Fundamental Controls of Dissolution Rate Spectra: Comparisons of Model and Experimental Results

Real-time microscopic observations of reacting mineral surfaces have provided a significant advance in the understanding of mineral dissolution and growth. The kinetics of surfaces are often dominated by the distribution of defects, e.g., screw dislocations, that provide a critical means of sustaining step movement and kink creation that are fundamental to dissolution and growth processes. However, in natural settings, the discontinuities created by physical grain boundaries and contacts may constitute a critical contribution to “whole rock” reactivity, a point that has been recognized in the past. Because of the complex relationship between mineral surface characteristics such as area, roughness, and reactivity, this problem requires a modeling approach that examines the relationship between rate and surface morphology. This approach is relevant to the question of whether a critical size exists that is governed by surfaces kinetics, below which the reactivity of grains is dominated by contributions from boundary sites. We discuss these results in light of experimental observations of the statistical distribution of rates using the concept of rate spectra.