Improved mineral-dissolution kinetics in reactive-transport modeling

• Applicant: Tao Yuan, Ph.D.
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555157446

Reactive-transport models are essential tools for the predictive description of mineral-dissolution reactions and thus the evolution of the pore network, flow field, and permeability, which is important in critical-zone weathering, the evolution of karst systems, and carbon sequestration, among others. However, the reliability of reactive-transport models involving mineral-dissolution reactions is restricted by the assessment of reactive-surface sites. Implementing these insights into continuum-scale reactive-transport models is a major challenge because the intrinsic variability of surface reactivity at the micrometer scale is difficult to quantify, and the effects of the intricate interplay between the small-scale variability of flow and reactivity on effective reactive transport on larger scales is largely unknown. The aim of the proposed project is therefore to implement intrinsic surface reactivity in reactive-transport models to enhance the predictability of mineral dissolution at micrometer to centimeter scales. At the micrometer scale, we will assess the influence of surface nanotopography on calcite dissolution by comparing two parameterizations of the nanoroughness: one based on the standard deviation of the surface height, and the other on the distribution of surface slopes. The micrometer-scale reactive-transport models will be applied to test cases of mineral dissolution, ranging from single crystals to complex pore networks, for which datasets of measured nanotopography and net dissolution rates exist. Next, we propose an upscaling strategy to account for the variability of the intrinsic surface reactivity on the micrometer scale in centimeter-scale simulations that can be applied to rock cores. Moreover, new porosity-permeability relationships will be derived based on micrometer-scale simulations. Both the upscaled reaction rates and the petrophyscial relationships will be implemented in centimeter-scale models to enhance the predictability of mineral dissolution in larger-scale simulations. With the developed reactive-transport models, the project aims to reproduce experimentally derived heterogeneous rate distributions and observed preferential dissolution patterns. Finally, we will investigate the dependence of mineral dissolution kinetics on spatial and temporal scales in systems with heterogeneous intrinsic surface reactivity. Sensitivity studies will be carried out to understand the scale dependence of effective calcite dissolution in the presence of unresolved variability of the intrinsic surface reactivity. For different conditions we will provide a length scale, at which the intrinsic surface reactivity heterogeneity can be homogenized, thus leading to constant effective coefficients. We expect to confirm the general applicability of the developed reactive-transport models.

• DFG Programme: Research Grants