Extraction and separation of Li⁺ from high-ratio Mg/Li salt lake brines by [C₂mim][NTf₂] ionic liquid and a homemade extractor

The separation and recovery of Li+ from high-ratio Mg/Li salt lake brines possess a big significance, especially the demand for Li+ has grown rapidly in recently years. The ionic liquid [C(2)mim][NTf2] with tributyl phosphate (TBP) and sulfonated kerosene system was hired as an extractant to extract Li+ from salt lake brines with a high-ratio of Mg/Li experimentally by using a homemade membrane emulsification circulation (MEC) extractor. From the single-element extraction, the extraction efficiency of Li+ could be up to 96.0 % within 8 min. In view of the multi-element experiment, the MEC extractor manifested better extraction performance compared with oscillating and stirring extraction. The extraction ability of the extractant for Li+ could reach the ideal level without the addition of any co-extraction agents (Fe3+ and ClO4-). The new extraction system could have extensive applications since the extraction performance was insensitive to pH and temperature. The optimal extraction conditions for Li+ were V-TBP: V[C(2)mim][NTf2]: V-kerosene = 8:1:1, R(O/A) = 1. In addition, the stripping efficiency of Li+ could be improved by increasing the A/O and stripping stage. When the stripping stage reached 3, 94.5 % of Li+ could be extracted successfully by using 2 mol/L HCl. The slope method and FT-IR analysis manifested that the TBP-[C(2)mim][NTf2]-sulfonated kerosene system extracted Li+ by an anion coordination mechanism in the form of [Li.2TBP](+)(org). The DFT calculations were used for revealing the reaction between Li+ and P = O. The results are expected to provide experimental data and a theoretical basis for practical application.