Sulfide Mine Research Articles

Evaluation of bauxite residues (red muds) of different origins for environmental applications

Bauxite residue (red mud) samples from 11 Australian and overseas Bayer process refineries and variously treated red muds were investigated from the perspective of potential environmental uses for red muds. Red muds had pH (1:5 H 2O) values ranging from 8.4 to 12.6 and electrical conductivities of 0.7 to 18.2 mS/cm (1:5 extract), surface area ranged from 15 to 30 m 2/g and texture from sandy clay loam to clay. Red muds are mostly composed of crystalline compounds of Fe, Al, Si and Ca with some red muds containing moderate amounts of Ti and Na. Most red muds contain hematite, goethite, quartz, calcite, desilication product (sodalite), gibbsite, boehmite and anatase. Other minerals, including muscovite, halite and gypsum occur in some red muds. The acid buffering behaviour of red muds was investigated by incubation of red muds with various amounts of hydrochloric acid. Buffering curves changed with time and each red mud gave a different buffering curve although curves could be grouped into five different shapes. Most of the buffering occurs between about pH 6 and 8 where the pH is buffered by dissolution of calcite, sodalite and tricalcium aluminate (when present). X-ray diffraction (XRD) analysis of acid treated red muds at different pH values indicate that sodalite and calcite buffer (i.e. dissolve) simultaneously. Buffering at lower pH values (< 4) is due to dissolution of Fe oxides. Each red mud has different pH buffering characteristics so that the use of red mud for liming of acid soil, water, sulphidic mining residues and manufacturing wastes will require detailed characterisation of the buffering reactions for the particular system.

Plant Colonization on a Contaminated Serpentine Site

This study evaluated relationships between the serpentine soil from a waste-rock dump of the abandoned Libiola sulphide mine (NW Italy) and its pioneer vegetation. We identified the tolerance of various species to environmental conditions and evaluated physical or chemical factors that influenced the first plants to colonize this stressful environment. Thirteen sampling sites were identified in the rock dump from characterization of surface or near-surface oxidation zone and vegetation type. Sampling sites were analyzed for slope, pH, mineralogy, soil chemistry, floristic composition, and the percent coverage of each species. In all the plots, species richness and vegetation cover were extremely low. The flora showed an acidophilous character.

A regional soil and sediment geochemical study in northern California

Abstract Regional-scale variations in soil geochemistry were investigated in a 20,000-km 2 study area in northern California that includes the western slope of the Sierra Nevada, the southern Sacramento Valley and the northern Coast Ranges. Over 1300 archival soil samples collected from the late 1970s to 1980 in El Dorado, Placer, Sutter, Sacramento, Yolo and Solano counties were analyzed for 42 elements by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry following a near-total dissolution. These data were supplemented by analysis of more than 500 stream-sediment samples from higher elevations in the Sierra Nevada from the same study site. The relatively high-density data (1 sample per 15 km 2 for much of the study area) allows the delineation of regional geochemical patterns and the identification of processes that produced these patterns. The geochemical results segregate broadly into distinct element groupings whose distribution reflects the interplay of geologic, hydrologic, geomorphic and anthropogenic factors. One such group includes elements associated with mafic and ultramafic rocks including Cr, Ni, V, Co, Cu and Mg. Using Cr as an example, elevated concentrations occur in soils overlying ultramafic rocks in the foothills of the Sierra Nevada (median Cr = 160 mg/kg) as well as in the northern Coast Ranges. Low concentrations of these elements occur in soils located further upslope in the Sierra Nevada overlying Tertiary volcanic, metasedimentary and plutonic rocks (granodiorite and diorite). Eastern Sacramento Valley soil samples, defined as those located east of the Sacramento River, are lower in Cr (median Cr = 84 mg/kg), and are systematically lower in this suite compared to soils from the west side of the Sacramento Valley (median Cr = 130 mg/kg). A second group of elements showing a coherent pattern, including Ca, K, Sr and REE, is derived from relatively silicic rocks types. This group occurs at elevated concentrations in soils overlying volcanic and plutonic rocks at higher elevations in the Sierras (e.g. median La = 28 mg/kg) and the east side of the Sacramento Valley (median 20 mg/kg) compared to soils overlying ultramafic rocks in the Sierra Nevada foothills (median 15 mg/kg) and the western Sacramento Valley (median 14 mg/kg). The segregation of soil geochemistry into distinctive groupings across the Sacramento River arises from the former presence of a natural levee (now replaced by an artificial one) along the banks of the river. This levee has been a barrier to sediment transport. Sediment transport to the Valley by glacial outwash from higher elevations in the Sierra Nevada and, more recently, debris from placer Au mining has dominated sediment transport to the eastern Valley. High content of mafic elements (and low content of silicic elements) in surface soil in the west side of the valley is due to a combination of lack of silicic source rocks, transport of ultramafic rock material from the Coast Ranges, and input of sediment from the late Mesozoic Great Valley Group, which is itself enriched in mafic elements. A third group of elements (Zn, Cd, As and Cu) reflect the impact of mining activity. Soil with elevated content of these elements occurs along the Sacramento River in both levee and adjacent flood basin settings. It is interpreted that transport of sediment down the Sacramento River from massive sulfide mines in the Klamath Mountains to the north has caused this pattern. The Pb, and to some extent Zn, distribution patterns are strongly impacted by anthropogenic inputs. Elevated Pb content is localized in major cites and along major highways due to inputs from leaded gasoline. Zinc has a similar distribution pattern but the source is tire wear.

