Batch experiments were carried out to investigate the kinetics of adsorption of lead ions by steel slag on the basis of the external diffusion, intra-particle diffusion and adsorption reaction model (pseudo-first-order, pseudo-second-order). The results showed that the controlling step for the adsorption kinetics changed with the varying experimental parameters. When the particle size of steel slag was larger than 120 mesh, intra-particle diffusion of Pb2+ was the controlling step, and when the initial concentration of Pb2+ was less than 150 mg L-1 or the shaking rate was lower than 150 rpm, external diffusion of Pb2+ was promoted. Contrary to the former experimental conditions the adsorption reaction was the controlling step, and the adsorption followed second-order kinetics, with an adsorption rate constant of 13.26 g mg(-1) min(-1). The adsorption isotherm of Pb2+ with steel slag followed the Langmuir model, with a correlation coefficient of 0.99. (C) 2009 Elsevier B.V. All rights reserved.