JPH1160327A - Production of inorganic granular molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a lightweight tough granular molded body excellent in heat resistance by mixing coal ash with an alkali metallic silicate, a hardening regulator and a specified amt. of water, molding the resultant inorg. starting material compsn. in a granule shape and firing it. SOLUTION: An inorg. starting material compsn. is prepd. by mixing 100 pts.wt. coal has having <=15 wt.% carbon content with a 20-100 pts.wt. alkali metallic silicate, a 5-30 pts.wt. hardening regulator and water corresponding to 10-30 wt.% of the compsn. The alkali metallic silicate is, e.g. sodium silicate and is used as powder not substantially contg. free water. Oxides or hydroxides of one or more metals selected from among Al, Mg, Zn, B and Ca are used as the hardening regulator. The compsn. is molded in a granule shape by an extruder system or a rotating disk system. The resultant molded body is fired at 300-600 deg.C in an oxygen-contg. atmosphere or an inert gaseous atmosphere after heating at 50-100 deg.C/hr heating rate and then it is cooled at 50-100 deg.C/hr cooling rate.

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 inorganic granular molded product using coal ash as a main raw material, and more particularly, to a method for effectively utilizing coal ash discharged in large quantities as industrial waste. The present invention relates to a method for producing an inorganic granular molded product excellent in heat resistance, mechanical properties and the like at low cost. The inorganic granular molded product obtained by the method of the present invention provides a material useful in the field of civil engineering and building materials, for example, having high strength and light weight and being usable as an aggregate, for example.

[0002]

2. Description of the Related Art A large amount of coal is used as an energy source for thermal power generation, and a large amount of coal ash as a fired material is also discharged.

[0003] Among the coal ash, there is particularly fine fly ash. Fly ash melts coal ash generated when pulverized coal is burned at a thermal power plant, and is rapidly cooled while being transported to the flue with high-temperature combustion gas. It has become particles.
Since this has a self-hydrating action, some fly ash is used as fly ash cement.

[0004] Like flyland cement, fly ash cement has the property of setting by hydration. However, when heated to 500 ° C. or higher, water of crystallization in the cement condensate is released, and the mechanical strength is significantly reduced.

[0005]

On the other hand, coal ash is mixed with an inorganic binder such as Portland cement or water glass or an organic binder such as polyvinyl alcohol (PVA) or carboxymethyl cellulose (CMC).
It is also known to obtain a ceramic-like molded product by treating at a high temperature, but these methods require a large amount of water to be added, and require a very high firing temperature.
There are inevitable disadvantages in terms of energy costs.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that powdered sodium silicate obtained by removing water from water glass is used as an inorganic binder in coal ash such as fly ash. A predetermined amount of water is added to the mixture, and a predetermined amount of water is added to the mixture. The mixture is formed into a predetermined shape using a substantially powdery inorganic raw material composition obtained by baking at a relatively low temperature. The present inventors have found that an inorganic molded product having excellent mechanical properties can be obtained simply and inexpensively by suppressing the amount of water to be used, and proposed above.

Further, using the above-mentioned inorganic raw material composition,
By forming into granules and firing, it was found that an inorganic granular molded product having excellent mechanical properties as described above was obtained,
The present invention has been reached.

That is, the present invention relates to an inorganic raw material composition comprising coal ash and an alkali metal silicate, or coal ash, an alkali metal silicate and a hardening modifier, wherein
A substantially powdery composition obtained by adding and mixing water equivalent to 30% by weight is formed into a granular form, and then the composition is subjected to 300 to
The present invention relates to a method for producing an inorganic granular molded product, which is fired at a temperature as low as 600 ° C.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As coal ash used in the method of the present invention, coal ash discharged from a thermal power plant or other factories is used. Among these coal ash, "fly ash"
A uniform and fine coal ash referred to as ash is suitably used. This fly ash melts coal ash generated when pulverized coal is fired at a thermal power plant, etc., and is rapidly cooled while being transported to the flue together with the high-temperature firing gas. Light and fine particles.

The coal ash may be completely baked ash obtained by firing at a high temperature, or may contain a free carbon component formed by firing at a relatively low temperature, for example, fly ash having a carbon content of 15% by weight or less. Is preferably used.

