Three ionic liquids(ILs), namely, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide and 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide with the triisobutyl phosphate(TIBP) and kerosene system were respectively used to extract lithium ion from salt lake brine with a high concentration ratio of magnesium and lithium experimentally. Results indicate that the highest extraction selectivity for lithium was obtained with IL 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)-sulfonyl]imide. The effects of solution pH and phase ratio R(O/A) on the extractive step and the influence of acid concentration of the stripping solution and R(O/A) on the back extraction step were also investigated systematically. The single-step extraction efficiency of lithium ion was 83.71% under the optimal extraction conditions, and the single-step back extraction efficiency was 85.61% with a 1.0 mol/L HCl in 1.0 mol/L NaCl medium as stripping agent at R(O/A)=2. The liquid-liquid extraction mechanism and the complex of the ligand with lithium were proposed.

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Solubilities, densities, and refractive indices for the salt-water ternary system (LiCl + LiBO 2 + H 2 O) at T = 288.15 K and 298.15 K and p = 0.1 MPa were determined using the isothermal dissolution equilibrium method. According to the experimental data at two temperatures, the phase diagrams and the diagrams of densities and refractive indices versus lithium chloride composition in the solution were plotted, respectively. In the phase diagrams at 288.15 K and 298.15 K, in all there are three crystallizing regions corresponding to lithium metaborate octahydrate (LiBO 2 ·8H 2 O, Lb8), lithium metaborate dihydrate (LiBO 2 ·2H 2 O, Lb2), and lithium chloride monohydrate (LiCl·H 2 O, Lc1), three univariant curves and two invariant points corresponding to (Lb8 + Lb2) and (Lb2 + Lc1). It was found that there are two kinds of hydrates for lithium metaborates (Lb8 and Lb2) formed at both termperatures, and the hydrate for lithium metaborate belongs to hydrate type II. Neither double salts nor solid solutions were found. A comparison of the phase diagrams at two temperatures shows that the areas of the crystalline regions of Lb8 and Lc1 are decreased and that of Lb2 is increased with increasing temperature. The density and refractive index in the ternary system at two temperatures change regularly with the increasing LiCl mass fraction in the solution to reach the maximum values in the ternary-invariant-point. The correlation equations of density and refractive index were used, and the calculated results agree well with the experimental data.