JPH1157650A - Method for immobilization of collected waste incinerator ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To economically and efficiently lower elution of heavy metals out of collected waste incinerator ash by adding a treatment agent containing silicic acid to the collected waste incinerator ash, kneading the resultant ash with water, and then curing the resultant mixture at high temperature and high pressure under saturated steam pressure. SOLUTION: When the amount of elution of heavy metals out of collected waste incinerator ash is lowered by making harmful heavy metals such as lead contained in the collected ash insoluble and immobilize, a treatment agent containing silicic acid is added to the collected waste incinerator ash, the resultant ash is kneaded with water, and then the resultant mixture is cured at high temperature and high pressure under saturated steam pressure. As the treatment agent containing silicic acid component, clay minerals such as white clay, bentonite, attapulgite, sepiolite, illite, and allophane, fly ash, silica fume, silica stone fine powder or the likes is used. The added amount of treatment agent is not specifically limited and it is preferably to add within a range of 5-30 wt.% based on the collect ash weight. The high temperature and high pressure aging is preferably carried out at 100-300 deg.C temperature and 1-90 atmospheric pressure conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stabilizing waste incineration collected ash, and more particularly to a method for insolubilizing and fixing harmful heavy metals such as lead contained in collected ash. The present invention relates to a treatment method for reducing the amount of heavy metals eluted from waste incineration collected ash.

[0002]

2. Description of the Related Art Incinerated ash discharged from a waste incineration plant cannot be landfilled as it is, and intermediate treatment is performed so that the elution amount of heavy metals contained therein conforms to a predetermined standard value. It is required to do so. As the method of the intermediate treatment, cement solidification, treatment with various chemicals such as a polymer chelating agent, acid extraction treatment, melting treatment and the like are employed. In the process of incineration of waste, slaked lime etc. is blown for purifying exhaust gas, the collected ash is kneaded with water, granulated, and solidified by a steam autoclave using the waste heat of an incinerator. A method for reducing the elution of heavy metals has also been proposed (JP-A-55-3587).
0).

[0003]

However, recently, dust collection ash is often highly alkaline due to slaked lime blown for purifying exhaust gas from incinerators, and amphoteric heavy metals such as lead are eluted. The situation is easy. In addition, JP 55-35870 "Waste incineration method" is effective in preventing cadmium elution with respect to elution of heavy metals, only by solidifying the collected ash blown with lime such as slaked lime by autoclave curing. There is a statement to the effect. However, this is considered to be due to the fact that cadmium hydroxide is poorly soluble in water under high alkalinity.In this treatment method, the solidified ash still shows high alkalinity even after curing in an autoclave. It is difficult to prevent lead from being eluted.

[0004] Further, since the standard value of the elution amount of lead has been revised and strengthened, the solidified material is highly alkaline even by solidification of cement, and it is difficult to clear the standard value of the elution amount. In addition, in the treatment with a chemical such as a polymer chelating agent, even if the elution amount standard value can be cleared, a large amount of the chemical must be added, and the treatment cost must be expensive. In addition, there is a method in which dust ash is melted and turned into slag. In this method, the heavy metal is trapped in the structure of the slag, so that the heavy metal is very difficult to elute. However, a large amount of energy is required to melt the dust ash, and the equipment must be large. Further, in the melting process, a molten dust ash in which heavy metals such as lead are extremely concentrated is generated, and the treatment of the molten dust ash is much more difficult than the treatment of the dust ash before melting.

[0005]

In order to solve the above-mentioned problems, the present invention provides a method of adding a treating agent containing a silicic acid component to waste incineration collected ash, kneading the mixture with water, and then mixing the mixture under saturated steam pressure. High-temperature and high-pressure curing reduces the elution of heavy metals from waste incineration ash. After adding white clay or granulated blast furnace slag as a treating agent to the collected ash, kneading with water, and then simply curing at normal temperature and pressure, the elution of heavy metals such as lead contained in the collected ash The amount can be reduced (Japanese Patent Application No. 8-268547, Japanese Patent Application No. 8-06684)
3).

