DETERMINATION OF CHROMIUM AND IRON DISTRIBUTION COEFFICIENT IN MOLTEN SALTS BY THE METHOD OF LINEAR SWEEP VOLTAMMETRY

摘要

By the method of linear sweep voltammetry the coefficients of chromium and iron distribution during electrorefining in chloride and chloride-fluoride melts have been determined. In chloride melts the Fe(Ⅱ) and Cr(Ⅱ) complexes are shown to discharge reversibly. In order to determine the distribution coefficients in chloride melts it is sufficient to know the values of potentials of Fe(Ⅱ) and Cr(Ⅱ) peaks of discharge and their concentration in the melt. In chloride-fluoride melts the Fe(Ⅱ) and Cr(Ⅱ) fluoride complexes discharge irreversibly and for calculating the coefficients of chromium and iron distribution it is necessary to determine not only the thermodynamic parameters but the kinetic parameters as well, i.e. the transfer and diffusion coefficients and standard heterogeneous constants of the rate of charge transfer as well. It was established that transition from chloride to chloride-fluoride melt does not lead to a considerable change in the value of the distribution coefficient. The formal standard potentials E~*_(Fe(Ⅱ)/Fe), E~*_(Cr(Ⅱ)/Cr), though becoming more negative, change by virtually the same values owing to the proximity of the iron and chromium ionic moments resulting in practically the same complexing ability.