JP2003211122A - Treatment method for fly ash containing heavy metals - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method in which useful heavy metals in fly ash are separated from chlorine and separated/recovered in a recyclable form in a smelting process. <P>SOLUTION: This method includes a process in which fly ash is added with an alkaline agent, preferably, sodium hydroxide solution so as to leach the heavy metals, thereafter, the slurry is deluted and adjusted to pH 7-13 by adding a mineral acid, and then separated into precipitates containing the heavy metals and chlorine solution. If required, a heat-treating process in which the precipitates containing the heavy metals are further heated and treated, is added to the method. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heavy metals such as copper, zinc and lead generated from incinerators and melting furnaces in municipal waste incinerators and industrial waste incinerators or cement kilns for treating sludge, and chlorine. The present invention relates to a method for treating fly ash containing.

[0002]

2. Description of the Related Art Generally, garbage discharged from business establishments and households (referred to as "urban waste" or "general waste") is collected in municipal waste incinerators or industrial waste incinerators. It is incinerated. At that time, the incineration ash and fly ash generated from the incinerator and the like are deposited at the final disposal site after chemical treatment or intermediate treatment such as melting furnace and cement kiln treatment. However, according to the intermediate treatment such as the above melting furnace and cement kiln treatment, heavy metals with high vapor pressure such as zinc, lead, and cadmium volatilize in the furnace and enter the exhaust gas, and the heavy metal in this exhaust gas is processed by the exhaust gas treatment. There was a problem that it condensed in the facility and turned into fly ash again. Heavy metals such as copper, zinc, lead and cadmium as well as chlorine, sodium and calcium are concentrated and contained in a large amount in this fly ash again, and a stable fly ash treatment method including recovery of these heavy metals is available. It was wanted.

Regarding such fly ash, JP-A-7-10
No. 9533 discloses that fly ash is suspended in water in a tank, and the pH of the suspension is adjusted to an appropriate value in an alkaline range by adding an acid or an alkali to precipitate heavy metal in the fly ash as a hydroxide. And a method for recovering the precipitate is disclosed. In addition, the present applicant has also previously filed an invention of a method of coping with a wet processing method (Japanese Patent Laid-Open No. 8-117724 and Japanese Patent Laid-Open No. 8-14153).
No. 9).

In Japanese Unexamined Patent Publication No. 8-117724, a first step in which fly ash is slurried with water, pH is adjusted to perform solid-liquid separation, and a substance from the first step is repulped with an acid solution to obtain a pH value.
After adjusting to 3 or less, a second step of solid-liquid separation to obtain a lead residue and a neutralizer or sodium hydrosulfide are added to the acidic filtrate from the first step and the second step to add zinc and copper. A method comprising a third step of filtering the contained substances by filtration and using the filtered water as drainage liquid is disclosed in JP-A-8-141539, in which fly ash is neutralized with water and a neutralizing agent. From the second step, the first step of solid-liquid separation by repulping, the repulping of the sludge from the first step, pH adjustment to about 3 with sulfuric acid, and the solid-liquid separation to obtain lead residue A third step of adding an alkaline neutralizing agent to the filtrate of step 1 to filter out a precipitate containing zinc and copper, and
A method is disclosed in which the filtered water of the step is repeatedly used as the neutralizing solution of the first step, and a sulphating agent is added to the filtrate from the first step to perform drainage treatment. By such a wet treatment method, the heavy metals contained in the fly ash are separated in a stable form and are effectively recovered as heavy metal resources. It became possible to render it harmless in accordance with the regulations of Article 3, Paragraph 1 of the Water Pollution Control Law.

[0005]

However, according to the above-mentioned Japanese Patent Laid-Open No. 7-109533, there are cases where chlorine enters into the recovered heavy metal compound as an oxychloride which is a sparingly soluble compound such as lead and copper. Since chlorine is inconvenient in the smelting process, there still remains a problem in terms of recycling heavy metals. Especially, when the copper content in the fly ash is high, a large amount of copper oxychloride is produced, and the chlorine content in the heavy metal precipitates is considerably high. It is known that the copper content and the chlorine content are correlated. . Therefore, a smelting raw material having a higher copper grade and a higher value has a higher chlorine content and is difficult to be used as a smelting raw material, which is a paradoxical situation.

