Removal of hexavalent chromium from industrial wastewater by Cereal By-Product

Abstract

The present work is aimed at exploring carbon which was prepared by calcination of Cereal By-Product (CBP) and used as adsorbent for the removal of Chromium (VI) from a surface treating industry. The effect of various parameters such as adsorbent dosage, particle size, pH, contact time and stirring speed was studied. As the adsorption process is pH dependent, it showed maximum removal efficiency of Cr(VI) in the pH range of 6–8 for an initial chromium concentration of 132 mg/L. Effect of temperature on the equilibrium constant was studied and the thermodynamic parameters like standard Gibb's free energy (Δ(7°), standard enthalpy (AH°) and standard entropy (\S°) were evaluated. The positive values of ΔΗ° change indicate that adsorption is endothermic. The positive AG° values indicated that adsorption was non spontaneous thermodynamically. Pseudo second-order model was found to explain the kinetics of Cr(VI) adsorption most effectively. Intraparticle diffusion studies show that the mechanism of adsorption is mainly dependent on diffusion. The Langmuir, Freundlich and Temkin isotherm were used to describe the adsorption equilibrium studies of CBP activated carbon at 20°C. Temkin isotherm shows better fit than Freundlich and Langmuir isotherm. It is demonstrated that the removal effectiveness reached nearly 90.37% when using optimal conditions. The result shows also that the Cereal By-Product activated carbon can be efficiently used for the treatment of wastewaters containing chromium as a low cost alternative compared to commercial activated carbon and other adsorbents reported.