Iron silicate slag represents a significant by-product that derives from the primary production of metallic copper. After a cleaning step, which usually takes place in an electric furnace, the material can be sold to the construction industry or other industrial sectors. However, stricter environmental as well as legislative regulations limit the amount of remaining impurities even further, which is why the resulting slag has to be additionally treated. A second electric furnace treatment with a high reduction potential leads to a copper-iron-molybdenum alloy, which cannot be reintroduced in the primary production cycle due to the elevated amount of refractory metal. Therefore, an adequate treatment has to be found for the material in order to separate the impurity-rich copper phase from the high-melting molybdenum. After a detailed characterization of the newly accumulating Cu-Fe-Mo alloy, several treatment approaches are presented. While hydrometallurgical options lead to low energetic requirements, the pyrometallurgical concepts aim at a phase separation in a molten state. Since literature does not provide a feasible solution, a new approach has to be considered and developed. A hydro- as well as a pyrometallurgical option qualify for closer examination. The initial focus lies on thermodynamic calculations, followed by the kinetic verification in laboratory-scale trials. Since the primary copper industry produces significant amounts of sulfuric acid, a selective leaching of the present iron and molybdenum with a subsequent cementation delivers a promising approach. However, molybdenum shows no preferred tendency to enter the liquid state, which is why the pyrometallurgical method moves into the center of consideration. Thermodynamic calculations of stability diagrams reveal that a selective oxidation of iron and molybdenum is possible in a CO/CO2 atmosphere, whereas copper and all relevant impurities maintain their metallic behavior. Small-scale experiments using the differential thermal analysis confirm these findings, which is why the technological feasibility is further investigated on pilot scale. To sum up, the present thesis delivers a guideline for the treatment of a copper-iron-molybdenum alloy. By performing the recommended steps, two valuable products result from the process. The metallic copper phase can be reintroduced in the primary production cycle, whereas the clean ferromolybdenum slag may qualify for further processing in the iron and steel industry. While having proven the technological feasibility of a selective oxidation treatment, a special focus lies on the implementation on an industrial scale.