JP2003201524A - Waste treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waste treatment method in which lead and zinc are classified from wastes such as fly ash, and removed, the use of chemicals such as acids can be considerably reduced, and a raw material of cement (calcium carbonate) can be obtained. <P>SOLUTION: This waste treatment method comprises a step (A) of obtaining an aqueous solution containing lead and the solid part containing zinc by mixing wastes with a solution containing calcium ions to obtain a slurry, and separating the solid part from the liquid part, a step (B) of obtaining a solution containing lead sulfide and calcium ions by adding a sulfurizing agent to the aqueous solution containing lead, and separating the solid part from the liquid part, a step (C) of obtaining an aqueous solution containing calcium carbonate and zinc by obtaining the slurry by mixing the solid part containing zinc with the solution containing calcium ions, bringing the slurry into contact with gaseous carbon dioxide, adding hydrochloric acid thereto, and separating the solid part from the liquid part, and a step (D) of obtaining an aqueous solution containing zinc sulfide and calcium ions by adding sulfurizing agent to the aqueous solution containing zinc, and separating the solid part from the liquid part. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the separation of lead and zinc from wastes such as soot and dust discharged from incineration facilities, and the utilization of these heavy metals as useful mineral resources. The present invention relates to a waste treatment method for obtaining a high-quality cement raw material (calcium carbonate) having a low content of zinc and chloride ions.

[0002]

2. Description of the Related Art In recent years, soot dust such as incinerated fly ash and molten fly ash,
The amount of incinerated ash such as municipal waste has increased remarkably. on the other hand,
From the viewpoint of environmental protection and the like, it is required to reduce the amount of waste such as soot and dust containing a large amount of heavy metals and to remove heavy metals. On the other hand, heavy metals such as lead and zinc can be used as a useful mineral resource in a non-ferrous smelter without being disposed of as waste if they are separated and collected. Under such circumstances, various methods have been proposed for separating and recovering heavy metals such as lead and zinc from waste such as soot and dust, and recovering them. For example, in Japanese Patent Laid-Open No. 2000-281398,
Wastes such as municipal waste incineration ash are leached with sulfuric acid, copper and zinc contained in the wastes are eluted into the liquid to be separated, and the sulfuric acid leaching residue is leached with alkali at pH 13.5 or more, A waste treatment method is described in which lead in a residue is eluted in a liquid to be separated and gypsum in the residue is converted to calcium hydroxide to be used as a cement raw material.

Further, JP-A-6-170354 discloses a method for treating fly ash containing heavy metals generated from an incinerator or the like, in which a mineral acid is added to the fly ash and the fly ash is dissolved at a pH of 3 or less. , A first step of eluting heavy metals other than lead and filtering out a residue containing lead, and a neutralizing agent is added to the filtrate obtained in the first step to neutralize the pH to 7 or higher to obtain zinc. A method for treating fly ash, which comprises a second step of producing a precipitate of a heavy metal hydroxide mainly consisting of, and filtering the precipitate,
Have been described.

[0004]

SUMMARY OF THE INVENTION In the technique disclosed in the above publication,
Large amounts of acid (eg sulfuric acid) are required to elute heavy metals such as zinc from the waste. In particular, when the waste has a high calcium content and sulfuric acid is used as an acid for eluting heavy metals, the calcium contained in the waste reacts with the sulfuric acid and the sparingly soluble calcium sulfate. Therefore, in order to elute heavy metals such as zinc, there is a problem that more sulfuric acid must be added as compared with the case where calcium does not exist.

In view of the above problems, the present invention can separate lead and zinc from wastes (particularly, soot dust containing a large amount of calcium) and recover them to obtain useful mineral resources. The amount of acid and other chemicals required in the waste treatment process can be significantly reduced, and lead,
An object of the present invention is to provide a method for treating waste, which can obtain a high-quality cement raw material (calcium carbonate) having a low content of zinc and chloride ions.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has combined a specific deleading step and a lead recovery step with a specific dezincification step and a zinc recovery step, By treating waste such as soot and dust,
The inventors have found that the above-mentioned objects can be achieved and completed the present invention.

