6,149,883 Pressure oxidation process for the production of molybdenum trioxide from molybdenite

Patent Number/Link:

6,149,883

Nov. 21, 2000

[11]

[45]

111111111111111111111111111111111111111111111111111111111111111111111111111

US006149883A

Patent Number:

Date of Patent:

United States Patent [19]

Ketcham et al.

[54] PRESSURE OXIDATION PROCESS FOR THE

PRODUCTION OF MOLYBDENUM

TRIOXIDE FROM MOLYBDENITE

4,444,733

4,512,958

4,551,312

4,551,313

4/1984 Laferty et al. 423/24

4/1985 Bauer et al. 423/55

11/1985 Yuill 423/53

11/1985 Sabacky et al. 423/59

[75] Inventors: Victor J. Ketcham, Salt Lake City,

Utah; Enzo L. Coltrinari, Golden;

Wayne W. Hazen, Wheat Ridge, both

of Colo.

FOREIGN PATENT DOCUMENTS

2830394 1/1980 Germany.

3128921 10/1983 Germany.

331472 7/1930 United Kingdom 423/61

[73] Assignee: Kennecott Utah Copper Corporation,

Salt Lake City, Utah

References Cited

Appl. No.: 08/327,980

Filed: Oct. 24, 1994

Int. CI? BOlD 11/00; COlO 39/00;

C22B 34/30

U.S. Cl. 423/54; 423/55; 423/58;

423/61

Field of Search 423/58, 54, 61,

423/55

OTHER PUBLICATIONS

ABSTRACT

Molybdenum trioxide is produced from molybdenite by a

pressure oxidation process comprising of the steps of forming

an aqueous slurry of molybdenite, pressure oxidizing the

slurry to form soluble and insoluble molybdenum species,

converting the insoluble molybdenum species to soluble

molybdenum species by alkaline digestion, separating the

soluble molybdenum species from insoluble residue contaminants

(if present), removing the molybdenum species

from the aqueous media through solvent extraction, and

recovering the molybdenum values as molybdenum trioxide

from the organic solvent. Low grade molybdenite

concentrates, including concentrator slimes containing talc

and sericite, can be used as a feed. The process produces

technical grade molybdenum trioxide.

[57]

World Patent Index (Derwent) database printout of Acc't.

No. C83-014596 sharing the patent family and English

language abstract of DE 3,128,921, no date.

19 Claims, 6 Drawing Sheets

Primary Examiner~teven Bos

Attorney, Agent, or Firm-Whyte Hirschboeck Dudek SC

7/1969 Litz 75/84

8/1971 Chio!a et al. 423/54

4/1972 Barry et al. 23/15 W

11/1974 lema! 423/59

7/1975 Ammann 423/55

10/1975 lema! 23/264

12/1976 Miillerstedt 423/54

9/1977 Vertes et al. 423/58

3/1983 Sohn 423/61

4/1983 Bauer et al. 423/55

U.S. PATENT DOCUMENTS

3,455,677

3,598,519

3,656,888

3,848,050

3,896,210

3,910,767

4,000,244

4,046,852

4,376,647

4,379,127

[58]

[21]

[22]

[51]

[56]

[52]

I:h~cfe~e~11--1 Najor K Compound

Filter I

Alkaline I

Leach

NaHS-"1 Sulfide I

IPrecioitationl

Molybdic

Oxide

Ammonium Sulfate

=h~c~e~e~Ir-~~~~-.

Filter -I Copper Sulfide to Smelter

Limestone..-I':"N~eu~t~ra~l~iZ~a~t10~·.Iln}-~~-'Slurry to Tailings Pond

and Lime L: (Gypsum/iron precipitate)

u.s. Patent Nov. 21, 2000 Sheet 1 of 6 6,149,883

Figure 1

Molybdic

Oxide

- - - - - 1-----l~As/P precipitate

Filter to disposal

Ammonium Sulfate

I-------'l.~Residue to smel ter

or gold recovery

Slurry to Tailings Pond

(Gypsum/iron precipitate)

pper Sulfide to Smelter

Na or K Compound

1 Thickener

- - - - - Filter 1

IAlkaline I

Leach•

Thickener

- - - - -

Filter

ol( I

Stripped

Organic

Moly SX Llol( I Moly SX

Extraction • Stripping

Loaded

Organic

Hs~lsulfide LI

Precipitation

Thickener

- - - - - Co

Filter

L~·mes~one~INeutralization

and L~me

u.s. Patent Nov. 21, 2000 Sheet 2 of 6 6,149,883

Figure 2

Oxygen • Pressure

Oxidation

Moly 1st Cleaner

Concentrate

'---------'t 1 ~--'-------',

Thickener

- - - - - [-------

Filter

Thickener

Filter

- - - - - 1-- --. Residue to smelter

or gold recovery

Stripped

Organic

III

Loaded

Organic

Moly SX ------.

Stripping

.....1. ----- MgSO.

Thickener~ As/P precipitate

- - - - - to disposal

Filter

NaHS"- Molybdic

Oxide

Ammonium Sulfate

Thickener

_ - - - - f-----------...

Filter

Copper Sulfide to Smelter

Limestone..- Neutralization 1----------J~Slurry to Tailings Pond

and Lime (Gypsum/iron precipitate)

u.s. Patent Nov. 21, 2000 Sheet 3 of 6 6,149,883

Figure 3

Oxygen • Pressure

Oxidation

Moly 1st Cleaner

Concentrate

-----'t 1 0='---'----------"---,

Molybdic

Oxide

.....f----- MgSO.

Thickenerl .~. As/P precipitate

to disposal

Ammonium Sulfate

Filter

Slurry to Tailings Pond

(Gypsum/iron precipitate)

pper Sulfide to Smelter

smelter

covery

Lime or Magnesium Hydroxide

1 Thickener

I - - - - - Filter 1

I !Alkaline

Leach

I .. I

Thickener

I - - - - - .. Residue to

I Filter or gold re

I Stripped

I Organic

I Moly SX I .. I Moly SX ILoading

.. Stripping

I Loaded

Organic

aHs+1 Sulfide LI

Precipitation

Thickener

- - - - - Co

Filter

L imes~one+INeutralization

and LJ.me

u.s. Patent Nov. 21, 2000 Sheet 4 of 6 6,149,883

Figure 4

Final Cu

Concentrate

(to smelter)

tailings

lotation ~I'

slimes

conc.

I • Desliming

coarse

Cleaner ..

Mo Flotation

tailings

Bulk

Cu-Mo

Concentrate ---...·1 Rougher

Mo F

conc.

Heat

Treatment

4 L-_---,__---'

Final Mo

Concentrate

(to roas ter)

u.s. Patent Nov. 21, 2000 Sheet 5 of 6 6,149,883

Figure 5

Bulk Final Cu

Cu-Mo Concentrate

Concentrate -------J.~I Rougher 1-------... (to smelter)

Mo Flotation jconc,-------.

Cleaner

'--------}.~I Mo Flotation~

conc.

Cleaner Mo

Concentrate

(to autoclave oxidation)

u.s. Patent Nov. 21, 2000 Sheet 6 of 6 6,149,883

Figure 6

Concentrated

Ammonium Molybdate

Solution from Mo SX Stripping

----------MgS04

'If t

Purification III-------J.~As/P/Si02 precipitate

and filter

Technical

Grade

Molybdate

Oxide

.----------•• NH3 + H20 (recycled)

Evaporative

Crystallizer f--------l

--------.~Primary Mo SX

Extraction Stage

Barren---.~I Secondary

Organic SX "----------,--r1- H20

.--------'---=---'----, Evaporative

Crystalizer

1 Ammonium Sulfate

6,149,883

SUMMARY OF THE INVENTION

According to one embodiment of this invention, molybdenum

trioxide of at least technical grade is produced from

Various methods exist or have been proposed for producing

molybdenum trioxide from molybdenite concentrate.

The dominant technology is roasting in which the concentrate

is heated in the presence of excess air to form molyb-

5 denum trioxide and sulfur dioxide as a gaseous by-product.

While proven, this technology is environmentally difficult

and produces an off gas with a low concentration of sulfur

dioxide which requires upgrading before it is an economically

attractive feed to an acid plant. Additionally, roasting

10 is, as a practical matter, limited to molybdenum concentrates

that contain less than 5 wt % copper and less than a total of

10 wt % combined naturally floatable gangue minerals such

as talc and sericite. The presence of these substances results

in the formation of a sticky material in the roaster that

15 adheres to the rabble arms of conventional multihearth

roasters, and interferes with the rejection of fixed sulfur.

One variation on roasting is combining it with sublimation

as described in such patents as U.S. Pat. Nos. 3,848,050,

3,910,767, 4,555,387, 4,551,313 and 4,551,312. This pro-

20 cess has the merits of producing an off gas relatively rich in

sulfur dioxide but remains unproven (i.e. it is yet to be

commercialized) and suffers from relatively high losses of

molybdenum to byproduct slag produced in the process.

