JP2002136944A - Method for fixing heavy metal contained in ash and fixing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for fixing heavy metals by controlling pH of 10 wt.% of the aqueous solution of the heavy metals within a range of a low elution of the heavy metals if the pH of the ash to be treated is changed with time. SOLUTION: The pH of an aqueous solution containing ash and a heavy metal fixing agent (a total concentration of the ash and the heavy metal fixing agent is 10 wt.%) is made to be 8.5-11.5 by adding to the ash the heavy metal fixing agent consisting of one pt.wt. as alumina converted from aluminum sulfate and 1.7-6.0 pts.wt. as alumina converted from sodium aluminate. This method for fixing the heavy metal is also can be suitable for ash containing water or slurryed ash. This method for fixing the heavy metal is preferably carried out with the ash agitated or mixed. Further, a coagulation and sedimentation agent is preferably added to the ash. As the coagulation and sedimentation agent, a single one of, or a combination of two or more of, aluminum hydroxide, poly aluminum chloride, Fe(OH)3, FeCl3, Fe2(SO4)3 or the like is utilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for fixing heavy metals contained in ash generated from an incinerator and preventing elution thereof, and a heavy metal fixing agent used in the method. Specifically, incineration ash is required to undergo any one of intermediate treatments of melting, chemical treatment, cement solidification, and solvent extraction before landfill disposal, but this invention is an invention in the field of chemical treatment.

[0002]

2. Description of the Related Art Drugs used in a drug treatment method are roughly classified into three types: A) a pH adjusting agent such as an acidic drug, or a coagulation-precipitation agent added thereto, B) a chelate, and C).

[0003] The drugs of A) are generally inexpensive,
When the alkalinity of fly ash fluctuates, certain performance cannot be obtained. The chemicals B) and C) are expensive, and ash containing heavy metals such as molten fly ash requires a large amount of chemicals to be added, resulting in high processing costs.

[0004]

[0005] Currently, as a method of treating acidic gases such as HCl and SO ₂ contained in incinerator exhaust gas, dry processing blowing slaked lime in flue gas in a bag filter before flow is the mainstream. Therefore, fly ash collected by the bag filter contains unreacted slaked lime, and the aqueous solution thereof is alkaline. Many metals do not elute in alkaline water, but amphoteric metals such as Pb also elute in alkaline water having a pH of about 12. Therefore, in order to prevent the elution of heavy metals, it is necessary to adjust the pH of the 10% by weight aqueous solution to a range where the elution of heavy metals is small by adding a drug. Also, in an incinerator where the amount of acid gas changes with time, p
H also fluctuates. For example, when fly ash discharged near neutrality comes out, the ash after the treatment becomes acidic in the treatment using the acidic chemical, and the heavy metal cannot be fixed effectively.

In view of the above, it is an object of the present invention to fix the pH of a 10% by weight aqueous solution after treatment within a range in which heavy metal elution is small even if the pH of the ash varies with time. And a heavy metal fixing agent used in the method.

[0006]

The method for fixing heavy metals in ash according to the present invention is as follows: 1 part by weight of aluminum sulfate in terms of alumina, and 1.7 parts in weight of sodium aluminate in terms of alumina.
A heavy metal fixing agent consisting of 6.0 parts by weight is added to the ash, and an aqueous solution containing the ash and the heavy metal fixing agent (the concentration of the total weight of the ash and the heavy metal fixing agent is 10%) is adjusted to pH 8.5 to 11.5. Is indicated.

The method for fixing heavy metals in ash according to the present invention can also be applied to ash containing water or slurry ash.
The method for fixing heavy metals in ash according to the present invention is preferably performed while stirring or kneading the ash. Further, it is preferable to add a flocculant to the ash. Aluminum hydroxide, polyaluminum chloride, Fe (OH)
₃ , FeCl ₃ , Fe ₂ (SO ₄ ) _{3 and the} like are used alone or in combination of two or more.

The fixing agent for heavy metals according to the present invention comprises 1 part by weight of aluminum sulfate in terms of alumina and 1.7 to 6.0 parts by weight of sodium aluminate in terms of alumina.
The mixing ratio of the two drugs is adjusted so that a 2% by weight aqueous solution containing them has a pH of 9 to 11.5. The heavy metal fixing agent thus prepared has a strong buffering action in an aqueous solution having a pH of 8.5 to 11.5. That is, when this is added to alkaline ash having a pH of 12 or more, the pH of the 10% by weight aqueous solution drops to 8.5 to 11.5, and when it is added to neutral ash near pH 7, the pH of the 10% by weight aqueous solution decreases. Rises to 8.5 to 11.5. As described above, by adding this heavy metal fixing agent to the ash and treating it, Pb
PH range in which the elution of glycerol is extremely low (pH of 10% by weight aqueous solution)
PH can be adjusted to 8.5 to 11.5).

In a preferred embodiment, the incinerated ash and / or fly ash is sent to a stirrer, and the heavy metal fixing agent according to the present invention is added thereto at a ratio of 1 to 60% by weight, and the whole is uniformly mixed.

