Extraction and spectrophotometric determination of tungsten in ferro-niobium with TPAC-thiocyanate complexes

Abstract

One fifth gram of a sample was fused with potassium pyrosulfite and taken up with 50 ml of hydrochloric acid (1+2) containing 2 g of ammonium oxalate. It was diluted to 100 ml with water. To a 10 ml aliquot corresponding to ca. 100 μg of W were added 20 ml of hydrochloric acid and 5 ml of stannous chloride solution (20 w/v% in hydrochloric acid), and the mixture was boiled gently for about 2 min. to reduce tungsten. After cooling, it was transferred by washing with hydrochloric acid to a 200 ml polyethylene separatory funnel, and 5 ml of ammonium hydrogen fluoride solution (20 w/v%) was added as a masking agent for niobium. Each 3 ml of TPAC solution (0.025M) and sodium thiocyanate solution (15 w/v%) was added and shaken well. It was made up to 70 ml with hydrochloric acid and shaken vigorously with accurately 20 ml of chloroform for 2 min. The separated layer of chloroform was filtered through a dried paper, and the amount of tungsten was obtained by measuring absorbance at about 400 mμ. The method was successfully applied to the determination of about 0.5% of tungsten as an impurity in ferro-niobium.