JP2008280594A - Metal refining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal refining method where, upon electrolysis of a molten metal chloride, the evaporation of a metal salt can be effectively suppressed, and the reduction in the recovery efficiency of the molten metal chloride caused by evaporation from a liquid face and the sticking of the evaporated metal chloride to the inside of piping can be prevented. <P>SOLUTION: In the region from the upper end position of electrode members 11, 12, 13 dipped into a molten metal chloride 3 to the bottom face of an electrolytic cell 5, the heating temperature T1 of the electrolytic cell 5 is set to the melting point m of a metal composing the metal chloride or above and also to a temperature capable of electrolyzing, and, in the region from the upper part than the upper end position of the electrode members 11, 12, 13 to the liquid face 3a of the molten metal chloride 3, the heating temperature T2 of the electrolytic cell 5 is set to the temperature range from the melting point tc of the metal chloride or above to the melting point tc+100°C or below, the temperature T3 of a gas directly above the liquid face 3a of the molten metal chloride 3 is set to a temperature below the melting point tc of the metal chloride, and the molten metal chloride 3 is subjected to electrolytic treatment. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal refining method for separating molten metal chloride into metal and chlorine by electrolyzing the molten metal chloride.

  As a low-cost process for producing polycrystalline silicon for solar cells, the zinc reduction method for silicon tetrachloride can be considered. In this process, zinc chloride is discharged as a by-product, from which zinc is recovered as a process. It is required to be reused within.

  Therefore, a potential difference is given to a plurality of electrode members immersed in the molten zinc chloride in the electrolytic bath while heating the molten zinc chloride stored in the electrolytic bath to a temperature that can be electrolyzed by a heat source arranged around the electrolytic bath. A metal refining process that separates molten zinc chloride into zinc and chlorine by electrolyzing molten zinc chloride has been considered.

  However, since the melting point of zinc chloride is 283 ° C., the electrolyzing temperature is about 500 to 650 ° C. Therefore, when the electrolytic cell is heated to an electrolysis temperature of 500 to 650 ° C., Evaporation of the stored molten zinc chloride from the liquid surface is activated.

  The activation of zinc chloride evaporation not only leads to a decrease in zinc recovery efficiency, but also the evaporated zinc chloride may stick to the pipe connected to the electrolytic cell and block the pipe. There is also.

  Therefore, by surrounding the electrode member immersed in the molten metal chloride in the electrolytic cell with a heat insulating material, only the molten metal chloride around the electrode member involved in the electrolytic reaction is maintained at a temperature capable of electrolysis, It is known that the outer molten metal chloride is lower than the electrolyzing temperature to prevent evaporation of the metal chloride (see, for example, Patent Document 1).

JP 2005-200759 A

  In the technique of Patent Document 1 in which the periphery of the electrode member is surrounded by a heat insulating material, in theory, the molten metal chloride at a position more than a certain distance from the electrode member is kept at a temperature lower than the electrolyzable temperature, and the metal chloride Evaporation can be reduced.

  However, in actuality, since the heat generated by the electrode member during the electrolytic reaction escapes upward, the temperature of the molten metal chloride located above the electrode member is sufficiently lowered only by surrounding the electrode member with a heat insulating material. It is difficult to increase the evaporation suppression effect of the metal salt. Therefore, it is difficult to sufficiently prevent the recovery efficiency due to evaporation of the molten metal chloride from the liquid surface and the adhesion of the evaporated metal chloride to the pipe.

  Accordingly, the object of the present invention is to effectively suppress the evaporation of the metal salt when electrolyzing the molten metal chloride, and to reduce the recovery efficiency due to evaporation from the liquid surface of the molten metal chloride or to evaporate it. An object of the present invention is to provide a metal refining method capable of preventing metal chloride from adhering to a pipe.

  The metal refining method according to the present invention that can solve the above-mentioned problems is the above-mentioned electrolytic cell while heating the molten metal chloride stored in the electrolytic cell to a temperature capable of being electrolyzed by a heat source disposed around the electrolytic cell. A metal refining method for separating the molten metal chloride into metal and chlorine by applying a potential difference to a plurality of electrode members immersed in the molten metal chloride in the electrolysis of the molten metal chloride, The plurality of electrode members have a molten metal chloride such that the upper end position is positioned below the liquid level of the molten metal chloride by a predetermined distance L1 and the lower end position is positioned away from the bottom surface of the electrolytic cell. In the region from the upper end position of the electrode member to the bottom surface of the electrolytic cell, the heating temperature T1 of the electrolytic cell by the heat source is equal to or higher than the melting point tm of the metal constituting the metal chloride, Electrolysis is possible In the region from the upper end position of the electrode member to the liquid level of the molten metal chloride, the heating temperature T2 of the electrolytic cell by the heat source is set to the melting point tc + 100 ° C. above the melting point tc of the metal chloride. Electrolytic treatment is performed under the above temperature control, with the gas temperature T3 immediately above the liquid level of the molten metal chloride as the temperature below the melting point tc of the metal chloride.

