The Extraction of Uranium (VI) from Sulphuric Acid Solutions by Tri-n

9 The Extraction of Uranium (VI) from Sulphuric Acid Solutions by Tri-n-Octylphosphine Oxide TAICHI SATO

Downloaded by CORNELL UNIV on September 1, 2016 | http://pubs.acs.org Publication Date: April 16, 1980 | doi: 10.1021/bk-1980-0117.ch009

Department of Applied Chemistry, Faculty of Engineering, Shizuoka University, Hamamatsu, Japan

We have used tri-n-octylphosphine oxide (TOPO) as a solvent extractant of uranium(VI) and thorium(IV) from nitric and hydro chloric acid solutions (1-3). In contrast, the extraction of uranium(VI) and thorium(IV) from nitric and hydrochloric acid solutions has been investigated by tri-n-butylphosphate (TBP) (4, 5). However, since TBP reveals a poor efficiency for the extrac tion of metals from sulphuric acid solutions, this paper extends the work to the extraction of uranium(VI) from sulphuric acid solutions by TOPO. Experimental Reagent TOPO (Hokko Chemical Industry Co. Ltd., Tokyo) was used with out further purification and dissolved in kerosene, or benzene. The kerosene was purified by washing with concentrated sulphuric acid (4). The aqueous solutions of uranyl sulphate were prepared by dissolving uranyl sulphate hydrate (UO SO ·3Η O, Yokozawa Chemical Co. Ltd.) in sulphuric acid solutions of the required concentrations. All chemicals were of analytical reagent grade. Extraction and analytical procedures 2

4

2

E q u a l v o l u m e s (20 m l ) o f t h e TOPO s o l u t i o n i n t h e o r g a n i c s o l v e n t and u r a n y l s u l p h a t e s o l u t i o n c o n t a i n i n g s u l p h u r i c a c i d were s h a k e n f o r 10 m i n i n 50 m l s t o p p e r e d c o n i c a l f l a s k s i n a thermostatic water-bath at the r e q u i r e d temperature. P r e l i m i n a r y e x p e r i m e n t s showed t h a t e q u i l i b r a t i o n i s c o m p l e t e i n 10 m i n . T h e m i x t u r e was c e n t r i f u g e d and s e p a r a t e d , a n d u r a n i u m was s t r i p p e d f r o m t h e o r g a n i c p h a s e w i t h 0 . 5 M ammonium c a r b o n a t e s o l u t i o n , and then the d i s t r i b u t i o n c o e f f i c i e n t (the r a t i o o f the e q u i l i b r i u m c o n c e n t r a t i o n o f uranium i n the o r g a n i c phase t o t h a t i n the aque ous p h a s e , [ U ] / [ U ] q ) was o b t a i n e d . U r a n i u m ( V I ) was d e t e r m i n e d b y t i t r a t i o n w i t h EDTA u s i n g x y l e n o l o r a n g e (XO) as i n d i c a t o r ( 6 ) . T h e a c i d i t y o f t h e o r g a n i c p h a s e was d e t e r m i n e d b y a d d i n g 2 % s o d i u m o x a l a t e s o l u t i o n t o t h e a q u e ous s o l u t i o n b a c k - w a s h e d a n d t i t r a t i n g w i t h 0 . 0 1 M s o d i u m h y d r o x i d e o r g

a

0-8412-0527-2/80/47-117-117$05.00/0 © 1980 A m e r i c a n C h e m i c a l Society

Navratil and Schulz; Actinide Separations ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

118

ACTINIDE

SEPARATIONS

s o l u t i o n b y u s i n g t h e pH m e t e r . T h e w a t e r c o n t e n t o f t h e o r g a n i c s o l u t i o n was d e t e r m i n e d b y t h e K a r l F i s c h e r m e t h o d . T h e s u l p h a t e c o n c e n t r a t i o n o f t h e o r g a n i c p h a s e was d e t e r m i n e d a s f o l l o w s : t h e s u l p h a t e i n t h e aqueous s o l u t i o n b a c k - e x t r a c t e d f r o m t h e o r g a n i c p h a s e was c o m p l e t e l y p r e c i p i t a t e d as b a r i u m s u l p h a t e w i t h b a r i u m chloride solution. S p e c t r o p h o t o m e t r y , i n f r a r e d a n d NMR s p e c t r a l measurements A b s o r p t i o n s p e c t r a were o b t a i n e d on a Shimadzu Model QV-50 spectrophotometer, u s i n g 1 . 0 0 cm f u s e d s i l i c a c e l l s . Infrared s p e c t r a were d e t e r m i n e d o n a J a p a n S p e c t r o s c o p i c C o . L t d . M o d e l I R - S , e q u i p p e d w i t h p o t a s s i u m c h l o r i d e p r i s m s (4000-550 c m " ) u s i n g a m a t c h e d c e l l w i t h p o t a s s i u m b r o m i d e window ( a s p a c e r o f 0 . 1 mm) o r a c a p i l l a r y f i l m b e t w e e n t h a l l i u m h a l i d e . N u c l e a r mag n e t i c r e s o n a n c e (NMR) s p e c t r a were o b t a i n e d f o r s a m p l e s d i s s o l v e d i n c a r b o n t e t r a c h l o r i d e u s i n g a H i t a c h i P e r k i n - E l m e r Model R-20 H i g h R e s o l u t i o n NMR s p e c t r o m e t e r u t i l i z i n g a p e r m a n e n t magnet o f 14092 g a u s s , i n t h e u s e o f t e t r a m e t h y l s i l a n e a s a n i n t e r n a l r e f erence .


