Mechanism of solid/liquid interfacial reactions. The maleic acid driven dissolution of calcite: An atomic force microscopy study under defined hydrodynamic conditions

The dissolution of calcite (CaCO3) in the presence of aqueous solutions containing maleic acid (cis-HOOC-CH=CH-COOH) in the pH range 4.3-8.2 has been studied by means of atomic force microscopy utilizing a flow cell of known hydrodynamics and modelable convection/diffusion. The latter permits the interpretation of dissolution rate data as measured by the z-piezo voltage in terms of a mechanism involving concentrations of solution species local to the dissolving crystal surface. In this way the dissolution mechanism for the (<10(1)over bar 4>) cleavage plane is shown to proceed via reaction of the adsorbed monoprotonated anion, cis-HOOC-CH=CH-COO-, but to be inhibited by the adsorbed dianion, -OOC-CH=CH-COO-. Where available excellent quantitative agreement is noted with independent surface averaged kinetic data previously (J. Chem. Sec., Faraday Trans. 1 1989, 85, 4335) obtained using a channel flow cell.