The Influences of Manganese and Phosphorus on the Low-Temperature Oxidation of Coal

Coal is rich in a variety of elements and minerals, which influence the spontaneous combustion of coal. This study investigated the effects of manganese (Mn) and phosphorus (P) on the spontaneous combustion of coal. Six Mn- and P-containing additives were added to coal and the gases released by programmed temperature heating were collected. The results showed that Mn-containing additives promoted the spontaneous combustion of coal as the temperature increased to 60°C, while P-containing additives showed significant inhibition until the temperature reached 150°C. Infrared spectra suggested that Mn enhanced the decomposition of the R-O, C-O, and -CH2 in the coal, while P significantly inhibited the decomposition of R-O and C-H. Thermogravimetry/differential thermal analysis (TG/DTA) implied that Mn promoted the oxy-genolysis of coal and released more heat, while P delayed the critical temperature of the spontaneous combustion of coal. In addition, by investigating the contents of Mn and P in the coal from 18 coal fields in China, it was found that in general, spontaneous combustion seldom occurred in mine areas with a high P content. This could possibly be attributed to the fact that Mn enhanced the generation of free radicals through electron transfer, while P played an inhibiting role by capturing free radicals.