US3308948A - High voltage separation of fine particles - Google Patents

Description

Mamh 1967 R. E. BARTHELEMY HIGH VOLTAGE SEPARATION OF FINE PARTICLES 2 Sheets-Sheet 1 'Tileci Tab CHARGING MEANS CHARGING MEANS IN VEN TOR. 065? A. 54/?77/ELEM) A599 EK irraeA/fm Wimdl 3967 R. E. BARTHELEMY 3,308,948

HIGH VOLTAGE SEPARATION OF FINE PARTICLES Filed Feb. 20, 1963 2 Sheets-$heet 8 IN VENTOR. 20 5.61? 5. 54/? M51 EM) A TTORN E Y5 United States Patent Ofifice 3,308,948 Patented Mar. 14, 1967 3,308,948 HIGH VOLTAGE SEPARATION OF FINE PARTlCLES Roger E. Barthelemy, 1600 Holly Oaks Lake Road, Jacksonville, Fla. 32211 Filed Feb. 20, 1963, Ser. No. 259,952 20 Claims. (Cl. 209127) This application is a continuation-in-part of my co- .pending application, now abandoned, Ser. No. 175,896 filed Feb. 26, 1962, entitled, High Tension Separation.

This invention pertains to high voltage separation and particularly to separation processes employing ionic charging of granular materials, high voltage separation of such charged materials, and to apparatus therefor.

An object of the invention is to provide an improved high voltage separator and separation process and particularly to provide improved separation of very fine particles.

Particular objects are to combine in high tension roll separators means to treat ionic middlings, and particularly ionic middlings which include very fine particles, i.e. of -325 mesh, such as tend to occur more in crushed than in sand ores.

The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic representation of a machine in accord with the invention;

FIG. 2 is a fragmentary perspective view showing details of an electrode useful in the machine of FIGS. 1 and 3;

FIG, 3 is a schematic representation similar to FIG. 1 showing a modified embodiment in accord with the invention.

High voltage ionic roll type separators, i.e. high tension roll type separators, have been found particularly useful in separating minerals in beach sand types of granular ores. Beach sand types of ores are principally made up of rounded as opposed to jagged particles or granules, whereas crushed ores comprise jagged particles having sharp edges and, often, fiat cleaved sides. The generally rounded particles of beach sands, when subjected to separation in a high voltage ionic or high tension roll type separator, readjust themselves on the roll very rapidly under the influences of the electrical forces thereon, the latter including gravitational, windage, inertial and centrifugal forces as well as the frictional forces imposed thereon by the rotor surface and by other particles, whereby the conductive particles which have been charged in the ionic field very quickly lose that charge to the grounded rotor to be thrown therefrom. The non-conductors tend to retain the charges accumulated thereon and are thereby pinned by electrostatic attraction to the rotor surface.

It will be understood that'the type of separator to which this invention pertains comprises a moving surface element, typically in the form of an elongated roll, with' means to supply granular materials, typically comminuted or particulate ore, to an upwardly facing forwardly moving area of the surface. A discharge electrode is arranged forwardly of the area receiving the feed and spaced from the surface. This electrode, being'maintained at a high potential with respect to the conductive surface of the roll, provides ions in the space between the electrode and the roll by emitting a corona discharge. The electrode, or other electrodes nearby, or both, further provide an electrostatic field in this space. Typically the roll is grounded and the discharge electrodes, and electrostatic electrodes if any, are charged in prior art machines to the order of 10 to 20 kilovolts D.C., positively or negatively.

The grounded surface moves forwardly and thence downwardly through and beyond the primary discharge electrode area, and conductive particles, which lose their charges to the roll, are thrown forwardly from the roll adjacent and just beyond the primary electrode area under the combined influences of the electrostatic field and centrifugal force.

It has been found that good results are obtainable in beneficiating a crushed Laborador iron ore made up of sharp broken particles in accord with a process which may be practiced with the machine herein described. In separating round particle beach sands, the non-conductors become highly charged because, it is believed, of the ability thereof to roll about on the roll surface. Similarly conductors take on and lose charges readily in beach sand ores. Beach sands, accordingly, are satisfactorily separable, in roll machines having one primary electrode, into concentrate, tailings and middlings suitable for retreatment. Crushed ores separate less readily, apparently because of the greater amount of fines and the nonrounded shapes of the particles.

As seen in FIGURE 1 of the drawing, a high tension roll type separator in accord with this invention comprises a roll 1 onto the upper surface of which a mixture of particles to be separated is fed as represented by the arrow 2. The roll or rotor is conductive and is typically grounded. Means, not shown, are provided for rotating the roll at, for example a speed of between about 200 and 250 r.p.m. for a 14 inch diameter roll.

