JP2007268513A - Method for treating waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating waste, by which a toxic substance can be restrained from being eluted from waste containing the toxic substance, particularly, boron, fluorine, selenium or chromium. <P>SOLUTION: The method for treating waste comprises a mixing step of adding cement and lime to the waste containing the toxic substance and mixing them and a hydrothermal treatment step of subjecting the mixture obtained at the mixing step to hydrothermal treatment. The toxic substance is one or more of boron, fluorine, selenium and chromium. The ratio of the total amount of the cement and lime to be added to the waste to the amount of the waste is 5-60 mass%. The mass ratio of the amount of the lime to be added to the waste to the total amount of the cement and lime to be added to the waste is 0.1-0.9. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to a technical field related to a method for treating waste containing hazardous substances, and relates to a method for treating waste such as coal ash, incinerated ash, and contaminated soil containing harmful substances, in particular, fluorine, The present invention belongs to a technical field related to a waste treatment method for immobilizing harmful substances and controlling their dissolution with respect to wastes containing harmful substances such as boron, selenium and chromium.

  Conventional methods of fixing harmful substances in waste and suppressing the elution of harmful substances include a method of melting at high temperature, a method of solidifying using cement, a method of chemically fixing using a chelating agent, etc. Is known (for example, JP-A-2003-206172).

  However, although the method of melting at a high temperature is effective in preventing elution, it is not an inexpensive processing method because of the high running cost required for melting at a high temperature. Similarly, the method using a chelating agent has the disadvantage that the cost of the chelating agent is high and the processing cost is high, and the immobilization method using a chelate for fluorine and boron which are non-metallic elements. That is difficult. The method of solidifying using cement is an inexpensive method, but the effect of suppressing elution of boron and fluorine is not sufficient, and since cement may contain chromium, it is necessary to remove the waste from the solidified waste. There is a possibility that valent chromium is eluted.

As a method for treating contaminated soil, a technique is known in which mainly heavy metals are mixed, calcium compounds are mixed, and hydrothermal solidification is performed (Japanese Patent Laid-Open No. 2002-320952). This technique relates to a method for treating contaminated soil containing heavy metals.
JP 2003-206172 A JP 2002-320952 A

  The present inventors have already invented a method of fixing fluorine by forming crystalline calcium silicate on waste containing fluorine (Japanese Patent Application 2002-201306). In this method, crystalline calcium silicate (calcium silicate) is formed in the fluorine-containing waste, and fluorine contained in the waste is confined inside by this crystalline calcium silicate to prevent elution to the outside. According to this method, it is possible to effectively suppress the elution of fluorine in the waste, but once the harmful substances such as boron, selenium, and chromium, which are often contained in the incinerated ash together with the fluorine, are included. It was difficult to immobilize and suppress elution.

  The present invention has been made paying attention to such circumstances, and its object is to solve the problems of the prior art and to harmful substances, particularly wastes containing boron, fluorine, selenium and chromium. An object of the present invention is to provide a waste treatment method capable of suppressing the elution of materials.

  In order to achieve the above-mentioned object, the present inventors have conducted intensive studies and have completed the present invention. According to the present invention, the above object can be achieved.

  The present invention, which has been completed in this way and has achieved the above object, relates to a waste processing method, and the waste processing method according to claims 1 to 16 (first to sixteenth inventions). Waste disposal method), which has the following configuration.

  That is, the waste treatment method according to claim 1 includes a mixing step of adding and mixing cement and lime to a waste containing harmful substances, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. It is a waste processing method characterized by having [1st invention].

  The waste treatment method according to claim 2 is the waste treatment method according to claim 1, wherein the harmful substance is one or more of boron, fluorine, selenium, and chromium [second invention].

  The waste treatment method according to claim 3 is the waste treatment method according to claim 1 or 2, wherein the cement is at least one of Portland cement, blast furnace cement, fly ash cement, and silica cement. invention〕.

  The waste processing method according to claim 4 is the waste processing method according to any one of claims 1 to 3, wherein the lime is one or more of quicklime and slaked lime [fourth invention].

  The waste treatment method according to claim 5, wherein the total amount of cement and lime added to the waste is 5 to 60% by mass with respect to the amount of the waste. [5th invention].

  The waste treatment method according to claim 6, wherein the amount of the lime with respect to the total amount of cement and lime added to the waste is 0.1 to 0.9 by mass ratio. It is a processing method of a thing [6th invention].

  The waste treatment method according to claim 7, further comprising a curing treatment step at room temperature for 1 to 14 days before hydrothermal treatment of the mixture obtained by the mixing step. [Seventh Invention].

  The waste treatment method according to claim 8 includes a mixing step of adding and mixing cement and lime to the waste containing chromium, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. This is a featured waste disposal method [eighth invention].

  The waste treatment method according to claim 9 includes a mixing step of adding and mixing a calcium compound to a chromium-containing waste, a curing step of curing the mixture obtained by the mixing step at room temperature for two days or more, And a hydrothermal treatment step of hydrothermally treating the mixture after curing [9th invention].

  The waste treatment method according to claim 10 includes a mixing step of adding and mixing a calcium compound and an iron compound to a chromium-containing waste, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. This is a waste processing method characterized in that [10th invention].

  The waste treatment method according to claim 11 includes a mixing step of adding and mixing cement and lime to a waste containing boron or selenium, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. This is a waste processing method characterized in that [11th invention].

  The waste treatment method according to claim 12 includes a mixing step of adding and mixing a calcium compound and an iron compound to a waste containing arsenic, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. This is a waste processing method characterized in that [12th invention].

  The waste treatment method according to claim 13 includes a mixing step of adding and mixing a calcium compound and an organic acid salt of iron and / or iron phosphate to a waste containing selenium, and a mixture obtained by the mixing step. A waste heat treatment process comprising a hydrothermal treatment step [13th invention].

  The waste treatment method according to claim 14, wherein the calcium compound is at least one of slaked lime, quicklime, Portland cement, blast furnace cement, and fly ash cement. A waste disposal method [14th invention].

  The waste treatment method according to claim 15, wherein the waste is one or more of coal ash, incineration ash, sludge, sludge, slag, and contaminated soil. This is a processing method [15th invention].

  The waste treatment method according to claim 16, wherein the temperature of the hydrothermal treatment is 130 to 300 ° C, and the pressure is a pressure equal to or higher than a saturated water vapor pressure at the temperature. A waste disposal method [16th invention].

  According to the waste processing method according to the present invention, it is possible to suppress the elution of harmful substances with respect to wastes containing harmful substances.

  As described above, the waste processing method according to the present invention includes a mixing step in which cement and lime are added to and mixed with waste containing harmful substances, and a hydrothermal treatment step in which the mixture obtained by the mixing step is hydrothermally treated. A waste processing method characterized by comprising: [First invention].

  According to the waste processing method of the present invention, after adding cement and lime to a waste containing harmful substances such as boron, fluorine, selenium, and chromium, mixing the mixture, and then hydrothermally treating the mixture, the waste Elution of harmful substances such as boron, fluorine, selenium and hexavalent chromium therein can be prevented.

