Anion concentration-dependent partitioning mechanism in the extraction of uranium into room-temperature ionic liquids.

The mode of partitioning of uranyl ion between nitrate-containing aqueous phases and various N,N'-dialkylimidazolium-based room-temperature ionic liquids (RTILs) in the presence of tri-n-butyl phosphate (TBP) is shown to change from an ion-exchange process to one involving extraction of a neutral uranyl-TBP-nitrato complex as the aqueous nitrate concentration is increased. Increasing the hydrophobicity of the RTIL cation eventually leads to nitrato complex extraction as the predominant mode of partitioning, regardless of nitrate concentration.