Showing papers on "Tailings published in 1999"

Geochemistry of a Permeable Reactive Barrier for Metals and Acid Mine Drainage

Abstract: A permeable reactive barrier, designed to remove metals and generate alkalinity by promoting sulfate reduction and metal sulfide precipitation, was installed in August 1995 into an aquifer containing effluent from mine tailings. Passage of groundwater through the barrier results in striking improvement in water quality. Dramatic changes in concentrations of SO4 (decrease of 2000−3000 mg/L), Fe (decrease of 270−1300 mg/L), trace metals (e.g., Ni decreases 30 mg/L), and alkalinity (increase of 800−2700 mg/L) are observed. Populations of sulfate reducing bacteria are 10 000 times greater, and bacterial activity, as measured by dehydrogenase activity, is 10 times higher within the barrier compared to the up-gradient aquifer. Dissolved sulfide concentrations increase by 0.2−120 mg/L, and the isotope 34S is enriched relative to 32S in the dissolved phase SO42- within the barrier. Water chemistry, coupled with geochemical speciation modeling, indicates the pore water in the barrier becomes supersaturated with re...

Mineral surfaces and bioavailability of heavy metals : a molecular-scale perspective

Abstract: There is a continual influx of heavy metal contaminants and pollutants into the biosphere from both natural and anthropogenic sources. A complex variety of abiotic and biotic processes affects their speciation and distribution, including adsorption onto and desorption from mineral surfaces, incorporation in precipitates or coprecipitates, release through the dissolution of minerals, and interactions with plants and microbes. Some of these processes can effectively isolate heavy metals from the biosphere, whereas others cause their release or transformation to different species that may be more (or less) bioavailable and/or toxic to organisms. Here we focus on abiotic adsorption and precipitation or coprecipitation processes involving the common heavy metal contaminant lead and the metalloids arsenic and selenium in mine tailings and contaminated soils. We have used extremely intense x-rays from synchrotron sources and a structure-sensitive method known as x-ray absorption fine structure (XAFS) spectroscopy to determine the molecular-level speciation of these elements at concentrations of 50 to several thousand ppm in the contaminated environmental samples as well as in synthetic sorption samples. Our XAFS studies of As and Pb in the mine tailings show that up to 50% of these contaminants in the samples studied may be present as adsorbed species on mineral surfaces, which makes them potentially more bioavailable than when present in sparingly soluble solid phases. Our XAFS studies of Se(VI) sorption on Fe2+-containing sulfates show that this element undergoes redox reactions that transform it into less bioavailable and less toxic species. This type of information on molecular-level speciation of heavy metal and metalloid contaminants in various environmental settings is needed to prioritize remediation efforts and to assess their potential hazard to humans and other organisms.

Quantitative speciation of lead in selected mine tailings from Leadville, CO

Abstract: The authors have characterized Pb speciation in selected tailings from the Leadville, CO, area using a variety of analytical techniques, including X-ray absorption fine structure (XAFS) spectroscopy. Samples from three locations were analyzed, including two chemically distinct tailings piles located within the city limits and tailings material deposited as overbank sediments along the Arkansas River approximately 13 km downstream from Leadville. Extended XAFS (EXAFS) spectra of these multicomponent samples were fit using linear combinations of model compound spectra. In accordance with pH differences among the samples, adsorbed Pb accounts for {approximately}50% of total Pb (Pb{sub T}) in fine fractions of the near-neutral pH Hamms tailings, whereas Pb-bearing jarosites account for the majority of Pb{sub T} in the fine fractions of the low pH Apache and Arkansas River tailings. EXAFS analyses following sequential extraction by MgCl{sub 2} and EDTA show evidence of significant redistribution (readsorption) of Pb during the MgCl{sub 2} extraction and for removal of adsorbed Pb and dissolution of Pb-carbonates during the EDTA extraction. Changes in Pb speciation with water extraction are observed in one sample of Arkansas River tailings. These molecular-scale results show that Pb speciation varies dramatically among environments in the Leadville area and that Pb occursmore » in a number of phases not amenable to definitive characterization by conventional microanalytical and/or chemical extraction techniques.« less

XAFS determination of the chemical form of lead in smelter-contaminated soils and mine tailings; importance of adsorption processes

