4,754,953 Utilization of oxygen in leaching and/or recovery procedures employing carbon

Patent Number/Link:

United States Patent [19]

Brison. et ale

[11] Patent Number:

[45] Date of Patent:

4,754,953

Jut 5, 1988

[54] UTILIZATION OF OXYGEN IN LEACHING

AND/OR RECOVERY PROCEDURES

EMPLOYING CARBON

Related U.S. Application Data

Division of Ser. No. 732,637, May 10, 1985, abandoned.

Int. Cl.4 C22B 11/04

U.S. Cl 266/101; 266/168;

266/170; 75/101 R; 75/105; 75/108; 75/109;

75/118 R; 423/27; 423/29; 423/30; 423/31

Field of Search 423/27,29, 30, 31;

75/105, 101 R, 108, 109, 118 R; 266/101, 168,

170; 422/129, 211, 232

References Cited

U.S. PATENT DOCUMENTS

4,251,352 2/1981 Shoemaker 209/45

4,331,472 5/1982 King, Jr 266/170 5 Claims, 3 Drawing Sheets

[57] ABSTRACT

In gold and/or silver cyanide leaching-adsorption processes

employing solid adsorbents such as activated

charcoal, the overall efficiency in the recovery of gold

and/or silver from ores or the like is greatly increased

by contacting the cyanide slurry containing the gold

and/or silver, with oxygen gas instead of normal air. A

generally pure oxygen gas can be bubbled into a vessel

containing the slurry, and a cover (e.g. a floating cover)

may be provided on the vessel to reduce the oxygen

transfer out of the solution and to facilitate pressurization

of the system with an oxygen atmosphere. The

procedures of the invention are applicable to carbon-inpulp

(CIP), and carbon-in-Ieach (CIL) processes and

related processes using resins. Deaeration of the ore

slurry can be practiced prior to the introduction of the

oxygen.

4,416,774 1111983 Taylor 210/236

4,457,495 7/1984 Eder et al. 266/170

FOREIGN PATENT DOCUMENTS

0899119 111982 U.S.S.R 266/168

Primary Examiner-Robert L. Stoll

Attorney, Agent, or Firm-Nixon & Vanderhye

Robert J. Brison, Golden, Colo.; Carl

L. Elmore; Phillip Mitchell, both of

Glens Falls, N.Y.

Kamyr, Inc., Glens Falls, N.Y.

900,687

Aug. 27, 1986

Assignee:

Appl. No.:

Filed:

[75] Inventors:

[73]

[21]

[22]

[58]

[62]

[51]

[52]

[56]

ORE FEED

FROM

THICKENER

SO%SOUDS

-ISO MESH

LOADED

CARBON

TO GOLD

RECOVERY

..5"8 I

LOADED

CARBON

TO GOLD

RECOVERY

ORE FEED

FROM

THICKENER

50 % SOLIDS

-/50 MESH

WASTE

/3/

;:2

zz"

~.L

CARBON

ADDITION

COARSE PARTICLES+30

MESH

I~ I

CFl •

~a~

sa.

~F-

",UI ....

0'"

rt>

~....

-..A.

-..l

lJl

-..A.

lJl

u.s. Patent

ORE,

CYANIDE

SLURRY

Jul. 5, 1988

DEAERATE

Sheet 2 of 3

INJECTION

4,754,953

1SLURRY

FLOW

DIRECTION

ICARBON

GRANULE

DIRECTION

LOADED CARBON

TO STRIPPING,

ACID WASHING.

THERMAL

REGENERATION

AND REUSE

66 70

RESIDUE;

.....-.~:J----------l:::JCYANIDE DESTRUCT

oN a 01 SPOSAL

r.JJ

::r'

t't>

E=-

...A.

-.l

til

...A.

til

t;..)

.....

U'J •

I""+-

TAILING

CARBON

LOADED

CARBON

TO GOLD

RECOVERY

CIP

RECOVERY

7.f"

as-

FIBER

15 tt / TON

7.5 T /0

FLOCCULANT

.25 IS- /TON

250#/0

MILL WATER

169 GPM

OVERSIZE RETURN

TO REGRIND

NaCN IT/D

ORE FEED

FROM CLASSIFIER

1000

T/D 35%

SOLIDS

-~-i

I 02 /400 il /0 I 1i1r-E-tikJl I

According to the present invention, it has been found

that the combination of (1) the use of oxygen or oxygenenriched

air and (2) a leach-adsorption system employing

actuated carbon results in an extremely efficient

5process for treatment ofgold and/or silver ores, or the

like.