However, when the addition amount of the treating agent is reduced or the curing time is shortened, or when an inexpensive treating agent having low reactivity with dust collection ash at normal temperature and normal pressure is used,
In order to effectively reduce the dissolution of heavy metals from dust ash, it is effective to add a treating agent containing silicic acid, knead with water, and perform high-temperature and high-pressure curing under saturated steam pressure. Was found. Furthermore, in order to reduce the elution of heavy metals from the molten ash generated during the melting process, which was difficult with conventional chemical treatments such as cement hardening and polymer chelating agents, a treatment agent containing silicic acid is also required. After adding and kneading with water, it was found that it was effective to perform high-temperature and high-pressure curing under saturated steam pressure.

As the treating agent containing a silicic acid component, clay minerals such as clay, bentonite, attapulgite, sepiolite, illite, allophane, fly ash, silica fume, silica fine powder, silica gel, granulated blast furnace slag and the like can be used. Can be. However, there is no particular limitation as long as silicic acid is contained. The higher the fineness and specific surface area, the higher the reactivity. However, it is desirable to select a material that is as inexpensive as possible in terms of the treatment cost of the collected ash, including the amount added. Therefore, it is preferable to use white clay which is highly effective even with a small amount of addition, or fly ash which is very inexpensive. These treatment agents may be used alone for the dust collection ash, or a plurality of them may be used in any combination.

[0008] The amount of the treatment agent to be added is appropriately adjusted depending on the properties of the dust ash to be treated and the dust ash generated by the molten slag-forming treatment. Is preferably added. If you do not want to increase the amount of dust collected after treatment by adding a treatment agent, use clay minerals such as clay,
It is desirable to use fly ash or granulated blast-furnace slag when the treatment cost is more important than the increase in the amount of dust ash after the treatment.

[0009] The curing temperature needs to be higher than 100 ° C in order to make the saturated steam pressure in the closed vessel 1 atmosphere or more, and the pressure is determined depending on the heating temperature in the closed vessel. High-temperature and high-pressure curing conditions of the treatment method of the present invention,
A temperature of 100 to 300 ° C. and a pressure of 1 to 90 atm are desirable.
The effect of reducing the dissolution of heavy metals by the treatment method of the present invention becomes more pronounced as the curing temperature is higher, but if the temperature is too high,
As the pressure increases, the cost of a processing apparatus capable of withstanding high pressure is increased, and a large amount of heating energy is required. Is preferred.

[0010] The curing time is also appropriately adjusted depending on the properties of the target dust ash and the dust ash generated by the molten slag forming treatment. The longer the curing time, the longer the elution reduction effect increases, but it is desirable to perform the curing with a short curing time in consideration of the processing cost as in the case of the temperature conditions.

[0011]

[Function] After adding a treating agent containing a silicic acid component to a highly alkaline dust ash, kneading the mixture with water, and performing high-temperature and high-pressure curing under saturated steam pressure, calcium silicate hydrate and aluminum silicate hydrate are obtained. Etc. are generated.

That is, the silicic acid component of the treating agent reacts with calcium in slaked lime contained in a large amount in dust ash to produce calcium silicate. For example, crystalline calcium silicate hydrates such as tobermorite and zonotolite are produced, which take in heavy metals such as lead into the crystal structure by ion exchange and reduce elution of heavy metals from dust ash. In addition, calcium silicate hydrates other than crystalline are also produced, which physically confine heavy metals such as lead and chemically adsorb heavy metals to reduce elution of heavy metals from dust ash.

When the treating agent contains an aluminum silicate component in addition to the silicate component, an aluminum silicate hydrate such as hydrogarnet is formed by high-temperature and high-pressure curing,
These also physically confine heavy metals such as lead and chemically adsorb them. In addition, calcium in slaked lime contained in dust ash is consumed by the hydration reaction with the silicic acid component of the treating agent,
Neutralization of the alkaline dust ash also reduces elution of heavy metals such as lead.

