Study of Calcium Liquid-Liquid Extraction in Parallel Microchannels

Flow patterns of six liquid-liquid systems, including chloroform/butyl acetate/ethyl acetate/kerosene/butanol/octanol-water, in a numbered-up microfluidic set-up were studied in this work. Three distinct flow regimes were observed in the parallelized microfluidic device: slug flow, droplet flow and parallel flow. A uniform flow distribution with non-uniformity less than 10% indicates the high quality of microchannels and successful numbering-up procedure in the scaled-out microfluidic device. By flow pattern analysis, a parallel flow regime with complete phase separation was chosen as the desired flow regime for calcium ion separation. Chloroform-water system and DCH18C6 crown ether were identified to obtain the maximum extraction efficiency of calcium. In these conditions, the effects of crown ether concentration ([CE]), the concentration of calcium ion ([Ca2+]) and pH were studied in order to optimize the extraction efficiency using the Box-Behnken method. The extraction efficiency of more than 60% was achieved in three sequential microchips under optimized conditions within only 3.5 seconds. An excellent improvement was also observed in calcium separation efficiency using EMIM NTf2/n-butyl acetate mixture as the organic phase. Therefore, more than 95 % extraction efficiency was achieved within 1.6 seconds using ionic liquid–cosolvent mixtures utilizing a microfluidic cascade.