AbstractLiquid–liquid extraction, also known as solvent extracting, is a well‐established separation technique that depends on the unequal distribution of a solute between two immiscible liquids. The initial feed liquid containing the solute is brought into contact with a solvent that is selected to have a greater affinity for the solute. The partition of the solute can be enhanced by adding a chemical extractant to the solvent; this practice is widespread in the hydrometallurgical and nuclear industries. Most industrial extractors operate continuously with countercurrent flow of the two phases. In mixer–settlers, the phases are contacted as a well‐agitated dispersion of drops, which are then sent to settling tanks for phase disengagement. In extraction columns, the dispersed drops move countercurrently against the flow of the second (continuous) phase. The physics, chemistry, and practice of extraction, with brief descriptions of important industrial extraction processes and equipment, are presented. Research on hydrodynamic aspects of process design, eg, axial mixing, drop dispersion, and coalescence, is reviewed. New extraction techniques, eg, membrane extraction, supercritical exctraction, and two‐phase aqueous extraction, are discussed.
