Mine Waste Disposal Research Articles

ANALYSIS OF WATER QUALITY DETERIORATION IN NWORIE RIVER, OWERRI- IMO STATE, SOUTHEAST, NIGERIA

Due to indiscriminate activities of man through sand excavation, sand mining and illegal waste disposal within the watershed the study evaluated the effect of these activities on selected water quality parameters of Nworie River in Owerri -Imo State, Southeast Nigeria. The study area was divided into Upstream, Midstream and downstream. The river was sampled and the raw data from water sampling were subjected to laboratory analysis; results obtained were matched with standards. The results showed that the average pH of the river was 7.4; upstream and midstream had higher pH values than the downstream with low pH and these were within the permissible limit. Biological oxygen Demand (BOD) of the river were 75mg/l, 60mg/l and 56mg/l at the Upstream, Midstream and downstream with an average value of 64 mg/l . The river had a mean turbidity value of 76NTU and mean Total Dissolved solids (TDS) value of 272mg/l which were above the permissible limit. Calcium (Ca2+) did not exceed the standard limit while magnesium exceeded the standard limit by 68% at the Upstream. Nworie river had mean water conductivity value of 93S/cm; water conductivity at the Midstream and downstream were within the permissible limits while the Upstream had 6% increase above the acceptable limit. It was observed from this study that Nworie river exhibited three different colours of light-green, dark-green and brownish-muddy colour respectively at the Upstream, Midstream and Downstream which could be attributed to the level of erosional deposits and sediment loads from the degraded watershed. Further degradation of the watershed should be avoided by practising good soil conservation measures, ensuring that indiscriminate activities of inhabitants of the area are stopped and since environmental balance, land degradation, water management and food security are strongly linked, each must be addressed in the context of the other to have a measurable impact to the society.

Effect of crossflow on trapping depths of particle plumes: laboratory experiments and application to the PLUMEX field experiment

The fate and transport of sediment plumes in the ocean, such as those resulting from the disposal of deep-sea mining residuals, are affected by ambient crossflow. We present laboratory measurements of the depth at which a particle plume is trapped by ambient stratification for various crossflow and particle settling velocities. Results suggest that the trap depth declines exponentially with crossflow velocity but is relatively insensitive to settling velocity in the range studied. An empirical correlation based on the laboratory data is validated by a larger scale field experiment involving simulated disposal of deep-sea mining wastes.

Combining Satellite InSAR, Slope Units and Finite Element Modeling for Stability Analysis in Mining Waste Disposal Areas

Slope failures pose a substantial threat to mining activity due to their destructive potential and high probability of occurrence on steep slopes close to limit equilibrium conditions, which are often found both in open pits and in waste and tailing disposal facilities. The development of slope monitoring and modeling programs usually entails the exploitation of in situ and remote sensing data, together with the application of numerical modeling, and it plays an important role in the definition of prevention and mitigation measures aimed at minimizing the impact of slope failures in mining areas. In this paper, a new methodology is presented; one that combines satellite radar interferometry and 2D finite element modeling for slope stability analysis at a regional scale, and applied within slope unit polygons. Although the literature includes many studies applying radar interferometry and modeling for slope stability analysis, the addition of slope units as input data for radar interferometry and modeling purposes has, to our knowledge, not previously been reported. A former mining area in southeast Spain was studied, and the method proved useful for detecting and characterizing a large number of unstable slopes. Out of the 1959 slope units used for the spatial analysis of the radar interferometry data, 43 were unstable, with varying values of safety factor and landslide size. Out of the 43 active slope units, 21 exhibited line of sight velocities greater than the maximum error obtained through validation analysis (2.5 cm/year). Finally, this work discusses the possibility of using the results of the proposed approach to devise a proxy for landslide hazard. The proposed methodology can help to provide non-expert final users with intelligible, clear, and easily comparable information to analyze slope instabilities in different settings, and not limited to mining areas.

