Project

Discipline

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

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

Active participation

Active participation

Number	Title	Start	Funding scheme

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.