JP2000302498A - Production of artificial light-weight aggregate and artificial light-weight aggregate produced thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing an artificial light-weight aggregate capable of efficiently producing a harmless aggregate from refuse incineration ash and having high strength and low water-absorption while promoting the evaporation of heavy metals and harmful substances in the baking of the aggregate and provide an artificial light-weight aggregate produced by this process. SOLUTION: The objective process for the production of an artificial light- weight aggregate comprises the crushing of a mixture produced by mixing refuse incineration ash with a binder, a foaming agent, a reducing agent and silica and/or alumina as a composition controlling agent, the addition of water to the crushed mixture, the forming and optional drying of the product and two-stage baking of the formed material comprising the 1st stage baking at 850-1050 deg.C and the 2nd stage baking at 1060-1200 deg.C. The calcium content of the baked aggregate in the formed material is <=16 wt.% in terms of oxide, the foaming agent is iron oxide and/or silicon carbide and the reducing agent is a carbon material. The artificial light-weight aggregate produced by this process has an absolute-dry specific gravity of >=1.5 and <2.0, a uniaxial compressive strength of >=50 kgf and a water-absorption of <=5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an artificial lightweight aggregate for civil engineering and construction using garbage incineration ash generated from a garbage incineration facility or the like for recycling and effectively utilizing the ash. The present invention relates to a manufacturing method and an artificial lightweight aggregate obtained by the method.

[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, which collects ash scattered in exhaust gas. Most of the ash is landfilled as waste. I have. Above all, fly ash contains heavy metals such as lead, zinc, and cadmium.At present, it has been rendered harmless by melting and solidifying, cement solidifying, chelating, and acid washing to prevent elution of heavy metals. It has been later landfilled. However, the melt solidification method has a high processing cost, and in recent years it has been pointed out that the cement solidification method and the treatment for preventing elution of heavy metals are not sufficient, and other methods have a problem that they lack long-term reliability. Many municipalities are struggling to secure final disposal sites and extend the remaining years, so there is a long-awaited need to develop technology that effectively uses fly ash as waste instead of waste.

As one of the methods, the present inventors have previously described:
Using incinerated ash as a main raw material, add a composition control agent such as silica sand, pottery stone and feldspar, a binder, a foaming agent such as hematite and silicon carbide, and a reducing agent such as coke and calcinate it with a rotary kiln. Through this, we found a method of manufacturing artificial lightweight aggregates for civil engineering and construction with less elution of heavy metals,
This technique is disclosed in Japanese Patent Application Laid-Open No. 10-287675. According to the method described in this publication, incinerated ash can be used as artificial lightweight aggregate and can contribute to prolonging the remaining years of the final disposal site, but it mainly contains heavy metals and sulfides contained in the incinerated ash. The use of incinerated ash was limited due to the need to reduce the amount.

[0004]

SUMMARY OF THE INVENTION According to the present invention, the volatilization of heavy metals and harmful substances during the firing of aggregate is further promoted,
Provided is a method for producing an artificial lightweight aggregate capable of efficiently producing a harmless, high-strength, and low water absorption artificial aggregate using waste incineration ash as a main raw material, and an artificial lightweight aggregate obtained by the method. The purpose is to do so.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies on a method of converting waste incineration ash into aggregate and detoxifying the same, and as a result, the above-mentioned calcination is carried out in a two-stage method at a specific temperature range. The inventors have found that the object can be solved, and have completed the present invention.

[0006] That is, the first embodiment of the present invention is obtained by mixing waste incineration ash with a binder, a foaming agent, a reducing agent, and at least one of silica and alumina as a composition control agent. After the obtained mixture is pulverized, water is added to mold the mixture, and then, if necessary, the molded body is dried. Then, the molded body is subjected to a first step in a temperature range of 850 ° C. to 1050 ° C., and 1060 ° C. to 1200 ° C. Wherein the two-stage calcination with the second stage in the temperature range of ° C. is performed, wherein the calcium content in the baked aggregate of the molded body is 16% by weight or less in terms of oxide. And the foaming agent is at least one of iron oxide and silicon carbide.
And a method for producing an artificial lightweight aggregate using a carbon material as the reducing agent.

