Search

Abstract The objective of this work is to investigate the implications of geological influence factors on gas content and geochemical characteristics of deep-buried (> 800 m) coalbed methane (CBM) reservoirs. Results show that bituminous coal accounts for the majority, which exhibits similar maturity but differ in maceral and chemical constituents. CBM reservoirs show low porosity, low permeability and moderate temperature, with thickness of 0.85–4.15 m. In addition, the total gas content is 4.58–12.33 m3/t (average of 8.83 m3/t). CH4 is the main component with concentration of 92.83−99.22% (average of 96.68%), and the δ13CCH4 and δ13DCH4 is − 53.78‰–−44.62‰ (average of − 48.82‰) and − 223.93‰––−4.49‰ (average of − 215.37‰), respectively. All CBM samples are the mixtures of thermogenic gases and secondary biogenic gases with CO2 reduction. In addition, gas content characteristic at the critical point of burial depth is the result by positive and negative geological effects. CH4 concentration shows a wide range with the increases of buried depth, while the numerical values of which for the selected samples display complex variation characteristics. Furthermore, the values of δ13CCH4 and δ13DCH4 become heavier with the increases of buried depth. Besides, the above two geochemical parameters are related to R o, max and reservoir temperature.

In recent years, to liberate coal resources from high pressure limestone water on the coal seam floor, North China Coalfields have generally adopted surface directional drilling technology to carry out regional grouting reinforcement and transformation (commonly known as “floor regional treatment”) on the thin-layer limestone of the Taiyuan Formation in order to comprehensively seal karst cracks in limestone and block vertical guide water channels. In this technology, the design of the spacing between “horizontal branching holes” closely related to the diffusion range (radius) of the slurry has been widely studied by academia and industry. There is a large amount of grouting work in the bottom plate area of the Anhui North mining area, especially in the mining of deep resources, which will cost billions of yuan. It is necessary to verify the true data of the diffusion range of the grout. Therefore, based on the Hengyuan Coal Mine in the northern Anhui mining area as the research base, relying on the II63 mining area floor area treatment project, the slurry diffusion range tracing test was designed and implemented. The fluorescent agent (tracer) was added to the horizontal branch hole (Z8-7) in the middle, and the rock debris samples were taken from the horizontal branch holes (Z8-6, Z8-8) and cross branch detection holes (Z8JC) on both sides to identify fluorescent cement and obtain the diffusion range of the slurry. Furthermore, based on the analysis of the influencing factors of slurry diffusion, a formula for calculating the diffusion range of slurry in the grouting treatment of the bottom plate area of the Hengyuan Coal Mine was constructed. The results show that: ① Based on the analysis of on-site and indoor identification results of rock debris, the diffusion range of grouting slurry under the coal seam floor area of the Hengyuan Coal Mine II63 mining area was 38.3−44.0 m, and the cement distribution was dense within the diffusion range of horizontal branch hole slurry within 30 meters. The grouting effect was the best in this area. ② Through a rapid identification of on-site rock cuttings and precise identification of indoor rock cuttings, the diffusion range of the slurry obtained was basically consistent, proving the effectiveness of fluorescence tracing of the diffusion range of the slurry. ③ Through comparative analysis, it was believed that under actual grouting conditions such as calculation parameters and boundary constraints, the theoretical calculation and numerical simulation results of the slurry diffusion range were close to the measured results of on-site tracing experiments. ④ Using the data from water pressure tests, grouting parameters, drilling structures, and hydrogeological responses during the tracer test process, taking into account the factors such as gravity, structure, and groundwater runoff, and using SPSS nonlinear fitting software, a formula for calculating the diffusion range of grouting slurry in the bottom plate area of the Hengyuan Coal Mine II63 mining area was obtained. ⑤ Based on the actual geological and hydrogeological conditions of the injection layer in the Hengyuan Coal Mine, using the fitted slurry diffusion range calculation formula, the slurry diffusion range of Z8 site in the II63 mining area was obtained to be 37.8−42.9 m, which was similar to the measured results of the slurry diffusion range tracer test. The calculation formula could be promoted and applied under similar conditions. The on-site tracing engineering test of the diffusion range of grouting slurry in the coal mine floor area not only obtained real data on the diffusion range of slurry, but also clarified the inherent relationship between slurry diffusion and various geological and hydrogeological factors. The diffusion mechanism of grouting slurry for ultra deep and ultra long directional drilling was revealed, and a formula for calculating the diffusion range of slurry was constructed, providing a reference basis for the reasonable design of horizontal branch hole spacing in bottom plate area treatment projects under similar conditions.

