U.S. patent application number 10/468215 was filed with the patent office on 2004-05-06 for extraction of metals.
Invention is credited to Mukunthan, Kannappar, Osborn, Steve, Ratchev, Ivan, Strezov, Lazar.
Application Number | 20040084323 10/468215 |
Document ID | / |
Family ID | 3827191 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040084323 |
Kind Code |
A1 |
Strezov, Lazar ; et
al. |
May 6, 2004 |
Extraction of metals
Abstract
A method of producing a metal or an alloy from metalliferous
material by removing O,S, or N from a solid body of metalliferous
material by electrolysis in an electrolytic cell is disclosed. The
cell includes a molten halide salt or mixture of halide salts as an
electrolyte. The cation of the salt is selected from the group that
includes Ca, Ba, Li, Na, K, Mg, Sr, Cs and Y. In one aspect of the
invention the method includes conducting the electrolysis under
conditions wherein the solid body of metalliferous material is made
part of a cathode of the electrolytic cell, the cathode includes a
conductor for electrically connecting the cathode with an
electrical potential, the conductor has high resistance to chemical
attack by the electrolyte at high temperatures, and the conductor
is at least partly immersed in the electrolyte. In another aspect
of the invention the method includes conducting the electrolysis
under conditions wherein the potential applied between an anode and
the cathode of the electrolytic cell is chosen such that permanent
decomposition of the electrolyte is avoided to an extent that
substantial deposition of the electrolyte cation at the cathode is
avoided and anode material transport towards and into the cathode
is substantially prevented. A cathode for use in the method is also
disclosed, which cathode includes a body of metalliferous material
distributed around one or more electrical conductors that are
substantially inert in the electrolyte at high temperatures and
which provide a plurality of reduction zones at the cathode.
Inventors: |
Strezov, Lazar; (New South
Wales, AU) ; Ratchev, Ivan; (Georgetown, AU) ;
Osborn, Steve; (Valentine, AU) ; Mukunthan,
Kannappar; (Rankin Park, AU) |
Correspondence
Address: |
MILES & STOCKBRIDGE PC
1751 PINNACLE DRIVE
SUITE 500
MCLEAN
VA
22102-3833
US
|
Family ID: |
3827191 |
Appl. No.: |
10/468215 |
Filed: |
December 22, 2003 |
PCT Filed: |
February 18, 2002 |
PCT NO: |
PCT/AU02/00168 |
Current U.S.
Class: |
205/363 ;
205/367 |
Current CPC
Class: |
C22B 34/129 20130101;
C22B 34/1263 20130101; C25C 3/00 20130101; C25C 3/28 20130101 |
Class at
Publication: |
205/363 ;
205/367 |
International
Class: |
C25C 003/00; C25C
003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2001 |
AU |
PR 3172 |
Claims
1. A method of producing a metal or an alloy from metalliferous
material by removing an impurity (I) selected from the group
including O, S, or N from a solid body of metalliferous material by
electrolysis in an electrolytic cell that includes molten halide
salt or mixture of halide salts as an electrolyte, wherein the
cation of said salt is selected from the group that includes Ca,
Ba, Li, Na, K, Mg, Sr, Cs and Y, which method includes conducting
the electrolysis under conditions wherein: (a) the potential
applied between an anode and a cathode of the electrolytic cell is
chosen such that permanent decomposition of the electrolyte is
avoided to an extent that substantial deposition of the electrolyte
cation at the cathode is avoided; and (b) the body is made part of
the cathode of the electrolytic cell, the cathode includes a
conductor for electrically connecting the cathode with an
electrical potential, the conductor has high resistance to chemical
attack by the electrolyte at high temperatures, and the conductor
is at least partly immersed in the electrolyte; and (c) O, S, or N
is removed from the cathode and passes into solution and/or
chemically reacts with the electrolyte cation.
2. The method defined in claim 1 wherein the metalliferous material
contains an oxide, sulfide, carbide or nitride of said metal.
3. The method defined in claim 1 or claim 2 wherein the
metalliferous material is a titanium-containing material.
4. The method defined in claim 3 wherein the titanium-containing
material is titania.
5. The method defined in any one of the preceding claims wherein
the impurity is oxygen.
6. The method defined in any one of the preceding claims wherein
the anode is formed from graphite.