In the method of the present invention, an inorganic binder and, if necessary, a curing regulator are added to the coal ash to prepare an inorganic raw material composition.

The alkali metal silicate used as the inorganic binder in the present invention is represented by the following general formula: M ₂ O.nSiO ₂ .nH ₂ O (1) (wherein, M: an alkali metal such as Na or K; m: molar ratio to alkali metal oxide), and n (molar ratio of silicon dioxide to alkali metal oxide) in the above formula (1) is 1.5 to 3.5 (preferably 2.0 to 3). .
It is preferably in the range of 0).

Specific examples of the alkali metal silicate include sodium silicates called sodium disilicate and sodium trisilicate, and sodium silicate (powder) standardized as JIS-No. Powder and JIS-2 No. powder. ).

The amount of the alkali metal silicate used is preferably 20 to 100 parts by weight, more preferably 30 to 60 parts by weight, based on 100 parts by weight of coal ash.
If the amount used is less than 20 parts by weight, the molded product obtained by mixing and firing after molding is incompletely solidified and tends to become brittle, which is not preferable. Also, 100
If used in excess of parts by weight, excess alkali metal silicate that does not interact with coal ash will be mixed in, and may have drawbacks such as being weak to hot water immersion despite firing. Is not preferred.

In the general formula of the above alkali metal silicate, m represents the relative amount of water contained as water of crystallization, and is, for example, an ordinary amount such as sodium disilicate powder (Kishida Chemical Products) available as a reagent grade. Even in the form of a powder, m =
2.5-3 (corresponding to a water content of about 20% by weight of the silicate)
However, the composition of the present invention is a powdery inorganic binder. That is, the powdery inorganic binder is used even at the stage of preparing the composition, and the raw material composition itself can be substantially handled as a powdery substance, despite the addition of a controlled amount of water described below. It is possible, and simplicity in operation and apparatus can be realized.

In the present invention, one of the most important factors for obtaining a favorable inorganic granular molded product is the adjustment of the amount of water added (moisture percentage) in the inorganic raw material composition. That is, a composition comprising coal ash and an alkali metal silicate, or coal ash, an alkali metal silicate and a hardening agent, has a moisture content of 1%.
It is extremely important in the present invention to add and mix an amount of water corresponding to 0 to 30% by weight. When the water content is less than 5% by weight, even if the raw material composition is formed into granules by an extrusion method or a rotating dusk method, shape retention is insufficient, and strong solidification cannot be caused even in subsequent firing. . On the other hand, when a large amount of water exceeding 30% by weight as a water content is added and mixed, there is oozing of water on the surface due to excessive water in forming into granules, and due to adhesion between the granules, etc. In addition to this, it is difficult to form into the shape described above, and it takes a very long time to perform preliminary drying before firing, which is not preferable. The water content depends on the particle size of the target granular molded product, but is preferably in the range of 15 to 25% by weight in the inorganic raw material composition.

In the method of the present invention, a curing regulator can be added. This curing regulator has an effect of accelerating the curing reaction between coal ash and the inorganic binder when obtaining an inorganic granular molded product from a raw material composition obtained by mixing coal ash with an inorganic binder and a predetermined amount of moisture, An oxide or hydroxide of at least one metal selected from aluminum, magnesium, zinc, boron and calcium is preferably used. Particularly preferably, examples of the curing regulator include alumina, aluminum hydroxide, zinc oxide and the like.

The amount of the curing regulator used is 100 ash
1 to 30 parts by weight based on parts by weight (particularly 5 to 20 parts by weight)
Is preferred. If the amount of the curing regulator is excessive, the production cost of the molded product increases, which is not preferable.

As described above, the inorganic raw material composition used in the method of the present invention contains coal ash and an inorganic binder as main components and, if necessary, a curing control agent. Fine inorganic hollow particles, short fibers for reinforcement, whiskers and the like can be mixed.

