US2772777A - Apparatus for magnetic separation of ores - Google Patents

Description

Dec. 4, 1956 A. J. QUENEAU APPARATUS FOR MAGNETIC SEPARATION OF ORES Filed Oct. 20, 1954 4 Sheets-Sheet l INVENTOR AUGUST/N L. J QUENEAU ATTORNEY Dec.- 4, 1956 A. J. QUENEAU 2,772,7 7

APPARATUS FOR MAGNETIC SEPARATION OF ORES Filed Oct. 20, 1954 4 Sheets-Sheet 2 l T III INVENTOR JjA- AUGUS77N 1.. .1 QUENEAU ATTORNEY 4 Sheets-Sheet 3 A. L. J. QUENEAU APPARATUS FOR MAGNETIC SEPARATION OF ORES Dec. 4, 1956 Filed Oct. 20, 1954 INVENTOR a AUGUST/N L. .1 QUENEAU BY MIA-M a ATTORNEY a=r14- I Dec. 4, 1956 A. J. QUENEAU APPARATUS FOR MAGNETIC SEPARATION OF ORES Filed Oct. 20; 1954 4 Sheets-Sheet 4 AUGUST/N L. \J. GUENEAU I'Illilll lulmllimini Thur";

ATTORNE United States Patent APPARATUS FOR MAGNETIC SEPARATION OF ORES Augustin L. J. Queneau, Far Hills, N. J.

Application October 20, 1954, Serial No. 463,394

Claims. (Cl. 209 219) rials have been unsuitable for use directly in the blast furnace or for smelting according to other conventional smelting practices. Owing to the rapid exhaustion of the known deposits of high grade iron ores, the iron andsteel industry will in the near future be required to depend more and more on the available lower grade ores. Therefore, it has become important to develop economical means for separating the iron mineral values from the gangue materials of these lower grade ores.

The iron minerals in these ores occur in various forms. In many of the larger bodies, the iron minerals are of low magnetic susceptibility such as hematites, martites, goethites, siderites and limonites. In some of these deposits the iron minerals of low magnetic susceptibility occur in admixtures with varying amounts of magnetite which by itself does not present the same problem of separation from gangue constituents as the less susceptible iron minerals, but when present even in minor proportions in ad mixture with such minerals as hematite, creates serious operating problems when it is sought to separate the less susceptible minerals by magnetic separation procedures involving the use of high intensity magnetic fields.

For example, when an ore [containing a mixture of magnetite and hematite is suddenly brought under the influence of a high intensity mg-anetic field'suoh as may be produced by electromagnetic means, the attraction of the magnetite may be so great as to cause clogging of the relatively restricted passageway through which the ore is fed in the separation treatment past the poles of the high intensity magnet. Not only does the magnetite immediately collect directly on the pole pieces of the magnet, if they are directly exposed to contact with the mineral particles, or on the non-magnetic partition walls separating j the magnet from the flow passage for the ore when such an arrangement is provided, but it will tend to carry along with it less susceptible mineral particles and even nonmagnetic gangue particles. This sudden collection or clumping of the magnetite particles with the resultant entrapment of gangue particles tends to undesirable lowering of the grade of the recovered concentrate and to defeat the purposes of the separation.

This difficulty may be avoided by first passing the suitably ground ore through a relatively low intensity separator and then later passing the residue from this separation through a high intensity separator, but this involves provision of at least two separator installations with their appurtenant ore and pulp feeding and concentrates re- 2,772,777 Patented Dec. 4, 1956 2 ceiving and handling devices, with consequent increase in the capital investment for a plant of a given capacity and greatly increased operating expense for labor, power and maintenance.

A further disadvantage of a magnetic separation plant wherein the ore is treated in one separating unit and then transferred to a second separating unit resides in the fact that the magnetically susceptible particles rather quickly become demagnetized on removal from the influence of the magnetic field, so that on being fed to the second separator there is a short but nevertheless substantial time interval after the particles have again been brought under the influence of the magnetic field during which they become re-activated or magnetized and then responsive to the forces exerted upon them to attract them toward one or the other of the poles of the magnet.

