Arsenic mobility in natural systems is often linked to iron and sulfur cycling at redox boundarie... more Arsenic mobility in natural systems is often linked to iron and sulfur cycling at redox boundaries, apparently due to co-precipitation reactions of arsenic with poorly crystalline iron (oxy)hydroxides, iron monosulfides, and pyrite (e.g., Edenborn et al., 1986; Moore et al., 1988). The mobility of arsenic under anoxic, sulfate-reducing conditions is expected to be governed by interactions between arsenite or thioarsenite species with amorphous or crystalline iron sulfides. Iron sulfide minerals are especially common components of soil/sedimentary environments, and reactions at the surfaces of iron sulfides play pivotal roles in metal retention, mobility, and bioavailability (Huerta-Diaz and Morse, 1992). Although essential for predicting the fate of arsenic in anoxic environments, details of reaction mechanisms, geochemical pathways, and the limiting factors that govern metal uptake by iron sulfides (iron monosulfides and iron disulfides) are incompletely understood. The kinetic nat...
The white lines on the L2,3 absorption edges of the transition metals and on the M4,5 absorption ... more The white lines on the L2,3 absorption edges of the transition metals and on the M4,5 absorption edges of the rare earth elements are the most prominent feature in electron-energy-loss spectra (EELS). The white lines of these elements have been studied and used to determine valance and coordination of atoms in various systems. Fe-O compounds with valence 2, 3 and mixed valence states, for example, have been carefully examined and characterized. However, in spite of the importance of iron sulfides in geochemistry and environmental science, the EELS data of these compounds are not available. Pyrite (FeS2) is widespread in hydrothermal ores, modern sediments, and sedimentary rocks deposited throughout the geologic record. The ferromagnetic iron sulfide greigite (Fe3S4) is another important compound. It has been recognized as a carrier of magnetic remanence in young sediments. Sedimentary greigite may be precipitated inorganically or biogenically by magnetotactic bacteria.
Abiotic degradation of chlorinated solvents by reactive iron minerals such as iron sulfides, magn... more Abiotic degradation of chlorinated solvents by reactive iron minerals such as iron sulfides, magnetite, green rust, and other Fe(II)‐containing minerals has been observed in both laboratory and field studies. These reactive iron minerals form under iron‐ and sulfate‐reducing conditions which are commonly found in permeable reactive barriers (PRBs), enhanced reductive dechlorination (ERD) treatment locations, landfills, and aquifers that are chemically reducing. The objective of this review is to synthesize current understanding of abiotic degradation of chlorinated solvents by reactive iron minerals, with special focus on how abiotic processes relate to groundwater remediation. Degradation of chlorinated solvents by reactive minerals can proceed through reductive elimination, hydrogenolysis, dehydrohalogenation, and hydrolysis reactions. Degradation products of abiotic reactions depend on degradation pathways and parent compounds. Some degradation products (e.g., acetylene) have the potential to serve as a signature product for demonstrating abiotic reactions. Laboratory and field studies show that various minerals have a range of reactivity toward chlorinated solvents. A general trend of mineral reactivity for degradation of chlorinated solvents can be approximated as follows: disordered FeS > FeS > Fe(0) > FeS2 > sorbed Fe2+ > green rust = magnetite > biotite = vermiculite. Reaction kinetics are also influenced by factors such as pH, natural organic matter (NOM), coexisting metal ions, and sulfide concentration in the system. In practice, abiotic reactions can be engineered to stimulate reactive mineral formation for groundwater remediation. Under appropriate site geochemical conditions, abiotic reactions can occur naturally, and can be incorporated into remedial strategies such as monitored natural attenuation.
Pyrite formation has been investigated at 70° C and pH 68 by aging precipitated, disordered mack... more Pyrite formation has been investigated at 70° C and pH 68 by aging precipitated, disordered mackinawite, Fe9S8, and greigite, Fe3S4, in solutions containing aqueous H2S, HS−, Sx2−, S2O32−, SO32−, colloidal elemental sulfur, and the organic sulfur species ...
Introduction Arsenic in ground water and surface water poses a risk to ecosystem and human health... more Introduction Arsenic in ground water and surface water poses a risk to ecosystem and human health. Because of this risk, environmental concern is rising over arsenic levels in water resources. Arsenic has been documented at concentrations up to about 100 mg/L in ground water systems across the U.S., or about 4 orders of magnitude greater than the revised U.S. EPA maximum concentration limit (MCL) of 0.01 mg/L (effective in 2006). Arsenic contamination is associated with weathering processes, mineral deposits, mining activities, industrial, and agricultural uses. More detailed information is needed on the factors that govern arsenic transport and fate in the environment, especially natural processes that remove arsenic from the mobile phase such as reactions that occur at mineral surfaces. A clearer understanding of these processes is needed in order to optimize contaminant remediation systems and to better predict the long-term behavior of arsenic at hazardous waste sites.
