Experimental study on carbon sequestration during the synthesis of calcium silicate induced by microwave heating

During the preparation of Portland cement clinker, the decomposition of calcium carbonate(CaCO₃) releases a significant amount of CO₂, substantially exacerbating the greenhouse effect. Reducing CO₂ emissions has become a critical technological challenge that urgently needs to be addressed by the cement industry in the context of achieving the "dual carbon" goals. This study employs calcium carbonate(CaCO₃) and quartz sand as raw materials, with α-SiC and silicon(Si) serving as induction media. Utilizing microwave heating-induced technology, CO₂ is fixed to prepare in-situ β-SiC-graphitic carbon/calcium silicate composite powders. The results indicate that as the microwave synthesis temperature increases from 1150℃ to 1250℃, the concentrations of SiO₂ and CaO in the synthesized products gradually decrease, while the contents of dicalcium silicate(Ca₂SiO₄, C₂S) and tricalcium silicate(Ca₃SiO₅, C₃S) increase. Further increasing the synthesis temperature to 1350℃ results in no significant changes in the composition of dicalcium silicate(C₂S) and tricalcium silicate(C₃S) in the products. Additionally, at a microwave synthesis temperature of 1250℃, the residual amount of silicon(Si) in the product is minimized, and the product contains β-SiC along with graphitic carbon. During the microwave heating process, the solidification effect of carbon in the CO₂ produced during the reaction can be controlled by adjusting the temperature and holding time in the medium temperature stage(650-750℃). It was found that when the medium holding temperature increases from 650℃ to 750℃ and the holding time extends from 10 to 30 minutes, the amount of carbon sequestration first increases and then decreases. When the holding temperature is controlled at 700℃ and the holding time is 20 minutes, the carbon fixation reaches maximum theoretical value, which is 39.79%. Microwave-assisted in-situ synthesis of β-SiC-graphitic carbon/calcium silicate can effectively reduce CO₂ emissions during the production of cement clinker.