JPS5848635B2 - Aluminum electrolytic manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrially advantageous method for producing aluminum by subjecting aluminum chloride to molten salt electrolysis.

Traditionally, aluminum has been manufactured industrially by the so-called Hall-Heroux method, in which aluminum oxide (alumina) is dissolved in a metal fluoride molten salt electrolytic bath mainly composed of molten cryolite, and electrolyzed using carbon as an anode. .

However, in principle, the Hall-Heroux method requires a large amount of electrical energy for the electrolytic reduction of alumina, and in fact, the electric power required to produce one ton of aluminum, that is, the electric power consumption rate, is 14,000 KWh/t or more. Therefore, there has been a strong demand for the development of aluminum manufacturing technology that can reduce electrical energy consumption.

As an alternative to the Hall-Heroux process, a promising energy-saving method for producing aluminum is aluminum chloride electrolysis, in which aluminum chloride is dissolved in a molten alkali metal chloride bath such as Na(J!, KCII) and electrolyzed. The law is known.

This aluminum chloride melt electrolysis method can operate at an electrolysis temperature of around 700°C, which is approximately 300°C lower than the Hall-Heroux method, and since the anode reaction is a chlorine production reaction, the graphite electrode used as the anode is non-consumable. Tona? Things, etc.
Despite having many advantages, it has not been used industrially for a long time due to the difficulty of handling high-temperature aluminum chloride and generated chlorine gas, and the inability to obtain suitable bath-resistant materials industrially. It has been left unused.

However, in recent years, the American Alcoa Company, for example,
As shown in Japanese Patent Publication No. 52-15044, Japanese Patent Publication No. 52-15043, and Japanese Patent Publication No. 5215361, an aluminum chloride electrolytic method (Alcoa method) using a new electrolytic device and an electrolytic bath with a new bath structure was proposed, and it suddenly attracted industrial attention. It came to be.

This Alcoa method uses AlCl containing LiCl at a high concentration.
3 -L iCJ'-Na (J' type molten salt electrolytic bath is used, and a carbon (graphite) electrode plate is placed in the tank lined with a nitride-based refractory material with excellent fire resistance and bath resistance. Chlorine gas can be produced by electrolyzing at a bath temperature of approximately 700°C, a distance between electrodes of approximately 15 mm, and a current density of approximately 1 A/cIIL using an electrolytic cell in which horizontal double electrodes are stacked with a certain gap in between. The electrolytic bath is produced on the anode surface, while molten metal aluminum is produced on the cathode surface. By eliminating the metal aluminum produced on the cathode surface from between the electrodes and homogenizing the aluminum chloride present in the electrolytic bath between the electrodes, the electrolytic operation can be stabilized and the AlCl3-NaCl electrolytic bath can be stabilized. The cell voltage was reduced by introducing LiCl, which has high electrical conductivity, into the components.

However, when using this AlCl3 Licl NaCl based electrolytic bath or when using the conventional AlCl3-NaCl based or AICl3-KCl based electrolytic bath, the current efficiency is at most about 85%, so the power consumption rate is low. There is a limit to the improvement of the electrolytic bath, and therefore there is a desire to develop an electrolytic bath that is industrially more advantageous.

As a result of various studies, especially regarding electrolytic bath group precepts, the inventors found that
If a relatively large amount of MgCl2 or CaCl2 is first contained in the AlCl3-NaCl electrolytic bath components, aluminum chloride can be electrolyzed with a high current efficiency of more than 90% and close to 95 to 99%. revealed.

After further research, we found that when a small amount of barium chloride is added to the electrolytic bath mentioned above, the amount of aluminum generated at the cathode?
We have discovered that the flow of Ni from the cathode surface can be removed extremely smoothly and quickly.

