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Du Y, Chrysochoou M. Microstructural analyses of Cr(VI) speciation in chromite ore processing residue from the soda ash process. JOURNAL OF HAZARDOUS MATERIALS 2020; 393:122385. [PMID: 32114129 DOI: 10.1016/j.jhazmat.2020.122385] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2019] [Revised: 02/19/2020] [Accepted: 02/21/2020] [Indexed: 06/10/2023]
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.
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Affiliation(s)
- Yaguang Du
- Dept. of Civil and Environmental Engineering, Univ. of Connecticut, Storrs, CT, United States.
| | - Maria Chrysochoou
- Dept. of Civil and Environmental Engineering, Univ. of Connecticut, Storrs, CT, United States.
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2
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Cohen SX, Webb SM, Gueriau P, Curis E, Bertrand L. Robust framework and software implementation for fast speciation mapping. JOURNAL OF SYNCHROTRON RADIATION 2020; 27:1049-1058. [PMID: 33566015 DOI: 10.1107/s1600577520005822] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Accepted: 04/27/2020] [Indexed: 06/12/2023]
Abstract
One of the greatest benefits of synchrotron radiation is the ability to perform chemical speciation analysis through X-ray absorption spectroscopies (XAS). XAS imaging of large sample areas can be performed with either full-field or raster-scanning modalities. A common practice to reduce acquisition time while decreasing dose and/or increasing spatial resolution is to compare X-ray fluorescence images collected at a few diagnostic energies. Several authors have used different multivariate data processing strategies to establish speciation maps. In this manuscript, the theoretical aspects and assumptions that are often made in the analysis of these datasets are focused on. A robust framework is developed to perform speciation mapping in large bulk samples at high spatial resolution by comparison with known references. Two fully operational software implementations are provided: a user-friendly implementation within the MicroAnalysis Toolkit software, and a dedicated script developed under the R environment. The procedure is exemplified through the study of a cross section of a typical fossil specimen. The algorithm provides accurate speciation and concentration mapping while decreasing the data collection time by typically two or three orders of magnitude compared with the collection of whole spectra at each pixel. Whereas acquisition of spectral datacubes on large areas leads to very high irradiation times and doses, which can considerably lengthen experiments and generate significant alteration of radiation-sensitive materials, this sparse excitation energy procedure brings the total irradiation dose greatly below radiation damage thresholds identified in previous studies. This approach is particularly adapted to the chemical study of heterogeneous radiation-sensitive samples encountered in environmental, material, and life sciences.
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Affiliation(s)
- Serge X Cohen
- Université Paris-Saclay, CNRS, Ministère de la Culture, UVSQ, IPANEMA, F-91192 Saint-Aubin, France
| | - Samuel M Webb
- Stanford Radiation Lightsource (SSRL), SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Pierre Gueriau
- Université Paris-Saclay, CNRS, Ministère de la Culture, UVSQ, IPANEMA, F-91192 Saint-Aubin, France
| | - Emmanuel Curis
- Laboratoire de Biomathématiques, EA 7537 - BioSTM, Faculté de Pharmacie de Paris - Université Paris Descartes, 4 Avenue de l'Observatoire, F-75006 Paris, France
| | - Loïc Bertrand
- Université Paris-Saclay, CNRS, Ministère de la Culture, UVSQ, IPANEMA, F-91192 Saint-Aubin, France
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3
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Liu P, Ptacek CJ, Blowes DW, Finfrock YZ, Steinepreis M, Budimir F. A Method for Redox Mapping by Confocal Micro-X-ray Fluorescence Imaging: Using Chromium Species in a Biochar Particle as an Example. Anal Chem 2019; 91:5142-5149. [DOI: 10.1021/acs.analchem.8b05718] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Peng Liu
- School of Environmental Studies, China University of Geosciences, 388 Lumo Rd., Wuhan, Hubei 430074, People’s Republic of China
- Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON N2L 3G1, Canada
| | - Carol J. Ptacek
- Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON N2L 3G1, Canada
| | - David W. Blowes
- Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON N2L 3G1, Canada
| | - Y. Zou Finfrock
