eCLAY: Redox reactivity of iron-bearing clay minerals
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.
Partners
- Michael Sander (ETHZ / IBP)
- Michelle Scherer (University of Iowa)