Amine-promoted gypsum carbonation for efficient CO2 capture and selective synthesis of CaCO3 polymorph integrating with amine regeneration by bipolar membrane electrodialysis

Abstract

CO2 mineralization of waste gypsum not only reduces the carbon emissions of power plants but also improves gypsum utilization by recovering high-value-added CaCO3. However, the extensive consumption of various reagents limited its development. This paper proposed an amine-promoted waste gypsum carbonation process integrating with amine regeneration by bipolar membrane electrodialysis (BMED). The alkaline amine was expected to act as a multifunctional reagent for gypsum carbonation — alkaline reagent, CO2 absorbent, gypsum dissolution promoter, and CaCO3 crystal regulator. Seven typical amines with different amino types and pKa values were selected to investigate the feasibility of this process. Results show that promising CO2 removal efficiency (>95 %) from an artificial exhausting gas, gypsum carbonation efficiency (>93 %), and CO2 sequestration capacity (>340 g-CO2/kg-gypsum) can be achieved due to the additional alkalinity, fast CO2 absorption, high CO2 concentrations, and enhanced CaSO4 dissolution in amine solutions. In addition, the interactions of amine-CO2-gypsum and the CaCO3 growth mechanism in the gas–liquid-solid system were explored. Monoethanolamine (MEA), 3-amino-1-propanol (MPA), piperazine (PZ), and 1,3-Diaminopropane (DAP) could prolong the CaCO3 precipitation due to their strong affinity for Ca2+ and CO32−. In this case, CO2 absorption by the liquid phase dominated the carbonation process in the initial 30 min for these four amines, while CaCO3 precipitation mainly occurred within 30 ∼ 120 min. Amines’ different affinities for Ca2+ and CO32− provided an approach to selective synthesis of CaCO3 polymorph: 100 % calcite by PZ, 100 % vaterite by DAP, a calcite-vaterite mixture by MEA, and a calcite-vaterite-aragonite mixture by MPA. After the carbonation process, amines were recycled from the liquid residue by BMED, which could provide OH− for amines regeneration from protonated amines, recovery of H2SO4, and decrease the solution salinity.