Actinide Separations - American Chemical Society

10 Properties and Uses of Nitrogen and Sulfur Donors Ligands in Actinide Separations

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C. MUSIKAS, G. Le MAROIS, R. FITOUSSI, and C. CUILLERDIER Division de Chimie, Département de Génie Radioactif, Centre d'Etudes Nucléaires de Fontenay aux Roses, BP N° 6, Fontenay aux Roses, 92260 France

Most of the complexing agents used in actinide separations are oxygen donor ligands (1, 2), because of the hard acceptor character of the f series ions. The aqueous complexes of ligands of which the donor atoms are less electronegative than oxygen (Pauling's electronegativity 3.5) are weak because of the competition with water for the coordination sites of the metal. However, unusual actinide separations involving these weak complexes have been performed. For instance, the group of trivalent lanthanide ions has been separated from trivalent actinides by using concentrated aqueous chloride media (electronegativity 3.0) from which trivalent actinide ions are selectively absorbed in anion exchange resins (3) or extracted by organic solutions of t r i or tetraalkylamonnium chloride salts (4). 4f - 5 f group separation is also possible by using aqueous thiocyanate solutions, where the trivalent actinide ion can be selectively extracted in an organic solution of tetraalkylammonium thiocyanate (5) or fixed on an anion exchange resin (6). For the thiocyanate complexes of lanthanides or actinides, the coordination occurs via the nitrogen atom (electronegativity 3.0). F o r t h e s e two c a s e s , t h e r e i s no o b v i o u s e x p l a n a t i o n o f t h e o r i g i n o f g r o u p s e p a r a t i o n . F o r m a t i o n c o n s t a n t s o f weak c o m p l e x e s are d i f f i c u l t t o measure and t h e expected g r e a t e r c o v a l e n t effect f o r a c t i n i d e has n o t been c l e a r l y e s t a b l i s h e d . This paper reports the r e s u l t s of i n v e s t i g a t i o n s of the complex f o r m a t i o n between a c t i n i d e o r l a n t h a n i d e i o n s and a z i d e o r o r t h o p h e n a n t h r o l i n e . The a i m o f t h i s work was f i r s t t o c o n f i r m whether these r e l a t i v e l y s o f t l i g a n d s give complexes of d i f f e r e n t s t a b i l i t i e s w i t h t h e t r i v a l e n t l a n t h a n i d e and a c t i n i d e i o n s , as a consequence o f t h e b r o a d e r e x t e n s i o n o f 5f o r b i t a l s as compared w i t h 4 f . S e c o n d l y , we a t t e m p t e d t o u s e t h e r e s u l t s i n a c t i n i d e chemical separation processes. Dialkyldithiophosphates are also soft ligands (electronegat i v i t y o f s u l f u r 2.5) and as p a r t o f a s y s t e m a t i c study f o r t h e i r b i n d i n g p r o p e r t i e s t o t h e a c t i n i d e s i o n s we r e p o r t t h e r e s u l t s o f

0-8412-0527-2/80/47-117-131$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.

132

ACTINIDE

solvent

extraction

o f U ( V I ) a n d Np

SEPARATIONS

(IV).

Experimental Chemicals. A l l r e a g e n t s used i n t h i s s t u d y were a n a l y t i c a l g r a d e a n d were s u p p l i e d by P r o l a b o o r M e r c k . T h e n o y l t r i f l u o r o a c e t o n e (TTA) s u p p l i e d by Koch L i g h t was p u r i f i e d by s u b l i m a t i o n . The a c t i n i d e elements were p r o v i d e d by CEA-SPT (Fontenay aux Roses) a s o x i d e o r n i t r a t e s o l u t i o n s . We u s e d t h e i s o t o p e s 23cy » ?Np, 239 , 241 244 . 152 , 147 169 t r a c e r s were 2 3


