of Ce(IV)

Aqueous 0.5N H S 0 2

0.1M TLMA-Sulfate

IN H S0

0.1M T L M A - H N O ; ,

I N HNO

0.1M TLMA-HNO3

6N H N O 3

2

4

; î

4

Ce(IV) Beta Counting of Ce (-bNaBiOs) ni

7.7

7.4

2.6

2.7

110

78

200

240


21.

MusiKAS

Oxidation

A N D BERGER

301

Potential

Table II. 0.1M Trilaurylmethylammonium Nitrate—Carbon Tetrachlo ride Extraction of Cerium and Berkelium from N i t r i c A c i d Solutions in the Presence of Sodium Bismuthate


Aqueous IN IN IN 4N 4N 6N 6N 8N ΙΟΝ

HN0 HNO3 HNO3 HNO3 HNO3 HNO3 HNO3 HNO3 HNO3

E° a

3

+

1.5M A l ( N O )

H

+

1.5M A 1 ( N 0 ) ,

s

3

H

1 1 65 12 20 6 9 3.6 2

110 110 100 100 100 100 100

3

(without N a B i O ) + 1.5M A 1 ( N 0 )

% of Initial Bk Extracted

Ce(IV)

3

C e ( I V ) initial aqueous concentration = 6.0 X 1 0 " M E ° C e (III) < 0.005 when [ H N O 3 ] < 6 N 3

a

Experimental

Apparatus. T h e f o l l o w i n g apparatus was u t i l i z e d for this s t u d y : a P R T 2000 t y p e potentiostat ( T a c u s s e l ) for the electrolysis; a G r a p h i s p e c t r a l spectrophotometer ( J o u a n ) for the a b s o r p t i o n measurements; a T S 6 t y p e m i l l i v o l t m e t e r ( T a c u s s e l ) for p o t e n t i o m e t r i c analysis; a 2?r w i n d o w l e s s flow gas counter ( S . A . I . P . ) for m e a s u r i n g the soft b e t a f r o m B k ; a n d a b e l l t y p e G e i g e r counter for C e and C e beta counting. 2 4 9

1 4 1

1 4 4

Reagents. B E R K E L I U M . A n a m o u n t of 5μ C i of b e r k e l i u m 249 was s u p p l i e d b y E u r a t o m . Its p u r i t y was c h e c k e d b y a l p h a a n d b e t a c o u n t i n g a n d b y a l p h a a n d g a m m a s p e c t r o g r a p h y . T h e y i e l d of soft b e t a was greater t h a n 9 8 % . T h e s a m p l e was d i s s o l v e d i n 6 N n i t r i c a c i d , a n d the c o n v e r s i o n to s u l f u r i c a c i d m e d i u m was m a d e b y f u m i n g d o w n one a l i q u o t three times a n d d i s s o l v i n g the r e s i d u e i n the a p p r o p r i a t e s o l u t i o n . C E R I U M . C e r i u m 141 a n d 144 isotopes w e r e s u p p l i e d b y the " D é p a r t e m e n t des Radioéléments" of Saclay. C e r o u s n i t r a t e solutions w e r e p r e p a r e d b y d i s s o l v i n g the reagent ( P r o l a b o N o . 2 2 5 8 5 ) . C e r i c n i t r a t e was o b t a i n e d b y e l e c t r o l y t i c o x i d a t i o n of the p r e v i o u s s o l u t i o n i n a c e l l w i t h s e p a r a t e d c o m p a r t m e n t s . C e r i c sulfate a n d f e r r o a m m o n i u m sulfate solutions w e r e p r e p a r e d f r o m the g u a r a n t e e d reagent ( M e r c k N o . 2274 a n d N o . 3793). C e r o u s sulfate w a s o b t a i n e d s i m i l a r l y b y e l e c t r o l y t i c r e d u c t i o n . T R I L A U R Y L M E T H Y L A M M O N I U M SALTS. A s o l u t i o n of 0.1 M t r i l a u r y l m e t h y l a m m o n i u m c h l o r i d e i n c a r b o n t e t r a c h l o r i d e was p r e p a r e d for e a c h e x p e r i m e n t b y d i s s o l v i n g the reagent ( R h ô n e - P o u l e n c ) . T r i l a u r y l m e t h y l a m m o n i u m n i t r a t e a n d sulfate solutions w e r e o b t a i n e d b y m i x i n g f o u r times the p r e v i o u s o r g a n i c s o l u t i o n ( 3 v / v ) r e s p e c t i v e l y w i t h 4 N H N O 3 a n d 1 M N a S 0 . I n a d d i t i o n , the solvents w e r e p r e - e q u i l i b r a t e d b y m i x i n g t h e m t w i c e ( 3 v / v ) w i t h the c o r r e s p o n d i n g a c i d solutions. T R I B U T Y L P H O S P H A T E . T h e reagent t r i b u t y l p h o s p h a t e ( E a s t m a n K o d a k ) w a s p u r i f i e d b y s c r u b b i n g w i t h s o d i u m carbonate s o l u t i o n ( 5 % v / v ) a n d t h e n w i t h d i s t i l l e d w a t e r a n d b y d i s t i l l a t i o n in vacuo. 2

