A series of 1,3-dialkylimidazolium-based ionic liquids (ILs) have been evaluated as substitutes for the conventional organic solvents (i.e., n-alcohols) frequently employed in the extraction of alkali and alkaline earth cations from acidic aqueous phases by crown ethers. Insight into the fundamental aspects of metal ion extraction in these systems has been obtained by analysis of the acid and extractant dependencies of metal ion distribution ratios, measurements of the IL phase water content and of the solubility of the ILs in the aqueous phase, determination of the partitioning of the extractant and of inorganic ions, and consideration of the relative hydrophobicities of the ILs employed. In contrast to the single pathway (i.e., neutral complex extraction) observed using molecular diluents, metal ion extraction in these systems has been shown to proceed through as many as three competing pathways over a wide range of conditions. Despite this added complexity, the favorable physicochemical characteristics of the ILs (e.g., non-flammability and unprecedented structural tunability), along with the higher extraction efficiencies and selectivities for strontium over alkali metal cations sometimes observed with these solvents, suggests that they may have a role to play in various separations applications on both the industrial and analytical scale. In addition to their immediate practical utility, the results of these studies represent an important step toward developing guidelines for the rational design of IL-based metal ion separation systems.

Room-temperature ionic liquid-based solvent extraction systems for improved fission product separations

244th National Meeting (2012)

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