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

Abstract

In view of the complex problems for the ionic liquids (ILs) recovery with the system containing ILs and TBP, this work proposed a NaNTf2-based synergistic extraction system, NaNTf2 + 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 Mg2+ 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 PO in TBP and the chemical shift changes of P in 31P NMR, the interaction strength between TBP and different metal ion followed the sequence: ETBP−H >> ETBP−Li > ETBP−Mg > ETBP−K > ETBP−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.