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Maria Chrysochoou - One of the best experts on this subject based on the ideXlab platform.

  • Microstructural analyses of Cr(VI) speciation in Chromite Ore processing residue from the soda ash process.
    Journal of hazardous materials, 2020
    Co-Authors: Maria Chrysochoou
    Abstract:

    Abstract The microstructure of Chromite Ore Processing Residue (COPR) derived from the soda ash roasting process was investigated prior to and after removal of water exchangeable chromate using a host of microscopy and spectroscopy techniques. Soda ash COPR consists mostly of a magnesioferrite (MgFe2O4) matrix that has substantial substitution of trivalent chromium (Cr) for iron. The Chromite particles are generally larger than the overall particle size distribution of COPR, containing most of the Cr mass in areas that are greater than 20 μm in diameter; Chromite particles are also associated with most of the non-exchangeable hexavalent Cr (Cr(VI)), even though the binding mechanism is not well understood. The remaining non-exchangeable Cr(VI) was found in association with the surrounding Si- and Al-matrix, with spectroscopic evidence of the presence of Cr(VI)-hydrotalcite.

  • Importance of Mineralogy in the Geoenvironmental Characterization and Treatment of Chromite Ore Processing Residue
    Journal of Geotechnical and Geoenvironmental Engineering, 2010
    Co-Authors: Maria Chrysochoou, Dimitris Dermatas, Deok Hyun Moon, Dennis G Grubb, Christos Christodoulatos
    Abstract:

    The geoenvironmental characterization of COPR at two deposition sites (New Jersey and Maryland) included geotechnical, chemical, mineralogical, and leaching analyses of three main Chromite Ore processing residue (COPR) types [gray-black (GB), hard brown (HB), clayey (C)]. Quantitative mineralogical analyses were instrumental in the delineation of the geochemical differences between the three COPR types, which enabled a framework to predict COPR response to potential remediation schemes. Overall, COPR mineralogy resembled cement, with hydration and pozzolanic reactions dominating its geochemistry. GB COPR was largely unreacted despite its prolonged exposure to humid conditions, while HB COPR was completely hydrated and contained high Cr(VI) concentrations. The two materials were chemically similar, with dilution accounting for the chemical and density differences. While the total acid neutralization capacity (ANC) of GB and HB was the same, the ANC at high pH (8–12) was higher in HB due to the dominance of...

  • Experimental Studies on Coupled Treatment of Chromite Ore Processing Residue
    Journal of ASTM International, 2009
    Co-Authors: Maria Chrysochoou, Dimitris Dermatas, Christos Christodoulatos
    Abstract:

    A study was performed to investigate the combined treatment of hexavalent chromium (Cr(VI)) and heaving in Chromite Ore Processing Residue (COPR). Treatment of heaving focused on the intentional exhaustion of the mineral brownmillerite, the hydration of which is considered responsible for volume expansion in COPR deposition sites in New Jersey. The addition of sufficient amounts of sulfate under different conditions of temperature, acidity, and particle size aimed in the quick transformation of brownmillerite to ettringite, a phenomenon observed during a COPR pilot scale study. Simultaneously, the reductive treatment of hexavalent chromium (Cr(VI)) in COPR was pursued using calcium polysulfide (CPS) and ferrous sulfate (FS). X-ray Absorption Near Edge Spectroscopy (XANES) analyses showed that neither reductant was able to reduce Cr(VI) below 1,000 mg/kg after three months (FS) and six months (CPS) of treatment. However, competitive sulfide oxidation by oxygen was much slower compared to ferrous iron oxidation, as evidenced by chemical analyses. Quantitative X-ray diffraction analyses showed that brownmillerite dissolved to form ettringite only in a sample treated with FS at 50°C; neither acidity or temperature alone were able to trigger brownmillerite dissolution and ettringite formation. Particle size reduction to

