5,837,210
*Nov. 17, 1998
[11]
[45]
111111111111111111111111111111111111111111111111111111111111111111111111111
US005837210A
Patent Number:
Date of Patent:
United States Patent [19]
Simmons et al.
[73] Assignee: Newmont Gold Company, Denver,
Colo.
[75] Inventors: Gary L. Simmons, Albuquerque, N.
Mex.; John C. Gathje, Longmont,
Colo.
[54] METHOD FOR PROCESSING GOLDBEARING
SULFIDE ORES INVOLVING
PREPARATION OF A SULFIDE
CONCENTRATE
[ *] Notice: The term of this patent shall not extend
beyond the expiration date of Pat. No.
5,653,945.
OTHER PUBLICATIONS
Burger, "Froth Flotation Developments: This Industry
Workhorse Goes From Strength to Strength,"E&MJ (Sep.
1983) pp. 67-75.
Onstott et aI., "By-Product Molybdenum Flotation From
Copper Sulfide Concentrate With Nitrogen Gas In Enclosed
Wemco Nitrogen Flotation Machines," Preprint No. 84-65
(1984) Society of Mining Engineers ofAIME, Feb. 26-Mar.
1, 1984.
Berglund et aI., "Influence of Different Gases In Flotation of
Sulphide Minerals," Proceedings ofAn Engineering Society
Foundation Conference on Advances in Coal and Mineral
Processing Using Flotation (1989) pp. 71-76, Society for
Mining, Metallury and Exploration, Inc., Littleton, Colorado,
Dec., 1989.
FOREIGN PATENT DOCUMENTS
References Cited
Related U.S. Application Data
Appi. No.: 735,783
Filed: Oct. 23, 1996
[57] ABSTRACT
Provided is a method for processing a gold-bearing sulfide
ore which involves maintaining the ore in a substantially
oxygen free environment, preferably beginning with comminution
of the ore and ending when a desired final
concentrate, enriched in sulfide minerals, is obtained by
flotation. In one embodiment, nitrogen gas is used to substantially
prevent contact between the ore and air during
comminution of the ore and during flotation operations. It is
believed that oxygen gas present in air detrimentally affects
the recovery of sulfide minerals in a flotation concentrate
through surface oxidation of sulfide mineral particles. The
use of a gas such as nitrogen can significantly reduce the
potential for such surface oxidation. Additionally, gases
separated from an oxygen plant may be beneficially used,
with an oxygen gas stream being used, for example, for
pressure oxidation of sulfide mineral materials, and with a
nitrogen gas stream being used in comminution and/or
flotation operations, resulting in advantageous use of a
nitrogen gas by-product stream which has previously been
vented to the atmosphere as waste.
(List continued on next page.)
Primary Examiner~teven Bos
Attorney, Agent, or Firm-Holme Roberts & Owen
5/1906 Lovett ... ... 209/39
5/1991 Fair et al. 423/26
12/1991 Kerr et al. 423/26
5/1995 Kelebek et al. 252/61
8/1997 Gathje et al. 423/26
U.S. PATENT DOCUMENTS
Continuation-in-part of Ser. No. 423,839, Apr. 18,1995, Pat.
No. 5,653,945.
Int. C1.6 B03D 1/00; COlO 7/00;
C22B 11/00
U.S. CI 423/26; 423/27; 423/29;
209/166; 209/167
Field of Search 423/26,27,29,
423/DIG. 15; 209/39, 166, 167
821,516
5,013,359
5,074,993
5,411,148
5,653,945
[56]
[21]
[22]
[63]
[51]
[52]
[58]
2608462 6/1988 France 209/39
833320 5/1981 U.S.S.R 209/39 40 Claims, 24 Drawing Sheets
MINERAL
MATERIAL
FEED
102
GAS
SOURCE
ill
FLOTATION
CONCENTRATE
116
FLOTATION
TAIL
118
5,837,210
Page 2
OlliER PUBLICATIONS
Martin et aI., "Complex Sulphide Ore Processing With
Pyrite Flotation by Nitrogen," International Journal of Mineral
Processing, 26 (1989) pp. 95-110, Elsevier Science
Publishers B.Y., Amsterdam, no month.
Jones, "Some Recent Developments in the Measurement
and Control of Xanthate, Perxanthate, Sulphide, and Redox
Potential in Flotation," International Journal of Mineral
Processing, 33 (1991) pp. 193-205, Elsevier Science Publishers
B.Y., Amsterdam, no month.
Berglund, "Pulp Chemistry in Sulphide Mineral Flotation,"
International Journal of Mineral Processing, 33 (1991) pp.
21-31, Elsevier Science Publishers B.Y., Amsterdam, no
month.
Klymowsky et aI., "The Role of Oxygen in Xanthate Flotation
of Galena, Pyrite and Chalcopyrite," CIM, Bulletin
for Jun., pp. 683-688 (1970), Jun.
Rao et aI., "Possible Applications of Nitrogen Flotation of
Pyrite," Minerals, Materials and Industry (ed. M.T.Jones),
Institute of Mining and Metallurgy, pp. 285-293 (1990), no
month.
Rao et aI., "Adsorption ofAmyl Xanthate at Pyrrhotite in the
Present of Nitrogen and Implications in Flotation," Can.
Metall. Q., vol. 30, No.1, pp. 1-6 (1990), no month.
Xu et aI., "Sphalerite Reverse Flotation Using Nitrogen,"
Proc. Electrochem Soc., vol. 92-17, Proc. Int. Symp. Electrochem.
Miner. Met. Process. III, 3rd, pp. 170-190 (1992),
no month.
Van Deventer et aI., "The Effect of Galvanic Interaction of
the Behavior of the Froth Phase During the Flotation of a
Complex Sulfide Ore," Minerals Engineering, vol. 6, No. 12,
pp. 1217-1229 (1993), no month.
Author unknown, title unknown, Chapter IV, Gases and
Aeration, pp. 63-70, date unknown.
Plaskin et aI., "Role of Gases in Flotation Reactions,"
Academy of Sciences, U.S.S.R. Moscow, date unknown.
Kongolo et aI., "Improving the efficiency of sulphidization
of oxidized copper ores by column and inert gas flotation,"
Proceedings of COPPER 95-COBRE 95 International Conference,
vol. II, The Metallurgical Society of CIM, pp.
183-196, 1995, no month.
Rao and Finch, "Galvanic Interaction Studies on Sulphide
Minerals," Canadian Metallurgical Quarterly, vol. 27, No.4,
pp. 253-259 (1988), no month.
u.s. Patent Nov. 17, 1998
MINERAL
MATERIAL
FEED
102
108
COMMINUTION
104
Sheet 1 of 24
GAS
SOURCE
110
5,837,210
106
FLOTATION
112
FLOTATION
TAIL
118
114
FLOTATION
CONCENTRATE
116
Fig. 1
u.s. Patent Nov. 17, 1998
PARTICULATE
MINERAL
MATERIAL
+ 110
FLOTATION
112
FLOTXTION
TAIL
118
114
116
Sheet 2 of 24
AIR
132
OXYGEN
PLANT 130
128
Ir
PRESSURE
OXIDATION
124
t
OXIDIZED
MATERIAL
126
5,837,210
Fig. 2
u.s. Patent Nov. 17, 1998
FIRST
MINERAL MATERIAL
FEED
138
Ir
Sheet 3 of 24
SECOND
MINERAL MATERIAL
FEED
~ 140
MIXING
142
144
5,837,210
FLOTATION 116
112
114
PRESSURE
OXIDATION
124
128
OXYGEN
PLANT 130
,
FLOTATION
TAIL
118
Fig. 3
OXIDIZED
MATERIAL
126
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00
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u.s. Patent Nov. 17, 1998 Sheet 10 of 24 5,837,210
102
116
4
8
118 Fig. 10
Ir
COMMINUTION
1,---104 I'----
1\ 10
106
ACID
TREATMENT \
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(
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\ SOURCE
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u.s. Patent Nov. 17, 1998 Sheet 11 of 24 5,837,210
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102
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Sheet 14 of 24 5,837,210
COMMINUTION
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/ SEPARATION
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)
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118
Fig. 15
u.s. Patent
250 l
248
Nov. 17, 1998
102
Sheet 15 of 24 5,837,210
DEOXYGENATION
\ 104
110
/
COMMINUTION
108 1 GAS --..
SOURCE
~
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(114
+
FLOTATION 116
\
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240~
,
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242 ~_
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246
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u.s. Patent Nov. 17, 1998 Sheet 16 of 24 5,837,210
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u.s. Patent Nov. 17, 1998 Sheet 17 of 24 5,837,210
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u.s. Patent Nov. 17, 1998 Sheet 20 of 24 5,837,210
.. PAX
+ 8-703
... AP 5100
e AP 412
25 30
•
10 15 20
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5
20
10 l..--.__-L-__--L__-----J~__~______L_____l
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u.s. Patent Nov. 17, 1998 Sheet 21 of 24 5,837,210
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u.s. Patent Nov. 17, 1998 Sheet 23 of 24 5,837,210
30
10 5 10
Float Time (min)
22
• Tap H20
-<> De-Ox H20
Fig. 25
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---.
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Float Time (min)
Fig. 27
u.s. Patent Nov. 17, 1998 Sheet 24 of 24 5,837,210
FIRST
MINERAL MATERIAL
FEED
SECOND
MINERAL MATERIAL
FEED
-138 ---140
'r
.r
- 108\ ACID
COMMINUTION PRETREATMENT
\
Ii L104
,r
106
~ 114)
PRESSURE
.. OXIDATION )
FLOTATION T
I 124
~112 1
116
1
126 Ir
118
Fig. 28
5,837,210
2
SUMMARY OF THE INVENTION
The present invention involves a method for processing
gold-bearing sulfide ores to facilitate gold recovery without
the burden of pressure oxidizing or roasting a whole ore and
without the substantial loss of gold value associated with
preparation of an ore concentrate by conventional flotation.
It has been found that air, which is used as the flotation gas
25 in conventional flotation, detrimentally affects flotation
separation of gold-bearing sulfide minerals, and that significantly
enhanced flotation performance may be obtained by
maintaining the sulfide ore in an environment substantially
free of air until a desired final flotation concentrate is
30 obtained.
It is believed that oxygen gas present in air tends to
oxidize the surface of certain gold-bearing sulfide mineral
particles, with the effect that flotation of those sulfide
35 mineral particles is reduced, resulting in a significant
amount of sulfide mineral which fails to float during
flotation, and, therefore, remains with the gangue.
By using a flotation gas that is deficient in oxygen gas
relative to air, however, the problems associated with the use
40 of air can be reduced. The result is an increased recovery of
sulfide materials in the concentrate, and correspondingly, an
increase in the recovery of gold in the concentrate. It is also
believed that the presence of oxygen promotes increased
galvanic interaction, which tends to depress sulfide minerals
45 during flotation.
In one embodiment, the gold-bearing sulfide minerals in
a sulfide ore are maintained in an environment that is
substantially free of oxygen beginning with comminution of
the ore and ending with recovery of a desired final sulfide
50 mineral concentrate. An oxygen deficient gas can be introduced
prior to or during comminution to displace any air that
may be present in the ore feed and to prevent air from
entering during comminution. Oxygen in the air that would
otherwise be present during comminution is, thereby, press
vented from oxidizing newly exposed sulfide mineral surfaces
created during comminution. Although comminution
in an atmosphere of the oxygen deficient gas is preferred, an
alternative to reduce detrimental effects of oxygen is to seal
the entire comminution process to prevent air from entering
60 into the process during comminution. With this alternative,
only oxygen initially in feed to comminution will be present,
so that damage to the mineral material will be limited.
In addition to reducing oxygen levels during comminution
and flotation, the use of an oxygen deficient gas tends
65 to decrease galvanic interaction, with a corresponding
increase in floatability of sulfide minerals. In one
embodiment, galvanic interaction is further reduced by
through a slurry of ore particles which have been treated
with reagents and the particles of the ore which are less
hydrophilic tend to attach to and rise with the air bubbles,
thereby permitting separation of the ore into two fractions.
