JP3796819B2 - Detoxification treatment method of aluminum dross - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is able to remove as much and as efficiently as possible aluminum nitride that reacts with water to generate ammonia and cause environmental pollution from aluminum dross generated in the melting process during aluminum refining and alloy casting. The present invention relates to a method for detoxifying aluminum dross.
[0002]
[Prior art]
Aluminum dross (hereinafter simply abbreviated as “dross”) has a different composition depending on the generation source, but metal aluminum ranges from 20 to 80%, aluminum oxide ranges from 10 to 40%, and aluminum nitride ranges from 10 to 10. In the range of 30%, other flux components are contained in the range of several percent. Of these components, metallic aluminum and aluminum oxide are usually in a granular state, and aluminum oxide is usually in a powdery state. In addition, its use is gradually increasing as a deoxidizer and a temperature raising agent for steel.
[0003]
However, when this dross is used for various purposes, unit operations such as pulverization, sieving, storage, etc. are required, but the aluminum nitride contained in the dross during these steps is at room temperature. As it reacts with water to generate ammonia gas, the working environment is easily polluted, and when aluminum carbide or fine metal aluminum is included, acetylene gas or hydrogen gas may be generated. When dross is used for various purposes, its detoxification treatment is required.
[0004]
Regarding the detoxification of aluminum nitride in the dross, in Japanese Patent Application Laid-Open No. 7-51652, the nitrogen component is removed by treating the dross at a temperature of 700 to 1000 ° C. in the presence of carbon dioxide and water vapor. A method of α-aluminaization has been proposed. However, this method has high removal efficiency and is effective for removing chlorine components, but requires a high temperature of at least 700 ° C., consumes a lot of energy, and exists in a high-temperature flux. There is a problem that the maintenance of the kiln lining material is not easy because of the halogen to be remarkably corroded.
[0005]
Japanese Patent Laid-Open No. 4-173930 proposes a method of decomposing aluminum nitride and neutralizing ammonia generated at that time by holding a mixed slurry of dross and water at 80 ° C. or more for 3 hours. Has been. However, in this method, the treatment time is excessive, the ammonia decomposition rate is only about 90%, and the amount of waste liquid discharged from the treatment process is large, so that the equipment cost and waste liquid treatment cost become high. There is a problem.
[0006]
Further, JP-A-2-270920 discloses that dross powder is mixed with a caking additive such as tar, pitch, asphalt and the like, and is agglomerated by pressure molding, encapsulating aluminum nitride which is an ammonia generation source and harmless. It has been proposed to However, in this method, when aggregates are crushed for some reason, aluminum nitride is exposed on the new surface and reacts with water, and there is a concern that ammonia may be generated. For example, there is a problem that it is difficult to apply when recovering aluminum by electrolytic reduction.
[0007]
[Problems to be solved by the invention]
For this reason, in the above prior art, problems still remain in terms of energy cost, equipment cost, amount of waste liquid, lining material deterioration, incomplete harmlessness, etc., and new dross that solves all these problems There is a need to develop a detoxification process.
[0008]
Therefore, the object of the present invention is to decompose and remove aluminum nitride in the dross as much as possible, and the dross treated product obtained by this treatment is, for example, a product when used as a cement auxiliary material. Aluminum dross that has favorable characteristics such as improving the quality of the steel, reducing the cost, and improving the production efficiency of the process when used as an additive in the iron making process. It is to provide a detoxification treatment method.
[0009]
Another object of the present invention is to provide dross-treated products having excellent characteristics as described above with low energy costs, downsizing of equipment, high productivity, reduction of waste liquid amount, or none, and reduction of deterioration of lining materials. Or it is providing the detoxification processing method of the aluminum dross which can be obtained while achieving inequality.
[0010]
[Means for Solving the Problems]
The present invention is basically an aluminum dross detoxification treatment method in which aluminum dross and water are allowed to coexist with milling and stirring to react aluminum nitride in the aluminum dross with water. This dross detoxification treatment method increases the contact efficiency between aluminum nitride contained in this dross and water under grinding and stirring conditions in which the dross is vigorously stirred and finely pulverized. This is characterized in that aluminum nitride is decomposed and removed as completely as possible.
