Activation of calcium oxide as a sorbent

A method of producing calcium oxide of increased sorbent capacity with respect to sulfur dioxide from stones of 400-2000 microns particle size containing calcium carbonate and magnesium carbonate, which comprises:

• a. heating said stones at 700.degree. up to 900.degree. C. in an atmosphere in which the partial pressure of carbon dioxide is greater than the equilibrium partial pressure of CO.sub.2 over CaCO.sub.3 at the reaction temperature to calcine the magnesium fraction of the stones;
• and,
• b. additionally heating said stones in an atmosphere containing an amount sufficient of carbon dioxide to delay calcination and for a time sufficient to cause sufficient CO.sub.2 back pressure to produce large mouthed pores, at a temperature greater than that in step (a) in the range 900.degree.-950.degree. C. for a time sufficient to effect decomposition of the CaCO.sub.3 to CaO, the CO.sub.2 partial pressure being greater than 40% but not exceeding 85% of the equilibrium partial pressure of CO.sub.2 over CaCO.sub.3 at the reaction temperature.