JPH10113634A - Solidification treatment of flying ashes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the elution of harmful materials, such as heavy metals by treating flying ashes with a mineral acid or acidic salt, then subjecting the flying ashes to a solidification treatment by making combination use of a hydraulic material and a solidification assistant. SOLUTION: The flying ashes and the mineral acid or the acidic salt are mixed by a mixer, etc., to lower the alkalinity thereof. The hydraulic material and the solidification assistant are then added thereto simultaneously or in this order to solidify the flying ashes. For example, about 85% phosphoric acid is added at about 2 pts.wt. to about 100 pts.wt. flying ashes recovered by a dust collector of municipal waste incineration plants and the flying ashes are mixed, by which the pH thereof is lowered by about 0.5 to 2. Ordinary Portland cement is added as the hydraulic material thereto at about 3 to 30 pts.wt. and higher fatty acid salt, etc., such as zinc steerage, are added as the solidification assistant thereto at about 0.5 to 5 pts.wt. to solidify the flying ashes. The solidified molding is cured to form the solidified matter. The pH elution amt. of the solidified matter attains a value smaller than an elution reference value of 0.3mg/l and the elution of the harmful materials, such as heavy metals, is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the solidification of fly ash containing harmful substances such as lead and cadmium discharged from incinerators for municipal solid waste and sewage sludge or the like, or for melting and solidifying such incineration ash. Regarding the processing method.

[0002]

2. Description of the Related Art Laws concerning the treatment and cleaning of industrial waste have been enacted, and strict regulations have been set for industrial waste. Disposers cannot dispose of them unless they comply with these regulations. For example, for industrial waste containing heavy metals, etc., a leach test is performed, and if mercury, cadmium, lead, hexavalent chromium, etc. are not below the regulated value, it is prohibited to landfill or dispose of it at the final disposal site. ing.

[0003] Fly ash (fly) collected by a dust filter such as an incinerator or a melting furnace for municipal solid waste or sewage sludge, or a melting and solidifying furnace for these incinerated ash, and an electric dust collector. Ash) contains harmful substances such as heavy metals, and cannot be disposed of as it is without any treatment. In particular, fly ash contains metals and salts with low melting points such as cadmium, lead, and zinc, and has extremely high dissolution values in dissolution tests, and falls under specially controlled waste.

When municipal garbage or sewage sludge is incinerated or melted in an incinerator or the like, acidic substances such as hydrogen chloride caused by chlorine compounds and sulfur oxides caused by sulfur compounds contained therein are generated. I do. For this reason, when incinerating garbage, etc., alkaline substances such as lime are mixed to suppress the generation of acidic substances, or alkaline substances such as slaked lime and caustic soda are introduced into a dust collector that collects fly ash, and these air Measures have been taken, such as suppressing emissions to the public. Therefore, the collected fly ash exhibits extremely strong alkalinity and corresponds to alkaline waste.

As a technique for treating such fly ash, for example,
In addition to solidification treatment with hydraulic material such as cement, solidification treatment with asphalt and solidification treatment with plastic, neutralization with exhaust gas from incinerators etc.
A method has been proposed in which acid extraction is followed by immobilization as a sulfide or stabilization with a heavy metal immobilizing agent such as a liquid chelate. However, few of these conventional processing technologies completely comply with the regulation values of the dissolution test. Especially,
Fly ash containing a large amount of soluble heavy metals and the like often does not conform to the dissolution test even after solidification of cement or the like, and cannot be finally disposed of only by solidification. Further, the strong alkalinity of fly ash hinders solidification treatment with a hydraulic material such as cement. Even if this strong alkali is neutralized with an acid, a large amount of acid is required, resulting in an increase in processing cost.

[0006] Recently, in order to stabilize the solidified material for a longer period of time, a method of solidifying fly ash after performing some pretreatment in advance has been studied. For example, a method of washing fly ash with acid to transfer salts and heavy metals to the cleaning solution, a method of overheating fly ash to re-evaporate heavy metals, and a method of fixing heavy metals contained in fly ash with chemicals And the method of suppressing their dissolution. However, in the acid washing method, naturally, waste acid and sludge containing heavy metals and the like are generated, and these treatments become a new problem. Further, in the superheating method, there remains a problem of treating superheated exhaust gas containing harmful substances. In addition, the chemical fixation method is effective at a wide range of pH, does not generate harmful gas, and has the effect of reducing the volume of waste to one third, but is extremely expensive and practical. Poor.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for solidifying fly ash with a hydraulic material to seal harmful substances such as heavy metals in the solidified material and to suppress their elution. To provide.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve such problems, and as a result, firstly treated fly ash with a mineral acid or the like, and then separated the hydraulic material and the solidification aid. The present inventors have found that heavy metals and the like are contained in the solidified product and the elution thereof is suppressed by performing the solidification assisting treatment in combination, and the present invention has been completed.

