JPS5839789A - Electrolyzing method for molten chloride - Google Patents

Abstract

PURPOSE:To facilitate the recovery of a produced metal and to improve the yield thereof by removing the upper layer of an electrolytic bath, cooling part thereof, supplying the same to the lower part of an electrolytic cell, recovering the produced metal from the other part and supplying part of the electrolytic bath to the upper part of the electrolytic cell. CONSTITUTION:In electrolyzing of metallic chloride such as magnesium chloride, a part of the upper layer of an electrolytic bath contg. molten chloride in an electrolytic cell 1 is removed. The removed part is passed through a cooling passage and is cooled to the extent of maintaining a molten state. The cooled electrolyte is supplied to the bottom part of an electrolytic chamber 2. The other part of the electrolyte is conducted to an upper bath/magnesium separating cell 7, where at least a part of the produced metal such as metallic magnesium is recovered. At least a part of the electrolytic bath after the separation is supplied into the another part in the chamber 2. According to this method, electrolyzing operations are accomplished at adequate temp. and the ascending flow and surface flow in the chamber 2 are accelerated, whereby the floating magnesium etc. in the entire area in the chamber 2 are recovered in good yields.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of magnesium metal by electrolysis of metal chlorides, particularly molten magnesium chloride.

Magnesium metal is produced by electrolysis of a molten chloride bath containing magnesium chloride, sodium chloride, calcium chloride, etc., but the precipitated metal magnesium has a lower specific gravity than this electrolytic bath and rises in the electrolytic bath. Therefore, the electrolyzer needs a configuration to prevent recombination with the chlorine gas deposited on the surface of the cathode and floating in the bath. For this purpose, for example, in the device described in U.S. Pat. No. 2,785,121, the deposited liquid phase metal magnesium rises along the cathode surface, is received by a gutter provided above the cathode plate, and the inclination of the gutter is According to the structure, the electrolytic cell is collected at the upper side of the electrolytic cell. At this time, since only a slight difference in specific gravity with respect to the electrolytic bath can be used as a force for moving the magnesium floating above the cathode to the collection section, the angle of inclination of the gutter must be set sufficiently large. For this purpose, the cathode must be immersed deep below the surface of the electrolytic bath, which requires an excessively large cross-sectional area of the electrolytic bath compared to the cross-sectional area of the electrodes, making it difficult to expect an improvement in electrolytic efficiency per cross-sectional area of the electrolytic bath. The disadvantage of not having one is unavoidable.

On the other hand, even in an electrolytic cell that collects chlorine gas generated on the anode side, it is necessary to collect the magnesium floating on the electrolytic bath surface in one place. In an electrolytic cell, it is required that the floating magnesium be led out of the cell more quickly.

Further, in operating such an electrolytic cell, it is desirable to use a bath temperature as low as possible from the viewpoint of the life of the graphite electrode and the yield of produced metal. This is particularly required when a large number of anode-cathode electrode pairs are immersed in the same bath, or when a large number of intermediate electrodes are used between the two electrodes.

Therefore, the present invention uses a forced circulation flow in an electrolytic bath to separate and move the magnesium deposited on the surface of the cathode part of the cathode and the intermediate electrode from the electrode surface, and further uses a forced circulation flow in the electrolytic bath to carry out the floating formed metal to the outside. This method overcomes the above-mentioned drawbacks of the conventional technology by utilizing liquid flows forcibly formed in the upper layer, and by placing metallic magnesium on these flows so that they can be quickly collected into a magnesium reservoir. The gist is that an electrolytic bath containing a molten metal chloride and held within an electrolytic chamber is immersed in an electrolytic bath, and at least one anode and at least one anode are disposed horizontally within the electrolytic chamber. When recovering metal and chlorine gas generated by electrolysis using one cathode, the upper layer of the electrolytic bath is flowed out from one end of the electrolytic chamber to the outside, and a portion of the electrolytic bath that has flowed out is removed from the electrolytic chamber. The electrolytic bath thus cooled is cooled to a temperature lower than that of the metal remaining in the electrolytic bath and remains in a molten state, and the cooled electrolytic bath is allowed to flow into the lower part of the electrolytic chamber, while at least the produced metal is removed from other parts of the electrolytic bath that has flowed out. By collecting a portion of the electrolytic bath and supplying at least a portion of the remaining electrolytic bath to another portion of the electrolytic chamber, the electrolytic bath within the electrolytic chamber is forced to form an upward flow and a surface flow, thereby removing the produced metal. The present invention relates to a method for electrolyzing molten chloride, which is characterized in that it can be easily carried out and recovered from an electrolysis chamber.

