U.S. patent application number 13/577678 was filed with the patent office on 2013-09-19 for separation of tungsten from ammonium molybdate solutions.
This patent application is currently assigned to Orchard Material Technology, LLC. The applicant listed for this patent is John E. Litz, Lawrence F. McHugh, Leonid N. Shekhter, Xiong Wei. Invention is credited to John E. Litz, Lawrence F. McHugh, Leonid N. Shekhter, Xiong Wei.
Application Number | 20130243673 13/577678 |
Document ID | / |
Family ID | 49157831 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130243673 |
Kind Code |
A1 |
Shekhter; Leonid N. ; et
al. |
September 19, 2013 |
SEPARATION OF TUNGSTEN FROM AMMONIUM MOLYBDATE SOLUTIONS
Abstract
Disclosed is process for the separation of tungsten from
molybdenum and more particularly from ammonium molybdate solutions.
The method comprises dissolving technical grade molybdenum trioxide
in an aqueous ammonium hydroxide solution and further adding
certain metal generating compounds to the aqueous solution thereby
generating a tungsten-containing precipitate. Calcium, iron and
manganese are the preferred metal generating compounds of the
invention. Certain temperature and pH values of the system, as
disclosed, are preferred for the precipitation of the tungsten from
the ammonia molybdate solution.
Inventors: |
Shekhter; Leonid N.;
(Ashland, MA) ; Litz; John E.; (Lakewood, CO)
; Wei; Xiong; (North Andover, MA) ; McHugh;
Lawrence F.; (North Andover, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shekhter; Leonid N.
Litz; John E.
Wei; Xiong
McHugh; Lawrence F. |
Ashland
Lakewood
North Andover
North Andover |
MA
CO
MA
MA |
US
US
US
US |
|
|
Assignee: |
Orchard Material Technology,
LLC
North Andover
MA
|
Family ID: |
49157831 |
Appl. No.: |
13/577678 |
Filed: |
February 7, 2011 |
PCT Filed: |
February 7, 2011 |
PCT NO: |
PCT/US2011/023852 |
371 Date: |
October 19, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12875385 |
Sep 3, 2010 |
|
|
|
13577678 |
|
|
|
|
61302378 |
Feb 8, 2010 |
|
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Current U.S.
Class: |
423/58 |
Current CPC
Class: |
C01G 49/0018 20130101;
C22B 34/34 20130101 |
Class at
Publication: |
423/58 |
International
Class: |
C22B 34/34 20060101
C22B034/34 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The present invention was not developed with the use of any
Federal Funds, but was developed independently by the inventors.
Claims
1. A process for the separation of tungsten from molybdenum
comprising the steps of (a) dissolving a compound containing
molybdenum and tungsten in an ammoniacal solution and (b) adding at
least one metal ion generating compound to the solution, the metal
ion generating compound being selected from calcium, iron and
manganese; wherein a precipitate comprising tungsten is
generated.
2. The process of claim 1, wherein the precipitate comprising
tungsten is generated in an amount of less than 125 ppm.
3. The process of claim 1, wherein the molybdenum containing
compound is technical grade molybdenum trioxide.
4. The process of claim 1, wherein the ammoniacal solution is
ammonium hydroxide.
5. The process of claim 1, wherein the calcium ion generating
compound is selected from calcium acetate, calcium hydroxide,
calcium chloride, and calcium nitrate.
6. The process of claim 5, wherein the temperature of the system is
between 10.degree. C. and 50.degree. C.
7. The process of claim 1, wherein the iron ion generating compound
is selected from ferric sulfate, ferrous molybdate, ferric
molybdate, ferric nitrate, and ferric chloride.
8. The process of claim 7, wherein the temperature of the system is
between 50.degree. C. and 70.degree. C.
9. The process of claim 1, wherein the manganese ion generating
compound is manganous chloride or manganous nitrate.
10. The process of claim 9, wherein the temperature of the system
is between 10.degree. C. and 60.degree. C.
11. The process of claim 1, wherein the pH of the system is between
7 and 10.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a U.S. National Stage application
under 35 U.S.C. .sctn.365 of PCT Application No. PCT/US2011/23852
filed Feb. 7, 2011, which claims priority under 35 U.S.C. .sctn.120
to U.S. Non-provisional patent application Ser. No. 12/875,385
filed on Sep. 3, 2010; which priority Under 35 U.S.C. .sctn.119(e)
to U.S. Provisional Patent Application Ser. No. 61/302,378 filed on
Feb. 8, 2010, the subject matter of which are hereby incorporated
by reference in their entirety.