Submarine Tailings in Chile—A Review

This review aims to understand the environmental impact that tailings produce on the land and marine ecosystem. Issues related to flora, fauna, and the environment are revised. In the first instance, the origin of the treatment and disposal of marine mining waste in Chile and other countries is studied. The importance of tailings’ valuable elements is analyzed through mineralogy, chemical composition, and oceanographic interactions. Several tailings’ treatments seek to recover valuable minerals and mitigate environmental impacts through leaching, bioleaching, and flotation methods. The analysis was complemented with the particular legislative framework for every country, highlighting those with formal regulations for the disposal of tailings in a marine environment. The available registry on flora and fauna affected by the discharge of toxic metals is explored. As a study case, the “Playa Verde” project is detailed, which recovers copper from marine tailings, and uses phytoremediation to neutralize toxic metals. Countries must regularize the disposal of marine tailings due to the significant impact on the marine ecosystem. The implementation of new technologies is necessary to recover valuable elements and reduce mining waste.

ПЕРСПЕКТИВЫ РАЗРАБОТКИ МЕСТОРОЖДЕНИЙ ОСЕТИИ

Goal. Substantiation of the ecological and economic efficiency of innovative technologies for the development of deposits of the Sadonsky ore cluster during the period of restoration of the lost industrial potential of the depressed region. Methods. Analysis of the theory and practice of mining, with priority given to the experience in the development of North Caucasian deposits. Laboratory experiment in the study of the properties of filling mixtures and options with different activation methods, including reagent leaching in a disintegrator. Mathematical and economic modeling of the efficiency of recycling tailings utilization at the cost of commercial products, taking into account the prevented environmental damage. Results. The information on the dynamics of mining and processing of ores from the Sadonsky deposits is presented. The results of studies of the properties of base concrete mixtures based on ore dressing tailings and local available components are systematized and generalized. The results of changes in the properties of hardening mixtures are given depending on the presence of metals in the tailings of enrichment with various activation options by alternative methods, including an innovative method of mechanochemical leaching in a disintegrator with electrochemically activated water. The equivalent of 1 kg of cement using binders from processing tailings has been determined. The advantages of mechanochemical activation of tailings in a disintegrator in comparison with the option of irrigation by irrigation using various reagents have been experimentally determined. A quantitative indicator of an increase in the strength of the compositions of hardening mixtures under equal conditions has been established. The efficiency of utilization of tailings and metallurgy has been determined as a set of effects of reducing the amount of environmental damage from storage of tailings, the cost of metals obtained during processing, raw materials for the construction industry and associated marketable products. The nomenclature of tailings processing products has been detailed. A model for determining the profit from processing tailings and metallurgy is recommended. A forecast is given at the level of engineering expertise of the prospects for tailings processing. The hardware diagram of the tailings disposal section is detailed. A universal scheme for the disposal of mining and processing waste was recommended. Conclusion. The prospects for the development of the deposits of the Sadonsky ore cluster depend on conversion to technologies with filling voids with solidifying mixtures and leaching of metals at the processing stages. The combined mining technology will reduce the output of tailings, strengthen the base of the construction industry, eliminate the need to build a second stage of tailings and improve the environment.

Circle Economy in Mining Industry-Hydraulic Backfill Use in Velenje Coal Mine

Adverse impacts on human environment are growing daily. Possible new locations for mining activities in Slovenia and worldwide are becoming very scarce. Particularly sensitive issue usually is to find appropriate location for disposal of mining waste, generated by process of excavation and processing/transformation of metal/non-metal minerals and coal. By establishing of closed ecological and technological circle of winning, processing or energy transformation and returning mining waste materials into excavated open space it is possible to organize environment friendly, sustainable metal/non-metal/coal mining or circle economy in mining industry. By depositing mining waste into underground space, earth surface can be disburdened. Suitable location should take existing natural barriers into account otherwise technical measures have to be taken to protect surrounding formation against adverse impact. Essential conditions for underground mining and processing or transformation mining waste depositing is reliable and durable protection against spreading of adverse impact of deposited waste materials into surroundings, particularly in hydrosphere. For this, natural and/or technical barriers should be thoroughly used. The good results of this research should assure by selection of appropriate waste materials mixtures preparation, transport and deposition by proper technology, future mining to be ecologically sustainable/green and economically effective. A brief outline of backfilling by thick suspension mixtures performed in Velenje coal mine will be presented.

