DISSOLUTION-RESISTANT MATERIALS FOR SPECIFIED HAZARDOUS SUBSTANCES (HEAVY METALS OR SIMILAR SUBSTANCES)

Abstract

The invention provides a highly applicable anti-dissolution material which, when applied to contaminated soil, fly ash, or similar substances containing heavy metals or similar substances, will provide a useful effect, preventing the leaching of heavy metals or similar substances much more quickly than conventional anti-dissolution materials. This anti-dissolution material is an anti-dissolution material for regulated hazardous substances (heavy metals or similar substances), containing at least aluminum oxide cement powder and gypsum powder. Preferably, in the anti-dissolution material, the amount of gypsum based on 1 mole of tricalcium aluminate (C3A) in aluminum oxide cement is between 0.3 mole and 6.4 mole. This anti-dissolution material exhibits a more useful effect, to the extent that even fluorine and boron, heavy metals and similar substances readily soluble by conventional anti-dissolution materials, can also be effectively prevented from dissolving.

Description

Insolubilizing material for specific hazardous substances (heavy metals, etc.)

[0001] The present invention relates to an insolubilizer for specified hazardous substances (also referred to as "heavy metals, etc."; details will be described later). More specifically, the present invention relates to a technology for providing an insolubilizer for specified hazardous substances that can effectively inhibit the elution of heavy metals, etc. from contaminated soil or fly ash containing heavy metals, etc., and that can rapidly and effectively insolubilize heavy metals, etc., in a shorter time (e.g., within 6 hours) than conventional insolubilizers.

[0002] Class II specified hazardous substances (heavy metals, etc.) are designated as substances requiring soil contamination countermeasures, and standards for their elution into water have been established. Currently, the following heavy metals are designated: cadmium and its compounds, hexavalent chromium compounds, cyanide compounds, mercury and its compounds (including alkyl mercury), selenium and its compounds, lead and its compounds, arsenic and its compounds, fluorine and its compounds, and boron and its compounds.

[0003] Conventionally, insolubilizing materials have been proposed and used to inhibit the elution of heavy metals from contaminated soil containing any of the above-mentioned heavy metals, etc. For example, Patent Documents 1 and 2 propose an insolubilizing material that uses a light-burned magnesia partial hydrate obtained by hydrating a portion of light-burned magnesia obtained by firing a mineral at 550 to 1400°C.

[0004] Patent No. 4481360 Patent No. 4343259

[0005] In the course of examining the above-mentioned conventional technologies, the present inventors have discovered the following problems to be solved. First, they noted that the above-mentioned conventional technologies add an insolubilizing agent to contaminated soil to obtain improved soil with a 7-day aging. They then discovered that the above-mentioned conventional technologies add the insolubilizing agent to the treated material by adding water, which requires several days of curing after mixing the insolubilizing agent, resulting in a significant practical problem: it takes a long time for heavy metals and other contaminated materials to be insolubilized. If heavy metals and other contaminated materials are not insolubilized quickly, it becomes difficult to achieve sufficient insolubilization treatment, especially when a large amount of contaminated soil needs to be treated. This indicates that a technology is needed that shortens the curing period for insolubilization as much as possible, and preferably eliminates the curing period altogether. The present inventors considered a solution to this problem by adding an insolubilizing agent in powder form to contaminated soil, thereby achieving rapid and effective insolubilization treatment and eliminating the need for a curing period after adding the insolubilizing agent. That is, the inventors recognized the importance of developing an insolubilizing agent that can be quickly applied in powder form to heavy metals and other substances in contaminated soil to effectively insolubilize them. Furthermore, in the case of the prior art using the light-burned magnesia partial hydrate mentioned above, there was another problem in that when used on contaminated soil following a flood, for example, the added insolubilizing agent would be washed away in the water. Furthermore, the inventors recognized that the soot and dust known as fly ash collected by dust collectors at the exhaust gas outlet tends to contain large amounts of heavy metals, and therefore recognized the need for the development of a simple technology that can quickly insolubilize fly ash, similar to contaminated soil, to prevent the elution of heavy metals.