[0006] As a method for reducing the chlorine content in the recovered heavy metal precipitate, the present applicant has filed a Japanese Patent Application No. 2000-1706.
Proposed in No.52. In this treatment method, fly ash is repulped with water to a pulp concentration of 40 wt% or more, an alkaline agent is added to adjust the pH to 13 or more, and an alkali leaching solution and an alkali insoluble residue are obtained, and the alkali leaching step. After re-pulping the alkali-insoluble residue filtered off from water with water, mineral acid is added to adjust the pH to 2 to 5,
The mineral acid leaching step and the mineral acid leaching step for obtaining a mineral acid insoluble residue, and the alkaline leaching solution from the alkali leaching step are mixed with the mineral acid leaching solution from the mineral acid leaching step to obtain a pH of 10 to 13 p.
A method for recovering heavy metals from fly ash, comprising: a heavy metal compound neutralized in the H region and containing at least one heavy metal of copper, zinc or lead; and an alkali neutralization step for obtaining an alkali neutralizing solution. Therefore, it became possible to obtain heavy metal impurities with high quality and low chlorine content. However, since the number of processes is large, problems remain in terms of equipment cost and drug cost.

Further, as a method using alkali leaching, JP-A-10-5736 discloses that copper, zinc and lead are leached in an alkaline region having a pH of 12.5 or higher and solid-liquid separation is carried out.
A method of recovering the eluted heavy metals in the liquid as sulfides has been proposed. However, in the method using this sulfiding agent, chlorine in the leachate is mixed in the recovered material, which also leaves a problem in the use as a smelting raw material. In view of such a situation, the present invention collects useful heavy metals in fly ash, and by reducing chlorine to the maximum, a fly ash that can be separated and collected in a reusable form in a smelting process. The purpose is to provide a processing method.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object. Firstly, a fly ash containing at least one heavy metal of copper, zinc and lead and chlorine is used as an alkali. Containing a heavy metal, characterized in that after leaching the heavy metal by adding an agent, water is added, then mineral acid is added to adjust the pH to 7 to 13 and solid-liquid separation is carried out into a heavy metal-containing substance and a chlorine-containing liquid. Secondly, the method of treating fly ash is
An alkali agent is added to fly ash containing at least one heavy metal of lead and chlorine to leach the heavy metal, and then a mineral acid is added to adjust the pH to 7 to 13 to fix the heavy metal-containing substance and the chlorine-containing liquid. Thirdly, a method for treating fly ash containing heavy metal, characterized in that liquid separation is carried out. Thirdly, the fly ash containing at least one heavy metal of copper, zinc and lead and chlorine is added with an alkali agent to obtain the heavy metal. The method for treating fly ash containing heavy metal is characterized in that solid-liquid separation is carried out into a heavy metal-containing substance and a chlorine-containing liquid. Fourth, at least one heavy metal of copper, zinc and lead and chlorine A method for treating fly ash containing heavy metal, comprising adding an alkali agent to fly ash containing leaching the heavy metal, and then adding water to perform solid-liquid separation into a heavy metal-containing precipitate and a chlorine-containing liquid. Fifth, the slurry temperature during the leaching is set to 30 ° C. The above method for treating fly ash containing heavy metal according to any one of the first to fourth, and sixthly, the heavy metal-containing substance is heated to 100 to 1000 ° C. to volatilize chloride contained therein. The method for treating fly ash containing the heavy metal according to any one of the first to fifth aspects,
The oxygen concentration in the atmosphere during the heat treatment is 0.1 to 2
The method for treating fly ash containing a heavy metal according to the sixth aspect, which is 1%, and the eighth aspect, containing the heavy metal according to any one of the first to fifth aspects, wherein the heavy metal-containing substance is used as a smelting raw material. Ninth, there is provided a method for treating fly ash containing heavy metal according to the sixth or seventh aspect, wherein the heat-treated heavy metal-containing precipitate is used as a smelting raw material.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A method for treating secondary fly ash (hereinafter simply referred to as fly ash) generated in the incineration ash treatment of an urban refuse incineration plant or the like is claimed as an embodiment of the present invention. The processing steps of Item 1 will be described with reference to FIG. Copper for fly ash,
Those containing at least one of zinc and lead and chlorine are suitable for the present invention, and it is even better if the copper content is 1 wt% or more. In the treatment method using leaching with a mineral acid, it is difficult to reduce chlorine when the copper content is 1 wt% or more, but the treatment method according to the present invention can reduce chlorine even if the copper content is high. Unless otherwise specified, the embodiments of the invention described below are performed at a liquid temperature of 30 to 40 ° C. under an air atmosphere.

