JP2000290050A - Production of artificial lightweight aggregate and artificial lightweight aggregate obtained by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for inexpensively producing high quality artificial lightweight aggregate reduced in the absolute dry specific gravity with the addition of a small quantity of an easily obtainable low cost additive and capable of exhibiting high strength with a relatively low temp. treatment and the artificial light weight aggregate obtained by the method. SOLUTION: The producing method of the artificial lightweight aggregate is by mixing a foaming agent and if necessary, a binder with coal ash of a main raw material and crushing, wet-kneading the crushed material with a m.p. decreasing agent consisting of an alkali metal silicate, molding, drying and firing. The firing is performed at 950-1300 deg.C, the adding quantity of the alkali metal silicate per total aggregate blending materials is >=0.5 wt.% to <=10 wt.%. The foaming agent is composed of iron oxide and at least one kind of silicon carbide or a carbonaceous material. The artificial lightweight aggregate obtained by the method has a absolute dry specific gravity of 0.5-1.5, >=50 kgf compression breaking load and <=15% water absorption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to artificial lightweight aggregates, and more particularly, to recycling coal ash generated from coal-fired power plants and coal-fired boilers as artificial lightweight aggregates for civil engineering and construction. The present invention relates to a method for producing an artificial lightweight aggregate for effective use and an artificial lightweight aggregate obtained by this method.

[0002]

2. Description of the Related Art Coal has abundant resources compared to petroleum and a low price per unit calorific value. Therefore, the domestic energy policy is planning or implementing a large increase in the amount of fuel used especially as fuel for power generation. is there. As a result, the amount of coal ash generated from coal-fired power plants and coal-fired boilers has increased almost in proportion to the amount of coal used. As effective utilization of such coal ash, utilization as artificial lightweight aggregate is suitable in terms of mass processing because of its large demand.
However, although coal ash is partially aggregated by the sinter great method, its use as artificial aggregate is extremely small in Japan at present. The cause is that coal-fired power plants and coal-fired boilers use coal that generates high melting point ash in order to reduce the adhesion of ash to boiler water pipes and boiler walls. is there.

That is, coal ash generated from a coal-fired power plant or a coal-fired boiler generally has a high melting point,
In order to make a lightweight aggregate, it is necessary to mix a large amount of low melting point clay or shale and fire it. However, it is difficult to secure a large amount of these clays and shale, and many steps and costs are required to mine, transport, pre-process, and mix these clays and shale. That the cost is high, and that the utilization rate of coal ash per unit product is low,
In addition, the absolute dry specific gravity of the artificial lightweight aggregate obtained by using coal ash is about 1.3 to 1.4, which limits the application. The artificial dry aggregate having a smaller absolute dry specific gravity and a lighter and stronger strength is used. Coal ash has not been effectively reused as artificial lightweight aggregate due to problems such as the fact that the technology for producing lightweight aggregate has not been developed yet.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of such circumstances, and can reduce the absolute dry specific gravity, which is suitable for adding a small amount of easily available and inexpensive additives. It is an object of the present invention to provide a method for inexpensively producing a high-quality artificial lightweight aggregate that exhibits high strength even at a low temperature treatment and an artificial lightweight aggregate obtained by this method.

[0005]

Means for Solving the Problems The present inventors have increased the use rate of coal ash per unit product to increase its effective utilization rate, can reduce the absolute dry specific gravity, can exhibit high strength, and can reduce the cost. As a result of intensive studies on a suitable production method, the above problem can be solved by mixing a foaming agent, a binder if necessary, and a melting point depressant composed of an alkali metal silicate into coal ash as a main raw material. This led to the completion of the present invention.

That is, in order to achieve the above object, in a first embodiment of the present invention, coal ash as a main raw material is mixed with a foaming agent and, if necessary, a binder, and ground, and the ground material is treated with an alkali. The method is characterized by a method for producing an artificial lightweight aggregate, which is formed by wet-kneading with a melting point depressant made of a metal silicate, molding, and then drying and firing.
The process was carried out at a temperature of 0 ° C., and the amount of the alkali metal silicate added to the total raw material for the aggregate was 0.5% by weight or more and 10% by weight in terms of the total alkali metal oxide contained in the alkali metal silicate. % Or less, and the foaming agent is made of iron oxide and at least one of silicon carbide and carbonaceous material.

