The Enrichment of Lithium Isotopes by Extraction Chromatography

4

The Enrichment of Lithium Isotopes by

Extraction Chromatography

D.

A . LEE

Downloaded by UNIV OF TEXAS AT DALLAS on July 22, 2016 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0089.ch004

Chemistry Division, O a k Ridge National Laboratory, O a k Ridge, T e n n .

Lithium

isotopes

tography.

were

fractionated

The chemical

ous lithium

hydroxide

exchange

equilibrated

supported

a dodecane

mobile

hydroxide.

concentrated

by

nature

magnitude

an

analysis

made

by

at

phase.

exchange

of the isotopic

species

of the separation

Granulated

solution factor

of

phase. lithium

was 1.003, as 6

"breakthrough" Separation

chromatography ion

aque-

dibenzoyl-

as the stationary

aqueous

in the aqueous

lithium

of d i b e n z o y l m e t h a n e -

stage separation

frontal

by extraction

separations The

was

The single

determined

isotopes

phase

chroma-

used was

in dodecane.

solution

-trioctylphosphine oxide in dodecane The

extraction

with

-methane-trioctylphosphine oxide Teflon

by

reaction

was

Li

lithium

compared

resin involved

of

with

chromatography. determined

the

factor.

' T ' h e r e are t w o isotopes of l i t h i u m ,

6

L i a n d L i , w h i c h occur i n nature 7

w i t h a L i / L i a b u n d a n c e r a t i o o f 0.080. S e v e r a l m e t h o d s h a v e b e e n 6

employed

7

f o r t h e f r a c t i o n a t i o n of these isotopes.

National Laboratory,

6

L i has been

A t the O a k Ridge

enriched to 99.999%

e l e c t r o m a g n e t i c separator ( C a l u t r o n )

purity i n a n

( 1 8 ) . T r a u g e r , et al. (27) h a v e

d e s c r i b e d t h e s e p a r a t i o n o f l i t h i u m isotopes

b y molecular distillation.

E l e c t r o m i g r a t i o n (8) has also b e e n u s e d to fractionate these

isotopes.

O k a m o t o a n d K a k i h a n a (20) h a v e e n r i c h e d l i t h i u m isotopes b y electrom i g r a t i o n i n a c a t i o n exchange m e m b r a n e . processes h a v e b e e n i n v e s t i g a t e d .

Several reversible chemical

L e w i s a n d M a c D o n a l d (17) s t u d i e d

the exchange o f l i t h i u m b e t w e e n l i t h i u m a m a l g a m a n d l i t h i u m c h l o r i d e i n absolute e t h y l a l c o h o l . L a t e r , L . P e r r e t , L . R o z a n d , a n d E . Saito (22) equilibrated lithium amalgam w i t h lithium bromide i n d i m e t h y l forrnam i d e a n d m e a s u r e d a s e p a r a t i o n factor of 1.05. E x t e n s i v e investigations h a v e b e e n m a d e o f i o n exchange t e c h n i q u e s (4, 10, 19, 23, 25, 26). I n 57

Spindel; Isotope Effects in Chemical Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1969.

58

ISOTOPE E F F E C T S IN C H E M I C A L PROCESSES

these systems the m e a s u r e d s e p a r a t i o n factors w e r e g e n e r a l l y v e r y s m a l l (1.000-1.005). T h e influence of v a r i o u s p h y s i c o - c h e m i c a l parameters u p o n the s e p a r a t i o n f a c t o r f o r l i t h i u m isotopes

i n i o n exchange

systems has

been

s t u d i e d . I n c r e a s i n g the c r o s s l i n k i n g of the r e s i n f r o m 2x to 24x i n c r e a s e d the s e p a r a t i o n factor (11)

f r o m 1.0006 to 1.0038.

T h e c h a n g e i n the

s e p a r a t i o n factor w a s a t t r i b u t e d to changes i n h y d r a t i o n o f t h e l i t h i u m species i n the r e s i n phase. G l u e c k a u f (3) u s e d the s o l u t i o n m o l a l i t i e s of


the r e s i n phase a n d the difference i n the c r y s t a l l o g r a p h i c r a d i i of and

7

L i to c a l c u l a t e the s e p a r a t i o n factors.

6

Li

H i s c a l c u l a t e d values agree

v e r y w e l l w i t h these o b s e r v e d s e p a r a t i o n factors. T h e effect of t e m p e r a t u r e u p o n the separation factor was s t u d i e d (12).

