- Email: [email protected]
G.T. Seaborg and G.H. Higgins
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G.T. SEABORG and G.H. HlGGlNS
GLENN THEODORE SEABORG w a s born i n 1912, i n Ishpeming, Michigan. H e s t u d i e d a t t h e Univ e r s i t y o f C a l i f o r n i a , a t Los Angeles, where h e was named P h i Beta Kappa i n h i s j u n i o r y e a r and r e c e i v e d t h e A.B. d e g r e e i n chemist r y i n 1934. In 1937 he was awarded t h e Ph. D. d e g r e e from 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 a t Berkeley. Between 1937 and 1939 h e w a s t h e p e r s o n a l r e s e a r c h a s s i s t a n t o f Berkel e y ' s famous p h y s i c a l c h e m i s t , G i l b e r t Newt o n L e w i s . S i n c e 1939, h e h a s been on t h e F a c u l t y of 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 a t Berkeley. Between 1958 and 1961, he was Chancellor of t h e Un i v e r s i t y of C a l i f o r n i a a t Berkeley and p r e s e n t l y he is U n i v e r s i t y P r o f e s s o r o f Chemistry and A s s o c i a t e Direct o r of t h e Lawrence Berkeley L a b o r a t o r y . During World War 11, D r . Seaborg headed t h e group a t t h e U n i v e r s i t y o f C h i c a g o ' s M e t a l l u r g i c a l L a b o r a t o r y which d e v i s e d t h e chemical e x t r a c t i o n p r o c e s ses used i n t h e p r o d u c t i o n of plutonium f o r t h e Manhattan P r o j e c t . H e s e r v e d between 1946 and 1950 as a member of t h e Atomic Energy Commiss i o n ' s f i r s t General Advisory Committee and from 1959 t o 1961 on t h e P r e s i d e n t ' s S c i e n c e Advisory Committee. Between 1961 and 1971 h e s e r v e d a s t h e Chairman o f t h e United S t a t e s Atomic Energy Commission under t h r e e p r e s i d e n t s . I n 1963 he headed t h e U.S. d e l e g a t i o n t o t h e U.S.S.R. f o r t h e s i g n i n g o f t h e "Memorandum on Cooperation i n t h e F i e l d o f U t i l i z a t i o n of Atomic Energy f o r P e a c e f u l Purposes" and was i n t h e U.S.A. d e l e g a t i o n t o Moscow f o r t h e s i g n i n g o f t h e Limited Nuclear T e s t Ban T r e a t y . I n September 1971, he was p r e s i d e n t o f t h e F o u r t h United N a t i o n s Conference a t Geneva on t h e P e a c e f u l Uses o f Atomic Energy. I n 1973, D r . Seaborg v i s i t e d t h e P e o p l e ' s Republic o f China as a member o f t h e f i r s t s c h o l a r l y d e l e g a t i o n sponsored by t h e U.S. Committee on S c h o l a r l y Communication w i t h t h e P e o p l e ' s Republic o f China w h i l e i n S p r i n g 1978 he s e r v e d a s t h e chairman o f t h e D e l e g a t i o n on Pure and Applied Chemist r y v i s i t i n g t h e same c o u n t r y . D r . Seaborg i s t h e a u t h o r o f o v e r 300 s c i e n t i f i c p a p e r s and a dozen books as w e l l as works on t h e p e a c e f u l u s e s of n u c l e a r e n e r g y . H i s w r i t i n g s have been t r a n s l a t e d i n t o many f o r e i g n l a n g u a g e s . I n 1951, a t t h e age o f 39, D r . Seaborg was awarded ( w i t h E.M. M c M i l l a n ) t h e Nobel P r i z e f o r Chemistry f o r h i s work on t h e c h e m i s t r y o f t r a n s u r a n i u m e l e m e n t s . H i s o t h e r r e c o g n i t i o n s i n c l u d e t h e Atomic Energy Commission's E n r i c o Fermi Award, t h e Arches of S c i e n c e Award of t h e P a c i f i c S c i e n c e C e n t e r , t h e U.S. Department of S t a t e D i s t i n g u i s h e d Honor Award, t h e John E r i c s s o n Gold Medal o f t h e American S o c i e t y of
