The carbonaceous char forms in the chamber during pyrolysis. The char residue produced is generally proportional to the level of contaminants which are adhering to the feedstocks. Since the char passes acid leaching tests it can simply be land filled. Inorganic additives such as cadmium pigments from the plastics end up in the char stream. The carbon matrix has a metal .fixing. effect and binds up the metal ions so that no leaching occurs after disposal.