Mineral Dissolution Kinetics: Pathways to Equilibrium

• Published in: ACS earth and space chemistry Vol. 5; no. 7; pp. 1657 - 1673
• Main Authors: Kurganskaya, Inna, Luttge, Andreas
• Format: Journal Article
• Language: English
• Published: American Chemical Society 15.07.2021
• Subjects: dissolution mechanisms; Gibbs free energy; Monte Carlo; carbonates; rate law; saturation state
• ISSN: 2472-3452; 2472-3452
• DOI: 10.1021/acsearthspacechem.1c00017

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.