JP6933936B2 - Molten salt electrolytic cell - Google Patents

Description

The present invention relates to a molten salt electrolytic cell used in a molten salt electrolysis method for obtaining a metal by electrolyzing a molten salt containing magnesium chloride.

Titanium metal is industrially produced based on titanium sponge produced by the Kroll process. The titanium sponge titanium production process by this Kroll process is roughly divided into four steps: a chloride distillation step, a reduction separation step, a crushing step, and an electrolysis step.

In the electrolysis step, which is one of these steps, magnesium chloride, which is a by-product of the reduction step of reducing titanium tetrachloride with metallic magnesium to produce sponge titanium, is electrolyzed by molten salt to regenerate metallic magnesium. It is a process to do.

The molten salt electrolytic cell used in the electrolysis step is composed of, for example, an electrolysis chamber for electrolyzing the molten salt and a metal recovery chamber for recovering the produced metallic magnesium, as disclosed in Patent Document 1. Will be done.

Chlorine gas is generated by the electrolysis of the molten salt. Therefore, for the recovery of the generated chlorine, the exhaust gas pipe is connected to the upper space of the electrolysis chamber (Patent Document 2), and the exhaust gas pipe is connected to the electrolysis chamber. It has been proposed to connect to both the upper space and the upper space of the metal recovery chamber (Reference 3).

Japanese Unexamined Patent Publication No. 2012-149301 Japanese Patent Publication No. 2004-502879 Japanese Unexamined Patent Publication No. 2001-35589

However, in the structures disclosed in Patent Documents 2 and 3, chlorine gas is insufficiently defoamed from the metallic magnesium and the molten salt, so that chlorine gas is mixed and disturbed in the flow of the metallic magnesium and the molten salt. As a result, chlorine decomposed by electrolysis and metallic magnesium re-react to magnesium chloride, which must be electrolyzed again, and there is a problem that the current is not used effectively. In addition, due to insufficient defoaming of chlorine, chlorine gas enters the metal recovery chamber beyond the partition wall, and chlorine and metallic magnesium re-react in the metal recovery chamber, resulting in a decrease in current efficiency and the metal recovery chamber. There was a problem of corroding metal devices such as thermometers and liquid level control devices installed in.

Therefore, an object of the present invention is to provide a molten salt electrolytic cell having good defoaming property of chlorine gas from metallic magnesium and molten salt produced in an electrolysis chamber.

The above problem is solved by the present invention shown below.
That is, in the present invention (1), a cathode having a prismatic space inside, a prismatic anode arranged inside the cathode, and one or more multiple poles arranged between the cathode and the anode. A molten salt consisting of an electrolysis chamber in which the molten salt is electrolyzed and a metal recovery chamber having a metal magnesium holding portion in which the metallic magnesium generated by the electrolysis of the molten salt is held. It ’s an electrolytic tank,
The upper part of the electrolysis chamber and the metal recovery chamber is separated by a partition wall.
At the lower part of the boundary between the electrolysis chamber and the metal recovery chamber, a molten salt inflow path for the molten salt to flow from the metal recovery chamber into the electrolysis chamber is formed, and the electrolysis chamber and the metal recovery chamber and the molten salt inflow path are formed. Above the molten salt inflow path at the boundary of the metal recovery chamber, the metal magnesium and the molten salt produced in the electrolysis chamber pass over the cathode on the metal recovery chamber side and flow laterally. After that, a metal magnesium inflow route is formed, which flows downward through the vertical portion of the metal magnesium inflow route and then flows into the metal recovery chamber.
The distance from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path is 100 to 500 mm.
The height of the cathode is 500 to 2000 mm.
The present invention provides a molten salt electrolytic cell characterized by the above.

Further, in the present invention (2), the ratio (B) of the distance (B) from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path with respect to the height (A) of the cathode (B). / A) provides the molten salt electrolytic cell of (1), which is characterized by having a value of 0.05 to 0.6.

Further, the present invention (3) provides a molten salt electrolytic cell according to either (1) or (2), wherein the width of the vertical portion of the metallic magnesium inflow path is 50 to 300 mm.

Further, in the present invention (4), the distance (B) from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path with respect to the width (C) of the vertical portion of the metal magnesium inflow path. ) Is 0.8 to 10, and the molten salt electrolytic cell according to any one of (1) to (3) is provided.

Further, in the present invention (5), an L-shaped or inverted L-shaped defoaming region forming member in a cross-sectional view is arranged outside the cathode on the metal recovery chamber side at a distance from the partition wall. This provides the molten salt electrolytic cell according to any one of (1) to (4), wherein the metal magnesium inflow path is formed.

Further, in the present invention (6), the flat plate-shaped defoaming region forming member is arranged on the outside of the cathode on the metal recovery chamber side at a distance from the partition wall, so that the metal magnesium inflow path is established. It provides the molten salt electrolytic cell according to any one of (1) to (4), which is characterized by being formed.

According to the present invention, it is possible to provide a molten salt electrolytic cell having good defoaming property of chlorine gas from metallic magnesium and molten salt produced in an electrolysis chamber.

