Preparation and study of a sodium alginate film for preventing spontaneous combustion of water-soaked coal in goaf

Considering the high risk of spontaneous combustion of soaked coal compared to raw coal and the limitations of existing technology in preventing spontaneous combustion of coal in goaf water, a sodium alginate film has been developed which can effectively solve the problem of preventing spontaneous combustion of soaked coal by oxygen insulation, heat absorption and inhibition. The optimum composition ratio and the properties of the film are evaluated by film formation and thermogravimetric experiments. The results show that the film properties are best when the ratio of sodium alginate to gelatin is 8:2, the sodium tripolyphosphate concentration is 0.5 %, the ammonium polyphosphate concentration is 0.2 %, and the concentration of CaCl2 for the first and second cross-linking is 0.01 % and 0.2 %, respectively. The combination of sodium alginate and CaCl2 forms a stable and compact spatial network structure that can reduce the temperature of the covered coal by approximately 36 °C. Throughout the field trials, the temperature change of the goaf treated with sodium alginate film is opposite to that of the untreated area, showing a downward trend, with a total decrease of 0.4 °C in 20 days. This study provides a new idea for preventing spontaneous combustion of soaked coal.