Determination of antimony in concentrates, ores and non-ferrous materials by atomic-absorption spectrophotometry after iron-lanthanum collection, or by the iodide method after further xanthate extraction

Abstract

Methods for determining trace and moderate amounts of antimony in copper, nickel, molybdenum, lead and zinc concentrates and in ores are described. Following sample decomposition, antimony is oxidized to antimony(V) with aqua regia, then reduced to antimony(III) with sodium metabisulphite in 6 M hydrochloric acid medium and separated from most of the matrix elements by co-precipitation with hydrous ferric and lanthanum oxides. Antimony (≥ 100 μg/g) can subsequently be determined by atomic-absorption spectrophotometry, at 217.6 nm after dissolution of the precipitate in 3 M hydrochloric acid. Alternatively, for the determination of antimony at levels of 1 μg/g or more, the precipitate is dissolved in 5 M hydrochloric acid containing stannous chloride as a reluctant for iron(III) and thiourea as a complexing agent for copper. Then tin is complexed with hydrofluoric acid, and antimony is separated from iron, tin, lead and other co-precipitated elements, including lanthanum, by chloroform extraction of its xanthate. It is then determined spectrophotometrically, at 331 or 425 nm as the iodide. Interference from co-extracted bismuth is eliminated by washing the extract with hydrochloric acid of the same acid concentration as the medium used for extraction. Interference from co-extracted molybdenum, which causes high results at 331 nm, is avoided by measuring the absorbance at 425 nm. The proposed methods are also applicable to high-purity copper metal and copper- and lead-base alloys. In the spectrophotometric iodide method, the importance of the preliminary oxidation of all of the antimony to antimony(V), to avoid the formation of an unreactive species, is shown.