JPH07109533A - Method for recovering heavy metals in molten fly ash - Google Patents

Abstract

(57) [Summary] [Structure] The molten fly ash discharged from the melting furnace is introduced into a treatment tank and suspended in water in the tank, and this suspension is adjusted to an appropriate value in the alkaline range by the addition of acid or alkali. After adjusting the pH
The precipitate formed is separated. [Effect] Zn, Pb, Cd, C contained in the molten fly ash
Since heavy metals such as u precipitate as hydroxides at a pH of 10 to 10.5, such harmful heavy metals can be removed and recovered from the molten fly ash. The recovered heavy metal can be reused as a metal raw material in Yamamoto reduction and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering heavy metals in molten fly ash generated when melting wastes and the like.

[0002]

2. Description of the Related Art Conventionally, wastewater containing heavy metals and dust such as molten fly ash are treated as heavy metal sludge by being subjected to heavy metal treatment, and are then landfilled after intermediate treatment such as cement solidification and chelate fixation by chemicals. Has been done.

[0003]

However, when cement solidification is carried out as an intermediate treatment of heavy metal sludge, in order to keep it below the regulation value in the waste treatment method, several times to several tens of times are required depending on the concentration of heavy metal contained. There is a problem that the amount of cement required is doubled and the volume of the landfilled material increases. Even if the cement is solidified and landfilled, heavy metals may be eluted in the long term due to the influence of acid rain and the like. Further, when the chelate is immobilized, the cost of the drug is high and it is not economically advantageous.

The present invention solves the above problems, and when treating the molten fly ash, the heavy metal in the molten fly ash can be removed and recovered in an economically advantageous manner without increasing the amount of the treated material. The purpose is to do.

[0005]

In order to solve the above problems, the present invention introduces molten fly ash discharged from a melting furnace into a treatment tank and suspends it in water in the tank. Alternatively, it is characterized in that the heavy metal in the molten fly ash is precipitated as a hydroxide by adjusting the pH to an appropriate value in the alkaline range by adding an alkali, and the precipitate is recovered.

In the present invention, the molten fly ash discharged from the melting furnace is introduced into a treatment tank, suspended in water in the tank, and a water-soluble sulfide is added to this suspension to remove the molten fly ash. The heavy metal of (1) is precipitated as a sulfide, and the precipitate is recovered.

Further, in the present invention, the molten fly ash discharged from the melting furnace is introduced into a treatment tank and suspended in water in the tank, and the suspension is adjusted to a suitable pH in the alkaline range by adding an acid or an alkali. After the adjustment, the water-soluble sulfide is added to the suspension to precipitate the heavy metal in the molten fly ash as hydroxide and sulfide, and the precipitate is recovered.

[0008]

According to the above construction, the molten fly ash is collected and suspended in water in the treatment tank, and the pH of this suspension is adjusted to an appropriate value in the alkaline range, 10 to 10.5, by adding an acid or an alkali. By doing so, heavy metals such as Pb, Zn, Cd, and Cu, which are usually contained in the molten fly ash in the form of chloride, can be precipitated as hydroxides as shown in the following formula. Therefore, the heavy metal in the molten fly ash can be removed and collected by collecting the precipitate.

[0009]

[Chemical 1] When the water-soluble sulfide is added to the suspension, the heavy metal M in the molten fly ash precipitates as sulfide as shown in the following equation.

[0010]

[Chemical 2] Further, when the pH of the suspension is adjusted to an appropriate value in the alkaline range by adding an acid or an alkali and then a water-soluble sulfide is added to the suspension, the heavy metal M in the molten fly ash is Precipitates as sulfide.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of a processing apparatus in which the heavy metal recovery method of the present invention is performed. 1 is a dissolution tank, 2 is a first reaction tank, 3 is a second reaction tank, and 4 is a precipitation tank. Is.

The molten fly ash discharged from the melting furnace is melted into a tank 1.
And mixed with water and stirred by the stirrer 5 to sufficiently dissolve the water-soluble substance contained in the molten fly ash in water. The obtained suspension 6 is sent to the reaction tank 2, and while monitoring with the pH meter 7 and stirring with the stirrer 8, acid or alkali is added to adjust the pH to 10 to 10.5. Then,
Since a water-soluble substance, that is, a chloride of heavy metal, is dissolved in the suspension 6, a precipitate of heavy metal hydroxide is generated.

