Borer, P. ., Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich , Zurich, Switzerland, paul.borer@env.ethz.ch
Sulzberger, B. ., Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dubendorf, Switzerland, barbara.sulzberger@eawag.ch
Hug, S. J., Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dubendorf, Switzerland, stephan.hug@eawag.ch
Kraemer, S. M., Department of Environmental Geosciences, University of Vienna, Vienna, Austria, stephan.kraemer@univie.ac.at
Kretzschmar, R. ., Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, Switzerland, ruben.kretzschmar@env.ethz.ch

PHOTOREDUCTIVE DISSOLUTION OF LEPIDOCROCITE AND OTHER IRON (HYDR)OXIDES IN THE ABSENCE OF ORGANIC LIGANDS: EXPERIMENTAL STUDIES AND KINETIC MODELING

Photoreductive dissolution of lepidocrocite (gamma-FeOOH) was investigated in the absence of organic ligands. The formation of dissolved Fe(II) was observed under irradiation with artificial sunlight up to pH 6. Combined irradiation/dark experiments at pH 3 revealed that after the light source was turned off, dissolved Fe(II) was reoxidized on a timescale of minutes/hours in aerated suspensions. The presence of H2O2 was confirmed by additional measurements. A kinetic model for photoreductive dissolution of lepidocrocite was developed, which was based on the assumption that photolysis of Fe(III)-hydroxo groups at the surface of lepidocrocite leads to the formation of surface Fe(II) and OH radicals. The model suggests that H2O2 can only be formed in considerable amounts if the surface-catalyzed reoxidation of Fe(II), incorporated in the lattice surface structure, by molecular O2 is much faster than the corresponding reoxidation of adsorbed Fe(II). Additional photodissolution experiments conducted in the presence of radical scavengers or an iron-binding ligand (desferrioxamine B) showed that photodissolution of crystalline Fe(III) (hydr)oxide phases can be significanty enhanced and also occurs at seawater pH.

Oral presentation

Presentation is given by student: Yes
Session #:SS01
Date: Friday, June 13, 2008
Time: 10:30 AM

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