Green Leaching and Selective Recovery of Ni, Co, and Mn from Lithium-Ion Battery Black Mass with Citric Acid and H ₂ O ₂

End-of-life battery waste poses environmental risks while representing a valuable source of metals. This study presents a green hydrometallurgical route for metal recovery from black mass via citric acid–H 2 O 2 leaching and a two-stage selective precipitation process. We optimized the leaching conditions as follows: 90 °C leaching temperature, 3 vol% H 2 O 2, 1.0 mol L −1 citric acid, a liquid-to-solid ratio of 30 mL g −1, and a duration of 2 h. Copper was selectively removed (>99.4%) using Na 2 S precipitation, with minimal loss of target metals. Subsequent oxalic acid precipitation (metal:oxalate molar ratio 1:3, 30 °C, and 30 min) produced mixed Ni–Co–Mn oxalate dihydrates with precipitation efficiencies of 98.1% (Ni), 98.7% (Co), and 92.0% (Mn). The highly pure and crystalline recovered product is a suitable precursor for cathode resynthesis. This integrated process demonstrates an efficient, environmentally benign route for the closed-loop recycling of critical metals from spent batteries.