JPH11116300A - Artificial aggregate and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniaxial squeezing strength and to lower specific gravity by substantially having components produced by the firing of a fly ash, containing a specific composition of Fe and C, forming substantially from an outer layer and inner layer, forming Fe in the outer layer from hematite and forming Fe in the inner layer from wustite and/or magnetite. SOLUTION: An artificial aggregate contains silicon oxide, alumina, iron oxide, slaked lime and magnesia as the components produced by the firing of the fly ash. And the artificial aggregate contains 3-5 wt.% Fe and 0.2-0.3 wt.% C. The aggregate is produced as follows. A finder, a composition blending material and a foaming agent are mixed with the fly ash, further coal or coke is added as a reducing agent and the resultant mixture is pulverized to have <=15 μm average particle diameter. The pulverized material is molded with the addition of water. The molding is fired at 1000-1200 deg.C firing temp. with a retention time in the temp. range controlled to 2-5 min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to the recovery and recycling of incinerated fly ash (hereinafter referred to as fly ash) accompanying exhaust gas when incinerating general waste such as municipal waste. The present invention relates to a method for producing harmless architectural aggregates for construction and civil engineering.

[0002]

2. Description of the Related Art Most fly ash generated during incineration of municipal solid waste is disposed of as landfill. But,
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.

[0003] With respect to a technique for preventing heavy metals from being eluted from fly ash, that is, a detoxification technique, those which are currently adopted or studied are as follows.

A. Melt solidification method This method uses fly ash and incineration ash (main ash) remaining in the incinerator.
Are heated and melted, and then cooled and solidified, and some are vitrified.

[0005] 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. Also, it is difficult to recycle the generated slag glass.

B. Cement solidification method In this method, as the name implies, cement is mixed and solidified.

[0007] Since the amount of landfill 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. In terms of cost, it is cheap, but far from economic.

C. Chelating method In this method, heavy metals such as lead and zinc are reacted with a chelating agent to convert them into a stable compound to prevent elution.

[0009] The chelating agent is expensive and has low reliability in terms of long-term stability of heavy metals. In addition, there is a problem in volume reduction of fly ash and main ash.

D. Acid Washing Method In this method, fly ash is subjected to acid washing to remove metal components which are likely to elute in advance, to reclaim fly ash after washing, and to separately treat washing water.

This method requires a large-scale treatment facility, and has a problem in reducing the volume of incinerated ash.

E. Baking method In addition to the above four methods, a method for baking fly ash, volatilizing and separating heavy metals to make them harmless, and making effective use of the burned material is being studied. For effective use, concrete aggregates used in large quantities are desirable, but important properties required for artificial aggregates include crush strength and specific gravity. In order to make the above-mentioned artificial aggregate have a uniaxial crushing strength of 30 kg / cm ² or more and to use it as a concrete aggregate for a high-rise building, the specific gravity needs to be 2.0 or less. Fly ash generally contains a large amount of alkali metals, lime, and chlorine, and its composition is significantly different from that of conventional lightweight aggregates. It is not possible.

[0013]

In each of the above-mentioned various methods, except for the artificial aggregate method, not only the fly ash is mostly disposed of in landfills, but also new waste that must be landfilled may be produced. It has become something.

In Japan, where the land is narrow, the problem of waste
Not only the environment but also securing a final disposal site is a major social issue. Especially in the Tokyo metropolitan area, the remaining years of disposal sites are less than 5 years, so the effective use of waste is being actively studied in order to extend the life of the current disposal sites.
No effective use other than roadbed material has been found.

[0015] Remaining 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. .

On the other hand, there is a danger of depletion of high-quality gravel resources that are in competition with artificial aggregates used as concrete raw materials in the market, and inexpensive and high-quality artificial aggregates are required.

An object of the present invention is to provide an artificial aggregate having the above-mentioned properties having a uniaxial crushing strength of 30 kg / cm ² or more and a specific gravity of 2.0 or less, and a method for producing the same.

[0018]

The artificial aggregate of the present invention substantially contains components produced by firing fly ash, specifically, silicon oxide, alumina, iron oxide, slaked lime, and magnesia.
〜5% by weight of iron and 0.2-0.3% by weight of carbon, consisting essentially of an outer layer and an inner layer, wherein the iron in the outer layer is mainly hematite (Fe ₂ O ₃ ) and the iron in the inner layer Is mainly wustite (FeO) and / or magnetite (Fe
₃ O ₄ ).

