JP2006015290A - Fixing method for heavy metal in fly ash using no mixing nor kneading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a safe and efficient fixing method of heavy metals in fly ash produced during incineration of waste without using a mixing nor kneading apparatus, but using a selected treating chemical agent, and without reforming existing facilities. <P>SOLUTION: In this fixing method for heavy metals, a heavy metal-containing waste treating chemical agent comprising an inorganic compound composed of an aluminum compound or a sulfate with a decomposition point of 150°C or higher, and an organic compound composed of a dithiocarbamate or a metal salt as the principal components, is injected into flue gas to complete a reaction with metal-containing fly ash in exhaust gas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for immobilizing heavy metals in fly ash generated when incinerating waste.

The conventional method for immobilizing heavy metals contained in fly ash is collected by a dust collector installed at a waste incineration facility, discharged from the dust collector, and then treated with water and heavy metals. An immobilization method is used in which a chemical is added and the reaction is completed by a mixing and kneading apparatus.
(See Patent Document 1.)

In addition, as a method of spraying the treatment chemical into the exhaust gas, a method of reacting with mercury or the like with an aqueous solution of piperidine dithiocarbamate is disclosed.
(See Patent Document 2.)

In addition, zinc iodide is supported on bag filter aids such as diatomaceous earth, alumina, silica, and activated carbon, and pre-coated on the surface of the bag filter in the same manner as the bag filter aid, and then adsorbs mercury and other heavy metals. The method of processing is shown.
(See Patent Document 3)

JP-A-9-99215 JP 05-208117 A Japanese Patent Laid-Open No. 10-109016

The fly ash collected by the collection device is often mixed and mixed with a kneading device, and water and a treatment chemical are added to immobilize heavy metals contained in the fly ash. The installation cost is high, a space for installation is necessary, and labor such as maintenance work is also required.

In addition, as a method of spraying the treatment chemical in front of the fly ash dust collector attached to the incineration facility, a method of spraying an aqueous solution of piperidine dithiocarbamate aqueous solution or other dithiocarbamate is disclosed. Since it is an aqueous solution, there is a problem in safety such as the working environment such as generation of harmful gas of spray medicine, and a device for spraying the aqueous solution needs to be installed separately. Furthermore, the dust collector is also limited, for example, fly ash contained in flue gas sprayed with an aqueous solution cannot be applied to electric dust collectors in terms of corrosion and flammability.

In addition, Hg and other heavy metals such as Hg can be sprayed into the flue by supporting zinc iodide (ZnI ₂ ) on filter aids for bag filters such as diatomaceous earth, alumina, silica and activated carbon. Although a method has been disclosed that can reduce the amount of ash that can be adsorbed and simplify the treatment method, the highly volatile mercury gas contained in the exhaust gas is an activated filtration aid with a large specific surface area. The agent is physically or chemically adsorbed, but other heavy metals such as lead (Pb), cadmium (Cd), and chromium (Cr) are contained in the fly ash discharged from the lower part of the collector. However, since the standard value for discharging cannot be satisfied, a fixing process such as a cement solidifying apparatus or a melting processing apparatus is necessary, and there is a problem that processing costs become enormous.

The present invention provides a dust collecting device attached to an incineration facility, a slaked lime sprayed for exhaust gas treatment, highly reactive slaked lime, activated carbon, dolomite and other chemicals and existing devices, and without mixing, mixing and kneading devices. It aims at providing the heavy metal processing chemical | medical agent and processing method which are not required.

In order to solve the above-mentioned problems, the present invention injects a heavy metal immobilization treatment chemical into the flue and selects a chemical that sufficiently reacts with the heavy metal in the fly ash. The flue exhaust gas contains acid gas such as hydrogen chloride gas and sulfur oxide, dioxin, etc., and the temperature is generally about 100 to 250 ° C. and the water also contains 5 to 30%.

In selecting a chemical, it is necessary that the chemical does not adversely affect slaked lime, highly reactive slaked lime, dolomite, or activated carbon injected for removing acidic gas or adsorbing dioxin. For example, as disclosed in JP-A No. 05-208117, an ammonium or potassium salt of dithiocarbamate is expected to be adsorbed on activated carbon injected for dioxin adsorption and inhibit the dioxin adsorption effect. In the filter aid for bag filters activated by supporting zinc iodide on diatomaceous earth, alumina, silica and activated carbon, fly ash is discharged as before, using heavy metal immobilization chemicals and processing equipment Need to be processed.