  • Assessment of brownmillerite and periclase hydration in Chromite Ore processing residue at elevated temperature
    GeoCongress 2008, 2008
    Co-Authors: Deok Hyun Moon, Adriana M. Sanchez, Dimitris Dermatas, Maria Chrysochoou, Mahmoud Wazne, Dennis G Grubb
    Abstract:

    Chromite Ore processing residue (COPR) is a solid waste that was generated by the high temperature process of chromium extraction from Chromite Ore using soda ash and lime. The purpose of this study was to evaluate whether brownmillerite and periclase could be transformed into other minerals to understand and predict phase transformation during weathering in COPR. In this study, brownmillerite hydration to hydrogarnets and periclase to brucite in COPR materials were respectively assessed at elevated temperatures (100 o C and 200 o C) for 30 days because these reactions are very slow at ambient temperatures. The results showed that no apparent phase transformation was observed at 100 o C. However, brownmillerite and periclase started dissolving the first day at 200 o C, forming hydrogarnets and brucite, and completely dissolving after 15 days. MOreover, hydrogarnets were the main phase after 30 days of reaction. This indicated that the phase transformation could be possible when the initial COPR materials with high content of brownmillerite are exposed to long-term weathering.

  • Current Knowledge on Heaving Mechanisms of Chromite Ore Processing Residue
    GeoCongress 2008, 2008
    Co-Authors: Dimitris Dermatas, Deok Hyun Moon, Maria Chrysochoou, Maria Kaouris, John J. Morris, Chris French
    Abstract:

    Chromite Ore Processing Residue (COPR) has in certain cases been associated with heaving phenomena. To understand the COPR heave mechanism, the site owner sponsOred research that included extensive field investigation, site characterization and laboratory programs. Based on the results, this paper presents the current knowledge on COPR heave mechanisms. Among the different heaving mechanisms considered, ettringite formation had previously been reported as an expansion mechanism in cements and lime-treated soils. While site investigation revealed significant, localized presence of ettringite, it could not be correlated to the observed heave features. However, observations from test-trench activities and heave phenomena in ferrous sulfate treated COPR, confirmed that ettringite induced expansion constitutes a viable COPR heave mechanism. From other potential mechanisms that were evaluated, brownmillerite hydration to hydrogarnets remains the most viable. Although brownmillerite hydration proceeds extremely slowly at ambient temperature, hydrogarnet-rich material has been found in discrete layers in trenches at different sites, and has lately been associated with a major heave feature at SA-7. Accordingly, the conditions for rapid brownmillerite hydration and its associated potential for heave manifestation remain open to further investigation.

Hainan Kong - One of the best experts on this subject based on the ideXlab platform.

  • Treatment of Chromite Ore Processing Residue by pyrolysis with rice straw
    Chemosphere, 2009
    Co-Authors: Dalei Zhang, Luwei Dai, Kangjin Peng, Hao Pang, Hainan Kong
    Abstract:

    Abstract Chromite Ore Processing Residue (COPR) is the byproduct of chromate production process, which contains a large amounts of Cr(VI). The present work developed a new technique to treat COPR, and the process involved mixing the COPR with rice straw followed by pyrolysis. It was found that the gaseous organic fraction generated during pyrolysis of straw was beneficial to Cr(VI) reduction. In the study, process variables, such as the amount of straw added to COPR, heating temperature and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were all investigated. After pyrolysis, Cr(VI) decreased greatly, from 3400 for untreated COPR to less than 30 mg kg −1 for treated COPR at 600 °C.

  • Remediation of Chromite Ore processing residue by pyrolysis process with sewage sludge
    Bioresource technology, 2009
    Co-Authors: Dalei Zhang, Hainan Kong
    Abstract:

    Abstract The present work developed a novel technique to treat Chromite Ore processing residue (COPR). The process involved mixing the COPR with sewage sludge followed by pyrolysis. The gaseous organic fraction generated during pyrolysis of sludge was beneficial to Cr(VI) reduction. Process variables, such as the amount of sludge added to COPR (sludge-to-COPR (S/C) ratio), heating temperature, reaction time and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were investigated. Cr(VI) content had decreased greatly, from 3384 mg kg−1 for untreated COPR to less than 30 mg kg−1 for COPR treated at 600 °C.

