Abandoned Coal Mines Research Articles

Assessment of Carbon Storage Capacity of Stands in Abandoned Coal Mine Forest Rehabilitation Areas over time for its Development of Management Strategy

Assessment of Carbon Storage Capacity of Stands in Abandoned Coal Mine Forest Rehabilitation Areas over time for its Development of Management Strategy

Pointwise Modelling and Prediction for Ground Surface Uplifts in Abandoned Coal Mines from InSAR Observations

Interferometric synthetic aperture radar (InSAR) is a useful tool for monitoring surface uplifts due to groundwater rebound in abandoned coal mines. However, InSAR-based prediction for surface uplifts has rarely been focused on so far, hindering the scientifical assessment and controlling of uplift-related geohazards in a wide area. In this study, we firstly revealed that the temporal evolution of surface uplifts caused by groundwater rebound at a surface point approximately followed an exponential distribution. Following the result, a varied cumulative distribution function (CDF) of the Weibull distribution was then used to model the temporal evolution of surface uplifts on a point-by-point basis. Finally, the parameters of the varied Weibull CDF were inverted from historical InSAR observations of surface uplifts and were forward used to predict uplift trends. Two abandoned coal mines in Beipiao city, China, were chosen to test the presented method. The results suggest that the varied Weibull CDF is able to well describe the processing of time-series uplifts, and the root mean square errors of the predicted uplifts were about 1.2 mm. The presented pointwise method predicts surface uplifts based on historical uplift observations and a mathematical function (i.e., the varied Weibull CDF), without the requirement of in situ geological and hydrological information about the focused abandoned coal mines. Therefore, it offers a new tool for predicting surface uplifts in abandoned mines, especially in case they lack in situ geological and hydrological information.

Urban landscapes and legacy industry provide hotspots for riverine greenhouse gases: A source-to-sea study of the River Clyde

There is growing global concern that greenhouse gas (GHG) emissions from water bodies are increasing because of interactions between nutrient levels and climate warming. This paper investigates key land-cover, seasonal and hydrological controls of GHGs by comparison of the semi-natural, agricultural and urban environments in a detailed source-to-sea study of the River Clyde, Scotland. Riverine GHG concentrations were consistently oversaturated with respect to the atmosphere. High riverine concentrations of methane (CH4) were primarily associated with point source inflows from urban wastewater treatment, abandoned coal mines and lakes, with CH4-C concentrations between 0.1 - 44 µg l−1. Concentrations of carbon dioxide (CO2) and nitrous oxide (N2O) were mainly driven by nitrogen concentrations, dominated by diffuse agricultural inputs in the upper catchment and supplemented by point source inputs from urban wastewater in the lower urban catchment, with CO2-C concentrations between 0.1 - 2.6 mg l−1 and N2O-N concentrations between 0.3 - 3.4 µg l−1. A significant and disproportionate increase in all GHGs occurred in the lower urban riverine environment in the summer, compared to the semi-natural environment, where GHG concentrations were higher in winter. This increase and change in GHG seasonal patterns points to anthropogenic impacts on microbial communities. The loss of total dissolved carbon, to the estuary is approximately 48.4 ± 3.6 Gg C yr−1, with the annual inorganic carbon export approximately double that of organic carbon and four times that of CO2, with CH4 accounting for 0.03%, with the anthropogenic impact of disused coal mines accelerating DIC loss. The annual loss of total dissolved nitrogen to the estuary is approximately 4.03 ± 0.38 Gg N yr−1 of which N2O represents 0.06%. This study improves our understanding of riverine GHG generation and dynamics which can contribute to our knowledge of their release to the atmosphere. It identifies where action could support reductions in aquatic GHG generation and emission.

Study of geochemical features of soils on the territory of an abandoned coal mining area using geoinformation technologies.