That is, in the method for treating waste according to claim 1 of the present application, the waste containing zinc and lead and the aqueous solution containing calcium ions are mixed to obtain a slurry, and then the slurry is subjected to solid-liquid separation. And a lead removal step (A) for obtaining a solid content containing zinc and an aqueous solution containing lead and calcium ions,
After adding a sulfidizing agent (for example, NaHS) to the aqueous solution containing the lead and calcium ions obtained in the lead removal step (A), solid-liquid separation is performed, and lead-containing solid content (PbS) and calcium ions are added. A lead recovery step (B) for obtaining an aqueous solution containing: and the zinc-containing solid content obtained in the lead removal step (A),
After mixing with an aqueous solution containing calcium ions to obtain a slurry, the slurry is brought into contact with carbon dioxide gas, hydrochloric acid is then added, and then solid-liquid separation is performed to obtain a solid content containing calcium carbonate and zinc and calcium. A dezincification step (C) for obtaining an aqueous solution containing ions, and a sulfurizing agent (eg, NaHS) added to the aqueous solution containing the zinc and calcium ions obtained in the dezincification step (C), followed by solid-liquid separation Then, a solid content (ZnS) containing zinc and a zinc recovery step (D) for obtaining an aqueous solution containing calcium ions are included.

According to this structure, it is possible to separate lead and zinc from the waste, remove the waste, and recover the waste to obtain a useful mineral resource. Most of the chlorine components (chloride ions) contained in the waste are also eluted in the solution and removed. In addition, during all steps of the method of the present invention, an acid (specifically hydrochloric acid) is used.
Is only added after the carbon dioxide gas is supplied in the dezincification step (C), and the amount used can be small. The calcium ion used for the elution of lead is also repeatedly circulated and used in all steps of the method of the present invention, so that the amount used can be small. Further, the calcium content in the waste is recovered as calcium carbonate containing almost no lead, zinc, or chloride ions, so that it can be suitably used as a raw material for cement.

In the waste treatment method, the calcium ion-containing aqueous solution obtained in the lead recovery step (B) can be used as the calcium ion-containing aqueous solution in the dezincification step (C) (claim). Item 2). According to this structure, the aqueous solution containing calcium ions can be effectively used without waste. In the waste treatment method, the calcium ion-containing aqueous solution obtained in the zinc recovery step (D) can be used as the calcium ion-containing aqueous solution in the lead removal step (A) (claim 3). . According to this structure, the aqueous solution containing calcium ions can be circulated and repeatedly used throughout the steps of the treatment method of the present invention.

In the dezincification step (C), the carbon dioxide gas supply source is, for example, an apparatus for generating exhaust gas containing carbon dioxide gas (claim 4). With this configuration, the exhaust gas emitted from the device (for example, the refuse incineration facility) that generates the waste (for example, the incineration fly ash generated when the refuse is incinerated) that is the target of this method is effective. Can be used for. In the lead removal step (A),
The pH of the slurry is preferably adjusted to 9 to 11.5 (Claim 5). Using an alkaline agent such as caustic soda,
By adjusting the pH within this numerical range, for example, even if the content of calcium in the waste is low and the pH of the slurry becomes about 6 if the pH is not adjusted, The elution rate can be increased.
The aqueous solution containing calcium ions used in the lead removal step (A) and the zinc removal step (C) preferably contains 45,000 to 160,000 mg / L of calcium ions (claim 6). Thus, by adjusting the content rate of calcium ions to 45,000 mg / L or more, lead can be sufficiently eluted, and the content rate is 160,000 mg / L.
By adjusting to L or less, the zinc content does not elute with the lead content in the lead removal step (A), and the chloride that adheres to the solid content when calcium chloride is used as the calcium ion supply source. It is possible to avoid an excessive amount of ions. The solid content containing the calcium carbonate obtained in the dezincification step (C) can be used as a raw material for cement (claim 7). That is, since the calcium carbonate obtained by the method of the present invention contains almost no components such as lead, zinc, and chloride ions that adversely affect the quality of cement, it can be suitably used as a raw material for cement.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the waste treated in the present invention include soot dust and incineration ash discharged from the furnace bottom of an incineration facility. Examples of soot dust include soot dust (melt fly ash) discharged from a facility for melting dust and incineration ash, soot dust (incinerator fly ash) emitted from a facility for incinerating dust and sewage sludge, cement kiln and industrial waste treatment. Examples include soot and dust emitted from the high temperature treatment process of the facility.

