Lithium recovery from mechanically activated mixtures of lepidolite and sodium sulfate

Mixtures of lepidolite ore and sodium sulfate (Na2SO4) at mass ratios of 1:0.5 and 1:1 were prepared and milled using zirconia media in a planetary ball mill for 5 h. The 5 h milled samples were heated in a furnace at temperatures of 700°C or 800°C for one h under an air atmosphere. XRD results showed the formation of new phases such as LiKSO4, LiNaSO4 and Li2NaK(SO4)2 in the calcine. Unmilled samples showed no such reactions. The presence of well crystalline Li2NaK(SO4)2 phase in the calcine after heating at 700 indicated that chemical reactions between the lepidolite and Na2SO4 occur at lower temperatures after 5 h milling. Hot water leaching of the calcines showed that phases such as LiKSO4, LiNaSO4 and Li2NaK(SO4)2 were responsible for the increase in solubility of lithium. Increasing the calcination temperature had a more significant effect on the lithium dissolution than increasing the fraction of Na2SO4.