The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Carol J. Ptacek - One of the best experts on this subject based on the ideXlab platform.
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hydrogeochemistry and microbiology of mine drainage an update
Applied Geochemistry, 2015Co-Authors: Kirk D Nordstrom, David W. Blowes, Carol J. PtacekAbstract:Abstract The extraction of mineral resources requires access through underground workings, or open pit operations, or through drillholes for solution mining. Additionally, mineral processing can generate large quantities of waste, including mill tailings, waste rock and refinery wastes, heap leach pads, and slag. Thus, through mining and mineral processing activities, large surface areas of sulfide minerals can be exposed to oxygen, water, and microbes, resulting in accelerated oxidation of sulfide and other minerals and the potential for the generation of low-quality drainage. The oxidation of sulfide minerals in mine wastes is accelerated by microbial catalysis of the oxidation of aqueous ferrous iron and sulfide. These reactions, particularly when combined with evaporation, can lead to extremely Acidic drainage and very high concentrations of dissolved constituents. Although Acid mine drainage is the most prevalent and damaging environmental concern associated with mining activities, generation of saline, basic and neutral drainage containing elevated concentrations of dissolved metals, non-metals, and metalloids has recently been recognized as a potential environmental concern. Acid Neutralization reactions through the dissolution of carbonate, hydroxide, and silicate minerals and formation of secondary aluminum and ferric hydroxide phases can moderate the effects of Acid generation and enhance the formation of secondary hydrated iron and aluminum minerals which may lessen the concentration of dissolved metals. Numerical models provide powerful tools for assessing impacts of these reactions on water quality.
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diavik waste rock project evolution of mineral weathering element release and Acid generation and Neutralization during a five year humidity cell experiment
Minerals, 2014Co-Authors: Jeff B Langman, Carol J. Ptacek, Mandy L Moore, Leslie Smith, David C Sego, David W. BlowesAbstract:Abstract: A five-year, humidity-cell experiment was used to study the weathering evolution of a low-sulfide, granitic waste rock at 5 and 22 °C. Only the rock with the highest sulfide content (0.16 wt %) released sufficient Acid to overcome a limited carbonate Acid-Neutralization capacity and produce a substantial decline in pH. Leached SO 4 and Ca quickly increased then decreased during the first two years of weathering. Sulfide oxidation continued to release Acid and SO 4 after carbonate depletion, resulting in an increase in Acid-soluble elements, including Cu and Zn. With the dissolution of Al-bearing minerals, the pH stabilized above 4, and sulfide oxidation continued to decline until the end of the experiment. The variation in activation energy of sulfide oxidation correlates with changes in sulfide availability, where the lowest activation energies occurred during the largest releases of SO 4 . A decrease in sulfide availability was attributed to consumption of sulfide and weathered rims on sulfide grains that reduced the oxidation rate. Varying element release rates due to changing carbonate and sulfide availability provide identifiable
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diavik waste rock project evolution of mineral weathering element release and Acid generation and Neutralization during a five year humidity cell experiment
Minerals, 2014Co-Authors: Jeff B Langman, Carol J. Ptacek, Mandy L Moore, Leslie Smith, David C Sego, David W. BlowesAbstract:A five-year, humidity-cell experiment was used to study the weathering evolution of a low-sulfide, granitic waste rock at 5 and 22 °C. Only the rock with the highest sulfide content (0.16 wt %) released sufficient Acid to overcome a limited carbonate Acid-Neutralization capacity and produce a substantial decline in pH. Leached SO4 and Ca quickly increased then decreased during the first two years of weathering. Sulfide oxidation continued to release Acid and SO4 after carbonate depletion, resulting in an increase in Acid-soluble elements, including Cu and Zn. With the dissolution of Al-bearing minerals, the pH stabilized above 4, and sulfide oxidation continued to decline until the end of the experiment. The variation in activation energy of sulfide oxidation correlates with changes in sulfide availability, where the lowest activation energies occurred during the largest releases of SO4. A decrease in sulfide availability was attributed to consumption of sulfide and weathered rims on sulfide grains that reduced the oxidation rate. Varying element release rates due to changing carbonate and sulfide availability provide identifiable geochemical conditions that can be viewed as Neutralization sequences and may be extrapolated to the field site for examining the evolution of mineral weathering of the waste rock.