It has been found that not only does oxygen increase

the rate of dissolution of gold and/or silver, but that the

overall efficiency of processes employing carbon ad10

sorption in gold and/or silver recovery is significantly

increased by the use of a gas containing a significantly

higher proportion of oxygen than is found in air.

Although activated carbon is well known to be a

catalyst in decomposition of cyanideion by oxygen,

surprisingly, it has been found that the use of oxygen

rather than air in CIP or CIL systems does not result in

unacceptable cyanide consumption, the cyanide consumption

being unexpectedly low.

It has been found that the increased efficiency that

results from the practice of the present invention has a

number of contributing factors. In CIL and CIP processes,

the oxygen increases the dissolution rate, which

therefore makes the gold and/or silver more readily

available for adsorption by the carbon. Also, since the

gas that is introduced has a higher proportion of oxygen

than natural air; it will also have a significantly lower

proportion of carbon dioxide than normal air. Reduced

carbon dioxide also increases carbonadsorption efficiency

since carbon dioxide reacts with lime in the

cyanide solution to form CaC03 (as well as causing

other problems), which deposits on the carbon granules.

Practicing the invention one can either get a higher

percentage of gold and/or silver extraction, or get the

same percentage extraction as in conventional facilities

omy using much less, and/or smaller, equipment, or a

combination of these advantages. For instance in a conventional

CIL plant. all of the CIL tanks could be reduced

to about one-fifth their normal size if oxygen

were utilized instead of air to contact the solution. Further,

if oxygen is utilized in a leaching process followed

by CIP the large· agitated leach tanks can each be reduced

to about one-fifth their usual size (with commensurate

reduction in the residence time in each).

Compared to conventional CIP processes, according

to the invention since the gold would be adsorbed almost

as soon as it was leached, the driving force for

leaching of the gold would be increased, and the "preg"

robbing effects in the case of carbonaceous ores would

be minimized. Also the tie-up of gold in the in-process

inventory would be significantly decreased.

Compared to conventional CIL processes, the process

according to the invention would reduce the agitated

tank size by a factor of about five or more, reduce

the carbon and gold loss due to abrasion of the carbon,

reduce the tie-up of gold in the in-process inventory,

and reduce the carbon inventory.

The process according to the invention also has the

potential for optimizing the leach time for differences in

the types of ore utilized. For instance for slow leaching

ores, a pressurized leach-adsorption system could be

utilized to obtain higher oxygen concentration in the

solution. For fast leaching ores, oxygen enriched air

could be utilized to provide only a moderate increase in

leach rate since little is gained by reducing the leach

time below the time required for carbon adsorption

(about 4-6 hours). In any event. the practice of the

process according to the invention, and the utilization

4,754,953

UTILIZATION OF OXYGEN IN LEACHING

AND/OR RECOVERY PROCEDURES

EMPLOYING CARBON

This is a division of application Ser. No. 732,637 ftled

May 10, 1985, now abandoned.

BACKGROUND AND SUMMARY OF THE

INVENTION

Procedures that have been gaining increasing acceptance

and widespread usage for the regovery of gold

and/or silver from ores, and the like, are the carbon-inpulp

(CIP), and carbon-in-leach (CIL) processes. These

procedures are versatile, and effect efficient recovery of 15

the gold and/or silver from the ore.

In a typical CIP process, milled ore is leached in a

series of agitated vessels (typically approximately six

vessels each having a retention time of about four

hours). In the leach vessels the gold and/or silver is 20

largely dissolved from the pulp. After leaching, the

pulp moves to the CIP adsorption system, which typically

contains about six vessels each having a retention

time of about one hour. The pulp is agitated in each of

these vessels, which are open to the atmosphere, and in 25

each vessel the pulp is contacted by activated charcoal

particles (i.e. carbon granules) that preferentially adsorb

gold and silver from the solution. The inventory of

carbon granules is continuously or periodically trans- 30

ferred from one vessel to the next in the opposite direction

of the flow of the pulp, with carbon discharged

from the first vessel in the series ultimately being passed

to a gold and/or silver recovery station, while the pulp

discharged from the last vessel in the series is leach 35

residue, which can be disposed of.

