Room-temperature ionic liquids:: new solvents for f-element separations and associated solution chemistry

Ionic liquids (ILs) are composed of organic cations and either organic or inorganic anions that remain liquid over a wide temperature range, including room temperature. IL characteristics can be dramatically adjusted (e.g., hydrophobic vs. hydrophilic) by changing the anion type, or subtly altered by changing the length or number of alkyl groups appended to the cation. Changing alkyl chain lengths in the l-alkyl-3-methylimidazolium cation, in combination with PF6- or N(SO2CF3)(2)(-) anions, produces hydrophobic ILs with theological properties suitable for their use in liquid/liquid separations. Actinides exhibit significant partitioning to these ILs from aqueous solutions with the addition of an extractant (e.g., octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide) to the IL. Ionic liquids can, thus, be considered for actinide chemistry as a new class of materials with adjustable solvent characteristics, unique properties, and the potential for enhancing the principles of "green" chemistry in various chemical processes. Here we highlight the unique physical properties of some ILs and their use in liquid/liquid separations. (C) 2003 Elsevier Science (USA). All rights reserved.