Simultaneous ion fractionation and concentration by selectrodialysis for saline wastewater valorization

Abstract

In order to desalinate saline wastewater and achieve energy-efficient recovery of mixed salt (Na2SO4 and NaCl), selectrodialysis (SED) stack with commercial monovalent selective anion exchange membranes (MVA) was utilized in this work. The experiments proved that the final concentration and purity of Na2SO4 in Product could reach 0.84 mol·L−1 and 94.9%, respectively, under the optimal testing conditions (initial concentration of Product solution was 15 wt.% NaCl and the current density of 200 A·m−2). Simultaneously, the concentration and purity of NaCl in Brine achieved 1.90 mol·L−1 and 97.1%, respectively. In order to guide the engineering application, a formula was established to predict the termination time of SED process according to the applied current density. Furthermore, glycerol retention rate of the SED stack in Feed solution could reach more than 95%. And low energy consumption on Na2SO4 and NaCl fractionation/concentration by 0.13–0.15 kWh·kg−1 at 200 A·m−2. Hence, this work illustrated the techno-economic feasibility of using SED for saline wastewater valorization.