In other words, in the electrolysis of aluminum chloride using a laminated double electrode, it is essential to remove metallic aluminum generated on the cathode from the cathode surface as quickly as possible in order to perform stable, high current efficiency operation. However, according to experiments conducted by the inventors, among alkaline earth metal chlorides, Ba (J!
It was confirmed that although 2 has a poor effect of improving current efficiency like MgCl2 and CaCl2, it has the effect of reducing the interfacial tension with respect to the aluminum metal bath and promoting flow.

Therefore, the present invention electrolyzes a metal chloride molten salt electrolytic bath containing aluminum chloride in an electrolytic cell in which a plurality of horizontal or inclined electrodes are stacked one above the other with an appropriate distance between the electrodes. In the method of generating chlorine gas on the surface and molten metal aluminum on the cathode surface, the molten aluminum generated on the cathode surface is flowed away from the electrode surface and settled at the bottom of the electrolytic cell. (J?3,
NaCA,Bacj? A method for producing aluminum by electrolyzing aluminum chloride while maintaining a stable high current efficiency by using a mixed bath consisting of 2t C acl2 and/or MgCl2 and specifying the mixing amount of each within the range described below. It is.

In the present invention, Na (J!) selected as a solvent salt for aluminum chloride improves the electrical conductivity of the electrolytic bath, and is used in an amount of 85 to 10% by weight.

Furthermore, the addition of 3 to 15% by weight of BaCl2 has the effect of reducing the interfacial tension of aluminum and making it easier to flow and discharge from the electrode surface. Below the lower limit amount, this effect is small, and when above the upper limit amount, the effect is small. The addition increases the density of the bath,
This is not preferred because it reduces the sedimentation rate of aluminum.

Next, CaCl2 sMgC#2 all contribute to improving current efficiency during electrolysis, and these salts exhibit the effect of improving current efficiency when contained in the bath at 10 to 60% by weight. be.

However, since CaCl2 has the property of separating into two layers from other electrolytic bath components, it is desirable to limit the content to 35% by weight or less.

Finally, if the AlCl3 concentration in the bath is increased too much, the electrical conductivity of the bath will decrease and the vapor pressure of the bath will become excessive, leading to an increase in cell voltage and unstable furnace operation. The concentration of AICll3 was in the range of 2 to 15% by weight.

Electrolytic conditions for stable operation of aluminum chloride electrolysis using the electrolytic bath of the present invention described above vary depending on the type and capacity of the bath, but generally the bath temperature is 680 to 7
By performing electrolysis within this range at 80°C and current density of 0.5 to 260 A/c/L, interelectrode distance of 10 to 25 degrees, electrolytic production of aluminum can be continued with a current efficiency of approximately 90% or more. I was able to do it.

Electrolysis is carried out using a closed electrolytic cell that has a raw material supply port at the top, a chlorine gas discharge port, a metal storage tank at the bottom, and a graphite electrode inside.

The electrodes may consist of a pair of graphite plates stacked in parallel at appropriate intervals, or three or more graphite plates may be stacked one above the other in parallel, with at least one intermediate between the anode and cathode. Any of those that constitute a double electrode may be used.

In addition, the electrodes can be arranged horizontally as in the Alcoa method, but in this type of electrolytic method, the distance between the electrodes is relatively small, and if the amount of aluminum generated on the cathode surface increases, the electrodes will short-circuit. In addition, the chance of reaction with chlorine increases, so in order to quickly remove this from the cathode surface, it is desirable to add BaCl2 to the bath and to tilt the plate electrode appropriately.

In this case, the electrolytic bath flows upward on the slope due to the lift effect caused by the rise of the chlorine gas generated on the cathode surface, and the aluminum generated on the cathode top surface falls downward on the slope and is eliminated by its own weight. become.

It is preferable that the inclination of the electrodes be at an angle of 10 to 45 degrees with respect to the horizontal. If the inclination angle exceeds 45 degrees, the flow of the electrolytic bath between the electrodes becomes extremely strong, which may cause reoxidation of the precipitated aluminum. This is disadvantageous because the current efficiency actually decreases.

