Special Issue on Hierarchical Organization in Solvent Extraction

Amongst the multitude of papers that report the phenomenological behavior of liquid–liquid extraction, a significant fraction are associated with the separation, purification, and recycling of metals (both for industrial metal production as well as energy portfolios – as in nuclear energy applications). Over the last decade, an exponential increase in publications has been supported by fundamental advances to the science of phase transfer in multiphase systems, which has evolved to include predictive capabilities that finally exceed rough apparent “stoichiometry” determinations. The trend was clearly articulated within the latest issue of the series edited by Bruce Moyer (Moyer, B. A., Ed. Changing the Landscape in Solvent Extraction. Ion Exchange and Solvent Extraction, A Series of Advances, Vol. 23, CRC Press: Philadelphia, PA, 2019.). There it was noted that, for carefully designed systems, distribution ratios can be directly related to the reaction free energy of transfer in a simple exact and unique formula. Further, any theory that predicts the energetic characteristics of phase transfer without fitting distribution ratios variation with temperature, mole ratios, solvent additives will help to design the separation processes of the future (Sholl, David S.; Lively, Ryan P. Seven chemical separations to change the world. Nature 2016, 532, 435–437.). In this special issue, we have assembled seven specially focused papers that emphasize the structure, function, and thermodynamic characteristics of the many interactions that contribute to this radically new approach toward the fundamental science of liquid–liquid phase transfer. Collectively, these works beautifully demonstrate how the organization and distribution of local and extended chemical environments at the interface and the organic phase can be used to re-interpret the traditional paradigms of liquid–liquid extraction. They also consolidate the simultaneous molecular, supramolecular and colloidal approach that moves towards predictive theories that are useful for the chemical engineer in charge of designing effective plants.