Iron(II) oxidation by SO 2/O 2 for use in uranium leaching

Abstract

Iron(III) can be used as an oxidant in the leaching of uranium ore in an acid medium. The oxidation of iron(II) to iron(III) using an SO 2/O 2 gas mixture was investigated in order to provide an iron(III) stream for uranium extraction. The effects of pH, temperature and SO 2/O 2 volumetric ratios were considered. Oxidation of iron(II) by SO 2/O 2 was controlled by diffusion of SO 2 or O 2 at pH 2 and 40 °C. However as the pH decreased below pH 1, the reaction was controlled by a slow chemical step and the reaction rate decreased. Increasing the temperature increased the oxidation rate at pH 0.8, and at 70 °C the rate again became dependent on SO 2 or O 2 diffusion. The oxygen efficiency for a fixed reactor set-up was dependent on the SO 2/O 2 ratio and total flow rate of the gas. In leach tests, the uranium extraction achieved with iron(III) solution prepared by SO 2/O 2 oxidation was the same as that for a standard uranium leach with conventional oxidant.