Résumé
Electrostatic separation processes rely on the triboelectric properties of particles to sort them in anelectrical field. This process has received increasing interest in many applications such as recycling ofplastics particles, removal of unburned carbon from fly ash or separation of the components of interestfrom low-value agricultural resources such as extraction of lignin from wheat straw residues [1]. To betterunderstand the triboelectric separation, we developed a numerical model based on the Discrete ElementMethod (DEM) to simulate the charging kinetics of a thin layer of particles subjected to vertical vibrationsand performed experiments for validation. This model is based combines the equation of Laurentie et al[2] for charge transfer at the particle scale and the conceptual approach of Matsuyama and Yamamoto [3]for charge relaxation. The experiments were used to calibrate and validate the model using a vibrated cellcontaining glass beads. The charging kinetics was monitored by means of a Faraday cage for several valuesof the total mass of the particle bed. In all cases, we find that the global charge increases rapidly beforeleveling off at a constant value. Furthermore, the global specific charge (per unit of mass) decreases as thethickness of the particle bed increases due to charge relaxation during collisions between particles. Weshow that the charging process is governed by a characteristic time which allows us to scale the chargingkinetics whatever the mass of particles. This scaling reveals the dynamic origin of the charging process ofa granular material.