Ferrous Hydroxy Carbonate is a Stable Transformation Product of Biogenic Magnetite

Journal Article · Wed Feb 02 04:00:00 EST 2005 · American Mineralogist

DOI:https://doi.org/10.2138/am.2005.1727· OSTI ID:15011219

Kukkadapu, Ravi K; Zachara, John M; Fredrickson, Jim K; Kennedy, David W; Dohnalkova, Alice; McCready, David E

A ~1:1 mixture of ferrihydrite and nanocrystalline akaganeite (β-FeOOH; 10-15 nm) was incubated with Shewanella putrefaciens (strain CN32) under anoxic conditions with lactate as an electron donor and anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. The incubation was carried out in a 1,4-piperazinediethanesulfonic acid (PIPES)-buffered medium, without PO³⁻₄ at circumneutral pH. Iron reduction was measured as a function of time (as determined by 0.5 N HCl extraction), and solids were characterized by X-ray diffraction (XRD), electron microscopy, and Mössbauer spectroscopy. The biogenic reduction of Fe³⁺ was rapid; with 60% of the total Fe (Feтот) reduced in one day. Only an additional 10% of Feтот was reduced over the next three years. A fine-grained (10 nm), cation-excess (CE) magnetite with a Fe²⁺/Feтот ratio of 0.5-0.6 was the sole biogenic product after one day of incubation. The CE magnetite was unstable and partially transformed to micron-sized ferrous hydroxy carbonate [FHC; Fe₂ (OH)₂CO_3(s)], a rosasite-type mineral, with time. Ferrous hydroxy carbonate dominated the mineral composition of the three year incubated sample. The Fe²⁺/Feтот ratio of the residual CE magnetite after three years of incubation was lower than the day 1 sample and was close to that of stochiometric magnetite (0.33). To best of our knowledge, this is the first report of biogenic FHC, and only the third observation of this material in nature. Ferrous hydroxy carbonate appeared to form by slow reaction of microbially produced carbonate with Fe²⁺-excess magnetite. The FHC may be an overlooked mineral phase that explains the infrequent occurrence of fine-grained, biogenic magnetite in anoxic sediments.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 15011219
• Report Number(s): PNNL-SA-41786; 4593; KC0303020
• Journal Information: American Mineralogist, Journal Name: American Mineralogist Journal Issue: 2-3 Vol. 90; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BINDING ENERGY
BIODEGRADATION
DIRB
Environmental Molecular Sciences Laboratory
Ferrihydrite-akagneite
IRON CARBONATES
IRON HYDROXIDES
MAGNETITE
MIXTURES
MOESSBAUER EFFECT
PHASE TRANSFORMATIONS
SEDIMENTS
biogenic magnetite
ferrous hydroxyl carbonate