Estimate of sulfur, arsenic, mercury, fluorine emissions due to spontaneous combustion of coal gangue: An important part of Chinese emission inventories

Characterizing carbonaceous aerosols in residential coal combustion: Insights from thermal/spectral carbon analyzer coupled with photoionization mass spectrometry analysis

This study aims to identify unique signatures from residential coal combustion in China across various combustion conditions and coal types. Using a Thermal/Spectral Carbon Analyzer with a Photoionization Time-of-Flight Mass Spectrometer (TSCA-PI-TOF-MS), we focus on the optical properties and organic mass spectra of the emissions. Bituminous coal emerged as the primary emitter of total carbon, releasing 729 μg C/mg PM2.5 under smoldering and 894 μg C/mg PM2.5 under flaming. Carbon fractions mainly comprised OC1 and OC2, except for anthracite's dominance of EC1 under smoldering. Pyrolysis carbon absorption shifted from 405, 445 and 532 nm during smoldering to near-infrared bands (635-980 nm) during flaming for both bituminous and anthracite coal. Conversely, clean coal exhibited an inverse trend, attributed to additives enhancing oxygen-containing organic compounds and long-chain hydrocarbons released in charring process. Sample of bituminous coal began charring at OC3 step, while anthracite began earlier at OC2 step, particularly pronounced under flaming. Clean coal displayed unconventional charring at OC1 step under smoldering condition, producing signature compounds like butenal, methylfuran, furanylalcohol, and naphthol. The mass spectra of bituminous coal featured characteristic peaks, including m/z 192 (methylphenanthrene), 206, 220 (alkylated phenanthrenes), and 234 (retene). Anthracite coal showed a potential tracer at m/z 223, shifting from OC1 in smoldering to OC2 in flaming. Clean coal under flaming condition exhibited elevated levels of aromatic compounds, indicating potential toxicity, with peaks at m/z 178 (phenanthrene), 228 (chrysene/benz[a]anthracene), 234 (retene), 242 (methylchrysene), and 252 (benzo[a]pyrene, benzo[k]fluoranthene). Results also showed that the broader mass spectra range in the OC3 and OC4 steps across all coal types suggests that high-temperature pyrolysis promotes diversity. These findings contribute to refined source apportionment of carbon emissions from residential coal combustion and provide the scientific basis for the formulation of air pollution prevention strategies, crucial for coal-dependent regions.

Research on long-term migration behaviors of heavy metals after close-distance coal seam backfill mining

The backfill mining of coal-based solid waste in goaf poses a potential risk of heavy metal pollution to the groundwater environment, and the migration behavior of heavy metals differs significantly under the disturbance of backfill mining in close-distance multi-layer coal seams and single-layer coal seams. In this study, a migration model of heavy metals after solid backfilling in the goaf of shallow-buried close-distance thick coal seams was established, and the impact of the overburden damage and the layered distribution of the filling body on the long-term migration behavior of heavy metals were analyzed. The results show that the migration of heavy metals after close-distance coal seam backfill mining exhibits a higher risk of heavy metal pollution. The peak permeability of overburden after close-distance coal seam backfill mining is about 600 × 10-19 m2 higher than that after single-layer coal seam backfill mining. The migration distance of heavy metals in the floor after backfill mining of close-distance coal seams is 7.41 m farther than that of single-layer coal seam backfill mining, and its migration time of heavy metals to the surface is 27 a earlier than that of single-layer coal seam. This research provides theoretical and empirical support for the ecological risk assessment and heavy metal pollution control in close-distance coal seam backfill mining. ENVIRONMENTAL IMPLICATION: The main filling material of close-distance coal seams backfill mining is coal gangue. Heavy metal elements such as Mn and Cr will be released in the underground environment for a long time, and the migration behavior of heavy metal elements will have an impact on the groundwater environment for more than 1000 years. This research provides theoretical and empirical support for the ecological risk assessment of close-distance coal seam backfill mining and the mitigation of heavy metal pollution.

Study on the secondary oxidation behavior and microscopic characteristics of oxidized coal gangue

Spontaneous combustion of coal gangue (CG) hills has caused varieties of secondary disasters that seriously endanger the ecological environment of the world. The emission law of index gases and their oxidation kinetics during the secondary oxidation process of CG with different ranks of oxidation were studied by using the temperature programmed device and online mass spectrometer (MS). Fourier transform infrared spectroscopy (FTIR) was used to reveal the changes of the CG internal active functional groups. The results showed that the energy required for the combustion of CG with low rank of pre-oxidation was significantly lower than that of the raw sample. However, as the oxidation rank increased, due to amounts of volatile components were released in the process of oxidation reaction, the CG in the combustion process of the emission of index gases and its oxygen consumption rate gradually reduced; the rapid oxidation stage shifted to the direction of the high temperature. In this study, the risk of spontaneous combustion of CG after oxidation at 80 ℃ under 3% oxygen concentration was the strongest. The results of this paper are of great guiding significance for exploring the spontaneous combustion characteristics of CG hills and their prevention by traditional covering method.

Efficient benzo(a)pyrene degradation by coal gangue-based catalytic material for peroxymonosulfate activation

A low cost and green peroxymonosulfate (PMS) activation catalyst (CG-Ca-N) was successfully prepared with coal gangue (CG), calcium chloride, and melamine as activator. Under the optimal conditions, the CG-Ca-N can remove 100 % for benzo(a)pyrene (Bap) in an aqueous solution after 20 min and 72.06 % in soil slurry medium within 60 min, which also display excellent reuse ability toward Bap after three times. The removal of Bap is significantly decreased when the initial pH value was greater than 9 and obviously inhibited in the presence of HCO3- or SO42-. The characterization results indicated that the addition of calcium chloride could stabilize and increase the content of pyridinic N during thermal annealing, resulting in the production of •OH, SO4•- and 1O2. Based on electron paramagnetic resonance (EPR) and active radical scavenging experiments, 1O2 could be identified to be the dominant role in Bap degradation. Overall, this work opened a new perspective for the low cost and green PMS catalysts and offered great promise in the practical remediation of organic pollution of groundwater and soil.

Comprehensive study on the spatial distribution of heavy metals and their environmental risks in high-sulfur coal gangue dumps in China

The accumulation of coal gangue (CG) from coal mining is an important source of heavy metals (HMs) in soil. Its spatial distribution and environment risk assessment are extremely important for the management and remediation of HMs. Eighty soil samples were collected from the high-sulfur CG site in northern China and analyzed for six HMs. The results showed that the soil was heavily contaminated by Mn, Cr and Ni based on the Nemerow index, and posed seriously ecological risk depended on the geo-accumulation index, potential ecological risk index and risk assessment code. The semi-variogram model and ordinary kriging interpolation accurately portrayed the spatial distribution of HMs. Fe, Mn, and Cr were distributed by band diffusion, Ni was distributed by core, the distribution of Cu had obvious patchiness and Zn was more uniform. The spatial autocorrelation indicated that all HMs had strong spatial heterogeneity. The BCR sequential extraction was employed to qualify the geochemical fractions of HMs. The data indicated that Fe and Cr were dominated by residual fraction; Cu, Ni and Zn were dominated by reducible and oxidizable fractions; Mn was dominated by reducible and acid-extractable (25.38%-44.67%) fractions. Pearson correlation analysis showed that pH was the main control factor affecting the non-residue fractions of HMs. Therefore, acid production from high sulfur CG reduced soil pH by 2-3, which indirectly promoted the activity of HMs. Finally, the conceptual model of HMs contamination at the CG site was proposed, which can be useful for the development of ecological remediation strategies.

