Plutonium Chemistry - American Chemical Societypubs.acs.org/doi/pdf/10.1021/bk-1983-0216.ch021Similara. Species: Pu(0H)...
0 downloads
557 Views
1MB Size
21 Complexation of the Plutonium(IV) Ion in Carbonate-Bicarbonate Solutions J. I. KIM, CH. LIERSE, and F. BAUMGARTNER
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
Institut für Radiochemie, TU München,8046Garching, Federal Republic of Germany
The complexation of Pu(IV) with carbonate ions is investigated by solubility measurements of PuO in neutral to alkaline solutions containing sodium carbonate and bicarbonate. The total concentration of carbonate ions and pH are varied at the constant ionic strength (I = 1.0), in which the initial pH values are adjusted by altering the ratio of carbonate to bicarbonate ions. The oxidation state of dissolved species in equilibrium solutions are determined by absorption spectrophotometry and different i a l pulse polarography. The most stable oxidation state of Pu in carbonate solutions is found to be Pu(IV), which is present as hydroxocarbonate or carbonate species. The formation constants of these complexes are calculated on the basis of solubility data which are determined to be a function of two variable parameters: the carbonate concentration and pH. The hydrolysis reactions of Pu(IV) in the present experimental system assessed by using the literature data are taken into account for calculation of the carbonate complexation. 238
2
With growing i n t e r e s t i n the c h e m i c a l behaviour o f a c t i n i d e i o n s i n the environment ( 1 ) , the complexation o f these i o n s with c a r b o n a t e a n i o n s h a s been r e c e n t l y a t t r a c t i n g p a r t i c u l a r a t t e n t i o n ( 2 - 1 0 ) due t o t h e u b i q u i t o u s p r e s e n c e o f c a r b o n a t e i o n s i n n a t u r e ( 1 1 , 12) a n d t h e i r p r o n o u n c e d t e n d e n c y t o f o r m c o m p l e x e s w i t h heavy m e t a l i o n s (7^, 1 0 - 1 4 ) . In s p i t e o f t h e c a r b o n a t e c o m p l e x a t i o n of a c t i n i d e s being considered important chemical reactions for understanding the chemistry of a c t i n i d e s i n n a t u r a l f l u i d s , n o t many e x p e r i m e n t s have been d e v o t e d up t o now t o t h e q u a n t i t a t i v e s t u d y o f t h e s u b j e c t , t h o u g h numerous q u a l i t a t i v e o b s e r v a t i o n s a r e d i s c u s s e d i n t h e l i t e r a t u r e . A l t h o u g h t h e r e a r e a few papers r e p o r t i n g the formation c o n s t a n t s o f carbonate complexes 0097-6156/ 83/0216-0317$06.00/0
© 1983 American Chemical Society
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
318
PLUTONIUM CHEMISTRY
o f P u ( I I I ) and P u ( V I ) ( 1 5 , 1 6 ) , i n a c r i t i c a l c o m p i l a t i o n o f s t a b i l i t y c o n s t a n t s ( 1 3 ) none o f t h e s e d a t a h a s b e e n c o n s i d e r e d w o r t h y o f i n c o r p o r a t i o n . To o u r p r e s e n t k n o w l e d g e no r e c o r d e d d a t a have been known f o r t h e c a r b o n a t e c o m p l e x a t i o n o f P u ( I V ) i n t h e l i t e r a t u r e e x c e p t one f o r t h e f o r m a t i o n o f PuCO* species (17). The s t u d y o f c a r b o n a t e c o m p l e x e s o f Pu i s c o m p l i c a t e d by v a r i o u s e x p e r i m e n t a l d i f f i c u l t i e s . The low s o l u b i l i t y o f many c a r b o n a t e s (7), l e a v i n g a v e r y d i l u t e Pu c o n c e n t r a t i o n i n s o l u t i o n , r e s u l t s i n d i f f i c u l t i e s to the experiments with e l e c t r o c h e m i c a l o r s p e c t r o p h o t o m e t r y methods. However, t h e r a d i o m e t r i c method w i t h s o l v e n t e x t r a c t i o n o r s o l u b i l i t y measurement i s e a s i l y a p p l i c a b l e f o r the purpose. U n l i k e the s o l u t i o n with anions, l i k e CI"*, N 0 " e t c . , t h e c o n c e n t r a t i o n o f w h i c h c a n b e v a r i e d at a constant pH, t h e p r e p a r a t i o n o f s o l u t i o n s w i t h v a r y i n g c a r b o n a t e c o n c e n t r a t i o n a c c o m p a n i e s i n d i s p e n s a b l y t h e c h a n g e o f pH o f t h e s o l u t i o n . As a r e s u l t , t h e f o r m a t i o n o f c a r b o n a t e c o m p l e x e s i n v o l v e s a c c o r d i n g l y t h e h y d r o l y s i s r e a c t i o n s o f Pu i o n s i n s o l u t i o n s u n d e r i n v e s t i g a t i o n . I t i s t h e r e f o r e p r e r e q u i s i t e t o know the s t a b i l i t y constants o f Pu(lV) hydroxides p r i o r to the study of i t s carbonate complexation. The p r e s e n t s t u d y i s c o n d u c t e d u n d e r c o n s i d e r a t i o n o f t h u s m e n t i o n e d d i f f i c u l t i e s . The s o l u b i l i t y measurement i s a p p l i e d t o t h e p r e s e n t i n v e s t i g a t i o n , s e l e c t i n g t h e pH r a n g e 6 ^ 12 i n w h i c h t h e c a r b o n a t e c o n c e n t r a t i o n c a n be m a i n t a i n e d g r e a t e r t h a n 5xl0~* M / l . The c a r b o n a t e c o n c e n t r a t i o n a n d pH o f e x p e r i m e n t a l s o l u t i o n s , both b e i n g m u t u a l l y dependent i n a g i v e n s o l u t i o n , a r e taken i n t o a c c o u n t a s two v a r i a b l e p a r a m e t e r s i n t h e p r e s e n t e x p e r i m e n t a n d h e n c e t h e f i n a l e v a l u a t i o n o f f o r m a t i o n c o n s t a n t s i s b a s e d on three dimensional f u n c t i o n s . For c a l c u l a t i o n purpose, the hydrol y s i s c o n s t a n t s o f Pu(IV) a r e t a k e n from t h e l i t e r a t u r e ( 1 8 ) . In o r d e r t o d i f f e r e n t i a t e t h e i n f l u e n c e o f h y d r o l y s i s r e a c t i o n s on the c a r b o n a t e complexation so f a r as p o s s i b l e , t h e c a l c u l a t i o n i s b a s e d on t h e s o l u b i l i t i e s f r o m s o l u t i o n s o f c a r b o n a t e c o n c e n tration > lCf M / l a n d pH > 8.
