Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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APPARATUS AND METHOD FOR REMOVING MAGNETIC MATERIAL FROM
GRINDING CIRCUITS
FIELD OF THE INVENTION
The present innovation relates to apparatuses and methods used to remove
magnetic materials from grinding circuits, for example in the mining and
minerals
industries.
BACKGROUND OF THE INVENTION
The mining and minerals industries utilize various devices to separate
valuable
minerals from host contaminants after extraction from the earth. Initially the
ore
preparation procedure typically involves crushing ore from several feet in
size
down to approximately 1-3 inches in a crusher (e.g. gyratory, cone or jaw
crushers). The preliminary crushing step is typically followed by one or more
stages of grinding to reduce the ore to an average size of less than 1 mm
(generally between 75 and 300 microns). The grinding stage typically utilizes
large rotating cylindrical mills (e.g. ball or semi-autogenous grinding
("SAG")
mills) containing grinding media such as spherical steel balls. The balls are
in a
constant tumbling motion due to the rotation of the mill. The ore is typically
fed
into one end of the mill, it progresses through the grinding chamber and is
discharged from the opposite end. As the ore progresses through the mill the
grinding media impacts the material resulting in fracture and breakage of the
individual pieces of ore into smaller particles.
The tumbling motion of the grinding media results in the fracture of the
grinding
media (e.g. the steel balls). Additionally, mechanical abrasion will wear the
grinding media surface causing a reduction in size of the grinding media. The
result of this process is generation of various shapes of steel which are
significantly smaller than the original spherical ball. A new grinding ball
will
typically range from 3 to 5 inches in diameter. The broken or worn ball
components can be as large as a hemisphere of the original ball or fragments
having dimensions of less than 1/4 inch. Depending on the mill design, these
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fragments will discharge with the mineral/crushed material and report to
downstream equipment.
The ball fragments cause numerous problems in ore processing facilities. Most
notably such fragments increase wear on downstream equipment within the
grinding circuit, for example on pumps, piping and valves. The costs
associated
with maintenance downtime and equipment rebuild can be substantial.
Secondly, such fragments negatively impact mill efficiency (i.e. lower
throughput).
The circuit design for most grinding operations is such that a large portion
of the
fragments that discharge the mill will return with the new feed to the
grinding
circuit. As a result, a substantial build-up of fragments can occur in the
grinding
mill occupying volume that would otherwise be filled by mineral slurry. This
loss
in active mill volume can de-rate the mill capacity by as much as
approximately
10%. Furthermore, the small mass of the fragments does not provide a
sufficient
impact force to effectively fracture the mineral particles in the mill. Third,
the
recovery of precious metals by downstream gravity concentrators is reduced and
downstream upgrading (tabling) is less efficient. For example, the steel
particles
report in very high proportions to a gravity concentrate, such as a Knelson
concentrate, which recover heavy particles. The amount of unwanted steel in a
Knelson concentrate typically varies from 15%-45%.
It will be clearly understood that any reference herein to background material
or
information, does not constitute an admission that any material, information,
forms part of the common general knowledge in the art, or is otherwise
admissible prior art.
SUMMARY OF THE INVENTION
An apparatus for removing magnetic material from a grinding circuit is
provided.
The apparatus may comprise a screening device configured for separating
undersized material from oversized material; an outfeed table, at least a
portion
of the outfeed table being positioned below the screening device, the outfeed
table being operatively configured for receiving the oversized material from
the
screening device and for spreading the oversized material into a layer of
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oversized material; and a magnetic device, at least a portion of the magnetic
device located above the outfeed table, the magnetic device being operatively
configured for removing the magnetic material from the layer of oversized
material.
In an exemplary embodiment of the apparatus, the apparatus may further
comprise a frame, wherein the screening device and the outfeed table are
supported by the frame. In some embodiments, the magnetic device may be
supported by the frame.
In an exemplary embodiment of the apparatus, the apparatus may further
comprise an oversize discharge located adjacent a first end of the screening
device and positioned between the screening device and the outfeed table.
In an exemplary embodiment of the apparatus, the apparatus may further
comprise a washing device positioned between the screening device and the
outfeed table, the washing device being operatively configured to wash the
oversized material. In some embodiments, the layer of oversized material
comprises pre-washed oversized material.
In an exemplary embodiment of the apparatus, the apparatus may further
comprise an oversize discharge located adjacent a first end of the outfeed
table
wherein at least at least a portion of the oversize discharge is positioned
below
the outfeed table.