Abstract: We investigated smelter-contaminated soils from Evin-Malmaison, Nord-Pas-de-Calais, France, and mine tailings from Leadville, Colorado, U.S.A. Bulk Pb concentrations range from 460 to 1900 ppm in the topsoils at Evin-Malmaison site and from 6000 to 10000 ppm in the tailings samples from the Leadville site. These concentrations necessarily raise human health and environmental concerns, but bioavailability and chemical lability of Pb in these materials vary dramatically and show little correlation with bulk concentrations. This study provides detailed information on the speciation of Pb in these materials. Emphasis is on the identification and characterization of poorly crystalline and/or fine-grained species, such as sorption complexes and poorly crystalline (co)precipitates, which are likely to control Pb bioavailability and mobility in these natural systems. Because these samples are heterogeneous, multi-phase mixtures, a variety of bulk analytical methods were used including powder X-ray diffraction (XRD) and Rietveld refinement, scanning electron microscopy, electron probe microanalysis, synchrotron-based X-ray absorption, and micro-fluorescence spectroscopies. The synchrotron-based techniques enable identification of amorphous or nanocrystalline Pb-containing phases and the spatial distribution of Pb at the 25 mu m scale. These techniques, in conjunction with physical and chemical separation techniques, allowed identification and characterization of several species not amenable to detection by conventional microanalytical techniques. In the Evin-Malmaison samples, direct spectroscopic evidence for Pb sorbed to humic acids was found, as well as to both manganese and iron (oxyhydr)oxides. In the Leadville samples, variations in Pb speciation with pH are consistent with predictions based on simplified model system studies of adsorption processes: specifically, the carbonate-buffered tailings with near-neutral pH contain up to 50% of total Pb as adsorption complexes on iron (oxyhydr)oxides, whereas Pb speciation in sulfide-rich low pH samples is dominated by Pb-bearing jarosites with no evidence for adsorbed Pb in these latter samples.

Mercury contaminated sites : characterization, risk assessment, and remediation

Abstract: I Reviews.- 1 Natural and Anthropogenic Mercury Sources and Their Impact on the Air-Surface Exchange of Mercury on Regional and Global Scales.- 2 Mercury Mines in Europe: Assessment of Emissions and Environmental Contamination.- 3 Mercury Contamination from New World Gold and Silver Mine Tailings.- 4 Mercury-Contaminated Industrial and Mining Sites in North America: an Overview with Selected Case Studies.- 5 Remediation Techniques for Hg-Contaminated Sites.- 6 Advanced Technology Available for the Abatement of Mercury Pollution in the Metallurgical Industry.- 7 Mercury Contamination of Minamata Bay: Historical Overview and Progress Towards Recovery.- 8 Chemical Interactions Between Mercurial Species and Surface Biomolecules from Structural Components of Some Biological Systems.- II International Case Studies.- 1 Distribution, Bioavailability and Speciation of Mercury in Contaminated Soil and Groundwater of a Former Wood Impregnation Plant.- 2 Relative Importance of Non-Point Sources of Mercury to an Industrialized Coastal System, Sepetiba Bay, SE Brazil.- 3 Monitoring and Assessment of Mercury Pollution in the Vicinity of Electrical Engineering Plants in the CIS.- 4 Mercury in Gas and Oil Deposits.- 1 Atmospheric Mercury in Abandoned Mine Structures and Restored Mine Buildings at Mt. Amiata, Italy.- 2 Mercury in the Town of Idrija (Slovenia) After 50o Years of Mining and Smelting.- 3 Evaluation of Internal Doses of Mercury at Intermittent Exposure to Elemental Mercury at the Mine in Idrija.- 4 Mercury in Terrestrial Food Webs of the Idrija Mining Area.- 5 Vegetation on Contaminated Sites near an Hg Mine and Smelter.- 6 Modern Mercury Contamination from Historic Amalgamation Milling of Silver-Gold Ores in the Carson River, Nevada and Jordan Creek, Idaho: Importance of Speciation Analysis in Understanding the Source, Mobility, and Fate of Polluted Materials.- 7 Gold Mining in Siberia as a Source of Mercury Contamination of the Environment.- 1 Estimation of Gaseous Mercury Emissions in Germany: Inverse Modelling of Source Strengths at the Contaminated Industrial Site BSL Werk Schkopau.- 2 Removal of Mercury from Gases by Modified Zeolites in a Stationary Bed.- 3 Mercury Speciation of MSWI Flue Gas on Pilot and Industrial Scales.- 4 Mercury Saturation Profile Across the Sulphur-Impregnated Activated Carbon Bed.- 1 Basic Study on the Remediation Technology of Mercury Compound-Contaminated Soil by Low-Temperature Thermal Treatment.- 2 Electroleaching: a Mobile Cleanup Process for Mercury Contaminated Materials.- 3 Mercury Decontamination of a Chloralkali Plant in Alexandria, Egypt.- 1 Mercury Subsurface Maxima in Sediments: a Diagnostic for Anthropogenic Origins.- 2 Concentration of Mercury and Other Heavy Metals in Central India.- 3 Fluvial Transports of Mercury Pollution in the III River Basin (Northeastern France): Partitioning into Aqueous Phases, Suspended Matter and Bottom Sediments.- 4 Distribution of Total and Methyl Mercury in a Creek Ecosystem Near Bombay.

