The kinetics, equilibrium and thermodynamics of the biosorption of Cu(II), Cd(II) and Pb(II) onto Acacia leucocephala bark powder from aqueous solution were investigated at different experimental conditions. The biosorption characteristics of Cu(II), Cd(II) and Pb(II) ions on the bark powder was investigated with respect to well-established effective parameters including the effect of pH, initial metal ion concentration, biosorbent dosage, contact time and temperature. Optimum adsorption of Cu(II), Cd(II) and Pb(II) took place at pH values of 6.0, 5.0 and 4.0, respectively. Further, the biosorbent was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The Langmuir and Freundlich equilibrium adsorption models were studied and observed to fit well. The Langmuir model gives a better fit than the Freundlich model. The kinetic studies indicated that the biosorption process of the metal ions followed well pseudo-second-order model. The thermodynamic parameters Gibbs free energy (Delta G degrees), enthalpy (Delta H degrees), and entropy (Delta S degrees) changes were also calculated, and the values indicated that the biosorption process was exothermic and spontaneous. It was concluded that A. leucocephala bark powder can be used as an effective, low cost, and environmentally friendly biosorbent for the removal of Cu(II), Cd(II) and Pb(II) ions from aqueous solution. (C) 2009 Elsevier B.V. All rights reserved.