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Hailiang Dong - One of the best experts on this subject based on the ideXlab platform.
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effect of ligands on the production of oxidants from oxygenation of reduced fe bearing clay mineral Nontronite
Geochimica et Cosmochimica Acta, 2019Co-Authors: Qiang Zeng, Hailiang Dong, Xi WangAbstract:Abstract Oxygenation of reduced iron-bearing clay minerals produces highly reactive oxidants that are capable of transforming a range of organic compounds, which is of great environmental importance, but the effect of Fe-chelating ligands on this process has not been studied. In this work, oxidant production from oxygenation of reduced Nontronite was investigated in the presence of four common ligands. Addition of phosphate, tripolyphosphate (TPP), nitrilotriacetic acid (NTA) and ethylene diaminetetraacetic acid (EDTA) all significantly increased the oxidant yields, but the specific mechanisms varied, depending on the ligand types. NTA and EDTA addition promoted dissolution of structural Fe, forming aqueous NTA-Fe2+ and EDTA-Fe2+ complexes. Upon exposure to air, these complexed species rapidly oxidized through homogeneous Fenton reaction, forming chelated soluble Fe3+ species, which were rapidly reduced back to Fe2+ by electrons transferred from structural Fe(II) in reduced Nontronite. With increasing NTA and EDTA loadings, homogeneous Fenton reaction gradually dominated over heterogeneous oxidation of structural Fe(II). Because of rapid air oxidation of NTA-Fe2+ and EDTA-Fe2+ complexes, these species were maintained at low levels in aqueous solution, thus minimizing the quenching effect of oxidants by excess Fe2+and the probability of non-oxidant generation pathway, both of which contributed to the observed increase of the oxidant yields. In contrast, phosphate increased the oxidant yield through sorption to the surface of reduced NAu-2 and a subsequent shift of weak oxidant [possibly Fe(IV)] to strongly reactive hydroxyl radicals (HO ). TPP played a dual role by both changing the surface catalytic properties of Nontronite through sorption and enhancing homogeneous Fenton reaction by chelating with aqueous Fe2+ and Fe3+. These results shed lights on how commonly present natural and synthetic ligands affect the oxidation process of reduced iron-bearing clay minerals and oxidant production, hence providing a theoretical basis for understanding oxidant-promoted transformation mechanisms of organic matter in either natural or engineered systems.
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smectite illite and early diagenesis in south pacific gyre subseafloor sediment
Applied Clay Science, 2016Co-Authors: Kiho Yang, Hailiang Dong, Toshihiro Kogure, Hionsuck Baik, Bryce Hoppie, Robert N HarrisAbstract:Abstract Subseafloor sediment and basalt rock samples at seven sites in the South Pacific Gyre (SPG) were recovered by Integrated Ocean Drilling Program Expedition 329 (2010.10.8–2010.12.13). Microscopic and spectroscopic measurements on the structural Fe-redox states and the elemental composition of smectite, and polytypes of illite in the sediment at two sites (U1365 and U1369) were performed to understand the origin/formation mechanism of clay minerals in the oligotrophic open ocean. The dominant phases of clay minerals found in the present study were smectite and illite polytypes. Suggestive of non-uniform early diagenetic processes in the expansive SPG seafloor, higher ordering of illite polytypes (1 M , 2 M 1 , and 3 T ) were identified at site U1369 while disordered 1 M d illite were found at U1365. Smectites of hydrothermal origin (Al-rich beidellite, and saponite) were observed at U1369. Fe-rich montmorillonite minerals that are likely associated with the terrigenous input, were dominant at U1365. Nontronite (Fe-rich smectite) was detected at both sites. Red-brown to yellow-brown semiopaque oxide minerals (RSO) were widely distributed with Fe-rich smectite near the basaltic crust at U1365. Lower observed heat flow at U1365 relative to U1369 provides a possible explanation for the observed variability in clay mineral speciation between these two sites. The presence of K-Nontronite at the basalt/sediment interface at both sites indicates an oxidative basalt alteration; however variations in the oxidation states of structural Fe in Nontronite measured by EELS indicate that reductive environment persists locally at the basalt/sediment interface.
