Typical Acid Mine Drainage Research Articles

Assessment of heavy metals leachability characteristics and associated risk in typical acid mine drainage (AMD)-contaminated river sediments from North China

Acid mine drainage (AMD) is a worldwide environmental problem, characterized by low pH values and high concentrations of heavy metals. Heavy metal pollution of sediments caused by AMD has attracted widespread attention. However, research works on the leachability and distribution characteristics along with the ecological and health risks assessment of AMD-polluted sediment are limited. 15 sediments samples were collected from an AMD-polluted river, Shandi River, North China to analyze the leachability concentration, potential sources, and associated risk of eight metals, namely Ni, Cd, Cu, Zn, Fe2+, Fe3+, Pb, and Mn. Our results showed that Mn, Ni, Fe3+, and Fe2+ were the main leachate pollutants in the Shandi river. Certain levels of ecological risks existed in AMD-polluted stations and Ni was the common key metal that caused the high ecological risk factor in S1, S2, and S4. Cu, Ni, and Zn were the three metals that caused high or moderate risk to zebrafish. Mn and Fe were the main heavy metals that caused non-carcinogenic risks both for adults and children and Ni was another main heavy metal that caused non-carcinogenic risks for children. Ni and Cd can induce carcinogenic risks in these areas. Pearson's correlation and PCA results supported that these metals possibly originate from common AMD–polluted sources. The technology of “gravitational settling-neutralizing filter-aeration-coagulation-filtration” (GSNFACF) was an effective strategy to amend AMD and could be used for future cleaner production and environmental sustainability. These results suggested that the main contaminants in the sediments of the Shandi River should be preferentially treated by the government.

Rare earth elements - Source and evolution in an aquatic system dominated by mine-Influenced waters

Acid mine drainage (AMD), formed by the instability of sulfides, typically generates acidity and releases potentially toxic elements and sulfate to the environment, among other pollutants. An example is the group of rare earth elements (REE) that may have high toxic behavior. This toxicity leads to degradation of soils, water reservoirs and rivers, promoting serious risks for the ecosystems. So, the main goal of the present work is to study the hydrochemical properties of a system with mine-influenced waters during the rainy season, focusing on the origin, evolution/behavior, and concentration of REE. The study area is the São Domingos mining complex, located in one of the largest metallogenetic provinces in the world (Iberian Pyrite Belt), known by the evidences of AMD contamination. The obtained results reveal extraordinarily low pH (0.4), high electrical conductivity, reaching 26,200 μS/cm, and high values of sulfate and acidity. Regarding the REE, the determined concentration exceeded that observed in normal pH of neutral freshwaters by 2–3 times the order of magnitude. The results revealed that Y and Ce are distinguished in practically all sampled sites, due to its higher concentrations, with maximum values of 221.8 and 166.9 μg/L. In general, the concentrations increase as the water pH decreases. The statistical analysis indicates that REE elements may have a common origin, mutual dependence, and similar behavior during transport with typical AMD elements and composition of host rocks. Most samples show enrichment in middle REE (MREE) (Gdn/Lun), like the classic signature of AMD. In turn, colloids and AMD-precipitates may be participating in the incorporation of these elements. Therefore, due to potential risk of impacts on ecosystems, REE are a topic of relevant interest for future studies in order to assist monitoring processes and help government decisions related to water quality management.

Indicator species drive the key ecological functions of microbiota in a river impacted by acid mine drainage generated by rare earth elements mining in South China.

Acid mine drainage (AMD) generated by rare earth elements (REEs) deposits exploration contains high concentrations of REEs, ammonium and sulfates, which is quite different from typical metallic AMD. Currently, microbial responses and ecological functions in REEs-AMD impacted rivers are unknown. Here, 16S rRNA analysis and genome-resolved metagenomics were performed on microbial community collected from a REEs-AMD contaminated river. The results showed that REEs-AMD significantly changed river microbial diversity and shaped unique indicator species (e.g. Thaumarchaeota, Methylophilales, Rhodospirillales and Burkholderiales). The main environmental factors regulating community were pH, ammonium and REEs, among which high concentration of REEs increased REEs-dependent enzyme-encoding genes (XoxF and ExaF/PedH). Additionally, we reconstructed 566 metagenome-assembled genomes covering 70.4% of identifying indicators. Genome-centric analysis revealed that the abundant archaea Thaumarchaeota and Xanthomonadaceae were often involved in nitrification and denitrification, while family Burkholderiaceae were capable of sulfide oxidation coupled with dissimilatory nitrate reduction to ammonium. These indicators play crucial roles in nitrogen and sulfur cycling as well as REEs immobilization in REEs-AMD contaminated rivers. This study confirmed the potential dual effect of REEs on microbial community at the functional gene level. Our investigation on the ecological roles of indicators further provided new insights for the development of REEs-AMD bioremediation.

