JP2019001696A - Coal ash-cured substance - Google Patents

Abstract

To provide a coal ash-cured substance capable of: preventing heavy metals in coal ash from being eluted; and being used inexpensively as a civil-engineering material and an environmental material.SOLUTION: A coal ash-cured substance of this invention comprises a coal ash, a flush residue of chlorine bypass dust, and a cement. It is also preferable that: the substance contains 0.1-20 pts.mass of the flush residue of chlorine bypass dust based on 100 pts.mass of the coal ash; the content of AlOin the flush residue of the chlorine bypass dust is 1-10 mass%; and the content of SOin the flush residue of the chlorine bypass dust is 3-15 mass%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cured coal ash.

Coal ash generated from coal-fired power plants is mainly composed of quartz and mullite, which are minerals mainly composed of SiO ₂ and Al ₂ O _3. Conventionally, cement raw materials, concrete admixtures, backfill materials, It is used as environmental materials such as civil engineering materials such as embankment materials, bottom quality improvement materials, and water purification materials. Among them, with the recent increase in the amount of coal ash generated, it is considered promising to use it for civil engineering materials and environmental materials that are expected to be able to effectively use a large amount of coal ash. However, coal ash contains coal-derived heavy metals, and it has been reported that heavy metals exceeding soil environmental standards are eluted from coal ash. Therefore, in order to effectively use coal ash for civil engineering materials or environmental materials, it is necessary to suppress elution of heavy metals contained in coal ash.

  As a method for suppressing elution of heavy metals in coal ash, Patent Document 1 discloses a method in which cement ash, a reducing agent, and slaked lime are added to coal ash and hardened. Patent Document 2 discloses a method of granulating by adding a reducing agent and cement, lime, gypsum and the like to coal ash.

  On the other hand, in cement factories, the use of high chlorine-containing waste as a raw material for cement has been increasing in recent years, and the amount of chlorine bypass dust generated from chlorine bypass facilities installed to remove chlorine in cement kilns has increased. It has increased. Chlorine bypass dust has been treated by the method of adding water washing residue, which has been treated with water to remove chlorine, etc., to cement or the method of adding it to cement-based solidified materials. Development of effective use methods is desired.

Japanese Unexamined Patent Publication No. 2016-47519 JP 2007-119341 A

  In the methods disclosed in Patent Documents 1 and 2, since a material containing coal ash and at least one of cement, lime, and gypsum is used, heavy metals such as fluorine, boron, arsenic, and selenium contained in coal ash are used. The effect of insolubilization of hexavalent chromium is expected, but the effect of inhibiting elution of hexavalent chromium cannot be expected. In addition, since an expensive reducing agent is required to suppress the elution of hexavalent chromium, the material cost and the unit price of the product increase, making it difficult to effectively use it for civil engineering and environmental materials that require inexpensive materials. It becomes. Furthermore, like patent document 1, when only an acidic iron salt is used as a reducing agent, there exists a concern that the pH of coal ash hardened | cured material may fall and it may have a bad influence on the elution suppression effect, such as a boron.

  Therefore, the subject of this invention is providing the coal ash hardened | cured material which can suppress the elution of heavy metals in coal ash, and can be utilized cheaply as a civil engineering material or an environmental material. It is another object of the present invention to provide an effective method for using water residue of chlorine bypass dust, which has been generated in recent years.

  The present inventor has found that the washing residue of chlorine bypass dust contains calcium, aluminum and sulfuric acid, and ettringite is produced in the washing residue. Ettringite has the property of insolubilizing heavy metals by replacing sulfate ions and hydroxide ions contained in its structure with heavy metal anions, and adsorbing heavy metals on the surface, insolubilizing heavy metals in coal ash. And found that the elution can be reduced. Moreover, it discovered that the water washing residue of the chlorine bypass dust contained calcium hydroxide produced by hydration of free lime (hereinafter also referred to as “f.CaO”) in the chlorine bypass dust.

  Based on these findings, the present inventor mixed coal ash and water washing residue of chlorine bypass dust and cement, and cured coal ash obtained by curing by kneading with water is water washing residue of chlorine bypass dust. It has been found that the amount of elution of heavy metals from the hardened coal ash can be reduced as compared with the case where no additive is added, and the present invention has been completed.