- CLS@APS sector 20, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, Illinois 60439, United States
- Science Division,
Canadian Light Source, Inc., 44 Innovation Boulevard, Saskatoon, SK S7N 2 V3, Canada
| | - Mark Steinepreis
- Stantec Consulting,
Ltd., 100-300 Hagey Blvd., Waterloo, ON N2L 0A4, Canada
| | - Filip Budimir
- Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, ON N2L 3G1, Canada
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4
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Boesenberg U, Ryan CG, Kirkham R, Siddons DP, Alfeld M, Garrevoet J, Núñez T, Claussen T, Kracht T, Falkenberg G. Fast X-ray microfluorescence imaging with submicrometer-resolution integrating a Maia detector at beamline P06 at PETRA III. JOURNAL OF SYNCHROTRON RADIATION 2016; 23:1550-1560. [PMID: 27787262 DOI: 10.1107/s1600577516015289] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 09/28/2016] [Indexed: 05/20/2023]
Abstract
The high brilliance of third-generation synchrotron sources increases the demand for faster detectors to utilize the available flux. The Maia detector is an advanced imaging scheme for energy-dispersive detection realising dwell times per image-pixel as low as 50 µs and count rates higher than 10 × 106 s-1. In this article the integration of such a Maia detector in the Microprobe setup of beamline P06 at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg, Germany, is described. The analytical performance of the complete system in terms of rate-dependent energy resolution, scanning-speed-dependent spatial resolution and lower limits of detection is characterized. The potential of the Maia-based setup is demonstrated by key applications from materials science and chemistry, as well as environmental science with geological applications and biological questions that have been investigated at the P06 beamline.
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Affiliation(s)
- Ulrike Boesenberg
- Deutsches Elektronen Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
| | - Christopher G Ryan
- Commonwealth Scientific and Industrial Research Organisation (CSIRO), Clayton, Victoria, Australia
| | - Robin Kirkham
- Commonwealth Scientific and Industrial Research Organisation (CSIRO), Clayton, Victoria, Australia
| | | | - Matthias Alfeld
- Deutsches Elektronen Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
| | - Jan Garrevoet
- Deutsches Elektronen Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
| | - Teresa Núñez
- Deutsches Elektronen Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
| | - Thorsten Claussen
- Deutsches Elektronen Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
| | - Thorsten Kracht
- Deutsches Elektronen Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
| | - Gerald Falkenberg
- Deutsches Elektronen Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg, Germany
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5
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Chrysochoou M, Johnston CP. Polysulfide speciation and reactivity in chromate-contaminated soil. JOURNAL OF HAZARDOUS MATERIALS 2015; 281:87-94. [PMID: 25092639 DOI: 10.1016/j.jhazmat.2014.07.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 07/08/2014] [Accepted: 07/12/2014] [Indexed: 06/03/2023]
Abstract
Calcium polysulfide (CPS) has been observed to maintain a reducing capacity for prolonged time periods when used to treat Cr(VI)-contaminated soils. This study utilized bulk and micro-X-ray absorption near edge structure (XANES) spectroscopy to investigate sulfur speciation in soil samples treated with CPS in batch and column studies and to determine the source of the reducing potential. Bulk XANES spectra indicated the presence of two dominant sulfur species: elemental sulfur, which is the product of the sulfide-chromate redox reaction, and thiosulfate (S2O3(2-)). Micro-XANES analyses confirmed these findings and showed that elemental sulfur precipitated as large particles, while thiosulfate was diffused within the soil grains and thus available to react with chromate that leached from slowly dissolving PbCrO4. Micro-X-ray fluorescence (μXRF) analyses indicated a close association of Pb and thiosulfate, so that PbS2O3 is a likely sink for thiosulfate, accounting for up to 20% of the total S added. Sorption of thiosulfate on iron oxides below pH 8 is a second retention mechanism for thiosulfate in the solid. Given that thiosulfate cannot reduce chromate but can reduce solid-bound Fe(III) under neutral pH conditions, it is hypothesized that ferrous iron production is an additional mechanism to maintain reductive conditions in CPS-treated soils.