1

Results

and d i s c u s s i o n

Extraction

isotherm

The e x t r a c t i o n o f a q u e o u s s o l u t i o n s c o n t a i n i n g 5 g/1 o f u r a n y l s u l p h a t e i n s u l p h u r i c a c i d a t d i f f e r e n t c o n c e n t r a t i o n s was c a r r i e d o u t w i t h TOPO i n k e r o s e n e o r b e n z e n e a t 20 ° C . Some r e p r e s e n t a t i v e r e s u l t s a r e g i v e n i n F i g u r e 1 . The d i s t r i b u t i o n c o e f f i c i e n t a t f i r s t r i s e s w i t h a q u e o u s a c i d i t y , p a s s e s t h r o u g h a maximum a t about 3-4 M a c i d and t h e n f a l l s a t h i g h e r a c i d i t i e s . I t i s a l s o f o u n d t h a t t h e i n i t i a l aqueous a c i d i t y c o r r e s p o n d i n g t o t h e m a x i mum d i s t r i b u t i o n c o e f f i c i e n t i s n o t much i n f l u e n c e d b y v a r y i n g t h e TOPO c o n c e n t r a t i o n . When b e n z e n e i s u s e d as a d i l u e n t i n s t e a d o f k e r o s e n e , t h e shape o f t h e d i s t r i b u t i o n c o e f f i c i e n t curve w i t h t h e s o l u t i o n i n benzene resembles t h a t i n k e r o s e n e , a l t h o u g h the ex t r a c t i o n e f f i c i e n c y i s i n k e r o s e n e > b e n z e n e , as i l l u s t r a t e d i n Figure 1. I f we assume t h a t t h e e x t r a c t i o n o f u r a n i u m ( V I ) f r o m s u l p h u r i c a c i d s o l u t i o n s w i t h TOPO i s g o v e r n e d b y s o l v a t i n g r e a c t i o n as i n t h e case o f t h e e x t r a c t i o n from n i t r i c and h y d r o c h l o r i c a c i d solutions (2,3) v i z . 9

U 0 S 0 ( a ) + nTOPO(o) *=* U 0 S 0 . n T 0 P 0 ( o ) where (a) a n d (o) r e p r e s e n t a q u e o u s a n d o r g a n i c p h a s e s , t i v e l y , t h e f o l l o w i n g r e l a t i o n s h i p would be expected 2

4

2

(1) respec

4

l o g Eg = l o g Κ + n l o g ( C - nCy), (2) i n w h i c h Eg i s t h e d i s t r i b u t i o n c o e f f i c i e n t , Κ t h e e q u i l i b r i u m constant, C T O p o t o t a l TOPO c o n c e n t r a t i o n a n d C y t h e u r a n i u m concentration o f the organic phase. T

t

n

0

P

0

e

F o r t h e e x t r a c t i o n o f u r a n y l s u l p h a t e s o l u t i o n s (5 g/1) c o n t a i n i n g s u l p h u r i c a c i d a t v a r i o u s c o n c e n t r a t i o n s o f TOPO i n k e r o s e n e a t 20 ° C , t h e l o g - l o g p l o t s o f Eg v s . ( C 0 P 0 u) con s t a n t s u l p h u r i c a c i d c o n c e n t r a t i o n s showed t h a t t h e E q n . (2) i s n

T

C

a


t


9.

SATO

Extraction

of U(VI) by

0.1 Initial

119

TOPO

1 aqueous s u l p h u r i c

10 acid concn., M

Figure 1. Extraction of U (VI) from sulfuric acid solutions by TOPO in (O) kersosene and (A) benzene; numerals on the curves are TOPO concentrations, M .


