Formation Of Acid Mine Drainage Research Articles

Prediction of acid mine drainage formation and zinc migration in the tailings dam of a closed mine, and possible countermeasures

Acid mine drainage (AMD), the very acidic and highly contaminated leachate generated in closed/abandoned mines, is commonly managed by neutralization to raise the pH and precipitate most of the heavy metals. Although effective, this approach does not generate any product of economic value, so it is very costly and unsustainable in the long-term. Unfortunately, there are currently no effective alternatives to neutralization, and one way to improve the sustainability of this process is to reduce the volume of AMD generated and/or the concentration of heavy metals. The tailings dam investigated in this study is located in northern Hokkaido, Japan. Detailed characterization of borehole core samples showed that even after almost 40 years of exposure to the environment, the tailings still contain pyrite (FeS2) and substantial amounts of copper (Cu) and zinc (Zn). Reactive-transport modeling using Visual MODFLOW predicted that AMD quality would likely continue to deteriorate with time and that treatment should be continued for at least 1,000 years. The model also predicted that a barrier with low permeability installed downstream of the tailings dam or ground sealing techniques for recharge reduction could lower the volume of AMD and concentration of Zn from the site.

Application of biostimulant and CaO to remediate acid mine drainage on the coal mining land in Lampung Sumatra Island

Mining using an open pit system may lead to a deterioration in the quality of the environment in term of the extent of the cleared land, heavy metals contamination on the overburden rock, the formation of acid mine drainage (AMD) with a pH <5, high level of total suspended solid (TSS), and the content of the metal on it. Several research results on post-mining land indicated a change in the environmental quality of the mine. Handling of the AMD problem can be conducted by several methods, including the active method by spreading calcium oxide (CaO) in AMD with the aim of increasing pH to neutral. The purpose of this study was to study the alternative techniques to manage the AMD using biostimulant. The present study was conducted firstly in the vinil house by using 10 L of AMD water sample with 2 kinds of treatment, i.e. CaO with levels of 0.2 and 0.25. Biostimulant with four kinds of treatment (I, II, III and IV) which resulted from the combination of different types of biostimulants (A, B and C) with different in composition. Secondly, research on the 1000 L of AMD for scaling up applications in the field. CaO and Biostimulant doses were obtained from the first stage of the study. Analysis pH, TSS, Fe, and Mn of the AMD were done on the control, CaO, and biostimulant treatments. CaO treatment resulted in an increase in pH to 6.9, TSS decreased significantly decline so to 60 mg/L. Fe content in AMD decreased to 0.22 mg/L, and Mn levels decreased to 0.12 mg/L on day 10. Biostimulant treatment resulted in increase of pH to pH 6.7. The TSS value decreased to 40 mg/L. Fe and Mn levels decreased to 0.03 mg/L and Mn 2.98 mg/L, respectively.

Efeitos da drenagem ácida de mina sobre a qualidade das águas subterrâneas: preceitos legais e técnicos

Atividades de mineração podem causar degradação ambiental em grandes extensões, comprometendo solos, águas superficiais e subterrâneas, atmosfera e a biota. A exploração mineral tem como consequência a exposição de grandes quantidades de sulfetos a processos de intemperismo que geram ambientes ácidos em consequência da produção de drenagem ácida de mina (DAM), promovendo a solubilização de metais e o transporte destes para os fluxos de águas naturais. Entretanto, as variações hidroquímicas das águas subterrâneas em áreas de mineração e os efeitos da DAM sobre os aquíferos foram ainda pouco investigados no Brasil. Este trabalho visou identificar as principais normas legais que gerem a qualidade dos recursos hídricos subterrâneos no Brasil, de forma a integrar aspectos ambientais, técnicos e legais concernentes aos impactos da DAM sobre as águas subterrâneas, possibilitando, dessa forma, identificar os fatores mais urgentes a serem desenvolvidos com o intuito de proteger efetivamente tais recursos. Entre tais fatores, a definição de critérios de lançamento de efluentes sobre os solos e águas é essencial, inclusive para projetar-se um sistema de coleta, tratamento e disposição final de resíduos em áreas de mineração que atendam a preceitos básicos de qualidade ambiental. Para isso, uma avaliação criteriosa sobre os processos ambientais e geoquímicos operantes no meio é essencial durante o planejamento pré-mineração, operatório e pós-operação. Desta forma, os problemas concernentes aos efluentes ácidos gerados, que podem comprometer profundamente os ecossistemas, não serão resolvidos em curto prazo por meio de uma intervenção pontual e desarticulada com parâmetros legais e ambientais.