406 Swedish E n g i n e e r s , t h e F r a n k l i n Medal, t h e L e i f E r i k s o n Award, t h e John S c o t t Award and Medal o f t h e C i t y o f P h i l a d e l p h i a , t h e P e r k i n Medal o f t h e S o c i e t y o f Chemical I n d u s t r y , t h e Chemical P i o n e e r Award and t h e Gold Medal Award o f t h e American I n s t i t u t e o f C h e m i s t s . The American Chemical S o c i e t y h a s honored him w i t h i t s Award i n P u r e C h e m i s t r y , t h e William H , N i c h o l s Medal, t h e C h a r l e s L a t h r o p P a r s o n s Award, t h e W i l l a r d Gibbs Medal, t h e Madison M a r s h a l l Award, and w i t h i t s h i g h e s t h o n o r , t h e P r i e s t l e y Medal. D r . Seaborg s e r v e d a s P r e s i d e n t o f t h e American Chemical S o c i e t y ( 1 9 7 6 ) , t h e American A s s o c i a t i o n f o r t h e Advancement o f S c i e n c e ( 1 9 7 2 ) , and Chairman o f t h e AAAS Board o f D i r e c t o r s ( 1 9 7 3 ) . H e h a s r e c e i v e d o v e r 40 honorary d o c t o r a l d e g r e e s . H e i s a member o f t h e U.S. N a t i o n a l Academy of S c i e n c e s and n i n e f o r e i g n n a t i o n a l academies i n c l u d i n g t h a t I n 1973, h e w a s d e c o r a t e d as an O f f i c e r i n t h e L6gion of t h e U . S . S . R . d'Honneur o f t h e R e p u b l i c o f F r a n c e . In 1940-1941 D r . Seaborg c o - d i s c o v e r e d e l e m e n t 94 ( p l u t o n i u m ) , t h e f i r s t of t h e t r a n s u r a n i u m e l e m e n t s which h e and h i s coworkers d i s c o v e r e d , Am (element 9 5 ) , Cm (96), Bk ( 9 7 ) , Cf ( 9 8 ) , E s ( 9 9 ) , Fm (loo), Md ( 1 0 1 ) , No (102) and e l e m e n t 106. H e and h i s c o l l e a g u e s have d i s c o v e r e d more t h a n 100 i s o t o p e s t h r o u g h o u t t h e p e r i o d i c t a b l e s . A s t h e aut h o r ( i n 1944) o f t h e " a c t i n i d e c o n c e p t " of t h e heavy e l e m e n t e l e c t r o n i c s t r u c t u r e , D r . Seaborg i s t h e o n l y p e r s o n s i n c e Mendeleev t o have made a major change i n t h e p e r i o d t a b l e o f e l e m e n t s . D r . S e a b o r g ' s involvement i n chromatography i s r e l a t e d t o h i s a c t i v i t i e s i n t h e p i o n e e r i n g atomic e n e r g y r e s e a r c h : h e u t i l i z e d i o n - exchange chromatography f o r t h e s e p a r a t i o n and p u r i f i c a t i o n of uranium and p l u t o n i u m from e a c h o t h e r and from f i s s i o n p r o d u c t s , s e p a r a t i o n of t r a n s p l u t o n i u m e l e m e n t s from r a r e e a r t h s and from e a c h o t h e r . -0-o-oGARY HOYT HIGGINS w a s born i n 1927, i n S t . James, Minnesota. H e s t u d i e d a t M a c a l e s t e r C o l l e g e , i n S t . P a u l , Minnesota, where he r e c e i v e d h i s A.B. d e g r e e i n 1949. A f t e r b e i n g employed a t Minnesota Mining & Man u f a c t u r i n g Co. and s e r v i n g a s a t e a c h i n g a s s i s t a n t a t M a c a l e s t e r C o l l e g e , he j o i n e d t h e U n i v e r s i t y of C a l i f o r n i a a t Berkeley a s a t e a c h i n g a s s i s t a n t i n 1949. H e r e c e i v e d h i s Ph.D. t h e r e i n 1952 and t h e n j o i n e d t h e Lawrence Livermore L a b o r a t o r y . H e h a s been associated with t h i s laboratory ever since; h i s p r e s e n t p o s i t i o n i s t h a t of a technical. a d v i s o r t o t h e a s s o c i a t e d i r e c t o r f o r Ener-. gy & Resource Program. D r . H i g g i n s i s t h e and c o a u t h o r of o v e r 50 p u b l i c a t i o n s . H e h a s r e c e i v e d t h e Guggenheim F e l l o w s h i p Award and a h o n o r a r y D.Sc. d e g r e e from Macalester C o l l e g e . H i s r e s e a r c h i n t e r e s t h a s been c e n t e r e d on t h e c h e m i c a l and n u c l e a r p r o p e r t i e s o f t h e t r a n s u r a n i u m e l e m e n t s . H e i s t h e c o d i s c o v e r e r o f e l e m e n t s 99 and 1 0 0 , e i n s t e i n i u m and fermium. D r . H i g g i n s h a s been i n v o l v e d i n t h e u s e o f ion-exchange chromatography f o r t h e separation of transuranium elements.