[0011]
The aluminum dross to be detoxified by the method of the present invention is not particularly limited and is recovered from the melting step during refining of aluminum or casting of an alloy, and the composition thereof is the kind of alloy, Although it varies greatly depending on the dross generation process and the treatment method after dross collection, preferably aluminum aluminum contained in the dross is recovered as much as possible, and aluminum nitride in the dross that is an ammonia generation source Should be in a state that is easy to disassemble as much as possible. And for that purpose, for example, when the dross is pulverized, aluminum nitride is easily pulverized more finely than metal aluminum. It is preferable to obtain dross rich in aluminum nitride from the sieve under separation.
[0012]
Specifically, the pulverization and separation method using the difference in the pulverization characteristics between the metal aluminum and the aluminum nitride is, specifically, an ordinary grinding pulverizer such as a ball mill, a pulverizer, a ring roll mill, or a micron mill, or a shear pulverizer. The dross is pulverized to about 100 μm or less, preferably about 50 μm or less using a pulverizer, and the pulverized material of the dross is separated using, for example, a sieve having a mesh size of 16 to 150 mesh. Fractions are collected and used for recycling resources and the like, and dross rich in aluminum oxide, aluminum nitride and the like is collected from under the sieve, and the dross is rendered harmless by the method of the present invention. The smaller the particle size of the dross, the better the reaction rate. However, it is not preferable to finely pulverize the dross to the submicron level because of the high pulverization cost.
[0013]
When the particle size of the dross powder exceeds 100 μm, a thick aluminum hydroxide layer of the reaction product is formed around the unreacted aluminum nitride, the water contact with the aluminum nitride is obstructed, and the reaction rate becomes slow. . In order to prevent this, if the grinding and stirring conditions are strengthened, the stirring power increases, and since dross powder having a particle size exceeding 100 μm contains a relatively large amount of metallic aluminum, it reacts with water. As a result, hydrogen gas is generated and the risk of the reaction system increases, and the loss of useful aluminum content increases. When the dross powder is supplied to the reaction system with a particle size of preferably 50 μm or less, the time required for completion of the reaction is shortened, and the stirring power in the grinding and stirring can be reduced, which is industrially advantageous.
[0014]
The present invention is characterized in that when the aluminum nitride in the aluminum dross is detoxified by reacting with water, the dross and water are allowed to coexist in the reaction system under the conditions of grinding and stirring. Aluminum nitride reacts with water to form an aluminum hydroxide layer on its surface, but its thickness increases with time, and its density increases with temperature. In some cases, the decomposition reaction may be incomplete due to the fact that the aluminum hydroxide layer formed on the surface prevents the aluminum hydroxide layer from contacting the inner aluminum nitride, resulting in an incomplete decomposition reaction. Therefore, the aluminum hydroxide layer formed on the surface of the aluminum nitride is destroyed, and the contact between the aluminum nitride and water is performed efficiently.
[0015]
In the present invention, the state of water coexisting in the reaction system may be liquid or gaseous, and is not particularly limited, but according to experiments by the present inventors. The reaction rate of water is higher when it is in contact with aluminum nitride in the liquid state than in the gaseous state, and moreover, a liquid of about the amount of adhering water adheres around the aluminum nitride or dross particles, and the surrounding state is saturated. The condition in which water vapor close to or near it was the optimum condition in terms of reaction rate.
[0016]
Further, the amount of water used in the reaction system is not particularly limited. However, it is desirable that the amount of water used is minimal in consideration of the problem of waste liquid treatment, and preferably the reaction with aluminum nitride in the dross. It is 2.5-4 times equivalent with respect to an equivalent, More preferably, it exists in the range of 3-3.5 equivalent.
[0017]
That is, with respect to 100 parts by weight of dross used for the reaction, adhering around the dross particles on the part of water W1 of the reaction equivalent necessary for the reaction between aluminum nitride and water in the dross represented by the following reaction formula (1) Water and water necessary for saturating the atmosphere in the reactor W2 = (1.5-3) × W1 Total amount added by weight part WT = W1 + W2 = (2.5-4) × W1 Part by weight of water should be used.
