NOTES

be related to the smaller radius of cerium as comparedto europium.

References1. SEKINE, T. &. HASEGAWA, Y., Solvent extraction chemistry

(Marcel Dekker, New York), 1977.2. MARCUS, Y. & KERTES, A. S., Ion exchange and solvent

extraction of metal complexes (Wiley-Interscience,London), 1969.

3. HIROSE, K. & TANAKA, M., J. inorg: nucl, Chem., 38(1976), 2285.

4. SMITH, R. M. & MARTELL, A. E., Critical stability constants(Plenum Press, New York), 1975.

S. LEO, A., HANSCR, C. & ELKINS, D., Chem. Rev., 71(1971), 525.

6. PERRIN, D. D., Dissociation constants of organic bases inaqueous solution (Butterworths, London), 1965.

7. SUDERSANAN, M. & SUNDARAM, A. K., Proc. Indian Acad.Sci.,90 (1981), 137.

8. MORE, A. K. & SUDERSANAN, M., Proc. Indian Acad.sa., 89 (1980), 375.

Solvent Extraction of Uranium(VI) with Versatic-9.

U. S. RAy· & S. C. MODAKDepartment of Chemistry, Visva-Bharati. Santiniketan 731235

Received 10 October 1980; revised 28 November 1980; accepted20 January 1981

Solvent extraction of uranium(VI) from 0.1M acetic acidsolution has been investigated with a high molecular weight car-boxylic acid, Versatic 9, using benzene as a diluent. Quantitativeextraction of uranium is achieved at pH 5.4 to 5.65. Theinterference of magnesium, calcium, strontium, barium, lan-thanum, cerium, praseodymium, neodymium, samarium, gado-linium, terbium, dysprosium and thorium in the extraction ofU(VI) has been investigated. The probable composition of theextracted species as UOiR ••RH (RH = Versatic-9) has beenproposed.

THE commercially available Versatic-9, Versatic-911 and Versatic-IO, the water insoluble carbo-

xylic acid extractants, have been shown to conformto the general behaviour associated with liquid cationexchangers'. Attempts are being made to employthese extractants in some commercial plants for hydro-metallurgical separation of metals", The elucidationof the structure of the extracted species has beeninvestigated extensively by various workers=". Nosystematic attempt has, however, been made to studythe extraction behaviour of uranium(VI) withVersatic-9. This note reports the solvent extractionbehaviour of uranium(VI) with Versatic-9. Theprobable composition of the extracted species hasalso been suggested. The proposed method is verysimple, rapid, selective and applicable to milligramquantities of uranium.

Versatic-9, a mixture of highly branched saturatedaliphatic monocarboxylic acids containing nine

CHI CHaI I

HaC-C-CH.--C-COOHI I

CHI CHa

CHa CHII I

HaC-CH-C-COOHtH/,

CH. CHI(27%}(56%)

Versatic-9

carbon atoms", was supplied by Shell Chemical Com-pany (London) and was used as such.

Uranyl acetate solution (1.05 mg uranium/ml) wasprepared by precipitating uranyl hydroxide fromuranyl nitrate (BDH, AR) and subsequently dissolvingthe hydroxide in 0.2 M acetic acid. The solution wasstandardised by the complexometric titration withdisodium salt of EDTA using xylenol orange indica-tor-", All other reagents were of standard reagentquality.

Elico pH meter, model LI-I0, (Elico, Hyderabad)was used for pH measurements.

Procedure - The concentration of uranium(VI)in the aqueous phase initially was 2.2 X 1O-3Mandthat of the acetate ion was O.IM. The pH of theaqueous phase was measured before and after theextraction in all the experiments. The volumes of theaqueous phase and the organic phase were always20 ml and 10 ml respectively; the organic phase wasVersatic-9 (33 %), diluted with benzene. The amountof uranium(VI), taken for each experiment was10.5 mg. All experiments were carried out at 30° ±0.5°C. Contact time and the stipping time of 5 minwas used in all the experiments, though the distributionratio reached a constant value after 0.5 min ofshaking. After shaking the aqueous and the organicphases, the two layers were allowed to settle for 10 min,the aqueous phase separated and the equilibrium pHmeasured. To remove any trace of organic solvententrained in the separated aqueous phase, the latterwas washed with benzene (5 ml). The resulting ben-zene extract was mixed with the separated organicphase. The amount of uranium present in theaqueous phase was estimated by EDT A titration.Nitric acid (2N, 20 ml) was added to the organicphase, the mixture shaken for 5 min, the two phasesallowed to settle and separate. The aqueous layerwas carefully withdrawn and again washed with ben-zene (5 ml) to remove any entrained solvent presentin the separated aqueous phase (acid extract). Theamount of uranium extracted in that phase wasestimated. The procedure was followed except for thevariations indicated.

At constant metal concentration (2.2 X 10-3M),constant Versatic-9 concentration (1.942 M) andconstant acetate ion concentration (0.1M) the extrac-tion of uranium starts at pH 2.35 and increases withincreased pH, the extraction becoming quantitativeat pH 5.4-5.65. So, the pH of the aqueous phasewas maintained at 5.6 for quantitative extractionthroughout the experiments.

Extraction experiments were also carried out underoptimum condition using various diluents such asbenzene, toluene, xylene, carbon tetrachloride, chloro-form, diisopropyl ether and nitrobenzene. It was

933

INDIAN J. CHEM., VOL. 20A, SEPTEMBER 1981

found that except diisopropyl ether and nitrobenzenequantitative extraction of uranium was achieved withall other diluents. In the case of diisopropyl ether andnitrobenzene emulsion formation took place.