407 In the decade spanning the mid-1940's to the mid-1950's uses of chromatography in our laboratory were divided into three major areas. These were, of course, designed to solve three chemical separation problems, namely, separation and purification of uranium and plutonium from each other and from fission products, separation of transplutonium elements from rare earths and separation of transplutonium elements from each other. There are alternative chemical separation processes to solve each of these problems; however, because we were dealing with isotopes whose half lives were quite short, speed of separation was crucial. For example, we could not have used the fractional crystallization techniques to study isotopes of curium separated from americium. Chromatography, as we used the method, was restricted to use of various ion-exchange resins with complexing agents as eluants. In the uranium/plutonium purification and separation process chloride complexes which are anionic were alternately adsorbed and desorbed from anion-exchange resins of the quaternary amine type. Since plutonium in its higher oxidation state forms these complexes the Pu-U could be isolated as a group. Plutonium in its plus three state forms a very weak chloride complex while uranium always remained in its higher oxidation states in aqueous solution and is strongly complexed to anionic form at high chloride concentration. These facts make for easy separation of uranium and plutonium. Neptunium generally follows uranium but can be separated using ion exchange by strong reduction. During this period, particularly during the forties, the actinide concept was not universally accepted; however, the work in our laboratory by Burris Cunningham on ionic radii in compounds of the heavy elements confirmed the view that the 5f electron shell begins with actinium similar to the 4f shell with lanthanum. His work further convinced us that the stable aqueous ions of the transplutonium actinides would all have plus three oxidation states. Hence we started very early to adopt the ion-exchange techniques, used by F. Spedding for purification of the rare earths, to the new and then unknown actinides with atomic numbers 97 through 103. This technique involved use of sulphonic acid type cation-exchange resins with chelating agents for eluants. Citric acid with carefully adjusted pH was most common but EDTA, lactic acid, sodium thiocyanate and later, a-hydroxyisobutyric acid were also used. The early elution columns required 24 or more hours for separation of elements 95 and 96, americium and curium, with room temperature citric acid. This precluded study of isotopes with half lives shorter than several hours so development of faster separation was important. The problem was solved by two separate developments. The first, made in our laboratory, was achieved by increasing the column and eluant temperature to 87 OC. The temperature was maintained constant by condensing trichloroethylene vapor in a jacket surrounding the ion-exchange column. The second was due, probably, to the commercialization of ion-exchange water softeners. The quality of the resins became both better, in that more regular crosslinkage and
active sulfonic acid sites were produced, and more uniform in that different lots were alike. The result of both developments was separations which were complete in about 2 hours, a factor of ten improvement. By the mid-1950's further improvements due to use of a-hydroxyisobutyric acid reduced separation times of the same elements to about 10 minutes. The third area of application was separation of the plus three valence lanthanides from the plus three actinides. Early in the study of various eluants HC1 was used to separate rare earths from each other although the separations were not very clean. At first it was thought that the elution was due to competition between H30+ and the rare earths for the sorption sites but studies with various acids disclosed a special effect of HC1. When the HC1 concentration was raised to 13 N studies with Am, Cm, and Pm showed that the actinides were apparently complexed by the C1- ion, while the lanthanides either were not complexed or were weakly complexed.