BACKGROUND
Field and Background of the Invention
[0003] Tungsten was discovered and isolated in the late 18.sup.th
century. Tungsten is found in the minerals wolframite
(iron-manganese tungstate, FeWO.sub.4/MnWO.sub.4), scheelite
(calcium tungstate, (CaWO.sub.4), ferberite (FeWO.sub.4) and
hithnerite (MnWO.sub.4). In 2000, these minerals were mined and
used to produce about 37,400 tons of tungsten concentrates. China
produced over 75% of this total, with most of the remaining
production coming from Austria, Bolivia, Portugal, and Russia.
[0004] Tungsten is extracted from its ores in several stages. The
ore is eventually converted to tungsten(VI) oxide (WO.sub.3), which
is heated with hydrogen or carbon to produce powdered tungsten. It
can be used in that state or pressed into solid bars. Tungsten can
also be extracted by hydrogen reduction of WF.sub.6 or pyrolytic
decomposition. In its raw form, tungsten is a steel-gray metal that
is often brittle and hard to work, but, if pure, it can be worked
easily by forging, drawing, extruding or sintering. Of all metals
in pure form, tungsten has the highest melting point, 3,422.degree.
C. (6,192.degree. F.), lowest vapor pressure (at temperatures above
1,650.degree. C. (3,000.degree. F.)) and the highest tensile
strength.
[0005] Because it retains its strength at high temperatures and has
a high melting point, elemental tungsten is used today in many
high-temperature applications, such as light bulb, cathode-ray
tube, and vacuum tube filaments, heating elements, and rocket
engine nozzles. Its high melting point also makes tungsten suitable
for aerospace and high-temperature uses such as electrical,
heating, and welding applications, notably in the gas tungsten arc
welding process.
[0006] Because of its conductive properties and relative chemical
inertia, tungsten is also used in electrodes, and in the emitter
tips in electron-beam instruments that use field emission guns,
such as electron microscopes. In electronics, tungsten is used as
an interconnect material in integrated circuits, between the
silicon dioxide dielectric material and the transistors. It is used
in metallic films, which replace the wiring used in conventional
electronics with a coat of tungsten (or molybdenum) on silicon.
[0007] The electronic structure of tungsten makes it one of the
main sources for X-ray targets, and also for shielding from
high-energy radiations (such as radioactive samples). Tungsten
powder is used as a filler material in plastic composites, which
are used as a nontoxic substitute for lead in bullets, shot, and
radiation shields. Since this element's thermal expansion is
similar to borosilicate glass, it is used for making glass-to-metal
seals.
[0008] The hardness and density of tungsten are applied in
obtaining heavy metal alloys, such as high speed steel, Tungsten
high melting point makes tungsten a good material for applications
like rocket nozzles. Superalloys containing tungsten are used in
turbine blades and wear-resistant parts and coatings. Applications
requiring its high density include heat sinks, weights,
counterweights, ballast keels for yachts, tail ballast for
commercial aircraft, and as ballast in race cars for NASCAR and
Formula One.
[0009] High-density alloys of tungsten with nickel, copper or iron
are used for fishing lures (tungsten beads allow the fly to sink
rapidly). Some types of strings for musical instruments are wound
with tungsten wires. Its density, similar to that of gold, allows
tungsten to be used in jewelry as an alternative to gold or
platinum. Its hardness makes it ideal for rings that will resist
scratching, are hypoallergenic, and will not need polishing, which
is especially useful in designs with a brushed finish.
[0010] Tungsten played a significant role in World War II in
background political dealings. Portugal, as the main European
source of the element, was put under pressure from both sides,
because of its deposits of wolframite ore. Tungsten's resistance to
high temperatures and its strength in alloys made it an important
raw material for the weaponry industry. In armaments, tungsten,
usually alloyed with nickel and iron or cobalt to form heavy
alloys, is used in kinetic energy penetrators as an alternative to
depleted uranium, in applications where uranium's additional
pyrophoric properties are not required (for example, in ordinary
small arms bullets designed to penetrate body armor). Similarly,
tungsten alloys have also been used in cannon shells, grenades and
missiles, to create supersonic shrapnel.
