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 x 10-7 x[Li+]0.7882 & sdot;[Lix54]0.2337 & sdot;[TBP]0.2999. The thermodynamic parameters of the extraction reaction were calculated as Delta H=-2.41 kJ/mol, Delta G =-10.202 kJ/mol, Delta S = 26.1 J/(mol & sdot;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.