Hydrogels derived from 2-hydroxyethyl-methacrylate and 2-acrylamido-2-methyl-1-propanesulfonic acid, with ability to remove metal cations from wastewater

Synthesis, characterization, and study of the cation adsorption properties of four hydrogels are presented. The hydrogels were synthesized via radical copolymerization of a 1:1 mixture of 2-hydroxyethyl-methacrylate and 2-acrylamido-2-methyl-1-propanesulfonic acid, with different initiators and cross-linking reagents. HM1 hydrogel was obtained by adding only ammonium persulfate; HM2 hydrogel was synthesized using a redox initiator solution containing ammonium persulfate and sodium metabisulfite at room temperature. For HM3 hydrogel the initiator benzoyl peroxide and the cross-linking reagent ethylene glycol dimethacrylate were used. Finally, for HM4 hydrogel the polymerization was carried out using ammonium persulfate as initiator and poly(ethylene glycol) diglycidyl ether as cross-linking reagent. The sorption properties were analyzed by pH, contact time, maximum sorption capacity, and selectivity studies. The HM2 and HM3 hydrogels exhibited good ion sorption properties. These copolymers were capable of interacting and removing Cd(II), Cu(II), Pb(II), Ni(II), and Zn(II) ions from synthetic solutions and with real samples from mining wastewaters. The results obtained from the studies of maximum sorption capacity at different concentrations showed that the HM2 hydrogel was capable of adsorbing 226 mg/g Cd(II), 241 mg/g Pb(II), 166 mg/g Cu(II), 161 mg/g Zn(II), and 110 mg/g Ni(II) and the HM3 hydrogel was capable of adsorbing 184 mg/g Ni(II), 172 mg/g Cd(II), 126 mg/g Zn(II), 90 mg/g Pb(II), and 39 mg/g Cu(II). The experimental data were correlated with the Langmuir and Freundlich isotherm models. Thermodynamic parameters such as enthalpy (ΔH°), Gibbs free energy (ΔG°), and entropy (ΔS°) changes were obtained. The sorption kinetics were analyzed using Lagergren pseudo-second-order equation.