The kinetics of the noncatalytic solid-gas reaction between Ca(OH)(2) and SO2 at low temperature and in the presence of water vapor was investigated. The effect of relative humidity, temperature, and SO2 concentration on the desulfurization capacity, of the solid was evaluated, as well as the effect of NO2 concentration. A deactivation model (DM) and a new version of this model, by implementing an inverse shrinking core model (DM-ISCM) with an ionic solid-state diffusion control, were fitted to experimental kinetic data. The proposed model showed the best agreement with the experimental results. A chemical mechanism for the reaction on the solid surface was also discussed. (c) 2005 American Institute of Chemical Engineers.