Metal Recovery of LiCoO2/LiNiO2 Cathode Materials by Hydrothermal Leaching and Precipitation Separation

Here, Ni, Co, and Li ions in the leachate obtained from commercial LiCoO2/LiNiO2 cathode materials by hydrothermal leaching with citric acid were precipitated and separated in order using a series of precipitants, dimethylglyoxime (DMG), (NH4)2C2O4, and Na3PO4, respectively. The parameters including the pH value, precipitant amount, and reaction temperature were optimized during the metal separation step. Finally, the recovery rates of Ni, Co, and Li were 97.2, 96.1, and 94.1%, respectively, with the purities of Ni, Co, and Li in the corresponding precipitate being 96.3, 96.2, and 99.9%, respectively. The method of hydrothermal leaching was compared with the method of traditional leaching in terms of the leaching mechanism and the metal separation performance of the obtained leachates. Compared with the traditional leaching with a reductant (e.g., H2O2), hydrothermal leaching is performed at higher temperatures and requires pressure-resistant reactors, but it can reduce the consumption of chemicals such as reductants, promote the reaction rate, and improve industrial applicability. Even though the leaching mechanisms were different, the leachates obtained by hydrothermal and traditional leaching showed comparable performance in the metal separation step, indicating hydrothermal leaching is qualified to produce leachates for lithium-ion battery (LIB) recycling. With the success of isolating metal components from the leachate obtained by hydrothermal leaching, an upgraded hydrometallurgical method, composed of hydrothermal leaching and precipitation separation steps, was officially launched for LIB recycling and is subject to further development.