Effects of FeS2 on the process of coal spontaneous combustion at low temperatures

Abstract

Spontaneous combustion of coal has become an important disaster that threatens the safety of coal mines. FeS2 is the main component of pyrite, which is suspected to be a major contributor to coal spontaneous combustion (CSC). So, it has important significance to FeS2 on the characteristics of coal oxidation for prevention and treatment. This study used coal samples mixed with different proportions of FeS2 (2.0 mass%, 4.0 mass%, and 6.0 mass% mass percentage) were tested to investigate the characteristics of spontaneous combustion, as compared with the fresh sample. The CO and CO2 production rates, critical temperature, and dry cracking temperature during oxidation were analyzed. The temperature-programmed experiments was conducted to simulate low-temperature oxidation processes realistically. In-situ infrared spectroscopy was used to appraise the evolution of low-temperature (< 200.0°C) oxidation of aromatic hydrocarbons, aliphatic hydrocarbons, and oxygen-containing functional groups on the surfaces of the samples. Experimental results showed that FeS2 exhibited a strong influence as the temperature exceeded the dry cracking temperature. Adding 2.0 mass% and 4.0 mass% FeS2 showed a promoting effect on low-temperature oxidation; however, FeS2 became an inhibitor which reached 6.0 mass%. Furthermore, adding 2.0 mass% FeS2 showed the strongest promoting effect. From a microscale perspective, the promoting effect of FeS2 on coal oxidation was due to thermal release from FeS2 oxidation, enhancing the reaction between aliphatic hydrocarbons, such as methyl groups and methylene, and oxygen. Due to the reaction of FeS2, the acidic environment was conducive to the hydrolyzation of lipid structures into highly active alcohol or phenol structures, which in turn promoted the oxidation of the coal sample. These results are crucial for understanding the mechanism underlying the influence of FeS2 on CSC and mine safety protocols.