In recent years, shale logging has played a crucial role in the grouting reinforcement engineering of the floor limestone strata in “North China-type”coalfields. However, existing shale logging techniques are limited to the recognition of physical indicators such as color, particle size, and morphology. This limitation makes an accurate stratification challenging, and the “along-stratum rate” in borehole design is difficult to be ensured. These constraints hinder the effectiveness of water damage control in the floor limestone strata areas. This study, based on the elemental geochemical differences in the Carboniferous Taiyuan Formation thin-layered limestone and its clastic interlayers, selected the Taoyuan Coal Mine in the Huaibei Coalfield as the research area. Some vertical core samples were obtained from drill holes in the upper part of the Taiyuan Formation, including L1 limestone to L4 limestone (with L3 limestone as the grouting control target layer). Using the X-ray fluorescence spectrometry (XRF), the major elemental background values of thin-layered limestone and its interlayers were quantitatively determined. Also, a major elemental geochemical identification model was established for thin-layered limestone using mathematical statistical methods such as cluster analysis and factor analysis. Simultaneously, major elemental testing was conducted on shale samples from directional drilling horizontal branch holes. The identification pattern validation was completed through shale stratigraphic source analysis based on the established geochemical identification model. The results showed that high CaO content and Loss on Ignition (LOI) value could serve as characteristic indicators for the target layer L3 limestone in grouting and reinforcement. Abundances of MgO (0.5%±), MnO (0.03%±), and P2O5 (0.08%±) could be used as recognition indicators for the overlying marker layer J3. The cluster analysis identification model effectively distinguished the Taiyuan Formation L1 to L3 limestone. The model established using element factor scores effectively differentiated clastic interlayers from thin-layered limestone in the Taiyuan Formation. The Fisher discriminant equation obtained by running the model with rock geochemical background values achieved an accuracy rate of 100% in the source analysis of cuttings from grouting target layer L3 limestone. Based on the above findings, the feasibility of applying the elemental geochemical source analysis method, aimed at ensuring the “in-layer rate” in horizontal branch hole cuttings, was demonstrated. This, in turn, led to the proposal of a ground directional drilling “in-layer rate” control technology scheme. This study, grounded in elemental geochemical theory, identified the target layer stratification through characteristic geochemical information carried by cuttings from directional drilling. With the support of on-site rapid quantitative testing techniques, the technology offers new insights into addressing the challenge of grouting and modification at bottom limestone water hazard areas in the North China-type coalfields.

Recently, the ability of microbial-induced calcium carbonate precipitation (MICP) to remediate heavy metals has been widely explored. Sporosarcina pasteurii was selected to remediate heavy metal-contaminated solution and aged refuse, exploring the feasibility of Sporosarcina pasteurii bioremediation of heavy metals and analyzing the changes in heavy metal forms before and after bioremediation, as well as the mechanism of remediation. The results showed that Sporosarcina pasteurii achieved remediation rates of 95%, 84%, 97%, and 98% for Cd, Pb, Zn, and Cr (III) in contaminated solution, respectively. It also achieved remediation rates of 74%, 84%, and 62% for exchangeable Cd, Pb, and Zn in aged refuse, respectively. The content of exchangeable Cr (III) before bioremediation was almost zero. The content of heavy metals with exchangeable form and carbonate-bounded form in aged refuse decreased after bioremediation, while the content of heavy metals with iron–manganese oxide binding form and residual form increased. Simultaneously, the presence of Fe and Al components in aged refuse, as well as the precipitation of calcium carbonate produced during the MICP process, jointly promotes the transformation of heavy metals into more stable forms.

The migration, transformation, and accumulation of dissolved organic matter (DOM) in pore water of sediment cores play a pivotal role in lacustrine carbon cycling. In order to understand the dynamics of DOM in the sediments of large shallow eutrophic lakes, we examined the vertical profiles of DOM and the benthic fluxes of dissolved organic carbon (DOC) in sediment cores located in algae accumulated, dredged, and central areas of eutrophic Lake Taihu, China. Optical properties showed the significant influence of terrestrial inputs on the DOM components of pore water in the algae accumulated area but an abundant accumulation of autochthonous DOM in the central area. The benthic fluxes of DOC ranging from −458.2 to −139.4 mg·m−2·d−1 in the algae accumulated area displayed an opposite diffusion direction to the other two areas. The flux ranges of 9.5–31.2 mg·m−2·d−1 in the dredged area and 14.6–48.0 mg·m−2·d−1 in the central area were relatively smaller than those in the previously reported lake ecosystems with low trophic levels. Dredging engineering disturbed the pre-dredging distribution patterns of DOM in sediment cores. The deposition, accumulation, and transformation of massive algae scums in eutrophic lakes probably promoted the humification degree of sediments. HIGHLIGHTS Terrestrial input significantly affected the dissolved organic matter (DOM) components of the algae accumulated area.; DOC diffusion direction of the algae accumulated area was opposite to the other areas.; Dredging work disturbed the pre-dredging distribution patterns of DOM in sediment cores.; Biogeochemical processes of accumulated algae scums probably promoted humification.;