[0012] Since soot dust has a higher content of heavy metals such as zinc and lead than incineration ash and the like, it is suitable as a treatment object of the present invention for the purpose of separating and recovering heavy metals. Among them, molten fly ash, zinc, lead, recovered by the method of the present invention,
It is particularly preferable in that it has a high calcium content. In addition, molten fly ash is generally compared with municipal waste incineration ash, etc.
High chlorine (chloride ion) content. The average composition of molten fly ash is 30% by weight of calcium, 9% by weight of sodium, 10% by weight of potassium, 1.6% by weight of lead, 5.4% by weight of zinc, 24% by weight of chlorine (excluding chlorine, converted to oxides. Shows the weight ratio.

An example of the waste treatment method of the present invention will be described below with reference to the drawings. FIG. 1 is a process diagram showing an example of a method for treating waste (fly ash) according to the present invention. Figure 1
Among these, the waste treatment method of the present invention includes respective steps of a lead removal step (A), a lead recovery step (B), a dezincification step (C), and a zinc recovery step (D).

[Lead removal step (A)] First, fly ash to be treated is mixed with an aqueous solution containing calcium ions (eg, calcium chloride solution, calcium nitrate solution, calcium acetate solution, etc.) to form a slurry. . To mix,
For example, fly ash may be put into a dissolution tank that stores an aqueous solution containing calcium ions and stirred for a predetermined time.
As a result, most of the lead and chloride ions in the fly ash are eluted in the aqueous solution. Here, the content rate of calcium ions in the aqueous solution containing calcium ions is 45,000 to 160,
It is preferably 000 mg / L. If the concentration is less than 45,000 mg / L, the lead elution rate may decrease, and lead may not be sufficiently removed.If the concentration exceeds 160,000 mg / L, zinc in fly ash may be eluted at the same time, There is a possibility that the object of the present invention of recovering lead and zinc separately cannot be sufficiently achieved. After the waste and the aqueous solution containing calcium ions are mixed to obtain a slurry, the pH of the slurry is adjusted to 9 to 11.5, if necessary. For example, when the waste to be treated is fly ash having a low calcium content, the pH of the slurry may be about 6. In this case, since the lead elution rate becomes low, an alkaline agent such as caustic soda is added to adjust the pH to 9 to 11.5 to increase the lead elution rate. In an aqueous solution containing calcium ions,
Of the calcium content in fly ash, water-soluble calcium chloride is eluted with lead in the aqueous solution, and calcium hydroxide is
It remains as a solid with zinc.

When the molten fly ash having a high calcium content is to be treated, the aqueous solution containing calcium ions preferably has a low content of sulfate ions. This is because the elution of lead is suppressed when the aqueous solution contains a large amount of sulfate ions. Next, the slurry is solid-liquid separated into a solid content and a liquid content. As the solid-liquid separation method, for example, a method by filtration using a filtration device,
Examples thereof include a method using a thickener (for example, gravity sedimentation, centrifugation, sedimentation with a flocculant, etc.). The solids thus obtained contain zinc, calcium hydroxide and the like, and the liquids contain lead, calcium ions, chloride ions eluted from fly ash and the like. The separated solid content and liquid content are respectively dezincification step (C) and lead recovery step (B).
Is processed in.

