Investigation of mineral dissolution kinetics through Atomic Force Microscopy

We illustrate an experimental platform grounded on Atomic Force Microscopy (AFM) imaging enabling one to evaluate nanometer-scale absolute material fluxes across a mineral surface subject to precipitation/dissolution reaction under continuous flow. Reactive phenomena of this kind taking place at the solid-fluid interface have a pivotal role in driving alterations of the fundamental properties of natural geologic systems (including, e.g., porosity, permeability, and storage capacity). High resolution experimental observations document that several kinetic processes contribute to the overall reaction. These, in turn, yield a markedly heterogeneous distribution of reaction rates. The latter cannot be characterized through average rate values. Current challenges limiting our ability to characterize such heterogeneity include the establishment of a reliable integrated experimental platform that allows employing AFM imaging to evaluate real-time and in situ absolute material fluxes across the mineral surface. These can then be employed to enrich and expand typical analyses of the evolution of surface morphology. We overcome these barriers and provide spatial distributions of rates observed at the nanoscale across the surface of a calcite crystal subject to dissolution. We then interpret experimental observations through a stochastic approach. The latter is designed to embed the action of diverse kinetic modes corresponding to different mechanistic processes taking place across the surface and driving the spatial heterogeneity of the reaction.