Actinide Separations - ACS Publications - American Chemical Society

6 Actinide Extractants: Development, Comparison,

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and Future R. R. S H O U N and W . J. M c D O W E L L Oak Ridge National Laboratory, Oak Ridge, TN 37830

Actinide Separations Milestones In 1805 Bucholz noted that uranyl nitrate is very soluble in diethyl ether (1), and in 1842 Peligot purified uranyl nitrate by recrystallization from ether (2). These documented instances of the dissolution of an inorganic material in an organic solvent formed the basis for a method to separate and purify large quantities of high-purity uranium and plutonium for the Manhattan Project by solvent extraction, initially using ether as an extractant. One of its first uses was to isolate element 94 (plutonium) in the Chicago Metallurgical Laboratory during the period 1942-1944. This objective was accomplished by ether extraction of uranyl nitrate, leaving the plutonium in the aqueous phase. In one instance, 300 lb of neutron-irradiated uranyl nitrate was separated batchwise by using 2- and 3-liter separatory funnels (3). In addition to the actinide separations needs that were recognized in the 19th century and the first half of the 20th century, a multitude of other separations problems currently need to be resolved. F o r e x a m p l e , we a r e now f a c e d w i t h t h e p r o b l e m o f s e p a r a t i n g s e v e r a l new (man-made) a c t i n i d e s f r o m t h e o t h e r a c t i n i d e s , or other groups of elements, f o r a n a l y t i c a l , e n v i r o n m e n t a l , and n u c l e a r w a s t e h a n d l i n g p u r p o s e s . These needs have added s p e c i a l u r g e n c y t o t h e n e c e s s i t y f o r d e v e l o p i n g m e t h o d s f o r s e p a r a t i n g a c t i n i d e s from a wide range of u n d e s i r e d i o n s . It i s hoped t h a t t h i s r e v i e w w i l l n o t o n l y s e r v e t o c o r r e l a t e t h e r e f e r e n c e m a t e r i a l i n a u s e f u l manner, but a l s o p r o v i d e an u n d e r s t a n d i n g o f t h e a p p r o p r i a t e c o m b i n a t i o n o f m o i e t i e s n e e d e d t o make the most e f f i c i e n t s e p a r a t i o n s agents f o r s p e c i f i c a p p l i c a t i o n s , and t h e r e b y c o n t r i b u t e t o t h e d e v e l o p m e n t o f b e t t e r e x t r a c t a n t s . N a t u r a l s u c c e s s o r s t o d i e t h y l e t h e r as an e x t r a c t a n t w e r e v a r i o u s e t h e r s , p o l y e t h e r s , a n d a l c o h o l s s u c h as d i b u t y l c a r b i t o l , known as " t r i e t h e r d i b u t o x y t e t r a e t h y l e n e g l y c o l , known as " p e n t a e t h e r , " and k e t o n e s s u c h a s m e t h y l i s o b u t y l k e t o n e , known as " M I B K " o r " h e x o n e " ( 4 ) . Most a p p l i c a t i o n s f o r the e t h e r e x t r a c t a n t s r e q u i r e d the a d d i t i o n of h i g h c o n c e n t r a t i o n s of

0-8412-0527-2/80/47-117-071$05.00/0 ©

1980 A m e r i c a n C h e m i c a l Society

Navratil and Schulz; Actinide Separations ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


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s a l t i n g a g e n t s t o t h e aqueous phase t o e f f e c t t r a n s f e r o f t h e d e s i r e d metal species i n t o the extractant phase. T h i s was a d i s a d v a n t a g e b o t h e c o n o m i c a l l y and i n h a n d l i n g and d i s p o s i n g o f t h e aqueous r a f f i n a t e f o r p u r p o s e s o t h e r t h a n a n a l y t i c a l a p p l i c a t i o n s . S e e k i n g o t h e r e t h e r - l i k e , a q u e o u s - i m m i s c i b l e compounds w i t h electron-donor, coordinative properties l e d to the recognition t h a t t r i b u t y l p h o s p h a t e (TBP) h a d o u t s t a n d i n g q u a l i t i e s a s a n e x t r a c t a n t f o r u r a n y l , t h o r i u m , and c e r i u m ( I V ) n i t r a t e s f r o m solutions containing a d d i t i o n a l n i t r a t e i o n . This represented a m a j o r m i l e s t o n e i n t h e d e v e l o p m e n t o f new r e a g e n t s f o r s o l v e n t e x t r a c t i o n (4_, 5) . TBP i s p r e s e n t l y b e i n g u s e d i n a n i m p o r t a n t p r o c e s s (Purex) f o r s e p a r a t i n g and p u r i f y i n g u r a n i u m and p l u t o n i u m from spent f u e l s i n n i t r i c a c i d s o l u t i o n . TBP h a s g a i n e d w i d e a c c e p t a n c e i n s e p a r a t i o n s p r o c e s s e s f o r n u c l e a r f u e l r e p r o c e s s i n g and waste h a n d l i n g b e c a u s e o f i t s e x c e l l e n t e x t r a c t i o n c h a r a c t e r i s t i c s and r e a d y a v a i l a b i l i t y ; h o w e v e r , i t h a s some d i s a d v a n t a g e s w i t h r e s p e c t t o r a d i a t i o n s t a b i l i t y a n d aqueous-phase s o l u b i l i t y . A t l e a s t two h o m o l o g s o f T B P , t r i h e x y l p h o s p h a t e (THP) a n d t r i - ( 2 - e t h y l h e x y l ) phosphate (TEHP), a r e e x c e l l e n t e x t r a c t a n t s , a r e l e s s a q u e o u s s o l u b l e , a n d do n o t e x h i b i t t h e t e n d e n c y t o w a r d t h i r d - p h a s e f o r m a t i o n o b s e r v e d when t h o r i u m i s e x t r a c t e d b y TBP ( 6 , 7 ) . Other e l e c t r o n - d o n o r a l k y l phosphates w i t h e x t r a c t i o n p r o p e r t i e s s i m i l a r t o T B P , such as d i b u t y l p h e n y l p h o s p h a t e (DBPP) a n d d i - s e c - b u t y l p h e n y l p h o s p h o n a t e ( D S B P P ) , a r e b o t h r a d i a t i o n - s t a b l e a n d show h i g h e r e x t r a c t i o n power f o r u r a n i u m and p l u t o n i u m . I n s p i t e o f t h e a d v a n t a g e s o f s u c h c o m p o u n d s , TBP r e m a i n s l a r g e l y supreme i n i t s a p p l i c a t i o n b e c a u s e o f e s t a b l i s h e d use and commercial a v a i l a b i l i t y . T h e a l k y l p h o s p h o r i c a c i d s w e r e f i r s t r e c o g n i z e d as e x c e l l e n t a c t i n i d e e x t r a c t a n t s because d i b u t y l p h o s p h o r i c a c i d e x i s t e d as an i m p u r i t y i n TBP ( 8 ) . They e x t r a c t w e l l f r o m u n s a l t e d s o l u t i o n s a n d f r o m s y s t e m s s u c h a s s u l f a t e i n w h i c h TBP i s i n e f f e c t i v e . Organophosphorus a c i d s a r e thus s u i t a b l e f o r uranium h y d r o m e t a l l u r g i c a l a p p l i c a t i o n s where o r e i s l e a c h e d w i t h s u l f u r i c a c i d . T h e Dapex p r o c e s s i s an example i n w h i c h b i s ( 2 - e t h y l h e x y l ) p h o s p h o r i c a c i d (HDEHP) i s u s e d a l o n e o r i n s y n e r g i s t i c c o m b i n a t i o n w i t h n e u t r a l o r g a n o p h o s p h o r u s compounds f o r u r a n i u m a n d v a n a d i u m r e c o v e r y

(9,10). The a l k y l a m i n e s o f f e r g r e a t e r s e l e c t i v i t y t h a n o r g a n o p h o s p h o r u s compounds i n many a p p l i c a t i o n s , p a r t i c u l a r l y i n u r a n i u m h y d r o metallurgy. A m i n e e x t r a c t i o n i s t y p i f i e d b y t h e Amex p r o c e s s , w h i c h u s e s a t e r t i a r y o r b r a n c h e d s e c o n d a r y amine t o e x t r a c t u r a n i u m from s u l f a t e l e a c h l i q u o r s (11). A s i m i l a r process based on the use o f a p r i m a r y o r s t r a i g h t - c h a i n s e c o n d a r y amine (sometimes m o d i f i e d w i t h a n o r g a n i c - s o l u b l e a l c o h o l ) h a s g i v e n good r e s u l t s i n t h o r i u m r e c o v e r y (12). Amines c a n a l s o be used t o s e p a r a t e t h e t r i v a l e n t actinides from the c h e m i c a l l y s i m i l a r t r i v a l e n t l a n t h a n i d e s . I n t h e Tramex p r o c e s s , a t e r t i a r y amine i s u s e d a s t h e e x t r a c t a n t f r o m 10 t o 12 M L i C l , 0.1 t o 0.3 Ν AICI3, a n d 0.01 M HC1 ( 1 3 , 1 4 ) . The development


