Activation of calcium oxide as a sorbent

The sorbent capacity of calcium oxide with respect to sulfur dioxide is increased by calcining limestone or dolomite in an atmosphere where the partial pressure of carbon dioxide is greater than 40 percent of the equilibrium partial pressure of carbon dioxide over calcium carbonate at the reaction temperature. Where dolomite is the starting material, it may be calcined in a two-step heating process in which the atmosphere during the first heating stage contains carbon dioxide and the temperature is maintained in the dissociation range of magnesium carbonate (MgCO3); the atmosphere of the second heating stage also contains carbon dioxide, but the temperature is maintained in the calcium carbonate (CaCO3) dissociation range. Calcium oxide so produced in such an atmosphere of carbon dioxide sufficient to delay calcination is found to have relatively large mouthed pores capable of sorbing increased amounts of sulfur.