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
3
6
Experimental The Pu0 i s p r e p a r e d by p r e c i p i t a t i o n o f P u ( I V ) h y d r o x i d e f r o m n i t r i c a c i d s o l u t i o n w i t h a n a d d i t i o n o f c o n e . Nh^OH, w h i c h i s f o l l o w e d by w a s h i n g , f i l t r a t i o n , d r y i n g and c a l c i n a t i o n o f t h e h y d r o x i d e f o r 6 h r s a t 700 ° C . A t t h e t i m e o f p r e p a r a t i o n , the Pu0 i s f o u n d t o be i n c r y s t a l l i n e s t a t e w i t h t h e l a t t i c e c o n s t a n t o f 5.399 A a n d t h e a v e r a g e c r y s t a l s i z e o f 225 A . The i s o t o p i c c o m p o s i t i o n o f p l u t o n i u m i s known t o be 9 4 . 8 4 % Pu, 4.89 % Pu,.0.24 % P u , 0 . 0 2 4 % * P u , 0 . 0 0 4 % ?u and 6 . 2 ppm Pu. 2 3 8
2
2 3 8
2
0
2 3 8
2 3 9
2 I f 0
2 l
x
lhl
2 3 6
A b o u t 5 mg o f t h u s p r e p a r e d Pu0 i s i n t r o d u c e d i n each e x p e r i m e n t a l s o l u t i o n o f 10 m l , w h i c h i s p r e p a r e d w i t h v a r y i n g t h e c o n c e n t r a t i o n o f c a r b o n a t e i o n a n d pH by c h a n g i n g t h e N a H C 0 / Na C0 r a t i o a t t h e c o n s t a n t i o n i c s t r e n g t h (I = 1.0) a d j u s t e d 2 3 8
2
3
2
3
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
21.
Pu(IV) Ion in Carbonate-Bicarbonate Solutions 319
KIM ET A L .
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
by a d d i t i o n o f N a C l û \ . A fevi/ s o l u t i o n s p r e p a r e d w i t h h i g h c a r b o n a t e c o n c e n t r a t i o n , up t o 1 M / l , a r e a l s o i n c l u d e d . A l l s a m p l e s a r e p l a c e d i n g l a s s v i a l s vi/ith t i g h t l y c l o s e d c o v e r and a l l o w e d t o stand f o r a long p e r i o d o f time with o c c a s i o n a l s h a k i n g . Measu r e m e n t s a r e made a f t e r 4 , 9 and 12 months c o n t a c t t i m e . The s a m p l i n g o f s o l u t i o n f o r a c t i v i t y measurement i s c a r r i e d o u t by f i l t r a t i o n w i t h 0 . 2 2 μπι M i l l e x f i l t e r ( M i l l i p o r e C o . ) w h i c h i s e n c a p s u l e d a n d a t t a c h e d t o a s y r i n g e f o r handy o p e r a t i o n . The randomly s e l e c t e d f i l t r a t e s a r e f u r t h e r p a s s e d t h r o u g h Amicon C e n t r i f l o membrane f i l t e r ( C F - 2 5 ) o f 2 nm p o r e s i z e . The a c t i v i t i e s m e a s u r e d f o r t h e f i l t r a t e s f r o m t h e two d i f f e r e n t p o r e s i z e s a r e o b s e r v e d t o be i d e n t i c a l w i t h i n e x p e r i m e n t a l e r r o r . A c t i v i t i e s a r e m e a s u r e d by a l i q u i d s c i n t i l l a t i o n c o u n t e r . F o r e a c h s a m p l e s o l u t i o n , t r i p l i c a t e s a m p l i n g s and a c t i v i t y measurements a r e u n d e r t a k e n and t h e a v e r a g e o f t h r e e v a l u e s i s u s e d f o r c a l c u l a t i o n . A b s o r p t i o n s p e c t r a o f e x p e r i m e n t a l s o l u t i o n s a r e measured u s i n g a Beckman UV 5260 s p e c t r o p h o t o m e t e r f o r t h e a n a l y s i s o f o x i d a t i o n s t a t e s o f d i s s o l v e d Pu i o n s . T h i s a n a l y s i s i s f u r t h e r s u p p o r t e d by t h e measurements w i t h d i f f e r e n t i a l p u l s e p o l a r o g r a p h y ( P o l a r e c o r d Ε 5 0 6 , Metrohm C o . ) u s i n g a d r o p p i n g Hg e l e c t r o d e . To e x a m i n e t h e most s t a b l e o x i d a t i o n s t a t e o f Pu i o n s i n c a r b o n a t e s o l u t i o n s , t h e e x p e r i m e n t i s c o n d u c t e d by c o m b i n i n g an e l e c t r o c h e m i c a l r e a c t i o n c e l l t o t h e a b s o r p t i o n s p e c t r o p h o t o m e t r y . The Pu s o l u t i o n o f d i f f e r e n t o x i dation states prepared electrochemically i s continuously c i r c u l a t e d b e t w e e n t h e r e a c t i o n c e l l and t h e c u v e t t e i n t h e s p e c t r o p h o t o m e t e r . The o r i g i n a l s o l u t i o n o f 0.1 M HClOi, c o n t a i n i n g 10"~ M / l Pu i s t i t r a t e d w i t h N a C 0 s o l u t i o n and t h e c h a n g e i n o x i d a t i o n s t a t e s i s o b s e r v e d w i t h g r a d u a l l y v a r y i n g t h e pH and c a r bonate c o n c e n t r a t i o n . 3
2
3
