From serpentinization to carbonation : new insights from a CO2 injection experiment
Citable URI
https://hdl.handle.net/1912/6369As published
https://doi.org/10.1016/j.epsl.2013.08.017Keyword
Serpentinization; Methane formation; Mineral carbonation; Carbon sequestration; Hydrothermal injection experimentAbstract
We injected a CO2-rich hydrous fluid of seawater chlorinity into an ongoing,
mildly reducing (H2(aq) ≈ 3 mmol/kg) serpentinization experiment at 230°C and 35
MPa to examine the changes in fluid chemistry and mineralogy during mineral
carbonation. The chemistry of 11 fluid samples was measured, speciated, and
compared with MgO-SiO2-H2O-CO2 (MSHC) phase equilibria to approximate the
reaction pathway from serpentinization to carbonation. Although the overall system
was in apparent disequilibrium, the speciated activities of dissolved silica (aSiO2(aq))
and carbon dioxide (aCO2(aq)) evolved roughly along MSHC equilibrium phase
boundaries, indicative of 4 distinct mineral assemblages over time: 1) serpentine22
brucite (± magnesite) before the injection, to 2) serpentine-talc-magnesite 2 hours
after the injection, to 3) quartz-magnesite (48h after injection), and 4) metastable olivine – magnesite (623h after injection) until the experiment was terminated.
Inspection of the solid reaction products revealed the presence of serpentine,
magnesite, minor talc, and magnetite, in addition to relict olivine. Although quartz
was saturated over a short segment of the experiment, it was not found in the solid
reaction products. A marked and rapid change in fluid chemistry suggests that
serpentinization ceased and precipitation of magnesite initiated immediately after
the injection. A sharp decrease in pH after the injection promoted the dissolution of
brucite and olivine, which liberated SiO2(aq) and dissolved Mg. Dissolved Mg was
efficiently removed from the solution via magnesite precipitation, whereas the
formation of talc was relatively sluggish. This process accounts for an increase in
aSiO2(aq) to quartz saturation shortly after the injection of the CO2-rich fluid.
Molecular dihydrogen (H2(aq)) was generated during serpentinization of olivine by
oxidation of ferrous iron before the injection; however, no additional H2(aq) was
generated after the injection. Speciation calculations suggest a strong affinity for the
formation of methane (CH4(aq)) at the expense of CO2(aq) and H2(aq) after the
injection, but increased CH4(aq) formation was not observed. These findings suggest
that kinetically fast mineral carbonation dominates over sluggish CH4(aq) formation
in mildly reducing serpentinization systems affected by injection of CO2-rich fluids.
Description
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 379 (2013): 137-145, doi:10.1016/j.epsl.2013.08.017.
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Suggested Citation
Preprint: Klein, Frieder, McCollom, Thomas M., "From serpentinization to carbonation : new insights from a CO2 injection experiment", 2013-08, https://doi.org/10.1016/j.epsl.2013.08.017, https://hdl.handle.net/1912/6369Related items
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