120

ACTINIDE

SEPARATIONS

s a t i s f i e d f o r η = 2: t h e s l o p e s o f 2 . 0 , 2 . 0 , 2.3 and 2.3 a t 0 . 5 , 1, 2 and 3 M a c i d s r e s p e c t i v e l y . I t i s thus thought t h a t t h e v a l u e o f t h e d i s t r i b u t i o n c o e f f i c i e n t f o r u r a n i u m shows a s e c o n d - p o w e r dependence, i n d i c a t i n g the f o r m a t i o n o f the d i s o l v a t e U 0 S 0 2T0P0. Hence i t i s i n f e r r e d t h a t η = 2 i n t h e E q n . ( 1 ) , i . e . 2

U 0 S 0 ( a ) + 2T0P0(o) U0 S0 ·2T0P0(o) (3) In t h e e x t r a c t i o n o f u r a n y l s u l p h a t e s o l u t i o n s o f v a r i o u s concen trations c o n t a i n i n g 3 M s u l p h u r i c a c i d w i t h 0 . 0 3 M TOPO i n k e r o s e n e a t 20 ° C , t h e c o n c e n t r a t i o n o f u r a n i u m i n t h e o r g a n i c p h a s e as a f u n c t i o n o f i n i t i a l a q u e o u s u r a n i u m c o n c e n t r a t i o n a p p r o a c h e s a l i m i t i n g v a l u e ( 0 . 0 1 5 M) a s shown i n T a b l e 1 , s u p p o r t i n g t h e s o l v a t i o n number o f TOPO f o r u r a n i u m o b t a i n e d f r o m t h e s o l v e n t dependency, although the o r g a n i c phase i s n o t y e t s a t u r a t e d under the present experimental c o n d i t i o n s . F o r those o r g a n i c phases, the m o l a r r a t i o s o f t h e s u l p h a t e c o n c e n t r a t i o n and t h e water c o n t e n t t o t h e c o n c e n t r a t i o n o f u r a n i u m were a l s o d e t e r m i n e d : t h e f o r m e r i s n e a r l y u n i t y a t t h e d i f f e r e n t i n i t i a l aqueous u r a n i u m c o n c e n t r a t i o n , b a s e d o n t h e f a c t t h a t t h e s p e c i e s H S 0 - 2 T 0 P 0 (7) f o r m e d a t low a c i d i t y i s e x c h a n g e d b y t h e s p e c i e s U 0 S 0 . 2 T O P O a r i s i n g f r o m t h e e x t r a c t i o n o f u r a n y l s u l p h a t e a s w e l l as t h e e x t r a c t i o n o f u r a n y l n i t r a t e b y TBP ( 8 ) ; t h e l a t t e r d e c r e a s e s t o u n i t y a s i l l u s t r a t e d i n T a b l e 1 , i m p l y i n g t h a t t h e u r a n y l complex formed i n the o r g a n i c phase c o n t a i n s uranium/sulphate/water/TOPO i n t h e molar r a t i o 1 : 1 : 1 : 2 , i n d i c a t i n g the stoichiometry to the U0 S0 -H 0.2TOPO. Absorption spectra 2


4

2

4

4

2

4

2

4

2

4

2

Some r e p r e s e n t a t i v e r e s u l t s f o r t h e a b s o r p t i o n s p e c t r a o f b o t h t h e aqueous a n d o r g a n i c p h a s e s f r o m t h e e x t r a c t i o n o f a q u e ous s o l u t i o n s c o n t a i n i n g 5 g/1 u r a n y l s u l p h a t e i n s u l p h u r i c a c i d a t d i f f e r e n t c o n c e n t r a t i o n s w i t h 0 . 2 M TOPO i n k e r o s e n e a t 20 ° C a r e i l l u s t r a t e d i n F i g u r e s 2 a n d 3 . F o r t h e s p e c t r a o f aqueous uranyl sulphate containing sulphuric a c i d only (Figure 2), the f o l l o w i n g r e s u l t s were o b s e r v e d : w i t h i n c r e a s i n g u p t o 5 M H S 0 , t h e a b s o r p t i o n due t o u r a n y l i o n U 0 ( 9 , 10) , w h i c h e x h i b i t s a b a n d c e n t e r a t 420 n m , i s a c c o m p a n i e d b y a p r o g r e s s i v e i n c r e a s e i n t h e i n t e n s i t y o f t h e a b s o r p t i o n a t 430 nm b y t h e f o r m a t i o n o f the species U 0 S 0 ( 1 1 - 1 3 ) , t h e a b s o r p t i o n a t a r o u n d 455 nm d i s appears i n above 7 M H S 0 , i n d i c a t i n g t h e f o r m a t i o n o f t h e s p e c i e s U 0 ( S 0 ) 2 - ( 1 4 , 1 5 ) , a l t h o u g h A r d e n e t a l (16) i n s i s t t h e p r e s e n c e o f t h e complex i o n U 0 ( S 0 ) 3 ^ " P below 2 . 5 . In c o n t r a s t , t h e s p e c t r a o f t h e o r g a n i c p h a s e s ( F i g u r e 3) show l a r g e l y t h e a b s o r p t i o n s due t o t h e s p e c i e s o f t h e U 0 ( S 0 ) " type, e v e n t h o u g h t h e s p e c t r u m o f t h e a q u e o u s s o l u t i o n a t low s u l p h u r i c a c i d c o n c e n t r a t i o n does n o t i n d i c a t e t h e p r e s e n c e o f U 0 ( S 0 ) ? ~ . I t i s t h u s presumed t h a t t h e e x t r a c t e d s p e c i e s i s an s i x - c o o r d i n a t e d u r a n i u m complex i o n , a l t h o u g h t h e s p e c t r a o f t h e o r g a n i c phases r e v e a l the f i n e s t r u c t u r e a t t r i b u t e d t o t h e l i g a n d f i e l d effect. Infrared spectra The o r g a n i c phases from t h e e x t r a c t i o n o f u r a n y l s u l p h a t e 2