It is a schematic perspective view which shows the morphological example of the molten salt electrolytic cell of this invention. It is a figure which shows the molten salt inflow path and the metal magnesium inflow path of the molten salt electrolytic cell in FIG. It is an end view which cut the molten salt electrolytic cell in FIG. 1 by a vertical plane. It is an end view which cut the molten salt electrolytic cell in FIG. 1 by the vertical plane different from FIG. It is an enlarged view near the metal magnesium inflow path in FIG. It is a schematic end view which shows the morphological example of the molten salt electrolytic cell of this invention. It is an enlarged view near the metal magnesium inflow path in FIG. It is a figure which shows the positional relationship between the upper end of the cathode on the metal recovery chamber side, and the upper end of a defoaming region forming member. It is a figure which shows the positional relationship between the upper end of the cathode on the metal recovery chamber side, and the upper end of a defoaming region forming member. It is an end view which shows the form example of the installation method of the defoaming area forming member.

The molten salt electrolytic cell of the present invention has a cathode having a prismatic space inside, a prismatic anode arranged inside the cathode, and one or more duplexes arranged between the cathode and the anode. A molten salt consisting of an electrolysis chamber in which the molten salt is electrolyzed and a metal recovery chamber having a metal magnesium holding portion in which the metallic magnesium generated by the electrolysis of the molten salt is held. It ’s an electrolytic cell,
The upper part of the electrolysis chamber and the metal recovery chamber is separated by a partition wall.
At the lower part of the boundary between the electrolysis chamber and the metal recovery chamber, a molten salt inflow path for the molten salt to flow from the metal recovery chamber into the electrolysis chamber is formed, and the electrolysis chamber and the metal recovery chamber and the molten salt inflow path are formed. Above the molten salt inflow path at the boundary of the metal recovery chamber, the metal magnesium and the molten salt produced in the electrolysis chamber pass over the cathode on the metal recovery chamber side and flow laterally. After that, a metal magnesium inflow route is formed, which flows downward through the vertical portion of the metal magnesium inflow route and then flows into the metal recovery chamber.
The distance from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path is 100 to 500 mm.
The height of the cathode is 500 to 2000 mm.
It is a molten salt electrolytic cell characterized by.

The molten salt electrolytic cell of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 is a schematic perspective view showing a morphological example of the molten salt electrolytic cell of the present invention, and is a molten salt electrolytic cell for producing metallic magnesium. FIG. 2 is a diagram showing a molten salt inflow path and a metallic magnesium inflow path of the molten salt electrolytic cell in FIG. FIG. 3 is an end view of the molten salt electrolytic cell in FIG. 1 cut along a vertical plane. FIG. 4 is an end view of the molten salt electrolytic cell in FIG. 1 cut by a vertical plane different from that in FIG. FIG. 5 is an enlarged view of the vicinity of the metallic magnesium inflow path in FIG. In FIG. 1, for convenience of explanation, only the outlines of the side wall 2, the hearth 3, and the lid 4 are shown by dotted lines.

As shown in FIGS. 1 to 4, the outside of the molten salt electrolytic cell 1 is composed of a side wall 2, a hearth 3, and a lid 4. The side wall 2 and the hearth 3 are constructed of refractory bricks, and the lid 4 is constructed of castable refractory. Further, although not shown, the lid 4 on the upper portion of the metal recovery chamber 22 has a magnesium recovery port and a molten metal for recovering the metallic magnesium stored in the magnesium holding portion 14 continuously, at regular intervals, or irregularly. When the amount of salt consumed by electrolysis is reduced, a molten salt replenishment port for replenishing the molten salt is formed in the molten salt electrolytic cell 1, and chlorine is formed on the lid 4 of the upper portion of the electrolysis chamber 21. A gas recovery port is formed, and a chlorine gas discharge pipe for discharging chlorine gas to the outside is attached.

The upper part inside the molten salt electrolytic cell 1 is separated into an electrolysis chamber 21 and a metal recovery chamber 22 by a partition wall 5. At the lower part of the boundary between the electrolysis chamber 21 and the metal recovery chamber 22, a molten salt inflow route 8 which is an inflow route for the molten salt to flow from the metal recovery chamber 22 into the electrolysis chamber 21 is formed. At the boundary between the electrolysis chamber 21 and the metal recovery chamber 22, the portion above the molten salt inflow path 8 is a path for the metallic magnesium and the molten salt produced in the electrolysis chamber 22 to flow into the metal recovery chamber 22. A certain metallic magnesium inflow route 7 is formed. The lower part of the electrolysis chamber 21 and the metal recovery chamber 22 refers to a portion below each partition wall 5. Further, the boundary between the electrolysis chamber 21 and the metal recovery chamber 22 is a position where the cathode 25 on the metal recovery chamber 22 side is installed from the vicinity of the position where the partition wall 5 is installed when viewed in the lateral direction. Refers to the range up to the vicinity.

On the upper side of the electrolysis chamber 21, one or more pairs of cathode 25 and anode 23, and one or more double poles 24 charged between the cathode 25 and the anode 23 are installed. The cathode 25, the anode 23, and the double electrode 24 are provided at the lower part of the electrode support portion 151 provided on the lower side of the side wall 2 side of the electrolysis chamber 21, and the lower part of the boundary portion between the electrolysis chamber 21 and the metal recovery chamber 22. By being installed on the electrode support portion 152, it is installed on the upper side of the electrolysis chamber 21. Therefore, the electrolysis chamber 21 has a molten salt holding portion 26 on the lower side.

The shape of the cathode 25 is a shape having a prismatic space inside. The cathode of the cathode 25 that is parallel to the extension direction of the partition wall 5 and is closer to the metal recovery chamber 22 is the cathode 25a on the metal recovery chamber side.

