JP2002320942A - Method for stabilization processing of molten fly ash and/or burned fly ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of economically and securely stabilizing molten fly ash and/or burned fly ash including Se contained in these fly ashes in a form that handling is convenient. SOLUTION: After the molten fly ash and/or burned fly ash and powdered substances containing slaked lime are blended, a ferrous chloride aqueous solution is added so as to allow FeCl2 to be 5.5 pts.wt. or more per 100 pts.wt. of the molten fly ash and/or burned fly ash and allow Fe to be 30 to 100 pts.wt. per 100 pts.wt. of Ca in the slaked lime contained in the powdered substances and a blended solution is kneaded either as it stands or by further adding a required amount of water thereto to prepare a kneaded product so as to allow pH to be 9 to 12.5 and allow a water content to be 15 to 30 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for stabilizing molten fly ash and / or fired fly ash. In order to reduce the volume and detoxify the incineration residue of so-called refuse such as municipal waste, industrial waste, and sludge, melting treatment is performed. In addition, in order to recycle, reduce the volume, and render the harmless, refuse is pyrolyzed and gasified, and the pyrolysis residue is melted, that is, gasified and melted. Further, the incineration residue of refuse is calcined with limestone or the like to produce ecocement. In these melting and firing processes,
Exhaust gas accompanied by dust is generated. This exhaust gas is usually collected by collecting waste heat, cooled, and then subjected to dust collection by adding activated carbon or the like as necessary. The dust collected in this dust collection process, that is, the fly ash and the burnt fly ash, are ultimately landfilled. It is necessary to stabilize the ash and the incinerated fly ash. Such a stabilization process is shown in Showa 4
The dissolution test was carried out in accordance with the Environmental Agency Notification No. 13 “Testing Methods for Metals Contained in Industrial Waste” in 1996.
It is required to satisfy the revised version of “Criteria for Industrial Waste Including Metals”. The present invention relates to a newly regulated S
The present invention relates to a method for stabilizing molten fly ash and / or burnt fly ash, which can also stabilize e simultaneously with other restricted substances.

[0002]

2. Description of the Related Art Conventionally, as a method for stabilizing molten fly ash, a method has been proposed in which water and a fly ash stabilizing chelating agent are added to the molten fly ash and kneaded (Japanese Patent Laid-Open No. Hei 5-8732).
4). However, in the conventional method, the cations such as Pb, Cd, and Hg can be stabilized.
Those present as anions in the form of suboxides or oxides, such as e, As, and hexavalent Cr, are difficult to stabilize, and in particular, use a large amount of expensive fly ash stabilizing chelating agents, which is uneconomical. When the molten fly ash to be treated contains activated carbon, the fly ash stabilizing chelating agent is adsorbed on the activated carbon, so that a larger amount of the fly ash stabilizing chelating agent is required. There is a problem of becoming uneconomical.

[0003] Conventionally, as a method of stabilizing molten fly ash, water and ferrous chloride and / or ferrous sulfate have been added to the molten fly ash, and if necessary, a chelating agent for stabilizing the fly ash has been added. Has also been proposed for kneading by adding
0219). This conventional method has the advantage of being economical because no or only a small amount of a fly ash stabilizing chelating agent is added. However, in this conventional method, S
e cannot be stabilized, and Pb cannot be stabilized when the molten fly ash is acidic or neutral.

Conventionally, as a method for stabilizing acidic molten fly ash, required amounts of slaked lime, ferrous chloride and water are added to the acidic molten fly ash and kneaded, and the pH is 8.5 to 10.0 and the water content is reduced. 1
A method of preparing a kneaded material of about 5 to 20% by weight has been proposed (JP-A-8-192129). This conventional method includes Se.
It has the advantage of being economical because it can stabilize harmful substances such as heavy metals other than, and does not add a fly ash stabilizing chelating agent. However, in this conventional method, the amount of ferrous chloride added to the acidic molten fly ash is small, and the pH adjustment range of the kneaded material is narrow and slightly low.
There is a problem that it is difficult to reliably stabilize.

[0005]

The problem to be solved by the present invention is that the molten fly ash and / or the calcined fly ash, including Se contained therein, are economically and reliably provided in a form that is convenient to handle. To provide a method for stabilization.

[0006]

According to the present invention for solving the above-mentioned problems, after mixing molten fly ash and / or calcined fly ash with a powdered substance containing slaked lime, an aqueous ferrous chloride solution is added to the mixture. FeCl per 100 parts by weight of molten fly ash and / or calcined fly ash
₂ to 5.5 parts by weight or more, and 30 to 100 parts by weight of Fe per 100 parts by weight of Ca in slaked lime contained in the powdery substance. And the pH is 9 to 12.5
Further, the present invention relates to a method for stabilizing molten fly ash and / or fired fly ash, which is a kneaded product having a water content of 15 to 30% by weight.

