Carbon dioxide capture coupled with magnesium utilization from seawater by bipolar membrane electrodialysis

Carbon dioxide (CO₂) capture coupled with further mineralization in high value-added form is a great challenge for carbon capture utilization and storage (CCUS) processes. In this work, a bipolar membrane electrodialysis (BMED) technique integrated with crystallization chamber was proposed to utilize CO₂-derived carbonates and the residual magnesium resource from seawater to produce functional nesquehonite. To ensure the stable CO₂ storage and magnesium extraction by BMED process, the metastable zone during nesquehonite crystallizing was first measured to modulate crystallization rate, obtain high-quality crystal products and inhibit membrane fouling states. Subsequently, the effects of current density, temperature, and CO₂ flow rate during the whole BMED-crystallization process were further investigated. The increase in current density and temperature was conducive for the extraction of magnesium while the enlarged gas flow rate induced higher absorption of CO₂. Under the current density at 22 A/m², CO₂ flow rate at 50 mL/min and temperature at 30 °C, the optimal carbon absorption ratio and the magnesium extraction ratio reached 50.85% and 56.71%, respectively. Under this condition, the explosion nucleation of the nesquehonite was effectively avoided to inhibit membrane fouling and the generation of magnesium hydroxide was depressed to obtain the target product nesquehonite. This study on simultaneous carbon capture and magnesium utilization provides theoretical guidance for the industrial green storage of CO₂ and development of valuable magnesium products.