JP4826532B2 - Processing method of molten fly ash - Google Patents

Description

  The present invention treats molten fly ash that is generated when municipal waste and industrial waste are melted, and molten fly ash that is generated when incinerated fly ash generated when municipal waste and industrial waste are incinerated. It is about the method.

Conventionally, most of the molten fly ash has been solidified with chemicals and disposed of in landfills. However, in recent years, it has become difficult to secure landfills, and there has been a demand for volume reduction of fly ash. As a method for reducing the volume, a fly ash treatment method is disclosed (for example, see Patent Document 1). In this fly ash treatment method disclosed in Patent Document 1, after chlorine-containing molten fly ash is washed with water or acid in advance and dechlorinated, the solid content is put into a metal smelting furnace and used as a flux. This is a method for reducing the volume of fly ash. The processing method of the fly ash which used the water for washing | cleaning described in this patent document 1 as the smelter wastewater is disclosed (for example, refer patent document 2). Specifically, in the fly ash treatment method disclosed in Patent Document 2, the fly ash containing chlorine, calcium, and heavy metals is washed with water in the first step to separate the first residue and the first liquid, and then the second step. The first residue is washed with water and separated into a second residue and a second liquid, the second liquid obtained in the second step is used for the water washing in the first step, and the smelter is further washed with water in the second step. Use waste water. Moreover, the said 1st liquid is neutralized with a neutralizing agent at a 3rd process, and it isolate | separates into a 3rd residue and a 3rd liquid, and uses the liquid (acid liquid) in a smelter process as a neutralizing agent in a 3rd process. . The liquid in the smelter process refers to a liquid after leaching of the ore with acid, a liquid after use in electrolytic smelting, or other waste acid liquid generated from the inside of the smelter, and is mainly acidic.
The fly ash treatment method configured in this way prevents an increase in running costs of the water used for washing fly ash and the neutralizer used to neutralize the wash water obtained after the fly ash washing. It is possible to utilize the residue obtained after washing the fly ash with water.
Japanese Patent No. 3374728 (Claim 1) Japanese Patent Laying-Open No. 2003-290736 (Claims 1, 2, and 4, paragraphs [0027] and paragraph [0049])

Many fly ash contains alkali components such as unreacted slaked lime, sodium hydroxide, and calcium carbonate. Therefore, when the fly ash is washed with water, the slurry becomes strongly alkaline, and amphoteric metal ions (Zn, Pb , Al, etc.) are eluted, and there is a problem that a load is applied to wastewater treatment. Here, before sending the leachate fly ash in wastewater treatment, and pH adjusted by adding a mineral acid to leachate fly ash, that after, filtered and precipitated heavy metal content in the leachate of fly ash and the pH adjusted This method is known as a general method. However, this was an economically wasteful system. Instead of mineral acid, the fly ash treatment method disclosed in Patent Document 2 uses an acidic smelter process solution to neutralize the fly ash leachate.
However, in the conventional fly ash treatment method disclosed in Patent Document 2, alkaline components such as Ca (OH) ₂ and CaCO _{3 in} the fly ash hardly elute in the alkaline solution. The amount of necessary acid (liquid in the smelter process) is very small. For this reason, there was a problem that the volume reduction of fly ash did not progress so much and the heavy metal content was dissolved.
In addition, in the conventional fly ash treatment method disclosed in Patent Document 2, the second step is necessary, and gypsum generated in the neutralization step is sent to the smelting step as the main component of the neutralization residue. , step increases, unnecessary gypsum was also relatively large sent to want earthenware pots problem smelting process smelting process.
An object of the present invention is to provide a method for treating molten fly ash that can reduce the volume of fly ash without dissolving heavy metals, and that can efficiently utilize the acidic waste liquid generated in the smelting process. It is in.
Another object of the present invention is to provide a method for treating molten fly ash that can reduce the wastewater treatment load by reusing water washed with solids containing valuable metal components in a leaching / coprecipitation step. There is.