Fig. 46.1. Simple ion-exchange equipment in protection box used for actinide-lanthanide or anioncation separations. The sleeved curved roads used by the manipulators are shown in the foreground. The exchange column shown in this figure just left of center and immediately over the 1-liter polyethylene bottle is of the unjacketed type. The tubes in the circular tables were used to sequentially collect eluate.
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Thus separation of the two groups could be achieved by eluting the mixture on cation-exchange resin with concentrated HC1. By the decade of the 1950’s separations were improved by using the ethyl alcohol azeotrope saturated with HC1 gas. It was also found that anionic complexes of the actinides were formed in 36 N LiCl and that the actinides could be selectively adsorbed from an actinidelanthanide mixture thus providing an alternative separation procedure useful for handling massive amounts of the actinides. The first gram-quantity purification of curium was accomplished by this method. Construction of ion-exchange columns was, except for the jacketed column, very simple for the handling of the tracer quantities we usually processed. A 1 or 2 mm diameter thick-walled capillary tube 5 or 10 cm in length was drawn to a tip at one end and joined to a centrifuge cone test tube at the other. The tip was broken off and a small plug of glass wool inserted as a stopper for holding the resin. The test tube was closed with a one hole
Fig. 4 6 . 2 . Ion-exchange equipment in protection box used for higher temperature separation of members of the actinide and lanthanide series from each other. Note again the sleeved curved rods used for manipulations. The column seen here on the mount attached to the backwall directly in the center, swung above the right lazy Susan tube holder over tube No. 9 is typical of the jacketed type used for higher temperature separation of this type.
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Fig. 4 6 . 3 . D r . Seaborg in early 1950's with jacketed ion-exchange column used for the separation of actinides or lanthanides from each other. stopper and a tube leading to a separatory funnel reservoir of eluant was inserted through the hole. These were used for cationic resins mostly. Simple batch separations, for example in cases where cations were separated from anions, were carried out in fritted glass filter funnels with or without provisions for vacuum filtration. Because of concern for cross-contamination, resins were rarely regenerated for repeated uses and column, resin and all were discarded after use. Our ion-exchange equipment in use during the mid-fifties was placed in dry boxes to protect against the alpha particle radioactivity. Such equipment is typical of those used for remotely operated separation of actinide elements from reactor irradiated samples. The assemblieswere inserted in lead shields, for protection against gamma radiation, and the equipment operated with manipulators via sleeved curved rods. The ion exchange columns belonged to two general types. The first type was unjacketed and used for actinide-lanthanide or anion-cation separations. The jacketed columns were used for
411 higher temperature separation o f members o f t h e a c t i n i d e o r lanthan i d e s e r i e s from each o t h e r . This b r i e f report was r e s t r i c t e d t o d i s c u s s i o n only on the major ongoing chromatographic techniques used i n our laboratory, Naturally, there were a l s o numerous experimental procedures which were s h o r t - l i v e d or u n s u c c e s s f u l .