Deok Hyun Moon - One of the best experts on this subject based on the ideXlab platform.

  • Importance of Mineralogy in the Geoenvironmental Characterization and Treatment of Chromite Ore Processing Residue
    Journal of Geotechnical and Geoenvironmental Engineering, 2010
    Co-Authors: Maria Chrysochoou, Dimitris Dermatas, Deok Hyun Moon, Dennis G Grubb, Christos Christodoulatos
    Abstract:

    The geoenvironmental characterization of COPR at two deposition sites (New Jersey and Maryland) included geotechnical, chemical, mineralogical, and leaching analyses of three main Chromite Ore processing residue (COPR) types [gray-black (GB), hard brown (HB), clayey (C)]. Quantitative mineralogical analyses were instrumental in the delineation of the geochemical differences between the three COPR types, which enabled a framework to predict COPR response to potential remediation schemes. Overall, COPR mineralogy resembled cement, with hydration and pozzolanic reactions dominating its geochemistry. GB COPR was largely unreacted despite its prolonged exposure to humid conditions, while HB COPR was completely hydrated and contained high Cr(VI) concentrations. The two materials were chemically similar, with dilution accounting for the chemical and density differences. While the total acid neutralization capacity (ANC) of GB and HB was the same, the ANC at high pH (8–12) was higher in HB due to the dominance of...

  • leaching mechanisms of cr vi from Chromite Ore processing residue
    Journal of Environmental Quality, 2008
    Co-Authors: Mahmoud Wazne, Deok Hyun Moon, Christos Christodoulatos, Santhi Chandra Jagupilla, Agamemnon Koutsospyros
    Abstract:

    : Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from Chromite Ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values 10.5 and by adsorption at pH 10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH <8. As pH decreased to <10, most of the Cr(VI) bearing minerals become unstable and their dissolution contributes to the increase in Cr(VI) concentration in the leachate solution. At low pH ( <1.5), Cr(III) solid phases and the oxides responsible for Cr(VI) adsorption dissolve and release Cr(III) and Cr(VI) into solution.

  • Leaching mechanisms of Cr(VI) from Chromite Ore processing residue.
    Journal of environmental quality, 2008
    Co-Authors: Mahmoud Wazne, Deok Hyun Moon, Christos Christodoulatos, Santhi Chandra Jagupilla, Agamemnon Koutsospyros
    Abstract:

    Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from Chromite Ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values 10.5 and by adsorption at pH 10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH

  • Assessment of brownmillerite and periclase hydration in Chromite Ore processing residue at elevated temperature
    GeoCongress 2008, 2008
    Co-Authors: Deok Hyun Moon, Adriana M. Sanchez, Dimitris Dermatas, Maria Chrysochoou, Mahmoud Wazne, Dennis G Grubb
    Abstract:

    Chromite Ore processing residue (COPR) is a solid waste that was generated by the high temperature process of chromium extraction from Chromite Ore using soda ash and lime. The purpose of this study was to evaluate whether brownmillerite and periclase could be transformed into other minerals to understand and predict phase transformation during weathering in COPR. In this study, brownmillerite hydration to hydrogarnets and periclase to brucite in COPR materials were respectively assessed at elevated temperatures (100 o C and 200 o C) for 30 days because these reactions are very slow at ambient temperatures. The results showed that no apparent phase transformation was observed at 100 o C. However, brownmillerite and periclase started dissolving the first day at 200 o C, forming hydrogarnets and brucite, and completely dissolving after 15 days. MOreover, hydrogarnets were the main phase after 30 days of reaction. This indicated that the phase transformation could be possible when the initial COPR materials with high content of brownmillerite are exposed to long-term weathering.

