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.