When the molten salt is electrolyzed according to the method of the present invention, the precipitated metal, particularly magnesium, floats up on the upward flow of the bath and reaches the bath surface or traps near the surface.

Since a fast flow is formed on the surface or upper layer of the bath, magnesium rides on this bath flow and enters the cooling passage, where it is separated on the bath surface. Guide of magnesium from the electrolysis chamber to the cooling passage does not necessarily require a special guide odor, but the metallic magnesium collected on the upper part of the beach in the direction of travel is collected in a magnesium collection tank (e.g. The Ti11. or ZrC1, it can be sent to the chloro method reduction process. The separated bath is returned to the chamber from another part of the chamber.

Chlorine, one of the products produced by the electrolytic reaction, is a gas and has a large difference in density, so it easily floats up in the electrolytic bath and is collected in the space above the bath surface of the electrolytic bath, and is deposited on the side walls and ceiling of the bath. It is discharged outside the tank through the exhaust port installed in the tank.

In the present invention, the cooling passage is separated from the electrolytic chamber by a partition,
Further, it is connected to the electrolytic chamber at a height above the top of the cathode plate and at the bottom. The internal electrolytic bath is cooled by natural ventilation through the outer wall, which is thinner than other parts, or by an air cooling jacket installed in contact with the outer surface of this outer wall.
This can be carried out more effectively by forcibly introducing cold air or by feeding cold air into a pipe inserted into the cooling passage. The temperature difference between the bath leaving the electrolytic chamber and the bath entering the electrolytic chamber is suitably 10 μ or more, preferably about 50"Q.

The bath surface flow in the electrolytic chamber advantageously utilizes the bath returned from the produced magnesium collection tank as described above. This bath is optimally supplied near the bath surface at the end of the electrolytic chamber opposite the cooling passage, but in some cases it may be supplied along with a replenishing electrolytic bath to the bottom of the cell.

A wide range of chamber configurations can be utilized in the present invention. For example, the electrode configuration may be as described in the above-mentioned US patent, ie, several pairs of electrodes each consisting of one anode and two cathodes, or one anode and one cathode may be placed at each end of the electrolytic chamber. Patent application 12489/1989, which the applicant can file first
As described in No. 0, a series multi-electrode type electrolytic chamber configuration may be used in which an anode is placed in the center of the electrolytic chamber, one cathode is placed at each end of the chamber, and one or more intermediate electrodes are arranged between the two electrodes. , especially in the case of this series multipolar type, a great effect can be obtained. In either case, as the number of electrodes per volume of electrolytic bath increases,
The calorific value of the electrolytic bath also increases, and especially when operating at a higher current density, there is a greater risk of consumption of the anode material graphite and wear and tear of the produced metal, but in the present invention, this risk is eliminated by cooling the electrolytic bath outside the electrolysis chamber. It is effectively removed by pressure.

It is desirable that the circulating flow used in the method of the present application is not turbulent. For this purpose, (1) it is preferable that the ends of each electrode facing the wall surface of the electrolytic cell be closely fixed by fitting or the like, and gaps that would cause downward flow be removed from between them.

(2) Near the wall, the bath temperature in this area decreases due to heat radiation through the tank wall, and convection (circulation flow) occurs between the electrode surfaces.
If this happens, it will hinder the recovery of magnesium, so if the heat dissipation is large, it is desirable to reduce the electrode spacing near the wall surface and increase the current density particularly in this area to increase the amount of heat generated.

Note that the electrolytic bath used in the present invention is dissolved in a separate container equipped with heating means, and is also required! It is convenient to mix and store the ingredients according to the conditions and then replenish the stored material to the bottom of the electrolytic chamber.

Next, the invention of the present application will be explained in detail with reference to the drawings.

FIG. 1 is a side cross-sectional view of a molten chloride electrolyzer suitable for implementing the method of the present invention, FIG. 2 is a plan view of the electrolytic cell section at the location indicated by A-A in FIG. 1, and FIG. Furthermore, Figure 2 KB-
FIG. 3 is an elevational cross-sectional view at a portion indicated by B. FIG. In these figures, an electrolytic cell 1 has an electrolytic chamber 2 essentially made of refractory bricks and a cooling passage 3, both of which are separated by a partition wall 4. (near) and the bottom are connected to the electrolytic chamber 2 through openings 5-6, respectively.

A bath/magnesium separation tank 7 is provided above the bath level at the outer end of the electrolytic cell of the cooling passage 2, and is connected to the center of the outer end of the electrolytic cell 1 by a pipe 8.

