JPH10128304A - Ash cleaning method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently elute and remove heavy metals from ashes by promoting elution of heavy metals contained in ashes by cleaning the ashes with a solution having specified chlorine ion concentration and carrying out filtration. SOLUTION: The chloride ion concentration is adjusted to be 2.0wt.% or higher by introducing chlorides such as calcium chloride and a filtered liquid 10 of a cleaning liquid through a route 14 into a cleaning and stirring tank 2 to which ashes discharged out of a combustion furnace and cleaning liquid (water) are led through a route 1. Carbon dioxide is blown to the cleaning and stirring tank 2 from a introducing means 19 and mixed with the resultant mixture of the ashes and cleaning liquid. After cleaning, the suspended solution of the ashes is subjected to solid-liquid separation by a dewatering and filtering means (a filtering apparatus) 3 and since a large quantity of heavy metals together with chlorine ion are eluted in the resultant filtered liquid 10, the heavy metals of the filtered liquid 10 are classified by a removing means 11. Meanwhile, the filtered cake 4 is subjected to solid-liquid separation by a cleaning and filtering means 5. The filtered liquid 7 is led to a circulation route 12, joined to the filtered liquid 10 to adjust the chlorine ion concentration, and then re-circulated to the cleaning and stirring tank 2 and reused.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to ash or dust generated from a combustion furnace such as incineration ash and fly ash discharged from a garbage incinerator or dust from a cement kiln (including ash dust). The present invention relates to a method and an apparatus for performing a cleaning treatment suitable for use as a raw material or the like, recycling such as regeneration of heavy metals, or landfill disposal.

[0002]

2. Description of the Related Art Ash dust such as incineration ash and dust contains a considerable amount of chlorine, and also contains mercury, zinc, lead and the like (hereinafter referred to as heavy metals). Since these heavy metals and chlorine have an adverse effect on the quality of cement, it is necessary to remove heavy metals and chlorine as much as possible when these ash dusts are reused as cement raw materials and the like. Therefore, conventionally, when these ash dusts are reused as a cement raw material or the like, the ash dusts are washed with water and filtered to remove chlorine. Also, when collecting and recycling heavy metals from ash dust, the ash dust is washed with an acid such as hydrochloric acid or sulfuric acid to elute the heavy metals, and after filtering, the heavy metals are collected from the filtrate, and the cake is used as a raw material for cement. Attempts have been made to reuse it.

[0003]

As described above, conventionally, it has been attempted to wash ash dust with water and reuse it. However, simply washing ash dust with water can hardly remove heavy metals, and after filtration, Remains on the cake. When the ash dust contains Friedel's salt, the chlorine contained in Friedel's salt is not eluted only by washing with water, but also remains in the cake. In addition, the method of washing ash dust with an acid such as hydrochloric acid or sulfuric acid not only increases the cost of chemicals used, but also makes the treatment equipment acid-resistant and requires equipment for neutralizing the wastewater. Become.

[0004]

SUMMARY OF THE INVENTION The present invention provides a cleaning method and apparatus which solves the above-mentioned problems in the conventional cleaning method. (A) By using a cleaning liquid in which the chloride ion in the liquid has a certain concentration or more. Heavy metals can be effectively eluted from ash dust.
(B) Carbon dioxide is introduced into the cleaning solution, and ash dust is washed in the presence thereof to promote desalination of ash dust while suppressing elution of heavy metals, thereby obtaining a filtrate having a high chlorine concentration and containing almost no heavy metals. In addition, the use of this liquid for cleaning ash dust enhances the effect of chloride ions to elute and remove heavy metals.

That is, the first invention of the present application is characterized in that (1) washing of ash dust with a solution having a chloride ion concentration of 2.0 wt% or more promotes elution of heavy metals contained in the ash dust and performs filtration. This is a method of cleaning ash dust. The above-mentioned washing treatment method comprises the steps of (2) repeatedly using the washing filtrate from which heavy metals have been removed to reduce the chloride ion concentration in the solution to 2.0 watts.
Includes a method of cleaning ash dust by setting it to t% or more.

The second invention of the present application is to (3) promote the elution of chloride ions from Friedel's salt contained in the ash dust by suspending the ash dust in a cleaning solution in the presence of carbon dioxide.
This is a method for cleaning ash dust, characterized by suppressing elution of heavy metals in ash dust. The cleaning treatment method includes (4) a method of introducing carbon dioxide into the suspension by blowing exhaust gas from a combustion furnace into a cleaning solution in which ash dust is suspended.

According to a third aspect of the present invention, (5) carbon dioxide is introduced into a washing suspension of ash to wash it, thereby promoting elution of chloride ions from Friedel's salt contained in the ash, and This is a method of cleaning ash dust in which heavy metals in ash dust are eluted and removed by increasing the chlorine ion concentration and then increasing the chloride ion concentration to 2.0 wt% or more and washing and filtering the ash dust. The above-mentioned cleaning method includes: (6) a method of introducing carbon dioxide into a cleaning suspension of ash dust by blowing combustion exhaust gas into the suspension; (7) adding a chloride ion-containing solution;
Alternatively, a washing filtrate from which heavy metals have been removed is added to carry out washing with a chloride ion concentration of 2.0 wt% or more, (8) a method of repeatedly using the washing filtrate from which heavy metals have been removed,
(9) Includes a method in which ash dust from which chloride ions and heavy metals have been removed is used as a cement raw material.

