Alternative Thermodynamic Pathway for Producing Neodymium from Oxide Through Molten Solution Non-Ideality and Hydride Precipitation

Abstract We present a novel sustainable method for producing neodymium (Nd) metal. Environmentally sustainable production of rare-earth elements is critical for enabling green technologies. However, Nd, a key rare-earth element used in high-performance magnets for applications such as electric vehicles and wind turbines, is currently produced via an energy-intensive molten-salt electrolysis process. This process releases direct CO₂ emissions as well as perfluorocarbons, which possess a warming potential thousands of times higher than that of CO₂. In this article, we report the discovery of a two-step metallothermic pathway for producing Nd metal from Nd oxide (Nd₂O₃) with zero direct emissions. In this approach, magnesium (Mg) reduces Nd₂O₃, forming an Mg-Nd alloy containing up to 50% Nd by mass. Magnesiothermic reduction of Nd₂O₃ has historically been considered unfeasible because the free energy change of the reaction is positive under standard conditions. However, thermodynamic modelling and experiments in this work demonstrate that the free energy of mixing of the molten Mg-Nd alloy overcomes this energy barrier, enabling a thermodynamically unfavorable reaction to become favorable. Hydrogen is then used to precipitate solid Nd hydride (NdHy) from this alloy, separating the Nd from the alloy and enabling reduction of additional Nd₂O₃. This work demonstrates the thermodynamic viability of this pathway and provides a general approach that could inform the design of new metallothermic reduction pathways.