AlN + 3H ₂ O → Al (OH) ₃ + NH ₃ (1)
W1 = 100 * (a / 100) * (3 * 18) /41=1.32a [where a is the AlN content (% by weight) in the dross. ]
[0018]
Thus, the amount of water used for 100 parts by weight of dross is 2.5 to 4 times the theoretical amount W1 parts by weight necessary for decomposing aluminum nitride in the dross. When the amount of water used is less than 2.5 × W1 parts by weight, it becomes difficult for a water film in a liquid state to adhere to the surface of the dross particles, and water vapor and aluminum nitride come into direct contact with each other. The speed is reduced. Also, if the amount of water used exceeds 4 x W1 parts by weight, free water becomes excessive and the reactants adhere to the vessel walls and balls, leading to a decrease in yield and increasing the stickiness of the treated dross. Handling as powder becomes difficult. In addition, when the reaction vessel is an open system, the foamed material in which dross, water, and generated gas are mixed may be ejected from the opening without being reacted. By making the usage-amount of water into the said appropriate range, it can obtain as a powdery substance which is easy to handle a dross processed material with a high decomposition rate, without producing such various troubles.
[0019]
Moreover, although the decomposition reaction of aluminum nitride with water proceeds even at room temperature, the reaction temperature is usually in the range of 60 to 200 ° C., preferably 90 to 200 ° C., more preferably 100 to 150 ° C. in terms of reaction rate. Is good. If the reaction temperature is less than 60 ° C., the reaction rate becomes slow and the reaction apparatus becomes excessive. On the other hand, when the reaction temperature exceeds 200 ° C., the internal pressure of the reaction vessel becomes several tens of atmospheres, and the conditions as a pressure vessel become severe. Although the reaction rate increases as the reaction temperature increases, the above temperature range of 100 to 150 ° C. is industrially preferable as a temperature range in which water and water vapor coexist and the internal pressure of the reaction vessel does not become excessive.
[0020]
The reaction time is governed by the reaction temperature, dross particle size, grinding and stirring conditions, the amount of water used, etc., but is preferably in the range of 15 to 90 minutes. When the reaction time is less than 15 minutes, the reaction between aluminum nitride and water is not completed, and water is absorbed after the treatment and the slow reaction is continued. Even if it exceeds 90 minutes, the increase in the decomposition rate is almost saturated and the productivity is lowered.
[0021]
As a reaction vessel used in the method of the present invention, since the reaction system is subjected to grinding and stirring conditions, it is possible to use a lining with an abrasion-resistant material, and it is necessary to be able to stir while heating the material of the reaction system, (1) A powerful grinding and stirring action can be given to the mixture of dross and water, (2) Heating up to 200 ° C is possible, (3) Raw materials and products remain unreacted outside the system It is necessary to combine the following five conditions: (4) corrosion resistance, wear resistance, and (5) structural strength that can withstand internal pressure.
[0022]
Specifically, it is possible to use an apparatus of a type capable of performing a reaction while applying a strong grinding force to the reaction system material with a stirring medium such as a rolling ball mill, a vibration mill, a retort, a rotary kiln, or a stirring mill. However, a closed rolling ball mill having a heating mechanism is particularly preferable. The reaction vessel preferably has a structure and strength that can withstand an internal pressure corresponding to the saturated water vapor pressure at the reaction temperature, and has a closed structure to prevent the scattering of dross powder and moisture. However, if the reaction vessel has a trapping mechanism that prevents scattered matter from coming out of the rolling ball mill, an open type structure having some openings may be used.
[0023]
Therefore, it is also possible to apply a continuous system when productivity is not sufficient in the batch system, in which case the contents of dross powder, dross foam, product gas, steam mist, etc. react. It is necessary to provide a capture mechanism that does not scatter from the system to the outside, and return the captured products to the reaction system again from the viewpoint of the quality, yield, and environmental measures. In addition, it is necessary to suppress gas leakage so that the vapor-liquid equilibrium corresponding to the treatment temperature is established, that is, the adhering water tends to always exist in the liquid state around the dross powder. This is because, when the opening is excessive, the pressure in the reaction vessel decreases, evaporation of the adhering water occurs, the liquid water film around the dross preferable for promoting the reaction disappears, and the reaction rate decreases.
