Technique of solvent extraction:

You have been introduced to the technique of solvent extraction and it's potential. A partition law and its limitations have been elaborates. The important terms which are used to express the distribution of chemical species have been explained. That is clear in which the distribution of a chemical constituent will depend upon the composition of aqueous and organic phases. In other words, the extent of extraction will depend upon the aqueous and organic phase variables. Amongst the organic phase variables, a most significant is the nature and the category of the extractant. There are numerous extractants and they keep on flooding the market to meet certain requirements of the separations. A wide categorization of different types of extractants used for metal ions has been discussed in the earlier unit. In order to fruitfully utilize the aqueous and organic phase parameters for effective metal ion separations, we will have to look into the various equilibria existing in the two phases and the overall extraction equilibria.

This particular unit begins with a discussion on the metal ion extraction equilibria of some of the important extraction systems. The different steps involved give an idea of several factors which affect the metal ion extraction. Once the parameters influencing extraction are known, they could be varied to achieve separations along with high separation factors. The practical utility of the background discussed herein will be demonstrated by citing examples of various metal ion separations achieved by variation of different parameters. It may be important to point out here that the discussion on equilibria is confined to some typical examples. All the various types of systems cannot be covered because of the variability and complexity involved in the extraction systems. Towards the end, a brief discussion on criteria for the choice of organic phase is presented. It becomes particularly important because the technique finds extensive applications for industrial operations.

Objectives

After studying this Unit, you should be able to

• Explode the extraction of metal ions with some important class of extractants,
• Enumerate various aqueous and organic phase parameters which affect the extraction of metal ions,
• Define several approaches which are generally adopted for metal ion separations, and
• Choose the criteria for the selection of the organic phase particularly for commercial applications.