Showing papers in "Mine Water and The Environment in 2017"

Review of Passive Systems for Acid Mine Drainage Treatment

Abstract: When appropriately designed and maintained, passive systems can provide long-term, efficient, and effective treatment for many acid mine drainage (AMD) sources. Passive AMD treatment relies on natural processes to neutralize acidity and to oxidize or reduce and precipitate metal contaminants. Passive treatment is most suitable for small to moderate AMD discharges of appropriate chemistry, but periodic inspection and maintenance plus eventual renovation are generally required. Passive treatment technologies can be separated into biological and geochemical types. Biological passive treatment technologies generally rely on bacterial activity, and may use organic matter to stimulate microbial sulfate reduction and to adsorb contaminants; constructed wetlands, vertical flow wetlands, and bioreactors are all examples. Geochemical systems place alkalinity-generating materials such as limestone in contact with AMD (direct treatment) or with fresh water up-gradient of the AMD. Most passive treatment systems employ multiple methods, often in series, to promote acid neutralization and oxidation and precipitation of the resulting metal flocs. Before selecting an appropriate treatment technology, the AMD conditions and chemistry must be characterized. Flow, acidity and alkalinity, metal, and dissolved oxygen concentrations are critical parameters. This paper reviews the current state of passive system technology development, provides results for various system types, and provides guidance for sizing and effective operation.

Effects of Coal Mining on Shallow Water Resources in Semiarid Regions: A Case Study in the Shennan Mining Area, Shaanxi, China

Abstract: The Shennan mining area in northern Shanxi Province is located in a semiarid area where surface and near-surface water resources are very valuable. Mining-induced fractures can cause these shallow water resources to leak. The overburden strata were divided into engineering geology rock groups and a comparative analysis was calculated based on the height of the water-conducting fractured zone and the key stratum theory, using both an empirical formula and a fitting formula. The influence of coal mining on the shallow water resources was divided into four types: serious, moderate, slight, and no water loss. Finally, a water resource leakage differentiation graph was produced for the study area. The results can be used to guide coal extraction in the study area and to protect the area’s shallow water resources.

Numerical Analysis of Karst Water Inrush and a Criterion for Establishing the Width of Water-resistant Rock Pillars

Abstract: Water-bearing caves in the Maokou limestone have caused disastrous water inrushes in mines in southern China. A linkage analysis between the hydro-mechanical coupling and the strength reduction method was used to investigate the stability of water-resistant rock pillars. The factor of safety (FOS) of the pillar was established, and a criterion for establishing the required width of the pillar was proposed in engineering practice, i.e., the width of the pillar should be based on the blast hole depth and blast-disturbance depth, along with a FOS of 1.5. The permeability of the water-resistant pillar and the probability of water inrush both increase as the strength reduction factor increases because the effective width of the pillar narrows. A numerical analysis of the Qiyi coal mine “4·16” water inrush accident shows that the cause of the inrush was that the 3.0 m wide barrier left by roadway excavation was too narrow to withhold the karst water pressure of about 4.0 MPa.

Experimental Simulation of Fault Water Inrush Channel Evolution in a Coal Mine Floor

