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.