Note: Descriptions are shown in the official language in which they were submitted.
20737~9
SFPARATION OF FINF SULPHIDF MIN~RALS BY FRO~H FLOTATION
This invention relates to the separation of
sulphidic minerals by froth flotation in a mineral
separation process. More particularly this invention
relates to a new conditioning process to improve the
separation by differential froth flotation of ultrafine
sulphidic minerals present in polymetallic sulphides.
Froth flotation is a well-known mineral
processing operation for obtaining mineral concentrates of
a desired compound or element. In this process a
collector agent is added to the aqueous slurry of the
ground ore. Mixing is usually achieved in a mixing tank
called a conditioner or directly in the flotation cells.
The collector agent for a particular mineral is
preferentially adsorbed on the surface of the mineral
particles containing the desired compound, thereby
rendering the surface hydrophobic (non-wetting by water).
In a flotation device and in the presence of a frothing
agent, air bubbles will be attached to the particles of
the desired mineral thereby lifting them to the surface of
the slurry. The froth in most instances is collected by
mechanical means. The separated froth is usually dried or
dewatered, and the concentrate is treated in subsequent
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steps to recover the desired compound or element.
In addition to collector and frothing agents
being added to an ore slurry in the mineral separation
process, it is usual to add depressant agents, which will
be adsorbed on the surface of particles containing
unwanted compounds. Depressants can be added to the same
conditioner as the collector, or to a different one. The
surface of the particles are thereby rendered wettable,
i.e. hydrophillic and hence not floatable. The unwanted
minerals may contain minerals bearing certain compounds
which are to be recovered by subsequent flotation process
steps, by means of additions of a collector agent specific
to such a mineral. When two or more flotation circuits
are operated sequentially to selectively separate desired
compounds present in ores, the process is referred to as
differential flotation.
The usual practice of differential flotation is
to treat the ore pulp similarly to a single flotation
circuit but with reagents which will permit the flotation
of only one of the desired minerals by preventing or
minimizing flotation of other minerals. The residue from
the first flotation stage is then treated in a conditioner
with one or more chemical reagents to bring about
flotation and concentration of a second mineral. In the
second flotation process the desired minerals contained in
the froth will provide a concentrate of minerals which
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have been separated from the minerals contained in the
concentrate of the first flotation step. The residue or
tailing of the second flotation process step thus will
contain the unwanted minerals separated from the two
desired minerals originally present in the ore. Of
course, more than two flotation process circuits may be
introduced sequentially to result in more than two
concentrates of compounds and minerals which are of use to
the mineral processor.
The concentrates obtained still contain unwanted
compounds, but have been substantially enriched in the
desired compound or element, thereby reducing the cost of
further recovery steps. It is customary to refer to the
compound of metals in an ore which are to be recovered
from the ore under treatment as value metals.
Massive sulphidic ores can contain sulphides of
three or more metals which are to be separated and
recovered by separate process steps; they usually contain
also sulphides which are intimately mixed and disseminated
throughout the ore. The iron sulphides, quartz and
silicates are usually of no value to the metallurgist and
are to be separated from the value metals and discarded.
In most massive sulphides ores, the various
sulphidic value metals and the iron sulphides are so
finely disseminated and intimately mixed to require very
fine grinding or regrinding i.e. below 30 micrometers.
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Although the fine grinding is technically feasible, the
separation by froth flotation of the various metal values
from a very finely ground ore (i.e. minus 30 micrometers)
is difficult. Two major problems are usually encountered.
5The first problem is related to the recovery of
the very finely ground sulphidic metal values. It has
been well known in the industry that the recovery of minus
10 micrometer sulphidic minerals is much lower than the
recovery of the plus 10 micrometer sulphidic minerals. In
10other words, it has been often proven that the major
fraction of the sulphidic metal value losses in the
flotation tailings from milling operations using very fine
grinding (or regrinding) is generally contained in the
finest fraction of the tailing. Using conventional
15methods for processing finely ground sulphidic material,
a large proportion of the finest fraction of the value
metal escapes the process and is definitively lost to the
tailings.
