JP4584874B2 - Waste treatment method and treatment apparatus - Google Patents

Description

  The present invention belongs to a technical field related to a waste processing method and a processing apparatus.

  When soil and incineration ash containing harmful heavy metals come into contact with environmental water such as rain water, elution of heavy metals occurs and pollutes soil, groundwater, rivers, seawater, and the like. For this reason, it is disposed of in landfill after stabilizing heavy metals in the incineration fly ash by treating with cement solidification method, chemical addition method, melt solidification method and the like.

  However, these conventional methods still have many problems to be solved. For example, in the cement solidification method, since the cement added as a solidifying agent may contain chromium, hexavalent chromium may be eluted from the waste after the solidification treatment. In the chemical addition method, the cost of the chelating chemical to be added is high, and the treated soil and incinerated ash lose strength, making handling difficult. In the melt solidification method, the equipment cost for processing at a high temperature is high, and the equipment scale becomes complicated.

The present inventors have already proposed a hydrothermal treatment method that is an effective and less expensive elution prevention method for soil and incinerated ash containing heavy metals [Japanese Patent Laid-Open No. 2002-320952 ( Contaminated soil treatment method and treated product), Japanese Patent Application Laid-Open No. 2004-41890 (treatment method for fluorine-containing waste), Japanese Patent Application Laid-Open No. 2003-286066 (method for producing solidified body)]. However, in the hydrothermal treatment method, the object to be treated is heated with water vapor, so that the condensed water vapor becomes drain water, and it is inevitable that the drain water contacts the object to be treated and wets the object to be treated. If the hydrothermal reaction has progressed sufficiently and elution of heavy metals has been suppressed, even if drain water comes into contact with the material to be treated, heavy metals will not be eluted from the material to be treated, but the reaction is insufficient In particular, when drain water comes into contact with the temperature rising process to the reaction temperature, heavy metals are eluted from the material to be treated, and as a result, water containing heavy metals is discharged from the autoclave. It was found that it was necessary to install equipment for treating the water (drainage) containing this heavy metal.
JP 2002-320952 JP JP 2004-41890 A JP2003-286066

  The present invention has been made paying attention to such circumstances, and its purpose is to hydrothermally treat a mixture obtained by mixing a calcium compound and water with waste containing heavy metal, or further mixing silica. In doing so, an object of the present invention is to provide a waste treatment method and a treatment apparatus capable of treating wastewater containing heavy metals generated during hydrothermal treatment without providing wastewater treatment facilities.

  In order to achieve the above object, the present inventors have intensively studied, and as a result, completed the present invention. According to the present invention, the above object can be achieved.

  The present invention thus completed and capable of achieving the above object relates to a waste processing method and a processing apparatus, and the waste processing method according to claims 1 to 8 (first aspect). The waste processing apparatus according to any one of claims 9 to 10, which is configured as follows.

  That is, the waste treatment method according to claim 1 is a waste having a hydrothermal treatment step of hydrothermally treating a mixture obtained by mixing a calcium compound and water with a waste containing heavy metal, or further mixing silica. In this treatment method, when the hydrothermal treatment step is performed twice or more, the waste water containing heavy metal generated during the hydrothermal treatment in the preceding hydrothermal treatment step is mixed with water in the subsequent hydrothermal treatment step. Alternatively, it is a waste processing method characterized in that it is used as a part thereof [first invention].

  The waste treatment method according to claim 2 is the waste treatment method according to claim 1, wherein the calcium compound is at least one of slaked lime, quicklime, Portland cement, blast furnace cement, and fly ash cement. invention〕.

  The waste processing method according to claim 3 is the waste processing method according to claim 1 or 2, wherein the waste contains silica [third 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 waste is one or more of soil and incinerated ash [fourth invention].

  The disposal method according to claim 5, wherein the amount of the calcium compound in the mixture is 3 to 40% by mass with respect to the amount of silica in the mixture. It is a processing method of a thing [5th invention].

  The waste treatment method according to claim 6, wherein the amount of waste water containing the mixed water or heavy metal used as a part thereof is 10 to 60% by mass with respect to the total amount of calcium compound and silica in the mixture. A waste disposal method according to any one of claims 1 to 5 [Sixth Invention].

