Decarbonation rates of cycled CaO sorbent were measured for a wide range of particle sizes (0.25-4 mu m), temperatures (747-830 degrees C), and relative CO2 Concentrations (0-95%). The decarbonation rate was found to decay exponentially with an increase in partial CO2 pressure that can be explained by assuming CaO nuclei formation is the rate-limiting step. A differential particle model using two variable parameters was successfully applied to fit the experimental data. An approximate analytical expression is put forward for the decarbonation rate as a function of sorbent texture, temperature, CO2 pressure, particle size, and Sherwood number.