The article describes the results of a study of the geochemical features of soils on the territory of an abandoned mining area. The Kizel coal basin (Russia) is of particular interest for studying the consequences of technogenic and post-technogenic transformation of the natural environment. The study of the soil as a deposit medium made it possible to identify geochemical indicators of the negative impact. Such a detailed study of the distribution of chemical elements in this area was conducted for the first time. Geoinformation system and maps with interpolation were created to study the spatial distribution of metals and metalloids in soils. Umbric Retisols Abruptic and Haplic Retisols Abruptic soils are common in the territory. Sampling for geochemical testing was carried out from two horizons: humus and podzolic. Sampling from two depths made it possible to identify elements that continue to be contaminated at the time of the study. A total of 103 sample plots were established in the study area. The results obtained were compared with the background of the natural region of the Western Urals to identify the contribution of technogenesis. As a result, the coefficients of concentration and dispersion of chemical elements were calculated. Due to this, elements were identified, the accumulation of which occurs on the territory of the Kizelovsky coal basin. To identify the current and accumulated pollution, the ratio between the humus and podzolic horizons was calculated. As a result, it was found that at the moment in the humus horizon in some areas there is a high accumulation of Co, Mn, Ni and Sr. The geochemical series of the territory for the humus and podzolic horizons was obtained: Fe > Ti > Mn > Sr > Cr > V > Zn > Ni > Co > Pb > As. Data on the geochemical specificity of the territory of the Kizel coal basin have been obtained. The created geoinformation database reflects the physical and chemical properties of soils, metals and metalloids content, dispersion and accumulation coefficients, coefficients of the ratio of the humus and podzolic horizon. Based on it, it is possible to obtain data on the geochemical features of the territory, geoecological characteristics, spatial distribution of metals and metalloids and identification of pollution sources. Co (24 ± 2.8mg/kg), Mn (1100 ± 155mg/kg), Ni (69 ± 9.3mg/kg), As (10 ± 3.5mg/kg), Cr (178 ± 20mg/kg), Zn (80 ± 7.8mg/kg) and Sr (221 ± 26mg/kg) accumulate in the humus horizon. Co (24 ± 1.8mg/kg), Mn (1000 ± 103mg/kg), Ni (60 ± 6.4mg/kg) and Cr (153 ± 15.2mg/kg) accumulate in the podzolic horizon.

A new approach to evaluate abandoned mine methane resources based on the zoning of the mining-disturbed strata

Abundant abandoned mine methane (AMM) accumulates in the mining-disturbed coal/rock strata in abandoned coal mines. However, the simplified pore and fracture model of the mining-disturbed strata is often adopted to investigate AMM resources. In this case, AMM distribution needs to be more accurate, making it difficult to determine the appropriate location of surface wells. So the question is, how can the pore and fracture be characterized in different zones of the mining-disturbed strata? What is the distribution of AMM resources in the mining-disturbed strata? To address these problems, in this work, the mining-disturbed coal/rock strata of the abandoned mine are divided into five zones. The pore and fracture of the mining-disturbed strata in different zones are characterized by simulation experiments. On this basis, the new evaluation approach of AMM in the mining-disturbed strata is established to reveal the distribution of AMM in each zone. The results show that the mining-disturbed coal/rock strata are divided into five zones: stress concentration zone (I), shear fracture zone (II), separation fracture zone (III), compaction zone (IV), and bottom fracture zone (V). The pore and fracture of coal/rock strata and the distribution of AMM are different in each zone. The AMM resources in the mining-disturbed strata have great potential for development. The AMM in zone I account for 69% of the total, mainly the adsorbed gas in the remaining coal seam affected by mining disturbance. The AMM in the stress relief zone is mostly free gas remaining in the pore and fracture. The fractures in zone II are connected along the horizontal direction, forming a ring fracture body with abundant free AMM resources, which accounted for 19% of the total AMM resources. The AMM in zones III, IV, and V are limited. This work provides a new approach to evaluating the AMM and plays a guiding role in the layout of the surface wells in abandoned mines.