In an exemplary embodiment of the apparatus, the apparatus may further
comprise a washing device positioned between the outfeed table and the
oversize discharge, the washing device being operatively configured to wash
the
oversized material.
In an exemplary embodiment of the apparatus, the apparatus may further
comprise a magnetic discharge collection device, at least portion of the
magnetic
discharge collection device positioned below the magnetic device.
In an exemplary embodiment of the apparatus, the apparatus may further
comprise an adjusting means for adjusting or tilting the outfeed table, the
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adjusting means being operatively connected to the outfeed table. In an
exemplary embodiment of the apparatus, the outfeed table may be vertically
adjustable from a horizontal plane. In some embodiments, the magnetic device
may be vertically adjustable from a horizontal plane. In some embodiments, the
outfeed table is tiltable between approximately 0 degrees and 45 degrees from
the horizontal plane. In some embodiments, the magnetic device is tiltable
between approximately 0 degrees and 45 degrees from the horizontal plane.
In an exemplary embodiment of the apparatus the screening device may be
comprised of a vibrating screen.
In an exemplary embodiment of the apparatus the magnetic device may be a belt
magnet.
In an exemplary embodiment of the apparatus the outfeed table may be a non-
vibrating outfeed table.
An apparatus for removing a magnetic material from a grinding circuit may also
comprise a screening device configured for separating undersized material from
oversized material; and a belt magnet located above the screening device, the
belt magnet being operatively configured for removing the magnetic material
from
the layer of oversized material. In some embodiments, a horizontal gap between
the top portion of the screening device and the bottom portion of the belt
magnet
is minimal. In some embodiments, the apparatus further comprises a frame,
wherein the screening device is supported by the frame. In some embodiments,
the apparatus further comprises a magnetic discharge collection device, at
least
portion of the magnetic discharge collection device positioned below the belt
magnet. In some embodiments, the belt magnet is supported by the frame. In
some embodiments, the screening device is comprised of a vibrating screen. In
some embodiments, the belt magnet is vertically adjustable from a horizontal
plane. In some embodiments, the belt magnet is tiltable between approximately
0 degrees and 45 degrees from the horizontal plane.
A method for removing a magnetic material from a grinding circuit is also
provided. The method may comprise the steps of separating undersized material
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from oversized material using a screening device; transferring the oversized
material from the screening device to an outfeed table; spreading the
oversized
material into a layer of oversized material on the outfeed table; and removing
magnetic material from the layer of oversized material using a magnetic
device.
5 In some embodiments, the method may further comprise washing the
oversized
material after separating the undersized material from the oversized material
using a screening device but before transferring the oversized material from
the
screening device to the outfeed table.
In some embodiments the method may further comprise collecting the magnetic
material using a magnetic discharge collection device.
In some embodiments, the spreading the oversized material into a layer of
oversized material on the outfeed table comprises adjusting the angle of the
outfeed table from the horizontal plane.
Other details, objects, and advantages of the invention will become apparent
as
the following description of certain present exemplary embodiments thereof and
certain present exemplary methods of practicing the same proceeds.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of an apparatus for removing magnetic material from a
grinding circuit are shown in the accompanying drawings. It should be
understood that like reference numbers used in the drawings may identify like
components.
Figure 1 is a perspective view of an exemplary embodiment of the apparatus for
removing magnetic material from a grinding circuit.
Figure 2 is a perspective right side view of an exemplary embodiment of the
apparatus for removing magnetic material from a grinding circuit.
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Figure 3 is a perspective left side view of an exemplary embodiment of the
apparatus for removing magnetic material from a grinding circuit.
Figure 4 is a perspective top view of an exemplary embodiment of the apparatus
for removing magnetic material from a grinding circuit.
Figure 5 is a perspective front side view of an exemplary embodiment of the
apparatus for removing magnetic material from a grinding circuit.
Figure 6 is a perspective view of an exemplary embodiment of the apparatus for
removing a magnetic material from a grinding circuit.
Figure 7 is a flow chart of an exemplary grinding circuit showing one
exemplary
position of the apparatus.
Figure 8 is a perspective view of an exemplary embodiment of the screening
device.
Figure 9 is a perspective view of an exemplary embodiment of the magnetic
device and the outfeed table.
Figure 10 is a perspective view of an exemplary embodiment of the frame.
Figure 11 is a perspective view of an exemplary embodiment of the magnetic
device.
