With the increasing demand for lithium-ion batteries, key elements like lithium, graphite, cobalt, and nickel face heightened demand and classification as critical by the European Commission. This study investigates a bio-metallurgical approach for recovering these elements from NMC/C electrode material. The method leverages Aspergillus niger's acid production capacity. Lab experiments involved leaching pyrolyzed black mass using diverse multi-acid systems, including citric, DL-malic, gluconic, and oxalic acid. Parameters such as temperature, leaching time, solid-to-liquid ratio, and molasses as a reductant were varied. Nickel and cobalt recovery rates were modest, with highest rates (13% for Ni, 25.8% for Co) in DL-malic and gluconic acid-rich setups. Maximum lithium recovery (87.9%) occurred in a citric-rich medium. Analysis revealed organo-metallic components in solid residues and formed precipitates, implying oxalic acid's role in inhibiting recovery. Therefore, optimization of acid generation is crucial for effective bio-metallurgical recovery. In summary, this study highlights the potential of Aspergillus niger-mediated bio-metallurgical processes with organic acid mixtures for sustainable recovery of critical elements from spent lithium-ion batteries. The findings contribute crucial insights into optimizing leaching parameters and underscore the significance of bioleaching in addressing the demand for key battery materials. This work has important implications for advancing eco-friendly e-waste recycling practices and aligns with the principles of resource conservation and circular economy in the energy storage sector.