The extraction behaviour of dioxouranium(VI) from nitric acid solutions with tributylphosphate (TBP) dissolved (30%, v/v) in room temperature ionic liquids (viz. 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, [C(4)mirn][NTf2], 1-decyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, [C(10)mim][NTf2], and trihexyltetradecylphosphonium bis{(trifluoromethyl)sulfonyl}amide, [P-66614][NTf2]) was investigated. The experiments were performed in a capillary (0.5 mm internal diameter) made of Teflon, operated in the plug flow regime. The effects of ionic liquid type, initial nitric acid concentration, and residence time on dioxouranium(VI) extraction were studied. UV-vis spectroscopy was used for the determination of the dioxouranium(VI) concentration in the ionic liquid phase. For increasing [HNO3](aq,init), the %extraction decreased and then increased for [C(4)mim][NTf2], while for the other two ionic liquids it increased. The %extraction also increased with residence time in the channel. Overall mass transfer coefficients were about 0.2 s(-1) in all TBP/ionic liquid systems at the initial nitric acid concentration of 3 M when a 10 cm capillary was used. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.