INTRODUCTION Toxic metals are released into the environment in a number of ways. Coal combustion, sewage wastewaters, automobile emissions, battery industry, mining activities and the utilization of fossil fuels are just a few examples 1 . Excess heavy metals are introduced into aquatic ecosystems as by-products of industrial processes and acid-mine drainage residues. They are highly toxic as ions or in compound forms. They are soluble in water and may be rapidly absorbed into living organisms 2 . The release of heavy metals into the environment by industrial activities is a serious environmental problem because they tend to remain indefinitely, circulating and eventually accumulating throughout the food chain. Due to their extreme toxicity, metal ions are nowadays among the most important pollutants both in surface water and in ground water. Since levels of metals in the environment have increased because of industrial pollu- tion 3,4 , the elimination of such ions from water is essential to protect public health. Heavy metals, such as lead, copper, zinc, chromium, cadmium and nickel are among the most toxic pollutants present in marine, ground and industrial wastewaters. In addition to their toxicity effects even at low concentrations, heavy metals can accumulate throughout the food chain, which leads to serious ecological and health hazards as a result of their solubility and mobility 5 . It can cause mental retardation and Removal of Hexavalent Chromium from Aqueous Solution using Vigna Radiata Husk (Green Gram) K. SARAVANAKUMAR 1 and A. KUMAR 2,* 1 Department of Chemical Engineering, St. Peter's Engineering College, Avadi, Chennai-600 054, India 2 C. Abdul Hakeem College of Engineering & Technology, Melvisharam-632 509, India *Corresponding author: E-mail: ayanakumar@yahoo.com Asian Journal of Chemistry; Vol. 23, No. 6 (2011), 2635-2638 (Received: 13 August 2010; Accepted: 16 February 2011) AJC-9628 In this study, Vigna radiata Husk (VRH) activated carbon was prepared and used to remove Cr(VI) from aqueous solution. The influences of initial Cr(VI) ion concentration (250-1000 mg/L), pH (1-11), adsorbent dose (0.25-2.5 g), contact time (15-150 min) and particle size (0.15-0.85 mm) had been reported. A comparison of isotherm models applied to the adsorption of Cr(VI) ions on the adsorbent was evaluated for Langmuir, Freundlich and Redlich Peterson isotherms. Adsorption of Cr(VI) was highly pH dependent and the results indicate that the optimum pH for the removal was found to be 2. The obtained results showed that the adsorption of Cr(VI) by Vigna radiata Husk follows Redlich-Peterson isotherm equation with a correlation coefficient equal to 0.99. In addition, the kinetics of the adsorption process follows the pseudo second-order kinetic model. The results indicate that Vigna radiata Husk can be employed as a low cost alternative to commercial adsorbents in the removal of Cr(VI) from water and wastewater. Key Words: Vigna Radiata husk, Adsorption, Heavy metal removal, Isotherms, Kinetics. semi permanent brain damage in young children 6 . Chromium(VI) which has widespread use in leather tanning, paint and pigment manufacturing, chrome plating, wood preservation, fertilizers, textile dyeing, electroplating, cement, mining and photography industries 7 , is a major metal pollutant of the environment. The permissible limit of chromium(VI) in drinking water is 0.05 mg/L 8 . Among them, paint and pigment, chrome plating, textile and match industries discharge Cr(VI), which is a powerful epithelial irritant and a human carcinogen 9 . Additionally, Cr(VI) is toxic to many plants, aquatic animals and bacteria 10 . The United Nations Food and Agriculture Organization recommended maximum level of chromium for irrigation waters is 0.1 mg/L 11 . Wastewaters generated by these industries usually contain significant quantities of salts such as sodium chloride, so the effects of these salts on the removal of chromium(VI) should be investigated 12,13 . The removal of toxic metal ions and recovery of valuable ions from mine wastewaters, soils and waters have been important in economic and environmental problems 14-17 . Different conventional processes (precipitation, ion exchange, electrochemical processes and/or membrane processes) are usually applied to the treatment of industrial effluents but the application of such processes is often limited because of technical or economic constraints 18 . Among the various water-