Method and Apparatus for Producing Metal by Molten-Salt Electrolysis

Abstract

A method for production of metal by molten-salt electrolysis of the present invention is a method for production of metal by molten-salt electrolysis which is performed by filling a molten salt of calcium chloride in an electrolysis vessel having a anode and a cathode, one of the anode or cathode is arranged surrounding the other electrode, the cathode has at least one hole communicating the inner area surrounded by the cathode with the outer area, and the molten salt flows through the communicating holes from one area including the anode (the inner area or outer area) to the other area.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual cross sectional diagram showing a production process for calcium metal by molten-salt electrolysis in an embodiment of the present invention.

FIG. 2 is a conceptual cross sectional diagram showing a production process for calcium metal by molten-salt electrolysis in another embodiment of the present invention.

FIG. 3 is a conceptual cross sectional diagram showing a production process for calcium metal by molten-salt electrolysis in another embodiment of the present invention.

FIG. 4 is a conceptual cross sectional diagram showing a production process for calcium metal by molten-salt electrolysis in another embodiment of the present invention.

FIG. 5 is a conceptual cross sectional diagram showing a production process for calcium metal by molten-salt electrolysis in another embodiment of the present invention.

FIG. 6 is a conceptual cross sectional diagram showing a production process for calcium metal by molten-salt electrolysis and a production process of titanium metal in another embodiment of the present invention.

FIG. 7 is a conceptual cross sectional diagram showing a production process for calcium metal by molten-salt electrolysis and a production process of titanium metal in another embodiment of the present invention.

FIG. 8 is a conceptual cross sectional diagram showing a production process for calcium metal by molten-salt electrolysis and a production process of titanium metal in another embodiment of the present invention.

FIG. 9 is a conceptual cross sectional diagram showing a finned cylindrical cathode used in the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are explained below with reference to the drawings. The drawings show appropriate examples of apparatus construction to practice the present invention. FIG. 1 shows a conceptual cross sectional diagram of the first embodiment of the present invention. Reference numeral 1 is an electrolysis vessel, and an electrolysis bath 2 consisting of calcium chloride (melting point 780° C.) is filled in the vessel. The electrolysis bath 2 is heated to a temperature above the melting point of calcium chloride by a heater (not shown) to be maintained in a molten state. Reference numeral 3 indicates a anode. Reference numeral 4 indicates a cylindrical cathode, which is arranged surrounding the anode 3. Plural communicating holes are formed at a lower part of the cathode 4, and the molten salt can be moved between the inner area and the outer area of the cathode. Since the communicating holes are formed at the lower part of the cathode, the upper part of the cathode can function as a division wall.

Furthermore, a bath supplying pipe 6 is arranged at an inner part of the cathode 4, and calcium chloride which is a raw material of the molten-salt electrolysis is continuously supplied therethrough. An extracting pipe 7 is arranged at an upper and outer part of the cathode 4 to extract calcium metal.

Starting the electrolysis by connecting the anode 3 and cathode n 4 to a direct current power supply, which is not shown, calcium metal in a molten state is generated on an inner surface of the cathode 4. Since the molten salt is continuously supplied through the bath supplying pipe 6, the generated calcium metal is flowed from the inside of the cathode 4 against the outside, and the calcium metal is pushed out to the outside. The calcium metal 5 reaching the outside of the cathode 4 is partially dissolved in the electrolyte bath and floats up, forming a precipitated layer of calcium metal 5.

The molten calcium metal which is moved to the outside of the cathode 4 and floats up, and the calcium chloride in which calcium metal is precipitated, are continuously extracted by the extracting pipe 7. The molten calcium metal and the calcium chloride having precipitated calcium metal are both extracted and can be used in a reduction reaction of titanium oxide or titanium chloride using molten salt, for example.

On the other hand, chlorine gas is generated at the surface of the anode 3 and is emitted out of the system. The chlorine gas can be used in a chlorination reaction of titanium ore or the like.

FIG. 2 shows a conceptual cross sectional diagram of the second embodiment of the present invention. Reference numeral 1 is an electrolysis vessel, and an electrolysis bath 2 consisting of calcium chloride (melting point 780° C.) is filled in the vessel. The electrolysis bath 2 is heated to a temperature above the melting point of calcium chloride by a heater, which is not shown, so as to be maintained in a molten state. Reference numeral 3 indicates a anode which is unified with the electrolysis vessel. Reference numeral 4 is a cylindrical cathode, and it is immersed at the central part of the electrolysis vessel 1. Plural communicating holes are formed at a lower part of the cathode 4, and the molten salt can be moved between the outer area and the inner area of the cathode. Since the communicating holes are formed at the lower part of the cathode, an upper part of the cathode can function as a division wall.