In addition to the loss of values due to the low
20recovery of the fine sulphidic minerals, there is also a
second problem related to the poor selectivity observed
during the froth flotation of ultrafine minerals. It is
also well known from current operations processing very
finely divided sulphidic minerals that the finest (smaller
25than 10 micrometers) fraction of a final concentrate is
significantly lower grade than the coarsest fraction. The
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grade of the global concentrate is therefore quite lower,
and so its metallurgical value.
In the conventional froth flotation plants
processing sulphide ores, the conditioners (or
S conditioning tanks) are designed to blend various pulp
streams and to mix them with suitable chemical reagents
such as collectors, activators, depressants, modifiers.
The size of the conditioning tank is determined based on
the time required for the various chemical agents to
achieve full efficiency; in some cases, the action of the
chemical agent is so rapid that no conditioning time is
required; other chemical agents need a certain time to
perform their task, and they will be added to the ground
ore pulp in conditioners large enough to provide the
required contact time between the chemicals and the pulp.
Conditioners are tanks equipped with a motor driven
impeller to allow for proper suspension of the pulp.
There are a variety of impeller types which are
currently used in the industry in standard conditioner
units: propellers (marine type), turbines (pitched blade
turbine PBT), hydrofoils. In the last 8-10 years the low
shear, high flow, hydrofoil has become the standard mixing
impeller for slurry applications in all solid
concentrations. The hydrofoil replaced the pitched blade
turbine (PBT) due to its high efficiency (low shear)
characteristics in these solid suspension cases. The
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pitched blade turbine imparts too much shear and
turbulence to the slurry and too little axial flow when
compared to the hydrofoil. This high efficiency impeller
coupled with impeller diameter to tank diameter ratios
(D/T ratio) in the range of 0.25 to 0.30 have resulted in
the most efficient combination for solid suspension.
The design of the standard conditioner units is
based on minimizing the power draw of the conditioners
while ensuring complete agitation of the pulp and avoiding
settling of the coarsest particles. Installed power in
standard conditioners used in froth flotation plants
processing sulphide ores typically lies in the 0.04 to 1.5
kW/m3 range.
A new process has been developed to enhance the
recovery of ultrafine metal sulphides contained in finely
ground sulphide ores. Sulphidic ores that could be
successfully processed using the new conditioning process
of this invention include those of copper, lead, zinc,
nickel, molybdenum, gold, silver, and the platinum group
minerals (PGM).
The new process, called high intensity
conditioning, consists in modifying the conditioning stage
prior to flotation in such a way as to cause
flocculation/agglomeration of the ultrafine metal
sulphides in the conditioner; the flocs/agglomerates so
formed can then be recovered as usually in the subsequent
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flotation stage. To be effective, the new process (High
intensity conditioning) requires:
a) the use of a different conditioner unit
(called high intensity conditioner),
significantly different from the standard
conditioners used to process sulphide
minerals and briefly described above. The
high intensity conditioner consists of:
- a holding tank, usually fully baffledi
however baffle design is not critical
to the conditioning process
- a high shear impeller
- a motor and drive capable of providing
power draw for the impeller in the 5
to 150 kW/m3 range
b) imparting to the pulp the appropriate
amount of energy sufficient to overcome
t h e e n e r g y b a r r i e r f o r
flocculating/agglomerating the ultrafine
metal sulphide. The optimum energy
required has to be determined in each
specific case since it will depend on the
type of sulphide minerals present in the
pulp, their size and the reagents in the
pulp. In general, the energy requirements
for high intensity conditioning are in the
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1 to 10 k~/m3 range for the larger units
(>25m3~, in the 20 to 70 kWh/m3 range for
the smaller units (1-10 m3), and up to 100
kWh/m3 for the laboratory unit (2-30
liters). For comparison, energy
requir~ments in standard conditioners
larger than 25 m3 are usually in the 0.01
to 0.04 kWh/m3 range. Various impeller
designs could be used for high intensity
conditioning. An impeller suitable to be
used for high intensity conditioning can
be characterized by:
- one to three turbines mounted on the
same shaft. The turbines could be
opposed or not.
