JP2000054038A - Treatment of calcium-containing incineration fly ash and molten fly ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating method of fly ash capable of simply separating heavy metals such as lead and zinc in a stable form from incineration fly ash or molten fly ash containing calcium. SOLUTION: The treating method of the fly ash comprises of a 1st process of adding a dil. hydrochloric acid into the fly ash containing the heavy metals, salts and unreacted slaked lime to make into sludge, eluting the most part of the salts containing calcium chloride and zinc, and then solid-liquid separating and a 2nd process of adding an ammonium chloride aq. solution to the resultant residue to make into sludge again, solubilizing the unreacted slaked lime, and then solid-liquid separating to obtain a residue containing the heavy metal consisting essentially of lead. And further a 3rd process of making the residue obtained in the 2nd process into sludge in an aq. solution, adding sulfuric acid to make it acidic to elute the metals except lead and solid-liquid separating to obtain residue containing lead is provided and next, the liquid phases obtained in each process are mixed and after made it alkaline with an alkali agent, the hydroxides and the sulfides of the heavy metals consisting essentially of zinc are precipitated by adding a sulfidizing agent.

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 calcium, and more particularly to a method for treating waste gas generated from incinerators and melting furnaces in municipal garbage incineration plants and industrial waste incineration plants. The present invention relates to a fly ash treatment method capable of recovering heavy metals such as lead, zinc, and the like from a bag filter fly ash sprayed with slaked lime as a sum treatment agent.

[0002]

2. Description of the Related Art Conventionally, as a method for recovering heavy metals from fly ash containing heavy metals such as lead and zinc generated from incinerators and melting furnaces, fly ash is dissolved with an acid, and heavy metals other than lead are converted into a liquid phase. A process of eluting and recovering a residue containing lead as a main component, and adding a sulfide agent to the liquid phase to recover a sulfide precipitate mainly containing zinc (see Japanese Patent Application Laid-Open No. 8-141439). ). However, the current mainstream of exhaust gas treatment for incinerators or melting furnaces is dry neutralization treatment in which slaked lime is directly sprayed on exhaust gas. Therefore, fly ash obtained by the dry exhaust gas treatment method necessarily has a high content of slaked lime, that is, calcium. When the above-mentioned conventional heavy metal recovery process is applied to slaked lime-containing fly ash, sulfuric acid and calcium in slaked lime react to produce gypsum, and the quality of the recovered heavy metal is reduced.

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention solves the above-mentioned problems of the prior art, and stabilizes heavy metals such as lead and zinc contained in fly ash containing slaked lime. It is an object of the present invention to provide a method for recovering heavy metals in fly ash from an incinerator and a melting furnace, which can be separated into high-quality incinerators.

[0004]

In order to solve the above-mentioned problems, according to the present invention, heavy metals containing lead and zinc generated from an incinerator and a melting furnace sprayed with slaked lime, salts containing calcium chloride, and salts and unreacted materials containing calcium chloride In the method for treating fly ash containing slaked lime, the fly ash is added with diluted hydrochloric acid to form a muddy state, and after eluting most of salts and zinc containing calcium chloride, a first step of solid-liquid separation, The second step of solubilizing unreacted slaked lime by adding an aqueous solution of ammonium chloride to the obtained residue to re-slurry, and then performing solid-liquid separation to obtain a residue containing a heavy metal mainly composed of lead. This is a method for treating fly ash.

[0005] In the above treatment method, the liquid phase obtained by the solid-liquid separation in the first step and the second step is made alkaline by adding an alkali agent to form a heavy metal hydroxide mainly composed of zinc. Alternatively, solid-liquid separation may be performed, or the solid-liquid separation may be performed by further adding a sulfurizing agent to precipitate the remaining heavy metals as sulfides. In the above treatment method, the residue obtained in the second step is re-mudged in an aqueous solution, adjusted to acidic conditions by adding sulfuric acid, eluted with metals other than lead, and subjected to solid-liquid separation. And a third step of obtaining a residue containing Furthermore, in the present invention, the liquid phase obtained by the solid-liquid separation in the first, second and third steps is made alkaline by adding an alkali agent while mixing and stirring them.
The method may further comprise a fourth step of adding a sulfurizing agent to an equivalent or more of zinc in the fly ash to produce a hydroxide precipitate and a sulfurized precipitate of heavy metals mainly containing zinc.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating fly ash containing heavy metals such as lead and zinc generated from an incinerator and a melting furnace sprayed with slaked lime, calcium chloride and unreacted slaked lime. The fly ash is eluted with dilute hydrochloric acid to elute most of salts such as calcium chloride and zinc, followed by solid-liquid separation, and the resulting residue is re-mudged in an aqueous ammonium chloride solution (repulpable ), Solubilizing the unreacted slaked lime, and then solid-liquid separation of the residue containing heavy metals containing lead as a main component. Processing method.

Hereinafter, the present invention will be described in detail. First, slaked lime-added molten fly ash generated during the melting treatment of incinerated ash in an urban refuse incineration plant is added to dilute hydrochloric acid, repulped, and stirred at room temperature. Preferably, the stirring time is 30 minutes or more. Next, the slurry is subjected to solid-liquid separation,
A filtrate containing a Cl compound, a Ca compound, and a Zn compound;
It is separated into heavy metal-containing residues mainly composed of lead (first step). The residue obtained as described above is added to an aqueous solution of ammonium chloride in an amount equivalent to or more than calcium in the fly ash, and the mixture is stirred to solubilize unreacted slaked lime, thereby improving the lead content of the residue. To obtain a lead-containing residue (second step). The reaction between slaked lime and ammonium chloride in this step is as follows. Ca (OH) ₂ + 2NH ₄ Cl → CaCl ₂ + 2H
₂ O + 2 NH ₃ The ammonia gas generated by this reaction is transferred to an exhaust gas line of an incinerator or melting furnace and reused as a dry NOx remover.

