Controlling flow patterns and its evolution behavior in microchannel for intensified separation of rare-earth and Al(III) ions: Hints from the hydrodynamics parameters

Abstract Control of flow patterns and its evolution behavior in microchannel is crucial for microfluidic technology to achieve mass transfer intensification in the micro-scale and selective separation of target ions. In the present work, we found that the non-equilibrium extraction and selective separation behaviors of target metal ions from other co-existing background ions have a close relationship with the change of hydrodynamic parameters of the organic and aqueous two phases and the evolution of flow patterns in microchannel. Taking the separation of Er(III) and Al(III) ions in microchannel as a model system, it is revealed that the transition of the flow patterns from parallel flow to slug flow might originate from the decrease of the linear velocity of two phases flow, the increase of viscosity and the decrease of the interfacial tension between the two phases. The change of those hydrodynamic parameters would result in an obvious increase in specific interfacial areas between the two phases and a decrease in wall film thickness of the slug flow. A higher Capillary number corresponds to a larger specific interfacial area and a higher surface renewal rate between the two phases. Therefore, an intensified separation of Er(III) and Al(III) ions can be attributed to the change of those hydrodynamic parameters in microchannel. The present work highlights a novel approach by controlling the flow patterns of aqueous and organic two phases in microchannel for controllable selective separation of target metal ions.