JPS586550B2 - Asphalt solidification method for hazardous pollutants - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for solidifying hazardous pollutants into asphalt.

For example, in municipal waste incineration plants, Cb, P
Since waste containing hazardous heavy metals such as
In addition to components represented by 2O3, MgO, Na2O, K2O, etc., metals such as Pb, Cd, Fe, Cr, Zn, Cu, and Hg, or compounds thereof are included.

In addition, HCl and S are contained in the combustion gas discharged from the combustion furnace.
Because it contains Ox, etc., it is usually used as NaOH, Ca(O
H) After gas cleaning using a neutralizing agent such as 2, the salts generated by the reaction between HCl, SOx and the neutralizing agent are discharged in a state containing harmful heavy metals, in order to be released into the atmosphere. be done.

Therefore, in order to dispose of waste containing pollutants such as these toxic metals, it is mandatory to solidify the waste with asphalt or the like to prevent the pollutants from leaching out, and then dump the waste separately into the ocean.

However, if waste containing these harmful pollutants is solidified with asphalt and then landfilled or dumped, the strength of the solidified product may decrease due to the components contained in the waste or moisture from the outside. Phenomena such as swelling, cracking, and even collapse may occur, and there is a risk that harmful pollutants may be leached out.

For example, if the waste contains large amounts of water-soluble salts such as NaCl, KCl, CaCl2, etc., after dumping,
Dissolution of salts is observed, reducing the strength of the solidified product.

In addition, oxides of alkali metals such as Na2O and K2O in the waste react with metals such as Al and Fe, which are also mixed in the ash, and moisture, generating H2 gas, and forming solidified molded products. This increases the internal pressure locally, causing cracks, etc., from which harmful pollutants can be leached.

An object of the present invention is to provide a method for solidifying harmful pollutants into asphalt, which prevents the elution of harmful pollutants from waste solidified molded articles.

According to the invention, the above object is achieved by providing a pre-treatment of the waste containing hazardous pollutants by granulation with mixing of water and cement before solidification with asphalt.

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

The inventor first discovered that when waste is solidified with asphalt and then disposed of in a landfill or ocean, components that react with water in the waste react with water, making the solidified molded product brittle. After discovering the fact that water-soluble harmful pollutants were leached, we came up with the idea of pre-treatment.

In other words, if the above reaction occurs after solidification, if the reaction with water is completed before solidification, the above reaction with water will not occur after solidification, and it will be more The point is that good results may be obtained.

Therefore, the present inventors mixed ordinary Bortland cement in a weight ratio of 3 to 10 parts per 100 parts of waste having the components shown in Figure 1, and further adjusted the water/cement ratio to 30%. Add water and continue mixing with mixer for 10 minutes more.

At this time, if a mixer with a granulation function is used, water will act as a binder during mixing, and the mixture of waste and ordinary Portland cement will be subjected to the granulation action, and the second
A particle size distribution as shown in the figure could be obtained.

While undergoing this mixing action, components that react with water contained in the waste complete their reaction.

Next, when this granulated material was left in the atmosphere for 10 days,
The hydration reaction with cement further progressed, and hardened granules were obtained.

After that, the weight ratio of asphalt to the granules is 8 to 11.
% added and thoroughly kneaded, the diameter is 100mm and the height is 75m.
It was molded into a cylindrical shape of m.

Figure 3 shows the results of the Marshall stability test conducted on this cylindrical solidified molded product and the results of the Marshall stability test conducted on a solidified molded product of the same size that was not pretreated. show.

As is clear from FIG. 3, satisfactory results were obtained throughout the Marshall stability test.

Furthermore, the reason why there is a difference in the asphalt blending ratio in comparison with conventional products is that as a result of granulation in the present invention, the specific surface area is reduced and the amount of asphalt added to be kneaded is significantly reduced.

Furthermore, the results of the investigation of the compressive strength of the solidified molded product and its change over time when immersed in water are shown in FIGS. 4 and 5.

As is clear from both figures, the solidified molded product obtained by the method of the present invention had satisfactory results in terms of both compressive strength and change over time.

In addition, in Figure 5, the decrease in the volumetric expansion rate of the solidified molded product to which the method of the present invention was applied is thought to be the result of the reaction with water taking place in the pretreatment stage before solidification. .

Table 1 shows the results of the elution test for the solidified molded product, and as is clear from the table, neither Cd nor Pb was detected.

This is considered to be because the waste can be kept alkaline by the hydration reaction of cement, and water-soluble Cd and Pb are changed into insoluble salts in the alkaline region.

As is clear from the above description, according to the present invention, before solidifying waste containing hazardous pollutants with asphalt, water and cement are mixed, and components that react with water contained in the waste are mixed. It reacts with water and maintains the overall alkalinity through a hydration reaction with cement, making it possible to turn water-soluble harmful pollutants into insoluble salts, improving the strength of solidified molded products, expanding, No elution of contaminants due to cracks, etc.

In addition, since granulation is performed, the specific surface area is reduced, and the amount of asphalt to be added can be significantly reduced, resulting in excellent effects such as being extremely economically advantageous.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram explaining the components and properties of waste, Figure 2 is a diagram showing the particle size distribution after granulation, Figure 3 is a diagram showing the Marshall stability test results, and Figure 4 is a diagram showing the compression A diagram showing the strength test results, and FIG. 5 is a diagram explaining changes over time.

Claims (1)

[Claims] 1. Before solidifying waste containing hazardous pollutants with asphalt, water and cement are added and kneaded to cause the water-reactive substances contained in the waste to react with water, and at the same time granulation is performed. A method for solidifying hazardous pollutants into asphalt, which is characterized in that asphalt is then added and solidified.