Resin-in-pulp processes are similar to carbon-in-pulp

processes except that an ion exchange resin is used in

place of carbon granules. Such processes have not yet

received commercial acceptance for Au!Ag leaching. 40

Conventional CIL processes are similar to CIP processes

except that the dissolution and the adsorption of

the gold and silver are practiced essentially simultaneously.

In a typical CIL procedure, the ground and

thickened ore slurry typically passes to a series of about 45

six agitated leach-adsorption vessels,· each having a

retention time ofabout four hours. In the agitated leachadsorption

vessels the carbon and ore flow in countercurrent

paths in basically the same manner as in the CIP

process, with the loaded carbon passed to a recovery 50

stage and the discharged leach residue is disposed of. As

in most cyanidation operations, part of the gold and/or

silver is typically dissolved in the grinding circuit and in

other preliminary processing steps, such as thickening.

Although the proportion of the total metal dissolved in 55

these steps is often substantial, subsequent treatment in a

series of leach vessels, or leach-adsorption vessels, is

typically practiced in order to obtain more complete

gold and/or silver recovery.

It has been known for many years that. under certain 60

limiting conditions, the rate of gold dissolution in a

cyanide solution is approximately. proportional to the

partial pressure of oxygen, and that the rate of dissolution

can be significantly increased if generally pure

oxygen gas (e.g. gas having an oxygen content of about 65

99 percent or greater) is used instead of air to effect

oxidation during the cyanidation process. However this

fact has not been taken advantage of commercially.

of the apparatus according to the present invention, is

extremely advantageous.

It is the primary object of the present invention to

provide for the increased efficiency of the recovery of

gold and/or silver from ores or the like. This and other 5

objects of the invention will become clear from an inspection

ofthe detailed description ofthe invention, and

from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS 10

FIG. 1 is a schematic view, with parts of some components

shown in cross-section, of exemplary apparat1ls

for practicing a eIP process according to the present

invention;

FIG. 2 is a schematic view of exemplary apparat1ls 15

for practicing a CIL process according to the invention;

and

FIG. 3 is a schematic view of exemplary apparat1ls

for increased efficiency of ore leaching which can precede

the adsorption tanks of the enhanced ClP process 20

according to the invention.

4,754,953

DETAILED DESCRIPTION

ing about 99 percent or more oxygen). However the

desired results according to the invention, of increased

carbon .adsorption efficiency, and the like, can sometimes

be achieved even when generally pure oxygen is

not utilized, but rather merely a gas having a significantly

increased proportion of oxygen compared to

normal air. The gas from source 18 also desirably, and

usually inherently (merely by the increase in the proportion

of oxygen), has a decreased proportion of carbon

dioxide compared to normal air, which also results

in decreased cyanide consumption and reduced formation

of CaC03.

In the embodiment actually illustrated in FIG. I, a

single leach (or pre-leach) tank 22 is illustrated. In the

tank 22 no carbon is present, but rather only leaching

takes place. As described above, however, the presence

of the oxygen containing gas in the leach tank 22 also

increases the efficiency of the dissolution of the gold

and/or silver into the cyanide solution.

The tank 22 is preferably an agitated tank, having a

conventional mechanical agitator including blades 23

and shaft 24, powered by a powering device 25 or the

like. The slurry within the tank 22 will achieve a certain

The invention will be herein described with respect

to the recovery of gold and/or silver from gold and/or 25 level, and in accordance with the present invention it is

silver containing ores or the like. The term "ore or the desirable to provide a cover for the solution to minimize

like" as used in the present specification and claims the transfer of oxygen from the slurry to the air, and

means all materials conventionally considered as gold also to minimize the t:ansfer o~ nitrogen from the air to