Environmental and Health Risk Assessment of Soil Adjacent to a Self-Burning Waste Pile from an Abandoned Coal Mine in Northern Portugal

Abandoned mines and disposal of mining residues can be responsible for the release of potentially toxic elements (PTEs) into the environment causing soil and water contamination, with potential ecological damage and human health hazards. The quantification of the apportionment of PTEs in soils and the study of the associated ecological and human health risks are essential. This study aims to assess the environmental and human health risk of the soils surrounding an abandoned coal mine in São Pedro da Cova, whose waste pile has been affected by self-combustion for over 17 years. The soil environmental characterization of the study area regarding PTEs was accessed by different pollution indices, considering the elementary crustal abundance and the determined regional soil geochemical background. The soil contamination degree was evaluated using indices such as the contamination factor (Cf) and geoaccumulation index (Igeo), inferred for all soil samples, and the potential ecological risk index (PERI) was also accessed. The human health risk was evaluated for adults and children, considering the non-carcinogenic and carcinogenic risks. The pollution indices calculated for the PTEs using distinct reference values showed significant differences, resulting in lower pollution indices when using the regional reference values. The regional background proved to be a much more reliable geochemical baseline for environmental assessment. Regarding Igeo, the soils were found to be unpolluted to moderately polluted for most of the studied PTEs. The determined PERI for the soils surrounding the abandoned mine classifies them as low ecological risk. The evaluation of the non-carcinogenic and carcinogenic risks, resulting from exposure to the studied soils, suggests that there is no potential human health risk for children or adults regarding the considered PTEs.

Applied Methodological Approach for the Assessment of Soil Contamination by Trace Elements around Abandoned Coal Mines—A Case Study of the Jerada Coal Mine, Morocco

Previously conducted studies have established that soil contamination by trace elements (TEs) around coal mines affects ecological biodiversity and human health. One of the ways to protect the health of the surrounding population of coal mine sites is through the assessment of contamination impacts by accurate procedures for the establishment of relevant reclamation plan. The aim of the study is to develop an applied methodological approach to easily assess and quantify the impact of coal mining on the surrounding soils. To achieve this goal, a set of relevant geochemical indexes (enrichment factor—EF, geochemical background—GB, and geoaccumulation index—Igeo) and a geostatistical interpolation for mapping soil contamination were applied. It is experimentally established that the process of combining these techniques can be of great interest in highlighting the anomalous areas and revealing the contamination sources. A case study has been carried out on of the abandoned coal Jerada mine site in Morocco. Soils and coal mine waste rocks (CMWR) samples were collected from this site. Soil and CMWR samples were analyzed for their geochemical content. CMWRs were characterized further for their mineralogical composition and environmental behavior. Based on the EF, three TEs (As, Pb, and Zn) were targeted. The results of GB and Igeo calculations have established an evident relationship between the CMWR dump and the occurred soil contamination. TEs distribution pattern has been revealed using the obtained geochemical maps. The developed methodological approach may be in high demand when assessing soil contamination in most of abandoned coal mine sites around the word.

Bacterial succession in an abandoned circum-neutral opencast coal mine in India

Context Abandoned mines provide an ideal opportunity to study the succession of microbial communities, which is crucial for the development and stability of the soil. Aims We examined the diversity and temporal succession of the microbial community in an abandoned coal mine. Methods We investigated soil geochemical parameters and microbial succession using high-throughput 16S rRNA gene amplicon sequences over a 4-year period in a derelict opencast circum-neutral coal mine in Tasra colliery, Jharkhand, India. Results Soil pH (4.46–6.13), organic carbon (0.86–4.53%), available nitrogen (0.001–0.003%) and total cultivable heterotrophic microbial load increased, and concentrations of chloride (24 865–15 067 ppm), sulfate (26 417–417 ppm) and heavy metals reduced over the period of 4 years. The 16S rRNA gene sequences identified Proteobacteria as the dominant phylum across samples except for the fourth year, where Actinobacteria was predominant. Chlorobi, WPS-2 and Spirochaetes were exclusively identified in the first year. Twelve phyla present in the first year were completely absent by the end. In the fourth year, an abundance of nitrogen-fixing members such as Burkholderiales, Rhizobiales, Roseiflexales and Actinomycetales was noted and semi-quantitative PCR suggested that nitrogenases were predominately vanadium dependent (relative to molybdenum). Gradual shifts from purportedly chemolithotrophic to heterotrophic metabolic strategies were also observed. Conclusion This work establishes that soil improvement in abandoned coal mines involves the dynamic interplay of physicochemical parameters and shifts in microbial communities and dominant metabolic guilds. This knowledge can be used to plan and monitor remediation measures in such sites.

