Removal of zinc ions from aqueous solution using zinc extractant-encapsulated hydrogels formed by Pickering emulsion technique

Traditional extraction methods for the removal of metal ions from water were generally limited by the generation of third phases and leakage of extractant. In this work, Pickering emulsion hydrogels (PEHGs) containing zinc extractants 2-ethylhexyl hydrogen-2-ethylhexylphosphonate (P507) were prepared via the emulsions polymerization route for the removal of zinc ions (Zn(II)) from aqueous solutions. The PEHGs were characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and compressive tests. The adsorption performance of Zn(II) by PEHGs was investigated. The results showed that PEHGs have excellent stability, mechanical properties and a good encapsulation effect. No third phase was formed during the adsorption process. The actual Zn(II) adsorption by the PEHGs was 138.2 mg/g, which was almost consistent with the theoretical adsorption amount of 143.06 mg/g at 298 K. After ten adsorption–desorption cycles, the adsorption capacity of the PEHGs for Zn(II) could reach 95.7% of the initial adsorption capacity. In a mixed solution of Zn(II), Mg(II), Cu(II) and Ni(II), the adsorption rate of Zn(II) by the PEHGs exceeded 98%. The adsorption amount of Zn(II) by the PEHGs was fitted well with the data of the Langmuir adsorption isotherm model and followed the chemical adsorption process. In conclusion, the proposed PEHGs had the potential for Zn(II) removal in aqueous solutions.