JP2005171353A - Method of electrolyzing molten metal chloride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of electrolyzing molten metal chloride where the turbulence in the flow of a bath within an electrolytic cell is suppressed, the winding-up of impurities stored at the bottom part of the electrolytic cell is prevented, and the reduction of current efficiency is suppressed. <P>SOLUTION: For example, at the time of electrolyzing the molten chloride of magnesium to obtain molten metal, a buffer body 11 is arranged in an electrolytic bath comprising the molten metal chloride held in the electrolytic cell 1, suitably, in the lower part of the section at which the molten metal chloride reaches the electrolytic bath. Further, the injection rate of the molten metal chloride to the electrolytic cell is controlled to ≤100 cm/s. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for electrolyzing a molten metal chloride that is a high-temperature melt, and particularly to an electrolysis technique that suppresses a decrease in current efficiency.

  In the manufacturing technology of sponge titanium by the crawl method, molten magnesium is used as a reducing agent for titanium tetrachloride. The molten magnesium chloride by-produced by this reduction reaction is regenerated into magnesium and chlorine gas by molten salt electrolysis (hereinafter sometimes simply referred to as “electrolysis”).

  Therefore, in the manufacturing process described above, there are many occasions where molten magnesium and molten magnesium chloride are frequently handled, but since molten magnesium easily reacts with oxygen gas and nitrogen gas in the atmosphere, when handling these, contact with the atmosphere Care must be taken to avoid.

  However, for example, when pumping molten magnesium from an electrolytic cell into a transport container or injecting molten magnesium from a transport container into a reduction container, it is difficult to avoid contact of the molten magnesium with the atmosphere due to the device structure. It is difficult to eliminate the generation of oxides and nitrides.

  In order to solve such problems, the oxygen concentration in the argon gas maintained in the melting furnace atmosphere is constantly monitored, and if there is an abnormality, supply of raw materials to the melting furnace and discharge of molten metal should be stopped. Discloses a technique for suppressing the formation of magnesium oxide (see Patent Document 1).

JP 2002-059254 A

  However, in the technique described in Patent Document 1, it is difficult to completely disconnect the contact between the molten magnesium and the atmosphere due to the configuration of the apparatus. For this reason, when this apparatus is used, the production | generation of the impurity which has a magnesium oxide and nitride as a main component is unavoidable. If these impurities are mixed in the molten magnesium electrolytic bath, some of the impurities may be deposited on the anode surface and hinder the generation of chlorine gas. There is also a risk of promoting recombination with gas. Therefore, it is not preferable that the impurities float in the electrolytic bath.

  Since such impurities have a higher specific gravity than the electrolytic bath, they settle and separate at the bottom of the electrolytic bath when the electrolytic bath is left standing. However, when the electrolytic cell is continuously operated, it is necessary to supply molten magnesium chloride, which is a raw material of magnesium, to the electrolytic cell. At this time, the flow of the electrolytic bath is disturbed and deposited at the bottom of the electrolytic cell. Impurities can be rolled up in the bath flow. As a result, there arises a problem that the above-mentioned troubles occur in the anode and the cathode, and as a result, the current efficiency is temporarily lowered.

  The present invention has been made in view of the above circumstances, and a bath flow in an electrolytic cell is added when molten magnesium chloride is added to an electrolytic cell for performing molten salt electrolysis (hereinafter sometimes simply referred to as “electrolytic cell”). It is an object of the present invention to provide a molten metal chloride electrolysis method that suppresses the disturbance of electric current and consequently suppresses the decrease in current efficiency.

  The present inventors diligently studied to solve the above-mentioned problem. By providing a buffer in the vicinity of the region where the molten metal chloride is added in the electrolytic bath, the flow of the bath is locally turbulent. It has been found that it is possible to relax, thereby preventing the impurities accumulated in the bottom of the electrolytic cell from being rolled up into the bath flow and suppressing a decrease in current efficiency. The present invention has been made based on the above findings.

