JPH091104A - Treatment of flying ash - Google Patents

Abstract

PURPOSE: To make it possible to recover only the heavy metals by adding a slight amt. of acid to flying ashes contg. the heavy metals and water-soluble salts to dissolve the heavy metals, then adding a heavy metal complexing agent thereto to convert the dissolved heavy metals to complex and subjecting the complex to supercritical extraction by carbon dioxide supercritical fluid. CONSTITUTION: The flying ashes 1 are charged into a heavy metal treating vessel 2 and are agitated and mixed under addition of a slight amt. of the acid 3, such as hydrochloric acid, by which the heavy metals in the flying ashes 1 are dissolved at the time of treating the flying ashes 1. The heavy metal complexing agent # is then added to the flying ashes 1 and the flying ashes are agitated and mixed to convert the heavy metals to the complex. The complex-contg. flying ashes 5 contg. the heavy metal complex are introduced into a supercritical extraction vessel 6 where the heavy metal complex is extracted into the carbon dioxide supercritical fluid 7. The complex- contg. carbon dioxide supercritical fluid 8 is thereafter introduced into a reduced pressure vessel 9 where the pressure is reduced. The dissolving power of the fluid 8 is lowered by this pressure reduction and the fluid 8 is separate to the carbon dioxide fluid 10 and solid 11 contg. the heavy metal complex and, therefore, the solid 11 is recovered from the reduced pressure vessel 9.

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 fly ash containing heavy metals and water-soluble salts generated during incineration and melting of waste such as municipal solid waste and industrial waste.

[0002]

2. Description of the Related Art Conventionally, wastes such as municipal waste and industrial wastes are incinerated in an incinerator, and incinerator ash generated here is melted in an ash melting furnace. The molten slag produced by the melting process is very safe and stable because it is resistant to acids and alkalis and heavy metals are difficult to elute, and its volume is reduced to 1/2 to 1/3 of the incineration ash. Have advantages.

However, fly ash is generated during the incineration or melting of waste, and the fly ash contains a high concentration of water-soluble salts such as potassium chloride and sodium chloride and a small amount of heavy metals. Therefore, it has been proposed to separate the heavy metals in the fly ash to make the fly ash harmless and to separate and collect the water-soluble salts and the heavy metals for effective use.
For example, wash fly ash with water containing NaHS,
A method of separating and collecting sludge containing heavy metals and salt water in which water-soluble salts are dissolved has been proposed.

[0004]

However, in the above-mentioned conventional separation and recovery method, since salt water adheres to the heavy metal sludge, it is unavoidable that the recovered heavy metals are contaminated with salt, and the quality thereof is significantly improved. There is a problem of decrease.

The present invention solves the above problems, and an object of the present invention is to provide a method for treating fly ash which can efficiently separate and collect heavy metals.

[0006]

In order to solve the above problems, a method for treating fly ash according to the present invention is a method for treating fly ash generated in incineration or melting of waste. A small amount of acid is added to dissolve the heavy metals contained in the fly ash, a heavy metal complexing agent is added to the fly ash to convert the dissolved heavy metals into a complex, and fly ash containing this heavy metal complex is added. Is extracted with carbon dioxide supercritical fluid to extract the heavy metal complexes into carbon dioxide supercritical fluid, and the carbon dioxide supercritical fluid containing the obtained heavy metal complexes is decompressed to improve the dissolving power of this fluid. The amount is reduced and the heavy metal complex is recovered as a solid.

[0007]

Operation: Generally, heavy metals contained in fly ash exist in various forms such as oxides and chlorides. According to the above configuration, since such heavy metals are converted into a complex and easily extracted, when supercritical extraction of fly ash with a carbon dioxide supercritical fluid is performed, the heavy metal complex is converted into a carbon dioxide supercritical fluid. Extracted into the fluid, other salts remain. When the carbon dioxide supercritical fluid containing this heavy metal complex is decompressed, the dissolving power of the fluid is reduced and the heavy metal complex is separated as a solid, so only the heavy metals can be recovered.

