(280c) Electroytic Reduction of Zirconium Oxide in Molten LiCl-Li2O to Study Mass Transport of Li2O

Direct electrolytic reduction in molten chloride salt has been demonstrated for a number of different metal oxides. When using an electrolyte consisting of LiCl and Li₂O, minimization of lithium oxide retention in the reduced product is important for process efficiency and product quality.  In this study, zirconium oxide reduction in this salt has been experimentally investigated. Cyclic voltammetry with a basket containing zirconium oxide as the working electrode was used to assess the relative importance of lithium oxide electrowinning versus direct electrolytic reduction of the zirconium oxide.  It is theorized that a high rate of direct ZrO₂ reduction coupled with limited mass transport of Li₂O will result in excessive Li₂O buildup in the cathode basket. This effect was tested via electrolytic reduction experiments in which basket rotation and periodically interrupted cell current were used to minimize accumulation of Li₂O in the cathode basket.  To provide data for future modeling, the solubility of metallic lithium was measured as a function of lithium oxide concentration in the lithium chloride.  The reported experiments were performed in an argon atmosphere glove box, with low oxygen and moisture concentrations.  All experiments were run at a temperature of 650°C.  Electrode potentials were measured and controlled versus a nickel/nickel oxide reference electrode. The anode used for these experiments was made of platinum wire and was purged with argon to enable continuous measurement of oxygen gas produced from the reaction.