JP2002045824A - Method for treating aluminum dross residual ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating aluminum dross residual ash and for utilizing aluminum dross residual ash as useful resources, by which toxic impurities are efficiently removed and a granular, particulate or clumpy alumina composition which is extremely excellent in handleability when transported and used, high in compressive strength and industrially useful, can be obtained from the residual ash. SOLUTION: This method for treating aluminum dross residual ash remaining after metal aluminum or an aluminum alloy is recovered from the aluminum dross produced at the aluminum melting step to melt an aluminum raw material consisting of aluminum or an aluminum alloy comprises adding washing water to the aluminum dross residual ash to obtain slurry, washing the obtained slurry with the washing water while adjusting the pH of the obtained slurry to 5-9, subjecting the slurry to solid-liquid separation and firing the obtained solid residue.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aluminum dross residue inevitably generated from a basic and essential aluminum raw material melting step in the production of a variety of aluminum (hereinafter abbreviated as "aluminum") or aluminum alloy products. A method for obtaining harmless alumina compositions by firing at lower temperatures than conventional methods by removing chlorides and alkali metals, which are problematic in terms of environment and effective use, from ash (a general term for aluminum ash and dust ash). .

[0002]

2. Description of the Related Art Aluminum products made of aluminum or aluminum alloy have excellent properties in terms of touch resistance, light weight, electrical conductivity, and heat conductivity.
It is used in an extremely large number of fields such as construction, daily necessities, food and beverage containers, and its form is also ingots, rolled products, extruded products,
It is extremely diverse as forged products and their processed products. In the production of such aluminum products, an aluminum melting step of melting aluminum raw materials is essential as a basic step regardless of the form of use.

[0003] In the aluminum melting step, aluminum or aluminum alloy is originally a metal which is easily oxidized, and since the surface of the molten metal is always exposed to air and oxidized, a flux is usually used to prevent this. Have been. However, it is difficult to completely prevent oxidation of the surface of the molten metal in the aluminum melting step, and so-called aluminum dross containing aluminum oxide as a main component is inevitably generated on the surface of the molten metal.

[0004] Since this aluminum dross usually contains as much as 80% by weight of aluminum,
The aluminum dross scraped and solidified from the surface of the molten metal is melted again, and the molten metal aluminum is physically squeezed out at high temperature and under pressure using a squeezing machine such as a rotary blade, and collected. Metal aluminum is recovered as much as possible by repeating multiple times. In the course of this operation,
Since fine dust is generated, it is usually collected by a dust collector such as a bag filter.

[0005] In this manner, the residue containing the molten metallic aluminum as much as possible from the aluminum dross and the one containing dust ash are usually called aluminum dross residue ash. This aluminum dross residue ash is mainly composed of aluminum oxide (alumina), but still contains metallic aluminum and aluminum alloys, and furthermore, chlorides and alkali salts caused by fluxes that pose a problem on the environment or effective use. (NaCl, K
Cl, AlCl _3, etc.), aluminum nitride (AlN), and the like.

The halide contained in this aluminum dross residual ash reaches 1 to 10% by weight depending on the treatment history, is released as a gas when heated at a high temperature, and causes safety and environmental problems. Also produces white smoke. Of these, alkali halides are particularly stable at high temperatures and remain even after firing at high temperatures.For example, when used as raw materials for chemical industry, raw materials for ceramics, alumina-based slag-making agents for metal refining, etc. Has become.

[0007] Therefore, aluminum dross residual ash
Until now, various studies have been made on removing halides and alkali salts of these harmful impurities and also aluminum nitride and reusing them as an alumina source. As the method, a hydrothermal treatment method and a high-temperature calcination method have been known for a long time.

For example, in the classical hydrothermal treatment method, a large amount of water is added to aluminum dross residual ash, and chloride is dissolved and removed by stirring while heating in an open container, and at the same time, AlN is converted to AlN + 3H ₂ O → Al (OH). _Although it was decomposed and removed by the reaction of ₃ + NH ₃ ↑, the treatment required a long time, the load on a huge reaction tank was large, and the effect of removing aluminum nitride was not sufficient. In recent years, efficiency has been improved by devising operating conditions, but the recovery and disposal of ammonia is indispensable, and there has been a problem that equipment and operation are complicated. Furthermore, even if the aluminum dross residual ash treated by this method is to be granulated, a large amount of powdery product is generated unless a binder is added, and there is a problem that it is difficult to form a granular product.

