51
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Usman M, Byrne JM, Chaudhary A, Orsetti S, Hanna K, Ruby C, Kappler A, Haderlein SB. Magnetite and Green Rust: Synthesis, Properties, and Environmental Applications of Mixed-Valent Iron Minerals. Chem Rev 2018; 118:3251-3304. [PMID: 29465223 DOI: 10.1021/acs.chemrev.7b00224] [Citation(s) in RCA: 182] [Impact Index Per Article: 30.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Mixed-valent iron [Fe(II)-Fe(III)] minerals such as magnetite and green rust have received a significant amount of attention over recent decades, especially in the environmental sciences. These mineral phases are intrinsic and essential parts of biogeochemical cycling of metals and organic carbon and play an important role regarding the mobility, toxicity, and redox transformation of organic and inorganic pollutants. The formation pathways, mineral properties, and applications of magnetite and green rust are currently active areas of research in geochemistry, environmental mineralogy, geomicrobiology, material sciences, environmental engineering, and environmental remediation. These aspects ultimately dictate the reactivity of magnetite and green rust in the environment, which has important consequences for the application of these mineral phases, for example in remediation strategies. In this review we discuss the properties, occurrence, formation by biotic as well as abiotic pathways, characterization techniques, and environmental applications of magnetite and green rust in the environment. The aim is to present a detailed overview of the key aspects related to these mineral phases which can be used as an important resource for researchers working in a diverse range of fields dealing with mixed-valent iron minerals.
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Affiliation(s)
- M Usman
- Environmental Mineralogy, Center for Applied Geosciences , University of Tübingen , 72074 Tübingen , Germany.,Institute of Soil and Environmental Sciences , University of Agriculture , Faisalabad 38040 , Pakistan
| | - J M Byrne
- Geomicrobiology, Center for Applied Geosciences , University of Tübingen , 72074 Tübingen , Germany
| | - A Chaudhary
- Environmental Mineralogy, Center for Applied Geosciences , University of Tübingen , 72074 Tübingen , Germany.,Department of Environmental Science and Engineering , Government College University Faisalabad 38000 , Pakistan
| | - S Orsetti
- Environmental Mineralogy, Center for Applied Geosciences , University of Tübingen , 72074 Tübingen , Germany
| | - K Hanna
- Univ Rennes, École Nationale Supérieure de Chimie de Rennes , CNRS, ISCR - UMR6226 , F-35000 Rennes , France
| | - C Ruby
- Laboratoire de Chimie Physique et Microbiologie pour l'Environnement , UMR 7564 CNRS-Université de Lorraine , 54600 Villers-Lès-Nancy , France
| | - A Kappler
- Geomicrobiology, Center for Applied Geosciences , University of Tübingen , 72074 Tübingen , Germany
| | - S B Haderlein
- Environmental Mineralogy, Center for Applied Geosciences , University of Tübingen , 72074 Tübingen , Germany
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52
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Hens T, Brugger J, Cumberland SA, Etschmann B, Frierdich AJ. Recrystallization of Manganite (γ-MnOOH) and Implications for Trace Element Cycling. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:1311-1319. [PMID: 29325415 DOI: 10.1021/acs.est.7b05710] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The recrystallization of Mn(III,IV) oxides is catalyzed by aqueous Mn(II) (Mn(II)aq) during (bio)geochemical Mn redox cycling. It is poorly understood how trace metals associated with Mn oxides (e.g., Ni) are cycled during such recrystallization. Here, we use X-ray absorption spectroscopy (XAS) to examine the speciation of Ni associated with Manganite (γ-Mn(III)OOH) suspensions in the presence or absence of Mn(II)aq under variable pH conditions (pH 5.5 and 7.5). In a second set of experiments, we used a 62Ni isotope tracer to quantify the amount of dissolved Ni that exchanges with Ni incorporated in the Manganite crystal structure during reactions in 1 mM Mn(II)aq and in Mn(II)-free solutions. XAS spectra show that Ni is initially sorbed on the Manganite mineral surface and is progressively incorporated into the mineral structure over time (13% after 51 days) even in the absence of dissolved Mn(II). The amount of Ni incorporation significantly increases to about 40% over a period of 51 days when Mn(II)aq is present in solution. Similarly, Mn(II)aq promotes Ni exchange between Ni-substituted Manganite and dissolved Ni(II), with around 30% of Ni exchanged at pH 7.5 over the duration of the experiment. No new mineral phases are detected following recrystallization as determined by X-ray diffraction and XAS. Our results reveal that Mn(II)-catalyzed mineral recrystallization partitions Ni between Mn oxides and aqueous fluids and can therefore affect Ni speciation and mobility in the environment.
