JP2005118623A - Method for treating substance contaminated with dioxins, method for treating ash, and dioxins decomposing agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove dioxins simply, effectively and safely from a substance such as fly ash contaminated with dioxins. <P>SOLUTION: This method for treating the substance contaminated with dioxins comprises the steps of: preparing a mixture by adding an iron oxide and at least one of an alkali metal compound and an alkaline-earth metal compound to the substance contaminated with dioxins; and heating the prepared mixture. Triiron tetroxide, for example, is used as the iron oxide. The mixture is heated generally at ≥300°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for treating pollutants and a decomposing agent, and more particularly to a method for treating dioxins pollutants such as fly ash and a decomposing agent for dioxins.

  In the incineration process of industrial waste, household waste, and other waste, organic compounds contained in the waste and chlorine may react to produce dioxins, so they are discharged from the waste incineration facility Fly ash and incineration ash (incinerator bottom ash, etc.) are generally considered to be contaminated with dioxins. Dioxins are unprecedented highly toxic substances that can cause skin and visceral disorders and have teratogenic and carcinogenic properties. In particular, 2,3,7,8-tetrachlorodibenzo-para-dioxin, which is a dioxin in a narrow sense, is said to be one of the most toxic substances obtained by mankind.

  For this reason, incineration facilities for waste, a method is being adopted in which a dust removal device such as a bag filter is provided in an exhaust gas discharge system to collect fly ash and prevent discharge of fly ash to the atmosphere. However, in this method, since the collected fly ash contains a high concentration of dioxins, a separate treatment for detoxifying it is necessary.

  As an example of the treatment method for detoxification as described above, in Patent Document 1, a chemical having an oxidation catalyst function or a chemical having an oxidizing ability is added to fly ash or incineration ash (furnace bottom ash, etc.) A method for decomposing and removing halogenated aromatic compounds such as dioxins contained in ash, which comprises heating to a temperature of 300 ° C. or higher in the presence of oxygen and water vapor and then quickly cooling to 200 ° C. or lower. Has been described. In this method, dioxins contained in ash are oxidatively decomposed by the action of the drug and heating in the presence of oxygen atmosphere and water vapor. Moreover, since the ash after heat processing is rapidly cooled, the re-synthesis | combination of dioxins is prevented and the dioxin density | concentration of the ash after a process falls.

  However, the method described in Patent Literature 1 requires a rapid cooling of the ash after the heat treatment, so that the treatment work is complicated, and a complicated and expensive treatment device that combines the heating device and the cooling device is used. Since it is necessary, practical application is substantially difficult.

In addition, according to Table 5 of the same document, the method described in Patent Document 1 uses dioxins (PCDDs) even when a large amount (15% by weight) of α-Fe ₂ O ₃ which is easily available as a drug is used. And PCDFs) is at most 95.7%, and the degradation rate is improved only by about 10% even when no chemical is added, and the detoxification effect of dioxins is sufficient. Hard to say. Furthermore, since the method described in Patent Document 1 does not consider that dioxins may be gasified and volatilized from the ash during the heating process, the concentration of dioxins in the ash itself can be reduced. However, volatilizing dioxins may cause environmental pollution such as air pollution.

JP 2002-355638 A

  An object of the present invention is to easily and effectively remove dioxins from dioxins pollutants such as fly ash safely.

  In the present application, the term “dioxins” refers to polychlorinated dibenzo-para-dioxins (PCDDs) and polychlorinated according to the provisions of Article 2 of the Law No. 105 of 1999, “Dioxin Special Measures Law”. In addition to dibenzofuran (PCDFs), it is used to mean including coplanar polychlorinated biphenyls (Co-PCBs).

  A method for treating a dioxin pollutant according to the present invention comprises a step of preparing a mixture by adding iron oxide and at least one of an alkali metal compound and an alkaline earth metal compound to a dioxin pollutant, And heating the mixture. The iron oxide used in this method is, for example, triiron tetroxide. In this method, the mixture is usually heated to 300 ° C. or higher.

  The method for treating ash according to the present invention is a method for treating ash generated in a waste incineration facility equipped with an incinerator for incineration of waste, and the ash is treated with iron oxide, an alkali metal compound and an alkali. A step of preparing a mixture by adding at least one of the earth metal compounds, a step of containing the mixture in a container, and a container containing the mixture in the incinerator, and in the incinerator Heating the mixture in the container by incinerating the waste.

  The dioxin decomposing agent of the present invention is for decomposing dioxins contained in dioxin pollutants, and contains iron oxide and at least one of an alkali metal compound and an alkaline earth metal compound. Yes.

  The method for treating a dioxin pollutant according to the present invention prepares a mixture by adding iron oxide and at least one of an alkali metal compound and an alkaline earth metal compound to a dioxin pollutant. Because the mixture is heated, it can easily and effectively remove dioxins from dioxin pollutants, and gasification of dioxins into the work environment is unlikely to occur, allowing safe processing. be able to.

  In the ash treatment method according to the present invention, a mixture is prepared by adding iron oxide and at least one of an alkali metal compound and an alkaline earth metal compound to ash, and the mixture is accommodated in a container. Since the waste is heated in the incinerator during incineration, dioxins can be easily and efficiently removed from the ash effectively and gasified into the work environment. Volatilization is difficult to occur and the processing can be performed safely.

  Since the dioxin decomposition agent of the present invention contains iron oxide and at least one of an alkali metal compound and an alkaline earth metal compound, when mixed with a dioxin contaminant and heat-treated, the dioxin contamination Dioxins can be easily and effectively removed from a substance, and gasification of dioxins into the work environment is unlikely to occur, so that the treatment can be performed safely.

  Dioxins pollutants to which the treatment method of the present invention can be applied are not particularly limited, but are usually solids such as particles and powders contaminated by dioxins, such as household waste. It occurs in ash such as fly ash and incineration ash (incinerator bottom ash etc.) generated in refining facilities such as incineration facilities and industrial waste and aluminum recycling, demolition residue generated by incinerator demolition, sewage treatment, etc. Examples include sludge, soil, and sediments such as rivers and lakes.

  In carrying out the treatment method of the present invention, first, an iron oxide and at least one of an alkali metal compound and an alkaline earth metal compound are added to the above-mentioned dioxin contaminants to obtain a mixture. Prepare.

The iron oxide used in this step is not particularly limited as long as it is various oxides of iron. For example, iron oxide (FeO), diiron trioxide (Fe ₂ O ₃ ), and iron trioxide. (Fe ₃ O ₄ ). These iron oxides may be used alone or in combination of two or more. However, as iron oxide, it can be manufactured at a low cost, is easily available as a waste recycling product, and suppresses volatilization of dioxins in the gaseous state from dioxin pollutants in the heating process described later. It is particularly preferable to use triiron tetroxide for reasons such as ease.

Iron trioxide is a mixture of iron oxide (FeO) and ferric trioxide (Fe ₂ O ₃ ), and is usually referred to as magnetite. The production method and the like of triiron tetroxide are not particularly limited. For example, those obtained as a by-product in the production process of sulfuric acid method titanium oxide are preferable. Specifically, the iron-containing sulfuric acid obtained in the production process of sulfuric acid method titanium oxide is neutralized and then concentrated and separated. And the filtrate obtained by filtering the supernatant liquid in that case is further neutralized and oxidized. More specifically, sodium hydroxide is added while passing an air stream through the filtrate, and the pH is set to 6.0 to 6.3 and the oxidation rate is set to 75 to 80% while setting the temperature to 65 ° C. Process to become. Then, this neutralization, after separation by filtration of the product obtained by the oxidation treatment, and dried at about 120 ° C., the ratio of FeO and _{Fe 2 O 3 (FeO: Fe} 2 O 3) is 10 to 30: 90-70 iron trioxide is obtained. The final drying step is preferably performed in a nitrogen atmosphere. In this way, the ratio of FeO and Fe ₂ O ₃ is set as described above, easy decomposition efficiency higher triiron of dioxins were obtained.

  Since the iron oxide as described above is easily mixed with dioxins pollutants such as fly ash and incinerated ash, it is preferably granular or powdery, but the particle shape is not particularly limited. . However, in general, the finer the iron oxide, the higher the contact efficiency with the dioxins contained in the dioxins pollutant, and accordingly the decomposition efficiency of dioxins can be increased. Then, since it becomes expensive, what was normally manufactured using the present manufacturing line can be utilized as it is. Incidentally, the average particle size of the powdered iron oxide is preferably 0.05 to 50 μm, and more preferably 0.07 to 10 μm.

