U.S. patent application number 11/886323 was filed with the patent office on 2008-10-16 for method of high-melting-point metal separation and recovery.
Invention is credited to Katsunori Dakeshita, Masahiko Hori, Tadashi Ogasawara, Makoto Yamaguchi.
Application Number | 20080250901 11/886323 |
Document ID | / |
Family ID | 36991413 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080250901 |
Kind Code |
A1 |
Ogasawara; Tadashi ; et
al. |
October 16, 2008 |
Method of High-Melting-Point Metal Separation and Recovery
Abstract
A TiCl.sub.4 gas is supplied to a molten CaCl.sub.2 liquid held
in a reactor vessel 6 through a raw material feed pipe 11,
TiCl.sub.4 is reduced to produce granular metallic Ti by Ca melted
in the CaCl.sub.2 liquid. The molten CaCl.sub.2 liquid in which Ti
granules taken out downward from the reactor vessel 6 is mixed is
delivered to a separation process 12, the molten CaCl.sub.2 liquid
is heated in a heating vessel 15, and separation is generated by a
difference in specific gravity, whereby the molten CaCl.sub.2
liquid 16 is located in an upper layer while a metallic Ti 17 is
located in a lower layer. The metallic Ti 17 in the lower layer is
taken out from a high-melting-point metal discharge port 18, and
the metallic Ti 17 is solidified to yield an ingot. The molten
CaCl.sub.2 liquid 16 in the upper layer is delivered to an
electrolysis process 13 along with the molten CaCl.sub.2 liquid
taken out from the reactor vessel 6, and Ca generated by the
electrolysis and CaCl.sub.2 are returned into the reactor vessel 6.
A separation and recovery method of the invention is applied to the
separation process 12 in the above production process, and
high-quality Ti or Ti alloy is efficiently separated and recovered
from the CaCl.sub.2-containing molten salt with a small amount of
energies.
Inventors: |
Ogasawara; Tadashi; (Hyogo,
JP) ; Yamaguchi; Makoto; (Hyogo, JP) ;
Dakeshita; Katsunori; (Hyogo, JP) ; Hori;
Masahiko; (Hyogo, JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW, SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
36991413 |
Appl. No.: |
11/886323 |
Filed: |
March 8, 2006 |
PCT Filed: |
March 8, 2006 |
PCT NO: |
PCT/JP2006/304456 |
371 Date: |
June 27, 2008 |
Current U.S.
Class: |
75/621 ;
75/707 |
Current CPC
Class: |
Y02P 10/234 20151101;
C22B 34/1272 20130101; C25C 3/02 20130101; C22B 9/02 20130101; C22B
34/1295 20130101; Y02P 10/20 20151101 |
Class at
Publication: |
75/621 ;
75/707 |
International
Class: |
C22B 34/12 20060101
C22B034/12; C22B 9/02 20060101 C22B009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2005 |
JP |
2005-072854 |
Claims
1-11. (canceled)
12. A high-melting-point metal separation and recovery method,
wherein a molten salt in which a high-melting-point metal is mixed
is melted in an inert gas atmosphere to perform a liquid phase
separation of the high-melting-point metal, the molten salt being
used as a reaction field.
13. The high-melting-point metal separation and recovery method
according to claim 12, wherein a boiling point of said molten salt
is higher than a melting point of said high-melting-point
metal.
14. The high-melting-point metal separation and recovery method
according to claim 12, wherein said molten salt is used as the
reaction field in producing said high-melting-point metal and said
molten salt is the one in which the high-melting-point metal
obtained by a reaction in the reaction field is mixed.
15. The high-melting-point metal separation and recovery method
according to claim 14, wherein a boiling point of said molten salt
is higher than a melting point of said high-melting-point
metal.
16. The high-melting-point metal separation and recovery method
according to claim 15, wherein said molten salt contains
CaCl.sub.2.
17. The high-melting-point metal separation and recovery method
according to claim 16, wherein said molten salt contains Ca and the
high-melting-point metal obtained by a reaction is the one obtained
by causing a compound of said high-melting-point metal to react
with Ca in said molten salt.
18. The high-melting-point metal separation and recovery method
according to claim 17, wherein the high-melting-point metal is Ti
or a Ti alloy and said compound of the high-melting-point metal
contains TiCl.sub.4.
19. The high-melting-point metal separation and recovery method
according to claim 14, wherein all or part of the molten salt in
which the high-melting-point metal obtained by the reaction is
mixed is maintained in a molten state until being melted in an
inert gas atmosphere.
20. The high-melting-point metal separation and recovery method
according to claim 18, wherein all or part of the molten salt in
which the high-melting-point metal obtained by the reaction is
mixed is maintained in a molten state until being melted in an
inert gas atmosphere.
21. The high-melting-point metal separation and recovery method
according to claim 17, wherein Ca is vaporized and separated when
the molten salt with remnants of Ca is melted in an inert gas
atmosphere after the reaction with said compound of the
high-melting-point metal.
22. The high-melting-point metal separation and recovery method
according to claim 18, wherein Ca is vaporized and separated when
the molten salt with remnants of Ca is melted in an inert gas
atmosphere after the reaction with said compound of the
high-melting-point metal.