[0008]

EXAMPLES A method for treating fly ash according to an example of the present invention will be described below with reference to the flow chart shown in FIG.

In FIG. 1, the fly ash 1 to be treated is
It is generated in the incineration and melting processes of waste such as municipal solid waste and industrial waste. It contains a high concentration of water-soluble salts of sodium chloride and potassium chloride and a small amount of heavy metals such as mercury.

When treating such fly ash 1, the fly ash 1 is put into the heavy metal treatment tank 2, a small amount of acid 3 such as hydrochloric acid is added to the fly ash 1, and both are mixed by stirring. To dissolve heavy metals in fly ash 1. Next, the heavy metal complexing agent 4 is added to the fly ash 1 in the tank 2, and these are mixed by stirring to convert the heavy metals into a complex.

Then, the complex-containing fly ash 5 containing the heavy metal complex in the tank 2 is introduced into the supercritical extraction tank 6, and the carbon dioxide supercritical fluid 7 is subjected to supercritical extraction for an appropriate time to remove the fly ash 5. The heavy metal complex is extracted into the carbon dioxide supercritical fluid 7.

Thereafter, the complex-containing carbon dioxide supercritical fluid 8 containing the heavy metal complex in the tank 6 is introduced into the decompression tank 9 to be decompressed. This depressurization operation is carried out by complex-containing carbon dioxide supercritical fluid 8
May be performed within a range of maintaining the supercritical state, or the complex-containing carbon dioxide supercritical fluid 8 may be transitioned from the critical state to the gas phase by depressurization. The decompression reduces the dissolving power of the fluid 8 and the fluid 8 is separated into the carbon dioxide fluid 10 and the solid 11 containing the heavy metal complex, so that the solid 11 is recovered from the decompression tank 9.

The extraction residue 12 containing salts remaining in the supercritical extraction tank 5 is separately collected. The carbon dioxide fluid 10 in the decompression tank 9 is taken out of the tank 9, supplemented with supplemental carbon dioxide 13 if necessary, and then heated in the heat exchanger 14 and compressed in the compressor 15 so that the carbon dioxide is overheated. Convert to a critical fluid. The obtained carbon dioxide supercritical fluid 7 is recycled back to the supercritical extraction tank 6 for reuse.

As described above, since the heavy metals are converted into the complex, the heavy metals can be supercritically extracted using the carbon dioxide supercritical fluid, and the heavy metals can be efficiently separated and recovered.

[0015]

As described above, according to the present invention, by converting the heavy metals in the fly ash into the complex, only the heavy metals are supercritically extracted by using carbon dioxide which becomes a supercritical state at low temperature and low pressure. However, since it can be obtained as a dried product, it is advantageous in terms of cost and safety.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for treating fly ash according to an embodiment of the present invention.

[Explanation of symbols]

 1 Fly ash 3 Acid 4 Heavy metal complexing agent 5 Complex containing fly ash 7 Carbon dioxide supercritical fluid 8 Complex containing carbon dioxide supercritical fluid 10 Carbon dioxide fluid 11 Solid

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Shibaken 1-47 Shikitsuhigashi 1-47, Naniwa-ku, Osaka City, Osaka Prefecture Kubota Corporation

Claims (1)

[Claims] 1. A method for treating fly ash generated during incineration or melting of waste, comprising adding a small amount of acid to the fly ash to dissolve heavy metals contained in the fly ash. A heavy metal complexing agent is added to the above to convert the dissolved heavy metals into a complex, and fly ash containing the heavy metal complex is supercritically extracted with carbon dioxide supercritical fluid to convert the heavy metal complex into carbon dioxide supercritical fluid. A method for treating fly ash, which comprises recovering a heavy metal complex as a solid by decompressing the obtained carbon dioxide supercritical fluid containing the heavy metal complex to reduce the dissolving power of the fluid.