U.S. patent application number 10/569602 was filed with the patent office on 2006-10-05 for method and apparatus for producing metal.
Invention is credited to Masahiko Hori, Tadashi Ogasawara, Toru Uenishi, Makoto Yamaguchi.
Application Number | 20060219053 10/569602 |
Document ID | / |
Family ID | 34269262 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060219053 |
Kind Code |
A1 |
Ogasawara; Tadashi ; et
al. |
October 5, 2006 |
Method and apparatus for producing metal
Abstract
The present invention relates to a method for producing a metal
by a direct oxide reduction process with Ca. A CaCl.sub.2-based
molten salt containing Ca is held in a reduction chamber 1, a metal
oxide is introduced into the molten salt in the reduction chamber
1, and the metal oxide is reduced with the Ca in the molten salt to
form said metal. The metal formed in the molten salt is separated
from the molten salt in a separation means 2, and the molten salt
deprived of the metal is introduced into a chlorination chamber 7
and subjected to chlorination treatment with chlorine gas to
eliminate the byproduct CaO in the molten salt. The molten salt
after chlorination treatment is introduced into an electrolysis
chamber 8 and electrolyzed for the formation of Ca and chlorine
from CaCl.sub.2, and the thus-formed Ca or Ca-containing molten
salt is transferred from the electrolysis chamber 8 to the
reduction chamber 1. The chlorine obtained in the electrolysis
chamber 8 is used in the chlorination chamber 7. Thus, the present
invention provides a metal production method and an apparatus
wherein high levels of productivity are obtained and the product
metal can be inhibited from carbon contamination due to CaO,
without any generation of CO.sub.2 from the production process,
while their being based on the direct oxide reduction process
comprising the step of reducing a metal oxide with Ca.
Inventors: |
Ogasawara; Tadashi; (Hyogo,
JP) ; Yamaguchi; Makoto; (Hyogo, JP) ; Hori;
Masahiko; (Hyogo, JP) ; Uenishi; Toru; (Hyogo,
JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW
SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
34269262 |
Appl. No.: |
10/569602 |
Filed: |
July 14, 2004 |
PCT Filed: |
July 14, 2004 |
PCT NO: |
PCT/JP04/10024 |
371 Date: |
February 24, 2006 |
Current U.S.
Class: |
75/10.54 |
Current CPC
Class: |
C22B 34/1268 20130101;
C22B 34/129 20130101; C25B 1/26 20130101; C25C 3/02 20130101; C22B
5/04 20130101 |
Class at
Publication: |
075/010.54 |
International
Class: |
C22B 34/00 20060101
C22B034/00; C22B 34/12 20060101 C22B034/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2003 |
JP |
2003-304176 |
Claims
1. A method for producing a metal which comprises: a reduction step
in which a metal oxide is introduced into a CaCl.sub.2-based molten
salt containing Ca for the formation of said metal by reduction of
the metal oxide with Ca in the molten salt; a separation step in
which said metal formed in the molten salt is separated from the
molten salt; a chlorination step in which the molten salt after
separation of said metal is subjected to chlorination treatment
with chlorine gas to chlorinate the byproduct CaO in the molten
salt; and an electrolysis step in which the molten salt after
chlorination treatment is electrolyzed to form Ca and chlorine from
CaCl.sub.2, and the thus-formed Ca or Ca-containing molten salt is
sent to the above-mentioned reduction step.
2. A method for producing a metal which comprises: a reduction step
in which a metal oxide is introduced into a CaCl.sub.2-based molten
salt containing Ca for the formation of said metal by reduction of
the metal oxide with Ca in the molten salt; a separation step in
which the metal formed in the molten salt is separated from the
molten salt; a chlorination step in which the molten salt after
separation of said metal is subjected to chlorination treatment
with chlorine gas to chlorinate the byproduct CaO in the molten
salt; and an electrolysis step in which the molten salt after
chlorination treatment is electrolyzed to form Ca and chlorine from
CaCl.sub.2, and the thus-formed Ca or Ca-containing molten salt is
sent to the above-mentioned reduction step, wherein, in said
reduction step, the metal formed is allowed to settle and the metal
that has settled is drawn out together with the molten salt and
transferred to the separation step.
3. A method for producing a metal according to claim 1, wherein
said metal is one of titanium, tungsten, niobium, tantalum,
chromium, zirconium and neodymium.
4. A method for producing a metal according to claim 1, wherein
part of the molten salt after chlorination treatment is sent to the
electrolysis step and the remaining portion of the molten salt is
sent to the reduction step.
5. A method for producing a metal according to claim 1, wherein the
chlorine gas formed in said electrolysis step is used in said
chlorination step.
6. A method for producing a metal according to claim 1, wherein, in
said electrolysis step, an electrolysis chamber in which the anode
side and cathode side are separated from each other by a partition
wall is used.
7. A method for producing a metal according to claim 6, wherein a
flow of the molten salt from the anode side toward the cathode side
is formed in the electrolysis chamber.
8. A method for producing a metal according to claim 1, further
comprising the step of rinsing the metal separated from the molten
salt using part of the CaCl.sub.2 after completion of said
chlorination step.
9. A method for producing a metal according to claim 1, wherein, in
said separation step, said metal is separated from the molten salt
by physical compacting together.
10. A method for producing a metal according to claim 1, further
comprising the step of melting the metal obtained in the separation
step in an inert atmosphere to make an ingot.
