United States Patent [19]
Kindig et al.
[11 ]
[45)
4,229,209
Oct. 21, 1980
FOREIGN PATENT DOCUMENTS
119156 8/1959 V.S.S.R. 209/212
[54] PROCESS FOR BENEFICIATING GOLD
(75) Inventors: James K. Kindig, Arvada; Ronald L.
Turner, Golden, both of Colo.
[73] Assignee: Hazen Research, Inc., Golden, Colo.
[21] Appl. No.: 873,148
[22] Filed: Jan. 27, 1978
2.332,309
2.944,883
3.490,899
3,669,644
3,767,7fIJ
10/1943
7/1960
111970
6/1972
10/1973
Drummond 427/252
Queneau et aJ. 75/82
Krivisky et al 423/25
Salo 423/25
Hougen el al. 75/121
Related U.S. Application Data
[63] Continuation-in·part ofSer. No. 658,259, Feb. 17, 1976,
abandoned.
Primary Examiner-L. Dewayne Rutledge
Assistant Examiner-Michael L. Lewis
Attorney. Agent, or Firm-Sheridan, Ross, Fields &
McIntosh
19 Claims, No Drawings
A process for beneficiating particulate gold from nonmagnetic
foreign material with which it is mixed which
comprises contacting the mixture with an iron carbonyl
in order to selectively enhance the magnetic susceptibility
of the gold particles so that a magnetic separation
between the gold and foreign material may be effected.
[51) Int. CI,2 C22B 1/00; C22B 11/00
[52) U.S. Cl 75/1 R; 75/83;
209/212; 427/132; 427/252
[58) Field of Search 75/1 R, 17, 21, 28,
75/62,72,77,82,83;423/23,25,138;209/212,
213,214; 427/47, 252, 253, 254, 255, 132
[56] References Cited
U.S. PATENT DOCUMENTS
2,132,404 10/1938 Dean et aJ. 423/25
[57) ABSTRACT
1
PROCESS FOR BENEFICIATING GOLD
4,229,209
2
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
SUMMARY OF THE INVENTION
The magnetic susceptibility of gold associated with
foreign materials is increased to the point where mag- 50
netic separation of gold particles from the foreign material
is feasible. The magnetic susceptibility of the gold
particles is increased by contacting a mixture ofparticulate
gold and foreign materials, such as occurs with
placer deposits, with an iron carbonyl like iron pen- 55
tacarbonyl under conditions at which general decomposition
of the iron carbonyl into metallic iron and carbon
monoxide is not appreciable. The carbonyl-treated mixture
is then passed through a magnetic separator for
removal of the gold particles. 60
Placer gold ores usually do not require grinding to
achieve liberation; however, if required, they may be
ground. The liberated ore is then contacted with carbonyl
vapors in a gas treating chamber, either alone or
by means of a gas that is inert to the process, which is 6S
used to carry the iron carbonyl vapors. Physical separation
between gold and foreign material follows in a
magnetic separator.
Fe(COls-="Fe+ SCO
The process is applied by contacting the mixture of
gold and foreign material with iron carbonyl under
conditions wherein the iron carbonyl decomposes to
form a magnetic skin on the gold particles but not on the
foreign material. These conditions are determined by
the temperature, the type of carbonyl used, pressure,
gas composition, etc. Ordinarily, the reaction occurs at
a temperature just below the substantial decomposition
temperature of the carbonyl in the presence of an ore.
Various types of available equipment can be used for
contacting the gold and foreign material with iron carbonyl
vapors, such as, a rotating kiln used as a reaction
vessel with the material being contacted directly with
iron carbonyl vapors or the vapors carried into contact
with the tumbling contents of the kiln by a gas such as
nitrogen which is inert to the reaction process. It has
been found that the material which enhances the magnetic
susceptibility of the gold particles exercises a preferential
selectivity for the gold particles over the particles
of the foreign material.
The process must be carried out at a temperature
below the temperature of major decomposition of the
carbonyl under the reaction conditions so that there is
no opportunity for decomposition of the carbonyl on a
nonselective basis or, perhaps, for its reaction with
some material to produce the magnetic material with
which the gold particles are coated. Obviously, if the
temperature is allowed to rise above the decomposition
The invention is particularly useful for recovering
5 gold from placer type gold deposits wherein gold particles
which are either free or have an exposed surface
exist in small percentages with large amounts of sand
and other particulate material including dolomite, albite,
muscovite, gypsum, and calcite. In the case of
10 placer gold, grinding can ordinarily be dispensed with.
