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Publication numberUS3720312 A
Publication typeGrant
Publication dateMar 13, 1973
Filing dateJul 9, 1970
Priority dateJul 9, 1970
Also published asCA942709A, CA942709A1, DE2134298A1, DE2134298B2, DE2134298C3
Publication numberUS 3720312 A, US 3720312A, US-A-3720312, US3720312 A, US3720312A
InventorsDuncan R, Shook P, Sweeney E
Original AssigneeFmc Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Separation of particulate material by the application of electric fields
US 3720312 A
Abstract
A separator of particulate material by the use of electric fields is comprised of a pair of spaced plates of a dielectric material between which particulate material is arranged to be fed, the material being propelled in a given direction by a vibratory feeder attached to the lowermost plate. A set of parallel spaced electrodes are provided on each of said plates out of contact with the material and extending in a direction laterally of said given direction, and an AC voltage is applied between the sets of electrodes so that alternating electrical fields are set up at spaced locations along said plates in said given direction. Certain of said particulate material is caused to be repelled by said electrical fields and deflected thereby to move in said direction laterally of said given direction while the remainder of said material moves generally in said given direction.
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United States Patent 161 Shook et al. 51March 13, 1973 1 1 SEPARATION OF PARTICULATE 3,249,225 5/1966 Stuetzer et all ..2o9 129 MATERIAL BY THE APPLI OF 3,291,302 12/1966 Brastad..... ..209 129 x [75] Inventors: Paul 1 R. Shook, Colorado Springs; Assistant Examiner Ra] v ph J. H111 Earl Sweeney f Ralph AttmeyF. W. Anderson, C. E. Tripp and R. S. Duncan, Colorado Springs, all of CD 0 Kelly [73] Assignee: FMC Corporatiom'San Jose, Calif. [5 ABSTRAC [22] Filed: July 9, 1970 A separator of particulate material by the use of electric fields is comprised of a pair of spaced plates of a [21] Appl 53518 dielectric material between which particulate material is arranged to be fed, the material being propelled in a [52] U.S. CI .209/130, 209/127, 209/223 R, given direction by a vibratory feeder attached to the 209/226, 209/228 lowermost plate. A set of parallel spaced electrodes [51] Int. Cl ..B03c 7/04 are provided on each of said plates out of contact with [58] Field of Search ..209/127-l31, 223 R, the material and extending in a direction laterally of 209/223 A, 225,226, 228 said given direction, and an AC voltage is applied 1 between the sets of electrodes so that alternating elec- [56] References Cited trical fields are set up at spaced locations along said plates in said given direction. Certain of said particu- 1 UNITED STATES PATENTS late material is caused to be repelled by said electrical 1,179,937 4/1916 Kraus; .209 127 0 fields and deflected thereby to m in Said direction 1,355,477 /1920 Howell ..209/l29 laterally of said given direction while the remainder of 3,253, /1 fl i -2 said material moves generally in said given direction.

,869 1/1955 Gearu ....209/127 C 1 2,848,108 8/1958 Brastad et al ..209/127 R 28 Claims, 9 Drawing Figures A vI! \1 A I RT? T 1 *(v KC": I\\\\\\\\{\\ Q 42 t 73 J 1k 60 .'ii2. 7 1l o l I 7)- 2' 7"") -E)-- 1-3 fz ez I/ ;i 1 I .8 1 I I 1 I/ I x fa u! 4. .J 4 4 z .l z -1 v 1 [ll ELECTRIC FIELDS Primary Examiner-Tim R. Miles PATENTEUHAR 1 3197s SHEET l 0F 4 FIG EEI

TO SIDE ELECTRODES TO LOWER PLATE TO CENTER ELECTRODES ELECTRODES 1 SEPARATION OF PARTICULATE MATERIAL BY THE APPLICATION OF ELECTRIC FIELDS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention pertains to apparatus for separating fine particulate material in accordance with certain electrical characteristics of the material, and more particularly, it pertains to separators which utilize. high voltage electrical fields to cause a separation of the individual particles of a particulate material.

2. Description of the Prioi' Art The. separation of fine particulate material, particularly mineral matter, has been practiced for at least 60 years in the United States utilizing the basic principle of applying body forces by the application of an electric field to a mixture of charged or polarized solid particles in such a manner that a selective sorting of the particles will be effected dependent upon the degree of and nature of the charge on the individual particles. Early electrostatic separating devices generally comprised .machines for feeding a mixture of mineral particles over a grounded conveying surface and applying an electrostatic field across the surface by means of a high tension electrode placed thereabove. Certain of the particles would be attracted by the electrode and propelled over a divider bar while the remainder of the particles would be relatively unaffected by the presence of an electrostatic field and would either remain on the conveying surface or be propelled under the divider bar. An early U.S. Pat.,No. 476,991, embodying this principle was granted to Mr. Thomas A. Edison in 1892.

