JP2009144176A - Method of producing metal calcium and molten salt electrolytic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for efficiently producing metal calcium by a molten salt electrolysis. <P>SOLUTION: In the method of producing metal calcium by filling calcium chloride molten salt in an electrolytic bath and arranging so as to dip an anode and a cathode to carry out the molten salt electrolysis, metal calcium is deposited on the cathode in a solid state by cooling the cathode to a temperature equal to or below the melting point of the metal calcium in the molten salt electrolysis and after molten salt electrolysis, the deposited solid metal calcium is recovered by heating to be melted. The molten salt electrolytic apparatus is used for the manufacturing method and is composed of an electrolytic bath, the cathode, the anode and a partition wall dipped and arranged between the cathode and the anode and the cathode has a flow passage formed to pass a heating medium or a cooling medium to heat or cool the cathode itself. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to molten salt electrolysis of calcium chloride, and in particular, technology for efficiently recovering only high-purity metallic calcium from solid precipitate calcium containing molten salt obtained by molten salt electrolysis of calcium chloride. About.

  Sponge titanium has been manufactured by the conventional crawl method, and the production cost has been reduced by accumulating various improvements. However, because the crawl method is a batch process, the cost is greatly reduced by the efficiency improvement. It seems that the situation is difficult.

  In contrast, the University of Cambridge has reported an attempt to produce titanium metal directly by reducing titanium oxide with calcium in a molten salt (see, for example, Patent Document 1). Ono et al. Also discloses a similar process (see, for example, Patent Document 2). Furthermore, Okabe et al. Have reported calcium reduction of titanium oxide in molten salt based on a new concept called EMR method (see, for example, Patent Document 3).

  Recently, a method of directly producing titanium metal by using titanium tetrachloride as a raw material instead of titanium oxide and reducing it with metallic calcium has been disclosed (for example, see Patent Document 4).

  In the reduction reaction disclosed in the above-mentioned document, calcium chloride is finally produced as a by-product, so it is decomposed into metal calcium and chlorine gas by molten salt electrolysis, and the metal calcium is recycled for the reduction process. The

  However, since the metallic calcium produced by the above electrolytic reaction has solubility in calcium chloride, which is an electrolytic bath, the metallic calcium once deposited on the cathode is redissolved in the electrolytic bath. Therefore, a method for recovering only metallic calcium with a high yield is desired.

  In this regard, a method is disclosed in which a composite molten salt having a melting point lower than that of metallic calcium is used, and metallic calcium is deposited on the cathode in a solid state (see, for example, Patent Document 5). Further, after depositing metallic calcium produced at the cathode in the molten salt electrolysis on the cathode in a solid state, mechanically scraping or heating the entire cathode on which solid metallic calcium is deposited, the metallic calcium Is disclosed (for example, see Patent Document 6).

  FIG. 4 shows a method for dissolving and separating metallic calcium by a conventional method. As shown in FIG. 4 (a), a voltage is applied to the anode and the cathode, and a predetermined amount of metallic calcium is deposited on the cathode by molten salt electrolysis of calcium chloride. Then, as shown in FIG. 4 (b). The molten metal calcium was extracted out of the system while the electrolytic bath was heated above the melting point of metallic calcium by a heating means (not shown) to float the molten metallic calcium on the surface of the electrolytic bath.

  However, the above-described method does not solve the problem that metallic calcium is re-dissolved in the electrolytic bath, and requires heat energy for dissolving solid metallic calcium deposited on the cathode, and improvement is required.

  Thus, there is a demand for a technique for efficiently producing metallic calcium not containing an electrolytic bath deposited by molten salt electrolysis of calcium chloride in a molten state.

WO99 / 064638 JP 2003-129268 A JP 2003-306725 A WO2007 / 026565 US3226311 WO2006 / 003864

  The present invention relates to a method and apparatus for efficiently producing metallic calcium used for producing metallic titanium by reducing metallic titanium oxide or chloride, and in particular, produced by molten salt electrolysis. An object of the present invention is to provide a method and an apparatus capable of efficiently producing metallic calcium.

  As a result of extensive studies in view of such circumstances, solid metal calcium produced by molten salt electrolysis of calcium chloride was deposited on the cathode while cooling the cathode itself, and then the cathode itself was placed in an electrolytic bath. It has been found that high-purity metallic calcium can be efficiently produced by heating and melting and separating the solid metal from the cathode, and the present invention has been completed.

