Distribution pattern of polycyclic aromatic compounds in coal gangue from coal city-East China

Coal gangue is a by-product of coal, the output of which is as high as 30% of raw coal, whereas only 30% of it is recycled. The leftover remains in the environment from gangue backfilling areas and overlap with residential, agricultural, and industrial areas. Coal gangue accumulated in the environment is easily weathered and oxidized and becomes a source of various pollutants. In this paper, 30 coal gangue samples (fresh and weathered coal gangues) were collected from three mine areas in Huaibei, Anhui province, China. Gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) was used to qualitatively and quantitatively analyze thirty polycyclic aromatic compounds (PACs), including 16 polycyclic aromatic hydrocarbons (16PAHs), preferentially controlled by the United States Environmental Protection Agency (US EPA), and the corresponding alkylated polycyclic aromatic hydrocarbons (a-PAHs). The results showed that PACs existed objectively in coal gangue, and the content of a-PAHs was higher than that of 16PAHs (average values for 16PAHs ranged from 77.8 to 581 ng/g; average values for a-PAHs ranged from 97.4 to 3179 ng/g). Moreover, coal types not only affected the content and type of PACs but also affected the distribution pattern of a-PAHs at different substitution sites. With the increase of gangue weathering degree, the composition of a-PAHs kept changing; the low ring a-PAHs were more easily diffused to the environment, and the high ring a-PAHs remained enriched in the weathered coal gangue. The correlation analysis showed that the correlation between fluoranthene (FLU) and alkylated fluoranthene (a-FLU) was as high as 94%, and the calculated ratios were not more than 1.5. The basic conclusion is that not only 16PAHs and a-PAHs objectively existed in the coal gangue, but also the characteristic compound belonging to the pollution source of coal gangue oxidation have been discovered. The results of the study provide a new perspective for the analysis of existing pollution sources.