CA2054457A1 - Gravity separators having metallic troughs, particularly humphreys spirals - Google Patents

Abstract

Abstract A gravity-magnetic separator (10) for concentrating magnetic materials (28), particularly iron, is disclosed. The preferred separator is a cast-iron Humphreys spiral retrofitted with powerful rare earth magnets (22) beneath its separating surface (14), the magnets being sufficiently strong to overcome the shielding effect of the cast-iron spiral and induce a magnetic field at the separating surface of about 60 gauss to about 120 gauss. The resulting gravity-magnetic separator enhances the recovery of iron in a commercially significant way.

47\50175A.09 OCTOBER 29, 1990 25

Description

~OS~S7 s Technical Field This invent~on relates to apparatus ~or ~eparating magnetlc mat:erial~ from feed materials such a~ ores, and ~ore particularly to enhancing the recovery of iron ~n metallic gravity separators through the application of power~ul magnetic forces co-directional with the gravity force.

-Background Art In conventional gravity separators, dlfferences in thespecific gravities of the different components of the feed materi~l are used to accompli~h separation. More specifically, a stream of ~eed material is fed onto a downwardly sloping surfacQ, which ~ay b~ an lnclined plane, cone, or ~piral, where it flows und~r the influence of gravity. The higher speciric gravity particles settle near the bottom o~ the ~tream while thQ light materlal~ accumulate near the top. While typically the materials settling near the bottom o~ the ~tream represent the valuable part o~ the ore, that 18 not always the case. In any event, as is well ~nown ~n the art, Yarious separating means may be employed to separatQ the material~
settling at the bottom of the stream from those near the top.
In the case of ~ome metallic ores, it is highly beneficial to combine gravity ~eparation with magnetic separation, as disclosed 47\50175A.os OCTOBER 29, 1990 in commonly owned U.S. Patent ~o. ~,565,62~, thQ conte~s o5f which ~r~ incorpora~ed herein by re~erence ln their entirety. Thifi patent discloses a gravity-magnetic ore separator ~or concentrating magnetic or weakly ~agnetic ~inQrals having a relativQ~y higb 5 8peci~ic grav~ty and utillzes magnetic and gravltatlonal ~orces ~cting co-directlonally~ Under the influence of both magnetic and gravitational forces, magnetic particles are collected more efficiently at the bottom of the ~loped surface thereby enhancing recovery and ~educing costs.
The patent specifically describes gravity-magnetic separators constructed by modifying conventional gravity eparators, such as Reichert cone concentrators or Hu~phreys spirals. ~he Humphreys spiral, introduced in 1943, i8 typ~cally maae of cast-iron which ~hields the ~eed material from the magnetic forces. Ihis problem i8 empha~ized in U.S. Patent No. ~,565,624 ~see col. 7, lines 35-41) wherein it was concluded that it woul~ be imposslble to retro-~it a ca~t-iron 8piral with magnets to ac~leve satis~actory gr~vity-magnetic separation without ~irst replacing portions of the lron ~piral wlth a non-met~llic ~aterial. However, thQ hiqh cost of ~uch replace~ent has proved an impediment to the modiflcation of the cast-iron Humphreys spiral ~8 a gravity-magnetic separator.

Accordingly, it is an ob~ect o~ the present invention to pro~ida cost effective means for modi~ying existing gravity ~7\50175A.09 OCrOBER 29, 1990 2 205~S7 separators of the type havlng ~ 810plng ~ur~aca ~ade o~ ~etal to ~ake the~ qravlty-magnetic separators.

It i~ a further ob~ect of the invention to provido BUCh gravity-magnetic separator~ without, however, requiring the replacement of portlons of the sloping surface with non-metallic ~aterlal A

~7~50175A.09 OCTOBER 29, 1990 3 2 0 ~ 7 Disclosur~ o~ the Invention ~.:

Broadly speaking, the present lnvention compr~ses an apparatus for separating magnetic material from a feed ~ixture including non-magnetic material having a lower specific gravity than the magnetic material, the mixture being combined with a non-~agnetic fluid for - defining a pulp, the apparatus comprising: a downwardly 810PQd pa~sage having an upper, separating surface and a lower surface, the passage comprising metal and being of a sufficient length to achieve at least partial qravity separation o~ the magnetic ~5 material as the pulp flows downwardly over the separating surface:
mean~ for applying a magnetic force beneath the passage as the pulp flows down the separating 8urface, the magnetic force being ~u~iclently strong to overcome the shlelding e~fect of the ~etallic passage to thereby act on thQ pulp for producing a magnetic force at the 8eparating 8ur~ace for augmenting the gravity separation by attracting the magnetic material to the separating surface, the magnetic force not being 80 strong as to cause a build up of magnetic material on the separating sur~acs; and means for separating the magnetic material near the separating ~urface from t~e pulp.

In a preferred embodiment o~ the invention, the magnetic ~aterial comprises iron, e.g.! magnetite and hematite, the passags . .
47~50175A.09 OCTOBER 29, 1990 . -'` ` ~05~457 ¦ co~prise~ a ca~t-iron Humphreys ~piral and the ean~ for ~pplying ; a ~agnetlc force ~t the separat~ng surface comprl~es a plur~lity of rare earth magnets dl~posed beneath the separating surfac~ at t~e lower turn~ of the ~u~phreys splral. The maqnets ~ay comprise, for example, neodymium or samariu~.

A method in accordance with the present invention is also di~closed. Broadly speaking, the present invention disclosas a method for separating magnetic material from a feed mixture also co~prising non-magnetic material having a lower specific gravity than the magnetic material, the method comprising: combining the mixture with a non-magnetic fluid thereby forming a pulp; feedinq the pulp onto the upper, separating surface of a downwardly sloped passage at the raised feed end thereof, the passage comprising metal and being sufficiently long to achieve at least partlal gravity separation o~ the magnetic material as the pulp flows do~nwardly over the separating sur~aces applying a magnetic ~orce beneath the ~luica as the pulp tlow~ down the separating ~urface, the magnetic force bQing sufficiently strong to overcome the shielding effect of the metallic passage to thereby act on the pulp for producing a maqnetic force at the upper surface for auqmenting gravity ~eparation by attracting the magnetic material to the ~eparating surface, the magnetic force not being 80 strong as to cause build up of the magnetic material on the separating surface;
and ~eparatinq the magnetic ~aterial near the ~eparating ~urface froJ the pulp~
~7~50175A.09 OCTOBER 29, 1990 5 20~57 By retrofitting a cast-iron Humphreys ~piral in accordance ~ith the invention, recovery of the magnetic material in t~e feed mixtur~ i6 enhanced in ~ commercially significant ~ay, esp~cially S consldering the relat~vely min~mal cost o~ retro~itting a cast-lron Humphreys spiral in accordance with the invention. In this regard, once the preferred rare earth magnets are positioned beneath the cast-iron spiral, they are held in place by magnetic attraction, i.e., no special securing means are necessary.
The foregoing as well as further features and advantage~ of the apparatus and method in accordance with the present invention will be more fully apparent from the following detailed descr~ption and annexed drawings of the presently preferred e~bodiment thereof.

47\50175A.09 OCTOBER 29, 1990 6 -- 2 ~ 5 7 Brief Desc~E~ion of the Draw~nqs FIG. 1 is an elevational side view of an embodiment of the lnvention showing a conventional cast-iron Humphrey~ spiral geparator fitted with magnets according to the invention:
FIG. 2 is an enlarged sectional view of a portion of the trough of the spiral separator of FIG. l; and FIG. 3 is a perspective view of a magnet means in accordance with the invention.

~7\50175A.09 OCTOBER 29, 1990 7 `- 2 ~ 7 Best Mode For ~arrylng Out The Invent~on s The ~ollowing is a description of a cast-iron Humphreys spIral type gravity separator retro-fitted with ~agnets in accordance with the invention to achieve gravity-magnetic separation. A~ shown, the separator 10 includes a multl-turn (e.g. 5 turn) helical sluice having a trough 12 of modified seml-circular cross-section made of cast-iron. The feed material 25, which may co~prise an iron ore wherein the iron i8 in the form of magnetite and hematite, is introduced into trough 12 at the top of the spiral 10 and flows lS down the trough along separating surface 1~. In a typical Humphreys ~piral, the trough 12 i8 cast-iron approximately 3/8 inches thick and the ~eparating surface 14 comprises a rubberized liner approximately 1/2 inch thlck laid in the trouqh.

As is well Xnown in the art of gravity separation, the heavier fraction 28 of the feed material tends to collect at the bottom ~6 of trough 12 nearest the axis of the separator 10 where ports 18 fitted with cutter~ 19 ~erve to removQ thQ concentrate. The lighter materials 26, i.e. the non-magnetic matter, tends to accumulate near the top of the trough 12 for ultimate exit as tailings. The highest grade of concentrate is discharged from port~ 18 near the top of the spiral, whereas the ports near the lower end of the trough dischargQ middling. Materials discharged ~7\S0175A~09 OCTOB~R 29, 1990 8 2 0 ~ 7 by ports 18 are collected by cylindrical pipe ao positioned ~long the axis of the spiral separator 10 whereas the tailings ex~t t~
s turn ~piral 10 at the lower end 15 thereof. In practlce, the trough 12 may be filled substantlally to the top with feed ~atQrial 25, though in FIG. 2 it is shown only partially filled for purposes o~ clarity.

The present invention is intended for use witb ores, and particularly iron ores, wherein the heavier fract-ion 28 comprises a ~agnetic m~neral such that gravity and magnetic forces cooperate to enhance recovery. To create the qravity-magnetic separator of the invention, means 22 for producing a magnetic force are positioned beneath the cast-iron gpiral trough 12 at specific locations therealong. In accordance with an i~portant feature of the invention, the means 22 are suf~iciently strong to overcome the shi~lding e~fect of the cast-lron sp$ral trougb 12 wh$ch reduces the magnet$c field transmltted to the feed ~aterial. Before the present invention, it was the perception in the industry that it wa~ not possible to retro-fit cast-iron spiral separators with ~gnetic means suf~iciently strong to overcome the sh$elding effect of the cast-iron trough. Rather, and as indicated in the aforementioned U.S. Patent No. 4,565,624 (see col. 7, line~ 35-41), to avoid the shielding effect in the case of the cast-iron spiral, it was contemplated that openings retro-fitted with non-~agnetic material would be cut in the trough at locations where the ~agnets were to be placed~
47~50175A.09 OCTOB~R 29, 1990 9 2 ~ 7 The present invention provides magnetic means capable ofach~eving the desired gravity-magnetic separation in a ca~t-iron spiral without, however, the necessity of cuttiny openings in the trough. A preferred magnetic means 22 in accordance with the invention capable of overcoming the ~hislding effect of the cast-iron spiral is powerful permanent magnets. In particular, it was discovered that permanent magnets comprising a rare earth metal, e.g. neodymium or samarium, are capable o~ overcoming the shielding effect of the cast-iron trough 12 and producing the desired ~agnetic force. In one embo~iment, permanent magnets 22 comprising boron, neodymium and iron may be used. In another embodiDent, permanent magnets comprising cobalt and samariuD may be used. Both of the above magnets are capable of creating ~ magnetic field IS strength ln the range o~ from about 60 gauss to about 120 gauss, and pre~erably about 90 to about 105 gauss, at the separating surface 14 of the trough 12 along which the feed naterial 25 flowfi, whereby the concentrating capability of the cast-iron spiral ~eparator 10 is improved.
In particular, it has been found that if the magnetic field ~trength at the separating surface 14 is from about 60 gauss to about 120 gauss, and preferably about 90 to about 105 gauss, the resulting magnetic field is sufficiently strong to augment the gravity separation of magnetic minerals, whereby the separator 10 functions as a gravity-magnetic ~eparator for enhancing the 47~50175A.09 oK~DBER 29, 1990 10 i ~ ~ 2 0 5 ~ 7 separation of the ~agnetic materlals, e.g., magnetite and hematite, from the feed. The above noted upper l~m$t for the magnetl~ field strength is des$ra~1e because at this l~mit t~ere ~8 satisfactory gravity-magnetic ~eparation ~ithout, howevèr, excessiY~ build-up S of the maqnetic materlal on t~e ~ur~ace 14 abov~ the magnet ~eans 22.

Suitable compositions for rare earth ~agnets in accordance s with the invention are as f~llows, wherein all co~ponents are expressed in percentages by weight:

I. Neodymium-Boron-Iron (optionally containing dysprosium) Nd 30-35t B 1-2~
Dy 0-5%
Fe 56-59%
Other rare earths 0-2%
II. Samarlum - Cobalt Sm 30~40%
Co 60-80%
Other rare earths 0-5%

Re~erring now to FIG. 2, a portion of the spiral trough 12 and its separating ~urface 14 down which the feed material 25 ~lows is shown. The feed material 25 comprises crushed ore and non-maqnetic fluid, e.g., water. The resulting dens$ty of the feed material is typically about 15%-45% by we$ght, and preferably about 20%-35%. As shown, and as $8 known in the art, wagh water 24 Day be used at various locations along the trough 12 to flush 47\50175A.09 OCTOB~R 29, 1990 11 '` ` ~ 20~4~
lower density non-magnetic ~aterlal to thQ outslde o~ the trough away from the ports 18.

Tes~ Results wi~h Ca~t-iron ~pir~
The following examples lllustrate specific application of the invention. However, these examples are not to be construed as llmiting the invention or as expres-~ing optimu~ results.
s Example I

Referring to FIG. 3, each magnet means 22 comprised two permanent magnets 32, 34, each l-inch x 2-inch x V2-inch thick, ~oined by a mild-~teel plate 30 approximately 1/~ inch thick, such that the North pole of magnet 32 and the South pole of magnet 34 f4CQ Away ~rom the plate 30 and the space between the two ~agnets i8 approximately V 2-inch. Neodymium-boron-iron magnets from Eriez Magnetic~, Erie, Pennsylvania were used. In this example, nlne magnet means 22 were used. Each magnet mean~ 22 was secured directly beneath the trough 12 ln spaced relation therealong.
Specifically, three magnet means 22 were disposed alonq each of the last three turns of the spiral separator lo (each turn represents one 360 degree revolution of the trough 12), each magnet means 22 being spaced approximately m~d~ay between tbe neare~t two ports 18. In thi8 regard, lt has been found that if the magnet means 22 are placed on the upper turns of tbe spiral ~7\50175A.09 OCTOBER 29, 1990 12 0~4~7 6eparator 10, the flow o~ feed mat~rial i8 ~lowed by the ~ttraction o~ the heav~er, ~agnetic materi~l~ to the magnet means 22, with the result bein~ that the recovery and grado o~
concentrate are reduced.
.

The magnetic attraction b~tween the magnet ~eans 22 and the ca~t-iron trough 12 served to secure the magnet means to the trough, i.e. no separate securing means was necessary. Actually, with the thickness of rare earth magnets used, wood or plastic spacers between the magnet means 22 and the trough 12 were used to space the maqnets 22 from the undersurface of the trough 12 to produce a magnetic field of approximately 88 to 111 gauss at the separating surface 14 of the spiral separator 10. In this regard, placing the magnets directly ad~acent the trough 12, i.e., without spacer~, produced a magnetic field intensity too high for e~ectively recovering iron ore, as the ore would then build up on the sur~ace 14 abov~ the magnet~ 22 thereby precluding effective separation. 0~ course, the thic~nes~ and dimensions of the rare earth ~agnets 32 and 34 used affect the ~agnetic field strengtb at the separating surface 14. Therefore, it i8 possible to obtain the desired magnetic field strengtb without tbe use Or spacers by selecting the proper dimensions of the rare earth ~agnets.

A sample of ~ron ore ~rom the Labrador Trougb in Canada containing approximately 43.8% total iron (Fet) by weight was tested. The material was fed to a Humphreys cast-iron spiral ~7~50175A.09 O~DBER 29, 1990 13 C~` ~0~ 57 without t~e addition o~ ~agnets to determine the recovery and grade of the spiral without modification. A second sample of the ~a~e ore was then fed, under conditions as simil~r as possible to th~ above-mentioned test, to the ~piral 10 to which the nine S ab~>ve-described magnet means 22 had been attached such that readings on the separating surface 14 ranged from 88 to 111 gauss.
~he cutter or splitter settings on the spiral 10 were those conventionally used in the operating mill from which the sample came. The results are shown in Table A.

TAB~ A
Ca3t-iron ~umphreys ~piral ~est ~e~ult~
Magnets Witho~ 9~h No. Magnets o 9 Co~centrate ~ 68.5 72.5 F~ ~ in concentrate57.456.0 % Recovery 89.9 94.1 % Fe~ ln tailings 14.1 9.2 Feed rate, tph 2.~ 2.3 % Solids in ~eed 38.1 31.4 In the above table, ~Concentrate %~ is the welght percentage of concentrate recovered via the ports 18; ~FeT % in concentrate~
i~ the weight percentage of iron in the concentrate: ~% recovery~
i~ the weight percentage of the total iron (Fet) in the feed ~aterial that 18 contained in the concentrate; "% Fe~ in tailings~
i8 the weight percentage of iron in the tailings: "Feed rate, tph~
i~ the feed rate in ~hort ton8 per hour; and "% Solids in ~eed" is 3S the weight percentage of or~ in tho pulp. The increase o~
~7~50175A.09 OCTOBER 29, 1990 1 ~` ~` 2~5~7 ~pproximately 4% ~n the recovery of lron obtained by the U8Q of ~agnet means 22 in accordance with the invention, i.e., 89.9 to 9~.1, i8 a significant one. A Humphreys sp~ral modified in ~ccordance with the inventlon improve~ the economic return S significantly.

Exam,,ple I~

~he same sample as in Example I was fed to the spiral separator 10 but with different cutter ~ettings on the spiral to determine the effect of this variable on separation. Three tests were run in which no magnet mean~ 22 were used and then six and nine magnet means were added, in each case three magnet means 22 to each o~ thG lowermost turns of the separator 10. Gaussmeter reading~ on the 8eparating surface 14 were again 88 to 111 gauss.
The results are shown in ~able B whereln lt may be seen that adding magnet means 22 invariably increased the rate of iron recovery ~rom the ~eparator 10.
~ABL~ B
Ca8t-Iro~ ~u~phr~y~ 8plral ~est Result~
, ~agnets W/0 With No. Magnets o 6 9 Concentrate % 65.4 70.7 73.6 FeT % ln concentrate59.3 56.6 58.3 % recovery 89.9 91.6 93.2 % FeT ~n tailings 12.6 12.5 11.8 Feed rate, tph 2.2 2.4 2.3 % Solld~ ln ~eed 31.8 30.9 30.6 ~7\50175A.09 OCTOBER 29, 1990 15 ~ ~' C~ 2~457 In lieu of permanent magnets, it may be possiblo to substitute powerful electromagnets as magnet ~eans 22, provided 8uch electromagnets produce a magnetic field ~trength ~t the separating sUrface 14 in the range of a~out 60 gauss to about 120 galass. Such electromagnets would be placed ln the same manner as the permanent magnets, though means for securing the electromagnet8 to the trough 12 ~hould be provided so that ~hen the electromagnets are deactivated, they will not fall. Tha use of electromagnets i8 not presently preferred, as sufficiently strong electromagnets would be quite bulky.

It should now be appreciated by those of ordinary skill in the art that while the present invention has been particularly lS described in connection with the cast-iron ~Umphreys spiral 10, it could be applied to other types o~ metallic gravlty separators.
A~ thi8 as well additional changes and modifications ~ay be made without departing from the spirit and scope of the invention, the ~bove description should be construed as illustrative and not in a limiting sense, the scope o~ the invention being defined by the ~ollowing claims.

~7~50175A.09 OCrDBER 29, 1990 16

Claims (38)

1. A method for separating magnetic material from a feed mixture also comprising non-magnetic material having a lower specific gravity than said magnetic material, the method comprising:

combining said mixture with a non-magnetic fluid thereby forming a pulp;
feeding said pulp onto the upper surface of a downwardly sloped passage means at the raised feed end thereof, said passage means comprising metal and being sufficiently long to achieve at least partial gravity separation of said magnetic material as said pulp flows downwardly over said surface;
applying a magnetic force beneath said passage means as said pulp flows down said surface, said magnetic force being sufficiently strong to overcome the shielding effect of said metallic passage means to thereby act on said pulp to produce a magnetic force at said surface for augmenting said gravity separation by attracting said magnetic material to said surface, said magnetic force not being 80 strong as to cause build up of said magnetic material on said surface; and separating said magnetic material near said surface from said pulp.

2. The method according to claim 1, wherein said passage means comprises a cast-iron Humphreys spiral.

47\50175A.09 OCTOBER 29, 1990 17

3. The method of claim 2, wherein said step of applying a magnetic force comprises providing beneath said surface at least one magnet at least partially comprising a rare earth metal.

4. The method of claim 2, wherein said Humphreys spiral has a plurality of turns and wherein said step of applying said magnetic force comprises providing at least one magnet means beneath said surface on at least the two lowermost turns of said Humphreys spiral.

5. The method of claim 4, wherein said Humphreys spiral comprises ports at least in said lowermost turns, wherein said step of separating magnetic material from said pulp comprises removing said magnetic material through said ports, and wherein said step of applying said magnetic force comprises providing said magnet means between said ports.

6. The method of claim 5, wherein said step of providing said magnet means comprises providing a plurality of magnet means at each of at least the two lowermost turns of said Humphreys spiral.

7. The method of claim 1, wherein said magnetic force applying step comprises applying a magnetic force sufficient to generate a magnetic field at said upper surface of about 60 gauss to about 120 gauss.
47\50175A.09 OCTOBER 29, 1990 18

8. The method of claim 7, wherein said magnetic force applying step comprises applying a magnetic force generating a magnetic field at said upper surface of about 90 gauss to about 105 gauss.

9. The method of claim 1, wherein said step of applying a magnetic force comprises providing an electromagnet beneath said surface.

10. The method of claim 1, wherein said magnetic material comprises iron ore.

11. The method of claim 10, wherein said passage means comprises iron.

12. The method of claim 5, wherein said magnetic force applying step comprises applying a magnetic force sufficient to generate a magnetic field at said upper surface of about 60 gauss to about 120 gauss.

13. The method of claim 12, wherein said magnetic force applying step comprises applying a magnetic force generating a magnetic field at said upper surface of about 90 gauss to about 105 gauss.

47\50175A.09 OCTOBER 29, 1990 19

14. The method of claim 5, wherein said step of applying a magnetic force comprises providing an electromagnet beneath said surface.

15. The method of claim 5, wherein said magnetic material comprises iron ore,

16. The method of claim 15, wherein said passage means comprises iron,

17. The method of claim 16, wherein said plurality of magnet means comprises rare earth magnets.

18. An apparatus for separating magnetic material from a feed mixture also comprising non-magnetic material having a lower specific gravity than said magnetic material, said mixture being combined with a non-magnetic fluid for defining a pulp, comprising:

a downwardly sloped passage means having an upper surface and a lower surface, said passage means comprising metal and being of a sufficient length to achieve at least partial gravity separation of said magnetic material as said pulp flows downwardly over said upper surface;
means for applying a magnetic force beneath said passage means as said pulp flows down said upper surface, said magnetic force applying means applying a magnetic force sufficiently strong to overcome the shielding effect of said metallic passage means to thereby act on said pulp to produce a magnetic force at said upper surface for augmenting said 47\50175A.09 OCTOBER 29, 1990 20 gravity separation by attracting said magnetic material to said upper surface, said magnetic force not being so strong as to cause build up of said magnetic material on said upper surface: and means for separating magnetic material near said upper surface from said pulp.

19. The apparatus according to claim 18, wherein said passage means comprises a cast-iron Humphreys spiral.

20. The apparatus of claim 19, wherein said means for applying a magnetic force comprises at least one magnet at least partially comprising a rare earth metal.

21. The apparatus of claim 19, wherein said Humphreys spiral has a plurality of turns and wherein said means for applying said magnetic force comprises at least one magnet means disposed beneath said surface on at least the two lowermost turns of said Humphreys spiral.

22. The apparatus of claim 21, wherein said means for separating said magnetic material from said pulp comprises separating ports at least in said lowermost turns of said Humphreys spiral, and wherein said magnet means are disposed between said ports.

47\50175A.09 OCTOBER 29, 1990 21

23. The apparatus of claim 22, wherein said magnet means comprises a plurality of magnet means at each of at least the two lowermost turns of said Humphreys spiral.

24. The apparatus of claim 18, wherein said means for applying said magnetic force comprises means for applying a magnetic force sufficient to generate a magnetic field at said upper surface of about 60 gauss to about 120 gauss.

25. The apparatus of claim 24, wherein said means for applying said magnetic force comprises means for applying a magnetic force generating a magnetic field at said upper surface of about 90 gauss to about 105 gauss.

26. The apparatus of claim 18, wherein said means for applying a magnetic force comprises an electromagnet.

27. The apparatus of claim 18, wherein said magnetic material comprises iron ore.

28. The apparatus of claim 27, wherein said passage means comprises iron.

29. The apparatus of claim 21, wherein said means for applying said magnetic force comprises means for applying a 47\50175A.09 OCTOBER 29, 1990 22 magnetic force sufficient to generate a magnetic field at said upper surface of about 60 gauss to about 120 gauss.

30. The apparatus of claim 29, wherein said means for applying said magnetic force comprises means for applying a magnetic force generating a magnetic field at said upper surface of about 90 gauss to about 105 gauss.

31. The apparatus of claim 22, wherein said means for applying a magnetic force comprises an electromagnet.

32. The apparatus of claim 22, wherein said magnetic material comprises iron ore.

33. The apparatus of claim 32, wherein said passage means comprises iron.

34. The apparatus of claim 33, wherein said plurality of magnet means comprises rare earth magnets.

35. The apparatus of claim 34, wherein said rare earth magnets comprise neodymium.

36. The apparatus of claim 34, wherein said rare earth magnets comprise samarium.

47\50175A.09 OCTOBER 29, 1990 23

37. The apparatus of claim 3, wherein said rare earth magnets comprise neodymium.

38. The apparatus of claim 3.7, wherein said rare earth magnets comprise samarium.

47\50175A.09 OCTOBER 29, 1990 24