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Environmentally sustainable acid mine drainage remediation: Research developments with a focus on waste/by-products

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Abstract

Acid mine drainage (AMD) is a major environmental problem and remains so despite the availability of a vast array of remediation techniques and technologies. Many methods used to remediate AMD are limited in implementation due to poor performance, design inaccuracies, difficult understanding of functionality, high costs, usage of hazardous chemicals, depletion of natural resources and the generation of further waste. As a result of these limitations, and due to the need for sustainability, research is being conducted on the use of waste materials and by-products from other industries, such as the dairy, paper mill, steel mill, wine, tyre, seafood and even from AMD treatment itself, to remediate AMD. Materials from these industries have been shown to reduce or eliminate some of the drawbacks of conventional techniques and technologies such as lime neutralization, passivation, in-situ biological remediation, backfilling, waste-heap covers, adsorption, constructed wetlands, desalination, sulfidogenic bioreactors, anoxic limestone drains and permeable reactive barriers. This paper presents an overview of AMD and discusses research developments into various waste materials or by-products from other industries that have been successfully applied in remediating AMD.

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... The key challenges associated with active treatment include the high operational costs and the generation of hazardous sludge that requires additional management and safe disposal [6,24,25]. These disadvantages can lead to active methods being economically unfeasible for abandoned mines in remote regions [23,26]. ...
... Permeable Reactive Barriers (PRBs) are an emerging AMD treatment method characterised by their high porosity and various material compositions that can include alkaline materials such as concrete, cement, fly ash and lime as well as various organic materials and electron donor materials such as zero-valent iron [105][106][107][108][109]. PRBs can be installed underground, directly in the flow path of contaminated groundwater and used as in situ systems, which eliminates the costs associated with the pumping and distribution of mine water to treatment works [25,110]. Other advantages of PRB remediation include the low operational cost and the minimal operational supervision required [25,30,111]. ...
... Permeable Reactive Barriers (PRBs) are an emerging AMD treatment method characterised by their high porosity and various material compositions that can include alkaline materials such as concrete, cement, fly ash and lime as well as various organic materials and electron donor materials such as zero-valent iron [105][106][107][108][109]. PRBs can be installed underground, directly in the flow path of contaminated groundwater and used as in situ systems, which eliminates the costs associated with the pumping and distribution of mine water to treatment works [25,110]. Other advantages of PRB remediation include the low operational cost and the minimal operational supervision required [25,30,111]. However, the effectiveness of a PRB system for AMD remediation is limited by the depletion of the chemical components of the reactive barrier, armouring of the reactive surface and the physical clogging of the porous network with time [62,110,112]. ...
Article
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This paper reviews the Acid Mine Drainage (AMD) remediation potential and operational costs of twelve existing AMD remediation methods against Class 0 and Class I AMD geochemical characteristics as defined in the Modified Hill Framework. Of the twelve remediation options reviewed in this study, eleven required additional process steps either for further treatment to achieve the discharge limits or for the safe management of hazardous waste by-products. Chemical desalination showed the greatest potential with high quality treated water and operational costs between USD 0.25 and USD 0.75 per cubic meter treated. The management of the toxic metal and sulphide by-products remains a key challenge that requires further research for sustainable mine water remediation. Further development of end-to-end methods suitable for Class 0 AMD with economical operational costs is recommended in order to effectively address the ongoing environmental challenges posed by AMD globally.
... There are many conventional AMD treatment and prevention techniques such as passivation, backfilling, desalination, permeable reactive barriers, lime neutralisation, waste-heap covers, adsorption, in situ biological remediation, constructed wetlands, sulfidogenic bioreactors, backfilling, reverse osmosis, filtration, ion exchange and electrodialysis which have been developed over the years (Moodley et al. 2018;Saha and Sinha 2018). The implementation of traditional AMD treatment and prevention techniques is limited due to the constant depletion of natural resources, poor performances, high cost of construction and implementation, design inaccuracies, generation of additional wastes, difficulty in understanding the functionality and the use of hazardous chemicals (Moodley et al. 2018;Saha and Sinha 2018). ...
... There are many conventional AMD treatment and prevention techniques such as passivation, backfilling, desalination, permeable reactive barriers, lime neutralisation, waste-heap covers, adsorption, in situ biological remediation, constructed wetlands, sulfidogenic bioreactors, backfilling, reverse osmosis, filtration, ion exchange and electrodialysis which have been developed over the years (Moodley et al. 2018;Saha and Sinha 2018). The implementation of traditional AMD treatment and prevention techniques is limited due to the constant depletion of natural resources, poor performances, high cost of construction and implementation, design inaccuracies, generation of additional wastes, difficulty in understanding the functionality and the use of hazardous chemicals (Moodley et al. 2018;Saha and Sinha 2018). ...
... In the past few years, there has been an increase in research on the use of industrial waste or by-products to treat and prevent AMD. Waste materials and by-products from the paper mill, wine, seafood and steel mill industries have shown the ability to reduce and eliminate some of the limitations associated with conventional AMD treatment and prevention techniques (Moodley et al. 2018). There is a need to conduct more research on the use of industrial wastes and by-products to develop environmentally sustainable AMD prevention and treatment techniques. ...
Article
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Acid mine drainage (AMD) caused by the oxidation of sulphide minerals found in mine waste is a global environmental concern, especially in water-restricted countries with heavy mining industries. Implementing AMD treatment and prevention programs can be extremely expensive, hence the need to identify environmentally sustainable treatment and preventative techniques to mitigate the potential of AMD formation. Soil covers and blends have been identified as an attractive approach. However, prior studies on the characteristics of the soils concerned and the acid-neutralisation rate should be carried out before considering the implementation of a soil cover or blending system to mitigate AMD formation. This study evaluated the acid generation capabilities of acidic gold mine tailings (AG), alkaline gold mine tailings (AN) and blends (MIX25, MIX50). Acid–base accounting (ABA), net acid generation (NAG) and acid-buffering characteristic curve (ABCC) test methods were used to evaluate the acid-generating and acid-neutralising capabilities of AG, AN, MIX25 and MIX50 samples. Leach column tests were conducted using alkaline gold mine tailings (AN) as the top pH neutralising cover (COV25) to determine the potential of the alkaline gold mine tailing to serve as a pH neutralising cover material to prevent and treat AMD generated by the acidic gold mine tailings. The ABA, NAG and ABCC results showed that AN has a high acid-neutralising capacity while AG has the potential to generate acid. The results further indicated that the AN to AG blend ratio of 1:3 by weight (MIX25) would neutralise the acid generated by AG. Leach column experiment (COV25) found that using AN as a pH neutralising cover would be a feasible option.
... Acid mine drainage (AMD) refers to acidic runoff rich in high concentrations of metal ions, such as iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), lead (Pb), nickel (Ni), arsenic (As), cadmium (Cd), aluminum (Al), and mercury (Hg) [1][2][3]. AMD is associated with mining and mineral processing activities and comes from the natural oxidation of sulfide-bearing minerals (such as pyrite) exposed to water, oxygen, and microbes [4,5]. AMD is considered one of the most prevalent causes of environmental pollution which stems from its high acidity (pH < 3) and toxic metal content [6]. ...
... To tackle the issue of AMD, many attempts have been made to limit the generation and release of AMD by protecting sulfide minerals from air, water, and bacteria and minimizing their interactions [5,[8][9][10][11][12][13]. However, due to practical constraints involved in the prevention strategy [14], the next available option is AMD treatment by either active or passive methods [2]. The most common active methods include neutralization using caustic soda (sodium hydroxide), calcium hydroxide (Ca(OH)2) or limestone (CaCO3), as well as adsorption, ion exchange, and crystallization [6,15]. ...
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Acid mine drainage (AMD) is a serious environmental issue associated with mining due to its acidic pH and potentially toxic elements (PTE) content. This study investigated the performance of the Fe-Al bimetallic particles for the treatment of combined AMD-gold processing effluents. Batch experiments were conducted in order to eliminate potentially toxic elements (including Hg, As, Cu, Pb, Ni, Zn, and Mn) from a simulated waste solution at various bimetal dosages (5, 10, and 20 g/L) and time intervals (0 to 90 min). The findings show that metal ions with greater electrode potentials than Fe and Al have higher affinities for electrons released from the bimetal. Therefore, a high removal (> 95%) was obtained for Hg, As, Cu, and Pb using 20 g/L bimetal in 90 min. Higher uptakes of Hg, As, Cu, and Pb than Ni, Zn, and Mn also suggest that electrochemical reduction and adsorption by Fe-Al (oxy) hydroxides as the primary and secondary removal mechanisms, respectively. The total Al3+ dissolution in the experiments with a higher bimetal content (10 and 20 g/L) were insignificant, while a high release of Fe ions was recorded for various bimetal dosages. Although the secondary Fe pollution can be considered as a drawback of using the Fe-Al bimetal, this issue can be tackled by a simple neutralization and Fe precipitation process. A rapid increase in the solution pH (initial pH 2 to >5 in 90 min) was also observed, which means that bimetallic particles can act as a neutralizing agent in AMD treatment system and promote the precipitation of the dissolved metals. The presence of chloride ions in the system may cause akaganeite formation, which has shown a high removal capacity for PTE. Moreover, nitrate ions may affect the process by competing for the released electrons from the bimetal owing to their higher electrode potential than the metals. Finally, the Fe-Al bimetallic material showed promising results for AMD remediation by electrochemical reduction of PTE content, as well as acid-neutralization/metal precipitation.
... This approach is frequently regarded as an accurate remediation procedure for defiled soil waters because of its toxin expulsion plan and system. Specialists (Thiruvenkatachari et al., 2008;Moodley et al., 2018) have shown that one of the few instruments of contaminant expulsion (debasement, precipitation, and sorption) in the PRB process is the natural reaction. Large PRB is an In-situ method for treating groundwater contaminated with different contamination categories, comprising heavy metals and chlorinated chemicals (Table 3). ...
... A super-durable or semi-long receptive (medium) impediment is mainly composed of zero-valent iron for this process. The feasibility of this method is decided mainly by the kind of media employed and affected by toxic compounds, biogeochemical and hydrogeological conditions, natural and health effects, mechanical health, and price (Moodley et al., 2018;Liu et al., 2018). Throughout the appraisal of a PBR for the remediation of bankrupt chlorinated solvents in groundwater, the arrangement of carbonate acceleration in the iron zone was not considered as a key limit to the demonstration pragmatic (Wilkin et al., 2020). ...
Article
Nanotechnology, as an emerging science, has taken over all fields of life including industries, health and medicine, environmental issues, agriculture, biotechnology etc. The use of nanostructure molecules has revolutionized all sectors. Environmental pollution is a great concern now a days, in all industrial and developing as well as some developed countries. A number of remedies are in practice to overcome this problem. The application of nanotechnology in the bioremediation of environmental pollutants is a step towards revolution. The use of various types of nanoparticles (TiO2 based NPs, dendrimers, Fe based NPs, Silica and carbon nanomaterials, Graphene based NPs, nanotubes, polymers, micelles, nanomembranes etc.) is in practice to diminish environmental hazards. For this many In-situ (bioventing, bioslurping, biosparging, phytoremediation, permeable reactive barrier etc.) and Ex-situ (biopile, windrows, bioreactors, land farming etc.) methodologies are employed. Improved properties like nanoscale size, less time utilization, high adaptability for In-situ and Ex-situ use, undeniable degree of surface-region to-volume proportion for possible reactivity, and protection from ecological elements make nanoparticles ideal for natural applications. There are distinctive nanomaterials and nanotools accessible to treat the pollutants. Each of these methods and nanotools depends on the properties of foreign substances and the pollution site. The current designed review highlights the techniques used for bioremediation of environmental pollutants as well as use of various nanoparticles along with proposed In-situ and Ex-situ bioremediation techniques.
... Hydrophobic coating materials can be used to prevent the reactive mineral fractions from oxidizing. Organic materials and their derivatives, such as DETA, sodium oleate, phospholipids, and humic substances, are typically used towards that end, owning to their high hydrophobicity (Moodley et al., 2018;Park et al., 2019). However, similarly to covering materials, exposure to environmental conditions, substances emitted from the encapsulated material, along with (micro) organisms can degrade microencapsulation rendering it unable to isolate the covered material from the air, water, and/or bacteria, thus eventually leading to AMD formation (Villain et al., 2013). ...
... Hybrid treatment refers to the integration of active with passive processes for the treatment of AMD (Fig. 6). Most often, in hybrid systems neutralization with alkaline media (active) is combined with aerobic or anaerobic wetlands (passive) (Groudev et al., 2008;Moodley et al., 2018;Naidu et al., 2019). Therefore, treatment efficiency can be optimized and a relatively high quality effluent can be obtained. ...