[0006] Therefore, an object of the present invention is to provide an insolubilizing material of high practical value that, when applied to contaminated soil, fly ash, etc. containing heavy metals, can provide a useful effect of suppressing the elution of heavy metals, etc., much more quickly and rapidly than conventional insolubilizing materials. More specifically, an object of the present invention is to provide a highly practical and useful insolubilizing material that, when applied to contaminated soil, fly ash, etc., can rapidly and effectively insolubilize heavy metals, etc., within a short time, at least the six hours required for a leaching test to confirm the elution of heavy metals, etc. That is, an object of the present invention is to develop a new insolubilizing material that can achieve rapid insolubilization without requiring the long curing period required by conventional insolubilizing materials. In particular, if an insolubilizing material that can achieve rapid insolubilization when applied in powder form to contaminated soil, fly ash, etc. is developed, it can effectively suppress the elution of heavy metals, etc. from contaminated soil due to rain during the curing period, which is a problem with conventional insolubilizing materials, and therefore can be used as a more practical and useful insolubilizing material. Another object of the present invention is to provide an insolubilizing material that can effectively insolubilize fluorine and boron, among other heavy metals, which have been difficult to insolubilize with conventional insolubilizing materials, and that exhibits more excellent and useful effects.

[0007] The above object can be achieved by the present invention, which provides the following insolubilizer: [1] An insolubilizer for specified hazardous substances (heavy metals, etc.), comprising at least an alumina cement powder and a gypsum powder.

[0008] The preferred forms of the insolubilizing agent for specific hazardous substances (heavy metals, etc.) of the present invention are as follows: [2] Tricalcium aluminate (C ３A) The insolubilizer for specific hazardous substances (heavy metals, etc.) according to the above [1], wherein the ratio of gypsum to 1 mole of gypsum is within a range of 0.3 to 6.4 times by mole per mole of gypsum. [3] The insolubilizer for specific hazardous substances (heavy metals, etc.) according to the above [1] or [2], which is used by adding the powdered form to contaminated soil or fly ash containing specific hazardous substances (heavy metals, etc.). [4] The insolubilizer for specific hazardous substances (heavy metals, etc.) according to any one of the above [1] to [3], wherein the specific hazardous substance is at least one heavy metal selected from the group consisting of cadmium and its compounds, hexavalent chromium compounds, cyanide compounds, mercury and its compounds (including alkyl mercury), selenium and its compounds, lead and its compounds, arsenic and its compounds, fluorine and its compounds, and boron and its compounds.

[0009] The present invention provides an effective insolubilizing agent that, when applied to contaminated soil or fly ash containing heavy metals, etc., is significantly faster than conventional insolubilizing agents. Specifically, a sufficient inhibitory effect on the elution of heavy metals, etc. can be confirmed within the six hours required for the elution test to confirm insolubilization. This means that the present invention can provide an insolubilizing agent that can satisfactorily insolubilize heavy metals, etc., before the six hours required for the elution test have elapsed. Furthermore, the present invention can provide an insolubilizing agent that can rapidly insolubilize heavy metals, etc., by mixing the insolubilizing agent in powder form with contaminated soil or fly ash, etc., without requiring a long curing period. This eliminates the need for a long curing period, thereby preventing the elution of heavy metals, etc., from contaminated soil due to rain during the curing period, a problem that has been encountered with conventional insolubilizing agents. Furthermore, the present invention can provide an insolubilizing agent that can effectively insolubilize heavy metals, etc., even fluorine and boron, which have been difficult to insolubilize with conventional insolubilizing agents, and thus exhibits highly practical and useful effects. In terms of the materials used, the present invention also has the industrially important effect of being able to provide an insolubilizing material with excellent performance economically.

[0010] FIG. 1 is a graph showing the correlation between the ratio of alumina cement and gypsum used in the insolubilizing agent and the fluorine concentration of the filtrate obtained in an elution test, confirming the effectiveness of the insolubilizing agent of the present invention.

[0011] The present invention will be described in detail below with reference to preferred embodiments. The insolubilizing agent of the present invention is characterized by comprising at least an alumina cement powder and a gypsum powder. The inventors discovered that the combined use of an alumina cement powder and a gypsum powder can rapidly insolubilize heavy metals and the like contained in contaminated soil and fly ash, and can also effectively insolubilize fluorine and boron, which have been difficult to achieve with conventional insolubilizing agents, and thus arrived at the present invention.