Abstract: Mine water inrush is very common in China and can cause hysteresis and severe damage. The entire process of crack formation, concealed fault propagation, and evolution of a water inrush channel with high pressure water directly beneath the mine floor was physically simulated based on fluid–solid coupling mechanics and solid materials research. Activated materials were used to simulate fault damaged rock, including soybeans, sand, Vaseline, and calcium carbonate. The results indicate that water channels are mainly caused by the connection between tectonic rock zones and coal floor cracks, which are the direct cause for water inrush. Furthermore, the lagging water inrush mechanism from the coal floor in a confined water body under both a stress field and a seepage field were revealed. The formation of the water inrush path with temporal and spatial variations was analyzed by interpreting the monitoring data and phenomena. The data showed that the floor stress in front of the working face increased and was affected by the abutment pressure, and that floor stress under the mined-out area began to decrease simultaneously. The stress of the upper wall showed a drastic drop while the stress of the footwall continued to decline and then stabilized after the water inrush. This work provides new approaches and knowledge for research on deep mining water inrush structures.ZusammenfassungBergwassereinbrüche sind in China sehr häufig und können bleibende und schwere Schäden verursachen. Der gesamte Prozess der Bruchentstehung, die verdeckte Störstellenentwicklung und die Entstehung der Wassereinbruchswegigkeit durch gespanntes Wasser direkt unter der Abbausohle wurde basierend auf kombinierten Festkörper-/Fluidmechanik- und Gesteinsuntersuchungen bearbeitet. Aktivierte Werkstoffe (Sojabohnen, Sand, Vaseline und Kalkstein) wurden verwendet, um gestörtes Gebirge zu simulieren. Die Ergebnisse zeigen, dass die Wasserwegigkeiten hauptsächlich durch die Kombination von Störungszonen und Rissen im Kohleliegend—die der unmittelbare Auslöser für den Wassereinbruch sind—verursacht werden. Darüber hinaus wurde der verzögerte Mechanismus des Sohlwasserausbruchs innerhalb eines gespannten Wasserkörpers sowohl unter Druck- als auch unter Sickerwasserbedingungen entdeckt. Die Entstehung der Wasserwegigkeit wurde in zeitlichen und räumlichen Variationen durch Interpretation der beobachteten Daten und Phänomene untersucht. Die Daten zeigten, dass die Sohlspannung vor der Abbaufront anstieg und vom Überlagerungsdruck beeinflusst wird und, dass die Sohlspannung unter der abgebauten Fläche gleichzeitig abzunehmen begann. Die Spannung in der Firste zeigte einen drastischen Abfall während sie in der Sohle weiter abnahm und sich dann nach dem Wassereinbruch stabilisierte. Diese Arbeit stellt neue Ansätze und Erkenntnisse für die Erforschung von Wassereinbruchsstrukturen im tiefen Bergbau zur Verfügung.ResumenLa irrupción de agua de mina es muy común en China y puede causar histéresis y daños severos. Se simuló físicamente el proceso entero de formación de grieta, propagación de la falla y evolución del canal de irrupción de agua con alta presión de agua debajo del piso de la mina, basado en las investigaciones sobre materiales sólidos y la mecánica de acoplamiento sólido-fluido. Para simular la roca de la falla se utilizaron materiales activados como porotos de soja, arena, vaselina y carbonato de calcio. Los resultados indican que los canales de agua son principalmente causados por la conexión entre las zonas de roca tectónica y las grietas de carbón del piso y son la causa directa de la irrupción de agua. Además, se reveló el mecanismo de retraso de la irrupción de agua desde el piso de carbón en un cuerpo de agua confinada bajo tensión y filtración de campo. La formación de un paso de irrupción de agua con variaciones espacio-temporales fue analizado por la interpretación de los datos monitoreados y de los fenómenos. Los datos mostraron que la tensión del piso sobre la cara de trabajo se incrementó y fue afectado por la presión y que la tensión del piso bajo el área no explotada empieza a decrecer simultáneamente. Luego de la irrupción de agua, la tensión de la pared superior descendió drásticamente mientras que la tensión de la pared inferior descendió y luego se estabilizó. Este trabajo proporciona nuevas aproximaciones y conocimiento para la investigación sobre la irrupción de agua en minería de profundidad.抽象

Assessment of Water Inrush Risk Using the Fuzzy Delphi Analytic Hierarchy Process and Grey Relational Analysis in the Liangzhuang Coal Mine, China

Abstract: The exploitation of deep coal seams in North China’s coalfields is seriously threatened by water inrush. Water inrush is controlled by multiple factors and its processes are often not amenable to mathematical expression. To predict and prevent water inrush from the underlying Ordovician aquifer during mining of the No. 13 coal seam in the Liangzhuang coal mine, we used an innovative combination of methods to assess the risk of water inrush based on the fuzzy Delphi analytic hierarchy process (FDAHP) and grey relational analysis (GRA). Expert opinions and GRA were applied to obtain the relative importance of each of the major controlling factors, and the total weights of all factors were assigned using FDAHP. This allowed us to develop a risk index map in which the study area was divided into two zones and four subzones based on the risk index.

