Zirconium Metal Production by Electrorefining of Zr Oxycarbide

In the present study, a cost-affordable electrorefining process of zirconium (Zr) using an oxycarbide anode, which has been developed for titanium (Ti) smelting, was applied to Zr production. First, the synthesis of Zr oxycarbide by carbothermic reduction of ZrO2 was investigated, and a dense and conductive ZrC0.5O0.5 anode was successfully produced followed by sintering. The reduction steps of Zr ions in a chloride electrolyte were then electrochemically analyzed; the Zr (IV) ion was electrochemically reduced to Zr metal through the formation of a low-valence Zr (probably Zr (II)) ion. In contrast, Zr (IV) ion was stabilized by F− coordination in a chloride-fluoride electrolyte, and the reduction to Zr metal mainly occurred through a single step. The cathode reaction for electrorefining was checked, and Zr was obtained by galvanostatic electrolysis in a chloride-fluoride bath. The anode reaction using a ZrC0.5O0.5 anode was investigated, and the dissolution of Zr (IV) ion accompanied by CO evolution was observed. Electrorefining experiment showed that a series of electrorefining, anodic dissolution to form Zr ions, transportation of Zr ions from the anode to cathode, and cathodic reduction to produce metallic Zr were appropriately coordinated. For achieving good results in the electrolysis, it is essential to introduce F− ions into the electrolyte and to apply high cathode-current–density (optimally over 1000 mA·cm−2). Through the present study, the feasibility of Zr production based on the electrorefining of Zr oxycarbide synthesized by the carbothermic reduction of ZrO2 was demonstrated in principle.