JP3747246B1 - Asbestos detoxification method for composite materials containing asbestos - Google Patents

Abstract

An object of the present invention is to decompose a fibrous asbestos of a composite material into granular or powdery form by heating a reaction liquid containing a specific compound containing a fluorocarbon substitute material at a low temperature to a composite material containing fibrous asbestos. Provide a way to detoxify.
A composite material having a cement containing fibrous asbestos and a calcium oxide component is immersed in a reaction solution containing calcium chloride so that the reaction solution is impregnated in the composite material. By heating at a temperature, the chemical bond between Mg and Si in the asbestos compound is cut, and the fibrous asbestos is decomposed into particles or powders.
[Selection] Figure 2

Description

  The present invention relates to a method for detoxifying asbestos of an asbestos-containing composite material, and in particular, the fibrous asbestos of a sprayed fireproof coating layer composed of a composite material of fibrous asbestos and cement formed on the surface of a building material such as a steel frame, in granular or powder form It is related with the method of decomposing into asbestos and detoxifying it.

Asbestos is a naturally occurring mineral fiber. Examples include serpentinite chrysotile (white asbestos, Mg ₆ Si ₄ O ₁₀ (OH) ₈ ) and amphibolite amosite (tea asbestos, (Fe, Mg) ₇ Si ₈ O ₂₂ (OH) ₂ ). It is said that there are more than 3,000 types of usage such as construction materials, electrical products, automobiles and household products because of its excellent properties such as heat resistance, chemical resistance and insulation.

  However, although the causal relationship between asbestos exposure and various diseases (asbestosis, lung cancer, malignant mesothelioma, etc.) has been suggested since the 1960s, asbestos continues to be used in Japan. . Asbestos consumed in Japan between 1930 and 2002 reached 10 million tons, more than 90% of which was used as building materials.

  Asbestos can be used in a case where it is used alone as a textile product, and in a case where a cement-asbestos composite material is used for preventing the sound absorption and condensation of a steel fireproof coating material and wall material.

  Cement-asbestos composites can be broadly classified into three types: sprayed asbestos, asbestos heat insulating material, and asbestos molded board. Among them, sprayed asbestos has a large amount of use, a high asbestos content, and asbestos is likely to be scattered at the time of destruction.

  Sprayed asbestos is used as a fireproof coating layer for building materials such as steel frames. Specifically, cement and asbestos are mixed and sprayed from a spray gun or the like in order to prevent the steel frames from melting and collapsing in the event of a fire. The amount of asbestos contained in the spray material is usually about 50 to 95%. The asbestos in this spraying material has a fiber shape (cotton shape) as a whole and does not have mechanical strength, but has a function as a heat insulating material because it has many voids. When building materials with a fireproof coating layer containing asbestos are dismantled after the building is dismantled, the fireproof coating layer is peeled off from the building material, and the peeled fireproof coating layer is then disposed of as a specified controlled substance. .

  Recently (June 2005), health problems caused by asbestos became a social problem at a stretch, and public opinion regarding handling of sprayed asbestos became more severe. In the future, dismantling and disposal of buildings with building materials that have fireproof coating layers containing asbestos will peak, and it is expected that the problem of processing composite materials containing asbestos will become increasingly serious.

  Fireproof coated building materials produced in large quantities so far are disposed of as industrial waste when discarded after use. However, if the cement hardened material is neutralized, it is predicted that the fibrous asbestos will be scattered and released. Therefore, there are no special measures at present.

As a means for decomposing and detoxifying asbestos, for example, a closed electric furnace melting method described in Patent Document 1 and a slag bath melting method described in Patent Document 2 can be cited. It has not been put into practical use because it requires temperature and has enormous energy consumption problems.
There are also attempts to melt with high temperature plasma, but no attempt has been made.
Japanese Patent No. 3085959 Japanese Patent Laid-Open No. 7-171536

  For this reason, one of the inventors of the present invention, in Patent Document 3, mixes asbestos with a chlorofluorocarbon compound produced by chlorofluorocarbon decomposition detoxification treatment, and then detoxifies the asbestos by heating the mixture at a low temperature. A method was proposed.

That is, in order to detoxify asbestos, it was considered to be heated and melted. In order to solve the energy consumption problem, a melting agent that melts asbestos at the lowest possible temperature was sought. In the steel industry, a fluorine compound is used as a melting agent, and it was thought that the fluorocarbon decomposition products that the present inventor has worked on may be possible.
JP 2005-168632 A

  The "CFC decomposition product" here is a substance finally obtained in the CFC decomposition process. In the “plasma system”, which is one of the CFC decomposition methods, CFCs are first decomposed into hydrogen chloride, hydrogen fluoride, and carbon dioxide, which are absorbed by calcium hydroxide, and then washed with water to wash the calcium chloride. A fluorocarbon decomposition product containing calcium and calcium fluoride as components is obtained.

