Composition Control of Extractors

Abstract

Solvent extraction developed—with a few notable exceptions, particularly in the petroleum field—as a commercially important process operation only after intensive work on extraction processes for nuclear fuel reprocessing during World War II. Since then it has found increasing application in the separation of metals, aromatics, and more recently, the treatment of waste water. Whereas the early applications depended on simple differences in the solubility of a material distributed between two immiscible solvents, newer processes largely involve chemical reactions, temperature and pH sensitivity, and valence control to effect changes in distribution in multi-solute systems. Many of these new processes are drawn from our growing knowledge of more sophisticated extractants which form complexes with the solute to be extracted and are highly selective. It is this latter property that makes them especially useful in hydrometallurgical applications where one or two metals must be recovered from an impure, multicomponent system. Also, as these new developments in solvent extraction chemistry have appeared, the range of applicable metal extraction processes has broadened—from valuable metals in small volumes of solution to large flows of less valuable metals present in low concentrations.