Water hyacinth roots were employed as a biosorbent to remove Cu(II) in aqueous media. Nitrogen adsorption/desorption analysis revealed that the biosorbent was mesoporous with a relatively small surface area. Equilibrium biosorption isotherms showed that the water hyacinth roots possessed a high affinity and sorption capacity for Cu(II) with a monolayer sorption capacity of 22.7 mg g(-1) at initial pH 5.5. Kinetics study at different temperatures revealed that the sorption was a rapid and endothermic process. The activation energy for Cu(II) sorption was estimated to be 30.8 kJ mol(-1), which is typical of activated chemisorption processes. The sorption mechanism was investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, effect of pH and calcium release. These analyses suggested that the biosorption mainly involved the ion exchange of Cu(II) with cations and complex formation with functional groups on the surface of the roots. All the results showed that water hyacinth roots are an alternative low-cost biosorbent for the removal of Cu(II) from aqueous media. (c) 2009 Elsevier B.V. All rights reserved.