  Like asbestos, chlorofluorocarbon is a material that has been widely used to build an amenity society. Its stability, non-flammability, and non-toxicity make it a refrigerant for refrigerators and coolers, cleaning agents for semiconductors and precision equipment, and sprays for sprays. It was used.

  However, since chlorofluorocarbon is an ozone-depleting substance and is now prohibited to be used worldwide and is required to be recovered, asbestos can be decomposed and harmless within the scope of recycling and recycling the recovered chlorofluorocarbon decomposition products. Although it is preferable to use it in the process of decomposing it, it cannot generate harmful chlorofluorocarbons in order to detoxify asbestos, so it does not use chlorofluorocarbon degradation products and does not adversely affect the environment. It was necessary to develop a method for detoxifying asbestos using a compound containing. In addition, chlorofluorocarbon degradation products can decompose and detoxify asbestos as long as they can react with asbestos. For example, in the case of sprayed asbestos composed of a composite material of cement and asbestos, However, since it interferes with the reaction between asbestos and CFC decomposition products, it may not be possible to sufficiently decompose and detoxify asbestos. In addition, the form after decomposing the fibrous asbestos using the CFC decomposition product may maintain the fibrous form, and is not necessarily decomposed into a granular or powdery form. Therefore, it may not be said that asbestos has been sufficiently detoxified.

  The object of the present invention is to decompose the fibrous asbestos of the composite material into granular or powdery form by heating the composite material containing fibrous asbestos at a low temperature with a reaction liquid containing a specific compound containing a fluorocarbon substitute. Provide a way to detoxify asbestos.

In order to achieve the above object, the gist of the present invention is as follows.
(I) After a composite material having a cement containing fibrous asbestos and a calcium oxide component is immersed in a reaction solution containing calcium chloride and impregnating the reaction solution into the composite material, a temperature of 600 to 800 ° C. The asbestos detoxification method of the asbestos-containing composite material characterized by cutting the chemical bond between Mg and Si in the asbestos compound and heating the asbestos to decompose the fibrous asbestos into particles or powders.

(II) The asbestos detoxification method for an asbestos-containing composite material according to (I) above, wherein the composite material is a fireproof coating layer formed by being sprayed on a surface of a building material such as a steel frame.

(III) The method for detoxifying an asbestos-containing composite material according to (I) or (II), wherein the reaction solution is a reaction solution further containing another calcium compound in addition to calcium chloride.

(IV) The asbestos detoxification method for an asbestos-containing composite material according to (III), wherein the other calcium compound is calcium carbonate.

(V) The asbestos-containing composite material according to any one of (I) to (IV), wherein the reaction liquid further contains an auxiliary additive compound that forms a molten salt at a low temperature to increase a reaction rate with asbestos. Asbestos detoxification method.

(VI) The asbestos detoxification method for an asbestos-containing composite material according to (V), wherein the auxiliary additive compound is a chloride and / or fluoride other than calcium chloride.

  According to this invention, the composite material containing fibrous asbestos is decomposed into granular or powdery form by heating the reaction liquid containing a specific compound containing a fluorocarbon substitute material at a low temperature. It is possible to provide a method for detoxifying asbestos.

  In particular, it has been said that sprayed asbestos containing asbestos and cement cannot be decomposed, disintegrated or melted until now, or only at a high temperature of 1500 ° C or higher. In the handling of sprayed asbestos, it is necessary to improve the asbestos scattering property by wetting with water or the like. In the present invention, a reaction solution of various salts (preferably, a single salt of calcium chloride or a mixed salt of calcium chloride and calcium carbonate) is used for wetting, and a large sprayed asbestos mass can be crushed. Calcium chloride and calcium carbonate (or calcium hydroxide, etc.) that are insufficient for the decomposition of asbestos are re-impregnated and heated to 600-800 ° C. Can be detoxified.

  In addition, asbestos can be made stable and non-fibrous by adding about twice the calculated amount of calcium component. In addition, the reaction temperature can be lowered by using a molten salt.

  The present invention can reduce the cost of waste, detoxify a fireproof coating material containing asbestos, which is a harmful substance that has been harmful to health for many years, and has an upper limit of the detoxifying temperature. A certain 800 ° C. is a temperature that can be achieved by the use of energy from an urban cleaning plant, and as a result, the cost of detoxifying asbestos can be reduced.

An embodiment according to the present invention will be described below.
The present inventors evaluated the detoxification of asbestos in a composite material having asbestos and cement from the following viewpoint.

(1) Non-fibrosis of asbestos The present inventors considered that asbestos exhibits a fibrous form in a normal use form, and can be rendered harmless if the form is broken and the fibrous asbestos is decomposed into powder or granules. . This point was evaluated by observing with a scanning electron microscope. In order to examine this point in more detail, it was washed with water or acetic acid. Even if a substance other than asbestos is present, if it dissolves in acetic acid, it will be removed and separated, and evaluation will be easy.