Preparation and strength formation mechanism of alkali-stimulated spontaneous combustion gangue-granulated blast furnace slag backfill

Spontaneous combustion gangue (SCG) is often used as aggregate in traditional cemented paste backfill (CPB) for mine backfill, but the activation of SCG is insufficient. To stimulate the activity of SCG for the preparation of spontaneous combustion gangue-granulated blast furnace slag backfill (SGB), a new CPB was prepared by activating SCG via a mechanochemical composite activation method and adding ground granulated blast furnace slag (GGBS) to improve its activity. The mixing ratio was optimized by the response surface method and satisfaction function, and the strength formation mechanism was analyzed by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR). The results showed that SCG had a certain pozzolanic activity, and the optimal grinding time was 30 min. The optimal mix ratio was 82.58% mass concentration, 2.93% alkali content, 30% GGBS content, and 52.92% fine gangue rate. Calcium silicate hydrate (C-S-H) gel and calcium aluminate sulfate hydrate (C-A-S-H) gel were the main reaction products of backfill, and with increasing curing age, C-S-H gel in the reaction system was gradually converted into C-A-S-H gel. FTIR analysis results showed that there were H-O-H, Si-O, and Si-O-T (T was Si or Al) bonds in the product, indicating that C-S-H gel and C-A-S-H gel were formed in the product. A new damage constitutive model was developed. The damage constitutive model could completely describe the backfill stress-strain curve. The study verified the feasibility of preparing cemented paste backfill with SCG and GGBS, which was beneficial to clean coal mine production and environmental protection.

Detection of Spontaneous Combustion Areas of Coal Gangue Dumps and Comprehensive Governance Technologies: A Case Study

Spontaneous combustion of coal gangue dumps not only releases toxic and harmful gases, polluting the environment, but also leads to explosion accidents and casualties due to improper handling. This paper focuses on delineating the fire area, constructing a comprehensive fire prevention and extinguishing system, and restoring the ecological environment. Infrared thermal imaging was used to detect the shallow fire area, while intensive drilling was conducted to detect the deep fire area. The stability of the coal gangue dump was enhanced by perfusing three-phase foam for cooling and using a curing material to fill the cracks. Land reclamation was then performed to restore the ecological environment. The results indicate that spontaneous combustion of coal gangue dumps can trigger the spread of the fire area from the outside to the inside, gradually expanding due to the 'stack effect'. The sources of spontaneous combustion in gangue fire areas are mainly located 3-5 m below the flat surface, and the shallow and deep fire areas are interconnected, posing a significant danger. These research findings can serve as a reference for detecting fire areas in coal gangue dumps and controlling environmental pollution.

Partition pattern and environmental consequences of the widespread coalmines and host rocks on the water of selected regions, China

The massive exploration and random dumping of coals in various regions of China create serious environmental and health problems because of the presence of toxic trace elements (TTEs), which possibly transfer to environment and cause serious health issues. This study was conducted to probe the environmental consequences of coalmines on the aquifer water and their association with health risks and the environment. For this purpose, 100 s of water samples was collected from the typical coalmine regions of Hancheng, Huanglong, Binxian, Handan, Langao, and Fusui and analyzed for various parameters. In Handan mining areas, Se, Mn, Fe, TDS, SO42-, and total hardness were higher than the WHO standard, while in Hancheng, SO42- was > 95%, Ca2+ 40-96%, and Mg2+ was 0-40%, which caused permanent hardness. In the Fusui and Huanglong areas, the SO42- concentration was > 95%, Ca2+ 60-100%, and Mg2+ 20%, causing permanent hardness. In Binxian, HCO3- was 70-90%, Ca2+ 60-80%, and Cl- and SO42- were 20%, causing temporary hardness. In the Kashin-Beck disease (KBD) area, Se in the Middle Triassic was 0.3, Upper Triassic 0.23, and Quaternary 0.01, while fluoride (F) was 124.7, 141.6, and 159 in μg L-1. The Handan water is included in rock-evaporation dominance (a mixed controlling mechanism), Hancheng, Binxian, Huanglong, and Langao water was included in rock dominance, while the Fusui water was included in rock-precipitation dominance. The average daily intake ((ADI) mg kg-1 d-1) of Ba, Cd, Co, Cr, Cu, Fe, Ti, Tl, Mo, Ni, Zn, Pb, Be, U, and Sr was comparably higher than No Observed Adverse Effect Level (NOAEL), which surely causes high health risk in selected regions. The elemental contaminants in the water were attributed to the geological environment, geochemical processes, ion exchanges, redox reactions, and dissolution of mineralized rock. For aquifer safety, coal mining, and other geological activities should be avoided to protect the water for future generations.

Quantifying the impacts of coal mining activities on topsoil using Hg stable isotope: A case study of Guqiao mining area, Huainan City

The Hg released from coal mining activities can endanger soil ecosystems and pose a risk to human health. Understanding the accumulation characteristics of mercury (Hg) in coal mining soil is important for effectively controlling Hg emissions and developing measures for the prevention and control of Hg contamination. To identify the potential sources of Hg in soils, the Hg concentration and isotopic composition characteristics of raw coal and different topsoil types from the areas surrounding a coal mine were determined in this study. The results showed that Hg in coal mainly exists mainly in the form of inorganic Hg, and Hg has experienced Hg2+ photoreduction prior to incorporating into coal. In addition, the composition of Hg isotopes differed significantly among different topsoil types, and the δ202Hg value of the farmland soil exhibited large negative excursions compared to the coal mining soil. The ternary mixed model further revealed the presence of substantial differences in potential Hg sources among the two regions, with the coal mining soil being greatly disturbed by anthropogenic activity, and the relative contributions of Hg from raw coal, coal gangue, and background soil to coal mining soil being 33.42%, 34.4%, and 32.19%, respectively. However, Hg from raw coal, coal gangue and background soil contributed 17.04%, 21.46%, and 61.51% of the Hg in the farmland soil, indicating that the accumulation of Hg in farmland soil was derived primarily from the background soil. Our study demonstrated that secondary pollution in soil caused by immense accumulation of solid waste (gangue) by mining activities offers a significant challenge to ecological security. These findings provide new insights into controlling soil Hg in mining areas and further highlight the urgency of strict protective measures for contaminated sites.

A method for evaluating the coal spontaneous combustion index by the coefficient of variation and Kruskal-Wallis test: a case study

Focusing on the precise prediction of coal spontaneous combustion (CSC), temperature-programmed experiment was conducted to identify the coal spontaneous combustion indexes. Based on a conception that there should be no significant difference between the coal temperatures determined by different coal spontaneous combustion indexes with sufficient accuracy, an approach for evaluating the coal spontaneous combustion index by statistical analysis was developed. After mining data screening by the coefficient of variation (C_v), the arrays of coal temperature determined by different indexes were calculated with the curve fitting. The Kruskal-Wallis test was employed to analyze the differences between the arrays of coal temperature. Finally, the weighted grey relational analysis method was used to optimize the coal spontaneous combustion indexes. The results show that the production of gaseous compounds is positively correlated with coal temperature. In this case, O₂/CO₂ and CO₂/CO were selected as the primary indexes, and CO/CH₄ was used as the alternative index of coal at low-temperature stage (≤ 80 °C). The detecting of C₂H₄ and C₂H₆ were the confirmation indexes when the coal temperature reaches 90 °C ~ 100 °C. It could provide a reference to the determination of grading index of coal spontaneous combustion during mining and utilization.

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.

Investigation of thermal behavior and hazards quantification in spontaneous combustion fires of coal and coal gangue

To explore the thermal behavior and hazard during the spontaneous combustion fires (SCFs) of coal and coal gangue (CG), the characteristics of heat release and thermal transfer during the SCFs of coal and CG were tested. The results indicate that coal contains more combustibles and aromatic hydrocarbons, while CG possesses higher contents of ash and inorganic silicate. Coal has a stronger heat release capacity, while CG owns a smaller specific heat capacity, a larger thermal diffusivity and a greater thermal conductivity. Thus, CG performs better with respect to heat transfer. The apparent activation energy of coal is larger in the endothermic stage, whereas that of CG is more notable in the exothermic stage. Based on heat release and heat transfer performance, hazardous zones during the SCFs of coal and CG were identified, and the combustion growth index was established to quantify the hazard of SCF disasters. The results show that the hazard is determined by both heat release and thermal transfer capacities. Coal or CG with a combustible component of 31.3 %, which not only releases massive heat but also transfers heat quickly, corresponds to the most considerable hazard of SCF disasters.

