Intensified extraction and separation of zinc from cadmium and manganese by a slug flow capillary microreactor

Abstract

Selective extraction of zinc from sulphate effluents containing zinc, cadmium and manganese by liquid–liquid extraction with a capillary microreactor operating in the slug flow regime was elaborately investigated. Experiments were carried out at a flow rate ratio 1:1 of aqueous to organic phase, with a set-up consisting of a T-mixer connected to a PTFE capillary microreactor, and a subsequent membrane separator. The influences of extractant saponification degree, initial aqueous pH, residence time and mixture velocity on separation performance were studied, which indicated that separation enhancement of zinc from cadmium and manganese can be achieved by controlling the residence time and mixture velocity in the capillary microreactor without any aqueous pH adjustment. The βZn/Cd 2232.86 and βZn/Mn 1288.90 could be accomplished within 45 s in microfluidic extraction, whereas only 233.39 and 193.05 within 25 min in batch extraction, confirming the significant separation enhancement. Furthermore, the overall volumetric mass transfer coefficient kLa and overall mass transfer coefficient kL were also determined, high kLa of zinc (0.055 s−1–0.472 s−1) and low kLa of cadmium (0.009 s−1–0.076 s−1) and manganese (0.011 s−1–0.083 s−1) were responsible for the significant separation performance in the slug flow microfluidic system.