190 V. VEEaESW~R~ R~O Bd. 177

Potent ia le entsprechend den K u r v e n der A bb .4 ab. - - Auch durch e inen Zusatz yon Phosphors~ure wurden die Potent ia le auf negat ive Werte herabgedrtickt.

Wir un te r sueh ten auBerdem den EinfluB der Gesamtwolframkonzen- t ra t ion . Aus den Ergebnissen, die Tab .2 enth/ilt , wird ersiehtlich, dab diese ke inen wesentl ichen EinfluB auf die Potent ia le hat.

Zusammenfassung Die kathodische Reduk t i on salzsaurer Wolfram(VI)- lSsungen an

Blei- oder Quecksilberelektroden verl/~uft fiber die 5wertige Stufe bis zum 3wert igen Wolfram. Wolfram(IV) t r i t t n ieht auf. Reino LSsungen yon dreiwertigem Wolfram ha t t en stets eine griine Fa rbe ; nu r bei nied- rigen Wol f ramkonzen t ra t ionen t r a t ein gelbgriiner F a r b t o n hervor. Eine Reduk t ion fiber die 3wertige Stufe hinaus konn te n icht fest- gestellt werden.

Mit e lek t ro ly t i seh hergestell ten Wolfram(V)- u n d Wol f ram(I I I ) - 15sungen f i ihr ten wir Poten t ia lmessungen an den Sys temen W vI/v a n d WV/III in konzent r ie r t salzsauren L6sungen dutch. Es zeigte sieh ein

s tarker EinfluB der S/~urekonzentration auf die Potent ia lwerte .

Literatur 1 BABKO, A. K. : Bull. sci. Univ. Etat Kiev., Ser. chim. ; vgl. Chem. Zbl. 1937, I,

4400. -- ~ BE~N~A~DI-GmssoN, R. F. : Diss. Berlin (1910). -- a CER~IC~OV, Y., u. V. G. Gor~u~INA: Chem. Abstr. 1946, 1110. -- 4 COLLE~B~.~G, 0., U. J. B~KE~: Z. Elektrochem. 30, 230 (1924). -- ~ COLT.~BE~G, 0., U. A. GUT~E: Z. anorg. Mlg. Chem. 136, 252 (1924). -- 6 GEYE~, R., u. G. HENZE: diese Z. 172, 409 (1960). -- 7 I~LTJ:E, 1:~., n. R. GEYER: Z. anorg, allg. Chem. 246, 258 (1947). -- s LEISER, H.: Z. Elektrochem. 18, 690 (1907). -- 9 LI~GANE, J. g., u. L. A. S~ALL: J. Amer. chem. Soc. 71, 973 (1949). -- x0 TOURKY, A. 1~., I. M. IssA u. A. 1VI. AMIN: Anal. ehim. Aeta (Amsterdam) 10, 168 (1954); vgl. diese Z. 147, 53 (1955). -- 1~ Tg~A~)WELL, W. D., u. R. NIERIKE~: Helv. chim. Acta 24, 1067 (1941).

Prof. Dr. ~. GEYEg, Halle (Saale), Ncuwerk 7

Institute of Nuclear Sciences, Boris Kidrich, Belgrade (Yugoslavia)

A Titrimetrie Determination of Uranium in Presence of Organic Solvents

By U. VEERESWARA ~AO

(Received July 1, 1960)

A rapid and accurate volumetr ic method for the de te rmina t ion of u ran ium, i ron and v a n a d i u m in the presence of organic solvents usual ly employed in solvent extract ion processes is described. The method pro- posed is quite simple, rapid and requires no complicated apparatus .