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o f t h e T a l s p e a k p r o c e s s was a n i m p o r t a n t a d v a n c e i n l a n t h a n i d e actinide separation. H e r e , t h e l i q u i d c a t i o n e x c h a n g e r HDEHP i s used to e x t r a c t t h e l a n t h a n i d e s from a s o l u t i o n c o n t a i n i n g c a r b o x y l i c a c i d s and o t h e r a q u e o u s - s o l u b l e c o m p l e x i n g a g e n t s t h a t p r e f e r e n t i a l l y r e t a i n t h e t r i v a l e n t a c t i n i d e s i n t h e aqueous p h a s e . T h i s p r o c e s s , which has the advantage o f b e i n g l e s s c o r r o s i v e than Tramex, has had w i d e s p r e a d a p p l i c a t i o n s i n c e i t s development i n 1964 ( 1 5 , 1 6 ) . A l t h o u g h a v a r i e t y o f e x t r a c t a n t s have been s t u d i e d and t e s t ed f o r t h e i r s u i t a b i l i t y i n a n a l y t i c a l s e p a r a t i o n s o f a c t i n i d e s , p e r h a p s t h e most r e c e n t m i l e s t o n e i n t h e p r o c e s s u s e o f a c t i n i d e extractants i s the a p p l i c a t i o n of the bidentate carbamoylmethylphosphonates ( 1 7 , 1 8 , 1 9 ) . T h e p i o n e e r i n g work o n t h e s e compounds was d o n e 15 y e a r s ago b y S i d d a l l ( 2 0 , 2 1 ) . Their p r i n c i p a l advan tage i s t h e i r a b i l i t y t o e x t r a c t t h e t r i v a l e n t , t e t r a v a l e n t , and h e x a v a l e n t a c t i n i d e s f r o m c o n s i d e r a b l y more c o n c e n t r a t e d n i t r i c a c i d media than other e x t r a c t a n t s . The e x t r a c t i o n c h e m i s t r y o f t h e more i m p o r t a n t r e a g e n t s w i l l be e x a m i n e d , a n d t h e i r c h a r a c t e r i s t i c s c o m p a r e d , i n t h e f o l l o w i n g section. Classes of Coordinative

Extractants

Extractants

A l l neutral, electron-donor extractant ligands, L , bind n e u t r a l metal s a l t s , such as s a l t s o f the t r i v a l e n t a c t i n i d e s , MA3, b y c o m p l e t i n g t h e c o o r d i n a t i o n r e q u i r e m e n t s o f t h e m e t a l , M , to g i v e an adduct ΜΑβ^ηί. T h i s i s true o f e x t r a c t a n t s such as e t h e r s , the a l k y l phosphate e s t e r s , the phosphine o x i d e s , the amine s a l t s , a n d a l l e x t r a c t a n t s t h a t r e q u i r e t r a n s f e r o f a c h a r g e - e q u i v a l e n t amount o f a n i o n t o t h e o r g a n i c p h a s e t o f o r m the e x t r a c t e d s p e c i e s . Ethers. Although ethers hold an important h i s t o r i c a l place i n a c t i n i d e e x t r a c t i o n , they a r e not used e x t e n s i v e l y at p r e s e n t . T h e y a r e w e a k - L e w i s - b a s e c o o r d i n a t i v e e x t r a c t a n t s , whose c h e m i s t r y has been a d e q u a t e l y covered i n e a r l i e r r e v i e w s ( 2 2 ) . Monodentate phosphate compounds. The monodentate phosphate compounds a r e s t r o n g e r L e w i s b a s e s a n d h a v e a h i g h e r c o o r d i n a t i n g a b i l i t y than e t h e r s . Their b a s i c i t y i s i n the order: phosphate < phosphonate < phosphinate < phosphine o x i d e . Typical of t h e i r b e h a v i o r i s t h e e x t r a c t i o n o f a c t i n i d e n i t r a t e s by TBP, which has b e e n r e p o r t e d (23) a s : MA . + 3TBP ± MA - 3 T B P , . 3(aq) +· 3 (org) Q (

E x t r a c t i o n by any t r i a l k y l

phosphate,

or phosphine o x i d e would be s i m i l a r .

.

(1) phosphonate, In general,

phosphinate, compounds


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c o n t a i n i n g c a r b o n - t o - p h o s p h o r u s bonds g i v e h i g h e r D s than t h e corresponding esters. F o r example, phosphine o x i d e s , w i t h t h r e e c a r b o n - p h o s p h o r u s b o n d s , g i v e h i g h e r D ' s f o r U02(N03>2, UO2SO4, U 0 C l 2 , Th(N0 )4, P u ( ^ 3 ) 4 than does T B P , w h i c h h a s no c a r b o n phosphorus bonds ( 2 4 ) . The o r d e r o f e x t r a c t i o n o f t r i v a l e n t a c t i n i d e s b y TBP a t 5 M HNO3 i s : Am < Cm < Bk < C f i E s ( 2 5 ) . A comparison o f the e f f e c t o f t h e s t r u c t u r e o f phosphate e s t e r s o n u r a n i u m e x t r a c t i o n f r o m n i t r a t e m e d i a shows t h a t t h e e s t e r s from secondary a l c o h o l s g i v e h i g h e r uranium d i s t r i b u t i o n c o e f f i c i e n t s (Djj's) t h a n those from p r i m a r y a l c o h o l s , p h e n y l e s t e r s e x t r a c t uranium l e s s s t r o n g l y than a l k y l e s t e r s , and b e n z y l e s t e r s are intermediate i n e x t r a c t a n t s t r e n g t h f o r uranium ( 2 4 ) . The u s u a l e f f e c t o f i n c r e a s i n g t h e a c i d c o n c e n t r a t i o n i s r e p o r t e d t o b e a n i n c r e a s e i n t h e D ( d u e t o i n c r e a s e d amounts o f t h e e x t r a c t a b l e MA3 i n t h e a q u e o u s p h a s e ) f o l l o w e d b y a d e c r e a s e i n t h e D (due t o f o r m a t i o n o f t h e e x t r a c t a n t - H N C ^ a d d u c t ) , result i n g i n a maximum e x t r a c t i o n a t a n a c i d c o n c e n t r a t i o n b e t w e e n 2 a n d 6 M . However, one s t u d y h a s n o t e d an i n c r e a s e i n americium e x t r a c t i o n a t n i t r i c a c i d c o n c e n t r a t i o n s f r o m 12 t o 16 M . T h e s e data a r e not c o n s i s t e n t w i t h t h e u s u a l view of americium d i s t r i b u t i o n dependence on n i t r i c a c i d and n i t r a t e c o n c e n t r a t i o n , and t h e authors hypothesize that a ΤΒΡ·ΗΝ0 adduct, which i s a stronger e x t r a c t a n t f o r a m e r i c i u m t h a n TBP a l o n e , i s f o r m e d a b o v e 8 M HNO3 and a n o r g a n i c - p h a s e c o m p l e x o f A m i N C ^ ^ ^ n i T B P ^ m H N C ^ ) i s f o r m e d r a t h e r t h a n A m i N C ^ ^ n T B P (26) . W h i l e o n e may n o t a b s o l u t e l y d i s c o u n t t h i s p o s s i b i l i t y , a d d i t i o n a l f a c t o r s such as the e x t r a c t i o n o f HAm(N03)4 a n d d e v i a t i o n s f r o m i d e a l a c t i v i t i e s i n s u c h concentrated a c i d s o l u t i o n s should d e f i n i t e l y be c o n s i d e r e d . T


2

a

3

n

d

M

M

3

The p h o s p h i n e o x i d e most commonly u s e d a s a n e x t r a c t a n t i s t r i o c t y l p h o s p h i n e o x i d e (TOPO). The order o f e x t r a c t i o n o f U(VI) f r o m m i n e r a l a c i d b y TOPO i s : HNO3 > HC1 > HCIO4 ( 2 7 ) . Extensive i n f o r m a t i o n on e x t r a c t i o n w i t h t h i s reagent has been compiled ( 2 8 ) . R e c e n t p a p e r s (29) r e p o r t t h e u s e o f TOPO f o r t h e e x t r a c t i o n of a c t i n i u m from n i t r a t e media. T h e maximum e x t r a c t i o n c o e f f i c i e n t f r o m > 2 . 0 M N a N 0 a t pH 2 w i t h 0 . 0 5 M TOPO i n c y c l o h e x a n e was n o t e d t o b e g r e a t e r t h a n 10^, a n d t h e e x t r a c t e d c o m p l e x was r e p o r t e d a s Ac(N0 )3*4TOPO Q0) . The maximum a c t i n i u m e x t r a c t i o n f r o m c h l o r i d e s o l u t i o n s b y 0 . 1 M T O P O — c y c l o h e x a n e was f o u n d t o b e f r o m 8 M L i C l a t pH 2 ( Ac ^) · e x t r a c t e d compound i n t h i s s y s t e m h a s b e e n r e p o r t e d as L Î 2 A c C l 5 2 T O P O ( 3 0 ) . Reagent dependencies f o r a m e r i c i u m e x t r a c t i o n f r o m s l i g h t l y a c i d i c 1 M L i C l w i t h TOPO i n d i c a t e d t h a t t h e e x t r a c t e d s p e c i e s i s A m C l 3 * T 0 P 0 , w h i l e AmCl3»3TOPO i s i n d i c a t e d when t h e a q u e o u s p h a s e i s 5 M L i C l . T h e number o f e x t r a c t a n t m o l e c u l e s a s s o c i a t e d w i t h t h e Am s p e c i e s was n o t c o n s t a n t over t h e L i C l c o n c e n t r a t i o n range 1 t o 5 M , and n o n i n t e g r a l v a l u e s o f 1 . 2 and 2 . 7 were o b t a i n e d a t 1 M L i C l and 5 M L i C l , respectively. These r e s u l t s suggest a mixture o f o r g a n i c - p h a s e species (31). 3