A primary ionizing electrode 3 is disposed spacedly outward from the upper forward quadrant 4 of the roll at approximately 65 degrees above the horizontal measured about the roll axis, and spaced about 5 or 6 centimeters from the roll surface. A sharp blade, or thin wire, or a series of points, as at 5, comprising a conductive part of the electrode, is or are directed toward the rotor and when the electrode is charged to a potential of the order of 15,000 volts DC. or greater the air is ionized providing an ionized field into which the feed particles are carried. In accord with certain features of this invention, a primary electrode potential of between about 30,000 and 40,000 volts is desired.

The particles entering the ionized zone acquire charges and, inducing opposite charges on the roll surface, are pinned thereto so long as the particle retains a sufiicient charge. Conductive particles tend to discharge to the roll and to acquire a charge opposite in sign to the electrode potential. The conductive particles then leave the roll under the influences of the several forces acting thereon, including, usually, a relatively strong centrifugal force, and electrostatic forces and some gravitational force.

The principal electrostatic force on the particles is established by the electrode 3 which, as shown, may comprise in addition to the discharge element 5 a more massive portion 6, which may be in the form of a rounded conductive tube or rod. The net effect of the aforementioned forces will be to cause 'a substantial portion of the conductive particles to enter a zone 7 above a splitter 8, where the particles are collected as a concentrate fraction.

Such of the non-conductive particles as acquire a strong charge in the ionizing field are firmly pinned thereby to the roll surface, and if they are good insulators, these particles remain pinned to the roll for relatively long periods and may, for example, be carried through the forward lower quadrant 9 and remain pinned to the rotor past a splitter 10 located under the roll as, for example,

under the lower rear quadrant 11 thereof. A brush, A.C wiper, or similar means 12, as is wellknown in the art, may be employed beyond splitter to remove these non-conductive particles from the roll for collection as tailings. Between the splitters 8 and 10, particles may leave the roll and, in the case of beach sands, such particles may be collected as middlings for further separation processing, either in other machines or by recirculation. In accord with the present invention, the particleswhich leave the roll between the splitter 8 and the splitter lti are divided by a splitter 13 into a gravitational middlings fraction, which enters the zone 14 between splitters 8 and 13, and an ionic middlings fraction which enters the space 15 underlying the lower forward quadrant 9 of the roll.

Crushed ores, as mentioned above have two characteristics which distinguish them from beach sand types. The particles are sharp and do not roll freely on the surface of the roll and a relatively large proportion of the particles are of very small size. In a specific example given herein of crushed Laborador iron ore the ionic middlings comprise more than 50% particlesof finer,

than 74 microns, for example. Particularly with crushed ores, it is found that an appreciable fraction of larger particles behave statistically as though substantially unaffected by the fields and such particles enter the zone.

14 as gravitational middlings. These particles have not been lifted by the electrostatic field but take a path in leaving the rotor which is the free path which would be produced by centrifugal and gravitational forces alone with no substantial field effects. Itwill be understood that windage also may have some small effect in each case but this effect is not usually of important magnitude. In operation, when a comminuted crushed Laborador iron ore of, for example, 65 mesh, that is, ore comprising particles Which pass through a screen of 65 mesh, is fed tothe top of the roll, the ore comprising conductive particles such asiron carbonates and specular hematite which discharge to the roll surface but which, unlike rapidly discharging titanium beach sand ore conductors, discharge slowly, such conductive particles may be charged by the ionic field and may then discharge soon enough to be thrown in a concentrate path 7 to the right of splitter 8. These particles will have completely discharged to the rotor and as they leave the rotor will be liftedabove the trajectory which particles would travel inthe absence of electric fields. Specifically, these particles will be lifted by the electrostatic attraction of the electrode 3 because of their charge opposite to the charge of the electrode.

A mixture of conductive andnon-conductive particles will fall from the roll in a path 14 as gravitational middlings. These particles will have passed over the rotor and under the electrode but fall in a trajectory asfthough ing. While individual particles in the gravitational mid- 55 unaffected by the electrical field or by any ionic chargdlings path may have been affected by the fields, the effects for one reason or another have balanced out, and

the net effect, or statistical effect, is substantially. nil;

Gravitational middlings will, ordinarily, be recirculated, and, as seen from specific examples hereinafter set forth, may comprise a substantial proportion of the values sought to be recovered.

cientto overcome the electrostatic force attracting the particle to the roll surface. These fine particles, according to the invention, which leave the roll in charged condition as ionic middlings are acted upon by the field of an auxiliary electrode 16 charged to a potential preferably substantially higher than the potential of the primary electrode 3 and of the same sign. the ionic middlings zone, being strongly charged, repel each other and form a cloud or fog seen not as particles but as a haze. These particles in the example herein given comprise 30% particles of about 30 to 40 microns, and particles of less than about 74 microns. effect of this auxiliary electrode is to repel the particles leaving the roll and entering the ionic middlings zone 15,

