THE FC)RJ#ATION OF THALLIUM CHLORIDE COMP&EPS +4ND THEIR EXTRACTION INTO ETFER

BY I I Donald L e o n i d Borrocta A Voigt

November 1955,

Ames Laboratory Iowa State College Ames, Iowa

f&l Technical Information Service Extenshn, Oak Ridge, G i n 3

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ISC-703 iii

ABSrnCT

IN.TRODUCT ION

Page iv

JEVIEFV OF LITERATURE 1

A. Thallium Chemistry i n General 1 B. E x t r a c t i o n from Acid So lu t ions by E the r 3

A . Thallium-204 7 . B. Thakliumf111) P e r c h l o r a t e 8 C: Lithium.. Chlor ide . 9 D. ~i ' tkl ium P e r c h l o r a t e 1 0 E. Uisce l laneous . .: . . . . .

..! . .. . 1 0

A,, . .General. Proce,dure . . . . , : ,16 B .'. i ~ , r e ~ ~ i n i n ~ , r ~ . . ~ n ~ e s tigat i o n ' . . . . . . , . . . . . 1 8 C , ~6rnpe'G

ISC-703 . . . . . I .

THE FORMATION OF THALLIUM-,CHLURQE COMPLEXES AND THEIR I . . . . . .

Donald Leonard Horrocks and A. Voigt

ABSTRACT I

Thallium i s one of a l a rge group of elements which can be extracted i n t o e the r s from halogen'acid solutions. ' T,he general lack of knowledge of t h e extract ion process for these s a l t s has given strong impetus t o the study of a l l aspects of it.

Since there has been no previous invest igat ion on the fundamental nature of the ex t rac t ion of thallium-chloride complexes from H C 1 solutions, it was the purpose of t h i s work to study the ex t rac t ion under various condit ions, using radio t r ace r techniques a s t he tool . This invest igat ion, employing isopropyl e ther , had a s i t s immediate objective the determination of the empirical formula of the thall ium compound i n the e ther phase and t he equil ibrium constant f o r the ex t rac t ion process.

I n t h i s inves t iga t ion i t was found necessary to 'study the ex t rac t ion a t constant, but high, ionic s t rength . Since the extract ion equilibrium constant i s a function of the a c t i v i t i e s of the thallium-chloride complexes, t he a c t i v i t y coef f ic ien t s anu the concentrations of the various complexes need t o be known, and the usual methods of determining the a c t i v i t y co- e f f i c i e n t s , such a s simple extensions of the Debye-Huckel law, could not be used a t these high values o f , the ionic strength. Methods and equations were developed t o determine these a c t i v i t y coef f ic ien t s . This method i s appl icable t o systems i n which the ionic s t reng th i s constant, the complex ions a r e l a rge .and the concentrations of the complexes a re small.

It was found t h a t the compound present i n the e the r phase was e s s e n t i a l l y HTlCll, and the equil ibrium constant f o r .the extract ion was defined as:

,where the parentheses ind ica te a c t i v i t i e s and the subscr ipt J re fVndica tes the e the r phase. For invest igat ions performed a t constant a c id i t y a new ex t rac t ion equilibrium consta.nt was defined:,

* This repor t i s based on a Ph.D, t he s i s by Donald Leonard Horrocks submitted November, 1955 t o Iowa S t a t e College, Ames, Iowa.

The i n v e s t i g a t i o n r evea l ed t h a t f o r a given cons t an t a c i d concen t r a t ion K ' was e s s e n t i a l l y cons t an t w i t h vary ing LiCl concen t r a t ions f o r LiCl concen t r a t ions g r e a t e r t han 0.1 1\11. A t LiCl concen t r a t ions below 0 .1 M. K 1 i nc reased q u i t e markedly. This i nc rease .was be l i eved due t o t he e x t r a c t i o n of TIC13 and/or t h e i o n i z a t i o n of H T l C l 4 i n the* e t h e r phase a t low e t h e r a l concen t r a t ions of tha l l ium. The e x t r a c t i o n Gas dependent upon the i c n i c s t r e n g t h a s shown by t h e change i n K 1 , a t a given a c i d i t y , 1vith:change i n t h e va lue of t h e i o n i c s t r e n g t h . For 1.0 M. ~ ~ 1 0 4 the va lue . o f , K t was 2.50. a t t he va lue of i o n i c s t r e n g t h equal t o 2.0 and 5.35 a t an i o n i c s t r e n g t h va lue equa l t o 3.0.

IL: was observed t h a t K ! x a s dependent upon the: concen t r a t ion o f H C l O 4 ' . t o t he f i r s t power. Also the over a l l d i s t r i b u t i o n c o e f f i c i e n t ' o f t h a l l i u m

between t h e aqueous and e t h e r phases, KT, was observed t o be dependent upon t h e f i r s t power of t h e H C l O 4 concent ra t ion .

- The , t r u e e x t r a c t i o n equ i l i b r ium cons t an t was::

Although K, could n o t be d i r e c t l y c a l c u l a t e d , q u a n t i t i e s which were proport- i o n a l t o Kx were ca l cu la t ed . A t H C l O 4 concen t r a t ions g r e a t e r . t h a n ,0.4 M. and LiCl concen t r a t ions g r e a t e r than 0 .1 .M. t he s p e c i e s e x t r a c t e d i n t o i sop ropy l e t h e r was shown t o be HTlC14. A t very low LiCl concen t r a t ions , below 0.05 hl., t h e e x t r a c t i o n was a nore complicated process . :

The e x t r a c t i o n d a t a i n d i c a t e d t h e forma$ion of a pentachloro- tha l l ium complex. The Porma t i o n cons t an t f o r t he complex, T ~ c I - ~ , from tha l l i um

l s j (111) and c h l o r i d e i o n s was c a l c u l a t e d t o be 3.6 x 10 .

INTRODUCTION

L i .

Thallium i s one of a l a r g e group of e lements which. a r e e x t r a c t e d i n t o e t h e r from halogen a c i d s o l u t i o n s . The gene ra l l a c k of kr~owledge of ' t h e - . e x t r a c t i o n of t h e s e s a l t s has .g iven s t r o n g impetus t o t he s tudy of a l l a s p e c t s of the. e x t r a c t i o n process .

A s i s t h e case w i t h t h e t r i v a l e n t . c a t i o n s of Group I11 B and many o t h e r t r i v a l e n t ca t ions , tha l l ium, i n i t s +3 ox ida t ion s t a t e , forms a s e r i e s of halogen complexes i n an aqueous s o l u t i o n of the corresponding halogen a c i d . The p a r t i t i o n of t h e . m e t a l between an a c i d s o l u t i o n of t h e metal-halogen complexes and e t h e r has been s t u d i e d under many condi t ions , b u t v i r t u a l l y no i n v e s t i g a t i o n s have b e e n . c a r r i e d ou t a t cons t an t i o n i c s t r e n g t h on t h e

.fundamental dependence of the equi l ibr ium between t h e aqueous and e t h e r s o l u t i o n s upon the hydrogen and c h l o r i d e i o n concent ra t ion .

It i s t h e purpose of t h i s work t o s tudy, by means of radiochemical methods, t h e p a r t i t i o n of thallium(111) c h l o r i d e complexes between H 2104 - LiCl - LiC104 s o l u t i o n s and iso-propyl e t h e r . The i n v e s t i g a t i o n has a s i t s immediate o b j e c t i v e t h e de te rmina t ion of t he e G P i r i c a l formula of t h e tha l - l ium compound i n t h e e t h e r s o l u t i o n and t h e equ i l i b r ium cons tan t f o r t he e x t r a c t i o n p roces s . I n t h i s manner, i t i s hoped t h a t our knowledge of t h e e x t r a c t i o n p roces s of t r i v a l e n t metal-halogen complexes, and the more gen- e r a l t o p i c of l i q u i d - l i q u i d p a r t i t i o n , w i l l be increased b y another smal l * . amount.

REVIEW OF LITERATURE

A. Thallium Chemistry i n General . .

The chemistry and l i - t e r a t u r e of tha l l ium, p r i o r t o 1950, have been reviewed by Wag aman, Heffner and Gee (1 ) and Howe and Smith ( 2 ) . These reviews.which inc ' ude 5 a long l i s t of r e f e rences a r e exceedingly u s e f u l i n reviewing t h e chemistry of t ha l l i um. Waggaman, Heffner and Gee (1) review t h e . p r o p e r t i e s , sources , recovery a n d . u s e s of t h e e l e m e n t a n d its: com-

and r e p o r t on t h e methods of a n a l y s i s of tha l l ium, Howe and Smith (2) h

d i s c u s s t h e h i s t o r y , chemistry and p r o p e r t i e s of t ha l l i um w i t h s p e c i a l '

emphasis,, on , i t s m e t a l l u r ~ . . . ,- C ' -*

The .d i scove ry of t ha l l i um i s gene ra l ly c r d d i t e d t o W. Crookes (3 ) who noted a new element while making a spec t roscopic examination of s e l en i - f e r o u s d e p o s i t s i n the l e a d chambers of a s u l f u r i c a c i d f ac to ry . He named t h e new. element tha l l ium, de r ived 'from t h e La t in word t h a l l u s , meaning a

. .

budding twig, because'of the cha rac t e r i s t i c green l i n e i t imparted t o the spectrum.

I n an independent invest igat ion, A . Lamy (4) reported in 1862 t h a t he had observed the cha rac t e r i s t i c green l i n e while examining-the sediment from the chambers of a s u l f u r i c ac id plant . He made valuable contributions -in determining the physical and chemical proper t ies of the new el.ement.

Because of the comparative s ca r c i t y of thallium, it had continued t o be a laboratory c u r i o s i t y fo r many years. I n 1919 the use of thall ium i n photosensit ive c e l l s was patented. Several new uses fo r thall ium were developed i n 1'925, p a r t i c u l a r l y as a. poison for rodent^ and l a t e r as an insec t ic ide . Thallium has now become a very important element.

Thallium c1ource.3 are of ~ . W U Lruad groups, n a t w a l occurrences and in- d u s t r i a l wastes. The na tura l sources include deposits of thallium minerals i n roclts o r dissolved i n b r ine . Thallium can be derived from i r idust r ia l wastes and residues where. the thal l ium from the o r ig ina l raw n a t e r i a l s has been concentrated.

t

Hopkins ( 5 ) discussed the proper t ies of thall ium metal and i t s com- pounds qu i te thoroughly. He discussed a t length many compounds of the two oxidation s t a t e s o f . thallium; thal lous and t h a l l i c , Tl(1) and TL(111) respect ively . Thallous resembles the analogous compounds of the a l k a l i metals i n the soluble compounds and those of lead in the more d i f f i c u l t y soluble ones, while t h a l l i c resembles the compounds of i ron and aluminum. Tha l l i c compounds a r e considerably hydrolyzed and a r e s tab le only in the presence of an excess of ac id . Thallous compounds a r e oxidized t o t h a l l i c , by m04, C 1 Br2 and aqua reg ia but not by HNO alone. The reduction of t h a l l i c t o t f ~ l l o u s i s e a s i l y accomplished by ~ n 3 1 2 , HZSOg, metal l ic tha l - l ium and FeSoh. Thallous and t h a l l i c s a l t s read i ly form complex s a l t s wi th each other , such a s TlCl3 ' 3TlC1.

