Supramolecular chemistry in solvent extraction : toward highly selective extractants and a better understanding of phase-transfer phenomena

Solvent extraction provides the basis for important separation and concentration processes that are widely used in hydrometallurgy, waste treatment, ­ e ffluent purification, and material preparation 1- 3 . In a typical extraction process, the complexing agent, the extractant, plays a key role and is responsible for the phase transfer of one or more species of interest between the particular liquid- liquid phases employed. At present, four categories of metal extractants are used in industry: acidic and chelating cation exchanging reagents as well as solvating and anion exchanging reagents. An aim of this review is to show how supramolecular concepts may play a role in influencing extraction processes with the focus placed on the more recent work. Since both calixarene-derived extractants and metal salt extractants are treated in other chapters of this book, these areas have been given less emphasis in the discussion that follows.