US3382977A - Magnetic separator with a combination field - Google Patents

Description

May 14, 1968 F. FRAAS 3,382,977

MAGNETIC SEPARATOR WITH A COMBINATION FIELD Filed March 8, 1965 2 Sheets-Sheet 1 INVENTOR FOSTER F/MAS A'IT NEYS' F. v FRAAS May 14, 1968 3,382,977

MAGNETIC SEPARATOR WITH A COMBINATION FIELD Filed March 8, 1965 2 Sheets-Sheet 2 w m v V M N i 3w; oz 3 9. oz 53 Sum oz PC9234 O0 oowi 55 Bub oz 53 Sui oz 64m wtzmi MCJOQOII ("A-3903M NO 031031-100 uouovaa) M INVENTOR FOSTER FRAAS ATIOR EYS United States Patent 3,332,977 MAGNETIC SEPARATOR WITH A COMBHNATION FIELD Foster Fraas, Hyattsville, Md., assignor to the United States of America as represented by the Secretary of the Interior Filed Mar. 8, 1965, Ser. No. 438,132 7 Claims. (Cl. 209214) ABSTRACT OF THE DISCLQSURE Beneficiation separation of mineral substances having relatively low magnetic susceptibilities is efI'ectuated by passing the substances in a stream through a non-tractive, homogeneous magnetic field for a magnetization pretreatment, and directly thereafter passing the stream of pretreated substances through a tractive non-homogene ous magnetic field for separation of the more magnetically susceptible substances from the stream.

The present invention relates to improvements in a method and means which enlarge the capability of a magnetic separator to economically separate minerals having almost identical magnetic susceptibilities, and to provide for the separation of minerals of lower magnetic susceptibility. These improvements are achieved by forming and arranging the means producing the magnetic fields such that a stream of mineral particles introduced to the separator is first exposed to a strong magnetization eifect in a homogeneous magnetic field of high intensity wherein the effective magnetic property of the particles is increased, and thereafter exposed to a nonhomogeneous field wherein particles with a magnetic susceptibility higher than a predetermined value, are separated from particles with a lower magnetic susceptibility.

Heretofore magnetic separators have operated in accordance with the principle that particle pretreatment required the application of forces derived from nonhomogeneous magnetic fields. In such operations feiro and paramagnetic particles have forces directed on them in the direction of higher magnetic field intensity, and diamagnetic particles have forces directed on them in the opposite direction. It is well established that nonhom-ogeneous fields produce forces which act to alter the position of the treated particles, and as disclosed in Patent No. 2,065,460, issued to F. R. Johnson on Dec. 22, 1936, cause a pro-alignment of such particles before they enter a leaving point, or final separation area. Also characterizing the use of a nonhomogeneous field in particle pretreatment is a stratification of the particles into layers due to the magnetic particles being turned around their axis one or more times so as to be worked out of the nonmagnetic material, in a manner more fully described in Patent No. 765,013, issued to F. J. King on July 12, 1904. Actually, two processes occur simultaneously when particles are thus pretreated, namely a force or particle positioning process resulting from the nonhomogeneous field, and a magnetization process whereby the magnetic field increases the efiective magnetism of the particles. The latter is a rate process, the degree of magnetization depend-ing on the time that particles are in the magnetic field.

The advantageous mineral separating operation secured 3,382,977 Patented May 14, 1968 by means of the present invention results from the severance therein of the aforesaid force and magnetization processes into distinct stages. Magnetization for pretreating the particles is obtained in a homogeneous field applying no perceptible tractive or position disturbing forces on the particles, and separation is obtained in a nonhomogeneous field. Consequently, the magnetization preliminary to separation can be controlled to an optimum selectivity value, and the particles pass through the pretreatment field unrestrained with no accumulation so that each particle receive-s the same amount of magnetization. Because of this optimum selectivity and uniformity of magnetization of the particles made possible by the present invention, any separator in accordance therewith is responsive to a more precise regulation of its operational characteristics, including current strength in the windings ofits field coils, and speed at which the particles are moved through its pretreatment field, to accomplish a separation of par-ticles having nearly the same magnetic susceptibility.