The invention is applicable to recovering gold from
quartz, granite, other type rocks, and other material to
which it is attached; however, in the case of these materials
it is ordinarily first necessll'ry to grind the material
to a sufficiently fine particle size to liberate particulate
gold. This process also includes the recovery of more
than one metal value at a time from an ore or mixture.
The term "mixture" as used herein includes ore.
It is not known why the process of the invention
enhances the magnetic susceptibility of the gold partie
cles. It is well known that neither gold nor iron carbonyl
are magnetic. It is probable that the gold is coated
with a thin shell of metallic iron, which, of course, is
magnetic. What is not known is why there should be a
selective deposition of a film of magnetic material on
the gold while under essentially the same conditions
there is not decomposition of iron carbonyl producing a
magnetic film on all the ore particles. Ofcourse, a rapid
and complete decomposition of iron carbonyl would
result in coating particles of both gold and the foreign
material with iron so that an effective magnetic separation
would be obviated. Other metal carbonyls may be
used such as those of the Group VIII metals nickel and
cobalt.
Iron carbonyl decomposes under the proper temperature
conditions in accordance with the following reaction:
CROSS REFERENCES TO RELATED
APPLICATIONS
As is well known, since the government has lifted the
price on gold from 535.00 an ounce, the price of gold
has multiplied. As a result, many gold mines which 15
were forced out ot operation by the 535.00 an ounce
ceiling have now resumed operations, and gold exploration
and mining has greatly increased.
Because most gold ores contain less than a few
ounces of gold per ton of ore, large amounts of gangue 20
must be processed in order to recover the gold. In addition
to the low grade of gold ores, the gold is usually
present as very fine particles. Thus, gravity processes
for the separation of gold from gangue are inefficient.
This is due to the high viscous drag forces acting on 25
small particles in water relative to the force of gravity.
Typically, large amounts of water are needed for
beneficiating gold ores, particularly placer gold ores.
This is a significant problem in recovering gold from
low grade ores particularly placers existing in arid areas 30
such as deserts. There is, therefore, considerable time
and expense involved in recovering gold from its ores.
The above conditions have created a need for improved
and more efficient beneficiating procedures for
the recovery of gold from low grade ores, i.e., gold 35
associated with foreign materials with which the gold
exists in small percentages. Also, a process which operates
dry would be especially useful, because it would
provide a method for recovering gold which is located
in deserts. 40
Accordingly, it is a principal object of this invention
to provide an economically feasible method for separating
gold from foreign material by selectively enhancing
the magnetic susceptibility of the gold particles so that
they may be successfully separated from the foreign 4S
material by magnetic separation.
This application is a continuation-in-part application
of our now abandoned application Ser. No. 658,259
filed in the U.S. Patent and Trademark Office on Feb.
17,1976.
BACKGROUND OF THE INVENTION
4,229,209
3
temperature of the carbonyl for sufficient time, complete
decomposition of the carbonyl will occur with the
result that the particles of the foreign material as well as
the gold will be coated with metallic iron to give both
types of particles an enhanced magnetic susceptibility, 5
thus preventing their effective separation magnetically.
The amount of carbonyl used and the time of treatment
can be varied to effect substantially complete
magnetization of the gold present. The time, temperature
and injection rate of the treatment is a balance 10
between the reaction rate and the economics of the
magnetic separation process. Carbonyl will be added in
an amount of from about 0.1 to about 128 kilograms per
metric ton of feed with from about 0.25 to about 8 kilot5
grams per metric ton of feed being preferred and from
about 0.5 to about 4.0 kilograms per metric ton of feed
being more preferred. Additionally, it is preferred to
inject the carbonyl into the reactor during the first half
of the roast period and it is more preferred if it is in- 20
jected during the first quarter of the roast and most
preferred if injected during the first tenth of the roast
period.