A second embodiment of the present invention is obtained by the manufacturing method according to the first embodiment, and has an absolute dry specific gravity of 1.5 or more and less than 2.0, and a uniaxial compressive breaking load of 50 kg.
It is characterized by an artificial lightweight aggregate having a water absorption of not less than f and not more than 5%.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be described more specifically below. The main components of clay and shale, which are the raw materials of general artificial lightweight aggregate, are silica, alumina, calcia, and the like, and the components of incineration ash are almost the same. And to make the artificial lightweight aggregate have mechanical strength, the inside of the pellet should be made into a semi-molten state during sintering and vitrified, and in order to reduce the weight, the inside is melted and at the same time a moderate viscosity decrease What is necessary is just to catch the bubble by a volatile component. However, refuse incineration ash generated from refuse incineration facilities and the like has a low melting point and rapidly melts compared with the above-mentioned artificial lightweight aggregate raw material, making it difficult to convert it into aggregate. Since the chemical and physical properties differ depending on the state, etc., to obtain aggregate having desired physical properties, the composition is controlled so that the chemical composition of the raw material approaches the chemical composition of the natural mineral that is the raw material of general artificial lightweight aggregate There is a need to. Furthermore, since the incineration ash contains heavy metals and harmful substances, it is necessary to detoxify the aggregate after firing.

The present invention provides an aggregate-mixed raw material obtained by adding a small amount of a binder, a foaming agent, a reducing agent and at least one of silica and alumina as a composition controlling agent to the incinerated ash. By sintering in two stages of the temperature before softening and the sintering temperature, and controlling the composition so that the calcium content in the aggregate after sintering is 16% by weight or less in terms of oxide, harmful substances can be reduced. Low and absolute dry specific gravity of 1.5 or more and less than 2.0, uniaxial compressive breaking load of 50 kg
It is characterized in that an artificial lightweight aggregate having a water absorption of not less than f and not more than 5% can be produced. The refuse incineration ash targeted by the present invention is not particularly limited,
Main ash, fly ash or a mixture thereof can be used.
Also, there is no particular effect on the particle size of the incineration ash.

The composition control agent to be added to the refuse incineration ash is not particularly limited as long as it is mainly composed of silica and / or alumina because of its chemical composition and has no adverse effect on the quality of aggregate after calcination. Shale, clay, pottery stone, feldspar, kaolinite, kibushi clay, industrial chemicals, minerals containing silica and alumina, and industrial by-products such as coal ash and sewage sludge. Silica in the composition control agent contributes to vitrification for developing the mechanical strength of the aggregate, or alumina contributes to generation of a mineral or glass phase effective for the aggregate strength. The addition amount of such a composition control agent may be appropriately selected so as to obtain the required physical properties according to the aggregate application, but an artificial lightweight aggregate having an absolute dry specific gravity of 1.5 or more and less than 2.0 is used. In order to obtain it, it is preferable to add calcium such that the content of calcium in the aggregate after firing is 16% by weight or less in terms of oxide. The reason is that if it exceeds 16% by weight, the optimum firing temperature range becomes high and the temperature range in which firing is possible becomes narrow. The content of calcium is preferably as small as possible, but the lower limit is about 5% by weight because it is contained in the refuse incineration ash which is the main raw material.

Next, the reason why the two-stage firing is performed in the aggregate firing process in the present invention is to obtain an aggregate satisfying detoxification, high strength and light weight. That is, the first stage firing is preferably performed for detoxification, and is performed at a temperature at which a liquid phase is formed in the pellets and softening does not occur. This is because the volatile component is blocked by the liquid phase and the volatilization is not promoted even when firing at a temperature higher than the softening temperature. The firing temperature at this time is 850 ° C. to 1
This is because an artificial lightweight aggregate having desired physical properties cannot be obtained with an aggregate blending raw material having a chemical composition that is in the range of 050 ° C. and softens outside this temperature range. The residence time in the first stage firing is not particularly limited, and can be appropriately changed so that the aggregate after firing is rendered harmless.

