Selective lithium extraction from low-grade lepidolite leachate with a high Na/Li ratio using Lix54-TBP

During the hydrometallurgy process of low-grade lepidolite , a large amount of Na + is usually introduced. The high Na/Li ratio makes it difficult to sustainably precipitate and recover Li + . To improve the Li + recovery efficiency and the Na/Li separation coefficient, a Lix54-TBP extractant system with sec-octyl alcohol as phase modifier was proposed. The extraction efficiency of Li + reached 98.29 %, with a Na/Li separation coefficient of 5606.25 under the optimal conditions. The kinetic equation of the extraction was R (Li) = 9.397 × 10 −7 × [Li + ] 0.7882 · [Lix54] 0.2337 · [TBP] 0.2999 . The thermodynamic parameters of the extraction reaction were calculated as ΔH = -2.41 kJ/mol, ΔG = -10.202 kJ/mol, ΔS = 26.1 J /( mol · K) and Ea = 19.73 kJ/mol, indicating the exothermic, spontaneous and diffusion - controlled extraction. The molecular electrostatic potential, RDF , bond length, and binding energy were simulated based on the DFT. The selective extraction mechanism of Li + by Lix54-TBP system was further determined to be an ion exchange reaction . This study provides technical and theoretical references for efficient and stable extraction of Li from low-grade lepidolite, which is crucial for the full protection and utilization of strategic mineral resources. • A new extractant system Lix54-TBP is proposed. • Lix54-TBP can efficiently extract Li + with an extraction efficiency of 98.29 %. • Lix54-TBP can achieve a high separation factor β (Na/Li) of 5606.25. • The kinetics and thermodynamics of the ion exchange extraction is revealed. • The molecular dynamics are simulated based on the density functional theory.