Experimental research on the spontaneous combustion of coal with different metamorphic degrees induced by pyrite and its oxidation products

To study the effect of pyrite on the spontaneous combustion of coal, three types of low-sulfur coal samples with different metamorphic degrees, namely HQL (lignite), DR (bituminous), and YQ (anthracite), were selected to impregnate FeS2 and its oxidation products. The results of thermal analysis experiments showed that Fe3+, Fe2+, and H+ had evident catalytic effects on the low-temperature oxidation of the three samples, with the catalytic order being Fe3+ > Fe2+ > H+. A self-heating experiment on coal showed that Fe3+ reduced the shortest ignition time of the above samples by 55.4%, 49.8%, and 45.3%, respectively, and its catalytic ability was the strongest. With the increase in the degree of metamorphism, the promotion effect of Fe2+ gradually decreased, and the promotion effect of H+ on the low-temperature oxidation of DR was the greatest. Through an FTIR analysis, it was found that Fe3+, which is a strong oxidant and free radical, could catalyze the oxidation reaction of the active structures -CH2- and -OH. Fe2+ promoted O-2 and H+ in low-rank coals to generate H2O2 and made them to further generate hydroxyl radicals to oxidize the structure in the coal. In high-rank coals, Fe2+ catalyzed the oxidation reaction in the coal mainly through its oxidizability with decreasing H+ concentration. H+ promoted the low-temperature oxidation of coal mainly by adsorbing oxygen and removing ash to increase the specific surface area. Combining the oxidation reaction of pyrite under dry and wet conditions, pyrite could catalyze the spontaneous combustion of low-rank coals under dry conditions. Under humid conditions, pyrite could better catalyze the spontaneous combustion of high-rank coals.

Automated summary

This study shows that pyrite has a catalytic effect on the spontaneous combustion of coal. Fe3+ exhibits the strongest catalytic ability, significantly reducing the ignition time of coal. With increasing coal metamorphic degree, the promotion effect of Fe2+ weakens, while H+ has the greatest promotion effect on the low-temperature oxidation of coal. The oxidation reaction of pyrite mainly occurs through the oxidizability of Fe3+ and Fe2+, while H+ promotes coal oxidation by adsorbing oxygen and removing ash to increase the specific surface area.