  The present invention can be applied to waste containing boron, fluorine, selenium, chromium, and the like. Examples of the target waste include coal ash, incinerated ash, sludge, sludge, slag, and contaminated soil.

By performing hydrothermal treatment, SiO ₂ in the waste (or in the additive) reacts with calcium compounds such as CaO to produce crystalline calcium silicate (calcium silicate) such as tobermorite. Hazardous substances are effectively taken into crystalline calcium silicates (calcium silicate) such as tobermorite, and the amount of harmful substances can be reduced, but the effect on elements such as boron and selenium is sufficient. However, it is necessary to devise an additive material to be added. That is, by adding both cement and lime to the waste and then hydrothermally treating it, it becomes possible to effectively and sufficiently reduce the amount of the toxic substance eluted.

  In the waste processing method according to the present invention, as the cement, one or more of Portland cement, blast furnace cement, fly ash cement, and silica cement can be used [third invention]. These are used as additives along with lime. As lime, 1 or more types of quick lime and slaked lime can be used [4th invention].

  Regarding the amount of cement and lime to be added to the waste, it is desirable that the total amount be 5 to 60% by mass (wt%) relative to the amount of the waste [fifth invention]. When the total amount is less than 5% by mass, it is difficult to obtain a sufficient effect of fixing harmful substances, and adding over 60% by mass is not preferable from the viewpoint of economy. When the total amount is 5 to 60% by mass, a sufficient effect of fixing harmful substances can be obtained and the economy is excellent. From the viewpoint of immobilization effect of such harmful substances and economical efficiency, it is further desirable that the content is 10 to 40% by mass.

  Regarding the amount of the lime relative to the total amount of cement and lime added to the waste, it is desirable that this is 0.1 to 0.9 by mass ratio [Sixth Invention]. If this amount is less than 0.1 or more than 0.9, the effect on immobilization of harmful substances is reduced. When this amount is 0.1 to 0.9, a sufficient effect of immobilizing harmful substances can be obtained. From the viewpoint of the effect of immobilizing such harmful substances, it is further desirable that the ratio be 0.2 to 0.7.

  An autoclave can usually be used for the hydrothermal treatment. The mixture obtained by the mixing step can be hydrothermally treated immediately after the mixing step, but it can also be hydrothermally treated after curing at room temperature for 1 to 14 days. In this case, the cement is solidified during the curing treatment. Since the reaction proceeds and hydrothermal treatment produces crystalline calcium silicate (calcium silicate) such as tobermorite, a higher effect can be obtained. Therefore, it is desirable to perform the curing treatment as described above. That is, it is desirable to have a step of curing at room temperature for 1 to 14 days before hydrothermal treatment of the mixture obtained by the mixing step [seventh invention].

  The added cement reacts with water to produce calcium silicate hydrate, ettringite, and the like by a hydration reaction. Such a hydrated product has a certain effect on immobilization of harmful substances such as boron, fluorine, selenium and chromium, but this alone is insufficient to suppress the elution of the harmful substances. Crystalline calcium silicates (calcium silicate) such as tobermorite can also be produced by adding only cement and hydrothermally treating it, which is effective in suppressing elution, but it is effective in suppressing elution such as boron, fluorine, selenium, and chromium. In the case of difficult harmful substances, it is necessary to further improve the effect of hydrothermal treatment.

  By adding lime together with cement, the cement solidification reaction is advanced, and at the same time, the added lime increases alkalinity and dissolves silica in the cement and waste. In particular, crystalline calcium silicate (calcium silicate) such as tobermorite can be produced. By using this method, it becomes possible to suppress the elution of harmful substances such as boron, selenium, fluorine and chromium, which were not sufficiently suppressed by the conventional method.

  In hydrothermal treatment, among calcium silicates, it is preferable that crystals grow at a relatively low temperature of about 130 to 300 ° C. to produce tobermorite having high strength. As hydrothermal treatment conditions, reaction temperature (autoclave curing temperature): 130 to 300 ° C., reaction time (curing time): 1 to 24 hours are appropriate, and typical conditions are treatment at a temperature of 180 ° C. for 5 hours. When the reaction temperature is lower than 130 ° C., the tobermorite crystal is not sufficiently grown, and it becomes difficult to increase the effect of suppressing the elution of fluorine. When the reaction temperature exceeds 300 ° C., tobermorite crystals grow and an elution suppression effect can be expected, but the treatment cost becomes too high, which is not preferable from the viewpoint of economy.

  From the above points, the hydrothermal treatment temperature is desirably 130 to 300 ° C. The hydrothermal treatment pressure is preferably set to a pressure equal to or higher than the saturated water vapor pressure at the hydrothermal treatment temperature [16th invention]. When such a pressure is used, it is possible to sufficiently produce crystalline calcium silicate such as tobermorite, and elution of fluorine and the like can be suppressed.

  According to the waste processing method of the present invention, as described above, it is possible to suppress elution of boron, selenium, fluorine, and chromium, which was not sufficiently suppressed by conventional methods. Therefore, the waste treatment method according to the present invention can be suitably used particularly for waste containing one or more of boron, fluorine, selenium, and chromium, and suppress the elution of these harmful substances. [Second invention].

  Examples of the waste to be treated according to the present invention include coal ash, incinerated ash, sludge, sludge, slag, and contaminated soil [15th invention].

  Examples of the waste treatment method for suppressing the elution of chromium in the waste containing chromium include the following [Cr-1] to [Cr-3] waste treatment methods.

  [Cr-1]: This waste treatment method includes a mixing step of adding and mixing cement and lime to a waste containing chromium, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. This is a waste processing method characterized in that [8th invention]. According to this waste processing method, elution of chromium in the waste can be suppressed. Details will be described below.

By performing hydrothermal treatment, SiO ₂ in the waste (or in the additive) reacts with calcium compounds such as CaO to produce crystalline calcium silicate (calcium silicate) such as tobermorite. Then, the chromium in the waste is effectively taken into the crystalline calcium silicate (calcium silicate) such as tobermorite to be generated, and the amount of chromium elution can be reduced. By adding both cement and lime to the waste and then hydrothermally treating it, it becomes possible to effectively and sufficiently reduce the amount of chromium elution.

  Therefore, according to the [Cr-1] waste treatment method (waste treatment method according to the eighth invention), elution of chromium in the waste can be sufficiently suppressed. This waste disposal method can be suitably used particularly for soil contaminated with chromium.

  [Cr-2]: This waste treatment method includes a mixing step of adding and mixing a calcium compound to a chromium-containing waste, and a curing step of curing the mixture obtained by the mixing step at room temperature for two days or more. And a hydrothermal treatment step of hydrothermally treating the cured mixture [9th invention]. According to this waste processing method, elution of chromium in the waste can be suppressed. Details will be described below.