At the time o f sampling, the t o t a l c o n c e n t r a t i o n o f carbonate i o n s i n e a c h s o l u t i o n and i t s pH a r e d e t e r m i n e d u s i n g a C 0 - e l e c trode (Orion Research C o - T y p e 9 5 - 0 2 ) and a g l a s s e l e c t r o d e , r e s p e c t i v e l y . B a s e d on t h e s e r e s u l t s , t h e c o n c e n t r a t i o n s o f f r e e b i c a r b o n a t e and c a r b o n a t e i o n s i n e a c h s o l u t i o n a r e c a l c u l a t e d by t a k i n g a c c o u n t o f d e g r e e s o f d i s s o c i a t i o n o f N a H C 0 , N a C 0 , H C0 and H C 0 , w h i c h a r e t a k e n f r o m t h e l i t e r a t u r e ( 1 5 , 1 8 , 19) or assessed through i n t e r p o l a t i o n or e x t r a p o l a t i o n o f r e l e v a n t l i t e r a t u r e data (20, 21). 2
3
2
3
Results
2
3
3
and
discussion
Hydrolysis reactions. As t h e s y s t e m u n d e r i n v e s t i g a t i o n c o n t a i n s not o n l y c a r b o n a t e i o n s but a l s o h y d r o x i d e i o n s o f c o n s i d e r a b l e c o n c e n t r a t i o n , i t i s q u i t e p l a u s i b l e that the r e a c t i o n s o f h y d r o l y s i s a n d c a r b o n a t e c o m p l e x f o r m a t i o n compete w i t h e a c h o t h e r . S i n c e the h y d r o l y s i s r e a c t i o n i s not i n v e s t i g a t e d s e p a r a t e l y i n t h i s e x p e r i m e n t , t h e magnitude o f t h i s r e a c t i o n as a f u n c t i o n o f pH i s e v a l u a t e d on t h e b a s i s o f t h e f o r m a t i o n c o n s t a n t s a v a i l a b l e i n the l i t e r a t u r e ( 1 8 ) , which are reproduced
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
320
PLUTONIUM
CHEMISTRY
i n T a b l e I, t o g e t h e r w i t h t h e s o l u b i l i t y p r o d u c t o f P u 0 taken f r o m t h e same l i t e r a t u r e . The d i s s o l v e d c o n c e n t r a t i o n o f P l u t o n i u m , [ P u ] s , due t o h y d r o l y s i s r e a c t i o n i s t h e sum o f a l l h y d r o xide species: 2
[Pu]s
= [Ρυ* ] +
+ [Pu(0H)
3 +
]
+
+ [PuCOH). *- ] 1
(1)
1
wj^ich c a n be w r i t t e n i n t e r m s o f t h e s o l u b i l i t y p r o d u c t o f P u 0 K and f o r m a t i o n c o n s t a n t o f e a c h h y d r o x i d e s p e c i e s β ^ , s u c h a s : 2
s d
Pu0
+ 2H 0
2
1
t Pu ** +
2
P u * * + OH"
t Pu(0H)
Pu
t PuiOH) ?"
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
1
+ iOH"
Î +
40H"
K sp 3
3 +
1
H
U
3u*
1
1
[Pu^HOrT]
(2)
[PuCOHi^/CPu^lCOH"]
(3)
[Pu(0H)^ ]/[Pu i
l t +
][0H-]
i
Hi
and h e n c e K [
P
u
]
8
H
=
l_un J
5 ( Χ Ι β
[OH"] ) 1
Η
(4)
lrU
B a s e d on E q u a t i o n 4 , i t i s p o s s i b l e t o e v a l u a t e t h e d i s s o l v e d c o n c e n t r a t i o n o f Pu a s a f u n c t i o n o f pH, p r o v i d e d p o l y m e r and o t h e r complex s p e c i e s a r e not p r e s e n t . However, t h e p o l y m e r i z a t i o n o f h y d r o l y s e d s p e c i e s e n h a n c e s t h e s o l u b i l i t y o f P u 0 and h e n c e t h e d i s s o l v e d Pu c o n c e n t r a t i o n i s e x p e c t e d t o be g r e a t e r t h a n t h e q u a n t i t y c a l c u l a t e d by E q u a t i o n 4 . On t h e o t h e r h a n d , t h e p r e s e n c e o f a s t r o n g c o m p l e x i n g a n i o n , e . g . c a r b o n a t e i o n , may 2
Table
I.
Species:
Pu(0H)
The f o r m a t i o n c o n s t a n t s
Pu(0H)
of
Pu(IV)
i
l
0
3
24.6
+
34.7
Pu(0H)g
44.3
Pu(0H)I 2
52.7 -
log y
a) b) c)
a
HiCo
Pu(0H)f
Pu0 (s)
(18)
12,2
3 +
Pu(0H)!
9
hydroxides
c a l c u l a t e d b a s e d on t h e v a l u e s symbol used i n t h i s paper ( c f . the v a l u e taken as the average
K
H
= 52.0
c
)
sp
i n T a b l e s 4 . 4 and 9 . 9 E q u a t i o n 14) o f t h o s e g i v e n i n (7)
in and
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
(18) (18)
21.
K i M ET AL.
Pu(IV)
Ion
in Carbonate-Bicarbonate
321
Solutions
s u p p r e s s t h e p o l y m e r i z a t i o n and h i g h e r d e g r e e o f h y d r o l y s i s r e a c t i o n s through formation o f carbonate or hydroxocarbonate s p e c i e s o f the Pu(IV) i o n . By t h e a i d o f t h e l i t e r a t u r e d a t a o f h y d r o l y s i s c o n s t a n t s , t h e a b s o l u t e and r e l a t i v e amounts o f e a c h h y d r o x i d e s p e c i e s o f P u ( I V ) a s a f u n c t i o n o f pH a r e c a l c u l a t e d and g i v e n i n F i g u r e s l a and l b . I t i s shown i n t h i s f i g u r e t h a t i n t h e r e g i o n pH > 8 o n l y t h e P u ( 0 H ) i a p p e a r s i n t h e s o l u t i o n . By a d d i n g t h e c a r b o n a t e i o n o f i n c r e a s i n g c o n c e n t r a t i o n and t h u s i n c r e a s i n g pH, i t i s e x p e c t e d t h a t the Pu(0H)s i o n i s t r a n s f o r m e d t o d i f f e r e n t c a r b o n a t e com p l e x e s and a t t h e same t i m e t h e s o l u b i l i t y p a t t e r n o f P u 0 changes.