23. The high-melting-point metal separation and recovery method
according to claim 12, wherein the high-melting-point metal is Ti
or a Ti alloy, the molten salt contains CaCl.sub.2 and Ca, and said
melting is performed in an inert gas atmosphere or in vacuum.
24. The high-melting-point metal separation and recovery method
according to claim 23, wherein a Ca concentration of the molten
salt is adjusted in the range of 0.1 to 1.5% by mass before a mixed
substance of said molten salt and Ti or a Ti alloy is melted.
25. The high-melting-point metal separation and recovery method
according to claim 23, wherein Ca is added in said molten salt when
the Ca concentration in the molten salt is less than 0.1% by mass
before the mixed substance of said molten salt and Ti or the Ti
alloy is melted.
26. The high-melting-point metal separation and recovery method
according to claim 24, wherein Ca is added in said molten salt when
the Ca concentration in the molten salt is less than 0.1% by mass
before the mixed substance of said molten salt and Ti or the Ti
alloy is melted.
27. The high-melting-point metal separation and recovery method
according to claim 23, wherein all or part of the molten salt in
which the high-melting-point metal obtained by the reaction is
mixed is maintained in a molten state until being melted in an
inert gas atmosphere.
28. The high-melting-point metal separation and recovery method
according to claim 26, wherein all or part of the molten salt in
which the high-melting-point metal obtained by the reaction is
mixed is maintained in a molten state until being melted in an
inert gas atmosphere.
29. The high-melting-point metal separation and recovery method
according to claim 23, wherein Ca is vaporized and separated when
the molten salt with remnants of Ca is melted in an inert gas
atmosphere after the reaction with said compound of the
high-melting-point metal.
30. The high-melting-point metal separation and recovery method
according to claim 26, wherein Ca is vaporized and separated when
the molten salt with remnants of Ca is melted in an inert gas
atmosphere after the reaction with said compound of the
high-melting-point metal.
31. The high-melting-point metal separation and recovery method
according to claim 28, wherein Ca is vaporized and separated when
the molten salt with remnants of Ca is melted in an inert gas
atmosphere after the reaction with said compound of the
high-melting-point metal.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for separating and
recovering a high-melting-point metal such as Ti by heating and
melting a molten salt such as calcium chloride (CaCl.sub.2) in
which the high-melting-point metal.
BACKGROUND ART
[0002] A Kroll method for reducing titanium tetrachloride
(TiCl.sub.4) by Mg is generally used as an industrial production
method of the high-melting-point metal such as metallic Ti. In the
Kroll method, molten Mg is loaded in a reactor vessel, a TiCl.sub.4
liquid is supplied from above a liquid surface thereof, and the
metallic Ti is produced by reducing TiCl.sub.4 with Mg near the
liquid surface of the molten Mg. The high-purity sponge Ti is
obtained through the Kroll method.
[0003] However, in the Kroll method, a feed rate of TiCl.sub.4 is
restricted because reaction undergoes near the liquid surface of
the molten Mg in the reactor vessel. Additionally, Ti granules
produced are aggregated because of an adhesion property between Ti
and the molten Mg, and the Ti granules are sintered to generate
size-wise grown granules by the heat from the molten liquid.
Therefore, it is difficult to taking out the produced Ti to the
outside of the reactor vessel, and it is also difficult to
continuously produce Ti.
[0004] There have been conducted many researches and developments
in order to solve the above problems. For example, Japanese Patent
Application Publication No. 2004-52037 proposes a metallic titanium
refining method in which reduction is performed using Ca and a
univalent calcium ion (Ca.sup.+) which are generated by
electrolysis in a mixed molten salt including titanium oxide
(TiO.sub.2), calcium chloride (CaCl.sub.2), calcium oxide (CaO),
and/or calcium (Ca). International Patent Application No.
2002-517613 discloses a method for removing oxygen (O.sub.2) from a
metallic compound and the like (for example, TiO.sub.2) by the
electrolysis in the molten salt such as CaCl.sub.2.
[0005] The inventors have also proposed a method in which a
metallic chloride containing TiCl.sub.4 is used as a raw material
and Ti granules or Ti alloy granules are produced in the molten
salt by causing the metallic chloride to react with Ca melted in
the molten salt containing the molten CaCl.sub.2. For example, the
inventors disclose Japanese Patent Application Publication No.
2005-133195 in which, in order to economically replenish Ca in the
molten salt, the Ca being consumed by the reducing reaction between
TiCl.sub.4 and Ca, Ca produced by the electrolysis of the molten
CaCl.sub.2 is utilized and Ca is circularly used.
[0006] The titanium oxide or the titanium chloride is reduced to
produce Ti in these methods, and the obtained Ti exists in the
state in which Ti of a solid matter (powdery matter or granular
matter) is mixed with the molten salt because the molten salt
provides a reaction field where the reducing reaction undergoes at
that time. Therefore, a manipulation (process) is required to
separate Ti from the molten salt in which Ti exists in the mixed
state.
[0007] Currently, in the Kroll method generally used as an
industrial metallic Ti production method, because the
yet-to-be-reacted Mg and a magnesium chloride (MgCl.sub.2) which is
of a by-product are mixed in the sponge metallic Ti obtained
through the reducing process, the yet-to-be-reacted Mg and
MgCl.sub.2 are vaporized and removed by heating through a vacuum
separation process, and the high-purity sponge metallic Ti is
separated and recovered. According to the Kroll method, the
high-quality metallic Ti is obtained. However, a large amount of
thermal energy is required to evaporate Mg and MgCl.sub.2 which
permeated into the sponge's fine structure.
