Adsorption Studies on the Removal of Hexavalent Chromium-Contaminated Wastewater Using Activated Carbon and Bentonite

The pollution of heavy metal ions in the environment is a critical problem because of their toxicity and other adverse effects on the receiving waters and/or soils.They must be removed from wastewater before discharging them into water bodies.Water pollution by chromium is due to both, natural sources and man made activities.Chromium is found in rocks, animals, plants, soils and in volcanic dusts and gases.Various industrial processes such as steel production, electroplating, leather tanning, nuclear power plants, textile industries, wood preservation, anodizing of aluminum, water-cooling and chromate preparation 1 .Discharge chromium containing wastes with varied concentration between 5 and 220 mg/L into the environment, which contaminates soil and water 2,3 .The world mine production of chromite was estimated at a gross mass of 13 × 10 6 metric tons in 2002 4 .In nature chromium exists in two most stable oxidation states, i.e., trivalent and hexavalent forms in aqueous systems.Although, at trace level, the trivalent form is considered as an essential nutrient 5,6 , hexavalent form of chromium is toxic, carcinogenic and mutagenic in nature [7][8][9][10][11][12] .The hexavalent form is about 500 times more toxic than trivalent form 13 .Furthermore, Cr(VI) is highly mobile in soil and aquatic system and also is a strong oxidant capable of being adsorbed by skin 14 .Considering its toxicity and