Economic Performance of Active and Passive AMD Treatment Systems Under Uncertainty: Case Studies from the Brunner Coal Measures in New Zealand

Acid mine drainage (AMD) often requires management long after mining operations have ceased. Cost-effective long-term passive treatment systems (PTS) are required for closure of mine sites. However, PTS research seldom defines well-constrained operational and financial parameters to enable confident decision making by mining companies. PTS are generally assumed to be a lower-cost alternative to active systems when used in favorable circumstances, but there is little objective information to define when they are more suitable than active treatment. Instead, general ‘rules-of-thumb’ for flow rates or acid loads are used to determine when PTS are best used. We used well-characterized AMD from multiple historic and active coal mine sites in New Zealand to test these rules-of-thumb from a financial perspective by modelling capital and operational costs over a 100 year timeframe. We present static and uncertainty-based cost assessments of a mussel shell reactor PTS compared to typical active AMD treatment systems at six mine drainage sources from the Brunner Coal Measures. We show that for expected AMD characteristics and duration of treatment, savings on operational costs with PTS can exceed the higher initial capital costs. In addition, the financial advantage of PTS over time may be achieved at flow rates and acidity loads that exceed the industry rules-of-thumb PTS limits. However, in some circumstances, cost projections for high up-front capital costs of purchasing all treatment media for the life span of the PTS is less favorable than discounted treatment media in active treatment systems over time. Understanding financial models of AMD treatment options during mine site design can help reduce the costs of operating and closing mine sites.

High Diversity in Iron Cycling Microbial Communities in Acidic, Iron-Rich Water of the Pyhäsalmi Mine, Finland

Microbial communities of iron-rich water in the Pyhäsalmi mine, Finland, were investigated with high-throughput amplicon sequencing and qPCR targeting bacteria, archaea, and fungi. In addition, the abundance ofLeptospirillumandAcidithiobacilluswas assessed with genus-specific qPCR assays, and enrichment cultures targeting aerobic ferrous iron oxidizers and ferric iron reducers were established. The acidic (pH 1.4–2.3) mine water collected from 240 m, 500 m, and 600 m depth from within the mine had a high microbial diversity consisting of 63-114 bacterial, 10-13 archaeal, and 104-117 fungal genera. The most abundant microorganisms in the mine water were typical acid mine drainage (AMD) taxa, such as acidophilic, iron-oxidizingLeptospirillum,Acidiphilum,Acidithiobacillus,Ferrovum, andThermoplasma. The fungi belonged mostly to the phylum Ascomycetes, although a great part of the fungal sequences remained unclassified. The number of archaeal 16S rRNA genes in the mine water was between 0.3 and 1.2 × 107copies mL−1in the samples from 500 m and 600 m, but only 3.9 × 103at 240 m and archaea were in general not enriched in cultures. The number of fungal 5.8S rRNA genes was high only in the mine water from 500 m and 600 m, where 0.2–3.4 × 104spore equivalents mL−1were detected. A high number ofLeptospirillum16S rRNA genes, 0.6–1.6 × 1010copies mL−1, were detected at 500 m and 600 m depth and in cultures containing ferrous iron, showing the importance of iron oxidizers in this environment. The abundance of bacteria in general was between 103and 10616S rRNA gene copies mL−1. Our results showed a high microbial diversity in the acid- and iron-impacted waters of the Pyhäsalmi mine, whereLeptospirillumbacteria were especially prominent. These iron oxidizers are also the main nitrogen-fixing microorganisms in this ecosystem.

Novel and Unexpected Microbial Diversity in Acid Mine Drainage in Svalbard (78° N), Revealed by Culture-Independent Approaches.

