Extracting Lithium from the High Concentration Ratio of Magnesium and Lithium Brine Using Imidazolium-Based Ionic Liquids with Varying Alkyl Chain Lengths

摘要

The present study investigates the extraction of lithium ion from the high concentration ratio of magnesium and lithium salt lake brine in a series of 1-alkyl-3-methylimidazolium-based ionic liquids (ILs), in which the alkyl chain lengths were n-butyl (C-4), n-pentyl (C-5), n-hexyl (C-6), n-heptyl (C-7), n-octyl (C-8) or n-nonyl (C-9), in the presence of triisobutyl phosphate (TIBP) + kerosene systems. The results showed that with shorter alkyl chain length of imidazolium-based ILs there was higher extraction efficiency of lithium ion. The optimal novel FeCl3-free extraction system of [C(4)mim][PF6]+TIBP+kerosene was established, and the single-pass extraction and back extraction efficiencies for lithium ion were 74.14% and 86.37% under the optimal conditions of [C(4)mim][PF6] : TIBP : kerosene = 1 : 8 : 1 (v/v), pH = 5.0, R(O/A) = 2.0 in the extraction step, as well as 1 mol/L HCl eluent, R(O/A) = 3 in the back extraction step. A comparison of extraction behaviors in a multilevel cross-flow and multistage counter-current extraction process for lithium ion was also carried out. On the basis of infrared spectroscopy and slope analysis methods, a cation-exchange extraction mechanism in the system of [C(4)mim][PF6]+TIBP+kerosene for lithium ion extraction was demonstrated.