2

2

4

4

+

4

2

2

2

4

2

2

4

a

t

H

v

a

l

u

2

e

s

4

2

2

2


4

2


from the e x t r a c t i o n

phase

0.0045

0.0065

0.0078

0.0092

0.0274

0.0685

0.137

0.274

0.822

10

25

50

100

300

0.0109

0.0029

0.0137

5

M

0.00075

,

0.00274

M

[U]

1

g/1

Initial

content

0.01535

0.01480

0.01476

0.01345

0.01365

0.0101

0.0102

2.75

0.93

1.89

3.85

1.41

1.61

2.13 4.62

3.26

3.03

4.62

18.3

4

[so ]/[u]

phase

with

6.67

10.2

40.0

[T0P0]/[U]

i n the organic

1.11

1.36

1.66

0.0108 0.0106

2.53

4.00

15.7

2

[H 0]/[U]

Molar r a t i o

0.0114

0.0116

J

0.01358

o

0.0118

L

[H 0] 2 org' M

0.01370

>

acid

i n the organic

sulphate solutions containing 3 M sulphuric

4 org M J

of uranyl

o f uranium and s u l p h a t e and t h e w a t e r

0 . 0 3 M TOPO on k e r o s e n e a t 20 ° C .

1.

Table

The c o n c e n t r a t i o n s



122

ACTINIDE

350

370

390

410

430

450

470

SEPARATIONS

490

W a v e l e n g t h , nm

Figure 2. Absorption spectra of aqueous uranyl sulphate solutions containing sulfuric acid at different concentrations; numerals on curves are sulfuric acid concentrations, M .

W a v e l e n g t h , nm

Figure 3. Absorption spectra of the organic solutions from the extraction of aqueous uranyl sulphate solutions containing sulfuric acid at different concentrations with 0.2M TOPO in kerosene; numerals on curves are initial aqueous sulfuric acid concentrations, M .


9.

Extraction

SATO

of U(VI) by

TOPO

123

s o l u t i o n s ( 0 , 1 , 5 , 25 a n d 100 g/1) c o n t a i n i n g 3 M s u l p h u r i c a c i d w i t h 0 . 1 M TOPO i n k e r o s e n e were e x a m i n e d i n c o m p a r i s o n w i t h t h e aqueous s o l u t i o n o f u r a n y l s u l p h a t e a t 250 g/1 b y i n f r a r e d s p e c t r o s c o p y . The r e p r e s e n t a t i v e s p e c t r a o f t h e o r g a n i c phases are i l l u s t r a t e d i n Figure 4. T h e s p e c t r u m o f t h e aqueous u r a n y l s u l p h a t e s o l u t i o n r e v e a l s t h e a b s o r p t i o n b a n d s a t 1 1 4 0 , 1030 a n d 970 c m " , a s s i g n e d t o t h e v i b r a t i o n o f t h e b i s u l p h a t e group ( p o i n t group C symmetry) (17, 1 8 ) , and t h e asymmetric s t r e t c h i n g f r e q u e n c y o f t h e u r a n y l group (19) a t 950 c m ' i n a d d i t i o n t o t h e s t r o n g a b s o r p t i o n s o f t h e OH g r o u p d u e t o t h e OH s t r e t c h i n g a n d b e n d i n g v i b r a t i o n s a t 3320 a n d 1625 c m " , r e s p e c t i v e l y , a s c r i b e d t o t h e p r e s e n c e o f w a t e r . T h i s implies that the equilibrium U 0 + H S O 4 - 5F=* U 0 S 0 + H e x i s t s i n t h e aqueous s o l u t i o n a t low a c i d i t y , c o r r e s p o n d i n g t o t h e e l e c tronic spectral result. 1