1960 Titrimetrie Determination of Uranium 191

A simple and r a p i d vo lume t r i c m e t h o d for the d e t e r m i n a t i o n of ura- n ium when smal l quan t i t i e s of d issolved organic solvents are p resen t is no t r epo r t ed so far. The increas ing in te res t in the so lvent ex t r ac t i on processes as means for the sepa ra t ion of u ran ium e i ther f rom n a t u r a l sources or f rom i r r a d i a t e d m a t e r i a l requires a rap id , vo lumet r i c m e t h o d for the de t e rmina t i on of u ran ium, ferr ic i ron and v a n a d i u m and o ther s imilar e lements in presence of organic solvents . The usual m e t h o d con- sists of des t roy ing the organic m a t t e r b y t r e a t m e n t wi th a m i x t u r e of n i t r ic and perchlor ic acids a n d conver t ing the n i t r a t e s to sulfates and la te r e s t ima t ing the u r any l sulfa te thus formed wi th p e r m a n g a n a t e a f te r a pr ior r educ t ion in Jone ' s or c admium reduc tor . E v e n t hough m a n y au thors r epo r t ed the e s t ima t ion of u ran ium in organic solvent so lu t ions d i rec t ly , however , all the i r me thods were confined to f inding su i tab le reagents t h a t can form miscible mix tu res wi th the organic solvents and then f inal ly de te rmin ing the des i red e lement e i ther po la rograph ica l ly or spcc t ropho tomet r i ca l ly . Recen t ly , DIZDAR 1 has po in t ed out t h a t smal l quant i t i es of d isso lved organic so lvent in the aqueous ex t r ac t do no t exercise a n y significant influence on the accuracy of the color imetr ic m e t h o d proposed. Since all the above methods of analys is are a lways res t r i c t ed to less t h a n mi l l ig ram quant i t ies , i t is necessary to f ind a r a p i d b u t accura te m e t h o d for the analysis of larger quant i t i es of u ran ium in the presence of d issolved organic impur i t ies . G0rALA RAo 2 r epo r t ed t h a t among the ava i lab le ox id iz ing agents , sodium v a n a d a t e has been ex tens ive ly used for the es t ima t ion of u ran ium and i ron in the presence of organic substances . I n this inves t iga t ion , an a t t e m p t was made to examine whether the above oxidiz ing agent can be successful ly u t i l ized tbr the macro and microvo lumet r ic de t e rmina t i on of u ran ium, ferric i ron, vanad ium(V) . The v a n a d a t e has also the a d v a n t a g e t h a t i t is s table over long per iods of t ime and t h a t i t can be used even in the presence of chlorides.

Experimental Reagents. Sodium Vanadate. The requisite quantity of Merc/~'s ammonium meta

vanadate was weighed into a conical flask. Distilled water was added together with a slight excess of solid sodium carbonate and the solution was boiled until ammonia was completely driven off. The resulting solution of sodium vanadate was trans- ferred to a measuring flask and made up to the mark. The normality of the solution thus obtained was checked with standard permanganate solution as well as a Mohr's salt solution.

Diphenylbenzidine. A 0.1~ solution of diphenylbenzidine (m.p. 140--141 ~ C)in conc. sulfuric acid was used throughout. Fresh solutions were prepared each day.

Uranyl Sul/ate. Suitable quantity of reagent grade uranyl nitrate was dissolved in water and the solution was repeatedly evaporated with eonc. sulfuric acid till no more nitrous fumes evolved. The solution was standardized with standard per- manganate as well as sodium vanadate.

Ferric Sul/ate. Merck pro analisi ferric sulfate was dissolved in 0.1 N sulfuric acid and the same solution was used throughout. Sodium vanadate was prepared in

192 V. VEERESWARA RAO Bd. 177

the manner described above. Commercially available organic solvents were used as such without fur ther purification.

P r e l i m i n a r y e x p e r i m e n t s w e r e c a r r i e d o u t t o o b s e r v e t h e ef fec t o f

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

i n v e s t i g a t i o n .

2 ml of sodium vanada te solution was pipet ted into an Erlenmeyer flask fitted wi th a ground in stopper. Sufficient 10 IV[ acid (sulfuric or hydrochloric bu t not nitric acid) was added to give an overall acidity of 1 IV[ or 5 3I when di luted to 50 ml as indicated in the table, followed b y 2 ml of the solvent. The to ta l volume was always 50 ml. The vanada te remaining in the solution was es t imated by a t i t ra t ion with a s tandard Mohr 's salt solution.

T h e o b s e r v a t i o n s we re r e c o r d e d i n T a b l e 1.

1. Tributyl- phosphate

2. Ethyles ter

3. Butyle ther

4. Butylaceta te

5. Ethylaceta te

6. Amylalcohol

7. Hexone

8. Acetylacetone

9.10~ DDPA in kerosene

Table 1.2 ml o] the vanadate solution containing 0.425 mmoles + 2 ml o/the solvent -~ acid to give the acidity mentioned below ~ water to 50 ml

