Note: Descriptions are shown in the official language in which they were submitted.
CA 02335330 2001-02-09
METHOD AND APPARATUS FOR THE BENEFICIATION OF ORES
FIELD OF INVENTION
This invention relates to the beneficiating of ores and, more particularly, to
a method
and apparatus for classifying ores and concentrates by size, shape and density
while
concurrently leaching values therefrom, and for thickening, detoxifying and
dewatering
tailings.
BACKGROUND OF THE INVENTION
Heaping leaching involves crushing, but rarely grinding, of an ore and laying
the ore
by mechanical means as a layer onto a pad on the ground or other prepared
surface. A
leaching agent is sprayed onto the layer of ore, after which it percolates
through the pile,
dissolving some of the base metals, gold or precious metals. The solution is
then collected
by drainage underneath and around the pile to a sump, where the solution maybe
recirculated
to the top of the ore pile as often as is necessary to leach out the gold or
precious metals, or
pumped to a plant to have the gold or precious metals extracted from the
solution.
Vat leaching is similar to heap leaching, except that the ore is sometimes
ground and
placed in a pit or like tank instead of a pile such that the ore is immersed
for a more effective
soaking to improve contact of the leaching solution with the ore.
Heap leaching or vat leaching is not nearly as efficient as conventional
leaching in
agitated tanks because the larger particle sizes and lack of mixing does not
allow intimate
contact between the leaching agent and the gold or precious metals. Leaching
times are
typically 10 to 15 days for vat leaching and weeks or months for heap
leaching. In addition,
both methods are batch processes, requiring adding and removing the ore from
the leach area
by mechanical means.
It is known to beneficiate ores by classifying solids in slurries using beds
fluidized
by a countercurrent flow of a liquid or gas medium. Known methods, such as for
separating
bitumen from oil sands, use a continuous flow of rising fluid, usually water,
countercurrent
to descending solids to effect a separation according to size, shape and
density. The product
CA 02335330 2001-02-09
recovered usually is substantially diluted by the volume of separating medium
required and
must be thickened.
Paste backfilling is a relatively new technology-gaining acceptance in
underground
mines. Tailings are thickened to a paste in specially designed thickeners to a
solids content
of about 70 wt% solids. (Paste is defined as slurry being dewatered to the
point that no more
water will drain from it, e.g. in a standard concrete mix slump test.) A
mixture of pozzolanic
materials, such as cement, fly ash and/or slag, with sand or aggregates can be
applied to the
thickened tailings with the resulting material piped underground for backfill.
Tailings from cyanide processes need detoxification prior to being applied as
backfill,
but in cases where the backfill is taken from old tailings, it is assumed that
nature has
destroyed the cyanide or that levels are low enough to not pose a threat
underground. If there
are cyanide complexes in the tailings, they are pretty well fixed by
cementation. Leakage to
the environment, at best, would be slow enough to allow the half-life of the
complexes to be
reasonable.
Common practice since cyanide processing began is to use tailings ponds as a
means
of decanting and the return of cyanide solutions to the processing plant.
Operators are
reluctant to destroy cyanide in the tailings because of the cost ofNaCN, and
would rather risk
leakage from the tailings into the environment. Since most dams will leak to a
certain extent,
polishing ponds are commonly placed at the toes of the dams to destroy any
cyanide solution
seepage. It is assumed that natural degradation will take place and the
tailings can be
washed, as in heaps; however, there is concern that cyanide contained in the
solids cannot
be destroyed - at least by the S02/Air system - because sufficient air cannot
be contacted with
the solids, and that washing will not be completed due to channeling.
Extensively dewatered tailings by filtering can be conveyed to tailings
disposal areas.
Vacuum filters can be used to dewater the tailings. The tailings are washed in
the filters but
are not detoxified. The tailings are stacked with huge, moveable conveyors and
stackers, a
huge capital investment.
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CA 02335330 2001-02-09
SUMMARY OF THE INVENTION
In accordance with one of its aspects, the invention provides an apparatus for
treating
a particulate ore for the recovery of contained values therefrom. The
apparatus has a tank
for receiving a liquid, the tank including a feed end, a discharge end and a
bottom. The
apparatus also includes means for feeding the particular ore to the tank at
the feed end, a
manifold head tank for receiving the liquid for fluidizing the particular ore,
and distribution
means for intermittently distributing the liquid in the tank, to fluidize the
particulate ore in
the tank. In addition, the apparatus also has means for withdrawing the ore
particles at the
tank discharge end, and means at the bottom of the tank for withdrawing the
liquid
therefrom.
