The sulfation reaction of half-calcined dolomite particles at high CO2 partial pressures (around 1 bar) was investigated. The experiments were carried out in two different reactors : (a) a thermogravimetric analysis system (slow heating rates) and (b) a shock-microreactor (rapid heating rates). The experiments were carried out under isothermal conditions at temperatures between 650 and 875 degrees C. A natural dolomite sample was used. Different particle sizes were tested : 26, 128, 256 and 512 mu m. Under reaction conditions employed in the experiments (P-CO2 approximate to 1 atm and T < 900 degrees C), half-calcination of dolomite particles takes place and the sulfation reaction occurs between CaCO3 . MgO and SO2. The CaCO3 is the only active species during sulfation. The particle size and temperature have a strong influence on the variation in extent of conversion with time. Two different stages can be distinguished in the sulfation of half-calcined dolomite particles; chemical control at the onset of reaction and diffusional control at longer reaction times. When the sulfation reaction is carried out under conditions similar to those existing in a boiler (high heating rates and simultaneous calcination and sulfation), the measured reaction rates are higher than those observed from thermogravimetric experiments. At X = 0.1 an activation energy of 34 kcal mol(-1) (142 kJ mol(-1)) was measured. This value suggests that the process is controlled by a solid state diffusion mechanism.