Ion Insertion into Confined Solid Ionic Channels for Separation of Rare Earth Elements

Rare earth elements (REEs) play an indispensable role in the path towards a greener, renewable future. Despite its efficacy, the conventional industrial solvent extraction method suffers from substantial energy consumption and chemical intensiveness. Thus, there is an urgent need to develop sustainable methods for REEs separation. Ionic radius and Lewis acidity are the two key differences that have paved the way for many separation methods. Separation methods combining both size effect and binding affinity can promote selectivity among REEs, however, the effect of long-range confinement on separation is largely unexplored. Here we report a new method to achieve separation among REEs in aqueous systems without ligands via creating optimal long-range confinement to maximize the energy penalty among unfavored REEs. We observed two distinct group behaviors through ion insertion, based on which we achieved effective separation for cross-group elements. We further proposed a pinning strategy to boost the same-group separation by maintaining the confinement throughout the reaction process. As a result, we achieved a significant escalation in enrichment factors for La-Nd and La-Pr pairs from 1.6 ± 0.1 and 1.5 ± 0.1 without pinning, to 5.4 ± 0.1 and 4.2 ± 0.1 with pinning, respectively. This unique design delivers an impressive ~92.3% purity of Dy from a 1:1 Nd-Dy pair, and a ~97.0% purity of Nd from a 1:1 La-Nd pair, through a two-time separation process. Our work illuminates the potential of confinement design and its pivotal role in advancing sustainable REE separation methods.