Another variation on roasting is combining it with either

25 a pre- or post treatment step in which the concentrate is

contacted with a suitable reagent, e.g. ferric chloride, hydrochloric

acid, sodium cyanide, ferric sulfate, sulfuric acid,

etc., to remove deleterious base metal impurities such as

copper. While generally effective, these variations require,

30 by definition, an extra process step, and the various treatment

reagents all have their own undesirable baggage, e.g.

cyanide compounds are environmentally disfavored; chloride

ion, ferric sulfate and sulfuric acid are corrosive, etc.

35 Another class of processes for the production of molybdenum

trioxide from molybdenite concentrate are hydrometallurgical

in nature. In these processes, the concentrate is

leached with one of various reagents, e.g. hypochlorite ion.

While these processes avoid the production of an off gas, all

40 suffer other disabilities, e.g. hypochlorite is a relatively

expensive reagent, and most remain unproven.

One hydrometallurgical process with promising economics

and compatibility with the environment is pressure

oxidation. In this process, the molybdenite concentrate is

45 slurried with water, and then it is fed to an autoclave in

which it is contacted with oxygen under pressure. The

process can be conducted either continuously or on a batch

basis. Insoluble molybdenum trioxide (Mo03 ) is recovered

by filtration. Several varients of this process are described

50 generally in German patent documents DE3,128,921 and

DE2,830,394 as well as U.S. Pat. Nos. 3,656,888; 4,379,

127, and 4,512,958.

While all of the known processes for producing molybdenum

trioxide from molybdenite concentrate are effective

55 to one degree or another, the mining industry holds a

continuing interest for a process that is not only economically

efficient, but also has a low environmental impact. In

addition, the industry has a continuing interest in developing

the ability to process those grades of molybdenite concen-

60 trates that contain relatively high levels of impurities such as

copper and naturally floatable gangue, e.g. talc and sericite,

which are presently difficult to roast to yield molybdenum

trioxide of at least technical grade.

BACKGROUND OF THE INVENTION

PRESSURE OXIDATION PROCESS FOR THE

PRODUCTION OF MOLYBDENUM

TRIOXIDE FROM MOLYBDENITE

FIELD OF THE INVENTION

This invention relates to the production of molybdenum

trioxide. In one aspect, the invention relates to the production

of molybdenum trioxide from molybdenite concentrate

while in another aspect, the invention relates to the formation

of insoluble molybdenum trioxide during the pressure

oxidation of molybdenite concentrate. In yet another aspect,

the invention relates to solubilizing the insoluble molybdenum

trioxide through the action of an alkaline leach.

Molybdenum occurs in nature most commonly as molybdenite

(MoS2 ). While molybdenite may be the primary metal

value of an ore body, such as that at Climax, Colo., it is often

found as a secondary metal value in a copper ore body, such

as that at Bingham Canyon, Utah.

Copper ores only rarely contain sufficient copper to

permit direct smelting, and many ores contain less than 1%

copper. The copper content of these thin ores must be

significantly increased before these materials are worthy to

serve as a smelter feed and to this end, these thin ores are

subjected to concentration. In this process, the ores are

crushed and ground to expose their copper mineralization,

and then floated in a series of flotation cells in which the

copper minerals are recovered as a froth concentrate and the

noncopper-bearing minerals, e.g. silicates and carbonates

generally known as gangue, are recovered as tailings.

Many copper flotation facilities comprise three banks of

flotation cells, i.e. rougher cells, cleaner cells and scavenger

cells. The ore slurry produced during the crushing and

grinding of the ore is feed for the rougher cells in which most

of the copper mineralization is floated. The froth concentrate

from the rougher cells is collected and transferred to the

cleaner cells in which much of the remaining gangue is

rejected and recycled, while the clean copper concentrate is

dewatered and readied for use as a smelter feed. The material

that does not float in the rougher cells is transferred to the

scavenger cells in which additional copper is recovered. The

froth from the scavenger cells is processed to separate

gangue from copper mineralization, and the mineral values

are returned to the rougher cells.

If molybdenite is present in a copper ore body, then it will

usually float with the copper mineralization. As such, the

copper concentrate from the cleaner cells is usually processed

in a separate flotation circuit to remove the molybdenite

before the copper concentrate is readied as a feed to

the smelter. The molybdenite is recovered as a molybdenite

concentrate, e.g. typically in excess of 90% MoS2 with the

remainder mostly silicates and carbonates and various, usually

nominal, amounts of other metals such as copper, gold,

arsenic, etc. The molybdenite concentrate is then processed

to produce molybdenum trioxide which is used primarily as

an alloying agent in the production of specialty steels.

If the copper ore body contains nonmetal-bearing, naturally

floatable silicate gangue minerals, such as talc and/or

sericite, then these minerals will form slimes (because of

their soft character), and these slimes tend to follow the

copper mineralization during flotation. These slimes are

difficult to separate from the molybdenum values and when

such a separation is attempted (e.g. by flotation or 65

cycloning), it usually results in the loss of a relatively large

amount of the molybdenum values.

6,149,883

DESCRIPTION OF THE PREFERRED

EMBODIMENTS

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram of one embodiment of

the process of this invention in which insoluble Mo03 is

solubilized through the action of an alkali metal compound.

FIG. 2 is a schematic flow diagram of another embodiment

of the process of this invention in which insoluble

Mo03 is solubilized through the action of ammonium

hydroxide.

FIG. 3 is a schematic flow diagram of another embodiment

of the process of this invention in which insoluble

Mo03 is converted to a soluble form through the action of

lime.

FIG. 4 is a schematic flow diagram of a conventional

process for molybdenum recovery from coppermolybdenum

concentrate.

FIG. 5 is a schematic flow diagram of a modified molybdenum

flotation circuit.

FIG. 6 is a schematic flow diagram for the production of

technical grade molybdenum trioxide from concentrated

ammonium molybdate solution.

hydroxide, the gangue is rejected (typically by filtration) just

prior to the crystallization of the soluble molybdate values.

In the first and third embodiment of this invention, i.e. that

in which the insoluble molybdenum trioxide is converted to

soluble molybdate values through the action of a sodium or

potassium compound or lime, the gangue is rejected (again

typically by filtration) just prior to the solvent extraction

step.

The process of this invention can successfully recover

molybdenum trioxide from a wide range of molybdenite

concentrate grades including those which are unsuitable for

conventional multihearth roasting and are now routinely

combined with a copper smelter feed, i.e. those that contain

more than 5 wt %copper and more than 10 wt %of naturally

floatable gangue minerals, e.g. talc and sericite. As a

consequence, the process of this invention allows a greater

recovery of molybdenum values (as measured from ore body

to final product, i.e. Mo03 ) than by conventional techniques,

particularly roasting, and it produces a molybdenum trioxide

of higher purity than that produced by roasting.

Referring to FIG. 1, the molybdenite concentrate starting

materials of this invention (i) contain an economically

significant amount of MoS2 , e.g. as low as 10%, but typi-

50 cally at least about 20% and preferably at least about 50%,

(ii) are typically in the form of finely divided particles of a

size usually less than 100 mesh (U.S. standard), and (iii) can

include concentrates which were not processed previously

because they contained unacceptably large amounts of

insoluble gangue minerals, e.g. talc and sericite. The starting

material concentrates of this invention are the product of

typical ore beneficiation processes, and the concentrates

produced from the cleaner flotation cells in the molybdenum

recovery circuit are preferred. These concentrates are usu-

60 ally in the form of a slurry or filter cake containing small

amounts of hydrocarbon flotation oils. These concentrates

do not require pretreatment, but if desired, the concentrates

can be subjected to retorting, scrubbing with a strong alkali

solution, or other treatment which removes or reduces the

amounts of flotation oils in the concentrate.

The concentrates used in this invention contain other

materials such as silica, feldspars, naturally floatable gangue

a molybdenite concentrate containing molybdenum and

nonmolybdenum metal contaminants (e.g. copper, arsenic,

iron, etc.) in a process comprising of the steps of:

A. Oxidizing under pressure an aqueous suspension of the

concentrate to effect substantially complete conversion 5

of molybdenite to form a soluble hydrous molybdic

oxide and insoluble molybdenum trioxide;

B. Separating the soluble molybdic oxide from the

insoluble molybdenum trioxide;

C. Converting the insoluble molybdenum trioxide to 10

soluble molybdate values;

D. Mixing the soluble molybdate values of C with the

soluble molybdic oxide of A;

E. Extracting the molybdenum values with an organic 15

solvent from the mixture of D such that the majority of

the molybdenum values are extracted into the organic

solvent and a majority of the metal contaminants

remain in the aqueous phase;

F. Crystallizing the extracted molybdenum values of E; 20

and

G. Calcining the crystallized molybdenum values of F to

produce molybdenum trioxide.

In this embodiment, the insoluble molybdenum trioxide of

step C is converted to soluble molybdate values through the 25

action of a sodium or potassium based reagent, e.g. sodium

or potassium carbonate or hydroxide.

