Coal Mining Activities Research Articles

Towards an integrated approach for zero coal mine waste storage: solutions based on materials circularity and sustainable resource governance

ABSTRACT Around 25 million tons of coal mine waste rock (CMWR) are stored in many places in Morocco due to coal mining activities. As a result, air and water quality of the neighborhood is polluted and large lands are occupied. This study aimed to investigate the use of an integrated and circular approach based on coal recovery and waste rock recycling. More than 30 drill core samples were taken from the big coal dump reaching a depth of 60 m and analyzed to evaluate the chemical composition variability. Froth flotation was used to recover coal particles using diesel as a collector and Methyl Isobutyl Carbinol as a frother, 100 g/t each. The tailings of coal flotation process (CFT) were used to manufacture fired bricks at a pilot scale. The results of this study highlighted the possibility to valorize the whole waste material toward an objective of zero waste in the future. On a basis of 100t feed, (i) 10-15t can be recovered as high-quality anthracite coal with a calorific value over 7500 kcal/kg using flotation processing at a recovery yield over 80%, (ii) 45-60t can be reused as shales for bricks production with a compressive strength over 16MPa, (iii) 20-30t can be reused as aggregates for concrete production with a compressive strength over 20MPa. The remaining material can be reused as sand. The recovered anthracite can be reused to manufacture coal briquettes or used at it is in the thermal power plant next to the dump site.

Eco-environment vulnerability assessment using remote sensing approach in East Kalimantan, Indonesia

Indonesia is the world's largest island country blessed with abundant natural resources. Coal is one of the largest natural resources and commodities with an increased production rate annually. On the other hand, coal mining activities in East Kalimantan, Indonesia have been identified as one of the causes of environmental damage. Without proper regulation and comprehensive study, the environmental damage is predicted to increase every year. In order to provide a scientific analysis of the environmental damage prediction and evaluate ecological environmental conditions using remote sensing and geospatial approaches, this study aims to construct Eco-environment Vulnerability Index (EVI) in East Kalimantan and investigate spatial conditions and changes during 2017–2019. Spatial Principal Component Analysis (SPCA) method was applied to construct EVI by integrating satellite imagery and socio-economic data like Gross Regional Domestic Product (GRDP) per capita and population density. The results revealed that most of the areas in East Kalimantan are in good condition as indicated by very low EVI values (less than −0.0078). Meanwhile, very high EVI values (more than 0.4446) were found in the former mining, coastal, and urban areas. These areas have very high EVI because of lack of vegetation, high development of urban areas, and dense population. The mapping results of vulnerable areas are expected to be used as a guideline for governments, communities, and mining companies regarding the impacts exposed by coal mining activities and government plans for new capital city relocation towards the ecological environmental vulnerabilities.

Changes of SOC Content in China’s Shendong Coal Mining Area during 1990–2020 Investigated Using Remote Sensing Techniques

Coal mining, an important human activity, disturbs soil organic carbon (SOC) accumulation and decomposition, eventually affecting terrestrial carbon cycling and the sustainability of human society. However, changes of SOC content and their relation with influential factors in coal mining areas remained unclear. In the study, predictive models of SOC content were developed based on field sampling and Landsat images for different land-use types (grassland, forest, farmland, and bare land) of the largest coal mining area in China (i.e., Shendong). The established models were employed to estimate SOC content across the Shendong mining area during 1990–2020, followed by an investigation into the impacts of climate change and human disturbance on SOC content by a Geo-detector. Results showed that the models produced satisfactory results (R2 > 0.69, p < 0.05), demonstrating that SOC content over a large coal mining area can be effectively assessed using remote sensing techniques. Results revealed that average SOC content in the study area rose from 5.67 gC·kg−1 in 1990 to 9.23 gC·kg−1 in 2010 and then declined to 5.31 gC·Kg−1 in 2020. This could be attributed to the interaction between the disturbance of soil caused by coal mining and the improvement of eco-environment by land reclamation. Spatially, the SOC content of farmland was the highest, followed by grassland, and that of bare land was the lowest. SOC accumulation was inhibited by coal mining activities, with the effect of high-intensity mining being lower than that of moderate- and low-intensity mining activities. Land use was found to be the strongest individual influencing factor for SOC content changes, while the interaction between vegetation coverage and precipitation exerted the most significant influence on the variability of SOC content. Furthermore, the influence of mining intensity combined with precipitation was 10 times higher than that of mining intensity alone.