In the calcination method, aluminum dross residual ash is heated to a temperature higher than the red heat temperature in an oxidizing atmosphere to oxidize and decompose aluminum nitride to alumina (Al ₂ O ₃ ). It contains about 20% by weight of aluminum nitride. In order to decompose 90% by weight or more of this amount to reduce the amount of aluminum nitride in the product to 1% by weight or less, 1300% is used.
A high temperature as high as ° C. is required, and there are problems in terms of equipment and energy costs.

Further, in recent years, a method of obtaining a powdery treatment product containing aluminum oxide as a main component by heating aluminum dross residual ash to 400 to 1400 ° C. while maintaining an oxidizing atmosphere (Japanese Patent Application Laid-Open No. -135,761), a method of adding water to aluminum dross residual ash to adjust the water content to 5 to 30% by weight, and then burning at 700 to 1500 ° C (Japanese Patent Application Laid-Open No. 6-339,674), Add silicon dioxide in an amount equal to or greater than the amount of aluminum nitride contained in the residual ash from Amidroth,
A method of obtaining α-alumina as a raw material for cement by heating to a temperature of at least ℃ (Japanese Patent Application Laid-Open No. 7-96,265) and the like have also been proposed.

However, such a method also requires a high temperature exceeding 1300 ° C., requires the use of a large amount of auxiliary materials, and reduces the content of Al ₂ O _{3 in the} product, so that it is not suitable for special applications. However, this method is not always satisfactory because the use thereof is limited or a large amount of dust is generated when an economical direct heat furnace is used.

[0012] On the other hand, from the standpoint of using a fired product of aluminum dross residual ash, from the viewpoint of chemical composition, aluminum nitride is 2% by weight or less and chlorine compound (in terms of chlorine) is 1% by weight in terms of chemical composition. Must be:
In terms of physical properties, its transport safety and efficiency,
Furthermore, from the viewpoint of the strength in use, it is desirable that the particles are granular, granular, or massive.

However, the fired product of aluminum dross residual ash cannot be easily granulated into granules, granules, or agglomerates. It is necessary to perform calcination or granulation for granulation, granulation, or agglomeration using a separate binder.

For example, in order to use it as a slag-making agent for metal refining, it is necessary to form a granule or lump having a diameter of 3 to 80 mmφ, and its crushing strength is required to be 140 N or more, preferably 200 N or more. For this purpose, an adhesive synthetic resin such as carboxymethylcellulose (CMC) or a binder such as a natural resin, pitch, water glass, or cement is added to a powder obtained by drying or baking to granulate. (See, for example, JP-A-56-5)
In addition to the special auxiliary material cost, increase in the number of manufacturing steps and prolonged manufacturing time are unavoidable.

Further, the present inventors have found that in order to be able to efficiently remove to useful resources unwanted impurities such as aluminum nitride of aluminum dross residual ash, hydrated SiO ₂ compound in the aluminum dross residual ash etc. A method of kneading a mixture with water and granulating the mixture, followed by granulation and firing is proposed (JP-A-11-179,322).

However, although this method has the effect of decomposing AlN at a relatively low temperature, it still requires 1000 ppm to remove chlorine from aluminum dross residual ash having a high chlorine concentration.
A firing temperature of at least ℃ is required. This is because the chlorine compound is mainly an alkali metal chloride caused by flux and cannot be removed except by heating to a temperature higher than the melting point of these metal chlorides.

[0017]

Accordingly, the present inventors have developed a method of converting useful aluminum dross ash, which is difficult to treat, into an alumina resource having a shape that can be efficiently and economically used more easily. As a result of intensive studies, first, water was added to aluminum dross residual ash, the pH was adjusted to 5 to 9 when washing with stirring, and then the solid residue obtained by solid-liquid separation was calcined. It has been found that, even when calcined at a relatively low temperature, harmful impurities can be easily decomposed and removed to obtain useful resources, and that granules, granules or agglomerates can be easily granulated, and the present invention has been completed. .

