RU2483128C2 - Method of removing impurities from aluminium and furnace to this end - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises smelting the wastes in vertical furnace with boric anhydride at temperature above their melting point by 100°C and separate discharge of cleaned aluminium melt and that contaminated with impurities into moulds. Then, boric acid is, first, loaded into furnace crucible, its weight being calculated by the formula m_{H3BO3, kg} = 128.2·X², where X is crucible diameter, m. Then, aluminium wastes are loaded therein to melt height in furnace of 1000-1100 mm to hold the melt therein for 45-90 min. Top part of the melt contaminated with slag and low-weight impurities, medium part of the melt cleaned of impurities, and its bottom part are, then, separately discharged. Proposed furnace comprises jacket, lining, 300-1500 mm-dia 1290 mm-high crucible made of refractory bricks with wall thickness of 120 mm and bottom lined by refractory concrete to 90 mm height, furnace heating elements arranged between crucible and lining, crucible cover, ring to close lining top and space between lining and crucible, crucible lining and three tap holes. One of the latter is located at 900-1000 mm from furnace crucible bottom, second is located at 100 mm from said bottom and third is located level with crucible bottom.

EFFECT: higher efficiency, lower costs.

6 cl, 2 dwg, 1 tbl

Description

The invention relates to the metallurgical industry and can be used to produce pure aluminum from its waste.

The furnace can be heated using electricity, burning natural gas or liquid fuel.

A known method and installation for processing cages or waste non-ferrous metals and their alloys in a horizontal furnace, heating and melting of the loaded materials is carried out using an electric arc of direct current created by a single electrode introduced into the furnace.

The furnace is able to rotate in both directions (Patent RU 2007101902 A September 10, 2008, Bull. No. 25).

The disadvantages of the known invention are:

- complex hardware design of the method;

- in horizontal furnaces there is an ineffective separation of impurities and molten metal due to the large area and low height of the melt;

- the complexity of a clear separation of slag and molten metal during their discharge into the molds, therefore, there is a low yield of purified metal;

- low quality of the metal being cleaned.

A known method of purification of aluminum from impurities and a furnace for implementing the method, selected as a prototype.

Purification of aluminum from impurities is carried out in a vertical furnace by melting aluminum waste in a molten salt of sodium chloride and potassium, sodium fluoride, sodium tetraborate, boric acid anhydride.

Impurity metal oxides interact with boric acid anhydride and are removed from the salt melt, and the purified aluminum melt flows down the furnace and then it is sent to the molds. (Patent RU 2411297 C2, 07.20.2010, Bull. No. 20).

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

- inconvenience in the operation of the furnace due to the inability to stop the aluminum cleaning process for various reasons. To stop from the furnace, it is necessary to drain the molten aluminum remaining at the bottom of the crucible of the furnace, and the molten salt in a special container;

- increased safety requirements when working on the furnace.

The objectives of the proposed method and furnace for its implementation are:

- an increase in the ability to use furnaces of various capacities when using various heating methods - electricity, burning natural gas or liquid fuel;

- simplify the process of servicing furnaces;

- reduce capital and operating costs of the process of cleaning aluminum waste from impurities.

The solution of these problems is achieved by first loading boric acid into the crucible of the furnace, the mass of which is calculated by the formula: mH ₃ BO ₃ , kg = 128.2 · x ² , where x is the internal diameter of the crucible of the furnace, m, then they are loaded into the crucible of the furnace aluminum waste from the calculation of the formation of its melt with a height of 1000-1100 mm. The aluminum melt is heated 100 ° C above its melting temperature and held at this temperature for 45-90 minutes to separate the impurities along the height of the melt: lightweight impurities will float to the surface of the melt, heavy impurities will settle in the lower part of the melt, the middle part of the melt and will represent purified aluminum. After the molten aluminum is held in the crucible of the furnace, the molds are drained for the specified time: first, through the upper notch located at a height of 900-1000 mm from the bottom of the crucible of the furnace, then through the middle notch located at a height of 100 mm from the bottom of the crucible of the furnace, and finally through lower notch located at the bottom of the crucible bottom of the furnace.

