Gel Foam Loaded with Oxygen-Consuming Bacterial Communities for the Coupled Inhibition of Lignite Spontaneous Combustion

Abstract To improve the durability of microbial inhibition of coal spontaneous combustion, oxygen-consuming bacterial communities from mining environments were immobilized in gel foam to construct a bioactive carrier for lignite protection. Two previously screened aerobic communities, D2 and D3, were loaded into four candidate gel-foam systems and evaluated in terms of carrier stability, water retention, bacterial compatibility, and functional retention. The sodium alginate-based Y1 formulation exhibited the best overall carrier performance and maintained sustained microbial oxygen consumption. Importantly, after foam collapse and air replenishment, the residual Y1 gel phase remained metabolically active and decreased the O2 volume fraction from approximately 21% to approximately 10%, demonstrating that microbial function could persist beyond the lifetime of the foam structure. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses showed that the bacterial-loaded gel foam coated the coal surface and filled pores and fissures, while no major reconstruction of the overall XRD diffraction profile was observed after treatment. Thermogravimetric/derivative thermogravimetric (TG-DTG) and kinetic analyses further showed that Y1-D2 and Y1-D3 shifted the T2/T3 temperatures from 153.20/309.91 °C to 194.81/333.07 °C and 192.35/327.13 °C, respectively, and increased the apparent apparent activation energy of the oxygen-absorption stage by 93.59% and 109.20%. The inhibition results from the coupled effects of physical sealing, water retention and bacterial immobilization, sustained biological oxygen consumption, and local gas-environment modification. This work highlights gel foam as a functional microbial carrier rather than solely as a passive fire-retardant material.