Adsorption of hexavalent chromium from aqueous medium onto carbonaceous adsorbents prepared from waste biomass

This paper reports the adsorption of Cr(VI) ions from aqueous solution by sulphuric acid treated sunflower waste. Two adsorbents, namely SHC and SSC, were prepared from sunflower plant head and stem waste. The adsorbents were characterized by FT-IR, SEM and EDX The surface areas of SHC and SSC were 1.17 and 1.28 m(2) g(-1), respectively. The effect of various process parameters namely pH, temperature, initial metal ion concentration, adsorbent dosage and contact time has been studied. The optimum conditions for removal of Cr (VI) were found to be pH = 2, contact time = 2 h, adsorbent dosage = 4.0 g/L, concentration = 250 mg/L, temperature = 25 +/- 1 degrees C, rpm = 180. The percent removal at these optimum conditions was found to be 75.7% and 85.4% for SHC and SSC respectively. The Freundlich, Langmuir and D-R models were applied for mathematical description of adsorption equilibrium. Adsorption data were well described by the Langmuir isotherm with maximum adsorption capacities of 53.76 mg/g and 56.49 mg/g for SHC and SSC, respectively. Overall, the experimental results suggest that SHC and SSC could be used as low cost alternative adsorbents for the treatment of Cr(VI) containing wastewater. A comparison of different kinetic models showed that our data fitted well to the pseudo-second order model. (C) 2009 Elsevier Ltd. All rights reserved.