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 (K 2 CO 3 /Na 2 CO 3 ), which could form a eutectic molten salt system at 720°C, was used as a roasting agent to extract lithium from pyrometallurgical slag. Lithium was successfully extracted from the slag by K 2 CO 3 /Na 2 CO 3 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 LiAlSi 2 O 6 lattice after roasting with K 2 CO 3 /Na 2 CO 3 . Thermogravimetry—differential scanning calorimetry results indicate that the eutectic phenomenon of K 2 CO 3 and Na 2 CO 3 could 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 K 2 CO 3 with the concurrent formation of KAlSiO 4 , while Na 2 CO 3 mainly 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.