Invisible Effect of Virtual Water Transfer on Water Quantity Conflict in Transboundary Rivers—Taking Ili River as a Case

Water stress in countries within a drainage basin exacerbates the water quantity conflict in transboundary rivers. However, few studies considered the invisible effect of virtual water transfer on water quantity conflict by intensifying water stress. Therefore, this study, with Ili River as the case, collects data on Virtual Water Trade (VWT) from 1990 to 2015, uses water stress index (WSI) to assess water stress values under two scenarios (with or without virtual water transfer), and takes Grey Verhulst Model to predict two scenarios water stress values respectively. Next, based on the Levenberg—Marquardt (LM) Algorithm, this study compares the water quantity conflict intensity of the two scenarios, and further explores the invisible effect of virtual water transfer on the conflicts among transboundary rivers. Results show: (1) During the study period (1990–2015), water stress in China and Kazakhstan along the banks of Ili River increased in general. (2) China was basically a net exporter of virtual water during 1990–1995, and Kazakhstan became a net exporter after 1995. (3) During 2020–2025, water conflict value of Ili River without virtual water transfer is 0.458, while the value rises to 0.622 with virtual water transfer, indicating that virtual water transfer between China and Kazakhstan has an invisible enhancement on the water quantity conflict of Ili River. (4) The intensified water quantity conflict is mainly caused by the more and more serious water stress in Kazakhstan. On such basis, it is more urgent for Kazakhstan to restructure its economy and trade.

Adsorption and Desorption of Coal Gangue toward Available Phosphorus through Calcium-Modification with Different pH

The chemical reaction between calcium ions (Ca2+) and phosphate in the soil is the main way to maintain the availability of soil phosphorus. Thus, we believe stimulating coal gangue with Ca2+ solution would be an effective way to improve its adsorption and desorption capacity toward phosphate. In order to explore the effects of different pH of Ca2+ solution on the modified effect of coal gangue, we conducted mechanical grinding (<1 mm), high temperature calcination (800 °C), and the stimulation of Ca2+ solution with different pH (2, 7, 13), to prepare acidic calcium-modified coal gangue (Ac-CG) (Ac-CG, acidic calcium-modified coal gangue; Ne-CG, neutral calcium-modified coal gangue; Al-CG, alkali calcium-modified coal gangue; RCG, raw coal gangue), neutral calcium-modified coal gangue (Ne-CG), and alkali calcium-modified coal gangue (Al-CG); raw coal gangue (RCG) was regarded as the control. The results indicated that Al-CG had better phosphate adsorption (3.599 mg g−1); this favorable adsorption performance of Al-CG was related to the formation of hydrated calcium silicate gel and ettringite, which provided more Ca2+, Al3+, and hydroxyl groups, and a larger specific surface area (9.497 m2 g−1). Moreover, Al-CG not only held more phosphate but also maintained its availability longer for plants. It is suggested that stimulating coal gangue with Ca2+ solution under alkaline conditions is a perfect way to enhance its adsorption and desorption capacity toward phosphate; the Al-CG we prepared could be used as filling material and soil conditioner in the reclamation area.

Influence of lignin on coal gangue pyrolysis and gas emission based on multi-lump parallel reaction model and principal component analysis

The effects of lignin (LIG) on coal gangue (CG) pyrolysis characteristics, gas emissions, and multi-lump parallel reaction modeling are studied in this paper. The combined thermogravimetry and Fourier infrared spectrometer were used to obtain the weight loss and gas product functional group data of the co-pyrolysis of coal gangue and lignin. Gaussian peaks were used to analyze the reaction degree of different proportions of lignin added to coal gangue at different temperatures. Moreover, principal component analysis (PCA) is applied to further analyze pyrolysis reaction process. During the pyrolysis of C1L3 samples, a synergistic interaction was discovered. The optimal mixing ratio of coal gangue and lignin during pyrolysis was obtained. The influence mechanism of lignin on coal gangue pyrolysis is studied in this article, which can provide technical support for the reduction and resource utilization of coal gangue. There are six-lump parallel reactions in pyrolysis after CG and LIG are mixed. The addition of LIG changed the CO₂ release law of CG pyrolysis. The strengthening of coal gangue disposal research is of positive significance for improving the environment and increasing the utilization rate of coal.

Release characteristics of elemental mercury during low calorific value coal combustion

The dynamic release characteristics of Hg⁰ during low calorific value coal combustion were investigated in a combining laboratory-scale furnace coupled with atomic fluorescence spectroscopy. The results show that the sulfur has an inhibitory effect on the homogeneous oxidation of Hg⁰ in flue gas. The instant intensity of Hg⁰ release increases with increasing temperature while the amount of Hg⁰ release gradually decreases with increasing temperature. Compared with that under air, the instant intensity of Hg⁰ release under O₂/CO₂ atmosphere increases to some extent with a lower decreasing rate of Hg⁰ release peak. The release ratio of elemental mercury (Hg) from Yuwu (YW) and Qinxin (QX) coal increases while that from Yonghao (YH) coal decreases under O₂/CO₂ atmosphere. In the range of 800-1100°C, the release rate of Hg reaches more than 96% under the residence time of 50 s.

Using UAV and Field Measurement Technology to Monitor the Impact of Coal Gangue Pile Temperature on Vegetation Ecological Construction

Coal gangue is an inevitable product in coal mining and processing and is the most important source of pollution in mines. Vegetation restoration of coal gangue piles must consider its special site conditions. Therefore, we conducted unmanned air vehicle (UAV) temperature monitoring, field investigation and experimental analysis on spontaneous combustion coal gangue piles in Lu’an mining area. In the vegetation construction of coal gangue piles, high-temperature stress affects plant survival. The spontaneous combustion coal gangue piles have abnormal temperature, high surface temperature and few vegetation types. The plant community species diversity index (Shannon–Wiener index, Pielou’s index and Species abundance index) is small, the plant community is single and the plant diversity is low. Spontaneous combustion of coal gangue leads to soil acidification, reducing soil water content, soil organic carbon (SOM), available nitrogen (AN), available potassium (AK) and available phosphorus (AP). These factors are single or interactive in plants and have an impact on plant survival and growth. The research results are of great significance to the vegetation restoration of spontaneous combustion coal gangue piles, ecological reconstruction and the improvement of the ecological environment of coal mine areas.

The effect of biomass addition on pyrolysis characteristics and gas emission of coal gangue by multi-component reaction model and TG-FTIR-MS

The pyrolysis experiment of biomass added to coal gangue was studied by thermogravimetric-Fourier transform infrared spectroscopy-mass spectrometry (TG-FTIR-MS) method. The multi-component reaction model was used to simulate the pyrolysis reaction of coal gangue and biomass. The most suitable model was obtained, and the pyrolysis mechanism was analyzed. According to the two-component reaction model of CG pyrolysis, the decomposition temperature range of components in CG is 340-800 °C and 400-620 °C. The five-component reaction model can well simulate the pyrolysis process of coal gangue and biomass. Meanwhile, the effects of different proportions of biomass in the mixture on the gas products of coal gangue pyrolysis were analyzed. It was found that the addition of biomass to coal gangue could promote the release of gaseous organic matter during pyrolysis. CG75PS25 only has a synergistic effect in the high temperature zone greater than 600 °C. CG25PS75 only has a synergistic effect in a small range of 230-300 °C, and there is an inhibitory effect in other temperature ranges. In general, there is an inhibitory effect between coal gangue and biomass on CO₂ formation, which is of positive significance for greenhouse gas emission reduction.

