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

The effect of modified polymer on the change rule of physical properties of different gradation coal gangue

In this study, in order to improve the water retention of coal gangue matrix and accelerate the recovery of frozen soil layer in mining area, three different particle size gradations of coal gangue and modified polymer SAP (0.0, 0.1, 0.2, 0.3, 0.4%) were compounded and reconstructed. Based on the indoor soil column model, the change rule of SAP on the physical properties of coal gangue with different gradations is clarified. The results show that SAP can promote the reconstruction of coal gangue matrix. When the mass fraction of SAP is constant, the partial soil gradation reduces the bulk density, and improves the total porosity, capillary porosity and capillary water holding capacity. The inhibition degree of SAP on capillary water migration was different. The sand, soil and viscosity gradations without SAP reached the design height at 1340, 1380 and 1470 min, respectively. When SAP was 0.0% ~ 0.4%, the higher the dosage, the longer the action time. After continuous measurement for 6 days under natural ventilation, SAP was 0.3%. The partial soil gradation had strong water retention performance and could effectively inhibit water loss. With the increase of time, the water loss was the slowest. It is recommended that the preferred SAP mass fraction is 0.3%, the gradation is partial soil, and the bulk density is 1.30 g/cm3, which can provide suitable water and gas conditions for vegetation growth.

Distribution characteristics, source analysis and ecological risk assessment of PAHs in tea garden soil in China

In this study, we collected 177 soil samples from major tea-producing areas in China, systematically investigated the spatial distribution characteristics of the polycyclic aromatic hydrocarbons (PAHs) in the soil of these tea plantations and discussed the environmental factors influencing of the PAHs in tea garden soil. The feature ratio method and source analysis methods were used to determine the PAHs source in tea garden soil, and the potential risk of PAHs in tea garden soil was also evaluated. The results showed that the concentrations of the 16 PAHs in 177 samples ranged from 6.21 to 4068.91 ng g-1, with an average of 257.00 ng g-1. The majority of PHAs in tea garden soils predominantly contained a 5-6 ring pattern, and the highest content was indeno (1,2,3-cd) pyrene (InP, 23%) and benzo (b) fluoranthrene (BbF, 16%). In addition, 10.16% of the PAHs in tea plantation soils contained a 2-3-ring pattern, with naphthalene (NAP) having the highest content. PAH source in Chinese tea garden soil was predominantly mixed combustion, such as incomplete biomass combustion, petroleum combustion, coal combustion and wood combustion. The PAHs distribution was mainly affected by the industrial structure, geographical location of tea plantation, climatic conditions, soil properties and other factors in different regions. According to the Dutch Maliszewska-Kordybach grading standard, 79% of the soil samples from Chinese tea plantations were classified as unpolluted, 13% as mildly polluted, and 2% and 6% as moderately and severely polluted, respectively. Although the PAH pollution in tea plantations was generally low, BaP and InP pose significant ecological risk in some areas. Therefore, strategies such as effective guidelines and environmentally friendly technologies, must be developed to reduce the risk of PAH pollution in tea plantation soils.

Application of tree cores to investigate the historical pollution trends of atmospheric polycyclic aromatic compounds: A case study in a typical coal-contaminated region of China

In this study, 76 polycyclic aromatic compounds (PACs) were detected in air, soil, and tree core samples from Huainan, a typical coal-contaminated region of China. Concentrations of ΣPACs in soil and air samples were 2400 ± 5100 ng/g and 150 ± 63 ng/m3, respectively. Priority PAHs were predominant in both air and soil samples, contributing over 50 % of ΣPACs. Source analysis indicated that PAC contamination in Huainan primarily originated from local coal-related activities. The benzo[a]pyrene (BaP)-toxic equivalent concentrations (TEQBaP) of PACs in the air samples (5.6 ± 5.3 ng/m3) exceeded the threshold of 1 ng/m3. Some PACs, such as benzo[e]pyrene (BeP) and Alk-BaPs, demonstrated significant toxicity and are recommended for consideration as priority pollutants. The historical pollution trends of atmospheric PACs were obtained based on the tree core samples. PAC concentrations in tree core segments showed a strong correlation with atmospheric PM10 levels in Huainan. As air quality has improved in recent years, the PACs concentrations in tree core segments have also decreased. Historical fluctuations of atmospheric PACs were largely attributed to the changes in the gas treatment systems of a nearby coal-fired power plant and adjustments in environmental policies. By integrating trends observed in tree core segments with air concentrations, the historical atmospheric PAC concentrations were extrapolated. The extrapolated results showed similar concentration levels and trends when compared with historical data from other studies in China. Thus, tree cores can not only reflect the historical trends of atmospheric PACs with high temporal precision but also are feasible for extrapolating historical concentrations of airborne PACs.

