Rapid chelatometric determination of bismuth, titanium and aluminium using Semi-Xylenol Orange with visual end-point indication

Abstract

A rapid and simple general complexometric method was presented for the determination of bismuth, titanium and aluminium in laboratory synthesized alloys similar to those of some bauxites, clay, ilmenite, Portland cements and ceramic products. The precision and accuracy attainable in successive titrations of Bi 3+, Ti 4+ and Al 3+ with 0.01 and/or 0.001 M solutions of disodium ethylenediaminetetraacetate (Na 2EDTA) and standard ZnCl 2 of the same concentration, using Semi-Xylenol Orange (SXO) as a metallochromic indicator with visual end-point indication were studied. For one aliquot Bi 3+ was at first directly titrated at pH 1–2 (HNO 3) with Na 2EDTA using SXO as indicator in the presence of L-ascorbic acid to reduce Fe 3+ to Fe 2+. At the bismuth end-point, an excess of Na 2EDTA was added, the pH was adjusted with hexamine buffer (pH 5) and the excess of Na 2EDTA was back-titrated with solution of standard zinc(II) chloride for both the simultaneous and consecutive titrations in the presence of (SXO) as indicator. For the simultaneous titration, fluoride was added to release the Na 2EDTA combined with both Al 3+ and Ti 4+. For the consecutive titration, phosphate was added to release the Na 2EDTA combined with Ti 4+ and then fluoride to release the Na 2EDTA combined with Al 3+. The interference of various anions and cations in the determination of Bi 3+, Ti 4+ and Al 3+ was studied. A comparison of the accuracy of both the simultaneous and consecutive titration was also carried out. The proposed methods were applied successfully to some real samples of bauxites, clay, ilmenite, Portland cements and ceramic products and the results were satisfactory.