RU2411297C2 - Procedure for refinement of aluminium from impurities and furnace for implementation of procedure - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in charging aluminium in stand into melt of salts of sodium and potassium chlorides, sodium fluoride, tetra-boric-acidic sodium, and boric acid anhydride at temperature 700-800°C and of composition, wt %: NaCl - 64, NF - 20, KCl - 11, Na₂B₄O₇ - 3, B₂O₃ - 2. The furnace contains a crucible made as a shell out of refractory steel, a shell, a refractory lining of the crucible, burner devices, a cover of the furnace, tubes for refined melt process pouring and for pouring aluminium melt and salts during furnace repair or in case of emergency. A low end of the tube for refined aluminium melt process pouring is built-in into the crucible of the furnace at distance of 50-80 mm from the bottom of the furnace, while the level of melt of refined aluminium is at height of 860-900 mm from the bottom of the furnace.

EFFECT: raised efficiency of refinement of aluminium containing impurities as metal oxides or inter-metallic compounds and elimination of scull formation.

7 cl, 1 dwg, 1 tbl

Description

The invention relates to the metallurgical industry and can be used to clean various aluminum wastes from impurities to produce aluminum used for anticorrosion coating of steel strips, deoxidation of steel in open-hearth furnaces, the manufacture of various aluminum products, and the production of various aluminum-based alloys.

The method includes melting aluminum waste in a melt of salts of sodium chloride and potassium, sodium fluoride, sodium tetraborate, boric acid anhydride at a temperature of 700-800 ° C in a crucible furnace. At the bottom of the crucible of the furnace, a blocking layer of molten aluminum with a height of 200-220 mm is formed, above which there is a layer of molten salts with a height of 800-820 mm, and the drain of the purified molten aluminum is carried out at a height of 860-900 mm. The distance from the level of the molten salt to the top of the crucible furnace support equal to 350-400 mm The loading of aluminum waste into the molten salt is carried out in a cage made of refractory steel. After the smelting of aluminum, the crate is removed from the molten salt along with the impurities remaining in it, the purification of which is carried out by immersion in water of the crate and subsequent mechanical removal of impurities from the crate.

Aluminum is cleaned of impurities in a furnace containing a crucible made of refractory steel, a lid, heating devices, pipes for technological draining of the cleaned aluminum melt and for draining the molten aluminum and salts made of refractory ceramics and having an electric heater, a stand made of refractory steel and having fixing on the furnace supports by means of shoulders on the stand stock after immersing it in molten salts with aluminum waste.

The design of the furnace eliminates the contact of the molten aluminum with its metal parts and thereby contributes to the elimination of re-contamination of aluminum with metals and the reliability of long-term operation of the furnace.

The technical result is the purification efficiency of aluminum containing impurities in the form of metal oxides or intermetallic compounds. The content of aluminum metal in purified aluminum can reach 99.9%.

The technology for cleaning aluminum eliminates the formation of plaque on the walls of the crucible and allows you to conduct the process of cleaning aluminum in a continuous mode with maximum automation of the process.

The present invention relates to the metallurgical industry and can be used to clean aluminum from impurities. Purified aluminum can be used in the industry of anti-corrosion coatings of rolled steel, to obtain various alloys based on aluminum, the manufacture of various products, in the process of deoxidation of steel in open-hearth furnaces. A known method of purifying aluminum from impurity metal oxides, selected as a prototype, comprising melting aluminum in a melt of a mixture of salts: sodium chloride, sodium fluoride, potassium chloride, sodium tetraborate having a concentration in the molten salt of 5-7 wt.%, At a temperature of 750- 850 ° C. To transfer sodium metabisorbate (NaBO ₂ ), formed during the purification of aluminum, into sodium tetraborate, boric acid is periodically charged into the molten salt.

To implement the method of purification of aluminum, a furnace is used, which includes the following elements:

1. furnace crucible made of refractory steel;

2. a wall pocket for a shutter made of molten aluminum, which is a pipe made of refractory steel;

3. a branch pipe for draining purified aluminum into molds, which is a pipe made of refractory steel;

4. refractory steel grill;

5. supporting posts made of refractory steel;

6. a pipe for introducing nitrogen into the crucible space above the surface of the molten salt;

7. crucible cover (RF patent No. 2305712, published September 10, 2007, bull. No. 25).