In those embodiments of this invention in which the

residue from step A (the autoclaving step) filters and washes

well (i.e. the residue is quantitatively recovered and the 30

soluble impurities, e.g. copper and sulfates, are readily

removed by contacting the filter cake with rinse water), the

insoluble molybdenum trioxide of step C can be converted

to soluble molybdate values through the action of ammonium

hydroxide, and the soluble molybdate values are then 35

advanced directly to step F. This embodiment eliminates the

need of combining the soluble molybdate values with the

soluble hydrous molybdic oxide to form a mixture from

which the values are subsequently removed by solvent

extraction.

In yet another embodiment, the insoluble molybdenum

trioxide is converted to soluble molybdenum values in step

C through the action oflime (CaO) or magnesium hydroxide

(the former preferred for economic reasons). The soluble

molybdate values are then combined with the solution 45

containing soluble molybdic oxide of step A while maintaining

a pH of less than 2, and then filtered. The filtrate is

forwarded to step E for solvent extraction of the molybdenum

values for subsequent crystallization and calcination to

molybdenum trioxide.

Copper values present in the molybdenite concentrate are

also oxidized in step A, and the oxidized copper values from

the raffinate of step E are recovered by any conventional

technique, e.g. solvent extraction, electrowinning, precipitation

as a sulfide, etc. Precipitated copper sulfide is a 55

suitable smelter feed and depending upon its purity, copper

recovered by electrowinning may be sold as either cathode

copper or melted to make anodes for further processing. The

waste liquor from the copper recovery steps is neutralized

and disposed in an environmentally acceptable manner.

In all three of the above-described embodiments of this

invention, gangue is separated from the molybdenum and

copper values, and then typically returned to a smelter for

further processing to recover additional metal values. In the

second embodiment of this invention, i.e. those in which the 65

insoluble molybdenum trioxide is converted to soluble

molybdate values through the action of a ammonium

6,149,883

5 6

Rhenium, which is generally present in molybdenite

concentrates as a solid solution contaminate in the molybdenite

mineral, is oxidized to yield soluble perrhenic acid.

Similar equations can be written for the other metals

5 values that are oxidized during this process step.

After the oxidation reaction is completed, the solid fraction

of the reaction mass is separated from the liquid fraction

by any conventional technique, typically a combination of

10 thickening and filtration. In a hallmark feature of this

embodiment (FIG. 1), the undissolved molybdenum trioxide

in the solid fraction is converted to a soluble alkaline

molybdate, preferably a soluble sodium molybdate, with an

alkali metal, e.g. sodium, potassium, etc., compound. While

15 any alkali metal material that will solubilize the insoluble

molybdenum trioxide can be used in this step of the invention

(e.g. sodium and potassium hydroxide, carbonates and

bicarbonates), soda ash (Na2C03) is preferred because of its

low cost, wide availability, and ease of use. The reaction of

20 soda ash with molybdenum trioxide is described in equation

IV.

The digestion or solubilization of the molybdenum trioxide

with soda ash is conducted preferably at ambient pressure

conditions in two or more digestors operated continuously

in series, each equipped with agitation means. The

density of the reaction mass is a function of the molybdenum

content of the solids generated in the pressure oxidation

stage and of the alkali metal solution strength (e.g. the

greater the soda ash strength, the greater the molybdenum

content, and the greater the solids density). The pressure

oxidation and digestion stages are operated such that the

concentration of molybdenum in the liquid fraction of the

slurry at the liquid-solid separation phase of this step is

preferably between about 10 and 100 grams per liter (gil).

The slurry is subjected to any conventional liquid-solid

separation technique, e.g. belt filtration, and the filtrate is

then combined with the liquid fraction from the pressure

oxidation of the original feed slurry. The precipitate or filter

cake is treated by any conventional means for recovery of

the residual metal values, e.g. silver, gold, etc.

The mixture of the liquid fractions from the pressure

oxidation and alkaline leach steps, the former the dominant

portion of the mixture and typically comprising at least

about 70 volume percent of the mixture, is typically acid in

pH as a result of the acid produced during the pressure

oxidation stage. If the mixture is not sufficiently acid to

maintain the molybdenum values soluble during solvent

extraction for any reason, then it is re-acidified or in other

words, sufficient acid, e.g. sulfuric acid, is added to the

mixture such that the solubility of the molybdenum values is

maintained during the solvent extraction. The temperature of

the mixture during re-acidification, if necessary, can vary to

convenience, but the temperature of the mixture is usually

reduced to less than about 40 C prior to contact with the

extracting solvent. The chemistry of the re-acidification

reaction is described by equation V. (V)

(V)

(IV)

(I)

(II) 60

(III)

minerals such as talc and sericite, various phosphorus

values, and other (nonmolybdenum) metals such as copper,

iron, arsenic, gold, silver, rhenium, etc. These other materials

are present in varying amounts, particularly the metals,

although the process of this invention is particularly well

adapted for recovering molybdenum values from concentrates

with relatively large amounts of copper values, e.g. in

excess of 5 weight percent, and relatively large amounts of

naturally floatable gangue minerals, e.g. in excess of 10

weight percent, that create difficulties in traditional roasting

processes.

The particle size of the concentrate material, measured in

terms of Pso (80% by weight of the concentrate can pass

through a screen of designated mesh size), can vary,

although concentrates of relatively small particle size, e.g.

Pso at 200 or finer mesh and preferably Pso at 325 or finer

mesh, are preferred. This small particle size facilitates the

oxidation step by facilitating dispersion and maximizing

surface area.

In the first process step of this invention, molybdenite

concentrate is slurried with water or an aqueous solution of

metal salts and/or acid to a solids concentration of between

about 5 and 40, preferably between about 10 and 30, percent

by weight, and is fed to an autoclave on either a batch or

continuous basis. The autoclave itself can be of any suitable 25

design, but it is typically equipped with agitation means, e.g.

one or more propeller stirrers, and baffled into two or more

compartments. While the oxidation reaction proceeds at

ambient pressure and temperatures below 100 C, the reaction

conditions are chosen such that the sulfur bound to the 30

molybdenum is essentially completely oxidized in a reasonably

short period of time, e.g. one to five hours. "Essentially

completely oxidized", "substantially complete conversion of

molybdenite", and like terms means that at least about 90,

preferably at least about 95, and more preferably at least 35

about 97, percent of the MoS2 is oxidized to molybdenum

oxides, either soluble or insoluble.

Preferred reaction rates occur at temperatures in excess of

100 C, preferably in excess of 150 C, and more preferably

at or in excess of about 200 C, and at a partial pressure of 40

free oxygen in excess of 25 psi, preferably in excess of about

75 psi. The maximum partial pressure of free O2 is a

function of the autoclave design, but typically it does not

exceed about 600 psi, preferably it does not exceed about

200 psi. The oxygen can be introduced as pure oxygen, 45

oxygen-enriched air or air, although pure oxygen or oxygenenriched

air are preferred for obvious reasons.

The oxidation reaction is allowed to proceed to substantial

completion, the exact time dependent upon a host of factors

such as temperature, pressure, agitation rates, slurry density, 50

particle size, etc. The product of the oxidation reaction

includes soluble molybdic oxide, insoluble molybdenum

trioxide, and soluble metal sulfate values, e.g. copper and

ferric sulfate produced from the oxidation of chalcopyrite,

insoluble minerals such as talc and sericite, etc. These 55

oxidation reactions are described by the following equations:

The soluble molybdic oxide, represented as the general

chemical formula M003'H20Csoluble) for convenience, can

be present in solution as one or more of a range of anions 65

including M004- 2, HM030 11 - 3, H3M06021-3,

HgM02407S-3, etc. depending upon of the solution.

The chemistry of the molybdenum solvent extraction is

described in equations VI and VII for one possible anionic

form of soluble molybdic oxide. Similar equations can be

written for other possible anionic forms of the soluble

molybdic oxide.

6,149,883

7 8

(X)

(XI)

(IX)

(R3NHMH9M024078)+48NH40H~3R3N+24(NH4)2Mo04+

30H20 (VIII)

7(NH4)2Mo04+4H2S04~(NH4)6Mo7024'H20(,olid)+4(NH4)2S04+

3H20 (XII)

The purified and loaded strip liquor is admixed with a

crystallizer mother liquor at a ratio dictated by the desired

crystal size and performance characteristics of the

crystallizer, and the combination is subjected to crystallization

by any conventional technique. Typically, crystallization

is performed by evaporation at an elevated temperature

and/or reduced pressure. Crystals are recovered from the

mother liquor by centrifugation or other liquid-solid separating

technique, and the bulk of the molybdenum values are

recovered as diammonium molybdate (ADM) or diammonium

paramolybdate. The chemistry of crystallization, for an

ADM product, is described in equation X.

To avoid saturation of the mother liquor with impurities, a

portion of the mother liquor may be treated separately rather

than recycled to the crystallizer. In this side stream, the

residual molybdenum values in the crystallizer mother

liquor are recovered by precipitating molybdenum from

solution (generally accomplished by acidifying the mother

liquor with any suitable acid, e.g. sulfuric acid). The molybdenum

precipitates as a solid containing a mixture of

hydrous molybdenum trioxide and a range of possible

ammonium molybdate species-(NH4)sHM06021'H20,

(NH4)6M07024'H20, etc. -the compositions of which

depends on the precise pH and temperature of precipitation.