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
2
Complexation o f Pu(IV) i o n with carbonate a n i o n . The s o l u b i l i t i e s o f P u 0 a r e d e t e r m i n e d t o be v a r y i n g w i t h r e s p e c t t o t h e c a r b o n a t e c o n c e n t r a t i o n a s w e l l a s pH s i m u l t a n e o u s l y . The d i s s o l v e d c o n c e n t r a t i o n s o f Pu d e t e r m i n e d a f t e r 4 and 12 months c o n t a c t t i m e a r e g i v e n i n F i g u r e 2 a s a f u n c t i o n o f pH, w h e r e a s t h e c o n c e n t r a t i o n s o f f r e e c a r b o n a t e and b i c a r b o n a t e i o n s d e t e r m i n e d i n e a c h e x p e r i m e n t a l s o l u t i o n a r e p r e s e n t e d i n F i g u r e 3 . The s o l u b i l i t i e s m e a s u r e d a f t e r 9 and 12 months a r e f o u n d t o be a l m o s t i d e n t i c a l . In F i g u r e 2, i t i s o b s e r v e d t h a t t h e s o l u b i l i t y o f P u 0 a t f i r s t d e c r e a s e s s l o w l y w i t h i n c r e a s i n g pH u n t i l pH = 8 . 5 , t h e n d e c r e a s e s r a p i d l y between pH = 8.5 ^ 1 0 . 0 , and f i n a l l y i n c r e a s e s s t e e p l y above pH = 1 0 . 0 . T h i s d e v e l o p m e n t o f s o l u b i l i t y w i t h i n c r e a s i n g pH does n o t r e f l e c t a monotonous f u n c t i o n w i t h s i n g l e v a r i a b l e as shown by E q u a t i o n 4 b u t i n f e r s t o a f u n c t i o n o f two v a r i a b l e p a r a m e t e r s , i . e . pH and c a r b o n a t e c o n c e n t r a t i o n . The minimum s o l u b i l i t y o b s e r v e d a t pH = 10 and [ C 0 " " ] = 3 χ 10*" M/l implies that there i s a transformation of s o l i d species (s) t a k i n g p l a c e , i . e . from P u 0 ( s ) t o P u ( 0 H ) C 0 ( s ) . The e x i s t e n c e o f s u c h a p r o c e s s c a n be i n d i r e c t l y e v i d e n c e d by t h e i r r e g u l a r change o f d e c r e m e n t o b s e r v e d i n f r e e c a r b o n a t e ( a l s o b i c a r b o n a t e ) c o n c e n t r a t i o n s n e a r pH = 10 a s i l l u s t r a t e d i n F i g u r e 3 . T h i s may be a s c r i b e d t o t h e c o n s u m p t i o n o f f r e e c a r bonate ions f o r the formation o f the plutonium hydroxocarbonate p r e c i p i t a t e . The r e a c t i o n s i n v o l v e d i n t h i s p r o c e s s a r e i n t e r p r e t e d as f o l l o w s : 2
2
3
3
2
Pu0 (s) 2
+ 2H 0 2
Pu *"*" + 20H~ + C O ? " 1
h+
t Pu
2
+ 40H~
+ Pu(0H) C0 (s) 2
. Pu0 (s) 2
log -log
.
+ 2H 0 + C O P 2
where l o g
3
3
Κ c a n be
+ Pu(0H) C0 2
X-52
3
K^ K
p
= -52
(5)
= X
(6)
H C
SE! + 20H"
log
.
Κ = X-52
< 0
F o r c o n v e n i e n c e o f i l l u s t r a t i o n and f u r t h e r e x p l a n a t i o n s t o be followed l a t e r , the f r e e P u i o n i s t a k e n a s an i n t e r m e d i a t e r e a c t a n t i n t h e f o r m u l a t i o n o f E q u a t i o n s 5 and 6, a l t h o u g h t h i s 4
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
(7) (8)
322
PLUTONIUM CHEMISTRY
3.0 (1): P u 1.8 "h2 \ \ ^
(2): P u ( 0 H )
-ι.
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
-10 H -5.0
(5)
-9.0 -14.0
(a) 4 +
3 +
(3):
Pu(0H)2
(4):
Pu(0H)3
(5):
Pu(0H)°
(6):
Pu(OH)-
(7):
T o t a l Pu d i s s o l v e > r
+
\
ι -12.0
Λ \ ι ν ί \ -10.0
ι
.
-8.0 log
[0H"]
ι
-6.0
,
ι
,
-4.0
ι
,
-2.0
0.0
-2.0
0.0
(M/L)
f p e e
(b)
The r e g i o n o f i n te r e s t
-L -14.0
-12.0
-10.0
-8.0 log
[0H"]
-6.0 f r e e
-4.0
(M/L)
Figure 1. The a b s o l u t e ( a ) a n d r e l a t i v e ( b ) amounts o f P u ( I V ) h y d r o x i d e i o n c o n c e n t r a t i o n ( o r p H ) , c a l c u l a t e d by E q u a t i o n 4 b a s e d on t h e d a t a g i v e n i n T a b l e I. The r e g i o n o f i n t e r e s t f o r t h e p r e s e n t i n v e s t i g a t i o n i s marked by d o t t e d l i n e s .
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Pu(IV) Ion in Carbonate-Bicarbonate Solutions 323
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
KIM ET AL.
j
-4
h
-5
h
-6
h
-7
h
(·):
after
4 months c o n t a c t
time
(χ):
a f t e r 12 months c o n t a c t
time
*
-8
I
-9 -
9
-
8
-
7
-
I
I
I
6
I
I ι ι ι -5
l 0
9
H
[0 "]
ι
1 -4
-3
-2
M/L
free
< )
Figure 2. The s o l u b i l i t i e s o f P u 0 ( c ) a s a f u n c t i o n o f t h e pH o f e q u i l i b r i u m s o l u t i o n s . Up t o pH = 10 t h e s o l u b i l i t i e s a f t e r 4 and 12 months a r e a l m o s t i d e n t i c a l , w h i l e a t pH > 10 t h e v a l u e s a f t e r 12 months d i f f e r f r o m t h o s e a f t e r 4 months w h i c h a r e n o t i n e q u i l i b r i u m . The v a l u e s a f t e r 12 months and 9 months ( n o t p l o t t e d h e r e ) a r e f o u n d t o be i d e n t i c a l . 2 3 8
2
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
324
PLUTONIUM CHEMISTRY
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
_
* * · •
free HCO, ion -
·
··
"«
•
2- s o r p t i o n
"
•·
CO,
» «
. .ν·· °
·
"
-"*· m * •
. \
. «1. 1 · «. •·
. •. .·
* * · ·*
··
·
J
Λ
;••
-6 "
" - f r e e CO3" ion
-8
*
"
-1
-10 5
6
1
1
1
1
1
7
8
9
10
11
12
PH
Figure 3. The c o n c e n t r a t i o n s determined at
of
free carbonate
solubility
and b i c a r b o n a t e
e q u i l i b r i u m as
D e c r e m e n t s o f t h e c o n c e n t r a t i o n n e a r pH = 10 formation
of
solubilities
t h e Pu(0H) C0 2
of
Pu0
2
(cf.