G.T. SEABORG and G.H. HlGGlNS
GLENN THEODORE SEABORG w a s born i n 1912, i n Ishpeming, Michigan. H e s t u d i e d a t t h e Univ e r s i t y o f C a l i f o r n i a , a t Los Angeles, where h e was named P h i Beta Kappa i n h i s j u n i o r y e a r and r e c e i v e d t h e A.B. d e g r e e i n chemist r y i n 1934. In 1937 he was awarded t h e Ph. D. d e g r e e from 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 a t Berkeley. Between 1937 and 1939 h e w a s t h e p e r s o n a l r e s e a r c h a s s i s t a n t o f Berkel e y ' s famous p h y s i c a l c h e m i s t , G i l b e r t Newt o n L e w i s . S i n c e 1939, h e h a s been on t h e F a c u l t y of 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 a t Berkeley. Between 1958 and 1961, he was Chancellor of t h e Un i v e r s i t y of C a l i f o r n i a a t Berkeley and p r e s e n t l y he is U n i v e r s i t y P r o f e s s o r o f Chemistry and A s s o c i a t e Direct o r of t h e Lawrence Berkeley L a b o r a t o r y . During World War 11, D r . Seaborg headed t h e group a t t h e U n i v e r s i t y o f C h i c a g o ' s M e t a l l u r g i c a l L a b o r a t o r y which d e v i s e d t h e chemical e x t r a c t i o n p r o c e s ses used i n t h e p r o d u c t i o n of plutonium f o r t h e Manhattan P r o j e c t . H e s e r v e d between 1946 and 1950 as a member of t h e Atomic Energy Commiss i o n ' s f i r s t General Advisory Committee and from 1959 t o 1961 on t h e P r e s i d e n t ' s S c i e n c e Advisory Committee. Between 1961 and 1971 h e s e r v e d a s t h e Chairman o f t h e United S t a t e s Atomic Energy Commission under t h r e e p r e s i d e n t s . I n 1963 he headed t h e U.S. d e l e g a t i o n t o t h e U.S.S.R. f o r t h e s i g n i n g o f t h e "Memorandum on Cooperation i n t h e F i e l d o f U t i l i z a t i o n of Atomic Energy f o r P e a c e f u l Purposes" and was i n t h e U.S.A. d e l e g a t i o n t o Moscow f o r t h e s i g n i n g o f t h e Limited Nuclear T e s t Ban T r e a t y . I n September 1971, he was p r e s i d e n t o f t h e F o u r t h United N a t i o n s Conference a t Geneva on t h e P e a c e f u l Uses o f Atomic Energy. I n 1973, D r . Seaborg v i s i t e d t h e P e o p l e ' s Republic o f China as a member o f t h e f i r s t s c h o l a r l y d e l e g a t i o n sponsored by t h e U.S. Committee on S c h o l a r l y Communication w i t h t h e P e o p l e ' s Republic o f China w h i l e i n S p r i n g 1978 he s e r v e d a s t h e chairman o f t h e D e l e g a t i o n on Pure and Applied Chemist r y v i s i t i n g t h e same c o u n t r y . D r . Seaborg i s t h e a u t h o r o f o v e r 300 s c i e n t i f i c p a p e r s and a dozen books as w e l l as works on t h e p e a c e f u l u s e s of n u c l e a r e n e r g y . H i s w r i t i n g s have been t r a n s l a t e d i n t o many f o r e i g n l a n g u a g e s . I n 1951, a t t h e age o f 39, D r . Seaborg was awarded ( w i t h E.M. M c M i l l a n ) t h e Nobel P r i z e f o r Chemistry f o r h i s work on t h e c h e m i s t r y o f t r a n s u r a n i u m e l e m e n t s . H i s o t h e r r e c o g n i t i o n s i n c l u d e t h e Atomic Energy Commission's E n r i c o Fermi Award, t h e Arches of S c i e n c e Award of t h e P a c i f i c S c i e n c e C e n t e r , t h e U.S. Department of S t a t e D i s t i n g u i s h e d Honor Award, t h e John E r i c s s o n Gold Medal o f t h e American S o c i e t y of