Svalbard, situated in the high Arctic, is an important past and present coal mining area. Dozens of abandoned waste rock piles can be found in the proximity of Longyearbyen. This environment offers a unique opportunity for studying the biological control over the weathering of sulphide rocks at low temperatures. Although the extension and impact of acid mine drainage (AMD) in this area is known, the native microbial communities involved in this process are still scarcely studied and uncharacterized. Several abandoned mining areas were explored in the search for active AMD and a culture-independent approach was applied with samples from two different runoffs for the identification and quantification of the native microbial communities. The results obtained revealed two distinct microbial communities. One of the runoffs was more extreme with regards to pH and higher concentration of soluble iron and heavy metals. These conditions favored the development of algal-dominated microbial mats. Typical AMD microorganisms related to known iron-oxidizing bacteria (Acidithiobacillus ferrivorans, Acidobacteria and Actinobacteria) dominated the bacterial community although some unexpected populations related to Chloroflexi were also significant. No microbial mats were found in the second area. The geochemistry here showed less extreme drainage, most likely in direct contact with the ore under the waste pile. Large deposits of secondary minerals were found and the presence of iron stalks was revealed by microscopy analysis. Although typical AMD microorganisms were also detected here, the microbial community was dominated by other populations, some of them new to this type of system (Saccharibacteria, Gallionellaceae). These were absent or lowered in numbers the farther from the spring source and they could represent native populations involved in the oxidation of sulphide rocks within the waste rock pile. This environment appears thus as a highly interesting field of potential novelty in terms of both phylogenetic/taxonomic and functional diversity.

Long term fluctuations of groundwater mine pollution in a sulfide mining district with dry Mediterranean climate: Implications for water resources management and remediation

Water resources management and restoration strategies, and subsequently ecological and human life quality, are highly influenced by the presence of short and long term cycles affecting the intensity of a targeted pollution. On this respect, a typical acid mine drainage (AMD) groundwater from a sulfide mining district with dry Mediterranean climate (Iberian Pyrite Belt, SW Spain) was studied to unravel the effect of long term weather changes in water flow rate and metal pollutants concentration. Three well differentiated polluting stages were observed and the specific geochemical, mineralogical and hydrological processes involved (pyrite and enclosing rocks dissolution, evaporitic salts precipitation-redisolution and pluviometric long term fluctuations) were discussed. Evidencing the importance of including longer background monitoring stage in AMD management and restoration strategies, the present study strongly advise a minimum 5-years period of AMD continuous monitoring previous to the design of any AMD remediation system in regions with dry Mediterranean climate.

Microbial Community Composition in Acid Mine Drainage Lake of Xiang Mountain Sulfide Mine in Anhui Province, China

Acid mine drainage (AMD) lake of Xiang Mountain in Anhui Province, China, was characterized by acidic waters (pH around 2.8) containing high concentrations of soluble metals and sulfate. To investigate the function and dynamics of this extreme ecosystem, four water samples were collected from the lake in the fall of 2010. The acidophilic community structure was analyzed by molecular approaches, and bacterial and archaeal clone libraries of 16S rRNA genes were constructed. In contrast to dominance of chemolithotrophic acidophiles in typical AMD environments, autotrophic iron/sulfur-oxidizing bacteria were detected in only one sample with low abundance. Unexpectedly, the Cyanobacteria group was the predominant in all four samples (54.9%−77%). Chemoheterotrophs Acidiphilium and Acidisphaera were also abundant. These two heterotrophic groups contain bacteriochlorophyll that can perform photosynthesis, an advantage to grow and survive in such oligotrophic acidic environments. Only two clone sequences related to Legionella (2.8% of the total clones) were recovered from one sample in sharp contrast to its higher abundance (12.7%) in the summer of 2009. All archaeal sequences were affiliated to the phylum Crenarchaeota. The results of statistical analysis suggested that the water chemistry of the AMD lake controlled microbial composition of the AMD ecosystem.

