Origins of Clustering of Metalate–Extractant Complexes in Liquid–Liquid Extraction

Effective and energy-efficient separation of precious rare metals is very important for a variety advanced technologies. Liquid-liquid extraction (LLE) relatively less energy intensive technique, widely used in lanthanides, actinides, platinum group (PGMs). In LLE, the distribution an ion between aqueous phase organic determined by enthalpic (coordination interactions) entropic (fluid reorganization) contributions. The molecular scale details these contributions are not well understood. Preferential from usually correlated with resulting fluid organization phase, as longer-range increases metal loading. However, it difficult to determine extent which causes, or caused by, this study, we demonstrate that two systems same loading may impart different organizations investigate underlying mechanism. Small-angle X-ray scattering shows structure quaternary ammonium extractant solution toluene affected differently metalates (octahedral PtCl62- square-planar PdCl42-), although both completely transferred into phase. aggregates formed metalate-extractant complexes (approximated reverse micelles) exhibit more long-range order (clustering) compared PdCl42-. Vibrational sum frequency generation spectroscopy complementary atomistic dynamics simulations on model Langmuir monolayers indicate affect interfacial hydration structures differently. Furthermore, water These results support strong relationship organizational local present within complexes, independent metalate concentration.