Accordingly, an object of the present invention is to efficiently remove harmful impurities from aluminum dross residual ash to make it a useful resource, and it is extremely easy to handle in transportation and use, and has high crushing strength and is industrially useful. It is an object of the present invention to provide a method for treating aluminum dross residual ash that can obtain a granular, granular, or massive alumina composition.

[0019]

That is, the present invention provides an aluminum dross residue after recovering metallic aluminum or an aluminum alloy from aluminum dross generated in an aluminum melting step of melting an aluminum raw material made of aluminum or an aluminum alloy. When treating the ash, the pH of the slurry obtained by adding washing water to the aluminum dross residual ash was adjusted to 5 to
This is a method for treating aluminum dross residual ash by adjusting the water content in the range of 9 and washing with water and then baking the solid residue obtained by solid-liquid separation.

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,
Aluminum raw materials such as new aluminum ingots, aluminum mother alloys, aluminum scraps of products generated in the factory (return materials in the factory), secondary aluminum ingots, secondary aluminum mother alloy ingots, and aluminum scraps collected from automobile parts and aluminum cans It is aluminum dross residual ash obtained from aluminum dross which is by-produced in the aluminum melting process when producing aluminum ingots such as slabs, billets, aluminum ingots, aluminum alloy ingots and the like in a basic form. The composition of such aluminum dross residue ash is generally about 8 to 1 metal aluminum.
5% by weight, aluminum oxide (Al ₂ O ₃ ) 45 to 60% by weight,
Aluminum nitride (AlN) 5 to 15% by weight, silicon (Si)
0.5 to 10% by weight, iron (Fe) 0.5 to 2% by weight, magnesium (Mg) 0 to 6% by weight, alkali (Na +
K) 1.5 to 6% by weight, calcium (Ca) 0 to 1% by weight, chlorine (Cl) 1 to 8% by weight, fluorine (F) 0.5 to 4
% By weight.

In the method of the present invention, first, washing water is added to such aluminum dross residual ash, and the pH of the obtained slurry is adjusted to a range of 5 to 9, preferably 7 to 9. Wash under agitation while adjusting and maintaining. In the washing of aluminum dross residual ash, if the pH of the slurry is lower than 5, the amount of acid used increases, which is not economical and causes a problem that metal aluminum loss becomes remarkable. Then, there arises a problem that metal aluminum and aluminum nitride are extremely reduced.

The amount of washing water used for washing the aluminum dross ash depends on the content of impurities to be removed such as halogen compounds contained in the aluminum dross ash to be treated. 3 to 200 times the weight of the dross residue ash,
Preferably, it may be 5 to 100 times by weight.

Examples of the pH adjusting agent used for adjusting the pH of the slurry at the time of washing with water include organic acids such as gluconic acid, acetic acid and citric acid, and inorganic acids such as nitric acid, sulfuric acid and phosphoric acid. Those which are easily decomposed and removed by baking at a relatively low temperature are preferable, and organic acids are preferable. In addition, as it is in the alumina composition obtained after calcination, or when using a pH adjuster that may remain as a decomposition product, consider the use of the alumina composition obtained by calcination. In addition, it is necessary to determine the amount of the pH adjuster to be used within the range of the allowable residual amount.

In the present invention, the washing method is not particularly limited, and may be a batch type or a continuous type in which a plurality of washing tanks are connected in series. A large-capacity and relatively small-capacity flush tank in a continuous system is efficient. In addition, about the number of times of washing,
It is not particularly limited and may be determined according to the dilution ratio or the like. For example, when the dilution ratio is less than 10 times, it is preferable to perform the measurement twice or more. It may be times.

After washing the aluminum dross residual ash with water as described above, the obtained slurry is subjected to solid-liquid separation, and the obtained solid residue is fired to obtain an alumina composition. Here, the method for solid-liquid separation of the slurry is not particularly limited as long as it can be industrially adopted, and for example, decantation for separating a supernatant liquid by allowing to stand for a predetermined time, pressure filtration,
Filtration means such as filtration under reduced pressure, centrifugation and the like can be mentioned.

