ABSTRACT
The extraction and transport of the alkali metals have been studied intensively for over 40 years [1–5], and selective systems have by now been identified for each alkali metal ion. Ironically, the development of the field of solvent extraction in this century has been primarily driven by a desire to extract other metals away from the more abundant alkali metal ions. However, with the appearance of reagents specific for alkali metals, especially in the 1960s and 1970s, interest in this topic has grown, spurred by applications in analytical chemistry, hydrometallurgy, nuclear-waste treatment, medicine, and research. Now, the flourishing literature on alkali metal extraction could be scarcely covered in a single volume. In view of the intense recent interest in cesium separations in particular (as discussed more in the following), the authors focus here on the topic of cesium solvent extraction. Furthermore, in considering the approach to this topic it seemed that the most useful type of review would be one that deals with principles broadly applicable to cesium solvent extraction, from which many new extraction systems could be rationally devised and existing systems better understood and improved. Unifying solvent extraction principles relate fundamentally to ion solvation, namely the interactions of an ion with its solution environment. From an understanding of these phenomena, one can 296immediately see how to devise solvent extraction systems with extreme cesium selectivity based on ion solvation. Even if one’s interest lies in designed extractants such as crown ethers and cryptands, ion solvation must still be appreciated, for as essentially recognized over 20 years ago [6], the addition of many crown compounds, even those having an “appropriate” cavity size, to a diluent often does more to lower cesium selectivity than to raise it.
