Single and multicomponent equilibrium data for the extraction of SmCl 3 , NdCl 3 , and CeCl 3 in acidic chloride solutio
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T H E ion exchange m e c h a n i s m of e x t r a c t i n g lanthanide ions f r o m acidic aqueous s o l u t i o n s into d i - ( 2 - e t h y l hexyl) phosphoric acid ( h e r e a f t e r a b b r e v i a t e d D2EHPA) was p r o p o s e d by P e p p a r d e t a l . ~ as follows: M.3 + 3(H2G2) = M(HG2)3 + 3I-I*
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The above m e c h a n i s m holds for t r a c e r c o n c e n t r a t i o n s . H o w e v e r , the e x t r a c t i o n c h e m i s t r y of the l a n t h a n i d e s f r o m aqueous acidic solutions with D2EHPA at m a c r o c o n c e n t r a t i o n s is m o r e c o m p l e x and not well u n d e r stood. The fact that it is m o r e p r a c t i c a l to s e p a r a t e the r a r e e a r t h s at higher l a n t h a n i d e c o n c e n t r a t i o n s i n d i c a t e d the need for m o r e data at a higher c o n c e n t r a t i o n r a n g e . In r e c e n t y e a r s , data at g r e a t e r than t r a c e r c o n c e n t r a t i o n s w e r e made a v a i l a b l e by a n u m b e r of i n v e s t i g a t o r s . 2-s The p u r p o s e of this r e s e a r c h , in addition to a c q u i s i t i o n of m a c r o c o n c e n t r a t i o n e q u i l i b r i u m data, was to study the e x t r a c t i o n b e h a v i o r of the t e r n a r y s y s t e m Sm, Nd, and Ce. The above data w e r e f u r t h e r utilized in the d e v e l o p m e n t of e m p i r i c a l r e l a t i o n s p r e d i c t i n g e q u i l i b r i u m data of single and m u l t i c o m p o n e n t l a n t h a n i d e s y s t e m s . ~-7 EXPERIMENTAL Materials The r a r e e a r t h oxides u t i l i z e d throughout this study w e r e provided by the R a r e E a r t h S e p a r a t i o n
group of the A m e s L a b o r a t o r y . E m i s s i o n s p e c t r o s copy of the oxides showed a p u r i t y of g r e a t e r than 99.9 pct with r e s p e c t to other lanthanide oxides. T h e c e r i u m oxide was f o r m e d f r o m c e r i u m p e r c h l o r a t e ignited at a low t e m p e r a t u r e of about 250~ Acids and other c h e m i c a l s employed in this work w e r e of r e a g e n t grade p u r i t y . The D2EHPA was 98.8 pct m o n o a c i d i c . The h y d r o c a r b o n d i l u e n t ( m i n e r a l s p i r i t s ) was added to an a p p r o p r i a t e a m o u n t of D2EHPA in o r d e r to f o r m a 1 M D2EHPA solution on a m o n o m e r b a s i s . Stock Solutions The r a r e e a r t h oxides w e r e r e a c t e d with e x c e s s HC1 to f o r m the r a r e e a r t h c h l o r i d e s . The e x c e s s HC1 was e v a p o r a t e d after which a s m a l l a m o u n t of HC1 was added to m a i n t a i n the acidity of the solution. The low t e m p e r a t u r e f i r e d t e t r a v a l e n t c e r i u m was r e a c t e d with 100 pct e x c e s s HC1 and the slow r e a c t i o n was allowed to continue for 24 h at 90~ Some u n r e a c t e d fine m a t e r i a l s t i l l s u s p e n d e d in the solution was f i l t e r e d with a v e r y fine f i l t e r p a p e r . The e x c e s s HC1 was e v a p o r a t e d v e r y slowly and s e v e r
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