Method and device for the electrostatic separation of granular materials

A method for the electrostatic separation of a granular material comprising particles having an equivalent diameter ranging between 50 μm and 2 mm, said method comprising the following steps:

• A. introducing said granular material into a charging device at a constant flow rate allowing said particles to be charged as a function of their nature, then charging said particles;
• B. generating an electric field E between two coaxial cylindrical electrodes with a vertical axis (OZ) disposed in a separation chamber, the intensity of E varying between 1 kV/cm and 10 kV/cm;
• the two cylindrical electrodes being divided into an internal cylindrical electrode with an external axis diameter die and an external cylindrical electrode with an internal diameter dei;
• said cylindrical electrodes being connected to a high direct voltage generator, one of said electrodes being connected to the positive terminal of said generator and the other one of said electrodes being connected to its negative terminal or to ground;
• so as to create an electric field zone in the form of a cylindrical layer with a thickness e that complies with the formula:
• e=(dei−die)/2;
• (1)
• C. generating, by suction, in said electric field zone, a descending vertical air flow perpendicular to the direction of the electric field E and for which the effect, combined with the effect of gravity, allows said particles, once charged, to be continuously transferred to said electric field zone;
• D. moving said charged particles when they are located in said electric field zone toward the opposite polarity electrodes in order to adhere thereto;
• E. continuously detaching, using mechanical means for cleaning the surface of the electrodes, said particles adhering to the surface of said electrodes, said mechanical cleaning means being free to rotate about the vertical central axis (OZ) of the electrodes and said electrodes being fixed, or vice versa;
• F. continuously discharging said detached particles under the combined action of gravity and of said vertical air flow;
• then
• G. recovering said particles.