[0014]

Embodiments of the present invention will be described below.

[0015] As Examples 1-4 Examples 1-4 were discharged from a municipal waste incineration plant,
A treatment containing silicic acid in 100 parts by weight of dust ash with a lead content of 2800 (mg / kg) in the ash and a lead elution amount of 50 (mg / l) determined by the Environment Agency Notification No. 13 test. Commercial activated clay as an agent,
Add 10 parts by weight of acid clay, bentonite, and JIS standard fly ash, and mix thoroughly with water.
100 ° C / hour in an autoclave, 180 ° C1
Hydrothermal curing was performed at 0 atm for 1 hour under saturated steam pressure.

Comparative Examples 1 to 10 As Comparative Example 1, 10 parts by weight of ordinary Portland cement were added to 100 parts by weight of dust ash as in the example.
It was hydrothermally cured at 180 ° C. and 10 atm for 1 hour. Comparative Examples 2 to 9
As described above, 10 and 30 parts by weight of ordinary Portland cement, 1 and 3 parts by weight of a commercially available polymer chelating agent, and 10 parts by weight of the above-mentioned treating agent containing silicic acid, based on 100 parts by weight of dust ash similar to those in the examples. Each was added and cured at normal temperature and pressure for 1 hour. Further, as Comparative Example 10, dust ash was kneaded with only water and cured at normal temperature and pressure for 1 hour.

Embodiments 5 to 12 As Embodiments 5 to 12, dust ash 10 similar to that of the above embodiment was used.
10 parts by weight of a commercially available activated clay and a JIS standard fly ash were added to each of 0 parts by weight as a treating agent containing a silicic acid component, and after thoroughly kneading with water, the temperature was raised at 100 ° C./hour in an autoclave apparatus. , 120 ° C, 150 ° C, 180
It was hydrothermally cured at a temperature of 200 ° C. for 1 hour under a saturated steam pressure.

Comparative Examples 11 to 16 As Comparative Examples 11 and 12, hydrothermal curing was performed at 100 ° C. for 1 hour under a saturated steam pressure. Other conditions are the same as in Examples 5 to 1 above.
Same as 2. As Comparative Examples 13 to 16, dust ash was kneaded with water only and hydrothermally cured under the saturated steam pressure for 1 hour at each temperature of Examples 5 to 12 described above. The other conditions were the same as in Example 5 above.
Same as 12.

Examples 13 to 15 The lead content in the ash discharged in the process of melting slag collected from municipal garbage incineration plants was 18200 (mg / kg). 20 parts by weight of commercially available activated clay, JIS fly ash, and granulated blast furnace slag as a treating agent containing silicic acid were added to 100 parts by weight of dust ash having a lead elution amount of 120 (mg / l). After sufficiently kneading with water, the temperature was raised at 100 ° C./hour in an autoclave, and the temperature was raised to 180 ° C.
Hydrothermal curing was performed at 0 atm for 1 hour under saturated steam pressure.

Comparative Examples 17 to 25 As Comparative Examples 17 to 19, the same treating agents as in Examples 13 to 15 were added, and the composition was cured under normal temperature and normal pressure. Other conditions are the same as those in Examples 13 to 15 described above. Comparative Example 20-
As No. 23, 20 to 30 parts by weight of ordinary Portland cement, 3 and 5 parts by weight of a commercially available polymer chelating agent were added to 100 parts by weight of dust ash, and the mixture was cured under normal temperature and normal pressure. Other conditions are the same as in Examples 13 to 15. Comparative Example 24
And 25, the mixture was kneaded with water only and cured at 180 ° C. under 10 atm and at normal temperature and normal pressure. Other conditions are the same as in Examples 13 to
Same as 15.