It is an object of the present invention therefore to provide for use in a magnetic separation of particles, a method and apparatus in which fine operating adjustments are effective to cause the separation of particles whose similar magnetic properties would otherwise make difficult their separation by magnetic means.

A further object of the invention is to provide for use in a magnetic separation of particles, a method and apparatus in which a combination of homogeneous and nonhomogeneous magnetic fields is applied to successively magnetize and separate the par-ticles processed thereby.

These and other objects of the invention will more fully appear from the following detailed description when read in connection with the accompanying drawing wherein:

(FIG. 1 is a partly schematic view of an exemplary form of the magnetic separator improvement according to the present invention;

FIG. 2 presents a number of graphical representations of operational characteristics of the invention in its application to the processing of a number of different minerals;

FIG. 3 is a partly schematic view of an additional embodiment of the invention; and

- \IG. 4 is .a partial view of FIG. 3 taken along line 4--4.

Reference to FIG. 1 provides a simplified showing of basic elements in a cross-belt type magnetic separator 10, comprising the improvement of the present invention. A more detailed disclosure of a cross-belt magnetic separator can be found on page 213 of US. Bureau of Mines Bulletin No. 425. Separator 10 includes a magnetic pole 11, whose projecting face or pole cap is distinguished by a Vshaped notch 12, situated between broad and narrow fiat surfaces 13 and 15 of the cap, which creates along one end of this cap a wedge shaped conformation 16, where'on lies surface 15. Pole 11 is cooperatively related with an oppositely magnetized pole 13, whose projecting face or pole cap comprises an essentially flat surface 19 arranged to lie parallel to surfaces 13 and 15, and appropriately spaced therefrom to accommodate a particle conveying structure tor operation between the poles. This conveying structure includes a conveying means 22, such as a moving belt or vibrating channel, which functions to conduct feed particles 24 between the surfaces of the spaced pole caps in the direction indicated by the arrow in 'FIG. 1. The particles are thus first moved through a homogeneous magnetic field between surfaces 13 and 19, and thereafter through a nonhomogeneous or particle separating magnetic field generally defined in and about the area between surfaces 15 and 19. Further comprising the conveying structure is a cross-belt 26, serving to transport to a separate bin the particles attracted to the wedge 16 as a result of the action in the nonhomogeneous magnetic field.

All particles are processed in the homogeneous magnetic field for the same length of time, namely the interval required for a particle to move past the outer edge of surface 13 and arrive under the inner edge thereof at notch 12. Obviously, this time interval can be set as needed by means of a suitable speed control for conveying means 22. It is also evident that the effective span of surface 13 may be varied as needed to predetermine in the first instance the time during which the particles will be subjected to magnetization in the homogeneous field. A zero field gap existing between surfaces 13 and 15, due to presence of a notch 12, can also be varied to predetermine the degree of preliminary magnetization of the particles prior to a separation action thereon. Without this preliminary magnetization, a field magnetization would occur only in the particle separating nonhomogeneous field. Since the path for each separating particle would then be random, the actual magnetization would depend on the various random magnetic field intensities through which a particle passes. The spectrum of the number of separated particles versus ampere turns in the magnet would therefore be spread over a broad range. With a preliminary homogeneous magnetization field, the magnetization is fixed and substantially the same for every particle having the same composition. As a result, the tractive force in the nonhomogeneous field is effectively the same for every such paramagnetic particle, and the spectrum of the number of separated particles versus ampere turns in the magnet is confined to a narrow range.

To facilitate a substantive demonstration of the effectiveness of a preliminary magnetization in a homogeneous field, the apparatus of FIG. 1 was adapted to have its pole 11 rotatable such that it could be moved through an angle of 180 about a vertical axis. With this arrangement particles 24 moving on conveying means 22, as indicated by the arrow, could be passed through the nonhomogeneous field between surfaces 15 and 19, without a preliminary magnetization. In FIG. 2 are graphically illustrated the results of runs made to process four different minerals with and without employing a preliminary magnetization in a homogeneous field. The term field in the explanatory legends of the graphs signifies that the feed was first passed through the homogeneous field, whereas the phrase no field signifies that the feed passed first through the nonhomogeneous field. Further, the terms Slow and Fast found on the graphs, signify the speed at which the particles were moved through the fields and they correspond to passage velocities of 3.6 and 5.5 inches per second.

Examination of the curves shows tha the slope AW/AH, where AW is an increment in the amount collected at the Wedge when an increment AH is added to the magnetic field strength, is much greater when a preliminary homogeneous magnetization field is used, particularly for fast passage velocities. A large value for AW/AH represents a spectrum confined to a narrow range, and accordingly a high selectivity in particle separation. FIGURE 2 also illustrates that the use of a preliminary homogeneous magnetization field permits separation at lower magnetic field intensities, thus providing for an extension of the magnetic separation range tolower paramagnetic susceptibility values. The maximum field intensity in magnetic separators is limited by the permeability of the alloys used in the magnetic circuit.

The rate process wherein the degree of magnetization depends on time and intensity is different from particles of dilferent composition. Thus the magnetization difference between two particles of different composition may vary according to the preliminary homogeneous magnetization field which is selected. This is illustrated in Table 1 in the separation of ilmenite and hematite with two types of separation. In run 1, separation is obtained without a preliminary magnetization field, while in run 2 a preliminary magnetization field is used. Although the amount of collected fraction is the same, the composition of the concentrate varies according to the amount of magnetization in a preliminary homogeneous magnetization field, the respective values being 39 and 60 percent hematite.

TABLE L-SEPARATION 0F HEMATITE FROM ILMENITE Fraction attracted toward 1 Minus plus 65 mesh mixture of hematite and ilmenite. 2 Both separations at fast passage speed of 5.5 inches per second.

Although this invention has been described with the use of a cross-belt separator as an example, it is applicable to a variety of other structural forms wherein a combination of homogeneous and nonhomogeneous magnetic fields may be utilized. The specific characteristics of a design for any such form would depend upon whether the particles are carried through the fields by fluids, belts, vibrating conveyors, rolls, or by freefall.

Reference to FIGS. 3 and 4, provides a showing of a freefall type of separator comprising the present invention. Particles 29 are moved on a vibrating surface 30, in the direction indicated by the arrow, to pass between a lower magnetic pole 32 and upper magnetic pole 34. Pole 32 is fashioned to have a pole cap with an upwardly protruding frontal part 36 defined by a flat, horizontal upper surface 38, which terminates at one end as a Wedge shaped conformation 40. The protrusion 36 extends part way into a relatively deep notch in the face of pole 34, to define a passage between the poles wherein vibrating surface 30 can be made active to propel particles 29 through two distinct magnetic fields. Two flat surfaces 42 and 44, constituting horizontal and vertical faces, respectively, of the notch in pole 34, meet at a right angle whereby surface 42 is disposed parallel to surface 38 on pole 32, and surface 44 is located opposite wedge 40 of pole 32. A knife-edge particle diverting device 46 is located below wedge 40 and surface 44, and arranged in an area approximately between the wedge and face. In addition, a narrow cross belt 48, supported to move around a pair of spaced apart pulleys and 52, is arranged to traverse the area contiguous to the extended surfaces of wedge 40, for a purpose to be hereinafter more fully explained.

The magnetic field between surfaces 38 and 42 is homogeneous, while the magnetic field between wedge 40 and surface 44 is nonhomogeneous. Particles 29, moving along conveyor 30, therefore first receive a preliminary magnetization by passing through the homogeneous field and thereafter are affected by tractive forces in falling from the end of conveyor 30 into the nonhomogeneous magnetic filed. Diverting device 46 in the path of the falling particles is accordingly effective to divide or group these particles into distinct fractions 54 and 55, constituted respectively by the magnetic particles of the feed attracted toward wedge 40, and the remaining nonmagnetic, diamagnetic, or lower magnetic susceptibility particles. To safeguard against the possibility that some particles may be attracted so strongly as to adhere to wedge 4%, cross belt 48 is made operative 'by a drive from pulley 50 or 52, to pass in front of wedge 40 and to divert and remove any such wayward particles.

TABLE 2.CONCFINTRATION OF BERYL l\-IOUNTAIN ORE AFTER ONE PASS THROUGH SEPARATOR Weight Composition, Recovery Fraction class percent percent beryl of beryl,

percent 1 Nonmagnetic gangue minerals are feldspar and quartz.

While a preferred procedure and embodiment of the invention has been described and illustrated, it is understood that the invention is not limited thereby but is susceptible to change in form and detail.

What is claimed is:

1. A method for separating from a mass of particles of which individual particles have magnetic susceptibilities varying from negligi le values to perceptible values, the particles of greater magnetic susceptibilities, comprising the steps of feeding the particles in a positively controlled stream through a homogeneous magnetic field whereby the particles of the mass are subjected to a substantially non-tractive, magnetization treatment in said homogeneous magnetic field for a finite interval of time, directly thereafter passing the treated particles through a tractive nonhomogeneous magnetic field wherein the particles of greater magnetic susceptibility are removed from the stream, and collecting the removed particles.

2. In a magnetic separator adapted to separate a particle stream composed of a mixture of slightly magnetic particles and relatively non-magnetic particles, a combination comprising a pair of magnetic poles arranged to face each other across an air space comprising sequential air gaps, the first of said poles having a cap whose conformation includes a large flat area and an area inclined to said large fiat area, the second of said poles having a cap whose conformation includes a large flat area in parallel relationship with said flat area of said first pole cap to obtain in one of said air gaps a homogeneous magnetic field therebetween, and a second portion cooperatively related with said inclined area of said first pole cap to obtain in a second of said air gaps a nonhomogeneous magnetic field therebetween, a conveying structure disposed between said pole caps and operative in said air gaps thereof to carry said particles of said stream first through said homogeneous field and thereafter directly through said nonhomogeneous field, and means operatively related to said conveying structure in said nonhomogeneous field to collect said slightly magnetic particles removed from said particle stream toward said inclined area of said first pole cap.

3. In a magnetic separator for concentrating into fractions particulate matter of varying magnetic susceptibilities, a combination comprising first means for producing a homogeneous magnetic field of prescribed length and intensity, and 'second means for producing a nonhomogeneous magnetic field adjacent to said homogeneous field, wherein said first and second magnetic field producing means of said combination comprises two spaced apart magnetic poles, each having a flat surface disposed facing one another in a parallel relationship, between which is produced said homogeneous magnetic fields, and one of said magnetic poles having in addition a wedge shaped conformation on which a relatively narrow flat surface is disposed to face in a parallel relationship a further fiat surface on said other magnetic pole, whereby said narrow and further flat surfaces are cooperatively related to produce said nonhomogeneous magnetic field, means conveying said particulate matter as a flowing stream in successive order through said homogeneous magnetic field wherein said particulate matter is moved unrestrained and without accumulation so that each particle of said matter is equally treated with magnetization, and directly thereafter through said nonhomogeneous magnetic field wherein the particles of said matter of higher than a predetermined magnetic susceptibility are diverted into a path difierent from the path taken by the particles of said matter of lower magnetic susceptibility.

4. The magnetic separator of claim 3, wherein said first and second magnetic field producing means of said combination comprises two spaced apart magnetic poles, each having a fiat surface disposed facing one another in a parallel relationship and between which is produced said homogeneous magnetic field, and one of said magnetic poles having in addition a wedge shaped conformation disposed to face a further fiat surface arranged perpendicular to said fiat surface on said other magnetic pole, whereby said wedge conformation and further fiat surface are cooperatively related to produce said nonhomogeneous magnetic field.

5. The magnetic separator combination of claim 3 wherein said means conveying said particulate matter comprises a belt.

6. The magnetic separator combination of claim 3 wherein said means conveying said particulate matter comprises a vibrating conveyor.

7. The magnetic separator of claim 3 wherein said means conveying said particulate matter to pass through the homogeneous magnetic field is a vibrating conveyor so situated and controlled that said particulate matter leaves said vibrating conveyor to pass through said nouhomogeneous magnetic field by freefall.

References Cited UNITED STATES PATENTS 1,529,970 3/ 1925 Ullrich 209-219 X 1,536,541 5/1925 Ullrich 2092l9 2,056,426 10/ 1936 Frantz 209232 2,338,501 1/ 1944 Followill 209--223 2,591,121 4/1952 Blind 209-223 2,976,995 3 1961 Forrer 209-223 FOREIGN PATENTS 451,585 8/1936 Great Britain.

HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner.

Images