4


302

L A N T H A N I D E / A C T I N I D E

M I S C E L L A N E O U S . T h e c a r b o n t e t r a c h l o r i d e a n d acids u s e d w e r e r e agents of g r a d e R P ( P r o l a b o ) . ( C C 1 N o . 22521, H N O N o . 20420, H S 0 N o . 20700). Procedure. A q u e o u s phases w e r e p r e p a r e d f r o m samples of cerium ( I V ) , cerium (III), berkelium, and acid and diluted by distilled w a t e r to the p r o p e r concentrations. S a m p l e s of c e r i u m w e r e c h o s e n i n o r d e r to o b t a i n different c e r i u m ( I V ) / c e r i u m ( I I I ) ratios. T h e solutions w e r e a l l o w e d to s t a n d for six hours to r e a c h the o x i d a t i o n e q u i l i b r i u m . A 2 cc. s a m p l e of the solvent was a d d e d to the same v o l u m e of aqueous s o l u t i o n a n d m i x e d for 15 m i n u t e s . A f t e r s e p a r a t i o n b y a c e n t r i f u g e , samples of b o t h phases w e r e t a k e n for the b e t a c o u n t i n g of b e r k e l i u m a n d the s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n of c e r i u m ( I V ) . I n a d d i t i o n , one a l i q u o t of the l o a d e d solvent was t a k e n for d e t e r m i n i n g the d i s t r i b u t i o n coefficient of b e r k e l i u m ( I V ) . 4

2


C H E M I S T R Y

a

4

Results D a t a obtained with 0.1M and 0.05M tri-

Sulfuric A c i d Solutions.

l a u r y l m e t h y l a m m o n i u m s u l f a t e - c a r b o n t e t r a c h l o r i d e for d e t e r m i n i n g the f o r m a l o x i d a t i o n p o t e n t i a l of the B k ( I V ) - B k ( I I I ) c o u p l e i n I N a n d 0 . 5 N H S0 2

4

is s u m m a r i z e d i n T a b l e I I I ; the c o r r e s p o n d i n g curves

i 0 g l

[Bk(IV)]. [Bk(III)]

°

hS

-

a

l 0 g ,

°

of:

[Ce(IV)]. [Ce(III)L

are p l o t t e d i n F i g u r e s 5 a n d 6. T h e slopes are 0.92, c a l c u l a t e d b y the least squares m e t h o d ( F i g u r e 5 ) a n d close to 1 ( F i g u r e 6 ) , g r a p h i c a l l y e s t i m a t e d , for I N a n d 0 . 5 N H S 0 , r e s p e c t i v e l y . 2

