Abstract: The dissolution of Mg-Al hydrotalcites in aqueous solution and its mechanism were investigated, with the dissolution kinetics and thermodynamics at different temperatures and pH. The kinetic model with the outer diffusion and chemical reaction control can be used to describe the dissolution process appropriately, with different controlling steps in various pH ranges. In the pH range from 1.0 to 3.8, the hydrotalcites dissolve completely and the dissolution rate decreases as pH increases, with the dissolution controlled by desorption. In the pH range from 4.2 to 9.4, the hydrotalcites partly dissolve, independent of pH, with the dissolution controlled by surface exchange reaction. On the other hand, the Gibbs free energy change of the dissolution reaction from the Mg-Al hydrotalcite is estimated as 29.516 kJ·mol^-1 at 298 K. The result is consistent with the experimental evidence.

Key words: Mg-Al hydrotalcite, dissolution, kinetics, thermodynamics, kinetic modeling

摘要： 研究了Mg-Al水滑石在水溶液中的溶解性能及其机理，考察了温度和pH对其溶解性能的影响， 探讨了溶解过程中动力学和热力学规律。动力学研究表明，Mg-Al水滑石在水溶液中的溶解符合外扩散及表面化学反应控制模型，且不同pH区间其控制步骤不同。pH 1.0～3.8，水滑石完全溶解，其溶解速率随pH的提高而减小，受解吸控制。而pH 4.2～9.4，水滑石部分溶解，溶解速率与pH值无关，受表面交换反应控制。另一方面，对水滑石溶解反应的Gibbs自由能变进行定量估算，其值为29.516 kJ·mol^-1。经实验验证，理论估算可很好地与实验结果吻合。

关键词: 镁铝水滑石, 溶解, 动力学, 热力学, 动力学模型