Dhingra (Nee Madan), Usha

Kakkar, L R

English

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Indian Journal of ChemistryVol. 22A, February 1983, pp. 181-182Ferron as an Analytical Reagent forExtractive Separation of MolybdenumUSHA DHINGRA (nee MADAN) & L R KAKKAR *Department of Chemistry, Kurukshetra University,Kurukshetra 132 119Received 6 May 1982 ; revised 9 August 1982; accepted26 August 1982Molybdenum forms an yellow coloured complex withferron. This coloured complex is extractable in 1% tribenzyl-amine-chloroform mixture from aqueous acidic solutioncontaining ascorbic acid. This forms the basis of the selectivemethod for the separation of molybdenum. The methodovercomes the interference due to Re(VII), W(VI), U(VI)Cr(TIJ, YI), Y(V). Ce(IY), Th(IY), Ru(III), CoCH), Ni(Il),Fe(II), Mnm), Mg(lI), Cd(T1), Pb(II), SO,,-, cr,NO.-, PO.'-and C.O!- Zr(IY) and Pd(II) interfere. The ratio ofmolybdenum: ferron: tribenzylamine in the extracted speciesis found to be 1 : 1 : 3.Molybdenum, both in the pentavalent and hexavalentstates, is extractable into chloroform as 8-hydroxy-quinoline- and 8-hydroxy-2-methylquinoIine2 chelates.8-Mercaptoquinoline3 has also been used for theextraction of molybdenum. All these methods sufferfrom several interferences and, therefore, have seriouslimitations in their applications to various technicalsamples.In the present work, a highly selective method ofseparation of molybdenum is proposed. This involvesextraction of an yellow co loured complex formed bymo 1ybdenum with 7- iodo-8- hydroxyquino line- 5-sul p-honic acid (ferron) into tribenzylamine-chloroform.A stock solution of molybdenum containing10 mg/rnl of the metal ion was prepared by dissolvingsodium molybdate dihydrate (E. Merck) in distilledwater and standardised gravimetrically by the oxinemethod'. Solutions of lower concentrations areprepared by suitable dilution. Stock solution (5 or10 mg/ml) of other elements were prepared by dissol-ving their commonly available salts (CP grade). A0.5 % solution offerron (Riedel) was prepared in I :1water-acetone mixture. Tribenzylamine (TBA) (Fluka)was dissolved in chloroform to give 1% (w/v) solu-tion. Ascorbic acid (S. Merck) was used as such.Procedure-To a sample solution containing :(;0.5 mg Mo/ml were added 0.5 % ferron solution(10 ml) and 5M sulphuric acid (4ml). The volume wasmade up to 20 ml with distilled water and to this wasadded ascorbic acid (100 mg) and the solution shakenfor 1 min. The coloured species thus obtained wasextracted once by an equal volume of 1% TBA inchloroform if the content of molybdenum was .;;;;0.25 mg/rnl and twice if the molybdenum content was>0.25 mg/ml, each time for 3 min. The organicphase was separated and the metal ion back extrac-ted by shaking twice with an equal volume of watermade just alkaline with sodium hydroxide. To thecombined aqueous extracts, 4-5 drops of 30% H202was added and boiled for 2-3 min. The solution wasrendered just acidic with HCI, excess H202 boiledoff and the solution cooled. Milligram amounts ofmolybdenum in the solution were determined gravi-metrically by the oxine method" and micro amountscolourimetrically by the thiocyanate method",It is observed that under the optimum conditions,viz. an aqueous solution (20 ml) containing 0.5 mgMo/rnl, 10 ml ferron solution and 2N acid, theextraction of the metal ion in different acids decreasesin the order H2S04 (99%), CHaCOOH (55%),HCI (40%) H3P04 (35%), HN03 (18%). There ispractically no extraction from the neutral media.The extaction is 72 % at 0.25M and 80 % at 