Micro-pixe mapping of elemental distribution in arbuscular mycorrhizal roots of the grass, cynodon dactylon, from gold and uranium mine tailings

Abstract: A combination of PIXE, proton back-scattering (BS) spectrometry and confocal laser scanning microscopy (CLSM) was used to determine in situ elemental concentrations in arbuscular mycorrhizal (AM) grass roots and AM fungal spores from gold and uranium mine tailings in South Africa. AM regions of roots were characterised by locally elevated P and vesicles were defined by distinctive transition metal and radionuclide distributions. Vesicles (AM structures responsible for nutrient storage), accumulated Mn, Cu, Ni and U, whereas Fe and Zn were present at lower levels than in host tissue. AM spores from mine tailings accumulated Ca, Cr, Fe, Ni, Cu, Br, Y, Th and U, but were deficient in P and K. The sequestration of excess metals and radionuclides in vesicles may limit metal availability, and thus toxicity, to the host.

Copper, copper mine tailings and their effect on marine algae in Northern Chile

Abstract: Results are presented of a long-term research programme on the effect of copper contamination on biota in Chilean coastal waters In spite of the magnitude of the copper mining tailings that affected Caleta Palito and surroundings in northern Chile, the effects on the intertidal assemblages remain restricted to a small geographic area Even within the affected area, the effects are not homogeneous and there is evidence of active recovery in biological diversity in recent few years Experimental evidence suggests that the current low algal diversity and abundance is strongly influenced by herbivory, although chronic effects of the discharges cannot be ruled out Cellular changes in Enteromorpha compressa from the impacted area were characterised by abnormal granules in the cytoplasm, though these granules did not contain detectable levels of copper or other heavy metals

Characterization of Mine Wastes for Prediction of Acid Mine Drainage

Abstract: One of the environmental challenges the mining and minerals industry is facing today is the increased levels of metals in the environment due to mining, milling, and refining activities. Liquid effluents, mine waters, tailings, waste rocks, and dusts may contribute to the generation of potentially deleterious waste and contaminated groundwater and soil deposits in, around, and outside mine environments. Tailings which are unwanted silicate, oxide and sulfide minerals discarded during ore processing operations, are usually discharged into impoundments as a slurry with particle sizes that are predominantly in the silt to fine sand size range (1 µm-1 mm). Waste rock is essentially wall rock material removed to access and mine ore. Waste rock material, composed of particles ranging in size from silt to boulder size fragments, are often disposed of in large piles.

Microbiological and geochemical characterization of fluvially deposited sulfidic mine tailings

