Microbes are everywhere, but when they are in mined soils, they react with the mineral pyrite to speed up acidification of mine run-off water. Scientists have been trying to understand the chemistry behind this process that eventually leads to widespread acidification of water bodies and deposition of heavy metals. What a new study has found seems to defy the laws of chemistry: microbes react with the pyrite surface, coating it with chemicals that would be expected to hinder further reactions. Despite the formation of such coatings, however, microbe-mediated reactions occur tens of thousands of times faster than when no microbes are present.

''That's a puzzle,'' said Alfred Spormann, a co-principal investigator on the study. ''This changed surface chemistry should slow down the microbial oxidation but it doesn't.''

The collaborative study was led by co-principal investigators Scott Fendorf, Gordon Brown and Spormann at Stanford. Dartmouth Assistant Professor Benjamin Bostick, Fendorf's former doctoral student who coordinated the research effort, will present the group's findings Thursday, Dec. 11 at this year's San Francisco meeting of the American Geophysical Union (AGU). The AGU is an international scientific society with more than 35,000 members dedicated to advancing the understanding of Earth and its environment.

In mines, oxygen from the air initiates chemical reactions with pyrite, also known as fool's gold. Microbes subsequently react with the pyrite in cyclic processes that result in the rapid production of large amounts of sulfuric acid. The research team wanted to understand how the activity of the microorganisms controls the chemistry on mineral surfaces, and how that chemistry, in turn, controls the activity of the microorganisms. Specifically, they wanted to find out what kinds of iron species and precipitates can be found on microbe-treated pyrite surfaces.

The researchers grew the bacteria Thiobacillus ferrooxidans an
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Contact: Dawn Levy
dawnlevy@stanford.edu
650-725-1944
Stanford University
11-Dec-2003

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