[Lead recovery step (B)] When a sulfidizing agent is added to the liquid component (aqueous solution containing lead, calcium ion, chloride ion, etc.) obtained in the deleading process (A), lead in the liquid component ( Pb ²⁺ )
Reacts with the sulfide ion (S ^2- ) to produce lead sulfide (PbS), which precipitates. Here, examples of the sulfiding agent include sodium hydrosulfide (NaHS), sodium sulfide (Na ₂ S), and the like. It is desirable that the amount of the sulfurizing agent added is slightly less than the amount required to sulfurize all the lead in the liquid. The reason is that when the sulfiding agent remains in the liquid, the sulfiding agent suppresses the elution of zinc in the dezincification step (C). Even if a small amount of lead remains in the liquid due to a shortage of the sulfidizing agent for producing lead sulfide, this lead is removed together with zinc in the dezincification step (C).

After producing lead sulfide, solid-liquid separation is performed to recover lead sulfide. Examples of the solid-liquid separation method include the same methods as described above (for example, filtration and a method using a thickener). The obtained lead sulfide can be used as a refining raw material or the like. On the other hand, part of the liquid component containing calcium ions after removing lead sulfide is discharged to the outside of the system for wastewater treatment, and the rest is sent to the dezincification step (C) for reuse.

[Zinc removal step (C)] Solid content obtained in the lead removal step (A) (containing zinc, calcium hydroxide, etc.)
Is mixed with the liquid component (aqueous solution containing calcium ions) obtained in the lead recovery step (B) to form a slurry. First, carbon dioxide gas (CO ₂ ) is blown into this slurry. Carbon dioxide gas reacts with the calcium content in the slurry to produce calcium carbonate (CaCO ₃ ). Also, the pH of the slurry
Is reduced to 6 or less by blowing carbon dioxide gas. As the carbon dioxide gas, exhaust gas discharged from a refuse incineration facility, an incineration ash melting facility, or the like can be used.

Next, hydrochloric acid is added to the slurry. Then,
Most of the zinc contained in the solid content of the slurry elutes in the aqueous solution. At this time, the calcium carbonate contained in the solid content does not elute and remains as the solid content. The amount of hydrochloric acid is 10% per liter of slurry in an aqueous solution having a concentration of 35% by weight.
~ 80 ml. If the amount is less than 10 ml, the amount of zinc eluted will be small, and zinc may remain in the calcium carbonate used as a cement raw material, and if the amount exceeds 80 ml, calcium will elute in the liquid and the cement raw material Not only the amount of calcium carbonate used as
The use of a large amount of hydrochloric acid causes an increase in cost.

When zinc is eluted, the concentration of calcium ions in the slurry is preferably 45,000 to 160,000 mg / L. If the concentration is less than 45,000 mg / L, the dissolution rate of zinc may decrease, and if the concentration exceeds 160,000 mg / L, when high concentration chloride ions are present along with calcium ions, However, the amount of chloride ions adhering to the cake (solid content) increases, and the content of chloride ions in calcium carbonate used as a cement raw material increases, which may lead to deterioration in the quality of calcium carbonate. After the zinc is eluted, the slurry is subjected to solid-liquid separation to obtain an aqueous solution containing a solid content of calcium carbonate and zinc and calcium ions. Examples of the solid-liquid separation method include the same methods as described above (for example, filtration and a method using a thickener). The cake (solid content consisting of calcium carbonate) obtained by solid-liquid separation is thoroughly washed with water,
Chlorine (chloride ion) is removed. The calcium carbonate thus obtained has a low content of heavy metals such as lead and zinc and chloride ions, and can be suitably used as a raw material for cement.

