Solvent extraction of lithium from simulated shale gas produced water with a bifunctional ionic liquid

The recovery of lithium from brines is a major field of study with an increase in lithium-ion batteries consumption and the subsequent growth of lithium consumption. The recovery of lithium from shale gas produced water is promising since these sources could contain non-negligible concentrations of lithium. In this study, lithium extraction was investigated using solvent extraction with a bifunctional ionic liquid (IL) as an extracting agent diluted in n-dodecane. The components of these IL are cheap and commercially available products, namely Aliquat-336 (methyltrioctylammonium chloride) and DEHPA (di-(2-ethylhexyl)phosphoric acid), and its synthesis is straightforward. Lithium extraction was optimized by studying several experimental parameters (mixing time, aqueous phase acidity, IL concentration in the solvent phase, aqueous lithium concentration). The mechanism of extraction was detailed, and the stripping was shown to be complete with 0.5 mol.L-1 of HCl. A two stages strategy was defined to recover lithium from synthetic brine. In the first stage, divalent metals are removed using five successive cycles of extraction with DEHPA (1 mol.L-1) dissolved in n-dodecane. In the second stage, the IL extracting agent [Aliquat-336][DEHPA] (1 mol.L-1) allowed to remove 83% of lithium in one cycle of extraction, which is higher than reported solvent extraction results with conventional extracting molecules.