Adsorption of Cr(VI) onto a low-cost ceramsite: Preparation, kinetics, and thermodynamics

A novel composite ceramsite derived from bamboo powders and bentonite was developed as adsorbents for waste water treatment. The microstructure, morphology, and thermal properties of ceramsite were characterized by X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray fluorescence, and differential thermal analysis. The effect of compositions, sintering temperatures, sintering time, pH, and adsorption time on the adsorption performance of the ceramsites were studied. The results revealed that the maximum Cr(VI) removal rate of 99% can be obtained in the ceramsite with weight ratio bamboo to bentonite of 6:4, the annealing temperature of 1000 degrees C, the solution pH 1 and contact time of 12 h. The adsorption kinetics and adsorption isotherm analysis revealed that the adsorption process best followed pseudo-second-order reaction kinetics and the Freundlich adsorption isotherm. The adsorption mechanism was discussed and both chemisorption and physiosorption were proposed as adsorption mechanism of Cr(VI). Moreover, the thermodynamic parameters, including changes in Gibbs free energy, entropy, and enthalpy, were studied in detail. The bamboo powder/bentonite composite ceramsite developed in this work is a promising candidate as an effective and economical adsorbent for Cr(VI) ions removal.