11. An apparatus for producing a metal comprising: a reduction
chamber in which a CaCl.sub.2-based molten salt containing Ca is
held and a metal oxide introduced into the molten salt is reduced
with Ca in the molten salt to obtain said metal; means for
separating the metal formed in the molten salt from the molten
salt; a chlorination chamber in which the molten salt after
separation of the metal is held and the molten salt is subjected to
chlorination treatment with chlorine gas for the chlorination of
the byproduct CaO in the molten salt; an electrolysis chamber in
which the molten salt after chlorination treatment is held and the
molten salt is electrolyzed to form Ca and chlorine from CaCl2; and
means for transferring the thus-formed Ca or Ca-containing molten
salt from the electrolysis chamber to said reduction chamber.
12. An apparatus for producing a metal comprising: a reduction
chamber in which a CaCl.sub.2-based molten salt containing Ca is
held and a metal oxide introduced into the molten salt is reduced
with Ca in the molten salt to obtain said metal; means for
separating the metal formed in the molten salt from the molten
salt; a chlorination chamber in which the molten salt after
separation of the metal is held and the molten salt is subjected to
chlorination treatment with chlorine gas for the chlorination of
the byproduct CaO in the molten salt; an electrolysis chamber in
which the molten salt after chlorination treatment is held and the
molten salt is electrolyzed to form Ca and chlorine from
CaCl.sub.2; and means for transferring the thus-formed Ca or
Ca-containing molten salt from the electrolysis chamber to said
reduction chamber, wherein said chlorination chamber is unified
with said reduction chamber.
13. An apparatus for producing a metal comprising: a reduction
chamber in which a CaCl.sub.2-based molten salt containing Ca is
held and a metal oxide introduced into the molten salt is reduced
with Ca in the molten salt to obtain said metal; means for
separating the metal formed in the molten salt from the molten
salt; a chlorination chamber in which the molten salt after
separation of the metal is held and the molten salt is subjected to
chlorination treatment with chlorine gas for the chlorination of
the byproduct CaO in the molten salt; an electrolysis chamber in
which the molten salt after chlorination treatment is held and the
molten salt is electrolyzed to form Ca and chlorine from
CaCl.sub.2; and means for transferring the thus-formed Ca or
Ca-containing molten salt from the electrolysis chamber to said
reduction chamber, wherein said electrolysis chamber is integrated
with said reduction chamber.
14. An apparatus for producing a metal according to claim 11,
wherein said electrolysis chamber has, between the anode side and
cathode side, a partition wall through which the molten salt can
pass.
15. An apparatus for producing a metal according to claim 13,
wherein the cathode side of said electrolysis chamber is unified
with said reduction chamber.
16. An apparatus for producing a metal according to claim 15,
wherein said electrolysis chamber is configured in such a manner
that the molten salt introduced into the anode side can flow
through the cathode to the reduction chamber.
17. An apparatus for producing a metal according to claim 16,
further comprising a Ca reservoir for retaining Ca in the liquid on
the reduction chamber side from the cathode.
18. An apparatus for producing a metal according to claim 15,
wherein said electrolysis chamber is formed like a ring surrounding
the reduction chamber which has a cylindrical shape.
19. An apparatus for producing a metal according to claim 18,
wherein said electrolysis chamber comprises an outer cylinder
serving also as the anode and an inner cylinder serving also as the
cathode and allowing the molten salt to pass therethrough, the
inside of said inner cylinder being the reduction chamber.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing a
metal by a direct oxide reduction process wherein a metal oxide is
reduced with Ca to form a metal such as titanium, and to an
apparatus for use in practicing the method.
BACKGROUND ART
[0002] It is the Kroll process that is a general method for the
commercial production of metallic titanium. In this Kroll process,
metallic titanium is produced via a reduction step and vacuum
separation step. In the reduction step, titanium tetrachloride
(TiCl.sub.4) in a reaction vessel is reduced with Mg, whereby
titanium metal sponge is produced. In the vacuum separation step,
the unreacted Mg and the byproduct magnesium chloride (MgCl.sub.2)
are eliminated from the titanium metal sponge in the reaction
vessel, whereby the product titanium is produced.
[0003] In the production of metallic titanium by the Kroll process,
high-purity products can be produced but the production cost
becomes high, rendering the product price high. Therefore, it is a
limitation of the Kroll process that it can produce only
high-quality and highly-priced metallic titanium.
[0004] On the other hand, the production of low-priced metallic
titanium, though somewhat lower in purity, is demanded for use as
structural members, for instance. In response to such a demand,
works have been planned to develop a method for continuously
producing metallic titanium relatively low in purity at low cost
and, in line with above, direct oxide reduction processes
consisting in reducing titanium oxide with Ca have been
investigated.
[0005] FIG. 1 is an illustration of a direct oxide reduction
process known in the prior art. As a typical example of the known
direct oxide reduction processes, there is the Olson process
described in U.S. Pat. No. 2,845,386. In this process, a TiO.sub.2
powder is charged to a molten salt containing CaCl.sub.2 for the
formation of Ti as a result of the reduction of TiO.sub.2 with Ca,
as shown in FIG. 1. At the same time, CaO is electrolyzed in the
molten salt containing CaCl.sub.2 using an iron cathode and a
graphite anode.
[0006] In the Olson process mentioned above, CaO is formed as a
byproduct on the surface of the TiO.sub.2 powder with the progress
of the reaction. Since, however, the byproduct CaO is soluble in
CaCl.sub.2, the CaO formed on the surface of the TiO.sub.2 powder
is dissolved in the CaCl.sub.2 and the reaction between TiO.sub.2
and Ca progresses continuously on the surface of the TiO.sub.2
powder. Further, upon electrolysis of the CaO-containing molten
salt (CaCl.sub.2), the CaO is removed from the CaCl.sub.2, as shown
below by the chemical formulas (1)-(3).