The separation tank 7 has a pipe 9 for the recovery of the separated magnesium, a pipe 1o for supplying the bath to the other end of the electrolytic cell 1, as well as suitable means for pumping the bath into the separation tank (e.g. suction,
Heat-resistant metal pumps, etc. (not shown) is provided. To return the bath to the electrolytic cell, the pressure of the bath due to the height difference between the separation tank and the electrolytic cell can be used.

An anode 11 made of a graphite plate and a cathode 12 made of an iron plate are arranged at both ends of the electrolytic chamber 2, respectively, and the upper part of the anode 11 protrudes from the lid body for energization, and the end of the cathode is connected to the tank. protruding from the side wall of 1 and forming conductive parts, respectively. Between the anode plate 11 and the cathode plate 12, nine intermediate electrodes 15 are arranged in series, each consisting of a thick graphite plate and an iron plate, each having an insulating block 14 at the top that reaches above the bath level. is placed on an electrode support 16 made of an insulating material such as alumina and placed in the electrolytic chamber. The spacing between the intermediate electrodes and between them and the anode and cathode is approximately 52 cm, with essentially equal spacing between the electrodes and over the entire plate surface. Furthermore, by fitting the side surfaces of each electrode into grooves provided on the opposing walls of the electrolytic chamber 20, the effects of fixing the electrodes and preventing disturbance of the circulating flow of the electrolytic bath are achieved at the same time. An exhaust hole 17 for discharging chlorine gas from the electrolytic cell is provided in the upper peripheral wall of the electrolytic chamber 2 at a height spaced apart from the level of the upper ends of the intermediate electrode and the cathode. The shape of the cooling passage may be a rectangular planar cross section parallel to the electrolytic chamber as shown here. The top part is connected by the opening 5, which is located slightly above the top part of the intermediate electrode or cathode of the electrolytic chamber, and the bottom part is also connected by the opening 6. In this figure, the bottom surface is set at approximately the same height as the bottom surface of the electrolytic chamber 2, but it may be sloped to some extent to facilitate flow toward the electrolytic chamber side. In this example, the thickness of the wall material on the side opposite to the electrolytic chamber is reduced in order to cool the electrolytic bath in the cooling passage, and furthermore, a jacket 18 is provided on the outside thereof to force cold air to pass through.

The electrolytic bath is supplied from a bath supply pipe 19 connected to the bottom of the cooling passage 3 to the bottom of the electrolytic chamber 2 through the bottom of the cooling passage. This bath is created by melting magnesium chloride in a separate storage vessel (not shown) with heating means and is required! The composition is adjusted according to the conditions and maintained in a molten state.

The sludge formed during the electrolytic reaction is allowed to settle to the bottom of the tank,
The support stand 16 on which the electrode plate is placed is provided with a large number of gaps or slits in order to remove it from the tank, and the bottoms of the electrolytic chamber 2 and the cooling passage 3 have grooves that go down toward the outer ends of the cooling passage. The cooling passage has a slope, and the sludge accumulated at the bottom of the cooling passage is taken out using a discharger R (not shown).

Although it is preferable from an economic efficiency point of view to use such a cooling passage in a configuration having an intermediate electrode as described above, it can also be applied to a case where a conventional electrode pair consisting of only an anode and a cathode is used.

Next, an example of operation according to the method of the present invention is shown schematically in FIGS. 1 to 3 above.

The size of the example electrolytic chamber is 1111L in length x 511L in width x depth t8
Straw, cooling passage is length α211L x width 511L x depth T21
It is L.

The bath/magnesium separation tank installed above the cooling passage has a cylindrical shape with an inner diameter α6m and an axial length t21R.
It has the ability to pump up 0-strong melt and can return the separated bath to the electrolytic chamber at almost the same temperature as the bath in the electrolytic chamber. The outer peripheral wall of the electrolytic cell is 46 degrees thick (however, the circumference of the cooling passage is at least 25 aa), and the partition wall between the electrolytic chamber and the cooling passage is made of refractory bricks with a thickness of 20C11. Place an alumina support stand with many slits in the electrolytic chamber, and place a support stand made of alumina with many slits on it.
Then, a graphite plate with a slightly sloped surface at the bottom was placed on one end to serve as an anode, and the opposite side was made with a similar slope.11! ×αB
An iron plate of wing X5cIIL (thickness) was placed as a cathode.