5 Flotation has been used to prepare concentrates of goldbearing
sulfide minerals which are rich in the sulfide minerals
and relatively free of gangue material. One problem
with flotation of many gold-bearing sulfide ores, however, is
that a significant amount of the gold-bearing sulfide mineral
10 often reports to the wrong flotation fraction, representing a
significant loss of gold.
There is a significant need for an improved method for
processing many gold-bearing sulfide ores that avoids the
high costs associated with oxidatively treating whole ores
15 without the significant loss of gold associated with concentrating
sulfide ores by flotation.
FIELD OF THE INVENTION
CROSS-REFERENCE TO RELATED
APPLICATIONS
BACKGROUND OF THE INVENTION
1
METHOD FOR PROCESSING GOLDBEARING
SULFIDE ORES INVOLVING
PREPARATION OF A SULFIDE
CONCENTRATE
This application is a continuation-in-part of U.S. Pat.
application Ser. No. 08/423,839 filed Apr. 18, 1995, now
U.S. Pat. No. 5,653,945 the entire contents of which are
incorporated herein.
The present invention involves a method for processing
gold-bearing sulfide ores to facilitate recovery of gold from
the sulfide ore. In particular, the present invention involves
flotation processing of gold-bearing sulfide ores in a manner
that reduces problems associated with conventional flotation
to produce an ore concentrate. The present invention also 20
involves the flotation processing in combination with oxidative
treating, such as pressure oxidation, and use of
by-product gas from an oxygen plant used to supply oxygen
gas for the oxidative treating.
Significant amounts of gold are found in sulfide ores, in
which the gold is associated with sulfide mineralogy. The
gold is difficult to recover from such sulfide ores, because
the gold is typically bound in sulfide mineral grains in a
manner that renders the ore refractory to many traditional
gold recovery techniques, such as direct cyanidation of the
ore. Therefore, sulfide ores are commonly treated to chemically
alter the sulfide mineral to permit dissolution of the
gold during subsequent gold recovery operations.
One technique for treating a gold-bearing sulfide ore in
preparation for gold recovery is to subject the ore to an
oxidative treatment to oxidize sulfide sulfur in the sulfide
minerals, thereby rendering the gold more susceptible to
recovery. One method for oxidatively treating a sulfide ore
is pressure oxidation, in which a slurry of the ore is subjected
to oxygen gas in an autoclave at elevated temperature and
pressure to decompose the sulfide mineral, freeing the gold
for subsequent recovery. Other oxidative treating methods
include roasting and bio-oxidation of the ore in the presence
of air or oxygen gas.
Treating whole ores by pressure oxidation or by oxidative
roasting is expensive. Part of the expense is due to energy
consumed in heating gold-barren gangue material in the
whole ore, and especially the energy required to heat water
in which the gangue material is slurried in the case of
pressure oxidation. Also, process equipment for treating a
whole ore must be sized to accommodate the throughout of
gangue material, in addition to the throughput of the goldbearing
sulfide minerals, thereby significantly adding to the
cost of process equipment. Moreover, side reactions may
occur involving gangue material which can detrimentally
affect the oxidative treating or can produce hazardous materials
which require special handling.
One way to reduce the high energy and process equipment
costs associated with oxidative treating of a whole ore, as
well as the potential for problems associated with side
reactions, would be to remove gangue material from the ore
prior to the oxidative treatment. For example, one method
that has been used to remove gangue material from goldbearing
sulfide ores is flotation. In flotation, air is bubbled
5,837,210
3 4
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flow diagram showing one embodiment of the
present invention;
FIG. 2 is a flow diagram showing another embodiment of
the present invention;
FIG. 3 is a flow diagram showing yet another embodiment
of the present invention;
FIG. 4 is a graph of the grade of concentrate recovered
from flotation versus grind size Examples 1-6;
FIG. 5 is a graph of the grade of tails from flotation versus
grind size Examples 1-6;
FIG. 6 is a graph of concentrate weight percent recovery
from flotation versus grind size for Examples 1-6;
FIG. 7 is a graph of gold recovered in concentrate from
flotation versus grind size for Examples 1-6;
FIG. 8 is a flow diagram for one embodiment of the
present invention relating to a pilot plant for Example 7; and
FIG. 9 is a graph of gold recovery in concentrate from
flotation versus grind size for Example 8;
FIG. 10 is a flow diagram of one embodiment of the
present invention including acid pretreatment;
FIG. 11 is a process flow diagram of one embodiment of
the present invention showing recycle of flotation gas;
FIG. 12 is a sectional elevation showing features of one
embodiment of a flotation apparatus of the present invention;
FIG. 13 is a sectional elevation of another embodiment of
a flotation apparatus of the present invention;
FIG. 14 is a process flow diagram of a comminution
circuit of one embodiment of the present invention;
FIG. 15 is a process flow diagram of one embodiment of
the present invention including magnetic separation prior to
flotation;
FIG. 16 is a process diagram of one embodiment of the
present invention including a leach of flotation tails and
including the use of deoxygenated water;
FIG. 17 is a process flow diagram of one method of the
present invention having multiple flotation stages with comminution
occurring between flotation stages;
FIG. 18 is a graph with plots of sulfide sulfur recovery
versus pH for Examples 9-28;
FIG. 19 is a graph including plots of gold recovery versus
pH for Examples 9-28;
FIG. 20 is a graph including plots of incremental gold
recovery and incremental sulfide sulfur recovery for
Examples 9-28;
FIG. 21 is a graph including plots of gold recovery versus
flotation time for Examples 29-35;
FIG. 22 is a graph of gold recovery versus flotation time
for Examples 29-35;
FIG. 23 is a graph including plots of gold recovery and
oxidation-reduction potential versus flotation time for
Example 36;
oxidation, although another oxidative treatment such as an
oxidizing roast or bio-oxidation may be used instead. Such
oxidative treating often requires a source of purified oxygen
gas, which is often produced by separation from air in an
5 oxygen plant. A by-product gas from such an oxygen plant
is deficient in oxygen gas and rich in nitrogen gas. The
by-product gas is, therefore, an ideal source of gas for use
during comminution and/or flotation of a gold-bearing sulfide
ore. This by-product gas is normally vented to the
10 atmosphere in current gold processing operations and is,
therefore, wasted.
reducing the amount of iron introduced into the system
and/or by removing iron from the system. Iron contamination
in the system may be reduced by using comminution
media made of stainless steel or hardened steel, rather than
the normal mild steel, and/or by using a nonmetallic liner for
comminution equipment. Iron may be removed from the
system prior to flotation by magnetic separation. It has been
found that reducing galvanic interaction can significantly
improve recovery of gold-bearing sulfide minerals during
flotation, especially when flotation is conducted with an
oxygen deficient flotation gas.
Possible sources of the oxygen deficient gas include
by-product gas from an oxygen plant, a dedicated nitrogen
plant, combustion exhaust gases, and on-site delivery of
compressed or liquified gases. In one embodiment to reduce 15
the consumption of the oxygen deficient gas, flotation gas is
recycled in the flotation operation.
When using an oxygen-deficient flotation gas according to
the present invention, adjustment of other flotation operating
parameters have been found to be unusually important to 20
maximizing flotation performance. In that regard, it has been
found that the flotation should be operated at an acidic pH,
preferably below about pH 6. Also, use of a lead-containing
activator significantly enhances flotation performance, as
does the use of deoxygenated water during comminution and 25
flotation. These additional enhancements are particularly
important because it has been found that the gold is often
most associated with the mineralogical/morphological sulfide
species that are generally the hardest to float. Therefore,
for example, a flotation enhancement that increases sulfide 30
mineral recovery by just one percentage point may increase
gold recovery in the concentrate by a proportionately larger
amount. This is because the incremental sulfide mineral
particles that tend to float with each enhancement include
those most likely to contain significant quantities of gold. 35
Conversely, the sulfide minerals that are easiest to float, such
as coarse grain pyrite, often contain little gold.
Another embodiment according to the present invention
includes a leach of flotation tails to recover gold remaining 40
in the tail that is not associated with sulfide minerals. For
some sulfide ores, this may be a significant quantity of gold.
The tail leach generally involves a cyanide leach. A major
advantage of the present invention is that the flotation tail is
relatively clean of sulfide minerals. This is important to 45
effective cyanide leaching of the tail because of the significant
loss of cyanide that would occur if significant quantities
of sulfide minerals were present in the tail.
In a still further embodiment according to the present
invention, a significant operational enhancement is obtained 50
by performing a regrind operation intermediate between two
flotation stages. This permits a more coarse initial grind to
be used for an initial stage of flotation to recover a significant
quantity of the sulfide mineral particles. The regrind
then permits additional liberation of sulfide minerals that 55
may be locked in middling particles. Such staged processing
would not be possible with conventional air flotation
because of the detrimental effects of oxygen during conventional
grinding and flotation.
In one aspect, the present invention involves the advan- 60
tageous utilization, in the processing of gold-bearing sulfide
ores, of gases which may be separated from air. In one
embodiment, a flotation operation, conducted substantially
in the absence of oxygen gas, is combined with oxidative
treating to decompose sulfide minerals, freeing gold for 65
possible subsequent dissolution using a gold lixiviant, such
as a cyanide. The preferred oxidative treating is pressure
5,837,210
TABLE 11
0.08
Twin Creeks
0.03
Gold Loss (%) per 1.0% Loss
Iron Sulfide
Lone Tree
TABLE 12
Morphology
Iron Sulfide
Coarse Grained
Pyrite
25 'Not applicable.
2Average content from 5 high grade samples from fine grained/amorphous
material.
Gold Content
Iron Sulfide (ppm by wt.) Grain
15
Morphology Lone Tree Twin Creeks Size
Coarse Grained Pyrite 2 2 Coarse
Blastic Pyrite 25 NA' Coarse
Medium Grained Pyrite 48 9 Medium
Fine Grained/Framboidal Pyrite 103 58 Fine
20 Amorphous/Framboidal Pyrite NA' 96 Fine to very
fine
Framboidal Pyrite 1902 271 Very fine
Marcasite 34 16 NA
Orpiment NA 28 NA
Finer grain size and finer morphological character of a
sulfide mineral renders the sulfide mineral generally more
susceptible to the detrimental effects from the presence of
oxygen in a flotation system. To obtain a high recovery of
gold in a flotation concentrate it is, therefore, extremely
important that the flotation be operated in a manner to
maximize the flotation of those mineralogical morphologies
that are most difficult to float. To illustrate this problem,
calculated gold losses are shown in Table 12 in flotation
tailings for each one percent equivalent loss of sulfide
mineral to the tail for the various species. As seen in Table
12, if one percent of the iron sulfide of the Lone Tree ore is
lost to the tail, and that one percent is framboidal pyrite, then
the corresponding loss of gold to the tail is over three
percent, or a loss of gold that is proportionately more than
three times the loss of iron sulfide material. As seen for Twin
Creeks, the loss of framboidal pyrite results in a loss of gold
that is proportionately more than ten times the loss of the
iron sulfide. To further illustrate, experience on the Lone
Tree, Twin Creeks and other ores indicates gold recoveries
in only the 50 to 80 percent range with conventional flotation
50 recoveries of sulfide minerals in the 75 to 95 percent range.
For the Twin Creeks ore, 87 to 90 percent flotation gold
recovery in the concentrate is not achieved until sulfide
sulfur recovery exceeds about 97 percent. By promoting the
flotation of the most difficult-to-float mineralogical/
morphological species of the sulfide minerals, the present
invention addresses the need for extremely high sulfide
mineral recoveries in the flotation concentrate to obtain
acceptable gold recoveries.
6
Nevada, U.S.A. As shown in Table 11, the pyritic species
represent a variety of mineralogical/morphological types. A
common theme, however, is that the gold content of the iron
sulfides generally tends to increase as the grain size and/or
5 morphologic character becomes finer. Coarse grained pyrite
contains very low levels of gold, whereas fine grained,
amorphous and framboidal pyrite all contain much higher
levels of gold. The pyritic species shown in Table 11 are
arranged in decreasing coarseness of grain size.