Next, firing in the second stage is performed for the purpose of developing strength and reducing the weight, and is performed at a temperature in the range of 1060 ° C. to 1200 ° C. The reason for limiting to this temperature range is that if the temperature is lower than 1060 ° C., the aggregate is unsintered and the strength is not developed.
If the temperature exceeds 0 ° C., the pellets are melted and a desired aggregate cannot be obtained. At this time, the residence time in the second stage firing can be appropriately changed so that the obtained aggregate has desired physical properties. In addition, heavy metals and the like generated by volatilization can be recovered and used as a metal refining raw material, so that the effective utilization rate of resources can be further increased.

The reason why the binder is added in the present invention is to impart the moldability and mechanical strength of the pellets after the granulation with water. The reason for this is that the powder of the pellets reduces the yield of the product, and the powdered powder adheres to the pellet surface in the vicinity of the sintering zone, or adheres to the inner wall of the rotary kiln, thereby hindering 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, natural rubber, and pulp waste liquid. Further, the amount of the binder added is not particularly limited, but in consideration of the effect of the addition and the cost, is 0.5%.
The range of from 10% by weight to 10% by weight is preferred.

Next, the reason why the blowing agent and the reducing agent are added in the present invention is that when a liquid phase is formed inside the pellets after the first stage firing and the pellets are in a semi-molten state, the blowing agent and the reducing agent are added. This is because the specific gravity is controlled by generating gas by the action and trapping the gas as bubbles in the pellet.
The foaming agent or reducing agent used is not particularly limited as long as it exhibits such effects, but in the present invention, iron oxide or silicon carbide is preferable as the blowing agent, and carbonaceous material is preferable as the reducing agent. Further, as the iron oxide used as a foaming agent, hematite having a high degree of oxidation is particularly preferable. The particle size of the iron oxide used as the foaming agent is not particularly limited, but is preferably 10 μm or less in order to promote a deoxidation reaction by the carbon material during firing. Further, the preferable amount of the foaming agent such as hematite to the whole of the aggregate compounding raw material is 1
% By weight. 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 reducing the weight by the foaming agent does not increase.

Silicon carbide used as a foaming agent is used when the granulated pellets generate a large amount of liquid phase by heating.
It captures CO and CO ₂ gas generated by efficiently reacting with iron oxide to promote foam swelling of pellets. The amount of silicon carbide was 0.1% by weight based on the total weight of the raw material containing the aggregate.
It is preferably from 1.0 to 1.0% by weight. The reason is,
If the amount is less than 0.1% by weight, the effect of reducing the absolute dry weight is not sufficient, while if it exceeds 1.0% by weight, the effect of reducing the weight does not increase.

The carbonaceous material as a reducing agent has a small effect, but exhibits a function such as foaming by reacting with iron oxide, such as coke. Therefore, it is possible to replace a part of the silicon carbide with a carbon material, and the carbon material has a great effect of adjusting the degree of reduction inside the pellet during firing. The amount of carbon added to the aggregate raw material is
It is preferably from 0.2% by weight to 10% by weight. The reason is that if it is less than 0.2% by weight, the effect of weight reduction by foaming cannot be obtained, while if it exceeds 10% by weight, the effect of weight reduction by foaming expansion does not increase. This is because it may remain inside the pellet and reduce the strength of the artificial lightweight aggregate.

In the pulverization method used in the present invention, the mixed aggregate-mixed raw material has an average particle size of 20 μm or less, preferably 15 μm or less.
Any method may be used as long as it can be finely pulverized to the following, and examples thereof include a ball mill such as a pot mill, a vibration mill, and a planetary mill, a collision-type jet pulverizer, and a turbo pulverizer. Next, the mixed and pulverized material with the refuse incineration ash, the binder, the reducing agent, the foaming agent and the composition controlling agent is dried and wet-kneaded if necessary. An apparatus can be used.

