Polymeric Fe/Zr pillared montmorillonite for the removal of Cr(VI) from aqueous solutions

Four kinds of pillared montmorillonites were prepared by intercalating poly-hydroxyl iron, poly-hydroxyl iron/zirconium with different Fe/Zr molar ratios (4/1, 1/1) and poly-hydroxyl zirconium into the interlayer space of sodium-saturated montmorillonite (Na-Mt) via ion-exchange, termed Fe-Mt, Fe/Zr-4:1-Mt, Fear) 1-Mt and Zr-Mt, respectively. The obtained materials were characterized by X-ray fluorescence (XRF) spectra, X-ray diffraction (XRD) spectra, Fourier transform infrared (FTIR) spectra, point of zero charge measurement and BET analysis. Batch experiments were conducted to investigate the adsorption behavior of Cr(VI) on selected samples. The results showed that the equilibrium uptake of Cr(VI) was highly pH-dependent with an optimal pH range of 3.0-6.0. The kinetics of Cr(VI) adsorption could be described well by the Pseudo-second-order model. The Langmuir adsorption isotherm provided the best correlation of the equilibrium data, and the estimated maximum equilibrium uptake of Cr(VI) of Fe/Zr-4:1-Mt was 22.35 mg/g at pH 3.0, 25 degrees C, higher than those of other three samples. Also, the thermodynamic parameters demonstrated that the process of Cr(VI) adsorption onto pillared montmorillonites was spontaneous and exothermic in nature. The presence of phosphate, sulphate and tartrate inhibited markedly the adsorption of Cr(VI), whereas nitrate, chlorate and acetate exhibited no significant effect on Cr(VI) adsorption. The analyses combining characterization results with adsorption data revealed that the removal mechanisms of Cr(VI) by these pillared montmorillonites mainly involved electrostatic interaction and ion-exchange. Overall, the regeneration of Fe/Zr-Mt could be achieved using NaOH solution, enabling a promising application for removing Cr(VI) from aqueous solution. (C) 2010 Elsevier B.V. All rights reserved.