In order to solve the above-mentioned problems, the present invention has a high heat-resistant temperature and does not affect the injection of chemicals for gas treatment. Aluminum dihydroxide polymer [Al ₂ SO ₄ (OH) ₄ · XH ₂ O · 2Al (OH) ₃ ] One kind selected from inorganic compounds of _n and salts of diethyldithiocarbamic acid (alkali salts such as potassium, sodium, ammonium, calcium) and sulfides, chlorides, carbonates, and phosphorus oxides of zinc and iron Zinc diethyldithiocarbamate (C ₂ H ₅ ), which is a product of zinc diethyldithiocarbamate and iron synthesized by the above chemical reaction and is commercially available as a vulcanization accelerator and vulcanizing agent in the rubber industry and can be synthesized by a known production method. mixture or piperazine dithiocarbamates of) ₂ NCS ₂ Zn and diethyldithiocarbamate iron _{(C 2 H 5) 2 NCS} 2 Fe Is a heavy metal immobilization treatment agent characterized in that it contains at least one or more selected from among powdered medicament potassium _{(CH 2) 4 N 2 C} 2 S 4 organic chelates of K _2.

Since the heavy metal immobilization treatment chemical of the present invention is excellent in heat-resistant temperature (melting point 150 ° C. or higher), it is injected into the flue in the same manner as the exhaust gas treatment chemical. That is, one or more selected from slaked lime, highly reactive slaked lime dolomite (for acid gas adsorption), diatomaceous earth, perlite (filter aid for bag filter), activated carbon (for dioxin adsorption), etc. It can be used as a mixture.

Further, the heavy metal immobilization treatment agent of the present invention can be used alone by being injected into the flue. Furthermore, it can be mixed with water and injected into a kneading apparatus for use in fixing heavy metals in existing fly ash.

The above heavy metal fixation treatment chemicals are various cements, Portland cement, early strong cement, early cemented alumina cement, sodium bicarbonate, sodium carbonate, potassium carbonate, potassium bicarbonate, calcium carbonate, calcium bicarbonate, gypsum, ferrous sulfate It can be used as a mixture with one or more selected from sodium thiosulfate and the like.

The selected treatment agent is excellent in heat resistance and is a commercially available water-soluble dithiocarbamate, such as potassium diethyldithiocarbamate, tetra (dithiocarboxy) tetraethylenepentamine sodium or piperazinenium-1, Compared with potassium 4-piperazine dicarbodithiate and the like, the heavy metal in the fly ash can be fixed with an extremely small amount added by the fly ash weight ratio.

In general, fly ash discharged from a dust collector attached to an incineration facility is processed by adding the above water-soluble chelating agent and water in a mixing and kneading device, and the heavy metal in the fly ash is fixed. However, the use of the treatment chemical and treatment method selected in the present invention eliminates the need for mixing and kneading equipment and the addition of water, and eliminates the need for mixing and kneading equipment installation space, installation costs and related personnel. The heavy metal immobilization process in fly ash is dramatically streamlined.

In addition, the amount of processing chemicals added is small, and when used in combination with exhaust gas processing chemicals (slaked lime, highly reactive slaked lime, dolomite, activated carbon), the amount of fly ash discharged becomes extremely small, and it is carried into landfill sites The amount is reduced, which contributes to the reduction of landfill costs and the extension of the life of the treatment plant.

As mentioned above, although an Example is given and this invention is demonstrated concretely, this invention is not limited to this. As samples for explaining the treatment chemical and the treatment method of the present invention, ash collected with a bag filter type dust collector after blowing slaked lime into a municipal waste incinerator (stoker-type continuous operation) was used. The effect of immobilizing heavy metals is determined by the dissolution test method of the Environmental Agency Notification No. 13 and the test solution is adjusted, and typical lead (Pb) is analyzed from the heavy metal-containing items in the fly ash. Evaluation was performed using the value (0.3 mg / l).

As a method for treating fly ash discharged from the dust collector attached to the incineration facility of the present invention, as an embodiment not using a mixing and kneading device, a collection of facilities capable of incinerating 15 tons of waste for 12 hours of operation. A preliminary treatment chemical addition test is performed with the fly ash discharged from the dust device, the treatment chemical selected in the present invention is mixed with the exhaust gas treatment chemical (highly reactive slaked lime mixed with activated carbon), and the mixture is placed in an existing silo. A fixed amount was blown into the flue and evaluated by the amount of elution obtained by the elution test of lead (Pb) in the fly ash discharged from the lower part of the dust collector.