Hillabrahd, 'Lundell, Bright; and Hoffman (6') .discussed methods -of separat ion and determination of thall ium. ~ h a l l h n i s not p rec ip i ta ted by H2S i n strong ac id solut ions , however, separations based on t h i s f a c t a r e a s a r u l e worthless, s ince thall ium .forms compounds with members of the H2S group, such a s arsenic , antimony, t i n or copper. Thallium i s completely p r ec ip i t a t ed a s T12S i n a c e t i c acid solut ions by H2S or by ( ~ ~ 4 ) ~ s . Hillebrand, -- e t a l . (6) discuss the separation of thallium from lead, s i l ve r , cadmium, iron, aluminum, chromium, cobalt , nickel , zinc, mangnese, a lka l ine ea r ths , magnesium, eal3.i.um and a lka l i e s . Thoy a1 30 mention .thrj, separot ion of thall ium from a number of elements based upon the repeated extract ion of t h a l l i c . chloride from 6N H C 1 solut ion by means of e ther (7) .' They dis- cussed 'several methods of determination of thallium, of which the most important a r e weighing a s Tl2CIO4 (8), T1203 (9). and T 1 1 (10).

Noyes and Bray (11) discuss the qua l i t a t i ve behavior of thallium. (I) and thall ium (111). They review the methods of separation and detection of various compounds of thall ium. ..

B. Ex t r ac t ion from Acid So lu t ions by E the r

Rothe (12) was t h e f i r s t t o s tudy t h e method of e x t r a c t i o n of s a l t s from a c i d s o l u t i o n s by means of e t h e r . ' He s t u d i e d t h e extract i ion of FeC13 i n t o e t h e r from H C 1 s o l u t i o n s . Other e a r l y workers on the e x t r a c t i o n of ' . FeC13 : in to e t h e r included Langmuir (13) , who a p p l i e d it t o the ' s e p a r a t i o n of i r o n and n i c k e l , and Kern (14 ) , who a p p l i e d i t t o t h e sepa ra t ion of i r o n and uranium. The l a t t e r s t u d i e s inc luded work on t h e dependence of t h e e x t r a c t i o n upon t h e concen t r a t ion of t h e HC1. S p e l l e r (15) used t h e e 'xtrac- t i o n method t o s epa ra t e i r o n from copper, manganese, aluminum, ' chrominum, c o b a l t and n i c k e l .

I n 1908 Noyes, Bray and Spear ( 7 ) r epo r t ed t h e e x t r a c t i o n of TIC13 i n t o e t h e r from K C 1 s o l u t i o n . They noted t h a t 19 mg. of thal l i l im a s TlC13 i n H C 1 ( sp . g r . , 1.12) was completely removed from t h e aqueous s o l u t i o n a f t e r two e x t r a c t i o n s wi th e t h e r . They r e p o r t e d t h a t 90-95 pe rcen t of t h e o r i g i n a l t h a l l i u m a s TlC13 was e x t r a c t e d when a 6 M H C 1 s o l u t i o n was shaken w i t h e t h e r .

Swi f t (16) r epo r t ed t h a t gal l ium, along wi th i r o n and tha l l i um, was e x t r a c t e d by e t h e r from a H C 1 s o l u t i o n . Experiments, c a r r i e d ou t w i t h sma l l amounts of ga l l ium i n H C 1 s o l u t i o n s of v a r i o u s concen t r a t ions in - d i c a t e d t h a t t h e e x t r a c t i o n of ga l l ium by e t h e r was more n e a r l y complete when t h e i n i t i a l concen t r a t ions of t he H C 1 was 5.5 N . Swi f t (16) showed t h a t by t r e a t i n g a 4.9-5.9 N s o l u t i o n of H C 1 con ta in ing ga l l ium w i t h an equa l amount of e t h e r , p r e v i o u s l y s a t u r a t e d wi th a s o l u t i o n of I I C l o f t h e sarne concent ra t ion , abou t 97 pe rcen t o f t h e ga l l ium was e x t r a c t e d .

Wada and I s h i i (17) r e p o r t e d t h a t TlBr can be s e p a r a t e d from a l l o t h e r '

s a l t s . o f meta ls except gold by shaking t h e a Bk s o l u t i o n w i t h . e t h e r . They showed t h a t e x t r a c t i o n of TlCl and T1Br3 could be c a r r i e d o u t . a t much 2 lower concen t r a t ions of a c i d s han had been assumed e a r l i e r . They s t a t e d t h a t 99 pe rcen t of t h e o r i g i n a l tha l l ium, p r e s e n t a s TlRr3 i n H B r , w a s ex- t r a c t e d i n t o d i e t h y l e t h e r when t h e i n i t i a l H3r concen t r a t ion was 0 .lN. A t t h i s HBr concen t r a t ion no Fe(111), ~ a ( 1 1 1 ) o r I n (111) was e x t r a c t e d , . . however, 99 p e r c e n t of tb o r i g i n a l ~ ~ ( 1 1 1 ) was e x t r a c t e d .

"Solvent Ex t r ac t ion and I t s App l i ca t ions t o Inorganic ~ n a l ~ s i s l ~ i s t h e t i t l e o f a paper w r i t t e n by I r v i n g (18) i n which he a t t empt s t o p r e s e n t a comprehensive survey of l i q u i d - l i q u i d p a r t i t i o n of . inorganic subs tances . He d i s c u s s e s p a r t i t i o n i so therms, e x t r a c t i o n f o r removal and f r a c t i o n a t i o n , , f a c t o r s f avo r ing s o l v e n t e x t r a c t i o n and t h e e x t r a c t i o n of n i t r a t e s , c h l o r i d e s , bromides, f l u o r i d e s and o t h e r i no rgan ic compounds. IIe a l s o p r e s e n t s i n f o r - mation about t h e e x t r a c t i o n of organo-metal l ic complexes; d i t h i z o n a t e s , ox ina t e s , c u p f e r r a t e s and o t h e r meta l complexes.

I r v i n g (18) p o i n t e d ou t t h e cu r ious and a n a l y t i c a l l y important a l t e r - a t i o n s i n e x t r a c t a b i l i t y i n pas s ing down Group 111 B,. i n t h e e x t r a c t i o n

b '

from 6 N H C 1 by e the r the e x t r a c t a b i l i t i e s were approximately A 1 ( 0 percent) , gallium (40-60 percent) , indiun ( t race) and thallium (90-95 percent) . The ex t rac t ion of the metal bromides from 6 N KBr was approximately gallium (57 percent) , indium (99 percent) and thallium (92 percent) . Indium, which was ex t rac ted with d i f f i c u l t y from H C 1 solution, was removed completely from 4 t o 6 N HBr solut ions , The extract ion of thallium(111) was complete over a l a r g e range of H B r concentrations, a t l e a s t 99 percent extracti-on from 0 , l N t o 5.0 N H R r . Using 0.5 N HBr thal l ium(II1) was separated from a l l metals except gold, which was 99 percent extracted a s lUuBr4, The eff ic iency of extrac+,ion of i ron was reduced by replacing H C 1 by HBr and the a c i d i t y f o r maximum extract ion was a l s o lowered,

Oxidation produces g rea t changes i n the e x t r a c t a b i l i t y of metals. Edwards and Voigt '(19) f ~ u n d that, t,ha d.i..3.bribution ooo f f i c i e i~ t of 31r(V) be.tween iso-propyl, e t he r and 6,s-8.5 N H C 1 was greater than 200, whereas tha t o f ~L'(IIT) w a s only 0.016. I rving and Rossot t i (20) repor t t h a t ~ l (111 ) can be ex6racted from d i l u t e H C 1 so t h a t very l i t t l e i ron o r ga l l - ium a r e extracted, However, Tl(1) had a maximum ex t rac t ion of 7.66 per- cent i n 6019 N HC1. When ~ l (111 ) e ther ex t r ac t s a r e shaken with a re- ducing solut ion ~ l ( 1 ) i s t rans fe r red t o the aqueous phase; thus giving a very good separation method f o r thall ium, I rving (18) repor t s the follow- ing percentages of metal chloride oxidized-.reduced p a i r s extracted by . . e the r from 6 N HC1; Fe(11). (0 percent) and ~e(111) (99 percent) , ~ ~ ( 1 1 1 ) (68 percent) and AS(V) (2-4 percent) , Tl(1) (0 percent) and Tl(I I1) (90- 95 percent) , Sn(11) (15-30 percent) and Sn(IV) (.17 percent) and Sb(111) (66 percent) and s ~ ( v ) (81. percent) , .

I rving, k s s o t t i and Drysdale (21) i&es t iga ted the extract ion of indium by d ie thy l e the r from halogen acids of various concentrations. They sho~ved t h a t the percentage of indium hal ide extracted by d i e thy l e ther from the corresponding halogen acid increased i n the order c ~ < B ~ < I and the . maximum ,extract ion occurs a t decreasing acid concentrations i n the same .

' order , Indium iodide. was extracted quan t i t a t ive ly from H I o f ' normalit.ies between 0 , s and 2 -5 , the d i s t r i bu t i on coef f ic ien t being g r ea t e s t at , : 1.5 N.

The p a r t i t i o n of minute t r ace r amounts of GaC13 between e ther and H C 1 was s tudied by Grahame and Seaborg (22) , They observed t h a t the d i s t r i -

a bution r a t i o f o r CaC13 be.tween e ther and 6 N H C l was f a i r l y constant f o r i n i t i a l quan t i t i e s of 10-12 g. and 7 me., the dis ' . tribution r a t i o being 17,5-19.0 and 16.9 respect ively , Grahame and Seaborg (22) -a l so reported . the d i s t r i bu t i on r a t i o s of several meta l l i c halides between e ther .and H C I . a t low concentrat ions by the use of radioact ive isotopes , Thoy a tud iad . - Lho clfstributiurl uf h C 1 2 , CoC12 and FeCl between e ther arid H C 1 at . .various 2 H C 1 concentrations. They. observed t h a t t e maximum extract ion of GaC13 . occurred i n about 5.5 N H C l , t he same a s reported by Swift (16) .:. Grahame I ..- and Seaborg (22) reported t h a t the a c t i v i t y coef f ic ien t of the .GaC13 i n the e the r phase, a t very low concentrations, was proportional t o the concen- t ra t ion .because of t he r e l a t i v e l y l a rge amount.o.f H C 1 dissqlved i n the other.

I r v i n g and Rossot t i (20), with the a i d of radio-nuclides, s t u d i e d . t h e e x t r a c t i o n by e t h e r of GaSr3 and Gar3, InC13 and In13, T l 1 3 and TlC1,TlBr and T1I from t h e corresponding halogen a c i d s over a range of a c i d normal- ities.' They repor ted changes i n the volume a f t e r equi l ibr ium of e t h e r and aqueous phases increased with the s t r e n g t h of t h e halogen a c i d i n t h e order HCZ. < H B ~ ( H T , They r e p o r t only a small change i n the volume of the phases f o r HCI s t r e n g t h of up t o 5.0 N, while t h e volume change of the phases i s very l a r g e fo r HBr s t r e n g t h s a b v e 3.0 N and f o r H I s t r eng ths above 1 .0 N.

