JP3392293B2 - Neutral fly ash treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for treating neutral fly ash capable of suppressing the elution of heavy metals contained in the neutral fly ash discharged together with the exhaust gas from an incineration plant such as a refuse incinerator or a melting plant. It is about.

[0002]

2. Description of the Prior Art Neutral fly ash contains mercury, lead,
Since heavy metals such as chromium and cadmium are contained in large amounts, it is necessary to suppress the elution of these heavy metals. Conventionally, as a method for suppressing the elution of heavy metals, water and a phosphate compound which is a heavy metal fixing agent are added to neutral fly ash,
Method of kneading to adjust pH to the range of 6 to 12
No. 155725) or water and a pH adjusting agent such as calcium hydroxide or sodium hydroxide to neutral fly ash, and then kneading, followed by addition of a heavy metal fixing agent and kneading. .

[0003]

However, the method of treating neutral fly ash only with water and a heavy metal fixing agent has a problem that it is necessary to add a large amount of heavy metal fixing agent. Further, in the method of treating neutral fly ash with water, a pH adjusting agent such as calcium hydroxide or sodium hydroxide, and a heavy metal fixing agent, the amount of the heavy metal fixing agent can be reduced, but the expensive pH
Since the regulator is used, there is a problem that running cost becomes high. An object of the present invention is to provide a method for treating neutral fly ash that can be treated at low cost.

[0004]

Means for Solving the Problems As a result of intensive studies to solve such problems, the present inventors have used an expensive pH adjusting agent which has been conventionally used by using incinerated ash as the pH adjusting agent. The present inventors have found the fact that it is possible to reduce the amount of heavy metal fixing agent used and the amount of heavy metals contained in neutral fly ash and incinerated ash can be suppressed at the same time, and have reached the present invention. That is, the first invention is to knead neutral fly ash and incinerated ash as a pH adjuster to adjust the amount of incinerated ash as a pH adjuster so that the pH of the kneaded product becomes 9 to 11. The gist is a method for treating neutral fly ash, which is characterized by A second aspect of the invention is to knead neutral fly ash and incinerated ash as a pH adjuster to obtain a p
The method for treating neutral fly ash is characterized in that after adjusting the amount of incinerated ash as a pH adjuster so that H becomes 9 to 11, the kneaded product and a heavy metal fixing agent are further kneaded. To do.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The neutral fly ash referred to in the present invention is fly ash in which the pH of the supernatant water after shaking the fly ash as a 10% by weight aqueous solution for 6 hours falls within the range of 5 or more and less than 9 Examples of the neutral fly ash include neutral fly ash discharged from the refuse incinerator and the refuse melting furnace together with the exhaust gas. These neutral fly ash usually contain heavy metals such as mercury, lead, chromium and cadmium. Further, the incineration ash referred to in the present invention,
It refers to the incineration residue remaining on the bottom of the refuse incinerator, and the pH of the supernatant water after shaking the incineration residue as a 10% by weight aqueous solution for 6 hours usually ranges from 11 to 13.

In the present invention, neutral fly ash and incinerated ash as a pH adjusting agent are kneaded and treated. At this time, the amount of incinerated ash with respect to neutral fly ash is the kneaded product after kneading. It is necessary to adjust the pH to 9 to 11, and if the pH of the kneaded product after kneading is less than 9, the amount of heavy metals eluted will increase, and if it exceeds 11, lead will elute in the form of anions. Therefore, it is necessary to add a large amount of heavy metal fixing agent. The pH of the kneaded material in the present invention means
It is the pH of the supernatant water after the kneaded product was made into a 10 wt% aqueous solution and shaken for 6 hours.

As the mixing ratio of the neutral fly ash and the incinerated ash at this time, the properties of the neutral fly ash and the incinerated ash are influenced by the combustion products, the combustion time, the exhaust gas treatment conditions, and depending on the incineration site. As they differ, the composition of each ash should be analyzed and determined. Usually, the pH of the kneaded product after kneading can be set to 9 to 11 by selecting and mixing the incinerated ash in the range of 1 to 99 parts by weight with respect to 100 parts by weight of the neutral fly ash.

The amount of water at the time of kneading is not particularly limited, but if it is about 0 to 50 parts by weight with respect to 100 parts by weight of the mixture of neutral fly ash and incineration ash, the kneading is performed. It is preferable because it is easy to handle, and particularly preferably 2 to 35 parts by weight.

As the kneading method, in the present invention, since incineration ash containing foreign matters such as metal pieces and incombustibles is used,
It is preferable to use a vibration type kneader, but it is also possible to use other kneaders such as a rotary drum type and a twin-screw type. Also, the kneader may be a batch type,
A continuous type may be used. In addition, as the kneading time,
Although it is not particularly limited, it is preferably about 2 to 30 minutes because it is uniformly kneaded, and particularly preferably 5
~ 30 minutes.

Further, in the second aspect of the present invention, in order to further suppress the elution amount of heavy metals, the above kneaded product and the heavy metal fixing agent are kneaded. As the heavy metal fixing agent used in this case, Water-soluble compounds having a dithiocarbamic acid group, a thiol group, a xanthate group, a thioureido group, and the like, sulfur compounds such as sodium sulfide and sodium hydrosulfide, phosphoric acid compounds such as phosphoric acid and hypophosphorous acid, and the like are commercially available. Various heavy metal fixatives can be used.
The amount of the heavy metal fixing agent is usually 5 parts by weight or less with respect to 100 parts by weight of the kneaded product, and the elution of heavy metals can be sufficiently suppressed.