The natural balance system of deep groundwater is disturbed by coal mining and drainage depressurization, leading to temporal and spatial changes in microbial communities in different aquifers. Herein, groundwater samples of Permian coal measures sandstone aquifer and Carboniferous Taiyuan Formation limestone aquifer with depths of 600 and 750 m are collected from the mine hydrological holes in Huaibei coalfield, and 16S rRNA gene V4 region sequencing method is used to test and analyze the microbial community diversity of deep groundwater. The operational taxonomic units (OTUs) numbers of coal measure water and Taiyuan limestone water samples range from 968−3071 and 820−3894, respectively, with the average values being 1980.43 and 1847.81 respectively. ACE, Shannon and Chao values show that coal measure water > Taiyuan limestone water. Simpson index shows that coal measure water < Taiyuan limestone water, indicating that coal measure water > Taiyuan limestone water, regarding the diversity of microbial community composition in groundwater. Main dominant bacteria phylum in Taiyuan limestone water and coal measure water are Proteobacteria, Bacteroidota and Planctomycetota; their relative abundance ranging 41.48%−97.36%, 0.57%–48.01%, 0.13%–15.29%, respectively. Main dominant bacteria genera in coal measure water are Thiovirga, Hydrogenophaga, and Flavobacterium; their relative abundance accounting for 5.98%, 4.39% and 3.43%, respectively of the total bacteria in the coal measure water. Hydrogenopaga, Acinetobacter and Thiobacillus are the main dominant bacteria genera in Taiyuan limestone water, their relative abundance being 11.13%, 4.72% and 4.40% respectively. Unique OTUs in coal measure and Taiyuan limestone aquifers number 1759 and 4107, respectively. F−, K+ and ORP are the main environmental factors affecting the bacterial community in groundwater. K+ impacts the abundance of the bacterial community in the Taiyuan limestone water to a greater extent than that of coal measure water. Contrarily, F− affects the bacterial community in the coal measure water and Taiyuan limestone water is similar. As the aquifer depth increases, so does the influence of F− and K+ on the microbial community abundance. The increase of F− concentration of typical pollutants in Huaibei Coal strengthens some bacterial communities, resulting in changes in microbial community composition. The groundwater pollution caused by coal mining also enriches Thiothrix in the ash water. Huaibei coal measure water and Taihui limestone water are the main water filling sources for coal mining in Huaibei coalfield. Knowledge of the deep underground of the coalfield and how different water microbial community change, has been improved by this work, thereby providing a new method for identifying the water source of coal mine gushing (outburst), and a guarantee for the prevention and control of water disasters in coal mines.

The main threat source of coal mining in the lower formation of Huaibei Coalfield is limestone water from the coal seam floor (including the Carboniferous Taiyuan Formation and the Ordovician limestone water), and some well flooding accidents occur from time to time. For the control of water disaster in the limestone floor, at present, the ground directional drilling high-pressure grouting technology is mostly used for carrying out the regional reinforcement and reconstruction of the third layer of thin limestone (referred to as “three ashes”) in the Taiyuan Formation of the coal seam floor. Therefore, it seals the karst cracks of the three ashes and blocks the vertical water channel passing through the three ashes. However, with the implementation of large-scale high-pressure grouting project, the groundwater flow field in the injected aquifer will be disturbed. Because of the coupling effect of a large amount of slurry water, the groundwater chemical field will inevitably be seriously disturbed. Taking the limestone aquifer of the Taiyuan Formation (hereinafter referred to as “Taihui water”) in the Taoyuan Coalmine of the Huaibei Coalfield as the research object, based on the constant component monitoring data statistics, Piper diagram, ion combination ratio, and saturation index analysis, this paper studies the hydrogeochemical evolution law of the Taihui water before grouting, during grouting and after grouting (i.e. “three periods before, during and after regional grouting”). The results show that ① in the three periods, Na++K+, HCO3 −, Cl− in the Taihui water first decrease and then increase. Ca2+, SO4 2− and pH values first increase and then decrease, while Mg2+, TDS decrease as a whole. In the grouting control area, Ca2+ and SO4 2− are relatively high and alkalinity is relatively high, while Na++K+ and HCO3 − are relatively low. Before grouting, SO4·Cl−Na and SO4·Cl−Na·Ca (mixed type) are the main types. Since regional grouting, SO4·Cl−Na·Ca and SO4·Cl−Na are the main types in the Taihui water, and the proportion of mixed water increases. ② During grouting, the dissolution of carbonate and sulfate, the desalfation and the cation exchange in the Taihui water are weakened, the dissolution of calcite and dolomite is enhanced, and the mixing effect of the precipitates water of cement slurry is obvious. After grouting, the dissolution of carbonate and sulfate, desulphation and cation exchange are gradually enhanced, the dissolution of calcite and dolomite is gradually weakened, and the mixing effect of precipitates water is weakened. One year after the completion of grouting, the hydrochemical effect is gradually recovered toward the state before grouting, but it has not yet recovered to the state before grouting. It can be seen that the regional grouting treatment has a relatively obvious impact on the disturbance of the chemical field of the Taihui water. ③ The saturation index of dolomite and calcite in the Taihui water is large, and most of them are in precipitation state. The saturation index of gypsum and rock salt is small, and they mostly exist in the state of dissolution. In the three periods, the saturation indexes of calcite, dolomite and gypsum in the Taihui water increase first and then decrease, in which dolomite is more obvious, while the rock salt saturation index does not change significantly. The saturation index of most minerals has a strong positive correlation with pH value, while the saturation index of gypsum has a strong positive correlation with TDS. ④ Due to the mixing of the water from the grouting slurry with high pH value, the original ion balance is broken, which leads to the reduction of the correlation of the conventional indicators of the Taihui water since the regional grouting, and the correlation is lower after the grouting than that during the grouting.