[Zinc recovery step (D)] Dezincification step (C)
In an aqueous solution containing zinc and calcium ions obtained in
Add sulfiding agent. Here, as the sulfiding agent, the same one as the sulfiding agent used in the lead recovery step (B) (for example, sodium hydrosulfide or the like) can be used. By the addition of the sulfiding agent, zinc (Zn ²⁺ ) in the liquid content reacts with the sulfide ion (S ²⁻ ) to produce zinc sulfide (ZnS) and precipitate. On this occasion,
It is desirable that the addition amount of the sulfurizing agent is slightly less than the amount required for sulfurizing all the zinc in the liquid. The reason is that when the sulfiding agent remains in the liquid, the sulfiding agent suppresses the elution of lead in the deleading step (A). Even if a small amount of zinc remains in the liquid due to a shortage of the sulfidizing agent for producing zinc sulfide, the zinc is dissolved in the aqueous solution containing calcium ions, and the lead removal step (A) is performed. Are combined in the slurry and treated again by the same treatment step as described above.

As a chemical to be added to an aqueous solution containing zinc and calcium ions, a neutralizing agent such as sodium hydroxide can be used together with the sulfiding agent. For example, when sodium hydroxide is used, hydroxide ion reacts with zinc ion in addition to the neutralization reaction with acid (hydrogen ion), and produces sparingly soluble zinc hydroxide (Zn (OH) ₂ ). Let Zinc hydroxide can be recovered as a solid content together with zinc sulfide (ZnS). However, when the amount of the neutralizing agent becomes excessive, zinc hydroxide reacts with hydroxide ions and changes into water-soluble tetrahydroxozincate ions ([Zn (OH) ₄ ] ^2- ). Therefore, it is necessary to keep the amount of the neutralizing agent added below a certain level. After producing zinc sulfide, solid-liquid separation is performed to recover zinc sulfide. Examples of the solid-liquid separation method include the same methods as described above (for example, filtration and a method using a thickener). The obtained zinc sulfide can be used as a refining raw material or the like. On the other hand, the liquid component containing calcium ions after removing zinc sulfide is sent to the lead removal step (A), circulated and repeatedly used.

[0023]

[Example] [Example 1] Molten fly ash (CaO: 29%, Na ₂ O: 1)
5%, K ₂ O: 4.5%, Cl: 16%, Zn: 10.5%, Pb: 3.5%;
However, "%" is based on weight. ) To 1 kg, add 6 liters of an aqueous solution containing 20% by weight of calcium chloride,
It was made into a slurry. After stirring this slurry for 0.5 hour to elute lead, this slurry was filtered to obtain a solid content (cake) and a filtrate. Sodium hydrosulfide (10.5 g) was added to the filtrate to generate a precipitate, which was then subjected to solid-liquid separation using a filter press as a filtering means, and lead sulfide (34.3 g, dry weight).
Was recovered. Next, 0.75 kg of deleaded solids (cake)
After adding 5 liters of an aqueous solution containing 20% by weight of calcium chloride to (dry weight) to form a slurry, carbon dioxide gas was blown into the slurry to lower the pH of the slurry to 5.5. Further, 200 ml of 35% by weight hydrochloric acid was added to the slurry to elute zinc, and the slurry was filtered to recover 0.68 kg (dry weight) of solid content consisting of calcium carbonate. 75 g of sodium hydrosulfide was added to this filtrate to form a precipitate,
Solid-liquid separation using a filter press as a filtration means,
101.7 g (dry weight) of zinc sulfide was recovered.

[Example 2] Molten fly ash (Ca0: 29%, Na
₂₀ : 15%, K ₂₀ : 4.5%, Cl: 16%, Zn: 10.5%, Pb: 3.
5%) (1 kg) was added with 6 liters of a filtrate (calcium ion concentration: 68,000 mg / L) obtained by filtering zinc sulfide obtained in Example 1 to obtain a slurry. The slurry was stirred for 0.5 hours to elute lead and then filtered to remove solids (cake).
And a filtrate was obtained. Add 10 g of sodium hydrosulfide to this filtrate,
After forming a precipitate, solid-liquid separation was performed using a filter press as a filtering means, and 34.5 g (dry weight) of lead sulfide was recovered. Next, 5 liters of the filtrate from which lead had been removed was added to 0.76 kg of the deleaded solid content (cake) to form a slurry, and carbon dioxide gas was blown into the slurry to adjust the pH of the slurry.
Lowered to 5.5. Further, 200 ml of 35 wt% hydrochloric acid was added to the slurry to elute zinc, and then the slurry was filtered to collect 0.66 kg (dry weight) of solid content consisting of calcium carbonate. Sodium hydrosulfide (75 g) was added to the filtrate to form a precipitate, which was then subjected to solid-liquid separation using a filter press as a filtering means, and zinc sulfide (101.5 g (dry weight)).
Was recovered. The filtrate from which zinc sulfide was filtered off was returned to the initial lead removal step and repeatedly used as an aqueous solution containing calcium ions for slurrying the molten fly ash.