3

v

1

1


2

2 +

2

+

4

T h e s p e c t r u m o f t h e w a t e r - s a t u r a t e d TOPO e x h i b i t s t h e OH v i b r a t i o n s ( s t r e t c h i n g a n d b e n d i n g b a n d s a t 3380 a n d 1620 c m " , r e s p e c t i v e l y ) a n d t h e Ρ •> 0 s t r e t c h i n g b a n d a t 1185 c m " (actually a d o u b l e t a t 1185 a n d 1170 c m " ) , i n d i c a t i n g t h e p r e s e n c e o f a weak h y d r o g e n b o n d i n t h e compound Τ 0 Ρ 0 · Η 0 . I n t h e o r g a n i c s o l u t i o n from the e x t r a c t i o n o f 3 M s u l p h u r i c a c i d s o l u t i o n , the absorption assigned to the Ρ 0 s t r e t c h i n g b a n d o f TOPO s h i f t s t o the lower f r e q u e n c y , r e s u l t i n g from t h e f o r m a t i o n o f the s p e c i e s H S0 -2TOPO ( 7 ) . F o r the s p e c t r a o f the o r g a n i c s o l u t i o n s from the e x t r a c t i o n o f t h e aqueous s o l u t i o n s c o n t a i n i n g u r a n y l s u l p h a t e , the f o l l o w i n g p a t t e r n i s observed w i t h i n c r e a s i n g the concentra t i o n o f u r a n i u m : t h e i n t e n s i t y o f t h e OH v i b r a t i o n s c a u s e d b y t h e p r e s e n c e o f t h e compound Τ 0 Ρ 0 · Η 0 (7) d e c r e a s e s , a n d s i m u l t a n e o u s l y t h e OH s t r e t c h i n g a n d b e n d i n g b a n d s a p p e a r a t 2800 a n d 1700 c m , r e s p e c t i v e l y , d e m o n s t r a t i n g t h a t t h e complex has a c o o r d i n a t e d water m o l e c u l e i n agreement w i t h t h e r e s u l t o f t h e K a r l F i s c h e r t i t r a t i o n ( T a b l e 1) ; t h e a b s o r p t i o n due t o t h e Ρ 0 s t r e t c h i n g b a n d o f TOPO b o n d e d w i t h u r a n i u m i o n , a p p e a r s a t 1090 c m " ; t h e a b s o r p t i o n s o f t h e s u l p h a t e g r o u p ( p o i n t g r o u p C$ symmetry) (20) a t 1 2 5 0 , 1150 a n d 1020 cm"" a r e a c c o m p a n i e d b y t h e a s y m m e t r i c s t r e t c h i n g b a n d (19) o f t h e u r a n y l g r o u p a t 925 c m " " . Hence t h e i n f r a r e d r e s u l t s c o n f i r m t h a t u r a n i u m e x t r a c t e d i n t o TOPO s o l u t i o n i s b o n d e d t o t h e p h o s p h o r y l o x y g e n a t o m , s u g g e s t i n g t h a t t h e e x t r a c t e d s p e c i e s e x i s t s as a c o m p l e x [ U 0 S 0 4 ( H 0 ) ( T O P O ) ] i n an o c t a h e d r a l arrangement. NMR s p e c t r a 1

1

1

2

2

4

2

- 1

1

v

1

1

2

2

2

The o r g a n i c phases from t h e e x t r a c t i o n o f u r a n y l s u l p h a t e s o l u t i o n s ( 0 , 5 a n d 100 g/1) c o n t a i n i n g s u l p h u r i c a c i d w i t h 0 . 1 M TOPO i n c a r b o n t e t r a c h l o r i d e a t 20 °C were e x a m i n e d b y NMR s p e c t r o s c o p y . T h e NMR s p e c t r u m o f w a t e r - s a t u r a t e d TOPO s o l u t i o n shows a p e a k a t 9 . 1 1 ( τ v a l u e ) i n a t r i p l e t due t o t h e m e t h y l p r o t o n s , a s h a r p peak a t 8.68 a r i s i n g from methylene p r o t o n s , and a peak a t 5.53 from m e t h y l e n i c p r o t o n s a t t a c h e d t o a phosphorous atom, and the water p r o t o n s i g n a l at 7.58, i n d i c a t i n g the f o r m a t i o n o f the compound Τ 0 Ρ 0 · Η 0 . I n t h e o r g a n i c s o l u t i o n s f r o m t h e e x t r a c t i o n o f 2



124

ACTINIDE

_ι 1200

ι

ι 1000

ι

SEPARATIONS

I 800

F r e q u e n c y , cm ^

Figure 4. IR spectra of the organic solutions from the extraction of aqueous uranyl sulphate solutions containing 3M sulfuric acid with 0.1 M TOPO in kero sene; A, B, C, and D represent uranyl sulphate solutions of J , 5, 25, and 100 g/L, respectively.


9.

