Rare earth elements (REEs) are an essential component in permanent magnet materials used in consumer electronics, industrial motors, and renewable energy technologies needed to bring the world to a low carbon future. According to a U.S. Geological Survey, the world mined 350,000 metric tons of REEs in 2023, and the International Energy Agency (IEA) predicts the demand to grow six-fold by 2050. Due to the lack of concentrated deposits, mining is not sufficient to meet these growing demands and recycling consumer materials containing rare earths is a promising source of these critical materials. Current metallurgical methods such as hydrometallurgical leaching use large volumes of corrosive chemicals (H₂SO₄, HNO₃, HCl, etc.) to separate and produce rare-earth salts. Through subsequent roasting, oxides are formed as raw materials for conventional metal production. The ensuing acid waste has detrimental effects on the environment and is costly to treat, and thus it is imperative to employ environmentally friendly techniques to recycle REEs. One approach is recycling REEs in the absence of acids, which will significantly reduce waste generation and associated costs. For example, mechanochemistry uses mechanical (grinding or milling) forces for chemical transformations, and can be a powerful tool for rapid, and clean synthesis without the need for bulk solvents. To explore this capability for REE recycling, we have employed mechanochemistry to reduce various metal oxides and salts of Ce, Nd, Dy and Tb to their metal forms. First, thermodynamic calculations were conducted on the chemical conversion of REE salts and oxides to metal. Herein, cerium compounds were used as a case study for assessing the feasibility of mechanochemical reduction combined with subsequent melting consolidation. Mechanochemical reduction of CeF₃, CeCl₃, CeBr₃, CeI₃, and CeO₂to Ce metalwas observed, congruent with thermodynamic calculations. The separation of product metal from the oxide byproduct is still ongoing, however the formation of a Ce ingot was observed during initial trials. The combination of these solid-state techniques proves to be promising, with the potential for overall lower costs and less generation of waste. Future investigations will determine the feasibility of scaling up.

Sheeniza Shah

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