  The waste treatment method according to claim 7, wherein the hydrothermal treatment in the hydrothermal treatment step is performed for 1 to 48 hours in the presence of saturated steam at 130 to 300 ° C. [Seventh Invention].

  The waste treatment method according to claim 8, wherein the heavy metal is one or more of lead, arsenic, selenium, chromium, mercury, lead, cadmium, and boron. It is a processing method [8th invention].

  A waste treatment apparatus according to claim 9 is a waste treatment apparatus for performing the waste treatment method according to any one of claims 1 to 8, and is filled with a mixture for hydrothermal treatment in an autoclave. In a waste treatment apparatus having a piping and a pressure reducing valve for discharging water discharged from the autoclave to the outside of the autoclave, a receiver for receiving the water discharged from the hydrothermal treatment container; A waste disposal apparatus having a pipe and a pressure reducing valve for discharging water received by the receiver to the outside of the autoclave [9th invention].

  The waste treatment apparatus according to claim 10, further comprising protective means for preventing condensed water generated outside the hydrothermal treatment container in the autoclave from entering the hydrothermal treatment container. [Tenth Invention]

  According to the waste treatment method of the present invention, when a mixture obtained by mixing calcium compound and water with waste containing heavy metal or further mixing silica is hydrothermally treated, it is generated during hydrothermal treatment. Wastewater containing heavy metals can be treated without providing wastewater treatment equipment.

  According to the waste processing apparatus according to the present invention, the waste processing method according to the present invention can be performed. As a result, the wastewater containing the heavy metal generated in the hydrothermal treatment can be treated without providing a wastewater treatment facility.

  In order to achieve the above-mentioned object, the present inventors have conducted intensive research. As a result, when wastewater containing heavy metal is mixed with the object to be treated and hydrothermally treated, the drainage mixed with the object to be treated is treated in the same way that heavy metals in the object to be treated are suppressed from being eluted by hydrothermal treatment. It was found that heavy metal contained therein was also suppressed by hydrothermal treatment.

  The present invention has been completed based on such knowledge, and it relates to a waste processing method and a processing apparatus. In the waste processing method and processing apparatus according to the present invention thus completed, first, the waste processing method according to the present invention is a method of mixing calcium compounds and water with waste containing heavy metals, Alternatively, it is a waste treatment method having a hydrothermal treatment step of hydrothermally treating a mixture obtained by further mixing silica, and when the hydrothermal treatment step is performed twice or more, the hydrothermal treatment step in the preceding hydrothermal treatment step is performed. A waste treatment method characterized in that wastewater containing heavy metals generated at the time is used as water to be mixed or a part thereof in a subsequent hydrothermal treatment step [first invention].

  In the waste treatment method according to the present invention, wastewater containing heavy metal generated during hydrothermal treatment in the preceding hydrothermal treatment step (hereinafter also referred to as heavy metal-containing wastewater) is mixed in the subsequent hydrothermal treatment step. Use as water or part of it. That is, the heavy metal-containing wastewater generated during the hydrothermal treatment in the preceding hydrothermal treatment step is mixed with the mixture to be hydrothermally treated in the subsequent hydrothermal treatment step. Accordingly, as can be seen from the above knowledge, in the subsequent hydrothermal treatment step, the drainage mixed with the above mixture is controlled in the same manner as the heavy metals in the waste in the mixture are suppressed from being eluted by the hydrothermal treatment. Elution of heavy metals in the heavy metal-containing wastewater generated during the hydrothermal treatment in the preceding hydrothermal treatment step is also suppressed by the hydrothermal treatment.

  In this way, the heavy metal-containing wastewater generated during the hydrothermal treatment in the preceding hydrothermal treatment step can be treated in the subsequent hydrothermal treatment step.

  Therefore, according to the waste processing method according to the present invention, it is possible to treat heavy metal-containing wastewater generated during hydrothermal treatment without providing wastewater treatment equipment.

