JP2003181411A - Heavy metal elution preventing agent and treatment method of contaminated medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heavy metal elution preventing agent which efficiently prevents the elution of heavy metals from a contaminated medium such as incineration fly ash including the heavy metal and to provide a treatment method of contaminated medium using the same. <P>SOLUTION: This treatment method of contaminated medium features that the contaminated medium is mixed with powdery calcium hydroxide and, thereafter, is kneaded with water. Further, this treatment method also relates to treatment equipment of fly ash and incineration ash which is provided with a dust collector for treating the waste gas containing the fly ash and incineration ash discharged from an incineration furnace and separating the fly ash and incineration ash contained therein, a contaminated medium treatment agent adding device which adds a contaminated medium treating agent containing the powdery calcium hydroxide to the fly ash and incineration ash discharged from the dust collector and a kneader for kneading the fly ash and incineration ash mixed with the powdery calcium hydroxide with water. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heavy metal elution preventive agent and a method for treating a pollutant medium using the same. According to the heavy metal elution inhibitor and the treatment method of the present invention, lead, cadmium, which are discharged from various incinerators such as a refuse incinerator,
Contamination media such as fly ash and incineration ash (in this specification, these are collectively referred to as "incineration fly ash") containing harmful heavy metals such as arsenic, selenium, chromium, mercury, zinc and copper in a high concentration Elution of heavy metals from the can be prevented.

[0002]

2. Description of the Related Art Incineration treatment is indispensable for the treatment of general waste, industrial waste, sludge from sewage treatment plants, waste from human waste treatment plants, etc. from the viewpoint of weight reduction. When incinerating these wastes, incinerator fly ash is generated from various incinerators such as refuse incinerators, but this incinerator fly ash contains lead, cadmium,
Heavy metals harmful to the human body such as arsenic, selenium, chromium, mercury, zinc and copper are contained in high concentration. When they come into contact with environmental water such as rainwater, they elute and pollute soil, groundwater, rivers, seawater and the like.

Therefore, incineration fly ash is designated as a specially controlled industrial waste, and it is obliged to dispose of it after subjecting it to the following elution preventing treatment of heavy metals. (1) A method of stabilizing heavy metals with an acid or other solvent. (2) A method of melting and solidifying incineration fly ash containing heavy metals. (3) A method of solidifying incineration fly ash containing heavy metals with cement. (4) A method of treating incineration fly ash containing heavy metals with a chemical.

Among the above methods, the methods (3) and (4) have been put into practical use in recent years.

[0005]

However, the above conventional method has the following problems. (a) The melt solidification method requires a treatment temperature of 1200 to 1400 ° C., so that the amount of energy is large and the treatment cost is also high.

(B) In the cement solidification method, lead is liable to be leached out at a high pH value, which is not sufficient as a leaching prevention measure. Also, since cement is added, the volume of the treated material cannot be reduced.

(C) In the method of treating incineration fly ash containing heavy metals with a chemical, the liquid chelating agent used for this purpose is expensive, resulting in high cost. In particular, when the amount of heavy metal is large, the amount of expensive chelating agent used increases and the cost increases.

(D) By chemical treatment with a chelating agent or the like, it is possible to insolubilize cationic metals such as lead and cadmium, but it is difficult to insolubilize anionic metals such as arsenic and selenium.

(E) If the incineration fly ash is acidic, heavy metal ions such as lead, cadmium and arsenic cannot be insolubilized by the chelating agent alone. (f) The chelating agent has a high heavy metal immobilizing ability, but has a problem that long-term storage stability can be sufficiently expected.

The present invention solves the problems of these conventional methods and efficiently prevents the elution of heavy metals from contaminated media such as incinerated fly ash containing heavy metals, and A method for treating a contaminated medium using the same is provided.

[0011]

In order to achieve the above object, the present invention is characterized in that a contaminated medium such as incinerated fly ash is mixed with powdered slaked lime and then kneaded with water. Regarding the processing method of. The present invention also provides a heavy metal elution inhibitor that can be used in such a treatment method. That is, another embodiment of the present invention relates to a heavy metal elution preventive agent characterized by being composed of powdered slaked lime.

