JP2000117219A - Fly ash treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of gaseous CS2 while maintaining good working environment by adding a dithiocarbamic acid base chelating agent to fly ash to stabilize harmful metal and cooling kneaded matter, in which the dithiocarbamic acid base chelating agent is added to the fly ash, to keep the kneaded matter at specified temperature. SOLUTION: Stabilizing treatment of fly ash is done in two pressures. In a first process, fly ash and water are charged into a preliminary mixer 10 and are wetted to such a degree that the fly ash is not scattered. At this time, air is blown in to promote evaporation of the water and to cool the wetted fly ash. In temperature control of the fly ash in the preliminary mixer 10, quantity of the blown air is increased or decreased based on the measurement of a thermometer 13 to keep the temperature in the specified range in which the measured value of the thermometer 13 does not exceed 60 deg.C. The cooled fly ash is discharged from an exit port and is sent to a kneader 30. Next, in a second process, the cooled ash, a dithiocarbamic acid chelating agent, and water are loaded to the kneader 20 and are kneaded. In this way, while keeping a good working environment, harmful metal is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a harmful metal containing dithiocarbamate group in fly ash containing harmful metal, such as refuse incineration fly ash or molten fly ash generated by melting the same. The present invention relates to a treatment method for stabilizing harmful metals by adding an agent (hereinafter referred to as a dithiocarbamic acid-based chelating agent).

[0002]

2. Description of the Related Art Fly ash, such as incinerated fly ash and molten fly ash generated when it is melted, contains harmful metals such as lead and cadmium. Must be treated to stabilize harmful metals. One of the treatment methods for stabilizing this harmful metal is to add a stabilizer. As a stabilizer, a dithiocarbamic acid-based chelating agent having excellent processing performance is used in many cases. In the stabilization treatment with the dithiocarbamic acid-based chelating agent, the dithiocarbamic acid-based chelating agent and water are added to the fly ash and kneaded, and the harmful metal in the fly ash is reacted with the chelating agent to form a water-insoluble chelate complex. An operation for forming is performed. At this time, in order to prevent scattering of the processed material, cement may be further added as a hardening material to solidify the kneaded material.

[0003]

However, in the above prior art, carbon dioxide (CS ₂ ) is removed from the kneaded material during the stabilization treatment of the harmful metal which is added and kneaded by adding a dithiocarbamic acid-based chelating agent to fly ash. The problem of generating gas occurs. CS ₂ gas is a harmful gas, and the controlled concentration of the working environment is specified as 10 ppm by the Industrial Safety and Health Law.
For this reason, if the CS ₂ gas generated from the kneaded material stays in the building, it becomes impossible to maintain the CS ₂ concentration in the working environment at or below the regulation value.

[0004] The present invention provides a method for stabilizing harmful metals by adding a dithiocarbamic acid-based chelating agent.
_{(2) An} object of the present invention is to provide a fly ash treatment method capable of maintaining a favorable working environment with a small amount of gas.

[0005]

In order to achieve the above object, in the first invention, a kneaded product obtained by adding a dithiocarbamic acid-based chelating agent to fly ash is cooled, and the temperature of the kneaded material is reduced to 60 ° C. or less. To maintain.

[0006] In the second invention, water is added to the fly ash and mixed, and after cooling the mixture, a dithiocarbamic acid-based chelating agent is added and kneaded, and the temperature of the kneaded material is reduced to 60 ° C or lower. As such, the mixture is cooled.

In the third invention, fly ash, a dithiocarbamic acid-based chelating agent, and water are charged into a water-cooled kneader and kneaded while cooling, and the temperature of the kneaded material is maintained at 60 ° C. or lower.

In the fourth invention, fly ash and water are charged into a premixer, air is blown into the premixer to cool the fly ash, and the cooled fly ash is charged into a kneader. At the same time, a dithiocarbamic acid-based chelating agent, and if necessary, water and a curing agent are charged and kneaded, and the temperature of the kneaded material is 60 ° C.
Adjust the amount of air blown into the premixer so that:

The dithiocarbamic acid-based chelating agent is synthesized by reacting an amine compound with CS ₂ and contains unreacted CS ₂ and an unstable by-product compound that easily releases CS ₂ . Therefore, when a condition change such as a temperature rise occurs, CS ₂ in the dithiocarbamic acid-based chelating agent
And the decomposition reaction of by-product compounds are promoted. As described above, CS ₂ gas generated when a dithiocarbamic acid-based chelating agent is added to fly ash is generated by partially decomposing a dithiocarbamic acid-based chelating agent.

[0010] In fact, the temperature of high-temperature fly ash just discharged from a dust collector of a refuse incinerator or a fly ash that has been sent to a heat dechlorination apparatus (dioxin decomposing apparatus) and heat-treated has a temperature of 100 ° C or more. When a dithiocarbamic acid-based chelating agent and water are added to these fly ash and kneaded, the temperature of the kneaded material becomes 80 ° C. or higher, and a large amount of CS ₂ gas is generated.

