Direct Two Step Solar Metallothermic and Electrolytic Production of Rare Earth Elements from Oxides

Rare Earth Elements (REEs) exhibit a range of unique electronic, optical and magnetic properties which make them attractive for many niche applications, including metal alloys, catalysts, petroleum refining, glass additives, polishing compounds, and ceramics. The demand for rare earth elements is expected to grow in the coming years, especially in uses related to critical clean energy technologies such as PV devices, batteries, high-performance magnets, and phosphors for lighting and electronics. Cerium (Ce), lanthanum (La), neodymium (Nd), and praseodymium (Pd) account for ~86% of the total global REE consumption. The current electrolytic production route through molten chlorides is quite inefficient due to the stability of Re⁺² ion in chloride melt, whereas the oxide-fluoride route suffers from low solubility of oxides in fluorides. Additionally, these extractive processes are currently driven by fossil fuel based energy sources with very high greenhouse gas impacts and resource depletion potential.

Energy consumption and environmental concerns, coupled with the fact that the current electrolytic production method must occur at high temperatures, provides significant motivation for investigating solar driven metallothermic/ electrolytic processing routes as alternatives to conventional REE production for providing “clean” high temperature process heat and electricity. In this work, a new two-step REE production route consisting of direct metallothermic reduction of RE-oxides using Ca and subsequent electrolytic recovery of metallic Ca in a mixed chloride bath has been explored from the theoretical energy consumption perspective. The new process is critically evaluated using thermodynamic analysis and compared with the state-of-the-art. The two-step process shows promise in terms of significant improvement in the energy efficiency compared to the current electrolysis routes. The potential technological challenges in scale-up and impact of solar variability will be discussed as well.