Liquid-liquid extraction of calcium using ionic liquids in spiral microfluidics

Using microfluidic systems in liquid-liquid extraction process has distinctive advantageous, including lower consumption and high extraction efficiency. In this research, the separation of calcium metal ions from the aqueous phase is investigated by use of 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM NTf2) and 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIM NTf2) to enhance the performance of the liquid-liquid extraction. The main idea is to evaluate the geometrical effect of microchannel in the extraction efficiency. For this purpose, the spiral microchannel was constructed to induce the centrifugal force. Comprehensive parametric studies are done to reveal the effect of the main parameters on the extraction performance of the microfluidic device. At first, the effect of the alkyl chain of ionic liquids in the extraction efficiency is investigated. The results showed that the shorter length of the chain has the higher extraction efficiency. Then, the physical parameters such as calcium concentration, a crown ether concentration and the pH are optimized in the traditional extraction. The results of experiments show that the maximum extraction efficiency of 50% is achieved when the concentrations of calcium and crown ether are 75 ppm and 3.75 mM, respectively, and the pH value of aqueous phase is 7. In the final step, the microfluidic system was used to study the hydrodynamic parameters influencing on the mass transfer. These parameters are: different geometries of microchannel (spiral and Y-shaped), and different flow rates of aqueous phase and the ionic liquid in the droplet flow pattern. Our findings reveal that the spiral microchannel is more efficient when the flow rate of water and the ionic liquid phases is highest and extraction efficiency of 52% is obtained in this condition, which is equivalent to equilibrium extraction efficiency.