In another aspect of the present invention, there is provided a method for
beneficiating particulate ores containing soluble metal values. The method
includes
continuously feeding the particulate ore containing the values to a liquid in
a tank at the feed
end of the tank, intermittently uniformly fluidizing the ore with a liquid for
5 to 10 seconds,
and intermittently withdrawing the liquid for about 2 to 5 minutes across and
along the tank.
The method also includes continuously separately withdrawing classified
particles from the
tank for recovery of the values therefrom, and recycling the liquid for
intermittently
fluidizing the ore particles.
In another aspect of the present invention, there is provided a method of
leaching
particulate ores containing soluble metal values. The method includes forming
a tank having
a feed end and a discharge end for containing a leach solution, and
continuously feeding the
particulate ore containing the values soluble in the leach solution to the
tank at the feed end
thereof. The method also includes intermittently fluidizing the particulate
ore by adding
leach solution uniformly across and along the length of the tank for 5 to 10
seconds. The
leached solution is released intermittently to the tank from a manifold head
tank in
communication with the siphon assembly. The method also includes withdrawing
the leach
solution for about 2 to 5 minutes to result in a jigging action to move the
ore particles up and
down, to classify the particles into strata according to size, shape and
density, and also to
move the classified particles from the feed end to the discharge end of the
tank, so that the
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CA 02335330 2001-02-09
particles are stratified while soluble metal values are concurrently dissolved
by the leach
solution. The method also includes withdrawing classified particles from the
tank, treating
the leach solution for recovery of the values therefrom, and recycling the
leach solution for
intermittently fluidizing the particulate ore.
BRIEF DESCRIPTION OF THE DRAWINGS
The method and apparatus of the invention will now be described with respect
to the
accompanying drawings, in which:
Figure 1 is a plan view of the apparatus of the invention;
Figure 2 is a longitudinal section of the apparatus of the invention along
line
2-2 of Figure 1;
Figure 3 is a transverse section of the interior of the apparatus along line 3-
3
of Figure 1;
Figure 4 is a transverse section of the discharge end of the apparatus along
line
4-4 of Figure 1;
Figure 5 is an end section and plan of the tank discharge showing the
discharge
slot and belt discharge;
Figure 6 is a vertical section of a siphon head tank of the invention;
Figure 7 is a schematic illustration of the apparatus and flow sheet of the
invention;
Figure 8 is a schematic illustration of the apparatus and leaching flow sheet
of
the invention, showing a detoxification step;
Figure 9 is a schematic illustration of another embodiment of the apparatus
and flow sheet of the invention;
Figure 10 is a vertical section of four embodiments of paste thickeners of the
invention;
Figure 11 an end section of the apparatus of Fig. 1 at a discharge end, as
well as
a cross-section at the discharge end, and plan views of the apparatus
of Fig. 1 at discharge slots and above an endless belt;
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Figure 12 an end section of an embodiment of the apparatus of the invention at
a discharge end as well as a cross-section at the discharge end, and
plan views of an embodiment of the apparatus of the invention at
discharge slots and above the endless belt; and
Figure 13 is an end section of an embodiment of the apparatus of the invention
at a discharge end as well as a cross-section at the discharge end, and
plan views of an embodiment of the apparatus of the invention at
discharge slots and above the endless belt.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to Figures 1 - 5, the apparatus of the invention comprises a
tank 10
normally rectangular in plan with side walls 11, 13 having a feed end 12 and
discharge end
14 with a bottom surface 16 normally sloping downwardly from the feed end 12
to the
discharge end 14. Tank 10 maybe a metal, plastic, reinforced plastic or
concrete vessel. The
slope of bottom surface 16 should be sufficient to permit and promote
migration of
particulate solids, as will become evident as the description proceeds,
towards discharge end
14. A slope in the range of up to one inch per foot of length of the tank,
preferably 0.3 to 1
inch per foot of length of the tank, normally is sufficient for desired
migration of the
particles, the slope depending on the characteristics of the particulate
material such as size,
shape and density of the particles. It will be understood that some ores will
require no slope
of the bottom surface for effective migration of particles to the discharge
end.