either back to the ,roll surface or to one or the other of conducting belts 17 and 18 (which are disposed, respectively, adjacent splitters 13 and 10) defining one and the other side of zone 15. The non-conductive particles so repelled by electrode 16 attach themselves to theroll or belt surface, Whereas the conductive particles so repelled have a new and prolonged chance to lose their charge to the roll or belt and thereaftertobe attracted by the, electrode 16. The electrode 16 comprises a grid, as shown in FIGURE 2. Specifically, the. electrode may comprise a perforated metallic sheet material member 19 provided with a'plurality. of openings 20 separated by bars 21, the bars being about one-third as wide as the. openings whereby the openings comprise more than one-half of the whole area of the electrode. The sheet material member is folded .over. into inverted U-shape. ticles attracted toward the electrode enter one or another of the openings and strike a conductive divider plate 22, the plate comprising a part ofthe electrode and functioning to prevent the particles from passing all the way through the electrode, into an opening at one side, and out through an opening of the other side. The particles striking the plate 22 fall intozone 23 for collection as a concentrate. fraction. Some conductive particles will land upon the bars 21 instead of entering into the electrode, whereupon they will-become charged, and againbe rcpelledby electrode 16 to the roll or to one of the belts,

including wire 161.

Beyond the path of the gravitational middlings is an I The theory of separation in accord with the above outline is more fully given in my article entitled Modern As shown in FIG. 1 the portions comprising feed 2, roll 1,'electrode structure 3 and splitters 8, 10 and 14 1 thus function in accord with this invention as means lo supply into the space 15 conductive and non-conduc tive particles chargedsubstantially equally, thatis, having charges in proportion to their respective weights, in the same polarity as thepolarity of electrode 3. This feed of charged particles is, as herein explained, actedupon in a novel manner by the electrode 16 and the conductive surfaces 17 and 18,'and the associated elements. A high potential difference is maintained between the electrode 16 and the surfaces 17 and 18, and, accordingly,-there is provided separation between the conductiveand the non-conductive particles so fed into space 16...

While electrode 16 acts primarily as a static electrode, any uninsulated non-spherical objects or body charged to 65 or 75 kv. in the untreated atmosphere will discharge into the atmosphere, and some ionization will be.

The particles in The Conductive vpar- Good produced by this electrode. The electrode 3 is arranged to provide substantial ionic discharge from the thin wire or plural point or other known discharge electrode portion 5. Portion 6 usually included a high tension roll separators, being cylindrical and larger than thin wire, tends, as has been known to the art for many years, to focus the ionic discharge toward the roll. Of course, any object charged to 35 kv. establishes an electrostatic field whether or not it provides any substantial ionization.

It has been found that satisfactory operation is obtainable if electrode member 19 is completely covered with a synthetic resin plastic insulting fihn or coating 1%, in which case the charges of the conductive particles landing upon the bars 21 will not leak off to the electrode and the particles will collect until they fall ofi or are knocked off or otherwise mechanically removed. If electrode member 19 is so coated, it becomes, of course, substantially completely a static non-ionizing electrode, even at 65-80 kv. Since the grid 19 serves as a Faraday cage, it is immaterial whether bafile 22 therewithin is coated or uncoated, so long as it is maintained at the potential of member 19.

It is well understood by those skilled in the art that machines of the type to which this invention pertains embody splitters, feeds, electrodes and other elements adjustable in position with respect to the roll, which is usually fixed in position. Adjusting means for mounting such elements being commonplace and constituting no part of this invention, such means are omitted from the drawings for clarity.

The grounded conductive belts 17 and 18 are mounted on suitable rollers, such as rollers 24 and 25, and are suitably driven to move, as represented by the arrows 26 and 27, in a direction to carry downwardly non-conductive particles pinned thereto as a result of repulsion by the electrode 16. Belt 17 moving in the direction 26- carries non-conductive particles across a tailings splitter 28, where they may be removed as by a brush 29 and collected as tailings. A similar splitter 30 is similarly arranged in connection with belt 27 and a means 31 is similarly provided for removing the tailings from belt 27. Walls or partitions 32 and 33 extend downwardly from electrode 16, and these partitions are preferably of plastic material'and define between them the zone 23 through which falls the concentrate fraction collected interiorly of electrode 16. Between the splitter 28 and the wall 32 on the forward side of electrode 16, a middlings fraction is obtained which may be collected with a smaller quantity of middlings fraction falling between wall 33 and splitter 30. These middlings may be added to the gravitational middlings for recirculation or may be treated on other machines. Tailings collected on belt 26, along the forward side of zone are substantially greater in quantity than those collected on belt 18- at the rearward side of the zone 15. If bafiie 22 is omitted, a substantial quantity of concentrate falls outwardly adjacent to wall 33. The baffle causes this fraction to fall in zone 23.