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biological oxidation of fe ii in reduced Nontronite coupled with nitrate reduction by pseudogulbenkiania sp strain 2002
Geochimica et Cosmochimica Acta, 2013Co-Authors: Linduo Zhao, Abinash Agrawal, Hailiang Dong, Jing Zhang, Ravi K Kukkadapu, Deng Liu, Richard E EdelmannAbstract:Abstract The importance of microbial nitrate-dependent Fe(II) oxidation to iron biogeochemistry is well recognized. Past research has focused on oxidation of aqueous Fe 2+ and structural Fe(II) in oxides, carbonates, and phosphate, but the importance of structural Fe(II) in phyllosilicates in this reaction is only recently studied. However, the effect of clay mineralogy on the rate and the mechanism of the reaction, and subsequent mineralogical end products are still poorly known. The objective of this research was to study the coupled process of microbial oxidation of Fe(II) in clay mineral Nontronite (NAu-2), and nitrate reduction by Pseudogulbenkiania species strain 2002, and to determine mineralogical changes associated with this process. Bio-oxidation experiments were conducted using Fe(II) in microbially reduced Nontronite as electron donor and nitrate as electron acceptor in bicarbonate-buffered medium under both growth and nongrowth conditions to investigate cell growth on this process. The extents of Fe(II) oxidation and nitrate reduction were measured by wet chemical methods. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and 57 Fe-Mossbauer spectroscopy were used to observe mineralogical changes associated with Fe(III) reduction and Fe(II) oxidation in NAu-2. The bio-oxidation extent under growth and nongrowth conditions reached 67% and 57%, respectively. Over the same time period, nitrate was completely reduced under both conditions to nitrogen gas (N 2 ), via an intermediate product nitrite. Abiotic oxidation by nitrite partly accelerated Fe(II) oxidation rate under the growth condition. The oxidized Fe(III) largely remained in the Nontronite structure, but secondary minerals such as vivianite, ferrihydrite, and magnetite formed depending on specific experimental conditions. The results of this study highlight the importance of iron-bearing clay minerals in the global nitrogen cycle with potential applications in nitrate removal in natural environments.
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microbial reduction of fe iii in smectite minerals by thermophilic methanogen methanothermobacter thermautotrophicus
Geochimica et Cosmochimica Acta, 2013Co-Authors: Jing Zhang, Hailiang Dong, Abinash AgrawalAbstract:Abstract Clay minerals and thermophilic methanogens can co-exist in hot anoxic environments, including the continental subsurface, geysers, terrestrial hot springs, and deep-sea hydrothermal vent systems. However, it is unclear whether thermophilic methanogens are able to reduce structural Fe(III) in clay minerals. In this study, the ability of a thermophilic methanogen Methanothermobacter thermautotrophicus to reduce structural Fe(III) in iron-rich and iron-poor smectites, (Nontronite NAu-2 and Wyoming montmorillonite SWy-2) and the relationship between iron reduction and methanogenesis were investigated. M. thermautotrophicus reduced Fe(III) in Nontronite NAu-2 and montmorillonite SWy-2 with H2/CO2 as substrate. The extent of bioreduction was 27% for Nontronite and 13–15% for montmorillonite. Anthraquinone-2,6-disulfonate (AQDS) did not enhance the extent of bioreduction, but accelerated the rate. When methanogenesis was inhibited via addition of 2-bromoethane sulfonate (BES), the extent of bioreduction decreased to 16% for NAu-2 and 9% for SWy-2. These data suggest that Fe(III) bioreduction and methanogenesis were mutually beneficial. The likely mechanism was that Fe(III) bioreduction lowered the reduction potential of the system so that methanogenesis became favorable, and methanogenesis in turn stimulated the growth of the methanogen, which enhanced Fe(III) bioreduction. NAu-2 was partly dissolved and high charge smectite and biogenic silica formed as a result of bioreduction.
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fe2 sorption onto Nontronite nau 2
Geochimica et Cosmochimica Acta, 2008Co-Authors: Hailiang Dong, Deb P Jaisi, Chongxuan Liu, Ruth E Blake, Jeremy B FeinAbstract:The sorption of ferrous iron to a clay mineral, Nontronite (NAu-2, a ferruginous smectite), was investigated under strictly anoxic conditions as a function of pH (3-10), Fe2+ concentration (0.01-50 mM), equilibration time (1 to 35 days), and ionic strength (0.01 to 0.5 M NaClO4). The surface properties of NAu-2 were independently characterized to determine its fixed charge and amphoteric site properties for the interpretation of Fe2+ sorption. Fe2+ sorption to NAu-2 was strongly dependent on pH and ionic strength, reflecting the coupled effects of Fe2+ sorption through ion exchange and surface complexation reactions. Fe2+ sorption to NAu-2 increased with increasing pH from pH 2.5 to 4.5, reached the first plateau from pH 4.5 to 7.0, increased again with increasing pH from pH 7.0 to 8.5, and reached the maximum (the second plateau) above pH 8.5. The Fe2+ sorption below pH 7.0 increased with decreasing ionic strength. The differences of Fe2+ sorption at different ionic strength, however, diminished with increasing equilibration time. The Fe2+ sorption from pH 4.5 to 7.0 increased with increasing equilibration time up to 35 days and showed stronger kinetic behavior in higher ionic strength solutions. Increasing Fe2+ concentration nonlinearly decreased Fe2+ sorption, resulting from the mass actionmore » and site saturation. An equilibrium model that integrated ion exchange, surface complexation and aqueous speciation reactions reasonably well described the Fe2+ sorption data as a function of pH, ionic strength, and Fe2+ concentration measured at 24 hours of equilibration. Model calculations showed that species Fe(OH)+ was required to describe Fe2+ sorption above pH 8.0. Model calculation also implied that the ion exchange reactions was responsible for the kinetic behavior of Fe2+ sorption. Overall, this study demonstrated that Fe2+ sorption to NAu-2 was complexly affected by equilibrium and kinetic processes.« less
Joseph W Stucki - One of the best experts on this subject based on the ideXlab platform.