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mechanisms controlling Acid Neutralization and metal mobility within a ni rich tailings impoundment
Applied Geochemistry, 2006Co-Authors: M R Gunsinger, David W. Blowes, Carol J. Ptacek, John L Jambor, M C MoncurAbstract:Abstract Low-quality pore waters containing high concentrations of dissolved H + , SO 4 , and metals have been generated in the East Tailings Management Area at Lynn Lake, Manitoba, as a result of sulfide-mineral oxidation. To assess the abundance, distribution, and solid-phase associations of S, Fe, and trace metals, the tailings pore water was analyzed, and investigations of the geochemical and mineralogical characteristics of the tailings solids were completed. The results were used to delineate the mechanisms that control Acid Neutralization, metal release, and metal attenuation. Migration of the low-pH conditions through the vadose zone is limited by Acid-Neutralization reactions, resulting in the development of distinct pore-water pH zones at depth; the Neutralization reactions involve carbonate (pH ⩾ 5.7), Al-hydroxide (pH ⩾ 4.0), and aluminosilicate solids. As the zone of low-pH pore water expands, the pH will then be primarily controlled by less soluble solids, such as Fe(III) oxyhydroxides (pH 4 are principally controlled by the formation of gypsum and jarosite. Geochemical extractions indicate that the solid-phase concentrations of Ni, Co, and Zn are associated predominantly with reducible and Acid-soluble fractions. The concentrations of dissolved trace metals are therefore primarily controlled by adsorption/complexation and (or) co-precipitation/dissolution reactions involving secondary Fe(III) oxyhydroxide and hydroxysulfate minerals. Concentrations of dissolved metals with relatively low mobility, such as Cu, are also controlled by the precipitation of discrete minerals. Because the major proportion of metals is sequestered through adsorption and (or) co-precipitation, the metals are susceptible to remobilization if low-pH or reducing conditions develop within the tailings.
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Multicomponent reactive transport modeling of Acid Neutralization reactions in mine tailings
Water Resources Research, 2004Co-Authors: Jasna Jurjovec, David W. Blowes, Carol J. Ptacek, K. Ulrich MayerAbstract:[1] Multicomponent reactive transport modeling was conducted to analyze and quantify the Acid Neutralization reactions observed in a column experiment. Experimental results and the experimental procedures have been previously published. The pore water geochemistry was described by dissolution and precipitation reactions involving primary and secondary mineral phases. The initial amounts of the primary phases ankerite-dolomite, siderite, chlorite, and gypsum were constrained by mineralogical analyses of the tailings sample used in the experiment. Secondary gibbsite was incorporated into the model to adequately explain the changes in pH and concentration changes of Al in the column effluent water. The results of the reactive transport modeling show that the pH of the column effluent water can be explained by dissolution reactions of ankerite-dolomite, siderite, chlorite, and secondary gibbsite. The modeling results also show that changes in Eh can be explained by dissolution of ferrihydrite during the experiment. In addition, the modeling results show that the kinetically limited dissolution of chlorite contributes the largest mass of dissolved Mg and Fe (II) in the effluent water, followed by ankerite-dolomite, which contributes substantially less. In summary, reactive transport modeling based on detailed geochemical and mineralogical data was successful to quantitatively describe the changes in pH and major ions in the column effluent.
David W. Blowes - One of the best experts on this subject based on the ideXlab platform.
