Cobalt and lithium recovery from active mass of spent Li-ion batteries: Theoretical and experimental approach

The paper is focused on the experimental study of cobalt and lithium recovery from active mass of spent lithium batteries with theoretical explanation of behavior of components in this process. Two leaching agents— H2SO4 and HCl were used in order to compare their effects on cobalt and lithium extraction. It follows from the results that using HCl as a leaching reagent is more appropriate than using H2SO4. Optimal conditions for cobalt and lithium recovery were: 2 M HCl, 60–80 °C, leaching time 90 min. The work also explains the influence of temperature on cobalt and lithium extraction from active mass by activation energy in case of both leaching agents. It was found that the cobalt extraction in sulfuric acid occurs in two time periods. In the first time period, in 15 to 20 min from the beginning of leaching, the process is controlled by the rate of a chemical reaction (Ea(Co) = 43–48 kJ·mol−1). In the second time period, the process changes to diffusion controlled, as it is evidenced from the value of Ea(Co) = 3–3.5 kJ·mol−1. In the case of HCl, cobalt extraction in first time period is controlled by the rate of chemical reaction, Ea(Co) = 40–44 kJ·mol−1. In the second time period, process is converted to a mixed mechanism, Ea(Co) = 20–26 kJ·mol−1. Lithium extraction is controlled by the diffusion in both of time periods, or occurs in mixed mode. Ea(Li) is between 2 and 20 kJ·mol−1 in both of leaching agent. The study of the fine structure confirmed the hypothesis that on the cobalt and lithium extraction affects the internal structure of the active mass, which consists primarily of LiCoO2 and the cobalt extraction is dependent on lithium extraction from the LiCoO2 structure.