The fourth invention of the present application comprises (10) a stirring tank for suspending and washing ash dust, a means for filtering the ash dust suspension after washing, a means for removing heavy metals from the filtrate, and a method for removing heavy metals from the filtrate. This is a ash dust cleaning apparatus that includes a path for circulating the removed solution to a stirring tank, and cleans ash dust with a cleaning solution having a chlorine ion concentration of 2.0 wt% or more. The above-described processing apparatus is provided with (1)
1) A processing apparatus provided with a means for introducing carbon dioxide into a stirring tank, (12) a means for washing and filtering a filter cake of ash suspension, and a path for circulating the filtrate to a stirring tank are provided. Including processing equipment.

[0009]

DETAILED DESCRIPTION OF THE INVENTION (A) Elution of Heavy Metals by Chloride Ions In the first cleaning treatment method of the present invention, heavy metals contained in ash dusts are washed by washing ash dusts with a solution having a chloride ion concentration of 2.0 wt% or more. Filter to facilitate elution of the species. When ash dust is suspended in the washing liquid (water) and washed, the elution of heavy metals such as lead, zinc and mercury contained in ash dust is promoted by increasing the chloride ion concentration of the suspension to the above concentration and washing. Is done. It is considered that this is because a part of the water molecules is dissociated to generate hydrogen ions due to an increase in chloride ions, and the hydrogen ions ionize heavy metals. The chlorine ion concentration is suitably 2.0% by weight or more. The higher the concentration, the higher the elution effect, and it can be used up to a chloride ion saturated concentration. Incidentally, the chloride ion concentration in the saturated state of calcium chloride added as a chloride ion source is 4
About 34% by weight of water at 0 ° C. 2.0w chlorine ion concentration
If it is less than t%, the elution effect of heavy metals is low. Usually, at most 20 to 25 wt% is appropriate.

As means for increasing the chloride ion concentration to 2.0% by weight or more, chlorides such as calcium chloride, sodium chloride and potassium chloride are added, or a washing filtrate already used for washing ash dust is added. Chloride ions remain in the washing filtrate, and can be used for adjusting the chloride ion concentration by circulating the chloride ions in the washing step.
This washing filtrate may be used repeatedly. Since chlorine ions are eluted from the ash during washing, the chloride ion concentration at the start of washing may be less than 2.0 wt%, and the amount of chloride added to adjust the chloride ion concentration or the supply amount of washing filtrate. The amount may be such that the chlorine ion concentration in the liquid becomes 2.0 wt% or more while the cleaning proceeds.

The eluted heavy metals dissolve in the liquid as metal ions, and the chlorine ion concentration in the liquid gradually increases by repeatedly circulating the washing filtrate. The chlorine ion concentration is usually adjusted to at most about 20 to 25% by adding a washing filtrate for the filter cake or a new washing liquid.

Since the ash dust filter cake thus obtained is free of heavy metals, it is suitable for use as a cement raw material or landfill. On the other hand, since the filtrate contains a large amount of heavy metals, the heavy metals can be recovered from the filtrate and reused. Also, as already mentioned,
Since chlorine ions remain in the washing filtrate, the dissolved heavy metals can be removed from the washing filtrate, circulated to the washing step, and used as a chlorine ion source.
Means for removing heavy metals from the washing filtrate may be a conventional method such as a method using pH adjustment or a method using a chelating agent.

(B) Elution of Chloride Ion by Carbon Dioxide In the second cleaning treatment method according to the present invention, Friedel's salt contained in ash dust is washed by introducing carbon dioxide into a ash dust washing suspension. And promotes elution of chloride ions from ash while suppressing elution of heavy metals in ash dust. The introduction of carbon dioxide may be carried out by blowing and blowing carbon dioxide gas or a mixed gas containing carbon dioxide gas or combustion exhaust gas into a liquid in which ash dust is suspended. When the ashes are suspended in a washing liquid (water) and washed, washing in the presence of carbon dioxide promotes elution of chloride ions from Friedel's salt contained in the ashes.

