Citrate-EDTA-H ₂ O ₂ buffering system recovers Li/Co/Ni/Mn from battery black mass at pH 5.0 using a dual chelation mechanism.

The exponential growth in the consumption of lithium-ion batteries (LIBs) necessitates the development of environmentally benign recycling technologies to address the impending surge in end-of-life waste. This study presents a novel, sustainable hydrometallurgical approach for the recovery of critical metals (Li, Ni, Co) from spent NMC/LCO cathode materials utilizing a low-concentration ammonia system. In contrast to conventional methods relying on high ammonia concentrations (4-6 M), this work demonstrates efficient metal leaching using only 0.5 M NH4OH buffered with ammonium sulfate, employing sodium sulfite (Na2SO3) as a reducing agent to facilitate the breakdown of the oxide matrix. Through systematic optimization, the optimal process parameters were established: 0.5 M NH4OH, 0.273 M (NH4)2SO4, and 0.8 M Na2SO3 at pH 10.5 and 80 °C. Under these conditions, the system achieved leaching efficiencies of 99.6% for Ni, 96.4% for Li, and 89.1% for Co. A distinctive feature of the developed process is the selective retention of manganese; unlike acid leaching, this method retains 76% of manganese in the solid residue, significantly simplifying downstream purification and target component separation. The proposed method offers an eight-fold reduction in ammonia consumption compared to conventional ammoniacal schemes, substantially lowering both operational costs and the carbon footprint of the recycling process.

Recovery of critical metals from spent lithium-ion batteries commonly relies on single-pass chemical reductants, increasing reagent consumption and limiting opportunities for reductant reuse. In this study, electrochemically assisted leaching (EAL) with continuous regeneration of the Fe³⁺/Fe²⁺ redox mediator was investigated for nickel–cobalt–aluminum oxide (NCA)-containing black mass. The leaching kinetics of nickel, cobalt, and lithium were compared in H₂SO₄, H₂SO₄ + Fe²⁺, and in H₂SO₄ with continuous cathodic regeneration of Fe²⁺. Kinetic data were analyzed by nonlinear regression in fractional-conversion space, model selection using the corrected Akaike information criterion, and subsequent assessment of the physical plausibility of the selected kinetic schemes. Solid-state changes were examined by XRD, Raman spectroscopy, and SEM-EDS, while response surface methodology was used for multi-response process optimization. Nickel and cobalt were generally better described by two-stage kinetics, with a temperature-sensitive initial regime followed by a slower product-layer-affected stage. Reductive leaching was accompanied by reconstruction of the Ni-rich layered oxide toward a rock-salt NiO-type residual phase, which is considered a plausible contributor to the nearly temperature-independent cobalt extraction limit of approximately 69–74%. Multi-response optimization identified a mediator-to-solid ratio of approximately 0.8 mmol Fe²⁺ per gram of black mass, enabling sub-stoichiometric mediator use. At 45 °C and 120 min, leaching efficiencies reached 99.6% for lithium, 95.1% for nickel, and 70.4% for cobalt. These results demonstrate the feasibility of coupling chemical leaching with continuous electrochemical mediator regeneration while identifying the solid-state and mass-transfer limitations governing further process intensification.