JP3368166B2 - Method for producing hollow particles - Google Patents

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 hollow particles used for lightweight building materials, filter materials, etc., using raw materials mainly composed of incinerated ash of sewage sludge, coal ash, converter slag and the like.

[0002]

2. Description of the Related Art Natural shirasu produced in Kyushu is a typical raw material for hollow particles used for lightweight construction materials.
This natural shirasu is an amorphous body containing volcanic gas mainly containing H2O, and when the shirasu is heated, the dissolved H2O serves as a foaming source to produce hollow particles.
This natural shirasu is weathered and highly viscous on the surface.
By achieving low viscosity inside, a foam close to a sphere is obtained.

On the other hand, the previously proposed Japanese Patent Application No. 7-27545.
In No. 2, Fe, Cu, Ti, and Mn are at least 0.8 wt%
When the slag containing it is dissolved, the cations are made to have a low valence number and reheated in an oxidizing atmosphere after crushing, making the cations an expensive number and causing them to act as crystal nuclei, and to make the surface layer high. Hollow particles are obtained by forming a crystallized shell material.

[0004]

[Problems to be Solved by the Invention] Japanese Patent Application No. 7 proposed above
The cation limitation found in -275452 relates to crystallization or shell formation and is not sufficient for slag composition. That is, Japanese Patent Application No. 7-2754
In No. 52, in the reducing atmosphere, various gases, especially H2 and H
Although it is said that a large amount of 2 O is dissolved, it is natural that the amount of gas to be dissolved is originally different depending on the slag composition, and when waste having various composition variations is used as the starting material, There was no guidance on how to choose the composition of the whole slag.

Therefore, an object of the present invention is to provide a composition which can contain a large amount of dissolved gas and can form a shell when heated in an oxidizing atmosphere.

[0006]

[Means for Solving the Problems] That is, the present invention relates to a melting step of melting a raw material mainly composed of a waste in a non-oxidizing atmosphere to form a melt, and cooling the melt to reduce Fe to 2. A cooling step to obtain an amorphous body containing 3% by weight or more and 8.0% by weight or less; a pulverization step to pulverize the amorphous body into a granular body preferably having a particle size of 0.2 to 3 mm; Heating the particulate body in an oxidizing atmosphere, reacting the atmospheric gas with the amorphous body to form a shell-like substance, and releasing the gas to perform the foaming treatment, preferably 0.3 to
This is a method for producing hollow particles of 5 mm. Further, it has a composition in which the weight ratio of CaO / SiO2 in the amorphous form is 0.2 or more and 0.53 or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
First, the slag requirement that is the basis of the present invention will be described.
The slag must meet three basic requirements. That is, firstly, since the slag is manufactured by an industrially easy method, it has a composition that can be melted at a low temperature. Secondly, the gas component is dissolved in the molten slag and becomes amorphous when cooled. Thirdly, the basic requirement is to crystallize at the time of reheating and release gas from the slag to form a shell to create a highly viscous state in the surface layer and a low viscous state inside.

In the present invention, in order to satisfy the first and second requirements, the weight ratio of CaO / SiO2 of the amorphous body is 0.2.
It is practical to set to 0.53. First of all, a uniform melt must be formed by an industrially easy method, that is, at a low temperature of 1500 ° C. or lower, preferably 1350 ° C. or lower. Depending on the amount of Al2 O3 / SiO2, if Al2 O3 / SiO2 is in the range of 0.2 to 0.5, CaO / SiO2 must be 0.2 or more. Al2 O3 / SiO2 is in the range of 0.2 to 0.5 for both municipal waste incineration ash and coal ash, and CaO / SiO2 needs to be 0.2 or more from the first industrial melting point of view.

The second requirement is that the slag in which a large amount of gas is dissolved in a non-oxidizing atmosphere such as a reducing atmosphere is confined in the slag, and more specifically, it is cooled to be amorphous. It is a point to make slag. As a result of investigating various slags, the main crystalline phase generated during cooling is Gehlen.
It is an ite phase (2CaOSiO2 Al2 O3) and has a crystallization temperature of 700 ° C to 1000 ° C. This Gehlenite
The second requirement is to have a slag composition that does not form a phase. Since this is closely related to the foaming principle, the foaming principle will be mentioned first.