Risk Assessment of Water Inrush from Aquifers Underlying the Gushuyuan Coal Mine, China

Abstract: Mining of the No. 15 seam in the Gushuyuan coal mine is threatened by water inrush from the underlying Ordovician limestone aquifer. Water pressure and yield of the aquifer, the equivalent thickness of the water-resisting layer(s), and the properties of geologic structures are the major factors that control water inrush. The water inrush risk was evaluated using the vulnerability index (VI) method, which couples GIS with the analytic hierarchy process. Comparing the results with that of the traditional water inrush coefficient method in a specific mining area clearly showed the advantage of the VI method, especially in mines underlain by a thin water-resisting layer.

Risk Assessment of Water Inrush in an Underground Coal Mine Based on GIS and Fuzzy Set Theory

Abstract: A systematic method was developed to evaluate the risk of water inrush through a coal seam floor using the geographic information system (GIS) and the fuzzy set theory. The main geological and hydrogeological indicators that control water inrush were first considered using a fuzzy mathematics approach, in which fractal analysis was carried out to quantify the fault’s characteristics. The degree of membership was determined using GIS, the weight of every factor was considered by calculating the entropy in accordance with Shannon’s information entropy theory, and the level of risk of the evaluated object was derived using the maximum membership principle. The approach was validated by a case study at the Chensilou mine in Henan Province, China, where the aquifers that underlie an exploitable coal seam, II2, were made impermeable by grouting. Data from Nov. 2014 to April 2016 shows that the risk of water inrush was reduced in Panel 2517 of the II2 coal seam, that there were no serious disturbances in this panel and no groundwater inrush through the floor. This method can be a powerful tool for systematically assessing the risk of water inrush through the floor, since the influence of several factors can be quantitatively considered in accordance with the geological and mining conditions.

Formation and Height of the Interconnected Fractures Zone after Extraction of Thick Coal Seams with Weak Overburden in Western China

Abstract: Formation of a zone of interconnected fractures during coal mining is a key factor in mine flooding. Coal mines in western China are characterized by thick coal seams with mechanically weak overburden. In situ studies including drill core analysis, drilling fluid loss measurement, and borehole video monitoring were used at the working face 101 in Shaanxi Jinjitan coal mine to explore the maximum height of the interconnected fractures zone (IFZ). Also, tests on a scaled physical model and numerical simulation based on the drilling data were used to study the formation of the fractured zone. By considering data from other mines with similar mining conditions, a logarithmic relationship was found between the maximum height of the IFZ and the thickness of coal excavation. The maximum height of the IFZ was found to be 27 times the thickness of the excavated coal seam, which is far more than in coal mining areas in eastern China. Also, the IFZ in overlying strata of the study area was arch-shaped, not saddle-shaped, as had been observed in previous studies.

Evaluation of Floor Water Inrush based on Fractal Theory and an Improved Analytic Hierarchy Process

Abstract: A new evaluation model, based on fractal theory and an improved analytic hierarchy process (IAHP), was developed to predict the potential for water inrush. Fractal theory was used to quantitatively evaluate the complexity of the fault zones, which is a major water inrush factor. Study of the Lu-an mining area showed that the faults there can be subdivided into four levels of complexity: simple, medium, relatively complex, and complex. The overall complexity of the fault network in the study area was moderate. The IAHP was used to study the potential for coal floor water inrush through these faults. The results indicated that this mining district can be divided into risk-based zones. The extremely high risk zones were mainly located in the northern Tun-liu mine and the northern Chang-cun mine; high risk zones were primarily distributed in the Tun-liu mine and the southwestern Wang-zhuang mine. All other mines were classified as medium and low risk zones.

A Review of Geophysical Exploration Technology for Mine Water Disaster in China: Applications and Trends

Abstract: Geophysical exploration can be effective in detecting and monitoring potential sources of coal mine water in-rushes and underground watercourses. Generally, in-mine seismic, DC resistivity, and transient electromagnetic methods are used for such purposes in China. However, such technologies can be influenced by many factors, such as roadways, fissures in the surrounding rocks, and various secondary conditions. Our review of current geophysical methods and tools concludes that further basic research should be carried out on geophysical field propagation in the whole space, data collection methods, and inversion methods appropriate for the special environment of coal mines. Moreover, borehole and roadway space should be designed to incorporate effective geophysical drilling, cross-hole exploration, drilling–roadway exploration, and roadway–roadway exploration. Future hydrogeophysical exploration research should focus on comprehensive geophysical methods combining multi-field synergistic observations with multi-field data integration and automatic monitoring as well as early warning systems for mine water disasters combining real-time processing and analysis of exploration equipment with Internet of Things technology.

