[H-SC06] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC06-P02] Improvement of reactive transport models for observation-based estimates of CO₂ sequestration through Enhanced Rock Weathering in agricultural fields in Japan

*Masahiro Yoda¹, Shinnosuke Aoyama¹, Steven James Benbow², Tsutomu Sato³, Atsushi Nakao⁴, Taku Nishimura⁵, Hkaung Htut San³, Hiroyasu Takase¹ (1.QJ Science. Co. Ltd., 2.Quintessa Ltd., 3.Graduate School of Engineering, Hokkaido University, 4.Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 5.Graduate School of Agricultural and Life Sciences, The University of Tokyo)

Keywords:Enhanced Rock Weathering, CO2 Mineralization, Reaction Transport Model, NETs

Enhanced Rock Weathering (ERW) has recently gained attention as a potential Negative Emission Technology (e.g., Beerling et al., 2020; Kanzaki et al., 2022). Beerling et al. (2020) developed a one-dimensional reactive transport model (RTM) to estimate CO₂ sequestration due to ERW when crushed basaltic rock is applied to agricultural fields. They evaluated the time evolution of mineral weathering in the basaltic rock and estimated the potential for CO₂ sequestration through the precipitation of carbonate minerals (e.g., calcite) in agricultural fields and the release of alkalinity into the ocean via land surface runoff. Their model considers factors influencing CO₂ sequestration, such as precipitation rate, mineral grain size, and secondary minerals. However, their model is quite general and for more concrete and accurate estimates of CO₂ sequestration models should, as far as possible, reflect relevant field conditions and observations.

In this presentation, we will discuss the construction and improvement of the RTM for observation-based estimation of CO₂ sequestration through ERW in Japanese agricultural fields. Preliminary improvement for the RTM was conducted using the QPAC modelling software (Quintessa, 2013). A more accurate estimation of CO₂ sequestration through ERW was achieved by incorporating observational data obtained from agricultural fields (e.g., soil pore water quality and the soil gas phase) into the RTM.

In the improved RTM, we focused on the soil characteristics specific to Japan. There is a wide distribution of soils derived from volcanic activity (e.g., Andosols), which have pH-buffering effects. Therefore, alkalization due to the mineral weathering can be buffered, and the pH of soil pore water is expected to remain weakly acidic to neutral, in contrast to previous estimates (e.g., Beerling et al., 2020). Our improved model allows the pH of soil pore water to be set as an input to the model, enabling us to understand the dissolution behavior of previously undissolved minerals (e.g., augite) under more realistic field conditions. The gas phase in soil, particularly CO₂, is also an important factor in understanding the precipitation behavior of carbonate minerals. Our model, which considers depth gradients and temporal changes of pCO₂ in soil, can provide a more accurate estimation.

Finally, we will propose an observation-based estimation of CO₂ sequestration through ERW in Japan, based on the preliminary analysis by the improved model. We will also suggest further improvements to the model and the observation methods needed for future measurement, reporting, and verification (i.e., MRV).

*The outcome of this study was achieved through the commissioned project by the New Energy and Industrial Technology Development Organization (NEDO) (JPNP18016).