  That is, according to one molten metal chloride electrolysis method of the present invention, in obtaining molten metal by electrolyzing molten metal chloride, a buffer is disposed in an electrolytic bath containing molten metal chloride held in an electrolytic cell. It is characterized by doing.

  In addition, when the molten metal chloride is injected into the electrolytic cell, the present inventors have made the molten metal chloride in the electrolytic bath smaller by reducing the injection rate of the molten metal chloride into the electrolytic cell as compared with the conventional method. Reduces the current efficiency by mitigating local turbulent flow in the vicinity of the area where the material is added, thereby preventing the accumulation of impurities accumulated in the bottom of the electrolytic cell into the bath flow. The knowledge that it can suppress was obtained. The present invention has been made based on the above findings.

  That is, in another molten metal chloride electrolysis method of the present invention, in obtaining molten metal by electrolyzing molten metal chloride, the injection rate of molten metal chloride into an electrolytic cell is set to 100 cm / second or less. It is a feature. In addition, the fall of current efficiency can further be suppressed by combining the optimization of the injection | pouring speed | rate of such molten metal chloride, and arrangement | positioning of an above described buffer.

  In such a molten metal chloride electrolysis method, the molten metal is magnesium, the molten metal chloride is magnesium chloride, the buffer is a plate or a cone, and the buffer It is preferable to arrange a plurality of layers in the vertical direction in the electrolytic bath from the viewpoint that particularly excellent current efficiency can be obtained.

  According to the molten metal chloride electrolysis method of the present invention, when the molten metal chloride is added to the portion of the electrolytic bath where the molten metal chloride is added, or when the molten metal chloride is injected into the electrolytic cell, Adopting a method of reducing the injection rate of the molten metal chloride compared to the conventional method, that is, reducing the local turbulent flow of the electrolytic bath, thereby accumulating at the bottom of the electrolytic cell Impurities can be prevented from being rolled up in the bath flow, and a decrease in current efficiency can be suppressed.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
FIG. 1 is a view showing one electrolysis apparatus for carrying out the molten metal chloride electrolysis method of the present invention. In FIG. This is a container for molten magnesium chloride. As shown in FIG. 1, the electrolytic cell 1 includes an iron outer plate 3, a heat insulating brick layer 4, and a refractory brick layer 5, and a first partition wall 6 and a second partition wall 7 from an upper wall portion made of the heat insulating brick layer 4. It has a structure that hangs down. The inside of the electrolysis total is partitioned by a first partition wall 6 into a molten metal storage chamber 8 and an electrolytic chamber 9 connected to the storage chamber 8.

  The electrolytic bath 1 is filled with a high-temperature melt containing molten magnesium chloride up to an electrolytic bath level 10 in FIG. In addition, a buffer 11 is disposed in the electrolytic bath in the storage chamber 8, and an iron cathode 12 and a graphite anode 13 are inserted into the electrolysis chamber 9 from the outside.

Below, the case where the electrolysis method of this invention is implemented using the apparatus of the structure mentioned above is demonstrated.
Molten magnesium chloride by-produced in the production process of titanium sponge is injected into the electrolytic cell 1 from the container 2 through the supply / discharge port 14 of the electrolytic cell 1. Next, the traveling speed of the molten magnesium chloride is lowered by the buffer 11, and the course thereof is changed to the lower left direction in FIG. 1 and circulates along the direction of the annular arrow in the same figure.

  Thus, in the molten magnesium chloride poured from the container 2, an impurity called an electric stack is mixed. As shown in FIG. 1, the electric stack 15 has a specific gravity greater than that of molten magnesium chloride, and therefore deposits at the lower left corner of the electrolytic cell 1.

  In this way, the molten magnesium chloride from which the electrode stack 15 is naturally separated by gravity further changes the course in the direction of the arrow, passes under the first partition 6 and enters the electrolytic chamber 9 from the storage chamber 8. In the electrolysis chamber 9, molten magnesium chloride is electrolyzed into molten magnesium and chlorine gas.