  In the metal refining method according to the present invention, it is preferable to perform the electrolytic treatment by setting the pressure above the liquid level of the molten metal chloride stored in the electrolytic cell to a negative pressure.

  In the metal refining method according to the present invention, it is preferable to perform the electrolytic treatment by setting the pressure p above the liquid level of the molten metal chloride stored in the electrolytic cell to −10 Pa ≦ p ≦ −1 kPa.

  In the metal refining method according to the present invention, it is preferable that the metal chloride is zinc chloride and zinc is generated by electrolytic treatment.

  In the metal refining method according to the present invention, the heating temperature T1 is set to 420 ° C. ≦ T1 ≦ 650 ° C., the heating temperature T2 is set to 283 ° C. ≦ T2 ≦ 383 ° C., and the temperature T3 is about room temperature. It is preferable that zinc is generated by performing an electrolytic treatment under the above temperature control.

According to the metal refining method of the present invention, when the molten metal chloride is electrolyzed, the heating temperature of the electrolytic cell by the heat source itself is in a positional relationship with the electrode member immersed in the molten metal chloride in the electrolytic cell. The temperature of the molten metal chloride located in the region from the upper end position of the electrode member to the liquid surface of the molten metal chloride is set to the melting point tc + 100 ° C. above the melting point tc of the metal chloride. Further, the temperature of the gas region above the liquid level of the molten metal chloride is set to a temperature below the melting point tc of the metal chloride, so that the evaporation of the metal salt is effectively performed. Can be suppressed.
Therefore, it is possible to prevent the recovery efficiency due to evaporation of the molten metal chloride from the liquid surface and the adhesion of the evaporated metal chloride to the pipe.

Hereinafter, an example of an embodiment of a metal refining method according to the present invention will be described with reference to the drawings.
1A is a longitudinal sectional view showing a schematic configuration of an embodiment of a molten salt electrolysis apparatus for performing a metal refining method according to the present invention, and FIG. 1B is a molten salt electrolysis shown in FIG. It is a graph of the temperature of the molten metal chloride and gas in an electrolytic cell set when implementing the metal refining method which concerns on this invention in an apparatus.

  A molten salt electrolysis apparatus 1 shown in FIG. 1 includes an electrolytic bath 5 that stores molten metal chloride 3, and a plurality of heaters 7 and 8 that are heat sources arranged around the electrolytic bath 5 to heat the electrolytic bath 5. , 9, a plurality of electrode members 11, 12, 13 immersed in parallel in the upright state in the molten metal chloride 3, a predetermined potential difference is given to these electrode members 11, 12, 13, or the heater 7 , 8 and 9 are heated to a desired temperature, a controller (not shown), a heat insulating wall 15 surrounding the outer periphery of the electrolytic cell 5 and the heaters 7, 8 and 9, and the electrode members 11, 12, and 13. The lid member 17 that covers the upper opening 5a of the electrolytic cell 5 for taking in and out is provided.

On the upper end surface of the electrolytic cell 5, a chloride introduction path 21 for introducing the molten metal chloride 3 into the electrolytic cell 5 and a gas space 23 above the liquid level 3 a of the molten metal chloride 3 in the electrolytic cell 5 are provided. a gas introduction path 25 for introducing a nitrogen gas (N ₂₎ an inert gas such as a chlorine discharge path 27 for discharging the negative pressure suction attraction chlorine gas produced (Cl ₂₎ by electrolysis of a molten metal chloride 3 Is provided.
In addition, a generated metal recovery passage 29 for discharging metal generated by electrolysis of the molten metal chloride 3 is provided on the bottom side of the electrolytic cell 5.