3
suggest
p r e c i p i t a t e and h e n c e
Figure
ions
a function of
pH. the
lowering
2).
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
21.
Pu(IV) Ion in Carbonate-Bicarbonate Solutions 325
κ ί Μ ET AL.
i o n i s n o t v i a b l e s p e c i e s i n t h e s o l u t i o n o f pH > 8. The r e a c t i o n g i v e n by E q u a t i o n 7 c a n be f o r m u l a t e d a l t e r n a t i v e l y vi/ith more or l e s s r e a l i t y r e l e v a n t r e a c t i o n s : Pu0 (s) 2
t
2
Pu(0H)I
(9)
P u ( 0 H ) i + CO?"
+ Pu(0H) C0 (s)
+ 30H"
(10)
Pu0 (s)
*
+ 20H"
(11)
2
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
+ 2 H 0 + OH"
2
+ 2 H 0 + C01" 2
3
Pu(0H) C0 (s) 2
3
As i s a p p a r e n t i n F i g u r e s l a and l b , t h e P u ( 0 H ) i s p e c i e s i n p r e d o m i n a n t a t pH > 8 i n t h e a b s e n c e o f c a r b o n a t e i o n s . I t appears reasonable to expect that i n the presence of carbonate ions i n s o l u t i o n the Pu(0H)i i o n undergoes the f o r m a t i o n of the P u ( 0 H ) C 0 p r e c i p i t a t e , o f w h i c h t h e s o l u b i l i t y d e p e n d s on t h e c a r b o n a t e c o n c e n t r a t i o n as w e l l as pH. C o n s i d e r a t i o n o f P u ( 0 H ) C 0 as a l e a s t s o l u b l e s p e c i e s under the p r e s e n t e x p e r i m e n t a l system i s a t t r i b u t e d t o t h e s i m i l a r compound, i . e . T h O C 0 * n H 0 , w h i c h a p p e a r s s p a r ingly soluble i n a l k a l i n e carbonate s o l u t i o n s (22). Equation 8 may r e s u l t i n a p o s i t i v e o r n e g a t i v e v a l u e ; t h e f o r m e r i n d i c a t e s Pu(0H) C0 l e s s s o l u b l e than Pu0 while the l a t t e r s u g g e s t i n g the r e v e r s e . 2
2
3
2
3
3
3
2
2
The d i s s o l v e d s p e c i e s a r e c o n s i d e r e d t o be a c o m p o s i t e o f numerous h y d r o x i d e s , c a r b o n a t e s , and h y d r o x o c a r b o n a t e s o f P u ( I V ) , w h i c h c a n be e x p r e s s e d by [Pu]s
=
[Pu^ ]-r
[Pu(0H)
+
+[Pu(C0 ) 3
2 +
]+
3 +
+[Pu(0H) *~ ]+ 1
+[Pu(0H).(C0 ) " ]+
+
2
3
C0 )
2 j
3
3
i
i
[Pu(0H)(C0 ) ]+
+[Pu(C0 ) t" ]+[Pu(0H) J l
]+
2J
i
3
] + . . .+[Pu(0H) ( C O s ) ; - - ^ ] 1
1
(12) and i n a g e n e r a l
[Pu]s
, = [pu"*]
Γ J i-
form: _n ;>Z i=0
m
. β
j=0
Η
"
ί
Γ
ί
1
L
J
[OH"]
1
[C01"]
J
-1 ! :
/ -t -τ \ {
U
)
where
ο 3
HiCj
[Pu(0H).(C0,).] =
— - i
[Pu- ] +
J
r
[0H-] [C0i ] 1
-
(14)
J
The f r e e c o n c e n t r a t i o n o f P l u t o n i u m , [Pu *"*"], AS c o n t r o l l e d by either s o l u b i l i t y products, Κ f o r Pu0 or for Pu(0H) C0 , sp 1
2
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
2
3
326
PLUTONIUM CHEMISTRY
namely
K
[Pu" ]
=
+
[
P
u
i
+
]
=
HC S£
(15)
[0H"] [C0 "] 2
3
Which o f t h e two i s a p p l i c a b l e t o t h e p r e s e n t e x p e r i m e n t d e p e n d s m a i n l y on w h e t h e r E q u a t i o n 8 r e s u l t s i n a p o s i t i v e o r n e g a t i v e v a l u e . The s o l u b i l i t y c h a n g e s q u i t e d i f f e r e n t l y i n pH > 8 a n d r e a c h e s t h e minimum ( [ P u ] s = 2 χ l C f M / l ) a t pH = 10 and [ C 0 l ~ ] = 3 χ 1 0 " M / l . S i n c e t h e minimum i s much l o w e r t h a n t h e v a l u e a s s e s s e d by E q u a t i o n 4 ( c f . F i g u r e l a ) , i t i s p l a u s i b l e t h a t E q u a t i o n 8 becomes a p o s i t i v e v a l u e . As d e s c r i b e d a b o v e , i n pH < 8 t h e c a r b o n a t e c o n c e n t r a t i o n s a r e r e l a t i v e l y s m a l l , < 10 M / l , and i t i s t h e r e f o r e e x p e c t e d t h a t i n t h a t c o n d i t i o n d i f f e r e n t hydroxide s p e c i e s are predominant ( c f . F i g u r e l b ) . In pH > 8 where [ C 0 | ~ ] > 10" * M / l , t h e f o r m a t i o n o f h y d r o x o c a r b o n a t e and c a r b o n a t e c o m p l e x e s may t a k e p l a c e . F o r t h i s r e a s o n , e v a l u a t i o n o f t h e f i n a l r e s u l t s i s m a i n l y b a s e d on t h e e x p e r i m e n t a l d a t a f r o m t h e s o l u t i o n s o f pH > 8 and [ C O ^ ] > 10" * M / l . F o r t h e d e t e r m i n a t i o n o f 3^-Q - t h e c o m p u t a t i o n a l . s o l u t i o n o f e x p e r i m e n t a l r e s u l t s i s c a r r i e c h O u t by E q u a t i o n 1 3 . The B^iCo v a l u e s f o r h y d r o l y s i s r e a c t i o n s a r e taken i n t o a c c o u n t as g i v e n i n T a b l e 1. The i and j v a l u e s a r e v a r i e d f r o m 0 t o 5 f o r t h e f o r m a t i o n o f h y d r o x o c a r b o n a t e c o m p l e x e s . The i n p u t p a r a m e t e r s f o r E q u a t i o n 1 3 : [ P u ] s , [ O H " ] ( o r p H ) , and [ C O " ] a r e a l l e x p e r i m e n t a l v a l u e s a f t e r 12 months c o n t a c t t i m e . 9
