Spectrophotometric determination of indium in nickel alloys and zinc ores with 1-(2-pyridylmethylideneamine)-3-(salicylideneamine)thiourea

Tahmta,Vol. 33,No. 7,pp.607-610,1986 Printed in Great Britain

W39-9140/86$3.00+0.00

Pergamon Journals Ltd

SPECTROPHOTOMETRIC DETERMINATION OF INDIUM IN NICKEL ALLOYS AND ZINC ORES WITH 1-(2-PY RIDY LMETHY LIDENEAMINE)-3(SALICYLIDENEAMINE)THIOUREA DANIEL ROSALES, ISABEL MILLAN and JOSEL. GOMEZ ARIZA Department of Analytical Chemistry, Faculty of Chemistry, University of Sevilla, 41012 Sevitla, Spain

(Receiwd 12 September 1985. Accepted 23 Nooember 1985) Summary-A sensitive method for the spectrophotometric determination of indium with 1-(2-pyridylmethylideneaminef-3-(salicylideneamine)thiourea is proposed. A yellow complex is formed at pH 4.5 (succinate buffer) in a medium containing 40% dimethylformamide, and the absorbance is measured at 415 nm. The molar absorptivity is 6.2 x lo4 l.mole-’ .cme’l. The relative standard deviation of the procedure is 1.5%. The method has been applied to determination of indium in a nickel alloy and three zinc ores, with prior isolation of indium by co-precipitation with ammonia and extraction into n-butyl acetate from SM hydrobromic acid.

The content of indium in the earth’s crust is about IO-‘%. In sphalerites, chalcopyrites, sulphostannates and sulphogermanates, which are the principle sources of indium, the content ranges from less than 10m4% to IO-‘%.’ Indium is usually recovered as a by-product in the zinc industry, and is responsible, together with lead, cadmium and tin, for the embrittlenlent of zinc alloys.* Indium is used to protect bearings from corrosion, as a semiconductor, in non-ferrous me~liurgy, in electric contacts and reflectors, in the jeweilery trade, in fluorescent glass and in the dental profession, Certain indium compounds are also used as colouring matter in the ceramic industry. The indium content in different materials has been determined by several methods: polatographically in beryllium compounds,3 zinc and zinc alloys’,2,4 and pure tin5 by anodic-stripping voltammetry in tim6 by radioactivation methods in feldspars,7 cylindrite,” gallium,‘.’ zinc,‘,9.‘0rocks’,“.” and biological materials; 13 titrimetrically with EDTA in aluminium’” and sphalerite;’ by emission spectroscopy in minerals and rocks,‘.‘5 aluminium alloys,r6 cadmium” and zinc spectrometry in alloys;‘” by atomic-absorption foodstuffs,” sulphides,Z0,2’ aluminium,” zinc’* and nickel alioys;22 by infrared spectroscopy in silicon crystals, .23 fluorimetrically with Rhodamine 6Zh in gallium.‘~ with quinolin-8-01 in dusts* and with Butylrhodamine B, sulphonazo and Rhodamine 6G or 3B in minerals;20.24-26and spectrophotometrically with dithizone in uranium and thorium salts,2s mineral and zinc compoundszO.** and germanium,29 with diphenylcarbazone in germanium,24 with arsenazo,30 6F,33 Bromorin3’ salicylfluorone, 32 Rhodamine mopyrogailol Red, 34 S~7-dibromoquinolin-8-ol,2d~35~36 Methylthymol Bluer4 and Rhodamine 6Gz6 or B27in