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Affiliation(s)
- Tobias Hens
- School of Earth, Atmosphere & Environment, Monash University , Clayton, Victoria 3800, Australia
| | - Joël Brugger
- School of Earth, Atmosphere & Environment, Monash University , Clayton, Victoria 3800, Australia
| | - Susan A Cumberland
- School of Earth, Atmosphere & Environment, Monash University , Clayton, Victoria 3800, Australia
- Australian Synchrotron , Clayton, Victoria 3168, Australia
| | - Barbara Etschmann
- School of Earth, Atmosphere & Environment, Monash University , Clayton, Victoria 3800, Australia
| | - Andrew J Frierdich
- School of Earth, Atmosphere & Environment, Monash University , Clayton, Victoria 3800, Australia
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53
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Aeppli M, Voegelin A, Gorski CA, Hofstetter TB, Sander M. Mediated Electrochemical Reduction of Iron (Oxyhydr-)Oxides under Defined Thermodynamic Boundary Conditions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:560-570. [PMID: 29200267 DOI: 10.1021/acs.est.7b04411] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Iron (oxyhydr-)oxide reduction has been extensively studied because of its importance in pollutant redox dynamics and biogeochemical processes. Yet, experimental studies linking oxide reduction kinetics to thermodynamics remain scarce. Here, we used mediated electrochemical reduction (MER) to directly quantify the extents and rates of ferrihydrite, goethite, and hematite reduction over a range of negative reaction free energies, ΔrG, that were obtained by systematically varying pH (5.0 to 8.0), applied reduction potentials (-0.53 to -0.17 V vs SHE), and Fe2+ concentrations (up to 40 μM). Ferrihydrite reduction was complete and fast at all tested ΔrG values, consistent with its comparatively low thermodynamic stability. Reduction of the thermodynamically more stable goethite and hematite changed from complete and fast to incomplete and slow as ΔrG values became less negative. Reductions at intermediate ΔrG values showed negative linear correlations between the natural logarithm of the reduction rate constants and ΔrG. These correlations imply that thermodynamics controlled goethite and hematite reduction rates. Beyond allowing to study iron oxide reduction under defined thermodynamic conditions, MER can also be used to capture changes in iron oxide reducibility during phase transformations, as shown for Fe2+-facilitated transformation of ferrihydrite to goethite.
