Environmental impact assessment of acidic coal gangue leaching solution on groundwater: a coal gangue pile in Shanxi, China.

With the continual advancement of coal resource development, the comprehensive utilization of coal gangue as a by-product encounters certain constraints. A substantial amount of untreated coal gangue is openly stored, particularly acidic gangue exposed to rainfall. The leaching effect of acidic solutions, containing heavy metal ions and other pollutants, results in environmental challenges such as local soil or groundwater pollution, presenting a significant concern in the current ecological landscape of mining areas. Investigating the migration patterns of pollutants in the soil-groundwater system and elucidating the characteristics of polluted solute migration are imperative. To understand the migration dynamics of pollutants and unveil the features of solute migration, this study focuses on a coal gangue dump in a mining area in Shanxi. Utilizing indoor leaching experiments and soil column migration experiments, a two-dimensional soil-groundwater model is established using the finite element method of COMSOL. This model quantitatively delineates the migration patterns of key pollutant components leached from coal gangue into the groundwater. The findings reveal that sulfate ions can migrate and infiltrate groundwater within a mere 7 years in the vadose zone of aeration. Moreover, the average concentration of iron ions in groundwater can reach approximately 58.3 mg/L. Convection, hydrodynamic dispersion, and adsorption emerge as the primary factors influencing pollution transport. Understanding the leaching patterns and environmental impacts of major pollutants in acidic coal gangue is crucial for predicting soil-groundwater pollution and implementing effective protective measures.

Dynamics of carbon storage driven by land use/land cover transformation in coal mining areas with a high groundwater table: A case study of Yanzhou Coal Mine, China.

Intensive anthropogenic activities have led to drastic changes in land use/land cover (LULC) and impacted the carbon storage in high-groundwater coal basins. In this paper, we conduct a case study on the Yanzhou Coalfield in Shandong Province of China. We further classify waterbodies by using the Google Earth Engine (GEE) to better investigate the process of LULC transformation and the forces driving it in four periods from 1985 to 2020 (i.e., 1985-1995, 1995-2005, 2005-2015, and 2015-2020). We modeled the spatiotemporal dynamics of carbon storage by using InVEST based on the transformation in LULC and its drivers, including mining (M), reclamation (R), urbanization and village relocation (U), and ecological restoration (E). The results indicate that carbon storage had depleted by 19.69 % (321099.06 Mg) owing to intensive transformations in LULC. The area of cropland shrank with the expansion of built-up land and waterbodies, and 56.31 % of the study area underwent transitions in land use in the study period. U was the primary driver of carbon loss while E was the leading driver of carbon gain. While the direct impact of M on carbon loss accounted for only 5.23 % of the total, it affected urbanization and led to village relocation. R led to the recovery of cropland and the reclamation of water for aquaculture, which in turn improved the efficiency of land use. However, it contributed only 2.09 % to the total increase in carbon storage. Numerous complicated and intertwined processes (211) drove the changes in carbon storage in the study area. The work here provides valuable information for decision-makers as well as people involved in reclamation and ecological restoration to better understand the link between carbon storage and the forces influencing it. The results can be used to integrate the goals of carbon sequestration into measures for land management.

The Relationship between Acid Production and the Microbial Community of Newly Produced Coal Gangue in the Early Oxidation Stage.

Coal gangue is a solid waste formed during coal production, and the acid mine drainage it generates during open-pit storage severely pollutes the ecological environment of mining areas. Microorganisms play a crucial catalytic role in acidification, and their species and gene functions change during the oxidation process of coal gangue. In this study, the changes in microbial community structure were investigated during the initial acidification process for newly produced gangue exposed to moisture by monitoring the changes in pH, EC, sulfate ion concentration, and the iron oxidation rate of gangue leaching solutions. Moreover, the composition and functional abundance of microbial communities on the surface of the gangue were analyzed with rainfall simulation experiments and 16S rRNA sequencing. The study yielded the following findings: (1) The critical period for newly produced gangue oxidation spanned from 0~15 d after its exposure to water; the pH of leaching solutions decreased from 4.65 to 4.09 during this time, and the concentration and oxidation rate of iron in the leaching solutions remained at low levels, indicating that iron oxidation was not the main driver for acidification during this stage. (2) When the gangue was kept dry, Burkholderia spp. dominated the gangue microbial community. When the gangue was exposed to moisture, the rate of acidification accelerated, and Pseudomonas replaced Burkholderia as the dominant genus in the community. (3) In terms of gene function, the microbial community of the acidified gangue had stronger nitrogen cycling functions, and an increase in the abundance of microorganisms related to the sulfur cycle occurred after day 15 of the experiment. The microbial community in the acidified gangue had more stress resistance than the community of the newly formed gangue, but its potential to decompose environmental pollutants decreased.