Although the problem of clumping and entrapment of gangue particles is not present to the same degree when dealing with mixtures of magnetically susceptible minerals of the lower degrees of magnetic susceptibility such as hematite and the other iron minerals above mentioned that do not contain magnetite, it is nonetheless desirable to subject ore mixtures of these minerals to a succession of magnetic separations and also preferable to progressively increase the magnetic intensity of the fields to which the ore is subjected. Here again, if the retreatment is conducted in a diiferent separating unit the same objections from the standpoint of increased capital investment, labor costs and operating and maintenance expense are presented. What is of still greater importance from the technical point of view is the fact that the ore particles must be re-magnetized in the course of the initial stages of each subsequent separation, and since these minerals have lower magnetic susceptibilities the time intervals required for their remagnetization are greater. Furthermore, the orientations of the magnetized but as yet uncollected particles within the pulp with respect to one or the other of the poles of the magnet, or more particularly, with respect to their attraction toward the sides of the flow path where they can be more readily acted upon When they are brought under the influence of the next set of magnets, are destroyed and all advantage that would otherwise be derived from the fact that these particles have been drawn closer to one or the other side of the separation box is lost.

It is an object of the invention to provide improvements in methods and apparatus for separating mineral values from ore pulps in which values of high magnetic susceptibility, such as magnetite, as well as those of lower magnetic susceptibility, such as hematite, limonite, goethite and the like, may also be separated and recovered in the course of a single multiple stage operation.

It is a further object of the present invention to provide a multiple separator in which the material undergoing treatment is subjected successively and ina continuous operation to a series of magnetic fields of increasing intensity While maintaining the magnetically susceptible mineral constituents in a magnetized state throughout the course of their travel through the separator until they are collected at one of the several stages of the separation operation'and are removed from the liquid pulp suspen sion in which they are presented for the separation action;

It is a further object of the invention to provide a multiple separator of the wet type wherein a liquid suspension of magnetically susceptible mineral particles is caused to flow in the form of a liquid suspension under a constant hydrostatic head and at a substantially constant velocity successively through a series of magneticfields of progressively increasing intensity.

It is a further object of the invention to provide in a multiple separator means for varying the effective strength of the magnetic fields progressively and selectively as the ore pulp passes through the separator.

It is a still further object of the invention to provide in a multiple separator having at least three pairs of rotating poles arranged in vertically-spaced opposed relation on the opposite sides of the flow path for a descending column of ore pulp, means for withdrawing as a concentrate the mineral particles attracted at a plurality of the separating zones preceding the final separation zone and leading such concentrates to a common outlet, such means being so associated with the separator as not to obstruct or restrict the flow passage for the pulp through the several separating zones.

It is still another object of the invention to provide in a multiple separator of the wet type polar extensions energized by electromagnetic means and disposed in parallel relation to the flow path for the descending column of pulp in advance of the initial separating stage and the association with such polar extensions of means which serves both to counteract the tendency of the polar extensions to arrest the downward flow of the more magnetically susceptible mineral particles before they reach the point of concentrates withdrawal at the first high intensity zone and which cooperates with such polar extensions in promoting the magnetization and polar orientation of such susceptible particles that is favorable to their separation at the separation zones.

It is a further object of the invention to provide an electromagnetic separator of the opposed rotating pole piece type' wherein the effective strength of the magnetic field developed between the opposed rotating pole pieces is varied by varying the air gaps between such rotating pole pieces and the stationary poles, or polar extensions of said stationary poles, with which the rotating pole pieces are respectively associated.