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Affiliation(s)
- Meret Aeppli
- Institute of Biogeochemistry and Pollutant Dynamics, Swiss Federal Institute of Technology (ETH) , 8092 Zurich, Switzerland
- Swiss Federal Institute of Aquatic Science and Technology (Eawag) , 8600 Duebendorf, Switzerland
| | - Andreas Voegelin
- Swiss Federal Institute of Aquatic Science and Technology (Eawag) , 8600 Duebendorf, Switzerland
| | - Christopher A Gorski
- Department of Civil and Environmental Engineering, Pennsylvania State University, University Park , Pennsylvania 16802, United States
| | - Thomas B Hofstetter
- Swiss Federal Institute of Aquatic Science and Technology (Eawag) , 8600 Duebendorf, Switzerland
| | - Michael Sander
- Institute of Biogeochemistry and Pollutant Dynamics, Swiss Federal Institute of Technology (ETH) , 8092 Zurich, Switzerland
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54
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Schaefer MV, Handler RM, Scherer MM. Fe(II) reduction of pyrolusite (β-MnO 2) and secondary mineral evolution. GEOCHEMICAL TRANSACTIONS 2017; 18:7. [PMID: 29209871 PMCID: PMC5716966 DOI: 10.1186/s12932-017-0045-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Accepted: 11/27/2017] [Indexed: 05/05/2023]
Abstract
Iron (Fe) and manganese (Mn) are the two most common redox-active elements in the Earth's crust and are well known to influence mineral formation and dissolution, trace metal sequestration, and contaminant transformations in soils and sediments. Here, we characterized the reaction of aqueous Fe(II) with pyrolusite (β-MnO2) using electron microscopy, X-ray diffraction, aqueous Fe and Mn analyses, and 57Fe Mössbauer spectroscopy. We reacted pyrolusite solids repeatedly with 3 mM Fe(II) at pH 7.5 to evaluate whether electron transfer occurs and to track the evolving reactivity of the Mn/Fe solids. We used Fe isotopes (56 and 57) in conjunction with 57Fe Mössbauer spectroscopy to isolate oxidation of Fe(II) by Fe(III) precipitates or pyrolusite. Using these complementary techniques, we determined that Fe(II) is initially oxidized by pyrolusite and that lepidocrocite is the dominant Fe oxidation product. Additional Fe(II) exposures result in an increasing proportion of magnetite on the pyrolusite surface. Over a series of nine 3 mM Fe(II) additions, Fe(II) continued to be oxidized by the Mn/Fe particles suggesting that Mn/Fe phases are not fully passivated and remain redox active even after extensive surface coverage by Fe(III) oxides. Interestingly, the initial Fe(III) oxide precipitates became further reduced as Fe(II) was added and additional Mn was released into solution suggesting that both the Fe oxide coating and underlying Mn phase continue to participate in redox reactions when freshly exposed to Fe(II). Our findings indicate that Fe and Mn chemistry is influenced by sustained reactions of Fe(II) with Mn/Fe oxides.
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Affiliation(s)
| | - Robert M. Handler
- Sustainable Futures Institute, Michigan Technological University, Houghton, MI 49931 USA
| | - Michelle M. Scherer
- Civil and Environmental Engineering, University of Iowa, Iowa City, IA 52242 USA
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55
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Huhmann BL, Neumann A, Boyanov MI, Kemner KM, Scherer MM. Emerging investigator series: As(v) in magnetite: incorporation and redistribution. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2017; 19:1208-1219. [PMID: 28871292 DOI: 10.1039/c7em00237h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Exposure to As in groundwater negatively impacts millions of people around the globe, and As mobility in groundwater is often controlled by Fe mineral dissolution and precipitation. Additionally, trace elements can be released from and incorporated into the structure of Fe oxides in the presence of dissolved Fe(ii). The potential for As to redistribute between sorbed on the magnetite surface and incorporated in the magnetite structure, however, remains unclear. In this study, we use selective chemical extraction and X-ray absorption spectroscopy (XAS) to distinguish magnetite-sorbed and incorporated As(v) and to provide evidence for As(v) incorporation during magnetite precipitation. While As in the As-magnetite coprecipitates did not redistribute between sorbed and incorporated over a 4 month period, a small, but measurable increase in incorporated As(v) of up to 13% was observed for sorbed As(v). We suggest that Fe(ii)-catalyzed recrystallization of magnetite did not significantly influence the redistribution of sorbed As(v) because the extent of Fe atom exchange was small (∼10%). In addition, the extent of As redistribution was the same in the absence and presence of added aqueous Fe(ii), suggesting that aqueous Fe(ii) had, overall, a minor effect on As redistribution for both coprecipitated and sorbed As(v). Our results suggest that coprecipitation of As(v) with magnetite and redistribution of As(v) sorbed on magnetite are potential pathways for irreversible As(v) uptake and sequestration. These pathways are likely to play a significant role in controlling As mobility in natural systems, during human-induced redox cycling of groundwater such as aquifer storage and recovery, as well as in iron oxide-based As removal systems.