A Nonlinear Risk Evaluation Method for Water Inrush Through the Seam Floor

Abstract: A risk evaluation method based on principal component analysis, fuzzy mathematics, particle swarm optimization, and support vector classification, is proposed due to the limitations of the water inrush coefficient method. The many factors that influence coal floor water inrush were categorized as structural, hydrogeological, coal seam occurrence and mining condition principal components, according to principal component analysis, among which the structural and mining condition components were the most important. The principal component factors were then fuzzified. Finally, an evaluation method was established, with the parameters of the supporting vector classification optimized through the particle swarm algorithm. The validity of the method was demonstrated by comparing its predictions with actual conditions at ten coal seam mining faces.

Prediction Reliability of Water Inrush Through the Coal Mine Floor

Abstract: Inrush of Ordovician limestone karst water through the mine floor occurs frequently in the Carboniferous-Permian coalfield in northern China. A probability index method was proposed to predict water inrushes using five indices: an aquifer water-bearing index, a structural index, an aquifuge index, an aquifer water pressure index, and an underground pressure index. Expert input was used to obtain weights for these five factors. Expert evaluation and statistical probability were then used to determine weights of the subsidiary factors, allowing the calculation of a water inrush probability index (I) and a threshold water inrush value for the Feicheng coalfield of 0.65. The Dempster-Shafer evidence theory was then used to determine a 74% degree of confidence for this prediction. Finally, the method was applied to the No. 9901 working face of the Taoyang coal mine. A subsequent 1,083 m3/h water inrush that occurred there aligned with the statistical results.

Assessment of Metal Contamination in the Mine Water of the West Bokaro Coalfield, India

Abstract: This study was carried out in the West Bokaro coalfield area of the Jharkhand state of India to assess water quality for drinking and domestic purposes. Thirty mine water samples were collected from opencast and underground mines, and concentrations of Al, As, Ba, Cr, Cu, Fe, Mn, Ni, Se, and Zn were determined using ICP-MS. Spatial distribution maps were prepared using GIS software so that the quality of the mine water could be easily understood. Metal concentrations were higher in the pre-monsoon season than in the post-monsoon season, irrespective of location, but there were more significant seasonal variations in the opencast mine water than in the underground mine water. The concentrations of Al, Ba, Fe, Mn, and Ni exceeded the desirable as well as the permissible drinking water limits in both seasons. The quality of the surface water as well as the groundwater in the region may be adversely affected by the high metal concentrations in this mine water.

Hydraulic and Thermal Modelling of an Underground Mining Reservoir

Abstract: Flooded mines are a groundwater reservoir that can be used geothermally. Modelling such a reservoir can be complicated because it is necessary to simultaneously solve the equations of flow and heat transport within the mine voids and the surrounding medium, whose hydraulic parameters may have been affected by mining. We present a numerical model developed for the reservoir formed by the Barredo and Figaredo shafts in the Central Coal Basin of Asturias (Spain), using FEFLOW software. Both 2- and 3-D versions of the model were used to simulate the flooding of the mine. They were calibrated by comparing the results with actual water levels measured during flooding. The hydrogeological and thermal characteristics of the reservoir were adjusted to predict the long-term temperature of the water under different scenarios of water extraction and injection.

Characterization of Two Nanofiltration Membranes for the Separation of Ions from Acid Mine Water

Abstract: We evaluated nanofiltration for separation of ions from acid mine drainage (AMD), using two composite nanofiltration membranes (Nano-Pro-3012 and NF90) as examples of the polyamide class of acid-stable membranes. The structure of the NF membranes was characterized by scanning electron and atomic force microscopy. The NF90 displayed a higher permeate flux than Nano-Pro-3012, with higher relative roughness at both pH values. Both membranes suitably rejected most of the metals found in the AMD, but the Nano-Pro-3012 membrane proved unsuitable for sulphate removal.

