No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Fate of the naturally occurring radioactive materials during treatment of acid mine drainage with coal fly ash and aluminium hydroxide
Abstract
Mining of coal is very extensive and coal is mainly used to produce electricity. Coal power stations generate huge amounts of coal fly ash of which a small amount is used in the construction industry. Mining exposes pyrite containing rocks to H2O and O2. This results in the oxidation of FeS2 to form H2SO4. The acidic water, often termed acid mine drainage (AMD), causes dissolution of potentially toxic elements such as, Fe, Al, Mn and naturally occurring radioactive materials such as U and Th from the associated bedrock. This results in an outflow of AMD with high concentrations of sulphate ions, Fe, Al, Mn and naturally occurring radioactive materials. Treatment of AMD with coal fly ash has shown that good quality water can be produced which is suitable for irrigation purposes. Most of the potentially toxic elements (Fe, Al, Mn, etc) and substantial amounts of sulphate ions are removed during treatment with coal fly ash. This research endeavours to establish the fate of the radioactive materials in mine water with coal fly ash containing radioactive materials. It was established that coal fly ash treatment method was capable of removing radioactive materials from mine water to within the target water quality range for drinking water standards. The alpha and beta radioactivity of the mine water was reduced by 88% and 75% respectively. The reduced radioactivity in the mine water was due to greater than 90% removal of U and Th radioactive materials from the mine water after treatment with coal fly ash as ThO2 and UO2. No radioisotopes were found to leach from the coal fly ash into the mine water.
... Therefore, additional sources for coal supply must be discovered promptly to sustain the functionality of the coal industry into twenty-first century in South Africa. Meanwhile, the Waterberg Coalfield is being considered as a fit replacement of the Witbank Coalfield, because it could potentially contain (Madzivire et al., 2014;Lloyd, 2002;Lloyd, 2000) majority of the country's virgin coal resources remain in situ. The Highveld Coalfield reserves are vital to the long-lasting of Sasol Synthetic Fuels (SSF) and Sasol Chemical Industries (SCI) (Madzivire et al., 2014). ...
... Meanwhile, the Waterberg Coalfield is being considered as a fit replacement of the Witbank Coalfield, because it could potentially contain (Madzivire et al., 2014;Lloyd, 2002;Lloyd, 2000) majority of the country's virgin coal resources remain in situ. The Highveld Coalfield reserves are vital to the long-lasting of Sasol Synthetic Fuels (SSF) and Sasol Chemical Industries (SCI) (Madzivire et al., 2014). ...
... Coal fly ash (CFAs) are fine particulate materials, with major combustion waste product (normally 60-88%) produced when burning crushed coal in thermo-electric power stations (TPSs) to produce electricity (Madzivire et al., 2014;Vassilev & Vassileva, 2007). The coal type and technological procedures used in TPSs determine the constituent and properties of these fine particulate solid products (Vassilev & Vassileva, 2009). ...
Over the years, South Africa has generated vast amounts of coal fly ash and gold slime tailings, constituting over 70% of the country's waste materials. These byproducts contain elevated levels of trace metals, posing a potential threat to the environment upon release. Addressing this issue requires a comparative study of the environmental impact of coal fly ash and selected mine tailings on water resources and land pollution. This research aims to investigate and compare leachability, metal release, oxidation effects, and environmental pollution between coal fly ash and gold tailings. By contrasting these aspects, the study seeks to enhance understanding of the potential risks associated with these materials, aiding informed decision-making for their management and regulation. Additionally, the research explores the correlation between gold tailings' acid potential generation and coal fly ash's alkaline potential generation in terms of leachability, metal release, oxidation effects, and environmental pollution. The research employed comprehensive laboratory experiments and analytical investigations, including leaching tests under simulated weathering conditions. A total of 51 gold tailings samples and 66 coal fly ash samples were analysed through SEM and XRD for mineralogical insights and ICP-MS and XRF for geochemical analyses. Statistical analysis revealed the significant roles of pH, Fe ions, Ca2+, and Mg2+ in metal extraction from both materials. Notably, the study identified key factors contributing to the environmental impact of coal fly ash and gold tailings. SEM imagery highlighted heterogeneous characteristics in gold tailings, while factor analysis indicated the potential release of ferrous ionic species, contributing to acidity. Trace elements like Ni, Zn, Pb, and Cu were predominantly associated with Fe/Mn oxides during leaching experiments, facilitating their mobilization with acid-generating ions
... Another industrial byproduct, fly ash (FA), generated from coal mines, has proven an effective substitute, with [11],finding that FA increased the pH and reduced the concentrations of Fe, Al, Mn, and sulphate significantly. Another additive for the neutralization process, aluminum hydroxide (Al(OH) 3 ), has been added to mixtures to more efficiently neutralize acidity and precipitate contaminants, as Al(OH) 3 is known to slow the increase in pH by increasing the content of CaO solutions [12][13][14]. ...
... While these and other studies show that neutralizing agents are effective at reducing mineral contamination through precipitation [10,15], with [16], listing the corresponding pH levels for twelve contaminating metals, of which eleven are below pH 8.5 [16], previous work also shows that controlling neutralization is difficult. Some studies could not effectively neutralize the acidity with other agents [17], while many overshot neutralization [11,13,14,18,19]. Likewise, studies show that achieving a 6.5-8.0 pH range does not remove another major contaminant, sulfur, in its many forms [9,10]. ...
... Using two of the same reagents as this study, but adding them in two stages, [14], overshot neutralization to arrive at a pH of 10. Ref. [13], went back to the reagents of their previous studies, adding CaO and FA first, then Al(OH) 3 when the pH stabilized at 9.8, and then moved into active methods of carbonation to finally neutralize the samples. ...
The necessity of mining valuable metals must be balanced with the safe and effective disposal or remediation of the resulting waste. Water, one of our most valuable resources, is a major component of the mining process, and its post-operation storage often results in acid mine drainage. While many remediation methods have been studied, they have low economic feasibility, as minimally active methods alone were inadequate, and thus required additional, costly active methods for effective neutralization. This study looks to neutralize acid mine drainage with only minimally passive methods, through an optimized dosage of lime, fly ash, and aluminum hydroxide. Wastewater samples of pH 3.62 and 5.03, containing 1.36 and 2.21 percent sulfides, respectively, were experimentally treated, with the utilized dosage parameters generated using the Monte Carlo method for neutralizing acidity. The remediated water samples presented 0.01% and 0.16% sulfur content values, which corresponds to 99.3% and 92.8% reductions, respectively. These results present, for the first time, that minimally active methods could achieve a pH of 8.5 without active methods. While future studies should validate these results and provide a more complete characterization of the water samples, the major challenge of neutralization was addressed, and, thus, these results contribute process incentives for mining companies to economically remediate their waste water in order to safeguard their surrounding communities and return valuable water back to the water cycle.
... Motsi et al., 2009 80 SUKLA SAHA and ALOK SINHA Mg concentration decreased below detection limit when the pH was increased to 12.25 because of the formation of Mg(OH) 2 . Treatment of mine water with FA also reduced Mn concentration below detection limit as Mn precipitates in the form of Mn(OH) 2 at pH 8.5-9.5 (Madzivire et al., 2014). Along with various heavy metals, sometimes AMD contains different radioactive materials such as uranium (U) and thorium (Th) from the associated bedrock (Madzivire et al., 2014). ...
... Treatment of mine water with FA also reduced Mn concentration below detection limit as Mn precipitates in the form of Mn(OH) 2 at pH 8.5-9.5 (Madzivire et al., 2014). Along with various heavy metals, sometimes AMD contains different radioactive materials such as uranium (U) and thorium (Th) from the associated bedrock (Madzivire et al., 2014). FA interacted with U and Th present in the water and form UO 2 at ph≥3 and ThO 2 at pH >5. ...
... It was also reported that treatment of AMD with FA, can remove 90% of Ra and Pb. Hence, it can be used as a safe adsorbent to treat contaminated gold mine water as no leaching of radioactive materials from coal fly ash to acidic water was reported (Madzivire et al., 2014). ...
The present study systematically and comprehensively reviewed different aspects of treating Acid Mine Drainage (AMD) with active treatment and waste materials. The work also critically reviews the status and the factors associated with the treatment process. Although, conventional active methods are very efficient but they are mainly associated with costly material as well as high maintenance cost which enhances the cost of entire treatment system. Waste materials such as fly ash, metallurgical slag, zero valent iron (ZVI), cement kiln dust (CKD), organic waste such as peat humic agent (PHA) and rice husk can be efficiently used for the treatment of AMD. However, efficiency of different waste material varied from each other due to the variation in their physical and chemical characteristics. The results from the investigation showed that fly ash, metallurgical slag and CKD raise the pH of acidic solution more, in comparison to ZVI and organic waste, due to their richness in lime content. Furthermore, fly ash can be efficiently converted and utilized in its other derivative such as chemically modified fly ash and zeolite. Efficiency of ZVI is hindered by the presence of higher concentration of total dissolved solids. PHA can treat AMD that is mild acidic in nature. Besides, long retention time is required for the removal of heavy metals and sulfur with organic waste and sulfate reducing bacteria (SRB). The study also potentially reviewed that metal removal from AMD varied due to composition of AMD and the characteristics of waste materials. However, waste materials demand more attention for its practical applicability in field conditions due to its richness, higher possibility for recycling and reuse, low installation cost and harmless nature towards the environment.
... During liming of AMD to neutralize the pH, metals precipitate as hydroxides and the final product of the neutralization reaction is calcium sulphate dehydrate (gypsum), and produces waters, compositions of which exceed the Department of Water and Sanitation (DWS) (previously known as Department of Water Affairs and Forestry, DWAF) stipulated water guidelines for Domestic Water Use (Gitari et al., 2006, Madzivire et al., 2010, Madzivire et al., 2014. The mainly gypsum sludge may also contain toxic metal species, which require proper disposal and frequent long-term environmental hazard monitoring which is unsatisfactory. ...
... In their study, the authors noted that codisposal of coal fly ash and acid mine drainage raises the pH to circumneutral levels, and hence attenuation of metal species. Madzivire et al. (2014) reported that the application of a jet loop reactor for mine water treatment using fly ash, lime and aluminium hydroxide can lower the sulphate concentration to DWA water quality guidelines acceptability and raise the pH to >10. Bologo et al. (2012) reported that the application of magnesium hydroxide for treatment of AMD can lead to an increase of the pH to 9.6 and lower the TDS from 9242 to 6037 mg/L and remove other metals except for magnesium. ...
... The relevant criteria for discharge of acidic and sulphate-rich water are given in Table 2.6. , **), Coalmining AMD and † ), Neutral drainage water (Gitari et al., 2006, Madzivire et al., 2010, Madzivire et al., 2011, Madzivire et al., 2013, Madzivire et al., 2014, Masindi et al., 2014c. ...