Other objects and advantages of the invention will be made apparent by reference to the following specification and the accompanying drawings, in which:

Fig. 1 is a plan view of one form of separator that may be used in practicing the present invention;

Fig. 2 is a vertical section on the line 2-2 of Fig. 1;

Fig. 3 is an elevation taken on the line 3--3 of Fig. 1;

Fig. 4 is a part vertical section and part elevation on the line 4-4 of Fig. l;

Fig. 5 is a plan view of the bottom of the separator;

Fig. 6 is a section on the line 66 of Fig. 4;

Fig. 7 is a section on the line 77 of Fig. 4;

Fig. 8 is an end elevation of sleeve for modifying the gap in the magnetic field;

Fig. 9 is a view similar to Fig. 4 illustrating a modified form of the separator;

Fig. 10 is a section on the line 1010 of Fig. 9 with the fixed polar extension removed;

Fig. 11 is an elevation of the face of one of the fixed polar extensions; and

Fig. 12 is a section on the line 1212 of Fig. 11.

Fig. 13 is a view similar to Fig. 4 illustrating a modified form of separator; and

Fig. 14 is a part section of still another form of separator with parts omitted.

In U. S. Patent No. 2,088,364 of myself and Edwin E. Ellis and in my U. S. Patents Nos. 2,154,010, 2,258,194 and 2,290,892, there are disclosed certain methods and apparatus whereby the separation of mineral values of relatively low magnetic susceptibility from low grade ores can be accomplished. In the use of the apparatus disclosed in the aforesaid patents the ore, in the form of a pulp with water, is caused to flow under a constant hydrostatic head past rotating poles which attract and divert the magnetically susceptible material from the path of flow of the pulp and thus deliver valuable portions of the ore into containers separate from the gangue materials. In Patent No. 2,258,194, I have described a duplex separator in which the flowing material is subjected to the action of two concentrated magnetic fields successively to effect a more complete separation of values from the gangue.

In accordance with the embodiment of the invention shown in Fig. l12 inclusive, a magnetic field is established in a similar manner as described in the aforesaid patents by the provision of cores of highly permeable iron or steel which are each suitably wound with a multiplicity of turns of wire to form one or more coils for each core adapted to be supplied from any suitable source with direct current. Each pair of cores is connected by a yoke to complete the magnetic circuit except for the gap between the cores. Polar extensions are connected to the cores to afford a relatively long vertical gap. Between the extensions, a separator box is disposed through which the pulp flows. The pulp is supplied at the top. The bottom outlet of the separator box has a restricted opening and an overflow weir is provided at the top so that a constant hydrostatic head is maintained in the downwardly flowing pulp as described in the patents heretofore mentioned.

The walls of the separator box have a plurality of semi-cylindrical recesses formed therein. In each recess a rotating pole member is mounted on a suitable shaft. The shafts are driven so that all of the pole members on one side rotate in a clockwise direction, and those on the other side rotate in a counterclockwise direction. Each pole member is cylindrical in form and provided with a plurality of rows of teeth in the periphery thereof which serve to concentrate the lines of flux at the edges of the teeth in known manner.

At the top of the separator box there are two rotating cylindrical poles of relatively small diameters, the purpose of which is to prevent agglomeration of the mineral values at the top of the box due to the attraction of the polar extensions 42. The attracted particles are moved downwardly with the pulp to enter the fields of the lower and larger rotating poles which effect the initial separation by drawing the magnetically susceptible particles inwardly toward the walls of the separator box and downward laterally past partitions which separate the attracted particles from the bulk of the pulp. This operation is repeated as the pulp enters successively the zones of the lower rotating poles.

The attracted particles at each of the upper levels are directed by sloping walls toward and into a downwardlyextending pipe at the side of the separator box and are thus removed. The particles deflected by the lowermost set of rotating poles are separated similarly and are withdrawn through a separate outlet while the gangue remains in the pulp which is withdrawn at the bottom through a restricted outlet adapted to permit limited flow so that the hydrostatic head is maintained in the separator box.