First, fly ash is directly mixed with an alkaline agent. The mixed state has a good slurry state, and the leaching reaction is allowed to proceed while stirring or kneading the slurry, and an alkali leaching step of once transferring heavy metals such as copper, zinc and lead to the liquid side is performed. The alkaline agent used at this time is N
A solution of at least one metal hydroxide selected from a and K dissolved in water can be used. However, since the hydroxide of K is expensive, the hydroxide of Na is preferable.

When carrying out the alkali leaching step, a method of providing a water washing step as a pre-step and carrying out an alkali leaching reaction on the substance after the water washing can be considered. In this method, soluble salts are removed by washing with water, so that the leaching efficiency is increased, but since the number of steps is increased by one, the washing step must be omitted if there is no room in the equipment. It was found that chlorine can be sufficiently reduced by setting the temperature of the slurry to 30 ° C. or higher without the water washing step as in the present invention. Here, the temperature of the slurry is set to 30 ° C. or higher because the temperature is lower than 30 ° C., especially at a low temperature of 20 ° C. or lower, KCl, Na ₂ SO ₄ , and Na.
_{This is because} the solubility of salts such as ₂ CO ₃ decreases and a part of them remains in the precipitate, which reduces the leaching efficiency. In addition,
The upper limit of the slurry temperature is 100 ° C. or lower in view of the cost of heat resistance of the apparatus, the running cost of heating the slurry, the balance of the effects of leaching, dechlorination, etc. (that is, the slurry temperature range is 30 to 100 ° C.). Is preferred,
50 ° C or lower (that is, the slurry temperature range is 30 to 50)
° C. ) Is more preferable.

Further, the applicant of the present invention previously disclosed in Japanese Patent Laid-Open No. 2000-21.
2654 proposes a method in which fly ash is once slurried with water and then an alkaline agent is added. But,
This treatment method has a problem that chlorine content of 2% or more remains because the alkali concentration in the slurry is significantly reduced. Furthermore, when neutralizing with sulfuric acid after leaching, it has been known that gypsum and calcium chloride are produced when the alkali concentration is low, which has disadvantages such as an increase in chlorine concentration and an increase in the amount of substances generated. . The treatment method proposed by the present invention can surely reduce chlorine in the recovered precipitate while suppressing the addition amount of the alkaline agent.

The amount of the alkaline agent added is determined by the heavy metal content in the fly ash, and the higher the heavy metal content, the larger the amount of the alkaline agent to be used. Therefore, it is desirable to determine the addition amount of the alkaline agent in consideration of the heavy metal content rate and the heavy metal extraction rate in the fly ash. In addition, it should be taken into consideration that the leaching reaction with a slurry concentration as high as possible enables a large amount of heavy metal to be leached with a small amount of the alkali agent, and thus can reduce the cost of the alkali agent. From this point of view, the slurry concentration when leaching heavy metals by adding an alkaline agent to fly ash is 500 g / L.
The above is preferable, and 1000 g / L or more is more preferable.

Further, as shown in FIG. 3, the slurry in the alkali leaching step is subjected to solid-liquid separation into a heavy metal-containing substance and a chlorine-containing liquid without a diluting step and a neutralizing step, and the chlorine-containing solution is directly used as the alkali. It is also possible to repeat the leaching process.

