JP3204104B2 - Manufacturing method of artificial lightweight aggregate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the recycling of fly ash scattered in exhaust gas during incineration of municipal solid waste, and more particularly to a method for producing aggregates for buildings and civil engineering from the fly ash.

[0002]

2. Description of the Related Art In the present specification, fly ash refers to a substance obtained by collecting dust scattered in exhaust gas at the time of incineration of municipal waste. Most fly ash is landfilled as waste. However, this fly ash contains many heavy metals such as lead and zinc. For this reason, in order to prevent elution after landfill, a treatment for preventing elution of heavy metals is performed. Techniques currently adopted or studied to prevent heavy metals from being eluted from fly ash, that is, elution prevention techniques are as follows.

A. Melt solidification In this method, fly ash and main ash are heated and melted, and then cooled and solidified. At this time, some of the fly ash and the main ash contain vitrified materials. Although this method can reduce the volume of fly ash and main ash, it consumes a large amount of energy and may not be economical at all in terms of cost. In addition, it is difficult to recycle glass (slag glass) to be generated.

B. Cement solidification In this method, cement is mixed and solidified as the name implies. Since the amount of treated material is increased by the amount of the cement to be mixed, the life of the final disposal site is shortened, which is a serious problem. Although cheap in terms of cost, it is far from economic.

C. Chelation treatment In this method, heavy metals such as lead and zinc are prevented from being eluted by a chelating agent as a stable compound. The reliability is not always reliable in terms of the expensive chelating agent and the long-term stability of heavy metals. There is also a problem in reducing the volume of incinerated ash.

D. Acid Cleaning In this method, fly ash is acid-cleaned to remove metals that are likely to elute in advance, landfill the fly ash after cleaning, and separately treat washing water. The treatment equipment has become large-scale, and there is a problem in terms of volume reduction of incinerated ash.

[0007]

In each of the above methods,
Prevention of elution of heavy metals was devised exclusively, and its reuse is not considered. Therefore, not only most of fly ash is landfilled, but also new waste may be generated by mixing cement. However, landfills, especially managed landfills for processing fly ash, are decreasing in remaining years, and many municipalities are struggling to secure landfills and extend their life. In addition, in methods such as cement solidification, chelation treatment, and acid cleaning, for example, whether long-term elution of heavy metals can be reliably prevented, how much the processing cost can be reduced,
There are many points to be solved in terms of how to simplify the operation technology of the processing equipment.

In the present invention, these drawbacks are solved, the elution of heavy metals is prevented stably for a long time at low cost, and fly ash is not disposed of as waste but is used as a resource, particularly for buildings and structures. It is an object of the present invention to provide a technology for effectively utilizing concrete as artificial lightweight aggregate capable of significantly reducing the weight of concrete for use.

[0009]

In the method of the present invention for solving the above-mentioned problems, first, fly ash of municipal solid waste, which is a raw material, is mixed with bentonite as a binder and a composition mixture to form a mixture. When the chemical composition after firing is 20 to 8 silica
Adjust to 0% by weight and calcium oxide to 0.5 to 15% by weight. Further, as a foaming agent, 2 to 10% by weight of iron oxide and 0.1 to 2.5% by weight of silicon carbide are added at an average particle size of 10 μm or less. The mixture thus obtained is preferably pulverized so that the average particle size is 15 μm or less. Next, water is added to the obtained pulverized material to form a molded body, and after drying if necessary, the molded body is fired. Minerals containing silica, such as silica sand, pottery stone, feldspar, kaolinite, wood knot viscosity, and incineration main ash, can be used as the composition mixture. The firing temperature is desirably 1000 to 1250 ° C.

There is no problem as long as the molding device used in the present invention can be formed so that the molded body (pellet) has a predetermined diameter. However, it is convenient to use a punch pelletizer or an extrusion molding machine. In addition, it is preferable to use a rotary kiln as the firing apparatus in consideration of continuous operation and quality uniformity.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies to obtain an artificial lightweight aggregate foamed and expanded during firing by using fly ash, a composition mixture, a foaming agent and a binder. As a result, if the content of silica and calcium oxide after calcination is adjusted to be within a certain range, and iron oxide and silicon carbide having a certain particle size are added at a certain ratio and foamed, lead and zinc can be obtained. Elution of heavy metals such as
The present inventors have found that an artificial lightweight aggregate having sufficient strength and durability that can be used as a building aggregate can be fired, and the present invention has been accomplished. Hereinafter, each element of the present invention will be described in detail.

When the content of silica and the content of calcium oxide in the calcined product are 20 to 80% by weight or less and the content of calcium oxide is in the range of 0.5 to 15% by weight, It has less heavy metal elution than the fired material, has high strength for building use, and has excellent durability.

That is, in the method of the present invention, the reason for setting the silica content to 20% by weight or more is that if the silica content is lower than this, the strength after firing is low and the durability is poor. is there. On the other hand, when the content of silica exceeds 80% by weight, the amount of the composition mixture becomes several times as much as that of fly ash, and the firing temperature exceeds 1250 ° C., and the fuel cost increases. This is because high heat resistance is required and it is not practical.