The extraction dependency of uranium (VI) uponthe acetate concentration showed that the extractiondecreases with increase in acetate ion concentration.The experiments were carried out at constant pH,constant metal ion concentration and constant extrac-tant concentration. The plot of log D against log[acetate] was linear with a slope of -2.16, indicatingthe release of two acetate ions during the extractionprocess.

In hydro metallurgy, sulphide and oxide ores areleached by acids or ammonium salts. So largeamount of sulphate and ammonium ions exist in thesesolutions, which have an important effect on the ex-traction equilibriums. In order to clarify the effectof sulphate and ammonium ion in the extractionprocess the extraction experiments were carried outin presence of different concentrations of (NH4)aS04' The extraction of uranium is considerably dec-reased (Fig. 1) by the presence of ammonium sulphatein the concentration range 0.5 to 3.0 M at constantpH, constant metal concentration (2.2 X 1O-3M)andconstant Versatic-9 concentration (1.942 M), probablydue to inextractable complex formation in theaqueous media.

At constant metal concentration (2.2 x 10-3M),constant acetate concentration (O.lM) and constantpH the plot of log D against log [Versatic-9]was linearwith a slope of 1.56. Versatic acids are known to existas dimer in non-polar solvents", From this it can beinferred that three ligand molecules are entering intothe extracted species. The probable extraction me-chanism, can therefore be represented as

U02(CH3COO)z + 1.5 R2Hz ~ U02Ra.RH +2CH3COOH

where RzHa represents the dimeric form of Versatic-9in benzene and the barred species are in the organicphase.

The effect of the following diverse ions was studied:Mg2+ Ca2+ Sr2+- Ba2+ LaH CeH Pr3+ Nd3+Sm3+: Gd3+,'Tb3+,'Dy3+,'Th4+, 'CN-, SCN-,'EDTA:

100 r--------------,

80

??-360o

Ex., 40

20

3 5 74 6pH

Fig. 1 - Extraction of uranium from (NH.).SO. solutions withVersatic-9 [(Versatic 9-benzene,1 :2) vs [(NH.).SO,] for

curves I, 2, 3 and 4 are 0.5, I, 2 and 3 M respectively].

934

TABLE1 - EFFECT OF FOREIGN IONS ON THE EXTRACTIONOF URANIUM(VI)

[Amount of uranium (VI) taken 10.05 mg]

Foreign ion Uranium (VI) . Errorfound (mg) (%)

Mg(IJ) * 9.95 -0.99Ca(II)* 9.95 -0.99Sr(lI)* 9.97 -0.79Ba(ll) * 9.95 -0.99La (III) 9.97 -0.79Ce(IV) 9.95 -0.99Pr(III) 9.95 -0.99Nd(Ill) 9.94 -1.09Sm(IlI) 9.96 -0.89Gd(IIl) 9.94 -1.09Tb(IlI) 9.94 -1.09Dy(JII) 9.95 -0.99Th(VI) 9.95 -0.99SCN-* 10.01 -0.39CN-* 10.01 -0.39EDTA* 9.97 -0.79

*Amount taken = 40 mg; for the rest the amount takenwas 10 mg.

The results show that Mg(Il), Ca(II) , Sr(Il) andBa(Il) when present in concentration four times thatof uranium (VI) do not interfere in the extraction ofuranium (VI) by Versatic-9. Large amount of EDTA,cyanide and thiocyanide do not interfere (seeTable 1).Interference of La(III), Ce(IV), Pr(IlI), Nd(IlI),Sm(III), oanm, Tb(Ill), Dy(IlI) and Th(IV) can beremoved by masking them with EDTA (disodiumsalt). In those cases two consecutive extractions wererequired.

The authors are grateful to the UGC, New Delhifor financial help, to Shell Chemical Co. (London)for a gift sample of Versatic-9 and to Prof. A. K. Defor his interest in the research project.

References1. FLETT, D. S. & JAYCOCK,M. J., Ion exchange and solvent

extraction, Vol. 3 (Marcel Dekker, New York), 1973.2. FLETI, D. S., Trans. Min. Metall., 83 (1974), C 30.3. RAY, U. S. & MODAK, S. C., Sep. Sci. & Tech., 16 (1981),

87.4. RAY, U. S. & MODAK, S. C,; J. Indian chem. Soc.,

58 (1981), 38.5. ASHBROOK,A. W., J. inorg. nucl, Chem., 34 (1972),1721.6. SHIBATA, J. & NISHIMURA, S., Trans. JIM, 18 (1977),

794 .7. SHlGEMATSU,T. NISHIMURA, S., TANABE, T. & KONDO,

Y. Nippon Kinzoku Gakkaishi, 36 (1972), 445 : Chem,Abstr., n (1972), 10229 K.

8. SHIBATA, J., IZUTANI, M. KiROKI, K. & NISHIMURA,S.,Nippon Kinzoku Gakkaishi, 38 (1974) ,847; Chem. Abstr.,82 (1975), 33658 S.

9. SHIBATA,J. & NISHIMURA,S., Nippon Kinzoku Gakkaishi,39 (1975), 206 : Chem. Abstr., 82 (1975), 127877 q.

10. PRIBILRUDOLF, Chelometry-basic determinations (Chema-pol. Czechoslovakia), 1961.