[0011]

EXAMPLES Next, the present invention will be specifically described with reference to examples. In addition, the pH in the examples was obtained by adding 10 times the amount of distilled water to the sample, shaking frequency 200 SPM, shaking width 4 c.
m was shaken laterally for 6 hours, and the supernatant water after standing was measured with a pH meter. The heavy metal elution test was conducted according to the Environmental Agency Notification No. 13.

Examples 1 and 2, Comparative Examples 1 to 4 Neutral fly ash (pH 7.2) collected by a bag filter of an exhaust gas treatment facility in an municipal solid waste incinerator containing Pb 14, 200 mg / kg and Cd 351 mg / kg. ), And Pb776mg wet in an ashing facility for extinguishing and cooling
10/0 (Comparative Example 1),
8/2 (Example 1), 6/4 (Example 2), 4/6 (Comparative Example 2), 2/8 (Comparative Example 3), 0/10 (Comparative Example 4)
100 parts by weight of each mixture with 36 parts of water.
Parts by weight, 23 parts by weight, 10 parts by weight, 6 parts by weight and 2 parts by weight were added and kneaded for 5 minutes. Since the incinerated ash contained sufficient water for handling the kneaded product, no water was added.

Table 1 and FIG. 1 show the results of the pH of the kneaded product after kneading and the elution test of heavy metals. FIG. 1 is a diagram showing the relationship between the mixing ratio of neutral fly ash and incinerated ash, the elution concentration of lead and cadmium, and the pH of the kneaded product, and the elution concentration of lead and cadmium and the pH of the kneaded product on the vertical axis The horizontal axis shows the mixing ratio of neutral fly ash and incinerated ash.

[0014]

[Table 1]

As can be seen from Table 1 and FIG. 1, the elution of lead and cadmium can be suppressed by kneading the neutral fly ash and the incineration ash so that the pH of the kneaded product becomes 9 to 11. The lead and cadmium elution concentrations are "Prime Minister's Ordinance (Showa 48) which establishes criteria for industrial waste including metals.
February 17, 2014, Prime Minister's Office Ordinance No. 5) "was sufficiently cleared (Examples 1 and 2).

Example 3, Comparative Examples 5 and 6 The same neutral fly ash as in Example 1 and the same incinerated ash as in Example 1 were mixed at a ratio of 6/4, and water was added to 100 parts by weight of mixed ash. 10 parts by weight was added and kneading was carried out for 5 minutes (Example 3). For comparison, the same neutral fly ash as in Example 1 was used, with 36 parts by weight of water for 100 parts by weight of neutral fly ash (Comparative Example 5) and 34 parts by weight of water for 100 parts by weight of neutral fly ash. Parts and 15 parts by weight of 24% by weight sodium hydroxide as a pH adjuster (Comparative Example 6) were added and kneaded for 5 minutes. To the kneaded product after kneading, 0 to 4 parts by weight of UML-7200 manufactured by Unitika Ltd. having a dithiocarbamic acid group as a heavy metal fixing agent was added to the kneaded product, and the mixture was further kneaded for about 5 minutes. PH of the kneaded product after kneading
Table 2 and FIG. 2 show the results of the elution test for heavy metals. FIG. 2 is a diagram showing the relationship between the amount of heavy metal fixative added and the elution concentrations of lead and cadmium, where the vertical axis shows the elution concentrations of lead and cadmium and the horizontal axis shows the amount of heavy metal fixative added. There is.

[0017]

[Table 2]

As can be seen from Table 2 and FIG. 2, when attempting to treat neutral fly ash only with a heavy metal fixing agent (Comparative Example 5), “Prime Minister's Ordinance (which defines the criteria for industrial waste containing metals etc. February 17, 1973, Prime Minister's Ordinance No. 5
No. 4), it was necessary to add 4% by weight of a heavy metal fixative in order to clear the landfill landfill judgment standard. Further, in the treatment using 24 wt% sodium hydroxide as a pH adjusting agent and a heavy metal fixing agent together (Comparative Example 6),
The elution concentrations of lead and cadmium decreased and cleared the criteria for landfill landfill. On the other hand, when treated with incinerated ash (Example 3), the elution concentration was lower than when treated with 24 wt% sodium hydroxide as a pH adjuster, and the landfill landfill judgment standard was sufficiently cleared. Was.

[0019]

EFFECTS OF THE INVENTION According to the present invention, by treating neutral fly ash with incineration ash that is easily available, the amount of heavy metal fixing agent and pH adjusting agent used can be greatly reduced. , Can be processed at low cost. Further, according to the present invention, heavy metals contained in neutral fly ash and incinerated ash can be treated at the same time.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a mixing ratio of neutral fly ash and incinerated ash, pH of a kneaded product after kneading, and elution concentrations of lead and cadmium.

FIG. 2 is a diagram showing the relationship between the amount of a heavy metal fixing agent added and the elution concentrations of lead and cadmium.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields investigated (Int.Cl. ⁷ , DB name) B09B 3/00-5/00

Claims (2)

(57) [Claims] 1. An amount of incineration ash as a pH adjuster is adjusted such that neutral fly ash and incinerated ash as a pH adjuster are kneaded so that the pH of the kneaded product becomes 9 to 11. How to treat neutral fly ash. 2. A neutral fly ash and incinerated ash as a pH adjuster are kneaded to adjust the amount of incinerated ash as a pH adjuster so that the pH of the kneaded product is 9 to 11, and further A method for treating neutral fly ash, which comprises kneading a mixture with a heavy metal fixing agent.