JP2000210635A - Treatment of aluminum dross residual ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily suppress malodor by adding acidic water into aluminum dross residual ash after recovering aluminum or an aluminum alloy from aluminum dross to have specified water concentration and after kneading and granulating, incinerating the granulated aluminum dross residual ash. SOLUTION: Acidic water is added to the aluminum dross residual ash after recovering metallic aluminum or the aluminum alloy from the aluminum dross generated in an aluminum dissolving process for dissolving an aluminum raw material to have water concentration of 25-35 wt.%, kneaded and granulated. The granulated aluminum dross residual ash is incinerated. The kneading and the granulating is performed by applying such a method by kneading one prepared by adding the prescribed quantity of the acidic water to the aluminum dross residual ash in a rotary kneader or a continuous kneader and after that, compression tableting the kneaded material after kneaded in a granulating device to granulate. The firing of the granulated aluminum dross is performed in an acidic atmosphere at 800-1800 deg.C for 2-48 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal aluminum or aluminum alloy from aluminum dross inevitably generated in an aluminum melting step of melting an aluminum material made of aluminum (hereinafter abbreviated as "aluminum") or aluminum alloy. After collecting aluminum dross residual ash, there is no danger of generation of odor or ignition due to impurities contained in the residual ash,
The present invention relates to a processing method that can be turned into a useful resource.

[0002]

2. Description of the Related Art Aluminum products made of aluminum or aluminum alloy have excellent characteristics in corrosion resistance, electrical conductivity, heat conductivity, etc., so that they can be used in vehicles, ships, machinery, electricity, construction, daily necessities, beverage cans, etc. It is widely used in very many fields and its form is ingots, rolled products, extruded products,
Wide variety of products such as castings.

[0003] The production of such aluminum products is as follows.
Generally, it melts aluminum raw materials (raw materials) such as new aluminum ingots, aluminum mother alloys, aluminum scraps of products generated in the factory (return material in the factory), secondary aluminum ingots, secondary aluminum mother alloy ingots, and recovered aluminum scrap. Slab in basic form
After manufacturing aluminum ingots such as billets, aluminum ingots, aluminum alloy ingots, the aluminum ingot is subjected to rolling, extrusion, casting, and other processing to form a desired shape.
After that, by performing surface treatment such as anodic oxidation treatment for the purpose of cleaning the surface and imparting corrosion resistance and design to the surface, it is performed to make various aluminum products finally. .

Incidentally, in order to manufacture an aluminum ingot from an aluminum raw material, an aluminum melting step of melting the aluminum raw material is indispensable as described above. However, in the aluminum melting step, the surface of the molten metal is oxidized because aluminum or an aluminum alloy is originally a metal that is easily oxidized. In order to prevent the oxidation of the surface of the molten metal, a flash is usually used. However, it is difficult to completely prevent the oxidation, and a so-called aluminum dross containing aluminum oxide as a main component on the surface of the molten metal is inevitable. Is occurring.

[0005] Since the aluminum dross usually contains 80% by weight of aluminum, the aluminum dross scraped from the surface of the molten metal can be removed by using a rotary blade-type squeezing machine or under pressure. Squeezes out and collects molten metal aluminum. Further, the aluminum dross which has been cooled and solidified after the primary recovery treatment is again subjected to a melting treatment, and the above-mentioned recovery treatment is performed in the same manner to recover as much metallic aluminum as possible.

[0006] The residue after the metallic aluminum has been recovered from the aluminum dross as much as possible, that is, the aluminum dross ash is mainly composed of aluminum oxide.
It still contains metallic aluminum (including its alloys), and reacts with moisture to produce ammonia and hydrogen chloride, which can cause pollution such as offensive odors. Also included.