After adding calcium compound to waste containing chromium and mixing it, hydrothermal treatment makes SiO _{2 in} the waste (or in the additive) react with calcium compound such as CaO to produce crystalline calcium such as tobermorite. Generate silicate (calcium silicate). If it does so, chromium will be taken in effectively in crystalline calcium silicates (calcium silicate), such as a tobermorite to produce | generate, and it is possible to reduce chromium elution amount effectively and fully. However, if the chromium concentration is high or the form of chromium is easily dissolved in water, it is difficult to sufficiently suppress the elution of chromium. is necessary. Therefore, a period in which a mixture containing a chromium compound in a waste containing chromium is cured at room temperature before being hydrothermally treated. This is effective in suppressing elution of chromium from the treated product after hydrothermal treatment. The curing period must be 2 days or longer.

  Therefore, according to the [Cr-2] waste treatment method (waste treatment method according to the ninth invention), elution of chromium in the waste can be sufficiently suppressed. The period for curing may be two days or more as described above, but a curing period of about 2 days to 1 week is realistic. The waste treatment method according to the ninth aspect of the invention can be suitably used particularly for soil contaminated with chromium.

  [Cr-3]: This waste treatment method includes a mixing step of adding and mixing a calcium compound and an iron compound to a chromium-containing waste, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. (10th invention). According to this waste processing method, elution of chromium in the waste can be suppressed. Details will be described below.

  As described above, when calcium compounds are added to and mixed with waste containing chromium and then hydrothermally treated, it is possible to reduce the elution amount of chromium, but when the chromium concentration is high or the form of chromium is in water. Since it is difficult to sufficiently suppress elution of chromium when it is in a form that is easily dissolved, a device for obtaining a sufficient effect of suppressing elution of chromium is required. Therefore, the calcium compound is added to and mixed with the waste containing chromium, and the iron compound is added and mixed. This is effective for suppressing elution of chromium from the treated product after the hydrothermal treatment.

  Therefore, according to the [Cr-3] waste treatment method (waste treatment method according to the tenth invention), elution of chromium in the waste can be sufficiently suppressed. This waste disposal method can be suitably used particularly for soil contaminated with chromium.

  As a waste processing method for suppressing the elution of boron or selenium with respect to the waste containing boron or selenium, the following [B · Se] waste processing method can be exemplified.

  [B · Se]: This waste treatment method includes a mixing step of adding and mixing cement and lime to a waste containing boron or selenium, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. [11th invention]. According to this waste processing method, elution of boron and selenium in the waste can be suppressed. Details will be described below.

By performing hydrothermal treatment, SiO ₂ in the waste (or in the additive) reacts with calcium compounds such as CaO to produce crystalline calcium silicate (calcium silicate) such as tobermorite. Then, boron and selenium in the waste are taken into crystalline calcium silicate (calcium silicate) such as tobermorite to be generated, and the elution amount of boron and selenium can be reduced. However, it is not sufficient, and a device for obtaining a sufficient elution suppression effect is required. Then, after adding both cement and lime to the waste, hydrothermal treatment is performed. This makes it possible to effectively and sufficiently reduce the amount of boron and selenium eluted.

  Therefore, according to the waste treatment method [B · Se] (waste treatment method according to the eleventh invention), elution of boron and selenium in the waste can be sufficiently suppressed. This waste treatment method can be suitably used particularly for soil contaminated with boron or selenium.

  As a waste processing method for suppressing arsenic elution of waste containing arsenic, the following [As] waste processing method can be exemplified.

  [As]: This waste treatment method includes a mixing step of adding and mixing a calcium compound and an iron compound to a waste containing arsenic, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step. This is a waste processing method characterized in that [12th invention]. According to this waste treatment method, arsenic elution in the waste can be suppressed. Details will be described below.

After adding calcium compound to waste containing arsenic and mixing it, hydrothermal treatment causes SiO _{2 in} the waste (or in the additive) to react with calcium compound such as CaO to produce crystalline calcium such as tobermorite. Generates silicate (calcium silicate). Then, arsenic can be effectively taken into the crystalline calcium silicate (calcium silicate) such as tobermorite to be generated, and the amount of arsenic eluted can be reduced. However, it is not sufficient, and a device for obtaining a sufficient elution suppression effect is necessary. Therefore, the calcium compound is added and mixed to the waste containing arsenic and the iron compound is added and mixed. This is effective in suppressing elution of arsenic from the treated product after hydrothermal treatment.

  Therefore, according to the [As] waste processing method (waste processing method according to the twelfth aspect of the present invention), the elution of arsenic in the waste can be sufficiently suppressed. This waste treatment method can be preferably used particularly for soil contaminated with arsenic.

  In the waste treatment methods according to the ninth, tenth and twelfth inventions, quick lime, slaked lime, cement and the like can be used as the calcium compound added to the waste. Ferrous sulfate can be suitably used as the iron compound added to the waste. The amount of ferrous sulfate added at this time is preferably 1 to 10% by mass (% by weight). If it is less than 1% by mass, it is difficult to obtain a sufficient chromium elution inhibitory effect, and it is not preferable to add more than 10% by mass from the viewpoint of economy.

  Examples of the waste treatment method for suppressing selenium elution in the waste containing selenium include the following [Se] waste treatment method.

  [Se]: This waste treatment method comprises a mixing step of adding and mixing a calcium compound and an organic acid salt of iron and / or iron phosphate to a waste containing selenium, and a mixture obtained by the mixing step. A waste heat treatment process comprising a hydrothermal treatment step [13th invention]. According to this waste processing method, elution of selenium in the waste can be suppressed. Details will be described below.

Calcium compounds are added to and mixed with waste containing selenium. When this mixture is hydrothermally treated, SiO _{2 in} the waste (or in the additive) reacts with calcium compounds such as CaO, and tobermorite, etc. Of crystalline calcium silicate (calcium silicate). The selenium in the waste is effectively taken into the crystalline calcium silicate (calcium silicate) such as tobermorite that is produced. Therefore, it is possible to reduce the amount of selenium eluted, When the selenium concentration is very high, or when the selenium is present in a form that easily dissolves in water, selenium elution is not sufficiently suppressed, and a device for obtaining a sufficient elution suppression effect is required.

  It is effective to add an organic acid salt of iron and / or an iron phosphate compound to the waste together with the calcium compound.

  Selenite and selenate ions are known to form low-solubility salts with iron, but even if hydrothermal treatment is performed using an iron salt of a strong acid such as sulfate as an additive, sufficient elution suppression is achieved. There is no effect. On the other hand, when an organic acid iron salt or iron phosphate, which is a salt of a weak acid, is used as an additive, a decrease in the pH of the treated product is suppressed, and iron salts of selenic acid and selenious acid having low solubility can be formed. It is possible that the amount of selenium eluted can be effectively reduced by the combined effect of crystal formation by hydrothermal treatment.

  The waste treatment method according to the thirteenth aspect of the present invention (the above-mentioned [Se] waste treatment method) is, as described above, a waste containing selenium with an organic acid salt of calcium compound and iron and / or iron phosphate. And a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step.

  As can be seen from the above, according to the waste processing method according to the thirteenth aspect of the invention (the [Se] waste processing method), a calcium compound is added to and mixed with waste containing selenium. The amount of selenium eluted can be reduced as compared with the case where the resulting mixture is hydrothermally treated. That is, even when the concentration of selenium in the waste is very high or the selenium is present in a form that easily dissolves in water, selenium elution can be sufficiently suppressed, and a sufficient elution suppression effect can be obtained. it can.