[0011] Tungsten compounds are used in catalysts, inorganic pigments
(e.g. tungsten oxides), and as high-temperature lubricants
(tungsten disulfide). Tungsten carbide is used to make
wear-resistant abrasives and cutters and knives for drills,
circular saws, milling and turning tools used by the metalworking,
woodworking, mining, petroleum and construction industries and
accounts for about 60% of current tungsten consumption. Tungsten
oxides are used in ceramic glazes and calcium/magnesium tungstates
are used widely in fluorescent lighting, while tungsten halogen
bulbs are frequently used to light indoor photo shoots, and special
negative films exist to take advantage of tungsten's unique
disentangling properties. Crystal tungstates are used as
scintillation detectors in nuclear physics and nuclear medicine.
Other salts that contain tungsten are used in the chemical and
tanning industries.
[0012] Molybdenum minerals have been known from approximately the
same time as tungsten. Molybdenum is mined as a principal ore, and
is also recovered as a byproduct of copper and tungsten mining.
Molybdenum has similar physical properties as tungsten with the
sixth highest melting point of 2,623.degree. C. (4,753.degree.
F.).
[0013] The ability of molybdenum to withstand extreme temperatures
without significantly expanding or softening makes it useful in
applications that involve intense heat, including the manufacture
of aircraft parts, electrical contacts, industrial motors and
filaments. Most high-strength steel alloys contain 0.25% to 8%
molybdenum. More than 43,000 tons of molybdenum are used as an
alloying agent each year in stainless steels, tool steels, cast
irons and high-temperature superalloys.
[0014] Molybdenum is also used in steel alloys for its high
corrosion resistance and weldability. Molybdenum contributes
further corrosion resistance to "chrome-moly" type-300 stainless
steels (high-chromium steels that are corrosion-resistant already
due to their chromium content) and especially in the so-called
superaustenitic stainless steels. Molybdenum acts by increasing
lattice strain, thus increasing the energy required to dissolve out
iron atoms from the surface.
[0015] Because of its lower density and more stable price,
molybdenum is sometimes used instead of tungsten. An example is the
`M` series of high-speed steels such as M2, M4 and M42 as
substitution for the `T` steel series which contain tungsten.
Molybdenum can be implemented both as an alloying agent and as a
flame-resistant coating for other metals. Although its melting
point is 2,623.degree. C. (4,753.degree. F.), molybdenum rapidly
oxidizes at temperatures above 760.degree. C. (1,400.degree. F.)
making it better-suited for use in vacuum environments.
[0016] Other uses of molybdenum include radioisotopes in medical
procedures. Molybdenum disulfide (MoS.sub.2) is used as a solid
lubricant and a high-pressure high-temperature antiwear agent.
Molybdenum disilicide (MoSi.sub.2) is an electrically conducting
ceramic with primary use in heating elements operating at
temperatures above 1500.degree. C. in air. Molybdenum powder is
used as a fertilizer for some plants, such as cauliflower. The
element is also used in analyzers in power plants for pollution
controls acting as a catalyst for consistent readings by infrared
light. Ammonium heptamolybdate is used in biological staining
procedures. Lead molybdate (wulfenite) co-precipitated with lead
chromate and lead sulfate is a bright-orange pigment used with
ceramics and plastics.
[0017] Technical grade molybdenum oxide (TMO) is the most widely
traded molybdenum product worldwide. Molybdenum trioxide
(MoO.sub.3) is used as an adhesive between enamels and metals.
MoO.sub.3 is produced industrially roasting molybdenum disulfide,
the chief ore of molybdenum:
2MoS.sub.2+7O.sub.2.fwdarw.2MoO.sub.3+4SO.sub.2
[0018] Molybdenum trioxide is used to manufacture molybdenum metal,
which serves as an additive to steel and corrosion-resistant
alloys. The relevant conversion entails treatment of MoO.sub.3 with
hydrogen at elevated temperatures:
MoO.sub.3+3H.sub.2.fwdarw.Mo+3H.sub.2O
[0019] Technical grade molybdenum trioxide may contain from 50 to
1000 ppm of tungsten. High purity molybdenum powder requires that
the amount of tungsten be no greater than approximately 150 weight
ppm. Purification of tungsten from molybdenum solution is also
necessary in order to produce pure ammonium dimolybdate. The
separation of tungsten from molybdenum in aqueous solutions
presents a challenge due to the similarity of the chemical
properties of these two metals. The current invention presents a
method for separating tungsten from molybdenum trioxide in order to
obtain highly pure molybdenum and tungsten values.
