Flue gas produced from coal combustion contains CO2, O-2, and H2O in addition to SO2. The effects of these components, especially CO2, on the sulfation of a high surface area CaCO3 (73 m(2)/g) were studied using a differential fixed-bed reactor under conditions simulating the conventional and O-2/CO2 coal combustion atmospheres. The initial sulfation rate and ultimate (1 h) conversion for CaCO3 increased as the SO2 concentration (1000-5000 ppm) and reaction temperature (750-950 degrees C) increased, decreased as the CO2 concentration (0-95%) increased, and was independent of O-2 (5-20%) and H2O (0-10%) concentrations. Sulfation at temperatures and CO2 concentrations where CaCO3 can decompose gave higher conversions than the direct sulfation of CaCO3. CO2 impeded the sulfation of CaCO3 by inhibiting or delaying the decomposition of CaCO3 and enhancing the sintering of CaCO3 and CaO. Under the conditions where CaCO3 cannot be formed, CO2 had little effect on the sulfation of CaO; however, under the conditions where CaCO3 can be formed, CO2 had a negative effect by forming CaCO3. CaCO3 was more reactive than its calcine only at low CO2 concentrations (<12.5%). Under high CO2 concentrations (>50%), precalcination of CaCO3 and operation at temperatures where CaCO3 cannot be formed are more advantageous to SO2 removal.