Sulfate-induced changes in rheological properties of fibre-reinforced cemented paste backfill

Cemented paste backfill (CPB), a soft concrete-like material, is extensively used in underground mines worldwide for ground support and/or mine waste disposal. One of the most important ingredients in CPB is cement but it is expensive and can amount to 75% of the cost of the CPB. Therefore, CPB reinforced with fibres has been proposed and introduced in backfill operations to reduce the overall cement usage and cost, as well as improve the mechanical performance of CPB. However, the rheological properties of fibre-reinforced CPB and the factors that affect them are not well understood. The objective of this study is to therefore evaluate the effect of sulfate, which is commonly found in CPB, on the yield stress and viscosity of fibre-reinforced CPB through a series of experiments. The results show that the yield stress decreases with an increase in the initial sulfate content, while the viscosity increases as the sulfate content is increased. The sulfate ions significantly affect the amount and type of cement hydration products that form in the backfill matrix as well as the zeta potential of the fibre-reinforced CPB. The presented findings will contribute to improve the design and optimisation of backfill transport systems.

Integration of Environmental Information in a Mining Region Using a Geoportal

At present, the complex nature of the impact on the ecosystem in regions with intensive mining creates a multidimensional information “plume” consisting of data on mineral reserves, the state of mining operations, accumulated, current and future environmental pollution. The transition to the lean use of the subsoil and the reasonable disposal of mining waste requires fundamentally new forms of environmental information accumulation and processing during designing new enterprises and regulating the activities of existing ones. The most promising form of information support for the greening of mining is a geoportal. It is a complex of software and technological support for working with spatial data. Its key task is to provide the users with tools and services for storing and cataloging, publishing and loading spatial and environmental data, searching and filtering by metadata, interactive web visualization, direct access to geodata based on map web services.

Thermal conductivity models of sandstone: applicability evaluation and a newly proposed model

The thermal conductivity (TC) of rock has a general application in safety assessment and engineering optimization of deep geological engineering practices such as geothermal mining and nuclear waste disposal. Determining the TC of rock by using a TC model is a convenient and effective method for such evaluation, and selecting a suitable TC model is key for ensuring accurate calculation results. In this study, we firstly select eight two-phase TC models to evaluate the applicability to sandstone. Secondly, the TC values of sandstones in various porous media such as air, water, and ice are measured by using the transient plane source (TPS) method, and the mineral composition and content were determined by using X-ray diffraction (XRD) and the Cross, Iddings, Pirsson, and Washington (CIPW) norm. Thirdly, the TC values of sandstones in different porous media are also calculated by using the eight models, and their deviations are analyzed to compare their applicability. Finally, by considering of the influence of pore structure on the rock TC, a new TC model referred to as the thermal resistance–connectivity (TRC) model is proposed for sandstone based on pore connectivity, and the mean deviation is compared with the previous model. Several results are obtained. Among the eight common models, the geometric mean model is found to be more accurate than other models regardless of all three states. In particular, for the porous medium filled with ice, the calculated value of the Geometric mean model had the most significant agreement with the measured value. In addition, the mean deviation of the TRC model for all three states is shown to be more consistent with the measured value than the eight models. Therefore, we recommended the TRC model for calculating the TC of sandstone. This study provides a novel method for determining the TC value for deep geological assessment.

