Mössbauer Analysis of Microbial Redox Transformations of Naturally Occurring Fe(III)-bearing Phyllosilicates
EMSL Project ID
19846
Abstract
The abundance of ferric iron in sedimentary environments and its ability to accept and donate electrons makes it important electron acceptor for microbial metabolism. Fe(III) in the structure of phyllosilicates is one of two main sources of bio-available Fe(III) in subsurface sediments. While the most of studies were performed with model phyllosilicates without significant amounts of impurities and with formulas close to idealized, there are important differences between minerals found in soils and sediments and the model minerals that occur in relatively pure deposits. The objective of this study is to examine microbial redox transformations of both pristine sediments and sediments that have been stripped of their Fe(III) oxide content. Microbial transformations of naturally occurring phyllosilicates will be studied using background sediment consisting of shale-limestone saprolite obtained from a U.S. Department of Energy experimental site (Oak Ridge Field Research Center). Fe(III)hydroxides will be extracted from sediment using oxalate extraction in the presence of catalytic quantities of Fe(II). This will allow for dissolution of Fe(III) hydroxides without significantly altering the valence of Fe in phyllosilicates. To evaluate relative importance of Fe(III)-bearing phyllosilicates in microbially-mediated reactions of Fe(III), both Fe-oxide free and pristine sediments will be used for microbial reduction experiments. Two model cultures differing in the extent to which they reduce structural Fe(III) will be used for experiments: (1) Geobacter metallireducens and (2) Shewanella putrefaciens. Electron donor consumption, cell number, Fe(II)/Fe(III) content will be monitored over time. At the end of the experiment iron speciation in solid phase samples will be examined by chemical extraction (University of Wisconsin) and Mössbauer spectroscopy (PNNL). The following samples will be studied by Mössbauer spectroscopy: a) pristine sediment, b) Fe-oxide free sediment c) reduced pristine and Fe-oxide free sediments, d) re-oxidized pristine and Fe-oxide free sediments. Variable temperature Mössbauer studies are critical to understand changes in the Fe-mineralogy and will help us to elucidate the role of Fe(III)-bearing phyllosilicates in microbial cycle of iron.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2006-09-01
End Date
2009-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Mohanty, S., B. Kollah, D. Hedrick, A. Peacock, R. K. Kukkadapu, and E. E. Roden. 2008. Biogeochemical processes in ethanol stimulated uranium-contaminated subsurface sediments. Environ. Sci. Technol. 42(12):4384-4390.