Enhanced acid treatment to extract lithium from lepidolite with a fluorine-based chemical method

Lepidolite has recently become valued as an important lithium ore resource due to the rapidly increasing demand for lithium (Li) for lithium-ion batteries (LIBs). However, existing processes to extract Li from lepidolite are still difficult and uneconomical, since the amount of lithium contained is typically low. Here, a fluorine-based chemical method was proposed to enhance the lithium extraction and utilize the 2–4% F from lepidolite. Additionally, a mixture of hydrofluoric and sulfuric acid (HF/H2SO4) was employed to theoretically investigate the reaction mechanism of the fluorine-based chemical method, since HF molecules are main reaction forms in the reaction. The results showed that the HF/ore ratio played a dominant role in the acid treatment, especially in the generation of fluorides. The added H2SO4 slightly accelerated the dissolution and affected the coordination equilibrium between Al3+ and F−. The dissolution conditions were also optimized that 98% of Li and 90% of Rb and Cs were efficiently converted into lixivium as sulfates using an ore/HF/H2SO4 ratio of 1:2:3.5 (g/mL/mL) at 85 °C for 3 h. Lepidolite was selectively dissolved over quartz, resulting in the relatively selective leaching of Li over Si and leaving amorphous SiO rich layers and K2SiF6 in the residue, which will be beneficial for the downstream processes of purification and separation. This investigation leads to advances in the understanding of the dissolution behavior with this fluorine-based chemical method and reflects the application potential of introducing fluorine to utilize lepidolite.