  • Current Knowledge on Heaving Mechanisms of Chromite Ore Processing Residue
    GeoCongress 2008, 2008
    Co-Authors: Dimitris Dermatas, Deok Hyun Moon, Maria Chrysochoou, Maria Kaouris, John J. Morris, Chris French
    Abstract:

    Chromite Ore Processing Residue (COPR) has in certain cases been associated with heaving phenomena. To understand the COPR heave mechanism, the site owner sponsOred research that included extensive field investigation, site characterization and laboratory programs. Based on the results, this paper presents the current knowledge on COPR heave mechanisms. Among the different heaving mechanisms considered, ettringite formation had previously been reported as an expansion mechanism in cements and lime-treated soils. While site investigation revealed significant, localized presence of ettringite, it could not be correlated to the observed heave features. However, observations from test-trench activities and heave phenomena in ferrous sulfate treated COPR, confirmed that ettringite induced expansion constitutes a viable COPR heave mechanism. From other potential mechanisms that were evaluated, brownmillerite hydration to hydrogarnets remains the most viable. Although brownmillerite hydration proceeds extremely slowly at ambient temperature, hydrogarnet-rich material has been found in discrete layers in trenches at different sites, and has lately been associated with a major heave feature at SA-7. Accordingly, the conditions for rapid brownmillerite hydration and its associated potential for heave manifestation remain open to further investigation.

Christos Christodoulatos - One of the best experts on this subject based on the ideXlab platform.

  • Importance of Mineralogy in the Geoenvironmental Characterization and Treatment of Chromite Ore Processing Residue
    Journal of Geotechnical and Geoenvironmental Engineering, 2010
    Co-Authors: Maria Chrysochoou, Dimitris Dermatas, Deok Hyun Moon, Dennis G Grubb, Christos Christodoulatos
    Abstract:

    The geoenvironmental characterization of COPR at two deposition sites (New Jersey and Maryland) included geotechnical, chemical, mineralogical, and leaching analyses of three main Chromite Ore processing residue (COPR) types [gray-black (GB), hard brown (HB), clayey (C)]. Quantitative mineralogical analyses were instrumental in the delineation of the geochemical differences between the three COPR types, which enabled a framework to predict COPR response to potential remediation schemes. Overall, COPR mineralogy resembled cement, with hydration and pozzolanic reactions dominating its geochemistry. GB COPR was largely unreacted despite its prolonged exposure to humid conditions, while HB COPR was completely hydrated and contained high Cr(VI) concentrations. The two materials were chemically similar, with dilution accounting for the chemical and density differences. While the total acid neutralization capacity (ANC) of GB and HB was the same, the ANC at high pH (8–12) was higher in HB due to the dominance of...

  • Experimental Studies on Coupled Treatment of Chromite Ore Processing Residue
    Journal of ASTM International, 2009
    Co-Authors: Maria Chrysochoou, Dimitris Dermatas, Christos Christodoulatos
    Abstract:

    A study was performed to investigate the combined treatment of hexavalent chromium (Cr(VI)) and heaving in Chromite Ore Processing Residue (COPR). Treatment of heaving focused on the intentional exhaustion of the mineral brownmillerite, the hydration of which is considered responsible for volume expansion in COPR deposition sites in New Jersey. The addition of sufficient amounts of sulfate under different conditions of temperature, acidity, and particle size aimed in the quick transformation of brownmillerite to ettringite, a phenomenon observed during a COPR pilot scale study. Simultaneously, the reductive treatment of hexavalent chromium (Cr(VI)) in COPR was pursued using calcium polysulfide (CPS) and ferrous sulfate (FS). X-ray Absorption Near Edge Spectroscopy (XANES) analyses showed that neither reductant was able to reduce Cr(VI) below 1,000 mg/kg after three months (FS) and six months (CPS) of treatment. However, competitive sulfide oxidation by oxygen was much slower compared to ferrous iron oxidation, as evidenced by chemical analyses. Quantitative X-ray diffraction analyses showed that brownmillerite dissolved to form ettringite only in a sample treated with FS at 50°C; neither acidity or temperature alone were able to trigger brownmillerite dissolution and ettringite formation. Particle size reduction to

