JP3496610B2 - Alkaline fly ash treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating alkaline fly ash of refuse incineration fly ash discharged from a waste melting furnace or a waste incinerator, and more specifically to treating the fly ash after treatment. In this case, the present invention relates to a treatment method for suppressing elution of harmful heavy metals such as lead or cadmium contained in alkaline fly ash from fly ash.

[0002]

2. Description of the Related Art At present, soot dust (dust incineration fly ash) collected in a dust collection facility of a waste melting furnace or a waste incinerator is an alkaline fly ash containing harmful heavy metals in fly ash. Since alkaline fly ash is designated as specially controlled general waste by the waste treatment method, it is prohibited to dispose of it in landfill as it is, and it is obliged to dispose of it in landfill after intermediate treatment. ing. The intermediate treatment is a treatment performed to prevent elution of harmful heavy metals such as lead or cadmium contained in high concentration in alkaline fly ash, that is, stabilization of alkaline fly ash, detoxification and scattering prevention, The methods include (1) melt solidification, (2) cement solidification, (3) chemical treatment, and (4)
There are four extractions to acids and other solvents. Of these, the chemical treatment (3) is for immobilizing harmful heavy metals with a chemical, and is advantageous in that it is inexpensive because it requires only a small facility and is easy to operate and maintain.

Examples of chemicals used for chemical treatment include diethyldithiocarbamic acid-based organic liquid chelating agents, phosphoric acid-based inorganic liquid chelating agents, and organic or inorganic solids of these solids. As a chemical treatment method, any one of these chemicals is kneaded with alkaline fly ash together with water to detoxify harmful heavy metals in the fly ash.

The mechanism by which harmful heavy metals are rendered harmless is as described below. First, the mechanism by which diethyldithiocarbamic acid fixes lead is shown below.

[0005]

[Chemical 1]

In the chemical formula (A), a portion surrounded by □ is a structure called a chelate, and since the binding force is very strong, lead is hardly separated from this structure. Therefore, when diethyldithiocarbamic acid, which is an organic liquid chelating agent, is kneaded with alkaline fly ash together with water, lead in the alkaline fly ash is bonded and fixed with diethyldithiocarbamic acid as in the above chemical formula (A), and lead Prevent elution,
In other words, it is rendered harmless. Further, when the phosphoric acid-based inorganic liquid chelating agent is used, the reaction form is different from that when the diethyldithiocarbamic acid-based organic liquid chelating agent is used, and lead is combined with phosphoric acid to form lead phosphate. Form. Since this lead phosphate has a very low solubility in water, it is said that it does not dissolve in water, so that harmful heavy metals are rendered harmless.

The fly ash after the intermediate treatment (chemical treatment) is subjected to, for example, a dissolution test according to the Environmental Agency Notification No. 13 method, and it is confirmed whether the harmful heavy metals in the eluate are below the standard value, and then the landfill. Be disposed of. In addition, the elution test of the Environmental Agency Notification No. 13 method is 50 g of a sample with a particle size of 0.5 to 5 mm and water (pH
5.8 to 6.3) 500 ml was placed in a flask, shaken for 6 hours, and analyzed for components in a filtrate (eluate) obtained by filtering with a filter paper having a pore size of 1 μm.

However, since all the chemicals used in the chemical treatment of the above (3) are expensive, there is a problem that the treatment cost becomes high when the concentration of harmful heavy metals in the alkaline fly ash is high. It was Therefore, various fly ash treatment methods have been proposed in which the amount of chemicals added is reduced or the amount of harmful heavy metals eluted without using chemicals is set to a reference value or less.

