Article,
A model for crystal dissolution
Eur J Mineral, 15 (4): 603-615 (2003)
DOI: 10.1127/0935-1221/2003/0015-0603
Abstract
A comprehensive dissolution rate theory that integrates individual surface reactions into an overall rate is developed. The dissolution theory is based on the movement of dissolution stepwaves stemming from surface defects. The net bulk rate associated with dissolution stepwaves arises quite naturally from the equations describing the spreading of the train of steps from surface defects. The overall rate can be shown to approach a simple linear rate or transition-state theory-like equation far from equilibrium. However, one of the most important results is the strong nonlinear decrease in the rate as equilibrium conditions are approached, as is the case in most natural processes. The model is validated by extensive Monte Carlo simulations of crystal dissolution, which include a detailed treatment of surface defect energetics, adsorption, surface diffusion, transport of elements from solution, and the bonding dependence of detachment processes from the surface. Monte Carlo results show the generation of dissolution stepwaves and the nonlinear dependence of the overall rate on the saturation state. The final rate equations are consistent with both the far-from-equilibrium experimental work and several recent studies that approached equilibrium. The decrease in the rate as equilibrium is approached has far-reaching implications for both man-made problems (e.g., radioactive waste disposal, pollution, etc.) and natural processes from ground-water to metamorphic systems.
