Simultaneous extraction of lithium, rubidium, cesium and potassium from lepidolite via roasting with iron(II) sulfate followed by water leaching

Lepidolite is an important mineral resource containing lithium, rubidium, cesium and potassium. Most researches focused on the extraction of lithium from lepidolite, while the co-extraction of rubidium, cesium and potassium was ignored. In this study, the extraction of lepidolite at lower temperature was investigated by using iron(II) sulfates feedstock, aiming at enhancing the extraction of lepidolite, especially for rubidium and cesium. Thermodynamic predictions indicated that the co-extraction of lithium, rubidium, cesium and potassium from lepidolite by roasting with iron(II) sulfate was feasible, but high temperature worked against the extraction. The effects of process parameters on the extraction were investigated systematically. It was found that the optimal roasting conditions were as follows: 50% lepidolite particles <74 μm, temperature of 675 °C, iron(II) sulfate to lepidolite mass ratio of 2:1, and holding time of 90 min. The extraction efficiencies of Li, Rb, Cs and K were 92.7%, 87.1%, 82.6% and 86.2%, respectively. The reaction between lepidolite concentrate and iron(II) sulfate followed two pathways, i.e. gas-solid and liquid-solid reaction. The formation of pyrosulfates with low smelting point promoted the reaction by reacting with lepidolite through a circular transformation between sulfates and pyrosulfates. Compared with the conventional extraction of lepidolite, the proposed process operates at a lower temperature and co-extracts various metals, exhibiting great potential in industrial application.