JP2000247701A - Production of artificial lightweight aggregate and artificial aggregate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an artificial lightweight aggregate having sufficient characteristics as materials for civil engineering and construction, a bone-dry specific gravity of 1.0-1.5 g/cm3, an uniaxial compression breaking load of >=30 kgf and water absorption of <=5% and to provide a method for simply producing the same at a low cost from burned ash as a principal raw material. SOLUTION: When producing artificial lightweight aggregate by mixing refuse burned ash with a binder, a foaming agent, a reducing agent, and coal ash as a composition controlling agent, by crushing the mixture and adding water to the crushed product to mold a molded product and, if needed, by drying the molded product and baking it, this method can control the composition of the final product of the artificial lightweight aggregate so as for its calcium content to be <=16 wt.% in terms of oxides. The foaming agent is preferably iron oxide and/or silicon carbide and the reducing agent is preferably a carbon material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial lightweight aggregate for civil engineering and construction mainly using refuse incineration ash generated from a refuse incineration facility or the like, and a method for producing the same.

[0002]

2. Description of the Related Art Waste incineration ash generated from waste incineration facilities includes main ash, which is incineration residue, and fly ash collected from exhaust gas, and most of them are landfilled as waste. Since fly ash contains heavy metals such as lead and cadmium, it is treated to prevent leaching of heavy metals by melt solidification, cement solidification, chelate treatment, or acid washing, and is rendered harmless. ing.

However, the melting and solidification method has a high processing cost,
Other methods have the problem of lack of long-term reliability.In addition, many municipalities are struggling to secure final disposal sites and extend the remaining years, so fly ash is not recycled as waste but as recycled. The development of technology for effective use is expected.

As one of the methods, the present inventors have previously described:
Using fly ash as a main raw material, a binder, a silica sand, a composition controlling agent such as pottery stone and feldspar, a foaming agent such as hematite and silicon carbide, and a reducing agent such as coke are added, and pelletized.
By firing the obtained pellets in a rotary kiln, a method for producing an artificial lightweight aggregate for civil engineering and construction with a small amount of heavy metal elution was found, and this technique was disclosed in JP-A-10-287675.
Issue.

[0005] According to this method, fly ash can be effectively used as artificial lightweight aggregate and can contribute to the extension of the remaining years of the final disposal site. Since it varies greatly depending on the situation and the like, it is necessary to control the composition with additives in order to produce a desired aggregate according to the application. From such a viewpoint, the present inventors further describe a technique for adding a composition control agent to the present invention by Japanese Patent Application No. 10-360909.
However, a detailed study on a production method using a less expensive composition control agent was required.

[0006]

However, it has been pointed out that the thus produced artificial lightweight aggregate has high water absorption and is not always sufficient as a civil engineering / building material. Therefore, the present invention provides an artificial lightweight skeleton having a bone-dry specific gravity of 1.0 to 1.5 g / cm ³ , a uniaxial compression breaking load of 30 kgf or more, and a water absorption of 5% or less, and incineration ash using this as a main raw material. It is an object of the present invention to provide a cheaper and simpler manufacturing method.

[0007]

Means for Solving the Problems The present inventors have increased the effective utilization rate of the above incinerated ash, and have an absolute dry specific gravity of 1.0 to 1.5 g / c.
As a result of intensive studies to obtain an aggregate having a high strength and a low water absorption at m ³ , it was found that the above problem could be solved by adding a certain amount of coal ash as an agent for controlling the composition of the aggregate. The present invention has been completed.

That is, the first aspect of the present invention which achieves the above object is to mix a waste incineration ash with a binder, a foaming agent, a reducing agent and coal ash as a composition controlling agent, and pulverize the resulting mixture. Then, water is added to the pulverized material, and the molded body is dried, if necessary, and then fired to obtain an artificial lightweight aggregate. Is a method for producing an artificial lightweight aggregate in which the composition is controlled to be 16% by weight or less in terms of oxide. Preferably, iron oxide and / or silicon carbide is used as the foaming agent, and carbonaceous material is used as the reducing agent.