10
5
FIG. 24 is a graph including plots of gold recovery and
oxidation-reduction potential versus flotation time for
Example 37;
FIG. 25 is a graph including plots of weight recovery
versus flotation time for Example 38;
FIG. 26 is a graph including plots of gold-recovery versus
flotation time for Example 38;
FIG. 27 is a graph including plots of sulfide sulfur
recovery versus flotation time for Example 38;
FIG. 28 is a process flow diagram of one embodiment of
the present invention using gas generated in an acid pretreatment
step as a flotation gas.
The present invention provides a method for processing a
gold-bearing sulfide mineral material, such as a gold-bearing
sulfide ore, to facilitate recovery of the gold from the
mineral material. The method involves preparation of a
flotation concentrate in a manner that reduces problems
associated with conventional flotation. It has, surprisingly,
been found that the problems associated with concentrating
a gold-bearing sulfide ore by conventional flotation may be
significantly reduced by the use of a flotation gas which
comprises a lower volume fraction of oxygen gas than is
present in ambient air. Preferably, the flotation gas should be
substantially free of oxygen gas. When air is used as a
flotation gas, the oxygen gas in the air appears to detrimentally
affect the floatability of the sulfide minerals. This may 30
be due to a surface oxidation of sulfide mineral particles
caused by the presence of the oxygen gas. The surface
oxidation would tend to depress the sulfide mineral particles
during flotation. Furthermore, the detrimental effects of
oxygen gas may be further reduced by maintaining the ore 35
in an environment that is substantially free of oxygen gas
during comminution, mixing, pumping and all other processing
steps until a final flotation concentrate has been
obtained. For example, when multiple flotation steps are
used, it is desirable to maintain the ore in an environment 40
that is substantially free of oxygen gas between the flotation
steps.
By reducing the apparently detrimental effects of oxygen
gas, it is possible to recover a greater amount of the sulfide
mineral in the flotation concentrate. The present invention, 45
therefore, facilitates the recovery of gold from sulfide mineral
material which may have previously been discarded as
waste, either with the gangue in a flotation tailor as subgrade
ore previously believed to be uneconomical for gold recovery.
Enhanced concentration, according to the present
invention, of sulfide minerals into the flotation concentrate
provides a particular advantage with respect to gold recovery
from gold-bearing sulfide minerals. This is because it has
been found that gold in a refractory sulfide ore is often 55
predominantly associated with sulfide mineral
mineralogical/morphological species that are most difficult
to effectively float. Therefore, the increase in gold recovery
in the concentrate with the present invention will often be a
substantially greater percentage increase than the percentage 60
increase in recovery of sulfide minerals.
As an example of concentration of gold in difficult-tofloat
mineralogical/morphological species, a detailed mineralogical
characterization is shown in Table 11 of auriferous
pyritic species found in two refractory sulfide ore 65
samples. One ore sample is from the Lone Tree Mine and the
other ore sample is from the Twin Creeks Mine, both in
DETAILED DESCRIPTION OF IRE
PREFERRED EMBODIMENT
7
5,837,210
8
(l)Not applicable.
(2)Average content from 5 high grade samples from fine grained/amorphous
material
Morphology Lone Tree Twin Creeks
Blastic Pyrite 0.41 NA(l)
Medium Grained 0.80 0.36
Pyrite
Fine 1.71 2.29
Grained/Amorphous
Pyrite
Amorphous/Framboidal NA(l) 3.79
Pyrite
Framboidal Pyrite 3.15(2) 10.7
Marcasite 0.45 0.63
Orpiment NA 1.11
One embodiment in accordance with the present invention
is shown in FIG. 1. With reference to FIG. 1, a gold-bearing
mineral material feed 102 is provided for processing. The
mineral material feed 102 may be any gold-bearing material
comprising one or more sulfide mineral with which the gold
is predominantly associated, and from which the gold is
difficult to recover. The sulfide mineral could include one or
more mineralogy including pyrite, marcasite, arsenopyrite,
arsenous pyrite and pyrrhotite. The mineral material feed
102 is typically a whole ore, but may be a residue from other
processing or a previously discarded tail.
The mineral material feed 102 is subjected to comminution
104 to obtain a particulate mineral material 106 having
mineral particles of a size suitable for flotation. The particulate
mineral material 106 is preferably sized such that at
least 80 weight percent of particles in the particulate mineral
material are smaller than about 100 mesh, more preferably
smaller than about 150 mesh, and still more preferably
smaller than about 200 mesh. The size at which 80 weight
percent of a material passes is often referred to as a P80 size.
Any suitable grinding and/or milling operation may be used
for the comminution 104. Wet grinding and/or milling
operations are generally preferred due to their relative ease
and low cost compared to dry operations.
The comminution 104 is conducted in the presence of a
blanketing gas 108 which is obtained from a gas source 110.
During, or prior to, the comminution 104, the mineral
material feed 102 is mixed with the blanketing gas 108,
which contains oxygen gas, if at all, at a lower volume
fraction of oxygen gas than is present in ambient air, to
reduce problems that could be caused by the presence of air
during the comminution 104. During the comminution 104,
it is preferable to maintain a positive pressure of the blanketing
gas 108 into any grinding and/or milling apparatus to
assist mixing of the mineral material feed 102 with the
blanketing gas 108, and to displace any air which may have
been present with the mineral material feed 102.
After the comminution 104, the particulate mineral material
106 is subjected to flotation 112 to separate sulfide
minerals, with which the gold is associated, from non-sulfide
gangue material. During flotation, a slurry of the particulate
mineral material 106 is aerated with a flotation gas 114 from
the gas source 110. Any suitable flotation apparatus may be
used for the flotation 112, such as a one or more of a
conventional flotation cell or a flotation column. Preferably,
however, the flotation apparatus is such that a small positive
pressure of the flotation gas 114 may be maintained in the
Iron Sulfide
TABLE 12-continued
Gold Loss (%) per 1.0% Loss
Iron Sulfide
apparatus to prevent the entry of air into the apparatus. The
flotation gas 114 has oxygen gas, if at all, at a reduced
volume fraction relative to the volume fraction of oxygen
gas in ambient air, to reduce the problems associated with
5 using air as a flotation gas. Although not required, the
flotation gas 114 will normally be of substantially the same
composition as the blanketing gas 108 used in the comminution
104. Additionally, normal reagents may be added
during or prior to the flotation 112 to assist in flotation
10 separation. Such reagents may include frothing agents,
activators, collectors, depressants, modifiers and dispersants.
Preferably, the flotation 112 is conducted at ambient
temperature and a natural pH produced by the mineral
material. Operating conditions such as pH may, however, be
15 adjusted as desired to optimize flotation separation for any
particular mineral material.
Exiting from the flotation 112 is a flotation concentrate
116, which is recovered from the flotation froth and which
is enriched in sulfide minerals, and consequently is also
20 enriched in gold. Also exiting from the flotation 112 is a
flotation tail 118, which is enriched in non-sulfide gangue
materials, and consequently contains low levels of gold. The
flotation concentrate 116 may be further processed to
recover the gold by any suitable technique, if desired.
25 Alternatively, the flotation concentrate 116 may be sold as a
valuable commodity for processing by others to recover the
gold.
As noted previously, the flotation gas 114 and the blanketing
gas 108 each comprise oxygen gas, if at all, at a
30 volume fraction that is less than the volume fraction of
oxygen gas in ambient air. Preferably, however, the amount
of oxygen gas in the flotation gas 114 and/or blanketing gas
108 is less than about 15 volume percent, and more preferably
less than about 5 volume percent. Most preferably, both
35 the flotation gas 114 and the blanketing gas 108 are substantially
free of oxygen gas.
To aid in the understanding of the present invention, but
not to be bound by theory, it is believed that oxygen gas, if
present in any appreciable quantity, tends to oxidize the
40 surface of particles of certain gold-bearing sulfide minerals,
which can have the effect of depressing flotation of the
gold-bearing sulfide mineral particles during the flotation
112. By reducing the amount of oxygen gas that comes into
contact with a mineral material, it is believed that any
45 surface oxidation effect is reduced, resulting in enhanced
flotation of sulfide mineral particles and a corresponding
increase in the amount of sulfide mineral, and therefore gold,
recovered in the flotation concentrate 116. Therefore, it is
preferred that the flotation gas 114 and the blanketing gas
50 108 consist essentially of components which could not
oxidize the surface of gold-bearing sulfide mineral particles.
It is preferred that the flotation gas 114 and the blanketing
gas 108 predominantly comprise one or more gases other
than oxygen gas. Suitable gases include nitrogen, helium,
55 argon and carbon dioxide. Preferably, one or more of these
gases should comprise greater than about 95 volume percent
of the flotation gas 114 and the blanketing gas 108, and more
preferably greater than about 98 volume percent. Still more
preferable is for the blanketing gas 108 and the flotation gas
60 114 to consist essentially of one or more of these gases.
Nitrogen gas is particularly preferred because of its relatively
low cost. Carbon dioxide is less preferred because it
forms an acid when dissolved in water, which could corrode
process equipment or produce conditions less conducive to
65 optimum flotation.
The blanketing gas 108 and/or the flotation gas 114 may
be introduced into process apparatus in any appropriate
5,837,210
9 10
5
enriched stream from an oxygen plant. The nitrogen plant
may be based on separation of air into a nitrogen-enriched
stream and an oxygen-enriched stream by membrane
separation, cryogenic separation or otherwise.
Another possibility for the gas source 110 is a burner or
other combustion device to produce combustion exhaust
gases that are substantially depleted in oxygen. For example,
the gas source 110 could be exhaust from an electrical power
generator used to generate power for a mine or mineral
10 processing facility. When using combustion exhaust gases as
the blanketing gas 108 and/or the flotation gas 114, it is
preferred that the fuel combusted to produce the gases be a
clean-burning fuel such as natural gas, propane or another
liquified petroleum gas, or an alcohol such as methanol or
15 ethanol. Although less preferred, other fuels could be used
such as coal or fuel oils, including diesel fuel.
Yet another possibility for the gas source 110 is gas
generated during acid pre-treatment of a mineral material
feed 102 comprising carbonate minerals. Carbon dioxide gas
20 is generated from decomposition of the carbonate minerals.
The carbon dioxide may be used as the blanketing gas 108
and/or the flotation gas 114. Such an embodiment is shown
in FIG. 10. As shown in FIG. 10, the mineral material feed
102 is subjected to comminution 104 to form the particulate
25 mineral material 106. The particulate mineral material 106 is
then subjected to an acid pre-treatment 150 where acid 152
is added to the particulate mineral material 106 to decompose
carbonate minerals present in the particulate mineral
material 106. The particulate mineral material 106 remain-
30 ing following the acid pre-treatment is subjected to flotation
112, to form the flotation concentrate 116 and the flotation
tail 118. During the acid pre-treatment 150, a gas that is
enriched in carbon dioxide and deficient in oxygen is
produced, which is used as the blanketing gas 108 and the
35 flotation gas 114. An alternative to acid pretreatment of the
mineral material feed 102 is to use gases produced during
acid pretreatment of another carbonate-containing mineral
material, such as a whole ore, prior to pressure oxidation.
Such an embodiment is shown in FIG. 28.
A still further possibility for the gas source 110 is to have
liquid or compressed nitrogen, carbon dioxide or another gas
delivered to the site. On-site generation of the flotation gas
114 and the blanketing gas 108 is, however, preferred.
In one preferred embodiment of the present invention, the
flotation gas 114 is made up, at least in part, of recycled gas
from the flotation 112. One such embodiment is shown in
FIG. 11, where a recycle gas 156 from the flotation 112 is
used as part of the flotation gas 114. In this manner, make-up
50 flotation gas 114 from the gas source 110 may be kept to a
minimum. This recycling of gas from the flotation 112
provides the benefits of reducing the amount of make-up gas
that needs to be supplied by the gas source 110 and reduces
emission of oxygen-deficient gas from the flotation 112.