[0007] Thus, according to the Olson process, the byproduct CaO
formed on the surface of the TiO.sub.2 powder is dissolved in the
CaCl.sub.2 and, further, the dissolved CaO is continuously removed
from the CaCl.sub.2 as a result of electrolysis, hence is never
accumulated. The reaction for the formation of Ti from TiO.sub.2
thus continues. 2CaO+C.fwdarw.2Ca+CO.sub.2 (on the anode surface)
(1) 5Ca+2CO.sub.2.fwdarw.CaC.sub.2+4CaO (in the vicinity of the
anode) (2) 2Ti+CaC.sub.2.fwdarw.2TiC+Ca (on the cathode) (3)
[0008] As described above, the Olson process can form Ti from
TiO.sub.2 continuously without allowing accumulation of the
byproduct CaO. On the other hand, however, CaC.sub.2 is formed in
the molten salt as the electrolysis of CaO proceeds. The
thus-formed CaC.sub.2 deteriorates the quality of Ti by mixing Ti
with TiC, as shown by the chemical formula (3) given above.
[0009] In other words, the Olson process can form Ti continuously
and is therefore efficient but Ti is contaminated with TiC
resulting from the reaction of CaC.sub.2 formed in the molten salt
containing CaCl.sub.2 with the progress of electrolysis of CaO. The
deterioration in product quality due to contamination with carbon
(C) becomes a critical problem in the production of metallic
titanium and, therefore, any process based on direct oxide
reduction process has not yet been put to practical use.
DISCLOSURE OF THE INVENTION
[0010] It is an object of the present invention to provide a metal
production method which is highly productive and free from such
quality deterioration as contamination with carbon in spite of its
employing the direct oxide reduction process featured by reducing a
metal oxide with Ca, and a metal production apparatus for
practicing such method.
[0011] To accomplish the above object, the method for producing a
metal according to the present invention comprises a reduction step
in which a metal oxide is introduced into a CaCl.sub.2-based molten
salt containing Ca for the formation of the corresponding metal by
reduction of the metal oxide with Ca in the molten salt, a
separation step in which the metal formed in the molten salt is
separated from the molten salt, a chlorination step in which the
molten salt after separation of the metal is subjected to
chlorination treatment with chlorine gas to chlorinate the
byproduct CaO in the molten salt, and an electrolysis step in which
a part or the whole of the molten salt after chlorination treatment
is electrolyzed to form Ca and chlorine from CaCl.sub.2 and the
thus-formed Ca or Ca-containing molten salt is recycled to the
above-mentioned reduction step.
[0012] The metal production apparatus according to the present
invention comprises a reduction chamber in which a CaCl.sub.2-based
molten salt containing Ca is held and a metal oxide introduced into
the molten salt is reduced with Ca in the molten salt to obtain
said metal, means for separating the metal formed in the molten
salt from the molten salt, a chlorination chamber in which the
molten salt after separation of the metal is held and the molten
salt is subjected to chlorination treatment with chlorine gas for
the chlorination of the byproduct CaO in the molten salt, an
electrolysis chamber in which a part or the whole of the molten
salt after chlorination treatment is held and the molten salt is
electrolyzed to form Ca and chlorine from CaCl.sub.2, and means for
transferring the thus-formed Ca or Ca-containing molten salt from
the electrolysis chamber to the reduction chamber mentioned
above.
[0013] In producing metallic titanium, for instance, by the metal
production method of the present invention, the desired product
titanium is formed based on the reactions represented below by the
chemical equations (4)-(6): TiO2+2Ca.fwdarw.Ti+2CaO (reduction
step) (4) 2CaO+2Cl.sub.2.fwdarw.2CaCl.sub.2+O.sub.2 (chlorination
step) (5) CaCl.sub.2.fwdarw.Ca+Cl.sub.2 (electrolysis step) (6)
[0014] First, in the reduction step, the titanium oxide introduced
is reduced with Ca in the molten salt and, as a result, metallic
titanium is continuously formed and CaO is formed as a byproduct.
Therefore, the molten salt after reduction is composed of
CaCl.sub.2, metallic titanium and the byproduct CaO.
[0015] Then, in the separation step, the metallic titanium formed
in the molten salt is separated from the molten salt.
[0016] Further, in the chlorination step, the molten salt after
separation of the metallic titanium is subjected to chlorination
treatment with chlorine gas, whereby CaCl.sub.2 is formed from the
CaO formed as a byproduct of the reduction reaction. As a result,
the molten salt after chlorination treatment is almost free of CaO
and substantially comprises CaCl.sub.2 alone.
[0017] The molten salt substantially comprising CaCl.sub.2 alone
after chlorination treatment is partly or as a whole sent to the
electrolysis step, in which Ca is formed in the molten salt by the
electrolysis treatment. The CaCl.sub.2-based molten salt now
containing Ca again after the electrolysis step is recycled to the
reduction step. In this manner, continuous production of metallic
titanium becomes possible.
[0018] The present invention is based on a first and second
characteristic feature. The first feature consists in carrying out
the electrolysis outside the region of the reduction reaction. The
second feature consists in chlorinating CaO in the molten salt
prior to electrolysis. By combining these first and second
features, it becomes possible to prevent the accumulation of CaO in
the reduction step and at the same time prevent the generation of
CaC.sub.2 otherwise resulting from electrolysis of CaO and thus
avoid the carbon contamination of the product metal. Thus, it is
possible to continue the reduction reaction while preventing the
product from being contaminated.