Pit Lakes Affected by a River Contaminated with Brines Originated from the Coal Mining Industry: Evolution of Water Chemistry in the Zakrzówek Horst Area (Krakow, Southern Poland)

Long-term coal mining activities in the Upper Silesia significantly affect the environment in southern Poland. Discharges of brines (with TDS reaching over 110 g/L) from mines are the main source of pollution of many rivers in Poland, including the Vistula River. The Zakrzówek horst is a small geological structure composed of the Upper Jurassic limestones. These limestones were exploited in several quarries. In the largest one (the “Zakrzówek” quarry), exploitation reached the depth of 36 m below the water table, i.e., about 32 m below the average water level in Vistula River which flows 700 m from the quarry. An important part of this inflow into quarries came from the contaminated Vistula River, with a chloride concentration over 2 g/L. The exploitation ceased in 1991, and dewatering ended in 1992. In the old quarry area, pit lakes appeared, which are unique because they present an example of a post-mining site affected by the riverine water contaminated with brines. Investigations of physicochemical parameters of water in the Zakrzówek area were carried out in the period of 1990–2020. Results showed that the largest pit lake was initially meromictic with a distinct stratification. After several years, holomictic conditions developed due to the surface layer freshening and convective mixing.

Mining for Sovereignty? Norwegian Coal Companies and the Quest for Supremacy over Svalbard 1916-1925

At the outbreak of the First World War there was virtually no Norwegian coalmining activity on the Spitsbergen archipelago. The handful of small coal companies that were formed in Norway around the turn of the century were either idle or had been bought up by foreign interests after a few years. During the war, however, several new private companies were established, most notably the Store Norske Spitsbergen Kulkompani in 1916. Two years later, in 1918–1919, the Norwegian government stated its desire to acquire full sovereignty over the archipelago. The wish was granted by the treaty of 9 February 1920 that came as a result of the peace negotiations in Paris. This paper reviews the role of the Norwegian coal companies in Norway’s quest for supremacy over Svalbard during and after the First World War. Were private enterprises an instrument of the Norwegian government’s ambitions or was it the other way around? It is argued that private companies were instrumental in moving the political authorities from a passive to an active stance regarding sovereignty during the last phase of the war and through the peace conference in 1919. Their primary concern was to protect their own vested interests. However, as soon as sovereignty was secured in 1920, it was the government that actively used the companies as instruments to improve Norway’s position on the archipelago before implementing the treaty and settling the property rights.
 Note: I use the official toponym ‘Svalbard’, although before 1925 ‘Spitsbergen’ was more commonly used.

Effect of the Co-Application of Eucalyptus Wood Biochar and Chemical Fertilizer for the Remediation of Multimetal (Cr, Zn, Ni, and Co) Contaminated Soil

Contamination of soil with heavy metals is a worldwide problem, which causes heavy metals to release into the environment. Remediation of such contaminated soil is essential to protect the environment. The aims of this study are: first, to compare the effect of biochar and the joint application of biochar with fertilizer for the phytoremediation of heavy metals-contaminated soil using Acacia auriculiformis; second, to study the effect of the application rate of biochar in improving the physicochemical properties of the soil. The soil samples were collected from an active coal mine dump and assessed for their physicochemical properties and heavy metals toxicity. Initial results indicated that the soil has poor physicochemical properties and was contaminated with the presence of heavy metals such as Zn, Ni, Cu, Cr, and Co. Later, the heavy metals-contaminated soil was mixed with the 400 and 600 °C biochar, as well as the respective biochar–fertilizer combination in varying mixing ratios from 0.5 to 5% (w/w) and subjected to a pot-culture study. The results showed that the application of both varieties of biochar in combination with fertilizer substantially improved the physicochemical properties and reduced the heavy metals toxicity in the soil. The biochar and fertilizer joint application also substantially improved the soil physiochemical properties by increasing the application rate of both varieties of biochar from 0.5 to 5%. The soil fertility index (SFI) of the biochar and biochar–fertilizer amended soil increased by 49.46 and 52.22%, respectively. The plant’s physiological analysis results indicated a substantial increase in the plant’s shoot and root biomass through the application of biochar and biochar–fertilizer compared to the control. On the other hand, it significantly reduced the heavy metals accumulation and, hence, the secretion of proline and glutathione hormones in the plant cells. Therefore, it can be concluded that the joint application of biochar with the application rate varying between 2.5 to 5% (w/w) with the fertilizer significantly improved the physicochemical properties of the soil and reduced the heavy metals toxicity compared to the controlled study.