55 Reducing the emission of oxygen-deficient gas from the
flotation 112 is particularly important when the flotation 112
is conducted in an enclosed structure where people are
present, so that ambient air in the structure does not become
seriously deficient in oxygen. In that regard, oxygen moni-
60 tors should be placed in any such enclosed structure to
ensure that sufficient oxygen is present for human needs.
FIG. 12 shows features of one embodiment of a flotation
apparatus 160 that may be used with the present invention to
accomplish recycling of flotation gas. As shown in FIG. 12,
65 the flotation apparatus 160 has a sealed flotation tank 162,
above which is mounted a motor 164 for rotating a shaft 166
extending down into the flotation tank 162 to drive an
manner. Such gases may be fed under positive pressure or
may be induced into the apparatus by creating a suction
which pulls the gas in. Preferably, however, the apparatus is
designed to substantially prevent introduction of air into
comminution and flotation apparatus.
In one embodiment, the possible detrimental effects of
any surface oxidation of sulfide mineral particles that may
be present in a mineral material feed may be counteracted by
the addition of a sulfidizing agent, to at least partially replace
the oxidized coating with a sulfide coating. Any material
capable of reacting to form the desired sulfide coating of the
mineral particle could be used. Suitable sulfidizing agents
include alkali metal sulfides and bisulfides, such as Na2S,
NaHS, etc. Such sulfidizing agents could be added just
before or during any stage of the flotation 112.
With the present invention, greater than about 80 weight
percent of sulfide minerals from the particulate mineral
material 106 may be recovered in the flotation concentrate
116, and preferably greater than about 90 weight percent of
those sulfide minerals are recovered in the flotation concentrate
116.
One major advantage of the process of the present invention
is that, in addition to permitting a high recovery of
gold-bearing sulfide minerals in the flotation concentrate
116, it permits a high rejection of gangue material into the
flotation tail 118. Relative to the use of air as a flotation gas,
the present invention permits the same recovery of gold to
be obtained in a concentrate of smaller weight. This provides
a significant economic advantage because less gangue material
is present in the concentrate, from which the gold must
ultimately be separated to produce a purified gold product,
if desired.
The gas source 110 may be any source providing a
suitable flotation gas 114 and blanketing gas 108. One
preferred gas source 110 is a facility in which nitrogen gas
is separated from air, with the separated nitrogen gas being
used as the blanketing gas 108 and the flotation gas 114.
Several processes are known for separating nitrogen from
air, including cryogenic separation and membrane separa- 40
tion.
One particularly preferred gas source 110 is an oxygen
plant, which is commonly found at existing facilities where
gold-bearing sulfide ores are processed. An oxygen plant is
typically required, for example, when a pressure oxidation 45
operation or an oxidative roasting operation is used in the
processing of gold-bearing sulfide ores. In the oxygen plant,
oxygen is separated from air, such as by cryogenic separation
or membrane separation, and the separated oxygen gas
is used in the pressure oxidation or oxidative roasting
operation. A by-product of such an oxygen plant is an
effluent gas stream which is enriched in nitrogen gas and is
suitable for use as the blanketing gas 108 and/or the flotation
gas 114. This by-product stream has previously been vented
to the atmosphere and has, therefore, been wasted. With the
present invention, however, the by-product stream may be
beneficially used to produce the flotation concentrate 116, in
addition to using the oxygen gas product stream for the
pressure oxidation or oxidative roasting operation.
Another possibility for the gas source 110 is a nitrogen
plant dedicated to producing a nitrogen-enriched gas for use
as the blanketing gas 108 and/or the flotation gas 114. A
nitrogen plant differs from an oxygen plant in that the main
product stream is a nitrogen-enriched gas stream and the
by-product stream is an oxygen-enriched gas stream. The
oxygen-enriched gas stream from a nitrogen plant, however,
is normally of much lower purity in oxygen than an oxygen5,837,210
10
11
impeller 168. When the flotation apparatus 160 is operating,
a vapor headspace 170 exists above a liquid column 172.
Gas from the vapor headspace 170 is withdrawn via a
conduit 174 by a blower 176 to be forced through a conduit
178 for use as flotation gas. The flotation gas from conduit 5
178 is forced through an annular conduit 180 to the vicinity
of the impeller 168 so that the flotation gas may be
adequately distributed and dispersed throughout the liquid
column 172. Make-up flotation gas is provided via conduit
182 to compensate for any system losses of flotation gas.
FIG. 13 shows features of another embodiment of the
flotation apparatus 160 for effecting recycle of flotation gas.
In the embodiment shown in FIG. 13, the flotation apparatus
160 is designed such that a blower is not used. Instead, the
conduit 174 collects gases from the overhead vapor space 15
170 and cycles the gas to the annular conduit 180 for use as
a flotation gas. The action of the impeller 168 causes a
vacuum in the annular conduit 180 creating sufficient suction
to draw the flotation gas through the conduit 174 at a
sufficiently high rate. This type of flotation apparatus 160 20
design, therefore, is self-inducing with respect to the introduction
of flotation gas and does not require a blower or
other gas compression device. Cycling of the flotation gas
without the use of a blower is important because the recycled
flotation gas will normally contain a significant amount of 25
acid or corrosive mists or corrosive gases that could significantly
corrode interior surfaces of a blower.
Referring again to FIG. 1, as noted previously, the flotation
112 may be performed at a natural pH. It has been
found, however, that it is preferred that the flotation 112 be 30
conducted at an acidic pH, and preferably at an acidic pH
that is lower than about pH 6. Even more preferred is a
flotation pH range of from about pH 3 to about pH 6, and
most preferred is a pH range of from about pH 5 to about pH
6. Control of the pH may be accomplished by the addition 35
of an acid or a base as necessary to adjust the pH to within
the desired range. For example, sulfuric acid and/or any
other acid could be added to the flotation 112 to lower the pH
and lime, sodium carbonate, caustic or any other base could
be added during the flotation 112 to raise the pH. Acid for 40
reducing the pH could come from other mineral processing
steps, such as pressure oxidation or bio-oxidation, as discussed
below. Furthermore, acidification could be accomplished
by introducing sulfur dioxide into the flotation 112.
In its dissolved state in water, sulfur dioxide forms sulfurous 45
acid. The sulfur dioxide could be provided by exhaust gas
from a sulfur burner.
As noted previously, various reagents may be used during
the flotation 112. It has been unexpectedly found, however,
that copper-based activators generally do not perform as 50
well as lead-based activators used during the flotation 112.
Lead-based activators should contain lead in an oxidation
state of +2. One preferred activator is lead nitrate. Another
preferred activator is lead acetate. One benefit of using a
lead-based activator, relative to the use of a copper-based 55
activator such as copper sulfate, is that higher recoveries are
experienced in the flotation concentrate 116 for both sulfide
minerals and gold. Also, if the flotation tail is subjected to
cyanide leaching, as discussed below, the use of a lead-based
activator provides the additional advantage of lowering 60
cyanide consumption during the leaching operation relative
to a copper-based activator. An added advantage is that
cyanide consumption for eventual cyanide leaching of gold
contained in the flotation concentrate 116, such as after
pressure oxidation, will be lower with the use of a lead- 65
based activator compared to the use of a copper-based
activator.
12
Another reagent that has been found to be particularly
useful in the flotation 112 is a xanthate collector. The
appropriate xanthate collector may be provided by addition
to the flotation 112 of a xanthate salt such as potassium amyl
xanthate or sodium isopropyl xanthate. The enhanced performance
through use of a xanthate collector reagent is
significantly greater than would normally be expected, especially
when compared to the performance of other widely
used collector reagents.
When the mineral material feed 102 contains a significant
amount of organic carbon, the organic carbon can significantly
detrimentally interfere with recovery of gold and
sulfide minerals in the flotation concentrate 116. To reduce
the detrimental effects of organic carbon, when present in
the mineral material feed 102, it has been found to be
advantageous to add an aromatic oil to the flotation 112. One
example of such an aromatic oil is moly collecting oil,
commonly referred to as MCO.
As discussed above, the comminution 104 is conducted in
the presence of the blanketing gas 108. With reference now
to FIG. 14, one embodiment of a comminution circuit is
shown. As shown in FIG. 14, the mineral material feed 102
is fed to a first comminution unit 186, such as a sag mill. In
the first comminution unit 186, the mineral material particles
in the mineral material feed 102 are reduced in size. Output
from the first comminution unit 186 passes through a
trommel screen 188 in a sealed discharge box 190. Blanketing
gas 108 is fed into the discharge box 190 so that the
blanketing gas will flow back through the first comminution
unit 186 in counter-flow with the mineral material feed 102,
to ensure removal of air from the mineral material feed 102.
Material exiting the discharge box goes to a tank 192 for
delivery to a cyclone separator 194 via a pump 196. The
cyclone separator 194 classifies the mineral material by
particle size into an overflow 198 of smaller-size particles
and an underflow 200 of larger-size particles. The underflow
200 is then fed to sealed feed box 201 of a second comminution
unit 202, such as a ball mill, to further reduce the size
of mineral material particles in the underflow 200. Discharge
from the second comminution unit 202 passes through a
trommel screen 204 in a sealed discharge box 206. Blanketing
gas 108 is fed into both the feed box 201 and the
discharge box 206. Material exiting the discharge box 206
goes to a tank 208 where it is combined with the overflow
198 from the cyclone separator 194. Discharge from the tank
208 goes to a cyclone separator 210 via a pump 212. The
cyclone separator 210 makes a size separation of particles
into an overflow 214 comprising smaller-size particles and
an underflow 216 comprising larger-size particles. The
underflow 216 from the cyclone separator 210 is fed to the
second comminution unit 202 along with the underflow 200
from the cyclone separator 194. The overflow 214 from the
cyclone separator 210 goes to the tank 218 where particulate
mineral material in the overflow 214 may be held for feed to
flotation processing.
It should be noted that, as shown in FIG. 14, all process
equipment is sealed except for feed into the comminution
unit 186. Furthermore, the blanketing gas 108 is introduced
at various points in the comminution system to ensure that
minimal air makes its way into the system. As shown in FIG.
14, the blanketing gas 108 is specifically fed to the discharge
box 190 of the first comminution unit 186, to the tanks 192,
208 and 218; to the cyclone separators 194 and 210; and to
the feed box 201 and the discharge box 206 of the second
comminution unit 202.
In addition to maintaining the comminution environment
in the absence of any significant quantities of air, it is
5,837,210
13 14
enter into the system. With the present invention, however,
when it is not practical or economic to use a blanketing gas,
enhanced performance may still be obtained by sealing all
equipment involved with comminution processing so that
5 substantially the only oxygen entering into the comminution
processing enters with the mineral material feed 102 to be
processed. In that regard, such a comminution system could
be substantially as described with respect to FIG. 14, with all
process equipment sealed to prevent the entry of air and with
10 no blanketing gas 108 being fed to the process equipment.
Oxygen already present in the mineral material feed 102
would be consumed through oxidation of surfaces of sulfide
mineral particles exposed during comminution. Once all of
that original oxygen had been consumed, however, the
continued detrimental effects of oxygen would be substan-
15 tially eliminated. Although this mode of operation is not as
preferable as using the blanketing gas 108, it is preferred to
a system that it is open to the introduction of air, as is
commonly practiced.
To further reduce the amount of oxygen introduced in the
20 system to reduce the detrimental effects of surface oxidation
of sulfide minerals and of galvanic interactions, it is preferred
that process water used to slurry mineral material for
comminution processing and/or flotation processing has
been deoxygenated. Deoxygenation of process water can
25 significantly enhance recovery in the concentrate of sulfide
minerals and gold during flotation processing. The deoxygenation
may be performed in any convenient manner, such
as by bubbling an inert stripping gas, such as nitrogen or
carbon dioxide, through the process water to remove oxygen
30 from the process water or by adding an oxygen scavenger to
the water to tie-up the oxygen. It has been found that a
flotation tank works well for deoxygenation, with nitrogen
or carbon dioxide being introduced into the vessel to perform
the oxygen stripping function. Alternatively, the inert
35 stripping gas could be sparged into a tank containing the
process water. Preferably, the process water should be
deoxygenated to a dissolved oxygen level that is less than
about 1.0, and more preferably less than about 0.5, parts per
million of oxygen by weight.
