Conceptual evaluation of an integrated CCU technology based on Na-salts pH swing mineral carbonation

This work proposes an alternative indirect pH swing CO₂ Capture and Storage by Mineral Carbonation (CCSM) process in order to decrease the energy intensive salts regeneration. In the proposed process, NaHSO₄ is used to extract Mg from the mineral ore, which is then carbonated after a pH swing step. The remaining Na₂SO₄ is then separated from the carbonation solution taking advantage of its low solubility at temperatures close to 0 °C and then regenerated to NaOH and NaHSO₄ in three stages. The integrated process that uses both Mg-rich silicates and inorganic wastes, was experimentally proved, and their energy consumption calculated. The final CO₂ sequestration capacity was of 77.4% with enhanced recovery of metals in the pH swing step, which could offset the CCSM by about $50/t CO₂. The final regeneration step showed a 55% conversion of Na₂CO₃ to CaCO₃ at 120 °C under 3 bar and the conversion rate could be improved further by optimization. The energy consumption estimation without optimisation indicated that the sodium-based process would require about 19.6 GJ/tCO₂, which at this stage of development is larger than the optimised Åbo Akademi process (12-15.5 GJ/tCO₂), but considerably lower than the University of Nottingham's process (30 GJ/tCO₂).