Generally, a reaction' time not in excess of about two
hours is adequate, with a reaction time not in excess of 25
one hour being preferred and a reaction time not in
excess of a half hour being most preferred. The temperature
at which the reaction is formed at atmospheric
pressure can vary between about 100°-250° C., a preferred
temperature range is from about 100° to about 30
150° C. and a more preferred temperature range is from
about 110° to about 130° C. Generally, the higher the
temperature, the more complete the gold recovery with
lower gold concentration in both the tails and the magnetic
concentrate and the larger the amount of magnetic 35
concentrate. Therefore, for any feed material, the economics
of the situation will have to be considered and
conditions set to produce the most favorable balance
between the grade and recovery.
Ifdesired, prior to treating the gold and foreign mate- 40
rial with iron carbonyl, the mixture of gold and foreign
material can be magnetically cleaned to remove any
magnetic impurities. Thereafter, the non-magnetic fraction
of the mixture is treated with the iron carbonyl.
After the feed mixture containing the gold has been 45
treated with a metal carbonyl, it is then subjected to a
magnetic separation process to effect the separation of
gold. Any of many commercially available magnetic
separators can be used to remove the gold from the
50 gangue. For example, low or medium intensity separations
can be made with a permanent magnetic drum
separator (field strengths up to about 2,500 gauss), electromagnetic
drum separators (field strengths up to
about 7,000 gauss), induced roll separators (field 55
strengths of about 11,000 gauss) or other configurations
known to those skilled in the art. Additionally, newer
high-gradient magnetic separators are especially good
for separating fines, although they are generally operated
wet. A dry magnetic separation process for gold is 60
generally preferred. This avoids the expense of dewatering
and also allows for the recovery of gold from
deserts.
The invention is illustrated by the examples presented
below in which samples of placer gold and associated 65
foreign material were treated by the process of the
invention. The examples are illustrative of the invention
but not limiting thereof.
4
EXAMPLE I
In this example, a sample of placer gold concentrate
was diluted with gangue of essentially silicon dioxide
and aluminum dioxide. The resultant sample contained
4050 grams gold per metric ton of placer ore. For the
purpose of a blank, a comparative magnetic separation
was made on an untreated portion of the sample. Another
portion of the sample was treated with the process
of the invention at 135° C. and a third portion of the
sample was treated by the process of the invention at
temperatures up to 145° C. Both of the treated samples
were subjected to magnetic separation as in the first test,
and the magnetic and nonmagnetic fractions ofeach test
were analyzed as to gold content with the gold distribution
for the magnetic and nonmagnetic fractions of each
test computed. By "Gold Distribution" is meant the
percentage ofgold in the entire beginning sample which
is partitioned to the specified final fraction. The following
table sets forth the results obtained.
TABLE 1
Weight Gold Gold
Treatment % of Assay Distriof
Sample Fractions Sample oz/ton bution %
No Treatment Magnetic IU4 21.26 1.92
Non-Magnetic 88.46 142.<)4 98.08
Low Temperature
135' C.
30 min Magnetic 11.95 132.87 13.29
32 kg/m.ton
Fe(CO)s Non-Magnetic 88.05 117.68 86.71
High Temperature
up to
145' C. in
23 min Magnetic 14.18 200.83 26.79
Total 23 kg/
m.ton Fe(CO)S Non-Magnetic 85.82 90.70 73.21
EXAMPLE 2
To provide a test sample for this example, 4.7 grams
of the non-magnetic fraction of a placer gold concentrate
was blended with 195 grams of sand. Analysis of
this material showed a gold content of 84 grams per
metric ton. A one-fourth split of the above material (52
grams) was placed in a rotating glass reactor and heated
to 150° C. under nitrogen. At this temperature, the
mixture was exposed to vapors of iron carbonyl for
one-half hour at an amount equal to about 32 kilograms
of carbonyl per metric ton of material. Cool down was
under nitrogen. After treatment, magnetic separation
was effected by using a Dings crossbelt separator with
a 4.5 amp setting. Two recleanings of the magnetic
material were made.
The results of the above tests are set forth in the
following table:
TABLE 2
Yield Gold Distribution
(Wl.%) (OzrTon) of Gold %
Concentrate
(Magnetic) 0.96 225. 88.3
Gangue
(Non-Magnetic) 99.04 0.29 11.7
EXAMPLE 3
The sample of Clear Creek placer gold from Colorado
was diluted with silica to yield a gold content of
1.0 kilogram per metric ton. This placer gold ore was
Gold Gold
Added Magnetic Yield Assay Recovery
Mineral Fraction Wt.% oz/ton % or Total
S Calc head 100.0 26.0
IClear Creek gold ","'Oncenlrale added 10 silica s.and, no Vulture placer.
