JPH07268503A - Method for stabilizing aluminum dross - Google Patents

Abstract

PURPOSE:To stabilize aluminum dross, to facilitate handling and storing of the aluminum dross and to effectively utilize the aluminum dross by adding a specific amt. of water to the aluminum dross and mixing and stirring both, then holding the mixture and evaporating the added water by the heat of hydrolysis. CONSTITUTION:The water is added at 5 to 50wt.% to the aluminum dross in the form of fine powder recovered in primary and secondary refining process of aluminum and both are mixed and stirred by a mixer. The aluminum dross is thereafter held in a vessel where the added water is evaporated by the generation of heat according to the hydrolysis. Combustible gases contg. the harmful gases generated in part thereof at this time are preferably captured and burned. The stabilized aluminum hydroxide is formed by the hydrolysis. Particles of unreacted metal aluminum, aluminum nitride, magnesium silicate, etc., are stabilized as dense protective films.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a dross generated in a primary refining process of aluminum and a dross generated in a secondary refining process of aluminum (a melting process of aluminum scrap) (hereinafter, the former is referred to as a primary recovery dross, and the latter is referred to as a latter). Hereinafter, sometimes referred to as secondary recovery dross; both are simply referred to as aluminum dross).

[0002]

2. Description of the Related Art In addition to unrecovered metallic aluminum, aluminum oxide, aluminum chloride, potassium chloride, etc. derived from flux components are contained in finely powdered aluminum dross; aluminum nitride produced in the dissolution process, It contains intermetallic compounds, magnesium silicide, and other oxides, and the composition thereof also varies within a considerable range depending on the source.

It is known that such aluminum dross undergoes a vigorous hydrolysis reaction when brought into contact with water. For example, upon contact with rainwater at the stage of transportation, storage, etc., metallic aluminum is hydrolyzed to generate intense heat, and at the same time releases hydrogen gas. Further, aluminum nitride is also hydrolyzed to generate heat and generate ammonia gas. further,
Magnesium silicide is also hydrolyzed to generate highly toxic silane gas. The gases generated at this time are all flammable, and hydrogen gas and silane gas, especially silane gas, have a wide explosion limit and are extremely dangerous. For this reason,
Conventionally, during handling of aluminum dross or after landfill,
Explosion accidents occur repeatedly.

Conventionally, a part of aluminum dross has been used as it is as a heat retaining agent and a deoxidizing material for steel refining.
Most of it is dispersed in a large excess of water and is
After completing hydrolysis for about a week, it is landfilled with a large amount of water. This method requires a large amount of water and a long time, and the harmful gas generated at the time of decomposition is directly discharged to the atmosphere without being treated. In some cases, the harmful gas killed plants near the treatment plant. Also, securing land for landfill is becoming increasingly difficult. Therefore, the implementation of this method is expected to be subject to various restrictions in the future.

Further, while adding an appropriate amount of water to the aluminum dross to form a granular or lumpy form of about several cm, the gas generated at this time is collected and burned, and then again in the presence of an excessive amount of water for a long time. There is also a method of landfilling after hydrolyzing. However, according to this method, when the soil is acidified, for example, by acid rain after the landfill treatment, aluminum ions are eluted from the aluminum dross into the soil, which causes environmental problems such as death of trees. There is a nature.

[0006]

SUMMARY OF THE INVENTION Accordingly, the main object of the present invention is to stabilize chemically very active aluminum dross, thereby facilitating its handling and storage and effectively utilizing it. And

[0007]

In view of the above-mentioned problems of the prior art, the inventor of the present invention added water at a specific ratio to aluminum dross in a container in the course of research and after stirring. In the case of holding until the water evaporates due to the heat generated by hydrolysis, it is quite unexpected that the hydrolysis reaction proceeds gently and a chemically highly stable granular solid is obtained. I found it.

That is, the present invention provides the following method for stabilizing aluminum dross: Stabilization of aluminum dross by adding 5 to 50% by weight of water to aluminum dross in a container, mixing and stirring, and holding the aluminum dross until the added water evaporates due to the heat generated by hydrolysis. Method.

2. The method for stabilizing aluminum dross according to item 1, wherein 10 to 40% by weight of water is added to the almidros.

The objects of the method of the present invention are the primary recovered dross generated in the primary refining of aluminum (so-called insoluble aluminum residual ash) and the secondary recovered dross generated in the secondary refining of recovered aluminum. These aluminum dross are fine powder (about several to 100 μm)
Takes the form of. Representative examples of the composition of such primary recovery dross and secondary recovery dross are as follows.

[0011]

[Table 1]

The numerical values in Table 1 are% by weight.

In the present invention, the aluminum dross as described above is housed in a container, water corresponding to 10 to 50% (more preferably 15 to 40%) of its weight is added, and mixed by stirring. If the amount of water added is too small, the hydroxide film will not be sufficiently formed due to hydrolysis, and thus unreacted particles of metallic aluminum, aluminum nitride, magnesium silicide, etc. in the aluminum dross will not be sufficiently protected. On the other hand, if too much water is added,
Due to the evaporation of a large amount of water, the heat of reaction is taken away and the temperature does not rise sufficiently, so the hydroxide film produced is not dense and stable, and also unreacted metallic aluminum, nitriding Particles of aluminum, magnesium silicide, etc. are not sufficiently protected.

