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Numerical simulation can be a powerful tool in the research and development of any new electrostatic process. The aim of the present work is to introduce a simple mathematical model for simulating the outcome of a recently patented tribo-aero-electrostatic separation process for binary mixtures of granular materials. The process is characterized by the fact that the charging of the granules is produced in a fluidized bed device, in the presence of an electric field. The mathematical model assumed that the probability of a granule to be separated can be expressed as a function of the number of impacts with granules belonging to the other class of materials. When this probability was given by a normal distribution law, the results of the simulations differed significantly from those of an experiment conducted with a granular mixture of polyamide and polycarbonate particles, in a laboratory tribo-aero-electrostatic separator. In order to improve the predictive capability of the simulations, a polynomial function derived from the regression of the experimental data was employed for expressing the same probability. Thus, it was possible to calculate the evolution in time of the mass of granules separated at the electrodes for various compositions of the granular mixture. The computed results were in good agreement with the experiments.