Thermogravimetric study and modeling of direct sulfation of Iranian limestones by sulfur dioxide

The direct sulfation of three high purity limestones from different sources, all having more than 97% CaCO 3 , was studied in a thermogravimetric analyzer under atmospheric pressure, in the presence of excess CO 2 to prevent decomposition of CaCO 3 . Experiments were carried out over particle size levels ranging from 1.6 - 7.8 μm at four temperatures (700, 750, 800, and 850 °C), and two SO, concentrations (2400 and 3200 ppm). The particle size and temperature showed a dominant influence on the variation of conversion with time, while effect of SO 2 concentration was found to be weak. The results of experiments show that the Shrinking Core Model can be used to predict the performance of limestone sulfation. This simply reveals that the reaction rate and diffusion mechanism control are both important. The parameters of the model, such as chemical rate constant K s and effective diffusion coefficient (D eff ) were obtained as follows: K s = 3.8 exp(-14/RT) cm/s D eff = 18607 exp(-55.3/RT) cm 2 /s Model predictions are in good agreement with experimental data.