A method of treating spent sorbent from power plants containing materials including mercury absorbed from emission gases comprising putting said spent sorbent in an atmosphere isolated container or furnace chamber and heating said sorbent by microwave, radio frequency and/or infrared irradiation. The sorbent is heated to a temperature of at least the boiling point of the major contaminant, including mercury. No air or purge gas is added except to maintain safe pressure conditions, to control combustion of the sorbent and increase efficiency. The resulting vapor is released through an exhaust port of the chamber that leads to a condenser where mercury is condensed and separated. Other residual vapors are led to a scrubber for further cleansing and may be returned to the power plant for other applications. The hot treated sorbent is cooled down prior to contacting with air for later reuse in the power plant.