For more than a decade, considerable effort has been directed at the evaluation of the viability of ionic liquids (ILs) as replacements for the molecular organic solvents normally employed as diluents in the liquid-liquid extraction of metal ions.  While some studies have demonstrated that extraction efficiencies far superior to those observed in conventional solvent extraction systems can be achieved using ILs, other work indicates that this improved efficiency comes at the price of added mechanistic complexity and a greater likelihood of substantial solvent losses during the extraction process.   In this presentation, the results of a series of investigations of the extraction of alkali and alkaline earth cations by macrocyclic polyethers into various imidazolium-based ionic liquids are summarized, with emphasis on the factors found to be responsible for determining the balance among the several possible pathways for metal ion partitioning in IL-based extraction systems, among them IL cation and anion hydrophobicity, the nature of the aqueous phase anion, and the water content of the ionic liquid phase.  The significance of these factors as regards the improvement of IL-based metal ion extraction systems and their application in the development of guidelines for the rational design of these systems is described.

Ionic liquid-based metal ion extraction systems: Progress and prospects

248th National Meeting (2014)

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