  In the electrolytic cell 5, the height h1 of the gas space 23 above the liquid surface 3a is substantially equal to or higher than the height h2 of the electrode members 11, 12, 13 immersed in the molten metal chloride 3. The upper ends of the electrode members 11, 12, 13 immersed in the molten metal chloride 3 are positioned at a position below the liquid surface 3a by a predetermined distance L1, and the lower ends of the electrode members 11, 12, 13 are electrolyzed. The depth is set to be a position away from the bottom surface of the tank 5 by a predetermined distance.

  The distance L1 from the upper end of each electrode member 11, 12, 13 to the liquid level 3a is such that the molten metal chloride 3 in this region exceeds the set temperature, which will be described later, due to the heat generated by the electrode members 11, 12, 13. Set it deep enough to prevent the temperature from rising. For example, the distance L1 may be set within a range of 200 to 600 mm.

The plurality of heaters 7, 8, and 9 serving as heat sources have a height on the outer periphery of the electrolytic cell 5 in order to heat the molten metal chloride 3 in the electrolytic cell 5 according to the position with respect to the electrode members 11, 12, and 13. It is provided with a different position.
The uppermost heater 7 heats the region from the upper end position of the electrode members 11, 12, 13 to the liquid surface 3 a of the molten metal chloride 3 to a desired temperature range.
The intermediate heater 8 heats the region from the upper end to the lower end of the electrode members 11, 12, 13 to a desired temperature range.
The lowest heater 9 is provided so as to cover the bottom of the electrolytic cell 5, and heats the region from the lower end of the electrode members 11, 12, 13 to the bottom surface of the electrolytic cell 5 to a desired temperature range.
Thus, by arranging the heaters 7, 8 and 9 separately in the height direction of the electrolytic cell 5, the electrolytic cell 5 can be provided with a desired temperature gradient according to the height position.

Current supply rods 30A, 30B are connected to the electrode members 11, 13 at both ends of the plurality of electrode members 11, 12, 13, and one is operated as a cathode and the other as an anode.
The plurality of electrode members 12 arranged in parallel between the electrodes 11 and 13 at both ends are connected by a non-conducting member 31 in a state in which a predetermined gap is ensured between the adjacent electrode members. The potential difference corresponding to the distance from the electrode members 11 and 13 at both ends contributes to the electrolytic reaction.

Next, the metal refining method implemented with the said molten salt electrolysis apparatus 1 is demonstrated.
In the metal refining method of the present embodiment, the molten metal chloride 3 stored in the electrolytic cell 5 is heated to a temperature capable of being electrolyzed by the heaters 7, 8, and 9 which are heat sources arranged around the electrolytic cell 5. By applying a potential difference to the plurality of electrode members 11, 12, and 13 immersed in the molten metal chloride 3 in the electrolytic bath 5 to electrolyze the molten metal chloride 3, the molten metal chloride 3 is converted into metal and chlorine. Separated and recovered.

  The plurality of electrode members 11, 12, and 13 are located at the upper end position below the liquid surface of the molten metal chloride 3 by a predetermined distance L 1 and at the lower end position away from the bottom surface of the electrolytic cell 5. It arrange | positions in molten metal chloride 3 like this.

  In a region from the upper end position of the electrode members 11, 12, 13 to the bottom surface of the electrolytic cell 5, the heating temperature of the electrolytic cell 5 (temperature of the heaters 8, 9) T <b> 1 in this region is changed to metal by heating by the heaters 8, 9. The temperature is set to a temperature that is at least the melting point tm of the metal constituting the chloride and that can be electrolyzed.

  Further, in the region above the upper end position of the electrode members 11, 12, 13 and up to the liquid level 3 a of the molten metal chloride 3, the heating temperature of the electrolytic cell 5 in this region (the temperature of the heater 7) is heated by the heater 7. T2 is set to a temperature range between the melting point tc of the metal chloride and the melting point tc + 100 ° C. or less. For this purpose, the heaters 7, 8, and 9 are controlled by setting the distance L1 within the range of 200 to 600 mm.

  Furthermore, the temperature T3 of the gas region above the liquid level 3a of the molten metal chloride 3 (the temperature of the gas immediately above the liquid level) is adjusted by adjusting the temperature of the inert gas supplied from the gas introduction path 25, so that Set to a temperature below the melting point tc of the chloride.

  As described above, the electrolytic treatment is performed under temperature control in which the temperature of each part of the electrolytic cell 5 is set to a desired temperature. Thereby, in the area | region from the upper end position of the electrode members 11, 12, and 13 to the bottom face of the electrolytic cell 5, while performing electrolysis of a metal chloride favorably, it is molten metal above the upper end position of the electrode members 11, 12, and 13 It will be heated to such an extent that chloride 3 does not evaporate, and it can control evaporation of a metal salt effectively. Accordingly, the recovery efficiency due to the evaporation of the molten metal chloride 3 from the liquid surface 3a is not reduced, and the evaporated metal chloride can be prevented from adhering to the inside of the pipe (chlorine discharge path 27). .

