Mine Closure Research Articles

What is good mine closure?

The ability to close and relinquish a mine is becoming increasingly important. Over the past few decades the mining sector has been promoting sustainable practices (Lohdia, 2018). But mine closure challenges the industry’s sustainability intentions. The mining industry’s peak body has made available a set of mine closure guidelines (e.g. ICMM, 2019). However, mining companies avoid closure by putting a mine under care and maintenance or selling the assets to smaller firms (Owen & Kemp, 2018). Abandonment of mines is common worldwide and is still occurring. The global problem of abandoned or improperly closed mines makes it clear that “it’s not over, when it’s over” (World Bank, 2002).

Experiences of mine closure cover with geosynthetics in Peru

Peru is internationally recognized as one of the countries with significant mining reserves. According to the Department of Energy and Mines (MINEM), as of December 2021, a total of 672 mining concession holders were registered and declared in the Monthly Statistical Declaration (ESTAMIN). Likewise, 44 mining concessions are in the closure stage (progressive, post-closure and final). In addition, Peru has 7956 Mining Environmental Liabilities (MEL) as of 2020, according to the inventory approved by the Department of Energy and Mines, which need to be remediated as they constitute a permanent and potential risk to the health of the population, the surrounding ecosystem and property. As part of the closure of these MEL and closure of some mining components, the use of geosynthetics has increased in Peru, and we speak specifically of the closure cover in slopes, platforms, sidewalks and others, which has become relevant as an alternative solution for soils selected as part of a traditional closure, the objective of this work is to present a series of experiences of the application of geosynthetics in mine closure covers, which intervene in the physical, geochemical and hydrological stability. It is worth mentioning that geosynthetics have been applied in Peru for more than 30 years in mining projects.

The methodology for mine closure with geosynthetics applied in Brazil

Industrial and mining activities, exploring and processing minerals, often require specific treatment processes to avoid the generation of contaminants, as is the case with acidic waters, resulting from the contact of precipitation with the material to be treated. Therefore, closure projects are carried out, which require environmental treatment, a covering, so that the structure can be integrated into the environment. Therefore, there is a need to find alternatives to conventional systems for using natural materials for closing covers, due to the magnitudes involved in these projects, as well as the scarcity of natural material, considering the use of geosynthetics for this type. of solution. Thus, it is demonstrated how geosynthetics work in these structures, providing chemical, physical and biological stability to the scenario where it can often be an arduous task to ensure them with conventional solutions, resulting in an advantageous solution in technical and economic terms. Such factors are demonstrated methodologies developed for the application of geosynthetics used in coverage, which led to the elaboration of several projects to be carried out in Latin America in recent years, with practical examples completed in Peru. In this scenario, aiming to expand the application of the methodology, its peculiarities are addressed, aimed at application in tropical countries where, typically, there are effects generated by excessive precipitation, one of the main adverse agents to be considered, as is the case in Brazil.

Salt exploitation by dissolution – an alternative method to reduce post-closure risks

During the last century, the mine closure frequency had significantly increased, therefore important environmental issues affect the public safety and the sustainable development process of the mining areas. The customary method of salt exploitation by dissolution uses the flooding of the formed caverns as the last step of the exploitation, which permanently isolates the caverns. In this case the rock-mass equilibrium inside the cavern changes, calamities such as seismicity, subsidence and collapse occasionally occur. Quite a few times, human settlements, civil buildings or industrial constructions located at the surface are affected. The present paper discusses adopting an alternative salt exploitation method by dissolution which offers the possibility to extract the entire salt deposit. This allows monitoring the stability factors linked to the exploitation process - the collapse that will occur as monitored represents the latter part of the method. It finally offers the opportunity to reclaim the water surface formed as a sustainable development goal and to reduce the long-term risks for calamities.

Meso-level planning for mine closure and transition: How do we optimise closure benefits and minimise risk at the regional scale?

