Recovery of lithium from high Mg/Li ratio salt-lake brines using ion-exchange with NaNTf2 and TBP

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.