[0008] In the method proposed in Japanese Patent Application
Publication No. 2004-52037 in which the titanium oxide is reduced
by an electrolytic Ca and univalent calcium ion (Ca.sup.+), a
sponge metallic Ti is taken out to the outside of the reaction
tank, and the sponge metallic Ti is separated and recovered by
applying water washing and dilute hydrochloric acid washing to the
sponge metallic Ti to which the salt such as the calcium chloride
adheres. In the method disclosed in International Patent
Publication No. 2002-517613, Ti is obtained while mixed with the
molten salt such as CaCl.sub.2, the manipulation for removing Ti
from the adhering molten salt by the water washing is required
after Ti is appropriately comminuted.
[0009] Even in the metallic Ti production in which TiCl.sub.4 is
reduced by Ca, in the finial separation and recovery process, the
molten CaCl.sub.2 liquid in which the powdery and granular metallic
Ti is mixed is taken out to the outside of the reactor vessel and
Ti is separated by a squeezing manipulation of mechanical
compression. In this case, the adhering molten salt is removed by
the water washing or the like after the separation.
[0010] Although the water washing process is relatively simple
work, many man-hours and a large space are required due to a wet
process. It is not easy to remove a residual water after the water
washing. The insufficient removal of the water has possibly a
negative influence on the Ti quality such that an oxygen content
and a hydrogen content of the obtained Ti are increased. Even if
the produced Ti is exposed to an open air after cooling, an
oxidation takes place at a surface of Ti to decrease its quality.
Additionally, a large amount of energies are required in order that
CaCl.sub.2 which is melted once in the water and separated from Ti
is transformed from the aqueous solution state into the molten
CaCl.sub.2 liquid which can be used as a raw material of the
electrolysis for reusing Ca.
DISCLOSURE OF THE INVENTION
[0011] An object of the invention is to provide a method for
separating and recovering the high-quality high-melting-point metal
from the molten salt in which the high-quality high-melting-point
metal is mixed, particularly a method for with less energy
efficiently separating and recovering the high-quality Ti or Ti
alloy from the CaCl.sub.2-containing molten salt in which the Ti or
Ti alloy produced by reducing TiCl.sub.4 by Ca is mixed.
[0012] In order to achieve the object, the inventors studied a
method in which the mechanical squeezing manipulation and the water
washing were not used, and the inventors performed experiments to
study a possibility of the Ti separation (liquid phase separation)
in the state where the mixed substance is heated to a temperature
at which the Ti is melted (dissolved) and the mixed substance
exists in the liquid phase, when the metallic Ti is separated and
recovered from the mixed substance in which the metallic Ti
produced by the Ca reduction, the molten CaCl.sub.2, and the
remaining yet-to-be-reacted Ca are mixed.
[0013] The study is inspired by the following facts. That is,
CaCl.sub.2 has a boiling point (2008.degree. C.) higher than a
melting point (1680.degree. C.) of Ti, and CaCl.sub.2 has a
specific gravity of about 2 in the liquid-phase state while Ti has
a specific gravity of about 4.5, so that the liquid phase
separation between CaCl.sub.2 and Ti can be achieved when the mixed
substance is kept at temperatures not less than the melting point
of Ti.
[0014] In the experiment, the metallic Ti and CaCl.sub.2 whose
quantities are substantially equal to each other are loaded in a
water-cooled copper crucible, the metallic Ti and CaCl.sub.2 are
heated to temperatures not less than the melting point of Ti, and
the whole of the metallic Ti and CaCl.sub.2 is melted. As a result,
the experiment shows that the metallic Ti and CaCl.sub.2 are
clearly separated according to a difference in specific
gravity.
[0015] For both the Ti recovery achieved by the liquid phase
separation and the Ti recovery achieved by the vacuum separation
adopted in the conventional Kroll method, a composition (that is,
mixed ratio of "Ti, CaCl.sub.2, and residual Ca" or "Ti,
MgCl.sub.2, and yet-to-be-reacted Mg") of the mixed substance is
properly premised according to an actual condition to estimate
thermal energies (equivalent to electric power) necessary for the
recovery. In the required energy, given that the latter (Ti
recovery achieved by the vacuum separation) is set to 100, the
former (Ti recovery achieved by the liquid phase separation) is 38.
Accordingly, it is found that the energies can significantly be
saved by applying the liquid phase separation for the Ti
recovery.
[0016] The reason why the large amount of thermal energies are
required for the vacuum separation in the Ti recovery is that not
only the heat of vaporization is required to vaporize and separate
MgCl.sub.2 and yet-to-be-reacted Mg, but also it takes long time to
thoroughly allow vaporization and separation deep into a center
portion in the reactor vessel. On the other hand, in the Ti
recovery achieved by the liquid phase separation, CaCl.sub.2 is not
vaporized because of CaCl.sub.2 having the high boiling point. That
is one of advantages in the Ti recovery achieved by the liquid
phase separation.