[0007] In the stabilization method according to the present invention, the molten fly ash to be treated is collected by dust collection processing from the exhaust gas generated in the melting processing of the incineration residue of refuse and the gasification melting processing of refuse. It is dust. In addition, calcined fly ash
Dust collected by the dust collection process from the exhaust gas generated in the burning process of the refuse incineration residue. These molten fly ash and calcined fly ash include Pb, Cd, Hg, Se, As,
It contains harmful substances such as heavy metals such as hexavalent Cr.

In the stabilization method according to the present invention, first, molten fly ash and / or calcined fly ash are mixed with a powdered substance containing slaked lime. A typical example of such a powdery substance is slaked lime itself.
An aqueous iron solution is added and kneaded, and the pH of the kneaded product is 9 to 1
In the case of 2.5, ferrous hydroxide generated from ferrous chloride by slaked lime has a solubility near the minimum and is easy to settle, and at this time, harmful substances as described above are embraced. To coprecipitate and stabilize. Instead of powdered substances containing slaked lime, it is conceivable to use cement,
In this case, the obtained kneaded material is easily solidified, so that it is difficult to handle the material at the time of unloading or transporting.

The above-mentioned powdery substance preferably contains calcium chloride in addition to slaked lime. Calcium chloride is easily soluble in water and has a high hygroscopicity, so it is effective for retaining the water content of the obtained kneaded product and for terminating the stabilization reaction. It is also effective in suppressing dust generation during transportation and transportation. For example, in the case of Pb, Pb is easily extracted from molten fly ash or calcined fly ash by chloride ions derived from calcium chloride, and when the aqueous ferrous chloride solution is added and kneaded, the Pb once extracted is shared. It is easy to settle and stabilize.

[0010] Further, as the above-mentioned powdery substance, dust collection processing of exhaust gas generated from a refuse incinerator, a refuse gasification melting furnace, a refuse incineration residue melting furnace, or a refuse incineration residue firing kiln. In the dry exhaust gas treatment of the acidic exhaust gas later, it is advantageous to use a reaction product generated in a facility for neutralizing the acidic exhaust gas by blowing slaked lime or the like. Exhaust gas is generated from refuse incinerators, refuse gasification and melting furnaces, refuse incineration residue melting furnaces, and refuse incineration residue firing kilns. These exhaust gases are usually collected by waste heat, cooled, and then subjected to dust collection by adding activated carbon or the like as necessary. The exhaust gas after the dust collection process contains HCl, SOx, and the like, and exhibits acidity. The acidic exhaust gas after the dust collection treatment is usually subjected to a dry exhaust gas treatment, neutralized by blowing slaked lime or the like, and then subjected to a dust collection treatment again. The collected matter by the dust collection process again is a reaction product composed of unreacted slaked lime, neutralized material, and the like. Since such reaction products include some heavy metals that could not be collected by the dust collection process in the previous stage, they cannot be landfilled as it is, and it is difficult to dispose of them. is there. Therefore, in the present invention, such a reaction product is used as a powdery substance as described above.

[0011] In the stabilization method according to the present invention, an aqueous ferrous chloride solution is added to a mixture of molten fly ash and / or calcined fly ash and a powdered substance containing slaked lime. Ferrous chloride can reduce hexavalent Cr, and when ferrous hydroxide generated from the ferrous chloride coagulates with slaked lime, harmful substances as described above are embraced and coprecipitated. Even when the ferric hydroxide generated from the ferrous hydroxide by oxidation is coagulated, the harmful substance is coprecipitated to stabilize the harmful substance. Also, as described above for calcium chloride, chloride ions of ferrous chloride facilitate extraction of Pb from molten fly ash and calcined fly ash, and as a result, co-precipitate and stabilize Pb once extracted. . Although it is conceivable to use an aqueous ferrous sulfate solution in place of the aqueous ferrous chloride solution,
Ferrous sulfate is usually commercially available in powder form, its aqueous solution is unstable and reacts with slaked lime to form gypsum,
The resulting kneaded material tends to solidify, which hinders handling. On the other hand, the aqueous ferrous chloride solution itself is commercially available and is stable, and the kneaded material obtained by using the aqueous solution does not solidify, and the handling thereof is convenient.