Mining Waste Challenges: Environmental Risks of Gigatons of Mud, Dust and Sediment in Megadiverse Regions in Brazil

The management of long-lived mining wastes is a complex environmental challenge, but the subject is little discussed among the public, scientific community, and policymakers. The negative environmental impacts caused by mining wastes are severe and cause damage to human health and the loss and degradation of natural ecosystems. With the objective of stimulating discussion to advance the development of measures to contain threats to biodiversity and to mitigate negative impacts, we present an overview of total volumes of mining waste disposal in tailings dams and dump piles, discriminating them by ore type and biome. We highlight the major environmental risks and challenges associated with tropical forests, savannas, and freshwater ecosystems and possible limitations and advances in public policies and governance. The scale of this challenge is global, as some data show, for example, Brazil generated 3.6 billion tons of solid mining waste in dump piles in the period between 2008 and 2019. The volume is equivalent to 62% of the global mass of nonfuel minerals removed from the planet’s crust in 2006. Numerous socio-environmental disasters are caused by catastrophic mining dam failures, and over the last 34 years, an average of one failure has occurred every three years in Brazil.

Assessment of environmental and resource-saving technologies and technical means for processing and disposal of man-made formations and waste

The object of research is environmental and resource-saving technologies and technical means for the processing and disposal of man-made formations and waste in the underground mining of mineral deposits with backfilling of the worked-out space. One of the most problematic areas is the management of the state of ore-containing energy-disturbed massifs and the delivery of hardening filling mixtures to the place of their laying, as well as the shortage of components for their preparation. This increases the importance of the management of the stress-strain state (SSS) of the rock mass, ensuring the safety of the earth’s surface from destruction and vital activity of the population living in the zone of influence of the mining region.The paper presents the main scientific and practical results of the substantiation of technologies and technical means for the disposal of mining and metallurgical waste into underground goaf (man-made voids) as components of hardening filling mixtures of various composition and strength. Methods of theoretical generalizations with the use of mathematical statistics, physical and mathematical modeling, with the implementation of calculations and feasibility studies, laboratory and field experimental studies, industrial tests in the conditions of operating enterprises of mining and metallurgical production are described. On the basis of the study of the mechanism of stress-strain state of a rock mass using geophysical and surveying methods, an environmental technology for extinguishing technogenic voids in energy-disturbed massifs is proposed. This technology makes it possible to ensure the safety of the earth’s surface and the vital activity of the population living in the zone of influence of mountain objects (mines, dumps, industrial sites for stowing complexes, tailings, ore-processing plants (OPP), etc.). It was found that for the mines of the state enterprise «VostGOK» (Ukraine), the utilization rate of own production waste for hardening backfill is from 0.45 to 0.68; hydraulic – from 0.56 to 0.75; free-flowing – 0.62, and the extraction of each ton of commercial ore is accompanied by the output of 0.7-0.8 tons of waste. An assessment of the utilization level of wastes of mining and metallurgical production is given and an inventory for wastes of mining enterprises is given, which gives an estimate and directions of their possible use for the needs of the national economy. The research results can be used in underground mining of complex ore deposits and mining and metallurgical production.

Acute exposure to environmentally relevant lead levels induces oxidative stress and neurobehavioral alterations in larval zebrafish (Danio rerio)

The ubiquitous contamination of environmental lead (Pb) remains a worldwide threat. Improper Pb mine waste disposal from an abandoned lead-zinc mine has recently unearthed widespread Pb poisoning in children in Kabwe Zambia. Although the adverse effects of Pb on human health have begun to receive attention, the ecotoxicological effects on aquatic vertebrates still need further investigation. In addition, there is paucity in the knowledge on the behavioural and molecular subcellular responses in larval zebrafish exposed to Pb within the range of environmental relevant concentration (average 3 μg/L with maximum of 94 μg/L) on aquatic organisms such as zebrafish. The adverse effects of environmentally relevant levels of Pb on larval zebrafish was evaluated by measuring swimming behaviour under alternating dark and light conditions. Larval zebrafish acutely exposed to environmentally relevant Pb exhibited neuro-behavioural alteration including enhanced hyperactivity under light conditions evidenced by increased distanced covered and speed compared to the control. The alteration of entire behavioral profiles was further associated with the disturbed expression patterns of mRNA level of key genes associated with antioxidant (HO-1, Ucp-2 and CoxI), proapoptotic gene (TP53), and antiapoptotic gene (Bcl-2). To our knowledge, this is the first report on the effects of environmentally relevant Pb levels from Kabwe, Zambia and their adverse neurobehavioural effects and subcellular molecular oxidative responses in larval zebrafish acutely exposed within a 30 min period. The current results would be beneficial in our understanding of the effects of low Pb levels acutely discharged into an aquatic environment and the life of aquatic organisms.