Article
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Mining activities are notorious for their environmental impact, with acid mine drainage (AMD) being among the most significant issues. Specifically, AMD has recently been a topical issue of prime concern, primarily due to the magnitude of its environmental, ecotoxicological, and socioeconomic impacts. AMD originates from both active and abandoned mines (primarily gold and coal) and is encountered in Canada, China, Russia, South Africa, USA, and other countries with strong mining industries. Owing to its acidity, AMD contains elevated levels of dissolved (toxic) metals, metalloids, rare-earth elements, radionuclides, and sulfates. Practical and cost-effective solutions to prevent its formation are still pending, while for its treatment, active (driven by frequent input of chemicals and energy) or passive (based on oxidation/reduction), technologies are typically employed with the first being more efficient in contaminants removal, however, at the expense of process complexity, cost, and energy consumption. More recently, and under the circular economy concept, hybrid (combination of active and passive technologies) and particularly integrated (sequential or stepwise treatment) systems have been explored for AMD beneficiation and valorisation. These systems are costly to install and operate but are cleaner production systems since they can effectively prevent pollution and can be used for closed-loop and sustainable AMD management (e.g., zero liquid discharge systems). Herein, an insight into the body of knowledge on AMD treatment, beneficiation (metals/minerals recovery), valorisation (water reclamation), and life cycle assessment (LCA), is comprehensively reviewed and discussed with focus placed on circular economy. Future research directions are provided to introduce reuse, recycle, and resource recovery paradigms and inspire innovation in valorising this toxic and hazardous effluent. Overall, AMD beneficiation and valorisation appears promising since the reclaimed water and the recovered minerals/metals could offset the treatment costs and environmental impacts. However, the main challenges include high-cost, complexity, cross-contamination, and the generation of heterogeneous and highly mineralised sludge.
... Acid mine drainage, caused by weathering of sulfide-rich mine waste, is arguably the most critical environmental problem in the mining sector (Muniruzzaman et al., 2020). The best technique for managing acid mine drainage is to prevent its formation by minimizing contact between the sulfide ore and oxygen, water, and/or oxidizing bacteria (Chowdhury, Sarkar, & Datta, 2015;Moodley et al., 2018;Pozo-Antonio et al., 2014;Skousen, Ziemkiewicz, & McDonald, 2019;Suyasa, Hamdi, & Teguh, 2019). Data on the maximum potential acidity (MPA), nett acid producing potential (NAPP), and the net potential ratio (NPR) of samples in open land rocks are shown in Figure 3 above. ...
... The negative impact due to acid mine drainage can last a long time, long after the mine closure period, even hundreds of years or as long as sulfide minerals are still available and oxidized, and require large funds for remediation (Ali, 2017). Soils affected by acid mine drainage become useless for agricultural activities because of their high acidity and high metal concentrations affecting animal and plant life (Moodley et al., 2018). If it is formed or passes through land (soil) ecosystems, acid mine drainage can contaminate and poison soil organisms, including vegetation. ...
Article
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The phenomenon of acid mine drainage (AMD) is one of the serious environmental problems that is often encountered at a mine site. Controlling acid mine drainage is an important thing to do during mining activities and after mining activities end. This research aims to analyze the potential for rock and soil formation of acid mine drainage to the environment around the nickel mining area in Kabaena Timur District. Data obtained through the analysis of the laboratory of Limited Company of Narayana Lambale Selaras. The results showed that in open land the sulphure content range was 0.411-1.452 Kg H2SO4/ton. NAG values are in the equivalent range of 0-3.675 Kg H2SO4/ton. ANC ranges from 25.725-60.025 Kg H2SO4/ton. The range of MPA values is equivalent to 1.977-44.470 Kg H2SO4/ton. The NAPP values ranged from-40.526 to-3.839 and the NPR ranged from 1.116 to 3.776. Whereas in closed land the values for sulphure content, NAG, ANC, MPA, NAPP, and NPR were respectively = 0.418-1.364 Kg H2SO4/ton; 0-3.185 Kg H2SO4/ton; 25.725-57.575 Kg H2SO4/ton; 12.790-41.775 Kg H2SO4/ton;-36.846 to-1.276 and 1.037-3.927. Based on the criteria for NAPP and NPR values, shows that all rock and soil samples in the nickel mining area don't have the potential to form acid mine drainage because the NAPP value is < 0 and the NPR value > 1.
... Associated impacts include elevated cancer risks and deaths resulting from exposure to radioactive compounds and the dissolved hazardous metals associated with AMD. The lowered pH levels and increased sulphate (SO 4 ), salt and metal content of AMD contaminate surface water and groundwater resources which, in turn, have an impact on aquatic life and soil properties [1][2][3][4][5][6][7][8][9]. ...
... The analyses completed for Phase 1 included total organic carbon (TOC), total carbon (TC) and total inorganic carbon (TIC) and was required to understand the carbon composition of the selected substrate materials. The specific element of interest was TOC, as it is known to support microbial activity for SO 4 reduction in AMD [6,7,11,13,16,19,[22][23][24]. Phase 2 substrate mixtures were also analyzed for TOC, TC and TIC; however, additional analyses were requested for the substrate mixtures during Phase 2. These additional analyses included nitrogen (N), phosphorous (P) and water-soluble P ( Table 2) and were identified as potential electron donors for microbial activity. ...
Article
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Acid mine drainage (AMD) is a global problem with severe consequences for the environment. South Africa’s abandoned mines are a legacy from the country’s economic dependence on the mining sector, with consequent negative impacts on ecosystems. AMD remediation includes active and passive techniques. Constructed wetlands (a passive technique) have lower operational costs but require larger spaces and longer timeframes to achieve the remediation of AMD, and are supported by anaerobic sulphate-reducing bacteria (SRB), which capable of remediating high-sulphate-laden AMD while precipitating dissolved metals from the AMD. Organic substrates supporting these activities are often the limiting factor. When enhancing existing passive AMD remediation technologies, alternative waste material research that may support SRB activity is required to support the circular economy through the reduction in waste products. Chicken feathers show potential as a substrate enhancer, boosting organic carbon availability to SRB, which sustains passive AMD treatment processes by achieving pH elevation, sulphate and metal reductions in AMD water for reuse. Microbial biodiversity is essential to ensure the longevity of passive treatment systems, and chicken feathers are proven to have an association with SRB microbial taxa. However, the longer-term associations between the AMD water parameters, microbial diversity and the selected substrates remain to be further investigated.
... AMD is an extraordinarily acidic and highly contaminated leachate generated from underground workings of closed or abandoned mine sites and accumulations of tailings or mullocks, which is one of the most severe water pollution problems worldwide. 1 The leachate is mainly derived from the oxidation of sulfide mineral ores, which are initially exposed to the environment by intensive mining activities. Notably, among the metal sulfides, pyrite ore (FeS 2 ) is one of the primary minerals responsible for the generation of AMD owing to the tendency of oxidation when accessed to oxygen, water, and microorganisms. ...
... Nevertheless, large amounts of neutralizing agents are required in the process and will generate a considerable sludge after remediation of AMD. 1 Notably, adsorption is an essential technique for removing heavy metals from wastewater resulted from its strong affinity and high loading capacity, compared to other approaches. The advantages of adsorption in the purification of wastewaters are its high effectiveness and flexibility. ...
Article
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Technologies for remediation of wastewater by industrial solid waste have recently attracted interest. Acid mine drainage is an extraordinarily acidic and highly heavy metal ions contaminated leachate which posed some challenges for the environment. Nonetheless, steel slag shows significant potential application prospects in wastewater treatment, due to its excellent physicochemical properties and structures. This paper elaborately reviewed the structure, properties, water treatment applications of steel slags, and the mechanism for removing heavy metal ions from acid mine drainage, discussed the problems existing in industrial wastewater treatment by steel slag, and proposed the solutions for future research, aiming to provide theoretical references for the practical application of steel slag in AMD treatment.
... The man-made hazard sources can be defined as the ones obtained as a result of human activities (Sengupta & Agrahari, 2017). The researchers (Moodley et al., 2018), scientists (Fazzo et al., 2017), industrialists (Guan et al., 2019), agriculturalists (Abdel-Shafy & Mansour, 2018), laborers (Akkoyunlu et al., 2017), etc., keep on working on many scales for developing a nation and providing a better living to them. Although very useful to a certain extent, these practices may also contribute to hazard production (Burella et al., 2019;Shah et al., 2018). ...
Article
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There has been great concern about producing, converting, or disposing of the waste obtained from different sources. Waste production is a continuous phenomenon that can be minimized by taking certain measures; however, it cannot be eliminated completely. The wastes produced along with various useful processes, such as industrial operations or natural processes, may have hazardous effects on the living organisms. The hazards brought about by natural calamities or man-made operations can affect the integrity of the natural environment and the living entities in the worst possible ways. An insight into the hazardous effects and the associated causes intensifies the need to develop hazard management strategies. Hazard management policies have garnered prodigious attention due to the disastrous effects of hazardous materials. The hazard management policies are being addressed at the government as well as the individual levels benefitting mankind. Worldwide, different countries are working on hazard management in different capacities , depending upon the available resources. Attempts are being made to manage hazardous products obtained from different sources without the natural sources being worn out, ensuring environmental sustainability. The general escalation in world pollution, making it unfit for living organisms, ruining the aesthetic beauty of the environment, etc., has given rise to great concerns about waste management. The control and management of waste products have become the hottest topic being discussed on various platforms like symposia , workshops (both National and International), conferences, and a demanding topic in many journals. Considering the dire need for knowledge and awareness about waste management , this review focuses on the causes and effects of the hazards and measures being taken at different levels.
... Since the 1970s, PRBs have been installed in the flow path of groundwater and used as an in situ remediation method for various water contaminants including heavy metals, organohalogen compounds, nitrate and SO 4 , among others [9,12,13]. The major advantages of using PRBs for groundwater remediation include the low operational and maintenance costs, minimal operational supervision required and the potential for in situ installation, which limits land usage [12,14]. The major limitations of PRBs include the depletion of the reactive chemical compounds over time, the potential for armouring of the reactive surface and the gradual clogging from precipitant build-up in the flow path, all of which can necessitate the need for PRB replacement or the use of sequenced multi-barrier techniques [12,15]. ...
Article
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This paper investigates the Acid Mine Drainage (AMD) remediation capabilities of pozzolanic pervious concrete Permeable Reactive Barriers (PRBs) with a specific focus on the effects of flow configuration and contact time on the remediation efficiency. Raw AMD was collected from an abandoned coal mine. Two flow configurations, gravity flow and column flow, were tested at a laboratory scale with gradually increasing contact times. The gravity flow configuration with two orders of magnitude less liquid-concrete contact time achieved AMD treated water quality equivalent to the high retention column flow configuration. Concentrations of iron, aluminium, sulphate, magnesium and sodium were reduced by more than 99%, 80%, 17%, 22% and 20%, respectively, at the tested limits while calcium and potassium concentrations were increased by up to 16% and 300%, respectively. The study findings indicate that the lifecycle costs of pervious concrete PRBs can be significantly reduced when the PRBs are operated under gravity flow.
... There are two strategies to deal with AMD, (1) prevent its formation and (2) remediation (Moodley, 2018). Johnson and Hallberg (2005) divide the remediation approaches in two categories: (a) abiotic systems where a chemical agent is used to neutralize the AMD and (b) biological systems where the use of microorganisms favors the neutralization of AMD and immobilization of metals. ...
Article
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Mine wastes pollute the environment with metals and metalloids in toxic concentrations, causing problems for humans and wildlife. Microorganisms colonize and inhabit mine wastes, and can influence the environmental mobility of metals through metabolic activity, biogeochemical cycling and detoxification mechanisms. In this article we review the microbiology of the metals and metalloids most commonly associated with mine wastes: arsenic, cadmium, chromium, copper, lead, mercury, nickel and zinc. We discuss the molecular mechanisms by which bacteria, archaea, and fungi interact with contaminant metals and the consequences for metal fate in the environment, focusing on long‐term field studies of metal‐impacted mine wastes where possible. Metal contamination can decrease the efficiency of soil functioning and essential element cycling due to the need for microbes to expend energy to maintain and repair cells. However, microbial communities are able to tolerate and adapt to metal contamination, particularly when the contaminant metals are essential elements that are subject to homeostasis or have a close biochemical analog. Stimulating the development of microbially reducing conditions, for example in constructed wetlands, is beneficial for remediating many metals associated with mine wastes. It has been shown to be effective at low pH, circumneutral and high pH conditions in the laboratory and at pilot field‐scale. Further demonstration of this technology at full field‐scale is required, as is more research to optimize bioremediation and to investigate combined remediation strategies. Microbial activity has the potential to mitigate the impacts of metal mine wastes, and therefore lessen the impact of this pollution on planetary health.
