Chapter 3 - Chemistry of Metal Solvent Extraction

Abstract

The chapter gives an overview of the chemistry of metal solvent extraction; it provides the factors underlying the strength of metal extractant interactions, their influence for different metals and extracting reagents, and other parameters of complexation that are briefly reviewed and discussed. Solvent extraction of metals is an important technology in hydrometallurgical industry, analytical separations, and liquid waste treatment. Metal ions, cations, and anions are extracted from an aqueous phase into an organic phase through reversible chemical reactions, forming organic-soluble neutral complexes. Extractant usually has very low solubility in an aqueous phase, but interacts with metal ions and obtains high solubility in an organic phase complex. So, extraction is described by a heterogeneous chemical reaction on either side of the aqueous organic interface to the final equilibrium concentrations of the reaction product. In addition, the chemical reaction of solutes with organic compounds (termed as extractants, or reagents), dissolved in the organic solvent (diluent), is accompanied by the distribution of product complexes between two immiscible phases. The extent of complexation for any solute–ligand system is defined by equilibrium constant, which is termed stability or formation constant for metal–ligand interaction. Furthermore, the chapter explains metal extraction by anion exchangers and many equations.