The extraction behavior of europium(111) from nitric acid medium by a solution of n-octyl(pheny1)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and tri-n-butylphosphate (TBP) in the room temperature ionic liquid, 1-buty1-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (bmimNTf(2)), was studied. The distribution ratio (D-Eu) of Eu(III) in CMPO-TBP/bmimNTf(2) was measured as a function of various parameters such as the concentrations of nitric acid, europium, CMPO, and TBP and temperature. The distribution ratio of europium increases with the increase in the concentration of nitric acid reaches a maximum value around 1 M followed by decrease. Loading of europium in CMPO-TBP/bmimNTf2 increases with the increase in Eu(111) concentration without leading to the formation of third phase, which is usually observed in conventional diluents. The stoichiometry of metal-solvate in organic phase varies from 1:3 (Eu:CMPO) at trace levels to 1:1 at higher europium loadings. The viscosity of the TBP-CMPO/bmimNTf(2) system at various temperatures and the enthalpy change accompanied by the extraction of europium(111) were determined and reported in this paper. (C) 2010 Elsevier B.V. All rights reserved.