Figure 12 is a picture of an exemplary embodiment of the apparatus installed
during testing.
Figure 13 is an overhead picture of the outfeed table during operation and
testing.
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Figures 14A and 14B are pictures of the magnetic material which was recovered
during testing of the apparatus.
DETAILED DESCRIPTION OF THE INVENTION
Figures 1-6 depict exemplary embodiments of an apparatus for removing
magnetic material from a grinding circuit. As shown the apparatus may contain
a
screening device 10, an outfeed table 20 and a magnetic device 30. The
screening device 10 is configured to separate undersized material from
oversized
material. At least a portion of the outfeed table 20 is positioned below the
screening device 10 so that the outfeed table 20 can recieve the oversized
material from the screening device and therafter spread the oversized material
into a layer. At least a portion of the magnetic device 30 is located above
the
outfeed table 20 and is configured so that magnetic material which is present
in
the layer of oversized material on the outfeed table 20 can be removed. In
some
embodiments, the outfeed table is non-vibrating. The screening device 10 ahead
of the outfeed table 20 is advantageous in that such an arrangement provides a
higher efficiency of magnetic material removal, as the layer of oversize
material
can be thin.
The outfeed table 20 is advantageous in that in some embodiments it is
stationary (i.e. - non-vibrating) and spreads out the oversize material into a
layer
thereby allowing more efficient and easier collection of magnetic material via
closer magnetic attraction by the magnetic device 30 thereby requiring a
smaller
or lesser powered magnetic device 30 to be used.
Additionally, the outfeed table 20 allows the magnetic device to be placed in
closer proximity to the oversized material without risking the screening
device 10
damaging the magnetic device 30 and resulting in a more efficient magnetic
material recovery from the oversize material layer. For example, the outfeed
table 20 can spread out the oversize material into a layer thereby allowing
more
efficient and easier collection of magnetic material via closer magnetic
attraction
by the magnetic device 30 thereby requiring a smaller or lesser powered
magnetic device 30 to be used.
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In an exemplary embodiment, there may be an oversize discharge 40 located
adjacent to a first end of the screening device 10 for collecting oversize
material
as is passes off of the first end of the screening device 10. An oversize
discharge 40 may also be positioned adjacent to a first end 24 of the outfeed
table 20 for collecting additional oversize material as is passes off of the
first end
24 of the outfeed table 20.
One or more washing devices 50 (e.g. a spray header) may be positioned e.g. on
or above the screening device 10, between the screening device 10 and the
outfeed table 20 and/or between the outfeed table 20 and the oversize
discharge
which is positioned adjacent to a first end 24 of the outfeed table 20 for
collecting
additional oversize material as is passes off of the first end of the outfeed
table
20. The washing devices are operatively configured to wash the oversized
material. Washing the oversized material is advantageous in that it reduces
contaminants on theoversized material which allows for better quality and more
desirable magnetic material being collected by the magnetic device 30. Washing
the oversized material also increases the value of the product due to a low
contaminant level.
As shown in Figure 8, in an exemplary embodiment, the screening device 10 is a
vibrating screen. In other embodiments the screening device can be other well
known types of screens in the art, for example static screens or sieve bend
screens. As shown in Figure 8, the vibrating screen 10 may contain a vibrator
(or
motor) 13 for exciting or moving a screen 12. Typically the vibrator 13 is
mounted on a mounting plate 14 across the screening device 10. The screening
device may also contain feet 18 and spring feet 19 attached thereto. In some
embodiments, the screening device may contain a washing device 50, for
example a spray header, for washing material as it is screened and before it
passes onto the outfeed table 20.
As shown in Figure 11, in an exemplary embodiment, the magnetic device 30 is a
belt magnet. In other embodiments the magnetic device can be other well known
types of magnets in the art, for example a drum magnet. As shown in Figure 11,
the belt magnet 10 has a first longitudinal rail 34 and a second longitudinal
rail
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36. As shown rollers 37 are disposed between the longitudinal rails 34, 36 at
the
first end 38 and second end 39. A belt 31 may be disposed between the
longitudinal rails 34, 36 and is rotatable (via a drive device 32) around the
rollers
37. In some embodiments, the magnetic device 30 can be supported by the
frame 100. In other embodiments the magnetic device 30 can be suspended
above the outfeed table 20. The use of the belt magnet is advantageous in that
the belt magnet removes coarse scats (i.e. - metallic material). Grinding
media
generally breaks by spalling of the grinding ball. As the scat recirculates in
the
grinding circuit, it further breaks into smaller pieces. Thus it is
advantageous to
remove the scats at the coarsest size possible. An additional advatage is that
the belt magnet presents its magnetic effect over a large surface area of the
outfeed table 20 with a thin layer of slurry, allowing a long residence time
for pick
up of the magnetic material.