In the stabilization method according to the present invention, the ferrous chloride aqueous solution is preferably 5.5 parts by weight or more, preferably 5 parts by weight, as FeCl ₂ per 100 parts by weight of molten fly ash and / or calcined fly ash. 0.5 to 15 parts by weight. When the amount of the aqueous ferrous chloride solution is calculated as FeCl ₂ ,
5.5 per 100 parts by weight of molten fly ash and / or calcined fly ash
If the amount is less than 10 parts by weight, it is difficult to stabilize Se reliably. Conversely, the amount of Se should be more than 15 parts by weight per 100 parts by weight of molten fly ash and / or calcined fly ash in terms of FeCl _2. Although there is no particular problem, the effect of stabilizing harmful substances such as heavy metals described above is not so high.

In the stabilization method according to the present invention, the ferrous chloride aqueous solution contains 30 to 100 Fe as Fe per 100 parts by weight of Ca in slaked lime contained in the powdery substance.
Add by weight. When the amount of the aqueous ferrous chloride solution is out of the range of 30 to 100 parts by weight per 100 parts by weight of Ca in slaked lime contained in the powdery substance, the pH of the obtained kneaded material is 9 to It is difficult to make 12.5, preferably 10.5-12.5.

Finally, in the stabilization method according to the present invention,
Thus, the molten fly ash and / or the calcined fly ash and the powdered substance containing slaked lime are mixed, and the mixture obtained by adding an aqueous ferrous chloride solution is kneaded as it is or further by adding a required amount of water, pH of 9 to 12.5 and moisture of 15 to 30% by weight
Kneaded material. Depending on the concentration and the amount of the aqueous ferrous chloride solution to be used, the aqueous solution to which the aqueous ferrous chloride solution has been added can be kneaded as it is. A required amount of water, usually 25 parts by weight or less per 100 parts by weight of molten fly ash and / or calcined fly ash, is added to the iron iron aqueous solution and kneaded.

In the stabilization method according to the present invention, as described above, the pH is 9 to 12.5, preferably 10.5 to 12.5.
12.5 and a water content of 15 to 30% by weight, preferably 2
It is a kneaded material of 0 to 25% by weight. The pH of the kneaded material can be adjusted by the relative usage ratio of slaked lime in the powdered substance containing slaked lime and ferrous chloride in the ferrous chloride aqueous solution, and the water content is determined by the concentration of the ferrous chloride aqueous solution used and It can be adjusted by the amount as well as the amount of water added. The pH of the kneaded material is 9-
If it is outside the range of 12.5, it is difficult to stabilize the above-mentioned harmful substances such as heavy metals including Se, and if the water content is outside the range of 15 to 30% by weight, there is a problem in its handling. Is generated. For example, when carrying out or transporting kneaded materials,
It is very troublesome because it generates dust and leaks the aqueous solution.

In the stabilizing treatment method according to the present invention, as described above, after mixing the molten fly ash and / or the calcined fly ash with the powdered substance containing at least slaked lime, the mixture is mixed with ferrous chloride. An aqueous solution is added, and if necessary, a required amount of water is also added and kneaded, and the pH is 9 to 12.5 and the water content is 15 to
The kneaded product is 30% by weight, but it is also effective to knead by adding a small amount of a fly ash stabilizing chelating agent after adding and kneading an aqueous ferrous chloride solution. In this case, the amount of the fly ash stabilizing chelating agent used is 5 parts by weight or less per 100 parts by weight of molten fly ash and / or calcined fly ash. Adding more than that has no effect and is rather uneconomical. As such a fly ash stabilizing chelating agent, a per se known pyrrolidine-based sulfur compound, imine-based sulfur compound, carbamic acid-based sulfur compound, or the like can be used.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the stabilization method according to the present invention include the following 1) to 4). 1) After mixing 100 parts by weight of molten fly ash collected from the exhaust gas in the melting treatment of municipal solid waste incineration residue and 9.8 parts by weight of JIS special grade slaked lime, 33% by weight was added to the mixture.
16.7 parts by weight of an aqueous ferrous chloride solution (5.5 parts by weight as FeCl ₂ per 100 parts by weight of molten fly ash, 45.7 parts by weight as Fe per 100 parts by weight of Ca in JIS special grade slaked lime) and water (the above-mentioned melting point) Water extracted from the granulator used for granulating the melt generated in the treatment, the same applies hereinafter) 1
A method in which 8.7 parts by weight is added and kneaded to obtain a kneaded product having a pH of 12.0 and a water content of 20.6% by weight.

