The efficiency of the electrostatic separation process depends on the accurate control of particle trajectories. The aim of this article is to point out the role of the following factors that might affect the behavior of the insulating particles in roll-type corona-electrostatic separators: i) electrode system configuration, ii) applied high voltage, iii) roll speed, iv) particle size, and v) relative humidity of ambient air. The numerical simulation of particle trajectories, based on the balance equation of the electrical and mechanical forces that act on charged insulating particles, took into account both the charging and discharging phenomena. Pauthenier's equation for spheres in a uniform electric field served as the model for particle charging. The equation of particle discharging was established after the experimental study of the potential decay at the surface of a layer of millimeter size PVC granules in contact with an electrode. Samples of the same granular material were then processed in a laboratory roll-type corona-electrostatic separator. The analysis of the products collected after passage through the electric field of the separator validated the accuracy of the numerical simulations.