1. Field of the Invention
The invention generally relates to the separation of particulate materials including minerals, ores, industrial wastes and the like. More particularly, the invention deals with the separation of particulate and granular materials by utilizing a divergent electric field which effects the separation in accordance with the values of the dielectric constants of the materials being separated relative to the dielectric constant of a liquid dielectric medium within which the separation occurs.
2. Description of the Prior Art
The prior art recognizes that separation of various particulate materials in dry form or solids from liquids may be achieved by utilizing electrophoresis. Electrophoresis arises from the electrostatic attraction of charged electrodes for the charged particles. The direction of motion of the charged particles is dependent on the direction of the electric field, such that reversal of the field reverses the direction of travel. Electrostatic separation is generally conducted with air as the fluid dielectric medium within which two electrodes of opposite polarity are disposed. The high voltage electric field required to effect this type of separation is not necessarily divergent and, in most cases, is relatively uniform. It is generally accepted that optimum electrostatic separations are effected when the dielectric constant of the electrode gap be as near unity as possible.
The Tyson U.S. Pat. No. 2,485,335 is an example of a typical prior art system for separating materials by means of an electrostatic field. Tyson teaches that solid polymer particles may be separated from an associated reaction liquid by passing the slurry of liquid and particles through an electrostatic field created by an electrical discharge potential. The electrical discharge causes the polymer particles to adhere to the surface of the rotating drum which carries a charge opposite to that carried by the particles. The liquid is caused to drain away and the polymer particles adhering to the drum are subsequently removed therefrom.
By contrast, separation of materials through dielectrophoresis occurs because of the tendency of matter to become polarized in a non-uniform electric field and move into regions of highest field strength or intensity. Dielectrophoresis only occurs in a divergent or non-uniform electric field created in a fluid dielectric medium. In a divergent electric field, particles in a less-polar suspension migrate to and accumulate where the field is strongest. This movement does not require the particles to be charged but depends instead on the force experienced by all polarizable materials in non-uniform electric fields. The uncharged particle is believed to be polarized by the applied voltage and, consequently, moves due to the unequal pulls exerted by the forward and backward direction of the non-uniform electric field. The most polar material moves toward the area of greatest field intensity, independent of the direction of the field and the type of applied voltage, whether such voltage is in the form of alternating current, direct current or pulsating direct current. It is therefore recognized that for separation to occur, the dielectric constant of the particles to be separated must be higher than that of the liquid dielectric medium within which the divergent electric field is created.
The Walker U.S. Pat. No. 3,304,251 exemplifies a prior art system for separating particles by the utilization of dielectrophoresis or a non-uniform electric field. This is achieved by passing an inner wire electrode through an outer tubular electrode within which a contact zone is provided for the materials being separated. A liquid dispersion of the particles is contacted in the zone with a non-uniform electrical field such that the particles migrate and adhere to the wire electrode which removes the particles from the contact zone.