... As tailings contain a multitude of various contaminants, the integrity of these impoundments is a significant issue of global environmental concern [46]. One of the environmental issues related to mine tailings is acid mine drainage [47] which occurs due to the content of sulfide minerals in mine tailings when they are in contact with oxygen and water [48]. ...
Article
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The tailing storage facility is the largest water sink in most mines. An incorrect management of water content in mine tailings can become a threat to their stability, and consequently, their environmental safety. Also, water reuse and recycling are plausible options to mining companies for reasons pertaining to water scarcity. Dew-atering technologies for tailings, desalination and water transport are energy intensive. Proper handling of mine tailings and water supply management can considerably improve the water-energy nexus. This article evaluates the water-energy nexus in copper mining companies using a water reduction model focused on mine tailing facilities and water supply to the mine site to find the trade-offs between water and energy. The originality of this work consists in the application of a real options approach, enabling to increase the flexibility of decision-making thanks to quantitative analysis. This approach deploys the Monte Carlo simulation to perform sensitivity and 2 uncertainty analysis to evaluate every cost component of water management strategy. Results show that if seawater is the primary source of raw water to the mining plant, water transport represents the largest cost due to the use of energy. So, improving the reuse of water by using dewatering technologies will improve the water-energy nexus, by improving energy consumption. Even though the costs of these technologies are elevated because they are energy-intensive, reduction of water use requirements in the mine will reduce the cost of its treatment and transport.
... This is generally achieved through some combination of diversion of AMD from a surface water body, provision of a neutralizing agent (e.g. addition of limestone), and partial retardation of water flow to facilitate aeration of the water and allow metal (hydr)oxides to settle out of the water (Cravotta and Trahan 1999; Moodley et al. 2018). These treatment strategies can range from systems requiring extensive maintenance (referred to as "active treatment") to systems that can operate with minimal human intervention (referred to as "passive treatment) (Coulton et al. 2003;Johnson and Hallberg 2005;Kleinmann et al. 1998). ...
Article
Passive treatment of coal mining derived acid mine drainage (AMD) utilizes natural processes to neutralize acidity and remove dissolved metal contaminants. In some cases, microbial communities develop without human intervention that can induce the removal of harmful AMD components. To better understand how these beneficial processes might develop, we studied the Huff Run system in eastern Ohio, where a portion of the stream was artificially diverted to prevent direct entry of AMD into the stream. There are now two abandoned stream channels that receive raw AMD and we hypothesized that the increased residence time of the AMD in these abandoned channels could reduce the adverse effects of AMD on Huff Run. We tracked seasonal changes in the aqueous chemistry and microbiology in the two abandoned channels, referred to as Farr and Lyons. The Fe, Al, and Mn were partially removed from solution as AMD moved through the Farr channel, with net alkaline water, and abundant Bacillus and Paenibacillus phylotypes. Dissolved Fe was partially removed in the Lyons channel, but neither Al nor Mn were, and the sediments contained abundant phylotypes attributable to Alicyclobacillus sp., which are capable of oxidative precipitation of Fe(II) under acidic conditions. Our results indicate that enhanced AMD retention in abandoned channels can induce contaminant removal and that abiotic and biotic reactions in the channels are influenced by the AMD chemistry.
... As a series of AMD treatment, alkali agents (limestone, sodium hydroxide, calcium carbonate etc.)-induced pH neutralization method for metal(loid) precipitation/separation process has been mainly adopted in the closed/abandoned mine sites (Naidu et al. 2019;Yuan et al. 2019). The rehabilitation possibility of AMD through the introduction of natural alkaline agents (carbonated clay minerals, sandstone, and calcareous crust) has been also tested in terms of metal removal efficiency to pursue the environmentally sustainable remediation (Moodley et al. 2018). Thus, pH neutralization and metal removal in AMD based on the physicochemical treatment were primarily focused. ...
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This work introduced a new way of fabricating a granular material with the supply of Al-rich precipitates selectively obtained from acid mine drainage (AMD), and its potential as a promising adsorbent for fluoride (F) was evaluated. Through the selective sequential precipitation (SP) process in the field, Al-rich precipitates with high purity (>81%) were collected at the high recovery rate (>99.8%) as a raw material for adsorbent fabrication. The granular adsorbent (ALB) was synthesized through encapsulation of precipitate powders by chemically inducing polymeric bead formation. The characterization results revealed that ALB possessed a highly porous structure and embedded a large number of nanoparticles of amorphous Al hydroxides inside its framework. Less adsorption of F occurred at an alkaline pH condition due to the competitive effect of hydroxyl ions. The adsorption process can be divided into fast adsorption by the outer surface and slow diffusion in the inner phase. The maximum adsorption capacity of ALB for F was calculated to be 17.7 mg g−1 in the Langmuir isotherm model fitting results. By the repetitive adsorption/desorption and XPS results, it turned out that both chemisorption and physisorption gave a contribution in the removal of F, and the regeneration of adsorbent using NaOH was effective to restore the adsorption capability but accompanied the loss of adsorption sites. As a result, it can be concluded that a granule-type material fabricated using Al-rich precipitates selectively recovered from AMD neutralization can be considered as a promising adsorbent for F removal in aqueous solution.
... Meanwhile, the doping abandoned open pit mines or underground mines, and direct disposal into rivers, lakes and the ocean (Rusdinar et al. 2013;Torres et al. 2018). The dry-stacking of thickened tailings was widely used in mines around the world, such as Ekai Diamond Mine and Kidd Creek Mine of Canada, Bulyanhulu Gold Mine of Tanzania, Kubaka Mine of Russia, Hindustan Mine of India, and Shouwangfen Copper Mine of China (Hou et al. 2018;Liu 2020;Moodley et al. 2018). The tailings storage facility (TSF) could be several square kilometers of land with dams and was built in stages as mining and waste production progresses (Schoenberger 2016). ...
Article
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Impoundments of tailings and active surface subsidence zones induced by ore mining were the major environmental problems. The aim of this study was to investigate the technical feasibility of impoundment of tailings using active surface subsidence zones. The self-designed scaled physical model was conducted to investigate the movement laws of tailings under different heights of granular media and tailings, and then drawing ore in these experiments was performed to simulate the mining process. The experimental results showed that the isolated extraction zone and stoping sequence had a primary influence on the doping process of tailings. Besides, when the height of granular media was more than that of the isolated movement zone, the uniform mode of drawing ore could be decreased the amounts of tailings drawn from drawpoints. Meanwhile, the doping process was not impacted by continuously emission of tailings to active surface subsidence zones. Thus, the field test was employed in the Dabeishan Iron Mine and the mining schemes were put forward based on the experimental data. The results showed that the recovery ratio and dilution ratio were 80.9% and 24.3% respectively, and that the scheme established in this paper could be used in practice.
... An alternative approach for the efficient management of sulfide-bearing wastes is related to the development of artificial coatings to block the oxidant transport to the pyrite surfaces and thus prevent the progress of AMD. Several inorganic and organic compounds have been used for the development of artificial coating including phosphates, iron hydroxides, humic acids, polyamines, organosilanes, siloxane, phospholipids (BREF 2018;Moodley et al. 2017). ...
Article
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The prevention of acid generation from sulfidic mine wastes is a problem that challenges the global scientific community for decades. A promising strategy is related to the formation of coating layer around sulfides for inhibiting surface oxidation. In the current research, the conditions favoring the formation of an efficient silicate-based coating around pyrite and arsenopyrite were studied, using batch tests. The coating solutions contained silicate-oxyanions, an oxidant (H2O2) and buffered at pH 6. The effect of Si concentration (0.1–50 mM), liquid/solid ratio (5–100 mL/g) and contact time (up to 24 h) was investigated. Pyrite tailings treated with a solution of 1 mM Si/0.1 M H2O2 at L/S:100 mL/g for 24 h resulted in the optimum formation of a coating, which reduced the amount of SO4−2-released by 72%, compared to the sample treated in the absence of Si. However, silicate treatment had a negative effect on arsenopyrite tailings inducing As mobilization.
... Once generated, AMD formation is nearly impossible to stop leaving little options for its management. Chemical neutralization-mixing AMD and basic materials like limestone, lime or magnesia to precipitate the bulk of heavy metals-is the method of choice for historic TSFs and legacy mines because it is effective, easy to construct and operate, and can be tailored to the site-specific geochemical properties of AMDs (Kefeni et al., 2017;Moodley et al., 2018). In Japan, for example, chemical neutralization of AMDs from legacy mines have been subsidized by the government to the tune of ~70 B JPY (~US$ 770 M) for the last 40 years (Tomiyama et al., 2019). ...
Article
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Porphyry ores and E-wastes/WEEE are two of the most important copper-bearing materials on the planet. Over 60% of world copper output comes from porphyry copper ores while E-waste(s) is globally the largest copper-bearing waste category since the 1980s. They also contain critical elements for low-carbon technologies essential in the clean energy transition's success. In this review, a critical analysis of ore distribution/processing, metal extraction, E-waste generation and E-waste recycling is presented, focusing on identifying challenges and how to address them with emerging technologies and sustainable socio-environmental strategies. Access to ore deposits is a major hurdle for mine development while the absence of a consistent E-waste classification and legislation, including poor collection rates, remains serious problems in E-waste recycling. As lower grade porphyry ores are exploited, difficulties in processing/extraction due to mineralogical complexities, very fine particles and the generation of “dirty” concentrates will become more prevalent. For E-wastes recycling, current trends are to develop smaller, more mobile, and eco-friendly hydrometallurgical alternatives to pyrometallurgy that can handle localised compositional and feed variabilities. Finally, more sustainable mine waste management strategies, including better LCIA tools with spatial and temporal dimensions, are needed to limit socio-environmental impacts of resources exploitation and maintain the sector's SLO.
... The flexibility, density and anti-corrosion properties of lead are still actively used in the construction of tanks for storage of caustic liquors and as protection against X-rays and radiation. Lead is used in the manufacture of paints and pigments and other chemical compounds [16]. ...
Article
Information is given about the need to dispose of waste from the Shymkent lead plant in the form of slags, which have accumulated about 2 million tons. It is proved that lead production slags contain a large number of toxic compounds, such as lead, zinc, osmium, and cadmium, which are dangerous sources of environmental pollution. According to the results of X-ray diffractometric analysis and DTA, it was found that the slag of lead produc- tion contains a fairly high number of non-ferrous metal compounds: the content of lead oxide up to 2 %, zinc oxide up to 17% and copper oxide up to 1.25% of the total weight of the sample. The qualitative composition and content of non-ferrous metals of lead slags makes it possible to make the process of recycling toxic waste from lead production technically and economically feasible. The results of preliminary tests allow us to select a technology for more complete and selective extraction of lead and zinc oxides from the slag waste of lead production. When using a selective method for extracting non- ferrous metals, it is expected to improve the ecological state of the environment and reduce the negative impact on human health due to the disposal of toxic slags from lead production. At the same time, a significant contribution is made to the development of the system of rational use of natural and secondary resources.
... The result of such chemical feedback is acid mine drainage (AMD), which flows into old mining tunnels and groundwater, destroying local ecologies and compromising plant, animal and human health [2]. However, one form of bacteria, Acidithiobacillus ferrooxidans, thrives in highly acidic conditions and accelerates the acidification process [3]. ...
... Whether applied for AMD or NMD treatment, the performance of PBRs depends on the substrate depletion rate, clogging rates (e.g. biofouling or precipitation) and on the specific contaminant removal mechanisms [8,15]. For better PBR performance and longevity, suitable reactive mixtures must be carefully selected depending on material availability at the mine site, mine drainage quality and operating conditions [16]. ...
Article
Efficiency of passive bioreactors (PBRs) to treat mine drainage (acid-AMD and neutral-NMD), in northern climates, is evaluated using pilot-scale PBRs installed at the Raglan mine site (Quebec, Canada). Three reactors (PBR-AMD, PBR1-NMD and PBR2-NMD) were filled with reactive mixtures and operated (at hydraulic retention times of 2.5d and 1d, for AMD and NMD) for 48 days, 94 days and 44 days, respectively. The AMD quality was 27.6 mg/L Ni, 23.7 mg/L Fe, 2.4 mg/L Cu, and 3186 mg/L SO 4 2− , at pH 3.6, while the NMD quality was 23.9 mg/ L Ni, 0.06 mg/L Fe < 0.003 mg/L Cu, and 587 mg/L SO 4 2− , at pH 7.2. Removal efficiencies of the PBR-AMD reactor were 93-95 % vs 53-56 % Ni (at the beginning and end of the tests, respectively), 96-99 % Fe and 99 % Cu. In the PBR1-NMD reactor, 99 % vs 83 % Ni (in 2017 and 2018, respectively) was removed, while in the PBR2-NMD reactor, 95-99 % vs 61-83 % Ni (at the beginning vs at the end, respectively) was removed. However, all bioreactors failed to meet environmental criteria. None of the bioreactors developed favorable conditions for sulfate reducing bacteria (SRB). Ni retention was likely mainly governed by sorption mechanisms on organic matter or on Fe-oxy-hydroxides. Low temperatures, combined with salinity, may explain the lack of SRB growth in the reactors and the absence of SO 4 2− treatment. The treatment of Cu was not affected by the low temperatures and the primary mechanism of Fe removal in the PBR-AMD reactor was precipitation in the form of oxy-hydroxides.