Any molding method may be used as long as it can be molded to a predetermined diameter. For example, it is convenient to use a pan pelletizer or an extruder. The obtained molded product is then dried and fired if necessary, but the firing method is not particularly limited.For example, it is preferable to use a rotary kiln in consideration of continuous operation and uniformity of quality,
The atmosphere can be arbitrarily selected according to desired aggregate physical properties. For example, the oxygen concentration in the combustion gas is 3 to 12%, the temperature in the first stage firing is 850 ° C. to 1050 ° C., the residence time is 10 minutes to 60 minutes, and then the temperature in the second stage firing is It is preferable to operate the rotary kiln in such a manner that the kiln structure such as 1060 ° C. to 1200 ° C. and the residence time is 10 minutes to 120 minutes in consideration of the gradient of the rotary kiln, the number of rotations, the installation of the dam and the kiln structure such as the inner diameter, etc. The drying method applied as necessary before firing is not particularly limited.

[0019]

The present invention will be described by the following examples and comparative examples.
This will be described in more detail. However, the present invention is not limited to the following examples.
It is not limited. The main incineration fly ash used
The component is SiO₂: 27.36% by weight, Al₂O ₃: 1
2.78% by weight, Fe₂O₃1.61% by weight, Ca
O: 14.26% by weight, MgO: 3.35% by weight, Na
₂O: 8.46% by weight, K₂O: 7.24% by weight
It is. In addition, silica sand, coal ash and
The main components of shale are as shown in Table 1 below.

[0020]

[Table 1]

Example 1 70% by weight of incinerated ash, silica sand 1
An aggregate blending material consisting of 7.5% by weight, 5% by weight of bentonite, 5% by weight of hematite, 2% by weight of coke and 0.5% by weight of silicon carbide was prepared by using a ball mill to obtain an average particle size of 1%.
The mixture was pulverized to 5 μm. While adding water to the ground material,
After granulating into a spherical shape having a diameter of about 5 mm to 15 mm using a pan pelletizer, the resultant was air-dried at 105 ° C. Then, the dried aggregate was supplied to a rotary kiln having a brick inner diameter of 400 mm, a length of 6000 mm, a dam of 2000 mm from the front of the furnace and a height of 50 mm on the side of the furnace, and an oxygen concentration of 5% in the combustion gas.
After the first stage of baking at 1000 ° C. for about 40 minutes under the above atmosphere, the second stage of baking was performed at 1060 ° C. for about 10 minutes to obtain an aggregate a (Example 1).

JIS to evaluate the quality of the obtained aggregate a
The specific gravity and the water absorption were measured based on A1110, and the crushing strength was measured using a uniaxial compressive breaking load. The results are shown in Table 2 below. The crushing strength was measured for each aggregate having a diameter of about 10 mm by a crushing tester, and the average value was obtained.

The content of CaO, the elution of lead, and the residual amount of sulfide as SO ₃ were measured and are shown in Table 2 below. As can be seen from Table 2, the aggregate a of Example 1 had an absolute dry specific gravity of 1.75, a crush strength of 70 kgf, and a water absorption of 4.5%.
Met. The lead elution amount was less than 0.01 mg / liter (reference value: 0.01 mg / liter or less), and the residual amount of SO ₃ was 0.2% by weight or less (reference value: 0.5% or less). Value and the CaO content is 1
It was 5.05% by weight.