Synthesising acid mine drainage to maintain and exploit indigenous mining micro-algae and microbial assemblies for biotreatment investigations

The stringent regulations for discharging acid mine drainage (AMD) has led to increased attention on traditional or emerging treatment technologies to establish efficient and sustainable management for mine effluents. To assess new technologies, laboratory investigations on AMD treatment are necessary requiring a consistent supply of AMD with a stable composition, thus limiting environmental variability and uncertainty during controlled experiments. Additionally, biotreatment systems using live cells, particularly micro-algae, require appropriate nutrient availability. Synthetic AMD (Syn-AMD) meets these requirements. However, to date, most of the reported Syn-AMDs are composed of only a few selected heavy metals without considering the complexity of actual AMD. In this study, AMD was synthesised based on the typical AMD characteristics from a copper mine where biotreatment is being considered using indigenous AMD algal-microbes. Major cations (Ca, Na, Cu, Zn, Mg, Mn and Ni), trace metals (Al, Fe, Ag, Na, Co, Mo, Pb and Cr), essential nutrients (N, P and C) and high SO(4) were incorporated into the Syn-AMD. This paper presents the preparation of chemically complex Syn-AMD and the challenges associated with combining metal salts of varying solubility that is not restricted to one particular mine site. The general approach reported and the particular reagents used can produce alternative Syn-AMD with varying compositions. The successful growth of indigenous AMD algal-microbes in the Syn-AMD demonstrated its applicability as appropriate generic media for cultivation and maintenance of mining microorganisms for future biotreatment studies.

Effects of thin Covers on the Release of Coal Gangue Contaminants

The effects of the different ecological covers on the release of coal gangue contaminants were evaluated by the batch pot of experiments. The tests were carried for 12 weeks on the coal gangue by different approaches, which were the coverings with 1-2cm artificial matrix that contained acid buffer and plant ameliorant(Tr1:thin matrix cover), 1-2cm slurry of artificial matrix (Tr2: thin coating),and control groups(CK),and planted Lolium perenne, Chenopodium ambrosioides L, and sporopollen of Funaria hygrometrica Hedw on the surface layer, respectively. During the pot experiments, the leachates were collected and analyzed for pH, electrical conductivity (EC), and concentration of Fe, Mn, Cu, Zn, SO42-, F- .The results showed that the coal gangue was uninterruptedly oxidized to form acidic when it was exposed to open air, and 3 or 5 weeks later, dissolution of Fe, Mn, Cu, Zn and SO42-, F− in the coal gangue started and increased significantly, and this is a typical acid mine drainage (AMD) formation process. Compared to the CK, thin matrix cover could retard the allotted time of the production of acidity and release of contaminants, but was easily invalid to long-term. The pH of thin coating was at a high value with time, and the concentration of Fe, Mn, Cu, Zn, SO42− and F- reduced significantly. The data indicated that the thin coating could effectively stop or retard the production of acidity and the release of contaminants generated by coal gangue. It suggests that thin coating covers on the coal gangue could be a suitable method for pollution abatement and controlling on-site.

Role of iron colloids in copper speciation during neutralization in a coastal acid mine drainage, South Korea: Insight from voltammetric analyses and surface complexation modeling

A coastal acid mine drainage (AMD) of ~ 800 m length, Chonam-ri Creek flows through a neutralizing pond mid-stream before discharging to the Kwangyang Bay of South Korea. The creek water displays a low dissolved organic carbon (DOC) concentration of ~ 1 mg/L, with a wide range of pH from ~ 3 to ~ 7 and Fe concentration from 0.005 to 106 mg/L. Our previous field study showed that the fraction of labile Cu and Pb in the creek water, determined by anodic stripping voltammetry (ASV), decreases rapidly with increasing pH, but no such pH dependence was observed for Cd or Zn. To further understand geochemical processes governing metal speciation during neutralization in AMD, we conducted two sets of laboratory experiments using Chonam-ri Creek water samples and model solutions, as well as Visual MINTEQ modeling. When the natural pH of the creek water samples was adjusted to a range between 2 and 8 by adding acid or base, the pH dependence of metal speciation or lack thereof was reproduced. A model solution simulating the water of Chonam-ri Creek also demonstrated the pH dependence of Cu speciation, determined by competitive ligand exchange-cathodic stripping voltammetry (CLE-CSV) in the presence of Fe and strong organic ligand. Based on VMINTEQ modeling indicating that 0.45 μm filterable Fe in the downstream sites of Chonam-ri Creek is most likely in the form of Fe colloid, surface complexation modeling of Cu adsorption onto Fe colloid using 1-pK Three Plane Model (TPM) was successful (RMSE = 0.185) in predicting the labile Cu concentrations. VMINTEQ modeling suggests that Cu speciation is dominated by interaction with Fe colloids over dissolved organic matter (DOM) during neutralization in a typical AMD with high Fe and low DOM, and that Cu is discharged to the bay in the form of colloids. The coupled application of voltammetric technique and geochemical modeling provides useful information on metal speciation in AMD.