2Assay data not available for tails.
EXAMPLE 5
A synthetic placer containing 891 grams of gold per
metric ton (26 ounce per ton) was diluted with magnetically
scalped Vulture placer to 27.1 grams of gold per
metric ton of feed (0.79 ounce per ton). The gold particles
contained in this feed material were 28- X 150mesh.
A second sample of a placer containing a low
gold content was prepared by adding 49 flakes of 65X
loo-mesh gold (hand picked from Clear Creek concentrate)
to one kilogram of magnetically scalped Vulture
placer. This resulted in a placer ore containing 3.4
grams of gold per metric ton of feed (0.098 ounce per
ton). One kilogram samples of each of these mixtures
was then separately treated at 1220 C. for 15 minutes
with an iron pentacarbonyl dosage of one kilogram per
metric ton of feed. The carbonyl was injected into the
reactor by a syringe pump calibrated to deliver the
required amount of iron carbonyl in the first 1.5 minutes
of the roast. The test results are presented in Table 4.
TABLE 4
4,229,209
6
TABLE 3-continued
5
treated with 1 kilogram of iron pentacarbonyl per metric
ton feed at a temperature of 122' C. for 15 minutes.
The iron carbonyl was injected in 1.5 minutes coincident
with the start of the 15 minute roast and the reaction
chamber was purged with nitrogen during heating
and cool down. The reactor product was magnetically
separated yielding a magnetic concentrate of 57.4 kilograms
per metric ton of gold (1676 ounce per ton) and
1.6% of the feed. The non-magnetic tails contained 66.9
grams per metric ton gold (1.95 ounce per ton). The 10
overall gold recovery was 93.3%.
EXAMPLE 4
Gold
Recovery
% of Total
89.3
3S
89.9
76.5
40
87.4
85.9
Gold
Added Magnetic Yield Assay
Mineral Fraction WI. % ozlton
Muscovite Magnetic 28.6 82.6
Nonmagnetic 71.4 3.98
Calc head 100.0 26.5
Gypsum Magnetic 19.0 126.0
Nonmagnetic 81.0 3.34
Calc head 100.0 26.6
Hematite Magnetic 51.3 33.3
Nonmagnetic 48.7 10.8
Calc head 100.0 22.3
Albite Magnetic 19.8 125.0
Nonmagnetic 80.2 4.46
Calc head 100.0 28.3
Dolomite Magnetic 19.0 91.2
Nonmagnetic 81.0 3.52
Calc head 100.0 20.2
Calcite Magnetic 19.0 93.9
Nonmagnetic 81.0 3.37
Calc head 100.0 20.6
Silica l Magnetic 1.6 1676.0
Nonmagnetic 98.4 1.95
Calc head 100.0 28.7
Vulture2 Magnetic 20.4 99.1
Nonmagnetic 79.6
Calc head 100.0 28.7
Vulture2 Magnetic 20.2 106.0
Nonmagnetic 79.8
86.7
93.3
::::78.0
::::82.0
Gold
Yield, Gold Assay, Recovery
Fraction Wt% oz/ton % or Total
Magnetic 11.6 5.82 85.7
Nonmagnetic 88.4 0.127
Calc head 100.0 0.787
Magnetic 14.1 0.49 69.9
Nonmagnetic 85.1 0.034
Calc head 100.0 0.098
EXAMPLE 6
Eight 90 gram samples of a simulated gold placer ore
with a size range of 28- X 150-mesh were subjected to
two different roast durations, i.e. 15 minutes and 60
4S minutes. For each of these times two injection rates
were used, additionally the effect of varying roast time
and injection rates were analyzed with respect to different
size fractions. All of the samples were treated with
4 kilograms of iron carbonyl per metric ton at a temper-
50 ature of 1200 -122' C. For the "slow" injection rate, the
iron carbonyl was injected during the entire run, while
for the "fast" injection rate, all the iron carbonyl was
injected in the first 11% of the roast time, i.e. 1.65 minutes
for the 15 minute run and 6.6 minutes for the 60
55 minute run. The results are given below in Tables 5 and
6.