. - I r v i n g and ,&gsot t i (20) showed t h a t In13 was e x t r a c t i d q u a n t i t a t i v e l y , over t h e r&~~d',0:5. - 2.5' N H I , while Ga13 was not ex t rac ted un3.er':similar d&nditbirs:. -' . They, showed t h a t Tl13, 7.ike T l B r and TlC13, was quant i t i a t i v e l y e x t i a c t e d f r a q H I so&utions of s t r eng th 0.05 $0 2.0 N . Small amounts of T 1 I and T ~ B s , - , ~ u < no t TlC1, were ex t rac ted . q u a n t i t a t i v e l y from 0.5 - 2.5 W H2.and.,f~o&:~.O - 3.2, N HBr r e spec t ive ly . For a l l of the systems s t u d i e s by I r v i n g .arid R o s s o t t i (20) the percentage. e h r a c t i o n increased w i t h a c i d nornql,i$y. passest: through a maximum; and the order of the ha l ides f o r T+ieh. thg 'maxin!um e x t r a c t i o n o.ccurs a t lower a c i d concentra t ions was 1 4 @'

I n an inves t iga t ion of thallium, f o r the purpose of comparison it i s ' of i n t e r e s t . t o discuss in some d e t a i l t he extract ion from H C 1 solut iqns i n t o e the r of i t s well-known homolog, i ron. Since the ea r ly wobkers , (7,. , - 12-15), very l i t t l e ytork .was reported on the ex t rac t ion of FeCl from H C 1 so lu t ions by e the r u n t i l t he paper by Dodson, Forney and ~ w ? f t (26) ' .

-

i n 1936. They s tudied the e f f e c t s of varying the i ron and acid concen- - t r a t i o n s , and of peroxide and a lcohol upon the extract ion of FeC13 by isopropyl e ther . The optimum H C 1 concentration fo r e f f i c i e n t ex t rac t ion ' . with isopropyl, e t he r ranged from 6.5 t o 8.5 M. as compared t o a range of 5.5 t o 6.5 M. , f o r ex t rac t ion with d ie thy l e the r . A t acid concentrations between 7.5 and 9.0 M. t h ree phases were observed, two e ther l ayers and an aqueous layer . The "heavyv e ther l ayer of . in termediate density con- t a ined most of t h e ex t rac ted i ron. They reported t h a t a t a c id concen- t r a t i o n s . of 8 ..6 ,and 9 ..3 M the separate e ther phase was metastabze' and dissolved i n fhe .o ther phases on continued shaking. The percentage of i r on extracted'was found t o vary with t he t o t a l amount of iron. Iso- propyl e ther was found t o be super ior t o d ie thy l e the r f o r the extract ion of both small and l a rge quan t i t i e s of iron.

Axelrod and Swift (27) s tudied the ex t rac t ion of Fe(111) from H C 1 so lu t ions by dichloroethyl e the r and reported the formula of the i r on compound in t he e the r phase. They s t a t e d t h a t f o r t h e i r . s t u d i e s dichlor- e t h y l e the r had a p r a c t i c a l advantage overei ther e the r or isopropyl e t h e r i n t h a t i t separates a s the lower phase. They reported no evidence of a decrease i n t he d i s t r i bu t i on r a t i o a t H C 1 concentrations a s high as 11.5 M which i s contrary the r e s u l t s of Dodson, Forney and Swift (26) with d i e thy l and isopropyl e the r . This indicated a continuous increase with increas ing a c i d concentration of the concentration of the extracted com- pound. Axelro.4 and Swift (27) reported the empirical formula of the i r on compound i n the e the r phase a s IlFeCl40 4-5 H 0, neglecting polymerization, and poss ible presence of e the r in the molecu 1 e . This forrdula compared with the formula of 2 ( ~ e ~ 1 3 H C ~ ) .9H20 15 (C2H5) 20 reported by Ka t o and I s i i (28) .

Nachtrieb and Conway (24) and Nachtrieb and Fryxel l (29, 30) made a very thorough study of the ex t rac t ion of FeC13 by isopropyl e ther . Nachtrieb and Conway (24) showed tha t the empirical formula of the i ron compound extracted from aqueous FeCl which does not exceed 8 M. in H C 1 was HFeC14. However, f o r aqueous HC ? concentrations exceeding 8 M. the mole r a t i o of FeCl t o H C 1 exceeds 1:l. They reported r a t i o s f o r FeC13 t o H C 1 of l t1.94 a 2 8.0 M.HC1, 1:1.96 a t 9.0 M.HC1, 1:3.04 a t 10.0 M.HC1 and 1:b004 a t 11.0 M.HC1. The absorption s,qectrum of the ether phase did no t alter not iceably when the r a t i o of YeC1 t o KC1 exceeds 1:1, therefore i t d id not seem t o ind ica te the formation o 3 mixtures of higher complexes of t he type H2FeC15, N3FeC16, e t c . They studied the extract ion of leClg a s a funct ion of temperature. Using the v a n ' t Hoff equation a hea t of ex t r ac t i on of -1970 ca lo r i e s per mole was found f o r 0.9595 M.FeC13 i n 3.50 M.HC1.

Nachtr ieb and F r y j e l l (29) p e r f o i m e d experiment,^. i n which t h e concen t r a t ions of aqueous hydrogen and e l l lo r ide i o n s w-?rekept c o n s t a n t and t h e concen t r a t ion of t h e t o t a l + , r iva l en t ca t49ns was k e p t cons+,ant by making t h e . combined concen t r a t ions of A l C l 3 and FeC13 equal t o .O .500 'f i ; ' . '"~hey r epor t ed t h a t t h e e f f e c t of A l C l 3 was t o i n c r e a s e t h e e f i i c i e n e g of ex-

... t r a c t i o n of low concen t r a t ions o f . i r o n , b u t i t did n o t make t h e . d i s t r i - " bu t ion c o e f f i c i e n t independent of t h e t o t a l i r o n concent ra t ion . S ince a non-ext rac tab le s a l t was capable of i n c r e a s i n g t h e e f f i c i e n c y o f . e x t r a c t i o n ,

- $hey be l i eved t h a t a pol.ymerization wi th r i s i n g concen t r a t ions o f . i r o n .W

does not e x p l a i n t h i s i n c r e a s e i n t h e p a r t i t i o n c o e f f i c i e n t . , A s e l f - s a l t i n g o u t e f f e c t o f FeC13 was pos tu l a t ed . They ,s tudied t h e d i s t r i b u t i o n of FeC13.between aqueous H C 1 and i sop ropy l e t h e r a t a s e r i e s of ' cons tan t H C 1 concent ra t ions . They observed a c o n s t a n t p a r t i t i o n c o e f f i c i e n t f 6r a p a r t i c u l a r ' H C 1 . concent ra t ion f o r . s u f f i c i e n t l y d i l u t e FeC13. s o l u t i o n s . . . .

. S t o i c h i o m ~ t r i c a c t i v i t y c o e f f i c i e n t s a s determined by a n e.m.f. c e l l method . f o r FeC13 , i n 5 F H C 1 s a t u r a t e d wi th . FeC12.H20 were r epo r t ed by . . Nachtr ieb and F r y x e l l T30). They, s t a t e d t h a t t h e i n c r e a s e i n t h e p a r t i t i o n c o e f f i c i e n t of FeC13 between i sop ropy l e t h e r and aqueous H C 1 wi th t h e in - . c r e a s e i n i r o n concen t r a t ion was due t o t h e roemarkable decrease i n t h e a c t i v i t y c o e f f i c i e n t of t h e component w i t h i n c r e a s i n g concent ra t ion .

m e r s , Metzler and Swi f t (31) s t u d i e d t h e d i s t r i b u t i o n of Fe( I I1) between HC1 and i sop ropy l e t k e r s o l u t i o n s t o determine t h e compound ex- t r a c t e d . A t low a c i d i t i e s , 3 M. i n HC1, t h e r a t i o of c h l o r i d e t o i r o n :. and hydrogen t o i r o n i s a p p r o x i ~ l a t e l y h:l and l:1 r e spep t ive ly . A t h igher a c i d concen t r a t ions two e t h e r phases appeared and t h e r a t i o s were some- . what h ighe r i n both phases. The amount of water co-ordinated wi th t h e e t h e r e a l i r o n was determined at a nmber o f a c i d concent ra t ions . The r a t i o of moles o f . w a t e r t o moles 01 l r o n i n t h e e t h e r phase va r i ed from 5.5 t o 8 They a l s o s tud ied t h e e x t z a c t i o n of FeC13 by i sop ropy l e t h e r a t a cons t an t a c i d concent ra t ion , 5.6 WF.HC1. A t low i r o n concen t r a t ions t h e d i s t r i b u t i o n r a t i o was approximately cons t an t , b u t a s t h e i r o n concen- t r a t i o n inc reased t h e d i s t r i b u t i o n r a t i o i nc reased q u i t e sha rp ly . A t q u i t e h igh concen t r a t ions of i r o n t h e d i s t r i b u t i o n r a t i o n o t on ly ceased t o i n c r e a s e b u t a c t u a l l y decreased.

Myers and Metzler (32) c a l c u l a t e d t h e e f f e c t i v e p o l . p e r i z a t i o n o f t h e e t h e r e a l i r o n . They s tud ied t h e e f f e c t of t h e v a r i a t i o n . o f t h e d i s t r i b u t i o n c o n s t a n t w i th a c i d concen t r a t ion and t h e e f f e c t of a c i d upon t h e appa ren t polymerizat ion 0.f t h e e t h e r e a l i ron . .They observed t h e fbrmation of two e t h e r phases a t h igh a c i d concen t r a t ions and i n v e s t i g a t e d t h e e f f e c t o f ac id concen t r a t ion upon t h e composition of t h e two phases. . .

The v i s i b l e and u l t r a v i o l ' e t abso rp t ion spectrums of t h e i sop ropy l e t h e r l a y e r s were examined by Ne tz l e r and Meyers (33) . They a l s o s t u d i e d t h e ~601eculAi- weight and magnetkc kiis 'd 'eptibili ty of t he ' i r 6 n . compound i n .

.

t h e e t h e r l a y e r .

MATERIAL . .

. . 8.' Thallium - 204 . .

I n any i n v e s t i g a t i o n employing radiochemical methods it i s necessary t o s e l e c t t h e i s o t o p e which w i l l f a c i l i t a t e a n a l y s i s . The i s o t o p e s e l e c t e d

f o r t h i s inves t iga t ion was ~ 1 2 0 4 , which decays by emission of 0.76 Mev. beta (34) with p .4'.1 f 0.1 years h a l f - l i f e (35). . The thall ium was received as ac t i ve ~1NO)which was suppl ied by the Isotopes Branch, United S t a t e s Atomic Energy CoynLssion, Oak liidge, Tennessee.

. .

The .active TlNO had t o be pur i f ied, the main impurit ies, both being s tab le , were i ron an3 l e a d . The TlN03 wad dissolved i h aqua reg ia oxi-

- "

dizing, the T 1 ( I ) t o T 1 (111) which was extracted i n to isopropyl e the r from a 6 11.' H e 1 so lu t ion . The T 1 (111) was re-extracted i n t o water and re- duced t o T1 ( I ) wi th excess H2S03. After removing the excess HpS03 by . . boi l ing, the thall ium was precipitated as T11. The TI1 was' dissolved i n . . . aqua r?g ia and t he ex t rac t ion was repeated three times with p rec ip i ta t ion of T1(0:1)3 between ex t rac t ion s teps . The. T l (0 '1 )~ from. the f i n a l precipi - t a t i o n was d r ied a t 110' C . f o r approximately two tioura converting. it to T12U3. The dark reddish-brown powder wax s to red i n a weighing b o t t l e f o r . .

.use In preparation of stock thall ium solutions. . . , .

. . .. . . .

