Investigation on thermal analysis and FTIR microscopic characteristics of artificially-oxidized coal and chronic naturally-oxidized coal during secondary oxidation

Abstract

To reduce mine fire risk and ensure efficient resource utilization, an in-depth research must be conducted on the secondary oxidation of coal. Accordingly, the macroscopic oxidation characteristics and microscopic composition of newly-mined coal, artificially oxidized coal (the newly-mined coal oxidized at 70 °C and 180 °C) and repeated-mined coal (oxidized naturally over 10 years) were evaluated in this study. And these coal samples were labeled N, N-70, N-180, and R, respectively. The parameters indicating the oxidation characteristics of coal were analyzed by simultaneous thermal analysis-Fourier transform infrared spectroscopy (STA-FTIR) and Shimazu Fourier transform infrared spectrometry (FTIR-8400) from the perspective of coal thermal reaction and functional groups. The experimental results suggest that the temperature T2 required by N-70, N-180, and R to reach the oxidation stage was lower than that of N. In addition, CO and CO2 gases were released earlier from these coals than from N. The same release was earlier for N-180 and N-70 compared to that for R. Compared with N, the content of hydroxyl and aliphatic hydrocarbons in N-70, N-180 and R after the initial oxidation decreases, and the decrease of N-70, N-180 was greater than that of R. The content of oxygen-containing functional groups (-COOH, C=O, -COO-) increased significantly, and the increase for N-70, N-180 was greater than that of R. These results indicate that coal was more prone to secondary oxidization after primary oxidation. This is because the coal absorbed heat released during the primary oxidation and subsequently had a higher activity. The artificially-oxidized coal in the laboratory absorbed more heat and generated more oxygen-containing functional groups (-COOH, C=O, -COO-) than the chronic naturally-oxidized coal in the mine face, resulting in a higher risk of spontaneous combustion during secondary oxidation.