The bottom surface of the tank maybe covered with a coarse particulate
material such
as crushed stone to form a bed which may be restrained by means of a wire mesh
grid which
overlays the crushed stone to maintain the desired slope of the bottom
surface. This grid may
be underlain with a screen which has a mesh finer than the finer particles of
the particulate
ore to prevent infilling of the crushed stone with the ore particles. The
crushed stone
preferably is graded from coarse to fine in size from 1 %2 inch to 3/8 inch in
diameter. If the
particulate ore is 1/4 inch or larger in size, the screen preferably has '/4
inch mesh openings
CA 02335330 2001-02-09
to separate the ore from the crushed stone bed. This is disclosed in U.S.
Patent No.
5,096,678.
Particulate ore normally is fed by pipeline or launder as a slurry to tank 10
at feed.
Alternatively, particulate ore may be fed by a screw conveyor (not shown) or
by a belt
conveyor (not shown) adapted to uniformly distribute ore particles across the
tank (not
shown).
A plurality of equispaced pipes 26 extend from manifold head tank 28 at the
side 11
along the bottom surface 16 of tank 10 to through pipes 54 to vent 56 at side
13. Pipes 26 are
connected to vents 56 by pipes 55 to expel air from pipes prior to introducing
liquid to tank
10. Liquid is introduced to tank 10 through a plurality of spaced perforations
such as holes
provided along pipes 54 to form pool 32. Pipes 26, 54, 55 and 56 are uniformly
spaced apart
about 6 to 12 inches and holes are spaced along pipes 54 about 3 to 12 inches.
Holes may
be formed on the top, sides, or bottom of pipes 54 and preferably are formed
along the
bottom of pipes 54.
Figure 6 illustrates the siphon discharge from head tank 28 into the plurality
of
equispaced pipes 26. Each pipe 26 has a stationary funnel section 40 with a
vertically-
reciprocal pipe 42 slidably mounted therein. Pipe 42 is connected to a
vertical pipe 44
mounted in head tank 28 by a length of flexible pipe coupling 46. Pipe 42 is
biased into a
normally at-rest position "up" position shown by solid lines by a counter-
weight 48
connected thereto by a cable 50 passing over pulley 52.
In operation, liquid rising in head tank 28 fills pipe coupling 46 causing the
pipe
coupling 46 to drop due to the added weight of the liquid, initiating a siphon
sustained flow
of liquid into pipe section 40 until the head tank is emptied. Once tank 28 is
empty, counter-
weight 48 raises empty pipe 42, permitting tank 28 to fill until the next dump
cycle is
initiated.
The liquid from head tank 28 discharges downwardly through each pipe funnel 40
into a horizontal run 54 across the bottom surface 16 to discharge through the
holes in pipes
54 to fluidize the bed in the tank. With reference to Figure 6, the
supernatant liquid from
tank 10 flows along launder 24 to pump 58 and is recycled to head tank 28 or
preferably
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CA 02335330 2001-02-09
delivered under pressure to paste thickener 60 for cleaning of fine solids and
colloidal solids
before return to head tank 28.
Figure 10 illustrates four embodiments of a paste thickener in which liquid
under
pressure from pump 58 is fed tangentially into the conically-shaped feed well
65 for
discharge of collected solids downwardly through apex 62 and discharge
upwardly of
classified liquid through a weir with collecting launder 25. The feed pipe to
the thickener
utilizes an eductor 21 to dilute slurry feed to the feed well 65 with
classified liquid from the
collecting launder 25, since it is generally known that dilution of slurry
aids separation of
solid particles. The conical shape and tangential feed of feed well 65 is
designed to promote
effective mixing of flocculating agents added to the feed well 65 through the
top and to
impart centrifugal force to the solid particles to aid in separation from the
liquid. A
distribution cone 19 is sometimes used to spread settling particles to the
surface of the
discharge cone 59.
The paste thickener, Type B, is identical to Type A described above, except
that
lamella thickener elements 18, preferable made of plastic and commonly used in
water
treatment plants, are added to promote separation of fine particulates that
would otherwise
be carried with the rising liquid in the thickener.
Paste thickener, Type C, is identical to Type A described above, except that
an
agitating device 23 is employed to gently agitate settled solids to release
interstitial air and
liquid, thus improving the density of underflow from apex 62. The agitating
device 23
consists of a free rotating rod with blades extending into the solids with the
blade devices
made to move slowly up and down by an air or hydraulic cylinder 22. The blades
are set at
an angle to promote free rotation as they rise up and down in the underflow
slurry in cone
59.
Paste thickener, Type D, is identical to Type C described above, except that
cone 20
is arranged to have a larger open throat at the apex 62 by elongating the side
walls to a chisel
shape and discharging by means of a progressive cavity pump 63. The side walls
of the cone
20 may also be lined with low friction material such as TeflonTM. The purpose
of this
arrangement is to handle sticky material such as ores with high clay content.