Structurally, there are many gaps between atoms in which gas molecules can enter in an amorphous state, but in a crystal, gas molecules cannot enter due to their dense structure. When an amorphous material in which gas molecules are dissolved is crystallized, the dissolved gas becomes
As the crystallization progresses, it moves to the remaining non-crystallized amorphous phase, and when it exceeds the gas saturation solubility of the amorphous phase,
It is released from the glass as bubbles outside the system. On the other hand, the gas solubility of an amorphous material is generally larger in a reducing atmosphere than in an oxidizing atmosphere, and in order to more effectively promote the above-mentioned gas release, the gas should be reduced when the gas is dissolved in the amorphous material. atmosphere,
When crystallizing, it is necessary to use an oxidizing atmosphere.

That is, the crystallization of the slag in the cooling process results in the loss of the gas component dissolved in the melt during cooling, and the foaming does not occur even when reheated in an oxidizing atmosphere. Therefore, a cooling step of cooling the melt to an amorphous body is important.

When the melt is cooled, an amorphous body is generally obtained when the cooling rate is high, and a crystalline body is apt to be formed when the cooling rate is low. Therefore, in order to limit the composition range in which the amorphous body is obtained, it is meaningless unless the cooling rate is determined. The industrially cooling method of the molten slag is a method of receiving the molten slag in a heat-resistant pan and cooling it as it is. Therefore, in order to estimate a realistic cooling rate, the inventors have found that SiO2 is 45% by weight and Al2 is
Slag containing 18% by weight of O3 and 21% by weight of CaO is melted at 1450 ° C to obtain a size of 800 x 1200 mm.
It was poured into a water-cooled iron pan having a thickness of 300 mm, and the cooling rate of the slag at about 100 mm from the surface was measured.
As a result, 13 ° C / mi from 1100 ° C to 900 ° C
n at a cooling rate of 900 ° C. to 700 ° C. is 8 ° C./mi
It was n. The second slag requirement is the composition range of the slag capable of obtaining the amorphous body at the cooling rate described above.
Under this cooling condition, if CaO / SiO2 exceeds 0.53, a Gehlenite phase will be generated during cooling and the slag will crystallize.

Industrially, molten slag may be left to cool in a slag field. In this case, the cooling is considerably slower than in the case described above, which is disadvantageous to amorphous.
In order to reproduce this state in a simulated manner, we conducted an experiment in which the slag was cooled in an adiabatic box, and performed 1100 ° C to 900 ° C.
However, 900 ° C to 700 ° C is 2 ° C / min at 4 ° C / min
Realized the cooling rate of. Even with this slow cooling slag, CaO
When / SiO2 was 0.47 or less, a good amorphous material was obtained. That is, the value of CaO / SiO2 at which the amorphous silicon can be stably obtained at a rate that can be cooled at low cost is 0.4.
It is 7 or less.

As described above, the value of CaO / SiO2 at which an amorphous material is stably obtained varies depending on the cooling rate, but is practically 0.53 or less. Of course, there is no problem even if the cooling rate is increased.

Next, the third requirement mentioned above, that is, in order to avoid the release of gas from an amorphous body to form pumice-like particles and to produce hollow particles by foaming gas, It is necessary to form a shell-like substance capable of supporting the. That is, it is important for producing hollow particles to have a highly crystallized high-viscosity layer on the surface layer and a low-viscosity layer inside thereof as the crystallization progresses. For this reason, in the present invention, FeO
Fe is 2.3 wt% to 8 wt% in terms of conversion.

Regarding this specific action, Japanese Patent Application No. 7-
Although it is the same as No. 275452, if the Fe content, which is the cheapest and is contained in a large amount in waste, is 2.3 wt% or more in terms of FeO, it becomes sufficient for shell formation.

The Fe atoms in the slag usually exist in the form of Fe ^{+2 when} dissolved in a reducing atmosphere. Upon heating in an oxidizing atmosphere, changes from Fe ⁺² to Fe ^+3, is to form a highly viscous layer surface is highly crystallized Fe ⁺³ is a role of the crystal nuclei.