The chemistry of this precipitation is described generally in

equations XI and XII.

The residual molybdenum recovery solids are separated

from the solution, generally by filtration, and are recycled to

the crystallizer in which the molybdenum is converted to

ADM for subsequent drying and calcining.

The residual molybdenum recovery solids and ADM are

dried to a moisture content of less than about ten percent,

preferably less than about five weight percent, and then

calcined to remove ammonia and recover molybdenum

trioxide. Hydrous molybdenum trioxide is dehydrated during

calcination. Any conventional calciner can be used in

this step, and the calcination temperature is usually in excess

of 450 C, preferably at or in excess of 575 C. The process

chemistry of the calcination is described in equations XIII,

XIV and xv. Similar equations can be written for other

ammonium molybdate species.

removed from the aqueous phase (usually by filtration) for

ultimate recovery and disposal. If present, other deleterious

impurities, e.g. arsenic, phosphorus, etc., can be removed at

this stage by the addition of a precipitating agent such as

5 magnesium sulfate (MgS04). This precipitate is recovered

with the silica-containing precipitate for appropriate recycle

or disposal.

The stripped organic phase is cleaned of residual values,

and then recycled to the solvent extraction phase. The

10 chemistry of this solvent stripping step is described in

equations VIII and IX (and as noted earlier, similar equations

can be written for other possible anionic forms of the

soluble molybdic oxide).

(VI)

(VII)

3(R3NH)HS04+(H9Mo24078)-3~(R3NH)3(H9Mo24078)+

3(HS04t 3

Any conventional solvent extraction technique can be

used in the practice of this invention, and it can be conducted

in a single or multi-step manner. The extracting solvent

usually comprises an organic solvent in combination with a

nonprimary amine (e.g. a secondary or tertiary amine) in

which the extractant contacts the dissolved, molybdenumcontaining

liquid fractions of the pressure oxidation and

alkaline leach steps in a countercurrent manner. The contact

is conducted at or near ambient temperature and pressure,

and the extraction of the molybdenum values is near quantitative.

Representative tertiary amines include tri-caprylyl 15

amine (e.g. Alamine 336) and tri-auryl amine (e.g. Alamine

304). A wide range of other secondary and tertiary amines

may also be used provided that their molecular structure

includes at least one hydrocarbyl group of sufficient molecular

weight to effectively limit their solubility in the aqueous 20

phase (e.g. containing~6 carbon atoms).

Quaternary amines may also be used, but molybdenum

loaded on quaternary amines in the organic phase is more

difficult to recover in the stripping stage, requiring a stronger

stripping agent than ammonium hydroxide, and their use in 25

this stage of the process is therefore not preferred.

A range of organic solvents derived from petroleum or

coal liquids may be used, including those of aliphatic or

aromatic nature as well as mixtures of the two. In similar

applications of solvent extraction for recovery of 30

molybdenum, others (Mollerstad, U.S. Pat. No. 4,000,244,

Lafferty U.S. Pat. No. 4,444,733 and Litz, U.S. Pat. No.

3,455,677) teach that the addition of one or more modifiers,

such as a high molecular weight alcohol or alkyl phosphate

esters, to the organic solvent is required to prevent the 35

formation of stable emulsions (also known as a "third

phase") when molybdenum loadings of greater than about

10 gil Mo in the organic phase are desired. Although we

have found this to be true when using a solvent of full or

partial aliphatic nature, we have discovered that modifiers 40

are not required to prevent the formation of stable emulsions

if an exclusively aromatic solvent, such as that marketed

under the trademark Aromatic 150, is employed.

Excess organic material is removed from the aqueous

raffinate of the solvent extraction step by any conventional 45

technique, e.g. skimming, and the metal values in the

raffinate are then recovered by any conventional technique

such as solvent extraction/electrowinning (SXEW), direct

electrowinning, and precipitation as a sulfide through the

action of any sulfiding agent, e.g. hydrogen sulfide (H2S), 50

sodium hydrogen sulfide (NaHS), etc. The precipitate is then

separated from the filtrate by conventional technique, e.g.

thickening and filtering, and the solid fraction is transferred

to a smelter for recovery of copper and/or other metal values

while the aqueous fraction is neutralized with any suitable 55

neutralizing agent, e.g. limestone, milk of lime, etc. which

precipitates gypsum (CaS04'2H20) and iron hydroxides

which can then be transferred to a tailings pond for disposal.

The molybdenum-loaded organic phase from the solvent

extraction process is first scrubbed with an acid solution, e.g. 60

sulfuric acid, to remove any entrained raffinate (which

contains copper and iron values). The scrubbed organic

phase is then contacted with a stripping medium to recover

the molybdenum values. The stripping medium is typically

an aqueous alkaline solution, e.g. ammonium hydroxide, 65

that is selective for the molybdenum values. Silicacontaining

precipitate may form in the strip stages, and is

6,149,883

9 10

(XVII)

(XVIII)

>50

<0.5

<0.03

<0.05

Roaster

Feed

Molybdenite

Concentrate %

>55

<0.5

<0.03

<0.05

<0.15

Technical

Grade

Molybdenum

Trioxide %

TABLE 1

SPECIFIC EMBODIMENTS

Minimum Commercially Acceptable Quality

Specifications for Conventional

Molybdenum Trioxide Production Process

Mo03(soluble)+CaO--..,.CaMo04(acid soluble)

Species

Comparative Example: Conventional Technology

If lime replaces Mg(OH)2' then Mo03 is converted to an

acid soluble form according to equation XVIII.

In either case, the unseparated reaction product (both

liquid and solid fractions) is admixed with the liquid fraction

from the autoclave stage, if necessary additional acid is

added to maintain a pH of 2 or less, and then the resulting

mixture separated by any conventional technique into its

liquid and solid constituent parts. The solids fraction (e.g.

filter cake) is sent to a smelter or gold recovery operation for

further processing, while the liquid fraction is transferred to

the solvent extraction stage.

The process of this invention is more fully described by

the following Examples. Unless indicated to the contrary, all

parts and percentages are by weight.

Molybdenum is presently recovered from copper ore

mined at Bingham Canyon, Utah in the form of a molybdenite

concentrate. This concentrate is shipped to commercial

roasting facilities employing conventional multihearth

roasting technology for conversion of the molybdenite to

technical grade molybdenum trioxide which is sold to end

users, principally in the alloy steel manufacturing industry.

The molybdenum trioxide produced must meet a number

of minimum quality specifications for technical grade product

if it is to be successfully marketed. The most relevant of

these minimum quality specifications are listed in Table 1.

To achieve these quality specifications in the final molybdenum

trioxide product from a conventional roaster, the

molybdenite concentrate from which it is produced must

also meet a number of corresponding minimum quality

standards. Minimum quality specifications for molybdenite

concentrates required by the roasting facilities currently

processing molybdenite concentrate from Bingham Canyon

are also listed in Table 1.

embodiment or the NH40H of the FIG. 2 embodiment. This

embodiment of FIG. 3, like the embodiment of FIG. 1, is

well adapted for autoclave residues of all natures, i.e.

regardless of whether or not the residue filters or washes

5 well, and the Mg(OH)2 reacts with the insoluble Mo03

according to the equation XVII.

(XVI)

(XIII)

(XIV)

(XV)

After separation from the solid fraction, the soluble

molybdenum values are transferred directly to the crystallization

stage for further processing, as opposed to the

solvent extraction stage as in the embodiment described in

FIG. 1.

In yet another embodiment (FIG. 3), lime or magnesium

hydroxide replaces the alkali metal compound of the FIG. 1

Ammonia is recovered from the crystallizer and calciner off

gases as ammonium hydroxide, and recycled, as is process

water. Solution from the residual molybdenum recovery step

contains ammonium sulfate, which is recovered by evaporating

the solution to dryness. The recovered molybdenum 10

trioxide is cooled and packaged for shipment. Dust-laden off

gases are processed to recover product, recycle process

reagents, and to emit clean discharges to the environment.

Rhenium present in the molybdenite concentrate is substantially

completely recovered in step E of the process 15

(solvent extraction) and reports to the purified and loaded

strip solution as ammonium perrhenate, NH4Re04 . If

desired, this rhenium may be recovered by solvent extraction

or, preferably, ion exchange resin processing of the

purified and loaded strip solution, crystallizer mother liquor, 20

or ammonium hydroxide recycle stream using an extractant

or ion exchange resin with a high selectivity for rhenium

over molybdenum in alkaline solutions. Quaternary amine

extractants and ion exchange resins containing quaternary

amine functional groups such as that marketed under the 25

trademark Amberlite IRA-400, are preferred.

Rhenium can then be recovered from the loaded organic

(solvent extraction option or ion exchange resin using any

one of several established stripping and upgrading processes

for the production of crude or purified ammonium 30

perrhenate, perrhenic acid, or rhenium sulfide. Suitable

stripping agents include perchloric acid and ammonium

thiocyanate. As taught in U.S. Pat. No. 3,558,268, the later

is preferred due to its higher inherent safety and simpler

upgrading process for the production of ammonium perrhe- 35

nate.