The basic principles of Mr. Edisons electrostatic separator are used even today in the commercially adopted high tension machines and conductive induction machines wherein the particulate material is charged either by the corona discharge of a high voltage electrode or by an electrical field placed adjacent to a grounded rotor carrying the fine dry particulate material. In the high tension devices, the relatively nonconductive particulate material tends to remain pinned to the grounded rotor while the relatively conductive material is thrown-off due to centrifugal forces or due to an attracting electrode placed downstream from the corona discharge. In the conductive induction machines the relatively conductive material assumes the charge of the rotor and is attracted in the electrostatic field while the relatively non-conductive material remains on the rotor.

In addition to the machines hereinbefore mentioned wherein separation is performed by lifting or propelling certain of the particles in a mixture of particulate material a greater distance from a grounded surface than the rest of the particles, attempts have also been made to move material over a horizontal or inclined surface and, by electrostatic means, cause certain of the material to move laterally of the remainder of the material against the gravitational or vibrational feed of the material. One of the earliest disclosures of such an apparatus is contained in U.S. Pat. No. 1,020,063 to Sutton et al. issued on Mar. 12, 1912. In one embodiment of the electrostatic separator proposed by Sutton et al, an aligned series of charged electrodes are provided extending parallel to the direction of feed of particulate material on a conveying surface, and the electrodes are arranged to be moved in a direction laterally of the conveying surface so as to cause certain of the particles to also have a resultant direction of movement laterally of the direction of feed of the material. In another embodiment of the invention disclosed in the Sutton etal. patent, a plurality of spaced overhead electrodes are provided with a particular individual configuration wherein the greatest electrical field density is concentrated at the ends of the. electrodes laterally of the main feed path of the material so that, again, certain of the particulate material is caused to move in a deflected path relative to the main flow of material.

In recent years renewed attempts have been made to electrostatically or electrodynamically separate material which is moved along a generally horizontal conveying surface by causing a portion of the. material to be deflected laterally of the main body of material. Use of, special electrode configurations, AC as well as DC electrical fields, and grooves or deflecting barriers for aiding in the separation of material have all been utilized, sometimes in relatively complex ways, in order to achieve a truly efficient and highly sensitive method of separating dry particulate material. Examples of patents which disclose such apparatus are U.S. Pat. Nos. 2,699,869 to Gear, No. 3,096,277 to Maestas, and No. 3,217,880 to Benton.

Another method of achieving separation of mineral material by the application of high voltage electrical fields is disclosed in U.S. Pat. No. 3,009,573 to Whipple. In the separator disclosed in this patent an'electrical field of sufficient intensity is provided so as to prevent the passage of certain particulate matter through the field-A series of such electrical fields are presented to the particulate material which is delivered vertically so as to normally gravitate through the fields. Certain of the material is levitated away from the fields and deflected laterally to a position where it can be separately collected.

SUMMARY OF THE INVENTION v The electric field separating apparatus of the present invention comprises i an improvement over those separators of the prior art wherein separating was attempted in a generally horizontal or inclined plane by deflecting certain particles laterally of the direction of feed of the material. A passage for the flow of particulate material is provided and an electrical field is provided laterally across this passage by providing electrodes spaced above and below and electrically insulated from the path of the material which electrodes are in alignment and extend laterally of the path of feed of the material. When the electrical field is applied by oppositely charging the electrodes a certain portion of the mixed material will normally be prevented from moving through the field and will be caused to move in a direction parallel to the field and laterally of the direction of the remainder of the material which proceeds normally through the field in the feed direction. By adjusting the frequency and magnitude of i the voltage applied to the electrodes, separations of different conductive or dielectric materials can be obtained. In general, relatively conductive materials are most easily separated from relatively non-conductive materials as in other electric field separators; however,

by varying the frequency of the voltage, separations of relatively noniconductive materials having similar dielectric constants may even be obtained,

In the preferred embodiment of the invention a series of parallel spaced electrical fields are provided extending laterally of the-feed path of the material but at an angle thereto with at least a component thereof in the direction of propulsion of the material. These electrical fields are narrow so that a series of barriersare provided with a certain portion of the material being deflected along the upstream edge of each of the electrical fields with the bulk of such portion of the material being deflected by the first few electrical field barriers. An'AC voltage is provided between the sets of electrodes spaced above and below the feed path, and it has been found that by varying the frequency of this applied voltage, different materials can be caused to be repelled by the fields.

In contrast with the prior art structures, particle separation in the present invention is achieved positively at the upstream edges of the electrical fields which are sharply defined-by an electrode grid structure. With the separator of the present invention critical separations of mixed minerals such as chrysocolla and chalcopyrite can be achieved which mineral mixture has not been effectively separated hereinbefore; also, 'the separation of wolframite and monazite has been achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic side elevation of the electric field separator of the present invention in an operative assembly including the means for feeding the particulate material continuously to the separator.

FIG. 2 is an enlarged plan of the separator of FIG. 1 with a portion of the cover plate thereof being broken away for the purpose of clarity.

FIG. 3 is an enlarged side elevation of the apparatus of FIG. 2 with portions thereof being shown in section.

FIG. 4 is an exploded isometric illustration of the main structural components of the separator particularly illustrating the structure of one of the electrode 7 grids.

FIG. 5 is an enlarged plan view of the conveyor plate and portions of the overlying plate and cover structure of the separator of FIG. 2 particularly illustrating the location of the deflector members and the barrier means with respect to the underlying electrode grid structure.

FIG. 6 is an enlarged isometric view of one of the deflector members shown in FIG. 5.

FIG. 7 is an enlarged isometric view of a portion of the barrier means and collecting means for the repelled material as shown in FIG. 5 with portions thereof being broken away for the purpose of clarity.

FIG. 8 is an enlarged, partially diagrammatic section taken along lines 8-8 of FIG. 2 showing the dielectric plates between which the particulate material is moved and particularly illustrating the nature of the electrical fields and their effect upon the material.

FIG. 9 is a schemmatic illustration of the electrical circuitry for the separator of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The electric field separator 20 of the present invention, as shown in an operative material processing assembly in FIG. I, is adapted to be utilized in conjunction with a feeding apparatus 22 continuously feeding fine particulate material M to one end of the separator. The particulate material is propelled longitudinally along the separator in a horizontal direction and, if not repelled by the electric fields, is discharged at the other end of the separator upon a conveyor take-away belt 24. Particulate material which is repelled by the electric fields will be deflected laterally by the fields and collected in troughs 26 arranged adjacent the side edges of the separator. A middling product containing a mixture of the two separations of the particulate material will be discharged at the end of the separator adjacent the discharge conveyor belt 24 but at the sides thereof and into underlying collection containers 28. In accordance with standard mineral separation procedures, the middling product collected in the containers 28 will from time to time be transferred back to the feeding apparatus for reprocessing through the separator.

The feeding apparatus 22 may comprise a conventional vibratory feeder or vibratory conveyor trough and hopper combination. The trough 30 is vibrated by a vibratory feeder structure 31 for vibratorily conveying particulate material which feeder structure includes a base 32 which mounts the lower ends of a pair of flexible leaf springs 33 the other ends of which are connected to a mounting bracket 34 attached to the trough. The mounting bracket is vibrated by an electromagnetic drive motor 35. A hopper 37 containing a supply of the mixed particulate material M is attached at the reward end of the feeder trough, and, as the trough is vibrated, the material will be incrementally moved out of the open bottomed hopper and along the face of the trough to be deposited vertically upon the adjacent end of the separator 20. The trough is preferably provided with a heated liner (not shown) which will raise the temperature of the material to a sufficient degree before it is delivered to the separator so that the effects of ambient humidity or the initial presence of latent moisture in the material will not be allowed to alter the electrical characteristics of the particles.

The separator, as shown in the exploded view of FIG. 4, basically comprises a mounting plate 38, a lower electrode plate 40 upon which the material is adapted to be conveyed, an upper electrode plate 42 overlying the lower electrode plate with the undersurface thereof being spaced from the top surface of the lower electrode plate, and a cover plate 44 which overlies the top electrode plate and which is securely fastened to the side edges of the mounting plate by screws 45 (FIG. 3) to clamp the entire structure in place. The separator is driven by a conventional vibratory feeder 46, similar to the vibratory feeder or vibratory conveyor 31, including a base member 47 supporting the lower ends of a pair of leaf springs 48 the upper ends of which are rigidly connected to a mounting bracket 49 which is in turn, securely attachedto a stiffner plate 52 that is connected to the underside of the mounting plate 38 (FIG. 3). The vibratory feeder is driven by an electromagnetic drive member 50 which is mounted upon the base member and includes an oscillating shaft connected to one end of themounting bracket 49.*The vibratory I feeder is adapted to vibrate the entire separator struc' ture generally in an oscillatory path extending at an angle to thehorizontal so as to move the individual particles of the material in a progression of incremental steps from the feed end of the separator to the discharge end thereof and down a sloping discharge plate 54 which is attached to the edge of the lower elecand bottom surfaces of the upper and lower electrode plates, respectively.

When the upper electrode plate is positioned over the lower electrode plate it is usually preferable that the grids do'not directly overlie each other in a vertical plane. Consequently, the grids on the top electrode Electrode grid structures of matching configuration are I printed upon the top surface of the upper electrode plate 42 and upon the bottom surface of the lower electrode plate 40 in order to provide a plurality of electrical fields which extend between the electrodeplates and directly affect the movement of the materialupon the surface of the lower electrode plate. All of the structure of the electrostatic separator which encomthe separator is the material polycarbonate which has no known fatigue life, excellent abrasion resistance, and a high dielectric strengthwhich allows for extremely high density electric fields that enable large (8-l0 mesh) particles to be separated.

