JP4289673B2 - Heavy metal elution inhibitor and heavy metal elution prevention method and apparatus using the same - Google Patents

Description

  The present invention relates to prevention of elution of heavy metals, and in particular, incineration fly ash and incineration ash discharged from incineration plants such as municipal waste, industrial waste, sewage sludge (hereinafter referred to as “incineration fly ash” together) And a heavy metal elution prevention method and apparatus using the agent.

  Incineration fly ash generated during the incineration of industrial waste and municipal waste is finally landfilled, but these incineration fly ash is lead, cadmium, hexavalent chromium, mercury, arsenic, selenium, etc. Because it contains heavy metals that are harmful to human bodies, it must be fixed so that heavy metals do not elute by rainwater after landfilling. Regarding the immobilization of incineration fly ash, it is obliged to carry out any of the following methods: “cement solidification method”, “extraction method with acid or other solvent”, “melt fixation”, or “chemical addition method”. Yes. Among these, the “drug addition method” has been studied in various ways because it is generally easier to handle and handle than other methods. The chemical addition method is a method in which a predetermined amount of water, a chemical and incineration fly ash are kneaded and reacted to fix harmful heavy metals. As the chemical used for this purpose, a liquid chelate chemical is generally used. This liquid chelate agent is added in a large amount when the amount of elution of heavy metals such as molten fly ash is large. Since the liquid chelate agent is in a liquid state, if the amount added is increased, the treated ash loses its strength and is difficult to handle. In such a case, it is necessary to further use cement in order to give the treated ash strength, but there is a problem that the facility becomes complicated. Furthermore, since the liquid chelate agent has a strong alkalinity in the liquid, sufficient caution is required for handling. Furthermore, the liquid chelate agent has a problem that it causes water pollution when it leaks out, and sufficient care is required in handling.

As a solution to such a problem, in Japanese Patent Application Laid-Open No. 2003-301165, a powdery dithiocarbamate that is hardly soluble in water is used, and this is mixed with an object to be treated such as incineration fly ash. A method for preventing elution of heavy metals from the object to be treated has been proposed. However, this method is sufficient for harmful heavy metals such as lead, cadmium, and mercury, but is not sufficient for difficult-to-process heavy metals such as arsenic, selenium, and hexavalent chromium. As a method for treating difficult-to-treat heavy metals such as arsenic, selenium and hexavalent chromium, a method using an iron salt has been proposed. For example, in Japanese Patent Application Laid-Open No. 2004-209372, heavy metals such as hexavalent chromium, arsenic, and selenium are efficiently immobilized by adding a ferrous salt having a reducing property together with an inorganic flocculant such as a sulfate band. However, the effect of inhibiting elution of heavy metals such as lead that is eluted at a high concentration, such as molten fly ash, has not been sufficient. In addition, as a method for treating ash containing lead, hexavalent chromium, arsenic, and selenium, a method of adding a ferrous compound and a phosphate heavy metal fixing agent has been proposed. The elution suppressing effect on heavy metals is not sufficient, and there is a problem that the strength of the treated ash is lost as a result of increasing the amount of addition.
JP2003-301165A JP 2004-209372 A

  The present invention solves the above-mentioned problems of the prior art, and simultaneously processes heavy metals such as arsenic, selenium, hexavalent chromium, and lead eluted at a high concentration, which are difficult-to-process heavy metals, with a small addition amount and simple equipment. It is an object of the present invention to provide an agent capable of effectively preventing elution of heavy metals by treatment, and a method and apparatus for preventing elution of heavy metals using the agent.

In order to solve the above problems, the present invention, the incineration fly ash for heavy metals, which comprises a mixture of zinc or iron salt of a poorly soluble powdery dithiocarbamate and powdered ferrous salt in water This is an elution inhibitor .
Further, in the present invention, a mixture of zinc or iron salt of powder form dithiocarbamate slightly soluble in water and powdered ferrous salt, and water was added to the incineration fly ash containing heavy metals, the kneading and heavy metals elution prevention method, wherein, further, the incineration fly ash containing heavy metals, and a mixture of zinc or iron salt of powder form dithiocarbamate slightly soluble in water and powdered ferrous salt, and water An apparatus for preventing the elution of heavy metals, comprising an adding means for adding and a kneader for kneading the additive .
Wherein in the elution prevention method and apparatus, zinc or iron salt of powder form dithiocarbamate slightly soluble in the water to be added to the incineration fly ash (hereinafter, abbreviated as dithiocarbamate) and powdered ferrous salt (hereinafter, iron salts abbreviated) is cement, porous aluminum silicate, after mixing with one or more selected from porous silicon dioxide or silica sand, it can be added to the incineration fly ash.

According to the present invention, by adding dithiocarbamate and iron salt that are sparingly soluble in water to incineration fly ash, elution of heavy metals can be suppressed with a small addition amount even when the amount of elution of heavy metals is large. As in the case of using a liquid chelate agent, there is no problem that the added amount is increased and the strength of the treated ash is lost. For this reason, it is not necessary to use cement for imparting strength to the treated ash, and the equipment can be simplified. Furthermore, in the conventional treatment, it was difficult to treat heavy metals such as lead, cadmium and mercury and difficult-to-treat heavy metals such as arsenic, selenium, and hexavalent chromium at the same time. It becomes possible. That is, according to the present invention, heavy metals such as arsenic, selenium, hexavalent chromium and lead eluted at a high concentration, which are difficult to process, can be simultaneously processed with a small amount of addition with simple equipment.
Furthermore, according to the present invention, the effect of suppressing elution of heavy metals is enhanced as compared with the case where dithiocarbamate or iron salt, which is hardly soluble in water, is added alone.

  Hereinafter, various embodiments of the present invention will be described by taking incineration fly ash treatment as an example. According to the present invention, by using dithiocarbamate and iron salt, which are sparingly soluble in water, as a heavy metal elution inhibitor, preferably in the form of powder, and mixing them with an object to be treated such as incineration fly ash. The elution of heavy metals from the object to be treated can be effectively prevented. In the present invention, “slightly soluble in water” means that the solubility in water is less than 5% by weight, particularly preferably less than 1% by weight.

In the present invention, the water-insoluble dithiocarbamate that can be used as a heavy metal dissolution inhibitor includes zinc salts and iron salts of dithiocarbamic acid in a solid state at room temperature. The dithiocarbamic acid in the present invention can be easily obtained by reacting an amine with carbon disulfide. Examples of amines that can be used in this reaction include low amines such as methylamine, ethylamine, propylamine, and butylamine. Low molecular weight secondary amine such as molecular weight primary amine, dimethylamine, diethylamine, dipropylamine, dibutylamine, ethylenediamine, 1,3-propylenediamine, 1,4-butanediamine, hexamethylenediamine, octamethylenediamine, diethylenetriamine, Polyamines such as triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and iminobispropylamine, polyamines such as polyethyleneimine and polyallylamine, pyrrolidine, piperidine and piperazine Or a cyclic amine such as hexamethylene imine. Of these dithiocarbamic acids derived from these amines and salts thereof, those which are in a solid state at room temperature and hardly soluble in water can be preferably used.

Examples of iron salts in the present invention include ferrous sulfate (monohydrate, heptahydrate, etc.), ferrous chloride (tetrahydrate, etc.), ferrous chloride such as ammonium sulfate ferrous hexahydrate. The salt can be used preferably in the solid state, in particular in powder form .

In the present invention, the form of the heavy metal elution inhibitor when adding the heavy metal elution inhibitor to the object to be treated is as follows: (1) Powdered dithiocarbamate and powdered iron salt which are hardly soluble in water are added (2) Add powdered dithiocarbamate and powdered iron salt that are sparingly soluble in water separately, (3) Add powdered dithiocarbamate and liquid iron salt that are sparingly soluble in water separately, (4) If necessary, powdery dithiocarbamate and / or powdered iron salt which is hardly soluble in water, porous aluminum silicate such as cement, activated clay, acidic clay, porous silicon dioxide, silica sand The method of adding after diluting by mixing with suitable powder etc. etc. is mentioned.
Among these, according to the form (1), since one-agent treatment is possible, a plurality of medicine reservoirs are not required, and not only the equipment can be simplified, but also the medicine can be easily managed.