  That is, the present invention is a method for producing metallic calcium in which an electrolytic bath composed of a molten salt is filled in an electrolytic cell, and an anode and a cathode are immersed in the electrolytic bath to perform molten salt electrolysis. Is characterized in that the cathode is cooled to below the melting point of metallic calcium to deposit metallic calcium on the cathode in a solid state, and after completion of the molten salt electrolysis, the deposited solid metallic calcium is melted and recovered by heating the cathode. It is said.

  In the present invention, it is preferable that not only the metal calcium deposited on the cathode is heated by heating the cathode itself, but also that the electrolytic bath in contact with the cathode is simultaneously heated.

  Moreover, in this invention, it is set as a preferable aspect that the molten metal calcium is extracted out of the system at the same time as the metallic calcium deposited on the cathode is melted and separated.

  A molten salt electrolysis apparatus according to the present invention is a molten salt electrolysis apparatus used in the above-described method for producing calcium metal, and includes an electrolytic cell, a cathode, an anode, and a partition wall arranged so as to be immersed between the cathode and the anode. A flow path through which a heat medium or a refrigerant that can be heated or cooled can flow is formed.

  In the present invention, it is preferable that not only the partition wall is disposed so as to be immersed between the anode and the cathode, but also that the cathode partition wall is disposed around the cathode.

  According to this invention, there exists an effect that metal calcium with high purity can be efficiently manufactured from the solid deposit containing the molten salt manufactured by molten salt electrolysis. As a result, it is possible to produce metallic calcium suitable as a reducing agent for titanium oxide and titanium tetrachloride.

  A preferred apparatus configuration example for carrying out the present invention and a method for producing molten metal calcium by using molten salt electrolysis of calcium chloride will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a molten salt electrolysis apparatus E of the present invention. FIG. 1 (a) shows a molten salt electrolysis process, and FIG. 1 (b) shows a separation and recovery process. The electrolytic bath 1 is filled with an electrolytic bath 2 made of calcium chloride and held in a molten state by a heating means (not shown). An anode 3 and a cathode 4 are immersed in the electrolytic bath 2, and a partition wall 5 is provided between the anode 3 and the cathode 4. A lid 11 for shielding the inside of the electrolytic cell 1 from the atmosphere is provided at the upper part of the electrolytic cell 1. The lid 11 has a gas supply nozzle 12 and a gas for holding the inside of the electrolytic cell 1 in an arbitrary atmosphere. A discharge nozzle 13 is provided.

  The cathode 4 of the present invention incorporates heating means and cooling means for the cathode 4 itself. Specifically, as shown in FIG. 1A, the cooling means includes an inlet nozzle 41, an outlet nozzle 42, and a flow path 43, and cools the cathode 4 by circulating the refrigerant through the flow path 43. It is configured to be able to. Further, the heating means is a heater 44, which can heat the cathode 4.

  When energization is started in the molten salt electrolysis apparatus E shown in FIG. 1A and molten salt electrolysis is performed in the electrolytic bath 2, chlorine gas is generated from the anode 3 and metal calcium 6 is deposited on the surface of the cathode 4. . At this time, the metal calcium 6 can be deposited in a solid state by circulating a coolant through the flow path 43 of the cathode 4 and cooling to a temperature below the melting point of the metal calcium.

  Subsequently, when a predetermined amount of metallic calcium 6 is deposited on the cathode 4, the process proceeds to the separation and recovery step shown in FIG. In the separation / recovery step, the energization between the anode 3 and the cathode 4 and the supply of the refrigerant to the flow path 43 are cut off, and the heating by the heater 44 is started to keep the temperature above the melting point of calcium. As a result, the metallic calcium 6 is melted and floated, and is recovered as the molten metallic calcium 61 by the extraction tube 14.

  In the present invention, it is preferable that the surface temperature of the cathode 4 is controlled to be equal to or lower than the melting point of metallic calcium during calcium chloride molten salt electrolysis. As a result, solid metallic calcium can be effectively deposited on the cathode 4. On the other hand, the temperature of the electrolytic bath 2 is preferably controlled within a temperature range in which the molten state of the electrolytic bath 2 can be maintained, and specifically, maintained within a range of 800 ° C to 850 ° C. Is preferred.

