Spent CaO sorbent was taken from a com. semi-dry flue gas desulfurization plant and regenerated either by oxidn. with air O-2 under room conditions or by spontaneous air oxidn. during storage outside for 150 days. Every 30 days, samples of the sorbent were taken out from the surface layer and analyzed for elementary compn. (including the heavy metal content). The oxidn. degree of the spent sorbent was not satisfactory for its further use in prodn. of cement or fertilizers.