An experimental study of dolomite dissolution rates at 80 °C as a function of chemical affinity and solution composition

Abstract

Steady-state dissolution rates of Haute Vallée de l'Aude dolomite were measured as a function of chemical affinity and aqueous solution composition in mixed-flow reactors at 80 °C. Experiments were performed in HCl–NaHCO 3 bearing aqueous solutions with in-situ pH ranging from 6.36 to 7.17. Rates are found to be a strong function of aqueous carbonate concentrations at far-from-equilibrium conditions. Measured rates can be described using the dissolution mechanism of Pokrovsky and Schott [Pokrovsky, O.S., Schott, J., 2001. Kinetics and mechanism of dolomite dissolution in neutral to alkaline solutions revisited. Am. J. Sci., 301, 597–626] where rates are controlled by the detachment of the > MgOH 2 + species at the dolomite surface. Within this mechanism, dolomite dissolution rates can be described using r = k Mg + { K CO 3 ⁎ K Ca ⁎ K CO 3 ⁎ K Ca ⁎ + K Ca ⁎ a CO 3 2 − + a CO 3 2 − a Ca 2 + } n ( 1 − exp ( − n A / R T ) ) where r refers to the overall BET surface area normalized dolomite dissolution rate at both near and far-from-equilibrium conditions, k Mg + designates a rate constant equal to 4.0 × 10 − 12 mol cm − 2 s − 1 , K Ca ⁎ and K CO 3 ⁎ denote equilibrium constants equal to 3.5 × 10 − 5 and 4.5 × 10 − 5 , respectively, a i refers to the activity of the subscripted aqueous species, A corresponds to the chemical affinity of the dissolving dolomite, R represents the gas constant, T symbolizes absolute temperature and n designates a stoichiometric coefficient equal to 1.9.