16S rDNA Sequencing-Based Insights into the Bacterial Community Structure and Function in Co-Existing Soil and Coal Gangue.

Coal gangue is a solid waste emitted during coal production. Coal gangue is deployed adjacent to mining land and has characteristics similar to those of the soils of these areas. Coal gangue-soil ecosystems provide habitats for a rich and active bacterial community. However, co-existence networks and the functionality of soil and coal gangue bacterial communities have not been studied. Here, we performed Illumina MiSeq high-throughput sequencing, symbiotic network and statistical analyses, and microbial phenotype prediction to study the microbial community in coal gangue and soil samples from Shanxi Province, China. In general, the structural difference between the bacterial communities in coal gangue and soil was large, indicating that interactions between soil and coal gangue are limited but not absent. The bacterial community exhibited a significant symbiosis network in soil and coal gangue. The co-occurrence network was primarily formed by Proteobacteria, Firmicutes, and Actinobacteria. In addition, BugBase microbiome phenotype predictions and PICRUSt bacterial functional potential predictions showed that transcription regulators represented the highest functional category of symbiotic bacteria in soil and coal gangue. Proteobacteria played an important role in various processes such as mobile element pathogenicity, oxidative stress tolerance, and biofilm formation. In general, this work provides a theoretical basis and data support for the in situ remediation of acidified coal gangue hills based on microbiological methods.

Land Use Dynamic Evolution and Driving Factors of Typical Open-Pit Coal Mines in Inner Mongolia.

Although coal is difficult to replace in the short term, the large-scale production and consumption of coal have significant impacts on the ecological environment. The severe disturbances, such as land excavation and occupation, that accompany the mining of mineral resources have caused dramatic changes in land cover and a significant pressure on the sensitive and fragile ecological environment. To analyze the temporal and spatial evolution trends and the differences in land use in different typical mining areas in Inner Mongolia, as well as the evaluation system and driving mechanisms of land use evolution, this study takes the typical open-pit coal mines in Inner Mongolia as the research objects and, based on the Google Earth Engine (GEE) platform, analyzes the dynamic evolution characteristics and driving factors of land use in typical open-pit coal mines in Inner Mongolia from 2001 to 2020. The change trend of land use in typical open-pit mining areas in Inner Mongolia for the past 20 years is obvious, with the highest fluctuations for grassland, mining land, cropland, and residential/industrial land. Land use in the open-pit coal mining area is greatly affected by mining factors. From the perspective of spatial variation, the most important driving factor is the distance from national roads and railways, followed by the annual average temperature and annual average precipitation and topographical conditions, such as elevation. In terms of policy, land reclamation and ecological restoration in mining areas have a positive impact on land use change. Improving the mechanism for environmental compensation in mining areas can promote the efficient and rational use of mining areas and the protection of ecosystems.

Addition of carbon sources and nutrient salts can inhibit gangue acidification by changing microbial community structure.