The charge on electrode 16, which may be in the range of 50,000 or 60,000 volts or greater and is preferably about 65,000 to 75,000 volts, desirably results in ionic discharge which increases the charges on the nonconductive particles. The ionic discharge may result in a charging current of, typically, slightly less than 0.02 milliampere per foot of electrode at electrode potentials of about 75,000 volts, or of about 0.01 or 0.015 milliampere at potentials of from 50,000 to 60,000 volts. While such discharge desirably increases the charges on particles in space 15, electrode 16 acts primarily as a static electrode in cooperation with the grounded conductive surface elements 17 and 18. In-crushed ores, it may be theorized that non-conductors of other than round shapes may have acquired charges on one edge or one side from the primary electrode, and upon entering the zone 15, the electrode 16 may supply charges to another edge or side, thereby greatly increasing the total charge on the particle.

In a specific case and in accord with the invention, a crushed Laborador iron ore constituted as follows was supplied to the machine of FIGURE 1:

Percent Specular hematite 40 Magnetite 10 Manganese oxides l2 Carbonates (Fe, Mg, Ca) 10-12' Quartz 36-39 When this ore was treated on the machine with electrode 16 de-energized and therefore completely ineffective, and with 35,000 volts applied to electrode 3, collecting concentrates in the zone 7 above splitter 8, collecting tailings beyond splitter 10 and collecting the matrials in zones 14 and 15 as a middlings, the following rseults were obtained.

Percent Percent Fe Distr. Weight Fe Percent Concentrates 25.1 66.1 5357 Middlings. 44.8 28.9 42.0 Tailings 30. 1 4. 4 4. 3

Under the same conditions, by separtely collecting the middlings in zones 14 and 15 as gravitational middlings and ionic middlings, respectively, the following results were obtained.

Percent Percent Fe Distr. Weight Fe Percent Concentrates 25. 1 66. 1 53. 7 Gravitational Mi ddlings 16. 3 43. 0 22. 7 Ionic Mi ddlings 28. 5 20. 9 19. 3 Tailings 30. 1 4. 4 4. 3

With electrode 16 charged to 65,000 volts, concentrates Percent Percent Fe Distr. Weight Fe Percent Concentrates 25. 1 66. 1 53. 7 Gravitational Middlings 16. 3 43. 0 22. 7 Ionic Middlings split by auxiliary electrode 16:

Concentrate. 2. 9 64. 7 6. l 9. 1 37. 7 11. 1 10.2 3. 6 1. 2 36. 4 4. 4 5. 2

It will be noted that the tailings collected beyond splitter 10 are increased in amount by the effects of electrode 16, from 30.1% of theoriginal ore, by weight, to 36.4% of original ore, without increase in the percentage of iron contained in these tailings. The tailings extracted from belts 17 'and 18, constituting 10.2% of the original weight of ore, are somewhat cleaner than the t'ailings'collected beyond spiltter 10, whereby the total tailings collected in one pass is increased by 30% and such tailings are lower grade, containing less iron, thanthe tailings obtainable without electrode 16. The concentrate obtained in zone 7 is, as would be expected, unchanged, as are the gravitational middlings collected in zone 14, but a high grade concentrate is collected interiorly of the auxiliary electrode 16, which would be added to the concentrate at 7,

and a relatively high grade of middlings is collected outwardly of walls 32 and 33 and inwardly of splitters 28 and 30, which would be added to the gravitational middlings at 14 for recirculation or further treatment. The total tailings which may be discarded after one pass thus is increased from 30.1% to 46.6% of the weight of the feed, the concentrate is increased from 25.1% to 28.0%

and the middlings to be further treated or recirculated is,

of these adhered particles and ready collection thereof.

Such movement of the walls, it will be seen, is not essential to the separation function per se.

As an alternative construction, the belts 17 and 18 may be omitted it means are provided to vibrate splitters 13 and and thereby to cause particles attracted to the splitters from zone to move downwardly for collection as tailings, in which case the splitters 13 and 10 would I constitute the grounded conductive walls bounding the space 15.

The embodiment shown in FIGURE 3 may be in most respects in accord with the embodiment of FIGURES 1 and 2, and the above description of these figures applies to FIGURE 3 except as specifically noted hereafter; Portions and elements of the machine of FIGURE 3 which conform to FIGURES 1 and 2 and to the above description are identified by the same respective numbers as are applied in FIGURES l and 2, except that a prime is added. Thus roll 1, electrode 3, electrode 16, belt 18, splitter 10 and brush 12 find their counterparts in roll 1, electrode 3, electrode 16', belt 18', splitter 10 and brush 12, respectively.

The electrode 16' of FIGURE 3 is supplied with high voltage energy, of about 75 to 80 kv., by any convenient means, such as by a wire shown schematically at 161, connected thereto at any convenient point but, as is well known in connecting of high voltage electrodes, the wire should be in a position such as not to afiect the electrostatic field between electrode 16 and the grounded rotor 1' and belts 17' and 18', in accord with the arrangement of electrode 16 and conductor 161 connected thereto as shown in FIGURES 1 and 2.