In Huaibei coalfield, the technology of ground directional drilling and high-pressure grouting is widely used to control the karst water disaster of coal measures floor. After grouting, the filling and drainage path of the seepage field changes, and the grouting high pressure and the slurry water will change the distribution characteristics of the groundwater seepage field and chemical field of the injected target aquifer in a certain period of time. Taking Taoyuan Coal Mine in Huaibei Coalfield as the research object, the evolution model of seepage field and chemical field (referred to as “double field”) of the target layer under regional grouting disturbance is built by using the software of Feflow, the coupling mechanism of “double field” is discussed, and the Cl− which is less affected by the environment is selected as the simulation factor, and the analysis of the factors affecting solute transport under the “double field” coupling effect is carried out. On this basis, the mathematical model of solute diffusion under regional grouting disturbance is constructed. The results show that in the seepage field model after identification and verification, 71.9% of the points where the error between the simulated water level and the measured water level is less than 3m, and the simulation effect is good; Among the identified and verified chemical field models, the simulation effect of solute transport in mining area II4 is good, and the simulation value in mining area II1 is about 14.4 mg/L lower, with an error of about 6.6% of the actual value, less than 10%. The overall simulation effect is good. The Cl− in mining area II4 and II2 with relatively high permeability coefficient is easy to migrate and diffuse, while the rock in mining area II1 with low permeability coefficient is dense and has poor permeability. During the 50 years of model operation, it basically exists in the state of “stagnant water”. Based on the evolution characteristics of local seepage field in II4 mining area under grouting disturbance, it is considered that solute transport is mainly controlled by permeability coefficient, dispersion, hydraulic gradient, seepage velocity, grouting time, slurry specific gravity and other parameters. It is found that the concentration of Cl− reaches a peak within 18−22 years after the completion of grouting, and then begins to decrease, and reaching the equilibrium state before regional grouting approximately 40 years later. Based on the data obtained from multiple parameter setting operations, a mathematical model of solute diffusion under the “double field” coupling is established. The data with error rate less than 10% accounts for 81.4%, which indicates that the established mathematical model of solute diffusion is basically reliable. This study can provide scientific basis for the study of the water environment evolution of the injected target aquifer under the regional grouting disturbance and the prediction and early warning of coal mine water disasters, and has important theoretical and practical significance.

The project implementation of water inrush and its treatment ensures the safe mining of coal mines, but also causes certain disturbance to the hydrogeochemistry of primary limestone water. Based on the water inrush event in Taoyuan Coal Mine of Huaibei coalfield in 2013, the water rock interaction mechanism of Taiyuan Formation limestone water (namely, ‘Taihui water’) was discussed. The results showed that: (1) the relationship of cation mass concentration before and after water inrush was Na+ + K+ > Ca2+ > Mg2+; the correlation of anionic mass concentration before water inrush was SO42− > HCO3− > Cl−, while it was HCO3− > SO42− > Cl− after the event. Before the event, the main water quality types were SO4•Cl-Ca and SO4•Cl-Na; after the event, they mainly included HCO3-Na and SO4•Cl-Na; (2) There is a strong positive correlation between mineral saturation index and pH value, that is, minerals are easy to dissolve under acidic conditions, while alkaline conditions will inhibit the dissolution and transformation of minerals; (3) The hydrogeochemical processes of limestone aquifer mainly included cation exchange, carbonate dissolution, pyrite oxidation, sulfate and silicate dissolution. HIGHLIGHTS The hydrogeochemical characteristics of Taiyuan Formation limestone water disturbed by water inrush of collapse column was analyzed.; Based on saturation index, ion combination ratio and correlation analysis method, the evolution of hydrogeochemistry under the influence of water inrush was discussed.; The relationship between saturation index and TDS and pH value was studied.;

