GB1107574A - Method and apparatus for the electrostatic sorting of granular materials - Google Patents

Abstract

1,107,574. Combined pneumatic and electrostatic separation of solids. SOCIETE ANON- YME DE MACHINES ELECTROSTATIQUES. 21 May, 1965 [21 May, 1964; 18 Jan., 1965], No. 21730/65. Headings B2H and B2J. A mixture of substantially non-conducting particles to be sorted is continuously fed from a hopper 10, Fig. 1, by a screw 12 onto a perforated or porous wall 6 spaced from the bottom 4 of a tank 2 and made of electrically conductive or semi-conductive material such as sintered powder metals. Heated compressed air is 'blown via a pipe 8 through the wall 6 to produce a fluidized bed of the particles which as a result of their agitation, become electrostatically charged by contactor frictional electrification whereby charges of different polarities are imparted to particles of different constituents. An extracting electrostatic field is established between the wall 6, which is connected to the positive terminal of an electrostatic generator 34, and a grounded conductive conveyor belt 18. The positively charged particles of one or more of the constituents are attracted by the lower stretch 24 of the conveyor belt 18 from which they are brushed off into a collecting trough 26. The negatively charged particles of the other constituents remain in the tank 2 and are discharged through a calibrated outlet 14. As shown; the conveyor belt 18 is longitudinally offset from the input end of the tank 2 in order to provide in the tank an initial pre-charging zone in which no extracting field is present and in which the particles have the opportunity to become effectively charged. The wall 6 may consist of a rigid porous metal plate or of a fine-mesh wire screen. The effectiveness of the charging process may be enhanced by vibrating the fluidized bed by means of a vibrator unit 38 connected to the bottom wall 4 of the tank and by means of partition walls 40 which may or may not extend right to the side walls of the tank and which serve to transmit the vibrations to the interior of the bed and especially when made of epoxy resin, to transfer charge carriers between the particles of the different constituents of the mixture. Instead of partition walls, spaced cross-bars 41, Fig. 2, of poorly conductive or insulating material may be used. A grounded horizontal plate electrode 19 is positioned above the lower stretch 24' of the conveyor belt 18' which is made of poorly conductive material. Electrification of the particles may be further improved by introducing small spheres or beads of epoxy resin 42 in the tank 2 where they remain permanently and are free to move at random among the particles. An overflow-type outlet 41' is provided which permits discharge of the particles remaining in the tank but prevents escape of the spheres or beads. Materials treated include phosphate or potassium ores and powdered plastic resins. Reference has been directed by the Comptroller to Specifications 1,025,688.