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Isolation and microbial reduction of Fe(III) phyllosilicates from subsurface sediments.
Tao Wu1, Evgenya Shelobolina, Huifang Xu
1Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Environmental Science & Technology
|October 16, 2012
Summary
Citrate-dithionite-bicarbonate (CDB) extraction effectively isolates Fe(III) phyllosilicates from soil for microbial reduction studies. This method preserves mineral structure, enabling accurate research on iron reduction in anoxic environments.
Area of Science:
- Geochemistry
- Environmental Microbiology
- Soil Science
Background:
- Fe(III)-bearing phyllosilicates are crucial iron sources for microbial reduction in anoxic soils and sediments.
- Isolating these phases is essential for understanding their role in biogeochemical cycles.
Purpose of the Study:
- To isolate Fe(III) phyllosilicate and Fe(III) oxide phases from weathered shale saprolite for individual experimentation.
- To evaluate chemical extraction methods for their ability to isolate Fe(III) phyllosilicates without structural alteration.
Main Methods:
- Physical separation using density gradient centrifugation.
- Chemical extraction using acid ammonium oxalate (AAO) and citrate-dithionite-bicarbonate (CDB) at different temperatures.
- X-ray diffraction (XRD) and Mössbauer spectroscopy for mineralogical and redox speciation analysis.
- Microbial reduction experiments using Geobacter sulfurreducens.
Main Results:
- Density gradient centrifugation failed to separate phyllosilicate and Fe(III) oxide phases.
- AAO extraction altered phyllosilicate structures, while CDB extraction minimally impacted them.
- CDB extraction followed by H(2)O(2) reoxidation yielded Fe(III) phyllosilicates suitable for microbial reduction studies, with reduction extents comparable to pristine sediments.
Conclusions:
- Citrate-dithionite-bicarbonate (CDB) extraction is a suitable method for isolating Fe(III) phyllosilicates from complex soil matrices.
- The isolated Fe(III) phyllosilicates, after reoxidation, accurately represent the natural material for studying microbial iron reduction.
- This methodology facilitates detailed investigations into the role of phyllosilicates in microbial iron cycling.
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