Inorganic Thixotropic Gel for Controlling Coal Spontaneous Combustion Through the Prevention of Air Leakage

Cracks in coal goaf provide air leakage pathways and therefore increase the likelihood of coal spontaneous combustion, thus strongly affecting the safety of mining operations. Herein, an inorganic thixotropic gel (ITG) was proposed for inhibiting coal spontaneous combustion by blocking this leakage. The orthogonal experiments were designed to examine the effects of gel composition on gelation time and rheological/thixotropic properties. The three interval thixotropy test of the optimal-composition gel (4 wt% sodium bentonite, 3 wt% laponite, and 0.46 wt% silicate cement) revealed its good thixotropic recovery. The viscoelasticity test indicated that this gel retained elasticity-dominated behavior before being completely transformed into a sol and was not easy to break into pieces under pressure. By testing the characteristics of the ITG, it was proven that the ITG had an excellent water retention capacity, and high-temperature resistance and the apparent effects on blocking air leakage and extinguishing coal fire. By the thermogravimetric test, the influence of ITG on coal activation energy was calculated based on the ignition activation energy theory. FTIR was also introduced to analyze the effect of ITG on active groups of coal. In addition, structural characterization showed that ITG featured a tight surface and a stable overall structure, which further agreed with its prominent ability to block air leakage.