Mining activity can have small geographic footprints compared to the significant economic, employment, and environmental impacts that are experienced at a much larger scale. Likewise, the closure of these mines can lead to regional-scale transformations in economic and sociodemographic structure that exhibit cumulative or interactive effects with regional trends (Haggerty et al., 2018; Syahrir et al., 2021). Yet regional- or meso-level planning and regulation of mining activity and mine closure is often overlooked as extractive industries are typically regulated at state, provincial or national levels, with local oversight typically limited to where the mine is located (Lobao et al., 2009). Regional-level analysis also must include a diversity of rightsholders and stakeholders that may be impacted differently and with varying levels of influence or agency over how economic futures are defined (Monosky and Keeling 2021; Roemer and Haggerty, 2021).

A rapid dual-drive technology for extinguishing large high-gas coal mines fires

Fires formed by the high gas protrusion in coal mines are difficult and risky to extinguish during the mine closure process due to the mine’s large closed range and underground gas stock. To achieve efficient and safe unsealing, reduce the risk of re-ignition and gas explosion, and accurately determine the fire extinguishing effect, a dual-drive rapid fire extinguishing technology is proposed. This technology involves ground precise positioning of drilling holes, rapid and large flow of liquid nitrogen injection, and curtain grouting to block fires in ultra-large high-gas mines. The practical results demonstrate that the implementation of surface injection of liquid nitrogen for fire extinguishing and cooling, and plugging effectively reduces the concentration of CO in the underground space from 230 PPm to 0 PPm, and decreases the CH4 concentration content from 90% to less than 0.75%. The fire extinguishing and cooling effect is fast and significant. A technical scheme for unsealing the fire area of the whole mine is formulated on a large scale based on the state of pumping and releasing pressure in the closed space of the mine. This scheme has important guiding significance for safety rescue and rescue operations after serious fire accidents occur in similar high-gas prominent mines.

Multi-criteria analysis of deep pits sustainable development strategy

Relevance. Long periods of development of steeply dipping deposits necessitate multiple adjustments of mining and technical system throughout an open pit life cycle. The decisions made determine the development strategy of a mining enterprise for a long period. The complexity of making such strategic decisions depends on numerous influencing parameters. These parameters have a different impact, have a variety of units of measurement, target values, and are not only quantitative but also qualitative. There is a need for new approaches to the choice of development strategy of the mining and technical system of an open pit, as well as its main subsystem – the opening-up of an opencast system. It is proposed to base these approaches on multi-criteria decision-making methods that consider many influencing parameters. Aim. Development of a methodology for choosing a strategy for sustainable development of the deep open pit mining and technical system based on multi-criteria decision-making methods and assessment of the opening system parameters. Objects. Mining enterprise, mining and technical systems, opening system. Methods. Literature review, system analysis, multi-criteria decision making. Results. The authors have determined the main strategies for development of the mining and technical system for deep open pits. These strategies aim at achieving the sustainable development of the mining and technical system: adjustment of the current stage mining parameters; transition to a new stage of mining; transition to a combined open-underground mining; mine closure. The key role of the opening system in the structure of the mining and technical system is substantiated to ensure its sustainable development. The authors systematized the main parameters for evaluating the pit opening system and set target values for each parameter. A review of the main multi-criteria decision-making methods used to solve various problems in the mining industry is made. A rank coefficient is proposed for choosing the mining and technical system development strategy. The calculation of this coefficient is based on a combination of the fuzzy AHP and CRADIS multi-criteria methods. A method was developed for selecting a strategy for sustainable development of the mining and technical system of deep open pits. A case study was conducted on the conditions of the Maly Kuibas open pit. The obtained results strongly suggest that the best strategy with the highest ranking is the transition to the combined development method.

Hydrodynamic Groundwater Modeling and Hydrochemical Conceptualization of the Closure Mining Area of the WuMa River Watershed of China.

