JP2011224464A - Method of treating combustion ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the amounts of eluted environmental regulation target substances, e.g., fluorine, boron, lead and hexavalent chromium, below the environmental quality standards for soil contamination of the soil contamination countermeasures act, which substances are eluted simultaneously from combustion ash discharged by a boiler using coal as the main fuel and also burning RPF and wood waste together, and utilize the combustion ash safely in the soil field.SOLUTION: A method of treating combustion ash comprises adding dilute sulfuric acid to the combustion ash to make fluorine, boron, lead and hexavalent chromium eluted, rinsing the solid/liquid-separated residue to remove dilute sulfuric acid, fluorine and boron remaining in the treated residue and subjecting the residue to air drying, or dehydration, so as to reduce the amount of fluorine eluted from the residue to ≤0.8 mg/L and the amount of the eluted boron to ≤1.0 mg/L, measured by the elution test based on the Ministry of Environment notification No.18, 2003, and also control amounts of all other target elements of the soil contamination countermeasures act below the environmental quality standards for soil contamination.

Description

  The present invention relates to a method for suppressing elution of these harmful substances from combustion ash containing fluorine, boron, lead and hexavalent chromium. More specifically, the present invention uses combustion ash containing these harmful substances in the field of soil (such as roadbed materials and soil conditioners), so sulfuric acid is mixed with the combustion ash at a pH within an appropriate range. After mixing, solid-liquid separation is performed, and the residue is rinsed with water, so that the amount of fluorine eluted from combustion ash by an elution test based on Notification No. 18 of the Ministry of the Environment in 2003 is 0.8 mg / L or less and boron It is related with the processing method of combustion ash which makes the elution amount of 1.0 mg / L or less, the elution amount of lead 0.01 mg / L or less, and the elution amount of hexavalent chromium 0.05 mg / L or less.

  Conventionally, combustion ash such as household waste incineration ash, coal combustion ash (coal ash) from a thermal power plant, sewage sludge incineration ash, and various industrial wastes has been used as a raw material for cement and a soil conditioner. However, as a result of the enforcement of the Soil Contamination Countermeasures Law in 2003 and the addition of fluorine and boron elution standards, the combustion ash in most cases exceeds the soil environmental standard values stipulated in this law. It has become difficult to use in the soil field.

  Conventionally, fluorine and boron elution suppression methods from combustion ash exist separately, and fluorine elution suppression methods include melt solidification method, cement solidification method, and method of dissolving and removing by dissolving in solution. Further, as a method for suppressing the elution of boron, there is known a method in which the boron is extracted into an acidic solution and separated and removed.

  The melt-solidification method is known as a method in which waste is heated up to a high temperature of 1,400 to 1,600 ° C. to be sealed and fixed in slag that generates harmful substances (Patent Document 1). However, there is a problem that the processing cost including the equipment cost is high and the slag is not used much.

  The solidification method using cement is known as a method of solidifying and insolubilizing by adding a treatment agent composed of an inorganic agent or an organic agent (Patent Document 2). However, several steps are required for the treatment, and the treatment cost is high. In addition, the cement itself may contain harmful substances regulated by the Soil Contamination Countermeasures Law, such as hexavalent chromium and lead. There was a problem of coming.

  A method is also known in which a phosphoric acid compound and a calcium compound are added to combustion ash, kneaded and solidified (Patent Document 3). However, this method has a problem that the addition amount of the phosphoric acid compound is large and the cost of the phosphoric acid compound itself is high and the processing cost becomes enormous.

  Also known is a method in which combustion ash is mixed with water, dehydrated to remove water-soluble chlorine, and further thermally decomposed in water vapor at 400 ° C. or higher to gasify and remove fluorine as hydrofluoric acid. (Patent Document 4). However, this method has a problem in that it needs to be heated at a high temperature of 400 ° C. or higher, requires special equipment, and has a high processing cost.

  Furthermore, a method is known in which calcium aluminate (addition rate: 20 to 80% by mass) and gypsum (10 to 80% by mass) are added to suppress the elution of fluorine in the steelmaking slag (Patent Document 5). However, in this method, the fluorine content derived from fluorite (calcium fluoride) used in the iron making process is very high, so the addition rate of the treatment agent to make it less than the standard value of the Soil Contamination Countermeasures Law is very high. There is a problem that not only the chemical cost for processing the combustion ash but also the transportation cost is increased.

