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

Effectively extracting lithium from the pyrometallurgical slag of spent lithium-ion batteries at a relatively low temperature remains a great challenge. Herein, potassium carbonate/sodium carbonate (K₂CO₃/Na₂CO₃) which could form eutectic molten salts at 720°C were used as the roasting agents for extracting lithium from the pyrometallurgical slag. The lithium is successfully extracted from slag by K₂CO₃/Na₂CO₃ roasting followed by water leaching. According to the theoretical calculation results, lengths of Li-O bonds increase after adsorption of K⁺/Na⁺, resulting in easily release of Li⁺ from the lattice of LiAlSi₂O₆ after roasting with K₂CO₃/Na₂CO₃. Moreover, the TG-DSC results indicate that the eutectic phenomenon of K₂CO₃ and Na₂CO₃ is observed at 720°C and the reaction of slag and eutectic molten salts happens above 720°C. The X-ray diffraction results suggest that Li⁺ in slag is exchanged by K⁺ in K₂CO₃ which is accompanied by the formation of KAlSiO₄, while Na₂CO₃ is mainly employed as a fluxing agent. The lithium extraction efficiency can reach 93.87% under the following optimal conditions: roasting temperature of 740°C, roasting time of 30 min, leaching temperature of 50°C, leaching time of 40 min and water/roasted samples mass ratio of 10:1. This work provides a new system for extracting lithium from the pyrometallurgical slag of spent lithium-ion batteries.