US2466371A - Apparatus for electrostatic concentration and separation - Google Patents

Description

April 5, 1949. 'w. BYRD, JR 2,466,371

APPARATUS FOR ELECTROSTATIC CONCENTRATION AND SEPARATION Filed May 18, 1944 4 Sheets-Sheet 1 w. BYRD, JR 2,466,371

APPARATUS FOR ELECTROSTATIC CONCENTRATION AND SEPARATION 4 Sheds-Sheet 2 Filed May 18, 1944 Z'Snnentor (Ittorneg s April 5, 1949. 5m,- ;R 2,466,371

APPARATUS FOR ELECTROSTATIC CONCENTRATION AND SEPARATION Filed May 18, 1944 v 4 Sheets-Sheet 3 3nventor QQIIIFMQW BmQ-I April 5, 1949. w. BYRD, JR 2,466,371

APPARATUS FOR ELECTROSTATIC CONCENTRATION AND SEPARA ION Filed May 18, 1944 4 Sheets-Sheet 4 3nventor attorneg S Patented Apr. 5, 1949 AP PARATUS FOR ELECTROSTATIC CONCEN- TRATION AND SEPARATION William Byrd, Jr., Princeton, N. J. Application May 18, 1944, Serial No. 536,202 15 Claims. (01. 209-128) The present invention has as its primary object the provision of a simplified and comparatively cheap apparatus with which an electrostatic separation can be effectively and efficiently practiced.

Another object of the invention is the provision of a construction wherein centrifugal force is utilized to obtain. contact between the particles being separated and the charging or separating electrode so as to insure a positive and uniform contact of the particles with the electrode.

A further object of the invention is the provi-- sion of simple yet efl'ective means for controlling the speed of travel of the particles over the electrode and the force with which they engage said electrode and the angle of trajectory of said.

particles into the atmosphere after they leave the separating or charging electrode or such other support as they may be traveling upon.

Another and further object of the invention.

is the practice of an improved electrostatic separation with the use of an apparatus having no moving parts.

A still further object of the invention is the provision of a pivotally or otherwise movably mounted particle receiving, conveying and separating conduit or chute.

Other objects, novel features of construction and improved results of the invention will appear from the following description when read in the light of the accompanying drawings.

The present apparatus is directed to the separation and collection .of particles making up a comminuted mass chiefly in accord with their electrical conductivity characteristics but it may also be employed to effect separations on the basis of other physical properties of the particles, as for example, specific gravity, dielectric constant and particle shape.

The invention is not to be limited to the constructions appearing in the drawings and hereinafter specifically described but is to be limited only within the scope of the hereinafter appended claims.

The drawings, accordingly, are to berecognized as merely illustrative of constructions by which the present: invention can be practiced, and it is to be understood that departures from the drawings can be made without departing from the inventive concept.

In the drawings:

Fig. 1 is a perspective view through an apparatus suitable for practicingthe present method.

Fig. 2 is a vertical sectional view through the apparatus appearing in Fig. 1.

v Fig. 3 is a vertical sectional view of the lower end of the apparatus appearing in Figs. 1 and 2 of the drawings and illustrating a slight modification thereof.

Fig. 4 is a, perspective view of a modified form of apparatus suitable for practicing the present method.

Fig. 5 is a vertical sectional view through the apparatus appearing in Fig. 4.

Referring now to Fig. 1 of the drawings, A designates a feed hopper and B a feed pan the lower end of which is disposed above the upper open end 5 of a chute. The chute is completely closed at its front, back and ends and has its upper end pivotally supported upon a shaft 6 carried by the cross arm i of a standard or support 8. v

The chute itself is of a specific construction and configuration and comprises an upper portion or section C which is downwardly inclined and merges into an acutely curved portion or section D which in turn merges into a lower section E which terminates in a separating and discharge chamber F having a pair of outlet openings 9 and ill in its lower end. Preferably the upper portion 0 of the chute is reduced in width as it approaches the curved portion D and the curved portion is comparatively narrow. The portion E of .the chute is for descriptive purposes referred to as' a discharge throat and this throat is of increasing width from the curved portion D of the chute until the throat joins the discharge portion F.

