Reduction of ZrO2 in LiCl-Li2O Melt During Electrolysis

Abstract

Reduction of spent nuclear fuel (SNF) components to metals during the electrolysis of the LiCl-Li2O melt at 650 °C is extremely important in the framework of the development of fuel reprocessing technology. In the present paper the ZrO2 reduction by lithium during the electrolysis of the LiCl-Li2O melt at 650 °C was studied. Cathode processes on a molybdenum substrate in contact with different ZrO2 samples (powder, pressed pellet, dense ceramic) were analyzed using cyclic voltammetry and electrolysis. It was shown that the appearance of ZrO2 near the molybdenum cathode leads to increasing cathode currents and decreasing lithium oxidation current. Both effects indicate the consumption of reduced lithium for the reduction of ZrO2 samples. In order to analyze the reduction products X-ray phase analysis and scanning electron microscopy were used, and to estimate the reduction degree of ZrO2 samples three methods were tested: dissolution of samples in inorganic acid solution, dissolution of samples in EtOAc/Br2 solution, and carbothermal reduction. It was shown that during the electrolysis of dense samples only the lithium zirconate (Li2ZrO3) was formed at their surfaces, whereas the electrolysis of ZrO2 powder samples resulted in the formation of Li2ZrO3, Zr3O, and ZrO phases.