4,814,149 Process for recovering molybdenum from solution in a form that is substantially free from vanadium

Patent Number/Link:

United States Patent [19]

Litz

[11] Patent Number:

[45] Date of Patent:

4,814,149

Mar. 21, 1989

9 Claims, 1 Drawing Sheet

Primary Examiner-Patrick P. Garvin

Attorney, Agent, or Firm-S. R. La Paglia; T. G. De

Jonghej P. L. McGarrigle

149134 11/1980 Japan 423/55

OTHER PUBLICATIONS

Mellor, A Comprehensive Treatise on Inorganic and Theoretical

Chemistry, vol. XI, p. 595, (1948), pub. by Longmans,

Green & Co., N.Y., N.Y.

The present invention is a process for selectively precipitating

molybdenum in a form that is substantially

free from vanadium impurities. The molybdenum is

precipitated in the form of ammonium octamolybdate

which has a molybdenum to vanadium ratio of about

400:1 in an initial crystallization and a ratio of about

1300:1 in a subsequent recrystallization.

[57] ABSTRACf

[54] PROCESS FOR RECOVERING

MOLYBDENUM FROM SOLUTION IN A

FORM THAT IS SUBSTANTIALLY FREE

FROM VANADIUM

[75] Inventor: John E. Litz, Lakewood, Colo.

[73] Assignee: Chevron Research Company, San

Francisco, Calif.

[21] Appl. No.: 915,306

[22] Filed: Oct. 3, 1986

[51] Int. Cl.4 C01G 39/00; COIG 39/02

[52] U.S. Cl , 423/56; 423/55

[58] Field of Search 423/55, 56

[56] References Cited

U.S. PATENT DOCUMENTS

4,500,495 2/1985 Hubred et aI 423/55 X

FOREIGN PATENT DOCUMENTS

52895 4/1977 Japan 423/55

u.s. Patent Mar. 21, 1989 4,814,149

Mo, V

STRIPPING

MOLYBDENUMI VANADIUM SEPARATION

AND RECOVERY CIRCUIT r------------------.vI

SPENT

CATALYST

NH4 HC0 ~ 3 Mo,V, CO,+Ni ~

ORGANIC .-----'------.

SEPARATION ~

OF Mo +V FROM

Co +Ni

Co, Nil l I

RAFFINATE' T....---:-:OR::'":G:-:"A-:-N='C---J

SUBSEQUENT RECYCLE

TREATMENT

pH 8.0

I. INITIAL TREATMENT TO GET A

MIXED Mo, V STREAM---

n. V PRECIPITATION----m.

Mo CONCENTRATION----~.

AMMONIUM OCTAMOLYBDATE

PRECIPITATION---------

I PRECIPITATION

~' NH4 V03 I

AMMONIUM _--.--J I

METAVANADATEJ

-(-AM-V-) r . ,-lIT ----~H~S04 ~O-P'-':H::"2-.5--NH4 OH ...I~

I '-iN AQUEOUS PHASE + 1

I Mo EXTRACTION ORGANIC I

AND PHASE Mo STRIP AND \

II CONCENTRATION CONCENTRATION Org{AQ =1/5 Org/Aq =lOll I

I ORGANIC RECYCLE I J ~~FFINAT~ _ _ _:. ':'_-I':-~

H2S04 TO pH6.5 I

AT 50°C I

• I

S,02 I

HYDROLYSIS I

AND I

REMOVAL I

H2 S04 TO pH :

2.5 AT ao°c I,

AMMONIUM I

OCTAMOLYBDATEI--_-I-JI

PRECIPITATION

(AOM)

(NH4)4 MOB 026 '5H20 I

-------------- -----_....:_,

4,814,149

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow chart of the process of the present

invention. Here, the process for recovering molybdenum

(Mo) and vanadium (V) from spent catalysts is

divided up into five sections: the initial treatment; the

vanadium crystallization; the molybdenum concentration;

and the molybdenum precipitation. In the initial

treatment the spent catalyst is leached free of Mo, V,

and other metals and then the Mo and V are extracted.

The next section substantially removes all the V that is

present in the mixed MolY stream. The next step concentrates

the Mo in solution by organic and aqueous

extraction. And, the final section precipitates the Mo as

ammonium octamolybdate (AOM).

SUMMARY OF THE INVENTION

The present invention is a process capable of selectively

recovering a substantially pure molybdenum

precipitate from a solution that has molybdenum and

vanadium values by precipitating molybdenum as ammonium

octamolybdate. All the steps of the process

comprise: crystallizing most of the vanadium from the

initial solution; concentrating the molybdenum that

remains in solution; removing the impurities from the

concentrated solution; then precipitating the molybdenum,

that is in solution, as ammonium octamolybdate.