__ .and silver ores, and other materials such as tailings, the s~urry.A conven~lonal stan~nary c?ver tank may be

from which gold and/or silver may be recovered. Also, 30 p~oVlded, or, a floatIng c~ver IS provlde.d, such as the

the invention has applicability to the recovery of other disc-shaped cover 26 which has. a- generally flat top

.-metals. . surface 27, and a generally concave bottom surface 28

In the preferred embodiment according to the present which is actually in con~ct with the sl~, and which

invention, activated charcoal (also known as activated has an a~e 29 therem thr~ugh which the shaft 24

carbon, carbon, and the like) is used as the material for 35 passes. If desl1'ed, a permane~t hd 30 may a:tso be ~laced

adsorbing the gold and/or silver from the solution. on the tank 22, and the enure tank prOVided With an

However it is.to be understood that other materials can oxygen atmosphere at about one atmosphere pressure,

!:Ie utilized, besides activated charcoal granules or parti- or provided with an oxygen atmosphere at significantly

ccles, for adsorbing the gold and/or silver, such as ion greater than one atmospher~ pressure. .

_.-exchange resins (i.e. a resin-in-pulp process, as de- 40 Only one leach tank 22 IS shown..TypI~ally th~r~

':;.scribed in U.S. Pat. No. 4,502,952). would be about 4 to 6 more such tanks m senes to mml-

-~::: .In the utilization ofthe apparat1ls illustrated in FIG. 1 mize short-circ~ting of ~e sl~ particles.

for the practice ofa CIP process according to the inven- After the desl1'ed retennon t1me m the leach tank 22,

tion, the ore is milled in the presence of lime and possi- the. slurry overflows from tank 22, or thr~ugh.cut-out

bly cyanide, and ultimately fed through the flow con- 45 31 m the cover 26, and through the condUit 32 Into the

trol valve 11 to a separating screen assembly 12 which flI'St carbon adsorption tank 34 of a series of such tanks.

screens out the particles that are too large, and is Three tanks are shown in series in FIG. 1, however any.

dumped in discharge 13. If desired, the ore slurry may desired number of tanks may be provided.

be thickened by conventional means to remove part of Conventional components of the tank 34 include the

the solution, which may be treated separately for gold 50 mechanical agitator including blades 35 and shaft 36,

and/or silver recovery. The ore slurry that passes the slurry inlet 37, the slurry outlet 38 covered by a

through the screen 12 passes to the level control tank carbon screen 39 (e.g. see U.S. Pat. No. 4,416,774),

14, and is withdrawn from the tank 14 by the pump 15. carbon inlet 40 connected up to carbon pump 41, and

If desired, the ore slurry can be deaerated as by any carbon outlet 42. The pumps 41, 41' may be placed near

type of conventional deaeration means (such as a vac- 55 the top of the tank. The tank 34 may be a conventional

uum system) 16. covered tank, or may include a non-conventional float-

After the ore slurry passes through pump 15, a con- ing cover 44 which is substantially identical to the cover

ventional basic cyanide solution (such as NaCN) is 26 (except there is no necessity for the cut-out 31),

added to the ore from source 17, additional lime may be which floats on the top of the slurry within the tank 34.

added as needed, and oxygen containing gas from 60 The floating cover can be a plurality of floating balls.

source 18 is added through the flow control valve 19, Non-conventional components of the tank 34 also

and oxygen injector 20. If desired the cyanide solution include the sparger 46 located adjacent the bottom of

and the oxygen containing gas can be added to the the tank for sparging oxygen into the tank from the

slurry utilizing mixers, although since significant mixing source 18. The sparger 46. in addition to introducing the

will take place in subsequent vessels a separate mixer at 65 oxygen into the solution that is necessary for the inthis

point is not essential. creased efficiency according to the invention, also ef-

The oxygen containing gas from source 18 preferably fects some agitation oftile solution, facilitating efficient

comprises generally pure oxygen (that is a gas contain- dissolution of the oxygen.

4,754,953

Another non-conventional component of the tank 34

comprises the top 47. The top 47, as does the top 30, can

seal the tank so that an oxygen atmosphere (either at

one atmosphere pressure, or significantly greater than

one atmosphere pressure) may be maintained in the 5

tank.

