The projected raising demand for lithium-ion batteries is accompanied with a tremendous surge of lithium, graphite, cobalt, and nickel, which are classified as critical according to the European Commission. The future upcoming waste stream is considered as a viable resource for recovery, resulting consequently in mitigation of supply chain risks and environmental impact. This thesis aims to investigate the application of a biometallurgical method to obtain valuable elements from NMC/C electrode material based on the acid production of Aspergillus niger, a fungi. The laboratory experiments included the leaching of pyrolyzed black mass in different multi-acid systems. Citric, DL-malic, gluconic as well as oxalic acid were considered for usage in the acidic liquid mixture as all of them are generated during the fungal metabolization process. To investigate several influencing parameters the conditions for temperature, leaching time, solid-to-liquid ratio and amount of added molasses as reductant ranged between 30 to 60 °C, 45 to 180 min, 50 to 100 g/l and 0 to 0.6 g/gblack mass, respectively. Additional leaching tests omitting oxalic acid, with subsequent adding in different quantities were performed. The leaching efficiencies for nickel and cobalt were low for each multi-acid system. Highest achievable recovery rates of 13% for Ni and 25.8% for Co in the excess of DL-malic and gluconic acid, respectively were noted. The obtained maximum value for lithium was 87.9% determined in a citric rich acidic medium. The investigation with a scanning electron microscope (SEM) including energy dispersive X-Ray spectroscopy (EDS) mapping indicated organo-metallic components in the solid residues, obtained after filtration. Formed precipitates after storage in the pregnant solutions showed a similar composition. In addition, the observable solid components generation in the additional experiments were pointing to possible precipitation of transition metals with oxalic species. According to the results, oxalic acid mainly contributed to the low leaching efficiencies by two different ways. Hardly soluble oxalates get formed which secondly can cover the material surface of NMC particles resulting in a kinetic inhibition for further possible reaction. The findings of this study showed that a beneficial biometallurgical approach using Aspergillus niger has to exclude or minimize the generation of oxalic acid during the metabolization process because a fully recovery of valuable metals is desired according to their criticality and economic value.