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revisiting the Nontronite mossbauer spectra
American Mineralogist, 2017Co-Authors: Fabien Baron, Sabine Petit, Alain Decarreau, Martin Pentrak, Joseph W StuckiAbstract:The distribution of ferric iron (Fe 3+ ) between the octahedral and tetrahedral sheets of smectites is still an active problem due to the difficulty of identifying and quantifying the tetrahedral ferric iron ( [4] Fe 3+ ). Mossbauer spectroscopy has often been used to address this problem, with the spectra being fitted by a sum of doublets, but the empirical attribution of each doublet has failed to yield a uniform interpretation of the spectra of natural reference Fe 3+ -rich smectites, especially with regard to [4] Fe 3+ , because little consensus exists as to the [4] Fe 3+ content of natural samples. In an effort to resolve this problem, the current study was undertaken using a series of synthetic Nontronites [Si 4–x [4] Fe x 3+ ] [6] Fe 2 3+ O 10 (OH) 2 Na x with x ranging from 0.51 to 1.3. Mossbauer spectra were obtained at 298, 77, and 4 K. Statistically acceptable deconvolutions of the Mossbauer spectra at 298 and 77 K were used to develop a model of the distribution of tetrahedral substitutions, taking into account: (1) the [4] Fe 3+ content; (2) the three possible tetrahedral cationic environments around [6] Fe 3+ , i.e., [4Si]-(3 [6] Fe 3+ ), [3Si [4] Fe 3+ ]-(3 [6] Fe 3+ ), and [2Si 2 [4] Fe 3+ ]-(3 [6] Fe 3+ ); and (3) the local environment around a [4] Fe 3+ , i.e., [3Si]-(2 [6] Fe 3+ ) respecting Lowenstein’s Rule. This approach allowed the range of Mossbauer parameters for [6] Fe 3+ and [4] Fe 3+ to be determined and then applied to spectra of natural Fe 3+ -rich smectites. Results revealed the necessity of taking into account the distribution of tetrahedral cations ( [4] R 3+ ) around [6] Fe 3+ cations to deconvolute the Mossbauer spectra, and also highlighted the influence of sample crystallinity on Mossbauer parameters.
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comparisons of structural iron reduction in smectites by bacteria and dithionite ii a variable temperature mossbauer spectroscopic study of garfield Nontronite
Pure and Applied Chemistry, 2009Co-Authors: Fabiana R Ribeiro, Peter Komadel, J D Fabris, Joel E Kostka, Joseph W StuckiAbstract:The reduction of structural Fe in smectite may be mediated either abiotically by re- action with chemical reducing agents or biotically by reaction with various bacterial species. The effects of abiotic reduction on clay surface chemistry are much better known than the ef- fects of biotic reduction, and differences between them are still in need of investigation. The purpose of the present study was to compare the effects of dithionite (abiotic) and bacteria (biotic) reduction of structural Fe in Nontronite on the clay structure as observed by variable- temperature Mossbauer spectroscopy. Biotic reduction was accomplished by incubating Na-saturated Garfield Nontronite (sample API 33a) with Shewanella oneidensis strain MR-1 (Fe II /total Fe achieved was ~17 %). Partial abiotic reduction (Fe II /total Fe ~23 %) was achieved using pH-buffered sodium dithionite. The Nontronite was also reduced abiotically to Fe II /total Fe ~96 %. Parallel samples were reoxidized by bubbling O 2 gas through the re- duced suspensions at room temperature prior to Mossbauer analysis at 77 and 4 K. At 77 K, the reduction treatments all gave spectra composed of doublets for structural Fe II and Fe III in the Nontronite. The spectra for reoxidized samples were largely restored to that of the un - altered sample, except for the sample reduced to 96 %. At 4 K, the spectrum for the 96 % re- duced sample was highly complex and clearly reflected magnetic order in the sample. When partially reduced, the spectrum also exhibited magnetic order, but the features were com- pletely different depending on whether reduced biotically or abiotically. The biotically re- duced sample appeared to contain distinctly separate domains of Fe II and Fe III within the structure, whereas partial abiotic reduction produced a spectrum representative of Fe II -Fe III pairs as the dominant domain type. The 4 K spectra of the partially reduced, fully reoxidized samples were virtually the same as at 77 K, whereas reoxidation of the 96 % reduced sam- ple produced a spectrum consisting of a magnetically ordered sextet with a minor contribu- tion from a Fe II doublet, indicating significant structural alterations compared to the un - altered sample.
