Plutonium Chemistry - American Chemical Society

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1 Forty Years of Plutonium Chemistry: The Beginnings GLENN T. SEABORG

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University of California, Lawrence Berkeley Laboratory and Department of Chemistry, Berkeley, CA 94720

The first isolation of a chemical compound of plutonium (a flouride) took place on August 20, 1942 and the first weighing of a pure compound (2.77 micrograms of the dioxide) on September 10, 1942. Thus this Symposium marks quite precisely the 40th anniversary of these events, the beginnings of the investigation of the macroscopic (non-tracer) chemical properties of this important synthetic element. The immediately following ultramicrochemical studies led to a definition of the IV and VI oxidation states, some properties of the metallic state, the synthesis and characterization of numerous solid compounds and the crucial testing of the first method devised for its separation and isolation in pure form after its production in the nuclear chain reaction. Later work with larger amounts, available as the result of its production in a nuclear reactor, made it possible to characterize the III and V oxidation states and many more compounds. The l a s t f o r t y y e a r s have s e e n an e x t e n s i v e , w o r l d - w i d e i n v e s t i g a t i o n o f the chemical p r o p e r t i e s o f the s y n t h e t i c element, plutonium. As a r e s u l t , as much i s known a b o u t t h e c h e m i c a l p r o p e r t i e s o f t h i s e l e m e n t as i s known a b o u t t h e c h e m i c a l p r o p e r ­ t i e s o f most o f t h e n a t u r a l l y o c c u r r i n g e l e m e n t s . The p a p e r s i n t h i s v o l u m e , p r e s e n t e d a t t h e Symposium o n t h e C h e m i s t r y o f P l u t o n i u m h e l d d u r i n g t h e Kansas C i t y m e e t i n g o f t h e A m e r i c a n C h e m i c a l S o c i e t y , i n September, 1982, r e p r e s e n t an u p - d a t i n g o f t h i s l a r g e amount o f i n f o r m a t i o n . I n t h e t i m e a n d s p a c e a v a i l a b l e t o me, I s h a l l l a r g e l y c o n ­ f i n e my comments t o t h e o r i g i n o f t h e c h e m i c a l s t u d i e s on t h i s remarkable element. I n so doing I s h a l l i n c l u d e q u o t a t i o n s from my J o u r n a l i n o r d e r t o h e l p c a p t u r e some o f t h e f l a v o r o f t h i s p i o n e e r i n g work.

0097-6156/83/0216-0001$06.50/0 © 1983 American Chemical Society

Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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PLUTONIUM CHEMISTRY

The f i r s t i s o l a t i o n o f a c h e m i c a l compound o f p l u t o n i u m ( a f l u o r i d e ) t o o k p l a c e on A u g u s t 20, 1942 and t h e f i r s t w e i g h i n g o f a p u r e compound (2.77 m i c r o g r a m s o f the d i o x i d e ) on September 20, 1942 a t t h e w a r t i m e M e t a l l u r g i c a l L a b o r a t o r y o f t h e U n i v e r s i t y o f C h i c a g o . These e v e n t s r e p r e s e n t t h e b e g i n n i n g o f t h e i n v e s t i ­ g a t i o n of the m a c r o s c o p i c ( n o n - t r a c e r ) c h e m i c a l p r o p e r t i e s of p l u t o n i u m and t h i s Symposium c o r r e s p o n d s q u i t e p r e c i s e l y t o the 40th anniversary of these inaugural experiments.