[0017] The inventors also found that Ca melted in CaCl.sub.2 plays
an important role in separating Ti and CaCl.sub.2. That is, in
performing the liquid phase separation of Ti by heating and melting
CaCl.sub.2 in which Ti is mixed, Ti starts to dissolve in
CaCl.sub.2 and gets mixed in the granular form when Ca does not
exist. However, when Ca is melted in CaCl.sub.2 even slightly, the
melting of Ti into CaCl.sub.2 is suppressed and the Ti
concentration in CaCl.sub.2 is remarkably decreased after Ti is
separated.
[0018] Accordingly, in performing the liquid phase separation of
Ti, the decrease in Ti recovery percentage can be suppressed by
melting Ca in CaCl.sub.2. Furthermore, Ca is circulated while
CaCl.sub.2 is used as a medium in the method for producing Ti or Ti
alloys by reducing TiCl.sub.4 with Ca, proposed by the inventor.
Therefore, when Ti is mixed in CaCl.sub.2, there likely arises
problems in the electrolysis process. However, the risk of raising
the problem is erased by the invention.
[0019] The invention is made based on such ideas and the results of
the studies, and a gist of the invention pertains to a following
high-melting-point metal separation and recovery method.
[0020] That is, the invention is a high-melting-point metal
separation and recovery method in which a molten salt mixed with a
high-melting-point metal is melted in an inert gas atmosphere to
perform liquid phase separation of the high-melting-point metal,
the molten salt being used as a reaction field.
[0021] Ti and Zr can be cited as an example of the
"high-melting-point metal".
[0022] As used herein, "being mixed" shall mean that the mixed
state is not a homogeneous phase. That is, "(be) mixed" shall mean
that the high-melting-point metal in the solid phase exists in the
molten salt, whereas the substance containing the "mixed" component
is also referred to as "mixed substance".
[0023] The "reaction field" shall mean a region where the reaction
undergoes. In such cases, the "reaction field" shall mean the
molten salt which acts as the reaction field, i.e., the molten salt
where the reaction of some kind is in progress.
[0024] The "melting" shall mean a manipulation for heating the
molten salt, in which the high-melting-point metal is mixed, to
transform the whole of the molten salt into the liquid state.
[0025] The "liquid phase separation" shall mean, as described
above, the separation in a state of having the mixed substance in
the liquid phase. In such cases, the "liquid phase separation"
shall mean that the high-melting-point metal and the molten salt
are vertically separated by the difference in specific gravity
while existing in the liquid phase.
[0026] The molten salt in which the high-melting-point metal is
mixed is not one in which the high-melting-point metal is simply
mixed in the usual molten salt, but the one that acts as the
reaction field, i.e., the one that is taken out from an arbitrary
process. The molten salt may be solidified and apparently formed in
the solid-phase state, when the separation and recovery method of
the invention is applied. This is because the molten salt becomes
the molten state in the melting process.
[0027] The molten salt in which the high-melting-point metal is
mixed is melted to implement the separation and recovery method of
the invention. That is, the molten salt in which the
high-melting-point metal is mixed is heated until the whole of the
molten salt becomes the liquid state, which separates the
high-melting-point metal and the molten salt as the reaction field
in the liquid phase. That is, the separation undergoes by a
difference in specific gravity, whereby usually the molten salt is
located in an upper layer while the high-melting-point metal is
located in a lower layer.
[0028] Assuming that M is a melting point of the high-melting-point
metal to be separated and recovered and B is a boiling point of the
molten salt, when the molten salt satisfies a relationship of
B>M, the high-melting-point metal having the melting point M can
be used as the target. However, the kinds of the molten salt that
can be used in practice are relatively limited due to restrictions
by handling difficulties, characteristics (particularly, a harmful
effect on an environment), prices, and the like. For example, in
the case where Ti (melting point of 1680.degree. C.) is the target
high-melting-point metal, the molten salt may be represented by
CaCl.sub.2 (boiling point of 2008.degree. C.), LaCl.sub.3 (boiling
point of 1710.degree. C.), SnCl.sub.3 (boiling point of
2040.degree. C.), CaF.sub.2 (boiling point of 2510.degree. C.), or
BaF.sub.2 (boiling point of 2137.degree. C.).
[0029] FIG. 1 is a view schematically illustrating the way that the
high-melting-point metal separation and recovery method according
to the invention is implemented to separate the high-melting-point
metal from the molten salt.
[0030] In FIG. 1, the molten salt in which the high-melting-point
metal is mixed is loaded in a reactor vessel 1, and the molten salt
and the high-melting-point metal are heated to a molten state. The
liquid phase separation undergoes between the high-melting-point
metal and the molten salt in the molten state due to the difference
in specific gravity. In the example shown in FIG. 1, the liquid
phase separation undergoes in such a manner that a molten salt 2 is
located in the upper layer while a high-melting-point metal 3 is
located in the lower layer, and the high-melting-point metal 3 can
be taken out and recovered from a high-melting-point metal
discharge port 4 disposed at a bottom of the heating vessel 1. On
the other hand, the molten salt 2 can be taken from a molten salt
discharge port 5 disposed in the vicinity of an intermediate-height
portion of the reactor vessel 1.
