Glucose oxidase-based biocatalytic acid-leaching process for recovering valuable metals from spent lithium-ion batteries

An environmentally benign leaching process for recovering valuable metals from the cathodes of spent lithium-ion batteries was developed. Glucose oxidase produced by Aspergillus niger can oxidize glucose to give the leaching agent gluconic acid. The presence of gluconic acid was proven by mass spectrometry. The cathode material morphology was characterized by X-ray diffractometry and scanning electron microscopy, and the efficiencies with which valuable metals were leached from the Li(Ni_xCo_yMn_z)O₂ material were determined by inductively coupled plasma optical emission spectroscopy. More than 95% of the Co, Li, Mn, and Ni were leached from spent lithium-ion batteries using a solid/liquid ratio of 30 g/L, 1 M gluconic acid leaching solution, a 1 vol% H₂O₂ reductant solution, a temperature of 70 °C, and a reaction time of 80 min. The leaching kinetics were perfectly described by the Avrami equation. The apparent activation energies for leaching of Li, Ni, Co, and Mn were determined as 41.76, 42.84, 43.59, and 45.35 kJ/mol, respectively, indicating that the surface chemical reaction is the rate-controlling step during this leaching process. This mild biocatalysis-aided acid leaching process is a promising method for effectively recovering valuable metals from spent lithium-ion batteries.