  In the waste processing method according to the thirteenth aspect of the present invention (the [Se] waste processing method), as the calcium compound, for example, one or more of slaked lime, quicklime, Portland cement, blast furnace cement, and fly ash cement are used. [14th invention]. Examples of the waste include coal ash.

  After the mixing step, before the mixture is hydrothermally treated, if a period for curing at room temperature is set, the amount of selenium eluted from the treated product after the hydrothermal treatment can be further reduced. The period for curing at room temperature may be 2 days or more, and a curing period of about 2 days to 1 week is realistic.

  Examples of iron organic acid salts include iron citrate and iron oxalate. The amount of iron organic acid salt and / or iron phosphate added is desirably 1 to 10% by mass. If the amount is less than 1% by mass, the elution suppressing effect is lowered. If the amount is 1% by mass or more, a sufficient elution suppressing effect is obtained, and adding over 10% by mass is not preferable from the viewpoint of economy.

  The waste containing selenium (hereinafter also referred to as selenium-containing waste) may contain silica or may not contain silica. When the selenium-containing waste contains silica, if the silica content is sufficient, a calcium compound and an organic acid salt of iron and / or iron phosphate are added to the selenium-containing waste, When the amount is insufficient, the calcium compound and the organic acid salt of iron and / or iron phosphate are added to the selenium-containing waste and silica is added. When the selenium-containing waste does not contain silica, a calcium compound and an organic acid salt of iron and / or iron phosphate are added to the selenium-containing waste and silica is added.

  As a method for insolubilizing and fixing selenium in waste, a method is known in which selenium is insolubilized by generating ettringite by the reaction of gypsum and a calcium compound (such as slaked lime) (Cement and Concrete). Research, Vol 25, No. 3. 658-670, 1995). However, the method of generating ettringite has a problem that the use of recycling is limited because high strength cannot be obtained in the waste after treatment. On the other hand, in the waste processing method according to the thirteenth aspect of the present invention (the [Se] waste processing method), the treated waste has high strength and has a wide range of recycling applications. The effect of reducing the amount of selenium eluted is almost the same.

  In the present invention, the hydrothermal treatment of a mixture is a treatment of heating the mixture in steam, that is, a treatment of exposing the mixture to steam at a high temperature (usually 100 ° C. or higher).

  Examples of the present invention and comparative examples will be described below. The present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. include.

[Example A]
Table 1 shows the conditions and results of treatment of coal ash containing boron, fluorine, and chromium. This processing is roughly divided into two types, processing 1 and processing 2, and these were performed as follows.

<Process 1>:
One or more of normal Portland cement and quicklime and an appropriate amount of water are added to the coal ash containing boron, fluorine, and chromium, and these are uniformly mixed by a mixer, and further granulated by the same mixer. A granulated product was obtained (mixing step including granulation).

<Process 2>:
One or more of normal Portland cement and quicklime and an appropriate amount of water are added to the coal ash containing boron, fluorine, and chromium, and these are uniformly mixed by a mixer, and further granulated by the same mixer. A granulated product was obtained (mixing step including granulation). After this granulated material was cured indoors at room temperature for 2 days, it was subjected to hydrothermal treatment using an autoclave (hydrothermal treatment step). The hydrothermal treatment conditions were as follows: treatment temperature: 180 ° C., treatment pressure: 10 atm, treatment time: 5 hours. This treatment pressure (10 atm) is a pressure equal to or higher than the saturated water vapor pressure (10 atm) at a treatment temperature of 180 ° C.

  The sample after the above treatment was used as a sample, and a toxic substance elution test was performed on the sample. In addition, in the case of the process 1 (when it carries out to granulation), the thing after granulation (namely, granulated material) becomes a sample. In the case of treatment 2 (when hydrothermal treatment is performed), the sample after hydrothermal treatment becomes a sample. The above dissolution test was conducted in accordance with the attached table of Environmental Agency Notification No. 46 “Environmental Standards Concerning Soil Contamination”. The results of this dissolution test (ie, the dissolution amount) are shown in Table 1.

  As can be seen from Table 1, in the case of No. 1, it is the elution amount of boron, hexavalent chromium and fluorine for coal ash itself (when no treatment is performed on coal ash, that is, untreated coal ash), Environmental standard values of 1 mg / liter (hereinafter referred to as L), 0.05 mg / L, and 0.8 mg / L are exceeded. The case of No. 1 corresponds to a comparative example.

  In the case of No.2, 20% by weight (mass%) of cement (hereinafter referred to as wt%), 12% by weight of quick lime and appropriate amount of water are added to coal ash, and the coal ash, cement and quick lime are mixed uniformly by a mixer. And then subjected to a leaching test for harmful substances after curing at room temperature for 7 days. Hydrothermal treatment was not performed. In the case of No. 2, boron and fluorine are less than the amount of elution from coal ash (in the case of No. 1 above), and a certain elution suppression effect is recognized, but still exceeds the environmental standard value. It is a value to be satisfied, and a satisfactory effect cannot be obtained. Moreover, about hexavalent chromium, the elution amount increased rather than the case of the said No. 1 (when nothing is processed for coal ash). Usually, cement often contains chromium, and because cement and quicklime are added, it is assumed that the treated product became alkaline, and the elution amount of hexavalent chromium, which is alkaline and easier to elute, increased. Is done. Here, the amount of cement (wt%) and the amount of quicklime (wt%) are ratios (wt%) to the amount of coal ash (hereinafter the same). The case of No. 2 corresponds to a comparative example.

  In the case of No.3, add 20wt% of cement to coal ash, uniformly mix and granulate with appropriate amount of water, and after 2 days normal temperature curing, treatment temperature: 180 ℃, treatment pressure: 10 atmospheres, Treatment time: Results obtained when hydrothermal treatment was carried out for 5 hours. By carrying out the hydrothermal treatment, the elution amount of hexavalent chromium and fluorine is remarkably reduced, and the elution amount is reduced below the environmental standard value. On the other hand, for boron, although the elution amount is further reduced as compared with the case of No. 2, the environmental standard value is not satisfied. Note that No. 3 corresponds to a comparative example.

  In the case of No.4, the amount of cement added is increased from that in the case of No.3, 40 wt% cement is added, mixed, granulated, cured at room temperature for 2 days, and then hydrothermally treated. Similar to the case of No.3, a remarkable elution suppression effect is recognized for hexavalent chromium and fluorine. On the other hand, no significant improvement was observed for boron compared to No.3. The case of No. 4 corresponds to a comparative example.

  In the case of No.5, 12 wt% of quicklime is added instead of cement, and it is uniformly mixed with coal ash and water by a mixer, granulated, cured at room temperature for 2 days, and then hydrothermally treated. Even if lime is added and hydrothermal treatment is performed, the elution amount of hexavalent chromium and fluorine can be reduced, but the effect of reducing the elution amount of boron is insufficient. Note that No. 5 corresponds to a comparative example.