TABLE 5
Gold Gold Gold Distri-
Roast Injection Yield, Assay, Dist. bution %
Time Time Product % oz/ton % Per % Yield
15 min. Fast Magnetic concentrate 12.2 242.90 99.1 8.13
Nonmagnetic tails 87.8 0.29 0.9 om
Calculated feed 100.0 29.89 100.0
15 min Slow Magnetic concentrate 11.6 217.93 97.9 8.44
Nonmagnetic tails 88.4 0.61 2.1 0.02
Calculated feed 100.0 25.82 100,0
60 min Fast Magnetic concentrate 15.6 184.32 98.2 6.30
Nonmagnetic tails 84.4 0.61 1.8 om
Calculated feed 100.0 29.27 100.0
7
4,229,209
8
TABLE 5-continued
Gold Gold Gold Distri-
Roast Injection Yield, Assay, Dist. bUlion %
Time Time Product % oz/ton % Per % Yield
60 min. Slow Magnetic concentrate 21.1 148.99 97.9 4.64
Nonmagnetic tails 78.9 0.86 2.1 0.03
Calculated reed 100.0 32.12 100.0
TABLE 6
Size
Reaction Injection Fraction, Yield, % Gold Assay, oz/ton
Time, min Time Mesh Magnetic Nonmagnetic Magnetic Nonmagnetic
15 Fast 28 X 35 ) 32.72 ) 0.45
35 X 65 6.08 38.02 372.38 0.09
65 X 150 6.13 17.05 114.47 0.41
15 Slow 28 X 35 ) 35.71 ) 0.58
35 X 65 6.14 36.28 304.23 0.88
65 X 150 5.47 16.41 121.05 0.06
60 Fast 28 X 35 ) 31.36 ) L50
35 X 65 8.10 37.92 273.60 <0.005
65 X 150 7.52 15.10 88.16 0.29
60 Slow 28 X 35 ) 34.73 ) 1.80
35 X 65 11.l6 32.02 222.88 <0.005
65 X 150 9.90 12.20 65.70 0.44
EXAMPLE 7 metric ton of feed injected during the first I.S minutes of
A synthetic gold placer ore was prepared from the the roast.
nonmagnetic fraction of Vulture placer spiked to ap-
35
A total of 14 tests were performed in random order
proximately 920 grams gold per metric ton feed with with the magnetic separation of the reactor product
the nonmagnetic portion of Clear Creek gold concen- being carried out on the size fractions: 28 X6S-mesh and
trate. The size range of the feed was 28- X 150-mesh. 65 X ISO-mesh. For each size fraction three passes were
Four different samples were treated with 4 kilograms made over an induced magnetic separator at 75 rpm and
iron pentacarbonyl per metric ton offeed for a period of 8 amp coil current. The results of these tests are summa-
IS minutes at various temperatures. The results are 40 rized for the composited size fractions in Table 8.
given below in Table 7. TABLE 8
TABLE 7 Roast Iron Gold
Treatment Gold Gold Distri- Run Temp- Carbonyl Gold Re-
Temperature Yield Assay, bution Or- erature Dosage, Yield, Assay, covery
45 'c. Fraction Wt.% ozlton der 'c. kg/m.lon Fraction Wt% ozlton % %
110 Magnetic 9.42 245. 86.2
II 110 0.25 Magnetic 15.1 97.8 61.0
Nonmagnetic 90.58 4.09 13.8 Nonmagnetic 84.9 ILl
Calc head 100.0 26.8 Calc head 100.0 24.2
liS Magnetic 9.37 276. 937
12 1I0 0.25 Magnetic 12.2 86.3 40.9
Nontnagnetlc 9063 1.93 6.3 50 Nonmagnetic 87.8 17.3
Calc head 100.0 27.6 Calc head 100.0 25.7
125 Magnetic 2542 93.0 99.2 110 10 Magnetic 15.0 113 72.7
Nonmagnetic 7458 0.26 08 Nonmagnetic 85.0 7.48
Calc head 100.0 23.8 Calc head 100.0 23.3
135 Magnelic 73.42 39.2 99.98 6 110 40 Magnetic 16.5 135 78.4
Nonmagnetic 26.58 <0.02 <0.02 55
Nonmagnetic 83.S 7.35
Calc head 1000 28.8 Calc head 100.0 28.4
7 110 4.0 Magnetic 17.1 111 75.0
Nonmagnetic 82.9 7.65
Calc head 100.0 25.3
EXAMPLE 8 14 120 0.25 Magnetic 16.9 120 88.0
A synthetic gold placer was prepared from a non-
Nonmagnetic 83.1 3.32
60 Calc head 100.0 23.0
magnetic fraction of a Vulture placer spiked to approxi- 120 10 Magnetic 18.0 147 88.0