As shown in FIG. 1, the invention according to claim 1 is an improvement of a method for treating molten fly ash containing a valuable metal component containing at least one of Zn, Pb or Cu, a calcium component, and a chlorine component. .
The characteristic structure is that an acid solution containing sulfuric acid and hydrochloric acid in a mass concentration ratio (10: 1) to (1:10) is added to the molten fly ash and stirred, and most of the calcium component from the molten fly ash A leaching / coprecipitation step 11 for co-precipitation of valuable metal ions eluted in the acidic solution among the valuable metal components, and a calcium component in the molten fly ash And a solid-liquid separation step 12 for separating a solid content containing a part and the coprecipitate of the valuable metal from the leachate.
In the processing method for molten fly ash according to claim 1, PbCl ₂ present in molten fly ash and having low solubility in water is decomposed by sulfuric acid in an acidic solution as shown in the following reaction formula (1). The water-soluble NaCl · KCl · CaCl ₂ in the molten fly ash is dissolved in the water in the acidic solution.
PbCl ₂ + H ₂ SO ₄ → PbSO ₄ + 2HCl (1)
Moreover, most of the calcium components in the molten fly ash are leached with hydrochloric acid in the acidic liquid and are dissolved in the water in the acidic liquid, so that the volume of the molten fly ash can be reduced. Further, when sulfuric acid in the leachate reacts with Ca ions in the leachate to produce gypsum, valuable metal components are also removed mainly by coprecipitation.

The invention according to claim 2 is the invention according to claim 1, wherein the acidic liquid containing hydrochloric acid and sulfuric acid is an acidic waste liquid generated in the smelting process, as shown in FIG. .
In the method for treating molten fly ash according to claim 2, since the acidic waste liquid generated in the smelting process is used as the acidic liquid added to the molten fly ash in the leaching / coprecipitation step 11, expensive hydrochloric acid is used. The amount of wastewater used can be reduced and the load of wastewater treatment can be reduced.
The invention according to claim 3 is the invention according to claim 1, and further, as shown in FIG. 1, after the solid content from which the leachate has been removed in the solid-liquid separation step 12 is washed with water, It is characterized by supplying water to the leaching / coprecipitation process.
In the molten fly ash treatment method according to the third aspect, since the water containing the solid content containing the valuable metal component is reused in the leaching / coprecipitation step 11, the load of wastewater treatment can be reduced.

According to the present invention, an acidic liquid containing sulfuric acid and hydrochloric acid in a mass concentration ratio (10: 1) to (1:10) is added to the molten fly ash and stirred, and from the molten fly ash, most of the calcium component and Since the chlorine component was leached to produce a leachate having a pH of 7 to 10, PbCl ₂ having low solubility in water in the molten fly ash was decomposed by sulfuric acid in the acidic solution, and water-soluble NaCl · KCl · CaCl in the molten fly ash ₂ dissolves in the water in the acidic liquid, and most of the calcium component in the molten fly ash is leached by the hydrochloric acid in the acidic liquid and dissolves in the water in the acidic liquid. In addition, valuable metal ions eluted in the acidic liquid among the valuable metal components are coprecipitated and removed when sulfuric acid and Ca ions in the acidic liquid react to produce gypsum. As a result, chlorine components can be removed from the molten fly ash in a relatively small number of steps without dissolving valuable metal components in the leachate and without increasing the amount of chemical used, and the volume of molten fly ash can be reduced efficiently. it can.
Moreover, if the acidic waste liquid generated in the smelting process is used as the acidic liquid containing hydrochloric acid and sulfuric acid, the amount of expensive hydrochloric acid used can be reduced and the wastewater treatment load can be reduced.
Further, after the solid content from which the leachate has been removed in the solid-liquid separation process is washed with water, if the washed water is supplied to the leaching / coprecipitation process, the washed water need not be treated. As a result, the wastewater treatment load can be reduced.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
As shown in FIG. 1, the molten fly ash treatment method of the present invention includes a leaching / coprecipitation step 11 in which an acidic liquid is added to the molten fly ash and agitated, and a solid-liquid separation step 12 in which solid content is separated from the leachate. Including. The acidic liquid contains hydrochloric acid and sulfuric acid. Molten fly ash is molten fly ash that is generated when municipal waste and industrial waste are incinerated, as well as molten fly ash that is generated when municipal waste and industrial waste are incinerated. Including. This molten fly ash contains a calcium (Ca) component, a chlorine (Cl) component, and a valuable metal component (Zn, Pb, Cu, etc.). In this embodiment, the molten fly ash has an average composition of 15 to 20% by mass of chlorine (Cl), 15 to 30% by mass of calcium (Ca), 4 to 15% by mass of sodium (Na), and 4 to 15 2% by mass of potassium (K), 2-6% by mass of alumina (Al ₂ O ₃ ), 3-9% by mass of silica (SiO ₂ ), 0.5-1.5% by mass of iron (Fe), 1 to 10% by mass of zinc (Zn), 0.3 to 3% by mass of lead (Pb), 0.05 to 0.5% by mass of copper (Cu), 0.01 to 0.1% by mass % Cadmium (Cd) and the like. The molten fly ash is a compound in which the oxides, composite oxides, chlorides, carbonates, sulfates, etc. of the above composition are combined. Specifically, NaCl, KCl, CaCl ₂ , Ca (OH) Cl, a _{Ca (OH) 2, CaCO 3} , CaSO 4, PbCl 2, ZnO, compounds combining _{2CaO · Al 2 O 3 · SiO} 2 or the like. The acidic solution is a mixed acid aqueous solution containing hydrochloric acid and sulfuric acid, and the mass concentration ratio of sulfuric acid and hydrochloric acid is (10: 1) to (1:10), preferably (5: 1) to (1: 5). More preferably, it is (3: 1) to (1: 5). Here, the mass concentration ratio of sulfuric acid and hydrochloric acid in the acidic liquid was limited to the range of (10: 1) to (1:10). The elution amount of the calcium component is less than the elution amount in the conventional water leaching, so that the volume reduction of the molten fly ash cannot be achieved. If it is less than (1:10), that is, less than 1/10, the hydrochloric acid becomes too much and leaching is performed. This is because the elution amount of valuable metal ions such as lead increases near pH 7. The acidic liquid is preferably an acidic waste liquid generated in the smelting process. This has the advantage that the amount of expensive hydrochloric acid used can be reduced and the load of wastewater treatment can be reduced.