Geomicrobiology of Sulfidic Mine Dumps: A Short Review

The geomicrobiology of sulfidic mine dumps is reviewed. More than 30 microbiological studies of sulfidic mine dumps have been published. Mainly culturing approaches such as most probable number (MPN) or agar plates were used to study the microbial communities. More recently, molecular biological techniques such as FISH, CARD-FISH, Q-PCR, T-RFLP, DGGE, or cloning have been applied to quantify microorganisms and to investigate the microbial diversity. Aerobic Fe(II)- and sulfur compound oxidizing microorganisms oxidize pyrite, pyrrhotite and other metal sulfides and play an important role in the formation of acid mine drainage (AMD). Anaerobic microorganisms such as Fe(III)-reducing microorganisms dissolve Fe(III)(hydr)oxides and may thereby release adsorbed or precipitated metals. Sulfate-reducing microorganisms precipitate and immobilize metals. In addition to the microbial communities several biogeochemical processes have been analyzed in mine dumps. Pyrite or pyrrhotite oxidation rates have been measured by different techniques: Column experiments, humidity cells, microcalorimetry, or oxygen consumption measurements. Analyses of stable isotopes of iron, oxygen and sulfur have yielded valuable information on biogeochemical reactions. The microbiology and the biogeochemical processes in sulfidic mine dumps have to be understood for control and prevention of AMD generation and to provide different possibilities for remediation concepts. Today, remediation measures, e.g. under water storage of the waste or covering of the dumps, focus on the inhibition of pyrite oxidation to keep the toxic compounds inside the mine waste dumps. As an alternative to the inhibition of pyrite oxidation, metals which also have economic value could be extracted from mine dumps by the application of different metal extraction technologies including bioleaching.

Evaluation of a total reflection X-ray fluorescence spectrometer in the determination of arsenic and trace metals in environmental samples

ABSTRACT Suitability of the PicoTAX total reflection X-ray fluorescence (TXRF) spectrometer was studied for determination of As and trace metals in the Haveri Au-Cu sulphide mine tailings leached with aqua regia and in water affected by acid mine drainage. Results for 12 water and 16 tailings samples were compared with accredited methods, inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). Certified reference samples analysed were QC Metal LL from Eurofins A/S, and groundwater CRM 609 and lake sediment BCR-280R from the Institute for Reference Materials and Measurements (IRMM) of the European Commission. Approximate method detection limits (MDL) for water samples, based on reference sample analyses, are in the range of 20 μg l −1 for As, Cr, Pb and Zn and 5–10 μg l −1 for Co, Cu, Ni, V and Mn. MDLs for aqua regia leach, calculated using reagent blank values, were ≤20 (mg kg −1 ) for As, Co, Cr, Cu, Mn, Ni, V, and Zn. Random error of determination varied from 12 to 20 %. Inter-element interferences include: As and Pb on each other, and Fe on Cr and Co. Using the Mo anode of the X-ray tube excludes the determination of Cd, Mo, Nb, Tc and Zr. TXRF can be recommended merely as a preliminary technique for selecting samples.

