AbstractExperimental data on sulfation rates of CaO particles derived from CaCO3are compared to those derived from Ca(OH)2using a product layer diffusion control model differing only in the shape of the CaO grain. Both the model and the experimental data indicate slightly higher reactivity for the Ca(OH)2‐derived oxide due to the observed difference in grain shape. This effect is considered as a contributor to the greater performance of Ca(OH)2in pilot‐scale SO2removal stud