That is, the reason for washing with water or acetic acid is as follows.
In the product, excess CaCl ₂ melt added and unreacted CaO composite oxide remain, and when the product is observed with an electron microscope, the asbestos fiber itself is lost due to these remaining compounds. Although it may be difficult to observe, when washed with water, the molten CaCl ₂ dissolves in the water, so the CaCl ₂ can be removed, and when washed with acetic acid, the CaO-based easily soluble oxidation This is because the object can be dissolved and removed. In particular, an organic acid such as acetic acid is used because the above-described oxide dissolves but asbestos does not dissolve.

(2) Determination of asbestos in composite and determination method for decomposition Asbestos is a crystal containing magnesium (Mg) and silicon (Si), has a unique crystal structure, and is analyzed by X-ray diffraction. Can do. Also in the present invention, the presence or absence of asbestos was determined by this method. Moreover, the decomposition | disassembly of asbestos was determined by the presence or absence of magnesium oxide produced | generated when the chemical bond of Mg and Si was cut | disconnected.

(3) Preparation of sprayed asbestos Since discarded sprayed asbestos is difficult to obtain because it is a managed waste and its use history is unclear, Portland cement and chrysotile asbestos are used as research samples. Prepared by mixing and curing.
The sprayed asbestos used in the experiment was prepared by the following method of two types of samples (sample A is asbestos: cement = 6: 4 (mass ratio) and sample B is asbestos: cement = 9: 1 (mass ratio)). .

(I) Preparation method of sample A (asbestos: cement = 6: 4 (mass ratio))
Asbestos, the most used chrysotile type (manufactured by Kanto Chemical Co., Ltd.) was used. Asbestos and ordinary Portland cement (CaO content: approx. 65% by mass) are collected in a mass ratio of 6: 4, and aluminum powder is used as a foaming agent to fully demonstrate its effect as a heat insulating material. An amount corresponding to 10 mass.% Of the mass was added. Next, water was added in an amount corresponding to the mass equal to the sum of the amounts of cement, asbestos and aluminum powder used, and mixed in a beaker. Mixing was continued until asbestos, cement and aluminum powder were uniform. The mixture was allowed to stand and cured to prepare Sample A. Sample A had a bulk density of 0.83 g / cm ³ and a porosity of 64.8%.

(Ii) Preparation method of sample B (high asbestos-containing sprayed asbestos, asbestos: cement = 9: 1 (mass ratio))
Sample B, which is a sprayed asbestos with a high asbestos content, was prepared by the following method. Asbestos and ordinary Portland cement (CaO content: about 65% by mass) were collected at a mass ratio of 9: 1, and water was added in an amount equal to the total mass and mixed. Mixing was performed until asbestos and cement were uniform. The mixture was dropped on a heated hot plate, and moisture was rapidly evaporated to prepare a porous sample B. Sample B had a bulk density of 1.82 g / cm ³ and a porosity of 29.6%.

(4) Decomposition of asbestos in low asbestos-containing sprayed asbestos (composite material)
Study of detoxification (a) When using CFC decomposition products (Comparative Example 1)
About the produced sample A, it was investigated whether asbestos decomposes | disassembles and makes non-fiber by the asbestos detoxification method of patent document 3 which the inventor applied.
The CFC decomposition product used as a melting agent decomposed the CFC compound collected from the car air conditioner by the plasma method, and the generated decomposition product was absorbed by calcium hydroxide. It is a mixture with calcium carbonate, calcium fluoride and calcium chloride. Thereafter, the calcium chloride was removed by washing with water to obtain a dehydrated cake (provided by Car Steel Co., Ltd., main components CaCO ₃ and CaF ₂ ).

  Sprayed asbestos (sample A) (1.7 g) was pulverized in a mortar and mixed with 3.0 g of chlorofluorocarbon decomposition product and pure water (about 3 ml) to prepare a slurry asbestos-chlorofluorocarbon decomposition product. This was put into a magnetic crucible. The crucible is then placed in a muffle furnace (Muffle Furnace STR-13K ISUZU, 160 mm x 110 mm x 260 mm) at room temperature, heated to 800 ° C for 2.5 hours, held at this temperature for 2 hours, and then removed from the furnace. The mixture was allowed to cool to obtain a fired product. The obtained fired product was observed with a scanning electron microscope (SEM, JSM-5600).

  In the case of using chlorofluorocarbon decomposition products, signs of decomposition were observed from a heating temperature of 500 ° C., and asbestos fibers were powdered at 700 ° C. However, the decomposition temperature in this invention for sprayed asbestos was set to 800 ° C., which is even higher than that, because asbestos is covered with cement.

  When sprayed asbestos (sample A) heated at 800 ° C. for 2.5 hours was observed with an SEM, the asbestos retained the fiber form and was not decomposed (FIG. 1). The reaction between the CFC decomposition product and asbestos is a solid-solid reaction. It is considered that the decomposition of asbestos did not proceed in sprayed asbestos because the cement solidified product inhibited the contact between asbestos and the fluorocarbon decomposed product and prevented the reaction from proceeding.