The aluminum ingots obtained through the upper notch are collected separately and re-melted in the crucible of the furnace without the addition of boric acid, while maintaining the height, exposure and conditions of melt discharge, as described above, and the collected melt ingots from the lower notch are used to obtain metal alloys .

The furnace has a crucible with an internal diameter of 300-1500 mm, a height of 1290 mm and is laid out of refractory bricks on a refractory mortar and has a wall thickness of 120 mm, the bottom of the furnace crucible is lined with refractory concrete to a height of 90 mm.

The furnace has three slots for draining the molten aluminum located on one axis along the height of the crucible of the furnace, at heights: 900-1000 mm from the bottom of the crucible of the furnace, 100 mm from the bottom of the crucible of the furnace, at the bottom of the crucible of the furnace. The lathes are made in the form of pipes made of refractory ceramics, in which the locking devices are mounted in the form of two disks made of refractory ceramics and having side openings, the first disk from the crucible of the furnace is made stationary with an opening in the lower part, the second disk having a side opening is tightly attached to the fixed the disk and is made to be rotated by a special lever, when the holes in the disks are blocked, the notch is closed, when the holes coincide, the openings are open for draining the molten aluminum into the receiving bucket and further along the gutter in the molds. Such a system of constipation in letki allows you to adjust the intensity of the discharge of aluminum melt into the molds.

A general view of the furnace is shown in Figure 1. The furnace includes the following elements:

1. The casing of the furnace made of structural steel, δ - 5-10 mm

2. Sheet asbestos, δ - 10 mm.

3. Lining of the furnace with refractory bricks, δ - 350 mm.

4. The furnace crucible made of refractory brick, δ - 120 mm, height 1290 mm, inner diameter 300-1500 mm.

5. Space for accommodating furnace heating elements (nichrome tape, gas burners, liquid fuel nozzles), δ - 150 mm.

6. The bottom of the furnace crucible is lined with refractory concrete to a height of 90 mm.

7. Ring made of refractory steel, δ - 20 mm, lined on both sides with refractory concrete.

8. The crucible cover of the furnace is made of refractory steel, δ - 20 mm, lined on both sides with refractory concrete.

9. Rings for installing and removing the cover.

The tap hole and locking devices are shown in Figure 2:

10. Pipe made of refractory ceramics.

11. Fixed disk made of refractory ceramics with a lower side hole.

12. A movable disk made of refractory ceramics with a side opening.

13. Lever for turning the movable ceramic disc.

14. Lever support, refractory ceramic disc with side hole.

Cleaning waste aluminum from impurities is as follows. For example, take a furnace in which the crucible will have an internal diameter of 600 mm.

Using a crane beam, remove the lid (pos. 8) of the crucible of the furnace. First, boric acid is loaded into the crucible of the furnace, the mass of which is calculated by the formula:

mH ₃ BO ₃ , kg = 128.2 · x ² , where x is the internal diameter of the crucible of the furnace, m

mH ₃ BO ₃ , kg = 128.2 · 0.6 ² = 46.15 kg.

Then, aluminum waste containing 85% aluminum metal is charged into the crucible of the furnace.

The height of the molten aluminum should be 1000 mm. The mass of aluminum waste that needs to be loaded into the furnace is calculated by

formula: max.Al, t - 0.785 × 0.6 ² × 1.0 × 2.7: 0.85 = 0.9

where 0.6 is the inner diameter of the crucible, m;

1,0 - the height of the molten aluminum, m;

2.7 - specific gravity of aluminum, t / m ³ ;

0.85 - coefficient taking into account the 85% content of aluminum metal in aluminum waste.

