A mathematical model dealing with the removal Of SO2 by solid absorbent in a bag filter is proposed. The model assumes a situation similar to that of a fixed bed reactor and describes the phenomena and kinetics of the process for the SO2-Ca(OH)(2) reaction system. The model is based on the grain model concept, where the diffusion coefficient of gas in the particles/pellet is assumed to vary during the reaction. Runge-Kutta-Gill and finite difference methods were used to calculate the reaction rate constant, k(s), and the coefficient of gas diffusion in the solid grain, D-s, through best fitting with the experimental data under a temperature range of 120-190degreesC. The effects of certain parameters, such as humidity and temperature, were investigated. Assuming the validity of the Arrhenius law, the activation energies were calculated for both the reaction, E-r, and the coefficient of gas diffusion in the solid grain, E-d. The results thus obtained using the proposed model are in good agreement with those previously reported in the literature.