[0007] A second embodiment of the present invention is obtained by the method according to the first embodiment, and has an absolute dry specific gravity of 0.5 to 1.5, a uniaxial compressive breaking load of 50 kgf or more, It is characterized by an artificial lightweight aggregate having a water absorption of 15% or less.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be described more specifically below. The present invention adds the melting point depressant consisting of an alkali metal silicate to coal ash as a main raw material, so that the melting point of coal ash is from 950 ° C. to 1300 ° C.
° C, preferably 1000 ° C to 1250 ° C, and the absolute dry specific gravity is lowered by adding iron oxide and a carbon material such as silicon carbide and / or coal or coke as a foaming agent. It is characterized by a method for producing an artificial lightweight aggregate having a high strength of about 0.5 to 1.5. The carbonaceous material also functions to adjust the reduced state inside the granulated pellets during firing.

First, coal ash as a main raw material used in the present invention is not particularly limited. For example, raw powder which is a mixture of fly ash and synda ash, JIS A62
All coal ash can be used, including fly ash, coarse powder, clinker ash, etc., that meet 01. Also, there is no particular effect on the particle size of the coal ash.

Next, the blowing agent used in the present invention is iron oxide,
It is composed of at least one of silicon carbide and carbonaceous materials, and is added to control the absolute dry specific gravity of the artificial lightweight aggregate to about 0.5 to 1.5. The foaming agent is not particularly limited as long as it exerts the above-mentioned effects. For example, hematite having a high oxidation degree is preferable among iron oxides. The average particle size of the iron oxide is not particularly limited, but is preferably 10 μm or less in order to promote a deoxygenation reaction by the carbon material during firing. Further, the preferable addition amount of Fe ₂ O ₃ to the whole of the aggregate compounding raw material is 1% by weight to 10% by weight.
The reason is that if the content is less than 1% by weight, the effect as a foaming agent is small, and the absolute dry specific gravity of the artificial lightweight aggregate cannot be controlled to about 0.5 to 1.5. This is because the effect of weight reduction by the above does not increase any more. The specific gravity of iron oxide is significantly higher than that of coal ash, and if foaming is not promoted, the specific gravity of the artificial lightweight aggregate will increase.

Silicon carbide has the effect of promoting the foaming of pellets. First, when the granulated pellet is heated to generate a large amount of liquid phase, silicon carbide and iron oxide react efficiently to generate CO and CO ₂ . Then, these gases are trapped in the liquid phase, and the foaming of the pellets is promoted. It is preferable that the amount of silicon carbide to be added to the whole of the aggregate compounding raw material is 0.1% by weight to 1% by weight. That is, when the addition amount is less than 0.1% by weight, the absolute dry specific gravity is 1.5.
This is because the following aggregates cannot be obtained and the weight cannot be reduced. On the other hand, even if the weight exceeds 1% by weight, the lightening effect is not further increased. Further, coal and coke can be used as the carbonaceous material, and although the effect is small, it reacts with iron oxide to exert a function such as a foaming action. Therefore, it is possible to replace a part of silicon carbide with a carbon material. The carbon material has a great effect of adjusting the degree of reduction inside the pellets during firing. The amount of the carbonaceous material added to the whole of the raw material for the aggregate is 0.2% by weight or more.
Preferably it is 10% by weight. That is, if the addition amount is less than 0.2% by weight, the effect of weight reduction by foaming cannot be obtained. On the other hand, if the addition amount 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.

Since the alkali metal silicate described below has the function of the binder, it is not necessary to add a new binder, but if necessary, it can impart the moldability and strength of the granulated material. To be added. The type of the binder is not particularly limited, for example, inorganics such as bentonite, starch, molasses,
Lignin, polyvinyl alcohol, methyl cellulose,
Organics such as natural rubber and pulp waste liquid are exemplified. The amount of addition is not particularly limited, but is preferably in the range of 0.5% by weight to 10% by weight in consideration of the effect of addition and cost.

Next, the melting point depressant used in the present invention will be described below. Coal ash often has an extremely high temperature of 1400 ° C. to 1500 ° C. for forming and sintering a liquid phase. Firing the artificial lightweight aggregate at 1400 ° C. to 1500 ° C. is not practical in terms of the fire resistance of the firing equipment, energy cost, and difficulty in selecting a foaming agent. Conventionally, when baking such a high refractory raw material, a method of adding a large amount of a natural mineral such as low refractory clay or shale containing a large amount of alkali metals as a melting point depressant has been generally used.
The present inventors have conducted various studies on the effects of adding clay and shale, and as a result, it has been confirmed that a small amount of alkali metals among these constituents significantly lowers the liquidus temperature. It has been confirmed that the element exhibiting the effect of lowering the liquidus temperature is not limited to the above-described alkali, and that any element constituting the low-melting oxide, such as boron or lead, exhibits the effect. .

As a result of further study of a less expensive production method, the present inventors have found that an alkali metal silicate can be used as a melting point depressant. Alkali metal silicate used in the present invention is not specifically limited, for example, M _{2
O · nSiO 2 · mH 2 O} (M: sodium, potassium, lithium, etc.) or its but anhydride salts, sodium salts from the viewpoint of cost are preferred.