Also, with the present invention it is possible to use
recycled water as process water. When recycled water is
used, however, it is important that an activator be used
during flotation processing. This is because any cyanide in
the recycle water that is available for reaction with sulfide
45 sulfur or sulfide minerals will tend to depress flotation of the
sulfide minerals and, accordingly, reduce the recovery of
gold in the concentrate. The activators, however, counter the
depressing effect that cyanide has on flotation. Also, the
recycle water may be treated with a material such as
50 ammonium bisulfite, sulfur dioxide, a peroxide, Caro's acid
or any other known cyanide destruction technology used to
destroy the cyanide prior to using the recycle water for
flotation.
As noted with respect to FIG. 1, one preferred gas source
55 110 for the blanketing gas 108 and the flotation gas 114 is an
oxygen plant. FIG. 2 shows one embodiment of the present
invention in which both the oxygen gas product stream and
the nitrogen gas by-product stream from an oxygen plant are
both used to process gold-bearing sulfide mineral material.
60 Referring to FIG. 2, particulate mineral material 110 is
subjected to the flotation 112 to produce the flotation concentrate
116 and the flotation tail 118, as previously
described. The flotation gas 114 is a nitrogen gas enriched
by-product stream from an oxygen plant 130, in which air
65 132 is separated into an oxygen enriched gas stream
(treating gas 128) and nitrogen enriched gas stream
(flotation gas 114).
Eq. 1
auriferous pyrite surface (cathode):
Vz02+H20+2e-~20H- Eq.2
For example, during grinding, galvanic cells are created
every time an auriferous pyrite mineral surface comes into
contact with grinding media, mill liners, abraded tramp iron
or any other metal sulfide at a lower or higher rest potential.
These galvanic interactions create hydroxide coatings on
sulfide mineral surfaces, depressing their floatability.
According to the present invention, such detrimental galvanic
interactions can be hindered by reducing the amount
of oxygen present during comminution through use of the
blanketing gas 108.
It has been found, however, that, in addition to reducing
the amount of oxygen present during the comminution
operation, improved flotation results may be obtained by
further limiting iron contamination of the mineral material
being processed. The combination of reducing the amount of
iron introduced into the mineral material and the use of the
blanketing gas 108 provides an increase in gold recovery in 40
the flotation concentrate that would be unexpected based on
the contributions of each alone.
One way to reduce the amount of iron available for
galvanic interactions during the comminution processing is
to use comminution media made of a hardened steel or a
corrosion-resistant steel, such as stainless steel or a high
chromium alloy steel. Although ceramic comminution
media could be used, ceramic comminution media are
typically not of sufficient density for effective comminution.
Another way to reduce detrimental galvanic effects from
iron is to provide all comminution equipment, such as
grinders and mills, with non-metallic liners, and preferably
with rubber liners.
A further, and preferred method for reducing detrimental
galvanic interactions caused by iron during flotation is to
perform a magnetic separation step after comminution and
prior to flotation. Referring to FIG. 15, an embodiment is
shown including a magnetic separation step after comminution.
As shown in FIG. 15, the mineral material feed 102
is first subjected to comminution 104, followed by magnetic
separation 230 to remove particles of magnetic material 232
from the mineral material 106.
As an alternative to the embodiments discussed thus far,
it should be noted that many of the advantages of the present
invention may be obtained even without the use of the
blanketing gas 108. In that regard, most conventional comminution
circuits utilize equipment that freely permits air to
important to the performance of subsequent flotation operations
that the effects of galvanic interaction be reduced as
much as possible during comminution of the mineral material
feed 102. Such galvanic interactions are due to different
electrochemical activities at different material surfaces. The
combination of a cathodic surface (i.e., pyrite, pyrrhotite,
etc.) and an anodic surface (i.e., iron from comminution
media or from steel walls of mill liners) results in the
creation of galvanic cell during the comminution processing.
Galvanic cells also exist between different sulfide minerals
that may be present in the mineral material feed, with the
sulfide mineral with the higher rest potential acting as the
cathode and the sulfide mineral with the lower rest potential
acting as the anode. For example, the galvanic interaction
between grinding iron and various forms of auriferous pyrite
can be represented by the following reactions:
grinding iron surface (anode):
15
5,837,210
16
The flotation concentrate 116, which is enriched in goldbearing
sulfide minerals, is subjected to pressure oxidation
124 to decompose sulfide minerals, producing an oxidized
material 126 from which the gold could be recovered by
dissolution using any suitable gold lixiviant, such as a
cyanide. The pressure oxidation 124 involves treating a
slurry of the flotation concentrate 116 in an autoclave at a
temperature of greater than about 1500 C. and an elevated
pressure in the presence of an overpressure of a treating gas
128, which is rich in oxygen. It should be noted that other
oxidative treating steps could be used instead of the pressure
oxidation 124. For example, an oxidative roasting or biooxidation
could be used to produce the oxidized material
126 using the treating gas 128.
A further embodiment in accordance with the present
invention is shown in FIG. 3 which uses the product and
by-product gas streams from an oxygen plant to process a
gold-bearing sulfide mineral material provided in two separate
feed streams. Referring to FIG. 3, a particulate first
mineral material feed 138 is subjected to the flotation 112 to
produce the flotation concentrate 116 and the flotation tail
118, as previously described. The flotation gas 114 is a gas
stream enriched in nitrogen from the oxygen plant 130. A
particulate second mineral material feed 140 is combined
with the flotation concentrate 116 in a mixing step 142. The
combined stream 144, in the form of a slurry, is subjected to
the pressure oxidation 124 to produce the oxidized material
126, from which gold could be recovered.
One advantage of the embodiment shown in FIG. 3 is that
it permits the processing of multiple ores having different
characteristics. For example, the first mineral material feed
138 may comprise a lower grade gold-bearing sulfide ore
than the second mineral material feed, which may comprise
a higher grade gold-bearing sulfide ore. The higher grade ore
may be suitable for pressure oxidation in a whole ore form,
whereas the lower grade ore must be upgraded to a concentrate
form to be suitable for pressure oxidation.
Alternatively, the second mineral material feed may comprise
a gold-bearing sulfide ore which has a significant
amount of carbonate material which would require acid to be
added prior to pressure oxidation 124, and which could,
therefore, cause high operating costs compared to ores with
low carbonate levels detrimentally interfere with proper
operation of the pressure oxidation 124. A high sulfide sulfur
content in the flotation concentrate 116, however, tends to
produce additional acid during pressure oxidation to at least
partially offset the acid consuming effect of carbonate material
in the second mineral material feed. Most of the carbonate
material that may have been present in the first
mineral material feed, if any, would ordinarily have been
removed during the flotation 112.
With the present invention, most of the gold reports to the
flotation concentrate. Gold in the concentrate, which is
typically substantially all associated with one or more sulfide
mineral, may then be freed for recovery operations by
oxidative processing, such as pressure oxidation, oxidative
roasting or bio-oxidation. Many mineral material feeds,
however, contain a significant amount of gold that is not
associated with a sulfide mineral. For example, it is not
uncommon for a gold-bearing refractory sulfide ore to also
contain some gold in association with oxidized minerals. Up
to 50%, and in some instances even more, of the gold in a
refractory sulfide ore may be associated with minerals other
than sulfide minerals. Also, refractory sulfide ores that have
been stockpiled for a significant amount of time, and therefore
exposed to air for a significant amount of time, may
contain even larger amounts of gold that are no longer held
by the sulfide minerals. This is because a significant amount
of a sulfide mineral may become oxidized so that a significant
quantity of the gold is no longer associated with the
sulfide mineral. For example, a refractory sulfide ore stock-
S piled for several months may oxidize to a degree where 20%
to 30% or more of the gold is no longer associated with
sulfide minerals.
It has been found that the present invention works very
well for the treatment of mineral material feeds having both
10 gold associated with sulfide minerals and gold not associated
with sulfide minerals. Gold that is not associated with sulfide
minerals, and especially gold associated with oxidized
minerals, may be recovered following flotation processing
by leaching of the flotation tail. Although any compatible
15 leaching operation may be used, a preferred leaching operation
is cyanide leaching. One embodiment of the present
invention involving a leach of the flotation tail is shown in
FIG. 16.
With reference to FIG. 16, a mineral material feed 102 is
20 provided having both gold that is associated with a sulfide
mineral and gold that is not associated with a sulfide
mineral. The mineral material feed 102 is subjected to
comminution 104 to prepare the particulate mineral material
106, which is then subjected to flotation 112. Following the
25 flotation 112, the flotation tail 114 is subjected to oxygenation
240 followed by a leach 242 of the flotation tail 114.
Preferred for the leach 242 is a carbon-in-pulp cyanide
leach, although a carbon-in-Ieach cyanide leach could be
used instead. Exiting from the leach 242 is loaded carbon
30 244 that is loaded with gold. Also exiting from the leach 242
is a leach tail 246 that is depleted in gold. The loaded carbon
244 may be processed in any known manner for recovery of
the gold.
With continued reference to FIG. 16, the comminution
35 104 and the flotation 112 are performed in the presence of
the blanketing gas 108 and the flotation gas 114,
respectively, supplied from the gas source 110. As also
shown in FIG. 16 process water 248 is subjected to deoxygenated
prior to using the process water 248 in the process.
40 Therefore, according to the embodiment shown in FIG. 16,
the process water 248 is first deoxygenated in the deoxygenation
step 250 and, following the flotation 112, the water
with the flotation tail 118 is then oxygenated in the oxygenation
step 240 prior to the leach 246. The oxygenation 240
45 may be accomplished in any manner suitable for increasing
the amount of oxygen dissolved in the liquid of the slurry of
the flotation tail 118. Typically, the slurry of the flotation tail
118 is subjected to sparging or bubbling with air or an
oxygen-enriched gas. Oxygenation 240 may be conducted
50 using air or an oxygen-enriched gas, such as would be
suitable for pressure oxidation processing, as previously
discussed. Although the embodiment described with respect
to FIG. 16 includes deoxygenation of process water, such
deoxygenation is not required. The use of deoxygenated
55 process water does, however, tend to improve gold recovery
from the process.
The ability to successfully leach the flotation tail 118, as
shown in FIG. 16, results from the efficient separation of
sulfide minerals into the concentrate during the flotation 112.
60 If a significant amount of sulfide mineral were to report to
the flotation tail 118, then performance of the leach 242
could be significantly impaired because sulfide sulfur from
the sulfide mineral would consume cyanide during a cyanide
leach and the gold in the flotation tail associated with the
65 sulfide mineral would not be leachable. With the present
invention, however, cyanide consumption is reduced during
the leach 242 because of the efficient reporting of sulfide
5,837,210
17 18
0.063 OZ/st(l)
0.05 OZ/st(l)
1.75 wt. %
1.66 wt. %
1440 ppm. by wt.
TABLE 1
EXAMPLES
LONE TREE SUBGRADE SULFIDE ORE
REPRESENTATIVE HEAD ANALYSIS
Gold
Silver
Total Sulfur
Sulfide Sulfur
Arsenic
(l)ounces per short ton of ore
For each example, the ore sample is ground to the desired
size. A first portion of the ore sample is subjected to flotation
in a laboratory-scale flotation cell using air as the flotation
gas. A second portion of the ore sample is subjected to
flotation under the same conditions, except using a flotation
gas which consists essentially of nitrogen gas. During each
flotation test, a flotation froth is collected from the top of the
flotation cell to recover a flotation concentrate which is
enriched in sulfide minerals, and which is, therefore, also
enriched in gold. The flotation tail is that material which is
not collected in the froth. For each flotation test, the flotation
conditions are substantially as follows: A natural pH and
addition of potassium amyl xanthate and mercaptoben-
Examples 1-6
Examples 1-6 demonstrate the use of nitrogen gas as a
flotation gas during flotation of a gold-bearing sulfide ore to
produce a sulfide enriched concentrate which could be
further processed to recover gold, if desired.
