Moisture-driven carbonation kinetics for ultrafast CO₂ mineralization

CO₂ mineralization, a process where CO₂ reacts with minerals to form stable carbonates, presents a sustainable approach for CO₂ sequestration and mitigation of global warming. While the crucial role of water in regulating CO₂ mineralization efficiency is widely acknowledged, a comprehensive understanding of the underlying mechanisms remains elusive. This study employs a combined experimental and atomistic simulation approach to elucidate the intricate mechanisms governing moisture-driven carbonation kinetics of calcium-bearing minerals. A self-designed carbonation reactor equipped with an ultrasonic atomizer is used to meticulously control the water content during carbonation experiments. Grand Canonical Monte Carlo simulations reveal that maximum CO₂ uptake occurs at a critical water content where the initiation of capillary condensation significantly enhanced liquid-gas interactions. This phenomenon leads to CO₂ adsorption-driven ultrafast carbonation at an optimal moisture content (0.1 to 0.2 g/g, water mass ratio to total wet mass of the mineral). A higher moisture content decimates the carbonation rate by crippling CO₂ intake within mineral pores. However, at exceptionally high moisture levels, the carbonation reaction sites shift from internal mesopores to the grain surface. This results in surface dissolution-driven ultrafast carbonation, attributed to the monotonically decreasing free energy of dissolution with increasing surface water thickness, as revealed by metadynamics simulations. This study provides a fundamental and unified understanding of the multifaceted role of water in mineral carbonation, paving the way for optimizing ultrafast CO₂ mineralization strategies for global decarbonization efforts.