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75

B i d e n t a t e p h o s p h a t e compounds. The organophosphorus b i d e n t a t e e x t r a c t a n t s a r e n e u t r a l s p e c i e s e x t r a c t a n t s t h a t undergo no k e t o e n o l i z a t i o n a n d h a v e no e x c h a n g e a b l e h y d r o g e n s ( a s i s t h e c a s e i n e x t r a c t i o n by the b i d e n t a t e d i k e t o n e s ) . They c o n t a i n e i t h e r two P=0 g r o u p s o r o n e P=0 a n d one C=0 g r o u p . The c a r b a m o y l m e t h y l p h o s p h o n a t e s (CMPs) a n d c a r b a m o y l p h o s p h o n a t e s ( C P s ) a r e e x a m p l e s of t h e l a t t e r , w h i l e t h e t e t r a a l k y l d i p h o s p h o n a t e s and t e t r a a l k y l diphosphinedioxides [or b i s - ( d i s u b s t i t u t e d phosphinyl)-alkanes] are examples o f t h e f o r m e r . I t h a s been n o t e d (from a c i d and w a t e r e x t r a c t i o n data) t h a t t h e p h o s p h o r y l g r o u p s o f t h e d i p h o s p h o n a t e s do n o t a c t i n d e p e n d e n t l y o f each o t h e r (20). Thus e x t r a c t i o n power i s n o t a s i m p l e f u n c t i o n o f p h o s p h o r y l group c o n c e n t r a t i o n . W i t h more t h a n o n e b r i d g i n g m e t h y l e n e between p h o s p h o r y l g r o u p s , e x t r a c t i o n i s s i g n i f i c a n t l y poorer than expected f o r that phosphoryl concentra tion. This suggests the n e c e s s i t y of s p e c i a l s t e r i c requirements such as p o s s i b l y t h e c l a s s i c a l six-membered c h e l a t e r i n g (27,32) . N i t r i c a c i d i s e x t r a c t e d b y b i d e n t a t e compounds a n d , i n most c a s e s , competes w i t h t h e m e t a l e x t r a c t i o n a t h i g h e r a c i d i t i e s (>_8 M) . Comprehensive s t u d i e s o f a c i d e x t r a c t i o n and i t s e f f e c t on m e t a l i o n e x t r a c t i o n h a v e b e e n r e p o r t e d (21). The e x t r a c t i o n o f Cm a n d E s b y d i b u t y l ( d i e t h y l c a r b a m o y l ) p h o s p h o n a t e (DBDECP), w h i c h h a s no b r i d g i n g m e t h y l e n e g r o u p between t h e carbamoyl and p h o s p h o r y l g r o u p s , i s i n t h e o r d e r : HCIO4 > HNO3 > HC1. DBDECP a p p e a r s u n i q u e i n t h a t i t shows t h i r d power r e a g e n t d e p e n d e n c e a n d p r o v i d e s a d i s t r i b u t i o n c o e f f i c i e n t w h i c h i n c r e a s e s r a p i d l y w i t h a c i d c o n c e n t r a t i o n even above 8 M . T h i s s u g g e s t s e i t h e r t h a t t h e r e i s no c o m p e t i t i o n f r o m a c i d compound f o r m a t i o n w i t h t h e e x t r a c t a n t o r t h a t a n a c i d o c o m p l e x o f t h e m e t a l i s e x t r a c t e d a s i n E q . (2) (20,33): M

3

+

+ (3+X)A~ + X H + 3DBDECP -> H M A _ (DBDECP) . χ 3+x 3 +

OJ

0

(2)

The l a t t e r p o s s i b i l i t y i s s u p p o r t e d b y r e f e r e n c e s , s u g g e s t i n g t h e existence of anionic t r i v a l e n t actinide species at acid concentra t i o n s greater than 5 M (34). The o r d e r o f e x t r a c t i o n o f U ( V I ) f r o m m i n e r a l a c i d s b y b i s ( d i - n - h e x y l p h o s p h i n y l ) a l k a n e s i s : HCIO4 > HC1 > HNO3. T h e f a c t t h a t t h i s o r d e r i s t h e r e v e r s e o f t h e o r d e r o b s e r v e d f o r TOPO i s e x p l a i n e d b y t h e d i f f e r e n c e i n t h e a b i l i t y o f t h e m o n o d e n t a t e TOPO and t h e b i d e n t a t e compounds t o s a t u r a t e t h e u r a n i u m c o o r d i n a t i o n sphere. A p p a r e n t l y , TOPO i s u n a b l e t o r e p l a c e a l l t h e w a t e r i n t h e w e a k l y bound ( b u t more o r g a n o p h i l i c ) u r a n i u m p e r c h l o r a t e c o m p l e x , w h e r e a s t h e b i d e n t a t e compound h a s t h i s c a p a b i l i t y ( 2 7 ) . Numerous d e s c r i p t i v e s t u d i e s o f t h e e x t r a c t i o n b e h a v i o r o f t h e s e compounds f o r u r a n i u m a n d t h o r i u m s y s t e m s c a n b e f o u n d i n t h e l i t e r a t u r e (27,35-39). Work w i t h t h e o r g a n o p h o s p h o r u s b i d e n t a t e v i n y l e n e d i p h o s p h i n e , i n which t h e p h o s p h o r y l s a r e b r i d g e d !lP(0)CH = H C ( 0 ) P ' , illustrates the importance o f s t e r i c c o n s i d e r a t i o n s i n t h e e x t r a c t i o n o f u r a n y l


76

ACTINIDE

nitrate. ent.

Extraction

Extraction

was

greater

has

about

the

the

by c i s

by t h e than

same

and t r a n s

i s o m e r s was m a r k e d l y

cis-tetratolylvinylene

that

shown b y t h e

extraction

trans

power as

The

of magnitude g r e a t e r

than that

organophosphorus b i d e n t a t e

phosphate

(OETAPP),

noted

the

The


isomer;

for

a compound o f

extraction

maximum Djj r e p o r t e d

HC1.

The l i k e l y

U 0

2U

+

q )

Alkyl

2

N

0

;

a

(

q

is

+

)

(40).

the

type R 2 P ( 0 ) N H ( 0 ) P R ,

about

105

from 4 to

expression

0 E T A P P

t

(org)

ammonium c o m p o u n d s .

2

U 0

( N

°3Y

is

secondary,

are

commonly u s e d .

coordinators

since

may a l s o

equivalent

w r i t t e n b a s e d on e i t h e r

for

λ

extraction

negatively

by exchange

charged

salt

neutral-metal

under a p p r o p r i a t e Salts

of

the

sulfate

systems

LiCl

of

tertiary recovery

and i n t h e (11,12).

agents,

almost

more r a p i d l y t h a n

can

of

be

the

(4)

n

N

amine s a l t (n i s

neutral

the

for

a

charge

of

a l k y l ammonium

.

(5) equilibrium

shown t h a t

both can

operate

found wide a p p l i c a t i o n i n

They a r e

used e x t e n s i v e l y

of uranium from s u l f a t e

separation ions

amines,

very

is

is

separated

salts

extracted

power o f

example, the L 1 N O 3

the liquors

effectively (43).

from

The t r i v a l e n t from H N O 3 often

t h i r d - p o w e r dependence

For

system

the D

C

m

i n the

increase expected

increases

concentration

Among

concen

s l i g h t l y by secondary

(44).

inextractable

in

leach

o f u r a n i u m and t h o r i u m i n

in a nitrate

Am(III)

but n i t r a t e

the

of M A 3 .

seventh

have

by p r i m a r y amines

are

the

the

Plutonium(IV)

other

by t e r t i a r y

salting-out

to

anion of

amines have

actinides.

um e l e m e n t s

extraction

expressions

t h e m e t a l MAjJjJ^

(42)

transplutonium actinides, negligibly

thought

neutral-species

be d i s t i n g u i s h e d by

studies

f r o m u r a n i u m a n d most trated

amines,

conditions.

hydrometallurgical of uranium ore

are

process

species:

cannot

but k i n e t i c

extraction

often

+ MA , * (R NH) MA . , . n(aq) « - 3 m m+n(org)

two m e c h a n i s m s

studies,

the

assuming a d d i t i o n of

mR NHA. . 3 (org) These

of

)

is, f

complex o f

or,

the

That

N

the m e t a l ) ; to

equilibrium

3

R 3 N , and R^

R2NH,

b e c o n s i d e r e d as

mechanism.

and

(

+ MA~™ + (R NH) MA + TTIAT m+n(aq) • N a > N H j and B e > Mg > Ca . T r i a l k y l a m i n e s f r o m Cg t o C20 h a v e b e e n s t u d i e d f o r t h e i r p o t e n t i a l s u i t a b i l i t y i n t h e e x t r a c t i o n o f Am, Cm, and C f f r o m L 1 N O 3 and NaNO^. With the l o n g e r - c h a i n amines, t h e r e i s a lower dependence o f o n e x t r a c t a n t c o n c e n t r a t i o n and s a l t i n g - o u t a g e n t concentration. T h i s s u g g e s t s t h a t t h e l a r g e r , more s t e r i c a l l y h i n d e r e d e x t r a c t a n t m o l e c u l e s p e r m i t a s m a l l e r number o f l i g a n d s t o surround the m e t a l , thereby l e a v i n g f r e e c o o r d i n a t i o n s i t e s i n t h e complex f i l l e d w i t h w a t e r . A s a n example o f t h i s s e l e c t i v i t y , t r i o c t y l amine p r o v i d e s a s a t i s f a c t o r y Am-Cm s e p a r a t i o n b u t a p o o r A m - C f s e p a r a t i o n ; w i t h l o n g e r - c h a i n a m i n e s , t h e Am-Cm s e p a r a t i o n d e t e r i o r a t e s , w h i l e t h e A m - C f and C m - C f s e p a r a t i o n s i m p r o v e s u b s t a n t i a l l y (45). S e v e r a l p u b l i c a t i o n s on a c t i n i d e s s e p a r a t i o n s by t e r t i a r y a m i n e s a r e a v a i l a b l e s t u d y i n g P u ( V I ) a n d P u ( I I I ) e x t r a c t i o n (46); Np(V), N p ( V I ) ; P u ( V I ) , U(VI) (47); and Am, Cm (48,49). I n c e r t a i n a p p l i c a t i o n s , t h e q u a t e r n a r y ammonium s a l t s h a v e advantages o v e r t e r t i a r y amines f o r a c t i n i d e e x t r a c t i o n s . Quantit a t i v e e x t r a c t i o n of the t r a n s p l u t o n i u m elements from n i t r a t e m e d i a b y q u a t e r n a r y ammonium s a l t s c a n be a c h i e v e d w i t h a l o w e r aqueous-phase n i t r a t e c o n c e n t r a t i o n than i s r e q u i r e d f o r t e r t i a r y a m i n e s ; t h u s , a l u m i n u m n i t r a t e may b e u s e d i n s t e a d o f l i t h i u m nitrate. The s e p a r a t i o n f a c t o r b e t w e e n Am and Cm c a n b e as h i g h as t h r e e i n a q u a t e r n a r y ammonium n i t r a t e s y s t e m ( 5 0 ) . The e f f e c t o f t h e l e n g t h o f t h e a l k y l c h a i n on Cm, Am, B k , C f , and E s e x t r a c t i o n by a l k y l d i o c t y l a m m o n i u m n i t r a t e s s u g g e s t s t h a t s t e r i c factors s u b s t a n t i a l l y i n f l u e n c e the e x t r a c t i o n s e l e c t i v i t y (51). A c o m p a r i s o n of the e x t r a c t i o n of t e t r a v a l e n t and h e x a v a l e n t a c t i n i d e s b y t e t r a h e p t y l ammonium n i t r a t e shows t h a t tetravalent i o n s a r e more e a s i l y e x t r a c t e d t h a n h e x a v a l e n t i o n s : e.g., Pu(IV) > Np(IV) > Th(IV) > Np(VI) > Pu(VI) > U ( V I ) . Symmetrical q u a t e r n a r i e s u s u a l l y show h i g h e r e x t r a c t i o n power t h a n u n s y m m e t r i c a l ones ( 5 2 ) . A n e x c e l l e n t r e v i e w o f amine e x t r a c t i o n may b e found i n (42). C