T h e s e p a r a t i o n factor decreased as t h e t e m p e r a t u r e i n c r e a s e d . T h e

exothermic 6

Li(aq.) +

e n t h a l p y of 7

exchange

(—AH°)

L i ( r e s . ) ^± L i ( a q . ) + 7

6

for

the isotopic

reaction

L i ( r e s . ) w a s 2.26 c a l . / m o l e , a n d

the e n t r o p y change w a s —1.81 X 10" c a l . / m o l e degree at 2 5 ° C . 3

T h e influence of the h y d r a t i n g t e n d e n c y of cations co-sorbed

with

l i t h i u m isotopes o n a n i o n exchange c o l u m n w a s i n v e s t i g a t e d i n a series of experiments s u m m a r i z e d i n T a b l e I. A s the heat of h y d r a t i o n of the co-sorbed c a t i o n i n c r e a s e d , the isotopic s e p a r a t i o n factor i n c r e a s e d

(13).

T h e n a t u r e of the a n i o n i n the s o l u t i o n phase h a d v e r y little effect u p o n t h e s e p a r a t i o n factor.

H o w e v e r , for

systems

i n v o l v i n g complexes

of

l i t h i u m w i t h e t h y l e n e d i a m i n e t e t r a a c e t i c a c i d , there was a r e v e r s a l of the isotope effect.

T h a t is, L i c o n c e n t r a t e d i n the r e s i n phase i n s t e a d of 7

the aqueous phase as it u s u a l l y d i d i n i o n exchange r e s i n systems. Table I.

Variation of the Separation Factor with the N a t u r e of the Co-sorbed and E l u t i n g Cation (13) Cation NH K NH OH H Ca Cu Cr3 Al 4

Separation

+

+

3

+

+

2 +

2 + +

3 +

a

Factor

0

1.0023 1.0029 1.0033 1.0037 1.0037 1.0045 1.0053 1.0049

( L i / L i ) resin/( Li/ Li) aqueous. 6

7

6

7

K n y a z e v a n d S k l e n s k a y a ( 9 ) c a l c u l a t e d the i s o t o p i c s e p a r a t i o n f a c tors for exchange reactions b e t w e e n l i t h i u m complexes of n i t r i l o t r i a c e t i c acid, ethylenediaminetetraacetic acid a n d aminobarbituric-A^N'-diacetic a c i d , a n d aqueous l i t h i u m ions. T h e s e reactions w e r e p o s t u l a t e d for a single phase system; therefore, the separations cannot b e o b s e r v e d e x p e r i -


4.

LEE

mentally.

Extraction

59

Chromatography

A s the p K of the l i t h i u m c o m p l e x i n c r e a s e d , the c a l c u l a t e d

separation factor increased. T h e influence of eluent c o n c e n t r a t i o n i n i o n exchange

systems o n

the s e p a r a t i o n factor for l i t h i u m isotopes w a s e x a m i n e d b y s e v e r a l w o r k ers (2, 6, 21).

L e e a n d D r u r y (14)

f o u n d t h a t the s e p a r a t i o n factors

decreased w i t h i n c r e a s i n g eluent c o n c e n t r a t i o n w h e n D o w e x - 5 0 a n d Zeo K a r b resins w e r e used.

C o m p a r a b l e results w e r e o b t a i n e d w i t h either

c h l o r i d e or acetate eluents. Downloaded by UNIV OF TEXAS AT DALLAS on July 22, 2016 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0089.ch004

T h e s e p a r a t i o n factors for h t h i u m isotopes i n i o n exchange

systems

w e r e too s m a l l to b e p r a c t i c a l . T o increase the s e p a r a t i o n f a c t o r signific a n t l y , l i t h i u m species i n v o l v i n g other types of l i t h i u m c o m p o u n d s w o u l d h a v e to b e c o n s i d e r e d for e q u i l i b r a t i o n . T h e s e p a r a t i o n of isotopes

by

c h e m i c a l exchange d e p e n d s u p o n the fact t h a t the isotopic species i n t h e t w o phases are d i s s i m i l a r w i t h respect to c h e m i c a l b o n d i n g . T h a t is, i n one phase the i s o t o p i c species s h o u l d be s t r o n g l y b o n d e d , a n d i n t h e other phase the species s h o u l d b e w e a k l y b o n d e d .

