Citric Acid Leaching Performance at High Solid‑to‑Liquid Ratios for Lithium‑Ion Battery Recycling

This study investigated the performance of citric acid as lixiviant for cathode material from end-of-life lithium-ion batteries (LIBs). Black mass containing 84.2 wt% MNC (LiNi0.45Mn0.4Co0.15O2) and 15.8 wt% LCO (LiCoO2) material was leached at solid-to-liquid ratios of 20, 50, and 100 g/L. Leaching with 1.5 M citric acid, 2 vol.% H2O2, and a solid-to-liquid ratio of 20 g/L at 95 °C extracted 90% Co, 95% Li, 94% Mn, and 94% Ni within 20 min. At the highest solid/liquid ratio of 100 g/L with 1.5 M citric acid, 10 vol.% H2O2, and 95 °C, 84% Al, 84% Co, 87% Li, 86% Mn, and 96% Ni were leached after 40 min, producing a leach solution containing 0.68 g/L Al, 20.0 g/L Co, 6.0 g/L Li, 13.6 g/L Mn, and 19.3 g/L Ni. Using stepwise addition of H2O2, instead of initial bulk addition, did not significantly improve the leaching efficiency but did reduce the required leaching time. Temperature control of the reactor was also more manageable with stepwise addition of H2O2 and gas evolution was less vigorous. It was observed that the leaching efficiencies of Co, Li, and Mn decreased slightly at solid/liquid ratios of 50 g/L and 100 g/L, while the leaching of Ni increased slightly. The solution leached at 20 g/L could be stored for 6 weeks without any spontaneous precipitation, however, solutions leached at 50 g/L and 100 g/L showed changes in concentration after 1 month’s storage, suggesting that processes with high solid-to-liquid ratios must ensure that solutions are not stored for extended periods of time.