Mercury isotope fractionation and mercury source analysis in coal.

Understanding the sources of mercury (Hg) in coal is crucial for understanding the natural Hg cycle in the Earth's system, as coal is a natural Hg reservoir. We conducted analyses on the mass-dependent fractionation (MDF), reported as δ202Hg, and mass-independent fractionation (MIF), reported as Δ199Hg, of Hg isotopes among individual Hg species and total Hg (THg) in Chinese coal samples. This data, supplemented by a review of prior research, allowed us to discern the varying trend of THg isotope fractionation with coal THg content. The Hg isotopic composition among identified Hg species in coal manifests notable disparities, with species exhibiting higher thermal stability tending to have heavier δ202Hg values, whereas HgS species typically display the most negative Δ199Hg values. The sources of Hg in coal are predominantly attributed to Hg accumulation from the original plant material and subsequent input from hydrothermal activity. Hg infiltrates peat swamps via vegetation debris, thus acquiring a negative Δ199Hg isotopic signature. Large-scale lithospheric Hg recycling via plate tectonics facilitates the transfer of Hg with a positive Δ199Hg from marine reservoirs to the deep crust. The later-stage hydrothermal input of Hg with a positive Δ199Hg enhances coal Hg content. This process has resulted in an upward trend of Δ199Hg values corresponding with the increase in coal THg content, ultimately leading to near-zero Δ199Hg in high-Hg coals. Coal Hg reservoirs are affected by large-scale natural Hg cycling, which involves the exchange of Hg between continents and seas.

Native polycyclic aromatic hydrocarbons (PAHs) in coal and its preparation products-A mixed source of environmental contamination.

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants and inherent components of coal and coal gangue. The similarities and differences in PAH characteristics between these two source materials are largely unknown. In this study, raw coal, cleaned coal, slime, middlings, and gangue from the Wangjialing Coal Preparation Plant in China were analyzed to determine the concentration and distribution of extractable PAHs. The total concentrations of 41PAHs (∑41PAH), US EPA 16 priority parent PAHs (∑16PAH), and their alkylated derivatives (∑aPAH) ranged from 18.3 to 89.6, 8.70 to 34.5, and 8.40-48.0 mg/kg, respectively, and were ranked as raw coal > cleaned coal > slime > middlings > gangue. The PAH characteristics of raw coal and its preparation products were consistent, with predominant 2-3-ring PAHs and similar PAH isomer ratio distributions. The distribution of conventional PAH isomer ratios for different ranks of coal and coal gangue from different origins was compiled from the literature. The resulting distribution was consistent and overlapped with both petrogenic and pyrogenic sources defined by the ratios. Therefore, coal and coal gangue should be considered one category and classified as a mixed source (mixture of petrogenic and pyrogenic sources). To accurately identify environmental PAH sources, investigations of aPAHs in the environment and PAH characteristics in coal and coal gangue should be expanded.

Migration patterns and health risk assessment of polycyclic aromatic compounds in typical coal fire source.

The Wuda coal fire in Inner Mongolia, China, is a global catastrophic event. It emits a huge volume of organic pollutants, including polycyclic aromatic compounds (PACs), which are widely concerning due to their physiological toxicity and environmental persistence. However, there is no systematic study on the enrichment and migration patterns of PACs emitted from coal fires. Here, we compared samples from coal fire sponges and surrounding soil, and analyzed 47 PACs using GC × GC-TOFMS. Data analysis showed that the average content of 16 polycyclic aromatic hydrocarbons (16PAHs) in the coal fire sponge was 15400.65 ng/g, which is about 4.2 times higher than that in the surrounding soil. Meanwhile, 31 PACs were detected at levels far exceeding those of 16PAHs. The distribution pattern of PACs showed that coal fire sources are more likely to produce and store 16PAHs while surrounding soils are more likely to be enriched with PAH derivatives. The cancer risk assessment revealed a significant cancer risk in both the coal fires and the surrounding soil. The formation mechanism of oxygenated PAHs was also explored, and it was found that coal fires emit 16PAHs and alkylated PAHs, which oxidize to form oxygenated PAHs during migration to surrounding soils. The value of naphthaldehyde/alkylated naphthalene (< 2) can be referenced as characteristic markers of coal fire pollution. This provides a new perspective on the sources of PACs in the current environment.

Urine LMs quantitative analysis strategy development and LMs CWP biomarkers discovery.

