Emergent mutual separation strategy for rare-earth elements based on crystallization of coordination compounds

Over the past several decades, rare-earth (RE) elements have been widely used in industrial products due to their exceptional physical, chemical, and mechanical properties. The discovery and industrial applications of RE elements have largely been driven by advances in their mutual separation, as RE ions exhibit highly similar chemical properties. In recent years, the growing production of RE-based products has highlighted concerns over supply risks. Recovering RE ions from end-of-life industrial products, often referred to as "urban mines," offers a sustainable solution and supports a circular RE economy. To promote RE recycling, there is a pressing need to develop separation methods with higher selectivity and lower environmental impact. This mini-review focuses on a novel strategy for RE separation based on the crystallization of coordination compounds, as reported over the past decade. First, separation systems utilizing the crystallization of coordination polymers constructed with RE ions and organic bridging ligands are summarized. Then, separation through the crystallization of discrete RE complexes with organic ligands is described, with particular emphasis on ligand structure, separation factors, and crystallization conditions.