Name of Overall Time of Vanadate Vanadate the Solvent acidity contact taken in found l~emarks

in hours mmoles in mmoles

1 7 0.425 0.425 no reduction 5 7 0.425 0.335 no reduction

1 30 0.425 0.460 induced 5 30 0.425 0.675 reaction

1 30 0.425 0.275 reduction 5 30 0.425 --

1 7 0.425 0.425 no reduction 5 7 0.425 0.425 no reduction

1 30 0.425 0.425 no reduction 5 30 0.425 0.425 no reduction

1 7 0.425 0.425 no reduction 5 7 0.425 0.345 reduction

1 7 0.425 0.425 no reduction 5 7 0.425 0.250 reduced

1 30 0.425 0.001 rapid 5 30 0.425 -- reaction

1 7 0.425 0.425 no reaction 5 7 0.425 0.425 no reaction

F r o m t h e T a b l e 1 i t is e v i d e n t t h a t t h e r e is p r a c t i c a l l y n o r e a c t i o n

b e t w e e n m o s t o f t h e s o l v e n t s a n d t h e v a n a d a t e e v e n a f t e r m a n y h o u r s

o f c o n t a c t a t low ac id c o n c e n t r a t i o n s . A c e t y l a e e t o n e a n d d i b u t y l e t h e r

a r e t h e o n l y e x c e p t i o n s . A t h i g h e r a c i d c o n c e n t r a t i o n s , h o w e v e r , t h e r e is

c o n s i d e r a b l e r e a c t i o n . T h i s m a y b e a t t r i b u t e d t o t h e f a c t t h a t a t h i g h e r

a c i d c o n c e n t r a t i o n s t h e o x i d a t i o n p o t e n t i a l o f t h e v a n a d a t e i n c r e a s e s

1960 Titrimetric Determination of Uranium 193

f rom 1.02 to 1.3 vol ts vs. S.C.E. as r epo r t ed b y WILLA~D and ~Ah~ALO 5. As h igher acidi t ies can be s u i t a b l y d i lu t ed to the requ i red n o r m a l i t y the danger of ox ida t ion of t he organic so lvent and subsequent change in the t i t re does no t arise in the presen t case. Para l le l exper iments carr ied ou t under s imilar condi t ions wi th p e r m a n g a n a t e and d i ch romate have shown t h a t bo th ox idan t s r eac t i m m e d i a t e l y wi th the organic solvents. Hence, t h e y cannot be used for t he d i rec t vo lumet r ic de te rmina t ion .

The poss ib i l i ty for the exis tence of an induced reac t ion was invest i - g a t e d in the fol lowing way :

Aliquot portions of U t+ and Fe e+ (obtained after reducing the corresponding compounds at the higher oxidation level in a cadmium reductor) were taken in Erlenmeyer flasks. Varying amounts of ~he organic solvents e.g. tributylphosphate,

Table 2. Uranium solution -4- x ml o/ the solvent d- 5 ml o /10 M H2SO ~ 4- water to make up to 50 ml

Volume of Amount of Amount of Name of the solvent the solvent uranium taken uranium found

ml g g

30~ Tributylphosphate

Methylisobutylketone

Ethy]acetate

Dodecylphosphoric acid in kerosene

0.5 1.0 1.5 2.0

0.5 1.0 1.5 2.0

0.5 1.0 1.5 2.0

0.5 1.0 1.5 2.0

0.1380 0.1380 0.1380 0.1380

0.1380 0.1380 0.1380 0.1380

0.1380 0.1380 01.380 0.1380

0.1380 0.1380 0.1380 0.1380

0.1382 0.1381 0.1379 0.1380

0.1381 0.1383 0.1380 0.1381

0.1380 0.1380 0.1380 0.1380

0.1378 0.1382 0.1384 0.1380

methylisobutyl ketone, ethylacetate, dodeeyl phosphoric acid in kerosene were added and the acidity was adjusted to be about 1 M and the solutions were titrated with a standard solution of vanadate as recommended by PA~-DU~A~GA ~AO 4. Practically no difference in the titre values was observed indicating the absence of an induced reaction.

The resul ts ob t a ined are given in Table 2. The same effect was no t iced in the case of ferrous sulfa te also.

I n ano the r set of exper iments the amoun t s of u r a n ium and ferrous were va r i ed keeping the q u a n t i t y of one of the above solvents (300/0 TBP) ~ cons tant . I n th is case also, p r ac t i ca l ly no difference in the t i t re values was observed as is ev iden t f rom Table 3.

Z. analy~. Chem., Bd. 177 13

194 V. V~EgESWAgA RAO Bd. 177

The val id i ty of the above method was fur ther tes ted by a direct apphcat ion to an ext rac t ion process.

Uranyl sulfate was extracted by various solvents using sodium chloride as the salting out agent 3. Uranium was reextracted from an aliquot of the organic phase and then divided into two parts. A portion was directly determined by titration after reduction with vanadate and the other was evaporated to dryness and the

Table 3. 2 ml o/the solvent @ x g o] uranium or iron salt + 5 m110 M H~SO ~ ~- water to 30 ml

Solvent A m o u n t of A m o u n t of A m o u n t of ( A m o u n t o f Difference t aken i ron �9 u r a n i u m t aken i ron found u r a n i u m found

g g g g g )

0.1000 -- 0.1004 -- + 0.0004

30~ Tri- 0.2000 0.2000 0.0000 butyl- 0.3000 0.3012 @ 0.0012 phosphate I

I [

- - 0.1380 _ I 0.1383 + 0.0003 - - 0.2760 -- 0.2761 -[- 0.0001 - - 0.4140 -- 0.4140 0.0000

organic matter destroyed and finally converted into the form of either sulfate or chloride. The solution thus obtained was reduced in a cadmium reductor, and the U ~+ formed after aeration was determined by a titration with standard vanadate.