Thus it is possible to secure two sets of concentrates. Those from the upper rotating poles are mixed and form the high grade product. the lowermost set of poles constitute a middlings fraction of a lower grade. The tailings consist of the gangue materials in the pulp and are substantially free from values.

During the passage of the material through the separating path it is subject continuously to the stray magnetic current and hence the susceptible particles do not lose polarity. This materially assists the deflection of the susceptible particles as they enter the successive concentrated fields.

The separated materials from Referring to Figs. 1-12 of the drawings, 5 indicates the separator box which is supported in any suitable manner. Inlet pipes 6 permit the introduction of the pulp. The pipes have openings 7 below the upper surface of the pulp which is maintained by means of a weir 8 connected to an outlet pipe 9. At the bottom of the separator box, outlet pipes 10 are provided. Flow through these pipes is controlled by diaphragms 11 each having an opening 12 of restricted size therethrough to limit the fiow of the pulp through the separatorbox and maintain a constant hydrostatic head in the flowing pulp.

The sides of the separator box 5, as shown in Fig. 4, are provided with a plurality of arcuate recesses 13 on each side thereof. In these recesses, rotating polesg14, 15, 1 6, 17 and 18 are mounted: on shafts 19, 20, 21, 22 and 23 which are suitably journaled in frame members 24 and 25. The shafts 19-23inclusive are driven from any suitable source of power by gears 26 and 27 mounted on the shafts 19. As shown in Fig. 3, pinions 28 and 29 mesh with the gears 30 on shafts 20, 21, 22 and 23, so that the shafts on opposite sides of the separator box are driven in opposite directions, clockwise on one side and counter-clockwise on the other. Each of the rotating poles -18 inclusive is slotted longitudinally and peripherally of the surface portions thereof to provide a plurality of projecting teeth 32.

Beneath each of the arcuate recesses 13, an upwardly directed partition 33 defines a compartment to one side of the main downward flow path for the pulp suspension.

These partitions terminate in spaced relation to the arcupreferably at an angle of 45 although this angle may.

be modified. The magnetically susceptible particles which are withdrawn into the pipe 35 pass downwardly through the pipe and are discharged through an outlet 36 to a suitable receptacle (not shown) as the high grade concentrate.

The concentrates receiver is normally kept filled with water and preferably there will be hydraulic pressure maintained therein sufiicient to create a certain amount of back flow setting up a hydraulic barrierin the concentrates compartments at each separating zone and thereby minimizing any tendency for liquid to flow outwardly from the mainflow of the pulp suspension through the separator box into the concentrates compartments with the concentrates attracted to. and moved along thesurfaces of the arcuate wall sections. .The pulp remaining after the separations at the several higher intensity zones of the poles 15, 16 and 17 is finally subjected to the ac-. tion of the rotating'poles 18 which draw the remaining magnetically susceptible particles inwardly and past a partition 37. These particles pass into an outlet 38 and consist of a lower grade of concentrate. The gangue materialsin the pulp arev then withdrawn as previously described, through the outlet pipes 10. I v i a Th uppermost rotating poles 14 have no separating action. They are relatively'small, and their function is to prevent agglomeration or clumping at the top of the separator-box. The magnetic'fiux flowing between these small rotating poles i4 acts to magnetize the magnetically susceptible particles and render them more readily attracted toward and into the path of the flux between the rotating poles 15, thus accelerating the separating action.

'In order to supply the magnetic flux, cores 39 are 351 inch.

connected to a yoke 40 and provided with coils 41 each carrying a predetermined number of turns of wire. These coils are connected to a suitable source of direct current. Two coils are provided for each core member so that the strengh of the field developed may be varied by energizing one or both of the coils as operating conditions may require. The magnetic circuit is closed through the yoke 40 except for the gaps between polar extensions 42 which are secured to the cores 39. The polar extensions 42 extend upwardly along the sides of th separator box 5 and are provided with a plurality of arcuate recesses 43 in whichthe several rotating poles 14, 15, 16, 17 and 18 operate. The faces of the polar extensions 42 adjacent the sides of the separator box 5' are grooved to provide a plurality of projections 42'. The projections 42 afford a plurality of relatively concentrated magnetic fields extending through th path of travel of the pulp as it descends in the box. These concentrated fields have the effect of diverting the magnetically susceptible particles toward the sides of the separator box, so that they pass readily into the zones of maximum magnetic intensity provided by th rotating poles 15 to 18 inclusive. Consequently the separating elficiency of the rotating poles is increased and maximum separation is easily attained.