[0012] The inventors believe that the unprecedented effect of the present invention, obtained by using alumina cement powder and gypsum powder in combination, is realized by the insolubilization mechanism of heavy metals, etc., as described below. When the insolubilizer of the present invention is applied to the material to be treated, such as contaminated soil or fly ash, and mixed and kneaded, tricalcium aluminate (3CaO.Al), the main component of alumina cement powder, is insolubilized. ２ O ３ , Abbreviation; C ３ A hydration reaction occurs between the calcium sulfate of the gypsum powder and water contained in soil, fly ash, etc. at room temperature in a moderate to weak alkaline environment, resulting in the rapid generation of ettringite. It is believed that the heavy metals contained in the contaminated soil or fly ash, etc., are incorporated into the crystalline structure of ettringite during the crystal growth process of ettringite by using this alumina cement powder in combination with gypsum powder, and are then adsorbed onto the surface of ettringite after ettringite growth has been completed, thereby achieving rapid insolubilization. The inventors' studies have confirmed that the following unprecedented effects can be obtained by applying the insolubilizing agent of the present invention, which combines alumina cement powder and gypsum powder. That is, the insolubilizing agent of the present invention effectively and quickly insolubilizes both heavy metals, such as cations like cadmium (Cd) and lead (Pb), and anions like arsenic (As) and fluorine (F).

[0013] Regarding the above-described configuration and effects of the present invention, it is known that ettringite crystals adsorb and fix heavy metals, etc., but there have been no cases where the combined use of alumina cement and gypsum for the purpose of insolubilizing heavy metals, etc. contained in contaminated soil, fly ash, etc. has been studied or proposed. The materials that make up the insolubilizing agent of the present invention will be explained below.

[0014] <Alumina cement powder> Alumina cement is generally produced by melting a mixed powder of bauxite and limestone, the raw materials for alumina, at high temperatures (1500°C to 1600°C). The main component is tricalcium aluminate (C ３ A). Alumina cement has properties such as rapid hardening and attaining the required strength even at low temperatures, and excellent chemical resistance and fire resistance. However, alumina cement is more expensive than regular cement and is therefore not suitable for general use. However, due to the above-mentioned properties not found in regular cement, it is used in limited applications such as emergency construction, construction in cold regions, construction work at chemical plants, and refractories. The present invention proposes a new and unprecedented use of alumina cement. The insolubilizer of the present invention uses alumina cement in powder form. The average particle size of the alumina cement used in the present invention is not particularly limited, but a powdered form is desirable because the insolubilizer is mixed and kneaded with the material to be treated, such as contaminated soil containing heavy metals or fly ash. The average particle size of commercially available alumina cement is approximately 5.0 μm, and it can be used effectively in the present invention.

[0015] <Gypsum Powder> As the gypsum constituting the insolubilizing agent of the present invention, any gypsum selected from the group consisting of gypsum anhydride, gypsum hemihydrate (α-type, β-type), and gypsum dihydrate can be used. The raw material (source) of these gypsums is not particularly limited, and may be any of natural gypsum, by-products from thermal power plants, waste gypsum board, etc. According to the studies of the present inventors, it was found that, in terms of the influence on the effect aimed at by the insolubilizing agent of the present invention, the type of gypsum raw material constituting the insolubilizing agent tends to exhibit a higher effect in the following order: gypsum hemihydrate (α-type, β-type) > gypsum dihydrate > gypsum anhydride.

[0016] Furthermore, in the insolubilizing agent of the present invention, gypsum is used in powder form, similar to the alumina cement. The particle size of the gypsum powder is not particularly limited, and commercially available gypsum powders can be used. For example, gypsum powders with an average particle size of 200 μm or less, preferably 150 μm or less, can be suitably used. Gypsum powder that is too fine becomes difficult to handle, so it is preferable to use gypsum powder with an average particle size of 1 μm or more. In any case, when powdered gypsum is used as an insolubilizing agent for contaminated soil or fly ash containing heavy metals, etc., it quickly reacts with the powdered alumina cement used in combination and functions as an effective insolubilizing agent for specific hazardous substances (heavy metals, etc.).

