Removal of as(V), Cr(VI) and Cr(III) heavy metal ions from environmental waters using amidoxime and quaternized hydrogels

Acrylonitrile (AN) and 1-vinyl imidazole (VI) based hydrogel was prepared in bulk (macro) dimensions via redox polymerization technique. Afterward, this hydrogel was quaternized (positively charged) and exposed to the amidoximation reaction. The prepared hydrogels (quart-p(AN-co-VI), amid-p(AN-co-VI) and p(VI)) characterized using fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). Swelling experiments were performed gravimetrically at room temperature in deionized water and different pH solution. Water absorbencies of both amidoximated hydrogels and quaternized hydrogels were founded to be high. Prepared hydrogels were used to remove heavy metal ions such as arsenic(V) (As(V)), Chromium(VI) (Cr(VI)) and Chromium(III) (Cr(III)) from aqueous media. The sorption of As(V), Cr(VI) and Cr(III) metal ions by hydrogels were carried out at different initial metal ion concentrations, different pHs, different times in batch sorption experiments at 25oC. The maximum metal ion sorption capacity by all hydrogels was in the order: As(VI)>Cr(VI)>Cr(III). The maximum sorption capacity for As(VI), Cr(VI) and Cr(III) ions was found to be 598, 303.8 and 4.9 mg g-1 for amid-p(AN-co-VI), respectively. As result of, amidoximated hydrogels have more sorption capacity to metal ions than quaternized hydrogels. Three different kinetic models (pseudo first order, pseudo second order and intraparticle diffusion model) were also used to investigate the sorption mechanisms. Furthermore, the Langmuir and Freundlich sorption isotherms were investigated for these metal ions. As a result of, amidoximation and quaternization of AN and VI based hydrogels have been a promising technique to increase the sorption rate and capacity of hydrogels and are thought to provide great advantages in the removal of metal ions from wastewaters. Especially, among the p(AN-co-VI) modification processes, amidoximation reaction was found to give better results than quaternization reaction. Prepared hydrogels were found to be more selective than Cr(III) versus As(V) and Cr(VI).