' B . Thallium .(III) Perchlorate

The T1 needed t o make up solut ions t o the lequired concentrat ions was prepared a s the perchlorate i n order . t o be i n a non-conplexed s t a t e . A solu.tion of Tl(C10 ) 3 was s a t i s f a c t o r i l y prepared from T120 by re- ac t ion with ~ ~ 2 0 ~ . khe T 1 03 was obtained from thallium meta ? which was oxidized and puf l f i ed i n t i e same manner a s t h e act ive thallium.. Th6 de- .. s i r e d amounts of pu r i f i ed i nac t i ve and ac t i ve T 1 O3 wore dissolved i n ex- cess HC104. The r e su l t i ng solut ion was d i lu ted % o 2 1,i'ters volume.and . . used a s the stock so lu t ion i n the subsequent experiments..

A procedure f o r s tandardizat ion of 'thallium so lu t ions was repgrted . by Kleinberg (36) . This pr0ce.d-ure involved reduction with sulf i t e and p rec ip i t a t i on of T1 C r O from a bas ic solut ion. The resultls of the s tandardizat ion of $ he k l ( C 1 0 4 ) ~ solut ion a r e shown i n Table 1. The s tock so lu t ion was found t o contain 2.R mg. of T12Cr04 per m l . of solution, which equaled .0.0106 M.

To determine the exact concentration of H C l O 4 i n the stock solut ion, a l iquo ts ,were ' t i t r a t e d against standard NaCH tan tohe p h s n ~ l p h t h a l o i n ~ an'd- p o m t . Both the f r e e acid and the T l (C104)~ were t i t r a t e d . J u s t before the end-point the thall ium prec ip i ta ted a s T ~ ( G H ) ~ , leaving a c l ea r solut ion, so t h a t the end-point was e a s i l y detected. By c a l m l a t i o h , correcting f o r the Tl(C104)~, the concentration of H C l O 4 i n t h e stock go lu t ion was 4.05 M.

The stock so lu t ion of Tl(C10 )3, 0.0106 M. i n 4.05 M. HCIOb, hag 'been very s t ab l e and has shown v i r t u a l k y no evidence of decomposition a f t e r severa l months a t room temperature. The solution which i n i t i a l l y gave no t e s t f o r chlor ide ion, s t i l l gave no t e s t , a f t e r one year, ' Aliquots of the

s tock s o l u t i o n were t i t r a t e d p o t e n t i o m e t r i c a l l y w i t h Ce(S0 )p i n a Beckman P Model G pH Meter t o t e s t f o r t h e presence of any tha l l ium( ) . There was Q no apparent break i n t he po e n t i a 1 , r e a d i n s upon vary ing t h e amount of fi added c ~ ( s o ~ ) ~ from 3 x 10- moles t o 10- moles f o r an a l i q u o t of s tock

s o l u t i o n con ta in ing 10-3 moles of T ~ ( C ~ O ~ ) ~ . The amount o f t ha l l i um(1) which was p r e s e n t i n t h e s tock s o l u t i o n was l e s s than 3 x 10'3 pe rcen t .of' t h e t o t a l tha l l ium, a n e g l i g i b l e amount f o r t h i s i n v e s t i g a t i o n .

Table 1

Standa rd iza t ion of t h e Stock S o l u t i o n of T l ( t 3 1 0 ~ ) ~

d d2 Determinat ion

Average: 0.0201 5 0,0002 g o / 1 0 m l . 0.0002 2 0. ooooooo6

C , Li thium Chlor ide

The LiCl used i n t h i s i n v e s t i g a t i o n was Merck r eagen t grade LiCl . - which was d i s s o l v e d and f i l t e r e d through s i n t e r e d g l a s s t o remove any

i r i so luble mat te r . S e v e r a l s o l u t i o n s o f v a r i o u s concen t r a t ions were pre- pared, ranging from 0.496 M., t o 6.70 Me

Standa rd iza t ion of t he LiCl s o l u t i o n s was by a g rav ime t r i c method, a s AgC1. These AgCl s t a n d a r d i z a t i o n s were checked by two a l t e r n a t e . methods, a s ion-exchange and a volumetr ic method us ing an adso rp t ion in - d i c a t o r . In t h e ion-exchange method the LiCl sample was e l u t e d through a Dowex - 50 c a t i o n i c r e s i n column i n t h e a c i d i c c y c l e . The e f f u l e n t was

."A~

. t i t r a t e d with standard NaOM t o the phenolphthalein e n ~ i - ~ & 6 t . In the vol- , umetric method the LiCl samples were t i t r a t e d with s p n & r d AgNO) solut ions using di-chlorofluorescein a s the indicator . I n order t o obtain consis tent and co r r ec t r e s u l t s by t h i s method the s a m ~ l e has t o be neu t ra l during the t i t r a t i o n . 30th of the check methods gave r e s u f t s which agreed with those . of the AgCl method,

Do Lithium Perchlorate

Solut ions of LiClO4 were prepared from G. Frederick Smith's reagent grade LiC104 f o r inves t iga t ion of the ex t rac t ion a t constant ionic s t reng th ,

The LiClO so lu t ion was f i l t e r e d through a f i n e s in te red glass funnel and r e c r y s t a l l 4 zed from watey, A stock s a l u t i ~ n was prepared from the re- c r y s t a l l i z e d LiMO4, Two methods were used t o determine the concentration of the Lie104 solut ions , ion-exchange and a gravimetric method. Xn the ion-exchange 'method the LiC104 sa@le was e lu ted through a column of Dowex- 50 ca t ion ic r e s i n i n the ac id i c cycle. The e f fu l en t was t i t r a t e d with standard NaOH to t he phenolphthalein end-point . In the gravimetric pro-

h cedure the perch lora te was p r ec ip i t a t ed a s tetraphenylarsonium perchlorate by the add i t ion of tetraphenylarsonium chlor ide (37). The prec ' ipi tate was coagulated by the add i t ion of HC1, f i l t e r e d onto s in te red glass crucibles , washed with d i l u t e H C 1 solut ion, d r ied a t 1100 C. f o r one-half hour and weighed a s tetraphenylarsonium perchlorate. The r e s u l t s of these two methods were i n agreement.

E. Miscellaneous

Throughout the inves t iga t ion G, Frederick Smith 's doubly vacuum dis- t i l l e d H C l O was used. Standa-d solut ions of NaOH were prepared from Baker G and Adamson s reagent grade Nb OH Bakers s "Baker Analyzedf1 reagent grade AgN03 was used t o prepare AgN03 solut ions . The p ipe t tes andvolumetric f l a s k s used i n the preparat ion of solut ions were Kimblels Exax and Pyrex. A l l so lu t ions were prepared with double d i s t i l l e d water,

METHOD OF INTERPRETATION OF DATA

From the data fo r counting of samples of the aqueous and o ther . phases a d i s t r i bu t i on r a t i o was calculated,

where :

!@fie = concen t r a t ion of t o t a l t ha l l i um i n t h e e t h e r phase w

'?lTw L .- = concen t i a t i on pf t o t a l ; t ha~ i ium: : in : ihe aqueous phase. S ince t h e measurements o f KT were made a t equ i l i b r ium condi t ions , t h e

corlcentrat ion o f t h a l l i u m i n t h e e t h e r phase must be p r o p o r t i o n a l t o t h e leous a c t i v i t y of one o r more of t h e tha l l i um-ch lo r ide complexes i n t h e aqL.

phase, depending upon whether one o r more o f t he c h l o r i d e cornplexes a r e e x t r a c t e d .

It was o f importance t o cons ide r t h e v a r i o u s complexes p r e s e n t i n t h e system. Benoit (38) r e p o r t e d hhe d i s s o c i a t i o n cons t an t s f o r t h e di-, tri- and t e t r a - c h l o r o complexes of thal l ium: .

and t h e d i s s o c i a t i o n c o n s t a n t f o r t h e . f i r s t hydrolyzed t h a l l i u m species:

I n t h e above equa t ions t h e symbol ( ) d e s i g n a t e s t h e a c t i v i t i e s of t h e v a r i o u s s p e c i e s p r e s e n t ' i n t h e aqueous phase, By combining t h e s e . . equat ions a new s e t of c o n s t a n t s was defined:

. .

. . . . and. ( . . . . . ... .

. . . .

. , .. . . . , . A v a l u e of; &s ?b$ined from the experimental data and it6 . d6 tgmina t idn

i w i l l be . shown . . i n . S e c t i o n . . . . E o f Chapter V. ,.. . . ,', . . . .

. . . , . . F t yin .be . shown ip Sect ion D of chapter .V t h a t the t h a l l i u m species

presen t i n the:&her phase was HTLC14. Knowing th i s , t h e " e x t r a c t i o n equil i- . brium con3tant. may be' wri t ten , as: i

i . . . . . . . .

. .

where (x)~ d e s i g n a t e s the a c t i v i t y of X i n t h e e t h e r and (X) desig- n a t e s the a c t i v i t y of X i n the aqueous phase.

Since the only tha l l ium i n the e t h e r phase was present as HTlC14, t h e a c t i v i t y of HTlC14 i n the e t h e r phase may be written::

where y. ETir.,1i represen t s the a c t i v i t y coeff i o i e n t of H T l C l j , i n the e t h e r phase and B3 e equals t h e concentrat ion of HTlC14 i n the e t h e r phase. The t o t a l concentra t ion of tha l l ium in t h e aqueous ~ h a s e was equal t o the sum - . of the concentra t ions '.of t h e va r ious . tha l l ium spec.ies i n t h e aqueous phase:

Using the r e l a t i o n s h i p that the concentration i s equal t o the a c t i v i t y divided by the a c t i v i t y coef f ic ien t and the new s e t of constants obtained from the data of Benoit (38), name'ly K1, K2, K3, K 4 and Kg, equation (4) can be rewrititen:

Solving equation (5) f o r t he a c t i v i t y of T1+3 and subs t i t u t i ng t h i s quan- t i t y and equation (3) i n to equation (2) yields:

ISC- 703

KO = 1 and KT =bje /pb. It w3.s a.ss~nnsd. t:;at t h e act5.vj.Qjr cseTf i c i e n i of HTlC14 i-n e t h e r was

c o n s t a ~ t , s i n c e the . c o n c e n J ~ r a t i o n o f HTlC14 i n t h e e t h e r phase was, slw.1-1 ar,d t h e s i jec ies i s i10.t c!;a:-ged.' I t i.la:j als.:, assiiineci -;:dia.t t h e ~cki .v. i? ;~r t>f t h e hydrogen ion was cons t an t f o r a given i n v e s t i g a t i o n s i n c e t h e ex t rac- t i o n s were s t u d i e d a t cons t an t a c i d concentra ' t ion and cons t an t i o n i c s t r e n g t h . I n a l l o f tile' e x t r a c t i o n s s tud ied , t h e a c i d concen t r a t ion was always s u f f i c i e n t l y h i g h t h a t no liydrolyyed t h a . l l i u r was p r e s e n t and t h e tern, i n v o l v i n g t h e concen t r a t ion of Z'10P2was theref0r .e e l imina ted . When t h e s e cond i t i ons a r e i nco rpora t ed i n t o t h e e x t r a c t i o n equ i l i b r ium cons t an t of equat ion ( 6 ) a newf e x t r a c t i o n equ i l i b r ium cons t an t can b e ca l cu la t ed :

The va lue of K' shou ld 'be f a i r l y c o n s t a n t a t t h e d i f f e r e n t LiCl concen- t r a t i o n s , assuming t h a t t h e a c t i v i t y c o e f f i c i e n t s of t h e t!~allirun- c h l o r i d e complexes and f r e e c h l o r i d e i o n can b e c a l c u l a t e d .