P u

A n u

C m

E u

N d j

Y b

u

s

e

d

a

s

s u p p l i e d b y I s o t e c ( V e r s a i l l e s ) . B i s - (2 e t h y l h e x y l ) d i t h i o p h o s p h o r i c a c i d ( H D E H D T P ) , t r i o c t y l p h o s p h i n e o x i d e (TOPO) a n d d i h e x y l m e t h o x i o c t y l p h o s p h i n e o x i d e ( P O X 11) w e r e s u p p l i e d b y I r c h a (Vert l e P e t i t ) . Apparatus. U l t r a v i o l e t , v i s i b l e and near i n f r a r e d spectra w e r e r e c o r d e d w i t h a C a r y 17 s p e c t r o p h o t o m e t e r , γ spectroscopy was c a r r i e d o u t w i t h a G e - L i d e t e c t o r a n d a Zoomax ( S e i n ) m u l t i c h a n n e l a n a l y z e r . p H m e a s u r e m e n t s w e r e t a k e n w i t h a n A r i e s 10000 ( T a c u s s e l ) p o t e n t i o m e t e r , α s p e c t r o s c o p y was c a r r i e d w i t h a s o l i d state α detector and a (Intertechnique) m u l t i c h a n n e l a n a l y z e r . Results

nide -

and D i s c u s s i o n

Azide complexes. a z i d e s complexes

The aqueous t r i v a l e n t a c t i n i d e were examined by two t e c h n i q u e s

and l a n t h a :

U . V . , v i s i b l e , near I . R . spectroscopy ( N d , E u , E r , P u , Am, Cm), S o l v e n t e x t r a c t i o n : ( N d , E u , Y b , Am) u s i n g r a d i o a c t i v e tracer techniques.

The s p e c t r a l c h a n g e s o b s e r v e d on a d d i t i o n o f a z i d e i o n s t o t r i v a l e n t a c t i n i d e o r l a n t h a n i d e p e r c h l o r a t e s o l u t i o n s a r e shown i n f i g u r e 1. T o c a l c u l a t e t h e f o r m a t i o n c o n s t a n t s o f t h e c o m p l e x e s we used e q u a t i o n (1),which c o r r e l a t e s t h e m o l e c u l a r e x t i n c t i o n c o e f f i c i e n t o f t h e v a r i o u s m e t a l l i c s p e c i e s ( ε · ) and t h e measured apparent molecular e x t i n c t i o n c o e f f i c i e n t ( ε ^ ) ,with the s t a b i l i ty constants o f the complexes ( 3 J i=i

S

= ε

ο

+ Σ

3

max

i"

i=1

[ N

3

_ ) I L

. 7

i = i max 1

+ Σ

β'-^ν

1

i=1

1

_ . m

1

3 . and ε . were c a l c u l a t e d by l e a s t s q u a r e a d j u s t m e n t . Good a d j u s t m e n t s a r e o b t a i n e d when i i s l i m i t e d t o 2 i n t h e range 0 t o 2Π i n a z i d e . G e n e r a l l y , t o m i n i m i z e t h e n u m b e r o f c o e f f i c i e n t s t o be f o u n d i n o n e a d j u s t m e n t , we u s e d a m a t h e m a t i c a l p r o g r a m (_7) m a k i n g i t p o s s i b l e t o f i x o n e o r m o r e c o e f f i c i e n t s f o u n d i n s e p a r a t e p r e v i o u s e x p e r i m e n t s o r c a l c u l a t i o n s . F o r t h e Nd c o m p l e x e s we u s e d a l s o a d e c o n v o l u t i o n m e t h o d t o o b t a i n t h e f o r m a tion constants. The r e s u l t s o f t h e c a l c u l a t i o n o f f o r m a t i o n m

a

x


Nitrogen

and Sulfur Donor

Ligands

133


10. MusiKAs E T AL.

Figure 1. Absorption spectra of trivalent actinide and lanthanide ions in the absence or presence of azide: ( ) perchloric media, μ = 5, θ = 25°C, pH = 5.4; ( ; 4M azide, = 5,θ = 25°C, pH = 5.4. μ


134

ACTINIDE SEPARATIONS

constants

are

stability the f i r s t

i s o b s e r v e d between a c t i n i d e and l a n t h a n i d e f o r m e r b e i n g more s t a b l e . F o r Eu ( I I I ) , t h e

given

i n Table

constants

were

calculated

I.