I An important feature of the present'invention is the particular arrangement of the electrode grid structures which provide the. electrical fields. As best seen in FIGS. 4 and 5, the electrode grid structures are of generally herringbone shape. The top electrode grid 60 (FIG. 4) includes a central grid member 60a extending inthe direction 'of vibratory movement of the material in the separator, and a plurality of grid members 60b connected with the central grid on both sides thereof and extendinglaterally at an angle thereto inclined in the direction of movement of the material in the separator; The grid members 60b are spaced a certain distance apart which, in the embodiment of the inven tion shown, is about one inch. At the outer ends of each of the grid members 60b there is a break (FIG. 4), and sets of interconnected grid members 60c areprovided in alignment with the grid members 60b so as to form a pair of separate electrode structures at each side of the upper electrode plate. The bottom electrode grid structure 62 (show'n in' dashed linesin FIG. 5) is virtually identicalto the top electrode grid structure 60 and includes a central grid member 62a and a plurality of interconnected, laterally extending grid members 62b. Separate electrode grid structures including grid members 620 are provided at the sides of the lower electrode plate. Preferably, the electrode grid structures are comprised of a good conducting medium such as silver print which can be sprayed or painted on the top plate are spaced slightly forward in the direction of movement of the material as is illustrated in FIG. 5 or,

particularly, in the enlarged sectional view of FIG. 8. Because of this relative positioning of the electrodes, the electrical fields, as indicated by the field line F in FIG. 8, will be inclined slightly forward in the direction of movement of material between the electrode plates (indicated by the arrow in FIG. 8) which inclination has been found to be more effective in achieving a separation of different. particulate matter. The upper electrode plate, in a manner to be explained hereinafter, is adjustable upon the lower electrode plate so that the relative positioning of the electrode grid structures in the horizontal plane may be altered to virtually any desired condition.

, .Material which is fed to the lower electrode plate 40 l will be received between a back wall 70 and a front wall 72 in a pocket 74 formed therebetween by short side wall sections 73.-The central lower edge of the front wall 72 is provided with a narrow opening 75 so that material within the pocket will be propelled forwardly upon the central surface of the lower electrode plate in a thin layer. As the material moves along the lower electrode plate a certain portion of the material which is relatively-unaffected by the presence of the electric fieldswill rnove'forward generally in the direction of the arrows A (FIG. 5) while another portion of the material will be deflected and caused to move in a direction parallel to the electrode grid members 62b as indicated by the arrows B (FIG. 5).

Positioned atopthelower electrode plate 40 arelocations overlying the space between the grid members b and 60c are a plurality of deflector members 80, one of which is shown in detail in'FIG. 6. These deflector members bridge the gap between the electrode plates so that the 'upperelectrode plate 42. rests upon the top surface 81 of the deflector member. Each deflector member has a leg'82 extending generally in an inward'direction towards the grid member 62a so as toredirect certain particles back toward the centerof the electrode plate which have undesirably been moved laterally not directly as a result of the electricfields but rather as a result of collision with other particles. Each deflector also includes a second leg 84 extending parallel to the underlying electrode grid members 62b and 620 and bridging the gap therebetween so that the particles which are repelled by the electrical field generated between the grid members 60b and 62b will not be permitted to move forwardly on the electrode plate 40 until they are subjected to the influence of the electrical field generated between'the grid members 60 c and 62c. In practice, it has been foundthatv material which is'repelled by the'electrical fields'will be caused to move along a line parallel to but somewhat rearwardly positioned from the grid members generally in the plane of the trailing face 86 of the deflector member. This is illustrated somewhat diagrammatically in FIG. 8 wherein heavy concentrations of the material are caused to be formed along lines located rearwardly of the electrical fields which material will gradually move laterally in an inclined direction as a result of the combination of the vibratory feeding forces and 'the repelling force of the fields.

Mounted upon the side portions of the top surface of the lower electrode plate 40 area pair of barrier structures 90, shown in detail in FIG. '7, which provide a further separation of the particulate material. A plurality of upright walls 92 extending between the electrode plates form physical extensions of the electrical fields. These walls are interconnected by low barrier walls 94 over which the repelled material must pass in order to be received within pockets 96 formed at the side edges of the lower electrode plate by the walls 94. Each of the pockets 96 is provided with a vertical discharge passage 97 which extends through the lower electrode plate and the underlying mounting plate 38 (FIG. 3) so that material received within the pockets will be ultimately delivered to the underlying collecting troughs 26. Material which does not move over the low barrier walls 94 will eventually be propelled down the face of the lower electrode plate and discharged into the collecting containers 28 for the middling product. In practicing the present invention, it has been found desirable to space the electrode plates by a distance of 3/ l 6ths of an inch and to make the barrier wall height. l/1'6th of an inch, or 55rd of the total height of the passage.

As shown in FIG. 4, the inclined discharge plate 54 at the downstream end of the separator is provided with a pair of upright guide walls 101 between which the non-repelled material is arranged to pass. To further aid in the separation of this material from the middling product, a pair of splitter bars 103 are pivotally mounted upon the downstream edge of the lower electrode plate 40. Each splitter bar is provided with a knife edge 104 at its inwardly projecting end in order to make a clean division between'the particulate material traveling down the discharge end of the lower electrode plate. The knife edge is positioned adjacent to the last of the deflector members at the end of the electrode grid structure. By pivoting the splitter bars 103 inwardly, only the material at the very center of the electrode plate will be separated from the remainder of the material, and the quality of this product may thereby be upgraded in certain instances, e.g., where the effect of the electrical fields is only such as to cause a slight deflection of certain mixed-mineral matter.

