Statistical mechanical treatment of reactive solvent extraction Original Research Article

A statistical mechanical lattice model of a reactive solvent extraction process involving two phase liquid-liquid ion exchange is presented. It is applied to literature data on the extraction of alipathic carboxylic acids by quaternary ammonium salts. The Helmholtz free energy of the system is constructed and minimised subject to the constraints of mass balance and electroneutrality. The equations defining the equilibrium conditions have been solved numerically for a range of interaction parameters and hence the equilibrium concentrations of the various partitioned species are obtained. These interaction parameters are compared with experiment. The intuitive notion that the extent of partition is dominated by electrostatic solute-extractant interactions is shown to neglect various other interactions that may, in some systems, be important.