Abstract
Dissimilatory iron reduction and the redox cycling of green rust
Mineralogical magazine, Vol.76(6), p.2188
Goldschmidt 2012
2012
Abstract
Green rusts (mixed Fe (super II) /Fe (super III) layered double hydroxides) have been identified in Fe (super III) /Fe (super II) transition zones in a variety of natural and engineered subsurface environments including groundwater, soils, and sediments, and among corrosion products in zero valent iron permeable reactive barriers. Many of these environments are characterized by periodic or seasonal cycling of redox conditions (e.g., redoximorphic soils in areas with seasonal flooding) that create the opportunity for cycling of Fe between oxidized and reduced forms. In recent years evidence has been building that suggests that the green rust mineral fougerite plays a central role in Fe redox cycling in these environments. Carbonate green rust was produced in anoxic defined mineral medium containing 75 mM formate and 80 mM Fe (super III) , in the form of phosphate doped (0.7 mass % P) lepidocrocite, inoculated with Shewanella putrefaciens CN32. The green rust was then oxidized by introducing sterile air into the headspace. After 24 h the suspensions were sparged with sterile Ar and re-inoculated with S. putrefaciens CN32. Samples were collected for measurement of Fe (super II) and characterization of the secondary mineralization products by powder X-ray diffraction, scanning electron microscopy, and (super 57) Fe Mossbauer spectroscopy. Results of the analysis of the product of green rust oxidation were consistent with ferric green rust. In our experiment, the oxidation of green rust by O (sub 2) to ferric green rust occurred over a period of 24 h without the formation of other Fe (super III) oxide phases. However, the initial green rust was formed in the presence of phosphate and sorption of phosphate or silicate by green rust has been shown to promote oxidation of green rust to ferric green rust by suppressing the dissolution of green rust, a prerequisite for the formation of other ferric phases such as lepidocrocite or goethite. After re-inoculation, total Fe (super II) concentrations rebounded to pre-oxidation concentrations and green rust was observed as the dominant secondary mineralization product. Since phosphate and silicate are typically available in soils and sediments, similar conditions may be encountered in-situ. Thus, our results indicate the potential for cycling of green rust between reduced and oxidized forms under redox dynamics similar to those encountered in environments that alternate between iron-reducing and oxic conditions and are consistent with the identification of green rust in soils/sediments with seasonal redox cycling.
Details
- Title: Subtitle
- Dissimilatory iron reduction and the redox cycling of green rust
- Creators
- Edward J O'Loughlin - Argonne National LaboratoryMaxim I BoyanovChristopher A GorskiMichael L McCormickMichelle M SchererKenneth M Kemner
- Resource Type
- Abstract
- Publication Details
- Mineralogical magazine, Vol.76(6), p.2188
- Conference
- Goldschmidt 2012
- Publisher
- Mineralogical Society
- ISSN
- 0026-461X
- eISSN
- 1471-8022
- Alternative title
- Goldschmidt 2012 abstract volume
- Language
- English
- Date published
- 2012
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984202245902771
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