First, in the leaching / coprecipitation step 11, 100 to 500% by mass, preferably 100 to 300% by mass of water is added to 100% by mass of the molten fly ash and mixed to prepare a slurry. Is added and stirred at a temperature of 5 to 50 ° C. for 30 minutes to 6 hours. At this time, the addition amount of the acidic liquid is adjusted so that the pH of the slurry is 7 to 10, preferably 8.5 to 9.5. This pH is detected by a pH sensor. In this leaching / coprecipitation step 11, PbCl ₂ present in the molten fly ash and having low solubility in water is decomposed by sulfuric acid in the acidic solution as shown in the following reaction formula (1), and water in the molten fly ash is dissolved. NaCl / KCl / CaCl ₂ is dissolved in water in an acidic solution.
PbCl ₂ + H ₂ SO ₄ → PbSO ₄ + 2HCl (1)
Further, most of the calcium component in the molten fly ash is leached by hydrochloric acid in the acidic liquid and is dissolved in the water in the acidic liquid. Thus, not only hydrochloric acid in the acidic liquid but also sulfuric acid and water contribute to dechlorination in the molten fly ash. Furthermore, valuable metal ions eluted in the acidic liquid among the valuable metal components are coprecipitated and removed when the sulfuric acid and Ca ions in the acidic liquid react to produce gypsum. Examples of the coprecipitate of metal ions include CaAsO ₄ (calcium arsenate), PbSO ₄ (lead sulfate), and the like. Here, the amount of water added is limited to the range of 100 to 500% by mass with respect to 100% by mass of the molten fly ash. When the amount is less than 100% by mass, stirring of the slurry becomes difficult. This is because when the acidic liquid is added, the solid-liquid ratio of the slurry is lowered, the liquid is increased, and the processing capacity of the molten fly ash is lowered. The reason why the pH of the slurry is limited to the range of 7 to 10 is to efficiently leach out most of the calcium component and almost all of the chlorine component.

  Next, in the solid-liquid separation step 12, a solid content containing a part of the calcium component in the molten fly ash, the valuable metal component not eluted in the acidic liquid, and the coprecipitate of valuable metal ions is converted into the above leachate. Separate from. The leachate after separation contains soluble alkali metal salts such as sodium component and potassium component in addition to the calcium component and chlorine component, but contains almost no valuable metal ions. Further, the solid content after the separation contains the concentrated valuable metals. Further, this separation is performed using a thickener or a filter press. In addition, the calcium component contained in solid content is about 50-150 mass% with respect to 100 mass% of calcium components contained in the leachate of molten fly ash. Further, after the solid content from which the leachate has been removed in the solid-liquid separation step 12 is washed with water, the washed water is supplied to the leaching / coprecipitation step 11 and mixed with molten fly ash to prepare a slurry. As a result, it is not necessary to treat the washed water, so that the wastewater treatment load can be reduced. Further, the weight of the washed solid is 50 to 80% by mass when the weight of the molten fly ash before treatment is 100% by mass. As a result, the volume of molten fly ash can be reduced efficiently.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
As shown in FIG. 1, in the leaching / coprecipitation step 11, 200 ml of water was mixed with 100 g of molten fly ash to prepare a slurry, and 300 ml of smelter process internal solution was added to and mixed with this slurry. As said water, the water after wash | cleaning the solid content isolate | separated at the solid-liquid separation process 12 was utilized. The leaching temperature in the leaching / coprecipitation step 11 was 30 ° C., the leaching time was 1 hour, and the rotation speed of the stirring bar was 150 rpm. Next, suction filtration using filter paper was performed in the solid-liquid separation step 12. This separated the solid content of molten fly ash (69.6 g) from the leachate (450 ml). The pH of the leachate was 9.
<Comparative Example 1>
Except for adding 390 ml of the smelter process liquid to the slurry, the leaching / coprecipitation process and the solid-liquid separation process were carried out in the same manner as in Example 1, and the solid content (70.7 g) of the molten fly ash was leached (550 ml). ). The pH of the leachate was 6.6.

