A novel modified guar gum antioxidant gel foam was fabricated to improve foam stability and suppress coal spontaneous combustion (CSC). Tert-butylhydroquinone (TBHQ) was introduced as an antioxidant into hydrophobically modified guar gum to prepare a physicochemical composite inhibitor, which was blended with surfactant and gel components. The CSC suppression relies on the synergistic effect of foam, gel and inhibitor. Single-factor experiments combined with response surface methodology (RSM) were used to optimize the gel foam formulation, and the foam microstructure was characterized. Cementation, film-forming and temperature-programmed oxidation tests were carried out to evaluate its inhibition performance. Results demonstrate that the optimal mass fractions of gelling agent, cross-linker, foaming component and antioxidant are 1.602 wt.%, 0.20 wt.%, 0.20 wt.% and 0.86 wt.%, respectively. The inhibitor forms a water-retentive foam skeleton with stable interfaces. The foam has small, uniformly distributed bubbles with low coarsening rate, which can fully wet coal and produce cooling effects. It exhibits outstanding cementation and film-forming capability to bind pulverized coal, form continuous gel films, block gas percolation and isolate coal from oxygen. Compared with water-based foam, polymer-stabilized foam and conventional gel foam, this material achieves stronger CSC inhibition. It reduces oxygen consumption, gas generation and heat release during coal oxidation, with an average inhibition efficiency of 86.5% at 120–170 °C. The developed material combines excellent foam properties and inhibition capacity. It physically delays coal oxidation through covering, wetting, cementation and pore plugging; chemically, it scavenges oxidative free radicals and terminates coal‑oxygen chain reactions to prevent coal spontaneous combustion.
 

coal spontaneous combustion; hydrophobically modified guar gum; gel foam; free radicals; synergistic inhibition mechanism