关键词: 二水硫酸钙, 溶解, 动力学, 速率常数, 活化能

Abstract:

Dissolution rate of a gypsum (CaSO₄·2H₂O) sample rotating in pure water was measured by automatically detecting electric conductivity of the solution, in one-second time interval of data acquisition. Superficial shape (7 cm×4 cm×2 cm) and surface area (100 cm²) of the sample were maintained constant basically during measurement. Under surface reaction-controlled dissolution experiment condition, the kinetics model was used for regression of dissolution rate constant (k_s) and reaction order (n). The values of k_s were 1.91×10^-8, 3.46×10^-8, 4.92×10^-8, 7.07×10^-8 mol·cm^-2·s^-1 respectively for temperatures 25, 45, 65, 85℃, accommodated by a value of 1.27 for reaction order n. Consequently activation energy of dissolution reaction was correlated 19.07 kJ·mol^-1 through the Arrhenius equation. Because of eliminating uncertainty of sample's surface area in dissolution experiment, the results calculated from the kinetics equation with the model parameters regressed in this paper were more consistent with experimental value and closer to theoretical expectation of dissolution rates in literature.

Key words: calcium sulfate dihydrate, dissolution, kinetics, rate constants, activation energy