406 Swedish E n g i n e e r s , t h e F r a n k l i n Medal, t h e L e i f E r i k s o n Award, t h e John S c o t t Award and Medal o f t h e C i t y o f P h i l a d e l p h i a , t h e P e r k i n Medal o f t h e S o c i e t y o f Chemical I n d u s t r y , t h e Chemical P i o n e e r Award and t h e Gold Medal Award o f t h e American I n s t i t u t e o f C h e m i s t s . The American Chemical S o c i e t y h a s honored him w i t h i t s Award i n P u r e C h e m i s t r y , t h e William H , N i c h o l s Medal, t h e C h a r l e s L a t h r o p P a r s o n s Award, t h e W i l l a r d Gibbs Medal, t h e Madison M a r s h a l l Award, and w i t h i t s h i g h e s t h o n o r , t h e P r i e s t l e y Medal. D r . Seaborg s e r v e d a s P r e s i d e n t o f t h e American Chemical S o c i e t y ( 1 9 7 6 ) , t h e American A s s o c i a t i o n f o r t h e Advancement o f S c i e n c e ( 1 9 7 2 ) , and Chairman o f t h e AAAS Board o f D i r e c t o r s ( 1 9 7 3 ) . H e h a s r e c e i v e d o v e r 40 honorary d o c t o r a l d e g r e e s . H e i s a member o f t h e U.S. N a t i o n a l Academy of S c i e n c e s and n i n e f o r e i g n n a t i o n a l academies i n c l u d i n g t h a t I n 1973, h e w a s d e c o r a t e d as an O f f i c e r i n t h e L6gion of t h e U . S . S . R . d'Honneur o f t h e R e p u b l i c o f F r a n c e . In 1940-1941 D r . Seaborg c o - d i s c o v e r e d e l e m e n t 94 ( p l u t o n i u m ) , t h e f i r s t of t h e t r a n s u r a n i u m e l e m e n t s which h e and h i s coworkers d i s c o v e r e d , Am (element 9 5 ) , Cm (96), Bk ( 9 7 ) , Cf ( 9 8 ) , E s ( 9 9 ) , Fm (loo), Md ( 1 0 1 ) , No (102) and e l e m e n t 106. H e and h i s c o l l e a g u e s have d i s c o v e r e d more t h a n 100 i s o t o p e s t h r o u g h o u t t h e p e r i o d i c t a b l e s . A s t h e aut h o r ( i n 1944) o f t h e " a c t i n i d e c o n c e p t " of t h e heavy e l e m e n t e l e c t r o n i c s t r u c t u r e , D r . Seaborg i s t h e o n l y p e r s o n s i n c e Mendeleev t o have made a major change i n t h e p e r i o d t a b l e o f e l e m e n t s . D r . S e a b o r g ' s involvement i n chromatography i s r e l a t e d t o h i s a c t i v i t i e s i n t h e p i o n e e r i n g atomic e n e r g y r e s e a r c h : h e u t i l i z e d i o n - exchange chromatography f o r t h e s e p a r a t i o n and p u r i f i c a t i o n of uranium and p l u t o n i u m from e a c h o t h e r and from f i s s i o n p r o d u c t s , s e p a r a t i o n of t r a n s p l u t o n i u m e l e m e n t s from r a r e e a r t h s and from e a c h o t h e r . -0-o-oGARY HOYT HIGGINS w a s born i n 1927, i n S t . James, Minnesota. H e s t u d i e d a t M a c a l e s t e r C o l l e g e , i n S t . P a u l , Minnesota, where he r e c e i v e d h i s A.B. d e g r e e i n 1949. A f t e r b e i n g employed a t Minnesota Mining & Man u f a c t u r i n g Co. and s e r v i n g a s a t e a c h i n g a s s i s t a n t a t M a c a l e s t e r C o l l e g e , he j o i n e d t h e U n i v e r s i t y of C a l i f o r n i a a t Berkeley a s a t e a c h i n g a s s i s t a n t i n 1949. H e r e c e i v e d h i s Ph.D. t h e r e i n 1952 and t h e n j o i n e d t h e Lawrence Livermore L a b o r a t o r y . H e h a s been associated with t h i s laboratory ever since; h i s p r e s e n t p o s i t i o n i s t h a t of a technical. a d v i s o r t o t h e a s s o c i a t e d i r e c t o r f o r Ener-. gy & Resource Program. D r . H i g g i n s i s t h e and c o a u t h o r of o v e r 50 p u b l i c a t i o n s . H e h a s r e c e i v e d t h e Guggenheim F e l l o w s h i p Award and a h o n o r a r y D.Sc. d e g r e e from Macalester C o l l e g e . H i s r e s e a r c h i n t e r e s t h a s been c e n t e r e d on t h e c h e m i c a l and n u c l e a r p r o p e r t i e s o f t h e t r a n s u r a n i u m e l e m e n t s . H e i s t h e c o d i s c o v e r e r o f e l e m e n t s 99 and 1 0 0 , e i n s t e i n i u m and fermium. D r . H i g g i n s h a s been i n v o l v e d i n t h e u s e o f ion-exchange chromatography f o r t h e separation of transuranium elements.
