4,721,526 Heap leaching with oxygen

Patent Number/Link:

United States Patent [19]

Elmore et al.

[11] Patent Number:

[45] Date of Patent:

4,721,526

Jan. 26, 1988

[56]

[54] HEAP LEACHING WITH OXYGEN

(75] Inventors: Carl L. Elmore; Phillip Mitchell, both

of Glens Falls, N.Y.; Robert J.

Brison, Golden, Colo.

[73] Assignee: Kamyr, Inc., Glens Falls, N.Y.

[21] Appl. No.: 895/)77

[22] Filed: Aug. 13, 1986

[51] Int. CI.4 C22B 11/04

[52] U.S. CI 75/118 R; 75/105;

423/29; 423/30;423/31; 266/168

[58] Field of Search 266/168, 101 R;

75/101 R, 105, 118 R, 2; 423/27, 29, 30, 31

References CJted

U.S. PATENT DOCUMENTS

2,009,667 7/1935 Keyes 423/29

4,190,436 2/1980 Hughes 75/105

4,256,705 3/1981 Heinen et al. 423/27

4,526,615 7/1985 Johnson 75/101 R

FOREIGN PATENT DOCUMENTS

3126234 4/1983 Fed. Rep. of Germany .

78/1184 7/1978 South Africa.

OTHER PUBLICATIONS

Davidson, R. J. et al, "The Intensive Cyanidation of

Gold-Plant Gravity Concentrates", J. of South African

Inst. of Min. and Metal., Jan., 1978, pp. 146-165.

"On the Dissolution ofPrecious Metals ... ", Tronev et

al., Comptes Rendus (Doklady) de l'Academie des Sciences

(1937), vol. 16, No.5, pp. 281-284.

"Chemistry of Cyanidation ... ", Hedley et al., American

Cyanamid Company, Dec. 1968.

"The Chemistry of the Extraction of Gold ... ", Gold

Metallurgy in South Africa, Finkelstein, Chapter 10, p.

309 (1972).

"Research on Pressure Leaching of Ores ... ", Pietsch

et al., Erzmetall, Jun. 1983, pp. 261-265.

"The Treatment of Refractory Gold-Bearing ... ",

Muir et al., Precious Metals: Mining Extraction and

Processing, 1984, pp. 309-322.

"Solubilities of Inorganic and Metal-Organic Compounds

(Seidel)", Linke, 4th Ed., 1958, vol. 1, p. 250,

vol. 2, pp. 1228-1230.

CARBON

COLUMNS

86../

Skillings I, Skillings Minning Review, vol. 75, No. 26,

Jun. 28, 1986, pp. 3-10.

Skillings II, Skillings Minning Review, May 25, 1985

pp.4-7.

McClelland I, Dept. of the Interior Report 8612 "Improvements

in Heap Leaching ... ", 1981.

McClelland II, Dept. of the Interior Circular 8945,

"Agglomeration-Heap Leaching ... ", 1983.

Arthur et al, "Development of a Small Scale ... ", pp.

XXIV-I, 3, 5, 7, 9, 11, 13, 17, 19 and 21.

Potter I, "Some Factors in the Design of ... ", 1980.

Potter II, "Extraction of Metallurgy 1981", "Some

Developments in Gold... ", pp. 128-136.

McQuiston et aI, "Gold and Silver Cyanidation ... ",

pp. 3-9, 1981.

Chamberland I, "Minning Congress Journal", Apr.,

1981, Heap Leaching ... , pp. 47-52.

Chamberland II, "Gold and Silver Leaching ... ",

Department of Interior Information Circular 8852.

Kappes, "Leaching of Small Gold and Silver Deposits",

Nov., 1978, pp. 1-18.

Sawyer, "Process Design and Operation ... ", pp.

CI87-191.

Duncan et al, Engineering and Minning Journal, Jul.,

1977, pp. 65-72, "How Cortez Gold Mine ... ".