Next, water is added to the slurry to dilute it, and then a mineral acid such as sulfuric acid is added to adjust the pH to 7 to 13, whereby the leached heavy metal is precipitated as a hydroxide, and the heavy metal-containing precipitate and chlorine are added. Solid-liquid separation into a chlorine-containing liquid containing sodium, etc. (heavy metal separation step). The obtained heavy metal-containing precipitate is washed with water as necessary and used as a smelting raw material. The reason for diluting by adding water here is that solid-liquid separation cannot be performed when the slurry concentration after alkali leaching is high, and there is a temperature rise due to heat of neutralization during neutralization treatment, This is because there is no need to specially protect the equipment for preventing this and the equipment cost can be reduced. Therefore, it is possible to omit adding water as shown in FIGS. 2 and 3 if there are facilities or circumstances that do not require consideration of temperature rise.
The amount of water for dilution added is 1 to 20 relative to the weight of the slurry.
Double is good. It should be noted that this addition amount is preferably an addition amount of water according to the properties of fly ash, since the addition amount of the alkali agent is determined by the properties of fly ash, particularly the heavy metal content.

The mineral acid used for neutralization is preferably sulfuric acid, and if the concentration is to be added after dilution, the temperature will not rise so much, so it is desirable to use sulfuric acid in the highest concentration possible.
When water is not added and dilution is not performed, it is necessary to use dilute sulfuric acid, if necessary. The pH at the time of neutralization is the pH at which the heavy metal quality in the heavy metal-containing precipitate becomes the highest between 7 and 13.
You can set it to. If the pH is less than 7, most heavy metals remain dissolved in the liquid and cannot be recovered.
When H is more than 13, the pH is not about 7 or less, but especially the amount of lead dissolved in the liquid is large, and it becomes impossible to send the filtrate to the wastewater treatment process.

Neutralization is performed in the steps shown in FIGS.
If it cannot be neutralized with sulfuric acid or the like due to some reason such as cost and equipment, a process of not neutralizing as shown in FIGS. 3 and 4 can be considered. In this case, since the chlorine-containing liquid after the heavy metal separation step is subjected to solid-liquid separation while heavy metals such as lead and zinc are dissolved, this chlorine-containing liquid cannot be discharged and needs to be repeatedly used. is there. For example, by repeatedly using it as an alkali leaching solution for heavy metals and a diluting solution after alkali leaching, the heavy metal quality of the heavy metal-containing concentrate becomes substantially the same as that when neutralization is performed. Since the chlorine-containing liquid is a highly alkaline solution having a pH of 13 or more, it needs to be mixed with water for dilution, but repeated use also leads to a reduction in water supply cost. In addition, the repeated use of the chlorine-containing liquid can be applied to the steps of FIGS.

The heavy metal-containing precipitate recovered in the above-mentioned heavy metal separation step has a very low chlorine content. This is not clear at present, but it can be inferred as follows. When a heavy metal is eluted (leached) on the acidic side, the metal is present in the liquid as an ion such as M ^{n +} . When these metal ions are neutralized in a liquid with high chlorine concentration, M
(ClO) _x · yH ₂ O forms and precipitates a sparingly soluble oxychloride. However, when heavy metals in fly ash are eluted (leached) in a high-concentration alkali as in the present invention, M
In the form of O _x ^n-of such ions present in the liquid. When this is neutralized, the oxychloride is not synthesized but precipitates as a hydroxide, and it is presumed that a heavy metal-containing precipitate having an extremely low chlorine content can be obtained.

Although the chlorine content of the heavy metal-containing concentrate obtained in the above-mentioned heavy metal separation step has been reduced to an extremely low level, it may not actually meet the acceptance criteria of the smelter. The smelter's raw material acceptance standard is a chlorine concentration of 2
It is less than wt%, and in the most severe case, a value of less than 0.05 wt% is common. If this strictest standard is required, it may not be possible to meet the above-mentioned processing steps alone. Therefore, by heating the heavy metal-containing precipitate, the chloride in the heavy metal-containing precipitate can be further reduced by volatilizing and separating chlorides having a high vapor pressure such as lead and zinc.