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Affiliation(s)
- Maria Chrysochoou
- Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269, USA.
| | - Chad P Johnston
- Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269, USA
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Boesenberg U, Marcus MA, Shukla AK, Yi T, McDermott E, Teh PF, Srinivasan M, Moewes A, Cabana J. Asymmetric pathways in the electrochemical conversion reaction of NiO as battery electrode with high storage capacity. Sci Rep 2014; 4:7133. [PMID: 25410966 PMCID: PMC4238016 DOI: 10.1038/srep07133] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Accepted: 11/04/2014] [Indexed: 11/09/2022] Open
Abstract
Electrochemical conversion reactions of transition metal compounds create opportunities for large energy storage capabilities exceeding modern Li-ion batteries. However, for practical electrodes to be envisaged, a detailed understanding of their mechanisms is needed, especially vis-à-vis the voltage hysteresis observed between reduction and oxidation. Here, we present such insight at scales from local atomic arrangements to whole electrodes. NiO was chosen as a simple model system. The most important finding is that the voltage hysteresis has its origin in the differing chemical pathways during reduction and oxidation. This asymmetry is enabled by the presence of small metallic clusters and, thus, is likely to apply to other transition metal oxide systems. The presence of nanoparticles also influences the electrochemical activity of the electrolyte and its degradation products and can create differences in transport properties within an electrode, resulting in localized reactions around converted domains that lead to compositional inhomogeneities at the microscale.
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Affiliation(s)
- Ulrike Boesenberg
- 1] Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA [2] Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, D-22607 Hamburg, Germany
| | - Matthew A Marcus
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Alpesh K Shukla
- Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Tanghong Yi
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Eamon McDermott
- Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SK, Canada
| | - Pei Fen Teh
- 1] Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA [2] School of Materials Science and Engineering, Nanyang Technological University, Singapore
| | - Madhavi Srinivasan
- School of Materials Science and Engineering, Nanyang Technological University, Singapore
| | - Alexander Moewes
- Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SK, Canada
| | - Jordi Cabana
- 1] Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA [2] Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
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Tack P, Garrevoet J, Bauters S, Vekemans B, Laforce B, Van Ranst E, Banerjee D, Longo A, Bras W, Vincze L. Full-Field Fluorescence Mode Micro-XANES Imaging Using a Unique Energy Dispersive CCD Detector. Anal Chem 2014; 86:8791-7. [DOI: 10.1021/ac502016b] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Pieter Tack
- X-ray
Microspectroscopy and Imaging Group (XMI), Ghent University, Krijgslaan
281 S12, B-9000 Ghent, Belgium
| | - Jan Garrevoet
- X-ray
Microspectroscopy and Imaging Group (XMI), Ghent University, Krijgslaan
281 S12, B-9000 Ghent, Belgium
| | - Stephen Bauters
- X-ray
Microspectroscopy and Imaging Group (XMI), Ghent University, Krijgslaan
281 S12, B-9000 Ghent, Belgium
| | - Bart Vekemans
- X-ray
Microspectroscopy and Imaging Group (XMI), Ghent University, Krijgslaan
281 S12, B-9000 Ghent, Belgium
| | - Brecht Laforce
- X-ray
Microspectroscopy and Imaging Group (XMI), Ghent University, Krijgslaan
281 S12, B-9000 Ghent, Belgium
| | - Eric Van Ranst
- Department
of Geology and Soil Science (WE13), Ghent University, Krijgslaan
281 S8, B-9000 Ghent, Belgium
| | - Dipanjan Banerjee
- European
Synchrotron Radiation Facility (ESRF), DUBBLE-CRG, FR-38043 Grenoble
Cedex, France
| | - Alessandro Longo
- European
Synchrotron Radiation Facility (ESRF), DUBBLE-CRG, FR-38043 Grenoble
Cedex, France
| | - Wim Bras
- European
Synchrotron Radiation Facility (ESRF), DUBBLE-CRG, FR-38043 Grenoble
Cedex, France
| | - Laszlo Vincze
- X-ray
Microspectroscopy and Imaging Group (XMI), Ghent University, Krijgslaan
281 S12, B-9000 Ghent, Belgium
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8
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Brinza L, Schofield PF, Hodson ME, Weller S, Ignatyev K, Geraki K, Quinn PD, Mosselmans JFW. Combining µXANES and µXRD mapping to analyse the heterogeneity in calcium carbonate granules excreted by the earthworm Lumbricus terrestris. JOURNAL OF SYNCHROTRON RADIATION 2014; 21:235-41. [PMID: 24365942 PMCID: PMC3874023 DOI: 10.1107/s160057751303083x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Accepted: 11/09/2013] [Indexed: 05/28/2023]
Abstract
The use of fluorescence full spectral micro-X-ray absorption near-edge structure (µXANES) mapping is becoming more widespread in the hard energy regime. This experimental method using the Ca K-edge combined with micro-X-ray diffraction (µXRD) mapping of the same sample has been enabled on beamline I18 at Diamond Light Source. This combined approach has been used to probe both long- and short-range order in calcium carbonate granules produced by the earthworm Lumbricus terrestris. In granules produced by earthworms cultured in a control artificial soil, calcite and vaterite are observed in the granules. However, granules produced by earthworms cultivated in the same artificial soil amended with 500 p.p.m. Mg also contain an aragonite. The two techniques, µXRD and µXANES, probe different sample volumes but there is good agreement in the phase maps produced.