The further tanks 48, 49, etc. in the adsorption system

are each substantially identical to the tank 34 except

that in the last tank 49 in the series the cover 44/ has

disposed therein a valved opening 50 which allows the 10

addition of activated charcoal particles, which are

coarser than the ore particles in the slurry [the difference

in coarseness allowing effective screening].

The slurry discharged through outlet 38' of the tank

49 goes to tank 52, and from tank 52 is withdrawn by 15

pump 53 and ultimately passed to a disposal site 54 for

the ore tailings (which is what the pulp has been reduced

to). The carbon particles outlet 42 from the first

tank 34 passes through flow control valve 55 to chute

56, and ultimately to the carbon screen 57, with sepa- 20

rated loaded carbon being passed to the gold and/or

silver recovery station 58, and separated slurry in conduit

59 being recirculated.

The apparatus of FIG. 1 can also be utilized for a

carbon-in-leach process merely by elimination of the 25

tank 22. Such an arrangement is especially advantageous,

and the size and/or number of tanks 34, 48, 49

would be less than for conventional CIL processes.

FIG. 2 schematically illustrates another form the

apparatus according to the invention can take for the 30

practice of a CIL process. The ore slurry, mixed with

oxygen, passes into the top of vertical vessel 60, and

flows continuously downwardly therein. Typical conditions

of the ore slurry would be 50 percent solids

(minus 100 mesh), 0.3 gil NaCN, solids specific gravity 35

of 2.7, and a slurry specific gravity of 1.46. The activated

charcoal granules would be introduced from

source 61 into the bottom of the vessel 60 at point 62,

and would flow upwardly in the vessel. Typically the

carbon granules would be relatively large, about 6-16 40

mesh, and would have a lower specific gravity than the

slurry (e.g. 1.2). The slurry density, carbon density and

size, and other factors (such as the addition offlocculent

or fibers to the slurry) could be adjusted to optimize the

carbon upflow rate relative to the slurry downflow rate. 45

The loaded carbon, with some entrained slurry, would

be withdrawn from adjacent the top of the vessel 60 at

point 63, and passed to a carbon screen 64, with the

loaded carbon stripped and regenerated for reuse in the

carbon injection system 61, and with separated slurry in 50

conduit 65 returning to the top of the vessel 60. The

residue withdrawn at the bottom 66 of the vessel 60 by

the pump 67 would either pass into conduit 68 to be

used as part of the liquid for carrying the recycled carbon

into the column within the vessel 60, or would pass 55

to conduit 69 and ultimately to cyanide destruction and

disposal site 70.

The vessel 60 may be operated at atmospheric pressure,

or at super-atmospheric pressure, and an oxygen

atmosphere may be provided at the top thereof in either 60

case. Also, the system could be operated so that the

slurry flowed upwardly and the carbon granules flowed

downwardly, if denser carbon were utilized, and/or if

the slurry solids had a lower specific gravity.

FIG. 3 schematically illustrates other exemplary ap- 65

paratus that can be utilized for effectively and efficiently

dissolving the gold and/or silver in the leaching

stage prior to CIP recovery in station 75. Utilizing the

apparatus of FIG. 3, the slurried ore in conduit 76 is

mixed with cyanide from conduit 77, and ultimately

mixed with oxygen from conduit 78 in a mixer 79. The

mixer may be any suitable mixer capable of mixing

components of a medium consistency slurry, such as an

MC® mixer sold by Kamyr, Inc, of Glens Falls, N.Y.

Also, as generally disclosed in U.S. Pat. No. 4,501,721;

flocculent and/or fiber can be added to the slurry to

facilitate locking of the particulized ore in a stable network

in the slurry. For instance cellulosic fibers, fiberglass

fibers, or the like are mixed with liquid in tank 80

and then metered to the inlet to mixer 79, while flocculents,

such as synthetic polymers of anionic, cationic, or

nonionic types are mixed with mill water in tanks 81,

and then ultimately passed to conduit 82 prior to introduction

into upflow 83. The leached slurry that is discharged

from the top 84 of vessel 83 will then pass to

the CIP recovery station 75, which can be as illustrated

in FIG. 1 (without the tank 22). The vessel 83 can also

be pressurized, as by utilizing pressure control valve 85,

and a one atmosphere, or super-atmospheric, oxygen

atmosphere maintained therein, or the vessel can be

completely slurry filled.