Furthermore, a bath supplying pipe 6 is arranged at an outer part of the cathode 4, and calcium chloride which is a raw material of the molten-salt electrolysis is continuously supplied therethrough. An extracting pipe 7 is arranged at an upper and inner part of the cathode 4 to extract calcium metal.

Starting the electrolysis by connecting the anode 3 and cathode 4 to a direct current power supply, which is not shown, calcium metal in a molten state is generated on an outer surface of the cathode 4. Since the molten salt is continuously supplied through the bath supplying pipe 6, the generated calcium metal is flowed from the outside of the cathode 4 against the inside, and the calcium metal is pushed into the inside. The calcium metal 5 reaching the inside of the cathode 4, is partially dissolved in the electrolyte bath and floats up, forming a precipitated layer of calcium metal 5.

The molten calcium metal which is moved to the inside of the cathode 4 and floats up, and the calcium chloride in which calcium metal is precipitated, are continuously extracted by the extracting pipe 7. The molten calcium metal and the calcium chloride having precipitated calcium metal are both extracted and can be used in a reduction reaction of titanium oxide or titanium chloride using molten salt, for example.

On the other hand, chlorine gas is generated at the surface of the anode 3 and is emitted out of the system. The chlorine gas can be used in a chlorination reaction of titanium ore or the like.

FIG. 3 shows a conceptual cross sectional diagram of the third favorable embodiment of the present invention. Explanations of reference numerals 1 to 8 are omitted since they are similar to those for FIG. 2. In FIG. 3, which is different from the case of FIG. 2, inert gas is injected from the bottom part of the inner area of the cathode 4 through an inert gas supplying pipe 9. A gas-lift effect occurs by the injection of the inert gas, and upward flow occurs in the inner area of the cathode 4. Accompanied by this effect, a flow from the outer area to the inner area occurs. As a result, calcium metal generated on the surface of the cathode 4 can be moved into the inside the cathode in a short time, and a loss by the back reaction with chlorine gas which is generated in the outer area of the cathode can be reduced.

FIG. 4 shows a conceptual cross sectional diagram of the fourth favorable embodiment of the present invention. Arrangement of reference numerals 1 to 8 is omitted since they are similar to those in FIG. 2. Differing from the above-mentioned embodiments, an oblique communicating hole inclining in a vertical direction is formed at a side wall of the cathode 4, as shown in FIG. 4. In addition, as shown in FIG. 9, which is a conceptual cross sectional diagram in which the cathode 4 is seen from above, the communicating holes are inclined uniformly from the normal line direction of the cylindrical electrode also in the horizontal direction. Furthermore, the cathode 4 is arranged so as to be rotatable. By rotating such a cathode 4, the molten salt can be forcibly moved from the outer area of the cathode 4 to the inner area. As a result, calcium metal generated on the outer surface of the cathode 4 can be moved into the inner area of the cathode in a short time, and a loss by the back reaction with chlorine gas which is generated in the outer area of the cathode can be reduced.

FIG. 5 shows a conceptual cross sectional diagram of the fifth favorable embodiment of the present invention. Explanation of reference numerals 1 to 8 is omitted since they are similar to those in FIG. 2. Differing from the above-mentioned embodiments, an agitating fin 10 is arranged at the bottom part of the inner area of the cathode 4. The agitating fin can be rotated via a driving axis to form a flow of molten salt from the bottom to the upper surface. As a result, calcium m 4 can be moved to the inner area of the cathode in a short time, and a loss by the back reaction with chlorine gas which is generated in the outer area of the cathode can be reduced.

It should be noted that calcium metal generated on the outer surface of the negative electrode 4 can be efficiently recovered by combining the apparatuses shown in FIGS. 3 to 5, if necessary.

As explained above, by the present invention, since calcium metal is continuously pushed out of the system soon after its generation, the back reaction with chlorine gas can be prevented, and the calcium metal can be efficiently produced. In particular, by the second embodiment of the present invention, since the anode and the electrolysis vessel are unified, the structure of the apparatus can be favorably simplified. In addition, by the third, fourth and fifth embodiments of the present invention, the back reaction of calcium metal and chlorine gas can be efficiently reduced.

During the molten-salt electrolysis of calcium chloride, chlorine gas is generated at the anode. Therefore, it is required to use a material having durability against the corrosion property of chlorine gas, and in addition, having conductivity and not having solubility in the electrolysis bath. As a material having such properties, carbon is desirable.