[0020] U.S. Pat. No. 4,525,331 to Cheresnowsky et al. describes a
conventional purification method for technical grade molybdenum
trioxide. An aqueous solution of nitric acid and ammonium nitrate
is contacted with impure molybdenum concentrate to solubilize a
major portion of the impurities. The resulting molybdenum
concentrate is digested in ammonium hydroxide under conditions that
maximize iron precipitation and removal. The resulting ammonium
molybdate solution is separated from the sludge and further
purified by chelating cation exchange resin in the ammonium form.
Although the process provides ammonium molybdate having low
impurity levels of various metals, because the chemistries of
tungsten and molybdenum are very similar, tungsten is not separated
from the molybdenum during such process.
[0021] Several methods are known for the separation of tungsten
from molybdenum. U.S. Pat. No. 4,303,622 to Huggins et al. is a
process for recovering tungsten and molybdenum values from tungsten
concentrates by dissolving the concentrate in hot sodium hydroxide
solution and adding a sulfide precipitating agent to precipitate
molybdenum trisulfide (and some tungsten).
[0022] U.S. Pat. No. 3,969,478 to Zelikman et al. in and U.S. Pat.
No. 4,275,039 to Ozensoy et al. disclose a process for the
separation of tungsten and molybdenum comprised of adding nitric or
hydrochloric acid to obtain a pH from 0.5 to 4.3, introducing
hydrogen peroxide as a complexing agent, and then selectively
extracting molybdenum with an organic solvent phase. These
processes cannot be applied for the separation of tungsten from
ammonium molybdate solutions.
[0023] A publication entitled "Use of Hydrated Oxides of
Multivalent Metals for Effective Removal of Tungsten from
Molybdenum Compounds", by M. I. Semenov et al published in the
Journal of Applied Chem. USSR (Leningrad, 1984, 57(7), 1501-6)
relates to the separation of tungsten from molybdenum by adding
hydrated oxides of multivalent metals to a molybdate solution
containing tungsten to cause sorption of the tungsten. The
procedure was performed according to the publication by the
inventors hereof and it was found that the process took as long as
seven days, making any industrial application of the process
impractical and undesirable.
[0024] A publication entitled "Ammonium Molybdate of High Purity"
by Papageorgios, Panajotis, Plonka, Marian, Walczak, Wladylsaw,
(Przedsiebiorstwo Przemyslowo-Handlowe "Polskie Odczynniki
Chemiczne") Pol. 54,639 (Cl. C 01 g), 20 Jan. 1968, Appl. 28 Mar.
1966; 2 pp, relates to obtaining spectrally pure ammonium molybdate
by absorption on a freshly prepared suspension of products of
hydrolysis of tin salts. However, preliminary purification is
recommended and methyl alcohol, which is highly toxic, is used to
precipitate the ammonium molybdate.
[0025] U.S. Pat. No. 4,999,169 also to Cheresnowsky discloses a
process of separating tungsten from ammonium hydroxide solutions
containing molybdenum by sorption of the tungsten on tin (IV) oxide
hydrate. The sorption is selective and the molybdenum is left in
the solution. The process is difficult to commercialize because it
requires significant amounts of tin (IV) oxide hydrate. It is
difficult to imagine a practical way of rejuvenation of tin oxide
and further utilization of tungsten.
[0026] Still desired is an efficient process for the separation of
tungsten from molybdenum, specifically from ammonium molybdate
solutions. The present invention addresses the need by teaching a
simple and effective metallurgical process for separating tungsten
from molybdenum and thereby providing metal forms with improved
purity. The invention enables a continuous process. These and other
objects of the invention will be more clearly defined when taken in
conjunction with the following disclosure, the accompanying figures
and the appended claims.
[0027] The above references are incorporated by reference herein
where appropriate for appropriate teachings of additional or
alternative details, features and/or technical background.
