Elucidation of the structure of organic solutions in solvent extraction by combining molecular dynamics and X-ray scattering

Abstract

Knowledge of the supramolecular structure of the organic phase containing amphiphilic ligand molecules is mandatory for full comprehension of ionic separation during solvent extraction. Existing structural models are based on simple geometric aggregates, but no consensus exists on the interaction potentials. Herein, we show that molecular dynamics crossed with scattering techniques offers key insight into the complex fluid involving weak interactions without any long-range ordering. Two systems containing mono- or diamide extractants in heptane and contacted with an aqueous phase were selected as examples to demonstrate the advantages of coupling the two approaches for furthering fundamental studies on solvent extraction. A terrific team: The ill-defined self-aggregation of metal-ion extractants in oils was determined by using a combination of molecular-dynamics simulation and small-/wide-angle X-ray scattering (SWAXS) techniques (see picture). In this way, it was possible to quantitatively describe the molecular and supramolecular organization of the extractant in the organic phase at a wide range of concentrations. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.