7. A method of producing a metal or an alloy from metalliferous
material by removing an impurity (I) selected from the group
including O, S, or N from a solid body of metalliferous material by
electrolysis in an electrolytic cell that includes molten halide
salt or mixture of halide salts an an electrolyte, wherein the
cation of said salt is selected from the group that includes Ca,
Ba, Li, Na, K, Mg, Sr, Cs and Y, which method includes conducting
the electrolysis under conditions wherein: (a) the potential
applied between an anode and a cathode of the electrolytic cell is
chosen such that permanent decomposition of the electrolyte is
avoided to an extent that substantial deposition of the electrolyte
cation at the cathode is avoided and anode material transport
towards and into the cathode is substantially prevented; (b) the
body is made part of the cathode of the electrolytic cells; and (c)
O, S, C or N is removed from the cathode and passes into solution
and/or chemically reacts with the electrolyte cation.
8. The method defined in claim 7 wherein the cathode includes a
conductor having high resistance to chemical attack by the
electrolyte at high temperatures for connecting the cathode with an
electrical potential and the conductor is at least partly immersed
in the electrolyte.
9. The method defined in claim 7 or claim 8 wherein the
metalliferous material contains an oxide, sulfide, carbide or
nitride of said metal.
10. The method defined in any one of claims 8 to 9 wherein the
metalliferous material is a titanium-containing material.
11. The method defined in claim 10 wherein the titanium-containing
material is titania.
12. The method defined in any one of claims 7 to 11 wherein the
impurity is oxygen.
13. The method defined in any one of claims 7 to 12 wherein the
anode is formed from graphite.
14. A cathode for use in the method defined in any one of the
preceding claims includes the body of metalliferous material
distributed around one or more electrical conductors that are
substantially inert in the electrolyte at high temperatures and
which provide a plurality of reduction zones at the cathode.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to methods of producing metals
from metalliferous materials such as metal oxides.
BACKGROUND OF THE INVENTION
[0002] It is well known to produce metals from metalliferous ores
by a methods that include the steps of: 1) concentrating an ore; 2)
reducing the ore concentrate under high temperature conditions in
the presence of a suitable reductant and producing a crude metal;
and 3) refining the crude metal.
[0003] The present invention is concerned with alternative methods
of producing metals from metalliferous materials that are based on
the use of electrochemical cells.
PRIOR ART
[0004] A. A paper entitled "Electrochemical deoxidation of
titanium" published in Metallurgical Transactions B, Volume 24B,
June 1993, pages 449-445 (Authors: T H Okabe, M Nakamura, T Oishi
and K Ono).
[0005] The Okabe et al paper discloses an electrochemical method of
removing oxygen dissolved in titanium.
[0006] The paper reports experimental work on an electrolytic cell
that included a cathode of titanium having up to 1400 ppm dissolved
oxygen and an anode of graphite. The cathode and the anode were
immersed in a molten CaCl.sub.2 electrolyte bath. Electrical
potentials between 0 and 6V were applied between the anode and the
cathode. CaCl.sub.2 was employed to produce calcium and to
facilitate the calcium reaction by decreasing the activity of the
electrolytic by-product CaO. The calcium potential in CaCl.sub.2
was increased at the titanium cathode surface as a result of the
application of the electrical potential across the anode and the
cathode. This resulted in deoxidisation of the cathode by the
electrolytically produced calcium or by calcium of high activity in
the CaCl.sub.2. The resulting oxygen ions, which were mainly
present in the deoxidisation product in the electrolyte, reacted at
the graphite anode to form CO or CO.sub.2 gas that was removed from
the system.
[0007] B. A paper entitled "Electrochemical deoxidation of
yttrium-oxygen solid solutions" published in Journal of Alloys and
Compounds, Volume 237, 15 Apr. 1996, pages 150-154 (Authors: T H
Okabe, T N Deura, T Oishi, K Ono and D R Sadoway).
[0008] The Okabe et al paper discloses an electrochemical method of
removing oxygen dissolved in yttrium.
[0009] The paper describes experimental work on solid yttrium
containing dissolved oxygen. The yttrium was placed in a titanium
basket cathode and thereafter immersed in a bath of molten
CaCl.sub.2 electrolyte. The CaCl.sub.2 electrolyte bath was
contained in a titanium crucible and a constant voltage of between
3.2 to 3.8V was applied between the cathode and a graphite anode
submerged in the electrolyte. Electrolysis was carried out at 1223K
(950.degree. C.) for a specified time.
