4,229,209 Process for beneficiating gold

Patent Number/Link:

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

PROCESS FOR BENEFICIATING GOLD

4,229,209

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

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.

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

TABLE 3-continued

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

89.9

76.5

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

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

4,229,209

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-

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

4,229,209

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;

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

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

Iron

Carbonyl

Dosage,

kg/m.ton

4.0

0.25

130

1.10

130

Roast

Temperature

'c,

Run

Order

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

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;

vapor to incorporate the iron carbonyl vapor in the IS

carrier gas;

(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.

• • • • •