A system and method for decomposing ammonia from fly ash contaminated with ammonia is provided which includes maintaining the temperature of a bed of ammonia-contaminated fly ash at a decomposition temperature greater than 500.degree. F. and less than 842.degree. F. to decompose the ammonia from the fly ash. In a preferred embodiment, the ammonia-laden fly ash is maintained at a temperature less than a lowest carbon combustion temperature at which substantial combustion of carbon in fly ash begins to occur. A preferred embodiment includes a first chamber operating at a decomposition temperature greater than 500.degree. F. and less than 842.degree. F. followed by a second chamber operating at a higher carbon combustion temperature for carbon burn-out.