On the upper side of the metal recovery chamber 22, a magnesium holding portion 14 for holding magnesium is provided. Further, a molten salt holding portion 27 is provided below the metal recovery chamber 22.

The metal magnesium inflow path 7 is formed by arranging the defoaming region forming member 6a on the outside of the cathode 25 on the metal recovery chamber 22 side with a space between the metal magnesium inflow path 7 and the partition wall 5. The defoaming region forming member 6a is installed on the electrode support portion 152.

As shown in FIG. 4, when molten salt electrolysis is being performed, the molten salt 11 containing magnesium chloride is used in the cathode 25, the anode 23, and the multi-pole 24 on the upper side of the electrolysis chamber 21 of the molten salt electrolytic cell 1. Is electrolyzed. Therefore, in the molten salt electrolytic tank 1, the molten salt 11 is electrolyzed in the vicinity of the cathode 25, the anode 23, and the compound pole 24 on the upper side of the electrolysis chamber 21 to generate molten magnesium and chlorine gas, both of which are molten salts. Since the specific gravity is smaller, a flow of molten salt that moves upward is generated, the molten salt 11 on the lower side of the electrolysis chamber 21 moves upward, and the movement of the molten salt causes the molten salt to move to the lower side of the metal recovery chamber 22. A flow 111 of molten salt is generated in which a certain molten salt 11 moves to the lower side of the electrolysis chamber 21 through the molten salt inflow path 8. Then, a flow 101 of metallic magnesium in which the metallic magnesium 10 generated by electrolysis on the upper side of the electrolysis chamber 21 moves to the upper side of the metal recovery chamber 22 through the metallic magnesium inflow path 7 together with the molten salt is generated. The metallic magnesium 10 that has moved to the upper side of the metal recovery chamber 22 is held by the magnesium holding portion 14 at the upper part of the metal recovery chamber 22. Further, chlorine gas 12 is generated together with the metallic magnesium 10 by the electrolysis of the molten salt 11, and the generated chlorine gas 12 is defoamed from the metallic magnesium and the molten salt and moves from the bath surface 9 to the upper space, which is not shown. It is discharged to the outside by the chlorine gas recovery port and the chlorine gas discharge pipe formed on the lid 4.

In the molten salt electrolytic cell 1, a defoaming region forming member 6a having a specified thickness is installed on the outside of the cathode 25a on the metal recovery chamber 22 side at a distance from the partition wall 5, thereby causing metallic magnesium. The inflow path 7 is formed. Therefore, as shown in FIG. 3, the metallic magnesium and the molten salt produced in the electrolysis chamber 21 pass over the cathode 25a on the metal recovery chamber 22 side and flow in the lateral direction (direction indicated by reference numeral 101a). , The metal magnesium inflow path vertical portion 7a flows downward (direction indicated by reference numeral 101b), and then flows into the metal recovery chamber 22.

Since the defoamed region forming member 6a has a specified thickness, the lengths of the metallic magnesium and the molten salt always flow sideways. At this time, chlorine gas is defoamed from the metallic magnesium and the molten salt. That is, chlorine is formed by forming a region in which the metallic magnesium and the molten salt flow laterally within a specified range on the outside of the cathode 25a on the metal recovery chamber 22 side, and passing the metallic magnesium and the molten salt through the region. It gives the gas time to defoam from the metallic magnesium and the molten salt, making it easier for the chlorine gas to defoam from the metallic magnesium and the molten salt.

If there is no member between the upper end of the defoaming region forming member 6a and the liquid level above it, the defoaming of chlorine gas is not hindered, but from the liquid surface above the defoaming region forming member 6a to the lid. It is preferable that there is no member in the space of.

The molten salt electrolytic cell of the present invention has a cathode having a prismatic space inside, a prismatic anode arranged inside the cathode, and one or more duplexes arranged between the cathode and the anode. A molten salt consisting of an electrolysis chamber in which the molten salt is electrolyzed and a metal recovery chamber having a metal magnesium holding portion in which the metallic magnesium generated by the electrolysis of the molten salt is held. It ’s an electrolytic cell,
The upper part of the electrolysis chamber and the metal recovery chamber is separated by a partition wall.
At the lower part of the boundary between the electrolysis chamber and the metal recovery chamber, a molten salt inflow path for the molten salt to flow from the metal recovery chamber into the electrolysis chamber is formed, and the electrolysis chamber and the metal recovery chamber and the molten salt inflow path are formed. Above the molten salt inflow path at the boundary of the metal recovery chamber, the metal magnesium and the molten salt produced in the electrolysis chamber pass over the cathode on the metal recovery chamber side and flow laterally. After that, a metal magnesium inflow route is formed, which flows downward through the vertical portion of the metal magnesium inflow route and then flows into the metal recovery chamber.
The distance from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path is 100 to 500 mm.
The height of the cathode is 500 to 2000 mm.
It is a molten salt electrolytic cell characterized by.

The molten salt electrolytic cell of the present invention is constructed of refractory bricks. For example, the side wall of the molten salt electrolytic cell of the present invention, the hearth, the partition wall between the electrolysis chamber and the metal recovery chamber, the support member for the electrode, and the like are made of refractory brick. The refractory brick may be any one having heat resistance to a temperature of 650 to 800 ° C. and corrosion resistance to molten salt and produced metal, and the material of the refractory brick is usually a molten salt electrolytic tank. The material of the refractory brick is not particularly limited as long as it is used as a construction material, and examples of the material of the refractory brick include Al ₂ O ₃ brick, SiO ₂ brick, and Mg O brick.