  In addition, since the heavy metal-containing wastewater generated during the hydrothermal treatment in the preceding hydrothermal treatment process is used as water to be mixed or a part thereof in the subsequent hydrothermal treatment process, only that much is used in the subsequent hydrothermal treatment process. The amount of clean water to be newly mixed can be reduced. Therefore, when water is mixed in the hydrothermal treatment step, the required amount of clean water can be reduced, thereby improving the economic efficiency.

  Here, the subsequent hydrothermal treatment step is a hydrothermal treatment step performed after the preceding hydrothermal treatment step. The subsequent hydrothermal treatment step is not limited to the hydrothermal treatment step performed after the preceding hydrothermal treatment step, and includes a hydrothermal treatment step performed after the hydrothermal treatment step. The preceding hydrothermal process is a hydrothermal process that is performed before the subsequent hydrothermal process. The preceding hydrothermal treatment step is not limited to the hydrothermal treatment step performed first, and may be a hydrothermal treatment step performed after the hydrothermal treatment step.

  In the waste processing method according to the present invention, the hydrothermal treatment step is a hydrothermal treatment of a mixture obtained by mixing calcium compound and water with waste containing heavy metal, or further mixing silica. At this time, the waste containing heavy metal (hereinafter also referred to as heavy metal-containing waste) may contain silica or may contain no silica. When the heavy metal-containing waste contains silica and the silica content is sufficient (sufficient to suppress elution of heavy metals by hydrothermal treatment), it can be obtained by mixing this waste with a calcium compound and water. The mixture is hydrothermally treated. If the heavy metal-containing waste does not contain silica or if the silica content is insufficient even if silica is contained (insufficient to suppress heavy metal elution by hydrothermal treatment), the waste will contain calcium. In addition to mixing the compound and water, the mixture obtained by mixing silica is subjected to hydrothermal treatment. From these, the hydrothermal treatment step in the waste processing method according to the present invention is a step of hydrothermally treating a mixture obtained by mixing calcium compound and water with heavy metal-containing waste or further mixing silica. It was.

  In the waste treatment method according to the present invention, as the calcium compound, for example, one or more of slaked lime, quicklime, Portland cement, blast furnace cement, and fly ash cement can be used [second invention].

  As described above, there are cases where the heavy metal-containing waste contains silica and cases where it does not contain silica. When the heavy metal-containing waste contains silica, if the silica content is sufficient, a mixture obtained by mixing the waste with a calcium compound and water may be hydrothermally treated. When the amount is insufficient, not only the calcium compound and water are mixed with the waste, but also the mixture obtained by mixing silica is hydrothermally treated [third invention].

  Examples of the heavy metal-containing waste include soil and incinerated ash, and one or more of these can be used [fourth invention].

In the hydrothermal treatment step, silica (SiO ₂ ) in the heavy metal-containing waste or the silica added and mixed with the calcium compound is reacted by hydrothermal treatment to produce crystalline calcium silicate (calcium silicate) such as tobermorite. Heavy metals in heavy metal-containing waste and wastewater mixed with heavy metal-containing waste by this crystalline calcium silicate (heavy metal-containing wastewater generated during hydrothermal treatment in the previous hydrothermal treatment process) It is confined to (immobilized) and is prevented from elution to the outside.

  In order to achieve such a high level of elution suppression effect, it is desirable that the amount of calcium compound in the mixture subjected to hydrothermal treatment is 3 to 40% by mass with respect to the amount of silica [No. 5 invention]. When this amount is less than 3% by mass or more than 40% by mass, the effect of immobilizing heavy metals is reduced. When this amount is 3 to 40% by mass, the effect of immobilizing heavy metals becomes a high level. From the viewpoint of the effect of immobilizing such heavy metals, it is further desirable that this amount be 5 to 25% by mass.