As shown in Figure 9, in an exemplary embodiment an outfeed table 20 has a
first side 21, a second side 22, a front end 28 and a back end 29. The outfeed
table may also contain a liner plate 23. In an exemplary embodiment, the liner
plate is made of ultra high molecular weight polyethyline ("UHMW"). The UHMW
may assist in providing a wear resisitant surface and allows a low coefficient
of
friction for the magnetic material. In other embodiments, other like materials
well
known in the art may be used as all of or part of the liner plate 23. As
further
shown in Figure 9, the magnetic device 30 is positioned above (but adjacent
and
close to) the outfeed table 20. By positioning the magnetic device close to
the
outfeed table 20, more magnetic material is able to be collected by the
magnetic
device 30.
Figure 10 depicts an exemplary embodiment of the frame 100 which may support
one or more of the screening device 10, the magnetic device 30 and the outfeed
table 20. In the embodiment shown in Figure 10, the frame contains skid beams
102. One or more vertical beams 104 may be attached to the skid beams 102.
Horizontal tie beams 106 and/or cross braces 108 may be used to provide
structural rigidity to the vertical beams 104. The frame may also contain feed
chute legs 17 for supporting the feed chute 16 on the frame 100 and or
screening
device 10.
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Figure 7 depicts a flow diagram of a typical grinding and gravity separation
circuit. In operation, an apparatus for removing a magnetic material from a
grinding circuit may be placed at e.g. location 200. The apparatus detailed
herein (as shown in Figures 1-6 and 12 and 13) was trialed on the screen
5 oversize of an existing Knelson feed screen. The oversize in the trial
was pre-
screened at 2 to 6 mm. During the trial the apparatus was operated continously
(24 hours per day, 7 days a week) with a feed rate of approximately 2 TPH with
a
+ 2 mm feed and a 2-6 mm screen aperture installed on the apparatus. The trial
resulted in an actual magnetic material recovery of 2 by 50 gallon drums per
shift
10 which would equate to an estimated plant wide magnetic material recovery
of
10% of total plant grinding media. If two of three screen oversize streams
were
treated the magnetic material recovery would be expected to be higher. As
shown in Figures 14A and 14B, visually, the recovered magnetic material was
clean, and was not a large gold carrier. Gold grade smeared onto the metallic
material was only -0.3 g/t. A sample of the magnetic material (e.g. scrap
steel)
recovered during the trial was shipped back to the grinding media supplier and
although the oxide (rust) component was higher than normal scrap steel, the
steel was suitable for use as scrap.
In operation, material or slurry is fed onto a screening device 10. The
material
may be fed onto the screening device via a feed chute 16. The material may
then be separated by the screening device 10 into oversized material (which
stays on top of the screen 12) and undersized material which passes through
the
screen 12. The oversized material can be washed using a washing device 50 on
the screen 12. The oversized material can be conveyed off of a first end of
the
screening device 10 into an oversize discharge 40. In an exemplary
embodiment, the oversized material can be washed by a washing device 50 (e.g.
between the screening device 10 and the outfeed table 20) before it is
conveyed
onto the outfeed table 20. The oversized material on the outfeed table 20
(which
may be pre-washed oversized material) can be spread into a layer on the
outfeed
table 20. To assist with spreading of the oversized material on the outfeed
table
20, the outfeed table 20 may be vertically adjustable from a horizontal plane
(H).
In some embodiments, the outfeed table 20 is tiltable between approximately 0
degrees and 45 degrees from the horizontal plane (H). In order to keep the
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magnetic device 30 as close to the outfeed table 20 as possible when it tilts
or
adjusts, the magnetic device 30 may also be vertically adjustable from a
horizontal plane (H). In some embodiments, therefore, the magnetic device 30
is
also tiltable between approximately 0 degrees and 45 degrees from the
horizontal plane (H). In some embodiments, an adjusting means 70 is used to
adjust the outfeed table 20. In an exemplary embodiment, the adjusting means
may be comprised of e.g. studs 72 and hinges 74.