The side wall and hearth of the molten salt electrolytic cell of the present invention may have a double structure in which the inside is constructed of fire-resistant bricks and the outside is constructed of heat-insulating bricks. The material of the heat insulating brick is not particularly limited as long as it is usually used as a material for constructing a molten salt electrolytic cell, and examples thereof include Al ₂ O ₃ brick, SiO ₂ brick, and Mg O brick.

The lid is constructed of castable refractory. The material of the castable refractory is not particularly limited as long as it is usually used as a material for constructing a molten salt electrolytic cell, and examples thereof include Al ₂ O ₃ castable and SiO ₂ castable. A chlorine gas recovery port is formed in the portion of the lid that closes the top of the electrolysis chamber, and a chlorine gas recovery pipe is attached. Further, a metal recovery port and a molten salt supply port are formed in a portion of the lid that closes the top of the metal recovery chamber.

The upper part of the inside of the molten salt electrolytic cell of the present invention is separated into an electrolysis chamber and a metal recovery chamber by a partition wall. A molten salt inflow path, which is an inflow path for molten salt to flow from the metal recovery chamber to the electrolysis chamber, is formed in the lower part of the boundary between the electrolysis chamber and the metal recovery chamber. At the boundary between the electrolysis chamber and the metal recovery chamber, above the molten salt inflow path, the metal magnesium inflow path, which is the path for the metal magnesium and molten salt generated in the electrolysis chamber to flow into the metal recovery chamber. Is formed. The lower part of the electrolysis chamber refers to the portion of the electrolysis chamber below the partition wall, and the lower part of the metal recovery chamber refers to the portion of the metal recovery chamber below the partition wall. Further, the boundary between the electrolysis chamber and the metal recovery chamber is the range from the vicinity of the position where the partition wall is installed to the vicinity of the position where the cathode on the metal recovery chamber side is installed when viewed in the lateral direction. Point to. In the present invention, the lateral direction refers to the left-right direction when viewed in a plane perpendicular to the extension direction of the partition wall, and the upper and lower directions refer to the plane viewed in a plane perpendicular to the extension direction of the partition wall. Refers to the upward and downward directions. Further, the lateral direction does not mean only the horizontal direction, but is a substantially horizontal direction, and includes a direction having a slight angle with respect to the horizontal direction within the range in which the effect of the present invention is exhibited. Further, the term "downward" does not mean only the vertical direction, but means a substantially vertical direction, and includes a direction having a slight angle with respect to the vertical direction within the range in which the effect of the present invention is exhibited.

A pair or more of cathodes and anodes are installed above the electrolysis chamber. The cathode has a shape having a prismatic space inside. The anode is located inside the cathode. The anode has a prismatic shape. One or more multi-poles are charged and installed between the cathode and the anode. The material of the cathode and the material of the anode are not particularly limited as long as they have excellent electrical conductivity and chemical durability against chlorine gas and high-temperature molten salt, and the combination of the material of the cathode and the material of the anode is particularly limited. Not limited. Examples of the material of the anode include graphite and the like. Further, as the material of the cathode, for example, iron, graphite and the like can be mentioned. The material of the multi-pole is not particularly limited as long as it has excellent electrical conductivity and chemical durability against chlorine gas and high-temperature molten salt, and examples thereof include graphite.

Since the shape of the cathode has a prismatic space inside, the cathode has a portion parallel to the extension direction of the partition wall and a portion perpendicular to the extension direction of the partition wall. In the present invention, the cathode of the cathode that is parallel to the extension direction of the partition wall and close to the metal recovery chamber is the cathode on the metal recovery chamber side.

The cathode, anode and duplex are supported above the electrolysis chamber by suitable supports such as support members. Therefore, the electrolysis chamber has a molten salt holding portion on the lower side.

The metal recovery chamber has a metal magnesium holding portion at the upper part, which holds the metal magnesium produced by electrolysis of the molten salt. The metallic magnesium holding portion is formed in the metal recovery chamber above the position of the outlet of the metallic magnesium inflow path. Further, the metal recovery chamber has a molten salt holding portion on the lower side.

When molten salt electrolysis is being performed using the molten salt electrolytic cell of the present invention, the molten salt is electrolyzed at the cathode, anode and multipole above the electrolysis chamber of the molten salt electrolytic cell. Therefore, in the molten salt electrolysis tank, the molten salt is electrolyzed in the vicinity of the cathode, the anode and the dipole on the upper side of the electrolysis chamber to generate molten magnesium and chlorine gas, both of which have a lower specific gravity than the molten salt. A flow of molten salt that moves to the upper side is generated, the molten salt on the lower side of the electrolysis chamber moves to the upper side, and the movement of the molten salt causes the molten salt on the lower side of the metal recovery chamber to move to the molten salt inflow route. There is a flow of molten salt that travels through to the underside of the electrolysis chamber. Then, the metal magnesium generated by electrolysis on the upper side of the electrolysis chamber, together with the molten salt, moves to the upper side of the metal recovery chamber through the metal magnesium inflow path, and a flow of metal is generated. The metallic magnesium that has moved to the upper side of the metal recovery chamber is held by the metallic magnesium holding portion at the upper part of the metal recovery chamber. In addition, chlorine gas is generated together with metallic magnesium by electrolysis of the molten salt, and the generated chlorine gas defoams from the metal and moves from the bath surface to the upper space, and the chlorine gas recovery port formed on the lid and the chlorine gas recovery port. It is discharged to the outside by the chlorine gas discharge pipe.