  In the waste treatment method according to the present invention, the heavy metal-containing wastewater generated during the hydrothermal treatment in the preceding hydrothermal treatment step is used as water or a part thereof mixed in the subsequent hydrothermal treatment step. The amount of the mixed water or heavy metal-containing wastewater used as a part thereof is desirably 10 to 60% by mass with respect to the total amount of calcium compound and silica in the mixture subjected to hydrothermal treatment [Sixth Invention]. This is because soil and incineration ash containing heavy metals generally contain fine particle components, and by using water as a binder, the fine particle components are prevented from going out of the reaction vessel during hydrothermal treatment. It is desirable to specify the amount of moisture. That is, when the amount of water added is less than 10% by mass, the fine particle component becomes dusty and dissipates from the reaction vessel, or leaks into the heavy metal drainage pipe at the bottom of the reaction vessel accompanying the drain water generated during the reaction. End up. On the other hand, if the amount of water added exceeds 60% by mass, the heavy metal-containing waste becomes a slurry and leaks into the heavy metal drainage pipe at the bottom of the reaction vessel. From this point, this amount is preferably 10 to 60% by mass, and further preferably 20 to 45% by mass.

  It is desirable to perform the hydrothermal treatment in the hydrothermal treatment step for 1 to 48 hours in the presence of saturated steam at 130 to 300 ° C. [Seventh Invention]. The reason is as follows. 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. For this reason, as hydrothermal treatment conditions, reaction temperature: 130-300 degreeC and reaction time: 1-48 hours are suitable. When the reaction temperature is lower than 130 ° C., the tobermorite crystal is not sufficiently grown, and it is difficult to achieve a high level of suppression effect of heavy metal elution. 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.

  Examples of heavy metals in waste containing heavy metals and wastewater containing heavy metals include lead, arsenic, selenium, chromium, mercury, lead, cadmium, and boron. There are cases of containing one of these and cases of containing two or more [eighth invention].

  A waste treatment apparatus according to the present invention is a waste treatment apparatus for performing any one of the waste treatment methods according to the present invention (first to eighth inventions), and hydrothermally heats the autoclave. A hydrothermal treatment container filled with the mixture is disposed, and receives water discharged from the hydrothermal treatment container in a waste treatment apparatus having a piping and a pressure reducing valve for discharging water discharged from the autoclave to the outside of the autoclave. A waste disposal apparatus comprising a receiver, a pipe for discharging water received by the receiver to the outside of the autoclave, and a pressure reducing valve [9th invention].

  Here, it is assumed that the mixture filled in the hydrothermal treatment container is a mixture containing a heavy metal and a calcium compound and clean water, or further mixed with silica. When steam is introduced into the autoclave and then heated, the mixture filled in the hydrothermal treatment container is hydrothermally treated. Water vapor condensed during this hydrothermal treatment becomes drain water, and a part of this drain water comes into contact with the mixture, and heavy metals are eluted from this mixture, resulting in heavy metal-containing wastewater (drainage containing heavy metals). The heavy metal-containing wastewater is received by a receiver, discharged to the outside of the autoclave through a pipe and a pressure reducing valve, and enters a heavy metal-containing wastewater container. The remainder of the drain water (drain water not in contact with the mixture) is discharged out of the autoclave via a pipe and a pressure reducing valve different from the above, and enters a container (a heavy metal-free drainage container) separate from the above.

  After completion of the hydrothermal treatment, water vapor is exhausted from the autoclave and the temperature in the autoclave is lowered. Thereafter, the hydrothermal treatment container is taken out from the autoclave together with the hydrothermally treated mixture. The hydrothermal treatment process is referred to as the preceding hydrothermal treatment process.

  In the preceding hydrothermal treatment step, the heavy metals in the waste in the mixture are suppressed from being eluted by the hydrothermal treatment. That is, such a mixture with suppressed elution is obtained.

  A mixture to be hydrothermally treated in a subsequent hydrothermal treatment step is prepared. This mixture is obtained by mixing a calcium compound and water with waste containing a heavy metal, or further mixing silica. At this time, the heavy metal containing wastewater put into the heavy metal containing wastewater container in the preceding hydrothermal treatment process is used as the water to be mixed or a part thereof. That is, this heavy metal-containing wastewater is mixed. If the amount of water is insufficient only by mixing this heavy metal-containing wastewater, water other than this heavy metal-containing wastewater is also mixed. As water other than this heavy metal containing waste water, industrial water, tap water, etc. can be used, for example.

