GEOC 129 |
| Mario Villalobos1, Brandy Toner2, Alain Manceau3, and Garrison Sposito2. (1) Environmental Bio-Geochemistry Group, Instituto de Geografía, UNAM, LAFQA, National Autonomous University of Mexico (UNAM), CU México 04510, Mexico, (2) Division of Ecosystem Sciences, UC Berkeley, 235 Hilgard Hall, Berkeley, CA 94720-3110, (3) Environmental Geochemistry Group, CNRS / University of Grenoble, LGIT - Maison des GéoSciences, Grenoble Cedex 9, 38041, France |
| Mn K-edge EXAFS spectroscopy was utilized to determine the short-range structural order of a poorly-crystalline layer type Mn oxide produced by a common soil and freshwater bacterium (Pseudomonas putida), and of its two closest synthetic analogs, δ-MnO2 and “acid birnessite”. EXAFS simulations revealed the presence of a near-neighbor O1 shell at a distance of 1.90 Å and of a Mn1 shell at 2.87 Å for all oxides. These distances are consistent with sheets formed from edge-sharing Mn(IV) octahedra. However, the number of Mn near-neighbors (N) obtained was significantly lower than the theoretical value of 6. Assuming this to be caused mainly by the presence of octahedral Mn vacancies, we used the experimental N values to estimate vacancy contents. The high vacancy values obtained are considered the main contributors to the negative structural charge borne by these oxides. |
|
Poster Session
6:00 PM-9:00 PM, Tuesday, March 30, 2004 Anaheim Convention Center -- Hall A, Poster
Division of Geochemistry |