SUMMARY OF THE INVENTION
[0028] The present invention is directed to a process for the
separation of tungsten from molybdenum and more particularly from
ammonium molybdate solutions. The method comprises dissolving
technical grade molybdenum trioxide in an aqueous ammonium
hydroxide solution and further adding certain metal generating
compounds to the aqueous solution thereby generating a
tungsten-containing precipitate. Calcium, iron and manganese are
the preferred metal generating compounds of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The embodiments will be described in detail with reference
to the following drawings in which like reference numerals refer to
like elements wherein:
[0030] FIG. 1 is a Pourbaix diagram of a calcium, tungsten,
molybdenum aqueous system at 25.degree. C.
[0031] FIG. 2 is a Pourbaix diagram of a calcium, tungsten,
molybdenum aqueous system at 50.degree. C.
[0032] FIG. 3 is a Pourbaix diagram of a calcium, tungsten,
molybdenum aqueous system at 75.degree. C.
[0033] FIG. 4 is a Pourbaix diagram of a calcium, tungsten,
molybdenum aqueous system at 10.degree. C.
[0034] FIG. 5 is a Pourbaix diagram of an iron, tungsten,
molybdenum aqueous system at 25.degree. C.
[0035] FIG. 6 is a Pourbaix diagram of an iron, tungsten,
molybdenum aqueous system at 50.degree. C.
[0036] FIG. 7 is a Pourbaix diagram of an iron, tungsten,
molybdenum aqueous system at 75.degree. C.
[0037] FIG. 8 is a Pourbaix diagram of a manganese, tungsten,
molybdenum aqueous system at 25.degree. C.
[0038] FIG. 9 is a Pourbaix diagram of a manganese, tungsten,
molybdenum aqueous system at 10.degree. C.
[0039] FIG. 10 is a Pourbaix diagram of a manganese, tungsten,
molybdenum aqueous system at 50.degree. C.
DETAILED DESCRIPTION
[0040] Technical grade molybdenum trioxide usually contains from
approximately 50 to 1000 ppm of tungsten, but any molybdenum
trioxide compound that contains tungsten may be used in the process
of the invention. Table 1 represents an example of the typical
composition of technical grade molybdenum trioxide. In methods
known to recover tungsten from wolframite and scheelite
concentrates, the ore is usually concentrated by gravity or
flotation methods and the concentrate is thereafter treated to
recover tungsten that is substantially pure and free of the
impurities listed in Table 1, except that due to the similarity of
the physical properties between tungsten and molybdenum, they
remain unseparated, as discussed in the background of the
invention. For purposes of definition in this specification,
"technical grade molybdenum trioxide" shall mean the technical
grade molybdenum trioxide that contains some or all of the
impurities listed in Table 1 and/or other minor metal impurities
not listed therein but that may be recovered or contained in the
ore.
TABLE-US-00001 TABLE 1 Composition of Technical Grade Molybdenum
Trioxide Metal % Metal % Mo 53.38 O 36.80 S 1.085 W 0.08 C 0.012 P
0.026 Cu 0.048 Fe 1.04 Si 4.0 Ca 1.97 Pb 0.035 Mg 1.0 Mn 1.33 K
0.07 Al 0.51 Ni 0.007
[0041] According to the process of the invention, the technical
grade molybdenum trioxide is added to an ammoniacal solution, most
preferably a solution of ammonium hydroxide. The technical grade
molybdenum trioxide ore is preferably added in a finely divided
state as this promotes dissolution of the compound. The ammonium
hydroxide is formed by the addition to water of either gaseous or
liquid anhydrous ammonia. Gaseous ammonia is the preferred form of
ammonia in the process of the invention. The ammonia can be
pre-dissolved in water. Dilute or concentrated solutions of
ammonium hydroxide are utilized, depending on the subsequent
process requirements. In a particularly preferred embodiment of the
process of the invention, a target of about 200 g to 280 g, more
preferably from 220 g to 260 g, and most preferably 240 g
molybdenum per liter of ammonium hydroxide is desired. To obtain
240 g molybdenum per liter of ammonium hydroxide, 175 g to 185 g
ammonium hydroxide per liter (85 g to 90 g ammonia per liter) is
required. Once the technical grade molybdenum trioxide is added to
the ammonium hydroxide solution, the ammonium hydroxide serves to
dissolve the molybdenum in the aqueous solution.