Coal workers' pneumoconiosis (CWP) is one of the most common inhalation occupational diseases. It is no effective treatment methods. Early diagnosis of CWP could reduce mortality. Lipid mediators (LMs) as key mediators in the generation and resolution of inflammation, are natural biomarkers for diagnosis inflammatory disease, such as CWP. The UHPLC-MRM technique was used to detect LMs in urine. The metabolic network of LMs in CWP and CT group samples was comprehensively analyzed. Screening for major difference compounds between the two groups. Aimed to contribute to the early diagnosis and treatment of CWP. Urinary levels of 13-OxoODE, 9-OxoODE, and 9,10-EpOME were significantly higher in the CWP group compared with the CT group (P < 0.05). In the model group, the area under the receiver operating characteristic (ROC) for 9-OxoODE,13-OxoODE,9,10-EpOME was 84.4%, 73.3%, and 80.9%, respectively. In the validation group, the area under the ROC was 87.0%, 88.8%, and 68.8% for 9-OxoODE,13-OxoODE,9,10-EpOME, respectively. According to the logistic regression model, the area under the ROC was 80.4% in the model group and 86.7% in the validation group. 13-OxoODE,9-OxoODE,9,10-EpOME could be used as biomarkers for early diagnosis. Significant abnormalities of LOX and CYP450 enzyme pathways were seen in CWP organisms. Changes in the CYP450 enzyme pathway may be associated with PAHs.

[Contamination Characteristics and Risk Assessment of Polycyclic Aromatic Compounds in Surface Dust of Suntuan Mining Area in Huaibei].

The Suntuan mining area of Huaibei is a typical coal resource mining base in the Huainan-Huaibei areas in North China. Previous environmental studies related to surface dust in coal mining areas mainly focused on heavy metals and water-soluble ions, with little research on polycyclic aromatic compounds (PACs). In this study, gas chromatography-triple tandem quadrupole mass spectrometry (GC-MS/MS) was used to determine the contents of 16 parent polycyclic aromatic hydrocarbons (16PAHs), alkyl polycyclic aromatic hydrocarbons (aPAHs), and some oxygenated polycyclic aromatic hydrocarbons (OPAHs) in surface dust from the Suntuan mining area and surrounding environment. The results showed that the ΣPACs concentration range of surface dust in the Suntuan mining area was 283.8-36852.5 µg·kg-1 (mean:4114.2 µg·kg-1). ΣaPAHs (mean:2593.8 µg·kg-1) was 2.4 times higher than Σ16PAHs (mean:1074.9 µg·kg-1), which was the main contributor to PAC pollution. The composition of 16PAHs and aPAHs in surface dust was dominated by low molecular polycyclic aromatic hydrocarbons. The average OPAH content was 445.6 µg·kg-1. At the same time, PAC pollution was mainly concentrated around the mining area and near the road of a coal gangue landfill. Based on the positive matrix factor (PMF) analysis, it was inferred that the study area was mainly affected by petroleum sources, followed by coal and biomass combustion, and traffic sources and petroleum product leakage accounted for a relatively small proportion. Based on the ratio and distribution pattern of 16PAHs and aPAHs, it was inferred that when Σ16PAHs/ΣPACs<0.25, it was mainly polluted by the coal mining area. The results of PMF combined with lifetime carcinogenic risk (ILCR) showed that there were potential carcinogenic risks for children near the study area, mainly from coal and biomass burning and coal mining. There are many coal mining areas in Huaihe River Basin in China. The results of this study can provide reference for pollution prevention and control of PACs in these coal mining areas.

Lipid Mediators Metabolic Chaos of Asthmatic Mice Reversed by Rosmarinic Acid.

BACKGROUND AND OBJECTIVE: Asthma is a common chronic inflammatory disease of the airways with no known cure. Lipid mediators (LMs) are a kind of inflammatory signaling molecules which are believed to be involved in the development of asthma. Hyssopus cuspidatus Boriss. is a traditional Uyghur medicine, which is widely used in the treatment of asthma and other respiratory diseases. Extraction of Hyssopus cuspidatus Boriss. was reported to neutralize asthma symptoms. The purpose of the study was to investigate both the anti-inflammatory and immunoregulation properties of the Hyssopus cuspidatus Boriss. extract (SXCF) and its main active constituent, rosmarinic acid (RosA), in vivo. The effect of RosA, a major constituent of SXCF, was evaluated on an asthmatic model, with both anti-inflammatory and immunoregulation properties. MATERIALS AND METHODS: Anti-inflammatory effect of SXCF and RosA was assessed using OVA-induced asthma model mice by UPLC-MS/MS method. RESULTS: Overall, RosA played a critical role in anti-asthma treatment. In total, 90% of LMs species that were significantly regulated by SXCF were covered. On the most important LMs associated with asthma, RosA equivalent induced similar effects as SXCF did. It is believed that some constituents in SXCF could neutralize RosA excessive impacts on LMs.