In the present invention, the contaminated medium is
General waste, industrial waste, sludge from sewage treatment plants, sludge from human waste treatment plants, etc., exhaust gas containing heavy metals discharged when incinerated in an incinerator, incinerated ash containing heavy metals, fly ash, Alternatively, it refers to soil containing heavy metals. In the following description, incineration fly ash will be described as a typical example.

[0013]

According to the present invention, heavy metals in a contaminated medium such as incinerated fly ash can be insolubilized.
Heavy metals that can be insolubilized by the present invention include lead, cadmium, arsenic, selenium, chromium, mercury, zinc, copper and the like. These heavy metals volatilized during incineration are contained in the incinerated fly ash, and if the incinerated fly ash is directly landfilled, it will be eluted as heavy metal ions by rainwater or the like.

Among these heavy metals, cadmium, lead,
Cationic metals such as mercury can be insolubilized by using a chelating agent having a functional group such as a dithiocarbamic acid group. However, arsenic exists in water as anions such as arsenate ion and arsenite ion, and selenium exists as anion such as selenite ion, so that it is difficult to insolubilize it with a chelating agent.

According to the present invention, a powdery slaked lime is brought into contact with a contaminated medium such as incineration fly ash containing these heavy metals, and then kneaded with water, whereby all of these heavy metals are insoluble. By converting the compound into a compound, it is possible to efficiently and simultaneously prevent the elution of all target heavy metals. According to the research conducted by the present inventors, it has been found that the slaked lime added to the incineration fly ash for this purpose needs to be in the form of powder, and the effect of insolubilizing heavy metals cannot be obtained in the form of slurry. This is considered to be because the use of powdered slaked lime causes an adsorption reaction to the undissolved portion of the slaked lime powder, which promotes insolubilization. Further, slaked lime in the form of slurry is more likely to absorb carbon dioxide gas in the air than that in the form of powder, and it is considered that the elution suppressing effect of heavy metals cannot be obtained even if the addition amount is increased.

The incineration fly ash includes acid fly ash and alkaline fly ash. Acid fly ash is a soot dust containing heavy metals collected in a dust collector through a flue after incineration. Alkaline fly ash is sprayed with slaked lime to protect the dust collector and improve the detachability of dust when it is collected by the dust collector through the flue after incineration.

In order to prevent heavy metal elution of acidic fly ash, heavy metal can be insolubilized by adding powdered slaked lime to fly ash and kneading with water. In this case, 5 to 20% by weight, more preferably 8 to 15% by weight, of powdered slaked lime is added to the acidic fly ash, and the anion of arsenic or selenium is reacted with excess calcium ion,
Elution of arsenic and selenium can be prevented by producing a sparingly soluble calcium salt such as calcium arsenate, calcium arsenite, calcium selenite, and calcium selenite. It is considered that the reaction for producing the sparingly soluble calcium salt proceeds as shown in the following equation.

[0018]

[Formula 1]

Further, by adding slaked lime to the acidic fly ash, the pH of the incineration fly ash eluate is increased from 4 to 4.5 to 6 to 12.
It is possible to prevent elution of lead, cadmium, etc. other than arsenic and selenium. If the amount of slaked lime added to the acid fly ash is less than 5% by weight, insolubilization of arsenic and the like due to the reaction of the above formula cannot be achieved,
Furthermore, since the pH does not rise, lead and cadmium are eluted. On the contrary, if the added amount of slaked lime exceeds 20% by weight,
The pH of the incineration fly ash eluate exceeds 12, leading to the elution of lead. For example, the insolubilization reaction of cadmium and lead is shown in the following formula. Regarding cadmium, a sparingly soluble salt is produced in the alkaline region according to the following formula, and lead is an amphoteric metal, and it is insolubilized as a hydroxide in the neutral region according to the formula below, but is redissolved in the alkaline region.

[0020]

[Formula 2]

On the other hand, when the alkaline fly ash is treated to prevent heavy metal elution according to the present invention, arsenic, selenium and the like can be insolubilized by adding powdered slaked lime to the fly ash. Most of the calcium ions in the alkaline fly ash are salts such as calcium chloride, and few calcium ions exist in the form of ions that can be used for insolubilizing arsenic and selenium.
Therefore, it is possible to insolubilize arsenic and selenium by newly adding slaked lime powder and kneading with water. However, when the pH of the incineration fly ash eluate exceeds 12 due to the addition of slaked lime, lead is eluted as described above. In that case, as described below, acid is added to adjust the pH. It is preferable to prevent lead elution by adjusting or adding a chelating agent.

