The behavior of the carbonation reaction of the calcined Cadomin limestone used for CO2 capture is described using the grain model and the changing grain size (CGS) model. To calculate the overall conversion over time, the mathematical modeling was solved semianalytically. The overall sorbent conversion obtained with the CGS model showed better agreement with the experimental data than the results obtained using the grain model. In the CGS model, the physical structure of the sorbent particle changes during the reaction. The CGS model was modified by considering a variable diffusion coefficient of the gaseous reactant through the development of the product layer. The modeling results showed the positive effects of increasing the reaction temperature and particle porosity on the rate of carbonation reaction. However, the rate of carbonation reaction decreased by increasing the sorbent particle size. Moreover, the modeling results demonstrated an initial kinetic control stage which was followed by a diffusion control step in the carbonation reaction of the calcined Cadomin limestone.