At the boundary between the electrolysis chamber and the metal recovery chamber, there is a vertical portion of the metal magnesium inflow path through which the metallic magnesium and the molten salt flow downward, and the metallic magnesium and the molten salt produced in the electrolysis chamber are present. A metal magnesium inflow path is formed, which passes over the cathode on the metal recovery chamber side, flows laterally, flows downward in the vertical portion of the metal magnesium inflow path, and then flows into the metal recovery chamber. That is, in the molten salt electrolytic cell of the present invention, a region is formed in which the metallic magnesium and the molten salt produced in the electrolysis chamber pass over the cathode on the metal recovery chamber side and flow in the lateral direction. Then, as the metallic magnesium and the molten salt flow laterally over a certain distance, the chlorine gas in the metallic magnesium and the molten salt is easily defoamed. The metal magnesium inflow path refers to a portion through which metal flows from the outside of the cathode on the metal recovery chamber side to the inside of the metal recovery chamber.

The distance from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path is 100 to 500 mm, preferably 150 to 300 mm. When the distance from the outer end of the cathode on the metal recovery chamber side to the end on the cathode side in the vertical portion of the metal magnesium inflow path is within the above range, the metal magnesium and molten metal are melted on the outside of the outer end of the cathode on the metal recovery chamber side. Since the salt flows sideways to form a chlorine gas defoaming region long enough for the chlorine gas to be defoamed, the defoaming property of the chlorine gas from the metallic magnesium and the molten salt is improved. The metal magnesium generated near the cathode on the metal recovery chamber side and the molten salt rising near the cathode on the metal recovery chamber side are sufficient for defoaming chlorine gas because the generation position is close to the metal magnesium inflow path. Without the chlorine gas defoaming region, the metallic magnesium and the molten salt would enter the metallic magnesium inflow path with the undefoamed chlorine gas contained. In the present invention, the metallic magnesium generated in the electrolysis chamber and passing over the cathode on the metal recovery chamber side and the molten salt rising near the cathode on the metal recovery chamber side flow laterally and then flow into the metallic magnesium. A metal magnesium inflow path is formed that flows downward into the metal recovery chamber after flowing downward in the vertical portion of the path, and from the outer end of the cathode on the metal recovery chamber side to the end on the cathode side of the vertical portion of the metal magnesium inflow path. Since the distance is specified to be 100 to 500 mm, preferably 150 to 300 mm, chlorine gas is produced from the metal generated near the cathode on the metal recovery chamber side and the molten salt rising near the cathode on the metal recovery chamber side. There is sufficient chlorine gas defoaming area for defoaming, in other words, the chlorine gas is given time to defoam from the metal magnesium produced and the molten salt. Therefore, in the molten salt electrolytic cell of the present invention, the defoaming property of chlorine gas from the produced metallic magnesium and the molten salt becomes good.

The distance from the outer end of the cathode on the metal recovery chamber side to the cathode side end in the vertical portion of the metal magnesium inflow path is the cathode on the metal recovery chamber side when viewed in the horizontal direction, as shown in FIG. It refers to the distance 33 from the position 32 of the outer end of 25 to the position of the cathode side end 31 of the vertical portion 7a of the metal magnesium inflow path.

The height of the cathode is 500 to 2000 mm, preferably 800 to 1500 mm. The height of the cathode refers to the length from the upper end to the lower end of the cathode.

The ratio (B / A) of the distance (B) from the outer end of the cathode on the metal recovery chamber side to the cathode side end in the vertical portion of the metal magnesium inflow path to the height (A) of the cathode is preferably 0.05 to 0. 6.6, particularly preferably 0.1-0.4. The ratio (B / A) of the distance (B) from the outer end of the cathode on the metal recovery chamber side to the end on the cathode side in the vertical portion of the metal magnesium inflow path to the height (A) of the cathode is within the above range. Defoamability from the generated metallic magnesium and molten salt of chlorine gas is improved.

The width of the vertical portion of the metallic magnesium inflow path is preferably 50 to 300 mm, particularly preferably 100 to 250 mm. Since the width of the vertical portion of the metal magnesium inflow path is within the above range, the defoaming property of chlorine gas from the metal becomes good. As shown in FIG. 5, the width of the vertical portion of the metallic magnesium inflow path refers to the width 34 of the vertical portion 7a of the metallic magnesium inflow path when viewed in the horizontal direction on the plane perpendicular to the extension direction of the partition wall.

The ratio (B / C) of the distance (B) from the outer end of the cathode of the metal recovery chamber to the cathode side end of the vertical portion of the metal magnesium inflow path to the width (C) of the vertical portion of the metal magnesium inflow path is preferably 0. It is 8 to 10, particularly preferably 1 to 3. The ratio (B / C) of the distance (B) from the outer end of the cathode of the metal recovery chamber to the cathode side end of the vertical portion of the metal magnesium inflow path to the width (C) of the vertical portion of the metal magnesium inflow path is within the above range. From the above, the defoaming property from the generated metallic magnesium of chlorine gas and the molten salt is improved.

In the molten salt electrolytic cell of the present invention, it is preferable that there is no member in the space from the liquid surface to the lid above the chlorine gas defoaming region so that chlorine gas can be easily defoamed.