[0019] Furthermore, the present invention provides an advantage
that no oxygen gas is formed although chlorine gas is formed on the
anode in the electrolysis. In ordinary electrolytic processes,
graphite is used as the anode material. As is indicated in FIG. 1
referring to the Olson process, the generation of oxygen gas on the
anode results in the generation of carbon dioxide.
[0020] In the electrolysis shown in FIG. 1, the Ca generated on the
cathode side has a high reducing power and therefore reduces the
metal oxide. However, as shown in the above chemical equations (2)
and (3), carbon dioxide, when it is present in the molten salt,
forms CaC.sub.2, and this CaC.sub.2 mixes the carbonized metal into
the product metal and thereby deteriorates the quality of the
product metal.
[0021] On the contrary, no oxygen gas is generated on the graphite
anode in the electrolysis according to the present invention and,
as a result, no carbon dioxide is generated, hence there is no risk
of carbon contamination of the product metal. In addition, now that
the graphite anode is not consumed, stable electrolysis conditions
can be secured.
[0022] In the production process according to the present
invention, it is necessary to control the molten salt temperature
at the melting point (780.degree. C.) or more of CaCl.sub.2 in the
reduction step, chlorination step and electrolysis step in which
the molten salt is circulated. In this connection, the melting
point of Ca is 848.degree. C. but when Ca is dissolved in the
molten salt CaCl.sub.2, Ca can be dissolved therein even at
848.degree. C. or less. While the exact solubility varies depending
on the dissolution temperature, Ca can be dissolved to a level of
about 1.5% by weight relative to CaCl.sub.2, and CaO can be
dissolved to a level of about 8.0% by weight relative to
CaCl.sub.2.
[0023] In the reduction step, powdery, granular or lumpy titanium
oxide is introduced into the molten salt. The metallic titanium
separated from the molten salt after reduction is also powdery,
granular or lumpy and wet with the molten salt. From the reduction
efficiency viewpoint, the use of powdery titanium oxide as the raw
material is desirable.
[0024] The separation of metallic titanium in the separation step
is effectively carried out in the manner of separation through
settling or a physical method such as compacting. The reasonable
amounting metallic titanium in bulk once separated and taken out by
settling or compacting can be made up into ingots by any of the
conventional melting methods, for example by the plasma melting
method.
[0025] In the melting step, either of a bottomless crucible or a
bottomed crucible may be used as the crucible for melting. The use
of the bottomless crucible makes it possible to carry out
continuous casting.
[0026] When titanium oxide is introduced in the form of particles
with small diameter, the formed metallic titanium also becomes
small in diameter and, therefore, the separation through settling
in the reduction step may become inefficient in some instances. In
such cases, an efficient method to be employed comprises the step
of carrying out the reduction step in a bottomed vessel,
extracting, from the vessel bottom, the molten salt with the
product metallic titanium suspended therein at a high concentration
as resulting from still and static separation and, thereafter,
separating the product metallic titanium from the molten salt by
compacting together, for instance. The remaining molten salt is
subjected to chlorination treatment, whereby the efficiency of
utilization of the molten salt can be improved.
[0027] In the chlorination step, the chlorination treatment can be
carried out continuously and efficiently by bubbling chlorine gas
into the molten salt.
[0028] If CaO remains in the metallic titanium formed in the
reduction step, the oxygen constituent of the CaO is included in
the metallic titanium in the step of melting and the oxygen
concentration in the titanium increases. For preventing this, it is
desirable to insert the so-called rinsing step, namely the step of
injecting CaO-free CaCl.sub.2 after chlorination treatment into an
appropriate location during the separation step to thereby rinse
the metallic titanium separated from the molten salt with the
CaCl.sub.2 after chlorination treatment.
[0029] Since up to about 8.0% by weight of CaO can be dissolved in
CaCl.sub.2, as mentioned hereinabove, the CaO remaining in the
metallic titanium is dissolved in the CaO-free CaCl.sub.2 that has
been injected and thus is removed from the metallic titanium.
[0030] In the electrolysis step, Ca is generated on the cathode
side, while chlorine gas is generated on the anode side. As the Ca
concentration in the Ca-containing CaCl.sub.2 extracted from the
cathode site in the electrolyzer increases, the reducing capacity
in the reduction step can be increased accordingly.
[0031] In case the Ca concentration in the electrolyzer exceeds the
solubility thereof in CaCl.sub.2, the excess Ca is suspended as a
solid or dissociated and floated to the surface. The CaCl.sub.2
with Ca suspended therein can be sent to the reduction step. Upon
consumption, in the reduction step, of the Ca originally being
contained, the suspended portion of Ca is newly dissolved to serve
to continue reducing reaction thereof.
[0032] It is not always necessary to transfer the whole of the
CaCl.sub.2 from the chlorination step to the electrolysis step.
Only part thereof may be transferred. In that case, the remaining
portion of CaCl.sub.2 may be directly sent from the chlorination
step to the reduction step without subjecting to the electrolysis
step. The reason why part of the CaCl.sub.2 is transferred from the
chlorination step to the electrolysis step is as follows.
[0033] The solubility of Ca in CaCl.sub.2 is low. Therefore, in
cases where the CaCl.sub.2 containing Ca dissolved therein is sent
to the reduction step, it becomes necessary to cycle a large amount
of CaCl.sub.2 so that the predetermined reducing capacity may be
secured. On the contrary, when molten Ca alone is transferred from
the electrolysis step to the reduction step, it is unnecessary any
more to cycle a large amount of CaCl.sub.2.
