From serpentinization to carbonation : new insights from a CO2 injection experiment
MetadataShow full item record
KeywordSerpentinization; Methane formation; Mineral carbonation; Carbon sequestration; Hydrothermal injection experiment
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.
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.
Showing items related by title, author, creator and subject.
Impact of intentionally injected carbon dioxide hydrate on deep-sea benthic foraminiferal survival Bernhard, Joan M.; Barry, James P.; Buck, Kurt R.; Starczak, Victoria R. (2008-10)Sequestration of carbon dioxide (CO2) in the ocean is being considered as a feasible mechanism to mitigate the alarming rate in its atmospheric rise. Little is known, however, about how the resulting hypercapnia and ocean ...
Removal of organic carbon by natural bacterioplankton communities as a function of pCO2 from laboratory experiments between 2012 and 2016 Passow, Uta; Brzezinski, Mark A.; Carlson, Craig A.; James, Anna K; Parsons, Rachel J; Trapani, Jennifer N (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: email@example.com, 2016-11-18)Factors that affect the removal of organic carbon by heterotrophic bacterioplankton can impact the rate and magnitude of organic carbon loss in the ocean through the conversion of a portion of consumed organic carbon to ...
Preindustrial-control and twentieth-century carbon cycle experiments with the Earth System Model CESM1(BGC) Lindsay, Keith; Bonan, Gordon B.; Doney, Scott C.; Hoffman, Forrest M.; Lawrence, David M.; Long, Matthew C.; Mahowald, Natalie M.; Moore, J. Keith; Randerson, James T.; Thornton, Peter E. (American Meteorological Society, 2014-12-15)Version 1 of the Community Earth System Model, in the configuration where its full carbon cycle is enabled, is introduced and documented. In this configuration, the terrestrial biogeochemical model, which includes ...