[0010] C. International application PCT/GB99/01781 (patent
publication WO99/64638)(Fray et al).
[0011] The Fray et al International application discloses two
potential applications of a "discovery" in the field of
metallurgical electrochemistry.
[0012] One application is the direct production of metal from a
metal oxide.
[0013] The other application is the removal of impurities that are
"dissolved" in a solid metal. The same basic process is said to be
applicable to both applications.
[0014] The "discovery" in the realisation that an electrochemical
method can be used to ionise oxygen contained in a solid metal so
that the oxygen dissolves in an electrolyte", compare page 5, lines
14-16. The International application discloses that when a suitably
negative potential in applied in an electrochemical cell with an
oxygen-containing metal as a cathode, a reaction occurs whereby
oxygen is ionised and is subsequently able to dissolve in the
electrolyte of the cell.
[0015] The International application discloses an electrolytic cell
that includes a body of a metalliferous material (such as a metal
oxide in which impurities are dissolved) as a cathode of the cell.
The cathode is immersed in a molten bath of a suitable electrolyte.
A predetermined electrical potential that is lower than the
decomposition potential of the electrolyte is applied between the
cathode and a suitable anode (either a separate graphite anode or
the electrolyte crucible). The potential is chosen such that it has
a value that allows a selected impurity (i.e. O, S, C or N) to be
ionised and thus diffuse through the body of metalliferous material
into the electrolyte where it dissolves.
[0016] The International application lists a substantial number of
metals that are said to be susceptible for use in the
above-described method. These metals are titanium (Ti), silicon
(Si), germanium (Ge), zirconium (Zr), hafnium (Hf), samarium (Sm),
uranium (U), aluminium (Al), magnesium (Mg), neodymium (Nd),
molybdenum (Mo), chromium (Cr), niobium (Nb) or any alloys
thereof.
[0017] All of the examples in the International application relate
to the "purification" and/or reduction of titanium, titania, and
specific titanium/aluminium alloys, namely Ti6Al4V, compare pages
9-14 of the International application. Example 12 relates to the
creation of a Ti--Al alloy starting from a mixture of TiO.sub.2 and
Al.sub.20.sub.3. The ranges of applied voltage in the different
samples varied from as low as 1.75V (see example 2) to 3.3V
(compare example 3). Most experiments were conducted at a
controlled voltage of 3.0V. Process times varied. Crucibles used
were made from alumina, graphite, or titanium whereby the anode was
either the crucible or a separate graphite rod. The only
electrolyte used in all of the examples was CaCl.sub.2.
SUMMARY OF INVENTION
[0018] Experimental work was carried out at the Minerals Technology
Centre, Newcastle Laboratories, of the applicant to reproduce the
experiments carried out the above-referenced prior art
documents.
[0019] The experimental work resulted in the following findings and
inventions.
[0020] 1. Titanium of very low oxygen concentration could be
produced directly from titania by electrolysis in molten
CaCl.sub.2.
[0021] However, cell modification was required to reduce titania in
an electrolytic cell, as the Fray et al International application
in particular is silent on how to set up an electrolytic cell in
order to achieve reduction of a good electrical insulator such as
titania. Reduction of titania could not be achieved within required
parameters by following the experimental set-up disclosed in the
Fray et al International application.
[0022] Accordingly, a first aspect of the invention in based on the
realisation that the type of cathode leads in electrical contact
with TiO.sub.2 and CaCl.sub.2 electrolyte severely influence the
titania reduction process. While there in only a preliminary
understanding of the mechanism, it is likely that proper selection
of the material and the type of electrical contact will be an
important part of the electrolytic cell design specific to metal
oxide to be reduced and the electrolyte employed therefor.
[0023] Accordingly, the first aspect of the invention is a method
of producing a metal or an alloy from metalliferous material by
removing an impurity (I) selected from the group including O, S, or
N from a solid body of metalliferous material by electrolysis in an
electrolytic cell that includes molten halide salt or mixture of
halide salts as an electrolyte, wherein the cation of said salt is
selected from the group that includes Ca, Ba, Li, Na, K, Mg, Sr, Cs
and Y, which method includes conducting the electrolysis under
conditions wherein:
[0024] (a) the potential applied between an anode and a cathode of
the electrolytic cell is chosen such that permanent decomposition
of the electrolyte is avoided to an extent that substantial
deposition of the electrolyte cation at the cathode is avoided;
and
[0025] (b) the body is made part of the cathode of the electrolytic
cell, the cathode includes a conductor for electrically connecting
the cathode with an electrical potential, the conductor has high
resistance to chemical attack by the electrolyte at high
temperatures, and the conductor is at least partly immersed in the
electrolyte; and
[0026] (c) O, S, or N is removed from the cathode and passes into
solution and/or chemically reacts with the electrolyte cation.