The above method and furnace for cleaning aluminum have the following disadvantages:

- high melting temperature of aluminum, which determines a significant melting rate of aluminum, which can reduce the efficiency of aluminum purification;

- the design of the furnace has not been sufficiently worked out, for example: a wall pocket will create inconvenience when loading stands with an aluminum block, a support grid and racks for installing a stand with an aluminum block made of refractory steel will create the bulkiness of the crucible of the furnace and there will be a possibility of gradual dissolution of the racks, made of refractory steel, in molten aluminum; the same applies to pipes made of refractory steel for draining molten aluminum into molds.

In this method, only a chemical method is indicated for purifying aluminum from impurity metals, while aluminum is also actually purified from intermetallic compounds of impurity metals with aluminum by the principle of zone melting of metals, since aluminum is melted in the molten salt layer by layer and the intermetallic compounds are not yet shifted to the side molten metal, that is, ultimately, to the center of the block, so they remain in the crate.

The objectives of the proposed method and furnace for its implementation are to ensure stable continuous operation of the furnace, increasing the efficiency of the process of cleaning impurities, improving the design of the furnace, improving working conditions and safety. The solution of these problems is achieved by the fact that the melting of aluminum is carried out at a temperature of 700-800 ° C in a molten salt having the following composition, wt.%:

NaCl - 64, NaF - 20, KCl - 11, Na ₂ B ₄ O ₇ - 3, B ₂ O ₃ - 2.

Aluminum is melted in a crucible with the formation of a height of the layer of molten aluminum at the bottom of the crucible of the furnace 200–220 mm and a height of the layer of molten salts above the level of the molten aluminum of 800–820 mm, and the discharge of the purified molten aluminum is carried out at a height of 860–900 mm from the bottom of the crucible of the furnace. The distance from the level of the molten salt to the top of the furnace is maintained equal to 350-400 mm. Aluminum is melted in a cage made of refractory steel immersed in molten salts. After removing the stand from the molten salt, it is cleaned of impurities remaining in it by immersion in a container with water, followed by mechanical removal of impurities from the stand.

The furnace is equipped with a steel casing lined with refractory bricks inside to form a space between the casing lining and the furnace crucible for placing heating devices, the crucible is made in the form of a shell with the refractory concrete lining on the inside of the crucible to a height of 500 mm from the bottom of the crucible of the furnace, the bottom of the furnace crucible is made made of refractory concrete, the lower end of the pipe for technological discharge of the cleaned aluminum melt is mounted in the crucible of the furnace and immersed in it at a distance from the furnace bottom of 50-80 mm, and the level of discharge of the melt is cleaned nnogo aluminum located at 860-900 mm from the furnace bottom. Pipes for technological discharge of refined aluminum and molten salts are made of refractory ceramics and have electric heating. The aluminum stand is configured to be fixed on furnace supports by means of shoulders on the stand rod after the stand is immersed in molten salts.

General view of the furnace is shown in the drawing. The furnace includes the following elements.

1. Crucible furnace. It is a tsar made of refractory steel, lined with refractory concrete inside to a height of 500 mm, the bottom of the crucible is also lined with refractory concrete. 2. The casing of the furnace is made of structural steel, as well as the spherical bottom of the furnace. 3. The sliding cover of the furnace is made of refractory steel and has a heat-insulating layer between the two sheets of the cover. 4. The bottom of the furnace lined with refractory concrete. 5. Pipe for draining purified aluminum, made of heat-resistant ceramics and having electrical heating. 6. Pipe for draining molten aluminum and salts during preventive repairs of the furnace or in case of emergency, made of refractory ceramics and having electrical heating. 7. Cork made of refractory clay. 8. Lining the crucible of the furnace from the inside with refractory concrete. 9. A crate for loading into an aluminum furnace made of refractory steel. 10. The molten aluminum at the bottom of the crucible furnace. 11. Melt of a mixture of salts.

To implement the method of purification of aluminum from impurities, the furnace is brought into operation. To do this, turn on the burners located in the space between the lining of the furnace casing (pos. 2) and the crucible of the furnace (pos. 1), heat the crucible of the furnace to 700-800 ° C, and the air is displaced from the crucible of the furnace with nitrogen. In a crate (item 9) made of refractory steel, ingots or aluminum blocks are loaded. Using a hydraulic actuator, the lid (pos. 3) of the crucible of the furnace (pos. 1) is opened, the crate with aluminum is immersed in the crucible of the furnace and fixed on the supports of the furnace by means of shoulders on the rod of the stand, the lid is closed. Nitrogen continues to be fed into the crucible space.

Thus, a locking layer of aluminum melt 250 mm high is deposited onto the bottom of the crucible of the furnace.