For example, in JP-A-11-192471 (hereinafter referred to as "prior art 1"), the pH of the fly ash to be treated is measured in advance. If the measured value is 11.0 or more, the fly ash to be treated is 580 to 580. Heat treatment at 800 ℃, the pH of the fly ash to be treated is adjusted to 8.5 or more and less than 11.0 to prevent elution of heavy metals in the fly ash to be treated, and the pH of the fly ash to be treated is measured in advance. However, if the measured value is neutral or acidic less than 8.5, an alkali source is added in advance to once set the pH of the fly ash to be treated to 11.0 or higher, and then the fly ash to be treated is adjusted to 58.
Heat treatment is performed at 0 to 800 ° C. to adjust the pH of the fly ash to be treated to 8.
A treatment method is disclosed in which the amount of the heavy metal in the fly ash to be treated is 5 or more and less than 11.0 to prevent elution of heavy metals.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 8-303741 (hereinafter referred to as "prior art 2"), incineration ash is 400 to 550
A treatment method is disclosed in which, after heat treatment at ℃, a heavy metal fixing agent and water are added, and the mixture is kneaded and molded and solidified.

Further, in Japanese Unexamined Patent Publication No. 10-151429 (hereinafter referred to as "prior art 3"), water is added to highly alkaline dust ash, and after mixing and stirring, the temperature is set to 200 to 600 ° C. in an air or carbon dioxide atmosphere. There is disclosed a method for detoxifying harmful heavy metals in highly alkaline dust ash which is heat-treated.

[0012]

The treatment method of the prior art 1 as described above does not use a chemical agent for immobilizing heavy metals, so that the treatment cost can be reduced. However, with this treatment method, heavy metals, such as lead, are only converted to lead hydroxide, etc., and lead, etc. is not fixed (detoxified), so leachate at the final disposal site (landfill) When pH is less than 8.5 or changed to 11 or more, lead may be eluted. Further, if the pH of the heat-treated fly ash does not fall below 8.5 or more and less than 11, there is a problem that the elution of heavy metals from the fly ash cannot be prevented and the fly ash cannot be disposed of in a landfill. . In this case, the fly ash is repeatedly heat-treated to readjust it to a pH that can be disposed of, or the pH is adjusted by adding an acidic chemical or the like, resulting in many and complicated treatment steps and high treatment cost. There is a risk that it will occur.

Further, in the treatment method of the prior art 2, since the heating temperature is 400 to 550 ° C., the heavy metal in the incinerated ash is difficult to dissolve in water at this treatment temperature, for example, in the case of lead, lead tetraoxide It is difficult to change to a complex oxide such as calcium or Ca ₂ PbO ₄ . By the way, according to the experiment by the present inventors, when heated at 400 ° C., the elution concentration of lead was about half that of untreated (unheated) fly ash, but when heated at 600 ° C. Has an elution concentration of 1/35
It is known to be reduced to.

Further, in the treatment method of the prior art 3, heat treatment is carried out at a relatively low temperature of 200 to 600 ° C. in an atmosphere of air or carbon dioxide, and harmful heavy metals in the dust ash are combined into a carbonate having a low solubility. Although it has been changed, if a large amount of harmful heavy metals are contained in the collected ash, the heavy metals that cannot be immobilized remain as they are, and the heavy metals may be eluted at the disposal site. If the same processing is repeatedly performed to prevent the above, there is a possibility that the processing cost will increase.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to reduce the amount of chemicals added and to detoxify harmful heavy metals easily, reliably, stably and inexpensively. It is an object of the present invention to provide an alkaline fly ash treatment method that can be performed.

[0016]

A method for treating alkaline fly ash according to the present invention is a method of treating alkaline fly ash discharged from a refuse incineration plant or the like at 550 in an air atmosphere or a high oxygen atmosphere.
This is a method of heating in a temperature range of up to 800 ° C. to change the heavy metal contained in the alkaline fly ash into a form insoluble in water, and then adding and kneading a chemical for immobilizing the heavy metal.

Further, the alkaline fly ash treatment method according to the present invention, when the heavy metal in the alkaline fly ash is changed to a form insoluble in water by heating in an air atmosphere, the pH of the alkaline fly ash is from 11.0 to. This is a method of controlling within the range of 13.0.

Further, the alkaline fly ash treatment method according to the present invention is a method of using an organic liquid chelating agent, an inorganic liquid chelating agent, an organic solid or an inorganic solid as a chemical for immobilizing heavy metals.

