Lithium recovery from lepidolite roasted with potassium compounds

Three different potassium compounds, namely K2SO4, KOH, and K2SO4 + KOH, were used as additives to extract lithium from lepidolite by roasting and water leaching. The effect of the additive/ore mass ratio on the extraction of Li, K, Si, and Al was compared among the different additives. Efficient extraction of Li and K was obtained by roasting lepidolite with the K2SO4 and K2SO4 + KOH additives. The Li extraction and K recovery were 92.78% and 81.72% respectively under the optimum conditions: K2SO4/KOH/ore mass ratio of 1:0.5:1, roasting at 900 °C for 2 h, and water leaching at 90 °C for 3 h with a liquid to solid (L/S) ratio of 5:1. The decomposition process of lepidolite with different additives was explored. The results indicate that lepidolite is decomposed into kalsilite when roasted with KOH and mixed phases of kalsilite, leucite, K2SO4, and LiKSO4 when roasted with K2SO4 and K2SO4 + KOH additives. Li in the lepidolite is converted into soluble LiKSO4, facilitating its extraction. The addition of KOH contributes to the formation of kalsilite, which makes K recovery easier.