JPH10194804A - Production of artificial aggregate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for effectively using a fly ash obtained by the incineration of municipal refuse and large in the content of lime as a resource. SOLUTION: A raw material composed of the fly ash, a caking agent and silica sand are mixed and adjusted to be 50-80wt.% in the silica content and 15-35wt.% in calcium oxide contained in an artificial aggregate, 1-10wt.% coke and 3-12wt.% hematite in the addition ratio to the raw material are added and uniformly mixed while being pulverized into <=15μm average particle diameter and water is added thereto to form a formed body, which is fired at 1000-1300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an artificial aggregate, and more particularly, to a method for producing an artificial aggregate using fly ash scattered in exhaust gas from incineration.

[0002]

2. Description of the Related Art At incineration facilities installed in various places, most of incineration ash generated when incinerating goods such as municipal solid waste and fly ash that collects dust scattered in exhaust gas are waste. Has been disposed of as landfill. At present, fly ash designated as a specially controlled waste is disposed of by landfill after performing the treatment to prevent elution of heavy metals such as the melt solidification method and the chelate treatment method.

However, when a treatment for preventing elution of heavy metals is performed,
The disposal costs are significantly higher than when landfilled without this. In addition, given that many municipalities are struggling to secure final disposal sites and extend their lives, it is not preferable to increase the volume of waste after elution prevention treatment of heavy metals.

Therefore, attention has been paid to a technique for solving these drawbacks, and effectively recycling and effectively using incinerated main ash and fly ash as wastes at low cost. That is, for example, using fly ash as a raw material, a binder and a composition formulating agent are added thereto so that the silica content and the calcium oxide content after firing become specific amounts, and if necessary, the mixture is added to the mixture. On the other hand, hematite and silicon carbide are added in specific amounts and fired.
As a result, an artificial aggregate is obtained in which the elution of lead, which is a heavy metal contained in fly ash, is relatively small, and has sufficient strength and durability for construction and civil engineering.

[0005]

Generally, when incinerators such as municipal waste are incinerated in an incineration facility, slaked lime is introduced before the exhaust gas enters a bag filter or an electric dust collector in order to remove hydrogen chloride contained in the exhaust gas. Is sprayed. For this reason, the lime content in fly ash varies greatly from about ten to several percent to about 50% based on calcium oxide, depending on the amount of slaked lime sprayed.

As described above, hematite and silicon carbide are added when fly ash having a low lime content is used as a raw material. Thereby, hematite and silicon carbide exhibit an effect as a foaming agent, and an artificial aggregate having a small specific gravity can be obtained. However, when fly ash having a high lime content such that the calcium oxide content after firing exceeds 15% by weight is used, the fired product is compacted, the specific gravity does not decrease, and hematite and silicon carbide are used as blowing agents. No effect.

Therefore, when the lime content is large, a lightweight artificial aggregate cannot be obtained because no foaming agent is added. Furthermore, when fly ash having a high lime content is used, the firing temperature becomes extremely high and the firing temperature range becomes extremely narrow, so that the strength of the fired product is not sufficient and the use is limited.

[0008] Therefore, depending on the demand destination, fly ash having a relatively low lime content is limited to fly ash, and fly ash having a high lime content is discarded. The contribution is also reduced.

An object of the present invention is to solve the above-mentioned problems and to provide means for effectively using fly ash having a high lime content as a resource.

[0010]

Means for Solving the Problems As a result of repeated studies to solve the above problems and achieve the above object, the present inventors have obtained:
In order to handle fly ash with high lime content as a raw material for artificial aggregate, it is necessary to sinter a compact (pellet) made from the fly ash at a relatively low temperature. The purpose is achieved by adjusting the silica content and the calcium oxide content after firing to specific amounts by blending fly ash, a binder and a composition preparation agent, and adding specific amounts of coke and hematite. The inventors have found that the present invention can be performed, and have completed the present invention.

