Mechanisms and Dynamics of Mineral Dissolution: A New Kinetic Monte Carlo Model

Abstract

Mineral dissolution is a fundamental process in geochemistry and materials science. It is controlled by the complex interplay of atomic level mechanisms like adatoms and terraces removal, pit opening, and spontaneous vacancy creation that can be gradually activated at different energies. Though the development of a comprehensive atomistic model is key to go deeper into the understanding of this phenomenon, existing models have failed to reproduce the abrupt dependence of the dissolution rate with the Gibbs free energy ( G). Herein, a new atomistic kinetic Monte Carlo (KMC) model is presented, which, invoking the microscopic reversibility of chemical reactions, captures the experimentally observed sigmoid dependence of the dissolution rate and provides new insights on the concomitant dissolution mechanisms. As a salient result, the model predicts the possible existence of unreported close-to-equilibrium dissolution modes where spontaneous vacancies creation and pit opening can occur before adatom and terrace removal.

KIMERA: A Kinetic Montecarlo Code for Mineral Dissolution

“…The implementation on KIMERA is based on the reversible Kinetic Model that we presented recently [29]. In this model, we take into account microscopic reversibility defining for every possible dissolution reaction two events, one of dissolution and one of precipitation, with their respective rates r D and r P :…”

“…The program is based on the N-fold-way algorithm, which ensures a good efficiency [40]. Moreover, to overcome the typical problem of KMC simulations of waste of computer power in fast and repeating events [41], we have implemented a Poisson approximation to handle opposite effects of dissolution and precipitation which shows no reduction of performance or biased results [29]. If faster simulations were needed, KIMERA has been parallelized using openMP library [42], which entails an easy way to divide the workload of some loops of the program between the number of cores available.…”

“…Of special interest is the KMC method which allows temporal scale studies comparable to experiments. The effect on dissolution of dislocations [26,27], grain sizes [25] or surface roughness [21], the inherent topographies associated to the dissolution mechanisms [22,23,26,27], the experimentally observed pulsating frequency at the nanoscale [28], or more recently the dissolution rate dependence with ∆G [29] are some of the milestones achieved by KMC simulations. Unfortunately, while many DFT, molecular dynamics and molecular mechanics programs are available both commercially and with free license [30][31][32][33], this is not the case with KMC.…”

“…A recent study demonstrates that the net dissolution of a mineral can be characterized using decoupled reactions of dissolution and precipitation [29]. Hence, we use that KMC scheme, so the fundamental frequency of the Arrhenius equation, f , splits into f D or f P , and E B into E D or E P depending if considering a dissolution or a precipitation event respectively.…”

“…This approximation arises from considering as limiting step the removal of the atom which leads to a kink atom, always with half of the mineral coordination [29,48].…”