Charging and discharging of insulating particles on the surface of a grounded electrode

The study of the ionic charging of insulating particles is intimately related to the technological developments in the field of electrostatic precipitation of dusts, deposition of powders, or separation of granular materials. The aim of the present paper is to analyze the corona charging of mm-size insulating disks, as well as their discharging when they are no longer exposed to the action of an external electric field. The experiments were carried out on a roll-type electrostatic laboratory separator, provided with a wire-type corona electrode, simulating the actual charging/discharging conditions in an industrial unit. Particles of various sizes were charged on the surface of the roll electrode, then the high voltage supplied to the corona electrode was turned off and the particles collected in a Faraday pail, connected to an electrometer. The charge measurements were performed at various time intervals from high-voltage turn-off. In this way, the charge decay could be recorded and the discharge process fully characterized. The measured data show that the discharge process depends on the nature, size and shape of the particles, as well as on the contact conditions between the particles and the grounded roll electrode. These data could guide the design of the electrostatic separation experiments that proceed any new industrial application of this technology.