Next, examples of the present invention are listed.

Example 1 AIC13 14.0% by weight, NaCl 51.0% by weight, MgCl227.

0% by weight, BaCl28. AlCl with a bath composition of O wt%
3. In an electrolytic bath lined with alumina refractory material using a mixed molten salt of NaCl MgCl2 BaCl2 as an electrolytic bath, an inclined graphite electrode plate (effective reaction surface 60 gm x 33 mm) with an angle of 30° to the horizontal was used to create an electrode gap between the electrodes. distance 14
Im, bath temperature 750℃, current 20A, current density IA
As a result of continuous electrolysis with /cIIL for 4.5 hours, 2 7
．． 6 r of aluminum was obtained.

The current efficiency at this time is 9l. 2%, and the cell voltage was 3.24V.

Example 2 AICll3 8.0% by weight, NaCl5. O weight%,
AIC with a bath composition of 224.0% by weight of MgCl2, 3.0% by weight of CaCl21, and 0.0% by weight of BaCl21
l3 -NaCl-MgCl2 CaCl2 Ba
Results 2 of electrolysis carried out under the same electrolytic conditions as Example 1 using a Cl2-based mixed molten salt as an electrolytic bath. 7. 7 f of alumium was obtained.

The current efficiency at this time was 91.7%, and the cell voltage was 3.
It was 28V.

Example 3 AICl 39.0% by weight, Na(J' 58.8% by weight, CaCl2 2 5.2% by weight, B acl2 7
．． O wt% (AlCl3-NaCl-Ca of D bath composition
As a result of performing electrolysis under the same electrolytic conditions as in Example-1 using a Cl2-BaClz mixed molten salt as an electrolytic bath, 27.4f was obtained.
t of aluminum was obtained.

At this time, the current efficiency is 90.7% and the cell voltage is 3.23■
Met.

Claims (1)

[Claims] 1. A metal chloride molten salt electrolytic bath containing aluminum chloride is electrolyzed in an electrolytic cell in which a plurality of horizontal or inclined electrodes are stacked one above the other with an appropriate distance between the electrodes. , in a method in which chlorine gas is generated on the anode surface and molten metal aluminum is generated on the cathode surface, and the molten aluminum generated on the cathode surface is settled to the bottom of the electrolytic tank, the molten salt electrolytic bath is
ICl32-15% by weight, CaCl210-35% by weight
, BaCl 23-15% by weight and NaCl 85-35
1. A method for electrolytically producing aluminum, characterized by forming a mixed composition consisting of % by weight. 2 A metal chloride molten salt electrolytic bath containing aluminum chloride is electrolyzed in an electrolytic cell in which multiple horizontal or inclined electrodes are stacked one above the other with an appropriate distance between the electrodes, and chlorine gas is applied to the anode surface. In addition, in a method in which molten metal aluminum is produced on the cathode surface and the molten aluminum produced on the cathode surface is allowed to settle to the bottom of the electrolytic bath, the molten salt electrolytic bath contains 32 to 15% by weight of AlCl, 10 to 60% by weight of MgC, BaCA! 23-15% by weight, NaCA85-1
Al? characterized by having a mixed composition consisting of 0% by weight? Electrolytic manufacturing method for Ni. 3 A metal chloride molten salt electrolytic bath containing aluminum chloride is electrolyzed in an electrolytic cell in which multiple horizontal or inclined electrodes are stacked one above the other with an appropriate distance between the electrodes, and the anode surface is In the method of obtaining chlorine gas and molten metallic aluminum on the cathode surface, and allowing the molten aluminum produced on the cathode surface to settle to the bottom of the electrolytic tank, the molten salt electrolytic bath is made of 32 to 15% by weight of AICl, MgCl2, and C.
aCl2 total of 10-60% by weight, BaCl23-
A method for electrolytically producing aluminum, characterized in that the mixed composition consists of 15% by weight of NaCl and 85-10% by weight of NaCl.