T h e c h e m i s t r y of

l i t h i u m l i m i t s the v a r i e t y of c h e m i c a l species a v a i l a b l e for isotope s e p a r a t i o n b y c h e m i c a l exchange.

I n aqueous s o l u t i o n , l i t h i u m exists almost

e x c l u s i v e l y as a h y d r a t e d i o n . T h e c o n c e n t r a t i o n of l i t h i u m i n the r e s i n phase of a n i o n exchange system is s o m e w h a t greater t h a n the c o n c e n t r a t i o n of l i t h i u m ions i n the exterior s o l u t i o n . A l t h o u g h there is association b e t w e e n the l i t h i u m ions a n d the f u n c t i o n a l groups of the r e s i n m a t r i x , s t i l l the l i t h i u m species i n v o l v e d is a h y d r a t e d h t h i u m i o n . T h i s s i m i l a r i t y of b o n d i n g o f the l i t h i u m species i n e a c h phase accounts for t h e s m a l l s e p a r a t i o n factors i n i o n exchange r e s i n systems.

Organolithium com-

p o u n d s , w h i c h are u s e d extensively i n c e r t a i n o r g a n i c syntheses,

are

b o n d e d differently. H o w e v e r , t h e y are v e r y r e a c t i v e c o m p o u n d s w h i c h are u n s t a b l e t o w a r d a i r a n d m o i s t u r e , a n d a n y use of o r g a n o l i t h i u m c o m p o u n d s i n isotope s e p a r a t i o n systems appears to b e i m p r a c t i c a l . R e c e n t l y , i t w a s f o u n d that l i t h i u m f o r m e d extractable

complexes

w i t h m i x t u r e s of d i b e n z o y l m e t h a n e ( H D B M )

and tri-n-octylphosphine

o x i d e ( T O P O ) or t r i b u t y l p h o s p h a t e

T h e /?-diketone a n d the

(TBP).

p h o s p h i n e oxide or p h o s p h a t e i n a h y d r o c a r b o n d i l u e n t w o r k e d synerg i s t i c a l l y to extract l i t h i u m f r o m b a s i c aqueous

solutions (15).

From

a l k a l i n e solutions of l i t h i u m salts, or f r o m m i x t u r e s of l i t h i u m a n d s o d i u m , or h t h i u m a n d a m m o n i u m salts, the extracted l i t h i u m LiDBM

complex

was

• 2 T O P O . F r o m a l k a l i n e solutions of l i t h i u m salt m i x e d w i t h

p o t a s s i u m , r u b i d i u m , or c e s i u m salts, the extractable l i t h i u m species w a s a dimer, L i ( D B M ) 2

2

• 2HDBM

• 4 T O P O (16).

T h e e n o l i c f o r m of

d i b e n z o y l m e t h a n e is a v e r y w e a k a c i d w h i c h , w h e n n e u t r a l i z e d , w i l l f o r m a chelate w i t h l i t h i u m i o n . T B P a n d T O P O are n e u t r a l a d d u c t - f o r m i n g donors w h i c h d i s p l a c e the w a t e r m o l e c u l e s a r o u n d the l i t h i u m i n the chelate, thus m a k i n g the c o m p l e x m o r e s o l u b l e i n the w a t e r - i m m i s c i b l e


60

ISOTOPE E F F E C T S IN C H E M I C A L PROCESSES

o r g a n i c phase.

I n the case of the d i m e r , excess H D B M

molecules

also

participate i n adduct formation. A l t h o u g h b o t h the l i t h i u m a t o m i n this n e w c o m p l e x a n d the l i t h i u m a t o m i n the h y d r a t e d l i t h i u m i o n are p r o b a b l y t e t r a h e d r a l l y c o o r d i n a t e d to o x y g e n atoms, s t i l l the force constants of the l i t h i u m - o x y g e n b o n d s are u n d o u b t e d l y i n f l u e n c e d differently i n the t w o species b e c a u s e of the structure of the l i g a n d s a n d the e n v i r o n m e n t of the p a r t i c u l a r solvent. T h e r e f o r e , i t w a s of interest to investigate the p o s s i b i l i t y of s e p a r a t i n g Downloaded by UNIV OF TEXAS AT DALLAS on July 22, 2016 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0089.ch004

l i t h i u m isotopes b y a n exchange r e a c t i o n i n w h i c h L i D B M • 2 T O P O i n a w a t e r - i m m i s c i b l e o r g a n i c solvent w a s e q u i l i b r a t e d w i t h h y d r a t e d l i t h i u m ions i n a basic aqueous

solution.