... A velocidade de geração de DM e sua composição são variáveis em razão da influência de vários fatores como pH, temperatura, quantidade de oxigênio, água, concentração de Fe 3+ , microrganismos quimiolitoautotróficos, que catalisam a geração de DM e a superfície de contato dos sulfetos metálicos com os 1998). Entre as fontes de carbono já testadas no tratamento biológico de DM, têm-se esgoto doméstico, esterco animal, serragem, casca de cereais, soro de leite, vinhaça, lodo de esgoto e resíduos sólidos municipais (HAO et al., 2014;JAMIL;CLARKE, 2013;KEFENI;MSAGATI;MAMBA, 2017;KUMAR et al., 2015;KUMAR et al., 2011;MOCKAITIS et al., 2014;MOODLEY et al., 2017;PLACE;FIGUEROA;WILDEMAN, 2006 Resíduos da indústria cervejeira: potencial e pertinência de uso no tratamento biológico de drenagem de mina Não foram encontrados trabalhos na literatura que tenham usado resíduos de cervejaria como fonte de carbono para redução de sulfato. São produzidos como resíduos da produção de cerveja grãos gastos, trub da produção de mosto e resíduos de levedura (PERIMENIS et al., 2018). ...
Article
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RESUMO Rochas contendo sulfetos metálicos podem ser oxidadas em um processo catalisado por procariotos quimiolitoautotróficos ou Fe3+. A atividade mineradora acelera esse processo ao gerar resíduos contendo sulfetos metálicos com grande superfície de contato. O lixiviado resultante, conhecido como drenagem de mina (DM), é rico em sulfato, íons hidrogênio e contaminantes químicos inorgânicos como ferro (Fe), zinco (Zn), cádmio (Cd), manganês (Mn), níquel (Ni), arsênio (As) e alumínio (Al). Para remover tais poluentes, atualmente, o principal tratamento utilizado é a adição de reagentes alcalinos. Entretanto, esse método tem limitada eficiência, alto custo e gera grandes volumes de resíduos sólidos tóxicos de relativa solubilidade. Bactérias redutoras de sulfato (BRS) podem oxidar matéria orgânica com geração de sulfeto. Algumas vias metabólicas do processo consomem H+neutralizando o pH. O sulfeto produzido pode reagir com contaminantes inorgânicos e precipitá-los, permitindo sua recuperação da fase líquida. O uso de subprodutos industriais e urbanos contendo diferentes fontes de carbono como doadores de elétrons no tratamento de DM tem sido investigado. Este artigo sumariza dados sobre as variáveis relevantes para a atividade microbiana durante o tratamento biológico de DM, analisando o atual cenário de pesquisas com fontes alternativas de carbono. Discute-se ainda novas fontes de matéria orgânica ainda não aplicadas para tratamento biológico de efluentes e que, sob aspectos de sustentabilidade, dos pontos de vista sustentável e econômico, podem ser usadas no tratamento de resíduos.
... The mixing of different fluids in nature causes various phenomena, which often have unexpected environmental impacts. Such impacts can be significant for chemically unusual fluids, like acid mine drainage (AMD) that exhibits low pH and particularly high concentrations of Fe and sulfates (Genty et al., 2016(Genty et al., , 2017Moodley et al., 2018). For example, the discharge of AMD into surface water causes severe environmental problems, such as high total dissolved solid concentrations and unpleasant colors and odors in the water (Gaikwad and Gupta, 2008;Galhardi and Bonotto, 2016;Simate and Ndlovu, 2014). ...
Article
Precipitates induced by the pore-scale mixing of iron sulfate solutions with simulated groundwater were investigated using a microfluidic pore model to assess the environmental impacts of the infiltration of acid mine drainage into a shallow aquifer. This model was employed to visualize the formation of precipitates in a porous network and to evaluate their physicochemical influences on pore flow. Four types of groundwater (Na-HCO3, Na-SO4, Na-Cl, and Ca-Cl) were evaluated, and precipitation rates were calculated by processing images of precipitates in the pores captured via microscopy. The results showed that all groundwater types formed a yellow-brownish precipitate at the interface of the iron solution and simulated groundwater flow. Microscopic X-ray analyses demonstrated that precipitate morphology varied with groundwater type. Faster precipitation was observed in the following order by groundwater type: Na-HCO3 > Na-Cl > Na-SO4 > Ca-Cl, which was attributed to the different stability constants of the major anions in each simulated groundwater with Fe ions. Chemical equilibrium models suggested that precipitates were Fe minerals, with FeOOH as the predominant form consistent with the results of X-ray photoelectron spectrometry. The presence of FeOOH implies that precipitates may serve as an effective sorption barrier against some nutrients and heavy metals for the underlying groundwater. However, dye-flow experiments suggested that the precipitates may clog aquifer pores, thereby altering hydrogeological properties in the aquifer.
... In the literature, different technologies have been proposed to treat surface water, groundwater and soil polluted by metalcontaining effluents. [4][5][6] Some of them, such as the addition of alkaline materials to precipitate the metal ions, reverse osmosis or passive technologies such as constructed wetlands or phytoremediation, have been used widely. 2,7 Sorption also is a costeffective solution for the removal of heavy metals 8 but requires a subsequent stage of desorption or removal of the contaminant by some other method. ...
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BACKGROUND This work studied the treatment and metal recovery of a synthetic acid mine drainage (AMD) containing 500 mg L−1 of Cu2+ and Fe+3 and 50 mg L⁻¹ of Ni²⁺ and Sn²⁺ by using a bioelectrochemical system (BES). The presence of electroactive bacteria improved the performance of such reactor configuration, in contrast to systems with abiotic anodes. RESULTS Operating as microbial fuel cell (MFC), all the Fe³⁺ was reduced to Fe²⁺ in about 24 hours and Cu²⁺ was electrodeposited onto the cathodic surface, a copper electrode, obtaining pure Cu⁰. Almost all the Cu in the catholyte was recovered after 4 days. The maximum current density attained in this stage was 0.136 mA cm⁻² and a maximum power of 0.0134 mW cm⁻². Then, a subsequent operation as microbial electrolysis cell (MEC) allowed to simultaneously recover the Fe²⁺, Ni²⁺ and Sn²⁺ by fixing the cathode potential at −0.7 V vs Ag/AgCl. The electrode material in this stage was titanium. The tin was completely deposited onto the cathodic surface after 1 day of electrolysis. After 3 days, 77% and 60% of nickel and iron, respectively, was recovered. CONCLUSION It was possible to recover Cu⁰ generating electricity at the same time. The cell potential difference required for the metal electrodeposition of Fe²⁺, Ni²⁺ and Sn²⁺ was lower than in the case of the BES because of the contribution of the electroactive bacteria. Sequential metal deposition is possible by adjusting the operating parameters of the BESs reactors. This article is protected by copyright. All rights reserved.
... This problem of the acidic nature of water is not restricted to a limited area near the source of generation but extended to a larger area if this water gets discharged to the main water stream [14]. The AMD has generally more impact on the groundwater than that of the quality of surface water [15]. If the mines which are producing acidic water are present in the permeable formation, this acidic water (low pH) penetrates the aquifer and spreads into and over a larger area with the movement of groundwater which is used by human beings in different ways like wells and bore wells. ...
Chapter
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Acid Mine Drainage (AMD) is the most severe environmental problem facing the mining sector in the current scenario because of low pH and high pollutants concentration. AMD contains a high amount of sulphate viz. pyrite, FeS 2 ,andtoalesser extent pyrrhotite and heavy metal ions, contaminate both surface water and groundwater. To treat AMD, extensive research projects have been initiated by governments, the mining industry, universities, and research establishments. The environmental impact of AMD can be minimized at these basic levels; prevention should be taken to control the infiltration of groundwater to the pollution site and control the acid-generating process. There are some conventional active methods to treat AMD, such as compost reactor and packed bed iron-oxidation bioreactors; however, these methods have associated with costly material and high maintenance cost, which increases the cost of the entire treatment. In an alternative, the use of low-cost materials such as fly ash, metallurgical slag, zero-valent iron (ZVI), cement kiln dust (CKD), and organic waste such as peat humic agent (PHA), rice husk, and eggshell can be a valuable measure for economic viability to treat the metal-rich wastewater.
... Physical, chemical, and biological methods have been developed for AMD treatment [12][13][14][15]. Among these, chemical precipitation has advantages over other procedures, such as short reaction time, high recovery efficiency, good selectivity, and minimal operational management [10]. ...
Article
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In this paper, a combined precipitation–flotation system is proposed for the removal of Fe(III), Zn(II), and Cd(II) as hydroxides. The efficiency of precipitation, as a function of pH, metal ion concentration, and dosage of the precipitating agent as the main variables, was evaluated. The results showed that 99% efficiency was attained from a mixture solution containing the three metal ions in sulfate media at pH 10.3 after 15 min of treatment. The sedimentation behavior showed that a larger precipitate facilitated solid/liquid separation at 30 min. The characterization of precipitates was performed by X-ray diffraction (XRD) identifying iron, zinc, and cadmium oxides; hydroxides; and sodium sulfate. For the flotation, a 20 mg/L solution of dodecylamine (DDA) was used as a collector. Such a solution allowed for the removal of 76% of precipitates in concentrate. An increase in the collector concentration diminished the float percentage due to the micelle formation and low adsorption of the collector on the surface of the precipitate. The results provide evidence of the effectivity of the removal of metal ions by the combined precipitation–flotation system as an alternative for the treatment of acid mine drainage (AMD) in less time in comparison with a sedimentation stage.
... In the co-bioremediation approach, reducing microorganisms can use the carbon from the organic wastewater stream as an electron donor to breakdown inorganic pollutants [10]. This dual treatment approach where a pollutant from one stream works as an intermediary for the remediation of another has been the topic of much research in recent years [11][12][13][14][15]. However, the research has currently mostly been limited to the use of complex organic matter sources such as primary sewage sludge for co-remediation with AMD [14,[16][17][18]. ...
Article
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This study evaluated the co-remediation performance of an active–passive process comprised of passive permeable reactive barrier acid mine drainage (AMD) pre-treatment and active anaerobic digestion treatment of AMD with effluent as a carbon source. The bioreactor was operated for 24 consecutive days with peak chemical oxygen demand (COD) and sulphate loading rates of 6.6 kg COD/m3/day and 0.89 kg SO42−/m3/day, respectively. The AMD pre-treatment was capable of removing 99%, 94% and 42% of iron (Fe), potassium (K), and aluminium (Al) concentrations, respectively. The biological treatment process was capable of removing 89.7% and 99% of COD and sulphate concentrations, respectively. The treated wastewater copper (Cu), sulphate (SO42−), and pH were within the effluent discharge limits and the potable water standards of South Africa. Fe, Al, manganese (Mn), nickel (Ni), and zinc (Zn) concentrations in the treated wastewater were marginally higher than the discharge and potable water limit with all concentrations exceeding the limit by less than 0.65 mg/L. The remediation performance of the process was found to be effective with limited operational inputs, which can enable low cost co-remediation.
... Contamination of soils and aqueous systems affected by acid mine drainage (AMD) is a serious threat that demands the attention of the scientific community (Moodley et al. 2018). Among the environmental risks derived from AMD, the extremely low pH of affected waters, the high concentration of sulphate and heavy metals either dissolved or accumulated in adjacent soils or the impact on the local flora and fauna, can be mentioned. ...
... Experiments using various reactive materials will be conducted using batch and column studies [7]. The selection of materials was carried out to consider their availability, cost and environmental sustainability [9]. This research is a batch study that focuses on the different reactivities of selected materials as a single source. ...