Shortly after the start of stirring, the hydrolysis reaction starts and gas is generated as the temperature rises. Due to this temperature rise, the hydrolysis reaction becomes more active, but when the temperature of the reaction system exceeds 100 ° C., the added water evaporates and the hydrolysis reaction stops. During this hydrolysis reaction, flammable gas (hydrogen,
(Ammonia, silane, etc.) is generated, so it is preferable to collect this and burn it to render it harmless.

The main reactions in the method of the present invention are as follows.

Al + 3H ₂ O → Al (OH) ₃ + 3 / 2H ₂ AlN + 3H ₂ O → Al (OH) ₃ + NH ₃ Mg ₂ Si + 4H ₂ O + 2Mg (OH) ₂ + SiH ₄ The temperature, heat generation duration, etc. differ depending on the composition and amount of aluminum dross, the proportion of water added, the stirring and mixing state of water and dross, the environmental temperature, etc., but the progress of the hydrolysis reaction as a whole is substantially There is no significant difference.

According to the analysis of the product after the completion of the reaction, the surfaces of the aluminum metal particles and the aluminum nitride particles are covered with aluminum hydroxide produced by the hydrolysis reaction, and the surfaces of the magnesium silicide particles are It was confirmed that it was covered with magnesium hydroxide produced by hydrolysis.

In one example of the hydrolysis reaction according to the present invention, the maximum temperature reached when 100 g of secondary recovered dross is mixed with 15 g of water is 150 ° C., and 450 g of water is mixed with 3 kg of secondary recovered dross. The highest temperature reached was 164 ° C.

Most of the aluminum dross is oxides and flux components that do not contribute to the exothermic reaction. The exothermic reaction is caused by metallic aluminum, aluminum nitride,
It is the surface of particles such as magnesium silicide, and it is considered that the surface temperature of these particles has reached a much higher temperature from a microscopic point of view. Therefore, the aluminum hydroxide formed on the surface of the particles as described above is stabilized by heating and is present in the form of boehmite, unlike aluminum hydroxide formed in an aqueous solution. it is conceivable that. Similarly, it is considered that magnesium silicide is in a stable state by heating.

As a result, aluminum dross particles (particle size 0.2 to 0.2) which have undergone the hydrolysis reaction in the presence of the above-mentioned specific amount of water.
(About 2 mm) has lost its original activity, and no longer undergoes a hydrolysis reaction even when it comes into contact with water again. Therefore,
Aluminum dross particles stabilized in this way sufficiently withstand normal storage, transportation, granulation, etc., and cause explosive hydrolysis reaction due to contact with moisture, intense heat generation, outflow of harmful metal ions, etc. Nothing. Therefore, even if the aluminum dross thus stabilized is used for landfilling, it does not cause pollution problems.

Further, the aluminum dross particles stabilized by the method of the present invention exhibit a unique function as a slag dusting inhibitor in iron and steel refining and are therefore extremely useful.
That is, when the stabilized or modified aluminum dross particles obtained in the present invention are added to, for example, a molten reducing slag produced in an electrolytic furnace, the electric furnace reducing slag after cooling is about 10 c.
It becomes a lump of about m and is extremely easy to handle.

On the other hand, when aluminum dross itself in the form of fine powder is added as a dusting inhibitor to the electric furnace reducing slag in a molten state in the same manner as in the conventional case, the dross rises up during the addition and the working environment is significantly deteriorated. Let Further, in this case, the electric furnace reducing slag after cooling collapses into powder and becomes difficult to handle.

[0023]

According to the present invention, active aluminum dross can be stabilized or modified by a simple method.

The obtained aluminum dross particles are chemically extremely stable, and even when they are subjected to landfill treatment,
It does not cause problems such as explosion, heat generation, generation of harmful gas, or elution of aluminum ions.

Further, the stabilized or modified aluminum dross particles obtained by the method of the present invention are extremely useful as a dusting inhibitor for electric furnace reducing slag.

When the stabilized aluminum dross particles obtained by the method of the present invention are used as a deoxidizing material for electric furnace reducing slag, a lump slag is obtained. This massive slag is useful as, for example, an aggregate for civil engineering and construction.

[0027]

EXAMPLES Examples will be shown below to further clarify the features of the present invention.

Example 1 100 g of secondary recovered dross having the composition shown in Table 1 was put into a household mixer, while rotating at 3600 rpm,
A predetermined amount of water was dropped. After the addition of water was completed, the rotary stirring by the mixer was continued for about 1 minute. Then, transfer the obtained mixture to a beaker provided with one opening for degassing, insert a thermocouple so that it reaches the center of the mixture,
The electromotive force of the thermocouple was taken into a personal computer, and the change in temperature with time was recorded.

