Removal of Cu(II), Zn(II), Cd(II) and Pb(II) complexes with IDS (iminodisuccinic acid) and EDDS (ethylenediaminedisuccinic acid) from the synthetic aqueous solutions through adsorption on chitosan (CS) under batch equilibrium experimental conditions at different phase contact time (1-120 min), pH values (1-12), temperatures (20-50 degrees C) has been investigated. The effect of CS modification by preparing the bead crosslinked by glutaraldehyde and epichlorhydrin was also tested. The appropriate model of adsorption was proposed for better understanding of the mechanism of adsorption on CS. For this aim the Langmiur, Freundlich, Temkin and Dubinin-Radushkevich (D-R) adsorption models were used. The parameters in the adopted adsorption isotherm models were discussed in detail. The study of equilibrium isotherm shows that the best model for analysis of experimental data is the Langmuir model, which is in agreement with high values of correlation coefficients (R-2). The results also showed that with the increasing pH and temperature, the adsorption ability of CS decreases. The maximum conditions for adsorption of Cu(II) in the presence of IDS were determined as CS dose 0.2 g. pH = 2-3, t 1 h and T 20 degrees C. The thermodynamic constants of adsorption such as Delta H degrees and Delta S degrees were also calculated. The negative value of the Gibbs free energy Delta G degrees demonstrates the spontaneous nature of the studied ions adsorption on CS in the presence of IDS. The obtained results showed that the pseudo second-order model was more suitable to describe the sorption kinetics on CS. (C) 2011 Elsevier B.V. All rights reserved.