The present invention will be described in more detail below. Note that the following description is for facilitating the understanding of the present invention and does not limit the present invention.

In the alkaline fly ash treatment method according to the present invention, first, the alkaline fly ash is heated in a temperature range of 550 to 800 ° C. in an air atmosphere or a high oxygen atmosphere to remove heavy metals contained in the alkaline fly ash with water. Change to a form insoluble in. When the alkaline fly ash is heated in the above temperature range in an air atmosphere, the pH of the alkaline fly ash is 11.0 to.
Control within the range of 13.0.

Heavy metals such as lead contained in alkaline fly ash are CaClOH (or calcium chloride), which is a non-reacted slaked lime in fly ash, or a double salt of calcium chloride / calcium hydroxide which is a neutralization product of slaked lime and hydrochloric acid.・ Calcium hydroxide monohydrate, CaCl ₂・ Ca (OH) ₂
-H ₂ O) and the above temperature range (550 to 800 ° C.), it has been clarified in the previous studies that complex oxides such as lead dicalcium tetroxide and Ca ₂ PbO ₄ are formed. Since this complex oxide is insoluble in water, there is no risk of elution of lead, which is a heavy metal. Therefore,
By heating the alkaline fly ash in the above temperature range, the heavy metal can be changed into a form insoluble in water.

In the above temperature range, as shown in FIG. 3, after heating the alkaline fly ash at each temperature, the results of the elution test according to the above-mentioned Environmental Agency Notification No. 13 and the flying temperature It can be explained from the relationship with the lead content in ash (lead volatilization rate from fly ash). That is, as is clear from FIG. 3, it is found that the elution concentration of lead is lowered by heating the alkaline fly ash in the air atmosphere. Then, this elution concentration becomes minimum around 550 ° C., and at a temperature higher than this, the elution concentration hardly changes. The lead volatilization rate is 80
It can be seen that the temperature gradually increases after the temperature exceeds 0 ° C. Therefore, lead evaporates at a high temperature exceeding 800 ° C., and new equipment is required to treat the lead. Further, it is desirable from the viewpoint of energy utilization that the heating temperature of fly ash is as low as possible. Therefore, the heating temperature of the alkaline fly ash is within the range of 550 to 800 ° C.

When heating in an air atmosphere, it is not necessary to control the pH if sufficient oxygen is present.
When oxygen is not sufficiently present, water is released from the alkaline fly ash by heating (equation described later), and calcium oxide (C
aO). When there is carbon dioxide gas, calcium oxide changes into calcium carbonate (Ca ₂ CO ₃ ) in the cooling process (the formula described later). That is, Ca (OH) ₂ → CaO + H ₂ O ... CaO + CO ₂ → Ca ₂ CO ₃ ... This calcium carbonate is not very soluble in water, and the pH of the solution becomes 10.0. On the other hand, when heating is performed in an air atmosphere or a high oxygen atmosphere in which water and sufficient oxygen are present, a reaction opposite to the above equation occurs, and calcium oxide (CaO) is again converted into calcium hydroxide (Ca (O
H) ₂ ) and the pH is in the range of 11.0 to 13.0. Here, the heavy metal contained in fly ash, especially lead, is a metal that dissolves on both the acid side and the alkali side, and the amount of elution becomes minimum at about pH 10. Therefore, the pH is set to 11.0 in this method.
It is not a method for immobilizing heavy metals by merely adjusting the pH because it controls the elution amount of lead by controlling the amount within a range of to 13.0.

In the following alkaline fly ash treatment method according to the present invention, the alkaline fly ash is heated to change the heavy metal into a form insoluble in water, and then a chemical for fixing the heavy metal is added and kneaded. .

Examples of agents for immobilizing heavy metals include diethyldithiocarbamic acid-based organic liquid chelating agents, phosphoric acid-based inorganic liquid chelating agents, and organic or inorganic solids of these solids. Any one of the chemicals is kneaded with alkaline fly ash together with water, and the harmful heavy metals in the fly ash are rendered harmless by the above-described immobilization mechanism (see chemical formula (A)).