Article
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Containing sulphates and heavy metals, acid mine drainage (AMD) should be managed strategically to mitigate and control the migration of the contaminants to the downstream area. Conventional treatment techniques such as using lime to increase pH levels and metal precipitation or using imported material are usually inefficient and unsustainable. The AMD treatment investigated in this study uses the permeable reactive barrier (PRB) technique to enhance bacterial sulphate reduction and metal sulphide precipitation. The AMD treated is seepage water from industrial mining waste rock dump. This study aims to calculate the removal efficiency percentage of reactive materials to reduce contaminants in a batch test. Reactive materials used were organic waste generated locally i.e. domestic sewage sludge (SE), municipal compost (CO), cocopeat (CP), and the inorganic waste material is fly ash (FA) from a coal-firing power plant. A batch test was conducted in 56 days in an anaerobic chamber using nitrogen gas to support an anaerobic environment during subsampling. Mine water used in this test has a low pH level of 3.2, alkalinity (as CaCO3) < 1 mg/L, high sulphate 3280 mg/L, and contains Fe 46 mg/l, Al 54 mg/L, Cu 2.3 mg/L and Zn 3.4 mg/L. The test result at day 56 from using individual reactive material shows increased pH levels to 6.9; 5.6; 3.7; and 11.6 for sewage (SE), compost (CO), cocopeat (CP), and fly ash (FA), respectively. Alkalinity was increased to 1450 mg/L (SE), 323 mg/L (FA), 15 mg/L (CO), 1 mg/L for CP. The highest sulphate removal was measured in 85% from addition of FA. Sulphate removed from organic material reactor were 52% by (SE), 17% by (CO), 20% by (CP). %RE of dissolved metals (Al, Cd, Co, Mn, Ni, Fe, Cu, Zn), from SE reactor was 80%, CO reactor 80%, CP reactor 52%, FA reactor 94%. Oxidation-Reduction Potential (ORP) was measured to determine reducing conditions. ORP were measured at -551 mv, 255 mv, 156 mv, and -113 mv for SE, CO, CP and FA respectively. SE has the potential to remove metals and favour reducing conditions for sulphide precipitation at medium pH levels. Meanwhile, metal precipitation from addition of FA is mainly due to hydroxide precipitation at high pH levels. FA was able to decrease the most sulphate due to ion adsorption.
... The pH decreased over time in the experiments with metals due to the formation of metal sulfides (Supplementary Material, Fig. B). With the metal sulfide formation, acidification of the medium occurs for two protons are released as a product of this reaction (Moodley et al., 2018). Consequently, the pH remained constant in the experiments without metals and in the chemical and disproportionation controls (Supplementary Material , Fig. B). ...
Article
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Biological sulfidogenic systems are advantageous over hydroxide precipitation methods to recover base metals from hot and acidic metallurgical streams. Sulfide precipitation is not widely used in the hydrometallurgical industry for the high operational and capital expenses associated with compartmentalizing the sulfidogenic and metal precipitation process. A single-stage elemental sulfur-reducing process in which sulfidogenesis and metal precipitation occur concurrently could significantly decrease these costs. This study examines the effect of metals on the sulfidogenic activity of an adapted thermoacidophilic sulfur-reducing culture. Batch tests were conducted with Cu²⁺, Ni²⁺, and Zn²⁺ in concentrations up to 100, 570, and 525 mg L⁻¹, respectively. All metal ions were completely precipitated (LOQ < 0.1 mg L⁻¹) with higher volumetric sulfide production rates than in the experiments without metals. Dissolved metals appear to stimulate the sulfur reduction metabolism in a redox-dependent process. Additionally, we investigated the use of an unadapted microbial inoculum from a full-scale anaerobic reactor as a fast start-up inoculum for a sulfidogenic process under high temperature (80 °C), low pH (pH 3), and high Cu²⁺ concentrations (up to 1143 mg L⁻¹). After seven days of operation, we found equivalent sulfidogenic rates to those obtained after 75 days of adaptation with the same inoculum. These results encourage the development of a single-stage metal precipitation and sulfur-reducing process under conditions suitable for thermoacidophilic microorganisms.
... In recent years, the technologies for removing pollutants in wastewater by industrial solid waste have attracted interest. Among industrial solid wastes, steel slag is favored in wastewater treatment due to its excellent physicochemical properties (Fisher and Barron 2019;Moodley et al. 2018). Steel slag as industrial solid waste is primarily composed of CaO, Fe 2 O 3 , MgO, SiO 2 , MnO, and other alkaline substances (Yildirim and Prezzi 2011), which could hydrolyze with H 2 O to release OH − , displaying superior acid neutralization and chemical precipitation capabilities (Yang et al. 2019). ...
Article
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Acid mine drainage is an extraordinarily acidic and highly heavy metal ion-contaminated leachate, seriously threatening the environment. In this work, an industrial solid waste of steel slag is the adsorbent to remediate the simulated acid mine drainage containing a large amount of Fe(II) ions. Due to the excellent physicochemical properties and structures, steel slag exhibited remarkable Fe(II) removal performance. Its maximum removal efficiency was up to 100%. The initial pH, the dosage and particle size of steel slag, and initial concentration of heavy metal ions on Fe(II) removal efficiency were determined. The pseudo-second-order model and Freundlich isotherm model well described the adsorption behavior of steel slag, implying that the adsorption of Fe(II) by steel slag was mainly multilayer chemisorption. The thermodynamic study demonstrated that the adsorption process was endothermic and spontaneous; the enthalpy change was calculated to equal 91.21 kJ/mol. Mechanism study showed that the entire removal process of Fe(II) by steel slag was completed by electrostatic adsorption, chemical precipitation, and surface complexation in cooperation, and the chemical precipitation was the dominant mechanism. Meaningfully, this study provides a valuable strategy and path for engineering applications of AMD remediation by steel slag, which is prospective as an ideal candidate for Fe(II) ions elimination, inspiring the future development of “Treating the wastes with wastes.”
... While there is substantial research on the technical strategies for mine remediation (Lottermoser 2010;Moodley et al. 2018;Rasafi et al. 2017), studies focused on public participation and community values regarding how to restore/rehab/reclaim an area where a mine was once located are also valuable (Banfield & Jardine 2013; Rixan & Blangy 2016;Beckett & Keeling 2019). Research has shown that the mining "industry prioritizes technical aspects of mine closure over the social, cultural, economic, and ecological" (Monosky & Keeling 2021), hence restoration strategies must be envisioned by all stakeholders if diverse goals are to be achieved. ...
Article
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The United Nations Decade on Ecosystem Restoration promises to educate society on the many ways ecological restoration projects can benefit humankind. One avenue of possibilities for restoration ecology lies with concerns of environmental justice. The concept of futuristic restoration, which posits a paradigm of ecological restoration that is future-oriented, aligns well with calls for policymakers to address the circumstances, processes, and systems within which environmental inequalities are typically produced. This article offers three policy arenas where futuristic restoration can be employed in order to further environmental justice goals: (1) land conservation prioritization; (2) urban development plans; and (3) mine remediation projects. The temporal dimension of sustainability and how it pertains to restoration projects will also be addressed. This article is protected by copyright. All rights reserved.
... Acid mine drainage (AMD) contamination of water resources is a concern in most regions impacted by previous mining activity. When the AMD enters the water systems (surface and groundwater), it causes biotic impact to the dams, rivers, lakes and streams through direct toxicity, disruption to nutrient cycle, visual changes from orange/yellow color staining of stream sediments, habitat alteration by metal precipitation resulting in waters becoming unstable or unsuitable for irrigation, domestic or even industrial uses [1,2]. AMD is formed as a result of the oxidation of sulphide minerals such as pyrite (FeS 2 ), chalcopyrite (CuFeS 2 ), galena (PbS), sphalerite (ZnS), and arsenopyrite (FeAsS) [3]. ...
Chapter
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In addition to known negative environmental impacts, acid mine drainage (AMD) contaminates freshwater resources, limiting the availability of clean water in mining regions. AMD is characterized by high elemental and sulphate concentrations and low pH. Nanomaterials are increasingly investigated for the remediation of AMD‐contaminated water due to their high reactivity and larger adsorptive surface areas). In addressing the treatment of contaminated waters sustainably, cellulose‐based materials offer a suitable alternative, as cellulose can be extracted from a wide range of plants, including agricultural wastes. This chapter reviews the synthesis of cellulose‐based nanomaterials and composites and their application in the remediation of AMD‐contaminated water. It begins with a discussion on cellulose sources, details on the structure, extraction techniques, and surface modifications that allow for use in AMD treatment. It also explores cellulose in composites with inorganic nanomaterials and with other biological compounds such as chitin. Finally, we examine the potential for cellulose‐based materials in the valorization of AMD‐contaminated water.
... The challenge with active technologies is the use of high dosages of virgin chemical, generation of heterogeneous and highly mineralised sludge, production of brine and regenerant wastewater and exorbitant energy inputs (Masindi and Tekere, 2020). On the other hand, passive treatment technologies include constructed wetlands (Allende et al., 2014;Luo et al., 2020), biological barriers (Moodley et al., 2018;Park et al., 2019), permeable reactive barriers (Naidu et al., 2019;Shabalala et al., 2014), aerobic wetlands (Johnson and Hallberg, 2005), anaerobic wetlands (Skousen et al., 2019), and lime drains (Skousen et al., 2017). However, Passive treatment systems have challenges of poor performance in concentrated solutions, clogging of the system, and catastrophic failures (Simate and Ndlovu, 2014). ...
Article
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In this novel study, acid mine drainage (AMD) was treated using a hybrid approach comprising a nano-and-biotic system synergistically integrated in a step-wise and modular fashion. Specifically, the treatment chains were made up of different stages, which comprise, neutralisation using activated magnesite or MgO-nanoparticles (NPs) (Stage 1) and polishing the product water using staged wetlands (Stage 2) or a series of wetland in a step-wise connection. In stage One (1), real AMD was treated with MgO-NPs at a ratio of 1:100 (1 g/100 mL), 500 rpm of mixing speed, and One (1) hour of hydraulic retention time (HRT) whilst in stage 2, the final water was fed into constructed wetlands, i.e. Three (3) interconnected wetland with different flow modalities [(I) subsurface vertical flow (SSVF-CW), (II) free water surface flow (FWS-CW), and (III) subsurface horizontal flow (SSHF-CW)], for further purification and polishing to the desired product. In this stage, i.e. stage 2, the product water and substrate were collected daily at the outlet and bottom of each wetland. Findings from this study demonstrated pH to have increased from 2.6 to 10.4. Significant removal of inorganic contaminants was also observed and the following removal sequence was registered, Fe (99.8%) ≥ Al (99.5%) ≥ Mn (99.24%) ≥ Zn (98.36%) ≥ Cu (97.38%) ≥ Ni (97.7%) ≥ SO42─ (80.59%). Reduction in electrical conductivity (EC) was also observed (86%). Specifically, the nano-part removed the metals and sulphate partially whereas the bio-part effectively removed sulphate and EC levels, thus denoting stellar combination and complementary performance for the hybrid system in integrated fashion. The state-of-the-art analytical instruments were used to underpin and succinct the fate of chemical species in raw and product MgO-NPs, substrates, and the grass. Finally, the product water conformed to the prescribed standards for effluent discharge hence proving that the synergy of neutralisation and bio-remediation, i.e. nano-and-biotic system, could potentially yield the desired results in mine water management and afield. This will go a long way in curtailing ecological footprints associated with mining activities thus fostering the concept of sustainable development.
... neutralizing AMD either through active or passive means. Active treatment involves the continuous 557 addition of alkaline substrates to neutralise the pH and subsequently remove metals, while passive 558 treatment involves natural and biological processes to treat AMD (Moodleya et al., 2017). However, 559 treatment of this AMD would require high costs (Kefeni et al., 2017). ...
... Several low-cost adsorbent materials were used to remove heavy metals from AMD, such as biochar (Oh and Yoon, 2013;Wibowo et al., 2022), chitosan-bentonite (Feng et al., 2019), clay , chicken eggshells (Zhang et al., 2017), attapulgite and schwertmannite (by-products of AMD treatment) (Moodley et al., 2018), shrimp shell waste (Núñez-Gómez et al., 2019), agricultural waste (Bandara et al., 2020;Yang et al., 2020), and organic biomixture (Levio-Raiman et al., 2021). Among those adsorbent materials, biochar, as a carbonaceous material produced by the thermal conversion of biomass, is promising to obtain a better heavy metals removal in AMD (Oh and Yoon, 2013). ...
Article
Acid mine drainage (AMD) contains numerous heavy metals, which need appropriate treatment before releasing to the environment. This study reports Fe and Mn removal from AMD by adsorption using ultra-fine biochar derived from coal, peat, and coconut shell. Clamshell waste was used and compared with pure CaO as a conventional precipitant. All adsorption materials were tested in an artificial solution at different pH conditions and contact time at room temperature. The adsorption process reached equilibrium at 100 min. Neutral pH was the best condition to achieve a higher removal efficiency. Results showed that biochar could successfully remove >90 % Fe and 80 % Mn. The isotherm model of each sorption fit with the Langmuir model. Metals can be precipitated in 10 min using clamshell waste, which is comparable with pure CaO. biochar, pure CaO, and clamshell are potential materials to solve heavy metal pollution and increase pH in wastewater.
