Abstract: A method is described for a thermal treatment of materials that can be pumped or blown, particularly for the pyrolysis of waste materials, An electric arc is established in a gap between a pair of concentric electrodes, and the material to be treated is pumped or blown into the gap and through the electric arc to effect the thermal treatment. The product of the thermal treatment is forced to pass through a high temperature smelt. The method can be carried out utilizing a sealed receptacle (11) equipped with an electrode tube (15) having a material supply at one end and an open end directed towards or located in the smelt. A sleeve or other wall means can be placed in the receptacle near the electrode tube to create circulation and spread the decomposition products in the smelt.