Abstract: The fluvial deposition of mine tailings generated from historic mining operations near Butte, Montana, has resulted in substantial surface and shallow groundwater contamination along Silver Bow Creek. Biogeochemical processes in the sediment and underlying hyporheic zone were studied in an attempt to characterize interactions consequential to heavy-metal contamination of shallow groundwater. Sediment cores were extracted and fractionated based on sediment stratification. Subsamples of each fraction were assayed for culturable heterotrophic microbiota, specific microbial guilds involved in metal redox transformations, and both aqueous- and solid-phase geochemistry. Populations of cultivable Fe(III)-reducing bacteria were most prominent in the anoxic, circumneutral pH regions associated with a ferricrete layer or in an oxic zone high in organic carbon and soluble iron. Sulfur- and iron-oxidizing bacteria were distributed in discrete zones throughout the tailings and were often recovered from sections at and below the anoxic groundwater interface. Sulfate-reducing bacteria were also widely distributed in the cores and often occurred in zones overlapping iron and sulfur oxidizers. Sulfate-reducing bacteria were consistently recovered from oxic zones that contained high concentrations of metals in the oxidizable fraction. Altogether, these results suggest a highly varied and complex microbial ecology within a very heterogeneous geochemical environment. Such physical and biological heterogeneity has often been overlooked when remediation strategies for metal contaminated environments are formulated.

Soil Covers for Controlling Acid Generation in Mine Tailings: a Laboratory Evaluation of the Physics and Geochemistry

Abstract: To evaluate the effectiveness of soil covers, column experiments were conducted on tailings protected by a three-layer soil cover and tailings directly exposed in the open laboratory for a period of 760 days. Periodic rain application was performed to simulate field conditions, and at four times during the experiments the pore water was completely flushed out of each column for analysis. Profiles of oxygen, temperature, and volumetric water content were measured throughout the experiment, and the post-testing pore water quality was also characterized. A one-dimensional semi-analytic diffusion model was used to simulate oxygen profiles in the uncovered tailings. Modelling performed using the geochemical code MINTEQ showed that in the laboratory, aluminium concentrations in the tailings pore water were controlled by Al(OH)SO4, sulphate by gypsum and Al(OH)SO4and iron by lepidocrocite in the upper half and by ferrihydrite in the lower half. In the field, however, the iron oxyhydroxide minerals formed in the oxidized zone appear to be dissolving. It was found that the cover was effective in preventing significant desaturation of the clay, even over a 150-day drying period. The covered tailings did not oxidize much during the experiments. In the uncovered tailings, oxygen modelling and examination of the geochemistry show that the rate of gross oxidation and the advancement of the oxidation front decreases with time. However, pore water quality is controlled by geochemical processes other than oxidation, as reported in the field.

Role of carbonates in mitigation of metal release from mining waste. Evidence from humidity cells tests

Abstract: Leaching of two contrasting types of sulphidic tailings in humidity cells has been performed The release of heavy metals and the oxidation rate have been studied Tailings from the Laver mine contain a few percent sulphides and lack carbonates, whereas tailings from the Stekenjokk mine are both sulphide- and carbonate-rich The results showed that in the leachates from the Laver samples, the metal concentrations increased and pH decreased with time, indicating an increased oxidation rate In the Stekenjokk samples, pH remained high during the experiment, thereby keeping the metal concentrations low in the leachates The oxidation rate also decreased with time, probably due to Fe-hydroxide coatings on sulphide surfaces The results show that addition of carbonates and the maintenance of a high pH not only reduce the solubility of heavy metals, but also decrease the oxidation rate of sulphides

Method for recovery of hydrocarbon diluent from tailings

Abstract: A method for recovery of hydrocarbon diluent from tailings produced in a bitumen froth treatment plant comprises introducing the tailings into a steam stripping vessel maintained at near atmospheric pressure, said vessel having a plurality of interior, vertically spaced shed decks, and distributing the tailings over said shed decks. Steam is introduced below the shed decks for vaporizing the major portion of the contained diluent and some water.

Biotic and abiotic characteristics of ecosystems on acid metalliferous mine tailings near sudbury, ontario

Abstract: INCO Ltd., a large mining company near Sudbury, Ont., deposits vast amounts of tailings on its property. These tailings contain elevated levels of Cu, Ni, and sulphides, and to curtail dust and aci...

