Feasibility study of electrochemical conversion of solid ZrO₂ to Zr metal in LiCl-(0-1 wt%)Li₂O melts with graphite and platinum anodes

Direct electrochemical reduction of solid ZrO₂ to Zr metal assumes importance in the context of pyrochemical reprocessing of spent oxide nuclear fuel. In this context, electrochemical reduction experiments were carried out with powder compacted and sintered ZrO₂ pellets as cathode in LiCl-x wt.% Li₂O (x = 0, 0.1, 0.25 and 0.5) melts against graphite anode and in LiCl-(0.5 and 1.0) wt.% Li₂O melts against platinum anode at 650 °C and the samples were analysed using XRD and SEM combined with EDS techniques. The pellets were found reduced to Zr in pure LiCl melt and to Zr and smaller amounts of Li₂ZrO₃ in LiCl-Li₂O melts under specific experimental conditions. Similar cathodic polarization experiments carried out with Li₂ZrO₃ pellets converted those to a mixture of Zr and Li₂ZrO₃. Contrary to the results reported in the literature by earlier workers, the results of this study make it quite clear that both solid ZrO₂ and Li₂ZrO₃ can be electro-reduced to Zr in LiCl-Li₂O melts. However, the study carried out with two different cathode configurations reveal that the efficiency of electro-reduction is strongly influenced by the design of the oxide electrode and to some extent the Li₂O content of the melt.