Therefore, 900 kg of aluminum waste is charged into the crucible of the furnace. The locking devices of the tap hole are brought into the closed state (Fig. 2) using the lever (pos. 13). The crucible of the furnace is closed with a lid (Fig. 1, pos. 8). They include gas burners located in the furnace space (Fig. 1, item 5). Figure 1 does not indicate the location of the gas burners in space (pos. 5) and the sampling of the products of gas combustion in the exhaust pipe, therefore, we recall that the gas burners in the space (pos. 5) are located in the upper part, and the sampling of the products of combustion of natural gas is carried out with lower part of the space (item 5). In this embodiment, heat from the combustion of natural gas in the furnace is most effectively used. The temperature inside the crucible of the furnace is set equal to 760-780 ° C (melting point of aluminum 660.2 ° C). Upon reaching the set temperature, the aluminum melt can withstand 60-90 minutes (the time should be set when working out the technological parameters for the treatment of aluminum waste containing 85% aluminum metal).

During the heating of the aluminum waste to a temperature of 760-780 ° C, the thermal decomposition of boric acid into boric acid anhydride (B ₂ O ₃ ) and water will occur, as well as the melting of boric anhydride (t _pl . About 600 ° C). During the sedimentation of the aluminum melt, the melt of boric acid anhydride will slowly rise upward, and it will react with impurity metal oxides to form metaborate metal salts [Me (BO ₂ ) ₃ , Me (BO ₂ ) ₂ ], which together with other lightweight impurities will float to the surface of the aluminum melt, heavy impurities (Fe, Cu, Pb, etc.) will settle down the aluminum melt. After the settling time has ended, a bucket with a trough is brought to the upper notch at a height of 900 mm from the bottom of the crucible, carefully lock the upper notch, regulate the rate of melt discharge and completely drain the upper layer into molds containing 500 kg of melt (slag together with aluminum melt) . These ingots are collected for remelting in a furnace.

Next, a ladle with a chute is brought to the middle notch at a height of 100 mm from the bottom of the crucible of the furnace, the chute is directed to the molds placed on the conveyor, the lock of the notch is carefully opened, the intensity of the melt draining into the molds is regulated and the purified aluminum melt is completely drained into the molds. And, finally, the ladle is led to the lower notch located at the bottom of the crucible of the furnace, the trough is sent to the molds containing 500 kg of aluminum melt, the lock of the notch is carefully opened, the intensity of the discharge of aluminum melt into the molds is regulated, the melt in the lower part of the furnace crucible is completely drained into molds. In all doors, the constipation is closed, the heating of the furnace is stopped and prepared for the next aluminum cleaning operation, as described above.

The set of features of the proposed technical solution - a method for cleaning aluminum from impurities and a furnace for implementing the method - have differences from the prototype and should not be explicitly studied from the prior art, therefore, the authors believe that the method and furnace are new and have an inventive step. The method of cleaning aluminum waste from impurities and the furnace for implementing the method can effectively clean aluminum waste and reduce capital and operating costs.

The results of the technical process of the proposed method for the treatment of aluminum waste are presented in table 1.

The composition of aluminum waste, wt.%:

Aluminum metal - 95.0;

impurity metal oxides - 2.5;

intermetallic compounds - 2.5.

Table 1 No. of experiments Name of process parameters U measurement Parameter Values Process results one. The mass of loaded boric acid in a crucible furnace kg 0.32 Received purified aluminum - 4.48 kg In% of the mass of waste - 80.0 The content of metallic aluminum in purified aluminum is 99.55% The mass of loaded aluminum waste in the crucible furnace kg 5,6 The mass of the melt obtained from the upper notch - 0.74 kg Melt temperature ° C 780 The content of aluminum metal - 0.42 kg The exposure time of the melt in the crucible furnace min 45 In% of the mass of loaded aluminum waste in the furnace - 7.5 The mass of the melt obtained from the lower tap hole - 0.56 kg Melt bed height mm 1000 The content of aluminum metal - 0.44 kg Inside diameter of crucible furnace mm fifty In% of the mass of loaded aluminum waste in the furnace - 7.9 2. The mass of loaded boric acid in a crucible furnace kg 0.32 Received purified aluminum - 4.48 kg In% of the mass of waste - 80.0 The content of metallic aluminum in purified aluminum is 99.7% The mass of loaded aluminum waste in the crucible furnace kg 5,6 The mass of the melt obtained from the upper notch - 0.74 kg Melt temperature ° C 780 The content of aluminum metal - 0,413 kg The exposure time of the melt in the crucible furnace min 60 In% of the mass of loaded aluminum waste in the furnace - 7.4 The mass of the melt obtained from the lower tap hole - 0.56 kg Melt bed height mm 1000 The content of aluminum metal - 0.44 kg Inside diameter of crucible furnace mm fifty In% of the mass of loaded aluminum waste in the furnace - 7.9

