Introduction 1) Heavy metal contamination of various water resources is of great concern because of their toxic effects to hu- man beings and other animals and plants in the environment. The presence of lead in drinking water is known to cause various serious health problems, leading to death in extreme cases. Severe exposure to lead has been associated with sterility, abortion, stillbirths, and neo-natal deaths [1,2]. Lead could exist either in organic or inorganic forms of Pb(II); it is known as a metabolic poison [3]. The several technologies for Pb(II) removal include ion exchange, chemical precipitation with lime, and electro- chemical treatment. However, these technologies are often inefficient and/or are very expensive when used for the reduction of Pb(II) ions to very low concentrations To whom all correspondence should be addressed. (e-mail: wookjin@mju.ac.kr) [4-6]. The adsorption process plays an important role in removing heavy metals, such as lead, from wastewater. There has been much research into the development of low-cost alternatives to activated carbon; these materials include fly ash, metal oxides, zeolites, peats, chitosans, and activated sludge [7-12]. New methods are required to reduce heavy metal concentrations to environmentally acceptable levels at affordable cost. The adsorption processes are generally among the most effective techniques for the removal of highly toxic metals. Adsorbents that have strong affinities and high loading capacities for targeted metal ions have been developed by modifications of various surfaces with metal-complexing groups [13-15]. Chitin, a natural polymer of acetylated and non- acety- lated glucosamine, has been widely postulated as being a cell wall component responsible for metal adsorption [16-19]. To increase the uptake capacity of chitin, the hydroxyl groups of the adsorbent, which has low affinity Adsorption of Lead(II) Ions using Surface-Modified Chitins Seoung-Hyun Kim, Hoon Song, Grace Masbate Nisola, Juhyeon Ahn, Melvin Maaliw Galera, Chang hee Lee , and Wook-Jin Chung Department of Environmental Engineering and Biotechnology, Myongji University, Yongin 449-728, Korea Korea Environment Institute, Seoul 122-706, Korea Received December 15, 2005; Accepted March 30, 2006 Abstract: To establish the feasibility of the removal of lead using chitin, adsorption characteristics were investigated at various temperatures and concentrations. The adsorption characteristics of chitin were analyzed by determining its adsorption equilibrium, kinetics, and thermodynamic properties. The data gathered favor the Langmuir over the Freundlich model. The adsorption capacity of the surface-modified natural chitin for Pb(II) removal increased significantly when the adsorbent was treated using the xanthation method. The homoge- neous surface diffusion model described the adsorption kinetic data well and can be used to predict the chitin performances; therefore, it could be helpful for design considerations. Under the steady-state reaction conditions, the change in Gibbs free energy ( G Δ 0 ) ranged from -19.03 to -21.50 kJ/mol, and the enthalpy (ΔH 0 ) and entropy ( S Δ 0 ) changes were 16.54 kJ/mol and 0.124 kJ/mol/K, respectively; i.e., a higher temperature favors a spontaneous Pb(II) adsorption by chitin when using the xanthation method. Thermodynamic calculations indicate that the adsorption of lead on the adsorbents was spontaneous and endothermic. Application of the chitin modified with the xanthation method to the removal of Pb(II) metals from wastewater is expected to be economical and effective. Keywords: adsorption, lead (II) ion, adsorbent, chitin, xanthation, phosphorylation