Simultaneous suppression of acid mine drainage formation and arsenic release by Carrier-microencapsulation using aluminum-catecholate complexes

Pyrite (FeS2), the most common sulfide mineral in nature, plays an important role in the formation of acid mine drainage (AMD), one of the most serious environmental problems after the closure of mines and mineral processing operations. Likewise, arsenopyrite (FeAsS) is an important sulfide mineral because its dissolution releases toxic arsenic (As) into the environment. To mitigate the serious environmental problems caused by pyrite and arsenopyrite, this study investigated carrier-microencapsulation (CME) using Al-catecholate complexes, a technique that selectively forms protective coatings on the surfaces of sulfide minerals, by electrochemical techniques and batch leaching experiments coupled with surface sensitive characterization techniques.Cyclic voltammetry (CV) of Al-catecholate complexes (mono-, bis-, tris-catecholate) suggest that these three species could be oxidatively decomposed in this order: [Al(cat)3]3–→[Al(cat)2]–→[Al(cat)]+→Al3+, and these reactions were irreversible. Among these three species, [Al(cat)]+ was the most effective in suppressing pyrite and arsenopyrite oxidations because it requires less steps for complete decomposition than the other two complexes. Analyses of CME treated minerals by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated that they were covered with Al-oxyhydroxide (γ–AlO(OH)), which became more extensive at higher [Al(cat)]+ concentrations. In addition, this coating was stable even at relatively high applied potentials that simulated surface oxidizing conditions. Based on these results, a detailed mechanism of Al-based CME is proposed: (1) adsorption of [Al(cat)]+ on the surface of mineral, (2) oxidative decomposition of [Al(cat)]+ and release of “free” Al3+, and (3) precipitation and formation of Al-oxyhydroxide coating.

KAJIAN POTENSI PEMBENTUKAN AIR ASAM TAMBANG DARI TANAH LAPISAN PENUTUP BATUBARA ASAL KABUPATEN TELUK BINTUNI

Acid mine drainage is formed when certain sulfide minerals in rocks are exposed to oxidizing. Upon exposure to oxidizing conditions, these sulfide minerals are oxidized in the presence of water and oxygen to form highly acidic, sulfate-rich drainage. Acidity levels, and metal composition and concentration depend on the type and amount of sulfide mineral and the presence or absence of alkaline materials. If acid mine drainage has formed, it will be very difficult to stop the process as it is a continuous process until one of the reactions runs out. Acidic water containing heavy metals when flowing into rivers, loker or swamps will damage the condition of the ecosystem in the river. This will certainly cause a decrease in water quality. The purpose of this study is to examine the potential for the formation of acid mine drainage based on the acid base balance method.&#x0D; The results obtained in samples A, B1, B2, and C for the pasta pH test were 5.25, 4.20, 4.71, and 3.14, respectively. The results of the other parameters for the four samples were total sulfur contents (0.005%, 0.021%, 0.008%, 0.47%), acid neutralization ability (3.1, 2.82, 2.45, 13.07 kg H2SO4/ton), maximum acidic potential (0.153, 0.643, 0.245, 14.394 kg H2SO4/ton) and acid-base balance expressed as potential acid production (-12.917, -2.177, -3.065, 11,944). Evaluation of sample C data based on acid-base balance values (11.944 kg H2SO4/ton) and KPA/PKM ratio (&lt;2, 0.17) indicating that sample C has the potential to form acid mine drainage if the coal mining process is carried out.