Wastewaters originating from mining activities are usually acidic and often contain high concentrations of Fe, Mn, Al and SO₄2⁻ in addition to traces of Pb, Co, Ni, Cu, Zn, Mg, Ca and Na. This wastewater impacts surface and subsurface water resources negatively and has to be treated before release to receiving aquatic ecosystems. Numerous wastewater treatment technologies have been developed and implemented. However, cost implications, ineffectiveness, selective treatment capabilities and generation of secondary sludge that is toxic and expensive to dispose-off to the environment due to stringent environmental regulations often limit their application. As such, mining companies are in a search for cheaper, brine free, effective and efficient mine water treatment technology. This study assessed the potential of applying mechanochemically modified cryptocrystalline magnesite-bentonite clay composite for acid mine drainage (AMD) treatment. To accomplish this, neutralization of acidity and removal of inorganic contaminants from mine effluents were studied using batch laboratory experiments and precipitation of chemical species was determined using pH Redox Equilibrium (in C language) (PHREEQC) geochemical modelling. The present study was divided into three parts which includes: (1) the application of magnesite for remediation of AMD, (2) the application of ball milled bentonite clay for remediation of AMD and (3) the application of magnesite-bentonite clay composite for remediation of AMD.In the first part of the study, AMD was reacted with cryptocrystalline magnesite. The reaction of AMD with magnesite at an optimum solid: liquid ratio of 1:100 and contact time of 60 min led to an increase in pH, reaching a maximum pH of 10, resulting in significant precipitation of most metal species. Increase of pH in solution with contact time caused the removal of the metal ions mainly by precipitation, co-precipitation and adsorption. SO₄2⁻ concentration was lowered from 4640 to 1910 mg/L. Fe was mainly removed as Fe(OH)3, goethite, and jarosite, Al as basaluminite, boehmite and jurbanite, Al(OH)3 and as gibbsite and diaspore. Al and Fe precipitated as iron (oxy)-hydroxides and aluminium (oxy)-hydroxides. Mn precipitated as rhodochrosite and manganite. Ca was removed as gypsum. Sulphate was removed as gypsum, and Fe, Al hydroxyl sulphate minerals. Mg was removed as brucite and dolomite. These would explain the decrease in the metal species and SO₄2⁻ concentration in the product water. Cryptocrystalline magnesite effectively neutralized AMD and attenuated concentration of inorganic species to within Department of Water and Sanitation (DWS) water quality guidelines for 1997. Though > 60% SO₄2⁻ removal was achieved, a polishing technology will be required to remove alkali and alkaline earth metal species and remaining SO₄2⁻ from the aqueous system.
In the second part of this study, AMD was reacted with ball milled bentonite clay. The contact of AMD with bentonite clay led to an increase in pH and a significant reduction in concentrations of metal species. At constant agitation time of 30 mins, the pH increased with the increase in dosage of bentonite clay. Removal of Mn2+, Al3+, and Fe3+ was greatest after 30 min of agitation. The adsorption affinity obeyed the sequence: Fe > Al > Mn > SO₄2⁻. The pH of reacted AMD was > 6. Bentonite clay showed high adsorption capacities for Al and Fe at concentration < 500 mg/L, while the capacity for Mn was lower. Adsorption efficiency for SO₄2⁻ was > 50%. Adsorption kinetics revealed that the suitable kinetic model describing data was pseudo-second-order hence confirming chemisorption. Adsorption isotherms indicated that removal of metals fitted the Langmuir adsorption isotherm for Fe and SO₄2⁻ and the Freundlich adsorption isotherm for Al and Mn, respectively. Gibbs free energy model predicted that the reaction is not spontaneous in nature for Al, Fe and Mn except for SO₄2⁻. Ball-milled bentonite clay showed an excellent capacity in neutralising acidity and lowering the levels of inorganic contaminants in acidic mine effluents. A polishing technology will be required to remove alkali and alkaline earth metal species and remaining SO₄2⁻ from the aqueous system.
The third part of the study evaluated the reaction of magnesite-bentonite clay composite in neutralisation of the acidity and attenuates levels of inorganic contaminants in metalliferous effluents. The interaction of the composite with AMD led to an increase in pH (pH >11) and lowering of metal concentrations. The removal of Al3+, Fe3+/2+, Mn2+ and SO42- was optimum at 20 min of equilibration and 1g of adsorbent dosage. The composite removed ≈99% (Al3+, Fe3+, and Mn2+) and ≈90% (SO42-) from raw mine effluent. Minor elements such as Co, Cu, Zn, Ni and Pb were also removed significantly. The synthesized composite showed a significantly better heavy metals and SO42- removal ability of from highly acidic solutions as compared to that obtained by cryptocrystalline magnesite and bentonite clay when used individually. Adsorption kinetics fitted better to pseudo-second-order kinetic than pseudo-first-order kinetic and intra-particle diffusion model hence confirming chemisorption. Adsorption data fitted better to Freundlich adsorption isotherm than Langmuir hence confirming multisite adsorption. Gibbs free energy model predicted that the reaction is spontaneous in nature for Al, Fe and SO₄2⁻ except for Mn. Geochemical model indicated that Fe was removed as Fe(OH)3, goethite, and jarosite, Al as basaluminite, boehmite and jurbanite, Al(OH)3 and as gibbsite and diaspore. Al and Fe precipitated as iron (oxy)-hydroxides and aluminium (oxy)-hydroxides. Mn precipitated as rhodochrosite and manganite. Ca was removed as gypsum. Sulphate (SO₄2⁻) was removed as gypsum, and Fe, Al hydroxyl sulphate minerals. Mg was removed as brucite and dolomite. This would explain the decrease in the metal species and SO₄2⁻ concentration in the product water. The composite removed the contaminants to below South African legal requirements for water use. It was concluded that the composite has the potential to neutralize acidity and attenuate potentially toxic chemical species from acidic and metalliferous mine drainage as compared to cryptocrystalline magnesite and bentonite clay when used individually. As such, it can be concluded that the new synthesized composite has a synergetic potential in wastewater treatment.
... [15] Fly ash helps in enhancing the precipitation process because it is capable of neutralizing acidity and precipitating out most of the potential elements to acceptable limits for irrigation or even potable water quality. [29,30] Treatment of wastewater with fly ash and Al(OH) 3 produces good quality water where thorium is precipitated into the form of ThO 2 which occurs at a pH greater than 5. [30] Besides that, the addition of coagulants such as alum, iron salts and organic polymers can also enhance the removal of metal ion from wastewater. [31][32][33] The precipitation of thorium hydroxide by adding MgCl 2 and NaOH needs an optimum pH range between 9.9 and 11.2. ...
... [15] Fly ash helps in enhancing the precipitation process because it is capable of neutralizing acidity and precipitating out most of the potential elements to acceptable limits for irrigation or even potable water quality. [29,30] Treatment of wastewater with fly ash and Al(OH) 3 produces good quality water where thorium is precipitated into the form of ThO 2 which occurs at a pH greater than 5. [30] Besides that, the addition of coagulants such as alum, iron salts and organic polymers can also enhance the removal of metal ion from wastewater. [31][32][33] The precipitation of thorium hydroxide by adding MgCl 2 and NaOH needs an optimum pH range between 9.9 and 11.2. ...
Thorium affects human health and causes environmental issues. The concentration of thorium in the environment may increase due to waste that is produced from human activities like mining, rare-earth extraction, and others. If this waste is not handled properly, thorium may leak and cause water contamination. This review summarises the methods of thorium removal from wastewater. The article addresses the main features of the techniques for thorium removal by physicochemical processes such as chemical precipitation, ion exchange, adsorption, electrochemical and membrane filtration. Their advantages and limitations in the applications are evaluated. Bioadsorption and natural material are widely used in the removal of thorium. However, in the near future, the electrosorption process seems to be the most promising method to treat wastewater since it can overcome limitations of adsorption techniques with the help of electric current to have a more efficient and rapid process. It should be noted that all the techniques able to remove thorium depend on pH, temperature, the concentration of thorium and other wastewater components. In general, the technical applicability, simplicity of technique and cost-effectiveness are the key factors in selecting the most suitable treatment for removal of thorium.
... It is a widespread environmental problem occurring at both working and abandoned mining operations. AMD has been identified as the second most serious environmental problem worldwide after global warming, and it is attracting increasing attention (Madzivire et al., 2014;Ríos, Williams and Roberts, 2008). The effects of AMD arising from active mine sites is of less concern compared to their abandoned counterparts due to ac- ...
... Amorphous aluminum hydroxide (Al(OH) 3 ) was then added to precipitate sulfate as ettringite, reducing the sulfate concentration from 1,043 ppm to 213 ppm. Further study (Madzivire et al., 2014) indicated that the treatment of AMD using coal fly ash also displayed the potential to remove radioactive elements, such as uranium and thorium, thereby purifying the water sufficiently to meet drinking standards. Sahoo et al. (2013) investigated the ability of coal fly ash to inhibit AMD generation in column leaching from waste containing abundant pyrite. ...
Acid mine drainage (AMD) derives from the oxidation of sulfide minerals, primarily pyrite (FeS2), and is the most severe environmental issue facing the minerals industry. The most common short-term approach to AMD treatment is migration control, such as acid neutralization and metal/metalloid and sulfate removal, through the addition of alkaline materials, including lime (Ca (OH)2), limestone (Ca CO3), gangue minerals and industrial wastes. This requires the continuous input of materials and may result in the production of a vast amount of secondary sludge requiring further treatment and disposal. Addition of chemicals is usually more important in metal/metalloid removal than in sulfate removal unless the sulfate is present in very high concentrations. A more promising long-term strategy for AMD prevention is source control through the complete removal of pyritic minerals and encapsulation of potential risk minerals by coating with impermeable surface layers. This is regarded as the most cost-effective approach, although the mechanisms underpinning this and the implementation procedures are yet to be fully elucidated. It is likely that long- A nd short-term practices can be combined to optimize the remediation of contaminated mining sites. Some factors such as differing geological and mineralogical characteristics and transportation costs must also be considered for the successful implementation of AMD prevention and remediation strategies. This review also considers some implications for AMD remediation, but the promising bioremediation of AMD is not discussed as it has been extensively reviewed.
... Heavy metals in active and abandoned mines in South Africa have impacted both surface and underground water. [40,42,45,[47][48][49][50][51]. Table 2. ...
... The legislative requirements for industrial effluents are primarily governed by the Department of Water Affairs DWS Water Quality Guidelines [46]. This purpose requires that any person who uses water for industrial purposes shall purify or otherwise treat such water in accordance with requirements of DWA [41,[46][47][48]. The relevant criteria for discharge of acidic and sulphate-rich water are given in Table 2. ...
... To reduce the above setbacks the research community have embarked on various initiatives to reduce the volume of sludge generated, the running costs and thereby improving the efficiency. Kefeni et al. [7] have proposed that such initiatives can be achieved through recovery of valuable resources such as metals [14,11,[15][16][17][18][19], gypsum [11,19], elemental sulphur [9], clean water [19] and the use readily available materials such as bentonite and clay [12] and waste materials such coal fly ash [20] It is estimated that South Africa produces 252 Mt of coal and exports about 58 Mt every year (DMR, 2009). The largest coal reserves are around Witbank, Highveld Ermelo and the Waterberg. ...
... Some of the proposed applications include using CFA as an additive in the manufacturing of cement and in road construction material as feedstock in zeolite synthesis and for neutralising and treating AMD from coal mines [23][24][25]. It has been shown that AMD can be treated with CFA, lime and Al(OH) 3 to acheive good quality with most parameters within the TWQR recommended by Department of Water and Sanitation (DWS) and World Health Organisation (WHO) for irrigation and potable water except for pH, EC and the concentration of elements such as Al 3+ and Ca 2+ [4,5,20]. ...
... All rights reserved. [10][11][12][13]. Mining houses are in a quest to come up with sustainable technologies that are economically viable and effective in the remediation of mine effluents. ...
... At pH > 10, brucite was precipitating. The results are consistent to what has been reported in literature [11,13,[45][46][47]. dissolution of CaO, MgO, Na 2 O and K 2 O with an increase in dosage, since these are alkaline earth metals and alkali metals. ...
