U.S. patent application number 11/631364 was filed with the patent office on 2009-08-27 for method and apparatus for producing metal by electrolysis of molton salt.
Invention is credited to Susumu Kosemura, Eiji Nishimura, Yuichi Ono, Masanori Yamaguchi.
Application Number | 20090211916 11/631364 |
Document ID | / |
Family ID | 35782673 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090211916 |
Kind Code |
A1 |
Yamaguchi; Masanori ; et
al. |
August 27, 2009 |
Method and apparatus for producing metal by electrolysis of molton
salt
Abstract
A process for production of a metal includes a step of filling a
metal chloride in an electrolysis vessel having positive and
negative electrodes, a step of heating and fusing the metal
chloride to make an electrolytic bath, and a step of electrolyzing
the electrolytic bath to deposit metal on the negative electrode in
a solid state. In addition, in an apparatus for production of a
metal in which a metal chloride is filled in an electrolysis vessel
having positive and negative electrodes, the metal chloride is
heated and molten to make an electrolytic bath and the electrolytic
bath is electrolyzed to deposit the metal on the negative electrode
in a solid state, the electrolytic bath is divided into an
electrolysis chamber and a dissolution chamber by a dividing wall,
the positive electrode is arranged in the electrolysis chamber, the
negative electrode is arranged to enable orbital movement in a
circle through the electrolysis chamber and dissolution chamber,
and the metal deposited on the negative electrode in the
electrolysis chamber is separated and recovered in the dissolution
chamber.
Inventors: |
Yamaguchi; Masanori;
(Kanagawa, JP) ; Ono; Yuichi; (Kanagawa, JP)
; Kosemura; Susumu; (Kanagawa, JP) ; Nishimura;
Eiji; (Kanagawa, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
35782673 |
Appl. No.: |
11/631364 |
Filed: |
June 27, 2005 |
PCT Filed: |
June 27, 2005 |
PCT NO: |
PCT/JP05/11747 |
371 Date: |
October 21, 2008 |
Current U.S.
Class: |
205/367 ;
204/260 |
Current CPC
Class: |
C25C 7/08 20130101; C25C
3/00 20130101; C25C 7/007 20130101 |
Class at
Publication: |
205/367 ;
204/260 |
International
Class: |
C25C 3/00 20060101
C25C003/00; C25C 7/00 20060101 C25C007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2004 |
JP |
2004-192905 |
Claims
1-10. (canceled)
11. A process for production of a metal by molten-salt
electrolysis, the process comprising: a step of filling metal
chloride in an electrolysis vessel having a positive electrode and
a negative electrode; a step of heating and fusing the metal
chloride to make an electrolytic bath; and a step of electrolyzing
the electrolytic bath to deposit metal on the negative electrode in
a solid state.
12. The process for production of a metal by molten-salt
electrolysis according to claim 11, wherein the temperature of the
electrolytic bath used in the molten-salt electrolysis is
maintained at not more than the melting point of the metal.
13. The process for production of a metal by molten-salt
electrolysis according to claim 11, wherein the temperature of the
electrolytic bath used in the molten-salt electrolysis is
maintained at not less than the melting point of the metal, and at
the same time the temperature of the negative electrode is
maintained at not more than the melting point of the metal.
14. The process for production of a metal by molten-salt
electrolysis according to claim 11, wherein the metal in a solid
state deposited on the negative electrode is scraped by a
mechanical means.
15. The process for production of a metal by molten-salt
electrolysis according to claim 12, wherein the metal in a solid
state deposited on the negative electrode is scraped by a
mechanical means.
16. The process for production of a metal by molten-salt
electrolysis according to claim 13, wherein the metal in a solid
state deposited on the negative electrode is scraped by a
mechanical means.
17. The process for production of a metal by molten-salt
electrolysis according to claim 11, wherein the negative electrode
on which the metal in a solid state is deposited is immersed in
metal chloride filled in a recovery vessel maintained at a
temperature not less than the melting point of the metal, so as to
recover the metal.