Surface structure-dependent pyrite oxidation in relatively dry and moist air: Implications for the reaction mechanism and sulfur evolution

Pyrite oxidation not only is environmentally significant in the formation of acid mine (or acid rock) drainage and oxidative acidification of lacustrine sediment but also is a critical stage in geochemical sulfur evolution. The oxidation process is always controlled by the reactivity of pyrite, which in turn is controlled by its surface structure. In this study, the oxidation behavior of naturally existing {1 0 0}, {1 1 1}, and {2 1 0} facets of pyrite was investigated using a comprehensive approach combining X-ray photoelectron spectroscopy, diffuse reflectance Fourier transform infrared spectroscopy, and time-of-flight secondary-ion mass spectrometry with periodic density functional theoretical (DFT) calculations. The experimental results show that (i) the initial oxidation rates of both pyrite {1 1 1} and {2 1 0} are much greater than that of pyrite {1 0 0}; (ii) the initial oxidation rate of pyrite {2 1 0} is greater than that of pyrite {1 1 1} in low relative humidity, which is reversed in high relative humidity; and (iii) inner sphere oxygen-bearing sulfur species are originally generated from surface reactions and then converted to outer sphere species. The facet dependent rate law can be expressed as: r{hkl}=k{hkl}haP0.5(t+1)-0.5, where r{hkl} is the orientation dependent reaction rate, k{hkl} is the orientation dependent rate constant, h is the relative humidity, P is the oxygen partial pressure, and t is the oxidation time in seconds. {1 1 1} is the most sensitive facet for pyrite oxidation. Combined with DFT theoretical investigations, water catalyzed electron transfer is speculated as the rate-limiting step. These findings disclose the structure–reactivity dependence of pyrite, which not only presents new insight into the mechanism of pyrite oxidation but also provides fundamental data to evaluate sulfur speciation evolution, suggesting that the surface structure sensitivity should be considered to estimate the reactivity at the mineral–water interface.

Mechanisms of interaction between arsenian pyrite and aqueous arsenite under anoxic and oxic conditions

Pyrite affects the conversion and migration processes of arsenic in soils and waters. Adsorption and redox reactions of arsenite (As(III)) occur on the surface of pyrite, and the interaction processes are influenced by the arsenic incorporated into pyrite. This work examined the effects of arsenic content, pH and oxygen on the interaction between arsenian pyrite and aqueous As(III) and investigated the underlying mechanisms. The results indicated that arsenic incorporation led to a high content of Fe(III) in pyrite, and that As(III) was mainly adsorbed on pyrite surface and part of As(III) was oxidized to As(V) by the newly formed intermediates including hydroxyl radicals and hydrogen peroxide. The oxidation rate increased with increasing arsenic content in the pyrite and the presence of air (oxygen), and first decreased and then increased with increasing pH from 3.0 to 11.0. Hydroxyl radicals and hydrogen peroxide significantly contributed to the oxidation of pyrite and aqueous As(III) in acidic and alkaline solutions, respectively. Although pyrite oxidation increased with increasing arsenic content as indicated by the elevated concentrations of elemental S and SO42−, the percentage of released arsenic in total arsenic of the arsenian pyrite decreased due to the adsorption of arsenic on the surface of newly formed ferric (hydr)oxides, especially the ferric arsenate precipitate formed in high pH solutions. The present study enables a better understanding of the important interaction process of dissolved arsenite and natural pyrites in the study of groundwater contamination, arsenic migration/sequestration, and acid mine drainage formation.

Potential Formation of Acid Mine Drainage In Putra Perkasa Abadi Coal Mining Company - Girimulya Site (BIB), Tanah Bumbu Regency, South Kalimantan

Coal is a combustible fossil fuel, formed from plants that have been consolidated between rock strata and can be used by geothermal. World Energy Council said Indonesia is the fifth world coal producer after China, United States, India and Australia. Acid Mine Drainage is become one of environmental damage from coal massive exploitation in Indonesia. Precautions are required to reduce risks and minimize the formation of acid mine drainage at overburden disposal in order to meet the quality standards set by the Government. The action is carried out by isolating Potential Acid Forming (PAF) materials with non-acidic (NAF / Non Acid Forming) materials to avoid exposure to air and water with sulphide minerals. Good PAF and NAF material management in the disposal area will minimize the potential of acid mine drainage.

