5,653,945
[45] Date of Patent: Aug. 5, 1997
I~I.~IIIIIIIIIIIIIII
US005653945A
United States Patent [19] [11] Patent Number:
Gatbje et aI.
[54] METHOD FOR PROCESSING GOLD·
BEARING SULFIDE ORES INVOLVING
PREPARATION OF A SULFIDE
CONCENTRATE
[75] Inventors: John C. Gathje, Longmont. Colo.;
Gary L. Simmons, Albuquerque, N.
Mex.
[73] Assignee: Santa Fe Pacific Gold Corporation,
Albuquerque, N. Mex.
[21] Appl. No.: 423,839
[22] Filed: Apr. 18, 1995
[51] filt. CI,6 B03D 1/00; COlG 7/00
[52] U.S. Cl. 423/26; 423/27; 423/29;
423/30
[58] Field of Search 423/26. 27, 29,
423/30, 579, DIG. 15
Berglund et al.. "Influence of Different Gases In Flotation Of
Sulphide Minerals," Proceedings of An Engineering Foundation
Conference on Advances in Coal and Mineral Processing
Using Flotation (1989) pp. 71-76, Society for Mining,
Metallurgy and Exploration, Inc., Littleton, Colorado,
Dec., 1989.
Martin et al.. "Complex Sulphide Ore Processing With
Pyrite Flotation By Nitrogen," International Journal of Mineral
Processing, 26 (1989) pp. 95-110, Elsevier Science
Publishers B.V.. 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.V., Amsterdam. no month.
(List continued on next page.)
Primary Examiner-Steven Bos
Attorney, Agent, or Finn-Holme Roberts & Owen LLP
Burger, "Froth Flotation Development: This Industry Workhorse
From Strength to Strength," E&MJ (Sep. 1983) pp.
67-75.
Onstott et al., "By-Product Molybdenum Flotation From
Copper Suliide Concentrate With Nitrogen Gas in Enclosed
Wemco Nitrogen Flotation Machines", Preprint No. 84-65
(1984) Society of Mining Engineers of AIME, no month. 39 Claims, 9 Drawing Sheets
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.
[56]
809,959
1,045,970
1,505,323
3,655,044
3,834,896
4,571,263
4,571,264
4,605,439
4,797,202
5,013,359
5,074,993
5,245,110
References Cited
U.S. PATENT DOCUMENTS
1/1906 Kirby 209/166
12/1912 Greenway 209/166
8/1924 Eberenz 209/166
4/1972 Delaney 209/167
9/1974 Eisele et aI 423/26
2/1986 Weir et aI 423/150.4
2/1986 Weir et aI 423/150.4
8/1986 Weir 423/140
1/1989 K1irnpe1 et aI 423/26
5/1991 Fair et aI 423/26
12/1991 Kerr et aI 209/167
9/1993 Van Dijk et aI. 423/579
OTHER PUBLICATIONS
[57] ABSTRACT
AIR
132
flOTATION
TAIL
118
OXIDIZEO
MATERIAL
126
5,653,945
Page 2
OTHER PUBLICATIONS
Berglund, ''Pulp Chemistry in Sulphide Mineral Flotation",
International Journal of Mineral Processing, 33 (1991) pp.
21-31. Elsevier Science Publishers B.V.• Arnbsterdam.
Klymowsky et al., 'The Role of Oxygen in Xanthate Flotation
of Galena, Pyrite and Chalcopyrite," CIM, Bulletin
for June. pp. 683-688 (1970), Jun., 1970.
Rao et al.. ''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 al., "Adsorption of Anyl Xanthate at Pyrrhotite in the
Presence of Nitrogen and Implications in Flotation." Can.
Metall. Q., vol. 30, No.1, pp. 1-6 (1990), no month.
Xu et al.. "Sphalerite Reverse Flotation Using Nitrogen,"
Proc. Electrochem Soc., vol. 92-17. Proc. Int. Syrup. Electrochem.
Miner. Met. Process. III, 3rd, pp. 170-190 (1992),
no month.
Van Deventer et al., 'The Effect of Galvanic Interaction of
the Behaviour 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 al.. "Role of Gases in Flotation Reactions."