Diversity of Iron Oxidizing Bacteria from Various Sulfidic Mine Waste Dumps

More than 100 cultures of acidophilic Fe(II)- and/or sulfur-oxidizing microorganisms from mine waste dumps in 10 different countries all over the world have been maintained in liquid media in the BGR-strain collection for many years. Our 16S rDNA analysis showed that most of the cultivated Fe(II)-oxidizers belong to four genera: Acidithiobacillus, Acidimicrobium, “Ferrimicrobium” and Leptospirillum. All analyzed Acidithiobacillus strains were identified as At. ferrooxidans. The Leptospirillum strains were affiliated with L. ferriphilum or L. ferrooxidans. The Gram-positive strains related to Acidimicrobium or ”Ferrimicrobium” were phylogenetically more diverse than the strains of the genera Acidithiobacillus and Leptospirillum and fell into three separate clusters. While several strains could be identified as syngeneic (16S rDNA) with “Ferrimicrobium acidiphilum”, two other 16S rDNA clusters were distantly related and might represent new species or even new genera. In addition, one new Sulfobacillus strain and one new Alicyclobacillus strain could be identified. Furthermore several strains related to Acidiphilium acidophilum have been detected and form one 16S rDNA cluster.

The Influence of Disimilatory Fe(III) Reducers on Iron Ore Dissolution

The biological reduction rate of Fe(III) was studied using dissimilatory ferric reducing bacterial cultures (FeRB) in an attempt to establish a biotechnological via for the metallurgical treatment of iron ores. Enrichment cultures of dissimilatory ferric reducers were obtained from samples collected from a flooded acidic open pit in an abandoned Pb and Zn sulphide mining site nearby La Unión (Murcia, Spain). Adapted cultures were able to reduce 3 g/L of soluble Fe(III) with 100 efficiency in 36 hours. The growth of mixed cultures was also tested in solids. Ferrihydrite and ammonium jarosite served as electron acceptors in cultures where lactate acted as electron donor. Bacterial growth was also positive in both cases. This result represents an effective alternative to the chemical reduction of ferric minerals that avoids extreme temperatures when pyrometallurgical reactors are used. In addition, three species of FeRB were isolated and identified as Serratia fonticola, Aeromonas hydrophila and Clostridium celerecrescens. One of them, Aeromonas hydrophila, results of particular interest and, at the present moment, is being studied in depth. The particular significance of Aeromonas hydrophila is related to the characteristics of its exhausted cultures, where ferrous iron remains solved at pH values next to 7. At the present moment, the identification and characterization of the Fe(II) soluble complex is being account.

Acidophilic bacterial community reflecting pollution level of sulphide mine impacted by acid mine drainage

To reveal the impact of mining on bacterial ecology around mining area, bacterial community and geochemical characteristics about Dabaoshan Mine (Guangdong Province, China) were studied. By amplified ribosomal DNA restriction analysis and phylogenetic analysis, it is found that mining pollution greatly impacts the bacterial ecology and makes the habitat type of polluted environments close to acid mine drainage (AMD) ecology. The polluted environment is acidified so greatly that neutrophil and alkaliphilic microbes are massively dead and decomposed. It provided organic matters that can make Acidiphilium sp. rapidly grow and become the most bacterial species in this niche. Furthermore, Acidithiobacillus ferrooxidans and Leptospirillum sp. are also present in this niche. The amount of Leptospirillum sp. is far more than that of Acidithiobacillus ferrooxidans, which indicates that the concentration of toxic ions is very high. The conclusions of biogeochemical analysis and microbiological monitor are identical. Moreover, because the growth of Acidithiobacillus ferrooxidans and Leptospirillum sp. depends on ferrous iron or inorganic redox sulfur compounds which can be supplied by continual AMD, their presence indicates that AMD still flows into the site. And the area is closer to the outfalls of AMD, their biomasses would be more. So the distinction of their biomasses among different areas can help us to find the effluent route of AMD.

Multiphase flow and reactive transport model in vadose tailings

Weathering processes affecting pyritic wastes may generate huge amounts of acid waters with high concentrations of potentially toxic contaminants (acid mine drainage). Acid mine drainage is mainly produced in the vadose zone. In the present study, a coupled non-isothermal multiphase flow and reactive transport model of the vadose zone of sulfide mine tailings was developed. The geochemical model included kinetically controlled reactions for Fe(II)-oxidation and for the dissolution of sulfide and aluminosilicate phases and the Pitzer ion-interaction model to describe the behavior of the pore-water solutions. Model results were compared with experimental observations in unsaturated column experiments under strongly evaporative conditions similar to arid or semiarid climates. Evolution trends for temperature, water saturation, evaporation rates, pore-water hydrochemistry and mineral phases observed during the drying experiment were adequately reproduced. The coupled model reproduced the increase of solute concentrations in the column top and the precipitation of a crust of secondary mineral phases. This crust became a barrier for water vapour diffusion to the atmosphere and modified the thermohydraulic behavior of the tailings. Enhanced downward migration of water vapour and its condensation in this colder end of the column were correctly taken into account by the model, which reproduced the dilution observed in the lower part of the column during the experiments.