High sulfate mine groundwater at the Huaibei coalfield has exceeded the permissible limit (250 mg/l) of World Health Organization, posing serious threat to nearby water resource. A total of 28 samples were collected from Taiyuan formation aquifer (TA) and Ordovician aquifer (QA). In view of the mean concentration in two aquifers, the TA and OA were identified as high sulfate group and low sulfate group. The contrast on hydrochemical characterization and water-rock interactions were analyzed to reveal the mechanism of sulfate enrichment in mine groundwater. Compared with low sulfate groundwater, the high sulfate groundwater possess a higher content of TDS, Na+ and Cl−, which elevated by 3.83, 4.0 and 3.29 times, respectively. The low sulfate groundwater is controlled by Ca-Na-HCO3 type (82%), whereas the high sulfate groundwater is dominated by Na-SO4-HCO3 type (88%). The geochemical process of low sulfate groundwater is influenced by dissolution of carbonate minerals and weak ion exchange. The mechanism of sulfate enrichment in mine groundwater are predominately controlled by both silicate and carbonate minerals weathering, strong ion exchange interaction and competitive effect. The outcomes enhance understanding of the mechanism of high sulfate mine water and provide theoretical support for mine wastewater treatment. HIGHLIGHTS Hydrogeochemistry mechanism contrasts between low and high sulfate in limestone aquifers were studied.; Water environment for high sulfate mine groundwater was revealed from comparative analysis with low sulfate mine groundwater.; Corresponding minerals dissolution dominated the hydro-chemistry process together with ion exchange and competitive effect.;

Due to the large amount of water supply, the water level difference between mid-layer water and shallow water increases. There is no authoritative answer whether there is a hydraulic connection between shallow and mid-layer water. Therefore, a clear understanding of hydrogeochemical characteristics and the water chemical connection of them is indispensable for groundwater protection and the safety of water supply. The results of the statistical analysis showed that shallow and mid-layer water were both neutral water. The content of SO42−, Cl− and Na+ in both exceeded the grade III standard limit in the Standard for Groundwater Quality of China. Piper diagram revealed shallow water was mainly of Na + Mg + HCO3− and Mg + Na + HCO3− type, and mid-layer water was mainly of Na + Mg + HCO3− + SO42− and Na + Mg + HCO3− type. Besides, using the coefficient variations method of comprehensive water quality index (pH, TDS, F−, and NO3−), it is found that except for a local area with thin thickness (less than 5 m) of the first aquiclude, the mid-layer water was not affected by shallow water in Sulin mining area. This study may be helpful for the safety of water supply in the study area and other mining areas in the Huaibei coalfield. HIGHLIGHTS First analysis on the hydraulic connection between shallow and mid-layer water by using comprehensive water quality indexes.; The relationship between the thickness of the first aquiclude and the vatiation of nitrate content in mid-layer water and shallow water.; Sources of fluorine in mid-layer water.;

Soil is the foundation of agricultural green development and human survival; the study of local environmental geochemical baselines can guide soil management and ensure the safe use of soil. In this study, a total of 100 shallow farmland soil samples were collected in each township of Yongqiao District, Suzhou City, Anhui Province, China. Herein, the contents of 10 heavy metal elements including As, Hg, Cd, Pb, Cr, Cu, Mn, Ni, Zn and Fe were determined. In addition, the geochemical baseline of heavy metals was calculated based on the relative cumulative frequency curve method, and the soil pollution status was evaluated. The results show that the average contents of As, Hg, Cd, Cu, Mn and Zn exceeded the soil background values of Anhui Province by 3.82%–64.74% (1.04–1.65 times), meanwhile, the average contents of Pb and Cr were lower than the soil background values of Anhui Province. The average contents of Cd, Cr, Cu, Mn and Ni exceeded the Chinese soil background values by 1.61%–64.74% (0.98–1.65 times). The geochemical baseline values of As, Hg, Cd, Pb, Cr, Cu, Mn, Ni, Zn and Fe were 9.585 mg/kg, 0.028 mg/kg, 0.112 mg/kg, 21.59 mg/kg, 53.66 mg/kg, 19.31 mg/kg, 543.8 mg/kg, 24.93 mg/kg, 50.57 mg/kg and 2.654%, respectively. The pollution assessment results also showed that most of the farmland soil samples in the study area were non-polluting or slightly polluted based on geochemical baselines. Hg and Cu in a few samples were moderately polluted, and Cd in only one sample was moderately intensely polluted. Combined with the distribution of pollution and field investigation, it is considered that Hg comes from atmospheric deposition and agricultural non-point source pollution of industrial pollution. Cu comes from animal husbandry and agricultural pollution. Meanwhile, Cd is related to natural sources, wood processing and agricultural fertiliser application. The study demonstrated that the calculation of soil geochemical background value should take full account of the differences between the various regions, combined with the current state, particularly the pre-consideration of the distribution of elements or pollutants. Then, reasonably select the evaluation standard value so that the evaluation results can truly reflect the state of soil pollution.