On the other hand, the material of the negative electrode is not limited in particular as long as the material has conductivity. For example, carbon steel, stainless steel, or material such as copper or the like can be used. From the viewpoint of processing the negative electrode to have a cylindrical shape and forming communicating holes, carbon steel having easy workability is desirable.

The electrolysis bath consisting of calcium chloride is required to be maintained at a temperature which is not lower than the melting point of calcium metal (845° C.). If the temperature is lower than the melting point of the calcium metal, calcium metal is generated in a solid state at the inner part of the cathode and blocks up the communicating holes, and this interferes with the flow-through of molten salt and calcium metal. On the other hand, if the temperature is much greater than the melting point of calcium metal, evaporation of the electrolysis bath is promoted and solubility of calcium metal in calcium chloride is increased. This is undesirable from the viewpoint of the yield. A range not exceeding 100° C. above the melting point of calcium metal is desirable.

The temperature of the electrolysis bath can be controlled by using a heating burner immersed in the electrolysis bath. Furthermore, if the burner has a cooling function, this is desirable because the temperature can be freely controlled in a target range. In addition, temperature control can be performed by another means of selection.

In the electrolysis bath, another salt can be added to calcium chloride. For example, the melting point of the electrolysis bath can be lowered by adding potassium chloride. By lowering the melting point of the electrolysis bath in this way, degrees of freedom of the electrolysis performing temperature are increased and the cost required for heating can be reduced. Potassium chloride added to calcium chloride is desirably in a range from 20 to 80 mass %. By adding potassium chloride in such a range, the melting point of the electrolysis bath can be lowered to 615 to 760° C.

FIG. 6 shows a conceptual cross sectional diagram of the sixth desirable embodiment of the present invention. Reference numeral 1 is an electrolysis vessel, an electrolysis bath 2 consisting of calcium chloride is filled therein, and it is heated to a temperature not less than the melting point of calcium chloride by a heater, which is not shown, to be maintained in a molten state. Reference numeral 3 indicates a anode unified with the electrolysis vessel, and a cathode 4 having cylindrical shape is arranged being immersed in a central part of the electrolysis vessel 1. Since the upper and lower parts of the cathode 4 are open, the molten salt can be moved between the outer area and inner area of the cathode. Furthermore, a titanium tetrachloride supplying pipe 11 is arranged in the inner area of the cathode 4.

The electrolysis is started by connecting the anode 3 and cathode 4 to a direct current power supply, which is not shown, and at the same time adding titanium tetrachloride 12 through the titanium tetrachloride supplying pipe 11. Calcium metal in a molten state is generated on an outer surface of the cathode 4 by the starting of the electrolysis. At the same time, since titanium tetrachloride 12 floats up in a bubbled state in the electrolysis bath 2, upward-flow occurs in the electrolyte bath 2 by this gas-lift effect, the electrolysis bath runs over from the inner area to the outer area at the upper part of the cathode, and downward-flow occurs in the outer area. In this way, flow in the electrolysis bath occurs along the arrowed line shown in FIG. 6. Calcium metal generated by the electrolysis floats up in the inner area of the cathode and sinks down in the outer area along the flow.

The above-mentioned upward-flow of the calcium metal generated in the inner area of the cathode contacts and reacts with the bubbles 12 of the titanium tetrachloride (TiCl₄+2Ca→2CaCl₂+Ti), to generate titanium metal. The titanium metal generated is carried to the upper or lower part of the electrolysis bath by the flow of the bath, so as to be recovered by a recovering device, which is not shown.

In this way, by the embodiment, it is not necessary that calcium metal be recovered to be sent to a titanium producing process. Calcium metal is generated and subsequently titanium metal can be desirably obtained almost at the same time.

FIG. 7 shows a conceptual cross sectional diagram of the seventh desirable embodiment of the present invention. Reference numeral 1 is an electrolysis vessel, an electrolysis bath 2 consisting of calcium chloride is filled therein, and it is heated at a temperature not less than the melting point of calcium chloride by a heater, which is not shown, so as to be maintained in a molten state. Reference numeral 3 indicates a anode unified with the electrolysis vessel, a cathode 4 having a cylindrical shape is arranged immersed in a central part of the electrolysis vessel 1. The lower part of the cathode 4 is open, and a hole communicating the outer part and inner part of the cathode is arranged at a side surface of the cathode. These communicating holes are inclined downward of the vertical direction. Furthermore, as shown in FIG. 9, the communicating holes of the cathode 4 are inclined from the normal line direction of the cylindrica 4 is arranged so as to be rotatable. A titanium tetrachloride supplying pipe 11 is arranged at the lower part of the inner area of the cathode 4.

