JPH105715A - Treatment of heavy metal-containing ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely stabilize heavy metals in ash even when the amts. of a chelating agent and a ferrite forming salt used are small. SOLUTION: Heavy metal-contg. ash is kneaded with water, a ferrite forming agent is added and they are kneaded at 50-100 deg.C. After ferrite formation reaction proceeds, a chelating agent is further added and they are kneaded. When the pH of the kneaded ash is <7 at the time of adding the ferrite forming agent, the pH is preferably adjusted to >=7 by adding alkali. The ferrite forming agent is preferably ferrous chloride and/or ferrous sulfate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating incinerated ash discharged from incineration or melting of solid waste such as municipal solid waste and industrial waste, and ash containing heavy metals such as exhaust gas collection ash.

[0002] Dust in exhaust gas generated from municipal solid waste incineration equipment is collected by an electric dust collector or a back filter. Since this collected dust is highly scattered and contains heavy metals harmful to the human body, such as lead hexavalent chromium, it is necessary to change this to a form that is convenient to handle and does not elute harmful metals. The present invention relates to a method for treating such heavy metal-containing ash.

[0003]

2. Description of the Related Art Conventionally, as a method for treating heavy metal-containing ash, a required amount of water, a chelating agent, and a ferrite-forming salt are added to a collected dust separated by a dust collector in a refuse incineration plant, and the mixture is kneaded. A method of treating dust in a refuse incineration plant characterized by setting the temperature and ferrite formation conditions is known (Japanese Patent Laid-Open No. 7-757).
No. 66).

[0004]

However, in the method of immobilizing heavy metals in heavy metal-containing ash using a chelating agent, it is difficult to immobilize heavy metals unless a large amount of a chelating agent is used, especially during dust collection ash treatment. In addition, in the method of treating a heavy metal-containing ash by simultaneously adding a chelating agent and a ferrite-forming salt to dust collection dust, the treatment effect is low unless the amount of ferrite-type salt used is increased.

[0005] In view of the above, an object of the present invention is to provide a method for treating heavy metal-containing ash which can reliably treat heavy metals in ash even when the amounts of chelating agents and ferrite-forming salts used are small. It is in.

[0006]

According to the method for treating heavy metal-containing ash according to the present invention, water is added to the heavy metal-containing ash and kneaded, and then a ferrite forming agent is added and further kneaded at a temperature of 50 ° C to 100 ° C. It is characterized in that a chelating agent is added and kneaded after the ferrite-forming reaction proceeds.

In the method of the present invention, when the pH at the time of adding the ferrite forming agent is less than 7, it is preferable to further add an alkali and add the ferrite forming agent to make the pH 7 or more. As the alkali, sodium hydroxide, calcium hydroxide and the like are often used.

The preferred ferrite former is a ferrous compound.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The amount of the chemical used in the method of the present invention is, for example, 100 parts by weight of heavy metal-containing ash and water
0 to 50 parts by weight, 4 to 15 parts by weight of ferrite-forming agent (the molar ratio should be at least equimolar to heavy metal forming ferrite), and 1 to 5 parts by weight of chelating agent.

The kneading temperature after adding the ferrite forming agent is 50.
C. to 100.degree. C., preferably 65.degree. If the temperature is too low, the ferrite-forming reaction does not easily proceed, while if it is too high, the evaporation of water becomes severe, which is not preferable in any case.

Ferrite forming agents include ferrous chloride,
Ferrous compounds such as ferrous sulfate are preferred. These may be used alone or in combination.

As the kneading means, it is preferable to use a vibratory kneader or a twin-screw kneading extruder in which a plurality of rods are loaded.

A typical example of the chelating agent is "Epolva" manufactured by Miyoshi Oil & Fats Co., Ltd.

[0014]

Next, the method of the present invention will be specifically described with reference to examples.

Example 1 100 g of dust ash A obtained by collecting dust in flue gas generated from municipal solid waste incineration equipment with a back filter was added water 10
0 g was added and the temperature was raised to 70 ° C. while mixing. Next, 4 g of ferrous sulfate (as FeSO ₄ ) was added to the mixture,
The mixture was stirred (300 rpm) for 2 hours while passing air through the mixture at 1 liter / min and violently to cause a ferrite-forming reaction. Next, a chelating agent was added to the reaction solution to collect 100 g of dust ash.
After stirring for 5 minutes, the precipitate was left for one day. The heavy metal content of the collected dust ash A was as follows: Pb = 0.39 wt%, Zn = 1.35 wt%, T-Cr = 150 mg / kg, Cd = 120 mg /
kg, T-Hg = 8.4 mg / kg, As = 12 mg / kg
kg.

Examples 2 to 4 The same operation as in Example 1 was carried out except that the amount of the chelating agent was changed to 2, 3, and 4 g for 100 g of dust ash, respectively.

Example 5 100 g of water was added to 100 g of dust ash B different from dust ash A, and the temperature was raised to 70 ° C. while mixing. Next, 4 g of ferrous sulfate (as FeSO ₄ ) was added to the mixture and the pH was adjusted to 7
After the mixture was adjusted to 1, the mixture was stirred for 2 hours (300 rpm) while passing air at 1 liter / min and violently to allow a ferrite formation reaction. Next, 2 g of a chelating agent was added to 100 g of dust collection ash to the reaction solution, and stirring was continued for 5 minutes. The heavy metal content of the collected dust ash B was Pb = 1.2% by weight, Zn =
3.1% by weight, T-Cr = 340mg / kg, Cd = 9
8 mg / kg, T-Hg = 1 mg / kg, As = 11 m
g / kg.

Comparative Example 1 The same operation as in Example 1 was performed except that no chelating agent was added.

Comparative Example 2 The same operation as in Example 5 was performed except that no chelating agent was added.

Comparative Examples 3 to 6 The same operations as in Examples 1 to 4 were carried out except that ferrous sulfate was not added and stirring was not performed under air storm.

Dissolution test The precipitates obtained in Examples 1 to 5 and Comparative examples 1 to 6 and the dust ash A point when neither ferrous sulfate nor a chelating agent was added were used to dissolve heavy metals. Tested. The test method followed the Notification of the Environment Agency No. 13 (TCL in the United States).

The results of these dissolution tests are summarized in Table 1.

[0023]

[Table 1] As can be seen from Table 1, the amount of heavy metal eluted from the precipitate obtained in the example is equal to or less than the criterion value for landfill disposal of cinders, dust, and sludge.

[0024]

As described above, the method for treating dust ash of the present invention is constructed as described above. Therefore, even if the amounts of expensive reagents such as chelating agents and ferrite forming salts are small, heavy metals in the ash can be reliably removed. It is economical and can fix Hg ²⁺ and other heavy metals that are unlikely to become ferrite. Moreover, it is possible to treat dust ash having a pH of 12 or more, which has been difficult with the conventional method, without any problem.

Claims (3)

[Claims] Claims 1. After adding and kneading water to a heavy metal-containing ash,
A method for treating heavy metal-containing fly ash, comprising adding a ferrite-forming agent, further kneading at a temperature of 50 ° C. to 100 ° C., and kneading by adding a chelating agent after the ferrite-forming reaction proceeds. 2. The method for treating heavy metal-containing ash according to claim 1, wherein when the pH at the time of adding the ferrite forming agent is less than 7, the pH is adjusted to 7 or more by further adding an alkali. 3. The method of claim 1, wherein the ferrite forming agent is ferrous chloride and / or
The method for treating heavy metal-containing ash according to claim 1, wherein the method is ferrous sulfate.