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.