407 In the decade spanning the mid-1940's to the mid-1950's uses of chromatography in our laboratory were divided into three major areas. These were, of course, designed to solve three chemical separation problems, namely, separation and purification of uranium and plutonium from each other and from fission products, separation of transplutonium elements from rare earths and separation of transplutonium elements from each other. There are alternative chemical separation processes to solve each of these problems; however, because we were dealing with isotopes whose half lives were quite short, speed of separation was crucial. For example, we could not have used the fractional crystallization techniques to study isotopes of curium separated from americium. Chromatography, as we used the method, was restricted to use of various ion-exchange resins with complexing agents as eluants. In the uranium/plutonium purification and separation process chloride complexes which are anionic were alternately adsorbed and desorbed from anion-exchange resins of the quaternary amine type. Since plutonium in its higher oxidation state forms these complexes the Pu-U could be isolated as a group. Plutonium in its plus three state forms a very weak chloride complex while uranium always remained in its higher oxidation states in aqueous solution and is strongly complexed to anionic form at high chloride concentration. These facts make for easy separation of uranium and plutonium. Neptunium generally follows uranium but can be separated using ion exchange by strong reduction. During this period, particularly during the forties, the actinide concept was not universally accepted; however, the work in our laboratory by Burris Cunningham on ionic radii in compounds of the heavy elements confirmed the view that the 5f electron shell begins with actinium similar to the 4f shell with lanthanum. His work further convinced us that the stable aqueous ions of the transplutonium actinides would all have plus three oxidation states. Hence we started very early to adopt the ion-exchange techniques, used by F. Spedding for purification of the rare earths, to the new and then unknown actinides with atomic numbers 97 through 103. This technique involved use of sulphonic acid type cation-exchange resins with chelating agents for eluants. Citric acid with carefully adjusted pH was most common but EDTA, lactic acid, sodium thiocyanate and later, a-hydroxyisobutyric acid were also used. The early elution columns required 24 or more hours for separation of elements 95 and 96, americium and curium, with room temperature citric acid. This precluded study of isotopes with half lives shorter than several hours so development of faster separation was important. The problem was solved by two separate developments. The first, made in our laboratory, was achieved by increasing the column and eluant temperature to 87 OC. The temperature was maintained constant by condensing trichloroethylene vapor in a jacket surrounding the ion-exchange column. The second was due, probably, to the commercialization of ion-exchange water softeners. The quality of the resins became both better, in that more regular crosslinkage and
active sulfonic acid sites were produced, and more uniform in that different lots were alike. The result of both developments was separations which were complete in about 2 hours, a factor of ten improvement. By the mid-1950's further improvements due to use of a-hydroxyisobutyric acid reduced separation times of the same elements to about 10 minutes. The third area of application was separation of the plus three valence lanthanides from the plus three actinides. Early in the study of various eluants HC1 was used to separate rare earths from each other although the separations were not very clean. At first it was thought that the elution was due to competition between H30+ and the rare earths for the sorption sites but studies with various acids disclosed a special effect of HC1. When the HC1 concentration was raised to 13 N studies with Am, Cm, and Pm showed that the actinides were apparently complexed by the C1- ion, while the lanthanides either were not complexed or were weakly complexed.