Enrichment of Sulfate, Acidity and Mercury in Native outcrop coal, Southwest China.

The coal found in the Longtan Formation of the Late Permian is widely distributed in Southwest China, including the northwestern Guizhou, southeastern Sichuan, and northern Yunnan regions. This coal typically has a high sulfur content. Eighty-two coal samples were collected from the coal strata in 11 counties spanning this area, including underground mine coal, native outcrop coal and man-made outcrop coal. The mercury, total fluorine, total sulfur, and sulfate contents and pH values were determined. The results showed that the average mercury content in native outcrop coal was 2233 ng/g, whereas that in underground mine coal was 306 ng/g, and the relative enrichment factor could reach 6.6. There was no significant difference in the total fluorine content among the three types of coals; furthermore, the total sulfur content in native outcrop coal and man-made outcrop coal was higher than that in underground mine coal because of the local policy, which strictly prohibits the mining of high-sulfur coal. Native outcrop coal is acidic, with a total average pH of 3.54 and an average sulfate content as high as 13,390 µg/g. In contrast, underground coal is almost neutral (average pH 7.33), with a low sulfate content (average 3221 µg/g). These characterizations indicate that native outcrop coal has been subjected to long-term weathering and the mercury enrichment is likely due to migration, oxidation, and precipitation of Hg from the underground coal seam and enriched in loose and pulverized coal particles. Further investigation is needed to determine whether other outcrop areas are affected by this phenomenon.

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.

Parent and alkylated polycyclic aromatic hydrocarbon emissions from coal seam fire at Wuda, Inner Mongolia, China: characteristics, spatial distribution, sources, and health risk assessment.

The Wuda coalfield in Inner Mongolia is a vital coal base in China, and it is the hardest-hit area for coal fires (spontaneous combustion of coal seams and coal gangue). Using gas chromatography-mass spectrometry, this work tested the concentration and analyzed the characteristics, distribution, sources, and health risks of polycyclic aromatic compounds (PACs) in the surface soil of the Wuda District, including the coal mine, coal fire, agricultural, and background areas. The soil of coal mine and coal fire area were heavily polluted with PACs, with mean concentrations of 9107 and 3163 µg kg-1, respectively, considerably higher than those in the agricultural (1232 µg kg-1) and background areas (710 µg kg-1). Alkyl polycyclic aromatic hydrocarbons (APAHs) were the dominant pollutants among these PACs, accounting for 60-81%. Alkyl naphthalenes and alkyl phenanthrenes are the primary pollutants in APAHs, accounting for 80-90% of the total amounts. Additionally, using the positive matrix factorization method, it can be concluded that the primary PAC sources are petrogenic sources, coal and biomass combustion, coal fires, and vehicle emissions. Finally, according to the cancer risk values of 16 PAHs, only the coal mine area showed a potential cancer risk. However, this result lacks a risk assessment of APAHs and underestimates the actual risk. The results of this study improved the understanding of PAC pollution in coal fire and surrounding areas and provided a reference for environmental and health risk investigations.

Contamination characteristics of polycyclic aromatic compounds from coal sources in typical coal mining areas in Huaibei area, China.

The Huaibei area is rich in coal resources and serves as the main energy production base in East China. However, serious environmental consequences are associated with coal mining and utilization. With increasing reports on distribution and risks by polycyclic aromatic compounds (PACs), the potential pollution of coal sources must be addressed. Here, the PAC concentrations in the topsoil, coal, and coal gangue of a typical coal mining area in Huaibei were evaluated. The mean ΣPACs in topsoil, coal, and coal gangue were 1528.3, 274,815.8, and 10,908.3 µg·kg-1, respectively. Alkyl polycyclic aromatic hydrocarbons (aPAHs) were identified as primary contributors to PACs, and the concentrations of oxygenated PAHs (oPAHs) were significantly higher in coal and coal gangue than in topsoil. PAC pollution was mainly concentrated in the coal mine area and near the coal gangue landfill road. Not only sixteen high priority pollutant PAHs (16PAHs), but PAH derivatives also contributed to the organic pollution from coal sources. Principal components analysis, multiple linear regression, characteristic ratios, and positive matrix factor analysis were used to trace PAC sources. The characteristic ratios for organic pollution from coal and gangue particles involving 16PAHs, aPAHs, and oPAHs were proposed. Further, the high-ring 16PAH ratio was also found suitable for coal mining areas. The Monte-Carlo risk assessment showed that coal particles were highly carcinogenic, and despite the low carcinogenicity of coal gangue and topsoil, they might also serve as potential carcinogens. This study aimed to disseminate knowledge on PACs from coal and coal gangue, provide a useful background for efficient resource utilization of coal gangue, and a reference for tracing PAC sources in coal mine environment media.

