Study on the thermal behaviour of spontaneous combustion of open-pit minerals

Jing-Yu Zhao; Zhao-Long Chi; Jia-Jia Song; Shi-Ping Lu; Yan-Ni Zhang; Chang-Kui Lei; Chi-Min Shu

doi:10.1016/j.scitotenv.2024.172477

Study on the thermal behaviour of spontaneous combustion of open-pit minerals

Sci Total Environ. 2024 Jun 15:929:172477. doi: 10.1016/j.scitotenv.2024.172477. Epub 2024 Apr 15.

Authors

Jing-Yu Zhao¹, Zhao-Long Chi¹, Jia-Jia Song², Shi-Ping Lu¹, Yan-Ni Zhang¹, Chang-Kui Lei³, Chi-Min Shu⁴

Affiliations

¹ School of Safety Science and Engineering, Xi'an University of Science and Technology, No. 58, Yanta Mid. Rd., Xi'an, Shaanxi 710054, PR China; Shaanxi Key Laboratory of Prevention and Control of Coal Fire, Xi'an University of Science and Technology, No. 58, Yanta Mid. Rd., Xi'an, Shaanxi 710054, PR China.
² School of Safety Science and Engineering, Xi'an University of Science and Technology, No. 58, Yanta Mid. Rd., Xi'an, Shaanxi 710054, PR China; Shaanxi Key Laboratory of Prevention and Control of Coal Fire, Xi'an University of Science and Technology, No. 58, Yanta Mid. Rd., Xi'an, Shaanxi 710054, PR China. Electronic address: songjiajia07@sina.com.
³ School of Safety and Emergency Management Engineering, Taiyuan University of Technology, No. 79, Yingze West Street, Taiyuan, Shanxi 030024, PR China.
⁴ Department of Safety, Health, and Environmental Engineering, National Yunlin University of Science and Technology, 123, University Rd., Sec. 3, Douliou, Yunlin 64002, Taiwan.

PMID: 38621544
DOI: 10.1016/j.scitotenv.2024.172477

Abstract

To study thermal behaviour during spontaneous combustion of an open-pit coal mine, mixed slag (coal, oil shale, and coal gangue) was taken as the research object. Laser thermal conductivity analyser and differential scanning calorimetry were used to test thermophysical parameters and heat release characteristics of the minerals. The parameters can be employed to calculate the apparent activation energy using the Arrhenius equation and evaluate the thermal behaviour of open-pit mixed slag. The results indicate that thermophysical parameters have stage characteristics. Thermal diffusivity and thermal conductivity of minerals, especially mixed slag, have a strong correlation with temperature. Heat flow of minerals exhibits five characteristic stages, and heat flow of the samples is consistent with the change in heating rate. During the heating process, thermal diffusivity and heat flow of the mixed slag are between those of a single mineral. Except for the mixed slag at 15 and 20 °C/min, the initial exothermic temperature of the other samples is mainly concentrated at 50-80 °C. Thermal energy release of the sample is mainly concentrated in the accelerated exothermic stage and rapid exothermic stage. Thermal energy release of mixed slag in rapid exothermic stage is always greater than that in accelerated exothermic stage, and the proportion of thermal energy release in these two stages exceeds 98 %. The apparent activation energy during the accelerated exothermic stage is lower, making it easier to release heat, and rapid exothermic stage is relatively high, which can readily lead to heat accumulation. Thermal analysis reveals that the thermal behaviour of mixed slag is significantly different from that of a single mineral. Its unique exothermic characteristics can provide a more accurate theoretical basis for the prevention and control of environmental pollution caused by slag spontaneous combustion.

Keywords: Apparent activation energy; Exothermic characteristic; Heating rate; Thermal energy release; Thermophysical parameters.