FIG. 1 shows the relationship between the proportion of water added (% by weight) to the secondary recovered dross and the maximum temperature reached during the hydrolysis reaction.
Shown in.

FIG. 2 shows the water addition ratio (% by weight) to the secondary recovered dross and the temperature change with time during holding. For simplification, FIG. 2 shows only the temperature change in the vicinity of the maximum reached temperature during holding.

Further, Table 2 shows the relationship between the water addition ratio and the residual water content of the reaction product after cooling and the presence or absence of odor in each reaction product. In addition, the numerical value in Table 2 shows weight%.

[0032]

[Table 2]

Example 2 20% of the sample weight of water was added to each of the 6 types of samples that had undergone the hydrolysis reaction in the same manner as in Example 1, and the mixture was mixed and stirred in a mixer, and then the same as in Example 1. The temperature was maintained and the change in the temperature with time was examined. At room temperature, no temperature change was observed in any of the samples during mixing and stirring and during the holding period.

Then, 20% of water was mixed with each of the 6 kinds of samples which had undergone the hydrolysis reaction in the same manner as in Example 1, and after stirring and holding at 50 ° C., the initial amount of water added was 5%.
%, A temperature rise of about 6 ° C. was observed only in the sample, but no temperature change was observed in the other samples.

From these results, it is clear that the aluminum dross treated by the method of the present invention is extremely stable.

Example 3 20% of the sample weight of water was added to each of the 6 types of samples that had undergone the hydrolysis reaction in the same manner as in Example 1, and the mixture was mixed and stirred with a mixer and then heated to 50 ° C. It was held in a glass bottle with a stopper, and the tip of the glass tube passed through the rubber stopper was immersed in water in a beaker to observe whether or not gas was generated.

A small amount of gas was observed only in the sample in which the initial amount of water added was 5%, but no gas was observed in the other samples.

From these results, it is clear that the aluminum dross treated by the method of the present invention is extremely stable.

Example 4 3500 kg of secondary recovered dross having the composition shown in Table 1 was placed in a mixer and 4500 cc of water was added dropwise while rotating. After the addition of water was completed, the rotary stirring by the mixer was continued for about 1 minute. Next, the obtained mixture was transferred to a beaker provided with one opening for degassing, the thermocouple was inserted so that it reached the center of the mixture, the electromotive force of the thermocouple was taken into a personal computer, and the temperature was aged. The change was recorded.

As a result, a rapid exotherm started at 38 ° C., and the maximum temperature (164 ° C.) was reached after 18 minutes.

Water was added to the obtained reaction product in the range of 5 to 50% by weight, and the mixture was stirred and mixed, and then held, but no heat generation was observed.

Example 5 10 kg of secondary recovered dross having the composition shown in Table 1 was placed in a mixing granulator, and 1.8 l of water was added to granulate to obtain granules having an average particle diameter of 0.3 mm. . In the process of this granulation,
A temperature rise and gas evolution were observed. The water content of the granule was zero.

When water was added to the obtained granules and the mixture was kept at 50 ° C., neither temperature rise nor gas generation was observed.

Example 6 19 kg of aluminum dross granulated in the same manner as in Example 5 was placed in a steel slag pot (Noro bucket), and 0.5 tons of molten electric furnace reducing slag was poured into this.

As a result, a lump-shaped electric furnace reducing slag having a crushed size of about 5 to 15 cm was obtained.

This massive slag is composed of 2CaO.SiO ₂
Since it is a main component, is chemically stable and has excellent mechanical strength, it can be further crushed to an appropriate size and used as an aggregate for civil engineering or construction if necessary.

Comparative Example 1 The same operation as in Example 6 was carried out except that non-granulated fine powder aluminum dross was used as the deoxidizing material. During operation, fine dross flew up and deteriorated the working environment.

Further, the obtained electric furnace reducing slag is pulverized and disintegrated, and is difficult to handle.
It was virtually impossible.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the proportion of water added (% by weight) to the secondary recovered dross and the maximum temperature reached during the hydrolysis reaction.

FIG. 2 is a graph showing a water addition ratio (% by weight) with respect to secondary recovered dross, and a temperature change state with time during a hydrolysis reaction and during subsequent holding.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yasuhiro Hatano 3-33-2 Miharadai, Sakai City, Osaka Prefecture (72) Inventor Kiyoshi Yamazaki 3-7-22-409 Shonai-cho, Toyonaka City, Osaka Prefecture (72) Inventor Ryozo Tanaka 28-7-201 Minami-tsuki, Suita-shi, Osaka Prefecture

Claims (2)

[Claims] 1. A feature of adding 5 to 50% by weight of water to aluminum dross in a container, mixing and stirring, and holding the aluminum dross until the added water evaporates due to heat generated by hydrolysis. A method for stabilizing almidross. 2. The method for stabilizing aluminum dross according to claim 1, wherein 10 to 40% by weight of water is added to the aluminum dross.