(B) When sodium fluoride (NaF) is used (Comparative Example 2)
In the case of Comparative Example 1 using a CFC decomposition product, it was considered that the cement solidified product inhibited the contact between asbestos and the CFC decomposition product, thereby preventing the progress of the decomposition reaction of asbestos. Therefore, it was considered that the asbestos can be decomposed by impregnating the cement-asbestos composite material with the melting agent reaction liquid so that the asbestos and the melting agent come into contact with each other. The main components of the CFC decomposition product are calcium carbonate and calcium fluoride. Since these are hardly soluble in water, a water-soluble decomposition agent containing both calcium and fluorine was used. Specifically, water-soluble sodium fluoride was used. In addition, since the calcium component contained calcium oxide in the cement covering asbestos, and this calcium oxide can be used, it was thought that it was not necessary to add to the melting agent.

  To 1.7 g of sprayed asbestos (sample A), 1.0 g of salt (sodium fluoride) was dissolved in 4 to 6 ml of pure water, added as a reaction solution, and placed in a magnetic crucible. Thereafter, the crucible was placed in a muffle furnace at room temperature, heated to 800 ° C. over 2.5 hours, held for 2 hours, then taken out of the furnace and allowed to cool to obtain a fired product.

  The mixing ratio of salt (sodium fluoride) and sprayed asbestos (sample A) is the mass of calcium carbonate and calcium fluoride, which are the main components of the fluorocarbon decomposition product, compared to asbestos 1 in the experiment using only the fluorocarbon decomposition product. Since the ratio was approximately 1: 1, a similar ratio was used.

  The obtained fired product was subjected to powder X-ray diffraction (XRD, RINT2100V / PC) analysis and SEM (JEOL Ltd., JSM-5600) observation.

  In order to clarify the observation of the form of asbestos present in the fired product, coexisting components covering asbestos were removed by washing with 1N acetic acid. Specifically, the heat-fired product was pulverized in an agate mortar, and about 100 mg thereof was taken and placed in a 100 ml Erlenmeyer flask. The operation of adding 40 ml of pure water or 20 ml of 20% aqueous acetic acid solution and then shaking the ground sample for about 30 seconds using an ultrasonic cleaner for 1 minute and 30 seconds was repeated 6 times. The sample was filtered by attaching a membrane filter (pore diameter 1 μm, thickness 80 μm, porosity 80%) to a suction filter. The taken out filter was dried for 24 hours with a dryer at 110 ° C. to obtain a sample for SEM observation.

The X-ray diffraction pattern of the obtained fired product is shown in FIG. The diffraction line peaks peculiar to asbestos were 12 ° and 25 ° at 2θ, but this diffraction line was not observed. There was no forsterite (Mg ₂ SiO ₄ ) produced when dehydrated asbestos at 600 to 700 ° C. Forsterite is a brittle crystal unlike asbestos, but it retains a fibrous structure like asbestos, and its presence in forsterite is not preferable from an environmental point of view. The diffraction line in FIG. 2 (a), was CaMgSiO and sodium fluoride unreacted _{4 (CaO · MgO · SiO 2} ).

FIG. 3 shows a part of a state in which the fired product is observed with a scanning electron microscope. In this case, the presence of acicular material was clearly observed.
Therefore, the decomposition of fibrous asbestos was insufficient with sodium fluoride.

(C) When sodium chloride is used (Comparative Example 3)
Fluorine compounds are generally environmentally hazardous substances, and the use of sodium fluoride is considered undesirable. For this reason, the same experiment was also performed on sodium chloride, which is the same salt as sodium fluoride.

  To 1.7 g of sprayed asbestos (sample A), 1.0 g of salt (sodium chloride) was dissolved in 4 to 6 ml of pure water, added as an aqueous solution, and placed in a magnetic crucible. Thereafter, the crucible was placed in a muffle furnace at room temperature, heated to 800 ° C. over 2.5 hours, held for 2 hours, then taken out of the furnace and allowed to cool to obtain a fired product.

The obtained fired product was subjected to powder X-ray diffraction (XRD, RINT2100V / PC) analysis and SEM (JEOL Ltd., JSM-5600) observation.
In order to clarify the observation of the form of asbestos present in the fired product, the coexisting component covering the asbestos was washed with 1N acetic acid and then observed.

The X-ray diffraction pattern of the obtained fired product is shown in FIG. The diffraction line peaks peculiar to asbestos were 12 ° and 25 ° at 2θ, but this diffraction line was not observed. Also, the characteristic diffraction lines (twin peaks at 35.7 ° and 36.5 ° in 2θ) of forsterite (Mg ₂ SiO ₄ ) dehydrated at 600 to 700 ° C were not observed in Fig. 2 (b). .
The confirmed diffraction lines were unreacted sodium chloride, CaMgSiO ₄ (CaO · MgO · SiO ₂ ), MgSiO ₃ (MgO · SiO ₂ ), and the like.

  Moreover, the result of having observed the heat-fired thing with the scanning electron microscope is shown in FIG. From FIG. 4, fibrous protrusions were present in the fired product, and non-fibrosis was insufficient.

