Acid and base recovery from softened reverse osmosis (RO) brines. Experimental assessment using model concentrates

Managing high salinity concentrates generated during membrane water desalination processes is a primary need due to the potential threat to the receiving ecosystems that brine discharge represents. Brines from desalting techniques contain inorganic salts that may be further purified to increase their commercial value. This study presents a beneficial reuse strategy for reverse osmosis (RO) brines generated in a seawater desalination plant. Bipolar membrane electrodialysis (BMED) has been the selected technology for the conversion of RO concentrates into acid and base products.The viability results presented prove that BMED can be considered a technically feasible option for the production of 1.0 M or higher concentrated acid and base with current efficiencies in the 60–90% range. Main factors affecting the current efficiency are proton and sulphate migration through anionic exchange membranes towards the acid stack and to a minor extent the migration of co-ions, Cl−, through cation exchange membrane towards the base stack. These results indicate that the application of the BMED process to real seawater RO brines needs the implementation of pre-treatment steps in order to eliminate interference compounds.From this work it can be further conclude that application of BMED process will contribute to ensure the recovery of valuable compounds.

► BMED for obtaining acid and base products from RO brines
► HCl and NaOH 1.0 M are obtained in bench scale setup
► Current efficiencies in the 60–90% range are obtained
► The proton and sulphate migration to the acid stack influence current efficiency