Actinide

A N D MCDOWELL

m

+

+

2 +

2 +

2 +

Sulfoxides. S u l f o x i d e s (R S0) are n e u t r a l e l e c t r o n - d o n o r type m o l e c u l e s s i m i l a r to the phosphine o x i d e s . A significant v o l u m e o f w o r k h a s shown t h a t l o n g - c h a i n d i a l k y l s u l f o x i d e s may have c o n s i d e r a b l e p o t e n t i a l u t i l i t y i n a c t i n i d e s e p a r a t i o n s . E x t r a c t i o n b e h a v i o r from n i t r a t e systems i s s i m i l a r to t h a t of TBP f o r some s u l f o x i d e s ; i n a d d i t i o n , t h e y o f f e r t h e p o s s i b i l i t y of producing l e s s troublesome degradation products than TBP. Howe v e r , t h e s e compounds a r e n o t p r e s e n t l y a v a i l a b l e i n c o m m e r c i a l q u a n t i t i e s , and we l a c k t h e e x p e r i e n c e w i t h them t h a t h a s b e e n amassed w i t h T B P . D i - n - p e n t y l s u l f o x i d e (DPSO) i n b e n z e n e p r e f e r e n t i a l l y e x t r a c t s u r a n i u m o v e r t h o r i u m f r o m 5 M HC1 c o n t a i n i n g a n e u t r a l s a l t i n g 2


78

ACTINIDE

SEPARATIONS

out agent, y i e l d i n g a s e p a r a t i o n f a c t o r o f 3690. The e x t r a c t e d s p e c i e s f o r t h o r i u m i s r e p o r t e d t o be ThCl4*2DPSO»HCl. Homologs d i o c t y l s u l f o x i d e (DOSO) a n d d i p h e n y l s u l f o x i d e (DS0) y i e l d c o m p l e x e s w i t h t h e f o r m u l a s T h C l 4 2 D O S O a n d ThCl4*3DSO, r e s p e c t i v e l y . The e x t r a c t i o n o f a m o n o a c i d i c T h C ^ H C l s p e c i e s b y DPSO a n d a n e u t r a l s p e c i e s b y DOSO i s i n d i c a t e d ( 5 3 ) . e

Two p a p e r s r e p o r t t h e u r a n y l s p e c i e s e x t r a c t e d b y DOSO t o b e U0 (N0 ) 2DOSO (54,55). The o r d e r of s t r e n g t h o f e x t r a c t i o n o f uranyl nitrate i s : diheptyl > decyl benzyl > diphenyl: the e x t r a c t i o n c o e f f i c i e n t from three d i l u e n t s i s i n the order: benzene > c a r b o n t e t r a c h l o r i d e > c h l o r o f o r m . In s t u d i e s of the e x t r a c t i o n o f P a ( V ) a n d U ( V I ) f r o m HC1 m e d i a b y DPSO, DS0, a n d DBSO, t h e o r d e r o f e x t r a c t a n t s t r e n g t h was f o u n d t o b e : DPSO > DBSO > DS0. T h i s s u g g e s t s t h a t t h e e x t r a c t e d s p e c i e s were P a O C l 3 3 R S O o r P a ( O H ) C l 3 3 R S O (56) . D i p e n t y l s u l f o x i d e was i n v e s t i g a t e d a s a n e x t r a c t a n t t o s e p a r a t e the a c t i n i d e s T h ( I V ) , U ( V I ) , and Pa(V) f r o m t h e t r i v a l e n t l a n t h a n i d e s L a , C e , Pm, E u , a n d T b . A c t i n i d e e x t r a c t i o n i s a t a maximum a t 7 M H C 1 , a n d t h e r e i s l i t t l e o r no lanthanide e x t r a c t i o n at t h i s a c i d concentration (57).


2

3

2

#

e

#

2

2

2

C a t i o n Exchange

Extractants

A l k y l phosphoric a c i d s . Perhaps the l a r g e s t s i n g l e group of extractants f o r a c t i n i d e s are the a l k y l p h o s p h o r i c acids of three main t y p e s : d i a l k y l p h o s p h o r i c a c i d s , d i a l k y l p h o s p h o n i c a c i d s , and d i a l k y l p h o s p h i n i c a c i d s ( R 0 ) P ( 0 ) 0 H , ( R 0 ) R P ( 0 ) 0 H , and R P ( 0 ) 0 H , respectively. M o n o a l k y l ( d i a c i d i c ) r e p r e s e n t a t i v e s of each type e x i s t , b u t t h e s e compounds a r e r a r e l y u s e d b e c a u s e o f t h e i r w a t e r s o l u b i l i t y and d i f f i c u l t y i n s t r i p p i n g . A l k y l phosphoric acids u s u a l l y form dimers o r h i g h e r aggregates i n nonpolar s o l v e n t s such as benzene o r n-hexane ( 5 8 ) . The e x t r a c t i o n o f a t r i v a l e n t a c t i n i d e b y a d i a l k y l p h o s p h o r i c a c i d s u c h a s HDEHP i n a n o n p o l a r d i l u e n t may b e d e s c r i b e d b y t h e r e a c t i o n T

2

M^ . (aq) +

In a p o l a r a monomer, M^ . (aq) +

2

+ n(HA) , •> Μ Α · ( η - 3 ) Η Α , . + 3H* . . 2(org) 3 (org) (aq) 0 /

0

(6)

s o l v e n t i n which the d i a l k y l p h o s p h o r i c a c i d i s p r i m a r i l y t r i v a l e n t a c t i n i d e e x t r a c t i o n has been d e s c r i b e d as ( 5 9 ) : + 3HA, ν -*· M A + 3H^ . ( o r g ) «3 (org) (aq) 0 f

N

N

(7)

The d i a l k y l p h o s p h o r i c a c i d m o s t commonly u s e d and s t u d i e d f o r t r i v a l e n t a c t i n i d e e x t r a c t i o n i s p r o b a b l y HDEHP. Even though t h i s compound i s n o t a s s t r o n g a n e x t r a c t a n t a s some o t h e r s t r a i g h t c h a i n a n a l o g s , i t o f f e r s advantages s u c h as l o w a q u e o u s - p h a s e s o l u b i l i t y , l e s s t e n d e n c y t o t h i r d - p h a s e f o r m a t i o n , and r e a d y a v a i l ability. I n americium and c u r i u m e x t r a c t i o n from c h l o r i d e s o l u t i o n s b y HDEHP i n η - h e p t a n e , d e p e n d e n c e o f t h e e x t r a c t i o n c o e f f i c i e n t on h y d r o g e n i o n c o n c e n t r a t i o n a n d HDEHP c o n c e n t r a t i o n i n d i c a t e s a n


6.