Note

from the

that

a

clear

occurence

of

difference

an

in

complexes, formation

a b s o r p t i o n band

i n the exists

U . V . p o r t i o n of the only i n the spectra

rather charge

s t a b l e d i v a l e n t i o n s , we a t t r i b u t e d i t t o a z i d e t o m e t a l t r a n s f e r s . F i g u r e 2 s h o w s how t h i s b a n d v a r i e s i n t h e

série

Eu,

Yb,

s p e c t r u m . As t h i s a b s o r p t i o n band of l a n t h a n i d e e l e m e n t s , w h i c h have

Sm.


The e n e r g y o f a b s o r p t i o n peak t e n d s t o w a r d s h i g h e r v a l u e s as the s t a b i l i t y o f the d i v a l e n t i o n s d e c r e a s e s , i n agreement w i t h t h e s e m i - e m p i r i c a l t h e o r y p o s t u l a t e d by N u g e n t e t a l ( 8 ^ . In order to v e r i f y the d i f f e r e n c e s observed i n 4 f - 5 f complex s t a b i l i t y , we u s e d a n a d d i t i o n a l s o l v e n t e x t r a c t i o n m e t h o d b a s e d on t h e c o m p e t i t i o n b e t w e e n a soluble organic chelatant (TTA) and t h e aqueous s o l u b l e a z i d e i o n s f o r b i n d i n g t h e m e t a l i o n s . The e x t r a c t i o n e q u i l i b r i u m i s shown by e q u a t i o n (2) a n d t h e distribution coefficients (D) o f t h e m e t a l a t c o n s t a n t p H a r e c o r r e l a ted

with

the

formation

(N3 ) +

a q

+ 3

•

constants (ΗΤΤΑ) g o r

= D 0

where D i s i s present i

max

c

by e q u a t i o n *

(n(TTA) ) 3

i=imax / Σ β. i= 0

.

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 i n the aqueous phase. a

n

D

e

determined

by

the

N

(3).

o

r

g

+ 3

(H ) +

a

q

(2)

(3)

Q

3

when no

maximum s l o p e

complexing of

the

agent

curve

D = f azide

(log N3-). Its value i s closed to three i n concentrated solutions. T y p i c a l e x t r a c t i o n s c u r v e s a r e shown i n f i g u r e 3 . By t h e least square adjustment of experimental D to equation (3), we c a l c u l a t e d t h e c o e f f i c i e n t s β/| a n d β 2 °^ w h i c h v a l u e a r e 2 a n d

8.

I t c a n be s e e n t h a t t h e r e s u l t s f o u n d by s p e c t r o p h o t o m e t r y are c o n f i r m e d . F i g u r e 4 shows t h e r a t i o o f Eu ( I I I ) t o Am ( I I I ) dis t r i b u t i o n c o e f f i c i e n t s as a f u n c t i o n of f r e e a z i d e c o n c e n t r a t i o n . T h i s c u r v e shows c l e a r l y t h e h i g h e r s t a b i l i t y o f t h e aqueous, Am ( I I I ) a z i d e c o m p l e x e s . D i s t r i b u t i o n c o e f f i c i e n t s o f Am (III) a n d E u ( I I I ) , p r e s e n t i n t h e same s o l u t i o n s , w e r e d e t e r m i n e d b y γ s p e c t r o s c o p y . I n c o n c l u s i o n , i t a p p e a r s t h a t the a z i d e com p l e x e s o f a c t i n i d e s a r e more stable. As shown by t h e v a l u e s o f t h e f o r m a t i o n c o n s t a n t s f o u n d by s o l v e n t e x t r a c t i o n ( o v e r a l l f o r m a t i o n c o n s t a n t s ) and by s p e c t r o photometry (inner sphere formation c o n s t a n t s ) , i t i s safe to assume t h a t a z i d e complexes a r e m o s t l y i n n e r s p h e r e . T h i s i s a l s o s u p p o r t e d by t h e v a l u e s o f t h e f o r m a t i o n c o n s t a n t o f Eu (III) c a l c u l a t e d u s i n g t h e c h a r g e t r a n s f e r band whose a p p e a r a n c e must be a t t r i b u t e d t o c l o s e c o n t a c t b e t w e e n a z i d e a n d m e t a l i o n .


