A comprehensive mathematical model for the CO 2 ‐catalyzed sintering of CaO is proposed. It takes into account the mechanisms of surface diffusion and grain boundary diffusion, catalyzed by CO 2 chemisorption and dissolution, respectively. In addition, the model proposed here considers the change in pore size distribution during sintering, grain growth, and the densification by lattice diffusion, which is the intrinsic sintering mechanism of the CaO. Model predictions are validated using experimental data on the sintering of two CaO samples, one of them derived from pure CaCO 3 and the other from limestone. It is found that impurities in limestone‐derived CaO do not significantly affect the CO 2 dissolution or chemisorption processes; however, they strongly increase the rate of sintering by lattice diffusion. It is also established that low temperatures and CO 2 partial pressures promote the coarsening by surface diffusion, whereas high temperatures and CO 2 partial pressures favor densification. © 2017 American Institute of Chemical Engineers AIChE J , 63: 3286–3296, 2017