F r o m the s t a n d p o i n t of d i s s i m i l a r

species i n t h e t w o phases, this system appears to h a v e advantages the aqueous i o n exchange

r e s i n system for h t h i u m isotope

a n d a l a r g e r s e p a r a t i o n factor s h o u l d b e expected.

over

separation,

T o determine whether

or not this solvent e x t r a c t i o n process w a s feasible w i t h respect to exchange rates a n d m a g n i t u d e of the single stage s e p a r a t i o n factor, the process w a s evaluated

by

a

technique

new

to

isotope

separation,

extraction

chromatography. Extraction chromatography

( r e v e r s e d phase p a r t i t i o n c h r o m a t o g r a -

p h y ) has b e e n u s e d i n a n a l y t i c a l a n d b i o c h e m i s t r y to effect c h e m i c a l separations.

It is a m e t h o d w h i c h c o m b i n e s

the s i m p l i c i t y of i o n ex-

change a n d the s e l e c t i v i t y of solvent extraction.

I o n exchange

theory

m a y b e u s e d to c a l c u l a t e the n u m b e r of t h e o r e t i c a l plates i n the c o l u m n a n d the e n r i c h m e n t coefficient.

E x t r a c t i o n c h r o m a t o g r a p h y as a s e p a r a -

t i o n m e t h o d has b e e n r e c e n t l y r e v i e w e d b y C e r r a i (1)

and Katykhin

(7).

T h e p r o c e d u r e for the e n r i c h m e n t of l i t h i u m isotopes b y e x t r a c t i o n chromatography

w a s as f o l l o w s .

A d o d e c a n e or p-xylene

s o l u t i o n of

H D B M - 2 T O P O w a s a b s o r b e d onto a n i n e r t s u p p o r t of g r a n u l a t e d T e f l o n . T h i s w a s the stationary p h a s e i n a c o l u m n 120 c m . l o n g X 2.5 c m . I . D . A n aqueous l i t h i u m h y d r o x i d e s o l u t i o n c o n t a i n i n g the m i x t u r e of isotopes to b e separated was passed t h r o u g h the c o l u m n .

A t e a c h p l a t e i n the

c o l u m n , isotopic e q u i l i b r i u m was e s t a b l i s h e d b e t w e e n the l i t h i u m species i n the t w o phases.

M u l t i p l i c a t i o n of the e n r i c h m e n t o c c u r r e d as l i t h i u m

p r o c e e d e d d o w n the c o l u m n .

A t the " b r e a k t h r o u g h " the isotopes

were

p a r t i a l l y f r a c t i o n a t e d a l o n g the profile of the e l u t i o n c u r v e . T h e c o n c e n t r a t i o n of l i t h i u m i n the e l u t r i a n t samples w a s d e t e r m i n e d b y spectrophotometry.

t h e n c a l c u l a t e d f r o m a p l o t of the e l u t i o n c u r v e . w a s also e x a m i n e d .

flame

T h e n u m b e r of t h e o r e t i c a l plates i n the c o l u m n w a s T h e reverse s i t u a t i o n

T h a t is, a c o l u m n l o a d e d w i t h h t h i u m d i b e n z o y l -

m e t h a n e - t r i o c t y l p h o s p h i n e oxide c o m p l e x w a s s t r i p p e d f r o m the c o l u m n w i t h d i l u t e h y d r o c h l o r i c a c i d a n d the i s o t o p i c

s e p a r a t i o n factor

d e t e r m i n e d . I n this case, t h e isotopes w e r e e l u t e d i n reverse order.


was

4.

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Extraction

61

Chromatography

T h e c a l c u l a t i o n of the n u m b e r of plates i n the c o l u m n w a s a c c o m plished by

u s i n g the t h e o r e t i c a l treatment of

through" chromatography c o l u m n (N)

(5).

was given b y N =

W ' / ( V

v o l u m e at the p o i n t of i n f l e c t i o n a n d V c e n t r a t i o n c', defined b y c ' / c °

G l u e c k a u f for

"break-

T h e n u m b e r of t h e o r e t i c a l plates i n t h e

=

— V ' ) , w h e r e V is t h e e l u t i o n 2

is the e l u t i o n v o l u m e at t h e c o n -

0.1587. G l u e c k a u f gave a n a l t e r n a t i v e

e q u a t i o n for the n u m b e r of plates i n the c o l u m n ( F i g u r e 1 ) :


