Solvent extraction of lithium from hydrochloric acid leaching solution of high-alumina coal fly ash

Highlights: :• A novel process of Li recovery from leaching liquor of fly ash was proposed. • Li recovery reached 99% through 2-stage counter-current extraction. • Complex ratio and thermodynamic parameters of extraction process were investigated. The present work used solvent extraction method to extract lithium from hydrochloric acid leaching solution of high-alumina coal fly ash. In extraction stage, the optimum conditions were explored, at 20 ℃ and O/A = 1:4, using 70%(Vol.) tributyl phosphate-30%(Vol.) sulfonated kerosene-0.36 mol/L Fe³⁺ as extractant, extraction of lithium could reach 99% by two-stage extraction. In scrubbing stage, 95% of Al³⁺ in loaded organic phase was scrubbed with 6 mol/L HCl at O/A = 40:1, then 97% of Ca²⁺ in the loaded organic phase was scrubbed by three-stage countercurrent scrubbing with 5.5 mol/L LiCl + 0.5 mol/L HCl at O/A = 30:1. In stripping stage, 99% of Li⁺ in scrubbed organic phase was stripped by five-stage countercurrent stripping with 6 mol/L HCl at O/A = 10:1. In regeneration stage, 2 mol/L NaOH was used as regenerant to remove free acid and exchange H⁺ of extractive compound. There were no third phase, emulsification and solid deposition during the whole experiment. The structure of extractive compound was determined by slope method, and extracted complex ratio of Li⁺, Fe³⁺, and TBP was 1:1:1. The extraction process was found to be exothermic and spontaneous by thermodynamic study. Therefore, it's a promising method to recover lithium from hydrochloric acid leaching solution of high-alumina coal fly ash by TBP-FeCl₃-sulfonated kerosene extraction system.