cation was worked out. These results are presentedin Table 1.

Determination of mercury - Mercury has beendetermined amperometrically by titrating with vari-ous reagents=". In the present case mercury solutionwas placed in a pyrex beaker containing 25 mlof 0.1 M ammonium tartrate-ammonia buffer (pH~9). The titration was carried out using a rotatingplatinum micro electrode at a potential of +0.2V(versus SCE) using TCH as a titrant. The diffusioncurrent remained constant till the whole mercurywas precipitated. After the end point, the anodiccurrent increased on adding excess of TCH. Theplot of volume of TCH versus diffusion current gavea reverse L shaped curve.

The determination of Ni2+, COH, Zn2+ and Cd2+was also feasible under the above operative con-ditions with only essential difference that the appliedpotential (-O.IV versus SCE) corresponded to theanodic wave of TCH. These titrations could alsobe carried out at dropping mercury electrode.

References1. DESHMUKH, G. S. & KULKARNI, A. G., Indian J. Chem.,

20A (I98I), 314.2. VOGEL, A. r., A text book of quantitative inorganic analysis

(Longmans Green, London), 1968.3. KOL"IHOFF, I. M. & JOHNSON, R. A., J. electrochem. Soc.,

98 (195I), 237.4. USATENKO, Yu. I & UVAROVA, K. A., Zav Lab, 26 (1960),

1098.S. KRYUKOVA. L. V. & USATENKO, Yu. I., Zav Lab, 41

(1975), 387.6. DESHMUKH, G. S. & SARASWATHI, K., Indian J. Chem., 3

(1965),489.7. NOVENKO. G. M. & FILENKO, A. I., Zh. analit Khim, 27

(1972), 755.8. RAO, A. L. J., BRAR, BIKRAM & VEERRAJU, B., J. electro-

chem Soc, (India) 27 (1978), 225.

Extractive Separation of Mo)ybdenum(VI) as itsThiocyanate by Ethyl Methyl Ketone

(Miss) USHA MADAN & L. R. KAKKAR*Department of Chemistry, Kurukshetra University,

Kurukshetra 132 119

Received 20 August 1981; revised 25 November 1981 and accepted18 January 1982

A method ror tbe separation of Mo(VI) rrom Re(Vll),W(VI), orm, Vl), U(VI), V(V), As(V), Sb(V), Di(V), Th(lV),Ce(lV), Ti(IV), Ni(lI), Fe(ll), Co(ll), Pb(lI), Cu(ll) and Cd(ll)has been developed. The method is based on the extraction orMo(Vl)-thiocyanate complex into ethyl methyl ketone-cllloroCormmixture in acidic media.

IN the oft used thiocyanate method! of molyb-denum determination, elements like rhenium

tungsten, chromium, uranium, vanadium etc. ar~extracted in the reduced state while molybdenum isextractable in both the oxidised and reduced statesHence it was considered worthwhile to study its

NOTES

extraction without using a reductant in order to sepa-rate it from interfering elements. In the presentnote, a highly selective method for the separationof molybdenum by extraction of Mo(VI)-SCN isdescribed.

Procedure - The acidity of a solution containingmolybdenum with or without other metal ions (0.5mg/ml) was adjusted to 2.5M (hydrochloric acid)followed by the addition of 2 ml of 2M ammoniumthiocyanate. The volume was made upto 20 ml.The orange-yellow complex, thus formed, was ex-tracted twice by equilibrating the aqueous solutioneach time for I min with an equal volume of themixture of ethyl methyl ketone (EMK) and chloro-form (3: I). Molybdenum, from the combined sol-vent phases, was recovered by back-extracting twiceeach time for 2 min with an equal volume of wate;(alkaline to litmus) containing a few drops of hydro-gen peroxide.

The thiocvanate in the back-extracts was des-troyed by boiling with 2 ml of 30% hydrogen pero-xide in acidic medium. After cooling, the solutionwas neutralised with dilute ammonia and molyb-denum or other ions (Pd, Hg) were determined byappropriate conventional methodss,

Iron, cobalt, copper and titanium, which werepartially extracted along with molybdenum wereeliminated by back-washing the organic phas~ oncefor 2 min with an equal volume of 2 % stannouschloride solution before recovering molybdenum byalkaline back -extraction.

The orange-yellow complex formed by molybde-num(VI) with thiocyanate in acid media is highlyextractable into ethyl methyl ketone-chloroformmixture. Chloroform alone does not extract anymolybdenum, but extracts 30 % with 10% EMKand 98.9 % with 75 % EMK in one extraction under

. the conditions given below. Though pure EMKextracts 99.4 ~~, it is not recommended due to itshigh solubility in the alkaline aqueous phase whileback-extracting the metal ion from the solvent. Theextraction from different acids decreases in the order:HCl > H, S04 > HlP04 > HNOJ•

For molybdenum up to 40 mg, the optimum con-ditions for the quantitative extraction are : 2.5 MHCI, 0.2M thiocyanate in a final volume of 20 mland equilibration twice (each time for 1 rnin) with aneaual volume of 3: I mixture of EMK and CHC\..Complet~ness of extraction was confirmed by testingfor Mo In the aqueous phase colorimetrically bySn(II)-SCN method'.

