Seminar title "Ion Transport through Liquid-Liquid Interfaces: X-Ray Studies of Interfacial Complexation"
Host: Dr. Heather Allen
The transport of ions through liquid-liquid interfaces occurs in many biological and chemical processes. As one example, the separations method known as solvent extraction is designed to extract a target species of ion from a multi-component aqueous mixture into an organic solvent, then return it to an aqueous phase containing only the targeted species. Ongoing developments of solvent extraction processes are aimed at optimizing the efficacy and kinetics of the separation of a wide variety of metals and molecules, including the recovery of base, rare earth, and precious metals, as well as the reprocessing of spent nuclear fuel and nuclear waste. During the solvent extraction of metal ions, extractants and complexants assist their transport across the liquid-liquid interface between an aqueous solution and an organic solvent. Complexation of metal ions with extractants and complexants is believed to take place at or near the organic-aqueous interface, as demonstrated recently by synchrotron x-ray measurements which locate and characterize metal ions and their complexes in the liquid-liquid interfacial region. This presentation will describe recent studies of model liquid-liquid systems relevant to the extraction of rare earth ions, both in the forward (water to organic) and backward (organic to water) directions. These results suggest a connection between the observed interfacial structures and the extraction mechanism, which ultimately affects the extraction kinetics.