In the artificial lightweight aggregate according to the present invention, the aggregate
Preferable alkali metal silicate with respect to the whole compounding raw material
The amount of addition depends on the total amount contained in the alkali metal silicate.
10 weight% at 0.5% or more in terms of alkali metal oxide
% Or less. This is because the chemical composition of coal ash differs depending on the type of coal.
Although, SiO₂: 40-75% by weight, Al
₂O ₃: 15 to 35% by weight, Na₂O: 0.2-2 weight
%, K₂O: 0.2 to 4% by weight, said alkali
The melting point drop increases with the amount of metal silicate added.
The temperature range for solubilization becomes longer, and the firing of aggregate
This is from the viewpoint of improving characteristics and coal ash utilization. And annex
The reason for setting the addition amount in the above range is that if the addition amount is less than 0.5% by weight,
The effect of point descent is not fully exhibited, and on the other hand, exceeds 10% by weight
Even if it is added, no more special effect can be obtained,
Costs due to increased use of alkali metal silicates
High and the utilization rate of coal ash decreases.
Because it is not.

In the pulverization method used in the present invention, the mixed aggregate-mixed raw material has an average particle size of 30 μm or less, preferably 20 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 product of the main raw material coal ash and the foaming agent and, if necessary, the binder is kneaded with a melting point depressant composed of an alkali metal silicate, but the kneading method to be employed is not particularly limited and a known kneading method is used. A kneading device can be used.
Here, kneading water may not be added depending on the amount of alkali metal silicate added, so that kneading can be performed more easily. The molding method to be subsequently performed is not particularly limited as long as it can be molded to a predetermined diameter, and it is convenient to use a known molding device. In addition, since an alkali metal silicate has a function as a binder, molding can be performed more easily without newly adding a binder.

Although the firing method is not particularly limited, for example, a rotary kiln is preferably used in consideration of continuous operation and uniformity of quality, and the atmosphere can be arbitrarily selected according to desired aggregate characteristics. For example, the oxygen concentration in the combustion gas is 3% to 12%, and the firing zone temperature is 950 ° C to 1300 ° C.
C., preferably 1000 ° C. to 1250 ° C., and the kiln gradient, the number of rotations, the kiln structure such as the dam installation and the inner diameter, etc., so that the residence time of the molded body at the firing zone temperature is 10 minutes to 120 minutes. It is preferable to operate the rotary kiln taking into account. The drying method to be performed before firing is not particularly limited. However, in some cases, the molded body can be directly charged into a rotary kiln, and drying and firing can be simultaneously performed in the rotary kiln.

[0018]

The present invention will be further described below with reference to examples and comparative examples. However, the present invention is not limited to the following examples. The coal ash used was SiO ₂ : 56.2.
0% by weight, Al ₂ O ₃ : 32.10% by weight, Fe
₂ O ₃ : 3.57% by weight, CaO: 0.59% by weight, M
gO: 1.40 _wt%, Na 2 O: 0.22 wt%, K
₂ O: 0.48% by weight as a main component. Example 1 An aggregate-mixed raw material composed of 87.5% by weight of coal ash, 5% by weight of bentonite, 5% by weight of hematite, 0.5% by weight of silicon carbide and 2% by weight of coke was averaged in a ball mill to have an average particle diameter of 20 μm. And pulverized. After adding 42.1% by weight (Na ₂ O = 4% by weight) of commercially available No. 3 water glass as an alkali metal silicate to the total amount of the pulverized product, kneading, extrusion molding and ventilation drying at 105 ° C. And then a rotary kiln (brick inner diameter 400mm x length 6000m
m), the oxygen concentration in the combustion gas is 10%, 101
The artificial lightweight aggregate was prepared by firing at 0 ° C. for 10 minutes. As the evaluation of the obtained artificial lightweight aggregate, the absolute dry specific gravity and the water absorption were measured based on JIS A1110, and the crushing strength was measured by a uniaxial compressive breaking load. The crushing strength was measured for each aggregate having a diameter of 10 mm by a crushing tester, and the average value was obtained. The obtained measurement results are shown in Table 1 below.

