Selective Recovery of Cerium as High-Purity Oxides via Reactive Separation Using CO2-Responsive Structured Ligands

Development of new ligand systems that selectively extract and release critical elements, such as lanthanides, in the presence of other metal ions at significantly higher concentrations can provide a sustainable alternative to conventional mining and ligand-based flotation reagents. In this work, the rational design of a highly tunable molecular scaffold based on tris(2-aminoethyl)amine is elaborated. When functionalized with salicylaldehydes, the corresponding imine ligands were observed to effectively extract Ce from aqueous solutions in the presence of a large excess of both Mg and Ca. Furthermore, the re-extraction and reactive separation of Ce was observed using CO2 as a stimulus trigger for release and precipitation, synthesizing cerium carbonate and high-purity ceria that could be used for a wide range of applications. The pH swing driven by the controlled partial pressure of CO2 allowed the efficient recovery of energy-relevant elements from unconventional resources through green chemistry.