[0007] For this reason, various studies have been made so far on making the aluminum dross residual ash non-polluting or reusing it as an alumina source. However, this aluminum dross residual ash contains aluminum nitride as an impurity, and the content of aluminum nitride is usually 5 to 5.
20% by weight, and aluminum nitride reacts with moisture in the air to generate ammonia during standing or storage.
It causes safety and environmental problems, and its aluminum nitride is fairly stable even at high temperatures in a neutral or reducing atmosphere. This is an obstacle to the conversion of useful resources.

Further, the present applicant has proposed that water (actually water-containing) be added to aluminum dross residual ash in order to efficiently remove harmful impurities such as aluminum nitride from the aluminum dross residual ash so as to be a useful resource. There has already been proposed a processing method of kneading the mixture (together with an SiO ₂ compound or the like), granulating the mixture, and firing the mixture (Japanese Patent Application No. 9-349457).

However, when water is simply added to the aluminum dross residual ash to perform granulation, the aluminum nitride contained in the aluminum dross residual ash is not allowed during the granulation stage or during the storage of the granulated material. Combustible ammonia is always generated due to decomposition of odor, which may cause odor and ignition. In addition, the ammonia generated in this way becomes an aqueous solution and reacts with metal aluminum to produce aluminum hydroxide. At the same time, hydrogen gas is rapidly generated in a short time, so that the reaction is further accelerated and instantaneous. Explosive limits may be reached. In particular, such phenomena that cause ignition or reach the explosion limit occur sporadically and the timing of their occurrence is not clear, making it difficult to take preventive measures.

[0010] Incidentally, when it is necessary to remove ammonia, hydrogen gas or the like during a general work process, usually, air in the surrounding environment of the work equipment is collected and led to a clean tower, and the clean tower cleans the air. In many cases, the method of releasing to the outside is adopted. However, this method has a large gas generation in a short time as described above, and can cope even with the maximum gas generation in an operation process in which the generation time is not constant. When a facility having a normal gas processing capacity is installed, it is not possible to cope with a sudden generation of gas. For this reason, this method alone cannot sufficiently and properly cope.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has as its object to remove impurities such as aluminum nitride in the process of treating aluminum dross residual ash. Treatment of aluminum dross residual ash that can easily suppress bad odors that occur due to accidents and can easily prevent phenomena such as ignition and explosion caused by unexpected generation of ammonia, hydrogen gas, etc. It is to provide a method.

[0012]

SUMMARY OF THE INVENTION The present invention, which can achieve the above object, is a method for recovering metallic aluminum or aluminum alloy from aluminum dross generated in an aluminum melting step of melting an aluminum raw material made of aluminum or aluminum alloy. To the aluminum dross residual ash after the addition, acidic water is added to adjust the water concentration to 25 to 35% by weight, kneaded and granulated, and the granulated aluminum dross residual ash is calcined. Is the way.

The aluminum dross residue ash to be treated in the present invention is not particularly limited as long as it is by-produced in an aluminum melting step of melting an aluminum raw material made of aluminum or an aluminum alloy. Specifically, for example,
Dissolve aluminum raw materials (raw materials) such as the new aluminum ingots, aluminum mother alloys, aluminum scraps of products generated in the factory, secondary aluminum ingots, secondary aluminum mother alloy ingots, and recovered aluminum scrap as described above. It is a residue obtained from aluminum dross by-produced in an aluminum melting step when manufacturing an aluminum ingot such as a slab, a billet, an aluminum ingot, an aluminum alloy ingot, or the like. The composition of such aluminum dross residual ash is generally
10-15% by weight of metal aluminum, aluminum oxide (Al
₂ O ₃ ) 50 to 60% by weight, aluminum nitride (AlN) 5 to
20% by weight, silicon (Si) 0.5 to 10% by weight, iron (F
e) 0.5-2 wt%, magnesia (MgO) 0-6 wt%, alkali (Na + K) 1.5-3 wt%, calcium (Ca) 0-1 wt%, chlorine (Cl) 0.5- 5% by weight, and 0.5 to 2% by weight of fluorine (F).