  In the case of No.6, 20 wt% cement and 12 wt% quick lime are added to coal ash, and after adding the appropriate amount of water and mixing and granulating the mixture, the granulated product is cured at room temperature for 2 days, followed by hydrothermal treatment ( 180 ° C., 10 atm, 5 hours). When both cement and lime are added and hydrothermally treated, the boron elution amount is remarkably reduced together with hexavalent chromium and fluorine, and the elution amount can be reduced to a level that satisfies the environmental standard value. Note that No. 6 corresponds to an example of the present invention, and the requirements of the fifth invention and the requirements of the sixth invention are also satisfied.

  In the case of No. 7, the addition amount of cement and the addition of quicklime are increased from those in the case of No. 6, and 40 wt% and 20 wt% are added, respectively. As in the case of No. 6, the elution amount of boron, hexavalent chromium and fluorine is sufficiently reduced. The case of No. 7 corresponds to an example of the present invention, and satisfies the requirements of the fifth invention and the sixth invention.

  In the case of No.8, 54 wt% cement and 6 wt% quicklime (lime addition / total addition = 0.1) are added, and the elution amount of boron, hexavalent chromium and fluorine is below the environmental standard value. Has been reduced. On the other hand, in the case of No.9 to which 57 wt% cement and 3 wt% quicklime (lime addition / total addition = 0.05) were added, the elution amount of boron and fluorine was suppressed to a sufficiently low value. Chromium elution amount slightly exceeds the environmental standard value. Here, lime addition amount / total addition amount is lime addition amount / [total cement addition amount and lime addition amount] (hereinafter the same). Note that No. 8 corresponds to an example of the present invention, and satisfies the requirements of the fifth and sixth inventions. The case of No. 9 corresponds to the embodiment of the present invention and satisfies the requirements of the fifth invention, but does not satisfy the requirements of the sixth invention and can be positioned as a comparison with No. 8. is there.

  In the case of No.16, cement 4.5 wt%, quick lime 0.5 wt% (lime addition amount / total addition amount = 0.1) is added, and sufficient elution suppression effect of boron, hexavalent chromium and fluorine is obtained. ing. On the other hand, in the case of No. 17 to which 4.75 wt% cement and 0.25 wt% quick lime (lime addition amount / total addition amount = 0.05) were added, a sufficient elution suppression effect was not obtained with hexavalent chromium. The case of No. 16 corresponds to the embodiment of the present invention, and satisfies the requirements of the fifth invention and the sixth invention. The case of No. 17 corresponds to the embodiment of the present invention and satisfies the requirements of the fifth invention, but the requirements of the sixth invention are outside the mass ratio (0.1 to 0.9). It can be positioned as a relative to 16.

  Thus, if the amount of cement added is increased too much compared to the amount of lime added, the amount of hexavalent chromium eluted from the added cement increases, so that a sufficient elution suppression effect cannot be obtained. In order to obtain a sufficient elution suppression effect, the lime addition amount / total addition amount is desirably 0.1 or more. Lime addition amount / total addition amount: When 0.1 or more, a sufficient elution suppression effect can be expected for hexavalent chromium.

  In the case of No.16, the total addition amount of cement and lime is 5 wt%, but a sufficient elution suppression effect is obtained, and if the total addition amount of cement and lime is 5 wt% or more, A sufficient elution suppression effect can be expected.

  In the case of No. 10, 6 wt% cement and 54 wt% quick lime (lime addition / total addition = 0.9) are added. In this case, the elution amount of boron, hexavalent chromium and fluorine is sufficiently suppressed. Yes. Even in the case of No.14, a sufficient elution suppression effect is obtained even when the cement addition amount is 0.5 wt% and the quick lime addition amount is 4.5 wt% (lime addition amount / total addition amount = 0.9). On the other hand, in the case of No.15, 0.25 wt% cement and 4.75 wt% quick lime (lime addition / total addition = 0.95) were added, and the elution amount of hexavalent chromium and fluorine can be reduced. , Boron elution suppression effect is not sufficient. When the addition ratio of cement is too small, it is considered that sufficient calcium silicate hydrate is not formed and the elution suppression effect is not sufficient. The addition ratio of cement and quick lime can be expected to have a sufficient elution suppression effect if the lime addition amount / total addition amount is 0.9 or less, but if the lime addition amount / total addition amount is 0.9 or more, the elution suppression effect is insufficient. The fear that becomes. Note that No. 10 and No. 14 correspond to the examples of the present invention, and satisfy the requirements of the fifth invention and the sixth invention. The case of No. 15 corresponds to the embodiment of the present invention and satisfies the requirements of the fifth invention, but does not satisfy the requirements of the sixth invention and can be positioned as a comparison with No. 14. is there.

  In the case of No.11 and No.12, the total addition amount of cement and lime is 60wt% and 30wt%, and the addition amount of lime / total addition amount is 0.667 and 0.333, respectively, boron, hexavalent chromium, fluorine Sufficient elution suppression effect is exhibited. Note that No. 11 and No. 12 correspond to the examples of the present invention, and the requirements of the fifth invention and the requirements of the sixth invention are also satisfied.

  Table 2 shows the conditions and results of the treatment of coal ash generated in a power generation facility different from the case of Table 1 (that is, cases of Nos. 1 to 17). This coal ash contains boron, fluorine, and chromium.

  In the case of No.18, it is the result of analyzing the leaching amount of harmful substances from coal ash itself (untreated coal ash), and the leaching amount of boron, hexavalent chromium and fluorine exceeds the environmental standard value. . Note that No. 18 corresponds to a comparative example.

  In the case of No.19, 20 wt% of ordinary Portland cement is added to coal ash, an appropriate amount of water is added, and the mixture is uniformly mixed by a mixer, and the granulated product obtained by granulation is treated for 2 days at room temperature. After the curing treatment, hydrothermal treatment was performed in an autoclave under hydrothermal treatment conditions of 180 ° C., 10 atm, and 5 hours. With respect to the amount of elution from the sample (after hydrothermal treatment), a remarkable reduction effect is observed in boron and fluorine, but the effect of boron is not sufficient when compared with the environmental standard value. Hexavalent chromium has a slight elution reduction effect, but the effect is insufficient. Note that No. 19 corresponds to a comparative example.

  In the case of No.20, the amount of cement added was increased to 40 wt% and hydrothermal treatment was performed. As a result, the boron elution amount further decreased. However, the elution amount of hexavalent chromium is not improved compared to the case where the cement addition amount is 20 wt% (in the case of No. 19). The case of No. 20 corresponds to a comparative example.

  In the case of No. 21, 12 wt% lime (total addition amount 32 wt%, lime addition amount / total addition amount = 0.375) was added to coal ash together with 20 wt% cement. Compared with No.19 and No.20, the amount of boron, hexavalent chromium, and fluorine eluted significantly decreased, and the addition of both cement and lime suppresses the release of harmful substances by hydrothermal treatment. The effect is very high. The case of No. 21 corresponds to the embodiment of the present invention, and satisfies the requirements of the fifth invention and the sixth invention.

  In the case of No.22, cement 20wt%, quick lime 9wt% (total addition amount 20wt%, lime addition amount / total addition amount = 0.310) are added, and toxic substances are eluted as in the case of No.21. The amount is sufficiently reduced. The case of No. 22 corresponds to the embodiment of the present invention, and satisfies the requirements of the fifth invention and the sixth invention.