N =

2TT(V/AV)2

A l o n g t h e g r a d i e n t of the " b r e a k t h r o u g h " c u r v e , the l i t h i u m samples w e r e i s o t o p i c a l l y assayed b y mass spectrometry. m e n t factor was d e t e r m i n e d as f o l l o w s

e

~

a

"

1

~~ *

i=l

T h e single stage e n r i c h -

(24):

cm

V^o

where a

=

Vi = d

the L i - L i s e p a r a t i o n f a c t o r 6

7

the v o l u m e of the i - t h f r a c t i o n c o l l e c t e d

(ml.)

— the m o l a r c o n c e n t r a t i o n of L i i n the i - t h f r a c t i o n


62

ISOTOPE E F F E C T S I N C H E M I C A L PROCESSES

Ri =

the r a t i o of L i t o L i i n the i - t h f r a c t i o n

R =

the r a t i o o f L i to L i i n the o r i g i n a l l i t h i u m c o m p o u n d

0

Q

=

6

7

6

7

the t o t a l c a p a c i t y of the exchange b e d i n m i l l i e q u i v a l e n t s .

It w a s f o u n d t h a t L i c o n c e n t r a t e d i n the aqueous phase, as s h o w n 6

i n F i g u r e 2. T h i s w a s a r e v e r s a l f r o m the u s u a l results o b t a i n e d i n i o n

1

1

r


1—'—I—'—I— —I— —I— ~ 8.00 7.00 6.005.00-

5 o

4.003.00 2.001.00

10 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0

500 SAMPLE

Figure 2. Lithium chromatography.

10 2 0 3 0

600 NUMBER

isotope enrichment by extraction Li DBM • 2 TOPO vs. LiOH

exchange systems. I n the latter systems, L i u s u a l l y c o n c e n t r a t e d i n t h e 6

r e s i n phase. T h e single stage s e p a r a t i o n factor w a s 1.003, a v a l u e c o m p a r a b l e t o the s e p a r a t i o n f a c t o r t y p i c a l l y f o u n d f o r i o n exchange r e s i n systems.

I t w a s u n f o r t u n a t e that t h e significant c h a n g e i n t h e isotope

effect r e s u l t e d i n a n isotope r e v e r s a l i n s t e a d o f a n a d d i t i o n t o t h e effect f o u n d f o r aqueous i o n exchange systems. I f complexes of l i t h i u m c o u l d be f o u n d i n w h i c h l i t h i u m w a s c o o r d i n a t e d t o atoms other t h a n o x y g e n i n one phase, a l a r g e r isotope effect m i g h t b e expected.


4.

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Extraction

63

Chromatography

Conclusion T h e present w o r k has b e e n the first a p p l i c a t i o n of e x t r a c t i o n c h r o m a t o g r a p h y to isotope separation. T h i s t e c h n i q u e p r o v e d t o b e a s i m p l e a n d convenient

laboratory-scale

method

for studying lithium

isotope

s e p a r a t i o n b y l i q u i d - l i q u i d extraction. T h e m e t h o d m a y h a v e e v e n m o r e i n t e r e s t i n g possibilities f o r isotopes of elements w h i c h f o r m a v a r i e t y of complexes w h i c h are s o l u b l e i n o r g a n i c solvents.


T h e prospect o f separating l i t h i u m isotopes o n a l a r g e scale b y the e x t r a c t i o n o f l i t h i u m f r o m aqueous solutions is n o t v e r y p r o m i s i n g . I n the system w e h a v e s t u d i e d , reflux c o u l d b e a c c o m p l i s h e d b y a n acid-base m e c h a n i s m ; h o w e v e r , because o f the s m a l l s e p a r a t i o n factor, a n e x t r e m e l y large reflux r a t i o w o u l d b e r e q u i r e d . T h i s w o u l d necessitate a v e r y large p l a n t u s i n g enormous q u a n t i t i e s o f a c i d a n d base, a n d t h e cost w o u l d b e excessive. F r o m a n a c a d e m i c s t a n d p o i n t , the s e p a r a t i o n of isotopes b y extract i o n c h r o m a t o g r a p h y presents a u s e f u l t o o l f o r s t u d y i n g isotopic

species

i n s o l u t i o n . T h e n a t u r e of the species m a y sometimes b e e l u c i d a t e d b y d e t e r m i n i n g s m a l l v a r i a t i o n s i n the single stage s e p a r a t i o n factor i f isot o p e s e p a r a t i o n is p r o m o t e d

b y certain physico-chemical

parameters.

