Experimental Study on a Metal-Chelating Agent Inhibiting Spontaneous Combustion of Coal

In order to inhibit the intrinsic metal in coal to catalyze the spontaneous combustion of coal, three different types of metal-chelating agents were selected to react fully with coal, and thermogravimetric and differential scanning calorimetry curves of coal samples and gas generated during coal oxidation were obtained through temperature-programmed experiments. The effects of these additives on coal spontaneous combustion were analyzed by characteristic temperature, exothermic peak parameters, and CO and CO2 emission laws. The results show that the addition of oxalic acid promotes the spontaneous combustion of coal, ethylenediaminetetraacetic acid, and phytic acid and can inhibit the spontaneous combustion of coal, and the inhibition effect of phytic acid is better. The mechanism of phytic acid inhibition of coal samples was analyzed by Fourier transform infrared spectroscopy. It was found that phytic acid can capture metal ions in coal to form stable chelates. The oxygen-containing functional groups in coal combine to form an ether, ester, and hydrogen-bonded cross-linking structure, which improve the stability of coal macromolecules. In the oxidation reaction, phytic acid reduces the free radical content of the system and inhibits the chemical adsorption of coal to oxygen, thereby delaying the spontaneous combustion of coal. The inhibitory effect of phytic acid on the spontaneous combustion of coal with different metamorphic degrees was compared. It was found that phytic acid had a significant inhibitory effect on low rank coal. The minerals in the coal were analyzed by water and hydrochloric acid treatment, and it was found that the phytic acid was mainly combined with the exchangeable minerals in the coal. It is considered that phytic acid is a new type of high-efficiency low rank coal spontaneous combustion inhibitor, and it is very friendly to the environment. The results can provide new ideas for preventing the spontaneous combustion of coal.