Trace metal and As solid-phase speciation in sulphide mine tailings – Indicators of spatial distribution of sulphide oxidation in active tailings impoundments

Abstract Redistribution of potentially harmful metals and As was studied based on selective extractions in two active sulphide mine tailings impoundments in Finland. The Hitura tailings area contains residue from Ni ore processing, while the Luikonlahti site includes tailings from the processing of Cu–Co–Zn–Ni and talc ores. To characterize the element solid-phase speciation with respect to sulphide oxidation intensity and the water saturation level of the tailings, drill cores were collected from border zones and mid-impoundment locations. The mobility and solid-phase fractionation of Ni, Cu, Co, Zn, Cr, Fe, Ca, Al, As, and S were analysed using a 5-step non-sequential (parallel) selective extraction procedure. The results indicated that metal redistribution and sulphide oxidation intensity were largely controlled by the disposal history and strategy of the tailings (sorting, exposure of sulphides due to delayed burial), impoundment structure and water table, and reactivity of the tailings. Metal redistribution suggested sulphide weathering in the tailings surface, but also in unsaturated proximal areas beside the earthen dams, and in water-saturated bottom layers, where O 2 -rich infiltration is possible. Sulphide oxidation released trace metals from sulphide minerals at both locations. In the Hitura tailings, with sufficient buffering capacity, pH remained neutral and the mobilized metals were retained by secondary Fe precipitates deeper in the oxidized zone. In contrast, sulphide oxidation-induced acidity and rise in the water table after oxidation apparently remobilized the previously retained metals in Luikonlahti. In general, continuous disposal of tailings decreased the sulphide oxidation intensity in active tailings, unless there was a delay in burial and the reactive tailings were unsaturated after deposition.

Hydrochemical characteristics and seasonal influence on the pollution by acid mine drainage in the Odiel river Basin (SW Spain)

The Odiel river Basin is heavily affected by acid mine drainage (AMD) from the sulphide mining areas in the Iberian Pyrite Belt (IPB). A thorough study has been conducted along this fluvial system, monitoring the seasonal influence on the pollution level and its hydrochemical characteristics. From 2002 to 2006, surface water samples were collected at 91 different points throughout the Odiel river Basin and analyzed by field and laboratory methods for dissolved metals and metalloids. Acid mine drainage affects 37% of the length of the drainage network, which shows a great diversity of geochemical conditions as well as significant variations through the hydrological year. Unaffected streams show different water types depending on the lithological substrate and the marine aerosol influence. Mean concentrations in the contaminated streams are very high: 231 mg/L of Fe, 135 mg/L of Al, 56 mg/L of Zn, 16 mg/L of Cu, etc. Four types of contaminated streams were recognized based on hydrochemical and physicochemical characteristics. There are important seasonal variations depending on the precipitation regimen, level of pollution and proximity to the AMD sources. In the more contaminated samples the M/Fe ratio (M = metals other than Fe) decreases during the summer season. Slightly contaminated samples show an inverse evolution as this ratio increases in spring and summer due to substantial Fe precipitation. A recomparison of contaminant loads suggests that the Odiel river Basin (including the Tinto river) accounts for 15% of the global gross flux of dissolved Zn and 3% of the global gross flux of dissolved Cu transported by rivers into the ocean.

Effects of sewage sludge on solution chemistry and plant uptake of Cu in sulphide mine tailings at different weathering stages

This climate chamber experiment examines the effects of sewage sludge (SS) on sulphide mine tailings from the Aitik Cu mine in northern Sweden. The effects of SS were determined from Cu in solution ...

