## 3 Results and Discussion
### Results of the Single-Stage Acid Leaching Method with the Addition of Hydrogen Peroxide
Incredibly important is the fact that nickel and cobalt were leached from the feed with high efficiencies, confirming the results presented in a number of publications, e.g., in the work of [PERSON] et al. [54] and [PERSON] et al. [55], in which the authors obtained over a 93% recovery of metals from battery masses using sulfuric acid. Although increasing the concentration of sulfuric acid for leaching in most cases resulted in an increase in the leaching efficiency of individual components, it also resulted in an increase in the content of free sulfuric acid in the solution formed after leaching. It is an unquestionable problem in carrying out subsequent operations aimed at the recovery of individual components in industrial conditions. For this reason, the tests were carried out using the auxiliary substance in the form of 2 dm\({}^{3}\) of 30% aqueous solution of hydrogen peroxide. 1.2 Results of the Single-Stage Acid Leaching with the Addition of 2 dm\({}^{3}\) of Hydrogen Peroxide--Selection of the Leaching Agent  
From the results of the tests listed in Table 3, it can be concluded that with the use of a larger portion of the aqueous solution of hydrogen peroxide, along with the increase in concentration of H\({}_{2}\)SO\({}_{4}\), there was no unequivocal increase in the leaching efficiency of both nickel and cobalt for all tested battery masses. It should be emphasized that the obtained leaching efficiencies depended to a large extent on the type and composition of the material directed to the leaching process. Thus, the leaching efficiencies obtained for cobalt ranged from 55.03% to 91.37%, and that for nickel ranged from 55.78% to 92.43%. The content of free acid in the solutions after leaching was also very diverse, but it proved that in all the studies, an appropriate, excessive amount of leaching agent was used. The average concentration of the free acid was 36 g/dm\({}^{3}\) and was very similar to the concentration obtained in the tests using the smaller portion of hydrogen peroxide. Obtaining high concentrations of cobalt and nickel was also an important element of this research. The highest cobalt concentrations were obtained for Materials II and III (materials with high initial Co content). These concentrations ranged from 25.10 g/dm\({}^{3}\) to 38.20 g/dm\({}^{3}\) and were lower than those obtained with the use of the smaller portion of hydrogen peroxide. In the case of nickel, the highest concentrations were obtained for Material I (material with high initial content of Ni), which ranged from 13.60 g/dm\({}^{3}\) to 15.40 g/dm\({}^{3}\) and were also lower than those obtained with the addition of 1 dm\({}^{3}\) of hydrogen peroxide. Also, in the case of lithium, copper and manganese, the leaching efficiencies of these components behaved differently with increasing H\({}_{2}\)SO\({}_{4}\) concentration. For lithium, the concentrations in the solutions obtained after leaching ranged from 4 g/dm\({}^{3}\) to 6 g/dm\({}^{3}\) and was slightly lower than the concentrations obtained using 1 dm\({}^{3}\) of hydrogen peroxide. The leaching efficiency of manganese ranged from 59% to 93% and that of copper ranged from 54% to 84%. It should be emphasized that these values were also lower than those obtained with the smaller portion of H\({}_{2}\)O\({}_{2}\). In the case of iron, phosphorus and fluorine, the leaching efficiencies of these components in most cases increased with increasing H\({}_{2}\)SO\({}_{4}\) concentration. The exception was fluorine; when leaching was carried out with Material I, the leaching efficiency decreased as the concentration of H\({}_{2}\)SO\({}_{4}\) increased, but the decrease was insignificant. In the case of iron, the concentration in solutions obtained after leaching ranged from 0.37 g/dm\({}^{3}\) to 0.51 g/dm\({}^{3}\) and was only slightly lower than the one obtained with the smaller dose of hydrogen peroxide. The leaching efficiency of phosphorus ranged from 54% to 100% and that of fluorine ranged from 41% to 78%.