<b>Copyright information:</b>Taken from "Microbial sulfate reduction and metal a... more <b>Copyright information:</b>Taken from "Microbial sulfate reduction and metal attenuation in pH 4 acid mine water"http://www.geochemicaltransactions.com/content/8/1/10Geochemical Transactions 2007;8():10-10.Published online 23 Oct 2007PMCID:PMC2211471. a) At pH 4, covellite (CuS), greenockite (CdS), and sphalerite (ZnS) precipitate, but mackinawite (FeS) remains undersaturated. b) At pH 7, all metal sulfides precipitate. The model was also run with the Eh fixed at 0.0 mV. At this condition elemental sulfur (dashed line) precipitation is favored at pH 4 following metal sulfide precipitation. Initial metals concentrations were Fe (150 mg L), Zn (100 mg L), Cd and Cu (15 mg L).
<b>Copyright information:</b>Taken from "Microbial sulfate reduction and metal a... more <b>Copyright information:</b>Taken from "Microbial sulfate reduction and metal attenuation in pH 4 acid mine water"http://www.geochemicaltransactions.com/content/8/1/10Geochemical Transactions 2007;8():10-10.Published online 23 Oct 2007PMCID:PMC2211471. PM01: water from culture experiments; PM02: low-pH cultures; PM03: near-neutral-pH cultures.
Resource Conservation and Recovery Act Offices (RCRA). The Forum is focused on exchanging informa... more Resource Conservation and Recovery Act Offices (RCRA). The Forum is focused on exchanging information related to ground-water characterization, monitoring, and remediation. The application of monitored natural attenuation (MNA) for inorganic contaminants in ground water is a topic of concern to the Forum. The purpose of this Issue Paper is to provide scientists and engineers responsible for assessing remediation technologies with background information on MNA processes at mining-impacted sites. Some of the key issues concerning the application of natural attenuation for inorganic contaminants are discussed, such as the geochemical mechanisms responsible for attenuation, attenuation capacity, monitoring parameters, and evaluating whether attenuated metal and metalloid contaminants will remain immobile.
The term “monitored natural attenuation, ” as used in the following discussion and in the Office ... more The term “monitored natural attenuation, ” as used in the following discussion and in the Office of Solid Waste and Emergency Response (OSWER) Directive 9200.4‑17P (hereafter referred to as the 1999 OSWER Directive; USEPA, 1999), refers to “the reliance on natural attenuation processes (within the context of a carefully controlled and monitored site cleanup approach) to achieve site‑ specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. ” When properly employed, monitored naturalattenuation(MNA)mayprovideaneffectiveremedy for ground water where a thorough engineering analysis informs the understanding, monitoring, predicting, and documenting of the natural processes. In principle, MNA provides a reasonable remedy for attaining groundwater
Arsenic mobility in natural systems is often linked to iron and sulfur cycling at redox boundarie... more Arsenic mobility in natural systems is often linked to iron and sulfur cycling at redox boundaries, apparently due to co-precipitation reactions of arsenic with poorly crystalline iron (oxy)hydroxides, iron monosulfides, and pyrite (e.g., Edenborn et al., 1986; Moore et al., 1988). The mobility of arsenic under anoxic, sulfate-reducing conditions is expected to be governed by interactions between arsenite or thioarsenite species with amorphous or crystalline iron sulfides. Iron sulfide minerals are especially common components of soil/sedimentary environments, and reactions at the surfaces of iron sulfides play pivotal roles in metal retention, mobility, and bioavailability (Huerta-Diaz and Morse, 1992). Although essential for predicting the fate of arsenic in anoxic environments, details of reaction mechanisms, geochemical pathways, and the limiting factors that govern metal uptake by iron sulfides (iron monosulfides and iron disulfides) are incompletely understood. The kinetic nat...
The white lines on the L2,3 absorption edges of the transition metals and on the M4,5 absorption ... more The white lines on the L2,3 absorption edges of the transition metals and on the M4,5 absorption edges of the rare earth elements are the most prominent feature in electron-energy-loss spectra (EELS). The white lines of these elements have been studied and used to determine valance and coordination of atoms in various systems. Fe-O compounds with valence 2, 3 and mixed valence states, for example, have been carefully examined and characterized. However, in spite of the importance of iron sulfides in geochemistry and environmental science, the EELS data of these compounds are not available. Pyrite (FeS2) is widespread in hydrothermal ores, modern sediments, and sedimentary rocks deposited throughout the geologic record. The ferromagnetic iron sulfide greigite (Fe3S4) is another important compound. It has been recognized as a carrier of magnetic remanence in young sediments. Sedimentary greigite may be precipitated inorganically or biogenically by magnetotactic bacteria.
