Kinetics of H2–O2–H2O redox equilibria and formation of metastable H2O2 under low temperature hydrothermal conditions
Foustoukos, Dionysis I.
Houghton, Jennifer L.
Seyfried, William E.
Sievert, Stefan M.
Cody, George D.
MetadataShow full item record
KeywordKnallgas reaction; H2 oxidation; Metastable hydrogen peroxide; Anaerobic chemolithoautotrophic metabolism; Fenton reaction; Hydrothermal systems
Hydrothermal experiments were conducted to evaluate the kinetics of H2(aq) oxidation in the homogeneous H2-O2-H2O system at conditions reflecting subsurface/near-seafloor hydrothermal environments (55-250 oC and 242-497 bar). The kinetics of the water-forming reaction that controls the fundamental equilibrium between dissolved H2(aq) and O2(aq), are expected to impose significant constraints on the redox gradients that develop when mixing occurs between oxygenated seawater and high- temperature anoxic vent fluid at near-seafloor conditions. Experimental data indicate that, indeed, the kinetics of H2(aq)-O2(aq) equilibrium become slower with decreasing temperature, allowing excess H2(aq) to remain in solution. Sluggish reaction rates of H2(aq) oxidation suggest that active microbial populations in near-seafloor and subsurface environments could potentially utilize both H2(aq) and O2(aq), even at temperatures lower than 40 oC due to H2(aq) persistence in the seawater/vent fluid mixtures. For these H2-O2 disequilibrium conditions, redox gradients along the seawater/hydrothermal fluid mixing interface are not sharp and microbially-mediated H2(aq) oxidation coupled with a lack of other electron acceptors (e.g. nitrate) could provide an important energy source available at low-temperature diffuse flow vent sites. More importantly, when H2(aq)-O2(aq) disequilibrium conditions apply, formation of metastable hydrogen peroxide is observed. The yield of H2O2(aq) synthesis appears to be enhanced under conditions of elevated H2(aq)/O2(aq) molar ratios that correspond to abundant H2(aq) concentrations. Formation of metastable H2O2 is expected to affect the distribution of dissolved organic carbon (DOC) owing to the existence of an additional strong oxidizing agent. Oxidation of magnetite and/or Fe++ by hydrogen peroxide could also induce formation of metastable hydroxyl radicals (•OH) through Fenton-type reactions, further broadening the implications of hydrogen peroxide in hydrothermal environments.
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 75 (2011): 1594-1607, doi:10.1016/j.gca.2010.12.020.
Showing items related by title, author, creator and subject.
Klein, Frieder; Grozeva, Niya G.; Seewald, Jeffrey S.; McCollom, Thomas M.; Humphris, Susan E.; Moskowitz, Bruce; Berquo, Thelma S.; Kahl, Wolf-Achim (2014-10-20)The exposure of mantle peridotite to water at crustal levels leads to a cascade of interconnected dissolution-precipitation and reduction-oxidation reactions—a process referred to as serpentinization. These reactions have ...
French, Katherine L. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2015-02)Tracing the evolution of Earth’s redox history is one of the great challenges of geobiology and geochemistry. The accumulation of photosynthetically derived oxygen transformed the redox state of Earth’s surface environments, ...
Modeling sulfate reduction in methane hydrate-bearing continental margin sediments : does a sulfate-methane transition require anaerobic oxidation of methane? Malinverno, Alberto; Pohlman, John W. (American Geophysical Union, 2011-07-12)The sulfate-methane transition (SMT), a biogeochemical zone where sulfate and methane are metabolized, is commonly observed at shallow depths (1–30 mbsf) in methane-bearing marine sediments. Two processes consume sulfate ...