The growing demand for lithium-ion batteries (LiBs) for energy storage has intensified the need for the critical raw materials (CRMs) they contain, including Li, Co, Ni, and Mn. Consequently, the incentive to recycle LIBs is increasing. However, the commonly used hydrometallurgical processes often have a significant environmental footprint. Moreover, the relatively low value of certain battery materials (e.g., LiFePO₄, LFP) results in a limited incentive for their recycling. This study explores the simultaneous recycling of LFP with various types of LiNi_xMn_yCo_zO₂-containing Black Mass (BM). Leaching studies over time were conducted using stepwise additions of LFP and H₂O₂ solution (1 vol%) to a mild lixiviant of 0.63 mol/L H₂SO₄ at 50°C_. For pristine NMC 532, ± 95% leaching of Li, Ni, Co, and Mn was achieved. The Fe(II) present in LFP, as well as H₂O₂, acts as a reductant for the dissolution of Ni, Co, and Mn, later precipitating as FePO₄ to the leaching residue. The Al and Cu present in industrially treated BM further enhanced the dissolution of the transition metals via a catalyzed reaction with the iron from LFP. This resulted in complete leaching of Li, Ni, Co, and Mn for mechanically pre-treated industrial black mass samples. However, the leaching residues acquired from these samples were highly contaminated with graphite. Also, while pyrolysis of the black mass benefits the leaching of Co and Mn, it results in difficulties in subsequent removal of Fe from the pregnant leach solution. The chemical processes and their performance are described in this work.