Lithium extraction from salt‐lake brines using dicationic ionic liquids: ePC‐SAFT modeling and molecular mechanisms

This work proposes a novel strategy for enhancing Li+ extraction from salt‐lake brines with the high Mg2+/Li+ ratio using dicationic ionic liquid (DIL)‐based extractants. The ternary mixture of the DIL [DOMIM][Tf2N]2, tributyl phosphate (TBP), and dichloromethane (DCM) as a diluent achieved a higher single‐stage Li+ extraction efficiency (86.40%) and separation selectivity of Li+/Mg2+ (302.37) compared with the ternary mixture based on monocationic IL [OMIM][Tf2N] instead of the DIL. The high Li+ extraction performance could be maintained over five‐cycle regeneration. Electrolyte perturbed‐chain statistical associating fluid theory was used to qualitatively predict activity coefficients of Li+ and Mg2+ in the organic phase of the so‐called “organic–inorganic complex strong electrolyte system.” The DIL‐enhanced extraction mechanisms at the molecular level (i.e., Li+ extracted the form of 2Li+ + 3TBP + 2[Tf2N]− complex) was revealed by slope analysis spectrum characters and quantum chemical calculations. This study provides guidance for the rational design of new IL‐based extractants for high‐efficiency Li+ extraction from brines.