Hexavalent chromium extraction from aqueous solutions in a liquid-liquid slug flow microreactor

[Display omitted] •High Cr6+ removal was obtained with no emulsion formation even at a flow of 0.3 L/h.•Equilibrium was achieved inside microreactor in less than 19 s.•There is an A/O ratio leading to a maximum Cr6+ removal that has to be determined.•Changing T-junction to cross-shaped junction slightly improved removal efficiency. Solvent extraction system for removal of Cr (VI) from acidic aqueous solutions with trioctylamine in toluene was developed in a microreactor operating in slug flow regime to eliminate some disadvantages of conventional contactors. The microreactor consisted of a T-junction followed by a 0.7 or 1.0 mm circular microchannel. Excellent extraction efficiency and prompt two-phase separation at the outlet (no emulsion was formed) was successfully achieved even at a total flow rate of 0.3 L/h. The equilibrium was attained in less than 19 s (yielding the extraction efficiency of 98.9 %) which is one order of magnitude shorter than that reported for batch extraction in the literature. This can lead to significantly smaller contactor volume in favor of the plants suffering from space limitations. Cross-shaped junction was also employed for slug generation and the results were compared to those of T-junction, revealing that cross-shaped junction slightly improved the extraction efficiency. Thus, T-junctions can be preferred for a simpler manufacturing of distributors. In a nutshell, slug flow microreactors have a great potential to intensify solvent extraction of pollutants from wastewaters.