(712c) Solar Metallothermic Production of Rare Earth Elements

Rare earth elements (REEs) have many applications in metal alloys, catalysts, petroleum refining, glass additives, polishing compounds, and ceramics; they also underpin many critical clean energy technologies such as PV devices, batteries, high-performance magnets, and phosphors for lighting and electronics. The demand for rare earth elements is expected to grow in the coming years, especially in uses related to the energy sector. At present, the extractive processes for REEs and rare earth oxides (REOs) are driven by fossil fuel based energy sources with very high greenhouse gas impacts and resource depletion potential. The separation and reduction stages of the REO/REE production process have the highest energy and material consumption requirements.

Cerium (Ce), lanthanum (La), neodymium (Nd), and praseodymium (Pd) REEs and REOs accounts for 54, 25, 4, and 3% (86% combined) of the global REE supply and usage. Ce, La, Nd, and Pr metals are commercially produced by electrolytic processes where the anhydrous chlorides of the metals are dissolved in molten NaCl, KCl, CaCl₂, or other salts. The electrolysis of these rare earth chlorides must occur at approximately 50°C above the melting point of these metals, which are 795, 920, 1021, and 931°C for cerium, lanthanum, neodymium, and praseodymium, respectively.

Energy consumption and environmental concerns, coupled with the fact that the current electrolytic production method must occur at high temperature, provides significant motivation for investigating solar thermal processing as an alternative to conventional REE production. Here, the potential for solar metallothermic production of rare earth elements, especially Ce, La, Nd, and Pr, is critically evaluated using thermodynamic analysis.