C.L. Tolbert, S.S. Bamane, G.M. Pawar, M.E. Case, C.M. Hill, R.V. Fox
Idaho National Laboratory,
United States
Keywords: critical materials, rare earth elements, lanthanides, capillary electrophoresis, separations, carboxylate ligands
Summary:
Enhancing the Electrophoretic Separation of Rare Earth Elements Through Complexation with Carboxylate Ligands 1,2Chloe L. Tolbert, 2Swapnil S. Bamane, 2Gorakh M. Pawar, 2Mary E. Case, 1Caleb M. Hill, and 2Robert V. Fox 1University of Wyoming, Department of Chemistry, 1000 E University Ave, Laramie, WY 82071 2Idaho National Laboratory, Energy Innovation Laboratory, 755 MK Simpson Blvd, Idaho Falls, ID 83401 The rare earth elements (REEs) consist of the lanthanides plus scandium and yttrium. REEs are categorized as critical materials, as they are vital in technologies including electronics, magnets, sensors, and defense weapons systems, and are at high supply risk. In order to be useful in such technologies, REEs must first be separated from one another- though this remains a challenge due to their physical and chemical similarities. Traditional separation approaches such as solvent extraction rely on large volumes of volatile organics and acids to discriminate these subtle differences and report low separation efficiencies, making this an unsustainable approach. Using a transport-based separation technique such as capillary electrophoresis (CE), REEs can be separated in completely aqueous systems at high efficiency by the introduction of partially-complexing ligands into the electrophoretic medium by maximizing differences in mobility between REE species, though the mechanisms through which this is achieved are poorly understood. Here, an investigation of the transport behavior of four REEs (La, Sm, Dy, and Lu) in solutions of different carboxylate ligands is conducted via CE. Experimental and computational approaches are performed to rigorously assign complexation configurations between the chosen REE-ligand groups, helping to explain the performance of well-performing ligands. The competition induced by dual-ligand systems is also studied to help further elucidate the behavior responsible for enhanced separations.