Further, the method for producing an artificial aggregate of the present invention comprises:
The fly ash was mixed with a binder, a composition mixture, and a reducing agent, and coal or coke was used as the reducing agent. The resulting mixture was pulverized so that the average particle size became 15 μm or less, and then the obtained mixture was obtained. In a method of obtaining a molded body by adding water to the pulverized material and molding the molded body, and firing the molded body to obtain an aggregate, the firing temperature is set to 1
100 to 1200 ° C, and the residence time at 1100 to 1200 ° C is 2 to 5 minutes. Preferably, the oxygen concentration in the exhaust gas at the exhaust gas outlet of the firing furnace is 7 to 10% by volume. Note that the molded body is dried if necessary before firing.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is obtained by mixing a fly ash, a composition mixture, a binder and a reducing agent, and using a foaming agent as necessary to obtain a molded body, and firing the molded body. The artificial aggregate contains 3 to 5% by weight of iron and 0.2 to 0.3% by weight of carbon, and is substantially composed of an outer layer and an inner layer. The iron in the outer layer is mainly hematite (Fe ₂ O ₃ ). , The inner layer of iron is mainly wustite (FeO) and / or magnetite (F
e ₃ O ₄ ) has a crushing strength of 30 kg / cm ² or more and a specific gravity of 2.0 or less.

In the artificial aggregate of the present invention, since the melting point of the outer layer is higher than the melting point of the inner layer, only the inner layer can be melted and foamed uniformly, and the surface is sintered to make it dense and smooth. It becomes possible. It is considered that the alkali chlorides and volatile heavy metal salts (lead and zinc) in the fly ash are mostly volatilized during the calcination stage, and the remainder is confined in a matrix of iron oxide.

As a method for obtaining such an artificial aggregate, for example, fly ash as a raw material, bentonite as a binder, silica sand, pottery stone, feldspar, kaolinite, wood At least one kind of mineral containing silica such as modest viscosity, and a calcined chemical composition of the obtained mixture is 20 to 80% by weight of silica and 0.5 to 15% of calcium oxide.
% By weight and a foaming agent having an average particle size of 10%.
2 to 10% by weight of iron oxide or silicon carbide having a particle size of 1 μm or less is added, and 2 to 9% by weight in terms of carbon content is further added using coal or coke as a reducing agent.
In a method of pulverizing so as to have a particle size of 5 μm or less, and then adding water to the pulverized material to form a molded body, and then, if necessary, drying and firing to obtain a foamed artificial aggregate,
The firing temperature is set to 1100 to 1200 ° C.,
The residence time at 00C is 2-5 minutes.

The type of the furnace used for firing is not particularly limited as long as it can satisfy conditions such as temperature and heating time. However, a rotary kiln is preferred because it is easy to handle and control. This is because the rotary kiln has simple facilities, has little variation in the quality of the baked artificial aggregate, and has high reliability in detoxification by reducing elution of heavy metals such as lead.

In the case where a rotary kiln is used as an incinerator, the residence time can be adjusted by adjusting the rotation speed of the kiln and the inclination of the kiln.

The carbon quality in the calcined product can be adjusted by adjusting the blending amount, more preferably by adjusting the oxygen concentration in the exhaust gas at the kiln exhaust gas outlet to 7 to 10% by volume.

When an artificial aggregate is obtained by firing using a rotary kiln, usually, a liquid phase is generated in the raw material of the aggregate to exhibit the strength of the aggregate or expand the foam. Therefore, adhesion of the pellets obtained by granulating the raw materials or adhesion of the pellets to the inner wall of the kiln is likely to occur. However, according to the conditions of the present invention, only the inner layer is in a molten state while the outer layer of the pellet remains in a sintered state, and foams and expands.

Water is added to the mixture obtained by pulverization and mixing, and a compact is obtained by rolling granulation, extrusion granulation, pressure molding and the like. At this time, the method to be adopted and the size of the formed article mainly depend on the size of the artificial lightweight aggregate obtained as a product. Generally, it is often 5 to 15 mm.

[0028]

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

[Examples 1 and 2, Comparative Example 1] The chemical composition of fly ash used in the experiment is shown in Table 1.

[0030]

[Table 1]

Coke (reducing agent), silica stone (component adjusting agent) and hematite (foaming agent) were added to this raw material at a carbon content of 3.2% by weight, Fe ₂ O ₃ content of 4.7% by weight, SiO
_{(2) The} powder was added so that the added amount was 16.0% by weight, and pulverized using a ball mill so that the average particle diameter became 15 μm. The particle size distribution of the pulverized raw material was measured using a laser diffraction type particle size distribution system.

