JPH11114536A - Method for producing fired product with low cadmium elution amount - Google Patents

Abstract

An object of the present invention is to provide a technique for detoxifying incinerated fly ash, which has the same long-term reliability as the melt-solidification method and is lower in cost than the melt-solidification method. SOLUTION: A municipal solid waste incineration fly ash or the like is mixed with a binder and a composition mixture, coal or coke is added as a reducing agent, the obtained mixture is pulverized, and then water is added to the obtained pulverized material. In addition, a molded body is obtained by molding, and then, if necessary, dried and roasted to obtain a fired product.
The residence time is 15 minutes or more, and preferably a rotary roasting furnace is used as the roasting furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for detoxifying dust containing cadmium, such as fly ash from incineration of municipal solid waste.

[0002]

2. Description of the Related Art In Japan, from the viewpoint of disinfection and hygiene,
Combustible waste is actively incinerated. Most of the incinerated ash and fly ash are landfilled. However, incinerated ash and fly ash, particularly fly ash, contain a large amount of harmful metals, and environmental pollution by cadmium eluted from landfill fly ash has become a major social issue.

[0003] Various techniques have been proposed to solve this problem, and some of them have been put into practical use. For example, cement solidification method,
Examples include a chemical treatment method and a melt solidification method. The cement solidification and chemical treatment methods physically or chemically fix harmful metals such as cadmium and insolubilize them, and the treatment cost is low, but there is a problem in long-term reliability due to acid rain and the like.

[0004] The melt-solidification method is a technique practically used only in Japan, in which incinerated fly ash is melted at 1300 ° C or more to form vitreous slag. This method
Many harmful metals such as cadmium can be volatilized and removed during melting,
Also, since the remaining harmful metals can be wrapped and fixed in the network structure of silica in the slag, even if they are landfilled, they have high long-term reliability and are excellent incineration fly ash treatment technology. However, there is a problem that equipment costs and processing costs are relatively high due to high-temperature processing.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique for detoxifying incinerated fly ash which has the same long-term reliability as the melt-solidification method and is less expensive than the melt-solidification method.

[0006]

A binder and a composition mixture are mixed with municipal solid waste incineration fly ash and the like, coal or coke is added as a reducing agent, and the resulting mixture is pulverized. In a method of obtaining a molded product by adding water to the pulverized product and forming the product, and then, if necessary, drying and roasting to obtain a baked product, the residence time at 1000 ° C. or more is set to 15 minutes or more, preferably roasting. A rotary roaster is used as the roaster.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Cadmium metal has a high vapor pressure,
The boiling point is 777 ° C. In addition, since the boiling point of chloride is as low as 961 ° C., if it is present in fly ash in the form of metal or chloride, it is considered that it can be easily volatilized and separated by high-temperature roasting from the viewpoint of thermodynamics. Can be However, oxides
Although there is no data on vapor pressure, it is known that sublimation occurs at 1559 ° C., so if it exists as an oxide, it is expected that it will be difficult to volatilize and separate. Therefore, incineration fly ash obtained from three municipal solid waste incineration plants in Japan was examined by X-rays and the like, but no form of cadmium in the incineration fly ash could be confirmed.

Based on the above findings, the inventor of the present invention has used a sample obtained by mixing municipal solid waste incineration fly ash containing 0.2% of cadmium with bentonite as a binder and granulating it to a diameter of about 10 mm. A basic roasting test using an electric furnace was performed. After roasting at 1050 ° C. for 10 minutes in an air atmosphere, the residual concentration of cadmium was 0.01% or less, but the elution concentration according to Notification No. 13 of the Environment Agency showed a high value of 1.4 mg / l. It is considered that the reason for this is that cadmium is oxidized during roasting and becomes an oxide having a low vapor pressure, so that volatilization and separation are insufficient and the cadmium is eluted.

Next, a basic roasting test using a small electric furnace was conducted in a simulated LPG combustion gas atmosphere containing a mixture of nitrogen, oxygen and water vapor. As a result, it was confirmed that after roasting at 1050 ° C. for 10 minutes, the residual concentration of cadmium was 0.01% or less, and the elution concentration according to Environment Agency Notification No. 13 was 0.01 mg / l or less.

Based on the above basic test results, tests were conducted under various conditions using a small rotary kiln. As a result, the cadmium elution concentration of the fired product tends to decrease as the roasting temperature increases. It was found that the fluctuation was large and that the maximum temperature depended on how long the residence time in a temperature castle of 1000 ° C. or higher rather than what the maximum temperature was.

The conditions of the present invention have been selected in this manner, and the amount of cadmium eluted from the calcined product is 0.01 mg /
and at least one of minerals containing silica such as silica sand, porcelain stone, feldspar, kaolinite, and wood knot viscosity as a composition mixture.
Using a seed, these are mixed, and the resulting mixture is mixed so that the roasted chemical composition is 20 to 80% by weight of silica and 0.5 to 15% by weight of calcium oxide. Iron oxide and / or silicon carbide having an average particle size of 10 μm or less are mixed in an amount of 2 to 10% by weight, and 2 or 9% in terms of carbon amount is further added using coal or coke as a reducing agent at 1000 ° C. The roasting is performed at the above-mentioned temperature for 15 minutes or more. In this case, even if the oxygen concentration in the roasting atmosphere is 3 to 5%, the elution concentration can be made 0.01 mg / 1 or less. is there.