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structural perturbations in the solid water interface of redox transformed Nontronite
Journal of Colloid and Interface Science, 2000Co-Authors: Laibin Yan, Joseph W StuckiAbstract:Redox reactions of structural Fe affect many surface and colloidal properties of Fe-containing smectites in natural environments and many industrial systems, but few studies have examined the clay-water interface under oxidizing and reducing conditions. Infrared (FTIR) spectroscopy was used to investigate the effects of structural Fe oxidation state and hydration on layer Si-O stretching vibrations in Na-Nontronite. Aqueous gels of unaltered, reduced, and reoxidized smectites were equilibrated at different swelling pressures, Pi, and water contents, m(w)/m(c), using a miniature pressure-membrane apparatus. One part of each gel was used for the gravimetric determination of m(w)/m(c); the other was transferred to an attenuated total reflectance cell in the FTIR spectrometer, where the spectrum of the gel was measured. The frequencies of four component peaks of Si-O stretching, nu(Si-O), in Nontronite layers and of the H-O-H bending, nu(H-O-H), in the interlayer water were determined by using a curve-fitting technique. Reduction of structural Fe shifted the Si-O vibration to lower frequency and desensitized the Si-O vibration to the hydration state. A linear relation was found between nu(Si-O) and nu(H-O-H) for Nontronite in each of its various oxidation states. These observations were interpreted to mean that structural Fe oxidation state has a significant impact on interfacial processes of the aqueous colloid system of Fe-rich phyllosilicates. Copyright 2000 Academic Press.
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oxidation reduction mechanism of iron in dioctahedral smectites ii crystal chemistry of reduced garfield Nontronite
American Mineralogist, 2000Co-Authors: Alain Manceau, Victor A Drits, Will P. Gates, Bruno Lanson, D Chateigner, Dongfang Huo, Joseph W StuckiAbstract:The crystallochemical structure of reduced Garfield Nontronite was studied by X-ray absorption pre-edge and infrared (IR) spectroscopy, powder X-ray diffraction, polarized extended X-ray absorption fine structure (P-EXAFS) spectroscopy, and texture goniometry. Untreated and highly reduced (>99% of total Fe as Fe 2+ ) Nontronite samples were analyzed to determine the coordination number and the crystallographic site occupation of Fe 2+ , changes in in-plane and out-of-plane layer structure and mid-range order between Fe centers, and to monitor the changes in structural and adsorbed OH/H 2 O groups in the structure of reduced Nontronite. Contrary to earlier models predicting the formation of fivefold coordinated Fe in the structure of Nontronites upon reduction, these new results revealed that Fe maintains sixfold coordination after complete reduction. In-plane P-EXAFS evidence indicates that some of the Fe atoms occupy trans-sites in the reduced state, forming small trioctahedral domains within the structure of reduced Nontronite. Migration of Fe from cis- to trans sites during the reduction process was corroborated by simulations of X-ray diffraction patterns which revealed that about 28% of Fe 2+ cations exist in trans sites of the reduced Nontronite, rather than fully cis occupied, as in oxidized Nontronite. Out-of-plane P-EXAFS results indicated that the reduction of Fe suppressed basal oxygen corrugation typical of dioctahedral smectites, and resulted in a flat basal surface which is characteristic of trioctahedral layer silicates. IR spectra of reduced Nontronite revealed that the dioctahedral nature of the Nontronite was lost and a band near 3623 cm −1 formed, which is thought to be associated with trioctahedral [Fe 2+ ] 3 OH stretching vibrations. On the basis of these results, a structural model for the reduction mechanism of Fe 3+ to Fe 2+ in Garfield Nontronite is proposed that satisfies all structural data currently available. The migration of reduced Fe ions from cis-octahedra to adjacent trans-octahedra is accompanied by a dehydroxylation reaction due to the protonation of OH groups initially coordinated to Fe. This structural modification results in the formation of trioctahedral Fe 2+ clusters separated by clusters of vacancies in which the oxygen ligands residing at the boundary between trioctahedral and vacancy domains are greatly coordination undersaturated. The charge of these O atoms is compensated by the incorporation of protons, and by the displacement of Fe 2+ atoms from their ideal octahedral position toward the edges of trioctahedral clusters, thus accounting for the incoherency of the Fe-Fe1 and Fe-Fe2 distances. From these results, the ideal structural formula of reduced Garfield Nontronite is Na 1.30 [Si 7.22 Al 0.78 ] [Fe 2+ 3.65 Al 0.32 Mg 0.04 ]O 17.93 (OH) 5 in which the increased layer charge due to reduction of Fe 3+ to Fe 2+ is satisfied by the incorporation of protons and interlayer Na.
