Particle carbonation kinetics models and activation methods under mild environment: The case of calcium silicate

CO₂ mineralization is an economical technology with a low carbon footprint and has been considered an effective means to achieve carbon fixation. The slow diffusion and reaction in the gas-solid system of CO₂ mineralization is a common issue affecting the normal carbonation depth. The surface water plays a critical role as an ionic mass transferring medium in the reaction systems. By studying the CO₂ mineralization of dispersed calcium silicate (CS) particles, this work systematically revealed the kinetics and mechanisms of carbonation under mild environments (below 80°C). It was interesting to find that carbonation of CS particles followed different kinetic mechanisms depending on the temperature and with the migration of surface water. At 20°C, the CO₂ mineralization reaction conformed to the unreacted shrinking-core mechanism with the primary reaction rate-limiting step of product layer diffusion. For higher temperatures (40–80°C), the carbonation process was controlled by the surface water coverage. The leaching behavior of CS indicated that electrical double layer (EDL) formed at the particle interface and limited Ca²⁺ activity in water film might be the mechanism of surface water coverage controlled kinetics. Accordingly, the enhanced CO₂ mineralization of CS, 58.16% CO₂ uptake increment, was realized at 80°C through rehydration activation. The evolution of mineral micromorphology with process of leaching and carbonation is characterized by semi-quantitative XRD analysis and mercury intrusion porosimetry analysis. CO₂ mineralization kinetics and the proposed activation method under mild environment open the door to efficient CO₂ mineralization with low energy consumption.