[0017] <Usage ratio of alumina cement powder and gypsum powder> A preferred use ratio of gypsum powder and alumina cement powder constituting the insolubilizing agent of the present invention will be described. First, as shown below, in order to generate ettringite, which is necessary to obtain the effects of the present invention, theoretically, the C in the alumina cement is ３ Three times the molar amount of gypsum as A is required. ３ A + 3CaSO ４ ・nH ２ O+mH ２ O=C ３ A.3CaSO ４ ・32H ２ O (ettringite)

[0018] However, when the theoretically required amount of gypsum powder is used for the alumina cement powder, the amount of Ca in the contaminated soil or fly ash that is the object to be treated is small. ２＋ Ions and SO ４ ２－ If ions, etc. are contained, the amount of gypsum will be excessive relative to the amount of alumina cement. This means that the amount of treated soil or fly ash containing the insolubilizer after the insolubilization treatment will be unnecessarily large, which means that a burden will be placed on secondary treatment. ２＋ Ions and SO ４ ２－ If there are too many ions, they will take away the sites in the ettringite structure where certain harmful substances (heavy metals, etc.) can be adsorbed, preventing insolubilization. Therefore, the amount of gypsum powder used in combination with alumina cement powder should be determined based on the amount of Ca contained in the material to be treated.２＋ Ions and SO ４ ２－ It is preferable to determine the amount taking into consideration the amount of ions.

[0019] According to the investigations of the present inventors, the insolubilizing agent of the present invention is, for example, tricalcium aluminate (C ３ A) It is preferable that the mixing ratio of gypsum is within the range of 0.3 to 6.4 times by mole, more preferably within the range of 0.3 to 3.2 times by mole, and even more preferably within the range of 1.0 to 3.2 times by mole, per mole of 1 alumina cement. As mentioned above, alumina cement is more expensive than ordinary cement, so the present invention, which uses gypsum powder, makes it possible to realize an economical insolubilizing agent. For example, the amount of gypsum powder relative to the alumina cement powder is preferably within the range of approximately 50 to 1,000 parts by mass of gypsum powder per 100 parts of alumina cement powder. More preferably, the amount of gypsum powder is within the range of approximately 50 to 500 parts by mass of gypsum powder per 100 parts of alumina cement powder, and even more preferably within the range of approximately 150 to 500 parts by mass of gypsum powder per 100 parts of alumina cement powder.

[0020] <Other Additives> The insolubilizing agent of the present invention contains alumina cement powder and gypsum powder, and other additives can be added as needed within the scope of the present invention. Examples of additives include insolubilizing agents using light-burned magnesia, which have been proposed and used in conventional technology. As mentioned above, conventional light-burned magnesia-based insolubilizing agents have the practical problem of taking a long time to insolubilize heavy metals, etc., but they do have the ability to insolubilize heavy metals, etc. Furthermore, since they do not affect the rapid reaction between the powdered gypsum and alumina cement that constitute the insolubilizing agent of the present invention, which is a characteristic of the present invention as described above, they can be used in combination with the insolubilizing agent of the present invention.

[0021] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are by mass unless otherwise specified.

[0022] (Method for testing elution of heavy metals, etc.) First, the elution test method used to confirm the effect of the insolubilizing material of the present invention will be described. In the present invention, a test was conducted based on the elution test method of Ministry of the Environment Notification No. 46 of 1991 to confirm the effect of the insolubilizing material in suppressing the elution of heavy metals, etc. The elution test method is outlined below. The specimen to be treated is dried, passed through a 2 mm sieve after drying, and then mixed with the insolubilizing material (powder). Then, immediately after mixing, a solvent (distilled water) for the elution test is added in an amount 10 times the amount of the specimen obtained above to form a suspension, and the following elution procedure is carried out.