[0008] Zinc is made alkaline by adding an alkali agent such as sodium hydroxide to the liquid phase obtained by the solid-liquid separation in the first step and the second step. Generate oxides and perform solid-liquid separation, or
Instead of solid-liquid separation, a sulfurizing agent such as sodium hydrosulfide is further added to precipitate the remaining heavy metals as sulfides, and these precipitates are collected by solid-liquid separation. Furthermore, in order to raise the lead quality of the lead-containing residue, the residue of the second step is dissolved in water to form a slurry. Solubilize heavy metals. The lead in the slurry is recovered as a sulfuric acid precipitate (third step).

The recovery of zinc is carried out by mixing the filtrates obtained in the first, second and third steps, adding an alkali agent such as sodium hydroxide while stirring, and hydrolyzing under alkaline conditions. By adding a sulfurizing agent such as sodium,
Precipitating heavy metals such as zinc as hydroxides and sulfides,
This solution is subjected to solid-liquid separation (fourth step). As described above, in the present invention, heavy metals contained in slaked lime-containing fly ash can be separated and recovered into high-grade lead-containing residues and zinc-containing residues without being disturbed by the added slaked lime,
These recovered materials can be used as secondary raw materials for non-ferrous smelting.

[0010]

The present invention will be described below in more detail with reference to examples. Example 1 FIG. 1 shows an overall flow process diagram of the processing method of the present invention.
In this embodiment, fly ash in an incinerator and a melting furnace is treated according to the flow shown in FIG. 1 liter of 1N hydrochloric acid
100 g of fly ash is added and stirred for 30 minutes. This slurry is subjected to solid-liquid separation, separated into a residue containing heavy metals and a filtrate containing a Cl compound, and the obtained residue is added to 1 liter of a 1.6 N aqueous ammonium chloride solution and extracted with stirring for 30 minutes. This slurry can be separated into an aqueous solution containing calcium and zinc and a residue containing lead and zinc by solid-liquid separation.

The residue obtained here is repulped with 1 liter of water, sulfuric acid is added to the solution, and stirring is continued for at least 30 minutes while maintaining acidic conditions. Here, lead is precipitated. Next, this slurry is separated into a filtrate containing heavy metals other than lead and a lead-containing residue by solid-liquid separation. The filtrate obtained above, the filtrate, and the filtrate are combined, and a 5N sodium hydroxide solution as a neutralizing agent is added thereto, and the mixture is adjusted to alkaline conditions. After the pH adjustment, stirring is continued for at least 30 minutes to form a hydroxide precipitate such as zinc. Then, add sodium hydrosulfide to 15
g (equivalent of zinc contained in fly ash) is added, and stirring is maintained for at least 30 minutes to convert heavy metals other than zinc into sulfide precipitates. By subjecting this solution to solid-liquid separation, a zinc-containing residue and comprehensive wastewater can be obtained.

Table 1 shows the analysis values of the lead-containing residue, the zinc-containing residue, and the total wastewater when the treatment was carried out by the conventional method and the present method.

[Table 1]

As can be seen from Table 1, in the conventional treatment, the lead-containing residue contains about 25% calcium, so that the lead content is about 4%. The zinc content of the zinc-containing residue was 40%. However, when the present invention is used, the lead content in the lead-containing residue is 2%.
6.1%, and the zinc content in the zinc-containing residue is 72.1%. These are higher in quality than the conventional method, and can be sufficiently used as a secondary nonferrous smelting raw material. In addition, general wastewater is below the wastewater standard and can be discharged directly to rivers and the sea.

[0014]

According to the present invention, heavy metals contained in slaked lime-containing fly ash can be separated as high-quality lead-containing residues and zinc-containing residues without being hindered by calcium compounds. The product can be used as a secondary material for non-ferrous smelting.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of a processing method according to the present invention.

Claims (4)

[Claims] 1. A method for treating fly ash containing heavy metals containing lead and zinc, salts containing calcium chloride, and unreacted slaked lime generated from an incinerator and a melting furnace sprayed with slaked lime. After adding dilute hydrochloric acid to make muddy and elute most of salts and zinc containing calcium chloride,
The first step of solid-liquid separation, and by adding an aqueous solution of ammonium chloride to the obtained residue to re-slurry, solubilize unreacted slaked lime, and then perform solid-liquid separation, and mainly contain lead A method for treating fly ash, comprising a second step of obtaining a residue containing a heavy metal. 2. The liquid phase obtained by the solid-liquid separation in the first step and the second step is made alkaline by adding an alkali agent, and solidified by generating a heavy metal hydroxide containing zinc as a main component. 2. The method according to claim 1, wherein the liquid heavy is separated or solid-liquid separated, and a sulfurizing agent is further added to precipitate remaining heavy metals as sulfides, and these precipitates are subjected to solid-liquid separation. Fly ash treatment method. 3. The residue obtained in the second step is re-slurried in an aqueous solution, adjusted to an acidic condition by adding sulfuric acid, and eluted with a metal other than lead to perform solid-liquid separation. The method for treating fly ash according to claim 1, comprising a third step of obtaining a contained residue. 4. A liquid phase obtained by the solid-liquid separation in the first, second and third steps is made alkaline by adding an alkali agent while mixing and stirring them, and furthermore, fly ash is added to the fly ash. 4. The method for treating fly ash according to claim 3, comprising a fourth step of adding an amount of zinc or more contained therein to an amount equivalent to or greater than zinc to form a hydroxide precipitate and a sulfide precipitate of heavy metals mainly containing zinc.