The inner or rear wall of the chute on its inner face and within the chute is provided with an insulator strip II which extends from a point H which is slightly above the bend in the chute to a point I 3 which is approximately the termination of the lower end of the discharge throat at the point where it meets the upper end of the discharge chamber F. On its external side or face this insulator plate carries a current conducting plate or electrode H the extent or length of which is less than the insulator but is suflicient to extend around the bend of the chute and substantially throughout the entire length of the chute throat portion.

The plate electrode is connected by a conductor ii to a suitable source It of high voltage direct electric current supply.

The discharge openings 9 and ill-of the chamof the chamber. The bottom of the chamber between its outlets extends upwardly into a V- shape so as to provide an apex l'l above which is pivotally mounted a divider 18 which from a point exterior of the chamber may be manually adjusted.

A threaded adjusting arm 20 is pivotally connected to the discharge chamber portion of the chute as at 2| and has its opposite threaded end 22 extending through a suitable opening 23 in the upright 8., A finger-operable nut 25 is threadedly mounted on the arm 20 and is of a size and shape to cooperate with the opening 23 to provide a means for swinging the chute on its pivot 6 and holding the chute in its adiusted position. I

The front wall 26 of the chute should be constructed of some good current conducting material and have its inner surface preferably polished. Stainless steel ground and polished would constitute a satisfactory material. The front wall 26 is electrically connected to ground as at 21 and inasmuch as the chute in its entirety would, for manufacturing simplicity. be no doubt made of metal the inner wall 28 of the chute is likewise connected to ground as at 29.

The adjustment afforded the concentrator by reason of thepivotal support of the chute or conduit is important and very advantageous. This construction enables a control of .the speed of movement of the descending particles by varying the degree of inclination of the downwardly inclined portions of the chute. Thus the inertia of the particles is under control and likewise the centrifugal force exerted by the particles upon the curved portion D of the chute is under control. This is of importance because it is highly desirable to assure a good sliding electrical contact of the particles with the outer or front wall of the chute as the particles travel around the bend or curved portion D. In concentrators as heretofore constructed and operated one of the greatest weaknesses lay in the inability to control the contact between particles and the separating electrodeinapositive and uniform manner. The present construction provides such a control and overcomes the recited deficiency in prior concentrators. In the present construction the particles are forced to move downwardly in sliding contact with the curved surface of the outer or front wall of the chute and thus positive and good electrical contact between all of the particles and the separating electrode is assured, as is likewise an electrical charging of all of the particles in accordance with their electrical conductivity characteristics, which charging is essential to a successful separation. It is to be understood of course that the rate of feed of the material is controlled so that a thin stream or layer only of particles is moving down the chute.

The pivotal support for the chute also aifords a convenient and efficient meansof controlling the angle of projection of the particles into the throat portion E of the chute and thence into the separating and discharge chamber F. All of the particles after having been subjected to the electrical charging process in the region of the curved portion D will be discharged into the throat portion E along a substantially fixed angle of trajectory.

The insulation ll may be glass or some suitable form of plastic or rubber. Porcelain enameled steel might possibly be used by spacing it rmmihe grounded body of the separator through the medium of a suitable insulating gasket. The

use of insulation in combination with the plate electrode I4 is however not essential. The purpose of its use if to prevent the possibility of any of the particles tending to reverse their electrical charge and as a consequence be attracted back toward that portion of the front wall of the chute opposed to the plate electrode H. In other words, if any substantially electrical conducting particles reached the plate which would not be impossible, in the absence of the insulator II, an undesired change in the state of revision of the electrical charge of these particles would occur. is a feature which could be dispensed with, and particularly so if the spacing of the front and rear walls of the chute and other variables were proprly controlled to reduce to the minimum the possibility of any particles actually engaging the plate electrode It. By the use of the insulation higher voltages which produce higher forces may be used.

The degree of the curve of the curved portion D of the chute can be varied in very wide limits as can also the length of the curved portion of the chute. The important point is to assure a comparatively prolonged contact or series of contacts under centrifugal force or pressure between the particles and the stationary separating electrode. It has been found that even the more or most electrically conducting particles require this prolonged contact to insure the proper transfer of electrical charge.

For the best results the mixed mass of particles to be separated should be heated or dried before being fed to the hopper A. It could also be desirable to size said particles within reasonable limits. From the hopper the material is uniformly fed to the feed pan B which extends throughout the full transverse length of the upper end of the chute.

