Modified polyacrylamide hydrogels and their application in removal of heavy metal ions

Modified crosslinked polyacrylamides having different functional groups were prepared by Mannich reaction using different amine compounds such as ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA) and sulfomethylation reaction. Products were characterized by determination of their basic group content (BGC), hydroxymethyl group content (HMG), equilibrium degree of swelling (EDS) and FT-IR spectra. For Mannich reactions, BGC and EDS changed with amount of employed amine compounds, reaction time and temperature. Sulfomethylation reactions gave products with high BGC and very high EDS. FT-IR spectroscopic analysis confirmed that a parallel hydrolysis reaction occurred along with the expected modification reactions. The products were used for removal of Cu(II), Cd(II) and Pb(II) ion under competitive and non-competitive conditions at different pH. The metal ion removal capacities changed depending their BGC and EDS. While the Mannich products were selective towards Cu(II) ion, the sulfomethylation products were highly selective to Pb(II) ions. The polymers were used several times by regeneration without loss of adsorption capacity and changing of selectivity properties.