10.

Nitrogen

MUSIKAS E T AL.

TABLE

I

:

Formation


actinide data.

Complex

β. 1

2 +

1,2

Eu(N )

2 +

4,0

3

3

E r ( N

3

2 r 2

+

2

+

3

3

Sulfur Donor

of

azides

Ligands

complexes

135

of

trivalent

lanthanide

derived

from

Electronic

trar

Calculation

sition

f-f

observée

(800

charge

nm)

spectrophotometry

method

deconvolution

transfer

see

ref.

(16)

+

Pu(N )

Am(Ν

constants and

Nd(N )

and

)

1,2

f-f

(525

nm)

adjustment t o equation

(4)*

f-f

(665

nm)

deconvolution

10

f-f

(503

nm)

adjustment

to

equation

(1)

23

f-f

(503

nm)

adjustment

to

equation

(1)

8

f-f

(397

nm)

adjustment

to

equation

(1)

24

f-f

(397

nm)

adjustment

to

equation

(1)

(1)

Am(N )2 3

CmCN ) 3

2 +

Cm(N )* 3

χ A t pH 5 , 4 lue

is

Pu

less

(III)

is

reliable

partially than

oxidizied and Pu(N )

Am(l\L)

+

2 +

or

Cm(l\L)

2 +

3

,

value.


β

va


136


Figure 2. UV absorption band of aqueous mixtures of selected lanthanide ions in the presence of azide (1-mm cell); C = 0.05M, 2.4M azide, pH = 5.4, μ = 5. M

Nd

Figure 3. Distribution coefficients of Nd (III) between aqueous azide solu tions and 0.0075M ΗΤΤΑ in benzene at 23°C; aqueous phases μ = 5, Nd ~ 10 M. 5

(III)

0.1


1

C j (M) N

10.

Nitrogen

MUSIKAS E T AL.

Orthophenanthroline chemical

affinity with

behavior

line

(Ci2HôN )

which

has

and g i v e

bonds

in

2

lent

lanthanide,

Many

solids

have but

been

as

prepared

complexes

We s t u d i e d potentiometry. competition of

complexes.

bidentate two the

by

This

between

donors

precipitation in

of

of

method

is

based

H

the

and

χ HL

constants and (6).

+

(L)

stability

check

A from of

each

triva-

methods

and

from aqueous the

lanthanides

(_9).

lanthanides

solutions of

the

(JUD),

aqueous

3 +

the

-

a

ions

5.2),

Χ χ H

+

the

by

due

to

. L

1

the

coordination

shown by e q u a t i o n

+ Ν Ι_

were

χ

(4).

(4)

3 +

calculated

by

V

i =4 i η = Σ 1=1

for as

complexes

(H,

a n d Am [ I I I )

o n pH v a r i a t i o n s

metal

(pk

+ Π

of

2.75 sphere

spectroscopic

to

ghenantro-

literature.

complexes +

1-10

at

coordination

several

greater

we t r i e d

We c h o s e

nitrogen

measurement

orthophenanthroline

The f o r m a t i o n equations [5)

ligand.

137

exhibit

ions,

orthophenanthroline

appears

the

Ligands

As a z i d e s

actinide

first

shown by

containing

no q u a n t i t a t i v e

soluble

site

a

Sulfur Donor

trivalent

this other


for

and

using

[5)

i=4 / Σ

(6)