A Study of Water-Inrush Mechanisms Based on Geo-Mechanical Analysis and an In-situ Groundwater Investigation in the Zhongguan Iron Mine, China

Abstract: The Zhongguan iron mine is strongly threatened by water inrushes because of the thick Ordovician limestone aquifer and a variety of concealed faults. An inrush event occurred at −260 m below sea level (bsl), inundating the mine during the mineral deposit developing stage. It was very important to understand why and how this occurred to prevent its recurrence. A numerical simulation of a process-based model of the excavation, together with an in-situ groundwater investigation, showed that the event was related to the normally impermeable X1 fault, which was gradually activated from the bottom of the aquifer to the mine roof as excavation developed. The activated fault transformed into an inrush channel, hydraulically connecting the aquifer and the roadway. Thus, faults and other geological structures have to be mapped before mining. Moreover, sealing possible water channels before excavation in potential inrush areas is much better than advance dewatering because of the aquifer’s transmissivity and the limited effectiveness of grout curtains.

Using a Fluid–Solid Coupled Numerical Simulation to Determine a Suitable Size for Barrier Pillars When Mining Shallow Coal Seams Beneath an Unconsolidated, Confined Aquifer

Abstract: Barrier pillars are an effective and fundamental measure to prevent water inrush when mining shallow coal seams under an unconsolidated, confined aquifer. Based on the complex geological and hydrogeological conditions in the southern area of the Qidong coal mine, the no. 61 coal seam there was selected for a research demonstration. A fluid–solid coupled numerical simulation was carried out using the universal distinct element code. The hydraulic pressures and seepage rates in overlying strata were analyzed for two mining cases, near the aquifer and near the fault. The results showed that the degree of interconnection between the bed-separated and vertical fractures, and increases in hydraulic pressures and seepage rates in overlying strata were key factors in predicting potential water inrush when mining shallow coal seams under an unconsolidated, confined aquifer. Combining the numerical simulation results with China’s coal mining requirements, the no. 61 coal seam can be mined up to 90 m beneath the unconsolidated, confined aquifer, which limits mining to an altitude of −509.36 m. The width of the barrier pillar should be 30.7 m near the fault.

Physical Simulation of High-Pressure Water Inrush Through the Floor of a Deep Mine

Abstract: When mining at great depth, high-pressure karstic water inrush can pose a serious threat. We used physical simulations to investigate channel inception, evolution, and catastrophic flooding. Using newly developed coupled solid–liquid materials and physical simulations of high-pressure water intrusion, a laboratory test was carried out that reproduced the spatial and temporal characteristics of channel formation and crack generation, extension, connection, and failure. Floor failure features caused by the effects of mining and confined water were analyzed, and the formation and evolution of catastrophic flooding were investigated. The results showed that the evolution of a water-inrush channel can be divided into three stages: floor crack development, water channel initiation, and channel evolution. Extrapolating the simulation results to a real-world example, a floor fracture formed when the working face advanced to 45 m, and a water-inrush channel formed when the push distance of the working surface was about 70 m. Thereafter, the point of water eruption widened, water flow increased, and the main cracks in the floor rock mass showed obvious changes. The crack in the lower interface was angled 56° upward, and finally a water eruption point formed in the middle of the mined cavity. These results provide theoretical support for the prediction of water inrush into deep coal mines.

Delineating the Origin of Groundwater in the Golgohar Mine Area of Iran Using Stable Isotopes of 2 H and 18 O and Hydrochemistry

Abstract: The Golgohar iron ore mine in southern Iran is a large open pit that uses dewatering (≈4000–5000 m3/day) to prevent flooding. A vast cone of depression has formed, and water from a large area flows into the pit. A study of the different sources of this water was necessary to plan a proper dewatering project. Moreover, the discharged water is saline and contains high levels of contaminants. Based on hydrochemical and isotope (18O and 2H) analysis, it was concluded that the area’s deep saline groundwater is coming from the Sirjan (Kheirabad) salt playa (north of the mine) by saltwater intrusion while the chemistry of more distant groundwater was due to dissolved minerals.