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hydrogeochemistry and microbiology of mine drainage an update
Applied Geochemistry, 2015Co-Authors: Kirk D Nordstrom, David W. Blowes, Carol J. PtacekAbstract:Abstract The extraction of mineral resources requires access through underground workings, or open pit operations, or through drillholes for solution mining. Additionally, mineral processing can generate large quantities of waste, including mill tailings, waste rock and refinery wastes, heap leach pads, and slag. Thus, through mining and mineral processing activities, large surface areas of sulfide minerals can be exposed to oxygen, water, and microbes, resulting in accelerated oxidation of sulfide and other minerals and the potential for the generation of low-quality drainage. The oxidation of sulfide minerals in mine wastes is accelerated by microbial catalysis of the oxidation of aqueous ferrous iron and sulfide. These reactions, particularly when combined with evaporation, can lead to extremely Acidic drainage and very high concentrations of dissolved constituents. Although Acid mine drainage is the most prevalent and damaging environmental concern associated with mining activities, generation of saline, basic and neutral drainage containing elevated concentrations of dissolved metals, non-metals, and metalloids has recently been recognized as a potential environmental concern. Acid Neutralization reactions through the dissolution of carbonate, hydroxide, and silicate minerals and formation of secondary aluminum and ferric hydroxide phases can moderate the effects of Acid generation and enhance the formation of secondary hydrated iron and aluminum minerals which may lessen the concentration of dissolved metals. Numerical models provide powerful tools for assessing impacts of these reactions on water quality.
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diavik waste rock project evolution of mineral weathering element release and Acid generation and Neutralization during a five year humidity cell experiment
Minerals, 2014Co-Authors: Jeff B Langman, Carol J. Ptacek, Mandy L Moore, Leslie Smith, David C Sego, David W. BlowesAbstract:Abstract: A five-year, humidity-cell experiment was used to study the weathering evolution of a low-sulfide, granitic waste rock at 5 and 22 °C. Only the rock with the highest sulfide content (0.16 wt %) released sufficient Acid to overcome a limited carbonate Acid-Neutralization capacity and produce a substantial decline in pH. Leached SO 4 and Ca quickly increased then decreased during the first two years of weathering. Sulfide oxidation continued to release Acid and SO 4 after carbonate depletion, resulting in an increase in Acid-soluble elements, including Cu and Zn. With the dissolution of Al-bearing minerals, the pH stabilized above 4, and sulfide oxidation continued to decline until the end of the experiment. The variation in activation energy of sulfide oxidation correlates with changes in sulfide availability, where the lowest activation energies occurred during the largest releases of SO 4 . A decrease in sulfide availability was attributed to consumption of sulfide and weathered rims on sulfide grains that reduced the oxidation rate. Varying element release rates due to changing carbonate and sulfide availability provide identifiable
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diavik waste rock project evolution of mineral weathering element release and Acid generation and Neutralization during a five year humidity cell experiment
Minerals, 2014Co-Authors: Jeff B Langman, Carol J. Ptacek, Mandy L Moore, Leslie Smith, David C Sego, David W. BlowesAbstract:A five-year, humidity-cell experiment was used to study the weathering evolution of a low-sulfide, granitic waste rock at 5 and 22 °C. Only the rock with the highest sulfide content (0.16 wt %) released sufficient Acid to overcome a limited carbonate Acid-Neutralization capacity and produce a substantial decline in pH. Leached SO4 and Ca quickly increased then decreased during the first two years of weathering. Sulfide oxidation continued to release Acid and SO4 after carbonate depletion, resulting in an increase in Acid-soluble elements, including Cu and Zn. With the dissolution of Al-bearing minerals, the pH stabilized above 4, and sulfide oxidation continued to decline until the end of the experiment. The variation in activation energy of sulfide oxidation correlates with changes in sulfide availability, where the lowest activation energies occurred during the largest releases of SO4. A decrease in sulfide availability was attributed to consumption of sulfide and weathered rims on sulfide grains that reduced the oxidation rate. Varying element release rates due to changing carbonate and sulfide availability provide identifiable geochemical conditions that can be viewed as Neutralization sequences and may be extrapolated to the field site for examining the evolution of mineral weathering of the waste rock.