<Comparative example 2>
First, 500 ml of water was mixed with 100 g of molten fly ash to prepare a slurry, and the slurry was stirred and washed with water. The slurry temperature at this time was 30 ° C., the washing time was 1 hour, and the rotation speed of the stirrer was 150 rpm. Next, suction filtration using filter paper was performed. This separated the solid content (69 g) of the molten fly ash from the leachate (450 ml). The pH of the leachate was 11.3.
<Comparative Example 3>
22 ml of the smelter process internal solution was added to the leachate separated in Comparative Example 2 to neutralize the leachate. The solid content (26.3 g) produced by this neutralization was taken as Comparative Example 3.
<Comparative example 4>
Of the 390 ml of the smelter in-process solution used in Comparative Example 1, 13.2 g of slaked lime as a reagent is added to 368 ml remaining after subtracting 22 ml used in Comparative Example 3 so that the pH is around 9. Neutralized. The process liquid (810 ml) in the smelter after this neutralization was used as Comparative Example 4.

<Comparative test 1 and evaluation>
The composition of the molten fly ash of Example 1 and Comparative Examples 1 and 2 (composition before treatment) and the composition of the solid content of Example 1 and Comparative Examples 1 and 2 (composition after treatment) were analyzed, and the results were Table 1 shows. Moreover, the composition of the liquid in the smelter process of Example 1 and Comparative Examples 1, 3 and 4 was analyzed, and the results are shown in Table 2. Moreover, the composition of the leachate of Example 1 and Comparative Examples 1 and 2 was analyzed, and the results are shown in Table 3. Further, the composition of the solid content after neutralization in Comparative Example 3 was analyzed, the results are shown in Table 4, the composition of the process liquid in the smelter after neutralization in Comparative Example 4 was analyzed, and the results are shown in Table 5. Show.

表３から明らかなように、比較例２ではｐＨ１１．３の浸出液中に２ｇ／リットルのＯＨ^-イオンが存在するとともに、７４０ｐｐｍの鉛が溶出しており、比較例１ではｐＨ６．６の浸出液中にＯＨ^-イオンが存在しなかったけれども、鉛の溶出量が２５ｐｐｍと多くなったのに対し、実施例１ではｐＨ９の浸出液中にＯＨ^-イオンが存在せず、鉛が溶出せず、亜鉛や銅などの有価金属も溶出しなかったことが分った。
表１、表４及び表５から明らかなように、比較例２〜４の固形分の合計が９５．３ｇ（６９ｇ＋２６．３ｇ）と多かったのに対し、比較例１及び実施例１では固形分がそれぞれ７０．７ｇ及び６９．６ｇと少なくなったことが分った。なお、比較例１の固形分が少なくなったのは、ｐＨが比較的高い６．６であったためと考えられる。

As is apparent from Table 3, in Comparative Example 2, 2 g / liter of OH ^- ion was present in the leachate at pH 11.3, and 740 ppm of lead was eluted. In Comparative Example 1, in the leachate at pH 6.6. Although no OH ^- ion was present in the sample, the amount of lead elution increased to 25 ppm, whereas in Example 1, no OH ^- ion was present in the pH 9 leachate, lead did not elute, It was found that valuable metals such as copper did not elute.
As is clear from Tables 1, 4 and 5, the total solid content of Comparative Examples 2 to 4 was 95.3 g (69 g + 26.3 g), whereas in Comparative Example 1 and Example 1, the solid content was high. Were reduced to 70.7 g and 69.6 g, respectively. In addition, it is thought that the solid content of the comparative example 1 decreased because the pH was relatively high 6.6.

<Example 2>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the smelter process liquid was 10: 1. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.
<Example 3>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the smelter process liquid was 5: 1. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.
<Example 4>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the smelter process liquid was 2: 1. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.
<Example 5>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the smelter process liquid was 1: 1. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.

