Bipolar membrane electrodialysis as part of a CO2 mineralization process: A comparison of three different input sulfate salt solutions

This study investigates efficient methods for regenerating sulfuric acid and alkaline solutions required in the CO 2 mineralization process known as the “wet ÅA route”. The performance of three sulfate salts, K 2 SO 4 , Na 2 SO 4, and (NH 4 ) 2 SO 4, was compared by applying a three-compartment bipolar membrane electrodialysis (BMED) stack, enabling the regeneration of acid and base solutions from the remaining sulfate solution left at the end of the ÅA route. Na 2 SO 4 or K 2 SO 4 as input salt solutions proved most energy-efficient in terms of kJ electricity/kg (or mol) salt separated. Using K 2 SO 4 also results in a higher conversion rate (mol or kg salt separated/h), compared to the other two salts. 3.4 kJ/kg K 2 SO 4 separated was required and a conversion rate of 0.1 kg K 2 SO 4 separated/h was achieved with a Eurodia EUR2 pilot stack (7 cells, active membrane area of 0.02 m 2 /membrane and maximum container volume of 4 L). The potential for separating any un-carbonated magnesium from the process solution via monovalent-selective electrodialysis was also assessed. Approximately 8 % of the magnesium ions were transported across the membranes, indicating a risk of fouling in downstream BMED operations. To meet purity requirements (<1 ppm Mg²⁺), alternative separation methods such as ion exchange resins should be considered. • Bipolar membrane electrodialysis was applied to three sulfate salt solutions. • K 2 SO 4 outperforms in terms of conversion rate, compared to (NH 4 ) 2 SO 4 and Na 2 SO 4 . • By using 0.5 M K 2 SO 4 input salt, 3.4 kJ/kg K 2 SO 4 and 0.1 kg K 2 SO 4 /h was achieved. • Monovalent selective membrane electrodialysis retained 92 % of the magnesium input.