In the heat treatment, only PbCl ₂ is volatilized if it is performed in an oxidizing atmosphere, but if it is performed in a reducing atmosphere, PbCl ₂ is evaporated.
Both Cl ₂ and ZnCl ₂ are volatilized, and chlorine can be efficiently reduced. When gas blowing is not performed in a gas blowing type or closed type furnace, it is considered that the furnace is in a reducing atmosphere. Therefore, when the heavy metal-containing substance of the present invention is heat-treated, it can be performed in the atmosphere at the time of charging and at the time of heating start, and it is not necessary to use a special atmosphere gas, and the heat treatment can be safely performed at low cost.

The heat treatment temperature at this time is 100 to 10
00 ° C, preferably 800 volatilizes lead and zinc chloride
Treatment at ~ 1000 ° C is good. It is known that the weight of chlorine is reduced by 90% or more by the heat treatment, and this reduction rate is much larger than that of the substance obtained by the conventional treatment method. This is because oxychlorides of heavy metals such as copper and lead are not generated in the heavy metal-containing precipitates leached with an alkaline agent, and chlorides or chlorine remaining from adhering water are mainly present. This is because it volatilizes more easily than chlorine.

The chlorine-containing filtrate that has been subjected to the heavy metal separation step can be rendered harmless by being subjected to wastewater treatment by a coprecipitation method of iron salts that is widely used industrially or by passing it through a chelating agent. is there.

As described above, in the present invention, fly ash from a refuse incineration facility or the like is treated to condense contained heavy metals such as copper, zinc and lead to remove chlorine to an extremely low level. It can be recovered as a raw material for smelting.

[0024]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the technical scope of the present invention is not limited to the description of these examples.

Example 1 As shown in FIG. 5, 20%
200 g of fly ash A shown in Table 1 was put into a 1 liter beaker containing 80 g of a NaOH solution and 175 g of water to form a slurry, which was strongly stirred for 10 minutes for alkali leaching. In addition,
The alkali leaching was performed by adjusting the slurry temperature to 40 ° C. (the same applies to other examples and comparative examples). Then, dilute by adding 500 ml of water, add 98% sulfuric acid as a neutralizing agent to adjust pH to 12 and maintain for 30 minutes, and then filter by filtration to remove heavy metal-containing impurities and salts mainly containing heavy metals. It separated into the chlorine-containing liquid. At that time, 400 ml of tap water was used as the cake washing water.

[0026]

[Table 1]

Example 2 As shown in FIG. 5, 20%
200 g of fly ash B shown in Table 1 was put into a 1 liter beaker containing 80 g of a NaOH solution and 175 g of water to form a slurry, which was vigorously stirred for 10 minutes. After that, 500 ml of water was added to dilute, 98% sulfuric acid was added as a neutralizing agent to adjust the pH to 11 and maintained for 30 minutes, followed by filtering to remove heavy metal-containing impurities and salts containing mainly heavy metals. It separated into the chlorine-containing liquid. At that time, 400m as cake washing water
l of tap water was used. The heavy metal-containing substance obtained here was heat-treated at 800 ° C. for 1 hour without gas blowing, and the substances before and after the heat treatment were analyzed and shown in Table 1.

COMPARATIVE EXAMPLE 1 As shown in FIG. 6, 700 ml of water and 20 parts of fly ash A shown in Table 1 were placed in a 1 liter beaker.
Add 0 g to make a slurry and add 98% sulfuric acid to adjust the pH.
After adjusting to 4 and maintaining for 30 minutes, 20% NaOH was added to adjust pH to 11 and maintaining for 30 minutes, and then filtration operation was performed to remove the heavy metal-containing precipitate containing mainly heavy metals and chlorine containing mainly salts. Separated into the containing liquid. At that time, 400 ml of tap water was used as the cake washing water. The heavy metal-containing substance obtained here was heat-treated at 800 ° C. for 1 hour without gas blowing, and the heavy metal-containing substance before and after the heat treatment was analyzed and shown in Table 1.

[Comparative Example 2] The same operation as in Comparative Example 1 is performed in Table 1.
The fly ash B shown in FIG. The results are shown in Table 1.