... This weathering process is accelerated, however, due to the increase in surface area (fine particles). Because of this rapid reaction, AMD is considered one of the most serious environmental issues in the mining industry [108,117,118]. The continuous production of acid from mine waste causes a drop in pH, which creates favorable conditions for autochthonous microorganisms found in these wastes. ...
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Mining has advanced primarily through the use of two strategies: pyrometallurgy and hydrometallurgy. Both have been used successfully to extract valuable metals from ore deposits. These strategies, without a doubt, harm the environment. Furthermore, due to decades of excessive mining, there has been a global decline in high-grade ores. This has resulted in a decrease in valuable metal supply, which has prompted a reconsideration of these traditional strategies, as the industry faces the current challenge of accessing the highly sought-after valuable metals from low-grade ores. This review outlines these challenges in detail, provides insights into metal recovery issues, and describes technological advances being made to address the issues associated with dealing with low-grade metals. It also discusses the pragmatic paradigm shift that necessitates the use of biotechnological solutions provided by bioleaching, particularly its environmental friendliness. However, it goes on to criticize the shortcomings of bioleaching while highlighting the potential solutions provided by a bespoke approach that integrates research applications from omics technologies and their applications in the adaptation of bioleaching microorganisms and their interaction with the harsh environments associated with metal ore degradation.
... McCullough [17] investigated the effects on physical and chemical characteristics of the waste rock dump material caused by intermixing of heterogeneous materials in the disposed soil volumes. McCullogh and Lund, and Sloss, as well as Moodley et al. [20,31,32] demonstrated the significance of the backfilling methods used in the reinstatement of holds, pits, and hollows of mines and the effects of acid mine drainage phenomena as a high-criticality problem of reclamation. Sloss [20] examined the use of coal by-products in mined sites backfilling works and their suitability for use as substitute natural rock residuals and improper soil volumes. ...
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The reclamation of lignite surface mines is a long-term commitment of high complexity. These reclamation projects consist of land use repurposing, reinstatement of landforms and landscape , remediation of polluted soils and water bodies, restoration of ecosystems, and other related activities, which are usually developed when mines enter the ultimate phase of their operational life. Nowadays, reclamation is supported by regulatory settings and legislative provisions, which motivate the affected communities to move towards a circular economy and sustainable development. This paper investigates the geoenvironmental and socioeconomic problems of reclamation and draws research questions on how the strategic planning of a reclamation project can be performed and how the relevant project risks can be investigated and managed. In turn, a prototype methodology based on experts' judgment is suggested with a case study combining: (a) the IDEF0 (Integrated DEFinition Function) modelling technique, as a low cost and easy-to-develop tool enabling strategic planning of reclamation projects, and (b) the Weighted Risk Factor analysis WRF as a suitable method for effective risk analysis and response planning in post-mining frameworks. Finally, a discussion on the methodology and proposals for further research are provided.
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Ecologically engineered passive treatment systems have been successfully implemented world-wide to decrease concentrations of ecotoxic metals in mine drainage without continuous energy or material inputs. Typical design life of such treatment systems is approximately 20 years, at which point rehabilitative maintenance must occur. For example, oxidation ponds, designed to accumulate iron (oxyhydr)oxide solids, must be dredged to sustain effective hydraulic retention time, creating large volumes of potentially hazardous waste. In this study, total recoverable and leachable metals in iron (oxyhydr)oxide solids from the oxidation ponds of two multi-cell passive treatment systems in the historic and now derelict Tri-State Lead-Zinc Mining District in Ottawa County, Oklahoma, United States were characterized using several batch leaching tests. This assessment informs potential disposal and reuse scenarios for the solids once they have been removed from the systems. Solids leached nonhazardous concentrations of metals under Resource Conservation and Recovery Act guidelines. However, some metals exceeded Oklahoma Water Resources Board criteria for protection of public water supplies, and total metals exceeded some consensus-based toxicity benchmarks for soils and sediments. Beneficial reuse plans for the iron (oxyhydr)oxides must consider these potential risks.
Article
Aiming at the prevention and control of acid mine drainage (AMD) at the source for a long-term period, herein, we report for the first time an active passivation coating with self-healing function to protect metal sulfide minerals from oxidation. Benzotriazole (BTA) inhibitor was loaded into halloysite nanotube (HNT) under vacuum condition and encapsulated by Cu-BTA complexes stoppers, and then the PropS-SH/HNT-BTA (PSHB) coating was prepared by mixing HNT-BTA nanoparticles with γ-mercaptopropyltrimethoxysilane (PropS-SH) to inhibit pyrite oxidation. The morphology and composition of HNT nanocontainers were characterized by SEM, TEM, EDS and FTIR methods. The loading capacity of BTA in HNT-BTA lumen was determined by TGA measurements. The releasing behavior of BTA under different pH conditions was investigated by UV–vis spectrophotometer and the release mechanism of BTA from HNT-BTA lumen was validated using Ritger-Peppas model. It was found that HNT-BTA could achieve stimulus-responsive release of BTA under acidic conditions. The passivation and self-healing properties of PSHB coating were studied by electrochemical measurements, chemical leaching tests and scratch tests. The experimental results showed that the novel PSHB coating had long-term oxidation resistance and active self-repair function after damage. Meanwhile, the passivation and self-healing mechanism of the PSHB coating is also introduced. It is thought that this study is helpful to bring new ideas in the field of metal sulfide mineral passivation.
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Coal mining represents one of the primary economic incomes in the department of Boyacá, Colombia. However, the acid mine drainage (AMD) generated has a tremendous environmental impact in the area due to the presence of sulfate ions (SO4-2), heavy metals, and low pH This article studies the behavior in the content of Fe and sulfates in AMD samples when treated within an artificial anaerobic vertical flow wetland, analyzing the concentration of these elementsand the content of dissolved oxygen (DO) and pH at different time intervals. The treatment of a MAD from the department of Boyacá was carried out using a bioreactor prototype with an organic substrate to provide the necessary conditions for the development of sulfate-reducing bacteria. Measurements were made with hydraulic retention times between 24 to 120 hours, monitoring the changes in the content of total Fe, SO4-2, pH, and DO. The data obtained show a reduction for total Fe of 88.3%, established at 5.61g∙m-2∙day-1, and for SO4-2 of 34.3% with 9.35g∙m-2∙day-1; reaching a maximum removal degree of 52.32% at 120h for sulfates and 92% for Fe, where the maximum removal peak is achieved, reducing the Fe removal rate for longer times. The reduction in the concentration of Fe is related to the reduction of DO and regulation of the pH, in addition to favoring the reduction of sulfate ions through the formation of the mineralogical phases pyrite and siderite. These data show that the anoxic conditions of the organic environment are maintained, for which a subsequent aeration stage is suggested.
Article
Covering coal mining tailings with layers of soil reduces the generation of acid mine drainage. These layers are designed to minimize water seepage and the flow of oxygen into tailing deposits. In Brazil, tailings from mineral coal processing are rich in pyrite, are often stored in piles, and are covered with layers of soil on the surface. This study provides results on the performance of four experimental soil cover models on tailings resulting from coal mining in southern Brazil. Pilotscale physical models were constructed on-site, and the water balance of the covers, suction, volumetric moisture content, temperature in the tailings/cover layers, and quality of released effluent were measured. The covers designed with soil and bottom ash significantly reduced the volume of water seepage through the tailings and improved the quality of the generated effluents. Moreover, the results demonstrated that the performance of the cover depends on climate variations, and its behavior varies seasonally.
Article
Bentonite is widely used in industrial wastewater treatment due to its large reserves and excellent physicochemical properties. In order to further improve the properties of bentonite, natural bentonite needs to be modified before application. The common modification methods of bentonite include thermal activation, acid activation, and microwave activation. In recent years, bentonite composite has been applied to the treatment of the mine wastewater including all kinds of waters influenced by mining activity. In this paper, the main modification methods of bentonite, the preparation methods of bentonite composite materials, and the application of bentonite composite materials in the treatment of the mine wastewater including toxic metals are summarized. Also, these technologies are compared and discussed in depth. All kinds of bentonite calcined at 400 ~ 450 ℃ can better improve the surface area. The structure of bentonite is not damaged, and have enough activity to facilitate the adsorption of organic matter at 400 ~ 450 ℃. The acid concentration of Ca-bentonite acidification process is higher than that of Na-bentonite acidification. The microwave activation method of bentonite has faster reaction rate and better modification effect. The combination of microwave activation and other bentonite activation technologies will significantly improve the activation efficiency. The interlayer spacing of organic bentonite generally increases with the increase of modifier concentration, but it will not increase when the added surfactant dose exceeds the cation exchange capacity of the original bentonite. When the concentration of modifier used in modification is the same, the longer the carbon chain of modifier, the greater the layer spacing of organic bentonite. The magnetic bentonite can adsorb Cu2+, Cd2+, Mn2+, and Cr6+ and can be separated and recovered. The composite of graphene/graphene oxide bentonite can significantly increase the spacing between the bentonite layers, improve the pore structure of the composite obviously, and avoid agglomeration. But the price of graphene is much higher than other adsorption materials, which limits the industrial application of the technology. Investigation and research show that bentonite composites have high removal potential for pollutants in mine wastewater. This paper aims to scientifically summarize and analyze the treatment of mine wastewater with bentonite, and discusses some influencing factors.
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The successful acid mine drainage (AMD) treatment needs site-specific installation and implementation, as well as the deployment of technology that is compatible with the pollutants contained in the AMD. If key by-products of the AMD can be recovered, the financial sustainability of the AMD remediation method may be greatly improved. Additional research into novel and innovative solutions is necessary to advance in this direction. To accomplish this, it is necessary to have a complete awareness of current remediation technologies that are available and accessible. Active physical treatment methods such as ion exchange, adsorption, electrochemistry, and membrane techniques were examined in this article. Membrane technology excels in terms of ease of use, versatility, and environmental effect but produces brine streams the management of which remains vital for future adoption of the technology. Liquid membranes (LM), Micellar Enhanced Ultra-Filtration (MEUF), and Polyelectrolyte Enhanced Ultra-Filtration (PEUF) are all innovative membrane technologies that may provide some possibilities for metal recovery from chemical sludge and/or brine streams. Electrochemical technologies are considered an attractive alternative for AMD treatment, because they require only electricity as a consumable and can treat AMD to high standards by removing metals via (co)precipitation and sulfate via ionic migration (when an anion-exchange membrane is used in the configuration), while producing significantly less sludge. However, the accepted shortcomings include membrane/electrode fouling produced by (co)precipitates on the active surfaces necessary for the process, a lack of understanding regarding the effective scaling up to industrial scale, and the relatively expensive capital expenditure (CAPEX) required. The removal of heavy metals from AMD effluents by adsorption has a number of technical and environmental benefits, including high efficiency, and environmental friendliness. Despite its benefits, this technique has certain hurdles, such as the production process for low-cost adsorbents.
Chapter
Acid Mine Drainage (AMD) is a severe environmental problem in the area of metal and mining industries throughout the world. AMD becomes a pollutant for the surface and groundwater due to its highly acidic nature and high toxicity. From mineral exploration to the closing stage, mining methods, both opencast as well as underground, have serious environmental impacts with large‐scale consequences. Sulphide minerals, mainly pyrite, present in coals when exposed to air and water and get oxidized and hydrolyzed to form sulphuric acid, which further dissolves heavy metals. Formation of AMD is a natural process but it is accelerated by large‐scale indiscriminate, unscientific mining and construction activities. AMD is characterized by low pH, high acidity, and elevated concentration of sulphate, TDS (total dissolved solids), and heavy metals. Globally, groundwater quality deterioration is influenced by mine drainage. Leachates of AMD originating from overburdened mine waste have the potential to penetrate through the ground surface to the subsurface and contaminate groundwater. During the rainy season, leaching of heavy metals (Cu, Pb, Hg, etc.) from mine spoils happens more easily, thereby polluting groundwater. AMD treatment is mostly costlier than its control and it will take some years, even after mining activity has stopped. Initial identification of the problem has the potential to limit the factors accountable for AMD generation. This chapter conceives the fundamental science of AMD generation and its impact on groundwater quality, and also suggests the measures for its treatment and management.
