Abbasi, Shahid Abbas

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Aqueous-ethanol medium has been found to producestable colour. Interfering ions like Fe3+, Ti4+, etc.,are removed during carbonate fusion and subsequentaqueous extraction. The vanadium present in thesolution reacts immediately with SHA under theexperimental conditions and full colour is developedimmediately which remains stable for more than24 hr. This procedure is particularly suitablefor the estimation of vanadium in bauxite, magnetite,ilmenite, etc. In view of purity, availability, goodsolvent property and bettor extraction efficiency,methyl isobutyl ketone (MIBK) has been preferredas the extracting solvent to alcohols or esters usedby other workers. The coloured complex can bequantitatively extracted by a single extractionwith MIBK at pH 3, which makes the proceduresimple and rapid. The method is sensitive as wellas accurate and can be applied successfully for thedetermination of vanadium in various types ofrocks, minerals, ores, etc., where vanadium ispresent in the p.p.m. Icvel.References1. BHADUI<I, A. S. & RAY, P., Z. analyt . Chem., 154 (1957),103.2. KORISCH. J .. Modern methods for the separation of raremetal ions (Pergamon, London) 1969, 444.3. MAXWELL. J. A., Rocks and minerals analysis (Lo terscio tce,LOIl<ton), 1968, 273.4. BHADURI, A. S.• Z. analyt, Chem., 151 (1956), 109.5. ROUBAULT, M., ROCHE. H. L. & GOVINDARAJU. K.,Sciences Terre, 13 (1968), 381.6 FLANAGAN, F J., Geochim, cosmochim: Acta, 33 (1969),81.Rapid Separation & SimultaneousSpectrophotometric Determination of U(VI)Using N -m- Tolyl-o-methoxybenzohydroxamicAcidSHAHIn ABBAS ABBASIDepartment of Chemistry, Iridian Institute of TechnologyPow;,i, Bombay 400076Received 29 August 1975; accepted 1 November 1975A method is presented for rapid liquid-liquid extrac-tion and simultaneous spectrophotometric determina-tion of U(VI) in the presence of various anions andcations which are usually associated with it using N-m-tolyl-o-methoxybenzohydroxamic acid (TMBHA) inchloroform. The effect of various parameters such aspH reagent concentration, volume of mother liquor,forei~n iOIlS, etc., on the extraction and determina-tion of uranium is discussed. The sensitivity ofcolorimetric determination of U(VI) with the presentmethod is about 8 times more than the sensitivityof the most sensitive hydroxamic acid method usedhitherto.THE first dC.t<l.iled.cxaminat inn of N -phcnylbcnzo-~ydrox;,.m1C ~:cld (PBHA) as a reagent foruranium w.is carried out reccnt ly-, It was foundthat in the extraction of U(VI), manv c.uiorr.interfered and the colour of the extracted U(VI)-PBHA complex with Am~x = 510 nm was suitableNOTESonly for the determination of milligram quantitiesof uranium, the molar absorptivity at Aam:l beingas low as 230. The selectivity was also low andno attempt was made to counter the interferenceof various common and less-common metals whichare associated with uranium in minerals and fissionproducts. Subsequently N -phenyl-Z-naphthohydro-xamic acid (PNHA) was prepared and tried as areagent for U(VI)2. PNHA, though proving highlysensitive and selective for V(V)3, came off as onlya marginal improvement on PBHA in case of U(VI),in both sensitivity and selectivity.N - m - tolyl - 0 - methoxybenzohydroxamic acid(TMBHA) is now presented as a reagent moreselective than either PBHA or PNHA and abouteight times more sensitive than PNHA for theextractive colorimetric determination of U(VI).All the chemicals used were of reagent gradeunless specified. Conductivity water was used forall purpose. A stock solution of U(VI) was preparedby dissolving uranyl nitrate (0'5 g) in water (1 litre)and standardizng the solution for uranium'.TMBHA was prepared by the method of Guptaand Tandon-, and recrystallized repeatedly, m.p.110° (liP m. p. 1110). The reagent is very stableif stored out of contact of light and air. A O'IMsolation of TMBHA in ethanol-free doubly distilledchloroform was us cd for extraction work.PH measurements were carried out with a radio-meter j)H meter type PHM-29. The absorptionspectra were recorded on a Perkin-Elmer model402 r pcctrophotomctcr and measurements at aconstant wavelength were done with a SF-4 (USSR)spectrophotometer. All optical measurements werecarried out using matched quartz cells with 10 mmpath-length,Extraction procedure ~ An aliquot solution ofU(VI) containing 15 to 950 f.tg/ml of uranium wasadjusted at PH 4·4-5,2 with the help of dil. NaOHor HNOs' To it was added TMBHA solution(4 