  In addition, when the iron oxide is triiron tetroxide, the method and conditions for making it into powder are not particularly limited, but normally, the triiron tetroxide reacts with moisture and oxygen to dioxin. In order to avoid a reduction in the resolution of the class, it is preferable to grind and dry the iron tetroxide in an anhydrous inert gas stream (for example, in a nitrogen stream).

  On the other hand, the alkali metal compound used in this step is not particularly limited as long as it is a compound containing an alkali metal such as sodium or potassium. For example, an alkali metal oxide, hydroxide, carbonate, sulfate And nitrates. However, in the implementation process of the treatment method of the present invention, from the viewpoint of preventing the generation of nitrogen oxides or sulfur oxides that cause air pollution, alkali metal oxides, hydroxides or carbonates are usually added. It is preferable to use it. In addition, as the alkali metal compound, one type may be used, or two or more types may be used in combination. In addition, it is preferable to use a granular or powdery alkali metal compound for the same reason as the iron oxide.

  Further, the alkaline earth metal compound used in this step is not particularly limited as long as it is a compound containing an alkaline earth metal such as magnesium, calcium and barium. For example, an alkaline earth metal oxide, water Oxides, carbonates, sulfates and nitrates. However, for the same reason as in the case of an alkali metal compound, it is usually preferable to use an oxide, hydroxide or carbonate of an alkaline earth metal. In particular, it is more preferable to use calcium oxide or magnesium oxide that is inexpensive and easily available. In addition, as the alkaline earth metal compound, one type may be used, or two or more types may be used in combination. In addition, it is preferable to use a granular or powdery alkaline earth metal compound for the same reason as the iron oxide.

  In this step, dioxins pollutants, iron oxides and at least one mixture of alkali metal compounds and alkaline earth metal compounds are mixed with iron oxides, alkali metal compounds and alkaline earth metals against dioxins pollutants. A dioxin decomposing agent prepared by adding at least one of the compounds individually and mixing, or by premixing at least one of iron oxide and alkali metal compound and alkaline earth metal compound It can be prepared by adding to and mixing with dioxin contaminants.

  At this time, the mixture is preferably prepared in a granular or slurry form by adding an appropriate amount of water in order to suppress scattering of dioxin contaminants and facilitate handling.

  In addition, in the preparation process of the mixture, the amount of iron oxide used is usually preferably set to 3 to 40% by weight, and preferably 5 to 20% by weight, based on the total weight of the dioxin contaminants. It is more preferable to set. When the amount of iron oxide used is less than 3% by weight, dioxins contained in dioxins pollutants may not be sufficiently decomposed. On the contrary, when it exceeds 40% by weight, the weight of the mixture increases, so that there is a possibility that the final disposal cost such as transportation and transportation increases.

  On the other hand, the amount used of at least one of the alkali metal compound and the alkaline earth metal compound is usually preferably set to 3 to 40% by weight with respect to the total weight of the dioxin contaminant, It is more preferable to set the weight%. When the amount of the compound used is less than 3% by weight, dioxins are easily re-synthesized in the heat treatment step described later and the cooling process after the heat treatment step, and as a result, the dioxin concentration of the dioxin pollutant is reduced. It may be difficult to reduce, or the dioxin concentration of dioxins pollutants may increase instead. On the contrary, when it exceeds 40% by weight, the weight of the mixture increases, so that there is a possibility that the final disposal cost such as transportation and transportation increases.

  In the adjustment step of the mixture described above, the ratio between the amount of iron oxide used and the amount of at least one of the alkali metal compound and the alkaline earth metal compound is preferably adjusted according to the properties of the dioxins pollutant. . For example, when the dioxin pollutant contains a large amount of chlorine, in order to suppress the resynthesis of dioxins after the heat treatment process described later, at least one of the alkali metal compound and the alkaline earth metal compound is used as iron. It is preferable to relatively increase the amount of oxide used.

  In the description of the amount of each substance used above, the total weight of the dioxin pollutant is based on the solid content of the dioxin pollutant when the dioxin pollutant contains water such as soil and sediment. Is.

  Next, the mixture obtained in the above process is heat-treated. Here, it is preferable to heat the mixture to a temperature range higher than a temperature range suitable for synthesizing dioxins by reaction of various organic substances with chlorine. Specifically, it is preferable to heat the mixture to 300 ° C. or higher. When the heating temperature is lower than this temperature range, that is, when it is lower than 300 ° C., it may be difficult to effectively decompose and remove dioxins contained in the dioxin contaminants. In addition, although the upper limit of the heating temperature in this process is not specifically limited, It is preferable to set to 600 degrees C or less normally from practical viewpoints, such as implementation cost.

