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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]

Lithium is a vital aspect of the strategic development of the alternative energy and nuclear industries, and the demand for this metal is currently increasing rapidly. China possesses significant lithium resources, nearly 80 % of which are situated in salt lake brine. Solvent extraction is a viable means of extracting lithium ions from brine that has high magnesium-to-lithium ratio, and provides high selectivity along with ready scale-up to industrial production levels. The most common extraction technology for such scenarios is the tributyl phosphate (TBP)-FeCl 3 -kerosene system. However, this system tends to lose Fe3+ during the extraction process and the concurrent use of acid and alkali can seriously affect the stability of the organic phase. The present work demonstrates a new extraction process employing TBP as the main extractant, sodium tetraphenyl boron as a co-extractant and phenethyl isobutyrate as a diluent. Optimization of the relative amounts of these components along with the phase ratio provided a single-stage lithium ion extraction efficiency of 85.70 % together with a separation factor of lithium to magnesium ions of 1175. The organic phase was washed with a LiCl + NaCl solution to remove impurity ions then stripped five times with a NaHCO 3 solution, with a Li+ stripping efficiency >99 %. During ten replicate extractions, the Li+ extraction efficiency remained stable at approximately 84 %, demonstrating good stability. NMR spectra verified that the binding strength of metal cations to TBP decreased in the order of Li+ > Na+ ≫ Mg2+, indicating selectivity for the extraction of Li+. This single step NaHCO 3 method was adopted to simplify the extraction process. The overall strategy avoids the use of strong acids or bases that otherwise corrode equipment and provides greatly improved long-term stability of the organic phase. • TBP-sodium tetraphenyl boron-phenethyl isobutyrate extraction system was proposed. • A single-stage extraction efficiency of 85.70 % for lithium ion could be obtained. • The maximum separation factor of lithium to magnesium ions reached up to 1175. • NaHCO 3 was used as stripping agent to simplify the extraction process. • The proposed extraction system showed high stability and reusability. [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]

[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]