Pre-determine the mass of aluminum that needs to be melted in the crucible of the furnace so that the height of the aluminum melt is 250 mm according to the formula

m = 0.785 × d ² × h × q,

where m is the mass of aluminum that must be melted in the furnace to form a layer of molten aluminum at the bottom of the crucible of the furnace, having a height of 250 mm, t;

d is the diameter of the crucible of the furnace directly near the bottom of the crucible of the furnace, m;

h is the height of the molten aluminum at the bottom of the crucible furnace, equal to 0.25 m;

q is the specific gravity of aluminum equal to 2.7 t / m ³ .

After the formation of a layer of a molten aluminum with a height of 250 mm at the bottom of the crucible of the furnace, a mixture of salts, which is prepared in advance, begins to be loaded into the furnace. The composition of the mixture of salts is as follows, wt.%:

NaCl - 61.4; NaF - 19.2; KCl - 10.5; Na ₂ B ₄ O ₇ · 10H ₂ O (borax) - 5.5; boric acid (H ₃ BO ₃ ) - 3.4.

After thermal decomposition of borax into sodium tetraborate and water, boric acid into boric acid anhydride (B ₂ O ₃ ) and water, the composition of the mixture of salts will be as follows, wt.%:

NaCl - 64; NaF - 20; KCl - 11; Na ₂ B ₄ O ₇ - 3; B ₂ O ₃ - 2.

As soon as a melt layer of a mixture of salts with a height of 20-50 mm is formed over the surface of the aluminum melt, nitrogen supply to the furnace is stopped. The mixture of salts is loaded into the crucible of the furnace periodically in small portions of 20-30 kg. Re-loading the next portion of the salts is carried out after the full melting of the previously loaded portion of the salts. The loading of the salt mixture into the crucible of the furnace continues until the height of the layer of molten salts above the level of the molten aluminum reaches 800-820 mm There should be free space from the level of salt melt to the top of the crucible of the furnace to prevent splash of the molten salt from the crucible of the furnace at the moment of loading new portions of the mixture of salts and boric acid into the crucible of the furnace. The height from the level of molten salts to the top of the crucible furnace should be 350-400 mm

At the end of the deposition of the necessary mixture of salts in the crucible of the furnace, the molds are substituted for the technological drain and include electrical heating of the heat-resistant ceramic pipe (item 5). After that, the furnace is ready for continuous work on cleaning aluminum from impurities in a continuous mode. The oven must be continuously running. If it is planned to stop the furnace for a long time, then the burners are left in working condition and the temperature of the molten salt is maintained at 700 ° C.

The purification of aluminum in the furnace is as follows.

800-1000 kg of aluminum waste is loaded into the crate, the lid of the crucible of the furnace is opened using a hydraulic actuator, the crate with aluminum waste is slowly immersed in the molten salt. Aluminum waste in the cage should be completely immersed in the molten salt. The temperature of the melt is maintained in the range of 700-800 ° C, increasing or decreasing the temperature of the molten salt within this interval, depending on the task in terms of the melting rate of aluminum and its quality. After complete melting of the aluminum immersed in the crate into the furnace and draining it to the bottom of the crucible of the furnace for about 1-1.5 hours, the lid of the crucible of the furnace is opened, the crate with impurities is removed from the molten salt and left in a hanging position over the molten salt in for 5-10 minutes to drain the molten salt from the stand. Then the crate is completely removed from the furnace and transported to the place of purification from impurities. The boric acid weighing 70-100 kg is loaded into the molten salt, depending on the content of impurities in aluminum waste, after thermal decomposition of boric acid into boric acid anhydride (B ₂ O ₃ ) and water and melting of boric acid anhydride into the molten salt, the waste is immersed in another stand aluminum. Thus, a continuous process of purification of aluminum from impurities is carried out.

During preventive repairs or in emergency situations, aluminum and salt melts are poured out of the furnace through a heat-resistant ceramic pipe (pos. 6) into molds, the volume of which allows to obtain aluminum and salt masses equal to 500 kg. To drain the molten aluminum and salts through a pipe (pos. 6), a tube of refractory clay (pos. 7) is knocked out with a bar from the outside.

The set of features of the proposed technological and technical solutions of the method of purification of aluminum from impurities and the furnace for implementing the method are different from the prototype and do not follow explicitly from the studied prior art, therefore, the method and furnace are new and have an inventive step.

