9 Multigram Group Separation of Actinide and Lanthanide Elements by LiCl-Based Anion Exchange E. D. COLLINS, D. E . BENKER, F. R. CHATTIN, P. B. ORR, and R. G. ROSS Transplutonium Elements—Production and Recovery Downloaded from pubs.acs.org by FUDAN UNIV on 12/07/16. For personal use only.
Oak Ridge National Laboratory, Oak Ridge, T N 37830
A chromatographically operated, LiCl-based anion exchange (LiCl AIX) process (1) was adapted from the l a b o r a t o r y s c a l e t o the multigram s c a l e and has been used s u c c e s s f u l l y i n the Trans uranium Processing P l a n t (TRU) a t Oak Ridge N a t i o n a l Laboratory (ORNL) f o r over ten years t o separate lanthanide fission products from the transplutonium a c t i n i d e s and t o partition americium and curium from the heavier elements. During e a r l y process design s t u d i e s f o r TRU, the LiCl AIX process was recognized as one of the few methods t h a t had been used s u c c e s s f u l l y i n l a b o r a t o r y o p e r a t i o n s ; however, the use of solid i o n exchangers was c o n s i d ered i m p r a c t i c a l f o r the l a r g e r - s c a l e operations a t TRU, p r i m a r i l y because of the l o c a l i z e d h e a t i n g and radiolytic gas generation t h a t would occur. Thus, a continuously operated s o l v e n t e x t r a c t i o n process (Tramex) was developed t o accomplish the a c t i n i d e -lanthanide s e p a r a t i o n (2). T h i s process was c h e m i c a l l y s i m i l a r to the anion exchange process because it utilized a mixed ter tiary amine ( p r i m a r i l y o c t y l and decyl) t o e x t r a c t transplutonium a c t i n i d e s from a concentrated LiCl s o l u t i o n . A second s o l v e n t e x t r a c t i o n process (Pharex) was developed to p a r t i t i o n the transcurium a c t i n i d e s from the americium and curium i n the Tramex product (3^) · The Pharex process u t i l i z e d 2-ethylhexyl phenylphosphonic a c i d as the e x t r a c t a n t f o r the transcurium a c t i n i d e s . During e a r l y o p e r a t i o n s , the s e l e c t i v i t y of the Pharex e x t r a c t a n t was found t o be s e v e r e l y reduced by the presence of zirconium i o n s , which were introduced i n t o the process s o l u t i o n s by c o r r o s i o n of Z i r c a l o y - 2 equipment i n TRU. At z i r conium concentrations above 10 ppm, the achievable s e p a r a t i o n began t o be diminished and, a t 100 ppm, a p r a c t i c a l separation c o u l d not be made ( 4 ) . Thus, a replacement f o r the Pharex pro cess was needed, and the L i C l AIX process was the most immediate alternative. Temporary g l a s s equipment was i n s t a l l e d , and the L i C l AIX process was s u c c e s s f u l l y s c a l e d t o a u s e f u l l e v e l {5). Tramex product s o l u t i o n s c o n t a i n i n g from 4 t o 10 g of C m (11 t o 28 W of decay heat) were processed i n i t i a l l y , u s i n g a 38-mm-diam column c o n t a i n i n g 450rnl^o f Dowex^-X8 an^on exchange r e s i n . 2 4 4
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1981
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1155 16th St. N. W. Washington, D. C. 20038
TRANSPLUTONIUM ELEMENTS
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Dowex 1-X10 r e s i n i s now used. Subsequently, a l a r g e r glass column, having a diameter of 50 mm and c o n t a i n i n g 1.2 L of r e s i n , was used. F i n a l l y , the l a r g e glass column was replaced with a tantalum column o f i d e n t i c a l s i z e . A l o a d i n g c a p a c i t y o f 19 g o f C m (54 W) or 35 g o f t o t a l a c t i n i d e mass has been e m p i r i c a l l y e s t a b l i s h e d f o r the tantalum column. L o c a l i z e d heating and cumu l a t i v e r a d i a t i o n exposure of the r e s i n are problems, although not as extensive as expected. R a d i o l y t i c gas generation has not caused any s i g n i f i c a n t d i f f i c u l t y , and downflow operation i s used with l i t t l e evidence of channeling. At the l o a d i n g l i m i t s that have been e s t a b l i s h e d , three column loadings and e l u t i o n s can be made s u c c e s s f u l l y on each batch of r e s i n .
Transplutonium Elements—Production and Recovery Downloaded from pubs.acs.org by FUDAN UNIV on 12/07/16. For personal use only.
2 4 4
Process Chemistry The L i C l AIX process i s based on ( i ) the formation o f a n i o n i c c h l o r i d e complexes of the t r i p o s i t i v e a c t i n i d e and l a n thanide metals i n concentrated L i C l s o l u t i o n s , ( i i ) the s o r p t i o n of these complexes onto a strong base anion exchange r e s i n con t a i n e d i n a column, and ( i i i ) the p r e f e r e n t i a l chromatographic e l u t i o n of the lanthanides as a group p r i o r t o e l u t i o n of the a c t i n i d e s . The g e n e r a l i z e d formation of the t r i v a l e n t metal a n i o n i c c h l o r i d e complexes i s i l l u s t r a t e d i n equation (1)·
M
3 +
aq
+ xCl"
3
^
MC1 " χ
X
χ > 3
(1)
There i s no evidence of the s t r u c t u r e of the species or group of species that i s sorbed by the r e s i n . However, f o r purposes of i l l u s t r a t i o n , the formation and s o r p t i o n of the d i v a l e n t a n i o n i c complex are shown i n equations (2) and ( 3 ) : 3+ M
+
5C1
aq
MCI 5
aq
2R NCl 4 4
2^
o r o r a
9
+
,
MCl|- ^ 5 a q
(2)
aq
(R N) MC1 * org
At e q u i l i b r i u m , the a c t i v i t i e s r e l a t e d as f o l l o w s :
4
Δ
2
3
5
+ 2C1" aq
.
(a) of the r e a c t i n g species are
(3)
9.
COLLINS ET
[ a
]
(R N) MCl org 4
κ
LiCl-Based
AL.
2
5
Anion
[
a
J c
l
Exchange
aq (3a)
=
2
149
Separation
aq
where K