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.

High-resolution satellite estimates of coal mine methane emissions from local to regional scales in Shanxi, China

Coal mines are significant anthropogenic sources of methane emissions, detectable and traceable from high spatial resolution satellites. Nevertheless, estimating local or regional-scale coal mine methane emission intensities based on high-resolution satellite observations remains challenging. In this study, we devise a novel interpolation algorithm based on high-resolution satellite observations (including Gaofen5-01A/02, Ziyuan-1 02D, PRISMA, GHGSat-C1 to C5, EnMAP, and EMIT) and conduct assessments of annual mean coal mine methane emissions in Shanxi Province, China, one of the world's largest coal-producing regions, spanning the period 2019 to 2023 across various scales: point-source, local, and regional. We use high-resolution satellite observations to perform interpolation-based estimations of methane emissions from three typical coal-mining areas. This approach, known as IPLTSO (Interpolation based on Satellite Observations), provides spatially explicit maps of methane emission intensities in these areas, thereby providing a novel local-scale coal mine methane emission inventory derived from high-resolution top-down observations. For regional-scale estimation and mapping, we utilize high-resolution satellite data to complement and substitute facility-level emission inventories for interpolation (IPLTSO+GCMT, Interpolation based on Satellite Observations and Global Coal Mine Tracker). We evaluate our IPLTSO and IPLTSO+GCMT estimation with emission inventories, top-down methane emission estimates from TROPOMI observations, and TROPOMI's methane concentration enhancements. The results suggest a notable right-skewed distribution of methane emission flux rates from coal mine point sources. Our IPLTSO+GCMT estimates the annual average coal mine methane emission in Shanxi Province from 2019 to 2023 at 8.9 ± 0.5 Tg/yr, marginally surpassing top-down inversion results from TROPOMI (8.5 ± 0.6 Tg/yr in 2019 and 8.6 ± 0.6 Tg/yr in 2020). Furthermore, the spatial patterns of methane emission intensity delineated by IPLTSO+GCMT and IPLTSO closely mirror those observed in TROPOMI's methane enhancements. Our comparative assessment underscores the superior performance and substantial potential of the developed interpolation algorithm based on high-resolution satellite observations for multi-scale estimation of coal mine methane emissions.

Overlooked emerging polycyclic aromatic hydrocarbons and benzofuran derivatives in soil from coking plant

Coking releases large quantities of multiple polycyclic aromatic hydrocarbons (PAHs), yet previous research has often focused on only a limited subset. This may not fully represent the overall risk posed by aromatic compounds. Here, a novel non-target analysis method was developed to identify more emerging PAHs and benzofuran derivatives. Beyond the 16 US Environmental Protection Agency priority PAHs (EPA PAHs), 56 emerging PAHs, 64 alkylated PAHs, and 32 furans were identified, with 69 compounds identified for the first time. The Σ16 EPA PAHs, Σ56 emerging PAHs, Σ64 alkylated PAHs, and Σ32 furans concentration ranges were 0.30-6910, 0.01-2187, 0.52-1649, and 0.06-588 μg/g, respectively. Emerging PAHs and furans had higher contributions in the plant area than the control area. Some PAHs and furans' concentrations were not significantly associated with the EPA PAHs; therefore, the EPA PAHs are insufficient to represent the totals PAHs concentration or risk. In the top 20 % of toxicological priority compounds, the emerging PAHs concentrations were 50 % of those of the EPA PAHs but posed 3.4 times the carcinogenic risk. Four of these compounds had higher carcinogenic risks than the EPA PAHs, while another nine had comparable risks. Thus, the risks of emerging PAHs cannot be ignored. Future monitoring and control of PAHs and furan emissions by the coking industry are highly recommended.