The intermixed particles cascade down the upper downwardly inclined portion 0 of the chute and by inertia against the outer or front wall 26 of the chute at its curved section D. The curved portion D as well as the discharge throat portion E of the chute are traversed by an intense electrostatic field. The curved portion D of the chute by reason of the centrifugal force of the traveling particles around the bend causes the particles to engage the front wall of the chute under pressure and to slide downwardly over said wall, for a considerable distance, in firm and good electrical contact. The particles being in contact with the front wall 26 of the chute will acquire an electrical charge of the same region of the chute traversed by the electrostatic field will acquire an electrical charge in different degrees.

The front wall 26 of the chute where'it forms the front or bottom wall of the discharge throat portion of the chute is curved to provide a convex surface 30.

Those particles having the greatest degree of electrical conductivity will be repelled by the Hence the insulator is a safety feature butencasvi front wall .26 .of the chute and tend to move towards the inner wall 28 of the chute. The degree to which the particles are repelled will be in accord with their acquired charge and hence their degree of conductivity. Those particles which are either poor or non-conductors and have therefore failed to acquire a substantial charge will tend to travel along the inner face of the front wall 26 of the chute.

When the particles reach the chute discharge throat they enter into the separating and discharge chamber F which is comparatively large. The good conductors by reason of being drawn toward the inner chute wall 28 are projected and fall into the far or rear end of the separating chamber, that is, to the left side of the divider finger i8 and pass outwardly through the chamber outlet III for collection in any suitable manner. The poorer and non-conductingparticles which are traveling along the front wall 26 of the chute will when they reach the convex surface 30 thereof move outwardly from this surface but will not be projected sufiiciently far to pass over to the left side of the divider l8. Consequently these particles will fall through the space at the right side of the divider l8 and be discharged through the opening 9 for suitable collection separate and apart from the collection of the particles of good electrical conductivity.

In the separation the speed of downward travel of the particles in the upper portion C of the chute is of importance because it will determine the inertia'of the particles and the centrifugal force exerted by the particles as they are constrained to travel around the bent or concave portion D of the chute. The angle of trajectory of the particles from the discharge throat into the spac or separating chamber F is also important. Adjustment of particle speed and angle of particle trajectory can be nicely and conveniently taken care of due to the pivotal mounting of the chute. The degree of downward inclination of the upper chute portion and the angle of trajectory imparted to the particles can be quickly and properly adjusted by the mere manipulation of the finger nut 25.

Final segregation of the better from the poorer or nonconducting particles is obtained by proper positioning of the divider i8.

The construction appearing in Figure 3 of the drawings is a modification of the apparatus appearing in Figure 1 and discloses the use of an air suction on or in combination with the Figure 1 apparatus.

The construction of Figure 3 is identical to the Figure 1 construction with the exception of the .air suction feature and accordingly, for the most part, identical reference numerals and characters are used on both Figures 1 and 2 of the drawings, and the following description is limited to making clear the manner of applying the air suction.

' chamber 3'! which is provided with an outlet 38 adapted for connection with any suitable air suction mechanism (not shown) so as to create an air current. This air current is indicated by the arrows 33 and 40 from which it will be seen that air is drawn into the upper open end 5 of the chute or passageway along with the delivery of through the open ends 45 of these socks. The

air suction normally tends to close the open ends of the socks but the weight of the discharging particles is suflicient to force the socks open and to discharge against the slight negative air pressure.

The provision of an air suction is not essential to the apparatus of Figure 1 but under some conditions could be found desirable in assisting the particles, particularly the smaller ones which might not fiow so freely from gravitational force, to acquire the velocity desirable for obtaining the best possible separationand in some instances to step up the speed of travel of the particles so as to increase the capacity of the concentrator.

In connection with this use of airflow, it is desirable that the air be conditioned by cleaning, drying and heating. If desired the air may be recirculated by use of a closed system.

This particular form of apparatus has all of the advantages and benefits enumerated in respect to the Figure 1 construction.

