Environmental characterization of burnt coal gangue banks at Yangquan, Shanxi Province, China

The environmental characteristics of coal gangue dumps in Yangquan (Shanxi Province, China) were investigated. The amounts of coal gangue are very high in this coal region given the large coal production. As a result, widespread spontaneous coal gangue combustion gives rise to serious environmental problems. Coal gangue (including bulk gangue and specific lithologies, such as coal, kaolinite-rich material, sandstone, carbonate minerals, and sulfide mineralizations), fired coal gangue and condensate products from gas vents were fully characterized with respect to mineralogy, chemistry and leaching potential. The mineral paragenesis of the fired coal gangue (cristobalite, mullite, hematite, trydimite, cordierite) showed that the combustion temperature could reach 1200 °C. This was also corroborated by laboratory calcination tests. During this combustion some elements such as C, Cl, F, S, N, As, Cd, Hg, Pb, Sn, Ge and Se are emitted into the atmosphere. However, condensation processes accounted for the partial trapping of gaseous emissions of As, S, N, Hg and Se. Thus, condensate mineralizations of elemental sulfur and ammonium salts enriched in Se, As and other trace elements are frequent in the gas vents. The leaching potential of trace elements in the fresh coal gangue was relatively low, but the leaching of weathered coal gangue and the gas vents condensates could give rise to environmental problems, as these materials produce acidic leachates and yield relatively high leachable levels of a number of elements.