Fundamental studies on the continuous electrolytic reduction of uranyl sulfate

Abstract

With the aim of developing a process for continuous electrolytic reduction of uranyl sulfate, the effects of temperature and HF concentration on the electrolytic reduction were investigated using both a rectangular cell and a bipolar cell. Some tests on the semicontinuous-type elec-trolytic reduction of U(VI) and the continuous monitoring of U(VI) in a catholyte were carried out to examine the feasibility of a process for continuous electrolytic reduction. The reduction rate and current efficiency of the electrolysis were increased with increasing temperature up to 333 K, due to an increase in the diffusion coefficient of uranyl sulfate. The presence of a small amount of HF in the catholyte improved the polarization characteristics of the electrolysis. The precipitation of uranous sulfate occurring in electrolysis above 323 K was eliminated by the addition of HF of 2.3 g dm^-3. However, the addition of the excess amount of HF causes the precipitation of UF₄ on the cathode surface during electrolysis. Increase in electric current was not effective in the semicontinuous electrolytic reduction of U(VI) for catholytes with high reduction ratios, and a catholyte with a composition of around 50 pct reduction ratio is pref-erable for continuous operation. The concentration of U(VI) in a catholyte can be monitored continuously either in the absence or in the presence of HF by using a device consisting of three small electrodes.