The chlorine in the ash dust is Friedel's salt (3CaO.Al ₂ O
₃・ CaCl ₂・ 10H ₂ O), or a form similar to ettringite when there is a lot of chlorine (3CaO ・ Al ₂ O ₃・ 3CaCl ₂・ 32H ₂ O)
These are hardly soluble in water, so that they are hardly removed by simply washing with water. (In the present invention, chloride ions from Friedel's salt, including ettringite-like forms, Elution). However,
If carbon dioxide is present in the ash suspension, the carbonate ion CO ₃ ^2- is replaced with chloride ion as shown in the following formula, and chloride ion is eluted. _{CO 2 + H 2 O → 2H} + + CO 3 2- 3CaO · Al 2 O 3 · CaCl 2 · 10H 2 O + CO 3 2- → 3CaO · Al 2 O 3 · CaCO 3 · 10H 2 O + 2Cl - 3CaO · Al ₂ O ₃・ 3CaCl ₂・ 32H ₂ O ＋ CO ₃ ^2- → 3CaO ・ Al ₂ O ₃・ CaCO ₃・ 32H ₂ O ＋ 2Cl ⁻

The concentration of carbon dioxide introduced into the washing suspension is about 1
It may be 0 wt% or more. The carbon dioxide concentration of the combustion exhaust gas of the cement kiln is approximately 18 to 20% by weight and can be used as a carbon dioxide source. The amount of carbon dioxide introduced into the washing suspension was determined by adding a carbon dioxide concentration of 20 kg to a liquid obtained by suspending 5 kg of fly ash in 55 liters of washing water as described in Examples described later.
In the case of injecting flue gas of wt%, theoretically, it is sufficient if the amount of exhaust gas is 4 liters or more per liter of suspension, and in actual operation, it may be about 5 to 10 times this amount.

As shown in the above formula, chloride ions are eluted by the introduction of carbon dioxide, while heavy metal ions react with carbonate ions as shown in the following formula to precipitate carbides and become insoluble. Pb ²⁺ + CO ₃ ^2- → PbCO ₃ Zn ²⁺ + CO ₃ ^2- → ZnCO ₃ Therefore, no harmful heavy metals are eluted in the filtrate obtained by dehydration filtration, and a high concentration of chlorine is dissolved. Therefore, it is suitable for chloride regeneration.

(C) Combined Use of Chloride Ion and Carbon Dioxide The third treatment method according to the present invention comprises the above-described method of increasing the concentration of chloride ions to promote elution of heavy metals and the method of introducing carbon dioxide to reduce the elution of chloride ions. It is a combination of the prompting method. According to this treatment method, by introducing carbon dioxide into the washing suspension of ash and washing, the elution of chloride ions from Friedel's salt contained in the ash is promoted to increase the chloride ion concentration in the washing solution, Next, the ash dust is washed and filtered by adjusting the chlorine ion concentration to 2.0 wt% or more to elute and remove heavy metals in the ash dust.

As described above, in order to introduce carbon dioxide, carbon dioxide or a mixed gas containing carbon dioxide or combustion exhaust gas may be injected into the liquid in which the ash dust is suspended while stirring and bubbling. The introduction of carbon dioxide to wash the ashes promotes the elution of chloride ions from the ashes, thereby improving the desalting effect of the ashes and facilitating the adjustment of the chloride ion concentration in the next step. Next, after stopping the injection of the combustion exhaust gas, etc., chlorides such as calcium chloride, sodium chloride, and potassium chloride are added, or
The washing filtrate from which heavy metals have been removed is added to adjust the chloride ion concentration in the washing suspension to 2.0 wt% or more. As described above, since chloride ions are dissolved in the washing filtrate, chlorine ions are accumulated in the solution by repeated use, and can be used as a supply source of chlorine ions. The amount of chloride added to adjust the chloride ion concentration or the supply amount of the washing filtrate may be such that the chloride ion concentration in the solution becomes 2.0 wt% or more while the washing proceeds. Note that the adjustment of chlorine ions and the introduction of carbon dioxide may be performed simultaneously.

The chlorine ion concentration of the ash suspension is 2.0 wt.
%, The ash dust is stirred and washed, and then the suspension is subjected to dehydration filtration. The cake obtained in this way is sufficiently free of heavy metals and chlorine and is suitable for reuse as a cement raw material. In addition, the filtrate contains a large amount of heavy metals, and thus is suitable for regeneration of heavy metals. The filtrate from which heavy metals have been removed is circulated and reused as a washing solution.

(D) Configuration of Cleaning Processing Apparatus FIG. 1 schematically shows the configuration of an apparatus for performing the above-described cleaning processing method according to the present invention. The cleaning apparatus 20 shown in FIG. 1 is designed to be able to carry out a combination of the adjustment of chlorine ions and the introduction of carbon dioxide. The agitation tank 2 for suspending and cleaning ash dust, the ash dust suspension after cleaning , A means 11 for removing heavy metals from the filtrate 10, and a path 14 for circulating the solution from which the heavy metals have been removed to the washing and stirring tank 2.
Means 19 for introducing carbon dioxide into the washing and stirring tank 2
Is attached. Further, as a preferred embodiment, the washing and filtering means 5 for treating the filtered cake 4 after washing, and the path 14 for circulating the filtrate in the washing and stirring tank 2 are connected to the washing and filtering means 5. These processing means are communicated with each other by paths 9, 10, 12, 13, 16, and 18, respectively, and these paths are provided with valves for opening and closing the flow paths.

The ash dust and the washing liquid (water) discharged from the combustion furnace are introduced into the washing and stirring tank 2 through the path 1, and further, chlorides such as calcium chloride and sodium chloride, or in the case where washing processing has already been performed, Route 1 the washing filtrate
4 to the washing and stirring tank 2 to adjust the chloride ion concentration. This chlorine ion concentration was 2.0 wt.
% May be adjusted so as to be not less than%.

