Removal of hexavalent chromium by new quaternized crosslinked poly(4-vinylpyridines)

New quaternized crosslinked poly(4-vinylpyridines) prepared by nucleophilic substitution reactions of 4-vinylpyridine: divinylbenzene copolymers of gel and porous structure with halogenated compounds such as benzyl chloride and 2-chloracetone, were used to remove Cr(VI) from the aqueous solution. Batch adsorption studies were carried out to determine the effect of the initial concentration of Cr(VI), pH, temperature and the presence of sulfate anions. The process was found to be pH and concentration dependent. The adsorption capacities increase with the increase of the initial concentration of Cr(VI) and both resins exhibited the degrees of usage of the exchange capacities higher than 90% and good efficiency in the chromium removal. 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. The thermodynamic parameters (free energy change ΔG, enthalpy change ΔS and entropy change ΔH) for the adsorption have been evaluated and therefore, it was showed the spontaneous and endothermic process of the adsorption of Cr(VI) on the pyridine resins. In the competitive adsorption studies, chromate/sulfate revealed the selectivity of the pyridine adsorbents towards chromium ions. At acidic pH the synthesized pyridine resins offer much greater chromate removal capacities compared to alkaline pH. In the competitive adsorption studies, chromate/sulfate revealed the selectivity of the pyridine adsorbents towards chromium ions due to the formation a sandwich arrangement with the chromium anion and functional groups attached to the quaternary nitrogen atom.