Ionic liquid-assisted selective lithium extraction from magnesium-rich brines containing various alkali metals: Experimental and molecular insights

This study first systematically investigated selective Li+ extraction from Mg2+-rich brines with Na+ and K+ using ionic liquid (IL) based synergistic extractant (SE) systems from molecular mechanisms to extraction performances. The ternary combination 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([AMIM][Tf2N]), tri-iso-butyl phosphate (TIBP) and dichloromethane (DCM), i.e., [AMIM][Tf2N]-TIBP-DCM was selected as a suitable SE from the diverse organic phosphorus ligands, ILs and diluents. The single-stage Li+ extraction efficiency was as high as 96.87 %, and selectivities of βLi+/Mg2+, βLi+/Na+, and βLi+/K+ were up to 1161.94, 76.74, and 1263.46, respectively. It was found that Li+ is extracted from the aqueous phase to organic phase in Li+-4TIBP-[Tf2N] complex. The molecular-level mechanism was identified as the multi-type interaction formed between metal ions and [AMIM][Tf2N]-TIBP to destroy the hydration of metal ions through quantum chemical (QC) calculations. The work proposes valuable theoretical guidance to develop novel IL-related SE systems for the high-efficiency Li+ extraction from salt lake brines.