Macrocyclic Chelators for Aqueous Lanthanide Separations via Precipitation: Toward Sustainable Recycling of...

Rare-earth elements (REEs) are critical materials in modern industry, but their production has a significant environmental footprint. Environmentally friendly separation methods would enable efficient, sustainable recycling of REEs. This work introduces a class of cyclen-based macrocyclic chelators that induce significant differences in solubility for REE chelates, enabling their selective precipitation from pH-neutral aqueous solution. The process was refined using simple coordinating additives (e.g., acetate) to form ternary coordination compounds to fine-tune these chelate solubilities. Conditions were optimized for the REEs found in NdFeB magnets, allowing separations of even adjacent lanthanides by repeated precipitations. Separation factors comparable to those of industrial solvent extraction methods were achieved without organic solvents. Analysis of NdFeB magnets from current electric car motors revealed an unexpected presence of holmium as a supplement and/or replacement for terbium and dysprosium, suggesting shifting industrial trends with implications for future recycling efforts. In a case study, one such automotive magnet was processed to obtain a 99.7% pure neodymium product. Scalable, tunable, and entirely aqueous, this approach advances the sustainable use of REEs toward a circular economy.