In respect to both the Figure 1 and Figure 2 constructions the mass is illustrated and deo therewith so as to have three, four or even more separate streams of particle discharge.

r A still further modification of the invention is illustrated in Figures 4 and 5 of the drawings. Here the same feed hopper A and feed pan B are utilized. The mass composed of the particles discharges from the lower end of the feed pan into a feed device J the upper end of which is open and has at its front a downwardlyand rearwardly inclined wall over which the particles which slide in response to gravity enter the upper end of a feed spout which is downwardly and forwardly inclined so that the particles slide downwardly and forwardly over the bottom or rear wall 5| of the spout to-discharge in a forwardly direction upon the top of a separating roll electrode K which is continuously rotated, as indicated by arrow, in the direction of the discharge of particles from the particle feed spout.

The separating electrode K is provided with a shaft 52 the ends of which are rotatable within bearings 53 mounted upon the horizontally disposed arms 54 of any suitable support or standard such as for instance that illustrated in Figure 1 of the drawings. At one end the shaft is provided with a pulley 55 overwhich is trained a belt or the like 56 for connection with any suitable source of power to impart arotary motion to the shaft and its electrode K.

It is desirable to maintain the electrode Kin a clean and polished condition and for this purpose a suitable brush 51 is provided. This brush has a shaft 56 extending beyond its ends and these extending end portions are rotatably supported in suitable bearings 53 mounted upon the horizontal supportin arm 5!. At one end the e an shaft 58 is provided with a pulley 60 and at the :same end the roller electrode shaft is provided with a pulley Si. A belt 82 or the like provides a connection for driving the brush 51' so that it may accomplish its cleaning and polishing function in respect to the roller electrode.

High voltage direct current is provided from a suitable source 62 from which extends a conductor 63 for supplying current to a fine tautly drawn wire electrode 84 which extends throughout the length of the separating electrode K and in parallel relation thereto but spaced therefrom a suitable distance preferably from 1% to 2 inches. This wire electrode is positioned forwardly of the point of contact of the particles with the upper surface of the roller electrode K and is maintained at a potential suflicient to cause ionization but below the sparking point and can be of either positive or negative polarity. The position of the wire electrode and its potential is such as to create an electric field of considerable extent through which the particles must pass and during which passage the particles are subjected to an electrical bombardment so that said particlesare charged electrically.

The wire electrode 54 can be of either positive or negative potential and the roller separating electrode K is grounded at 65. I

The feed is such that the particles are delivered to the roller electrode with an initial movement in the same direction as the movement of the electrode and are deposited on the roller in a manner to reduce to the minimum any bouncing of the particles. Additionally the overhang 66 of the lower front end of the feed spout tends to shield the particles from the electric field until the particles are actually on the roller.

This shielding of the particles is obtained by grounding the feed mechanism J as indicated at 96.

A particle receiving and conducting conduit or chute having close similarity to that illustrated in Figure 1 of the drawings is associated with the roller electrode K. This conduit or chute has an open upper end 61 closely associated with but in separated relationship to the outer face or surface of the roller. This open end is disposed in front of the roller so that it faces the direction of rotation of the roller and is positioned at approximately a point where the curved surface of the roller is disposed in a perpendicular plane.

The conduit or chute has an upper downwardly and forwardly inclined portion L which extends from the Open upper end 61 downwardly to communicate with an acutely curved portion M which preferably is of reduced width in respect to the width of the conduit throughout the greater extent of the length of its upper end por tion L. The portion M merges into a throat-like portion N which throughout its length is of greater width than the curved portion M. The front or bottom wall of the throat is curved reversely to the portion M so as to provide a con vex curved portion 68 which constitutes the front wall of a separating and discharge chamber 1? in the lower end ofwhich is positioned the discharge outlet openings 69 and 10. The wall separating the discharge openings is V-shaped terminating in an apex H above which is positioned the manually adjustable pivotally mounted dividing finger 12.

The rear wall of the conduit or chute throughout the extent of the curved portion M of the chute and the throat portion N is provided with 8 a suitable insulator 13 having on its outer or rear face a current conductor constituting a plate electrode 14 to which high voltage direct current is supplied by a conductor 15 connected to the current supply element 62.

At its innermost or rear side the conduit or chute is provided with a particle receiving and directing element 15 which is of plate-like form and extends from the upper end 61 of the conduit or chute to merge into the lower end ll of the rear or top wall of the chute, as indicated at 18. At its upper end where this element 18 is closely associated with the separator roller K it is given a curvature 19 similar to the curvature of the roller.

