Iron(II) oxidation by SO2/O2 for use in uranium leaching

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 SO2/O2 gas mixture was investigated in order to provide an iron(III) stream for uranium extraction. The effects of pH, temperature and SO2/O2 volumetric ratios were considered. Oxidation of iron(II) by SO2/O2 was controlled by diffusion of SO2 or O2 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 SO2 or O2 diffusion. The oxygen efficiency for a fixed reactor set-up was dependent on the SO2/O2 ratio and total flow rate of the gas. In leach tests, the uranium extraction achieved with iron(III) solution prepared by SO2/O2 oxidation was the same as that for a standard uranium leach with conventional oxidant.