Li⁺ Extraction from Aqueous Medium Using Tetracyanoborate Ionic Liquids─Experiments and ePC-SAFT Modeling

The global need for rechargeable batteries has increased significantly, leading to a corresponding rise in demand for lithium. This study explores the use of tetracyanoborate-based ionic liquids (IL) and tributyl phosphate (TBP) for the liquid–liquid extraction of lithium ions (Li+) from aqueous sources. The investigation includes comprehensive experimental analyses and modeling with the electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT). The Experimental Section investigates the process conditions for the extraction efficiency of the extraction system. It includes investigations into the best TBP/IL ratio of the TBP/IL extraction agent mixture and the influence of the phase ratio (mass of IL + TBP/mass of the aqueous salt solution) on extraction efficiency. The results proved the synergetic effects of the two extraction agents, IL and TBP, providing maximum efficiency at TBP/IL = 0.85. Li+ was almost completely extracted from an aqueous LiCl solution using optimized conditions. The ePC-SAFT modeling approach accounted for the ion-pair-assisted extraction of Li+ into the organic phase, enabling the description of the experimental behavior as quantitatively correct. This provided deeper understanding of the thermodynamic behavior within the liquid–liquid extraction system and paves the way for the screening of numerous IL systems for Li+ extraction and the prediction of optimal process conditions in the future.