Design and Applicability of an Abandoned Coal Mine Roadway for Landfill Sites

Design and Applicability of an Abandoned Coal Mine Roadway for Landfill Sites

Coal and Coal Byproducts as Potential Sources of Rare Earth Elements (REE) in Indiana

The purpose of this study is to evaluate coal and coal byproducts (coal waste, coal ash, and acid mine drainage) in Indiana as potential sources of rare earth elements (REE). On a whole-rock basis, most Indiana coal samples have REE content below 100 ppm, and only some samples of the Brazil and Staunton Formations (Lower and Upper Block and Viking B coals) reach 100 ppm. Because REE concentrations vary between locations and within individual coal beds, and the correlations of coals within the Brazil and Staunton Formations are often uncertain, a better understanding of the stratigraphy of these formations is needed to identify the most promising REE horizons. Owing to a long history of coal mining, Indiana has numerous coal preparation plants and associated coarse-and fine-grained coal refuse (known, respectively, as gobs and slurry ponds). This paper reviews the available data on locations and volumes of these deposits. The total extent of slurry pond deposits was estimated at 2,765 acres, and the total volume estimates ranged from 94,000,000 to 136,000,000 cubic yards. No estimates are available for gob deposits in Indiana. To our knowledge, no REE data are available for coal preparation plant waste in Indiana, except for minimal data from coal slurry in Warrick County. Water streams from abandoned coal mines and coal processing (acid mine drainage, AMD) could also be a source of REE or other critical minerals; we review available data from AMD sites. Indiana, having many coal-fired power plants, has accumulated a large quantity of coal ash during its mining history. Our estimates indicate that coal ash deposits occupy ~2,184 acres, storing ~52,566,153 m3 of ash. Volume estimates for individual coal ash sites come from various sources and present our best estimates at this time. To our knowledge, no REE data are available on coal ash in Indiana. Such data would be of great value because coal ash deposits could be an important resource for REE, other critical minerals, or other high-value carbon products.

Study on Characteristics of Overburden Strata Structure above Abandoned Gob of Shallow Seams—A Case Study

To understand the change in overburden structure after coal seam group mining, we investigated the overburden characteristics and bearing capacity of abandoned coal mines in a coal seam group. We provide a theoretical basis for the construction and utilization of a coal mining subsidence area under a complex geological environment. This paper takes the construction project of Zhongtie Huizhi Square in Zhangqiu District, Jinan City, Shandong Province as the engineering background. According to the occurrence conditions of the study area, theoretical analysis, similar simulation, numerical simulation, and engineering practice verification are used. The overburden structure characteristics of abandoned mines in a shallow-buried coal seam group were studied. The results show that the development height of the water-carrying fractured zone after the mining of the 3#, 4#, and 9# coal seams is 17 m, 19.5 m, and 27.1 m, respectively, which shows that the height of water flow in the fractured zone is proportional to the buried depth of the coal seam after coal seam mining. After the model is set aside for three months, the degree of development of the residual fracture in the goaf is analyzed, and the distribution law of residual porosity in the longwall old goaf of a shallow-buried multiple coal seam is obtained. The development rate of residual fissures on both sides of the goaf is between 20.31% and 42.31%. The residual fracture development rate in the middle is relatively small, being between 8.21% and 18.53%. We comprehensively analyzed the characteristics of overlying strata in the abandoned mine under actual stratum conditions, and compared the empirical calculation results, theoretical research, similar simulation, and numerical simulation results in the specification with the engineering practice to prove the reliability of the research.

Technological avenues and market mechanisms to accelerate methane and nitrous oxide emissions reductions.