Acacemy of Sciences, U.S.S.R Moscow. date unknown.
u.s. Patent Aug. 5, 1997 Sheet 1 of 9 5,653,945
N
RATE
MINERAL
MATERIAL
FEED
102 l'
1--08 GAS COMMINUTION SOURCE
104 110
106 1
114 I
r •
FLOTATION -- FLOTATIO 112 CONCENT
116 '. FLOTATION
TAIL
118
Fig. 1
u.s. Patent Aug. 5, 1997
PARTICULATE
MINERAL
MATERIAL
110
Sheet 2 of 9
AIR
132
OXYGEN
PLANT 130
5,653,945
.Ir
FLOTATION
112
• r
FLOTATION
TAIL
118
_ 114 -
116
128
.,
PRESSURE
OXIDATION
124 -
+
OXIDIZED
MATERIAL
126
Fig. 2
u.s. Patent Aug. 5, 1997 Sheet 3 of 9 5,653,945
FIRST
MINERAL MATERIAL
FEED
138
, Ir
FLOTATION 116
112
114
FLOTATION
TAIL
118
-...
OXYGEN
PLANT 130
Fig. 3
SECOND
MINERAL MATERIAL
FEED
,Ir 140
MIXING
142
,Ir 144
PRESSURE
OXIDATION
124
,~
OXIDIZED
MATERIAL
126
u.s. Patent Aug. 5, 1997 Sheet 4 of 9 5,653,945
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5,653,945
2
5
gold-bearing sulfide ores. however, is that a significant
amount of the gold-bearing sulfide mineral 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
without the significant loss of gold associated with concentrating
sulfide ores by flotation.
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
15 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
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
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
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
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.
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
mineral concentrate. An oxygen deficient gas can be intro-
40 duced 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, prevented
from oxidizing newly exposed sulfide mineral surfaces
created during comminution.
In one aspect, the present invention involves the advantageous
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
50 in the absence of oxygen gas, is combined with oxidative
treating to decompose sulfide minerals. freeing gold for
possible subsequent dissolution using a gold lixiviant. such
as a cyanide. The preferred oxidative treating is pressure
oxidation, although another oxidative treatment such as an
55 oxidizing roast 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 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,
60 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 atmosphere in
current gold processing operations and is, therefore, wasted.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flow diagram showing one embodiment of the
present invention;
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
1
METHOD FOR PROCESSING GOLDBEARING
SULFIDE ORES INVOLVING
PREPARATION OF A SULFIDE
CONCENTRATE
20
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 25
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 30
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 35
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 45
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
through a slurry of ore particles which have been treated
with reagents and the particles of the ore which are less
hydrophilic tend to rise with the air bubbles. thereby permitting
separation of the ore into two fractions. Flotation has
been used to prepare concentrates of gold-bearing sulfide 65
minerals which are rich in the sulfide minerals and relatively
free of gangue material. One problem with flotation of many
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 10
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
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.
5,653,945
4
mineral particles of a size suitable for flotation. The particulate
mineral material 106 is preferably sized such that at
least 80 weight percent ofparticles in the particulate mineral
material are smaller than about 100 mesh. more preferably
5 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
10 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
15 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,
20 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
30 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
35 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
using air as a flotation gas. Although not required, the
40 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 III to assist in flotation
separation. Such reagents may include frothing agents,
45 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
adjusted as desired to optimize flotation separation for any
50 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
enriched in gold.. Also exiting from the flotation 112 is a
55 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..
Alternatively, the flotation concentrate 116 may be sold as a
60 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
volume fraction that is less than the volume fraction of
65 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 prefer-
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 25
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
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
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
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,
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 tail or as subgrade
ore previously believed to be uneconomical for gold recovery.
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, butmay 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
3
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 Examples 8-15.
DErAILED DESCRIPTION OF THE
PREFERRED EMBODIMENT
5
5,653,945
6
ably less than about 5 volume percent. Most preferably, both The gas source 110 may be any source providing a
the flotation gas 114 and the blanketing gas 108 are sub- suitable flotation gas 114 and blanketing gas 108. One
stantially free of oxygen gas. preferred gas source 110 is a facility in which nitrogen gas
To aid in the understanding of the present invention, but is separated from air, with the separated nitrogen gas being
not to be bound by theory, it is believed that oxygen gas, if 5 used as the blanketing gas 108 and the flotation gas 114.
