The dissolution and precipitation kinetics of solid particles: the influence of adsorption

The dissolution or growth of solid particles, analogous to electro-dissolution and deposition processes, can occur either under mass transport or surface kinetic control with the latter considered increasingly likely as the size of the particle decreases since the rate of diffusion scales inversely with particle size. The conditions under which these processes are influenced by the adsorption of species onto the dissolving or growing surface are explored both generically and illustrated by the specific case of calcite (CaCO3) particle formation/dissolution in aqueous solution forming or from the component ions. Under surface control, the presence of adsorbed species leads to ‘blocking’ of the reactive surface, and a corresponding reduction in the observed rate. Under mass transport control, the concentrations of the various species in the layer of solution next to the solid are in equilibrium with the solid. They are thus pinned by the pertinent solubility product coupled with the solute fluxes in and out of the diffusion layer. In this situation, adsorption effects on the kinetics of dissolution/growth emerge in the observed effective thermodynamic solubility product as inferred from experiment. The predictions for the reduction in the rate of calcite dissolution in aqueous solution in the presence of dissolved Mg2+ cations are in quantitative agreement with experiment suggesting that for solids such as calcium carbonate, the effective solubility product and hence dissolution or precipitation rate is generically dependent on the identity and coverage of the adsorbate.