Upcycling of mechanically treated silicate mine tailings as alkali activated binders

Mining activity is inevitable in human societies, and thus, disposal of mining waste in a proper and effective way is crucial to preserving our environment. In this context, studies on the reuse potential for mine tailings in the construction sector are booming. However, utilizing tailings as binder material is complicated due to the high variation in mineralogical composition and the low reactivity of these materials. In this study, an attempt was made to understand the effect of mechanical treatment on silicate mine tailings in order to improve their properties for use as a sole precursor in alkali-activated binders. Two different silicate tailings from Finland were studied: one rich in tremolite, which is high in magnesium (HM tailings) and one rich in anorthite and epidote, which is high in aluminum (HA tailings). Interestingly, grinding activity performed at different durations affected the properties of the tailings with various intensities, including their mineralogical and physical properties and characteristics and, thus the reactivity of tailings. Tremolite does not respond to milling for longer durations, and layered anorthite was easily distorted by the mechanical disturbance. Irrespective of the type of tailings, the compressive strength of alkali-activated milled tailings increased with an increase in grinding time from 1 to 16 min. However, the percentage of compressive strength increase varied with the type of tailings and their mineralogy.

Substantiation of technologies and technical means for disposal of mining and metallurgical waste in mines

The object of research is environmental and resource-saving technologies in underground mining of mineral deposits with the laying of the developed space. One of the most problematic places is the delivery of hardening filling mixtures to the place of their installation and the lack of components for their preparation. This increases the importance of managing the state of ore-bearing massifs and the preservation of the earth’s surface.The paper presents the main scientific and practical results of the substantiation of technologies and technical means for the disposal of mining and metallurgical production wastes into underground mined spaces (man-made voids) as components of hardening filling mixtures. Methods of theoretical generalizations are described using mathematical statistics, physical and mathematical modeling, with calculations and feasibility studies, laboratory and field experimental studies, industrial tests in operating enterprises. It is established that the use of vibration, mechanical and electroactivation of the components of the hardening filling mixture in mining enterprises leads to an increase in the activity of substandard materials by up to 10–40 % for each device. In particular, the enrichment of substandard inert materials at the vibrating screen GV-1.2/3.2 (Ukraine) increases the activity by 15–20 %. It is proved that the activation of binders (blast furnace granulated slag) in the DU-65 disintegrator (Disintegrator, Estonia) increases the activity of the binder by 20–25 %, with the output of the active class of fractions of 0.074 mm in size – by 55 % versus 40 % in ball mills. Vibration transport unit are recommended, which increase the activity of the solid components of the hardening filling mixture by 10–15 %, and electrodialysis apparatus for activating mixing water increase its activity by 30–40 %. It is shown that the use of vibration gravity transport systems ensures the filling of the filling mixture at a distance exceeding the height of the vertical stand by 15–20 times. A set of technical means is proposed for activating the components of hardening filling mixtures (binder, inert aggregate and electrochemically purified mine mixing water) during the manufacture and transportation of them to the installation site. This complex was introduced at such mining enterprises as:– State Enterprise «Eastern Mining and Processing Plant» and Balaklava Mining Administration (Ukraine);– Joint-stock company «Tselinnyi Mining and Chemical Combine» (Republic of Kazakhstan);– Public Joint-Stock Company «Priargunsky Industrial Mining and Chemical Association» and Closed Joint-Stock Company «Uralzoloto» (Russian Federation) in other developed mining countries.

