Study on the distribution characteristics and ecological risk of heavy metal elements in coal gangue taken from 25 mining areas of China

Aliphatic and polycyclic aromatic compounds in coal and coal-based solid wastes: Relationship with coal-forming paleoenvironment and implications for environmental pollution

In this study, coal and coal-based solid wastes (coal gangue, fly ash, bottom ash, desulfurized gypsum and tar residue) were collected from major coal mines, power plants and coking plants in Lianghuai mining area (LH), China, and were analyzed for 76 polycyclic aromatic compounds (PACs), 27 n-alkanes and 2 isoprenoids (phytane and pristane). The total n-alkanes concentrations and ∑76 PACs in raw coals (640 ± 600 and 180 ± 87 μg/g) were higher than those in coal-based solid wastes (47 ± 40 and 24 ± 25 μg/g), but were lower than those in tar residue (3700 and 63,000 μg/g). It was discovered that the depositional paleoenvironment in LH was mostly a lacustrine and freshwater environment with oxidizing conditions and mixed organic matter input, but the Huainan coalfield had stronger oxidizing conditions and more input of terrestrial organic matter than that of the Huaibei coalfield. Alkylated PACs made up 56 ± 12 % of the ∑76PACs in raw coals, whereas solid wastes mainly consisted of 16 EPA PAHs (66 ± 16 %). Coal combustion and gangue weathering altered the structural properties of n-alkanes and PACs, resulting in a significant loss of n-alkanes and PACs, a higher proportion of parent PACs, and an increased abundance of short n-alkanes in the products (No apparent change of n-alkanes composition was observed through gangue weathering). The toxicity of PACs in raw coal and its solid wastes in LH from high to low was tar residue, raw coal, coal gangue, and coal-fired products. This investigation further confirmed that traditional diagnostic ratios may distort source information, and that they should not be used to assess PACs sources from raw coal particles or coal gangues, but rather to identify combustion sources near the point source. In addition, Retene/(Retene + Chrysene) < 0.03 may indicate direct contamination of raw coal particles.

Dynamic leaching behaviors of heavy metals from recycled coal gangue aggregate under loading conditions during solid backfill mining

In solid backfill coal mining, recycled coal gangue aggregate (RCGA) is subject to the combined effects of overlying strata stress and leaching by mine water in the goaf. This process causes heavy metals to be leached and released from RCGA, which can lead to groundwater contamination. In this study, the release patterns of heavy metals in RCGA under the coupled effects of stress, solution pH, and solution flow rate were investigated, and the interactions between RCGA and the surrounding environment were explored. The findings indicate that: (1) The combined action of effective stress and mine water promotes the leaching of heavy metals. Specifically, the leaching of Pb, Zn, and Mn of RCGA is primarily influenced by the pH value of the leaching solution, while the leaching of Cu and Cr of RCGA is more closely related to the stress level; (2) Acidic environments accelerate the release of carbonate-bound fraction (CAR) in elements, facilitating the transformation of Fe/Mn oxide-bound fraction (XXI) into soluble forms; (3) The leaching ratios (Lr) of heavy metals follow the order: LrZn> LrPb> LrMn> LrCu> LrCr. This research provides guidance for the safe application of RCGA in solid backfill coal mining.

Reproductive strategy response of the fungi Sarocladium and the evaluation for remediation under stress of heavy metal Cd(II)