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Affiliation(s)
- Brittany L Huhmann
- Department of Civil and Environmental Engineering, University of Iowa, Iowa City, IA 52242, USA
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56
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Joshi P, Fantle MS, Larese-Casanova P, Gorski CA. Susceptibility of Goethite to Fe 2+-Catalyzed Recrystallization over Time. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:11681-11691. [PMID: 28895726 DOI: 10.1021/acs.est.7b02603] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Recent work has shown that iron oxides, such as goethite and hematite, may recrystallize in the presence of aqueous Fe2+ under anoxic conditions. This process, referred to as Fe2+-catalyzed recrystallization, can influence water quality by causing the incorporation/release of environmental contaminants and biological nutrients. Accounting for the effects of Fe2+-catalyzed recrystallization on water quality requires knowing the time scale over which recrystallization occurs. Here, we tested the hypothesis that nanoparticulate goethite becomes less susceptible to Fe2+-catalyzed recrystallization over time. We set up two batches of reactors in which 55Fe2+ tracer was added at two different time points and tracked the 55Fe partitioning in the aqueous and goethite phases over 60 days. Less 55Fe uptake occurred between 30 and 60 days than between 0 and 30 days, suggesting goethite recrystallization slowed with time. Fitting the data with a box model indicated that 17% of the goethite recrystallized after 30 days of reaction, and an additional 2% recrystallized between 30 and 60 days. The decreasing susceptibility of goethite to recrystallize as it reacted with aqueous Fe2+ suggested that recrystallization is likely only an important process over short time scales.
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Affiliation(s)
- Prachi Joshi
- Department of Civil & Environmental Engineering, Pennsylvania State University , 212 Sackett Building, University Park, Pennsylvania 16802, United States
| | - Matthew S Fantle
- Department of Geosciences, Pennsylvania State University , 212 Deike Building, University Park, Pennsylvania 16802, United States
| | - Philip Larese-Casanova
- Department of Civil & Environmental Engineering, Snell Engineering Center, Northeastern University , 360 Huntington Avenue, Boston, Massachusetts 02115, United States
| | - Christopher A Gorski
- Department of Civil & Environmental Engineering, Pennsylvania State University , 212 Sackett Building, University Park, Pennsylvania 16802, United States
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57
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Zarzycki P, Rosso KM. Stochastic Simulation of Isotopic Exchange Mechanisms for Fe(II)-Catalyzed Recrystallization of Goethite. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:7552-7559. [PMID: 28602094 DOI: 10.1021/acs.est.7b01491] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Understanding Fe(II)-catalyzed transformations of Fe(III)-(oxyhydr)oxides is critical for correctly interpreting stable isotopic distributions and for predicting the fate of metal ions in the environment. Recent Fe isotopic tracer experiments have shown that goethite undergoes rapid recrystallization without phase change when exposed to aqueous Fe(II). The proposed explanation is oxidation of sorbed Fe(II) and reductive Fe(II) release coupled 1:1 by electron conduction through crystallites. Given the availability of two tracer exchange data sets that explore pH and particle size effects (e.g., Handler et al. Environ. Sci. Technol. 2014 , 48 , 11302 - 11311 ; Joshi and Gorski Environ. Sci. Technol. 2016 , 50 , 7315 - 7324 ), we developed a stochastic simulation that exactly mimics these experiments, while imposing the 1:1 constraint. We find that all data can be represented by this model, and unifying mechanistic information emerges. At pH 7.5 a rapid initial exchange is followed by slower exchange, consistent with mixed surface- and diffusion-limited kinetics arising from prominent particle aggregation. At pH 5.0 where aggregation and net Fe(II) sorption are minimal, that exchange is quantitatively proportional to available particle surface area and the density of sorbed Fe(II) is more readily evident. Our analysis reveals a fundamental atom exchange rate of ∼10-5 Fe nm-2 s-1, commensurate with some of the reported reductive dissolution rates of goethite, suggesting Fe(II) release is the rate-limiting step in the conduction mechanism during recrystallization.
