H.B. Vibbert, A.W.S. Ooi, A.-H.A. Park
Keywords: ligand extraction, cerium, rare earth elements, separation, ligand design
Summary:Developing new chelating lixiviants that increase selectivity for critical element separations – ones that bind and release under mild conditions – hold the potential to provide a sustainable alternative to conventional mining and ligand-based flotation strategies. Here, we discuss the design principles, selectivity, and approaches to release Ce found in a large background of Ca or Mg ions, as is the case for waste-to-energy ashes or other types of alkaline industrial waste. We investigate how a pH responsive Schiff-base ligand based on tris(2-aminoethyl)amine can affect this separation using more environmentally friendly solvents and conditions than are typically employed. We discuss the design principles that guide the development of this class of ligand, examine the optimal selective extraction conditions, and show that more sustainable acids can be used to release bound Ce. Finally, we discuss heterogenized applications of this design and the selective removal of Ce without organic solvent.