The direct sulfation reaction of SO2 with CaCO3 has been investigated by thermogravimetry (TG) under the condition that the CaCO3 does not decompose to CaO prior to sulfation by controlling CO2 partial pressure. The direct sulfation process can be described by using a shrinking-core model for constant particle size. The model shows that the reaction rate and the diffusion rate or SO2 through the product layer are equally important. Temperature effects can be correlated by the activation energy of 35.9 kJ mol(-1) for the sulfation reaction and 66.5 kJ mol(-1) for the product layer diffusion. The sulfation reaction is found to be first order with respect to SO2. With larger pore volume and surface area of limestone samples, the sorbents have a stronger reactivity of SO2 removal. A 70% CaCO3 conversion can be achieved in 10 min at 800 degrees C and 2000 ppm SO2.