  Next, the molten magnesium and chlorine gas electrolyzed in this way change the course in the direction of the arrow in FIG. 1 and pass through the hole 6 a of the first partition 6, and the molten magnesium passes under the second partition 7. The chlorine gas passes through and is discharged to the outside through the opening 16. Finally, the molten magnesium that has reached the storage chamber 8 is taken out from the supply / discharge port 14.

  The above is a series of flow from injecting molten magnesium chloride into the electrolytic cell 1 and taking out the molten magnesium obtained by electrolysis. The amount of molten magnesium chloride in the electrolytic cell 1 as electrolysis continues. Gradually decreases. For this reason, it is necessary to supply molten magnesium chloride to the electrolytic cell 1 when a certain time has elapsed after the operation of the electrolytic cell 1. At this time, molten magnesium chloride can also be supplied to the electrolysis chamber 9 side, but in this case, the supplied molten magnesium chloride may hinder generation of chlorine gas or precipitation reaction of molten magnesium in the electrolysis chamber 9. is there. Accordingly, the molten magnesium chloride is preferably supplied to the storage chamber 8 side as shown in FIG.

  Further, a separation zone for molten magnesium chloride and molten magnesium is formed at the bottom of the molten metal storage chamber 8 in the electrolytic cell 1 shown in FIG. For this reason, when supplying molten magnesium chloride, it is preferable to suppress the bath flow in these separation zones as much as possible.

  As one means for suppressing the bath flow in the separation zone as much as possible, it is preferable to provide a bath flow buffer 11 below the portion where the molten magnesium chloride reaches the electrolytic bath, as shown in FIG. . It is preferable to hold the buffer body 11 in the horizontal direction in the bath. Moreover, the buffer body 11 can be made into a simple plate shape, and a plurality of through holes can be provided in the plate. By providing such a perforated plate, it is formed in the electrolytic bath by moving and diffusing molten magnesium chloride to the bottom of the electrolytic bath while appropriately suppressing the downward flow generated near the electrolytic bath surface where the molten magnesium chloride reaches. The flow from the storage chamber 8 to the electrolysis chamber 9 can be combined. When a plurality of such buffer bodies 11 are arranged in the vertical direction in the electrolytic bath, the bath flow in the separation zone can be further suppressed.

  In addition, the size and number of the holes provided in the buffer 11 can be determined as appropriate. However, when the deposit 15 that is an impurity in the electrolytic bath accumulates in the buffer 11, the bottom of the electrolytic cell 1 is reached. Therefore, it is preferable that a hole having a certain size is made to pass through the buffer body 11. Moreover, the buffer body 11 can be comprised with a refractory material or carbon, or can also be comprised with carbon steel. In the case where the buffer body 11 is made of carbon steel, it is preferable to periodically extract the buffer body 11 and check the surface corrosion status.

  Another means for suppressing the bath flow in the separation zone as much as possible is to set the injection rate of molten magnesium chloride into the electrolytic cell 1 to 100 cm / second or less. Moreover, although the molten magnesium chloride poured into the electrolytic cell 1 is supplied from the molten magnesium container 2, it is preferable to provide a plurality of molten magnesium chloride supply nozzles (not shown). In this way, by supplying molten magnesium chloride to the electrolytic cell 1 through a plurality of nozzles, it is possible to further disperse the disturbance of the bath when supplying molten magnesium chloride. When such an apparatus configuration is employed, the turbulence of the bath due to the floating separation of the molten magnesium from the electrolytic bath can be further suppressed at the bottom in the storage chamber 8.