mately 891 grams gold per metric ton of feed (26 ounce Nonmagnetic 82.0 4.41
per ton) with a nonmagnetic portion of Clear Creek Calc head 100.0 30.0
4 120 LO Magnetic 16.1 160 88.7
gold concentrate. The size range of the feed was 28- Nonmagnetic 83.9 3.93
X ISO-mesh. Each sample was roasted in a small reactor 65 Calc head 100.0 29.1
for 15 minutes at the specified temperatures of either 9 120 4.0 Magnetic 16.3 116 80.6
110·, 120· or 130· C. at a prescribed iron carbonyl dos- Nonmagnetic 83.7 5.44
Calc head 100.0 23.4
age of 0.25, I or 4 kilograms of iron pentacarbonyl per 13 120 4.0 Magnetic 20.9 108 83.8
9
4,229,209
10
What is claimed is:
1. A process for beneficiating particulate gold from
foreign material with which it is mixed which comprises
contacting the mixture with an iron carbonyl under
conditions which cause the iron carbonyl to decompose
and then cause a coating at the surface of the gold particles
to the substantial exclusion of the foreign material
so as to alter the surface characteristics of the gold
particles thereby causing a selective enhancement of the
magnetic susceptibility of the gold particles to the substantial
exclusion of the foreign material so that a magnetic
separation between the gold and foreign material
may be effected.
2. The process of claim 1 in which the treated mixture
is subjected to a magnetic field to remove gold particles
from the foreign material.
3. The process of claim 1 in which the iron carbonyl
is iron pentacarbonyl.
4. The process of claim 3 in which the carbonyl is in
20 gaseous form and is contacted with the mixture in an
inert carrier gas.
5. The process of claim 1 wherein the foreign material
is selected from the group consisting of granite, quartz,
muscovite, alumina, gypsum, albite, dolomite, calcite,
25 hematite and silica.
6. The process of claim 1 wherein the mixture is magnetically
cleaned and the non-magnetic fraction of the
mixture is then contacted with iron carbonyl.
7. The process of claim 1 wherein the mixture of gold
and foreign material is contacted with iron carbonyl at
a temperature between 100° C. and 250· C.
8. A process for beneficiating gold mixed with foreign
material, which comprises the steps of:
(a) reducing the mixture to a particulate form;
(b) placing the particulate mixture in a gas treatment
chamber;
(c) introducing iron carbonyl vapor into said chamber
under conditions which preclude substantial
non-selective decomposition of the iron carbonyl,
and
(d) maintaining the iron carbonyl vapor in contact
with said mixture for a sufficient time for the iron
carbonyl to selectively enhance the magnetic susceptibility
of substantially all of the gold particles
in the mixture.
9. The process of claim 8 wherein the temperature of
the chamber is not in excess of about 250· C.
10. The process of claim 8 wherein the iron carbonyl
vapor is contacted with said mixture at a temperature
between 110° C. and 130· C.
11. The process of claim 8 wherein from about 0.25 to
about 8 kilograms of iron carbonyl per metric ton of
mixture are introduced into said chamber.
12. The process of claim 8 wherein the iron carbonyl
vapor is maintained in contact with said mixture for less
than one-half hour.
13. The process of claim 8 wherein the iron carbonyl
gas is first contacted with an inert carrier gas and then
introduced into said chamber.
