1:45 PM - 3:15 PM
[HSC04-P07] Carbon dioxide removal using mafic–ultramafic rocks and Mg hydroxide
Keywords:Mafic rock, Geochemical trapping, Enhanced rock weathering
CO2 fixation in mafic or ultramafic rocks has recently attracted much interest in geochemical trapping. For CO2 capture and storage (CCS), results of some field tests in basalt (e.g., CarbFix project in Iceland and Wallula basalt pilot project in the US) significantly showed CO2 mineralization within several years. The application of enhanced rock weathering (ERW) is also an important issue worldwide, using weathering processes of crushed mafic or ultramafic rocks in croplands. Japan possibly has a high potential for the above technologies because mafic–ultramafic rocks in Japan show a large abundance and wide varieties. In this context, it is crucial to study the mechanism and application of CO2 removal using mafic–ultramafic rocks in Japan.
In this study, experiments for CCS and ERW were conducted with various rocks in Japan: basalt (Iki, Mishima, Sado, Hokkaido), peridotite (Hokkaido), and serpentinite (Hokkaido). Mg hydroxide (or Mg oxide) was also used as a reactant in the experiments to focus on the behavior of Mg2+, which is one of the main cations in mafic–ultramafic rocks.
To understand the geochemical reaction in CCS sites, the laboratory experiments were run in a closed reactor at 40°C and 60°C with 10 MPa CO2 and water (water/solid ratio = 10). Although dissolved Mg2+ ions were detected, precipitation of Mg carbonate was kinetically inhibited in the experiments. Magnesite (MgCO3) was presumably formed in long time scales as Mg carbonate hydrate (e.g., nesquehonite; MgCO3·3H2O) initially forms as metastable phases.
The experiments for ERW were started on the rooftop of the AIST Tsukuba Central 7 office. The samples were exposed to outside weather conditions and sometimes interacted with rainwater. The results of 6-month monitoring demonstrated that pH and dissolved metal concentrations (e.g., Mg2+) of the water passing through the solid samples were higher than those of the original rainwater. The weathering reaction of serpentinite was significantly observed as brucite (Mg hydroxide mineral) in serpentinite was dissolving.
To summarize, the reactivity of mafic–ultramafic rocks in CO2–water–rock systems was discussed in this study. Further works need to investigate other mafic–ultramafic rocks from different locations in Japan.
In this study, experiments for CCS and ERW were conducted with various rocks in Japan: basalt (Iki, Mishima, Sado, Hokkaido), peridotite (Hokkaido), and serpentinite (Hokkaido). Mg hydroxide (or Mg oxide) was also used as a reactant in the experiments to focus on the behavior of Mg2+, which is one of the main cations in mafic–ultramafic rocks.
To understand the geochemical reaction in CCS sites, the laboratory experiments were run in a closed reactor at 40°C and 60°C with 10 MPa CO2 and water (water/solid ratio = 10). Although dissolved Mg2+ ions were detected, precipitation of Mg carbonate was kinetically inhibited in the experiments. Magnesite (MgCO3) was presumably formed in long time scales as Mg carbonate hydrate (e.g., nesquehonite; MgCO3·3H2O) initially forms as metastable phases.
The experiments for ERW were started on the rooftop of the AIST Tsukuba Central 7 office. The samples were exposed to outside weather conditions and sometimes interacted with rainwater. The results of 6-month monitoring demonstrated that pH and dissolved metal concentrations (e.g., Mg2+) of the water passing through the solid samples were higher than those of the original rainwater. The weathering reaction of serpentinite was significantly observed as brucite (Mg hydroxide mineral) in serpentinite was dissolving.
To summarize, the reactivity of mafic–ultramafic rocks in CO2–water–rock systems was discussed in this study. Further works need to investigate other mafic–ultramafic rocks from different locations in Japan.