JP3424609B2 - Detoxification method of dioxin pollutants - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a substance contaminated with dioxins which are considered to be harmful to the human body (in addition to polychlorinated dibenzoparadioxin, polychlorinated dibenzofuran, coplana PCB, etc.), particularly The present invention relates to a method for detoxifying a substance that has been contaminated at a relatively low concentration such as soil.

[0002]

2. Description of the Related Art Dioxins such as polychlorinated dibenzoparadioxin are generated in garbage incineration facilities, especially when treating waste plastic containing chlorine at a relatively low temperature, and are now becoming a social problem. . Therefore, although suppression of generation by continuous high temperature combustion and improvement of dust collection methods such as bag filters have been carried out, it is not possible to suppress generation of dioxins themselves, and dioxin in incineration ash and dust collection dust. It is included. Therefore, it is necessary to treat dioxin contained in incinerated ash and dust, but treatment using high-temperature plasma is only attempted experimentally. In addition, the detoxification treatment method of soil contaminated with dioxins, which is currently proposed and studied, is a method of melting the contaminated soil itself at high temperature and is not a practical method. It is the current situation that development of various treatment methods is desired.

On the other hand, Japanese Patent Publication No. 8-504665 discloses that dioxins can be rendered harmless by a mechanochemical treatment. However, there is no specific description about the existence state of dioxins and the conditions for making them harmless. Dioxins, unlike the other toxic substances described in the above publication, do not exist as pure substances or in a state where the dilution ratio is not so large, and even when the concentration is high, less than 1 ppm ng / g.
Dioxin is mixed in incineration ash, dust fly ash, dust collection dust, soil, etc. at an extremely low concentration represented by the unit of (10 ⁻⁹ g / g), and is in such a state. It is extremely difficult to render the kind harmless.

As described above, some methods for treating dioxins have been proposed, but, for example, treatment of contaminated soil has not progressed in practice. This is partly due to the high treatment cost, but the concentration of dioxins is low in the actual pollutants such as contaminated soil, and the amount to be treated is enormous. ,
This is also because the processing efficiency is poor.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and an object thereof is a substance which is contaminated with actually existing dioxins, particularly a relatively low amount such as soil. An object of the present invention is to provide an efficient method for detoxifying a substance that has been contaminated at a concentration.

[0006]

The gist of the present invention resides in the following method for detoxifying dioxin pollutants.

A substance polluted with dioxins is washed with water and separated into a coarse particle portion and wash water consisting of water and fine particle portions, and water is removed from the wash water consisting of water and fine particle portions. A method for detoxifying a dioxin pollutant, which comprises mixing at least one of calcium oxide and a substance containing calcium oxide in a portion and performing a mechanochemical treatment.

In the above invention, after at least one of the substances containing aluminum oxide and silicon dioxide is added to the washing water consisting of water and fine particles, the water content is removed, and thereafter, calcium oxide and calcium oxide are added to the fine particles. Mixing at least one of the substances containing
Mechanochemical treatment may be performed.

As used herein, the term "dioxins" refers to polychlorinated dibenzofuranoxins, polychlorinated dibenzofurans, coplanar PCBs and the like, as described above.

The term "substance containing calcium oxide" means
A substance containing calcium oxide as a main component.

Steel slag may be used as the substance containing calcium oxide.

"Steel slag" is slag generated in steel production, and includes, for example, blast furnace slag (either slowly cooled slag or granulated slag is acceptable), converter slag, ladle residual slag, electric furnace slag, Next refining slag, ladle refining slag, etc.

The "mechanochemical treatment" is, for example, a treatment for mixing and pulverizing an object to be treated while applying mechanical energy in an impact pulverizing device such as a ball mill, and is a process of pulverizing by an impact force caused by dropping a ball. The object to be treated is physically torn off, resulting in a highly active molecular surface. Therefore, by performing the mechanochemical treatment, a reaction (mechanochemical reaction) that cannot occur at room temperature can proceed.

Dioxins, which are chemically stable organic chlorine compounds, can be detoxified by mixing them with at least one of calcium oxide and a substance containing calcium oxide and subjecting them to mechanochemical treatment. Among the bonds between the constituent elements, the binding force between carbon and chlorine is relatively weak, and the two can be separated by applying mechanical energy, and the released chlorine and calcium oxide react to give stable calcium chloride. It is based on the principle of generating.