4

F r o m these d a t a i t appears that i n s u l f u r i c a c i d the f o r m a l o x i d a t i o n potentials

of

the

Ce(IV)-Ce(III) H S0 2

4

Bk(IV)-Bk(III)

couple

differ

from

those

of

the

c o u p l e b y 0.022 a n d 0.017 volts, r e s p e c t i v e l y i n I N

and 0.5N H S 0 2

4

m e d i a . A s s u m i n g the p u b l i s h e d values of

1.44

a n d 1.46 volts for the f o r m a l o x i d a t i o n potentials of the C e ( I V ) - C e ( I I I ) couple i n I N and 0.5N H S 0 2

4

respectively (3, 6 ) , we obtain

£/

B k

=

1.42 volts i n I N H S 0

£/

B k

=

1.44 volts i n 0 . 5 N H S 0

2

2

4

4

N i t r i c A c i d Solutions. T h e d a t a o b t a i n e d w i t h 0 . 1 8 M t r i b u t y l p h o s p h a t e - c a r b o n t e t r a c h l o r i d e are s u m m a r i z e d i n T a b l e I V . It is a p p a r e n t that i n 6 N H N 0

3

F/

B k

-

Efce =

- 0 . 0 2 3 volts

I n this case the slope of the s t r a i g h t l i n e r e p r e s e n t i n g [Bk(IV)]

e

,

[Ce(IV)]

t t

is e s t i m a t e d to b e 1.1 ( F i g u r e 7 ) .


21.

MusiKAs

A N D

Oxidation

B E R G E R

B y accepting

1.58

303

Potential

volts as the f o r m a l o x i d a t i o n p o t e n t i a l of

the

Ce(IV)-Ce(III) couple (6) we obtain: E/

B k

== 1.56 volts i n 6 N

HN0

3

O n the other h a n d v e r y l i t t l e b e r k e l i u m is extracted b y t r i b u t y l p h o s p h a t e f r o m I N to 2 N H N 0

3

as s h o w n i n T a b l e I V . T h e d e t e r m i n a t i o n of the

f o r m a l o x i d a t i o n p o t e n t i a l of the B k ( I V ) - B k ( I I I ) c o u p l e i n this m e d i u m Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch021

is n o t r e l i a b l e . A s s u m i n g that a l l the b e r k e l i u m e x t r a c t e d is tetravalent a n d t h a t the d i s t r i b u t i o n coefficient of b e r k e l i u m ( I V ) is the same as that of c e r i u m ( I V ) , c a l c u l a t i o n shows that the difference b e t w e e n the f o r m a l o x i d a t i o n p o t e n t i a l of the t w o couples s h o u l d be greater t h a n + 0 . 0 8 volts. Table III. Trilaurylmethylammonium Sulfate—Carbon Tetrachloride Extraction of Cerium and Berkelium from Sulfuric A c i d Solutions Aqueous: I N H SO^ Solvent: 0.1 M TLMA

Aqueous: 0 . 5 N H SO^ Solvent: 0.05M TLMA

2

iCe(IVn

a

E° a

[Ce(Iim

Bk(IV)

a

2

Sulfate-CCl^

lCe(IVn

a

1.35 1.41 1.32 1.22 1.40 1.28 1.47 1.28 1.36 1.25 1.50 1.18 1.23 1.43

Bk(IV)

a

a

a

0.022 0.052 0.040 0.065 0.13 0.11 0.12 0.17 0.19 0.24 0.34 0.44 0.65 0.85

E°

iCe(III)}

[Bk(IIin

It

[Bk(IV)]

a

iBk(Iim

a

4.9 5.1 5.3 6.4 6.1 5.5

0.0087 0.014 0.036 0.08 0.085 0.1

0.035 0.08 0.15 0.21 0.24 0.31 0.44 0.48 0.6 0.75 0.65 0.85 1.10 1.35

Sulfate-CCl

0.02 0.038 0.065 0.13 0.15 0.17

E ° B k ( I I I ) < 0.005 i n a l l cases. a

Discussion I n I N to 2 N n i t r i c solutions, b e r k e l i u m was n o t extracted either i n T L M A nitrate or T B P , whereas c e r i u m was extracted. berkelium ( I V )