The solid residue obtained by the above solid-liquid separation is then calcined to turn it into a useful resource as an alumina composition. Since the halogen compound and the alkali metal have already been removed by washing and solid-liquid separation of the solid residue, aluminum nitride (AlN) contained in the solid residue is calcined.
As long as the baking temperature is usually 600 to 1000
C., preferably at 600-800.degree. If the firing temperature is lower than 600 ° C., aluminum nitride tends to remain. Conversely, if the firing temperature is higher than 1000 ° C., the energy cost only increases unnecessarily, and the product becomes too dense during the firing process. On the contrary, decomposition of aluminum nitride may be hindered.

The firing furnace used for firing the solid residue may be any of a gas combustion type, a fuel oil combustion type, an electric heating type, etc., and may be a direct heating type or an indirect heating type. Further, any type such as a stationary type, a tunnel type, a rotary type, and a shuttle type may be used.

In the method of the present invention, if necessary, the water content of the solid residue is adjusted to 25 to 50% by weight, preferably 25 to 50% by weight.
The mixture may be adjusted to about 35% by weight and kneaded, and the resulting kneaded product may be granulated into granules, granules, or a predetermined mass, and then fired. If the water content at this time is less than 25% by weight, it becomes difficult to granulate the solid residue into a required shape, and if it exceeds 50% by weight, the solid residue becomes a slurry and also has a required shape. Granulation becomes difficult.

The method of kneading and granulation is not particularly limited, and for example, a paddle mixer, a kneader mixer,
Kneading with a rotary kneader such as a double circular mixer, or a continuous kneader such as a screw mixer, and granulating the obtained kneaded material such as a briquetter, a rotary dish granulator, an extrusion granulator, etc. Granular, granular, or in a predetermined shape such as a lump, also, in consideration of the ease of transport and decomposition efficiency of aluminum nitride during firing, a predetermined particle size, preferably 3 to 80 mmφ,
More preferably, it is granulated to a size of 3 to 30 mmφ.

In the method of the present invention, the pH of the slurry is adjusted to 5
By washing with water which is adjusted and maintained within the range of 10 or less and stirred, most of impurities such as halogen compounds and alkali metals (Na + K) present in the aluminum dross residual ash are dissolved and removed, and the aluminum dross residual ash is removed. Almost all of the aluminum nitride (AlN) and metallic aluminum (Al) in the solid content remain after solid-liquid separation after washing with water.

The Al remaining in the solid residue
N and Al react with water at the beginning of the sintering process when the solid residue is sintered, and aluminum hydroxide ｛Al (OH)
_It is considered that the aluminum hydroxide acts as a binder, and the reaction heat serves as a heat source to improve the crushing strength after firing and prevent the fired product from being powdered.

The calcined product obtained by the method of the present invention has an AlN content of at most 2% by weight, preferably at most 1% by weight, and a chlorine content of at most 1% by weight.
% By weight, preferably 0.5% by weight or less, having an average particle diameter of 3 to 80 mmφ, and a crushing strength of 140 to 350 N (Newton), preferably 200 to 350 N (Newton).
It is a 300N alumina composition.

Such an alumina composition can be used as it is for applications such as ceramics, chemicals, and auxiliary materials for cement, as well as slag-making agents, soil stabilizers, and sludge solidifying agents for steelmaking. It is also industrially useful.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of a preferred embodiment of the present invention will be specifically described based on test examples, comparative test examples, and examples. In the following test examples, comparative test examples, and examples, as aluminum dross residual ash, the following composition recovered in the step of dissolving aluminum raw materials, metallic aluminum (Al) ... 8.1% by weight, aluminum nitride (AlN ) ... 8.
9% by weight, chlorine (Cl): 5.5% by weight, sodium (Na): 2.9% by weight, potassium (K): 2.4
%, Alumina (Al ₂ O ₃ ): 48.2% by weight, and silica (SiO ₂ ): 12.8% by weight.

