The Release of Dissolved Organic Matter and Inorganic Nitrogen from Coal Gangue of Different Geologic Ages in North China

Static leaching experiments lasting 480 h were performed to investigate the release of dissolved organic matter (DOM) and inorganic nitrogen from coal gangues collected from the Jurassic Middle-Lower Yan′an formation in the Bulianta coal mine (CG1) and the Permian Shanxi formation in the Baode coal mine (CG2) in North China. The amounts of dissolved organic carbon (DOC), NH4+–N, NO3−–N, and NO2−–N released from CG1 were all much higher than those from CG2, as was the electrical conductivity. These were highly correlated with the mineral and chemical composition and lithology. The fluorescence, biological, and humification indices for the leachates were indicative of autochthonous microbial processes that occurred during DOM formation. In addition, the specific ultraviolet absorbance at 254 nm (SUVA254) and fluorescence intensities (divided by DOC) of peaks B1, B2, T2, and A indicated that more microbial and less plant precursors in the DOM were released from CG2 than from CG1. Adsorption and denitrification of NH4+–N and NO3−–N released from CG1 and CG2 were observed. These results should be useful in assessing the environmental impacts caused by the DOM and nitrogen released from coal gangue.