[0024]
According to the present invention, aluminum dross and water are allowed to coexist under grinding and the aluminum nitride in the dross is reacted with water, so that the aluminum hydroxide layer formed on the surface of the aluminum nitride contacting with water is formed. The aluminum hydroxide layer can be broken or cracked, so that water coexisting in the reaction system can efficiently come into contact with aluminum nitride, and the reaction system does not need to be heated to 700 ° C. or higher. Usually, it can be carried out at a low temperature of 60 to 200 ° C, and in many cases 100 to 150 ° C.
[0025]
In addition, the amount of water used can be sufficiently reacted if the amount of water adhering around the dross particles is maintained, thereby preventing the dross from adhering to the wall and dusting. The reaction mixture after completion of the reaction can be handled in the form of powder and the operation becomes extremely easy, and the waste liquid can be eliminated. Furthermore, the reaction rate is increased as a synergistic effect of the stirring effect and the presence form of water, and aluminum nitride can be efficiently decomposed and removed in a shorter time than before.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
As a reaction vessel, a rolling ball mill made of SUS316 lined with silicon nitride ceramics was used. In this rolling ball mill, 100 parts by weight of dross powder of 100 μm or less, preferably 50 μm or less after pulverizing and separating and recovering metal aluminum And water corresponding to 2.5 to 4 times equivalent of the theoretical amount W1 part by weight required for decomposing aluminum nitride in the dross are added in a uniform mixed state.
[0027]
Here, the volume ratio of the mixture of dross powder and water charged into the rolling ball mill to the volume of the rolling ball mill, that is, the holding amount of the mixture of dross powder and water in the rolling ball mill (hold up) The higher the productivity, the higher the productivity, but the reaction rate becomes maximum when the pulverization efficiency and the stirring efficiency as the rolling ball mill are the optimum holding amount, so the rolling ball mill operates as a pulverizer. A holding amount in the range of 15 to 40% (volume ratio) of the internal volume, which is an appropriate range at the time, is preferable. Here, if the volume ratio of the mixture of dross powder and water introduced into the rolling ball mill is lower than 15%, there arises a problem that the productivity is lowered, and if it exceeds 40%, the decomposition rate of aluminum nitride is reduced. There is a possibility that a problem of reduction occurs.
[0028]
Further, the rolling balls thrown into the rolling ball mill are preferably in the range of 15 to 50% by volume ratio. If the volume ratio of the rolling balls to be put into the rolling ball mill is lower than 15%, the grinding efficiency is low and the decomposition rate is lowered, and if it exceeds 50%, the rolling does not contribute to the grinding. On the contrary, the amount of balls increases, so that the grinding efficiency is lowered and the decomposition rate is lowered.
[0029]
The rolling ball used as the stirring medium needs to be a wear-resistant material that is stable against water and water vapor up to 200 ° C., and preferably a cobblestone or alumina material.
[0030]
In addition, the rotational speed of the rolling ball mill may be an appropriate value when used as a pulverizer, but it is preferable to select as high a speed as possible below the critical speed, and the rotational speed is within an appropriate range commonly used as a pulverizer. The critical rotational speed may be 65 to 80%. Below the lower limit, the stirring effect is reduced and the reaction rate is reduced. On the other hand, when the upper limit is exceeded, the dross and the ball are pressure-bonded to the vessel wall, so that the stirring effect does not appear and the reaction rate decreases.
[0031]
Furthermore, since it is difficult to directly measure the temperature of the dross powder with respect to the reaction temperature, the atmosphere temperature is 100 to 200 ° C., and the reaction time is 15 to 90 minutes. Good.
[0032]
【Example】
Hereinafter, based on an Example and a comparative example, this invention is demonstrated more concretely.
[0033]
[Example 1]
10 kg of dross is crushed by using an air-flow type pulverizer, the metal aluminum content and dross powder such as aluminum oxide, aluminum nitride, etc. are separated from the mixed state, and then the 1 mm sieve is applied to the metal rich material on the sieve Was recovered and returned to a melting furnace for producing a new lump, and the dross pulverized product under the sieve was further passed through a 44 μm sieve, and the sieve was used as a sample.
