JPS5821550B2 - 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 often contains harmful heavy metals such as Cd and PB (and when these are to be landfilled or dumped into the ocean, they must be shaped into a specified shape with asphalt, cement, etc.). It is mandatory to do this after solidifying the product.

However, Cd, PB, NaCl, KCI, etc. contained in these wastes are water-soluble, and if they come into contact with rainwater or groundwater after landfilling, or with seawater when dumped into the ocean, they will be released. The components react with water, reducing the strength of the solidified molded product and causing harmful contaminants to be leached from cracks and damaged areas.

An object of the present invention is to provide a method for solidifying waste containing harmful pollutants, which prevents the elution of water-soluble harmful substances as described above and improves water resistance.

According to the present invention, the above object is achieved by adding basic substances into the waste containing hazardous pollutants before solidification and
This is achieved by adding pre-treatment to adjust H to 10-12.

The details of the method of the present invention will be explained below.

The inventor believes that the fact that water-soluble substances contained in these solidified molded products react with water and elute when they are solidified and then disposed of in landfills, ocean dumping, etc. reduces the water resistance strength. After discovering that this was the cause of the elution of harmful pollutants, we considered pretreatment as one way to eliminate this cause.

That is, better results may be obtained if water-soluble harmful pollutants are made insoluble in advance and then solidified.

Therefore, we added a basic substance such as slaked lime to the waste, variously adjusted the pH value of the eluate, and investigated the relationship between the amount of harmful pollutants eluted, and obtained the results shown in the figure.

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 it can be seen that 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, so in that case the range of PH value will be narrower, but in any case, slaked lime should be limited to a certain range around 11 for the eluate OPH value. By adding basic substances such as, the elution amount of Cd and PB can be lowered below the elution standard.

It is clear that the above results are based on the following facts.

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

cd+Ca(OH)2→Cd(OH)2+Ca+...
...(1) Pb 10 Ca(OH)2→Pb(OH)2+Ca2-・
...(2) As is clear from the figure, Pb(OH)2 obtained by the above formula (2) dissolves again in the high PH value region, so C
In order to make Pb and Pb insoluble at the same time, it is necessary to adjust the pH value of the eluate to between 10 and 120.

As is clear from the above explanation, before solidifying waste containing water-soluble hazardous pollutants such as Cd and Pb with asphalt, etc., basic substances such as slaked lime are added to the eluate until the pH value of the eluate reaches 10. -12 to make it insoluble, and then knead it with asphalt etc. and solidify it into a predetermined shape. Even in the case of landfilling, ocean dumping, etc., it will react with water and have waterproof strength. It is possible to obtain a solidification method that reduces the amount of harmful contaminants and prevents them from eluting beyond the standard value.

[Brief explanation of the drawing]

The figure shows the pH value and C of the eluate when the method of the present invention is adopted.
d is a diagram explaining the relationship with the elution amount of Pb.

Claims (1)

[Claims] 1 In a method in which waste containing hazardous pollutants is kneaded with asphalt etc. and solidified into a predetermined shape, a basic substance is added before the waste is kneaded with asphalt to make water-soluble harmful pollutants insoluble. 1. A method for solidifying waste containing hazardous pollutants, the method comprising pre-treating it as a salt.