In the molten salt electrolytic tank of the present invention, the metallic magnesium inflow path has a vertical portion of the metallic magnesium inflow path through which metallic magnesium flows downward, is generated in the electrolysis chamber, and passes over the cathode on the metal recovery chamber side. The metal magnesium and the molten salt are not particularly limited as long as they flow in the lateral direction, then flow downward in the vertical portion of the metal magnesium inflow path, and then flow into the metal recovery chamber.

As a method of forming the metal magnesium inflow path, for example, as in the morphological examples shown in FIGS. 1 to 5, a defoaming region forming member having a predetermined thickness and having an L-shaped cross section or an inverted L-shape is used as a metal recovery chamber. A method of forming a metal magnesium inflow path by arranging the outside of the cathode 25 on the side at a distance from the partition wall can be mentioned. That is, as an example of the form of the molten salt electrolytic cell of the present invention, the defoaming region forming member having an L-shape or an inverted L-shape when viewed in a cross section perpendicular to the extension direction of the partition wall is on the metal recovery chamber side. An example is a molten salt electrolytic cell in which a metal magnesium inflow path is formed by arranging the outside of the cathode at a distance from the partition wall.

Further, as a method of forming the metal magnesium inflow path, for example, as in the morphological examples shown in FIGS. 6 and 7, a flat plate-shaped (I-shaped cross-sectional view) defoaming region forming member having a predetermined thickness is made of metal. A method of forming a metal magnesium inflow path by arranging the cathode 25 on the recovery chamber side at a distance from the partition wall can be mentioned. That is, as an example of the form of the molten salt electrolytic cell of the present invention, a flat plate-shaped (I-shaped when viewed in a cross section perpendicular to the extension direction of the partition wall) defoaming region forming member is on the metal recovery chamber side. An example is a molten salt electrolytic cell in which a metal magnesium inflow path is formed by arranging the outside of the cathode at a distance from the partition wall.

FIG. 6 is a schematic end view showing a morphological example of the molten salt electrolytic cell of the present invention. FIG. 7 is an enlarged view of the vicinity of the metallic magnesium inflow path in FIG. The outside of the molten salt electrolytic cell 41 is composed of a side wall 2, a hearth 3, and a lid 4. Further, although not shown, the lid 4 on the upper portion of the metal recovery chamber 22 has a metal recovery port for recovering the metal magnesium stored in the metal magnesium holding portion 14 continuously, at regular intervals, or irregularly. A metal extraction pipe for taking out metallic magnesium is attached so as to be formed so as not to come into contact with the outside air, and a chlorine gas recovery port is formed on the lid 4 of the upper portion of the electrolysis chamber 21. A chlorine gas discharge pipe is attached to discharge chlorine gas to the outside.

The upper part inside the molten salt electrolytic cell 41 is separated into an electrolysis chamber 21 and a metal recovery chamber 22 by a partition wall 5. At the lower part of the boundary between the electrolysis chamber 21 and the metal recovery chamber 22, a molten salt inflow route 8 which is an inflow route for the molten salt to flow from the metal recovery chamber 22 into the electrolysis chamber 21 is formed. At the boundary between the electrolysis chamber 21 and the metal recovery chamber 22, the portion above the molten salt inflow path 8 is a path for the metallic magnesium and the molten salt produced in the electrolysis chamber 22 to flow into the metal recovery chamber 22. A certain metallic magnesium inflow path 71 is formed.

On the upper side of the electrolysis chamber 21, one or more pairs of cathode 25 and anode 23, and one or more double poles 24 charged between the cathode 25 and the anode 23 are installed. The cathode 25, the anode 23, and the double electrode 24 are provided at the lower part of the electrode support portion 151 provided on the lower side of the side wall 2 side of the electrolysis chamber 21, and the lower part of the boundary portion between the electrolysis chamber 21 and the metal recovery chamber 22. By being installed on the electrode support portion 152, it is installed on the upper side of the electrolysis chamber 21. Therefore, the electrolysis chamber 21 has a molten salt holding portion 261 on the lower side. The shape of the cathode 25 is a shape having a prismatic space inside.

On the upper side of the metal recovery chamber 22, there is a metal magnesium holding portion 141 in which the metal magnesium is held. Further, a molten salt holding portion 271 is provided below the metal recovery chamber 22.

In the metal magnesium inflow path 71, a flat plate-shaped (I-shaped cross-sectional view) defoaming region forming member 6b is arranged outside the cathode 25a on the metal recovery chamber 22 side at intervals from the partition wall 5. By that, it is formed. The defoaming region forming member 6b is installed on the electrode support portion 152.

In the molten salt electrolytic cell 41, the defoaming region forming member 6b having a specified thickness is installed on the outside of the cathode 25a on the metal recovery chamber 22 side at a distance from the partition wall 5, so that the metal magnesium is formed. The inflow path 71 is formed. Therefore, as shown in FIG. 5, the metallic magnesium and the molten salt produced in the electrolysis chamber 21 pass over the cathode 25a on the metal recovery chamber 22 side and flow in the lateral direction (direction indicated by reference numeral 101a). , The metal magnesium inflow path vertical portion 71a flows downward (direction indicated by reference numeral 101b), and then flows into the metal recovery chamber 22.

Since the defoamed region forming member 6b has a specified thickness, the lengths of the metallic magnesium and the molten salt always flow sideways. At this time, chlorine gas is defoamed from the metallic magnesium and the molten salt. That is, a chlorine gas defoaming region in which the metal magnesium and the molten salt flow laterally is formed on the outside of the cathode 25a on the metal recovery chamber 22 side within a specified range.

