X-ray absorption spectroscopy of extractant binding to rare earth ions at aqueous surfaces relevant to solvent extraction*

Solvent extraction processes are designed to extract a target species of ion from a multi-component aqueous mixture into an organic solvent, then return the target species to a fresh aqueous phase. Several structural aspects of this process have been studied, including the hydration of ions in water, the local atomic coordination of ion-extractant complexes in the organic phase, and ion-extractant ordering at both the liquid-liquid interface and at the surfaces of model aqueous solutions. Missing from these previous investigations is a study of local atomic coordination of the ion-extractant complex at the interface. However, this interfacial coordination has been shown to play a critical role in the formation of the ion-extractant complexes which are responsible for the transportation of the ions across the interface. This presentation will describe our advancements of synchrotron X-ray absorption spectroscopy to investigate the local coordination of ion-extractant binding at the surface of water, which serves as a model system relevant to the extraction of rare earth ions. These measurements were done at NSF's ChemMatCARS at the Advanced Photon Source, Argonne National Laboratory.