JP3395724B2 - Detoxification method of dioxin pollutants - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dioxins which are considered to be harmful to the human body (in addition to polychlorinated dibenzoparadioxin, polychlorinated dibenzofuran and coplanar PCB). The present invention relates to a method for detoxifying a contaminated substance, particularly a substance contaminated at a relatively low concentration such as soil. 2. Description of the Related Art Dioxins such as polychlorinated dibenzoparadioxin are generated in waste incineration facilities, particularly when waste plastics containing chlorine are treated at a relatively low temperature, and are presently a social problem. Has become. For this reason, continuous high-temperature combustion has been used to control the generation and improvement of dust collection methods such as bag filters.However, the generation of dioxins itself cannot be suppressed, and dioxin is not contained in incinerated ash or dust collected. It is included. Therefore, treatment of dioxin in incineration ash and dust dust is required, but treatment using high-temperature plasma is only experimentally attempted. The detoxification method of dioxin-contaminated soil that has been proposed and studied at present is a method of melting the contaminated soil itself at a high temperature, which is not a practical method. At present, the development of a new treatment method is desired. On the other hand, Japanese Patent Publication No. Hei 8-504665 describes that dioxins can be rendered harmless by mechanochemical treatment. However, there is no specific description of the existing state of dioxins and conditions for detoxifying them. Dioxins, unlike the other toxic substances described in the above-mentioned publications, 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 of ng / g.
(10 ⁻⁹ g / g), a very low concentration that is contained in incineration ash, dust fly ash, dust dust, soil, etc. It is extremely difficult to detoxify species. As described above, several methods for treating dioxins have been proposed, but for example, treatment of contaminated soil has not actually been advanced. This is partly due to the high cost of treatment, but the actual concentration of dioxins in contaminated soil and other contaminants is low, and the amount of substances to be treated is enormous. ,
This is also due to poor processing efficiency. SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to include substances contaminated by dioxins that actually exist, especially soil and the like. An object of the present invention is to provide an efficient detoxification method for a substance contaminated with a relatively low concentration. SUMMARY OF THE INVENTION The gist of the present invention resides in the following method for detoxifying dioxin contaminants. A method for detoxifying dioxin-contaminated substances by drying a substance containing at least one of aluminum oxide, silicon dioxide and these compounds contaminated with dioxins and mechanochemically treating the substances. [0008] The combination of substances containing at least one of aluminum oxide, silicon dioxide and these compounds, which is intended in the present invention, is selected from the group consisting of aluminum oxide, silicon dioxide, and a compound of aluminum oxide and silicon dioxide. Is a combination that selects at least one of the following. As used herein, the term "dioxins" refers to polychlorinated dibenzofurandioxane, polychlorinated dibenzofuran, coplanar PCB, and the like, as described above. [0010] The "mechanochemical treatment" is a process of mixing and pulverizing an object to be processed while applying mechanical energy with an impact pulverizing device such as a ball mill. The object to be treated is physically torn off, and a highly active molecular surface is formed. Therefore, by performing the mechanochemical treatment, a reaction (mechanochemical reaction) that cannot occur at normal temperature can be advanced. The present inventors have been conducting research on mixing dioxins with a calcium oxide-containing substance and detoxifying the mixture by mechanochemical treatment. In this treatment method, the bond between carbon and chlorine is relatively weak among the bonds between the elements constituting the dioxins, can be separated mechanically even with a small energy, and the separated chlorine reacts with calcium oxide. Based on the principle of producing stable calcium chloride. Further, in this reaction, it has been found that when a mixture of aluminum oxide and silicon dioxide or a compound thereof is mixed with the object to be treated, the dechlorination detoxification reaction is promoted. As a result of examining these phenomena in detail, it is found that a mixture of aluminum oxide and silicon dioxide, or a compound thereof, has a polishing action, and therefore, when mechanical energy such as an impact force is applied, It was found that separation of chlorine from dioxins and destruction of the structure of dioxins were promoted. [0014] Further, as in the case of dioxins, even when the concentration is high, it is present at an extremely low concentration of less than 1 ppm expressed in units of ng / g (10 ^-9 g / g). In this case, the amount of chlorine separated by the mechanochemical reaction is extremely small, and the amount of calcium oxide required to react with the released chlorine to produce stable calcium chloride is also extremely low. However, usually the amount of calcium oxide required for the reaction with chlorine is low, but the concentration of the separated chlorine is also extremely low.Therefore, in order to react this chlorine with calcium oxide, about the same amount of calcium oxide as the material to be treated is used. It is considered necessary to mix. That is, in order to convert the separated very low concentration of chlorine into stable calcium chloride, calcium oxide far exceeding the amount required for the reaction is mixed.
This is causing an inefficient reaction. On the other hand, incineration ash, dust fly ash,
Dust collected, soil, and the like originally contain a large amount of a mixture of aluminum oxide and silicon dioxide or a compound thereof, which has an effect of promoting a mechanochemical reaction. In consideration of these facts, when the contamination by dioxins is relatively low and the object to be treated contains a mixture of aluminum oxide or silicon dioxide, or a large amount of such a compound, the contamination is reduced. Since the dechlorination detoxification reaction is promoted, it is considered that mixing of calcium oxide is not necessarily required when performing the mechanochemical treatment, and it is considered that the mechanochemical treatment may be performed directly on the object to be treated. However, as will be described later, since the moisture contained in the object to be treated greatly affects the reaction rate, it is necessary to dry the object in advance to remove the water. . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the method for detoxifying dioxin contaminants of the present invention will be described in detail. The detoxification treatment method of the present invention comprises, as described above, aluminum oxide contaminated with dioxins,
