Multiple length-scale kinetics: an integrated study of calcite dissolution rates and strontium inhibition

Abstract

Through an integrated experimental approach, utilizing both vertical scanning interferometry (VSI) and atomic force microscopy (AFM), we have been able to directly link calcite (104) dissolution rates over multiple spatial and temporal scales. By adjusting the concentration of Sr²⁺ in both CO₂-saturated and CO₂-free solutions, we have determined that “rough” step edge retreat across the surface controls the rate of overall dissolution. An exciting result of our study is that measurements of rough step velocity can be directly correlated with rates of calcite (104) surface-normal retreat. The effect of added Sr²⁺ on the dissolution kinetics of calcite is variable, depending on the presence or absence of dissolved inorganic carbon (DIC). Results show that, under CO₂-saturated conditions and pH 8.6 to 8.9, increases in Sr²⁺ concentration lead to decreased etch pit growth rate and reduced etch pit density, resulting in a partial passivation of the crystal surface. An important result is that these events seemingly have little effect on the rates of overall dissolution, supporting our suggestion that the dissolution mechanism is controlled by rough step retreat.