Extraction of lithium from coal fly ash by low-temperature ammonium fluoride activation-assisted leaching

Abstract A novel process for extracting lithium from coal fly ash by low-temperature salt activation with ammonium fluoride was proposed in this study. The glass phase in coal fly ash was converted to water-soluble fluoride salts after the salt activation process, which was followed by the extraction of lithium from the glass phase via water leaching. The effects of activation temperature and SiO2/NH4F mass ratio on the extraction of lithium were investigated in detail. The results showed that more than 90% of lithium was recovered under the optimized conditions: 155 °C of activation temperature, 1:1.35 of SiO2/NH4F mass ratio. A possible reaction mechanism for lithium extraction was also proposed based on thermodynamic, thermogravimetry, X-ray diffraction, scanning electron microscopy, and solid nuclear magnetic resonance analyses. This work provides a unique platform reference for further studies on the efficient extraction of resources with similar mineral compositions.