In the present invention, when powdered slaked lime is added to incineration fly ash, exhaust gas containing incineration fly ash discharged from various combustion furnaces is subjected to dust collection processing, and incineration fly ash discharged from the dust collector is collected. It can be stored in an ash hopper and powdered slaked lime can be added to it. In this case, it is preferable to add slaked lime to incineration fly ash at a temperature in the range of 30 to 180 ° C, preferably 50 to 120 ° C. That is, the powdered slaked lime can be added at a temperature at which the incineration fly ash discharged from the dust collector is naturally air-cooled. The contact time between the incinerated fly ash and the slaked lime is not particularly limited, and it is usually retained in the ash hopper for about 1 to 3 days.

According to the method of the present invention, heavy metals can be insolubilized by mixing incineration fly ash and powdered slaked lime and then kneading by adding water. As the kneader used for this purpose, a kneader known in the art, such as an extrusion granulator or a tumbling granulator, can be used. The kneading is performed at 20 ° C to 80 ° C, more preferably 3
It is preferable to carry out at a temperature of 0 to 70 ° C. until the mixture is uniformly mixed. If the kneading temperature is lower than 20 ° C., the kneading machine needs to be cooled during operation, which leads to an increase in cost. On the other hand, if it exceeds 80 ° C., the water added to the incineration fly ash is evaporated, which is not preferable. The amount of water added to the incineration fly ash is preferably 10 to 50% by weight, preferably 20 to 30% by weight, based on the incineration fly ash, and appropriate operation is possible within this range. If the amount of water added is less than 10% by weight, the ash after the kneading treatment may be scattered, while if it exceeds 50% by weight, the amount of water is too large and it is difficult to mold the ash for disposal. Therefore, it is not preferable.

In the present invention, a water-soluble alkaline agent such as sodium hydroxide or potassium hydroxide, a chelating agent, or phosphorus is added according to the pH of the eluate of incinerated fly ash after adding powdered slaked lime to the incinerated fly ash. Elution of all heavy metals in the neutral range can be suppressed by further adding an aqueous solution containing at least one aqueous acid solution such as acid or sulfuric acid. That is, with respect to incineration fly ash in which leaching of arsenic, selenium and the like is suppressed by adding slaked lime powder, an acid / alkali is added to adjust the pH of the eluate to a neutral region to a weak alkaline region, or a chelate. By adding the agent, insolubilization of lead and cadmium in fly ash can be promoted.

For example, when the incineration fly ash to be treated is acidic fly ash, a powdery slaked lime is added to the incineration fly ash, and then a water-soluble alkaline agent is added to the incineration fly ash to obtain the incineration fly ash eluate. It is possible to raise the pH efficiently and suppress the elution of heavy metals more efficiently. As the water-soluble alkaline agent used for this purpose, sodium hydroxide, potassium hydroxide, sodium carbonate and the like can be used.

Further, by adding powdered slaked lime to acidic fly ash or alkaline fly ash and then adding a chelating agent, cation metals such as cadmium and lead can be efficiently eluted. As the chelating agent used for this purpose, a dithiocarbamic acid-based or dithiocarboxy-based chelating agent can be used.

Furthermore, after adding powdered slaked lime to alkaline fly ash and then adding an acidic aqueous solution, the pH of the eluate of the treated ash can be lowered and the elution of heavy metals can be efficiently suppressed. As the acidic aqueous solution used for this purpose, an aqueous solution of phosphoric acid, sulfuric acid or hydrochloric acid can be used. Above all, it is effective to use phosphoric acid that forms a salt that is hardly soluble with heavy metals.

