Steelmaking and plating industry benerates large quantities of dusts and sludge. They are regarded as hazardous wastes because of the leaching out of their toxic components. Therefore, particular wastes are stockpiled at high cost. Our work aimed at RF thermal plasma processing of a steelmaking flue dust and sludge from the hot plating of steel products. Waste samples were treated in reducing atmosphere, respectively, to produce fine metallic powders and in neutral/oxidizing atmosphere to synthesize zinc ferrite nanopowders. Starting powders and products were characterized by their chemical (ICP-AES) and phase (X-ray diffraction, XRD) composition, particle size and morphology (scanning electron microscopy, SEM). It was found that iron and zinc content of the particular wastes can be reduced to metals in the presence of hydrogen. In neutral/oxidizing conditions spinel ferrites of variable composition were formed even during the very short residence time in the reactor. (C) 2004 Elsevier B.V. All rights reserved.