The present study was developed with the aim of beneficiating two waste materials by converting them into a resource. Magnesite tailings, which is the byproduct of magnesite mining, was used to remediate acid mine drainage (AMD) which is the byproduct of gold mining. This will go a long way in minimizing the use of virgin resources and thus fostering the process of sustainable development. AMD was reacted with magnesite tailings at an optimum equilibration time of 30 min and 1 g of magnesite tailings dosage. Contact of AMD with magnesite tailings led to an increase in pH (pH > 10) and a drastic reduction in inorganic contaminants (>99%), except for sulphate that achieved >80% for sulphate removal efficiency. Kinetic studies showed that ·adsorption of chemical species by magnesite tailings fitted well to pseudo-second-order adsorption kinetics hence confirming chemisorption. Pore diffusion was also determined to be one of the principal mechanisms acting as a major rate governing step. pH Redox Equilibria (PHREEQC, in C language) geochemical modelling predicted that Fe removed as Fe(OH)3, goethite (FeOOH), and jarosite (KFe3(SO4)2(OH)6), Al as basaluminite (Al4(SO4)(OH)10·5(H2O)), boehmite (γ-AlO(OH)), jurbanite (AlSO4(OH)·5H2O, and Al(OH)3 as gibbsite and diaspore. Al and Fe also precipitated as iron (oxy)-hydroxides and aluminium (oxy)-hydroxides. Mn precipitated as rhodochrosite (MnCO3) and manganite (MnOOH). Ca was removed as gypsum (CaSO4·2H2O) and dolomite (CaMg(CO3)2). Sulphate was removed as gypsum and Fe, Al hydroxyl sulphate minerals. Mg was removed as brucite (Mg(OH)2) and dolomite (CaMg(CO3)2). This would explain the reduction in the chemical species contents in the treated water. Based on the above, it was concluded that magnesite tailings can neutralize and attenuate elevated concentrations of chemical species in AMD to within prescribed legal frameworks for water use in agricultural and industrial sectors in South Africa.
... The adsorption method can be divided into physical and chemical adsorption and can be classified according to the underlying mechanism, e.g., ion exchange, surface complexation, and precipitation [46]. Common AMD adsorbent materials include diatomaceous earth, clay minerals, bentonite, zeolite, seafoam, fly ash, and a variety of newly modified materials with layered structures and good adsorption properties [47]. ...
Acid mine drainage (AMD), arising from mineral resource exploitation, has transformed into a significant global environmental issue for the mining sector, posing considerable risks to water, soil, ecosystems, and human health. In this study, the current status and cutting-edge dynamics of AMD remediation research were evaluated using a bibliometrics approach. Publications on AMD remediation were collected from the Web of Science Core Collection (WOSCC) database, and the relevant literature was analyzed quantitatively using various statistical methods, including keyword co-occurrence and burst analysis. In total, 2743 articles related to AMD remediation published from 1990 to 2023 were obtained. The number of publications tended to increase annually, with a relatively fast rate of increase in recent years. Recent research related to AMD remediation has mainly focused on the ecological risks, the environmental geochemical cycling, the application of sulfate-reducing bacteria and adsorption, and the recovery of heavy metals (HMs) and rare earth elements (REEs). It is anticipated that these topics of AMD remediation research are expected to be at the forefront of future research endeavors. In addition, the current status, advantages, and challenges of AMD remediation technologies are discussed from both active and passive management perspectives, providing a theoretical basis and reference for AMD remediation.
... This hybrid process makes use of synergies between adsorption, ion exchange, and precipitation primarily due to the chemical components embedded in its matrices. pH of AMD was observed to increase from 2 to 10.9 ( The presence of Fe 3+ and 2 4 SO − ions at elevated concentrations suggests that the mine water being treated in this study originates from the oxidation of pyrite [20]. Thenceforth, other inorganic contaminants denote the presence of other sulfide minerals, i.e., Zn 2+ , Cu 2+ , Zn 2+ and Ni 2+ associated with coal strata and those were possibly incorporated into coal matrices during their genesis process [21]. ...
In this study, the efficacy of Ca-rich MgO nanoparticles for effective treatment of real acid mine drainage was evaluated. The optimized parameters include the feedstock dosage and contact time. Experimental results were underpinned using the state-of-the-art analytical techniques and instruments, such as the FTIR, HR-FIB/SEM, EDS, XRF, and XRD. The PH REdox EQuilibrium (in C language) (PHREEQC) model was also employed to complement experimental results. Optimum conditions were observed to be 45-60 mins of mixing time, ≥10 000 mg/dm3 of feedstock dosage, i.e. Ca-rich MgO nanoparticles, and ambient temperature and pH. The metal content (Fe, Mn, Cr, Cu, Ni, Pb, Al, and Zn) embedded in real AMD matrices was practically removed (≥99% removal efficacies) whilst the sulphate (SO₄) was also attenuated humongously (≥40%). The PHREEQC predicted metals to exist as multi-valents including carbonates and other chemical complexes. Chemical species in real AMD were predicted to precipitate as metals hydroxides, (oxy)-hydroxides, carbonates, and (oxy)-hydro-sulphates. Henceforth, the use of Ca-rich MgO nanoparticles proved to be effective in the treatment of real AMD from coal mining activities. However, a polishing technology will be required to further remove residual sulphates. This could be pursued to recover sulphate in a valuable form and then reclaim drinking water for domestic purposes or other defined uses (end-use). This will then be the most effective closed-loop approach in the management of real AMD under the circular economy (CE) concept.
... Decreasing the cost of AMD treatment is an urgent issue, and one method to decrease the cost is by substituting neutralizing materials with alkaline wastes. Neutralization of AMD with a variety of wastes, such as paper mill waste (Pérez-López et al., 2010), red mud and its related materials (Couperthwaite et al., 2013;Douglas et al., 2010;Duchesne, 2005, 2003;Kaur et al., 2018;Paradis et al., 2006;Tuazon and Corder, 2008;Zijlstra et al., 2010), cement kiln dust Duchesne, 2005, 2003;Mackie and Walsh, 2015;Paradis et al., 2006), and coal fly ash (Gitari et al., 2018(Gitari et al., , 2013(Gitari et al., ,2008b(Gitari et al., ,2008aMadzivire et al., 2019Madzivire et al., , 2010Madzivire et al., , 2011Madzivire et al., , 2014 have been examined. The use of alkaline wastes can reduce carbon dioxide (CO 2 ) emissions from AMD neutralization because conventional neutralization agents emit CO 2 during their production or during AMD neutralization; i.e. ...
A novel neutralizing agent (PAdeCS) was produced from concrete sludge generated during the production of secondary concrete products by centrifugal molding, and the effect on actual acid mine drainage (AMD) was evaluated. The effect was compared with a conventional neutralizing agent (i.e., calcium hydroxide). Nine reaction tanks were temporarily installed and operated, imitating the treatment of actual AMD. The amount of discharged water and sediment generated was evaluated. The amount of PAdeCS required to neutralize the actual mine wastewater was 1.5 times that of Ca(OH)2, and the amount of sludge generated was less with PAdeCS than with Ca(OH)2. The coagulation sedimentation performance of PAdeCS is greater than that of Ca(OH)2, determined by comparing the thickness of the sludge layer and the transparency of the supernatant. The reduction of CO2 emissions for the substitution of Ca(OH)2 and CaCO3 by PAdeCS was evaluated, and the neutralization performance of this novel neutralizing agent prepared from concrete sludge in AMD was determined.
... For instance, circumneutral MIW generally exhibits a pH greater than 5.6 [64], which causes the precipitation of many metals, with the exception of Ca and Mg. Therefore, this type of MIW is often characterized by low EC (< 1 000 µm cm -1 ), low concentrations of Fe and Al (< 1 mg L -1 ), average concentrations of − SO 4 2 (> 4 000 mg L 1 ), and elevated concentrations of Ca and Mg (> 500 mg L -1 ) [65][66][67]. The remediation challenge encountered with this type of water is the extraction of Ca and − SO 4 2 . ...
Mine‐influenced water (MIW), also popularly known as acid mine drainage (AMD), is one of the pressing environmental challenges that the South African government and the mining industry are currently faced with. MIW is typically characterized by low pH, high acidity and sulfate content, and elevated concentrations of various host rock elements, impacting negatively on the environment at local and regional scales. In South Africa, millions of rands are allocated from the government fiscus to address and mitigate the environmental challenges associated with MIW, mainly through the building of active treatment plants, as in the case of the Witwatersrand Gold Basin. However, MIW treatment or remediation also presents economic opportunities through the recovery of valuable minerals and metals, which could offset the treatment costs. Moreover, treated MIW can represent an alternative source of water for various uses such as industrial, agricultural, recreational, or potable, depending on the water quality achieved. In recent years, nanofiltration has emerged as a promising MIW remediation method owing to several factors, including water recovery, low energy consumption, high efficiency, simple operation processes and the fact that no chemical reagents are required. In this review, nanofiltration is discussed in the context of South African MIW remediation, and its benefits and limitations are examined. The technology is still in its infancy, and some perspectives and research directions are considered.
... Using alkaline industrial by-products to treat AMD can reduce the amount of waste and the treatment cost, which benefits economic and ecological environmental protection. Fly ash not only removes toxic metal pollutants and radioactive metals in AMD, but also produces good quality water, which is suitable for irrigation (Madzivire et al., 2014). After treatment with recycled concrete aggregates, the concentrations of Cr, Cu, Fe, Mn, Zn, and sulfate in AMD reduced significantly (Jones and Cetin, 2017). ...
Acid mine drainage (AMD) causes serious environmental pollution owing to its high acidity, toxic metal content, and sulfate content. This review describes the mechanism of formation and the effects of AMD, presents the prevention and treatment technologies, identifies critical research gaps, and explores the challenges and opportunities encountered by AMD prevention and treatment technologies. Although passivation and microencapsulation technology have good prospects, they are in the early experimental stage and focus on pure pyrite systems. Remediation technologies such as chemical neutralization, adsorption, microbial activity, and membrane technologies have been developed to reduce the negative impacts of AMD on environment and human health; however, a continuous supply of chemicals and energy, expensive maintenance costs, and long-term monitoring of the affected ecosystem are some of its limitations. The recovery and reuse of valuable resources (sulfuric acid, metals, and rare earth elements) during AMD treatment can reduce its cost and is crucial in achieving a sustainable treatment. Membrane technology can produce high-quality water, but cannot.
... Coal is a discontinuous and heterogeneous multiphase complex engineering rock mass that often contains associated minerals and irregular pores and fractures. When there is pyrite nearby or the coal seams have a high sulfur content, the mine water is prone to be acidic due to chemical and microbial action (Galhardi and Bonotto 2016;Madzivire et al. 2014). In acidic water environments, coal pillar dams undergo complex physical and chemical reactions that can change their bearing structure and stability. ...
We investigated the effects of acidic and circumneutral water on coal samples by uniaxial compression, acoustic emission, and a series of physical tests. In acidic water, the coal samples were damaged, and their ultrasonic velocities decreased, as minerals such as kaolinite and calcite underwent dissolution. When the pH was < 7, the uniaxial compressive strength and elastic modulus decreased, while the duration of the residual strength stage tended to increase. The reactions were stronger at higher H ⁺ concentrations and the number of large pores increased; there was a significant increase in the accumulated acoustic emission counts and maximum average energy near the unstable crack growth stage. The post-peak stage of the coal samples was characterized in the different acidic waters and the failure modes were identified by spectrum analysis. Acidic water damaged the weak areas of coal samples by complex physical and chemical reactions, which made direct tensile failure more likely when the coal samples were loaded.
... In addition, some of the radioactive elements present in fly ash include uranium (U), thorium (Th) and their numerous decay products, including radium (Ra) and radon (Rn). Furthermore, the radioisotopes of these elements such as 238 U, 226 Ra, and 232 Th have been identified in coal fly ashes (Eze et al., 2013;Madzivire et al., 2014;Peppas et al., 2010). ...
A 1500 L batch jet loop reactor pilot plant was designed, constructed, and evaluated for performance in the treatment of acid mine drainage (AMD) using coal fly ash with a view to optimize its operation and generate performance data. Results showed that concentration of major contaminants (sulfate, Al, Fe, Ca, Mg), and minor contaminants in the treated AMD can be significantly lowered (between one and four orders of magnitude) compared to the raw AMD. It was shown that the one-step treatment process recovered at least 66.6% (728.56 kg) of treated water depending on the degree of dewatering required for slurry pumping. The energy consumption of 2.655 kW used for pumping indicated that an oversized centrifugal pump (15 kW capacity) was used for the neutralization cycle, as only a small fraction of the pump capacity was utilized. The treated water met the target water quality range (TWQR) limit for agricultural irrigation in South Africa. The analysis of the solid residue shows its suitability for backfilling of mine voids or for making geopolymer such that AMD treatment with fly ash results in a zero discharge process. The treatment process offers a cradle-to-cradle solution to acid mine drainage and coal fly ash.