Several processes are known for separating nitrogen from
present in any appreciable quantity, tends to oxidize the air, including cryogenic separation and membrane separasurface
of particles of certain gold-bearing sulftde minerals, tion. One particularly preferred gas source 110 is an oxygen
which can have the effect of depressinE: flotation of the
~ plant, which is commonly found at existing facilities where
gold-bearing su1fi.de mineral particles during the flotation 10 gold-bearing sulftde ores are processed. An oxygen plant is
112. By reducing the amount of oxygen gas that comes into typically required, for example, when a pressure oxidation
contact with a mineral material, it is believed that any operation or an oxidative roasting operation is used in the
surface oxidation effect is reduced, resulting in enhanced processing of gold-bearing su1fi.de ores. In the oxygen plant,
flotali'on of su1fi.de lDl'neral parti'cles and a corresponding
oxygen is separated from air, such as by cryogenic separaincrease
in the amount of su1fi.de mineral, and therefore gold, 15 tion or membrane separation, and the separated oxygen gas
recovered in the flotation concentrate 116. Therefore, it is
is used in the pressure oxidation or oxidative roasting
preferred that the flotation gas 114 and the blanketing gas operation. A by-product of such an oxygen plant is an
108 consist essentially of components which could not effluent gas stream which is enriched in nitrogen gas and is
oxidize the surface of gold-bearing su1fi.de mineral particles. suitable for use as the blanketing gas 168 an<:L'or the flotation
It is preferred that the flotation gas 114 and the blanketing 20 gas 114. This by-product stream has previously been vented
gas 108 predominantly comprise one or more gases other to the atmosphere and has, therefore, been wasted. With the
than oxygen gas. Suitable gases include nitrogen, helium, present invention, however, the by-product stream may be
argon and carbon dioxide. Preferably, one or more of these beneficially used to produce the flotation concentrate 116, in
gases should comprise greater than about 95 volume percent addition to using the oxygen gas product stream for the
of the flotation gas 114 and the blanketing gas 108, and more 25 pressure oxidation or oxidative roasting operation.
preferably greater than about 98 volume percent. Still more FIG. 2 shows one embodiment of the present invention in
preferable is for the blanketing gas 108 and the flotation gas which both the oxygen gas product stream and the nitrogen
114 to consist essentially of one or more of these gases. gas by-product stream from an oxygen plant are both used
Nitrogen gas is particularly preferred because of its rela- to process gold-bearing su1fi.de mineral material. Referring
tively low cost. Carbon dioxide is less preferred because it 30 to FIG. 2, particulate mineral material 110 is subjected to the
forms an acid when dissolved in water, which could corrode flotation 112 to produce the flotation concentrate 116 and the
process equipment or produce conditions less conducive to flotation tail 118, as previously described. The flotation gas
optimum flotation. 114 is a nitrogen gas enriched by-product stream from an
The blanketing gas 108 andlor the flotation gas 114 may oxygen plant 130, in which air 132 is separated into an
be introduced into process apparatus in any appropriate 35 oxygen enriched gas stream and nitrogen enriched gas
manner. Such gases may be fed under positive pressure or stream. The flotation concentrate 116, which is enriched in
may be induced into the apparatus by creating a suction gold-bearing sulftde minerals, is subjected to pressure oxiwhich
pulls the gas in. Preferably, however, the apparatus is dation 124 to decompose su1fi.de minerals, producing an
designed to substantially prevent introduction of air into oxidized material 126 from which the gold could be recovcomminution
and flotation apparatus. 40 ered by dissolution using any suitable gold lixiviant, such as
In one embodiment, the possible detrimental effects of a cyanide. The pressure oxidation 124 involves treating a
any surface oxidation of sulfide mineral particles that may slurry of the flotation concentrate 116 in an autoclave at a
be present in a mineral material feed may be counteracted by temperature of greater than about 1500 C. and an elevated
the addition of a sulfidizing agent, to at least partially replace pressure in the presence of an overpressure of a treating gas
the oxidized coating with a su1fi.de coating. Any material 45 128, which is rich in oxygen. It should be noted that other
capable of reacting to form the desired su1fi.de coating of the oxidative treating steps could be used instead of the pressure
mineral particle could be used. Suitable su1fi.dizing agents oxidation 124. For example, an oxidative roasting or bioinclude
alkali metal su1fi.des and bisulftdes, such as Na2S, oxidation could be used to produce the oxidized material
NaHS, etc. Such su1fi.dizing agents could be added just 126 using the treating gas 128.
