Microfluidic solvent extraction of Cd(II) in parallel flow pattern: Optimization, ion exchange, and mass transfer study

Micro solvent extraction of cadmium ion from nitrate solution with a cationic extractant (MDEHPA) was performed in parallel flow pattern utilizing Y-Y microchannels. At first, the effects of the operating parameters on the extraction efficiency were studied. The optimum condition was determined using response surface methodology based on the central composite design (extractant concentration 6% (v/v), feed phase pH 6.3 and residence time 20 s). Additionally, for the first time, a correlation for the estimation of the aqueous phase Sherwood number in liquid-liquid parallel flow in the microchannels was developed. In this correlation, the aqueous phase Sherwood number was defined as a function of the aqueous phase Reynolds and Schmidt numbers. This model was able to predict the aqueous phase Sherwood number precisely with an average error of 9.91%. The influence of microchannel dimensions on the extraction efficiency was also examined. The increase in the channel length and the decrease in the channel width enhanced the extraction efficiency. Using the microchannel with optimal dimensions, the extraction percentage was obtained 99.3% at residence time 8 s. Moreover, the overall volumetric mass transfer coefficient (K(L)a) decreased with increasing residence time, channel width, and also channel length at a constant volumetric flow rate but increased with raising the channel length at an equal residence time. The K(L)a of the microfluidic system was much higher than the batch extractor.

Automated summary

This study investigated the micro solvent extraction of cadmium ion from nitrate solution and its influencing factors, determined the optimal conditions, and established a correlation for the estimation of the aqueous phase Sherwood number. It was found that microchannel dimensions had an impact on the extraction efficiency, with optimal dimensions achieving a 99.3% extraction rate.