[0034] When the Ca from the electrolysis step is stored on the melt
surface in the reduction step, Ca is dissolved from the Ca layer
formed on the liquid surface into the CaCl.sub.2 layer, whereby the
Ca concentration in the CaCl.sub.2 layer can be increased. Thus,
that portion of Ca consumed for the reduction of TiO.sub.2 by the
dissolved Ca in the CaCl.sub.2 layer is supplemented by the
dissolution of Ca from the Ca layer into the CaCl.sub.2 layer.
[0035] The production apparatus of the present invention is an
apparatus for producing a metal utilizing the above-mentioned
production method of the present invention. In the production
apparatus of the present invention, the electrolysis chamber is
desirably configured such that a partition wall is provided for
separating the anode side and cathode side from each other. By
providing such a partition wall, it becomes possible to prevent the
chlorine gas generated on the anode side from travelling into the
cathode side and further prevent the Ca generated on the cathode
side from returning to the anode side. In case of providing a
partition wall, the use of a porous ceramic plate (diaphragm) is
recommended.
[0036] On the other hand, by continuously extracting the
Ca-containing CaCl.sub.2 from the cathode side while continuously
introducing the CaCl.sub.2 fed from the chlorination step into the
anode side, it becomes possible to form a steady flow from the
anode side to the cathode side. Once such a flow is formed, the
same Ca separation effect as in case of using a porous plate can be
expected by using a solid/non-porous plate being disposed below the
liquid level and having an opening or hole(s) through which a small
amount of the molten salt can pass, for example a slit metal plate,
without using a porous plate as the partition wall.
[0037] The chlorine gas generated on the anode side in the
electrolysis chamber is used for bubbling in the chlorination
step.
[0038] For reducing the size of the apparatus, the chlorination
chamber may be integrated with the reduction chamber. For the same
purpose, it is also possible to integrate the electrolysis chamber
with the reduction chamber together. By using the word "integrate"
herein, it is meant that another chamber is arranged next to a
specific chamber; the partition wall for separating both chambers
from each other may be provided or may not be provided. The case of
no partition wall being provided is touted as unification, which
will be described later herein.
[0039] The cathode side of the electrolysis chamber integrated with
the reduction chamber can be unified with the reduction chamber by
removing the partition wall separating both chambers from each
other. This electrolysis chamber can be formed in a ring-like
manner around the reduction chamber which has a cylindrical shape.
More specifically, the system can comprise an outer cylinder
serving as the anode as well and an inner cylinder serving as the
cathode as well and allowing the passage of the molten salt, where
the inside of the inner cylinder serves as the reduction
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a drawing explaining a direct oxide reduction
method known in the art.
[0041] FIG. 2 is a drawing explaining the configuration of a
titanium production apparatus according to a first embodiment of
the present invention.
[0042] FIG. 3 is a drawing explaining the configuration of a
titanium production apparatus according to a second embodiment of
the present invention.
[0043] FIG. 4 is a drawing explaining the configuration of a
titanium production apparatus according to a third embodiment of
the present invention.
[0044] FIG. 5 is a drawing explaining the configuration of a
titanium production apparatus according to a fourth embodiment of
the present invention.
[0045] FIG. 6 is a drawing explaining the configuration of a
titanium production apparatus according to a fifth embodiment of
the present invention.
[0046] FIG. 7 is a drawing explaining the configuration of a
titanium production apparatus according to a sixth embodiment of
the present invention.
[0047] FIG. 8 is a drawing explaining the cross-sectional
configuration, seen from the direction of an arrow X-X, shown in
FIG. 7.
BEST MODE FOR CARRYING OUT THE INVENTION
[0048] In the following, the first to sixth embodiments of the
present invention are described referring to the drawings.
First Embodiment
[0049] FIG. 2 is a drawing explaining the configuration of a
titanium production apparatus according to the first embodiment of
the present invention. In the first embodiment, the apparatus
comprises a tower-shaped reduction chamber 1 and a horizontal
separation means 2 connected to the lower part of the chamber 1. A
CaCl.sub.2-based molten salt containing Ca is contained in the
reduction chamber 1, and the raw material titanium oxide
(TiO.sub.2) in the form of a powder is continuously introduced into
the molten salt.
[0050] Thus, in the reduction chamber 1, TiO.sub.2 charged into the
molten salt is reduced by Ca in the molten salt and metallic
titanium (Ti) is formed and, at the same time, CaO is formed as a
byproduct. Both the product Ti and the byproduct CaO settle and are
separated from the molten salt and flow into the separation means 2
together with a certain amount of CaCl.sub.2.
[0051] A CaCl.sub.2-based molten salt containing Ca, together with
the raw material titanium oxide, is additionally supplied from the
upper part to the reduction chamber 1. On the other hand, the
molten salt is extracted sideways from the lower part of the
reduction chamber 1 by the separation means 2. As a result, a
downward flow or current of the molten salt is formed in the
reduction chamber 1. This molten salt flow promotes the
above-mentioned settling and separation of the product Ti and
byproduct CaO.
[0052] In the separation means 2, the molten salt abundant in
product Ti and byproduct CaO, after flowing thereinto, is
physically compressed by means of a perforated cylindrical screw 3
in a cylindrical body. This physical separation procedure makes it
possible to squeeze out the molten salt from the product Ti and
compact together said product Ti. The compacted porous product Ti
is successively discharged from the separation means 2 and melted
in a melting means 4.
[0053] The product Ti separated from the molten salt by compression
in the separation means 2 can be subjected to rinsing with a
CaO-free molten salt containing CaCl.sub.2 as a main component.
This treatment is to prevent CaO from remaining in the product Ti
since the retention of CaO therein results in an increased oxygen
concentration in the step of melting due to the oxygen constituent
in CaO being included in the metallic titanium. More specifically,
a CaO-free molten salt after chlorination treatment in a
chlorination chamber 7, which is to be mentioned later herein, is
used for rinsing to dissolve the CaO remaining in the product Ti in
CaCl.sub.2, consequently removing the same from the product Ti.
