The ability of batteries to store energy is an indispensable feature for technical and consumer applications. Metal-containing residues from the battery industry can be processed in principle both pyro- and hydrometallurgical. However, in the pyrometallurgical route only the main metals are recovered, while valuable components such as e.g. rare earths get slagged. In hydrometallurgy, there are also ways to recover these, however, the processes are often relatively immature or provide contaminated products. For this reason, a process combination of leaching and precipitation should be tested in order to obtain pure products and improved leaching efficiencies. For this purpose, leaching with inorganic acids takes place in different modifications. In addition, optimized leaching parameters are determined using the MODDE12 statistical experimental design software.