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T r a c e r i n v e s t i g a t i o n s d u r i n g 1941 and e a r l y 1942 a t B e r k e l e y l e d t o a g r e a t d e a l o f i n f o r m a t i o n about the c h e m i c a l p r o p e r t i e s of plutonium. I t was l e a r n e d t h a t i t has a t l e a s t two o x i d a t i o n s t a t e s , t h e h i g h e r o f w h i c h i s n o t c a r r i e d by l a n t h a n u m f l u o r i d e or c e r i u m f l u o r i d e , w h i l e the lower s t a t e i s q u a n t i t a t i v e l y c o p r e c i p i t a t e d w i t h t h e s e compounds. I t was e s t a b l i s h e d t h a t t h e h i g h e r o x i d a t i o n s t a t e can be o b t a i n e d by t r e a t m e n t o f t h e l o w e r s t a t e w i t h o x i d i z i n g a g e n t s s u c h as p e r s u l f a t e and a r g e n t i c i o n s , d i c h r o m a t e , p e r m a n g a n a t e , o r p e r i o d a t e , and t h a t the u p p e r s t a t e can be r e d u c e d t o a l o w e r ( r a r e e a r t h f l u o r i d e - c a r r i a b l e ) s t a t e by t r e a t m e n t w i t h s u l f u r d i o x i d e o r b r o m i d e i o n . The a p p r o x i m a t e p o t e n t i a l of the couple p l u t o n i u m (reduced)~*plutonium ( o x i d i z e d ) was b e l i e v e d t o be between -1.0 and -1.4 v o l t s . I t was e s t a b l i s h ­ ed t h a t p l u t o n i u m i n aqueous s o l u t i o n i s n o t r e d u c e d t o t h e m e t a l by z i n c , and t h a t i t does n o t f o r m a v o l a t i l e t e t r o x i d e . I t was shown t h a t a s t a b l e l o w e r s t a t e o f p l u t o n i u m — p r o b a b l y p l u t o n i u m ( I V ) — i s c a r r i e d by T h d O s ) ^ . E t h e r e x t r a c t i o n was u s e d t o s e p a r a t e l a r g e amounts o f u r a n y l n i t r a t e f r o m p l u t o n i u m . Methods a l s o were d e v i s e d f o r the s e p a r a t i o n o f p l u t o n i u m f r o m e l e m e n t s 90, 91, and 93. On the b a s i s o f t h e s e f a c t s , i t was s p e c u l a t e d t h a t p l u t o ­ nium i n i t s h i g h e s t o x i d a t i o n s t a t e i s s i m i l a r to uranium (VI) and i n a l o w e r s t a t e i s s i m i l a r t o t h o r i u m ( I V ) and u r a n i u m ( I V ) . I t was r e a s o n e d t h a t i f p l u t o n i u m e x i s t e d n o r m a l l y as a s t a b l e p l u t o n i u m ( I V ) i o n , i t w o u l d p r o b a b l y f o r m i n s o l u b l e compounds o r s t a b l e c o m p l e x i o n s a n a l o g o u s t o t h o s e o f s i m i l a r i o n s , and t h a t i t w o u l d be d e s i r a b l e (as s o o n as s u f f i c i e n t p l u t o n i u m became a v a i l a b l e ) t o d e t e r m i n e t h e s o l u b i l i t i e s o f s u c h compounds as the f l u o r i d e , o x a l a t e , p h o s p h a t e , i o d a t e , and p e r o x i d e . Such d a t a were needed t o c o n f i r m d e d u c t i o n s b a s e d on t h e t r a c e r e x p e r i m e n t s . When t h e P l u t o n i u m P r o j e c t was e s t a b l i s h e d e a r l y i n 1942, f o r the purpose o f p r o d u c i n g p l u t o n i u m v i a the n u c l e a r c h a i n r e a c t i o n i n u r a n i u m i n s u f f i c i e n t q u a n t i t i e s f o r i t s use as a n u c l e a r e x p l o s i v e , we were g i v e n t h e c h a l l e n g e o f d e v e l o p i n g a c h e m i c a l method f o r s e p a r a t i n g and i s o l a t i n g i t f r o m t h e u r a n i u m and f i s s i o n p r o d u c t s . We had a l r e a d y c o n c e i v e d the p r i n c i p l e o f t h e o x i d a t i o n - r e d u c t i o n c y c l e , w h i c h became t h e b a s i s f o r s u c h a separations process. T h i s p r i n c i p l e a p p l i e d t o any p r o c e s s i n ­ v o l v i n g t h e use o f a s u b s t a n c e w h i c h c a r r i e d p l u t o n i u m i n one o f i t s o x i d a t i o n s t a t e s b u t n o t i n a n o t h e r . By use o f t h i s

Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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SEABORG

Plutonium Chemistry: The Beginnings

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p r i n c i p l e , f o r e x a m p l e , a c a r r i e r c o u l d be u s e d t o c a r r y p l u t o ­ n i u m i n one o x i d a t i o n s t a t e and t h u s t o s e p a r a t e i t f r o m u r a n i u m and t h e f i s s i o n p r o d u c t s . Then t h e c a r r i e r and t h e p l u t o n i u m c o u l d be d i s s o l v e d , t h e o x i d a t i o n s t a t e o f t h e p l u t o n i u m c h a n g e d , and t h e c a r r i e r p r e c i p i t a t e d a g a i n , l e a v i n g t h e p l u t o n i u m i n solution. The o x i d a t i o n s t a t e o f t h e p l u t o n i u m c o u l d a g a i n be changed and the c y c l e s r e p e a t e d . W i t h t h i s t y p e o f p r o c e d u r e , o n l y a c o n t a m i n a t i n g element h a v i n g a chemistry n e a r l y i d e n t i c a l w i t h p l u t o n i u m w o u l d f a i l t o s e p a r a t e i f a number o f o x i d a t i o n r e d u c t i o n c y c l e s were employed. T h i s p r i n c i p l e , o f c o u r s e , a p p l i e s t o o t h e r t y p e s o f p r o c e s s e s , s u c h as v o l a t i l i t y , s o l v e n t e x t r a c t i o n , or a d s o r p t i o n methods.

