Chapter 11 - Final Remarks on the Competitive Complexation/Solvation Theory of Solvent Extraction and its Application

Abstract

The main objective of this chapter is to present a novel, competitive complexation/ solvation (CCS) theoretical approach to solvent extraction separation processes. CCS theory was developed for interpretation and quantification of interactions in solvent extraction systems. According to the theory the molecules of an extracting mixture compete for solute (hydrated or solvated metal ions, acids, etc.) by the extent of their affinity to association and concentration. The solute is partitioned among the solvent components (i.e., extractant, synergistic agent, diluent, and water) forming, as a first step, H-bonded solvation shells or reversible reactive intermediates (adducts). The following step is proton/electron transfer with the formation of ion-exchange or ion-pair structures. As a consequence, a given measured property in mixed solvents can be calculated from values, measured in single solvent component systems. The theory establishes the correlation between complexation and solvation. At low concentrations of the solute in the organic phase the solute–extractant complex with its solvation shell forms a geometric structure, which is denoted as a single nucleus aggregate. Active solvents are considered amphoteric and may behave as acids or bases, depending on the nature of their functional groups and composition of the organic phase and on the nature of solute species and composition of the aqueous phase. The presented CCS modeling approach constitutes a general and useful framework for interpretation of ion–molecular interaction data in the solvent extraction systems.