a l r e a d y extracted f r o m 6 N H N 0

3

F u r t h e r m o r e , the

i n t o T B P was

com-

p l e t e l y b a c k - e x t r a c t e d b y I N H N 0 , w h i l e c e r i u m was not s t r i p p e d as 3

m u c h . A s i m i l a r e x p e r i m e n t m a d e after a d d i n g s o d i u m b i s m u t h a t e p r o v e d t h a t aqueous c e r i u m was e n t i r e l y at the f o u r v a l e n c e state, w h i l e b e r k e l i u m s h o w e d a l o w d i s t r i b u t i o n coefficient s p o n d i n g m a i n l y to the t r i v a l e n t state.

( s m a l l e r t h a n 0.01)

corre-

T h i s result was c o n f i r m e d b y a


304

LANTHANIDE

ACTINIDE

CHEMISTRY


iBMlVJa |Bk

tracer e x p e r i m e n t , c a r r i e d o u t w i t h extracted from I N H N 0

3

2 4 i )

Bk and

into T L M A

1 4 4

C e isotopes. C e r i u m w a s

i n the presence of s o d i u m

bis-

m u t h a t e whereas b e r k e l i u m w a s not. T h e last t h r e e experiments

seem to c o n f i r m that t h e difference

in

b e h a v i o r b e t w e e n b e r k e l i u m a n d c e r i u m i n I N to 2 N n i t r i c a c i d solutions does n o t result f r o m a difference i n the r e a c t i o n rate. I t is m o r e p r o b a b l y c a u s e d b y the h i g h e r f o r m a l o x i d a t i o n p o t e n t i a l of t h e B k ( I V ) - B k ( I I I ) c o u p l e . A t s u c h a h i g h f o r m a l o x i d a t i o n p o t e n t i a l tetravalent b e r k e l i u m s h o u l d b e less stable t h a n tetravalent c e r i u m , even i f the difference

is

s m a l l e r t h a n the e s t i m a t e d v a l u e ( + 0 . 0 8 v o l t s ) . T h e s e results suggest that t h e s t a n d a r d potentials of the C e ( I V ) — C e ( I I I ) a n d the B k ( I V ) - B k ( I I I )

couples s h o u l d b e rather


different.

21.

MUSiKAS

A N D

Oxidation

B E R G E R

305

Potential

Bk(IV)|a

Bk(lll)U


h

/ /

+

•

/

/

/

10

/ >

/+ / /

+

/

/

/ /

/

+/

Sic pe 1

/

/ / /

10'

/

/

> •*

/

/

/

/

/ / /

/

10"'

/

/

/

/

10"

10"

10"

1

jCe(lV)ja ICe(ll|)|a

Figure 6.

Formal potential of the Bk(IV)-Bk(III)

couple in 0.5N

H SO, 2

t

T h e f a c t that i n c o m p l e x i n g m e d i u m the t w o couples h a v e close values c o u l d i m p l y t h a t the B k ( I V ) complexes

are m o r e t i g h t l y b o u n d t h a n

those of the C e ( I V ) . A l t h o u g h b e r k e l i u m ( I V ) was o b t a i n e d i n c o n c e n t r a t e d n i t r i c a c i d (4, 6),

it was n o t extracted i n T L M A n i t r a t e C C 1 whereas 4

w a s extracted. concentration lium (IV)

cerium(IV)

W h e n d e c r e a s i n g the a c i d i t y for the same n i t r a t e i o n [e.g., i n I N H N 0

was e x t r a c t e d

3

+

(Table II).

1.5M A 1 ( N 0 ) 3 solution], berke3

This phenomenum

c o u l d be

at-

t r i b u t e d to the c o m p e t i t i o n b e t w e e n the n i t r i c a c i d a n d the t e t r a v a l e n t b e r k e l i u m species w h i c h c o u l d b e extracted.


