JPH0947740A - Method for restraining lead in fly ash from being eluted and lead elution inhibitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely restrain lead in fly ash of municipal refuse incineration from being eluted by adding amorphous aluminum hydroxide to the fly ash of municipal refuse incineration and kneading it with water to solidify it. SOLUTION: Amorphous aluminum hydroxide is added to fly ash of municipal refuse incineration and is kneaded with water to restrain lead in the fly ash from being eluted. Here the added quantity of amorphous aluminum hydroxide is made 3-50 pts.wt. to 100 pts.wt. of the fly ash. In addition to amorphous aluminum hydroxide, ferrous sulfate and/or thiourea is further added. The fly ash is made electric precipitator ash or bag filter ash of 10-30wt.% calcium content of a stoker furnace or a fluidization roaster. In this way, the elution of lead in ash of municipal refuse incineration is surely and economically restrained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for suppressing the elution of lead in municipal waste incineration fly ash and a lead elution suppressor.

[0002]

2. Description of the Related Art Municipal solid waste is usually incinerated in a mechanical furnace (stalker furnace) or a fluidized bed furnace, but the waste gas generated at that time is treated by an electric dust collector or a bag filter and is discarded. The solid fine particles contained in the gas are removed. The solid fine particles, that is, the incineration fly ash of municipal solid waste, contains heavy metals, which makes its treatment a problem. Conventionally, a cement solidification method or a chemical treatment method using a liquid chelating agent is often employed as the heavy metal stabilization treatment in such fly ash.

Generally, the heavy metal which is a problem in fly ash is mainly lead, but in the conventional method, the elution amount of lead may be set to a reference value of 0.3 mg / l or less depending on the properties of fly ash. There are many difficult cases.

Particularly, the above-mentioned waste gas contains H contained therein.
In order to suppress the emission of Cl gas, calcium compounds such as slaked lime are blown in powder (dry type) or slurry state (semi-dry type).
The regulation value of Cl is also different, and there are places where the amount of calcium compound blown in is large and places where it is small. Since this is collected by an electrostatic precipitator or a bag filter, the calcium content in the fly ash has a wide range of about 10% to 35%. In this case, for example, fly ash having a calcium content of 25% or less has a pH of 12 or more, but since the alkali content is relatively small, the pH is unstable and unstable. Therefore, the effect of suppressing the elution of heavy metals by cement and liquid chelating agents cannot often be expected with an economical addition amount. This is because both the cement and the liquid chelating agent have high pH themselves, so that the pH of the fly ash treated product becomes higher and the solubility of lead, which is an amphoteric metal, becomes higher, and this action has a stronger influence than the heavy metal suppressing effect. Presumed.

That is, in the fly ash (EP ash) collected by the electrostatic precipitator having a calcium content of about 20% and the fly ash (BF ash) collected by the bag filter, the lead content is 5,00.
There are some which show 0 mg / kg and a lead elution amount of 200 mg / l, but a lead elution standard value of 0.
Satisfying 3 mg / l or less is difficult only by using the usual amount of cement or liquid chelating agent, and a considerably large amount is required to satisfy this, and even if such a large amount is used, it is certain It does not always satisfy the standard value.

It is also conceivable that the pH of the fly ash is lowered to about 10 using a liquid acidic material such as liquid aluminum sulfate, and then a liquid chelating agent is added. The required addition amount of liquid aluminum sulfate is large, and the strength development of the kneaded product is low,
It is not practical because it has problems such as handling problems.

The present invention has been made in view of the above circumstances,
An object of the present invention is to provide an economical method with good handleability capable of reliably suppressing the elution of lead in incineration fly ash of municipal solid waste, and a lead elution inhibitor used in this method.

[0008]

Means for Solving the Problems and Modes for Carrying Out the Invention As a result of intensive studies to achieve the above object, the present inventor has added amorphous aluminum hydroxide to municipal waste incineration fly ash. By kneading with water and solidifying, lead elution in fly ash can be reliably suppressed with a relatively small amount of 0.3 mg /
The inventors have found that a lead elution standard value of 1 or less can be easily achieved, and that the fly ash treated with this can also be handled easily, resulting in the present invention.

Therefore, according to the present invention, a method for suppressing the elution of lead in fly ash, which comprises adding amorphous aluminum hydroxide to municipal waste incineration fly ash and kneading with water, and amorphous aluminum hydroxide To provide a lead elution inhibitor for municipal waste incineration fly ash.

The present invention will be described in more detail below.

As the municipal solid waste incineration fly ash to be treated in the present invention, a dry or semi-dry mechanical furnace (stoker furnace) in which a calcium compound such as slaked lime is blown in a powder or slurry state to remove HCl gas. ) And E of fluidized bed furnace
P ash or BF ash may be mentioned, and among these, fly ash having a calcium content of 10 to 30% by weight is particularly preferable. Fly ash having an excessively high calcium content needs to be used in a large amount when using amorphous aluminum hydroxide alone.