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
3
- l f
1
2
1
2
V e r i f i c a t i o n of Pu(IV) i o n i n s o l u t i o n . Whether t h e d i s s o l v e d Pu i o n s a r e t e t r a v a l e n t i s v e r i f i e d by t h e f o l l o w i n g e x p e r i m e n t s . The a b s o r p t i o n s p e c t r o p h o t o m e t r y o f t h e s o l u t i o n s w i t h h i g h e r c a r b o n a t e c o n c e n t r a t i o n (> 0.1 M / l ) , i n w h i c h t h e [ P u ] s v a l u e s a r e g r e a t e r t h a n 1 0 " M / l , shows t h a t t h e d i s s o l v e d s p e c i e s a r e P u ( I V ) i o n s . The i n d i r e c t c o n f i r m a t i o n o f a s t a b l e s p e c i e s o f Pu i o n s i n c a r b o n a t e s o l u t i o n s i s made by a g r a d u a l a d d i t i o n of Na C0 s o l u t i o n t o 0.1 M HClOif s o l u t i o n c o n t a i n i n g Pu i o n s o f d i f f e r e n t o x i d a t i o n s t a t e s . With i n c r e a s i n g the carbonate i o n c o n c e n t r a t i o n i n t h e s o l u t i o n , where pH b e i n g a l s o i n c r e a s e d a c c o r d i n g l y , i t i s o b s e r v e d t h a t the d i s t i n c t i v e a b s o r p t i o n peaks o f P u ( I I I ) , P u ( I V ) , Pu(VI) i n HCIO4 s o l u t i o n d i s a p p e a r g r a d u a l l y and the a b s o r p t i o n spectrum o f Pu(IV) i n c a r b o n a t e s o l u t i o n i s f i n a l l y observed. F i g u r e 4 manifests the t r a n s f e r process o f d i f f e r e n t o x i d a t i o n s t a t e s o f Pu i o n s f r o m t h e HClOt* s o l u t i o n t o P u ( I V ) i n t h e c a r b o n a t e s o l u t i o n . The s p e c t r o p h o t o m e t r y r e s u l t s a r e f u r t h e r s u p p o r t e d by t h e measurements w i t h d i f f e r e n t i a l p u l s e p o l a r o g r a p h y , w h i c h d e m o n s t r a t e s t h a t t h e most s t a b l e Pu o x i d a t i o n state i n carbonate solutions i s Pu(IV). 5
2
3
The l o w e s t s o l u b i l i t y o b s e r v e d i n o u r e x p e r i m e n t s i s 2 x l 0 " a t pH = 10 and [ C 0 ~ ] = 3 χ 1 0 ~ M / l . When t h e d i s s o l v e d s p e 9
M/l
3
3
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Pu(IV) Ion in Carbonate-Bicarbonate Solutions
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
21. κίΜ ET AL.
Wavelength / nm
Figure 4. The a b s o r p t i o n tions.
Curve
Pu(IV), after
of
Pu(V)
and P u ( V I ) of Na C0
1
lution is
2
c u r v e 3:
(pH = 1 0 . 4 ; (1-5)
t h e Pu i o n s
The s t a r t i n g
addition
10" * M / l ) ; tion
spectra
1:
χ 10~
3
after [COi""] 5
ions
solution in
0.1
solution
in different containing M HClOt,;
(pH = 6 . 7 ;
further addition = 0.3
M/l).
of
The Pu
solu
Pu(III),
curve
2:
[C0|~] Na C0 2
= 3
so
concentra
M/l.
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
327
328
PLUTONIUM CHEMISTRY
c i e s may be o t h e r t h a n P u ( I V ) i o n , i t i s t o e x p e c t t h a t t h e s o l u b i l i t y u n d e r t h i s c o n d i t i o n must be h i g h e r t h a n t h e o b s e r v e d v a l u e , s i n c e the o x i d a t i o n o r r e d u c t i o n enhances the s o l u b i l i t y o f t h e l e a s t s o l u b l e P u ( I V ) compound. I t i s q u i t e w e l l known t h a t t h e t e t r a v a l e n t a c t i n i d e compounds a r e l e s s s o l u b l e t h a n t h e same c o m p l e x compounds o f o t h e r o x i d a t i o n s t a t e s . In t h e l i t e r a t u r e ( 3 ) , t h e p o s s i b l e f o r m a t i o n o f p l u t o n y l b i c a r b o n a t e complex i s d i s c u s s e d . In o r d e r t o v e r i f y w h e t h e r we a r e d e a l i n g w i t h b i c a r b o n a t e o r c a r b o n a t e c o m p l e x e s , t h e Pu(IW) s o l u t i o n s p r e p a r e d i n NaHC0 a n d N a C 0 s o l u t i o n s a r e examined by s p e c t r o p h o t o m e t r y . The a b s o r p t i o n s p e c t r a m e a s u r e d up t o 900 nm show no v i s i b l e d i f f e r e n c e f o r b o t h s o l u t i o n s . F o r t h i s r e a s o n i t i s b e l i e v e d t h a t t h e Pu(IV) i o n forms c a r b o n a t e complexes i r r e s p e c t i v e o f carbonate or bicarbonate ions present i n s o l u t i o n .
