Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Mineral dissolution plays a key role in many environmental and technical fields, e.g., weathering, reservoir and host rock characterization, as well as building materials. The rate of mineral dissolution in water is determined by two parameters: (1) transport of dissolved species over and from the interface determined by advective fluid flow and diffusion (transport control) and (2) crystal surface reactivity (surface reactivity control). Current reactive transport models (RTM) simulating species transport commonly calculate mineral dissolution by using rate laws (e.g., Agrawal et al., 2020). These rate laws solely depend on species concentration in the fluid and therefore do not include intrinsic surface reactivity. Experimental studies at surface reactivity controlled conditions have shown a heterogeneous distribution of reaction rates (e.g., Bibi et al., 2018). This rate heterogeneity is caused by nanotopographical structures on the crystal surface, such as steps and etch pits that are generated at lattice defects. At these structures, the high density of reactive kink sites is leading to a local increase in dissolution rates.
In this study, we test whether experimentally observed rate heterogeneities can be reproduced by using current RTMs. We apply a standard RTM approach combined with the measured surface topography of a calcite single crystal (Bibi et al., 2018). The calculated surface dissolution rate maps are compared to experimentally derived rate maps. The results show that the measured rate heterogeneities cannot be reproduced with the existing RTM approach. To improve the predictive capabilities of RTMs, the surface reactivity that is intrinsic to the mineral needs to be implemented into dissolution rate calculations. We discuss parameterization of surface reactivity via proxy parameters, such as surface roughness or surface slope.

Agrawal, P., Raoof, A., Iliev, O. and Wolthers, M. (2020): Evolution of pore-shape and its impact on pore conductivity during CO2 injection in calcite: Single pore simulations and microfluidic experiments. Advances in Water Resources, 136, 103480.
Bibi, I., Arvidson, R.S., Fischer, C. and Lüttge, A. (2018): Temporal Evolution of Calcite Surface Dissolution Kinetics. Minerals, 8, 256