  From the viewpoint of the fluidity of the electrolytic bath 2, the temperature of the electrolytic bath 2 is preferably higher. Therefore, it is preferable to regulate the temperature of the electrolytic bath 2 in consideration of the mixing state of the electrolytic bath 2 into the metal calcium 6 deposited on the cathode 4 and the current efficiency. In the present invention, the temperature of the electrolytic bath 2 is preferably maintained below the melting point of metallic calcium. Note that the temperature of the electrolytic bath needs to be maintained at a temperature equal to or higher than the melting point of the molten salt constituting the electrolytic bath in order to facilitate the molten salt electrolysis. However, if the temperature of the electrolytic bath 2 becomes too high, the evaporation of the electrolytic bath 2 proceeds, and the amount of metallic calcium 6 dissolved in the electrolytic bath increases, which is not preferable. Therefore, in this invention, it is preferable that the temperature of the said electrolytic bath 2 sets 900 degreeC as an upper limit.

  The electrolytic bath used for the molten salt electrolysis of the present invention preferably contains calcium chloride and potassium chloride or sodium chloride. By blending such components into a composite salt, the melting point of calcium chloride can be suitably reduced.

  Specifically, the melting point of the electrolytic bath can be lowered from 772 ° C. (melting point of calcium chloride) to 600 ° C. by adding 5 mol% to 75 mol% of potassium chloride to calcium chloride. As a result, since the molten salt electrolysis can be performed at a lower temperature, the energy for melting the molten salt and the cooling energy for the cathode 4 are reduced, and the surface temperature of the cathode 4 is appropriately maintained while being below the melting point of metallic calcium It is possible to maintain the electrolytic bath in a molten state while maintaining excellent fluidity.

  In the molten salt electrolysis of the present invention, the cathode 4 through which a refrigerant can be circulated is used. As this refrigerant, it is preferable to use air from the viewpoint of cost, but if possible, dry air should be used. More preferred.

  After a predetermined amount of metallic calcium 6 is deposited on the surface of the cathode 4, the supply of the refrigerant to the cathode 4 is stopped, and the cathode 4 is immersed in the electrolytic bath 2 when the temperature of the cathode 4 is heated to the melting point of metallic calcium or higher. It is preferable to deposit the metallic calcium 6 so that a part of the cathode 4 remains in direct contact with the electrolytic bath 2.

  By taking the form of metal calcium deposited on the cathode 4 as described above, not only can the metal calcium 5 in contact with the cathode 4 be heated, but also the cathode separated by the partition walls 5 inside the electrolytic cell 1. The temperature of the electrolytic bath 2 held in the side range can be effectively increased.

  The molten metal calcium 61 produced by melting the metal calcium 6 deposited on the cathode 4 can be floated on the bath surface of the electrolytic bath 2 as shown in FIG. In the present invention, the molten metal calcium 61 is preferably extracted out of the system through the extraction tube 14 in as short a time as possible.

  As described above, the molten metal calcium 61 melted and separated from the cathode 4 is taken out of the system in a short time, so that the melting loss to the electrolytic bath 2 can be suppressed, and as a result, the molten metal calcium 61 is recovered. The effect is that the yield can be maintained at a high level.

  The cathode 4 can be heated by energizing and heating a heater 44 mounted inside the cathode, but a gas burner can be used instead of the heater 44. By using a gas burner, the cathode 2 can be heated in a short time.

  Instead of the heater 44 or the gas burner, heating may be performed by circulating a heat medium through a flow path for circulating the refrigerant. According to such an aspect, a heater and a gas burner for heating are unnecessary, and if only the flow path is formed in the cathode, cooling and heating can be performed by switching between the refrigerant and the heat medium.

  Chlorine gas is generated from the anode 3 immersed in the electrolytic cell 1. Chlorine gas is sucked and exhausted from a gas discharge nozzle 13 provided on the lid 11, and can be recycled, for example, as a chlorinating agent for titanium ore.

  It is preferable to immerse the partition wall 5 between the cathode 3 and the anode 4 in the electrolytic bath 2 held inside the electrolytic cell 1. By providing such a partition wall 5, it is possible to effectively suppress the re-reaction between the solid metallic calcium 5 deposited on the cathode 2 and the chlorine gas generated at the anode 3. .

  Further, the partition wall 5 melts the solid metallic calcium 5 deposited on the cathode 4 after the molten salt electrolysis step shown in FIG. 1A is completed and then the separation and recovery step shown in FIG. Prior to separation, the partition wall 5 is preferably lowered to the bottom of the electrolytic cell 1. By performing such an operation, the amount of the electrolytic bath to be heated can be reduced by partitioning the electrolytic bath 2 in contact with the cathode 4 from the entire electrolytic bath 2, and as a result, the solid metallic calcium 5 can be reduced. This has the effect that it can be efficiently melted and separated from the cathode 4.

