Adsorption of hexavalent chromium from aqueous solution on raw and modified activated carbon

Hexavalent chromium [Cr(VI)] is toxic and readily adsorbed by some adsorbents; therefore, its removal from wastewater is extremely important. Batch adsorption of Cr(VI) from aqueous solution using raw and acid-modified activated carbon was investigated in this study. The Cr(VI) sorption was found to be dependent on pH, contact time, initial concentration of solution, adsorbent dose, and temperature. The maximum efficiencies of Cr(VI) removal were 97.67 and 99.87% for activated carbon (AC0) and modified activated carbon (AC1), respectively. The maximum adsorption capacity was found to be 4.75 and 5.95 mg/g for AC0 and AC1, respectively. Thermodynamic parameters indicate that the adsorption process was endothermic and spontaneous in nature. Freundlich adsorption isotherm model was fitted well the equilibrium data for both adsorbents. The Cr(VI) uptake by AC0 and AC1 followed pseudo first-order and second-order kinetics, but was best described by the pseudo second-order rate model. The results also showed that both film diffusion and intraparticle diffusion were concurrently operating, but that intraparticle diffusion controlled the adsorption mechanism.