Hydrodynamic experiments were conducted in a microbore helix based passive mixer for the system of HNO3/30% TBP/n-dodecane under non-mass transfer conditions. Hold up and drop sizes were experimentally measured for an aqueous phase flow rate of 0.15-0.80 mL/min and organic phase flow rate of 0.10-0.75 mL/min for various A/O ratios from 0.2 to 5. Although a fine dispersion was generated in the mixer, it did not affect coalescence and clear streams emerged from exit points of a mini settler (similar to 1.2 mL). Due to smaller drop sizes generated, the observed specific interfacial area was huge and for the experimental conditions reported, it was ranged about 2.84 x 10(4) to 8.56 x 10(4) m(2)/m(3). It is of the same order of that observed in a 50-mm centrifugal extractor with identical aqueous-organic pair. (C) 2016 Elsevier B.V. All rights reserved.