[0023] The suspension obtained above was subjected to an elution procedure by continuously shaking at 200 rpm for 6 hours with an amplitude of 4 to 5 cm. The suspension was then centrifuged and filtered through a 0.45 μm membrane filter, and the resulting filtrate was used as a measurement sample to examine the elution concentration of heavy metals, etc. The heavy metals, etc. contained in the measurement sample were then quantified by analytical methods such as inductively coupled plasma atomic emission spectroscopy (IPC-AES), ion chromatography (IC), and atomic absorption spectroscopy (AAS), and the elution concentration was determined.

[0024] Test Example 1 (Confirmation Test for Fluorine Elution from Fly Ash) Fly ash discharged from a coal-fired boiler was used as a specimen. Using fly ash as the specimen and distilled water as the solvent for the elution test, a sample (suspension) for the elution procedure described above was obtained based on the elution test method described above. The following insolubilizing agents were used to mix with the fly ash used to obtain the sample (suspension) for the elution procedure described above, and differences in the effectiveness of the insolubilizing agents in inhibiting the elution of fluorine (F) from fly ash, which arise due to differences in their compositions, were investigated.

[0025] First, in the case of any insolubilizing agent, the alumina cement powder was mixed with the fly ash so that the fly ash sample contained 0.5% alumina cement powder by mass. Then, the amount of gypsum powder used together with the alumina cement powder was adjusted to 0.5% by mass of tricalcium aluminate (C ３A) was used to obtain samples (suspensions) for the elution operation. The alumina cement powder used to obtain the suspensions was Denka Alumina Cement No. 1 (trade name) manufactured by Denka Co., Ltd. This alumina cement powder was used to obtain the samples (suspensions) for the elution operation. The ... ３ The content of A is approximately 100%. The gypsum used to obtain the suspension is calcined gypsum (Kita Grade 1) manufactured by Kanto Chemical Co., Ltd.

[0026] Next, the elution procedure described above was carried out on each sample (suspension) obtained using different amounts of gypsum powder as insolubilizers, as described above. After the elution procedure, measurement samples for measuring the elution concentration in the filtrate were obtained in the same manner as described above. For each of the obtained measurement samples, the fluorine (F) concentration in the filtrate was measured using ion chromatography (manufactured by Shimadzu Corporation). The measurement results are shown in the graph in Figure 1. The vertical axis of the graph shown in Figure 1 represents the fluorine concentration (mg / L) in the filtrate, plotted in logarithmic notation. The horizontal axis represents the fluorine concentration (mg / L) in the filtrate, which is the main component of alumina cement powder. ３ The molar ratio is the molar ratio of the gypsum powder used in combination with A to 1 mole of A. Figure 1 shows the fluorine concentrations in the filtrates obtained from a blank case in which the above-mentioned elution test was conducted using only the fly ash as a specimen, and from a case in which the fly ash as a specimen was mixed with Portland cement powder, magnesium oxide powder, and gypsum powder, respectively, without using alumina cement powder as the insolubilizing agent, to obtain suspensions, and then the above-mentioned elution test was conducted on the obtained suspensions.

[0027] As shown in Figure 1, the results of the fluorine elution test conducted on samples in which the fly ash specimen was mixed with Portland cement and magnesium oxide were almost the same as those of the blank sample in which the fly ash specimen was subjected to the elution test alone, regardless of the substance used. Furthermore, when the fly ash specimen was mixed with gypsum alone without the addition of alumina cement, no significant elution suppression effect was observed in the fluorine elution test. These findings confirm that the mixture of any of the above substances hardly had any effect on suppressing the elution of fluorine from the fly ash specimen.

[0028] In contrast to the above, the results of a fluorine elution test conducted on a sample in which alumina cement was mixed with the fly ash specimen showed that the fluorine elution concentration was significantly reduced without the use of gypsum powder, as shown in Figure 1, confirming that alumina cement is effective as a substance that constitutes an insolubilizer for heavy metals, etc. However, as mentioned above, the use of gypsum powder alone did not reduce the fluorine elution concentration at all.