14. A process for recovering gold from a mixture of
gold with other material which comprises contacting
the mixture with a carbonyl of a Group VIII metal
under conditions which cause the Group VIII metal
carbonyl to decompose and then cause a coating at the
65 surface of the gold to the substantial exclusion of the
other material so as to alter the surface characteristics of
the gold thereby causing a selective enhancement of the
magnetic susceptibility of the gold to the substantial
60
45
TABLE 10
Gold
Gold Re·
Yield, Assay, covery
Fraction Wl% oz/ton % 5
Nonmagnetic 79.1 5.54
Calc head 100.0 27.0
Magnelic 31.8 74.8 89.2
Nonmagnetic 68.2 4.24
Calc head 100.0 26.6
Magnelic 19.4 133 95.0 IO
Nonmagnetic 80.6 1.69
Calc head 100.0 27.2
Magnetic 16.3 123 81.1
Nonmagnetic 83.7 5.57
Calc head 100.0 24.7
Magnetic 23.7 128 93.3 15
Nonmagnetic 76.3 2.84
Calc head 100.0 32.5
EXAMPLE 10
TABLE 8-continued
1.0
1.0
Iron
Carbonyl
Dosage,
kg/m.ton
4.0
0.25
130
130
1.10
130
Roast
Temperature
'c,
8
Run
Order
10
Iron
Carbonyl Yield, WI. % Gold, oz/lon Gold
Dosage Mag- Non- Mag- Non- Calc Recovery,
kg/m.ton netic magnetic netic magnetic Head % of Feed
1 9.3 90.7 560 8.14 59.5 87.6
2 9.6 90.4 491 5.06 51.7 91.2
4 10.1 89.9 558 4.19 60.1 93.7
8 11.0 89.0 496 3.80 57.9 94.2
16 15.8 84.2 368 2.59 60.3 96.4
Gold 30 Sample Treatment Gold Re-
Before Yield Assay, covery
Magnetic Separation Fraction % ozlTon %
Aged One Month Magnetic 39.7 36.3 96.8
in Dry Air Nonmagnelic 60.3 0.78
Calc head 14.9 35
Aged Two Months Magnetic 35.9 35.3 95.8
in Dry Air Nonmagnetic 64.1 0.87
Calc head 13.2
Aged Two Months in Magnetic 34.9 33.2 97.2
Dry Air, Tumbled 24 Nonmagnetic 65.1 0.52
Hours in Blender Calc head 11.9 40 Aged Two Months in Magnetic 37.2 30.5 91.4
Dry Air, Exposed 48 Nonmagnetic 62.8 1.70
Hours to 100% Calc head 12.4
Humidity, Stored
24 Hours in Vial
EXAMPLE 9
A placer ore containing 446 grams gold per metric
ton of feed (13 ounces per ton) which had been treated
with 4 kilograms of iron pentacarbonyl per metric ton
of feed for one hour at a temperature of 125· to 130· C.
in a large reactor was subjected to abrasive and weathering
conditions prior to magnetic separation of the
gold. The results are given below in Table 9.
TABLE 9
Samples of a non-magnetic fraction of 28- X65-mesh
Vulture placer were spiked with non-magnetic 28-
X65-mesh Clear Creek gold concentrate to obtain 1.99 50
kilograms of gold per metric ton of synthetic placer (58
oz/ton). The synthetic placer was then wet-screened at
65-mesh to remove fines. Thereafter, each sample was
treated with iron carbonyl at varying levels at 122' C. in
a small glass rotary reactor for 15 minutes. In each case, 55
the carbonyl was injected during the first 1.5 minute of
the roast. Results are given below.
4,229,209
10
11
exclusion of the other material so that a magnetic separation
between the gold and said other material may be
effected.
15. The process of claim 14 in which the Group VIII
metal is a member selected from the group consisting of 5
iron, nickel and cobalt.
16. The process of claim 15 in which the metal is iron.
17. A process for beneficiating gold mixed with foreign
material, comprising:
(a) reducing the mixture to a particulate form;
(b) placing the particulate mixture in a gas treatment
chamber;
(c) contacting an inert carrier gas with iron carbonyl
vapor to incorporate the iron carbonyl vapor in the IS
carrier gas;
12
(d) introducing the iron carbonyl vapor carried in the
carrier gas into said chamber at a rate of from about
0.5 to about 4.0 kilograms of iron carbonyl per
metric ton of particulate material and at a temperature
from about 110' C. to about 130' C.
(e) maintaining the iron carbonyl vapor in contact
with said mixture for less than one-half hour to
selectively enhance the susceptibility of substantially
all of the gold particles in the mixture;
(f) separating the gold particles from the mixture by
magnetic separation.
18. The process ofclaim 17wherein the iron carbonyl
is iron pentacarbonyl.
19. The process of claim 8 wherein the iron carbonyl
is iron pentacarbonyl.
• • • • •
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6S