Water-Isolating Capacity of an Inclined Coal Seam Floor Based on the Theory of Water-Resistant Key Strata

Abstract: A model of an inclined coal seam floor with linearly increasing water pressure was developed based on theories of ground pressure and key strata. The stability metrics of the water-resistant key strata in the inclined coal seam was deduced using Mohr–Coulomb yield criterion. Five principle factors were selected: the distance that the workface had advanced, the tilted length of workface, the thickness and pitch of the water- resistant key strata, and the elasticity modulus. A sensitivity analysis was then conducted using an orthogonal design. The thickness of the water-resistant key strata was the most important factor, with a 44.8% ranking, followed by the distance that the workface had advanced at 34.4%. The influence of the elasticity modulus, pitch, and tilted length of the workface, were 9.3, 5.8, and 5.7%, respectively. The maximum water pressure possibly tolerated by the inclined aquiclude were found to rise with the increasing load of the caved overburden, and decrease with the increasing workface initial or periodic weighting distance, workface length, and pitch of the water-resistant key strata. A parabolic relationship exists between the maximum allowable water pressure and thickness of the key aquiclude. Water-resistant key strata located in the lower part of the confining layer offers better protection from floor water inrush. These findings provide an important theoretical basis to determine the potential of water inrush from an inclined coal seam when mining above confined aquifers.

Predicting Open Pit Mine Inflow and Recovery Depth in the Durvuljin soum, Zavkhan Province, Mongolia

Abstract: Increasingly, mine issues and water resources are being managed on a watershed basis, while addressing problems at the local mine scale. A good example of this developed when empirical and analytical modelling of the potential inflow to an open pit mine in the Durvuljin soum, a region in northwest Mongolia, indicated that inflow would be on the order of 0.3 to 10.5 L/s. In this study, the radius of influence due to open pit mining was estimated to be between 0.6 and 3 km. Based on simulated drawdown contours and transient pit inflow figures that captured the impact of mining and groundwater inflow rate variations over a period of time, it appeared that advanced dewatering will not be required at this mine, unless currently unknown major fractured structures are intercepted. In-pit basal sumps and pumps should be sufficient to remove water from the mine floor. However, an assessment of the final pit level is also crucial to planning the post-mining surface and groundwater quality/eco-system and mitigation requirements during recovery. Our post-mining water table recovery estimate indicated that inflow will exceed evaporation and that a shallow lake will likely form. While such solutions, which do not rely on complex numerical models nor excessive input data, are not appropriate for all hydrogeologic situations, they are relevant to the conditions encountered at most mine sites.

Numerical Study of the Effects of Drainage Systems on Saturated/Unsaturated Seepage and Stability of Tailings Dams

Abstract: The stability of tailings dams is affected by seepage characteristics such as the location of the phreatic surface inside the dam, the effects of the capillary fringe, and the unsaturated zone above the zero pore pressure level. In this study, the performance of drainage systems in tailings dams was investigated by analyzing saturated and unsaturated seepage in the dam, considering the effects of the construction method, tailings properties, and the type of drainage systems. First, general seepage characteristics in tailings dams were studied and the effects of non-homogeneity were investigated. Our results show that in a silty tailings dam with a height of 15 m, unsaturated plus capillary seepage flux can reach 13% of the total seepage. The total head vs. discharge volume curves under various conditions were compared and their practical implications are presented. Then, stability analyses were carried out using the results of seepage analyses for different construction methods, material properties, and drainage systems. Finally, a number of practical conclusions are drawn regarding dam stability and the efficiency of toe, blanket, and chimney drains in different construction methods. Using a blanket and/or a chimney drain can increase the stability safety factor by up to two times, depending on the type of material.

Removal of Trace Metals from Acid Mine Drainage Using a Sequential Combination of Coal Ash-Based Adsorbents and Phytoremediation by Bunchgrass (Vetiver [Vetiveria zizanioides L])

Abstract: Potentially scalable low-cost treatment methods for acid mine drainage (AMD) are very limited. We used a sequential combination of adsorption and phytoremediation by bunchgrass (Vetiver [Vetiveria zizanioides L]) in a semi-batch system to remove Zn, Mn, Ni, and Cu from AMD. The objectives were: (1) to compare the removal of these metals by raw and NaOH-activated coal ash (NaOH-CA); and (2) to determine the effect of sequencing adsorption and phytoextraction on metal removal. The NaOH-CA adsorbed significantly more metals than raw coal ash (RCA) in both batch and semi-batch fixed column experiments, demonstrating the effectiveness of NaOH hydrothermal activation, which forms zeolites. Adsorption by NaOH-CA removed 59.1, 95.7, 67.6, and 77.9% of the Zn, Mn, Ni, and Cu, respectively, compared to 50.6, 95.1, 30.2, and 60.5% for the RCA. Metal removal by phytoremediation was generally less than that by adsorption, accounting for between 3.4 and 54.6% for both adsorbents. Phytoremediation following adsorption by NaOH-CA removed 89.2–99.9% of the metals compared to 70.8–98.5% when phytoremediation followed adsorption by RCA. Overall, relatively high metal removal efficiencies were attained, considering the acidic conditions (pH <4), at hydraulic residence times of 1 to 5 days. Using coal ash to treat AMD is potentially a low-cost and environmentally friendly option for minimizing the adverse public health and environmental risks associated with both wastes.

