THE KINETICS OF BARITE DISSOLUTION AND PRECIPITATION IN WATER AND SODIUM-CHLORIDE BRINES AT 44-85-DEGREES-C

The dissolution rate of natural barite cleavage fragments was measured in deionized water and NaCl brines over the temperature range 44-85-degrees-C. Dissolution followed first-order kinetics, with an activation energy of 24.9 +/- 10.1 kJ/mol. The observed insensitivity to stirring rate and low absolute value of the rate constant (extrapolated k at 25-degrees-C = 3.30 +/- 1.31 X 10(-3) L/m2 s) indicated desorption rather than volume diffusion as the rate-determining step. The NaCl concentration had no effect on k up to 0.1 M. Barite growth from supersaturated aqueous solutions was also studied. Precipitation followed a second-order rate law, k(25-degrees-C) = 162 +/- 65 L2/sm2 mol, E(a) = 22.0 +/- 14.3 kJ/mol, and was not sensitive to pH variation. A different rate law is likely to apply at high supersaturations, where a change in secondary growth morphology was observed.