The invention provides apparatus and a method for exothermic treatment of feed material to provide an ash. The apparatus includes a housing extending about a central axis and having first and second ends, and a central mixing zone adjacent the first end. A material intake carries the feed material into the housing and gas enters through a first gas inlet at the first end through guides to create an inner vortex extending axially about said axis and the gas then follows an outer vortex which also extends axially but in the opposite direction from that of the inner vortex. However the inner and outer vortices rotate in the same direction. A gas outlet is positioned to receive spent gas from the housing and an ash outlet is positioned remotely from the mixing zone to receive the ash. If preferred, the position of the ash outlet may be incorporated into the gas outlet. A control system is provided to limit the temperature in the feed material in the housing. As a result, in operation, gases can be fed into the first and second gas inlets carrying sufficient oxygen for exothermic combustion of the feed material and having a flow rate to create said inner and outer vortices. The outer vortex meets the inner vortex in the mixing zone to mix both with the inner vortex and with the feed material which will be subjected to exothermic combustion as the feed material is entrained in the inner and outer vortices. The material will pass through the mixing zone repeatedly until the feed material is converted to the desired ash having escape criteria needed to reach and exit through the ash outlet.