Research and development of a sodium alginate/calcium ion gel based on in situ cross-linked double-network for controlling spontaneous combustion of coal

To combine the advantages of polymer gels and inorganic sodium silicate gels for preventing and controlling the spontaneous combustion of coal, a new type of SA/P/B/Ca (sodium alginate/non-ionic polysaccharide/inorganic boron crosslinking agent/calcium carbonate) gel was designed in this paper. Based on the ionic crosslinking reaction of sodium alginate and Ca2+, the inorganic boron crosslinker was used to release the masked Ca2+ to achieve rapid in-situ gelation and a controllable gelation time. Simultaneously, the complex reaction between cis-diols and B(OH)4− formed a second network. The formulation of the SA/P/B/Ca gel was studied by orthogonal experiments. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), temperature-programmed oxidation experiments, and thermogravimetric analysis were used to study the synthesis mechanism and inhibitory effects of the gel. The results showed that only 5 wt% additives (total mass of SA, P, B, Ca/Total mass of the gel) was needed to obtain a gelation time of 50 s. This can greatly reduce material transport burdens. The double-crosslinked network of SA/P/B/Ca also showed improved stability and water retention compared with traditional water glass gels and single-network gels. It delayed the characteristic temperature of coal by 11–12 ℃, reduced the heat release by 19%, and showed superior inhibition and fire extinguishing performance against coal spontaneous combustion.