GEOC 155 |
| Peter J. Heaney1, Jeffrey E. Post2, Christina Lopano1, Sridhar Komarneni3, and Jonathan C. Hanson4. (1) Department of Geosciences, Pennsylvania State University, 309 Deike Bldg, University Park, PA 16802, (2) Department of Mineral Sciences, Smithsonian Institution, 10th Street and Constitution Avenue, NW, Washington, DC 20560-0119, (3) Dept. of Crop and Soil Sciences, The Pennsylvania State University, 205 Materials Research Lab, University Park, PA 16802, (4) Department of Chemistry, Brookhaven National Laboratory, Upton, NY 11973 |
| Biogenically precipitated Mn oxide minerals commonly display layered or tunneled structural topologies that promote aqueous cation exchange. These isomorphic substitutions often ensure a greater persistence than surface sorption in the extraction of dissolved cations from contaminated fluids, since diadochic replacement can lead to structural transformations that stabilize the exchanged solid. Using time-resolved powder synchrotron X-ray diffraction, we have observed the replacement of cations in layer structures (e.g., birnessite, buserite) by variable concentrations of dissolved transition metals (e.g., Ni, Zn) and proxies for radioisotopes (e.g., Ba, Rb, Cs). These experiments have documented the rapid kinetics of ion exchange, and they have provided a mechanistic understanding of the highly selective exchange process. Using Rietveld analysis of our XRD data, we have mapped systematic positional shifts among the interlayer species during the exchange reactions and the framework distortions that accompany interlayer reconfiguration. |
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Microbially Mediated Manganese and Iron Oxidation in the Biosphere
1:45 PM-6:20 PM, Wednesday, March 31, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |