Eco-friendly recovery process of lithium from reduction roasting residue powder based on hydrothermal extraction

To cater to the increasing demand for secondary lithium-ion batteries, the recovery of valuable metal species in spent batteries is increasingly important, particularly for lithium, for which a few effective recovery techniques have been reported. This study investigated the behavior of lithium extraction from the reduction roasting residue (R–R–R) powder under hydrothermal conditions with and without CaCl₂. The analysis results revealed that the hydrothermal treatment with CaCl₂ can effectively extract lithium from the R–R–R powder. Additionally, the optimal conditions were identified as powder treatment at 200 °C for more than 18 h with CaCl₂ (Ca/(P + F) = 4 (mol/mol)). This optimal condition did not rely on the volume scale of the pressure vessel; therefore, the proposed method can be practically effective. Furthermore, the separation of calcium and lithium cations in the extraction solution was investigated using sodium carbonate as a precipitator. The calcium cation was successfully separated as calcium carbonate from the extraction solution, and a pure lithium aqueous solution was collected. Based on our analysis, we propose a novel eco-friendly recycling process for extracting metals from spent lithium-ion batteries.