Extraction

SATO

of Ό (VI) by

TOPO

125

aqueous s o l u t i o n s c o n t a i n i n g u r a n y l s u l p h a t e a t 5 a n d 100 g/1 i n 3 M s u l p h u r i c a c i d the methylenic protons attached to the carbon atoms i m m e d i a t e l y a d j a c e n t t o a p h o s p h o r o u s atom a p p e a r a t 8 . 4 5 , 8.42 and 8 . 2 0 , r e s p e c t i v e l y , and t h e water p r o t o n r e s o n a n c e s a t 4.00, 3 . 8 5 and 3 . 7 0 , r e s p e c t i v e l y . T h e f a c t t h a t t h e s i g n a l s o f the m e t h y l e n i c p r o t o n and water p r o t o n s h i f t t o a lower f i e l d w i t h i n c r e a s i n g i n i t i a l aqueous c o n c e n t r a t i o n o f u r a n y l s u l p h a t e i s c o n s i s t e n t w i t h t h e i n f r a r e d d a t a , i n d i c a t i n g t h a t t h e compound H S 0 4 « 2 T 0 P 0 i s d i s p l a c e d b y t h e s p e c i e s UO2SO4·2T0P0. A l s o t h i s corresponds to the r e s u l t s f o r the a c i d i t y o f the organic phase. Temperature e f f e c t T h e e x t r a c t i o n o f aqueous s o l u t i o n s c o n t a i n i n g 5 g/1 o f u r a n y l s u l p h a t e i n 3 M s u l p h u r i c a c i d w i t h 0 . 1 M TOPO i n k e r o s e n e a t t h e t e m p e r a t u r e s b e t w e e n 20 a n d 50 ° C g a v e t h e d a t a shown i n T a b l e 2, i n d i c a t i n g t h a t t h e d i s t r i b u t i o n c o e f f i c i e n t d e c r e a s e s w i t h r i s i n g temperature. T h i s i s analogous to the r e s u l t s f o r the ex t r a c t i o n from n i t r i c and h y d r o c h l o r i c a c i d s (2,3) . The heat o f r e a c t i o n (change i n e n t h a l p y ) f o r E q u a t i o n (3) was e s t i m a t e d t o b e 2 4 . 5 6 and 2 3 . 9 3 k J / m o l i n 0 . 0 5 a n d 0 . 1 M TOPO, r e s p e c t i v e l y ( 2 4 . 2 5 k J / m o l as a v a r a g e v a l u e ) . S i m i l a r r e s u l t s were o b t a i n e d b y v a r y i n g t h e TOPO c o n c e n t r a t i o n . From t h i s i t i s f o u n d t h a t t h e h e a t o f r e a c t i o n i s i n t h e o r d e r 38.91 > 25.31 > 24.25 (kJ/mol) f o r t h e e x t r a c t i o n systems from n i t r i c , h y d r o c h l o r i c and s u l p h u r i c a c i d s , respectively, corresponding to t h e i r extraction e f f i c i e n c i e s f o r uranium(VI). Comparison o f t h e e x t r a c t i o n systems from n i t r i c , h y d r o c h l o r i c and s u l p h u r i c a c i d s o l u t i o n s Some r e p r e s e n t a t i v e r e s u l t s f o r t h e e x t r a c t i o n o f a q u e o u s s o l u t i o n s c o n t a i n i n g 5 g/1 o f u r a n y l s a l t s i n n i t r i c , h y d r o c h l o r i c and s u l p h u r i c a c i d s , r e s p e c t i v e l y , a t d i f f e r e n t c o n c e n t r a t i o n s w i t h 0 . 0 3 M TOPO i n k e r o s e n e a t 20 ° C a r e shown i n F i g u r e 5 , s u g g e s t i n g t h e i r e x t r a c t i o n e f f i c i e n c i e s o f TOPO f o r u r a n y l s a l t s are i n the order n i t r a t e > c h l o r i d e > s u l p h a t e . The d i s t r i b u t i o n c o e f f i c i e n t p a s s e s t h r o u g h a maximum a l t h o u g h t h e r e s p e c t i v e maxima a p p e a r a t a b o u t 0 . 3 M HNO3, 5 M HC1 a n d 4 M H2SO4. A c c o r d i n g l y , as t h e shape o f t h e i r e x t r a c t i o n c u r v e s c l o s e l y r e s e m b l e t o each o t h e r , i t i s e v i d e n t t h a t t h e i r e x t r a c t i o n e q u i l i b r i a a r e expressed by the s o l v a t i n g reactions (2,3): U 0 2 ( N 0 ) ( a ) + 2T0P0(o) 3=* U 0 ( N O 3 ) · 2 T 0 P 0 ( o ) (4) U 0 C l ( a ) + 2T0P0(o) U0 Cl2 ·2Τ0Ρ0(ο) (5) and E q u a t i o n ( 3 ) . H o w e v e r , s i n c e t h e c o m p l e x e s f o r m e d i n t h e o r g a n i c p h a s e s h a v e no c o o r d i n a t e d w a t e r m o l e c u l e s e x c e p t t h e u r a n y l s u l p h a t e complex c o n t a i n i n g a water m o l e c u l e , i t i s t h o u g h t t h a t e x t r a c t e d s p e c i e s e x i s t as t h e c o m p l e x e s [U02(02N0)2(TOPO)2], [ U 0 C l ( T O P O ) ] and [ U 0 ( 0 S 0 ) ( 0 H ) ( T O P O ) ] i n the coordination numbers o f e i g h t , s i x and s i x , r e s p e c t i v e l y , o n t h e b a s i s o f t h e r e s u l t s f o r t h e a b s o r p t i o n and i n f r a r e d s p e c t r a . A d d i t i o n a l l y , when t h e r e s p e c t i v e d a t a ( 1 1 6 3 , 1110 a n d 938) f o r t h e a p p a r e n t m o l e c u l a r w e i g h t s o f t h e u r a n y l n i t r a t o , c h l o r o a n d s u l p h a t o com p l e x e s w i t h TOPO a r e compared w i t h t h e t h e o r e t i c a l v a l u e s ( 1 1 6 8 ,