Primary Examiner-Robert L. Stoll

Attorney, Agent, or Firm-Nixon & Vanderhye

[57] ABSTRACf

A method and system for the percolation leaching of

gold and silver ores applies a cyanide leaching liquid to

a pile of gold and silver ore. Heap leaching, vat leaching,

or the like may specifically be practiced. The cyanide

leaching liquid is applied to the pile by spraying,

flooding, or via a foam of oxygen gas and cyanide liquid

on top of the pile. Gold and silver are recovered from

the pregnant liquor. The leach rate is increased and/or

the recovery of gold and silver from the ore is increased

by supplying to the pile a gas containing oxygen at a

significantly higher percentage than in ambient air (e.g.

pure oxygen gas). The oxygen gas may be supplied to

the leaching liquid, and/or into the pile itself (as with a

plurality of perforated pipes adjacent the bottom of the

pile).

19 Claims, 4 Drawing Figures

u.s. Patent Jan. 26, 1988

TFIG. I

.36

Sheet 1 of2 4,721,526

<L.---~:J"

IFIG. 4

TO HOWING TANKS

..'

57 68

PREGNANT

LIQUOR

HOLDING

TANIG

90 ----1/

~TRIPPING

GOLD

UNIT

+---'

88/

fF/G.3

u.s. Patent Jan. 26, 1988 Sheet 2 of2 4,721,526

MAKE-UP 50

WATER NaCN ~

02 66

72 SOURCE

CYANIDE 74

STORAGE

TANKS

CARBON

COLUMNS

{FIG. 2

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic view of exemplary

apparatus for practicing a heap leaching method according

to the present invention;

FIG. 2 is a perspective detail view of a portion of an

exemplary oxygen introducing pipe utilizable in the

system of FIG. 1;

FIG. 3 is a box diagram illustrating an exemplary

system for the preactive of vat leaching according to

the method of the present invention; and

FIG. 4 is a partial, side, cross-sectional view illustrating

equipment utilized with one of the vats schematically

illustrated in FIG. 3.

DETAILED DESCRIPTION OF THE

DRAWINGS

An exemplary heap leaching system for practicing a

method of heap leaching of gold and silver ore according

to the present invention is illustrated schematically

by reference numeral 10 in FIG. 1. Ore 11 is heaped in

any suitable conventional manner on a sloping leach

pad 12. The leach pad 12 may be of conventional design,

having a substantially impervious surface 14 on

which the ore 11 is heaped, such as a plastic heap laid

over a prepared surface, a reusable pad, a locallyobtained

clay lined pad, etc. The impervious surface 14

of the pad 12 is sloping, such as illustrated in FIG. 1,

having a higher portion and a lower portion, and pregnant

liquid is withdrawn from the lower portion, as

utilizing the conventional pregnant solution trough 16.

The pregnant liquid passes via conduit 20 to a conventional

gold recovery station 22, which may comprise a

conventional carbon-adsorption system, a conventional

zinc precipitation system, or the like. The barren solution

(cyanide leaching liquid) from the gold recovery

station 22 passes in line 24 ultimately to be applied to the

ore pile 11 via line 26 in conventional sprayheads 28, or

the like. Desirably a portion of the pregnant liquor is

recycled from line 20 to line 24 via line 30.

According to the present invention, the leach rate

and/or the recovery of gold or silver in the same total

leach time, is achieved by supplying oxygen to the ore

in the pile 11. Oxygen gas is supplied which has a significantly

greater percentage of oxygen therein than does

ambient air; desirably, "pure oxygen" is utilized, that is

oxygen gas having a purity approaching about 99 percent

or so, however gases having lower percentages of

oxygen, but higher than in ambient air, also will be

effective. The oxygen gas is supplied from a tank of

oxygen, 34, via line 36. The oxygen gas can be supplied

to the ore in pile 11 by one of, or both of, two ways.

According to a first procedure, the oxygen gas from

source 34 is applied to the cyanide leaching liquid in line

24 utilizing a conventional ejector 32, the oxygen gas

being supplied to the suction 38 of the ejector 32. Preferably

enough oxygen gas is supplied to essentially

saturate the leaching liquid with oxygen gas.

rate as in conventional pile leaching, resulting in a

higher concentration of gold in solution (and thereby

permitting a smaller recovery system).

