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Characterization of the redox properties of iron minerals by combined electrochemical and spectroscopic analyses

English title Characterization of the redox properties of iron minerals by combined electrochemical and spectroscopic analyses
Applicant Hofstetter Thomas
Number 149283
Funding scheme Project funding
Research institution Swiss Federal Institute of Aquatic Science and Technology (EAWAG)
Institution of higher education Swiss Federal Institute of Aquatic Science and Technology - EAWAG
Main discipline Geochemistry
Start/End 01.01.2015 - 31.12.2018
Approved amount 506'083.00
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All Disciplines (4)

Discipline
Geochemistry
Hydrology, Limnology, Glaciology
Other disciplines of Environmental Sciences
Pedology

Keywords (8)

microbial iron reduction; clay minerals; iron; iron oxides; pollutant dynamics; redox thermodynamics; biogeochemistry; electrochemistry

Lay Summary (German)

Lead
Eisen kommt in Böden und Sedimenten in verschiedenen Mineralien wie z.B. Goethit oder Hämatit vor und spielt eine wichtige Rolle im Kohlenstoffkreislauf und für die Mobilität und Toxizität von Schadstoffen. Die Redox-Reaktivität von eisenhaltigen Mineralien hängt davon ab, ob das Eisen in dreiwertiger (FeIII) oder zweiwertiger Form (FeII) vorliegt, wie es in der Mineralstruktur gebunden ist, und ob es Elektronentransferreaktionen eingehen kann.So können beispielsweise Mikroorganismen unter sauerstoffarmen Bedingungen amorphe Eisenmineralien besser veratmen als kristalline in dem sie FeIII zu FeII reduzieren und dabei das Mineral auflösen. Eine Quantifizierung dieser Redoxeigenschaften von eisenhaltigen Mineralien in der Umwelt ist aber trotz guter Kenntnis der Mineralstruktur noch nicht möglich.
Lay summary

Im vorliegenden Projekt geht es darum, die Redoxeigenschaften typischer eisenhaltiger Mineralien wie Eisenoxiden und eisenhaltigen Tonmineralien zu quantifizieren. Weil Elektronentransferreaktionen mit mehreren parallel ablaufenden Reaktionen an der Mineraloberfläche und Änderungen der Mineralphasen einhergehen können sind typische Parameter wie Standard-Reduktionspotentiale schwierig zu bestimmen und zu interpretieren. Diesen Herausforderungen wollen wir mit neuen elektrochemischen Methoden in Kombination mit spektroskopischer Mineralcharakterisierung begegnen. In Laborexperimenten werden wir damit die Veränderung der Redoxeigenschaften von Eisenmineralien beschreiben können, die durch mikrobielle Reduktion von FeIII zu FeII hervorgerufen werden.

Unsere Erkenntnisse ermöglichen ein besseres Verständnis von Redoxprozessen an welchen eisenhaltige Mineralien beteiligt sind. Beispiele hierfür sind die Mineralisierung von organischem Kohlenstoff unter sauerstoffarmen Bedingungen in Böden und Mooren oder die Retention von toxischen Metallen in Deponien und Endlagern. Damit liefert unser Projekt wichtige Informationen, welche zur fundierten Beurteilung in Klima- und Endlagerfragen benötigt werden.

 

Direct link to Lay Summary Last update: 01.09.2014

Responsible applicant and co-applicants

Employees

Publications

Publication
Electrochemical Analysis of Changes in Iron Oxide Reducibility during Abiotic Ferrihydrite Transformation into Goethite and Magnetite
Aeppli Meret, Kaegi Ralf, Kretzschmar Ruben, Voegelin Andreas, Hofstetter Thomas B., Sander Michael (2019), Electrochemical Analysis of Changes in Iron Oxide Reducibility during Abiotic Ferrihydrite Transformation into Goethite and Magnetite, in Environmental Science {&} Technology, 0.
Linking Thermodynamics to Pollutant Reduction Kinetics by Fe 2+ Bound to Iron Oxides
Stewart Sydney M., Hofstetter Thomas B., Joshi Prachi, Gorski Christopher A. (2018), Linking Thermodynamics to Pollutant Reduction Kinetics by Fe 2+ Bound to Iron Oxides, in Environmental Science & Technology, 52(10), 5600-5609.
Mediated Electrochemical Reduction of Iron (Oxyhydr-)Oxides under Defined Thermodynamic Boundary Conditions
Aeppli Meret, Voegelin Andreas, Gorski Christopher A., Hofstetter Thomas B., Sander Michael (2018), Mediated Electrochemical Reduction of Iron (Oxyhydr-)Oxides under Defined Thermodynamic Boundary Conditions, in Environmental Science & Technology, 52(2), 560-570.
Thermodynamic Characterization of Iron Oxide–Aqueous Fe 2+ Redox Couples
Gorski Christopher A., Edwards Rebecca, Sander Michael, Hofstetter Thomas B., Stewart Sydney M. (2016), Thermodynamic Characterization of Iron Oxide–Aqueous Fe 2+ Redox Couples, in Environmental Science & Technology, 50(16), 8538-8547.