The electrolysis is started by connecting the anode 3 and cathode 4 to a direct current power supply, which is not shown, and at the same time rotating the cathode 4 and adding titanium tetrachloride 12 through the titanium tetrachloride supplying pipe 11. Calcium metal in a molten state is generated on an outer surface of the cathode 4 by the starting of the electrolysis. At the same time, the electrolysis bath flows from the outer area of the cathode 4 into the inner area by the rotation of the cathode 4, and furthermore, since a downward flow occurs, calcium metal which is generated is gathered in the inner area and flows downward. Since titanium tetrachloride 12 floats up in bubbled state in the electrolysis bath and contacts with this calcium metal flow, they react to generate titanium metal. The titanium metal generated is carried to the lower part of the electrolysis bath by the flow of the bath so as to be recovered by a recovering device, which is not shown.

In this way, in the embodiment, it is not necessary that calcium metal be recovered and be sent to a titanium producing process. Calcium metal is generated, and subsequently, titanium metal can be desirably obtained almost at the same time. Furthermore, since calcium metal is gathered in the inner part of the cathode and is reacted with titanium tetrachloride, a back reaction with chlorine gas can be desirably reduced.

FIG. 8 shows a conceptual cross sectional diagram of the eighth desirable embodiment of the present invention. Reference numeral 1 is an electrolysis vessel, an electrolysis bath 2 consisting of calcium chloride is filled therein, and it is heated to a temperature not less than the melting point of calcium chloride by a heater, which is not shown, to be maintained in a molten state. Reference numeral 3 is a anode which is unified with the electrolysis vessel, and a cathode 4 having cylindrical shape is arranged being immersed in a central part of the electrolysis vessel 1. The lower part of the cathode 4 is open, and a hole communicating the outer part and inner part of the cathode is arranged at a side surface of the cathode. A titanium tetrachloride supplying pipe 11 is arranged at the lower part of the inner area of the cathode 4. An agitating fin 10 is rotatably arranged at the inner area of the cathode 4.

The electrolysis is started by connecting the anode 3 and cathode 4 to a direct current power supply, which is not shown, and at the same time rotating the agitating fin 10 and adding titanium tetrachloride 12 through the titanium tetrachloride supplying pipe 11. Calcium metal in a molten state is generated on an outer surface of the cathode 4 by the starting of the electrolysis. At the same time, the electrolysis bath flows from the outer area of the cathode 4 into the inner area by the rotation of the agitating fin 10, and furthermore, since a downward flow occurs, calcium metal which is generated is gathered in the inner area and flows downward. Since titanium tetrachloride 12 floats up in bubbled state in the electrolysis bath and contacts with this calcium metal flow, they react to generate titanium metal. The titanium metal generated is carried to the lower part of the electrolysis bath by the flow of the bath, so as to be recovered by a recovering device, which is not shown.

In this way, also by this embodiment, it is not necessary that calcium metal be recovered, washed, and be sent to a titanium producing process. Calcium metal is generated, and subsequently titanium metal can be desirably obtained almost at the same time. Furthermore, since calcium metal is gathered in the inner part of the cathode and is reacted with titanium tetrachloride, the back reaction with chlorine gas can be desirably reduced.

EXAMPLES

Using the electrolysis vessel shown in FIG. 1, electrolysis of a molten salt of calcium chloride was performed. The temperature of the electrolysis bath consisting of calcium chloride was maintained at 850±5° C., and the temperature of the circular cathode 4 was also maintained at 850±5° C., and they were not particularly being cooled.

Molten calcium chloride which is a raw material was continuously supplied to the inside the cathode through the bath supplying pipe 6, and at the same time, the precipitated layer of calcium metal was extracted to the outside of the system through the extracting pipe immersed in the outside the cathode. Calcium metal extracted out of the system was used in a reduction reaction of titanium oxide. On the other hand, chlorine gas generated at the anode was used in a chlorination reaction of titanium ore. Calcium metal was produced corresponding to 80% of theoretical weight calculated from the amount of electricity applied to the cathode and anode.

By the present invention, calcium metal can be efficiently produced by the electrolysis of calcium chloride. Furthermore, the calcium metal can be used in the production of titanium metal, without recovery.

Claims

1. A process for production of a metal by molten-salt electrolysis, the process comprising a step of filling calcium chloride in an electrolysis vessel having a anode and a cathode; wherein one of the negative or anode is arranged surrounding the other electrode,the cathode has at least one hole which communicates an inner area surrounded by the cathode and an outer area, andthe molten salt is flowed from one of the inner or outer area having the anode therein to the other area through the communicating hole.