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Highly acidic and toxic metal ion containing acid rock drainage (ARD) can cause severe environmental problems and endanger aquatic life. However, due to the high metal ion containing ARD is an auspicious source of metals for recovery and reuse. The feasibility of using waste digested activated sludge (WDAS) as a biosorbent for selective metal recovery from a highly complex mine water characterized by low pH (2.6), high sulfate concentration (80.8 g L⁻¹) and a multitude of metals (Co, Cr, Cu, Fe, Mn, Ni, Th, U, V, Y, and Zn) at concentrations from few mg L⁻¹ to several g L⁻¹ was investigated. The effect of pH (2.0–10.0) and WDAS concentration (3.8–22.2 g L⁻¹) on metal ion removal and the effect of several recovery solutions and their concentrations on metal recovery were explored in batch experiments. Metal removal was influenced by pH and WDAS concentration. A strong selectivity was observed in the recovery step employing 1 M Na2CO3 solution. The combination of a one-step removal and a two-step recovery approach enabled recovery of U (108.0 ± 6.6%), Cu (39.2 ± 2.5%), and Th (53.7 ± 7.7%) due to formation of strong carbonate complexes increasing the purity of U and Cu up to tenfold compared to the mine water. The results revealed that careful adaption of pH, WDAS concentration, and number of steps of the process according to the combination of metals present in solution is of great importance.
Article
Two constructed wetlands, unplanted (CCW) and planted (PCW) units were investigated to assess the role of plants (Typha latifolia) and the impact of hydraulic loading rates in the remediation of acid mine drainage (pH ≤ 2) and metal attenuation. Results revealed significant differences (p < 0.05) between metal removal efficiencies of CCW and PCW, except for Al, Mn and Cr. CCW (92–42%) exhibited higher sulfate removal efficiency than PCW (85–30%), indicating significant impairment of microbial sulfate reduction in the presence of plants. The overall activity decreased from 2.55 and 2.21 to 2.04 and 1.90 mg chemical oxygen demand (COD) removed mg (total volatile solids) TVS–1 day⁻¹, whereas specific sulfidogenic activity decreased from 0.79 and 0.76 to 0.62 and 0.59 mg sulfate reduced mg TVS–1 day⁻¹ in CCW and PCW, respectively. Wetland media retaining metals (>90% of the total metal mass removed) was further extracted, good metal extraction efficiencies (%) were achieved for Fe (57.7–97.6), Al (39.2–61.3), Zn (65.9–98.8), Co (70.8–77.3), Ni (78.3–89.2) and Cr (82.2–87.1) using different chelating acids. Following extraction, metals were recovered as 49.1–97.6% Fe, 29.7–47.9% Al, 57.4–94.9% Zn, 50.3–73.6% Co, 67.0–86.5% Ni and 68.3–83.8% Cr.
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Вирішення проблем водозабезпечення та охорони вод в рамках водних екосистем є актуальним питанням сьогодення. В роботі вирішено важливу науково-технічну проблему розробки високоефективних методів водопідготовки та очищення стічних вод від забруднень, що дозволяє створити маловідходні технології демінералізації. Нанофільтраційні технології водопідготовки дозволяють отримувати високоякісну питну воду та технологічну воду з необхідними показниками. Концентрати, які утворюються при нанофільтраційному очищенні високомінералізованих природних та шахтних вод, характеризуються підвищеним вмістом іонів жорсткості і сульфатів. Ефективного очищення води від сульфатів можна досягти при застосуванні синтезованого алюмінату натрію та вапна. Ступінь пом’якшення та очищення концентратів від сульфатів залежить від дози вапна та алюмінату натрію, співвідношення реагентів, реакції середовища. Ефективність вилучення сульфатів з води зростає з підвищенням дози вапна при постійній дозі коагулянту та з підвищенням дози гідроксоалюмінату натрію при постійній дозі вапна. Перевищення дози вапна на 20 % більше від стехіометричного співвідношення є недоречним, оскільки призводить до незначного підвищення ефективності вилучених сульфатів з води. Ефективність вилучення сульфатів за постійних доз вапна зростає з підвищенням дози коагулянту до 20–60 % від стехіометричної кількості сульфатів. При доведенні рН середовища до 7–8 за допомогою вуглекислого газу досягнуто підвищення ефективності вилучення іонів жорсткості та сульфатів. При знесоленні високомінералізованих вод при оптимальній дозі реагентів концентрація сульфатів знизилась до 69–89 мг/дм3 та іонів жорсткості – до 0.44–1.15 мг-екв/дм3. В роботі були розраховані рівняння регресії для залежності залишкових концентрацій сульфатів і іонів жорсткості у воді в залежності від дози вапна і алюмінату натрію.
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Paste and Thickened Tailings (PTT) technology has the advantages of water-saving, dam safety, and environmentally friendly, which can improve tailings disposal and backfill operation. In the process of thickening preparation, the ultra-fine tailings particles are prone to form suspended water-locking flocs, which are severely detrimental to the underflow concentration improvement in the thickener. This study focuses on the deep cone thickener underflow density improvement. The high-precision CT scanning and three-dimensional reconstruction technology were used to explore the pore structure shear evolution to enhance underflow slurry dewatering behavior and reveal the thickening mechanism. Results show that when the shearing rate of the rake is two revolutions per minute (rpm), the concentration of tailings underflow rises from 59.2% wt to 68.5% wt, increases by 15.71%. The rake shearing breaks the pore structure of the flocs network, the pores quantity increases and the porosity decreases by 21.74%. After shearing, suspended particles fill the pores, the pore connectivity decreases by 26.74%, the absolute permeability decreases by 31.35%, the sealed pore water is discharged, and the bed slurry can be thickened. The study can improve the utilization rate of tailings (from classified tailings to whole tailings), make the thickening process going deep(raising high concentration slurry to paste slurry), and increase the backfill capacity (backfill underground goaf in time), so as to effectively reduce the tailing pond and goaf quantity.
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For more than 30 years, sulfide gold ores were treated in metallurgic plants located in Nova Lima, Minas Gerais, Brazil, and accumulated in the Cocoruto tailings dam. Both flotation and leaching tailings from a deactivated circuit, as well as roasted and leaching tailings from an ongoing plant, were studied for their acid mine drainage potential and elements’ mobility. Detailed characterization of both tailings types indicates the presence of fine-grain size material hosting substantial amounts of sulfides that exhibit distinct geochemical and mineralogical characteristics. The samples from the ongoing plant show high grades of Fe in the form of oxides, cyanide, and sulfates. Differently, samples from the old circuit shave higher average concentrations of Al (0.88%), Ca (2.4%), Mg (0.96%), and Mn (0.17%), present as silicates and carbonates. These samples also show relics of preserved sulfides, such as pyrite and pyrrhotite. Concentrations of Zn, Cu, Au, and As are higher in the tailings of the ongoing circuit, while Cr and Hg stand out in the tailings of the deactivated circuit. Although the obtained results show that the sulfide wastes do not tend to generate acid mine drainage, leaching tests indicate the possibility of mobilization of toxic elements, namely As and Mn in the old circuit, and Sb, As, Fe, Ni, and Se in the tailings of the plant that still works. This work highlights the need for proper management and control of tailing dams even in alkaline drainage environments such as the one of the Cocoruto dam. Furthermore, strong knowledge of the tailings’ dynamics in terms of geochemistry and mineralogy would be pivotal to support long-term decisions on wastes management and disposal.
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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.
Conference Paper
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Acid mine drainage (AMD) remains a major environmental challenge for the mining industry. The preferred options for effectively limiting the environmental impact of AMD consist in controlling the reactions through the use of preventative techniques. Their principal objective is to exclude at least one of the constitutive elements of the chemical reactions, i.e. water, oxygen, or sulfidic minerals. The article recalls the basic principles and reviews different approaches for the prevention and control of AMD upon mine closure. The main methods include multi-layer covers, water covers, and an elevated water table (with a mono-layer cover). Their main advantages, limitations and uncertainties are addressed. Alternative approaches, such as environmental desulphurization and co-disposal of waste rock and tailings, are also discussed.
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Underground and opencast coal mining has been ongoing since 1896 on the Stockton Plateau, West Coast, New Zealand. Acid Rock Drainage (ARD) from historic and current mine workings has had an adverse environmental impact on the surrounding aquatic environment. Current mining operations now cover a total area of some 700 hectares, and approximately 220 hectares contain historic underground workings. Total disturbed overburden is 140 million tonnes averaging 1% sulfur. One of the main catchments affected by ARD includes the Mangatini stream, which has a base flow of 350 L s-1 and a pH that can be as low as pH 2.8 Solid Energy New Zealand Ltd has a dual approach to ARD mitigation including minimisation strategies (such as oxygen-excluding covers; alkaline oxygen-excluding covers, selective placement, and strategic mine planning to prioritise capping) and treatment strategies that include at-source treatment options (engineered wetlands, limestone leach beds) and catchment treatment systems (fine limestone dosing (20 tonnes per day) and a lamellar treatment plant using 60 tonnes per week of Ca(OH) 2 to remove coal fines and raise pH). This paper looks at some of these projects. A daily tip-head sampling programme for total S of active overburden areas is undertaken by Solid Energy. Data is used to prioritise overburden areas for capping, audit overburden areas to ensure PAF rock is placed with overburden area cores, and identify hot spots for additional ARD management requirements. As part of its effort to achieve company-wide net environmental gain, environmental research projects have focused on the use of waste streams for beneficial use at Solid Energy mining operations. To date this includes coal ash, cement kiln dust (CKD), and mussel shells. Results demonstrate that coal ash and cement kiln dust (CKD) placed as covers over acidic rock are very efficient oxygen-excluding layers. pH rebound associated with acidic drainage under a 5,000 tonne CKD cover occurs after ~1 year. Widespread capping using CKD and coal ash is proposed based on this success. Waste mussel shells have been trialled on site as a method to control ARD in-dump. Trial results were exceptional with pH > 6, and Solid Energy has applied for consents to use up to 60,000 t/a that volume being available in the South Island. A full scale fine lime dosing plant has been installed in the Mangatini Stream, and this has been operating 24 hours a day since April 2007. pH has generally consistently been above pH 4.7, and aluminium has been < 1mg L-1 since this plant started operation. This has met community stakeholder expectations, and the project has an anticipated life of 100 years. Solid Energy's dual approach to ARD mitigation is starting to have significant effects. In the short term the effects of ARD are being treated in-dump, and by catchment treatment
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This paper reviews the environmental issues and management practices in the mining sector in the North America. The sustainable measures on waste management are recognized as one of the most serious environmental concerns in the mining industry. For mining activities, it will be no surprise that the metal recovery reagents and acid effluents are a threat to the ecosystem as well as hazards to human health. In addition, poor air quality and ventilation in underground mines can lead to occupational illness and death of workers. Electricity usage and fuel consumption are major factors that contribute to greenhouse gases. On the other hand, many sustainability challenges are faced in the management of tailings and disposal of waste rock. This paper aims to highlight the problems that arise due to poor air quality and acid mine drainage. The paper also addresses some of the advantages and limitations of tailing and waste rock management that still have to be studied in context of the mining sector. This paper suggests that implementation of suitable environmental management tools like life cycle assessment (LCA), cleaner production technologies (CPTs), and multicriteria decision analysis (MCD) are important as it ultimately lead to improve environmental performance and enabling a mine to focus on the next stage of sustainability.
Conference Paper
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The Fisher site is a backfilled and reclaimed (in 1984) surface coal mine in western Pennsylvania, USA. A post-closure toe seep at the site discharged acid rock drainage generated in pyritic rock zones that were identified using geophysical techniques. In 1995, sodium hydroxide and bactericide solutions were injected through cased boreholes into the pyritic zones in a two-step process: sodium hydroxide followed by bactericide. Prior to the event, the toe seepage had been treated with the addition of sodium hydroxide followed by a series of settling ponds and wetland zones. Post-injection, the seepage exhibited net-alkaline chemistry and the sodium hydroxide amendment was discontinued. Based on the prevailing wisdom at the time, the effects of the injection event were expected to be temporary. Almost two decades later, the beneficial effects of the two-step injection event persist and bond release for the site is pending. The seep chemistry has been monitored for over 25 years and the data suggest that the steady-state condition of net alkalinity in the seep water entering the ponds and wetland may be permanent. One current view is that the initial suppression of Acidithiobacillus ferrooxidans bacterial community with the sodium hydroxide and bactericide has been maintained by the seasonal infusion of bactericidal organic acids derived from the robust vegetative cover. The situation appears to be self-sustaining.
Conference Paper
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The passive treatment of acid rock drainage (ARD) impacted waters using waste mussel shells utilises vertical flow successive alkalinity producing system (SAP) technology, with considerable industry acceptance in New Zealand. This paper discusses the seven year R&D pathway for this technology. The process is attractive to the mining industry as the shells are free-to-site in some instances, and the installation process is relatively straightforward. Sulfate Reducing Bioreactors (SRB’s) and oxic and anoxic treatment of ARD impacted waters are common passive treatment technologies employed by the mining industry. Mussel shells have significant advantages over these systems, being negative value (and thus free-to site, or even delivered for profit), having a high acid neutralisation capacity (> 80 wt% CaCO3 equivalent), good hydraulic conductivity (~1x10-3 m/s), and sufficient organics to support sulfate reducing bacteria catalysts for metal removal. This means that processing costs are reduced and the shells can be placed directly into the reactor for treatment. Down-flow bioreactors using shells have been investigated to encourage the calcium carbonate induced neutralisation of ARD followed by SRB alkalinity generation and trace metal removal. Details are presented of two systems (fresh and weathered shells) that were established at the Solid Energy Stockton Coal Mine, West Coast, New Zealand. Results show the formation of an upper zone dominated by sediment transitioning into underlying Fe then Al precipitate zones that is eventually replaced by a deeper sulfate reducing zone. Metal removal efficiencies range from 96 – 99% for Fe, Al, Ni, and Zn. The longevity of the system is linked to permeability, which is controlled by layers of sludge that develop during treatment.