In the method of the present invention, when the acidic aqueous solution or the water-soluble alkaline agent is added after the powdered slaked lime is added to the incinerated fly ash, the addition amount of the acidic aqueous solution or the water-soluble alkaline agent is the incinerated fly ash after the addition. The amount of the eluate is preferably 6-12. This is because the suppression of elution of lead, etc. is achieved by setting the pH within this range as described above, so by controlling the pH of the incineration fly ash eluate within this range, all target heavy metals This is because it is possible to prevent the elution of Therefore, the proper addition amount of the acidic aqueous solution or the water-soluble alkaline agent varies depending on the pH of the incineration fly ash eluate to be treated and the addition amount of powdered slaked lime. Further, when a chelating agent is added to the incineration fly ash, if the amount of the chelating agent added is 1% by weight or more based on the incineration fly ash, the heavy metal elution suppressing effect is increased.

As described above, in the present invention, incineration fly ash is collected in the dust collector discharged from the combustion furnace,
Powdered slaked lime can be added to what is stored in the ash hopper. As a result, it is possible to control fluctuations in the properties of the incineration fly ash, and to realize stable treatment of the incineration fly ash. Further, as a result, the curing period of the treated fly ash can be shortened, so that the incinerated fly ash can be efficiently treated by improving the treatment capacity of the incinerator and the like. Further, in the present invention, it is more preferable to add powdered slaked lime to the incineration fly ash at the outlet of the dust collector. As a result, the incinerated fly ash and slaked lime can be sent to the ash hopper in a more evenly mixed state, and the incinerated fly ash can be stably maintained without being affected by the operating conditions and temperature conditions of the incinerator and the flue. The heavy metal elution prevention treatment can be performed.

The present invention also relates to a chemical agent used for preventing elution of heavy metals from polluting media such as incineration fly ash described above. That is, another aspect of the present invention relates to a heavy metal elution preventive agent for incineration fly ash, which comprises powdered slaked lime.

Furthermore, the present invention also provides an apparatus used for performing the heavy metal elution prevention treatment of the contaminated medium described above. That is, still another aspect of the present invention is a dust collector for treating exhaust gas containing fly ash and incinerated ash discharged from an incinerator to separate fly ash and incinerated ash contained therein; A device for adding a polluting medium treating agent containing powdered slaked lime to fly ash and incinerated ash discharged from a dust device; a fly ash and incinerated ash mixed with powdered slaked lime are mixed with water The present invention relates to a processing device for fly ash and incineration ash, which comprises:
Still another aspect of the present invention is further characterized by further comprising a chemical addition device for adding an aqueous solution containing at least one of a water-soluble alkaline agent, a chelating agent, and an aqueous acid solution to fly ash and incineration ash. It also relates to processing equipment for fly ash and incineration ash.

The configuration of the fly ash and incineration ash processing apparatus according to the present invention will be described below with reference to the drawings. The following description relates to a specific example of the apparatus for treating fly ash and incineration ash according to the present invention, and the present invention is not limited to this.

FIG. 1 shows an outline of an incineration facility incorporating a fly ash and incineration ash treatment apparatus according to the present invention.
In FIG. 1, 1 is an incinerator, 2 is a gas cooling tower, 3 is a flue, 4 is a dust collector, 5 is an ash hopper, 6 is a contaminated medium treating agent hopper, 7 is a chemical tank, and 8 is a kneader. . The exhaust gas discharged from the incinerator 1 has a high temperature of 900 ° C. to 950 ° C., but is usually cooled to an appropriate temperature by the gas cooling tower 2. The exhaust gas cooled in the cooling tower 2 is sent to a dust collector 4 through a flue 3 optionally provided, where it is subjected to dust collection processing, incinerator fly ash is separated from the exhaust gas, and sent to an ash hopper 5. .

In the apparatus shown in FIG. 1, a hopper 6 accommodating the polluting medium treating agent according to the present invention is arranged, and the polluting medium treating agent is added to the outlet of the dust collector 4 or the ash hopper 5 through a pipe. To be done. In the present invention, the contaminated medium treating agent can be added at any place from the outlet of the dust collector to the inlet of the kneader. A chemical tank 7 containing a water-soluble alkaline agent, an aqueous acid solution, a chelating agent, or the like is also connected, and similarly, these chemicals are appropriately added to incineration fly ash.