[0015] The present inventors have mixed soil which is contaminated with dioxin and washed with water, water containing particulate portion of the soil used for washing and dewatering drying, the material containing calcium oxide or calcium oxide Then, it was found that dioxins can be rendered harmless by the mechanochemical treatment.

Further, when the dioxins are detoxified by the mechanochemical treatment, water has a great influence on the reaction rate, and in some cases, the detoxification reaction is stopped or a more harmful substance (eg, octachloride). It was found that dibenzoparadioxin, and further, dibenzoparadioxin tetrachloride) are produced.

The soil that is actually contaminated with dioxins usually contains several tens of percent of water. Also,
Water is usually sprayed on incinerated ash, dust fly ash, dust collection dust, etc. to prevent dust generation. Therefore, if a substance contaminated with these dioxins is directly subjected to mechanochemical treatment to render it harmless, it will always be affected by moisture.

[0018] Therefore, the present inventors, the dioxins and wash stream to wash the soil or the like is contaminated dioxins first with water, for detoxification by mechanochemical treatment of dioxins of the rinse wash water By paying attention to the influence of moisture, the inventors have made repeated studies and have completed the invention described above.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The method for detoxifying dioxin pollutants of the present invention will be described in detail below by taking a contaminated soil as an example.

In the detoxification treatment method of the present invention, as described above, the substance (soil) contaminated with dioxins is washed with water and separated into coarse particles and washing water consisting of water and fine particles.
After removing the water from the wash water consisting of water and fine particles,
Contains calcium oxide and calcium oxide in the grain
Mix at least one of the substances
This is a method of making pollutants harmless by treating them.

In this method, washing with water and fine particles is performed.
Clean water containing aluminum oxide and silicon dioxide
After adding at least one of the
Then, calcium oxide and calcium oxide are added to the fine particles.
Mix at least one of the substances containing
It may be subjected to no chemical treatment .

The amount of dioxins in soil polluted with dioxins is originally very small even if contained in the soil, and most of the dioxins generated in incinerators are exhaust gas. It has come in contact with the fine dust inside. Therefore, if washed with water, almost all of it can be washed away together with fine dust, and the contaminated soil can be made harmless.

The washing of the contaminated soil with water is specifically
It may be performed as follows.

In the present invention, first, the soil is washed with water, whereby washing water containing fine particles such as fine dust and soil particles (washing water consisting of water and fine particles), and coarse particles, that is, detoxification. Separated into soil.

As an example of the separating method, first, the soil is put into water and stirred to form a suspension. When the stirring is stopped, coarse particles are precipitated and fine particles are suspended in the supernatant, so that the supernatant is separated. The particle size to be separated can be changed by adjusting the time from the stop of stirring to the separation of the supernatant (standing time), and the separation efficiency of dioxins is determined by the adjustment of this standing time. Even if the stationary time is the same, the separation efficiency differs depending on the soil generation place. Therefore, the optimum stationary time at which the required separation efficiency is obtained can be obtained in advance for each place.

The amount of water used for washing may be at least twice the volume of soil contaminated with dioxins as a guide.

Another separation method is, for example, 0.1 m
Soil is put into a vibrating sieve having a mesh size of about m, and the fine particle portion of the soil is washed away with water. In this case, since the separation efficiency of dioxins is determined by the selection of the sieving mesh, the optimum sieving mesh may be selected for each soil generation site.

By adopting such a method, washing water containing fine particles such as fine dust and soil particles (water and fine particles
Wash water) and coarse particles, ie detoxified soil
Can it to separated into the soil.

Next, water is removed from the wash water consisting of water and fine particles . This is to reduce the amount of water, which has a great influence on the reaction rate, when detoxifying it.

As for the action of water, the action of water changes the mixed calcium oxide into calcium hydroxide, which deteriorates the absorption of chlorine desorbed from the dioxins by the mechanochemical treatment, and the action of water acts on calcium oxide. Then, a granulation phenomenon of the object to be treated (a substance polluted with dioxins) is caused, the impact energy at the time of crushing is alleviated, and the crushing effect is lowered.