The thickness of the shell varies depending on the amount of FeO contained, but is 10 to 3 for slag containing 1 wt% FeO.
When a shell of 0 μm is formed and FeO is 8 wt%, it is 200
Form ˜500 μm shells. When FeO is less than 2.3 wt%, the shell is too thin and is easily damaged during the foaming process, so that the low viscosity slag inside cannot be held by the shell and the low viscosity slag inside the shell is not retained. However, hollow particles cannot be obtained. FeO is 2.3 wt%
In order to form a shell of 40 to 70 μm with the contained slag, the slag has a sufficient thickness to hold the slag of about 0.2 to 2 mm. On the other hand, if the FeO content exceeds 8 wt%, the shell becomes too thick and virtually no foaming occurs.

A method for producing hollow particles from slag satisfying the above three requirements will be described below. First, as the waste, municipal waste incineration ash, sewage sludge incineration ash, coal ash, converter slag, etc. can be widely used. In the melting step of melting these raw materials mainly composed of waste materials in a non-oxidizing atmosphere to form a melt, it is desirable that the Fe ⁺² valence is dissolved at an oxygen partial pressure capable of stably existing. When it is difficult to control the Fe ⁺² valence within a range of stable oxygen partial pressure, metallic Fe can be dissolved by stable oxygen partial pressure and coexistent with metallic Fe. At the time of melting, the atmosphere is C
It is dissolved in an atmosphere rich in O gas, H2 gas, N2 gas, and H2 O gas, and the gas is dissolved in slag. If it is extremely difficult to control the atmosphere, add water glass to the raw material and melt it in an N2 atmosphere in which carbon coexists.
It is also possible to produce a slag in which a large amount of gas is dissolved.

In the cooling step of cooling the melt to an amorphous body, 1100 ° C. to 900 ° C., 4 ° C./min, 9
It is preferable to cool from 00 ° C. to 700 ° C. at a cooling rate of 2 ° C./min or more to produce an amorphous body. The slag composition at this time must contain Fe in an amount of 2.3% by weight or more and 8.0% by weight or less in terms of FeO as described above.
The weight% ratio of 2 is preferably 0.2 or more and 0.53 or less.

In the pulverization step of pulverizing the amorphous body into a granular body, it is pulverized to 0.2 mm to 3 mm. Fe amount is F
In the range of 5 to 8 wt% in terms of eO, 1 to 3 mm, Fe
When it is 2.3 to 5 wt% in terms of O, it is preferable to grind to 0.2 to 2 mm. Heating the amorphous body in an oxidizing atmosphere,
In the step of reacting the atmospheric gas and the amorphous body to form a shell-like substance and releasing the gas to perform the foaming treatment,
Baking in an atmosphere in which the Fe ⁺³ value is stable and in the air.
When the particles come into contact with each other and stick to each other, the particles are appropriately immersed in a powder such as alumina having a particle size of 50 μm or more to perform a foaming treatment, and after foaming, the alumina particles and the foam are separated with a sieve. Further, it can be avoided by performing the foaming process while rotating the slag like a rotary kiln. It is also possible to blow off the melt with a large amount of water, that is, to perform the cooling step and the crushing step at the same time by water granulation.

[0022]

EXAMPLES Examples of the present invention will be described below. (Example 1) Urban waste incineration ash and CaO generated from K city
In a predetermined proportion, and in a resistance heating type electric furnace using a carbon electrode, non-oxidizing atmosphere (water vapor 15-35%, remaining gas,
Carbon monoxide 40-70vol%, hydrogen 10-30vol
%, The remaining nitrogen) was melted at 1450 ° C. in the presence of metallic Fe, and was poured into a water-cooled iron pan having a size of 800 × 1200 mm to a thickness of 300 mm to be cooled. At this time, the cooling rate from 1100 ° C to 900 ° C is about 12 to 18 minutes, 9
The temperature from 00 ° C to 700 ° C was 25 to 32 minutes.

The slag composition thus obtained is shown in Table 1. Grind this slag to 1-2 mm, weigh 100 g, and
The tap density was determined 100 times using a 00 cc graduated cylinder. 3 parts by weight of particle size 30 for 1 part by weight of slag
Dry mix alumina powder of 0 μm or less, and
Heat treatment was performed at 000 ° C. and 1050 ° C. for 30 minutes. The heat-treated slag / alumina mixture was separated into slag-bearing slag on the sieve and alumina under the sieve using a 1 mm sieve. 100 g of the obtained foamed slag was weighed and the tap density was determined 100 times using a 200 cc graduated cylinder. The foaming rate of the slag was obtained from the ratio of the tap density before and after the heat treatment.