It is the primary object of the present invention to

5 enhance the effectiveness of pile leaching of gold and

silver ores. This and other objects of the invention will

become clear from an inspection of the detailed description

of the invention and from the appended claims.

4,721,526

HEAP LEACHING WITH OXYGEN

BACKGROUND AND SUMMARY OF THE

INVENTION

Pile leaching of gold and silver ores has been increasing

in popularity since pile leaching techniques can be

practiced with low capital and operating costs, and may

be cost-effective for use with low grade ores. "Pile

leaching" as used in the present specification and claims 10

covers what are conventionally known as heap leaching

processes, vat leaching processes, and like processes in

which a pile of ore particles or the like have a cyanide

leaching liquid applied thereto, with recovery of pregnant

liquor from the bottom of the pile. The term "ore" 15

as used in the present specification and claims covers

tailings, uncrushed ore, crushed ore, agglomerated

crushed ore, and the like. Pile leaching normally encompasses

the percolation leaching of relatively coarse

gold-siver ore piled on a surface which allows collec- 20

tion of the pregnant liquor obtained from the percolation

leaching.

According to the invention it has been found that the

leach rate can be increased, and/or the recovery can be

increased in the same total leach time, by utilizing oxy- 25

gen in the leaching process. That is oxygen containing

gas, having a significantly higher precentage of oxygen

therein than is obtained utilizing ambient air, is supplied

to the pile. This may be practiced by introducing oxygen

containing gas, such as "pure oxygen" (e.g. gas 30

having about 99 percent oxygen) into bottom portions

of the pile utilizing a plurality of pipes having gas passages

therein. Additionally, or alternatively, the oxygen

can be supplied to the pile by adding the oxygen to the

cyanide leaching liquid that is applied to the pile to 35

leach the gold and/or silver from the ore into the pregnant

liquor. An ejector may be utilized to add the oxygen

gas to the liquid prior to applying it to the pile, as by

spraying it on top of the pile (particularly where heap

leaching is utilized), flooding the top of the pile (partic- 40

ularly where vat leaching is practiced), or applying it as

a foam (the oxygen gas and cyanide leaching liquid

foaming) on top of the pile.

While the invention is applicable to a wide variety of

"ores", as that term is used in the present specification 45

and claims, it is particularly advantageous for use in

leaching gold from those ores which typically consume

oxygen and therefore tend to deplete the oxygen from

leached solutions in conventional systems. Where agglomeration

of the ore particles is desirable, that may be 50

practiced utilizing any desirable conventional technique,

such as shown in U.S. Pat. No. 4,256,705.

The gold and/or silver may be recovered from the

pregnant liquor utilizing a number of conventional techniques.

For instance the pregnant liquor may be with- 55

drawn from adjcent the bottom of a heap and then

treated by a carbon-adsorption system or a zinc precipitation

system, or it may be withdrawn from the bottom

of a rock filter of a vat leaching apparatus, and similarly

treated by carbon-adsorption or zinc precipitation. 60

By practicing the present invention, it is possible to

significantly increase the leach rate, or to increase recovery

in the same total leach time, or a combination of

both. Because of the increased leach rate that may be

obtained by utilizing oxygen in the practice of the in- 65

vention, the flow of solution to a pile could be increased

to maintain the same gold concentration in solution, or,

alternatively, the flow could be maintained at the same

4,721,526

Alternatively, or additionally, the oxygen gas is applied

to the pile 11 utilizing line 40, connected to line 36,

header 41, and pipes 42. The pipes 42 are disposed adjacent

the bottom of the pile 11, and extend substantially

the length thereof. The pipes 42 have gas passages, such 5

as illustrated by the openings 44 in FIG. 2, therein. The

passages 44 are designed with respect to the size of

particles expected to be provided in the pile 11, so that

the particles of ore do not readily clog the passages 44.