T h e s e parameters m a y i n c l u d e the p K o f t h e c o m p l e x , p H of t h e aqueous s o l u t i o n , t e m p e r a t u r e , c o n c e n t r a t i o n , n a t u r e o f t h e o r g a n i c solvent, a n i o n c o m p l e x i n g i n t h e aqueous phase, a n d other factors d e p e n d i n g o n t h e c h e m i s t r y o f the p a r t i c u l a r isotope.

Literature (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17)

Cited

Cerrai, E., Chromatog. Rev. 6, 129 (1964). Ciric, M . M . , Pupezin, J. D . , Bull. Boris Kidrich Inst. Sci. 13, 29 (1962). Glueckauf, E., J. Am. Chem. Soc. 81, 5262 (1959). Glueckauf, E . , Barker, K. H . , Kitt, G. P., Disc. Faraday Soc. 7, 199 (1949). Glueckauf, E . , "Isotope Separation by Chromatographic Methods," AERE-R2896, Atomic Energy Res. Estab., Harwell, Berkshire, 1959. Katal'nikov, S. G., Revin, V. A., Andreev, B. M . , Minev, V. A., Atomnaya Energiya 11, 528 (1961). Katykhin, G. S., Zh. Analit. Khim. 20, 615 (1965). Klemm, A., J. Naturforsch 6a, 512 (1951). Knyazev, D . A., Sklenskaya, E . V., Russ. J. Phys. Chem. 37, 1134 (1963). Lee, D . A., J. Chem. Eng. 6, 565 (1961). Lee, D. A., Begun, G. M . , J. Am. Chem. Soc. 81, 2332 (1959). Lee, D. A., J. Phys. Chem. 64, 187 (1960). Lee, D . A., J. Am. Chem. Soc. 83, 180 (1961). Lee, D . A., Drury, J. S., J. Inorg. Nucl. Chem. 27,1405 (1965). Lee, D . A., J. Chromatog. 26, 342 (1967). Lee, D . A., Taylor, W. L . (unpublished data, 1966). Lewis, G. N., MacDonald, R. T., J. Am. Chem. Soc. 58, 2519 (1936).



64

ISOTOPE E F F E C T S IN C H E M I C A L

PROCESSES

(1 8) Love, L . O., Bell, W . A., Jr., Prater, W . K., Banic, G . M . , Cameron, A. E . , "Proceedings of the International Symposium on Isotope Separation," J. Kistemaker, J. Bigeleisen, A. O. C . Nier, Eds., North-Holland Publishing Co., Amsterdam, 1958. (19) Menes, F . , Saito, E . , Roth, E . , "Proceedings of the International Symposium on Isotope Separation," J. Kistemaker, J. Bigeleisen, A. O. C . Nier, Eds., North-Holland Publishing Co., Amsterdam, 1958. (20) Okamoto, M . , Kakihana, H . , Nippon Kagaku Zasshi 88, 313 (1967). (21) Panchenkov, G . M . , Kuznetsova, E . M . , Kaznadzei, O. N . , Atomnaya Energiya 7, 556 (1959). (22) Perret, L., Rozand, L., Saito, E . , "Second International Conference on the Peaceful Uses of Atomic Energy," Vol. 4, 595, United Nations, New York, 1958. (23) Powell, J. E . , J. Inorg. Nucl. Chem. 24, 183 (1962). (24) Spedding, F . H . , Powell, J. E., Svec, H . J., J. Am. Chem. Soc. 77, 6125 (1955). (25) Taylor, T. I., Urey, H . C., J. Chem. Phys. 5, 597 (1937). (26) Ibid., 6, 429 (1938). (27) Trauger, D . B., Keyes, J. J., Jr., Kuipers, G. A., Lang, D . M . , "Proceedings of the International Symposium on Isotope Separation," J. Kistemaker, J. Bigeleisen, A. O. C. Nier, Eds., North-Holland Publishing Co., Amsterdam, 1958. RECEIVED August 28, 1967. Research sponsored by the U . S. Atomic Energy Commission under contract with the Union Carbide Corporation.


The Enrichment of Lithium Isotopes by Extraction Chromatography

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