Redox transformations of nutrients and contaminants and their bioavailability in soils are controlled by heterogeneous chemistry on mineral surfaces. Structural iron Fe(II)/Fe(III) couple in the octahedral sheet of clay minerals can directly participate in electron transfer reactions. The direction and kinetics of electron transfer was quantified in batch laboratory experiments, where we used redox active elements - arsenic (As) and antimony (Sb) - to probe the reactivity of clay structural iron as a function of Fe(II)/Fe(III) ratio in NAu-1 clay. The ability of the structural Fe(III) in NAu-1 to promote oxidation of As(III) or Sb(III) is controlled by the Fe(II)/Fe(III) ratio in clay substrate: if all structural Fe is in the oxidized Fe(III) form, no oxidation is observed; however, when the clay is partially reduced (Fe(II)/Fe total = ~0.2), NAu-1 promotes the most extensive oxidation under both oxic and anoxic conditions. Apparent surface reactivity is decreasing with time.Figure 1. Oxidation of arsenic by partially reduced nontronite NAu-1. The reactive surface sites are blocked by Fe(III) adsorption or precipitation on the clay mineral surface.

Reactivity of structural Fe(II)/Fe(III) redox couple in Fe-rich clay minerals

246th National Meeting (2013)

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