Optimization of LiF dissolution with Al2(SO4)3 and its application to lithium extraction by fluorination of α-spodumene

Numerous Li extraction methods from minerals and e-waste have been reported in the literature. Among them, direct fluorination processes appear to be a viable alternative due to their high lithium extraction efficiencies (>90%) as LiF. However, a drawback is the low water solubility of LiF, which requires acids for its separation and to obtain other commercial lithium salts. An interesting alternative for dissolving salts with low solubility is through the formation of coordination complexes. In this case, aluminum forms highly stable soluble complexes with the F⁻ anion, such as AlF²⁺, AlF₂⁺, AlF₃, AlF₄⁻, AlF₅²⁻, AlF₆³⁻.

This study proposes an acid-free LiF dissolution methodology using aluminum sulfate as a leaching agent. The LiF dissolution was modeled and optimized using Response Surface Methodology (RSM). The investigated operating parameters for LiF dissolution were the solid/liquid ratio (A), reaction temperature (B), and leaching time (C). Thus, a predictive mathematical model was successfully optimized (R² = 0.9445). The results indicated that the S/L ratio negatively influences the dissolution of LiF, while temperature and time have a positive effect. The LiF dissolutions of 90 ± 3% were achieved with a leaching time of 31 min, a S/L ratio of 20 g/mL, and a temperature of 45 °C.