Both the effect of particle size and initial concentration on the adsorption of lead by sawdust of two timber species were investigated using batch experimental equilibrium and kinetic studies. A 100% lead removal efficiency was recorded for the optimum particle size of 1.18 mm for Pycnanthus angolensis and 0.85 mm for Khaya ivorensis at an initial lead concentration of 10 mg/L. Freundlich isotherm (0.83 ≤ R 2 ≤ 0.96 for Khaya ivorensis and 0.94 ≤ R 2 ≤ 1.0 for Pycnanthus angolensis) performed better than Langmuir and Temkin isotherms. The Dubinin-Radushkevich isotherm was used to ascertain the sorption mechanism. Mean sorption energy (12.48 kJ/mol for Pycnanthus angolensis and 13.42 kJ/mol for Khaya ivorensis) indicated that adsorption was by ion exchange. The pseudo-first order kinetic model (0.96 ≤ R 2 ≤ 1.0 for Khaya ivorensis and 0.90 ≤ R 2 ≤ 1.0 Pycnanthus angolensis) performed better than others with respect to R 2 values, while the intraparticle diffusion model performed better than the other kinetic models with respect to absolute mean error (AME).

Experiments investigating lead adsorption by activated sawdust of different particle sizes of two timber species were conducted. The experimental data were fitted to isothermal and kinetic models. The optimum particle size was 0.85 mm for Khaya ivorensis and 1.18 mm for Pycanthus angolensis. The adsorption of lead by Khaya ivorensis and Pycanthus angolensis conformed to the Langmuir isotherm (0.83 ≤ R2 ≤ 0.96 and 0.86 ≤ R2 ≤ 0.98, respectively) and Freundlich isotherm (0.69 ≤ R2 ≤ 0.97 and 0.94 ≤ R2 ≤ 1.0, respectively). The adsorption process for the two species of timber was controlled by solute transport in the bulk liquid and intraparticle diffusion which was confirmed by good agreement of experimental data with pseudo-first-order kinetics (0.96 ≤ R2 ≤ 1.0 for Khaya ivorensis and 0.9 ≤ R2 ≤ 1.0 for Pycanthus angolensis) and the intraparticle diffusion model (0.9 ≤ R2 ≤ 0.99 for Khaya ivorensis and 0.84 ≤ R2 ≤ 0.97 for Pycanthus angolensis). A new kinetic model was developed with R2 of 0.93 ≤ R2 ≤ 0.99 for Khaya ivorensis and 0.88 ≤ R2 ≤ 1.0 for Pycanthus angolensis.