ABSTRACT
Using solvent extraction to effect the separation and concentration of metal values in extractive metallurgy in flowsheets of the type shown in Figure 2.1 is now well established.1-4 Processes can be operated continuously and on large scales using technology first established in the Manhattan Project in the 1940s.2,5
For most large-scale operations, relatively high-boiling hydrocarbons are the preferred water-immiscible solvents on the grounds of cost and safety. Also, their very low solubility in water reduces the risk of pollution and promotes phase disengagement. The very low polarity of these solvents favors the formation of secondary bonds, particularly hydrogen bonds (H-bonds) between the ligands
2.1 Introduction ............................................................................................... 49 2.2 Extraction of Metal Cations ....................................................................... 51 2.3 Extraction of Metalate Anions................................................................... 60 2.4 Metal Salt Extraction ................................................................................. 68 2.5 Conclusions ................................................................................................ 72 Acknowledgments ............................................................................................... 73 References ........................................................................................................... 73
used as metal extractants. While it has been recognized for some time6,7 that the formation of supramolecular assemblies arising from such secondary bonding is very important in defining the modes of action of extractants, only relatively recently have attempts been made at the design stage to exploit such interactions in the outer spheres of metal complexes to control the strength and selectivity of new reagents. Supramolecular chemistry is involved in most aspects of the formulation of extractant mixtures to achieve the criteria needed for an efficient process. These criteria are listed in Figure 2.2, in which “separation” refers to phase disengagement and “system” to ensuring that all components of the pregnant leach solution are accounted for.