[0029] In response to the above, an elution operation was carried out on a sample in which the insolubilizer of the present invention, which is a combination of alumina cement powder and gypsum powder, was mixed with the fly ash as a specimen, and the measurement results of the fluorine concentration in the filtrate obtained after the elution operation are shown in Figure 1. As a result, as shown in Figure 1, it was found that the use of the insolubilizer of the present invention can significantly reduce the elution of fluorine from fly ash. In particular, in the present invention, as shown in Figure 1, C, which is the main component of alumina cement powder, is used. ３ It has been found that it is preferable to use gypsum in a ratio of 0.3 to 6.4 times by mole per mole of A, and that this provides a high effect of reducing fluorine elution. ３It is preferable that gypsum is contained in a ratio of 1.0 to 6.4 times by mole per mole of A, and further preferably in a ratio of 1.5 to 3.0 times by mole. By configuring in this manner, it is possible to obtain a more stable and high level of effect of reducing the eluted fluorine concentration without using an excessive amount of gypsum. Thus, according to the present invention, by using gypsum powder in combination, it is possible to obtain a more effective effect of reducing the eluted fluorine concentration while reducing the amount of alumina cement powder used. This means that, since alumina cement is expensive, the use of gypsum powder in combination can provide an insolubilizing agent that is economical, which is an industrially useful effect.

[0030] As shown in Figure 1, the standard value for fluorine elution is 0.8 mg / L. As shown in Figure 1, C, the main component of alumina cement powder, ３ If gypsum powder is added at a molar ratio of about 1.0 to 1 mole of A, and the alumina cement powder and gypsum powder are used together and mixed and kneaded with the fly ash sample, the fluorine elution concentration will easily satisfy the elution standard described above. ３ It was confirmed that even when gypsum was used in an amount of more than 6.4 times by mole per mole of A), the increase in the effect of suppressing fluorine elution was small. In this case, since a large amount of gypsum was contained in the fly ash after treatment, a load was placed on the secondary treatment of the treated material, which is also undesirable.

[0031] [Test Example 2] (Confirmation test for elution of F, Cd, Pb, and As from simulated contaminated soil) As specimens to be treated, simulated contaminated soils were prepared by adding predetermined specific hazardous substances to be tested to 200-300 mesh silica powder, and these soils were used in the elution test described below. The alumina cement powder constituting the insolubilizer was contained in an amount of 0.5% per 100 parts by mass of the above-mentioned simulated contaminated soil. Furthermore, the amount of gypsum powder used in combination with the alumina cement powder constituting the insolubilizer was adjusted to 1 / 4 of the amount of tricalcium aluminate (C), the main component of the alumina cement powder. ３A solution of 3.0 times the molar amount of fluorine (F) per 1 mol of cadmium (Cd), lead (Pb), and arsenic (As) was used. An elution test was conducted using the same procedure as in Test Example 1. The elution concentration of the obtained filtrate measurement sample was measured by ion chromatography, as in Test Example 1. The elution concentrations of cadmium (Cd), lead (Pb), and arsenic (As) were measured by atomic absorption spectrometry. The results are shown in Table 1. In Table 1, the values ​​"<0.001" for cadmium (Cd) and lead (Pb) indicate that the elution concentration was lower than the lower elution limit. The elution test took six hours, and the results in Table 1 confirm that the use of the insolubilizing material of the present invention successfully insolubilized all of fluorine (F) and arsenic (As) (both anions) and cadmium (Cd) and lead (Pb) (both cations) in this short time.

[0032]

Claims

1. An insolubilizing material for specific hazardous substances (heavy metals, etc.) characterized by comprising at least alumina cement powder and gypsum powder.

2. The tricalcium aluminate (C) in the alumina cement ３ The insolubilizing material for specific hazardous substances (heavy metals, etc.) according to claim 1, wherein the ratio of gypsum to 1 mole of A is within a range of 0.3 to 6.4 moles.

3. The insolubilizing material for specific hazardous substances (heavy metals, etc.) according to claim 1 or 2, which is added in powder form to contaminated soil or fly ash containing specific hazardous substances (heavy metals, etc.).

4. An insolubilizing material for specific hazardous substances (heavy metals, etc.) according to claim 1 or 2, wherein the specific hazardous substance is at least one substance selected from the group consisting of cadmium and its compounds, hexavalent chromium compounds, cyanide compounds, mercury and its compounds (including alkyl mercury), selenium and its compounds, lead and its compounds, arsenic and its compounds, fluorine and its compounds, and boron and its compounds.

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