S ince t h e concen t r a t ions of t h e tha l l ium-chlor ide complexes i n t h e aqueous phase were k e p t small , i t was assumed t h a t t h e i r a c t i v i t y co- e f f i c i e n t s could b e c a l c u l a t e d by t h e ex tens ion of t h e Debye-Buckel expression:

- l o g )Ji = A z $ F (8 1 + B --'

where:

zi = c h a r ~ e o f t ha l l i um-ch lo r ide complex,

8 B = 0.3290 x 3.0 f o r h a t e r a t 30° C. ,

f i = i o n i c s t r e n g t h o f t h e s o l u t i o n and

a i = " e f f e c t i v e diameter" of t h e i o n i n t h e s o l u t i o n . I n most c a s e s o f l a r g e i o n s i n aqueous s o l u t i o n s t h e product o f ' B a i .is assumed t o b e 3.0. Sknce a l l of t h e tha l l i um-ch lo r ide complexes a r e l a r g e i o n s , equat ion (8) may b e r e w r i t t e n :

The a c t i v i t y c o e f f i c i e n t of t h e c h l o r i d e i o n was e s t i m a t e d ' b i . two methods. For t he f i r s t , t h e c h l o r i d e a c t i v i t y c o e f f i c i e n t was assumed t o be c o n s t a n t a s c h l o r i d e and p e r c h l o r a t e concen t r a t ions were changed a t a given i o n i c ' s t r e n g t h . Success ive approx ima t ions fa rva lues of c h l o r i d e a c t i v i t y c o e f f i c i e n t were s u b s t i t u t e d i n t o equat ion ( 7 ) u n t i l t h e va lues of K 1 were f a i r l y cons t an t over t h e range of LiCl concen t r a t ions used.

The second method was more d i f f i c u l t . A cons t an t va lue of c h l o r i d e a c t i v i t y c o e f f i c i e n t ' a t a given i o n i c s t r e n g t h was n o t assumed b u t t h e va lues of t h e a c t i v i t y c o e f f i c i e n t s of HC1 and LiCl r e p o r t e d by Harned and Owen (39) and byhS tokes and Hobinson (40) were used. I n t h e cases i n which t h e c o n c e r ~ t r a t i o n of a c i d was g r e a t e r t han the concen t r a t ion of t h e ' f r e e c h l o r i J e the a c t i v i t y c o e f f i c i e n t of t h e c h l o r i d e i o n was taken a s equal t o t h e mean a c t i v i t y c o e f f i c i e n t of H C 1 a t t h e concen t r a t ion o f t h e f r e e ch lo r ide . I n t hose c a s e s i n which t h e ' c o n c e n t r a t i o n of f r e e c h l o r i d e was g r e a t e r than t h e concen t r a t ion of a c i d t h e a c t i v i t y c o e f f i c i e n t of the c h l o r i d e ion was taken a s equal t o t he weighted average of t h e a c t i v i t y c o e f f i c i e n t s of H C 1 and LiCl a t t h e concen t r a t ion of t he f r e e ch lo r ide ,

Before K t could b e c a l c u l a t e d the f r e e c h l o r i d e ion concen t r a t ion had t o be determined. A t h igh LiCl concen t r a t ions t h e f r e e c h l o r i d e i o n con- c e n t r a t i o n was assumed t o be equal t o t h e i n i t i a l concen t r a t ion of t he LiCl. A t i n t e rmed ia t e LiCl concen t r a t ion e s s e n t i a l l y a11 o f t h e aqueous t h a l l i u m was p r e s e n t a t TlClG. S ince t h e t h a l l i u m p r e s e n t i n t he e t h e r

. phase a s HTlC11) a l s o had f o u r moles of c h l o r i d e p e r mole of t ha l l i um, t h e f r e e c h l o r i d e lon concen t r a t ion was taken a s t h e i n i t i a l LiCl concen- t r a t i o n minus f o u r t imes t h e i n i t i a l concen t r a t ion of T l ( ~ 1 0 4 ) ~ .

A t v e r y low LiCl concen t r a t ions the c a l c u l a t i o n of t h e f r e e c h l o r i d e ion concen t r a t ion became r a t h e r d i f f i c u l t . The t o t a l concen t r a t ion -o f t he aqueous c h l o r i d e was equal t o t he i n i t i a l concen t r a t ion of t h e LiCl minus f o u r t imes t h e concen t r a t ion of t he e t h e r a l +fhallium. Also t h e t o t a l aqueous c h l o r i d e concen t r a t ion was equal to:

/- -- where El>, i s t h e t o t a l aqueous concen t r a t ion o f c h l o r i d e i o n and k13 '

, i s t h e f r e e c h l o r i d e ion concent ra t ion . To f a c i l i t a t e t he c a l c u l a t i o n of t h e f r e e c h l o r i d e ion concen t r a t ion t h e a c t i v i t y c o e f f i c i e n t s were neg lec t ed and K1, K2, K3, K4 and K were assumed t o be a r a t i o of t h e concen t r a t ion ' 5 of t h e va r ious spec i e s . Applying t h i s assumption t o equa t ions (4) and (10) y i e l d s :

. . . , * . . . ' I

and

Solving these two equations f o r P1+3Jy equating and separating terms y i e l d s ::

, . . .

From equation (11) the concentration df f ree chloride ion can be determined by successive approximations.

It should be pointed out t h a t t h i s method gives a very good determin- a t i on of the equil ibrium constant , K t , s ince i t i s evaluated a t a number of d i f f e r en t chloride concentrat ions, The accuracy of the constant is dependent not only upon t he accuracy of the physical measurements, but a l so upon the accuracy of the assumption t h a t the values of Kly Kp, Kg and K 4 a s ca lcu la ted from data repor ted by Benoit (38) and the value of K5 as calcula ted from the ex t rac t ion data can be applied t o a l l of the conditions employed i n t h i s invest igat ion, It a l so i s very much dependent upon the assumptions made about the a c t i v i t y coef f ic ien t s of the many species pre- s en t i n t h i s complicated system,

EXPERIMENTAL INVESTIGATION

. . A. General Procedure

preliminary invest igat ions showed t h a t Tl(111) chloride complexes .. ex t rac ted very rap id ly i n to isopropyl e ther . A more complete i nves t i - gation revealed t h a t complete equilibri1.1m was reached between the aqueous and e the r phases i n approximately ten minutes. However, i n most o f the inves t iga t ions the samples were shaken i n a constant temperature bath : f o r about 40 minutes and allowed t o s e t t l e f o r about 30 minute?. This :

b -,

longer contact time was used t o ensure complete thermal equilibrium a s well a s the extract ion equilibrium.

. .

A. simple extract ion. apparatus was assembled t o study the d i s t r ibu t ion of Tl(111) chlor ide complexes between the e ther and aqueous phases. An E. H. Sargent and Company constant temperature bath with a thermo-regulator mercury.re$ay switch was used t o regulate the temperature of the experi- ments. A Burre l l Wrist-Action Shaker with automatic timer was.used t o shakecthe reac t ion tubes. Two types of react ion f l a sks were used i n t h i s invest igat ion, 50 ml. pyrex v o l u m e t r i c f l a sks and 35' mm. pyrex 'tubes with 34/45 ground glass female j o in t s and accompaning 34/45 ground g lass male caps.

I n the ensuing invest igat ions the aqueous l ayer was prepared by placing the desi red concentration of reac tan t s i n the reac t ion tubes and adding an equal volume of isopropyl e ther . I n a l l of the ex?eriments, the i n i t i a l aqueous and e the r phases were each 10 m l .

After tho reac t ion tubes were shaken i n the constant temperature bath and allowed t o s e t t l e , the samples viere withdrawn with pyrex volumetric p ipe t t e s . During the ea r ly invest igat ions , a f t e r the e ther samples V~ere withdrawn, the remaining e the r phase and a small amount of the aqueous phase were rem0ve.d with 'a p ipe t t e before the aqueous samp'les were with-' drawn. In the' l a t e r experiments the, remaining port ion of the e ther phase was not removed before t h ~ aqueous samples were withdrawn. The p i p e t t e was passed through the remaining e the r phase i n t o the aqueous phase, a small' amount of a i r was blown through the p.ipctte t o discharge any of the

1

e ther phase which might have been trapped i n the p ipe t t e and the aqueous sample was withdrawn. The r e s u l t s obtained, by these two sampling method's agreed within ' the l i m i t s . of e r ro r of the experimental methods. . . . .

Approxir.latelg. 2 t o 3 ~ r t l . of vra.ter -\!ere arltieci .to. the ether. ,samples- _ , .. ... .-

and the e t h e r evaporated by a1lo::;ing the sa r~p les t o stand a t room temper- a tu re f o r :f r o m : 6 t o 12 , hours. Analyses were rnade f o r acid, ' .chloride. and thallium. The acid and chlor ide analyses were done volurnetrically, the thall ium a n a l j s i s radiochemically . Since the amount of thallium ' pre-' . sent was not su f f i c i en t f o r p r ec ip i t a t i on and f i l t r a t i o n , c a r r i e r T l ( ~ 0 . j ) ~ i n HN03 was " added, i n a known amount. , ..

Three rnetkiods of mounting the thallium samples were invest igated with' . only. one of them proving su i t ab l e . The two unacceptable methods were simple evap.oration of an aliquo't of each phase, and p rec ip i t a t i on of the tha l l ium a s T ~ ( o H ) ~ . The evaporation method gave unreprddu i b l e and very f l aky simples with considerable self-absorption of t h s beta p a r t i - c l e s by the s a l t s which remained upon evaporation. Since T ~ ( o H ) ~ i s a very f i n e p r ec ip i t a t e which adheres t o glass , i t w a s , d i f f i c u l t . t o f i l t e r . . and mount.

The procedure f o r the, thall ium analysis ,which was used in'' a1 fur t l ier ..' . .. inves t iga t ions was t h a t used a l so f o r the standardization of the II"[CZO~;-)~ so.lution (see page 8 , ) , with a few changes. The T12Cr04 prec ip i ta tes were* allowed t o d iges t a t room temperature f o r Prba 1 l louri ' to' 1 2 ho,G?.b - : I , .

4

i n various . invest igat ions . The time of diges'tion was not too 'critical-..; ' . , . . . , . . . .

d

The T12CrOh sanlples were f i l t e r e d onto 23 m. d iscs of 3ch le icher ; and Schilell, . N O . 589, f i l t e r paper vvi'th. the use of chimney and s-l'nter'ed .

.. g la s s f i l t e r apparatus. The. p r ec ip i t a t e s ivere washed with wate'i.. anil absolute alcbholancj d r ied - a t 110° C .' ' for approximately 5 minutes.. The samples'were coo led . io room temperature before mounting. . .

During the e a r l y invest igat ions a , chemical y5.el.d de te r i ina t ion was: made by weighing t he T12Cr04 p rec ip i t a t e . The counting data we*corrected .Lo 100 percent 'chemical yield. . ,.However, in,. every case the chemical y i e ld was between 93 and. 104 percent, with the g rea tes t majority of the y i e ld s being between 98 and 101 percent, It was believed t h a t these y i e ld s were wel l wi thin the l i m i t s of e r r o r of the radiochemical methods employed. . . The determination of the, chemical y i e ld was discontinued a f t e r the ea r ly investi ,gations. and the yields. were asscned t o be 100 ~ e r c e n t i n . a l l the

. . . . . l a t e r invest igat ions . . . . . . .

