Abstract: Fly ash is thermally processed in electrically heated, closed pre-heat and combustion chambers. In the combustion chamber, the fly ash is tumble mixed to produce maximum combustion of carbon in the fly ash. Further, the tumble mixing is done while injecting air and oxygen into the tumbling heated fly ash. The tumble mixing is accomplished by feed screws. The screw shafts are hollow with air orifices at regular intervals. As a result, an oxygenated air mixture may be injected into the tumbling fly ash to aid the combustion of the carbon in the fly ash. The flow rates for air and oxygen, the temperature of the pre-heat chamber and the combustion chamber, and the ash flow rate (speed of feed screws) may be adjusted to obtain the proper combustion to get the desired Loss On Ignition (LOI) value for the fly ash. Spectrometers monitoring the color of the output of the fly ash may be calibrated to adjust one or more of the above variables.