  In the present invention, powder is defined as having an average particle size of 1 mm or less. The ratio of the powdered dithiocarbamate to the powdered dithiocarbamate and iron salt can be set as appropriate according to the heavy metal elution characteristics of the object to be treated. The ratio of the powdery dithiocarbamate salt hardly soluble in water and the iron salt to the powdered dithiocarbamate salt is 1 to 99% by weight, more preferably 10 to 90% by weight. If it is less than 1% by weight, the effect of preventing the dissolution of heavy metals such as lead eluting at a high concentration becomes insufficient, and if it exceeds 99% by weight, the effect of preventing the dissolution of selenium, arsenic, hexavalent chromium, etc. becomes insufficient. .

In the present invention, the addition rate of the heavy metal dissolution inhibitor (dithiocarbamate and iron salt which is hardly soluble in water) to the object to be treated is 0.05% by weight or more, more preferably 1% or more as dithiocarbamate which is hardly soluble in water. % By weight or more.
In addition, when kneading by adding water, the amount of water to be added varies depending on the properties of the object to be treated, the amount of heavy metal dissolution inhibitor added, etc., but generally 10 to 60 with respect to the object to be treated. It is preferable that it is weight%. As for the temperature at the time of knead | mixing the to-be-processed objects, such as incineration fly ash, adding the heavy metal elution inhibitor concerning this invention, 0-100 degreeC is preferable. The kneading time is not particularly limited, but generally 5 to 30 minutes is preferable. The kneaded product may be naturally dried. However, the effect of preventing heavy metals from leaching can be promoted by positively applying humidity to the kneaded product under atmospheric contact and heat curing.

  Hereinafter, the flow configuration diagram of the present invention shown in FIG. 1 will be used. The incineration fly ash which is a target in the present invention is not particularly limited, but is collected by incineration fly ash (EP, BF, multi-cyclone, etc.) discharged from incineration facilities for municipal waste, industrial waste, and sewage sludge. ). Usually, the dust 1 is filtered by the dust collector 2, and the incineration fly ash separated by the dust collector 2 is stored in the storage silo 3. The incineration fly ash 5 is weighed from the storage silo 3 by the weight meter 4 and sent to the kneader 6 where the humidified water from the humidified water tank 11 and the heavy metal elution inhibitor from the storage tank 12 are removed. Is added. The kneaded material that has come out of the kneader is sent to the treated ash pit 10 by the carry-out conveyor 9. Usually, the kneaded material which came out of the kneading machine is cured (dried and solidified) until it is carried out from the carry-out conveyor and the ash pit 10. In the present invention, the kneaded product (or kneaded molded product) humidified at the time of kneading is not only brought into contact with the atmosphere on the carry-out conveyor 9 or the treated ash pit 10 and then naturally dried, but the kneaded product is actively brought into contact with the atmosphere. The effect of preventing heavy metal elution can be promoted by applying humidity and curing by heating.

The following examples illustrate the invention.
Examples 1-7 and Comparative Examples 1-7
Test method The test method is as follows.
(1) Table 1 shows the properties of the bag filter fly ash used for the sample.

(2) Heavy metal elution test 40% water and a predetermined amount of chemicals were added to the sample, kneaded sufficiently, and then cured under predetermined conditions for 24 hours. Thereafter, the sample was pulverized to 5 mm or less, and a heavy metal dissolution test was conducted based on the Environmental Agency Notification No. 13 test method.
(3) Additives ○ Zinc diethyldithiocarbamate (powder)
○ Diethyldithiocarbamic acid iron salt (in powder form)
○ Potassium diethyldithiocarbamate (concentration 50% aqueous solution)
○ Ferrous sulfate monohydrate (in powder form)
○ Ferrous chloride solution: Fe content 10% by weight
(4) Dissolution test results The dissolution test results are shown in Table 2.