2) 100 parts by weight of molten fly ash collected from exhaust gas in the melting treatment of municipal solid waste incineration residue;
After mixing 5 parts by weight of S-grade slaked lime and 20 parts by weight of calcium chloride powder, the mixture was mixed with 35 parts by weight of a 33% by weight aqueous ferrous chloride solution (FeCl per 100 parts by weight of molten fly ash).
11.6 parts by weight _2, Ca1 in JIS special grade slaked lime
51.5 parts by weight of Fe per 100 parts by weight) and water 2
A method of adding 9.7 parts by weight and kneading to obtain a kneaded product having a pH of 10.5 and a water content of 28.0% by weight.

3) After mixing 100 parts by weight of molten fly ash collected from the exhaust gas and 50 parts by weight of the following reaction product in the melting treatment of the incineration residue of municipal waste, 33% by weight of 30 parts by weight of iron aqueous solution (melt fly ash 10
9.9 parts by weight as FeCl ₂ per 0 parts by weight, Fe per 100 parts by weight of Ca in slaked lime contained in the reaction product
37.2 parts by weight) and 10.4 parts by weight of water, and kneaded to obtain a kneaded product having a pH of 11.0 and a water content of 16.0% by weight. Reaction product: In the dry exhaust gas treatment of the acidic exhaust gas after the dust collection process of the exhaust gas generated from the incinerator of municipal solid waste, a slight excess of slaked lime is added to the acidic exhaust gas to neutralize the waste gas, and the dust is collected again by the dust collection treatment. Gathered

4) 100 parts by weight of molten fly ash collected from exhaust gas in the melting treatment of municipal waste incineration residue;
After mixing with 9.8 parts by weight of S-grade slaked lime, 16.7 parts by weight of a 33% by weight aqueous ferrous chloride solution (5.5 parts by weight as FeCl ₂ per 100 parts by weight of molten fly ash) was added to the mixture.
45.7 parts by weight of Fe per 100 parts by weight of Ca in JIS special grade slaked lime) and 19.3 parts by weight of water were added and kneaded, and 1 part by weight of a carbamate-based sulfur compound was added as a chelating agent for fly ash stabilization. Knead again and adjust the pH to 12.
1 and a method of making a kneaded material having a moisture content of 21.1% by weight.

[0021]

EXAMPLES Examples of the stabilization method according to the present invention will be described below, but the present invention is not limited to these examples. It should be noted that the molten fly ash collected from the exhaust gas generated in the melting process of the waste incineration residue, the molten fly ash collected from the exhaust gas generated in the gasification melting process of the waste, and the exhaust gas generated in the firing process of the waste incineration residue are collected. Although there is a difference in the composition between the collected fired fly ash, all of them can be stabilized almost in the same manner by the stabilization method according to the present invention.
The test result about the molten fly ash collected from the exhaust gas generated in the melting treatment of the refuse incineration residue is illustrated.

Example 1 In a melting treatment of municipal solid waste incineration residue, 100 parts by weight of molten fly ash having the composition shown in Table 1 collected from the exhaust gas by a bag filter and 9.8 parts by weight of JIS special grade slaked lime were padded. The mixture was mixed by a mixer. Then, 16.7 parts by weight of a 33% by weight aqueous ferrous chloride solution and 18.7 parts by weight of water (water withdrawn from a granulation tank used for granulating the melt produced in the above-mentioned melting treatment) were added to the mixture. And add
A kneaded product was obtained by kneading with a vibrating kneader. This kneaded material is subjected to a dissolution test according to the Environment Agency Notification No. 13 of 1974 “Testing method for metals and the like contained in industrial waste”, and the dissolution value is reported to the Prime Minister's Ordinance No. 51, 1995 Stability was determined in comparison with "Criteria for waste."

Examples 2 to 6 In the same manner as in Example 1, melt fly ash was used as a kneaded material, and a dissolution test was performed on each kneaded material to determine stabilization. However, in Example 3, calcium chloride powder was used together with JIS special grade slaked lime, and in Example 4, instead of JIS special grade slaked lime,
In dry exhaust gas treatment of acidic exhaust gas after dust collection using a bag filter for exhaust gas generated from incinerators of municipal solid waste, a slight excess of slaked lime was blown into the acidic exhaust gas for neutralization, and a bag filter was used again. In Examples 5 and 6, a liquid chelate was further added as a chelating agent for fly ash stabilization to a kneaded material obtained by adding a 33% by weight aqueous solution of ferrous chloride and water and using the reaction product collected in the dust collection process. In addition, it was kneaded.

Comparative Example 1 The same molten fly ash as in Example 1 was directly subjected to a dissolution test and determined.