In addition, when the above-mentioned chelating agent and water are added to the alkali fly ash collected during the treatment of removing hydrogen chloride by blowing slaked lime into exhaust gas generated from a refuse incinerator, Since fly ash contains unreacted lime, this unreacted lime reacts with water to generate heat,
The temperature of the kneaded material increases. Therefore, a large amount of CS ₂ gas is generated. In addition, when the above-mentioned chelating agent and water are added to the fly ash and kneaded, even when a hardening material, for example, cement is added, the temperature of the kneaded material increases due to heat generation due to heat of hydration of the cement. , CS ₂ gas generation amount increases.

The relationship between the temperature of the kneaded material and the amount of generated CS ₂ gas was examined based on the above operational knowledge, and the result was as shown in FIG. FIG. 3 is a plot of values measured by inserting a detector tube for measuring CS ₂ into the kneader when the dithiocarbamic acid-based chelating agent and water were charged into the kneader and kneaded into the fly ash. is there. As shown in this figure, the amount of generated CS ₂ gas tends to increase when the temperature of the kneaded material exceeds 50 ° C., and particularly, the amount of generated CS ₂ gas sharply increases when the temperature exceeds 60 ° C. Therefore, when the kneading was added dithiocarbamic acid chelating agent to fly ash, the kneaded product was cooled, the temperature 60 ° C. or less, preferably be below 50 ° C., CS ₂ generation amount of the gas is very Processing can be performed in a small number of states.

[0013]

FIG. 1 is a diagram showing an example of an embodiment according to the present invention. 20 is a kneader for stabilizing the fly ash, in which a biaxial paddle 22 is provided. Although not shown, the kneader 20 does not
Both or one of the casing 21 and the paddle 22 has a water cooling structure, and a cooling water pipe is connected.
In this embodiment, the kneading machine 20 is provided with a biaxial paddle, but a vibrating kneading machine or the like can be used as the kneading machine.

The fly ash stabilization process is performed as follows. Fly ash, a dithiocarbamic acid-based chelating agent, and water are charged into the kneader 20 and kneaded. The kneaded material is extruded from the discharge port and is carried out to the pit by a conveyor. During this kneading operation, while the kneaded material is cooled by passing water through the cooling structure of the kneader 20, fly ash and the like are charged. Although heat is generated in the kneader 20 due to a hydration reaction or the like, the temperature rise of the kneaded material is suppressed by cooling one or both of the casing 21 and the paddle 22 of the kneader. The temperature of the kneaded material is adjusted by changing the flow rate of the cooling water based on the measurement value of the thermometer 23 provided in the kneader 20 so that the temperature does not exceed 60 ° C.

In the description of FIG. 1, only fly ash, a dithiocarbamic acid-based chelating agent, and water are used as materials to be charged into the kneader 20. However, in the present invention, the materials are charged into the kneader 20. The material is not limited to those described above, but may be further charged with cement or charged with other additives.

FIG. 2 is a diagram showing another example of the embodiment according to the present invention. Reference numeral 10 denotes a premixer for adding water to the fly ash for cooling, and a stirring blade 12 is provided therein. An air blowing pipe and an exhaust gas pipe are connected to the premixer 10. Reference numeral 20 denotes a kneader for stabilizing fly ash discharged from the pre-mixer 10, and its structure is shown in FIG.
And a two-axis paddle 22 is provided. Further, both or one of the casing 21 and the paddle 22 has a water cooling structure, and a cooling water pipe is connected.

The operation for stabilizing fly ash in this embodiment is performed in two steps. In the first step, fly ash and water are charged into the premixer 10 and wetted to such an extent that the fly ash is not scattered. In the premixer 10, since heat is generated by the hydration reaction or the like when water is added to the fly ash, air is blown to accelerate the evaporation of the water, and the wet fly ash is cooled. The temperature of the fly ash in the premixer 10 is adjusted by using a thermometer 1
The amount of air blown is increased or decreased based on the measurement value of 3, so that the measurement value of the thermometer 13 is maintained in a predetermined range not exceeding 60 ° C. The fly ash cooled as described above is discharged from the discharge port and sent to the kneader 20.

In the second step, the cooling fly ash sent from the premixer 10, a predetermined amount of a dithiocarbamic acid-based chelating agent, and water for obtaining an appropriate kneaded product are charged into the kneader 20 and kneaded. . Since the second step is a step of stabilizing the fly ash that has been cooled by the pre-mixer 10, usually,
No cooling of the kneaded material is required. However, if the cooling load in the pre-mixer 10 in the first step is too large and the internal temperature cannot be reduced to 60 ° C. or less, one or both of the casing 21 and the paddle 22 of the kneading machine are provided. And then cooled.