[0034]
As shown in FIGS. 1 and 2, as shown in FIGS. 1 and 2, a reaction vessel cylinder 1 made of SUS316 having an internal dimension φ164 mm × 164 mm and having a silicon nitride ceramic lining 2 and a SUS316 made of silicon nitride ceramic lining 5 is used. 4, a porous ceramic plate 6 as a filter body (used in Example 7), and an alumina ball 7 having a diameter of 20 mm inserted in the reaction vessel cylinder 1. The external electric heater 3, the thermoelectric A rolling ball mill provided with a protective tube 8, a roller 9, a mount 10 and a thermocouple 13 was used.
[0035]
In this rolling hole mill, 2000 g of the alumina ball 7, 30 g of the test dross 11, and 30 g of water 12 corresponding to 3 times the reaction equivalent of aluminum nitride in the dross were respectively sealed and sealed. The mixture was heated to 120 ° C. by electric heating, rotated at 65 rpm, and reacted for 60 minutes while stirring and stirring.
[0036]
After completion of the reaction, the aluminum nitride content in the dross after cooling and detoxification treatment was quantified, and the decomposition rate with respect to the aluminum nitride content before the detoxification treatment and the adhering moisture of the obtained dross treated product were determined. As a result, the decomposition rate of aluminum nitride was 93%, the moisture content of the treated dross was 12%, and no ammonia odor was felt in the treated dross. In addition, the dross-treated product was in a state that can be handled as a powder, and adhesion to the wall surface of the ball mill was very small.
[0037]
[Example 2]
The dross detoxification treatment was performed in the same manner as in Example 1 except that the reaction temperature was 200 ° C. and the reaction time was 40 minutes. As a result, the decomposition rate of aluminum nitride was 93%, the moisture content of the treated dross was 10%, and no ammonia odor was felt in the treated dross. In addition, the dross-treated product was in a state that can be handled as a powder, and adhesion to the wall surface of the ball mill was very small.
[0038]
[Example 3]
The dross detoxification treatment was performed in the same manner as in Example 1 except that the reaction temperature was 90 ° C. and the reaction time was 90 minutes. As a result, the decomposition rate of aluminum nitride was 80%, the moisture content of the treated dross was 16%, and no ammonia odor was felt in the treated dross. In addition, the dross-treated product is in a state that can be handled as a powder, the adhesion to the wall surface of the ball mill is small, and no waste liquid is generated.
[0039]
[Example 4]
The dross detoxification treatment was performed in the same manner as in Example 1 except that the particle size of the test dross was 105 μm or less. As a result, the decomposition rate of aluminum nitride was 81%, the moisture content of the treated dross was 13%, and no ammonia odor was felt on the treated dross. In addition, the dross-treated product was in a state where it could be handled as a powder, there was almost no adhesion to the wall surface of the ball mill, and no waste liquid was generated.
[0040]
[Example 5]
The dross detoxification treatment was carried out in the same manner as in Example 1 except that a porous ceramic plate was disposed as a heat-resistant and wear-resistant filter on part of the lid on the outlet side of the ball mill. As a result, the decomposition rate of aluminum nitride was 83%, the moisture content of the treated dross was 10%, and no ammonia odor was felt on the treated dross. Further, the treated dross was in a state that can be handled as powder, there was almost no adhesion to the wall surface of the ball mill, no waste liquid was generated, and there was little scattering of the dross outside the mill.
[0041]
[Example 6]
The dross detoxification treatment was performed in the same manner as in Example 1 except that the reaction temperature was 80 ° C. As a result, the decomposition rate of aluminum nitride was 64%, the adhered moisture of the treated dross was 16%, and a slight ammonia odor was felt in the treated dross. In addition, the dross-treated product was in a state where it could be handled as a powder, there was almost no adhesion to the wall surface of the ball mill, and no waste liquid was generated.
[0042]
[Comparative Example 1]
30 g of the test dross and 30 g of water corresponding to three times the reaction equivalent to aluminum nitride in the dross were put into a vertical inner cylinder container, and a propeller type stirrer was inserted and stirred at 100 rpm, The reaction was allowed to proceed for 60 minutes. The lid was not completely sealed and was partially open to the atmosphere. As a result, the decomposition rate of aluminum nitride was 28%, the dross-treated product was 4% of adhered powder, and the ammonia odor remained.
