Review—Metallic Lithium and the Reduction of Actinide Oxides

Abstract

Extensive research and process development has been conducted on the electrolytic reduction of actinide oxides in molten LiCl-Li2O. It is now accepted that the reduction of these metal oxides occurs via two separate reduction mechanisms: direct electro-chemical reduction and mediated chemical reduction by metallic lithium. The deposition of metallic lithium at the cathode (mediated chemical reduction mechanism) during the process is known to be essential in order to achieve high process throughputs and reduction yields, and yet a knowledge gap exists regarding the nature of metallic lithium in this system. This review summarizes the formation of lithium during the process and its dispersion into the molten salt electrolyte. Previously reported aspects of the physical chemistry of the LiCl-Li2O-Li system are presented with a specific focus on the dispersion of Li in the solution. Finally, issues regarding the effect of the presence of lithium on the electrolytic reduction process are discussed. Evidence shows that electrochemically generated metallic lithium is likely a significant source of experimental uncertainty, low current efficiency and Li2O consumption in the oxide reduction process.