The concentrate splitter 34' of FIGURE 3 conforms generally to splitter 8 of FIGURE 1, defining a con centrate collection zone 7', but particles falling in the direction in which gravitational middlings were collected in the FIGURE 1 machine fall in the FIGURE 3 embodiment into the ionic middlings zone identified, at 35, which, accordingly would be a combined ionic and gravitational middlings zone, the gravitational middings being, however, substantially less, quantitatively, than the ionic middlings. It will be apparent that with some ores and operating conditions it may be preferred to collect gravitational middlings separately, as in the FIGURE 1 machine, and with other ores and conditions, to direct the gravitational rniddlings into the ionic 'rniddlings zone in accord with FIGURE 3.

In FIGURE 3, the grounded conductive belt 36 extends upwardly to an upper roller 37 disposed behind a small shield 38 at the operative end of the concentrate fraction splitter-34. middlings'frorn passing to the upper side of the belt.

Splitters 39 and 40, in addition to splitters 28 and are provided in the ionic and gravitational'rniddlings zone- =of the-FIGURE 3 machine for it has been found desirable with iron ores of the above defined Laborador type under some conditions and depending upon the re- Shield 38 prevents gravitational,

sults desired to collect as concentrate not only particles falling within the electrode 16 or 16' but also those particles. which fall outwardlyof but adjacent to the electrode 16', and, in typical operation of the FIGURE3 machine, the particles falling between splitters 39 and 40, including those falling between insulating plates 32 and33, will all-be collected together as a concentrate. With this arrangement the baffie 22' becomes less important, and it may be omitted, if desired, in those cases where it is found that no appreciable loss of values occurs from particles so accelerated that they pass through the electrode and over one or the other splitter 39 or 40.

A middlings for recirculation is collected in spaces 41 splitter 10" and there falling or being brushed off by.

brush 12.

It will be recognized that the electrostatic field gradients produced by electrodes 3 and 16 are substantial'gradients in the order of magnitude of tens of thousands of volts per inch between the roll and the electrode 3 and between electrode 16 and the roll and'are of the same order of magnitude but somewhat greater in the typical case between electrode 16 and each of walls 17 and 18. The field gradient becomes substantially Zero, however, in the vicinity of the roll throughout the area designated which extends from the upper forward quadrant just below the leaving point area for lifted conductive. particles, through the area from which gravitational middlings leave the roll and into the area where theionic middlings 1 leave the roll, that is, past splitter 13. .This interruption in the field occurringbetweenthe areas of influenceof electrode 3 and electrode 16 permits negatively charged particles, both conductors and non-conductors, to be thrown from the roll into the space 15 to be separated in the space 15 by the electrode 16and the grounded walls 17, 18. It will be understood by those skilled in the art that the word grounded as used herein refersto a reference potential which usually is earth potential as a matter of convenience.

Similarly, the fields established by electrodes 3' and 16' in the machine of FIGURE 3 do not provide any substantial gradient near the roll adjacent splitter portions 38, whereby, since they are not being held to the roll by electrostatic forces of negative polarity, the negatively charged ionic ,middlings leave the roll in the space 35, as, in effect, a feed of particles, both conductive and non-cons ductive, and with the particles substantially equally charged, that is with each particle carrying a charge substantially proportional to its weight, for the separator which comprises the electrode 16 and at leastone co-- operating grounded wall, such as wall 36.-

The feed, in the case of the ore used in the tests reported here, which leaves the rotor as ionic middlings, and which is so effectively treated by the electrode 16 or 16 of this invention, comprises a substantial portion of 325 mesh'pa rticles, and particles of this size are extremely difficult to handle in high tension roll type separators. The present invention, accordingly, has particular applicability with crushed ores, and ores comprising particles of about 300 mesh and finer. It will be recognized that the crushed ores commonlyinclude in substantial proportion fine and very fine particles.

The grounded belts should move slowly to provide time for reversal of charge by conductors before leaving the,

course, it is necessary to operate the belts at a sufiicient speed to transport the non-conductors out of the field before they build up to a depth to interfere with contact of conductors with the belt.

A series of separation tests have been conducted of industrially ground iron ore as identified above, containing 40 percent (40%) 200 mesh material, that is, material which will pass through a 200 mesh screen. The results of these tests are given below.

Test A This test was run on a standard high tension separator, comprising elements comparable to electrode 3 or 3', roll 1 or 1', feed 2 or 2' and with suitable splitters set to collect: (l) concentrate above a splitter comparable to splitter 8 or 34, (2) middlings between such concentrate splitter and a tailings splitter comparable to splitter 10 or 10, and (3) tailings from beyond the tailings splitter, with the electrode corresponding to electrode 3 charge to -38 kv., and with the splitters adjusted to effect an optimum separation of a high grade concentrate and low grade tailing:

Percent Percent Fe. Distr.