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mechanisms controlling Acid Neutralization and metal mobility within a ni rich tailings impoundment
Applied Geochemistry, 2006Co-Authors: M R Gunsinger, David W. Blowes, Carol J. Ptacek, John L Jambor, M C MoncurAbstract:Abstract Low-quality pore waters containing high concentrations of dissolved H + , SO 4 , and metals have been generated in the East Tailings Management Area at Lynn Lake, Manitoba, as a result of sulfide-mineral oxidation. To assess the abundance, distribution, and solid-phase associations of S, Fe, and trace metals, the tailings pore water was analyzed, and investigations of the geochemical and mineralogical characteristics of the tailings solids were completed. The results were used to delineate the mechanisms that control Acid Neutralization, metal release, and metal attenuation. Migration of the low-pH conditions through the vadose zone is limited by Acid-Neutralization reactions, resulting in the development of distinct pore-water pH zones at depth; the Neutralization reactions involve carbonate (pH ⩾ 5.7), Al-hydroxide (pH ⩾ 4.0), and aluminosilicate solids. As the zone of low-pH pore water expands, the pH will then be primarily controlled by less soluble solids, such as Fe(III) oxyhydroxides (pH 4 are principally controlled by the formation of gypsum and jarosite. Geochemical extractions indicate that the solid-phase concentrations of Ni, Co, and Zn are associated predominantly with reducible and Acid-soluble fractions. The concentrations of dissolved trace metals are therefore primarily controlled by adsorption/complexation and (or) co-precipitation/dissolution reactions involving secondary Fe(III) oxyhydroxide and hydroxysulfate minerals. Concentrations of dissolved metals with relatively low mobility, such as Cu, are also controlled by the precipitation of discrete minerals. Because the major proportion of metals is sequestered through adsorption and (or) co-precipitation, the metals are susceptible to remobilization if low-pH or reducing conditions develop within the tailings.
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Multicomponent reactive transport modeling of Acid Neutralization reactions in mine tailings
Water Resources Research, 2004Co-Authors: Jasna Jurjovec, David W. Blowes, Carol J. Ptacek, K. Ulrich MayerAbstract:[1] Multicomponent reactive transport modeling was conducted to analyze and quantify the Acid Neutralization reactions observed in a column experiment. Experimental results and the experimental procedures have been previously published. The pore water geochemistry was described by dissolution and precipitation reactions involving primary and secondary mineral phases. The initial amounts of the primary phases ankerite-dolomite, siderite, chlorite, and gypsum were constrained by mineralogical analyses of the tailings sample used in the experiment. Secondary gibbsite was incorporated into the model to adequately explain the changes in pH and concentration changes of Al in the column effluent water. The results of the reactive transport modeling show that the pH of the column effluent water can be explained by dissolution reactions of ankerite-dolomite, siderite, chlorite, and secondary gibbsite. The modeling results also show that changes in Eh can be explained by dissolution of ferrihydrite during the experiment. In addition, the modeling results show that the kinetically limited dissolution of chlorite contributes the largest mass of dissolved Mg and Fe (II) in the effluent water, followed by ankerite-dolomite, which contributes substantially less. In summary, reactive transport modeling based on detailed geochemical and mineralogical data was successful to quantitatively describe the changes in pH and major ions in the column effluent.
Soren Kiil - One of the best experts on this subject based on the ideXlab platform.
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mixed flow reactor experiments and modeling of sulfuric Acid Neutralization in lube oil for large two stroke diesel engines
Industrial & Engineering Chemistry Research, 2019Co-Authors: Kasper Hartvig Lejre, Peter Glarborg, Henrik Willads Houmann Christensen, Stefan Mayer, Soren KiilAbstract:Lubrication oil for marine diesel engines contains additives in the form of CaCO3-based reverse micelles, which can neutralize condensing H2SO4, and thereby limit uncontrolled corrosive wear of the piston rings and cylinder liner. In the present work, the Neutralization mechanism was studied experimentally and through modeling. Using a mixed flow reactor (MFR), the rate of the Acid–base reaction was measured as a function of relevant process parameters. In addition, the competition between CaCO3 reverse micelles and NaOH droplets for a reaction with H2SO4 droplets in a lube oil emulsion was explored in a batch reactor. For the residence times investigated, the results show that CaCO3 conversion is significantly reduced when reaching a critically low Ca/S ratio. Furthermore, a mathematical model for the Neutralization of H2SO4 droplets by CaCO3 reverse micelles in lube oil under well-mixed conditions was developed. Both the experimental data and simulations support previous results, suggesting that the lim...