Emission characteristics of PM2.5 and components of condensable particulate matter from coal-fired industrial plants

Particulate matter (PM), including condensable particulate matter (CPM) and filterable particulate matter (FPM), emitted from coal combustion is one of the major contributors to air pollution. In this study, CPM and FPM were sampled from two coal-fired industrial boilers with air pollution control devices (APCDs). The emission concentration of total PM (CPM and FPM) and inorganic components of CPM were studied. The organic fractions in CPM and raw coal were analyzed using a gas chromatograph/mass spectrometer (GC/MS). The concentrations of total PM in the flue gas decreased from 1475.61 to 7.68 mg/Nm³ in unit 1, and from 2451.62 to 29.38 mg/Nm³ in unit 2 after the flue gas passed through the APCDs. CPM accounted for 51.42-91.93% of total PM emitted from stacks, of which organic components (73.87-96.30%) were one of the main constituents. Although aromatic hydrocarbons are one of the major components of raw coal, they were almost nonexistent in the CPM emitted from coal combustion. Saturated hydrocarbons accounted for the largest proportion of organic components in CPM, 49.19% in unit 1 and 61.16% in unit 2. The proportion of esters in the oxygen-containing derivatives of CPM emitted from two units was relatively high. SO₄^2- was the inorganic component with the largest concentration in CPM emitted from the boiler units. This study will improve the understanding of the emissions levels of PM_2.5 and the properties of CPM that originate from the coal-fired industrial processes.

Effect of the Coal Preparation Process on Mercury Flows and Emissions in Coal Combustion Systems

Coal preparation is effective in controlling primary mercury emissions in coal combustion systems; however, the combustion of coal preparation byproducts may cause secondary emissions. The inconsistent coal preparation statistics, unclear mercury distribution characteristics during coal preparation, and limited information regarding the byproduct utilization pathways lead to great uncertainty in the evaluation of the effect of coal preparation in China. This study elucidated the mercury distribution in coal preparation based on the activity levels of 2886 coal preparation plants, coal mercury content database, tested mercury distribution factors of typical plants, and then traced the mercury flows and emissions in the downstream sectors using a cross-industry mercury flow model. We found that coal preparation altered the mercury flows by reducing 68 tonnes of mercury to sectors such as coking and increasing the flows to byproduct utilization sectors. Combusting cleaned coal rather than raw coal reduced the mercury emissions by 47 tonnes; however, this was offset by secondary mercury emissions. Coal gangue spontaneous combustion and the cement kiln coprocessing process were dominant secondary emitters. Our results highlight the necessity of whole-process emission control of atmospheric mercury based on flow maps. Future comprehensive utilization of wastes in China should fully evaluate the potential secondary mercury emissions.

Investigation of the Adsorption Behavior of Organic Sulfur in Coal via Density Functional Theory (DFT) Calculation and Molecular Simulation

In this paper, we have investigated the chemical adsorption behavior of O₂ on five types of organic sulfur (thiol, sulfoxide, thioether, sulfone, and thiophene) in polycyclic aromatic hydrocarbon (PAH) sheets using density functional theory (DFT) calculations. Here, the adsorption energy of O₂-organic sulfur exceeds that of O₂-PAH. Sulfone tends to be more favorable for oxidation reactions than other organic sulfur compounds and PAH by energy gap and deformation charge density analyses. A large charge transfer occurs between O₂ and organic sulfur compounds by charge analysis. A radical distribution function (RDF) analysis shows that O₂/CO₂/N₂ is preferentially adsorbed on nitrogen/sulfur/oxygen-containing functional groups in coal. To inhibit the reaction of sulfur-containing coal with oxygen, the physical adsorption of pure gas (CO₂/O₂/N₂) and binary mixed gases (CO₂ + O₂/N₂ + O₂/CO₂ + N₂) is conducted at different temperatures and geological depths using molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The adsorption capacities of five types of organic sulfur with respect to the pure gases decrease with increasing temperature and increase with increasing depth. For O₂/CO₂, CO₂/N₂, and O₂/N₂ binary gas systems, the order with respect to adsorption amount is CO₂ > O₂ > N₂. The factor of adsorption capacities is also evaluated, and the results show that pore volume plays a key role in adsorption behavior.

An Experimental Study of the Road Performance of Cement Stabilized Coal Gangue

The research into the road performance of coal gangue is of great significance for the consumption of coal gangue and reducing pollution. In this paper, the coal gangues were prepared by separation and crushing processes, and their gradations were also optimized. Aiming to identify the possible problems of coal gangue as a pavement base, an unconfined compressive strength test, a splitting test, a freeze–thaw test, and a drying shrinkage test of cement stabilized gangue with varying cement amounts were carried out, and the test results were compared and analyzed. The test results showed that the maximum dry density and optimum moisture content (OMC) of the optimized cement stabilized gangue and cement stabilized macadam increased with cement content. The maximum dry density and OMC of cement stabilized macadam were larger than that of cement stabilized gangue with the same cement content. The optimized 7-day unconfined compressive strength of cement stabilized gangue can meet the requirements for a secondary and lower highway base and subbase. The OMC and cement content are the critical factors affecting the compressive strength loss rate of cement stabilized gangue after freeze–thaw cycles. The smaller the OMC of cement stabilized gangue and the larger the cement content, the lower the compressive strength loss rate. With an increase in cement content, the drying shrinkage strain of cement stabilized gangue increased. The results show that a cement content of 4% is optimal for the cement stabilized coal gangue, which can be used for the light traffic base and heavy traffic subbase of class II and below highways. It provides a basis, guide, and reference for the application of coal gangue materials in a high-grade highway base.

Heavy metal- and organic-matter pollution due to self-heating coal-waste dumps in the Upper Silesian Coal Basin (Poland)

This study provides potential insight between self-heating coal-waste dumps and related environmental pollution in southern Poland. Samples collected from dumps in the Upper Silesian Coal Basin were used to quantify released contents of organic- and inorganic pollutants, i.e., polycyclic aromatic hydrocarbons (PAHs) and trace elements (Pb, Cd, Cr, Cu, Zn, Ni, Hg, As). Elevated Hg concentrations (~100-1078 mg/kg) and Pb (~600-2000 mg/kg) attest to the evaporation of these metals from deeper parts of the dumps. The acidic pH levels (3.0-4.5) may help to mobilize these elements. Pearson's correlation coefficients for samples analyzed by AAS and ICP-MS indicate a similar origin for Cd, Zn, and As. Mostly 2- and 3-ring PAHs, especially anthracene in burnt soil, dominate in the samples. Chlorinated PAHs, thiophenol, pyridines, quinolines (and derivatives) in thermally-altered samples, and waste containing pyrolytic bitumen indicate coking conditions. The high levels of Hg, Pb, and Cd, and chlorinated PAHs and nitrogen heterocycles formed or enriched during self-heating in these dumps should be deemed a significant environmental hazard. Calculating the lifetime cancer risks due to PAHs and heavy metals accumulations in the dumps are substantial, and access to these dumps should be prohibited.

