WO2006003865A1 - Method for producing metal by molten salt electrolysis - Google Patents

Abstract

Disclosed is a method for producing a metal by molten salt electrolysis which is characterized in that molten salt electrolysis is performed using an electrolysis vessel which comprises an anode, a cathode and a diaphragm composed of graphite and arranged between the anode and the cathode and is filed with a molten salt containing a metal chloride. The voltage applied between the anode and the cathode is set not more than two times as high as the theoretical decomposition voltage of the molten salt.

Description

 Method of producing metal by molten salt electrolysis

 Technical field

 The present invention relates to recovery of metal from metal salts, and more particularly to a method for producing metal by molten salt electrolysis.

 Background art

 [0002] Conventionally, elemental metallic titanium has been manufactured by the Kroll method to obtain titanium sponge by reducing titanium tetrabasic with molten magnesium, and manufacturing costs have been reduced by stacking various improvements. The However, since the crawling method is a batch process that repeats a series of operations discontinuously, the efficiency is limited.

 [0003] Under the above conditions, there is a method of producing titanium directly by reducing titanium oxide with metallic calcium in molten salt (see, for example, Patent Documents 1 and 2), calcium, etc. There is disclosed an EMR method (see, for example, Patent Document 3) in which a reducing metal containing a metal or an alloy is produced, and a titanium compound is reduced by electrons emitted from the reducing metal to obtain titanium metal. . In these methods, calcium oxide by-produced in the electrolytic reaction is dissolved in chloride and then molten salt electrolysis is used to recover and reuse metallic calcium. As a result, metallic calcium produced by the electrolytic reaction has a problem that it is easily dissolved and dissipated due to its high solubility in calcium chloride due to its liquid state, and the yield is lowered.

 Furthermore, an attempt is made to deposit metallic calcium on a cathode in the solid state using a composite molten salt having a melting point lower than metallic calcium (see, for example, Patent Document 4). While this method requires the special preparation of the complex molten salt, the cost increase and the problem will be solved.

 As described above, in the conventional method, it is difficult to efficiently recover metals such as calcium metal, and even if possible, there is a problem that the cost is high! .

 Patent document l: WO99Z064638

Patent Document 2: Japanese Patent Application Laid-Open No. 2003-129268 Patent Document 3: Japanese Patent Application Laid-Open No. 2003-306725

 Patent Document 4: US 3226311

 Disclosure of the invention

 Problem that invention tries to solve

The present invention has been made in view of the above situation, and it is possible to efficiently recover, for example, a metal used to reduce an acid or a salt of metal titanium. Of course, the object is to provide a method for producing a metal by molten salt electrolysis which can be carried out by an inexpensive method.

 Means to solve the problem

 The method for producing a metal by molten salt electrolysis according to the present invention comprises an anode and a cathode, and an electrolysis cell having a diaphragm composed of graphite and disposed between the anode and the cathode. It is characterized in that molten salt is filled and molten salt electrolysis is performed. Also, the voltage applied between the anode and the cathode is characterized in that it is not more than twice the theoretical decomposition voltage of the molten salt.

 In the electrolysis of metal salts, the reaction occurs in proportion to the voltage applied between the anode and the cathode, but an intermediate electrode (conductor) is placed between the anode and the cathode and it is necessary for the electrolysis. When the voltage more than twice the voltage is applied, this intermediate pole is polarized, and electrolysis occurs not only between the anode and the cathode but also between the anode and the intermediate pole, and in two regions of the intermediate pole and the cathode. Chlorine is generated on one side of the intermediate electrode and metal is deposited on the other side of the cathode and the intermediate electrode. According to the present invention, since the diaphragm composed of graphite is disposed between the anode and the cathode, the chlorine generated at the anode and the metal deposited at the cathode are separated, and the reverse reaction can be suppressed. In addition, since a voltage equal to or less than twice the theoretical decomposition voltage of the molten salt is applied, the reaction can be promoted efficiently without polarization of the membrane.

 BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described below with reference to the drawings. Hereinafter, the case where the metal is metallic calcium, the metallic salt is calcium chloride, the refractory metal salt is tetrabasic titanium, and the electrolytic bath is calcium chloride will be described as an example. The same applies to the case where is metal sodium and the metal salt is sodium chloride. FIG. 1 shows an example of a preferred apparatus configuration for practicing the present invention. In FIG. 1, reference numeral 1 denotes an electrolytic cell, the inside of which is filled with an electrolytic bath 2 consisting of calcium chloride (melting point 780 ° C.), and the heating means (not shown) It is heated and kept molten. Reference numeral 3 is an anode, and reference numeral 4 is a cathode, which are immersed in the electrolytic bath 2. A diaphragm 5 made of, for example, graphite is disposed between the anode 3 and the cathode 4.

 When the anode 3 and the cathode 4 are connected to a DC power supply (not shown) and electrolysis of the electrolytic bath 2 is started, chloride ions in the electrolytic bath 2 are attracted to the anode 3 to emit electrons and chlorine It is released out of the system as gas 6. Calcium ions are attracted to the cathode 4 to receive electrons, and become metallic calcium 7 and deposit on the surface of the cathode 4.

 Here, solid metallic calcium is deposited on the cathode 4 by setting the temperature of the electrolytic bath 2 to the melting point of metallic calcium (845 ° C.) and the melting point of calcium chloride (780 ° C.) or higher. be able to. On the other hand, the present invention can be practiced even if the temperature of the electrolytic bath 2 is selected to be higher than the melting point of metallic calcium. In this case, the metallic calcium deposited on the cathode 4 floats in the electrolytic bath 2 while a part thereof is dissolved, and stays on the surface of the electrolytic bath 2. The metallic calcium and the electrolytic bath enriched with metallic calcium can be used, for example, as a reducing agent by direct electrolysis of titanium oxide.

