JPS5821549B2 - Method for solidifying waste containing hazardous pollutants - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for solidifying waste containing harmful pollutants, and particularly to a method for solidifying electrostatically precipitated dust from a municipal waste incinerator using asphalt.

Electrostatic precipitated dust from municipal waste incinerators contains heavy metals such as Cd and PB, which are harmful pollutants, so if this dust is to be landfilled or dumped into the ocean, it will be treated with asphalt, cement, etc. It is mandatory to do this after it has solidified.

However, the above dust contains components that react with water, and when it comes into contact with rainwater or groundwater after landfilling, these components react with water, reducing the strength of solidified molded products. This can cause harmful contaminants to be leached from cracks and damaged areas.

For example, Na2 is contained in electrostatically collected dust from municipal waste incinerators.
It contains oxides such as O and CaO and metals such as AI and Zn, and these substances cause the following reaction with water.

CaO+H20→Ca(OH)2+ 15.1 Kca
l”・”・ke)2Al+Na2O+3H20→2NaA
IO2+3H2・・・・・・(2) In the case of the above equation (1), heat and a mechanically extremely fragile substance called Ca(OH)2 are generated, and in the case of the equation (2), H
2 gas and heat will be produced.

These substances, gas, heat, etc. have a synergistic effect, lowering the mechanical strength of the solidified molded product, causing cracks and breakage as mentioned above, and causing harmful contaminants such as Cd and Pb to be leached out. Become.

On the other hand, Cd, Pb, NaCl,
KCI and other substances are water-soluble, and when they come into contact with rainwater or groundwater after being landfilled, these components react with water, reducing the strength of solidified molded products and releasing harmful pollutants from cracks and damaged areas. This causes elution.

An object of the present invention is to provide a method for solidifying waste that does not cause a decrease in the water resistance of a solidified waste product and prevents the elution of harmful pollutants.

According to the present invention, the above objective is to complete the reaction of the reactive components with water in the waste by adding water and basic substances before solidification and to render water-soluble hazardous pollutants insoluble. This is achieved through processing.

The present invention will be explained in detail below.

The inventors of the present invention have found that when waste is solidified and then landfilled or dumped into the ocean, the water-reactive components and harmful water-soluble substances contained in the waste react with water, causing a decrease in water resistance. After discovering that this is the cause of harmful substances leaching out from cracks, etc., they considered pretreatment as one way to eliminate this cause.

That is, better results will be obtained if the reactive components are made to react with water to make water-soluble harmful substances insoluble before solidification.

Therefore, before solidifying the waste, we added a treatment process in which water and a basic substance such as slaked lime were added and kneaded, and the mixing ratio of water and the OPH value of the eluate were changed to prevent harmful pollution after solidification. The elution amount and intensity of the substance were investigated.

First, to explain the relationship with water, pretreatment is performed while changing the mixing ratio of water, and after the reaction with water is completed, this is dried, then kneaded with asphalt, and this is made into a cylindrical shape. After immersing the molded product in water for 7 days, a crushing test was conducted, and the results shown in FIG. 1 were obtained.

As is clear from the diagram in Figure 1, as the mixing ratio of water (weight %...mixed amount of water per 100 parts of waste) increases (as shown by curve A), , the crushing strength increased significantly, reaching 200 kg/c77f at a mixing ratio of 50%.
Great strength was obtained.

In comparison, it was found that the crushing strength of the solidified molded product made by the conventional method, which did not perform a pretreatment reaction with water, was significantly lower as shown at point B, and the result was satisfactory. I couldn't get it.

On the other hand, as a result of conducting a Cd and PB elution test in parallel with the crushing strength test, the results shown in FIG. 2 were obtained.

In the figure, the vertical axis indicates the elution amount (ppm).

In other words, according to the industrial waste standards, Prime Minister's Office Ordinance No. 5 (1972) and No. 66 (1972), the amount of Cd eluted is 0.
．． 3 ppm or less, and that of Pb is 3 ppm or less, and as is clear from the figure, the pH value that satisfies this standard is 10 to 12 in the case of Cd and Pb.

Of course, this standard may be more severe depending on the local government, and in that case the range of PH values will be narrower.

In any case, by adjusting the pH value of the eluate to a certain range around 11, drying it, and then mixing it with asphalt, the elution amount of Cd and Pb can be lowered below the elution standard.

It is clear that such a decrease in elution amount is based on the following facts.

That is, in general, heavy metals such as Cd and Pb become insoluble salts in basic regions through the following reaction.

Cd 10 Ca(OH) → Cd(OH) 2+Ca ・
・・・・・・・・・・・・(3) 廿廿 廿0601. .

Pb + Ca (OH) 2 → Pb (OH) 2 + Ca
...(4) Pb(OH)2 obtained by the above formula (2) is
As is clear from the figure, the high pH value region dissolves again, so in order to make Cd and Pb insoluble at the same time, the pH
The value needs to be adjusted between 10 and 120.

As is clear from the above explanation, according to the present invention, waste materials that react with water and are brittle, such as adult cow sludge, and waste containing water-soluble harmful pollutants, are solidified into a predetermined shape using asphalt, etc. Before the treatment, water and a basic substance are added to complete the reaction with water, and a pretreatment process is added to turn the hazardous substances into insoluble ones, so the water resistance is also high. A solidification method can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the relationship between the amount of water mixed and the crushing strength, and FIG. 2 is a diagram illustrating the relationship between the pH value and the amount of harmful substances eluted.

Claims (1)

[Claims] 1. In a method in which waste containing hazardous pollutants is kneaded with asphalt etc. and solidified into a predetermined shape, water and a basic substance are added to the waste before kneading it with asphalt to prevent the reaction with water. 1. A method for solidifying waste containing hazardous pollutants, which comprises the steps of: terminating water-soluble hazardous substances and performing pretreatment to convert water-soluble hazardous substances into insoluble salts.