The circuitry for applying an AC voltage of a variable frequency between the upper and lower electrode grid structures 60 and 62 is shown diagrammatically in FIG. 9. A conventional audio oscillator 110 is used to generate a variable frequency voltage including frequencies within the range of from about 30 cycles per second to about 400 cycles per second. Transformer T1 connects the output of the audio oscillator to a linear amplifying circuit which separately amplifies each half cycle of the applied sine wave and transfers the amplified voltage to the primary of a high voltage transformer T2, the secondary of which is directly connected to the electrode grid structures. Each half cycle of the applied voltage is amplified by a cascaded threestage amplifier section comprising transistors TR], TR2 and TR3 with the output of transistor TR3 being applied to the base of a power switching transistor TR4 which is connected in series with the transformer primary. In order to aid in maintaining the output linear with respect to the input from the oscillator 110, a pair of cascaded transistors TR5 and TR6 are connected between ground and the emitter lead of each of the switching transistors TR4. The amplifier sections are emitter biased by a positive voltage +V through the biasing resistors R1 and R2 and are collector biased by a negative voltage -V, the negative voltage also serving to drive the switching transistors TR4 through a grounded center tap on the high voltage transformer primary. One end of the secondary of the high voltage transformer includes leads L1, L2 and L3 which are connected to the side electrode grid members 620 and to the center electrode grid member 620, respectively, on the lower electrode plate as shown in FIG. 5. The other end of the secondary is connected to the center electrode grid member 60a on the upper electrode plate through a lead L4 extending within an upright insulator post 112 (FIG. 3). A variable voltage tap is provided in the secondary of the high voltage transformer T2 and includes a pair of leads L5 and L6 which are connected to the side electrode grid members 60c through upright insulator posts 1 14.

It will be noted that the voltage between the overlying side electrode grid members 600 and 620 will be less than that between the overlying center electrode grid members 60b and 62b. Thus, the tendency to separate two dissimilar materials will be decreased, i.e., made more sensitive, in the side sections of the separator, and a further separation of material can be made in the side sections in order to obtain a high quality concentrate in the collecting troughs 26.

' In assembling the separator of the present invention, the upper electrode plate 42 is placed upon the top of the deflector members and the barrier structures on the lower electrode plate 40. The cover 44 is then placed over the top electrode plate with elongated slots 116 at one end thereof being received over the upright insulator posts 114 and 112 connecting the electrode structures to the transformer. The cover is then securely fastened to the mounting plate 38 by the screw 45 which serves to clamp the electrode plates tightly together. Since the slots 116 are elongated it will be apparent that the upper electrode plate can be slid horizontally with respect to the lower electrode plate before the plates are clamped together. In practicing the present invention, it is normally desirable to have the electrode grid structure on the upper electrode plate spaced slightly forward of the electrode grid structure on the lower electrode plate as pointed out previously. The angle of inclination thus imparted to the electrical fields can be varied to achieve different separationeffects, and, in some instances, the top electrode grid structure may directly overlie the lower elec trode grid structure in order to obtain the maximum effectiveness in separating certain minerals.

While the theory of operation of the electric field separator of the present invention is not entirely understood, it is believed that the degree of separation of any mixture of different particles primarily depends upon the dielectric properties of the material, the particle size and density, the net charge upon the surface of the particle, the intensity and frequency of the varying electrical fields applied to the material, the feed rate, and the importance of deflections due to random collision with other particles.

in general, the larger the particle size the less the degree of activity, i.e., the less the particle will be effected by the electrical fields. This factor can be directly compensated for by increasing the electrode voltage; therefore, for larger article sizes the voltage between the electrodes must be increased accordingly. Obviously this factor imposes a upper limit upon the particle size for any given separator structure since the electrode voltage can only be increased to a certain maximum amount before dielectric breakdown occurs. When particles in a mixture are of different size groups, it is the normal practice to first separate the particles into different size groups and to process each group separately since the operating voltage during any one run of the separator will only effectively separate particles of a given size range.

The density factor appears to effect the distance that the particles are repelled from the electrical field. Hence, as the density of the particles varies it may be necessary to vary the horizontal position of the upper electrode plate with respect to the lower electrode plate in the manner hereinbefore explained to thereby vary the inclination of the electrical field in the path of movement so that the main body of repelled particles will be able to be moved laterally between the deflector members 80 without being physically impeded.

