Extraction of lithium from lepidolite by sodium bisulphate roasting, water leaching and precipitation as lithium phosphate from purified leach liquors

This paper presents the extraction process of lithium from lepidolite concentrate by roasting with NaHSO4 followed by water leaching. Results from TG-DSC analysis of feed material and XRD scans of solids justified the thermodynamic modelling of chemical reactions predicted using HSC software package. The roasting of NaHSO4/lepidolite concentrate mixture of mass ratio 2.5/1.0 at 500 °C followed by water leaching at 95 °C yielded 96% of Li extraction. Under these conditions, about 79% Rb and 73% Cs were also leached from calcined lepidolite material. Purification of the lepidolite leach liquor by adjusting the solution pH to 9 using caustic soda resulted in the precipitation of cryolite (NaAlF6) as a primary phase. The purified liquor with pH adjusted to 12 was treated with phosphoric acid to precipitate Li3PO4 to achieve a recovery of about 93%.