Removal of minor and trace impurities from lithium leach liquors

It is relatively straightforward to extract lithium from minerals and clays. However, the number and amount of impurities that are co-leached can vary significantly. Limiting lithium losses during removal of impurities can pose significant challenges in the production of battery grade lithium chemicals. Typically leach liquors from lithium mica ores and clays contain higher levels of impurities than from spodumene. Sighter testwork is required to identify the best technology to remove each impurity. This then needs to be followed by locked cycle testwork. It is necessary to simulate as many of the recycle loops as possible to determine the effect of each loop, to understand what level of impurity removal is possible and how impurities will build up in the circuit. In most cases a process bleed is required to limit the build-up to be able to produce battery grade lithium chemicals. This paper presents the typical impurities found in the extraction of lithium from various ores and reviews some of the issues with removal of minor and trace impurities from leach liquors such as: boron, fluoride, caesium, rubidium, calcium and magnesium. Techniques discussed are chemical precipitation, crystallisation, adsorption, selective ion exchange and solvent extraction for the production of battery grade lithium carbonate.