The WuMa River (WMR) watershed is located in Renhuai City, Guizhou Province of China, which is a first-class tributary of the Chishui River. The geochemical investigation mainly included the determination of groundwater pH, total hardness, total dissolution solid, major cationic and anionic, and the geochemical groundwater modeling. The principal component analysis (PCA) and Gibbs model were used to analyze the pollution type and geochemical composition. The geochemical investigation results show that the cations of groundwater are dominated by Ca2+ and the anions are dominated by HCO3-; therefore, two main hydrochemical types in the study area are identified as Ca2+-Mg2+-HCO3- and Ca2+-Mg2+-SO42-. The chemical composition of groundwater in this area is mainly controlled by weathering of the carbonate rocks. The ion concentration of groundwater in the study area exhibited significant spatial variability between dry and wet seasons, while temporal changes of cationic and anionic concentrations exhibited irregularities. In PCA and FA analysis, PC1, PC2, and PC3 were extracted, which could explain 51.92, 26.98, and 12.61% of the total information, respectively. F1 explained 67.44% of the total variance, among which Ca2+, Mg2+, K+, SO42-, and Cl- contributed the most among the factors and were the main factors controlling the chemical composition of groundwater. The relative error between the measured water level and the simulated water level is less than 2%, which meets the requirements of simulation accuracy. During the simulation period of the model, a total recharge of 339.05 × 104 m3 was observed in the simulated area, primarily attributed to infiltration from rainfall. The total excretion amounted to 330.78 × 104 m3, primarily through evaporation, with a minor amount of lateral outflow. The migration pathway of pollutants in groundwater primarily follows the direction of groundwater flow while diffusing vertically. The migration range of the pollutant is in accordance with the direction of groundwater flow and extends along the larger hydraulic gradient, demonstrating consistency. The findings of this study serve as a reminder that the closure of coal mines can constitute a significant source of water pollution. Simultaneously, they offer empirical data and theoretical references for the simulation and prediction of groundwater contamination in enclosed coal mines.

Co-Benefits Analysis of Coal De-Capacity in China

China is the world’s largest carbon emitter and coal de-capacity is a policy with immediate and substantial CO2 reduction effects. However, the carbon emission reduction and health co-benefits arising from the coal de-capacity are often ignored. Here, we assessed the carbon emission reductions and quantified the health co-benefits from coal de-capacity based on an analysis of the spatial and temporal distribution characteristics of the mine closures and phase out during 2016–2022. Our findings show that China had closed/phased out a total of 4027 mines with a total de-capacity of 8.75 × 108 t, spatially concentrated in Southwest and North China from 2016 to 2022. The coal life cycle emitted 1859 million t of carbon during the coal de-capacity. Importantly, 11,775 premature deaths were avoided during 2016–2022 due to reduced PM2.5 exposure as a result of coal mining. This study highlights the significant effects of coal de-capacity on carbon reduction and health co-benefits in China and provides scientific evidence and data to support the achievement of the sustainable development goals and the ‘dual carbon goals’.

Best Practices in Mine Closure: A Case Study of Cultural Ecosystem Services in the Kenyan Mining Sector

Mining operations leave behind quarries with inhospitable conditions, characterized by steep drop-offs, deep water, flooding and poor drainage, and in some cases, abandoned industrial waste. Increasingly, innovations in mine closure and ecological restoration are integratinghuman activities into post-project land uses. Drawing from the Bamburi Haller Park, a former limestone quarry, this study demonstrates that with suitable environmental practices and policy interventions, mine closure can lead to positive projects that spur economic and social benefits. As a policy tool, this paper examines cultural ecosystem services (CES) as part of best practices in mine closure and mine restoration. Visitation data and revenue records were collected covering the period from 2014 to December 2018. Results show that over 566 hectares are now under various land uses with 56.51 per cent of the quarry having been ecologically rehabilitated. The site attracted over 181,000 visitors annually with an average annual revenue of US$330,745 from CES, including ecotourism, recreation and sports and environmental and conservation education. CES can form a strong foundation for promoting ecosystems restoration, biodiversity conservation and sustainable land use activities while showcasing best practices in environmental social governance. The resulting ecosystem is a unique model and showcase for sustainable and responsible mine closure in the extractive industry.

Dianthus sylvestris subsp. sylvestris as a promising candidate for phytostabilization of copper-contaminated post-mining sites in Alpine ecosystems.

