Recovery of aluminium and lithium from gypsum residue obtained in the process of lithium extraction from lepidolite

Lepidolite has an Al2O3 content of greater than 22%. Using it efficiently will be very important for the economic extraction of lithium from this low-grade lithium ore if an industrial-scale extraction process is to be developed. This paper presents a novel technique for recovering aluminium and lithium from the gypsum residue generated during the extraction of lithium from lepidolite. The alkali digestion conditions were considered based on the principles behind the Bayer process. Maximum extraction of aluminium (100%) and 96.4% extraction of lithium were recorded at caustic ratio (Na2O/Al2O3 molar ratio) of 1.7, digestion temperature of 136 °C and digestion time of 60 min. After digestion, aluminium hydroxide was precipitated by cooling and seeding of the digestion solution. Li+ ion was not adsorbed by aluminium hydroxide during this process. Therefore, Li could easily be recovered by adding sodium phosphate (Na3PO4). In addition, the precipitation of lithium at several different molar ratios of Li+/PO43 − was performed to investigate its influence on the recovery process.