Examples 2 to 5 and Comparative Examples 1 to 5 65% by weight of incinerated ash, 22.5% by weight of silica sand, 950 ° C. in the first stage firing, and 1100 ° C. in the second stage firing Aggregate c (Example 3) in the same manner as Example 2 except that the aggregate b (Example 2) was changed to silica sand and coal ash was changed to 22.5% by weight in the same manner as in Example 1. 55% by weight of incinerated ash, 32.5% by weight of coal ash,
Aggregate d (Example 4) was replaced with 67.5% by weight of incinerated fly ash, and shale was replaced with 20% by weight of silica sand in the same manner as in Example 1 except that 0 ° C. and then the firing in the second stage were performed at 1140 ° C. %, First
The stage baking was about 1005 ° C., then the second stage baking was 1
Aggregate e (Example 5) in the same manner as in Example 1 except that the temperature was set to 080 ° C., and the same as Example 1 except that the first-stage firing was set to 820 ° C. and then the second-stage firing was set to 1050 ° C. Aggregate f (Comparative Example 1), and aggregate g (Comparative Example 2) in the same manner as in Example 1 except that the first stage firing was not performed.
Aggregate h in the same manner as in Example 4 except that the first stage firing was 1055 ° C. and then the second stage firing was 1140 ° C.
(Comparative Example 3) Aggregate i (Comparative Example 4) was prepared in the same manner as in Example 5 except that the first-stage firing was performed at 1000 ° C. and then the second-stage firing was performed at 1230 ° C. %, Silica sand 12.5% by weight, an aggregate j (Comparative Example 5) was obtained in the same manner as in Example 1 except that the first stage firing was performed at 1000 ° C., and then the second stage firing was performed at 1050 ° C. .

The obtained Examples 2 to 5 and Comparative Examples 1 to 5
The same measurement as in Example 1 was performed for the aggregates b to j according to Example 1. The evaluation results and the amount of lead eluted, the amount of residual SO ₃ and the content of CaO are also shown in Table 2 below.

[0026]

[Table 2]

As can be seen from Table 2, the aggregates b to e according to Examples 2 to 5 have an absolute dry specific gravity of 1.55 to 1.75, a crush strength of 63 to 100 kgf, and a water absorption of 2.4 to 4.0. %Met. In contrast, the aggregate f of Comparative Example 1 had a water absorption of 6.
5% and a lead elution amount of 0.08 mg / liter,
The residual amount of SO ₃ was 1.97% by weight and did not meet the standard value.
In the aggregate g of Comparative Example 2, the residual amount of SO ₃ was 1.99% by weight.
And the aggregate h of Comparative Example 3 had an absolute dry specific gravity of 2.05.
And the lead elution amount was 0.05 mg / liter and the residual amount of SO ₃ was 1.54% by weight, which did not meet the standard values. Aggregate i of Comparative Example 4 could not be converted to an aggregate by meltdown. The aggregate j of Comparative Example 5 had a CaO content of 16
%, And neither crushing strength nor water absorption had desired physical properties.

[0028]

As described above, according to the present invention, it is possible to efficiently produce harmless, high-strength, low-water-absorbing artificial lightweight aggregates using waste incineration ash as a main raw material. Therefore, without having to reclaim industrial waste,
Since it can be recycled into building materials, it is extremely useful in environmental conservation and effective use of resources.

Continuing on the front page (72) Inventor Atsushi Katakei 3-18-5, China, Ichikawa, Chiba Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Koji Kawamoto 3-18-5, China, Ichikawa, Chiba Sumitomo Metal Mining Co., Ltd.

Claims (6)

[Claims] 1. A mixture obtained by mixing incineration ash with a binder, a foaming agent, a reducing agent, and at least one of silica and alumina as a composition controlling agent, is pulverized, and then ground. And molded, and then 8
A first stage with a temperature range of 50 ° C to 1050 ° C;
A method for producing an artificial lightweight aggregate, comprising performing a two-stage firing including a second stage in a temperature range of 60C to 1200C. 2. The method for producing an artificial lightweight aggregate according to claim 1, wherein the two-stage firing is performed after the molded body is dried. 3. The method for producing an artificial lightweight aggregate according to claim 1, wherein the calcium content in the fired aggregate of the molded body is 16% by weight or less in terms of oxide. 4. The method according to claim 1, wherein the foaming agent is at least one of iron oxide and silicon carbide.
The method for producing an artificial lightweight aggregate according to any one of claims 1 to 3. 5. The method for producing an artificial lightweight aggregate according to claim 1, wherein the reducing agent is a carbonaceous material. 6. The method of claim 1, wherein the absolute specific gravity is 1.5 or more and 2.0 or more.
Less than, uniaxial compression breaking load is 50 kgf or more, water absorption is 5
% Artificial artificial aggregate, characterized in that the amount is not more than 10%.