The lack of remediation of inactive mine sites is a serious global concern, as they pose risks to the environment, human health, and safety. The potential of Dianthus sylvestris subsp. sylvestris to remediate post-mining sites contaminated with copper (Cu) at high altitudes, which is a challenging task for most management strategies, was explored in this study. More than 1300 mg Cu kg-1 in shoots were found in plants collected at the Monte Avanza legacy mine site (Alps). However, it is unclear whether this is due to hyperaccumulation or foliar contamination. To address this gap, field samples were washed with two different protocols, and a controlled Cu-tolerance test was conducted. While very high Cu concentrations, exceeding the Cu hyperaccumulation threshold of 300 mg kg-1, were found in samples washed with water, results for the plants cleaned with a more rigorous approach with EDTA suggested Cu exclusion strategy. Under controlled conditions, the plant showed Cu hypertolerance but did not hyperaccumulate Cu. Thus D. sylvestris presents a Cu exclusion strategy rather than hyperaccumulation potential, making it a suitable candidate for Cu phytostabilization at high altitude legacy mine sites. The study emphasizes the need for experiments under controlled conditions when assessing the phytoremediation potential.

Advancements in Mine Closure and Ecological Reclamation: A Comprehensive Bibliometric Overview (1980–2023)

Faced with the ongoing energy transition and the escalating fragility of our natural ecosystems, ecological reclamation emerges as an imperative necessity. Investigation within this field has been in progress since the early 20th century. To gauge the advancements in this realm, elucidate the evolving research trends, and emphasize pertinent metrics, it is essential to perform a comprehensive overview of the subject. Undertaking this bibliometric study is necessary to clarify research’s current state of play, grasp research hotspots, showcase outstanding researchers, and predict future research trends. In this work, 40,386 articles were retrieved from the Scopus and Web of Science databases, and bibliometric analysis was carried out using the Biblioshiny R package (Version 4.0.0, K-Synth Srl, Naples, Italy), and Python (PyCharm Community Edition 2023.2.1)o understand the progress in this research field from 1980 to 2023. The findings reveal a consistent upward trend in the publication rate within the field of mine closure and ecological reclamation over this timeframe, culminating in 6705 articles by 2022. Notably, authors and institutions from China have taken the lead, followed closely by those from the USA and Canada in terms of article publications. This prominence can be attributed to these countries’ rapid economic growth and energetic transition, which has frequently come at the expense of environmental quality, and a rise in reclamation challenges. In this sense, the circular economy has risen in force recently, which highlights the withdrawal of the old linear economy. In coming research on mine closure and ecological reclamation, multi-scale ecological reclamation research should be reinforced, and social and economic concerns should be integrated. This study pinpointed current research hotspots and forecasted potential future research areas, providing a scientific baseline for future studies in mine closure and ecological reclamation.

Assessing economic vulnerability in South African municipalities: A focus on mining-dependent regions using the Economic Complexity Index

South Africa’s historical reliance on mineral resources has established thriving towns and settlements, sustaining households for decades. However, the decline in demand for these resources and mine closures pose significant threats to the future of these areas, creating vulnerabilities in towns and their dependent regions. This article addresses concerns about the vulnerability of certain South African municipalities, particularly those heavily dependent on mining. Employing an Economic Complexity Index (ECI), the study identifies and classifies vulnerable mining towns and regions. The methodology involves applying the concept of economic vulnerability, utilising sub-national economic and trade data to determine the complexity of municipal economies. In addition, geospatially linked data is employed to identify mining-dependent areas at risk. The results highlight municipalities with low economic complexity, signalling the need for targeted interventions and emphasising the importance of economic diversification in mitigating risks. The study not only serves as a warning for current planning, but also lays the groundwork for future research and evidence-based policymaking to ensure the sustainability and resilience of regional economies in South Africa.

Vegetation change on mine sites in the most arid part of the Succulent Karoo Biome and their implications for mine closure

Restoring biodiversity is an important component of mine site rehabilitation. It needs to be evaluated regularly to assess success or failure of restoration methods and compliance with mine closure completion criteria. Yet vegetation dynamics in the driest part of the Succulent Karoo Biome are poorly understood. This study contributes to the question whether succession theory applies in this ecosystem by investigating 40 sites in a completely altered mining landscape and accompanying reference sites in the southern Namib within a 17-year time interval. Plant cover and species composition of the same site were compared between a field survey in 2005 and 2022. Multivariate analyses indicated that the importance of investigated environmental variables shifted between the survey periods, affecting the secondary vegetation on altered landforms as well as the undisturbed reference sites. This complicated the interpretation of perceived changes between the 2005 and 2022 surveys, making it difficult to detect successional trends. A drying of the general area is indicated which reduced species richness and cover overall and may have precipitated a change in habitat from stabilised to shifting dunes with concomitant changes to more sand-tolerant species in the southern part of the study area. These changes in both natural and secondary vegetation pose challenges when deciding on appropriate measures for restoration monitoring and setting completion criteria for mine closure.