[0031] The positions where the high-melting-point metal discharge
port 4 and molten salt discharge port 5 are disposed may
appropriately be determined in consideration of a mixed ratio of
the high-melting-point metal and the molten salt. Using the heating
vessel in which the discharge ports are provided at plural
positions, any of discharge ports may selectively be used according
to each liquid level of the upper layer and lower layer. Loading
the molten salt in which the high-melting-point metal is mixed and
taking out the high-melting-point metal 3 and the molten salt 2 are
performed systematically, which allows the recovery to be
semi-continuously or continuously performed.
[0032] It is necessary that a heating vessel having high resistance
to high temperatures is used so as not to allow a melt leakage of
the loaded materials. For example, a water-cooled copper vessel can
be used in the case where CaCl.sub.2 is used as the molten salt
while Ti is the high-melting-point metal.
[0033] For example, a plasma melting method and a high-frequency
induction melting method can be employed as a heating and melting
means.
[0034] The reason why the melting is performed in the inert gas
atmosphere is that the reaction of the high-melting-point metal
with oxygen or other gases and absorption of the oxygen or other
gases by the high-melting-point metal are prevented because
reactivity is enhanced in any substance in the system under the
high-temperature condition. Although a pressure of the inert gas
during melting is not particularly limited, usually the melting is
performed at a normal pressure (atmospheric pressure).
[0035] In the high-melting-point metal separation and recovery
method of the invention, it is conceived that "the molten salt may
be used as the reaction field in producing the high-melting-point
metal and the molten salt mixed with the high-melting-point metal
obtained by a reaction in the reaction field is used (this
embodiment mode is referred to as Embodiment 1).
[0036] The method of Embodiment 1 is the method in which a
condition that a molten salt is used as the reaction field in
producing the high-melting-point metal to be mixed in said molten
salt is added as the subject-matter.
[0037] In the high-melting-point metal separation and recovery
method (including the method of Embodiment 1), a condition that a
boiling point of the molten salt is higher than a melting point of
the high-melting-point metal is clearly expressed as one of
subject-matters, and the condition may be added (Embodiment 2).
[0038] The prerequisite that the boiling point of the molten salt
is higher than the melting point of the high-melting-point metal is
required in order to implement the separation and recovery method
of the invention to perform the liquid phase separation of the
high-melting-point metal. The method of Embodiment 2 is the one
which clearly specifies this.
[0039] In the high-melting-point metal separation and recovery
method (including the methods of Embodiments 1 and 2) of the
invention, the molten salt containing CaCl.sub.2 may be used
(Embodiment 3). The "molten salt containing CaCl.sub.2" shall mean
a molten salt containing only the molten CaCl.sub.2 or a molten
salt in which CaF.sub.2 and the like are added to the molten
CaCl.sub.2 to lower the melting point or to adjust its viscosity or
the like.
[0040] The suitable reaction field can be formed by applying the
method of Embodiment 3 in the case of the embodiment mode in which
the high-melting-point metal obtained by reducing a after-mentioned
high-melting-point metal compound (for example, TiCl.sub.4) with Ca
is separated and recovered.
[0041] In the high-melting-point metal separation and recovery
method (any of the methods of Embodiments 1 to 3) of the invention,
it is conceived that "the molten salt contains Ca and the
high-melting-point metal may be obtained by causing the
high-melting-point metal compound to react with Ca in the molten
salt" (Embodiment 4).
[0042] A high-melting-point metal chloride such as TiCl.sub.4 can
be cited as an example of the high-melting-point metal compound.
That is, in the method of Embodiment 4, a molten salt is specified
as the molten salt in which the high-melting-point metal obtained
by causing the high-melting-point metal chloride such as TiCl.sub.4
to react with Ca is mixed.
[0043] In the method (the method of Embodiment 4) of the invention,
it can be conceived that "the high-melting-point metal is Ti or a
Ti alloy and the high-melting-point metal compound contains
TiCl.sub.4 (Embodiment 5)".
[0044] For example, as schematically shown in an after-mentioned
application example of the separation and recovery method of the
invention, the mode wherein the liquid phase separation of the
metallic Ti is performed by melting the molten salt, in which the
metallic Ti obtained by causing TiCl.sub.4 to react with Ca is
mixed, corresponds to the method of Embodiment 5. When TiCl.sub.4
and other metallic chloride are caused to react with Ca, the other
metallic chloride is simultaneously reduced with Ca to thereby end
up having the Ti alloy mixed in the molten salt, so that the Ti
alloy can be separated and recovered.
[0045] In the high-melting-point metal separation and recovery
method of the invention, desirably a high-melting-point metal is Ti
or a Ti alloy, the molten salt contains CaCl.sub.2 and Ca, and the
melting is performed in an inert gas atmosphere or in vacuum
(Embodiment 6).
[0046] Ca melted in the CaCl.sub.2-containing molten salt
suppresses the melting of Ti or the Ti alloy in the molten salt and
significantly decreases the Ti concentration in the molten salt
after the Ti or the Ti alloy is separated, when the molten salt in
which the high-melting-point metal is mixed is heated to perform
the liquid phase separation between the molten salt and such a
metal. In an example of the study results, Ti is melted in the
molten salt in the range of 0.5 to 1% by mass when the melted Ca
does not exists in CaCl.sub.2, and the Ti concentration in the
molten salt is decreased to 50 ppm when CaCl.sub.2 contains Ca of
1% by mass.