i =0

where_ η i s the metal. and

average

Cpj a r e

the

number ligand

of

ligand molecules

and m e t a l

bonded

concentrations

to

the

respec

tively. a n d Hjvj a r e t h e a b s c i s s a e v a l u e s o f t h e c u r v e s i n f i g u r e 5 and r e p r e s e n t t h e amounts of a c i d i n t h e p r e s e n c e o f m e t a l . $± i s t h e f o r m a t i o n c o n s t a n t o f t h e c o m p l e x N L ? . We l i m i t e d i to 4 because of s t e r i c hindrance. T h e c a l c u l a t i o n r e s u l t s a r e s h o w n i n t a b l e I I . We a l s o report f o r m a t i o n c o n s t a n t s d e t e r m i n e d f r o m s p e c t r o p h o t o m e t r y f o r Ho a n d N d , and by s o l v e n t e x t r a c t i o n f o r E r . W i t h o u t g o i n g i n t o d e t a i l f o r t h e s e t w o m e t h o d s , i t may b e n o t e d t h a t t h e r e s u l t s s h o w f a i r agreement. That f a c t p o i n t s out the i n n e r sphere c h a r a c t e r of o r t h o p h e n a n t h r o l i n i u m l a n t h a n o u s c o m p l e x e s . The m a i n a b s o r p t i o n b a n d o f Am ( I I I ) i s m o d i f i e d by t h e p r e s e n c e o f orthophenanthro l i n e . We u s e d t h e s e s p e c t r a l v a r i a t i o n s t o c a l c u l a t e t h e f o r m a t i o n c o n s t a n t s o f Am ( I I I ) , a s d e s c r i b e d i n t h e p r e v i o u s p a r a g r a p h . A s f o r a z i d e c o m p l e x e s , we o b s e r v e d t h a t Am m o n o o r t h o p h e n a n t h r o l i n e i s more s t a b l e t h a n t h e e q u i v a l e n t l a n t h a n i d e c o m p l e x , and f o r t h e b i s o r t h o p h e n a n t h r o l i n e s p e c i e s , the difference


138

ACTINIDE

' E u (III) /

D

SEPARATIONS

Am(lll

60 J


40 J

Figure

4.

Variation in the ratio as a function of azide concentration at 25°C; organic phase ΗΤΤΑ in benzene, aqueous phase μ = 5, pH = 5.4. ^Eu(iii)/^Am(ni)

'U (VI) 100 J

10

0.1

Figure 5. Distribution coefficients of U (VI) between 5 M aqueous phosphoric acid and mixture of HDEHDTP and neutral oxygen donors in solution in dodecane as a function of the reagent con centration ratio; (1) 0.5M (HDEHDTP + POX 11), (2) 0.5M (HDEHDTP + TOPO), (3) 0.5M (HDEHDTP + TBP).

OXYGEN DONOR

0.01 . 0.25

0.50

0.75

1

REAGENTS FRACTION


10.

Nitrogen

MUSIKAS E T AL.

TABLE

II

:

Formation actinide


from

and

constants complexes

various

Log

3

1

of

Log

Nd

1.09

3.99

Sm

1.17

3.99

Eu

1.31

4.02

Gd

1.22

4.00

Dy

1.50

4.10

Ho

1.66

4.16

Er

1.78

4.16

Lu

1.88

4.3

Am

2.68

4.66

lanthanide

orthophenanthroline techniques

Spectrophotometry

B

2

Log

1.67

2.56

139

Ligands

trivalent

with

investigation

Potentiometry

Element

Sulfur Donor

β

1

Log

β

2

and derived

data.

Solvent

Log

extraction

^

Log

e>

0.79

3.53

1.99

4.03

3.95

4.03


2

140


between

t h e two s e r i e s

We a t t e m p t e d For a

this

purpose

reagent

able

phenanthroline poor

i t

to

because

Eu [ I I I ] At

neutralize

metallic i t

organic

shown

by t h e

mixture

significant.

We c h o s e

phases.

soiubilizes

phase

and i t s

higher

acid,

an

extractant.

charge

of

nonanoic

Nitrobenzene

mixture

i n the

acid

is

higher

affinity

and E u ( I I I )

ions

phase,

the

ortho

w h i c h has

suitable The

as

a

results

nitrobenzene/ortho-

are given is

i n Table present

III. mostly

f o r Am ( I I I ) i o n s

distribution coefficients.

Am ( I I I )

nonaoic

as

i n the organic

orthophenanthroline.

extraction

acid

have,

the t r i p o s i t i v e

species.

a n d Am ( I I I )

to

t h e w o r k i n g pH o r t h o p h e n a n t h r o l i n e

nanthroline


not as

was n e c e s s a r y

phenanthroline/nonaoic the

is

use o r t h o p h e n a n t h r o l i n e

s o l u b i l i t y i n aqueous

diluent of

to

Without

are not extracted

in

is

orthophe i n the

nitrobenzene.