before or during any stage of the flotation 112. 50 A further embodiment in accordance with the present
With the present invention, greater than about 80 weight invention is shown in FIG. 3 which uses the product and
percent of su1fi.de minerals from the particulate mineral by-product gas streams from an oxygen plant to process a
material 106 may be recovered in the flotation concentrate gold-bearing su1fi.de mineral material provided in two sepa-
116, and preferably greater than about 90 weight percent of rate feed streams. Referring to FIG. 3, a particulate first
those sulftde minerals are recovered in the flotation concen- 55 mineral material feed 138 is subjected to the flotation 112 to
trate 116. produce the flotation concentrate 116 and the flotation tail
One major advantage of the process of the present inven- 118, as previously described. The flotation gas 114 is a gas
tion is that, in addition to permitting a high recovery of stream enriched in nitrogen from the oxygen plant 130. A
gold-bearing sulftde minerals in the flotation concentrate particulate second mineral material feed 140 is combined
116, it permits a high rejection of gangue material into the 60 with the flotation concentrate 116 in a mixing step 142. The
flotation tail 118. Relative to the use of air as a flotation gas, combined stream 144. in the form of a slurry, is subjected to
the present invention permits the same recovery of gold to the pressure oxidation 124 to produce the oxidized material
be obtained in a concentrate of smaller weight. This provides 126, from which gold could be recovered.
a significant economic advantage because less gangue mate- One advantage of the embodiment shown in FIG. 3 is that
rial is present in the concentrate, from which the gold must 65 it permits the processing of multiple ores having different
ultimately be separated to produce a purified gold product, characteristics. For example, the first mineral material feed
if desired. 138 may comprise a lower grade gold-bearing su1fi.de ore
5,653,945
7 8
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
5 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 mercaptobenzothiazole
as collectors, copper sulfate for activation of
sulfides and MIBC as a frother. Flotation times range from
20 to 30 minutes.
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 fonn,
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 consume acid
produced during the pressure oxidation 124, and which
could, therefore, detrimentally interfere with proper opera- 10
tion 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. Almost all carbonate 15
material that may have been present in the first mineral
material feed, if any, would ordinarily have been removed
during the flotation 112.
The present invention is further described by the following
examples, which are intended to be illustrative only and 20
are not intended to limit the scope of the present invention.
EXAMPLES
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.
The results for examples 1-6 are shown tabularly in Table
2 and graphically in FIGS. 4-7 and reveal a significant
25 increase in the amount of gold recovered in the concentrate
when nitrogen gas is used as the flotation gas, especially at
smaller grind sizes.
TABLE 2
LONE TREE SUBGRADE BATCH JESTS
CoIlCentrate Concentrate Gold Reporting
Grind Grade Tail Grade Recovery to Concentrate
Exam- P80 oz goldlstC') oz goldlstC2) wt. %(4) %(5)
pIe Mesh(l) air nitrogen air nitrogen air nitrogen air nitrogen
1 100 0.31 0.35 0.19 0.20 15 15 75 75
2 150 0.28 0.31 0.21 0.16 15 16 71 79
3 200 0.33 0.29 0.21 0.16 15 19 74 81
4 270 022 0.25 022 0.12 20 24 72 86
5 325 0.23 0.20 0.22 0.16 20 25 73 81
6 400 0.14 0.14 0.29 0.12 29 33 67 85
(1)g0 weight percent of material passing the indicated size
(2)01mces of gold per short ton of cOIlCenlrate
(3)onnces of gold per short ton of tail
(4lweight percent of ore sample feed reporting to concentrate
(5)% of gold in ore sample feed reporting to cOIlCenlrate
LONE TREE SUBGRADE SULFIDE ORE
REPRESENOOIVE HEAD ANALYSIS
TABLE 1
(1)onnces per short ton of ore
For each ofExamples 1-6, an ore sample is provided from 50
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
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,
55 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
60 grade of the concentrate recovered. FIG. 6 shows that the
---------------------- amount of material recovered in the concentrate may be
~~~r O~~~ ~~:;:; significantly higher when using nitrogen gas as a flotation
Total Sulfur 1.75 wt. % gas than when using air, especially at the smaller grind sizes.
