A mathematical model has been developed that could predict kinetic parameters for the adsorption of divalent cations (lead, copper and zinc) onto low-grade rock phosphate using experimental data. The experiments were conducted with the initial concentrations of metal ions ranging from 10 to 100 mg/L. The mathematical model is based on application of Freundlich isotherm to mass transfer across the film surrounding the adsorbent. A code in C programming is used to numerically integrate the model equation, and to obtain the best simulated values of Freundlich constants K, N, order of reaction n, and film transfer coefficient, a. It is observed that the adsorption of metal ions on rock phosphate is more sensitive to N, n, and a in comparison to K, and lead is adsorbed more favorably than copper and zinc. (c) 2007 Elsevier Inc. All rights reserved.