Iron oxide: Difference between revisions

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=== Methanogenesis replacement by iron oxide reduction ===
Under conditions favoring iron reduction, the process of iron oxide reduction can replace at least 80% of methane production occurring by [[methanogenesis]].<ref name=":4">{{Cite journal|last=Sivan|first=O.|last2=Shusta|first2=S. S.|last3=Valentine|first3=D. L.|date=2016-03-01|title=Methanogens rapidly transition from methane production to iron reduction|journal=Geobiology|language=en|volume=14|issue=2|pages=190–203|doi=10.1111/gbi.12172|pmid=26762691|issn=1472-4669}}</ref> This phenomenon occurs in a nitrogen-containing (N<sub>2</sub>) environment with low sulfate concentrations. Methanogenesis, an [[Archaea]]n driven process, is typically the predominate form of carbon mineralization in sediments at the bottom of the ocean. Methanogenesis completes the decomposition of organic matter to methane (CH<sub>4</sub>).<ref name=":4" /> The specific electron donor for iron oxide reduction in this situation is still under debate, but the two potential candidates include either Titanium (III) or compounds present in yeast. The predicted reactions with Titanium (III) serving as the electron donor and [[Phenazine|phenazine-1-carboxylate]] (PCA) serving as an electron shuttle is as follows:
:Ti(III)-cit + CO<sub>2</sub> + 8H<sup>+</sup> → CH<sub>4</sub> + 2H<sub>2</sub>O + Ti(IV) + cit&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ΔE = &ndash;240 + 300 mV
:Ti(III)-cit + PCA (oxidized) → PCA (reduced) + Ti(IV) + cit&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ΔE = &ndash;116 + 300 mV