In this work, the sorption capacity behavior of copper and cadmium divalent ions in single and binary systems has been investigated. Batch metal sorption experiments to obtain the kinetic and equilibrium data for the dry biomass of the Eichhornia crassipes species were performed under controlled temperature, constant shaking and pH 5. An equilibrium time of 60. min was achieved for both Cu(II) and Cd(II) ions in mono-component system as well as in binary one. It was found that the overall adsorption data were best described by the pseudo second-order kinetic model. Six adsorption isotherms have been tested to fit the mono-component equilibrium data, obtaining the best description by the Langmuir-type one. A modified extended-to-multi-component Langmuir-type isotherm model was applied to predict the binary adsorption data and its adjustable parameters were estimated by the PSO method. Finally, the results have shown that the affinity of each metal ion onto the E. crassipes surface is influenced by the presence of the other one. © 2010 Elsevier B.V.