Mechanism of arsenic sorption onto laterite iron concretions

We investigated arsenic sorption mechanisms onto laterite iron concretions (LIC) using electrophoretic mobility (EM) measurements, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and surface complexation modeling. Competitive sorption experiments were also conducted in the presence of phosphate and sulfate, as these compounds may interfere with arsenic sorption in waters from sulfide mining waste and ore stock piles. Electrophoretic mobility measurement results indicate that arsenic sorption lowered the point of zero charge of the LIC at pH 3–10. This observation implies both As (III) and As (V) form inner-sphere complexes on the LIC. The FTIR studies suggest that both As (III) and As (V) also form inner-sphere complexes with LIC. Arsenic sorption onto LIC was modeled by surface complexation modeling using the generalized composite approach. The model assumes that all mineral phases contributing to sorption are represented by one type of surface group. Adsorption edge experimental data was used to verify model performance. Arsenic (III) sorption onto LIC, which is markedly reduced by increasing ionic strength, was modeled using the triple-layer model, while As (V) sorption onto LIC was modeled using both the diffuse and the triple-layer models. The presence of phosphate reduces the amount of both As (V) and As (III) sorbed, while sulfate only reduces adsorption of As (III).

Metal dispersion in groundwater in an area with natural and processed black shale – Nationwide perspective and comparison with acid sulfate soils

Black shale is often rich in sulfides and trace elements, and is thus a potential environmental threat in a manner similar to acid sulfate soils and active or abandoned sulfide mines. This study aims at characterising how exposed and processed (mined and burnt) black shale (alum shale) in Degerhamn, SE Sweden, affects the chemistry (Al, As, Ba, Cd, Ca, Cr, Co, Cu, Fe, Pb, Mg, Mn, Mo, Ni, K, Si, Na, Sr, S, U, V and Zn) of the groundwater. There were large variations in groundwater chemistry between nearby sampling points, while the temporal variations generally were small. Acidic groundwater (around pH 4), found in deposits of burnt and carbonate-poor shale where the conditions for sulfide oxidation were favourable, was strongly elevated in Al, U and several chalcophilic metals (Cd, Co, Cu, Ni and Zn). Cadmium and U were also, together with Mo, abundant in many of the near-neutral waters, both in the non-mined black shale bedrock and in the deposits of burnt shale. An extrapolation to a national level suggests that the dispersion of Ni from naturally occurring black shale is similar to that from anthropogenic point sources, while for Cd and As it is assessed to be approximately one tenth of that from point sources. The processed shale was, however, a much larger source of metals than the black shale bedrock itself, showing this material's potential as a massive supplier of metals to the aquatic environment. A comparison of waters in contact with the processed Cambrian-Ordovician black shale in Degerhamn and acid sulfate soils of the region shows that these two sulfide-bearing materials, in many respects very different, delivers basically the same suite of trace elements to the aquatic environment. This has implications for environmental planning and protection in areas where these types of materials exist.

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.

Evaluation of sulfidic mine tailings solidified/stabilized with cement kiln dust and fly ash to control acid mine drainage

Deficient surface disposal systems of sulfidic mine waste often cause severe contamination of surface streams and groundwater reservoirs due to the oxidation of sulfide phases. The subsequent generation of leachates characterized by high acidity and elevated concentrations of toxic elements (commonly known as acid mine drainage) jeopardize the health of contiguous ecosystem. Stabilization/solidification (S/S) is recognized as a promising solution for treating such wastes. S/S processes generally mobilize alkaline and/or cementing materials/additives that act as neutralizing and/or binding agents. In the present research, industrial byproducts, namely, cement kiln dust (CKD) and Class C fly ash (FAC) have been used as candidate materials along with the partial addition of sulfate-resistant cement (SRC) in the S/S of polymetallic sulfidic mine tailings (MT). The effectiveness of S/S was assessed by comparing laboratory experimental values obtained from unconfined compressive strength, hydraulic conductivity and leaching propensity tests of S/S samples with regulatory standards for safe surface disposal of such wastes. Despite general regulatory compliance of compressive strength and hydraulic conductivity, some solidified/stabilized-cured matrices were found unable to provide the required immobilization of pollutants. Solidified/stabilized and 90-day cured mine tailings specimens made with composite binders containing (10% CKD + 10% FAC), (5% SRC + 75% FAC) and (5% SRC + 5% CKD + 10% FAC) significantly impaired the solubility of all contaminants investigated and proved successful in fixing metals within the matrix, in addition to achieving adequate unconfined compressive strength and hydraulic conductivity values, thus satisfying U.S. EPA regulations. Laboratory investigations revealed that, for poly metallic mining waste, leachate concentrations are the most critical factor in assessing the effectiveness of S/S technology.