The method of purification of aluminum from impurities and the furnace for implementing the method make it possible to create, in an industrial environment, a reliable installation and efficient purification of aluminum from impurities, to create safe and labor-intensive working conditions. The results of the technological process for the purification of aluminum from impurities are presented in table 1.

The composition of contaminated aluminum, wt.%:

Aluminum - 94.8; impurities - 5.2.

Table 1 No. of experiments Name of process parameters Units Parameter Values Process results Oven temperature ° C 750 Melting rate The composition of salts: wt.% aluminum - 1430 kg / h NaCl 64 Content one. NaF twenty metal Kcl eleven aluminum in peeled Na ₂ B ₄ O ₇ 3 aluminum - 99.4% B ₂ O ₃ 2 Oven temperature ° C 700 Melting rate The composition of salts: wt.% aluminum - 1095 kg / h NaCl 64 Content 2. NaF twenty metal Kcl eleven aluminum in peeled Na ₂ B ₄ O ₇ 3 aluminum - 99.7% B ₂ O ₃ 2 Oven temperature ° C 670 Melting rate The composition of salts: wt.% aluminum - 825 kg / h NaCl 64 Content 3. NaF twenty metal Kcl eleven aluminum in peeled Na ₂ B ₄ O ₇ 3 aluminum - 99.9% B ₂ O ₃ 2 Oven temperature ° C 800 Melting rate The composition of salts: wt.% aluminum - 1570 kg / h NaCl 64 Content four. NaF twenty metal Kcl eleven aluminum in peeled Na ₂ B ₄ O ₇ 3 aluminum - 99.4% B ₂ O ₃ 2 Oven temperature ° C 830 Melting rate The composition of salts: wt.% aluminum - 1724 kg / h NaCl 64 Content 5. NaF twenty metal Kcl eleven aluminum in peeled Na ₂ B ₄ O ₇ 3 aluminum - 99.2% B ₂ O ₃ 2

Thus, the use of the proposed method for purification of aluminum from impurities and the furnace for implementing the method allow us to complete the tasks and obtain positive results of the technical solution.

Claims (7)

1. The method of purification of aluminum from impurities by remelting it in a melt of salts of sodium chloride and potassium, sodium fluoride, sodium tetraborate, boric acid anhydride, characterized in that the melting of aluminum is carried out at a temperature of 700-800 ° C in a molten salt having the following composition, wt.%:
NaCl 64 NaF twenty Kcl eleven Na ₂ B ₄ O ₇ 3 B ₂ O ₃ 2
while the melting of aluminum is carried out in a crucible with the formation of a height of the layer of molten aluminum at the bottom of the crucible of the furnace 200-220 mm and a height of the layer of salts above the level of the molten aluminum of 800-820 mm, and the discharge of the purified molten aluminum is carried out at a height of 860-900 mm from the bottom of the crucible of the furnace . 2. The method according to claim 1, characterized in that the distance from the level of the molten salt to the top of the crucible furnace is maintained equal to 350-400 mm 3. The method according to claim 1, characterized in that the melting of aluminum is carried out in a stand made of refractory steel immersed in a molten salt. 4. The method according to claim 3, characterized in that after removing the crate from the molten salt, it is cleaned of impurities remaining in it by immersion in a container of water, followed by mechanical removal of impurities from the crate. 5. Furnace for the purification of aluminum from impurities by remelting it in a molten salt of sodium chloride and potassium, sodium fluoride, sodium tetraborate, boric acid anhydride, containing a crucible made of refractory steel, a lid, heating devices, pipes for the technological discharge of purified aluminum melt and for draining molten aluminum and salts and a stand for aluminum, characterized in that it is equipped with a steel casing, lined with refractory bricks from the inside with the formation of a space between the lining of the casing and the crucible of the furnace for Further heating devices, the crucible is made in the form of a shell with a lining of refractory concrete on the inside of the crucible 500 mm high from the bottom of the furnace, the bottom of the crucible is made of refractory concrete, the lower end of the pipe for technological discharge of the cleaned aluminum melt is mounted in the crucible of the furnace and immersed in it a distance of 50-80 mm from the bottom of the furnace, and the melt discharge level of purified aluminum is located at a height of 860-900 mm from the bottom of the furnace. 6. The furnace according to claim 5, characterized in that the pipes for the technological discharge of the purified aluminum melt and the discharge of the aluminum melt and salts are made of refractory ceramics and have electric heating. 7. The furnace according to claim 5, characterized in that the aluminum stand is made with the possibility of fixation on the furnace supports by means of shoulders on the stand rod after the stand is immersed in molten salts.

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