It is desirable to vary the magnetic flux at various levels of the separator. This is accomplished by the provision of gaps of different widths between the surfaces of the arcuate recesses 43 and the several rotating poles. It will be seen, for example, that the gap surrounding the rotating pole 15 is considerably wider than that surrounding the pole 16, which in turn is wider than the gap surrounding the pole 17. These gaps may vary in width from, for example, 1 /2" to approximately th of an In order to permit adjustment of the gaps or clearances, semi-cylindrical sleeves 44 of magnetic material are provided as shown in Fig. 8. These may be inserted in the gaps and secured by screws applied through openings 45 as shown in Fig. 8. Sleeves of different thicknesses may be available so that any desired adjustment-of the gap may be made to modify the available magnetic flux in connection with the rotating poles at different levels of the separator box.

Instead of sloping partitions 34 as shown. in Fig. 2, I may utilize, as shown in Figs. 9 and 10, a partition 33' having its edge spaced from the wall of the separator box and forming a trough in which a screw conveyor 46 is supported on a shaft 47 and driven from any-suitabl source of power to feed the separated material into a pipe 35 which discharges the concentrate at the bottom of the separator in the manner previously described.

It will be understood that the poles 39 and the polar extensions 42 should be made of iron or steel of'relatively high magnetic permeability so as to afford the maximum concentration ofmagnetic flux at the desired points for the current-consumed. The rotatable poles 14, 15, 16, 17 and 18 should likewise be made of similar iron'orsteel. The shafts uponwhioh the rotatable poles are mounted should be made of stainless steel or other nonmagnetic material of suitable strength to withstand the powerful force of the magnetic field which tends to distort the shafts. The separator box 5."and is appurtenant parts must be made of non-magnetic material such as brass, aluminum and the like, in order that the magnetic flux may function properly to draw the magnetically suscepticle particles into the desired channels and thus separate it from the pulp.

The arrangements which insure that the downwardly flowing suspension of magnetically susceptible ore'particles will be subjected to progressively stronger magnetic fields as it passes through the multiple stage separator may be provided in various ways other than as-above described. Amodified form of multiple stage separator having the above objective is shQ n in Fig. 13. This separator has a generally" similar arrangement of the arcuately recessed wall portions and the common concentrates discharge connections as is shown in Fig. 4. In thisseparator the pulp suspension is caused to flow downwardly p'ast opposed pairs of rotating pole members 15, 16, 17 and 18 in succession.

The two upper pairs of opposed pole members 1.5 and 16 are supplied with magnetic flux by means of cores 39a which are connected to a yoke 40a and carry coils 41a. The cores 3911 are provided with polar extensions 4211 having arcuate recesses 43 in their faces directed toward the separator box to receive th pole members 15 and 16. The magnetic circuit is closed through the yoke 40a except for the gaps between the polar extensions 42a and the rotating pole members on the one hand and the opposed rotating pole members themselves on the other. The gaps between the polar extensions and the rotating pole members are usually kept as small as possible without interferring with the clearance and free rotation of these members. The maximum concentration of flux is maintained at the throat areas between the opposed pole members.

The two lower pairs of opposed pole members 17 and 18 are similarly supplied with magnetic flux by means of cores 3911 which are connected to a yoke 40b and carry coils 41b. The cores 3% are associated with polar extensions 42b which receive the pole members 17 and 18 in the arcuate recesses 43 as in the case of the upper electromagnetic assembly.