[0054] In the melting means 4, a plasma device is used. The lumpy
product Ti is melted in an inert atmosphere and the molten Ti is
collected in a water-cooled primary mold 5. In the water-cooled
primary mold 5, the molten Ti settles, while the molten salt floats
to the surface. The molten Ti separated from the molten salt is
allowed to flow into a water-cooled secondary mold 6 and thus is
cast to give a Ti ingot.
[0055] In spite of its separation from the molten salt by
compression in the separation means 2, the Ti melted in the melting
means 4 still contains a certain amount of the molten salt.
Therefore, the molten Ti is once collected in the water-cooled
primary mold 5, where the molten salt floats to the surface and can
be separated. The molten salt separated is sent to a chlorination
chamber 7, which is to be described later herein.
[0056] The molten salt separated from the product Ti in the
separation means 2 and the molten salt separated by floating in the
water-cooled primary mold 5 are sent to the chlorination chamber 7.
Since these molten salt portions contain the byproduct CaO in large
amounts, chlorine gas is bubbled into the molten salt introduced
into the chlorination chamber 7 to chlorinate the CaO in the molten
salt. This chlorination of CaO converts the CaO contained in the
molten salt to CaCl.sub.2, and a CaO-free molten salt substantially
consisted CaCl.sub.2 is formed.
[0057] The above CaO-free molten salt is then sent to an
electrolysis chamber 8. Part thereof is sent to the separation
means 4 for rinsing treatment, as mentioned above. In the
electrolysis chamber 8, the molten salt introduced is electrolyzed
by using a graphite anode and an iron cathode. Chlorine gas is
generated on the anode side in the chamber and Ca is formed on the
cathode side. In this way, a CaCl.sub.2-based molten salt
containing Ca is formed.
[0058] In the chlorination chamber 7, the CaO to be eliminated is
chlorinated. On the other hand, the reduction chamber 1 requires a
Ca-containing molten salt and, therefore, the Ca-containing molten
salt formed in the electrolysis chamber 8 is sent to the reduction
chamber 1. Thus, it is substantially unnecessary to supplement
CaCl.sub.2 and Ca from the outside source. The chlorine gas formed
as a byproduct in the electrolysis chamber 8 is sent to the
chlorination chamber for reuse.
[0059] In this electrolysis chamber 8, the anode side and cathode
side are separated from each other by a porous partition wall 9.
The molten salt sent from the chlorination chamber 7 is introduced
into the anode side, and the Ca-containing molten salt is drawn out
from the cathode side and sent to the reduction chamber 1. In this
way, a flow from the anode side toward the cathode side is formed.
As a result, the molten salt is inhibited from flowing backward
from the cathode side to the anode side. The chlorine gas is also
prevented from entering the cathode side from the anode side.
Second Embodiment
[0060] FIG. 3 is a drawing explaining the configuration of a
titanium production apparatus according to the second embodiment of
the present invention. The second embodiment differs from the
above-mentioned first embodiment as shown in FIG. 2 in that part of
the molten salt after completion of the chlorination treatment in
the chlorination chamber 7 is sent to the electrolysis chamber 8,
while almost whole of the remaining molten salt is returned to the
reduction chamber 1 and that the transfer of Ca from the
electrolysis chamber 7 to the reduction chamber 1 is carried out in
the form of a metal. In the second embodiment, however, the
transfer of Ca in the metal form to the reduction chamber 1 may be
combined with the method comprising the step of transferring Ca
being dissolved in CaCl.sub.2.
[0061] Therefore, in the electrolysis chamber 8, the molten salt
from the chlorination chamber 7 is introduced into the anode side,
and the Ca formed on the liquid surface on the cathode side, either
alone or together with a certain amount of CaCl.sub.2, is sent to
the reduction chamber 1. The Ca transferred to the reduction
chamber 1 floats to the surface of the molten salt in the chamber
and is dissolved in CaCl.sub.2. Therefore, the Ca concentration in
the CaCl.sub.2 in the reduction chamber 1 is maintained at a high
level in spite of the fact that the amount of the molten salt or Ca
transferred from the chlorination chamber 7 to the reduction
chamber 1 via the electrolysis chamber 8 is small.
[0062] Considering that the solubility of Ca in CaCl.sub.2 is low,
as mentioned above, part of the molten salt is transferred from the
chlorination chamber 7 to the electrolysis chamber 8. In this way,
the total production efficiency can be improved while avoiding the
cycle involving a large amount of CaCl.sub.2.
Third Embodiment
[0063] FIG. 4 is a drawing explaining the configuration of a
titanium production apparatus according to the third embodiment of
the present invention. The third embodiment differs from the
production apparatus according to the second embodiment as shown in
FIG. 3, featured in that the chlorination chamber 7 is integrated
with the reduction chamber 1. Otherwise, the configuration is
substantially the same as that of the production apparatus
according to the second embodiment.
[0064] The chlorination chamber 7 is laterally disposed being
annexed to the vertical type reduction chamber 1 via a partition
wall 10. In the reduction chamber 7, titanium oxide is introduced
into the CaCl.sub.2-based molten salt within the chamber through a
feeding tube 11 inserted into the CaCl.sub.2. The titanium formed
from titanium oxide upon reduction with Ca in the CaCl.sub.2
settles on the bottom of the reduction chamber 1 and downwardly
extracted and sent to the lower separation means 2.