The conditions under which these effects appear are the mixing ratio of the object to be treated with calcium oxide and / or a substance containing calcium oxide, the content of calcium oxide in the substance containing calcium oxide, the particle size of the substance to be treated, surface properties, etc. However, the upper limit of the water content whose influence can be ignored cannot be uniquely determined.

As a measure of the amount of water, it is desirable to set it to 30% by weight or less (hereinafter, "%" means "% by weight") with respect to the weight of calcium oxide mixed in the object to be treated. It is more preferably 20% or less, and even more preferably 15% or less. The amount of calcium oxide mixed is at least 30% of the total weight, as described below.
Therefore, it is preferable that the mixed calcium oxide and the substance containing calcium oxide also have a low water content.

To remove water from the washing water consisting of water and fine particles, a suspension containing fine particles is charged with a flocculant such as a polymer flocculant to cause flocculation and precipitation, or fine mesh (for example, , 0.01 μm) filter. As a method for dehydrating the mud-like matter separated by the coagulation liquid or the filter, dehydration by a screw decanter or filter press generally used in the dehydration treatment of mud, roll press dehydration, high pressure thin layer dehydration, etc. However, since the soil composed of fine particles becomes a state called “silt or clay” and hardens at the time of dehydration, it is necessary to dry and then pulverize the soil.

As a recommended method, the water content of the suspension containing fine particles is adjusted to an appropriate water content, and hot air accompanied by a shock wave is blown to the flow of this suspension to evaporate water. For example, it can be carried out by a drying device equipped with a pulse jet engine. Further, a method of evaporating the water by using a dryer equipped with a spray dryer or a medium fluidized bed dryer may be used.

In each case, a suspension containing fine particles is
The particles can be directly dispersed.

If a substance containing aluminum oxide and / or silicon dioxide is added to the suspension containing fine particles before removing water, the mechanochemical reaction to be performed later can be promoted.

[0037] As described above, the contaminated soil is washed with water, the crude
It consists of particles, i.e. detoxified soil, water and fines.
It is separated into the washing water and the washing water consisting of the water and fine particles.
The amount of the fine particles obtained by removing the Luo water (soil containing dioxins) depends on the type of soil, consisting 5 to 30% of the processed soil.

Next, the water-removed fine particles obtained as described above are mixed with calcium oxide and / or a substance containing calcium oxide, and subjected to a mechanochemical treatment of pulverizing with a planetary ball mill or the like.

The crushing treatment time depends on the structure of the crusher used, that is, the larger the crushing impact force, the larger the number of balls, the larger the unit weight of the balls, and the object to be treated (contamination of dioxins with respect to the balls). The smaller the weight ratio of the substance), the shorter it becomes. However, if the ratio of the object to be processed to the ball is reduced to shorten the processing time, the overall processing efficiency will be reduced. Therefore, in practice, the relationship between the processing time and the concentration change of dioxins is calculated in advance for each object to be treated according to the individual pulverizer and operating conditions, and the final concentration required for each object to be treated is determined. It may be determined according to.

The larger the amount of calcium oxide (in the case of mixing the substance containing calcium oxide) of calcium oxide, the lower the concentration of dioxins can be reduced in a short time. % Is preferable. It is more preferable that the weight of the object to be treated is approximately the same as that of the object to be treated, which enables efficient detoxification treatment. After the treatment, chlorine removed from the object to be treated is calcium chloride, and therefore it is harmless if it is discarded as it is.

As calcium oxide, quicklime or the like may be used.

The substance containing calcium oxide to be mixed has a particle size of 5 before being mixed with the object to be treated (dehydrated dried product).
It is desirable to pre-mill to less than or equal to mm or screen to remove particles greater than 5 mm. In this case, in consideration of the influence of the water content described above, it is desirable to mix with the object to be treated immediately after the preliminary pulverization. This is because, for example, even if the particles are preliminarily pulverized to a particle size of 1 mm or less, if they are stored for 1 week or more, the reaction rate remarkably decreases due to a moisture absorption phenomenon and a decrease in surface activity.

Steel slag can be used as the above-mentioned substance containing calcium oxide. As the iron and steel slag, as described above, blast furnace slag (either slowly cooled slag or granulated slag is acceptable), converter slag, ladle residual slag, electric furnace slag, secondary refining slag, ladle refining slag, etc. Among them, slag containing aluminum oxide or silicon dioxide is particularly preferable because the mechanochemical reaction is promoted as described below.