That is, this invention relates to the hardened coal ash containing coal ash, the washing residue of chlorine bypass dust, and cement.
The present invention relates to a cured coal ash containing 0.1 to 20 parts by mass of chlorine bypass dust washing residue with respect to 100 parts by mass of coal ash.
The present invention relates to a cured coal ash having an Al ₂ O ₃ content of 1 to 10% by mass in the water washing residue of the chlorine bypass dust.
The present invention relates to a cured coal ash having a SO ₃ content of 3 to 25% by mass of the water washing residue of the chlorine bypass dust. The present invention relates to f. The present invention relates to a cured coal ash having a CaO content of 0.1 to 45% by mass. This invention relates to the hardened | cured coal ash whose selenium elution amount of the water washing residue of the said chlorine bypass dust is 0.001-1.0 mg / L.
The present invention relates to a hardened coal ash having a selenium content of the water washing residue of the chlorine bypass dust of 10 to 250 mg / kg.

The present invention relates to a cured coal ash containing 3 to 25 parts by mass of cement with respect to 100 parts by mass of coal ash.
The present invention relates to a hardened coal ash in which the water washing residue of the chlorine bypass dust is obtained by washing and dewatering the chlorine bypass dust.
The present invention relates to a hardened coal product in which the hardened coal ash contains 1 to 15 parts by weight of gypsum with respect to 100 parts by weight of coal ash. The present invention relates to a cured coal ash containing 1 to 15 parts by mass of lime with respect to 100 parts by mass of the coal ash.
The present invention further relates to a cured coal ash containing a water reducing agent.

  The hardened coal ash of the present invention contains coal ash, washing residue of chlorine bypass dust, and cement, so that the amount of elution of heavy metals is reduced to below the soil environmental standard, so civil engineering materials and environmental materials Can be suitably used.

  In addition, since the hardened coal ash of the present invention uses the washing residue of chlorine bypass dust, which is industrial waste, as an elution inhibitor for heavy metals, when using a conventional commercially available heavy metal elution inhibitor Compared to the above, it can be used as an inexpensive civil engineering material or environmental material, so that the effective use of coal ash can be expanded and the washing residue of chlorine bypass dust can be used effectively.

FIG. 1 is a diagram showing X-ray diffraction (XRD) patterns of 28 days of age of hardened coal ash A to D of Examples 1 to 3 and Comparative Example 1 of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail. In addition, this invention is not limited to the following embodiment.

  The hardened coal ash according to the present invention includes coal ash, a residue of washing water of chlorine bypass dust, and cement.

  The coal ash used in the present invention is not particularly limited as long as it is generated by coal combustion. Examples include ash produced when pulverized coal is burned at a coal-fired power plant, and fly ash collected by an electric dust collector or the like and clinker ash collected by dropping from a combustion boiler. In particular, fly ash contains a large amount of heavy metals compared to clinker ash and has a large amount of elution, so that it is suitably used effectively as a raw material for the hardened coal ash of the present invention.

Coal ash contains heavy metals derived from coal such as arsenic (As), selenium (Se), and hexavalent chromium (Cr ⁶⁺ ). In addition to heavy metals, coal ash contains elements such as fluorine (F) and boron (B). In the following description, these heavy metals and other elements such as fluorine and boron are collectively referred to as “heavy metals”. Heavy metals may leach out of coal ash in excess of soil environmental standards. As a method for insolubilizing these heavy metals, cement is added and cured, and it is physically contained in the cured product and insolubilized, and coal ash pozzolanic reaction and cement hydration reaction. There is known a method of immobilizing and insolubilizing. Fluorine, arsenic and selenium can sufficiently suppress elution from coal ash by using these methods.

  On the other hand, boron is insolubilized by a hydrate produced by cement hydration reaction or coal ash pozzolanic reaction, but it is an element whose elution amount tends to increase when pH is lowered due to neutralization or the like. Hexavalent chromium is insolubilized by adding a reducing agent and reducing it to the form of trivalent chromium, but it is difficult to suppress elution except by the method of reducing to the form of trivalent chromium. The hardened coal ash of the present invention contains rind residue of chlorine bypass dust to produce ettringite that insolubilizes heavy metals, and is less susceptible to pH reduction due to neutralization, etc., and has an effect of suppressing elution of hexavalent chromium. Therefore, coal ash eluting at least one or more of fluorine, boron, arsenic, selenium and hexavalent chromium can be effectively used, and coal ash eluting at least one or more of boron and hexavalent chromium is more suitable. Can be used effectively.