The provision of two separate yokes with corresponding cores and coils has the advantage that the magnetic intensity at the different levels of the separator may be varied by varying the number of turns of wire on the cores so as to obtain any desired difference in the intensity of the magnetic fields obtainel.

The polar extensions 42a and 42b have their faces adjacent the sides of the separator box 5 grooved to provide a plurality of projections 42'. The projections afford a plurality of relatively concentrated magnetic fields extending across the path of travel of the pulp as it descends in the separator box, and these fields have the effect of diverting the magnetically susceptible particles toward the sides of the separator box so that they pass readily into the zones of maximum intensity provided by the rotating poles 15 to 18 inclusive. Consequently the separating efficiency of the rotating poles is increased.

In addition to the variation in the magnetic intensity at the different levels of the separator that is brought about by using at least two yokes with their associated cores and coils wound to develop differing magnetic intensities, I propose further to vary the flux concentrations between the rotating pole pieces by appropriately varying the construction and composition of the individual rotating pole pieces with that end in view. Thev magnetic permeability and tendencies for flux concentrations at select- 7 ed portions of the surfaces of the rotating pole pieces may be regulated in various ways known'to the art and described in my early patents above mentioned. As disclosed by way of example in my copending application Ser. No. 463,392 filed or even date herewith, and which is likewise a continuation-in-part of my copending application Serial No. 179,458, the poles 15 may be formed of laminations consisting of alternate sheets of low metalloid steel and of zinc. In the example given the thickness of the sheets used in forming these poles is .075 inch. These pole pieces are appropriately cut or scored in their surface areas to develop teeth and sharp edges at which the flux becomes still further concentrated. As shown in Fig. 13, the pole pieces 15' are also preferably formed with larger longitudinally extending recesses 50, and the pole piece 15 on one side is so mounted with relation to the pole piece at the opposite side as to insure'that the recesses 50 on the one side are in out of phase relation to'the recesses in the pole piece on the other side. This arrangement is more particularly described and claimed in my copending application Ser.

No. 463,392 aforesaid, and is particularly useful for separating particles of high magnetic susceptibility such as magnetite from a mixed ore pulp without danger of bridging.

Preferably the next set of rotating poles 16 is constructed in a similar manner of laminations of low metalloid steel and zinc which may be of similar thickness as in the case of the poles 15 but without provision of the deep recesses as was the case with the poles 15. The cylindrical surfaces are provided with cuts or grooves extending both in a direction parallel to the axis of the pole piece and peripherally to provide teeth and sharp edges at which the flux concentrations may occur.

The rotating poles of the third and fourth sets are similar to the first and second sets as regards the cuts or toothed areas formed at the surfaces, but in the case of the third set they are preferably constructed of laminations of low metall oid steel and zinc, laminations of the steel being .075 inch thick and the zinc .050 inch thick, thus providing a greater cross-section of the ferrous metal for the magnetic flux than in either the first or the second pair of rotating poles. The rotating poles 18 of the fourth set are preferably made of solid low metalloid steel provided with teeth at the cylindrical surface thereof as in the preceding sets. It will be understood that the proportions of the respective laminations where mentioned above are subject to variation and that other modifications may be made in the form of the poles used at the various stages to develop differences in the concentrations of the magnetic flux at the surfaces of the rotating poles according to the particular operating conditions desired to be maintained, those mentioned being merely illustrative of suitable constructions for use in practicing the invention.

The separator illustrated in Fig. 13 is operated in a generally similar manner as that shown in Fig. 4 and which has been previously described herein. The pulp is introduced into the separator box through the pipes 6 and the level is maintained constant by means of a weir adjacent the top of the separator box 5. At the bottom of the separator box, outlet pipes 10 are provided. Flow of the residue of the pulp suspension through the outlet pipes is controlled by means of orifice plates 11 each having an opening 12 of restricted size. By using an orifice plate having an opening 12 of suitable size the flow of pulp through the separator box is so regulated as to maintain a constant hydrostatic head.

