Reduction of ZrO2 during SNF Pyrochemical Reprocessing

Abstract

Reduction of ZrO₂ by lithium during electrolysis of LiCl-KCl-Li₂O melt at 650 °C was studied using a set of physicochemical methods of analysis. Influence of ZrO₂ in the space near a molybdenum cathode on the kinetics of the cathode process was established. Possible variations of the electrode reaction associated with the zirconium reduction were proposed. The appearance of ZrO₂ in the cathode space resulted in consumption of reduced lithium and in increase in the potential relaxation time of the molybdenum cathode after cathode polarization. Long-term galvanic impulse electrolysis of LiCl-KCl-Li₂O melt at 650 °C was carried out using the molybdenum cathode which was immersed into the ZrO₂ powder. According to the X-ray fluorescence analysis as well as the method of nuclear reactions the reduction product was presented by the ZrO₂, Li₂ZrO₃, Zr₃O phases. Additionally, by alloying the reduction product with tin, the ZrO₂ reduction degree to metallic zirconium was estimated, which was close to zero. It was assumed that the main pathway for the appearance of the metallic zirconium in the ZrO₂ reduction product during electrolysis of the LiCl-KCl-Li₂O melt was direct electroreduction of dissolved zirconium in the melt.