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.

Alkylated Polycyclic Aromatic Hydrocarbons Are the Largest Contributor to Polycyclic Aromatic Compound Concentrations in the Topsoil of Huaibei Coalfield, China.

Alkyl polycyclic aromatic hydrocarbons (APAHs) are more toxic and persistent than their parent compounds. Here, the concentrations, composition profiles, and spatial distribution of polycyclic aromatic compounds (PACs) in 127 topsoil samples from Huaibei coalfield were analyzed. The PAC concentrations in different functional areas were significantly different: mining area > industrial area > residential area > agricultural area. APAHs were the major contributors to PACs, accounting for 71-83% of total PACs. Alkylnaphthalenes and alkylphenanthrenes were the primary APAH components, accounting for 83-87% of APAHs. Principal component analysis showed that petrogenic source, coal and biomass combustion, and vehicle emissions were the primary sources of PACs. By comparing the fingerprint information of soil, coal, and coal gangue, it was hypothesized that the petrogenic source of PAC pollution in typical mining areas and surrounding areas are coal particle scattering and coal gangue weathering. Some coal mining and industrial areas potentially pose risks to children, whereas others do not. There are limited evaluation criteria for alkyl PAHs; hence, the estimated risk is likely lower than the actual risk. In addition to the conventional 16 PAHs, it is critical to consider a broader range of PACs, especially APAHs.

Characteristics of Water-Soluble Inorganic Ions in PM2.5 in Typical Urban Areas of Beijing, China.

Following the implementation of "coal-to-gas conversion" policy in the Haidian District of Beijing during summer, the present comparative study was performed employing 41 PM2.5 samples as precursors to analyze the characteristics of water-soluble inorganic ions. The concentrations of water-soluble inorganic ions in PM2.5 were analyzed by ion chromatography, and the occurrence form of ions was characterized via time-of-flight secondary ion mass spectrometry (TOF-SIMS). Results revealed that the daily average mass concentration of PM2.5 in Beijing during the sampling period was 94.28 ± 52.49 µg/m3. As compared to the winter of 2016, the average daily PM2.5 concentration in Beijing decreased by 29 µg/m3 in 2017 (28.2% decrease), with a remarkable decline in the number of days with pollution. During the pollution period, the concentrations of NO3 -, SO4 2-, and NH4 + were significantly higher in PM2.5 as compared to the cleaning period. The ratio of the concentrations of [NO3 -]/[SO4 2-] was greater than 1, and the contribution from mobile sources was relatively large, indicating that the implementation of the "coal-to-gas conversion" policy in Beijing has led to the reduction of SO4 2- emissions from fixed sources, such as coal. Furthermore, TOF-SIMS analysis results showed that NH4 + tended to exist in the form of molecular ammonium sulfate or ammonium hydrogen sulfate during the period of pollution.

Causes of PM2.5 pollution in an air pollution transport channel city of northern China.

To develop effective mitigation policies, a comprehensive understanding of the evolution of the chemical composition, formation mechanisms, and the contribution of sources at different pollution levels is required. PM2.5 samples were collected for 1 year from August 2016 to August 2017 at an urban site in Zibo, then chemical compositions were analyzed. Secondary inorganic aerosols (SNA), anthropogenic minerals (MIN), and organic matter (OM) were the most abundant components of PM2.5, but only the mass fraction of SNA increased as the pollution evolved, implying that PM2.5 pollution was caused by the formation of secondary aerosols, especially nitrate. A more intense secondary transformation was found in the heating season (from November 15, 2016, to March 14, 2017), and a faster secondary conversion of nitrate than sulfate was discovered as the pollution level increased. The formation of sulfate was dominated by heterogeneous reactions. High relative humidity (RH) in polluted periods accelerated the formation of sulfate, and high temperature in the non-heating season also promoted the formation of sulfate. Zibo city was under ammonium-rich conditions during polluted periods in both seasons; therefore, nitrate was mainly formed through homogeneous reactions. The liquid water content increased significantly as the pollution levels increased when the RH was above 80%, indicating that the hygroscopic growth of aerosol aggravated the PM2.5 pollution. Source apportionment showed that PM2.5 was mainly from secondary aerosol formation, road dust, coal combustion, and vehicle emissions, contributing 36.6%, 16.5%, 14.7%, and 13.1% of PM2.5 mass, respectively. The contribution of secondary aerosol formation increased remarkably with the deterioration of air quality, especially in the heating season.

