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β-Diketones are often used to separate brine with a high sodium-to‑lithium ratio but cannot be widely used because of their high toxicity and water solubility. In this work, a functionalized ionic liquid was synthesized from 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1-hexyl-3-methylimidazolium chloride, which was verified by FT-IR and 1H NMR spectroscopy. An organic phase system was formed with this ionic liquid as the extractant and 2-octanone as the diluent, which had the advantage of achieving good extraction and separation performances without co-extractant. In addition, the brine used in this work is the real Chaka salt lake brine in Tibet, which provides a reference value for industrial application of separation of metal ions. The experimental conditions were optimized and the single-stage extraction efficiency of Li+ reached up to 94 %. Using LiCl solution and HCl as the washing and stripping reagents, the washing efficiency of Na+ and stripping efficiency of Li+ were above 98 % and 99 %, respectively. The raffinate was used to regenerate the organic phase, which reduced the use of alkaline reagents. Over 10 cycles of the extraction process, the extraction efficiency of Li+ maintained at approximately 86 %. The extraction mechanism was identified as ionic association using slope analysis and ultraviolet and infrared measurements. • A novel extraction system was developed for selective extraction of lithium from Tibetan brine. • The single-stage extraction efficiency of Li+ with the extraction system reached up to 94 %. • The impurity ions could be washed out by using LiCl solutions. • The raffinate could be used to regenerate the organic phase. • The extraction system showed good reusability over 10 cycles of the extraction process. [ABSTRACT FROM AUTHOR]

• A novel ionic liquid of [Bmim]Bph 4 was used as co-extractant for extraction of Li+. • The single-stage Li/Mg separation factor was higher than 2500. • Li 2 CO 3 was obtained and the process flow was reduced with Na 2 CO 3 as stripping agent. • The binding capacity of TBP to metal ion followed the sequence Li+ ≫ Na+ > K+ ≈ Mg2+. • The whole extraction process with novel extraction system was green and efficient. A novel ionic liquid named 1-butyl-3-methylimidazolium tetraphenylboron ([Bmim]Bph 4) containing a stereo symmetric structure of Bph 4 - was synthesized and used as co-extractants with TBP and CH 2 BrCl as extractant and diluent for selective extraction of lithium ions from salt lake brines with high molar ratio of magnesium to lithium. The effects of extraction conditions containing molar ratio of co-extractant to lithium ion, volume percentage of TBP and O/A phase ratio on extraction performance were investigated. Under the optimal extraction conditions, the maximum separation factor of lithium to magnesium reached up to 2754 after one single-stage extraction process. After four stages of counter-current extraction process, the extraction efficiency of Li+ reached up to 99.47%. Then the washing and stripping conditions were optimized with the combination of LiCl and NaCl solution as the washing agent and Na 2 CO 3 solution as the stripping agent. After that, 10 cycles of the whole extraction experiments were carried out and the organic phase exhibited excellent reusability and stability. Since no acid and alkaline were used throughout the extraction process, the novel extraction process is greener and more environmentally friendly than the traditional solvent extraction process. [ABSTRACT FROM AUTHOR]