2

3

2

2

2

2

2

2

2

2

2

2

3

2

2


126

ACTINIDE

Table the

2.

Temperature

extraction

phuric

dependence

solutions

containing

Distribution

°C

0.05

3 M sul

coefficient 0.1

M TOPO

M TOPO

20

0.977

3.34

30

0.760

2.29

40

0.487

1.78

50

0.388

1.42

0.01

on

kerosene.

Temperature


of d i s t r i b u t i o n coefficient

of uranyl sulphate

a c i d w i t h TOPO i n

SEPARATIONS

0.01 Initial

0.1

1

10

aqueous a c i d c o n c n . , M

Figure 5. Extraction of U (VI) from aqueous solutions containing nitric, hydro chloric, and sulfuric acids with 0.03M TOPO in kerosene at 20°C; (Ο), (V), and (O) represent the extractions of uranyl nitrate, chloride, and sulphate, respec tively.



3.

o f aqueous

0. 006 0 . 036

o f 0.03

and 0.05 M .

and s u l p h a t e

are the respective

0 065 0 . 195

6.27

5 .30

of uranyl nitrate

0. 042 0 . 153

12.4

30 . 1

f o r the extractions

concentrations

a The v a l u e s

o-Dichlorobenzene

Chlorobenzene

Chloroform

0.236

0. 034 0 . 072

10.3

12 . 7

Toluene 1 .44

0 . 025 0 . 325

tetrachloride 21.8

Carbon 20 . 8

0 . 016

0 . 250

n-Hexane

0 . 022

0 . 068

2

TOPO

0.1 M H S04 + 0 . 9 M Na2S04 0 . 051

4

0 . 270

2

1M H S0

0 . 031

16.7

3

i n n i t r i c and

0 . 042

15 .9

Cyclohexane

8.62

12.6

3

0.01 M HN0 +0.99 M N a N 0

coefficient

of uranyl salts

4.37

15 . 7

Benzene

3

Distribution

solvents.