Test Examples 1 to 5 and Comparative Test Examples 1 to 3 100 g of the above aluminum dross residual ash was placed in a beaker.
Add the amount of washing water shown in
Was adjusted to the values shown in Table 1, and washed with water by stirring with a propeller for the washing time shown in Table 1. After washing with water, the mixture was filtered and dried, and the components in the solid residue were analyzed. Table 1 shows the results.

Next, water was added to the solid residue obtained above, and the mixture was sufficiently kneaded to obtain a paste-like kneaded product. The obtained kneaded product is granulated into a sphere having a size of about 20 mmφ using a rotary dish granulator, and then 650 ° C., 1 using an electric furnace.
It was fired under the condition of time. The crushed strength, Cl, AlN, and alumina content of the obtained granular fired product were examined. Table 1 shows the results.

[0037]

[Table 1]

As is clear from the test examples and comparative test examples in Table 1, when the acid was added to adjust the pH to 9 or less and washed with water, the solid residue after the solid-liquid separation was reduced. It can be seen that while most of aluminum nitride and metallic aluminum remain, chlorine, sodium and potassium are largely removed and reduced.

When the pH of the cleaning water exceeds 9.0 without controlling the pH, the chlorine content is removed as shown in Comparative Test Example 1, but at the same time, metallic aluminum and aluminum nitride are also removed. It can be seen that it decreases. Furthermore, the fired product of Comparative Test Example 2 obtained by firing at a firing temperature of 650 ° C. in the same manner as in each test example without washing with water contains a large amount of aluminum nitride and chlorine. White smoke was also generated when put on top. Further, in the fired product of Comparative Test Example 3 obtained by firing at 1200 ° C. without washing with water, both the aluminum nitride and the chlorine content were sufficiently reduced, but high-temperature firing at 1200 ° C. was necessary. It indicates that there is.

Example 1 Using aluminum dross residual ash washed, filtered and dried in accordance with Test Example 4, granulation was performed while spraying water in a rotary dish granulator.
Bake for hours. Even when it was fired or poured into molten steel as a slag-making agent for steel, it did not produce white smoke, and was extremely excellent in terms of environment and operation. When the particle size of the calcined product of the rotary kiln was measured, 90% of the calcined particles had a particle size of 5 mm or more.
That was all.

[0041]

According to the method for treating aluminum dross residual ash of the present invention, it is possible to efficiently remove harmful impurities from aluminum dross residual ash and use it as a useful resource, and it is extremely easy to handle in transportation and use. An industrially useful granular, granular, or massive alumina composition having high crushing strength can be obtained.

Continuation of the front page (72) Inventor Masatoshi Nanba 2-2-2, Higashishinagawa, Shinagawa-ku, Tokyo F-term (reference) in Japan Light Metal Co., Ltd. 4D004 AA44 AB05 BA05 CA13 CA14 CA15 CA30 CA35 CA40 CC12 DA03 DA06 DA10

Claims (5)

[Claims] 1. An aluminum dross residual ash which is obtained by recovering metallic aluminum or an aluminum alloy from an aluminum dross generated in an aluminum melting step of dissolving an aluminum raw material comprising aluminum or an aluminum alloy. Aluminum dross residual ash, wherein the slurry obtained by adding washing water to the slurry is adjusted to have a pH of 5 to 9, washed with water, and then solid-liquid separated and calcined to obtain a solid residue. Processing method. 2. The sintering of the solid residue according to claim 1, wherein the solid content residue is kneaded while adjusting the water content to 25 to 50% by weight, and the obtained kneaded product is granulated and fired. Of aluminum dross residual ash. 3. The method for treating aluminum dross residual ash according to claim 1, wherein the pH adjustment at the time of washing the alumidros residual ash with water is performed by adding an acid to the slurry. 4. The method for treating aluminum dross residual ash according to claim 1, wherein the acid for adjusting the pH of the slurry is an organic acid and / or an inorganic acid which disappears by baking. 5. The method for treating aluminum dross residual ash according to claim 1, wherein the calcination temperature is 600 to 1000 ° C.