Removal of Cr(VI) from aqueous solution by pyrolytic charcoals

Bio-chars produced by the pyrolysis of walnut shells at 450 °C (BC450)and theco-pyrolysis of walnut shells and 20 wt% tar sand (BCTS20)at the same temperature, were investigated as potential adsorbents for the removal of Cr(VI) ions from aqueous solutions using batch experiments. The BCTS20 has more abundant surface functional groups than BC450. The Cr(VI) removal percentages under optimal conditions were 80.47 and 95.69%for BC450 and BCTS20, respectively. Langmuir, Freundlich and D-R models were used to fit the adsorption isotherms and the Langmuir model described the adsorption isotherms best. The adsorption of Cr(VI)was by a chemical process dominated by ion-exchange, electrostatic attraction and chelation. The maximum Langmuir adsorption capacities were 36.55 and 49.76 mg per g of BC450 and BCTS20, respectively. The maximum Langmuir adsorption capacity of BCTS20 is comparable to that of some reported commercial activated carbons.