That is, according to the present invention, a raw material comprising fly ash, a binder and silica sand is ground and uniformly mixed to an average particle size of 15 μm or less, and water is added to form a molded product.
When producing the artificial aggregate by firing at 000 to 1300 ° C., the raw material is mixed with the silica having a silica content of 50 to 8 in the artificial aggregate.
0% by weight, calcium oxide content is adjusted to be 15 to 35% by weight and mixed. Coke and hematite are added at a rate of 1 to 10% by weight,
It is added so as to be in a range of 12% by weight. And it is preferable to use bentonite as a binder, and it is further preferable to set the addition rate of bentonite to 1 to 10% by weight. Further, it is preferable that the molded body is in the form of a pellet and the size is 5 to 15 mm.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The silica content in an artificial aggregate obtained by firing is set to 50 to 80% by weight. This allows
The firing temperature can be lowered and the strength of the fired product can be increased.
That is, if the silica content is less than 50% by weight, the strength of the fired product may not be sufficient, and if it exceeds 80% by weight, the adhesiveness of the molded article (pellet) in the kiln increases, and In addition, the amount of the composition preparation to be used for fly ash that should be treated is increased, and the meaning of waste treatment is reduced. To mix the silica content in this range, silica sand is used as a composition preparation.

Further, the content of calcium oxide in the fired product is set to 15 to 35% by weight. Calcium oxide content is 15
Less than% by weight is the effect of lowering the firing temperature of hematite (described later).
Is not good. On the other hand, when the calcium oxide content is 3
If it exceeds 5% by weight, the firing temperature exceeds 1300 ° C., which is not practical, and the temperature range in which the artificial aggregate can be fired is narrowed. If the temperature exceeds the appropriate firing temperature, the pellets adhere to the inner wall of the kiln, or sintering becomes insufficient due to firing at a temperature lower than the appropriate temperature, causing a problem that the strength of the fired product is not developed or heavy metal elution increases. .

[0014] The reason for adding coke is that, as a combustion aid, it has the effect of lowering the firing temperature, and when a predetermined amount is added, the elution of lead and chloride can be extremely reduced. The addition of coke promotes the volatilization of lead, and the amount of residue in the fired product becomes extremely small. Although the reason why such an effect can be brought about cannot be determined, (1) the addition of coke causes a reducing atmosphere in the furnace, and lead is easily volatilized. (2)
It is presumed that the coke and the lead compound in the fly ash react in the compact (pellet) to form a form that is easy to volatilize, and these are intertwined in a complicated manner, thereby producing a synergistic effect. It is thought to be due to this.

Note that only one of the above (1) and (2)
For example, even if the reducing atmosphere alone is strengthened, it is expected that the same effect as the effect of the present invention can be obtained if the conditions are selected, but this requires a long kiln and a large amount of coke. The addition of coke can be performed separately from the production of the molded product (pellet). However, if the effect of suppressing the elution of lead is due to the above-mentioned estimation reason, coke is added at the same time as the production of the molded product (pellet). Mixing is more efficient in reducing lead compounds.

[0016] The reason why the addition rate of coke is set to 1 to 10% by weight is that if it is less than 1% by weight, volatilization of the lead compound is not sufficient due to uneven distribution of the lead compound in the molded article (pellet) and elution is caused. This is because if the addition ratio exceeds 10% by weight, unreacted coke remains in the fired product after firing, so that the strength as an artificial aggregate decreases.

Hematite acts as a foaming agent, but has the effect of lowering the firing temperature when added in a predetermined amount. That is, as described above, the calcium oxide content is 15 to
If it is within the range of 35% by weight, the firing temperature can be lowered. Therefore, even when fly ash having a high lime content is used, problems such as furnace durability and fuel cost can be solved, and an artificial material having sufficient strength can be obtained. Aggregate is obtained.

The reason for setting the addition ratio of hematite to 3 to 12% by weight is that if it is less than 3% by weight, the effect of lowering the sintering temperature to solve the problems such as furnace durability and fuel cost cannot be obtained. Even if hematite exceeds 12% by weight, the effect of lowering the firing temperature does not increase, and the long-term durability of the artificial aggregate is adversely affected.

Further, the reason for using the binder is to suppress the powdering of the compact (pellet) in the rotary kiln when the firing is performed in the rotary kiln. In other words, when the powder of the compact (pellet) is remarkably powdered, not only the yield of the artificial aggregate decreases, but also the powder adheres to the surface of the compact in the firing zone in the kiln, and this serves as an adhesive. As a matter of fact, the compacts adhere to the kiln and adhere to each other, which hinders continuous operation.

When bentonite is used as a binder, the addition rate is preferably 1 to 10% by weight. This is because if the bentonite addition rate is less than this range, the effect of suppressing powdering cannot be obtained, and even if added beyond this range, no further effect can be expected.