  The heat treatment method in this step is not particularly limited, but it is usually preferable that the mixture is accommodated in a container and heated so that the temperature of the mixture in the container becomes the above-described temperature. In addition, as the container, it is particularly preferable to use an airtight container and a sealed container that can discharge a gas such as water vapor generated in the temperature rising process during heating to the outside. When the mixture is heated to 300 ° C. or higher, dioxins are likely to gasify. However, when such a closed container is used, the gas flow is reduced in the container, and dioxins contained in dioxin pollutants are gas. Therefore, it is possible to effectively prevent dioxins from diffusing into the atmosphere or the like, and as a result, it is possible to effectively prevent contamination of the working environment or air pollution during the implementation of the present invention. Moreover, since the gasified dioxins stay in the container and the contact efficiency with the above-mentioned iron oxide or the like increases, the removal efficiency of the dioxins can also be increased. Furthermore, when the mixture is accommodated in the container and heat-treated, the dioxin concentration reducing effect in the mixture can be easily confirmed.

  In the case of ash such as fly ash and incineration ash (furnace bottom ash, etc.) generated in an incineration facility equipped with an incinerator for incineration of waste, dioxin pollutants can be treated as, for example, these The mixture obtained by mixing the above-mentioned iron oxide or the like with ash of ash is placed in a container, preferably in an airtight sealed container and placed in an incinerator, and the incinerated product is incinerated in the incinerator. A method of heating the mixture in the container is conceivable. If it does in this way, an incinerator and a waste can each be utilized effectively as an installation and fuel for heating a mixture, and fly ash and incineration ash can be processed more efficiently and economically.

  In general, the heat treatment time in the heat treatment step is preferably set so that the above-described required temperature is maintained for at least about 1 hour. When the heat treatment time is less than 1 hour, the dioxins contained in the dioxin contaminants may not be effectively decomposed and removed for reasons such as the temperature inside the mixture is not sufficiently increased.

  In addition, what is necessary is just to naturally cool the mixture after heat processing to normal temperature, but it can also be forcedly cooled using cooling equipment as needed.

  In the above heat treatment step, dioxins contained in dioxins pollutants such as fly ash and their precursors are subjected to the action of iron oxide, at least one of an alkali metal compound and an alkaline earth metal compound, It is considered that scattering due to gasification is suppressed and that it is effectively decomposed. In addition, the mixture after the heat treatment tends to increase the concentration of dioxins by resynthesis in the cooling process, particularly in the temperature range of about 200 to 300 ° C. during the cooling. It is considered that the oxide is effectively suppressed by the action of at least one of the alkali metal compound and the alkaline earth metal compound. For this reason, the treatment method of the present invention is safe in that it can effectively prevent environmental pollution due to gasification of dioxins in the heat treatment step, and the re-synthesis of dioxins is less likely to occur at 200 ° C. or less. Even if the dioxin pollutant after the heat treatment is not rapidly cooled, the dioxin concentration in the dioxin pollutant can be greatly reduced.

  In addition, dioxins pollutants as described above, especially ash such as fly ash and incinerated ash, may contain harmful elements such as heavy metals and may cause environmental pollution due to their elution, but the method of the present invention is implemented. If it is done, it will become difficult to elute harmful elements. Therefore, the dioxins pollutants for which the treatment method of the present invention has been implemented can greatly reduce the dioxin concentration, and the amount of elution of harmful elements such as heavy metals can be below the soil standard or the landfill treatment standard.

Example 1
Iron trioxide and calcium oxide were uniformly mixed with the fly ash generated in the incineration facility, and an appropriate amount of water was added thereto to obtain a slurry-like mixture. Here, both powdered iron tetroxide and calcium oxide were used. Moreover, the addition amounts of triiron tetroxide and calcium oxide were set to 15% by weight with respect to the weight of fly ash. The amount of dioxins in the fly ash was measured in advance.

  A predetermined amount of the obtained mixture was collected in a combustion dish, and this combustion dish was inserted into a ceramic tube installed in a preheated tubular furnace. And after heating the mixture at 300 degreeC for 1 hour, the combustion dish was taken out from the ceramic-made tubes, it cooled naturally to normal temperature, and the dioxin residual rate in a mixture was measured. In the heating step of the mixture, air is circulated through the ceramic tube at a flow rate of 1.2 L / min, and the dioxins in the gas state contained in the exhaust air from the ceramic tube are collected by a filter for collecting dioxins (Miura Industry). The product was continuously collected using a trade name “Dioana” (“Dioana” is a registered trademark of Miura Kogyo Co., Ltd.), and the dioxin volatilization rate into the air was measured. The results are shown in Table 1.