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Move t o M e t a l l u r g i c a l

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The w o r k on t h e P l u t o n i u m P r o j e c t i n e a r l y 1942 was c e n t r a l i ­ zed i n t h e M e t a l l u r g i c a l L a b o r a t o r y o f t h e U n i v e r s i t y o f C h i c a g o . The f o l l o w i n g e x t r a c t f r o m my j o u r n a l d e s c r i b e s my a r r i v a l i n C h i c a g o w i t h my c o l l e a g u e I s a d o r e P e r l m a n : Sunday, A p r i l 19, 1942. T h i s m o r n i n g a t 9:30 a.m. I s a d o r e P e r l m a n and I a r r i v e d i n C h i c a g o a b o a r d t h e C i t y o f San F r a n c i s c o . A l t h o u g h our t r i p from B e r k e l e y took a l m o s t two f u l l d a y s , we f e e l t h a t t h e t i m e has n o t been w a s t e d . Many l i v e l y d i s c u s s i o n s e n s u e d i n t h e p r i v a c y o f o u r bedroom and, w i t h a p p r o p r i a t e c a r e , i n t h e c l u b c a r r e g a r d i n g ways t o s e p a r a t e e l e m e n t 94 c h e m i c a l l y f r o m u r a n i u m ( t h a t w i l l be n e u t r o n - i r r a d i a t e d i n c h a i n - r e a c t i n g p i l e s ) and f r o m t h e f i s s i o n b y - p r o d u c t s t h a t w i l l be p r o ­ duced c o n c u r r e n t l y i n t h e n e u t r o n - i r r a d i a t i o n p r o c e s s . T h i s o v e r a l l p r o b l e m o f e l e m e n t 94 i s o l a t i o n w i l l o c c u p y most o f o u r a t t e n t i o n f o r some t i m e t o come. The work o f my g r o u p i n t h e D e p a r t m e n t o f C h e m i s t r y a t t h e U n i v e r s i t y o f C a l i f o r n i a , B e r k e l e y , d u r i n g t h e p e r i o d A u g u s t 1940 t o t h e p r e s e n t , has p r o d u c e d much o f t h e b a c k g r o u n d i n f o r m a t i o n w h i c h i s the b a s i s of the M e t a l l u r g i c a l P r o j e c t . ( T h i s i s t h e code name f o r t h e p r o j e c t whose m i s s i o n i s t o p r o d u c e f i s s i o n a b l e e l e m e n t 94 i n s u f f i c i e n t q u a n t i t y f o r use i n a n u c l e a r weapon, and t h e p r o j e c t i s c e n t e r e d a t t h e U n i ­ v e r s i t y of Chicago.) Our r e s e a r c h a t B e r k e l e y has r e s u l t e d i n t h e d i s c o v e r y o f e l e m e n t 94, d e m o n s t r a t i o n o f the s l o w n e u t r o n f i s s i o n a b i l i t y of i t s isotope 9 4 , d i s c o v e r y and d e m o n s t r a t i o n o f the slow n e u t r o n f i s s i o n a b i l i t y of U , spontaneous f i s s i o n measurements on t h e s e i s o t o p e s , d i s c o v e r y o f 9 3 , i s o l a t i o n o f and n u c l e a r measurements on U * , s t u d y o f the c h e m i c a l p r o p e r t i e s and methods o f c h e m i c a l s e p a r a t i o n o f e l e m e n t 94, d e m o n s t r a t i o n o f t h e p r e s e n c e o f s m a l l c o n ­ c e n t r a t i o n s o f 94 i n n a t u r e and much r e l a t e d i n f o r m a t i o n . I have known P e r l m a n s i n c e o u r u n d e r g r a d u a t e days a t 2 3 9