[0042] The content of the molybdenum in the ammonium molybdate
solution can be anywhere from 100 to 250 grams per liter. In such
solutions, the content of the tungsten which is to be separated
from the molybdenum in the solution is in the range of
approximately 5 to 250 ppm.
[0043] Once the ammonium molybdate solution is prepared, the
solution is then contacted with certain metal compounds that are
capable of reacting with the tungsten and causing precipitation of
the tungsten out of solution. In the preferred embodiments of the
invention, calcium, iron, and manganese compounds are used to
precipitate the tungsten from the ammonium molybdate solution.
Combinations or mixtures of the metal compounds can be utilized,
for example a calcium compound can be added together with an iron
compound. Once the metal compound is added, the components can be
further stirred, mixed or agitated in order to enhance the speed of
reaction.
[0044] It has been identified that the temperature and pH of the
system have an impact on the precipitation of the tungsten from the
ammonia molybdate solution. Though in general, an increase in
temperature increases the rate of any particular reaction, it has
been discovered that in the process of the invention, an increase
in temperature serves to effect the selectivity of the reaction and
therefore particular parameters as disclosed herein are necessary
in order to effectuate the operability of the method of the
invention.
[0045] A preferred tungsten precipitate generating metal of the
invention is calcium. Calcium ion forms a very strong compound with
the tungstate ion. FIGS. 1-4 are Pourbaix diagrams that demonstrate
the selective precipitation of tungsten with calcium ions at
various temperatures, 10.degree. C., 25.degree. C., 50.degree. C.
and 75.degree. C., respectively. It was determined that the
preferable temperature range for precipitation with calcium
compounds is from 10.degree. C. to 50.degree. C., more preferably
from 15.degree. C. to 40.degree. C. and more preferably from
20.degree. C. to 30.degree. C. In a preferred embodiment, the
selective precipitation of tungsten is attained using calcium
acetate or calcium hydroxide at room temperature (approximately
25.degree. C.). Using calcium compounds in the process of the
invention, the pH of the system will be maintained at greater than
approximately 2.0, preferably greater than 7.0 and increasing
slightly depending on the temperature of the system with the
preferred pH range being from 7.5 to 10. Other calcium compounds
useful in the process of the invention include, but are not limited
to, calcium chloride, and calcium nitrate.
[0046] Iron is another operable metal in the process of the
invention. It can be seen from FIGS. 5, 6 and 7 that iron may be
used to selectively precipitate tungsten from ammonium solutions in
a wide range of temperatures and pH values. Iron tungstate
(FeWO.sub.4) is the major precipitate formed during the process
demonstrated in FIGS. 5-7. Beyond operable conditions, other
unwanted precipiates will form, such as ferrous molybdate
(FeMoO.sub.4). Tables 2 and 3 demonstrate that although the
molybdenum content in the solution is much higher than that of
tungsten, selective precipitation of tungsten is possible with iron
compounds within certain temperature and pH conditions. Based on
the data derived from FIGS. 5-7, the operable range of the process
has a pH range of between 1.0 and 11.8 and temperature between
10.degree. C. and 70.degree. C.; more preferably the pH is between
6 and 10 and temperature between 40.degree. C. and 70.degree. C.;
and more preferably the pH range is 7 to 9 and the temperature is
60.degree. C. to 70.degree. C. In a preferred embodiment, the
temperature of the system using ferric sulfate is at approximately
50.degree. C. having a pH of between 7 and 10. Other iron compounds
useful in the process of the invention include, but are not limited
to ferrous molybdate, ferric molybdate, ferric nitrate, and ferric
chloride.
[0047] Manganese is another metal compound useful in the process of
the invention. FIGS. 8, 9 and 10 demonstrate that manganese ions
form both molybdate and tungstate species in a wide pH range,
preferably from 3 to 11, and can be used to precipitate tungsten
from ammonium molybdate solutions. Decreasing temperature improves
selectivity of tungsten precipitation with manganese compounds. The
preferred temperatures for the process using manganese compounds is
from 10.degree. C. to 60.degree. C. Some useful manganese compounds
include, but are no limited to, manganous chloride, and manganous
nitrate.