Collaboration

Group / person Country
Types of collaboration
Christopher Gorski / Penn State Univerity United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Ralf Kägi Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Michael Plötze / Institute of Geotechnical Engineering ETH Zürich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
Ruben Kretzschmar Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Synchrotron ESRF France (Europe)
- Research Infrastructure
Bart Baeyens / Paul Scherrer Institute Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
Synchrotron ANKA Germany (Europe)
- Research Infrastructure
Jonathan Llyod / University of Manchester Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Exchange of personnel

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Symposium on "Clay mineral redox chemistry and the disposal of radioactive waste", Utrecht University, Individual talk Characterization of the Redox Properties of Iron Minerals by Electrochemical Analyses 23.11.2018 Utrecht, Netherlands Hofstetter Thomas;
Gordon Research Conference (GRC) on Environmental Science Water Poster Fe(II)-induced transformation of ferrihydrite: Linking iron oxide reducibility to mineralogy 25.06.2018 Holderness NH, United States of America Aeppli Meret;
Gordon Research Conference (GRC) on Environmental Science Water Poster Linking Thermodynamics to Pollutant Reduction Kinetics by Fe 2+ Bound to Iron Oxides 25.06.2018 Holderness NH, United States of America Hofstetter Thomas;
Gordon Research Seminar (GRS) on Environmental Science Water Poster Fe(II)-induced transformation of ferrihydrite: Linking iron oxide reducibility to mineralogy 23.06.2018 Holderness, NH, United States of America Aeppli Meret;
Interfaces Against Pollution IAP18 Talk given at a conference Ferrous-iron induced transformation of ferrihydrite: Linking changes in oxide mineralogy and reducibility 10.06.2018 Montpellier, France Aeppli Meret;
Inst. of Biogeochemistry & Pollutant Dynamics (IBP) PhD congress 2018 Poster Fe(II)-induced transformation of ferrihydrite: Linking iron oxide reducibility to mineralogy 06.04.2018 Zürich, Switzerland Aeppli Meret;
American Chemical Society 255th National Meeting, Division of Geochemistry Talk given at a conference Mediated electrochemical reduction of iron (oxyhydr-)oxides under defined thermodynamic boundary conditions 18.03.2018 New Orleans, LA, United States of America Hofstetter Thomas;
The 9th National Conference on Environmental Chemistry (NCEC) Talk given at a conference Characterization of the Redox Properties of Iron Minerals by Electrochemical Analyses 18.10.2017 Hangzhou, China Hofstetter Thomas;
Goldschmidt conference 2017, session on "Biotic and abviotic iron redox transformations in natural and engineered systems" Talk given at a conference Electrochemical Characterisation of Microbial Fe(III) Reduction 13.08.2017 Paris, France Brown Ashley;
Goldschmidt conference 2017, session on "Biotic and abviotic iron redox transformations in natural and engineered systems" Talk given at a conference Assessing Iron Oxide Reduction Using Mediated Electrochemical Analysis 13.08.2017 Paris, France Aeppli Meret;
International Conference on the Biogeochemistry of Trace Elements (ICOBTE) Talk given at a conference Electrochemical analysis of electron transfer to iron(oxyhydr-)oxides: effects of solution pH and reduction potential 16.07.2017 Zürich, Switzerland Aeppli Meret;
International Conference on the Biogeochemistry of Trace Elements (ICOBTE) Poster Electrochemical characterisation of microbial Fe(III) reduction 16.07.2017 Zürich, Switzerland Brown Ashley;
Inst. of Biogeochemistry & Pollutant Dynamics (IBP) PhD congress 2017 Talk given at a conference Investigating iron oxide reduction using mediated electrochemical analysis 21.04.2017 Dübendorf, Switzerland Aeppli Meret;
European Mineralogical Congress Talk given at a conference Reductive dissolution of iron(oxyhydr)oxides assessed by mediated electrochemical analysis 15.09.2016 Rimini, Italy Aeppli Meret; Brown Ashley;
European Mineralogical Congress Talk given at a conference Electrochemical characterisation of microbial iron oxide reduction 11.09.2016 Rimini, Italy Brown Ashley; Aeppli Meret;
Inst. of Biogeochemistry & Pollutant Dynamics (IBP) PhD congress 2016 Poster Reductive dissolution of iron (oxyhydr)oxides assessed by mediated electrochemistry 01.04.2016 Zürich, Switzerland Aeppli Meret;