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Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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UCLA. When I went t o B e r k e l e y t o b e g i n my g r a d u a t e w o r k , he a l s o t r a n s f e r r e d t o B e r k e l e y t o c o m p l e t e h i s w o r k f o r a B.S. d e g r e e i n c h e m i s t r y . He l a t e r o b t a i n e d h i s Ph.D. i n p h y s i o l o g y a t B e r k e l e y and a f t e r some p o s t d o c t o r a l w o r k t h e r e j o i n e d my g r o u p i n J a n u a r y and s o o n became a k e y man i n t h i s effort. When we s t e p p e d i n t o t h e s t r e e t f r o m t h e C h i c a g o and Northwestern R a i l r o a d S t a t i o n a t Canal and Madison S t r e e t s t h e t e m p e r a t u r e was a c o l d 40°F, a r a t h e r s h a r p c o n t r a s t t o t h a t i n B e r k e l e y when we l e f t . S t a r i n g us i n t h e f a c e was t h e h e a d l i n e i n t h e C h i c a g o S u n , "Tokyo F e a r s New Bombings; R e p o r t s F i r e s i n F o u r C i t i e s " w i t h sub-heads " F i v e - H o u r R a i d on J a p a n e s e L a i d t o Y a n k s " a n d " C a p i t a l , Yokohama, Kobe and Nagoya B l a s t e d . " The a c c o u n t went on t o s a y , " E a r l i e r J a p a n e s e b r o a d c a s t s s a i d a t t a c k s , w h i c h began a t noon y e s t e r ­ day, were c a r r i e d o u t by h i g h - f l y i n g U n i t e d S t a t e s p l a n e s w h i c h swept i n f r o m s e v e r a l d i r e c t i o n s a n d s t a r t e d f i r e s among t h e f l i m s y wood and p a p e r homes o f t h e h e a v i l y popu­ l a t e d a r e a s , " and c o n t i n u e d w i t h , " N e i t h e r W a s h i n g t o n n o r General Douglas McArthur's headquarters o f t h e U n i t e d N a t i o n s f o r c e s i n A u s t r a l i a would say t h a t Japan has been a t t a c k e d by a i r . " We t o o k a cab f r o m t h e s t a t i o n t o t h e S h o r e l a n d H o t e l (55th S t r e e t a t Lake M i c h i g a n ) near t h e U n i v e r s i t y o f Chicago campus. We r e g i s t e r e d h e r e and a b o u t noon r e t u r n e d t o t h e downtown a r e a v i a t h e I l l i n o i s C e n t r a l commuter l i n e . F o l l o w i n g l u n c h we a t t e n d e d t h e C h i c a g o T h e a t e r f o r a Sun­ day m a t i n e e and saw a s t a g e show f e a t u r i n g K a y K a y s e r ' s band and a m o v i e , " D e s i g n f o r S c a n d a l , " w i t h W a l t e r P i d g e o n . We had d i n n e r , r e t u r n e d h e r e t o o u r h o t e l , a f t e r w h i c h I w r o t e t o H e l e n , my b r i d e - t o - b e . T h i s d a y marks my 3 0 t h b i r t h d a y and a t r a n s i t i o n p o i n t i n my l i f e , f o r tomorrow I w i l l t a k e on t h e added r e s p o n s i ­ b i l i t y o f t h e 94 c h e m i s t r y g r o u p a t t h e M e t a l l u r g i c a l L a b o r a ­ t o r y on t h e U n i v e r s i t y o f C h i c a g o campus, t h e c e n t r a l com­ ponent o f t h e M e t a l l u r g i c a l P r o j e c t . We went t o w o r k i m m e d i a t e l y . O t h e r c h e m i s t s were added t o my g r o u p and b e f o r e t h e end o f t h e month we w e r e a s s i g n e d s p a c e i n and moved t o t h e a r e a on t h e f o u r t h f l o o r o f George H e r b e r t J o n e s L a b o r a t o r y on t h e U n i v e r s i t y o f C h i c a g o campus ( F i g u r e 1 ) . Although the o u t l i n e o f a chemical separation process could be o b t a i n e d by t r a c e r - s c a l e i n v e s t i g a t i o n s , t h e p r o c e s s c o u l d n o t be d e f i n e d w i t h c e r t a i n t y u n t i l s t u d y o f i t was p o s s i b l e a t t h e a c t u a l s e p a r a t i o n p l a n t s . T h e r e f o r e , t h e q u e s t i o n i n t h e summer o f 1942, was as f o l l o w s : How c o u l d any s e p a r a t i o n s p r o c e s s be t e s t e d at the c o n c e n t r a t i o n o f plutonium t h a t would e x i s t s e v e r a l years l a t e r i n t h e p r o d u c t i o n p l a n t s when, a t t h i s t i m e , t h e r e was n o t even a m i c r o g r a m o f p l u t o n i u m a v a i l a b l e ? T h i s p r o b l e m was s o l v e d t h r o u g h a n u n p r e c e d e n t e d s e r i e s o f e x p e r i m e n t s e n c o m p a s s i n g two m a j o r o b j e c t i v e s . F i r s t , i t was d e c i d e d t o a t t e m p t t h e p r o d u c t i o n

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