Table 1 shows the heavy metal grades of the heavy metal-containing concentrates obtained in the above Examples and Comparative Examples and the weight reduction rate of chlorine due to heat treatment. In Example 1, the content of chlorine, which is unfavorable for carrying into the smelting process, is 0.3 wt% or less, whereas
In Comparative Example 1 using the same fly ash A, sulfuric acid was used as a leaching agent, but chlorine in the heavy metal-containing substance was as high as 3% or more. In Example 2 and Comparative Example 2, fly ash B containing copper in an amount 3 times or more that of fly ash A is used, and it is more difficult to reduce chlorine than fly ash A. In Example 2, the chlorine content was 1.3% by weight, and the chlorine content was reduced by 98% after the heat treatment.
It can be reduced to 0.02 wt%. On the other hand, in Comparative Example 2 using sulfuric acid as the leaching agent, chlorine was 10 wt.
%, And even if the heat treatment is carried out, there is only a 20% weight reduction of chlorine, indicating that the treatment method according to the present invention is very effective in reducing chlorine.

[0031]

EFFECTS OF THE INVENTION Heavy metals in fly ash are leached with an alkaline agent and then neutralized with a mineral acid, so that the recovery rate of heavy metals is high, and the production of chlorine into a smelting process is extremely low. The effect is that a smelting raw material can be obtained and the equipment cost is low. In addition, it is possible to separate and collect heavy metals, and it is possible to reduce the burden of heavy metal recovery processing work in the smelting process.

[Brief description of drawings]

FIG. 1 is a process chart of the present invention in which dilution and neutralization are performed after alkali leaching.

FIG. 2 is a process chart of the present invention in which neutralization is performed after alkali leaching.

FIG. 3 is a process chart of the present invention in which solid-liquid separation is directly carried out after alkali leaching.

FIG. 4 is a process chart of the present invention in which dilution is performed after alkali leaching.

FIG. 5 is a process chart showing an embodiment of the present invention.

FIG. 6 is a process chart showing a comparative example of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22B 19/00 C22B 15/08 19/24 (72) Inventor Kenji Ichigo 1-8 Marunouchi, Chiyoda-ku, Tokyo No. 2 Dowa Mining Co., Ltd. F term (reference) 4D004 AA37 AB03 AB06 AC05 BA05 CA13 CA22 CA35 CC12 DA03 DA06 DA20 4K001 AA09 AA20 AA30 BA14 DB08 DB23

Claims (9)

[Claims] 1. An alkaline agent is added to fly ash containing at least one heavy metal of copper, zinc, and lead and chlorine to leach the heavy metal, water is added, and then mineral acid is added to adjust the pH.
A method for treating fly ash containing heavy metals, which comprises adjusting to 7 to 13 and performing solid-liquid separation into a heavy metal-containing precipitate and a chlorine-containing liquid. 2. A fly ash containing at least one heavy metal of copper, zinc and lead and chlorine is added with an alkali agent to leach the heavy metal and then a mineral acid is added to adjust the pH to 7 to 13 A method for treating fly ash containing heavy metals, which comprises solid-liquid separation into a substance and a chlorine-containing liquid. 3. An alkali agent is added to a fly ash containing at least one heavy metal of copper, zinc, and lead and chlorine to leach the heavy metal and to perform solid-liquid separation into a heavy metal-containing substance and a chlorine-containing liquid. A method for treating fly ash containing a heavy metal, characterized by: 4. A fly ash containing at least one heavy metal of copper, zinc and lead and chlorine is added with an alkali agent to leach the heavy metal and then water is added to form a heavy metal-containing substance and a chlorine-containing liquid. A method for treating fly ash containing heavy metals, characterized by solid-liquid separation. 5. The method for treating fly ash containing a heavy metal according to claim 1, wherein the slurry temperature during leaching is set to 30 ° C. or higher. 6. The heavy metal-containing compound is 100-1000.
Heat treatment at ℃ to volatilize and separate the chloride contained,
A method for treating fly ash containing the heavy metal according to claim 1. 7. The method for treating fly ash containing heavy metal according to claim 6, wherein the oxygen concentration in the atmosphere in the heat treatment is 0.1 to 21%. 8. The method for treating fly ash containing heavy metal according to claim 1, wherein the heavy metal-containing precipitate is used as a smelting raw material. 9. The method for treating fly ash containing heavy metal according to claim 6, wherein the heat-treated heavy metal-containing precipitate is used as a smelting raw material.