  The mixture thus obtained is filled into a hydrothermal treatment container, which is placed in an autoclave, and steam is put into the autoclave and then heated. Then, the mixture filled in the hydrothermal treatment container is hydrothermally treated. Water vapor condensed during this hydrothermal treatment becomes drain water, and a part of this drain water comes into contact with the mixture, and heavy metals are eluted from this mixture. As a result, heavy metal-containing wastewater is generated, and this heavy metal-containing wastewater is received. It is received by the vessel, discharged out of the autoclave through the piping and pressure reducing valve, and enters the heavy metal containing drainage container. The remainder of the drain water (drain water not in contact with the mixture) is discharged out of the autoclave via a pipe and a pressure reducing valve different from the above, and enters a container (a heavy metal-free drainage container) separate from the above.

  After completion of the hydrothermal treatment, water vapor is exhausted from the autoclave and the temperature in the autoclave is lowered. Thereafter, the hydrothermal treatment container is taken out from the autoclave together with the hydrothermally treated mixture.

  In the subsequent hydrothermal treatment step, the heavy metal in the waste in the mixture is suppressed from being eluted by the hydrothermal treatment, and the heavy metal in the mixed heavy metal-containing waste water is also suppressed from being eluted by the hydrothermal treatment. That is, such a mixture with suppressed elution is obtained.

  As can be seen from the above, according to the waste processing apparatus of the present invention, the waste processing method of the present invention can be performed. As a result, the wastewater containing the heavy metal generated in the hydrothermal treatment can be treated without providing a wastewater treatment facility.

  In addition, a hydrothermal treatment container filled with a mixture to be hydrothermally treated is disposed in the autoclave, and is a waste treatment apparatus having a pipe and a pressure reducing valve for discharging water discharged from the autoclave to the outside of the autoclave. In the case of a device that does not have a receiver for receiving water (heavy metal containing wastewater) discharged from the heat treatment vessel, the drainage containing heavy metal that is not in contact with the mixture (drainage containing no heavy metal) ) And is discharged out of the autoclave and mixed into the container. The wastewater that has entered this container is heavy metal-containing wastewater (heavy metal-containing wastewater in the preceding hydrothermal treatment step). However, the amount of heavy metal-containing wastewater in the preceding hydrothermal treatment step is significantly larger than the amount of water required to obtain the mixture in the subsequent hydrothermal treatment step [for example, in the case of the comparative example described later (12.4 Ton / 4.9 ton) times = 2.53 times more], part of the heavy metal-containing wastewater from the preceding hydrothermal treatment process can be used to obtain the mixture in the subsequent hydrothermal treatment process, but the rest should be used Therefore, most of the heavy metal-containing wastewater in the preceding hydrothermal treatment process cannot be hydrothermally treated and remains. As a result, a separate facility for treating this heavy metal-containing wastewater is required.

  On the other hand, in the case of the waste treatment apparatus according to the present invention, the heavy metal-containing wastewater discharged from the hydrothermal treatment container and the drain water that does not come into contact with the mixture (heavy metal-free wastewater) are separated separately. It can be discharged out of the autoclave and put into separate containers. The amount of this heavy metal-containing wastewater (heavy metal-containing wastewater in the preceding hydrothermal treatment step) is less than the amount of water required to obtain the mixture in the subsequent hydrothermal treatment step (for example, in the case of the examples described later, 4.9 tons-4 tons = 0.9 tons less), so that all of the heavy metal-containing wastewater from the preceding hydrothermal treatment step can be used to obtain a mixture in the subsequent hydrothermal treatment step. it can. Therefore, it is not necessary to provide a separate wastewater treatment facility.

  In view of this, the waste treatment apparatus according to the present invention also has a receiver for receiving water discharged from the hydrothermal treatment container, and further for discharging the water received by the receiver to the outside of the autoclave. A pipe and a pressure reducing valve are also provided. That is, as described above, the heavy metal-containing wastewater discharged from the hydrothermal treatment vessel and the drain water that did not come into contact with the mixture (heavy metal-free wastewater) are separately discharged outside the autoclave and separated into separate containers. In order to be able to put in, a hydrothermal vessel filled with a mixture to be hydrothermally treated is disposed in the autoclave, and waste having a pipe and a pressure reducing valve for discharging water discharged from the autoclave to the outside of the autoclave This processing apparatus has a receiver for receiving water discharged from the hydrothermal treatment container, and a pipe and a pressure reducing valve for discharging water received by the receiver to the outside of the autoclave.