Strategies targeting methane (CH4) and nitrous oxide (N2O) emissions are critical to meeting global climate targets. Existing literature estimates the emissions of these gases from specific sectors, but this knowledge must be synthesized to prioritize and incentivize CH4 and N2O mitigation. Accordingly, we review emissions sources and mitigation strategies in all key sectors (fuel extraction and combustion, landfilling, agriculture, wastewater treatment, and chemical industry) and the role of carbon markets in reducing emissions. The most accessible reduction opportunities are in the hydrocarbon extraction and waste sectors, where half (>3 Gt-CO2e/year) of the emissions in these sectors could be mitigated at no net cost. In total, 60% of CH4 emissions can be mitigated at less than $50/t-CO2. Expanding the scope of carbon markets to include these emissions could provide cost-effective decarbonization through 2050. We provide recommendations for carbon markets to improve emissions reductions and set prices to appropriately incentivize mitigation.

Which Provincial Regions in China Should Give Priority to the Redevelopment of Abandoned Coal Mines? A Redevelopment Potential Evaluation Based Analysis

Abandoned mines have a double nature consisting of resources and assets, and their rational redevelopment is one of the most important practices of the recycling economy. To direct the layout of the regional abandoned mine redevelopment, this paper constructs a comprehensive assessment framework for abandoned mine redevelopment potential based on the driving force–state–response (DSR) model. It is quantitatively evaluated by three-dimensional cloud models, and the results are coupled using a four-quadrant approach. From the perspective of space control, this paper proposes classification principles of redevelopment potential and redevelopment sequence and summarizes the important policy implementations for each category. The paper studies the redevelopment potential of abandoned mines from the provincial perspective in 25 coal-producing provinces of China. The results indicate that not all areas with high resource potential are suitable for redevelopment. In the northern and western regions, the regional abandoned mines have high resource potential and strong redevelopment drivers. However, the spatial pattern of the suitability of the development conditions is not distributed in the same way as the resources. The distribution of the abandoned mine redevelopment potential reveals that the eastern and east-central regions should give priority to the construction of demonstration projects. Different driving force scenarios confirm that most provinces have no obvious driving factor preference, with a few exceptions. This evaluation model is established from a more comprehensive perspective and is a valuable aid for decision makers when arranging abandoned mine regeneration projects.

Effects of Coal Gangue on the Hydrochemical Components under Different Types of Site Karst Water in Closed Mines

In order to explore the potential effects of abandoned coal mines on the water quality of Ordovician limestone aquifers, water-rock interaction simulations were conducted. After the closure of the coal mine, the karst water in the goaf area and the waste gangue had a geochemical reaction, and the above-mentioned water-rock process was simulated by an indoor static immersion experiment to explore the differences in the effect of different types of karst water on the dissolution of gangue. The basic water quality parameters pH, EC (electrical conductance), and ORP (oxidation-reduction potential) showed different trends in karst hydro-immersion solution and ultra-pure hydro-immersion solution; pH and EC had greater fluctuations in two sets of ultrapure hydro-immersion solutions, while ORP fluctuated more widely in three groups of karst hydro-immersion solutions. In addition, gangue minerals dissolved more significantly in bodies of water where limestone was added. The results of chemical component clustering showed that TDS (total dissolved solids) and EC were homopolymerized in each immersion solution, and subsequent correlation analysis showed that TDS and EC clusters were more significantly affected by mineral properties in ultrapure water-immersion solutions, and more affected by dominant ions in karst water-immersion solutions.