In this method, a substance containing at least one of silicon dioxide and these compounds is dried and subjected to mechanochemical treatment. The content of at least one of aluminum oxide, silicon dioxide, and these compounds may be at least 40% by weight in total (however, on a dry weight basis). If less than 40%, steel slag (blast furnace slag, converter slag, ladle residual slag, electric furnace slag,
Secondary refining slag, ladle refining slag, etc.) may be mixed and supplemented. The detoxification method of the present invention will be specifically described by taking soil contaminated with dioxins as an example.
The contaminated soil is dried at, for example, 110 ° C. for about 2 hours,
Thereafter, the mixture may be cooled to room temperature and pulverized by a planetary ball mill or the like. The pulverization time is 3 to 4 hours, but the reaction rate is slow and may exceed several hours. The pulverization time depends on the structure of the pulverizer used, such as a larger pulverization impact force, a larger number of balls, a larger single weight of the balls, and an object to be treated for the balls (contamination with dioxins). The smaller the weight ratio of the (substituted substance), the shorter it becomes. However, if the ratio of the processing object to the ball is reduced in order to shorten the processing time, the overall processing efficiency will be reduced. Therefore, in practice, the relationship between the processing time and the change in the concentration of dioxins is determined in advance for each processing object according to the individual crushing apparatus and operating conditions, and the final concentration required for each of the processing objects is determined. May be determined according to The purpose of drying the substance contaminated with dioxins in advance is to minimize the amount of water which greatly affects the reaction rate when detoxifying the substance. This is because moisture has a function of causing a granulation phenomenon of a processing target (substance contaminated by dioxins), reducing impact energy at the time of pulverization, and reducing a pulverization effect. The conditions under which this effect appears are determined by the relationship between the main components of the object to be treated and their proportions, the particle size of the object to be treated, the surface properties, and the like. It cannot be decided. As a standard of the water content, it is desirable to set the water content to 10% by weight or less based on the weight of the processing object. But,
In practice, it is desirable to examine the relationship between the granulation phenomena of the object to be treated and the amount of water in advance with respect to the crushing device to be used, and to obtain conditions under which the granulation phenomena do not occur. The drying method is not particularly limited. Any of heating drying, vacuum drying, solar drying, and a combination of these drying methods may be used. Since dioxins have a low vapor pressure, they do not evaporate by any method. By subjecting the substance contaminated with the dioxins to a pulverizing treatment (preliminary pulverizing treatment) in advance, a mechanochemical reaction can be promoted. In particular, when the object to be treated is soil, or when incinerated ash has a large particle size, the efficiency of mechanochemical treatment can be improved. In this case, it is desirable to carry out preliminary pulverization to a particle size of 5 mm or less. When the particles having a large particle size are contained, not only the detoxification treatment time is prolonged, but also the reaction may be stopped in some cases. Examples of the pulverizer that 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 them, a pulverizer of a type to which an impact of several times or more the gravitational acceleration is applied, for example, a planetary ball mill is preferable. The material of the crushing container and the crushing ball is not particularly limited, but stainless steel, chromium steel, tungsten carbide, agate and the like are preferable. According to the method of the present invention, a substance which is contaminated with dioxins which actually exist and which is contaminated at a relatively low concentration, such as soil, contains calcium oxide or calcium oxide. Detoxification treatment can be performed without using a substance. Since the amount of the processing object can be increased about twice, the effect of reducing the processing cost is great. Further, since calcium oxide is not mixed, there is no elution of alkali from the material after the treatment. EXAMPLE A 200 g of soil (containing 54.2% by weight of SiO _{2 and} 17.2% of Al ₂ O ₃ ) contaminated with dioxins was dried, and then dried with a planetary ball mill.
The mechanochemical treatment was performed for a long time, and dioxin analysis was performed on the obtained sample by GC-MS (gas chromatography mass spectrometry). Drying process is 110 ° C
And then cooled to room temperature in a desiccator. For comparison, 100 g of soil was similarly dried, then 100 g of calcium oxide was mixed and subjected to a mechanochemical treatment for 4 hours in a planetary ball mill.
Dioxin analysis was also performed on the obtained mixed sample. Table 1 shows the results of dioxin analysis. [Table 1] In the example of the present invention in which mechanochemical treatment was performed without mixing calcium oxide, the dioxin concentration after the treatment was slightly higher than that in the comparative example in which calcium oxide was mixed. 100pg
And the result was sufficiently satisfactory. In addition, even if the amount charged to the planetary ball mill was the same (200 g), in the example of the present invention, twice as much contaminated soil could be treated. According to the detoxification method of the present invention, a substance contaminated with dioxins, which is contaminated with a relatively low concentration such as soil, can be treated with calcium oxide or oxidized substance. Detoxification treatment can be performed without using a substance containing calcium. Since the amount of the processing object can be increased about twice, the effect of reducing the processing cost is great. Further, since calcium oxide is not mixed, there is no elution of alkali from the material after the treatment.

────────────────────────────────────────────────── (5) References JP-A-11-124463 (JP, A) JP-A-5-168727 (JP, A) JP-A-10-43732 (JP, A) JP-A-2000-70401 (JP, A) International Publication No. 8-504665 (JP, A) International Publication 01/12352 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B09C 1/08 A62D 3/00 B01D 53/70 WPI (DIALOG) JICST file (JOIS)

Claims (1)

(57) [Claim 1] A substance containing at least one of aluminum oxide, silicon dioxide and these compounds contaminated with dioxins is dried and mechanochemically treated. Method for detoxifying dioxin pollutants.