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 Delta G 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 R-dis and the macroscopic dissolution activation energy E-a 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 R-dis and E-a 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 Delta G 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.