Experimental study on dynamic mechanical characteristics and fracture behaviors of coal under water–gas-temperature coupling conditions

The stability of underground spaces in abandoned coal mines is affected by water, gas, temperature, and other dynamic disturbances. Thus, it is important to understand the dynamic behavior of coal in a complex environment for reusing abandoned mines. To this end, a multi-field coupled test system was independently developed to investigate the dynamic behaviors of coal under water–gas-temperature coupling conditions. The results revealed that in the presence of water and gas, the upper part of the coal sample was surrounded by gas, while the lower part was soaked in water. The dynamic stress–strain curve of the coal samples in the coupled water–gas-temperature environment includes a linear elastic deformation stage, rapid crack propagation stage, and post-peak fracture stage. The presence of the water–gas mixing pressure changes the failure of coal from ductile to brittle, whereas an increase in temperature changes the failure of coal from brittle to ductile. The dynamic strength of the coal samples increased linearly with an increase in the impact velocity, strain rate, and water–gas mixing pressure but decreased with an increase in temperature. The failure strain of the coal samples increased linearly with an increase of impact velocity, strain rate, and temperature, but decreased with an increase in the water–gas mixing pressure. In addition, the fracture process of the coal was captured using a high-speed camera, and the results indicated that the cracking degree of the gas part was greater than that of the water-soaked part. Moreover, the influence of various factors on the impact fracture behavior and deterioration mechanism of coal under water–gas-temperature coupling conditions were revealed.

Managing Methane Emissions in Abandoned Coal Mines: Comparison of Different Recovery Technologies by Integrating Techno-Economic Analysis and Life-Cycle Assessment.

Methane emissions from worldwide increasing abandoned coal mines have posed multiple challenges of global warming, energy waste, and explosion risk. This study first profiles the dynamic patterns of coal mine methane emissions in different recovery technologies, methane extraction with drainage (MEWD, mine-water concurrently extracted and treated) and direct methane extraction (DME, noncontrol on mine-water), in two abandoned mines from Ningxia and Inner Mongolia as China's leading coal provinces. Then, we conducted a techno-economic analysis and life-cycle assessment to quantify their comprehensive benefits. The key findings are as follows: (1) MEWD can long recover methane, although the economic profits decrease with declining methane extraction volume. DME can only work for ∼5 years, after which the mine is flooded, where methane is sealed underground and not recoverable. (2) MEWD drains and further treats the mine-water with an additional 29.4-35.9 million CNY cost compared with DME, while MEWD can achieve greater life-cycle environmental benefits with more cumulative methane recovery, whose CO2-eq (GWP-100) and SO2 reductions are 64.4 and 53.4% higher than those of DME. (3) MEWD is more promising for large-scale implementation, where feed-in tariffs and carbon market measures can improve the economics for sustainable management of incremental abandoned mine methane.

Energy evolution and water immersion-induced weakening in sandstone roof of coal mines

The instability of underground spaces in abandoned coal mines with water-immersed rocks is one of the main hazards hindering the geothermal energy use and ecological restoration of post-mining areas. This study conducted graded cyclic loading–unloading tests of five groups of sandstone samples with different water contents. The evolution of input, elastic, dissipated, damping, and plastic energies were explored, considering the damping effect. The normalized plastic energy serves to characterize the damage evolution of sandstone samples, whose failure characteristics were analyzed from both the macroscopic and microscopic perspectives. X-ray diffraction technique and scanning electron microscopy were used to reveal the softening mechanism of sandstone. The results show that under graded cyclic loading, input energy, elastic energy, and dissipated energy all increase gradually, and the fraction of elastic energy increases gradually at first and then tends to stabilize. The variation in the fraction of dissipated energy is opposite to that of elastic energy. In each cycle, the input energy is stored primarily in the form of elastic energy, whereas the dissipated energy is used primarily to overcome the damping of sandstone. When the normalized number of cycles approached unity, the plastic energy fraction sharply increases, while that of the dampening energy drops abruptly. With increasing water content, the effect of pore water on the lubrication, the water wedge, and dissolution of mineral particles becomes more obvious, reducing the elastic-storage limit of sandstone, meanwhile the sandstone damage factor increases significantly under the same cycle and the failure mode changes from brittle to ductile.