- The cooled samples were covered with 3.3 mg./cme2 cellophane d i scs o f 26 mm. diameter. The s a ~ p l e s were mounted on cardboard backing and counted.

. .

B, . Prelkninary Invest igat ion

A s e r i e s of preliminary invest igat ions were preformed'in order to observe the optimum condit ions f o r the study of t h e extraction. . .

1. Time and r a t e of shaking

The ex t rac t ion was s tudied a t two r a t e s of shaking f o r varying times of contact f o r the two phases. A t the lower r a t e of shaking, approxi- mately 350 v ibra t ions per minute and 314 inch stroke, the equilibrium was not obtained with a contact time of l e s s than 30 minutes. However, a f t e r a contact time of only 10 minutes a t the higher shaking r a t e , approxi- mately 350 v ibra t ions per minute and 1 inch s t roke, equilibrium was observed. i n t h i s inves t iga t ion it i s a l so necessary t o obtain a thermal equil ibrium between the two phases. Complete separation of the two phases i s an important condition. To s a t i s f y these requirements, a l l subsequent inves t iga t ion w i l l be 'prformed with the l i i iher shaking r a t e , a contact time of 30 minutes and a s t a t i ona ry period of 30 minutes f o r separation.

2. Varying Lithium Chloride concentrations \ '

The ex t rac t ion was observed a t various LiCl concentrations and con- s t a n t ac id concentration. The r e s u l t s of severa l runs a re s h o k i n Figure 1.

ISC -703

. - Figure 1 - Extraction at va ing'MCl concentration, w 1 o 4 1 =

0.4, M. F1(~104)3 = 1.06 x lo-3.a. . . . , . . . . . . . .. . . - .. .. .

Curve ,A. M C ~ was LUX. , . . :; ' 3 . .

Curve B. MCl was. NaC1.

2 0 _C_

ISC -7 0 3

Hoxvever, s i n c e t h e i o n i c s t r e n g t h was n o t k e p t cons tan t , t he a f f e c t of t he cor lcent ra t ion of LiCl upon t h e e x t r a c t i o n could no t be determined from t h e s e da t a .

3. Varying Hydrochloric Acid. concen t r a t ion , I _ . . _ _. .. .., _.... . - I n previous i n v e s t i g a t i o n s (17, l c , 20) t h e e x t r a c t i o n was. s t u d i e d

a t va ry ing MC1 concen t r a t ions , ' t h e concen t r a t ion of t ha l l i um kept cons tan t . The work of the p rev ious i n v e s t i g a t o r s was ropoated and the r e s u l t s ' shown i n F igu re 2. However, s i n c e t h e i o n i c s t r e n g t h was n o t maintained con-. ' . s t a n t , t h e t r u e e f f e c t a:r t h e concen t r a t ion of H C 1 could n o t be' determined.

I

:The optimum e x t r a c t i o n of about 92 pe rcen t occurred a t approximately 6.5 M. NC1. However, t h e e a r l i e r i n v e s t i g a t o r s (17, 18, 20) r e p o r t e d t h a t T1( 121) was e x t r a c t e d q u a n t i t a t i v e l y from sn1.v t i o n s o'f H C 1 concerl~trat ions as low a s 2 M. by d i e t h y l e t h e r . L i t t l e comparison was made be.tween t h e r e s u l t s of t h e p r e s e n t anti t h e e a r l i e r i n v e s t i g a t i o n s because of t h e d i f f - e r e n t e x t r a c t i o n s o l v e n t and concen t r a t ion of t h a l l i u m used. ..

. . '1 . 4. Varying Sodium Chlor ide concen t r a t ions

The e x t r a c t i o n was s t u d i e d a t cons t an t a c i d concent ra t ion us ing NaCl t o v a r y t h e c h l o r i d e i o n concen t r a t ion and t h e r e s u l t s a r e compared t o t h e experiments u s ing LiCl i n - F i g u r e 1. Once a g a i n no r e s u l t s were concluded' from t h e s e d a t a because t h e i o n i c s t r e n g t h was no t kep t cons tan t .

5 . Varying i o n i c . s t r e n g t h . . . .

: I

The e x t r a c t i o n was i n v e s t i g a t e d a t cons t an t H C l O and. LiCl concen t r a t ions wh i l e vary ing t h e i o n i c s t r e n g t h wi th k ~ l O ~ . e r e s u l k s of one of t h e runs a r e shown i n F i g u r e . 3 . The ve ry marked. 'effect o f th'o : i o n i c s t r e n g t h i s shown by t h e approximately 5.3 f o l d i n c r e a s e . $n t h e e x t r a c t i o n c o e f f i c i e n t f o r an i n c r e a s e i n t h e conccn t r a t i o n of LiClOb *from , 0 . 1. t o 2.4 1 . These d a t a i n d i c a t e d a v e r y s t r o n g s a l t i n g - o u t e f f e c t .

6. P u r i t y of Iso-propyl E the r

The need t o p u r i f y t h e iso-nropyl e t h e r ob ta ined from'the st6ck room, Matheson, Coleman and Bell i s o - p q y l e t h e r , was s tud ied . The iso-propyl e t h e r was p u r i f i e d by shaking ~vvlch a l k a l i n e - KMnO4 s o l u t i o n , d ry ing over ' CaC12 and d i s t i l l i n g . The middle f r a c t i o n b o i l i n g i n t h e range 68.5 t o 69.00 C. a t a tmospheric p r e s s u r e was cnll.ected. S e v e r a l exLrac t lons were ruil aL l d e n t i c a l coridi t ions u s i n g the normal and p u r i f i e d iso-propyl e t h e r and t h e r e s u l t s a r e shown i n F igure 4. Within t h e l i m i t of e r r o r of t h e methods used no d i f f e r e n c e i n t h e e x t r a c t i o n was observed and i n a l l f u r t h e r s t u d i e s t h e s tock room iso-propyl e t h e r was used.

7. . Varying i o n i c s t r e n g t h w i t h ~ o d h P e r c h l o r a t e

S ince NaC104 is m o r e s o l u b l e than LiClO),, thk e x t r a c t i o n could b e

;Ftgure: 2 - Extrac.tion a t varying HC1 concentrat ions 1.06 x 1073 M.-. T l ( c 1 . 0 ~ ) ~ .

Temperature = 2Q0. C.. . , . . . . ! . . . . . ' f '

. , ~ i ~ u r e 3 - Extract ion a's function of increas ing - ~ I C 1 0 4 concentrat ion.

. .

Fig

ure .4

- Ex

trac

tion

as

fun

ctio

n o

f e

the

r pu

rity.

. .

. .

0-

Ex

trac

tion

usin

g u

ntre

ate

d e

the

r. 4 - E

xtra

ctio

n u

sing

- pu

rified

eth

er.

. ..

s tud ied a t higher sa l t con$ihtrations. ~ o & v e r , when NaC104. was added t.o t he r e a c t i o n mixtures, t he chlor ide was oxidiz ld t o chlorine because NaC104 : i s such a Strong :.oxidizing agent. Thus, in a l l f u r t h e r invest igat ions LiC104 w ~ s . ~ s ~ d , $ o maintain the ion ic s t reng th constant. , . ' - ,

. . * ,. , . . .. . . . ,

, C. " ~ s @ & & i & i e . . . Dbpendence of the p a r t i t i o n Coeff ic ient . .

Two ssri$& ,.of & t r i c t i o & o f 0.00106 M, ~ 1 ( 6 1 0 4 ) ~ , i n 0.4 M.' HCIOb and 0.6 M. HClOh, i t varying concentrat ions of L i C l were c a r r i e d gut a t three d i f f e r e n t temperatur'es The ion ic s t rength w a s kept constant ,by. adding the required. amount'of LiC104. The r e s u l t s of :these runs a r e shown, i n Figure 5 j hgure6, and h b l e 2. ,

..

'The? of ' t h ~ ' ' ~ 'log, 6 / sgeins t 1 / ~ i s shcvuri i n Figures , 7 and 8.. AppXyiiig ' khe v a n l t Hoff on, a p a r t i a l molar .beqta of sxtrac- . Llorl, AH, : w a s calculated. Since r a t i o i s propor t iona l t o the ove~.-dLL ihermaeipimic equil ibrium cons tan t f o r the s x t ~ a c tion, . v t h i s ~ppl ica t io r i ' : of..' the. van l ' t Hoff equation i s . va l id and t.hc 'slope o f , t he curve i s th&..negative" of . , the part ial : molar hea t of extract ion. The c a l - cu la t ions 9% .th6 4 H 'are - sho~vn i n Table 3. The average 4 H 1 s' a'rh -9500 cal./ mole and -9900 ca$./mole, for t he extract ion from 0.4 M. and 0.6 M. ' l ~ l 0 4 so lu t ions , rcspec t ive ly . . .

More sxac t ly j the van1 t off equation i s written: . . . .

' Table 2

Temparature Dependence of the P a r t i t i o n Coeff ic ient

. . I n i t i a l : @!clod = 0.s4 M. A ueous K a t , KT a t KT a t F'. eLiC1_1 : 30 C. $ 0 ~ . . 200c .a 300 K~ C. 2.50 C. 200 C.

, . . . . . ' , . aAverage o f ' two runs..

ISC -703

0 TEMPERATURE = 20°C. o TEMPERATURE =2S°C. A TEMPERATURE =30°C.

Figure 5 - Ext rac t ion a s - func t ion of temperature a.t HC1Oh concen t ra t ion equal t o 0.4 M.

INIT lAL [L I CI ] IN MOLES / LITER

0 - TEMPERATURE = 20° C, 0 - f EMPERATUAE = .2S0 C. A - TEMPERATURE 2 30' C.,

Figure 6 - Extraction as function of temperature at ~ ~ 1 0 ~ concentration equal to 0.6 M.

ISC -703

Figure 7 - Vanlt Hoff P lo t f o r p a r t i a l molar h e a t of e x t r a c t i o n from 0.4 M e HC104.

Curve 1 - 0;22 M. L i C l Curve 2 - 0.43 M. L i C l Curve 3 - 0.86 M. L i C l Curve 4 - 1.08 M. L i C l

C'urve 5 - 1.30 .M. L i C l Curve 6 - 1.73 M. L i C l Curve 7 - 1.94 M . L i C l

Figure 8 - Vantt Hoff Plot fo r , p a r t i a l molar heat a t ex t rac t ion from 0.6 M. ~ ~ 1 0 ~ .

Curve 1 - 0.22 M. L i C l Curve 2 - 0.43 M. L i C l Curve 3 - 0.65 M. LiCl

Curve 4 - 1.08 M. L i C l Curve 5 - 1.51 M. L i C l

Table 3 .. . i . ,

P a r t i a l Molar Heat of Ext rac t ion ,A H

I n i t i a l Aqueous @ ~ 1 0 ~ I= 0.4 M. Curve I n i t i a l Slope . AH % 5 No. LiCl (per .001 deg-l) (kcal ./mole)

\ /

5 1.30 0.87 6

- 8.7 1.73 0.90 - 9.0

: 7 ' 1-94 0.96 - 9-6 / Average A H = -9 .5 . t - 0.66 kcal./mole

I n i t i a l Aqueous HCl04 = 0.6 M.

1 0.22 0.98 - 9.8 1

2 0.43 1.00 -10.0 3 0.65 1.02 4

-10.2 1.08 1.02

5 -10 .'2 .

