Enhanced lithium leaching from lepidolite in continuous tubular reactor using H2SO4+H2SiF6 as lixiviant

An acidic mixture of sulfuric and fluosilicic acid (H2SO4+H2SiF6) was employed as lixiviant to enhance leaching of lithium from lepidolite. The H2SiF6 was obtained as a byproduct of anhydrous hydrofluoric acid production, aiming to provide HF molecules. It was found that the HF molecules were the main reaction component and played a key role in strengthening the dissolution of lepidolite. Different factors, including mass ratio of ore/H2SO4/H2SiF6, concentrations of H2SO4 and H2SiF6, leaching temperatures (40−80 °C) and time (15−75 min), were investigated. Moreover, an efficient tubular reactor was employed to improve this acid leaching system. Under the optimal conditions (ore/H2SO4/H2SiF6 mass ratio of 1:0.8:1.6, 80 wt.% H2SO4, 15 wt.% H2SiF6, 80 °C, 15 min), 97.9% of Li, 96.4% of K, 97.6% of Rb, 96.7% of Cs and 81.4% of Al (mass fraction) were leached. Additionally, a two-step thermal process was proposed to remove fluorine of leaching slurry. This acid treatment using an acidic mixture of H2SO4 and H2SiF6 in a continuous tubular reactor shows potential as an alternative process to extract lithium from lepidolite.