Competitive Ion Migration and Process Optimization of Carbon Sequestration and Seawater Decalcification in a Bipolar Electrodialysis Process

In the process of carbon dioxide mineralization and seawater decalcification via bipolar membrane electrodialysis (BMED), HCO3– can act with OH– to form CO32–, and there are complex reactions between Ca2+/Mg2+ ions in seawater and OH–/HCO3–/CO32–. In this study, the competitive reaction and migration rates between HCO3–, CO32–, and OH– were investigated. It is interesting to find that if the reaction rate between OH– and HCO3– is higher than the migration rate, then it is possible that no OH– exists in the membrane system by controlling the current density and the rate of CO2 entry. Seeding in the crystallizer is a good strategy for avoiding the scaling in the membrane system as for the relatively wider metastable zone of CaCO3. However, long operation run and massive crystals would bring the risk of particle introduction to the membrane stack and large energy consumption. The dispersion of CO2 is enhanced by adequate ventilation equipment and the metastable zone is fully utilized by a self-crystallization process, thus the carbon fixation is increased to 100% and the decalcification ratio to 94.43%, but the operation time and the energy consumption of the electrodialysis process are sharply shortened. These findings suggest potential applications in mineral carbonation and seawater decalcification by BMED.