Chromium removal using modified poly(4-vinylpyridinium) bentonite salts

A new composite material able to remove hexavalent chromium [Cr(VI)] ions from aqueous solutions was obtained by reacting poly(4-vinylpyridine) (P4VP) with bentonite clay [Bf]. Two composite samples, Bf0.06 and Bf0.3, were prepared by varying initial amounts of P4VP. Thermogravimetric analysis revealed good stability of the new materials at high temperatures. FTIR technique clearly showed that P4VP was adsorbed on bentonite. The good efficiency in removing chromium ions from acidic solutions was demonstrated by adsorption kinetics. Freundlich and Langmuir isotherm models were used to determine adsorption capacity of Bf, Bf0.06 and Bf0.3 composites at 25°C and at pH = 1. The specific role of P4VP salt in the new composite materials was evaluated by comparing the kinetics of the original bentonite and polymer-modified composites. The obtained results showed clearly that the pyridinium positive charges on the polymer were efficient in hexavalent chromium removal from aqueous solutions. The thermodynamics of the rate processes showed the adsorption of chromium ions to be endothermic, accompanied by decreases in Gibbs free energy. The results showed the potentiality of these composites as an adsorbent for chromium ions from aqueous solutions.