5:15 PM - 6:45 PM
[HSC07-P13] Weathering monitoring of mafic and ultramafic rocks in outdoor experiments
Keywords:enhanced rock weathering, mafic rocks, carbon dioxide removal, carbonate mineral, magnesium oxide
Enhanced rock weathering (ERW) has been receiving a lot of attention and recognized to be a new technology for carbon neutrality in addition to carbon dioxide capture and storage (CCS). Some mafic rocks may have the potential for CO2 fixation as demonstrated by recent basalt CCS projects in Iceland and the United States. For the ERW study, it is necessary to evaluate the CO2 reduction potential in weathering processes of crushed mafic or ultramafic rocks on the Earth’s surface (e.g., croplands).
In this study, outdoor weathering experiments were conducted with a variety of mafic or ultramafic rocks in Japan: basalt (Iki, Mishima, Sado, Hokkaido), peridotite (Hokkaido), and serpentinite (Hokkaido). Mg oxide (MgO) was also used as a starting material in the experiments to focus on the behavior of Mg2+, which is one of the main cations in mafic or ultramafic rocks. The starting materials were sieved to a particle size of 1–2 mm and have been exposed to outside weather conditions on the rooftop of the AIST Tsukuba Central 7 office since September 1st, 2022.
The results of 12-month monitoring demonstrated the weathering process of the rocks. Within a few days after each rain event, we collected water samples: the original rainwater and the water passing through each of the solid samples. pH values increased as the rainwater passed through the solid samples, suggesting that atmospheric CO2 was chemically trapped as dissolved species during the rock weathering. The pH values the highest in the experiment with MgO (~9), followed by serpentinite (~8), peridotite and Sado basalt (~7), implying that the efficiency of chemical trapping of CO2 depends on the characteristics of the solid phase. In the experiments with MgO and serpentinite, results of the solution analyses showed particularly high Mg concentration and significant dissolution of the staring materials, which was a reason for the pH increase. The solid samples were collected after 1, 6, and 12 months. In the MgO experiments, powder X-ray diffraction analysis showed formation of hydrated Mg carbonate mineral (dypingite), and infrared microscopy and scanning electron microscopy revealed that dypingite precipitated on the MgO surface.
To summarize, this work succeeded in obtaining data on long-term rock weathering and CO2 fixation under the outside weather conditions. Since unreacted particles remained in the 12-month aged samples, we continue monitoring the rock weathering and plan new experiments to accelerate weathering and CO2 mineralization.
In this study, outdoor weathering experiments were conducted with a variety of mafic or ultramafic rocks in Japan: basalt (Iki, Mishima, Sado, Hokkaido), peridotite (Hokkaido), and serpentinite (Hokkaido). Mg oxide (MgO) was also used as a starting material in the experiments to focus on the behavior of Mg2+, which is one of the main cations in mafic or ultramafic rocks. The starting materials were sieved to a particle size of 1–2 mm and have been exposed to outside weather conditions on the rooftop of the AIST Tsukuba Central 7 office since September 1st, 2022.
The results of 12-month monitoring demonstrated the weathering process of the rocks. Within a few days after each rain event, we collected water samples: the original rainwater and the water passing through each of the solid samples. pH values increased as the rainwater passed through the solid samples, suggesting that atmospheric CO2 was chemically trapped as dissolved species during the rock weathering. The pH values the highest in the experiment with MgO (~9), followed by serpentinite (~8), peridotite and Sado basalt (~7), implying that the efficiency of chemical trapping of CO2 depends on the characteristics of the solid phase. In the experiments with MgO and serpentinite, results of the solution analyses showed particularly high Mg concentration and significant dissolution of the staring materials, which was a reason for the pH increase. The solid samples were collected after 1, 6, and 12 months. In the MgO experiments, powder X-ray diffraction analysis showed formation of hydrated Mg carbonate mineral (dypingite), and infrared microscopy and scanning electron microscopy revealed that dypingite precipitated on the MgO surface.
To summarize, this work succeeded in obtaining data on long-term rock weathering and CO2 fixation under the outside weather conditions. Since unreacted particles remained in the 12-month aged samples, we continue monitoring the rock weathering and plan new experiments to accelerate weathering and CO2 mineralization.