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Affiliation(s)
- Piotr Zarzycki
- Energy Geoscience Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
- Institute of Physical Chemistry, Polish Academy of Sciences , 01-224 Warsaw, Poland
| | - Kevin M Rosso
- Pacific Northwest National Laboratory, Richland, Washington 99354, United States
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58
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ThomasArrigo LK, Mikutta C, Byrne J, Kappler A, Kretzschmar R. Iron(II)-Catalyzed Iron Atom Exchange and Mineralogical Changes in Iron-rich Organic Freshwater Flocs: An Iron Isotope Tracer Study. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:6897-6907. [PMID: 28590131 DOI: 10.1021/acs.est.7b01495] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In freshwater wetlands, organic flocs are often found enriched in trace metal(loid)s associated with poorly crystalline Fe(III)-(oxyhydr)oxides. Under reducing conditions, flocs may become exposed to aqueous Fe(II), triggering Fe(II)-catalyzed mineral transformations and trace metal(loid) release. In this study, pure ferrihydrite, a synthetic ferrihydrite-polygalacturonic acid coprecipitate (16.7 wt % C), and As- (1280 and 1230 mg/kg) and organic matter (OM)-rich (18.1 and 21.8 wt % C) freshwater flocs dominated by ferrihydrite and nanocrystalline lepidocrocite were reacted with an isotopically enriched 57Fe(II) solution (0.1 or 1.0 mM Fe(II)) at pH 5.5 and 7. Using a combination of wet chemistry, Fe isotope analysis, X-ray absorption spectroscopy (XAS), 57Fe Mössbauer spectroscopy and X-ray diffraction, we followed the Fe atom exchange kinetics and secondary mineral formation over 1 week. When reacted with Fe(II) at pH 7, pure ferrihydrite exhibited rapid Fe atom exchange at both Fe(II) concentrations, reaching 76 and 89% atom exchange in experiments with 0.1 and 1 mM Fe(II), respectively. XAS data revealed that it transformed into goethite (21%) at the lower Fe(II) concentration and into lepidocrocite (73%) and goethite (27%) at the higher Fe(II) concentration. Despite smaller Fe mineral particles in the coprecipitate and flocs as compared to pure ferrihydrite (inferred from Mössbauer-derived blocking temperatures), these samples showed reduced Fe atom exchange (9-30% at pH 7) and inhibited secondary mineral formation. No release of As was recorded for Fe(II)-reacted flocs. Our findings indicate that carbohydrate-rich OM in flocs stabilizes poorly crystalline Fe minerals against Fe(II)-catalyzed transformation by surface-site blockage and/or organic Fe(II) complexation. This hinders the extent of Fe atom exchange at mineral surfaces and secondary mineral formation, which may consequently impair Fe(II)-activated trace metal(loid) release. Thus, under short-term Fe(III)-reducing conditions facilitating the fast attainment of solid-solution equilibria (e.g., in stagnant waters), Fe-rich freshwater flocs are expected to remain an effective sink for trace elements.
