Method for producing metal and method for producing refractory metal

Abstract

Provided is a method for producing metal by molten salt electrolysis, by which the metal can be efficiently produced. A method for producing metal by using an apparatus for molten salt electrolysis having an electrolytic cell and an electrode pair, wherein the molten salt electrolysis in the electrolytic cell and heating of the molten salt by a Joule heat generation between a pair of electrodes for electrolysis are simultaneously performed; and wherein the apparatus for molten salt electrolysis has at least two sets of electrode pair, and at least one set of the electrode pairs is electrically opened.

Claims

1. A method for producing metal by using an apparatus for molten salt electrolysis having an electrolytic cell and at least two electrode pairs, wherein the molten salt electrolysis in the electrolytic cell and heating of the molten salt by Joule heat generated by a pair of electrodes for electrolysis of the at least two electrode pairs are simultaneously performed; wherein at least one electrode pair of the at least two electrode pairs is electrically opened, and wherein the at least one electrically opened electrode pair is connected after the molten salt in the electrolytic cell is completely kept in the molten state.

2. The method for producing metal according to claim 1, wherein an electrically non-opened electrode pair of the at least two electrode pairs is arranged such that the molten salt is uniformly heated by a Joule heat generation in the neighborhood of the electrically non-opened electrode pair.

3. The method for producing metal according to claim 1, wherein the electrolytic cell is a bipolar cell.

4. The method for producing metal according to claim 1, wherein the metal is magnesium, aluminum, or zinc.

5. A method for producing refractory metal comprising, producing magnesium, aluminum, or zinc using the method of claim 4; and reducing metal chloride by using the magnesium, aluminum, or zinc produced.

6. The method for producing refractory metal according to claim 5, wherein the refractory metal is any one of titanium, zirconium, hafnium, and silicon.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 It is a diagrammatic view of an apparatus for molten salt electrolysis.

(2) FIG. 2 It is a diagrammatic view showing a mode and a connecting method of electrode pairs.

DESCRIPTION OF EMBODIMENTS

(3) A preferred embodiment of the production method of metal according to the present invention is explained by using schematic views of an apparatus for molten salt electrolysis which can be used in the present invention and also a mode and a connecting method of electrode pair.

(4) As shown in FIG. 1, an apparatus for molten salt electrolysis N is surrounded by walls of an electrolytic cell 1 and a ceiling wall 7 each constituted of a refractory, and a first wall 5 and a second wall 6 partitioning a metal storing chamber L and an electrolysis chamber M from each other are installed in an interior of the apparatus for molten salt electrolysis N.

(5) An electrolytic bath 8 filled with a molten salt is installed into the metal storing chamber L and the electrolysis chamber M, and furthermore, an anode 2 and a cathode 3 constituting an electrode pair are dipped and arranged in the electrolytic bath 8 of the electrolysis chamber M. In addition, non-illustrated plural bipolar electrodes are interposed between the anode 2 and the cathode 3.

(6) In particular, it is preferred to perform the production method of metal according to the present invention in a state where the apparatus for molten salt electrolysis N has at least two sets of electrode pair constituted of the anode 2 and the cathode 3, and at least one set of the electrode pairs is electrically opened. According to this way, the temperature of the electrolytic bath 8 can effectively ascend while being activated between the non-opened anode 2 and cathode 3 installed in the apparatus for molten salt electrolysis N to perform electrolysis of the molten salt.

(7) FIG. 2 schematically expresses an electrode pair 11 composed of the anode 2 and the cathode 3 installed in the apparatus for molten salt electrolysis N and a bipolar electrode 10 installed therebetween. FIG. 2 expresses the state where three or more sets of electrode pair having two bipolar electrodes arranged therein are connected in parallel. These electrode pairs are connected to a non-illustrated constant-current power source (rectifier via a main busbar).

(8) In an embodiment shown in FIG. 2, by electrically opening a part of the sets among the plural sets of electrode pair, the electrically opened electrode pair is not activated, and the applied voltage is constant, and therefore, the amount of energization of the electrode pair connected to the power source can be increased by an amount corresponding to that portion.

(9) As a result, the amount of a Joule heat generation can be increased on the electrically non-opened electrode pair. As a result, the Joule heat generation in the molten salt intervening between the electrode pairs can be increased, thereby bringing about an effect that the temperature of the electrolytic bath 8 can be efficiently increased.

(10) That is, a current (I) flowing through the plural electrode pairs increases, and when a resistance related to the electrolytic bath existing between the electrodes is designated as R, this means that the current flowing through the electrolytic bath existing between the electrode pairs increases. That is, a Joule heat generation W between the electrodes is calculated by I.sup.2R and exceeds a decrement of the Joule heat generation following the opening of a pair of electrodes.

(11) When this is expressed by a general formula, the Joule heat generation W relative to sets of electrode pair in the number of n is defined as n*(I/n).sup.2R, and this can be expressed in the form of I.sup.2R/n.