In order to introduce carbon dioxide into the washing and stirring bed 2 from the introducing means 19, the exhaust gas 17 from the combustion furnace or the mixed gas 15 containing carbon dioxide is blown into the washing and stirring tank 2 through the passages 16 and 18, respectively, and mixed. When the introduction of carbon dioxide and the adjustment of the chloride ion concentration are used together, the combustion exhaust gas or the mixed gas is blown, the carbon dioxide is introduced, the gas blowing is stopped, and then the chloride is added or the washing filtrate is added. To adjust the chloride ion concentration of the suspension.

After the above washing, the suspension of ash dust is dehydrated and filtered.
(Filtration machine) 3, and is subjected to solid-liquid separation. Since a large amount of heavy metals are eluted together with the chloride ions in the filtrate 10, the filtrate 10 is sent to the heavy metal removing means 11, where the heavy metals are separated, and then, if necessary, guided to the circulation path 14 through the path 13 to the circulation path 14. It is circulated to the washing and stirring tank 2 through the passage 14 and reused as a supply source of chlorine ions. The separated heavy metal is recovered and regenerated as needed. Therefore, the means for separating heavy metals may also serve as the regenerating means. The washing filtrate not circulating in the washing and stirring tank 2 is discharged to the outside through the passage 12.

On the other hand, the filter cake 4 is sent to the washing and filtering means 5, where the filtrate 7 separated into solid and liquid is led to the circulation path 14 through the path 9 and combined with the washing filtrate 10 to adjust the chloride ion concentration. It is circulated to the washing and stirring tank 2 through the path 14 and reused. The filtrate 7 which is not reused is discharged to the outside through the path 8. Since the solid content 6 recovered from the washing filtrate means 5 hardly contains heavy metals and chlorine,
It can be used as a raw material for cement. In addition, there is no risk of becoming a source of contamination by heavy metals and chlorine even when landfilled. Since the washing filtrate 10 from which heavy metals have been removed contains a large amount of chloride ions, as described above, in addition to being reused as a chlorine ion supply source in the washing step, the filtrate is used for chloride regeneration. can do.

Although the description has been made mainly with reference to FIG. 1, the present invention can appropriately change the introduction paths of the carbon dioxide and the washing filtrate as long as the gist of the invention is not changed as follows. (A) The washing filtrate is introduced into the washing and stirring layer 2 through the circulation path 14 and the concentration of chloride ions is adjusted to promote elution of heavy metals, while carbon dioxide is introduced from the introducing means 19 into the washing and filtering apparatus 5.
To break down Friedel's salt. (B) Carbon dioxide is blown into the washing and stirring layer 2 from the introducing means 19 to decompose Friedel's salt, while the circulation path 14 is connected to the washing and filtering device 5 to wash the washing filtrate into the washing and filtering device 5.
The filtrate 7 is circulated or drained through a heavy metal removing device 11. (C) Both the carbon dioxide introduction means 19 and the washing filtrate circulation path 14 are connected to the washing and filtering device 5, only washing is performed in the washing and stirring tank 2, and carbon dioxide and the washing filtrate are introduced into the washing and filtering device 5. The Friedel's salt is decomposed and heavy metals are eluted, and the filtrate 7 is circulated or drained through a heavy metal removing device 11.

[0026]

Examples and Comparative Examples Examples of the present invention are shown below.
In addition, these are illustrations and do not limit the scope of the present invention.

[0027] The cleaning apparatus used in Examples 1 1, firstly, the washing water 55 l calcium chloride dihydrate was dissolved _{(CaCl 2 · 2H 2 O)} 1140g, and the concentration of chloride ions in 1 wt% Further, a 0.1 mol / l solution of sodium hydroxide was added, and the washing solution was adjusted to pH 8. Next, fly ash A (Cl: 16.9wt
%, Pb: 969mg / kg, Zn: 4420mg / kg, Hg: 0.766mg / kg) 5kg
And 55 liters of the above calcium chloride aqueous solution
And stirred and mixed for about 5 minutes. Next, the suspension was led to a dewatering filter 3 and filtered. Since the cake 4 contains water containing a high chlorine concentration, the cake 4 was guided to a washing and filtering device 5, washed with water (about 21 liters), and filtered to remove chlorine from the cake 4 to obtain a treated cake 6. The washing filtrate 7 was drained through a passage 8. On the other hand, the washing filtrate 10 discharged from the dewatering filter 3 was sent to a heavy metal removing device 11, where the heavy metal was removed and then drained through a passage 12. In order to confirm the effect of removing heavy metals from fly ash, the washing filtrate 10 was sampled and analyzed. As a result, as shown in Table 1, the pH of the washing filtrate was 12.4, the chloride ion concentration was 2.6 wt%, the lead content was 31.0 mg / l (removal rate from fly ash was 35.2%), and the zinc content was 8.4 mg. / l (removal rate from fly ash 2.1
%), Mercury content 0.010 mg / l (removal rate from fly ash 14.4
%)Met.

Example 2 Calcium chloride dihydrate (CaCl ₂ .2H ₂
O) Fly ash A of the above-mentioned municipal garbage incinerator in the same manner as in Example 1 except that 3420 g was dissolved to make the chlorine ion concentration 3 wt%.
Was washed. In order to confirm the effect of removing heavy metals from fly ash, the washing filtrate 10 was sampled and analyzed.
As a result, as shown in Table 1, the pH of the washed filtrate was 12.
2. Chloride ion concentration 3.9wt%, lead content 57.0mg / l
(Removal rate from fly ash: 64.7%), zinc content: 13.5 mg / l (removal rate from fly ash: 3.4%), mercury content: 0.018 mg / l (removal rate from fly ash: 25.8%). Was.

Example 3 In 55 liters of water for washing, calcium chloride dihydrate (CaCl ₂ .2H ₂
O) Fly ash A of the above-mentioned municipal garbage incinerator in the same manner as in Example 1 except that 5700 g was dissolved to make the chlorine ion concentration 5 wt%.
Was washed. In order to confirm the effect of removing heavy metals from fly ash, the washing filtrate 10 was sampled and analyzed.
As a result, as shown in Table 1, the pH of the washed filtrate was 12.
0, chloride ion concentration 5.8wt%, lead content 74.0mg / l
(Removal rate from fly ash: 84.0%), zinc content: 23.5 mg / l (removal rate from fly ash: 5.8%), mercury content: 0.021 mg / l (removal rate from fly ash: 30.2%). Was.

Example 4 A solution of calcium chloride dihydrate (CaCl ₂ .2H ₂
O) Fly ash A from the above-mentioned municipal garbage incinerator was washed in the same manner as in Example 1 except that 10150 g was dissolved to make the chlorine ion concentration 7 wt%. In order to confirm the effect of removing heavy metals from fly ash, the washing filtrate 10 was sampled and analyzed. As a result, as shown in Table 1, the pH
2.0, chlorine ion concentration 7.3wt%, lead content 76.0mg /
l (removal rate from fly ash 86.3%), zinc content 23.3mg / l
(5.8% removal rate from fly ash), mercury content 0.020mg / l
(Removal rate from fly ash: 28.7%), and almost the same processing results as in Example 3 were obtained.

From the results of Examples 1 to 4, it was confirmed that the elution of heavy metals from fly ash was increased by increasing the chlorine concentration in the cleaning solution. Also, from the results of Example 1, it is clear that the chlorine ion concentration of the cleaning solution is suitably 2.0 wt% or more, and the higher the chloride ion concentration, the larger the amount of heavy metal eluted.

Example 5 Using the cleaning apparatus shown in FIG. 1, fly ash A from a city garbage incinerator (Cl: 16.9 wt%, Pb: 969 mg / kg, Zn: 4420 mg / kg, Hg: 0.76)
5 kg of 6 mg / kg) and 55 liters of washing water were introduced into the washing and stirring tank 2 and stirred and mixed for about 5 minutes. Next, the suspension was led to a dewatering filter 3 and filtered. Since the filter cake 4 contains water having a high chlorine concentration, it was further guided to a washing and filtering device 5 and washed with water (about 56 liters), and filtered to remove chlorine from the cake 4. Part of the filtrate 7 (about 5 liters) with the valve of the path 8 adjusted
To the washing and stirring tank 2 through a path 14, and the remaining filtrate 7 was drained through a path 8. On the other hand, after the filtrate 10 discharged from the dewatering filter 3 is guided to the heavy metal removing device 11 to remove heavy metals, a part (about 50 liters) of this filtrate 10 is passed through the path 13 through the path 9 to the filtrate 7 and the filtrate 7. They were merged and circulated to the washing and stirring tank 2 through the path 14. Here, 5 kg of fly ash from the city garbage incinerator was newly added,
After mixing and stirring, the same steps were repeated. After repeating this operation five times, the valve of the passage 12 was opened, and adjustment was made so that a part (about 6.4 liters) of the filtrate 10 was drained per one switch. Also, by adjusting the valve of the passage 8, a part of the filtrate 7 is adjusted.
(About 11.4 liters) was adjusted to circulate. In this way, the same process was repeated twice more so that 55 liters of the washing filtrate was circulated through the circulation path 14 to the washing and stirring tank. When the system was sufficiently stable, the filtrate 10 was sampled and analyzed in order to confirm the effect of removing heavy metals from fly ash. As a result, the pH of the washing filtrate was 12.3, the chlorine ion concentration was 7.1 wt%, the lead content was 79.0 mg / l (removal rate from fly ash 89.7%), and the zinc content was 24.1 mg / l (fly ash). And the mercury content was 0.024 mg / l (removal rate from fly ash was 34.5%).

As described above, it was confirmed that the effect of removing heavy metals can be improved by circulating the washing filtrate without adding a chloride such as calcium chloride. Similar results can be obtained not only for fly ash from a municipal garbage burning furnace but also for dust from a burning furnace such as dust from a cement kiln if it contains heavy metals and chlorine.

COMPARATIVE EXAMPLE 1 In Examples 1 to 5, ash dust was washed by adding chloride or circulating the washing filtrate to adjust the chloride ion concentration of the washing solution to 2.0 wt% or more. In this comparative example, the ash dust was washed only with the washing water as described below without performing such adjustment of the chloride ion concentration. First, 5 kg of the fly ash A and 55 liters of water from the municipal garbage incinerator were introduced into the stirring tank 2 and stirred and mixed for about 5 minutes. Next, the suspension was led to a dewatering filter 3 and filtered. This filter cake 4 is led to a washing and filtering device 5 and washed with about 13 liters of water,
After filtration, a dehydrated cake 6 was obtained. The filtrate 7 was drained to the outside through a route 8. On the other hand, the washing filtrate 10 is guided to a heavy metal removing device 11 to remove heavy metals, and then the route 1 is removed.
Drained to the outside through 2. In order to confirm the effect of removing heavy metals from fly ash, the washing filtrate 10 was sampled and analyzed. As a result, the pH of the filtrate was 12.5, the chloride ion concentration was 1.6 wt%, the lead content was 19.0 mg / l (removal rate from fly ash: 21.6%), and the zinc content was 8.0 mg / l (from fly ash). Removal rate
2.0%), mercury content 0.003mg / l (removal rate from fly ash 4.
3%). As is clear from this comparative example, heavy metals are not sufficiently eluted from ash dust when the chloride ion concentration in the cleaning solution is about 1.6 wt%.

Example 6 Fly ash B (Cl: 7.0 wt%, Pb: 4890 mg / kg, Zn: 5) from a municipal garbage incinerator containing Friedel's salt was used by using the cleaning apparatus shown in FIG.
5 kg of water (410 mg / kg, Hg: 0.672 mg / kg) and 55 liters of water were introduced into the washing and stirring tank 2 and stirred and mixed for about 5 minutes. Next, a standard mixed gas (CO ₂ : 20%,
(O ₂ : 10%, N ₂ : 70%) were mixed for 10 minutes while blowing at a rate of 0.5 Nm ³ / min. Thereafter, the suspension was immediately introduced into the dewatering filter 3 and filtered. Since the filter cake 4 contains water having a high chlorine concentration, it was further led to a washing and filtering device 5 where it was washed with about 10 liters of water and filtered to remove chlorine from the cake 4 to obtain a dehydrated cake 6. This filtrate 7 passes through route 8
Drained to the outside. On the other hand, the washing filtrate 10 was guided to a heavy metal removing device 11, and after removing heavy metals, was drained to the outside through a path 12. The heavy metals contained in the washing filtrate are small and may be discharged without being removed. To confirm the effect of removing heavy metals from fly ash,
The washing filtrate 10 was sampled and analyzed. as a result,
As shown in Table 2, the pH of the washing filtrate was 6.0, the chlorine ion concentration was 0.6 wt% (removal rate from fly ash: 94.3%), and the lead content was 0.1 mg / l (removal rate from fly ash was 0.0%). %), Mercury content 0mg / l
(0.0% removal rate from fly ash).

Example 7 As a source of carbon dioxide, the combustion exhaust gas (CO ₂ : about 20%) of a cement kiln was replaced with a standard mixed gas at 0.5 Nm ³ / min.
The fly ash B of the above-mentioned municipal garbage incinerator was washed in the same manner as in Example 6 except that the fly ash B was introduced. In order to confirm the effect of removing heavy metals from fly ash, the washing filtrate 10 was sampled and analyzed. As a result, as shown in Table 2, the pH of the washing filtrate was 6.3, the chlorine ion concentration was 0.6 wt% (removal rate from fly ash: 94.3%), and the lead content was 0.1 mg / l (from fly ash). Removal rate 0.0%), mercury content 0mg / l (removal rate from fly ash 0.0%)
Met.

COMPARATIVE EXAMPLE 2 In Examples 6 and 7, carbon dioxide gas was introduced into the cleaning suspension to remove ash dust. In this comparative example, the following process was performed without introducing carbon dioxide. Ash dust was washed only with washing water. 5 kg of the above fly ash B and 55 liters of water in the municipal garbage incinerator were put into the washing and stirring tank 2 and stirred and mixed for about 5 minutes. Next, this suspension was guided to the dehydration filter 3 and filtered.
This filter cake 4 is further led to a washing and filtering device 5 and is then washed for about 10 minutes.
Wash with 1 liter of water and filter to remove chlorine from cake 4,
Dehydrated cake 6 was obtained. The filtrate 7 was drained to the outside through a route 8. On the other hand, the washing filtrate 10 was guided to a heavy metal removing device 11, and after removing heavy metals, was drained to the outside through a path 12. In order to confirm the effect of removing heavy metals from fly ash, the washing filtrate 10 was sampled and analyzed.
As a result, as shown in Table 2, the pH of the washing filtrate was 12.
7. Chloride ion concentration 0.4 wt% (removal rate from fly ash 62.9
%), Lead content 6.0 mg / l (removal rate from fly ash 1.3%), and mercury content 0.002 mg / l (removal rate from fly ash 3.3%).

As is clear from this comparative example, Examples 6 and 7, by stirring and mixing while blowing a gas containing carbon dioxide into the liquid in which fly ash is suspended, Friedel that does not elute only by washing with water is used. Chloride ions from salt can be eluted, and at the same time, elution of heavy metals such as lead and mercury can be suppressed. Similar processing results can be obtained not only for fly ash from municipal garbage furnaces but also for dusts from combustion furnaces such as dust from cement kilns if they contain Friedel's salt and heavy metals.

Example 8 In this example, the washing filtrate was circulated to adjust the chloride ion concentration of the washing suspension, and the exhaust gas of the combustion furnace was blown into the suspension for washing. Fly ash C from municipal waste incinerator containing Friedel salt (Cl: 17.3wt%, Pb: 972mg / kg,
5 kg of Zn: 4398 mg / kg, Hg: 0.802 mg / kg) and 55 liters of water were introduced into the stirring tank 2 and stirred and mixed for about 5 minutes. Next, the combustion exhaust gas (CO ₂ : about 20%) of the cement kiln was mixed into the suspension for 10 minutes while blowing at a rate of 0.5 Nm ³ / min. Thereafter, the blowing of gas was stopped, and the mixture was further stirred and mixed for 10 minutes. Next, this suspension was guided to the dehydration filter 3 and filtered. The filter cake 4 was further guided to a washing and filtering device 5, washed with about 56 liters of water, and filtered to remove chlorine from the cake 4 to obtain a dehydrated cake 6. This filtrate 7 passes through route 8
A part (about 5 liters) was guided to the path 14 and circulated to the washing and stirring tank 2 by adjusting the valve. The remaining filtrate was drained outside through route 8. On the other hand, the washing filtrate 10 is led to the heavy metal removing device 11, and about 50 liters of the filtrate is led to the path 14 by adjusting the valve in the path 13, and is combined with the washing filtrate 7 flowing in the path 9 and circulated to the washing and stirring tank 2. did. Further, 5 kg of fly ash C from the municipal garbage incinerator was newly introduced into the washing and stirring tank 2, and the same process was repeated. After repeating this operation five times, the valve in the path 12 is adjusted to drain about 6.4 liters per 11 pieces, and the valve in the path 8 is adjusted to circulate about 11.4 liters of washing filtrate. Was adjusted to do so. Thus, 55 liters of washing water were circulated to the washing and stirring tank 2 through the passage 14, and the same process was repeated twice. When the system was sufficiently stable, the washing filtrate 1 was used to confirm the effect of removing heavy metals from fly ash.
0 was sampled and analyzed. As a result, as shown in Table 3, the pH of the washing filtrate was 12.3 and the chloride ion concentration was 7.
6wt%, lead content 78.0mg / l (removal rate from fly ash 88.4%)
%), Zinc content 24.0 mg / l (removal rate 6.0 from fly ash)
%), Mercury content 0.023mg / l (removal rate from fly ash 31.5%)
%)Met. Further, the chlorine in the dehydrated cake 6 was analyzed to confirm the effect of removing chlorine from fly ash, and the chlorine removal rate from the fly ash was examined. The chlorine removal rate was 99.8%.

Comparative Example 3 In contrast to Example 8, in this comparative example, ash dust was washed only with water as follows without introducing carbon dioxide into the ash dust suspension and circulating the washing filtrate. did. 5 kg of the above fly ash C and 55 liters of water in the municipal garbage incinerator were charged into the washing and stirring tank 2 and mixed by stirring for about 5 minutes. Next, this suspension was filtered with a dehydration filter 3
And filtered. The filter cake 4 was further guided to a washing and filtering device 5, washed with about 10 liters of water and filtered to remove chlorine from the cake 4 to obtain a dehydrated cake 6. The filtrate 7 was drained to the outside through a route 8. On the other hand, the washing filtrate 10 was guided to a heavy metal removing device 11, and after removing heavy metals, was drained to the outside through a path 12. In order to confirm the effect of removing heavy metals from fly ash, the washing filtrate 10 was sampled and analyzed. As a result, as shown in Table 3, the pH of the washing filtrate was 12.2, the chloride ion concentration was 0.9 wt% (removal rate from fly ash: 59.3%), and the lead content was 18.0 mg / l (from fly ash). Removal rate 20.4%), zinc content 7.5mg / l (1.9% removal rate from fly ash), mercury content 0.003mg / l (removal rate from fly ash)
4.2%).

As is clear from this comparative example and Example 8, the washing filtrate was circulated to increase the chloride ion concentration of the washing suspension, and further washed by stirring and mixing while blowing gas containing carbon dioxide. Can elute chloride ions from Friedel's salt, which cannot be eluted only by washing with water, and further promote elution of heavy metals such as lead, zinc and mercury contained in ash dust. Similar results can be obtained not only for fly ash from municipal solid waste furnaces but also for dusts from combustion furnaces, such as dust from cement kilns, if they contain Friedel's salt and heavy metals.

[0042]

[0043]

[0044]

[0045]

According to the cleaning method and apparatus of the present invention, the following effects can be obtained. (1) The leaching of heavy metals from these ash dusts is promoted by washing the ash or dust of the combustion furnace with the chlorine ion concentration of the washing liquid being 2.0 wt% or more, and the heavy metals are effectively removed from the ash dusts. Can be. Since the obtained ash or dust cake contains almost no heavy metals,
Suitable for use as a cement raw material and landfill. on the other hand,
Since the washing filtrate contains a large amount of heavy metals, it is suitable for regenerating heavy metals. In the case where the washing filtrate is used in circulation, cost reduction by water saving can be expected.

(2) Washing of Ash Dust In the case where ash or dust of a combustion furnace contains a hardly soluble Friedel salt by introducing carbon dioxide into the suspension and stirring and washing while bubbling the dust and ash. However, the Friedel salt can be decomposed to sufficiently elute the chloride ions. No harmful heavy metals are eluted in the washing filtrate, and a high concentration of chlorine is eluted, which is suitable for chloride regeneration and the like. Further, since no acid or the like is used, the cost required for treating chemicals and acids can be reduced.

(3) Washing of ash Dust is stirred and washed while bubbling by blowing a gas containing carbon dioxide into the suspension, so that even if hardly soluble Friedel's salt is contained, this free ash is removed. Del salt is decomposed and chloride ions are sufficiently eluted to make it easier to adjust the chloride ion concentration in the next step.Then, stop blowing gas and add chloride to this washing suspension, The washing filtrate containing chlorine ions from which heavy metals have been removed is circulated and added to adjust the chloride ion concentration in the washing suspension to at least 2.0 wt. Can be eluted. After stirring and washing, the cake obtained by dehydrating and filtering the suspension contains almost no heavy metals and chlorine, and is suitable for reuse as a cement raw material. Also,
Since the washing filtrate contains a large amount of heavy metals, it is suitable for regenerating heavy metals. The filtrate from which heavy metals have been removed can be circulated to the washing step and reused as a chlorine ion supply source, and cost reductions can be expected by saving water.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an apparatus for performing a cleaning method of the present invention.

[Explanation of symbols]

2: washing and stirring tank, 3: dehydration filter, 4: cake,
5: washing filtration device, 6: dehydrated cake, 7: washing filtrate,
10: washing filtrate, 11: heavy metal removal (regeneration) device,
15: Standard mixed gas supply source (bomb), 1, 8, 9, 1
2, 13, 16, 18, 14: route 19: carbon dioxide introducing means 20: cleaning treatment device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuma Sakae 2-14-1, Nishishinbashi, Minato-ku, Tokyo Inside Chichibu Onoda Co., Ltd.

Claims (12)

[Claims] 1. A method for cleaning ash dust, comprising washing ash dust with a solution having a chlorine ion concentration of 2.0 wt% or more to promote elution of heavy metals contained in the ash dust and filtering the ash dust. 2. The chlorine ion concentration in the solution is reduced to 2.0 wt. By repeatedly using the washing filtrate from which heavy metals have been removed.
The cleaning treatment method according to claim 1, wherein the ash dust is washed at a rate of not less than 10%. 3. Introducing carbon dioxide into the ash dust washing suspension to wash it, thereby promoting the elution of chloride ions from Friedel's salt contained in the ash dust, while suppressing the elution of heavy metals in the ash dust. A method for cleaning ash dust. 4. The cleaning method according to claim 3, wherein carbon dioxide is introduced into the ash dust cleaning suspension by blowing combustion exhaust gas into the suspension. 5. A cleaning suspension of ash, wherein carbon dioxide is introduced into the ash for washing to promote the elution of chloride ions from Friedel's salt contained in the ash to increase the chloride ion concentration in the washing liquid. A method for cleaning ash dust in which heavy metals in the ash dust are eluted and removed by washing and filtering the ash dust with a chloride ion concentration of 2.0 wt% or more. 6. The cleaning method according to claim 5, wherein carbon dioxide is introduced into the ash dust cleaning suspension by blowing combustion exhaust gas into the suspension. 7. The cleaning method according to claim 5, wherein a chlorine ion-containing solution is added, or a washing filtrate from which heavy metals have been removed is added to make the chlorine ion concentration 2.0% by weight or more for washing. 8. The method according to claim 6, wherein the washing filtrate from which heavy metals have been removed is used repeatedly. 9. The cleaning method according to claim 1, wherein the ash dust from which chlorine ions and heavy metals have been removed by the cleaning process is used as a cement raw material. 10. A stirring tank for suspending and washing ash, means for filtering the ash suspension after washing, means for removing heavy metals from the filtrate, and circulating the solution from which the heavy metals have been removed to a stirring tank. With a channel for chlorine ion concentration of 2.0 wt%
A ash dust cleaning apparatus that cleans ash with the above cleaning liquid. 11. The cleaning apparatus according to claim 10, further comprising means for introducing carbon dioxide into the stirring tank. 12. The cleaning apparatus according to claim 10, further comprising means for washing and filtering the filter cake of the ash dust suspension, and a path for circulating the filtrate in a stirring tank.