A NEW PARAMETER TO CHARACTERIZE LIMESTONES AS SO2 SORBENTS

A study of the CaO-SO2 reaction at 573 K in a thermobalance has been p erformed both in the absence and in the presence of O-2, with samples of eight different limestones and commercial CaCO3. Limestones and CaO obtained from it were both widely characterized. The ''classical'' te xtural parameters (BET surface area, pore volume, etc.) of the limesto ne or the CaO do not explain the behaviour of the CaO-SO2 system at 57 3 K, i.e., the SO2 retention degree at 573 K. On the contrary, a good correlation has been obtained between the SO2 retention degree at 573 K and the new parameter introduced in the present study: the specific surface area of CaO, determined by means of the CO2 chemisorption meth od at 573 K. In addition, the results obtained confirm and support the interpretation given for previous results, so it has been proved that CaSO3 formed a 573 K is restricted at the surface of the particles an d that at 573 K, both in the absence and in the presence of O-2, the s pecies formed is CaSO3.