If rhenium is not selectively recovered, a portion of it

co-precipitates with molybdenum in the ADM and the

residual molybdenum recovery solids. As these intermediate

products are calcined to molybdenum trioxide, their con- 40

tained rhenium is converted to rhenium oxide, Re20 7 , which

is volatile at calcination temperatures, is driven off with

ammonia, and is recovered and recycled in an ammonium

hydroxide solution. In a continuous process, this rhenium

recycle continues to build up until that portion of the 45

rhenium contained in purified strip solution which reports to

the ammonium sulfate product represents substantially all of

the rhenium solubilized in the autoclave, at which point the

rhenium in recycle is maintained at a stable steady-state

level. In another embodiment of this invention (FIG. 2), 50

ammonium hydroxide (NH40H) replaces the sodium or

potassium compound (e.g. soda ash) in the alkali leach stage

(Step C). This embodiment is particularly well adapted for

use on those residues from the autoclave stage (Step A) that

filter and wash well, and thereby leaving low levels of 55

soluble contaminants, such as copper or arsenic, in the filter

cake. The NH40H reacts with the insoluble Mo03 according

to equation XVI.

6,149,883

11 12

49.9

52.3

0.39

78.8

57.3

0.43

50.4

84.3

TABLE 2

Molybdenum Recoveries and Product Grades for

Conventional Process at Bingham Canyon Mine

Molybdenum recovery from ore, %

to Cu-Mo bulk concentrate feeding rougher

Mo flotation stage:

to Mo rougher concentrate produced in rougher

Mo flotation stage:

to final Mo concentrate produced in insol

flotation stage:

to saleable technical grade molybdenum trioxide

product (after roasting stage losses):

Final molybdenum concentrate grade, %

Equivalent grade of molybdenum trioxide produced

from final molybdenum concentrate, %

EXAMPLE 1

Improved Flotation Recovery Without Desliming for

Removal of Talc and Sericite

A modification of the Bingham Canyon molybdenum

concentrating circuit described in the Comparative Example

was tested. These modifications are illustrated in FIG. 5 and

described below.

Rougher Molybdenum Flotation.

This stage, which treats bulk copper molybdenum concentrates

to produce a rougher molybdenum flotation

concentrate, is identical to the rougher molybdenum flotation

stage in the Comparative Example.

Cleaner Molybdenum Flotation.

The rougher molybdenum concentrate produced in the

rougher molybdenum flotation stage is, without desliming or

regrinding, subjected to a single stage of cleaner flotation

60 where additional copper is rejected to a molybdenum cleaner

tailings stream which joins rougher molybdenum tailings to

form final copper concentrate. The cleaner molybdenum

concentrate produced in this stage, which also contains a

majority of the naturally floatable talc and sericite minerals

contained in the bulk copper molybdenum concentrate,

forms the feed of the autoclave oxidation stage of Examples

2 through 4.

Insol Flotation.

The heat-treated concentrate is subjected to several stages

of insol flotation. In this "reverse" flotation process (where

the more valuable sulfide mineral is depressed and the less

5 valuable gangue minerals are floated), talc and sericite are

removed as a froth concentrate and molybdenite is depressed

and remains in the tailings stream from this flotation stage.

This "tailings" stream from insol flotation is the final molybdenite

concentrate from the process, meeting the minimum

10 quality specifications listed in Table 1. It is filtered, dried and

bagged for shipment to roasting facilities. The insol flotation

"concentrate" reports to the final copper concentrate.

In the above process, overall recovery of molybdenum

contained in Bingham Canyon ore to the final molybdenite

concentrate averages about 50%, and multi-hearth molyb-

15 denum roasting facilities typically achieve about 99% stage

recovery of molybdenum contained in concentrate to technical

grade molybdenum trioxide product. Actual average

performance of the existing Bingham Canyon molybdenite

recovery process over eight days during which samples were

20 taken for the tests described in Examples 1 through 6 is

summarized in Table 2.

<10

Roaster

Feed

Molybdenite

Concentrate %

Technical

Grade

Molybdenum

Trioxide %

TABLE 1-continued

Minimum Commercially Acceptable Quality

Specifications for Conventional

Molybdenum Trioxide Production Process

Species

Naturally

floatable

gangue minerals

(talc &

sericite)

Copper and molybdenum are recovered from Bingham

Canyon ore in a multiple-stage process beginning with

crushing and grinding of the ore, followed by three stages of

flotation to produce a bulk copper and molybdenum sulfide

mineral concentrate containing about 27.5% Cu as copper

sulfide minerals, about 1.8% Mo as molybdenite, and about

14% gangue minerals including about 1% to 5% naturally

floatable talc and sericite.

The bulk copper and molybdenum concentrate is subjected

to further processing to separate a majority of the 25

contained molybdenum into a molybdenite concentrate

meeting the minimum specifications listed in Table 1. The

remaining material forms a final copper concentrate which is

fed to smelters for recovery of its contained copper and

precious metals values. This separation process is shown in 30

FIG. 4 and consists of the following stages:

Rougher Molybdenum Flotation.

Copper minerals are depressed by the addition of a

suitable chemical reagent and molybdenite is collected in the

concentrate. Because of their natural floatability, a majority 35

of the talc and sericite minerals in the bulk concentrate

follow the molybdenite. Tailings from this stage report to the

final copper concentrate which is feed to copper smelters,

and the rougher concentrate reports to the desliming stage.

Desliming.

The rougher molybdenum concentrate is deslimed in 40

cyclones for removal of talc and sericite fines which cannot

be successfully separated from molybdenite by flotation

processes. In addition to talc and sericite, the fines produced

in this cycloning step also contain copper and precious

metals values. These fines report to final copper concentrate. 45

Fine molybdenite is also unavoidably removed in cycloning

and forms a portion of the fines stream reporting to copper

concentrate, thereby causing a significant loss in molybdenum

recovery for this conventional process. The deslimed

concentrate proceeds to the cleaner molybdenum flotation 50

stage.

Cleaner Molybdenum Flotation.

The deslimed concentrate is reground and subjected to

further cleaning flotation steps where additional copper is

rejected to an intermediate molybdenum cleaner tailings 55

stream which is recycled and combined with bulk copper

molybdenum concentrate feeding rougher molybdenum flotation.

Cleaner molybdenum flotation concentrate

(consisting predominantly of molybdenite, talc and sericite)

advances to the heat treatment stage.

Heat Treatment.

Cleaner molybdenum concentrate is filtered, dried, and

subjected to a thermal treatment which removes flotation

reagents from the contained molybdenite mineral, thereby

inhibiting the floatability of molybdenite in the insol flota - 65

tion stage. The natural floatability of talc and sericite is not

effected by this heat treatment.

6,149,883

13 14

Assay, % solids. gil solutions

TABLE 4

Soda Ash Digestion Test Results

during the first stage of the cake washing which contains

autoclave discharge solution slightly diluted with wash

water) from the autoclave discharge were combined with the

primary filtrate from the digestion phase. Secondary wash

filtrates, containing low concentrations of molybdenum,

were weighed and assayed in this laboratory example but in

a commercial-scale application would be recycled and used

as feed water in earlier stages of the process for recovery of

their contained molybdenum values.

10 Molybdenum was recovered from the combined filtrate by

solvent extraction using a tertiary amine extractant in an

aromatic organic solvent. Molybdenum was recovered from

the loaded organic phase by stripping with a 3 to 4 normal

ammonium hydroxide solution producing a concentrated

15 ammonium molybdate aqueous solution. After stripping, the

barren organic phase was reused in the solvent extraction

stage of the next locked cycle test (Example 4).

Feed and product assays as well as stage recoveries of

molybdenum and copper achieved in this test are summarized

in Table 4.