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Mixed Flow Reactor Experiments and Modeling of Sulfuric Acid Neutralization in Lube Oil for Large Two-Stroke Diesel Engines
2018Co-Authors: Kasper Hartvig Lejre, Peter Glarborg, Stefan Mayer, Henrik Christensen, Soren KiilAbstract:Lubrication oil for marine diesel engines contains additives in the form of CaCO3-based reverse micelles, which can neutralize condensing H2SO4, and thereby limit uncontrolled corrosive wear of the piston rings and cylinder liner. In the present work, the Neutralization mechanism was studied experimentally and through modeling. Using a mixed flow reactor (MFR), the rate of the Acid–base reaction was measured as a function of relevant process parameters. In addition, the competition between CaCO3 reverse micelles and NaOH droplets for a reaction with H2SO4 droplets in a lube oil emulsion was explored in a batch reactor. For the residence times investigated, the results show that CaCO3 conversion is significantly reduced when reaching a critically low Ca/S ratio. Furthermore, a mathematical model for the Neutralization of H2SO4 droplets by CaCO3 reverse micelles in lube oil under well-mixed conditions was developed. Both the experimental data and simulations support previous results, suggesting that the limiting step in the Neutralization mechanism is adsorption of reverse micelles onto the much larger H2SO4 droplets. Using the video-microscopy experiments of Fu et al. [Tribol. Lett. 2006, 22 (3), 221], it was possible to estimate kinetic parameters for the adsorption-controlled reaction. The model was used to predict conversion of H2SO4 in a lube oil film at the cylinder liner surface for conditions relevant for a full-scale application. Calculations indicated that H2SO4 may reach the liner surface regardless of how well-wetted the surface is
Olivia L Fraser - One of the best experts on this subject based on the ideXlab platform.
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mineral weathering and podzolization control Acid Neutralization and streamwater chemistry gradients in upland glaciated catchments northeastern united states
Frontiers in Earth Science, 2019Co-Authors: Scott W Bailey, Kevin J Mcguire, Donald S Ross, Mark B Green, Olivia L FraserAbstract:Headwater streams in the White Mountains, NH, USA have been shown to have downstream gradients of increasing pH and concentrations of base cations coupled with decreasing concentrations of aluminum. A two-stage Acid Neutralization model involving shallow soil exchange processes in headwaters coupled with deeper mineral weathering downstream had been proposed to explain these gradients. We conducted synoptic sampling of three headwater catchments in this region that showed variations in this longitudinal pattern, ranging from streams that remain Acidic throughout their length to streams with circumneutral pH beginning at their source. To explain these differences, we mapped soils using a hydropedologic approach that emphasizes the influence of groundwater saturation frequency and water table regime on soil formation processes. Stream segments with lower pH and base cation concentrations, coupled with higher concentrations of dissolved organic carbon, aluminum, and in one case iron, were in subcatchments mapped with shallow to bedrock soils where eluvial soil forming processes dominated. In contrast, stream segments with higher pH and base cation concentrations coupled with low concentrations of dissolved organic carbon and aluminum were associated with subcatchments with deeper soils where illuvial processes were more dominant. Concentrations of sodium and silicon were relatively uniform across these gradients. Coupled with the higher concentrations of dissolved aluminum and small pools of exchangeable aluminum in the areas of bedrock outcrops and shallow soils, these data suggest that primary mineral dissolution is an important process influencing upper stream reaches. Some stream reaches with obvious groundwater springs show a more abrupt transition suggesting that Neutralization along deeper flowpaths may play a role as well. These data suggest a new three stage model of stream chemistry evolution with introduction of organic Acids by frequent flushing of organic soils on shallow bedrock along ridge areas, Acidic reaches controlled by shallow mineral weathering processes coupled with eluvial soil development, giving way to downstream reaches influenced by illuviation as organometallic complexes precipitate in spodic soil horizons. This new model highlights differences in critical zone evolution along hillslopes in glaciated catchments with implications for understanding gradients in water quality, soil fertility, and response and recovery from disturbances.