  A method of dissolving fluorine in a solution and separating and removing the fluorine is also known. For example, by contacting a mineral or mineral species with a leaching solution containing metal ions to form a soluble fluorine double complex (Patent Document 6), or washing fluorine-containing gypsum with washing water containing aluminum ions. There is also a method of separating and removing fluorine in gypsum (Patent Document 7).

On the other hand, as a method of suppressing the dissolution of boron, an acidic solution is added to the boron-containing combustion ash containing coal as the main fuel, boron is eluted, and then solid-liquid separation is performed. A method for separating and removing boron is known in which the acidic solution and boron to be removed are removed, and then the solid residue after rinsing and washing is dehydrated (Patent Document 8). However, this method is intended for the separation of only boron, and there is no description about the amount of elution of fluorine, and as boiler fuel, for example, in many cases in paper mills, in addition to coal, RPF, wood chips, etc. From the combustion ash discharged from the boiler co-fired, fluorine is also eluted at the same time as boron, so a separate measure for suppressing the elution of fluorine is required.
Japanese Patent Laid-Open No. 2003-119057 JP-A-6-15248 JP 2002-331272 A JP-A-9-165243 JP 2001-259570 A Japanese Patent No. 3665067 Japanese Patent Laid-Open No. 2004-299962 JP 2003-320342 A

  In the present invention, it is possible to treat fluorine and boron at the same time, simply and inexpensively, in place of the complicated and time-consuming process such as cement solidification and melting as described above, and the elution of fluorine or boron cannot be suppressed at the same time. In addition, we provide a method that can suppress the elution of lead and hexavalent chromium at the same time, and the soil field (backfill material, embankment, soil improvement material, roadbed material, etc.) without fear of causing soil contamination and water contamination of the treated combustion ash The purpose is to make effective use for the purpose.

  The inventors of the present invention are simple and inexpensive to suppress fluorine, boron, lead, and hexavalent chromium from combustion ash that elutes more than the soil environment standard value regulated by the Soil Contamination Countermeasures Law. As a result of diligent research on methods that can be treated, the sulfuric acid is added to the combustion ash and stirred sufficiently, and then the residue after solid-liquid separation is rinsed with water to thoroughly wash away the sulfuric acid remaining in the residue. The elution pH in the elution test method based on the Ministry of the Environment Notification No. 18 is reduced to 6-9, the fluorine elution amount is 0.8 mg / L or less, and the boron elution amount is 1.0 mg at the same time. / L or less, lead elution amount 0.01 mg / L or less, hexavalent chromium elution amount 0.05 mg / L or less, and all other elements regulated by the Soil Contamination Countermeasures Law Can be below environmental standards Heading the door, which resulted in the completion of the present invention.

  In the present invention, sulfuric acid is added to the combustion ash and stirred to elute fluorine, boron, lead, etc. contained in the combustion ash, and then the residue after solid-liquid separation is rinsed with water, Elution of fluorine, boron, lead and hexavalent chromium contained in combustion ash can be suppressed at the same time. As a result, the treated combustion ash can be used as a raw material for a backfill material, embankment, soil improvement material, roadbed material and the like without adversely affecting the environment.

The flow schematic diagram of the present invention is shown.

  The combustion ash in the present invention means that fluorine, boron, lead, and hexavalent chromium are eluted at the same time. Combustion ash using coal collected by a filter or the like as the main fuel is more preferable.

  However, the combustion ash used in the present invention is not necessarily limited to the combustion ash from which fluorine, boron, lead, and hexavalent chromium are eluted at the same time.