78.8

76.1

84.3

Range % Average %

65.2--85.8

74.2--88.4

76.1-91.7

TABLE 3

Simplified Flotation Process

Molybdenum recovery from ore to:

Over the same eight days for which Table 1 documents

performance of the conventional Bingham Canyon molybdenum

recovery process, this modified flotation flowsheet

was tested by sampling rougher molybdenum concentrate in

the commercial plant and performing the cleaner molybde- 5

num flotation stage in a laboratory flotation machine. Average

recoveries and product grades for this modified flotation

process during these eight days is shown in Table 3.

bulk copper molybdenum concentrate

feeding the rougher molybdenum

flotation stage:

rougher molybdenum concentrate

produced in the rougher molybdenum

flotation stage:

cleaner molybdenum concentrate

produced in the cleaner molybdenum

flotation stage:

Grade of cleaner molybdenum concentrate

produced in the cleaner molybdenum flotation

stage:

Mo Cu S-2 H2SO4

15.7 3.80 14.4

0.063 24.4 53

29.0 29.1 109

3.6 0.01 0.24

14.8

0.24 .014 0.25

26.9 24.8 86

0.12 24.8 64

15.2

135 nil

<0.2

99.0

85.7 99.8

13.3 0.0 N/A

99.0 99.8

99.5 <0.1

98.5 <0.1 N/A N/A

0.5 99.8

1.0 0.2

EXAMPLE 3

N/A - Not Applicable

45 cone. strip solution

Mo SX raffinate solution

digestion residue solids

Ammonia Digestion

A portion of bulk molybdenum concentrate sample PP2,

the source of which is described in Example 2, was used as

feed material in a test of the embodiment of the invention

55 shown in FIG. 2. This test employed a continuous pilot-scale

autoclave for the oxidation stage of the process. The concentrate

was reground to an 80% passing size of about 33

microns. A slurry of about 10% solids was prepared from

this reground concentrate using demineralized water. The

slurry was continuously injected into a horizontal autoclave

of approximately 25 L working volume containing four

separately agitated, equal-sized compartments in series. The

temperature and pressure of the autoclave were maintained

at about 220 C and 423 psig. Additional demineralized water

65 was continuously injected into the second, third, and fourth

compartments of the autoclave in amounts calculated to

mimic the cooling water requirements of a commercial-scale

Autoclave feed solids

Autoclave feed solutions

Primary & first wash autoclave filtrate

30 Autoclave residue solids

Na2C03 digestion primary filtrate

Na2C03 digestion residue solids

Combined filtrates, feed to Mo SX

Aqueous raffinate from Mo SX

Loaded organic phase

35 Conco. ammonium molybdate

strip solu.

Barren organic phase after stripping

Oxidation in autoclave stage, %

Dissolution in autoclave stage, %

Dissolution in digestion stage, %

40 Stage recovery from autoclave feed

solids to Mo SX feed solution, %

Stage recovery from SX feed solution

to cone. strip solution, %

Distribution of metal values, %

20.7

3.3

12.0-31.7

2.1-4.9

EXAMPLE 2

Soda Ash Digestion

Several bulk samples of cleaner molybdenum

concentrate, including samples PPI and PP2, were produced

at the Bingham Canyon mine by temporarily repiping the

existing circuit to match the flowsheet shown in FIG. 5.

These samples were used as feed material to laboratory tests

of various embodiments of the invention, including the

embodiment illustrated in FIG. 1 in which insoluble Mo03

is solubilized through the action of an alkali metal hydroxide

and, as an optional step in the process, a portion of the

molybdenum solvent extraction (MoSX) raffinate solution

can be recycled to the autoclave.

As one step in a series of locked cycle tests (tests in which

the intermediate products of one batch test are recycled to

the subsequent test thereby mimicking a continuous

commercial-scale process), a 19% solids slurry of the PPI

sample was prepared using molybdenum solvent extraction

raffinate solution from a previous test cycle. The slurry

mixture was placed in an agitated batch autoclave, the

temperature and pressure of the autoclave was brought to

and controlled at about 200 C and 310 psig, and oxygen gas 50

was sparged into the slurry for a period of 2 hours. Pressure

on the autoclave was then relieved and the oxidized slurry

was cooled to about 90 C, a small sample of the slurry was

removed for assay, and the remaining slurry was filtered.

The filter cake was washed with demineralized water.

Filtered and washed autoclave residue solids were

repulped at about 55 C with demineralized water and

Na2C03 at 30% solids. A total of 2.7 kg of Na2C03 per kg

of Mo in the autoclave residue was used, yielding a digestion

pH of about 8.5. The slurry was agitated for 2 hours, after 60

which the slurry was filtered and the filter cake washed with

demineralized water. Accounting for the removal of assay

samples, digested residue solids contained 63% of the original

mass of autoclave feed solids and consisted predominantly

of gangue minerals.

The primary filtrate (containing undiluted autoclave discharge

solution) and first wash filtrate (filtrate collected

6,149,883

15 16

Mo eu S-2 H2SO4

Autoclave feed solids 27.1 1.85 18.1

Autoclave feed solutions 45

Autoclave discharge filtrate solution 4.74 2.59 63

Autoclave residue solids 29.0 <0.01 0.05

NH40H digestion primary filtrate >50

NH40H digestion residue solids 0.14 <0.01 0.1

Oxidation in autoclave stage, % N/A N/A 99.5 N/A

Distribution of metal values, %

cone. digestion filtrate 85.2 <0.1 N/A N/A

Autoclave disch. solution 14.5 >99.9

digestion residue solids 0.3 <0.1

Projected Distribution of metal values N/A N/A

with inclusion of Mo SX stage, %

cone. digestion filtrate 85.2 <0.1

cone. SX strip solution "';14.0 <0.1

Mo SX raffinate solution ~0.5 >99.9

digestion residue solids 0.3 <0.1

N/A - Not Applicable 60

EXAMPLE 4

Lime Digestion

A portion of bulk molybdenum concentrate sample PP2,

the source of which is described in Example 2, was used as 65

feed material in a test of the embodiment of the invention

shown in FIG. 3 in which solid Mo03 is converted to an acid

soluble molybdate through the action of lime and, as an

optional step in the process, a portion of the molybdenum

solvent extraction raffinate solution can be recycled to the

autoclave.

As one step in a series of locked cycle tests, a 13% solids

slurry of the PP2 sample was prepared using a mixture of

molybdenum solvent extraction raffinate solution from

Example 2 (56% of total mass) and demineralized water

(31% of total). The slurry mixture was placed in an agitated

batch autoclave, the temperature and pressure of the autoclave

was brought to and controlled at about 200 C and 310

psig, and oxygen gas was sparged into the slurry for a period

of 2 hours. Pressure on the autoclave was then relieved and

the oxidized slurry was cooled to about 90 C, a small sample

of the slurry removed for assay, and the remaining slurry

was filtered. The filter cake was washed with demineralized

water.

Molybdenum was recovered from the combined filtrate by

solvent extraction using a tertiary amine extractant in an

aromatic organic solvent (the barren organic phase produced

in Example 2). Molybdenum was recovered from the loaded

organic phase by stripping with a 3 to 4 normal ammonium

hydroxide solution producing a concentrated ammonium

molybdate aqueous solution. After stripping, the barren

organic phase was reused in the solvent extraction stage of

the next locked cycle test.

Feed and product assays as well as stage recoveries of

molybdenum and copper achieved in this test are summarized

in Table 6. In this Example, a majority of the molybdenum

lost to the digestion residue solids is present as

unoxidized molybdenite. Overall molybdenum recovery to

concentrated ammonium molybdate solution could be

improved from the 94.8% achieved in this Example though

the use of autoclave conditions which will achieve more

complete oxidation of sulfide sulfur, such as those shown in

Example 3.

Filtered and washed autoclave residue solids were

repulped at about 55 C with demineralized water and

hydrated lime at 30% solids. Atotal of 0.8 kg of Ca(OH)2 per

kg of Mo in the autoclave residue was used, yielding a pH

of about 9. The limed slurry was agitated for 2 hours, during

which the solid molybdenum trioxide in the residue was

converted to calcium molybdate (which is soluble in acid

solutions).

The limed slurry was then recombined with the acidic

autoclave discharge filtrate solution and the mixture was

agitated for an additional 1 hour during which the calcium

molybdate formed in the liming stage was digested to form

soluble molybdic acid and a calcium sulfate precipitate. The

slurry was then filtered and the filter cake washed with

demineralized water. Accounting for removal of assay

samples, digested residue solids contained 68% of the original

mass of autoclave feed solids.

The primary and first wash filtrates from the autoclave

40 discharge were combined with the primary filtrate from the

digestion stage. Secondary wash filtrates, containing low

concentrations of molybdenum, were weighed and assayed

in this laboratory example but in a commercial application

would be recycled and used as feed water in earlier stages of

the process for recovery of their contained molybdenum

values.

Assay. % solids. gil solutions

TABLE 5

Ammonia Digestion Test Results

autoclave. Gaseous oxygen was sparged into the slurry in

each compartment in amounts slightly in excess of that

required for the sulfide oxidation reactions expected to occur

in each compartment. Unreacted oxygen was vented from

the vapor space of the autoclave.

Product slurry was periodically discharged from the last

compartment of the autoclave to a flash vessel where the

sudden drop in pressure to ambient conditions caused steam

to flash from the slurry, cooling it to about 95 C. Average

residence time of solids in the autoclave was about 2.8

hours. Autoclave discharge slurry from the flash vessel, at

about 15% solids, was collected in buckets and sampled for

assay. A solids weight loss of 33% occurred in the autoclave

treatment.

A portion of the collected autoclave discharge slurry was 15

filtered, and the filter cake was washed with demineralized

water. The washed cake was reslurried with a 3 normal

ammonium hydroxide solution and agitated for 1 hour. The

digestion slurry was filtered, yielding a concentrated ammonium

molybdate solution, and the filter cake was washed 20

with demineralized water. A solids weight loss of 44%

occurred in digestion. Digestion residue solids, consisting

predominantly of gangue minerals, represented 38% of the

original mass of autoclave feed solids. Wash filtrates, containing

low concentrations of molybdenum, were weighed 25

and assayed in this laboratory test but would, in a commercial

application, be recycled as feed water to earlier stages

of the process for recovery of their contained molybdenum.

