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Goethite reduction



Hi David,

If you become irritated by my mailing you please let me know.  Pursuant to
your email yesterday I've been trying to simulate goethite to mackinawite
inclusion with the sulfate reduction. Including these phases did, as you
predicted, initially buffer the pH to a somewhat higher value, however  only
for small amounts of sulfate reduction and it seemed as though maybe the
results were too complex to interpret. So I simplified the system and
considered organic matter degradation without sulfate in the presence of
goethite. My question here is with regards to this:

Goethite was not reduced... the system underwent methanogenesis. I don't
think that this result is possible? From what I've read, iron reduction is
much more favourable than methanogenesis having a more negative Gibbs energy
(I could cite papers, but I'm sure you're already familiar with these).
There was some goethite reduction, however, only 1/40 of that required if
CH2O used goethite as the terminal electron acceptor. Am I doing something
wrong?  

Dan

Daniel LaRiviere
Chemical Engineering Department
Texas A&M University
College Station, TX 77843-3136
phone: 979 845 5854




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