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• 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]

[Display omitted] • NaBPh 4 and CH 2 ClBr were used as co-extractant and diluent for extraction of Li+. • The new extraction system showed excellent extraction performance and reusability. • Using Na 2 CO 3 as stripping agent obtained Li 2 CO 3 product and reduced the process flow. • The binding capacity of TBP to metal ion followed the sequence Li+ > Na+ > K+ > Mg2+. • None of acid and alkali were used in the whole extraction process. It is very difficult to selectively extract lithium ions from high Mg/Li salt lake brine efficiently and environmentally. Among the conventional extraction system, FeCl 3 as the co-extractant has the disadvantages of easy to loss and reducing stability of the organic phase. Therefore, a new co-extractant must be developed and applied for selective extraction of lithium ions. TBP was used as the extractant. According to the optimization of extraction conditions, NaBPh 4 and CH 2 ClBr were selected as the suitable co-extractant and diluent. Under the optimal extraction conditions (molar ratio of NaBPh 4 to Li+ = 2.0, TBP volume fraction = 50%, and R (O/A) = 1.0), the one-stage extraction efficiency of Li+ and Li/Mg separation factor reached up to 87.65% and 2260.71, respectively. Effects of washing and stripping conditions on washing and stripping performances were investigated too. Under optimal conditions of washing and stripping processes, the stripping efficiency of Li+ reached up to 98.84% and Li 2 CO 3 product could be directly obtained in the aqueous phase. Then ten continuous cycles of the whole extraction processes were performed and the results verified that the extraction system showed excellent extraction stability and reusability. The extraction mechanism was deeply studied by using simulation calculation on Materials Studio software and nuclear magnetic resonance characterization. The binding capacity of TBP to metal ions follows the sequence: Li+ > Na+ > K+ > Mg2+. This proposed extraction technology not only avoids the use of acid and alkali, but also reduces the process flow, which has great research potential and industrialization value. [ABSTRACT FROM AUTHOR]