1.51 0.94 - 9-04 /

where K is the e q u i l i b r i u m constant measured i n terms of concentration and 8 1 are the a c t i v i t y coef f ic ien t s f o r the various compounds i n the two

phases. These a c t i v i t y coef f ic ien t terms a r e included i n the A H deter- mined from Figures 7 and 8, and hence the temperature dependence of the

/

concentration equil ibrium constant does not determine t he ' hea t of extrac- t ion unless the various a c t i v i t y coef f ic ien t terms cancel.

. D. Empirical Formula of Compound in ~ t h e r Phase . ~

I n the determination of the formula of the thal l ium compound i n the e ther phase the ana ly t i c a l procedure was e s s e n t i a l l y a s 'follows, although minor refinements and modifications were made a s the experiments progressed. Equal volumes of 1 0 m l . of the e the r and the ~ l ( C l 0 h ) ~ - HC104 - LiCl -

LiC104 solut ions were shaken togethqr, :allowed to separate and the e ther l aye r was analyzed f o r chlor ide , ionizable hydrogen and thallium content. The chlor ide content was determineLd.by adding water t o :the: e ther sample and t i t r a t i n g with standard AgN03.to the dichlorofluorescein end-point.

- A second port ion of the e the r phase was analyzed fo r acid and thall ium(II1) by &dding water and t i t r a t i n k it with. standard ~ a 0 : i t o a phen6lphEhaIGin end-point . 'The amount of thal l ium. i.n the &her .phase, was determined - radiochemically by counting the T12CrOb precipi ta te . , The r e s u l t s a r e presented i n ,Tables 4, 5 and .6 f o r three typ ica l ex.tracti.on experiments., , '

The amount's of hydrogen and chloride ions passing' into ' the e the r "'

l aye r from so lu t ions of the same compositign of HC104, . LiCl . and LiC104 . with no T ~ ( c ~ o ~ ) present were determined. The r e s u l t ? a r e shown i n Tables 4, 5 and 2 , compared with the! d.ata of the extract ion experiment w1.Lh TI(CI.04) 3, present.

The r a t i o s of associa ted chloride and 'of associated hydrogen t o thal l ium were. ca lcula ted and a r e shown i n Tables 7, 8 and 9. The corrected :chloride ion concentration was equal to the amount extracted minus the amount of chloride ion . so lub le i n e ther a t the given ionic strength,..and ac id concentratri.on, .: Since tho amount of chloride soluble i n the e ther was below the l i m i t s of detect ion of the method o'f analysis i n every experiment, it was considered t h a t t h e , a s soc i a~ t ed~ch lo r ide was equal t o t he extracted chlor ide , The average r a t i o s of associated chlor ide t o thall ium i n the e the r phase were 4.72, 4.42 and 4,38. The amounts of -chlor ide t i t r a t e d i n the e the r samples were between 4 . x 10-5 and 1 x 10-4 moles and any small e r r o r in t i t r a t i o n wruld pro'duce a l a rge . e r r o r i n ' the. r a t i o s . The calcula ted r a t i o s a r e consisten.t.ly higher than . )the predic ted r a t i o of 4,0. This digference could be due t o two fac tors , . the t i t r a t i o n of the indicator or the s o l u b i l i t y of amounts of chloride i n the ether. whdch ape r'e,lativaly important but undetcctible by the method of t i t r a t i o n , The high chlor ide r ,a t ios might a l so be due . -. t o the extrac- t i o n of thall-ium polymers o f t h e type L I ~ T ~ C ~ ~ o r H2T1C1s. The r a t i o o f . associa ted chloride t o thal l ium i n the e ther phasc was accepted a s 4.0 i n a l l f u r t h e r invest igat ions .

.. .., . The ;corrected hydrogen ion concentration was equal t o .the equivalents.

of base used.mtnus th ree times the thallium concentration Tn the e the r phase. and minus.the amount of ac id which i s soluble in e ther a t the givcn ionic

and acid concentrat ion, The average ratkos of as.socia t ed hydrogen t o thal l ium were 0.98, 0.90, and 1.08. Since the amount of associated. hydrogen was obtained a s a small difference between three l a rger numbers, a small e r r o r i n the t i t ~ a t i o n would produce a l a rge e r r o r i n the r a t i o s . The calcula ted r a t i o s a r e f a i r l y close t o 1.0:- In a l l fu r%her . inves t i - gat ions the r a t i o of associa ted hydrogen t o thallium i n the e ther phase w i l l be l o o , . , . .

I . . From ' t h i s da ta it i s assumed t h a t -there i s only one thallium compound * . . .

in Lhe e t h e r phase. The empirical formula of t h i s comp~,und i s . HT1C14.

'Table .&

I. S o l u b i l i t y of J1ydrogen, Chloride and . . . ., Thallium i n Ether . :. - , . . .

T o t a l S a l t and Acid Concefltration = 3.0 bl. ''I . ' b4.. 1:: I n i t i a l :Aqueous H C l O 4 , concen t ra t ion =

. . . . . . . . . . , . . ' L . I.

. . . . . . . . . . . . - .................. -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I n i t i a f

. . . . . . . . . . . . . . . . . . . . . [Q,! concent ra t ion i n . . . . . molos / l i t e r - in t h e e t h e r phase? - . . -, , , .,, ..,, ,, . . . . . h . . . . . L : , I . . ' . . . . . . . . . . . . 8 . . ,.. . : , . . . . . . . . . .

Table- 5

. .. . 4 ' .., . . ' ; 1 . ' Solubility of Hydrogen, &lor ide and , .

- . . .

... . , . Thalliwn ' i n Ether :: . . , , . . . . . . . . . .. . .. . . . .. . , . . . -

. , .

. I . . S o l u b i l i t y o f Hydrogen, Chloride and . . Thallium i n Ether . -

Tota l S a l t and Acid con cent ratio^ = 3.0 M. I n i t i a l Aqueous H C l O 4 Concentrat ion = 1.6 14-

. . . .

I n i t i a l ., .

L 3 = concent ra t ion i n i co les / l i t e r i n the e t h e r phase.

I. R a t i o of Associated Chloride and Ilydrogen Ions t o Thallium i n the Ether. Phase

. .

Total S a l t and Acid Concentration = 3.0 M. . I n i t i a l Aqueous H C l O 4 Concentrat ion. =. 0.4 M.

Cori-e.c t e 3 'Ttatios ' .. A ueous Corrected "' (tLiiC1-J . pl] x 104 , p12 x 103 CI+] x 104 ~ 1 - / T; HI / T I '

., .

. . . Average '4,42 ' U. YU

Table 8

11, R a t i o of Assoc ia ted c h l o r i d e and Hydrogen Ions t o Thallium i n the E the r Phase

T o t a l S a l t .and Acid Concent ra t ion ' -- 2.0 M. I n i t i a l . A q u e o u s ' . ~ ~ 1 0 ~ Concentrat ion = 1 , O M,

I n i t i a l . . A ueous s ~ o r r e c t e d . Correc ted Rat ios ' bicl~ , x 104 - 1 x 0 3 E.2 x 104 . m- / Tr - H+. / TI

Average 4.72 0 ,98

Table 9

III, Rat io of Associated Chloride,and Hydrogen Io.ns 'to "l'hallium i n the Ether Phase

Total S a l t and Acid ,Concentration .= 3.0 M. - I n i t i a l Aqueous HC104 Concentration = 1.6 1.

I n i t i a l A ueous corrected Corrected Ratios

$Cl] kQ x 104 . E1-7 x 103 x 104 C1- / T 1 ~f / T1

Average b Q 38, l,08

E. Determination of KS

- Using the values fo r the formation constants of the thallium-chloride

complexes a s reported by Ben0i.t (38) t o calcula te the values of K1, Kp, K3 ' .- . and K4 and the 1ong:equation ( 7 ) i n Chapter I?!, values of Ks were deter- .

mined by successive approximations. The approximate .values of K were de- - termined a t high L i C l concentrations where the assumption was ma 2 o t h a t the i n i t i a l aqueous chloride concentration was nearly.equa1 t o the f i n a l aqueous f r e e chloride concentration, . The va e of K 5 which gave consis t - I? en t ly the be s t evaluation of K v was 3,6 x 10

F. Low Lithium Chloride Concentrations

The extract ion of 0.00106 M. T l ( c 1 0 ~ ) ~ from ac id solut ions w& studied a t very low LiCl concentrations, not exceeding 0,009 M. Since the t o t a l s a l t and acid concentration was 1.0 M., the ionic s t reng th was e s sen t i a l l y constant in these experiments,

The ex t rac t ion was s tudied a t 250 C. f o r two acid concentrations, 0.4 M. and 1.0 M. HClO),, I n the extraction'study a t 0.4 M. H C l O 4 the so lu t ion was 0.6 h J o . i n LiC104 t o maintain the t o t a l s a l t and ac id concentration a t 1 , O Me The p l o t of t he r a t i o of thall ium i n the e ther phase t o thall ium i n the aqueous phase, KT, agains t the i n i t i a l concentration of LiCl i s shown i n Figure 9, The r e s u l t s a re tabula ted i n Tables 10 and 11.

Using the method o u t l i n e d a ChapOerIV .thevalue of K t was determined f o r both HC104 concentrations over the range of 'LiC1 concentrations em- ployed. In t h i s invest igat ion the ac t iv i ty . coef f ic ien t 'of the f r e e chloride was assumed t o be the mean a c t i v i t y coef f ic ien t of HC1 a t the - same concentration, s ince the concentration of H C l O 4 was i n excess of the LiCl concentration a t a l l times,

The a c t i v i t y coef f ic ien t s of the thallium-chloride complexes were . ca lcu la ted from the extension of the Debye-Huckel theory:

- l o g y i ~ z f JF - 1 + 3 \ t - ' ,

, The ion ic strength,^, was 1.0, neglecting the concentrations of T l ( ~ 1 0 ~ ) and LiCl s ince they were too small to e f f e c t the calcula t ion. The constan . A i s 0.5085 a t 250 C. The values of the a c t i v i t y coef f ic ien t s of the

2 thallium-chloride complexes which were calcula ted i n t h i s manner a r e shorn - i n Table 12. It was not necessary t o know the a c t i v i t y coef f ic ien t s f o r T l C 1 - P and ~ 1 + 3 since the concentration of these species a t any given LiCl connCce*- t r a t i o n was too small to e f f e c t the calcula t ion of Kg,

Figure 9 - Ext rac t ion a t very l o w LiCl concent ra t ions . Temperature = 25O C .

, 1' - 1.0 M. H C 7 0 4 Curve 2 - 0.41. H C ~ O ~ . .

' Table 10

Ext rac t ion of Thallium (111) chloride from O ; L M . ~ ~ 1 0 4 - and 0.6 Bd. LiC104 ' a t - Low ~ i ~ 1 .Concentrations

- - . . . . ..

. . . . . . . - . .

8 . .

~q.uqueous C~icTj x 103 m./ l . . . . ... . . - .. I n i t i a l Residual KT . @Qe x 104 m./ l . .- ',

Table 11

Extraction of Thallium (III) Chloride, from 1.0 M. H C l O 4 . - a t Low LiCl Concentrations

Aqueous fii~g x 103 m . / l . I n i t i a l . Residual

Temperature 2s0 C,

A c t i v i t y C o e f f i c i e n t s f i r ' Thallium-Chloride Complexes a t I o n i c S t r eng th o f 1 .0. .

