The extraction of both UO2(2+) and trivalent lanthanide and actinide ions (Am3+, Nd3+, Eu3+) by dialkylphosphoric or dialkylphosphinic acids from aqueous solutions into the ionic liquid, 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide has been studied and compared to extractions into dodecane. Radiotracer partitioning measurements show comparable patterns of distribution ratios for both the ionic liquid/aqueous and dodecane/aqueous systems, and the limiting slopes at low acidity indicate the partitioning of neutral complexes in both solvent systems. The metal ion coordination environment, elucidated from EXAFS and UV-visible spectroscopy measurements, is equivalent in the ionic liquid and dodecane solutions with coordination of the uranyl cation by two hydrogen-bonded extractant dimers, and of the trivalent cations by three extractant dimers. This is the first definitive report of a system where both the biphasic extraction equilibria and metal coordination environment are the same in an ionic liquid and a molecular organic solvent.

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Partitioning of sodium ions between aqueous nitrate media and 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imides (C n mim + Tf 2 N 2 ) in the presence of dicyclohexano-18-crown-6 is shown to take place via as many as three pathways: conventional nitrato complex extraction and/or either or both of two ion-exchange processes, the relative importance of which is determined by aqueous acidity and the hydrophobicity of the ionic liquid cation. Contrary to expectations, increasing the alkyl chain length of the IL cation (from C 5 mim + to C 10 mim + ) is insufficient to eliminate the possibility of ion exchange as a mode of metal ion partitioning between the two phases, an observation with negative implications for the utility of ILs as environmentally benign extraction solvents.

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