Preparation and performance study of coal-gangue-based fire prevention gel via mechanical-thermal-chemical activation

Coal gangue, a solid waste generated as a by-product of coal mining, poses multiple challenges when stockpiled, including land occupation, environmental pollution, and spontaneous combustion. This research develops a high-performance fire-extinguishing material by valorizing gangue into a coal gangue-sodium alginate-polyacrylic acid (GSP) multi-network hydrogel via a mechanical-thermal-chemical synergistic activation protocol. Alkali activation of calcined gangue (800 °C) facilitates the release of active Al³⁺, Fe³⁺, and Ca²⁺ ions, which catalyze coordination crosslinking with the organic carboxyl groups to form a robust, densified inorganic-organic framework. SEM-EDS characterization confirms a complex dual-network architecture where gangue particles serve as rigid reinforcements within the porous gel matrix. The GSP gel exhibits superior engineering functionality, including advanced fracture sealing, excellent high-temperature stability, and efficient long-distance pumpability, which effectively isolates oxygen and suppresses coal spontaneous combustion (CSC). Thermal analysis (TG-DSC) demonstrates that the gel treatment delays the coal ignition temperature by 14 °C and elevates the oxidation activation energy by 30.1%, effectively raising the kinetic threshold for thermal runaway. Crucially, FTIR spectroscopy reveals a molecular passivation mechanism: the gel encapsulates active surface sites, retarding the dehydrogenation of aliphatic C-H groups and significantly suppressing the evolution of reactive carbonyl (C=O) intermediates during low-temperature oxidation. Small-scale trials validate that the system rapidly suppresses high-temperature coal fires (800 °C) to ambient levels within 180 min without re-ignition. This research offers an integrated approach to mitigating the environmental footprint of gangue stockpiles while providing a high-efficiency material for mine fire suppression through synergistic physical-chemical inhibition.