Fig. 46.1. Simple ion-exchange equipment in protection box used for actinide-lanthanide or anioncation separations. The sleeved curved roads used by the manipulators are shown in the foreground. The exchange column shown in this figure just left of center and immediately over the 1-liter polyethylene bottle is of the unjacketed type. The tubes in the circular tables were used to sequentially collect eluate.
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Thus separation of the two groups could be achieved by eluting the mixture on cation-exchange resin with concentrated HC1. By the decade of the 1950’s separations were improved by using the ethyl alcohol azeotrope saturated with HC1 gas. It was also found that anionic complexes of the actinides were formed in 36 N LiCl and that the actinides could be selectively adsorbed from an actinidelanthanide mixture thus providing an alternative separation procedure useful for handling massive amounts of the actinides. The first gram-quantity purification of curium was accomplished by this method. Construction of ion-exchange columns was, except for the jacketed column, very simple for the handling of the tracer quantities we usually processed. A 1 or 2 mm diameter thick-walled capillary tube 5 or 10 cm in length was drawn to a tip at one end and joined to a centrifuge cone test tube at the other. The tip was broken off and a small plug of glass wool inserted as a stopper for holding the resin. The test tube was closed with a one hole
Fig. 4 6 . 2 . Ion-exchange equipment in protection box used for higher temperature separation of members of the actinide and lanthanide series from each other. Note again the sleeved curved rods used for manipulations. The column seen here on the mount attached to the backwall directly in the center, swung above the right lazy Susan tube holder over tube No. 9 is typical of the jacketed type used for higher temperature separation of this type.
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Fig. 4 6 . 3 . D r . Seaborg in early 1950's with jacketed ion-exchange column used for the separation of actinides or lanthanides from each other. stopper and a tube leading to a separatory funnel reservoir of eluant was inserted through the hole. These were used for cationic resins mostly. Simple batch separations, for example in cases where cations were separated from anions, were carried out in fritted glass filter funnels with or without provisions for vacuum filtration. Because of concern for cross-contamination, resins were rarely regenerated for repeated uses and column, resin and all were discarded after use. Our ion-exchange equipment in use during the mid-fifties was placed in dry boxes to protect against the alpha particle radioactivity. Such equipment is typical of those used for remotely operated separation of actinide elements from reactor irradiated samples. The assemblieswere inserted in lead shields, for protection against gamma radiation, and the equipment operated with manipulators via sleeved curved rods. The ion exchange columns belonged to two general types. The first type was unjacketed and used for actinide-lanthanide or anion-cation separations. The jacketed columns were used for
411 higher temperature separation o f members o f t h e a c t i n i d e o r lanthan i d e s e r i e s from each o t h e r . This b r i e f report was r e s t r i c t e d t o d i s c u s s i o n only on the major ongoing chromatographic techniques used i n our laboratory, Naturally, there were a l s o numerous experimental procedures which were s h o r t - l i v e d or u n s u c c e s s f u l .