This last step selectively precipitates molybdenum and

rejects 80% of the vanadium that has not been removed

in the vanadium crystallization. Any vanadium or molybdenum

that remains in solution may be recycled back

to the process for further recovery.

Generally, the present invention is a process capable

of selectively recovering a substantially pure molybdenum

precipitate from a mixed solution comprising molybdenum

and vanadium, by crystallizing vanadium as

ammonium metavanadate and subsequently precipitating

molybdenum as ammonium octamolybdate so that

said precipitated molybdenum is substantially free from

vanadium.

A more specific embodiment of the present invention

involves the process steps of:

(a) crystallizing vanadium from a solution having a

mixture of vanadium and molybdenum;

(b) extracting molybdenum from the remaining solution

of molybdenum with an organic amine;

ammonia;

(d) heating said aqueous solution to boiling;

(e) adjusting the pH of said heated solution to between

5.5 and 8.5 to precipitate impurities; and

(f) adjusting the pH of said heated solution to between

1.5 and 3.0 to precipitate molybdenum;

whereby the molybdenum precipitate is substantially

free of vanadium.

Hubred et al precipitates vanadium then removes

nickel, cobalt, and molybdenum by serial ion exchange.

However, the prior art has not addressed or adequately

solved the problem of vanadium contamination

5 of molybdenum when evaporative crystallization or a

chemical precipitation method is used.

It is an object of this invention to chemically precipitate

molybdenum from a mixed solution of molybdenum

and vanadium. It is a further object of this invention

to precipitate molybdenum while rejecting at least

80% of the associated vanadium.

BACKGROUND OF THE INVENTION

PROCESS FOR RECOVERING MOLYBDENUM

FROM SOLUTION IN A FORM THAT IS

SUBSTANTIALLY FREE FROM VANADIUM

The present invention relates to the recovery of molybdenum

from solution. Here, the more specific use of

the process is to recover molybdenum as ammonium 10

octamolybdate in a form that is substantially free from

vanadium.

Many hydrocarbon feedstocks contain high percentages

of metals as contaminants, e.g., iron, nickel, or

vanadium. Because of the growing shortages of petro- 15

leum in the world refmers are forced to use feedstocks

that contain larger amounts of these metals. Once they

are in the feed, they tend to deposit on the surfaces of

and/or in the interstices between hydroprocessing catalysts

which contain catalytic metals (e.g., cobalt, nickel, 20

molybdenum, or tungsten). When the hydroprocessing

catalysts no longer give the desired conversion rates

(due to plugging of the catalyst pores by coke or the

contaminant metals or due to reactor plugging), they

are replaced and subsequently disposed of (and are 25

called "spent catalysts"). Because of environmental and

economic considerations, it is therefore desirable to

recover the heavy metal values from the spent catalyst,

leaving the catalyst support in an environmentally benign

form. 30

The recovery of metals such as molybdenum and

vanadium from spent catalysts is nothing new of course,

as indicated by U.S. Pat. No. 4,500,495, issued Feb. 19,

1985 to Hubred et al; U.S. Pat. No. 4,554,138, issued

Nov. 19, 1985 to Marcantonio; as well as U.S. Pat. Nos. 35

4,434,140 and 4,434,141, both issued Feb. 28, 1984 to

Hubred et al, just to name a few which are totally incorporated

by reference. However, these patents have

never addressed the separation of molybdenum from

vanadium into a substantially pure form. 40

The recovery of molybdenum from various sources

has been described in the prior art [see U.S. Pat. No.

3,458,277, issued July 29, 1969 to Platzke et al and U.S.

Pat. No. 3,957,946, issued May 18, 1978 to Ronzio et al; 45

and J. Litz, "Solvent Extraction of W, Mo, and V:

Similarities and Contrasts", Extractive Metallurgy of

Refractory Metals, 69-81 (1980)]. See also, U.S. Pat. No.

3,455,677, issued Aug. 1, 1972 and U.S. Pat. No.

3,681,016, issued July 15,1969 to John E. Litz. U.S. Pat. 50

No. 3,455,677 involves evaporative crystallization of

and precipitation molybdenum in a process to recover

copper and molybdenum from ore COncentrates. This

patent describes two methods of forming a molybdenum

compound. The first is by evaporative crystalliza- 55

tion to force molybdenum out of solution at its solubility

limit and the second is a high temperature polymerization

which causes molybdenum precipitation. U.S.