[0010]

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

Example 1 1 part by weight of aluminum sulfate in terms of alumina and 2.2 parts by weight of sodium aluminate in terms of alumina were mixed to prepare a heavy metal fixing agent. The pH of a 2% by weight aqueous solution of the heavy metal fixing agent was 10. This chemical was added to fly ashes A to F having different alkalinities at a ratio of 20% by weight, and the fly ash was stirred to carry out a process for immobilizing heavy metals in the fly ash.

The fly ash containing the heavy metal fixing agent was subjected to a Pb elution test according to Notification No. 13 of the Environment Agency. as a result,
PH 6.8 to 12.3 of 10% by weight aqueous solution of raw fly ash,
After the immobilization treatment of heavy metals, the pH becomes 9.2 to 10.5 with an aqueous solution having a total weight concentration of 10% of fly ash and heavy metal fixing agent.
b. The elution amount is the elution standard value for all fly ash.
3 mg / liter or less was achieved.

[0013]

[Table 1]

Example 2 1 part by weight of aluminum sulfate in terms of alumina and 1.9 parts by weight of sodium aluminate in terms of alumina were mixed to prepare a heavy metal fixing agent. The pH of the 2% by weight aqueous solution of the heavy metal fixing agent was 9.5. This chemical was added to fly ashes A to F having different alkalinities at a ratio of 20% by weight, and the fly ash was stirred to carry out a process for immobilizing heavy metals in the fly ash.

[0015] The fly ash containing the heavy metal fixing agent was subjected to a Pb elution test according to Notification No. 13 of the Environment Agency. as a result,
PH 6.8 to 12.3 of 10% by weight aqueous solution of raw fly ash,
After the heavy metal immobilization treatment, the pH of the aqueous solution of the fly ash and the heavy metal fixing agent at a total weight concentration of 10% became 8.2 to 10.1.
The elution amount of Pb at pH 8.2 exceeded the reference value of 0.3 mg / liter. Therefore, when the amount of the drug added was set to 30% by weight, the pH became 8.9 to 9.9 with an aqueous solution having a total weight concentration of fly ash and heavy metal fixing agent of 10%, and the reference value of all ash was 0.3 mg / liter. The following has been achieved.

[0016]

[Table 2]

Example 3 1 part by weight of aluminum sulfate in terms of alumina and 2.5 parts by weight of sodium aluminate in terms of alumina were mixed to prepare a heavy metal fixing agent. The pH of a 2% by weight aqueous solution of the heavy metal fixing agent was 10.5. This chemical was added to fly ashes A to F having different alkalinities at a ratio of 20% by weight, and the fly ash was stirred to carry out a process for immobilizing heavy metals in the fly ash.

The fly ash containing the heavy metal fixing agent was subjected to a Pb elution test according to Notification No. 13 of the Environment Agency. as a result,
PH 6.8 to 12.3 of 10% by weight aqueous solution of raw fly ash,
After the immobilization treatment of the heavy metal, the pH was adjusted to 9.5 to 11.7 with an aqueous solution of fly ash and the heavy metal fixing agent having a total weight concentration of 10%.
The elution amount of Pb at pH 11.7 was the standard value 0.3 mg /
It has exceeded liters. Therefore, the amount of drug addition is
In terms of weight%, the pH was 10 to 10.9 with a 10% total aqueous solution of fly ash and heavy metal fixing agent, and the reference value of all ash was 0.3 mg / liter or less.

[0019]

[Table 3]

[0020]

[0021]

When aluminum sulfate and sodium aluminate are used as a heavy metal fixing agent in ash, it is possible to fix heavy metals with stable performance even for ash whose pH varies. Therefore, the ash whose pH fluctuates can be continuously processed by a simple device such as a quantitative supply device and a stirrer.

The method using a pH adjuster such as an acidic agent can be applied only to fly ash having a pH of 10 or more in a 10% by weight aqueous solution. Can also be applied.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kiichi Nagaya 1-7-89 Minami Kohoku, Suminoe-ku, Osaka F-term in Tachibai Shipbuilding Co., Ltd. 4D004 AA36 AA37 AB03 CA15 CA34 CA35 CC06 CC11 CC20 DA10 DA20

Claims (5)

[Claims] 1. An aluminum sulfate of 1 part by weight in terms of alumina and a sodium aluminate in terms of alumina of 1.7 to 1 part by weight.
A heavy metal fixing agent consisting of 6.0 parts by weight is added to the ash, and a 10% by weight aqueous solution containing the ash and the heavy metal fixing agent is adjusted to pH.
8.5 to 11.5.
A method for fixing heavy metals contained in ash. 2. The method of fixing heavy metals contained in ash according to claim 1, wherein the ash is ash containing water or slurry ash. 3. The method for fixing heavy metals contained in ash according to claim 1 or 2, wherein the method is performed while stirring or kneading the ash. 4. The method for fixing heavy metals contained in ash according to claim 1, further comprising adding a coagulating sedimentation agent to the ash. 5. An aluminum sulfate of 1 part by weight in terms of alumina, and a sodium aluminate in terms of alumina of 1.7 to 1 part by weight.
6.0 parts by weight of a fixing agent for heavy metals contained in ash.