Abstract
Although spodumene is the primary lithium ore deposit, Li extraction from secondary deposits like lepidolite is of growing scientific interest. This is due to reasons such as ensuring diversified supply in the face of potential price swings and forecast supply deficits.
Conventional processing technologies currently in use for lithium extraction from spodumene (LiAlSi2O6) and lepidolite (K(LiAl)3(Al,Si)4O10)(F,OH)2) are based on thermal pre-treatment and the sulphuric acid process. These technologies involve energy intensive steps such as decrepitation (1100°C) and sulphuric acid digestion (250°C) in spodumene processing and roasting (750-1000 °C) for lepidolite processing. Although lithium is critical in the transition to a green economy, the lithium refining process itself is largely environmentally unfriendly and incurs a large carbon footprint.
There is a need to reduce the carbon footprint of the metallurgical processing of this strategic metal. This work investigates the direct acid leaching of lithium from lepidolite and beta spodumene. Lepidolite is a mineral which contains Li and valuable elements such as Cs, Rb and K. The acids, H2SO4, HNO3, HClO4 and H3PO4 with different anions show different leaching efficiencies of Li and other valuable elements. The results show that high Li extractions (above 90%) were achieved with minimal silica dissolution in the lepidolite systems whilst extractions above 60% were obtained within 1 hour of optimised leaching of beta spodumene.