  Table 3 shows the conditions and results of coal ash treatment different from those in Table 1 (No. 1 to 17) and Table 2 (No. 18 to 21). This coal ash contains boron, chromium, and selenium. It also contains fluorine.

  In the case of No.23, it is the dissolution test result for the sample that was added only 23% by weight of cement to coal ash and was subjected to hydrothermal treatment. Although the elution amount of fluorine satisfies the environmental standard value, the elution suppression effect of boron, hexavalent chromium and selenium is not sufficient, and all of them are more than the environmental standard value. Note that No. 23 corresponds to a comparative example.

  On the other hand, in the case of No. 24 and No. 25, in which both cement and quicklime were added to coal ash and hydrothermal treatment was performed, the leaching amount of fluorine was not only below the environmental standard value, but also boron, hexavalent Both chromium and selenium showed a significant reduction in the amount of elution compared to the case of No.23. The cases of No. 24 and No. 25 correspond to the examples of the present invention, and satisfy the requirements of the fifth invention and the sixth invention.

  Table 4 shows the conditions and results of incineration ash treatment. This coal ash contains boron, chromium, and fluorine.

  In the case of No.26, add only 20wt% of cement to incineration ash, add water, mix uniformly, granulate, cure for 2 days, and then autoclave under conditions of 180 ° C, 10 atm, 5 hours. Hydrothermally treated. Among toxic substances, boron and fluorine can be suppressed to below the environmental standard value, but the hexavalent chromium elution amount exceeds the environmental standard value. Note that No. 26 corresponds to a comparative example.

  In the case of No.27, only 12% by weight of quicklime is added to the incinerated ash, water is added, mixed uniformly, granulated, then cured for 2 days, and then autoclaved at 180 ° C, 10 atm for 5 hours. Hydrothermally treated. Among harmful substances, boron and hexavalent chromium have been reduced to less than the environmental standard value, but the amount of fluorine eluted is higher than that of No. 26, and before the environmental standard value is satisfied. Not reached. Note that No. 27 corresponds to a comparative example.

  On the other hand, in the case of No.28, after adding cement 10wt% and quick lime 5wt% (total addition amount 15wt%, lime addition amount / total addition amount = 0.333) to incineration ash, uniformly mixing and granulating After two days of normal temperature curing, hydrothermal treatment was performed under conditions of 180 ° C., 10 atm, and 5 hours. By adding cement and quicklime, the amount of elution is reduced with respect to all boron, hexavalent chromium, and fluorine, which were difficult by themselves, respectively, and the environmental standard value can be cleared. In the case of No. 28, it corresponds to an embodiment of the present invention, and the requirements of the fifth invention and the requirements of the sixth invention are also satisfied.

  In the case of No. 29, add 5% by weight of cement and 2% by weight of quicklime (total added amount 7% by weight, lime added amount / total added amount = 0.286), mix uniformly, granulate, Cured and hydrothermally treated by the same method as in the case. As in the case of No. 28, sufficient elution amount reduction effect is obtained for all of boron, hexavalent chromium and fluorine. The case of No. 29 corresponds to the embodiment of the present invention, and satisfies the requirements of the fifth invention and the sixth invention.

  In the above example, coal ash or incineration ash was used as waste, and the above results were obtained. However, when using one or more of sludge, sludge, slag, and contaminated soil, the absolute value is Although different, the result of the same tendency as described above is obtained, and the amount of harmful substances eluted is reduced in the case of being processed by the processing method according to the present invention.

  When the granulated product is cured, the curing treatment conditions are room temperature curing at room temperature for 2 days. However, when other curing treatment conditions are used, the results of the same tendency as above are obtained although the absolute values are different. It is done.

  In the case of hydrothermal treatment, the hydrothermal treatment conditions were as follows: treatment temperature: 180 ° C., treatment pressure: 10 atm, treatment time: 5 hours. A trend result is obtained.

[Example B]
Table 5 shows the treatment conditions and results of contaminated soil containing chromium. Details of the treatment conditions and results of the contaminated soil containing chromium will be described below.

  Contaminated soil was prepared by adding potassium dichromate to the soil and mixing it uniformly. The chromium concentration in the contaminated soil was adjusted to a concentration of 250 mg / kg, which is the chromium content standard defined in the Soil Contamination Countermeasures Law.

  The prepared contaminated soil was mixed with ordinary Portland cement or quicklime and an appropriate amount of water using a mixer. Moreover, the contaminated soil prepared above, ordinary Portland cement, iron sulfate, and an appropriate amount of water were uniformly mixed with a mixer. The mixture thus obtained was subjected to hydrothermal treatment at high temperature and high pressure using an autoclave without being cured. Further, the mixture thus obtained was subjected to a curing treatment at room temperature for 2 days or more, and then subjected to a hydrothermal treatment at a high temperature and a high pressure using an autoclave. At this time, the standard hydrothermal treatment conditions were as follows: treatment temperature: 180 ° C., treatment pressure: 10 atm, treatment time: 5 hours (some treatment temperatures were 200 ° C.).

  The sample after the hydrothermal treatment was used as a sample, and a hexavalent chromium elution test was performed on this sample. The elution amount of hexavalent chromium in this dissolution test was determined by conducting an analysis in accordance with the attached table of Environmental Agency Notification No. 46 “Environmental Standards Concerning Soil Contamination”. Table 5 shows the results of this dissolution test (that is, the amount of hexavalent chromium eluted).

As can be seen from Table 5, No.1B is the hexavalent chromium elution test result for the contaminated soil itself (when the contaminated soil obtained by the preparation is not treated at all, ie, untreated contaminated soil). The elution amount of hexavalent chromium (Cr ⁶⁺ elution amount) is 15 mg / L, greatly exceeding the environmental standard value of 0.05 mg / L.

  In the case of No.2B, 12 wt% of quicklime and appropriate amount of water are added to the contaminated soil, and the sample mixed uniformly with a mixer is cured at room temperature (room temperature) for 7 days, then hexavalent chromium is eluted. It is the result of having conducted the test. The elution amount of hexavalent chromium is reduced to 0.64mg / L by the stabilization treatment using lime, and a certain elution suppression effect is recognized. However, the elution amount of hexavalent chromium is still a value exceeding the environmental standard value of 0.05 mg / L, and a satisfactory elution suppression effect cannot be obtained by the stabilization treatment in which lime is added.

  In the case of No. 3B, 20 wt% of Portland cement and appropriate amount of water are added to the contaminated soil, and the sample mixed uniformly with a mixer is cured at room temperature for 7 days (cement solidification treatment), and then a hexavalent chromium elution test is performed. It is the result of having gone. Compared to the stabilization treatment with quicklime added, the cement solidification treatment can further reduce the elution amount of hexavalent chromium, but the elution amount exceeds the environmental standard value of 0.05 mg / L.