Release behavior of iodine during leaching and calcination of phosphate rock

A series of experiments of column leaching under different pHs (pH 1.8, 3.8, 6.5, and 8.5) and calcination at different temperatures (200-1100 °C) were carried out for evaluation of release behavior of iodine in phosphate rock. The modes of occurrence of iodine in the phosphate rock and its leaching and calcination residues were extracted with sequential chemical extraction. Iodine in solution and solid samples was measured with ion chromatography (IC) and pyrohydrolysis combined ion chromatography (PIC), respectively. Mineralogical compositions of phosphate rock and the leached and calcined residues were determined by XRD (X-ray diffraction) and FT-IR (Fourier infrared spectrum). The results show that iodine in phosphate rock occurred in a descending order of significance, as forms of residual, carbonate bound, ion-exchange, organic bound, Fe-Mn oxide bound, and water soluble. Under pH 1.8, 3.8, 6.5, and 8.5, the release iodine may almost reach the maximum at the leaching time of 65, 93, 90, and 165 h, with leaching rates of 5.28%, 1.24%, 0.550%, and 1.08% and the average iodine concentrations in the leachates of 2300 μg/L, 378 μg/L, 164 μg/L, and 189 μg/L, respectively. The forms of the leached iodine were mostly ion-exchange and carbonate-bound iodine under pH 1.8 and water soluble and ion-exchange iodine under pH 3.8, 6.5, and 8.5. By calcination, the total iodine was released rapidly in 200-300 °C and 700-1000 °C, and almost released completely at 1000 °C, with a leaching rate of 96.6%. The ion-exchange and organic-bound iodine were, respectively, released at 200-1000 °C and at less than 300 °C; the carbonate-bound and residual iodine were mainly released at more than 700 °C. The release iodine in phosphate rock leached by natural water and calcined at a high temperature may lead to the increase of iodine concentration of water body and atmosphere.

Microbially-driven sulfur cycling microbial communities in different mangrove sediments

Microbially-driven sulfur cycling is a vital biogeochemical process in the sulfur-rich mangrove ecosystem. It is critical to evaluate the potential impact of sulfur transformation in mangrove ecosystems. To reveal the diversity, composition, and structure of sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) and underlying mechanisms, we analyzed the physicochemical properties and sediment microbial communities from an introduced mangrove species (Sonneratia apetala), a native mangrove species (Kandelia obovata) and the mudflat in Hanjiang River Estuary in Guangdong (23.27°N, 116.52°E), China. The results indicated that SOB was dominated by autotrophic Thiohalophilus and chemoautotrophy Chromatium in S. apetala and K. obovata, respectively, while Desulfatibacillum was the dominant genus of SRB in K. obovata sediments. Also, the redundancy analysis indicated that temperature, redox potential (ORP), and SO₄^2- were the significant factors influencing the sulfur cycling microbial communities with elemental sulfur (ES) as the key factor driver for SOB and total carbon (TC) for SRB in mangrove sediments. Additionally, the morphological transformation of ES, acid volatile sulfide (AVS) and SO₄^2- explained the variation of sulfur cycling microbial communities under sulfur-rich conditions, and we found mangrove species-specific dominant Thiohalobacter, Chromatium and Desulfatibacillum, which could well use ES and SO₄^2-, thus promoting the sulfur cycling in mangrove sediments. Meanwhile, the change of nutrient substances (TN, TC) explained why SOB were more susceptible to environmental changes than SRB. Sulfate reducing bacteria produces sulfide in anoxic sediments at depth that then migrate upward, toward fewer reducing conditions, where it's oxidized by sulfur oxidizing bacteria. This study indicates the high ability of SOB and SRB in ES, SO₄^2-_,S₂^- and S^2- generation and transformation in sulfur-rich mangrove ecosystems, and provides novel insights into sulfur cycling in other wetland ecosystems from a microbial perspective.

Ambient PM2.5 and Related Health Impacts of Spontaneous Combustion of Coal and Coal Gangue

Coal and coal gangue spontaneous combustion (CGSC) occurs globally, causing significant environmental pollution. However, its emissions are poorly quantified and are overlooked in global or regional air pollutant emission inventories in previous studies, resulting in the underestimation of its impacts on climate, environment, and public health. This study quantified the emissions of various air pollutants originating from CGSC in Wuhai, a city in China, investigated emission characteristics, and estimated the contribution of CGSC emissions to fine particulate matter (PM_2.5) air pollution and related health impacts on a regional scale. The results revealed that the CGSC-related PM_2.5 emissions were approximately 4643 t a^-1 (95% confidence interval (95% CI): 721; 10447), accounting for 26.3% of the total PM_2.5 emissions. Alkanes, alkenes, and aromatics accounted for 69.4, 17.9, and 2.9%, respectively, of the total emissions of volatile organic compounds (VOCs). Due to CGSC emissions, the ambient PM_2.5 concentration in Wuhai increased by 5.7 μg m^-3 on average, while the nitrate concentration decreased. The number of premature deaths caused by exposure to ambient PM_2.5 associated with CGSC reached 381 (95% CI: 290; 452) in Wuhai and surrounding cities in 2017. Urgent control strategies and engineering techniques are needed to mitigate CGSC to protect public health.

Evaluating the distribution and potential ecological risks of heavy metal in coal gangue

The heavy metals, which derived from accumulated coal gangue, are important source of environmental pollution. In this study, coal gangue dumps, collected in Shaanxi Province, China, were used to evaluate the potential ecological risks and release characteristics of heavy metals, including the chemical forms, release characteristics, and potential ecological risks by using the methods of Tessier's sequential extractions, leaching experiments, gray GM (1, 1) forecasting mode, and potential ecological risk index. The results indicated that gangue samples contained high levels of metals, especially of Pb, which was the 20-31 times of the background value, whereas the sum of exchangeable and carbonate fractions in Co and Cu was a large proportion (4-11%) of the total. Potential ecological risks were at strong level regardless of the type of the coal gangue because of Mo and Pb and the comprehensive ecological risk index of 351.51-412.27. Weathering promotes the release of heavy metals in the gangue. Furthermore, the contents of Cu and Pb in leaching solution and their release times in weathered gangue were significantly higher than those of the fresh one. This research provides a scientific basis for the prevention and control of heavy metal pollution in coal-containing areas.

Release of fluorine and chlorine during increase of phosphate rock grade by calcination and digestion

A series of experiments for calcination and subsequent digestion to increase the grade of phosphate rock were performed. Fluorine and chlorine released by calcination and digestion were investigated. The forms of both elements were studied by sequential chemical extraction. The grades of raw and calcined phosphate rocks, and their phosphorus concentrates were confirmed according to the value of P₂O₅%. The results showed that fluorine and chlorine in phosphate rock mainly existed in carbonate-bound and residual forms. The grade of phosphate rock can be well increased by calcination and subsequent digestion. By digestion at the optimal condition of 2.5:1 for liquid-solid ratio, 60 °C for digestion temperature and 50 min for digestion time, the phosphorus concentrates digested from the calcined phosphate rock of 1000 °C reached the highest grade (P₂O₅% = 33.24%). By calcination, the released fluorine was mainly HF at a low temperature and SiF₄ at a high temperature, with fluorine release amount of 1.61 × 10⁴-3.82 × 10⁴ g/t at 900-1100 °C. Cl₂, HCl and Cl^- were mainly released at 200-500 °C, less than 800 °C and more than 800 °C, which release amount were 9.40 × 10-2.54 × 10² g/t, 2.10 × 10²-1.53 × 10⁴ g/t and 2.24 × 10²-5.61 × 10² g/t, respectively. By digestion with water for the calcined phosphate rock of 900-1100 °C, the concentrations of fluorine and chlorine in effluent were respectively 77.2-160 mg/L and 7.99-19.6 mg/L. It can be concluded that fluorine and chlorine released by calcination for phosphate rock contribute greatly to atmospheric acid rain and equipment corrosion; by digestion, the discharge of fluorine seriously exceeds the standard and may cause greater pollution to the water body.

Pyrolysis characteristics, artificial neural network modeling and environmental impact of coal gangue and biomass by TG-FTIR

The harm done to the environment by coal gangue was very serious, and it is urgent to adopt effective methods to dispose of coal gangue in order to prevent further environmental damage. Co-pyrolysis experiments of coal gangue (CG) and peanut shell (PS) were carried out using thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) under nitrogen atmosphere. The heavy metal was detected using the inductively coupled plasma-optical emission spectroscopy (ICP-OES). CG and PS were mixed according to the mass ratio of 1:0, 3:1, 1:1, 1:3 and 0:1. The samples were heated to 1000 °C at the heating rate of 10 °C/min, 20 °C/min and 30 °C/min. The comprehensive pyrolysis index (CPI) of CG, C3P1, C1P1, C1P3 and PS is 0.17 × 10^-8, 9.75 × 10^-8, 35.47 × 10^-8, 100.94 × 10^-8 and 192.72 × 10^-8%² ·min^-2·°C^-3. The kinetic parameters were calculated by model-free methods (Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose). The gas products generated at different temperatures during the pyrolysis experiment were detected by Fourier transform infrared spectrometer. The heating rate, temperature and mixing ratio are the input parameters of artificial neural network (ANN), and the remaining mass percentage of sample during the pyrolysis is the output parameter. The ANN model was established and used to predict thermogravimetric experimental data. The ANN18 model is the best model for predicting the co-pyrolysis of CG and PS.