[0047] The application of the method of Embodiment 6 can suppress
the melting of Ti or the Ti alloy in the molten salt by a factor of
1/100 or less. The lower limit of the Ca concentration in the
molten salt is not limited because this effect can be recognized
even if Ca is slightly melted in the molten salt. The upper limit
of the Ca concentration in the molten salt is not particularly
limited because the effect exhibits even if the Ca concentration is
close to a saturation concentration in the CaCl.sub.2-containing
molten salt. To stretch a point, the upper limit of the Ca
concentration is the saturation concentration (in the case of
CaCl.sub.2, about 1.5% by mass) in the CaCl.sub.2-containing molten
salt.
[0048] The Ca may be contained in a molten salt before the molten
salt mixed with Ti or the Ti alloy is melted (i.e., at any time
before the melting is started). In other words, in the case where
Ca is not contained in the molten salt in which the
high-melting-point metal initially produced by the reaction with Ca
is mixed, the same effect as the case where Ca is initially
contained is obtained even if Ca is added just before the melting
is started.
[0049] In the separation and recovery method of the invention, as
described above, the melting is performed in the inert gas
atmosphere. This is because the reaction of the high-melting-point
metal with oxygen or other gases and the absorption of the oxygen
or other gases in the high-melting-point metal are prevented.
Usually the inert gas such as Ar is used. Like Embodiment 6, the
melting may be performed in vacuum in melting the
CaCl.sub.2-containing molten salt in which Ti or the Ti alloy is
mixed. As used herein, the "vacuum" shall mean a low-pressure
state. A level of vacuum may appropriately be set to an extent in
which the oxidation of Ti or the Ti alloy or reaction of the
high-melting-point metal with oxygen or other gases in the
high-melting-point metal are prevented.
[0050] In the high-melting-point metal separation and recovery
method (the method of Embodiment 6) of the invention, desirably a
Ca concentration of the molten salt is adjusted in the range of 0.1
to 1.5% by mass before a mixed substance of the molten salt and Ti
or the Ti alloy is melted (Embodiment 7).
[0051] The effect of suppressing the melting of Ti or the Ti alloy
in the molten salt is rather low when the Ca concentration in the
molten salt is lower than 0.1% by mass, and a risk of Ca
precipitation is generated by a fluctuation in operation condition
when the Ca concentration exceeds 1.5% by mass. More desirably the
Ca concentration ranges from 0.3 to 1.0% by mass.
[0052] As described above, the effect of suppressing the melting of
Ti or the Ti alloy in the molten salt is discerned even if Ca is
slightly melted in the molten salt. Furthermore, the melting of Ti
in CaCl.sub.2 can effectively be suppressed when the method of
Embodiment 7 in which the Ca concentration in the molten salt is
adjusted within the above range is applied before the melting.
[0053] In the method of Embodiment 6 or 7, preferably Ca is added
in the molten salt when a Ca concentration in the molten salt is
lower than 0.1% by mass before the mixed substance of the molten
salt and Ti or the Ti alloy is melted (Embodiment 8).
[0054] The method of Embodiment 8 is the one specifying an
operational mode in which the Ca concentration in the molten salt
is controlled and properly adjusted before the melting. The melting
of Ti can effectively be suppressed to assuredly perform the
separation between CaCl.sub.2 and Ti or the Ti alloy.
[0055] Although measurement of the Ca concentration can be made by
a hydrogen generation method, a neutralization titration method, or
the like, the Ca concentration may indirectly be controlled based
on material balances of an actual operation performance.
[0056] In the separation and recovery method of the invention, the
methods of Embodiments 4 to 8 are the ones which can be suitably
performed when the molten salt contains CaCl.sub.2 while Ti or the
Ti alloy is the high-melting-point metal. That is, the presence of
the melted Ca in CaCl.sub.2 suppresses the melting of Ti or the Ti
alloy in CaCl.sub.2 to significantly decrease the Ti concentration
in CaCl.sub.2 after the liquid phase separation, which allows the
Ti recovery percentage to be enhanced.
[0057] Further, in the production of Ti or the Ti alloy by the Ca
reduction in which Ca is circularly used by virtue of CaCl.sub.2 as
a medium, although the melting of Ti or the Ti alloy in CaCl.sub.2
should possibly become troublesome in the electrolysis process, the
risk of the melting of Ti or the Ti alloy in CaCl.sub.2 can be
eliminated.
[0058] In the high-melting-point metal separation and recovery
method (any of the methods of Embodiments 1 to 8) of the invention,
"desirably all or part of the molten salt in which the
high-melting-point metal obtained by the reaction is mixed is
maintained in a molten state until melted in an inert gas
atmosphere" (Embodiment 9).
[0059] As specifically described later, the application of the
method of Embodiment 9 can save the thermal energies necessary to
melt the solidified-state mixed substance consisted of the
high-melting-point metal and the molten salt. Desirably the whole
of the mixed substance is maintained in a molten state. However,
the thermal energies can be saved even if part of the mixed
substance is melted.
[0060] In the high-melting-point metal separation and recovery
method (any of the methods of Embodiments 4 to 9) of the invention,
Ca may be vaporized and separated when the molten salt with
remnants of Ca is melted in an inert gas atmosphere after the
reaction with the high-melting-point metal compound (Embodiment
10).