  In the waste treatment apparatus according to the present invention, when the condensed water generated outside the hydrothermal treatment container in the autoclave is provided with a protective means for preventing entry into the hydrothermal treatment container, the mixture filled in the hydrothermal treatment container The amount of water in contact with is reduced. Therefore, the elution amount of heavy metals from this mixture decreases, and the generation amount of heavy metal-containing wastewater decreases. As a result, the amount of heavy metal-containing wastewater that needs to be mixed and hydrothermally treated in the subsequent hydrothermal treatment step is reduced [10th invention].

  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.

  In FIG. 1, the temperature rising pattern in the process of hydrothermally treating heavy metal containing soil and incineration ash is shown. An object to be treated mixed with an additive such as slaked lime at room temperature is heated by pressurized steam in an autoclave. The temperature rise time (T1) in FIG. 1 is the time until the workpiece reaches the same temperature as the water vapor. During this time, the condensed water vapor (condensed water) wets the workpiece, and the drain contains heavy metals. It becomes water. The holding time (T2) in FIG. 1 is after the workpiece is heated to the same temperature as the water vapor. During this time, only water vapor condensation occurs for the autoclave to dissipate heat to the outside air. Since the drain water wets the inner wall of the autoclave, heavy metals are not eluted from the object to be treated. The temperature lowering time (T3) in FIG. 1 is after the hydrothermal treatment of the object to be treated is completed. During this time, since the elution of heavy metals in the object to be processed has already been suppressed, the heavy metals will not be eluted from the object to be processed even when the drain water comes into contact therewith. Therefore, only drain water generated by condensation during the temperature raising time in FIG. 1 may contain heavy metals.

  FIG. 2 shows a processing flow in the waste processing method according to the first embodiment. Raw material 1 (object to be treated) is incinerated ash containing silica. This article to be treated is mixed with clean water and an additive (slaked lime), molded into a granulated product having a diameter of about 5 mm or less, and then hydrothermally treated ( Hereinafter, this was also referred to as No. 1 hydrothermal treatment) (hereinafter, this process is also referred to as No. 1 hydrothermal process). No. 1 hydrothermal treatment yielded hydrothermally treated product 1, drained water 1 containing heavy metal discharged during temperature rise, and drained water 2 not containing heavy metal discharged during holding time and temperature falling time. The heavy metal-containing drain water 1 generated during the heating (T1) time was 4 tons and the heavy metal-free drain water 2 was 8.4 tons per 10 tons of dry weight of the raw material (processed material). .

  Next, the same raw material 1 (incinerated ash containing silica), additive (slaked lime), the above heavy metal-containing drain water 1 and clean water as in the case of No. 1 hydrothermal treatment step are mixed. In the same manner as in the hydrothermal treatment step, granulation and hydrothermal treatment (hereinafter also referred to as No. 2 hydrothermal treatment) were performed to obtain hydrothermally treated product 2 (hereinafter, this step is also referred to as No. 2 hydrothermal treatment step). ). At this time, since the water weight necessary for mixing and granulation was 4.9 tons, all of the heavy metal-containing drain water 1 (4 tons) was added as water, and water 0.9. Tons were added.

  FIG. 3 shows a processing flow in the waste processing method according to Comparative Example 1. Raw material 1 (object to be treated) is incinerated ash containing silica similar to that in Example 1. This object to be treated is mixed with clean water and an additive (slaked lime), and the same as in Example 1 above. After forming into a granulated product having a diameter of about 5 mm or less, hydrothermal treatment (Comparative Example 1) was performed. By hydrothermal treatment, hydrothermally treated product 3, heavy metal-containing drain water 3 discharged during temperature rise, holding time and temperature fall time was obtained. The weight of this heavy metal-containing drain water 3 was 12.4 tons.

  Table 1 shows raw water 1, hydrothermally treated product 1 and hydrothermally treated product 2 obtained in No. 1 hydrothermal process and No. 2 hydrothermal process in Example 1, and water obtained in Comparative Example 1. The heavy metal elution amount for each of the heat-treated products 3 is shown. In addition, heavy metal-containing drain water 1 discharged in No. 1 hydrothermal treatment step of Example 1, heavy metal-free drain water 2 and heavy metal-containing drain water 3 discharged in the case of Comparative Example 1 The concentration is also shown.