[0027] The metalliferous material may contain an oxide, sulfide,
carbide or nitride of said metal.
[0028] Preferably the metalliferous material is a
titanium-containing material.
[0029] Preferably the impurity in oxygen.
[0030] Preferably the titanium-containing material is titania.
[0031] Preferably the anode is formed from graphite.
[0032] Preferably the electrolyte is CaCl.sub.2.
[0033] 2. Carbon was detected in reduced metal pellets produced in
the experiments.
[0034] While the source of the carbon was the carbon anode employed
in the experiments, the mechanism by which carbon found its way
Into the reduced metal is not fully understood. The absolute levels
of carbon in some spots of the metal pellet were too high to
ignore.
[0035] Accordingly, in a second aspect of the invention there is
provided a method of producing a metal or an alloy from
metalliferous material by removing an impurity (I) selected from
the group including O, S, or N from a solid body of metalliferous
material by electrolysis in an electrolytic cell that includes
molten halide salt or mixture of halide salts as an electrolyte,
wherein the cation of said salt is selected from the group that
includes Ca, Ba, Li, Ha, A, Mg, Sr, Cs and Y, which method includes
conducting the electrolysis under conditions wherein:
[0036] (a) the potential applied between an anode and a cathode of
the electrolytic cell to chosen such that permanent decomposition
of the electrolyte is avoided to an extent that substantial
deposition of the electrolyte cation at the cathode is avoided and
anode material transport towards and into the cathode is
substantially prevented;
[0037] (b) the body is made part of the cathode of the electrolytic
cell; and
[0038] (c) O, S, or N is removed from the cathode and passes into
solution and/or chemically reacts with the electrolyte cation.
[0039] Preferably the cathode includes a conductor having high
resistance to chemical attack by the electrolyte at high
temperatures for connecting the cathode with an electrical
potential and the conductor is at least partly immersed in the
electrolyte.
[0040] The metalliferous material may contain an oxide, sulfide,
carbide or nitride of said metal.
[0041] Preferably the metalliferous material is a
titanium-containing material.
[0042] Preferably the impurity in oxygen.
[0043] Preferably the titanium-containing material is titania.
[0044] Preferably the anode is formed from graphite.
[0045] Preferably the electrolyte is CaCl.sub.2.
[0046] 3. In using the above-described inventive methods, it was
confirmed that Al.sub.2O.sub.3 in contact with a TiO.sub.2 pellet
body can be reduced and forms alloys with the reduced titanium.
[0047] 4. It was found that silicon could be reduced from SiO.sub.2
by electrolysis in molten CaCl.sub.2 when employing the
above-described methods. However, chlorine evolution in the cane of
SiO.sub.2 reduction was observed to a higher degree compared to
TiO.sub.2 reduction.
[0048] 5. Reduction of Al from Al.sub.2O.sub.3 pellets by the
above-described method was also attempted.
[0049] It was observed that reduction to Al took place only around
the site of contact between the pellet and the electric leads
connecting the cathode to the potential source. The portion of the
pellet away from the cathode leads was not reduced at all.
[0050] This observation again suggests that the electrical
conductivity of the cathode was a factor that affected the
reduction process.
[0051] Accordingly, in another aspect of the invention, there is
provided a cathode for use in the above described methods, wherein
the cathode includes the body of metalliferous material distributed
around one or more electrical conductors that are substantially
inert in the electrolyte at high temperatures and which provide a
plurality of reduction zones at the cathode.
[0052] 6. The mechanisms of removal of oxygen from titanium,
titania, yttrium and aluminium-titanium alloys suggested by the
Fray et al International application and the Okabe et al papers
using the electrolytic methods described are far from clear at
present. The Fray et al International application suggests that the
mechanism disclosed in the Okabe papers is incorrect. It is
believed that both mechanisms are speculative insofar as other
metals and oxides are concerned. Also, while there is evidence that
the type of electrolyte influences the process parameters, its
properties and role in the presented mechanisms is vague and only
qualitative.
