Critical Review of the Kinetics of Calcite Dissolution and Precipitation

Abstract

Abstract Kinetic results of published laboratory studies of calcite dissolution and precipitation in the system CaO-MgO-Na 2 O-K 2 O-CO 2 -H 2 SO 4 - HCl-H 2 O are used to test the surface mechanism model of Plummer, Wigley, and Parkhurst (1978; Amer. Jour. Sci. 278, 179-216). This mechanism model includes: 1) three simultaneous reactions at the mineral-aqueous solution interface, 2) heterogeneous equilibrium within the adsorption layer, 3) forward reaction first order in the boundary layer activities of H +, H 2 CO * 3 and H 2 O, and 4) backward reaction controlled by interaction of boundary layer Ca 2+ and HCO - 3 species with the adsorption layer speciation. Concentration - time curves predicted by this model have shapes similar to those observed in dissolution experiments. Most calculated rates are within a factor of 10 of the observed and many are within a factor of 2 or better. Discrepancies larger than a factor of 2 are probably significant and identify three problem areas: 1) quantification of transport aspects of the rate of dissolution under differing hydro-chemical conditions, 2) uncertainties in reaction surface area and reaction site density per unit surface area, and 3) difficulties in defining surface (adsorption layer) pH, which is essential in determining rate of backward reaction.