The extraction of Eu(III) from nitric acid solutions was studied in intensified small scale separation units using an ionic liquid solution (0.2 M n-octyl(phenyl)-N,N-diisobutylcarbamoylmethyphosphine oxide (CMPO)-1.2 M Tributylphosphate) (TBP)/1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyll amide; ([C(4)min][NTf2])as the extraction phase. The investigations were carried out in channels with 0.2 mm and 0.5 mm diameter for phase flowrates that result in plug flow with the aqueous solution as the dispersed phase. The interfacial area in plug flow and the velocity profiles within the plugs were studied with high speed imaging and bright field micro Particle Image Velocimetry. Distribution and mass transfer coefficients were found to have maximum values at nitric acid concentration of 1 M. Mass transfer coefficients were higher in the small channel, where recirculation within the plugs and interfacial area are large, compared to the large channel for the same mixture velocities and phase flow rate ratio. Within the same channel, mass transfer coefficients decreased with increasing residence time indicating that significant mass transfer takes place at the channel inlet where the two phases come into contact. The experimental results were compared with previous correlations on mass transfer coefficients in plug flows. (C) 2016 Published by Elsevier Ltd.