Extraction of lithium from the simulated pyrometallurgical slag of spent lithium-ion batteries by binary eutectic molten carbonates

The effective and low-temperature extraction of lithium from the pyrometallurgical slag of spent lithium-ion batteries (LIBs) remains a great challenge.Herein,potassium carbonate/sodium carbonate (KCO/NaCO),which could form a eutectic molten salt system at720°C,was used as a roasting agent to extract lithium from pyrometallurgical slag.Lithium was successfully extracted from the slag by KCO/NaCOroasting followed by water leaching.Theoretical calculation results indicate that the lengths of Li–O bonds increase after K~+/Na~+adsorption,resulting in the easy release of Li~+from the LiAlSiOlattice after roasting with KCO/NaCO.Thermogravimetry–differential scanning calorimetry results indicate that the eutectic phenomenon of KCOand NaCOcould be observed at 720°C and that the reaction of the slag and eutectic molten salts occurs at temperatures above 720°C.X-ray diffraction results suggest that Li~+in the slag is exchanged by K~+in KCOwith the concurrent formation of KAlSiO,while NaCOmainly functions as a fluxing agent.The lithium extraction efficiency can reach 93.87%under the optimal conditions of a roasting temperature of 740°C,roasting time of 30 min,leaching temperature of 50°C,leaching time of 40 min,and water/roasted sample mass ratio of 10:1.This work provides a new system for extracting lithium from the pyrometallurgical slag of spent LIBs.