Application of a life cycle assessment to compare environmental performance in coal mine tailings management

Enhancing shear strength and handleability of dewatered clay-rich coal tailings for dry-stacking

Mineral tailings dams pose high pollution risks to the environment and catastrophic failures. Dry stacking has been identified as a promising alternative to mitigate these risks and offers various benefits to the mining industry but lacks systematic research outcomes. To facilitate dry stacking, coal tailings slurries were dewatered using either filtration or centrifugation methods, resulting in a semi-solid form (cake) that can be safely disposed of. The handleability and disposability of these cakes are greatly influenced by the selection of chemical aids (such as polymer flocculants) and the mechanical dewatering technique employed. The effects of polyacrylamide (PAM) flocculants with a range of molecular weight, charge, and charge density are presented. Coal tailings samples with differences in clay mineralogy were dewatered using press filtration, solid bowl centrifugation, and natural air drying. Handleability and disposability of the tailings were assessed by their rheological properties, including yield stress, adhesive and cohesive stresses, and stickiness. Residue moisture, type of polymer flocculants, and clay mineralogy were found to be crucial factors affecting the handleability and disposability of the dewatered cakes. The tailing yield stress (shear strength) increased as the solid concentration increased. In the semi-solid regime (above 60 wt% solids), the tailings displayed stiff exponential growth. Similar trends were observed for stickiness and adhesive/cohesive energy of the tailings with a steel (truck) surface. Adding polymer flocculants increased the shear strength of the dewatered tailings by 10-15%, thus favouring disposability. However, the polymer selection for coal tailing handling and processing is a trade-off between its disposability and handleability, which requires a multi-criteria decision-making process. The current results also suggested that cationic PAM could be most suitable for dewatering by press filtration, while anionic PAM should be selected for dewatering by solid bowl centrifugation.

Toward sustainable reprocessing and valorization of sulfidic copper tailings: Scenarios and prospective LCA

There has been increasing attention recently to reprocessing of mining waste, which aims to recover potentially valuable materials such as metals and other byproducts from untapped resources. Mining waste valorization may offer environmental advantages over traditional make-waste-dispose approaches. However, a quantitative environmental assessment for large-scale reprocessing, accounting for future trends and a broad set of environmental indicators, is still lacking. This article assesses the life cycle impacts and resource recovery potential associated with alternative waste management through mine tailings reprocessing at a regional scale. Sulfidic copper tailings in the EU were selected as a case study. We perform prospective life cycle assessments of future reprocessing scenarios by considering emerging resource recovery technologies, market supply & demand forecasts, and energy system changes. We find that some reprocessing and valorization technologies in future scenarios may have reduction potentials for multiple impact indicators. However, results for indicators such as climate change and energy-related impacts suggest that specific scenarios perform sub-optimally due to energy/resource-intensive processes. The environmental performance of reprocessing of tailings is influenced by technology routes, secondary material market penetration, and choices of displaced products. The trade-off between climate change and energy related impacts, on the one hand, and toxicity impacts, on the other hand, requires critical appraisal by decision makers when promoting alternative tailings reprocessing. Implementing value recovery strategies for building material production, can save up to 3 Mt. CO₂-eq in 2050 compared to business as usual, helping the copper sector mitigate climate impacts. Additional climate mitigation efforts in demand-side management are needed though to achieve the 1.5 °C climate target. This work provides a scientific basis for decision-making toward more sustainable reprocessing and valorization of sulfidic tailings.

Coal tailings as a soil conditioner: evaluation of tailing properties and effect on tomato plants

The global coal industry yields a vast amount of tailings waste, and the utilisation of these tailings necessitates innovative efforts contributing to the United Nations Sustainable Development Goals. One of such novel initiatives is to reuse coal tailings (CT) safely, ecofriendly, and cost-effectively in agroecosystems as a soil conditioner to enhance the productivity of lands. This study aimed to evaluate the potential utilisation of coal tailings waste in the soil amelioration to improve plant performance. The physico-chemical characteristics of coal tailings from two Australian mining sites (CT1 and CT2) showed that the tailings samples are alkaline with loamy and loamy sand textures, respectively. The tailings have ~ 3% of macronutrients, high carbon (C), and low heavy metals and metalloids (As, Cd, Se, Cu, Zn, and Pb). The germination rate of tomato seeds was improved in the low-rate CT treatment. Greenhouse tomato plants exhibited an increase in leaf's K, Ca, and Mg contents in CT1 and CT2 treatments. More importantly, the CT treatment-induced accumulation of heavy metals in plants was mostly insignificant in both CT treatments. Therefore, we highlight the potential application of coal tailings as a soil conditioner because of the beneficial effect of improved carbon and nutrients (N, P, K, Mg, and Ca) in tomato leaves. Further amendment of the coal tailings should focus on the adjustment of pH and the addition of other beneficial materials for the improvement of soil properties for crops in both the greenhouse and the field.

