John Villinski won the "Association of Environmental Engineering and Science Professors Award for Best Student Presentation" of the Environmental Chemistry Division of the American Chemical Society Symposium "Chemical Speciation and Reactivity in Water Chemistry and Water Technology: A Symposium in Honor of James J. Morgan" at the 220th American Chemical Society National Meeting. The abstract for his presentation follows.
REDUCTIVE DISSOLUTION OF MnO2 BY Fe(II): EFFECTS OF CHEMICAL GRADIENTS AND INTERMEDIATE PHASE STRUCTURAL INFORMATION.
John E. Villinski1, Peggy A. O'Day2, John R. Bargar3 and Martha H. Conklin1 1Department of Hydrology and Water Resources, The University of Arizona, Tucson, AZ 85721-0011, 2Geology Department, Arizona State University, Tempe, AZ, 85287 3Stanford Synchrotron Radiation Laboratory, PO Box 4349, MS 69, Stanford, CA 94309
An in situ, real-time, synchrotron X-ray absorption spectroscopy study of the reductive dissolution of MnO2 be Fe(II) at pH 3 was performed in a novel flow-through reaction cell at SSRL. While the path length was only 7 mm, different results were obtained from collecting spectra at the inlet (upgradient) and downgradient portions of the bed. Analysis of XAS spectra indicated that Mn(IV) reduction occurred without a detectable presence of a reaction intermediate phase upgradient. Both XANES and pre-edge spectra indicated an intermediate phase containing tetrahedrally-coordinated Mn, and most likely Fe(III), was present downgradient. This is consistent with the observed advection and precipitation of Fe(III). The absorbance of the intermediate phase reached a constant value after 30 minutes of a 2 hour experiment, and thus the intermediate phase appears to exert control over the release of Mn(II) to solution. By probing different regions of a mineral-solution reaction path spectroscopically, a more complete picture of the reactions controlling the reductive dissolution is obtained.