Substantial methane emissions from abandoned coal mines in China

China has shut down and abandoned a substantial number of coal mines since 1999, which have been releasing methane (CH4) for many years. However, the characteristics of China's abandoned mine methane (AMM) emissions are still unclear; this is a concerning knowledge gap because coal mines are the largest contributor to China's anthropogenic CH4 emissions. This study used two methods to estimate China's historical AMM emissions over the past 40 years (1980–2020) and to project its AMM emissions to 2060 which is the target year for China's carbon neutrality goal. The results show that China's AMM emissions increased substantially from 0.11 ± 0.03 million tons per year (Mt/yr) (3.1 ± 0.84 Mt/yr CO2-eq) in 1980 to 4.7 ± 0.94 Mt/yr (131 ± 26 Mt/yr CO2-eq) in 2020. An accelerated growth rate was found during 1998–2005, with AMM emissions rapidly increasing by approximately three times, which was consistent with the high number of mine shutdowns. In 2019, we found that AMM emissions had become the fourth largest anthropogenic source in China, higher than the national anthropogenic CH4 emissions of individual United Nations Framework Convention on Climate Change Annex I countries excluding the United States of America and the Russian Federation. If unabated, China's AMM emissions are projected to peak at 8.7 ± 2.6 Mt/yr in 2040 and reach approximately one-third of China's anthropogenic carbon dioxide emissions in 2060. This study reveals that understanding AMM emissions can help more accurately quantify China's total CH4 emissions and guide their future mitigation.

A two-stage framework for site selection of underground pumped storage power stations using abandoned coal mines based on multi-criteria decision-making method: An empirical study in China

With the continued transformation of the energy structure, more and more coal mines have been abandoned. The construction of underground pumped storage power stations using abandoned coal mines not only solves the problem of renovating abandoned coal mines, but also ensures a high level of photovoltaic and wind integration. However, the most basic site selection problem of underground pumped storage power plants using waste coal mines has rarely been studied due to the complexity of the technical scheme and the uncertainty of the decision environment. Therefore, a two-stage fuzzy evaluation model is proposed in this paper. Firstly, two sets of site selection index systems are established, namely the veto assessment system and the comprehensive evaluation criteria system. Triangular intuitionistic fuzzy numbers are used for information representation. Then, the veto assessment system is applied for the initial screening of the alternatives. Afterward, the alternatives are evaluated by the comprehensive evaluation criteria system. The entropy method and step-wise weight assessment ratio analysis are utilized to calculate the objective and subjective weights respectively, and the Lagrange optimization method is used to obtain the combined weights. The sorting results of the alternatives are obtained through multi-attributive border approximation area comparison. Finally, an empirical analysis based on eight abandoned coal mines in Datong, Shanxi Province, proves the rationality of the decision-making framework. The weights of natural condition, society, resources, and economy are 29.52%, 23.83%, 28.42% and 18.23% respectively. Natural condition is the most important factor to consider when choosing the site for underground pumped storage power stations. The ranking results of the alternatives is A5 > A2 > A3 > A8 > A7. Therefore, A5 is the optimal location. The results have a guiding role for both governments and investors in the construction of underground pumped storage power stations and transformation of abandoned coal mines.

Effects of Soil Amelioration and Vegetation Introduction on the Restoration of Abandoned Coal Mine Spoils in South Korea

In order to ecologically restore coal mine spoils, tolerant species were selected through vegetation surveys on the abandoned coal mine spoils and natural forests established on the poor environment similarly to there. In addition, tolerant species were selected through cultivation experiments in the laboratory. Many C4 plants were included among the tolerant species selected through cultivation experiments. Soil was ameliorated by applying commercial organic fertilizer that can improve both physical and chemical properties of soil at the same time. Vegetation introduced for restoration was prepared by combining plant species tolerant to the degraded environment of coal mine spoils and the reference information. The treatment with a soil ameliorator improved the chemical properties of soil, such as the pH and nutrient contents, and promoted the growth of sample plants significantly. However, additional improvements were required compared with the chemical properties of healthy forest soil. The sites restored by ameliorating soil and introducing tolerant species showed a more similar species composition to the reference sites compared with the afforested and non-restored sites in both lowland and upland areas. However, such restoration did not play a significant role in increasing species diversity or excluding exotic plants. In this respect, more active restoration is recommended.