  In the simultaneous elution suppression treatment of fluorine, boron, lead and hexavalent chromium of combustion ash according to the present invention, sulfuric acid is always used. Some elution progresses when the pH becomes acidic, and if it is an acid, there is an elution effect, but sulfuric acid is preferred because it has the highest elution effect. The concentration of sulfuric acid at this time is 0.2 N to 1.0 N. If the concentration of sulfuric acid is less than 0.2N, when sulfuric acid is added to the combustion ash, fluorine, boron, lead and hexavalent chromium will not be sufficiently eluted, and as a result, a sufficient cleaning effect cannot be obtained. Not suitable for. Conversely, when the sulfuric acid concentration is higher than 1.0 N, fluorine, boron, lead, and hexavalent chromium are sufficiently eluted when sulfuric acid is added to the combustion ash. When the dissolution test according to Notification No. 18 was performed, the pH of the eluate was 4 or less, and as a result, the elution amount of these elements did not fall below the reference value, which is not suitable.

  The amount of sulfuric acid having the above-mentioned concentration in the present invention is preferably as much as possible if it is limited to elution, but the optimum amount is 10 to 15 times the mass of combustion ash in view of post-treatment and cost. . When 0.2N sulfuric acid is used, if less than 10 times the amount, when sulfuric acid is added to the combustion ash, fluorine, boron, lead and hexavalent chromium are not sufficiently eluted, resulting in a sufficient cleaning effect. Not suitable for not being able to. In addition, when using 1.0 N sulfuric acid, if it exceeds 15 times, there is no problem in eluting these elements from the combustion ash, but it is costly and the amount of rinse water after washing, which will be described later, is large. Because it is necessary, it is not suitable. Adjust and use according to the normality of the sulfuric acid used.

  The method for adding sulfuric acid in the present invention is not particularly limited, but it is desirable that the combustion ash and sulfuric acid are sufficiently mixed. As the equipment for mixing and dehydrating combustion ash and sulfuric acid, a known mixer can be used. However, since the present invention requires the rinsing of the residue described later, the filter cloth or A filter press made of polypropylene having a filter plate that is acid resistant and capable of washing the cake after dehydration is preferred.

The amount of water for rinsing the cleaning residue in the present invention is required to be 2 to 5 times as much as the ash mass ratio.
If the amount is less than 2 times, the rinsing effect is insufficient, and even if an amount exceeding 5 times is used, the effect reaches a peak, which is not preferable.
The purpose of rinsing was to adjust the pH of the elution test according to the Ministry of the Environment Notification No. 18 method to 6.0 to 9.0 by washing off the washing liquid remaining in the residue after washing the combustion ash with sulfuric acid. As a result, the elution amount of fluorine, boron, lead, and hexavalent chromium from the residue can be suppressed below the soil environment standard value of the Soil Contamination Countermeasures Law.

  The water used for rinsing in the present invention is not particularly limited as long as it does not contain a substance specified by the Soil Contamination Countermeasures Law. For example, pure water, ion-exchanged water, tap water, and the like can be used. In consideration of subsequent trace analysis, pure water or ion-exchanged water is preferably used. However, if the facilities are expanded and a large amount of rinse water is required, tap water or industrial water may be used.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Unless otherwise indicated, the combustion ash is the combustion ash (= coal ash) according to claim 1, and coal ash (1) and coal ash (2) having different lots (fuel composition at the time of boiler incineration) were used.

1. Properties of coal ash (1) Properties of coal ash (1) are as follows.
As the boiler fuel composition, fly ash collected by a bug filter of a fluidized bed boiler, which is 70% coal (low-grade coal), 20% RPF, 5% wood chips, and 5% others, was used. The main composition of the present coal ash, the result of measurement by X-ray fluorescence, 50.62% as SiO _2, 26.54% in _Al 2 _{O 3,} 8.43 percent CaO, was others. Moreover, as a result of measuring the amount of elution from coal ash according to the dissolution test method based on Notification No. 18 of the Ministry of the Environment in 2003, the amount of fluorine eluted was 8.0 mg / L, and the amount of boron eluted was the lower limit of detection. .1 mg / L or less, the elution amount of lead was 0.02 mg / L, and the elution amount of hexavalent chromium was 0.02 mg / L. The amount of elution of other elements stipulated by the Soil Contamination Countermeasures Law was below the standard value. The pH of the eluate was 12.6.