Investigating the formation of acid mine drainage of Toledo pyrite concentrate using column cells

Acid mine drainage (AMD) is an inevitable problem in mining and has adverse effects in water quality. Studying AMD formation will be valuable in controlling the composition of mine waters and in planning the rehabilitation method for a mine. In this research, kinetics of AMD formation of Toledo pyrite was studied using two column experiments. The mechanisms of AMD formation and the effects of various factors on pH drop were first studied. Another column test was done for validation and to study the role of Fe2+/Fe3+ ratio in the change of leachate pH. The first experiment revealed that time and particle size are the most significant factors. It was also observed that the sudden pH drop during the starting hours was due to cracks formed from beneficiation, and the formation of Fe(OH)3. The laddered behavior of pH thereafter was due to decrease in formation of Fe(OH)3, and the precipitates in pyrite surface that lowered the surface area available for pyrite oxidation. The results of the second experiment validated the laddered behavior of pH. It was also observed that particle size distribution and pyrite surface were affected by the change in pH. Fe2+/Fe3+ ratio of leachate generally decreased as pH dropped.

Microalgae-bacteria biofilms: a sustainable synergistic approach in remediation of acid mine drainage.

Microalgae and bacteria offer a huge potential in delving interest to study and explore various mechanisms under extreme environments. Acid mine drainage (AMD) is one such environment which is extremely acidic containing copious amounts of heavy metals and poses a major threat to the ecosystem. Despite its extreme conditions, AMD is the habitat for several microbes and their activities. The use of various chemicals in prevention of AMD formation and conventional treatment in a larger scale is not feasible under different geological conditions. It implies that microbe-mediated approach is a viable and sustainable alternative technology for AMD remediation. Microalgae in biofilms play a pivotal role in such bioremediation as they maintain mutualism with heterotrophic bacteria. Synergistic approach of using microalgae-bacteria biofilms provides supportive metabolites from algal biomass for growth of bacteria and mediates remediation of AMD. However, by virtue of their physiology and capabilities of metal removal, non-acidophilic microalgae can be acclimated for use in AMD remediation. A combination of selective acidophilic and non-acidophilic microalgae together with bacteria, all in the form of biofilms, may be very effective for bioremediation of metal-contaminated waters. The present review critically examines the nature of mutualistic interactions established between microalgae and bacteria in biofilms and their role in removal of metals from AMDs, and consequent biomass production for the yield of biofuel. Integration of microalgal-bacterial consortia in fuel cells would be an attractive emerging approach of microbial biotechnology for AMD remediation.

Management of coal processing wastes: studies on an alternate technology for control of sulfate and chloride discharge

Management of coal mining and coal processing wastes, particularly of high sulfur coals, can generate excessive amounts of sulfate (SO42−) and chloride (Cl−) in mine drainage that are known to negatively impact quality of both surface and ground water. The U.S. Environmental Protection Agency provides guidance to states on allowable SO42− and Cl− discharges from mine sites. This research evaluates the hypothesis that co-disposal of CCPW and FCPW with appropriate compaction can result in improved geochemical and geotechnical environments that will minimize acid mine drainage formation and SO42− and Cl− discharges. Addition of ground limestone (ag-lime) to the mix was also evaluated as a drying agent and for improvement in overall geochemistry by buffering higher pH values within the coal waste. These objectives were to develop and implement innovative concepts for engineered co-management of CCPW and FCPW at coal mining sites. The authors performed long-term field column leaching studies to analyze improvement in SO42− and Cl− in water quality. Requirements for stricter standards in some states led to the need for development of potentially improved environmental practices. This paper presents the overall encouraging results of the field kinetic studies.

Mineralogical and geochemical characterization of waste rocks from a gold mine in northeastern Thailand: application for environmental impact protection.