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Acid mine drainage is the most significant environmental pollution problem associated with mining industry. The main cause of acid mine drainage is the occurrence of pyrite and sulphide minerals with the rock of coal seams. During mining these sulphide minerals get exposed to air and mine water, then oxidation and hydrolysis results in the generation of acid mine drainage. The low pH value of the discharge mine water results in the further dissolution of minerals and release of toxic metals, when it allowed getting discharge into other water bodies. This acidity and high toxic metals concentration are harmful to the vegetation, aquatic life and wild life. This review paper describes the general chemistry of acid mine drainage generation; its impact on environment; different treatment techniques as remedial and control measures and future trend in treatment technology.
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The aim of this research is to reduce heavy metal and sulfate content of acid mine drainage (AMD) through the methods of passive filtration by combining permeable concrete and organic materials to achieve a low cost, yet effective temporary treatment method for rural/poor communities who are affected by AMD. The acids are filtered through layers of alternating pervious concrete and biological composting layers. The concrete layers target removal of heavy metals such as iron, manganese, potassium, magnesium, etc. through precipitation as well as reduce sulfate content to a small degree along with total dissolved solids. The concrete layers aid in raising the pH of the AMD to more acceptable levels. The biological layers achieve sulfate reduction through the metabolism of sulfate-reducing-bacteria (SRB)-this process however will require time and the organic layer thus will be thicker and less permeable than the concrete layers in order to allow seepage to take place at a reduced rate. A wide variation of composting layers were tested including cow manure, chicken manure, sawdust, straw, zoo manure, leaf compost, grass cuttings and river mud to find an optimum mix of materials which allows for the greatest sulfate reduction through SRB's. Long-term testing and effectiveness of the rigs will be undertaken to establish limitations and lifespan of the filtration system. AMD from the Witwatersrand gold fields and Mpumalanga coal fields with exceptionally high sulfate content were used to test effectiveness of the organic materials over a short period of time with long term testing being conducted with a synthetic AMD due to limited supply of the reagent. The short term testing yielded reductions of sulfates in the region of 56% when using kraal manure as the biological reagent mixed with sawdust for added organic carbon. The filter also successfully raised the pH to 8 while removing a significant portion of heavy metals. The results show promise for using the technology as a low cost, temporary measure to protect locally impacted groundwater, especially for isolated and/or rural communities.
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Gardner, W.C., Naeth, M.A., Broersma, K., Chanasyk, D.S. and Jobson, A.M. 2012. Influence of biosolids and fertilizer amendments on element concentrations and revegetation of copper mine tailings. Can. J. Soil Sci. 92: 89-102. A 3-yr field study on copper mine tailings in British Columbia determined the effects of fertilizer and biosolids on element concentrations in tailings and vegetation and on plant biomass. Bios lids applied at 50, 100, 150, 200 and 250 Mg ha(-1) (dry weight) increased total carbon, iron, magnesium, nickel, nitrogen, phosphorus, sulphur and zinc and available ammonium, iron, manganese, nitrate, phosphorus and zinc in tailings. With highest applications on silt loam tailings, total zinc (214 mg kg(-1)) exceeded Canadian Council of Ministers of the Environment guidelines for agricultural soils. Total chromium and copper exceeded these guidelines but not due to biosolids, being high in controls (chromium 38, 8; copper 647, 1291 mg kg(-1); silt loam and sandy sites, respectively). Plant tissue calcium, phosphorus, magnesium, manganese, nitrogen and zinc increased with increasing biosolids. Plant tissue calcium (20 g kg(-1)) and molybdenum (5 mg kg(-1)) exceeded National Research Council maximums for beef cattle. Total molybdenum in unamended silt loam (35 mg kg(-1)) and sandy tailings (18 mg kg(-1))and vegetation on silt loam (112 mg kg(-1)) were high. Biosolids had variable effects on tailings molybdenum and decreased total plant tissue molybdenum. Fertilizer and control treatments had limited plant growth. Managed biosolids use in reclamation can ameliorate sites and facilitate vegetation establishment, with low environmental risk.
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This study focused on the removal of heavy metals from a synthetic acid mine water by using continuous column experiments and Phosphate carbonated Wastes as alkaline drains. The passive treatment system targeted aims in neutralizing the acid mine drainage (AMD) containing high concentrations of dissolved iron and other metals. In Morocco, the phosphate mine industry produces huge quantities of overburden waste rocks (named herein PLW) which contain significant quantities of carbonates (calcite (46 wt %) and dolomite (16 wt %). The column experiments were set-up in laboratory and the testing were run under anoxic and oxic conditions by using a hydraulic retention time was 15 hours. The inflow to the treatment system ranged 5.5 mL/min, with acidic pHs of around 3, concentrations of dissolved Fe, Mn, Al, Ca, Zn and Cu were 600, 20,166, 350, 15 and 23 mg/L respectively, containing also some traces of Co, Cr and Ni. The test results showed that pH became neutral and a significant decrease in terms of metal concentrations; in particular for Fe (600 to 120 mg/L), Al (160 to 1.7 mg/L) and Cu (23 to 0.002 mg/L).
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This study reports on mine water treatment with apatite containing bone meal filters. Bone meal has earlier been used to immobilize lead, copper and zinc from solution by formation of metal phosphates. Two different mine waters were tested, one neutral and one acidic. Trace elements, especially lead, was efficiently retained by the bone meal in the acidic system. In the neutral system pH was too high for apatite dissolution and the decrease in metal concentrations were thus only due to physical filtering.
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Unactivated attapulgite was characterised and utilised as an adsorbent for the removal of heavy metal and neutralisation of acid mine drainage (AMD) from a gold mine. Adsorption experiments were carried out by agitation of a fixed amount of attapulgite with a fixed volume of AMD in a thermostatic shaker for varying times. Attapulgite showed that it can neutralise acid mine drainage as the pH after 4 h was 7.11. The results showed that metal ion removal after 4 h was 100% for Cu(II) and Fe(II), 93% for Co(II), 95% for Ni(II) and 66% for Mn(II) using a 10% (w/v) attapulgite loading. The experimental data best fit the Langmuir Isotherm with maximum adsorption capacities for Cu(II), Co(II), Mn(II), Fe(II) and Ni(II) being 0.0053, 0.0044, 0.0019, 0.01, and 0.0053 mg/g, respectively. The adsorption process fitted well the pseudo first order kinetics for Co(II) and Cu(II) and pseudo second order for Ni(II), Mn(II) and Fe(II). Thermodynamic data show that Cu(II), Co(II), Fe(II) and Ni(II) adsorption was thermodynamically spontaneous whilst Mn(II) was not thermodynamically spontaneous. The process is endothermic for Cu(II), Co(II), Mn(II), and Ni(II) and exothermic for Fe(II). Spent attapulgite (attapulgite that has already been used to remove metals) could be reused twice without regeneration.
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Recent studies have shown that a combination of coal fly ash (FA) and Al(OH)3 can be used to treat neutral mine drainage (NMD) and reduce sulphate concentration to within South African drinking water quality levels, Class II (400–600 mg/L). The short- comings of this method were the large amounts of FA required to raise the pH to greater than 11 (3:1 liquid- to-solid ratio) so that Al(OH)3 can be added to facilitate removal of sulphate ions through ettringite precipitation. This requires large silos to store FA, making up- scaling of this treatment technology using normal mixing methods to be unrealistic. In the current study, a jet loop reactor was used to reduce the amount of FA needed to increase the pH to greater than 11. The pH was raised to greater than 11 by mixing 0.25 % of lime (w/v ratio) and 13 kg of coal FA with 80 L of NMD in a jet loop reactor. After the pH of the mixture was above 11, amorphous Al(OH)3 (83.2 g) was added to the mixture. This resulted in the sulphate concentration decreasing to less than 500 mg/L. Bench-scale studies using 0.25 % (w/v) of lime and 6:1 coal mine water to FA ratio could not reduce the sulphate concentration to below 500 mg/L. Therefore, the impingement and cavitation mixing techniques that happen in a jet loop reactor played an important role in enhancing sulphate removal.
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High rate sulfate reducing bioreactors can be effectively used in the treatment of acid mine drainage (AMD). The main disadvantage of sulfate reducing bioreactors is the requirement of a suitable carbon source and electron donor as the dissolved organic carbon content of AMD is usually quite low. In this study, a landfill leachate was used as a low-cost carbon source for sulfate reducing bacteria in a fluidized-bed (FBR) reactor for the treatment of synthetic AMD. Ethanol was replaced with leachate in the feed of FBR operated longer than 150 days at 35 °C. Although sulfate reduction rates decreased appreciably when ethanol (3.44 g sulfate/L/d) was replaced with leachate (0.90 g sulfate/L/d), leachate-fed FBR still performed well as the pH increased to neutral values, soluble metal removals were 82–99.9%, and total metal removals were 80–99.9%. In the case of leachate, electron flow to sulfate reduction decreased significantly. Higher performance may be achieved at chemical oxygen demand (COD)/sulfate ratios higher than 1.0. This study showed that leachate may be used as a low-cost soluble substrate for sulfate reducing bacteria in high rate bioreactors for AMD treatment.
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Limestone drains are often implemented in the treatment of acid mine drainage (AMD), but when the AMD contains high levels of dissolved Fe their lifetime is dependent on the rate of precipitation of Fe hydroxide on the limestone surface. This study used a small-scale laboratory experiment to define the longevity of a limestone drain by determining the thickness of the Fe coating encapsulating the limestone particles when the system lost its maximum neutralising potential. Synthetic AMD (100 mg/L Fe, pH 4–4.8) was pumped through a column containing limestone particles for 1110 h, when the effluent pH had dropped from a maximum of 6.45–4.9. The decline in neutralisation during the experiment was due to the formation of Fe hydroxide coatings on the limestone grains. These coatings are composed of lepidocrocite/goethite in three distinct layers: an initial thick porous orange layer, overlain by a dense dark brown crust, succeeded by a layer of loosely-bound, porous orange globules. After 744 h, a marked increase in the rate of pH decline occurred, and the system was regarded as having effectively failed. At this time the Fe hydroxide crust effectively encapsulated the limestone grains, forming a diffusion barrier that slowed down limestone dissolution. Between the coating and the limestone substrate was a 60 μm wide void, so that agitation of the limestone sample would readily remove the coating from the limestone surface.
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Acid mine drainage poses severe environmental pollution problems due to its high acidity, toxic metals and sulphate contents. In this review, the available prevention of acid mine drainage generation, treatment options and their importance in light of the future perspectives are briefly discussed. The possible resources to be recovered such as ferric hydroxide, ferrite, rare earth metals, sulphur and sulphuric acid and their economic benefit are discussed. Furthermore, the importance of mine tailing for stabilisation of contaminated soil and production of building materials are highlighted. Overall, this review has shown that the resource recovery and reuse is a non-debatable holistic approach to environmental sustainability and acid mine drainage pollution reduction. Finally, the future perspective and areas that deserve in-depth exploration are underscored.
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Chicken eggshells (ES) as alkaline sorbent were immobilized in a fixed bed to remove typical heavy metals from acid mine drainage (AMD). The obtained breakthrough curves showed that the breakthrough time increased with increasing bed height, but decreased with increasing flow rate and increasing particle size. The Thomas model and bed depth service time model could accurately predict the bed dynamic behavior. At a bed height of 10 cm, a flow rate of 10 mL/min, and with ES particle sizes of 0.18–0.425 mm, for a multi-component heavy metal solution containing Cd²⁺, Pb²⁺ and Cu²⁺, the ES capacities were found to be 1.57, 146.44 and 387.51 mg/g, respectively. The acidity of AMD effluent clearly decreased. The ES fixed-bed showed the highest removal efficiency for Pb with a better adsorption potential. Because of the high concentration in AMD and high removal efficiency in ES fixed-bed of iron ions, iron floccules (Fe2(OH)2CO3) formed and obstructed the bed to develop the overall effectiveness. The removal process was dominated by precipitation under the alkaline reaction of ES, and the co-precipitation of heavy metals with iron ions. The findings of this work will aid in guiding and optimizing pilot-scale application of ES to AMD treatment.