The amount of water to be added in the premixer 10 in the first step is limited to an amount that allows the kneaded product obtained in the second step to maintain an appropriate amount of water.

In the first step, the exhaust gas generated by blowing air contains a small amount of scattered fly ash.
Alternatively, the gas is released after washing with water by providing a gas washing tower. While circulating the washing liquid in the gas washing tower, a part thereof is extracted and supplied to the premixer 10.

In the description of FIG. 1, only the cooled fly ash, the dithiocarbamic acid-based chelating agent, and water are used as the materials to be charged into the kneader 20 in the second step. What is charged into the kneading machine 20 is not limited to the above-mentioned one, but may be further charged with cement or charged with other additives.

Next, the fly ash stabilization process is performed by the method of the present invention.
The result of the process will be described. Waste incineration fly ash (Table 1)
Shows the component analysis value), cement, dithiocarbamic acid
Chelating agent (trade name A200 of Nippon Kokan Co., Ltd.), water
With a mixing ratio of 70: 30: 5: 28 in a twin-screw paddle type kneader
And kneading while cooling the water cooling structure of the kneading machine.
Was. At this time, the temperature of the fly ash charged into the kneader was 60 ° C.
However, the temperature of the kneaded material in the kneader was 50 ° C. So
Then, the gas in the kneader is sampled and_TwoMeasure gas concentration
As a result, the concentration was 30 ppm. Also, kneading
CS around the machine _TwoGas concentration measured, less than 1 ppm
Met.

On the other hand, the results of the fly ash stabilization treatment without cooling the kneader were as follows. In this stabilization process, processing conditions other than the presence or absence of kneader cooling were the same as those in the above-described process. During this treatment, the temperature of the fly ash charged into the kneader was 60 ° C, and the temperature of the kneaded material in the kneader was 80 ° C. And C in the kneader
The S ₂ gas concentration was 200 ppm. The CS ₂ gas concentration around the kneader was 40 ppm.

As is clear from the above test results, fly ash
When adding a dithiocarbamic acid-based chelating agent to kneading
In addition, if the temperature of the kneaded material is cooled to a predetermined value or less,
CS _TwoThe generation of gas is extremely low, and the work around the kneader
It was confirmed that the business environment could be maintained in good condition.

[0025]

[Table 1]

[0026]

According to the present invention, the kneaded product obtained by adding a dithiocarbamic acid-based chelating agent to fly ash is cooled and maintained at 60 ° C. or less, so that the amount of CS ₂ gas is small and a good working environment is maintained. can do.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment according to the present invention.

FIG. 2 is a diagram showing another example of the embodiment according to the present invention.

FIG. 3 is a graph showing the results of examining the relationship between the temperature of a kneaded material obtained by adding a dithiocarbamic acid-based chelating agent to fly ash and the amount of generated CS ₂ gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Premixer 11 Casing 12 Stirring blade 13 Thermometer 20 Kneader 21 Casing 22 Paddle 23 Thermometer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takuya Shinagawa 1-2-2 Marunouchi, Chiyoda-ku, Tokyo F-term in Nihon Kokan Co., Ltd. 4D004 AA36 AA37 AB03 CA15 CA32 CA34 CA45 CB28 CB31 CB37 CC03 CC06 CC13 DA03 DA06

Claims (4)

[Claims] 1. A fly ash treatment method for stabilizing harmful metals by adding a dithiocarbamic acid-based chelating agent,
A method for treating fly ash, comprising cooling a kneaded product obtained by adding a dithiocarbamic acid-based chelating agent to fly ash, and maintaining the temperature of the kneaded product at 60 ° C. or lower. 2. A method for treating fly ash, wherein a toxic metal is stabilized by adding a dithiocarbamic acid-based chelating agent,
Water is added to the fly ash and mixed, and after cooling the mixture, a dithiocarbamic acid-based chelating agent is added and kneaded, and the mixture is cooled so that the temperature of the kneaded product is 60 ° C. or less. Characteristic fly ash treatment method. 3. A method for treating fly ash in which a toxic metal is stabilized by adding a dithiocarbamic acid-based chelating agent,
A method for treating fly ash, comprising charging fly ash, a dithiocarbamic acid-based chelating agent, and water into a water-cooled kneader, kneading the mixture while cooling, and maintaining the temperature of the kneaded material at 60 ° C. or lower. 4. A method for treating fly ash, which comprises adding a dithiocarbamic acid-based chelating agent to stabilize harmful metals,
Fly ash and water are charged into a premixer, air is blown into the premixer to cool the fly ash, the cooled fly ash is charged into a kneader, and a dithiocarbamic acid-based chelating agent and Water and a hardening material are charged and kneaded according to the conditions, and the amount of air blown into the premixer is adjusted so that the temperature of the kneaded material becomes 60 ° C. or less. .