Assessing the Influence of Reacting Pyrite and Carbonate Minerals on the Geochemistry of Drainage in the Coeur d'Alene Mining District

Abstract: The relative abundance of minerals that react to generate or consume acid in mineralized areas is critical in determining the quality of water draining from such areas. This work examines the fundamental reactions that influence the pH and composition of drainage from mine adits and tailings piles. The authors construct triangle diagrams that predict stoichiometric relationships between concentrations of dissolved SO{sub 4}{sup {minus}}, dissolved Ca and Mg, and either alkalinity or acidity by considering reactions involving the oxidation of pyrite, dissolution of carbonate minerals, and precipitation of iron oxide and iron hydroxysulfate minerals. Drainage data from the Coeur d'Alene mining district are used to test their stoichiometric approach. Comparisons between theoretical predictions and drainage data indicate that the range of pH values in the mining district is due to reacting pyrite to carbonate mineral ratios that range from near 0/1 to 1/1. Calcite and ankerite are the dominant carbonate minerals that buffer the acid produced during pyrite oxidation and ferrihydrite or schwertmannite precipitation.

Secondary copper enrichment in tailings at the Laver mine, northern Sweden

Abstract: Field and laboratory studies of the sulphide-bearing tailings at Laver, northern Sweden, show that the present release of metals from the tailings is low, especially with regard to Cu. A large part of the Cu released by sulphide oxidation is enriched in a distinct zone just below the oxidation front. The enrichment zone occurs almost all over the tailings area except in areas with a shallow groundwater table. The Cu enrichment is caused by formation of covellite and adsorption onto mineral surfaces. The transport of Zn, Co, Cd, Ni and S seems to be controlled mainly by adsorption. No secondary zone or secondary minerals containing these metals have been found. Just below the groundwater table, metals are released into solution when the enrichment zone reaches the groundwater due to the low pH. An increased release of metals, especially Cu, can be expected in the future, since the enrichment zone is moving towards the groundwater table.

Comparison of the Ames Salmonella Assay and Mutatox Genotoxicity Assay for Assessing the Mutagenicity of Polycyclic Aromatic Compounds in Porewater from Athabasca Oil Sands Mature Fine Tailings

Abstract: The oil sands in the Athabasca region of northeastern Alberta, Canada, represent a significant hydrocarbon resource that is currently exploited by mining, followed by separation of bitumen from sand using hot water flotation. This process generates large quantities of bitumen-contaminated tailings. Current research involves an assessment of whether the tailings ponds can ultimately be converted to biologically productive lakes, with one unresolved issue being the toxicity of the polycyclic aromatic compounds (PACs) that might be released from the tailings. In this paper, we have identified several polycyclic aromatic hydrocarbons in the porewater from oil sands mature fine tailings and have compared the responses of 17 PACs in the Ames and Mutatox genotoxicity assays. The Mutatox assay was unsuitable as a surrogate for the Ames test in this application; poor (50%) concordance between the two assays occurred because the mechanism of light emission in the Mutatox assay is uncertain, leading to positive resp...

Environmental Impacts of Mining Activities: Emphasis on Mitigation and Remedial Measures

Abstract: Evaluation of the effects of mining in the environment treatment methods for mine effluents and rehabilitation of mine tailings and overburden materials study cases.

Heavy Metal Leaching from Mine Tailings as Affected by Plants

Abstract: A column experiment was conducted to determine the impact of soil cover and plants on heavy metal leaching from mine tailings and heavy metal contaminated soil. Columns made of PVC were constructed with 30 cm subsoil covered by 30 cm of mine tailings followed by 0, 30, or 60 cm subsoil covered by 30 cm of mine tailings followed by 0, 30, or 60 cm of clean topsoil. Two grasses, tall fescue (Festuca arundinacea Schreb.) and big bluestem (Andropogon gerardii), were grown in the columns. The columns were leached at a slow rate for 1 yr with a 0.001 M CaCl{sub 2} solution under unsaturated conditions. The presence of both tall fescue and big bluestem increased Zn and Cd concentrations in the leachate. Lead concentrations in leachates were not affected by the presence of plants. Although plants generally reduced the total amount of water leached, total mass of Zn and Cd leached generally was not impacted by plants. Total mass of Pb leached was positively correlated with total leachate collected from each column. Covering the mine tailings with 60 cm of topsoil increased the mass of Zn and Cd leached relative to no topsoil. When the subsoil was absent, Znmore » and Cd leaching increased by as much as 20-fold, verifying the ability of soil to act as a sink for metals. Mine tailing remediation by establishing vegetation can reduce Pb movement but may enhance short-term Cd and Zn leaching. However, the changes were relatively small and do not outweigh the benefits of using vegetation in mine tailings reclamation.« less