Like the particle conduit or chute of the Figure 1 construction the chute of the present form of' the invention is pivotally supported. This pivotal support comprises extending the end walls 80 of the chute rearwardly to provide fln-like members 8| the upper ends of which are provided with openings through which the shaft 520i the separating roller K extends. By this construc-' tion the conduit or chute is pivotally supported upon the shaft 52. The manner of manually swinging the conduit or chute upon its pivotal support and maintaining it in any desired set position is similar-to that illustrated in Figure 1 and heretofore described. Repetition of this description is unnecessary and accordingly similar reference numerals are used on this constructional feature to the like constructional feature in Figure 1 of the drawings.

The chute is composed of a smooth highly polished current conducting material and is grounded as at 83. i

The operation of the apparatus illustrated in Figures 4 and 5 is as follows: The mass composed of the particles which have been preferably although not necessarily previously heated or dried is delivered to the top of the separating roller K. As they feed out upon the roller the particles are carried thereby through the field of ionic bombardment created by the wire electrode 64. The speed of rotation given the roller K is that which it is determined will result in the best separation in view of the nature of the particles being operated upon and the particular size range of said particles.

5 All of the particles as they pass through the electrical field 84 will receive an electrical charge. Those particles which are the best conductors will rapidly and promptly lose this charge due to their electrical contact with the roller while the 5 remaining particles will lose their charge less rapidly until those particles having little or no property of electrical conductivity will retain their charge for a very considerable length of time. Due to inertia and centrifugal force as well as the force of gravity these particles when they have been carried to a point just above the open upper end 61 of the chute will for the most part be projected outwardly from the roller. The particles having the highest degree of electrical conductivity will be projected from the roller at the greatest angle and at an earlier stage than the remaining particles with the result that they will pass over the top of the open upper end of the chute and fall into the space 85 between the chute anda wall 94 or the like and can be col- 9 with good and poor conductors whose trajectory has been affected by interference from other particles. This intermediate portion of the mass will be projected into the open upper end 61 of the chute and will traverse the same and be separated as described in respect to the Figure 1 construction of the invention. In other words, this intermediate or middlings portion of the mass will be separated into two separate streams for separate discharge through the outlets 69 and 10. Those particles of this middlings group which are the best conductors will pass to the left of the cutting finger 12 for discharge at 69 while the poorer conductors will pass at the opposite side of the cutting finger for discharge through the outlet 10. These poorer conductors will tend to retain some of their initial charge sprayed on by the wire electrode 64. This residual charge is of opposite polarity to that of portions M, N of the front wall of the chute. The consequent attraction of these particles to the front wall will assist in causing them to report as desired at the outlet There will be a portion of the mass which by reason of the particles thereof having poor or no attribute of electrical conductivity will remain on or travel with the roller into the space between the roller and the separating element or plate 16. Some of these particles will drop from the roller and slide down the plate element 16 but others of them will remain adhered to the roller until they are forcibly removed therefrom by the brush 51. These particles are commonly referred to as tailings and are all carried into the space 88 between the chute and the wall or partition 89 and are discharged for collection at the lower end 90 of this space.

It will be obvious that like my Figure 1 construction those particles which traverse the conduit or chute will move in a curved path in contact by reason ofinertia and centrifugal force with a stationary electrode which is of course the front wall of the portion M of the chute. The advantages of this feature need not again be recited. The primary object of this particular form of-the invention is to obtain a more accurate separation than that obtained in the Figure 1 construction. In the Figure 1 construction the particles are separated into only two streams, whereas in the Figure 3 construction the particles are separated into four streams and those particles constituting the middlings are worked twice, that is to say, they are worked when on the separating roller K and are again worked in the conduit or chute.

The advantages of a-pivotally mounted conduit or chute have been enumerated in respect to the Figure 1 construction of the apparatus and need not be here repeated. It is suflicient to state that this apparatus will perform efficiently in making a fully acceptable separation of the mass. It might however be mentioned that particle size and mass will influence the chute dimensions and angle of inclination and the height and position of the feed pan B. When particles of small size and/or mass are being treated it has been found desirable to give to the particles a relatively long drop so as to give to them a comparatively high speed of travel and to reduce the radius of the curvature of the part D of the chute. "Particle velocity can also be controlled to a considerable extent by the positioning of the feed pan B.