Microbial communities in acid water environments of two mines, China

To understand the compositions and structures of microbial communities in different acid-aqueous environments, a PCR-based cloning approach was used. A total of five samples were collected from two mines in China. Two samples, named as G1 and G2, were acid mine drainage (AMD) samples and from Yunfu sulfide mine in Guangdong province, China. The rest of the three samples named as D1, DY and D3, were from three sites undertaking bioleaching in Yinshan lead–zinc mine in Jiangxi province, China. Phylogenetic analysis revealed that bacteria in the five samples fell into six putative divisions, which were α- Proteobacteria, β- Proteobacteria, γ- Proteobacteria, Firmicutes, Actinobacteria and Nitrospira. Archaea was only detected in the three samples from Yinshan lead–zinc mine, which fell into two phylogenentic divisions, Thermoplsma and Ferroplasma. In addition, the results of principal component analysis (PCA) suggested that more similar the geochemical properties in samples were, more similar microbial community structures in samples were.

Archaeal diversity in acid mine drainage from Dabaoshan Mine, China

Three acid mine drainage (AMD) samples collected from Dabaoshan Mine (Guangdong Province, China) were studied. In addition to physicochemical analyses, the diversity and community structures of the archaeal communities in these samples were described at the genetic level by amplified ribosomal DNA restriction analysis (ARDRA). Nine different ARDRA patterns were obtained from 146 clones and were studied as operational taxonomic units (OTUs), which were re-amplified and sequenced. Sequence data and phylogenetic analysis showed that most of the clones belonged to the Thermoplasmatales, and that archaea belonging to the Sulfolobales were absent. Only 1 OTU attributed to Ferroplasma was found and was observed to be abundant in all 3 samples. Eight OTUs were related to 2 new undefined groups in the Thermoplasmatales. Of the 8 OTUs, the clones in 2 similar units were isolated from samples collected from an abandoned sulfide mine (Huelva, Spain) and those in 5 similar units were isolated from samples collected from a closed copper mine (Tonglushan, China). These diversities were characterized by the reciprocal of Simpson's index (1/D) and correlated with the concentrations of ferrous ions and toxic ions in the AMD samples. The high temperature of the sampling sites was one of the factors that could explain why archaea belonging to the Thermoplasmatales were abundant in the analyzed AMD samples while those belonging to the Sulfolobales were absent.

Time Evolution of an AMD-Affected River Chemical Makeup

Acid mine drainage is the main problem encountered by sulphide mining operations, not only because of its ecological aspects, but also because, once it appears, it is very difficult to remediate both technologically and economically. This paper characterises the response of an acid mine drainage-affected channel in the Iberian Pyrite Belt (Southwest of the Iberian Peninsula, Huelva, Spain) to the stimulus of rainfall in its drainage basin by studying the cause–effect relationships between sulphate, iron, copper, zinc, manganese, arsenic and cadmium concentrations in water samples taken at three points and rainfall in the zone.

English

In watersheds of the mid-Atlantic region of the US where sulfide spoils occur from mining operations, geochemical reactions develop additional acids in the soil and water supply. The resulting condition lowers ambient pH to very low values (2 to 4 SU). The low pH impairs the soil chemistry and water quality to the extent that native flora and fauna can not survive on the site. This work presents the design and evaluation of remedial work implemented to abate acid mine drainage from a sulfide mine (Valzinco Mine) in the Piedmont Provence of Virginia, USA. Water quality conditions were measured before and after the remediation work, and documented the re-establishment and abundance of native wetland and aquatic vegetation within the site. Data showed that average pH increased from 3.4 to 5.1 and a decrease in total dissolved solids (Fe, Al, Zn, Pb, Cu, Cd, and SO4 2- ) over the study period. Initial wetland vegetation, both planted and volunteer, quickly colonized the site with an average ground cover of >74% after five years. Aquatic vegetation cover averaged >50% after 2 years and many plots had coverage >100%. Composition, species richness, and abundance of the new vegetation communities was similar to that of near-by reference (un-affected by mine activities) wetland (>75%, 6.0 spp. m -2 vs. 5.5 spp. m -2 , average cover 74% vs. 67%, respectively). Two amphibians (southern leopard frog, pickerel frog) and two aquatic reptiles (brown water snake and northern water snake) were captured on the site during the fifth year, indicating a return of herpatifauna to the wetland and aquatic communities. We conclude that the increase in pH, decline in total dissolved minerals, success of the re- vegetation of the site, and return of the reptiles to the site, is a strong indication that the remedial work successfully restored the soil and water chemistry closer to pre- mining conditions. Therefore, we suggest that the successful restoration of this site was based on sound hydrological and biogeochemical principles that can be applied to restoration efforts in other acid damaged watersheds in the mid-Atlantic region.