S u l f u r donor l i g a n d s . Complexes o f a c t i n i d e s o r l a n t h a n i d e s i o n s w i t h s u l f u r donor l i g a n d s such as d i t h i o c a r b a m a t e (S2CNR2) (11) and d i a l k y l d i t h i o p h o s p h a t e s ( ( R 0 ) Ρ S ) Π 2 ) have been o b t a i n e d i n non-aqueous s o l u t i o n s . The uses o f d i a l k y l d i t h i o p h o s 2

2

p h a t e s as e x t r a c t a n t s f o r u r a n i u m (VI) have been r e p o r t e d (13) , (14). Dialkyldithiophosphates are poorer extractants than d i a l k y l phosphates because t h e s o f t s u l f u r atom has l e s s a f f i n i t y t h a n oxygen f o r the hard f c a t i o n s . However, the P $ group has a lower tendency than P^Q|_J t o d i m e r i z e v i a hydrogen bonds. F u r S

H

thermore, the d i s t r i b u t i o n c o e f f i c i e n t s of m e t a l l i c species bet ween a q u e o u s p h a s e s a n d o r g a n i c p h a s e s c o n t a i n i n g d i a l k y l d i t h i o p h o s p h a t e s c a n h a v e h i g h e r v a l u e s d e s p i t e t h i s l o w e r a f f i n i t y . We found one example o f t h i s e f f e c t i n U (VI) e x t r a c t i o n from concen t r a t e d p h o s p h o r i c a c i d s o l u t i o n s . We i n v e s t i g a t e d t h e s y n e r g i s t i c e x t r a c t i o n o f U ( V I ) by m i x t u r e s o f d i (2 e t h y l h e x y l ) d i t h i o p h o s p h o r i c a c i d (HDEHDTP) a n d n e u t r a l o x y g e n d o n o r s s u c h a s t r i b u t y l phosphate (TBP), t r i o c t y l p h o s p h i n e oxide ( Τ 0 Ρ 0 ) , and dihexylmet h o x i o c t y l p h o s p h i n e o x i d e (POX 11) i n d o d e c a n e . Distribution coefficients o f U ( V I ) a s a f u n c t i o n o f t h e com p o s i t i o n o f t h e o r g a n i c p h a s e a r e shown i n f i g u r e 5 . T h e maximum of the d i s t r i b u t i o n c o e f f i c i e n t s always occurs f o r the proportion 1 : 1 o f HDEHDTP a n d n e u t r a l o x y g e n d o n o r . T h i s s u g g e s t s t h a t t h e e x t r a c t e d s p e c i e s have t h e f o r m u l a U 0 (DEHDTP) ( R P0) ( H P 0 ) 2

3

2

4

w h e r e R3PO r e p r e s e n t s t h e n e u t r a l oxygen d o n o r . The v a r i a t i o n o f d i s t r i b u t i o n a s a f u n c t i o n o f HDEHDTP o r Τ 0 Ρ 0 o r g a n i c concentra t i o n s a r e shown i n l o g a r i t h m i c c o o r d i n a t e s i n f i g u r e 6. The s l o p e 1 f o r the s t r a i g h t l i n e observed supports the proposed formula the extracted species. The e f f e c t o f t h e aqueous c o n c e n t r a t i o n

of of

phosphoric a c i d on the d i s t r i b u t i o n c o e f f i c i e n t s of U (VI) i s shown i n f i g u r e 7. They d e c r e a s e p r o b a b l y b e c a u s e o f U ( V I ) p h o s p h a t e complex f o r m a t i o n i n aqueous s o l u t i o n s . The h i g h e r v a l u e s ο 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 s o f U ( V I ) i n m i x t u r e s o f HDEHDP a n d Τ 0 Ρ 0 as compared w i t h e q u i v a l e n t m i x t u r e s o f d i ( 2 e t h y l h e x y l ) p h o s p h o r i c a c i d and Τ 0 Ρ 0 (15) a r e p r o b a b l y due t o t h e d i f f e r e n c e i n n a t u r e o f t h e e x t r a c t e d s p e c i e s as s u g g e s t e d by t h e p o s i t i o n o f


10.