Application of Hydro Borehole Mining (HBM) Technology for Lignite Extraction—An Environmental Assessment (LCA) and a Comparative Study with the Opencast Method

The article presents the impact of lignite mining on the environment associated with the introduction of hydro borehole mining (HBM) technology. The results are partially based on the HydroCoal Plus project results, where an environmental assessment of lignite HBM technology was performed. In order to reach the goals of the task, a life cycle assessment (LCA) study was used to assess selected environmental aspects of the HBM single-borehole lignite production process covering selected environmental impact categories such as energy consumption, fuel consumption, water consumption and carbon footprint. The LCA procedure was adapted in an innovative way, constituting another added value to the shown research. The second part of this paper describes opportunities identified by the authors to minimize the environmental impact of lignite production by implementing the HBM method compared to the conventional opencast method.

Life cycle assessment of underground coal mining in China

Coal is not only the main fossil fuel in China but also a pollution source. To evaluate the impact of coal production on the environment, a life cycle assessment (LCA) was conducted on the mining process of a typical coal mine in China by using the SimaPro 9.0.0 software. The Ecoinvent v3 database was used to provide the background data, and midpoint results with uncertainty information were calculated using the ReCiPe Midpoint (H) method. After normalising the midpoint results, fossil depletion was identified as the most predominant environmental impact category, followed by marine ecotoxicity, freshwater ecotoxicity, climate change, freshwater eutrophication, and human toxicity. The contribution analysis indicates that coal mining activities, consumption of steel and electricity, and mine ventilation are the key processes causing the above-mentioned environmental impact categories, which should be paid special attention. According to the sensitivity analysis, the primary countermeasures for addressing the environmental issues are to reduce the mining activities and improve the efficiency of coal mining and utilisation. In addition, the quantitative and comparative analyses show that the gas extraction production mode is beneficial to the environment. Finally, technical measures were proposed to promote green and sustainable development of the coal industry. This research can provide guidance for ensuring national energy security and promoting healthy development of the national economy.

Sustainable Strategies for the Exploitation of End-of-Life Permanent Magnets

The growing production of green technologies (such as electric vehicles and systems for renewable electricity production, e.g., wind turbine) is increasing the rare earth element (REE) demands. These metals are considered critical for Europe for their economic relevance and the supply risk. The end-of-life permanent magnets are considered a potential secondary resource of REEs thanks to their content of neodymium (Nd), praseodymium (Pr) or dysprosium (Dy). The scientific literature reports many techniques for permanent magnet recovery. This work used a life cycle assessment (LCA) to identify the most sustainable choice, suggesting the possible improvements to reduce the environmental load. Three different processes are considered: two hydrometallurgical treatments (the first one with HCl and the other one with solid-state chlorination), and a pyrometallurgical technique. The present paper aims to push the stakeholders towards the implementation of sustainable processes for end-of-life permanent magnet exploitation at industrial scale.

A real-time light-scattering technique for tailings solids measurement

This study presents the concept of an economic in situ light-scattering sensor for real-time measurement of the solid content in tailings facilities. An experimental setup using a blue (405 nm wavelength) laser diode and silicon photodiodes was constructed to measure the angular distribution of the intensity of scattered light. It was found that the angular intensity of scattered light for tailing samples follows a cosⁿ (θ) relation with n ≈ 1.5, where θ is the angle between the laser beam and the photodiode. An angular value of θ = 20° was chosen for the sensor design based on a high signal-to-noise ratio. The setup was used to determine the relation between scattered light intensity and solids content using a thickened tailings underflow from an oil sands facility and Kaolin as a model material. It was observed that the intensity of scattered light tends to increase with an increase in solids content, with qualitatively similar settling behavior for the two materials but at largely different time scales. An insertion-based prototype was built and tested in a large (2.7 m height) settling column with treated mature fine tailings, and the light-scattering data were verified by standard gravimetric method and gamma-ray measurements. In general, good agreement was established between these measurements in the absence of optical fouling, which demonstrates the potential of the sensor as an effective tool for tailings management.

Environmental Sustainability Analysis of Case Studies of Agriculture Residue Exploitation

The agriculture sector produces significant amounts of organic residues and the choice of the management strategy of these flows affects the environmental sustainability of the sector. The scientific literature is rich with innovative processes for the production of bio-based products (BBP) from agriculture residues, aimed at the implementation of circular economy principles. Based on literature data, the present paper performed a life cycle assessment and assessed the environmental sustainability of five processes for the exploitation of rice and wheat straw, tomato pomace, and orange peel. The analysis identified as significant issues the high energy demand and the use of high impact organic solvent. The comparison of BBP with conventional products showed higher environmental loads for the innovative processes that used organic residues (except for rice straw case). The obtained results do not want to discourage the circular strategy in the agriculture sector, but rather to draw the attention of all stakeholders to the environmental sustainability aspects, focusing on the necessity to decrease the electricity demand and identify ecological agents to use in BBP manufacturing, in agreement with the most recent European policies.