[0012]

Next, the present invention will be further described with reference to examples.

(Example 1) Table 1 shows the chemical composition of fly ash used in the experiment.

[0014] The composition ratio after mixing bentonite with municipal solid waste incineration fly ash containing 0.02% of cadmium is 5%, silica sand is 13%, hematite is 5%, coke is 2%.
%, And the mixture was sufficiently mixed and pulverized using a vibrating ball mill, and then granulated into a spherical shape having a diameter of 5 to 15 mm using a pan pelletizer and dried. This was put into a rotary kiln and roasted.

The rotary kiln was provided with a gas burner on the side opposite to the raw material inlet, and the high-temperature combustion gas generated by the burner was countercurrent to the flow of the granulated material. Therefore, the charged granules are heated as they approach the burner, reach a maximum temperature near the burner, and are discharged outside the furnace.

The raw material inlet gas temperature of this rotary kiln is 650 ° C., and the maximum temperature near the burner is 1105 ° C.
, And the number of rotations was adjusted to set the roasting time (time from input to discharge) to 90 minutes, and the roasting was performed.
In addition, from the measured value of the temperature using a thermocouple, 100
It was found that the residence time in the high temperature part of 0 ° C. or more was 17 minutes.

After cooling the calcined product, quantitative analysis of cadmium was performed by ICP. As a result, the residual amount of cadmium was 0.0
It was less than 1%. When a dissolution test was performed according to the notification of the Environment Agency Notification No. 13, the dissolution amount of cadmium was 0.005 m.
g / l or less.

Example 2 5% by weight of bentonite mixed with municipal solid waste incineration fly ash containing 0.03% of cadmium, 15% of silica sand, 5% of hematite and 5% of coke %, Sufficiently mixed and crushed using a vibrating ball mill, and then, with a pelletizer, a diameter of 5 to 5%.
It was granulated into a 15 mm spherical shape and dried. This was put into a rotary kiln and roasted.

The roasting conditions are as follows: the temperature of the granulated material inlet is 670 ° C.
The maximum temperature of the burner section was set at 1110 ° C., the number of rotations was adjusted, and the roasting time (the time from input to discharge) was set at 90 minutes. In addition, from the actual measurement value of the temperature using the thermocouple, the residence time of the granulated material in the high temperature part of 1000 ° C. or more at this time was 18 minutes.

After cooling the calcined product, quantitative analysis of cadmium was performed by ICP. As a result, the residual amount of cadmium was 0.01% or less. In addition, when a dissolution test was performed according to the notification of the Environment Agency Notification No. 13, the dissolution amount of cadmium was 0.0
It was 1 mg / l or less.

COMPARATIVE EXAMPLE 5% by weight of bentonite mixed with municipal solid waste incineration fly ash containing 0.02% cadmium, 15% silica sand, 5% hematite, and 3% coke. And sufficiently mixed and pulverized using a vibrating ball mill.
It was granulated into a spherical shape of 5 mm and dried. This was put into a rotary kiln and roasted.

The roasting conditions are as follows: the raw material charging port temperature is set at 540 ° C., the maximum temperature of the burner section is set at 1070 ° C., the number of rotations is adjusted, and the roasting time is set (time from input to discharge).
Was set to 90 minutes. In addition, from the measured value of the temperature using the thermocouple, the residence time of the raw material in the high temperature part of 1000 ° C. or more at this time was 11.7 minutes.

After cooling the obtained fired product, quantitative analysis of cadmium was performed by ICP. As a result, the residual amount of cadmium was 0.01% or less. However, when a dissolution test was performed according to the notification of the Environment Agency Notification No. 13, the dissolution concentration of cadmium was 0.72 mg / l.

[0024]

According to the method of the present invention, notice 13 of the Environment Agency
Concentration of cadmium in fly ash by incineration
g / l or less. This satisfies the environmental grave value of soil (elution concentration of cadmium: 0.01 mg / l), and cadmium-containing dust can be detoxified by using the present invention. Further, the method of the present invention is lower in cost and more economical than the melt-solidification method.

Continued on front page (72) Inventor Junichi Takahashi 2600 Ishigami Sojuku, Tokai-mura, Naka-gun, Ibaraki Pref. Sumitomo Metal Mining Co., Ltd.

Claims (2)

[Claims] Claims 1. A binder and a composition mixture are mixed with municipal solid waste incineration fly ash and the like, coal or coke is added as a reducing agent, the obtained mixture is pulverized, and water is added to the obtained pulverized substance. To obtain a molded body, and then, if necessary, drying and roasting to obtain a fired material having a low cadmium elution amount. A characteristic method for producing a fired product having a low cadmium elution amount. 2. The method according to claim 1, wherein a rotary roasting furnace is used as the roasting furnace.