  Moreover, in the metal refining method of this embodiment, the electrolytic treatment is performed by setting the pressure of the gas space 23 above the liquid surface 3a of the molten metal chloride 3 stored in the electrolytic bath 5 to a negative pressure. Therefore, the chlorine gas generated by the electrolytic reaction can be exhausted more safely. Further, when the atmospheric pressure of the gas space 23 above the liquid surface 3a of the molten metal chloride 3 is set to a negative pressure, nitrogen gas or other inert gas is used as a cooling gas by using a negative pressure suction force. If it supplies to the liquid level 3a of the molten metal chloride 3, the liquid level 3a temperature of the molten metal chloride 3 can be more reliably set to a desired temperature range, and the evaporation of the metal chloride is more reliably suppressed. be able to.

  Further, in the metal refining method of the present embodiment, the pressure p in the gas region above the liquid surface 3a of the molten metal chloride 3 stored in the electrolytic cell 5 is set to −10 Pa ≦ p ≦ −1 kPa to perform electrolysis. Process. Therefore, the atmospheric pressure in the gas space 23 above the liquid surface 3a of the molten metal chloride 3 can be prevented from becoming an excessive negative pressure, and the excessive negative pressure affects the exhaust of chlorine gas generated by the electrolytic reaction. Can be prevented.

  A specific example of the above embodiment is shown below.

In the metal refining method of Example 1, the metal chloride charged into the electrolytic cell 5 is zinc chloride, and zinc is generated by electrolytic treatment.
In that case, the heating temperature of the electrolytic cell 5 is set as follows.

The heating temperature T1 of the electrolytic cell 5 in the region from the upper end position of the electrode members 11, 12, 13 to the bottom surface of the electrolytic cell 5 is set to 420 ° C. ≦ T1 ≦ 650 ° C. The melting point of zinc is 419.5 ° C.
The heating temperature T2 of the electrolytic cell 5 in the region up to the liquid surface 3a of the molten metal chloride 3 above the upper end position of the electrode members 11, 12, 13 is set to 283 ° C. ≦ T2 ≦ 383 ° C. The melting point of zinc chloride is 283 ° C.
The temperature T3 of the gas immediately above the liquid level 3a of the molten metal chloride 3 is set to about room temperature by adjusting the temperature of the inert gas (nitrogen gas) supplied from the gas introduction path 25.

FIG. 1B shows the temperature gradient in the height direction of the molten metal chloride and gas in the electrolytic cell 5 when the temperature is set as described above.
In Example 1, the electrolytic treatment is performed under the above temperature control to generate zinc.

  In the metal refining method of Example 1, since the metal chloride is zinc chloride and zinc is generated by electrolytic treatment, for example, polycrystalline silicon for solar cells is produced by the zinc tetrachloride reduction method. In this case, zinc can be efficiently recovered from the zinc chloride discharged as a width product and reused in the polycrystalline silicon manufacturing process.

  Further, in the metal refining method of Example 1, the heating temperature T1 of the electrolytic cell 5 in the region from the upper end position of the electrode members 11, 12, 13 to the bottom surface of the electrolytic cell 5 is set, and the melting point tm of zinc is 419.5. Considering that the temperature is higher than or equal to ° C., the electrolytic cell is set to 420 ° C. ≦ T1 ≦ 650 ° C. and in the region above the upper end position of the electrode members 11, 12, 13 to the liquid surface 3 a of the molten metal chloride 3. In consideration of the fact that the melting point tc of zinc chloride is 283 ° C., the heating temperature T2 of 5 is set to 283 ° C. ≦ T2 ≦ 383 ° C., and the gas region above the liquid level 3a of the molten metal chloride 3 The temperature T3 is set to about room temperature.

  Therefore, during the electrolytic treatment of molten zinc chloride, the temperature of the molten zinc chloride located above the electrode members 11, 12, 13 is appropriately set within the range of 283 ° C. to + 100 ° C. of the melting point tc of zinc chloride. The temperature of the gas region above the liquid surface 3a of the molten zinc chloride is appropriately set to about room temperature, and the gas region above the liquid surface 3a of the molten zinc chloride exhibits a cooling effect on the molten zinc chloride. Therefore, the temperature in the vicinity of the liquid surface 3a of the molten zinc chloride can be reliably suppressed below the desired temperature, and evaporation of the molten zinc chloride from the liquid surface 3a can be more reliably prevented.

