Recovery of Lithium from Brine with a High Mg/Li Ratio Using Hydroxyl-Functionalized Ionic Liquid and Tri-n-butyl Phosphate

In this study, a hydroxyl-functionalized ionic liquid 1-hydroxyethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([OHEMIM][NTf2]) and tri-n-butyl phosphate (TBP) were used as co-extraction reagent and extractant, respectively, to improve the extraction efficiency of Li+ and the separation factor of Li–Mg from brine with a high Mg/Li ratio. The extraction efficiency of Li+ is 94.2% and the separation factor of Li–Mg is 539 under the optimal condition. The washing efficiency of Mg2+ and K+ is close to 100% using 0.6 mol L−1 LiCl and 1.8 mol L−1 NaCl as the washing solution at an organic-to-aqueous phase ratio (O/A) of 4, and the stripping efficiency of Li+ is about 98.0% using 1.0 mol L−1 HCl as the stripping agent at an O/A phase ratio of 1. The extraction efficiency of Li+ is reduced by less than 4.4% after seven cycles, indicating that the extraction system is stable and reusable.