Test Example The lead leaching test was performed on the collected dust ash obtained in Examples 1 to 15 and Comparative Examples 1 to 25. The dissolution test was performed 24 hours after kneading according to the notification of the Environment Agency No. 13. That is, the kneaded material was pulverized, and 50 g of the material remaining between 0.5 to 5 mm of sieve opening was collected, 500 ml of distilled water was added thereto, and the mixture was shaken for 6 hours. The shaker was filtered, and lead was eluted from the filtrate. The amount and pH of the eluted filtrate were measured. Tables 1 to 3 show the measurement results.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

As a result of the test, when a treating agent containing a silicic acid component was added and then hydrothermally cured in an autoclave (Examples 1 to 3)
4) The pH of the eluted filtrate of the solidified ash falls to about 11 and the amount of lead eluted is reduced effectively, and the elution standard value specified by the Environment Agency [less than 0.3 (mg / l)] I found that I could clear it. On the other hand, when normal Portland cement is added in the same amount as in Examples 1 to 4 and hydrothermally cured under the same conditions (Comparative Example 1), when ordinary Portland cement and a polymer chelating agent are added and cured under normal temperature and normal pressure (Comparative Examples 2 to 5), when the same silicic acid content as in Examples 1 to 4 was added and cured under normal temperature and normal pressure (Comparative Examples 6 to 9), and when kneaded only with water (Comparative Example 10), In all cases, the pH of the solidified ash was about 12, indicating that the elution amount of lead could not be sufficiently reduced.

In addition, when a treating agent containing a silicic acid component was added and hydrothermal curing was performed in an autoclave, it was found that the higher the curing temperature, the lower the pH of the eluted filtrate and the less the amount of lead eluted. In particular, when hydrothermal curing at 180 ° C or higher,
It is possible to effectively reduce the amount of lead eluted (Example 5
To 12). On the other hand, when hydrothermal curing was performed at 100 ° C. for 1 hour (Comparative Examples 11 and 12), the amount of lead eluted could not be reduced to the extent that the reference value could be cleared.
It was found that, under the same curing conditions as above, when the dust ash was kneaded only with water (Comparative Examples 13 to 16), the amount of lead elution could not be reduced. In addition, JIS standard fly ash has lower reactivity than activated clay, and the difference is remarkable especially when the temperature is low.

Further, with respect to the dust ash generated by the molten slag-forming treatment, when a treating agent containing a silicic acid component was added and hydrothermal curing was performed at 180 ° C. for 1 hour using an autoclave (Examples 13 to 15), It was found that the lead elution amount could be effectively reduced, and the elution standard value was cleared. On the other hand, when a silicic acid component is added and cured at normal temperature and normal pressure (Comparative Examples 17 to 19), when ordinary Portland cement and a polymer chelating agent are added (Comparative Examples 20 to 2)
3) When kneaded only with water (Comparative Examples 24 and 25)
It was found that none of them could sufficiently reduce the amount of lead eluted.

[0028]

As described above, according to the treatment method of the present invention, elution of amphoteric heavy metals such as lead from waste incineration dust ash or dust ash generated by molten slag conversion treatment can be performed at low cost. It can be reduced effectively.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Michio Kimita 1, Kanda Midoshirocho, Chiyoda-ku, Tokyo Sumitomo Osaka Cement Co., Ltd. (72) Inventor Takeshi Kuninishi 7-1-1 Minamienkajima, Taisho-ku, Osaka-shi No. 55 Sumitomo Osaka Cement Co., Ltd. Cement Concrete Research Laboratory

Claims (3)

[Claims] 1. A method for reducing the dissolution of heavy metals by adding a treating agent containing a silicic acid component to waste incineration collected ash, kneading the mixture with water, and performing high-temperature and high-pressure curing under saturated steam pressure. Waste incineration dust ash stabilization method. 2. The disposal according to claim 1, wherein the treating agent containing silicic acid is at least one selected from clay minerals such as clay and bentonite, fly ash, silica stone, and granulated blast furnace slag. A method for stabilizing incineration collected ash. 3. The method according to claim 1, wherein the curing is performed at a temperature of 100 to 300 ° C. and a pressure of 1 to 90 atm.
The method for stabilizing waste incineration collected ashes described in the item.