As a device used in the practice of the present invention, it is preferable to use a ball mill for pulverization. The average particle size after pulverization is preferably 15 μm or less, and if the average particle size is larger than this, the strength of the fired product is not sufficient. Note that pulverization of 1 μm or less is not practical in actual operation using a ball mill or the like, and therefore, pulverization of about 1 μm will be the lower limit.

For molding, for example, a bump pelletizer or an extrusion molding machine can be used, and the size of the molded product (pellet) is preferably 5 to 15 mm. This takes into account the appropriate dimensions for the utilization of the artificial aggregate obtained by firing.

In the firing, it is preferable to use a rotary kiln in consideration of a processing amount. And the firing temperature is 10
00 to 1300 ° C., which means that the firing temperature is 100 ° C.
If the temperature is lower than 0 ° C., the sintering is not sufficient, and if the temperature exceeds 1300 ° C., there is a problem in the furnace durability and fuel cost. In addition, when using a rotary kiln, the residence time depends not only on the progress of volatilization of lead and chloride, but also on the compact (pellet).
It is known that it affects the progress of the sintering, the adhesion to the inner wall of the rotary kiln, and the progress of the oxidation of the surface of the molded body. Therefore, it is necessary to set the residence time in consideration of these effects. That is, if the residence time is too short, the volatilization of lead, chloride and the like is insufficient, or the sintering is insufficient, so that the strength of the artificial aggregate decreases. Conversely, if the residence time is too long, the oxidation of the molded body will proceed too much and the strength of the artificial aggregate will be reduced, and if the residence time in the sintering zone is too long, the molded body will adhere to the kiln inner wall. It is preferable that the heating time is about 20 to 90 minutes.

As described above, even when fly ash having a high lime content is used, the elution of lead and chloride is extremely small, and an artificial aggregate having sufficient strength and durability for construction and civil engineering can be obtained. Obtainable.

[0025]

Next, examples of the present invention will be described together with comparative examples.

Example 1 The artificial aggregate obtained after firing had a silica content of about 57% and a calcium oxide content of about 1
Using fly ash A, silica sand and bentonite having the chemical composition shown in Table 1 so as to be 7% by weight, as shown in Table 2, fly ash A 55% by weight, silica sand 40% by weight and bentonite 5% , 1% by weight of coke and 3% by weight of hematite were weighed, and pulverized and mixed using a ball mill, and the particle size distribution of the pulverized mixture was measured by a laser diffraction type particle size distribution meter.

The obtained ground mixture was granulated into a spherical shape having a diameter of 5 to 15 mm using a bumper while moistening with water, and then dried for 30 minutes. For firing, the inside diameter of the brick is 300m
m, 11 using a 4800 mm rotary kiln
Firing was performed at 50 ° C. so that the residence time was 40 minutes.

Table 3 shows the average particle size and firing temperature of the obtained raw materials.
Table 4 shows the content of silica and calcium oxide in the artificial aggregate obtained after firing.

Table 5 shows the results of the lead dissolution test performed by the method specified in the Environment Agency Notification No. 13 and the chloride dissolution test performed by the method specified in JIS A5002. Further, Table 6 shows the crushing strength of the fired product having a diameter of 10 mm and the measurement results of the specific gravity measured by the method specified in JIS A1110.

Example 2 Fly ash having a chemical composition as shown in Table 1 so that the artificial aggregate obtained after firing has a silica content of about 57% by weight and a calcium oxide content of about 17% by weight. A, silica sand, and bentonite were weighed as shown in Table 2 so as to obtain a raw material mixture of fly ash A 55% by weight, silica sand 40% by weight, bentonite 5% by weight, coke 1% by weight, and hematite 12% by weight. And the firing temperature is 1080
The same treatment as in Example 1 was conducted except that the temperature was changed to ° C., and the same test was performed. Tables 5 and 6 show the obtained results.

[Examples 3 to 8] Using fly ash A or fly ash B having a chemical composition as shown in Table 1, silica sand, and bentonite, the mixing ratios correspond to the example numbers shown in Table 2, respectively. In the same manner as in Example 1 at the corresponding firing temperatures shown in Table 3, the same test was conducted.
Tables 5 and 6 show the obtained results.