ml) in chloroform and the two phases equilibratedfor about 5 min, kept aside for complete separationand the chloroform layer removed. The aqueouslayer was again extracted with a fresh 4 ml portionof TMBHA for 5 min, the chloroform extract mixedwith the first ex ract , dried (N?'2S04), and madeup to 10 ml with TMBHA solution. The ab=orbanceof the orange-yellow extract was measured againstTMBHA solution as blank. The extracts containing15-90 f.tg/ml of uranium were measured at 360nm anti those containing 80-950 [J.g/ml of uraniumwere measured at 520 nm. A calibration curvewas set by extraction-colorimetric determinationof several known amounts of uranium and plottingthe optical density values against concentrationof uranium. The results were found reproduciblewithin ± 0·5%.The ab=orpt ion spectra of uranium extract ofTMBHA in chloroform against reagent (TMBHAsolution in chloroform) blunk exhibits a sharp peakat 360 nm and a broad peak at 518-522 nm. Beer'slaw is obeyed in the range 15-90 (J.g/ml of U(VI)at 360 nm and 80-950 f.tg/ml of U(VI) at 520 nm;the molar absorptivities being 2 X 1(,3 at 360 nmand 285 at 520 nm. Thus uranium, if present inconcentrations less than 90 (J.g/ml can be determined547INDIAN J. CHEM., VOL. 14A, JULY 1976using the 360 nm peak while milligram concentra-tions of uranium can be determined at 520 nm.The sensitivity of the present method, calculatedaccording to the definition of Sandells is 0-12 (log/mlof U{VI). This is about 8 times more than thesensitivity of PNHA methods. It is to be pointedout here that for the PNHA method, the sensitivityhas wrongly been reported as 0-01 (Jog/ml. Fromthe optical density values the sensitivity comes outto be 1·0 (J.g/ml. The colour of the U(VI)-T-MBHAcomplex, was found to be stable up to 12 days.The extraction is quantitative in the PH range4-4-5-1. Below and above these PH values theextraction decreases. The optimum reagent concen-tration is 0-IM for complete extraction. Higherreagent concentrations can be used without dis-advantage.A change in the ratio of volumes of chloroformto a9..ueousphases from 1 to 20 does not effect theUeVI) extraction so that the present method canbe used to concentrate uranium from its dilutesolutions.The tolerance limit for 10 ml aliquot of U(VI)solution containing 760 (logof U(VI) was set at theamount required to cause ±2'O% error in theuranium recovery. It wasobserved that the presenceof 30000 ppm of La(III); 20000 ppm of Mn(II),Na(I), K(I); 16000 ppm of Mg{II), bromide, iodide;10000 ppm of Pb(II), Zn(I1), Ba(I1); 8000 ppm ofCa{II), Sr(II), Hg(II), Ni(II), Co(II), As(III), Ge(IV);6000 ppm of Ga(I1I) and 1000 ppm of phosphate,cyanide are tolerated. The interference due toBi(III), Th(IV) and Ce(I1I) can be eliminated using548EDTA and magnesium chloride as masking agents.Tungsten (VI), Zr(IV), Mo(VI), Fe(llI) and V(V)should be removed prior to the extraction of U(VI).Composition of the U(VJ)-TMBHA complex-Job's method of continuous variation, as modifiedby Vasburgh and Cooper", was employed to studythe composition of the orange-yellowU(VI)-TMBHAcomplex. The stoichiometry was found to be 1: 2(metal-ligand).Formation of 1: 2 complex neutralizes the dipo-sitive charges of uranyl ion and renders the complexhydrophobic and susceptible to extraction in chloro-form.In the present method, the overall extractionand determination takes less than half an hour,and it is possible to extract and determine micro-gram to milligram amounts of U(VI) in the presenceof several ions. Thus the method is rapid, simpleand selective.The author is grateful to the CSIR, New Delhi,for a senior fellowship and to G. Kaparwan forassistance...---References1. AGRAWAL, Y. K, Separation su., 8 (1973), 387.2. AGRAWAL, v. K, Separation Sci., 8 (1973), 709.3. AGRAWAL. Y. K, Analyt. Chem., 47 (1975), 940.4. WELCHER, F. W., The analytical use of ethylenediamine-tetracetic acid (Van Nostrand, New York), 1958.5. GUPTA. Y. K. & TANDON, S. G., J. Indian chem. soc., 46(1969), 831.6. SANDELL, E. B., Colorimetric determination of traces ofmetals (Interscience, New York), 1959.7. VOSBURGH, W. C. & COOPER, G. R., J. Am. chem. Soc.,63 (1941), 437.Ii'

Rapid Separation & Simultaneous Spectrophotometric Determination of U(VI) Using N-m- Tolyl-o-methoxybenzohydroxamic Acid

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Rapid Separation & Simultaneous Spectrophotometric Determination of U(VI) Using N-m- Tolyl-o-methoxybenzohydroxamic Acid

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