Recovery of molybdenum contained in the autoclave

discharge filtrate solution by solvent extraction was not 30

included in this test, the efficiency of that portion of the

process having been adequately demonstrated in other tests,

including Examples 2 and 4.

Feed and product assays as well as stage recoveries of

molybdenum and copper achieved in this test are summa- 35

rized in Table 5.

6,149,883

TABLE 6

Lime Digestion Test Results

levels employed and the relatively high sulfur content the

ADM, the Mo03 produced easily met the minimum quality

specification for technical grade molybdenum trioxide,

ADM and Molybdenum Trioxide Grades Produced

TABLE 7

EXAMPLE 6

Comparative Molybdenum Recoveries From Ore

Examples 1 through 5 describe laboratory experiments on

various process stages of three embodiments of the

invention, and these Examples document the stage recoveries

of molybdenum achieved in the process steps, Table 8

illustrates the projected overall recovery of molybdenum

contained in Bingham Canyon ore which may be achieved

through the implementation of these three embodiments of

the invention, based on the results of Examples 1 through 5,

For comparative purposes, Table 8 also lists the molybdenum

recovery achieved at the Bingham Canyon mine using

conventional roasting technology as described in the Comparative

Example,

62.7

0.10

0.30

0.004

0.002

<0.001

Mo03 product

Assay, %

52.6

0.89

ADM product

Si02

Elementl

Compound

The crystallization filtrate contained 111 gil Mo, 103 gil

NH3 , and 206 gil S04' A portion of this filtrate was tested for

recovery of its residual contained molybdenum, The pH of

the filtrate was adjusted to between 4 and 5 by addition of

sulfuric acid, and it was held for 6 hours at a temperature of

about 45 C. Eighty seven percent of the contained molybdenum

was precipitated and recovered by filtration, The

precipitate contained 43.4% Mo, and its major crystalline

species (identified by x-ray diffraction) were (NH4)

6M07024,H20, and Mo03 ,H20, In a commercial operation

this precipitate would be recycled to the crystallizer where

the contained molybdenum would be converted to ADM,

recovered in the ADM product, and calcined to Mo03 ,

The Mo precipitation filtrate contained a residual 7,6 gil

Mo, This molybdenum was recovered by secondary solvent

extraction in a single stage with an organic solvent identical

to that used in Examples 2 and 4, The loaded organic

contained 3,1 gil Mo and was not processed further in this

test. In a commercial application, it would be returned to the

first extraction stage of the solvent extraction circuit used to

recover Mo from autoclave discharge solution, and its

contained molybdenum would be recovered in the concentrated

strip solution,

The raffinate solution from secondary solvent extraction

contained 387 gil S04' 145 gil NH3 , and<O,OI gil Mo, It was

evaporated to dryness producing an ammonium sulfate

crystalline product which was assayed and met all quality

criteria for marketing as a commercial fertilizer.

Based on these results, overall recovery of molybdenum

contained in concentrated strip solution to a final technical

grade molybdenum trioxide product for the fiowsheet illustrated

in FIG, 6 is>99,8%,

Assay, % solids, gil solutions 5

Mo Cu S-2 H2SO4

Autoclave feed solids 29.1 1.93 20.4

Recycled Mo SX raffinate to autoclave 0.12 24.8 64

Primary & first wash autoclave filtrate 7.88 18.1 132 10

Autoclave residue solids 29.1 0.01 0.88

Lime digestion solids 1.48 0.01 0.86

Digestion filtrate, feed to Mo SX 38.0 16.1 99

Aqueous raffinate from Mo SX 0.09 16.6 64

Loaded organic phase 15.8

Cone. ammonium molybdate strip solu. 140 nil 15

Barren organic phase <0.2

Oxidation in autoclave stage, % 96.6

Dissolution in autoclave stage, % 20.3 99.6

Dissolution in digestion stage, % 74.7 0.0

Stage recovery from autoclave feed 95.0 99.8 N/A

solids to Mo SX feed solution, %

Stage recovery from SX feed solution 99.8 <0.1

to cone. strip solution, %

Distribution of metal values, %

cone. strip solution 94.8 <0.1

Mo SX raffinate solution 0.2 99.6 N/A N/A

digestion residue solids 5.0 0.4 25

N/A - Not Applicable

EXAMPLE 5

Production of Technical Grade Mo03 from Concentrated 30

Ammonium Molybdate Solution

Concentrated ammonium molybdate strip solutions produced

in a series of 7 locked cycle tests of various embodiments

of this invention, including those tests described in

Examples 2 and 4, were combined for recovery of their 35

contained molybdenum in accordance with the fiowsheet

illustrated in FIG, 6, This combined strip solution contained

132 gil Mo and also contained 0,06 gil As, 0,38 gil P20 S' and

38 gil S04 as solution impurities as well as 0,09 gil Si02 as

a solid suspension, Magnesium sulfate was added at a rate 40

of 2,9 gil of solution to precipitate arsenic and phosphorous

impurities as magnesium salts, The solution was then filtered

to remove the precipitated impurities, and the filter cake

washed with demineralized water then dried, The recovered

solids totaled 5,7 gil of strip solution and contained 2,2% As, 45

8,3% P20 S' 47% Si02, and 2,8% Mo, representing a recovery

loss of 0,12% of the molybdenum contained in the strip

solution,

The purification filtrate was evaporated under vacuum at

about 70 C to 23% of the original strip solution volume 50

during which a majority of the contained molybdenum

precipitated as ammonium dimolybdate (ADM) crystals,

(NH4)2M0207' The resulting crystal slurry was filtered,

yielding 202 g of ADM product per L of purified strip

solution, The ADM product contained 805% of the Mo in 55

feed solution, The extent of evaporation in this test exceeded

optimum levels, and approximately 14% of the contained

sulfate in the purification filtrate was also precipitated as

ammonium sulfate salt, contaminating the ADM product. In

commercial practice, evaporation would be limited to a 60

volume reduction which would not exceed the solubility

limit of the contained ammonium sulfate,

A portion of the ADM product was calcined in a laboratory

furnace for 1 hour at about 550 C to drive off the

contained ammonia and impurity sulfate to produce Mo03 , 65

Assayed grades of the ADM and Mo03 products are summarized

in Table 7, Despite the nonoptimum evaporation

TABLE 8

6,149,883

EXAMPLE 7

Conven. Soda Ammo-

Roast- Ash nia Lime

ing Dig.* Dig.* Dig.* 10

Process (FIG. 1) (FIG. 2) (FIG. 3)

Recoveries & losses of Mo contained

in ore, %

Comparative Overall Molybdenum Recoveries

from Bingham Canyon Ore

Losses to bulk Cu-Mo flotation

tails

Losses to final Cu cone.,

smelter feed

Feed to Mo03 conversion process,

commercial roaster

this invention

Conversion process losses,

15.7

33.9

50.4

15.7

8.2

76.1

15.7

8.2

76.1

15.7

8.2

76.1

Comparison of Aliphatic and Aromatic Solvents

5 The use of aliphatic and aromatic solvents in the extraction

of soluble molybdenum values from an aqueous mixture

using an amine is demonstrated by the data presented below.

These data show the difference between aliphatic and aromatic

solvents as diluents for Alamine 336. These data show

that the solubility of molybdate-amine and the Si-, As-, Pmolybdate-

amine complexes are higher in the aromatic

solvent. In addition, no modifier (isodecanol) was needed

with the aromatic solvent. Normally, a modifier is added to

15 the amine when diluted with an aliphatic diluent to increase

the solubility of the extracted complex in the organic solvent.

The test procedure and reagents are described below:

commercial roaster

alkali digestion solids

Mo SX raffinate solution

Strip solution purification

solids

Ammonium sulfate product

Allowance for additional

unidentified losses not seen

in testwork

Overall Recovery to marketable

technical grade Mo03 product

*Dig. ~ Digestion

0.5

0.8 0.2 3.8

0.4 ~0.4 0.2

0.2 0.2 0.2 Leach solution Autoclave leach solution

Assay ~ 19 gil Mo, 53 gil Cu, 17 gil Fe, 81 gil H2SO4

nil nil nil Alamine 336 Tricaprylyl tertiary amine extractant

2.0 2.0 2.0 25 Exxal10 Isodecanol modifier

Escaid 110 Aliphatic petroleum solvent, diluent

Aromatic 150 Aromatic petroleum solvent, diluent

49.9 72.7 ';;73.3 69.9 Organics Organic 1 ~ 5 vol % Alamine 336 + 5 vol % Exxal10 in

aliphatic Escaid 110

Organic 2 ~ 5 vol % Alamine 336 in Aromatic 150

TABLE 9-A

Test 1 with organic 1 (aliphatic diluent)

3 min, 38 deg. C.

