Microfluidic solvent extraction of calcium: Modeling and optimization of the process variables

In this study, a new systematic method was proposed for the highly efficient separation of species with very low separation factor. Here, solvent extraction and microfluidic technology were integrated for the extraction and separation of Ca2+ ion. A cyclic compound (DC18C6) was used as the selective extractant. Full separation of organic and aqueous phases at the end of the microchannel was achieved by exploiting a flow regime map. N-butyl acetate was chosen as organic solvent among from other potential candidates with different characteristics. The Box-Behnken experimental design was used to provide data for modeling, while the variables of the model were DC18C6 concentration, flow rate and pH of the aqueous phase. The results showed that Ca2+ extraction efficiency was 62.28% under the optimum conditions: DC18C6 concentration was 0.014 M, the aqueous phase flow rate was 20 mu l/min and pH of the aqueous phase was 5.1. Multi-stage microfluidic solvent extraction in series was performed and the possibility of numbering-up with maintaining full phase separation was demonstrated. The overall volumetric mass transfer coefficients were determined quantitatively in a single microchannel, and their values were in the ranges of 0.19-0.41 s(-1), which are two orders of magnitude higher than those of conventional liquid-liquid contactors.