Sulfide Sulfur 1.66 wI. % FIG. 7 shows that gold recovery in the concentrate may be
Arsenic 1440 ppm. by wI. increased by almost 15% at a P80 grind of 270 mesh, when
_____________________ 65 using nitrogen gas as a flotation gas as opposed to air, again
without detrimental effect to the grade of concentrate recovered.
5,653,945
9
It should be noted that at a P80 grind of 100 mesh, there
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 5
at the smaller grind sizes. Typically, it is expected that
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 10
as the flotation gas is flat. at best When using nitrogen gas,
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 per- 15
formance when using air. to assist in the understanding in the
present invention but not to be bound by theory, is that some
detrimental chemical process may be occurring when air is
used as a flotation gas, with the detrimental chemical process
counteracting the normally beneficial effects of a smaller 20
grind size. It was observed that when air is used as the
flotation gas, the pH of the slurry in the flotation cell drops
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
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
increased surface oxidation, further depressing flotation of
the sulfide mineral particles. Nitrogen gas, however. would
not oxidize the surface of sulfide minerals and, therefore, 35
permits better flotation of sulfide mineral particles, resulting
in a higher recovery of sulfide minerals at the smaller grind
sizes, as would normally be expected.
10
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
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.
(1180 weight percent of material passing the indicated size
(2101mces of gold per short ton of respective concentrate
(310unces of gold per short ton of final tail
(4lweight percent of ore sample feed reporting to respective concentrate
(5)% of gold in concentrate relative to feed fur the respective flotation step
0.085 071~11
0.28 071~11
6.45 WI. %
6.27 WI. %
1630 ppm by wI.
TABLE 4
Twin Creeks SUBGRADE SULFIDE ORE
REPRESENTATIVE HEAD ANALYSIS
Gold
Silver
Total Sulfur
Sulfide Sulfur
Arsenic
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.
60 (110unces per short ton of ore
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
45 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
50 flotation conditions are used as described for Examples 1--6.
Example 7 40
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.
Aflotation 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 P80 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 col- 55
lected 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 65
cell, the scavenger flotation step 178 is accomplished in a
series of three dual compartment flotation cells, and the
5,653,945
35
45
15
40
12
10. The method of claim 1, wherein:
said step of providing a particulate gold-bearing mineral
material comprises comminuting a coarse gold-bearing
mineral material in an environment which is substantially
free of oxygen gas.
11. The method of claim 10, wherein:
said sulfide mineral is maintained in an environment that
is substantially free of oxygen between and during said
comminution and said flotation.
12. The method of claim 1, wherein:
subsequent to said flotation, at least a portion of said
flotation concentrate is subjected to oxidative treating
in the presence of a treating gas, which is enriched in
oxygen gas relative to ambient air, to oxidize at least a
portion of sulfide sulfur in said sulfide mineral, to assist
in freeing at least a portion of said gold from association
with said sulfide mineral and to facilitate possible
subsequent recovery of said gold.
13. The method of claim 12, wherein:
said oxidation treating comprises biooxidation of said
sulfide material.
14. The method of claim 12, wherein:
said flotation gas comprises an oxygen deficient
by-product gas from an oxygen plant which produces
an oxygen enriched gas from air; and
in said step of oxidative treating, said treating gas comprises
at least a portion of said oxygen enriched gas
from said oxygen plant.
15. The method of claim 12, wherein:
said oxidative treating comprises pressure oxidizing a
slurry of said sulfide mineral at an elevated temperature
and an elevated pressure in the presence of said treating
gas.
16. The method of claim 12, wherein:
said oxidative treating comprises roasting of said sulfide
mineral at an elevated temperature in the presence of
said treating gas.
17. The method of claim 12, wherein:
subsequent to said step of flotation, at least a portion of
said flotation concentrate is blended with a whole ore
comprising a sulfide mineral to form a blend; and
said blend is subjected to said oxidative treating.
18. The method of claim 17, wherein:
said oxidative treating comprises pressure oxidizing a
slurry of said sulfide mineral at an elevated temperature
and an elevated pressure in the presence of said treating
gas;
said whole ore comprises carbonate material which consumes
acid during said pressure oxidizing; and
said flotation concentrate is enriched in sulfide sulfur
which, during said pressure oxidizing, contributes to
production of sulfuric acid which at least partially
offsets acid consumption by said carbonate material.
19. The method of claim 12, wherein:
following said oxidative treating, gold which has been
freed from association with said sulfide mineral during
pressure oxidation, is recovered by dissolution into a
leach solution comprising a lixiviant for gold.
