JPH0919671A - Treatment of flying ashes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to completely separate and recover heavy metals and salts at the time of treating flying ashes contg. heavy metals and salts, such as NaCl and KCl, generated in an incineration treatment and melting treatment of waste. SOLUTION: A small amt. of acid 3 is added to flying ashes 1 to dissolve the heavy metals. The dissolved heavy metals are converted to complexes by addition of a heavy metal complexing agent 4. The flying ashes 5 contg. the complexes are supercritically extracted for suitable time by supercritical water 7, by which the flying ashes are separated to complex-contg. supercritical water 8 and extraction residues 11 contg. the salts. The complex-contg. supercritical water 8 is reduced in pressure and the heavy metal complex solids 10 precipitated by this pressure reduction are separate.

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 generated during incineration or melting of waste such as municipal solid waste and industrial waste.

[0002]

2. Description of the Related Art Conventionally, waste such as municipal waste and industrial waste is incinerated in an incinerator, and the incinerated ash generated here is melted in an ash melting furnace. The molten slag generated by melting is strong against acids and alkalis and difficult to elute heavy metals, so it is very safe and stable.
It has the advantage that the volume is reduced to 1/2 to 1/3 of the incineration ash.

However, fly ash is generated during the incineration or melting of waste, and the fly ash contains a high concentration of 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 render the fly ash harmless and to separate and collect the salts and heavy metals for effective use. For example,
A method has been proposed in which fly ash is washed with water containing NaHS or the like to separate and collect sludge containing heavy metals and salt water in which salts are dissolved.

[0004]

However, in the above-mentioned conventional separation and recovery method, since a large amount of water is used for cleaning fly ash, there is a problem that it is difficult to treat salt water after cleaning.

Further, since salt water adheres to the sludge of heavy metals, it is unavoidable that the recovered heavy metals are contaminated with salt, and there is a problem that the quality thereof is significantly lowered.
The present invention solves the above problems and provides a method for treating fly ash that can completely separate heavy metals and salts such as potassium chloride and sodium chloride, and can easily treat water and the like used for washing fly ash. It is intended to be provided.

[0006]

In order to solve the above problems, a method for treating fly ash according to the present invention is a method of treating heavy metals generated during incineration or melting of waste with salts such as sodium chloride and potassium chloride. A method of treating fly ash containing, wherein a small amount of acid is added to the fly ash to dissolve heavy metals in the fly ash, and then a heavy metal complexing agent is added to form a heavy metal complex, Supercritical water is extracted from the fly ash containing the complex with a supercritical water for a suitable time, the heavy metal complex is extracted into the supercritical water and the salts are left, and the supercritical water from which the heavy metal complex is extracted is decompressed. The solubility of the heavy metal complex is reduced, and thereby the heavy metal complex is deposited and separated.

Generally, heavy metals contained in fly ash exist in various forms such as oxides and chlorides. According to the above-mentioned configuration, since such heavy metals are converted into a complex and made into a form that is easily extracted into supercritical water, by the supercritical extraction, the heavy metal complexes extracted into supercritical water and unextracted sodium chloride are extracted. It can be separated into salts such as and potassium chloride. Further, when the pressure of the supercritical water is reduced, its dissolving power decreases, so that the heavy metal complex can be precipitated from the supercritical water from which the heavy metal complex has been extracted. Therefore, both the heavy metal and the salt can be obtained as a dried product.

In the method for treating fly ash according to the present invention, the water in the supercritical state or in the partial gas state after separating the heavy metal complex is heated and compressed to be made into supercritical water again, and is reused. It was done.

According to the above construction, the water is not discharged to the outside of the system, and the water treatment outside the system becomes unnecessary.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for treating fly ash according to the present invention will be described below with reference to the flow chart shown in FIG.

In FIG. 1, the fly ash 1 as the substance to be treated is
It is generated in the incineration and melting processes of waste such as municipal waste and industrial waste. It contains a high concentration of water-soluble inorganic 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 a heavy metal treatment tank 2, a small amount of an 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 dissolved in the acid 3 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 pressure 218a is applied.
Supercritical water 7 having a temperature of tm or higher and a temperature of 374 ° C. or higher is subjected to supercritical extraction for a proper time to extract the heavy metal complex in fly ash 5 into supercritical water 7.

Then, the complex-containing supercritical water 8 containing the heavy metal complex in the tank 6 is introduced into the decompression tank 9 to be decompressed. This depressurization operation may be performed within a range in which the complex-containing supercritical water 8 is maintained in the supercritical state, or the complex-containing supercritical water 8 may be transferred from the critical state to the gas phase by depressurizing. The reduced pressure reduces the dissolving power of the fluid 8 and the heavy metal complex 10 is deposited as a solid, and thus the deposited heavy metal complex 10 is recovered from the reduced pressure tank 9.

The extraction residue containing the salts 11 remaining in the supercritical extraction tank 5 is separately collected. The water 12 in the supercritical state or in the partial gas state in the decompression tank 9 is taken out from the decompression tank 9,
Make-up water 13 is added if necessary, and then heat exchanger 14
Is heated and compressed in the compressor 15 to be converted into supercritical water 7, and the supercritical water 7 is circulated back to the supercritical extraction tank 6 for reuse.

As described above, since the supercritical water is circulated and used, the water is not discharged to the outside of the system and the problem of the conventional salt water treatment can be avoided. In addition, by controlling the extraction time with supercritical water, it is possible to completely separate heavy metals from salts such as NaCl and KCl. Furthermore, since the heavy metals and salts separated by extraction are obtained as a dry matter,
Easy to handle.

[0017]

As described above, according to the present invention, heavy metals in fly ash are converted into complexes and extracted into supercritical water, and salts such as NaCl and KCl in fly ash are left as extraction residues. By doing so, heavy metals and salts can be completely separated, and each can be obtained as a dry solid.

Further, since the water after separating the heavy metals and the salts is made into the supercritical water and circulated for reuse, the water is not discharged to the outside of the system, and a large amount of the salt water which has been conventionally required. Processing is unnecessary.

[Brief description of the drawings]

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

[Explanation of symbols]

 1 Fly ash 3 Acid 4 Heavy metal complexing agent 5 Complex containing fly ash 7 Supercritical water 8 Complex containing supercritical water 10 Heavy metal complex (solid) 11 Salts (extraction residue) 12 Water in supercritical or partial gas state

Claims (2)

[Claims] 1. A method of treating fly ash containing heavy metals and salts such as sodium chloride and potassium chloride generated in the incineration and melting treatment of waste, which comprises adding a small amount of acid to the fly ash. After the heavy metals in the fly ash are dissolved, a heavy metal complexing agent is added to form a heavy metal complex, and the fly ash containing this heavy metal complex is supercritically extracted with supercritical water for an appropriate period of time to remove the heavy metals. The complex is extracted into supercritical water and the salts are left, and the supercritical water from which the heavy metal complex is extracted is decompressed to reduce its dissolving power, thereby precipitating and separating the heavy metal complex. Fly ash processing method. 2. The fly according to claim 1, wherein water in a supercritical state or in a partial gas state after separating the heavy metal complex is heated and compressed to be made into supercritical water again, and is recycled. Ash treatment method.