Pat. No. 3,681,016 involves the separation and recovery

of molybdenum and rhenium values from solution. 60

Recovery of vanadium has also been described in the

prior art. See U.S. Pat. No. 4,544,533, issued Oct. 1,

1985 and U.S. Pat. No. 4,551,315, issued Nov. 5, 1985 to

P. J. Marcantonio, and U.S. Pat. No. 4,432,949 to G. L.

Hubred et· al. The patents to Marcantonio involve the 65

recovery of vanadium from an aqueous ammonium

bicarbonate strip solution and a subsequent precipitation.

They are incorporated by reference. The patent to

EXAMPLE

concentrations in this aqueous solution (having a pH of

around 9.0) are approximately 1.5-2.0 gil V and

150-200 gil Mo. Because there are some impurities left

in solution (such as the vanadium and silica) the Mo

must be removed in a fourth and fmal step.

Impurities are then taken out by the following procedure.

The concentrated solution (of the previous step) is

heated to between 40· C. and 80· C., more preferably

50· C., and the pH is adjusted to between 5.5 and 9.0,

but more preferably 6.5-8.5 using sulfuric acid (other

mineral acids, Le., HCI, HN03 are also suitable). These

adjustments are made primarily to hydrolyze silica

which precipitates out of solution and the precipitate is

removed by ftltration.

The solution is then contacted with H2S04 (preferably)

to adjust the pH to between 1.5 and 3.5, more preferably

2.5. It is also heated to between 70· C. and 90· C.,

more preferably 80· C., to initiate Mo precipitation as

ammonium octamolybdate (AOM), (NH4)4Mos026.5H20.

The slurry is not cooled. If it is cooled, the

amount of vanadium reporting to the molybdenum precipitate

might increase due to its lower solubility. Also,

the rate of polymerization, of the soluble molybdenum

into the less soluble octamolybdate species, would slow.

Vanadium rejection at this precipitation is approximately

80% (Le., of all V present only 20% precipitates

out with the AOM). The precipitate is then removed by

ftltration and may be subjected to a second recrystallization

procedure to further remove V.

The ftltrate is then recycled back to the V precipitation

step to remove the soluble V and recycle the extra

(NH4hS04 that is formed from the strip ammonia that

reacts with the sulfate. This occurs during the solvent

extraction when sulfuric acid is used to adjust the pH.

This ftltrate solution from the AOM precipitation contains

both ammonium vanadate and molybdate. After

the AOM is crystallized, it is calcined. This decomposes

the AOM into Mo03 by driving off H20 and ammonia.

4,814,149

DETAILED DESCRIPTION OF THE

INVENTION

The present invention selectively recovers molybdenum

(Mo) from a mixed molybdenum/vanadium 5

stream. A mixed molybdenum/vanadium stream may

be obtained from many sources such as ore and spent

catalysts. However, this invention discusses the recovery

of molybdenum from spent catalysts.

To recover spent catalyst values, the spent catalyst 10

may be first roasted and then leached with a solution of

ammonia (ammonium hydroxide) and ammonium carbonate.

This removes cobalt, molybdenum, vanadium,

and nickel. Subsequently, molybdenum (Mo) and vanadium

(V) are separated from cobalt and nickel by an 15

organic solvent extraction step. Thereafter, ammonium

bicarbonate (NH4HC03) is used to strip the Mo and V

from the solvent. For a more detailed explanation of

these steps, see the patents to Hubred and Marcantonio

which are hereby incorporated by reference. 20

Vanadium is crystallizated from a solution comprising

molybdenum and vanadium. It is very important to

crystallize as much vanadium as possible before trying

to precipitate the molybdenum. This can be done as

follows. First, the solution is boiled to decompose am- 25

monium bicarbonate and expel C02, NH3, and some

H20. Then ammonium sulfate, (NH4hS04, is added to

the stripped solution and the pH is adjusted to between

7.0-7.5 and then cooled to 30· C. (This heating increases

V precipitation by destroying any vanadium/carbonate 30

complexes). This should crystallize the majority of vanadium

as ammonium metavanadate (AMV), but approximately

30-40 ppm ofV may be left in solution. For

a more detailed explanation, see the patents to Marcantonio

which are incorporated by reference. 35

At this point the solution may contain approximately

3-4 grams per liter (gil) of Mo so that it must be concentrated

prior to precipitation. Thus, the Mo in the

vanadium-free solution is concentrated by an aqueous

and organic extraction. The pH is adjusted between 2.0 40

and 4.0 or more preferably to 2.5 with H2S04 (or an- In this example, Mo was chemically crystallized as

other mineral acid which will not form complexes with AOM. An ammoniacal-ammonium carbonate leach

either vanadium or molybdenum, Le., HCI or HN03) solution, containing nickel, cobalt, vanadium, and moand

the solution is organic extracted with a combination lybdenum values, was fed to a continuous quaternary

of organic solvents, one of which is a tertiary amine 45 ammonium compound solvent extraction step where

