GEOC 158 |
| Mario Villalobos, Environmental Bio-Geochemistry Group, Instituto de Geografía, UNAM, LAFQA, National Autonomous University of Mexico (UNAM), CU México 04510, Mexico, Garrison Sposito, Division of Ecosystem Sciences, UC Berkeley, 235 Hilgard Hall, Berkeley, CA 94720-3110, and J. R. Bargar, Stanford Synchrotron Radiation Laboratory, PO BOX 4349, Stanford, CA 94309. |
| Macroscopic Pb(II) uptake experiments and Pb L3-edge EXAFS spectroscopy were combined to determine the modes of Pb(II) sequestration by a biogenic Mn oxide and its synthetic analogs. Relatively fast Pb(II) sorption was observed as well as extremely high sorption capacities, which are inconsistent with a purely surface phenomenon. EXAFS spectra simulations revealed a similar uptake mechanism regardless of the specific nature of the phyllomanganate, electrolyte background, total Pb(II) loading, or equilibration time. Two main Pb-O and Pb-Mn shells at distances of 2.30 Å and 3.74 Å were found, respectively. However, rather low numbers of Mn near-neighbors (N) were obtained (2 < N < 3), supporting the occurrence of a combination of bonding mechanisms involving a triple-corner sharing complex above/below cationic sheet vacancies (N theoretical=6), and a double corner sharing complex at particle edges on singly-coordinated dangling –O bonds (N theoretical=2). These results account for the widely noted relatively high affinity of environmental manganese oxides for Pb(II). |
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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 |