The mechanochemical reaction can be promoted by adding a substance containing aluminum oxide and / or silicon dioxide together with a substance containing calcium oxide and / or calcium oxide.

Even if a calcium oxide-containing substance having a low content of aluminum oxide or silicon dioxide is mixed with a substance containing aluminum oxide or silicon dioxide such as bauxite, alumina brick, silica sand or silica brick, the rate of mechanochemical reaction is increased. To do. Zirconium oxide, titanium oxide,
Chromium oxide, silicon carbide and the like have similar reaction promoting effects, but a mixture or compound of aluminum oxide or silicon dioxide is cheaper and harmless. The fine particles obtained by washing the soil are similar to the components contained in the soil, and are mainly a mixture or compound of aluminum oxide or silicon dioxide, and the mechanochemical reaction is naturally promoted.

Examples of the pulverizer which can be used in the detoxification treatment method of the present invention include a ball mill, a planetary ball mill, an attritor mill, a rod mill, a roll mill and a crusher mill. Among these, a crusher of the type that is subjected to an impact of several times or more the acceleration of gravity, for example, a planetary ball mill is preferable. The material of the crushing container and the balls for crushing is not particularly limited, but stainless steel, chrome steel, tungsten carbide, agate or the like is preferable.

According to the above-mentioned method of the present invention, a substance contaminated with actually existing dioxins, particularly a substance contaminated with a relatively low concentration such as soil, can be treated in a short time. The amount of calcium oxide, a substance containing calcium oxide, etc. used is small, and the detoxification treatment can be efficiently performed.

[0048]

[Example] 1 kg of soil contaminated with dioxins
Was put into 2 liters of water, stirred for 10 minutes, and then passed through a 0.1 mm mesh vibrating screen to separate coarse particle portions. At that time, the coarse particle portion was further washed with 1 liter of water. About 3 liters of the obtained washing liquid was dehydrated using an evaporator, and a solid substance was taken out.
It was dried at ° C for 2 hours. The weight of this dehydrated / dried product (dry sample) was 97 g.

Thereafter, calcium oxide 1 was added to the dried sample.
00g was mixed and subjected to mechanochemical treatment for 4 hours with a planetary ball mill.
Dioxins were analyzed by MS (gas chromatograph mass spectrometer). The analysis was also performed on soil contaminated with dioxins, soil after washing with water (coarse particles) and dried samples (fine particles containing dioxins obtained by dehydrating and drying the water used for washing). .

Table 1 shows the analysis results of dioxins.

[0051]

[Table 1]

According to this example, the dioxin concentration of the treated sample was low, and the amount of mechanochemical treated object was less than 1/10 of the original amount of soil. That is, it means that the amount of calcium oxide could be treated in a smaller amount than in the case of directly treating the original soil with mechanochemical treatment. Further, in the case of processing with a planetary ball mill having a processing unit of 200 g used in this example, 10 times of processing are required, and 40 hours are required for the total amount of processing.
Note that the soil (coarse-grained portion) of soil after being washed with water
The concentration of syn is also extremely low, so simply washing it with water will cause contaminated soil.
Lom was detoxified .

[0053]

According to the detoxification treatment method of the present invention, a substance contaminated with dioxins, particularly a substance contaminated with a relatively low concentration such as soil, can be treated with calcium oxide in a short time. The amount of contained substances, etc. used is small, and detoxification treatment can be performed efficiently, resulting in a large reduction in treatment costs.

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Claims (2)

(57) [Claims] 1. After washing a substance polluted with dioxins with water to separate into coarse particles and cleaning water composed of water and fine particles, and removing water from the cleaning water composed of water and fine particles. A method for detoxifying dioxin pollutants, which comprises mixing at least one of calcium oxide and a substance containing calcium oxide in the fine particle portion and performing mechanochemical treatment. 2. A substance contaminated with dioxins is washed with water to separate into coarse particles and washing water consisting of water and fine particles, and aluminum oxide and silicon dioxide are added to the washing water consisting of water and fine particles. After adding at least one of the substances containing, the water is removed, and then at least one of calcium oxide and a substance containing calcium oxide is mixed in the fine particle portion, and mechanochemical treatment is performed. Method for detoxifying dioxins pollutants.