From these results, the lead elution of the fired product obtained in this way was 0.01 mg / l which is an environmental standard.
The chloride elution satisfies the elution standard of artificial aggregate of 0.01% or less (NaCl standard) or less, and since sufficient strength has been obtained, it can be used for building and civil engineering bone. It shows that it can be used as a material.

Comparative Example 1 Fly ash having a chemical composition as shown in Table 1 such that the artificial aggregate obtained after firing has a silica content of about 37% by weight and a calcium oxide content of about 39% by weight. Using A, silica sand and bentonite, as shown in Table 2, fly ash A 80% by weight, silica sand 15% by weight, bentonite 5% by weight, coke 5% by weight, hematite 8% by weight
And sintering temperature of 1300 ° C
Other than that, the treatment was performed in the same manner as in Example 1, and the same test was performed. Tables 5 and 6 show the obtained results.

Comparative Example 2 Fly ash having a chemical composition as shown in Table 1 such that the artificial aggregate obtained after firing has a silica content of about 56% by weight and a calcium oxide content of about 16% by weight. As shown in Table 2, using A, silica sand and bentonite, the raw material mixture was such that fly ash A was 55% by weight, silica sand was 40% by weight, bentonite was 5% by weight, coke was 0.5% by weight, and hematite was 8% by weight. And the firing temperature is 112
The same treatment as in Example 1 was conducted except that the temperature was set to 0 ° C., and the same test was performed. Tables 5 and 6 show the obtained results.

[Comparative Example 3] The silica content after firing was about 5
Using fly ash A, silica sand, and bentonite having a chemical composition as shown in Table 1 so that the content of calcium oxide becomes 9% by weight and the content of calcium oxide becomes about 18% by weight, fly ash A55 as shown in Table 2
The same treatment as in Example 1 was carried out except that the raw materials were weighed so as to obtain a raw material mixture of 40% by weight of silica, 40% by weight of silica sand, 5% by weight of bentonite, 15% by weight of coke, and 8% by weight of hematite. A similar test was performed. Tables 5 and 6 show the obtained results.

Comparative Example 4 The silica content after firing was about 5
Using fly ash B, silica sand, and bentonite having the chemical composition shown in Table 1 so that the content of calcium oxide becomes about 28% by weight and fly ash B55 as shown in Table 2,
%, Silica sand 40%, bentonite 5%, coke 5%, and hematite 1% by weight. A similar test was performed. Tables 5 and 6 show the obtained results.

[Comparative Example 5] The silica content after firing was about 5
Using fly ash B, silica sand, and bentonite having a chemical composition as shown in Table 1 so that the content of calcium oxide becomes about 29% by weight and fly ash B55 as shown in Table 2,
Except that the raw materials were weighed so as to obtain a raw material mixture of 1% by weight, a sintering temperature of 1290 ° C, and a sintering temperature of 1290 ° C.
Processing was performed in the same manner as in Example 1, and a similar test was performed. Tables 5 and 6 show the obtained results.

From these results, those of the comparative examples cannot be used as artificial aggregates because one or both of the elution of lead and chloride and the crushing strength are out of specification. It clearly shows that even if the same raw material is used, the object cannot be achieved outside the specified range of the present invention.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

[Table 6]

[0045]

According to the present invention, even when fly ash having a high lime content is used, the calcined product obtained by adding the coke and the hematite to the specific range with the silica content after the calcination in a specific range is obtained. It can be reused as aggregate for construction and civil engineering, and has a remarkable effect that can solve the problem of shortage of final disposal sites.

Claims (3)

[Claims] 1. A raw material comprising a fly ash, a binder, and silica sand is pulverized to an average particle size of 15 μm or less, uniformly mixed, and water is added to form a molded body.
When the artificial aggregate is manufactured by firing at ℃, the raw materials are adjusted and mixed so that the silica content of the artificial aggregate is 50 to 80% by weight and the calcium oxide is 15 to 35% by weight, and further, coke is added. Production of artificial aggregate, characterized in that coke and hematite are added so that the ratio is in the range of 1 to 10% by weight based on the raw material and the addition ratio of hematite is in the range of 3 to 12% by weight based on the raw material. Method. 2. The method for producing an artificial aggregate according to claim 1, wherein bentonite is used as a binder, and the addition ratio is 1 to 10% by weight. 3. The method for producing an artificial aggregate according to claim 1, wherein the compact is a pellet having a size of 5 to 15 mm.