Effect of diverse ions - The effect of a numberof diverse ions was studied. W(VI), Cr(HI, VI),U(VI), V(V), As(V), Sb(V), Bi(V), Th(IV), Ce(IV)Ti(IV), Ni(II), Fe(II), Co(II), Pb(II), Cu(II), Cd(II)(up to 0.5 mg/ml), and Re(VII) (0.01 mg/rnl) werenot extracted. Pd(II) and Hg(II) interfered. SO!-(50 mg/mj): Cl-, NO;, acetate (25 rng/rnl): PO:-a~d tartrate (IO mg/rnl), did not have any effect.Citrate (25 mg/rnl), fluoride (5 mg/rnl) and oxalate(10 mg~ml) decreased the extraction by 1.5,2 and 9 %respectively.

Composition of the extracted species - The ratioof Mo(VI) to thiocyanate in the complex was deter-

661

INDIAN J. CHEM., VOL. 2lA. JUNE 1982

TABLE 1 -ANALYSIS OF SYNTHETIC MIXTUR.ES BY THE PROPOSEDMEmOD

SI. Sample composition Mo foundNo. (mg)

Matrix· Mo(mg)

1. Ti(IO) 10.0 10.22. V(lO), U(10) 1.0 0.993. V(S). W(S) 10.0 10.04. Fe(2). Cu(S) 20.0 20.3s. Co(lO). Cu(S) 30.0 29.76. V(2), Re(0.2) IS.0 14.87. V(5), U(5). Ni(S) S.O 4.98. Pb(5). Bi(2). As(2) 10.0 10.19. Fe«2). Cu(5). Co(2), Ti(2) Sot 48.8t

10. (Fe(IO), N i(36)ltt 11.4 11.411. (Fe(4). Ni(40), Cr(12),J 11.8 11.9

W(3.2)tt

.Numbcrs in brackets indicate the amount of metalion in mg; tlLg; ttsampJe Nos. 10 and 11 correspond toHastclloy A and C respectively.

mined by Job's method of continuous variations",The curves obtained at different wavelengths (425,465. 490 nm) indicate that Mo : SCN ratio in thecomplex is 1:4. This was further supported by thelinear plot in the mole ratio method- with a sharpbreak at Mo : SCN ratio of I :4. A slope of ",2 ofthe plot of logarithm of the extraction coefficientagainst the logarithm of free hydrogen ion concen-tration indicates the presence of 2H+ ions in the

metal complex existing in the organic phase. Hencethe extracted species is probably an ion pair of thecomposition 2H+.[MoV102(SCN)4P ....

The proposed method for molybdenum separa-tion is very simple and less time consuming « 10min). It does not involve any reduction step. Theanalytical importance of the method was checkedby the analysis of several synthetic mixtures (fable 1).The results 0btained by the present method comparefavourablv with those obtained by the existingmethods=w.

We are grateful to Prof. V. Yatirajam for helpfulsuggestions. One of us (U. M.) is thankful to theUGC. New Delhi, for the award of a junior researchfellowship.

References1. PERRYN,D. D., New Zealand J. scient. Tech., 27A (1946).

396.2. KODAMA. K., Methods of quantitative inorganic analysis

(Intersciencc, New York), 1963, 244, 155.3. JOB, P., Ann. Chim., 9 (1928), 113.4. YOE, J. H. & JONES, A. L., Ind. Engng. Chern. (Altalyl.

Edl1), 16 (1944), 111.S. MCKAVENCY, J. P. & FREISER, H., Analyt, Chem., 2~

(1957), 290.6. YATIRAJAM,V. & RAM, J., Mikrochim. Acta. (1973), 77.7. YATIRAJAM,V. & RAM, J .• Talanta, 21 (1974),439.8. PAL, C. K. & CHAKRABURTTY,A. K., J. Indian chem, Soc.,

52 (1975), 138.9. YATIRAJAM,V. & RAM, J., Talal1ta, 20 (1973), 88S.

10. YATIRAJAM,V. & RAM, J., Analyt, chim, Acta, 59 (1972).381.

Erratum

Paper entitled, "Some Cyclopentadienyl- & Indenyl-niobium (V) Dioximates", IndianJ. Chem., 21A(I982), pp. 190·193 : Structure (I) in the right hand column on page 192should be corrected as shown below.

662

(II