with zinc compounds matrices, or similar 4-(2-pyridylazo)resorcinol in minerals3’~37 and silver-tin alloys3s with quinalizarin in organic matter,’ with phenyl~uorone in lead concentrate,” with qu~nolin-8-01 in cylindrite,* germanium~ and ores,24,26 with trihydroxylfuorones in cassiterite,” with Malachite Green in galliumz6 and with f -(2-py~dylazo)-2-naphthol in zinc compounds39 and geranium films.@ In almost all these methods, a prior separation of indium from associated elements is necessary. Separations have been done by extraction of the bromide or iodide complex into diethyl ether,‘+3,26~29”t di-isopropyl ether,28s”,4’ n-butyl acetate,‘5j26 chloroform26 and diantipyrylmethane;26 with dithizone into chloroform;1*27*4’with an alkylphosphoric acid into octane;26 with thiosulphate into 15% tributyl phosphate in kerosine;42 with diethyldithiocarbamate into isobutyl methyl ketone;r6sz6 with quinolin-8-01 into chloroform;’ and with thiothenoyltrifluoroacetone.32 Separations have also been done by precipitation with hydrogen sulphide,41 ammonia’~26~41or sodium hydroxide; Is4by hydrolysis with potassium cyanate;’ and by ion-exchange’*14~20~41*U or chromatographic methods.‘~‘2~25Indium can be preconcentrated by co-precipitation with cadmium, aluminium or iron(111).26*” During studies on Schiff’s bases derived from thi~arbohydrazide~’ it was found that the asymmetric compound l-(2-pyridylmethylideneamine)-3(salicylideneamine)thiourea (PST) behaves as a sensitive reagent for the spectrophotomet~c determination of indium. In this paper, development and testing of the method involving the use of PST is described. The method has been applied to the determination of indium in several samples.

607

DANIELRO~ALE~el al

608 EXPERIMENTAL Apparatus

Perkin-Elmer Model 554 and Coleman Model 55 spectrophotometers and a Beckman Model 70 pH-meter with a combined SCE-glass electrode were used. Reagents

All chemicals used were of analytical-reagent grade or better. Water that had been glass-distilled and demineralized was used throughout. A 0.1% PST solution in dimethylformamide (DMF) was prepared from PST.H,O, which was synthesized as described previously.45 This solution was stable for 3 months. A standard solution of In(III) (4.742 g/l.) in 1M hydrochloric acid was prepared from indium nitrate pentahydrate and standardized by EDTA titration. Working solutions were prepared by suitable dilution. A succinate buffer of pH 4.5 was prepared by dissolving 12 g of succinic acid and 17 g of potassium hydroxide in distilled water and diluting to 1 litre. Recommended procedure

Into a 25-ml standard flask, transfer an aliquot of sample solution containing up to 37 fig of indium, 3-5 ml of pH 4.5 succinate buffer, 3 ml of 0.1% PST solution and 7 ml of DMF. Dilute to the mark with water and mix well. Measure the absorbance at 415 nm (1 .O-cm cell) against a similarly prepared reagent blank. Use a calibration graph or empirical equation to convert the absorbance into concentration. Determination of indium in alloys and ores

Weigh accurately about 1 g of sample, transfer it into a beaker, heat it first with 5 ml of concentrated hydrochloric acid and then with 10 ml of concentrated nitric acid and 2 ml of bromine, and evaporate the solution nearly to dryness, on a sand-bath. Then add 2 ml of concentrated sulphuric acid and heat until copious white fumes are evolved. After cooling, take up the residue with approximately 25 ml of 1.5M hydrochloric acid and filter the solution through a Whatman 41 filter paper into a 50-ml standard flask. Wash the beaker and filter paper with 1.5M hydrochloric acid to make up the volume to the mark. Place 25 ml of this solution in a 250-ml beaker and dilute it to -50 ml with water. Add concentrated ammonia solution dropwise with stirring until the solution is alkaline, then let it stand for 15 min. Filter (Whatman 44 filter paper) and wash the residue with 50 ml of 1% ammonium chloride solution adjusted to pH 9 with ammonia. Discard the filtrate. Dissolve the residue by adding l&20 ml of 5M hydrobromic acid dropwise and transfer the solution into a 100-m] separating funnel. Reduce iron(II1) by addition of several drops of 15% titanium(II1) chloride solution and extract the indium by shaking with 10 ml of n-butyl acetate for 3 min. Discard the aqueous layer and wash the extract by shaking it first for 1 min with 3 ml of 5M hydrobromic acid containing 2 or 3 drops of 15% titanium(II1) chloride solution and then with 3 ml of 5M hydrobromic acid for 30 sec. Strip the indium from the organic phase with two 20-ml portions of 6M hydrochloric acid containing 2 or 3 drops of 30% hydrogen peroxide. Evaporate the solution to dryness on a sand-bath, dissolve the residue in water and dilute it to volume in a 25-ml standard flask. Determine the indium content by the recommended procedure, using 5 ml of buffer solution. RESULTS AND DISCUSSION PST and In(II1) in weakly acid media form a yellow complex which has an absorption maximum at 415 nm. The intensity of the colour developed remains constant with at least a 7-fold molar excess of reagent, and a 3-ml volume of 0.1% reagent solution was therefore chosen. The absorbance of the complex

