A method and apparatus for treatment of unburnts utilizing oxygen carrier particles, which may be CLOU particles, oxidized in an air reactor and transmitted to a post oxidation reactor as shown in FIG. 2. A flue gas stream containing unburnts is injected into post oxidation reactor wherein unburnts are oxidized by oxygen supplied by oxygen carriers. Reduced oxygen carriers are separated from post oxidation reactor and transmitted back to air reactor for re-oxidation. An embodiment may include a post oxidation chamber, which may be catalytic, receiving a portion of flue gas stream and oxygen from a flue gas stream of post oxidation reactor.