0.5-1.25M H2S04 and thereafter decreases with increasein acid concentration (5 ml ferron reagent per 20 mlaqueous volume). With 2, 8 and 10-15 ml of ferron(0.5 %), the extraction is 58, 94 and 99 % respectively.Upto 0.25 mg Mo/ml, the extraction of molybdenumis !00 % and at 0.5 mg/rnl it is 99 %. At higherconcentrations, turbidity results.Ascorbic acid keeps Cr(VI), V(V) and Fe(III) insolution, while the extraction of molybdenumremains unaffected by its presence even upto 200mgin the aqueous solution.The extraction is 95 % if the equilibration time is1 min and is 99 % for equilibration for 3 min ormore.It is clear from the above observations that for~0.5 mg Mo/rnl, 1M H2S04, 10 ml 0.5% ferronreagent in 1: 1 water-acetone mixture equilibratingonce (twice when >0.25 mg Mo/ml are present inaqueous solution) for 3 min with an equal volume of1% tribenzylamine in chloroform (w/v) , are theoptimal conditions for the quantitative extraction ofmolybdenum.The effect of diverse ions on the extraction ofMo(VI)-ferron complex has been studied. W(VI),U(VI), V(V), Th(IV), Ru(III), Cr(III), Co(lI), Ni(II),Fe(II), Mn(H), Mg(Il), Cd(H), 2.5 mg/rnl each;Ce(IV) 1 mg/rnl ; Pb(II), 0.5 mg/rnl; Cr(VI) 0.05 mg/ml; Re(VII) 0.005 mg/rnl; are not at all extracted.Zr(IV) (0.5 mg/ml) and Pd(JI) (0.05 mg/ml) interfere.Sulphate, chloride, nitrate, phosphate (0.5 g/20 ml assodium salts) and oxalate (0.1 g/20 ml) do notinterfere. EDT A, acetate. tartrate. citrate andfluoride (O! g/20 ml) lower the extraction by 0.5. 1,1,1.5 and 3% respectively.The wide scope of the method is tested by theanalysis of several synthetic and technical samplemixtures (Table 1) and the results obtained are quitesatisfactory. The proposed method compares favour-ably with the existing methods1-s's-lo of extractiveseparation of molybdenum.] 81Composition of the extracted species-The ratio ofmolybdenum: ferron: TBA in the extracted specieswas determined as 1 : 1 : 3 by Job's method" of conti-nuous variations and mole ratio method".Our thanks are due to Prof. V. Yatirajam forhelpful suggestions. One of us (U.D.) is grateful tothe UGC, New Delhi for financial assistance.INDIAN J. CHEM., VOL. 22A FEBRUARY 1983Table I-Analysis of Molybdenum in Technical Samples bythe Proposed MethodSample No. Sample CompositionMatrix" Mc(mg)1. Re (0.1) 0.12. W(l),Y(l) 1.53. Co(lO), Ni(5) 1.04. Th(S), Zr(S) 2.2S. Fe(2), Cr(l) 6.36. U(lO), Ru(5) 10.07. Mn~S), Mg(lO), Zn(5) S.O8. [Fe(2.9), Ni(0.7S), Cr(1),Co(O.OOS), Mn(O.I),Si(O.OS),P(0.0025)lt 0.29. [Fe(7), Cu(O.I), Ni(0.9),Cr(1.9), CCO.02)lt 0.1Mo found(mg)0.11.491.052.236.410.104.9S0.1980.099*Figures in brackets indicate the amount of metal ion inmg ;+Sample Nos. 8 and 9 correspond to stainless steel and. stainless U respectively./182References1 Stary J, Analyt chim Acta, 28 (1963) 132.2 Motojima K & Hashitani H, Bunsekikagaku, 9 (1960) 151.3 Agrinskaya, N A & Petrashen V I, Zh Analit Khim, 16(1961) 701.4 Kodama K, .Methods of quantitative inorganic analysis(Interscience, New York) 1963,216.S Perrin D D, New Zealand J Sci Tech, 27A (1946) 396.6 Job P, Ann Chim, 9 (1929) 113,7 Yoe J H & Jones A L, Ind Engng Chem (Anal Edn), 16(1944) 111.8 Buscarons F & Canela J, Analyti chim Acta, 70 (1974)113.9 Yatirajam V & Ram J, Talanta 21 (1974) 439.10 Yatirajam V & Ram J, Talanta, 20 (1973) 885..•f

Ferron as an Analytical Reagent for Extractive Separation of Molybdenum

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Ferron as an Analytical Reagent for Extractive Separation of Molybdenum

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