... polluting the waters . There are few works worldwide about concentrations and behaviour of natural radionuclides in locations affected by AMD, but high activity concentrations in these polluted environments have been found mainly for U-isotopes (Fernandes et al., 1998;Yamamoto et al., 2010;Durand, 2012;Madzivire, et al., 2014). In the study area some previous works also shown large concentrations of natural radionuclides with enhanced contents of U-Th isotopes and 210 radionuclides (Hierro et al., 2013). ...
The Odiel and Tinto rivers show singular characteristics due to the significant acid mine drainage (AMD) generated
in the first section of their basins and the phosphogypsum (PG) stacks located on their common estuary.
AMD leads to low pH and high redox potential, which keep high amounts of toxic elements and radionuclides in
dissolution. The objective of this work was to analyse the seasonal evolution of U-Th isotopes and 210Po in these
rivers and the estuarine mixing zone. Four sampling points were selected (a fluvial point and an estuarine one for
each river) and water samples were collected monthly throughout a year. The concentrations of natural
radionuclides in the dissolved and particulate phases were determined by alpha spectrometry. The Odiel and
Tinto rivers show concentrations of U-Th isotopes and 210Po from one to three orders of magnitude higher than
background continental waters due to the strong effect of AMD, and 234U/238U activity ratios up to 2.
The studied radionuclides show a clear seasonal behaviour in these rivers, with three different stages during
the year: (1) concentration peaks observed during November and December due to the “washing effect” produced
by the first rainfalls of the hydrological year, (2) a “dilution effect” by runoff in the rainy winter, and (3) a
progressive “concentration effect” during the spring and summer. A non-conservative behaviour of the analysed
radionuclides in the estuaries was demonstrated due to precipitation processes produced by the increase of pH.
The polluted outflows from the PG stacks located in the Tinto estuary produce a significant radioactive impact,
mainly during the rainiest months, increasing the concentration of U-isotopes and 210Po in the particulate phase.
... Gold mining AMD (Tutu et al. 2008), Coal mining AMD and, neutral drainage water (Madzivire et al. 2010(Madzivire et al. , 2011(Madzivire et al. , 2013(Madzivire et al. , 2014Masindi et al. 2014;Gitari et al. 2008;Gitari et al. 2006 As shown in Table 17.2, Acid mine drainage emanating from coal and gold mining in South Africa is rich in dissolved Fe, Al, Mn, Ca, Na, Mg and traces of Cu, Co, Zn, Pb and Ni (Akinwekomi et al. 2017;Commission 2010;Dabrowski et al. 2014;Hobbs and Kennedy 2011). The quality of these water is above the required standards, limits and specifications. ...
Heavy metals emanate from geogenic (natural) and anthropogenic (man-made) sources. These chemical species can pose severe ecological pollution and environmental degradation due to their high toxicity and non-bio-degradable nature. In this book chapter, the sources of heavy metals in the environment, pathways, ecological fate and footprints, eco-toxicological effects, regulatory frameworks, treatment technologies, valorization options, and recovery in light of the future perspectives are discussed. Thenceforth, this book chapter has shown that heavy metals could pose mutagenic, teratogenic, and carcinogenic effects to living organisms on exposure. The link between heavy metals and various eco-toxicological studies and epidemiological reports are also discussed. Finally, the future research outlooks and potential avenues towards the minimization of ecological footprints of heavy metals pollution are duly underscored.
... However, oxygen still plays a vital role in sustaining the ferric iron concentration through oxidation of ferrous iron to ferric iron. The reaction mechanism of pyrite oxidation by ferric iron can be seen in (2) [42][43][44]. ...
Acid generated by coal mine tailing can have a detrimental effect on the environment and human health. Determining whether acid mine drainage (AMD) will occur is of the utmost importance to develop a remediation strategy. Acid base accounting (ABA) is one of the most populate test protocols used today to assess and classify the acid generating potential of mine waste rock (tailings) The results of the ABA test revealed the potential of coal tailings of a wash plant situated in Middleburg to generate acid, which will lead to AMD if adequate step are not taken to slow down the rate of acid generations and if suitable management plans are not implemented.
... Sustainability 2020, 12, 18 2 of 27 Current techniques for treating AMD containing heavy metals include the neutralization precipitation [11], electrochemical [12], membrane separation [13-15], microbial [16,17], constructed wetland [18], and adsorption [19,20] methods. Neutralization precipitation and adsorption are widely used [21,22]. However, neutralization precipitation requires a large amount of chemical agents, such as neutralizer and flocculent [23,24], which leads to difficulties in solid-liquid separation and high processing costs [25,26]. ...
Novel multifunctional adsorbent bentonite–steel slag composite particles (BSC) were developed for highly efficient and synergistic treatment of heavy metal ions in acid mine drainage (AMD). Single-factor experiments were performed to examine the influence of different parameters on the adsorption effect, alkalinity release quantity, and loss rate of the composite particles. Based on these results, an L9(4³) orthogonal experiment was carried out, and the optimum levels and order of the factors were determined by range analysis. Finally, the optimum preparation process of the composite particles was determined: a bentonite–steel slag proportion of 5:5, Na2CO3 content of 5%, aging time of 12 h, calcination particle size of 2 mm, calcination temperature of 500 °C, and calcination time of 60 min. The isothermal adsorption of optimum BSC fit well with Langmuir and Brunauer–Emmett–Teller (BET) isotherms (R2R2 > 0.997). A synergistic adsorption–coagulation effect occurs, leading to the appearance of multiple layers locally on the surface of BSC, which satisfies the BET model. To understand the preparation mechanism of the BSC, bentonite, steel slag, uncalcined BSC, and the optimum BSC were characterized using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, X-ray powder diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The results indicate that calcination led to an increase in the average pore radius, total pore volume, and specific surface area (SBET) in the optimum BSC; numerous pores were present on its layered surface. Although the layer spacing increased after calcination, the structure of the dioctahedra remained unchanged. Exchangeable Na⁺, montmorillonite, and alkaline components were present between the optimum BSC layers. Water and impurities were removed after calcination. The BSC not only released an alkalinity-neutralising acid but also induced a synergistic adsorption–coagulation effect that removed heavy metal ions. It is an excellent multifunctional protective material for the mining environment, that can treat AMD-containing heavy metal ions.
... To mitigate the negative effects of AMD on ecosystems and human health, several treatment approaches have been developed, including neutralization precipitation [7], electrochemical [8], membrane separation [9,10], microbial treatment [11,12], constructed wetland [13], and adsorption [14] methods. Among these, the neutralization precipitation and adsorption methods [15,16] are widely used. ...
Abandoned lead and zinc (Pb-Zn) mines around the world produce large amounts of acid mine drainage (AMD) containing Pb(II), which is toxic and accumulates in the environment and in living organisms. Bentonite-steel slag composite particles (BSC) are a new type of acid mine drainage (AMD) treatment material that can remove heavy metal ions and reduce acidity. To date, there have been no reports on the treatment of Pb(II)-containing AMD using BSC. Therefore, the effects of pH, reaction time, temperature, and Pb(II) concentration on the adsorption of Pb(II) onto BSC were studied. Moreover, the BSC before and after the reaction, as well as the precipitation after the reaction, were characterized by scanning electron microscopy and X-ray diffraction analyses. The effect of pH on the adsorption process is similar to that of the formation of soluble and insoluble hydrolysates of Pb(II) on pH. The adsorption mechanism includes ion exchange, complexation, precipitation, and synergistic adsorption–coagulation effect. Adsorption kinetics are best-fit with the pseudo-second order kinetics model (R2 > 0.98). Furthermore, the total adsorption rate is controlled by liquid film diffusion and in-particle diffusion, the liquid film diffusion rate being higher than the in-particle diffusion rate. The isothermal adsorption of Pb(II) onto BSC fit well with Langmuir and Brunauer Emmett Teller (BET) isotherms (R2 > 0.995), and both single layer adsorption and local multilayer adsorption were observed. Thermodynamic analysis revealed that the adsorption process is spontaneous and endothermic, and that the degree of freedom increases with time. In summary, this study provides a theoretical basis for the use of BSC in treating AMD containing Pb(II).
... Furthermore, with the rise in environmental concerns, and stringent regulations that require industries to manage their polluted waters resources prior release to the environment. Industries are forced to treat this effluent in order to reduce their environmental footprints and comply with regulatory requirements (Masindi et al., 2018a;Madzivire et al., 2011Madzivire et al., , 2014Madzivire et al., , 2017. In that regards, a number of passive, active, and integrated approaches for acid mine drainage treatment have been developed and they use the following mechanisms neutralisation, adsorption, filtration, ion-exchange, phytoremediation and distillation (Sahoo et al., 2013;Simate and Ndlovu, 2014;Skousen et al., 2017;Gibert et al., 2002;Lewis, 2010;Mayes et al., 2009;Nleya et al., 2016;Papirio et al., 2013). ...
... Entre los estudios hidrogeoquímicos enfocados a caracterizar la atenuación natural del DAR, están el realizado por Berger et al. (2000) y que revelan el efecto de la dilución con agua de río o la capacidad de atenuación de las rocas carbonatadas; Quispe et al. (2013) explican la disolución y precipitación de fases minerales causadas por eventos estacionales de lluvia-estiaje y Corrales-Pérez y Romero (2013) estudiaron el proceso natural de atenuación de un drenaje ácido de mina (DAM), en el que la disolución de calizas favorece la precipitación de sulfatos como yeso y además de fases secundarias de hierro (jarosita). Cuando los lixiviados se intentan neutralizar es posible emplear diversos materiales adsorbentes: compósitos de magnesita-bentonita (Masindi et al., 2015), óxidos de hierro y aluminio (Otero-Fariña et al., 2015), cenizas volcánicas (Madzivire et al., 2014) etc. Una de las preocupaciones principales asociadas a los depósitos de residuos minero-metalúrgicos no controlados, es la magnitud del impacto de sus efluentes en la calidad del agua superficial y subterránea. Una vez caracterizados tanto los residuos como el entorno geológico, es posible aplicar una metodología que considera la modelación hidrogeoquímica de las reacciones químicas entre el lixiviado y los materiales geológicos con los que está en contacto, lo que permite comprender su evolución y en todo caso atenuación. ...
A Hydrogeochemical modelling approach was used to understand differences between mine leachates and aqueous extracts of stream sediments and sulfide mine residues from the historical mine district of San Luis Potosí. In Both solutions, leachates and aqueous extracts, Al, Ca, Fe, SO4 and Zn species predominate. Concentration of these species was higher in mine residue extracts than stream sediment extracts. Residues present two types of conditions: free without protection and semi-confined. The concentration of aqueous species from extracts of mine residues exposed to the weather was higher than semi-confined ones. XRD mineralogical characterization indicates the presence of jarosites in aqueous extracts and leachates. Configuration of reaction path reaction as a titration model shows dissolution-precipitation of minerals: gibbsite Al (OH)3, gypsum (CaSO4.2H2O), galena (PbSO4), alunite KAl3 (OH)6(SO4)2 and melanterite FeSO4:7H2O occurring, as a function of the quantity of calcite reacted and pH. In general, Fe exists as Fe²⁺ and S as SO4²-The use of a mix model, mine leachate (pH < 3) vs rain water solution, originated a near neutral pH solution. Evaporation of leachates produced metallic sulfates, gypsum and melanterite, which were founded in mine residues XRD analysis too. Water evolves from HCO³- -Ca to SO4²⁻-Ca type, probably due to common ion effect. Moreover, the most contaminated water extracts come from mine residues, which correspond to leachates spatially, reflecting the limited capacity of stream sediments to retain metals. This paper shows the importance of complement mine residue characterization, based on current environmental standards in Mexico, in order to propose best basis remediation plans.