  In the case of raw material 1, the elution amounts of arsenic (As) and selenium (Se) exceeded the environmental standard (both 0.01 mg / L). In the case of No. 1 hydrothermal treatment step of Example 1, only clean water was used as water, and the amount of elution of heavy metal in the obtained hydrothermal treatment product 1 was below the environmental standard. In the case of the No. 1 hydrothermal treatment step of Example 1, the heavy metal-containing drain water 1 generated during the temperature rise exceeded the environmental standards for both arsenic and selenium, but the drain water 2 generated during the holding and temperature lowering was The heavy metal concentration was below the environmental standard.

  In the case of No. 2 hydrothermal treatment step of Example 1, the total amount (4 tons) of drain water 1 containing heavy metals and clean water (0.9 tons) are used as water, and the resulting heavy metals of hydrothermally treated product 2 are used. The amount of elution was below the environmental standard. Therefore, even if the water added to the raw material contains heavy metals as shown in Table 1, elution of heavy metals in the obtained hydrothermally treated product can be suppressed if a sufficient reaction proceeds in the subsequent hydrothermal treatment.

  This is because the heavy metals in the drain water containing heavy metals added to and mixed with the raw materials are suppressed by the hydrothermal treatment, similarly to the heavy metals in the raw materials being suppressed by the hydrothermal treatment. Because. In this way, the heavy metal-containing wastewater generated during the hydrothermal treatment in the preceding hydrothermal treatment step (No. 1 hydrothermal treatment step) is treated in the subsequent hydrothermal treatment step (No. 2 hydrothermal treatment step). Can do. Therefore, it is possible to treat heavy metal-containing wastewater generated during the hydrothermal treatment in the preceding hydrothermal treatment step without providing a wastewater treatment facility.

  In the case of Comparative Example 1, the heavy metal-containing drain water 3 generated during the temperature rising / holding and temperature lowering of the hydrothermal treatment contained heavy metals, and the selenium concentration exceeded the environmental standard. In the case of Comparative Example 1, this heavy metal-containing drain water 3 does not employ a process of using it as mixed water in the subsequent hydrothermal treatment step. Therefore, in addition to the autoclave, it is necessary to separately install a wastewater treatment facility for treating the drainage 3 (drainage) containing this heavy metal.

  4 to 5 show examples of the waste processing apparatus according to the present invention. In any case, the apparatus shown in FIGS. 4 to 5 is provided with a hydrothermal treatment container filled with a mixture to be hydrothermally treated in the autoclave, a pipe for discharging water discharged from the autoclave to the outside of the autoclave, and a reduced pressure. It has a valve and a receiver for receiving water discharged from the hydrothermal treatment vessel, and a pipe and a pressure reducing valve for discharging water received by the receiver to the outside of the autoclave. There is a mouth (hole) for drain water discharge at the bottom of the hydrothermal treatment container. According to this apparatus, the drain water which does not contact the drain water which contacted the mixture (to-be-processed object) can be discharged | emitted separately. The waste treatment apparatus according to the present invention is not limited to the structure shown in FIGS. 4 to 5, and may be any structure that can separately discharge drain water that does not come into contact with drain water that comes into contact with the object to be treated.

  FIG. 6 shows an example of a waste treatment apparatus according to the tenth aspect of the present invention. In the apparatus shown in FIG. 6, a lid is provided in the hydrothermal treatment container. This lid can prevent the drain water condensed at the ceiling in the autoclave from coming into contact with the object to be processed. Therefore, the effect of further separating heavy metal-containing drain water is high. That is, since the amount of water in contact with the mixture filled in the hydrothermal treatment vessel is reduced, the amount of heavy metal elution from this mixture is reduced, and the generation amount of heavy metal-containing wastewater is reduced. The amount of heavy metal-containing wastewater that needs to be mixed and hydrothermally treated in the heat treatment process is reduced.

