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
I
Alkaline I
Leach
NaHS-"1 Sulfide I
IPrecioitationl
Molybdic
Oxide
Ammonium Sulfate
I
=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•
I
Thickener
- - - - -
Filter
ol( I
Stripped
Organic
Moly SX Llol( I Moly SX
Extraction • Stripping
Loaded
Organic
,
Hs~lsulfide LI
Precipitation
,
Thickener
- - - - - Co
Filter
I
L~·mes~one~INeutralization
and L~me
Na
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
1 Thickener
I - - - - - Filter 1
I
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
I
if
aHs+1 Sulfide LI
Precipitation
Thickener
- - - - - Co
Filter
I
L imes~one+INeutralization
and LJ.me
N
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
2
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
1
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.
4
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.
40
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
3
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
<0.05
Roaster
Feed
Molybdenite
Concentrate %
>55
<0.5
<0.03
<0.05
<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)
Mo
Cu
As
P
Pb
S
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.
65
60
(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, %
Mo
Cu
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, %
Mo
Cu
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
25
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.
20
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
Mo
Cu
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, %
50
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, %
55
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.
5
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
10
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
17
TABLE 6
Lime Digestion Test Results
18
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
0.002
<0.001
Mo03 product
Assay, %
52.6
0.89
ADM product
Mo
S
Si02
Cu
As
P
Pb
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, %
20
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
19
TABLE 8
6,149,883
20
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
20
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
30
TABLE 9-A
Test 1 with organic 1 (aliphatic diluent)
3 min, 38 deg. C.
Phase break
min
3.5
Scum
no
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
~l
3 min, 35 deg. C.
PIS
min
.8
Scum
no
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
13
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
17
8.5
35
65
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
* * * * *
40
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(~