20. The method of claim 1, wherein:
said flotation concentrate comprises greater than about 80
weight percent of said sulfide mineral from said mineral
material.
21. The method of claim 1, wherein:
said flotation concentrate comprises greater than about 90
weight percent of said sulfide mineral from said mineral
material.
11
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 5
feature shown in anyone of FIGS. 1-3 and 8 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 10
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 processing a gold-bearing mineral material
having a sulfide mineral with which gold is associated,
the method comprising the steps of:
(a) providing a particulate gold-bearing mineral material,
wherein said mineral material comprises gold and a 20
sulfide mineral with which said gold is associated, and
wherein said mineral material also comprises nonsulfide
material as gangue;
(b) subjecting said mineral material to flotation with a
flotation gas to separate said mineral material into at 25
least two fractions, a first fraction being a flotation
concentrate, collected from flotation froth, enriched in
said sulfide mineral and said gold and a second fraction
being a flotation tail enriched in said non-sulfide material
and depleted in said gold; 30
wherein said flotation gas comprises no greater than
about 15 volume percent of oxygen gas;
and wherein, when pyrrhotite is present in said mineral
material, said flotation concentrate is enriched in said
pyrrhotite.
2. The method of claim 1, wherein:
said flotation gas comprises a by-product gas, enriched in
nitrogen gas relative to air, from an oxygen plant in
which an oxygen enriched gas is produced from air.
3. The method of claim 1, wherein:
said flotation gas comprises less than about 5 volume
percent oxygen gas.
4. The method of claim 1, wherein:
said flotation gas is substantially free of oxygen gas.
5. The method of claim 1, wherein:
said flotation gas comprises greater than about 85 volume
percent nitrogen gas.
6. The method of claim 1, wherein:
said flotation gas comprises greater than about 95 volume 50
percent nitrogen gas.
7. The method of claim 1, wherein
said flotation gas is substantially free of components
capable of oxidizing, during said flotation, sulfide sul- 55
fur in said sulfide mineral.
8. 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, helium gas, argon gas, carbon dioxide gas 60
and combinations thereof.
9. The method of claim 1, wherein:
said step of providing a particulate gold-bearing mineral
material comprises comminuting a coarse gold-bearing
mineral material in the presence of a blanketing gas 65
comprising no greater than about 15 volume percent of
oxygen gas.
5,653,945
13
22. The method of claim 1. wherein:
said flotation concentrate is enriched in, and said flotation
tail is depleted in, said gold and at least one of pyrite,
marcasite, arsenopyrite. arsenous pyrite and pyrrhotite.
23. A method for processing a gold-bearing mineral 5
material having a sulfide mineral with which gold is
associated. the method comprising the steps of:
(a) providing a coarse gold-bearing mineral material.
wherein said mineral material comprises gold and a
sulfide mineral with which said gold is associated. and 10
wherein said mineral material also comprises nonsulfide
material as gangue;
(b) mixing a blanketing gas with said mineral material;
(c) comminuting said course mineral material in the 15
presence of said blanketing gas to form a particulate
gold-bearing mineral material;
(d) subjecting said particulate mineral material to flotation
with a flotation gas, to separate said mineral material
into at least two fractions. a first fraction. collected 20
from flotation froth, being a flotation concentrate
enriched in said sulfide mineral and said gold, and a
second fraction being a flotation tail enriched in said
non-sulfide material and depleted in said gold;
wherein, when said blanketing gas comprises oxygen gas 25
said blanketing gas comprises less than about 15 volume
percent of said oxygen gas.
24. The method of claim 23. wherein:
during said mixing, said blanketing gas displaces air from 30
the vicinity of said coarse mineral material.
25. The method of claim 23. wherein:
said blanketing gas comprises less than about 5 volume
percent oxygen gas.
26. The method of claim 23. wherein: 35
said blanketing gas comprises greater than about 95
volume percent nitrogen gas.