Sputum Microbiota in Coal Workers Diagnosed with Pneumoconiosis as Revealed by 16S rRNA Gene Sequencing.

Coal worker’s pneumoconiosis (CWP) is an occupationally induced progressive fibrotic lung disease. This irreversible but preventable disease currently affects millions across the world, mainly in countries with developed coal mining industries. Here, we report a pilot study that explores the sputum microbiome as a potential non-invasive bacterial biomarker of CWP status. Sputum samples were collected from 35 former and active coal miners diagnosed with CWP and 35 healthy controls. Sequencing of bacterial 16S rRNA genes was used to study the taxonomic composition of the respiratory microbiome. There was no difference in alpha diversity between CWP and controls. The structure of bacterial communities in sputum samples (β diversity) differed significantly between cases and controls (pseudo-F = 3.61; p = 0.004). A significant increase in the abundance of Streptococcus (25.12 ± 11.37 vs. 16.85 ± 11.35%; p = 0.0003) was detected in samples from CWP subjects as compared to controls. The increased representation of Streptococcus in sputum from CWP patients was associated only with the presence of occupational pulmonary fibrosis, but did not depend on age, and did not differ between former and current miners. The study shows, for the first time, that the sputum microbiota of CWP subjects differs from that of controls. The results of our present exploratory study warrant further investigations on a larger cohort.

Use of machine learning algorithms to assess the state of rockburst hazard in underground coal mine openings

The risk of rockbursts is one of the main threats in hard coal mines. Compared to other underground mines, the number of factors contributing to the rockburst at underground coal mines is much greater. Factors such as the coal seam tendency to rockbursts, the thickness of the coal seam, and the stress level in the seam have to be considered, but also the entire coal seam–surrounding rock system has to be evaluated when trying to predict the rockbursts. However, in hard coal mines, there are stroke or stress-stroke rockbursts in which the fracture of a thick layer of sandstone plays an essential role in predicting rockbursts. The occurrence of rockbursts in coal mines is complex, and their prediction is even more difficult than in other mines. In recent years, the interest in machine learning algorithms for solving complex nonlinear problems has increased, which also applies to geosciences. This study attempts to use machine learning algorithms, i.e. neural network, decision tree, random forest, gradient boosting, and extreme gradient boosting (XGB), to assess the rockburst hazard of an active hard coal mine in the Upper Silesian Coal Basin. The rock mass bursting tendency index W TG that describes the tendency of the seam–surrounding rock system to rockbursts and the anomaly of the vertical stress component were applied for this purpose. Especially, the decision tree and neural network models were proved to be effective in correctly distinguishing rockbursts from tremors, after which the excavation was not damaged. On average, these models correctly classified about 80% of the rockbursts in the testing datasets.

Long-term analysis of cryoseismic events and associated ground thermal stress in Adventdalen, Svalbard

Abstract. The small-aperture Spitsbergen seismic array (SPITS) has been in continuous operation at Janssonhaugen for decades. The high-Arctic location in the Svalbard archipelago makes SPITS an ideal laboratory for the study of cryoseisms, a nontectonic class of seismic events caused by freeze processes in ice, ice–soil, and ice–rock materials. We extracted a catalog of > 100 000 events from the nearly continuous observation period between 2004 and 2021, characterized by short-duration ground shaking of just a few seconds. This catalog contains two main subclasses where one subclass is related to underground coal-mining activities and the other is inferred to be dominated by frost quakes resulting from thermal-contraction cracking of ice wedges and crack-filling vein ice. This inference is supported by the correspondence between peaks in observed seismicity with peaks in modeled ground thermal stress, based on a Maxwellian thermo-viscoelastic model constrained by borehole observations of ground temperature. The inferred frost quakes appear to be dominated by surface wave energy and SPITS proximal source positions, with three main areas that are associated with dynamic geomorphological features, i.e., erosional scarps and a frozen-debris/solifluction lobe. Seismic stations providing year-round, high-temporal-resolution measurements of ground motion may be highly complementary to satellite remote sensing methods, such as InSAR (interferometric synthetic aperture radar), for studying the dynamics of periglacial environments. The long-term observational record presented in this study, containing tens of thousands of cryoseismic events, in combination with a detailed record of borehole ground temperature observations, provides a unique insight into the spatiotemporal patterns of cryoseisms. The observed patterns may guide the development of models that can be used to understand future changes to cryoseismicity based on projected temperatures.

Zinc in soil reflecting the intensive coal mining activities: Evidence from stable zinc isotopes analysis

In the mining area affected by coal mining activities for a long time, heavy metal Zn pollution poses a serious threat to soil quality and human health, and direct evidence showing the relationship between Zn accumulation mechanism in soils and mining activities is lacking. In this study, the Zn content and isotopes composition (δ66Zn) from soil and environmental samples around mining area were determined and analyzed to clarify the Zn characteristics in soil. Moreover, the distribution and source of Zn content in soil of mining area were analyzed by mathematical statistics, correlation analysis and isotope mass mixing model. The results showed that: (1) the Zn content in soil ranged from 95 to 327 mg·kg−1 (mean: 233 mg·kg−1), exceeding the control point and the soil background value of Anhui Province; (2) the results of Zn isotope analysis showed that Zn in soil mainly derived from the wind dispersion input of fine particles in gangue and fly ash, followed by the natural weathering of parent material; (3) isotopic mass mixing model can be used to distinguish the contribution of anthropogenic and natural Zn sources. Mining input was the main contribution source of Zn in soil (mean: 67%), followed by natural background (mean: 33%). The employment of Zn isotopes can effectively evaluate the impact of anthropogenic and natural long-term processes on Zn in the soil of the mining area, and provide important information for the formulation of soil metal pollution control measures.

Influence of Open-Pit Coal Mining on Ground Surface Deformation of Permafrost in the Muli Region in the Qinghai-Tibet Plateau, China

The Qinghai-Tibet Plateau (QTP) is the largest mid-to low latitude and high-altitude permafrost. Open-pit coal mining and other activities have caused serious damage to the alpine ecological environment and have accelerated the degradation of permafrost on the QTP. In this study, the influence of open-pit coal mining on the time series ground surface deformation of the permafrost in the Muli region of the QTP was analyzed from 19 January 2018 to 22 December 2020 based on Landsat, Gaofen, and Sentinel remote sensing data. The primary methods include human-computer interactive visual interpretation and the small baseline subsets interferometric synthetic aperture radar (SBAS-InSAR) method. The results showed that the spatial distribution of displacement velocity exhibits a considerably different pattern in the Muli region. Alpine meadow is the main land use/land cover (LULC) in the Muli region, and the surface displacement was mainly subsidence. The surface subsidence trend in alpine marsh meadows was obvious, with a subsidence displacement velocity of 10–30 mm/a. Under the influence of changes in temperature, the permafrost surface displacement was characteristics of regular thaw subsidence and freeze uplift. Surface deformation of the mining area is relatively severe, with maximum uplift displacement velocity of 74.31 mm/a and maximum subsidence displacement velocity of 167.51 mm/a. Open-pit coal mining had resulted in the destruction of 48.73 km2 of natural landscape in the Muli region. Mining development in the Muli region had increased the soil moisture of the alpine marsh meadow around the mining area, resulting in considerable cumulative displacement near the mining area and the acceleration of permafrost degradation.

Polycyclic aromatic hydrocarbons (PAHs) in riparian soils of the middle reach of Huaihe River: A typical coal mining area in China

ABSTRACT In the present research work, the concentration, distribution, composition, sources, potential toxicity, and ecological risk of PAHs in riparian soils of the middle reach of Huaihe River (along a 430-kilometer stream gradient) were studied. The total concentrations of PAHs varied from 210 to 39000 ng g−1, with a mean concentration of 3400 ± 8400 ng g−1 and a median value of 760 ng g−1. The middle section (Huainan-Bengbu section) with frequent coal mining and utilization activities was found to be the most contaminated region. High molecular weight (5- and 6- ring PAHs) and medium molecular weight (4- ring PAHs) PAHs were predominant. Based on the diagnostic ratios method and positive matrix factorization (PMF) model, PAHs in riparian soils were mainly originated from pyrogenic sources including vehicle emissions, and biomass and coal combustion. The calculation of total TEQBaP concentrations and risk quotient (RQ) indicated a low to moderate risk level of PAHs in most regions of the study area, but some specific sites showing high toxicity and ecological risk should be caused alarm and attention.