In the present invention, acidic water is added to such aluminum dross residual ash so as to have a water concentration of 25 to 35% by weight, and the resulting mixture is kneaded while being adjusted. Granulate. At this time, the water concentration is 25 to 3
The adjustment to be 5% by weight is specified from the viewpoint of granulating the aluminum dross residual ash to such an extent that it becomes aggregated. If the water concentration is less than 25% by weight, the aluminum dross residual ash is not sufficiently aggregated, and
If the content is more than 10% by weight, aluminum dross residual ash becomes slurry and cannot be aggregated.

The kneading and granulation are performed, for example, by adding a predetermined amount of acidic water to aluminum dross residual ash using a paddle mixer.
After kneading with a rotary kneader such as a kneader mixer and a double circular mixer or a continuous kneader such as a screw mixer, the wet kneaded material after kneading is compressed and compressed with a granulating device such as a briquetter to form a tablet. It may be carried out by a method of granulating, or a method of kneading and granulating by spraying a predetermined amount of acidic water in a state where the aluminum dross residual ash is put in a rotating dish and rotated in a rotating dish granulator. The average particle diameter of the granulated aluminum dross ash is preferably about 3 to 30 mm from the viewpoints of easy transportation and securing the decomposition efficiency of aluminum nitride during firing.

In the present invention, the aluminum dross residual ash thus granulated is fired. The firing at this time is performed in an acidic atmosphere at a firing temperature of 800 to 1800 ° C. for about 2 to 48 hours. Further, the type of the firing apparatus and the firing method for performing the firing are not particularly limited, and a known apparatus is appropriately selected and applied.

The acidic water used in the present invention is usually
Any water having a pH of about 4 or less may be used. Preferably, the water is adjusted to have a pH of 1 or more and 4 or less, more preferably 1 or more and 2 or less with an organic acid or an inorganic acid. This acidic water p
When H is larger than “4”, it becomes difficult to suppress the decomposition of aluminum nitride contained in aluminum dross residual ash,
In addition, the ability to neutralize ammonia generated by the decomposition is reduced. From the viewpoint that the effect of suppressing the decomposition of aluminum nitride and the effect of neutralizing ammonia can be more reliably obtained, the pH is preferably “2” or less. Conversely, if the pH value is less than “1”, it promotes the decomposition of metallic aluminum contained in aluminum dross residual ash, which promotes the generation of hydrogen gas. Economically disadvantageous.

The acid for adjusting the pH of the acidic water may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, but is preferably an organic acid from the viewpoint of reducing the load of exhaust gas treatment and preserving equipment. is there. Further, the organic acid is preferably acetic acid, gluconic acid or citric acid from the viewpoint of good solubility in water and good mixing with aluminum dross.

According to the treatment method of the present invention, by firing the granulated aluminum dross residual ash, the aluminum nitride contained in the residual ash is decomposed and the metallic aluminum is also oxidized, so that the aluminum oxide is removed. (Alumina), and ammonia gas and hydrogen gas generated during the calcination are burned and decomposed to be harmless. During the granulation of aluminum dross residual ash, acid water is added to achieve a specific water concentration, thereby suppressing (or averaging) the decomposition of aluminum nitride during granulation and storage of the granulated material. This suppresses the production of ammonia. Further, the generated ammonia is neutralized to suppress the generation of basic water, thereby suppressing the decomposition of metallic aluminum. The effect by adding such acidic water can be reliably obtained by setting the pH to 1 or more and 4 or less.

Further, when the pH of the acidic water is adjusted using an organic acid, the decomposition of aluminum nitride during the granulation of aluminum dross residual ash is more reliably suppressed, and thus the generation of ammonia is more surely achieved. Can be suppressed. In addition, when the granulated product is fired, the organic acid is decomposed into water and carbon dioxide, so that no special treatment of the exhaust gas is required during firing.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to examples and comparative examples.