Determining the scale of coal mining in an ecologically fragile mining area under the constraint of water resources carrying capacity

A reasonable mining scale is very important for the development of mining areas. In view of the lack of water resources in arid and semi-arid areas, this paper studies the scale of coal mining in arid and semi-arid areas under the constraint of the water resources carrying capacity (WRCC) with the aim of realizing the conservation mining of ecological environment. From the perspectives of market demand side, production side and the constraint side, a "trinity" decision model was constructed to investigate the main factors influencing the scale of coal mining. By introducing the optimal control theory with profit taken as objective function, the coal price and coal reserves were regarded as boundary conditions, and WRCC was set as constraint condition. Based on H-J-B equation algorithm, the decision-making equation for mining scale under the constraints of market demand and WRCC was obtained. Through comparing the mining scales under the two constraints, the mode of "water-based mining scale" was formulated, which is conductive for realizing the balance between coal mining and ecological environment development.

Environmental and Business Challenges Presented by Mining and Mineral Processing Waste in the Russian Federation

Using Murmansk Region, one of Russia’s largest mining regions, as a case study, this paper examines the environmental safety challenges arising in the storage of mining and mineral processing waste (MMPW). It was found that MMPW causes environmental damage even after the deposit’s exhaustion. While being stored, the MMPW composition experiences a major change in the process properties of the recoverable minerals. As a consequence, the potential value of the MMPW as a mineral resource falls. Imperfections of the regulatory framework, leading to a higher unit cost of recovery and a reduced profitability of MMPW processing, are demonstrated. Potential amendments to the Russian laws are proposed in order to make MMPW processing commercially more viable.

Assessing the sustainability of acid mine drainage (AMD) treatment in South Africa

The environmental sustainability of acid mine drainage (AMD) treatment at semi-industrial scale is examined by means of the life cycle assessment (LCA) methodology. An integrated process which includes magnesite, lime, soda ash and CO₂ bubbling treatment was employed to effectively treat, at semi-industrial scale, AMD originating from a coal mine in South Africa. Economic aspects are also discussed. AMD is a growing problem of emerging concern that cause detrimental effects to the environment and living organisms, including humans, and impose on development, health, access to clean water, thus also affect economic growth and cause social instability. Therefore, sustainable and cost effective treatment methods are required. A life cycle cost analysis (LCCA) revealed the viability of the system, since the levelized cost of AMD treatment can be as low as R112.78/m³ (€7.60/m³ or $9.35/m³). Moreover, due to its versatility, the system can be used both at remote locales, at stand-alone mode (e.g. using solar energy), or can treat AMD at industrial scale, thus substantially improving community resilience at local and national level. In terms of environmental sustainability, 29.6 kg CO_2eq are emitted per treated m³ AMD or its environmental footprint amount to 2.96 Pt/m³. South Africa's fossil-fuel depended energy mix and liquid CO₂ consumption were the main environmental hotspots. The total environmental footprint is reduced by 45% and 36% by using solar energy and gaseous CO₂, respectively. Finally, AMD sludge valorisation, i.e. mineral recovery, can reduce the total environmental footprint by up to 12%.

Coal-water slurries containing petrochemicals to solve problems of air pollution by coal thermal power stations and boiler plants: An introductory review

This introductory study presents the analysis of the environmental, economic and energy performance indicators of burning high-potential coal water slurries containing petrochemicals (CWSP) instead of coal, fuel oil, and natural gas at typical thermal power stations (TPS) and a boiler plant. We focus on the most hazardous anthropogenic emissions of coal power industry: sulfur and nitrogen oxides. The research findings show that these emissions may be several times lower if coal and oil processing wastes are mixed with water as compared to the combustion of traditional pulverized coal, even of high grades. The study focuses on wastes, such as filter cakes, oil sludge, waste industrial oils, heavy coal-tar products, resins, etc., that are produced and stored in abundance. Their deep conversion is very rare due to low economic benefit. Effective ways are necessary to recover such industrial wastes. We present the cost assessment of the changes to the heat and power generation technologies that are required from typical power plants for switching from coal, fuel oil and natural gas to CWSPs based on coal and oil processing wastes. The corresponding technological changes pay off after a short time, ranging from several months to several years. The most promising components for CWSP production have been identified, which provide payback within a year. Among these are filter cakes (coal processing wastes), which are produced as a ready-made coal-water slurry fuel (a mixture of flocculants, water, and fine coal dust). These fuels have the least impact on the environment in terms of the emissions of sulfur and nitrogen oxides as well as fly ash. An important conclusion of the study is that using CWSPs based on filter cakes is worthwhile both as the main fuel for thermal power stations and boiler plants and as starting fuel.