A green alternative to lithium recovery from end life batteries: Understanding the mechanism of oxalic acid-based early lithium recovery from spent NMC batteries

The rising demand for lithium-ion batteries, particularly in electric vehicles, underscores the urgent need for sustainable and efficient recycling strategies to recover critical raw materials such as lithium. This study explores early-stage lithium recovery (ESLR) using oxalic acid from industrial end-of-life black mass obtained from end-of-life (EoL) NMC 622 batteries, contrasting untreated and thermally treated black mass. Unlike traditional late-stage recycling methods that suffer from material losses and complex processing, ESLR simplifies the recovery of lithium A systematic screening of organic acids identified oxalic acid as the most effective, followed by optimization of acid molarity and solid-to-liquid ratios using a 2 3 factorial design of experiments (DoE). Comparative kinetic studies revealed distinct leaching behaviors for untreated and thermally treated black mass, both fitting the Avrami model, with activation energies determined for each case. DoE trials achieved 81.49% Li recovery (untreated) and 84.63% (thermally treated), with optimized conditions reaching ~91.3% in kinetic runs. Beyond leaching, a straightforward purification route was demonstrated by controlled pH adjustment with LiOH, yielding >99% Li purity in the pregnant leach solution (PLS) through selective precipitation of impurities. Further remediation of the Li depleted residue proved critical, direct sulfuric acid leaching (3 mol/ L H₂SO₄, 60 °C, 2.5 vol% H₂O₂) of the metal-oxalate-rich residues showed poor leachability. In contrast, thermal breakdown of oxalates at ≤350 °C effectively transformed the residues, enabling subsequent leaching of Ni, Co, and Mn recovery by solvent extraction. Collectively, these findings highlight the novelty of combining oxalic acid–based ESLR with a simple purification step and low-temperature residue remediation, providing a green, straightforward pathway that achieves high lithium recovery and solution purity without mandatory high-temperature pretreatment of NMC black mass. • Optimization of leaching conditions for thermally treated and untreated end of life NMC black mass • High Li leaching of 81.49% for untreated black mass, 84.63% for thermally treated black mass • Kinetic analysis: metal leaching and oxalic acid kinetics were measured and analyzed • Transition metal precipitation: identified leaching precipitation mechanism for Co, Cu, Mn, Ni