JP3344896B2 - Treatment method for heavy metal-containing ash - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fly ash collected from an incineration plant such as a garbage incineration plant by means of an electric dust collector or a bag filter from flue gas, incineration ash from residual incineration, and incineration of a garbage incineration plant. Heavy metal-containing ash, such as fly ash generated from a melting furnace for reducing the volume and recycling of incineration ash collected from electric dust collectors and bag filters from flue gas at plants, and incineration ash from incineration residue. The present invention relates to a method for treating heavy metal-containing ash that can suppress elution of contained heavy metals.

[0002]

[Prior Art] Fly ash and incineration ash generated in waste incineration plants, etc.
Alternatively, heavy metal-containing ash such as molten fly ash contains a large amount of heavy metals such as lead, cadmium, mercury, and chromium that are harmful to the body. Therefore, it is necessary to detoxify these heavy metals. As a processing method, for example,
Japanese Patent No. -6889 discloses a method of adding and kneading water and a heavy metal fixing agent to fly ash. However, in this method, it is necessary to add a large amount of a heavy metal fixing agent, so that there is a problem that running cost is increased. Therefore, JP-A-7-39846 discloses that
A method has been proposed in which aluminum sulfate is added to the fly ash and kneaded to adjust the pH, and then a heavy metal fixing agent is added and kneaded.

[0003]

However, a dithiocarbamic acid-based compound is generally used as a heavy metal fixing agent. However, when a dithiocarbamic acid-based heavy metal fixing agent and an aluminum compound pH adjuster are used in combination, a large amount of There was a problem that carbon disulfide was generated. The present invention
It is an object of the present invention to provide a method for treating heavy metal-containing ash, which can suppress the generation of carbon disulfide and the elution of heavy metals.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve such problems, and as a result, a magnesium compound has been used as a pH adjuster and a dithiocarbamic acid-based compound has been used as a heavy metal fixing agent. By treating the contained ash, it is possible to suppress the generation of carbon disulfide and to find out the fact that the elution of heavy metals can be suppressed.
The present invention has been reached. That is, the gist of the present invention is a method for treating heavy metal-containing ash, which comprises kneading a heavy metal-containing ash with a magnesium compound and a dithiocarbamic acid-based heavy metal fixing agent.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
As the heavy metal-containing ash used in the present invention, fly ash collected by an electric dust collector or a bag filter from flue gas in an incineration plant of a garbage incineration plant, incineration ash of incineration residue, incineration plant of a garbage incineration plant Fly ash collected by electric dust collectors and bag filters from flue gas and molten fly ash generated from a melting furnace to reduce and recycle incinerated ash from incineration residue When the pH of the supernatant water after shaking the contained ash as a 10% by weight aqueous solution for 6 hours is measured, it is usually 12%.
That is all.

The magnesium compound used in the present invention includes solid magnesium chloride hexahydrate, liquid magnesium chloride, solid magnesium sulfate heptahydrate, liquid magnesium sulfate, etc., such as sodium chloride, calcium chloride, sodium sulfate, and the like. 5 impurities such as calcium sulfate
Those having 0% or less are preferable. In the present invention, these magnesium compounds may be used alone, or a mixture of a plurality of them may be used. Usually, liquid magnesium chloride (28% by weight in terms of MgCl ₂ ,
When calculated as MgCl ₂ · 6H ₂ O 60% by weight containing) or 21 wt% when converted as a liquid magnesium sulfate _{(MgSO 4, MgSO 4 · 7H} 2 O may be used to the 43 wt% content) calculated as but containing heavy metals When the water content of the kneaded product obtained by kneading the ash, the magnesium compound and the heavy metal fixing agent becomes excessive, it is preferable to use solid magnesium chloride hexahydrate or solid magnesium sulfate heptahydrate.

Examples of the dithiocarbamic acid-based heavy metal fixing agent used in the present invention include sodium, potassium and lithium salts of diethyldithiocarbamic acid, dibutyldithiocarbamic acid, and tris (dithiocarboxy) diethylenetriamine. Various heavy metal fixing agents can be used.

In the present invention, the heavy metal-containing ash, the magnesium compound and the heavy metal fixing agent are kneaded. The magnesium compound at this time is adjusted so that the pH of the kneaded product after kneading is in the range of 9 to 11. It is preferable to adjust the properties of the heavy metal-containing ash, which greatly varies depending on the combustion conditions, combustion conditions, and exhaust gas treatment conditions, and also varies depending on the incineration plant. . Usually, if the magnesium compound is selected and kneaded in a range of 5 to 100 parts by weight with respect to 100 parts by weight of the heavy metal-containing ash, the above range can be adjusted. Also,
The heavy metal fixing agent is preferably determined in advance depending on the properties of the heavy metal-containing ash and the pH of the kneaded material after kneading the magnesium compound according to the kneaded material after kneading the magnesium compound. Usually, at 5 parts by weight or less based on 100 parts by weight of the heavy metal-containing ash, elution of heavy metals can be sufficiently suppressed.

When kneading, it is preferable to add water. The magnesium compound and the heavy metal fixing agent are kneaded with the heavy metal-containing ash, and the mixture is adjusted so that the moisture content of the kneaded product becomes 30 to 40%. This is preferred because the handling of the product is good.