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
3
2
3
Formation constants o f carbonate complexes. The c o m p u t a t i o n a l t r e a t m e n t o f e x p e r i m e n t a l r e s u l t s by E q u a t i o n 13 i s made by an i t e r a t i o n p r o c e s s . F i g u r e s 5 a n d 6 d e m o n s t r a t e c o m p a r i s o n s o f computed v a l u e s w i t h e x p e r i m e n t a l d a t a a s a f u n c t i o n o f two d i f f e r e n t v a r i a b l e p a r a m e t e r s , [OH"] and [ C 0 § ~ ] . S i n c e t h e e x p e r i m e n t a l e r r o r i n t h e measurement o f c a r b o n a t e c o n c e n t r a t i o n i s r e l a t i v e l y l a r g e due t o s m a l l volume o f s o l u t i o n a v a i l a b l e t o u s e , a c e r t a i n e x t e n t o f d e v i a t i o n i s e x p e c t e d from t h e comparison o f computed v a l u e s w i t h e x p e r i m e n t a l d a t a . H o w e v e r , F i g u r e s 5 and 6 show t h a t r e a s o n a b l e a g r e e m e n t s between t h e two v a l u e s a r e a t t a i n e d a s a f u n c t i o n o f pH a s w e l l a s o f t h e c a r b o n a t e c o n c e n t r a t i o n . S i n c e e a c h s o l u b i l i t y p o i n t i s r e l a t e d w i t h t h e two p a r a m e t e r s s i m u l t a n e o u s l y , t h e computed p o i n t s do n o t f o l l o w smooth c u r v e s b u t s e n s i t i v e l y f l u c t u a t e i n a c c o r d a n c e w i t h t h e v a r i a t i o n o f the conjugate parameter. Because t h e carbonate c o n c e n t r a t i o n a n d pH a r e m u t u a l l y d e p e n d e n t i n a g i v e n s o l u t i o n and b e c a u s e t h e OH" a n d C 0 | " i o n s a r e c o m p e t i t i v e l i g a n d s f o r c o m p l e x a t i o n o f the Pu(IV) i o n , i t i s found necessary t o i n v e s t i g a t e t h e c a r b o n a t e c o m p l e x a t i o n o f P u ( I V ) by v a r y i n g t h e two p a r a m e ters simultaneously. The c a l c u l a t e d f o r m a t i o n c o n s t a n t s o f B u - p presented i n T a b l e 2. Among c a l c u l a t e d v a l u e s f o r p r o b a D i e complex s p e c i e s , t h e r e l a t i v e amounts o f d o m i n a n t a n d l e s s d o m i n a n t c o m p l e x s p e c i e s a r e d i s t i n g u i s h e d by a
'HaCb
r°H-] [C0!-] a
η 1 I
r
e
b
(a,b
m III
=
const.)
(16)
The r e l a t i v e amount o f d o m i n a n t s p e c i e s u n d e r t h e e x p e r i m e n t a l c o n d i t i o n a r e shown i n F i g u r e 7 . F i v e s p e c i e s a r e p r e d o m i n a n t i n the s o l u t i o n : Pu(0H)C0 , P u ( C 0 ) § , P u ( C 0 ) r , Pu(C0 )iT, and P u ( C 0 ) " . The s p e c i e s o t h e r t h a n t h o s e g i v e n h e r e a r e n o t p r e s e n t i n s i g n i f i c a n t amount. +
3
3
3
3
3
5
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
21. KiM ET AL.
Pu(IV) Ion in Carbonate-Bicarbonate Solutions 329
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
M
H
(χ): experimental value ( · ) : calculated value
J -
6
-
I
5
I
I
-
fm
I
I
-
4
log [0H"]
-J
free
I
L_
_l
I
3
(M/L)
Fiqure 5. The c o m p a r i s o n o f c a l c u l a t e d s o l u b i l i t i e s by E q u a t i o n 13 vi/ith t h e v a l u e s f r o m e x p e r i m e n t (12 months c o n t a c t t i m e ) . The v a l u e s a r e p l o t t e d as a f u n c t i o n o f t h e c o n c e n t r a t i o n of free hydroxide ion at s o l u b i l i t y e q u i l i b r i a (cf. Figure 6).
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
l_
-2
330
PLUTONIUM CHEMISTRY
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
_
Μ
Κ
*• • • •
(χ): experimental value ( · ) : calculated value
Κ
-
•
··
:
-
: -
χ l
l
-5
l
l
i
l
· l
.
·
l
l
-4
l
J
1
-3 l
Figure 6.
l
o
g
1 L
-2 [ 3 ]free C0
_
(
M/L
i .-I
L
l i i ]
-1
>
The c o m p a r i s o n o f c a l c u l a t e d s o l u b i l i t i e s by E q u a t i o n 13 w i t h t h e v a l u e s f r o m e x p e r i m e n t (12 months c o n t a c t t i m e ) . The v a l u e s a r e p l o t t e d a s a f u n c t i o n o f t h e c o n c e n t r a t i o n o f free carbonate i o n at s o l u b i l i t y e q u i l i b r i a (cf. Figure 5 ) .
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
ι
0
Pu(IV) Ion in Carbonate-Bicarbonate Solutions 331
KIM ET A L .
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
1.0
-
^ \
P
U
(
C
0
/»u(C0 )|-
) 2
3
3
Pu(C0 )^
/
3
-
\
XPU(C0 )\ 3
.
Pu(OH)(C0 )
+
3
1
0.0 -4.0
1
1
l.Tfc
1
log [ C 0 ^ ]
1 1
-1.1
-2.0
-10
1. 1
1 ^ — \
f r e e
0.0
(M/L)
Figure 7. The
relative
carbonate
amounts o f
species
of
predominant
Pu(IV)
in
the
hydroxocarbonate investigated
and
solutions.