  FIG. 2 shows another preferred embodiment according to the present invention. In this embodiment, a cathode partition 51 is further provided around the cathode 4. In this embodiment, after the metal calcium 6 is deposited on the cathode 4 as shown in FIG. 2A by the molten salt electrolysis step, the cathode 4 itself is heated as shown in FIG. After the total amount of the solid metallic calcium 6 deposited on is dissolved, the molten metallic calcium 61 dissolved and separated from the cathode 4 is extracted out of the system from the extraction tube 14 immersed in the electrolytic bath 2. .

  As described above, since the predetermined range is surrounded by the cathode partition wall 51, the heating of the metallic calcium 6 deposited on the cathode 4 and the temperature of the electrolytic bath 2 in which the metallic calcium 6 is immersed also rise in a short time. There is an effect that it can be warmed. As a result, there is an effect that the recovery loss of the metallic calcium 6 to the electrolytic bath 2 can be effectively suppressed.

  FIG. 3 shows another preferred embodiment according to the present invention. In this embodiment, the electrolytic cell 15 has a cylindrical shape, and FIG. 3 is a plan view of the electrolytic cell 15 as viewed vertically downward from above. The electrolytic bath 15 is filled with the electrolytic bath 2, an anode 31 is disposed at the center, and a plurality of cell spacing walls 52 are disposed radially from the anode 31 toward the outside.

  One cathode 45 and one cathode partition wall 53 are respectively immersed in the electrolytic bath 2 inside the sector-shaped unit electrolytic cell 16 surrounded by the cell spacing wall 52. These cathodes 45 incorporate their own cooling means and heating means, similarly to the cathode 4 described in FIG. The cathode barrier 53 can employ the same structure as the cathode barrier 51 described in FIG.

  In the embodiment shown in FIG. 3, a part of the surface of the anode 31 and the cathode 45 facing the anode 31 constitute a set of electrolytic cells. As a result, a plurality of electrolytic cells are used despite being one electrolytic cell. The electrolytic reaction can be carried out at the same time, and high productivity can be secured.

  The electrolytic cell 15 shown in FIG. 3 is composed of six sets of unit electrolytic cells 16. Of these, three sets can be subjected to a molten salt electrolysis step for the cathode 45, and the remaining three sets can be subjected to a separation and recovery step for metallic calcium deposited on the cathode 45. By taking such an operation mode and alternately switching the steps, it is possible to produce metallic calcium apparently continuously from the electrolytic cell 15.

  The metallic calcium produced by the method of the present invention described above can be efficiently used as, for example, a reducing agent for titanium oxide or titanium tetrachloride. In addition, when used as a reducing agent for titanium tetrachloride, calcium chloride is by-produced. By returning the calcium chloride to the electrolytic cell 1 or the electrolytic cell 15 according to the present invention, molten salt electrolysis is performed. Metal calcium can be recycled.

  Moreover, in this invention, since the metal calcium 6 deposited on the cathode is melted and floated on the surface of the electrolytic bath, it is possible to recover high-purity metallic calcium with little entrainment of the electrolytic bath. Is.

  According to the present invention described above, there is an effect that it is possible to efficiently produce high-purity metallic calcium from a solid precipitate recovered by molten salt electrolysis of calcium chloride.

Hereinafter, the present invention will be described in more detail by way of examples.
[Example 1]
1. Molten Salt Electrolysis Molten salt electrolysis of calcium chloride was performed with the following configuration using the molten salt electrolytic cell shown in FIG.
1) Equipment configuration anode ・ Material: Graphite ・ Size: φ35mm × L60mm
Cathode ・ Material: Carbon steel ・ Size: φ35mm × L60mm
Partition: Material: Silicon nitride Size: T5mm x W200mmxL400mm
2) Electrolytic bath Composition: Calcium chloride: Potassium chloride = 85: 15
Melting point: 720 ° C

2. Electrolysis conditions 1) Electrolysis temperature: 750 ° C
2) Cathode cooling: Air was supplied from the outside to cool the cathode surface temperature below the melting point of metallic calcium.
3) Cathode heating: After the partition wall was lowered to the bottom of the container, the cathode was heated to a temperature equal to or higher than the melting point of metallic calcium by passing through an electric heater built in the cathode.

3. Dissolution / Separation Conditions When a predetermined amount of metallic calcium is deposited, the electrode is turned off, the air supply to the cathode is stopped, and then the heater built in the cathode is turned on to control the temperature of the cathode itself. Heated above the melting point of.