It is preferable that there is no member between the upper end of the defoaming region forming member 6b and the liquid surface so that the chlorine gas can be easily defoamed.

Examples of the material of the defoaming region forming member include refractory bricks, castable refractories, and silicon nitride when installed adjacent to the cathode. When installed not adjacent to the cathode, refractory bricks, castable refractories, carbon, silicon nitride, silicon carbide and the like can be mentioned.

Regarding the relationship between the upper end position of the cathode on the metal recovery chamber side and the upper end position of the defoaming region forming member, as in the embodiment shown in FIGS. 1 to 5, the position of the upper end of the cathode 25a on the metal recovery chamber side and the position of the upper end. The position of the upper end of the defoaming region forming member 6a may be the same, or the position of the upper end of the cathode 25a on the metal recovery chamber side is the upper end of the defoaming region forming member 6c as in the embodiment shown in FIG. The position of the upper end of the defoaming region forming member 6d may be higher than the position of the upper end of the cathode 25a on the metal recovery chamber side, as in the embodiment shown in FIG. good. In the embodiment shown in FIGS. 8 and 9, the distance from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path is indicated by reference numeral 33 in FIGS. 8 and 9. The distance.

In the embodiment shown in FIGS. 1 to 5, the defoaming region forming member 6a is installed in contact with the cathode 25a on the metal recovery chamber side, but the present invention is not limited to this. For example, as in the embodiment shown in FIG. 10, the metal magnesium produced by a method such as closing the space between the lower part of the cathode 25a on the metal recovery chamber side and the lower part of the defoaming region forming member 6a with the closing member 21 and the like. If the molten salt is prevented from flowing between the cathode 25a on the metal recovery chamber side and the defoaming region forming member 6a, it is between the cathode 25a on the metal recovery chamber side and the defoaming region forming member 6a. There may be a gap 20 in. That is, in the present invention, there may be no gap between the cathode on the metal recovery chamber side and the defoaming region forming member, or between the cathode on the metal recovery chamber side and the defoaming region forming member. If the produced metallic magnesium and the molten salt do not flow, there may be a gap between the cathode on the metal recovery chamber side and the defoaming region forming member. The gap between the cathode on the metal recovery chamber side and the defoaming region forming member serves as a cushioning gap when the defoaming region forming member and the cathode thermally expand.

The molten salt that undergoes molten salt electrolysis in the molten salt electrolytic cell of the present invention may be a molten salt that is electrolyzed by application of a voltage to produce metallic magnesium, and is a molten salt containing magnesium chloride. That is, the molten salt electrolytic cell of the present invention is a molten salt electrolytic cell for producing metallic magnesium that electrolyzes a molten salt containing magnesium chloride to produce metallic magnesium.

The molten salt containing magnesium chloride can contain one or more of potassium chloride, calcium chloride and sodium chloride for adjusting the electrical conductivity, the specific gravity, the melting point, and the like. In addition to magnesium chloride, potassium chloride, calcium chloride and sodium chloride, the molten salts containing magnesium chloride include magnesium fluoride, hydroxides, magnesium salts such as carbonates and nitrates, magnesium oxide, and metallic magnesium. It may be included.

Molten salts containing magnesium chloride include 10 to 30% by mass of magnesium chloride, 20 to 40% by mass of calcium chloride, and 40 to 60% by mass in terms of electrical conductivity, specific gravity, melting point, vapor pressure, and viscosity. Molten salt containing% sodium chloride is preferred, with 20 ± 5% by weight magnesium chloride, 30 ± 5% by weight calcium chloride, 49 ± 5% by weight sodium chloride, and 1 ± 1% by weight. A molten salt containing magnesium chloride and is particularly preferable.

Hereinafter, the present invention will be described in more detail with reference to examples, but this is merely an example and does not limit the present invention.

(Preparation of molten salt electrolytic cell)
The molten salt electrolytic cell having the structure shown in FIGS. 1 to 5 was produced, and the molten salt electrolytic cell having the detailed shape shown below was produced.
<Structure of molten salt electrolytic cell>
-Refractory bricks: HIGH ROZX-98, Al ₂ O ₃ manufactured by Rozai Kogyo Co., Ltd. 98.0% by mass, SiO ₂ 0.5% by mass
-Mortar: HR95 mortar manufactured by Rozai Kogyo Co., Ltd., Al ₂ O ₃ by 95.0 mass, SiO ₂ by 3 mass%
・ Electrolysis room: 2m ³
・ Metal collection room: 1m ³
-Number of unit electrolysis cells: 2
-Cathode shape: A shape with a square columnar space inside, height (A) 800 mm
-Anode material: Graphite-Cathode material: Iron-Multipole material: Graphite-Number of double poles between cathode and anode: 2
-Material of defoaming area forming member: Refractory brick HIGH ROZX-98 manufactured by Rozai Kogyo Co., Ltd.
-Thickness (X) of the defoaming region forming member: Shown in Table 1.
-Distance (B) from the outer end of the cathode on the metal recovery chamber side to the end on the cathode side in the vertical portion of the metal magnesium inflow path: Table 1.
-Width of vertical portion of metallic magnesium inflow route (C): Shown in Table 1.