For each of Examples 1-6, an ore sample is provided from
Santa Fe Pacific Gold Corporation's Lone Tree Mine in
Nevada. The ore samples are of a low grade sulfide ore
which would be unsuitable for economic pressure oxidation
in a whole ore form. A representative assay of an ore sample
is shown in Table 1.
the cleaner flotation 292 and the cleaner scavenger flotation
294. Use of the blanketing gas 108 and the flotation gas 114
substantially prevents problems that could occur if comminution
and/or flotation operations were conducted in the
5 presence of air. Furthermore, because the detrimental effects
from air are reduced, it is possible to have the second
comminution step 284 intermediate between the first flotation
stage 256 and the second flotation stage 290 without
destroying the floatability of sulfide minerals in the reground
10 mineral material 286. The second comminution step 284
significantly improves performance of the flotation circuit.
This is because it will not be necessary to comminute all of
the mineral material feed 102 to a very fine size that may be
required for liberating gold-bearing sulfide minerals from
15 middling particles in the first comminution step 254. Having
a coarser grind for the particulate mineral material 106 is
significantly less expensive than comminuting all of the
mineral material feed 102 to a size small enough to liberate
gold-bearing sulfide mineral fragments from middling. Also,
20 a coarser comminution to produce the particulate mineral
material 106 simplifies operation of the first flotation stage.
Middling particles from the first flotation stage 256 are, then
further comminuted in the second comminution step 284 to
liberate the locked gold-bearing sulfide mineral fragments
25 for recovery in the second flotation stage 290.
The present invention is further described by the following
examples, which are intended to be illustrative only and
are not intended to limit the scope of the present invention.
minerals to the flotation concentrate 116 and the relative
absence of sulfide minerals in the flotation tail 118.
Another significant advantage of the process of the
present invention is that it permits interim regrinding of
particulate mineral material between flotation stages (to
enhance gold recovery in the concentrate). Such intermediate
grinding can significantly enhance recovery of gold in
sulfide minerals fragments locked in middling particles. By
comparison, with conventional flotation using air as the
flotation gas, such intermediate grinding would further
reduce the floatability of the particulate mineral material due
to the detrimental effects of oxygen.
FIG. 17 shows a process diagram for one embodiment
according to the present invention involving regrinding of
particulate mineral material intermediate between flotation
stages. As shown in FIG. 17, a mineral material feed 102 is
subjected to a first comminution step 254 to produce a
particulate mineral material 106, which is then subjected to
a first flotation stage 256. The first flotation stage 256
includes rougher flotation 258 and rougher scavenger flotation
260. In the rougher flotation 258, the particulate mineral
material 106 is separated by flotation into a rougher concentrate
262, which forms part of a final concentrate 264,
and a rougher tail 266, that is fed to the rougher scavenger
flotation 260. The rougher scavenger flotation produces a
rougher scavenger concentrate 268 and a rougher scavenger
tail 270. The rougher tail 266, the rougher scavenger concentrate
268 and the rougher scavenger tail 270 often
include a substantial amount of middling particles. Such
middling particles include gold-bearing sulfide mineral frag- 30
ments locked with gangue material, such as silica.
Additionally, the rougher scavenger tail 270 will typically
include a substantial amount of very fine slime particles.
To remove the slime particles and to permit recovery of
the sulfide mineral fragments from middling particles, the 35
rougher scavenger tail 270 is subjected to a size separation
274, such as may be accomplished using a screen or a
classifying cyclone. A first fraction 276, comprising the
smaller-size slime particles becomes part of a final tail 278.
For example, a 500 mesh screen may be used in the size 40
separation 274 with all particles passing through the screen
being sent to the final tail 278 as slimes.
Asecond fraction 280 from the size separation 274, which
comprises larger-size particles, is sent to a second comminution
step 284 along with the rougher scavenger concen- 45
trate 268. In the second comminution step 284, particles are
comminuted to a smaller size to break up middling particles
and liberate gold-bearing sulfide mineral fragments. The
reground mineral material 286 is sent to a second flotation
stage 290 for concentration of the sulfide mineral fragments 50
liberated from middling particles. The second flotation stage
290 includes cleaner flotation 292 and cleaner scavenger
flotation 294. In the cleaner flotation 292, a cleaner concentrate
296 is produced, which is sent to form part of the final
concentrate 264. The cleaner flotation 292 also produces a 55
cleaner tail 298 which is sent to the cleaner scavenger
flotation 294. In the cleaner scavenger flotation 294, a
cleaner scavenger concentrate 300 is prepared, which is
recycled to the second comminution step 284 for further
processing. The cleaner scavenger flotation 294 also pro- 60
duces a cleaner scavenger tail 302 that is sent to form part
of the final tail 278.
Also shown in FIG. 17 is the gas source 110 that supplies
blanketing gas 108 to the first comminution step 254, the
second comminution step 284 and the size separation 274. 65
The gas source 110 also provides flotation gas 114 to the
rougher flotation 258, the rougher scavenger flotation 260,
5,837,210
19
zothiazole as collectors, copper sulfate for activation of
sulfides and MIBC as a frother. Flotation times range from
20 to 30 minutes.
The results for examples 1-6 are shown tabularly in Table
2 and graphically in FIGS. 4-7 and reveal a significant
increase in the amount of gold recovered in the concentrate
when nitrogen gas is used as the flotation gas, especially at
smaller grind sizes.
20
used as a flotation gas, with the detrimental chemical process
counteracting the normally beneficial effects of a smaller
grind size. It was observed that when air is used as the
flotation gas, the pH of the slurry in the flotation cell drops
5 rapidly for several minutes, sometimes falling by as much as
0.5-2 pH units. Therefore, it appears that oxygen in the air
may be oxidizing the surface of sulfide mineral particles,
producing sulfuric acid and lowering the slurry pH. Such
surface oxidization of the sulfide mineral particles could
TABLE 2
LONE TREE SUBGRADE BATCH TESTS
Concentrate Concentrate Gold Reporting
Grind Grade Tail Grade Recovery to Concentrate
P80 oz gold/st(2) oz gold/st(3) wt. %(4) %(5)
Example Mesh(1) air nitrogen air nitrogen air nitrogen air nitrogen
1 100 0.31 0.35 0.019 0.020 15 15 75 75
2 150 0.28 0.31 0.021 0.016 15 16 71 79
3 200 0.33 0.29 0.021 0.016 15 19 74 81
4 270 0.22 0.25 0.022 0.012 20 24 72 86
5 325 0.23 0.20 0.022 0.016 20 25 73 81
6 400 0.14 0.14 0.029 0.012 29 33 67 85
(1)80 weight percent of material passing the indicated size
(2)ounces of gold per short ton of concentrate
(3)ounces of gold per short ton of tail
(4)weight percent of ore sample feed reporting to concentrate
(5)% of gold in ore sample feed reporting to concentrate
Example 7
This example further demonstrates the beneficial use of
nitrogen gas in the flotation of gold-bearing sulfide ores, and
the use of a rougher-scavenger-cleaner arrangement of flotation
to enhance recovery of concentrate.
A flotation pilot plant is operated using a low grade sulfide
ore from the Lone Tree Mine, as previously described with
Examples 1-6. The pilot plant flow is shown in FIG. 8.
With reference to FIG. 8, the ore sample 166 is subjected
to comminution 168 in a ball mill to a PSO size of 270 mesh.
The ground ore, in a slurry 170, is introduced into a rougher
flotation step 172. In the rougher flotation step 172, an initial
flotation separation is made with a rougher concentrate 174
being collected with the flotation froth and a rougher tail 176
being sent to a scavenger flotation step 178, material collected
in the flotation froth of the scavenger flotation step
178 is repulped and introduced, as a slurry 179, to a cleaner
flotation step 180, where a final flotation separation is made
to produce a cleaner concentrate 182 from the froth and a
cleaner tail 184. The cleaner tail 184 is combined with a
scavenger tail 186, from the scavenger flotation step 178, to
produce the final tail 188. The rougher concentrate 174 and
the cleaner concentrate 182 are combined to form a final
concentrate 190. In this example, the rougher flotation step
172 is accomplished in a single dual compartment flotation
cell, the scavenger flotation step 178 is accomplished in a
30 render them less responsive to flotation. As the grind
becomes smaller, the surface area available for oxidation of
the sulfide minerals increases significantly and, accordingly,
any beneficial effect from more complete liberation of
sulfide mineral due to the smaller grind size is offset by
35 increased surface oxidation, further depressing flotation of
the sulfide mineral particles. Nitrogen gas, however, would
not oxidize the surface of sulfide minerals and, therefore,
permits better flotation of sulfide mineral particles, resulting
in a higher recovery of sulfide minerals at the smaller grind
40 sizes, as would normally be expected.
FIG. 4 graphically shows the grade of the flotation concentrate
(measured as ounces of gold per short ton of
concentrate material) as a function of the grind size. As seen
in FIG. 4, no identifiable effect on the grade of the concentrate
is apparent from using nitrogen gas relative to using air
in the flotation. FIG. 5, however, shows that the flotation tail,
at smaller grind sizes, contains a significantly lower gold
value when using nitrogen gas as a flotation gas than when
using air. Therefore, when using nitrogen gas, more of the
gold-bearing sulfide minerals are recovered in the
concentrate, apparently without any detrimental effect to the
grade of the concentrate recovered. FIG. 6 shows that the
amount of material recovered in the concentrate may be
significantly higher when using nitrogen gas as a flotation
gas than when using air, especially at the smaller grind sizes.
FIG. 7 shows that gold recovery in the concentrate may be 45
increased by almost 15% at a PSO grind of 270 mesh, when
using nitrogen gas as a flotation gas as opposed to air, again
without detrimental effect to the grade of concentrate recovered.
It should be noted that at a PSO grind of 100 mesh, there 50
is no significant difference in flotation performance when
using nitrogen gas as opposed to air as the flotation gas. It
is, therefore, surprising and unexpected that the performance
using nitrogen gas would improve so markedly relative to air
at the smaller grind sizes. Typically, it is expected that 55
flotation performance should improve with a smaller grind
size due to a more complete liberation of sulfide minerals
from non-sulfide gangue material. As seen in FIG. 7,
however, the gold recovery in the concentrate when using air
as the flotation gas is flat, at best. When using nitrogen gas, 60
however, gold recovery generally increases with decreased
grind size due to increased sulfide mineral particle
liberation, as would normally be expected.
One way to explain the unexpectedly poor flotation performance
when using air, to assist in the understanding in the 65
present invention but not to be bound by theory, is that some
detrimental chemical process may be occurring when air is
21
5,837,210
22
Examples 9-28
These examples demonstrate the importance of flotation
pH and the choice of activators for use during flotation with
the present invention.
A series of laboratory flotation tests are performed using
Lone Tree low grade gold-bearing sulfide ore samples. Prior
to flotation, each sample is ground to a p80 size of about 60
microns. One series of tests are performed using a nitrogen
atmosphere in the grind and nitrogen flotation gas with
10 varying flotation pH using lead nitrate as an activator. A
second series of tests are performed using air as the grinding
atmosphere and air as the flotation gas at varying flotation
pH's and using lead nitrate as an activator. A third series of
tests are performed using nitrogen as the grinding environ-
15 ment and nitrogen flotation gas with varying flotation pH
and using copper sulfate as an activator. The pH is adjusted
by either the addition of sulfuric acid or calcium hydroxide,
as required. Also, other normal flotation reagents are used in
each test. Conditions for the grind and flotation for each
20 example are shown in Table 5 and specific reagents used
with each example are shown in Table 6.