Complex a Charge

The v a l u e s of Kt ob ta ined by u s i n g t h e d a t a of t h e e x t r a c t i o n and t h e c a l c u l a t e d a c t i v i t y c o e f f i c i e n t s a r e shown in Table 13 and Figure 10 ,

The va lues o f K 9 tended toward a c o n s t a n t va lue a t t h e h igher LiCl concen t r a t ions employed f o r b o t h a c i d concent ra t ions , whi le t he va lue of K v i nc reased q u i t e markedly a t t h e lower LiCl concent ra t ions . This

. v a r i a t i o n i n - ' t h e va lue of K P i n d i c a t e d a d i f f e r e n t mode of e x t r a c t i o n was occuring than was o r i g i n a l l y assumed. However, s i n c e t h e a c t u a l t h a l l i u m

, s p e c i e s p re sen t i n t h e e t h e r phase a t t h e s e low LiCl concen t r a t ions was no t determined, i t might we l l be t h a t a tha l l ium-chlor ide spec i e s o t h e r t han HTlCl4 wao c x t r a c t c d , namely TlC13.

,

. D r . Pau l Schonken o f t he Univers i tB de Louvain, Belgium, i n a p r i v a t e communication, s t a t e d tha - t i n t h e e x t r a c t i o n of a u r i c gold-chloride com- p lexes t h e determining f a c t o r i n t h e e x t r a c t i o n p roces s a t low e t h e r a l concen t r a t ions of Au(II1) was t h e i o n i z a t i o n of HBuC14 i n t h e e t h e r phase. Since t h e e x t r a c t i o n of Au(II1) and T l ( I I 1 ) - c h l o r i d e complexes a r e q u i t e s i m i l a r , it m i g h t . a l s o be assuned t h a t a t low va lues of 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 , and hence low concen t r a t ions o f t h a l l i u m in t h e e t h e r phase, t h e amount of t h a l l i u m e x t r a c t e d might be p a r t i a l l y c o n t r o l l e d by t h e i o n i z a t i o n of HTlC14 i n t h e e t h e r phase. A t l o w ' e t h e r a l concen t r a t ions of HTlC14 t h e i o n i z a t i o n w i l l be q u i t e complete, t hus decreas ing t h e a c t i v i t y o f HTlCl i n t he e t h e r phase, and t h e amount of HTlCl4 e x t r a c t e d would i n c r e a s e un k il bo th t h e i o n i z a t i o n equ i l i b r ium cons t an t of HTlClh

Table 13

Evaluation of K t a t Very Low 'LiC1 concentrat ions - .

Tota l S a l t and Acid Concentration = 1 . 0 M, Temperature = 250 C.

I n i t i a l A ueous bicll

i n e ther and the ex t r ac t i on equil ibrium constant were s a t i s f i e d . This ' process would give r i s e t o l a r g e 'values of K t a t very low values of KT, bu t tde values of K P would decrease q i ~ i t e markedly sc KT ificreased.

\ Since both of these c r i t e r i a a r e s a t i s f i e d by the data, it may be

assumed t h a t both T l C l and IITlCl4 could be extracted a t these low Li,C1 concentrations. With 3 he data reported here the di f ference between these two processes of ex t rac t ion can not be determined.

G o Extract ion Studies a t constant Ionic .St rength and High LiC1 Concentrat i6ns'

I n order t o determine the ac tua l values of K P and t o study the e f f e c t s of LiCl andHC104 concentrat ions the ex t rac t ion was s tudied a t constant i on i c s t rength . The t o t a l s a l t and ac id concentrat.ions employed were 2.0 M., 3.0 M. and 5.0 M. The ' resu l t s of these inves t iga t ions .a re presented i n the following sec t ionso

Figure 10 - Dependence of Kt upon- Bica f o r very low . L i C l concentrat ions. .

1, Tota l ' s a l t and a c i d concent ra t ion equal t o 5.0 M.

In t h i s i n v e s t i g a t i o n t h e H C l O 4 concent ra t ion was k,O M. and t h e sum of t h e concent ra t ions of LiCl and ~ i C l O 4 was 1 , O Ma The i n i t i a l aqueous concent ra t ion of ~ l ( ~ 1 0 4 ) ~ was 1.06 x 10-3 M. The r e s u l t s of t h i s

, i n v e s t i g a t i o n a r e shown i n Table 14,

Three phases were observed a f t e r t h e e x t r a c t i o n equi l ibr ium was obtained; a * l i g h t f 1 e the r , a Ifheavy" e t h e r and an' aqueous phase, The volume of each phase changed a s t h e E C 1 - c o n c e r i t r a t i a va r i ed , It was a l s o noted t h a t a t every LiCl concent ra t ion t h e t o t a l f i n a l volume obtained was 0 . 5 - 1.0 m l . l e s s than t h e i n i t i a l t o t a l volume. The heavy etfier

.!- phase contained nea r ly a l l of t h e tha l l ium, B ~ t w e e n 90 1 9 6 percent of t h e o r i g i i l a l Lhalllum. ..-

The t h r e e phase reg inn has been obocrved by Dudson, Forney and Swi f t ( ~ 6 ) ~ %ers and Metzler (32) and Nachtrieb and Fryxe l l (30) i n t h e i n v e s t i - g a t i o n of t h e e x t r a c t i o n of FeC.13 i n t n e ther . Nachtrieb a d Fryxell ' ( 2 3 ) observed a t h r e e phase r e s i o n i n t h e e x t r a c t i o n of GaC13 i n t o i sopropyl e t h e r . Nachtrieb and Fr-yxell (30) suggested t h e explanat ion f o r t h e d i s t r i b u t i o n anomaly of t h e t h r e e phase syst,em was no t provided by thermo- dynamics, b u t would r e q u i r e s t r u c t u r a l evidence. They s t a t e d t h a t i n t h e case of ~ e ( 1 1 1 ) e x t r a c t i o n it was n o t unreasonable t o suppose t h a t t h e normal e x t r a c t i o n was a kind of genera l ized acid-base r e a c t i o n i n which hydrogen bonding l i n k s t h e HFeCl4 t o t h e e t h e r t o form an tloniumll s a l t :

Devia t ion from t h e normal extoraction may be due Lu polymers, Conceivably, chains might be formed by mul t ip l e hydrogen bonding.

R R R I .

I I I . . . 0 . . . HFeC15.f . , . 0 , . . HFeC15II . . . 0 . . . I I Y I R R R

I n this i n v e s t i g a t i o n , al though ein2ir ical formulas have no t been 'determined f r , t h e tha1l.j i l m species cxtraCtedp suine approximate r a t i o s of C ~ l - / T l and H /T1 i n t h e e t h e r phases have been ca lcu la t ed , . T11e s o l u b i l i t y of L i C l and H C l O 4 i n i sopropyl e t h e r was determined f o r t h e same s a l t and a c i d concent ra t ions wi th no T l ( ~ 1 0 4 ) ~ present . The same t h r e e phases were present , but . t h e volumes o f l i k e phases were no t t h e same a s when T l ( ~ 1 0 4 ) ~ was p resen t . For t h i s reason t h e a c t u a l co r rec t ion of t h e e t h e r a l c h l o r i d e and hydrogen i o n concent ra t ions f o r t h e i r s o l u b i l i t y i n e t h e r could n o t be determined. Some of t h e approximate r a t i o s were ca lcu la t ed and i n t h e heavy e t h e r phase i t was noted t h a t t h e r a t i o s of ~ 1 - / T 1 and I - f / T l were g r e a t e r than 4.0 and 1 , 0 r e spec t ive ly , which' would i n d i c a t e t h e

Table 14 45

Extraction Data f o r Total S a l t and Acid . Concentration of 5.0 M.

I n i t i a l Aqueous H C l O 4 Concentration = !loo Me " -. I n i t i a l Aqueous ~ l ( c 1 0 4 ) ~ , = 1.06 x 10-3 M0

Temperature. = 300 C.

-

Percent Thallium . I n i t i a l Volume of'Each Phase

. . .. i n Each Phase

A U ~ O U S Light Heavj Light Heavy * k i c i j e ther ,ether Aqueous . . e ther e ther .Aqueous

1.0 7.0 ml, 3.0 ml. 9.5 ml: 8.6 89.0 2:0 4

p o s s i b l e format ion of polymers i n t h e heavy e t h e r phase o f t h e t y p e %TIC$, where x>1.0 and y > 4.0.

However, i t i s be l i eved t .hat a t t h e s e v e r y low e t h e r a l concen t r a t ions o f t ha l l i um, f r o m ~ 0 . 0 0 1 t o 0 ,01 Me i n t h e "heavyn e t h e r phase, t h e f o r - mation o f polymers which i n c l u d e t h a l l i u m seemed ve ry un l ike ly , These same t h r e e phases were observed with..no t h a l l i u m p resen t , keeping t h e . . concen t r a t ions of LIC1, L i C l O 4 and H C l O b t h e same. T t seems t h a t t h e . format ion of t h i s . t h i r d phase was most l i k e l y due t o t h e s o l u b i l i t i e s of HC1, HC10G and t h e i r l i t h i u m s a l t s i n t h e iso-propyl e the r .

Upon.allowing t h e e x t r a c t f o n mixture t o s t and f o r l ong pe r iods o f t ime, one of t h e e t h e r l a y e r s disappeared i n d i c a t i n g t h a t it i s a meta- s t a b l e phase. However, t h e reason f o r t h i s i s unknown,

2. Total . s a l t and a c i d concen t r a t ions equal t o 2.0 M, . . . . Since t h e system was s o complicated a t t h e h igher a c i d and s a l t

concen t r a t ions t h e i n v e s t i g a t i o n was s h i f t e d t o a s tudy a t a lower t o t a l sal t and'. a c i d concen t r a t ion equal t o 2,O M, The e x t r a c t i o n e a u i l i b r i h was s t u d i e d a t t h r e e d i f f e r e n t H C l O 4 concent ra t ions ; 0 .4 M., 1 . 0 M, and 1.6 M. For each H C l O 4 concen t r a t ion t h e LiCl concen t r a t ion was v a r i e d - a k eep ing t h e t o t a l sa l t and a c i d concen t r a t ion equal t o 2.0 M; by t h e a d d i t i o n o f r e a u i r e d amounts of LiC10b so lu t ions . A t theqe lower. concen t r a t ions o f a c i d t h e r e was no n o t i c e a b l e d i f f e r e n c e i n t h e volume o f t h e e t h e r and aqueous phase be fo re and a f t e r t h e e x t r a c t i o n e q u i l i - brium, The r e s u l t s of t h i s i n v e s t i g a t i o n a r e shown i n F igure 11 and Tab le s 15, 16 and 17.

I

The gene ra l shape of t h e p l o t of KT a g a i n s t t h e in i t ia l LiCl c o n c e n t r a t i o n w a s similar f o r t h e e x t r a c t i o n a t t h e t h r e e a c i d concen- t r a t i o n s , A t LiC1 concen t r a t ions below 0 , l - 0.2 M, KT i nc reased very r a p i d l y a s t h e L i C l concen t r a t ion increased. , There was a maximum i n t h e p l o t a t L iC l concen t r a t ion o f 0 , l - 0.2 M. For LiCl concen t r a t ions g r e a t e r t h a n 0.2 M. t h e KT va lues decreased 'as t h e concen t r a t ion o f LiCl increased .

S ince t h e concen t r a t ions of t h e thallium-chloride'complexes were ve ry small i n every case, t h e i r a c t i v i t y c o e f f i c i e n t s were ca l - c i~ l a t ed from t h e ex tens ion o f the.Debye-Hu