4). Recovery conditions of metallic calcium Solid metallic calcium deposited on the cathode was melted and separated from the cathode, and at the same time, the molten metallic calcium floated and separated on the surface of the electrolytic bath was transferred to another container.

5). Results When metallic calcium was produced by the above-mentioned method, the yield of the recovered metal amount was in the range of 60% to 85% with respect to the theoretical precipitation amount calculated from the input electricity amount, and good current efficiency. showed that.

[Comparative Example 1]
Using the apparatus shown in FIG. 4, the electrolytic bath was the same as in Example 1, and metallic calcium was deposited on the cathode in a solid state. Next, the electrolytic bath, not the cathode, is heated from the outside to the melting point of the metallic calcium or more, and the solid metallic calcium deposited on the cathode is melted and floated on the electrolytic bath surface. Was recovered. The yield of metallic calcium recovered relative to the metallic calcium calculated from the amount of electricity supplied during molten salt electrolysis was calculated, and the rate was in the range of 40% to 65%.

  From the above examples and comparative examples, it was confirmed that the recovery yield when molten metal calcium was recovered according to the present invention was improved by 20% compared to the conventional case. It was also confirmed that the power consumed to dissolve the solid metallic calcium deposited on the cathode was also improved by 50%.

  According to the present invention, calcium metal can be efficiently produced by electrolysis of calcium chloride.

It is a schematic cross section which shows the molten salt electrolysis apparatus of this invention, (a) shows a molten salt electrolysis process, (b) shows a separation-and-recovery process. It is a schematic cross section which shows the cathode vicinity in the other molten salt electrolysis apparatus of this invention, (a) shows a molten salt electrolysis process, (b) shows a separation collection process. It is a top view which shows the other molten salt electrolysis apparatus of this invention. It is a schematic cross section which shows the conventional molten salt electrolysis apparatus, (a) shows a molten salt electrolysis process, (b) shows a separation and recovery process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolysis tank 11 Lid 12 Gas supply nozzle 13 Gas discharge nozzle 14 Extraction pipe 15 Electrolysis tank 16 Unit electrolysis tank 2 Electrolytic bath 3 Anode 31 Anode 4 Cathode 41 Inlet nozzle 42 Outlet nozzle 43 Channel 44 Heater 45 Cathode 5 Partition 51 Cathode partition 52 Cell spacing wall 53 Cathode partition 6 Metal calcium 61 Molten metal calcium

Claims (11)

  A method for producing metallic calcium by molten salt electrolysis, wherein during the molten salt electrolysis, the cathode is cooled below the melting point of metallic calcium to deposit the metallic calcium on the cathode in a solid state, and after completion of the molten salt electrolysis A method for producing metallic calcium, characterized in that the solid metallic calcium deposited by heating the cathode is melted and recovered.   2. The method for producing metallic calcium according to claim 1, wherein after the molten salt electrolysis is finished, the cathode and the electrolytic bath in contact with the cathode are simultaneously heated.   The method for producing metallic calcium according to claim 1 or 2, wherein solid metallic calcium deposited on the cathode is melted and separated from the cathode while being extracted from the electrolytic cell.   Prior to melting and separating solid metallic calcium deposited on the cathode, the partition wall immersed in the anode and the cathode is lowered to the bottom of the electrolytic cell. The manufacturing method of metallic calcium as described in any one of.   The method for producing metallic calcium according to any one of claims 1 to 4, wherein molten salt electrolysis of calcium chloride by-produced in the reduction step of titanium tetrachloride with metallic calcium is performed.   It is composed of an electrolytic cell, an electrolytic bath, a cathode, an anode, and a partition wall arranged so as to be immersed between the cathode and the anode. The cathode has a flow path through which a heat medium or a refrigerant that can heat or cool the cathode itself can flow. A molten salt electrolyzer characterized by being formed.   The molten salt electrolysis apparatus according to claim 6, wherein a heater or a gas burner is disposed inside the cathode.   The molten salt electrolysis apparatus according to claim 6, wherein a cathode partition is provided around the cathode in addition to the partition.   The molten salt electrolysis apparatus according to any one of claims 6 to 8, wherein a plurality of cathodes are radially arranged around the anode via a tank interval wall.   The molten salt electrolysis apparatus according to any one of claims 6 to 9, wherein the cathode is made of stainless steel, carbon steel, or titanium metal.   The molten salt electrolysis apparatus according to any one of claims 6 to 10, wherein the electrolytic bath is composed of a molten salt containing calcium chloride and at least one of potassium chloride and sodium chloride. .

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