Abiotic degradation of chlorinated solvents by reactive iron minerals such as iron sulfides, magn... more Abiotic degradation of chlorinated solvents by reactive iron minerals such as iron sulfides, magnetite, green rust, and other Fe(II)‐containing minerals has been observed in both laboratory and field studies. These reactive iron minerals form under iron‐ and sulfate‐reducing conditions which are commonly found in permeable reactive barriers (PRBs), enhanced reductive dechlorination (ERD) treatment locations, landfills, and aquifers that are chemically reducing. The objective of this review is to synthesize current understanding of abiotic degradation of chlorinated solvents by reactive iron minerals, with special focus on how abiotic processes relate to groundwater remediation. Degradation of chlorinated solvents by reactive minerals can proceed through reductive elimination, hydrogenolysis, dehydrohalogenation, and hydrolysis reactions. Degradation products of abiotic reactions depend on degradation pathways and parent compounds. Some degradation products (e.g., acetylene) have the potential to serve as a signature product for demonstrating abiotic reactions. Laboratory and field studies show that various minerals have a range of reactivity toward chlorinated solvents. A general trend of mineral reactivity for degradation of chlorinated solvents can be approximated as follows: disordered FeS > FeS > Fe(0) > FeS2 > sorbed Fe2+ > green rust = magnetite > biotite = vermiculite. Reaction kinetics are also influenced by factors such as pH, natural organic matter (NOM), coexisting metal ions, and sulfide concentration in the system. In practice, abiotic reactions can be engineered to stimulate reactive mineral formation for groundwater remediation. Under appropriate site geochemical conditions, abiotic reactions can occur naturally, and can be incorporated into remedial strategies such as monitored natural attenuation.
Pyrite formation has been investigated at 70° C and pH 68 by aging precipitated, disordered mack... more Pyrite formation has been investigated at 70° C and pH 68 by aging precipitated, disordered mackinawite, Fe9S8, and greigite, Fe3S4, in solutions containing aqueous H2S, HS−, Sx2−, S2O32−, SO32−, colloidal elemental sulfur, and the organic sulfur species ...
Introduction Arsenic in ground water and surface water poses a risk to ecosystem and human health... more Introduction Arsenic in ground water and surface water poses a risk to ecosystem and human health. Because of this risk, environmental concern is rising over arsenic levels in water resources. Arsenic has been documented at concentrations up to about 100 mg/L in ground water systems across the U.S., or about 4 orders of magnitude greater than the revised U.S. EPA maximum concentration limit (MCL) of 0.01 mg/L (effective in 2006). Arsenic contamination is associated with weathering processes, mineral deposits, mining activities, industrial, and agricultural uses. More detailed information is needed on the factors that govern arsenic transport and fate in the environment, especially natural processes that remove arsenic from the mobile phase such as reactions that occur at mineral surfaces. A clearer understanding of these processes is needed in order to optimize contaminant remediation systems and to better predict the long-term behavior of arsenic at hazardous waste sites.
<b>Copyright information:</b>Taken from "Microbial sulfate reduction and metal a... more <b>Copyright information:</b>Taken from "Microbial sulfate reduction and metal attenuation in pH 4 acid mine water"http://www.geochemicaltransactions.com/content/8/1/10Geochemical Transactions 2007;8():10-10.Published online 23 Oct 2007PMCID:PMC2211471. a) At pH 4, covellite (CuS), greenockite (CdS), and sphalerite (ZnS) precipitate, but mackinawite (FeS) remains undersaturated. b) At pH 7, all metal sulfides precipitate. The model was also run with the Eh fixed at 0.0 mV. At this condition elemental sulfur (dashed line) precipitation is favored at pH 4 following metal sulfide precipitation. Initial metals concentrations were Fe (150 mg L), Zn (100 mg L), Cd and Cu (15 mg L).
<b>Copyright information:</b>Taken from "Microbial sulfate reduction and metal a... more <b>Copyright information:</b>Taken from "Microbial sulfate reduction and metal attenuation in pH 4 acid mine water"http://www.geochemicaltransactions.com/content/8/1/10Geochemical Transactions 2007;8():10-10.Published online 23 Oct 2007PMCID:PMC2211471. PM01: water from culture experiments; PM02: low-pH cultures; PM03: near-neutral-pH cultures.
Resource Conservation and Recovery Act Offices (RCRA). The Forum is focused on exchanging informa... more Resource Conservation and Recovery Act Offices (RCRA). The Forum is focused on exchanging information related to ground-water characterization, monitoring, and remediation. The application of monitored natural attenuation (MNA) for inorganic contaminants in ground water is a topic of concern to the Forum. The purpose of this Issue Paper is to provide scientists and engineers responsible for assessing remediation technologies with background information on MNA processes at mining-impacted sites. Some of the key issues concerning the application of natural attenuation for inorganic contaminants are discussed, such as the geochemical mechanisms responsible for attenuation, attenuation capacity, monitoring parameters, and evaluating whether attenuated metal and metalloid contaminants will remain immobile.
The term “monitored natural attenuation, ” as used in the following discussion and in the Office ... more The term “monitored natural attenuation, ” as used in the following discussion and in the Office of Solid Waste and Emergency Response (OSWER) Directive 9200.4‑17P (hereafter referred to as the 1999 OSWER Directive; USEPA, 1999), refers to “the reliance on natural attenuation processes (within the context of a carefully controlled and monitored site cleanup approach) to achieve site‑ specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. ” When properly employed, monitored naturalattenuation(MNA)mayprovideaneffectiveremedy for ground water where a thorough engineering analysis informs the understanding, monitoring, predicting, and documenting of the natural processes. In principle, MNA provides a reasonable remedy for attaining groundwater
Uploads