SHOUN

Actinide

A N D MCDOWELL

79

Extractants

e x t r a c t e d s p e c i e s s t o i c h i o m e t r y o f ΜΑ(ΗΑ2)2· benzene, the i n d i cated s p e c i e s i s M(HA2)3« ^ a m p l of the e f f e c t of s t e r i c h i n d r a n c e may b e s e e n f o r t h e e x t r a c t i o n o f Am^+ a n d C m ^ b y t h e i s o m e r s b i s - n - o c t y l p h o s p h o r i c a c i d (HDOP), b i s - 2 - e t h y l h e x y l p h o s p h o r i c a c i d (HDEHP), a n d b i s - 2 , 2 - d i m e t h y l h e x y l p h o s p h o r i c a c i d (HDNOP); t h e o r d e r o f d e c r e a s i n g 1 ^ f o r a m e r i c i u m i s HDOP > HDEHP > HDNOP (60). D i i s o d e c y l p h o s p h o r i c a c i d (HDIDP) i s r e p o r t e d t o b e a s t r o n g e r e x t r a c t a n t t h a n HDEHP f o r t h e t r i v a l e n t a c t i n i d e s ( 6 1 ) . HDEHP i s a l s o u s e d a s a t o o l i n t h e s t u d y o f a q u e o u s c o m p l e x a tion. One o f t h e more u n u s u a l o f s u c h s t u d i e s i s t h e e x a m i n a t i o n of t h e complex f o r m a t i o n o f n o b e l i u m w i t h c i t r a t e , o x a l a t e , and a c e t a t e i o n s and comparison w i t h other d i v a l e n t i o n s . Nobelium was f o u n d t o r e s e m b l e C a a n d S r , b e i n g s l i g h t l y more l i k e S r ( 6 2 ) . S i n c e HDEHP i s b o t h a c a t i o n e x c h a n g e r a n d a c o o r d i n a t o r i n most e x t r a c t i o n s i t u a t i o n s , c o o r d i n a t e d w a t e r must b e removed f r o m the metal i o n i n the e x t r a c t i o n . Because t h i s sometimes l e a d s t o a s l o w r e a c t i o n s t e p , t h e k i n e t i c s o f HDEHP e x t r a c t i o n i s i m p o r t a n t . The k i n e t i c s o f t h e T a l s p e a k p r o c e s s ( 1 4 , 1 5 ) h a s b e e n i n v e s t i g a t e d ( 6 3 ) ; t h e k i n e t i c s o f A m ( I I I ) a n d T h ( I V ) e x t r a c t i o n b y HDEHP i n a n u n s t i r r e d system has a l s o been s t u d i e d ( 6 4 ) . D i o c t y l p h e n y l p h o s p h o r i c a c i d (HDOPP) h a s b e e n f o u n d t o b e a more p o w e r f u l e x t r a c t a n t f r o m m i n e r a l a c i d s t h a n HDEHP ( 6 5 , 6 6 ) . The d i s t r i b u t i o n c o e f f i c i e n t o f U ( V I ) f r o m s u l f u r i c a c i d s o l u t i o n s i s t h r e e t o f i v e t i m e s h i g h e r w i t h HDOPP t h a n w i t h HDEHP u n d e r t h e same c o n d i t i o n s . E x t r a c t i o n o f U ( V I ) f r o m m i n e r a l a c i d s b y HDOPP i s i n the order: HCIO4 3 > 2S04 (67). A c i d i t y and r e a g e n t d e p e n d e n c i e s a t l o w r e a g e n t l o a d i n g s and m e t a l - t o - r e a g e n t r a t i o s under f u l l y loaded c o n d i t i o n s i n d i c a t e the f o r m a t i o n of compounds s u c h a s UO2A4H2 a n d ( U 0 2 ) A 2 2 f ° respective c o n d i t i o n s , a s h a s b e e n t h e c a s e f o r HDEHP i n e a r l i e r work ( 6 8 ) . The a d d i t i o n o f a n e t h e r l i n k a g e i n t h e a l k y l c h a i n s o f d i a l k y l p h o s p h o r i c a c i d s has been found to i n c r e a s e i t s e x t r a c t i v e power f o r t r i v a l e n t a c t i n i d e s , r e s u l t i n g i n a n e x t r a c t a n t t h a t i s more e f f e c t i v e f r o m a c i d s o l u t i o n s t h a n i s H D E H P (69) . Bis(hexoxye t h y l ) p h o s p h o r i c a c i d ( H D H Q E P ) i s a compound o f t h i s t y p e t h a t h a s been s t u d i e d e x t e n s i v e l y ( 7 0 , 7 1 ) . T h e e t h e r l i n k a g e may c o n t r i bute to the c o o r d i n a t i o n o f the metal i o n , r e s u l t i n g i n the forma t i o n o f a seven-membered r i n g . In the e x t r a c t i o n of t r i v a l e n t a c t i n i d e s , the d i a l k y l p h o s p h o n i c a c i d s b e h a v e i n a manner s i m i l a r t o t h a t o b s e r v e d f o r t h e d i a l k y l phosphoric a c i d s . H o w e v e r , i n some s y s t e m s , t h e y o f f e r a g r e a t e r i n t e r g r o u p s e p a r a t i o n between l a n t h a n i d e s and a c t i n i d e s . The s e p a r a t i o n o f C f a n d Cm f r o m n i t r i c a c i d s o l u t i o n s h a s b e e n s t u d i e d u s i n g 2 - e t h y l h e x y l p h e n y l p h o s p h o n i c a c i d [ΗΕΗ(ΦΡ)] and 1 - m e t h y l h e p t y l p h e n y l p h o s p h o n i c a c i d [HMeH(P)]. ORNL h a s d e v e l o p e d a process f o r i n t e r g r o u p a c t i n i d e s e p a r a t i o n , c a l l e d Hepex, based on t h e u s e o f ΗΕΗ(ΦΡ) ( 7 2 , 7 3 ) . One s t u d y c o n c l u d e s t h a t t h e o r g a n i c - p h a s e s p e c i e s r e s u l t i n g f r o m A m ( I I I ) a n d C m ( I I I ) e x t r a c t i o n b y ΗΕΗ(ΦΡ) a r e a 3 : 2 m i x t u r e o f ΜΑο·ΗΑ a n d Μ Α · 2 Η Α , w h i l e C f i s e x t r a c t e d e x c l u s i v e l y a s MA3·ΗΑ ( 7 4 ) . I

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Sulfonic acids. S u l f o n i c a c i d s a r e v e r y s t r o n g c a t i o n exchange e x t r a c t a n t s f o r a wide v a r i e t y of metal i o n s . However, t h e i r use i n p r o c e s s a p p l i c a t i o n s as l i q u i d e x t r a c t a n t s ( a l t h o u g h e x t e n s i v e l y u s e d as r e s i n o u s c a t i o n e x c h a n g e r s ) h a s b e e n q u i t e l i m i t e d b e c a u s e of the d i f f i c u l t y o f o b t a i n i n g r e a g e n t s t h a t have s u f f i c i e n t l y h i g h o r g a n i c s o l u b i l i t y and s u f f i c i e n t l y l o w d i s t r i b u t i o n t o t h e a q u e o u s p h a s e when i n t h e s a l t ( p a r t i c u l a r l y t h e a l k a l i s a l t ) f o r m . T h e u s a b l e compounds t h a t a r e p r e s e n t l y a v a i l a b l e a r e d i n o n y l n a p h t h a l e n e s u l f o n i c a c i d (HDNNS) and d i d o d e c y l n a p h t h a l e n e s u l f o n i c a c i d (HDDNS). The f i r s t o f t h e s e has been used e x t e n s i v e l y i n s t u d y i n g aqueous complexes o f a c t i n i d e s ( 7 5 , 7 6 ) . Stability c o n s t a n t s f o r t h e s u l f a t e and f l u o r i d e c o m p l e x i n g o f U ( V I ) , N p ( V I ) , and P u ( V I ) w e r e f o u n d t o f o l l o w t h e o r d e r : U(VI) > Np(VI) > Pu(VI) (77). Diketones. B e t a - d i k e t o n e s s u c h as a c e t y l a c e t o n e , benzoyla c e t o n e , and i s o p r o p y l t r o p o l o n e a r e w e l l known f o r t h e i r a p p l i c a t i o n s i n a n a l y t i c a l e x t r a c t i o n of a c t i n i d e s . T h e s e compounds a r e weak a c i d s due t o t a u t o m e r i z a t i o n ; t h u s t h e y c a n a c t a s c a t i o n exchange e x t r a c t a n t s . T r i v a l e n t a c t i n i d e [M(III)] e x t r a c t i o n by t h e r e a g e n t (HA) a t l o w a q u e o u s a c i d c o n c e n t r a t i o n w h e r e t h e c o m pound b e h a v e s b o t h a s c a t i o n e x c h a n g e r a n d c o o r d i n a t o r p r o b a b l y f o l l o w s the r e a c t i o n Μ* + (aq) +

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I n h i g h - a c i d s y s t e m s w h e r e t h e compound c a n b e o n l y a n e u t r a l b i d e n t a t e c o o r d i n a t o r , the r e a c t i o n would be expected to b e : MX

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S i n c e f l u o r i n a t e d β - d i k e t o n e s a r e more a c i d i c t h a n n o n f l u o r i n a t e d compounds, t h e y h a v e u s e f u l e x t r a c t i o n c o e f f i c i e n t s f r o m more acidic solutions (78). T h e e x t r a c t i o n o f P a ( I V ) b y b e n z o y l a c e t o n e (HBA) f r o m p e r c h l o r i c a c i d and s o d i u m p e r c h l o r a t e was i n v e s t i g a t e d i n a r e c e n t study of the e q u i l i b r i a i n d i k e t o n e e x t r a c t i o n . The i n d i c a t e d r e a c t i o n i s r e p o r t e d t o be t h e same a s t h a t g i v e n i n E q . (8), where M?- = P a 0 ^ " o r P a ( 0 H ) | (79) . D i k e t o n e s have a l s o been used i n the s t u d y of aqueous c o m p l e x a t i o n . Oxalate (80), s u l f a t e , and f l u o r i d e c o m p l e x i n g o f N p ( I V ) , P u ( I V ) and T h ( I V ) have b e e n s t u d i e d b y t h e n o y l t r i f l u o r o a c e t o n e (TTA) e x t r a c t i o n . The 1 ^ i s a l w a y s h i g h e r when TTA i s d i s s o l v e d i n b e n z e n e t h a n when i t i s d i s s o l v e d i n n-hexane (81), which i s c o n t r a r y to the u s u a l o b s e r v a t i o n of higher D's i n a l i p h a t i c d i l u e n t s . +

Synergistic mixtures. A s o l v e n t e x t r a c t i o n system i s s a i d t o b e s y n e r g i s t i c when t h e d i s t r i b u t i o n c o e f f i c i e n t o b t a i n e d f r c m a m i x t u r e o f e x t r a c t a n t s i s g r e a t e r t h a n t h e sum o f d i s t r i b u t i o n c o e f f i c i e n t s of each e x t r a c t a n t a l o n e . Such systems a r e u s u a l l y



