Concentration of NaCl from seawater reverse osmosis brines for the chlor-alkali industry by electrodialysis

Abstract

Currently, numerous studies are focused on the valorisation of seawater desalination reverse osmosis brines. Electrodialysis can be used to concentrate one of the primary components (NaCl) and obtain a suitable raw material for industrial applications, such as the chlor-alkali industry. An electrodialysis pilot plant was used to evaluate the efficiency of concentrating a seawater reverse osmosis (SWRO) brine under representative full-scale operational conditions covering the temperature range of a semiarid climate. The results indicate that electrodialysis is a technology that can concentrate SWRO brines from approximately 70 to 245g/L NaCl, achieving an additional intrinsic purification of major multivalent ions (Ca2+, Mg2+, SO42−) due to the selectivity patterns of ion exchange membranes and the ion-complexation reactions in the concentrated brines. However, minor components, such as Ni and Cu, are concentrated due to the formation of Cu and Ni complexes with chloride ions to form monocharged species (e.g., NiCl+ and CuCl+). Energy consumption values of 0.12kWh/kg NaCl for 185g NaCl/l at 27°C and 0.35kA/m2 or 0.19kWh/kg NaCl for 203g NaCl/l at 27°C and 0.50kA/m2 were reached. These results were compared with the data obtained from the literature for salt production by electrodialysers.