That is, the present invention relates to a method of solidifying alkaline fly ash discharged from an incinerator or the like of municipal waste and sewage sludge and containing harmful substances with a hydraulic material,
This is a method for solidifying fly ash, comprising treating fly ash with a mineral acid or an acid salt thereof, and then solidifying using a hydraulic material and a solidification aid.

Hereinafter, the solidification treatment method of the present invention will be described in detail. As fly ash to which the solidification treatment method of the present invention can be applied, fly ash collected by a dust collector such as a bag filter or an electric dust collector installed in an incinerator or a melting furnace of municipal waste or sewage sludge or the like. Fly ash). Further, fly ash collected by a dust collecting device such as a bag filter or an electric dust collector installed in a melting and solidifying furnace for reducing the volume of the incinerated ash and the like can be treated by the present invention. In addition, those discharged from incinerators of various industrial wastes and the like and containing harmful substances such as heavy metals can be treated by the present invention. The fly ash is added with an alkaline substance in an amount equivalent to 2 to 3 times the amount of the acidic substance in the exhaust gas in order to suppress the emission of hydrogen chloride and sulfur oxides into the atmosphere.
It exhibits strong alkalinity exceeding H12.

In the present invention, this strongly alkaline fly ash is
First, it is treated with a mineral acid or an acid salt thereof. Mineral acids used in this treatment include, for example, sulfuric acid, hydrochloric acid, phosphoric acid and the like. When the alkaline component of fly ash is slaked lime, sulfuric acid or phosphoric acid which reacts with slaked lime to form an insoluble compound is preferred.

Examples of the acid salts of mineral acids include iron sulfate, aluminum sulfate, alum, iron chloride, aluminum chloride, iron phosphate, aluminum phosphate, calcium monohydrogen phosphate, calcium dihydrogen phosphate, and the like. Can be The acid salt must not, of course, be a harmful substance itself, nor should it inhibit the hydration of hydraulic materials such as cement. In particular, when reducing acid salts such as ferrous sulfate are used for fly ash treatment, they react with lime, which is a neutralizing agent for fly ash, to produce stable gypsum and be contained in small amounts in fly ash. Cr ⁶⁺ , which is a harmful substance, can be reduced and ^converted to a harmless chromium compound, and since it is an inexpensive compound, it is useful for reducing processing costs.

This treatment can be carried out by adding a mineral acid or an acid salt thereof to the water-containing fly ash and mixing with a mixer or the like. The amount of the mineral acid or acid salt thereof added is 0.5 to 20 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of fly ash (based on dry weight). The pH of fly ash may be lowered by about 0.5 to 2 by adding a mineral acid or a weak base salt thereof. Of course, the amount of mineral acid
Can be further reduced, but this is not preferable because it increases the processing cost.

Next, the fly ash treated with a mineral acid or a weak base salt thereof is solidified using a hydraulic material and a solidification aid in combination. Examples of such hydraulic materials include various portland cements such as portland cement, early-strength portland cement, ultra-high-strength portland cement, and moderately heated portland cement, as well as mixed cements such as blast furnace cement and fly ash cement. In addition, a cement-based special hydraulic material which is commercially available as a ground improvement material and is mixed with cement, such as blast furnace slag, lime, and gypsum, is also effective.

The solidification aid used in the solidification treatment method of the present invention, when used in combination with a hydraulic material, promotes the solidification of harmful substances, increases the strength of the solidified material, and increases the density of the solidified material. It is desirable to have a physical effect such as the formation of a compound, form an insoluble complex with heavy metals in harmful substances, and have a chemical effect such as a molecular bonding effect with pollutants and the like.

[0016] Such a solidification aid mainly comprises a metal salt of a higher fatty acid and an organic amino compound.
Those containing a regulator, a dispersant, a flocculant and the like are preferred. The higher fatty acid metal salt not only combines with the heavy metal to form an insoluble complex, but also prevents elution of contaminants from the solidified material. In addition, the organic amino compound promotes the hydration reaction and helps to insolubilize harmful substances by forming an insoluble complex.

In the solidification method of the present invention, the mixing ratio of the hydraulic material and the solidification aid to the fly ash is usually 1
Hydraulic material is 5 to 00 parts by weight (dry weight basis)
30 parts by weight, and the amount of the solidification aid is about 0.5 to 5 parts by weight.
If the hydraulic material is less than 5 parts by weight, it will hinder the solidification of fly ash, and if it exceeds 30 parts by weight, the economic efficiency will be reduced. If the amount of the solidification aid is less than 0.5 part by weight, the effect of reducing the elution concentration is small, and if it exceeds 5 parts by weight, the effect does not increase.