[Examples 2 to 9] Aggregate-mixed raw materials were 89.5% by weight of coal ash, 5% by weight of bentonite, and 5% by weight of hematite.
Example 2 was repeated in the same manner as in Example 1 except that the weight of the raw material was changed to 0.5% by weight, silicon carbide and 0% by weight of coke.
Hematite 5% by weight, Silicon carbide 0.5%, Coke 2
Example 3 was repeated in the same manner as in Example 1 except that the weight% was used.
Example 1 was repeated in the same manner as in Example 1 except that the raw material for the aggregate was 92.5% by weight of coal ash, 0% by weight of bentonite, 5% by weight of hematite, 0.5% by weight of silicon carbide and 2% by weight of coke. 4, the temperature of the low-kill kiln is 1030 ° C,
Example 5 and Example 6 were obtained in the same manner as in Example 1 except that the temperature was changed to 1,050 ° C. In Examples 2 to 6, the amount of commercially available No. 3 water glass was the same as in Example 1.

Further, the amount of the commercially available No. 3 water glass added to the same aggregate-mixed raw material as in Example 1 was 8.4% by weight (Na
Water was added and kneaded as _{2 O} = 0.8 wt%), Example 7 in the same manner as in Example 1 except that the firing temperature was 1170 ° C. in a rotary kiln, the addition of commercial water glass No. 3 Amount 21.1% by weight (Na ₂ O = 2% by weight)
The firing temperature in a rotary kiln is 1030 ° C., 1050
Example 8 and Example 9 were obtained in the same manner as in Example 1 except that the temperature was changed to ° C.

Comparative Examples 1 and 2 Comparative Example 1 was repeated in the same manner as in Example 1 except that the sintering temperature in the rotary kiln was changed to 900 ° C. 1 _wt% (Na 2 O = 0.2 wt%) and water was added and kneaded, the sintering temperature of the rotary kiln 119
Comparative Example 2 was obtained in the same manner as in Example 1 except that the temperature was changed to 0 ° C. The same evaluation test as in Example 1 was performed on the artificial lightweight aggregates obtained in Examples 2 to 9 and Comparative Examples 1 and 2, and the measurement results are shown in Table 1 below.

[0022]

[Table 1]

As can be seen from Table 1, according to Example 1, the absolute dry specific gravity was 1.18, the crush strength was 69 kgf, and the water absorption was 1
2.9% of artificial lightweight aggregate was obtained. Further, Examples 1 to
According to 5, 7 to 9, the absolute dry specific gravity is 1 to 1.5 and the water absorption is 1
A high-strength artificial lightweight aggregate having a crushing strength of 5% or less and a crushing strength exceeding 60 kgf was obtained. In addition, according to Example 6, an aggregate having a crushing strength equivalent to that of a commercially available artificial lightweight aggregate and a water absorption of 12.6% was obtained even when the absolute dry specific gravity was less than 1. On the other hand, according to Comparative Example 1, as a result of insufficient foaming due to a low firing temperature, an artificial lightweight aggregate having an absolute dry specific gravity of 1.5 or less was not obtained. As a result of insufficient melting point drop due to a small amount of metal silicate added, an artificial lightweight aggregate having an absolute dry gravity of 1.5 or less could not be obtained.

[0024]

As described above, according to the present invention, an extremely light, high-strength, high-quality artificial lightweight aggregate can be produced at a low cost using coal ash generated from a coal-fired power plant or a coal-fired boiler as a raw material. Can be produced efficiently and without having to reclaim and dispose of industrial waste.In particular, it can be recycled into civil engineering and building materials that require lighter weight. A great effect can be achieved.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shingo Sudo 3-18-5, China, Ichikawa, Chiba Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Koji Kawamoto 3-18-, China, Ichikawa, Chiba 5. Sumitomo Metal Mining Co., Ltd. Central Research Laboratory

Claims (6)

[Claims] 1. A method of mixing a coal ash as a main raw material with a foaming agent, pulverizing the mixture, wet-kneading the pulverized material with a melting point depressant comprising an alkali metal silicate, molding, and then drying and firing. A special method of manufacturing artificial lightweight aggregate. 2. The method for producing an artificial lightweight aggregate according to claim 1, wherein a binder is mixed with the coal ash together with a foaming agent. 3. The method for producing an artificial lightweight aggregate according to claim 1, wherein the firing is performed in a temperature range of 950 ° C. to 1300 ° C. 4. The amount of the alkali metal silicate to be added to the total raw material of the aggregate is 0.5% by weight or more and 10% by weight or less in terms of the total alkali metal oxide contained in the alkali metal silicate. The method for producing an artificial lightweight aggregate according to any one of claims 1 to 3, characterized in that: 5. The production of an artificial lightweight aggregate according to claim 1, wherein the foaming agent comprises iron oxide and at least one of silicon carbide and carbonaceous material. Method. 6. A method according to claim 1, wherein the absolute specific gravity is 0.5 to 1.5, the uniaxial compressive breaking load is 50 kgf or more, and the water absorption is 15%. An artificial lightweight aggregate characterized by the following.