[0065] The CaCl.sub.2 containing the byproduct CaO flows from the
lower part of the reduction chamber 1 into the chlorination chamber
7 and undergoes chlorination treatment with chlorine gas injected
thereinto from a site at the lower part thereof, whereby CaO is
chlorinated. The CaCl.sub.2 rises through the chlorination chamber
7 together with the chlorine gas flow (gas lift) rising within the
chlorination chamber 7. The CaCl.sub.2 separated from the metallic
titanium in the separation means 2 is also introduced into the
lower part of the chlorination chamber. On the other hand, the
oxygen gas formed as a byproduct in the chlorination chamber 7 is
drawn out upwards.
[0066] Most of the CaCl.sub.2 outgoing from the chlorination
chamber 7 is returned from the upper part of the chlorination
chamber 7 to the reduction chamber 1. The remaining portion of
CaCl.sub.2 is transferred to the electrolysis chamber 8. In the
electrolysis chamber 8, Ca is formed from the CaCl.sub.2 thus
introduced. The Ca formed in the electrolysis chamber 8 is
transferred, either alone or together with a small amount of the
Ca-rich CaCl.sub.2, to the reduction chamber 1. The byproduct
chlorine gas is sent to the chlorination chamber 7 for reuse.
[0067] The Ca introduced into the reduction chamber 1 forms a layer
covering over the CaCl.sub.2 in the reduction chamber 1. The
feeding tube 11 mentioned above serves for charging titanium oxide
into the CaCl.sub.2 through the Ca layer over the CaCl.sub.2.
[0068] In the titanium production apparatus comprising the
chlorination chamber 7 integrated with the reduction chamber 1, the
transfer of CaCl.sub.2 between both chambers becomes easy. It is
also possible to transfer whole of the CaCl.sub.2 coming out of the
chlorination chamber 7 to the electrolysis chamber 8.
Fourth Embodiment
[0069] FIG. 5 is a drawing explaining the configuration of a
titanium production apparatus according to the fourth embodiment of
the present invention. As compared with the production apparatus
according to the third embodiment as shown in FIG. 4, the
electrolysis chamber 8 is further added to the integrated reduction
chamber 1 in the fourth embodiment. Otherwise, the configuration is
substantially the same as that of the production apparatus
according to the third embodiment.
[0070] The electrolysis chamber 8 is sideways disposed, as opposed
to the chlorination chamber 7, having the reduction chamber 1
between them, and there is no partition wall provided between the
reduction chamber and electrolysis chamber. The electrolysis
chamber 8 is provided with a graphite anode 12 and an iron cathode
13, and the anode side is separated from the cathode side by a
partition wall 9. The cathode side is located on the side of the
reduction chamber 1 and unified with the reduction chamber 1
without any partition wall. The partition wall 9 is configured so
that the molten salt can pass therethrough, like the case of the
first embodiment.
[0071] The CaCl.sub.2 transferred from the chlorination chamber 7
is introduced into the anode side. The chlorine gas generated as a
byproduct on the anode side is sent to the chlorination chamber 7.
The CaCl.sub.2 introduced into the anode side passes through the
partition wall 9 and migrates to the cathode side. Thus, to let the
molten salt pass through the partition wall 9, there is formed, in
the electrolysis chamber 8, a bath flow from the anode 12 side to
the cathode 13 side with the supply of the molten salt to the anode
side.
[0072] On the cathode side of the electrolysis chamber 8, Ca is
formed on the surface of the iron cathode 13, and the Ca thus
formed migrates to the reduction chamber 1 side while floating to
the surface being carried by the bath flow. In the vicinity of the
bath surface from the cathode 13 to the reduction chamber 1 side,
there is provided a Ca reservoir 14. The Ca reservoir 14 is a
box-like body whose bottom is open. It catches up the Ca that is
formed on the surface of the cathode 13 and migrates toward the
reduction chamber 1 side, and thus prevents the same from being
cropped out above the bath surface. The Ca collected in the Ca
reservoir 14 is dissolved in the CaCl.sub.2 in the reduction
chamber 1 and used for the reduction reaction within the reduction
chamber 1.
[0073] In the fourth embodiment, the Ca reservoir 14 is made of
iron, like the cathode 13, and it may be unified with the cathode
13 so that it can have the same potential as the cathode 13. The
aim of providing the Ca reservoir 14 is to inhibit the Ca layer
from being cropped out above the bath surface. In case that the
space above the liquid surface on the reduction chamber side from
the cathode 13 can be filled with an inert gas atmosphere, the Ca
layer may be cropped out above the bath surface. However, in case
the ingress of air is unavoidable for some or other operational
reasons, the Ca layer cropping out above the bath surface leads to
the formation of CaO by oxidation. In this regard, the Ca reservoir
14 is provided to avoid the formation of CaO as a result of
oxidation as such.
[0074] Further, in the fourth embodiment, the upper part of the
partition wall 9 is protruded toward the cathode 13 and is in
contact with the cathode 13. This structure inhibits the Ca
generated on the surface of the cathode 13 from staying between the
cathode 13 and the partition wall 9.
[0075] In the titanium production apparatus in which the
electrolysis chamber 8 is integrated with the reduction chamber 1,
the transfer of Ca from the electrolysis chamber 8 to the reduction
chamber 1 becomes easy. In particular, the cathode side where Ca is
formed within the electrolysis chamber 8 can be unified with the
reduction chamber 1 and therefore the partition wall between both
the chambers can be eliminated. Therefore, the structure of the
apparatus can be particularly simplified and the apparatus can be
rendered small-sized.
