ELECTRICAL DOUBLE LAYER AT THE CALCIUM CARBONATE/ELECTROLYTE INTERFACE: MOLECULAR MODELING AND EXPERIMENTAL INSIGHTS

Calcium carbonate (CaCO₃) is one of the most common reactive minerals in the environment; important in biomineralization, scale formation and in the global carbon cycle. Understanding how the processes occurring at the carbonate surfaces, such as dissolution, (re/co)precipitation are controlled by the environment is of importance for predicting soil and groundwater acidity, the fate of contaminants and the security of geological carbon storage. A central component of carbonate surface reactivity is the electric double layer (EDL) that develops when carbonate minerals are immersed in water and that controls the surface affinity of ions. However, we lack the ability to predict carbonate surface stoichiometry and charge as a function of important variables including CO₂ partial pressure and solution pH or composition.

We use simulation to predict the surface charge, surface potential and the dielectric properties of carbonate-electrolyte interfaces and test these predictions using dielectric relaxation spectroscopy (DRS) and electrophoretic/potentiometric measurements. We find that the surface potential of calcite is more than order of magnitude larger than that of amorphous calcium carbonate – a clear indication that surface electrostatics contribute significantly to the surface energies and stabilities of carbonate polymorphs in solution.

Our results are relevant for developing a new generation of atomistic-surface complexation models of the carbonate/electrolyte interface, with implications for the carbonate dissolution/precipitation, pressure dissolution, growth and transformations in the environment.