The surface water from subsidence lakes and shallow groundwater plays an important role for agriculture, industry and local communities in coal mining areas. The connection between the two types of water and quality, however, remains unclear. In this study, 37 samples were collected from a subsidence lake and shallow groundwater around Luling coal mine. The hydrogeochemisty data and formation mechanisms were analyzed to reveal the connection proof. Compared with shallow groundwater, the surface water from the subsidence lake has a higher content of Na+ and HCO3−. For the two types of water samples, Na+ and Mg2+ are two most abundant cations, followed by Ca2+. The contents of anions followed the same order: HCO3− > SO42− > Cl−. The water samples were controlled by NaHCO3 (99.3%) type. The chemical composition of the two types of water were similar, which are all mainly influenced by silicate minerals weathering and ion-exchange interactions, among which ion-exchange interactions were more intense than in shallow groundwater. The recharging source of the two types of water mainly came from atmospheric precipitation. The two waters in the study area, in general, showed the risk of high salt and low-moderate alkali damage. The outcomes provide a better understanding of the subsidence lake and groundwater and it will help utilization of water resources. HIGHLIGHTS First analysis on the connection between a subsidence lake caused by coal mining and shallow groundwater.; Formation mechanisms of subsidence lake for coal mining area.; Recharging source of subsidence lake.; Water quality for irrigation purpose of subsidence lake.;

Nitrate pollution in groundwater is a global environmental concern. As a result, accurate identification of potential sources for such pollution is of critical significance to the effective control of groundwater quality. In this study, forty-nine shallow groundwater samples were collected from the Huaibei mining area. Hydro-chemical characterization, geospatial analysis technique, dual nitrate isotopes (δ15N-NO3- and δ18O-NO3-), Bayesian model and health risk assessment model were adopted for exploring the conditions, sources, proportion, and potential health risks of nitrate pollution for the first time in the study area. The results showed that the nitrate concentration ranged from 0.00 to 293.21 mg/L, and that 18.37% groundwater samples exceeded the standard of drinking water in China (GB 5749–2006). Based on the dual isotopic values of nitrate, it could be concluded that nitrification was dominated migration and transformation process of nitrogen. The results of Bayesian model showed that the proportional contributions of the potential nitrate pollution sources in shallow groundwater were manure and sewage (M&S) (39.54 %), NH4+ in fertilizer and precipitation (NHF&P) (34.93 %), soil nitrogen (SN) (14.89 %), and NO3- in atmospheric deposition (NAD) (10.64 %). The health risk assessment indicated that non-carcinogenic risks posed by NO3--N was higher for children than adults. The primary exposure pathway was oral ingestion. Monte Carlo simulation were applied to evaluate model uncertainty. The probabilities of non-carcinogenic risks were up to 12.54 % for children and 5.22 % for adults. In order to protect water quality and drinking water safety, it was suggested that effective nitrate reduction strategies and better management practices can be implemented.

High-fluoride (F-) deep groundwater in the vicinity of mining areas poses severe ecological risks. In this study, we aimed to characterize and reveal the seasonal distribution and influencing factors of elevated F- concentrations in the deep groundwater in the Shendong mining area, Shaanxi and Inner Mongolia province, China. In addition, the ecological risks associated with F- concentrations in irrigation water were assessed. During the wet and dry seasons, the F- concentrations in mine water samples ranged between 0.12 and 13.92 mg/L (mean: 4.24 mg/L) and between 0.20 and 17.58 mg/L (mean: 4.59 mg/L), respectively. The F- content of mine water was clearly higher during the dry season than that during the wet season. F- concentrations in deep groundwater exhibited consistent spatial distributions during both the dry and wet seasons, with an evident increase from southeast to northwest. The dissolution and precipitation of F--bearing and calcium minerals, cation exchange, competitive adsorption, evaporation, and anthropogenic activities during both the wet and dry seasons were identified as important factors influencing F- concentrations in deep groundwater. In addition, the ecological assessment revealed that 100% and 88.89% of low-F- deep groundwater samples were suitable for practices during the dry and wet seasons, respectively. In contrast 84.00% and 84.62% of high-F- deep groundwater samples were unsuitable for irrigation practices during the dry and wet seasons, respectively. This research provided useful prevention policies of deep groundwater extraction to mitigate environment problems associated with excessive F- irrigation.

The new modality of inter-regional joint prevention and control is increasingly important to the integrated process of collaborative governance of air pollutants. Therefore, it has become necessary to analyze the degree of interaction among air pollutants within and between cities, master the dynamics of their spatiotemporal distribution and its influencing factors, and diagnose the primary obstacle factors. Long-term data on the concentrations of six air pollutants among 16 cities of Anhui province from 2015 to 2020 were analyzed using harmonic regression, the coupling coordination degree model, the obstacle degree model, the logarithmic mean Divisia index (LMDI), and exploratory spatial data analysis (ESDA). Over all, the annual mean concentrations of five of these pollutants (NO2, SO2, CO, PM10, and PM2.5) decreased to a certain extent over time, whereas O3 concentrations increased. The biggest decrease was observed in BZ city, where SO2 decreased by 80.60% (halving time: −2.03 ± 0.02 years), and the biggest increase was observed in CZ city, where O3 increased by 113.85% (doubling time: 1.74 ± 0.01 years). The O3 concentrations in most cities reached their break points starting in 2018, but the break points of other air pollutants appeared earlier than that of O3, mostly before 2018. With the exception of NO2 and O3, the halving times of other air pollutants were basically shorter than the doubling times. The high degree of interaction among air pollutants within and between cities contrasted sharply with the low degree of coordination. An analysis of hotspot evolution revealed that particulate matter (PM10 and PM2.5) migrated to northern Anhui, NO2 and O3 agglomerated to central Anhui, and CO eventually gathered in the Wanjiang City Belt. The primary obstacle factors of air pollutants in Anhui were particulate matter, SO2 and NO2. The seasonal differences in primary obstacle factors were most evident in 2020: NO2 dominated in winter (in 10 cities), SO2 dominated in southern Anhui, and particulate matter dominated in northern and central Anhui in spring. Other seasons were almost entirely dominated by particulate matter. Industrial structure was found to be more effective in reducing industrial carbon emissions, and technological improvement was found to be more advantageous in reducing industrial particulate matter, NOx and SO2. Finally, the policy implications of these results and suggestions for strengthening the inter-city joint prevention and control of air pollutants are discussed.

