JP2641102B2 - Method for producing porous material using fly ash as main raw material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a porous material from fly ash produced as a by-product during coal combustion, and more particularly to a method for producing a porous material during coal combustion. It is used in a method for producing a porous material using raw fly ash and smoke desulfurized gypsum as raw materials.

(Conventional technology) Conventionally, coal ash produced as a by-product of coal combustion has been recovered as fly ash by dust collectors, and a part of it has been mixed and used in Portland cement. Environmental problems are developing.

In recent years, various studies have been conducted on the effective use of fly ash. For example, fly ash and lime are reacted in a strong alkaline solution in a high-temperature, high-pressure steam atmosphere to make fly ash particles porous, and to make fly ash particles tomobalite needle-like crystals (Ca ₅ (Si ₆ O ₁₈ H ₂ ) ・ 4
H ₂ O) (see JP-B-28858), or
In the reaction of fly ash and lime in an alkaline solution, ettringite crystals (Ca ₆ Al
_{2 (OH) 12 (SO 4} ) 3 · 26H 2 O) to produce a method of mixing the cement to activate the fly ash (JP-B 58
However, all of these methods have complicated production processes due to the reaction conditions of a high-temperature and high-pressure steam atmosphere, and require cumbersome equipment.

There is also known a method of producing a porous material by granulating fly ash or foamed clay, firing it at a high temperature using a kiln, producing a lightweight aggregate, and fixing the foamed clay particles with Portland cement.

However, this method requires 1200
There are drawbacks such as requiring a high temperature of ° C.

(Problems to be Solved by the Invention) The present inventor has conducted various studies so that fly ash can be effectively used in a simple manner without the need for complicated manufacturing steps and complicated equipment as described above. The present invention has been completed, and an object of the present invention is to provide a method for producing a porous material from fly ash by a very simple means.

(Means for Solving the Problems) That is, the present invention mixes fly ash 19 to 86 parts by weight, gypsum 10 to 50 parts by weight and lime 4 to 43 parts by weight,
After water was added to the mixture to form a slurry, the mixture was poured into a mold, held for 5 to 30 minutes to solidify, and then taken out of the mold to form a precursor.
This is a method for producing a porous material using fly ash as a main raw material, wherein steam curing is performed under the conditions of 0 ° C. and a relative humidity of 50 to 100%.

In the present invention, fly ash, gypsum and lime are mixed at the above-mentioned specific ratios, and the mixture is steam-cured at normal pressure and at a slight temperature to form a hydrate in the cured product after curing. On the fly ash surface, gypsum, lime and water react with each other to form ettringite crystals, monosulfate hydrate crystals and CSH on and around the fly ash, thereby forming a high-strength porous material. Is obtained. The added gypsum and lime generally do not react, and usually remain partially unreacted.

 The present invention will be described in more detail.

The composition of the fly ash used in the present invention is slightly different depending on the raw coal, but is generally as follows.

SiO ₂ 40 ~ 75 CaO 0.3 ~ 17 Al ₂ O ₃ 10 ~ 36 MgO 1-4 Fe ₂ O ₃ 1 ~ 18 SO ₃ 10 or less Total 100 And, in the present invention, of these, coarse ones due to cyclones It is preferable to use fine particles having a particle size of 30 μm or less. If particles having too large a particle size are used, the reactivity is poor, the surface area of the cured product becomes coarse, and the film becomes unstable. Bulk density of the resulting porous material, primarily because it depends on the secret of the density of the fly ash, in order to obtain a light-weight material, a low fly ash are preferred of possible covert bulk density, especially from about 0.97 g / cm ³ of about Things are good.

Gypsum has two molecules of water as crystallization water, usually represented as CaSO ₄ .2H ₂ O, but when used in the present invention, it is previously dehydrated at a temperature of about 200 ° C., III
It is preferable to use a type CaSO ₄ state because hydration of the reverse reaction occurs quickly and the slurry hardens in a short time. In addition, hemihydrate gypsum or calcium carbonate can be used as gypsum or lime. However, in this case, these are rarely used as they are, and are generally used after dehydration and decarburization.

In addition, coal contains sulfide minerals in addition to the clay content, which is a source of ash, and the sulfur dioxide gas generated by the combustion is recovered as flue gas desulfurization gypsum by lime treatment. The use of gypsum as a source of gypsum, which is slightly larger than the amount of ash, has the advantage that both fly ash and flue gas desulfurization gypsum, which are by-produced during coal combustion, can be used.

The gypsum particles used were all 100 mesh.

Slaked lime is used as lime, but quick lime can also be used. The particle size is 60 meshes.

The mixing ratio of these three was determined as follows. Gypsum / lime molar ratio _{(CaSO 4 · 2H 2 O /} Ca (OH) 2) 0.1~1.0
, The amount of gypsum (calculated as CaSO ₄ .2H ₂ O) for the ratio is 10 to 50% by weight.
Change every%. If the total mixed weight is 100, the amount of gypsum +
Lime amount by weight obtained by subtracting from the _{(CaSO 4 · 2H 2 O +} Ca (OH) 2) 100 becomes the fly ash quantity. Table 1 shows the results of examining the properties of the lightweight material or the porous material obtained by applying the means of the present invention to the three raw material mixtures having a predetermined mixing ratio.