As a kneading method, it is preferable to add a magnesium compound to the heavy metal-containing ash and knead the mixture, and then add a heavy metal fixing agent and further knead the mixture. The kneading may be performed using a kneading machine such as a vibration type, a rotating drum type, a twin-shaft kneading type, and the kneading machine may be a batch type or a continuous type. Further, the kneading time is preferably 2 to 20 minutes, particularly preferably 5 to 10 minutes.

[0011]

Next, the present invention will be described specifically with reference to examples. Examples 1 and 2, Comparative Example 1 28% by weight of magnesium chloride and 48% by weight of fly ash collected by a bag filter of an exhaust gas treatment facility in a municipal waste incineration plant containing pH 12.6, Pb6 and 290 mg / L Parts and 17 parts by weight of water (Example 1), 2
After adding 83 parts by weight of 1% by weight magnesium sulfate (Example 2) and kneading for about 5 minutes, a dithiocarbamic acid-based heavy metal fixing agent UML-7200 manufactured by Unitika Ltd.
Part by weight was added and kneaded for another 5 minutes. Separately, a heavy metal fixing agent is added to 100 parts by weight of the above fly ash.
Only parts by weight were added and kneaded for about 5 minutes (Comparative Example 1). The kneaded product thus obtained was made into a 10% by weight aqueous solution, shaken for 6 hours, and the pH of the supernatant water was measured, and a heavy metal dissolution test was carried out according to the method specified in Notification No. 13 of the Environment Agency. . Table 1 shows the results.

[0012]

[Table 1]

As shown in Table 1, by using a magnesium compound and a dithiocarbamic acid-based heavy metal fixing agent in combination, the elution of lead can be suppressed. Prime Minister's Ordinance Establishing Criteria for Waste (February 17, 1973, Prime Minister's Ordinance No. 5
No.) which is the landfill landfill judgment standard value of 0.3 mg /
Cleared the liter significantly. In addition, when a magnesium compound was used in combination, the elution of lead could be sufficiently suppressed by adding only 1 part by weight of the heavy metal fixing agent. However, the heavy metal fixing agent required for treatment with only the heavy metal fixing agent was 5 parts by weight. there were.

Example 3, Comparative Example 2 After enclosing 50 parts by weight of fly ash as in Example 1 in a Tedlar bag having a capacity of 1 liter, degassing was carried out, and 300 ml of pure air and 24 parts by weight of 28% by weight magnesium chloride were added. (Example 3) or 12 parts by weight of 52% by weight aluminum sulfate 18 hydrate (Comparative Example 2) and 8.8 of UML-7200 manufactured by Unitika, a dithiocarbamic acid-based heavy metal fixing agent.
A part by weight was injected, hand kneaded for 5 minutes, left to stand for 10 minutes, and the generated gas was transferred to another Tedlar bag. The concentration of carbon disulfide in the generated gas thus collected was measured with a gas chromatograph (manufactured by Hitachi, Ltd.). As a result, when 28% by weight of magnesium chloride was used as a pH adjuster, the amount of generated carbon disulfide was 11 ppm, and p
When 52% by weight of aluminum sulfate was used as the H adjuster, the amount of generated carbon disulfide was 410 ppm. From these results, when the treatment is performed with the magnesium compound and the dithiocarbamic acid-based heavy metal fixing agent, the amount of carbon disulfide generated is suppressed to about 1/40 that of the case where the treatment is performed using the aluminum compound and the dithiocarbamic acid-based heavy metal fixing agent. We can see that we can do it.

Reference Example 1 and Comparative Example 3 Assuming that fly ash was not supplied to the kneader due to a bridge or the like in the heavy metal-containing ash storage tank, 300 ml of pure air and 28 ml of pure air were stored in a 1-liter tedlar bag.
19 parts by weight of magnesium chloride by weight (Reference Example 1) or 10 parts by weight of aluminum sulfate 18 hydrate by 52% by weight (Comparative Example 3) and 10 parts by weight of a dithiocarbamic acid-based heavy metal fixing agent UML-7200 manufactured by Unitika Ltd. Part injection, 5
The mixture was hand-kneaded for 10 minutes, allowed to stand for 10 minutes, and then the generated gas was transferred to another Tedlar bag. The amount of carbon disulfide in the generated gas thus collected was measured in the same manner as in Example 3. As a result, the generation of carbon disulfide when 28% by weight of magnesium chloride and a dithiocarbamic acid-based heavy metal fixing agent were kneaded. The amount was 320 ppm, while the amount of carbon disulfide generated when kneading 52% by weight of aluminum sulfate and a dithiocarbamic acid-based heavy metal fixing agent was 3,500 pp.
m. From this result, even when the magnesium compound is in direct contact with the dithiocarbamic acid-based heavy metal fixing agent, the amount of carbon disulfide generated is 1/10 as compared with the case where the aluminum compound is directly contacted with the dithiocarbamic acid-based heavy metal fixing agent. It can be seen that:

[0016]

According to the present invention, the generation of carbon disulfide generated when a dithiocarbamic acid-based heavy metal fixing agent and a pH adjuster are used in combination can be suppressed.

Claims (1)

(57) [Claims] 1. A method for detoxifying heavy metal-containing ash, which comprises kneading a heavy metal-containing ash, a magnesium compound and a dithiocarbamic acid-based heavy metal fixing agent.