Effect of Addition of Treatment Agent of the Present Invention FIG. 1 shows an outline of a stalker-type incineration facility. Garbage is introduced from 1 and a drying process is performed in 2 to lead to combustion, and 3 is a residue that cannot be burned completely. Falls and cools. 4 recombusts the unburned matter in the exhaust gas, and 5 prompts the exhaust gas to make it difficult to generate dioxins, or lowers the temperature to below the heat resistance temperature of the filter portion of the bag filter. 6 is a silo for chemicals for exhaust gas treatment (slaked lime or activated carbon), which is sprayed (injected) before the bag filter type dust collector 7. The fly ash and chemicals for exhaust gas treatment collected by the bag filter type dust collector of No. 7 are used as fly ash. It is discharged into the 8 fly ash storage silo in Detailed Description 1 and fixed with a mixing and kneading device of 10 together with 9 heavy metal immobilizing agents and 11 water tanks and 12 water injection pumps. , 13 trucks, etc., are carried out to the landfill site.

Confirmation of the effect of adding the treatment chemical of the present invention was performed by reproducing the same operation procedure as that of the above-mentioned system that is generally used at present on a beaker scale in a laboratory. Using the fly ash collected from No. 8 fly ash silo, various treatment chemicals were added until the detoxification treatment was completed, and 40 parts by weight of water was added to the fly ash weight.

〔実施例〕
＊１ 処理薬剤 Ｐ：形状（粉体）ピペラジンジチオカルバミン酸カリウム
＊２ 処理薬剤 Ｈ：形状（粉体）ジエチルジチオカルバミン酸鉄・亜鉛の合成生成物
＊３ 処理薬剤 Ｍ：形状（粉体）ニ水酸化アルミニウム化合物
〔比較例〕
＊４ 市販品処理薬剤 Ａ：形状（液体）ジエチルジチオカルバミン酸カリウム
＊５ 市販品処理薬剤 Ｂ：形状（液体）テトラエチレンペンタミンナトリウム
＊６ 市販品処理薬剤 Ｃ：形状（液体）ピペラジンジチオカルバミン酸カリウム
飛灰試料（薬剤無添加）：ｐＨ＝12.5 Ｐｂ溶出量＝204mg/l
検定方法：環境庁告示第１３号法
陸上埋立処分基準値：Ｐｂ0.3mg/l以下
表１に見られるように本発明に使用する粉体状処理薬剤は市販されている液状の処理薬剤に較べて、Ｐｂ溶出量を埋立処分基準値（0.3mg/l）以下にするための薬剤の添加率が低い事が認められた。したがって、現状行われている混合、混練装置を用いての飛灰の重金属固定化用薬剤としての適用も排出する処理後の飛灰量も減量化して埋立処分場へ搬出できる事になり、経費節減も含めて合理的にできる事が明らかになった。

〔Example〕
* 1 Treatment agent P: Shape (powder) potassium piperazine dithiocarbamate * 2 Treatment agent H: Shape (powder) Synthesis product of iron and zinc diethyldithiocarbamate * 3 Treatment agent M: Shape (powder) dihydroxide Aluminum compound (comparative example)
* 4 Commercial treatment agent A: Shape (liquid) potassium diethyldithiocarbamate * 5 Commercial treatment agent B: Shape (liquid) sodium tetraethylenepentamine * 6 Commercial treatment agent C: Shape (liquid) potassium piperazine dithiocarbamate Ash sample (no chemical added): pH = 12.5 Pb elution amount = 204 mg / l
Test method: Environmental Agency Notification No. 13 landfill disposal standard value: Pb 0.3 mg / l or less As shown in Table 1, the powdery treatment chemical used in the present invention is compared with the commercially available liquid treatment chemical Thus, it was confirmed that the rate of addition of the drug to make the Pb elution amount equal to or less than the landfill disposal standard value (0.3 mg / l) was low. Therefore, it is possible to reduce the amount of fly ash after processing and to apply it as a chemical for immobilizing fly ash using heavy mixing and kneading equipment currently used, and to transport it to a landfill site. It became clear that we can do rationally, including savings.

The treatment chemical of the present invention (zinc diethyldithiocarbamate / iron synthesis product) is mixed with the exhaust gas treatment chemical (80% slaked lime: 20% activated carbon) and directly blown into the flue together with the exhaust gas treatment chemical. The heavy metal contained therein was detoxified at the same time, and the fly ash discharged from the bag filter dust collector was mixed and treated without using a kneader. The mixture ratio with the exhaust gas treatment chemical was blown into the flue at 15 kg / h using 76% slaked lime: 19% activated carbon: 5% fly ash treatment chemical. The exhaust gas amount was 11000 Nm ³ / h, and the exhaust gas temperature before the bag filter dust collector was 160 to 175 ° C. The discharged fly ash was collected 1 hour after the start of operation, and then collected every hour, and evaluated based on the Pb elution amount.