 Chlorine gas and metallic calcium generated as described above tend to diffuse and cause reverse reaction with each other, but in the present invention, since a diaphragm is provided between the anode and the cathode, the reverse reaction is suppressed. can do.

When the voltage applied to the anode and the cathode is increased, the amount of current supplied to the electrolytic cell 1 is increased, and the metal deposition rate can be increased. While the pressure is applied, both surfaces of the diaphragm 5 are polarized as the applied voltage increases, and when the applied voltage reaches twice the theoretical decomposition voltage, metal is deposited on the anode side of the diaphragm 5 and the cathode side of the diaphragm 5 Begins to generate chlorine gas. The chlorine gas generated on the cathode side of the diaphragm 5 causes a reverse reaction with the metal deposited on the cathode 4 to lower the yield of calcium metal. Therefore, the voltage applied to the anode 3 and the cathode 4 is preferably an electrolytic voltage which does not cause the polarization of the diaphragm 5. Such a voltage range is not less than the theoretical decomposition voltage of calcium chloride and not more than twice thereof, and specifically, 3.2 V to 6.4 V It is a range.

 The anode used in the present invention is required to be a material resistant to high-temperature chlorine gas, and graphite is preferable as such a material. Not only does Graphite withstand high temperature chlorine gas, it is also durable in high temperature electrolytic baths and has good conductivity and conductivity. In addition, the anode may be formed by immersing the upper lid of the electrolytic cell 1 (not shown) into the electrolytic bath 2 so that the surface of the anode 3 made of graphite penetrating the upper lid may be coated with ceramic. . With such a configuration, wear and tear on graphite can be minimized.

 [0017] Since no chlorine gas is generated from the cathode, any material resistant to high temperature molten salt can be used, and it can be made of common carbon steel or stainless steel. In the cathode, it is preferable to be made of carbon steel because of the possibility of forming refined metals and carbides. Carbon steel is preferred to withstand high temperature molten salts or metallic calcium. It is also cheap, durable and practical.

 Like the anode, the diaphragm used in the present invention is required to be made of a material resistant to high temperature calcium chloride or chlorine gas, and specifically, Graphite is preferable. Even if the entire septum is made of graphite, the strength at high temperature can be maintained for a long time by making the center part of ceramic and making the outside part of dolaphyte.

 Although the diaphragm is required to be as compact as possible, the porosity of the diaphragm is to be within the scope of the present invention even if there is a gap that metal calcium produced in the cathode 4 does not penetrate and move to the anode side. There is no hindrance to the above. Also, the lower end of the diaphragm does not have to reach the bottom of the electrolytic cell, and the calcium metal formed at the cathode 4 or the calcium chloride layer enriched with metal calcium can not move to the anode. It is enough.

 The generated chlorine gas is extracted out of the system and can be used, for example, for chlorination reaction of titanium ore. In addition, metallic calcium can be used for the reduction reaction of titanium oxide or titanium chloride using a molten salt.

As described above, the diaphragm is made of graphite and the voltage applied to the anode and the cathode is equal to or higher than the theoretical decomposition voltage of calcium chloride and equal to or lower than twice the theoretical decomposition voltage. The metal calcium can be efficiently generated without generating chlorine gas due to the polarization on the diaphragm surface.

 Example 1

 Between the anode made of carbon and the cathode made of carbon steel, using the apparatus shown in FIG. 1, using a diaphragm made of Graphite and maintaining the electrolytic bath made of calcium chloride at 850 ° C. Furthermore, a voltage of OV was applied to carry out molten salt electrolysis of calcium chloride. A part of the metal calcium formed at the cathode was dissolved in a sodium chloride calcium bath, and the remainder was dissolved as molten metal calcium and floated on the sodium chloride calcium bath surface to form a metal calcium enriched layer. After being extracted out of the system from the metal calcium enrichment layer, it was used for direct reduction of titanium oxide. Electrostatic force to the cathode The metallic calcium equivalent to 75% of the calculated theoretical value could be recovered.

 Comparative Example 1

 In Example 1, when the molten salt electrolysis of calcium chloride was performed by setting the voltage applied to the anode and the cathode to 7. OV, metallic calcium corresponding to 20% of the theoretical value could not be recovered.

 Industrial applicability

[0024] The acid oxide of metallic titanium can efficiently recover the metal used to reduce chloride.

 Brief description of the drawings

FIG. 1 is a schematic cross-sectional view showing an electrolytic cell in molten salt electrolysis of the present invention.

 Explanation of sign

1 Electrolyzer

 2 Electrolysis bath

 3 Anode

4 Cathode Metallic calcium

Claims

The scope of the claims  [1] It is characterized in that a molten salt containing a metal salt is filled in an electrolytic cell provided with an anode and a cathode, and a separator composed of graphite is arranged between the anode and the cathode and the molten salt is electrolyzed. Method of producing metal by molten salt electrolysis  [2] The method for producing a metal by molten salt electrolysis according to claim 1, wherein a voltage applied between the anode and the cathode is not more than twice the theoretical decomposition voltage of the molten salt. [3] The method for producing a metal by molten salt electrolysis according to claim 1, wherein the metal is recovered as a mixture with the molten salt or as a melt. [4] The method for producing a metal by molten salt electrolysis according to claim 1, wherein the metal is magnesium, sodium or calcium. [5] The method for producing a metal by molten salt electrolysis according to claim 1, characterized in that the molten salt is sodium chloride sodium, magnesium chloride, calcium chloride.