A remarkable improved Li+/Mg2+ selectivity and Li+ recovery simultaneously by adding crown ether to tributyl phosphate-ionic liquid extraction system as co-extractant
The high similarity in chemical properties between Li + and Mg 2+ poses a substantial challenge for their selective separation from salt lake brine with high Mg-Li (m/m) ratios. Herein, a highly efficient solvent extraction system was reported for Li + /Mg 2+ selective separation, with tributyl phosphate (TBP) and di(aminobenzo)-14-crown-4 (CE) as extractants, [C 4 mim][NTf 2 ] (IL) as co-extractant, and methylene chloride as a diluent. Simulated brines included 0.01 M LiCl and 0.01 and 0.2 M MgCl 2 with Mg/Li mass ratios of 3.5 and 70, respectively. Molecular dynamics (MD), density functional theory (DFT), and 1 H NMR analysis were employed to reveal the hydrogen bond interaction and compatibility between CE, TBP, and IL. Under the optimal extraction conditions containing a concentration of 20 mg/mL CE and 0.61 mmol/mL IL, the maximum single-stage Li + extraction rate of the TBP-CE-IL extraction system with Mg/Li mass ratios of 3.5 and 70 were 89.5 and 81.8 %, and the separation factor of Li to Mg were up to 515 and 422. Compared with the TBP-IL extraction system, the addition of CE effectively improved the extraction rate of Li + and the selectivity of Mg-Li, which was due to the hydrogen bond interaction between CE and TBP/IL and the cavity size effect between CE and Li + , improving CE coordination and endowing the complex generated in the organic phase with greater stability. The possible structure of the complex in the organic phase was determined to be 2TBP·Li·NTf 2 -CE·Li·NTf 2 through Li + extraction dynamic analysis. In summary, this work provides an efficient separation technology for Li + extraction from salt lake brine.
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