Weight Fe Percent C oncentrates 26. 2 66. 3 57. 1 Middlings. 37. 1 31. 6 38. 6 Tailings. 36. 7 3.6 4.3

Feed 100. 3o. 4 100. o

The screen analysis of the three products inpercent of Test A was:

Test B This test was run on the same ore and on the same separator as Test A, with the same feed rate, the same rotor speed, the same concentrate and tailings. splitter positions, and the same voltage on the primary electrode,

but splitters 28?, 30', 39 and 40 and electrode 16 were utilized, with electrode 16' energized at -75 kv. Con.-

centrate C, was collected above concentrate splitter 34.

and tailings T were collected beyond splitter Concentrate C was collected between splitters 39 and 40, tailings T was collected outwardly of splitters 28 and 30, and the middlings was collected in zones 41,and 42. The results given were from a straight run, with no recirculation of middlings.

Percent Percent Fe Fe Distr.

Weight Percent Concentrate C 26.3 66.6 57. 9 Concentrate C 10. 3 67. 7 23.1 Middlings- 9. 8 32. 3 10. 5 Tailings T 43.4 4.5 6.4 Tailings T2 10.2 6. 2 2.1

100. 0 so. 2 I 100. 0

The screen analysis of the products of Test B was:

Concentrates Tailings Tyler Mesh Middlings C C: T T2 +100 23. 7 14. 4 55. 9 8. 2 58. 2 16. 5 l2. 9 14. 5 20. 7 25. 5 23. 8 20. 8 11. 3 32. 4 ll. 8 36. 0 51. 9 18. 3 38. 7 4. 5

Mean Mesh in microns... 92 72 181 161 A comparison of the results from Test A and Test B shows that the provision of electrode 16 results in the recovery on the same rotor of an important amount of a second and substantially finer particle size concentrate C tailing T and the promotion of increased regular tailing T accompanied by a drastic reduction in middlings from, in this case 37.1% to only 9.8%. Accordingly, one straight initial pass through the machine of FIGURE 3 yields slightly more than of the feed separated into final tailings and final concentrate fractions, with only about 10% of total feed tonnage as middlings. This middlings fraction, being such a small proportion of the feed, may be conveniently recirculated for retreatment on the same rotor. This procedurewas followed in the following test which, except for recirculation of middlings (closed lock test), was run under conditions identical to Test B.

The screen analysis of the products of Test C was as follows:

Concentrates Tailings Tyler Mesh C C2 T T2 Mean Mesh in microns 93 71 85 158 It will be seen from a comparison of Test A with Test B and Test C, that electrode 16' is responsible for adding some coarse'tailingsto the tailings T carried past splitter 10 with an overall increase of such tailings from 36.7% by weight of the feed on Test A to 43.4% of the feed in Test B or 44.2% in Test C. There is, of course, no substantial effect of electrode 16 on the amount or type of concentrates collected above splitter 34, in space 7', except that such concentrate collection is increased upon recirculation of middlings as in Test C.

11 I It has been found that on electrode 16, or 16' current ashigh as 0.4 milliampere per foot of electrode results in less clean tailings T than. the lower current suggested.

Current levels of less than about 0.01- milliampere may be difficult to obtain in actual practical operation at 75 to 80 kv. on electrode 16.

It will be understood from the explanation herein of the invention that the particles leaving the rotor between the splitters 13 and of FIGURE 1 are very nearly all charged to a potential with respect to ground which results in a force Fe between the particle and rotor equal "to, substantially (but actually an immeasurably small' amount less than) the centrifugal force on the particle, mw R,.plus the gravitational force on the particles, mg cos u, where m is the particle mass, to is the angular velocity of the roll, R is the radius of the roll, g is gravitational acceleration and on istheangle between the radius fromthe center of the roll to the point of departure of the particle and the vertical. The space of FIGURE 1 or 35 of FIGURE 3 is filled, accordingly, with a cloud of dispersed particles which repel each other since they are similarly charged to nearly the same potentials. It will be seen that the angle on is not precisely the same for all particles and that the cos a term varies to some extent depending on the specific leaving point for each particle. Since the centrifugal force is normally several times greater than the. gravitational force on the leaving ionic middlings, however, the potential of the particles asthey leave the roll in zone 15 or 35 is nearly thesame, whether they leave the roll closely below splitter 13 or further along. With the ore usedin the tests reported hereinabove, the cloud in space 15 or 35 was of suchsmall particles so completely dispersed that thecloud was normally visible only as a haze. The electrostatic field existing between electrode 16 or 16 and the roll and grounded belts 18 and-17 or 18 and 36 is such as to urge these charged particles to move away from electrode 16 or 16'. Uncharged particles, that is particles at or near the potential of the belts and roll, are, of course, attracted to electrode 16 or 16, and it will be seen that the greatest proportion of uncharged particles are those which, having originally left the roll while carrying a charge Fe, have been repelled by the electrode to a belt, there to lose the charge or, in other words, to take on the charge of the belt, and thereafter to be repelled by the belt and to be attracted by the electrode. The belts 17, 18, 17' and 36 act, accordingly, as groundedwalls, that is to say, walls at a potential opposite to the potential of the electrodes 3 and 16, or 3 and 16; The separation eifectuated in zone 15 or zone 35, is not dependant upon :movement of 'the'belts, but moving belts constitute a' convenient and effective means for mechanically removing theseparated.non-conductors from the electrostatic field of the ionic middlings separation zone.

