Liquid-liquid extraction of calcium in a scaled-out microfluidic device: Process intensification using a crown ether-ionic liquid system

Solvent extraction of calcium was investigated in four microchannels parallelized on a microfluidic chip. Uniform flow distribution of observed flow patterns in parallel microchannels shows successful numbering-up of the microfluidic device. First, flow regime maps were plotted for six liquid-liquid systems. A parallel flow regime with complete phase separation was chosen as the desired flow regime for extracting the calcium ion. Organic phase and crown ether types were tested to obtain the maximum extraction of calcium from the aqueous phase. In these conditions, the effects of crown ether concentration, the concentration of calcium ion and pH were studied in order to optimize the extraction efficiency using the Box-Behnken method. The mass transfer coefficient was also determined as a function of residence time at different concentrations of calcium metal ions. In the second step, ionic liquid-based solvent extraction was studied. In this regard, the performance of the diluent (conventional organic solvent) type on the calcium separation efficiency was investigated. An excellent improvement in separation efficiency (7.1-64.2%) was achieved for the EMIM NTf2/n-butyl acetate mixture compared to butyl acetate. In the final step, continuous multistage liquid-liquid extraction of the calcium ion was performed using three series microchips to evaluate the microfluidic cascade's performance.