Waste rocks from gold mining in northeastern Thailand are classified as sandstone, siltstone, gossan, skarn, skarn-sulfide, massive sulfide, diorite, and limestone/marble. Among these rocks, skarn-sulfide and massive sulfide rocks have the potential to generate acid mine drainage (AMD) because they contain significant amounts of sulfide minerals, i.e., pyrrhotite, pyrite, arsenopyrite, and chalcopyrite. Moreover, both sulfide rocks present high contents of As and Cu, which are caused by the occurrence of arsenopyrite and chalcopyrite, respectively. Another main concern is gossan contents, which are composed of goethite, hydrous ferric oxide (HFO), quartz, gypsum, and oxidized pyroxene. X-ray maps using electron probe micro-analysis (EPMA) indicate distribution of some toxic elements in Fe-oxyhydroxide minerals in the gossan waste rock. Arsenic (up to 1.37wt.%) and copper (up to 0.60wt.%) are found in goethite, HFO, and along the oxidized rim of pyroxene. Therefore, the gossan rock appears to be a source of As, Cu, and Mn. As a result, massive sulfide, skarn-sulfide, and gossan have the potential to cause environmental impacts, particularly AMD and toxic element contamination. Consequently, the massive sulfide and skarn-sulfide waste rocks should be protected from oxygen and water to avoid an oxidizing environment, whereas the gossan waste rocks should be protected from the formation of AMD to prevent heavy metal contamination.

Suppression of the release of arsenic from arsenopyrite by carrier-microencapsulation using Ti-catechol complex

Arsenopyrite is the most common arsenic-bearing sulfide mineral in nature, and its weathering contributes to acid mine drainage (AMD) formation and the release of toxic arsenic (As). To mitigate this problem, carrier-microencapsulation (CME) using titanium (Ti)-catechol complex (i.e., Ti-based CME) was investigated to passivate arsenopyrite by forming a protective coating.Ti4+ ion dissolved in sulfuric acid and catechol were used to successfully synthesize Ti(IV) tris-catecholate complex, [Ti(Cat)3]2−, which was stable in the pH range of 5–12. Electrochemical studies on the redox properties of this complex indicate that its oxidative decomposition was a one-step, irreversible process. The leaching of As from arsenopyrite was suppressed by CME treatment using the synthesized Ti-catechol complex. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicate that this suppression was primarily due to the formation of an anatase (β-TiO2)-containing coating. Based on these results, a detailed 4-step mechanism to explain the decomposition of [Ti(Cat)3]2− and formation of TiO2 coating in Ti-based CME is proposed: (1) adsorption, (2) partial oxidation-intermediate formation, (3) non electrochemical dissociation, and (4) hydrolysis-precipitation.

Prediction of Acid Mine Drainage (AMD) and Metal Release Sources at the Küre Copper Mine Site, Kastamonu, NW Turkey

Waste and lithological rocks were subjected to aqueous leaching, acid base accounting (ABA), and net acid generation (NAG) tests, and detailed mineralogical investigations were conducted to predict acid mine drainage (AMD) formation at Turkey’s largest historical copper deposits. The field water chemistry from springs and seeps on the mine site were compared with the static and long term aqueous leaching test results. During the ABA, NAG and long term paste pH tests, ore rich and ore bearing wastes showed a paste pH <4, implying their acid generating nature. The relationship between net neutralization potential and acid producing potential revealed that waste rocks with a low sulfur content were generally low potential sources of AMD. Consistent with the static test results, aqueous leaching tests revealed that greater concentrations of Fe, Cu, Zn, Ni, Pb, Cd, Co and As were released from the wastes rich in pyrite. The test methods all generally agreed that the ore-rich wastes (O, P1C, P1D) were the main sources of AMD and metal contamination in the district.

Microbial acceleration of aerobic pyrite oxidation at circumneutral pH.