The rotating poles 15', 16, 17 and 18 are mounted on shafts 20-, 21,22 and 23, respectively, which are suitably journaled in frame members, not shown. The shafts 2123 are driven through appropriately interconnected gears from a suitable source of power in such manner that the shafts on the opposite sides of the separator box are driven in opposite directions, clockwise on one side and counterclockwise on the other, so that the toothed areas of the respective rotating poles, as they come close to and travel along adjacent to the respective arcuate wall portions, will travel in the same direction as the fiow of the pulp downwardly through the separator box.

Instead of a single" partition beneath each of the recesses at each side of the main downward flow path of the ore pulp suspension, twopartitions 33a and 33b'are provided in the separator box of Fig. 13. These partitions serve to divide the space within the box beneath each of the rotors into a middlings compartment and a concentrates compartment. Suitable connections similar to those described in my copending application Ser. No. 463,392 are provided for leading the concentrates and the middlings that are collected at the different levels to common dicsharge outlets; The discharge outlet for the concentrates is shown at 36 and the discharge outlet for middlings is shown at 38.

A still further embodiment of the apparatus invention is shown in Fig. 14. multiple stage separator includes a separator box having common concentrates discharge outlets and a separate Accordingto this modification thev outlet for the lower grade concentrate or middlings all similarly arranged as in the separator shown in Fig. 4. Provision is made for maintenance of four zones of relatively high magnetic intensity at different levels along the vertical extent of the separator box. The three lower Zones are established by means of rotating pole pieces 16, 17 and 1S suitably supported for rotation within corresponding arcuate recesses 13 and 43, the recesses 13 being formed in the adjacent sides of the separator box and the recesses 43 being formed in the adjacent sides of the polar extensions 42. These extensions are respectively secured to the core members 39 of the electromagnet constituted by such cores, the yoke 40 and the coils 41.

The first or uppermost zone of relatively high magnetic intensity is produced by means of a pair of rotors 50 each carrying a plurality of permanent magnets. These rotating magnet assemblies are of the type more particularly described and claimed in my copending application Ser. No. 463,393 filed of even date herewith. The permanent magnets 50 are disposed in equispaced relation about the peripheries of the rotors with their pole ends secured to spaced bars made of highly permeable iron or steel and extending around the rotors. These bars act as polar extensions of the permanent magnets. Preferably all of the positive or north poles are secured to one of the bars and all of the negative or south poles are secured to the opposite bar. The outer surface portions of the respective bars are provided with appropriate cuts both lengthwise and cross-wise to develop thereby sharp edges having for their purpose to provide surfaces which serve to concentrate the lines of force and thereby increase the magnetic attraction in localized areas.

The rotors 50 and the rotating pole pieces 16, 17 and 8 are mounted on shafts 20, 21, 22 and 23, respectively, and are journaled in frame members, not shown. The shafts are driven through appropriately connected gears from a suitable source of power in a similar manner as the generally corresponding rotors of the embodiments of Figs. 4 and 13, so that the toothed areas of the respective rotors 54 and the respective rotating pole pieces 16, 17 and 18, as they come close to and travel along adjacent to the respective arcuate wall portions, Will travel in the same direction as the flow of the pulp downwardly through the separator box.

Various changes may be made in the details of the procedure and in the apparatus as described without departing from the invention or sacrificing the advantages thereof.

This application is a continuation-in-part of application Serial No. 784,804 filed November 8, 1947 and application Serial No. 179,458 filed August 15, 1950, both now abandoned.