Fifth Embodiment
[0076] FIG. 6 is a drawing explaining the configuration of a
titanium production apparatus according to the fifth embodiment of
the present invention. In the configuration according to the fifth
embodiment, the partition wall 9 in the electrolysis chamber 8 as
found in the configuration of the production apparatus according to
the fourth embodiment as shown in FIG. 6 has been eliminated. The
other structural elements are substantially the same as those in
the titanium production apparatus according to the fourth
embodiment.
[0077] In the electrolysis chamber 8 unified with the reduction
chamber 1, the molten salt is introduced into the anode side, as
mentioned above, so that a flow of the molten salt from the anode
12 side to the cathode 13 side is formed. Therefore, even when the
partition wall 9 separating the anode side and cathode side from
each other is omitted, the efficiency can be prevented from
decreasing because of the reflux of the molten salt. However, the
cathode 13, like the partition wall 9, has a structure such that
the molten salt can pass therethrough.
[0078] Above the cathode 13, however, there is provided a curtain
wall type partition wall 15 made of a chlorine gas-resistant
material such as a refractory material. It may be conceived that
the cathode 13 be lengthened beyond the liquid surface level in
lieu of the newly provided partition wall 15. In this case,
however, there arises the problem that the lengthened portion of
the cathode 13 may be corroded by the chlorine gas generated on the
anode side. Thus, it becomes necessary to provide the partition
wall 15 separately from the cathode 13.
[0079] By omitting the partition wall 9 separating the anode side
and cathode side from each other in the electrolysis chamber 8
according to the fifth embodiment, the apparatus structure is still
more simplified and can be reduced the size more. On the other
hand, there is no Ca reservoir on the reduction chamber side of the
cathode 13 and, therefore, it is necessary to control the space
above the liquid surface level on the reduction chamber side of the
cathode 13 with an inert gas atmosphere.
Sixth Embodiment
[0080] FIG. 7 is a drawing explaining the configuration of a
titanium production apparatus according to the sixth embodiment of
the present invention. FIG. 8 is a drawing explaining the
cross-sectional configuration, seen along the line X-X, of the
titanium production apparatus shown in FIG. 7.
[0081] Like the fourth and fifth embodiments, the sixth embodiment
has a configuration such that the electrolysis chamber 8 is
integrated with the reduction chamber 1. However, it has a
configuration such that the reduction chamber 1 is formed like a
cylinder and the electrolysis chamber 8 is formed like a cylinder
surrounding the reduction chamber 1.
[0082] The cylindrical electrolysis chamber 8 provided outside the
reduction chamber 1 has a cylindrical anode 12 serving also as the
outer wall and a cylindrical cathode 13 serving also as the inner
wall. All of the CaO and the Ca-free CaCl.sub.2 obtained in the
chlorination chamber 7 positioned sideways to the reduction chamber
1 are introduced into the ring-like space between the anode 12 and
cathode 13. The inside cathode 13 serves also as part of the
cylindrical outer wall of the reduction chamber 1, and the inside
thereof is unified with the reduction chamber 1.
[0083] As shown in FIG. 8, the cathode 13 in the sixth embodiment
comprises a plurality of cathode segments arranged in a swirling
manner in the circumferential direction, and there is provided a
slit 13a between every two cathode segments 13. This slit 13a is
configured so as to pass the molten salt from the outside to the
inside and thus it has a shape such that the space thereof
gradually increases from the inside toward the outside. This
configuration of each slit 13a causes the formation of an internal
swirling flow and external swirling flow on each side of the
cathode 13 and, at the same time, it promotes the flow of the
molten salt from the outside to the inside.
[0084] Above the cathode 13, as a continuum, there is provided a
cylindrical partition wall 15 made of a chlorine gas-resistant
material, for example a refractory material. For the same reason as
in the fifth embodiment, it becomes necessary to provide the
partition wall 15 in addition to the cathode 13.
[0085] In the sixth embodiment, a swirling flow is generated on the
external side of the cylindrical cathode 13 and, further, the
molten salt flowing into the inside of the cathode 13, while
swirling, comes down in the reduction chamber 1 and, thus, the Ca
formed on the surface of the cathode 13 is smoothly drawn into the
inside thereof. The Ca flowing into the inside of the cathode 13
floats to the surface above the CaCl.sub.2 in the reduction chamber
1 and is dissolved in the CaCl.sub.2, and the dissolved Ca
contributes to the reduction reaction in the reduction chamber
1.
[0086] By configuring the electrolysis chamber 8 integrated with
the reduction chamber 1 cylindrically and externally to the
reduction chamber 1, it becomes possible to increase the areas of
the anode 12 and cathode 13 in the electrolysis chamber 8. This
enables more efficient apparatus designing. While, in the case
described herein, the whole amount of the CaCl.sub.2 obtained in
the chlorination chamber 7 is introduced into the electrolysis
chamber 8, it is also possible to introduce only a partial amount
thereof into that chamber.
[0087] Although the cases of metallic titanium production have been
described hereinabove, the metal to be produced in accordance with
the present invention includes not only titanium but also tungsten,
niobium, tantalum, chromium, zirconium and neodymium.
INDUSTRIAL APPLICABILITY
[0088] In accordance with the metal production method and metal
production apparatus of the present invention, the electrolysis in
the direct oxide reduction method comprising the step of reducing a
metal oxide with Ca is carried out in a region outside the
reduction area and the CaO is eliminated from the molten salt to be
subjected to electrolysis, so that the problems encountered in the
prior art of direct oxide reduction processes, namely the low
productivity and the product quality deterioration due to
contamination with carbon, can be avoided. The present invention
thereby can greatly contribute to the practical use of the oxide
reduction method in the field of metal production.
* * * * *