In this study, a magnetic iron-zirconium modified zeolite (FeZrMZ) was synthesized. Through sediment culture experiments, the influence of the addition of modified materials on the migration and transformation of phosphorus in river sediments was investigated. The results showed that the modified zeolite could not only effectively reduce the phosphorus concentration in the overlying water, but also significantly reduce the phosphorus concentration in the pore water of sediments. The addition of modified zeolite makes the unstable weakly adsorbed phosphorus (NH4Cl-P) and redox phosphorus (BD-P) transform into the more stable metal oxide-bound phosphorus (NaOH-P) and very stable residual phosphorus (Res-P). The four types of bioavailable phosphorus (BAP), including water-soluble phosphorus (WSP), readily desorbable phosphorus (RDP), algae-available phosphorus (AAP), and NaHCO3 extractable phosphorus (Olsen-P). Under anoxic conditions, they were reduced by 53.5%, 14.1%, 23.8%, and 49.9% respectively. Under aerobic conditions, they were reduced by 23.2%, 16.6%, 32.1%, and 50.0%. The addition of magnetic iron-zirconium modified zeolite could clearly reduce the release potential of phosphorus in sediment, and it could be recovered through the action of an external magnetic field, so it could be used as an effective sediment modifier to control the sediment release of phosphorus. HIGHLIGHTS Synthesize and characterize FeZrMZ, which has a good magnetic separation ability.; FeZrMZ can effectively reduce the concentration of phosphorus in overlying water and interstitial water.; FeZrMZ can convert unstable phosphorus in sediments into stable phosphorus.;

Previously, systematic studies of distribution, sources, and health risks of high F− groundwater used as a drinking-water source in the Sulin coal district, northern Anhui Province of China have not been carried out. In this study, 30 groundwater samples were collected in May 2019, and the data were analyzed using geographic information system, factor analysis, positive matrix factorization, and risk-based corrective action models. The results indicated that the F− concentration of the groundwater samples ranged from 0.16 to 2.06 mg/L, with a mean value of 1.10 mg/L. The F− concentrations of 53.33% of the groundwater samples exceeded China's maximum permissible limit for drinking water (1.00 mg/L). Quantificational source apportionment revealed that the weathering of F-bearing minerals is the main source (66.20%). Cation exchange (16.30%), agricultural activities (13.20%), and natural geological processes (4.30%) were the other sources of F−. The percentages of infants, children, teens, male adults, and female adults that face health risks due to excess F− intake were approximately 20.00%, 70.00%, 6.67%, 20.00%, and 10.00%, respectively. This research provided useful insights into the proper management of groundwater extraction to mitigate health problems associated with excessive F− intake. HIGHLIGHTS Quantificational source apportionment of F− in groundwater was carried out.; Health risk assessment of F− exposure was evaluated for individuals in different groups.; Spatial distribution was analyzed between low and high F− groundwaters in the Sulin coal district.;

Samples of river water and groundwater from Quaternary (QA), sandstone (SA), Taiyuan formation (TA), and Ordovician limestone (OA) aquifers in the Suxian coal-mining district, Anhui Province, China were collected. Their physicochemical properties, and major ion and isotopic compositions were determined. The samples were alkaline, with pH values exceeding 8, and the total dissolved solids concentrations depended on the water source. The δD and δ18O contents were highest in the river water samples and lowest in the SA groundwater. The isotopic characteristics of the QA and OA groundwaters suggest recharge by rainfall and surface water. The isotopic characteristics of river water were controlled mainly by evaporation. Water–rock interactions, the flow rate, and the main water sources were the most important influences on groundwaters in QA, OA, and TA, but the properties of SA groundwater were controlled by static reserves. Two discriminant functions, explaining more than 98.2% of the total variances, indicated that QA, TA, and OA were hydraulically connected. Three groundwater sources were identified as end-members, and a conceptual model was established to calculate water mixing ratios. Highlights This paper systematically discusses the chemical characteristics of elements and isotopes of groundwater in multi aquifers in coal mine area, and establishes a mixed water source identification model by using statistical method. The research results have certain significance for the establishment of groundwater chemistry and water source identification model.;