(primary and secondary amines may work, but not as the vanadium and molybdenum were extracted by an

well). The solvent may include most of the commercial organic solvent. The solvent comprised 80% Kermac

tertiary amines, such as tricapryl (Alamine 336 [trade- 470B (as diluent), 10% Aliquat 336 (trademark of Genmark

of General Mills, now owned by Henkel] or Ado- eral Mills, now owned by Henkel) (as an extractant),

gen 364 [trademark of Sherex Chemical]. The diluent 50 10% isodecanol (as a modifier). The loaded solvent was

may be a kerosene (Kermac 470B [trademark of Kerr stripped of the vanadium and molybdenum with an

McGee], Standard Odorless Thinner, Escaid [trade- ammonium bicarbonate solution that approached satumark

of Exxon] or something similar) or it can be an ration, i.e., approximately 2.5M. A composite of ammoaromatic,

such as "butylated" xylene (Solvent 150). If nium bicarbonate strip solutions was boiled to evolve

an aromatic diluent is used, there is no need to use an 55 the carbon dioxide, the pH of the solution was adjusted

alcohol modifier. Modifiers other than isodecanol may to 7.0 (with H2S0oi, if necessary), ammonium sulfate

be decanol, trimethyl nonanol, and similar alcohols. was added, and the mixture was cooled under agitation

The actual combination of organic solvents may be: to form a crop of ammonium metavandate crystals. A

10% Adogen 383; 10% isodecanol; and 80% Kermac composite of f1ltrates from the crystallization was ad-

47GB. The volume of this organic phase is approxi- 60 justed to a pH of 2.5 with sulfuric acid and served as

mately 1 part per 5 parts of original aqueous phase so feed to a continuous tertiary amine solvent extraction

that the Mo may be concentrated. The organic phase is where the molybdenum and residual vanadium were

then separated from the aqueous phase and contacted extracted by the solvent. The solvent comprised 10%

with an aqueous strip solution such as NH40H (this Adogen 383, 10% isodecanol and 80% Kermac 470B.

forms an ammonium molybdate strip concentrate solu- 65 The loaded solvent was then stripped of the molybdetion).

The volume of ammonium hydroxide is 1 part per num and vanadium with an ammonium hydroxide solu-

10 parts of organic phase. Both the extraction and strip- tion (120 gil NH3) to form an ammonium molybdate

ping steps are non-selective for either V or Mo, so their strip concentrate.

'The initial precipitates from Batches 1and 2 were consolidated and recrystallized.

Feed MolY Initial Recrystallization

--------------.......;~--- 25

whereby the molybdenum precipitate is substantially

free of vanadium.

2. A process for selectivity recovering a substantially

pure molybdenum precipitate from a solution used to

extract molybdenum from spent catalysts comprising

the following steps:

(a) separating molybdenum and vanadium from other

metal values with an organic solvent;

(b) stripping molybdenum and vanadium from said

organic solvent with an aqueous solvent;

and vanadium to boiling;

(d) cooling said boiled solution and adjusting the pH

to between 7.0 and 7.5 to crystallize a majority of

the vanadium that is in said solution;

(e) adjusting the pH of the remaining solution to

between 2.0 and 4.0;

(f) solvent extracting said molybdenum from the solution

of step (b) to increase the molybdenum concentration;

(g) stripping the organic solution having the molybdenum

with an aqueous strip solution to further

increase the molybdenum concentration;

(h) adjusting the pH of the aqueous molybdenum

solution to between 6.5 and 9.0 with sulfuric acid to

hydrolyze impurities;

(i) adjusting the pH of the remaining solution to between

1.5 and 3.5 to precipitate the molybdenum as

ammonium octamolybdate; and

G) recycling the remaining solution to a point immediately

upstream of the vanadium precipitation in

step (e).

3. The process as recited in claim 1 or 2 in which the

ammonium octamolybdate precipitate is washed with

demineralized water.

4. The process of claim 1 or 2 where the ammonium

octamolybdate precipitate is redissolved in pure water

and the process is repeated.

5. The process of claim 1 or 2 where the ammonium

octamolybdate precipitate is calcined to convert the

ammonium octamolybdate to molybdenum trioxide.

