Preparation and application of high accumulation solidified foam for preventing coal spontaneous combustion

Air leakage is an important cause of coal spontaneous combustion in mines, which affect the normal production of the mine. In order to solve the problems of long gelling time and weak stacking ability of traditional inorganic solidified foam (TISF) in the process of filling and plugging, a rapid setting inorganic solidified foam (RISF) modified by liquid sodium silicate (LSS) was proposed. The influence of different dosages of LSS on the gelling time, stacking capacity and other properties of foam slurry was studied. By means of compressive strength, stability test and other characterization methods, the optimal addition amount of LSS was determined to be 5% (mass fraction). The 28 d compressive strength of RISF reached 2.49 MPa, 1.7 times that of TISF. The maximum density ratio R was 1.11, and the stability increased by about 20%; The test results of gelation time and stacking ability showed that compared with TISF, the setting time of RISF was significantly shortened (from 683 s to 52 s), and the stacking ability was improved (the maximum stacking height is increased by 1.9 times). Based on this, the rapid curing mechanism of RISF was explored by combining scanning electron microscope (SEM) and X-ray diffraction (XRD). The test results showed that RISF had more hydration products and different hydration products were closely intertwined. During the particle hydration process, LSS hydrolyzed to generate the orthosilicate and combined with calcium ions in the solution, which accelerated the hydration reaction and shortened the gelling time of foam slurry. However, it was also found that when the amount of LSS added exceeded 5%, the compressive strength and stability of RISF decreased. This is mainly because excessive LSS caused the calcium silicon ratio in the solution to be lower than 1.0, resulting in the formation of low strength hydration products. The results of air blockage and fire extinguishing tests showed that compared with TISF, RISF had higher air blockage efficiency and excellent fire prevention and extinguishing performance, with a maximum increase of 26.3% in blockage efficiency, and no reignition occurred when extinguishing coal fires. The on-site application of RISF in the gangue hill of Limin Coal Mine has shown that it has good cooling and fire extinguishing effects, effectively solving the high temperature problem of the gangue hill, and ensuring the normal production of the mine.