A 6-year review status on soil pollution in coal mining areas from Europe

Coal is an essential component in achieving the goal of fulfilling the energy demands of the world. Nevertheless, the extensive practice of coal mining has resulted in environmental contamination through the release of both organic and inorganic pollutants, including polycyclic aromatic compounds and potentially toxic elements, into various mediums, notably soil. The escalating coal-mining activities across Europe have amplified the concentration of specific elements in the soil. Therefore, a thorough and meticulous assessment of these environmental impacts is imperative to furnish policymakers, industries, and communities with valuable insights, facilitating the formulation and adoption of effective mitigation strategies. Considering the results of studies from 2018 to 2023, this review thoroughly evaluates the current state of soil pollution in the coal mining areas of Europe, focusing on polycyclic aromatic hydrocarbons and potentially toxic elements. By analyzing the acquired data, this study aims to evaluate the levels of contamination by these pollutants in soils. The findings reveal that low molecular weight polycyclic aromatic hydrocarbons dominate the polycyclic aromatic compounds present, while potentially toxic elements including Zn, Pb, Mn, and Cr emerge as major contributors to soil contamination in coal mining areas from Europe.

Stress distribution and roof subsidence of surrounding strata considering in situ coal conversion and CO2 mineralization backfilling: Photoelastic experiments using 3D-printed models of mining faces and goafs

Coal, a reliable and economical fuel, is expected to remain the primary energy source for power generation for the foreseeable future. However, conventional mining and utilization of coal has caused environmental degradation and infrastructure damage. An in situ coal conversion method has been proposed to mitigate environmental problems and reduce CO2 emissions resulting from coal extraction and utilization. This method involves the in situ conversion and utilization of coal, backfilling of waste rock, and CO2 mineralization to backfill the goaf. In this study, the impact of mining and conversion activities on the surrounding strata was evaluated to ascertain the effectiveness and advantages of the in situ coal conversion method. Transparent stope models were created using three-dimensional printing technology. The stress distribution and deformation characteristics of the surrounding strata were examined using photoelasticity and digital image correlation methods. The results were compared with those obtained using the traditional backfill mining method. The comparison revealed that the disturbance to the surrounding strata was 14.4 times less in the in situ conversion method than in the traditional backfill mining method. Additionally, the disturbance height at the roof and the disturbance depth at the floor were 4.2 and 2.1 times lower, respectively. The roof subsidence in the in situ conversion method was 1.97 times less than that in the traditional backfill mining method. These results confirm the advantages of minimizing the disturbance to surrounding rocks and controlling the subsidence of roof strata.

Investigation of the effect of different distilled water, rainwater and seawater mass ratios on coal spontaneous combustion characteristics

When water comes into contact with coal, the risk of coal spontaneous combustion should be reassessed. In order to analyze the effect of distilled water, rainwater and seawater on the coal self-heating, thermogravimetric analysis (TGA) was applied to investigate the differences between the macroscopic oxidation properties of raw coal and water-immersed coal. The risk of coal spontaneous combustion increases after water immersion, but different types of water have different degrees of influence on the spontaneous combustion of coal. The microscopic pore structure and elemental changes on the surface of coal samples before and after water immersion were studied by Scanning Electron Microscope (SEM), low-pressure nitrogen gas adsorption (LP-N2GA) and Energy Dispersive Spectroscopy (EDS) experiments. Fourier infrared spectroscopy (FTIR) was used to investigate the change of active groups. The results show that the pore structure of coal samples immersed in water is much more developed than that of raw coal. In the low-temperature oxidation stage, moisture evaporation consumes much oxidation heat and inhibits the coal self-heating. After the stage, it promotes the coal spontaneous combustion. The content of the hydroxyl group increases, and the content of carbonyl and carboxyl decreases. The alkali metal elements can act as catalysts and active carriers of oxygen, enhancing the oxidation activity of coal. The results are helpful to understand the mechanism of different distilled water, rainwater and seawater mass ratios on coal spontaneous combustion and avoid potential self-heating after immersion.