JPH09136072A - Fly ash treatment method - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To ensure the insolubilization of heavy metals in incineration ash by using a water-soluble sulfide, and to make a dry fly ash containing a large amount of lime content of 10 to 50% To provide a method for surely insolubilizing heavy metals and rendering them harmless. SOLUTION: This is a method for stabilizing fly ash by mixing dry fly ash with cement and water, then adding calcium sulfide and kneading. A blending amount of 1 to 30 parts by weight of cement, 30 to 60 parts by weight of water, and 1 to 5 parts by weight of calcium sulfide is preferable with respect to 100 parts by weight of dry fly ash.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to heavy metals such as lead, cadmium, arsenic and mercury in dry fly ash generated from incinerators and melting furnaces for municipal waste, industrial waste, radioactive waste, sludge and the like. It relates to a treatment method for insolubilizing and stabilizing.

[0002]

2. Description of the Related Art In recent years, while the amount of waste and waste generated from cities and factories has increased remarkably, heavy metals are entrained in fly ash from incineration, etc. As a result, sufficient detoxification processing is required.

Conventionally, as a treatment method for making heavy metals such as lead, cadmium, and arsenic in incineration ash discharged from a general incinerator insoluble and harmless, it has already been disclosed in JP-A-55-1830.
JP-A-59-73091, JP-A-63-
Those disclosed in Japanese Patent No. 111990, Japanese Patent Application Laid-Open No. 1-231981 and the like are known. These prior inventions are insoluble sulfides such as sodium sulfide and calcium sulfide in incineration ash, or kneading mixture with cement, so heavy metals in the incineration ash are insoluble sulfides such as lead sulfide, It makes it harmless.

For example, the method disclosed in Japanese Patent Laid-Open No. 55-1830 is a method in which water is mixed with industrial waste such as dust collecting dust, cement and water-soluble sulfides and sufficiently mixed. It is desirable to keep industrial waste as dry as possible before it is cemented. Further, the method disclosed in Japanese Patent Application Laid-Open No. 1-231981 is a method in which a water-soluble sulfide is mixed with collected dust, an insolubilized precipitate is separated, and cement is kneaded with the precipitate to be solidified.
However, in these prior inventions, insolubilization of heavy metals in incinerated ash by water-soluble sulfides is not always perfect.

Further, in the above-mentioned prior invention, the incinerated ash contains almost no lime component, and even if it contains lime, it is 8% by weight or less. By the way, some dry fly ash contains a large amount of lime. Such dry fly ash sprays lime and slaked lime water dispersion liquid (lime milk) on high temperature and acidic combustion exhaust gas (off gas) generated from garbage incinerators, etc. to cool and neutralize the combustion exhaust gas and exhaust gas. Is an incineration ash produced by adsorbing and collecting ash entrained in, which contains harmful heavy metals such as lead, cadmium, and arsenic, and contains 10 to 50 wt% quicklime, slaked lime, It also contains lime such as lime carbonate and other calcium salts. In the dry fly ash mentioned above,
Since the lime component is contained in a relatively large amount of 10 to 50% by weight, the treatment method disclosed in the conventional prior art has a disadvantage that the heavy metal cannot be completely insolubilized.

[0006]

Therefore, an object of the present invention is to use water-soluble sulfides to completely insolubilize heavy metals in incinerated ash and to reduce CaO content to 1%.
An object of the present invention is to provide a method for surely insolubilizing and detoxifying even heavy metals contained in a large amount of 0 to 50% by weight in dry fly ash.

[0007]

The method of the present invention is characterized by adding cement and water to dry fly ash, mixing them, and then adding calcium sulfide and kneading. Preferably,
The present invention is a dry fly ash 10 containing 10 to 50% by weight of lime.
This is a method in which 1 to 30 parts by weight of cement and water are added to 0 parts by weight and mixed, and then 1 to 5 parts by weight of calcium sulfide is added and kneaded.