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Affiliation(s)
- Loredana Brinza
- Science Division, Diamond Light Source, Harwell Campus, Didcot, Oxon OX11 0DE, UK
| | - Paul F. Schofield
- Mineral and Planetary Sciences Division, Natural History Museum, Cromwell Road, London SW7 5BD, UK
| | - Mark E. Hodson
- Environment Department, University of York, York YO10 5DD, UK
| | - Sophie Weller
- Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
| | - Konstantin Ignatyev
- Science Division, Diamond Light Source, Harwell Campus, Didcot, Oxon OX11 0DE, UK
| | - Kalotina Geraki
- Science Division, Diamond Light Source, Harwell Campus, Didcot, Oxon OX11 0DE, UK
| | - Paul D. Quinn
- Science Division, Diamond Light Source, Harwell Campus, Didcot, Oxon OX11 0DE, UK
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9
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Singer DM, Fox PM, Guo H, Marcus MA, Davis JA. Sorption and redox reactions of As(III) and As(V) within secondary mineral coatings on aquifer sediment grains. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:11569-11576. [PMID: 24041305 DOI: 10.1021/es402754f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Important reactive phenomena that affect the transport and fate of many elements occur at the mineral-water interface (MWI), including sorption and redox reactions. Fundamental knowledge of these phenomena are often based on observations of ideal mineral-water systems, for example, studies of molecular scale reactions on single crystal faces or the surfaces of pure mineral powders. Much less is understood about MWI in natural environments, which typically have nanometer to micrometer scale secondary mineral coatings on the surfaces of primary mineral grains. We examined sediment grain coatings from a well-characterized field site to determine the causes of rate limitations for arsenic (As) sorption and redox processes within the coatings. Sediments were obtained from the USGS field research site on Cape Cod, MA, and exposed to synthetic contaminated groundwater solutions. Uptake of As(III) and As(V) into the coatings was studied with a combination of electron microscopy and synchrotron techniques to assess concentration gradients and reactive processes, including electron transfer reactions. Transmission electron microscopy (TEM) and X-ray microprobe (XMP) analyses indicated that As was primarily associated with micrometer- to submicrometer aggregates of Mn-bearing nanoparticulate goethite. As(III) oxidation by this phase was observed but limited by the extent of exposed surface area of the goethite grains to the exterior of the mineral coatings. Secondary mineral coatings are potentially both sinks and sources of contaminants depending on the history of a contaminated site, and may need to be included explicitly in reactive transport models.
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Affiliation(s)
- David M Singer
- Earth Sciences Division, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States
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Mitchell S, Michels NL, Majano G, Pérez-Ramírez J. Advanced visualization strategies bridge the multidimensional complexity of technical catalysts. Curr Opin Chem Eng 2013. [DOI: 10.1016/j.coche.2013.04.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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11
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Zeng T, Arnold WA, Toner BM. Microscale characterization of sulfur speciation in lake sediments. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:1287-96. [PMID: 23282039 DOI: 10.1021/es303914q] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Prairie pothole lakes (PPLs) are naturally sulfur-enriched wetlands in the glaciated prairie region of North America. High sulfate levels and dynamic hydrogeochemistry in combination render PPLs a unique environment to explore the speciation of sedimentary sulfur (S). The goals of this research were to define and quantify the solid-phase S pools in PPL sediments and track seasonal dynamics of S speciation. A quantitative X-ray microprobe method was developed based on S 1s X-ray absorption near-edge structure (XANES) spectroscopy and multienergy X-ray fluorescence mapping. Three S pools-pyritic S, reduced organic S (organic mono- and disulfide), and oxidized S (inorganic sulfate, ester sulfate, and sulfonate)-were identified in PPL sediments. No significant seasonal variation was evident for total S, but S speciation showed a seasonal response. During the spring-summer transition, the reduced organic S decreased from 55 to 15 mol %, with a concomitant rise in the oxidized S. During the summer-fall transition, the trend reversed and the reduced organic S grew to 75 mol % at the expense of the oxidized S. The pyritic S, on the other hand, remained relatively constant (∼22 mol %) over time. The seasonal changes in S speciation have strong potential to force the cycling of elements such as mercury in prairie wetlands.