Oxygen isotope evidence for sorption of molecular oxygen to pyrite surface sites and incorporation into sulfate in oxidation experiments

Abstract Experiments were conducted to investigate (i) the rate of O-isotope exchange between SO4 and water molecules at low pH and surface temperatures typical for conditions of acid mine drainage (AMD) and (ii) the O- and S-isotope composition of sulfates produced by pyrite oxidation under closed and open conditions (limited and free access of atmospheric O2) to identify the O source/s in sulfide oxidation (water or atmospheric molecular O2) and to better understand the pyrite oxidation pathway. An O-isotope exchange between SO4 and water was observed over a pH range of 0–2 only at 50 °C, whereas no exchange occurred at lower temperatures over a period of 8 a. The calculated half-time of the exchange rate for 50 °C (pH = 0 and 1) is in good agreement with former experimental data for higher and lower temperatures and excludes the possibility of isotope exchange for typical AMD conditions (T ⩽ 25 °C, pH ⩾ 3) for decades. Pyrite oxidation experiments revealed two dependencies of the O-isotope composition of dissolved sulfates: O-isotope values decreased with longer duration of experiments and increasing grain size of pyrite. Both changes are interpreted as evidence for chemisorption of molecular O2 to pyrite surface sites. The sorption of molecular O2 is important at initial oxidation stages and more abundant in finer grained pyrite fractions and leads to its incorporation in the produced SO4. The calculated bulk contribution of atmospheric O2 in the dissolved SO4 reached up to 50% during initial oxidation stages (first 5 days, pH 2, fine-grained pyrite fraction) and decreased to less than 20% after about 100 days. Based on the direct incorporation of molecular O2 in the early-formed sulfates, chemisorption and electron transfer of molecular O2 on S sites of the pyrite surface are proposed, in addition to chemisorption on Fe sites. After about 10 days, the O of all newly-formed sulfates originates only from water, indicating direct interaction of hydroxyls from water with S at the anodic S pyrite surface site. Then, the role of molecular O2 is as proposed in previous studies: acting as electron acceptor only at the cathodic Fe pyrite surface site for oxidation of Fe(II) to Fe(III).

Geochemical Characterisation of Seepage and Drainage Water Quality from Two Sulphide Mine Tailings Impoundments: Acid Mine Drainage versus Neutral Mine Drainage

Seepage water and drainage water geochemistry (pH, EC, O2, redox, alkalinity, dissolved cations and trace metals, major anions, total element concentrations) were studied at two active sulphide mine tailings impoundments in Finland (the Hitura Ni mine and Luikonlahti Cu mine/talc processing plant). The data were used to assess the factors influencing tailings seepage quality and to identify constraints for water treatment. Changes in seepage water quality after equilibration with atmospheric conditions were evaluated based on geochemical modelling. At Luikonlahti, annual and seasonal changes were also studied. Seepage quality was largely influenced by the tailings mineralogy, and the serpentine-rich, low sulphide Hitura tailings produced neutral mine drainage with high Ni. In contrast, drainage from the high sulphide, multi-metal tailings of Luikonlahti represented typical acid mine drainage with elevated contents of Zn, Ni, Cu, and Co. Other factors affecting the seepage quality included weathering of the tailings along the seepage flow path, process water input, local hydrological settings, and structural changes in the tailings impoundment. Geochemical modelling showed that pH increased and some heavy metals were adsorbed to Fe precipitates after net alkaline waters equilibrated with the atmosphere. In the net acidic waters, pH decreased and no adsorption occurred. A combination of aerobic and anaerobic treatments is proposed for Hitura seepages to decrease the sulphate and metal loading. For Luikonlahti, prolonged monitoring of the seepage quality is suggested instead of treatment, since the water quality is still adjusting to recent modifications to the tailings impoundment.