The feed rate of the material across the separator is important from two standpoints, the volume of material moved per unit area and the speed at which the particles are propelled. The volume of the feed is important in that it theoretically should provide for all of the particles to be separated by the time they reach the discharge end of the separator. If the volume feed rate is too high, a particle which would normally be deflected by the electrical fields may be physically forced through the fields due either to random collision with the other particles or to the masking effects encountered when there is a high concentration of particles in the area of the fields. The feed rate also has a direct bearing on the frequency of variation of the electrical fields, as previously pointed out. Considered in another manner, it can be seen that a high feed rate means a higher propelling force upon the particles which will tend to offset the deflecting forces due to the presence of the electrical fields.

Particles to be separated can generally be grouped into two classesactive and non-reactive. Active particles can be defined as the particles which will be deflected by the electrical fields, and non-reactive particles can be defined as those particles will move through the fields. Whether or not particles which can be classified as active or non-reactive will depend upon the frequency and intensity of the applied AC voltage as well as the particular mixture of particles being separated. As the frequency is varied certain particles which were formerly non-reactive become active and vice versa.

It has been found that a mixture of chalcopyrite and chrysocolla particles at a particle size of between 65 and 100 mesh can be separated with the separator of the present invention by applying a frequency of alternation of the electrical fields of about 162 cycles per second. Examples of non-reactive particles are those with usually perfect or near perfect crystalline structures, such as galena, quartz crystals, and some varieties of garnet and tourmaline. Active and non-reactive particles in fields generated by AC voltages of five to ten thousand volts with a frequency of 60 cycles per second can roughly be classified into two groups as follows:

Active Particles Non-active Particles 1. All micaceous minerals l. Calcite 2. Feldspar 2. Scheelite 3. Chalcopyrite 3. Apatite 4. Pyrite 4. Fluorite 5. Cobaltite 5. Azurite 6. Magnetite 6. Malachite 7. Hematite 7. Barite 8. Rutile 8. Limonite 9. Gold (native) 9. Zircon 10. Silver (native) l0. Garnet l 1. Gold (tellurides) l l. Sulphur 12. Silver (sulphides) l2. Monazite 13. Diamond 13. Cerussite 14. wolframite l4. Tourmaline 15. Cinnabar l5. Psilomelane 16.Thorite 16. Beryl 17. Molybdenite 17. Cassiterite l8. Chrysocolla l8. Sphalerite (all but Marmatite) 19. Copper (native) 20. Sphalerite (black).

21. lllmenite It must be remembered that these groups are for illustrative purposes only, and some particles in the active group may become non-reactive, or vice versa, depending upon the particle size and the particular mixture of particles being separated.

As an example of a separation that can be accomplished with the separator 20 of the present invention, a mixture of 20.7 percent wolframite and 79.3 percent monazite was processed at an effective feed rate of approximately 30 pounds per hour between electrode plates of 10 X 16 inches or roughly one square foot in area. A voltage of approximately 6,000 volts was utilized between the center electrode grid structures and approximately 4,500 volts between each of the side electrode grid structures at a frequency of 60 cycles per second. After one pass through the separator 97.6 percent of the wolframite was deflected by the electrical fields and collected at thesides of the separator while another 1.4 percent was found in the middling product collected at the discharge ends of the separator. It can therefore be said that a total of 99 percent of the wolframite was recovered since the middling product would normally have been recycled through the separator. The concentrate separated at the sides of the separator was found to be 99 percent wolframite with the original wolframite percentage being only 20.7 per cent of the total material processed.

Feed rates of up to 100 pounds per hour can be achieved in a separator as disclosed with electrode plates of approximately l0 inches by 16 inches..- Furthermore, while the separator of the present invention is disclosed as including only a single separating zone, it will be recognized that various separating zones may be provided one on top of the other with the entire structure being driven by a single vibratory feeding device. That is to say, the upper electrode plate 42 may be placed below a second lower electrode plate 40 which, in turn, may have another upper electrode plate 42 placed thereon, and so forth, until a considerable number of material feeding channels are thus provided in vertically spaced positions. in this way, the feed capacity of the separatormay be multiplied while the power requirements and space requirements are increased only slightly.

Multiple separations of the material can be achieved by isolating individual or, preferably, sets of electrode grid members 60b and 62b spaced along the length of the separator. AC voltages of different frequencies are then applied to each set of grid members. Since it has been found that particles may be rendered active or non-reactive in accordance with the frequency of the applied electrical field, it can be seen that different particles might be repelled at different longitudinal positions in the separator and that a progressive separation of several mineral materials is possible with but a single pass through the separator. It is also possible to increase the number of separations in a single pass by utilizing gravitational effects in addition to the electric field effects as by tilting the electrode plates about their longitudinal axis and/or using a riffled conveying surface for example.

It can be seen that the electric field separator of the present invention comprises a highly efficient apparatus which has been found to be very effective for separating mineral material from mesh to 500 mesh which would other wise be difficult if not impossible to separate by conventional electrostatic or other electric field separating procedures. For example, separations of cassiterite from pyrite, monazite from euxenite, sheelite from wolframite, cerussite from pyrite, and garnet from magnetite and illmenite are possible. The present invention can therefore be used to clean and separate various fractions derived from conventional gravity, flotation and electric mineral separating processes. Furthermore, a great degree of flexibility is present in the device of the present invention since the magnitude and frequency of the applied voltage may be varied to vary the effects of the electrostatic fields upon the different mineral particles. In addition, the location of the fields relative -to the path of movement of the particles is easily changed by shifting the relative horizontal positions of the electrode plates.

