Microbial Reduction of Structural Fe3+ in Nontronite by a Thermophilic Bacterium and its Role in Promoting the Smectite to Illite Reaction
Abstract
The illitization process of Fe-rich smectite (nontronite NAu-2) promoted by microbial reduction of structural Fe(1*) was investigated by using a thermophilic metal-reducing bacterium, Thermoanaerobacter ethanolicus, isolated from the deep subsurface. T. ethanolicus was incubated with lactate as the sole electron donor and structural Fe(1*) in nontronite as the sole electron acceptor, and anthraquinone-2, 6- disulfonate (AQDS) as an electron shuttle in a growth medium (pH 6.2 and 9.2, 65 deg C) with or without an external supply of Al and K sources. With an external supply of Al and K. the extent of reduction of Fe-(1*) in NAu-2 was 43.7 and 40.4% at pH 6.2 and 9.2, respectively. X-ray diffraction and scanning and transmission electron microscopy revealed formation of discrete illite at pH 9.2 with external Al and K sources, while mixed layers of illite/smectite or highly charged smectite were detected under other conditions. The morphology of biogenic illite evolved from lath and flake to pseudo-hexagonal shape. An external supply of Al and K under alkaline conditions enhances the smectite-illite reaction during microbial Fe(1*) reduction of smectite. Biogenic Si02 was observed as a result of bioreduction under all conditions. The microbially promoted smectite-illite reaction proceeds via dissolution of smectite and precipitation of illite. Thermophilic iron reducing bacteria have a significant role in promoting the smectite to illite reaction under conditions common in sedimentary basins.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2007
- Accession Number
- ADA499114
Entities
People
- D. D. Eberl
- Gengxin Zhang
- Hailiang Dong
- Jinwook Kim
Organizations
- United States Naval Research Laboratory