Removal of Hg(II) from acid aqueous solutions by poly(N-vinylimidazole) hydrogel

Caption of Hg(II) from acid aqueous solution by immersed poly(N-vinylimidaz ole) hydrogel particles was studied as a function of pH, counterion, and ca tion concentration. Fitting parameters to several sorption isotherms have b een determined. Their values depend mostly on pH and less, on temperature a nd counterion, and suggest a large affinity of imidazole groups in the gel and mercury cations. Practically total removal (94.4%) of Hg(II) is achieve d at pH = 2, with 10 g of dry gel per liter of solution, when cation concen tration was as large as 15,000 ppm (0.075 M). Polymer protonation decreases about fourfold the cation affinity, supporting competitive protonation-com plexation mechanisms. By its side, metal uptake decreases polymer protonati on. Thermal stability of loaded gels decreases with respect to metal free h ydrogels. Scanning electron micrographs reveal no changes in the gel morpho logy upon cation binding, but T-g increases significantly with the Hg(II) c ontent of loaded gels and swelling decreases moderately, indicating the rol e of the cation as ionic crosslinker. Practically total elution of Hg(II) i s achieved with 1 M HNO3 in consecutive loading-elution cycles. (C) 2000 Jo hn Wiley & Sons, Inc.