The obtained ground raw material is kneaded while adding water and bentonite (binder), extruded into a rod shape by an extruder, cut into a length approximately equal to the diameter, and cut with a pan pelletizer. Was rounded. After drying the spherical particles having a diameter of about 15 mm thus obtained,
Rotary kiln (brick inner diameter 300mm x length 4800
mm) and fired.

As firing conditions, a temperature of 1100 ° C. to 12
Firing was performed in the range of 00 ° C., and the residence time in this temperature range was 2 minutes (Example 1), 5 minutes (Example 2), and 8 minutes (Comparative Example 1). Table 2 shows the obtained results. Table 3 shows the components of the fired product of Example 1.

Further, the obtained pellet was cut, and the cross section was observed. The results are also shown in Table 2. In addition,
The specific gravity of the fired artificial aggregate was measured based on JIS A1110. The obtained results are also shown in Table 2.

[0035]

[Table 2]

[0036]

[Table 3]

As a result of X-ray morphological analysis of the cross section of the pellet having 0.2 to 0.3% by weight of residual carbon (Examples 1 and 2), the pellet had a double structure, and iron in the inner layer was wustite ( FeO) and / or magnetite (Fe ₃ O ₄ ), iron in the outer layer is hematite (Fe
₂ O ₃ ). On the other hand, when the cross section of a pellet having 0.14% by weight of residual carbon (Comparative Example 1) was analyzed in the same manner, about 20% by weight of iron
The degree was found to be hematite.

From the results of cross-sectional observation, it was found that the inner layer was melted and the outer layer was partially melted in pellets having high uniaxial crushing strength. In the pellets of Examples 1 and 2, no large bubbles were found in the molten portion of the inner layer, and it was found that small bubbles of 1 mm or less were scattered. It seems that the specific gravity could be reduced to 1.2 without lowering the uniaxial crushing strength by making the bubbles finer.

According to the method of the present invention, it is possible to obtain an artificial aggregate having a uniaxial crushing strength of 30 kg / cm ² or more even using chloride-containing fly ash, which is said to be difficult to obtain an artificial aggregate having high uniaxial crushing strength. Obviously, is possible. It goes without saying that the present invention can be applied to other fly ash having a composition similar to that of general incinerated fly ash.

[0040]

According to the method of the present invention, in detoxifying incinerated fly ash and effectively utilizing it as aggregate for civil engineering and construction,
After firing, the artificial aggregate has a double structure, the inner layer is kept in a molten state, and the outer layer is kept in a sintered state.
An artificial aggregate having a specific gravity of 2.0 or less at kg / cm ² or more can be obtained.

Claims (7)

[Claims] 1. Substantially containing components produced by firing fly ash, 3 to 5% by weight of iron and 0.2 to 0.3% by weight of carbon
And that the iron in the outer layer is mainly hematite (Fe ₂ O ₃ ) and the iron in the inner layer is mainly wustite (FeO) and / or magnetite (Fe ₃ O ₄ ). A characteristic artificial aggregate. 2. Silicon oxide, alumina, iron oxide, slaked lime,
In artificial aggregates mainly composed of magnesia, iron
5% by weight, containing 0.2 to 0.3% by weight of carbon, substantially consisting of an outer layer and an inner layer, wherein iron in the outer layer is mainly hematite (Fe ₂ O ₃ ) and iron in the inner layer is mainly wustite (FeO ₂ ). ) And / or magnetite (Fe ₃ O ₄ ). 3. A fly ash mixed with a binder, a composition mixture, and a reducing agent, and using coal or coke as a reducing agent, pulverizing the resulting mixture so that the average particle size is 15 μm or less; Next, water is added to the obtained pulverized product to form a molded body, and the molded body is calcined. In the method for producing an artificial aggregate, the calcining temperature is set to 1100 to 1200 ° C.
A method for producing an artificial aggregate, wherein the residence time at 1200 ° C. is 2 to 5 minutes. 4. Use of bentonite as a binder, use of a mineral containing silicon oxide as a composition mixture, and a chemical composition of the obtained mixture after calcination containing 20 to 80% by weight of silicon oxide.
4. The method according to claim 3, wherein the calcium oxide is mixed in an amount of 0.5 to 15% by weight, and coal or coke as a reducing agent is added in an amount of 2 to 9% by weight in terms of carbon amount. Method. 5. The method according to claim 3, wherein 2 to 10% by weight of iron oxide and / or silicon carbide having an average particle size of 10 μm or less is mixed as a foaming agent. 6. An oxygen concentration in exhaust gas at an exhaust gas outlet of a sintering furnace is set to 7 to 10% by volume.
The production method according to any one of the above. 7. The carbon grade in the artificial aggregate is 0.2 to 0.3.
%.
The production method according to any one of the above.