The above-mentioned inorganic hollow particles have an average particle size of 0.01.
To 2 mm (particularly preferably 0.1 to 0.5 mm), apparent specific gravity 0.05 to 0.8 (particularly preferably 0.1 to 0.5 mm).
The hollow particles of 7), specific examples thereof include fine inorganic hollow particles called glass balloons, shirasu balloons, silica balloons and the like. As a specific example of the glass balloon, a glass bubble made by Sumitomo 3M: K-1 (apparent specific gravity 0.125; 50% particle size 68 μm)
m), K-37 (apparent specific gravity 0.37; 50% particle size 50)
μm), Cellstar Z28 manufactured by Asahi Glass Co., Ltd. (apparent specific gravity 0.28; average particle size 55 μm), glass balloon HGS-16 manufactured by Tomoe Kogyo Co., Ltd. (apparent specific gravity 0.17 to 0.18;
Average particle size of 110 μm). Specific examples of the shirasu balloon include Q cell 300 (apparent specific gravity 0.21; average particle diameter 65 μm) manufactured by Asahi Glass Co., Ltd. and Sankilite Y02 manufactured by Sanki Kogyo (apparent specific gravity 0.23 to 0.26;
(Particle size: 44 to 75 μm). Further, as a specific example of the silica balloon, Nippon Philite Co., Ltd.'s Philite 52 / 7FG (specific gravity 0.7; particle size 30 to 100 µm)
And the like.

As fibers for reinforcement, glass fibers, carbon fibers, silicon carbide fibers and the like are used, and short fibers having a very small fiber length / fiber diameter such as milled fibers are particularly preferable.

The mixing of the raw material composition such as coal ash, an inorganic binder, a curing regulator, a predetermined amount of water and various additives in the method of the present invention is substantially a powder mixing state, and can be performed by simple mechanical mixing. Although sufficient, it is preferred to use a mixing device commonly referred to as a kneader or blender.

As a means for shaping the raw material composition obtained by the mixing operation into granules, for example, the raw material composition is put into a rotating disk type granulator and the disk is grown to a desired particle size while rotating the disk. And a method in which a rod-like material obtained by extruding through a die having small holes corresponding to a desired grain size is cut into granules.

The calcination in the method of the present invention is usually carried out by raising the temperature to 300 ° C. to 600 ° C. in an atmosphere containing oxygen such as air, or in an atmosphere of an inert gas such as oxygen gas, or further in an atmosphere of combustion gas or the like. Will be implemented.
Firing at a temperature lower than 300 ° C. solidifies or cures, but a part of the inorganic binder used cannot sufficiently participate in the reaction, and it is difficult to obtain an inorganic molded product having sufficient strength, which is not preferable. In addition, a high temperature exceeding 600 ° C., for example, 10
Firing in a high temperature atmosphere such as 00 to 1300 [deg.] C. can provide a molded product having similar strength characteristics, but it is difficult to say that it is preferable in terms of manufacturing cost because energy cost for obtaining a high temperature is high.

The temperature rise and fall during firing is preferably to avoid a rapid temperature change, for example, 50 to 100 ° C.
It is particularly preferable to slowly raise and lower the temperature such as / 1 hour.

Prior to the above-mentioned firing, it is desirable to pre-dry the granular solid obtained by various molding methods. The amount of water used in the method of the present invention is a relatively small amount as described above. However, in the stage before firing, it depends on the amount of water added and the molding method. Contains equivalent free water.

Therefore, if the rapid heat treatment is performed as it is, swelling or cracking of the granular molded product may occur, so that it is desirable to carry out preliminary drying before firing. The pre-drying temperature is preferably about 100 ° C., which is the boiling point of water at normal pressure.

Thus, according to the method of the present invention, coal ash,
From a raw material composition comprising an alkali metal silicate as an inorganic binder, a curing regulator and moisture, an inorganic granular molded product having good mechanical properties such as strength can be obtained. The granular molded product thus obtained is basically nonflammable,
It becomes a high-strength, low-specific-gravity inorganic granular material, and can provide a material useful as a lightweight aggregate in the field of civil engineering and construction materials.

[0029]

Next, the method of the present invention will be described in detail with reference to Examples and Comparative Examples, which are for the purpose of understanding the present invention, and the scope of the present invention is limited by these Examples. Not something. In the examples and comparative examples, “parts” means “parts by weight” unless otherwise specified.

