Factors affecting the extraction of lithium from lepidolite

Key factors controlling the extraction of lithium from a lepidolite concentrate (2.55% Li) using a two-stage process based on roasting with Na2SO4 and water leaching were determined in this study. HSC software was used to predict lepidolite decomposition characteristics and products yielded from roasting. From this simulation roasting was conducted at 850–1000 °C with different sodium sulphate additions (set at sodium sulphate-lithium molar ratios of 1:1 to 3:1) in 0.5–2 h to yield several calcines for leaching. Stabcal modelling was applied to investigate the stability of various Li species formed during water leaching. From the simulation it was identified that LiKSO4, as one of the main Li-containing products formed in the calcine, has a low solubility and therefore controls the release of Li into water during leaching. The low solubility of LiKSO4 at 25 °C indicated by Stabcal was confirmed during leaching at different water–calcine mass ratios from 5:1 to 15:1. Leaching under these conditions only yields liquors containing < 1.0 g/L Li, corresponding to Li extractions of 45–48%. The Li extraction was significantly improved at 85 °C, yielding liquors containing 1–3 g/L Li, corresponding to extractions of 47–90%, with lower extractions of Li achieved at higher Li concentrations. At best, 90.4% of lithium was extracted (at water–calcine mass ratio 15:1, 85 °C and 3 h) using calcines roasted at 1000 °C for 0.5 h (using Na2SO4 — Li molar ratio of 2:1).