(D) When calcium chloride is used (Example 1)
Those having a melting point lower than that of sodium chloride generally used as a melting agent were investigated. As a result, the melting point of calcium chloride was 774 ° C., which was lower than the melting point of sodium chloride (800 ° C.).

  Sprayed asbestos (sample A) 1.7 g (asbestos amount: about 1 g) was immersed in 4 ml of 25% by volume calcium chloride aqueous solution and impregnated, then placed in an alumina crucible and dried in a 110 ° C. drier. It was. At this time, the amount of calcium chloride adhering to the sprayed asbestos (sample A) was 1 g.

  Thereafter, the crucible was placed in a muffle furnace, heated from room temperature to 800 ° C. over 2.5 hours, held at this temperature for 2 hours, then taken out of the furnace and allowed to cool to obtain a fired product.

The obtained fired product was analyzed by a powder X-ray diffraction method. The result is shown in FIG. In this diffraction line, a diffraction line of magnesium oxide (MgO) was confirmed together with Ca ₁₂ Al ₁₄ O ₃₃ containing Mg used as a foaming agent and MgSiO ₃ . The presence of magnesium oxide indicates that the chemical bond between Si and Mg, which are constituent elements of asbestos, has been broken, which means that asbestos has been decomposed.

  Furthermore, the result of having observed the heat-fired thing with the scanning electron microscope (SEM) is shown in FIG. From FIG. 5, asbestos is granular, and the fibrous form of the original asbestos was not observed.

  In addition, although the said experiment is an experimental result in case heating temperature is 800 degreeC, also when heating temperature is performed in the range of 600 degreeC or more and less than 800 degreeC, asbestos fiber becomes granular or powder form similarly. As the fiber became non-fibrous, the asbestos peak disappeared even by X-ray diffraction. Therefore, it was found that asbestos in the composite material can be decomposed by impregnating the reaction solution containing calcium chloride and heating at a temperature of 600 to 800 ° C. The heating time is preferably 2 hours or longer.

From the above, the effect of decomposing asbestos was the most effective in the order of NaF <NaCl <CaCl ₂ and CaCl ₂ . This is attributed to the melting point of the salt (NaF 992 ° C., NaCl 800 ° C., CaCl 2 774 ° C.), and it is considered that the formation of the low-temperature melt promotes the decomposition reaction of asbestos.

(5) Decomposition of asbestos in sprayed asbestos (composite material) containing high asbestos
Examination of detoxification Next, examination was carried out to decompose and detoxify asbestos in asbestos sprayed with high content asbestos (sample B).

(I) When calcium chloride (0.4 g) is used and the heating temperature is 800 ° C. (Comparative Example A)
Highly asbestos-containing sprayed asbestos (sample B) 1.1 g (asbestos amount: about 1 g) was impregnated with a 25 vol% calcium chloride-containing reaction solution, placed in an alumina crucible, and dried in a 110 ° C. drier. It was. At this time, the amount of calcium chloride adhering to the sprayed asbestos (sample B) was 0.4 g.

Thereafter, the crucible was placed in a muffle furnace, heated from room temperature to 800 ° C. over 2.5 hours, and then held at this temperature for 2 hours. Thereafter, the product was taken out from the furnace and allowed to cool to obtain a fired product. The obtained fired product was subjected to powder X-ray diffraction analysis. The analysis results are shown in FIG. In this diffraction line, _two peaks of 35.7 ° and 36.5 ° at 2θ peculiar to forsterite (Mg ₂ SiO ₄ ) were clearly recognized. In addition to forsterite, the presence of calcium silicate hydrate (Ca ₃ Si ₂ O ₇ .H ₂ O) was observed. Other than that, the diffraction lines of magnesium oxide were also observed in the vicinity of 62 ° and 43 °, although the intensity was low. Since magnesium oxide is present, it can be said that decomposition of asbestos has occurred. However, in a sample having a high asbestos content, impregnation of the reaction solution containing only calcium chloride did not sufficiently decompose asbestos even when heated. As will be described later, the amount of calcium chloride (0.4 g) adhering to the sprayed asbestos (sample B) is asbestos / CaCl ₂ = 1/1 (molar ratio), and the amount of calcium necessary for the decomposition of asbestos (2 mol) This is probably because it was less than the above.

(B) When calcium chloride (0.4 g) is used and the heating temperature is 700 ° C. (Comparative Example B)
A fired product was obtained in the same manner as in Comparative Example A, except that the heating temperature was 700 ° C. The obtained fired product was subjected to powder X-ray diffraction analysis. The analysis result is shown in FIG. In this diffraction line, _two peaks of 35.7 ° and 36.5 ° at 2θ peculiar to forsterite (Mg ₂ SiO ₄ ) were clearly recognized. In addition to forsterite, the presence of calcium silicate hydrate (Ca ₃ Si ₂ O ₇ .H ₂ O) was observed. Other than that, the diffraction lines of magnesium oxide were also observed in the vicinity of 78 °, 62 ° and 43 °, although the intensity was low. Since magnesium oxide is present, it can be said that decomposition of asbestos has occurred. However, in a sample having a high asbestos content, impregnation of the reaction solution containing only calcium chloride did not sufficiently decompose asbestos even when heated. As will be described later, this is considered to be because the amount of calcium chloride (0.4 g) adhering to the sprayed asbestos (sample B) was less than the amount of calcium necessary for the decomposition of asbestos.