Utilizing the apparatus heretofore described, according

to the present invention a process of gold and/or

silver recovery from ore and the like may be practiced.

The process comprises the steps of: leaching gold and/

or silver from the ore or the like, to dissolve the gold

and/or silver, utilizing a basic cyanide solution; and (b)

recovering the leached gold and/or silver in solution by

contacting the solution with solid material for adsorbing

the gold and/or silver from the solution; wherein

step (b) is practiced by providing oxygen gas in the

solution in an amount significantly greater than can be

obtained by contacting the solution with air so as to

greatly increase the solution rate of the gold and/or

silver, and by minimizing the amount of carbon dioxide

in the solution so that it is significantly less than would

be obtained by contacting the solution with air, so as to

possibly increase the gold and/or silver adsorption efficiency

of the adsorbing material, and certainly to reduce

the production of CaC03. Preferably step (b) is

practiced by substantially saturating the solution with

oxygen, and preferably by utilizing generally pure oxygen.

The following table I indicates the results achieved

by preparing a gold cyanide solution by leaching a

common gold ore sample (the gold ore sample, as is

typical, also contained a small amount of silver), and

then exposing the solution to carbon adsorption in a

rotating bottle for six hours, with atmospheres of air,

oxygen, and nitrogen, respectively.

TABLE I

Atmosphere

Oxygen Air Nitrogen

Approx. % 02 100 21 0

in atmosphere

Leach solution 4.14 4.14 4.14

assay, Au, mgII

Final solution assay, 0.032 0.041 0.079

Au. mgll

Final carbon assay, 23.4 23.1 23.1

AU,oz/ton

Au adsorption, %1 99.23 99.01 98.10

Leach solution assay, 1.8 1.8 1.8

Ag, mgll

Final solution 0.2 0.2 0.2

assay, Ag, mgII

Final carbon assay, 8.77 8.97 8.36

Test #1 Test #2

Conditions 65

Grind 77.9%-200 77.9%-200

% Solids 27 27

pH: initial/adj. 8.7/10.9 8.7/10.9

In the following table III, further bottletype tests 50

were conducted for a carbon-in-leach cyanidation, confirming

that simultaneous leaching and carbon adsorption

in an oxygenated slurry results in rapid high gold

extraction with low cyanide consumption. The ore

tested in each of the two tests in table III was Gencor's 55

Buffelsfontein ore. With gold extractions of about

91-92%, in six hours, cyanide consumption was only

0.37-0.47 Ibs. per ton. If the pulp density and carbon

concentration was closer to expected plant conditions,

cyanide consumption is expected to be as little as 60

O.19-0.271bs. per ton. The low cyanide consumption is

very unexpected and advantageous.

TABLE III

The following table II indicates the results from a

carbon-in-pulp cyanidation test utilizing three different 10

types of Gencor ore samples from, respectively, Buffeisfontein

(No. 1), Leslie (No.2), and 81. Helena (No.3).

The tests indicate high gold extractions (in the range of

90-95%), and, surprisingly, low cyanide consumption.

All tests were performed in rotated bottles with oxygen 15

atomsphere at the local atmospheric pressure of 12.1

psia. The time in each case (total of 10 hours) was a six

hour cyanide leach plus a four hour elP process.

