Junyuan Hua,Feidong Yang,Jintao He,Jiahui Du,Bo Dong,Xiaohua Ma,Jianxin Li
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.
In view of the complex problems for the ionic liquids (ILs) recovery with the system containing ILs and TBP, this work proposed a NaNTf 2 -based synergistic extraction system, NaNTf 2 + TBP, which could realize the effective reutilization of the extraction system without reducing the lithium separation ability. Under the optimal extraction parameters, the extraction efficiency of Li + exceeded 98%, while that of Mg 2+ was only ~1%. The results of mass spectrometry (ESI-MS) and slope analysis showed that two TBP molecules involved in the extraction process of Li + , and the Li + extraction mechanism obeyed the cation-exchange process. According to the red shift of the FT − IR peak of P O in TBP and the chemical shift changes of P in 31 P NMR, the interaction strength between TBP and different metal ion followed the sequence: E TBP−H >> E TBP−Li > E TBP−Mg > E TBP−K > E TBP−Na . It was also found that after a three−stage countercurrent extraction process, [Li + ] org was 0.42 g L −1 , and the total recovery efficiency of Li + was about 98%. The saturated extraction capacity for Li + could be as high as 5.4 g L −1 , and Li + could be stripped with the aqueous solution containing 0.2 mol L -1 HCl. In addition, the extraction efficiency of Li + was almost not attenuated after 6 extraction cycles. This new extraction system shows a certain industrial application prospect for Li + separation from the salt lake bine with high Mg/Li ratio.
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