Removal of Fluoride from Water Using a Calcium-Modified Dairy Manure-Derived Biochar

This study investigated the removal of fluoride from water using a calcium-modified dairy manure-derived biochar (Ca-DM500). The Ca-DM500 showed a 3.82 - 8.86 times higher removal of fluoride from water than the original (uncoated) manure-derived biochar (DM500). This is primarily attributed to strong precipitation/complexation between fluoride and calcium. The Freundlich and Redlich-Peterson sorption isotherm models better described the experimental data than the Langmuir model. Additionally, the removal kinetics were well described by the intraparticle diffusion model. The Ca-DM500 showed high reactivity per unit surface area [0.0001, 0.03, 0.16 mg F per m² for Douglas fir-derived biochar (DF-BC), DM500. and Ca-DM500, respectively] for retention of fluoride reflecting the importance of surface complexation. The copresence of anions reduced removal by Ca-DM500 in the order SO 4 2 - ≈ PO 4 3 - > NO 3 - . The sorption behavior of fluoride in a continuous fixed-bed column was consistent with the Thomas model. Column studies demonstrated that the Ca-DM500 shows a strong affinity for fluoride, a low release potential, and a stable (unreduced) removal capacity through regeneration and reuse cycles.

Frost Resistance of Coal Gangue Aggregate Concrete Modified by Steel Fiber and Slag Powder

Coal gangue, a by-product produced during the process of coal mining and washing, has a serious impact on the environment. Using coal gangue as a concrete aggregate has been proven helpful in potentially improving its value and reducing its environmental impact to a certain extent. However, the high water absorption and low strength of coal gangue aggregate cause a poor frost resistance of coal gangue aggregate concrete (CGAC), and thus limits its application in cold areas. This study attempted to modify the CGAC with steel fibers (including hooked-end, undulated, and copper-plated steel fiber) and slag powder, and investigated its frost resistance. Moreover, the impact that steel fiber and slag powder had on air-void characteristics of CGAC was also analyzed. The results show that when steel fibers were incorporated into CGAC, the compressive strength and splitting tensile strength of CGAC reduced significantly after freezing/thawing and that they experienced the smallest reduction when the content of the steel fiber was 1 vol.% and the undulated steel fibers worked best. However, the effect of slag powder on frost resistance of CGAC at an early age was not obvious, which may be related to the slower pozzolanic reaction of slag powder. Incorporating steel fiber or slag powder into CGAC can optimize its mesostructure and make the air-voids of concrete smaller, which is beneficial to its frost resistance. The results provide a good way to improve the performance of CGAC, expand its application in cold regions, and reduce the pollution caused by coal gangue.

Effects of plant additives on the concentration of sulfur and nitrogen oxides in the combustion products of coal-water slurries containing petrochemicals

The active use of solid fossil fuels (coal) in the production of heat and electricity has led to significant pollution, climate change, environmental degradation, and an increase in morbidity and mortality. Many countries (in particular, European ones, China, Japan, the USA, Canada, etc.) have launched programs for using plant and agricultural raw materials to produce heat and electricity by burning them instead of or together with traditional fuels. It is a promising solution to produce slurry fuels, based on a mixture of coal processing, oil refining and agricultural waste. This paper presents the results of experimental research into the formation and assessment of the most hazardous emissions (sulfur and nitrogen oxides) from the combustion of promising coal slurry fuels with straw, sunflower and algae additives, i.e. the most common agricultural waste. A comparative analysis has been carried out to identify the differences in the concentrations of sulfur and nitrogen oxides from the combustion of typical coal, coal processing waste, as well as fuel slurries with and without plant additives. It has been shown that the concentration of sulfur and nitrogen oxides can be reduced by 62-87% and 12-57%, respectively, when using small masses of plant additives (no more than 10 wt%) and maintaining high combustion heat of the slurry fuel. However, the use of algae and straw in the slurry composition can increase the HCl emissions, which requires extra measures to fight corrosion. A generalizing criterion of slurry fuel vs. coal efficiency has been formulated to illustrate significant benefits of adding plant solid waste to coal-water slurries containing petrochemicals. Straw and sunflower waste (10 wt%) were found to be the best additives to reduce the air pollutant emissions.

Study on Urbanization Level, Urban Primacy and Industrial Water Utilization Efficiency in the Yangtze River Economic Belt

Considering the undesirable output, this paper adopted the data envelopment analysis (DEA) model with the slack variable and super efficiency improvement, to measure industrial water utilization efficiency in the Yangtze River Economic Belt. The paper also creatively introduces urbanization level and urban primacy into driver factors’ estimation by stochastic and fixed Tobit models, exploring how urbanization characteristics affected the water utilization in regional industrial production. The results showed that industrial water efficiency has maintained an upward trend during the whole period, while most central and western provinces have shown a U-shaped trend of decreasing first and then rising. However, the industrial water utilization efficiency of central regions is the lowest, and the eastern regions are the highest, catching up with western regions. Utilization efficiency shows an overall convergence during the research period from 2005 to 2017. Regarding the factors’ estimation, both population urbanization and land urbanization negatively affected industrial water utilization efficiency, particularly blind expansion and disorderly development. The urban primacy meant the unbalance of urbanization, which would lead to urban diseases and pollution transfer, while the effects of urban primacy depended on the urbanization level. However, the utilization efficiency of industrial water did not become better automatically along with urbanization development; therefore, the scale and speed of urbanization should be scientifically formulated. The effects of the level of economic development, the advanced industrial structure, and the level of foreign investment are significantly negative.

Research on N2-inhibitor-water mist fire prevention and extinguishing technology and equipment in coal mine goaf

In this study, a new type of N2-inhibitor-water mist (NIWM) technology was proposed to resolve the problem of fire prevention and extinguishing in the goaf of coal mine. The corresponding equipment was designed and manufactured. Under the condition that both gas pressure and liquid pressure were 0.5-2MPa, the NIWM equipment produced the water mist with Sauter mean diameter (SMD) range of 166-265μm. The experimental results of the operating parameters of NIWM equipment were in agreement with the theoretical derivation. The theory of two-phase flow atomisation can be used as theoretical guide for this technology. After that, on the basis of the NIWM equipment, the experiments of inhibiting low temperature (30-100°C) oxidation and extinguishing high temperature combustion of large dosage of coal sample were carried out. Water mist with SMD = 188μm had good diffusivity in the container. The inhibiting effect of N2-inhibitor-water mist on low temperature oxidation of coal was obviously greater than that of single material. N2-water mist extinguished the burning coal completely in 20 minutes. The addition of water mist solved the shortcoming of poor cooling effect of N2. In different stages of coal-oxygen reaction, N2, inhibitor and water mist play very different role in controlling the process of coal-oxygen reaction, which was not simple accumulation of the three. The combination of N2, inhibitor and water mist should be determined according to the state of the coal mine goaf fire. On the basis of the research conclusions, the onsite arrangement diagram of the NIWM fire prevention and extinguishing equipment in the goaf was designed. The research results proved the feasibility and effectiveness of this technology, and it is of great significance to the prevention and control of coal spontaneous combustion in goaf.