  Therefore, when generating zinc by the electrolytic reaction of molten zinc chloride, the recovery efficiency of zinc can be increased, and evaporated zinc chloride can be prevented from adhering in the chlorine discharge path 27.

  The molten salt electrolysis apparatus 1 and the metal refining method of the present embodiment described above are particularly effective in the following scenes.

  When producing polycrystalline silicon by the chloride method, silicon chloride (for example, silicon tetrachloride or silane trichloride) is reduced with zinc to obtain polycrystalline silicon, and the reducing zinc is converted into zinc chloride. It is taken out. And pure zinc can be obtained by electrolyzing zinc chloride, and this pure zinc can be used again for reduction of silicon chloride. In the step of electrolyzing zinc chloride, the molten salt electrolysis apparatus 1 and the metal refining method of this embodiment are preferably used.

  In addition, the use of the molten salt electrolysis apparatus 1 and the metal refining method shown in the above embodiment is not limited to the electrolysis of zinc chloride. It may be used when various metals chloride other than zinc chloride is separated and recovered by electrolysis from metal and chlorine gas.

(A) is a longitudinal cross-sectional view showing a schematic configuration of an embodiment of a molten salt electrolysis apparatus for performing a metal refining method according to the present invention, and (B) shows the present invention in the molten salt electrolysis apparatus shown in FIG. 1 (A). It is a graph of the temperature in the electrolytic cell set when implementing the metal refining method which concerns on.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molten salt electrolysis apparatus 3 Molten metal chloride 3a Liquid surface 5 Electrolyzer 7, 8, 9 Heater (heat source)
DESCRIPTION OF SYMBOLS 11, 12, 13 Electrode member 15 Heat insulation wall 17 Lid member 21 Chloride introduction path 23 Gas space 25 Gas introduction path 27 Chlorine discharge path 29 Production metal recovery path 30A, 30B Current supply rod 31 Non-conduction member

Claims (5)

While the molten metal chloride stored in the electrolytic cell is heated to a temperature capable of being electrolyzed by a heat source disposed around the electrolytic cell, a potential difference is applied to a plurality of electrode members immersed in the molten metal chloride in the electrolytic cell. A metal refining method for separating the molten metal chloride into metal and chlorine by providing and electrolyzing the molten metal chloride,
The plurality of electrode members are made of molten metal chloride such that the upper end position is positioned below the liquid level of the molten metal chloride by a predetermined distance L1 and the lower end position is positioned away from the bottom surface of the electrolytic cell. Placed in things,
In the region from the upper end position of the electrode member to the bottom surface of the electrolytic cell, the heating temperature T1 of the electrolytic cell by the heat source is equal to or higher than the melting point tm of the metal constituting the metal chloride and can be electrolyzed. age,
In the region from the upper end position of the electrode member to the liquid level of the molten metal chloride, the heating temperature T2 of the electrolytic cell by the heat source is set to a temperature not lower than the melting point tc of the metal chloride and not higher than the melting point tc + 100 ° C. ,
The temperature T3 of the gas immediately above the liquid surface of the molten metal chloride is set to a temperature not higher than the melting point tc of the metal chloride,
The metal refining method characterized by performing an electrolytic treatment under said temperature control. The metal refining method according to claim 1,
A metal refining method, wherein the electrolytic treatment is performed by setting the pressure above the liquid level of the molten metal chloride stored in the electrolytic bath to a negative pressure. The metal refining method according to claim 2,
The metal refining method characterized by performing an electrolysis process by setting the pressure p above the liquid level of the molten metal chloride stored in the electrolytic bath to −10 Pa ≦ p ≦ −1 kPa. A metal refining method according to any one of claims 1 to 3,
A metal refining method, wherein the metal chloride is zinc chloride, and zinc is generated by electrolytic treatment. The metal refining method according to claim 4,
The heating temperature T1 is set to 420 ° C. ≦ T1 ≦ 650 ° C.,
The heating temperature T2 is set to 283 ° C. ≦ T2 ≦ 383 ° C.,
The temperature T3 is set to about room temperature,
A metal refining method characterized in that zinc is generated by performing an electrolytic treatment under the above temperature control.

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