Precipitation of Iron, Tungsten, Molybdenum, and Chromium for Determination of Selenium and Tellurium in Alloy Steel by Inductively Coupled Plasma Atomic Emission Spectrometry

Selenium and tellurium impurities in metallurgical materials are difficult to determine directly by inductively coupled plasma atomic emission spectrometry (ICP-AES) as a consequence of spectral and nonspectral interferences from their major components. In this paper, we report separation of trace components (Se and Te) and macrocomponents (Fe, W, Mo, Cr, Cu, Ni, and Co) of alloy steel via precipitation. We demonstrate that the use of barium acetate and sodium fluoride as precipitants enables effective separation of selenium and tellurium from iron, tungsten, molybdenum, and chromium (less than 0.1 wt % of the initial concentration in the test solution) and partial separation from copper, nickel, and cobalt (25 to 55 wt % of the initial concentration in the test solution). We have optimized conditions for precipitation of the macrocomponents (iron, tungsten, molybdenum, and chromium) for subsequent ICP-AES determination of impurities: precipitation of the macrocomponents at pH 1; weight of the barium acetate and sodium fluoride precipitants, 10 and 3 g, respectively. We propose that hydrofluoric acid can be used to inhibit coprecipitation of selenium and tellurium on precipitates of macrocomponents. The optimal volumes of hydrofluoric and hydrochloric acids are 3 and 6 cm³, respectively. The procedure we developed for separation of trace components and macrocomponents was tested in analysis of alloy steel reference standards. The results of Se and Te determination by ICP-AES are characterized by satisfactory accuracy and reproducibility. The determination limit for the analytes after separation of the macrocomponents is 10^–3 wt %.