- at least one turbine comprises 3-6
blades.
- the ratio of the impeller diameter to
the tank diameter, or the D/T ratio,
ranges between 0.3 and 0.6; such a
high ratio would be considered
inefficient by conventional solid
suspension requirements.
- the impeller, called HIC, differs from
the radial flow impeller also because
of the pitch ~40 to 70~ to the
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blades. This develops an axial
component to the flow ensuring top to
bottom turnover of the slurry
preventing any stagnant zones. The
HIC impeller has a lowwer blade width
(W) to diameter (D) ratio compared to
conventional impellers, as shown in
Table 1.
Table 1: W/D ratio for Various Impellers
Impeller Type PBT Radial HIC
W/D Ratio 0.19-0.25 0.15-0.19 0.10-0.20
Due to its design, the HIC impeller imparts more
shear and turbulence to the pulp as compared to other
impellers; the HIC impeller develops a high power draw, or
high power number. It is believed that high shear is
necessary to achieve selective agglomeration and/or
flocculation of ultrafine particles in the pulp. These
flocs or agglomerates then respond similar to coarse
particles in the subsequent s~paration process of froth
flotation resulting in good selectivity and recoveries.
Those skilled in the art will recognize that
specific power requirements ~kW/m3) for processes
involving mixing, in particular flotation and
conditioning, significantly decrease with increase of the
unit volume. This is also the case for the conditioner in
this invention.
20737~9
Small high intensity conditioning units (less
than 1 m3) could require specific power inputs larger than
100 kW/m3 to achieve the turbulent mixing needed to
produce the desired results. Intermediate units
(1 - 10 m3) could require a power input comprised between
25 and 100 kW/m3, while larger units (larger than 25 m3)
could require power inputs in the 5 - 25 kW/m3 range.
The minimum power requirement to obtain the
desired effect depends on the ore treated, the pulp
density, the pulp viscosity, the reagents added to the
conditioner and the tank volume. The number of impellers
and their particular design will also depend on the tank
height since it is necessary to achieve violent, turbulent
conditioning throughout the entire vessel.
This invention will now be disclosed by way of
example with reference to the accompanying drawings in
which:
Figures la and lb illustrate side and plan
views, respectively, of an impeller design suitable to be
used in high intensity conditioning.
Figure 2 is a copper-lead-silver rougher and
cleaner flotation flowsheet with no high intensity
conditioning; and
Figure 3 is a flowsheet as shown in Figure 2
with the addition of high intensity conditioning.
Referring to Figures la and lb, there is shown
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11
an impeller design comprising three, six blade turbines 10
mounted on a shaft 12 suspended in a tank 14. In this
particular example, the laboratory turbine used had the
following dimensions: D = 10.2 cm, W = 1.8 cm and a = 35.
Three such turbines were mounted on the same shaft
although less than three turbines may be used in some
applications. The tank was a fully baffled cylindrical
tank (8L nominal volume) with a diameter L of 20.3 cm and
a height of 25 cm. Installed power was 190 watts.
A detailed description of this invention and its
application for the treatment of fine sulphide minerals
will be provided herein below with reference to working
examples.
ExamDle 1:
A massive sulphidic ore from Canada, which is
treated in a commercial operation for the recovery of
copper, lead, silver and zinc as major value metals, was
treated in a laboratory flotation circuit using the same
flotation reagents as used in the plant. The major
difficulty in treating this ore is that the sulphide
minerals are so disseminated that a very fine grinding is
necessary to achieve liberation; however, using the
standard flotation practice, low grade concentrates are
produced at a low recovery.
In this example, two laboratory tests were
conducted on pulp samples taken directly from the plant in
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12
the copper-lead-silver circuit. In the first test, the
standard plant conditions were simulated, i.e. the
collectors and frother were added directly to the
flotation cell. In this test, collector agents A343, A355
and R2~1 (American Cyanamid) were added as well as the
frothing agent MIBC (methyl isobutyl carbinol). In the
second test, the same dosage of the same reagents was
added to another sample of the same pulp, which was then
treated for 20 minutes in the high intensity conditioner
described above, before being submitted to the same froth
flotation procedure.