(Examples 1 to 4, Comparative Examples 1 to 3)
To the molten salt electrolytic cell prepared as described above, 2900 kg of a molten salt having a composition of 20% by mass of _{MgCl 2 , 30% by mass of CaCl 2} , 49% by mass of NaCl, and _{1% by mass of MgF 2 was charged.}
Then, the molten salt was electrolyzed for 30 days under the conditions shown below. While the electrolysis of the molten salt is being continued, in order to replenish magnesium chloride corresponding to the amount of metallic magnesium produced, magnesium chloride, which is a by-product of the Kroll process, is supplied to the electrolytic tank as a replenished molten salt. The content of magnesium chloride in the molten salt was adjusted to be 15 to 25% by mass.
The current efficiency was measured 30 days after the start of electrolysis of the molten salt. Further, an iron plate made of SS400 and having a thickness of 50 mm, a width of 100 mm and a length of 500 mm was installed in the metal recovery chamber, and the amount of thinning of the iron plate 30 days after the start of electrolysis of the molten salt was measured. The results are shown in Table 1.
In Table 1, in Comparative Example 1, the defoaming region forming member was not installed.

<Melted salt electrolysis conditions>
-Molten salt temperature: 660 ° C on average
・ Anode immersion length: 800 mm
・ Distance from defoaming region forming member to liquid level: 50 mm
・ Applied voltage: 10V
-Current density: 0.48 A / cm ²
-Theoretical Mg production: 21.8 kg / hour-Supply molten salt: Magnesium chloride produced by the Kroll process

１）メタル回収室側の陰極の外側端から金属マグネシウム流入経路縦部の陰極側端までの距離
２）金属マグネシウム流入経路縦部の幅

1) Distance from the outer end of the cathode on the metal recovery chamber side to the end on the cathode side of the vertical part of the metal magnesium inflow path 2) Width of the vertical part of the metal magnesium inflow path

1, 41 Molten salt electrolytic tank 2 Side wall 3 Hearth 4 Lid 5 Partition 6a, 6b, 6c, 6d Metal magnesium inflow path forming member 7, 71 Metal magnesium inflow path 7a, 71a Metal magnesium inflow path Vertical part 8 Molten salt inflow path 9 Bath surface 10 Metal magnesium 11 Molten salt 12 Chlorine gas 14,141 Magnesium holder 20 Gap 21 Electrolysis chamber 22 Metal recovery chamber 23 Anodic 24 Polypole 25, 25a Cathode 26, 27, 261, 271 Molten salt holder 31 Metal End of the vertical part of the magnesium inflow path on the cathode side 32 Outer end of the cathode on the side of the metal recovery chamber 33 Distance from the outer end of the cathode on the side of the metal recovery chamber to the end of the vertical part of the metal magnesium inflow path on the side of the cathode 34 Metal magnesium inflow path Vertical part Widths 101, 101a, 101b Metallic magnesium flow 111 Molten salt flow 151, 152 Electrode support

Claims (7)

A cathode having a prismatic space inside, a prismatic anode arranged inside the cathode, and one or more duplexes arranged between the cathode and the anode are installed, and molten salt is formed. A molten salt electrolysis tank comprising an electrolysis chamber for electrolysis and a metal recovery chamber having a metal magnesium holding portion for holding metal magnesium generated by electrolysis of the molten salt at the upper part.
The upper part of the electrolysis chamber and the metal recovery chamber is separated by a partition wall.
At the lower part of the boundary between the electrolysis chamber and the metal recovery chamber, a molten salt inflow path for the molten salt to flow from the metal recovery chamber into the electrolysis chamber is formed, and the electrolysis chamber and the metal recovery chamber and the molten salt inflow path are formed. At the boundary of the metal recovery chamber, above the molten salt inflow path, metallic magnesium and molten salt generated in the electrolysis chamber and passed over the cathode on the metal recovery chamber side flow laterally. After that, a metal magnesium inflow route is formed, which flows downward through the vertical portion of the metal magnesium inflow route and then flows into the metal recovery chamber.
The metal magnesium inflow path is formed by arranging a defoaming region forming member on the outside of the cathode on the metal recovery chamber side at a distance from the partition wall, and the defoaming region forming member is formed. , There is no member in the space from the liquid surface to the lid above the defoaming region forming member, which is provided below the liquid level.
The distance from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path is 100 to 500 mm.
The height of the cathode is 500 to 2000 mm.
A molten salt electrolytic cell characterized by. The ratio (B / A) of the distance (B) from the outer end of the cathode on the metal recovery chamber side to the cathode side end of the vertical portion of the metal magnesium inflow path to the height (A) of the cathode is 0.05 to 0. The molten salt electrolytic cell according to claim 1, wherein the temperature is 6. The molten salt electrolytic cell according to claim 1 or 2, wherein the width of the vertical portion of the metallic magnesium inflow path is 50 to 300 mm. The ratio of the distance from the outer end of the cathode of the metal recovery chamber side with respect to the magnesium metal inflow path longitudinal portions of the width (C) to the cathode side end of the metal magnesium inflow path longitudinal portions (B) (B / C) is The molten salt electrolytic cell according to any one of claims 1 to 3, which is 0.8 to 10. The molten salt electrolytic cell according to any one of claims 1 to 4, wherein the defoaming region forming member has an L-shape, an inverted L-shape , or a flat plate shape in a cross-sectional view. The molten salt electrolytic cell according to any one of claims 1 to 5, wherein a gap is provided between the cathode on the metal recovery chamber side and the defoaming region forming member. The molten salt electrolytic cell according to any one of claims 1 to 6, wherein there is no member between the upper end of the defoaming region forming member and the liquid level.

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