Continuation of table 1. No. of experiments Name of process parameters U measurement Parameter Values Process results one. The mass of loaded boric acid in a crucible furnace kg 0.32 Received purified aluminum - 4.48 kg In% of the mass of waste - 80.0 The content of aluminum metal in purified aluminum is 99.9% The mass of loaded aluminum waste in the crucible furnace kg 5,6 The mass of the melt obtained from the upper notch - 0.74 kg Melt temperature ° C 780 The content of aluminum metal - 0.404 kg The exposure time of the melt in the crucible furnace min 90 In% of the mass of loaded aluminum waste in the furnace - 7.2 1000 The mass of the melt obtained from the lower tap hole - 0.56 kg Melt bed height mm The content of aluminum metal - 0.44 kg Inside diameter of crucible furnace mm fifty In% of the mass of loaded aluminum waste in the furnace - 7.9

Thus, the use of the proposed method for the purification of aluminum waste from impurities and the furnace for implementing the method make it possible to achieve the objectives and obtain positive results.

Claims (6)

1. A method of cleaning aluminum waste from impurities, including melting the waste in a vertical furnace together with boric anhydride at a temperature above their melting point by 100 ° C and separately pouring into the molds the melt of purified aluminum and the melt contaminated with impurities, characterized in that in the crucible of the furnace boric acid is first charged, the mass of which is calculated by the formula:
m _H3BO3 , kg = 128.2 · x ² ,
where x is the inner diameter of the crucible furnace, m,
then the aluminum waste is charged based on the formation of the height of the melt in the crucible of the furnace of 1000-1100 mm and the melt is held in the crucible of the furnace for 45-90 minutes, followed by separate discharge of the upper part of the melt contaminated with slag and lightweight impurities, the middle part of the melt purified from impurities, and the lower part of the melt contaminated with heavy impurities. 2. The method according to claim 1, characterized in that after holding the molten aluminum in the crucible of the furnace for 45-90 minutes, the molten aluminum is first drained through the upper groove located at a height of 900-1000 mm from the bottom of the crucible of the furnace, then through the middle groove, located at a height of 100 mm from the bottom of the crucible of the furnace and finally through the lower notch located at the bottom of the furnace. 3. The method according to claim 1 or 2, characterized in that the ingots of aluminum obtained through the upper notch are collected separately and re-melted in the crucible of the furnace without the addition of boric acid. 4. A furnace for cleaning aluminum waste from impurities, comprising a casing, lining, furnace crucible, furnace heating elements located in the space between the crucible and the lining, a furnace crucible cover, a ring for closing the top of the lining and the space between the lining and the crucible, and the crucible masonry , notch, characterized in that the crucible of the furnace is made with an internal diameter of 300-1500 mm, a height of 1290 mm, is made of refractory bricks on a refractory mortar and has a wall thickness of 120 mm, and the bottom of the crucible of the furnace is lined with refractory concrete to a height of 90 mm. 5. The furnace according to claim 4, characterized in that it has three slots located at heights from the bottom of the crucible of the furnace 900-1000 mm, 100 mm, at the bottom of the crucible of the furnace. 6. The furnace according to claim 4, characterized in that the slots are made in the form of pipes made of refractory ceramics, in which the locking devices are mounted in the form of two disks made of refractory ceramics and having side openings, the first disk from the crucible of the furnace is made stationary with an opening in the lower part , the second disk having a side hole is tightly attached to the fixed disk and is made to rotate.

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