The results obtained for these two tests are
summarized in Table 2.
Table 2
Te6t Products Weigh~ Assays %, gtt 9'o Distribution
% Cu Pb Ag Cu Pb A8
No bigb Copper-lead-silvorCone I 17.95 1.40 14.24 436 59.6 64.7 58.8
intensity Copper-lead-silvor Cone 2 5.20 0.78 7.91 259 9.6 10.4 10.1
conditioner Copper-lead-silvor Cone 3 1.89 0.54 7.60 233 2.4 3.6 3.3
2 0 Copper-lead-silver Tail 74.96 0.16 1.12 49A 28.4 21.3 27.8
Hoad (Cale~ 100.00 0.42 3.95 133 100.0 100.0 100.0
20rnimrb Coppor-lesd-silver Cone 1 12.44 2.28 23.86 685 67.8 77.6 70.3
high Copper-lead-silvor Cone 2 2.28 05~5.08 180 2.8 3.0 3A
inbnsiq Copper-lead-silvor Cone 3 2.56 0.28 3.70 115 1.7 25 2.4
2 5 condi~nin~ Copper-lesd-silver Tail 82.72 0.14 0.78 35.0 27.7 16.9 23.9
Head (Calc) 100.00 OA2 3.82 121 100.0 100.0 100.0
By comparing the flotation test results shown in
Table 2, it is clearly observed that the use of the high
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13
intensity conditioning of this invention significantly
improves both the grade and the recovery of the copper,
lead and silver minerals.
Ex~m~le 2:
Two other pulp samples were taken from the same
plant as discussed in Example 1 and were used in two
laboratory tests. In the first test, standard plant
practice was simulated; no high intensity conditioning was
carried out and the flowsheet illustrated in Figure 2 was
followed.
In the second test, the same general flowsheet
and reagents were used but the pulp was treated in the
laboratory high intensity conditioner for 30 minutes
before rough flotation, and the crude concentrate after
regrinding was treated for 10 minutes in the high
intensity conditioning before being submitted to cleaning
stages. The flowsheet used during the second test is
illustrated in Figure 3.
The results obtained during these two tests are
summarized in Table 3.
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14
Tabl e 3
Test Products Weigbt Assays %. g/t % Dis~ributio~
% Cu Pb Ag Cu Pb Ag
No higb Copper-lead-silver Cl Conc8.79 2.68 27.32 694 67.7 67.8 58.7
intensity Copper-lead-silver Ro Conc20.45 1.31 13.28 351 77.2 76.7 69.0
conditioner Copper-lead-silver Ro Tail 79.55 0.10 1.04 40.5 22.8 23.3 31.0
Head (Calc) 100.00 0.35 3.54 104 100.0 100.0 100.0
high Copper-lead-silver Cl Conc8.36 3.12 32.73 786 71.2 76.1 65.4
intensi~y Copper-lead-silver Ro Conc18.44 1.54 16.06 402 77.7 82.3 73.8
0 conditioning Copper-lead-silver Ro Tail 81.56 0.10 0.78 32.2 22.3 17.7 26.2
Head (Calc) 100.00 0.37 3.60 100.5 100.0 100.0 100.0
From the results in Table 3, it is clearly seen
that the introduction of high intensity conditioning after
primary grind (before rougher flotation) and after
regrinding (before cleaner flotation) has greatly
increased the grade of the concentrates, and recovery
kinetics as well as selectivity (due to a better rejection
of iron sulphides) were improved due to the new invention.
~xam~le 3:
A massive sulphide ore originating in Quebec
(Canada) containing copper, silver and zinc as major value
metals was treated in a laboratory batch flotation
circuit. Plant pulp samples from the zinc circuit were
used. Two rougher flotation tests were conducted on the
plant pulp.
In the first test, standard plant reagents were
conditioned for 10 minutes in the flotation cell before
zinc rougher flotation. In this case, copper sulphate,
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lime and collector were added to the cell.