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Actiniae Extradants

81

m i x t u r e s o f c a t i o n exchange e x t r a c t a n t s and c o o r d i n a t i v e e x t r a c t a n t s , and t h e s y n e r g i s t i c e f f e c t i s t h o u g h t to o p e r a t e by a n enhancement o f t h e e a s e w i t h w h i c h t h e c o o r d i n a t i o n s p h e r e o f t h e m e t a l can be s a t i s f i e d . Two methods o f a c c o m p l i s h i n g t h i s h a v e been proposed f o r t r i v a l e n t a c t i n i d e s ( 7 8 ) . In the f i r s t , the s y n e r g i s t , S, r e p l a c e s c o o r d i n a t e d w a t e r on an e x t r a c t e d m e t a l c o m p l e x , t h u s m a k i n g t h e r e s u l t i n g c o m p l e x more o r g a n o p h i l i c . In the s e c o n d , t h e o r i g i n a l e x t r a c t e d complex i s s i m p l y c o o r d i n a t i v e l y u n s a t u r a t e d a n d t h e s y n e r g i s t adds t o t h e c o m p l e x , t h e r e b y e n h a n c ing i t s s t a b i l i t y . T h e r e a r e a number o f p r a c t i c a l s y n e r g i s t i c s y s t e m s t h a t make use o f organophosphorus compounds. A c l a s s i c e x a m p l e i s t h e com b i n a t i o n o f HDEHP a n d TOPO. T h e TOPO i s t h o u g h t t o r e p l a c e w a t e r o r HDEHP i n t h e c o o r d i n a t i o n s p h e r e o f t h e m e t a l . Some e a r l y w o r k i n t h i s area i n c l u d e d a study of the e x t r a c t i o n of uranium i n such systems ( 8 2 ) . C o m m e r c i a l p r o c e s s e s now e x i s t f o r t h e r e c o v e r y o f uranium from wet-process phosphoric a c i d u t i l i z i n g s y n e r g i s t i c systems ( 8 3 , 8 4 ) . D e s c r i p t i v e s t u d i e s of such systems have a l s o b e e n made ( 8 5 , 8 6 ) . E x a m p l e s o f TTA s y n e r g i s m w i t h A l i q u a t 3 3 6 - S c h l o r i d e show a s t r o n g s y n e r g i s t i c e f f e c t f o r Am, Cm, a n d C f . T h e e x t r a c t e d s p e c i e s i s r e p r e s e n t e d as an o r g a n i c - p h a s e i o n p a i r [ M ( T T A ) 3 C l ] " A , w h e r e A i s t h e q u a t e r n a r y ammonium i o n ( 8 7 ) . F o r TTA-TOPO e x t r a c t i o n o f Cm, t h e e x t r a c t e d s p e c i e s i s r e p o r t e d as Cm(TTA)2 X · ( T O P O ) , w h e r e X i s NO3 o r H S 0 g (88) . S y n e r g i s m was f i r s t r e p o r t e d i n t h e o p e n l i t e r a t u r e (TTA + TBP) i n 1954 ( 8 9 ) , a n d t h e i n v e s t i g a t i o n o f a d d i t i o n a l s y n e r g i s t i c s y s t e m s was d e s c r i b e d soon t h e r e a f t e r (90,82). S y n e r g i s t i c systems have a l s o been r e p o r t e d i n which one o f the a d d u c t s i s i n t h e aqueous p h a s e . T h e c o m b i n a t i o n o f TOPO ( i n CCI4) a n d b e n z o i c a c i d ( i n a q u e o u s a n d o r g a n i c ) was shown t o e x t r a c t uranium w i t h a s y n e r g i s t i c e f f e c t . The o r g a n i c - p h a s e adduct was r e p o r t e d t o b e I K ^ i C l O ^ « 0 6 ^ 0 0 0 · 2 T 0 P 0 . A n optimum b e n z o i c a c i d / T 0 P 0 r a t i o e x i s t s , a b o v e w h i c h compound f o r m a t i o n b e t w e e n T0P0 a n d b e n z o i c a c i d d e c r e a s e s t h e s y n e r g i s t i c e f f e c t (91). I n r e c e n t y e a r s , t h e p y r a z o l o n e s h a v e b e e n shown t o b e e x c e l l e n t e x t r a c t a n t s i n s y n e r g i s t i c c o m b i n a t i o n w i t h TBP a n d T 0 P 0 . The e x t r a c t i o n o f b o t h P u ( I V ) (92) a n d Am (93) b y l - p h e n y l - 3 m e t h y l - 4 - b e n z o y l - 5 - p y r a z o l o n e (ΦΜΒΡ) w i t h TBP shows s i g n i f i c a n t synergistic effects. T h r e e p y r a z o l o n e s i n c o m b i n a t i o n w i t h T0P0 and TBP a r e compared f o r t h e e x t r a c t i o n o f U ( V I ) i n ( 9 4 ) . Two pyrazolones e x h i b i t i n g improved s o l u b i l i t y characteristics, l - p h e n y l - 3 - m e t h y l - 4 - d e c a n o y l - 5 - p y r a z o l o n e (ΦΜ0Ρ) a n d l - p h e n y l - 3 m e t h y l - 4 - t e r t - b u t y l b e n z o y l - 5 - p y r a z o l o n e (ΦΜΒΒΡ), h a v e b e e n s y n t h e s i z e d and t e s t e d i n s y n e r g i s t i c c o m b i n a t i o n w i t h T0P0. The r e s u l t s show t h a t ΦΜ0Ρ i s s i g n i f i c a n t l y more s o l u b l e i n n - h e x a n e a n d t h u s a l l o w s h i g h e r e x t r a c t a n t c o n c e n t r a t i o n s t o be p r e p a r e d . The r e a g e n t d e p e n d e n c e i s 3 . 2 power t o ΦΜ0Ρ a n d 5 power f o r ΦΜΒΒΡ w i t h 2 : 1 p y r a z o l o n e : T 0 P 0 s o l u t i o n s i n DEB f o r a m e r i c i u m e x t r a c t i o n f r o m g l y c o l i c acid or n i t r i c a c i d (95). e

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ACTINIDE

SEPARATIONS


Future A c t i n i d e Extractants I n c o n s i d e r i n g t h e p o s s i b i l i t i e s f o r new and b e t t e r a c t i n i d e e x t r a c t a n t s , one must a s k t h e q u e s t i o n , " I n what way i s t h e e x t r a c t a n t t o b e made b e t t e r ? " T h e answer w i l l v a r y , o f c o u r s e , d e p e n d i n g on the p a r t i c u l a r need o r a p p l i c a t i o n . For example, h y d r o m e t a l l u r g i s t s may want a r e a g e n t t h a t i s more s e l e c t i v e f o r u r a nium o v e r i r o n i n s u l f a t e s y s t e m s . N u c l e a r f u e l r e p r o c e s s i n g may require high radiation s t a b i l i t y . N u c l e a r w a s t e management w o u l d need a r e a g e n t which would e x t r a c t a c t i n i d e s f r o m h i g h l y a c i d n i t r a t e systems, p o s s i b l y h a v i n g the a b i l i t y to r e j e c t t r i v a l e n t lanthanides. How a r e t h e s e v a r i o u s r e q u i r e m e n t s t o b e met? S e l e c t i v i t y a p p e a r s t o be b e s t i n t h o s e systems w h i c h t a k e advantage of d i f f e r e n c e s i n c o o r d i n a t i v e requirements of the m e t a l i o n ( e . g . , i n the e x t r a c t i o n by alkylammonium s a l t s ) . The c o o r d i n a t i v e n e u t r a l s p e c i e s e x t r a c t a n t s a r e t h e n e x t most s e l e c tive. L e a s t s e l e c t i v e a r e the c a t i o n exchange e x t r a c t a n t s ; h o w e v e r , t h o s e t h a t o f f e r c o o r d i n a t i v e p o s s i b i l i t i e s a r e more s e l e c t i v e t h a n t h o s e t h a t do n o t . Bidentate extractants offer enhanced e x t r a c t i o n s t r e n g t h because o f t h e i r a b i l i t y to f o r m chelate-type rings. No c l a s s o f e x t r a c t a n t s i s known t o h a v e c l e a r l y superior r a d i a t i o n s t a b i l i t y , although aromatic molecules a r e g e n e r a l l y t h o u g h t t o b e l e s s s u s c e p t i b l e t o r a d i a t i o n damage. R e a g e n t s t h a t a r e b o t h c a t i o n e x c h a n g e r s and s t r o n g a c i d s , s u c h as the s u l f o n i c a c i d s , s h o u l d be s u p e r i o r e x t r a c t a n t s from h i g h l y acid solutions. U n f o r t u n a t e l y , no member o f t h i s s u l f o n i c a c i d c l a s s t h a t i s s u f f i c i e n t l y o r g a n o p h i l i c h a s b e e n made a v a i l a b l e . Added t o the p r i m a r y e f f e c t o f t h e f u n c t i o n a l group a r e the e f f e c t s o f t h e s i z e , p l a c e m e n t , and b r a n c h i n g o f the o r g a n i c p o r t i o n of the m o l e c u l e . S u f f i c i e n t o r g a n i c " w e i g h t " must be a d d e d t o t h e f u n c t i o n a l g r o u p ( s ) so t h a t t h e e x t r a c t a n t m o l e c u l e , a n d w h a t e v e r s a l t s and a d d u c t s i t f o r m s i n t h e e x t r a c t i o n process, are s o l u b l e i n a reasonably simple h i g h - f l a s h - p o i n t organic diluent. A l s o , t h e r e a g e n t as w e l l a s i t s s a l t s and a d d u c t s must have a v e r y low d i s t r i b u t i o n t o the aqeuous phases to be u s e d . A r o u g h a p p r o x i m a t i o n i s t h a t a m o l e c u l a r w e i g h t o f a b o u t 300 i s r e q u i r e d , but the e f f e c t of a g i v e n organic l o a d i n g i s h i g h l y dependent on i t s f o r m . S t r a i g h t - c h a i n a l i p h a t i c s t e n d t o make m o s t compounds t o o i n s o l u b l e i n t h e o r g a n i c p h a s e b e f o r e t h e i r d i s t r i b u t i o n t o t h e a q u e o u s p h a s e becomes l o w e n o u g h ; t h u s a r o m a t i c , and e s p e c i a l l y b r a n c e d a l i p h a t i c , r a d i c a l s a r e much b e t t e r g r o u p s t o add t o an e x t r a c t a n t m o l e c u l e . The a d d i t i o n o f b r a n c h e d r a d i c a l s , however, l i m i t s the a b i l i t y of the f u n c t i o n a l group to a p p r o a c h t h e m e t a l i o n a n d t h e number o f e x t r a c t a n t m o l e c u l e s t h a t can be grouped around t h e i o n . For t h i s reason, i t i s often d e s i r a b l e t h a t t h e b r a n c h i n g b e somewhat removed f r o m t h e f u n c t i o n a l group. The s e l e c t i v i t y o f e x t r a c t a n t s may be a l t e r e d b y t h e t y p e o f o r g a n i c g r o u p s s u b s t i t u t e d on t h e f u n c t i o n a l g r o u p , w i t h t h e more s t e r i c a l l y h i n d e r e d ( h i g h l y branched) e x t r a c t a n t s t e n d i n g to favor larger ions or ions having strong coordinative bonding.