Deb P Jaisi - One of the best experts on this subject based on the ideXlab platform.
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fe2 sorption onto Nontronite nau 2
Geochimica et Cosmochimica Acta, 2008Co-Authors: Hailiang Dong, Deb P Jaisi, Chongxuan Liu, Ruth E Blake, Jeremy B FeinAbstract:The sorption of ferrous iron to a clay mineral, Nontronite (NAu-2, a ferruginous smectite), was investigated under strictly anoxic conditions as a function of pH (3-10), Fe2+ concentration (0.01-50 mM), equilibration time (1 to 35 days), and ionic strength (0.01 to 0.5 M NaClO4). The surface properties of NAu-2 were independently characterized to determine its fixed charge and amphoteric site properties for the interpretation of Fe2+ sorption. Fe2+ sorption to NAu-2 was strongly dependent on pH and ionic strength, reflecting the coupled effects of Fe2+ sorption through ion exchange and surface complexation reactions. Fe2+ sorption to NAu-2 increased with increasing pH from pH 2.5 to 4.5, reached the first plateau from pH 4.5 to 7.0, increased again with increasing pH from pH 7.0 to 8.5, and reached the maximum (the second plateau) above pH 8.5. The Fe2+ sorption below pH 7.0 increased with decreasing ionic strength. The differences of Fe2+ sorption at different ionic strength, however, diminished with increasing equilibration time. The Fe2+ sorption from pH 4.5 to 7.0 increased with increasing equilibration time up to 35 days and showed stronger kinetic behavior in higher ionic strength solutions. Increasing Fe2+ concentration nonlinearly decreased Fe2+ sorption, resulting from the mass actionmore » and site saturation. An equilibrium model that integrated ion exchange, surface complexation and aqueous speciation reactions reasonably well described the Fe2+ sorption data as a function of pH, ionic strength, and Fe2+ concentration measured at 24 hours of equilibration. Model calculations showed that species Fe(OH)+ was required to describe Fe2+ sorption above pH 8.0. Model calculation also implied that the ion exchange reactions was responsible for the kinetic behavior of Fe2+ sorption. Overall, this study demonstrated that Fe2+ sorption to NAu-2 was complexly affected by equilibrium and kinetic processes.« less
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partitioning of fe ii in reduced Nontronite nau 2 to reactive sites reactivity in terms of tc vii reduction
Clays and Clay Minerals, 2008Co-Authors: Hailiang Dong, Deb P Jaisi, John P MortonAbstract:Clay minerals impart important chemical properties to soils, in part, by virtue of changes in the redox state of Fe in their crystal structures. Therefore, measurement of Fe(III)/Fe(II) and partitioning of Fe(II) in different reactive sites in clay minerals (during biological and chemical Fe(III) reduction) is essential to understand their role and their relative reactivity in terms of reduction and immobilization of heavy metal contaminants such as technetium. This study had three objectives: (1) to understand the degree of dissolution of Nontronite (Fe-rich smectite) as a result of chemical and biological reduction of Fe(III) in the structure; (2) to quantify partitioning of chemically and biologically produced Fe(II) into different reactive sites in reduced Nontronite, including aqueous Fe2+, ammonium chloride-extractable Fe(II) (mainly from the ion-exchangeable sites, denoted as ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ ), sodium acetate-extractable Fe(II) (mainly from the surface complexation sites, denoted as Fe(II)acetate), and structural Fe(II) (denoted as Fe(II)str); and (3) to evaluate the reactivity of these Fe(II) species in terms of Tc(VII) reduction. Chemical and biological reduction of Fe(III) in Nontronite (NAu-2) was performed, and reduced Nontronite samples with different extents of Fe(III) reduction (1.2–71%) were prepared. The extent of reductive dissolution was measured as a function of the extent of Fe(III) reduction. Our results demonstrated that chemically and biologically produced Fe(II) in NAu-2 may be accommodated in the NAu-2 structure if the extent of Fe(III) reduction is small ( ∼30%, dissolution of Nontronite occurred with a corresponding decrease in crystallinity of residual Nontronite. The Fe(II) produced was available for partitioning into four species: ${\rm{Fe}}_{\left( {{\rm{ab}}} \right)}^{2 + }$ , Fe(II)acetate, ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ , and Fe(II)str. The increase in Fe(II)acetate during the early stages of Fe(III) reduction indicated that the Fe(II) released had the greatest affinity for the surface-complexation sites, but this site had a limited capacity (∼60 µmol of Fe(II)/g of NAu-2). The subsequent increase in ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ indicated that the released Fe(II) partitioned into the exchangeable sites once the amount of Fe at the surface-complexation sites reached half of its maximum site capacity. The fraction of Fe(II)str decreased concomitantly, as a result of Fe(II) release from the NAu-2 structure, from 100% when the extent of Fe(III) reduction was <30% to nearly 65% when the extent of Fe(III) reduction reached 71%. The Fe(II)acetate and Fe(II)str exhibited greater reactivity in terms of Tc(VII) reduction than the ${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ . Clearly, the surface-complexed and structural Fe(II) are the desirable species when reduced clay minerals are used to reduce and immobilize soluble heavy metals in contaminated groundwater and soils. These results have important implications for understanding microbe—clay mineral interactions and heavy metal immobilization in clay-rich natural environments.