Although thebest mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

What is claimed is:

l. A method of separating fine particulate material of which a portion of said material is attracted to an electrical field to a different degree than the remainder of said material, said method comprising the steps of providing an electrical field which extends in a generally vertical plane by applying an electric potential between a pair of spaced electrodes, moving said material along a path at least a component of which lies in the horizontal direction and into and out of said electrical field, said electrodes being spaced above and below said path and electrically insulated from said path and which electrodes extend transversely to said path, and moving that material which does not pass through said electrical field along said electrical field in a direction generally parallel to the electrodes, whereby a portion of said material is caused to move laterally of said path in a direction parallel to said electrical field without moving across said field while the remainder of said material will be moved across said electrical field generally in the direction of said path.

2. A method of separating fine particulate material according to claim 1 wherein a plurality of parallel electrical fields are provided with said fields extending laterally of said path and being spaced in the direction of said path.

3. A method of separating fine particulate material according to claim 1 including the step of providing a second electrical field aligned end to end with the first electrical field in the direction of movement of said portion of said material, said second electrical field being of a lower intensity than the first electrical field.

4. A method of separating fine particulate material according to claim 3 including the step of redirecting material toward the center of said path in the area between said first and second electrical fields.

5. A method of separating fine particulate material according to claim 2 including the step of further separating said remainder of said material at the downstream end of said path by separating the material at a side of the path from the material in the central portion of the path.

6. A separator for separating fine particulate material comprising a material conveyor having a conveying surface at least a component of which lies in a horizontal plane, means for conveying said material in a first direction along said conveying surface, a pair of electrodes extending in generally parallel planes and in a second direction transversely to said first direction, said electrodes being spaced above and below said conveying surface and being electrically insulated from said conveying surface, and means for applying a voltage between said electrodes to provide an electrical field across said conveying surface with the conveying surface extending both upstream and downstream of said electrical field whereby a portion of said material will be deflected by said electrical field and caused to move in said second direction while the remainder of said material moves through said electrical field in said first direction.

7. A separator for separating fine particulate material as set forth in claim 6 wherein said second direction has a component thereof parallel to said first direction.

8. A separator for separating fine particulate material as set forth in claim 7 including a pair of sets of electrodes spaced above and below said conveying surface, each of said sets of electrodes comprising a plurality of parallel electrodes extending in said second direction and being spaced apart in said first direction.

9. A separator for separating fine particulate material as set forth in claim 8 wherein said conveying surface lies in a horizontal plane and wherein said means for conveying said material comprises a vibratory conveymg means.

10. A separator for separating fine particulate material as set forth in claim 8 wherein said voltage is conveyor comprises a first flat plate of dielectric material having one of said sets of electrodes provided on the undersurface thereof and said conveying surface being provided on the flat top surface thereof and a second flat plate of dielectric material spaced above said first plate and having the other of said sets of electrodes provided on the top surface thereof.

13. A separator for separating. fine particulate material as set forth in claim 12 including a second pair of sets of electrodes with one set of said second pair being provided on the undersurface of said first flat plate adjacent to and in alignment with the electrodes of the first set but spaced therefrom in said second direction and with the other set of said second pair being provided on the top surface of said second flat plate adjacent to and in alignment with the electrodes of the first set but spaced therefrom in said second direction, and means for providing a voltage between the electrodes of said second pair of sets of electrodes which voltage is lower than that between said first pair of sets of electrodes.

14. A separator for separating fine particulate material as set forth in claim 13 including a plurality of deflector means provided between said flat plates in positions overlying the space between said first and second sets of electrodes for deflecting a certain portion of said material generally in said first direction and away from said second direction.

15. A separator for separating fine particulate material as set forth in claim 13 including a plurality of barrier means provided upon the top surface of said first flat plate in positions overlying the outermost ends of said second set of electrodes, and means positioned outwardly of said barriers for collecting that portion of said material which is caused to move over said barrier means.

16. A separator for separating fine particulate material comprising a conveying member having a conveying surface with at least a component thereof extending in a horizontal direction, means for moving said material in incremental movements in a longitudinal direction along said conveying surface, a first electrode grid structure positioned below said conveying surface, said grid structure being electrically insu lated from said conveying surface and including a V- shaped grid member with the legs extending from the apex of the Vin said longitudinal direction of movement of said material and being equiangularly located with respect to said longitudinal direction, a second electrode grid structure similar to said first electrode grid structure, said second electrode grid structure being positioned above said conveying surface in alignment with said first electrode grid structure, and means for applying a voltage between said electrode grid structures to create an electrical field with the conveying surface extending both upstream and downstream of said electrical field whereby a portion of said material will be deflected and caused to move laterally of said longitudinal direction and along the upstream edges of said electrical field.