6.

SHOUN

A N D MCDOWELL

Actinide

Extractants

83


T h e q u e s t i o n t h e n a r i s e s , " I s i t p o s s i b l e t o t a i l o r new, more p o w e r f u l , and more s e l e c t i v e e x t r a c t a n t s f o r t h e a c t i n i d e e l e m e n t ? " T h e answer must c e r t a i n l y b e y e s , A w e a l t h o f i n f o r m a t i o n now e x i s t s as a b a s i s f o r f u t u r e r e s e a r c h and d e v e l o p m e n t i n new e x t r a c t i o n s y s t e m s , and t h e p o s s i b i l i t i e s h a v e h a r d l y b e e n t o u c h e d . It d o e s a p p e a r , h o w e v e r , t h a t a more o r g a n i z e d a p p r o a c h t o t h e p r o b l e m w i l l be r e q u i r e d t h a n h a s b e e n t y p i c a l i n t h e p a s t . The s y s t e m a t i c c h a n g e s t o be made i n t h e s t r u c t u r e o f e x t r a c t a n t m o l e c u l e s , u s i n g p a s t e x p e r i e n c e as a b a s i s , w i l l r e q u i r e t h e c o o p e r a t i o n o f s y n t h e t i c o r g a n i c c h e m i s t s and s o l v e n t e x t r a c t i o n c h e m i s t s . Such e f f o r t s s h o u l d b e p u r s u e d more i n t e n s i v e l y i n t h e f u t u r e . W h i c h f u n c t i o n a l g r o u p s a p p e a r t o b e most p r o m i s i n g i n t h e p r e p a r a t i o n o f new and b e t t e r e x t r a c t a n t s ? B o t h s u l f o n i c a c i d s and s u l f o x i d e s o f f e r p r o m i s i n g , u n e x p l o r e d p o s s i b i l i t i e s because of the v e r y s t r o n g l y a c i d i c n a t u r e o f t h e f o r m e r and t h e c o o r d i n a t i n g a b i l i t y of the l a t t e r . F l u o r i n a t e d β - d i k e t o n e s a p p e a r p r o m i s i n g as v e r s a t i l e c h e l a t i n g e x t r a c t a n t s i f the aqueous s o l u b i l i t y can be r e d u c e d t o a s u f f i c i e n t l y l o w v o l u m e f o r p r o c e s s a p p l i c a t i o n s and a c i d s t r e n g t h c a n be i n c r e a s e d t o t h e p o i n t where t h e y a r e u s e f u l from a c i d i c s o l u t i o n s . S y n e r g i s t i c combinations o f f e r continuing f i e l d s f o r i n t e r e s t i n g e x p l o r a t i o n , even w i t h a v a i l a b l e r e a g e n t s . One o f t h e more i n t e r e s t i n g p o s s i b i l i t i e s may be t h e c o m b i n a t i o n of o r g a n i c - p h a s e c a t i o n e x c h a n g e r s w i t h t h e s i z e - s p e c i f i c crown ethers to produce s i z e - s p e c i f i c or s e l e c t i v e s y n e r g i s t i c m i x t u r e s . Many y e a r s a g o , someone i n t h e AEC o r g a n i z a t i o n commented t h a t , " S u r e l y t h i s s o l v e n t e x t r a c t i o n problem has been s o l v e d by now." T h e p o s s i b i l i t i e s o f s o l v e n t e x t r a c t i o n a p p e a r t o be a v e r y l o n g way f r o m e x h a u s t i o n e v e n now. Acknowledgment Research Department of

sponsored by the D i v i s i o n

of

Chemical Sciences,

Energy under c o n t r a c t W-7405-eng-26 w i t h the

U.S.

Union

Carbide Corporation.

5.

Literature Cited

1. 2. 3. 4.

Bucholz, C. F. J. Chem. von. A. F. Gehlen 1805, 4(17), 134. Peligot, E. Ann. Chim. Phys. 3rd Series 1842, 5, 5-47. Seaborg, G. T. Berkeley, CA, May 1978, USERDA Report PUB-112. Coleman, C. F.; Leuze, R. E. J. Tenn. Acad. Sci. 1978, 53(3), 102-107. References [1], [2], [3] contained therein. Warf, J. C. J. Am. Chem. Soc. 1949, 71, 3257-3258. Private communication, W. D. Arnold, Oak Ridge National Laboratory, Oak Ridge, TN, January 1979. Arnold, W. D. In: Oak Ridge, TN, November 1975, USERDA Report ORNL-5111, p. 56. Stewart, D. C. Livermore, CA, January 1950, Report UCRL-585. Blake, C. Α.; Brown, Κ. B.; Coleman, C. F. Oak Ridge, TN, May 1955, AEC Report ORNL-1903.

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84

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14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34.

ACTINIDE SEPARATIONS

Blake, C. Α.; Crouse, D. J.; Coleman, C. F.; Brown, Κ. B.; Kelmers, A. D. Oak Ridge, TN, December 1956, AEC Report ORNL2172. Brown, Κ. B.; Coleman, C. F.; Crouse, D. J.; Denis, J . O.; Moore, J. G. Oak Ridge, TN, May 1954, AEC Report ORNL-1734. Crouse, D. J.; Brown, Κ. B.; Arnold, W. D. Oak Ridge, TN, December 1956, AEC Report ORNL-2173. Baybarz, R. D.; Weaver, B. S.; Kinser, Η. B. Nucl. Sci. Eng. 1963, 17, 457-462. Leuze, R. E.; Baybarz, R. D.; Weaver, B. Nucl. Sci. Eng. 1963, 17, 252-258. Weaver, B.; Kappelmann, F. A. Oak Ridge, TN, 1964, AEC Report ORNL-3559. Weaver, B.; Kappelmann, F. A. J . Inorg. Nucl. Chem. 1968, 30, 263-272. McIsaac, L. D.; Baker, J. D.; Tkachyk, J . W. Idaho Falls, ID, August 1975, ERDA Report ICP-1080. Schulz, W. W. Hanford, WA, 1973, ERDA Report ARH-2901. Schulz, W. W. Hanford, WA, 1974, ERDA Report ARH SA-203. Siddall, III, T. H. J . Inorg. Nucl. Chem. 1963, 25, 883-892. Siddall, III, T. H. J . Inorg. Nucl. Chem. 1964, 26, 1991-2003. Sekine, T.; Hasegawa, Y. "Solvent Extraction Chemistry"; Marcel Dekker, Inc.; New York and Basel, 1977. Healy, T. V.; McKay, H. A. C. Rec. Trav. Chem. des Pay-bas 1956, 75, 730-736. Higgins, C. E.; Baldwin, W. H.; Ruth, J. M. Oak Ridge, TN, July 1952, AEC Report ORNL-1338. Best, G. F.; Hesford, E.; McKay, H. A. C. J . Inorg. Nucl. Chem. 1959, 12, 136. Zemlyanukhin, V. I.; Savoskina, G. P. Radiokhimiya 1961, 3(4), 411-416. English Translation: Sov. Radiochem. 3, 182-188. Mrochek, J . R.; Banks, C. F. J . Inorg. Chem. 1965, 27, 589-601. White, J. C.; Ross, W. J . Oak Ridge, TN, February 1961, NAS -NRC Report NAS-NS 3102. Karlova, Ζ. K.; Rodionova, L. M.; Pyzhova, Ζ. I.; Myasoedov, B. F. Radiokhimiya 1977, 19(1), 38-41. English Translation: Sov. Radiochem. 19, 31-33. Karolova, Ζ. K.; Rodionova, L. M.; Pyzhova, Ζ. I.; Myasoedov, B. F. Radiokhimiya 1977, 19(1), 42-45. English Translation: Sov. Radiochem. 19, 34-36. Harmon, H. D.; Peterson, J. R.; McDowell, W. J.; Coleman, C. F. J. Inorg. Nucl. Chem. 1976, 38, 155-159. Shoun, R. R.; McDowell, W. J.; Weaver, B. "Proceedings of ISEC '77," Toronto, Sept. 1977, in press. Aly, H. F.; Latimer, R. M. J. Inorg. Nucl. Chem. 1970, 32, 3081-3089. Horwitz, E. P.; Bloomquist, C. Α. Α.; Sauro, L. J.; Henderson, D. J. J . Inorg. Nucl. Chem. 1966, 28, 2131-2324.


6. SHOUN AND MCDOWELL 35. 36. 37. 38. 39. Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 5, 2016 | http://pubs.acs.org Publication Date: April 16, 1980 | doi: 10.1021/bk-1980-0117.ch006

40.