Impact of Expanding Coal Industry on the Regional Environment in an Indian Coal-Belt - A Case Study from Jharkhand, India

Environmental sustainability of coal industry is a major concern considering the trends of its exponential effect on the region and towards climate change. The study examines the land use/land cover changes using spatio temporal datasets of the years 2000 and 2020 in Dhanbad district which comes under the major coal-belt of India. The study shows the impact of expanding industries on the environment depicting a remarkable decrease in vegetation (18.89%), increase in built-up land (14.32%) and coalfields (0.9%) exhibiting massive deforestation activities. The study focuses on the increase in emissions from coal mining activities including GHGs, SOx, PMs, etc. over the years and their harmful impacts on the region. The sustainability evaluation of the coalfields of the study area is done through 15 predetermined indicators, suggesting the urgency and need of actions for sustainable functioning of coal mining industry in order to limit global warming to below 2 °C as suggested in the Paris Agreement-2016. The study also lays stress on the changing economic pattern of the region as an effect of increasing industrialization and changes in the land use.

Observational constraints on methane emissions from Polish coal mines using a ground-based remote sensing network

Abstract. Given its abundant coal mining activities, the Upper Silesian Coal Basin (USCB) in southern Poland is one of the largest sources of anthropogenic methane (CH4) emissions in Europe. Here, we report on CH4 emission estimates for coal mine ventilation facilities in the USCB. Our estimates are driven by pairwise upwind–downwind observations of the column-average dry-air mole fractions of CH4 (XCH4) by a network of four portable, ground-based, sun-viewing Fourier transform spectrometers of the type EM27/SUN operated during the CoMet campaign in May–June 2018. The EM27/SUN instruments were deployed in the four cardinal directions around the USCB approximately 50 km from the center of the basin. We report on six case studies for which we inferred emissions by evaluating the mismatch between the observed downwind enhancements and simulations based on trajectory calculations releasing particles out of the ventilation shafts using the Lagrangian particle dispersion model FLEXPART. The latter was driven by wind fields calculated by WRF (Weather Research and Forecasting model) under assimilation of vertical wind profile measurements of three co-deployed wind lidars. For emission estimation, we use a Phillips–Tikhonov regularization scheme with the L-curve criterion. Diagnosed by the emissions averaging kernels, we find that, depending on the catchment area of the downwind measurements, our ad hoc network can resolve individual facilities or groups of ventilation facilities but that inspecting the emissions averaging kernels is essential to detect correlated estimates. Generally, our instantaneous emission estimates range between 80 and 133 kt CH4 a−1 for the southeastern part of the USCB and between 414 and 790 kt CH4 a−1 for various larger parts of the basin, suggesting higher emissions than expected from the annual emissions reported by the E-PRTR (European Pollutant Release and Transfer Register). Uncertainties range between 23 % and 36 %, dominated by the error contribution from uncertain wind fields.

Anorganické zatížení říčních sedimentů řeky Olše a jejích významných přítoků

The main objective of research was to assess the current level of bottom sediment and water pollution of the Olše River and its tributaries. The Olše River is an important stream in the Upper Silesian Basin which was significantly affected by coal mining and industrial activities in the past (Martinec et al. 2006). Monitoring of the area by the Povodí Odry State Enterprise (the Odra River management) has shown that the water quality in the river has significantly improved due to the development of municipal wastewater treatment plants. Currently, saline waters from coal mines in the Karviná sub-basin are considered to be the biggest threat to the river environment. A total of 19 river sediment and 9 surface water samples were collected (Fig. 1). The elemental content was determined using X-ray florescence spectroscopy (XRF); for selected river sediments, the organic carbon content was determined using the Elementar Vario TOC CUBE device. The loading of river sediments by elements was evaluated using Igeo Class. The content of major ions (HCO3–, K+, Ca2+, Na+, Mg2+, SO42– and Cl–) in the surface water samples was determined in the laboratory. The water in the Olše River belongs to the hydrochemical type of Ca-HCO3. The water in the Karvina Creek near the mining works is highly mineralised and represents a single case of the Na-Cl hydrochemical type. Despite the significant mineralisation level, the water from this creek does not significantly affect the quality of the water in the Olše River. The highest enrichment of river sediments compared to the natural background was found for Zn (Table 1) at all sites. Zinc is one of the elements with rather high mobility and tends to be bound to hydrated Fe and Mn oxides that occur in rather large quantities on adjacent spoil heaps in the area and can thus enter the system very quickly. The Mn (340 to 2,553 mg/kg) as well as Sr (71 to 1,836 mg/kg) concentrations are elevated compared to those in global shales (850 mg/kg and 300 mg/kg, respectively; Turekian – Wedepohl 1961). Their contents in the Upper Silesian Coal Basin river sediments should be systematically monitored. The Olše River sediments were slightly to moderately contaminated with Cr and Pb (Table 1). This is not considered to be related to mining but rather to road runoffs and the fact that the river flows through industrial areas.

