HR: 1340h
AN: B13C-1380    [Abstracts]
TI: Zinc and Arsenic Immobilization and Magnetite Formation Upon Maghemite Reduction by Shewanella putrefaciens ATCC 8071
AU: * Cismasu, C
EM: cismasu@stanford.edu
AF: Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94301, United States
AU: Ona-Nguema, G
EM: onanguem@stanford.edu
AF: Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94301, United States
AU: Bonnin, D
EM: dominique.bonnin@espci.fr
AF: Laboratoire de Physique Quantique, Ecole Supérieure de Physique et Chimie Industrielle, 10 rue Vauquelin, Paris, 75005, France
AU: Menguy, N
EM: nicolas.menguy@impmc.jussieu.fr
AF: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR 7590, CNRS, Université Paris 6 & 7, IPGP, 140, rue de Lourmel, Paris, 75015, France
AU: Brown, G E
EM: gordon@pangea.stanford.edu
AF: Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94301, United States
AU: Brown, G E
EM: gordon@pangea.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, United States
AB: Dissimilatory reduction of ferric iron oxides is recognized as an important component of the iron biogeochemical cycle, causing the dissolution of iron oxide minerals and the possible formation of Fe(II)-bearing minerals such as magnetite, green rusts, siderite, etc. These mineralogical transformations affect the mobility of surface- associated toxic metal(loid)s, which may be released into solution, adsorbed, or incorporated into newly formed minerals. Maghemite (γ-Fe2O3) is an iron oxide mineral that is found in certain tropical soils and as isolated deposits in more temperate regions. In these settings, maghemite may play an important role in the biogeochemical cycling of iron and of surface-associated trace metal(loids). However, the reduction of maghemite by iron-respiring bacteria, the impact of reductive dissolution on the release of associated contaminants, and the nature of biogenic Fe(II)-containing reaction products are not well documented. In the present study, we incubated samples of pure maghemite and As(V)- and Zn-adsorbed maghemite with an iron reducing bacterium, Shewanella putrefaciens strain ATCC 8071, in a batch system under anoxic conditions. As a result of Fe(III) bioreduction, all mineral suspensions turned from brown to black during the first hour of incubation, indicating the onset of magnetite formation. The presence of this mineral was confirmed by transmission Mössbauer spectroscopy at room temperature, which showed the formation of an almost stoichiometric magnetite. High-resolution transmission electron microscopy images indicate that the parent maghemite and the biogenic magnetite particles are octahedral in shape and of similar size (5 to 20 nm). The presence of 50 mg/L adsorbed Zn(II) did not affect the initial rate of iron reduction with respect to the Zn-free maghemite sample (0.62 mM Fe(II)/h and 0.66 mM Fe(II)/h, respectively). However, adsorption of 50 and 100 mg/L As(V) on maghemite decreased the initial iron reduction rate to 0.35 mM Fe(II)/h and 0.16 mM Fe(II)/h, respectively. Results show that before inoculation, the proportion of As(V) adsorbed on the maghemite surface is significantly higher (90%) than Zn(II) (50%) after a two-day equilibration period. During bioreduction, the remaining soluble zinc and arsenic content decreases progressively as a function of time, possibly as a result of coprecipitation or adsorption reactions on the newly formed biogenic magnetite. Overall, this study shows that magnetite formation induced by the bioreduction of maghemite is particularly effective for the removal of zinc and arsenic from solution.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0419 Biomineralization
DE: 0463 Microbe/mineral interactions
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0489 Trace element cycling (4875)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting