Amidines as extractants: spectrophotometric determination of rhenium in ores as its ternary thiocyanato complex

Abstract

A sensitive method for the spectrophotometric determination of Re^IV is described. The method is based on the reduction of Re^VII to Re^IV by tin(II) chloride in H₂SO₄ and the extraction of the thiocyanato complex of the metal with amidine into chloroform over an acidity range of 3.5–6.5 M H₂SO₄. The complexes formed with 11 different amidines have molar absorptivities in the range 1.46 × 10⁴–2.35 × 10⁴ l mol^–1 cm^–1 with absorption maxima at ca. 435 nm in chloroform. Of the amidines investigated, N-(4-methylphenyl)-N′-phenylbenzamidine gave the highest sensitivity and was therefore selected for detailed studies. The detection limit of the method is 8 p.p.b. of Re. The effect of foreign ions on the extraction of Re was examined. The method is highly reproducible; it was applied to the determination of Re in an ore sample containing 40 p.p.m. of Re, with a relative standard deviation of 1.1%.