Chapter 7 - Competitive Complexation/Solvation Theory of Solvent Extraction: General Mechanisms and Kinetics

Abstract

This chapter deals with the competitive complexation/solvation theory of solvent extraction that is particularly based on four statements that are well-known facts in chemistry. The four statements are as follows. The first statement is that the extraction act is initiated by solvation of the solute compounds in organic solvents with formation of hydrogen- (coordinate-) bonded intermediates (adducts). The second statement is that strong (ion-exchange, chemical, electrostatic), weak (solvating, physical, intermolecular, H-bond, coordinate) interactions and aggregation are the basic interactions, which have to be taken into consideration in all range of extracted solute concentrations. The third statement is that solutes, extractants, active solvents, and their interacting species are considered amphoteric and may perform as acids (electron acceptors) or bases (electron donors), depending on the structure of their functional groups and composition of the organic phase, and on the structure of the solute species and composition of the aqueous phase. Lastly, the fourth statement is that aggregation mechanisms and species formed are changing with increasing loading of the organic phase by solute, and should be considered and analyzed in all regions of the general extraction isotherm. Furthermore, the chapter provides detailed study of extraction systems with low solute concentrations in the organic phase, systems with medium concentrations of the solute, systems with high concentrations of solute, and also provides the comparison of conventional and theories descriptions.