Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-GC Geochemistry

[S-GC41] Solid Earth Geochemistry, Cosmochemistry

Wed. May 29, 2019 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Gen Shimoda(Geological Survey of Japan, AIST), Katsuhiko Suzuki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Katsuyuki Yamashita(Graduate School of Natural Science and Technology, Okayama University), Akira Ishikawa(Department of Earth and Planetary Sciences, Tokyo Institute of Technology)

[SGC41-P02] H2 production and CO2 storage during peridotite serpentinization under CO2-rich hydrothermal conditions: Influence of pyroxene

*Jiajie Wang1, Noriaki Watanabe1, Atsushi Okamoto1, Kengo Nakamura1, Takeshi Komai1 (1.Tohoku Univ.)

Keywords:Pyroxene, Olivine, Hydrothermal, H2 production, CO2 storage

Serpentinization of peridotite (mainly includes olivine and pyroxene) usually produces molecular H2, which may potentially contribute to today’s always-increasing energy demands. On the other hand, peridotite also appears to be a good candidate for CO2 sequestration by mineralization. Based on this, our previous research has successfully combined the strategies of H2 production and CO2 mineralization by olivine alteration in CO2-rich hydrothermal system. However, olivine may not necessarily act as a peridotite equivalent during alteration, and the pyroxene influence is still poorly understood.
In this study, we examined the reactions in H2O-olivine/pyroxene-CO2 systems by performing hydrothermal experiments in 0.5 mol/L NaHCO3 solutions under conditions of 300 oC and 10 MPa. The results show that H2 was produced when olivine and/or pyroxene reacted in NaHCO3 solution, and the presence of pyroxene in starting material suppressed H2 production from per kg of mineral. Pyroxene was converted solely to serpentine, rather than brucite and magnesite even in CO2-contained solutions, which indicates CO2 mineralization was only realized in olivine-contained systems. In addition, the pyroxene serpentinization process is quicker than olivine. In the experiment with olivine/pyroxene weight ratio of 3/2, all of the pyroxene was altered after 72 h reaction, whereas half of the olivine particles have remained. Based on experimental results, we propose that the presence of pyroxene in starting material will suppress the H2 production and CO2 storage during peridotite alteration; however, the inhibition effect will be decreased along the reaction time.