Adsorption of Hexavalent Chromium from Aqueous Solution by a Chitosan/Bentonite Composite: Isotherm, Kinetics, and Thermodynamics Studies

In this work, the chitosan/bentonite composite was favorably prepared and further used for Cr(VI) removal from aqueous solutions via a batch adsorption process. The characteristics of the chitosan/bentonite composite were determined by using scanning electron microscopy, Brunner-Emmet-Teller measurement, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction, and the results reveal the evidence of the interaction between functional groups of chitosan with bentonite, which is helpful for the adsorption of Cr(VI). The adsorption performance of the chitosan/bentonite composite is better than that of chitosan or bentonite, and the effects of adsorbent dosage, shaking speed, pH, and temperature were investigated. The results indicate that the percentage removal of Cr(VI) increases with an increase in adsorbent dosage, the external diffusion resistance is maintained constant when the shaking speed exceeds 210 rpm, and the optimum pH is 3. The isotherm and kinetic experimental data of Cr(VI) adsorption onto the chitosan/bentonite composite were best-fitted by Redlich-Peterson and Elovich models, respectively. The adsorption process is an exothermic and of the multilayer variety. The desorption rates of Cr(VI) can be achieved at 60.1% with 0.1 M NaOH. The analysis FT-IR of adsorbents before and after adsorption, adsorption thermodynamics and kinetics, and desorption experiment reveal that the adsorption of Cr(VI) on the chitosan/bentonite composite is predominantly a chemical interaction. The above results suggested that the chitosan/bentonite composite can be employed as a cost-effective and environmentally friendly adsorbent for Cr(VI) removal from wastewater.