The magnetic device 30 operates where at least a portion of the magnetic
device
30 is above the outfeed table 20. In operation the magnetic device 30 collects
magnetic material from the layer of oversized material on the outfeed table
20. A
magnetic discharge collection device 60 may be positioned at least partially
below the magnetic device 30. The magnetic discharge collection device 60
collects magnetic material. Such magnetic material may include one or more of
the following: iron (Fe), nickel (Ni), or cobalt (Co), Magnetite (Fe304),
Ulvospinel
(Fe2Ti02), Hematite (aFe203), Ilmenite (FeTi02), Maghemite (yFe203),
Jacobsite (MnFe204), Trevorite (NiFe204), Magnesioferrite (MgFe204),
Pyrrhotite (Fe758), Greigite (Fe354), Troilite (FeS), Goethite (aFe0OH),
Lepidocrocite (yFe0OH), Feroxyhyte (OFe0OH), Awaruite (Ni3Fe) or Wairauite
(CoFe). In some embodiments the magnetic discharge collection device 60
contains a protective cover 62 for preventing magnetic material spray or
discharge and/or a collection bin 61 for storing or collecting the magnetic
material.
In an alternative embodiment of an apparatus for removing magnetic material
from a grinding circuit, the apparatus may comprise a screening device 10
configured for separating undersized material from oversized material and a
belt
magnet located above the screening device 10, the belt magnet being
operatively
configured for removing the magnetic material from the layer of oversized
material. In an exemplary embodiment, the belt magnet is placed very close to
the screening device 10 so that there is a minimized horizontal gap between
the
top portion of the screening device and the bottom portion of the belt magnet.
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A method for removing a magnetic material from a grinding circuit is also
provided. In an exemplary embodiment, the method includes separating
undersized material from oversized material using a screening device 10;
transferring the oversized material from the screening device 10 to an outfeed
table 20; spreading the oversized material into a layer of oversized material
on
the outfeed table 20; removing magnetic material from the layer of oversized
material using a magnetic device 30. In an exemplary embodiment, the step of
spreading the oversized material into a layer of oversized material on the
outfeed
table includes adjusting the angle of the outfeed table 20 from the horizontal
plane (H).
In one embodiment, the method may further include washing the oversized
material after separating the undersized material from the oversized material
using a screening device 10 but before transferring the oversized material
from
the screening device 10 to the outfeed table 20. In another exemplary
embodiment, the method may further include collecting the magnetic material
using a magnetic discharge collection device 60.
The apparatus described herein is further advantageous in that significant
costs
are recouped by recovering the magnetic material (i.e. - steel scrap) and
thereby
reducing costs spent on new grinding media. Typical economics are as follows:
= Grinding ball consumption ¨Typical is 1.2 kg/tonne ore (SAG/Ball circuit)
= Media cost - $1,500/tonne
= Media cost - $1.80 per tonne ore processed
= Grinding ball recovery as scrap ¨ approximately 30%
= Ball scrap price ¨ approximately 30% of new
= Net benefit $0.16 per tonne processed, or 9% reduction in media cost.
Other benefits may include decreased wear on downstream equipment within the
grinding circuit, for example on pumps, piping and valves; an increase in
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efficiency within the grinding circuit and a decrease in the amount of
unwanted
materials in gravity concentrates.
It is to be understood that the form of this invention as shown is merely a
preferred embodiment. Various changes may be made in the function and
arrangement of parts; equivalent means may be substituted for those
illustrated
and described; and certain features may be used independently from others
without departing from the spirit and scope of the invention as defined in the
following claims.
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List of Components:
- screening device
12 - screen
13 - vibrator
5 14 - mounting plate
16 - feed chute
17- feed chute legs
18 - legs
19 - spring feet
10 20 - outfeed table
21 - first side outfeed table
22 - second side outfeed table
23 - liner plate
24 - first end outfeed table
25 - second end outfeed table
30 - magnetic device
31 - belt
32 - drive device
34 - first longitudinal rail of magnetic device
36 - second longitudinal rail of magnetic device
37 - roller
38 - first end of magnetic device
39 - second end of magnetic device
40 - oversize discharge
50 - washing device
60 - magnetic discharge collection device
61 - collection bin
62 - protective cover
70 - adjusting means
72 - stud
74 - hinge
100 - frame
102- skid beam
104- vertical column
106- horizontal tie beam
108 - cross brace
200 - location of apparatus within grinding circuit
a - angle
h- horizontal plane