The second invention is an artificial lightweight aggregate obtained by the first invention, and has an absolute dry specific gravity of 1.0 to 1.0.
It is characterized by an artificial lightweight aggregate having 5 g / cm ³ , a uniaxial compressive breaking load of 30 kgf or more, and a water absorption of 5% or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be more specifically described below. The main components such as clay and shale, which are the raw materials of general artificial lightweight aggregate, are silica, alumina, calcia, and the like, and the components of fly ash are almost the same. Then, in order to impart mechanical strength to the artificial lightweight aggregate, the inside of the pellet may be made into a semi-molten state at the time of firing and vitrified, and in order to reduce the weight, the inside is melted, and a suitable viscosity reduction and At the same time, air bubbles due to volatile components may be captured inside. Specific gravity control can be performed by adjusting such a foaming state.

However, incineration ash generated from refuse incineration facilities and the like has different chemical and physical properties depending on the incineration facilities, combustion products, operating conditions, and the like, and is incomparable with natural minerals that are raw materials for general artificial lightweight aggregates. Therefore, since the content of silica, alumina, and the like is low, it is difficult to vitrify the inside of the pellet in a semi-molten state and to impart mechanical strength.

According to the present invention, a binder, a foaming agent, a reducing agent and a composition controlling agent are added to the refuse incineration ash to obtain pellets, which are fired to obtain an artificial lightweight aggregate. By using ash, the absolute dry specific gravity is 1.0 to 1.0
An artificial lightweight aggregate having 1.5 g / cm ³ , a uniaxial compressive breaking load (hereinafter, referred to as “crush strength”) of 30 kgf or more, and a water absorption of 5% or less can be produced.

[0013] The incineration ash that is the subject of the present invention is not particularly limited, and main ash, fly ash, or a mixture thereof can be used. Also, it is not particularly affected by the particle size of the incinerated ash. Although coal ash is used as a composition control agent, silica in the coal ash contributes to vitrification at the time of firing, and increases the mechanical strength of the aggregate. Therefore, the amount of coal ash to be added may be appropriately selected so as to obtain required physical properties according to the use of the aggregate, but in order to obtain an aggregate having an absolute dry specific gravity of 1.0 to 1.5 g / cm ^3. It is preferable to add coal ash so that the calcium content of the aggregate obtained by firing is 16% by weight or less in terms of oxide. If it exceeds 16% by weight, the optimum firing temperature range becomes high and the temperature range in which firing can be performed becomes narrow.

The coal ash is not particularly limited as long as it is generated from a thermal power plant or a coal-fired boiler. For example, the raw powder is a mixture of fly ash and synda ash, and fly ash conforming to JISA6201. All coal ash can be used, including coal, coarse powder and clinker ash. Also, the particle size of the coal ash is not particularly limited. Certain types of coal ash include unburned carbon. However, when such coal is used, the carbon exhibits a function as a reducing agent to be described later.
There is an advantage that it is not necessary to newly add a reducing agent depending on the amount of bon.

The reason for using the binder in the present invention is to add the moldability and mechanical strength of the pellets after the hydration granulation. If the mechanical strength is weak, during firing in a rotary kiln, pellets will be powdered and the product yield will be reduced, and powdered materials will adhere to the pellet surface near the firing zone,
Alternatively, they adhere to the inner wall of the rotary kiln and hinder continuous operation. The type of the binder is not particularly limited, and examples thereof include inorganics such as bentonite and water glass, and organics such as starch, molasses, lignin, polyvinyl alcohol, methylcellulose, and natural rubber pulp waste liquid. The amount of addition is not particularly limited, but is preferably in the range of 0.5 to 10% by weight in consideration of the effect of addition and cost.

The foaming agent and the reducing agent are used to generate gas by the action of the foaming agent and the reducing agent when the inside of the pellets becomes semi-molten during firing. The generated gas is captured as bubbles in the pellet, and the specific gravity of the aggregate is determined by the amount of the generated gas. That is, the specific gravity is adjusted by the amount of captured bubbles.

The foaming agent and the reducing agent are not particularly limited as long as they exhibit such effects. In the present invention, the foaming agent is preferably iron oxide or silicon carbide, and the reducing agent is preferably carbonaceous material. Hematite having a high degree of oxidation is particularly preferable as iron oxide used as a foaming agent. The particle size of the iron oxide used as the foaming agent is not particularly limited, but is 10 μm to promote the deoxidation reaction by the carbonaceous material during firing.
It is preferable to set the following. The preferred amount of hematite added is 1 to 10% by weight based on the total amount of the aggregate-mixed raw material. The reason is that if it is less than 1% by weight, the effect as a foaming agent is small, and if it exceeds 10% by weight, the effect of lightening by foaming does not increase.