Example 1 100 parts of fly ash (carbon content: 10% by weight) obtained as coal ash from a thermal power plant were mixed with sodium silicate (reagent "Sodium disilicate powder" manufactured by Kishida Chemical; silicon dioxide) as an inorganic binder. / Molar ratio of sodium oxide = 2.0) A powder composition consisting of 50 parts of alumina powder as a curing regulator and 10 parts of alumina was mixed in a kneader, and further mixed with 44 parts of water (water content in the total composition). (Corresponding to 21.6% by weight) was added little by little, and the mixing was continued to obtain a substantially powdery raw material composition.

The above raw material composition was placed in a rotating disk shear granulator set at an inclination angle of 45 °, and granulated while rotating at 60 rpm. The obtained granular material having a particle size of about 5 mm was transferred into a dryer set at about 100 ° C. and preliminarily dried. Then, the dried granules were set in a firing furnace, heated from room temperature to 300 ° C. over 3 hours, and maintained at 300 ° C. for 2 hours, and then naturally cooled in the firing furnace. The apparent specific gravity of the obtained granular molded product is 1.3.
It was 0 and the crushing strength was 20 to 30 kgf, confirming that it had good mechanical properties.

Using 60 parts of the above granular molded product as an aggregate, 40 parts of Portland cement and 20 parts of water were mixed, and 4c
pour into a bar mold of mx 4cm x 16cm,
After natural curing for a day, aggregate-reinforced blocks were prepared. The apparent specific gravity of the obtained block is 1.6, the compressive strength is 263 kgf / cm ² , and the compressive modulus is 28,000 kg.
f / cm ² was good. The specific compression strength and the specific compression elastic modulus obtained by dividing each characteristic by the specific gravity are 163 kgf /
cm ² and 17,000 Kgf / cm ² .

For comparison, a mortar molded product using sea sand as an aggregate instead of the granular molded product of the present invention was prepared. The apparent specific gravity was 2.0 and the compressive strength was 243 kgf / cm.
² , the compression modulus is 35,000 Kgf / cm ² , the specific compression strength is 122 Kgf / cm ² , the specific compression modulus is 18,
It was 000 kgf / cm ² , and it was confirmed that the compounding of the granular molded product according to the method of the present invention was light and showed a good mixing effect as an aggregate.

Comparative Example 1 When the amount of water added to the raw material composition of Example 1 was reduced to 8 parts (corresponding to 4.8% as the water content in the raw material composition), the raw material composition was uniformly mixed. However, even if a granulating apparatus using a rotating disk method was used, the powder surface had no tackiness and could not be formed into granules.

On the other hand, when the amount of water added to the raw material composition of Example 1 was increased to 160 parts (corresponding to 50% by weight as the water content in the raw material composition), it was just at the stage of mixing the raw material composition. In addition, the powdery state could not be maintained, and a desired granular molded product could not be obtained. That is, it was confirmed that controlling the moisture content in the raw material composition in the method of the present invention within a predetermined range is an important point.

[Example 2] Sodium silicate JIS as an inorganic binder was added to 100 parts of fly ash as in Example 1.
No. 1 powder (Fuji Chemical Co., Ltd .; molar ratio of silicon dioxide / sodium oxide = 2.19) 40 parts, powder glass fiber (Nitto Boseki PF A101) 5 parts and water 40 parts (in the raw material composition, (Corresponding to 21.6% by weight) to obtain a raw material composition, which was obtained in the same manner as in Example 1 by using a rotary disk type granulator to obtain a granulated product having a particle size of 5 to 8 mm. After preliminary drying, the granulated material was placed in an electric furnace, heated from room temperature to 350 ° C., heated, and kept at the same temperature for 1 hour to obtain a granular molded product. After natural cooling, the apparent specific gravity of the obtained granular molded product is 1.54, and the crushing strength is 80 to 1
It was extremely good at 00 kgf. The granular molded product is
It could be used as an aggregate component of cement mortar, and was found to be useful as an artificial lightweight aggregate.

