Mineral Dissolution Kinetics: Pathways to Equilibrium

Abstract

Dependence of dissolution rate from undersaturation is a fundamental problem that has been traditionally approached from thermodynamic arguments and empirical observations. Commonly used rate laws predicting dissolution kinetics are constructed based on these considerations. A persistent issue is the poor reproducibility of some kinetic parameters in the experimental measurements with 2−3 orders of magnitude in their parameter value variance. Some puzzling functional dependencies of rates on reaction Gibbs free energies became a subject of debate during the last two decades. In the present paper, we have derived new generic rate laws based on statistical mechanics considerations. These rate laws are implemented into a kinetic Monte Carlo model for calcium carbonate (calcite) dissolution at fixed concentrations of the dissolved ions. The saturation state was gradually changed from far-from-equilibrium towards equilibrium conditions. We showed how different kinetic pathways can be easily generated for systems with different types and amounts of lattice defects. The analysis of these pathways showed that a reactive system never repeats the same pathway when it enters a saturation state visited previously. This behavior reflects intrinsic mineral−water interface kinetics incorporated into the new rate laws including reactive site population statistics. We discuss the underlying theoretical issues in rate law definitions, leading to large rate variances and uncertain ΔG-dependencies. We also discuss the physical meaning of n in the (1 − Ω) n term arising from experimental and field studies. An alternative way to treat mineral−fluid kinetics is offered.

Effect of Solution Stoichiometry on BaSO4 Crystallization from Turbidity Measurements and Modeling

“…This in turn was related to differences in dehydration rates or surface complexation . To obtain more mechanistic insight on the stoichiometric effect on particle growth alone, one could also employ kinetic Monte Carlo calculations as previously used for particle dissolution . For nucleation, the formation of initial complexes might be relevant.…”

“…46 To obtain more mechanistic insight on the stoichiometric effect on particle growth alone, one could also employ kinetic Monte Carlo calculations as previously used for particle dissolution. 52 For nucleation, the formation of initial complexes might be relevant. To avoid highly charged particles, the amount of formed particles might be severely restrained to the concentration of the limiting ion.…”

Statistical Description of Calcite Surface Roughness Resulting from Dissolution at Close-to-Equilibrium Conditions

“…One should emphasize that our results are not intended to imply that Model 3 can be considered a universal descriptor of mineral dissolution that would apply to any mineral reacted at close-to-equilibrium conditions. As opposed to mechanistic models such as kinetic Monte Carlo simulations (e.g., refs , , ), Model 3 is essentially phenomenological and its parameters need to be estimated against experimental observations. Nonetheless, and more importantly, the development and analysis of these various models underlined the need to consider some key elements that have to be implemented into any future model to ensure its ability to capture major features of the statistics of surface roughness, as described in the following: The dissolution probability of a given voxel is dynamic as it depends on its immediate neighboring environment.…”

“…While such a simplification rests on the assumption that reactivity is immutable in time and homogeneous at the surface of the minerals, the heterogeneous nature of the surface reactivity appears as a universal feature of solid dissolution, as documented through a variety of material degradation studies ranging from the corrosion of metals, − glasses, and ceramics − to the weathering of rocks and minerals (e.g., refs − ). At the heart of the heterogeneous nature of surface reactivity is the concept of surface energy and its distribution in space and time throughout the evolution of the dissolution process (e.g., refs , ), which is then mirrored by the gradual development of surface roughness.…”

Discontinuous Dissolution Mechanism of Olivine Deduced from a Topography Observation Method

“…This model connects the Gibbs free energy to step retreat and dissolution rate. 21 The heterogeneities of mineral dissolution rates have been reported more recently on pyrochlore, 22 zinc oxide, 23 calcite, 24−26 limestone, 27 and feldspar 28 by the measurement of surface topography measurements with vertical scanning interferometry (VSI), atomic force microscopy (AFM), 27 and X-ray macroscopy. 25,26 These results have repeatedly validated the step-wave model.…”