Spatial–temporal variations and multi-statistical analysis of contaminants in the waters affected by acid-mining drainage in Karst area: a case of coal-mining area in Zhijin County

Due to the adverse effects of coal-mining activities in Karst areas, it is necessary to monitor the contaminants, analyze their fate in the transport and identify the sources. Therefore, concentrations of contaminants were measured in both groundwater and surface water samples collected from coal-mining area in Karst, located in Zhijin County, Guizhou Province (China). The analysis of spatial–temporal variations of contaminants indicates that (1) the concentrations of metal elements (except Ba) and SO42− tend to decrease along the water flow direction, while the concentrations of Ba and nitrate still show an upward trend and (2) the concentrations of metal elements and SO42− have seasonal variations. Furthermore, the results of multi-statistical analysis which combine Pearson correlation coefficients (PCC) with the principal component analysis (PCA), identify five factors for the data structure of contaminants. What is more, the assessment of the water quality was evaluated by Nemerow index method to better understand the status. The results indicate that water quality in the area was poor, while 52.6% of water samples were identified into Grade IV and 16.7% were identified into Grade V by the Nemerow index method.

EFFECTS OF COAL MINING ON FISHES OF MEGHALAYA, INDIA: A REVIEW

Coal mining activities generate huge quantity of effluent containing tremendous amount of several metals, nitrate, sulphate, dissolved, and suspended solids as well as other harmful pollutants. These toxic effluents are regularly being released into the neighbouring ponds, lakes and rivers. Significant discharge of untreated coal mining effluent into the aquatic environment contributes to a variety of toxic effects on aquatic fauna including fish. Coal mining activities specifically in the region of Meghalaya located in North-east India is posing severe threats to the aquatic biota. The purpose of the paper is to pay special emphasis on the fish fauna that lives in this region that has large effluents of acid mine drainage. Many authors have previously described the different histopathological changes in a fish that suffer from severe toxicity of acid mine drainage. This study has been prepared taking into account the various works of different authors and is thus a review of their work. The whole aim of the study is to give a general idea that acid mine drainage from coal mines has tremendous impact on the fish fauna and may completely wipe out the population that thrives therein in the long run.

EFEKTIVITAS METODE COVERING DALAM PENGELOLAN AIR ASAM TAMBANG DI PT. BINUANG MITRA BERSAMA BLOK DUA, KABUPATEN TAPIN, KALIMANTAN SELATAN

