Reactive transport modeling of carbon capture in soil amended with fast weathering silicate minerals

Abstract Mineralization of powder form of fast-weathering silicate minerals (e.g., wollastonite and diopside) is reckoned as a stable and relatively low-cost method for sequestrating atmospheric CO2 in agricultural and urban soils. While the process, called terrestrial enhanced weathering, has well shown the capacity of carbon drawdown in lab and field scale studies, the long-term evolution of formation/redissolution of weathering product is less discussed in the literature. This study assesses long-term carbonate formation and migration over the soil profile with a reactive transport model built within the Geochemist Workbench software package. The model is built on the basis of experimental design/ procedure conditions and accounts for intermittent irrigation regimes and kinetic dissolution/precipitation of minerals as well as calcite formation. Simulation results are indicative of the growth of sequestrated carbon beyond the short-term duration (up to 8.3 t CO2/ha) with dissolved form (e.g., bicarbonates) growing over time. The model also predicts a slow migration of carbonates to deeper layers over five years. The modeling outputs are inconsistent with experimental observations, highlighting inflow rate as a driving factor in the formation of carbonates and mass of dissolved carbonate efflux from the system.