Available online at www.sciencedirect.com Journal of Hazardous Materials 157 (2008) 277–285 Biosorption of Cu(II) from aqueous solutions by mimosa tannin gel ˙ I. Ayhan S ¸ engil a,∗ , Mahmut ¨ Ozacar b a Department of Environmental Engineering, Engineering Faculty, Sakarya University, 54100 Sakarya, Turkey b Department of Chemistry, Science & Arts Faculty, Sakarya University, 54100 Sakarya, Turkey Received 6 October 2007; received in revised form 25 December 2007; accepted 28 December 2007 Available online 15 January 2008 Abstract The biosorption of Cu(II) from aqueous solutions by mimosa tannin resin (MTR) was investigated as a function of particle size, initial pH, contact time and initial metal ion concentration. The aim of this study was to understand the mechanisms that govern copper removal and find a suitable equilibrium isotherm and kinetic model for the copper removal in a batch reactor. The experimental isotherm data were analysed using the Langmuir, Freundlich and Temkin equations. The equilibrium data fit well in the Langmiur isotherm. The experimental data were analysed using four sorption kinetic models – the pseudo-first- and second-order equations, and the Elovich and the intraparticle diffusion equation – to determine the best fit equation for the biosorption of copper ions onto mimosa tannin resin. Results show that the pseudo-second-order equation provides the best correlation for the biosorption process, whereas the Elovich equation also fits the experimental data well. Thermodynamic parameters such as the entropy change, enthalpy change and Gibb’s free energy change were found out to be 153.0 J mol -1 K -1 , 42.09 kJ mol -1 and -2.47 kJ mol -1 , respectively. © 2008 Elsevier B.V. All rights reserved. Keywords: Mimosa tannin gel; Copper(II); Biosorption 1. Introduction Copper is a very common substance that occurs naturally in the environment and spreads through the environment through natural phenomena. The production of copper has lifted over the last decades and due to this copper quantities in the envi- ronment have expanded. Copper is present in the wastewater of several industries, such as metal cleaning and plating baths, refineries, paper and pulp, fertilizer, and wood preservatives and it is highly toxic [1]. Most copper compounds will bound to nat- ural organic materials and soil particles which will settle down to sediments. Soluble copper compounds form the largest threat to human health. Copper and its compounds are ubiquitous in the environment and thus copper is found frequently in surface water. Organization (WHO) recommended a maximum accept- able concentration of Cu 2+ in drinking water of 1.5 mg L -1 [2]. Copper does not break down in the environment and because of that it can accumulate in plants and animals when it is found in soils. On copper-rich soils only a limited number of plants ∗ Corresponding author. Fax: +90 264 2955601. E-mail address: asengil@sakarya.edu.tr ( ˙ I.A. S ¸ engil). has a chance of survival. The excessive intake of copper by man leads to severe mucosal irritation, widespread capillary damage, hepatic and renal damage, central nervous problems followed by depression, gastrointestinal irritation, and possible necrotic changes in the liver and kidney [3]. The main techniques that have been used on copper con- tent reduction from industrial waste are chemical precipitation, ion exchange, membrane filtration, electrolytic methods, reverse osmosis and solvent extraction. These conventional techniques can reduce metal ions, but they do not appear to be highly effective due to the limitations in the pH range as well as the high material and operational costs. Among these various treat- ment techniques, activated carbon adsorption is one of the most commonly used due to its high efficiency and easy operation [4,5]. In recent years, considerable attention has been focused on the removal of copper from aqueous solution using adsorbents derived from low-cost materials [6–8]. Tannins, natural biomass containing multiple adjacent hydroxyl groups and exhibiting specific affinity to metal ions, can probably be used as alternative, effective and efficient adsor- bents for the recovery of metal ions. During the last years, the interest on biomaterials and specifically in tannins was growing. 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2007.12.115