In the second test, the pulp was treated with
the same reagents for 20 minutes in the high intensity
conditioner before being submitted to zinc rougher
flotation.
The results obtained during these two tests are
summarized in Table 4.
Table 4
Test Products Weight Assays % % Dis~ibulion
% Zn Zn
No high Zn Rougher Conc 1 2.54 30.10 44.9
intensiiy ZnRoqgberCooc 2 1.75 27.00 27.7
conditioning Zn Rougher Conc 3 1.70 13.60 13.6
Zn Total Rougher Conc 6.00 24.51 B6.2
Zn Rougher Tail 94.00 0.25 13.8
Head (Calc) 100.00 1.70 100.0
High in~ensity Zn Rougher Conc 1 4.71 31.0 85.2
conditioning Zn Rougher Conc 2 1.32 9.9 7.6
(20 minutes) Zn ~ougber Conc 3 2.11 1.53 1.9
2 0 Zn Total Rougher Conc 8.14 19.96 94.6
Zn Rougher Tail 91.86 0.10 5A
Hoad (Calc) 100.01.72 100.0
By comparing the flotation test results in Table
4, it is clear that the use of high intensity conditioning
25of this invention has greatly improved the selectivity and
kinetics of zinc rougher flotation: the concentrate
produced after 3 minutes of flotation assayed 31% Zn and
contained 85% of the zinc in the feed when the high
intensity conditioner of this invention was used, while it
30assayed 30.1~ Zn and contained only 44.9% of the zinc in
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1~
the feed, when the high intensity conditioner was not
used.
~xam~le 4:
A massive sulphide ore originating in British
Columbia (Canada), containing copper as major value metal
was treated in a laboratory batch flotation circuit. The
major gangue minerals in the ore were iron sulphides
(pyrrhotite and pyrite). Three laboratory rougher
flotation tests were conducted on this ore using identical
conditions and reagent scheme except for the conditioning
before copper rougher flotation.
In the first test, the ground pulp and
appropriate reagents were not conditioned before rougher
flotation. In the second test, the ground pulp and the
same appropriate reagents were conditioned for 20 minutes
in the high intensity conditioner before rougher
flotation. In the third test, the ground pulp and the
same appropriate reagents were conditioned for 20 minutes
in the flotation cell before rougher flotation.
The results of the three flotation tests are
summarized in Table 5.
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17
Table 5
Test Products Weight Assays % % Distribution
% Cu Cu
No high Cu Rougher CODC I 7.97 8.59 32.9
intensity Cu Tolal Rougher Conc 31.25 5.94 89.1
conditioning Cu Rougber Ta~ 68.75 0.33 10.9
Head (Calc) I00.0 2.08 100.0
High intensity Cu Rougher CODC I 8.87 17.60 74.2
conditioning Cu Tot~ Rougher Conc 23.94 8.15 92.8
(20 ~ninutes) Cu Rougher Ta~ 76.06 0.20 7.2
Head (C~c) I00.00 2.10 100.0
20 rninute Cu RougheT Conc 1 14.13 5.87 38.8
conditioning Cu Tot~ Rougher Conc 36.00 5.41 91.0
in the Denver Cu Rougher Ta~ 64.00 0.30 9.0
Head (Calc) 100.00 2.14 1000
By comparing the results of the two first
flotation tests in Table 5, it is again seen that the
introduction of high intensity conditioning greatly
increases the kinetics of copper flotation and the
selectivity versus iron sulphides.
By comparing the results of the two last
flotation tests in Table 5, it is also clearly seen that
the beneficial effect observed when introduciny high
intensity conditioning cannot be attributed to prolonged
conditioning times but to the high shear developed in the
pulp by the high intensity conditioning unit itself.
It has been shown by numerous examples conducted
on a number of different massive sulphide ores that the
high intensity conditioning of this invention is highly
efficient in improving the froth flotation separation of
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18
ultrafine metal sulphides.
Although the present invention has been
described with reference to the preferred embodiment, it
is to be understood that modifications and variations may
be resorted to without departing from the spirit and scope
of the invention, as those skilled in the art will readily
understand.
