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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]