For the apparent kinetics of the carbonation reaction of calcium oxide by carbon dioxide, as a kind of noncatalytic gas-solid reaction, a model equation has been proposed as follows: X = kbt/(b + t), where X is the conversion of CaO; k, a kinetic rate constant (time(-1)); b, a constant (time) equivalent to the time taken to attain half the ultimate conversion of CaO, and t, the time. As a result of analyses for some literature-reported data of CaO-carbonation conversion, it has been found that the rate of the carbonation can be well represented by dX/dt = k(1 - X/X-u)(2), where X-u is the ultimate conversion of CaO, which is given by the product of two parametric constants, k and b. The constants k and b in the two rate control regimes of CaO-carbonation, chemical reaction control and diffusion control, have been determined as functions of temperature, respectively. The activation energy in the carbonation of surface CaO with CO2 is estimated to about 72 kJ/mol regardless of the sources of CaO, however, that in the diffusion control regime appears differently as 102.5 (mesoporous CaO) or 189.3 kJ/mol (commercial-available CaO), possibly due to the morphological differences of the two CaO samples. From a practical point of view, the simple model equation proposed in this study deserves attention in that the CaO-carbonation behavior at working temperatures hi-her than 700degreesC could be closely predicted. (C) 2004 Elsevier B.V. All rights reserved.