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Published July 11, 1997 | Published
Book Section - Chapter Open

Formation of magnetite and iron-rich carbonates by thermophilic iron-reducing bacteria


Laboratory experiments were performed to study the formation of iron minerals by a thermophilic (45 - 75 degree(s)C) fermentative iron-reducing bacterial culture (TOR39) obtained from the deep subsurface. Using amorphous Fe(III) oxyhydroxide as an electron acceptor and glucose as an electron donor, TOR39 produced magnetite and iron-rich carbonates at conditions consistent, on a thermodynamic basis, with Eh (-200 mV to -415 mV) and pH (6.2 to 7.7) values determined for these experiments. Analyses of the precipitating solid phases by X-ray diffraction showed that the starting amorphous Fe(III) oxyhydroxide was nearly completely converted to magnetite and Fe-rich carbonate after 20 days of incubation. Increasing bicarbonate concentration in the chemical milieu resulted in increased proportions of siderite relative to magnetite and the addition of MgCl2 caused the formation of magnesium-rich carbonate in addition to siderite. The results suggest that the TOR39 bacterial culture may have the capacity to form magnetite and iron-rich carbonates in a variety of geochemical conditions. These results may have significant implications for studying the past biogenic activities in the Martian meteorite ALH84001.

Additional Information

© 1997 Society of Photo-Optical Instrumentation Engineers (SPIE). This research was sponsored by the Subsurface Science Program managed by Frank Wobber, by the Geoscience Research Program of the Office of Basic Energy Science, of the U.S. Department of Energy under contracts No. DE-AC05-960R22464. C. Zhang and S. Liu were supported through Oak Ridge Associated universities.

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