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Low-temperature dunite hydration: evaluating CH4 and H2 production from H2O and CO2
Stockholm University, Faculty of Science, Department of Geological Sciences.ORCID iD: 0000-0002-1291-5529
2016 (English)In: Geofluids, ISSN 1468-8115, E-ISSN 1468-8123, Vol. 16, no 3, 408-420 p.Article in journal (Refereed) Published
Abstract [en]

Abiotic methane (CH4) and hydrogen (H2) produced after hydration of mafic/ultramafic rocks represent energy sources for microbes that may thrive in the deep subsurface regions of Earth and possibly on other planets. While H2 is a direct product of serpentinization, CH4 can form via Fischer–Tropsch Type (FTT) reactions (carbon reduction) that, due to potential H2 migration, can be spatially and temporally detached from serpentinization. We tested an alternative process hypothesized by some scholars, in which CO2 can be reduced through dunite hydration without initially added H2, implying that CH4 can form in the same serpentinized fluid–rock system. The experiment used natural dunite sand (Forsterite 92), CO2 with δ13C ~ −25‰ (VPDB), and a 1 mm dissolved SiO2 solution mixed in 30 glass bottles (118 mL) stored for up to 8 months at low temperature (50°C) to simulate land-based serpentinization systems. In addition, 30 control bottles without olivine were used as blanks. Trivial amounts of CH4 (orders of 0.2–0.9 ppmv) were detected in both samples and blanks, likely representing analytical noise; essentially, no significant amount of CH4 formed under the experimental conditions used in this work. Low amounts of H2 (~2.55 ± 1.39 ppmv) were generated, with production yields that were one order of magnitude lower than in previously published experiments. Moderate concentrations of SiO2 appeared to hinder low-temperature H2 production. Our experiment confirms that the low-temperature reduction of CO2 into CH4 through direct olivine hydration, without initial H2, is sluggish and not straightforward, which is consistent with previous studies. The presence of substantial amounts of H2, as well as suitable metal catalysts, appears to be essential in the low-temperature production of abiotic CH4, as observed in published FTT experiments.

Place, publisher, year, edition, pages
2016. Vol. 16, no 3, 408-420 p.
Keyword [en]
Fischer – Tropsch reactions, hydrogen, methane, olivine hydration, serpentinization
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-128988DOI: 10.1111/gfl.12159OAI: oai:DiVA.org:su-128988DiVA: diva2:918698
Available from: 2016-04-11 Created: 2016-04-11 Last updated: 2016-09-09Bibliographically approved

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Neubeck, AnnaEtiope, Giuseppe
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