  In the case of No.4B, add 12wt% of quicklime and appropriate amount of water to the contaminated soil, mix uniformly with a mixer, and then perform hydrothermal treatment at 180 ° C for 5 hours using an autoclave. It is the result of having performed a dissolution test. Compared to No.2B without hydrothermal treatment, the elution amount of hexavalent chromium is remarkably reduced by hydrothermal treatment, and it can be seen that hydrothermal treatment is effective in suppressing elution of hexavalent chromium. . However, since the chromium concentration in the contaminated soil is high and it exists in a form that is easy to elute, it does not reach the environmental standard value.

  In the case of No. 5B, the hydrothermal treatment temperature is different from that of No. 4B, and this temperature is 200 ° C. Except this point, the same treatment as in No. 4B is performed, and then hexavalent chromium It is the result of having carried out the elution test. The elution amount of hexavalent chromium can be further reduced by increasing the temperature of the hydrothermal treatment.

  In the case of No. 6B, cement was used as the solidifying material, and the same hydrothermal treatment as in the case of No. 4B was performed, and then the elution test for hexavalent chromium was conducted. The hexavalent chromium elution amount was 0.049mg / L, which was lower than the environmental standard value of 0.05mg / L. By using cement as compared with the case where quick lime is used as the solidifying material, the elution amount of hexavalent chromium is suppressed to a low level, and it can be seen that it is more effective to use cement as the solidifying material. Although the mechanism by which the elution amount of hexavalent chromium can be suppressed by using cement as the solidification material compared to when quicklime is used is not clear, the silica content in the cement is a crystalline calcium silicate such as tobermorite (silicic acid) during hydrothermal treatment. The amount of elution of hexavalent chromium may be reduced because it becomes a raw material for generating calcium.

  In the case of No. 7B, cement is used as the solidification material, the sample after uniform mixing is cured at room temperature for 2 days in the room, then hydrothermally treated at 180 ° C for 5 hours, and then the hexavalent chromium elution test is performed. It is the result of having performed. It can be seen that the elution amount of hexavalent chromium from the contaminated soil after the hydrothermal treatment is significantly reduced by curing at room temperature after the mixing treatment. By providing a curing period before hydrothermal treatment, the calcium in the solidified material acts as an alkali during the curing period, dissolves silica in the soil, and generates crystalline calcium silicate (calcium silicate) during hydrothermal treatment This is considered to be a result of supplying a large amount of silica.

  In the case of No. 8B, 10 wt% ferrous sulfate was added as an additive at the same time as cement as the solidifying material, hydrothermal treatment was performed after uniform mixing, and then the elution test for hexavalent chromium was performed. is there. The elution amount of hexavalent chromium from the contaminated soil after hydrothermal treatment was 0.008 mg / L, and the elution amount was remarkably suppressed compared to the case where cement was added alone. The elution suppression mechanism when ferrous sulfate is added is not clear, but chromium is confined in the crystalline calcium silicate (calcium silicate) produced during hydrothermal treatment by the chemical reaction between chromium and iron in the contaminated soil. It is thought that it becomes easy to be done.

  In the case of No. 9B, cement and ferrous sulfate are added, and after 2 hours of normal temperature curing treatment after uniform mixing, hydrothermal solidification treatment is performed. By adding ferrous sulfate and curing treatment, it is possible to suppress the elution amount of hexavalent chromium to 0.005 mg / L or less.

  In the case of No. 10B to No. 13B, the effect of the addition amount in the case of adding ferrous sulfate was investigated. As the amount of ferrous sulfate added is increased, the elution amount of hexavalent chromium can be reduced. When the addition amount of ferrous sulfate is 0.5 wt%, the effect of reducing the elution amount of hexavalent chromium is small, and when the addition amount of ferrous sulfate is 1 wt% or more, the effect of reducing the elution amount of hexavalent chromium is increased.

[Example C]
Table 6 shows the treatment conditions and results of contaminated soil containing arsenic. Details of the treatment conditions and results of the contaminated soil containing arsenic will be described below.

  The contaminated soil was prepared by adding sodium arsenite to the soil and mixing it uniformly. The arsenic concentration in the contaminated soil was adjusted to 150 mg / kg, which is the arsenic content standard stipulated in the Soil Contamination Countermeasures Law.

  The above-prepared contaminated soil was mixed with ordinary Portland cement and an appropriate amount of water using a mixer. Moreover, the contaminated soil prepared above, ordinary Portland cement, iron sulfate, and an appropriate amount of water were uniformly mixed with a mixer. The mixture thus obtained was subjected to hydrothermal treatment at high temperature and high pressure using an autoclave without being cured. Further, the mixture thus obtained was subjected to a curing treatment at room temperature for 2 days or more, and then subjected to a hydrothermal treatment at a high temperature and a high pressure using an autoclave. At this time, the hydrothermal treatment conditions were a treatment temperature: 180 ° C., a treatment pressure: 10 atm, and a treatment time: 5 hours.

  The sample after the hydrothermal treatment was used as a sample, and an arsenic elution test was performed on this sample. The amount of arsenic dissolved in this dissolution test was determined by conducting an analysis in accordance with the attached table of Environmental Agency Notification No. 46 “Environmental Standards Concerning Soil Contamination”. Table 6 shows the results of this dissolution test (that is, the amount of arsenic dissolution).

  As can be seen from Table 6, in the case of No. 1C, the arsenic dissolution test results for the contaminated soil itself (the case where no treatment is performed on the contaminated soil obtained by the above preparation, that is, the untreated contaminated soil) The amount of elution was 2.4 mg / L, greatly exceeding the environmental standard value of 0.01 mg / L.

  In the case of No.2C, add 20wt% of cement and appropriate amount of water to the contaminated soil, mix uniformly with a mixer, and then perform hydrothermal treatment at 180 ° C for 5 hours using an autoclave, and then conduct an arsenic elution test. It is the result of having performed. The amount of arsenic elution was reduced to 0.021 mg / L by adding a solidifying material and performing hydrothermal treatment, and adding a solidifying material and performing hydrothermal treatment has a great effect on suppressing arsenic elution. I understand. However, the arsenic elution amount still exceeds the environmental standard value of 0.01 mg / L.

  In the case of No.3C, 20 wt% of cement and 10 wt% of ferrous sulfate were added to the contaminated soil, hydrothermal treatment was performed at 180 ° C for 5 hours, and then the arsenic elution test was conducted. Compared to No.2C without ferrous sulfate, the arsenic elution amount is reduced, and by adding ferrous sulfate, the elution amount can be suppressed to the environmental standard value.

  In the case of No.4C, 20 wt% of cement was added to the contaminated soil, and after 2 days of normal temperature curing treatment, hydrothermal treatment was performed at 180 ° C for 5 hours, and then the arsenic dissolution test was conducted. Compared with the case where curing is not performed, arsenic elution can be suppressed by performing normal temperature curing before hydrothermal treatment, and the elution amount can be reduced to an environmental standard value or less.

  In the case of No. 5C, 20 wt% cement and 10 wt% ferrous sulfate are added to the contaminated soil, and after 2 days of normal temperature curing treatment, hydrothermal treatment is performed at 180 ° C for 5 hours, after which arsenic is eluted. It is the result of having conducted the test. The amount of arsenic elution is reduced to 1/10 of the environmental standard value, and a remarkable elution suppression effect is recognized.