Abstract The aim of this study is to evaluate the hydrogeochemical characteristics and water environmental quality of shallow groundwater in the Suxian mining area of Huaibei coalfield, China. The natural formation process of shallow groundwater in Suxian is explored using Piper trilinear charts and Gibbs diagrams, and by examining the ratios between the major ions. United States Salinity Laboratory (USSL) charts, Wilcox diagrams, and the water quality index (WQI) are further employed to quantify the differences in water quality. The results reveal that the main hydrochemical facies of groundwater are HCO3–Ca, and that silicate dissolution is the main factor controlling the ion content in shallow groundwater. The USSL charts and Wilcox diagrams show that most of the water samples would be acceptable for use in irrigation systems. The WQI results for each water sample are compared and analyzed, and the quality of groundwater samples around collapse ponds is found to be relatively poor.

Spreading magnetic anomalies recorded the paleo-geomagnetic field variation that has great significance in the investigation of the extension process of ocean basins. Interpreting spreading magnetic anomalies under complex geological environments is challenging, especially for marginal sea basins. We proposed nested elliptical directional filters to separate the spreading magnetic anomalies of the South China Sea (SCS). The results show that the spreading magnetic anomalies separated by the nested elliptical directional filters depict the expansion process of the oceanic crust, and the interference magnetic anomalies are effectively suppressed. The separated spreading magnetic anomalies indicate that the expansion process of the SCS is affected by the interactions between the surrounding plates. The spreading magnetic anomalies of the SCS are warped, interrupted, and not strictly parallel. The pattern of the spreading magnetic anomalies reflects multiple ridge jumps during the expansion process and the post-spreading magmatic disturbances. The long-wavelength magnetic anomalies indicate lithospheric fractures and Curie surface variations in the SCS, which are affected by the post-spreading magmatic rejuvenation. The magnetic anomalies of the SCS resulted from the superposition of magnetic anomalies in the ocean crust and the uppermost mantle.

Abstract Bed-separation water is one of the major water hazards in coal mines. Targeted researches on the preventive technologies are of paramount importance to safe mining. This article studied the restrictive effect of geological and mining factors, such as lithological properties of roof strata, coal seam inclination, water source to bed separations, roof management method, dimensions of mining working face, and mining progress, on the formation of bed-separation water hazard. The key techniques to prevent bed-separation water-related accidents include interception, diversion, destructing the buffer layer, grouting and backfilling, etc. The operation and efficiency of each technique are corroborated in field engineering cases. The results of this study will offer reference to countries with similar mining conditions in the researches on bed-separation water burst and hazard control in coal mines.

Only little information is available on combined effects of abiotic environmental factors on algal arsenate (AsV) metabolic biokinetics. Herein, we demonstrated the methods of using the Taguchi statistical method to investigate four environmental factors including AsV, nitrate (N), orthophosphate (P) and pH for their combined effects on algal growth and arsenic (As) uptake but also extracellular adsorption of Microcystis aeruginosa, as well as As release from dead algal cells. Results showed that an increase of N facilitated M. aeruginosa growth and thus was the principal factor for the algal maximum specific growth rate ( μmax). P was vital to AsV bioconcentration factor (BCF) and As partition coefficients (LogKd) released from deal algal cells. AsV impacted the extracellular As adsorption onto the algal cells, which thereby increased with increasing initial AsV level. The initial pH had an imperative effect on the AsV uptake (ku) and release rate (Ke) from the dead cells. Collectively, the condition of low P, high N and alkaline pH level was favorable to As accumulation rate of living cells and restrictive to As release rate from dead cells of M. aeruginosa. The obtained information can pave a road for extensive understanding on efficient utilization of As bioremediation of algae in practical environment. • Principal factors were identified on AsV metabolic biokinetics by Taguchi method. • High N and pH but low P fasten AsV uptake and reduce As efflux from dead cells. • AsV only as the main factor impacted As extracellular adsorption on algal cells. Method name: Taguchi experimental design for arsenic metabolic biokenetics, Keywords: Algal bioremediation, Accumulation, Release, Dead algae, Taguchi

The thermochemical and kinetic behavior of co-combustion of coal, municipal sludge (MS) and their blends at different ratios were investigated by thermogravimetric analysis. Simulation experiments were performed in a vacuum tube furnace to determine the conversion behavior of toxic elements. The results show that the combustion processes of the blends of coal and municipal sludge are divided into three stages and the combustion curves of the blends are located between those of individual coal and municipal sludge samples. The DTGmax of the sample with 10% sludge addition reaches a maximum at the heating rate of 20 °C/min, indicating that the combustion characteristics of coal can be improved during co-combustion. Strong interactions were observed between coal and municipal sludge during the co-combustion. The volatilization rates of toxic elements decrease with an increasing proportion of sludge in the blends during co-combustion, which indicates that the co-combustion of coal and sludge can effectively reduce the volatilization rate of toxic elements. The study reflects the potential of municipal sludge as a blended fuel and the environmental effects of co-combustion of coal and municipal sludge.