Results of the flotation are shown tabularly in Table 7 and
graphically in FIGS. 18-20. FIG. 18 has plots of sulfide
series of three dual compartment flotation cells, and the
cleaner flotation step 180 is accomplished in a series of three
dual compartment flotation cells. As shown in FIG. 8,
nitrogen gas 192 is supplied from gas tank 194 and is fed to
each of the comminution step 168, the rougher flotation step 5
172, the scavenger flotation step 178 and the cleaner flotation
step 180. The nitrogen gas 192 is used as the flotation
gas in each of the flotation steps and is used as a blanketing
gas to prevent air from oxidizing ore particles during the
comminution 168. The nitrogen gas is also used to blanket
all other process equipment, not shown, such as pumps and
mixing tanks. Gold-bearing sulfide minerals in the ore
sample 166 are, therefore, maintained in a substantially
air-free environment through the entire pilot plant, until the
gold-bearing sulfide minerals have been recovered in a
desired concentrate product.
The results of the pilot plant are shown in Table 3, which
shows that the final concentrate 190 from the pilot plant is
of a higher quality than the concentrates shown in Examples
1-6. Addition of the scavenger flotation step 178 and the
cleaner flotation step 180 in the pilot plant significantly
improves the grade of concentrate finally recovered, without
any appreciable loss of gold recovery.
TABLE 3
LONE TREE PILOT PLANT
Example
Grind
P80
Mesh(1)
Final Concentrate Tail Grade Final Concentrate
Grade oz Recovery
oz gold/st(2) gold/st(3) wt %(4)
Gold Reporting
to Final
Concentrate
% gold
recovery(5)
7 270 0.57 .0095 9.4 86.4
(1)80 weight percent of material passing the indicated size
(2)ounces of gold per ton of respective concentrate
(3)ounces of gold per short ton of final tail
(4)weight percent of ore sample feed reporting to respective concentrate
(5)% of gold in concentrate relative to feed for the respective floatation step
40
TABLE 4
Twin Creeks SUBGRADE SULFIDE ORE
REPRESENTATIVE HEAD ANALYSIS
The results of Example 8 are graphically shown in FIG.
9 which shows a plot of gold recovery in the concentrate as
a function of grind size. As seen in FIG. 9, the use of
nitrogen gas generally results in a significantly higher recovery
of gold in the concentrate compared to the use of air as
a flotation gas.
Example 8
Laboratory tests are performed on samples of a low grade
gold-bearing sulfide ore from Santa Fe Pacific Gold Corporation's
Twin Creeks Mine in Nevada. A representative
analysis of an ore sample is shown in Table 4. For each test,
a sample is ground to the appropriate size and a portion of
each sample is then subjected to flotation using air as a
flotation gas and another portion is subjected to flotation
using nitrogen as a flotation gas. Substantially the same
flotation conditions are used as described for Examples 1-6.
sulfur recovery in the flotation concentrate versus flotation
pH for each of the three test series. FIG. 19 has plots of gold
recovery in the flotation concentrate versus flotation pH for
each of the three test series. As seen in Tables 5-7 and FIGS.
45 18 and 19, grinding and flotation using nitrogen gas provides
significantly enhanced performance relative to air for all but
the highest pH's. Furthermore, gold recoveries in the concentrate
are best at acidic pH's, and particularly at pH's
below about 6. Moreover, quite surprisingly, lead nitrate as
50 an activator consistently shows a significantly higher gold
recovery in the concentrate than the more standard activator
of copper sulfate.
FIG. 20 includes a plot of the difference in percentage
gold recoveries in the concentrate using nitrogen versus air
55 for various flotation pH's and a plot of the difference in
percentage recovery of sulfide sulfur in the concentrate
using nitrogen versus air for various flotation pH's. A
dramatic effect of pH is revealed in FIG. 20 at lower pH's.
For example, at pH 6, gold recovery in the concentrate
60 increases by greater than 15 percentage points for nitrogen
versus air with less than a 5 percentage point increase in
sulfide sulfur recovery. These results further indicate that
gold is often associated with sulfide mineral types that are
particularly difficult to recover in a concentrate using con-
65 ventional flotation with air as a flotation gas. These difficultto-
float sulfide mineral types float extremely well, however,
with the use of nitrogen, especially when a lead-containing
0.085 OZ/st(1)
0.28 OZ/st(1)
6.45 wt. %
6.27 wt. %
1630 ppm by wt.
Gold
Silver
Total Sulfur
Sulfide Sulfur
Arsenic
(l)ounces per short ton of ore
5,837,210
23
activator is used at an advantageously acidic pH. These
results, especially at pH's below about 6, are particularly
surprising.
24
TABLE 7-continued
Recovery in Concentrate
Examples 29-35
This example demonstrates the importance of the choice
of collector reagent in performing the flotation of the present
25 invention.
Laboratory flotation tests are performed on samples of
Twin Creeks low grade gold-bearing sulfide ore at a pH of
from about pH 5 to about pH 6 using various collector
TABLE 5
Grind
P-80 size Floatation
Example Atmosphere (microns) Floatation Gas pH
9 nitrogen 62 nitrogen 3
10 nitrogen 62 nitrogen 4
11 nitrogen 60 nitrogen 5
12 nitrogen 60 nitrogen 6
13 nitrogen 60 nitrogen 7
14 nitrogen 60 nitrogen 8
15 nitrogen 60 nitrogen 9
16 nitrogen 60 nitrogen 10
17 nitrogen 60 nitrogen 11
18 air 60 air 3
19 air 60 air 6
20 air 60 air 8
21 air 60 air 9
22 air 60 air 10
23 air 60 air 11
24 nitrogen 64 nitrogen 4
25 nitrogen 64 nitrogen 5
26 nitrogen 64 nitrogen 6
27 nitrogen 64 nitrogen 7
28 nitrogen 64 nitrogen 8
5
10
15
20
Example Gold (%) Sulfide Sulfur (%)
13 82.6 97.5
14 81.1 95
15 76.5 95.9
16 67.7 88.6
17 30.8 67.7
18 77.7 93.9
19 70.1 94
20 63.8 88.2
21 65.2 89.2
22 65.8 89.4
23 59.6 88.1
24 84.8 96.3
25 81.6 96.9
26 77.8 96.7
27 82.4 96.4
28 70.8 90.4
TABLE 6
Reagents (Ib/ton)
Calcium
Example Sodium Silicate MIBC(l) DF250(2) Sulfuric Acid Hydroxide PAX(3) Lead Nitrate Copper Sulfate
9 0.1 0.14 0.24 8.86 0 0.5 0.2 0
10 0.1 0.12 0.27 4.22 0 0.5 0.2 0
11 0.1 0.14 0.25 2.1 0 0.5 0.2 0
12 0.1 0.14 0.2 1.3 0 0.5 0.2 0
13 0.1 0.1 0.1 0 0.27 0.5 0.2 0
14 0.1 0.12 0.15 0 2.49 0.5 0.2 0
15 0.1 0.11 0.11 0 3.24 0.5 0.2 0
16 0.1 0.1 0.07 0 3.96 0.5 0.2 0
17 0.1 0.11 0.11 0 5.56 0.5 0.2 0
18 0.1 0.2 0.21 6.56 0 0.5 0.2 0
19 0.1 0.15 0.16 0 1.16 0.5 0.2 0
20 0.1 0.15 0.13 0 2.84 0.5 0.2 0
21 0.1 0.15 0.14 0 3.44 0.5 0.2 0
22 0.1 0.16 0.14 0 4.54 0.5 0.2 0
23 0.1 0.15 0.13 0 5.82 0.5 0.2 0
24 0.1 0.20 0.20 4.15 0 0.5 0 0.2
25 0.1 0.19 0.19 2.17 0 0.5 0 0.2
26 0.1 0.18 0.18 0.85 0 0.5 0 0.2
27 0.1 0.16 0.13 0 0.3 0.5 0 0.2
28 0.1 0.18 0.11 0 2.34 0.5 0 0.2
(l)Methyl isobutyl carbanol
(2)Polyethylene glycol
(3)Potassium amyl xanthate
TABLE 7
Recovery in Concentrate
Example Gold (%) Sulfide Sulfur (%)
9 86.7 96.8
10 86.7 95.3
11 85 97.3
12 86 97.3
reagents in cost equivalent amounts. A list of the different
collector reagents, companies that supply the reagents and
60 the amount of each collector reagent used are shown in Table
8. Nitrogen gas is used in the grind and as the flotation gas.
Particles are sized at a P80 size of about 46 microns and
flotation is conducted in a slurry with 30% solids. The ore
samples are of a low grade gold-bearing sulfide ore having
65 about 0.072 ounces per ton of gold and about 5.58 weight
percent sulfide sulfur. Other reagents used during the flotation
tests are shown in Table 9.
5,837,210
Other Reagents (Ib/ton)
TABLE 9
Sodium
Example Sulfuric Acid MIBC DF250 Lead Nitrate Silicate
(l)potassium amyl xanthate
(2)ethyl octyl sulfide, dialkyl dithiophosphate, polyglycol alkyl ether
(3)alkyl thionocarbonate
(4)Na-mercapto-benzothiazole and Na-di-iso-amyl dithiophosphate
(5)Na di-iso butyl dithiophosphate
(6)t-dodecyl mercaptan
(7)xanthogen formate
Example 38
This example demonstrates the important effect with the
25 present invention of using deoxygenated process water.
Samples of a Twin Creeks low grade gold-bearing sulfide
ore are subjected to laboratory flotation. Samples contain
about 0.072 ounces per ton of gold and about 5.58 weight
percent of sulfide sulfur. Grinding is performed in a nitrogen
atmosphere for each sample and flotation is performed using
nitrogen as the flotation gas. Both samples are sized at a P80
size of about 46 microns. One sample is slurried with regular
tap water for the flotation. The other sample is slurried with
tap water that has been deoxygenated by bubbling nitrogen
gas through the water for a sufficient time to remove most of
the oxygen previously dissolved in the water.
20
26
Samples of Lone Tree subgrade gold-bearing sulfide ore
are subjected to laboratory flotation. Both samples are
comminuted to a P80 size of approximately 270 mesh.
Following comminution, one sample is subjected to mag-
S netic separation to remove magnetic iron particles prior to
flotation while the other sample is not.
Results are shown graphically in FIG. 24, which includes
a plot of percent gold recovery in the flotation concentrate
10 versus flotation time and a plot of oxidation-reduction
potential in the flotation slurry versus flotation time. As seen
in FIG. 24, gold recovery is significantly higher for the
sample subjected to the magnetic separation. The effect is
15 particularly pronounced at shorter flotation times, but even
after 30 minutes of flotation, the sample having been subjected
to magnetic separation exhibits gold recovery that is
approximately ten percentage points higher than the sample
with no magnetic separation.
0.50
0.14
0.17
0.30
0.50
0.18
0.17
Amount lb/ton
30
0.12 0.25 0.3 1.0
0.11 0.07 0.3 1.0
0.07 0.07 0.3 1.0
0.09 0.09 0.3 1.0
0.04 0.04 0.3 1.0
0.17 0.17 0.3 1.0
35
0.11 0.11 0.3 1.0
Source
TABLE 8
Kerly Mining, Inc.
Minerals Reagents Inc.
Cytec Industries, Inc.
Cytec Industries, Inc.
Cytec Industries, Inc.
Phillips 66 Company
Minerec Mining Chemicals
Collector
PAX(l)
S-703(2)
AP-5100(3)
AP-412(4)
AP-3477(5)
CO-200(6)
Minerec A(7)
29
30
31
32
33
34
35
Example
29 7.76
30 4.8
31 4.37
32 5.0
33 5.04
34 5.74
35 5.49
25
Results of the flotation tests are shown in FIGS. 21 and
22, which plot percent gold recovery in the concentrate
versus flotation time for the various collector reagents. As
shown in FIGS. 21 and 22, potassium amyl xanthate performs
anomalously better than the other collectors with the
flotation of the present invention.
