Enhanced rock weathering in agricultural lands for carbon removal: a reactive transport modeling perspective
In this study, a reactive transport model was used to investigate constraints on the weathering rates of rock materials applied to agricultural lands for the purpose of carbon removal from the atmosphere. Enhanced weathering is a promising carbon removal technology. Application of ground rocks as soil amendments in agricultural lands can also provide other co-benefits, such as improved soil health, crop yield, etc. Adoption of this technology at a meaningful scale requires systematic assessment of its feasibility and scalability. Our simulations were designed to compare the relative importance of factors that are controlled by engineering operations (e.g., grain size and surface area, composition of the applied materials, and application depth) and soil properties (e.g., hydraulic properties, composition, and abundance of organic ligands), in order to inform optimized practices and carbon credit accounting. For instance, our results have highlighted the trade-off between water availability and reactive surface area. While grain size has been considered as a critical parameter and is typically refined to enlarge the reactive surface area and accelerate reaction rates, our results showed that in water limited systems, refinement of the grain size becomes ineffective. Given that grinding is a major contributor of the energy penalty associated with enhanced weathering, it is important to consider the land management practices such as irrigation at the applied locations while identifying optimized grain size. In addition, our results pointed out that with the same infiltration rate, well-drained soils allowed for more carbon removal due to more effective transport of the gas phase, including CO2.