Lithium fluoride dissolution in sulfuric acid solution: Optimization and application in the extraction of lithium from fluorinated α-spodumene

Abstract

Fluorination processes have been presented as an alternative to Li extraction and recovery processes from minerals and electronic waste. One of the possible products is LiF, a salt insoluble in water. Depending on market demands, it may be necessary to transform it into another lithium compound for technological applications. In this work, LiF was synthesized from LiCl and HF and characterized by the XRD and Rietveld method. The dissolution of LiF in sulfuric acid solution was modeled and optimized by Response Surface Methodology (RSM). The operating parameters investigated for leaching LiF were the solid/liquid ratio (A), sulfuric acid concentration (B), and leaching time (C). A mathematical model was obtained using RSM to predict the response at any point in the experimental domain (R2 = 0.9970). Analysis of variance (ANOVA) of the reduced quadratic model indicated that A, B, and AB, A2, and B2 interactions were significant. The optimal conditions selected were A = 13.0 LiF g/L, B = 5% v/v and C = 15 min to obtain a LiF dissolution of 100 ± 1% in sulfuric acid. Furthermore, optimal acid leaching conditions were tested on the fluorination products of α-spodumene with NaF. The results indicated that 98 ± 3% of the LiF in the fluorination products dissolves in the acid medium, in agreement with RSM. These results indicate the potential to double the solid/liquid ratio and halve the acid concentration and time to leach lithium from fluorinated α-spodumene, compared to other reported processes.