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Nontronite particle aggregation induced by microbial fe iii reduction and exopolysaccharide production
Clays and Clay Minerals, 2007Co-Authors: Deb P Jaisi, Hailiang Dong, Jinwook Kim, John P MortonAbstract:Clay particle aggregation affects a number of environmental processes, such as contaminant sorption/desorption, particle movement/deposition, and sediment structure and stability, yet factors that control clay aggregation are not well understood. This study was designed to investigate how microbial reduction of Fe(III) in clay structure, a common process in soils and sediments, affects clay-particle aggregation. Microbial Fe(III) reduction experiments were conducted with Shewanella putrefaciens CN32 in bicarbonate buffer with structural Fe (III) in Nontronite as the sole electron acceptor, lactate as the sole electron donor, and AQDS as an electron shuttle. Four size fractions of Nontronite (D5–D95 of 0.12–0.22 µm, 0.41–0.69 µm, 0.73–0.96 µm and 1.42–1.78 µm) were used to evaluate size-dependent aggregation kinetics. The extent of Fe(III) bioreduction and the amount of exopolysaccharide (EPS), a major biopolymer secreted by CN32 cells during Fe(III) bioreduction, were measured with chemical methods. Nontronite particle aggregation was determined by photon correlation spectroscopy and scanning electron microscopy. The maximum extent of Fe(III) bioreduction reached 36% and 24% for the smallest and the largest size fractions, respectively. Within the same time duration, the effective diameter, measured at 95% percentile (D95), increased by a factor of 43.7 and 7.7 for these two fractions, respectively. Because there was production of EPS by CN32 cells during Fe(III) reduction, it was difficult to assess the relative role of Fe(III) bioreduction and EPS bridging in particle aggregation. Thus, additional experiments were performed. Reduction of Fe(III) by dithionite was designed to examine the effect of Fe(III) reduction, and pure EPS isolated from CN32 cells was used to examine the effect of EPS. The data showed that both Fe(III) reduction and EPS were important in promoting clay mineral aggregation. In natural environments, the relative importance of these two factors may be dependent on local conditions. These results have important implications for understanding factors in controlling clay particle aggregation in natural environments.
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control of fe iii site occupancy on the rate and extent of microbial reduction of fe iii in Nontronite
Geochimica et Cosmochimica Acta, 2005Co-Authors: Deb P Jaisi, Ravi K Kukkadapu, Dennis D Eberl, Hailiang DongAbstract:Abstract A quantitative study was performed to understand how Fe(III) site occupancy controls Fe(III) bioreduction in Nontronite by Shewanella putrefaciens CN32. NAu-1 and NAu-2 were Nontronites and contained Fe(III) in different structural sites with 16 and 23% total iron (w/w), respectively, with almost all iron as Fe(III). Mossbauer spectroscopy showed that Fe(III) was present in the octahedral site in NAu-1 (with a small amount of goethite), but in both the tetrahedral and the octahedral sites in NAu-2. Mossbauer data further showed that the octahedral Fe(III) in NAu-2 existed in at least two environments- trans (M1) and cis (M2) sites. The microbial Fe(III) reduction in NAu-1 and NAu-2 was studied in batch cultures at a Nontronite concentration of 5 mg/mL in bicarbonate buffer with lactate as the electron donor. The unreduced and bioreduced Nontronites were characterized by X-ray diffraction (XRD), Mossbauer spectroscopy, and transmission electron microscopy (TEM). In the presence of an electron shuttle, anthraquinone-2,6-disulfonate (AQDS), the extent of bioreduction was 11%–16% for NAu-1 but 28%–32% for NAu-2. The extent of reduction in the absence of AQDS was only 5%–7% for NAu-1 but 14%–18% for NAu-2. The control experiments with heat killed cells and without cells did not show any appreciable reduction (
Jing Zhang - One of the best experts on this subject based on the ideXlab platform.