2. Properties of coal ash (2) Properties of coal ash (2) are as follows.
As boiler fuel composition, fly ash collected with a bug filter of a fluidized bed boiler, which is 65% coal (low-grade coal), 25% RPF, 5% wood chips, and 5% others, was used. The main composition of the present coal ash, the result of measurement by X-ray fluorescence, 46.52% as SiO _2, 25.14% in _Al 2 _{O 3,} 11.37 percent CaO, was others. Moreover, as a result of measuring the amount of elution from coal ash according to the dissolution test method based on Notification No. 18 of the Ministry of the Environment in 2003, the amount of fluorine eluted was 6.7 mg / L, and the amount of boron eluted was the lower detection limit. .1 mg / L or less, the elution amount of lead was 0.04 mg / L, and the elution amount of hexavalent chromium was 0.02 mg / L. The amount of elution of other elements stipulated by the Soil Contamination Countermeasures Law was below the standard value. The pH of the eluate was 13.0.

(A) Dissolution test method The dissolution test was conducted in accordance with the Ministry of the Environment Notification No. 18 in 2003. That is, after the sample was sufficiently air-dried, 50 g of a non-metallic sieve having a mesh opening of 2 mm was passed through a 1,000 mL polyethylene container with a lid, and 500 mL of pure water (pH 5.8 to 6.3) was added. In addition, a sample solution was prepared. This sample solution was shaken continuously for 6 hours at room temperature and atmospheric pressure using an industrial waste elution shaker (manufactured by Tytec Co., Ltd.) (shaking width: 4 to 5 cm, vibration frequency: 200 times / min). Next, the sample solution after shaking was allowed to stand for 30 minutes, and then centrifuged at about 3,000 rpm for 20 minutes. The supernatant was filtered through a membrane filter having a pore size of 0.45 μm, the filtrate was taken, the amount required for quantification was accurately measured, and this was used as a test solution.
(B) Fluorine measurement method The test solution was quantified with an ion chromatograph (ICS-2000 / manufactured by Nippon Dionex Co., Ltd.) (JIS K 0102 34.2, Table 6 with water quality environmental standard notice).
(C) Boron Measurement Method The test solution was quantified with an ICP emission spectroscopic analyzer (CIROS-120 / manufactured by Rigaku Corporation) (47.3 of JIS K 0102).
(D) Method for measuring hexavalent chromium The test solution was quantified with a diphenylcarbamide absorptiometer (JIS K 0102 65.2.1).
(E) Method for measuring selenium The test solution was quantified by hydride generation ICP emission spectrometry (JIS K 0102 67.2).
(F) Arsenic Measurement Method The test solution was quantified by hydride generation ICP emission spectrometry (JIS K 0102 61.3).
(G) Lead measurement method The test solution was quantified by ICP emission spectroscopic analysis (JIS K 0102 54.3).
(H) Method for measuring cadmium The test solution was quantified by ICP emission spectroscopic analysis (JIS K 0102 55.3).
(I) Measurement of pH The test solution was measured with an electrode-type pH meter (manufactured by Metra Co., Ltd.) (JIS Z 8802-1984).

Example 1
To coal ash (1) having an absolute dry mass of 100 g, 1,000 mL of 0.2 N sulfuric acid was mixed, and then sufficiently stirred with a magnetic stirrer for 30 minutes. After stirring, the mixture was placed in a Buchner funnel with No. Two qualitative filter papers were drawn, and solid-liquid separation was performed by suction filtration using an aspirator. After sufficiently separating the cleaning solution, 200 mL of rinse water for rinsing was poured into the residue while suctioning with an aspirator, and then the rinsing solution was sufficiently sucked and separated to obtain a residue. After the residue was air-dried, the residue was subjected to a dissolution test in accordance with 2003 Ministry of the Environment Notification No. 18. The pH of the washing filtrate is 3.8, the pH of the eluate of the residue after rinsing is 8.1, the elution amount of fluorine is 0.6 mg / L, the elution amount of boron is 0.3 mg / L, the elution amount of lead Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 2
The same operation as in Example 1 was performed except that the amount of sulfuric acid in Example 1 was changed from 1,000 mL to 1,200 mL. The pH of the washing filtrate is 3.5, the pH of the residue eluate after rinsing is 8.1, the fluorine elution amount is 0.6 mg / L, the boron elution amount is 0.2 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 3
The same operation as in Example 1 was performed except that the concentration of sulfuric acid in Example 1 was changed from 0.2 N to 0.3 N. The pH of the washing filtrate is 2.4, the pH of the eluate of the residue after rinsing is 8.2, the elution amount of fluorine is 0.7 mg / L, and the elution amount of boron is 0.1 mg / L or less (lower limit of detection) Below) The lead elution amount is 0.01 mg / L or less which is the detection limit, the elution amount of hexavalent chromium is 0.01 mg / L or less which is the detection limit, and other elements are also soil environmental standards of the Soil Contamination Countermeasures Law. It was below the value.

Example 4
The same operation as in Example 1 was performed, except that the concentration of sulfuric acid in Example 1 was changed from 0.2 N to 0.3 N and the amount of sulfuric acid was changed from 1,000 mL to 1,200 mL. The pH of the washing filtrate is 2.1, the pH of the eluate of the residue after rinsing is 7.8, the fluorine elution amount is 0.4 mg / L, the boron elution amount is 0.5 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 5
The same operation as in Example 1 was performed except that the concentration of sulfuric acid in Example 1 was changed from 0.2 N to 0.5 N. The pH of the washing filtrate is 2.1, the pH of the eluate of the residue after rinsing is 7.5, the elution amount of fluorine is 0.3 mg / L, the elution amount of boron is 0.6 mg / L, the elution amount of lead Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 6
The same operation as in Example 1 was performed, except that the concentration of sulfuric acid in Example 1 was changed from 0.2 N to 0.7 N, and the stirring time of the ash and sulfuric acid mixed solution was changed from 30 minutes to 20 minutes. The pH of the washing filtrate is 2.0, the pH of the residue eluate after rinsing is 7.2, the fluorine elution amount is 0.1 mg / L, the boron elution amount is 0.8 mg / L, the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 7
The same operation as in Example 1 was performed, except that the sulfuric acid concentration in Example 1 was changed from 0.2 N to 1.0 N. The pH of the washing filtrate is 0.47, the pH of the eluate of the residue after rinsing is 7.5, the fluorine elution amount is 0.6 mg / L, the boron elution amount is 0.8 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 8
The same operation as in Example 1 was performed except that the amount of sulfuric acid in Example 1 was changed from 1,000 mL to 1,500 mL. The pH of the washing filtrate is 2.4, the elution amount of fluorine is 0.3 mg / L, the elution amount of boron is 0.7 mg / L, the elution amount of lead is 0.01 mg / L or less, which is the detection limit, hexavalent The amount of chromium elution was 0.01 mg / L or less, which is the detection limit, and other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 9
The same operation as in Example 3 was performed except that the coal ash of Example 3 was changed from coal ash (1) to coal ash (2). The pH of the washing filtrate is 3.1, the pH of the eluate of the residue after rinsing is 7.1, the fluorine elution amount is 0.4 mg / L, the boron elution amount is 0.4 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 10
The same operation as in Example 1 was performed, except that the coal ash of Example 1 was changed from coal ash (1) to coal ash (2) and the stirring time was changed from 30 minutes to 20 minutes. The pH of the washing filtrate is 2.9, the pH of the eluate of the residue after rinsing is 8.3, the elution amount of fluorine is 0.5 mg / L, the elution amount of boron is 0.3 mg / L, and the elution amount of lead Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 11
The same operation as in Example 10 was performed except that the stirring time in Example 10 was changed from 20 minutes to 60 minutes. The pH of the washing filtrate is 3.2, the pH of the eluate of the residue after rinsing is 7.9, the fluorine elution amount is 0.3 mg / L, the boron elution amount is 0.5 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 12
The same operation as in Example 3 was performed except that the coal ash of Example 3 was changed from coal ash (1) to coal ash (2) and the amount of rinse water for rinsing was changed from 200 mL to 500 mL. The pH of the washing filtrate is 3.9, the pH of the eluate of the residue after rinsing is 8.1, the elution amount of fluorine is 0.5 mg / L, the elution amount of boron is 0.4 mg / L, and the elution amount of lead Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 13
Except for changing the coal ash of Example 3 from coal ash (1) to coal ash (2), the amount of sulfuric acid from 1,000 mL to 1,500 mL, and the amount of rinse water for rinsing from 200 mL to 500 mL, The same operation as in Example 3 was performed. The pH of the washing filtrate is 3.8, the pH of the eluate of the residue after rinsing is 7.9, the fluorine elution amount is 0.6 mg / L, the boron elution amount is 0.4 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 14
After 10 L of 0.3 N sulfuric acid was mixed with 1 kg of coal ash (2) having an absolutely dry mass, the mixture was sufficiently stirred for 30 minutes with a stirrer. After stirring, the mixed solution was adsorbed on a filter press filter plate using a “pressing filter press” manufactured by Makino Co., Ltd. with a slurry supply pump, and 2 L of rinsing water was pressurized with a backwash method using a water injection pump. . Thereafter, the filter mud was peeled off by air blow to obtain a residue. About the residue after a process, the elution test was done based on the Ministry of the Environment notification No. 18 in 2003. The pH of the washing filtrate is 3.6, the pH of the residue eluate after rinsing is 7.6, the fluorine elution amount is 0.2 mg / L, the boron elution amount is 0.5 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 15
The same operation as in Example 14 was performed except that the amount of rinse water by backwashing in Example 14 was changed from 2 L to 5 L. The pH of the washing filtrate is 3.7, the pH of the eluate of the residue after rinsing is 7.5, the fluorine elution amount is 0.4 mg / L, the boron elution amount is 0.4 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Example 16
The same operation as in Example 14 was performed, except that 0.3 N sulfuric acid in Example 14 was changed to 0.4 N sulfuric acid. The pH of the washing filtrate is 3.5, the pH of the residue eluate after rinsing is 8.1, the fluorine elution amount is 0.4 mg / L, the boron elution amount is 0.3 mg / L, and the lead elution amount Was 0.01 mg / L or less, which was the detection limit, and the elution amount of hexavalent chromium was 0.01 mg / L or less, which was the detection limit. Other elements were also below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 1
In Example 1, after mixing and stirring with sulfuric acid, after solid-liquid separation and dehydration, no rinsing treatment was performed, and a residue elution test was performed in accordance with Notification No. 18 of the Ministry of the Environment in 2003. The pH of the washing filtrate was 3.8, the pH of the residue eluate was 7.4, the fluorine elution amount was 1.4 mg / L, and the boron elution amount was 1.0 mg / L. Elution was more than the environmental standard value of the law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 2
In Example 3, after mixing and stirring with sulfuric acid, after solid-liquid separation and dehydration, no rinsing treatment was performed, and a residue elution test was performed in accordance with Notification No. 18 of the Ministry of the Environment in 2003. The pH of the washing filtrate is 1.7, the pH of the residue eluate is 7.7, the fluorine elution amount is 2.5 mg / L, and the boron elution amount is 0.9 mg / L. Elution exceeded the environmental standard value of the law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 3
In Example 8, after mixing and stirring with sulfuric acid, after solid-liquid separation and dehydration, no rinsing treatment was performed, and a residue elution test was performed in accordance with Notification No. 18 of the Ministry of the Environment in 2003. The pH of the washing filtrate is 3.1, the pH of the residue eluate is 7.7, the fluorine elution amount is 1.9 mg / L, and the boron elution amount is 0.9 mg / L. Elution exceeded the environmental standard value of the law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 4
In Example 1, the same operation as in Example 1 was performed, except that the concentration of sulfuric acid was changed from 0.2 N to 0.1 N. The pH of the washing filtrate is 10.9, the pH of the eluate of the residue after rinsing is 9.2, the elution amount of fluorine is 3.9 mg / L, and the elution amount of boron is 0.6 mg / L. Elution exceeded the soil environmental standard value of the Soil Contamination Countermeasures Law.

Comparative Example 5
In Example 1, the same operation as in Example 1 was performed except that the concentration of sulfuric acid was changed from 0.2 N to 1.5 N. The pH of the washing filtrate is 0.7, the pH of the eluate of the residue after rinsing is 4.0, the elution amount of fluorine is 7.1 mg / L, and the elution amount of boron is 1.0 mg / L. Both boron were eluted above the environmental standard value of the Soil Contamination Countermeasures Law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 6
In Example 1, the same operation as in Example 1 was carried out except that 0.2 N sulfuric acid for washing was changed to water (ion exchange water). The pH of the washing filtrate is 12.8, the pH of the eluate of the residue after rinsing is 9.3, the elution amount of fluorine is 4.1 mg / L, and the elution amount of boron is 5.2 mg / L. Both boron were eluted above the environmental standard value of the Soil Contamination Countermeasures Law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 7
In Example 1, the same operation as in Example 1 was performed except that 0.2 N sulfuric acid for washing was changed to 0.1 N dilute hydrochloric acid. The pH of the washing filtrate is 11.7, the pH of the eluate of the residue after rinsing is 9.2, the elution amount of fluorine is 5.0 mg / L, and the elution amount of boron is 2.8 mg / L. Both boron were eluted above the environmental standard value of the Soil Contamination Countermeasures Law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 8
In Example 1, the same operation as in Example 1 was performed except that 0.2 N sulfuric acid for washing was changed to 0.2 N dilute hydrochloric acid. The pH of the washing filtrate is 11.5, the pH of the eluate of the residue after rinsing is 9.1, the fluorine elution amount is 3.9 mg / L, and the boron elution amount is 1.2 mg / L. Both boron were eluted above the environmental standard value of the Soil Contamination Countermeasures Law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 9
In Example 1, the same operation as in Example 1 was performed except that 0.2 N sulfuric acid for washing was changed to 0.3 N dilute hydrochloric acid. The pH of the washing filtrate is 8.1, the pH of the eluate of the residue after rinsing is 8.4, the elution amount of fluorine is 1.7 mg / L, and the elution amount of boron is 2.2 mg / L. Both boron were eluted above the environmental standard value of the Soil Contamination Countermeasures Law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

Comparative Example 10
In Example 1, the same operation as in Example 1 was performed except that 0.2 N sulfuric acid for washing was changed to 0.5 N dilute hydrochloric acid. The pH of the washing filtrate is 5.1, the pH of the eluate of the residue after rinsing is 8.2, the fluorine elution amount is 0.9 mg / L, and the boron elution amount is 2.4 mg / L. Both boron were eluted above the environmental standard value of the Soil Contamination Countermeasures Law. In addition, other elements were below the soil environment standard value of the Soil Contamination Countermeasures Law.

As is clear from comparing Examples 1 to 16 and Comparative Examples 1 to 10, coal is mainly used as a fuel, and a certain concentration of sulfuric acid is added to and mixed with the combustion ash of a boiler that also co-fires RPF and wood chips. Then, the sulfuric acid solution and the fluorine and boron remaining in the treatment residue are washed by pouring a certain amount of water into the residue obtained by eluting fluorine, boron, lead and hexavalent chromium and then separating the solid and liquid. , Lead and hexavalent chromium are removed, and then the residue after rinsing is dehydrated, so that the amount of fluorine eluted from the residue by the dissolution test based on the Ministry of the Environment Notification No. 18 in 2003 is 0.8 mg. / L or less, boron elution amount 1.0 mg / L or less, lead elution amount 0.01 mg / L or less, hexavalent chromium elution amount 0.05 mg / L or less (other soils) Pollution control law regulatory elements All equal to or less than the soil environment reference value).
As a result, the amount of elution of all environmental impact elements from coal ash could be reduced below the soil environment standard value of the Soil Contamination Countermeasures Law, and it became possible to use it safely in the soil field.

Claims (2)

Combustion ash and a sulfuric acid solution having a concentration of 0.2 N to 1.0 N are mixed at a solid-liquid ratio of 1:10 to 1:15, and then solid-liquid separation is performed to elute and remove fluorine and boron. By rinsing and washing the separated combustion ash and further solid-liquid separation, the elution pH of combustion ash when measured by the dissolution test method of the Ministry of the Environment Notification No. 18 in 2003 is set to 6-9, Combustion ash treatment method in which the elution amount of fluorine, boron, lead and hexavalent chromium is simultaneously below the soil environmental standard value. The combustion ash is mainly produced from coal, mixed with RPF (Refuse Paper & Plastic Fuel) and wood chips, etc., and discharged from combustion facilities such as fluidized bed boilers, using bag filters and electric dust collectors. The method for treating combustion ash according to claim 1, wherein the combustion ash is collected.

Images