(285f) Phase Transitions and Mesoscale Aggregation in Liquid-Liquid Extraction of Rare Earth Elements

Understanding the molecular-scale origins of structure and phase transitions in multicomponent, hierarchically structured liquid phases is a fundamental challenge. One important application affected by these phenomena is liquid-liquid extraction, a predominant low-energy separations technique that is a go-to process for metal ion separations, including recovery and recycling of rare earth elements. A fundamental limitation of liquid-liquid extraction is the undesirable liquid-liquid phase transition, called third phase formation, that occurs upon sufficient loading of metal ions into the extractant-containing organic phase. In this talk, we present ongoing work relating solution structure to that phase transition, connecting the two through the concentration fluctuations associated with the liquid-liquid critical point. We use small angle x-ray scattering and high-speed x-ray photon correlation spectroscopy to measure static and dynamic critical exponents in the organic phase. Further from the critical point, we combine small angle x-ray scattering and molecular dynamics simulations to investigate how process conditions, such as extractant concentration and aqueous feed acidity, affect fluctuations in the organic phase. Connecting these fluctuations to the underlying phase transition will deepen our understanding of how extractant design and molecular-scale interactions control phase behavior, enabling the design of more efficient separations processes.