  In FIG. 7, the equipment flow for the treatment of the waste which concerns on the above-mentioned comparative example 1 is shown. FIG. 8 shows an equipment flow for the treatment of waste according to Example 1 described above. In the case of the comparative example 1, the heavy metal containing drain water discharged | emitted from an autoclave enters the container arrange | positioned out of an autoclave, is supplied to a waste water treatment facility, and is drained. In the case of Example 1, the heavy metal-containing drain water can be returned to the mixing step through the pipes (b) and (d) and reused. In the mixing process, when water is insufficient with only this heavy metal-containing drain water, piping for supplying clean water, industrial water, etc. (a ). In FIG. 8, symbol (c) indicates a drainage channel for drainage water containing no heavy metal.

  According to the waste treatment method of the present invention, when a mixture obtained by mixing calcium compound and water with waste containing heavy metal or further mixing silica is hydrothermally treated, it is generated during hydrothermal treatment. Wastewater containing heavy metals can be treated without providing wastewater treatment facilities, so that the waste treatment method according to the present invention has few facilities and is economically efficient, and wastes containing heavy metals It can use suitably as a processing method.

It is a figure which shows the temperature change in a hydrothermal treatment process. It is a figure which shows the processing flow in the processing method of the waste which concerns on Example 1. FIG. It is a figure which shows the processing flow in the processing method of the waste which concerns on the comparative example 1. FIG. It is a figure which shows the example of the processing apparatus of the waste which concerns on this invention. FIG. 5 is an example of a waste treatment apparatus according to the present invention, and is a diagram showing an example different from that shown in FIG. 4. It is an example of the waste processing apparatus which concerns on this invention, Comprising: It is a figure which shows another example from what is shown in FIGS. It is a schematic diagram which shows the equipment flow for performing the processing method of the waste which concerns on the comparative example 1. FIG. It is a schematic diagram which shows the equipment flow for performing the processing method of the waste which concerns on Example 1. FIG.

Explanation of symbols

  (a) --Piping, (b) --Piping, (c) --Drainage channel, (d) --Piping.

Claims (10)

  A waste treatment method comprising a hydrothermal treatment step of hydrothermally treating a mixture obtained by mixing a calcium compound and water with a waste containing heavy metal or further mixing silica, wherein the hydrothermal treatment step is performed twice. When performing the above, wastewater containing heavy metals generated during hydrothermal treatment in the preceding hydrothermal treatment step is used as water to be mixed or part thereof in the subsequent hydrothermal treatment step. Processing method.   The waste treatment method according to claim 1, wherein the calcium compound is at least one of slaked lime, quicklime, Portland cement, blast furnace cement, and fly ash cement.   The waste treatment method according to claim 1 or 2, wherein the waste contains silica.   The method for treating waste according to any one of claims 1 to 3, wherein the waste is one or more of soil and incinerated ash.   The amount of the calcium compound in the said mixture is 3-40 mass% with respect to the quantity of the silica in the said mixture, The processing method of the waste in any one of Claims 1-4.   The amount of waste water containing the mixed water or heavy metal used as a part thereof is 10 to 60% by mass with respect to the total amount of calcium compound and silica in the mixture. Waste disposal method.   The waste treatment method according to any one of claims 1 to 6, wherein the hydrothermal treatment in the hydrothermal treatment step is performed for 1 to 48 hours in the presence of saturated steam at 130 to 300 ° C.   The waste treatment method according to any one of claims 1 to 7, wherein the heavy metal is one or more of lead, arsenic, selenium, chromium, mercury, lead, cadmium, and boron.   A waste treatment apparatus for performing the waste treatment method according to any one of claims 1 to 8, wherein a hydrothermal treatment container filled with a mixture for hydrothermal treatment is disposed in the autoclave and discharged from the autoclave. In a waste treatment apparatus having a pipe and a pressure reducing valve for discharging water to be discharged out of the autoclave, a receiver for receiving water discharged from the hydrothermal treatment container, and water received by the receiver outside the autoclave A waste disposal apparatus comprising a pipe for discharging and a pressure reducing valve. The waste treatment apparatus according to claim 9, further comprising protection means for preventing condensed water generated outside the hydrothermal treatment container in the autoclave from entering the hydrothermal treatment container.

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