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Affiliation(s)
- Laurel K ThomasArrigo
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich , Universitätstrasse 16, CH-8092 Zurich, Switzerland
| | - Christian Mikutta
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich , Universitätstrasse 16, CH-8092 Zurich, Switzerland
| | - James Byrne
- Geomicrobiology Group, Centre for Applied Geosciences (ZAG), University of Tübingen , Sigwartstrasse 10, D-72076, Tübingen, Germany
| | - Andreas Kappler
- Geomicrobiology Group, Centre for Applied Geosciences (ZAG), University of Tübingen , Sigwartstrasse 10, D-72076, Tübingen, Germany
| | - Ruben Kretzschmar
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich , Universitätstrasse 16, CH-8092 Zurich, Switzerland
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59
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Joshi P, Gorski CA. Anisotropic Morphological Changes in Goethite during Fe(2+)-Catalyzed Recrystallization. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:7315-24. [PMID: 27345864 DOI: 10.1021/acs.est.6b00702] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
When goethite is exposed to aqueous Fe(2+), rapid and extensive Fe atom exchange can occur between solid-phase Fe(3+) and aqueous Fe(2+) in a process referred to as Fe(2+)-catalyzed recrystallization. This process can lead to the structural incorporation or release of trace elements, which has important implications for contaminant remediation and nutrient biogeochemical cycling. Prior work found that the process did not cause major changes to the goethite structure or morphology. Here, we further investigated if and how goethite morphology and aggregation behavior changed temporally during Fe(2+)-catalyzed recrystallization. On the basis of existing literature, we hypothesized that Fe(2+)-catalyzed recrystallization of goethite would not result in changes to individual particle morphology or interparticle interactions. To test this, we reacted nanoparticulate goethite with aqueous Fe(2+) at pH 7.5 over 30 days and used transmission electron microscopy (TEM), cryogenic TEM, and (55)Fe as an isotope tracer to observe changes in particle dimensions, aggregation, and isotopic composition over time. Over the course of 30 days, the goethite particles substantially recrystallized, and the particle dimensions changed anisotropically, resulting in a preferential increase in the mean particle width. The temporal changes in goethite morphology could not be completely explained by a single mineral-transformation mechanism but rather indicated that multiple transformation mechanisms occurred concurrently. Collectively, these results demonstrate that the morphology of goethite nanoparticles does change during recrystallization, which is an important step toward identifying the driving force(s) of recrystallization.
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Affiliation(s)
- Prachi Joshi
- Department of Civil & Environmental Engineering, Pennsylvania State University , 212 Sackett Building, University Park, Pennsylvania 16802, United States
| | - Christopher A Gorski
- Department of Civil & Environmental Engineering, Pennsylvania State University , 212 Sackett Building, University Park, Pennsylvania 16802, United States
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60
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Frierdich AJ, Spicuzza MJ, Scherer MM. Oxygen Isotope Evidence for Mn(II)-Catalyzed Recrystallization of Manganite (γ-MnOOH). ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:6374-6380. [PMID: 27249316 DOI: 10.1021/acs.est.6b01463] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Manganese is biogeochemically cycled between aqueous Mn(II) and Mn(IV) oxides. Aqueous Mn(II) often coexists with Mn(IV) oxides, and redox reactions between the two (e.g., comproportionation) are well known to result in the formation of Mn(III) minerals. It is unknown, however, whether aqueous Mn(II) exchanges with structural Mn(III) in manganese oxides in the absence of any mineral transformation (similar to what has been reported for aqueous Fe(II) and some Fe(III) minerals). To probe whether atoms exchange between a Mn(III) oxide and water, we use a (17)O tracer to measure oxygen isotope exchange between structural oxygen in manganite (γ-MnOOH) and water. In the absence of aqueous Mn(II), about 18% of the oxygen atoms in manganite exchange with the aqueous phase, which is close to the estimated surface oxygen atoms (∼11%). In the presence of aqueous Mn(II), an additional 10% (for a total of 28%) of the oxygen atoms exchange with water, suggesting that some of the bulk manganite mineral (i.e., beyond surface) is exchanging with the fluid. Exchange of manganite oxygen with water occurs without any observable change in mineral phase and appears to be independent of the rapid Mn(II) sorption kinetics. These experiments suggest that Mn(II) catalyzes manganese oxide recrystallization and illustrate a new pathway by which these ubiquitous minerals interact with their surrounding fluid.