(C) When a complex salt of calcium chloride and calcium carbonate is used and the heating temperature is 800 ° C. (Example A)
For this reason, the present inventors further examined detoxification of the high content sprayed asbestos (sample B).
Highly sprayed asbestos (sample B) 1.1 g (asbestos amount: about 1 g) is ground in a mortar, and 1.0 g of calcium carbonate and 1.0 g of calcium chloride dissolved in about 4 ml of pure water are added and mixed. Placed in a porcelain crucible. Thereafter, the crucible containing the sample was placed in a muffle furnace, and the temperature was raised from room temperature to 800 ° C. in 2.5 hours. The temperature was maintained at this temperature for 2 hours, then taken out of the furnace and cooled to obtain a fired product.

  The obtained fired product was observed by SEM and powder X-ray diffraction analysis (XRD). In addition, since the fired product contains an excessive amount of salt, the SEM observation was also performed on the sample after washing with water.

The XRD result of the heat-fired sample is shown in FIG. From this XRD result, magnesium oxide (MgO) is observed in addition to calcium chloride (CaCl ₂ ), Ca ₃ Cl ₂ SiO ₄ and Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ , and a forsterite-specific diffraction line peak is observed. There wasn't. Since the diffraction line has a magnesium oxide (MgO) peak, it is considered that asbestos was decomposed.

  FIG. 9 shows a state observed with a scanning electron microscope (SEM). Note that FIG. 9 was observed before washing with water or acetic acid, and from this figure, it was found that the film was partially melted.

  Further, the result of observing the fired product with an electron microscope after washing with 1N acetic acid is shown in FIG. From FIG. 10, the fired product was granulated, and the fiber form of asbestos was not recognized.

For these reasons, for composite materials with a small amount of cement relative to asbestos, more strictly, calcium oxide (CaO), the shortage of calcium oxide is separately added to calcium carbonate (CaCO ₃ ) and calcium hydroxide (Ca It was found that fibrous asbestos can be decomposed by adding other calcium compounds such as (OH) ₂ ).

(D) When a complex salt of calcium chloride and calcium carbonate is used and the heating temperature is 700 ° C. (Example B)
A fired product was obtained in the same manner as in Example A except that the heating temperature was 700 ° C.
The obtained fired product was observed by SEM and powder X-ray diffraction analysis (XRD). In addition, since the fired product contains an excessive amount of salt, the SEM observation was also performed on the sample after washing with water.

The XRD result of the fired product is shown in FIG. From this XRD result, magnesium oxide (MgO) is observed in addition to calcium chloride (CaCl ₂ ), Ca ₃ Cl ₂ SiO ₄ and Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ , and a forsterite-specific diffraction line peak is observed. There wasn't. Since the diffraction line has a magnesium oxide (MgO) peak, it is considered that asbestos was decomposed.

For these reasons, for composites with a lower amount of cement than asbestos, more strictly, calcium oxide (CaO), the shortage of calcium oxide is added separately to calcium carbonate (CaCO ₃ ) and calcium hydroxide (Ca ( It was found that fibrous asbestos can be decomposed by adding other calcium compounds such as OH) ₂ ).

  In addition, although the said Example A and B is an experimental result in case heating temperature is 800 degreeC and 700 degreeC, respectively, when heating temperature is performed at 600-800 degreeC, similarly, asbestos fiber is granular or While becoming powdery and non-fibrous, the asbestos peak disappeared even by X-ray diffraction. Therefore, it was found that asbestos in the high content sprayed asbestos can be decomposed by impregnating a reaction solution containing calcium chloride and calcium carbonate and heating at a temperature of 600 to 800 ° C. The heating time is preferably 2 hours or longer.

In the present invention, in the case of low asbestos-containing sprayed asbestos (composite material), the asbestos in the composite material is obtained by impregnating a reaction solution containing only calcium chloride and heating at a temperature of 600 to 800 ° C. In the case of sprayed asbestos with high asbestos content (composite material), in addition to calcium chloride, the calcium oxide deficiency is separated separately from calcium carbonate (CaCO ₃ ) and calcium hydroxide (Ca (OH ₂ ) Asbestos in the composite material can be decomposed by impregnating a reaction solution containing another calcium compound such as ₂ ) and heating at a temperature of 600 to 800 ° C.

