Efficient Extraction of Lithium Ions from High Mg/Li Ratio Brine through the Synergy of TBP and Hydroxyl Functional Ionic Liquids

Abstract

The extraction of Li+ from the high Mg/Li ratio brine was performed using hydroxyl functional ionic liquids (ILs) as the coextractant and tributyl phosphate (TBP) as the extractant. Firstly, the extractive system, 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HOEmim][NTf2]) + TBP was proved to exhibit the highest extraction efficiency of Li+ (88.15%) from LiCl aqueous solutions among the extractants composed of different ILs, TBP, and ILs + TBP. Effects of various extraction parameters on the extraction efficiencies of Li+ and Mg2+ were then investigated. 95.01% of Li+ was extracted and the Li/Mg separation factor reached 405.76 in a single-stage at 278.15 K and O/A of 2 : 1. The extraction complexes were determined by the slope analysis method and ESI-MS analysis, and the metal complexes in the organic phase were indicated to be mainly [Li·2TBP][NTf2]. The striping study showed that 92.86% of Li+ was stripped with 1.0 mol·L–1 HCl. 98% extraction capacity of the synergy extractants was remained after 5 regeneration cycles. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°), together with the mechanism of the Li+ extraction were further demonstrated finally. According to the results, [HOEmim][NTf2] + TBP extraction system showed promising performance in extracting lithium from salt lake brine with high Mg/Li ratio.