[0043]
[Comparative Example 2]
30 g of the test dross and 120 g of water corresponding to 12 times the reaction equivalent of aluminum nitride in the dross were charged into the autoclave and reacted at 200 ° C. for 60 minutes with propeller stirring at 250 rpm. The container was sealed. As a result, the decomposition rate of aluminum nitride was 80%, and the ammonia odor of the dross treated product remained somewhat. The internal pressure of the reaction vessel was as high as 17 atm. Further, the amount of waste liquid after the treatment was as large as 100 g or more.
[0044]
[Comparative Example 3]
The dross detoxification treatment was performed in the same manner as in Example 1 except that the amount of water used was 45 g corresponding to 4.5 times the reaction equivalent to aluminum nitride in the dross with respect to 30 g of the test dross. went. As a result, the decomposition rate of aluminum nitride was 90%, the moisture content of the treated dross was 16%, and no ammonia odor was felt on the treated dross. The dross-treated product was in a state where it could be handled as a powder, and the adhesion to the wall surface of the ball mill was slightly increased as compared with Example 1, and there was no generation of waste liquid.
[0045]
[Comparative Example 4]
The dross detoxification treatment was performed in the same manner as in Example 1 except that the amount of water used was 5 times the reaction equivalent with aluminum nitride in the dross. As a result, the decomposition rate of aluminum nitride was 60%, the moisture content of the dross-treated product was 18%, and no ammonia odor was felt on this treated dross product. Further, this dross treated product was slightly inferior in handling property as a powder, hardly adhered to the wall surface of the ball mill, and there was no generation of waste liquid.
[0046]
[Comparative Example 5]
The dross is the same as in Example 1 except that the amount of water used is 5 times the reaction equivalent of aluminum nitride in the dross and that the ball mill lid is opened with a small hole of φ10 mm. Was detoxified. As a result, the decomposition rate of aluminum nitride was 52%, the moisture content of the treated dross was 12%, and no ammonia odor was felt on the treated dross. Further, this dross treated product was slightly inferior in handling property as a powder, hardly adhered to the wall surface of the ball mill, and there was no generation of waste liquid.
[0047]
【The invention's effect】
According to the present invention, compared with the dross detoxification treatment method in which the aluminum nitride in the dross has been decomposed over a long period of time of 3 hours or more at a high temperature of 700 ° C. or higher or in water at 80 ° C. The dross can be detoxified at a low temperature of about 60 to 200 ° C. in a short time of about 60 minutes and with almost no waste liquid.
[0048]
In addition, the dross-treated product obtained by the detoxification treatment of the present invention has a reduced aluminum nitride as a barrier during electrolytic reduction as much as possible, so that it is only possible to recycle high value as a new aluminum ingot. In addition, it can be used as a secondary material or process additive for steel and cement.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a rolling ball mill used in an embodiment of the present invention.
FIG. 2 is a cross-sectional explanatory view of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Reaction container cylinder, 2, 5 ... Silicon nitride ceramic lining, 3 ... External electric heater, 4 ... Cover, 6 ... Porous ceramic board, 7 ... Alumina ball, 8 ... Thermocouple protective tube, 9 ... Roller, 10 ... frame, 11 ... test dross, 12 ... water, 13 ... thermocouple.

Claims (3)

In a reaction system in which aluminum dross and water coexist with stirring under stirring to react aluminum nitride in the aluminum dross with water, 3 to 3.5 times equivalent to the reaction equivalent with aluminum nitride in aluminum dross A method of detoxifying aluminum dross, characterized by coexisting water so that liquid water and gaseous water coexist.   The method for detoxifying aluminum dross according to claim 1, wherein the reaction temperature is in the range of 90 to 200 ° C.   3. The aluminum dross detoxification according to claim 1 or 2, wherein the agitation is performed by rolling a number of corrosion-resistant and wear-resistant balls existing in a proportion of 15 to 50% of the volume in the reaction system. Processing method.

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