Experimental data for the Inventions
A. Reduction of Titania
First Experiment
[0053] The purpose of the first experiment was to confirm (or
otherwise) the feasibility of producing metallic titanium from
titania by direct electrochemical reduction in molten
CaCl.sub.2.
[0054] Specifically, the purpose of the first experiment was to
confirm (or otherwise) the set-up described in the Fray et al
International application. Accordingly, the conditions of the
experiment were kept as close as possible to the conditions in the
examples of the International application.
[0055] The underlying principle of the process, according to the
Fray et al International application, is based on ionization of
oxygen in an oxide as a result of applying suitable negative
potential to it in electrochemical cell and subsequent dissolution
in the electrolyte.
II. Experimental Method and Equipment
[0056] The experimental set-up is shown in FIG. 1.
[0057] With reference to FIG. 1, the electrochemical cell included
a graphite crucible equipped with a graphite lid. The crucible was
used as the cell anode. A stainless steel rod was used to secure
electrical contact between a d/c power supply and the crucible. The
cell cathode consisted of Kanthal or platinum wire connected at one
end to the power supply and TiO.sub.2 pellets suspended from the
other end of the wire. An alumina tube was used as an insulator
around the cathode.
[0058] A type B thermocouple, contained in an alumina sheath, was
immersed in the electrolyte in close proximity to the pellets.
[0059] Two types of pellets were used. One type was slip-cast and
the other type was pressed. Both types of pellets were made from
analytical grade TiO.sub.2 powder. Both types of pellets were
sintered in air at 850.degree. C. One pressed and one slip-cast
pellet were used in the experiment.
[0060] The experiment was conducted at 950.degree. C. Voltages up
to 3V were applied between the crucible wall and the Kanthal or
platinum wire.
[0061] The power-supply maintained a constant voltage throughout
the experiment. The voltage and resulting cell current were logged
using LabVIEW.TM. data acquisition software.
III. Experimental Results
[0062] With reference to FIGS. 2 and 3, the constant voltage (3V)
used in the experiment produced an initial current of approximately
1.2 A. A continuous drop in the current was observed during the
initial 2 hours. After that a gradual increase in the current up to
1 A was observed.
[0063] At the end of the experiment the cell was removed from the
furnace and quenched in water. The solid CaCl.sub.2 was dissolved
by water and the two pellets were recovered.
[0064] SEM images of the cross-sections of the two pellets are
shown in FIGS. 4 and 5.
[0065] The presence of virtually pure metallic titanium in both
pellets was confirmed by EPMA analysis. The analysis also showed
areas of partially reduced titania. The EPMA results are shown in
FIGS. 6 and 7.
[0066] Carbon was detected at various locations within the pellets
and its content varied up to 18 wt %.
B. Reduction of Silicon
I. Experimental Method and Equipment
[0067] The experimental set-up was essentially the same an in the
case of titanium. The cathode consisted of platinum-rhodium wire
and SiO.sub.2 pellets suspended from the end of the wire.
[0068] The experiment was conducted at 950.degree. C.
II. Experimental Results
[0069] The voltage used in the experiment was 3V, which produced
initial current of approximately 1.5 A as shown in FIG. 8. After
that a gradual decrease in the current to 0.65 A was observed.
[0070] The working potential was selected as 3V in order to
overcome resistance and overvoltage. However, chlorine liberation
was observed at 3V although it is below the theoretical
decomposition potential of CaCl.sub.2, which is 3.25V at
950.degree. C.
[0071] The experiment was terminated after 4 hours. The partially
reduced pellets were isolated by dissolution of the CaCl.sub.2 in
water. The surface and interior of the sample were analysed by
SEM.
[0072] Analysis of the surface of the pellets showed the presence
of some oxygen, indicating that there was partial reduction only in
these regions.
[0073] However, the oxygen concentration in these regions was much
lower than the oxygen concentration in SiO.sub.2--as is shown in
FIG. 9.
[0074] The structure of the partially reduced regions of the
pellets in shown in FIG. 10. Regions of different phases, such as
SiO.sub.2 and 2CaO.SiO.sub.2, were detected--see FIGS. 11 to
13.
[0075] Pure unreduced SiO.sub.2 was present in the centre of the
pellets.
[0076] Pure Si was identified in the proximity of the platinum
leads--as shown in FIGS. 14 to 17.
[0077] Many modifications may be made to the inventions as
described above without departing from the spirit and scope of the
inventions.
* * * * *