Journal of Colloid and Interface Science 292 (2005) 354–362 www.elsevier.com/locate/jcis Kinetic and isotherm studies of Cu(II) adsorption onto H 3 PO 4 -activated rubber wood sawdust M. Helen Kalavathy, T. Karthikeyan, S. Rajgopal, Lima Rose Miranda ∗ Department of Chemical Engineering, Alagappa College of Technology, Anna University, Chennai 600 025, India Received 2 March 2005; accepted 26 May 2005 Available online 22 July 2005 Abstract Adsorption of Cu(II) from aqueous solution onto H 3 PO 4 -activated carbon using rubber wood sawdust (RSAC) was investigated in a batch system. Kinetic and isotherm studies were carried out by considering the effects of various parameters, such as initial concentration, contact time, pH, and temperature. The optimal pH value for Cu(II) adsorption onto RSAC was found to be 6.0. Thermodynamic parameters such as standard Gibbs free energy (G 0 ), standard enthalpy (H 0 ), and standard entropy (S 0 ) were evaluated by applying the Van’t Hoff equation. The thermodynamics of Cu(II) adsorption onto RSAC indicates its spontaneous and exothermic nature. Langmuir, Freundlich, and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The Langmuir isotherm fits the experimental data significantly better than the other isotherms. Adsorption kinetics data were tested using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The initial sorption rate, pseudo-first-order, pseudo-second-order, and intraparticle diffusion rate constants for different initial concentrations were evaluated and discussed. Adsorption mechanism studies revealed that the process was complex and followed both surface adsorption and particle diffusion. The rate-controlling parameter and effective diffusion coefficient were determined using the Reichenberg plot. It was found that the adsorption occurs through film diffusion at low concentrations and at higher concentration the particle diffusion becomes the rate-determining step.  2005 Elsevier Inc. All rights reserved. Keywords: Adsorption; Rubber wood sawdust; Activated carbon; Copper; Isotherms; Diffusion; Kinetics 1. Introduction Copper is present in the wastewater of several indus- tries, such as metal cleaning and plating baths, refineries, paper and pulp, fertilizer, and wood preservatives and it is highly toxic [1,2]. The excessive intake of copper by man leads to severe mucosal irritation, widespread capillary damage, hepatic and renal damage, central nervous prob- lems followed by depression, gastrointestinal irritation, and possible necrotic changes in the liver and kidney [2]. The World Health Organization (WHO) recommended a max- imum acceptable concentration of Cu(II) in drinking wa- * Corresponding author. Fax: +91 44 2235 5373. E-mail address: limarmiranda@yahoo.co.in (L.R. Miranda). ter of 1.5 mg l −1 [3]. It is essential that potable waters be given some treatment to remove copper before domestic sup- ply. In wastewater treatment technology, various techniques have been used for copper ion removal. Among these, physicochemical and biosorption methods have been suc- cessfully applied. An effective method for copper ion re- moval is chemical precipitation. However, disposal of large quantities of sludge is found to be difficult [4]. Conven- tional methods that have been used include ion exchange, reverse osmosis, electrochemical treatment, evaporative re- covery, and adsorption. These conventional techniques can reduce metal ions, but they do not appear to be highly ef- fective due to the limitations in the pH range as well as the high material and operational costs [5]. Among these vari- ous treatment techniques, activated carbon adsorption is one 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.05.087