... Therefore, knowledge of their quantitative and qualitative distributions is important to monitor environmental contaminations [12]. In South Africa, studies have been conducted on water quality from different water sources [3,[13][14][15][16] but no work has been done on water quality within and around D DAVID PUBLISHING Chemical Contamination and Radiological Risk Assessment of Water Sources in Richards Bay 9 phosphate storage facilities in Richards Bay. This study is conducted in Richards Bay about 190 km north of Durban. ...
... Precipitation is discouraged since it generates secondary sludge that is difficult to handle hence imposing additional disposal costs. Other methods require exorbitant energy and are tedious and laborious (Gitari et al., 2008;Jiang et al., 2009Jiang et al., , 2010Madzivire et al., 2010;Madzivire et al., 2011;Luptakova et al., 2012;Macías et al., 2012;Madzivire et al., 2014;Zhou et al., 2014). Masindi et al. (2014a) reported that cryptocrystalline magnesite from Folovhodwe, Limpopo Province, South Africa has the ability to remove heavy metals from industrial effluents and may be a good method for metal removal and recovery since it has low solubility that enables its potentials for metal recovery at varying pH gradients. ...
Soil is the basic foundation for the ecosystem functioning in urban green spaces and provides key ecosystem services for a livable city. Urban soils are a mixture of the natural soil-forming factors and other anthropogenic activities. Soil quality is part of the three constituents of environmental quality, with water quality and air quality included. Soil health on the other hand, is an integration of physical, chemical & biological properties and processes & the interactions among them. Cities in the global south, where urbanization is accelerating at a very high rate, experience negative impacts of legacy and contemporary anthropogenic activities, and studies have shown that these soils, often contain high levels of many different contaminants including heavy metals. Most of the soils in these urban ecosystems are severely depleted of most of both macro and micronutrients as well. Despite several studies and publications that have been done on urban soils in the past decades, the understanding of urban soils is still quite limited and many issues surrounding these soils are not well known. These include challenges to human and environmental health (from toxins in soil, food, air and water), limitations on their ability to provide ecosystem services (due to impaired physical, chemical and biological properties) and the critical role that these soils play if properly utilized. This study aimed at an in-depth understanding of these complex issues of soil health and soil quality using a case study of Cape Town (Gugulethu, Fairdale and Mfuleni regions). The specific objectives were; to assess the chemical/physical /biological properties & to determine the level/quantity of different heavy metals present in urban soils in Cape Town and finally to provide recommendations building on the results of the soil tests from Cape Town. A case study research approach was used; Cape Town (Gugulethu, Fairdale and Mfuleni regions). In total 15 urban gardens were sampled (8-Gugulethu, 5-Fairdale and 2-Mfuleni) for soil chemical/physical/biological properties which were analyzed using Haney Haney, Hossner Arnold (H3A) procedure. 7 urban gardens from Gugulethu {sampled and analyzed in Dec 2020} utilized Mehlich 3 procedures for heavy metal analyses. N, K, Fe, Mn, Cu and Volumetric Aggregate Stability (VAS) were not significantly different in the three regions (Gugulethu, Fairdale and Mfuleni), and all of them were below their respective required ideal levels, that means that they are deficient in Cape Town urban soils. pH on the other hand, was not significantly different in the three regions (Gugulethu, Fairdale and Mfuleni), and the results showed that most of the soils in Cape Town are slightly alkaline hence they lock out availability of some nutrient elements to plants. P, S, Ca and Mg were not significantly different in the three regions (Gugulethu, Fairdale and Mfuleni), and all of them were within their (or adequate) respective required ideal levels. Zn was significantly highest in Gugulethu (p˂0.05), followed by Fairdale, then significantly lowest (p˂0.05) in Mfuleni. SOM was conspicuously below the required ideal level in Fairdale and Mfuleni. The mean concentrations of the heavy metals in Gugulethu gardens varied significantly and decreased in the order of Pb > Cr > V > As > Ni > Co > Cd > Se > Hg. The mean values were Pb (20.19 mg/kg); Cr (6.42 mg/kg); V (5.08 mg/kg); As (2.99 mg/kg); Ni (2.3 mg/kg); Co (0.21 mg/kg); Cd (0.81 mg/kg); Se (˂1.2 mg/kg) and Hg (˂ 0.36 mg/kg). Lead, however, was above the maximum permissible levels according to the recommended levels by the South Africa government, though; As, Cd and Hg are harmful even in small concentrations. In conclusion, it is important for the urban planners to address (through policy/legislation) the soil health and soil quality as a critical issue in urban settings because it has serious implications to the whole urban ecosystem.
Acid mine drainage (AMD) is an emerging global and environmental threat in catchments and water systems that surrounds the gold and coal mining areas. The legacy of mining continues to further impact on water resources (surface and groundwater) long after mining operations have ceased. Specifically, heavy metals and sulphates released by AMD create an economic burden in remediating the contaminated environment and water systems, locally and further afield. Various treatment technologies, such as ion exchange, neutralization, adsorption, filtration crystallization, freeze desalination, thermal desalination, and bioremediation have been developed and implemented on temporospatial scales to remediate the effects of AMD in the receiving environments. This chapter discusses the emerging knowledge on the formation of AMD, source-related chemical composition, abatement techniques, treatment technologies, and challenges. Also, the feasibility of using native and pristine materials for mine water management is meticulously discussed. Further perspectives, potential outlooks, and avenues of AMD management will also be elucidated.
The oxidation of pyrite has attracted significant attention due to its predominant contribution to the serious environmental issue of acid mine drainage (AMD). However, relatively few studies have been conducted investigating the oxidation characteristics of individual pyrite crystal faces. The oxidation rates, under acidic, neutral and alkaline conditions, of three typical pyrite surfaces have been examined with their contrasting behaviors explored in terms of surface structure. Electrochemical and surface analytical measurements were conducted across the pH range 1 to 11, showing surface formation of Fe(OH)3, S⁰ and SO4²⁻. Tafel plots, electrochemical impedance spectroscopy and surface analyses demonstrate that the oxidation rate follows the order of {2 1 0} > {1 1 1} > {1 0 0}. This rate trend is directly related to the breakage of bonds on surface formation with formation of the {2 1 0} surfaces requiring the greatest bond breakage; hence this surface is the most unstable, and the {1 0 0} surface owns the least bond breakage and the greatest stability. The oxidation rate of all pyrite surfaces under strongly acidic conditions (pH = 1) is greater than for strongly alkaline conditions (pH = 11), with the slowest rates being observed under neutral condition, since S⁰, iron oxyhydroxide (Fe-OOH) and Fe(OH)3 formed under neutral or alkaline conditions cover the pyrite surface, thus inhibiting further oxidation. However, a more aggressive oxidant of hydroxo–Fe(III) complex is present under alkaline conditions, resulting in greater oxidation rate compared to that under neutral conditions that determined by the oxidation of Fe²⁺ by O2. DFT calculations suggest that H2O has the greatest affinity for the {2 1 0} surface as compared to the {1 0 0} and {1 1 1} surfaces but does not dissociate. However, after the dissociative adsorption of O2, H2O can dissociate on all the pyrite surfaces, enhancing further oxidation. Under acidic conditions this process is likely to be rate determining. Under alkaline and neutral conditions the oxidation process is dependent on the transfer of hydroxyls to the surface S group and surface cycling of Fe(II) − Fe(III).
The concomitant generation of concrete fines as a byproduct during aggregate recycling is problematic in entire concrete recycling system. The properties of concrete fines mostly composed of hydrated cement limits the availability in construction use. Effective utilization of concrete fines must be explored to improve the negative environmental impact from the cement and concrete industries. Developing concrete fines as alternative material is one of promising options. This study investigated the potential of concrete fines as novel neutralizer for acid mine drainage (AMD) to explore the effective use of concrete fines. The neutralization performance, including identification of main substance that provide alkalinity, removal mechanism of As, Fe, and comparison with conventional neutralizers were confirmed by discussing the effect of dosage and particle size on AMD neutralization. The sedimentation performance was determined, and the neutralized sludge that was derived from concrete fines showed good settling properties: compactness, and dewatering ability. Moreover, CO2 emissions in AMD neutralization were considered, and CO2 emission reduction by Ca(OH)2 and CaCO 3 substitution by concrete fines was assessed. This first fundamental investigation of concrete fines utilization in AMD treatment determined the potential for neutralization and established the prime consideration of CO2 emissions.
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.
Implementing an economical and effective measure for treating acid mine drainage (AMD) from abandoned mines using low-cost restoration reagents present a significant challenge. In this study, natural attapulgite (AT) and soda residue (SR) composite particles (AT-SR) were firstly prepared and utilized in AMD treatment. The efficiencies and mechanisms of AT-SR composites for regulating acidity and removing metals in AMD, the critical factors influencing the treatment efficiencies, and the regeneration performance and environmental risk were investigated. It is illustrated that AT and SR quality ratio of 5:5, dosage of 0.5 g L-1, particle size < 1.5 mm, concentrations of 150 mg L-1 for Fe, 75 mg L-1 for Mn and 100 mg L-1 for Cu, Zn, Cd and Pb, and adsorption time of 120 min were the optimized conditions. The maximum adsorption capacities of Fe, Mn, Cu, Zn, Cd and Pb under single metal scenarios were 51.61, 22.30, 37.05, 40.21, 37.39 and 49.53 mg g-1, respectively. Under the mixed metal scenarios, competitive adsorption was predominated with the rate constants in the reducing order of 3.169 for Fe > 0.841 for Cu > 0.657 for Pb > 0.083 for Zn > 0.024 for Cd > 0.006 for Mn. The experimental data was fitted well with the pseudo-second-order and the Freundlich isotherm models. AT-SR is an outstanding neutralizer for AMD due to its richness in calcium and magnesium oxides and the spent AT-SR composites could be easily regenerated while maintaining high metal removal efficiencies under the subsequent usages. It is determined under the aqua regia digestion and Toxicity Characteristic Leaching Procedure (TCLP) tests that AT-SR can be used safely without posing environmental risks, thus promoting the resource recovery and utilization of soda residue and providing a green and effective method for treating AMD.
To effectively restore the groundwater environment of the Shiping Mine (SPM) area, which is contaminated by acid mine drainage (AMD), a hydrogeochemical conceptual model was constructed based on groundwater chemistry and environmental stable isotopes. The contribution rate of various pollution sources in the groundwater environment was quantitatively analyzed using an optimized stable isotope mass balance model. A total of 68 groups of water samples were collected. The sampling period covered the dry, intermediate, and wet periods of a complete hydrological year. Samples were taken from rain, springs, mine drainage, tailings leachate, and surface water; and the detection and analysis indicators included 24 parameters, such as inorganic salts, heavy metals, and isotopes. A hydrogeochemical and statistical data analysis was performed. The main source of groundwater replenishment was found to be atmospheric precipitation, with the water-rock interaction of calcite and pyrite, and mining activities being the main controlling factors of hydrogeochemical processes. Acid mine drainage significantly enhanced the dissolution of various minerals, and the detection rate of Zn, Cu, As, Cd, and Pb increased from 0–30%–100% when compared with groundwater in the area upstream of the mines. The optimized mass balance model results revealed that the contribution rates of upstream groundwater, mine water and leachate were 0.78–0.86, 0.08–0.18, and 0.04–0.06 for Heidong underground river, respectively; were 0.27–0.36, 0.62–0.68, and 0.03–0.05 for Tiantang underground river, respectively. Furthermore, based on the water balance analysis, 34–70% of the mine water was found to infiltrate directly through karst fissures and karst pipes and could not be collected at the mine entrance. Acid mine drainage that directly infiltrated through runoff could easily be ignored due to the hidden migration path, which may cause the groundwater environment to be remediated less effectively than expected.