  • leaching mechanisms of cr vi from Chromite Ore processing residue
    Journal of Environmental Quality, 2008
    Co-Authors: Mahmoud Wazne, Deok Hyun Moon, Christos Christodoulatos, Santhi Chandra Jagupilla, Agamemnon Koutsospyros
    Abstract:

    : Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from Chromite Ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values 10.5 and by adsorption at pH 10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH <8. As pH decreased to <10, most of the Cr(VI) bearing minerals become unstable and their dissolution contributes to the increase in Cr(VI) concentration in the leachate solution. At low pH ( <1.5), Cr(III) solid phases and the oxides responsible for Cr(VI) adsorption dissolve and release Cr(III) and Cr(VI) into solution.

  • Leaching mechanisms of Cr(VI) from Chromite Ore processing residue.
    Journal of environmental quality, 2008
    Co-Authors: Mahmoud Wazne, Deok Hyun Moon, Christos Christodoulatos, Santhi Chandra Jagupilla, Agamemnon Koutsospyros
    Abstract:

    Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from Chromite Ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values 10.5 and by adsorption at pH 10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH

  • ettringite induced heave in Chromite Ore processing residue copr upon ferrous sulfate treatment
    Environmental Science & Technology, 2006
    Co-Authors: Dimitris Dermatas, Deok Hyun Moon, Maria Chrysochoou, Dennis G Grubb, Mahmoud Wazne, Christos Christodoulatos
    Abstract:

    A pilot-scale treatment study was implemented at a deposition site of Chromite Ore processing residue (COPR) in New Jersey. Ferrous sulfate heptahydrate (FeSO4·7H2O) was employed to reduce hexavalent chromium in two dosages with three types of soil mixing equipment. XANES analyses of treated samples cured for 240 days indicated that all treatment combinations failed to meet the Cr(VI) regulatory limit of 240 mg/kg. MOre importantly, the discrepancy between XANES and alkaline digestion results renders the latter unreliable for regulatory purposes when applied to ferrous-treated COPR. Regardless of Cr(VI), the introduction of reductant containing sulfate, mechanical mixing, water, acidity, and the resulting temperature increase in treated COPR promoted dissolution of brownmillerite (Ca2FeAlO5), releasing alumina and alkalinity. The pH increase caused initially precipitated gypsum (CaSO4·2H2O) to progressively convert to ettringite (Ca6Al2(SO4)3·32H2O) and its associated volume expansion under both in situ a...

Mahmoud Wazne - One of the best experts on this subject based on the ideXlab platform.

  • leaching mechanisms of cr vi from Chromite Ore processing residue
    Journal of Environmental Quality, 2008
    Co-Authors: Mahmoud Wazne, Deok Hyun Moon, Christos Christodoulatos, Santhi Chandra Jagupilla, Agamemnon Koutsospyros
    Abstract:

    : Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from Chromite Ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values 10.5 and by adsorption at pH 10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH <8. As pH decreased to <10, most of the Cr(VI) bearing minerals become unstable and their dissolution contributes to the increase in Cr(VI) concentration in the leachate solution. At low pH ( <1.5), Cr(III) solid phases and the oxides responsible for Cr(VI) adsorption dissolve and release Cr(III) and Cr(VI) into solution.