[0025]

According to the waste treatment method of the present invention, lead and zinc can be separated and removed from the waste to be recovered and used as a raw material for the Yamamoto reduction in a smelting plant. Further, in the method of the present invention, since the amount of the drug used can be small, the processing cost can be reduced and the processing can be efficiently performed. That is, in the whole process, hydrochloric acid is added only in a relatively small amount after the carbon dioxide gas is supplied in the dezincification process (C), and calcium ions are repeatedly circulated and repeatedly used, and it is necessary to constantly supply a large amount. Absent. Further, the calcium content in the waste is recovered as calcium carbonate containing almost no lead, zinc, or chloride ions, and is therefore preferably used as a raw material for cement.

[Brief description of drawings]

FIG. 1 is a process chart showing an example of a method for treating waste (fly ash) according to the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22B 13/00 C22B 13/04 19/30 3/00 RQ F term (reference) 4D004 AA36 AA37 BA02 BA05 CA12 CA13 CA15 CA34 CA35 CA41 CB05 CC01 CC11 CC12 DA03 DA10 DA20 4K001 AA20 AA30 AA36 BA14 CA02 DB08 DB23 DB24

Claims (7)

[Claims] 1. A waste containing zinc and lead is mixed with an aqueous solution containing calcium ions to obtain a slurry, and the slurry is subjected to solid-liquid separation to obtain a solid content containing zinc and lead and calcium ions. Lead removal step (A) for obtaining an aqueous solution containing
And, after adding a sulfiding agent to the aqueous solution containing lead and calcium ions obtained in the lead removal step (A), solid-liquid separation is performed to obtain an aqueous solution containing lead-containing solids and calcium ions. After the recovery step (B), the solid content containing zinc obtained in the lead removal step (A), and the aqueous solution containing calcium ions are mixed to obtain a slurry, the slurry is brought into contact with carbon dioxide gas. Then, hydrochloric acid is added, and then solid-liquid separation is performed to obtain a solid content containing calcium carbonate and an aqueous solution containing zinc and calcium ions, and a dezincification step (C) obtained in the dezincification step (C). And a zinc recovery step (D) for obtaining an aqueous solution containing calcium ions and a solid content containing zinc after solid-liquid separation after adding a sulfiding agent to the aqueous solution containing zinc and calcium ions. Waste to be Processing method. 2. The aqueous solution containing the calcium ions obtained in the lead recovery step (B) is the dezincification step (C).
The method for treating waste according to claim 1, wherein the method is used as an aqueous solution containing the calcium ion according to claim 1. 3. The aqueous solution containing the calcium ions obtained in the zinc recovery step (D) is the lead removal step (A).
The method for treating waste according to claim 1 or 2, wherein the method is used as an aqueous solution containing the calcium ion. 4. The waste according to claim 1, wherein in the dezincification step (C), the carbon dioxide gas supply source is a device that generates an exhaust gas containing carbon dioxide gas. Processing method. 5. The method for treating waste according to claim 1, wherein in the lead removal step (A), the pH of the slurry is adjusted to 9 to 11.5. 6. The aqueous solution containing the calcium ions used in the lead removal step (A) and the dezincification step (C) contains 45,000 to 160,000 mg / L of calcium ions, respectively. The method for treating waste according to any one of items. 7. The method for treating waste according to claim 1, wherein the solid content containing the calcium carbonate obtained in the dezincification step (C) is used as a raw material for cement.