Cadmium (Cd) is documented as one of the most lethal metals and poses a major threat to all life forms in the environment due to its toxic effects. Bioremediation of hazardous metals has received considerable and growing interest over the years. The functional fungi with tolerance to the heavy metal Cd were screened from the mining soil samples. Two fungi isolates from coal mine soil were characterized as Sarocladium sp. M2 and Sarocladium sp. M6 based on morphological and partial ITS sequencing analysis. M2 and M6 exhibited high levels of resistance to cadmium, and they were investigated for their micro-morphology and application in heavy metal removal with different concentration Cd(II) (0, 50, 100, 150 and 200 mg/L). The colony morphology of M2 and M6 gradually become very similar to that of bacteria with the increase of cadmium concentration (150-200 mg/L). Micro-morphological studies showed that Cd(II) exposure caused the disappearance of conidial heads and the occurrence of hyphae breakage (100-200 mg/L Cd(II), which is consistent to the colony morphology results. The surface/volume ratio of the spores decreased with the presence of Cd(II). The removal potential of fungi for cadmium was quantified by atomic absorption spectrometry. M2 and M6 showed great potential as bioremediators for highly Cd(II)-contaminated environment. The highest Cd(II) biosorption capacity was 5.13 ± 0.21 mg/g for M2 and 6.04 ± 0.21 mg/g for M6. The highest heavy metal sorption by M2 removed 57.11% ± 4.45% Cd(II) while that of M6 removed 48.35% ± 1.44% Cd(II) in 200 mg/L initial concentration Cd(II). To the best of our knowledge, this is the first report that cadmium induced the change of reproduction mode of the Sarocladium, from conidia to arthrospores, which made the colony morphological modifications, from the fungi colony morphology to the bacteria colony morphology. The arthrospore-modified (hyphae breakage) seemed to accumulate greater amounts of heavy metals than filamentous hyphae formation.

Geochemical characteristics and health risks of heavy metals in agricultural soils and crops from a coal mining area in Anhui province, China

Soil contamination by heavy metals (HMs) in mining areas is a major issue because of its significant impact on the environmental quality and physical health of residents. Mining of minerals used in energy production, particularly coal, has led to HMs entering the surrounding soil through geochemical pathways. In this study, a total of 166 surface soil and 100 wheat grain samples around the Guobei coal mine in southeast China were collected, and trace metal levels were determined via inductively coupled plasma mass spectrometry (ICP-MS). The average HMs (Ni, As, Cr, Cu, Pb, Cd, and Zn) concentrations were lower than the screening values in China (GB 15618-2018) but higher than the soil background values in the Huaibei Bozhou area of Anhui Province (except Zn), indicating HMs enrichment. Based on the geoaccumulation index (Igeo) and ecological risk index (IER), Cd pollution levels were low, while for the other metals the samples were pollution-free, and therefore no ecological risk warning was issued for the mining area. Both Cr and Pb had a higher noncarcinogenic health risks for adults and children. The lifetime carcinogenic risks (LCR) of Cr, Pb, and Cd were within acceptable levels. A positive matrix factorization (PMF) model identified two factors that could explain the HMs sources: factor 1 for Zn, Cd, and Pb, factor 2 for Ni, As, Cr, and Cu. Furthermore, HMs enrichment was observed in surface soil and the Carboniferous-Permian coal seams in the Guobei coal mine, which may suggest that coal mining is an important source for HMs enrichment in surface soil. Overall, this study provides a theoretical basis for undertaking the management and assessment of soil HMs pollution around a coal mine.

Contamination characteristics of alkyl polycyclic aromatic hydrocarbons in dust and topsoil collected from Huaibei Coalfield, China

Alkyl polycyclic aromatic hydrocarbons (APAHs) are more toxic and persistent than their parent compounds. In this study, the concentrations of polycyclic aromatic compounds (PACs) in dust, topsoil and coal gangue from Huaibei Coal mine, China were analyzed by gas chromatography-mass spectrometry, confirming APAHs were the dominant pollutants. The mean concentrations of APAHs were substantially higher than those of 16 PAHs in both dust and topsoil. The mean concentration of APAHs in dust was 9197 µg kg^-1, accounting for 80% of the total mean concentration of PACs. The mean concentration of APAHs in topsoil was 2835 µg kg^-1, accounting for 77% of the mean concentration of PACs. Alkyl naphthalenes and alkyl phenanthrenes were the primary pollutants in APAHs. Their mean concentrations in dust and topsoil were 7782 µg kg^-1 and 2333 µg kg^-1, respectively. This accounted for 85% and 82% of the concentration of APAHs, respectively. Additionally, low-molecular-weight APAHs dominated the PACs of the coal mine, exhibiting petrogenic characteristics; distribution of C1-C4 NAP and C1-C4 PHE exhibited "bell shape" pattern indicated as petrogenic source. Source identification indicated that the PACs were mainly derived from petrogenic sources and vehicle emissions, followed by biomass and coal burning. Fingerprinting information of dust and topsoil were consistent with coal gangue, indicating that PACs are most likely derived from coal gangue. Coalfields comparable to our study area are widely distributed in China. Therefore, investigating PAC pollution derived from coal gangue warrants further attention.

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.