Slags are so-called by-products which appear during pyrometallurgical processes and usually represent waste. Many of these are no longer just residues, but can be seen as useful by-products and important secondary resources. The annual production of metallurgical slags is more than one billion tonnes, with an estimated amount of 64 million tonnes in the ferronickel and 50 million tonnes in the copper industry. In addition to the ecological aspects, high landfill costs and huge disposal facilities are significant problems. This thesis deals with the investigation and production of refractory materials out of slags from the copper and nickel industry. In the first instance, thermodynamic calculations are carried out for both oxide melts at different temperatures and variable Al2O3 and MgO additions. From these check-ups, parameters for empirical studies can be determined. The investigation of the melting behaviour is carried out in the heating microscope from Hesse Instruments to determine the characteristic temperatures of the slags with different oxide additions. The following production of refractory masses by using FeNi slag occurred at RHI Magnesita in Leoben. Varying compositions regarding oxides, binder and additives served for the determination of the physical and chemical characteristics of the molten mixtures of metal oxides and silicates. The results show that magnesium oxide leads to higher temperature resistances than equivalent alumina additions, and that the supplement of Al2O3 increases the temperature of softening more significantly than bauxite or chamotte additives. Finally, the physical properties of the produced refractory masses are appropriate for industrial applications. In summary, this study analyses the use of molten by-products in the refractory industry with the aim to save landfill capacities and to ensure a sustainable application of modified slags.