When the content of calcium oxide is set to 15% by weight or less, when the content of calcium oxide is higher than this, even if a foaming agent is added, foaming expansion does not occur at the time of sintering of the aggregate, and the weight is reduced. Because you can't. On the other hand, since the content of calcium oxide in the raw material fly ash and chemical modifier does not fall below 0.1%, it is meaningless to reduce the content of calcium oxide to less than 0.1% by weight. is there.

[0015] Iron oxide is used as a foaming agent foaming agents function as an oxygen source of CO or CO ₂ generated as a blowing gas at high temperatures.
If the addition ratio of iron oxide is set to 2% by weight or more, the effect of reducing the weight of the aggregate is insufficient below this, and even if it exceeds 10% by weight, the effect of weight reduction does not increase. This is because the raw material becomes easily slag and becomes difficult to be fired. The reason why the average particle size of the iron oxide is set to 10 μm or less is that if the particle size is coarser, the efficiency of weight reduction becomes worse.

The silicon carbide functions as a carbon source of CO or CO ₂ gas. The reason why the addition rate of silicon carbide is set to 0.1% by weight or more is that if less than this, the effect of reducing the weight is not exhibited, and the addition rate of 2.5% by weight or less is
This is because the addition of more than this does not increase the light weight effect.

Here, carbon-containing coal, coke,
It is possible to use one or more of the heavy oils as the carbon source of the foaming gas in the same manner as silicon carbide, by using 2 to 10% by weight and 1 to 5% by weight in terms of carbon in terms of carbon fraction. But,
Since coal, coke, and heavy oil react with iron oxide from a low temperature stage of firing, the foaming efficiency, that is, the lightening effect is lower than that of silicon carbide. The reason why the addition ratio of coal or the like is set to 1% by weight or more in terms of carbon is that the weight reduction efficiency cannot be exhibited below this value. The reason why the content is set to 5% by weight or less is that the addition of more than 5% does not increase the light weight effect.

[0018] The composition of the fly ash to fly ash in Table 1. Since the content of silica is often less than the appropriate composition, use silica such as silica sand, pottery stone, feldspar, kaolinite, wood knot viscosity, incineration main ash, or a mineral containing the silica and alumina as a composition preparation material It is possible.

When firing in a rotary kiln such as a binder rotary kiln, the pellets are tumbled and abraded when moving in the kiln to generate powder. When the amount of generated powder is large, the actual yield decreases and the load on the soot collection equipment increases. In addition, the powder adheres to the surface of the pellets in the firing section in the kiln, and this serves as an adhesive, which makes it easier for the pellets to adhere to each other and to adhere to the inner wall of the kiln. If the formation of these deposits becomes excessive, the firing operation becomes difficult. The use of binder
Bentonite is suitable for this purpose to reduce powdering in the kiln. Good results can be obtained by adding the binder in an amount of 0.2 to 10% by weight based on the amount before firing. If the addition amount is less than this range, the effect as a binder will not be obtained, and if it is more than this range, further increase in the binding effect cannot be expected.

[0020] In the method of the particle size present invention mixtures, average particle diameter and 15μm greater than the mixture obtained by mixing a fly ash with a composition formulated material and caking additive, finally obtained strength of the artificial lightweight aggregate is descend. Therefore, it is necessary to form after pulverization so that the average particle size is 15 μm or less. Needless to say, this grinding plays a role of uniform mixing. Water is added to the mixture obtained by grinding and mixing, and the mixture is formed into pellets by tumbling granulation or extrusion granulation. The size of the molded body obtained in this way depends on the size of the artificial lightweight aggregate obtained as a product, but is generally 5 to 15 mm.

[0021] The firing is carried out at 1000 to 1250 ° C. However, at a temperature lower than this composition, the firing is not sufficient. At a temperature higher than this range, the cohesiveness of the molded article (pellet) is increased, and the molded article (pellet) is increased. The probability that the operation becomes impossible due to the adhesion of the metal becomes high.
Further, when the firing temperature is higher than 1250 ° C., the fuel cost is increased, and the firing equipment needs to have high heat resistance, which is not practical. The furnace used for firing is preferably a rotary kiln. The rotary kiln is preferable as a facility for sintering artificial lightweight aggregates in that the facility is simple, the quality of the baked artificial lightweight aggregate is small, and the reliability of detoxification by reducing elution of heavy metals is high. Needless to say, drying is performed as necessary before firing the molded body.

A dry bulk specific gravity obtained by adding a composition mixture and a binder using a bulk specific gravity fly ash as a main raw material, further adding a foaming agent, pulverizing, mixing, and granulating the resulting mixture. When the pellets of No. 9 are heated in a kiln, they temporarily bake and shrink, but expand and expand, resulting in an artificial lightweight aggregate having an absolute dry weight of about 0.6 to 1.3 and excellent in lightness.

[0023]

The present invention will be described below with reference to examples. [Example 1-1-1 to 2-2-3] Table 1 shows the chemical compositions of the two types of fly ash, quartz sand, feldspar, bentonite and hematite used in the experiment. These raw materials and silicon carbide were weighed and collected in the proportions shown in Tables 2 and 4 and pulverized and mixed in a ball mill. The particle size distribution of the pulverized raw material was measured with a laser diffraction type particle size distribution meter. After adding water to the obtained pulverized raw material, the mixture is granulated into a spherical shape having a diameter of about 5 to 15 mm using a pan pelletizer and dried.
× length 4800 mm) and fired. Tables 3 and 5 show the chemical composition of the artificial lightweight aggregate (fired product) after firing, and Table 10 shows the average particle size and firing temperature of the raw materials.

The specific gravity of the fired artificial lightweight aggregate is JIS A 1110
The crushing strength was measured for an artificial lightweight aggregate having a diameter of about 10 mm. The results obtained are shown in Table 10. The specific gravity varies depending on the production conditions from 0.6 to 1.3, but in any case, about 10%
In addition to a decrease in specific gravity due to a reduced amount of volatilization due to a chlorine compound (present in fly ash) of about 20% by weight or the like, foaming expansion proceeds by the addition of a foaming agent, and the specific gravity is greatly reduced. While the absolute dry specific gravity of the commercially available artificial lightweight aggregate is 1.2 to 1.4, in the present embodiment, the weight is reduced to about equal to or half thereof,
An artificial lightweight aggregate having a very small specific gravity can be obtained.

Comparative Example 1-1 A fired product was obtained under the conditions shown in Tables 6, 7, and 11. Although the crushing strength of this fired product is about twice that of commercially available artificial lightweight aggregates, it cannot be used particularly for concrete aggregates that require weight reduction.

[Comparative Example 1-2] A fired product was obtained under the conditions shown in Tables 6, 7 and 11. The crushing strength of this fired product was less than the crushing strength of a commercially available artificial lightweight aggregate, and was not particularly suitable for concrete requiring lightening.

Comparative Example 1-3 A fired product was obtained under the conditions shown in Tables 6, 7 and 11. Although the crushing strength of this calcined product is superior to that of a commercially available artificial lightweight aggregate, it cannot be used particularly for concrete aggregates that require weight reduction.

Comparative Examples 2-1 to 2-3 A fired product was obtained under the conditions shown in Tables 8, 9 and 11. 1-1-1 to 1- of Examples
This is the condition when no blowing agent is added to 3-3. The absolute dry specific gravity was 1.45 to 1.73, and the weight reduction was small.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

[0034]

[Table 6]

[0035]

[Table 7]

[0036]

[Table 8]

[0037]

[Table 9]

[0038]

[Table 10]

[0039]

[Table 11]

[0040]

According to the present invention, as described above, the present invention makes it possible to detoxify heavy metals which are liable to be eluted after landfilling, and to reduce the weight of buildings for civil and architectural use, which has recently been reduced in weight. Aggregate can be produced at relatively low cost. Thereby, the conventional waste can be detoxified and effectively used as aggregate resources, and the problem of securing a landfill disposal site can be solved. In addition, enormous costs involved in detoxification of heavy metals and volume reduction of ash can be reduced, which is extremely significant in terms of environmental problems and effective use of resources.

Claims (7)

(57) [Claims] 1. A method for producing an artificial lightweight aggregate by firing using fly ash as a raw material, wherein bentonite and a composition-mixed material are mixed with the fly ash, and a foaming agent is further added to form a mixture. An artificial material characterized in that the chemical composition after firing is adjusted to be 20 to 80% by weight of silica and 0.1 to 15% by weight of calcium oxide, and the mixture is pulverized and a molded product is fired. Manufacturing method of lightweight aggregate. 2. The method for producing an artificial lightweight aggregate according to claim 1, wherein the mixture has an average particle diameter of 15 μm or less. 3. The method for producing an artificial lightweight aggregate according to claim 1, wherein the firing is performed at 1000 to 1250 ° C. 4. A method for producing an artificial lightweight aggregate by firing using fly ash as a raw material, wherein bentonite and a composition mixture are mixed with the fly ash, and a foaming agent is added to form a mixture. At this time, the chemical composition after firing is adjusted to be 20 to 80% by weight of silica and 0.1 to 15% by weight of calcium oxide, and the mixture is pulverized and shaped so that the average particle size becomes 15 μm or less. A pellet is obtained by drying the pellet, and the pellet is dried and fired at 1000 to 1250 ° C. 5. The artificial lightweight bone according to claim 1, wherein at least one of silica sand, pottery stone, feldspar, kaolinite, wood knot viscosity and incinerated main ash is used as the composition mixture. The method of manufacturing the material. 6. A foaming agent, each of which has an outer ratio of 2 to 10
The artificial lightweight aggregate according to any one of claims 1 to 4, wherein iron oxide of 0.1% by weight and / or silicon carbide of 0.1 to 2.5% by weight are added in an average particle size of 10 µm or less. Method. 7. The method for producing an artificial lightweight aggregate according to claim 1, wherein a rotary kiln is used as a firing furnace.