Characterization and risk assessment of polycyclic aromatic hydrocarbon emissions by coal fire in northern China.

Coal spontaneous combustion is known to emit a variety of organic carcinogenic pollutants, polycyclic aromatic hydrocarbons (PAHs) are the most prominent. The Wuda coalfield is a coal fire-prone region in northern China. Coal fire sponges (CFS), a sponge-like contaminated soil protrusion, occur widely in the Suhaitu mining area. PAHs concentrations in CFS were measured via GC × GC-TOFMS. The average total PAHs concentration in the central annulus (A) was 17,416 µg kg-1 and ranged from 292 to 218,251 µg kg-1. Moreover, the study exhibited a heavily contaminated level (1000 µg kg-1). Low molecular weight PAHs were dominant, accounting for more than 50% of the total PAHs. Among them, naphthalene (Nap) and phenanthrene (Phe) were the most prominent, and the correlation between Phe and Nap + Phe was highly significant (R2 > 0.9). Our findings indicated that Nap and Phe contents may constitute a novel indicator to identify coal fire emission sources. Cancer risk calculations indicated that all annulus is already at a potential risk stage (10-6-10-4) for child or adults. CFS is not only a coal fire-associated PAH sink but also an atmospheric PAH emission source and, therefore, warrants the attention of local authorities.

Concentration and speciation of mercury in atmospheric particulates in the Wuda coal fire area, Inner Mongolia, China.

Coal-seam fire is a source of atmospheric mercury that is difficult to control. The Wuda Coalfield in Inner Mongolia, China, is one of the most severe coal fire disaster areas worldwide and has been burning for more than 50 years. To investigate atmospheric mercury pollution from the Wuda coal fire, gaseous elemental mercury (GEM) concentrations and atmospheric particulate mercury (PHg) speciation were measured using a RA-915+ mercury analyzer and the temperature-programmed desorption method. Near-surface GEM concentrations in the Wuda Coalfield and adjacent urban area were 80 ng m-3 (65-90 ng m-3) and 52 ng m-3 (25-95 ng m-3), respectively, which are far higher than the local background value (22 ng m-3). PHg concentrations in the coalfield and urban area also reached significantly high levels, 33 ng m-3 (25-45 ng m-3) and 22 ng m-3 (14-29 ng m-3), respectively (p < 0.05). There is no clear evidence that PHg combines with organic carbon or elemental carbon, but PHg concentration appears to be controlled by air acidity. PHg mainly exists in inorganic forms, such as HgCl2, HgS, HgO, and Hg(NO3)2·H2O. This work can provide references for the speciation analysis of atmospheric PHg and the safety assessment of environmental mercury.

Role of H+, HF, SO42- and kaolin in fixing Hg of coal fire sponge.

Coal fire sponges (CFS) are common in coal-fire areas. Due to the enrichment of Hg in CFS, large amounts of Hg are released by CFS into the atmosphere via natural weathering or solar radiation. Therefore, CFS should be of concern in Hg pollution management and control globally. In addition, CFS changes the Hg cycle path by capturing Hg from coal fires that would have entered the atmosphere. In this study, the concentration, distribution, species, and enrichment mechanism of CFS Hg were investigated. The results showed that the Hg concentration in CFS ranged from 1008 to 35,310 ng/g, with an average of 8932 ng/g (CFS number, n = 153). The Hg concentration of CFS in different types of land was found to be significantly inhomogeneous. To determine the status of subterranean spontaneous combustion, the Hg concentration was added, which can improve the effect of coal-fire monitoring. Compared to the background area topsoil, CFS was enriched in Hg, acid, SO42-, and total fluoride. The Hg species in CFS was primarily HgSO4, followed by HgO. However, the primary Hg species in the surrounding topsoil were HgCl2 and HgO. By the simulation experiment, it was determined that hydrofluoric acid (HF) was beneficial to activate the stable species in the coal-fire areas. HgCl2, HgO, or Hg0 were ionized by acid liquor or HF, which can promote Hg migration and increase the adsorbed ratio; in the presence of SO42-, the primary Hg species was HgSO4. Ultimately, Hg was absorbed by clay minerals and organic matter. The high-efficiency activation of steady Hg species by the coal-fire HF should be studied further.

