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

摘要：

采用电导率法测量匀速旋转的石膏块试样(CaSO₄·2H₂O,质量分数为98%)在纯水中的溶解速率,数据采集时间间隔1 s,测试期间试样表观形状(7 cm×4 cm×2 cm)和面积(100 cm²)基本不变。在溶解过程为表面反应控制条件下,依据溶解反应动力学模型,拟合得到25、45、65、85℃下二水硫酸钙溶解反应速率常数分别为1.91×10^-8、3.46×10^-8、4.92×10^-8、7.07×10^-8 mol·cm^-2·s^-1,反应级数为1.27。经Arrhenius公式回归得到溶解反应表观活化能为19.07 kJ·mol^-1。本实验方法排除了溶解过程试样面积不确定因素,拟合得到的模型参数使动力学方程计算值与实验值更为吻合,更接近溶解速率理论预测文献值。

关键词: 二水硫酸钙, 溶解, 动力学, 速率常数, 活化能