Inequality of female health and its relation with urbanization level in China: geographic variation perspective

Urbanization development plays a vital role in the health of modern residents; however, there have been very limited researches to specifically and comprehensively explore the relationship between urbanization level evaluating indicators (ULEIs) and female health outcomes. The mortality rate of breast cancer (BC), cervical cancer (CC), and ovarian cancer (OC) and classified urbanization factor are collected at provincial level. Stepwise regression model (SRM) and geographically weighted regression model (GWRM) are conducted to obtain spatial relationship between the mortality rate of those cancer and ULEI. Our results show that there is remarkable difference of mortality rate of BC, CC, and OC in different provinces as well as higher BC, CC, and OC distributed in northern regions. The increase of value added of primary industry (VAPI), taxi, and coal consumption has detrimental effect on BC and CC. Fuel oil consumption (FOC) ultimately results in increase of mortality rate of BC and OC, and urban fixed asset investment (UFAI) poses a risk to increase the mortality rate of OC. Contrarily, natural gas consumption (NGC) appear to mitigate mortality rate of BC. In particular, our findings demonstrate that there exist spatial differences for VAPI, FOC, NGC, taxi, and coal consumption influencing BC, CC, and OC. It is suggested that policy makers should take account of regional discrepancy and implement a sustainable urbanization development considering female health.

Impact of the coal mining-contaminated soil on the food safety in Shaanxi, China

The study aimed to investigate the impacts of coal mining-contaminated soil on the locally grown food crops and humans health. For the active investigation and assessment, the study collected 175 samples including contaminated and control soil and various types of food crops (corn, wheat, mixed food (egg, pork meat, potato, pepper)) from Shaanxi Province. All these samples were analyzed through ICP-MS and ICP-OES. Results show that in Weibei soil, the average concentration (mg kg^-1) of Cr (194 ± 94), Cu (27 ± 13), Cd (0.6 ± 0.3), Ni (83 ± 35), Be (1.98 ± 0.8), Rb (115 ± 68), Li (74 ± 78), Sr (148.5 ± 67), and Zn (3056 ± 2380) was higher than that of the Chinese soil standard (CSS) and upper continental crust (UCC) (P < 0.01-0.05). In Langao soil, the average concentration (mg kg^-1) of Cr (99.5 ± 48), Cu (77 ± 32), Ni (113 ± 37), Pb (45 ± 19.8), Cd (2.9 ± 1.7), Co (13.9 ± 2.4), Mo (28.7 ± 16), Be (2.98 ± 0.5), Li (81.8 ± 9.7), V (430 ± 166), Zn (255 ± 105), and Ba (1347 ± 445) was higher than that of the CSS and UCC. However, in Binxian Jurassic all the toxic trace elements (TTE) were higher than the CSS and UCC. In Langao contaminated vegetable, Na, Cd, Tl, In, Mo, Li, U, Bi, and Th may cause very high risk, whereas Al, Mn, P, Fe, Ca, Cr, Ni, Pb, Co, Cs, Rb, and Ba may cause considerable risk. However, the average daily intake (ADI) of Al, Mn, P, Fe, Cd, Mo, and Ba was higher than the No Observable Adverse Effect Level (NOAEL). However, the non-carcinogenic risk of Al, Mn, P, Fe, Cr, Cu, Ni, Pb, Cd, Co, Tl, Mo, Li, V, Ba, and Th was higher than acceptable level (HQ = 1). In Binxian wheat, Al, Tl, Cs, Bi, and Th may cause very high risk, and Ti, Na, K, Fe, Ca, Cr, Ni, Cd, Pb, Sr, Bi, and U may cause considerable risk. However, ADI of Al, Mn, P, Ti, Fe, Cu, Ni, Pb, Mo, Ba, and U for both adults and children was higher than the NOAEL. In Weibei, the wheat crops are prone to considerable-to-moderate elemental risk. The non-carcinogenic risk of Al, Mn, P, Fe, Cr, Cu, Pb, Co, Tl, Mo, Li, Zn, and Th was higher than the acceptable level. In countryside adults and children, ADI was lower than the NOAEL except Al, P, and Zn. The study concluded that human activities of coal mining release a high amount of TTE to the soil. Majority of arable land, grain food and vegetable were contaminated through TTE, which may cause high risks to human's health and the environment.

The Potential Environmental Impact of PAHs on Soil and Water Resources in Air Deposited Coal Refuse Sites in Niangziguan Karst Catchment, Northern China

Long-term deposition of coal spoil piles may lead to serious pollution of soil and water resources in the dumping sites and surrounding areas. Karst aquifers are highly sensitive to environmental pollution. In this study, the occurrence and release/mobilization of polycyclic aromatic hydrocarbons (PAHs) in coal waste and coal spoils fire gas mineral (CSFGM) were evaluated by field and indoor investigations at Yangquan city, one of the major coal mining districts in the karst areas of northern China. Field investigations showed that dumping of coal waste over decades has resulted in soil and water pollution via spontaneous combustion and leaching of coal spoil piles. Indoor analysis revealed that the 2-ring and 3-ring PAHs contribute to 65-80% of the total PAHs in coal spoils, with naphthalene (Nap), Chrysene (Chr), and Phenanthrene (Phe) as the dominant compounds. Based on a heating/burning simulation experiment, the production of PAHs is temperature-dependent and mainly consists of low-ring PAHs: 2-ring, 3-ring, and part of the 4-ring PAHs. The PAHs in the leachate are light-PAHs (Nap, 20.06 ng/L; Phe, 4.76 ng/L) with few heavy-PAHs. The distribution modes of PAHs in two soil profiles suggest that the precipitation caused downward movement of PAHs and higher mobility of light-PAHs.

Geochemical valuation and intake of F, As, and Se in coal wastes contaminated areas and their potential impacts on local inhabitants, Shaanxi China

This study probe the human health risk of fluoride (F), arsenic (As), and selenium (Se) and their daily intake available quantity to human through different sources in different regions of Shaanxi, China. For this purpose, a number of samples, including coal and coal wastes, rocks, soil, and vegetables were collected from south Qinling Mountain stone-like coal (Geo type-I), Binxian-Jurassic (Geo type-II), Hancheng Permo-Carboniferous (Geo type-III), and countryside (Huanglong County) of Shaanxi province. All these samples were analyzed through atomic fluorescence spectroscopy and combustion hydrolysis methods. Results showed that Geo type-I was enriched with As, Se, and F, Geo type-II, III, and the countryside were slightly enriched with As and F and deficient in Se. The average daily intake (ADI) of Se in Geo type-I was 0.005-0.0045, Geo type-II 0.0005-0.0004, Geo type-III 0.0006-0.0005, and countryside 0.0002-0.001 in mg kg^-1 day^-1 adult-children, respectively, which was lower than the optimum level (0.06-0.075 mg kg^-1day^-1). ADI of As at Geo type-I was 0.0085-0.0075, Geo type-II 0.004-0.0037, Geo type-III 0.0008, and countryside 0.00022-0.00019 in mg kg^-1 day^-1 adult-children, respectively, which was above the acceptable range (10^-6-10^-4). ADI of F at Geo type-I was 0.0047-0.0041, Geo type-II 0.0098-0.0087, Geo type-III 0.002-0.0017 and countryside 0.0015-0.0013 in mg kg^-1 day^-1 adult-children, respectively. The toxicity level of Se and F at all the regions was lower than the NOAEL and LOAEL, while As was higher at Geo type-II and I. The extreme deficient of Se than the optimum range along with high F could deregulate the normal body growth especially causes bones and joint problems. However, the study found a rare patient with bone and joint disease (maybe Kashin-Beck disease) in the countryside. To find the exact cause of Kashin-Beck disease, the study needs further medical investigation in Se-deficient regions and their association with selenium deficiency and enriched fluoride.

