Modeling of Adsorption of Chromium(VI) on Activated Carbons Derived from Corn (Zea mays) Cob

Chromium in its trivalent and hexavalent form in the environment is toxic above certain concentrations. Cr(VI), which is more toxic than Cr(III), was chosen in this work and removed from aqueous solutions of potassium dichromate by adsorption onto physically and chemically activated carbons derived from Zea mays( corn or maize) cob, an agricultural waste product. Adsorption studies were done at the optimum pH of 2 and at the room temperature of 30 degrees C. The aim of the work was to study the adsorption equilibrium and kinetic data with various isotherm and kinetic models. The best fit to the equilibrium data was provided by the 3-parameter Fritz-Schluender model followed by the 2-parameter Langmuir model. The adsorption isotherms were favorable and the adsorption on chemically activated carbons improved as the impregnation ratio was increased. Kinetic modeling showed that the fractional power model provided the best fit followed by the second-order Ritchie's equation. The adsorption of Cr(VI) on the activated carbons was film-diffusion controlled.