<Example 6>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the liquid in the smelter process was 1: 2. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.
<Example 7>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the smelter process liquid was 1: 5. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.
<Example 8>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the smelter process liquid was 1:10. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.

<Comparative Example 5>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the smelter process liquid was 22: 1. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.
<Comparative Example 6>
The solid content of the molten fly ash was separated from the leachate in the same manner as in Example 1 except that the mass concentration ratio of sulfuric acid and hydrochloric acid in the smelter process liquid was 1:25. The pH of the leachate was adjusted to about 7, and the ratio of solid to liquid was 1: 5.

<Comparative test 2 and evaluation>
The amount of the leachate obtained in Examples 2 to 8 and Comparative Examples 5 and 6, the elution amount of lead, and the weight of the solid content were measured and analyzed. The results are shown in Table 6 and FIG.

表６及び図２から明らかなように、硫酸が塩酸より多く含まれると、固形分の発生量が増えることが分った。これはＣａＳＯ₄が生成されるためである。このため硫酸の含有量の多い比較例５では固形分が７４．３ｇと多かったのに対し、硫酸の含有量が比較的少ない実施例２〜８及び比較例６では固形分が５０．３〜７２．７ｇと比較的少なかったことが分った。
一方、塩酸が硫酸より多く含まれると、溶融飛灰からの鉛成分の溶出量が多くなり、廃水処理への負荷が大きくなることが分った。このため塩酸の含有量の多い比較例６では鉛の溶出量が５６．５ｐｐｍと多かったのに対し、塩酸の含有量の比較例少ない実施例２〜８及び比較例５では４．０〜４８．０ｐｐｍと比較的少なかったことが分った。
上述のことから、硫酸：塩酸を質量濃度比で（１０：１）〜（１：１０）の範囲に設定することが望ましいことが分った。なお、鉛成分の溶出量は浸出液のｐＨを調整することにより制御できる。

As is apparent from Table 6 and FIG. 2, it was found that the amount of solid content increased when sulfuric acid was contained in a larger amount than hydrochloric acid. This is because CaSO ₄ is produced. For this reason, in Comparative Example 5 with a large content of sulfuric acid, the solid content was as high as 74.3 g, whereas in Examples 2 to 8 and Comparative Example 6 in which the content of sulfuric acid was relatively small, the solid content was 50.3 to 72.7g was found to be relatively small.
On the other hand, it was found that when hydrochloric acid is contained in a larger amount than sulfuric acid, the amount of lead components eluted from the molten fly ash increases and the load on wastewater treatment increases. For this reason, in Comparative Example 6 with a large hydrochloric acid content, the lead elution amount was as high as 56.5 ppm, whereas in Comparative Examples 5 and 8 and Comparative Example 5 with a small comparative hydrochloric acid content, 4.0 to 48. It was found that it was relatively low at 0.0 ppm.
From the above, it has been found that it is desirable to set sulfuric acid: hydrochloric acid in a mass concentration ratio in the range of (10: 1) to (1:10). The elution amount of the lead component can be controlled by adjusting the pH of the leachate.

It is process drawing which shows the method of processing the molten fly ash of embodiment of this invention. It is a figure which shows the relationship between the elution amount of lead with respect to the mass concentration ratio of hydrochloric acid to sulfuric acid, and the generation amount of solid content, respectively.

Explanation of symbols

11 Leaching / coprecipitation process 12 Solid-liquid separation process

Claims (3)

In a method for treating molten fly ash containing a valuable metal component containing at least one of Zn, Pb or Cu, a calcium component, and a chlorine component,
An acidic liquid containing sulfuric acid and hydrochloric acid in a mass concentration ratio (10: 1) to (1:10) is added to the molten fly ash and stirred, and most of the calcium component and the chlorine component are added from the molten fly ash. A leaching / coprecipitation step of co-precipitating ions of the valuable metal eluted in the acidic liquid among the valuable metal components;
A solid-liquid separation step of separating a solid content containing a part of the calcium component in the molten fly ash and the coprecipitate of the valuable metal from the leachate. Method.   The method for treating molten fly ash according to claim 1, wherein the acidic liquid containing hydrochloric acid and sulfuric acid is an acidic waste liquid generated in a smelting process.   The processing method of the molten fly ash of Claim 1 which supplies the water after washing | cleaning to the leaching and coprecipitation process after wash | cleaning the solid content from which the leaching solution was removed by the solid-liquid separation process.

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