18. The process for production of a metal by molten-salt
electrolysis according to claim 12, wherein the negative electrode
on which the metal in a solid state is deposited is immersed in
metal chloride filled in a recovery vessel maintained at a
temperature not less than the melting point of the metal, so as to
recover the metal.
19. The process for production of a metal by molten-salt
electrolysis according to claim 13, wherein the negative electrode
on which the metal in a solid state is deposited is immersed in
metal chloride filled in a recovery vessel maintained at a
temperature not less than the melting point of the metal, so as to
recover the metal.
20. The process for production of a metal by molten-salt
electrolysis according to claim 11, wherein the electrolytic bath
is divided into an electrolysis chamber and a dissolution chamber
by a dividing wall, the positive electrode is arranged in the
electrolysis chamber, and the negative electrode is arranged to
enable orbital movement in circle through the electrolysis chamber
and dissolution chamber, wherein the temperature of the negative
electrode is maintained at a temperature not more than the melting
point of the metal when the negative electrode passes through the
electrolysis chamber and the temperature of the negative electrode
is maintained at a temperature not less than the melting point of
the metal when the negative electrode passes through the
dissolution chamber.
21. The process for production of a metal by molten-salt
electrolysis according to claim 20, wherein the negative electrode
comprises plural electrodes and the electrodes are arranged on the
orbital path.
22. The process for production of a metal by molten-salt
electrolysis according to claim 11, wherein the metal chloride is
calcium chloride and the metal is calcium metal.
23. An apparatus for production of a metal by molten-salt
electrolysis, in which metal chloride is filled in an electrolysis
vessel having a positive electrode and a negative electrode, the
metal chloride is heated and molten to make an electrolytic bath,
and the electrolytic bath is electrolyzed to deposit metal on the
negative electrode in a solid state, wherein the electrolytic bath
is divided into an electrolysis chamber and a dissolution chamber
by a dividing wall, the positive electrode is arranged in the
electrolysis chamber, the negative electrode is arranged to enable
orbital movement in a circle through the electrolysis chamber and
dissolution chamber, and wherein the metal deposited on the
negative electrode while the electrode is in the electrolysis
chamber is separated and recovered while the electrode is in the
dissolution chamber.
24. The apparatus for production of metal by molten-salt
electrolysis according to claim 23, wherein the negative electrode
comprises plural electrodes and the electrodes are arranged on the
orbital path.
Description
TECHNICAL FIELD
[0001] The present invention relates to the recovery of metal from
a chloride thereof, and in particular, relates to a method and an
apparatus for producing metal by electrolysis of molten salts
containing metal chlorides.
BACKGROUND ART
[0002] Conventionally, titanium metal, which is a simple substance,
is produced by the Kroll method in which titanium tetrachloride is
reduced by molten magnesium to obtain sponge titanium, and various
kinds of improvements have been made to reduce the cost of
production. However, since the Kroll method is a batch process in
which a set of operations is repeated noncontinuously, there is a
limitation to its efficiency.
[0003] To resolve such a situation, a method in which titanium
oxide is reduced by calcium metal in molten salt to obtain titanium
metal directly (see WO99/064638 and Japanese Unexamined Patent
Application Publication No. 2003-129268), one in which an EMR
method in which a reducing agent containing an active metal such as
calcium or an active metal alloy is prepared, and one in which a
titanium compound is reduced by electrons emitted from the reducing
agent to yield titanium metal (see Japanese Unexamined Patent
Application Publication No. 2003-306725) have been proposed. In
these methods, calcium oxide, which is a by-product of the
electrolytic reaction, is dissolved in calcium chloride, and
molten-salt electrolysis is performed to recover and reuse calcium
metal. However, since the calcium metal generated during the
electrolytic reaction is in a liquid state and has high solubility
in calcium chloride, it dissolves easily in the calcium chloride.
There has been no disclosure of a technique to recover calcium
metal in a solid state alone.
[0004] Furthermore, a technique in which a molten salt electrolysis
is performed at a temperature lower than the conventional
electrolysis using a complex molten salt having a melting point
lower than that of calcium metal to deposit calcium metal on a
negative electrode in a solid state is disclosed (see U.S. Pat. No.