From this table, it can be seen that in the present invention, fly ash 19 to 86
Parts by weight, 10 to 50 parts by weight of gypsum and 4 to 43 parts by weight of lime, especially fly ash of 20 to 60 parts by weight.
Those having a gypsum / lime molar ratio of about 0.3 to 0.4 and 0.7 to 0.9 by weight are preferred.

First, water is added to the three raw material mixture to be uniformly dispersed to form a slurry. The slurry is solidified by a hydration reaction with type III anhydrous gypsum.
The amount of water to be added is not particularly specified, but if the amount of water is too large relative to the mixture, it takes a long time to solidify,
Or, since it does not solidify and it is difficult to obtain a uniform dispersion in a small amount, a water / solidification weight ratio of about 0.60 is usually preferable. With this amount of water, water can be uniformly dispersed within about 2 minutes. .

When it is in a slurry state, it is poured into a mold and solidified. After the solidification has progressed sufficiently and the strength has become sufficient to release the mold, it is removed from the mold as a precursor. The time required for this coagulation is about 5 to 30 minutes.

Next, steam curing is performed on the precursor removed from the mold. If the precursor does not have sufficient strength to perform steam curing, it is preferable to perform pre-curing. This pre-curing is carried out by leaving at room temperature for about 10 to 20 minutes, thereby increasing the strength. However, it is not necessary when the strength is more sufficient than at the beginning, and in some cases, it may take 10 to 20 minutes or more, or even longer.

The porous material can be obtained without steam curing. That is, a porous material is obtained only by drying, but only a product having poor water resistance can be obtained.

The conditions of steam curing are as follows: normal pressure, temperature 50 ~ 100 ℃,
80-100% relative humidity, temperature 50 ° C or less, relative humidity 8
If it is 0% or less, the steam curing time becomes long, which is not preferable. When the temperature is 100 ° C. or higher and the relative humidity is 100%, an autoclave is required, which is not practical. It is preferable to carry out the reaction at a temperature of about 80 ° C. and a relative humidity of 90% or more. The time required for this is about 20 hours, and preferably about 24 hours from water injection to the end of steam curing.

As a result of steam curing, the resulting porous body has a bulk specific gravity of 0.97 ~
There is light water resistant and 1.17 g / cm ^3, it is possible to machining. As mechanical properties, it has a bending strength of 0.5 to 3 MPa and a compressive strength of 1.2 to 9 MPa.

In the present invention, the precursor becomes a porous material without performing steam curing, but the water resistance is inferior to the case where steam curing is performed.

 Next, the present invention will be described in more detail with reference to examples.

Example 1 For fly ash having a density of 0.97 g / cm ³ , coarse particles were removed by a cyclone, and fine particles of 30 μm or less were used. As gypsum, use flue gas desulfurization gypsum,
After drying for 16 hours with 100 mesh all through, then 200
C. for 16 hours to obtain type III anhydrous gypsum. Lime is reagent 1
A grade of slaked lime was used to make the whole mesh 60 mesh.

The raw materials adjusted as described above were mixed and used. The mixing ratio was 51 parts by weight of fly ash, 20 parts by weight of gypsum, and 29 parts by weight of lime (CaSO ₄ .2H ₂ O / Ca (OH) ₂ mol ratio 0.3), mixed, and water was added thereto to form a slurry. Shape. As for the amount of water to be added, the weight ratio of water / solid content is set to 0.6, and this is poured into a 2 × 2 × 8 cm mold to solidify. The time required for demolding was 10-20 minutes, after which the precursor was left at room temperature for 30 minutes starting from the water injection. 80 ℃, RH
Steam curing was performed for 23 hours and 30 minutes under the condition of 90% to obtain a porous body. The specific gravity of the obtained porous body is 1.09 g / cm ³ , and the bending strength is
2.9MPa, Compressive strength 8.5MPa, water-resistant, easy to machine.

(Effects) As described above, the method according to the present invention has the following effects.

The use of fly ash by-produced during coal combustion as a raw material and the use of flue gas desulfurization gypsum, which is by-produced particularly during coal combustion, as gypsum help to solve environmental problems.

Manufacturing conditions are 10-100 ° C under normal pressure, 50-100 relative humidity
%, Particularly 80 ° C. and 90% RH, does not require complicated manufacturing processes and cumbersome equipment as in the past.

The porous material obtained by the method of the present invention is not inferior to the conventional one in mechanical strength, and can be used as a building material.

Claims (2)

(57) [Claims] (1) 19-86 parts by weight of fly ash, 10-50 gypsum
Parts by weight and 4 to 43 parts by weight of lime, and water was added to the mixture to form a slurry. The mixture was poured into a mold and held for 5 to 30 minutes to solidify. Producing a porous material using fly ash as a main raw material, wherein the precursor is subjected to steam curing under normal pressure at a temperature of 10 to 100 ° C. and a relative humidity of 50 to 100%. . 2. The method for producing a porous material using fly ash as a main raw material according to claim 1, wherein the gypsum is a type III anhydrous gypsum.