Factors affecting the transformation of a pyritic tailing: scaled-up column tests

Two different methods for predicting the quality of the water draining from a pyritic tailing are compared; for this, a static test (ABA test) and a kinetic test in large columns were chosen. The different results obtained in the two experimental set-ups show the necessity of being careful in selecting both the adequate predictive method and the conclusions and extrapolations derived from them. The tailing chosen for the weathering tests (previously tested in shake flasks and in small weathering columns) was a pyritic residue produced in a flotation plant of complex polymetallic sulphides (Huelva, Spain). The ABA test was a modification of the conventional ABA test reported in bibliography. The modification consisted in the soft conditions employed in the digestion phase. For column tests, two identical methacrylate columns (150 cm high and 15 cm diameter) were used to study the chemical and microbiological processes controlling the leaching of pyrite. The results obtained in the two tests were very different. The static test predicted a strong potential acidity for the tailing. On the contrary, pH value in the effluents draining from the columns reached values of only 5 units, being the concentration of metals (<600 mg/L) and sulphate ions (<17,000 mg/L) very small and far from the values of a typical acid mine drainage. In consequence, the static test may oversize the potential acidity of the tailing; whereas large columns may be saturated in water, displacing the oxygen and inhibiting the microbial activity necessary to catalyse mineral oxidation.

Macrofilamentous microbial communities in the metal-rich and acidic River Tinto, Spain

A novel type of macroscopic microbial community consisting of large dendritic filaments (up to 1.5 m) in a pH 2.0 dam of the River Tinto (South-western Spain) is described. The combined use of 16S rRNA-gene surveys and fluorescent in situ hybridisation (FISH) suggested that γ-proteobacteria and a relative large diversity of α-proteobacteria dominated these structures. β-Proteobacteria, Actinobacteria and Firmicutes were also detected. Whereas acidophilic bacteria of the genera Acidithiobacillus, Leptospirillum and Acidiphilium, and archaea belonging to the Thermoplasmatales dominate mine acid drainage waters and streamers (riverbed filamentous biofilms), none of the lineages identified in this study affiliate to typical acid mine drainage acidophilic bacteria. Bacteria of the Tinto macrofilaments might be heterotrophic, and could be feeding on the organic matter entrapped in the filamentous structure.

99/00713 Reversed air staging—a method for reduction of N 2O emissions from fluidized bed combustion of coal

A coastal acid mine drainage (AMD) of ~ 800 m length, Chonam-ri Creek flows through a neutralizing pond mid-stream before discharging to the Kwangyang Bay of South Korea. The creek water displays a low dissolved organic carbon (DOC) concentration of ~ 1 mg/L, with a wide range of pH from ~ 3 to ~ 7 and Fe concentration from 0.005 to 106 mg/L. Our previous field study showed that the fraction of labile Cu and Pb in the creek water, determined by anodic stripping voltammetry (ASV), decreases rapidly with increasing pH, but no such pH dependence was observed for Cd or Zn. To further understand geochemical processes governing metal speciation during neutralization in AMD, we conducted two sets of laboratory experiments using Chonam-ri Creek water samples and model solutions, as well as Visual MINTEQ modeling. When the natural pH of the creek water samples was adjusted to a range between 2 and 8 by adding acid or base, the pH dependence of metal speciation or lack thereof was reproduced. A model solution simulating the water of Chonam-ri Creek also demonstrated the pH dependence of Cu speciation, determined by competitive ligand exchange-cathodic stripping voltammetry (CLE-CSV) in the presence of Fe and strong organic ligand. Based on VMINTEQ modeling indicating that 0.45 μm filterable Fe in the downstream sites of Chonam-ri Creek is most likely in the form of Fe colloid, surface complexation modeling of Cu adsorption onto Fe colloid using 1-pK Three Plane Model (TPM) was successful (RMSE = 0.185) in predicting the labile Cu concentrations. VMINTEQ modeling suggests that Cu speciation is dominated by interaction with Fe colloids over dissolved organic matter (DOM) during neutralization in a typical AMD with high Fe and low DOM, and that Cu is discharged to the bay in the form of colloids. The coupled application of voltammetric technique and geochemical modeling provides useful information on metal speciation in AMD.