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.
Acid mine drainage (AMD) is one of the serious environmental pollutants due to its high acidity, toxic metals and sulfate concentration. In this study, Namibian hardwood charcoal ash leachate, sparingly soluble charcoal ash residue in deionized water and 25% NH4OH (aq.) solution were used for AMD treatment. The ICP-OES analysis results of treated AMD filtrate revealed that almost complete removal of Al, Co, Fe, Mn, Ni, Sb and Zn, and partial removal of Ca, Mg, and Na. The sulfate removal of charcoal ash leachate, residue and 25% NH4OH (aq.) was 66, 56 and 46%, respectively. The removal capacity of charcoal ash leachate and residue were almost better than 25% NH4OH (aq.). About 81% sludge composition recovered at pH 3.7 composed of Fe and O, while the sulfate recovered from the finally treated filtrate of AMD was with above 99% purity. This reveals the possibility of selective resource recovery with high purity from AMD using charcoal ash leachate. Furthermore, the formation of industrially important magnetic nanoparticles such as Fe3O4, Mg0.2Mn0.8Fe2O4 and Mg(Al, Fe)2O4 makes the sludge an eye-catching for future use. Indeed, waste for waste treatment for AMD pollution remediation and simultaneous double resource recovery are interesting findings of this study.
Acid treatment changes the evolution of coal microstructure, and exploring the internal relationship between different acid treatment and coal oxidation is of great significance for the prevention of coal spontaneous combustion. In this paper, lignite collected from Ximeng mine was treated with hydrochloric acid and nitric acid. The oxidation performance and microstructure parameters of treated coal were analyzed by gas chromatograph, mercury intrusion, FTIR and XPS. According to test results, low-temperature (T < 200 °C) oxidation process of coal involves the slow oxidation and rapid oxidation stages owing to different apparent activation energy. HCl and HNO3 treatment improved the pore volume and porosity, and enhanced the oxygen adsorption capacity, thus both accelerating oxidation reaction of coal during slow oxidation stage with temperature below 100 °C. However, in the rapid oxidation stage above 100 °C, HCl treatment inhibited oxygen reaction because the number of oxygen-containing groups including ether and carbonyl band reduced and the hydrogen bonding force for strengthening the stability of coal molecular enhanced. Whereas HNO3 treatment exerted promoting effect on coal oxidation for its pre-oxidation effect and the decrease of coal molecular stability. Further, the conversion mechanism of main active functional groups in acid-treated coal was proposed.
In the aftermath of intensive mining, the generation of acid mine drainage (AMD) has been an issue of prime concern to national, regional, and international scientific and water care communities. Elevated concentrations of Al, Fe, Mn, and sulfate, among other contaminants, dominate AMD. This makes AMD a viable source of valuable metals and minerals. Lately, recovery of metals from AMD has been intensively pursue, albeit, with minimal success. Ongoing research has been widespread due to the need for effective, efficient, and working solutions that aims to responds to increasingly stringent environmental regulations. Drainages from mining activities are being considered in a fresh light with a prime attempt of them being beneficiated through the recovery and synthesis of valuable minerals. To achieve that, different approaches and techniques are used to recover valuable minerals with a wide range of industrial applications. A series of laboratory, pilot, and industrial scale technologies have been employed for the treatment of AMD with value recovery, beneficiation, and material synthesis. Despite a wide range of available AMD treatment technologies, secondary sludge, which is complex, heterogeneous, and highly mineralized, require innovative approaches to harness value and advance the concept of circular economy. The need for sustainable and economic viable AMD treatment approaches has led to much focus on clean water reclamation, reuse, and recovery. Systematically, this chapter underscores (i) the composition of AMD, (ii) environmental and ecotoxicological impacts, (iii) developed remediation techniques, (iv) valorization routes, and (v) a case study in South Africa. Different configurations and approaches for the treatment of AMD with an option of acquiring valuable secondary minerals have been reported as well. Furthermore, the employment of membrane technology for AMD treatment has been emphasized. The advantages and disadvantages of individual approaches and their synergistic products were also discussed. Overall, this chapter gives insights to various routes for AMD valorization and how they can respond to circular economy. Future perspective and research avenues were also discussed.
Aminated peat (termed PG-Peat) produced using polyethylenimine and glycidyltrimethylammonium chloride was used for the removal of sulphate from real acid mine drainage (AMD) in batch and column mode sorption studies. In the batch tests, the highest sulphate removal capacity achieved was 125.7 mg/g. PG-Peat was efficient and rapid in sulphate removal from AMD even at low temperatures (2-5 °C), achieving equilibrium within a contact time of 30 min. The PG-Peat column treating real AMD showed even higher sulphate uptake capacity (154.2 mg SO42-/g) than the batch sorption studies. The regenerative and practical applicability of PG-Peat was also tested in column set-ups using synthetic sulphate solutions (at pH 5.8 and pH 2.0). The sulphate uptake capacity obtained was higher in column mode when the solutions were treated at acidic pH (2.0) compared to pH 5.8. This could be attributed to the presence of cationized amine groups on PG-Peat under acidic pH conditions. Almost complete sulphate desorption was achieved with NaCl in the column that treated synthetic sulphate solution at pH 5.8, while the lowest desorption rates were observed in the column that treated acidic synthetic sulphate solution (pH 2).
The accumulation and increase in radionuclide activities of NORMs beyond permissible levels, will lead to health hazards and environmental damages if proper measures are not taken to control their occurrence as well as protect the lives of drillers and the environment. Therefore, evaluations and risk assessments of subsurface lithofacies is inevitable in order to protect people and the environment. Lack of existing Federal environmental regulations to address the presence of NORMs in oil and gas exploration activities in Nigeria, gives credence to this study. However, before these regulations can be developed, adequate research knowledge is needed to better understand the occurrence and distribution of Norms in subsurface lithofacies, as well as quantify the hazards posed by these NORMs to the people in the environment. This study then investigates the occurrence of natural radiation in lithofacies of an oil field region in Niger-Delta area using Hyper Germanium (HPGe) detector. Six (6) samples of different subsurface layers of lithofacies were collected during drilling, and analyzed. The results showed that the measured activity concentration of ²³⁸U decreased as the depth increased; the activity concentration of ²³²Th ranged between 11.8 ± 9.29 Bq/kg and 23.1 ± 8.43 Bq/kg, while the activity concentration of ⁴ K ranged from 161.8 Bq/kg to 245.4 Bq/kg. The estimated radiological risks such as absorbed dose rates, annual effective dose rates, radium equivalent index, external hazard index and internal hazard index were determined. The mean values for the estimated radiological parameters were 12.32 nGyh⁻¹, 15.1049 Svy⁻¹, 44.7720 Bqkg⁻¹, 0.1209 and 0.1318 respectively. The gamma index estimated for the samples used were within the standard values recommended by Unscear, 2000. Significantly, this study reveals a distinctive decrease in 232Th activity with depth within the area under consideration. Based on the compared results, the measured radioactive concentrations and estimated radiological risks were below international reference values.
Acid mine drainage is globally recognized as one of the environmental pollutants, due to its highly toxic metals and sulfate concentration. In this study, the effect of metal and sulfate removal capacity of Namibian hardwood charcoal ash from acid mine drainage was investigated. The experimental results have shown that charcoal ash has dual pollutant removal capacity via adsorption and precipitation. For adsorption, insoluble charcoal ash minerals and precipitates produced during treatment are responsible. While soluble metal oxides and sparingly soluble carbonates are essential for neutralization of the acid mine drainage and metal hydroxide precipitation. Based on the treated acid mine drainage analysis results, almost complete and partial removal of toxic metals and sulfate from acid mine drainage was observed, respectively. Unlike commonly used lime or limestone obtained by purchasing and also which requires crushing to form a powder, charcoal ash obtained for free, need no modification due to its nanoparticle size (20–96 nm) and environmentally friendly nanomaterials. Collection and use of charcoal ash for pollution remediation is one way of creating a clean environment. Overall, charcoal ash performed well in metals and sulfate removal and has been found an attractive and novel-alternative for acid mine drainage treatment, with an added-value of resource recovery.
Since human daily demands for fresh water have been increased significantly, the supply of fresh water for the mining industry, especially froth flotation, should be considerably reduced. In addition, stricter environmental standards have been implemented in many countries to reduce the risks due to the disposal of wastewater, many flotation operators have to seek more efficient ways to utilize the limited fresh water sources. Recycling water with high concentrations of impurities is a normal strategy for most of the mineral processing plants; however, water quality should be carefully considered to guarantee a smooth flotation process. Recently, the application of seawater in flotation has attracted much attention due to its availability and abundance rather than fresh water. However, the influencing mechanisms due to the application of seawater in flotation have not been fully understood especially the reactions between mineral particles and bubbles in the presence of high concentrations of cations and anions. This would impede the application of alternatives to fresh water in the flotation. Therefore, this paper reviews the current water sources and the technologies for water recycling in the flotation process. Specifically, the life cycle of water in flotation was proposed. In addition, the strategies including high pulp density flotation as well as the most promising alternatives to fresh water have been discussed in details, with the related mechanisms being demonstrated.
Although the acid generating properties of pyrite (FeS2) have been studied extensively, the impact of galvanic interaction on pyrite oxidation, and the implications for acid and metalliferous drainage, remain largely unexplored. The relative galvanic effects on pyrite dissolution were found to be consistent with relative sulfide mineral surface area ratios with sphalerite (ZnS) having greater negative impact in batch leach tests (sulfide minerals only, controlled pH) and galena (PbS) having greater negative impact in kinetic leach column tests (KLCs, uncontrolled pH, >85 wt% silicate minerals). In contrast, the presence of pyrite resulted consistently in greater increase in galena than sphalerite leaching suggesting that increased anodic leaching is dependent on the difference in anodic and cathodic sulfide mineral rest potentials. Acidity increases occurred after 44, 20, and 12 weeks in the pyrite–galena, pyrite–sphalerite, and the pyrite containing KLCs. Thereafter acid generation rates were similar with the Eh consistently above the rest potential of pyrite (660 mV, SHE). This suggests that treatment of waste rocks or tailings, to establish and maintain low Eh conditions, may help to sustain protective galvanic interactions and that monitoring of Eh of leachates is potentially a useful indicator for predicting changes in acid generation behavior.
In this study, magnetite and cobalt ferrite nanoparticles were used as seeds for acid mine drainage (AMD) treatment at pH of 7.05?0.35. Duplicate samples of AMD, one without heating and another with heating at 60?C was treated under continuous stirring for 1h. The filtrate analysis results from ICP-OES have shown complete removal of Al, Mg, and Mn, while for Fe, Ni and Zn over 90% removals were recorded. Particularly, settling time has significant effect on the removal of Mg, Ca and Na. The results from SQUID have shown superparamagnetic properties of the synthesised magnetic nanoparticles and ferrite sludge. The recovered nanoparticles from AMD are economically important and reduce the cost of waste disposal.
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.
The leaching and carbonation performances of indirect mineral carbonation are investigated using coal fly ash (FA) as the raw source and water as the solvent. The reactions were conducted at ambient temperature and pressure with a gas mixture comprised of 15 and 33 mol% CO2. The overall CO2 storage and mineral carbonation capacities of FA suspended solution in which alkaline components had been previously leached for 2 h (2S33) were 31.06 and 17.36 mg CO2/g FA, respectively. The mineral carbonation capacity of FA in 2S33 was 18% of the theoretical value and its mineral carbonation storage capacity ratio was 55.9%. The performance of 2S33 was higher than that of its filtrate because the alkaline components were leached from the suspended FA simultaneously with the mineral carbonation. Submicrometer-sized particles were present in raw FA and their size was reduced by stirring during the leaching, as well as slightly increased, compared to the original raw FA, due to the carbonation. These submicro FA particles strongly affected the performance of the mineral carbonation of the FA-water solution.