Understanding Abiotic and Biotic Conditions in Post-Mining Pit Lakes for Efficient Management: A Case Study (Poland)

Abstract: This study was aimed at determining whether the origin, morphometry, and hydrology of post-mining lakes affect their hydrochemical and hydrobiological parameters (i.e. water quality). The investigated post-mining lakes were very young compared to glacial lakes and represent early stages of ecosystem succession. Despite their different ages and morphometries, they are all mesotrophic and have good water quality. They have not been supplied with phosphorus and nitrogen, which can cause excessive development of pelagic phytoplankton; as a result, they share low chlorophyll a (Chl a) content, low phytoplankton biomass, and relatively high water transparency. Low abundance and species richness of zooplankton indicate low trophic levels in all of the lakes. Chl a in Lakes Przykona and Bogdalow were within the range typical of mesotrophic lakes, while Lake Janiszew had very low Chl a, typical of an oligotrophic water body. The low N:P ratios (4–6), especially in summer, indicates nitrogen limitation of primary production. There is a risk that such a proportion of the major biogenic elements could lead to harmful cyanobacterial blooms. The lake basins were formed using quaternary deposits (sand, clay) at their bottoms; as a result, the lakes had a slightly alkaline pH (>8), which favors the development of aquatic organisms. Optimum depth helps establish lake stratification and ensures ecological stability. This applies to post-mining lakes as well; an optimum depth should be determined to ensure the development of thermal stratification, which affects lake processes.

Relationship Analysis of the Degree of Fault Complexity and the Water Irruption Rate, Based on Fractal Theory

Abstract: Fault structure significantly affects the likelihood of mine water inrush events. In this study, fractal theory was applied to the distribution of fault structures in a deep mining area of the No. 2 mine, Pingdingshan City, China. The results revealed a fractal dimension ranging from 0.602 to 1.672 for fault structures in 35 planes. Using the fractal dimension as a fundamental characteristic, the complexity of fault structures was quantified and categorized into five levels, with the overall complexity of the fault network in the study area classified as moderate. Nine mine water inrush events were used to establish a relationship between the fault fractal dimension and the water irruption rate, which was found to increase with the fractal dimension. Finally, differences in fault fractal dimension and fault complexity level are discussed and analyzed.

Quantitative Prediction of Water Volumes Within a Coal Mine Underlying Limestone Strata Using Geophysical Methods

Abstract: Mine water and mine inflow water are closely linked to the risk of mine water disasters. The relationships between various geophysical parameters and the volume of water in mine tunnels were considered by using an integrated suite of appropriate geophysical methods [i.e. direct current (DC) resistivity, transient electromagnetic method (TEM), and the seismic scattered wave method], and knowledge of the essential features of seam floor water in karst coal mine settings. By constructing a 3-dimensional physical simulation of water-bearing limestone, a quantitative predictive formula for water volume in abnormal bodies was derived in terms of the parameters of the selected suite of geophysical methods. Water volume was determined by using apparent resistivity (obtained from the DC resistivity survey and TEM), a measure of the amount of potentially water-containing space, and a correction coefficient. The quantitative formula was adjusted for accuracy using field data, and then tested at a specific field site. The average accuracy of predictions using the composite quantitative formula was 75.8 %, which is considered to be high. The formula presented in this paper could contribute significantly to the prevention and mitigation of water-related disasters in karst coal mines.