  FIG. 2 is a diagram showing another electrolysis apparatus for carrying out the molten metal chloride electrolysis method of the present invention. The apparatus shown in the figure is the same as the apparatus shown in FIG. 1 except for the shape of the buffer 21. Therefore, the reference numerals are omitted for the same components as those in the apparatus shown in FIG. In this apparatus, the buffer body 21 has a conical shape, and this shape can effectively suppress the bath flow generated when pouring molten magnesium chloride. The shape of the buffer is not limited to a plate shape or a conical shape as long as the above-described effects can be obtained, and other shapes can also be used.

  Thus, by providing the buffer bodies 11 and 21 shown in FIG. 1 or FIG. 2 in the electrolytic bath, the floating separation of the molten magnesium from the electrolytic bath is suppressed, and the deposits deposited on the bottom of the electrolytic bath are The problem of having an adverse effect upon entering the electrolytic chamber by being wound up and riding on the flow of the electrolytic bath can also be suppressed.

(Experimental example 1)
The apparatus shown in FIG. 1 is used, and a porous plate (corresponding to the buffer body of 11 in the figure) is immersed in an electrolytic bath on the side of the storage chamber 8 in the electrolytic cell 1, and an electrolytic cell for molten magnesium chloride The electrolytic cell was operated for 15 months at a rate of 60 cm / sec. As a result, almost no decrease in the current efficiency generated immediately after the injection of molten magnesium chloride was observed, and the current efficiency throughout the operation period was 80%.

(Experimental example 2)
The same device as in Experimental Example 1 was used. However, the perforated plate was not soaked, and the electrolytic cell was operated for 15 months at the same injection rate of molten magnesium chloride into the electrolytic cell as 200 cm / second. As a result, a decrease in current efficiency generated immediately after injection of molten magnesium chloride was observed, and the current efficiency throughout the operation period was 75%.

  As described above, according to the present invention, a method of mitigating local turbulent flow of the electrolytic bath is employed, and thereby impurities accumulated in the bottom of the electrolytic cell are introduced into the bath flow. Winding up can be prevented, and a decrease in current efficiency can be suppressed. Therefore, the present invention can be used for molten salt electrolysis represented by molten salt electrolysis of molten magnesium chloride by-produced during the production of sponge titanium by the crawl method.

It is a figure which shows one electrolysis apparatus for enforcing the electrolytic method of the molten metal chloride of this invention. It is a figure which shows the other electrolysis apparatus for enforcing the electrolytic method of the molten metal chloride of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolytic cell 2 ... Container 3 ... Iron outer plate 4 ... Heat insulation brick layer 5 ... Fireproof brick layer 6 ... 1st partition 6a ... Hole 7 ... 2nd partition 8 ... Storage chamber 9 ... Electrolytic chamber 10 ... Electrolytic bath level 11 ... buffer 12 ... iron cathode 13 ... graphite anode 14 ... supply / discharge port 15 ... electrode 16 ... opening

Claims (6)

  A method for electrolyzing a molten metal chloride comprising disposing a buffer in an electrolytic bath containing a molten metal chloride held in an electrolytic bath when the molten metal chloride is electrolyzed to obtain a molten metal.   A method for electrolyzing a molten metal chloride, characterized in that when the molten metal chloride is electrolyzed to obtain a molten metal, the injection rate of the molten metal chloride into the electrolytic cell is 100 cm / second or less.   In obtaining molten metal by electrolyzing the molten metal chloride, a buffer is disposed in the electrolytic bath containing the molten metal chloride held in the electrolytic cell, and the injection rate of the molten metal chloride into the electrolytic cell is 100 cm. A method for electrolyzing molten metal chloride, characterized in that the rate is not more than 1 second.   The method for electrolyzing a molten metal chloride according to any one of claims 1 to 3, wherein the molten metal chloride is magnesium chloride, and the molten metal is magnesium.   5. The molten metal chloride electrolysis method according to claim 1, wherein the buffer is a plate or a cone.   The method for electrolyzing molten metal chloride according to any one of claims 1 to 5, wherein a plurality of the buffer bodies are arranged in a vertical direction in the electrolytic bath.

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