The proposed magnesium-barium-oxide process consists of metal removal with Mg(OH)2, magnesium and sulphate removal with Ba(OH)2 and calcium removal with CO2. The raw materials, Mg(OH)2 and Ba(OH)2 are recovered from the BaSO4 and Mg(OH)2 sludges that are produced. Laboratory studies showed that metals are removed to low levels. This includes iron(II), the dominant metal ion in mine water, which is first oxidised to iron(III), whereafter it precipitates as Fe(OH)3 resulting in residual levels of Fe(II) in the mine water of less than 20 mg/ℓ. Sulphate is also removed to less than 25 mg/ℓ. The final sulphate concentration is a function of the amount of Ba(OH)2 dosed, as the amount of sulphate removed is stoichiometrically equivalent to the Ba(OH)2 dosage. During CO2-dosing, CaCO3 is precipitated to the saturation level of CaCO3.
High volume utilization of industrial wastes and by products is the solution for high disposal costs. Acceptable radioactivity levels in addition to other environmental factors is a key factor for safe utilization of wastes and byproducts of coal burning power plants. In general the radioactivity levels of most fly ashes are similar to natural materials. For higher radioactivity fly ash the radioactivity values must be reduced to acceptable limits. This can be done by mixing the fly ash with less radioactive natural materials. In this study a new technique involving the use of snow as an additive to the compaction water of fly ash is presented. Fly ash at optimum water content, and fly ash with additional 10% by weight snow are compacted, hermetically sealed to allow for equilibrium of 226Ra and 232Th with their decay products and cured for 28days at the curing room. Radioisotope activity analysis are conducted with a gamma analyst integrated gamma spectrometer. The activities of 235U, 226Ra, 238U, and 232Th of the fly ash and snow-added fly ash samples compacted at optimum moisture content are determined. The control samples revealed radioactivity values above UNIPEDE maximum allowable limits. Addition of snow caused a decrease of 31–42% in the radioisotope activity levels to that of control samples in Bqkg−1.The decrease in radioactivity is linked to increased void ratio after melting of ice, increased densification of matrix around the pores due to higher level of cementitious mineral formation. The decrease in the radioisotope activity levels will allow utilization of fly ash in highway embankment construction where large surface area exposure and large volume usage makes it more critical for human health. Another advantage of the developed technology is the reduction of transportation costs by more than ten per cent by using less material for construction.
The water treatment performances of two anoxic limestone drains (ALDs) were evaluated. Anoxic limestone drains are buried beds limestone that are intended to add bicarbonate alkalinity to flow-through acid mine drainage. Both ALDs received mine water contami-nated with Fe 2+ (216-279 mg -I) and Mn (41-51 m g L -~). F low through the Howe Bridge ALD increased alkalinity by an average 128 mg L-~ (CaCO3 equivalent) and Ca by 52 mg L -i, while concentrations of Fe, K, Mg, Mn, Na, and SO~-were unchanged. The Morrison ALD increased alkalinity by an average 248 mg L -I and Ca by III mg L-~. Concentrations of K, Mg, Mn, and SO~-all decreased by an average 17%, an effect attributed to dilution with uncontaminated water. Iron, which decreased by 30%, was partially retained within the Morrison ALD. Calcite dissolution was enhanced at both sites by high Pco2. Untreated mine waters at the Howe Bridge and Morrison sites had average calculated Pco~ values of 6.39 kPa (I0-1.z0 atm) and 9.24 kPa (I0 -I'°~ atm), respectively. At both sites, concentrations of bicarbonate alkalinity stabilized at undersaturated values (SIc~k~t~ I0 -I"~ at Howe Bridge and I0 -°'s at Morrison) after flowing through approximately half of the limestone beds. Flow through the second half of each ALD had little additional effect on mine water chemistry. At the current rates of calcite solubilization, 17.9 kg d-i CaCO3 at Howe Bridge and 2.7 kg d-i CaCO3 at Morrison, the ALDs have theoretical effective lifetimes in excess of 20 yr. By significantly increas-ing alkalinity concentrations in the mine waters, both ALDs increased metal removal in downstream constructed wetlands.
The Barium Sulphide Process removes sulphates from mine water by precipitating BaSO4 with BaS. Barium sulphide is regenerated thermally by reducing the BaSO4 with coal at 1000–1100°C for about 15 minutes. The process produces elemental sulphur and CaCO3 as by-products. Laboratory studies achieve typical sulphate reductions of about 95%. Metals such as Fe, Ni, Co and Mn are
also removed and pH can be increased from 1,4 to 8,3. The process has a water recovery of about 70%. For a 25 Ml/d plant (2g/l
SO4
2−), the capital cost is estimated at US$ 0,48m/Ml/d, while the detailed running costs amount to a net value of 27 c/m3. This compares well with that of other processes for desalination and is less than the fresh water price for new mines in
South Africa, viz. 30c/m3.
The removal of sulphate and metals from mine water was assessed using the integrated barium carbonate process and the co-precipitation
of barium sulphate with calcium carbonate. The rate of sulphate removal was influenced by the BaCO3 concentration and the cation associated with sulphate, and increased with increasing BaCO3-concentration. BaCO3 can only be used for removal of sulphate that is associated with calcium, as calcium is needed to remove the added carbonate
associated with the barium cation. Sulphate removal was only marginally influenced by alkalinity. Sulphide can be stripped
with CO2 from a BaS-solution. The (CO2 dosed/sulphide removed) molar ratio was close to unity for the first 50% of sulphide in solution. The stripped H2S-gas can be absorbed into zinc acetate. BaSO4 and CaCO3 can be converted simultaneously to BaS and CaO, respectively at an optimum temperature of 1050°C. The CaCO3/BaSO4 molar ratio has little influence on the yield of BaS. The running cost of the barium carbonate process for the removal of
2 g/L of sulphate totalled ZAR1.28/m3 (US$1.00 = ZAR7.0, Feb 2007), the capital redemption cost was R1.08/m3, and the value of the products (water and sulphur) totalled R2.76/m3.
Acid mine drainage (AMD) has been reacted with coal fly ash in a 24 h equilibration time using 1:3 and 1:1.5 FA:AMD ratios by weight to produce neutral and alkaline process waters. The capacity of the fly ash to remove the major inorganic contaminants was examined. The elemental concentration trends with time for the two ratios were used to discern which elements have solubility control in the neutralization process. The geochemical computer code PHREEQC and WATEQ4 database was used for geochemical modeling of the process water. The resulting solid residues (SR) were analyzed by X-ray diffraction (XRD), and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDX) in an attempt to detect the minerals phases controlling the inorganic contaminants concentration in solution. The relative quantities of soluble bases (CaO, MgO) in fly ash and hydrolyzable constituents in AMD dictated whether the final solution at a given contact time will have a dominant acidic or basic character. Concentration of Fe, Al, B were observed to be controlled by mineral solubility for the entire reaction time while mineral solubility control for Ca, Na, Mg, Si and Mn concentrations developed after the initial rapid dissolution. Initial concentration was controlled by precipitation of gypsum and adsorption on iron-oxy-hydroxides at pH > 5.5. Increase of pH in solution with contact time caused the removal of the metal ions mainly by precipitation, co-precipitation and adsorption. Fe was mainly removed as Fe(OH)3(a), goethite, Al as basaluminite, boehmite and alunite at pH 5.28–6.95 and as gibbsite and diaspore at pH 5.53–9.12. Cu and Zn were removed by adsorption onto the precipitating iron(oxy)-hydroxides and aluminum (oxy)-hydroxides. Si is released by dissolution of SiO2(a) at pH < 5. Na was removed as Na-jarosite at pH 3.96–6.95 and Ca as gypsum and anhydrite. The treatment of AMD with fly ash was observed to be site-specific, i.e., the effectiveness of the treatment process will depend on the quality of the fly ash and the AMD. The product water meets the DWAF water quality limits for domestic use and irrigation at pH > 8 except for species Na, B, Mg, Ca, Sr and Ba which remain in solution. In addition B, Mg, Sr, Mo and Ba are released from dissolution of fly ash and will be of concern in the proposed treatment process.
The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca2+. This resulted in increased removal of sulphate as CaSO4·2H2O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO4·2H2O. The results of this study would have implications on the design of treatment methods relevant for different mine waters.
The full-spectrum analysis (FSA) method was used to determine primordial activity concentrations (ACs) in soil, sand and ore samples, in conjunction with a HPGe detector. FSA involves the least-squares fitting of sample spectra by linear combinations of (238)U, (232)Th and (40)K standard spectra. The differences between the FSA results and those from traditional windows analyses (using regions-of-interest around selected photopeaks) are less than 10% for all samples except zircon ore, where FSA yielded an unphysical (40)K AC.
Mine waters become contaminated to a varying degree with the oxidation products of pyritic materials associated with the minerals. Waters containing from 6 000 to 13 000 mg/L of sulphates and up to almost 5 000 mg/L of iron are reported. For practical or economical reasons it is not yet possible to prevent this contamination of mine water. Prevention of pollution of surface water in South Africa is mostly confined to the neutralisation of acid mine water with lime. The neutralisation reaction results in the precipitation of a voluminous sludge containing mostly iron hydroxide and calcium sulphate, when the latter is formed in excess of its solubility in water.
The sludge usually settles to volumes equal to 10 percent of the volume of the water treated, but volumes as high as 50 per cent have been found.
Through application of the “High Density Sludge” process, which comprises sludge recirculation and conditioning with lime in addition to conventional neutralisation and sedimentation, the volume of these sludges has been reduced to 0,4-2,0 per cent of the volume of water treated. The seeding of calcium sulphate resulting in a reduction of scale build-up on plant equipment seems to be an advantage of the process.
Dissolved air flotation was found an attractive alternative means of solids/liquid separation to gravity settling for water producing relatively low amounts of sludge (100 to 200 mg solids per litre). At hydraulic loadings of 7 m3/m2.h (seven times higher than gravity settling) the flotation process produced an effluent containing less than 15 mg/L suspended matter and a sludge with a density of 50 g/L.
This book provides a thorough, up-to-date overview of wastes accumulating at mine sites. It deals comprehensively with sulfidic mine wastes, mine water, tailings, cyanidation wastes of gold-silver ores, radioactive wastes of uranium ores, and wastes of phosphate and potash ores. The book emphasizes the characterization, prediction, monitoring, disposal and treatment as well as environmental impacts of problematic mine wastes. The strong pedagogical framework is supported by case studies from around the world, presentation of crucial aspects of mine wastes as scientific issues; end-of-chapter summaries as well as lists of resource materials and www sites for each waste type. The considerably updated third edition has novel and notable changes including: revision of text to reflect major developments and contemporary issues that are taking place in the field of mine waste science; new web pages at the end of each chapter; over 20 case studies and scientific issues; over 150 figures and tables; and an updated bibliography with over 1200 references. This newly balanced text will continue to equip the student and the professional with a thorough understanding of the principles and processes of mine wastes. © Springer-Verlag Berlin Heidelberg 2010. All rights are reserved.
