Synthesis, Characterization, and Cementitious Activity of the Magnesium Silicate Hydrate and Calcium Silicate Hydrate from Coal Gangue

Coal gangue, a prevalent solid waste in the coal industry, has long been a significant concern due to its substantial production volume and potential environmental hazards. However, it contains valuable components such as silica and alumina, making it a promising raw material for synthesizing cementitious materials. This study focused on the synthesis of coal gangue-based magnesium silicate hydrate (M-S-H) and calcium silicate hydrate (C-S-H) through mechanical–thermal–chemical composite activation treatment. The cementitious activity of coal gangue samples and the characterization of the resulting cementitious materials were analyzed using ICP-AES, FTIR, XRD, SEM, and DSC-TG. Results indicated that calcination temperature, calcination time, the Ca/Si molar ratio, and the Mg/Si molar ratio were key factors influencing the cementitious activity of coal gangue, exhibiting a positive correlation with the dissolution amounts of Si4+ and Al3+. When kaolin in coal gangue was fully decomposed into active Al2O3 and SiO2, the cementitious activity of coal gangue reached its peak. M-S-H and C-S-H were successfully synthesized after 7 days of curing at room temperature, significantly reducing the synthesis time. The synthesized M-S-H and C-S-H exhibited large specific surface areas, good mechanical properties, and well-developed pore structures, making them suitable as mesoporous materials that provide numerous active sites for adsorbing metal ions.