What is the experience with governance models that manage and engage diverse stakeholders through a closure transition?

Traditionally understood in technical, environmental and (to a lesser extent) socio-economic terms, mine closure and transition is increasingly recognized as a significant governance challenge. Governance, in this context, refers not merely to the legal aspects of mine reclamation or closure regulation but rather the broader suite of actors, institutions, processes, methods, rules and practices that guide and oversee mine site transitions. Governance structures, interactions and practices are shaped by power relations as well as reflecting embedded norms and values. Since the 1980s, mine closure governance has expanded from a preoccupation by industry and governments with hazard mitigation, environmental reclamation and, in some cases, economic and social ‘adjustment,’ to encompass a wider set of social, economic and environmental aspects of closure (Kendall 1992; Laurence 2006). These issues may affect workers, local and regional development agencies, Indigenous rightsholders, fenceline communities and environmental advocates, among others (Bainton and Holcombe 2018; Everingham et al. 2020). This broad range of actors and issues, in turn, has generated reactions and responses from individual companies, industry associations and governments at all levels seeking to mitigate closure and transition impacts (Morrison-Saunders et al. 2016; Owen and Kemp 2018; Hodge and Brehaut 2023).

Life cycle assessment of coal mines of diverse scales over time in China

Coal mining has important detrimental effects on the environment and human health. By the end of 2022, China mined more than 4 billion tons of raw coal, and coal mining contributed to adverse environmental impacts. The objective of this work is to evaluate the environmental impacts emanated from coal mines in different periods (construction period, production period and closing period) and to find the relationship between coal mine scale and ecological impacts. This study uses coal mines that produce 0.45 Mt/a (considered a medium sized mine), 3 Mt/a and 8 Mt/a (both classified as large mines in this study) and a 12 Mt/a extra-large coal mine. Based on the time dimension, the mine life cycle was classified into construction, production and closing period, and the life cycle assessment method was used to conduct environmental assessment. The main influencing substances and key processes were tracked. The results indicated that mining engineering and gangue are the main factors affecting the construction and production periods of coal mines. Freshwater ecotoxicity, marine ecotoxicity, and human toxicity are the main environmental effects of coal produce, and they are mostly brought up by the release of hazardous elements like copper, chromium, zinc, nickel, and copper. Furan, formaldehyde, and chromium emissions during mine closure can be effectively reduced through environmental compensation, however coal mines' environmental compensation during mine closure is minimal. The environmental impact of coal mines producing 3 Mt and 8 Mt annually is minimal. The environmental impact of 0.45 Mt/a and 3 Mt/a coal mines is more prominent in the construction period. The pollutant discharge throughout the production phase, particularly the metal leaching discharge from gangue, needs to receive more attention from the 8 Mt/a and 12 Mt/a coal mines. Additionally, the larger the scale of coal mine production, the greater the proportion of the total environmental impact in the production stage.

Assessment of Heavy metal pollution and its health implications in groundwater for drinking purpose around inactive mines, SW region of Cuddapah Basin, South India

Assessment of Heavy metal pollution and its health implications in groundwater for drinking purpose around inactive mines, SW region of Cuddapah Basin, South India