3,226,311). However, in this production method, it is necessary to
prepare the complex molten salt specially, and the cost is
considerable.
[0005] As explained above, there is a problem in that it is
difficult to recover an active metal such as calcium metal alone,
and there is a problem in that the cost is high even if the
recovery is possible.
[0006] The present invention has been completed in view of the
above situation, and an object of the present invention is to
provide a method for production of metal by molten-salt
electrolysis, in which a metal used for reducing, such as an oxide
or chloride of titanium metal, is recovered in a solid state and at
low cost.
DISCLOSURE OF THE INVENTION
[0007] That is, a method for production of metal by molten-salt
electrolysis of the present invention has a step of filling an
electrolysis vessel having a positive electrode and negative
electrode with a metal chloride, a step of heating to fuse the
metal chloride to make an electrolytic bath, and a step of
electrolyzing the electrolytic bath to deposit metal in a solid
state on the negative electrode.
[0008] By the present invention, a metal can be deposited on the
negative electrode in a solid state, which is a state having low
solubility in the molten salt, and it can be recovered.
Furthermore, the recovery of the metal can be performed at low
cost.
[0009] An apparatus for production of metal by molten-salt
electrolysis of the present invention has an electrolysis vessel
having a positive electrode and a negative electrode therein and a
metal chloride filled in the vessel, the metal chloride is heated
and molten to make an electrolytic bath, and the electrolytic bath
is electrolyzed to deposit metal in a solid state on the negative
electrode. Furthermore, in the apparatus, the electrolytic bath is
divided into an electrolysis chamber and a dissolution chamber by a
dividing wall, the positive electrode is arranged in the
electrolysis chamber, and the negative electrode is arranged to
enable orbital movement in a circle through the electrolysis
chamber and the dissolution chamber. Metal which is deposited on
the negative electrode in the electrolysis chamber is recovered in
the dissolution chamber.
[0010] By the present invention, electrolysis of metal chloride is
promoted and the metal is deposited on the negative electrode while
the negative electrode is passing through the electrolysis chamber,
and the metal deposited can be recovered during the negative
electrode passing through the dissolution chamber. Furthermore,
since the negative electrode revolves and passes through the
electrolysis chamber and dissolution chamber regularly, deposition
and recovery of the metal can be automatically and efficiently
performed.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a conceptual diagram showing the method for
production of calcium metal in an embodiment of the present
invention.
[0012] FIG. 2A is a conceptual diagram showing the method for
production of calcium metal in another embodiment of the present
invention, and FIG. 2B is a conceptual diagram showing a scraping
device on the negative electrode in the case in which FIG. 2A is
seen from direction A.
[0013] FIG. 3A is a conceptual diagram showing the method for
production of calcium metal in another embodiment of the present
invention, and FIG. 3B is a conceptual diagram in the case in which
FIG. 3A is seen from direction A, and FIG. 3C is a conceptual
diagram in the case in which FIG. 3A is seen from direction B.
EXPLANATION OF REFERENCE NUMERALS
[0014] 1 . . . Electrolysis vessel, [0015] 1a . . . Electrolysis
chamber, [0016] 1b . . . Dissolution chamber, [0017] 2 . . .
Electrolytic bath, [0018] 3 . . . Positive electrode, [0019] 4 . .
. Negative electrode, [0020] 5 . . . Metal (calcium), [0021] 6 . .
. Molten salt, [0022] 7 . . . Recovery vessel, [0023] 8 . . .
Chlorine gas, [0024] 9 . . . Scraping device, [0025] 10 . . .
Dividing wall
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] Embodiments of the present invention are explained below
with reference to the drawings. FIGS. 1 to 3 show embodiments of an
apparatus to perform the present invention. Next, a case in which
the electrolytic bath is one of calcium chloride and the metal
generated is calcium metal, is explained.
[0027] In FIG. 1, reference numeral 1 is an electrolysis vessel,
and electrolytic bath 2 comprising calcium chloride is filled
therein and heated to a temperature not less than the melting point
of calcium chloride by a heating means, which is not shown, to keep
the electrolytic bath in a molten state. Reference numeral 3 is a
positive electrode and reference numeral 4 is a negative electrode,
and they are immersed in the electrolytic bath 2.