at 415 nm is independent of pH over the range 4.0-5.5. In preliminary studies it was found that large amounts of acetate decrease the absorbance of the complex, so a succinate buffer of pH 4.5 was selected for the analytical procedure. The amount of this buffer added (l-5 ml) has no effect on the absorbance. The absorbance of the reagent blank at 415 nm was 0.037 &-0.003 (7 samples). Choice of solvent

The absorption spectra of the In(IIItPST complex at pH 4.5 in various water-soluble solvents were similar. A mixture of water and DMF was chosen because the reagent was more soluble in it. The concentration of DMF affects the absorbance of the complex, but the absorbance is constant over the range 2848% v/v DMF and a medium containing 40% DMF is recommended. In this medium the complex is stable for more than 1 month. The order in which the reagents are added was found to be immaterial. Stoichiometry of the complex

The continuous-variation and mole-ratio methods failed because the complex is weak. Therefore, a modified Holme and Langmhyr method46 and that of Asmus4’ were applied to the mole ratio data. Both methods showed that the composition of the complex was 1: 1. The conditional formation constant at pH 4.5 was 5.25 f 0.10.45 Calibration and precision

Beer’s law is obeyed over the range O-1.5 ppm indium. The molar absorptivity is 6.2 x lo4 1.mole-‘. cm-‘, which compares well with the values obtained for other complexes used for spectrophotometric determination of indium. The optimum working range, as evaluated by Ringbom plot, is 0.3-1.5 ppm indium. The relative standard deviation (P = 0.05) found was 1.0% for 0.57 ppm of indium (11 samples). For investigation of betweenday variation, single determinations were made on eleven different days. All absorbances were within the range 0.301-0.320 (0.57 ppm indium) and the relative standard deviation was 1.5%. This is a better value than the 5% obtained in the extractive spectrophotometric determination of indium with dithizone.48 Interferences

Results of the interference studies are given in Table 1. The tolerance criterion was taken as the largest amount of foreign ion causing an error of not more than k 5% in the determination of 0.57 ppm indium. Cations interfered by giving higher absorbance or opalescence, whereas anions gave lower absorbance, except for iodate, periodate and nitrite, which oxidized the reagent, giving a yellow colour. Attempts to eliminate the interferences by addition of masking agents were unsuccessful. It must be noted

Spectrophotometric Table 1. Tolerance for foreign ions in the dete~ination 0.57 ppm indium

determination of

Tolerance, Ion or species

PPm

> 1000

Alkali metals, Be(B), Mg(II), Ca(II), Sr(II), Ba(II), AKIII), ThI). NH:, B&O:-, NO;, SO:-, ClO,,

SO:--,

SCN-,F--i

Cl’,

‘Br-,

I’,

CIO;, BrO;, CO:-., acetate, trichloroacetate, ascorbate 100 Ga(III), Y(IIi), La(III), Ce(IV), Th(IV), U(VI). Zr(IV), NO;, As@-, AsO;, SeO:-, IO;, IO;, tartrate 30 Mo(VI), W(VI), Mn(II) 20 Sn(II), Sb(III), Ti(IV), Cr(II1) 10 PUi-. p20;-, s>o;.5 C,O:-, citrate 3 Os(VIII), Ag(I), Au(II1) 0.5 Pb(I1) 0.1 Bi(III), V(V), Cu(II), Hg(I1) 0.05 Fe(H), Fe(III), Co(I1). Ni(II), Pd(II), Zn(II), CdjII) <0.05 EDTA, Sz-

that there were high tolerance levels for Be, Al, TI(1) and Ca.