[0026]

1 is a schematic diagram of a fly ash treatment system for carrying out the method for treating alkaline fly ash according to the present invention, and FIG. 2 is a schematic view of a refuse incineration system incorporating the fly ash treatment system. With reference to these drawings, an embodiment of the present invention will be described with reference to the drawings.

In the refuse incineration system, as shown in FIGS. 1 and 2, the dust sent into the incinerator 1 is agitated with the combustion air to burn and become dust. Next, the dust is agitated with the secondary combustion air in the secondary incinerator 2 and burned, and the unburned components are burned to form fly ash, which is heat-exchanged in the boiler 3. Next, the exhaust gas is cooled by the cooler 4, the hydrochloric acid gas in the exhaust gas is dechlorinated by the slaked lime 5 blown into the flue, and sent to the dust collector 7 of the fly ash processing device 6. Then, there, it is separated into fly ash and gas, and the separated and clean gas is discharged from the chimney 8 to the atmosphere.

The fly ash, which becomes alkaline by blowing slaked lime 5 and is separated by the dust collector 7 of the fly ash processing apparatus 6, is heated in the air atmosphere or high oxygen atmosphere in the heater 9 within a range of 550 to 800 ° C. The heavy metal in the fly ash that is heated is insoluble in water, for example, Ca ₂ PbO _{4 in} the case of lead.
Is converted (generated) into a complex oxide such as. At this time, if heating is performed in an air atmosphere, the pH of the fly ash should be 11.0.
When the temperature is controlled to ˜13.0 and heating is performed in a high oxygen atmosphere, sufficient oxygen can be supplied to change to a form insoluble in water (complex oxide, etc.), so the pH is not specified. And
The water-insoluble form (complex oxide, etc.) does not elute in water after the treatment and does not depend on pH. By providing the heater 9 in, for example, a boiler section in a factory, new energy required for heating is not required.

Next, the fly ash heated within the range of 550 to 800 ° C. is a chemical for fixing heavy metals from the chemical tank 11 in the kneading machine 10, an organic liquid chelating agent of diethyldithiocarbamic acid, and phosphoric acid. Inorganic liquid chelating agent or one of these solid organic or inorganic solids is kneaded with water from the industrial water (or tap water) tank 12 and is insoluble in water in the above heat treatment. A heavy metal that has not changed to a different form (composite oxide, etc.) is immobilized as shown in the chemical formula (A). At this time, the addition amount of the chemicals used is only the amount necessary to immobilize the heavy metal that has not changed to the water-insoluble form (complex oxide, etc.) in the heat treatment in the previous step of kneading. It is possible to significantly reduce the amount of added chemicals as compared with the case of the chemical treatment. Further, there is no dependence on the pH after the treatment. Then, after being fixed, it is disposed of in the disposal site 13 such as a landfill.

As described above, alkaline fly ash is heated in the temperature range of 550 to 800 ° C. in an air atmosphere or a high oxygen atmosphere, and the heavy metal contained in the alkaline fly ash is insoluble in water (complex acidity etc.). ), And then kneading by adding the necessary amount of a heavy metal immobilizing agent that has not changed to a water-insoluble form (complex acidic substance, etc.) by heat treatment. Since it is a method, it is possible to reduce the amount of addition of the chemicals, and to detoxify harmful heavy metals easily, reliably, and with good stability without tedious adjustment of pH and the like. In addition, the amount of chemicals added is reduced, and conventional equipment can be used, so that the method can be performed at low cost. The effect of this method will be specifically described with reference to the following examples.

[0031]

EXAMPLES First, Table 1 shows the composition of heavy metals contained in the alkaline fly ash discharged from the waste gasification and melting furnace.