Acidic pollution from gangue oxidation has become a primary environmental problem in coal mining areas in China. The use of microorganisms to remediate acidic pollution in coal gangue piles has been indicated to be effective, but environmental differences and carbon sources in different mining areas have become important factors restricting microbial activity. Instead of the addition of new functional bacteria to gangue piles, carbon sources and nutrient salts were added to recently discharged gangue to enhance the activity of beneficial bacteria in the indigenous microbial community. The changes in pH and electrical conductivity (EC) of the gangue leachate as well as the composition and abundance of the functional microbial community on the surface of the gangue were analyzed by leaching simulation experiments and 16S rRNA sequencing. The results showed that the addition of a carbon source maintained the pH of the gangue leachate at 6.31~6.65 in 14 d, which was significantly higher than that of the control group, but the pH of the leachate decreased significantly after the addition of the carbon source was stopped. The most effective treatment is adding a low concentration of nutrient salt (20% concentration) and sodium lactate (0.02 g/L) to the gangue first, and then adding sodium lactate (0.1 mg/L) every 7 days. The addition of carbon sources and nutrient salts changed the microbial community composition on the surface of the gangue, and the species diversity index decreased. The dominant genera in the experimental group were Listeria, Arthrobacter, and Enterococcus. The functional gene types in the experimental and control groups were almost the same, but their relative abundance changed. The abundance of functional genes related to the sulfur cycle increased substantially in the experimental group, and the abundance of genes involved in the nitrogen and carbon cycles also increased, albeit to different degrees.

Rapid synthesis of self-propelled tubular micromotors for "ON-OFF" fluorescent detection of explosives.

We report a rapid strategy to construct self-propelled functional tubular micromotors. Based on the established strategy, magnetic covalent-organic-framework-functionalized micromotors were fabricated to implement sensing of explosives in water. Such micromotors can complete fluorescent "On-Off" detection of trace explosive 2,4,6-trinitrophenol within 10 min.

Evaluation of the soil profile quality of subsided land in a coal mining area backfilled with river sediment based on monitoring wheat growth biomass with UAV systems.

Underground coal mining leads to land subsidence, and the situation is particularly serious in the Coal-Grain Complex in eastern China, causing the crop production to be reduced or to be taken out. Backfilling with Yellow River sediment is one of the effective methods to solve the land subsidence in this area, but a key issue is how to select the optimal soil reconstruction profile so that the crop yield after backfilling and reclamation is unaffected. The main purpose of this study is to verify the feasibility of selecting the optimal soil reconstruction profile by rapid monitoring of crop growth and judging soil quality with the aid of unmanned aerial vehicle systems (UAVs). A control treatment and 13 experimental treatments were established for the study area. The control treatment consisted of using 30 cm topsoil and 90 cm subsoil and the topsoil is a proxy for native (undisturbed) soil from the study sites. All other treatments consisted of using varying combinations of subsoil and sediment overlain by 30 cm of topsoil. The vegetation indices from the UAV multispectral images, and the plant height and vegetation coverage from the UAV RGB images were used for estimation of the winter wheat biomass in a random forest regression. The results showed that the random forest regression model yielded accurate estimation of the aboveground biomass. Furthermore, knowledge of plant height and vegetation coverage improved the accuracy of prediction such that crop growth was well characterized. The optimal soil profile consisted of 0.3 m topsoil + 0.2 m subsoil + 0.2 m sediment + 0.2 m subsoil + 0.3 m sediment. A fast and effective airborne monitoring method for soil quality was established, thus providing greatly improved monitoring efficiency.

Dual-stimuli-responsive CuS-based micromotors for efficient photo-Fenton degradation of antibiotics.

Antibiotics as emerging pollutants in water pose great risks to human health. Due to their persistence in the environment, advanced oxidation processes (AOPs) have been proposed for the degradation of antibiotics. Therefore, developing efficient catalysts for AOPs becomes critical for the removal of antibiotics. Herein, we develop self-propelled CuS-based micromotors (CuS@Fe3O4/Pt) as active heterogenous catalysts for efficient photo-Fenton degradation of antibiotics. Combining the merits of conventional heterogenous and homogenous catalysts, the prepared micromotors are easy to recycle and free of secondary pollution risks, while demonstrating high degradation efficiency due to self-induced intensification of mass transfer via autonomous motion and microbubble generation. The H2O2 in the Fenton reagents can serve as the fuel for the micromotors to drive their self-propulsion by bubbles generated from catalytic decomposition of H2O2 by the platinum layer. The dual-stimuli-responsiveness of the micromotors to magnetic field and light irradiation allows multi-modes of propulsion and guidance in different systems. The efficient photothermal effect of CuS enables the micromotors to achieve collective phototactic motion toward light, whereas magnetic responsiveness facilitates the recovery and collection of the micromotors. The synergistic effect of CuS and Fe3O4 NPs in H2O2 under visible light irradiation generates a large amount of OH· and ·O2- to effectively degrade tetracycline within several minutes. With these advantages, the dual-stimuli-responsive CuS-based micromotors provide a new strategy for enhanced degradation of antibiotics in water purification applications.

