Cr(VI) adsorption by montmorillonite nanocomposites

Abstract

Various montmorillonite (Mt) nanocomposite adsorbents were prepared with Al13 cations, dodecyl trimethyl ammonium chloride (DTAC) or dodecyl amine (DA) and characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and BET surface area and pore size analyses. The adsorption of hexavalent chromium, Cr(VI) onto various Mt nanocomposites as a function of adsorbent dosage, initial Cr(VI) concentration, contact time and solution pH was investigated. The results showed that the obtained nanocomposites had large basal spacing and good porous structure, and the specific surface areas followed the order: OH-Al-Mt>DA-Al-Mt>DTAC-Al-Mt>Na+-Mt>DTAC-Mt>DA-Mt. The removal efficiency of Cr(VI) ions increased with increasing the adsorbent dosage and contact time, but decreased with increasing initial Cr(VI) concentration, as expected. The adsorption of Cr(VI) was highly pH-dependent and the maximum removal efficiency of Cr(VI) was found in the acid environment. The adsorption equilibrium time was 2h and the adsorption kinetic data of Cr(VI) on various adsorbents were well described by the pseudo-second-order kinetics model, which indicated that the adsorption reaction of Cr(VI) ions with the adsorbents was mainly due to chemical adsorption. Both the Langmuir model and Freundlich model fitted the equilibrium data well, which suggested that the Cr(VI) adsorption onto various adsorbents was both as monolayer and on heterogeneous surface conditions. The adsorption results indicated that among all the adsorbents used in this experiment, the dodecyl amine and Al13 cations composited with Mt (DA-Al-Mt) was the most effective for removing Cr(VI) from wastewater.