Hydrochemical Prediction of Mine Water Inrush at the Xinli Mine, China

Abstract: Seawater poses a great threat to the Xinli Mine, an undersea gold mine in China. A hydrochemical method was used to assess the risk of sea water inrush into the mine. A detailed hydrochemical survey and sampling were carried out and the concentrations of conservative ions in the mine water were analyzed. Principal component analysis indicated that the potential water inrush channels were located in the hanging wall of the ore-controlling fault. A composite principal component was calculated from the Na+, Cl−, Mg2+, SO4 2−, and K+ concentrations, which reflected the effects of potash feldspathization and cation exchange, to assess the risk of seawater inrush.

Quantifying Iron Concentration in Local and Synthetic Acid Mine Drainage: A New Technique Using Handheld Field Spectrometers

Abstract: Pit lakes present a concern for public safety and environmental quality. With continuing advancement of imaging satellites, remote sensing spectroscopy may provide a useful tool for monitoring pit water quality across vast mining districts. Visible to shortwave infrared remote sensing has been widely used to monitor acid mine drainage (AMD) mineralogy at mine sites. However, few studies have examined the spectral signatures of mine-affected waters and open pit water bodies from a remote platform. The motivation for this study was to identify the spectral characteristics of AMD in a controlled laboratory setting in order to better interpret mine water bodies in remote sensing imagery. The spectral response of synthetic and local AMD were measured using a field spectrometer. Solutions with increasing Fe3+ and Fe2+ concentrations were mixed to mimic the chemical properties of local AMD. Synthetic solutions with known Fe concentrations were compared with local AMD for quantitative assessment. The spectral signatures of Fe3+ dominated waters possessed distinct characteristics that may be used for diagnostic identification. Specifically, the region between 0.35 and 0.625 µm was used to approximately quantify Fe3+ concentrations. Subtle changes in Fe concentrations in local AMD were identified using a field spectrometer alone. These findings suggest that subtle changes in open pit water quality may also be qualitatively and quantitatively measured by remote sensing spectroscopy.

Exploration of Diffuse and Discrete Sources of Acid Mine Drainage to a Headwater Mountain Stream in Colorado, USA

Abstract: We investigated the impact of acid mine drainage (AMD) contamination from the Minnesota Mine, an inactive gold and silver mine, on Lion Creek, a headwater mountain stream near Empire, Colorado. The objective was to map the sources of AMD contamination, including discrete sources visible at the surface and diffuse inputs that were not readily apparent. This was achieved using geochemical sampling, in-stream and in-seep fluid electrical conductivity (EC) logging, and electrical resistivity imaging (ERI) of the subsurface. The low pH of the AMD-impacted water correlated to high fluid EC values that served as a target for the ERI. From ERI, we identified two likely sources of diffuse contamination entering the stream: (1) the subsurface extent of two seepage faces visible on the surface, and (2) rainfall runoff washing salts deposited on the streambank and in a tailings pile on the east bank of Lion Creek. Additionally, rainfall leaching through the tailings pile is a potential diffuse source of contamination if the subsurface beneath the tailings pile is hydraulically connected with the stream. In-stream fluid EC was lowest when stream discharge was highest in early summer and then increased throughout the summer as stream discharge decreased, indicating that the concentration of dissolved solids in the stream is largely controlled by mixing of groundwater and snowmelt. Total dissolved solids (TDS) load is greatest in early summer and displays a large diel signal. Identification of diffuse sources and variability in TDS load through time should allow for more targeted remediation options.

Assessment of Soil and Water Contamination at the Tab-Simco Coal Mine: A Case Study

Abstract: In 1996, the Tab-Simco site, an abandoned coal mine 10 km southeast of Carbondale, Illinois, was listed as one of the most highly contaminated AMD sites in the mid-continent region. A suite of impacted soil and water samples were collected from various locations to characterize the current extent of AMD pollution, following standard U.S. EPA protocols. The mean pH of soil and water samples were found to be 2.69 and 2.07, respectively. The mean sulfur content of the soil samples was 0.5 %. The AMD-impacted soils contained high concentrations of Fe, Zn, Ni, Cr, Cu, Pb, and As. The AMD also contained high concentrations of Fe, As, Zn, Pb, Cr, Al, Cd, Cu, and Ni, as well as $${\text{SO}}_{4}^{2 - }$$ , all of which were significantly above their U.S. EPA permissible limits for surface water.