[Examples 1 to 12] To 25 kg of aluminum dross residual ash, 10 liters of acidic water having the acid and pH shown in Table 1 (10 liters of tap water in the comparative example) were added, and the residual ash was removed. Dross granules were obtained by granulation according to each granulation method shown in Table 1. In addition, the moisture concentration of the dross residual ash when adding acidic water etc. was all 30 weight%. Sulfuric acid having a concentration of 5% (specific gravity 1.05) was used. The obtained dross particles were stored in an iron storage box until firing. Next, the dross particles were fired at 1000 ° C. for 1 hour using a firing furnace in an oxidizing atmosphere. This calcination was performed before 8 hours from the addition of the acidic water to the residual ash.

In the "tablet-type" granulation method, aluminum dross residual ash to which acidic water has been added is kneaded by a rotary kneader and then embossed by a briquetter granulator to form dross particles having an average particle diameter of 15 mm. I tried to get. On the other hand, in the granulation method of the "rotating dish type", dross grains having an average particle diameter of 20 mm are formed by spraying acidic water onto the rotating aluminum dross ash housed and rotated by a rotating dish-type granulating apparatus to perform granulation. I got it. In this processing equipment, each kneading machine,
A canopy hood is installed at the upper part of the granulating device and the storage box, respectively, and each canopy hood is connected by an exhaust duct.
Air around each device was collected and sucked at a suction force of 0 m ³ / min, and then discharged outside after passing through an exhaust gas cleaning device.

During this process, the exhaust gas sucked in front of the exhaust duct cleaning device is sampled to determine the ammonia concentration according to JIS K0099-83.
It is continuously measured in accordance with the measurement method of the above, the maximum value of the concentration and the content of the processing steps at the time of the concentration (at the time of kneading, at the time of granulation,
Was checked during storage). In addition to the measurement of the ammonia concentration, the ammonia concentration in the working space of each processing step collected from a height of 1.5 m above the floor at a position 1 m away from the kneader, granulator and storage box equipment. Was measured by the same measurement method, and the maximum value of the ammonia concentration in the working space of the equipment related to the treatment process at the time when the maximum concentration reached in the exhaust duct was examined. Table 1 shows the measurement results at this time.

Further, each dross grain after granulation and after sintering is chemically analyzed, and aluminum nitride (Al
N) and the reduction rate of metallic aluminum (M-Al) were measured. At this time, the respective reduction rates were measured by the Kjeldahl method for aluminum nitride and the content of metallic aluminum by Br-methanol decomposition filtration ICP emission method,
It was determined as a reduction rate with respect to the initial content of aluminum nitride and metallic aluminum in aluminum dross residual ash used as a raw material. Table 1 shows the measurement results at this time.

[Comparative Examples 1 and 2] Comparative Examples 1 and 2
Except for using the tap water having the pH shown in Table 1 in place of the acidic water in Examples 1 and 2, the treatment of aluminum dross residual ash is performed through the same steps as in Examples 1 and 2, respectively. In addition, various similar measurements were performed. Table 1 shows the measurement results at this time.

[0027]

[Table 1]

As is clear from Table 1, Examples 1 to 12
In each of the Examples, the reduction rate of aluminum nitride and metallic aluminum after firing was almost 99% in each of the examples, and aluminum nitride and metallic aluminum were efficiently removed from the dross tablets by firing.

Examples 1 and 2 in which acidic water of pH 2 using acetic acid was added to aluminum dross residual ash and kneaded and granulated.
In addition, in Examples 9 and 10 in which acidic water of pH 2 using sulfuric acid was added to aluminum dross residual ash and kneaded and granulated, the reduction rates of aluminum nitride and metallic aluminum after granulation were both 0%. Also, during and after granulation, aluminum nitride and metallic aluminum remain without reduction. This indicates that, in other words, neither aluminum nitride nor metallic aluminum is substantially decomposed during and after granulation, and the decomposition is surely suppressed. In particular, since the amount of aluminum nitride has hardly decreased, the ammonia concentration is also lower than those of the other examples (3 to 8, 11 to 12). Further, in the example, no ignition or explosion occurred in the processing equipment.