17. A separator for separating fine particulate material as set forth in claim 16 wherein each of said electrode grid structures comprises a plurality of parallel V-shaped grid members spaced in said longitudinal direction and with the legs thereof extending from the apices of the Vs in said longitudinal direction of movement of said material, the apices of said grid members being interconnected by a further grid member extending in said longitudinal direction with the legs of said V- shaped grid members being equiangularly positioned with respect to said further grid member.

18. A separator for separating fine particulate material as set forth in claim 16 wherein said voltage is an AC voltage with a variable frequency range of from about to about 400 cycles per second.

19. A separator for separating fine particulate material as set forth in claim 17 including adjustment means for moving the electrode grid structures relative to one another in said longitudinal direction so as to alter the inclination of the electrical fields provided thereby with respect to a horizontal plane.

20. A separator for separating fine particulate material as set forth in claim 18 wherein said conveying member comprises a flat plate of dielectric material having said first electrode grid structure provided upon the undersurface thereof, and a second flat plate of dielectric material overlying said conveying member in parallel relationship thereto, said second flat plate having said second electrode grid structure provided upon the upper surface thereof.

21. A separator for separating fine particulate material as set forth in claim 17 including third electrode grid structures provided adjacent to the lateral edges of said first electrode grid structure, said third electrode grid structures including a plurality of interconnected grid members aligned end to end with but spaced from the grid members of said first electrode grid structure, fourth electrode grid structures similar to said third electrode grid structures provided adjacent to but spaced from the lateral edges of said second electrode grid structure and in alignment with said third electrode grid structures, and means for providing a voltage between said third and fourth electrode grid structures independent of the voltage between said first and second electrode grid structures.

22. A separator for separating fine particulate material as set forth in claim 21 including a plurality of deflector means provided upon said conveying member in positions generally overlying the space between the grid members ofsaid first and said third electrode grid structures for deflecting a certain portion of said material generally toward a position between said further grid members of said first and said second electrode grid structures.

23. A separator for separating fine particulate material as set forth in claim 21 including a plurality of barrier means provided upon said conveying member in positions overlying the outer ends of the grid members of said third electrode grid structures, and means positioned outwardly of said barrier means for collecting that portion of said material which is caused to move over said barrier means.

24. A separator for separating fine particulate material as set forth in claim 20 including a pair of splitter bars pivotally mounted upon the downstream edge of said conveying member adjacent the side edges thereof for separating the material conveyed along said conveying member into a first portion moving along the central section of the conveying member and a second portion moving along the sides of the conveying member.

25. A separator for the separation of fine particulate material comprising a pair of flat plates of dielectric material arranged in parallel spaced relationship in a generally horizontal plane, means for conveying said material between said plates in incremental movements along the upper surface of the lowermost plate in a longitudinal direction, a first electrode provided above the uppermost plate, a second electrode provided below the lowermost plate, said electrodes being mounted in parallel relationship to each other and extending transversely of said plates but inclined in said longitudinal direction, said conveying means being effective to move said material up to and over said second electrode, and means for providing a voltage between said electrodes for providing an electrical field across said plates of an intensity whereby a portion of said material is prevented from passing through said electrical field in said longitudinal direction and is caused to move laterally along the upstream edge of said electrical field.

26. A separator for the separation of fine particulate material as set forth in claim 25 including a plurality of said first and said second electrodes with said first electrodes being arranged in parallel relationship in a generally horizontal plane and with said second electrodes being similarly arranged in parallel relationship in a generally horizontal plane in alignment with the said first electrodes whereby a plurality of spaced parallel electrical fields are provided between said plates extending transversely thereof.

27. A separator for the separation of fine particulate material as set forth in claim 25 wherein said voltage is an AC voltage of a predetermined frequency.

28. A separator for the separation of fine particualte material as set forth in claim 27 including means for varying the frequency of said AC voltage in the range of from about 30 cycles per second to about 400 cycles per second.

2353 UNITED STATES PATENT oEElcE CERTIFICATE OF CORRECTION Patent No. 72 312 Dated M h 13, 1973 I fl PAUL R. SHOOK. EARL G. SWEENEY, RALPH E. DUNCAN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r Column 4, line 29, after feeder insert or vibratory "T conveyor,-. Column 4, line 60, after feeder insert --or vibratory conveyor' Column 4, line 61, delete "or vibratory conveyor". Column 9, line 5, "article should .be -particle-.

Column 9, line 50, delete the comma after "fields". Column 9, line 51, after particles insert which-. Column 9, line 52 after particles delete "which". Column 11, line 37, "electrostatic" should be ---'eleCtric--. Column 16, line 28, "particualte should be -.part:icul ate--. I 1 I Signed and sealed this 3rd day of. December 1974.

(SEAL) Attest:

:McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents

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Classifications
U.S. Classification209/130, 209/226, 209/127.3, 209/223.1, 209/228
International ClassificationB03C7/02, B03C7/00
Cooperative ClassificationB03C7/023
European ClassificationB03C7/02B