NUMERICAL MODELLING TOXIC SUBSTANCE TRANSPORT IN MINE WATER FLOWS

The purpose of this work is to develop and test a methodology for modelling the migration of toxic substances left after mining in mine water flows in a system of hydraulically connected mine workings of various sizes and elevations depending on the drainage parameters. Methods of research include the analysis of factors that influence the formation of the hydraulic regime in flooded mines, the accumulation and transport of toxic substances. Parameters of moving toxic substances in mine waters are calculated using hydraulic flow equations written for mining workings, with flooded workings being considered as pipelines with distributed recharge. Modelling of non-stationary 1D transport in water from local sources of toxic substances was performed using the finite difference method. Results. Flow rates and velocities in flooded mine workings on two hydraulically connected horizons of different elevations were calculated. For different locations of sources of toxic substances on the example of polychlorinated biphenyls, their concentrations in mine waters along the migration path and at the water hoisting at different flow rates were calculated. The influence of increased water withdrawal, dilution with additional recharge along the migration path and the position of potential sources of substances in the flooded mine were investigated. It wasshown that for the considered example, increasing the water outflow rate by two times accelerates the stabilisation of mass transport with an increase in the daily removal of substances by 3.4–6.4 times, which is more active from the upper horizon. Scientific novelty. For the first time, the transport of substances in flooded workings was simulated by combining a hydraulic flow model with a numerical transport model. Unlike 2D and 3D numerical transport models based on solid mechanics, which average the concentration in the grid blocks, the proposed approach allows the reproduction of the geometry of the mined-out space more accurately. It provides a more realistic distribution of flow velocities and concentrations depending on the parameters of the mine water withdrawal, depth of mine workings, and the mine water level. Practical significance. Using the tested methodology will make it possible to perform engineering predictions of the quality of groundwater and surface water near closed mines for different periods at different levels of flooding, water withdrawal rates and depths of the pumps for mine water drainage. In addition, the proposed technique can be used to justify the conceptual scheme of the numerical hydrogeochemical model of the post-mining areas. Keywords. Close mines, toxic substances, flooded workings, hydraulic flow, water hoisting, transport model.

Irrigation Should be Explored as a Sustainable Management Solution to the Acid Mine Drainage Legacy of the Witwatersrand Goldfields

Mine closure in the Witwatersrand Goldfields of South Africa has resulted in an acid mine drainage (AMD) legacy that is difficult to manage and costly to address. As a short-term measure, three large high-density sludge (HDS) plants were erected that treat 185 megalitres of AMD per day (ML/day), at great cost to taxpayers. Longer-term solutions are sought, as the salt load to the Vaal River System is unacceptable. Long-term modelling was used to assess whether the untreated and HDS-treated AMD could be used for irrigation and to determine the scale of the potential opportunity. The Goldfields waters are not very acidic, and simulations indicate it should be feasible to utilise even the untreated water for irrigation, especially if growers commit to applying limestone to their fields. HDS treatment lowers the corrosivity and trace element concentrations, and because the water is gypsiferous, double cropping will precipitate more than a third of the salts in solution as gypsum in the soil profile, thereby reducing salt load to the water environment. The potential irrigated area depends on the cropping system; it is about 9000 ha for rotational cropping and 30,000 ha for supplemental maize irrigation. It is prudent to seriously consider irrigation as a potential long-term water management option for the Goldfields AMD.

Wastes in Underground Coal Mines and Their Behavior during Mine Water Level Rebound—A Review

Backfill materials of various origin and composition, abandoned machinery, oils, PCB, gallery support material and cables are the main wastes occurring in underground coal mines during the period of their abandonment. Bearing in mind that under increasing societal pressure most if not all underground coal mines are going to close sooner rather than later, it is important to understand the interactions of these waste materials with rising mine water during mine water level rebound to prevent adverse environmental effects, especially on surface and groundwater. To this end, the composition of mine water at decant points as well as the hydrogeochemical, temporal and spatial dynamics of mine water during rebound requires quantification. In the first part of this paper, an overview of waste materials in underground coal mines is presented. The second part focusses on the experiences gained in the Ruhr area, a closed underground coal mining region in western Germany, where mine water rebound has been ongoing for decades. In this regard, the mine water modeling program Boxmodell was applied during regulatory approval procedures to predict the hydrodynamics and hydrogeochemical development of the water rebound. The results of these investigations allow deep insights into the interactions of rising mine water with wastes as well as the complex chemical evolution of mine water and potentially occurring contaminants (e.g., PCB). The experiences regarding wastes in underground coal mines and the geochemical evolution of rising mine water gained in the Ruhr area can be utilized to support the planning of mine closure in currently still active underground coal mining areas worldwide.