I claim:

1. An apparatus for electrostatically separating and separately collecting in accordance with their electrically responsive characteristics the particles making up a comminuted mass of material comprising, fa stationary separating conduit having downwardly and reversely inclined elongated upper and lower end portions connected by a curved intermediate portion, means to feed a stream of particles into the upper end portion of the'conduit, means to set up an electrical field in the curved intermediate portion of the conduit, and the lower end portion of the conduit having an outlet for the discharge of the particles from the conduit.

2. A construction as defined in claim 1 wherein, means is provided for creating a suction downwardly through said conduit.

3. A construction as defined in claim 1 wherein,

said conduit is pivotally supported and means is provided for swinging said conduit on its support'and securing the conduit in any one of a plurality of adjusted positions about its pivot.

4. A construction as defined in claim 1 wherein,

the means to feed the stream of particles into the conduit comprises a rotating roller electrode to which the stream of material is fed at a point remote to the conduit, and means subjecting the stream of material to an ionic bombardment throughout a portion of its travel on said roller electrode to the conduit. 1

5. An apparatus for electrostatically separating and separately collecting in accordance with their electrically responsive characteristics the particles making up a comminuted mass of material comprising a closed chute having open upper and lower ends, said chute having a downwardly inclined upper portion and a reversely downwardly inclined lower portion interconnected by a curved intermediate portion, the inner wall of the curved portion of the chute being connected to a source of high voltage current supply and the puter wall I in the bottom of said chamber, and means within said chamber for dividing the falling particles into two separate streams in accord with the distance the particles are projected forwardly into said chamber.

6. A constructoin as defined in claim 5 wherein, said chute is pivotally, supported, and means is provided for swinging said chute about its support and securing the chute in any one of a plurality of selected positions.

"7. A construction as defined in claim 5 wherein, means is provided for creating a suction downwardly and transverse the chamber of the lower end portion of the chute.

8. An apparatus for electrostatically separating and separately collecting in accordance with their electrically responsive characteristics the particles making up a comminuted mass of material comprising a rotatable roller separating electrode and means for rotating the same, means to feed a stream of particles to the top of said roller, a charging electrode in spaced relationship to said roller electrode for subjecting the material fed to said roller to ionic bombardment, a chute associated with said roller and having an open roller quickly after their deposit on the roller to ascaari 11 pass over the-top of said chute, the upper end of said chute being additionally positioned to provide a space between its upper end and the roller to permit the particles which adhere to the roller to pass in back of the chute, said chute having elongated upper and lower end portions downwardiy and reversely inclined and connected by a curved intermediate portion, the lower end portion of said chute provided with an outlet, and the outer wall of the curved portion or said chute constituting a plate of a charged condenser whose dielectric is the air space between said outer chute wall and the inner wall 01 said chute.

9. A construction as defined in claim 1 wherein, the lower end portion of the conduit is provided with at least two outlets for the discharge therefrom of two separate streams of particles.

10. A construction as defined in claim 5 wherein, the chamber is provided with a pair of outlets in its bottom one each of which is for the passageway 01 one of the two streams into which the tailing particles are divided.

11. A construction as defined in claim 8 wherein, means is provided in back of the chute to receive and direct the particles which pass in back of the chute to a place of discharge.

12. A construction as defined in claim 1 wherein, said chute is supported to permit it to be moved to vary the'degree oi downward inclinatrode to permit the chute to be swung to vary the degree of downward inclination of the upper and lower end portions of the chute.

15. An apparatus for electrostatically separating and separately collecting in accordance with their electrical responsive characteristics the particles making up a comminutedmass of material comprising, an open ended 'se'parating conduit having therein intermediate itsends a curved portion, means to reed astream oi! particles into one of the open ends of the said conduit, means to cause said stream of particles to move at a considerable speed through said conduit toward its opposite end for discharge therefrom, the inner wall of the curved portion of the conduit being connected to a source of high voltage current supply and the outer wall of said curved conduit portion being electrically grounded to create in said conduit portion an electric field through which the stream of particles must pass, the discharge end or the conduit being enlarged to form a chamber into which the particles composing the stream are projected and may fall in response to the forces exerted upon them, and means within said chamber dividing the falling particles into at least two separate streams for discharge through the outlet end or the conduit.

\ j H WILLIAM 'BYRD, Ja.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS

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