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Affiliation(s)
- Teng Zeng
- Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive Southeast, Minneapolis, Minnesota 55455, United States
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12
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Majumdar S, Peralta-Videa JR, Castillo-Michel H, Hong J, Rico CM, Gardea-Torresdey JL. Applications of synchrotron μ-XRF to study the distribution of biologically important elements in different environmental matrices: A review. Anal Chim Acta 2012; 755:1-16. [DOI: 10.1016/j.aca.2012.09.050] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2012] [Revised: 09/24/2012] [Accepted: 09/30/2012] [Indexed: 10/27/2022]
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13
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Chrysochoou M, Johnston CP, Dahal G. A comparative evaluation of hexavalent chromium treatment in contaminated soil by calcium polysulfide and green-tea nanoscale zero-valent iron. JOURNAL OF HAZARDOUS MATERIALS 2012; 201-202:33-42. [PMID: 22169240 DOI: 10.1016/j.jhazmat.2011.11.003] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2011] [Revised: 10/28/2011] [Accepted: 11/02/2011] [Indexed: 05/31/2023]
Abstract
A column study for hexavalent chromium (Cr(VI)) removal from contaminated soil was performed using calcium polysulfide (CPS) and nanoscale zero-valent iron stabilized with green tea extract (GT-nZVI). Injection of CPS at 12 times the stoichiometric requirement (12×) resulted in quantitative Cr(VI) removal for up to 195 days of equivalent groundwater flow. Solid-bound Cr(VI) was reduced up to >99% (<2mg/kg). Treatment with CPS resulted in a short-term release of high sulfur concentrations. Injections of 12× and 24× stoichiometric GT-nZVI resulted in decrease in leachate pH from 6 to 2.5, which rebounded to 4.5 after the equivalent of 45 days and remained stable for the next equivalent 3 years. Metals concentrations in the effluent (Pb, Cr and Fe) increased following injection and quickly decreased, such that the mass flux was low with respect to the total amounts in the solid. Aqueous Cr(VI) was non-detect for the majority of the monitoring time, but concentrations eventually increased with respect to the control sample. Solid-bound Cr(VI) concentrations decreased by 30% and 66% in the 12× and 24× treatments, respectively. The low efficiency was attributed to increased sorption to iron surfaces at pH 2.5 and slow dissolution of PbCrO4, both of which were identified by micro-X-ray fluorescence and absorption analyses.
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Affiliation(s)
- Maria Chrysochoou
- University of Connecticut, Department of Civil and Environmental Engineering, Storrs, CT 06269, United States.
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14
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Mayhew LE, Webb SM, Templeton AS. Microscale imaging and identification of Fe speciation and distribution during fluid-mineral reactions under highly reducing conditions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2011; 45:4468-4474. [PMID: 21517061 DOI: 10.1021/es104292n] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The oxidation state, speciation, and distribution of Fe are critical determinants of Fe reactivity in natural and engineered environments. However, it is challenging to follow dynamic changes in Fe speciation in environmental systems during progressive fluid-mineral interactions. Two common geological and aquifer materials-basalt and Fe(III) oxides-were incubated with saline fluids at 55 °C under highly reducing conditions maintained by the presence of Fe(0). We tracked changes in Fe speciation after 48 h (incipient water-rock reaction) and 10 months (extensive water-rock interaction) using synchrotron-radiation μXRF maps collected at multiple energies (ME) within the Fe K-edge. Immediate PCA analysis of the ME maps was used to optimize μXANES analyses; in turn, refitting the ME maps with end-member XANES spectra enabled us to detect and spatially resolve the entire variety of Fe-phases present in the system. After 48 h, we successfully identified and mapped the major Fe-bearing components of our samples (Fe(III) oxides, basalt, and rare olivine), as well as small quantities of incipient brucite associated with olivine. After 10 months, the Fe(III)-oxides remained stable in the presence of Fe(0), whereas significant alteration of basalt to minnesotaite and chlinochlore had occurred, providing new insights into heterogeneous Fe speciation in complex geological media under highly reducing conditions.
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Affiliation(s)
- L E Mayhew
- Department of Geological Sciences, UCB 399, University of Colorado, Boulder, Colorado 80309, USA.
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