In the solidification treatment method of the present invention, a preferable mixing ratio of the hydraulic material and the solidification aid to the fly ash is 10 to 25 parts by weight of the hydraulic material with respect to 100 parts by weight of the fly ash (dry weight basis). The solidification aid is 1.5 to 3 parts by weight.

The solidification aid used in combination with the main hydraulic material may be any effective amount for achieving its compounding purpose, but depending on the type and amount of heavy metal contained in the fly ash, It is preferable to appropriately change the mixing ratio of the two within the range of the ratio.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solidify fly ash by the method of the present invention, first, a fly ash and a mineral acid or an acid salt thereof are mixed with a mixer or the like to reduce alkalinity, and then the hydraulic ash is hardened. The material and the solidification aid may be added and mixed simultaneously, or they may be sequentially mixed with fly ash.

[0021]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited by these examples.

Examples 1 and 2 and Comparative Examples 1 and 2 Fly ash collected by a dust collector (electric dust collector) at a municipal waste incineration plant was subjected to a solidification test according to the following formulation. The fly ash had a pH of 12.5, a moisture content of 2.1% by weight,
The Pb content was 2730 mg / kg.

Phosphoric acid (85%) is added to 100 parts by weight of the fly ash.
Was added and mixed with a mixer, and the pH of the fly ash was reduced to 12. The phosphoric acid-treated fly ash was solidified in Examples 1 and 2, and the untreated fly ash was solidified in Comparative Examples 1 and 2.

As a hydraulic material, ordinary Portland cement (hereinafter, referred to as cement) was used, and as a solidification aid, Geodol (trademark) of Nippon Chemi-Tac Corporation was used. Geodol is obtained by dispersing and dissolving a higher fatty acid salt such as zinc stearate, an organic amino compound such as ethanolamine, a surfactant and the like in an aqueous ammonia solution, and diluting a commercially available stock solution 20-fold.

After a predetermined amount of water is added to the above fly ash and sufficiently kneaded, cement and a solidification aid are added and further kneaded.
The kneaded material was cast into a 4 × 4 × 16 cm metal mold. One day later, the molded product was removed from the mold and cured in a room at room temperature for about 4 weeks to prepare a solidified product.

Next, the solidified product was subjected to a heavy metal dissolution test to measure the content of lead (Pb). The dissolution test was performed based on the notification of the Environment Agency No. 13 (S4.2.17). The latest elution standard is Pb of 0.3
mg / l. Table 1 shows the mixing ratio of each component and the results of the dissolution test of the solidified product. In Table 1, fly ash is on a dry weight basis, and water is represented by the sum of kneading water and water in the fly ash. The Pb content is m per liter of eluate.
It is represented by g.

[0027]

[Table 1]

Examples 3, 4 and Comparative Example 3 Fly ash collected by a dust collector (bag filter) at an incineration plant for municipal garbage was subjected to a solidification test according to the same recipe as above. The fly ash had a pH of 12.5, a water content of 0.4% by weight, and a Pb content of 1570 mg / kg. The obtained solidified material and untreated fly ash were similarly subjected to a heavy metal elution test to measure the content of lead (Pb). Table 2 shows the mixing ratio of each component, the pH after the phosphoric acid treatment, and the dissolution test result of the solidified product. In Table 2, fly ash is on a dry weight basis, and water is represented by the sum of kneading water and water in fly ash. The Pb content is expressed in mg per liter of eluate.

[0029]

[Table 2]

[0030]

According to the present invention, there is provided a method for solidifying fly ash contaminated with heavy metals or the like, particularly lead, with a hydraulic material. First, the fly ash is treated with a mineral acid or an acid salt thereof, and then solidified with the hydraulic material. By performing the solidification treatment in combination with an auxiliary agent, it is possible to satisfy the regulation value of the elution test for heavy metals and the like, which was difficult with the conventional treatment technology, and the treatment cost is low.

Claims (4)

[Claims] 1. A method of solidifying alkaline fly ash containing harmful substances discharged from an incinerator of municipal waste and sewage sludge with a hydraulic material, wherein the fly ash is treated with a mineral acid or an acid salt thereof. And then solidifying using a hydraulic material and a solidification aid in combination. 2. The method for solidifying fly ash according to claim 1, wherein the pH of the fly ash is lowered by about 0.5 to 2 by treating the fly ash with a mineral acid or an acid salt thereof. 3. The method for solidifying fly ash according to claim 1, wherein the solidification aid comprises a metal salt of a higher fatty acid and an organic amino compound. 4. The mixing ratio of the hydraulic material and the solidification aid to the fly ash is 5 to 30 parts by weight of the hydraulic material and 0.5 to 0.5 parts by weight of the solidification aid with respect to 100 parts by weight of the fly ash (dry weight basis). ~
The method for solidifying fly ash according to any one of claims 1 to 3, wherein the amount is 5 parts by weight.