* 実施例１、２、３、４についてはジエチルジチオカルバミン酸塩と鉄塩を混合した状態で焼却飛灰に添加した。
** 参考例１、２、３については、焼却飛灰に鉄塩を添加し混合した後、ジエチルジチオカルバミン酸塩を添加した。
*** 実施例５、６については、ジエチルジチオカルバミン酸亜鉛塩と硫酸第１鉄１水和物とセメントを混合した状態で焼却飛灰に添加した。

* Examples 1, 2 , 3 , and 4 were added to incinerated fly ash in a mixed state of diethyldithiocarbamate and iron salt.
** For Reference Examples 1 , 2 , and 3 , iron salt was added to incineration fly ash and mixed, and then diethyldithiocarbamate was added.
*** For Examples 5 and 6 , zinc diethyldithiocarbamate, ferrous sulfate monohydrate and cement were added to the incinerated fly ash in a mixed state.

In Comparative Example 1 in which only zinc insoluble diethyldithiocarbamate was added to water and Comparative Example 2 in which only iron insoluble diethyldithiocarbamate was added to water, lead elution could be suppressed to less than the landfill reference value. However, elution of hexavalent chromium, arsenic, and selenium could not be suppressed to less than the landfill standard value. In Comparative Example 4 in which only ferrous sulfate monohydrate was added, elution of hexavalent chromium, arsenic and selenium could be suppressed to less than the landfill standard value, but lead elution was suppressed to less than the landfill standard value. I couldn't. On the other hand, Examples 1, 2 , and 4 were added with diethyl dithiocarbamate zinc salt insoluble in water and ferrous sulfate monohydrate, and zinc diethyldithiocarbamate insoluble in water and ferrous chloride solution were added. the reference example 1, water was added diethyl dithiocarbamate iron salt insoluble and the ferrous monohydrate sulfate example 3, in reference examples 2 and 3, lead, hexavalent chromium, arsenic, elution of selenium It was possible to suppress to less than the landfill standard value.

In the case of potassium diethyldithiocarbamate (50% aqueous solution), even when 10 w / w% was added, the elution concentration of lead could not be suppressed to less than the landfill reference value (Comparative Example 5), but according to the present invention, 4 w / w %, The elution of lead, hexavalent chromium, arsenic and selenium could be suppressed to less than the landfill standard value (Example 2 ).
Example 3 in which diethyldithiocarbamate iron salt and ferrous sulfate monohydrate were added to the incineration fly ash in a mixed state, after adding ferrous sulfate monohydrate to the incineration fly ash and mixing, Compared with Reference Example 3 to which iron diethyldithiocarbamate was added, the elution suppression effect of heavy metals was high.

The flow block diagram which shows an example of the elution prevention apparatus of this invention.

Explanation of symbols

1: Soot and dust, 2: Bag filter (dust collector), 3: Storage silo, 4: Weight meter, 5: Fly ash, 6: Kneading machine, 9: Unloading conveyor, 10: Treated ash pit, 11: Humidified water tank, 12: Heavy metal dissolution inhibitor storage tank

Claims (4)

Incineration fly ash for heavy metal elution preventive agent which comprises a mixture of zinc or iron salt of a poorly soluble powdery dithiocarbamate and powdered ferrous salt in water. A mixture of sparingly soluble powdered zinc or iron salt of dithiocarbamic acid and powdered ferrous salt in water, and water was added to the incineration fly ash containing heavy metals, heavy metals elution, which comprises kneading Prevention method. Powdered zinc or iron salt of dithiocarbamic acid and powdered ferrous salt sparingly soluble in water, a mixture of cement, a porous aluminum silicate, one or more selected from porous silicon dioxide or silica sand, and water It was added to the incineration fly ash containing heavy metals, heavy metals elution preventive way to said kneading to Rukoto. The incineration fly ash containing heavy metals and kneading the mixture of zinc or iron salt of powder form dithiocarbamate slightly soluble in water and powdered ferrous salt, and adding means for adding the water, the additives An apparatus for preventing elution of heavy metals, comprising a kneader .

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