  • Leaching mechanisms of Cr(VI) from Chromite Ore processing residue.
    Journal of environmental quality, 2008
    Co-Authors: Mahmoud Wazne, Deok Hyun Moon, Christos Christodoulatos, Santhi Chandra Jagupilla, Agamemnon Koutsospyros
    Abstract:

    Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from Chromite Ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values 10.5 and by adsorption at pH 10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH

  • Assessment of brownmillerite and periclase hydration in Chromite Ore processing residue at elevated temperature
    GeoCongress 2008, 2008
    Co-Authors: Deok Hyun Moon, Adriana M. Sanchez, Dimitris Dermatas, Maria Chrysochoou, Mahmoud Wazne, Dennis G Grubb
    Abstract:

    Chromite Ore processing residue (COPR) is a solid waste that was generated by the high temperature process of chromium extraction from Chromite Ore using soda ash and lime. The purpose of this study was to evaluate whether brownmillerite and periclase could be transformed into other minerals to understand and predict phase transformation during weathering in COPR. In this study, brownmillerite hydration to hydrogarnets and periclase to brucite in COPR materials were respectively assessed at elevated temperatures (100 o C and 200 o C) for 30 days because these reactions are very slow at ambient temperatures. The results showed that no apparent phase transformation was observed at 100 o C. However, brownmillerite and periclase started dissolving the first day at 200 o C, forming hydrogarnets and brucite, and completely dissolving after 15 days. MOreover, hydrogarnets were the main phase after 30 days of reaction. This indicated that the phase transformation could be possible when the initial COPR materials with high content of brownmillerite are exposed to long-term weathering.

  • Swelling related to ettringite crystal formation in Chromite Ore processing residue
    Environmental Geochemistry and Health, 2007
    Co-Authors: Deok Hyun Moon, Adriana M. Sanchez, Dimitris Dermatas, Maria Chrysochoou, Mahmoud Wazne, Dennis G Grubb
    Abstract:

    Several million tons of Chromite Ore Processing Residue (COPR) were deposited at two sites in New Jersey and Maryland, USA, and over time they exhibited extensive heaving phenomena. Ettringite, a needle-shaped mineral and an expansive mineral commonly recognized in the literature concerning cement- and soil, has been identified extensively in numerous COPR samples collected from these sites. It was therefOre believed that ettringite formation and its crystal growth are strongly associated with COPR heaving. We investigated the correlation between ettringite and the heaving phenomena in COPR materials that contained no initial ettringite. Two identical COPR samples were exposed to a 4% w/w sulfate solution (25°C, 50°C) in a confined swell test apparatus. Both swell test samples were analyzed by means of X-ray powder diffraction. The peak intensities of newly formed ettringite were mOre pronounced in the sample tested at 50°C, and swell development was only observed in this sample. Scanning electron microscopy analyses revealed well-crystallized ettringite needles exceeding 40 μm in length for this sample, while ettringite crystals less than 15 μm in length formed in the sample tested at 25°C. TherefOre, the results suggest that the quantity of ettringite and the extent of crystallization play a key role in the heave of COPR.

  • ettringite induced heave in Chromite Ore processing residue copr upon ferrous sulfate treatment
    Environmental Science & Technology, 2006
    Co-Authors: Dimitris Dermatas, Deok Hyun Moon, Maria Chrysochoou, Dennis G Grubb, Mahmoud Wazne, Christos Christodoulatos
    Abstract:

    A pilot-scale treatment study was implemented at a deposition site of Chromite Ore processing residue (COPR) in New Jersey. Ferrous sulfate heptahydrate (FeSO4·7H2O) was employed to reduce hexavalent chromium in two dosages with three types of soil mixing equipment. XANES analyses of treated samples cured for 240 days indicated that all treatment combinations failed to meet the Cr(VI) regulatory limit of 240 mg/kg. MOre importantly, the discrepancy between XANES and alkaline digestion results renders the latter unreliable for regulatory purposes when applied to ferrous-treated COPR. Regardless of Cr(VI), the introduction of reductant containing sulfate, mechanical mixing, water, acidity, and the resulting temperature increase in treated COPR promoted dissolution of brownmillerite (Ca2FeAlO5), releasing alumina and alkalinity. The pH increase caused initially precipitated gypsum (CaSO4·2H2O) to progressively convert to ettringite (Ca6Al2(SO4)3·32H2O) and its associated volume expansion under both in situ a...