A variable order kinetic (VOK) model derived from the Langmuir equation was applied to specify the kinetics of the fluoride removal reaction for electrocoagulation (EC). Synthetic solutions were employed to elucidate the effects of the initial fluoride concentration, the applied current and the initial acidity on the simulation results of the model. The proposed model successfully describes the fluoride removal reaction, except in a system in which the initial concentration of the acid is less than the initial fluoride concentration. The violent change of pH companying with the appearance of equivalence point in the titration curves should be the main reason the VOK model fails to simulate the defluoridation in the systems with an initial acidity higher than initial fluoride concentration. (c) 2006 Elsevier B.V. All rights reserved.