It has been found that the amount of tailings collected from belt or wall 17 or 36 defining the front wall of the ionic middlings space is much greater than the amount collected from the rear Wall belt 18 or 18. Accordingly,

it is'possible to operate the machine without wall 18 or,

18', although under the conditions of the tests herein given, and with the specific machine geometry shown, operation with belt 18 or 18 has proven, preferable, for reasons of efiiciency and economy.

The machine dimensions are such that the electrode 3 is spaced from the roll surface by a distance about.one-, half or two-thirds of the distance between electrode 16 and the roll surface, and the electrode 16 is approximately equidistant from belts 17 and 18 and from roll 1. Accordingly, ifelectrode 16 is charged to a potential between approximately 2 to 2.2 times the potential of electrode 3, the field gradient between electrode. 16 and the belts and roll Will be at least as great as and up to about one and one-half times as great as the gradient between electrode 3 and roll 1.

While only certain preferred embodiments of this in- 12 vention have been shown and described by way of illustration, .many modifications will occur to those skilled in the art and it is, therefore, desired that it be understoodthat it is intended in the appended claims to cover all such modifications as fall withinthe true spiritrandscope of this invention.

What is claimed as new and what it is desired to secure by Letters Patent of the United States is:

1. In a high tension roll type separator comprising a grounded roll and an ionizing electrode charged to a potential of at least 30 kilovolts spaced from the upper forward quadrant of said roll, an auxiliary static electrode disposed below and in the path ofparticles'thrown from thelower forward quadrant of the roll, a conductive grounded wall extending from a forward .portion of said roll and disposed betweenand spaced from each of said electrodes, means to charge said auxiliary e1ec-- trode to a potential in excess of substantially 60 kilovolts the same sign as said ionizing electrode, and means for separately collecting particles attracted respectively toward said auxiliary electrode and toward said wall.

2. In a high tension roll type separator comprising a grounded roll and an ionizing electrode, charged in predetermined polarity and disposed opposite and affecting a portion of the upper forward quadrant of the roll, whereby gravitational and ionic middlings leave said roll below said portion, wall means comprisinga conductive.v

back'surface having substantially the same potential as said roll disposed between said portion and the zone, of departure from the roll of said. ionic middlings, means establishing a unidirectional field of said predetermined.

polarity beyond and with the back surface of said wall means in said zone, said field being of sufficient intensity to pin non-conductive particles to said back surface, said field terminating spacedly below .and'rearwardly from said portion and beyond the leaving point area for gravitational middlings, and means for separately collecting from said ionic middlings those particles which cling to said back surface and those particles which are pulled in a direction away from said back surface by said field.

3. In a high tension roll and an ionizing primary electrode typeseparator adapted and arranged to be fed with ore particles including a substantial percentage of conductive and non-conductive particles smaller than 200 mesh, said separator having a roll, a pair of conductive wall means defining therebetween a space generally un derlying the roll into which charged particles are thrown from the roll under the influence of gravity and centrifugal forces thereon which substantially equal ,the electrostatic attractive force of such particles to the roll, said separatorcomprising means driving'said roll at a speed sufficient to impose centrifugal forces on said particles at least several times as great as the force of gravity, whereby said. space receives and contains a cloud of dispersed substantially equally charged conductive and non-conductive particles, said walls being at. substantially the potential of said roll, means beyond said space for collecting tailings pinned to the roll, a secondary electrode in said space, and means maintaining. said secondary electrodeat a potential with respect to the roll in excess of sixty thousands of volts and of the same polarity as the charges on said charged particles.

4. In a high tension roll type separator having a roll and a high potential primary electrode, front and back conductive walls defining therebetween a space generally underlying the roll in which charged particles leave the roll under the influence of gravity and centrifugal forces the roll, a second electrode in said space, and means maintaining said second electrode at a potential with respect to the roll in excess of substantially sixty thousands of volts and of the same polarity as the primary electrode, said electrodes being sufficiently spaced and shielded by said grounded front wall and said grounded roll as to provide a substantially field-free portion of the roll between the respective fields of the electrodes.

5. The combination in accord with claim 4 in which the roll speed provides centrifugal forces on said charged particles at least several times greater than the gravity forces and in which said electrode is perforate with openings for passing particles attracted thereto.

6. The process of electrically beneficiating crushed granular ore material comprising the steps of passing the materials to be separated on a conductive rotating roll surface into an ionizing field of predetermined polarity whereby to pin non-conductors to said surface and to throw and lift conductors from said surface as a concentrate fraction in a first path, collecting said fraction in said path, defining between spaced conductive walls maintained at substantially the potential of said roll surface a space beyond said first path into which an ionic middlings fraction leaves said roll surface, repelling substantially all of the ionic middlings particles outwardly toward said roll and walls from an electrode of said polarity disposed in said space spaced from said roll and inwardly between said walls, attracting toward said electrode such of said repelled particles as lose their charge to said walls and roll, collecting such attracted particles as a concentrate fraction, and collecting the particles so repelled to said walls which do not lose their charge thereto as tailings.

