Combined Carbothermal Reduction–Acetic Acid Leaching Strategy for the Stepwise Recovery of Lithium and Manganese from Spent Electrode Materials

Carbothermal reduction roasting is an important medium-temperature pyrometallurgical process for efficiently recovering valuable elements from spent lithium-ion batteries (LIBs). In this study, combined carbothermal reduction–acetic acid leaching was proposed, aiming to stepwisely recover Li, Ni, Co, and Mn from spent ternary LIBs containing lithium nickel cobalt manganese oxide (LiNi_xCo_yMn_zO₂, NCM). The biomass waste materials, chitosan, and chitin were chosen as sustainable reducing agents for carbothermal reduction roasting. The synergistic effect of the reducing gases and biochar produced during pyrolysis led to the reduction of transition metals in NCM into Ni, Co, and MnO, separately. Meanwhile, lithium reacted with CO₂ to form Li₂CO₃. Additionally, an acetic acid leaching process was employed to treat the roasting slag, achieving selective leaching of Li and Mn with leaching efficiencies of 98.45% for Li, 1.20% for Ni, 3.10% for Co, and 98.43% for Mn under optimal conditions. Compared to traditional carbothermal reduction roasting methods, this approach used extracts from shrimp/crab shell solid waste as a source of reducing atmosphere and biochar. More importantly, the leaching behaviors of Li, Ni, Co, and Mn were also investigated. Li and Mn were subsequently recovered as lithium carbonate (Li₂CO₃) and manganese carbonate (MnCO₃), respectively. An economic evaluation was also conducted to present a promising strategy for efficiently recycling valuable metals from spent LIBs.