Awards

Title Year
Silbermedaille der ETH Zürich für ausgezeichnete Doktorarbeiten 2019
2017 Chemistry Travel Award by SCNAT and SCS 2017

Associated projects

Number Title Start Funding scheme
159692 Dissolved phenols in ombrotrophic bogs: occurrence and enzymatic transformations 01.01.2016 Project funding
152993 Iron(III) precipitates formed by iron(II) oxidation in natural waters: Structure, reactivity and impact on arsenic 01.04.2014 Project funding
129476 Redox Reactivity of Iron-Bearing Clay Minerals 01.06.2010 Project funding
135515 Humic substance redox properties and redox reactions with oxygen 01.01.2012 Project funding

Abstract

Electron transfer reactions involving Fe3+/Fe2+ couples associated with iron (oxyhydr-)oxides and iron-bearing clay minerals play a key role in biogeochemical redox cycles and affect the availability, mobility, persistence, and toxicity of trace elements and many organic and inorganic contaminants. The iron in the-se minerals can serve as both electron acceptor and electron donor in abiotic and biotic reactions. Electron transfer to Fe3+ minerals is thought to affect the formation of carbon dioxide and methane in anoxic envi-ronments and therefore has implications for global warming. Despite the importance of Fe (oxyhydr-)oxides and Fe-bearing clay minerals as redox-active geochemical phases, their fundamental redox proper-ties have been investigated in only a few experimental studies. The characterization of the redox proper-ties is both conceptually and experimentally challenging. The conceptual challenges arise from the fact that electron transfer to/from Fe minerals is linked to other processes such as the adsorption and desorp-tion of Fe2+, precipitation reactions, and mineral re-crystallization. Experimental work using traditional electrochemical approaches is confronted with redox-nonequilibria and slow electron transfer kinetics be-tween electrodes and the Fe minerals. The work proposed herein aims at overcoming these challenges by combining mediated electrochemical analysis with spectroscopic studies. With this approach, we will char-acterize the redox properties of a series of different Fe (oxyhydr-)oxides and clay mineral specimen prior to and after their abiotic and biotic reduction. The proposed work will be carried out by one PhD student (focus on the Fe (oxyhydr-)oxides) and a postdoctoral researcher (focus on clay minerals).Mediated electrochemical analysis relies on water-soluble redox mediators to facilitate electron transfer and redox equilibration between the Fe minerals and working and redox electrodes. We will use mediated electrochemical reduction and oxidation (MER & MEO) to (i) directly quantify the total number of elec-trons that are accepted (i.e., reduction of Fe3+ to Fe2+) and donated (i.e., oxidation of Fe2+ to Fe3+) by a given Fe mineral sample as a function of the applied potential and solution pH, (ii) to follow changes in the re-dox states (i.e., ratio of Fe2+ to Fe3+) of Fe minerals when reacted with dissolved Fe2+ and when incubated with the iron-reducing bacteria Shewanella oneidensis MR-1 and Geobacter sulfureducens, and, (iii) for the clay mineral specimens, to determine their apparent reduction potentials (i.e., the potential at which there is an equimolar ratio of Fe2+ to Fe3+ in the clay) as a function of solution pH. The MER and MEO experiments will be complemented by mediated potentiometric EH measurements of the Fe minerals, both in their un-reacted forms and after reaction with dissolved Fe2+ and after incubation with iron reducing bacteria. This work will result in a compilation of EH ranges over which the tested Fe minerals accept/donate electrons from/to abiotic and biotic reaction partners. This thermodynamic data will provide a basis on which to incorporate Fe minerals into models describing biogeochemical and pollutant redox reactions. Finally, Mössbauer and X-ray absorption spectroscopy and X-ray diffraction analyses will be employed to charac-terize structural alterations in the Fe minerals during reaction with dissolved Fe2+ and during incubation with iron reducing bacteria. The combined electrochemical and spectroscopic analysis will allow us to link macroscopically measured redox properties to the molecular binding environments of mineral-associated iron.
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