Pyrite (FeS2 ) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro-organisms in pyrite oxidation under acidic-pH conditions is well known, to date there is very little known about the capacity for aerobic micro-organisms to oxidize pyrite at circumneutral pH. Here, we describe two enrichment cultures, obtained from pyrite-bearing subsurface sediments, that were capable of sustained cell growth linked to pyrite oxidation and sulfate generation at neutral pH. The cultures were dominated by two Rhizobiales species (Bradyrhizobium sp. and Mesorhizobium sp.) and a Ralstonia species. Shotgun metagenomic sequencing and genome reconstruction indicated the presence of Fe and S oxidation pathways in these organisms, and the presence of a complete Calvin-Benson-Bassham CO2 fixation system in the Bradyrhizobium sp. Oxidation of pyrite resulted in thin (30-50nm) coatings of amorphous Fe(III) oxide on the pyrite surface, with no other secondary Fe or S phases detected by electron microscopy or X-ray absorption spectroscopy. Rates of microbial pyrite oxidation were approximately one order of magnitude higher than abiotic rates. These results demonstrate the ability of aerobic microbial activity to accelerate pyrite oxidation and expand the potential contribution of micro-organisms to continental sulfide mineral weathering around the time of the Great Oxidation Event to include neutral-pH environments. In addition, our findings have direct implications for the geochemistry of modern sedimentary environments, including stimulation of the early stages of acid mine drainage formation and mobilization of pyrite-associated metals.

The use of Mössbauer spectroscopy in environmental research

The impact that mining has on the environment is becoming an ever increasing problem all over the world. South Africa, Brazil and India are main producers of various valuable resources such as for example iron ore, platinum, gold and coal, of which coal and platinum mining will be discussed in this paper. Dumping of ash, waste and discards, result in the formation of acid mine drainage (AMD) due to the high sulphur content of the coal and the waste products. The main Fe-S-bearing minerals in the coals investigated were pyrite, jarosite and ferrous sulphate, a weathering product of pyrite. In the ash produced due to combustion or gasification of the coal, the main Fe-constituents are Fe2+,3+ glass (≈ 30%) and hematite (70%). The amorphous phase of the sample was composed mainly of SiO2 and Al2O3 with trace element inclusions of Hg, Ti, Cd and As. The soil, sediment and overburden in the coal mining areas contain pyrite as Fe-S-mineral and also ferrous sulphate as weathering product, with illite the main clay mineral. From laboratory leaching products of coal and ash, sulphur in the form of SO\(_{4}^{2-}\), was found to be one of the most leached ions with a concentration ranging between 100–1000 ppm. The amount of Fe leached out from the ash samples was between 2–5 ppm, but the Fe-leachability depends on the pH, with higher amounts leached out at pH ≤ 1.5. Magnetite losses, to the amount of about 1kg per tonne of magnetite used, occur during the dense medium separation process (DMS) used in cleaning the coal, which also reports in the waste product. South Africa is the largest producer of platinum and smelting of the ore can lead to various forms of pollution. Magnetite formation in the 2-stage furnace process is used as an indicator of the effectiveness of the reduction and the Fe2+ and Fe3+ ratio is used to monitor the process. In the flash furnace the ratio is 2–6, whilst in the electric furnace it is ≤0.02. If not monitored closely a large amount of nickel loss will occur if sent to the waste dump. Mossbauer spectroscopy was used to identify the Fe-species and the results were augmented by High Resolution-Transmission Electron microscopy (HR-TEM), Field Emission-Scanning Electron Microscopy (FE-SEM)/EDS, X-Ray Diffraction (XRD) and ICP-EOS results.

Electrochemical oxidation of pyrite in pH 2 electrolyte

The oxidation of pyrite under acidic conditions, an important process leading to the formation of acid mine drainage, has been the subject of intense research yet remains incompletely understood. In this study, the mechanism of the electrochemical oxidation of pyrite in a pH 2 electrolyte was investigated using electrochemical techniques. The morphological changes and oxidation products of pyrite were studied using atomic force microscopy (AFM), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS). At low potential of 0.50V, electrochemical oxidation of pyrite was diffusion-limited due to a sulfur-rich layer (S0) that formed and covered the pyrite surface, resulting in surface passivation. As the potential increased to 0.60V, diffusion-limitation and surface passivation of pyrite oxidation ceased due to the conversion of amorphous elemental sulfur (S8) to crystalline S8, resulting in the previously covered active sites being re-exposed which allowed continued oxidation of pyrite. At higher potentials of 0.70 and 0.80V, more S8 and polysulfides (Sn2−), together with an iron-rich layer composed of Fe(OH)3, FeO and Fe2O3, formed and accumulated on the pyrite surface. These products led to a decreased rate of oxidation rather than a complete passivation of the surface. AFM imaging revealed that surface roughness increased with oxidation potential and that the oxidation of the pyrite surface was inhomogeneous. These findings provide further insight into the physical and chemical changes that pyrite undergo during electrochemical oxidation, which deepens our understanding of this important process.

