The role of iron oxide surfaces in biogeochemistry

Theme 1

Lepidocrocite_PollokThe surfaces of iron minerals are known to mediate a number of biogeochemical reactions. Adsorption of a reactive species can alter the coordination sphere of a surface bound species through bond weakening, which is in many reactions mediated by electron transfer processes. As a consequence Fe2+ detaches and is being released into the solution.

Recent findings suggest that Fe2+ interferes with the bulk mineral to generate new and potentially highly reactive mineral phases at the surface, the mechanisms of which are completely unknown. Understanding the role of Fe2+ at iron oxide surfaces is therefore a key to understand the biogeochemistry of iron.


Based on the currently available experimental data and observations made both in well defined systems and in the field, several knowledge gaps are evident regarding the nature and dynamics of electron transfer processes at iron mineral surfaces:

  • The mineralogy of iron mineral phases formed from reduction of Fe(III) and oxidation of Fe(II) on minerals by various reactants are not well characterized.
  • The geochemical controls on the mineral formation and evolution are not well understood.
  • The natures of surface properties, how surface chemistry changes, transient intermediate phases, and steady-state endpoints are unknown.

57Fe Mössbauer spectroscopy has turned out to be a powerful tool in studying these questions. It allows to directly observe the chemical nature of 57Fe atoms without disturbing the geochemical environment of the sample. Of all Fe isotopes, Mössbauer is sensitive only to 57Fe and invisible to other Fe isotopes. Mössbauer spectroscopy offers also other practical advantages including the preservation of wet, anoxic conditions and sensitivity to adsorbed, amorphous, and particulate Fe forms without any sample matrix effects.

Research Theme 1 supports activities aimed at unravelling biogeochemical processes at the mineral surfaces of iron oxide minerals.


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last modified 2010-03-05