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biological oxidation of fe ii in reduced Nontronite coupled with nitrate reduction by pseudogulbenkiania sp strain 2002
Geochimica et Cosmochimica Acta, 2013Co-Authors: Linduo Zhao, Abinash Agrawal, Hailiang Dong, Jing Zhang, Ravi K Kukkadapu, Deng Liu, Richard E EdelmannAbstract:Abstract The importance of microbial nitrate-dependent Fe(II) oxidation to iron biogeochemistry is well recognized. Past research has focused on oxidation of aqueous Fe 2+ and structural Fe(II) in oxides, carbonates, and phosphate, but the importance of structural Fe(II) in phyllosilicates in this reaction is only recently studied. However, the effect of clay mineralogy on the rate and the mechanism of the reaction, and subsequent mineralogical end products are still poorly known. The objective of this research was to study the coupled process of microbial oxidation of Fe(II) in clay mineral Nontronite (NAu-2), and nitrate reduction by Pseudogulbenkiania species strain 2002, and to determine mineralogical changes associated with this process. Bio-oxidation experiments were conducted using Fe(II) in microbially reduced Nontronite as electron donor and nitrate as electron acceptor in bicarbonate-buffered medium under both growth and nongrowth conditions to investigate cell growth on this process. The extents of Fe(II) oxidation and nitrate reduction were measured by wet chemical methods. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and 57 Fe-Mossbauer spectroscopy were used to observe mineralogical changes associated with Fe(III) reduction and Fe(II) oxidation in NAu-2. The bio-oxidation extent under growth and nongrowth conditions reached 67% and 57%, respectively. Over the same time period, nitrate was completely reduced under both conditions to nitrogen gas (N 2 ), via an intermediate product nitrite. Abiotic oxidation by nitrite partly accelerated Fe(II) oxidation rate under the growth condition. The oxidized Fe(III) largely remained in the Nontronite structure, but secondary minerals such as vivianite, ferrihydrite, and magnetite formed depending on specific experimental conditions. The results of this study highlight the importance of iron-bearing clay minerals in the global nitrogen cycle with potential applications in nitrate removal in natural environments.
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microbial reduction of fe iii in smectite minerals by thermophilic methanogen methanothermobacter thermautotrophicus
Geochimica et Cosmochimica Acta, 2013Co-Authors: Jing Zhang, Hailiang Dong, Abinash AgrawalAbstract:Abstract Clay minerals and thermophilic methanogens can co-exist in hot anoxic environments, including the continental subsurface, geysers, terrestrial hot springs, and deep-sea hydrothermal vent systems. However, it is unclear whether thermophilic methanogens are able to reduce structural Fe(III) in clay minerals. In this study, the ability of a thermophilic methanogen Methanothermobacter thermautotrophicus to reduce structural Fe(III) in iron-rich and iron-poor smectites, (Nontronite NAu-2 and Wyoming montmorillonite SWy-2) and the relationship between iron reduction and methanogenesis were investigated. M. thermautotrophicus reduced Fe(III) in Nontronite NAu-2 and montmorillonite SWy-2 with H2/CO2 as substrate. The extent of bioreduction was 27% for Nontronite and 13–15% for montmorillonite. Anthraquinone-2,6-disulfonate (AQDS) did not enhance the extent of bioreduction, but accelerated the rate. When methanogenesis was inhibited via addition of 2-bromoethane sulfonate (BES), the extent of bioreduction decreased to 16% for NAu-2 and 9% for SWy-2. These data suggest that Fe(III) bioreduction and methanogenesis were mutually beneficial. The likely mechanism was that Fe(III) bioreduction lowered the reduction potential of the system so that methanogenesis became favorable, and methanogenesis in turn stimulated the growth of the methanogen, which enhanced Fe(III) bioreduction. NAu-2 was partly dissolved and high charge smectite and biogenic silica formed as a result of bioreduction.
Ravi K Kukkadapu - One of the best experts on this subject based on the ideXlab platform.