More preferably, the present invention has a lime content of 1
100 parts by weight of dry fly ash containing 0 to 50% by weight of cement 1
-30 parts by weight and water are added and mixed, then 1 to 5 parts by weight of calcium sulfide is added and kneaded, and the total amount of water is 30 to 60 parts by weight. Further, it is preferable that the kneading is carried out in an alkaline condition having a pH of 10 or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
The dry fly ash in the present invention is dry ash generated from an incinerator and a melting furnace for municipal waste, industrial waste, radioactive waste, sludge and the like. Of these dry fly ash, high temperature and acidic combustion exhaust gas discharged from various incinerators is introduced to a gas cooling tower, and lime and slaked lime water dispersion (lime milk) are sprayed from the top of the tower to cool the exhaust gas. The ash that is neutralized and adsorbs and collects the ash that accompanies the exhaust gas, and collects the ash collected at the bottom of the tower and the exhaust gas discharged from the gas cooling tower to an electric dust collector or a bag filter, and collects the ash here. It is especially targeted for, but in addition to this, lime content is 10-50
Other incineration ash containing by weight% is also subject to the treatment method of the present invention.

As described above, such a dry fly ash normally contains 10 to 50% by weight of lime, and has a water content (free water) of 5% or less. Regarding the content of lime, if it is too low, the pH will be 10 or more.
Is not maintained, harmful hydrogen sulfide may be generated,
On the other hand, when the amount is large, the dissociation of calcium sulfide is suppressed, and the amount of calcium sulfide added inevitably increases.
A weight% range is particularly desirable.

Examples of the cement used in the present invention include inorganic cements such as Portland cement, blast furnace cement and fly ash cement. The cement content is preferably 1 to 30 parts by weight with respect to 100 parts by weight of dry fly ash. When the amount is less than 1 part by weight, the insolubilization of heavy metals is not sufficient. If it exceeds 30 parts by weight, the amount of water required for mixing fly ash and cement will increase,
The concentration of calcium sulfide becomes thin, and the insolubilizing effect of heavy metals is likely to decrease.

The components in the cement (ettringite) are
In the presence of water, it reacts with the heavy metals in the fly ash and insolubilizes most of the heavy metals. For example, in the method of the present invention, even if calcium sulfide is not used, the amount of heavy metals such as lead, zinc, chromium, mercury, and arsenic detected in the waste-treated kneaded product is about 1 m due to the insolubilizing effect of heavy metals only in cement.
down to g / l (milligram / liter). In addition, cement keeps the pH of the mixture above 12 and thus relatively lowers the solubility of heavy metals and reduces the required amount of calcium sulfide.

1 to 2 are process drawings showing an embodiment of the method for treating fly ash according to the present invention. As shown in FIGS.
It is important to add cement and water to dry fly ash and mix them to form a slurry-like mixture, and then add calcium sulfide to the mixture and knead. With such a mixing order, the effect of insolubilizing heavy metals by calcium sulfide is great. Therefore, heavy metals such as lead are not substantially eluted into water from the landfilled waste-treated kneaded matter containing fly ash.

By premixing fly ash, cement and water, the trace amount of heavy metals remaining after insolubilizing most of the heavy metals in the fly ash due to the components in the cement,
The point is insolubilization with calcium sulfide. With such a mixing order, the amount of calcium sulfide added can be reduced, and the heavy metal can be reliably insolubilized and the heavy metal can be reliably stabilized. The mixing time of fly ash, cement and water is 3 minutes to 1 hour or less, preferably 5 to 10 minutes. If it is less than 3 minutes, the mixing becomes insufficient, and the cement hardly insolubilizes most of the heavy metals. If it exceeds 1 hour, solidification of cement will start, the amount of the mixture adhering to the mixing vessel and the blade of the stirrer will increase, and cleaning of these will be difficult.

Methods other than the above mixing order, such as fly ash,
By a method such as mixing calcium sulfide and water and then adding cement to the mixture, it is difficult for the heavy metal to be completely insolubilized, as described later.

Calcium sulfide is added as a powder, preferably as an aqueous calcium sulfide solution or an aqueous calcium sulfide dispersion, to a mixture of fly ash, cement and water. Examples of calcium sulfide (CaS _x ) include calcium monosulfide (CaS) and calcium disulfide (CaS).
S _2), trisulfide calcium (CaS _3), tetrasulfide calcium (CaS _4), five calcium polysulfide such as calcium sulfide (CaS ₅₎ is used, a lot of sulfur calcium polysulfide large insolubilization effect of heavy metals Is preferred.
Since calcium sulfide has a low solubility in water, it is usually used in the form of an aqueous dispersion obtained by dispersing calcium sulfide powder in water. The concentration in the calcium sulfide aqueous dispersion is not particularly limited, and may usually be 5 to 30% by weight. This dispersion may contain gypsum, slaked lime or the like as a solid content depending on the composition of calcium sulfide used.