306

LANTHANIDE/ACTINIDE CHEMISTRY

|Bk (iV)fa I B K (iu)|i


•

Figure 7.

Formal potential of the Bk(IV)-Bk(III)

couple in 6N

HN0

3

T h e a c c u r a c y of the m e t h o d was c h e c k e d f r o m the d a t a p l o t t e d i n F i g u r e 5. C a l c u l a t i o n gives a m e a n v a l u e for F/

-

R k

F/ce =

0.023 volts

w i t h a s t a n d a r d d e v i a t i o n of: σ

== ± 0 . 0 0 9 volts

T h e scattering of the results d e p e n d s u p o n the soft b e t a c o u n t i n g of B k w h i c h is sensitive to the self a b s o r p t i o n of the source; the spectro p h o t o m e t r i c d e t e r m i n a t i o n of u n s t a b l e c e r i u m ( I V ) ; a n d the great n u m b e r of e x p e r i m e n t a l d e t e r m i n a t i o n s n e e d e d for c a l c u l a t i n g the p o t e n t i a l . 2 4 9


21.

MUsiKAs

A N D

Oxidation

B E R G E R

307

Potential

Table IV. 0.18M T r i b u t y l Phosphate—Carbon Tetrachloride Extraction of Cerium and Berkelium from N i t r i c A c i d Solutions E° Ce(IV)

[CeflV;]. [Ce(lII))

0.2 0.2

2.7

—

—

a

Aqueous" IN H N 0 + C e ( I V ) I N H N 0 + Ce(IV) + C e (III) I N H N 0 + 1.5M A l ( N 0 ) + Ce(IV) + NaBi0 2 N H N 0 + Ce(IV) + NaBi0 2 N H N 0 + Ce(IV) + Ce (III) 6N H N 0 + Ce(IV) + Ce (III) - d ° - d ° - d ° 3


3

3

3

a

InltidBk Extracted

E° Bk(IV) a

1 1

JBk(lV)] [Bk(III)]

a

a

0.05

a

0.02

a

70

3

3

3

1.9

2.5

3

a

3

1.9

0.55

3

8.9

0.034

1.3

8.4 8.1 8.4

0.065 0.4 0.465

1.2 1.25 1.05

e

0.055 0.16 1.0 1.6

E s t i m a t e d values assuming that only B k ( I V ) is extracted a n d that E ° B k ( I V ) = a

Ce(IV).

T o t a l c e r i u m i n i t i a l aqueous concentration = a l l cases. I n 6N H N O s E ° B k ( I I I ) < 0.005. b

c

3

6.0 X 1 0 " M . 3

E ° Ce (III) < a

E ° a

0.01 i n

a

Acknowledgments T h e authors w i s h to t h a n k A . Chesné for the h e l p f u l discussions a n d M . M a r t e a u for e x p e r i m e n t a l assistance. J . K o o i is g r a t e f u l l y a c k n o w l e d g e d for s u p p l y i n g b e r k e l i u m - 2 4 9 , thus e n c o u r a g i n g this w o r k .

Literature Cited (1) Haissinsky, M., Pluchet, E., J. Chim. Phys. 76, 608 (1962). (2) Jones, M. E., Cunningham, B. B., U. S. At. Energy Comm. AECD-2913 (1950). (3) Kunz, A. H., J. Am. Chem. Soc. 53, 98 (1931). (4) Matsuura, N., Haissinsky, M., J. Chim. Phys. 55, 475 (1958). (5) Peppard, D. F., Moline, S. W., Mason, G. W., J. Inorg. Nucl. Chem. 4, 344 (1957). (6) Smith, G. F., Getz, C. Α., Ind. Eng. Chem. Anal. 10, 191 (1938). (7) Thompson, S. G., Cunningham, Β. B., Seaborg, G. T., J. Am. Chem. Soc. 72, 2798 (1950). RECEIVED December 27,

1966.


(IV) Couple in Various Media - ACS Publications

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