Owing to the fact that the reagent PST is not enough for the direct determination of indium in alloys and ores, a prior separation from interfering ions is necessary. Attempts were made to separate indium by extraction into diethyl ether or selective

Table 2. Determination

n-butyl acetate from hydrobromic acid solution, following the method described by Busev et al.” but were unsuccessful because anodic-stopping voltammetry tests showed that the extracts were contaminated with lead, zinc and nickel (this last only in the case of the nickel alloy), and chemical tests also showed the presence of iron. Therefore, a double separation of indium by co-precipitation with Fe(III) or Al(III) hydroxide, then extraction of HInBr, into n-butyf acetate, after reduction of Fe(II1) with Ti(III), was chosen. When this method was used, anodic-stopping voltammetry showed only the presence of trace amounts of lead, which could be removed by treating the sample with sulphuric acid. The procedure was used to determine the indium content of a nickel alloy and three zinc ores. The results obtained are given in Table 2 and are in good agreement with those quoted in the certificates of with analysis, and with the results obtained 1-(2-pyridylazo)-2-naphthoi. Other reagents have been proposed for the spectrophotometric dete~ination of indium (Table 3), but most of them are less sensitive than PST. The disadvantage of the low selectivity of PST, which is common to all reagents for the spectrophotometric determination of indium, may be overcome by coprecipitation with Fe(M) or AI(M) hydroxide and extraction with n-butyl acetate from hydrobromic acid solution. In this manner, indium contents as low as 20 @g/g in alloys and ores can be accurately

of indium in a nickel alloy and zinc ores

Amount taken, g

Indium found,* %

Zn-Sn-Cu-Pb Ore Zinc concentrate Zinc blende

1.0120 1.0147 I .0200

0.0330 & 0.0006 0.0187 f o.ooo2 0.00288 f O.OOOl I

Nickel alloy

1.3966 0.00228 f 0.~8

Sample

609

of indium

Indium content, % 0.033t o.or9t 0.00269$ 0.~20~ 0.00222§

*Mean and range of three determinations. *Certificate content. (jBy the I-~Z-pyridyla~o)-2-naphthol method.‘@ Mean of three determinations. SApproximate content given in the BCS certificate.

Table 3. Comparison with other reagents used for the spectrophotometric Optimum PH

I._,, nm

a* 1031.mofe-‘.ctn-i

5.2-6.2

630

123

6.5-10.5 4.0-5.5 6.5-9.0

510 415 540

69 62 42.5

4-(2-PyridyIazo)resorcinol I-(2-Pyridylazo)-2-naphthol

3.4-4.5 5.&&O 5.4-6.7

510 545 560

32.7 24.5 21.2

Rhodamine S 5,7-Dibromoquinoiin-8-01 Quinolin-8-01 Xylenol Orange

HBr 3.c4.5 3.2-4.5 3.7-6.5

530 415 400 560

23.5 17.6 15.0 IS.0

Reagent Chrome Azurol S and cetrimide Dithizone PST Bromopyrogallol Red

determination of indium Remarks

Ga(III), Al(JI1) interfere Extraction into 40% DMF Extraction into alcohol Ga(III), AI(II1) 24% DMF Extraction into Extraction into Extraction into Extraction into Ga(III), Al(II1)

Ref. 49

CHCI,

48 This work

benzyl

34

interfere

24 40 40 41 36 41 41

CHCI, benzene CHCI, CHCI, interfere

DANIELRO~ALESet al.

610

determined with a l-g sample. A further advantage of the method is the high stability of the complex. Acknowledgement-We

Roldan Gonzales tests.

thank D. Gonzalez Arjona and E. for the anodic-stripping voltammetry

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