Reducing Acid Mine Drainage Formation Using Locally-Available Soil Ameliorants

Reducing Acid Mine Drainage Formation Using Locally-Available Soil Ameliorants

Application of Pb-Zn tailings for surface paste disposal: geotechnical and geochemical observations

Surface paste disposal (SPD) technology has been investigated recently to solve the geotechnical (tailings dam failure) and geochemical (acid mine drainage formation) problems relating to tailings disposal. The tailings dam accidents occurred in the last few years have expedited the researches to search for safer tailings disposal methods in mining industry. The aim of this study is to investigate which parameters affect the geotechnical and geochemical stability of sulphidic paste tailings as SPD. The pH, EC and crack intensity of paste tailings placed in layers were measured to observe how the parameters affect their stability. In this study, it can be seen that solid concentration of the paste material increases above ~80 wt.%, and its shear strength is above 20 kPa. In addition, the pH values reduced from 7.4 to 6.6 and the EC values increased from 2.9 to 3.3 mS/cm in seepage water of the paste layers. According to these values, it can be said that there is a very low environmental risk using the SPD. Results showed the applicability of the SPD method by obtaining geochemical and geotechnical stability.

Assessment of acid mine drainage potential of flotation slurry from a tailing dam in a copper mine, Murgul, Northeastern Turkey

Acid mine drainage potential of flotation slurry from a tailing dam in an active copper mine (Murgul) in Turkey was evaluated using an integrated approach combining static and kinetics tests, mineralogical and geochemical characterization and geochemical modeling. Acid mine drainage potential of the tailing waste was determined by acid base accounting tests and humidity cell experiment. During ABA tests, paste pH, fizz rating, sulfur speciation, acid and neutralization potentials of the slurry were measured. The rates of metal release and mechanism were determined from the humidity cell experiment. Leachates sampled weekly from the humidity cell were monitored for their pH, electrical conductivity, oxidation–reduction potential, alkalinity, sulfate and metal contents. In addition, at the end of the experiment, cell material was sampled along the flow path to determine the possible AMD products formed. Results of the ABA tests indicated that the tailing waste exhibited acidic character. Paste pH of the waste was 4.35. Acid potential (116.5 kg CaCO3/t) of the waste was about 34-folds more than its neutralizing potential (3.44 kg CaCO3/t), indicating that tailing waste had a high acid producing potential. In contrary to the ABA tests, the results of humidity cell experiment indicated that leachates of the tailing waste exhibited neutral to alkaline pH values (pH 7.4–8.2) throughout the experiment. The rates of metal (e.g., Fe: 0.04–0.001 mg/kg/week, Cu: 0.005 mg/kg/week) and sulfate release (24 mg/kg/week) were very low. Metals in leachate showed similar elution behavior. The rates of metal release were initially fast and then decreased significantly, suggesting that different processes including desorption, mineral dissolution/precipitation and oxidation played a role on metal elution behavior. Neutral to alkaline pH values observed throughout the humidity cell experiment suggesting that acidity produced by the pyrite oxidation was buffered by the low neutralizing capacity of the waste. Low permeability of the tailing waste and the presence of the unaltered pyrite grains significantly limited the kinetics of the acid mine drainage formation. Evidence of pyrite oxidation and the formation of ferrihydrite precipitates was visible especially at surface of the waste that was in contact with air and water. Dissolution of gypsum also controlled the observed sulfate release behavior from the tailing waste. Mass balance calculations performed on each metal showed that the percentage of mass eluted from humidity cell for Mn, Zn and Cu was 8.6, 4.9 and 3.6%, respectively, while it was <1% for the rest of the metals investigated. Results of this study suggest that slow metal leaching kinetics of the tailing waste reduce the risk of metal contamination in the surrounding surface water bodies that is in contact with the waste material.