As can be seen in Table 2, about 4 hours after the start of incinerator operation, fly ash that does not contain heavy metal immobilization treatment chemical remaining in the bag filter dust collector and heavy metal immobilization treatment chemical contained It is clear that fly ash substituted with ash was discharged, and the fly ash after 4 hours was mixed with Pb elution amount below the detection limit (0.05 mg / l) and processed without using a kneader. Became.

  The treatment agent for immobilizing heavy metals of the present invention is used by mixing with various materials according to the purpose of use such as improvement of solidification strength, improvement of dispersibility in silos, and improvement of physical adsorption performance. The test was conducted using fly ash discharged from a bag filter dust collector of a stoker-type incinerator, adding 10% and 20% of various materials to the fly ash weight, and adding 40% water. The amount of Pb elution was determined by the specified dissolution test method. Table 3 below shows the effect of suppressing the amount of Pb eluted from various materials and examples of the purpose of use.

飛灰試料（薬剤無添加）：ｐＨ＝12.7 Ｐｂ溶出量＝329mg/l
検定方法：環境庁告示第１３号法

Fly ash sample (no chemical added): pH = 12.7 Pb elution amount = 329 mg / l
Examination method: Environmental Agency Notification No.13

  The heavy metal immobilization treatment chemical for fly ash of the present invention is used by mixing various materials shown in Table 3 according to the purpose of use even in the case of processing using a mixing and kneading apparatus or when using a mixing and kneading apparatus. Depending on the situation, the application will be further expanded. Improvement in dispersibility is often used for the purpose of preventing bridging in stock silos, and the addition ratio is generally in the range of 0.5 to 5%. The physical adsorption performance is improved by adsorbing and fixing mercury (Hg), dioxin (DXN) or PCB. The addition ratio also varies due to the content and elution amount of the target substance. Strength improvement is often performed to prevent scattering when transported to a landfill after heavy metal immobilization treatment, and generally inexpensive polyland cement is used.

Overview of stalker-type incinerator Method for immobilizing heavy metals in fly ash using existing stalker-type mixing and kneading equipment)

Explanation of symbols

1 Waste input hopper 2 Stoker-type incinerator 3 Incineration residue cooling water tank 4 Secondary combustion chamber 5 Gas cooling chamber 6 Exhaust gas treatment chemical silo 6A Heavy metal fixation chemical exhaust gas treatment chemical silo 7 Bag filter type dust collector 8 Storage silo 9 Drug silo for immobilization of heavy metals 10 Mixing and kneading device 11 Water tank 12 Pump for tap water 13 Fly truck 14 Incentive blower 15 Chimney 16 Fly ash treatment bunker pit

Claims (5)

In waste incineration facilities, treatment agents that are injected into flue exhaust gas and react with toxic heavy metals are aluminum hydroxide, magnesium hydroxide, sulfate, silicate, phosphate carbonate with a decomposition temperature of 150 ° C or higher. Treatment that uses one or more selected from inorganic compounds as a main constituent and reacts with heavy metals contained in fly ash to produce sparingly soluble hydroxides, sulfates, silicates, phosphates, and carbonates Method. The treating agent according to claim 1 reacts with a heavy metal contained in fly ash as one of at least one selected from a dithiocarbamic acid salt or a metal salt organic compound having a decomposition temperature of 150 ° C. or higher, and hardly soluble. A processing method for producing a compound. Each of the treatment agents according to claim 1 and claim 2 is special slaked lime, highly reactive slaked lime, dolomite, sodium hydrogen carbonate, calcium carbonate or dioxin used for removing exhaust gas from waste incineration equipment. It can also be used by mixing with at least one of powdered activated carbon used for adsorption or diatomaceous earth or pearlite used for protecting filter cloth type dust collectors. The treatment agent mixed in claim 3 is sent into the exhaust gas by using a silo in the exhaust gas treatment device in the waste incineration facility, a cutting device, and an injection device, together with hydrogen chloride, sulfur oxide, dioxin, etc. in the exhaust gas, A heavy metal immobilization method in which heavy metals contained in fly ash in exhaust gas are treated as insoluble compounds. The treatment agent according to claim 1 and claim 2 is mixed with at least one selected from various cements, solidification materials, gypsum, diatomaceous earth, perlite, activated carbon, metal powder, metal salt compound, reducing agent, oxidizing agent, and the like. It can also be used for the purpose of improving solidification strength, dispersibility, physical adsorption performance and the like.

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