The decomposition mechanism of asbestos in sprayed asbestos (composite material) is asbestos changes into forsterite by heating after impregnating the reaction solution, and reacts with the calcium component in the impregnated calcium compound, and finally Specifically, it is considered that asbestos is decomposed by separating into magnesium oxide and calcium silicate. At this time, in the case of sprayed asbestos containing low asbestos (composite), calcium oxide (CaO) contained in a large amount in the cement can be used, so the amount of calcium chloride (CaCl ₂ ) to be added is In the case of sprayed asbestos (composite material) containing high asbestos, the amount of calcium oxide (CaO) contained in the cement is low, so calcium chloride (CaCl ₂ ) and carbonic acid should be added. The amount of calcium (CaCO ₃ ) added is twice as much as asbestos in terms of molar ratio.

That is, when 1 mole of asbestos (Mg ₃ Si ₂ O ₅ (OH) ₄ ) is decomposed, 3 moles of magnesium oxide and 2 moles of calcium silicate are generated according to the reaction formula shown below. The amount of calcium chloride and calcium oxide required for this reaction is 2 mol each.
Reaction formula: Mg ₃ Si ₂ O ₅ (OH) ₄ + 2CaO + 2CaCl ₂ → 2Ca ₂ SiO ₃ Cl ₂ + 3MgO + 2H ₂ O
For example, when 1 mol of chrysotile asbestos is 277.1 g, 1 mol of CaCl ₂ is similarly required. At this time, since CaO of Portland cement is said to be approximately 65% by mass, when the proportion of CaO contained in Portland cement is 65% by mass, the required CaO addition amount is as shown in FIGS. Referring to the product of FIG. 11, 2 mol of CaO is required for 1 mol of Si contained in asbestos, and 1 mol of CaO is 56 g, so that 2 mol is 56 × 2 = 112 g. As Portland cement, unless it is 112g / 0.65 = 172g or more, CaO will be insufficient. Therefore, when the number is larger than asbestos / cement = 277.1 / 172 = 1.6, it is necessary to add a CaO component.

  The sprayed asbestos (composite material) used in the above experiment has 1 g of asbestos, but 1 g of asbestos is 0.0036 mol. In this case, the amount of calcium chloride required to decompose 1 g of asbestos is 0.00. 0072 mol (0.80 g).

  In the case of Comparative Examples A and B, the amount of asbestos is 1 g, whereas calcium chloride is 0.4 g, and only about 50% of 0.8 g, which is an amount necessary for decomposition of asbestos, is added to the reaction system. It was considered that the reaction was not sufficient because it was not.

Therefore, in the case of Example A, the shortage of the added amount of calcium oxide is supplemented by adding another calcium compound such as calcium carbonate (CaCO ₃ ) or calcium hydroxide (Ca (OH) ₂ ) separately. As a result, the fibrous asbestos was almost completely decomposed. That is, in the case of Example A, 1.0 g (0.013 mol) of calcium chloride and calcium oxide in the cement of sprayed asbestos (0.1 g × 65% = 0.065 g / 56 g / mol = 1 g (0.0036 mol) of asbestos = 0.0011 mol) and 1.0 g (0.01 mol) of calcium carbonate were added, and the calcium content of both was 0.013 mol for calcium chloride and 0.011 mol for the calcium oxide system. Since each calcium component required to decompose 1 g (0.0036 mol) of asbestos is 0.0072 mol, in the case of Example A, 1.8 times the amount of calcium chloride required to decompose asbestos. The amount of calcium oxide was more than 1.5 times that of calcium oxide.
In the Examples, asbestos decomposition experiments were performed at a specific weight ratio, and the product was identified from the powder X-ray diffraction result of the fired product. Since the reaction ratios of asbestos, calcium chloride, and calcium oxide (calcium carbonate, calcium hydroxide, etc.) are obtained based on the identification results, the charged mixture ratios of the examples are different from the theoretical values.

  Thus, decomposition | disassembly became possible by heating in presence of a calcium chloride component more than twice the required amount which decomposes | disassembles asbestos, and a calcium oxide component more than twice.

  In particular, utilizing the chloride (calcium chloride) used in the method of the present invention causes the decomposition reaction of asbestos from a low temperature when the reaction solution is impregnated by lowering both the melting point and the reaction activation temperature. It is effective because it can be made.

Therefore, in order to decompose asbestos, it is necessary to add a calcium chloride component that is twice or more the calculated amount and a calcium oxide component that is twice or more the calculated amount, and it is preferable to use calcium chloride that lowers the melting temperature. . Therefore, in order to decompose asbestos, it is necessary to add CaO components such as CaCO ₃ and / or Ca (OH) ₂ so that the CaO component is more than twice the calculated amount of asbestos. It is desirable to use CaCl ₂ having a high value.

  In addition, it is preferable to form a molten salt by adding a salt from the viewpoint of lowering the reaction temperature between asbestos and calcium or forming a molten salt to improve the uniformity of the reaction. Examples of the molten salt system that can be used include the following systems.