[0061] That is, Ca can be removed from the molten salt after Ti or
the Ti alloy is separated, and the method of Embodiment 10 is a
desirable method when the molten salt separated from the
high-melting-point metal compound is reused. However, in this case,
it is considered that Ca is not completely removed but part thereof
is retained in CaCl.sub.2.
[0062] The separation and recovery method of Embodiment 10 will
specifically be described later in an application example of the
separation and recovery method of the invention. For example, in
the case where TiCl.sub.4 is reduced with Ca to produce the
metallic Ti, when the method of Embodiment 10 is applied to the
process of separating the metallic Ti, desirably Ca which obstructs
the electrolysis can be removed in performing the electrolysis of
the molten salt including CaCl.sub.2.
BRIEF DESCRIPTION OF THE DRAWINGS
[0063] FIG. 1 is a view schematically illustrating a state in which
a high-melting-point metal separation and recovery method according
to the invention is implemented to separate a high-melting-point
metal from a molten salt; and
[0064] FIG. 2 is a view illustrating a configuration example of an
apparatus for producing a metallic Ti by reducing TiCl.sub.4 with
Ca.
BEST MODE FOR CARRYING OUT THE INVENTION
[0065] A best mode for carrying out the invention will be described
below with reference to the drawing. FIG. 2 is a view illustrating
a configuration example of an apparatus for producing a metallic Ti
by reducing TiCl.sub.4 with Ca. A process enabling to implement a
separation and recovery method of Embodiment 6 is incorporated into
the configuration of FIG. 2.
[0066] Referring to FIG. 2, a reducing agent feed pipe 7 for
feeding Ca which is of a reducing agent is provided in a ceiling
portion of a reactor vessel 6. A bottom of the reactor vessel 6 is
tapered downward while a diameter of the reactor vessel 6 is
gradually reduced in order to promote discharge of produced Ti
granules. A Ti discharge pipe 8 is provided in a central portion at
lower end of the reactor vessel 6 to discharge the produced Ti
granules.
[0067] On the other hand, a cylindrical separation wall 9 is
disposed inside the reactor vessel 6 while a predetermined gap is
provided between the separation wall 9 and an inner surface of a
straight body portion of the reactor vessel 6. A molten salt
discharge pipe 10 is provided in an upper portion of the reactor
vessel 6 to discharge CaCl.sub.2 in the reactor vessel 6 to the
side. A raw material feed pipe 11 for feeding TiCl.sub.4 which is
of a raw material to Ti is provided in a lower portion of the
reactor vessel 6 while piercing through the separation wall 9 to
reach a central portion of the reactor vessel 6.
[0068] The molten CaCl.sub.2 liquid in which Ca is melted is held
as the molten salt in the reactor vessel 6. A level of the molten
CaCl.sub.2 liquid is set higher than the molten salt discharge pipe
10 and lower than an upper end of the separation wall 9. The molten
Ca liquid is held on the molten CaCl.sub.2 liquid inside the
separation wall 9.
[0069] Under this condition, a TiCl.sub.4 gas is supplied to the
molten CaCl.sub.2 liquid located inside the separation wall 9
through the raw material feed pipe 11. This enables TiCl.sub.4 to
be reduced by Ca in the molten CaCl.sub.2 liquid inside the
separation wall 9 to produce the granular metallic Ti in the molten
CaCl.sub.2 liquid. The Use of the raw material in which the
TiCl.sub.4 gas and other metallic chloride gas are mixed can
produce the Ti alloy. The TiCl.sub.4 gas and other metallic
chloride gas are simultaneously reduced by Ca, so that the Ti alloy
granules can be produced.
[0070] The Ti granules produced in the molten CaCl.sub.2 liquid
located inside the separation wall 9 in the reactor vessel 6 move
downward through the molten CaCl.sub.2 liquid and deposited on the
bottom of the reactor vessel 6. The deposited Ti granules are
appropriately taken out downward from the Ti discharge pipe 8 along
with the molten CaCl.sub.2 liquid, and the deposited Ti granules
are delivered to a separation process 12. In this case, some amount
of yet-to-be-reacted Ca remains in the CaCl.sub.2 liquid taken
out.
[0071] The molten CaCl.sub.2 liquid whose Ca is consumed by the
reducing reaction inside the separation wall 9 moves upward at the
outside of the separation wall 9 via the bottom of the separation
wall 9, and the molten CaCl.sub.2 liquid is discharged from the
molten salt discharge pipe 10. The discharged molten CaCl.sub.2
liquid is delivered to an electrolysis process 13.
[0072] Inside the separation wall 9, Ca is replenished to the
molten CaCl.sub.2 liquid from the molten Ca liquid held on the
molten CaCl.sub.2 liquid. At the same time, Ca is replenished onto
the molten CaCl.sub.2 liquid through the reducing agent feed pipe
7.
[0073] On the other hand, in the separation process 12, the Ti
granules taken out along with the molten CaCl.sub.2 liquid are
loaded in a heating vessel 15, the Ti granules are also heated to
be in a molten state, and the separation is generated by the
difference in specific gravity, whereby a molten CaCl.sub.2 liquid
16 is located in an upper layer while a metallic Ti 17 is located
in a lower layer. The molten CaCl.sub.2 liquid 16 in the upper
layer is taken out from a molten salt discharge port 19, and the
molten CaCl.sub.2 liquid 16 is delivered to the electrolysis
process 13 along with the molten CaCl.sub.2 liquid taken out from
the reactor vessel 6. The metallic Ti 17 in the lower layer is
taken out from a high-melting-point metal discharge port 18, and
the metallic Ti 17 is solidified to yield an ingot.