The suspension 9 containing the precipitate is sent to the reaction tank 3,
Na as a water-soluble sulfide while stirring with a stirrer 10.
Add aqueous HS solution. At the same time, while monitoring with the pH meter 11, the pH of the suspension 12 in the reaction tank 3 is 10 to 1
Keep at 0.5. As a result, the unreacted heavy metal contained in the suspension 12 reacts with NaHS to generate a heavy metal sulfide precipitate.

The suspension 12 containing the precipitate is sent to the settling tank 4, and a precipitate 13 composed of heavy metal hydroxide and heavy metal sulfide is formed.
And supernatant water 14 are separated. By processing as described above, harmful heavy metals can be separated and removed as the precipitate 13 to render the molten fly ash harmless. Since the heavy metal in the molten fly ash is concentrated, the precipitate 13 can be used as a heavy metal raw material in Yamamoto reduction or the like.

Instead of the above structure, the heavy metal hydroxide may be precipitated in the reaction tank 2 and then the heavy metal sulfide may be precipitated in the same tank 2, or the heavy metal sulfide may be suspended in the reaction tank 2. A configuration in which the precipitation of heavy metal hydroxide is taken out from the liquid 9 or the suspension 6 is sent to the reaction tank 3 without passing through the reaction tank 2 and the precipitation of heavy metal sulfide is taken out from the suspension 12 in the reaction tank 3. May be Instead of NaHs as the water-soluble sulfide, Cas, Na ₂ S, etc. may be used.

A specific example of recovering heavy metals from molten fly ash will be shown below. This example shows a small-scale treatment, in which 450 ml of water was added to 50 g of molten fly ash and stirred for 30 minutes, and NaHS (1.23 g,
15%) was added, and the mixture was stirred for 1 hour and then filtered to recover a solid matter (heavy metal sludge) and a filtrate. As can be seen from the analysis results shown in Table 1 below, the heavy metal is contained in the solid matter and the other components are contained in the filtrate, and the two are almost completely separated. The heavy metal content in the solid at this time was Pb 10.8%, Zn 26.3
%, Cd 0.35%, Cu 1.89%, and is 10 to 12 times more concentrated than the molten fly ash. This corresponds to a 100-fold concentration compared to incinerated fly ash, so it can be said that the separated solid matter can be sufficiently reused as a non-ferrous metal raw material. Table 2 is an example of the components of the molten fly ash.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

As described above, according to the present invention, the molten fly ash is collected and suspended in water, and the pH of this suspension is adjusted to an appropriate value in the alkaline range by adding an acid or an alkali, and the molten fly ash is melted. By precipitating heavy metals in fly ash as hydroxides, harmful heavy metals can be separated and removed to render molten fly ash harmless, and the heavy metals can be reused by reducing the separated heavy metals. .

The heavy metal can be removed and recovered from the molten fly ash by adding a water-soluble sulfide to the suspension and precipitating the heavy metal in the molten fly ash as a sulfide. After adjusting the pH of the suspension to an appropriate value in the alkaline range by adding acid or alkali, add water-soluble sulfide to the suspension and precipitate the heavy metals in the molten fly ash as hydroxides and sulfides. The heavy metal can be removed and recovered from the molten fly ash also by the above.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a processing apparatus in which a heavy metal recovery method of the present invention is performed.

[Explanation of symbols]

 1 Dissolution tank 2 1st reaction tank 3 2nd reaction tank 4 Precipitation tank 9 Suspension 12 Suspension 13 Precipitate

Claims (3)

[Claims] 1. A method in which molten fly ash discharged from a melting furnace is introduced into a treatment tank and suspended in water in the tank, and the pH of the suspension is adjusted to an appropriate value in an alkaline region by adding an acid or an alkali. A method for recovering heavy metals in molten fly ash, characterized in that heavy metals in the molten fly ash are precipitated as hydroxides and the precipitate is recovered. 2. The heavy fly ash discharged from the melting furnace is introduced into a treatment tank, suspended in water in the tank, and a water-soluble sulfide is added to this suspension to remove heavy metals in the molten fly ash. A method for recovering heavy metals in molten fly ash, which comprises precipitating as sulfide and recovering the precipitate. 3. The molten fly ash discharged from the melting furnace is introduced into a treatment tank and suspended in water in the tank, and the pH of the suspension is adjusted to an appropriate value in an alkaline range by adding an acid or an alkali. , A method for recovering heavy metals in molten fly ash, characterized in that heavy metals in the molten fly ash are precipitated as hydroxides and sulfides by adding a water-soluble sulfide to the suspension, and the precipitates are recovered. .