I claim:

1. In an apparatus for the wet magnetic separation of materials consisting of mixtures of magnetically susceptible particles and magnetically nonsusceptible particles, the combination which comprises a vertically-extending separator box having enclosing side and bottom Walls for receiving and maintaining a liquid suspension of such material under a controlled hydrostatic head, means defining a restricted discharge opening in the bottom portion of said box through which to maintain a controlled discharge of a residue of such a liquidsuspension, said box having opposite side walls provided with opposed inwardly extending arcuate recesses defining between them a relatively narrow fioW passage for the liquid suspension being treated therein, a pair of electromagnetic poles pieces positioned at opposite sides of said separator box and having arcuate recesses therein positioned in registering relation -to the arcuate recesses in the side Walls of said box, cylindrical end pieces mounted for rotation within said registering recesses, said arcuate recesses in said pole pieces being developed on radii of circles of a relatively large diameter as compared to the diameter of I 10 material fitting in seating engagement with the side walls of said pol'e piece recesses.

2. In an apparatus for the wet magnetic separation of materials consisting of mixtures of magnetically susceptible particles and magnetically non-susceptible particles, the combination which comprises a vertically-extending separator box having enclosing side and bottom walls for receiving and maintaining a liquid suspension of such material under a controlled hydrostatic head, means defining a restricted discharge opening in the bottom portion of said box through which to maintain a controlled discharge of a residue of such a liquid suspension, said box having opposite side wall portions provided with opposed inwardly extending arcuate recesses at at least three vertically spaced levels therein, said recessed wall portions defining between them relatively narrow flow passages for the liquid suspension being treated therein, a pair of electromagnetic pole pieces positioned at opposite sides of said separator box and having extensions thereof extending along said opposite sides in parallel relation thereto, said extensions having arcuate recesses therein positioned in registering relation to the arcuate recesses in the side wall portions of said box, cylindrical end pieces mounted for rotation within said registering arcuate recesses at the opposite sides of said box and at a plurality of levels along the extent thereof, said arcuate recesses in said pole piece extensions at at lea-st one level being developed on radii of circles of a relatively large diameter as compared to the cylindrical end pieces mounted for rotation in registering relation therewith, whereby relatively wide air gaps may be established between said pole piece extensions and said end pieces without relative adjustment of the positions of said extensions of said end pieces, and means for regulating said air gap comprising semi-cylindrical sleeves of magnetic material adapted to be seated in said recesses.

3. In an apparatus for the wet magnetic separation of materials consisting of mixturesof magnetically susceptible particles and magnetically nonsusceptible particles, the combination which comprises a vertically-extending separator box having enclosing side and bottom walls for receiving and maintaining a liquid suspension of such material under a controlled hydrostatic head, means defining a restricted discharge opening in the bottom portion of said box through which to maintain a controlled discharge of a residue of such a liquid suspension, said box having opposite side wall portions provided with opposed inwardly extending arcuate recesses at a plurality of vertically spaced levels therein, said recessed wall portions defining between them relatively narrow flow passages for the liquid suspension being treated therein, rotors disposed within said recesses and cooperating to maintain localized magnetic fields acting to attract magnetically susceptible particles from said suspension to said arcuate wall sections, means for rotating said rotors and thereby moving said localized magnetic fields and said magnetically susceptible particles downwardly and laterally along said recessed wall sections out of the main flow path for the suspension, a common discharge conduit disposed outside the confines of said separator box for receiving the magnetically susceptible particles separated at each of said levels, and means disposed beneath each of 'said'recessed wall sections for directing the thus attracted magnetically susceptible particles axially of said rotors to said common discharge conduit. 7 a

4. An apparatus according to claim 3 in which the means fordirecting the magnetically susceptible particles into said common discharge conduit includes partitions extending downwardly and transversely of the width of said box beneath said recesses.

5. An apparatus according to claim 3 in which the means for directing the magnetically susceptible particles into said common discharge conduit includes a trough extending axially of said rotors beneath said recesses and screw conveyors mounted in said trough. 2,258,194

References Cited in the file of this patent UNITED STATES PATENTS 5 15,027

2,045,098 Payne June 23, 1936 12 Stearns Apr. 27, 1937 Queneau Oct. 7, 1941 FOREIGN PATENTS Great Britain Nov. 14, 1884

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