New Kinetic Monte Carlo Model to Study the Dissolution of Quartz

Quartz
dissolution is a frequent process in geochemistry and materials
science. It is controlled at the atomic scale by the sequential hydrolysis
reactions and breakage of siloxane bonds, the surface topography,
and the Gibbs free energy difference ΔG between
the solid and the solution. Atomistic simulations have provided valuable
topographic information about quartz dissolution and reaction energy
barriers. However, with the current interpretation of the data, serious
discrepancies persist between the predicted dissolution rates Rdis and the macroscopic dissolution activation
energy Ea compared to their experimental
counterparts. In this work we show that both quantities can be reconciled
using a kinetic Monte Carlo (KMC) atomistic model based on bond-by-bond
reactions and Rdis and Ea can be jointly reproduced. In addition, the obtained
etch pit shapes for different quartz planes are in agreement with
the experimentally reported ones: V-shape striations in {001}, rectangular
pyramidal pits in {100}, and trapezoidal semipyramidal pits in {101}.
We also study the dissolution rate dependence with ΔG by introducing chemical reversibility in the KMC model, obtaining
again results in good agreement with experiments. This work highlights
the importance of understanding the mechanisms taking place at the
nanoscale to describe macroscopic properties and provides the basic
ingredients to extend this study to other minerals and/or dissolution
conditions.