Amines as Extractants

Abstract

Both study and use of extractions with high molecular weight amines (including quaternary ammoniums) in organic solution are increasing extensively. While equilibria have been measured in extraction of an increasing range of acids and metal ions, a difficulty remains unresolved in that the amine concentration power-dependence of extraction often indicates a different complex stoichiometry than do limiting loading and other considerations. Nevertheless, amine extraction serves as a useful tool in studying aqueous complex systems. Process applications have progressed especially in nitrate and chloride systems, in addition to the sulfate systems first emphasized. Systematic surveys together with information accruing from process development have extended the ranges of extractions that can be correlated in usefully generalized patterns, which in turn should accelerate the development of new applications. However, many more areas remain to be surveyed before the many pertinent variables will have been covered. New amines of all classes have become available at commercial, development, or researchsample levels, while a few previously promising amines have become less available. Descriptions and current sources are reviewed.