Liquid-liquid extraction is a chemical separations technique commonly utilized in radiochemical applications. A fundamental limitation to this technology is third phase formation, where sufficient loading of metal ions into the organic phase induces a liquid-liquid phase transition. The molecular-scale origins of this phase transition are challenging to understand in complex, hierarchically structured organic phases. We propose that organic phase structure and phase behavior are fundamentally connected in a way that can be understood by applying critical phenomena theory. By combining small angle X-ray scattering with molecular dynamics simulations, we demonstrate that organic phase mesostructure over a wide composition space is dominated by critical fluctuations. These fluctuations originate from the critical point associate with the third phase formation phase transition. For a range of liquid-liquid extraction systems with varying complexity, we find these fluctuations are consistent with the 3D Ising model. Scaling relations provided by critical phenomena theory provide a robust physical connection between aggregation in the organic phase and its phase behavior, deepening our understanding of both. These results will inform the design of more efficient third phase formation-resistant separations processes.

Critical phenomena and organic phase mesostructure in liquid-liquid extraction

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.