TABLE II

20 Test #1 Test #2 Test #3

Conditions

Grind 77.9%-200 80%-200 80%-200

% Solids 27 27 27

pH: initial/adj. 8.7/10.9 9.0/10/8 9.0/10.7

NaCN, initial gil 0.3 0.3 0.3 25

Time, hr. 10 10 10

Feed

Weight, g 300.0 300.0 300.0

AU,oz/ton 0.217 0.110 0.186

Reagents added, tola1

CaO,g 0.12 0.12 0.12 30

NaCN, g 0.25 0.25 0.25

Carbon

Mesh size Tyler 6 X 14 6 X 14 6 X 14

Initial wt, g 22.00 22.00 22.00

Final wt, g 22.05 22.11 22.09 35 AU,oz/ton 2.631 0.966 1.779

Sol'n, end of test

NaCN, gil 0.276 0.245 0.264

pH 10.6 10.6 10.4

Filtrate, total

Volume. m1 1414 1453 1399 40

Au, mgll 0.004 0.002 0.003

Residue

Weight, g 298.7 298.6 298.6

Au.oz/ton 0.017 0.004 0.015

0.015 rerun

Reagents consumed 0.16 0.33 0.26 45

NaCN, 1b/ton

Extraction. % 92.0 94.7 89.8

Oxygen Air Nitrogen

TABLE III-continued

Test #1 Test #2

NaCN, initial gil 0.3 0.3

Time, hr 61 62

Feed

Weight, g 399.9 399.9

Au? oz/ton 0.217 0.217

Reagents added, total

CaO,g 0.12 0.12

NaCN, g 0.25 0.25

Carbon

Mesh size Tyler 6 X 14 6 X 14

Initial wt, g 22.00 22.00

Final wt, g 22.26 22.07

AU,ozlton 2.684 2.695

Sol'n, end of test 10.5 10.6

Filtrate. total

Volume, mI 1412.67 1417.76

NaCN, gil 0.24 0.22

Residue

Weight, g 298.24 298.48

AU,oz/ton 0.019 0.018

Reagents consumed 0.37 0.47

NaCN, 1b/ton

Extraction, % 91.3 91.7

Calculated heads 0.219 0.217

AU,oz/ton

Ipre-saturated with 02 at ambo press. for 16 hours previous to leach.

2During 6-hr elP leach, purge with 02 at T = 0 ht and T = 1 hr. Also add 11 g

carbon at each of these times.

In conclusion, according to the present invention, a

method and apparatus are provided for the extremely

efficient and effective recovery of gold and/or silver

from ore or the like. 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 mddiflcations 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 process

and apparatus.

What is claimed is:

1. In a leach-adsorpton system for the recovery of

one of gold and silver from ore slurry containing the

same and also a gas containing a substantially higher

proportion of oxygen than is contained in natural air

wherein one of the gold and silver is leached from the

ore and recovered by contacting the slurry with solid

material for adsorbing the one of said sold and silver

from solution, apparatus therefor comprising:

a vessel having an inlet for the introduction of the ore

slurry and an outlet for the ore slurry;

means for controlling the level of slurry within the

vessel;

floating cover means disposed at the top of the slurry

level of the vessel for reducing the transfer of oxygen

out ofthe slurry and the transfer of nitrogen or

carbon dioxide into the slurry; and

a mechanical agitator disposed in said vessel, said

mechanical agitator including a central shaft, and

said floating cover means comprising means defining

an aperture therein for receipt of said shaft so

that said shaft may pass therethrough into the

slurry.

2. Apparatus as recited in claim 1 further comprising

sparger means for sparging oxygen into the slurry adjacent

the bottom of the vessel.

4,754,953

88.6 88.6 88.1

Atmosphere

TABLE I-continued

Ag,oz/ton

Ag adsorption, %1

'Based on final carbon and final solution.

4,754,953

3. Apparatus as recited in claim 2 further comprising

means for introducing activated charcoal particles into

the vessel, means for withdrawing said particles from

the vessel, and screening means at said slurry outlet for

screening the particles out of the slurry passing through 5

said outlet.

4. Apparatus as recited in claim 3 wherein said floating

cover means comprises a bed of floating balls.

5. In a leach-adsorption system for the recovery of 10

one of gold and silver from ore slurry containing the

same and also a gas containing a substantially higher

proportion of oxygen than is contained in natural air

wherein one of the gold and silver is leached from the

ore and recovered by contacting the slurry with solid 15

material for adsorbing the one of said gold and silver

from solution, apparatus therefor comprising:

a vessel having an inlet for the introduction of the ore

slurry and an outlet for the ore slurry;

means for controlling the level of slurry within the

vessel; and

floating cover means disposed at the top of the slurry

level of the vessel for reducing the transfer of oxygen

out of the slurry and the transfer of nitrogen or

carbon dioxide into the slurry, said floating cover

means comprising a disc-shaped cover having a top

substantially flat surface, and having a bottom surface

that is substantially concave, said substantially

convcave bottom in contact with the slurry.

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