6. A process for selectively recovering a substantially

pure molybdenum precipitate from a solution comprising

molybdenum and vanadium values, the process

comprises:

(a) crystallizing vanadium from said solution to form

a substantially vanadium-free mother liquor;

(b) concentrating molybdenum in said vanadium-free

mother liquor to form a molybdenum-rich concentrate;

concentrate by adjusting the pH of said concentrate

to between 5.0 and 9.0; heating said concentrate

to between 20° C. and 70° C.; allowing said

concentrate to digest for between 0.5 and 2 hours;

and fIltering out said impurities; and

(d) precipitating molybdenum as ammonium octamolybdate

from said concentrate to recover a

substantially vanadium-free molybdenum value.

7. A process a recited in claim 6 wherein the molybdenum

is concentrated according to step (b) by first

extracting an aqueous molybdenum solution with an

organic solvent oflesser volume and then extracting the

molybdenum with an aqueous solvent of lesser volume

than said organic solvent.

8. A process as recited in claim 6, step (d) wherein the

molybdenum is precipitated as ammonium octamolybdate

by adjusting the pH of the solution of step (c) to

4,814,149

) -1300:\'

AOM Precipitate, MolY

463:\

333:\

106:\

58:\

Batch \

Batch 2

Calcium impurities may be avoided by using deminer- 30

alized water for the molybdenum solvent extraction

strip solution. Additionally, silicon does not re-solubilize

if the crystals are dissolved for recrystallization.

Once silicon precipitates, it stays as a precipitate. Also,

nickel cannot be separated from Mo if it goes through 35

the first separation.

The vanadium content of the molybdenum product

can best be controlled by attaining low vanadium levels

in the ammonium metavanadate mother liquor. If this 40

crystallization is operated ideally, less than 50 milligrams

per liter vanadium in the mother liquor, the feed

to the molybdenum recovery will have a molybdenum/

vanadium ratio greater than 200.

Since many modifications and variations of the pres- 45

ent invention are possible within the spirit ofthis disclosure,

it is intended that the embodiments disclosed are

only illustrative and not restrictive. For that reason,

reference is made to the following claims rather than to

the specific description to indicate the scope of this 50

invention.

What is claimed is:

1. A process for recovering molybdenum in a purified

form substantially free from vanadium impurities, said

process comprises: 55

(a) crystallizing vanadium from a solution having a

mixture of vanadium and molybdenum;

(b) extracting molybdenum from the remaining solution

of molybdenum with an organic solvent;

aqueous solvent;

(d) heating said aqueous solution from step (c) to

between 40° C. and 80° C.;

(e) adjusting the pH of said heated solution to between

5.5 and 8.5 to precipitate impurities; and 65

(f) adjusting the pH of said heated solution to between

1.5 and 3.0 to precipitate molybdenum as

ammonium octamolybdate;

Thereafter, a composite of the ammonium molybdate

strip concentrate was heated to 50° C., the pH was

adjusted to 6.5 with sulfuric acid, and the solution was

allowed to digest for I hour. The hydrolyzed impurities

were removed by fIltration. The purified fIltrate was 5

heated to 80° C., adjusted to 2.5 pH with sulfuric acid

and seeded with ammonium octamolybdate (AOM).

The resulting slurry was digested for 4 to 5 hours, ftltered,

and the chemically precipitated crystals were

washed with a pH 2.5 sulfuric acid solution. The crys- 10

tallization above showed 80% of the initial vanadium to

be separated from the molybdenum product.

The fIltrates from the AOM crystallization were recycled

to the ammonium metavanadate (AMY) crystal- 15

lization as a source of ammonium sulfate and for the

purpose of recycling the contained vanadium and molybdenum.

The molybdenum concentrations in the fIltrates

are in the range from 1.9 to 4.7 grams per liter.

Table I shows the relative concentrations of the metals 20

that have been precipitated.

TABLE I

4,814,149

dium values from said solution as a precipitate of ammonium

metavanadate, concentrating the fIltrate of said

solution to assist removal of impurities in the resulting

concentrate by fIltration, and then concentrating the

5 concentrated solution of molybdenum and residual vanadium

values with an acid to precipitate ammonium

octamolybdate therefrom while rejecting greater than

80% of said vanadium values into the extract from such

precipitation of said ammonium octamolybdate.

* * * * *

between 2.0 and 5.0 with sulfuric acid; heating the solution

to between 50° C. and 95° C.; allowing the solution

to digest for between 3 and 6 hours; seeding the solution;

removing the precipitated ammonium octamolybdate;

and recycling the remaining solution to the vanadium

crystallization step.

9. A process for selectively recovering a substantially

pure molybdenum precipitate from a solution comprising

a mixture of molybdenum and vanadium values, said

process comprising crystallizing a majority of the vana- 10

#2hinPA�<-layout-grid-align:none;text-autospace:none'>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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