AN EXPERIMENTAL STUDY OF DOLOMITE DISSOLUTION RATES AS A FUNCTION OF PH FROM -0.5 TO 5 AND TEMPERATURE FROM 25 TO 80°C

Abstract

Steady-state dissolution rates of Haute Vallee de l'Aude dolomite were measured in mixed-flow reactors using rotating disk techniques. Experiments were performed in aqueous HCl solutions over the bulk solution pH range -0.39 to 4.44, and at temperatures of 25, 50 and 80°C. Dissolution rates were found to depend on disk rotation speed at all temperatures and pH. Interpretation of these rates using equations reported by Gregory and Riddiford [Gregory, D.P., Riddiford, A.C., 1956. Transport to the surface of a rotating disk. J. Chem. Soc., 33, 37-56] yields steady-state dissolution rates as a function of the solution pH adjacent to dolomite surface (pHsurf). Rates at all temperatures and 1<pHsurf<5 are found to be consistent with r=k1an1H+,surf, where r refers to surface area normalized steady-state dissolution rates, k1 stands for a rate constant, and aH+,surf designates hydrogen ion activity in the solution adjacent to the dolomite surface, and n1 denotes a constant equal to 0.63, 0.73 and 0.80+/-0.05 at 25, 50 and 80°C, respectively. Rates tend towards pH independence at more acidic conditions suggesting the saturation of dolomite surfaces with rate controlling protonated species. Additional experiments performed to assess the effect of the presence of aqueous Ca2+ and Mg2+ demonstrate that these species have little to no effect on dolomite dissolution rates at pH=2 and 50°C.