Removal of hexavalent chromium from aqueous solution using low-cost activated carbons derived from agricultural waste materials and activated carbon fabric cloth

This paper examines an efficient adsorption process for the treatment of tannery wastewater. A variety of low-cost activated carbons were developed from agricultural waste materials, characterized, and utilized for the removal of hexavalent chromium from wastewater. Systematic studies on chromium(VI) adsorption equilibrium and kinetics by low-cost activated carbons as well as commercially available activated carbon fabric cloth were carried out at different temperatures, particle size, pH, and adsorbent doses. Both Langmuir and Freundlich models fitted the adsorption data quite reasonably. The results indicate that the Langmuir adsorption isotherm model fits the data better than the Freundlich adsorption isotherm model. Further, the data are better correlated with the nonlinear form than the linear one. The kinetic studies were conducted to delineate the effects of temperature, initial adsorbate concentration, adsorbent particle size, and solid-to-liquid ratio. The adsorption of Cr(VI) follows pseudo-second-order rate kinetics. On the basis of these studies, various parameters such as the effective diffusion coefficient, activation energy, and activation entropy were evaluated to establish the mechanisms. The adsorption capacities of the tested adsorbents was found to be comparable to those of the available adsorbents/activated carbons.