JP6441086B2 - Effective use of coal ash - Google Patents

Description

  The present invention relates to a composition in which elution of trace components such as heavy metals from coal ash generated from coal-fired power generation and the like, and an effective utilization method of coal ash using the composition as a soil solidifying material.

  Coal ash generated from coal-fired power generation, etc. is a residue generated when coal is burned, and when combined with the electric power business and general industries, it is generated more than 10 million tons per year in Japan. At the same time, the effective use of coal ash is being promoted. According to the “Coal ash national fact-finding report (2012 results) / Coal Energy Center”, the effective use of coal ash in fiscal 1995 was generated. However, the effective utilization rate has been increasing year by year, reaching 97.6% in 2012, and it can be said that awareness of effective utilization has generally permeated.

  Coal ash is effectively used in a wide range of fields such as the cement field, civil engineering / architecture field, agriculture / forestry / fishery field, and the effective use in the cement field is a total of 67 .9%. In the cement field, it is used for cement raw materials, cement admixtures and concrete admixtures.

  In pulverized coal slags in coal-fired power generation, coal ash is roughly classified into fly ash and clinker ash according to the location of generation. Examples of fly ash cement mixtures include fly ash cement and cement-based solidified material. Examples of concrete admixtures include fly ash concrete.

  Fly ash concrete has features such as increased long-term strength and reduced drying shrinkage due to pozzolanic reaction, suppression of alkali-silica reaction, reduced heat of hydration, and improved chemical resistance. The problem is that color unevenness due to darkening occurs on the concrete surface after hardening due to the unburned carbon content in the steel. As these solutions, it is generally known to use an AE water reducing agent, a special admixture, and a special AE agent in combination.

  In addition, there are concerns about the elution of trace components from coal ash. In particular, when applied to cement-based solidification materials, trace components may elute from the improved soil when cement-based solidification materials are mixed into improved soil.

  Regarding the use of cement and cement-based solidification material for ground improvement, the notification “Use of cement and cement-based solidification material for ground improvement and re-use of improved soil is already targeted for projects under the direct control of the Ministry of Construction (currently the Ministry of Land, Infrastructure, Transport and Tourism). About the immediate measures for use (March 24, 2000 / Ministry of Construction, Technical Development No. 48) "was issued, and the elution test of hexavalent chromium using the soil to be improved and the solidified material to be used Has been scolded. In addition, “Environmental Standards Concerning Soil Contamination (August 1991 / Environmental Agency Notification No.46)” specifies 27 soil environmental standards containing hexavalent chromium. Fluorine, selenium, boron, and other trace components may be eluted from coal ash.

  Therefore, Patent Document 1 discloses a method for suppressing elution by adding and hardening blast furnace cement (particularly, blast furnace cement B) and / or blast furnace slag to coal ash instead of ordinary Portland cement.

JP 2000-301107 A

  About the method of patent document 1, since coal ash is hardened in order to suppress the elution of the trace component from coal ash, this coal ash cannot be used as an additive to a cement-type solidification material.

  By the way, in connection with this invention, the present inventors measured about the trace component from coal ash. The measurement results are shown in Table 1. No. 1-No. 6 Coal ash is coal ash generated at the same thermal power plant of electric power company A, and is the result of irregular sampling.

  With respect to Table 1, the pH was measured with reference to the Geotechnical Society standard “pH test method for soil suspension”. In addition, the amount of trace component elution was measured based on the method defined in “Environmental standards for soil contamination (August 1991 / Environment Agency Notification No.46)”.

  As shown in Table 1 above, even when coal ash generated from the same thermal power plant is used, it can be said that the values of pH and trace component elution amount differ greatly if the sampling time is different. This is thought to be due to changes in the coal type of coal used for thermal power generation. In addition, arsenic, selenium, fluorine, and boron were confirmed to be in excess of the soil environmental standards. In addition, the eluted concentration varies greatly depending on the coal ash.

  Based on this result, the concentration of trace components eluted from coal ash varies greatly depending on the coal type of the original coal, so these factors must be taken into account in order to keep it within the soil environmental standards. There is.

  Accordingly, an object of the present invention is to keep coal ash in a powdery state that can be used as an additive to a soil solidifying material, and to prevent elution of trace components.

  In order to achieve the above-mentioned problems, the present inventors have intensively studied. Therefore, the amount of trace component elution from coal ash is determined by using additives such as calcium hydroxide and blast furnace slag without using solvent washing, electrostatic classification, and cement solidification. The inventors have studied to suppress the elution amount and have arrived at the present invention. Furthermore, we have found a method for effectively using coal ash that can be stored in a state where the obtained modified coal ash is shielded from water, and can be used as an additive for soil solidifying materials as required by users. .

That is, the present invention relates to calcium ash and blast furnace slag in coal ash generated from a thermal power plant, 3.4 to 16.7 parts by mass of calcium hydroxide, and 11.5 to Add in the range of 50 parts by mass to make modified coal ash, keep the modified coal ash shielded from water, and mix the modified coal ash with cement and gypsum according to the order from the user. This is an effective utilization method of coal ash that is shipped as soil solidification material.

In addition, it is an effective utilization method of coal ash in which the cement shipped as soil solidification material is cement containing blast furnace slag.

  ADVANTAGE OF THE INVENTION According to this invention, the composition which reduced the elution of trace components, such as heavy metals from the coal ash generated from coal thermal power generation etc., can be obtained. Further, since the modified coal ash is in a powder form, it can be used as a mixed material such as another material, for example, a soil solidifying material, and the coal ash can be effectively used. Furthermore, since the elution of trace components from the modified coal ash is suppressed within the soil environmental standards, there is no need to take special measures for storage, transportation, etc., and it is extremely easy to handle.

  The present invention will be described in detail below. The modified coal ash in the present invention comprises coal ash, calcium hydroxide, and blast furnace slag. Furthermore, it can be shipped as a mixed material such as a soil solidifying material.

  The coal ash used in the present invention is obtained as a residue generated when coal is burned. By classifying coal ash by product, raw powder that is a mixture of fly ash and cinder ash, fine powder obtained by classifying and selecting raw powder, JIS fly ash and raw powder that conform to the Japanese Industrial Standard “Fly Ash for Concrete” Coarse powder that has been classified and adjusted in particle size, and ash dropped on the clinker hopper are collected and classified into clinker ash that has been crushed, dewatered, and adjusted in particle size, but is not particularly limited in the present invention. Moreover, although coal ash is generated in the electric business such as coal-fired power generation and general industries, the generated business is not particularly limited.

  The calcium hydroxide used in the present invention is generally called slaked lime. By containing calcium hydroxide in coal ash, the elution amount of arsenic, selenium, fluorine, and boron among trace components contained in the coal ash can be suppressed. In addition, when the powdered composition of the present invention containing slaked lime is mixed with water when used as a solidifying material or the like to form a slurry, the viscosity of the slurry is increased and the exudation of unburned carbon is suppressed. The effect that it can be also expressed.

  In the modified coal ash of the present invention, the calcium hydroxide is preferably 3.4 to 16.7 parts by mass with respect to 100 parts by mass of the coal ash. It is more preferably 3.4 to 14.3 parts by mass, and particularly preferably 3.4 to 10.4 parts by mass. When the amount of calcium hydroxide is large, the viscosity when the modified coal ash is used as a slurry becomes very high, and the effect on the viscosity of the slurry when the modified coal ash is used as a soil solidifying material increases. The cost tends to increase as a soil solidifying material. In addition, the effective use of coal ash itself decreases.

  As the calcium hydroxide, commercially available slaked lime, agricultural slaked lime, calcium hydroxide reagent, and the like can be suitably used. Preferably, it is calcium hydroxide specified in Japanese Industrial Standard “Industrial Slaked Lime”, and more preferably, it is more preferably a special product in terms of economy, market distribution, and the amount of calcium contained. .

  The blast furnace slag used in the present invention refers to blast furnace granulated slag. The blast furnace slag is preferably 11.5 to 50 parts by mass, more preferably 11.5 to 46.2 parts by mass, and most preferably 11.5 to 26.7 parts by mass with respect to 100 parts by mass of coal ash. . By using this blast furnace slag in combination with calcium hydroxide, the blast furnace slag exhibits an effect of suppressing the amount of selenium in particular, among trace components contained in coal ash.

  Also, by increasing the amount of blast furnace slag used, the cost of blast furnace slag increases, but the amount of calcium hydroxide used can be reduced, and the cost of the modified coal ash can be kept equal or low. It can be said that it is economical.

  The modified coal ash according to the present invention can be produced by adding and mixing calcium hydroxide and blast furnace slag to the generated coal ash, and since there is no elution of metals, etc. It can be stored and distributed in the same way as the above powder. Preferably, it is preferable to store a large amount of products manufactured in a long term and store them in a container shielded from water so that they can be shipped quickly in response to an order from the user.

  The modified coal ash in the present invention contains calcium hydroxide and blast furnace slag, and thus has a property of hardening when water is added. Therefore, it can be used as an additive for ready-mixed concrete and mortar materials. More preferably, it can be used as an additive for a soil solidifying material. That is, it can be used as an extender or modifier for soil solidifying materials containing Portland cement clinker, gypsum and other components.

  The storage of the modified coal ash in the present invention is not particularly limited as long as it is a container cut off from water. Considering the use of the modified coal ash as a soil solidifying material, it is preferably stored in a cement silo or the like.

  As the cement clinker used for the soil solidifying material, a known cement clinker can be used without particular limitation. Especially, the Portland cement clinker used for manufacture of a normal Portland cement, an early strong Portland cement, an ultra-early strong Portland cement, a moderately hot Portland cement, and a low heat Portland cement can be used conveniently.

  In the present invention, the amount of use when the modified coal ash is used as an additive for the soil solidifying material is not particularly limited, but generally it is derived from the modified coal ash with respect to 100 parts by mass of the cement clinker. The coal ash is preferably 1 to 55 parts by mass, and more preferably 1 to 30 parts by mass.

  As the gypsum used for the soil solidifying material, known gypsum can be used without particular limitation as gypsum used for cement or cement-based solidifying material. For example, dihydrate gypsum, hemihydrate gypsum, type I or type II anhydrous gypsum and the like can be mentioned. Natural gypsum and chemical gypsum may be used. Examples of the chemical gypsum include flue gas desulfurization gypsum, phosphate gypsum, titanium gypsum, and hydrofluoric gypsum.

The above-mentioned gypsum can be used alone or in combination of two or more as required. Preferably, anhydrous gypsum and dihydrate gypsum are used alone or in combination. The amount of gypsum is preferably 1 to 25 parts by mass and more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the cement clinker. Although powders of the gypsum is not particularly limited to be used is generally from 2,500~10,000cm ² / g in Blaine specific surface area, many 2,500~7,000cm ² / g It is.

  The soil solidification material may contain calcium hydroxide (slaked lime) for the purpose of lowering the plasticity index of the soil by ion exchange reaction and promoting the pozzolanic reaction. The soil solidification material to which the modified coal ash is added In addition, in addition to calcium hydroxide derived from the modified coal ash, calcium hydroxide may be included separately. The amount of calcium hydroxide is preferably such that the amount combined with the calcium hydroxide derived from the modified coal ash is 15 parts by mass or less with respect to 100 parts by mass of Portland cement clinker, and 10 parts by mass or less. preferable.

  Blast furnace slag has latent hydraulic properties, and when used as a solidifying component, it can contribute to long-term strength development. Moreover, since it has the effect | action which reduces elution of hexavalent chromium, it is preferable also from the point of environmental impact. Therefore, also in the soil solidification material to which the modified coal ash is added in the present invention, a blast furnace slag may be separately included in addition to the blast furnace slag derived from the modified coal ash. In order to express the above effects, the amount of blast furnace slag contained in the soil solidification material is preferably an amount that is 150 parts by mass or less with respect to 100 parts by mass of Portland cement clinker together with the amount derived from the modified coal ash. 40 parts by mass or less is more preferable.

  The soil solidification material to which the modified coal ash of the present invention is added includes, in addition to the above-mentioned components, other components known as blending components of the soil solidification material, specifically naphthalenesulfonic acid formalin condensate salt system, lignin Various dispersants and fluidizers such as sulfonate, melamine sulfonate formalin condensate, polycarboxylate and polyether dispersants, ferrous salts, trivalent titanates, sulfurous acid A reducing agent such as a salt, bisulfite, and thiosulfate, silica fume, limestone, and alkali metal phosphate may be blended.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

1. Coal ash and materials used (a) Coal ash Coal ash generated from electric power company A was used as coal ash. As the coal ash, five types of coal ash (1) to (5) were used depending on the timing of collection.

(B) Calcium hydroxide The calcium hydroxide (referred to as “slaked lime” in the following description) was a special industrial slaked lime manufactured by Nakayama Lime Industry Co., Ltd. The particle size of the slaked lime used was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd.), and the minimum particle size was 0.26 μm and the maximum particle size was 262.38 μm.

(C) Blast Furnace Slag Blast furnace granulated slag generated at the Kakogawa Works, Kobe Steel, Ltd. was used as the blast furnace slag. The chemical components measured using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation: ZSX) are MgO: 7.0%, Al ₂ O ₃ : 12.8%, SiO ₂ : 28.1%, SO ₃ : It was 4.55%, CaO: 45.6%.

2. Preparation of trial coal ash Coal ash and the above-mentioned additive materials were appropriately mixed to produce modified coal ash. In blending, each material was weighed, put into a plastic bag, and mixed in the bag.

3. Preparation of modified coal ash and elution test specimens The prepared modified coal ash is mixed with tap water (Shunan City, Yamaguchi Prefecture) at a water / modified coal ash ratio of 0.4 to form a slurry. Then, it was poured into a cylindrical metal mold having a diameter of 5 cm and a height of 10 cm, and sealed and cured for 7 days to produce a hardened modified coal ash. The mixing method was set to 400 rpm / 5 minutes using a three-one motor (“Tornado” manufactured by ASONE Corporation). The modified coal ash cured body sealed and cured for 7 days was finely pulverized and sieved using a non-metallic sieve (screen opening 2 mm), and the passed sample was used as a specimen for dissolution test.

4). Measurement of measurement components and trace component elution amount The trace components to be measured were five items of hexavalent chromium, arsenic, selenium, fluorine, and boron, which are classified as Class 2 specified hazardous substances in the Soil Contamination Countermeasures Law. As described above, the amount of trace component elution was measured based on the method defined in “Regarding Environmental Standards Concerning Soil Contamination (August 1991 / Environment Agency Notification No. 46)”.

4-1. Effect of slaked lime and blast furnace slag on elution of trace components The effect of coal ash on leaching lime and blast furnace slag was examined. Table 2 shows the composition and measurement results of coal ash and trial coal ash. In addition, for the dissolution test using only coal ash, the hardened body cannot be prototyped, so the sample used was a powder after mixing. The composition is expressed in parts by mass.

  Although Examples 1-10 have confirmed the elution reduction effect by containing slaked lime and blast furnace slag with respect to coal ash (1), it is suppressing to the elution amount within the soil environment standard in all the items. is made of.

  Examples 11-14 differ only in the lot of coal ash and have confirmed the elution reduction effect in the same content of slaked lime and blast furnace slag. Despite some differences in Examples 2 to 5), it is possible to suppress the amount of elution within the soil environment standard in any of the Examples.

  As described above, according to the present invention, it is possible to obtain a composition in which elution of trace components such as heavy metals from coal ash generated from coal thermal power generation or the like is reduced.

4-2. Trace component elution from improved soil using cement-based solidification material containing modified coal ash The amount of trace component elution from modified soil using cement-based solidification material containing modified coal ash was verified. The cement-based solidified material is ordinary Portland cement, blast furnace cement type B (from Tokuyama Co., Ltd.) and anhydrous gypsum, and the cement-based solidified material containing modified coal ash is further mixed with modified coal ash in a plastic bag. And made a prototype. The coal ash used at this time is the coal ash (5) shown in Table 2, and the dissolution test results are as shown in Comparative Example 5 shown in Table 2. The modified coal ash having the same composition as in Example 14 was used.

The sample soil was sandy soil (natural water content 15.29%, wet density 2.084 g / cm ³ ) and fine-grained soil (natural water content 26.82%, wet density 1.906 g / cm) collected in Osaka Prefecture. cm ³ ) was used. Solidifying material amount is 1 level 50kg in the case of the powder added in a target sample soil 1 m ³ per sandy soil, in the case of in fine grained soil powder was 100 kg, and 2 levels of 200 kg, the case of the slurry addition, All the sample soils were set to one level of 300 kg per 1 m ^{3 and} 80% water cement ratio.

  The improved soil was prepared by adding the cement-based solidified material or solidified material slurry to the target sample soil and mixing for 5 minutes using a soil mixer (manufactured by Aikosha Seisakusho). The prepared improved soil is Cement Association standard test method JCAS L-01 “Strength test method of improved body with cement-based solidified material” in the case of powder addition, and JGS0821 “Stable treated soil” in the case of slurry addition. The specimens were filled in accordance with the “Method for making specimens without compaction”, respectively, to produce specimens. The curing period was 7 days.

  In the dissolution test, five items of hexavalent chromium, arsenic, selenium, fluorine and boron were used, and specimens cured for 7 days were used as specimens. The dissolution test was carried out based on the method defined in “Environmental standards for soil contamination (August 1991 / Environment Agency Notification No.46)”.

  Table 3 shows the composition of the cement-based solidified material containing the modified coal ash and the results of the cement-based solidified material not containing the modified coal ash carried out as a reference example and the results of the dissolution test.

  Examples 15 to 19 show the amount of trace components eluted from the improved soil in the cement-based solidified material containing modified coal ash. Regardless of the type of soil to be improved, the form of addition, and the amount of solidifying material added, the elution of trace components from the improved soil is controlled within the soil environmental standards.

  Reference Examples 1 to 5 show the amount of trace component elution in a general cement-based solidified material that does not contain modified coal ash. Compared with these reference examples, Examples 15 to It can be said that the elution amount of 19 trace components is almost the same. Therefore, it is clear that even if coal ash containing a reduced amount of trace components as modified coal ash is contained in the cement-based solidified material, no trace components from coal ash are eluted. It can be usefully used as a compounding component such as a system solidifying material.

Claims (3)

Calcium hydroxide and blast furnace slag are added to coal ash generated from a thermal power plant, and the range of 3.4 to 16.7 parts by weight of calcium hydroxide and 11.5 to 50 parts by weight of blast furnace slag with respect to 100 parts by weight of coal ash. The modified coal ash is stored in a state shielded from water and mixed with the modified coal ash, cement and gypsum according to the order from the user. As an effective method of using coal ash.   The method for effectively using coal ash according to claim 1, wherein the cement is cement containing blast furnace slag. The component ratio in the modified coal ash is 3.4 to 10.4 parts by mass of calcium hydroxide and 11.5 to 26.7 parts by mass of blast furnace slag with respect to 100 parts by mass of coal ash. Effective utilization method of coal ash as described in 1.