[0074] Desirably a temperature during melting ranges from 1680 to
1750.degree. C. Because the melting temperature of Ti is
1680.degree. C., the Ti granules are not melted when the
temperature is lower than this. The temperature exceeding
1750.degree. C. easily reduces durability of facilities such as the
heating vessel. The temperature exceeding 1750.degree. C. is
disadvantageous from the viewpoint of energies necessary for
heating.
[0075] In the electrolysis process 13, the molten CaCl.sub.2 liquid
introduced from the reactor vessel 6 and the separation process 12
is separated into Ca and the Cl.sub.2 gas through the electrolysis.
Ca and CaCl.sub.2 are returned to the reactor vessel 6. Because
CaCl.sub.2 in which Ca is melted is used in the reactor vessel 6,
it is not necessary to separate Ca and CaCl.sub.2.
[0076] The Cl.sub.2 gas generated in the electrolysis process 13 is
delivered to a chlorination process 14. In the chlorination process
14, TiO.sub.2 is chlorinated to produce TiCl.sub.4. The oxygen of
the by-product is discharged in the form of CO.sub.2 by
simultaneously using carbon powders (C). The produced TiCl.sub.4 is
introduced into the reactor vessel 6 through the raw material feed
pipe 11. Thus, Ca which is of the reducing agent and Cl.sub.2 gas
are circulated by the circulation of CaCl.sub.2.
[0077] That is, the metallic Ti production process is an example to
which the separation and recovery method of Embodiment 6 is
applied. In the separation and recovery method of Embodiment 6, the
molten salt in which the metallic Ti is mixed is melted to perform
the liquid separation of the metallic Ti. According to the metallic
Ti production process, the metallic Ti is continuously produced
just by essentially replenishing TiO.sub.2 and C.
[0078] In the separation and recovery method (any of the methods of
Embodiments 1 to 8) of the invention, all or part of the molten
salt in which the high-melting-point metal obtained by the reaction
is mixed is desirably maintained in a molten state until being
melted in an inert gas atmosphere (Embodiment 9).
[0079] When Embodiment 9 is applied to the example of the metallic
Ti production process shown in FIG. 2, the mixed substance of the
Ti granules taken out from the Ti discharge pipe 8 and the molten
CaCl.sub.2 liquid is maintained in a molten state until being
delivered to the separation process 12 and loaded in the heating
vessel 15. That is, the mixed substance of the Ti granules is
loaded in the heating vessel 15 while the Ti granules are mixed in
the molten CaCl.sub.2 liquid. Even if part of the molten CaCl.sub.2
liquid is solidified, although the energy is required to melt the
part of the molten CaCl.sub.2 liquid again, there is no trouble on
the separation and recovery manipulation. Application of the method
of Embodiment 9 can save the thermal energies necessary to heat and
melt the mixed substance to put the whole of the mixed substance in
a molten state.
[0080] The method of Embodiment 10 is a method for vaporizing and
separating Ca when the molten salt having the remnants of Ca after
the reaction with the high-melting-point metal compound is melted
in an inert gas atmosphere, in the separation and recovery method
(one of methods of Embodiment 4 to 9) of the invention.
[0081] For example, in the metallic Ti production method shown in
FIG. 2, the molten CaCl.sub.2 liquid is separated into Ca and the
Cl.sub.2 gas by the electrolysis in the electrolysis process 13.
However, when the yet-to-be-reacted Ca remains in the molten
CaCl.sub.2 liquid, a reverse reaction in which Ca reacts with
Cl.sub.2 produced by the electrolysis to return to CaCl.sub.2 is
generated near the anode electrode, which decreases current
efficiency. In this case, when the separation and recovery method
of Embodiment 10 is applied, Ca in the molten CaCl.sub.2 liquid is
removed, so that the decrease in current efficiency caused by the
reverse reaction can be suppressed.
[0082] In the case where the molten salt contains only CaCl.sub.2
like the above example, because Ca is melted at 845.degree. C. and
vaporized at 1420.degree. C., the large amount of Ca is vaporized
and removed in the procedure of melting the mixed substance of the
Ti granules and the molten CaCl.sub.2 liquid which are taken out
from the Ti discharge pipe 8.
INDUSTRIAL APPLICABILITY
[0083] According to the high-melting-point metal separation and
recovery method of the invention, compared with the sponge metallic
Ti recovery achieved by the vacuum separation used in the Kroll
method, the metallic Ti or the Ti alloy can be recovered with the
extremely small amount of energies. The continuous work and saving
in labor can also be achieved in the high-melting-point metal
separation and recovery method of the invention, and the
high-melting-point metal separation and recovery method of the
invention can contribute largely to the reduction of production
costs. The obtained Ti has good quality because there is no risk of
mixing water having the adverse effect on the Ti quality.
[0084] Accordingly, the high-melting-point metal separation and
recovery method of the invention can effectively be utilized as the
separation and recovery method in producing the high-melting-point
metal, particularly producing Ti or the Ti alloy through the Ca
reduction of TiCl.sub.4.
* * * * *