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
332
PLUTONIUM CHEMISTRY
The complex formation constants obtained from t h i s experiment are very l a r g e i n comparison w i t h the complexation o f the Pu(IV) i o n w i t h other l i g a n d s , l i k e OH", F" e t c . In view o f s o l u b i l i t i e s observed i n higher carbonate c o n c e n t r a t i o n ([Pu]s ^ 10" M/l) i t i s considered p o s s i b l e t h a t the formation constants o f carbon ate complexes o f the Pu(IV) i o n must be r e l a t i v e l y l a r g e . The p o s t u l a t i o n made i n t h i s work as f o r the formation o f the very i n s o l u b l e Pu(0H) C0 under the present experimental c o n d i t i o n i s p r i m a r i l y based on the e a r l i e r works (22) on ThOC0 «nH 0, which i s found t o be not much s o l u b l e i n a l k a l i n e s o l u t i o n . However, the experimental v e r i f i c a t i o n o f the p o s t u l a t i o n i s s t i l l i n pro gress f o r the moment. The r a d i o l y s i s e f f e c t due t o the P u nu c l i d e used i n the present experiment i s not i n v e s t i g a t e d sepa r a t e l y . The recent paper (23) d e a l i n g w i t h the s o l u b i l i t y o f P u 0 i n pure water d i s c u s s e s the change o f pH due t o the r a d i o l y s i s e f f e c t , i . e . decrease o f pH on account o f the formation of HN0 i n the s o l u t i o n open t o a i r and hence i n c r e a s i n g the so l u b i l i t y o f P u 0 . In our separate experiment made i n a system c l o s e d t o a i r c o n t a c t , the s o l u b i l i t i e s o f P u 0 a f t e r 200 days i n water w i t h v a r y i n g pH = 5 'v* 9 are observed t o be i d e n t i c a l w i t h the values reported i n the l i t e r a t u r e f o r Pu0 •nHzOiam) (24) which were measured a f t e r 250 days. From experience, i t i s b e l i e v e d t h a t the r a d i o l y s i s e f f e c t can be o f two k i n d s : the d i r e c t e f f e c t which changes the c r y s t a l l i n e s t r u c t u r e o f the oxide and thus a l t e r s the k i n e t i c s o f d i s s o l u t i o n ; the i n d i r e c t e f f e c t which changes the s o l u t i o n and components t h e r e i n , e.g. producing HN0 i n case o f the s o l u t i o n being i n contact with a i r , and hence l e a d i n g t o a d i f f e r e n t s t a t e o f e q u i l i b r i u m , namely higher s o l u b i l i t y . However, the thus i n c r e a s e d s o l u b i l i t y f o l l o w s the e q u i 3
2
3
3
2
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
2 3 8
2 3 8
2
3
2 3 8
2
2 3 8
2
239
2
3
Table I I . The formation constants o f Pu(IV) carbonates and hydroxocarbonates log 3
Species: P u ( 0 H ) ( C 0 ) . i
PuC0
(
3
2+
47.1
+
3.0
Pu(C0 )°
55.0 ± 2.5
Pu(C0 )I"
57.9
+
2.7
59.6
+
2.9
62.4
± 2.4
3
3
Pu(C0 )ÎT 3
Pu(C0 )|" 3
55.2 ± 2.3
Pu(0H)C0Î
- log K r 68.8 ± 2.4 sp aT symbol used i n t h i s paper ( c f . Equation 13) H C
Pu(0H) C0 (s) 2
3
y
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
21. KIM ET AL.
Pu(IV) Ion in Carbonate-Bicarbonate Solutions 333
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
librium function with respect to pH, unless other complexing agents are present in solution. In a carbonate solution, the ra diation effect changes pH and therewith the carbonate concentra tion, and the Pu02 solubility varies accordingly. The solubility function shown in Figure 2 is not altered after 9 months, not after 4 months at :pH < 10, although individual experimental points are shifted to other positions in accordance with new val ues of pH and the carbonate concentration determined. The primary mechanisms of radiolysis effect on the solubility of Pu02 are, however, an important subject for separate investigation. Similar experiments with 2 3 9 Pu0 2 are in progress in our la boratory and will be used to verify or to improve the preliminary results presented in this paper. Acknowledgments The authors are much indebted to Dr. F. X. Koppold for the computer calculation. Thanks are due to Mr. Y. X. Xia for his help in measuring the absorption spectra and the technical assist ance of Miss Ch. Rahner throughout this work is acknowledged. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
Hanson, W. C., Ed.; "Transuranic Elements in the Environ ment"; DOE/TIC-22800, 1980. Billon, Α., Ed.; "Techniques for Identifying Transuranic Speciation in Aquatic Environments"; STI/PUB/613, IAEA: Vienna, 1981; p 65. Sullivan, J. C.; Bertrand, P. Α.; Choppin, G. R. Radiochim. Acta, in press. Wood, M.; Mitchell, M. L.; Sullivan, J. C. Inorg. Nucl. Chem. Lett. 1978, 14, 465. Rai, D.; Seme, R. J. J. Environ. Qual. 1977, 6, 89. Langmuir, D. Geochim. Cosmochim. Acta 1978, 42, 547. Edelstein, W. M., Ed.; "Actinides in Perspective"; Pergamon Press: New York, 1981; p 553. Bidoglio, G. Radiochem. Radioanal. Lett. 1982, 53, 45. Brückl, N.; L i , G. H.; Kim, J. I. Paper presented in the meeting of German Chemical Society, Nuclear Chemistry: Karlsruhe, Sep. 21-25, 1982. Jensen, B. S. RIS-Report on Critical review of available information on migration phenomena of radionuclides into the geosphere, 1981. Stumm, W.; Morgan, J. J., Eds.; "Aquatic Chemistry"; John Wiley & Sons: New York, 1981. Lindsay, W. L., Ed.; "Chemical Equilibria in Soils"; John Wiley & Sons: New York, 1979. Smith, R. M.; Martell, A. E . , Eds.; "Critical Stability Constants"; Plenum Press: New York, 1976.
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
334 14. 15. 16. 17.
Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch021
18. 19. 20. 21. 22. 23. 24.
PLUTONIUM CHEMISTRY
Saltelli, Α.; Avogadro, Α.; Bertozzi, G. "Proc. Workshop on the Migration of Long-lived Radionuclides in the Geo sphere"; OECD/NEA: Paris, 1979; p 147. Sillen, L. G.; Martell, A. E . , Eds.; "Stability Constants of Metal Ion Complexes"; The Chemical Society: London, 1964. Cleveland, J. M., Ed.; "The Chemistry of Plutonium"; Gordon & Breach Science, 1970. Moskvin, A. I.; Gel!man, A. D. Russ. J. Inorq. Chem. 1958, 3, 962. Baes, C. F.; Mesmer, R. G., Eds.; "The Hydrolysis of Cations"; John Wiley & Sons: New York, 1976. Walker, J.; Cormack, W. J. Chem. Soc. 1900, 77, 11. Frary, F. C.; Nietz, A. H. J. Am. Soc. 1915, 37, 2271. Seyler, C. A.; Lloyd, P. V. J. Chem. Soc. 1917, 111, 138. Gmelin Handbuch der Anorg, Chem. "Thorium und Isotope"; Sys. Nr. 44, Verlag Chemie: Weinheim, 1955; p 300. Rai, D.; Ryan, L. Radiochim. Acta in press. Rai, D.; Serne, R.; Moore, D. A. Soil Sci. Soc. Am. J. 1980, 44, 490.
RECEIVED December 21,1982
In Plutonium Chemistry; Carnall, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