[0028] The positive and negative electrodes 3 and 4 are connected
to a direct current power supply, which is not shown, and
electrolysis of the electrolytic bath is started. Chloride ions in
the electrolytic bath 2 are attracted to the positive electrode 3
and emit electrons to generate chlorine gas which is lost from the
system. Calcium ions are attracted to the negative electrode and
receive electrons to generate calcium metal 5 which is deposited on
the surface of negative electrode 4.
[0029] The present invention can be efficiently performed even in
the cases in which the temperature of the electrolytic bath 2 is
above or below the melting point of calcium metal 5 (845.degree.
C.). In particular, if the temperature of the electrolytic bath 2
is below the melting point of calcium metal, calcium metal 5 can be
deposited in a solid state on the surface of the negative electrode
4. On the other hand, even if the temperature of the electrolytic
bath 2 is above the melting point of calcium metal 5, calcium metal
5 can be deposited in a solid state on the surface of the negative
electrode 4 in the case in which a cooling structure is installed
in the negative electrode 4.
[0030] In both cases, since calcium metal 5 generated in the
electrolytic reaction is deposited in a solid state, the solubility
of the solid calcium metal 5 in calcium chloride contacting
therewith is extremely small. Therefore, calcium metal can be
recovered at high yield.
[0031] After a certain amount of calcium metal 5 is deposited on
the negative electrode 4, the negative electrode 4 is taken out of
the electrolytic bath 2 and is immersed in a recovery vessel 7
having molten salt 6 for which the temperature is maintained above
the melting point of calcium metal 5 (845.degree. C.). The calcium
metal 5 deposited on the negative electrode 4 is partially
dissolved in the molten salt 6 held in the recovery vessel 7, and
the rest floats up from the negative electrode 4 to be condensed
around the surface of the liquid. The condensed part is collected
and recovered. In this case, since evaporation loss becomes larger
as the temperature is increased, the temperature is practically set
at not more than 900.degree. C.
[0032] Calcium can be dissolved, floated and recovered in a liquid
state as explained above, and in addition, it can be cooled to not
more than the melting point of calcium metal (845.degree. C.) as
long as the molten salt 6 is not solidified. By performing such a
cooling operation, calcium metal 5 floats in a solid state, and it
can be efficiently recovered. Since the melting point of calcium
chloride is about 780.degree. C. and the melting point of calcium
metal is about 845.degree. C., by decreasing the temperature of the
recovery vessel 7 to about 800.degree. C., calcium metal 5 molten
in the molten salt 6 can be recovered in a solid state.
[0033] The negative electrode 4, after separating and recovering
the calcium metal 5 deposited, can be transferred from the recovery
vessel 7 to the electrolysis vessel 1 to perform molten-salt
electrolysis again. By repeating the above-mentioned set of
operations, calcium metal can be efficiently recovered. The calcium
metal 5 generated in the recovery vessel 7 in this way can be used
in the reduction of titanium tetrachloride using molten salt.
[0034] Alternatively, calcium metal is not recovered in the
recovery vessel 7 leaving the concentration of calcium metal in the
molten salt 6 high, and the molten salt containing calcium can be
used in the reduction reaction of titanium tetrachloride.
[0035] Chlorine gas 8 generated on the positive electrode 3 in the
electrolysis vessel 1 can be separately recovered and can be reused
in a chlorination reaction of titanium ore. Alternatively, it can
be used for other purposes.
[0036] As a material of the positive electrode 3, a material having
an electrical conductivity which does not dissolve in the
electrolytic bath and does not react with chlorine gas, is
desirable. As such a material, carbon is desirable.
[0037] The negative electrode 4 can be constructed by an electrical
conductive material, for example, carbon steel, stainless steel,
copper, aluminum or the like can be used. The negative electrode 4
desirably has a structure in which a cooling medium can be
circulated therein. The structure can promote deposition of calcium
metal on the negative electrode 4.