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Affiliation(s)
- Andrew J Frierdich
- School of Earth, Atmosphere & Environment, Monash University , Clayton, VIC 3800, Australia
| | - Michael J Spicuzza
- Department of Geoscience, University of Wisconsin , Madison, Wisconsin 53706, United States
| | - Michelle M Scherer
- Department of Civil and Environmental Engineering, University of Iowa , Iowa City, Iowa 52242, United States
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61
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Lan Y, Butler EC. Iron-Sulfide-Associated Products Formed during Reductive Dechlorination of Carbon Tetrachloride. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:5489-5497. [PMID: 27138348 DOI: 10.1021/acs.est.5b06154] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This paper investigated the mackinawite (FeS)-associated products formed during reaction between FeS and carbon tetrachloride (CT) at pH 7 and 8. At pH 8, reaction of FeS with CT led to formation of abundant spherical particles with diameters between 50 and 400 nm on the FeS surface and in solution; far fewer such particles were observed at pH 7. Analysis of the FeS surface by energy dispersive X-ray spectroscopy after reaction with CT at pH 8 showed decreased sulfur and elevated oxygen compared to unreacted FeS. The spherical particles that formed upon FeS reaction with CT were mostly amorphous with localized areas of poorly crystalline two-line ferrihydrite. X-ray photoelectron spectroscopy indicated that the predominant Fe surface species after reaction with CT at pH 8 was Fe(III)-O, consistent with ferrihydrite and other amorphous iron (hydr)oxides as major products. Powder X-ray diffraction analysis suggested formation of greigite upon reaction of FeS with CT at pH 7. Both ferrihydrite and Fe(2+), which is a product of greigite dissolution, can react with dissolved HS(-) to form FeS, suggesting that, after oxidation by chlorinated aliphatics, FeS can be regenerated by addition or microbial generation of sulfide.
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Affiliation(s)
- Ying Lan
- School of Civil Engineering and Environmental Science, University of Oklahoma , Norman, Oklahoma 73019, United States
| | - Elizabeth C Butler
- School of Civil Engineering and Environmental Science, University of Oklahoma , Norman, Oklahoma 73019, United States
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62
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Martin S, Shchukarev A, Hanna K, Boily JF. Kinetics and Mechanisms of Ciprofloxacin Oxidation on Hematite Surfaces. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:12197-12205. [PMID: 26419340 DOI: 10.1021/acs.est.5b02851] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Adsorption of antibiotics at mineral surfaces has been extensively studied over the past 20 years, yet much remains to be learned on their interfacial properties and transformation mechanisms. In this study, interactions of Ciprofloxacin (CIP), a fluoroquinolone antibiotic with two sets of synthetic nanosized hematite particles, with relatively smooth (H10, 10-20 nm in diameter) and roughened (H80, 80-90 nm in diameter) surfaces, were studied by means of liquid chromatography (LC), mass spectrometry (MS), and spectroscopy (vibration and X-ray photoelectron). Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy provides evidence for inner-sphere bidentate complex formation of CIP at hematite surfaces in 0.01 M NaCl, irrespective of pH and particle size. ATR-FTIR spectroscopy also revealed that the sorbed mother CIP molecule decayed to other surface species over a period of at least 65 h. This was supported by the detection of three daughter products in the aqueous phase by LC/MS. The appearance of NH3(+) groups during the course of these experiments, revealed by cryogenic XPS, provides further evidence that CIP oxidation proceeds through an opening of piperazine ring via N-dealkylation. Additional in vacuo FTIR experiments under temperature-programmed desorption also showed that oxidation of sorbed byproducts were effectively degraded beyond 450 °C, a result denoting considerably strong (inter)molecular bonds of both mother and daughter products. This work also showed that rougher, possibly multidomainic particles (H80) generated slower rates of CIP decomposition but occurring through more complex schemes than at smoother particle surfaces (H10). This work thus uncovered key aspects of the binding of an important antibiotic at iron oxide surfaces, and therefore provided additional constraints to our growing understanding of the fate of emerging contaminants in the environment.
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Affiliation(s)
- Sébastien Martin
- Ecole Nationale Supérieure de Chimie de Rennes, UMR CNRS 6226 , 11 Allée de Beaulieu, F-35708 Rennes Cedex 7, France
- Department of Chemistry, Umeå University , Umeå, SE-901 87, Sweden
| | | | - Khalil Hanna
- Ecole Nationale Supérieure de Chimie de Rennes, UMR CNRS 6226 , 11 Allée de Beaulieu, F-35708 Rennes Cedex 7, France
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