Research progress on the thermal activation treatment process of coal gangue

Coal gangue is one of the largest solid wastes generated during coal mining and washing, and its low intrinsic reactivity greatly restricts direct high-value utilization. Thermal activation is an effective strategy for converting low-activity coal gangue into reactive aluminosilicate materials. This review systematically summarizes the mineral transformation mechanisms, key process parameters, property evolution, and resource utilization pathways of thermally activated coal gangue. During calcination, kaolinite-rich coal gangue undergoes dehydroxylation and structural disordering, forming metakaolinite and amorphous Si-Al phases that contribute to pozzolanic activity. The activation effect is strongly controlled by calcination temperature, holding time, particle size, cooling mode, and atmosphere. Moderate thermal activation generally promotes the release of reactive SiO2 and Al2O3, improves grindability, adsorption capacity, and cementitious reactivity, whereas excessive calcination may induce crystallization into inert phases such as mullite and cristobalite, resulting in activity loss. The review further discusses the applications of activated coal gangue in cementitious materials, adsorbents, porous materials, wastewater treatment, and soil improvement. Finally, future research directions are proposed, including process scale-up, low-carbon assessment, quantitative characterization of amorphous phases, and long-term environmental safety evaluation. This review provides a mechanistic and application-oriented basis for the high-value utilization of coal gangue.