[0048] The tungsten containing precipitate may be separated from
the solution in any convenient way known in the art, such as
filtration. The tungsten can then be recovered from the filter
cake, washed, and utilized in ferroalloy processes. In a continuous
production industrial process of the invention, clean technical
grade molybdenum trioxide is generated. The resulting clean
technical grade molybdenum trioxide is substantially free of
tungsten, containing tungsten in an amount of less than
approximately 125 ppm, and depends greatly on the efficiency of the
removal procedure. The iron, calcium and manganese metal compounds
can also be separated and recovered after the separation of the
tungsten from the solution and further used as alloys and/or formed
into useful compounds of such metals.
EXAMPLES
[0049] In order to identify the possibility of tungsten removal,
thermodynamic simulations were carried out using HSC CHEMISTRY.RTM.
for Windows Thermodynamic Software 6.0 by Outokumpu Research Oy of
Finland. Two software modules were used: Reaction Equations and
Pourbaix Diagrams. The results are presented in the tables and
figures herein. The Pourbaix diagrams, also known as a potential/pH
diagrams, map out the potential stable or equilibrium phases of the
particular aqueous electrochemical system. The predominant ion
boundaries are represented by the lines indicated on the
diagrams.
[0050] Thermodynamic Analysis
[0051] Iron molybdate precipitation was obtained based on the data
of thermodynamic stability of iron tungstate in water based
solutions. Table 2 presents the thermodynamic stability of iron
molybdate (FeMoO.sub.4) in an aqueous solution.
TABLE-US-00002 TABLE 2 Thermodynamic Analysis of FeMoO.sub.4
Formation Fe(+2a) + MoO4(-2a) = FeMoO.sub.4 T deltaH deltaS deltaG
C. kcal cal/K kcal K Log (K) 0.000 1.799 40.803 -9.346 3.010E+007
7.479 10.000 2.965 44.996 -9.776 3.519E+007 7.546 20.000 3.908
48.274 -10.243 4.336E+007 7.637 30.000 4.731 51.033 -10.740
5.538E+007 7.743 40.000 5.497 53.519 -11.263 7.263E+007 7.861
50.000 6.242 55.863 -11.810 9.723E+007 7.988 60.000 6.979 58.110
-12.380 1.324E+008 8.122 70.000 7.720 60.299 -12.972 1.830E+008
8.262 80.000 8.479 62.481 -13.586 2.561E+008 8.408 90.000 9.265
64.676 -14.222 3.626E+008 8.559 100.000 10.087 66.906 -14.879
5.193E+008 8.715
[0052] Iron molybdate precipitation values for negative delta G
were obtained based on the data of thermodynamic stability of iron
tungstate (FeWO.sub.4) in an aqueous solution, demonstrated in
Table 3.
TABLE-US-00003 TABLE 3 Thermodynamic Analysis of FeWO.sub.4
Formation Fe(+2a) + WO4(-2a) = FeWO.sub.4 T deltaH deltaS deltaG C.
kcal cal/K kcal K Log (K) 0.000 -7.042 40.861 -18.203 3.677E+014
14.565 10.000 -6.182 43.956 -18.628 2.394E+014 14.379 20.000 -5.540
46.185 -19.079 1.679E+014 14.225 30.000 -5.019 47.932 -19.550
1.245E+014 14.095 40.000 -4.557 49.434 -20.037 9.663E+013 13.985
50.000 -4.116 50.819 -20.538 7.788E+013 13.891 60.000 -3.686 52.129
-21.053 6.489E+013 13.812 70.000 -3.256 53.402 -21.581 5.569E+013
13.746 80.000 -2.809 54.686 -22.121 4.909E+013 13.691 90.000 -2.337
56.002 -22.675 4.437E+013 13.647 100.000 -1.834 57.370 -23.241
4.105E+013 13.613
[0053] Tables 2 and 3 demonstrate that the formation of both
species, iron molybdate and iron tungstate, is thermodynamically
favorable, indicated by the negative delta G values. However, the
equilibrium constant for the formation of iron tungstate is seven
(7) orders of magnitude greater than that of iron molybdate.
Therefore, in principle, the selective precipitation of tungsten
seems to be thermodynamically feasible. In order to establish the
correct values of temperature and pH it was necessary to build
Pourbaix diagrams (FIGS. 1 through 8). These diagrams were built
using the ratios of the species contents from Table 1 that
represents the typical composition of technical grade molybdenum
trioxide.
Example 1
[0054] Calcium acetate and calcium hydroxide were used to
experimentally verify the general concept of the feasibility of
using calcium to precipitate tungsten from ammonium molybdate
solutions.