Examples 39-57
Samples of Lone Tree subgrade gold-bearing sulfide ore
are subjected to laboratory flotation. Each sample is ground
to a P80 size of approximately 270 mesh in a nitrogen
atmosphere. Flotation is conducted with a nitrogen flotation
gas. Following flotation for each sample, the flotation tail is
subjected to a carbon-in-Ieach cyanidation to recover gold
remaining in the flotation tail.
Results are shown in Table 10, where it is seen that the
leach of the flotation tail significantly contributes to gold
recovery according to the process of the present invention.
These examples demonstrate the benefit of a tail leach
55 with the present invention.
Results of flotation for each sample are shown in FIGS.
40 25-27. FIG. 25 includes a plot of weight recovery in the
concentrate versus flotation time for each sample, and shows
that flotation with the deoxygenated water attains a greater
weight recovery in the flotation concentrate. FIG. 26
includes a plot of gold recovery in the concentrate versus
45 flotation time for each sample, and shows that at the longer
flotation times, gold recovery is higher using the deoxygenated
water. FIG. 27 includes a plot of sulfide sulfur recovery
in the concentrate versus flotation time, and shows that, at
longer flotation times, sulfide sulfur recovery in the concen-
50 trate is higher using the deoxygenated water.
Example 36
Example 37
This example demonstrates a surprising effect of perform- 65
ing a magnetic separation on a ore sample prior to flotation
according to the present invention.
This example demonstrates the importance of grind media
on operation of the flotation of the present invention.
Laboratory flotation is conducted on Lone Tree low grade
gold-bearing sulfide ore samples using nitrogen during the
grind and during flotation as the flotation gas. All samples
were ground to a P80 size of about 44 microns. One sample
is comminuted using stainless steel rods while the other
sample is comminuted using conventional mild steel balls.
Results of the flotation are shown graphically in FIG. 23,
which includes a plot of percent gold recovery versus
flotation time for each sample and a plot of oxidation
reduction potential versus flotation time for each sample. As
shown in FIG. 23, the sample milled with stainless steel rods
exhibits substantially higher gold recovery at all flotation
times. More importantly, a high gold recovery is achieved in
a much shorter flotation time for the sample milled with the
stainless steel rods than for the sample milled with the mild
steel balls. This distinction is significant because it indicates
that flotation times may be reduced with the use of stainless
steel or other comminution media, such as a high chromium 60
alloy hardened steel, that would introduce less reactive iron
into the flotation system.
5,837,210
27 28
2. The method of claim 1, wherein:
said flotation gas comprises less than about 5 volume
percent oxygen gas.
3. The method of claim 1, wherein:
said flotation gas comprises greater than about 95 volume
percent of gas selected from the group consisting of
nitrogen gas, carbon dioxide gas, helium gas, argon gas
and combinations thereof.
4. The method of claim 1, wherein:
said flotation gas comprises combustion exhaust.
5. The method of claim 1, wherein:
relative to said mineral material feed, said flotation concentrate
is enriched in, and said flotation tail is depleted
in, substantially each and every sulfide mineral present
in said mineral material feed prior to said flotation.
6. The method of claim 1, wherein:
said flotation is substantially not selective to flotation of
said pyrite, marcasite, arsenopyrite, arsenous pyrite and
pyrrhotite, so that said flotation concentrate is enriched,
relative to said mineral material feed, in substantially
any of said pyrite, marcasite, arsenopyrite, arsenous
pyrite and pyrrhotite present in said mineral material
feed.
7. The method of claim 1, wherein:
after said flotation, said flotation tail is subjected to
leaching to remove from said flotation tail gold that is
not associated with a sulfide mineral.
8. The method of claim 7, wherein:
said leaching comprises cyanide leaching of gold from
said flotation tail.
9. The method of claim 1, wherein:
said liquid medium comprises deoxygenated water.
10. The method of claim 9, wherein:
said deoxygenated water comprises less than about 1.0
part per million by weight of oxygen.
11. The method of claim 9, wherein:
said deoxygenated water, prior to said flotation, had been
prepared by passing a gas through water to remove
oxygen from said water.
12. The method of claim 1, wherein:
prior to said flotation, said mineral material feed is
subjected to wet comminution to reduce the particle
size of said mineral material;
water used during said wet comminution comprising
deoxygenated water.
13. The method of claim 12, wherein:
said comminution is conducted in an environment that is
substantially free of air.
14. The method of claim 1, wherein:
before said flotation, said mineral material feed is subjected
to comminution to reduce the particle size of said
mineral material feed;
said comminution being conducted in equipment sealed to
substantially prevent air from being drawn into said
equipment.
15. The method of claim 14, wherein:
said comminution comprises processing said mineral
material through a sealed comminution unit having an
inlet and an outlet;
a blanketing gas being introduced into at least one of said
inlet and said outlet;
said blanketing gas comprising no greater than about 10
volume percent oxygen.
5
45
20
65
40
10
15
5.7 93.0
9.1 90.7
10.3 83.2
11.4 87.0
9.2 88.2
12.3 86.8
12.8 88.3
8.9 88.8
4.3 86.7
9.8 93.4
5.4 90.9
4.6 90.2
3.9 91.8
3.5 82.3
5.8 84.2
1.5 85.9
6.1 82.7
5.4 92.5
4.0 84.7
Gold Recovery from Total
Flotation Tail Gold Recovery
TABLE 10
87.3
81.6
72.9
75.6
79.0
74.5
75.5
79.9
82.4
83.6
85.5
85.6
87.9
78.8
78.4
84.4
76.6
87.1
80.7
Gold Recovery(1)
Form Flotation
Concentrate
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Example
25 The present invention has been described with reference
to specific embodiments of the present invention. According
to the present invention, however, any of the features shown
in any embodiment may be combined in any way with any
other feature of any other embodiment. For example, any 30
feature shown in anyone of FIGS. 1-3,8, 10-17 and 28 can
be combined with any other feature shown in any of those
figures. Furthermore, while various embodiments of the
present invention have been described in detail, it is apparent
that modifications and adaptations to those embodiments 35
will occur to those skilled in the art. It is to be expressly
understood that such modifications and adaptations are
within the scope of the present invention, set forth in the
following claims.
What is claimed is:
1. A method for flotation processing of a gold-bearing
mineral material feed that is refractory to gold recovery due
to association of gold in the mineral material with one or
more iron-containing sulfide mineral species, the method
comprising the steps of:
subjecting to flotation in a liquid medium said mineral
material feed in particulate form, said mineral material
feed comprising at least one iron-containing sulfide
selected from the group consisting of pyrite, marcasite,
arsenopyrite, arsenous pyrite, and pyrrhotite, said flo- 50
tation including passing bubbles of a flotation gas
through said liquid medium;
during said flotation, a first portion of said mineral material
feed rising through said liquid medium with said
bubbles and said first portion being collected from a 55
flotation froth as a flotation concentrate, a second
portion of said mineral material feed being collected as
a flotation tail;
said flotation concentrate being enriched, relative to said 60
mineral material feed, in said iron-containing sulfide
and in gold;
said flotation tail being depleted, relative to said mineral
material feed, in said iron-containing sulfide and in
gold;
wherein, said flotation gas comprises no greater than
about 10 volume percent of oxygen gas.
(1)Assumes 96% of gold in concentrate removed in elL leach following
pressure oxidation.
5,837,210
29 30
5
40
25
35
* * * * *
subjected to further flotation to produce a second
flotation concentrate enriched, relative to said first
flotation tail, in said at least one iron-containing sulfide
and in gold and to produce a second flotation tail
depleted, relative to said first flotation tail, in said at
least one iron-containing sulfide and in gold;
after said first flotation stage and prior to said second
flotation stage, said first flotation tail being subjected to
comminution to reduce the size of particles in said first
flotation tail.
30. The method of claim 29, wherein:
after said comminution and prior to said second flotation
stage, said first flotation tail is subjected to size separation
to separate said first flotation tail into two
fractions, a first fraction of smaller-size particles and a
second fraction of larger-size particles, said second
fraction being subjected to said second flotation stage
and said first fraction not being subjected to said second
flotation stage.
31. The method of claim 1, wherein:
said flotation is conducted in a sealed flotation apparatus
having a vapor headspace above said liquid medium;
gas is withdrawn from said vapor headspace and recycled
for introduction into said liquid medium to form at least
a part of said flotation gas.
32. The method of claim 31, wherein:
said flotation apparatus comprises means for dispersing
said flotation gas in said liquid medium, said means for
dispersing creating a vacuum to suck said gas from said
vapor headspace to introduce said gas into said liquid
medium.
33. The method of claim 22, wherein:
said lead-containing activator includes lead in a +2 oxidation
state.
34. The method of claim 22, wherein:
said flotation tail, after said step of flotation, is subjected
to cyanide leaching to recover gold from said flotation
tail.
35. The method of claim 34, wherein:
during said cyanide leaching of said flotation tail, consumption
of cyanide is lower using said lead-containing
activator relative to use of a copper-containing activator
during said step of flotation.
36. The method of claim 22, wherein:
said flotation concentrate, after said step of flotation, is
subjected to cyanide leaching to remove gold from said
flotation concentrate.
37. The method of claim 36, wherein:
during said cyanide leaching of said flotation concentrate,
consumption of cyanide is lower using said leadcontaining
activator relative to use of a coppercontaining
activator during said step of flotation.
38. The method of claim 22, wherein:
said liquid medium of said flotation comprises at least
some recycled process water.
39. The method of claim 38, wherein:
said recycled process water includes cyanide.
40. The method of claim 39, wherein:
said lead-containing activator at least partially counters a
depressing effect of said cyanide on said at least one
iron-containing sulfide.
10
50
said lead-containing activator comprises at least one of
lead nitrate and lead acetate.
24. The method of claim 1, wherein:
a copper-containing activator contacts said mineral material
feed during said flotation.
25. The method of claim 1, wherein:
a xanthate collector contacts said mineral material feed 45
during said flotation.
26. The method of claim 1, wherein:
during said flotation, said liquid medium is at an acidic
pH.
27. The method of claim 1, wherein:
during said flotation, said liquid medium is at a pH of
smaller than about pH 6.
28. The method of claim 1, wherein:
during said flotation, said liquid medium is at a pH of 55
from about pH 3 to about pH 6.
29. The method of claim 1, wherein:
said flotation comprises a first flotation stage of said
mineral material feed to produce a first flotation concentrate
enriched, relative to said mineral material feed, 60
in said at least one iron-containing sulfide and in gold
and to produce a first flotation tail depleted, relative to
said mineral material feed, in said at least one ironcontaining
sulfide and in gold;
said flotation further comprising a second flotation stage 65
wherein at least a portion of said first flotation tail is
16. The method of claim 15, wherein:
said blanketing gas comprises greater than about 95
volume percent of gas selected from the group consisting
of nitrogen gas, carbon dioxide gas, helium gas,
argon gas and combinations thereof.
17. The method of claim 14, wherein:
beginning with said comminution and ending with said
flotation, said mineral material feed is processed in an
environment that is substantially free of oxygen gas.
18. The method of claim 1, wherein:
before said flotation, said mineral material feed is subjected
to comminution to reduce the particle size of said
mineral material feed;
said comminution being performed in the interior of a 15
vessel having a nonmetallic interior lining to reduce the
potential for contamination of said mineral material by
Iron.
19. The method of claim 1, wherein:
before said flotation, said mineral material feed is sub- 20
jected to comminution in the presence of grinding
media to reduce the particle size of said mineral material;
said grinding media comprising at least one of a corrosion
resistant steel and a hardened steel alloy.
20. The method of claim 19, wherein:
said grinding media comprises at least one of stainless
steel and chromium alloy steel.
21. The method of claim 1, wherein:
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before said flotation, said mineral material feed is subjected
to magnetic separation to remove particles of
magnetic iron to reduce galvanic interaction involving
iron during said flotation.
22. The method of claim 1, wherein:
a lead-containing activator contacts said mineral material
feed during said flotation.
23. The method of claim 22 wherein: