JPH1029841A - Production of artificial aggregate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique by which fly ash that is obtained by collecting dust scattered into a flue gas at the time of incinerating municipal waste, is not disposed as waste but handled as a resource and effectively utilized as artificial aggregate. SOLUTION: In this production, fly ash is mixed with bentonite used as a binder and a blending material used as a composition adjuster to obtain a mixture and then, the mixture is fired. At this time, the mixing ratios are adjusted so that the chemical composition of the mixture after firing contains 20 to 80wt.% silica and 10 to 35wt.% calcium oxide and the fired mixture thus obtained is pulverized into a pulverized material having a <=15μm average particle size. Then, water is added to the resultant pulverized material to form formed bodies and thereafter, if necessary, the formed bodies are dried and then, the resulting formed bodies are fired to produce the objective artificial aggregate.

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.

[0003] 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.

[0004] Techniques currently adopted or studied to prevent heavy metals from being eluted from fly ash, ie, 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.

[0009]

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, methods such as cement solidification, chelating treatment, and acid washing, for example, make it possible to reliably prevent the elution of heavy metals for a long period of time, reduce the processing cost, and simplify the operation technology of the processing equipment. There are many issues to be resolved in terms of what to do.

According to the present invention, there is provided a technique which solves these drawbacks, inexpensively prevents the elution of heavy metals for a long time, and effectively utilizes fly ash as a resource instead of disposing it as waste. As an issue.

[0012]

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
It is adjusted so that calcium oxide becomes 10 to 35% by weight at 0% by weight. The mixture 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.

[0013] As the composition-combining material, a mineral containing silica such as silica sand, pottery stone, feldspar, kaolinite, and wood knot viscosity is added to the above-mentioned chemical composition, and if necessary, calcium oxide is added. It is desirable to use minerals containing calcium oxide, such as limestone, slaked lime and quicklime, as a source. 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 molded so as to have a predetermined diameter.
It is convenient to use a pan 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.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies to obtain an artificial aggregate using fly ash, a composition mixture and a binder, and as a result, have found that fly ash and a composition mixture are used. During firing, if the content of silica and calcium oxide after firing is adjusted to be within a predetermined range, elution of heavy metals such as lead and zinc can be extremely reduced and can be sufficiently used as an aggregate for civil engineering and construction. The present inventors have found that an artificial aggregate having strength and chemical quality can be fired, and have reached the present invention. less than,
Each element of the present invention will be described in detail.

Silica Content and Calcium Oxide Content When the content of silica in the fired product is 20 to 80% by weight or less and the content of calcium oxide is in the range of 10 to 35% by weight, It has less elution of heavy metals than products, has high strength for construction, and has excellent durability. That is, the reason why the silica content is set to 20% by weight or more in the method of the present invention is that if the silica content is lower than this, the strength after firing is low and the durability is poor. 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 sintering temperature exceeds 1250 ° C., and the fuel cost increases. This is necessary and is not practical.

The reason why the content of calcium oxide is set to 10% by weight or more is that if the content of calcium oxide is lower than this, foam expansion occurs at the time of sintering of the aggregate, and high strength cannot be achieved. On the other hand, if the content of calcium oxide exceeds 35% by weight, the firing temperature exceeds 1250 ° C., and the range of the appropriate firing temperature at which the aggregate can be fired becomes narrow, which is not preferable. In other words, if the temperature exceeds the proper firing temperature, it settles on the inner wall of the kiln or aggregates with each other. If the temperature is lower than the appropriate temperature, the sintering is insufficient, the aggregate strength is small, and the elution of heavy metals is increased. The material cannot be fired stably. Therefore, the range of the appropriate firing temperature is ensured at 35% by weight or less.

[0018] The composition of the fly ash to fly ash in Table 1. Since the content of silica is often less than the proper composition, it is supplemented by using silica such as silica sand, pottery stone, feldspar, kaolinite, silica such as wood knot viscosity, or a mineral containing the silica and alumina as a composition mixture. . Calcium oxide is often within the proper composition or higher,
A composition preparation containing calcium oxide is not necessarily required. Rather, calcium oxide may exceed the proper composition range. In this case, the composition is adjusted to be within the proper composition range by using a composition preparation containing silica.

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] Firing is carried out at a temperature of 1000 to 1250 ° C, but at a temperature lower than this composition, the firing is not sufficient, and at a temperature higher than this range, the stickiness of the pellets is increased, and the operation becomes impossible due to the adhesion of the pellets. Will be higher. Furthermore, the firing temperature is 1
If the temperature is higher than 250 ° C., the fuel cost increases, 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 preferred as a facility for sintering aggregates because the facility is simple and the quality of the baked 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 of 1.2 to 1.1 obtained by adding a composition mixture material and a binder using the bulk specific gravity fly ash as a main raw material, pulverizing, mixing, and granulating.
When the pellets of No. 9 were heated in the kiln, they shrank and shrunk,
It becomes a high-strength artificial aggregate having a bone-dry specific gravity of about 1.9 to 2.3.

[0023]

The present invention will be described below with reference to examples.

Examples 1-1-1 to 3-1-2 The chemical compositions of the three types of incinerated fly ash, quartz sand, feldspar, bentonite and limestone used in the experiments are shown in Table 1. These raw materials were weighed and collected in the composition shown in Table 2 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. The obtained crushed raw material was granulated into a spherical shape with a diameter of about 5 to 15 mm by a pan pelletizer while adding water, dried, and then supplied to a rotary kiln (brick inner diameter 500 mm × length 4800 mm) for firing. Tables 2 to 4 show the chemical composition of the aggregate (fired product) after firing, and Table 7 shows the average particle size and firing temperature of the raw materials. The specific gravity of the fired aggregate is JIS
The crushing strength was measured on an aggregate having a diameter of about 10 mm based on A1110. The results obtained are shown in Table 7.

The specific gravity varies depending on the production conditions from about 1.9 to 2.3, but in any case, the firing is caused by shrinkage due to the shrinkage of the raw material due to the loss of volatilization by the chlorine compound of about 20 to 30% by weight. The compaction strength is high. The crushing strength of commercially available artificial lightweight aggregate is about 50k
gf, in the embodiment, 90 kgf to 260 kgf.
It is about kgf and can be used not only as an aggregate for general structural concrete but also as an aggregate for high-strength concrete.

With respect to the dissolution property of heavy metals from the fired aggregate, the dissolution test of lead and zinc was carried out for acidity of hydrochloric acid and alkalinity of sodium hydroxide in accordance with the method prescribed in Notification No. 13 of the Environment Agency. As a result, in all of the examples in Tables 2 to 4, lead was 0.01 PPM or less as an environmental standard, and zinc was 5 PPM or less as a drainage standard regulated by the Water Pollution Control Law.

Comparative Examples 1-1 and 1-2 A fired product was obtained under the conditions shown in Tables 5 and 8. The crushing strength of this fired product was about the same as a commercially available artificial lightweight aggregate, and could not be used for high-strength concrete aggregate.

Comparative Examples 2-1 and 2-2 A fired product was obtained under the conditions shown in Tables 6 and 8. The crushing strength of this fired product was lower than the crushing strength of commercially available artificial lightweight aggregate, and was not suitable for structural concrete.

[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]

According to the present invention, since the present invention is constituted as described above, heavy metals which are easily eluted after landfill are made harmless and civil engineering. An excellent aggregate having high strength for construction can be produced at a 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)

[Claims] 1. A method for producing an artificial aggregate by firing using fly ash as a raw material, wherein bentonite and a composition-mixed material are mixed with the fly ash to form a mixture. -80% by weight silica and 10-35% by weight
A method for producing an artificial aggregate, characterized in that the mixture is adjusted to be calcium oxide, and the mixture is pulverized and the molded body is fired. 2. The method for producing an artificial 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 aggregate according to claim 1, wherein the firing is performed at 1000 to 1250 ° C. 4. A method for producing an artificial aggregate by firing using fly ash as a raw material, wherein bentonite and a composition-mixed material are mixed with the fly ash to form a mixture. -80% by weight silica and 10-35% by weight
The mixture is adjusted to be calcium oxide, and the mixture is pulverized so that the average particle size is 15 μm or less, molded to obtain pellets, and the pellets are dried and dried.
A method for producing an artificial aggregate, comprising firing at 50 ° C. 5. The artificial aggregate 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. Manufacturing method. 6. The composition mixture uses at least one of silica sand, porcelain stone, feldspar, kaolinite, wood knot viscosity and incineration main ash as a silica source, and one of limestone, slaked lime and quick lime as a calcium oxide source. The method for producing an artificial aggregate according to any one of claims 1 to 4, wherein the above is used. 7. The method for producing an artificial aggregate according to claim 1, wherein a rotary kiln is used as the firing furnace.