When the granulated pellets generate a large amount of liquid phase by heating, silicon carbide efficiently reacts with iron oxide to generate CO and CO ₂ gas. These gases are trapped in the liquid phase to promote foam swelling of the pellets. The amount of silicon carbide to be added to the whole of the aggregate compounding raw material is 0.1-1.
It is preferably 0% by weight. If the content is less than 0.1% by weight, the effect of reducing the absolute dry specific gravity is not sufficient.
This is because even if it exceeds 0% by weight, the light weight effect does not increase.

The carbon material as a reducing agent mainly serves to adjust the degree of reduction inside the pellets during firing. Although the effect is small, it reacts with iron oxide and contributes to the foaming action. Examples of the carbon material include coal and coke. Note that a part of silicon carbide can be replaced with a carbon material.

It is preferable that the amount of the carbonaceous material to be added to the whole raw material of the aggregate is 0.2 to 10% by weight. 0.2
If the amount is less than 10% by weight, the effect of reducing the weight by foaming cannot be obtained. On the other hand, if the amount exceeds 10% by weight, the effect of reducing the weight by foaming expansion does not increase, and unburned carbonaceous material remains inside the pellet. As a result, the strength of the artificial lightweight aggregate may be reduced.

The method of pulverizing the mixture obtained by mixing the respective raw materials is not particularly limited as long as the mixed aggregate-mixed raw material can be finely pulverized to an average particle diameter of 20 μm or less, preferably 15 μm or less. And ball mills such as planetary mills, collision type jet pulverizers and turbo pulverizers.

Next, the obtained pulverized product is wet-kneaded as necessary, but the kneading method to be employed is not particularly limited, and a known kneading apparatus can be used. Also, as a molding method,
What is necessary is just to be able to mold to a predetermined diameter, and for example, it is convenient to use a pan pelletizer or an extruder.

Next, the obtained molded product is fired after drying if necessary, but the firing method is not particularly limited. For example, in consideration of continuous operation and uniformity of quality, it is preferable to use a rotary kiln. The atmosphere can be arbitrarily selected according to the physical properties of the aggregate. For example, the oxygen concentration in the combustion gas is 3 to 12%, and the firing zone temperature is 1000 to 130%.
0 ° C., the residence time of the molded body at the firing zone temperature is 10 to 1
It is preferable to perform a rotary kiln operation in consideration of a kiln structure such as a kiln gradient, a rotation speed, a dam installation, and an inner diameter so as to be 20 minutes. In addition, the drying method applied as needed before firing is not particularly limited.

[0024]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. However, the present invention is not limited to the following examples. The main components of the used refuse incineration fly ash were SiO ₂ : 27.36% by weight and Al ₂ O ₃ : 1
3.00 wt%, Fe ₂ O _3: 1.51 wt%, CaO:
15.70% by weight, MgO: 3.31% by weight, Na
₂ O: 8.70% by weight, K ₂ O: 7.39% by weight. The main components of the coal ash used as the composition control agent were: SiO ₂ : 56.2% by weight, Al ₂ O ₃ : 32.1% by weight, Fe ₂ O ₃ : 3.57% by weight, CaO: 0. 59 wt%, MgO: 1.40 wt%, Na ₂ O: 0.22 wt%, K ₂ O: 0.48 wt%.

Example 1 47.5% by weight of incinerated fly ash, 5% by weight of bentonite, 5% by weight of hematite, coke 2
Wt%, silicon carbide 0.5 wt% and coal ash 40 wt%
Was mixed and ground to an average particle size of 15 μm using a ball mill. While adding water to the pulverized product, the mixture was granulated into a spherical shape having a diameter of about 5 to 15 mm using a pan pelletizer, and then dried at 105 ° C. with ventilation. Next, the dried aggregate was supplied to a rotary kiln having a brick inner diameter of 400 mm and a length of 6000 mm, and was fired under the conditions of an oxygen concentration of 5% in combustion gas and a temperature of about 1,120 ° C. As a quality evaluation of the aggregate a thus obtained, specific gravity and water absorption were determined by JI.
The measurement was performed based on SA1110, and the crushing strength was measured using a crushing tester. In addition, the said measurement was performed about each aggregate about 10 mm in diameter, and the average value was calculated | required. As can be seen from Table 1, the aggregate a of Example 1 has an absolute dry specific gravity of 1.40 g /.
cm ³ , crush strength was 75 kgf, and water absorption was 0.7%. In addition, as a result of a chemical analysis, calcium in the aggregate in terms of oxide was 7.8% by weight.

