The overall biosorption rate of lead(II) onto mansonia wood sawdust has been determined. Kinetic modeling revealed that pseudo-second-order kinetics described the experimental data fully while pseudo-first kinetics followed for only 5 min. Ion-exchange constant, S, was similar to the pseudo-first-order rate constant, k(1), indicating that ion-exchange is important only in the first 5 min. Intraparticle diffusion increased with lead(II) concentration while film and pore diffusion decreased. The initial biosorption factor, R(i), showed that initial biosorption was intermediate. Addition of calcium ions reduced initial biosorption almost completely, reduced the amounts of lead(II) removed and increased ion-exchange phenomenon indicating significance of ion-exchange. Increase in temperature was found to increase intraparticle diffusion rate and reduce film and pore diffusion. Activation energy of film diffusion and pseudo-second-order kinetics were highest indicating that film diffusion-controlled the overall rate with active participation of ion-exchange from pseudo-second-order model. (C) 2010 Elsevier Ltd. All rights reserved.