The total amount of heavy metals contained in the dry fly ash is usually about 1% by weight. The amount of the calcium sulfide powder, aqueous solution or aqueous dispersion to be mixed with the dry fly ash is determined to be 1 to 5 parts by weight as calcium sulfide with respect to 100 parts by weight of the dry fly ash. If the content of calcium sulfide is less than 1 part by weight, the effect of insolubilizing heavy metals is difficult to obtain due to lack of calcium sulfide, and if it exceeds 5 parts by weight, the effect cannot be expected to increase any more, which is not only uneconomical. However, harmful hydrogen sulfide gas may be generated from unreacted calcium sulfide.

Water is used for mixing fly ash and cement, adding calcium sulfide, etc., and the total amount thereof is preferably 30 to 60 parts by weight with respect to 100 parts by weight of dry fly ash. If the amount is less than 30 parts by weight or exceeds 60 parts by weight, the insolubilization of heavy metals is reduced. If the amount is less than 30 parts by weight, insufficient mixing of fly ash and cement tends to occur, and 60
If it exceeds the parts by weight, the concentration of calcium sulfide becomes too thin, and the effect of insolubilizing heavy metals decreases. Water slurries a mixture of fly ash and cement to facilitate their mixing, ionizes heavy metals, calcium, sulfur and the like, and facilitates addition of calcium sulfide.

In a mixture of fly ash, cement and water,
After adding calcium sulfide, this is kneaded. For mixing and kneading, a mixer such as an Eirich mixer, an omni mixer, or a continuous / batch type mixer with a horizontal shaft rotating at high speed / low speed is used, and the kneading time is 5 to 5.
It may be about 30 minutes, and the kneading temperature may be room temperature. During this kneading, the pH of the kneaded product is always 10 or more, preferably 12
It is preferable that it is above. This is because when the pH is less than 10, especially on the acidic side, the sulfur content of calcium sulfide becomes hydrogen sulfide and volatilizes, which is harmful. The pH is maintained at 10 or higher due to the presence of cement and the presence of 10% by weight or more of lime in fly ash, but the pH is less than 10 depending on the amount of lime or the composition of fly ash. In such a case, it is desirable to add alkali such as slaked lime and caustic soda.

By this kneading, the fly ash becomes wet soil or paste, and the lead ash contained in the fly ash,
Heavy metals such as zinc react with sulfur ions from calcium sulfide to form water-insoluble sulfides such as lead sulfide. This kneaded product is cured for several days and then disposed of by landfilling. According to the treatment method of the present invention, heavy metals such as lead and zinc in dry fly ash are insolubilized, and the heavy metals do not elute from the waste kneaded product after treatment, and the Environment Agency Notification No. 13 (Showa 48) In the metal elution test based on the method of assaying hazardous substances contained in industrial waste specified in the Official Gazette (March 17, 2003), the elution amount of lead, cadmium, and arsenic was below the regulation value (0.3 ppm or less for Pb). can do.

[0021]

EXAMPLES Hereinafter, the working effects of the present invention will be clarified by showing specific examples. (Examples 1 to 3, Comparative Examples 1 to 3) Dry fly ash, cement,
First, the influence of the difference in the mixing order of water and calcium sulfide on the insolubilizing effect of heavy metals was clarified. Figures 1-5
[FIG. 4] is a process diagram of 5 types in which the order of mixing calcium sulfide and the like is different. 23-25% by weight of lime, moisture 1.6
Prepare dry fly ash of up to 1.7% by weight.
kg, cement 5 kg, calcium sulfide (CaS ₅ ).
Calcium sulfide aqueous dispersion containing 0.3 kg and water 7.5
As shown in FIGS. 1 to 5, kg (total amount) was mixed by changing the mixing order to prepare five kinds of processed products having different mixing orders.

In the process A of the present invention shown in FIG. 1, cement is added to dry fly ash and dry mixed, and then water is mixed to form a slurry (mud).
After mixing for minutes, add the calcium sulfide aqueous dispersion,
This was a method of curing by kneading for 5 minutes to insolubilize heavy metals. In the method of the process B of the present invention shown in FIG. 2, water is added to dry fly ash and cement to form a uniform slurry, which is wet-mixed for 10 minutes, and then an aqueous dispersion of calcium sulfide is added to inactivate the heavy metal. Was kneaded for 5 minutes for curing.

