Liquid/liquid extraction (LLE) is a standard method of solute separation and purification in the fields of chemistry, engineering, and industry, where a solute distributes from one liquid phase to another based on the favorability of solvation free energies between the two phases. Understanding the mechanism by which simple solute like water, and highly organized ion-pair adducts selectively partition into two immiscible liquids has recently gained attention to enable controlled molecular extraction and design strategies. The experimental elucidation of the solute transport mechanisms face difficulties associated with the probation of biphasic fluidic interfaces and to characterize ion speciation, complexation, and adsorption phenomenon that occurs within the instantaneously evolving, dynamic, and heterogeneous regions of the liquid/liquid interface. The extraction mechanisms of metal ions in solvent extraction involve variations in ion-solvent-extractant adduct formation at the capillary wavefronts and perturbations in free energy of the adduct as it passes from the interface to the organic phase. Moreover, the extraction of water is characterized to occur via the formation of specific surface morphologies like the protrusions, water-fingers, and hinges depending on the choice of extractants and system compositions, via unconstrained molecular dynamics simulations. The presentation will describe the recent developments that are elucidating solute transport mechanisms, for example - water extraction by amphiphilic extractant like tri-butyl phosphate that involves protrusion formation, and octanol transport of water via molecular hinges. Of specific interest is the extent to which the mechanisms that transport water across a phase boundary are extensible to larger solutes like ion-pairs or metal-ligand (ML) complexes under equilibrium conditions.

Solute transport mechanisms in liquid/liquid extraction

ACS Fall 2021

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