Efficient lithium recovery from lithium-containing spent aluminium electrolyte via NaF fluorination roasting and Al2(SO4)3 leaching

Abstract

Recently, there has been a growing interest in lithium-containing spent aluminium electrolyte (LSAE) as a potential new source of lithium. However, the current method of using strong inorganic acids for leaching lithium from LSAE has several drawbacks, which not only consume a lot of acids but raise safety and environmental concerns due to the release of HF. Herein, a novel process combining NaF fluorination roasting and Al2(SO4)3 leaching is proposed for the efficient extraction of lithium from LSAE. LSAE with NaF additive was first roasted at temperatures between 900 and 980 °C to convert Na2LiAlF6 into easily leachable LiF. Then, environmentally friendly Al2(SO4)3 solutions were used to selectively leach LiF from roasted LSAE. Gibbs free energy change calculated by DFT confirms the thermodynamic feasibility of the NaF fluorination roasting and Al2(SO4)3 leaching process, and it was found that Al2(SO4)3 could react more readily with LiF than with Na3AlF6. Under optimal process conditions, a lithium leaching rate of 94.05% was achieved. After leaching, 99.26% of Al and 97.21% of F in the leachate were recycled as AlF1.5(OH)1.5(H2O)0.375 precipitation by adding NaOH solution to adjust the pH to 6.6. Then, AlF3 and Al2O3 with metallurgical grade were obtained by roasting AlF1.5(OH)1.5(H2O)0.375 at temperatures between 500 and 600 °C. Lastly, Li2CO3, with a purity of 99.0%, was precipitated using Na2CO3 from lithium-containing leachate after purification and evaporation concentration. The overall Li recovery rate for the entire process is 86.2%. Collectively, this research proposes an efficient and environmentally friendly extraction process for lithium from LSAE.