The formation of AMW is basically unavoidable in mining activities, AMW can be formed in pit and disposal area that are contaminated with potential acid forming material (PAF). The magnitude of the potential impact that AMW can have on mining activities certainly encourages every business actor to conduct a study on various preventive measures that are effectively implemented in AMW management, one of which is covering method. This thesis research aims to analyze the preventive covering method in the management of AMW and its effectiveness in meeting quality standards of liquid waste in coal mining activities. The Object of research is surface water that is in contact with covering treatment area (soil) which is also given additional treatment by planting cover crops and pioneer plants at OPD Sitarum. Surface water quality was tested in the laboratory with reference to BMLC standard of South Kalimantan Governor Regulation Number 36 of 2008. The results of the laboratory tests were then calculated for effectiveness and proved statistical analysis using normality test, homogeneity test, CRD test and DMRT to be able to conclude the effect of covering treatment in the management of AMW. The results showed that the application of covering method in OPD Sitarum was able to have a positive and significant effect on improving surface water quality. Where based on the results of laboratory tests, the SA4 and SA5 treatments have met the BMLC standard of the South Kalimantan Governor Regulation Number 36 of 2008. The laboratory results are strengthened by statistical data which shows that all treatment data are normally distributed and homogeneous, the results of CRD and DMRT analysis show the parameters of pH, TSS, and total-Fe was significantly different between SA2, SA3, SA4, and SA5 treatments against SA1 (control). Meanwhile, total-Mn parameter stated that SA2 and SA3 were not significantly different from the control, SA4 and SA5 were significantly different from the control. And for Cadmium (Cd) parameter, all treatments (SA2, SA3, SA4, and SA5) were not significantly different from the control. The conclusion of this research, the covering method applied in OPD Sitarum is considered effective in the management of AMW in a preventive manner. This is proven in SA4 treatment (covering + cover crop + Pioneer 1-2 years), where the results of the surface water quality test have met the BMLC standards of the South Kalimantan Governor Regulation Number 36 of 2008 with values: pH 6.95; TSS 159 mg L -1 ; total-Fe 1.93 mg L-1 ; total-Mn 0.031 mg L-1 ; and Cd 0.0045 mg L-1 . And the best covering treatment and effectiveness were found in SA5 treatment (covering + cover crop + 3-4 years pioneer plant) with values: pH 6.67; TSS 76.5 mg L-1 (97.22%); totalFe 1.13 mg L-1 (88.71%); total-Mn 0.019 mg L-1 (87.58%); and Cd 0.0058 mg L-1 (8.00%).

An experimental study on precursor identification for gas-bearing coal failure from electric potential responses in the loading process

The occurrence of coal and rock dynamic disasters threatens and restricts the safe production of underground coal mining activities seriously. For the prevention and control of the dynamic disasters, it is the foundation and premise to monitor the damage evolution and forecast the failure of coal mass under joint action of loading stress and gas pressure. For this, the stress loading and electric potential (EP) measuring experimental system of gas-bearing coal specimen was established, to test and analyze the precursor information for the failure of gas-bearing coal from EP response. The results show that the EP intensity of gas-bearing coal is positively correlated with loading stress level. The EP signals show step-like changes once the specimen is severely damaged at local moment. Based on mathematical statistics, the multifractal and critical slowing down paratemers of temporal EP data were analyzed, to reveal the nonlinear characteristics of gas-bearing coal during the loading and damaging process. In the critical failure stage, the multifractal parameter Δα rapidly increases to the peak and another parameter Δfm changes significantly to a negative value. Furthermore, the variance (V), as a critical slowing down parameter, rapidly rises to the peak value very shortly (0.3 s) before the failure occurs. Simultaneously, the autocorrelation coefficient (ac) also exhibits abnormal responses. Analysis combining the above indexes enables comprehensive monitoring and identification of precursor information for the failure of gas-bearing coal from temporal EP data.

Prediction of soil organic carbon in mining areas

Coal mining activities have destroyed natural landscapes and surface vegetation, resulting in a large loss of soil organic carbon (SOC) storage in farmlands. Therefore, farmland SOC mapping in mining areas is of great significance to low-carbon reclamation and ecological compensation. Natural factors such as topography, climate, vegetation, and soil properties are key variables for SOC mapping. Human activities, including crop rotation and farmland damage caused by coal mining, also severely interfere with farmland SOC in mining areas. Here, we use take mining areas of the Changhe watershed as a case study to explore the effects of these activities on farmland SOC storage. Farmland damage was quantified using mining area geological hazard data, and four random forest (RF) models were constructed to predict SOC content based on natural variables alone (RF-N), natural variables + crop rotation (RF-C), natural variables + farmland damage (RF-F), and natural variables + crop rotation + farmland damage (RF-A). We found that: (1) the RF-A model most accurately captured SOC spatial differentiation information (followed by RF-C, RF-F, and RF-N). (2) There were significant differences in the SOC of different crop rotation areas and between low and high damage farmlands; specifically, the SOC content of wheat-corn rotations (one-year two cropping system) was higher than wheat-soybean-corn rotations (two-year three cropping system) and wheat (one-year one cropping system), and the SOC of high damage farmlands was lower than that of low damage farmlands. (3) Variable importance analysis showed that crop rotation and farmland damage were the two most important variables for predicting SOC in mining areas—demonstrating the effectiveness of common farming practices in predicting SOC in mining areas. Our results provide a scientific basis for land reclamation, soil carbon input, and land remediation planning in mining areas.