The incineration fly ash mixed with the contaminated medium treating agent and various chemicals is then guided to the kneading machine 8, where water is added through the pipe 9 and kneaded. By this kneading step, elution preventing treatment of heavy metals is performed. The compound derived from the pollutant treatment agent compound (which functions as a heavy metal trapping component) produced by the decomposition reaction of dioxins and the heavy metals in the incineration fly ash react with each other to produce a water-insoluble compound. This prevents elution of heavy metals from the fly ash. The incineration fly ash, which is kneaded in the kneading machine 9 and the heavy metals are converted into water-insoluble compounds, is discarded to the outside through the discharge pipe 10, or
After being cured for a certain period of time, it is discharged to the outside.

On the other hand, the exhaust gas from which the incineration fly ash has been separated and removed in the dust collector 4 is discharged outside the system through the IDF (Induced Draft Fan) 21 and the chimney 22.

[0037]

The present invention will be described more specifically by the following examples. The following examples are illustrative of preferred embodiments of the invention and are not limiting of the invention.

In the following examples, the elution concentration of heavy metals was measured according to the Environmental Agency Notification No. 13 method. Example 1 As a sample of incineration fly ash, acid fly ash collected from the melting furnace of the sewage sludge incinerator was used. 30 g of humidified water was added to 30 g of the incinerated fly ash sample, and the mixture was kneaded for about 1 minute and cured for 1 day. Take 30 g of the cured sample in a beaker and add distilled water 30
A dissolution test of heavy metals was performed by adding 0 mL. The results of the dissolution test are shown in Table 1 together with the landfill standard values stipulated by the "Prime Minister's Office Ordinance (Prime Minister's Office Ordinance No. 5) that defines the criteria for determining industrial waste including metals and the like".

[0039]

[Table 1]

Next, 30 g of the incinerated fly ash sample was taken and 5 to 25% by weight of powdered slaked lime (per dry incineration fly ash sample, in the following examples, "% by weight" is the same standard). Was added. 30% by weight of humidified water was added to carry out a kneading treatment, followed by curing for 1 day. After curing, 30 g of the sample was placed in a beaker and a heavy metal dissolution test was performed. Table 2 shows the results of the elution test and the pH of the sample eluate after the treatment.

Comparative Example 1 The same incineration fly ash sample as in Example 1 was used, 5 to 25% by weight of calcium hydroxide slurry was added thereto, and kneading treatment and curing were carried out in the same manner as in Example 1, and then heavy metal was added. Dissolution test was performed. The results are shown in Table 2.

[0042]

[Table 2]

As is clear from Table 2, in Comparative Example 1, the elution concentrations of the three heavy metals of lead, cadmium and arsenic could not be made less than the landfill standard value under most conditions. On the other hand, in Example 1 of the present invention, the elution concentration of three types of heavy metals could be made less than the landfill standard value in a wide pH range.

Example 2 To the incineration fly ash sample of Example 1, 5% by weight of powdered slaked lime was added, and further sodium hydroxide was added as an alkaline chemical and dithiocarbamate as a chelating agent. Similarly, after carrying out kneading treatment and curing, an elution test of heavy metals was conducted. The results are shown in Table 3.

Comparative Example 2 An experiment was conducted in the same manner as in Example 2 except that slurry slaked lime was used instead of powdered slaked lime. The results are shown in Table 3.

[0046]

[Table 3]

As is clear from Table 3, in Comparative Example 2, elution of heavy metals was confirmed. On the other hand, in Example 2 of the present invention, by adding powdered slaked lime to incineration fly ash and further adding an alkali agent / chelating agent, the elution concentration of all heavy metals can be made less than the landfill standard value. It was Especially by raising the pH to near neutral range,
It was very effective in suppressing the elution of cadmium, which is stable in the alkaline region.

Example 3 5% by weight of powdered slaked lime was added to the incinerated fly ash sample of Example 1 and mixed, and the mixture was kept in a constant temperature bath at 30 to 120 ° C. for 12 hours, then air-cooled to 60 ° C. and humidified. 30% by weight of water was added and the mixture was kneaded for about 1 minute. After the fly ash after kneading was cured for 2 to 24 hours, the elution test of heavy metals was performed in the same manner as in Example 1. The pH of the eluate and the elution concentration of lead were measured. Also, p
The time during which the H and lead elution concentrations were stable was investigated, and it was examined whether the curing time could be shortened. The results are shown in Table 4.

Comparative Example 3 The same experiment as in Example 3 was carried out except that powdered slaked lime was not added. The results are shown in Table 4.

[0050]

[Table 4]

As is clear from Table 4, when the incineration fly ash is mixed with powdered slaked lime according to the present invention and kneaded to prevent the elution of heavy metals, the curing time of the fly ash after treatment is increased. It was possible to shorten the time, and efficiently prevent the elution of heavy metals in a short time.

Example 4 As a sample of incineration fly ash, alkaline fly ash collected from the melting furnace of the incineration facility was used. 30 g of incinerated fly ash sample and 3 humidifying water
0% by weight was added, and the mixture was kneaded for about 1 minute and cured for 1 day.
Take 30g of the cured sample in a beaker and add 300mL of distilled water.
Was added to carry out a dissolution test of heavy metals. The results of the dissolution test are shown in Table 5 together with the standard values for landfill.

[0053]

[Table 5]

Next, 30 g of incinerated fly ash sample was taken, 5% by weight of powdered slaked lime was added, and orthophosphoric acid was added as an acid agent.
30% by weight of humidified water containing a dithiocarbamate as a chelating agent was added, and the mixture was kneaded for about 1 minute and cured for 1 day. After curing, 30 g of the sample was placed in a beaker and 300 mL of distilled water was added to carry out an elution test of heavy metals. The results of the dissolution test are shown in Table 6.

Comparative Example 4 An experiment was conducted in the same manner as in Example 4 except that slurry slaked lime was used instead of powdered slaked lime. The results are shown in Table 6.

[0056]

[Table 6]

From the data in Table 6, according to the present invention, alkaline fly ash was mixed with powdered slaked lime, and an acid was further added to adjust the pH to a neutral to weakly alkaline range, or a chelating agent was added to produce lead. It can be seen that by promoting the insolubilization of, it was possible to efficiently prevent the elution of heavy metals.

[0058]

According to the present invention, incineration fly ash from various combustion furnaces containing heavy metals can be efficiently subjected to elution prevention treatment for all heavy metals.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an incinerator facility incorporating a device for treating incinerated fly ash according to the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Omote             11-1 Haneda Asahi-cho, Ota-ku, Tokyo Co., Ltd.             Inside the EBARA CORPORATION F-term (reference) 4D004 AA36 AA37 AB03 CA15 CA34                       CA35 CB28 CB42 CB43 CB45                       CC06 CC12 DA03 DA20

Claims (7)

[Claims] 1. A method for treating a contaminated medium, which comprises mixing the contaminated medium with powdered slaked lime and then kneading with water. 2. A treatment of a contaminated medium, which comprises mixing the contaminated medium with powdered slaked lime and further adding an aqueous solution containing at least one of a water-soluble alkali agent, a chelating agent and an aqueous acid solution and kneading the mixture. Method. 3. The method according to claim 1, wherein the contaminated medium eluate is adjusted to pH 6 to 12 and kneaded. 4. A heavy metal elution preventive agent for a pollutant medium, which comprises slaked lime in powder form. 5. A dust collecting apparatus for treating exhaust gas containing fly ash and incinerator ash discharged from an incinerator to separate fly ash and incinerator ash contained therein, which is discharged from the dust collecting apparatus. An apparatus for adding a polluting medium treating agent containing powdered slaked lime to fly ash and incinerated ash; a kneading device for kneading the fly ash and incinerated ash mixed with powdered slaked lime together with water; A device for processing fly ash and incinerated ash, which is characterized by being provided. 6. The device according to claim 5, wherein the pollutant treatment agent addition device is connected to the outlet of the dust collector. 7. A dust collector for treating exhaust gas containing fly ash and incinerator ash discharged from an incinerator to separate fly ash and incinerator ash contained therein; discharge from the dust collector An apparatus for adding a polluting medium treating agent containing powdered slaked lime to fly ash and incinerated ash; an aqueous solution containing at least one of a water-soluble alkaline agent, a chelating agent, and an aqueous acid solution for fly ash and incinerated ash. And a kneading device for kneading powdered slaked lime and fly ash and incinerated ash mixed with the aqueous solution.
Equipment for processing fly ash and incinerated ash.