Any suitable construction of passages can be provided 10

in order to effect the desired results, such as by providing

the entire pipes 42 of gas porous sintered material or

the like, providing the passages in the side or bottoms of

the pipe, etc. A second plurality of pipes, perpendicular

to pipes 42, may also be provided adjacent the bottom 15

of the pile and connected to tank 34.

Optionally, according to the invention, a cover 46

may be provided on top of the pile 11. The cover 46

would be formed ofgas impermeable plastic, or the like,

which would prevent or minimize diffusion of oxygen 20

out of the pile 11. An oxygen atmosphere could be

maintained beneath the cover 46, and/or the leaching

liquid could be applied by spraying it on top of the

cover 46 (if the cover were water permeable while still

preventing or minimizing diffusion of oxygen there- 25

through).

FIGS. 3 and 4 illustrate the practice of an exemplary

method according to the invention in a process conventionally

referred to as vat leaching. An exemplary system

for practicing this process is illustrated generally by 30

reference numeral 50 in FIG. 3 and preferably includes

a plurality of vats 52, 53, 54, and 55. A typical vat, such

as the vat 55, has an end wall 56, and sidewalls 57, 58. At

least a portion of the bottom of the vat slopes downwardly

from the open end between the walls 57, 58, 35

toward the wall 56. The bottom of the vat 55 typically

would contain rocks 60 providing a rock bed or filter, a

layer of burlap 61, a wood support 62 or the like, and a

filter 63 below the support 62 and burlap 61. The ore is

provided in a pile 59 above the rocks 60. Pregnant Ii- 40

quor is withdrawn from the bottom of the rocks 60 via

the filter 63 into lines 63', pump 64 pumping the pregnant

liquid from the vat 55. A sump 65 is provided

adjacent the filter 63.

According to the present invention, oxygen is sup- 45

plied to the pile 59 from oxygen source 66, as via line 67

which is connected up to individual headers 68 within

each vat (e.g. vat 55), with a plurality of pipes 70 extending

from each header 68. The pipes 70 have gas

passages therein, as described above with respect to 50

pipes 42. The pipes 70 may be provided adjacent the

bottom of the pile 59, to introduce oxygen gas into the

pile 59 so that it flows generally upwardly therein.

Alternatively, or additionally, oxygen gas is supplied

to the pile 59 by adding it to the cyanide leaching liquid 55

from storage tank 72, which passes in line 74. An ejector

76 in line 74 has oxygen supplied to the suction 78

thereof, the outlet 80 from the ejector 76 applying the

leaching liquid to each of the vats 52-55. In this particu~

lar embodiment, the cyanide leaching liquid is typically 60

applied to the piles 59 by flooding; for example see the

liquid 82 above the ore 59 in FIG. 4. Alternatively, the

oxygen gas and cyanide liquid could be caused to foam,

and the material 82 above the ore pile 59 could be a

foam. 65

The pregnant liquor from each of the lines 63' associated

with the vats 52-55 passes into lines 84, which

ultimately pass to pregnant liquor holding tanks 86.

From there the liquor is passed to a recovery station, as

to the carbon columns 88 having stripping unit 90 associated

therewith, from which the gold (and/or silver) is

recovered.

While exemplary apparatus has been utilized in order

to describe the process according to the invention, it

will be understood that other types of apparatus also

may be utilized. The method, in its broadest concepts,

envisions the percolation leaching of gold and silver ore

by practicing the following steps: (a) Piling leachable

gold and silver ore (as defined above) into a pile. (b)

Applying a cyanide leaching liquid to the pile to leach

gold and silver from the ore into a pregnant liquor. (c)

Supplying gas to the pile, the gas containing oxygen in

an amount greater than in ambient air, to increase the

leach rate or recovery, of gold and silver. And, (d)

recovering gold and silver from the pregnant liquor, as

by withdrawing the pregnant liquor from the bottom of

the pile and subjecting it to carbon-adsorption or zinc

precipitation techniques, or the like. While the invention

is applicable to all types of "ores", as defined

above, it is particularly applicable to the recovery of

gold from those ores which tend to consume oxygen.

It will thus be seen that according to the present

invention an effective method for the percolation leaching

of gold and silver from ore piles has been provided.