Between these, there were nine intermediate electrodes made by welding iron plates with the same cross section and a thickness of t5cIrL as the top traps of bolts embedded in a graphite plate of 1st x 18m and 12cm thick, so that the opposing surfaces were almost parallel to each other. It was placed as follows. Magnesium chloride 20%,
Using an electrolytic bath with a composition of 30% calcium chloride and 50% sodium chloride, a voltage of 57V was applied between the anode and the cathode, and a voltage of 367V was applied between each adjacent electrode, and the current density was (15)y' (-tl, electrolysis operation was continued for 24 hours at an electrolysis current of 4000A. During this time, the upper temperature of the electrolysis chamber was 710℃.
0, cold air is passed through the cooling jacket so that the temperature at the bottom of the cooling passage is maintained at 670'C,K, while the bath is pumped up at a rate of 120'4 in the bath/magnesium separation tank to remove the melt consisting mainly of the bath. While returning to the electrolytic chamber, the bath surface was maintained at a constant level by appropriately replenishing the molten bath composition.

Through the above operations, 405 M of magnesium metal and 137 tons of chlorine gas were obtained. This is similar to methods without such surface flow (Mg39ohp, CLt32
It shows an improvement of 3% compared to 4L), and an improvement of &5 cm compared to the method using neither surface flow nor forced circulation flow.

As described in detail above, according to the present invention, the electrolytic bath heated in the electrolytic chamber is forcibly radiated heat in the cooling passage, so that electrolysis can be performed at an appropriate temperature with less electrode consumption. What is more important is that this operation increases the density and creates a forced downward flow in the passageway, which promotes the formation of an upward flow in the electrolytic chamber, thereby separating the produced magnesium from the electrode surface. In addition, the formation of a surface flow makes it possible to recover the floating magnesium throughout the electrolytic chamber, thereby improving the yield.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view of a molten chloride electrolyzer suitable for carrying out the method of the present invention, Fig. 2 is a cross-sectional view of a portion indicated by A-A in Fig. 1, and Fig. 5 is a further cross-sectional view of FIG. 2 is a front cross-sectional view of the portion shown on line B-H. In the figures, each reference number indicates the following member. 1... Electrolytic cell; 2... Electrolytic chamber;
G... Cooling passage; 4...-... Partition wall; 5.6...
...Bullet opening; 7...Bath/magnesium separation tank; 8...Connecting pipe; 9...Mg
Recovery pipe; 1o... river/electrolytic bath supply pipe; 11...
Anode plate; 12... Cathode plate; 13... Electrolytic cell lid: 14. Mountain... Insulation block; 15...
・Intermediate electrode; 16... Electrode support stand; 17...
...C1, exhaust hole; 18, old... cooling jacket; 1
9... Electrolytic bath supply pipe; Patent applicant Hiroshi Ishizuka

Claims (1)

[Scope of Claims] t. An electrolytic bath containing a molten metal chloride and held in an electrolytic chamber, at least one anode and at least one anode immersed in the electrolytic bath and arranged horizontally in parallel within the electrolytic chamber. When recovering the metal and chlorine gas produced by electrolysis using one cathode, the upper part of the electrolytic bath is drained from one end of the electrolytic chamber to the outside of the chamber, and a portion of the electrolytic bath that has flowed out is removed. The electrolytic bath is cooled to a temperature lower than the temperature of the 11 ml of electrolytic chamber and still maintains a molten state, and the cooled electrolytic bath is allowed to flow into the lower part of the electrolytic chamber, while the produced metal is removed from other parts of the electrolytic bath that flowed out. Collecting a portion of the electrolytic bath and supplying at least a portion of the remaining electrolytic bath to another portion of the electrolytic chamber.
A method for electrolyzing molten chloride, characterized in that an upward flow and a surface flow are forcibly formed in an electrolytic bath in an iron electrolysis chamber, thereby facilitating the transport and collection of produced metals from the electrolysis chamber. 2. The method for electrolyzing molten chloride according to claim 1, wherein the metal chloride is magnesium chloride. (5) The method for electrolyzing molten chloride according to claim 1, wherein the electrolytic bath that has flowed out of the electrolytic chamber and from which the produced metal has been separated is introduced near the surface of the electrolytic bath in the electrolytic chamber. 4. The method for electrolyzing molten chloride according to claim 1, wherein the electrolytic bath that has flowed out of the electrolytic chamber and from which the produced metal has been separated is introduced near the bottom of the electrolytic chamber. i. The molten salt electrolyzer according to any one of claims 1 to 4, wherein the cooling means for the electrolytic bath essentially consists of an electrolytic cell wall structure that is thinner than other parts. 6. The molten salt electrolyzer according to any one of claims 1 to 4, wherein the cooling means for the electrolytic bath essentially consists of a cold air passage provided within the external flow path. Z. The molten salt electrolyzer according to claim 5 or 6, wherein the cooling means is further configured to forcibly bring a flow of cold air into contact with the outer wall surface of the external flow path.