Reductive acid leaching of valuable metals from spent lithium-ion batteries using hydrazine sulfate as reductant

Hydrazine sulfate was used as a reducing agent for the leaching of Li, Ni, Co and Mn from spent lithium-ion batteries. The effects of the reaction conditions on the leaching mechanism and kinetics were characterized and examined. 97% of the available Li, 96% of the available Ni, 95% of the available Co, and 86% of the available Mn are extracted under the following optimized conditions: sulfuric acid concentration of 2.0 mol/L, hydrazine sulfate dosage of 30 g/L, solid-to-liquid ratio of 50 g/L, temperature of 80 degrees C, and leaching time of 60 min. The activation energies of the leaching are determined to be 44.32, 59.37 and 55.62 kJ/mol for Li, Ni and Co, respectively. By performing X-ray diffraction and scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy, it is confirmed that the main phase in the leaching residue is MnO2. The results show that hydrazine sulfate is an effective reducing agent in the acid leaching process for spent lithium-ion batteries.