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Mineral Weathering and Podzolization Control Acid Neutralization and Streamwater Chemistry Gradients in Upland Glaciated Catchments, Northeastern United States
Frontiers Media S.A., 2019Co-Authors: Scott W Bailey, Kevin J Mcguire, Donald S Ross, Mark B Green, Olivia L FraserAbstract:Headwater streams in the White Mountains, NH, United States have been shown to have downstream gradients of increasing pH and concentrations of base cations coupled with decreasing concentrations of aluminum. A two-stage Acid Neutralization model involving shallow soil exchange processes in headwaters coupled with deeper mineral weathering downstream had been proposed to explain these gradients. We conducted synoptic sampling of three headwater catchments in this region that showed variations in this longitudinal pattern, ranging from streams that remain Acidic throughout their length to streams with circumneutral pH beginning at their source. To explain these differences, we mapped soils using a hydropedologic approach that emphasizes the influence of groundwater saturation frequency and water table regime on soil formation processes. Stream segments with lower pH and base cation concentrations, coupled with higher concentrations of dissolved organic carbon (DOC), aluminum, and in one case iron, were in subcatchments mapped with shallow to bedrock soils where eluvial soil forming processes dominated. In contrast, stream segments with higher pH and base cation concentrations coupled with low concentrations of DOC and aluminum were associated with subcatchments with deeper soils where illuvial processes were more dominant. Concentrations of sodium and silicon were relatively uniform across these gradients. Coupled with the higher concentrations of dissolved aluminum and small pools of exchangeable aluminum in the areas of bedrock outcrops and shallow soils, these data suggest that primary mineral dissolution is an important process influencing upper stream reaches, not just along longer, deeper flowpaths in downslope areas. In contrast, some stream reaches with obvious groundwater springs show a more abrupt transition in pH and base cation concentrations higher along the stream, suggesting that Neutralization along deeper flowpaths may play a role in upslope areas as well. These data suggest a new three stage model of stream chemistry evolution. First, organic Acids are introduced by frequent flushing of organic soils on shallow bedrock along ridge areas. Second, upper Acidic reaches are controlled by mineral dissolution coupled with eluvial soil development. Third, downstream reaches are influenced by illuviation as organometallic complexes precipitate in spodic soil horizons, removing organic Acids, and Acid-mobile metals from drainage waters. This new model highlights differences in critical zone evolution along hillslopes in glaciated catchments with implications for understanding gradients in water quality, soil fertility, and response and recovery from disturbances
Anders Lagerkvist - One of the best experts on this subject based on the ideXlab platform.
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accelerated carbonation of steel slags in a landfill cover construction
Waste Management, 2010Co-Authors: Silvia Diener, Lale Andreas, Inga Herrmann, Holger Ecke, Anders LagerkvistAbstract:Steel slags from high-alloyed tool steel production were used in a full scale cover construction of a municipal solid waste (MSW) landfill. In order to study the long-term stability of the steel slags within the final cover, a laboratory experiment was performed. The effect on the ageing process, due to i.e. carbonation, exerted by five different factors resembling both the material characteristics and the environmental conditions is investigated. Leaching behaviour, Acid Neutralization capacity and mineralogy (evaluated by means of X-ray diffraction, XRD, and thermogravimetry/differential thermal analysis, TG/DTA) are tested after different periods of ageing under different conditions. Samples aged for 3 and 10 months were evaluated in this paper. Multivariate data analysis was used for data evaluation. The results indicate that among the investigated factors, ageing time and carbon dioxide content of the atmosphere were able to exert the most relevant effect. However, further investigations are required in order to clarify the role of the temperature.