The comparat ive data is given in Table 4.

Table 4

~ a m e of the so lvent

3 0 0 / 0 T r i b u t y l -

p h o s p h a t e

Ethylacetate

10~ Dodecyl- phosphoric acid

A m o u n t of u r a n i u m t aken f o r

i i rec t t i t ra- t ion in the presence of he dissolved

organic so lven t

(a)

A m o u n t of urani - am t aken

where the] o rgan ic ]

mat terwasl l e s t r o y e d

(b)

0.0600 0.0600

0.0750 0.0750 0.0432 0.0432

A m o u n t found

(a) (b) (a)

0.0601

0.0752 0.04322

0.0600

0.0750 0.04321

Difference

(b)

V e r y li t t le difference due to exper imental error was observed when ferric salts were t rea ted and es t imated in the same way as for u ran ium.

F rom the above results, i t can be concluded tha t using sodium vana- date as the oxidizing agent, macro quant i t ies of u ran ium and ferric i ron may be determined accurately even in the presence of most of the organic solvents employed in usual practice.

+0.0001 0.0000

0.0002 ] +0.00001@ 0"0000 @ 0.00002

1960 Titrimetric Determination of Uranium 195

Since vanada t e can always be de te rmined indi rec t ly th rough its

reac t ion with ferrous salts, an a t t e m p t was made to es t imate v a n a d i u m

also by this sodium v a n a d a t e me thod .

Aliquot portions of vanadium were pipetted out and to them a known excess of ferrous sulfate solution was added followed by various amounts of organic solvent. The ferrous sulfate left unreacted was determined by titration with standard vana- date solution.

The da ta were presen ted in Table 5.

All the foregone observat ions lead us to conclude t h a t the es t imat ion

of those cations which can be reduced to lower oxida t ion s ta te by cad-

m i u m reduetor and la ter oxidized by vanada t e can be carr ied out in the

Table 5. 5 ml 0.1 N sodium vanadate + 10 ml 0.1 N/errous sul/ate solution + x ml o/ the organic solvent + 5 m110 M H2SO a + water to 50 ml

Amount of Amount of Difference Name of the solvent vanadar taken vanadate found

g g g

300/0 Tributylphosphate in kerosene

Ethylacetate

10~ Dodecylphosphoric acid in kerosene

Methylisobutylketone

0.02520

0.02520

0.02520

0.02520

0.02524

0.02522

0.02521

0.02520

+0.00004

+0.00002

+0.00001

0.00000

presence of organic solvents provided t h a t the acid concent ra t ion a t the

t ime of t i t r a t ion is not ve ry high. The possibi l i ty for the existence of any

even tua l induced reac t ion was also explored but i t was found t h a t under

the exper imenta l conditions, there was no such effect.

Recommended Procedure. The acidity of the solution containing the reduced cation was adjusted to be 1.0 M and titrated with a standard solution of sodium vanadate using diphenylbenzidine as the indicator. 2 ml of 10~ oxalic acid should be added to obtain better color change towards the cndpoint. Nitrates should not be present in the solution.

Acknowledgment. Thanks are due to the authorities of the Institute of Nuclear Sciences, Boris Kidrich for the award of a scholarship to work in the Institute.

The author feels highly indebted to Professor PAvL~ SAvid for the encouragement he has given.

References

1 DIZDAR, Z. I., and I. D. OsR]~ovId: Analyst 83, 177 (1958); cf. Z. analyt. Chem. 165, 287 (1959). -- ~ l%AO, G. GOPALA: Current. Sci. 13, 180 (1956). -- a l%Ao, U. VSERESWA~A: Bull. Inst. Nucl. Sci., Boris Kidrich (Belgrade) 8, 75 (1958). -- a RAo, V. PANDURANGA, B.V.S . 1:~. i~URTY and ~no G. GOPALA: Z. analyt. Chem. 147, 161 (1955). -- ~ WILLARD, H. g . , and G. D. MANALO: Ind. Engng. Chem., anal. Edit. 19, 462 (1947).

U. VEE~ESWA~A RAO, Florida State University, Tallahassee, Florida (USA)

13"