Due to the increasing amount of battery waste containing a variety of critical raw materials the structural policy framework and technical solutions for a sustainable product life cycle must be elaborated and implemented today. The processing of end-of-life batteries can generally be divided into mechanical, hydro- and pyrometallurgical treatment. The recycling steps vary depending on the cell system. Due to the different material fractions the recycling efficiencies show a tremendous development potential depending on the processing technology. BATREC Industrie AG is a recycling service provider that focuses on the stabilization, processing, and regeneration of toxic waste materials. Zinc containing primary batteries are treated in a pyrometallurgical process to recover the containing metals. In the recycling plant the batteries get pyrolyzed in a shaft furnace and melted in an electric arc furnace. Iron and manganese are reduced with carbon and form ferromanganese. The accompanying elements, additives and partly ignoble metals get slagged. Volatile substances such as zinc and chlorides evaporate and enter a condenser through the exhaust duct. Zinc metal and a zinc-containing salt slag occur at a condenser. The residue consists of oxides, chlorides, and metallic components. The practical part of this work consists of the investigation and characterization of the slag residue as well as the operational introduction of the rotary drum furnace into the plant. With the thermal treatment in the furnace the metal in the salt slag can be recovered which improves the in-house resource cycle. The chemical, pyro- and hydrometallurgical analysis methods enable the optimization and material-specific setting of the parameters for the thermal treatment. The investigations show that the viscosity of the salt slag in the molten state increases with rising oxide content. The content of the chloride compounds determines the melting point. When remelting the residue in the rotary drum furnace, a dry, solid state of the non-metallic phase allows a higher metal recovery. According to a statistical test evaluation the optimal melting conditions result at 478 °C and 05:00 hours duration. With the aim of reducing waste and thus also reducing costs, the rotary drum furnace is an ecological and economical significant expansion of the recycling plant.