Lithium recovery from an alumina electrolysis slag leaching solution with strong acidity: Separation of lithium-ion and production of battery grade lithium carbonate

Lithium (Li) with excellent physicochemical properties is widely used in modern industries. However, the shortage and depletion of Li resources has hindered the sustainable economic development. Li recovery from waste resource was an effective approach, in particular, alumina electrolysis slag is exemplified as Li riched solid waste. In this work, separation of Li from alumina electrolysis slag leaching solution (AESLS) via solvent extraction using bis(2-ethylhexyl) hydrogen phosphate (P204) system was explored. Effects of saponification degree, phase ratio, and reaction time on metal ions impurities and Li extraction were investigated. Operational parameters including extraction, scrubbing, saponification and precipitation were optimized. Results showed that the extraction efficiencies of Mg²⁺, Ca²⁺, Al³⁺, Fe³⁺ and Li⁺ were 100 %, 100 %, 99.99 %, 100 % and 20.71 %, respectively, under the optimal single extraction conditions. The loss of Li after scrubbing of loaded organic phase using hydrochloric acid was as low as 1.59 %. The P204 extraction process was proved to be a thermodynamic process with spontaneous entropy increase, and the extraction order of metal ions was Al³⁺ > Fe³⁺ > Ca²⁺ > Mg²⁺ > Li⁺ according to the extraction driving force (ΔC); The solvent-extracted ligand mechanism was elucidated by infrared spectroscopy and nuclear magnetic resonance. Additionally, battery-grade lithium carbonate was produced. Our study paves a new way for recovery of Li in AESLS.