  The boron elution amount of coal ash used in the present invention is preferably 0.001 to 15 mg / L, more preferably 0.001 to 10 mg / L, and still more preferably 0.001 to 7.5 mg / L. If the boron elution amount of coal ash is within these ranges, the boron elution amount from the hardened coal ash of the present invention can be suppressed to a soil environment standard or less.

  The arsenic elution amount of coal ash used in the present invention is preferably 0.0001 to 0.5 mg / L, more preferably 0.0001 to 0.4 mg / L, and still more preferably 0.0001 to 0.3 mg / L. . If the arsenic elution amount of coal ash is within these ranges, the arsenic elution amount from the cured coal ash of the present invention can be suppressed to a soil environment standard or less.

  The selenium elution amount of coal ash used in the present invention is preferably 0.0001 to 0.3 mg / L, more preferably 0.0001 to 0.2 mg / L, and still more preferably 0.0001 to 0.1 mg / L. . Selenium is also eluted from the washing residue of the chlorine bypass dust contained in the hardened coal ash of the present invention. If the amount of selenium eluted from the coal ash is within the above range, the selenium from the hardened coal ash of the present invention The amount of elution can be suppressed below the soil environmental standard.

  The hexavalent chromium elution amount of coal ash used in the present invention is preferably 0.001 to 0.3 mg / L, more preferably 0.001 to 0.2 mg / L, and 0.001 to 0.1 mg / L. Further preferred. If the elution amount of hexavalent chromium in the coal ash is within these ranges, the elution amount of hexavalent chromium from the hardened coal ash of the present invention can be suppressed below the soil environmental standard.

  0.001-15 mg / L is preferable, as for the fluorine elution amount of coal ash used by this invention, 0.001-12.5 mg / L is more preferable, and 0.001-10 mg / L is still more preferable. If the fluorine elution amount of coal ash is within these ranges, the fluorine elution amount from the hardened coal ash of the present invention can be suppressed to a soil environment standard or less.

  The boron elution amount, the arsenic elution amount, the selenium elution amount, the hexavalent chromium elution amount and the fluorine elution amount from coal ash are measured by the methods described in Examples described later.

  Chlorine bypass dust means that when raw fuel with a high chlorine content is used in the cement manufacturing process, part of the exhaust gas containing chlorine contained in the cement kiln of the cement factory equipment is extracted by the chlorine bypass equipment. It is dust (powder) generated when the exhaust gas is cooled. Chlorine bypass dust is a chloride such as potassium chloride, f. It is composed of a calcined material of cement raw material such as CaO, chlorine, aluminum, sulfuric acid and the like.

  The washing residue of chlorine bypass dust used in the present invention is an insoluble residue generated when the above-described chlorine bypass dust is washed with water. The water washing treatment refers to a treatment of washing with water and dehydrating.

  Due to the fact that chlorine bypass dust contains a plurality of components such as chlorine and calcium, the washing residue of the chlorine bypass dust obtained by filtering the chlorine bypass dust after washing with water is the same as the chlorine bypass dust. In addition, it contains chloride, calcium, aluminum and sulfuric acid. On the other hand, the washing residue of chlorine bypass dust has a reduced amount of selenium and chlorine as compared with the chlorine bypass dust before washing due to the fact that it has undergone a washing treatment. For these reasons, in the present invention, the washing residue of chlorine bypass dust is suitably contained in the hardened coal ash as a heavy metal elution inhibitor.

  Although the reason why the washing residue of chlorine bypass dust has an effect as an elution inhibitor of heavy metals is not clear, the present inventor presumes as follows (1) to (4).

(1) Due to the fact that the washing residue of chlorine bypass dust contains calcium, aluminum, and sulfuric acid, the calcium and aluminum in the washing residue of chlorine bypass dust and the sulfuric acid content are hydrated to remove heavy metals. writing ettringite _{(3CaO · Al 2 O 3 ·} 3CaSO 4 · 32H 2 O) is produced. It is considered that ettringite can be generated satisfactorily in the hardened coal ash by adding the washing residue of chlorine bypass dust, and the effect of insolubilizing boron and other heavy metals in the hardened coal ash is expected to increase. .
(2) f. Contained in washing residue of chlorine bypass dust. CaO (calcium hydroxide) accelerates the pozzolanic reaction of coal ash and / or the hydration reaction of cement, thereby promoting the hardening of the hardened coal ash, and the heavy metals contained in the coal ash are physically contained in the hardened material. It is considered that the effect of containment is improved and the elution suppression effect is improved by increasing the amount of hydrates that immobilize heavy metals. Further, it is considered that calcium hydroxide increases the pH of the hardened coal ash and improves the boron elution suppression effect that is easily insolubilized in a high pH region.

