Removal of Cr(VI) onto functionalized pyridine copolymer with amide groups

New pyridine strong base anion exchange resin has been prepared by the nucleophilic substitution reaction of 4-vinylpyridine:divinylbenzene copolymer of gel structure with 2-chloroacetamide as halogenated compound. The resulting resin was used to remove Cr(VI) from the aqueous solution. Batch adsorption studies have been carried out to determine the effect of the initial concentration of Cr(VI), adsorbent dose, pH, temperature and the presence of sulfate anions as counter ions. The process was found to be pH, solid/liquid ratio and concentration dependent. The adsorption capacities increase with the increase of the initial concentration of Cr(VI) and therefore, the resin exhibited the degree of usage of the strong base exchange capacities higher than 90% and the good efficiency in the chromium removal. At acidic pH and low concentration of the hexavalent chromium the synthesized pyridine resin offer much greater chromate removal capacities compared to alkaline pH. Equilibrium modeling of the process of Cr(VI) removal was carried out by using the Langmuir and Freundlich isotherms. The experimental data obeyed these isotherm models. Thermodynamic studies were performed and the parameters namely, ΔG°, ΔH° and ΔS° showed the spontaneous and endothermic process of the adsorption of Cr(VI) on the pyridine resin. In the competitive adsorption studies, chromate/sulfate revealed the selectivity of the pyridine adsorbents towards chromium ions. This selectivity is explained by the adsorption of the transition metal anion on the π bonds of the pyridine ring and the formation a sandwich arrangement with chromium anion and amide functional groups attached to the quaternary nitrogen atoms.