Hydrometallurgical Leaching of Metals from Button Batteries: Effect of the Citric Acid‑to‑Manganese Ratio on Extraction Efficiency

Sustainable recovery of critical metals from spent lithium-ion batteries requires high extraction efficiencies under mild conditions and elevated solid loadings. In this work, a citric acid-based hydrometallurgical system was investigated for manganese and lithium recovery from spent LiMnO2, focusing on the effect of the citric acid-to-manganese (CA:Mn) molar ratio at different solid-to-liquid (S/L) ratios. Experiments were conducted at 60 °C and 60 min, varying CA:Mn from 1.5 to 12.0 mol mol−1 and S/L from 7.5 to 30.0 g L−1. Manganese extraction reached 96.0 ± 3.5%, 95.0 ± 2.6%, 91.4 ± 2.9%, and 85.0 ± 1.7% at S/L ratios of 7.5, 15.0, 22.5, and 30.0 g L−1, respectively, at CA:Mn ratios between 4.5 and 9.0. Notably, high extraction efficiencies were maintained even at 30 g L−1, demonstrating the effectiveness of molar ratio adjustment under intensified conditions. At higher S/L ratios and extreme CA:Mn values, the formation of a white precipitate suggests secondary phase formation and reprecipitation phenomena. Lithium extraction remained consistently high (> 90%), reaching ~ 95% across most conditions, with a slight decrease to 88.3 ± 0.3% at the lowest CA:Mn ratio and highest S/L ratio. These results demonstrate that tuning the CA:Mn ratio enables efficient metal recovery under mild conditions, providing a more sustainable alternative for battery recycling.