[0032]

[Table 1]

Next, the alkaline fly ash having the heavy metal composition shown in Table 1 was heated in an air atmosphere at 600 ° C. for 30 minutes to obtain an organic liquid chelating agent (here, a diethyldithiocarbamic acid type, manufactured by NKK: A-200). ) And knead with water. The fly ash after this treatment is referred to as Example 1. Further, the alkaline fly ash having the heavy metal composition shown in Table 1 is not heated, but the same chemicals as in Example 1 are added and kneaded with water. The fly ash after this treatment is referred to as Comparative Example 1. Then, Example 1 and Comparative Example 1 are subjected to a dissolution test according to the Environmental Agency Notification No. 13 method. The results of the elution concentration of each heavy metal are shown in Tables 2 and 3.

[0034]

[Table 2]

[0035]

[Table 3]

As is apparent from Tables 2 and 3, in order to keep the elution concentration of each heavy metal below the reference value, Comparative Example 1 requires 10% (weight ratio) of the organic liquid chelating agent. In contrast, in Example 1, 5% (weight ratio) of the amount of the organic liquid chelating agent added was sufficient. From this, it is understood that the required amount of the organic liquid chelating agent to be added can be reduced to 1/2 by heating the fly ash as in Example 1. Therefore, if the treatment method as in Example 1 is performed, it is possible to reduce the amount of the agent for immobilizing the heavy metal to a necessary amount, and it is possible to easily and reliably detoxify the harmful heavy metal simply by performing the heat treatment, and It can be performed with good stability and at low cost.

[0037]

As described above, according to the method for treating alkaline fly ash according to the present invention, the alkaline fly ash discharged from the refuse incinerator is 550 in an air atmosphere or a high oxygen atmosphere.
This is a method of heating in a temperature range of up to 800 ° C. to change the heavy metal contained in the alkaline fly ash into a form insoluble in water, and then adding and kneading a chemical for immobilizing the heavy metal. Also,
The method of treating alkaline fly ash according to the present invention, when the heavy metal in the alkaline fly ash is changed into a form insoluble in water by heating in an air atmosphere, the pH of the alkaline fly ash is set to 11.
This is a method of controlling within the range of 0 to 13.0. further,
The method of treating alkaline fly ash according to the present invention is a method of using an organic liquid chelating agent, an inorganic liquid chelating agent, an organic solid or an inorganic solid as a drug for immobilizing heavy metals.

As a result, the amount of the harmful heavy metal-immobilizing agent added may be the amount required to immobilize the harmful heavy metal that has not been changed into a water-insoluble form by the heat treatment. The amount of drug can be significantly reduced. In addition, when heating alkaline fly ash, if the atmosphere is controlled, the amount of elution can be reduced while the harmful heavy metals are dissolved without complicated adjustment of pH. It can be done easily, reliably and with good stability. Further, since conventional equipment can be used, it is possible to obtain a method for treating alkaline fly ash that can be treated at low cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a fly ash treatment system for carrying out a method for treating alkaline fly ash according to the present invention.

FIG. 2 is a configuration diagram schematically showing a refuse incineration system incorporating the fly ash treatment system of FIG.

FIG. 3 is a diagram showing a relationship between a heating temperature of fly ash, a lead elution concentration, and a lead volatilization rate.

[Explanation of symbols]

1 incinerator 6 Fly ash processing equipment 7 dust collector 9 heating machine 10 kneader 11 drug tank 12 Industrial water (or tap water) tank

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Matsudaira 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) Reference JP 2000-51816 (JP, A) JP 2001-205218 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B09B 3/00-5/00

Claims (3)

(57) [Claims] 1. Alkaline fly ash discharged from a refuse incineration plant or the like in an air atmosphere or a high oxygen atmosphere at 550 to 550.
After heating in a temperature range of 800 ° C to change the heavy metal contained in the alkaline fly ash into a form insoluble in water, an agent for immobilizing the heavy metal is added and kneaded. Ash treatment method. 2. The pH of the alkaline fly ash is controlled within a range of 11.0 to 13.0 when the heavy metal in the alkaline fly ash is changed into a form insoluble in water by heating in an air atmosphere. Item 1. The alkaline fly ash treatment method according to Item 1. 3. The alkaline fly ash according to claim 1, wherein an organic liquid chelating agent, an inorganic liquid chelating agent, an organic solid or an inorganic solid is used as the agent for immobilizing heavy metals. Processing method.