Solubility as well as solution density in aqueous systems (LiCl + MgCl 2 + H 2 O) and (Li 2 SO 4 + MgSO 4 + H 2 O) at 288.15 K have been studied using the isothermal dissolution method. In the ternary system (LiCl + MgCl 2 + H 2 O) at 288.15 K, two invariant points, three isothermal dissolution curves and three crystallization regions including MgCl 2 •6H 2 O, LiCl•2H 2 O, and double salt LiCl•MgCl 2 •7H 2 O were detected. Experimental results compared with values of this system at (273.15, 348.15, and 323.15) K shows that the LiCl•MgCl 2 •7H 2 O crystallization region is increased slightly with the increasing of temperature, while that of MgCl 2 •6H 2 O and LiCl•2H 2 O are decreased obviously. In the ternary system (Li 2 SO 4 + MgSO 4 + H 2 O) at 288.15 K, there are one invariant point, two isothermal dissolution curves, and two crystallization regions corresponding to Li 2 SO 4 •H 2 O and MgSO 4 •7H 2 O. When this experimental phase diagram at 288.15 K was compared with that at (298.15, 303.15, and 348.15) K, it shows that the Li 2 SO 4 • H 2 O crystallization region is increased with the increasing of temperature, while that of MgSO 4 •7H 2 O is decrease obviously. A Pitzer and Harvie−Weare thermodynamic model were applied to calculate the solubility for this ternary system, and the calculated solubilities agree reasonably with the experimental results.

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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