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synthesis and characterization of redox active ferric Nontronite
Chemical Geology, 2017Co-Authors: Anastasia G Ilgen, Ravi K Kukkadapu, D R Dunphy, Kateryna Artyushkova, Jose M Cerrato, Jessica Nicole Kruichak, Matthew T Janish, Chengjun Sun, J M Argo, Rachel Elizabeth WashingtonAbstract:Abstract Heterogeneous redox reactions on clay mineral surfaces control mobility and bioavailability of redox-sensitive nutrients and contaminants. Iron (Fe) residing in clay mineral structures can either catalyze or directly participate in redox reactions; however, chemical controls over its reactivity are not fully understood. In our previous work we demonstrated that converting a minor portion of Fe(III) to Fe(II) (partial reduction) in the octahedral sheet of natural Fe-rich clay mineral Nontronite (NAu-1) activates its surface, making it redox-active. In this study we produced and characterized synthetic ferric Nontronite (SIP), highlighting structural and chemical similarities and differences between this synthetic Nontronite and its natural counterpart NAu-1, and probed whether mineral surface is redox-active by reacting it with arsenic As(III) under oxic and anoxic conditions. We demonstrate that synthetic Nontronite SIP undergoes the same activation as natural Nontronite NAu-1 following the partial reduction treatment. Similar to NAu-1, SIP oxidized As(III) to As(V) under both oxic (catalytic pathway) and anoxic (direct oxidation) conditions. The similar reactivity trends observed for synthetic Nontronite and its natural counterpart make SIP an appropriate analog for laboratory studies. The development of chemically pure analogs for ubiquitous soil minerals will allow for systematic research of the fundamental properties of these minerals.
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biological oxidation of fe ii in reduced Nontronite coupled with nitrate reduction by pseudogulbenkiania sp strain 2002
Geochimica et Cosmochimica Acta, 2013Co-Authors: Linduo Zhao, Abinash Agrawal, Hailiang Dong, Jing Zhang, Ravi K Kukkadapu, Deng Liu, Richard E EdelmannAbstract:Abstract The importance of microbial nitrate-dependent Fe(II) oxidation to iron biogeochemistry is well recognized. Past research has focused on oxidation of aqueous Fe 2+ and structural Fe(II) in oxides, carbonates, and phosphate, but the importance of structural Fe(II) in phyllosilicates in this reaction is only recently studied. However, the effect of clay mineralogy on the rate and the mechanism of the reaction, and subsequent mineralogical end products are still poorly known. The objective of this research was to study the coupled process of microbial oxidation of Fe(II) in clay mineral Nontronite (NAu-2), and nitrate reduction by Pseudogulbenkiania species strain 2002, and to determine mineralogical changes associated with this process. Bio-oxidation experiments were conducted using Fe(II) in microbially reduced Nontronite as electron donor and nitrate as electron acceptor in bicarbonate-buffered medium under both growth and nongrowth conditions to investigate cell growth on this process. The extents of Fe(II) oxidation and nitrate reduction were measured by wet chemical methods. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and 57 Fe-Mossbauer spectroscopy were used to observe mineralogical changes associated with Fe(III) reduction and Fe(II) oxidation in NAu-2. The bio-oxidation extent under growth and nongrowth conditions reached 67% and 57%, respectively. Over the same time period, nitrate was completely reduced under both conditions to nitrogen gas (N 2 ), via an intermediate product nitrite. Abiotic oxidation by nitrite partly accelerated Fe(II) oxidation rate under the growth condition. The oxidized Fe(III) largely remained in the Nontronite structure, but secondary minerals such as vivianite, ferrihydrite, and magnetite formed depending on specific experimental conditions. The results of this study highlight the importance of iron-bearing clay minerals in the global nitrogen cycle with potential applications in nitrate removal in natural environments.
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control of fe iii site occupancy on the rate and extent of microbial reduction of fe iii in Nontronite
Geochimica et Cosmochimica Acta, 2005Co-Authors: Deb P Jaisi, Ravi K Kukkadapu, Dennis D Eberl, Hailiang DongAbstract:Abstract A quantitative study was performed to understand how Fe(III) site occupancy controls Fe(III) bioreduction in Nontronite by Shewanella putrefaciens CN32. NAu-1 and NAu-2 were Nontronites and contained Fe(III) in different structural sites with 16 and 23% total iron (w/w), respectively, with almost all iron as Fe(III). Mossbauer spectroscopy showed that Fe(III) was present in the octahedral site in NAu-1 (with a small amount of goethite), but in both the tetrahedral and the octahedral sites in NAu-2. Mossbauer data further showed that the octahedral Fe(III) in NAu-2 existed in at least two environments- trans (M1) and cis (M2) sites. The microbial Fe(III) reduction in NAu-1 and NAu-2 was studied in batch cultures at a Nontronite concentration of 5 mg/mL in bicarbonate buffer with lactate as the electron donor. The unreduced and bioreduced Nontronites were characterized by X-ray diffraction (XRD), Mossbauer spectroscopy, and transmission electron microscopy (TEM). In the presence of an electron shuttle, anthraquinone-2,6-disulfonate (AQDS), the extent of bioreduction was 11%–16% for NAu-1 but 28%–32% for NAu-2. The extent of reduction in the absence of AQDS was only 5%–7% for NAu-1 but 14%–18% for NAu-2. The control experiments with heat killed cells and without cells did not show any appreciable reduction (
