Molten salt electrolysis of neodymium: electrolyte selection and deposition mechanism

Abstract

Molten salt electrolysis of neodymium from Nd2O3 can be a viable alternative to calciothermic reduction. Two important issues merit attention: selection of an appropriate electrolyte and the mechanism of the neodymium deposition reaction. Cyclic voltammetry experiments and melting point considerations point to the eutectic LiF–CaF2 as an appropriate electrolyte. The presence of CaF2 polarises the Li deposition reaction to more cathodic potentials, thereby providing a larger potential window for the deposition of neodymium. Experiments with the LiF–CaF2–NdF3–Nd2O3 and LiF–CaF2–LaF3–Nd2O3 melts suggest that both [NdF6]3− and [NdOF5]4−, depending on their molar ratios, can be reduced to neodymium.