On the role of analytical chemistry in solvent extraction processing

Analytical chemistry plays a vital role in both the development and operation of any chemical process, and the process of solvent extraction as applied in hydrometallurgical operations is no exception. Because of the increasing attention being given today to solvent extraction as a means of separating metals in solution, it seemed appropriate that the analytical chemistry associated with solvent extraction studies, process development, and operations be reviewed. In this review, consideration is given only to analysis of the aqueous and organic phases for the determination of solvent components, rather than to the determination of metals in these phases. Furthermore, the major emphasis is placed on analytical methods which are applicable to process studied and plant control, and which require a minimum of instrumentation and operator skill. The importance of sampling is discussed first, and problems encountered in obtaining representative samples from the solvent, aqueous, and slurry phases are considered in some detail. This is followed by a review of methods of analysis which are directly applicable, or are considered as having application, to the analysis of the organic and the aqueous phases of the solvent extraction process. Analytical methods for the determination of the various extractants, modifiers, and diluents presently being used, or considered for use, in commercial solvent extraction processes are surveyed. First, those methods which are applicable to the determination of reagents in the solvent phase are considered, followed by those which are available for analysis of the aqueous phase for the determination of soluble components of the solvent phase. In both cases extractants, modifiers, and diluents are considered separately. Finally, some of the more obvious analytical needs, and areas where research is required in order that a more complete understanding of the solvent extraction process can be obtained, are discussed.