While the invention has been herein shown and described

in what is presently conceived to be the most

practical and preferred embodiment thereof, it will be

apparent to those of ordinary skill in the art that many

modifications may be made thereof within the scope of

the invention, which scope is to be accorded the broadest

interpretation of the appended claims so as to encompass

all equivalent methods, procedures, and systems.

What is claimed is:

1. A method for increasing the total amount of gold

or silver recoverable in pile leaching gold or silver ore

comprising the steps of:

(a) piling leachable gold or silver ore into a pile;

(b) applying a cyanide leaching liquid to the pile

adjacent the top thereof to leach gold or silver

from the ore into a pregnant liquor;

amount of oxygen greater than in ambient air, said

gas being supplied adjacent the bottom of the pile

such that at least part of the gas flows countercurrently

to the cyanide leaching liquid and remains in

gaseous form thereby to increase the total leached

yield or amount of gold or silver recovered at the

completion of the leaching process in comparison

with the total leached yield or amount of gold or

silver recovered using air as the supplied gas; and

(d) recovering gold or silver from the pregnant liquor.

2. A method as recited in claim 1 wherein the method

is heap leaching, and wherein step (a) is practiced by

piling ore particles on a sloping pad having a high end

portion at an elevation enabling flow of pregnant liquor

to a low end portion of said pad, and wherein step (d) is

practiced by withdrawing pregnant liquor from the low

end portion of the pad.

3. A method as recited in claim 2 wherein step (b) is

practiced by spraying the cyanide leaching liquid onto

the top of the heap.

4. A method as recited in claim 2 wherein step (c) is

practiced by adding oxygen gas to the cyanide leaching

liquid before applying the leaching liquid to the pile.

4,721,526

5. A method as recited in claim 4 wherein step (c) is

practiced by saturating the cyanide leaching liquid with

oxygen gas.

6. A method as recited in claim 5 wherein step (c) is

further practiced by introducing pure oxygen gas, into 5

the bottom of the pile.

7. A method as recited in claim 4 wherein step (c) is

practiced by adding the gas to the liquid utilizing an

ejector.

8. A method as recited in claim 2 wherein step (c) is 10

practiced by introducing pure oxygen gas, directly into

the bottom of the pile.

9. A method as recited in claim 8 wherein step (c) is

further practiced by providing a plurality of pipes adjacent

the bottom of the pile, the pipes having gas pas- 15

sages therein, and introducing the oxygen gas into the

pile through the gas passages in the pipe.

10. A method as recited in claim 2 wherein step (b) is

practiced by spraying the liquid onto a water permeable

cover covering the heap. 20

11. A method as recited in claim 1 wherein the ore

consumes oxygen, and wherein steps (a) through (d) are

practiced to recover gold.

12. A method as recited in claim 1 wherein the

method comprises vat leaching, and wherein step (a) is 25

practiced by piling the ore on a rock bed, and wherein

step (d) is practiced by withdrawing the pregnant liquor

from the bottom of the vat, below the rock bed.

13. A method as recited in claim 12 wherein step (b)

is practiced by flooding.

14. A method as recited in claim 12 wherein step (c)

is practiced by adding oxygen gas to the cyanide leaching

liquid before applying the leaching liquid to the pile.

15. A method as recited in claim 14 wherein step (c)

is further practiced by introducing pure oxygen gas into

the pile itself.

16. A method as recited in claim 12 wherein step (c)

is practiced by introducing gas containing pure oxygen

gas directly into the pile itself.

17. A method as recited in claim 16 wherein step (c)

is further practiced by providing a plurality of pipes

adjacent the bottom of the pile, the pipes having gas

passages therein, and introducing the oxygen gas into

the pile through the gas passages in the pipe.

18. A method as recited in claim 1 wherein steps (b)

and (c) are practiced by applying oxygen gas and cyanide

leaching liquid as a foam to the top of the pile.

19. A method as recited in claim 1 wherein step (c) is

practiced by covering the pile to minimize the loss of

oxygen from the pile, and pure oxygen gas is introduced

below the covering, into the pile.

* * * * *