Self-Propelled Aerogel Solar Evaporators for Efficient Solar Seawater Purification.

A solar evaporator is regarded as a prospective approach to solve the problem of water shortage. Here, we report an aerogel-based solar evaporator with self-propulsion and self-healing behavior to achieve efficient desalination and enhanced heavy-metal removal. The aerogel solar evaporator is prepared from a Schiff-base hydrogel with an asymmetric Au deposition layer via a simple freeze-drying method. The hydrogel is composed of chitosan and dialdehyde starch, and the Au layer generates a thermal gradient to drive the self-propulsion of the aerogel solar evaporator. Also, the dynamic linkages involved in the Schiff-base hydrogel endow the aerogel solar evaporator with self-healing ability upon external damage. Meanwhile, the Schiff-base framework is used as the interaction site between the aerogel evaporator and water molecules to lower the water evaporation enthalpy. Moreover, the aerogel evaporators are designed into small elliptical spheres and a porous structure, which offer the aerogel evaporators excellent water evaporation behavior with an evaporation rate of 3.12 kg m-2 h-1 in natural seawater under 1-sun irradiation. The self-propulsion ability and self-healing property of such solar evaporators provide the advantages of enhanced purification efficiency, good durability, stability (maintain over 88.2% at the 10th day), and high salt resistance (maintain 80% at 200 g kg-1). More notably, heavy-metal ions in water have been removed effectively to a drinkable level after evaporation. These results prove that the self-propelled aerogel solar evaporator holds great promise for practical applications for on-site water desalination and purification.

Land damage assessment using maize aboveground biomass estimated from unmanned aerial vehicle in high groundwater level regions affected by underground coal mining.

Underground coal mining inevitably causes land subsidence, while negatively impacting land and ecological environments. This is particularly severe in coal-grain overlap areas (CGOA) in eastern China, which have high groundwater levels. Mining subsidence has substantially altered the original topography, and raised the groundwater level, which threatens grain security in the region. Therefore, it is necessary to determine the damaged farmland area in the CGOA. The traditional method to define the range of coal mining disturbance is usually based on surface subsidence. However, this fails to consider the multidimensional impacts of coal mining on the ecology, which is considered unreasonable. Therefore, this paper introduces a low-cost, fast, and non-destructive method for land damage assessment in a typical CGOA in eastern China, using maize aboveground biomass (AGB) as estimated from an unmanned aerial vehicle (UAV). There were three key results from the survey. (1) underground coal mining caused significant ecological problems in the study area, including subsidence (approximately 6 m) and the degradation of vegetation (maize AGB in a range of 192.73-1338.06 g/m2). In addition, the degradation of maize was affected by subsidence (0.61** Pearson coefficient found between the AGB and surface elevation). (2) An UAV combined with multispectral and digital cameras, allowed precise estimation of the AGB and the red-edge chlorophyII index (CIrededge) combined with the elevation factor had the best explanatory power using the random forest (RF) method (R2 = 0.96, RMSE = 65.03 g/cm2). (3) The maize AGB could be used to assess land damage affected by underground coal mining, which accounted for 82.12% of the study area. The results of the study could provide a reference for land damage assessments in the CGOA, while also providing a guide for land reclamation and agricultural management decisions in the region.

Understanding the Capability of an Ecosystem Nature-Restoration in Coal Mined Area.

