Author Proof A Kinetic, Equilibrium and Thermodynamic Studies on Removal of Cr(VI) by Activated Carbon Prepared from Ricinus communis Seed Shell P. Thamilarasu 1 and K. Karunakaran 2 * 1. Department of Chemistry, AMS Engineering College, Namakkal 637 013, Tamil Nadu, India 2. Department of Chemistry, Sona College of Technology, Salem 636 005, Tamil Nadu, India A study on the removal of hexavalent chromium ions from aqueous solution by using activated carbon prepared from Ricinus communis has been done. In this process, it was carbonised and activated by treating with concentrated sulphuric acid followed by heating for 5 h at 500 ◦ C. Batch adsorption experiments are also carried out as a function of pH, contact time, initial concentration of the adsorbate, adsorbent dosage and temperature. The experimental data are fitted well to the Freundlich adsorption isotherm. Thermodynamic parameters such as H ◦ , S ◦ and G ◦ are calculated, which indicated that the adsorption is spontaneous and endothermic in nature. Adsorbent used in this study is characterised by FT-IR and SEM before and after the adsorption of Cr(VI). Keywords: adsorption, isotherm, activated carbon, chromium and seed shell INTRODUCTION T he pollution caused because of heavy metals has received widespread attention in the recent years (Bishnoi et al., 2004) due to the toxicological importance in the ecosys- tem, agriculture and human health. It leads to the development of alternative technologies for the removal of these pollutants from aqueous effluents. The use of low-cost and waste biomaterials as adsorbents of dissolved metal ions has been shown to provide economic solutions to this global problem (Park et al., 2005). In this context, our adsorbent (RCC: Ricinus communis seed shell) could be used as an effective and environment-friendly adsorbent for the removal of Cr(VI) containing water and wastewater. Chromium is a highly toxic pollutant generated from many industrial processes such as leather tanning processes, electro- plating and manufacturing of dye, paint and paper. Chromium exists in the aquatic environment mainly in two states; trivalent chromium and hexavalent chromium. Hexavalent chromium is primarily present in the form of chromate and dichromate ions (Khezami and Capart, 2005). The USEPA has set the permissi- ble level for chromium in drinking water at 0.05 mg/L. These standards are based on the total concentration of the trivalent and hexavalent forms of dissolved chromium. Chromium has the potential to cause the following health effects from long-term exposure to above the minimum cleanliness level (MCL); damage to liver, kidney circulatory Q1 []and nerve tissues (USEPA, 1995). Conventional methods for removal of dissolved heavy metal ions included the chemical precipitation, chemical oxidation and reduction, ion exchange, filtration, electrochemical treatment and evaporative recovery. However, these high-technology pro- cesses have significant disadvantages, including incomplete metal removal, requirements for expensive equipment and monitoring systems, high-cost reagents, energy requirements, generation of toxic sludge and other waste products that require disposal (Aksu et al., 2002). Adsorption on activated carbon has been found to be an effec- tive process for Cr(VI) removal, but it is too expensive. Natural materials are available in large quantities; certain waste products ∗ Author to whom correspondence may be addressed. E-mail address: drkk@sonatech.ac.in Can. J. Chem. Eng. 9999:1–10, 2012 © 2011 Canadian Society for Chemical Engineering DOI 10.1002/cjce.20675 Published online in Wiley Online Library (wileyonlinelibrary.com). | VOLUME 9999, 2012 | | THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING | 1 |