7. In a high voltage ionic roll type particle separator of the type comprising a conductive roll, an ionic discharge electrode operable to pin non-conductive particles to the roll surface through and beyond the area from which discharged conductive particles are thrown by gravitational and centrifugal forces, first splitter means for dividing and collecting as concentrate the fraction of the conductive particles which is lifted by said electrode from the forward portion of the roll, and second splitter means for dividing and accumulating as tailings the fraction of the non-conductive particles which adhere longest to said roll, means for further separating the particles which leave the roll surface between said first splitter means and said second splitter means and which enter into a space generally below said roll, said further separating means including high potential means establishing an electrostatic field limited in extent to portions of the roll below and beyond said first splitter means and forwardly of said second splitter means, said high potential means comprising an electrostatic electrode in said space charged to a potential with respect to the roll substantially higher than the potential of said discharge electrode and of the same polarity as said discharge electrode, and means to collect conductive particles attracted by said electrostatic electrode.

8. The combination according to claim 7 wherein said dividing means comprises a grounded conductive surface facing said electrostatic electrode.

9. The combination according to claim 7 wherein said electrostatic electrode is perforated.

10. In combination, in a high tension separating machine comprising a rotating roll, a primary discharge electrode maintained at a high potential of predetermined polarity with respect to said roll and a head feed, there being a space below the roll into which ionic middlings are thrown from the roll, a secondary electrode having a high potential of said predetermined polarity with respect to said roll disposed in said space, a wall below said roll having a conductive surface portion disposed toward said space and facing and spaced from said secondary electrode, said wall surface having substantially the same potential as said roll, the potential of said secondary electrode being sufficiently high to pin nonconductive particles of said ionic middlings to said surface portion, means to remove such pinned particles from said surface portion, and means for collecting con ductive particles attracted toward said secondary electrode.

11. The combination according to claim 10 wherein the means to remove the pinned particles comprises means for mechanically removing such particles from said surface portion.

12. The combination according to claim 10 wherein the wall comprises a belt, and wherein the means to remove the pinned particles comprises means to drive the belt.

13. The combination according to claim 10 wherein said secondary electrode is a grid electrode having openings through which conductive particles pass.

14. The combination according to claim 13 wherein the secondary electrode is provided with an electrically insulating coating thereon.

15. The combination according to claim 10 further comprising a second wall below said roll having a con ductive surface portion disposed toward said space and having substantially the same potential as said roll, said portion of said second roll facing and spaced from said secondary electrode and disposed with respect to said secondary electrode opposite to the surface portion of the first wall, and means to remove particles pinned to said surface portion of said second wall.

16. The combination according to claim 15 wherein the secondary electrode is a grid electrode having respective spaced perforate portions facing the respective surface portions of said walls, said perforate portions having openings for admitting particles attracted toward said grid electrode into the space between said perforate portions.

17. The combination according to claim 16 wherein the perforate portions of the grid electrode are provided with an electrically insulating coating thereon.

18. The combination according to claim 16 wherein said secondary electrode further comprises a baflie spaced from and between said perforate portions thereof in position to be impinged by particles passing through the openings of said perforate portions.

19. The combination according to claim 18 wherein the perforate portions of the secondary electrode are provided with an electrically insulating coating thereon.

20. The combination according to claim 10 wherein the secondary electrode is provided with an electrically insulating coating thereon.

References Cited by the Examiner UNITED STATES PATENTS 859,998 7/1907 Wentworth 209l28 X 1,926,025 9/1933 Anderson -l54 X 2,314,940 3/1943 Hewitt 209-127 2,466,371 4/1949 Byrd 209-128 3,031,079 4/1962 Boss 209-128 FRANK W. LUTTER, Primary Examiner.

Claims (1)

1. IN A HIGH TENSION ROLL TYPE SEPARATOR COMPRISING A GROUNDED ROLL AND AN IONIZING ELECTRODE CHARGED TO A POTENTIAL OF AT LEAST 30 KILOVOLTS SPACED FROM THE UPPER FORWARD QUADRANT OF SAID ROLL, AN AUXILIARY STATIC ELECTRODE DISPOSED BELOW AND IN THE PATH OF PARTICLES THROWN FROM THE LOWER FORWARD QUADRANT OF THE ROLL, A CONDUCTIVE GROUNDED WALL EXTENDING FROM A FORWARD PORTION OF SAID ROLL AND DISPOSED BETWEEN AND SPACED FROM EACH OF SAID ELECTRODES, MEANS TO CHARGE SAID AUXILIARY ELECTRODE TO A POTENTIAL IN EXCESS OF SUBSTANTIALLY 60 KILOVOLTS THE SAME SIGN AS SAID IONIZING ELECTRODE, AND MEANS FOR

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