[Example 3] Sodium silicate JIS as an inorganic binder was added to 100 parts of fly ash as in Example 1.
50 parts of No. 1 powder (manufactured by Nippon Chemical Co., Ltd .; molar ratio of silicon dioxide / sodium oxide = 2.19) and 10 parts of alumina powder as a curing modifier were mixed using a kneader, and further 30 parts of water (raw material composition) (Equivalent to 14.9% by weight in the product) was added little by little and mixed to obtain a raw material composition. Then
This raw material composition was supplied to an extruder having a cap surface having a large number of small holes having a diameter of 2 mm, and a short rod was prepared by rotating a screw. This was dried in a dryer at about 100 ° C., and then processed into a columnar granular shape using a rotary crusher (for example, “Flush Mill”, a particle sizer manufactured by Fuji Paudal Co., Ltd.). The granules thus obtained were placed in an electric furnace in the same manner as in Example 1,
The temperature was raised to 400 ° C. for firing. The obtained granular molded product has an apparent specific gravity of 1.30 and a crushing strength of 40 to 50 kg.
f, which proved to be useful as an aggregate.

Example 4 25 parts of JIS No. 1 sodium silicate powder (manufactured by Fuji Chemical Co., Ltd .: used in Example 2) as an inorganic binder and 100 parts of fly ash same as in Example 1 and JIS-2 No. sodium silicate powder (manufactured by Fuji Chemical; ratio of silicon dioxide / sodium oxide = 2.52) 2
5 parts, 10 parts of alumina powder as a curing accelerator, 2 parts of polyvinyl alcohol as a shape-maintaining additive, and 3 parts of water
6 parts (corresponding to a water content of 18.2% by weight in the raw material composition) was added to obtain a raw material mixture. This mixture is then
Granulation was performed using the same rotary disk granulator as in Example 1 to obtain granules having a particle size of 2 to 5 mm. This granular material,
After preliminary drying in a dryer at 100 ° C., it was placed in an electric furnace at 300 ° C. and calcined for 3 hours to obtain a granular molded product.

[0039]

According to the method of the present invention as described above, it is possible to obtain an inorganic granular molded product which is lightweight, tough, and excellent in heat resistance. In particular, by controlling the moisture content in the raw material composition to a predetermined range, a light-weight, inorganic granular molded product having a desired size and shape and excellent in mechanical properties can be obtained. Therefore, the inorganic granular molded product according to the method of the present invention is effectively used for a wide range of applications as an aggregate of civil engineering and building materials, or as a carrier for various catalysts, agricultural chemicals, fertilizers, and the like, and further as a filling material. I can do it.

Claims (10)

[Claims] An inorganic raw material composition obtained by mixing coal ash, an alkali metal silicate and 10 to 30% by weight of water in the composition is formed into granules and then fired. A method for producing an inorganic granular molded product. 2. An inorganic raw material composition obtained by mixing coal ash, an alkali metal silicate, a hardening modifier and 10 to 30% by weight of water in the composition is formed into granules and then fired. A method for producing an inorganic granular molded product, characterized in that: 3. 20 to 10 parts by weight of coal ash
0 parts by weight of alkali metal silicate and 10 to 3 parts by weight in the composition
A method for producing an inorganic granular molded product, comprising forming an inorganic composition obtained by mixing water equivalent to 0% by weight into granules, and firing. 4. The method for producing an inorganic granular molded product according to claim 1, wherein the alkali metal silicate is sodium silicate. 5. The inorganic particulate molding according to claim 1, wherein said alkali metal silicate is sodium silicate and is in the form of powder substantially free of water. Method of manufacturing a product. 6. The alkali metal silicate is sodium silicate, and the molar ratio of silicon dioxide (SiO ₂ ) to sodium oxide (Na ₂ O) is in the range of 1.5 to 3.5. The method for producing an inorganic granular molded product according to any one of claims 1 to 5. 7. The inorganic particulate material according to claim 2, wherein the curing regulator is an oxide or hydroxide of at least one metal selected from aluminum, magnesium, zinc, boron and calcium. Manufacturing method of molded product. 8. The method according to claim 8, wherein the amount of the curing regulator is 100 ash.
The method for producing an inorganic granular molded product according to claim 2, wherein the amount is 5 to 30 parts by weight based on parts by weight. 9. The method according to claim 1, wherein the calcination is performed in an oxygen-containing atmosphere or an inert gas atmosphere at 300 to 600 ° C. 10. The method for producing an inorganic granular molded product according to claim 1, wherein an extruder method or a rotating disk method is used for forming the granular material.