Conventional desalination technologies such as electrodialysis reversal and reverse osmosis cannot be directly used to economically treat those waters encountered in the South African gold mining industry which are scaling with regard to calcium sulphate. The Chamber of Mines of South Africa Research Organisation therefore decided, in the early 1980's, to undertake research into the development of seeded reverse osmosis technology for treating scaling mine waters. This research culminated in the development of the Slurry Precipitation and Recycle Reverse Osmosis (SPARRO) technology. Extensive pilot plant investigations were undertaken and it was shown that the SPARRO process is technically capable of producing a high quality product water at water recoveries of around 95 per cent. Problems were encountered, however, with fouling of the tubular cellulose acetate membranes, resulting in declines in the flux rate. It is postulated that the fouling is mainly due to the presence of quartzitic suspended material, although the mechanism of fouling cannot be explained. Further research is being undertaken to clarify the potential fouling mechanisms and to optimize the membrane cleaning regimes. The capital cost for a 46.3l/s (4Ml/d) SPARRO plant has been estimated at R16.2 million, with an estimated operating cost of R1.48/m3 of product water.
The feasibility of using sulfate-reducing bacteria to remove heavy metals from aqueous streams such as acid mine drainage was evaluated using three anaerobic reactors: an upflow anaerobic sludge blanket (UASB) reactor, a packed filter reactor, and a filter reactor that was partially
packed with floating plastic pall rings. The packed filter reactors removed more than 99% of the influent metals. The performance of the partially packed reactor was superior based on effluent metal and sludge concentrations. Although the UASB reactor reduced the concentration of dissolved
iron, the effluent concentration of total suspended solids remained greater than 18 g/L. This elevated solids concentration indicated that the UASB reactor was not operating as an effective clarifier, and, as a result, UASB reactor operation was discontinued after 4 months. The packed filter
reactors were operated in parallel and received influent containing a combination of heavy metals. By withdrawing sludge from the bottom of these reactors, the accumulation of solids such as metal precipitates and biomass was controlled. The effluent concentrations of most metals were low,
often less than drinking water standards, with the exception of manganese.
The Witwatersrand has been subjected to geological exploration, mining activities, parallel industrial development and associated settlement patterns over the past century. The gold mines brought with them not only development, employment and wealth, but also the most devastating war in the history of South Africa, civil unrest, economical inequality, social uprooting, pollution, negative health impacts and ecological destruction. One of the most consistent and pressing problems caused by mining has been its impact on the water bodies in and adjacent to the Witwatersrand. The dewatering and rewatering of the karstic aquifer overlying and adjacent to the Witwatersrand Supergroup and the pollution caused by Acid Mine Drainage (AMD) are some of the most serious consequences of gold mining in South Africa and will affect the lives of many South Africans.
The objective of this study is to determine radiological characteristics of pulverized fly ash (PFA) collected from the 15 coal-burning thermal power plants (TPPs) in operation by means of gamma spectrometric technique and to assess the radiological impacts from the utilization of PFA samples examined as filling and cover material in earthwork applications. Also, the annual effective doses received by workers handling PFA and members of the public living in a house near the PFA pile/landfill were estimated using methods specified in the Radiation Protection 122. The activity concentrations of 226Ra, 232Th and 40K measured in PFA samples were tabulated for each TPP. The activity results show that Turkish PFA may have relatively high natural radioactivity content, depending on its origin reaching in the case of Kangal PFA 2720 Bq kg−1 of 226Ra. The values of external exposure indexes (radium equivalent activity index and gamma index) calculated for PFA samples are within the recommended safety limits. As well, the highest mean total annual effective doses estimated as 7.3 × 10−5 Sv y−1 for workers and 1.5 × 10−4 Sv y−1 for members of the public are significantly lower than the annual limit of 1.0 × 10−3 Sv y−1.
The concentration of trace elements and radionuclides in fly ash particles of different size can exhibit significant variation, due to the various processes taking place during combustion inside a coal-fired power plant. An investigation of this effect has been performed by analyzing samples of fly ash originating in two different coal-fired power plants, after separation into size fractions by sieving. The samples were analyzed by gamma-ray spectrometry, including low-energy techniques, radon exhalation measurement and instrumental neutron activation analysis for the determination of Al, As, Ga, K, La, Na, Mn, Mg, Sr, Sc, and V. Variations are observed in the results of various samples analyzed, while the activity balances calculated from the results of individual size fractions are consistent with those of the raw ash samples. Correlations among the radionuclides examined are also observed, while individual nuclide behavior varies between the two types of fly ash examined.
Coal, like most materials found in nature, contains trace quantities of the naturally occurring primordial radionuclides, i.e. of (40)K and of (238)U, (232)Th and their decay products. Therefore, the combustion of coal results in the released into the environment of some natural radioactivity (1.48 TBq y(-1)), the major part of which (99%) escapes as very fine particles, while the rest in fly ash. The activity concentrations of natural radionuclides measured in coals originated from coal mines in Greece varied from 117 to 435 Bq kg(-1) for (238)U, from 44 to 255 Bq kg(-1) for (226)Ra, from 59 to 205 Bq kg(-1) for (210)Pb, from 9 to 41 Bq kg(-1) for (228)Ra ((232)Th) and from 59 to 227 Bq kg(-1) for (40)K. Fly ash escapes from the stacks of coal-fired power plants in a percentage of 3-1% of the total fly ash, in the better case. The natural radionuclide concentrations measured in fly ash produced and retained or escaped from coal-fired power plants in Greece varied from 263 to 950 Bq kg(-1) for (238)U, from 142 to 605 Bq kg(-1) for (226)Ra, from 133 to 428 Bq kg(-1) for (210)Pb, from 27 to 68 Bq kg(-1) for (228)Ra ((232)Th) and from 204 to 382 Bq kg(-1) for (40)K. About 5% of the total ash produced in the coal-fired power plants is used as substitute of cement in concrete for the construction of dwellings, and may affect indoor radiation doses from external irradiation and the inhalation of radon decay products (internal irradiation) is the most significant. The resulting normalized collective effective doses were 6 and 0.5man-Sv(GWa)(-1) for typical old and modern coal-fired power plants, respectively.
Acid mine drainage (AMD) causes environmental pollution that affects many countries having historic or current mining industries. Preventing the formation or the migration of AMD from its source is generally considered to be the preferable option, although this is not feasible in many locations, and in such cases, it is necessary to collect, treat, and discharge mine water. There are various options available for remediating AMD, which may be divided into those that use either chemical or biological mechanisms to neutralise AMD and remove metals from solution. Both abiotic and biological systems include those that are classed as "active" (i.e., require continuous inputs of resources to sustain the process) or "passive" (i.e., require relatively little resource input once in operation). This review describes the current abiotic and bioremediative strategies that are currently used to mitigate AMD and compares the strengths and weaknesses of each. New and emerging technologies are also described. In addition, the factors that currently influence the selection of a remediation system, and how these criteria may change in the future, are discussed.
Acid mine drainage (AMD), characterized by low pH and high concentrations of sulfate and heavy metals, is an important and widespread environmental problem related to the mining industry. Sulfate-reducing passive bioreactors have received much attention lately as promising biotechnologies for AMD treatment. They offer advantages such as high metal removal at low pH, stable sludge, very low operation costs, and minimal energy consumption. Sulfide precipitation is the desired mechanism of contaminant removal; however, many mechanisms including adsorption and precipitation of metal carbonates and hydroxides occur in passive bioreactors. The efficiency of sulfate-reducing passive bioreactors is sometimes limited because they rely on the activity of an anaerobic microflora [including sulfate-reducing bacteria (SRB)] which is controlled primarily by the reactive mixture composition. The most important mixture component is the organic carbon source. The performance of field bioreactors can also be limited by AMD load and metal toxicity. Several studies conducted to find the best mixture of natural organic substrates for SRB are reviewed. Moreover, critical parameters for design and long-term operation are discussed. Additional work needs to be done to properly assess the long-term efficiency of reactive mixtures and the metal removal mechanisms. Furthermore, metal speciation and ecotoxicological assessment of treated effluent from on-site passive bioreactors have yet to be performed.
Sulfate-reducing passive bioreactors treat acid mine drainage (AMD) by increasing its pH and alkalinity and by removing metals as metal sulfide precipitates. In addition to discharge limits based on physicochemical parameters, however, treated effluent is required to be nontoxic. Acute and sublethal toxicity was assessed for effluent from 3.5-L column bioreactors filled with mixtures of natural organic carbon sources and operated at different hydraulic retention times (HRTs) for the treatment of a highly contaminated AMD. Effluent was first tested for acute (Daphnia magna and Oncorhynchus mykiss) and sublethal (Pseudokirchneriella subcapitata, Ceriodaphnia dubia, and Lemna minor) toxicity. Acute toxicity was observed for D. magna, and a toxicity identification evaluation (TIE) procedure was then performed to identify potential toxicants. Finally, metal speciation in the effluent was determined using ultrafiltration and geochemical modeling for the interpretation of the toxicity results. The 10-d HRT effluent was nonacutely lethal for O. mykiss but acutely lethal for D. magna. The toxicity to D. magna, however, was removed by 2 h of aeration, and the TIE procedure suggested iron as a cause of toxicity. Sublethal toxicity of the 10-d HRT effluent was observed for all test species, but it was reduced compared to the raw AMD and to a 7.3-d HRT effluent. Data regarding metal speciation indicated instability of both effluents during aeration and were consistent with the toxicity being caused by iron. Column bioreactors in operation for more than nine months efficiently improved the physicochemical quality of highly contaminated AMD at different HRTs. The present study, however, indicated that design of passive treatment should include sufficient HRT and posttreatment aeration to meet acute toxicity requirements.
The impact of gold mining on the Witwatersrand on the rivers and karst system of Gauteng and North West Province, South Africa Uti-lization of fly ash for treatment of coal mines waste water: solubility controls on major inorganic contaminants
- J F Durand
- W M Gitari
- L F Petrik
- O Etchebers
- D L Key
- E Iwuoha
- C Okujeni
Durand, J.F., 2012. The impact of gold mining on the Witwatersrand on the rivers and karst system of Gauteng and North West Province, South Africa. J. Afr. Earth Sci. 68, 24e43. Gitari, W.M., Petrik, L.F., Etchebers, O., Key, D.L., Iwuoha, E., Okujeni, C., 2008. Uti-lization of fly ash for treatment of coal mines waste water: solubility controls on major inorganic contaminants. Fuel 87, 2450e2462.
Flooding of Central and East Rand Gold Mines e an Investigation into Controls over the Inflow Rate, Water Quality and the Predicted Impacts of Flooded Mines (Report No. 486/1/95)
- R Scott
Scott, R., 1995. Flooding of Central and East Rand Gold Mines e an Investigation into
Controls over the Inflow Rate, Water Quality and the Predicted Impacts of
Flooded Mines (Report No. 486/1/95). Water Research Commission, Pretoria,
South Africa.
Active Neutralization and Amerioration of Acid Mine Drainage with Fly Ash (MSc thesis)
- D Surender
Surender, D., 2009. Active Neutralization and Amerioration of Acid Mine Drainage
with Fly Ash (MSc thesis). University of the Western Cape, South Africa.
Handbook, Council for Geoscience Council of Geosciences of South Africa, South Africa, pp. 642e652. Department of Water Affairs and Forestry
- D I Cole
Cole, D.I., 1998. Uranium. In: Wilson, M.G.C., Anhausser, C.R. (Eds.), The Mineral
Resources of South Africa, 16th ed., Handbook, Council for Geoscience Council
of Geosciences of South Africa, South Africa, pp. 642e652.
Department of Water Affairs and Forestry, 1996. South African Water Quality,
Guidelines, Agricultural Use: Irrigation, second ed., vol. 4. CSIR Environmental
Services, South Africa.
Application of a jet loop reactor to enhance removal of sulphates from mine water using coal fly ash, lime and aluminium hydroxide
- G Madzivire
- W M Gitari
- V R K Vadapalli
- T V Ojumu
- L F Petrik
Madzivire, G., Gitari, W.M., Vadapalli, V.R.K., Ojumu, T.V., Petrik, L.F., 2012. Application of a jet loop reactor to enhance removal of sulphates from mine water
using coal fly ash, lime and aluminium hydroxide. In: International Mine Water
Association Symposium, Australia, pp. 183e200.