Nitrogen

MUSIKAS E T A L .

TABLE

III

:

Distribution between

HN0

3

aq

and 0.25 nitric

equi

of

of

M nonanoic

°Eu

and Eu

0.25

acid

concentration

(III)

141

Ligands

Am ( I I I )

mixtures

acid

°Am

librium

(N)


aqueous

pH a t

coefficients

nitrobenzenic

nanthroline of

and Sulfur Donor

as

a

function

(μ =

(III)

(III)

ΙΊ 1 - 1 0 p h e 0.1) °Am

(III)

Eu

(III)

D

0.004

5.08

51

2.8

18.3

0.006

4.89

22.8

1.4

16.6

0.008

4.75

10.1

0.6

17.1

0.01

4.64

7.2

0.4

18.5

0.012

4.55

4.9

0.3

16.5

U (VI) 50

J

0.05

0.1

0.2

0.5

1

Figure 6. Distribution coefficients of U (VI) between 5 M aqueous phosphoric acid and mixtures of HDEHDTP and TOPO in solution in dodecane; (1) 0.01M HDEHDTP, TOPO variable, (2) 0.01 M TOPO, HDEHDTP variable.


142

ACTINIDE


D

U

SEPARATIONS

(VI)

100 J

10 J

1

4

0.1 J

Figure 7. Distribution coefficients of U (VI) as a function of aqueous phosphoric acid concentration; organic phases 0.25M HDEHDTP + 0.25M TOPO.

0.01

' 0

I 1

1

5

10

1

15 C H PO ( ) 3


4

M

10.

M u s i K A S E T AL.

Nitrogen

and Sulfur Donor

Ligands


Np(iv)

0.01

HDEHDTP

Figure 8.

Distribution coefficients of Np (IV) as a function of HDEHDTP ganic concentrations [(1 ),(2)] or aqueous HCl (3)

or

O.D.

Np (DEHDTP) C l

3

Np (DEHDTP) CI 2

2

Figure 9. Spectra of Ν ρ (IV) extracts in do de cane-Η DEHDTP solutions; C ( EHDTP) Cl2 = 0.001M; CNP(DEHDTP)CI = 0.00033M. NP D

700

λ nm

2


S

144

ACTINIDE

SEPARATIONS

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 s maximum a s a f u n c t i o n o f o r g a n i c p h a s e s c o m p o s i t i o n . The s t r o n g h y d r o g e n bonds i n HDEHP a r e p r o b a b l y e x t r a c t i o n i n h i b i t o r s by two e f f e c t s : l o w e r a c t i v i t y o f f r e e l i g a n d , and f o r m a t i o n o f s p e c i e s w h i c h do n o t e a s i l y a l l o w o t h e r l i g a n d s present i n the system t o e n t e r the c o o r d i n a t i o n sphere o f t h e m e t a l . A n o t h e r example o f h i g h number o f s p e c i e s w h i c h can be e x t r a c t e d i n o r g a n i c phase by u s i n g HDEHDTP a s l i g a n d i s shown i n f i g u r e 8, where we c a n s e e 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 s o f Np (IV) f r o m c h l o r i d e s o l u t i o n s a s a f u n c t i o n o f pH and HDEHDTP c o n c e n t r a t i o n . These c u r v e s s u g g e s t t h a t t h e s p e c i e s e x t r a c t e d have t h e f o r m u l a s :