2. The process for production of a metal by molten-salt electrolysis according to claim 1, wherein the cathode is arranged surrounding the anode,the cathode has at least one hole which communicates an inner area surrounded by the cathode and an outer area, andthe molten salt is flowed from the inner area to the outer area through the communicating hole.

3. The process for production of a metal by molten-salt electrolysis according to claim 2, wherein calcium chloride is supplied to the inner area.

4. The process for production of a metal by molten-salt electrolysis according to claim 2, wherein the molten salt containing calcium metal generated at the cathode is extracted from the outer area.

5. The process for production of a metal by molten-salt electrolysis according to claim 1, wherein the electrolysis vessel is made of carbon to enable functioning as the anode,a hollow cylindrical cathode is arranged in the electrolysis vessel,the cathode has at least one hole which communicates the inner area of the cathode and the outer area, andthe molten salt is flowed from the outer area to the inner area through the communicating hole.

6. The process for production of a metal by molten-salt electrolysis according to claim 5, wherein inert gas is supplied from the bottom part of the inner area of the cathode.

7. The process for production of a metal by molten-salt electrolysis according to claim 1, wherein a finned cylindrical cathode having plural communicating holes all inclined at a predetermined angle from the normal line direction of the side surface of the cylinder, is used as the hollow cylindrical cathode,the finned cylindrical cathode is rotated to flow the molten salt from the inner area to the outer area, or from the outer area to the inner area.

8. The process for production of a metal by molten-salt electrolysis according to claim 5, wherein calcium chloride is supplied to the outer area.

9. The process for production of a metal by molten-salt electrolysis according to claim 5, wherein the molten salt containing calcium metal generated at the cathode is extracted from the inner area.

10. The process for production of a metal by molten-salt electrolysis according to claim 1, wherein the metal is recovered as a mixed material with the molten salt or recovered as a molten material.

11. The process for production of a metal by molten-salt electrolysis according to claim 1, wherein the molten salt consists of calcium chloride, sodium chloride, barium chloride, and lithium chloride.

12. The process for production of a metal by molten-salt electrolysis according to claim 1, wherein a titanium tetrachloride supplying pipe is arranged in the inner area in which the metal is generated by the molten-salt electrolysis, andtitanium metal is generated by supplying titanium tetrachloride in a gas state through the titanium tetrachloride supplying pipe.

13. The process for production of a metal by molten-salt electrolysis according to claim 12, wherein an upward flow of the electrolysis bath is generated in the inner area by an upward flow of the titanium tetrachloride in a gas state, andthe metal generated is recovered at the electrolysis bath.

14. The process for production of a metal by molten-salt electrolysis according to claim 12, wherein the finned cylindrical cathode is used as the cathode,the titanium tetrachloride supplying pipe is arranged at the lower end of the inner area,a downward flow of the electrolysis bath is generated in the inner area by rotating the finned cylindrical cathode, andtitanium tetrachloride is supplied to be contacted against the downward flow, to generate metal.

15. The process for production of a metal by molten-salt electrolysis according to claim 12, wherein the titanium tetrachloride supplying pipe is arranged at a lower end of the inner area and the agitating fin is arranged at the inner area, anda downward flow of the electrolysis bath is generated in the inner area by rotating the agitating fin and titanium tetrachloride is supplied to contact the downward flow to generate titanium metal.

16. The process for production of a metal by molten-salt electrolysis according to claim 1, wherein the metal is calcium or titanium.

17. An apparatus for production of a metal by molten-salt electrolysis comprising: an electrolysis vessel anda anode and a cathode in the electrolysis vessel;wherein one of the negative or anode is arranged surrounding the other electrode,the cathode has at least one hole which communicates an inner area surrounded by the cathode and an outer area,the molten salt of calcium chloride is supplied to one of the two divided areas in which the anode is included therein,the molten salt of calcium chloride is flowed to the other area through the communicating hole,the molten salt of calcium chloride containing calcium metal generated at the cathode is extracted from the other area.

18. The apparatus for production of a metal by molten-salt electrolysis according to claim 17, wherein the cathode is arranged so as to be rotatable.

19. The apparatus for production of a metal by molten-salt electrolysis according to claim 17, wherein an agitating fin to enable the molten salt flowing from the inner area to the outer area or from the outer area to the inner area of the cathode, is arranged at the lower end of the inside of the cathode.

20. The apparatus for production of a metal by molten-salt electrolysis according to claim 17, wherein the metal is calcium metal or titanium metal.