Systems that melt at around 500 ° C-KCl-NaCl-CaCl ₂ , KCl-CaCl ₂ -MgCl ₂ , NaCl-CaCl ₂
Systems that melt from around 600 ° C -BaCl ₂ -CaCl ₂ , NaCl-CaCl ₂ -NaF-CaF ₂
Melts from the vicinity of 650 ℃ system -CaCl ₂ -CaF ₂

In addition, since the fluorine compound contains chlorofluorocarbon, which is an ozone depleting substance, it has a problem in processing the product, and the Ba compound is expensive. MgCl ₂ has a vapor pressure of 1 mmHg. It is 778 ° C, NaCl is 865 ° C, KCl is 821 ° C, and since the vapor pressure of the salt is high near the reaction temperature, these compounds can be used by using a molten salt appropriately contained as necessary. Good.

As a molten salt for melting asbestos, it is possible to apply other than the above system. There are other system changes due to the addition of trace amounts of salts.
Further, even when containing a salt having a high vapor pressure such as AlCl ₃ or FeCl ₃ , it is considered that the decomposition reaction of asbestos occurs at 600 to 800 ° C.

  In the above examples and comparative examples, both are shown as examples in which chrysotile type asbestos is used as asbestos, but the method of the present invention can be applied to other methods such as crocidolite, amosite, anthophyllite, tremolite, actinolite, etc. Needless to say, it can also be applied to asbestos.

  What has been described above is merely an example of an embodiment of the present invention, and various modifications can be made within the scope of the claims.

   According to the present invention, the fibrous asbestos of the composite material is decomposed into granular or powdery form by heating the composite material containing fibrous asbestos at a low temperature with a reaction solution containing a specific compound containing a fluorocarbon substitute. It is possible to provide a method for detoxifying asbestos.

  In particular, it has been said that sprayed asbestos containing asbestos and cement cannot be decomposed, disintegrated or melted until now, or only at a high temperature of 1500 ° C or higher. The present invention impregnates a reaction solution of various salts (preferably, a single salt of calcium chloride or a mixed salt of calcium chloride and calcium carbonate), and heats it to 600 to 800 ° C. The chemical bond of asbestos can be decomposed, and asbestos can be rendered harmless.

  In addition, asbestos can be made stable and non-fibrous by adding about twice the calculated amount of calcium component. In addition, the reaction temperature can be lowered by using a molten salt.

  The present invention makes it possible to reduce the cost of waste, to make harmless fire-resistant coating materials containing asbestos, a harmful substance that has been harmful to health for many years, and to make it the upper limit of the harmless temperature. A certain 800 ° C. is a temperature that can be achieved by the use of energy from an urban cleaning plant, and as a result, the cost of detoxifying asbestos can be reduced.

It is a photograph when the fired product of Comparative Example 1 is observed with a scanning electron microscope (SEM). (A) NaF-containing aqueous solution is a powder X-ray diffraction (XRD) pattern of the obtained baked product using a (b) NaCl solution and (c) CaCl ₂ solution. It is a photograph when the fired product of Comparative Example 2 is observed with a scanning electron microscope (SEM). It is a photograph when the fired product of Comparative Example 3 is observed with a scanning electron microscope (SEM). It is a photograph when the baked product of Example 1 is observed with a scanning electron microscope (SEM). 3 is a powder X-ray diffraction (XRD) pattern of a fired product of Comparative Example A. FIG. 3 is a powder X-ray diffraction (XRD) pattern of the fired product of Comparative Example B. FIG. 2 is a powder X-ray diffraction (XRD) pattern of the fired product of Example A. FIG. It is a photograph when the baking thing (before acetic acid washing | cleaning) of Example A is observed with a scanning electron microscope (SEM). It is a photograph when the baked product (after acetic acid washing) of Example A is observed with a scanning electron microscope (SEM). 3 is a powder X-ray diffraction (XRD) pattern of the fired product of Example B. FIG.

Claims (6)

A composite material having a cement containing fibrous asbestos and a calcium oxide component is immersed in a reaction solution containing calcium chloride so that the reaction solution is impregnated in the composite material, and then heated at a temperature of 600 to 800 ° C. The asbestos detoxification method of the asbestos-containing composite material which cuts | disconnects the chemical bond of Mg and Si in an asbestos compound, and decomposes | disassembles fibrous asbestos into a granular form or powder form. The asbestos detoxification method for an asbestos-containing composite material according to claim 1, wherein the composite material is a fireproof coating layer formed by spraying on a surface of a building material such as a steel frame. The method for detoxifying an asbestos-containing composite material according to claim 1 or 2, wherein the reaction solution further contains another calcium compound in addition to calcium chloride. The method for detoxifying asbestos of an asbestos-containing composite material according to claim 3, wherein the other calcium compound is calcium carbonate and / or calcium hydroxide. The method for detoxifying an asbestos-containing composite material according to any one of claims 1 to 4, wherein the reaction solution further contains an auxiliary additive compound that forms a molten salt at a low temperature. 6. The asbestos detoxification method for an asbestos-containing composite material according to claim 5, wherein the auxiliary additive compound is a chloride and / or fluoride other than calcium chloride.