Efficiently Removing Heavy Metals from High-Salinity Wastewater via Ionic Liquid-Based Aqueous Biphasic Systems

For the separationof metal ions, ionic liquid-based aqueous biphasicsystems (IL-ABSs) offer a promising alternative to solvent extraction.However, the incorporation of an extensive quantity of inorganic saltsrestricts their practical application. Because heavy metal wastewateroften contains high concentrations of inorganic salts, it offers goodprospects for the application of IL-ABSs in the separation of heavymetals. In this work, an IL-ABS was formed by tributyltetradecylphosphoniumchloride ([P-44414]Cl), and simulated high-salinity wastewater(NaCl and Na2SO4 as the main inorganic salts)was used for the separation of heavy metals. The phase diagram resultsindicated that the formation of a two-phase system required a relativelyhigh salt concentration. The extraction process followed the mechanismof anion exchange; thus, heavy metals such as zinc and cadmium thatformed complexes with chloride ions could be effectively extracted(extraction rate >99.5%) with a very fast rate (extraction time<1min) at a wide pH range (pH = 2-7). After extraction, the metalscould be stripped well (stripping rate >99.5%) after contact withthe NaOH solution. This research provided a new approach for treatingheavy metals in high-salinity effluents, which has the advantagesof IL-ABS and avoids the disadvantages of adding large amounts ofinorganic salts at the same time.