27. The method of claim 23. wherein:
said blanketing gas and said flotation gas have substantially
the same gas composition. 40
28.Amethod for using diverse gas streams separated from
air to assist in processing a gold-bearing mineral material
having a sulfide mineral with which gold is associated, the
method comprising the steps of:
(a) separating a quantity of air into at least two gas 45
streams, with a first gas stream being enriched in
nitrogen gas relative to said air and a second gas stream
being enriched in oxygen gas relative to said air;
(b) providing a feed of particulate mineral material com- 50
prising gold and a sulfide mineral with which said gold
is associated. and wherein said mineral material also
comprises non-sulfide material;
(c) subjecting at least a portion of said mineral material to
flotation to separate said mineral material into at least 55
two fractions, with a first fraction being a flotation
concentrate which is enriched in said sulfide mineral
and said gold relative to said mineral material and said
gold in said feed and a second fraction being a flotation 60
tail which is enriched in said non-sulfide material and
depleted in said gold relative to said mineral material in
said feed;
said flotation comprising subjecting at least a portion of
said feed to a flotation gas including at least a portion 65
of said first gas stream, which is enriched in nitrogen
gas; and
14
(d) oxidative treating of at least a portion of said mineral
material, said oxidative treating comprising contacting
said portion of said mineral material with at least a
portion of said second gas stream. which is enriched in
oxygen gas, to oxidize at least a portion of sulfide sulfur
in said sulfide mineral to produce an oxidized material
in which at least some of said gold is freed from
association with said sulfide mineral, facilitating possible
subsequent recovery of gold from said oxidized
material.
29. The method of claim 28, wherein:
said step of providing said feed of particulate mineral
material comprises comminuting a coarse mineral
material in the presence of at least some of said first gas
stream, which is enriched in nitrogen gas.
30. The method of claim 28, wherein:
at least a portion of said mineral material, which is
subjected to said step of oxidative treating, comprises
at least a portion of said flotation concentrate.
31. The method of claim 28, wherein:
at least a portion of said mineral material, which is
subjected to said step of oxidative treating. comprises
at least a portion of said feed blended with at least a
portion of said flotation concentrate.
32. The method of claim 28. wherein:
said oxidative treating comprises pressure oxidizing a
slurry of said sulfide mineral at an elevated temperature
and an elevated pressure in the presence of said second
gas stream. which is enriched in oxygen gas.
33. The method of claim 28. wherein:
said oxidative treating comprises oxidative roasting of
said mineral material at an elevated temperature in the
presence of said second gas stream, which is enriched
in oxygen.
34. The method of claim 28, wherein:
said first gas stream comprises greater than about 95
volume percent nitrogen gas.
35. A method for processing a gold-bearing mineral
material having a sulfide mineral with which said gold is
associated. the method comprising the steps of:
(a) providing, in at least two portions, particulate mineral
material comprising gold, with a first feed portion of
said mineral material having a first average gold concentration
and a second feed portion of said mineral
material having a second average gold concentration
that is smaller than said first average gold concentration;
each of said first feed portion and said second feed
portion comprising a sulfide mineral with which gold
is associated and from which gold is difficult to
recover, and each of said first feed portion and said
second feed portion also comprising non-sulfide
material;
(b) oxidative treating of said first feed portion, said
oxidative treating comprising contacting said first feed
portion with a treating gas comprising oxygen gas, to
oxidize at least a portion of sulfide sulfur in said sulfide
mineral to produce an oxidized material in which at
least some of said gold is freed from association with
said sulfide mineral; and
(c) subjecting said second feed portion, but not said first
feed portion, to flotation, comprising treating a liquid
5,653,945
15
slurry of said second feed portion with a flotation gas
to separate said second feed portion into at least two
fractions, a first fraction being a flotation concentrate
enriched in said sulfide mineral and said gold, and a
second fraction being a flotation tail enriched in said 5
non-sulfide material and depleted in said gold;
said flotation gas comprising no greater than about 15
volume percent of oxygen gas.
36. The method of claim 35, wherein: 10
said flotation gas comprises less than about 5 volume
percent oxygen gas.
37. The method of claim 35, wherein:
said flotation gas comprises greater than about 95 volume
percent nitrogen gas.
16
38. The method of claim 35, wherein:
at least a portion of said flotation concentrate is blended
with said first feed portion prior to said step of oxidative
treating.
39. The method of claim 35, wherein:
said oxidative treating comprises at least one of: (i)
pressure oxidizing a slurry of said first feed portion of
said mineral material in the presence of said treating
gas at elevated temperature and at elevated pressure,
(ii) oxidative roasting of said first feed portion in the
presence of said treating gas at elevated temperature,
and (iii) biooxidation of said first feed portion in the
presence of said treating gas.
* * * * *