Note: Descriptions are shown in the official language in which they were submitted.
~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
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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
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OCTOBER 29, 1990 3
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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~
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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.
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OCTOBER 29, 1990 7
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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