[0038] As the molten salt 6 in the recovery vessel 7, arbitrarily
selected one can be used, and in particular, calcium chloride is
desirable. Since calcium chloride is a by-product of molten-salt
electrolysis of titanium chloride and calcium metal, if the molten
salt 6 is calcium chloride, it will be unnecessary to remove
calcium chloride when condensed calcium metal is used in a
molten-salt electrolysis process for titanium chloride. In
addition, that is because after the molten-salt electrolysis
process for titanium chloride, the molten salt 6 can be reused with
calcium chloride which is a by-product of this process in the
electrolysis vessel 1.
[0039] The melting point of the electrolytic bath can be decreased
by adding potassium chloride to calcium chloride forming the
electrolytic bath 2. The amount of potassium chloride added to
calcium chloride is desirably in a range from 20 to 80 wt %. By
adding potassium chloride in this range, even if the temperature of
the electrolytic bath 2 is decreased below the melting point of
calcium metal by the temperature between 150.degree. C. and
250.degree. C., reliable operation can be performed without
solidification of the electrolytic bath.
[0040] The temperature of the electrolytic bath 2 can be
arbitrarily controlled within the target temperature range by using
a heating burner having a cooling function, which is not shown,
immersed in the electrolytic bath. Alternatively, another means can
be employed to control the temperature of the electrolytic bath
2.
[0041] FIG. 2 shows another embodiment of the present invention.
Electrolytic bath 2 comprising calcium chloride is filled in the
electrolysis vessel 1 of FIG. 2A, is heated to a temperature not
less than the melting point of calcium chloride by a heating means,
which is not shown, and is held in a molten state. Furthermore, the
positive electrode 3 and the negative electrode 4 having
cylindrical shape are immersed in the electrolytic bath 2. This
negative electrode 4 can be constructed so as to be rotatable, and
the scraping device 9 is arranged neighboring to an edge of a side
surface of the cylindrical negative electrode 4. FIG. 2B shows a
conceptual diagram of the negative electrode 4 and the scraping
device 9 seen from the direction A. As shown in the figure, by
rotating the negative electrode, calcium metal 5 deposited on the
surface of the negative electrode is efficiently scraped by the
scraping device 9.
[0042] Solid calcium metal 5 scraped from the negative electrode 4
floats up to the surface of the electrolytic bath 2 since the
density of calcium metal is lower than that of calcium chloride.
The calcium metal 5 which floated to the surface of the
electrolytic bath 2 is recovered from the electrolytic bath 2. The
solid calcium metal recovered from the electrolytic bath 2 is used
as a reducing agent for titanium oxide in molten-salt
electrolysis.
[0043] In this case, a basket having a net structure can be
arranged around the scraping device 9. By taking the basket out of
the electrolytic bath at appropriate times, solid metal deposited
can be efficiently recovered.
[0044] It is desirable that the dividing wall 10 be arranged around
the surface of electrolytic bath 2. Calcium metal deposited on the
negative electrode 4 is scraped and then floats and diffuses to the
bath surface. Finally, calcium metal can reach the positive
electrode 3, and it has a tendency to react oppositely with the
chlorine gas generated on the positive electrode 3. However, by
arranging the dividing wall 10, diffusion of floating calcium metal
can be prevented, and the back reaction can be effectively
suppressed.
[0045] The temperature of the electrolytic bath around the scraping
device 9 can be maintained, to a limited extent, at a temperature
not less than the melting point of calcium metal, by immersing and
arranging a heater near the scraping device 9. In this way, calcium
metal scraped from the negative electrode 4 can be recovered in a
molten state. The calcium metal in a molten state is partially
dissolved in calcium chloride, and the rest floats up in the
electrolytic bath 2. Therefore, calcium chloride having condensed
calcium metal is floating around the surface of the electrolytic
bath 2 via the dividing wall 10. By extracting floating calcium
chloride having condensed calcium metal, for example, it can be
used in reduction reactions for titanium tetrachloride.
