Separation of sodium hydroxide from post-carbonation brines by bipolar membrane electrodialysis (BMED)

Desalination brine is composed of two-fold higher Ca and Mg than seawater and is a promising candidate for the mineral carbonation process to reduce CO2. We previously obtained post-carbonation brine containing Na (2.6–2.8 wt%), Mg (60–147 mg/L), and Ca (4–7 mg/L) after mineral carbonation, followed by a conventional electrodialysis process using desalination brine. In the mineral carbonation process, NaOH was used as an essential reactant. This study aimed to use bipolar membrane electrodialysis (BMED) to produce NaOH solutions (>1.0 M to be recycled during mineral carbonation) from post-carbonation brine containing bivalent Mg ion concentrations >10 mg/L. In this study, we monitored the effects of applied voltage, temperature, the initial volume ratio of solutions (feed, base, and acid compartments), and the initial concentration of the acid/base solution on BMED performance. Proton leakage through the anionic exchange membrane could be utilized for the production of NaOH in the BMED process from Mg-containing brine by varying the volume ratio of the solutions. A total of 2.0 mol/L of NaOH was obtained from a brine containing 147 mg/L of Mg ions. These findings suggest potential efficiencies in the mineral carbonation processing of desalination brines. A further refinement of this method in a cyclic manner can help sequestrate CO2 through the mineral carbonation of desalination brines.