Glycopolymer-Mediated Selective Separation of Middle Rare Earth Elements

The selective separation of rare earth elements (REEs) remains a formidable challenge due to limitations of current methodologies, which struggle to achieve the separation efficiency required for their critical industrial applications. Middle REEs (MREEs), characterized by their intermediate ionic radii, are particularly challenging to separate without size-specific trapping mechanisms. In this study, we report a novel approach that synergistically combines heavy metal sequestration with size-selective separation, utilizing negatively charged glycopolymers to achieve the targeted separation of MREEs. We systematically investigated the binding affinities of these glycopolymers for various REEs, focusing on the selective isolation of MREEs through a controlled variation of glycopolymer properties, including degree of polymerization (DP) and charge density. Our findings reveal a distinctive U-shaped selectivity profile, with a marked preference for Samarium (Sm) and Europium (Eu) over other REEs such as Cerium (Ce), Gadolinium (Gd), and Holmium (Ho). This selectivity underscores the potential for designing tailored separation processes optimized for specific MREEs. Moreover, enrichment experiments demonstrated the practical viability of our methodology, achieving over 10 % selectivity for Sm in a Ce/Sm mixture with a 10 : 1 Ce/Sm ratio, a trend that held for Sm in a Ho/Sm Mixture with a 10 : 1 Ho/Sm ratio, indicating significant selectivity over both light and heavy REEs. A subsequent separation experiment using a 1 : 1 Ce/Sm mixture yielded a 15 % enrichment after only five passes through a filter containing minimal amounts of glycopolymer, highlighting the promise of further refinement for enhanced separation efficiency.