(12) The Joule heat generation W, that is I.sup.2R/n, generated in the electrolytic bath means that the smaller the number of electrode pairs during the operation, the more increased the amount of heat generated in the electrolytic bath.

(13) Accordingly, in the case where the temperature of the electrolytic bath turns into a tendency of descending, it is effective to decrease the number of electrode pairs in the operated state, thereby increasing the amount of heat generated in the electrolytic bath.

(14) Conversely, in the case where the temperature of the electric cell turns into a tendency of ascending, by increasing the number of operating electrodes, the amount of heat generated in the electrolytic bath can be suppressed, resulting in an effect that the temperature of the electrolytic bath can effectively descend.

(15) Though the metal which is produced by the method according to the present invention is not particularly limited so long as it can be produced by the apparatus for molten salt electrolysis, it is preferably magnesium, aluminum, or zinc.

(16) By allowing the metal which is produced by the method according to the present invention to react with metal chloride as a reducing agent, refractory metal can be obtained. For example, by allowing magnesium which is produced by the method according to the present invention to react with titanium chloride, zirconium chloride, or hafnium chloride, refractory metal, such as titanium, zirconium, hafnium, etc., can be produced. In addition, as for zinc which is produced by the method according to the present invention, by using silicon chloride as a reducing agent, silicon can be produced.

EXAMPLES

Example 1

(17) The apparatus for molten salt electrolysis N shown in FIG. 1 was prepared. The apparatus for molten salt electrolysis N has ten sets of electrode pair connected in parallel to a constant-current power source, three bipolar electrodes are arranged between the anode 2 and the cathode 3 constituting each of the electrode pairs, and a heat exchanger is installed in the electrolytic cell.

(18) A molten magnesium salt in a separate vessel was charged into the electrolytic cell 1 of the apparatus for molten salt electrolysis N where the heat exchanger was kept in the heated state.

(19) Subsequently, among the ten sets of electrode pair, seven sets of electrode pair were rendered in a connected state (three sets of electrode pair (electrode pairs of 30% of the total number of electrode pairs) were opened), and electrolysis was commenced. In addition, the heat exchanger was continuously kept in the heated state even during the electrolysis.

(20) On the seven sets of electrode pair, chlorine gas and molten metallic magnesium were smoothly produced immediately after energization. In addition, the metal salt solidified on the wall surface and the like was smoothly rendered in a molten state, and after a while, the solidified metal salt vanished, whereby it was fully rendered in a molten state.

(21) After the vanish of the solidified metal salt was confirmed through visual inspection, the electrically opened electrode pairs were connected, whereby the electrolysis of the molten salt by the ten sets of electrode pair in total could be performed.

(22) A time necessary for arriving at a target temperature from the starting of the electrolysis apparatus was measured.

(23) In addition, when titanium tetrachloride was reduced by using the produced magnesium to produce titanium, titanium could be produced without causing any problem.

Example 2

(24) The molten salt electrolysis was conducted under the same conditions as those in Example 1, except for performing molten salt electrolysis by using an electrolytic cell using nine sets of electrode pair in place of the ten sets of electrode pair and further using three sets of electrode pair as the electrode pairs of electrically opened electrodes (30% of the total number of electrode pairs), and a time necessary for arriving at a target temperature from the starting of the electrolysis apparatus was measured. It is to be noted that when titanium tetrachloride was reduced by using the produced magnesium to produce titanium, titanium could be produced without causing any problem.

Comparative Example 1

(25) An electrolysis cell was started in the same method as that described in Example 1, except that in all of the steps of electrolysis, all of the electrode pairs (ten sets) were connected to a power source without electrically opening a part of the electrode pairs. After commencing the starting operation of the electrolytic cell, the temperature of the molten salt exhibited a tendency of ascending; however, as compared with Example 1, a time required from starting of the electrolysis apparatus to arrival at a target preset temperature increased by an extra of about 50%.

(26) As described above, it was confirmed that the time necessary for arriving at a target preset temperature from the starting of the electrolysis apparatus is delayed as compared with that in Example 1.

(27) It may be considered that in the production method of magnesium in Example 1, in contrast, by electrically opening a part of the electrode pairs dipped and arranged in the molten salt, a Joule heat generation between the non-opened electrodes can be increased, and as a result, in Example 1, the temperature ascending time of the molten salt could be hastened as compared with that in Comparative Example 1.

(28) In addition, it may be considered that by electrically opening a part of the dipped and arranged electrode pairs, the electrolysis operation of the molten salt could be advanced from the time of starting of the electrolysis apparatus.

INDUSTRIAL APPLICABILITY

(29) The present invention can be applied to the production method for efficiently producing metal by using apparatus for molten salt electrolysis.

REFERENCE SIGNS LIST

(30) 1: Electrolytic cell 2: Anode 3: Cathode 4: Lid 5: First wall 6: Second wall 7: Ceiling wall 8: Electrolytic bath 9: Molten magnesium 10: Bipolar electrode 11: Electrode pair L: Metal storing chamber M: Electrolysis chamber N: Apparatus for molten salt electrolysis