Chelating Ligand Alters the Microscopic Mechanism of Mineral Dissolution

Ethylenediamine tetraacetate (EDTA)-mediated calcite dissolution occurs via a different process than water-promoted dissolution. Near-atomic-scale observations in EDTA solutions demonstrate that, after penetration through a critical pit depth barrier, step velocity increases linearly with pit depth for EDTA-promoted dissolution. The parallel processes of water-dominated dissolution at point defects and ligand-dominated dissolution at linear defects are clearly observable in real-time atomic force micrographs. EDTA and water initiate and propagate dissolution steps with pit-depth-dependent and -independent step velocities, respectively. The linear defects are susceptible to continuously increasing step velocities, but the point defects are not. The findings update the conceptual framework of the microscopic mechanism of mineral dissolution.