Mining in Papua New Guinea: A complex story of trends, impacts and governance

Mining is often portrayed as a contributor to sustainable development, especially so in developing countries such as Papua New Guinea (PNG). Since 1970, several large mines have been developed in PNG (e.g. Panguna, Ok Tedi, Porgera, Lihir, Ramu) but always with controversial environmental standards and social impacts often overlooked or ignored. In PNG, mine wastes are approved to be discharged to rivers or oceans on a very large scale, leading to widespread environmental and social impacts – to the point of civil war in the case of Panguna. The intimate links between indigenous communities and their environment have invariably been under-estimated or ignored, leading many to question mining's role in PNG's development. Here, we review the geology of PNG, its mineral resources, mining history, key trends for grades and resources, environmental metrics (water, energy, carbon), mine waste management, and regulatory and governance issues. The study provides a unique and comprehensive insight into the sustainable development contribution of the mining industry in PNG – especially the controversial practices of riverine and marine mine waste disposal. The history of mining is a complex story of the links between the anthroposphere, biosphere, hydrosphere and geosphere. Ultimately, this study demonstrates that the scale of environmental and social impacts and risks are clearly related to the vast scale of mine wastes – a fact which remains been poorly recognised. For PNG, the promise of mining-led development remains elusive to many communities and they are invariably left with significant social and environmental legacies which will last for decades to centuries (e.g. mine waste impacts on water resources). Most recently, the PNG government has moved to ban riverine tailings disposal for future projects and encourage greater transparency and accountability by the mining sector, including its interactions with communities. There remains hope for better outcomes in the future.

Electrical resistivity imaging for detection of hydrogeological active zones in karst areas to identify the site of mining waste disposal.

Hydrogeological active zones found in mine waste (tailings) dumping sites are a major source of concern that threatens the safety of the environment and groundwater, especially in karstic areas. Therefore, detecting and identifying these regions correctly will help in selecting the appropriate sites for tailings disposal and avoid consequential environmental problems. In this study, electrical resistivity imaging (ERI) surveys with high-resolution data were carried out to detect hydrogeological active zones in an area proposed as a settling pond for mining tailings accumulated from El Mochito mine property, located in the north-western section of Honduras. Two-dimensional (2-D) inversion results of thirty-four survey lines revealed several zones of low resistivity. These zones indicate water-/clay-bearing regions that are structurally weak. However, some survey lines, the limestone beneath the surface is entirely compacted; as such, it is considered to be an ideal site for tailings pond construction. In addition, on the eastern side of the valley, there is a large chunk limestone layer that is compacted and can be considered for tailings pond construction. The ERI method provided insight and developed an informative subsurface map to detect the hydrogeological active zones, thus proving it as a beneficial tool used for selecting disposal sites for mining tailings in karstic areas.

Environmental health perceptions in a superfund community

A disconnect between community perceptions and officially documented Superfund remedial actions and health outcomes may hinder the essential community engagement at Superfund sites. This study evaluates the extent of one such potential disconnect in Butte, Montana, which is part of the largest U.S. Superfund site in the U.S. Since the 1860s, when mining began in Butte, mine waste disposal practices in Butte and surrounding areas have left behind massive deposits that have contaminated the area's soil, sediment, groundwater and surface water with arsenic and heavy metals. Over the last four decades, a substantial amount of remediation work has been completed along with requisite community engagement and health studies at this Superfund site. The potential disconnect was evaluated using a new survey instrument that covered: (a) general environmental health perceptions, (b) mine-waste specific environmental health perceptions, (c) effectiveness of community engagement, (d) knowledge of health outcomes, and (e) demographics. The survey results demonstrated a disconnect in many instances where objective remedial improvements may not have resulted in improved environmental health perceptions in the community. The disconnect was most pronounced in the case of drinking water protection from mine waste and knowledge of health outcomes (cancer incidence rates and children's blood levels). The use of similar environmental health perception measurements may aid responsible agencies in monitoring for and addressing environmental health perception disconnects through better community engagement for the benefit of the impacted communities.