Assessment of heavy metal in coal gangue: distribution, leaching characteristic and potential ecological risk

In the process of excavation and utilization of the coal gangue hill, gangue at different weathering degree was exposed to the environment, which can be harmful to the surroundings. In order to find the law of heavy metal release and to evaluate the potential ecological risk, five kinds of coal gangue at different weathering degrees were collected from a coal mine named Suncun, an over 100-year-old mine of Xinwen coal mining field located in Tai'an city, Shandong Province of China. Samples were processed with microwave digestion for total content determination of heavy metals, and another part of samples was processed by Tessier sequential extraction for chemical forms analysis. Leaching tests at various pH were carried out to investigate the release of heavy metal. The laws of transformation and release of heavy metals were discussed and potential ecological risk was evaluated. The results indicated that the weathering degree had a significant impact on the content of heavy metal. Exchangeable and carbonate fractions of Cr and Pb were a large proportion of the total and should attract great attention. Potential ecological risk was at strong level (light black) and was up to very strong level (deep black) because of Cd. But Cr had contributed the most for gray gangue, which was 71% of the total. The species of heavy metal in gangue changed due to weathering and lead to the difference of the leaching characteristic and risk.

The influence of liquid plant additives on the anthropogenic gas emissions from the combustion of coal-water slurries

At present, coal is considered one of the main components for the production of cheap, high-energy and environmentally attractive slurry fuels. The latter can be produced on the basis of low-grade coal dust or coal processing wastes. Thus, coal-water slurries and coal-water slurries containing petrochemicals are produced. The involvement of coal and oil processing wastes expands the scope of raw materials, reduces the fuel costs from traditional energy sources and modifies the main economic characteristics of power plant performance. However, it also increases the impact of coal-fired thermal power stations on the environment. In the last 30-50 years, many efforts have been made to decrease the negative impact of human industrial activity on climate. Involving plant-based components in the process of energy generation to save energy and material resources looks very promising nowadays. This research studies the influence of adding typical bioliquids (bioethanol, turpentine, glycerol) on the concentration of anthropogenic emissions from coal-water slurry combustion. Relative mass concentrations of bioliquids varied in a small range below 20%. We focused on the concentration of the most hazardous sulfur and nitrogen oxides from the combustion of typical filter cakes, as well as plant-containing slurries. It was established that the concentration of sulfur oxides can be decreased (as compared to coal) by 75%, whereas that of nitrogen oxides by almost 30%. Using a generalizing criteria expression, we illustrated the main benefits of adding bioliquids to slurry fuels in comparison with coal. Adding 20% of glycerol was found to provide maximum advantages.

Trace elements concentration and distributions in coal and coal mining wastes and their environmental and health impacts in Shaanxi, China

This study probe the probable impacts of coal mining pollution and its impacts on human's health and environment. A total of 144 samples including coal and coal wastes, soil, plants, foods, and water were collected from the Hancheng county and countryside of Shaanxi, China. All the samples were analyzed for trace elements using ICP-MS, OES, and AFS. Results showed that the concentration of Se, As, Cr, Cu, Pb, Cd, Co, Ni, Mo, U, Th (mgKg^-1), Fe, Mn, Al, Ti (%) etc., in coal and coal wastes were 7.5, 12.1, 275, 55, 54.2, 0.8, 14.8, 94.5, 8.9, 4.9, 17.2, 3.5, 0.02, 19, 0.7, respectively. While in soil 0.6, 12, 194, 27.5, 7.4, 0.6, 11.3, 83.4, 0.7, 1.7, 9.9, 3.1, 0.04, 10.5, and 0.4 for the above elements, respectively. In Hancheng foods, the average concentration of Se-0.09, As-0.15, Cr-1.8, Cu-3.2, Pb-0.4, Cd-0.02, Co-0.09, Ni-0.4, Mo-0.64, U-0.01, Th-0.03, Fe-129, Mn-15.6, Al-234, and Ti-5.2 in mgKg^-1, respectively, which are comparably higher than the countryside. The elemental concentration in groundwater of both areas was below the WHO-2004 standard. In Hancheng, the average daily intake (mgKg^-1bw/d) of Se 0.004-0.0038, As 0.004-0.13, Cr 0.055-0.06, Cd 0.001-0.004, Ni 0.018-13.91, Pb 0.05-0.001 adult-children, respectively. The toxic trace elements such as Cr, Cu, Mn, Pb, Ti, Cd, Co, Th, Fe, Al, and Mo caused non-carcinogenic risk with high morbidity in children than adults. By assessing environmental risks, coal and coal wastes caused high risk, food and plants faced moderate to high risk, while mountain and agriculture soil are prone to low to considerable risk. The pollution in Hancheng County is extreme as compared to the countryside. The study concluded that the contamination is geogenic in both the areas but coal mining enhance the metals contamination and has extensive impacts on the living community and environment of Hancheng areas.

Evaluation of acidity in late Permian outcrop coals and its association with endemic fluorosis in the border area of Yunnan, Guizhou, and Sichuan in China

The junction area of Yunnan, Guizhou, and Sichuan provinces is the heaviest coal-burning endemic fluorosis zones in China. To better understand the pathogenicity of endemic fluorosis in this area, 87 coal samples from the late Permian outcrop or semi-outcrop coal seams were collected in eight counties of the junction area of Yunnan, Guizhou, and Sichuan provinces. The total fluorine and sulfate content, etc. in the coal was determined using combustion-hydrolysis/fluoride-ion-selective electrode method and ion chromatography, respectively. The results show that the total fluorine concentrations in the samples ranged from 44 to 382 µg g^-1, with an average of 127 µg g^-1. The average pH of the coals is 5.03 (1.86-8.62), and the sulfate content varied from 249 to 64,706 µg g^-1 (average 7127 µg g^-1). In addition, the coals were medium- and high-sulfur coals, with sulfur mass fraction ranging from 0.08 to 13.41%. By heating the outcrop coals, HF release from the coal was verified quantitatively without exception, while simulated combustion directly confirmed the release of sulfuric acid (H₂SO₄). The acid in coal may be in the form of acidic sulfate ([Formula: see text]/H₂SO₄) because of a positive relationship between pH and [Formula: see text] in the acidic coal. The possible reaction mechanism would be that a chemical reaction between the acid (H₂SO₄ or [Formula: see text]) and fluorine in the coal occurred, thereby producing hydrogen fluoride (HF), which would be the chemical form of fluorine released from coal under relatively mild conditions. The unique chemical and physical property of HF may bring new insight into the pathogenic mechanism of coal-burning endemic fluorosis. The phenomenon of coal-burning fluorosis is not limited to the study area, but is common in southwest China and elsewhere. Further investigation is needed to determine whether other endemic fluorosis areas are affected by this phenomenon.

Potentially useful elements (Al, Fe, Ga, Ge, U) in coal gangue: a case study in Weibei coal mining area, Shaanxi Province, northwestern China

Coal gangue has become one of the largest industrial solid waste in China, but it is also a kind of reserve resources. Representative coal gangue samples from different coal mines (mainly in Permo-Carboniferous and Jurassic) in Weibei area in Shaanxi Province are collected, and potentially useful elements (Al, Fe, Ga, Ge, U) in coal gangue are analyzed. The results show that the reserves of Al and Fe in Chinese coal gangue are 262 million tons and 196 million tons, respectively, based on the geometric mean values of Al₂O₃ (15.18%, weight percent) and Fe₂O₃ (6.24%, weight percent). Meanwhile, the crude reserves estimation of Ga, Ge, and U are 55,282, 6867, and 32,981 tons, respectively, based on the weighted mean contents of Ga, Ge, and U in coal gangue at 17.55, 2.18, and 10.47 mg/kg, respectively. Furthermore, Ga and Al contents in quite a large number of coal gangue mines exceed the cutoff value, which has a prospect of development and utilization from coal gangue. The policy implications from this study may include that (1) recycling of useful elements in Chinese coal gangue should be treated as an integral part of sustainable development with professional legislations and (2) establishing a basic database of coal gangue and authoritative system with relevant departments for solid waste management may effectively improve comprehensive utilization of coal gangue in the future.