(3) As a result of investigations by the inventor, chlorine bypass dust is caused by the fact that the gas atmosphere of the exhaust gas extracted from the vicinity of the kiln bottom of the cement kiln has a low oxygen concentration and is likely to generate reducing substances. It was also found that reducing substances were contained in the washing residue. It is considered that this reducing substance improves the elution suppression effect by reducing hexavalent chromium to trivalent chromium. In addition, the present inventors have actually measured that hexavalent selenate and tetravalent selenite coexist in the chlorine bypass dust, and it has been confirmed that the chlorine bypass dust is exposed to a reducing atmosphere. The inventor has confirmed.
(4) Since the water washing residue of chlorine bypass dust contains polyvalent metals such as TiO ₂ and MnO as trace components, heavy metals easily sorb on these polyvalent metals, resulting in a coal ash cured product. It is thought that elution of heavy metals is suppressed.

  There is no particular limitation on the type of water used for washing when producing the washing residue of chlorine bypass dust, and tap water, well water, ion-exchanged water, rain water, and the like can be used. The amount of water used for water washing is preferably 1 to 20 times, more preferably 3 to 15 times, and still more preferably 5 to 10 times the mass of chlorine bypass dust. If the usage-amount of water is the said range, since elution of heavy metals from a coal ash hardened | cured material is reduced more, it is preferable.

  There is no particular restriction on the washing method when producing the washing residue of chlorine bypass dust, and for example, the chlorine bypass dust and water can be stirred using a known apparatus such as a blender, and the mixture can be subjected to dehydration treatment such as filtration. it can. Moreover, the water-washing residue of the chlorine bypass dust after the dehydration treatment may be dried and powdered, or may be in a wet state after the dehydration treatment.

  0.1-20 mass parts is preferable with respect to 100 mass parts of coal ash, and, as for the quantity of the washing residue of the chlorine bypass dust contained in the hardened coal ash of this invention, 0.5-15 mass parts is more preferable, 1-10 mass parts is still more preferable. By making the content of the washing residue of the chlorine bypass dust within the above range, an effect of suppressing elution of heavy metals contained in coal ash can be obtained, and the amount of selenium eluted from the coal ash cured product can be made to be below the soil environment standard. it can.

The content of Al ₂ O _{3 in} the washing residue of chlorine bypass dust is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, and still more preferably 3 to 6% by mass. If the Al ₂ O ₃ content is in the above range, the production of ettringite that immobilizes heavy metals reduces the elution amount of heavy metals from the hardened coal ash, which is preferable. The Al ₂ O ₃ content of the washing residue of chlorine bypass dust is measured by the method described in the examples described later.

SO ₃ content of the washing residue chlorine bypass dust is preferably 3 to 25 wt%, more preferably from 4 to 20 mass%, still more preferably 5 to 15 wt%. If the SO ₃ content is in the above range, the coal ash hardened product is produced by generating ettringite that immobilizes heavy metals by reacting with water washing residue of chlorine bypass dust, calcium ash and calcium contained in cement, aluminum, and the like. Since the elution amount of heavy metals from is reduced, it is preferable. The SO ₃ content of the washing residue of chlorine bypass dust is measured by the method described in the examples described later.

  Chlorine bypass dust washing residue f. The CaO content is preferably 0.1 to 45% by mass, more preferably 5 to 40% by mass, and still more preferably 10 to 35% by mass. f. When the CaO content is within the above range, ettringite that immobilizes heavy metals can be sufficiently generated, and the pozzolanic reaction of coal ash and / or the hydration reaction of cement and / or the hardening of coal ash The elution inhibitory effect of heavy metals from the hardened coal ash due to the increase in the pH of the product can be effectively exhibited. Chlorine bypass dust washing residue f. The CaO content is measured by the method described in Examples described later.

  0.001 to 1.0 mg / L is preferable, 0.001 to 0.75 mg / L is more preferable, and 0.001 to 0.75 mg / L is more preferable as the selenium elution amount of the chlorine bypass dust washing residue contained in the hardened coal ash of the present invention. 001 to 0.5 mg / L is more preferable. When the selenium elution amount of the water washing residue of the chlorine bypass dust is within the above range, the selenium elution amount from the hardened coal ash can be made to be the soil environment standard or less. The amount of selenium eluted from the water washing residue of chlorine bypass dust is measured by the method described in the examples described later.

  The selenium content of the water washing residue of the chlorine bypass dust is preferably 10 to 250 mg / kg, more preferably 10 to 200 mg / kg, still more preferably 10 to 150 mg / kg. When the selenium content of the washing residue of the chlorine bypass dust is in the above range, the selenium elution amount of the washing residue of the chlorine bypass dust does not exceed the above elution range, and the selenium elution amount from the coal ash cured product is reduced to the soil. Can be below environmental standards. The selenium content of the water washing residue of the chlorine bypass dust is measured by the method described in the examples described later.

The content of TiO _{2 in} the water washing residue of the chlorine bypass dust is preferably 0.05 to 0.5% by mass, more preferably 0.1 to 0.4% by mass, and still more preferably 0.15 to 0.35% by mass. . If the content of TiO ₂ is the range is preferable because elution of heavy metals from coal ash cured product is further reduced. The TiO ₂ content of the washing residue of chlorine bypass dust is measured by the method described in the examples described later.

  0.001-0.2 mass% is preferable, as for the MnO content of the water washing residue of chlorine bypass dust, 0.005-0.15 mass% is more preferable, and 0.01-0.1 mass% is still more preferable. If MnO content is the said range, since elution of heavy metals from coal ash hardened | cured material is reduced more, it is preferable. The MnO content of the water washing residue of the chlorine bypass dust is measured by the method described in the examples described later.

Blaine specific surface area of the washing residue chlorine bypass dust is preferably 2000~20000cm ² / g, more preferably 3000~15000cm ² / g, more preferably 4000~10000cm ² / g. If the Blaine specific surface area is in the above-mentioned range, the water washing residue of chlorine bypass dust can react sufficiently in the hardened coal ash, and the elution of heavy metals from the hardened coal ash is further reduced, which is preferable. The method for measuring the specific surface area of branes will be described in detail in the examples described later.

  The cement used in the present invention is not particularly limited, and examples thereof include ordinary Portland cement, blast furnace cement, and early strength cement. From the viewpoint of reacting with sulfuric acid or calcium in the water washing residue of chlorine bypass dust and generating a large amount of ettringite, it is preferable to use a blast furnace cement containing blast furnace slag and containing a lot of aluminum. 3-25 mass parts is preferable with respect to 100 mass parts of coal ash, and, as for the amount of cement contained in hardened coal ash, 5-20 mass parts is more preferable, and 10-15 mass parts is still more preferable. When the amount of cement contained in the hardened coal ash is in the above range, it is possible to sufficiently obtain the effect of suppressing elution of heavy metals from the hardened coal ash while reducing the material cost.

  The hardened coal ash of the present invention may further contain gypsum. Examples of the gypsum used in the present invention include dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum. The amount of gypsum contained in the hardened coal ash is preferably 1 to 15 parts by weight, more preferably 3 to 12.5 parts by weight, and more preferably 5 to 10 parts by weight with respect to 100 parts by weight of coal ash. Is more preferable. When the amount of gypsum converted to dihydrate gypsum is within the above range, the effect of suppressing the elution of heavy metals from the hardened coal ash can be sufficiently obtained while reducing the material cost.

  The hardened coal ash of the present invention may further contain lime. Examples of lime used in the present invention include slaked lime and quicklime. When slaked lime is taken as an example, the amount of lime contained in the hardened coal ash is preferably 1 to 15 parts by weight, more preferably 3 to 12.5 parts by weight, and more preferably 5 to 10 parts by weight with respect to 100 parts by weight of coal ash. Part is more preferred. The amount of lime contained in the hardened coal ash is preferably 1 to 11.5 parts by weight, more preferably 2 to 9.5 parts by weight, based on quick lime as an example. 3-7.5 mass parts is still more preferable. Even when any lime is used, the amount of lime in the above range can sufficiently obtain the effect of suppressing elution of heavy metals from the hardened coal ash while reducing the material cost.

  The hardened coal ash of the present invention may further contain a water reducing agent. Examples of the water reducing agent used in the present invention include polycarboxylic acid-based, lignin-based, naphthalenesulfonic acid-based, and aminosulfonic acid-based water reducing agents. From the viewpoint of reducing the water / powder ratio at the time of producing the coal ash cured product and obtaining a coal ash cured product having a denser structure and preventing heavy metals from eluting, it is preferable to use a polycarboxylic acid-based water reducing agent. 0.1-10 mass parts is preferable with respect to 100 mass parts of coal ash, and, as for the quantity of the water reducing agent contained in hardened coal ash, 1-5 mass parts is more preferable.

  In addition, the hardened coal ash of the present invention is a reducing compound such as ferrous chloride, ferrous sulfate, calcium polysulfide, and calcium sulfide as long as the effects of the present invention are not impaired, and calcium compounds such as blast furnace slag and calcium carbonate. Further, magnesium compounds such as magnesium oxide, magnesium hydroxide and dolomite may be further contained.

  The particle size of the hardened coal ash according to the present invention is preferably larger from the viewpoint of suppressing elution of heavy metals from the hardened coal ash, but is preferably prepared as appropriate according to the application. For example, when used as a civil engineering material, the particle size of the hardened coal ash is preferably 0.01 to 100 mm, more preferably 0.075 to 75 mm, and still more preferably 2 to 40 mm.

  The method for producing the hardened coal ash according to the present invention is not particularly limited. For example, coal ash, washing residue and cement of chlorine bypass dust, gypsum, lime and / or water reducing agent, and water as necessary. Known methods such as a method of curing and curing the obtained kneaded product, and a method of curing and curing the granulated product obtained by further granulating the kneaded product can be applied. . From the viewpoint of suppressing the elution of heavy metals from the hardened coal ash, a method of curing and curing the obtained slurry-like kneaded material after adding and kneading an amount of water in which the kneaded material becomes a slurry. Is preferred. When the hardened coal ash obtained by the above method does not conform to the particle size range, the particle size can be further adjusted using a classifier or a crusher.

  The presence of ettringite in the cured coal ash obtained by the above production method can be confirmed by X-ray diffraction measurement of the cured coal ash. For example, the conditions for X-ray diffraction measurement of the hardened coal ash are as follows. Using D2PHASER (manufactured by BRUKER, X-ray source: CuKα ray) as an X-ray diffractometer, measurement range: 2θ = 5 to 25 °, scan speed: When a peak derived from the (010) plane of ettringite is observed in the range of 2θ = 8 ° or more and 10 ° or less when 0.5 second / step and step width: 0.02 °, and / or 2θ When a peak derived from the (110) plane of ettringite is observed in the range of 15 ° to 17 °, it can be said that ettringite is present in the hardened coal ash. By the presence of ettringite in the hardened coal ash, the elution suppression effect of heavy metals from the hardened coal ash can be further enhanced.

  The presence of mullite in the hardened coal ash obtained by the above production method can be confirmed by X-ray diffraction measurement of the hardened coal ash as in the case of confirming the presence of ettringite. . For example, when the X-ray diffraction measurement conditions of the hardened coal ash are the same as those described above, a peak derived from the (110) plane of mullite is observed in the range of 2θ = 15 ° to 17 °. It can be said that mullite is present in the hardened coal ash.

  Similarly, the presence of quartz in the hardened coal ash obtained by the above production method indicates that the conditions for the X-ray diffraction measurement of the hardened coal ash in the X-ray diffraction measurement of the hardened coal ash are described above. When a peak derived from the (010) plane of quartz is observed in the range of 2θ = 20 ° to 22 ° in the same condition as above, it can be said that quartz is present in the hardened coal ash. .

  When gypsum is included in the cured coal ash obtained by the production method, the presence of gypsum can be confirmed by X-ray diffraction measurement of the cured coal ash as described above. For example, when dihydrate gypsum is included in the coal ash cured product, in the X-ray diffraction measurement of the coal ash cured product, when the condition of the X-ray diffraction measurement of the coal ash cured product is the same as described above, 2θ = When a peak derived from the (020) plane of dihydrate gypsum is observed in the range of 11 ° to 13 °, it can be said that dihydrate gypsum is present in the hardened coal ash.

  Since the elution of heavy metals is suppressed below the environmental standard, the hardened coal ash of the present invention can be suitably used as a civil engineering material or an environmental material. Examples of uses of civil engineering materials include backfill materials, roadbed materials, embankment materials, landfill materials, ground improvement materials, backfill materials and the like. Examples of uses of environmental materials include bottom quality improving materials and water purification materials.

  Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. Note that the present invention is not limited to these examples.

1. Coal ash For the coal ash, fly ash recovered with an electric dust collector at a coal-fired power plant was used. Table 1 shows the amount of heavy metals eluted from the coal ash used. Analytical values shown in Table 1 are based on JIS K 0012 “Factory drainage test method” for the concentration of heavy metals in the test solution obtained from the elution test in accordance with Appendix No. 46 of the 1991 Environment Agency Notification. It is a measured value. In addition, the following soil environment standard used the description of the 1991 Environment Agency notification 46 separate table.

2. Washing residue of chlorine bypass dust Washing residue of chlorine bypass dust used was added 10 times the amount of water by weight with respect to chlorine bypass dust, stirred for 30 minutes, and then Buchner funnel and filter paper (manufactured by Advantech, No. The residue remaining on the filter paper was dried at 40 ° C. for 24 hours. Table 2 below shows the washing residue of the chlorine bypass dust used and the properties of the chlorine bypass dust before washing. The analysis values shown in Table 2 are values measured by the following methods (i) to (v).

(I) SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaO, MgO, SO ₃ , Na ₂ O, K ₂ O, R ₂ O, TiO ₂ , MnO content SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaO, MgO, SO ₃ , Na ₂ O, K ₂ O, TiO ₂ and MnO content were measured with reference to JIS M 8853 “Chemical analysis method of aluminosilicate materials for ceramics”. .
The R ₂ O content was calculated from the Na ₂ O and K ₂ O content (% by mass) measured by the above method according to the following formula (1). “0.658” is a coefficient for converting K ₂ O into a molar equivalent of Na ₂ O.
R ₂ O content (mass%) = Na ₂ O content + (0.658 × K ₂ O content) (1)

(Ii) f. CaO content f. The CaO content was measured in accordance with JCAS I-01: 1997 “Method for Quantifying Free Calcium Oxide” of the Cement Association Standard Test Method.
(Iii) Cl and Se contents Cl and Se contents were measured in accordance with JIS R 5202 "Cement chemical analysis method".
(Iv) Se elution amount The Se elution amount was prepared in accordance with the Appendix of Environment Agency Notification No. 46 in 1991, and the Se concentration of the test solution was determined in accordance with JIS K 0102 “Factory drainage test method”. Measured.
(V) Brain specific surface area The brain specific surface area was measured using a brain air permeation apparatus in accordance with JIS R 5201: 1997 “Cement physical test method”.

  As shown in Table 2, the washing residue of chlorine bypass dust contains calcium, aluminum, and sulfuric acid. It can also be seen that the chlorine washing dust washing residue is reduced in chlorine content, selenium elution amount and content as compared with chlorine bypass dust.

3. Preparation of hardened coal ash Coal ash, residual residue of chlorine bypass dust, blast furnace cement type B (manufactured by Ube-Mitsubishi Cement), dihydrate gypsum (exhaust gas desulfurization gypsum) and slaked lime (manufactured by Ube Materials, JIS special name) To obtain a mixture, a polycarboxylic acid-based water reducing agent (manufactured by BASF, master glenium SP8SV) and an amount of water in which the mixture is slurried are added to a Hobart mixer (manufactured by Hobart Japan Co., Ltd., And kneading at 591 rpm for 10 minutes. The obtained kneaded material was put into a rectangular container, and was shaken to form a slurry, which was uniformly filled in the container, and then cured by sealing for one day. The cured product was removed from the container and cut to a particle size of 10 to 15 mm to obtain a hardened coal ash. Coal ash hardened | cured material changed the addition amount of the washing residue of the chlorine bypass dust with respect to coal ash, and produced four types of hardened coal ash A thru | or D. Table 3 shows the blending ratio of the produced hardened coal ash.

4). Evaluation of elution amount of heavy metals in hardened coal ash

[Example 1]
Coal ash hardened material A prepared by adding 5 parts by mass of water washing residue of chlorine bypass dust to 100 parts by mass of coal ash was cured for 3 days, 7 days, or 28 days, and then the elution amount of heavy metals was reduced. evaluated. The evaluation of the elution amount of heavy metals was made according to JIS K 0058-1 5 “Testing method for chemical substances of slags”, and the pH and B, As, Se, Cr ⁶⁺ , And F concentration were measured in accordance with JIS K 0102 “Factory drainage test method”. The results are shown in Table 4.

[Example 2]
Heavy metals from hardened coal ash by the same method as in Example 1 except that hardened coal ash B prepared by adding 10 parts by weight of washing residue of chlorine bypass dust to 100 parts by weight of coal ash was used. The elution amount of was evaluated. The results are shown in Table 4.

Example 3
Heavy metals from hardened coal ash by the same method as in Example 1 except that the hardened coal ash C produced by adding 15 parts by weight of washing residue of chlorine bypass dust to 100 parts by weight of coal ash was used. The elution amount of was evaluated. The results are shown in Table 4.

[Comparative Example 1]
The amount of elution of heavy metals from the hardened coal ash was evaluated in the same manner as in Example 1 except that the hardened coal ash D prepared without adding the water washing residue of chlorine bypass dust was used. The results are shown in Table 4.

5. X-ray diffraction measurement of hardened coal ash About hardened coal ash of Examples 1 to 3 and Comparative Example 1 from the diffraction peaks obtained using an X-ray diffractometer, the hardened coal ash AD The presence of ettringite, gypsum (dihydrate gypsum), mullite and quartz contained therein was confirmed. X-ray diffraction measurement was performed in the same manner as described above. The results are shown in FIG.

  From Examples 1 to 3 and Comparative Example 1 shown in Table 4, the hardened coal ash A to C (Examples 1 to 3) to which the water washing residue of the chlorine bypass dust was added is the coal with no water washing residue added to the chlorine bypass dust. Compared with the ash cured product D (Comparative Example 1), the elution amounts of boron, arsenic, hexavalent chromium and fluorine were reduced. This is because the ettringite that hydrates calcium, aluminum, and sulfuric acid contained in the chlorine bypass dust washing residue and immobilizes heavy metals was formed, and in the chlorine washing dust washing residue f. It is considered that the pH of the hardened coal ash was increased by CaO.

  In particular, in the coal ash cured products B and C (Examples 2 and 3) in which the content of the water washing residue of the chlorine bypass dust was increased, as shown in Table 4, boron from the coal ash cured product at the age of 28 days, six It can be seen that the elution amount of valent chromium and fluorine can be further reduced. These results are supported by the results shown in FIG. 1 in which the presence of ettringite is confirmed.

Although the amount of selenium eluted from hardened coal ash tends to increase with the addition of water washing residue of chlorine bypass dust, the amount of water washing residue of chlorine bypass dust contained in hardened coal ash is set within a specific range. By doing so, it was found that the amount of selenium eluted could be suppressed below the soil environmental standard.

Claims (12)

  A hardened coal ash containing coal ash, chlorine bypass dust washing residue, and cement.   The cured coal ash according to claim 1, comprising 0.1 to 20 parts by mass of a water washing residue of the chlorine bypass dust with respect to 100 parts by mass of the coal ash. Coal ash cured product according to claim 1 or 2 Al ₂ O ₃ content of washing residues is from 1 to 10 weight percent of the chlorine bypass dust. The hardened coal ash according to any one of claims 1 to 3, wherein the SO ₃ content of the washing residue of the chlorine bypass dust is 3 to 25% by mass.   F. Water washing residue of the chlorine bypass dust. CaO content is 0.1-45 mass%, Coal ash hardened | cured material as described in any one of Claims 1-4.   The selenium elution amount of the washing residue of the chlorine bypass dust is 0.001 to 1.0 mg / L. The hardened coal ash according to any one of claims 1 to 5.   The selenium content of the washing residue of the chlorine bypass dust is 10 to 250 mg / kg, the cured coal ash according to any one of claims 1 to 6.   The cured coal ash according to any one of claims 1 to 7, comprising 3 to 25 parts by mass of the cement with respect to 100 parts by mass of the coal ash.   The cured coal ash according to any one of claims 1 to 8, wherein the washing residue of the chlorine bypass dust is obtained by washing and dehydrating the chlorine bypass dust.   The coal ash hardened | cured material as described in any one of Claims 1-9 which contains 1-15 mass parts of gypsum with respect to 100 mass parts of the said coal ash.   The cured coal ash according to any one of claims 1 to 10, comprising 1 to 15 parts by mass of lime with respect to 100 parts by mass of the coal ash.   Furthermore, the hardened coal ash as described in any one of Claims 1-11 containing a water reducing agent.