Iron sulphate roasting for extraction of lithium from lepidolite

• Lithium was extracted from lepidolite during roasting with FeSO4·7H2O and CaO.
• HSC modelling was used to simulate the roasting process.
• SO2, SO3 and HF gases were produced during roasting.
• About 93% lithium was extracted from roasting using a closed system.
• Leach liquors containing maximum ~ 8.7 g/L Li were obtained from leaching.

Iron sulphate roasting and water leaching were investigated to extract lithium from lepidolite in this study. HSC modelling was used to simulate the process of roasting lepidolite with FeSO4·7H2O and CaO. Based on HSC, three-dimensional models were derived to predict the effect of temperature, SO4/Li and Ca/F molar ratios on the production of S- and F-containing gases (SO2, SO3, HF) and Li species (Li2SO4, LiKSO4) during roasting. It is believed that temperature and SO2/SO3 gases controlled the extraction of lithium from lepidolite during roasting while more soluble Li sulphate species determined the recovery of lithium during leaching. Using optimum parameters selected from HSC, roasting tests were conducted to produce calcines for leaching. Optimum roasting conditions were experimentally determined as 850 °C, 1.5 h, and SO4/Li and Ca/F molar ratios of 3:1 and 1:1, respectively. Roasting in a closed environment led to more Li extracted than with an open system. Leaching the calcines obtained from the open and closed systems with a water/calcine mass ratio of 1:1 at room temperature for 1 h yielded leach liquors containing ~ 7.9 g/L Li and ~ 8.7 g/L Li, corresponding to ~ 85% and ~ 93% extractions of Li from lepidolite, respectively.