Specification of complex-PAHs in coal fire sponges (CFS) by high-resolution mass spectrometry with electrospray ionization.

Underground coal fires are considered an ecological disaster. While underground coal fires are prevalent in coal-producing areas throughout the world, they are most problematic in northern China. Previous studies have shown that underground coal fires stimulate the formation of cracks or gas outlets on the surface, as well as coal fire sponges (CFS) on the soil layer surface, which collect coal-fired pollutants. Herein, ultra-high-performance liquid chromatography (UHPLC) was used in conjunction with electrospray ionization (ESI) high-resolution mass spectrometry to analyze CFS samples collected from the No. 8 fire zone, located in Wuda coalfield, Inner Mongolia, China. The results show that CFS contain 233 oxy-substituted polycyclic aromatic hydrocarbons (O-PAHs), e.g., naphthaldehyde; 40 oxapolycyclic aromatic hydrocarbons (OPAHs), e.g., dibenzofuran; 40 alkyl-substituted polycyclic aromatic hydrocarbons (R-PAHs); and 11 parent polycyclic aromatic hydrocarbons (PPAHs). Thus, CFS are primarily composed of O-PAHs, which are 25 times and 5 times more prevalent than PPAHs and R-PAHs, respectively. As such, a high relative abundance of varied O-PAHs are discharged from underground coal fires, which is significantly different from what is released during industrial coal burning. Owing to their water solubility and condensability, the new facts disclosed in this paper may provide a new perspective for understanding complex organic pollutants from underground coal fires and their environmental impacts.

Characterization of acidity and sulfate in dust obtained from the Wuda coal base, northern China: spatial distribution and pollution assessment.

The coal fire in Wuda, Inner Mongolia of China, is one of the most serious coal fires in the world with a history over 50 years and endangers the neighboring downwind urban area. A lack of effective measures to control coal fires in this region can aggravate environmental pollution. In this study, the levels and spatial distributions of acid (pH) and SO42- in dust in the Wuda coalfield and its surrounding areas in Inner Mongolia, North China, were reported to identify the potential acid and SO42- pollution in the local environment with an area of 270 km2. The mean pH and SO42- content was to found to be 7.44 and 5981 µg·g-1, respectively. Through the analysis of the spatial distribution of pH and SO42- concentrations, it was found that most of contaminated areas are mainly distributed in coalfield and its affiliated industrial parks, and the Wuda urban area also suffered from pollution. Based on chemical equilibrium, the surface acid pollution might have resulted in the change of the dust type from the original weakly alkaline CaCO3 type to the CaSO4 type in coalfield and industrial parks. Finally, the pollution assessment revealed that the coalfield and industrial parks are both at heavy pollution levels, and the urban area is mostly moderately polluted, followed by farm and peripheral region with a certain pollution risk. The results indicated that the long-term release of acidic gas from the coal fires and industrial parks can led to significantly elevated acidity and SO42- levels in the dust of the local environment, while coal fires can aggravate surface pollution in industrial parks, but the extent of contamination was also closely related to the terrain and wind direction in the study area.

Study on Mercury Species in Coal and Pyrolysis-Based Mercury Removal before Utilization.

Coal-fired mercury (Hg) pollution control is an important global environmental context. Eight coal samples from different coal fields in China were used to investigate Hg species and the Hg removal effects under different pyrolysis conditions in the presence of nitrogen. These conditions included temperature, particle size, and residence time. The study concludes that the temperature is the most important factor affecting Hg removal from coal, and the mercury release activity at specific temperatures depends on the species and content of Hg present. Large particle size limits the removal rate of Hg, and coal particles smaller than 40 mesh are more favorable for the rapid removal of Hg. For most coal types, pyrolysis of 10-15 min can achieve the ultimate Hg removal effect. Rapid pyrolysis at 600 °C in nitrogen is feasible to remove Hg from coal. Consequently, the Hg removal rate reaches 88-100%, the loss rate of coal calorific value is 2-12%, and approximately 17-58% of S is removed synergistically. HgS, HgSe, HgSO4, organic matter Hg, and HgO are the main types of Hg species detected in coal, whose thermal decomposition characteristics are the essential criteria for determining the type of Hg removal process. This research will facilitate the improvement of pollution control methods for coal-source Hg pollution.