In the method of the comparative example of Process C, water was added to dry fly ash to obtain a uniform slurry, which was wet-mixed for 10 minutes, and then cement and an aqueous dispersion of calcium sulfide were added to the slurry almost at the same time. In this method, kneading for insolubilization of heavy metals was performed for 5 minutes to perform curing. Process D
In the comparative example method, water and an aqueous dispersion of calcium sulfide are added to dry fly ash to form a uniform slurry, which is wet mixed for 10 minutes, and then cement is added to the slurry to knead for insolubilization of heavy metals. Was carried out for 5 minutes for curing. In the process E of the comparative example, water and an aqueous dispersion of calcium sulfide were added to cement to form a uniform slurry, which was wet-mixed for 10 minutes, and then dry fly ash was added to the slurry to inactivate heavy metals. Was kneaded for 5 minutes for curing.

The kneading for the insolubilization of heavy metals in the above processes A to D was carried out by an Erich mixer. The pH during this kneading was 12.4 to 12.5.

The kneaded products obtained by the above-mentioned processes A to D were aged and cured for one day, and the waste-treated kneaded products were subjected to a lead elution test according to the Environmental Agency Notification No. 13. Table 1 shows the results. From these results, according to the method of Processes A and B (Examples 1 to 3) in which cement and water were added to dry fly ash and mixed, and then an aqueous dispersion of calcium sulfide was added, the lead detection amount (lead elution The amount is 0.3 mg / l or less, which means that lead insolubilization is large. Processes C to E (Comparative Examples 1 to 3) in which dry fly ash was not mixed with cement and water before adding the calcium sulfide aqueous dispersion were inferior in insolubilizing effect, and the stabilization of heavy metals was insufficient. .

[0026]

[Table 1]

(Examples 4 to 15) Next, the relationship between the blending amount of cement, water, calcium sulfide and the like and the insolubilization of heavy metals with respect to the amount of dry fly ash was examined by using the method of Process B. That is, 100 kg of the same dry fly ash as that used in Examples 2 to 3 was mixed by adding and mixing the amount of cement and the amount of water to prepare a slurry-like mixture, and then adding calcium sulfide to the mixture. The amount was changed and added and kneaded. The kneading conditions and the lead elution test measurement conditions are the same as those in Example 2 described above.
~ 3. Table 2 shows the results.

[0028]

[Table 2]

From the results of Examples 4 to 9 in Table 2, 1 to 30 parts by weight of cement, 1 to 5 parts by weight of calcium sulfide, and 30 to 60 parts by weight of total amount of water, relative to 100 parts by weight of dry fly ash, The lead detection amount is 0.3 mg /
It can be seen that lead insolubilization is large, for example, 1 or less.
As shown in Examples 11 to 15, if the compounding amount is out of the above range, the insolubilizing effect of lead is inferior or the amount of calcium sulfide used is large even in the method of the process B.

[0030]

As described above, according to the treatment method of the present invention, it is possible to reliably stabilize heavy metals such as lead in dry fly ash as insoluble sulfides such as lead sulfide. Can be made harmless and discarded.

[Brief description of the drawings]

FIG. 1 is a process chart showing an embodiment of a method for treating fly ash according to the present invention.

FIG. 2 is a process drawing showing another embodiment example of the present invention.

FIG. 3 is a process diagram of a comparative example.

FIG. 4 is a process drawing of another comparative example.

FIG. 5 is a process drawing of still another comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazunori Suzuki 2205 Narita-cho, Oarai-cho, Higashi-Ibaraki-gun, Ibaraki Pref. Inside the Oarai Nuclear Technology Development Center, JGC Corporation

Claims (4)

[Claims] 1. A method for treating fly ash, which comprises adding cement and water to dry fly ash, mixing them, and then adding calcium sulfide and kneading. 2. Cement 1 to 30 parts by weight and water are added to 100 parts by weight of dry fly ash containing 10 to 50% by weight of lime,
A method for treating fly ash, which comprises mixing 1 to 5 parts by weight of calcium sulfide after mixing and kneading. 3. Cement 1 to 30 parts by weight and water are added to 100 parts by weight of dry fly ash containing 10 to 50% by weight of lime,
After the mixing, 1 to 5 parts by weight of calcium sulfide is added and kneaded, and the total amount of water is 30 to 60 parts by weight. 4. The method for treating fly ash according to claim 1, wherein the kneading is performed in an alkaline solution having a pH of 10 or more.