In the present invention, the above fly ash is treated by adding amorphous aluminum hydroxide as a lead elution inhibitor.
In this case, as the amorphous aluminum hydroxide, one in an amorphous state by X-ray diffraction can be used, and the method for obtaining it is not particularly limited, but, for example, it is discharged in the anodizing step of aluminum. The acidic waste liquid may be obtained by neutralizing the acidic waste liquid to pH 6 to 7 with an alkali, and the use of amorphous aluminum hydroxide obtained from such waste liquid has great cost merit. In addition, the above-mentioned amorphous aluminum hydroxide is p of 2-5 weight% water slurry.
Those in which H is 5.8 to 6.5 are preferably used for the purpose of the present invention.

The amount of the amorphous aluminum hydroxide added is appropriately selected according to the calcium content of the fly ash, the pH value, etc., but the amount of the fly ash to be about 9 to 11 is usually used. It is preferably 5 to 50 parts by weight, more preferably 5 to 40 parts, and further preferably 5 to 30 parts, relative to 100 parts of fly ash (parts by weight, the same hereinafter). If the amount added is too small, the treatment effect will be reduced. On the other hand, if the amount of addition is too large, there is no problem from the viewpoint of treatment effect, but the effect is not further improved, it is not economical, and there may be a problem in operability.

In the present invention, fly ash is treated with the above-mentioned amorphous aluminum hydroxide. In this case, ferrous sulfate or thiourea can be used in combination with the amorphous aluminum hydroxide, and a lead elution inhibitor can be used. As amorphous aluminum hydroxide 5 to 95% by weight, ferrous sulfate as anhydrous ferrous sulfate 5 to 80% by weight, and if necessary, thiourea 0 to 15% by weight, especially 3% It is possible to use a mixture of ˜15% by weight, and by using ferrous sulfate or thiourea together with amorphous aluminum hydroxide, a more reliable lead elution suppressing effect can be given.

In the treatment of fly ash, the lead elution inhibitor as described above is added to fly ash and kneaded uniformly with water. In this case, however, this lowers the pH of the object to be treated (pH lowering). The degree is preferably 9 to 11), and amorphous aluminum hydroxide reacts rapidly with calcium compounds such as slaked lime in fly ash in the presence of water to form calcium aluminate and solidify, The elution standard value of 0.3 mg / l or less can be reliably achieved, and the handleability of this solidified product is good.

The amount of water to be added is not particularly limited, but is usually 15 to 50% by weight, preferably 20 to 45% by weight.

Incidentally, in treating fly ash, in addition to the above-mentioned components, cement, liquid chelating agent and other heavy metal treating agents may be used in combination as long as the object of the present invention is not impaired.

[0018]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example 1] Table 1 shows amorphous aluminum hydroxide and water having a pH of 5.8 to 6.5 in a 2 to 5 wt% water slurry based on 100 parts of fly ash shown in Table 1. The indicated amount was added, and the mixture was kneaded for 3 minutes to obtain a solidified product. The lead elution amount of this solidified product (treated product) was measured according to Notification 13 of the Environmental Agency.
The results are shown in Table 1.

[0020]

[Table 1] * Amorphous aluminum hydroxide 90 parts, anhydrous ferrous sulfate 1
A mixture of 0 parts

Comparative Example 1 Fly ash No. 1 in Table 1 3 of 100
After the liquid aluminum sulfate and water were added to the parts in the amounts shown in Table 2 and treated, the lead elution amount was examined. Table 2 shows the results.

[0022]

[Table 2]

Comparative Example 2 Fly ash No. 1 in Table 1 2 of 100
Cement, a liquid chelating agent (dithiocarbamic acid type) and water were added to the parts in the amounts shown in Table 3 and treated, and then the lead elution amount was examined. The results are shown in Table 3.

[0024]

[Table 3] Note: Since the price of liquid chelating agents is several times that of amorphous aluminum hydroxide, economically several times the amount of chelating agents added is comparable to the amount of amorphous aluminum hydroxide.

[Example 2] Ca content of 25 as fly ash
%, Pb content 2500 mg / kg, Pb elution amount 73 m
This fly ash 100 g / l is used with the fluidized bed furnace dry BF ash of g / l.
As a result of adding 20 parts of an inhibitor consisting of 40 parts of amorphous aluminum hydroxide, 50 parts of anhydrous ferrous sulfate and 10 parts of thiourea to the parts, the Pb elution amount was 0.02 mg / l.
Met.

[0026]

According to the present invention, it is possible to reliably and economically suppress the elution of lead in fly ash from incineration of municipal solid waste.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Iwaki 135 Nakamaruko Nakahara-ku, Kawasaki, Kanagawa Fuji Sash Co., Ltd. In the company

Claims (5)

[Claims] 1. A method for suppressing lead elution from fly ash, which comprises adding amorphous aluminum hydroxide to incinerator fly ash and kneading with water. 2. The amount of amorphous aluminum hydroxide added is 3 to 50 parts by weight with respect to 100 parts by weight of fly ash.
The described method. 3. The method according to claim 1, further comprising ferrous sulfate and / or thiourea. 4. The method according to claim 1, wherein the fly ash is an electrostatic precipitating ash or a bag filter ash of a stalker furnace or a fluidized bed furnace having a calcium content of 10 to 30% by weight. 5. A lead elution inhibitor for municipal waste incineration fly ash, which comprises amorphous aluminum hydroxide.