Construction of an Ionic Liquid Extraction System Assisted by COSMO-RS for Lithium Recovery from High Mg/Li Ratio Salt Lake Brines

Abstract Efficient recovery of lithium from high Mg/Li ratio salt lake brines remains a critical bottleneck for the sustainable development of the new energy industry, yet the directional design of ionic liquids (ILs) extraction systems is severely hindered by blind screening and ambiguous structure–activity relationships. Herein, a COSMO-RS-assisted strategy was proposed to rationally construct high-performance IL–tributyl phosphate (TBP) synergistic extraction systems. 870 candidate ILs were first rapidly screened via COSMO-RS simulation based on the infinite-dilution activity coefficients and chemical potentials (μ) of LiCl, NaCl, KCl, and MgCl2 in ILs, together with water-solubility parameters (lg Kow) and σ-profiles, thereby avoiding massive, inefficient trial-and-error experiments. The screened ILs were then incorporated into IL-TBP synergistic systems, and the effects of IL type, IL concentration, extractant type and concentration, temperature, and IL/TBP molar ratio on lithium extraction efficiency and Li/Mg selectivity were systematically investigated. Among the screened systems, [Emim][NTf2] + TBP offered the highest Li+ extraction efficiency, whereas [Bpy][NTf2] + TBP exhibited exceptional selectivity toward the simulated East Taiji’naier Salt Lake brine, achieving a separation factor βLi/Mg of 223.56 and βLi/Mg of 32.90. Notably, the developed systems allowed efficient stripping at a mild HCl concentration of only 1.0–1.5 mol·L–1, far below the 6–9 mol·L–1 required by the conventional TBP + FeCl3 route, significantly mitigating equipment corrosion and acidic wastewater generation. Moreover, the [Emim][NTf2] + TBP system maintained a Li+ extraction efficiency of 72–79% with βLi/Mg above 17 over five consecutive cycles, demonstrating outstanding reusability and long-term stability. This work provides an efficient and designable paradigm for the targeted construction of high-performance IL extraction systems and offers a rational screening platform transferable to other metal-separation applications.