On the other hand, Examples 3 and 4 in which acidic water having a pH of 4 using acetic acid was added to aluminum dross residual ash and kneaded and granulated, and acid water using gluconic acid was added to aluminum dross residual ash. In Examples 5 to 8 in which kneading and granulation were performed and Examples 11 to 12 in which acidic water having a pH of 4 using sulfuric acid was added to aluminum dross residual ash and kneaded and granulated, the above-described examples (1, 2, 9) were used. Compared with 10), the reduction rate of aluminum nitride and metallic aluminum after granulation was slightly increased, and the ammonia concentration (particularly in the exhaust duct) was slightly increased. Note that there was almost no difference in the ammonia concentration in the working environment.

On the other hand, in Comparative Examples 1 and 2 in which tap water having a pH of 6.8 was used in place of the acidic water, the reduction rates of aluminum nitride and metallic aluminum after calcination were as high as 99%. Although there was no difference from the case of Example 12, the reduction rates of aluminum nitride and metallic aluminum after granulation were as in Example 1.
The number was extremely large as compared with the case of ~ 12. In addition, when the maximum value of the ammonia concentration is compared with the cases of Examples 1 to 12, in Comparative Example 1 employing the “tableting” type granulation method, the exhaust duct is 7 to 47 times the work space. 5 times to 1
In Comparative Example 2 employing the "rotating dish" type granulation method, the ratio was as high as 8 to 34 times for the exhaust duct and 4 to 9 times for the working space. In fact , Comparative Examples 1 and 2
In the working space where the treatment was performed, an unpleasant odor due to ammonia or the like was confirmed by odor.

The fired product obtained by performing the treatments of Examples 1 to 12 had a very small content of aluminum nitride and metallic aluminum, and was a granular material mainly composed of aluminum oxide (alumina). Was.

[0033]

As described above, according to the treatment method of the present invention, in particular, acid water is added to aluminum dross residual ash and kneaded and granulated. Since the decomposition of aluminum and the decomposition of metallic aluminum are suppressed, ammonia generated by the decomposition of aluminum nitride during the processing of aluminum dross residual ash (particularly during granulation and storage after granulation and before firing) Odor and the like are easily and accurately suppressed. In addition, this makes it possible to easily prevent phenomena such as ignition and explosion caused by unexpected generation of ammonia and hydrogen gas. From this, it is possible to treat aluminum dross residual ash which is more excellent in working environment and safety.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B09B 3/00 301M (72) Inventor Akira Morita 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Nippon Light Metal Group Technology Center Co., Ltd. (72) Inventor Noboru Sugiyama 1-34-1, Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Nippon Light Metal Co., Ltd. Group Technology Center (72) Inventor Masatoshi Nanba 2-2-2 Higashishinagawa, Shinagawa-ku, Tokyo No. 20 Japan Light Metal Co., Ltd. F term (reference) 4D004 AA44 CA14 CA15 CA30 CC11 CC12 CC15 DA03 DA09 DA20 4G076 AA02 AB22 AB28 AC02 AC07 BA39 BD01 CA01 DA30 4K001 AA02 BA13 CA18 CA20 CA22 GA19

Claims (3)

[Claims] 1. An aluminum dross residue obtained by recovering metallic aluminum or an aluminum alloy from an aluminum dross generated in an aluminum melting step of melting an aluminum raw material made of aluminum or an aluminum alloy, into an aluminum dross residual ash having a water concentration of acidic water. A method for treating aluminum dross residual ash, comprising adding, kneading, and granulating the mixture so as to have a concentration of 25 to 35% by weight, and calcining the granulated aluminum dross residual ash. 2. The acidic water is adjusted to pH with an organic acid or an inorganic acid.
2. The treatment method according to claim 1, wherein water is water prepared in a range of 1 to 4. 3. The treatment method according to claim 2, wherein the organic acid is acetic acid, gluconic acid or citric acid.