Inhibitory Effect and Mechanism of QRC/AES/AEO-9 Gel Foam on Oxidation Activity of Coal During the Induction Period of Spontaneous Combustion

To mitigate the hazards of coal spontaneous combustion, a composite gel foam was developed based on quercetin (QRC), sodium fatty alcohol ether sulfate (AES), alcohol polyoxyethylene ether (AEO-9), and sodium alginate. Its inhibition efficiency was systematically evaluated against three conventional inhibitors. The effects of the four inhibitors on CO release during the induction period of coal spontaneous combustion were investigated using an isothermal flow reactor. While the raw coal emitted 5.33 ppm and 138.09 ppm of CO at 30°C and 70°C, respectively, these levels dropped markedly to only 1.57 ppm and 25.54 ppm after treatment with the composite gel foam. The composite gel foam exhibited a significantly higher inhibition efficiency than other inhibitors. The inhibition mechanism of the gel foam in suppressing the oxidation activity of coal during induction period was explored by SEM-EDS, FTIR, ESR, and quantum chemical calculations. AES and AEO-9 substantially reduce surface tension, enhancing foam coverage and forming a dense oxygen-blocking layer on the coal surface. Simultaneously, quercetin, bearing a catechol moiety, acts as an efficient radical scavenger. It donates phenolic hydrogen atoms to terminate key free radicals via a hydrogen atom transfer pathway, thereby breaking the oxidation chain. The resulting QRC radicals exhibit high stability due to resonance delocalization, preventing further radical propagation. The synergistic combination of physical isolation and radical quenching effectively suppresses low-temperature oxidation, underscoring the promise of this composite gel foam in preventing coal spontaneous combustion.