The research on the area of recycling of complex residues, especially zinc containing steel mill dusts, in the last 20 years was characterised by the development of new process routes to enable an economical recycling of such waste materials, mainly focussing on one special residue. In spite of the huge amount of steel mill dusts with a zinc content up to 40 %, the dusts were partly land filled or treated by processes that do not offer an environmental solution for the future. But environmental legislation in most countries makes a direct landfill only under strict conditions possible. Therefore in this thesis fundamental research concerning characterisation and melting behaviour of the used materials was realised. The results should enable the development of new or the improvement of existing recycling techniques. By means of granulometric analysis and scanning electron microscopy the bibliographical references regarding the extensive morphology of steel mill dusts were verified. The fusion and softening behaviour were analysed by a smelting microscope with a maximum temperature of 1650 °C as well as with scanning electron microscope analysis after an annealing up to 1500 °C. With this verification the complex fusion behaviour with melting points of some materials beyond 1650 °C was shown. The microstructure at these temperatures results in a segregation of a low melting calcium-silicate-slag and a high melting Fe-Cr-Mn-oxide. Further results were obtained from scanning electron microscopy, granulometric and thermal analysis, which complete the characterisation of these complex secondary raw materials.