[0055] Required aliquots of either calcium acetate solution or
calcium hydroxide (as set forth in Table 4) were added to 100 mL of
the ammonium molybdate solution at room temperature (25.degree.
C.). The pH was kept at about 10.1. The slurry was agitated for
three hours and the precipitate was filtered and washed. The
solutions were submitted for analysis. The results are set forth in
Table 4.
TABLE-US-00004 TABLE 4 Precipitation of Tungsten with Calcium
Compounds Vol- ume, Mo W % W Ml g/L mg g/L mg Removed Mo/W Feed
Solution Filtrate 100 263 26300 0.349 34.9 0 754 Calcium Acetate
Addition = 4 mL Filtrate 174 115 20010 0.089 15.5 42 1290 Calcium
Acetate Addition = 5 mL Filtrate 174 510 88740 0.098 17.1 86 5189
Ca(OH).sub.2 Addition = 0.3 g Filtrate 170 478 81260 0.077 13.1 88
6203 Ca(OH).sub.2 Addition = 0.3 g Filtrate 186 193 35898 0.100
18.6 61 1930
Example 2
[0056] In this example, ferric molybdate was used for tungsten
precipitation. A sample of ferric molybdate was prepared by
dissolving 100 grams of ferric sulfate (20 grams iron) in water and
then adding to an ammonium molybdate solution. The slurry was
agitated for an hour and the precipitate was filtered and washed.
The weight of the wet cake containing 5% iron was 400 grams. An
ammonia digestion of 440 grams of leached cake was started by
sequential additions of cake and ammonium hydroxide maintaining the
pH at 8.5 to 8.7 at approximately 60.degree. C. Thirty minutes
after the last addition, 100 grams of the ferric molybdate cake was
added (about 5 g Fe/L) and the slurry was agitated for another 30
minutes. The slurry was filtered and the cake was washed.
Afterwards, 200 mL aliquots were heated to 60.degree. C. and ferric
molybdate additions of 2, 4, 8, and 16 grams were made (0.5, 1.0,
2.0, and 4.0 g Fe/L). After one hour of agitation, the slurries
were filtered. The solutions and the solids the solids were
submitted for analysis. Major filtrate analysis data are set forth
in Table 5.
TABLE-US-00005 TABLE 5 Precipitation of Tungsten with Ferric
Molybdate Mo Volume, Weight, W mL g/L g g/L Mo/W pH Fe Addition =
0.5 g/L Filtrate ~200 228.9 45.78 0.067 3416 7.8 Fe Addition = 1.0
g/L Filtrate ~200 216.2 43.24 0.046 4700 7.4 Fe Addition = 2.0 g/L
Filtrate ~200 207 41.4 0.026 7962 7.8 Fe Addition = 4.0 g/L
Filtrate ~200 212 42.41 0.016 13253 7.8
[0057] Analysis of the data presented in Tables 4 and 5 confirmed
the thermodynamic calculations and demonstrated the feasibility of
tungsten removal from ammonium molybdate solutions.
[0058] Although the present invention has been described in
conjunction with preferred embodiments, it is to be understood by
those skilled in the art that modifications and variations thereto
may be resorted to without departing from the spirit and scope of
the invention. Such modifications and variations are considered to
be within the purview and scope of the invention and the appended
claims.
[0059] Any reference in this specification to "one embodiment," "an
embodiment," "example embodiment," etc., means that a particular
feature, structure, or characteristic described in connection with
the embodiment is included in at least one embodiment of the
invention. The appearances of such phrases in various places in the
specification are not necessarily all referring to the same
embodiment. Further, when a particular feature, structure, or
characteristic is described in connection with any embodiment, it
is submitted that it is within the purview of one skilled in the
art to effect such feature, structure, or characteristic in
connection with other ones of the embodiments.
[0060] Although embodiments have been described with reference to a
number of illustrative embodiments thereof, it should be understood
that numerous other modifications and embodiments can be devised by
those skilled in the art that will fall within the spirit and scope
of the principles of this disclosure. More particularly, various
variations and modifications are possible in the component parts
and/or arrangements of the subject combination arrangement within
the scope of the disclosure, the drawings and the appended claims.
In addition to variations and modifications in the component parts
and/or arrangements, alternative uses will also be apparent to
those skilled in the art.
* * * * *