A highly efficient ternary extraction system with tributyl phosphate/crown ether/NaNTf2 for the recovery of Li+ from low-grade salt lakes

A great challenge is to develop suitable techniques to extract Li + resources from low-grade salt-lake brines with high Mg/Li ratios. In this study, an efficient ternary extraction system has been constructed using tributyl phosphate (TBP) and crown ether (CE) as the extractant and sodium bistrifluoromethylsulfonimide (NaNTf 2 ) as the auxiliary extractant to extract Li + . Results showed that the single-stage E Li % and SF Li-Mg were up to 74.1 % and 757, respectively, when the O/A was 1, 0.02 mol/l Li + and 0.232 mol/l Mg 2+ . It is noteworthy that the elution of Li + was also as high as 100 % at an O/A volume ratio of 5, when 0.5 mol/l HCl was used as the counter-extractant to recovery Li + . The NMR and FTIR analysis and molecular dynamics (MD) and density functional theory (DFT) revealed that the exceptional performance of the three-component extraction system was attributed to the optimal matching between the diameter of Li + and the cavity size of the CE, as well as the strong affinity exhibited by CE, TBP, and NTf 2 − towards Li + . Specifically, the 2TBP-LiNTf 2 -CE-LiNTf 2 complex structure with the highest binding energy displayed the most structure. In summary, this work paves the way for the recovery of Li + from low-grade salt-lake brine.