c o n t a i n i n g 5 g/1

9 .57

10 . 4

Kerosene

1 M HN0

organic

solutions

b y TOPO i n v a r i o u s

Extraction

acids

Diluent

sulphuric

Table



128

ACTINIDE

SEPARATIONS

1114 a n d 1158) o f t h e m o l e c u l a r w e i g h t s f o r t h e i r m o n o m e r i c s p e c i e s , i t i s c o n s i d e r e d t h a t t h e c o m p l e x e s e x i s t as monomer. I n t h i s c a s e , t h e complexes a r e p r e p a r e d from t h e o r g a n i c s o l u t i o n s i n t h e e x t r a c t i o n u n d e r t h e f o l l o w i n g c o n d i t i o n s , b u t i t seems that the organic s o l u t i o n from the e x t r a c t i o n o f u r a n y l sulphate i s n o t y e t s a t u r a t e d w i t h u r a n i u m : t h e e x t r a c t i o n w i t h 0 . 1 M TOPO i n b e n z e n e a t 20 ° C o f u r a n y l n i t r a t e s o l u t i o n (50 g/1) containi n g 0.01 M n i t r i c a c i d and 0.29 M sodium n i t r a t e , o f u r a n y l c h l o r i d e s o l u t i o n (250 g/1) c o n t a i n i n g 0 . 1 M h y d r o c h l o r i c a c i d a n d 4 . 9 M l i t h i u m c h l o r i d e a n d o f u r a n y l s u l p h a t e s o l u t i o n (300 g/1) c o n taining 3 M sulphuric acid. F u r t h e r m o r e when t h e e f f e c t o f d i l u e n t o n t h e e x t r a c t i o n e f f i c i e n c y o f TOPO f o r u r a n i u m ( V I ) i s e x a m i n e d i n t h e e x t r a c t i o n o f a q u e o u s s o l u t i o n s c o n t a i n i n g 5 g/1 o f u r a n y l s a l t s i n n i t r i c and s u l p h u r i c a c i d s , i t i s f o u n d f r o m some r e p r e s e n t a t i v e data ( T a b l e 3) t h a t h y d r o c a r b o n s s u c h as a l k a n e o r c y c l o a l k a n e e n h a n c e the e x t r a c t i o n e f f i c i e n c i e s i n a l l systems, while h a l o g e n - s u b s t i t u t e d h y d r o c a r b o n such as c h l o r o f o r m r e d u c e s them. Conclusions The d i s t r i b u t i o n o f u r a n i u m ( V I ) between s u l p h u r i c a c i d s o l u t i o n s a n d s o l u t i o n s o f t r i - n - o c t y l p h o s p h i n e o x i d e (TOPO) i n o r g a n i c s o l v e n t has been i n v e s t i g a t e d under d i f f e r e n t c o n d i t i o n s . The aqueous and o r g a n i c p h a s e s a r e examined s p e c t r o p h o t o m e t r i c a l l y , and t h e o r g a n i c p h a s e s b y i n f r a r e d a n d n u c l e a r m a g n e t i c r e s o n a n c e s p e c t r o s c o p i e s . As a r e s u l t , i t i s found t h a t t h e e x t r a c t i o n i s expressed b y t h e e q u i l i b r i u m e q u a t i o n I K ^ S O ^ a q ) + 2T0P0(org) U 0 S 0 4 - 2 T O P O ( o r g ) , i n which t h e e x t r a c t e d s p e c i e s e x i s t s as a complex [ U 0 S 0 4 ( H 0 ) ( T O P O ) ] i n an o c t a h e d r a l a r r a n g e m e n t . A d d i t i o n a l l y t h e o b t a i n e d r e s u l t s a r e compared w i t h t h o s e f o r t h e e x t r a c t i o n from n i t r i c and h y d r o c h l o r i c a c i d s o l u t i o n s . 2

2

2

2

Acknowledgements The a u t h e r w i s h e s t o t h a n k M e s s r s . T . N i s h i d a a n d F . O z a w a f o r a s s i s t a n c e w i t h e x p e r i m e n t a l w o r k , a n d t h e Hokko C h e m i c a l I n d u s t r y C o . L t d . f o r t h e s a m p l e o f TOPO.

Literature Cited 1. Sato,T., and Yamatake,M., J.Inorg.Nucl.Chem. 1969 31,3633. 2. Sato,T., Nishida,T., and Yamatake,M., J.Appl.Chem.Biotechnol. 1973 23,909. 3. Sato,T., and Nishida,T., J.Inorg.Nucl.Chem. 1974 36,2087. 4. Sato,T., J.Appl.Chem. 1965 15,489. 5. Sato,T., J.Appl.Chem. 1966 16,53. 6. Kinnunen,J., and Wennerstrand, B., Chemist-Analyst 1957 46,92. 7. Sato,T., Watanabe,H., and Yamatake,M., J.Appl.Chem.Biotechnol. 1976 26,697. 8. Sato,T., J.Inorg.Nucl.Chem. 1959 9,188.



9. SATO

Extraction of U(VI) by TOPO

129

9. Sutton,J., J.Chem.Soc. 1949 s275. 10. Rabinowitch,E., and Belford,R.L., "Spectroscopy and Photo chemistry of Uranyl Compounds", Pergamon Press, Oxford, 1964 p.97. 11. Betts,R.H., and Michels,R.Κ., J.Chem.Soc. 1949 s286. 12. Ahrland,S., Acta Chem.Scand. 1951 5,1151. 13. As reference 10, p.116. 14. Day,Jr.,R.Α., and Powers,R.M., J.Am.Chem.Soc. 1954 76,3895. 15. Katz,J.J., and Seaborg,G.T., "The Chemistry of the Actinide Elements", Methuen, London, 1957 p.186. 16. Arden,T.V., and Wilkins,C.H., Anal.Chem. 1952 24,1253. 18. Walrafen,G.E., and Dodd,D.Μ., Trans.Faraday Soc. 1961 57,1286. 19. Gatehouse,B.M., and Comyns,A,E., J.Chem.Soc. 1958 3965. 20. Nakamoto,K., "Infrared Spectra of Inorganic and Coordination Compounds", 2nd ed., John Wiley, New York 1970, p.173. RECEIVED May 17, 1979.


The Extraction of Uranium (VI) from Sulphuric Acid Solutions by Tri-n

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