Comparative Examples 2 to 9 In the same manner as in Example 1, molten fly ash was used as a kneaded material, and a dissolution test was performed on each kneaded material to determine stabilization. However, in Comparative Example 2, ferric chloride was used instead of ferrous chloride, Portland cement was used in place of slaked lime in Comparative Example 3, slaked lime was not used in Comparative Example 4, and water was used in Comparative Example 5. In Comparative Example 6, a 33% by weight aqueous solution of ferrous chloride was first added and kneaded, and then JIS special grade slaked lime was added and kneaded again. In Comparative Example 7, the amount of water used was reduced. In Example 8, ferrous sulfate was used in place of ferrous chloride. In Comparative Examples 9 and 10, Ca100 derived from slaked lime was used.
The amount of Fe derived from ferrous chloride per part by weight was excluded from the scope of the present invention.

Table 2 shows the stabilization treatment conditions, the elution values and the results of the determination according to the method of notification by the Environment Agency No. 13, and Table 3 shows the results for Examples 1 to 6, and Table 3 shows the results for Comparative Examples 1 to 9. It is shown together.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

In Tables 2 and 3, ferrous chloride aqueous solution, ferrous sulfate aqueous solution, and ferric chloride aqueous solution: each having a concentration of 33% by weight Reaction product: exhaust gas generated from municipal waste incinerator In the dry exhaust gas treatment of the acidic exhaust gas after the dust collection process using the bag filter, a slight excess of slaked lime is blown into the acidic exhaust gas to neutralize, and the reaction product collected by the dust collection process using the bag filter again object. Water: Water extracted from a granulator used for granulating the melt generated in the melting treatment of municipal solid waste incineration residue FeCl ₂ / Molten fly ash: Used ferrous chloride aqueous solution per 100 parts by weight of molten fly ash of FeCl ₂ parts by weight of Fe / Ca: parts by weight pH of the Fe in the ferrous chloride aqueous solution was used per Ca100 parts in slaked lime used: dissolution test when values moisture kneaded product: in the kneaded material total % By weight of water

As is clear from the state and handleability of the kneaded material with respect to the stabilizing treatment conditions shown in Tables 2 and 3, and the results of the judgment, Comparative Examples 2 to 3 deviating from the stabilizing treatment conditions of the present invention. No. 9 shows that there is a problem in the judgment if there is no problem in the state and handling property of the kneaded material, and that there is a problem in the state and handling property of the kneaded material while there is no problem in the judgment. Example 1 that satisfies processing conditions
All of Nos. To 6 have no problem in the determination of the state and handleability of the kneaded material and the elution value.

[0032]

As is apparent from the above description, the present invention described above provides an economical and reliable method for handling molten fly ash and / or calcined fly ash, including Se contained therein, in a form convenient for handling. There is an effect that can be stabilized.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D004 AA37 AB03 CA15 CA35 CB26 CC03 CC06 CC11 CC13 DA02 DA03 DA10

Claims (5)

[Claims] After mixing molten fly ash and / or calcined fly ash with a powdered substance containing slaked lime, an aqueous ferrous chloride solution is added to the molten fly ash and / or 100 parts by weight of the calcined fly ash. F
eCl ₂ is added in an amount of not less than 5.5 parts by weight and Fe is added in an amount of 30 to 100 parts by weight per 100 parts by weight of Ca in slaked lime contained in the powdery substance. In addition, knead, pH 9-1
A method for stabilizing molten fly ash and / or calcined fly ash, which is a kneaded material having a water content of 2.5 to 15 to 30% by weight. 2. The method for stabilizing molten fly ash and / or burnt fly ash according to claim 1, wherein the powdery substance further contains calcium chloride. 3. An acidic exhaust gas as a powdery substance after dust collection of an exhaust gas generated from a refuse incinerator, a refuse gasification melting furnace, a refuse incineration residue melting furnace, or a refuse incineration residue firing kiln. The method for stabilizing molten fly ash and / or calcined fly ash according to claim 1 or 2, wherein in the dry exhaust gas treatment, a reaction product generated in a facility for injecting slaked lime or the like into the acidic exhaust gas for neutralization treatment is used. 4. The ferrous chloride aqueous solution is converted to FeCl _{2 by} 5.5 to 100 parts by weight of molten fly ash and / or calcined fly ash.
The method for stabilizing molten fly ash and / or burnt fly ash according to any one of claims 1 to 3, which is added so as to be 15 parts by weight. 5. An aqueous ferrous chloride solution is added and kneaded, and a fly ash stabilizing chelating agent is further added so as to be 5 parts by weight or less per 100 parts by weight of molten fly ash and / or calcined fly ash. The method for stabilizing molten fly ash and / or calcined fly ash according to any one of claims 1 to 4.