HR: 08:30h
AN: B21A-03    [PDF]
TI: Structural Characterization of Biogenic Manganese Oxides Produced in Sea Water
AU: * Webb, S M
EM: samwebb@slac.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 United States
AU: Bargar, J R
EM: bargar@ssrl.slac.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 United States
AU: Tebo, B M
EM: btebo@ucsd.edu
AF: Scripps Institute of Oceanography, University of California San Diego, La Jolla, CA 92093 United States
AB: Manganese oxides have been coined as the "scavengers of the sea" and play important roles in both marine and freshwater systems. Natural manganese oxide nanoparticles and grain coatings are ubiquitous in the environment and profoundly impact the quality of sediments via their ability to degrade and sequester contaminants. These oxides are believed to form dominantly via oxidation of Mn(II) by marine and freshwater bacteria and have extremely high sorptive capacities for heavy metals. We have used XANES, EXAFS, and synchrotron (SR)-XRD techniques to study biogenic manganese oxides produced by spores of the marine Bacillus sp., strain SG-1 in seawater as a function of reaction time under fully in-situ conditions. The primary biogenic solid-phase Mn oxide product is a hexagonal layered phyollomanganate with an oxidation state similar to that in delta-MnO2. XRD data show the biooxides to have a phyllomanganate 10 � basal plane spacing, suggesting the interlayer is hydrated and contains calcium. As the experiment continues, the initial biooxide changes to show triclinic symmetry. Fits to these EXAFS spectra suggest the octahedral layers have low Mn octahedral site vacancies in the lattice and the latyers bend to accommodate Jahn-Teller distortions creating the change in symmetry. The oxides observed in this study as models of Mn(II) bio-oxidation may be representative of the most abundant manganese oxide phase suspended in the oxic and sub-oxic zones of the oceanic water column.
DE: 0400 Biogeosciences
DE: 1045 Low-temperature geochemistry
DE: 3620 Crystal chemistry
DE: 4840 Microbiology
DE: 4851 Oxidation/reduction reactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting