JP6430212B2 - Coal ash treatment agent - Google Patents

Description

  The present invention relates to a coal ash treatment agent for suppressing elution of harmful components from coal ash.

  Coal ash, which is a combusted product of coal, is generated in large quantities due to an increase in demand for thermal power generation, and its treatment is an issue. As a treatment measure, it is being used for industrial resources, but a large amount of surplus that cannot be used is mainly disposed of in the ground. Coal ash is mainly used for construction and civil engineering materials such as cement raw materials, concrete admixtures, backfill materials and roadbed materials. However, coal ash contains trace components that elute to the surroundings due to water contact, and this includes soil such as fluorine, boron, arsenic, selenium and some heavy metals such as so-called hexavalent chromium. It also includes harmful components that are subject to environmental standards. Even in the coal ash resource utilization process and landfill disposal, it is difficult to completely eliminate the possibility of water contact over a long period of time, and measures to prevent the leaching of harmful components in coal ash have been studied. For example, a method of insolubilizing heavy metals in coal ash using a chelating agent is known. (For example, refer to Patent Document 1.) However, in addition to being very expensive, the chelating agent has a problem of being easily deteriorated and has not been widely spread. There is also known a method of solidifying coal ash with cement to suppress elution. (For example, refer to Patent Document 2.) This method has a relatively low processing cost and can generally prevent harmful components in coal ash from being eluted, but on the other hand, since cement contains chromium, There is concern about the possibility of elution. For this reason, there is also known a method in which hexavalent chromium eluted by using a reducing agent such as ferrous sulfate in combination with cement is made insoluble trivalent chromium. (For example, refer to Patent Document 3.) Furthermore, it is known that if the cement used is blast furnace cement, heavy metal ions such as hexavalent chromium are adsorbed on the blast furnace slag, so that the elution amount of hexavalent chromium and the like is reduced. It has been. (For example, see Patent Document 4)

  However, the use of a reducing agent requires a considerable amount of reducing agent to reduce hexavalent chromium eluted from both cement and coal ash, which increases the cost. In addition, there is almost no effect on eluted components other than heavy metals. In addition, the use of blast furnace cement generally has low strength, so there are restrictions on the utilization of resources, and it takes time to harden, so the time during which coal ash is exposed to water contact conditions becomes longer. Elution of harmful components easily proceeds, and the elution amount far exceeds the adsorption amount, which is a blind spot for preventing elution.

JP 2001-121133 A JP 2004-089816 A JP 09-314092 A JP 2007-22694 A

  The present invention is to solve the above-mentioned problems when suppressing the elution of harmful components from coal ash using inexpensive cement. In other words, as a means to seal off harmful components contained in coal ash, for example, eluting to surrounding soil, etc., it suppresses the elution of harmful components such as hexavalent chromium from cement used for treatment without using specific cement. However, the elution of harmful components from coal ash can be suppressed in a short time from the treatment, and the coal ash treatment agent suitable for continuing to suppress the elution over a long period of time and the simple and excellent workability treatment using the coal ash treatment agent Provide a method.

  As a result of investigations for solving the above problems, the present inventor has found that a hydraulic composition containing any kind of cement such as ordinary Portland cement and a specific component such as calcium aluminate can produce coal ash in a short time after water injection. It can be solidified, so there is almost no leaching of harmful components from coal ash during processing, and after solidification, the leaching of harmful components from coal ash can be stably suppressed over a long period of time, and hexavalent chromium from the cement used. Since the elution of heavy metals such as these was also sufficiently suppressed, the present invention was completed.

That is, the present invention is a coal ash treating agent represented by the following (1) to (3) and a method for treating coal ash represented by (4). (1) Coal ash treatment agent containing cement, calcium aluminate, gypsum, alkali metal carbonate and polycarboxylic acid water reducing agent. (2) Calcium aluminate, coal ash treatment agent of the molar ratio of CaO and _{Al 2 O 3 (CaO / Al} 2 O 3) is calcium aluminate 1.2-1.6 (1). (3) The coal ash treatment agent according to (1) or (2), which is used for coal ash eluting any one of fluorine, boron, arsenic, selenium and hexavalent chromium. (4) A method for treating coal ash, comprising mixing 20 to 35 parts by mass of any of the coal ash treating agents (1) to (3) and water with respect to 100 parts by mass of coal ash.

  According to the present invention, harmful components contained in coal ash, e.g., eluting into surrounding soil, etc., can be suppressed in a short time from the start of treatment, and can be maintained for a long period of time. Provided is a relatively inexpensive coal ash treatment agent in which elution of harmful components is sufficiently suppressed. Moreover, according to this invention, the processing method of the coal ash which is effective in order to suppress the elution of a harmful | toxic component and is easy and good workability | operativity is provided.

  The cement contained in the coal ash treatment agent of the present invention is not particularly limited as long as it is a hydraulic cement. Specifically, for example, various ordinary portland cements such as normal, early strength, ultra-early strength, moderate heat, and low heat generation, and mixed cement obtained by mixing portland cement with fly ash, slag powder, silica fume, etc. Can do. Of these, ordinary bolt land cement is preferable because it is relatively inexpensive and can be obtained stably, and has excellent versatility with respect to mixing and use.

The calcium aluminate contained in the coal ash treatment agent of the present invention may be any hydrated active substance having a structure of crystallized or advanced vitrification composed of CaO and Al ₂ O ₃ as chemical components. Further, a compound, a solid solution, a glassy substance or a mixture thereof in which other chemical components are added in addition to CaO and Al ₂ O ₃ may be used as long as the effects of the present invention are not substantially lost. Although not particularly limited, and preferably chemical components molar ratio of CaO and Al ₂ O ₃ uses calcium aluminate _{CaO / Al 2 O 3 = 1.2~1.6} , excellent rapid hardening In addition, it is good because instantaneous setting is difficult to be expressed in order to improve workability during processing. More preferably, when the content molar ratio of CaO and Al ₂ O ₃ is CaO / Al ₂ O ₃ = 1.2 to 1.6 and the vitrification rate is 25 to 75% or more, a calcium aluminate is further added. It may be easy to have an appropriate reaction activity. Containing calcium aluminate speeds up the setting, makes it possible to consolidate coal ash at an early stage and make it difficult to elute and diffuse the eluted components from the coal ash. The amount of calcium aluminate contained in the coal ash treatment agent is not particularly limited. However, in order to make the time to cure faster without affecting other properties with respect to 100 parts by mass of cement, -15 mass parts is preferable, and 8-12 mass parts is more preferable.

  As the gypsum contained in the coal ash treatment agent of the present invention, any one or more selected from the group consisting of anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum and calcium sulfate can be used. The inclusion of gypsum is important from the viewpoint of accelerating hardening, and contributes to making the coal ash difficult to elute and to make it harder quickly. In particular, when anhydrous gypsum is contained, this effect can be expressed more strongly. Although content of the gypsum in a coal ash processing agent is not specifically limited, 6-15 mass parts is preferable with respect to 100 mass parts of cement contents, and 8-12 mass parts is more preferable.

The alkali metal carbonate contained in the coal ash treatment agent of the present invention further enhances the suppression of harmful component elution in a short time from the treatment by promoting condensation from the time of water injection and shortening the hydration reaction time. To contribute. Moreover, since it has the effect | action which continues advancing until a hydration reaction stops, the improvement of an elution suppression effect is maintained in the meantime. As the alkali metal carbonate, any one or more of lithium carbonate, sodium carbonate, and potassium carbonate can be used. When lithium carbonate is preferably contained, better coagulation properties are easily obtained, and early strength development is enhanced. The content of the alkali metal carbonate in the coal ash treatment agent is not particularly limited, but is preferably 0.1 to 0.8 parts by mass, and 0.3 to 0 with respect to 100 parts by mass of the cement content. More preferably, 6 parts by mass.

  The polycarboxylic acid-based water reducing agent contained in the coal ash treatment agent of the present invention contains polycarboxylic acid as an active ingredient, and is referred to as a water reducing agent, a high-performance water reducing agent, a dispersant, and a fluidizing agent. Any thing is acceptable. The form may be either liquid or granular. Moreover, although it is possible to replace a part thereof with a water reducing agent having an active ingredient other than polycarboxylic acid, it is recommended to use only one having polycarboxylic acid as an active ingredient. By containing a polycarboxylic acid-based water reducing agent, it is beneficial to reduce the amount of water injected into the cement-based composition in order to suppress the dissolution of harmful elution components in coal ash. Moreover, the resistance at the time of coal ash kneading | mixing by calcium aluminate combined use can be reduced especially by using polycarboxylic acid as an active ingredient, and the elution suppression process of coal ash can be performed smoothly. In addition, this is particularly useful in effectively utilizing coal ash for mortar / concrete components and products. The content of the polycarboxylic acid-based water reducing agent in the coal ash treatment agent is not particularly limited, but is preferably 0.05 to 0.4 parts by mass with respect to 100 parts by mass of cement, -0.3 mass part is more preferable.

  Further, the coal ash treating agent of the present invention can contain components other than those described above unless the effects of the present invention are lost.

Moreover, the fineness of the coal ash treatment agent of the present invention is not limited. From the viewpoint of the elution suppression effect of harmful elution components from coal ash and cost, an appropriate value may be selected for each contained component. Specifically, Blaine specific surface area, for example, although cement about 2800~3600cm ² / g, calcium aluminate about 4000~7500cm ² / g, gypsum may generally can be given 3000~6500cm ² / g It is not limited to the description example.

  In addition, the coal ash to be treated with the coal ash treating agent of the present invention is not particularly limited, and may be ash derived from any coal. Preferably, the coal ash elutes at least one of fluorine, boron, arsenic, selenium, and hexavalent chromium. In the present invention, each of fluorine, boron, arsenic, selenium, and hexavalent chromium is referred to as a harmful component. And the coal ash processing agent of this invention is used for the process for carrying out the elution suppression of the coal ash which elutes such a harmful | toxic component.

  Moreover, the processing method of the coal ash of this invention adds and knead | mixes the said coal ash processing agent 20-35 mass parts and water to 100 mass parts of coal ash. Although the kneading method is not limited, for example, it can be performed using a commercially available mixing apparatus such as a Hobart mixer. The kneading time is usually about 1 to 2 minutes, but it is desirable to adjust appropriately depending on the kneading amount and the kneading apparatus. After kneading, a desired elution suppression function can be exhibited simply by leaving it in the air. If the addition amount of the coal ash treatment agent with respect to 100 parts by mass of coal ash is less than 20 parts by mass, curing may not proceed sufficiently or the time until curing may not be shortened sufficiently, and elution suppression may be insufficient. is not. Further, the amount of water added is not particularly limited, and the amount of hydration reactants such as cement and calcium aluminate used can be hydrated without excess or deficiency, and considering the blending amount of the water reducing agent, What is necessary is just to select the addition amount which the mixing resistance at the time of kneading | mixing does not become so high that it will interfere with mixing. For example, although it is preferable to select by preliminary experiment etc., as a specific standard, the addition amount of water with respect to 100 mass parts of coal ash can mention 10-30 mass parts, for example. Although not limited to this amount of water, if it is less than 10 parts by mass, the mixing resistance during the kneading operation may increase. Moreover, when it exceeds 30 mass parts, there exists a possibility that hardening time may become long.

  Moreover, in the said processing method, when adding the said coal ash processing agent and water to coal ash as an aspect of the processing method aiming at utilization of coal ash, according to a utilization use, it can be used for mortar and concrete, for example. A material selected from various aggregates, expansion materials, shrinkage reduction materials, short fibers, etc. can be added in combination as long as the effects of the present invention are not lost, and a cured product suitable for a desired application can be arbitrarily produced. . Furthermore, if necessary, the kneaded product after water injection may be subjected to molding or curing.

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

Using a commercially available powder reagent CaCO ₃ , Al ₂ O ₃ and SiO ₂ as raw materials, a raw material mixture formulated so as to obtain a calcium aluminate clinker having a chemical component content shown in Table 1 was obtained in an electric furnace at 1800 ° C. Heated for 1 hour. Immediately after the predetermined heating, the clinker was taken out of the furnace, and a cooling gas (N ₂ ) was sprayed onto the clinker surface as appropriate for rapid cooling. The rapidly cooled clinker was pulverized with a ball mill and sized with a classifier to prepare a calcium aluminate powder having a Blaine specific surface area of about 5000 cm ² / g. Using a powder X-ray diffractometer for this powder, the mass of each mineral contained in the calcium aluminate with a mass of M1 is quantified by an internal standard method, etc., and the total mass (M2) of the contained mineral phase that can be quantified is calculated. Was regarded as a pure glass phase, and the vitrification rate was calculated by the following formula.
Vitrification rate (%) = (1-M2 / M1) × 100
The vitrification ratio of calcium aluminate powder and the molar ratio of CaO and Al ₂ O ₃ as chemical components are also shown in Table 1.

Thus calcium aluminate powder obtained in both of the commercially available ordinary portland cement, blast furnace cement, II type anhydrous gypsum (Blaine specific surface area of 6000 cm ² / g), gypsum (Blaine specific surface area of 5500cm ² / g ), Lithium carbonate (powder reagent), sodium carbonate (powder reagent), polycarboxylic acid granular water reducing agent, naphthalenesulfonic acid liquid water reducing agent (solid content concentration 30%) A treatment agent was prepared by mixing for about 2 minutes using a Henschel mixer.

  The coal ash to be treated this time contains boron, fluorine, arsenic, selenium, and chromium, and as a result of measurement by a method according to Environment Agency Notification No. 46, the amount of boron elution is 2.9 mg / liter. Fluorine elution amount 1.4 mg / liter, arsenic elution amount 0.11 mg / liter, selenium elution amount 0.08 mg / liter, hexavalent chromium elution amount 0.15 mg / liter.

  First, the coal ash is transferred to a Hobart mixer, and then the treatment agent and water are added to the coal ash so as to have the composition shown in Table 3, and then the Hobart mixer is mixed at a low speed for about 2 minutes. did. Immediately after the mixing was stopped, the adhering matter on the inner wall of the mixer was quickly scraped off with a spatula and mixed again for about 2 minutes to treat the coal ash. All of these treatments were performed in an environment of about 20 ° C. ± 1 ° C.

  In order to evaluate the properties of the treatment body and the workability of the treatment, the mixing properties of the treatment bodies were examined. That is, during mixing, the mixing resistance is small and clearly exhibits a fluid state, and a visually uniform and uniform kneaded product is determined to be “good” for mixing, and other than that ( Including those that could not be mixed because the setting was too fast.

Further, a proctor penetration test using a proctor needle having a cross-sectional area of 0.125 cm ² was performed in an environment of 20 ° C. ± 1 ° C. with respect to the kneaded product after 2 hours from the end of mixing. The setting property was evaluated. Proctor penetration resistance value is 28N / mm ² or more and the end of the setting time is judged to be “good”, and if it does not reach 28N / mm ² or measurement is impossible Judged as “bad”.

  Further, the kneaded product of the processed body immediately after the mixing is filled into a cylindrical frame having an inner diameter of 5 mm and a height of 10 mm, and left to stand for 6 hours in an environment of 20 ° C. ± 1 ° C., and then demolded to form a cylindrical shape. A cured product (specimen) was obtained. Uniaxial compressive strength was measured by a method in accordance with JIS A 1108 for specimens of 1 day, 28 days, and 91 days of age, which were left in the atmosphere of about 20 ° C. ± 1 ° C., and evaluation on the curing properties of the treated body. It was. The above evaluation results relating to the treated body obtained by treating coal ash are summarized in Table 3. In addition, in the table, “−” was indicated for those in which the fluidity at the time of mixing was extremely low and the mold could not be filled or the mold could be filled but not cured.

  Further, the specimen prepared as described above was air-dried at 20 ° C. ± 1 ° C. for 7 days after demolding, then pulverized with a jaw crusher, and the pulverized product was passed through a 2 mm sieve to collect powder. 50.0 g of this powder was put into a plastic container having an internal volume of 1000 ml, 500 g of a solvent adjusted to pH 6.1 by adding 0.5 N hydrochloric acid to 1 liter of pure water, and 200 times with a commercially available shaker. Shaking / min for 6 hours. After shaking, it was allowed to stand for 30 minutes in a thermostat at 20 ° C. (± 1 ° C.), and the supernatant produced in the plastic container was filtered through a membrane filter having a pore size of 0.45 μm to obtain a test solution. With respect to this test solution, the elution amounts of boron, fluorine, arsenic, selenium and hexavalent chromium were measured by the following methods. Table 4 shows the elution amount detection values of the elution components from the treated body (specimen) at the age of 1 day. Further, Table 5 shows the detected values of the elution amounts of the elution components from the 91-day-old treated body (test body), which was performed in the same manner.

Both are the methods stipulated in Environment Agency Notification No. 46,
Boron: JIS K 0102-2008, 47.3 “ICP emission spectroscopy”
・ Fluorine: December, 1971 Environment Agency Notification No. 59, Appendix Table 6 Ion Chromatograph Method ・ Arsenic: 61.4 “ICP Mass Spectrometry” of JIS K 0102-2008
・ Selenium; JIS K 0102-2008 61.4 “ICP Mass Spectrometry”
Hexavalent chromium; JIS K 0102-2008 65.2.1 “Diphenylcarbazide absorptiometry”

  From the above results, it can be seen that the coal ash treatment agent of the present invention can exhibit the elution suppressing action of harmful components in the coal ash in a short time after the treatment, and this elution suppressing action lasts for a long time. Moreover, it can be seen that the treatment of coal ash for suppressing the release of harmful components can be carried out by a treatment method that is simple and excellent in workability. On the other hand, in the technology deviating from the present invention such as the prior art, elution of harmful components can hardly be suppressed in a short time after the processing, or even if it can be suppressed to some extent, a processing operation for that, for example, a load such as high mixing resistance is applied, It turns out that workability is inferior.

Claims (4)

A coal ash treatment agent for suppressing elution of harmful components from coal ash,
Cement, containing calcium aluminate, gypsum, alkali metal carbonate and polycarboxylic acid-based water reducing agent having a molar ratio of CaO to Al ₂ O ₃ (CaO / Al ₂ O ₃ ) of 1.2 to 1.6 Coal ash treatment agent. The amount of the calcium aluminate contained in the coal ash treatment agent is 6 to 15 parts by mass with respect to 100 parts by mass of the cement.
The amount of the gypsum contained in the coal ash treatment agent is 6 to 15 parts by mass with respect to 100 parts by mass of the cement.
The amount of the alkali metal carbonate contained in the coal ash treatment agent is 0.1 to 0.8 parts by mass with respect to 100 parts by mass of the cement,
The amount of the polycarboxylic acid-based water reducing agent contained in the coal ash treatment agent is 0.05 to 0.4 parts by mass with respect to 100 parts by mass of the cement.
The coal ash treatment agent according to claim 1. The coal ash treatment agent according to claim 1 or 2, which is used for coal ash eluting any one of fluorine, boron, arsenic, selenium and hexavalent chromium. Coal ash which suppresses the elution of harmful components from coal ash, wherein 20 to 35 parts by mass of coal ash treating agent according to any one of claims 1 to 3 and water are mixed with respect to 100 parts by mass of coal ash. Processing method.