Increase in Pb and Cd Adsorption by the Application of Peat in a Tropical Soil

Clayey soils have been used as liners at the base of waste deposits due to their geotechnical characteristics and capacity to adsorb metallic cations. However, a number of soils may not possess all required properties to ensure contaminant retention and therefore require additives. This study investigated whether the addition of commercial peat to a tropical residual soil (from the Ribeira Valley, Brazil) could improve its lead (Pb) and cadmium (Cd) adsorption capacity for its use as a liner in mining waste disposal. Pure soil and 10 and 20% soil-peat mixtures were compared. The application of peat increased the organic matter (OM) content (from 9 g kg−1 in soil to 58 g kg−1 in the 20% soil-peat mixture) and the cationic exchange capacity (CEC) (from 41.4 mmolc dm−3 in soil to 143.1 mmolc dm−3 in the 20% soil-peat mixture). Batch equilibrium test results revealed that the maximum Pb adsorption capacity of 623.6 μg g−1 also increased (to 1089.1 and 1270.0 μg g−1 in the 10 and 20% soil-peat mixtures, respectively). The soil Cd adsorption capacity of 261.2 μg g−1 increased to 304.0 and 631.3 μg g−1, respectively, with increasing peat proportions. The results suggest that peat can improve soil liner performance in waste deposits. Soil-peat mixtures are alternatives for minimizing potentially toxic metal contamination with available and low-cost materials.

Effect of drying treatment on the leachability of metallic elements from weathered solid mine wastes

Leaching of toxic metallic elements (Cu, Zn, As, Cd, and Pb) from two solid mine wastes was characterized under different drying treatments. During 14 batch decant-refill leaching steps, samples were intermittently dried four times in 40 °C oven or −20 °C freezer. For all leachates, the pH, pE, Fe2+/Fe3+, and SO42− were analyzed. The parameters of the two-site model (kfast, kslow, and ffast) and labile fractions (F1 + F2) were determined. High levels of toxic metallic elements were determined in waste samples; however, their leaching was limited, as evidenced by the magnitudes of F1 + F2, ffast, and kslow. Leachate solutions were acidic, at pH 3–4, and oxic, at 150 mV < Eh 300 < mV, thus having negligible Fe2+. Leachate concentrations of toxic metallic elements increased (4–58%) after drying at 40 °C and were strongly correlated (r2 = 0.780) with those of sulfate in liquid phase. The mass of element elution was in the order of 40 °C drying > −20 °C drying ≥ continuous wetting. Results indicate that the element leachability is increased through drying events and the leachate concentration is associated with the dissolution reaction of sulfur-bearing minerals. Frequent occurrence of prolonged droughts along with high temperatures over the mine waste disposal site, can enhance the leaching potential of toxic metallic elements.

Realizing Beneficial End Uses from Abandoned Pit Lakes

Pit lakes can represent significant liabilities at mine closure. However, depending upon certain characteristics of which water quality is key, pit lakes often also present opportunities to provide significant regional benefit and address residual closure risks of both their own and overall project closure and even offset the environmental costs of mining by creating new end uses. These opportunities are widely dependent on water quality, slope stability, and safety issues. Unfortunately, many pit lakes have continued to be abandoned without repurposing for an end use. We reviewed published pit lake repurposing case studies of abandoned mine pit lakes. Beneficial end use type and outcome varied depending upon climate and commodity, but equally important were social and political dynamics that manifest as mining company commitments or regulatory requirements. Many end uses have been realized: passive and active recreation, nature conservation, fishery and aquaculture, drinking and industrial water storage, greenhouse carbon fixation, flood protection and waterway remediation, disposal of mine and other waste, mine water treatment and containment, and education and research. Common attributes and reasons that led to successful repurposing of abandoned pit lakes as beneficial end uses are discussed. Recommendations are given for all stages of mine closure planning to prevent pit lake abandonment and to achieve successful pit lake closure with beneficial end uses.