Np ( D E H D T P ) C 1

3

Np ( D E H D T P ) C 1 2

2

Spectrophotometry c o n f i r m s t h e s e changes i n t h e Np ( I V ) e n v i r o n ment a s shown i n f i g u r e 9. Conclusions I n v e s t i g a t i o n s o f c o m p l e x e s o f 5 f i o n s and 4£ i o n s w i t h n i t r o g e n d o n o r l i g a n d s show t h a t t r i v a l e n t a c t i n i d e i o n s a r e more s t r o n g l y c o m p l e x e d t h a n t r i v a l e n t l a n t h a n i d e i o n s , and t h e s e p r o p e r t i e s c a n be e x p l o i t e d i n a c t i n i d e - l a n t h a n i d e g r o u p s e p a r a t i o n by t h e c h o i c e o f a p p r o p r i a t e e x t r a c t i o n s y s t e m s . The h i g h e r a f f i n i t y o f n i t r o g e n l i g a n d f o r 5f t r i v a l e n t ions i s not a t t r i b u t a b l e t o t h e o c c u r e n c e o f d i f f e r e n t t y p e o f complex f o r t h e two s e r i e s ( i n n e r v s o u t e r s p h e r e ) , a s shown by t h e u s e o f s e v e r a l c o m p l e x a t i o n t e c h n i q u e s . T h i s d i f f e r e n c e m i g h t be a t t r i b u t e d t o g r e a t e r c o v a l e n t bond c o n t r i b u t i o n s i n t h e a c t i n i d e c o m p l e x e s . D i a l k y l d i t h i o p h o s p h a t e s c a n be b e t t e r e x t r a c t a n t s t h a n t h e i r d i a l k y l p h o s p h a t e e q u i v a l e n t s , a s shown by t h e s y n e r g i s t i c e x t r a c t i o n o f U (VI) f r o m c o n c e n t r a t e d p h o s p h o r i c a c i d . T h i s e f f e c t i s p r o b a b l y due t o t h e w e a k e r h y d r o g e n bonds o f t h e P^||_j g r o u p which a l l o w the formation o f a g r e a t e r v a r i e t y o f e x t r a c t e d s p e c i e s . I n t h i s p a r t i c u l a r c a s e , we showed t h a t t h e e x t r a c t e d s p e c i e s has t h e f o r m u l a : U 0 ( H P 0 ) ( R PO) (DEHDTP). 2

2

4

3

Literature cited 1. 2. 3. 4.

Gmelin Handbuch der Anorganischen Chemie Band 21 Transurane Teil 2 von Günter Koch Springer Verlag 1975 Comprehensive Inorg. Chem. Bailar J.C., Emeleus H.A., Sir R. Nyholm, Trotman Dickenson A.F. - Vol 5 Actinides Pergamon Press (1973) Hulet E.K., Gutmacher R.G., Coops M.S. J. Inorg. Nucl. Chem. 1961 17, 350 Leuze R.E., Lloyd N.H. Process Chemistry 1970 4, 597


MUSIKAS ET AL.

5.

Gerontopoulos P. Th., Rigali L., Barbano P.G., Radiochimica Acta 1965 4, 75 Coleman J.S., Asprey L.B., and Chisholm R.C. J. Inorg. Nucl. Chem. 1969 31, 1167 Ngyen-Ngoc Η., Rapport D.I. n° 465 CEN-S (Mars 1971) Nugent L.J., Baybarz R.D., Burnett J.L., Ryan J.L., J. Phys. Chem. 1973 77, 1528 Sinka S.P., Butter E. Mol. Phys. 1969 16, 285 Mac Whinnie W.R., Niller J.D., in "Advances in Inorg. Chem. and Radiochem." - Academic Press 1969 12, 135 Bagnall K.W., Brown D., Holah D.G., J. Chem. Soc. (A) 1968 1149 Pinkerton Α.Α., Inorg. Nucl. Chem. Lett. 1974 10, 495 J. Chem. Soc. Dalton 1978 267 Curtui N., Haiduc I., Marcu Gh., J. of Radioanal. Chem. 1978 44, 109 Marcu G., Curtui Ν., Haiduc I., J. Inorg. Nucl. Chem. 1977 39, 1415 Bunus F.T., Domocos V.C., Dimitrescu P., J. Inorg. Nucl. Chem. 1978 40, 117 Ahrland S., Acta Chem. Scand. 1949 3, 783

6. 7. 8. 9. 10. Downloaded by GEORGE MASON UNIV on June 15, 2016 | http://pubs.acs.org Publication Date: April 16, 1980 | doi: 10.1021/bk-1980-0117.ch010

Nitrogen and Sulfur Donor Ligands

10.

11. 12. 13. 14. 15. 16.

RECEIVED

June 18, 1979.


145

Actinide Separations - American Chemical Society

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