  In addition, the dioxin residual rate in a mixture and the dioxin volatilization rate in the air are calculated | required by following Formula (1) and (2), respectively.

Examples 2-7
The heating conditions of the mixture and the air flow rate flowing through the ceramic tube were changed as shown in Table 1, and the dioxin residual rate in the mixture and the dioxin volatilization rate in the air were measured in the same manner as in Example 1. did. The results are shown in Table 1.

  In Example 5, the heating temperature of the mixture was initially set to 500 ° C., but was lowered to 400 ° C. after 1 hour, and maintained at 400 ° C. for an additional hour. Moreover, in Example 6, although the heating temperature of the mixture was initially set to 500 degreeC, after 1 hour progress, it reduced to 300 degreeC and maintained at 300 degreeC for 3 hours.

  For Example 2, the amount of harmful elements such as heavy metals contained in the fly ash before heat treatment is measured in advance, and the amount of toxic elements eluted from the fly ash before heat treatment and the fly ash after heat treatment Was measured respectively. The elution amount of harmful elements was measured based on the elution test method described in the Environmental Agency Notification No. 13 “Testing Methods for Metals in Industrial Waste” in February 1973. The results are shown in Table 2. For chromium (Cr) in Table 2, the content in the pre-treatment fly ash and the elution amount from the pre-treatment fly ash and the post-treatment fly ash are based on the total chromium content, and the standard value is landfill It means the hexavalent chromium concentration by the standard. The standard values are based on the revised 2000 Prime Ministerial Decree No. 1 “Criteria for Industrial Waste Containing Metals”.

Comparative Examples 1 and 2
Only fly ash was heat-treated under the conditions shown in Table 1, and the dioxin residual rate in the mixture and the dioxin volatilization rate in the air were measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Examples 3 and 4
Only triiron tetroxide was added to the fly ash and heat-treated under the conditions shown in Table 1, and the dioxin residual rate in the mixture and the dioxin volatilization rate in the air were measured in the same manner as in Example 1. . The results are shown in Table 1.

  According to Table 1, in each Example, since triiron tetroxide and calcium oxide were mixed with fly ash, the residual rate of dioxins in the mixture after heat treatment was small by heat treatment, and heat treatment was also performed. It can be seen that in the process, almost no gaseous dioxins are generated from the mixture. On the other hand, in each comparative example, it turns out that dioxins are hard to reduce even if it heat-processes. In Comparative Example 2, the ratio of volatilization of dioxins into the air is large because dioxins are re-synthesized on the surface of the fly ash and cannot be retained, so dioxins that volatilize into the air increase. This is probably due to the fact that In Comparative Example 4, the dioxins remaining rate in the mixture was high because dioxins and their precursors were prevented from evaporating from the fly ash, resulting in resynthesis of dioxins in the mixture. it is conceivable that.

  Moreover, according to Table 2, the amount of elution of harmful elements, particularly lead (Pb) and zinc (Zn), is significantly reduced in the fly ash after heat treatment compared to before heat treatment. It turns out that it is difficult to elute harmful elements such as heavy metals.

Claims (5)

A step of adding a mixture of iron oxide and at least one of an alkali metal compound and an alkaline earth metal compound to a dioxin pollutant; and
Heating the mixture;
Of Dioxin Contaminants Containing Gas   The processing method of the dioxin pollutant of Claim 1 whose said iron oxide is triiron tetraoxide.   The processing method of the dioxin contaminant of Claim 1 or 2 which heats the said mixture to 300 degreeC or more. A method for treating ash generated in a waste incineration facility equipped with an incinerator for incinerating waste,
A step of adding a mixture of iron oxide and at least one of an alkali metal compound and an alkaline earth metal compound to the ash; and
Containing the mixture in a container;
Placing the container containing the mixture in the incinerator and heating the mixture in the container by incinerating the waste in the incinerator;
Ash treatment method. A decomposition agent for decomposing dioxins contained in dioxin pollutants,
Iron oxide,
At least one of an alkali metal compound and an alkaline earth metal compound;
Dioxin decomposition agent containing.