41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58.

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Mrochek, J. E.; O'Laughlin, J . W.; Sakurai, H.; Banks, C. V. J. Inorg. Nucl. Chem. 1963, 25, 955-962. Mrochek, J. E.; O'Laughlin, J . W.; Banks, C. V. J. Inorg. Nucl. Chem. 1965, 27, 603-623. Mrochek, J . E.; Richard, J . J.; Banks, C. V. J. Inorg. Nucl. Chem. 1965, 27, 625-629. Parker, J . R.; Banks, C. V. J . Inorg. Nucl. Chem. 1965, 27, 583-587. Parker, J. R.; Banks, C. V. J . Inorg. Nucl. Chem. 1965, 27, 631-640. Berkman, Ζ. Α.; Bertina, L. E.; Kabachnik, M. I.; Kossykh, V. G.; Medved, T. Ya.; Nesterova, N. P.; Rozen, A. M.; Yudina, K. S. Radiokhimiya 1975, 17(2), 210-214. English Translation: Sov. Radiochem. 17, 213-216. Jankowska, M.; Kulawik, J.; Mekulski, J. J . Radioanal. Chem. 1976, 31, 9-29. Coleman, C. F. At. Energy Rev. 1964, 2(2), 3-54. Wilson, A. S. Progress in Nuclear Energy Series, III, Process Chemistry 1961, 3, 211. Moore, F. L. Anal. Chem. 1966, 38, 510. Derevyanko, E. P.; Chudinov, E. G. Radiokhimiya 1977, 19(2), 205-214. English Translation: Sov. Radiochem. 19, 172-179. Juznic, S.; Senegacnik, M. J. Radioanal. Chem. 1976, 30, 419424. Swarup, R.; Patil, S. K. J . Inorg. Nucl. Chem. 1976, 38, 1203-1206. Myasoedov, B. F.; Shkimev, V. M.; Kochetkova, Ν. E.; Chmutova, M. K.; Spivakov, B. Ya. Radiokhimiya 1975, 17(2), 234-237. English Translation: Sov. Radiochem. 17, 237-240. Nikolaev, V. M.; Lebedev, V. M.; Kovantsev, V. N. Radiokhimiya 1977, 19(5), 692-697. English Translation: Sov. Radiochem. 19, 575-580. Chudinov, E. G.; Pirozkhov, S. V.; Stepanchikov, V. I. Radio khimiya 1971, 13(2), 208-215. English Translation: Sov. Radiochem. 13, 208-214. Derevyanko, E. P.; Pirozkhov, S. V.; Shudinov, E. G. Radio khimiya 1975, 17(2), 291-296. English Translation: Sov. Radiochem. 17, 295-299. Swarup, R.; Patil, S. K. Radiochem. Radioanal. Lett. 1977, 29(2), 73-82. Mohanty, S. R.; Reddy, A. S. J . Inorg. Nucl. Chem. 1975, 37, 1977-1982. Korpak, W. Nukleonika 1964, 9, 1. Fedoezzhina, R. P.; Buchikhin, E. P.; Zarubin, A. I.; Kaneviskii, E. A. Radiokhimiya 1974, 16(5), 638-641. English Translation: Sov. Radiochem. 16, 626-629. Reddy, A. S.; Ramakrishna, V. V.; Patil, S. K. Radiochem. Radioanal. Lett., 1977, 28(5-6), 445-452. Reddy, A. S.; Reddy, L. K. Sep. Sci. 1977, 12(6), 641-644. Peppard, D. F.; Mason, G. W.; Driscoll, W. J.; Sironen, R. J. J. Inorg. Nucl. Chem. 1958, 7, 276-285.


86 59. 60. 61. 62.


63. 64. 65.

66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78.

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Marcus, Y.; Kertes, A. S. "Ion Exchange and Solvent Extrac tion of Metal Complexes"; Wiley-Interscience: London, New York, Sydney, Toronto, 1969. Mason, G. W.; Metta, D. N.; Peppard, D. F. J . Inorg. Nucl. Chem. 1976, 38, 2077-2079. Tachimori, S.; Sato, Α.; Nakamura, H. J. Nucl. Sci. Technol. 1978, 15(6), 421-425. McDowell, W. J.; Keller, O. L . ; Dittner, P. E.; Tarrant, J . R.; Case, G. N. J . Inorg. Nucl. Chem. 1976, 38, 1207-1210. Kasimov, F. D.; Nikolaev, V. M.; Kasimov, V. Α.; Skobelev, N. G. Radiokhimiya 1977 19(4), 442-446. English Translation: Sov. Radiochem. 19, 363-366. Choppin, G. R.; Nash, K. L. Rev. Chim. Miner. 1977, 14(2), 230-236. Barketov, E. S.; Vorob'eva, V. V.; Zaitsev, Α. Α.; Petukhova, I. V.; Spiryakov, V. I.; Filimonov, V. T. Radiokhimiya 1977, 19(4), 467-471. English Translation: Sov. Radiochem. 19, 382-385. Elesin, Α. Α.; Karaseva, V. Α.; Ivanovich, Ν. Α.; Zaitsev, A. A. Radiokhimiya 1974, 16(6), 772-777. English Transla tion: Sov. Radiochem. 16, 758-761. Nagle, R. Α.; Murthy, T. K. S. Sep. Sci. Technol. 1978, 13(7), 597-612. Baes, Jr., C. F.; Zingaro, R. Α.; Coleman, C. F. J. Phys. Chem. 1958, 62, 134. Horwitz, E. P. In: Oak Ridge, TN, October 1977, ERDA Report ORNL/TM-6056, Ed. Tedder, D. W.; Blomeke, J . O. Peppard, D. F.; Mason, G. W.; Griffin, G. J . Inorg. Nucl. Chem. 1965, 27, 1683-1691. Mason, G. W.; Bollmeier, A. F.; Peppard, D. F. J. Inorg. Nucl. Chem. 1967, 29, 1103-1112. Weaver, Boyd; Shoun, R. R. J. Inorg. Nucl. Chem. 1971, 33, 1909-1917. Weaver, Boyd; Shoun, R. R. Ind. Eng. Chem. Proc. Des. Dev. 1971, 10(4), 582. Barketov, E. S.; Zaitsev, Α. Α.; Filinonov, V. T. Radiokhimiya 1975, 17(3), 338-393. English Translation: Sov. Radiochem. 17, 383-387. Baisden, P. Α.; Choppin, G. R.; Kinard, W. F. J. Inorg. Nucl. Chem. 1972, 34(6), 2029-2032. Khopkar, P. K.; Narayankutty, P. J. Inorg. Nucl. Chem. 1968, 30, 1957-1962. Patil, S. K.; Ramakrishna, V. V. J . Inorg. Nucl. Chem. 1976, 38, 1075-1078. Myasoedov, B. F.; Guseva, L. I.; Lebeder, I. Α.; Milyukov, M. S.; Chmutova, M. K. "Analytical Chemistry of Transplutonium Elements," John Wiley and Sons, New York and Israel Program for Scientific Translations, Jerusalem, 1974. A translation from Russian of "Analiticheskaya Khimiya Transplutonievykh Elementov", Izdatel'stvo "Nauka", Moskova, 1972.


6. SHOUN AND MCDOWELL

Actinide Extractants

87


79. 80.

Ludqvist, R. Acta Chem. Scand. 1975, 29(2), 231-235. Bagawde, S. V.; Ramakrishna, V. V.; Patil, S. K. J. Inorg. Nucl. Chem. 1976, 38, 1669-1672. 81. Bagawde, S. V.; Ramakrishna, V. V.; Patil, S. K. J. Inorg. Nucl. Chem. 1976, 38, 2085-2089. 82. Blake, C. Α.; Horner, D. E.; Schmitt, J. M. Oak Ridge, TN, February 1959, USAEC Report ORNL-2259. 83. Hurst, F. J.; Crouse, D. J.; Brown, Κ. B. Ind. Eng. Chem. Proc. Des. Dev. 1972, 11(1), 122. 84. Hurst, F. J.; Crouse, D. J . Ind. Eng. Chem. Proc. Des. Dev. 1974, 13(3), 286. 85. Bunus, F. T.; Talanta 1977, 24, 117-120. 86. Bunus, F. T.; Pomocos, V. C.; Pumitrescu, P. J. Inorg. Nucl. Chem. 1978, 40, 117-121. 87. Khopkar, P. K.; Mathur, J . N. J . Inorg. Nucl. Chem. 1977, 39, 2063-2067. 88. Fardy, J. J.; Buchanan, J. M. J. Inorg. Nucl. Chem. 1976, 38, 149-154. 89. Cunningham, J . G.; Scargill, P.; Willis, H. H. 1950, British Report AERE, C/M215. 90. Blake, C. Α.; Coleman, C. F.; Brown, K. B.; Baes, C. F.; White, J. C. Proc. 2nd U.N. Intern. Conf. Peaceful Uses At. Energy, Geneva 1959, 28, 289. 91. Konstantinova, M. Anal. Chim. Acta 1977, 90, 195-197. 92. Chmutova, M. K.; Pribylova, G. Α.; Myasoedov, B. F. Radio khimiya 1975, 17(2), 220-226. English Translation: Sov. Radiochem. 17, 224-229. 93. Chmutova, M. K.; Pribylova, G. Α.; Myasoedov, B. F. Radio khimiya 1977, 19(2), 215-221. English Translation: Sov. Radiochem. 19, 180-185. 94. Rao, G. N.; Arora, H. C. J . Inorg. Nucl. Chem. 1977, 39, 2057-2060. 95. Weaver, B.; Shoun, R. R. Oak Ridge National Laboratory unpublished data, January 1979. RECEIVED

June 20, 1979.

Research sponsored by the Division of Chemical Sciences, U.S. Department of Energy under contract W-7406-eng-26 with the Union Carbide Corporation.


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