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Redox Reactivity of Iron-Bearing Clay Minerals

English title Redox Reactivity of Iron-Bearing Clay Minerals
Applicant Hofstetter Thomas
Number 129476
Funding scheme Project funding
Research institution Umweltchemie Eawag
Institution of higher education Swiss Federal Institute of Aquatic Science and Technology - EAWAG
Main discipline Other disciplines of Environmental Sciences
Start/End 01.06.2010 - 31.05.2012
Approved amount 252'064.00
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All Disciplines (2)

Discipline
Other disciplines of Environmental Sciences
Geochemistry

Keywords (8)

iron; electrochemistry; biogeochemistry; pollutant dynamics; redox reactions; clay minerals; compound-specific isotope analysis; Mössbauer spectroscopy

Lay Summary (English)

Lead
Lay summary
Iron is the most abundant redox-active element in the Earth's crust and the Fe(II)/Fe(III) redox couple plays a key role in biogeochemical cycles and pollutant dynamics. While the reactivity of iron in iron oxides and its implications for subsurface redox processes have been studied extensively, little is known on the contributions of reactive iron in clay minerals to the toxicity, mobility, and persistence of contaminants. Despite the importance of iron redox processes of clay minerals, few studies have characterized iron-bearing minerals with respect to redox properties thus compromising a general assessment of the availability and reactivity of structural iron in clays. Here, we propose a comprehensive approach that aims at quantifying the thermodynamic parameters as well as the redox capacities and kinetics of iron oxidation and reduction in a broad set of clay minerals. Our experimental setup makes use of novel electrochemical techniques for the mediated electrochemical reduction and oxidation using soluble radical redox mediators to facilitate electron transfer between the structural iron in a clay mineral and an electrode. Using Mössbauer spectroscopy, we will explore the binding and structural arrangement of iron in the clay lattice that gives rise to the electrochemically determined redox properties. Finally, these insights will be applied to establish an understanding of how the electrochemical properties of the characterized iron-bearing clay minerals determine their reactivity in the environment with electron transfer shuttles of biogeochemical relevance and important organic soil and groundwater contaminants.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
ACS National Meeting, GEOC Division, Session on "Redox Transformations of Metals in Sediments at Molecular to Pore Scales" 25.03.2012 San Diego, CA, USA
International Workshop on Uranium biogeochemistry: transformations and applications 11.03.2012 Ascona, Switzerland
ACS National Meeting, GEOC Division, Session on "Electron Transfer at Mineral Surfaces and Biogeochemical Implications" 28.08.2011 Denver, CO, USA
Goldschmidt 2011 "Chemical and microbial electron transfer processes at mineral surfaces " 14.08.2011 Prague, Czech Republic
Ninth international symposium on "Geochemistry of the Earth's Surface" 02.06.2011 Boulder, CO, USA


Knowledge transfer events

Active participation

Title Type of contribution Date Place Persons involved
4th Swiss Bentonite Meeting / Nagra 24.06.2011 Bern


Associated projects

Number Title Start Funding scheme
135515 Humic substance redox properties and redox reactions with oxygen 01.01.2012 Project funding
149283 Characterization of the redox properties of iron minerals by combined electrochemical and spectroscopic analyses 01.01.2015 Project funding
159692 Dissolved phenols in ombrotrophic bogs: occurrence and enzymatic transformations 01.01.2016 Project funding

Abstract

Iron is the most abundant redox-active element in the Earth’s crust and the Fe(II)/Fe(III) redox couple plays a key role in biogeochemical cycles and pollutant dynamics. While the reactivity of iron in iron oxides and its implications for subsurface redox processes have been studied extensively and are well understood, little is known on the contributions of reactive iron in clay minerals to mobility, persistence, and toxicity of contaminants. Despite the importance of iron redox processes of clay minerals, few studies have characterized iron-bearing clay minerals with respect to their redox properties, thus compromising a general assessment of the availability and reactivity of structural iron in clays. Here, we propose a comprehensive approach that aims at quantifying the reduction potentials of structural iron as well as the redox capacities and kinetics of iron oxidation and reduction in a broad set of clay minerals. Our experimental setup makes use of novel electrochemical techniques that allow for direct chronocoulometric quantification of reductively and oxidatively transferred electrons and coupled protons. Soluble radical redox mediators will be used to facilitate electron transfer between the structural iron in a clay mineral and the working electrode. Using Mössbauer spectroscopy, we will explore the molecular-level binding and structural arrangement of iron in the clay lattice that gives rise to the electrochemically determined redox properties. Finally, these insights will be used to establish an understanding of how the electrochemical properties of the characterized iron-bearing clay minerals determine their reactivity in the environment towards electron transfer shuttles of biogeochemical relevance and important organic contaminants. The proposed project will be carried out by a postdoctoral researcher and will allow the host institution to deepen and to expand its national and international collaborations.
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