Microbially-Induced Reduction of Iron Oxides: Impact of Flow on Secondary Mineral Phase Products
Abstract
Despite the acknowledged importance of ferric oxides in controlling contaminant behavior, there is limited understanding of the products and processes during reductive dissolution of these mineral phases under dynamic flow conditions. Factors potentially controlling the fate of iron during reduction include dissolved Fe and electron donor concentrations; therefore, the nature and reactivity of these products are expected to differ when a solute transport component is introduced. We have conducted column experiments using a common, iron-reducing bacterium (Shewanella putrefaciens, strain CN32) and 2-line ferrihydrite-coated silica within an artificial groundwater matrix. Changes in pore water chemistry were monitored and solids were characterized as a function of time and flow path (2-cm intervals) using a variety of methods including x-ray absorption fine structure (XAFS) and high-resolution transmission electron microscopy (TEM). Microbial Fe(III) reduction results in the conversion of ferrihydrite to goethite and magnetite. Sequestration of Fe(III) within these secondary phases results in decreased Fe(III) bioavailability and subsequent decreased rates of microbial reduction. Magnetite likely forms via topotactic conversion of ferrihydrite and is correspondingly associated with the ferrihydrite surface, while goethite appears to form via dissolution and reprecipitation and is concentrated on the cell envelope. Changes in flow velocity result in dramatic differences in secondary mineral phase accumulation suggesting that linking hydraulic conditions with biogeochemical processes is an important step to predict the fate of Fe and associated trace metals during reductive dissolution of iron oxides.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.B22A0143H
- Keywords:
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- 0400 BIOGEOSCIENCES;
- 1045 Low-temperature geochemistry