Examples 2 to 4 and Comparative Examples 1 to 3 57.5% by weight of incinerated fly ash, 5% by weight of bentonite, 5% by weight of hematite, 2% by weight of coke, 0.5% by weight of silicon carbide
Aggregate b (Example 2) was prepared in the same manner as in Example 1 except that the amount of coal ash was changed to 30% by weight.
Aggregate c (Example 3) was prepared in the same manner as in Example 1 except that 5% by weight of bentonite, 5% by weight of hematite, 2% by weight of coke, 0.5% by weight of silicon carbide and 55% by weight of coal ash were used. 67.5% by weight of incinerated fly ash, 5% by weight of bentonite, 5% by weight of hematite, 2% by weight of coke, 0.5% by weight of silicon carbide and 20% by weight of coal ash, except that the kiln temperature was 1080 ° C. Is the aggregate d in the same manner as in Example 1.
(Example 4) was obtained by incineration fly ash 77.5% by weight, bentonite 5% by weight, hematite 5% by weight, coke 2% by weight,
Aggregate e (Comparative Example 1) was prepared in the same manner as in Example 1 except that silicon carbide was 0.5% by weight and coal ash was 10% by weight, and incinerated fly ash was 77.5% by weight, bentonite was 5% by weight, and hematite was 5%. Wt%, coke 2 wt%, silicon carbide 0.5 wt%
Aggregate f (Comparative Example 2) was prepared in the same manner as in Example 4 except that coal ash was changed to 10% by weight,
Aggregate g (in the same manner as in Example 4 except that 5% by weight of bentonite, 5% by weight of hematite, 2% by weight of coke, 0.5% by weight of silicon carbide, 10% by weight of coal ash and 5% by weight of quicklime) Comparative Example 3) was obtained. The same measurement as in Example 1 was performed for the obtained aggregates b to g, and the evaluation result and the chemical analysis result of calcium in terms of oxide in the aggregate are shown in Table 1.

As can be seen from Table 1, aggregates b to d of the embodiment are shown.
Has a specific gravity of 1.25 to 1.45 and a crushing strength of 30 kg
f and the water absorption is 5% or less, whereas the aggregate e of the comparative example cannot be made into an aggregate by meltdown, and the aggregate f of the comparative example has a crushing strength as low as 4 kgf. The aggregate g had a crushing strength of 30 kgf or more, but an absolute dry specific gravity of more than 1.5.

Table 1 Aggregate Absolute Dry Specific Gravity Crushing Strength Water Absorption CaO g / cm ² Kgf% wt% Example 1 a 1.40 75 0.7 7.8 Example 2 b 1.45 77 0.5 9. 3 Example 3 c 1.25 70 0.1 5.6 Example 4 d 1.30 32 3.0 10.8 Comparative Example 1 e Comparative Example 2 f 0.64 4 9.6 12.2 Comparative Example 3 g 1.72 57 3.2 22.2

[0029]

As described above, the present invention can efficiently produce aggregate having high strength and low water absorption by using refuse incineration ash as a main raw material. Therefore, it is extremely useful in environmental conservation and effective use of resources, since industrial waste can be recycled, especially in civil engineering and building materials, without landfill treatment.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koji Kawamoto 3-18-5 China, Ichikawa City, Chiba Prefecture F-term in the Central Research Laboratory of Sumitomo Metal Mining Co., Ltd. 4D004 AA36 BA02 CA04 CA14 CA30 CC03 CC11 CC13 CC17 CC20 DA03 DA10

Claims (3)

[Claims] 1. A waste incineration ash is mixed with a binder, a foaming agent, a reducing agent, and a coal ash as a composition controlling agent, and the resulting mixture is pulverized. In the method of drying the molded body if necessary and then firing it to obtain an artificial lightweight aggregate, the calcium content in the finally obtained artificial lightweight aggregate is 16% by weight or less in terms of oxide. A method for producing an artificial lightweight aggregate, characterized in that the composition is controlled so as to be as follows. 2. The method according to claim 1, wherein iron oxide and / or silicon carbide is used as a foaming agent, and carbonaceous material is used as said reducing agent.
The described method. 3. An artificial lightweight aggregate obtained by the method according to claim 1 or 2, having an absolute dry specific gravity of 1.0 to 1.5.
g / cm 3, a uniaxial compressive breaking load of 30 kgf or more, and a water absorption of 5% or less.