FIG. 1 shows X-ray diffraction patterns of K3, K4, K5 and K6 slags. CaO / SiO2 value is 0.5
Amorphous products can be obtained up to 3, but above that Gehlenit
The e phase was precipitated. Table 2 shows the FeO content, basicity, and foaming rate. The slag having an FeO content of 2.3% or more and a C / S of 0.53 or less had a foaming ratio of more than 150%.

[0025]

[Table 1]

[0026]

[Table 2] (Example 2) Urban waste incineration ash and CaO generated from Y city
In a predetermined proportion, and in a resistance heating type electric furnace using a carbon electrode in a non-oxidizing atmosphere (water vapor 15 to 35%, in the remaining gas,
Carbon monoxide 40-70vol%, hydrogen 10-30vol
%, Remaining nitrogen), melted at 1450 ° C. in the coexistence of metallic Fe, and cooled in an adiabatic box. In this case, the cooling rate was 1100 ° C to 900 ° C for 45 to 62 minutes, and 900 ° C to 700 ° C for 82 to 117 minutes.

The obtained slag composition is shown in Table 3. The foaming rate of the slag was obtained by the same method as in Example 1. In Figure 2,
The X-ray-diffraction pattern of the slag produced by melt | dissolving the slag which has various compositions at 1450 degreeC, and making it cool in a heat insulation box is shown. When the value of CaO / SiO2 is 0.517 or more, Gehl
The enite phase precipitated. Table 4 shows the results of FeO content, basicity, and foaming rate. CaO / SiO2 (C /
When S) was 0.47 or less, the foaming rate exceeded 150%.

[0028]

[Table 3]

[0029]

[Table 4] (Example 3) Municipal refuse incineration ash generated from K city was heated in a resistance heating type electric furnace using a carbon electrode in a non-oxidizing atmosphere (water vapor 15-35%, residual gas, carbon monoxide 40-70 vo).
1% hydrogen, 10 to 30 vol% hydrogen, and remaining nitrogen), melted at 1450 ° C. in the presence of metallic Fe, and cooled in air.

The slag composition obtained is shown in Table 5. The slag was an amorphous material, and as a result of the same foaming test as in Example 1, the foaming rate was 254% at 1000 ° C. and 347% at 1050 ° C., and the Fe content (FeO conversion value) was 3. .5
%, And the foamability was good.

Put only this slag in a carbon crucible, 1
The FeO contained in the slag was precipitated as metallic Fe by melting in a nitrogen atmosphere at 450 ° C. for 1 to 24 hours, crushed after cooling and magnetically separated to produce a slag whose FeO content was controlled by the melting time. .

A foaming test similar to that of Example 1 was conducted using this remelted slag. The results of the Fe content (FeO conversion) and the foaming rate of the obtained slag are as shown in Table 6,
When it was 2.3 wt% or more, the foaming rate exceeded 150%.

[0033]

[Table 5]

[0034]

[Table 6]

[0035]

EFFECTS OF THE INVENTION According to the present invention, a large amount of dissolved gas can be contained, a shell can be formed when heated in an oxidizing atmosphere, and good hollow particles can be produced.

[Brief description of drawings]

FIG. 1 is a diagram showing an X-ray diffraction pattern of K3, K4, K5, and K6 slags obtained in Example 1.

FIG. 2 is a diagram showing X-ray diffraction patterns of slags prepared by melting slags having various compositions obtained in Example 2 at 1450 ° C. and cooling them in an adiabatic pox.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Yamagishi 61-1 Ono-cho, Tsurumi-ku, Yokohama-shi, Kanagawa NK Plant Construction Co., Ltd. (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 38 / 00-38/10 C04B 5/00-5/06

Claims (2)

(57) [Claims] 1. A melting step of melting a raw material mainly composed of waste in a non-oxidizing atmosphere to form a melt, and cooling the melt to convert Fe into 2.3 wt% or more in terms of FeO and 8.0.
A cooling step to obtain an amorphous body containing less than or equal to wt%; a pulverizing step to pulverize the amorphous body into a granular body; And a step of reacting the particles to form a shell-like substance and releasing gas to perform a foaming treatment. 2. The method for producing hollow particles according to claim 1, wherein the amorphous body has a CaO / SiO2 weight ratio of 0.2 or more and 0.53 or less.