Ecosystem issues have been severely concerned and studied when the coal resource is one of major energy generators, and green mining innovation techniques involving artificial-restorations have addressed and significantly lessened negative impacts on the ecological environment. The ecosystem of a coal-mined area, however, is able to naturally restore with the processes of natural succession, similar to the human body system that has the immune ability to self-heal a wound over time if the wound does not deeply hurt the health. Here we analyze multiple discipline real data from two mining sites, and evidently show an ability of nature that the coal mining related problems such as geological cracks, damaged aquifers and destroyed soils in Quaternary period can naturally recover around a half-year after the end of mining. Our results temporally and spatially demonstrate that the damaged ecosystem has a capability of unaided nature-remediation from the ground to the subsurface, which is very useful to the countries worldwide with abundant coal reserves and intense energy demands for their development.

A Novel Method to Monitor Coal Fires Based on Multi-Spectral Landsat Images.

Coal fires pose a serious threat to the environment worldwide, and they are responsible for atmospheric pollution, water contamination, land subsidence and the safety of miners. The multi-spectral Landsat images offer the possibility of detecting and monitoring coal fires at large scales. In this study, the thermal infrared spectral is extracted, and a mono-window algorithm is used for retrieving coal fire temperature. However, the surface emissivity and atmospheric water vapor content play important roles in determining the temperature for this algorithm. The surface emissivity is particularly difficult to obtain with satellite overpasses because it is affected by a variety of factors. In general, an average emissivity value is assigned to represent all land cover categories, which leads to a big error for retrieving coal fire temperature. Meanwhile, atmospheric water vapor content is calculated by simulating atmospheric profile through standard atmosphere models. However, it is difficult to obtain real water vapor content and atmospheric profile is affected by many factors with each satellite pass. The lack of knowledge of the real atmospheric profile is a large constraint, and inaccurate simulation can introduce big errors. Aiming at overcoming drawbacks mentioned above and increasing the accuracy for this algorithm, the NDVI threshold method is applied to estimate surface emissivity. The NDVI threshold method separates different land cover categories, and different emissivity is assigned to different land cover classifications. Based on the ground meteorological parameters' relationship between atmospheric water vapor and atmospheric water vapor pressure, an empirical relationship is found to estimate atmospheric water vapor content. For this method, the ground meteorological parameters are easily obtained from meteorological observation stations and it is convenient to estimate water vapor content. The mono-window algorithm is improved and coal fire temperature is retrieved. This methodology was applied to the Wuda coalfield, in China, and coal fire temperatures were retrieved and extracted from the background from 1988 to 2015 in the study area. A thorough inventory of coal fire areas and locations is annually presented, and area changes are qualitatively analyzed during the observation period. This method is considered as feasible and effective for retrieving and monitoring coal fires based on multi-spectral Landsat images in comparison to other techniques in the Wuda coalfield, China.

Attenuation of heavy metals by geosynthetics in the coal gangue-filled columns.

In the subsided areas backfilled with coal gangue, an issue of continuing environmental concern is the migration of hazardous metals to the subsurface soil and groundwater. As an effective isolation material, geosynthetics have been scarcely applied into mining areas reclamation of China. This paper describes research aimed at characterizing the behaviours of different geosynthetics in the leaching columns filled with coal gangues. Four types of geosynthetics were selected: fibres needle-punched nonwoven geotextiles, high-density polyethylene, needle-punched Na-bentonite geosynthetic clay liner (GCL-NP) and Na-bentonite geosynthetic-overbited film. Heavy metals were significantly attenuated and by monitoring aqueous solutions in the whole percolation period, negative correlation was found between pH value and concentration of heavy metals. Generally, GCL-NP showed comparatively better effects on attenuating the migration of heavy metals. According to the meta-analysis of heavy metals present in the leachates and retained in the columns, geosynthetics have good capabilities of sorption and retardation, which can delay the breakthrough time of heavy metals and retard the accumulation in the subsurface. Future research will use X-ray diffraction and micro-imaging (electron microprobe and scanning electron microscopy) to further explain retention mechanisms.