[0046] FIGS. 3A to 3C show another embodiment of the present
invention. FIG. 3B is a conceptual diagram of FIG. 3A seen from
direction A, and FIG. 3C is a conceptual diagram of FIG. 3A seen
from direction B. Electrolytic bath 2 comprising calcium chloride
is filled in the electrolysis vessel 1 of FIG. 3, and the
electrolytic bath 2 is heated to a temperature not less than the
melting point of calcium chloride so as to be maintained in a
molten state by a heating means, which is not shown. Furthermore,
the positive electrode 3 and the negative electrode 4 are immersed
and arranged in the electrolytic bath 2. The electrolysis vessel 1
is divided into the electrolysis chamber 1a in which the positive
electrode 3 is immersed and the dissolution chamber 1b is isolated
by the dividing wall 10 arranged around the surface of the
electrolytic bath 2. It should be noted that only the upper part of
the electrolytic bath 2 is divided by the dividing wall 10, and the
lower part thereof is unified. As shown in FIG. 3C, plural negative
electrodes 4 are arranged to enable orbital movement in a circle
through the electrolysis chamber 1a and dissolution chamber 1b.
These negative electrodes 4 can be revolved in a circle through the
electrolysis chamber and dissolution chamber by passing through a
sliced channel arranged at a part of the dividing wall 10.
[0047] Heating function and cooling function are provided to the
negative electrode 4. That is, a flow passage in which a heater and
a cooling medium can be circulated is arranged inside the negative
electrode 4. In this way, the temperature of the negative electrode
4 can be arbitrarily controlled from a temperature not more than
the melting point of calcium metal 5 to a temperature not less than
the melting point of calcium metal 5.
[0048] In the construction of apparatus explained above, when the
negative electrode 4 is in the electrolysis chamber side, the
temperature of the negative electrode 4 is maintained at a
temperature not more than the melting point of calcium metal to
deposit the calcium metal on the surface of the negative electrode
in a solid state. On the other hand, when the negative electrode
revolves and reaches to the dissolution chamber side, the
temperature of the negative electrode 4 is maintained at a
temperature not less than the melting point of calcium metal to
fuse the calcium metal deposited. Calcium metal 5 is molten and
released from the negative electrode 4 and is partially dissolved
in calcium chloride, and the rest floats up in the electrolytic
bath, to form a calcium metal condensed layer. The calcium metal
condensed layer formed at the bath surface of the dissolution
chamber of the electrolytic bath 2 is extracted at appropriate
times, and for example, it can be used as a reducing agent for
titanium oxide in molten-salt electrolysis.
[0049] In this way, by controlling the temperature of the negative
electrode from a temperature below the melting point of calcium
metal to a temperature above the melting point of calcium metal
depending on the position of the negative electrode 4 revolving
inside the electrolytic bath 2, calcium metal can be efficiently
recovered.
EXAMPLES
Example 1
[0050] Molten-salt electrolysis of calcium chloride was performed
by using both the electrolysis vessel and the recovery vessel shown
in FIG. 1. Calcium metal is deposited on the negative electrode by
controlling the temperature of the electrolytic bath comprising
calcium chloride at 800.+-.5.degree. C. As a result, calcium metal
having 85% of the weight of the theoretical weight calculated from
electricity applied between the positive electrode and negative
electrode was recovered.
Example 2
[0051] Using the apparatus shown in FIG. 2 and using calcium
chloride as an electrolytic bath, molten-salt electrolysis was
performed to deposit calcium metal continuously on the negative
electrode. The calcium metal was scraped by the scraping device to
recover it in a solid state. The amount of calcium metal produced
per unit time was about twice as much as that of Example 1.
Example 3
[0052] Using the apparatus shown in FIG. 3 and using calcium
chloride as an electrolytic bath, molten-salt electrolysis was
performed to deposit calcium metal continuously on the negative
electrode. The calcium metal in a molten state partially containing
the electrolytic bath was recovered. The amount of calcium metal
produced per unit time was about twice as much as that of Example
2.
[0053] As explained thus far, calcium metal can be efficiently
produced by electrolysis of calcium chloride by the present
invention.
* * * * *