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Ore or concentrate in the tank vat 10 is classified and washed of slimes which
are
collected in paste thickener 60 and discharged as a paste having a 35 to 70
wt% solids
content. As shown in Figures 1, 2, 3, 4, and 9 two-stage paste thickeners such
as 60 and 61
can be used to provide countercurrent washing or detoxification of the slimes
by discharging
the underflow from apex 62 to an agitated tank 35, which is located between
thickeners 60
and 61. Either fresh water, barren solution or a combination of the two can be
added to tank
35, along with detoxification or neutralization reagents.
Coarser ore in the tank travels to discharge end 14 and is lifted out and
decanted by
the discharge mechanism to about 20 wt% water content for 200 mesh size. The
discharge
mechanism is shown most clearly in Figures 3, 4 and 5 to comprise a pair of
linearly-aligned
wheels 66, 68 journalled for rotation by bearings 70, 72 in narrow trough 74
at discharge end
14 in communication with tank 10 through opening 76. A longitudinal tapered
slot 78 in the
floor 80 of trough 74 receives coarse solids from tank 10 to be picked up by
endless belt 82
which passes about wheel 66 under slot 78 to wheel 68. Belt 82 is held under
tension by
tensioned rolls 84, 86 before returning to wheel 66. Endless belt 90 passes
over belt 82 as
belt 82 wraps around wheel 68 to assist dewatering of the solids on belt 82
and to deliver the
solids to transverse conveyor 92.
Detoxification or neutralization of tailings can be done in a single stage
with leaching
as depicted in Figure 7 or in two stages as depicted in Figure 8. As is known
in the art,
detoxification of cyanide solutions can be achieved using various methods. For
instance,
detoxification of cyanide solutions is typically done by adding peroxygens or
SO2 with air
and copper sulfate as catalyst, sodium metabisulfite with air and copper
sulfate as catalyst,
or hypochlorate (chlorox), ferrous salts, ozone, or ultraviolet methods.
Neutralization of
tailings from acid leaches is typically done by adding hydrated lime or
caustic soda to the
solutions. Two sets of discharge mechanisms are depicted in Figure 8, with the
wheels
connected by common shafts. Spent ore is transferred from the leach section 37
of tank 10
to the detoxification section 38 of tank 10 by a chute or conveyor 93. A
separate head tank
65 is used to fluidize and mix liquid with the discharged ore from the first
section.
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Supernatant solution from the detoxification section 38 is pumped to tank 65,
where
detoxification or neutralization reagents are added to tank 65.
Figures 11, 12, and 13 depict other embodiments of the method of the
invention.
Figure 11 shows the use of wide belts 82 and 90 and multiple slots 78 for use
on wide vats
and fine particulate material, such as 200 mesh or smaller, or for cases where
a high rate of
discharge is required. Figures 12 and 13 show the use of a filter belt 90 that
is made from
filter cloth or perforated material such as polypropylene. The rim of wheel 68
is perforated,
beneath which are chambers 67 for collecting solution that is squeezed from
pressure
provided by encompassing belt 82 pressing onto filter belt 90. Filtrate is
drained through
pipes 71 to trough 74. As shown in Figure 12, the pipes 71 are arranged to
trail each
chamber 67 in wheel 68 in a curved manner such that when each pipe 71 and its
corresponding chamber 67 is submerged in the supernatant in trough 74, each
pipe 71
becomes full of liquid. As a pipe 71 is pulled out of the supernatant in
trough 74, suction is
created by the egress of the fluid, thus aiding in filtration on belt 90.
Figure 13 depicts a
similar arrangement to Figure 12, except that the suction is created by a
vacuum pump (not
shown). A vacuum is exerted on pipes 71 through a rotary valve 73. The ports
in the rotary
valve 73 are aligned with the pipes 71 in such a manner as to apply vacuum to
each chamber
67 as it emerges from the supernatant in trough 74 through 90 degrees of
rotation.
The method and apparatus of the invention can be used to leach ores and
concentrate
with recycle of the lixiviant and continuous removal of fine solids from the
system as a paste.
Tailings can be detoxified and dewatered by the system by feeding granular
tailings and
tailing slurries to the system with discharge of deslimed and dewatered
granular solids and
concurrent discharge of classified water and a colloidal paste.
It will be evident to those skilled in the art that the invention can take
many forms and
that such forms are within the scope of the invention as claimed.
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