Phase break

min

3.5

Scum

Clarity

Assay

q/LMo

1-------- L.Org.1, 10 ml

1-------- Raff.1, 30 ml

[70ml]

v.slt.mky*

clear

7.0

0.42

Leach soln .30 ml '-------,----'

3 min. 30 deg. C. 1.2 no

'--------.. precipitate formed, second organic phase

*very slightly murky

6,149,883

21 22

TABLE 9-B

Test 2 with organic 2 (aromatic diluent

3 min, 35 deg. C.

PIS

min

Scum

Clarity

Assay

q/LMo

f-------- L.Org.l, 10 ml

f-------- Raff.l, 30 ml

v.slt.mky*

clear

7.1

0.36

[90ml]

3 min. 30 deg. C. 1.2 no

f-------- L.Org.2, 10 ml

f-------- Raff.2, 30 ml

v.slt.mky*

clear

1.42

[80ml]

.f---------l~L.Org.3, 10 ml

'--------- Raff.3, 30 ml

3 min. 30 deg. C. 1.0 no

v.slt.mky*

clear

8.5

is selective for the molybdenum values such that a

majority of the metal contaminants remain in the aqueous

mixture while a majority of the molybdenum

values are extracted into the organic solvent;

G. removing the extracted molybdenum values of step F

from the organic solvent by contacting the organic

solvent with an aqueous solution containing a stripping

reagent selective for molybdenum values;

H. crystallizing the extracted molybdenum values of step

G; and

I. calcining the crystallized molybdenum values of step H

to produce molybdenum trioxide.

2. The process of claim 1 in which the solubilization

compound of step C is an alkali metal compound.

3. The process of claim 2 in which the alkali metal

compound of step C is a sodium or potassium compound.

4. The process of claim 3 in which the alkali metal

compound of step C is selected from the group consisting of

sodium and potassium hydroxides, oxides, carbonates and

55 bicarbonates.

5. The process in claim 4 in which the organic solvent is

an aromatic organic solvent.

6. The process of claim 5 in which the extractive compound

of Step E is a nonprimary amine, the molecular

structure of which includes at least one hydrocarbon group

60 containing 6 or more carbon atoms.

7. The process of claim 6 in which the extractive compound

of step E is a tertiary amine.

8. The process of claim 7 in which the gangue minerals

include talc and sericite.

9. The process of claim 8 in which the extracted molybdenum

values of step F are removed through the action of

ammonium hydroxide.

Although the process of this invention has been described

in considerable detail by the preceding examples. This detail

is for the purpose of illustration only and is not to be

construed as a limitation on the spirit and scope of the

invention as described in the appended claims. 40

What is claimed is:

1. A process for producing molybdenum trioxide of at

least technical grade from molybdenite concentrate containing

molybdenite, at least one of copper in excess of 5 wt %

or naturally floatable gangue minerals in excess of 10 wt %, 45

each based on the weight of the concentrate, the process

comprising the steps of:

A. contacting an aqueous suspension of the concentrate

with oxygen under a partial pressure of free oxygen of 50

between about 75 and 200 psi and at a temperature of

at least about 150 C such that at least about 95% of the

molybdenite is oxidized to form a soluble hydrous

molybdic oxide and insoluble molybdenum trioxide;

B. separating the soluble molybdic oxide from the

insoluble molybdenum trioxide;

C. contacting the insoluble molybdenum trioxide with a

solubilization compound to form an aqueous mixture of

soluble molybdate values and insoluble residue;

D. separating the soluble molybdate values from the

insoluble residue;

E. combining the soluble molybdate values of step D with

the soluble molybdic oxide of step A to form an

aqueous mixture containing soluble molybdenum values;

F. contacting the aqueous mixture of step E with an

organic solvent containing an extractive compound that

6,149,883

23 24

* * * * *

G. crystallizing the soluble molybdenum values of step F;

and

H. calcining the crystallized molybdenum values of step

G to form molybdenum trioxide.

17. The process of claim 16 in which the organic solvent

is an aromatic solvent.

18. A process for producing molybdenum trioxide of at

least technical grade from molybdenite concentrate contain-

10 ing molybdenite, at least one of copper in excess of 5 wt %

or naturally floatable gangue minerals in excess of 10 wt %,

each based on the weight of the concentrate, the process

comprising the steps of:

A. contacting an aqueous suspension of the concentrate

with oxygen under a partial pressure of free oxygen of

between about 75 and 200 psi and at a temperature of

at least about 150 C such that at least about 95% of the

molybdenite is oxidized to form a soluble hydrous

molybdic oxide and insoluble molybdenum trioxide;

B. separating the soluble molybdic oxide from the

insoluble molybdenum trioxide;

C. contacting the insoluble molybdenum trioxide with at

least one of lime and magnesium hydroxide to form a

mixture containing soluble molybdate values;

D. combining the mixture of step C with the soluble

molybdic oxide fraction of step B to form a mixture of

soluble molybdenum values;

E. contacting the aqueous mixture of step D with an

organic solvent containing an extractive compound that

is selective for the molybdenum values such that a

majority of the metal contaminants remain in the aqueous

mixture while a majority of the molybdenum

values are extracted into the organic solvent;

F. removing the extracted molybdenum values of step E

from the organic solvent by contacting the organic

solvent with an aqueous solution containing a stripping

reagent selective for molybdenum values;

G. crystallizing the extracted molybdenum values of step

F; and

H. calcining the crystallized molybdenum values of step

G to form molybdenum trioxide of at least a technical

grade.

19. The process of claim 18 in which the organic solvent

45 is an aromatic solvent.

D. contracting the soluble molybdic oxide with an organic 35

solvent containing an extractant that is selective for the

soluble molybdic oxide such that a majority of the

metal contaminants remain in the aqueous mixture

while a majority of the soluble molybdic oxide is

extracted into the organic solvent;

E. removing the extracted molybdic oxide of step D from

the organic solvent by contacting the organic solvent

with an aqueous solution containing a stripping reagent

selective for molybdenum;

F. combining the soluble molybdate values of step C with

the extracted molybdic oxide of step E to form a

mixture of soluble molybdenum values;

10. The process of claim 9 in which the concentrate is in

the form of finely divided particles.

11. The process of claim 10 in which the particles have a

size of less than about PSG at 200 U.S. standard mesh.

12. The process of claim 11 in which the metal contami- 5

nants include copper, and comprising the further step of

recovering the copper from the aqueous product of step F by

sulfide precipitation.

13. The process of claim 12 comprising the further step of

recovering the copper from the aqueous product of step F by

an electrowinning technique.

14. The process of claim 7 in which copper is present in

excess of 5 wt % and the gangue minerals are present in

excess of 10 wt %.

15. The process of claim 1 in which the solubilization 15

compound is ammonium hydroxide.

16. A process for producing molybdenum trioxide of at

least technical grade from molybdenite concentrate containing

molybdenite, at least one of copper in excess of 5 wt %

or naturally floatable gangue minerals in excess of 10 wt %, 20

each based on the weight of the concentrate, the process

comprising the steps of:

A. contacting an aqueous suspension of the concentrate

with oxygen under a partial pressure of free oxygen of

between about 75 and 200 psi and at a temperature of 25

at least about 150 C such that at least about 95% of the

molybdenite is oxidized to form a soluble hydrous

molybdic oxide and insoluble molybdenum trioxide;

B. separating the soluble molybdic oxide from the

insoluble molybdenum trioxide; 30

C. contacting the insoluble molybdenum trioxide with

ammonium hydroxide to form soluble molybdate values;

UNITED STATES PATENT AND TRADEMARK OFFICE

CERTIFICATE OF CORRECTION

PATENT NO. : 6,149,883

DATED : November 21,2000

INVENTOR(S) : Ketcham, VictOL, et al

It is certified that error appears in the above-identified patent and that said Letters Patent is hereby

corrected as shown below:

Front page, second column [56] References Cited: Add the following line after the

last line --4,555,387 1l/85 Sabacky et al. .423/59--.

Column 5, line 67: Insert "the pH" after --upon--.

Column 6, line 59: Delete (V).

Column 6, line 61: Replace "N~Mo04+ H2S04 .... N~S04 + Mo03_H20(so,uble)"

with --N~Mo04 + H2S04 ~ N~S04 + Mo03-H20(so'ubler-'

Column 8, line 49: Replace "(NH4hMo04 + H2S04 .... MoO~-H20(solid) +

(NH4)2S04" with --(NH4)2Mo04 + H2S04 .... Mo03-H20(solid) + (NH4)2S0C'

Column 9, line 59: Replace "M003(soluble) + 2NH40H .... (NH4)2 Mo04(soluble) +

H20" with --M003(insoluble) + 2NH40H .... (NH4)2 M004(soluble) + H20--.

Column 10, line 13: Replace "M003(soluble) + Mg(OH)2 .... MgMo04(acidsoluble) +

H20" with --M003(insoluble) + Mg(OH)2 .... MgMo04(acidsoluble) + H20--.

Signed and Sealed this

Fifteenth Day of May, 2001

Attest:

Attesting Officer

NICHOLAS P. GODICI

Acting Director of (he United StclfeJ Palen( and Trademark Olf{c(~