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 (K2CO3/Na2CO3), which could form a eutectic molten salt system at 720 degrees C, was used as a roasting agent to extract lithium from pyrometallurgical slag. Lithium was successfully extracted from the slag by K2CO3/Na2CO3 roasting 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 LiAlSi2O6 lattice after roasting with K2CO3/Na2CO3. Thermogravimetry-differential scanning calorimetry results indicate that the eutectic phenomenon of K2CO3 and Na2CO3 could be observed at 720 degrees C and that the reaction of the slag and eutectic molten salts occurs at temperatures above 720 degrees C. X-ray diffraction results suggest that Li+ in the slag is exchanged by K+ in K2CO3 with the concurrent formation of KAlSiO4, while Na2CO3 mainly functions as a fluxing agent. The lithium extraction efficiency can reach 93.87% under the optimal conditions of a roasting temperature of 740 degrees C, roasting time of 30 min, leaching temperature of 50 degrees 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.