[Example D]
Details of the conditions and results of the treatment of waste containing selenium (selenium-containing waste) will be described below.

  As the selenium-containing waste, coal ash containing selenium (hereinafter also referred to as selenium-containing coal ash) was used. This selenium-containing coal ash contains silica.

  To this selenium-containing coal ash, the solidifying material, additive and appropriate amount of water shown in Table 7 are added (additive may not be added), and mixed uniformly with a mixer. After curing for one day, hydrothermal treatment was performed using an autoclave at 180 ° C. for 5 hours. And the elution test of selenium was done about the mixture (hydrothermally processed material) after this hydrothermal treatment, and the elution amount of selenium was obtained. This dissolution test was conducted in accordance with Environmental Agency Notification No. 46. The results are shown in Table 7.

  As can be seen from Table 7, in the case of No. 1D, the selenium elution test results for selenium-containing coal ash (raw selenium-containing coal ash itself) that has not been treated at all, the selenium elution amount is 0.81 mg / L and the environmental standard value of 0.01 mg / L are greatly exceeded (Comparative Example 1).

  In the case of No.2D, the selenium elution test results of hydrothermally treated product obtained when Portland cement (20% by mass) and quicklime (12% by mass) are used as the solidifying material and no additive is added. is there. By using both cement and lime as solidification materials and hydrothermal treatment, the selenium elution amount was reduced to 0.020mg / L, and although the elution suppression effect was observed, it still exceeded the environmental standard value ( Comparative Example 2).

  In the case of No. 3D, in the case of No. 4D, normal Portland cement (20% by mass) is used as a solidifying material, and ferrous sulfate (5% by mass) or ferric sulfate (5% by mass) is used as an additive. It is the elution test result of the selenium of the hydrothermally processed material obtained when it was used. In any case, although the selenium elution amount is reduced compared to the selenium elution amount from the raw selenium-containing coal ash itself, the elution suppression effect is not sufficient (Comparative Example 3 and Comparative Example 4). .

  In the case of No.5D, the selenium dissolution test results of hydrothermally-treated product obtained when ordinary Portland cement (20% by mass) is used as the solidifying material and iron citrate (5% by mass) is used as the additive. is there. By adding iron citrate as an additive in addition to the solidifying material, the selenium elution amount is remarkably reduced, and the selenium elution amount can be reduced to a level that satisfies the environmental standard value (Example) 1).

  In the case of No. 6D, the selenium elution test results of hydrothermally-treated product obtained when ordinary Portland cement (20% by mass) is used as the solidifying material and iron oxalate (5% by mass) is used as the additive. is there. Although the elution amount of selenium does not satisfy the environmental standard value, the elution amount of selenium is greatly reduced by adding iron oxalate as an additive in addition to the solidified material (Example 2). In the case of No. 6D, the selenium elution amount does not satisfy the environmental standard value, but it satisfies the environmental standard value by increasing the amount of cement added or changing the conditions of hydrothermal treatment. Selenium elution amount can be reduced to the level.

  In the case of No. 6D, the selenium elution test results of hydrothermally-treated product obtained when ordinary Portland cement (20% by mass) is used as the solidifying material and iron phosphate (5% by mass) is used as the additive. is there. By adding iron phosphate as an additive in addition to the solidifying material, the selenium elution amount is remarkably reduced, and the selenium elution amount can be reduced to a level satisfying the environmental standard value (Example 3). ).

  In the above examples and comparative examples, ordinary Portland cement (or Portland cement and quicklime) is used as the calcium compound, but other calcium compounds (slaked lime, blast furnace cement, fly ash cement, etc.) are used. In the case of the above, a result having the same tendency as in the case of the example and the comparative example can be obtained. In the case of the above examples and comparative examples, iron citrate and iron oxalate are used as the organic acid salt of iron, but the above examples and comparative examples are also used when other iron organic acid salts are used. The result of the same tendency as in the case of. In the case of the above examples and comparative examples, the hydrothermal treatment is performed under the conditions of 180 ° C. and 5 hours, but also when performed under other conditions, the same tendency as in the case of the above examples and comparative examples is observed. Results are obtained.

  Moreover, in the case of the said Example and comparative example, although the selenium containing coal ash is used as a selenium containing waste, when using other selenium containing wastes (incineration ash containing selenium, etc.), The result of the tendency similar to the case of the said Example and a comparative example is obtained.

The waste treatment method according to the present invention is preferably used as a waste treatment method for immobilizing harmful substances and controlling their dissolution with respect to wastes containing harmful substances such as fluorine, boron, selenium and chromium. Can be useful.

Claims (16)

  A waste treatment method comprising a mixing step of adding cement and lime to a waste containing harmful substances and mixing, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step.   The waste treatment method according to claim 1, wherein the harmful substance is one or more of boron, fluorine, selenium, and chromium.   The waste treatment method according to claim 1 or 2, wherein the cement is at least one of Portland cement, blast furnace cement, fly ash cement, and silica cement.   The waste treatment method according to claim 1, wherein the lime is one or more of quicklime and slaked lime.   The waste processing method according to any one of claims 1 to 4, wherein a total amount of cement and lime added to the waste is 5 to 60% by mass with respect to the amount of the waste.   The method for treating waste according to any one of claims 1 to 5, wherein an amount of the lime with respect to a total amount of cement and lime added to the waste is 0.1 to 0.9 by mass ratio.   The waste treatment method according to any one of claims 1 to 6, further comprising a curing treatment step at room temperature for 1 to 14 days before hydrothermal treatment of the mixture obtained by the mixing step.   A waste treatment method comprising: a mixing step of adding cement and lime to a waste containing chromium and mixing; and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step.   A mixing step of adding and mixing a calcium compound to a waste containing chromium, a curing step of curing the mixture obtained by the mixing step at room temperature for two days or more, and a hydrothermal treatment step of hydrothermally treating the mixture after curing A waste treatment method comprising:   A waste treatment method comprising a mixing step of adding and mixing a calcium compound and an iron compound to a waste containing chromium, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step.   A waste treatment method comprising: a mixing step of adding and mixing cement and lime to a waste containing boron or selenium; and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step.   A waste treatment method comprising: a mixing step of adding and mixing a calcium compound and an iron compound to a waste containing arsenic; and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step.   A mixing step of adding and mixing a calcium compound and an organic acid salt of iron and / or iron phosphate to a waste containing selenium, and a hydrothermal treatment step of hydrothermally treating the mixture obtained by the mixing step Waste disposal method.   The waste treatment method according to any one of claims 9, 10, 12, and 13, wherein the calcium compound is at least one of slaked lime, quicklime, Portland cement, blast furnace cement, and fly ash cement.   The method for treating waste according to any one of claims 1 to 14, wherein the waste is one or more of coal ash, incineration ash, sludge, sludge, slag, and contaminated soil. The waste treatment method according to any one of claims 1 to 15, wherein a temperature of the hydrothermal treatment is 130 to 300 ° C and a pressure is a pressure equal to or higher than a saturated water vapor pressure at the temperature.