JP6296266B1 - Soil purification method - Google Patents

Abstract

[PROBLEMS] In a soil purification facility that purifies toxic metal-contaminated soil with washing water containing a chelating agent, the chelating agent is prevented from being taken away by sand and coarse aggregate, and rainwater that has fallen to the site of the soil purification facility Means are provided that enable processing without being processed and discharged to the outside. A soil purification facility S that purifies toxic metal-contaminated soil with washing water containing a chelating agent, and a rainwater supply unit 7 that recovers the chelating agent adhering to the sand and coarse aggregate separated in the classification unit. And a chelating agent removing unit 8 and a chelating agent collecting unit 9. In the soil purification method according to the present invention, cleaning wastewater is sprayed from the cleaning wastewater spraying device 93 onto the sand in the sand container 85, while the water of the cleaning wastewater adhering to the sand is evaporated into the air to sand. It removes from the accommodating part 85. FIG. The sand used in the sand container 85 and containing the chelating agent is introduced into the soil purification facility S to recover the chelating agent. A part of the sand discharged from the sand rinsing device 61 is used as sand to be accommodated in the sand accommodating portion 85. [Selection] Figure 6

Description

  The present invention relates to a soil purification method in a soil purification facility that purifies soil contaminated with a toxic metal or a compound thereof with washing water containing a chelating agent.

  In recent years, sites of production facilities that use harmful metals such as chromium, lead, cadmium, selenium, mercury and / or their compounds (hereinafter collectively referred to as “hazardous metals”) as raw materials or materials, or the vicinity thereof The problem is soil contamination due to soil contamination or industrial waste disposal including hazardous metals. Then, the soil contaminated with toxic metal (hereinafter referred to as “toxic metal-contaminated soil”) is insolubilized, for example, toxic metal at the position where the toxic metal-contaminated soil actually exists (hereinafter referred to as “original position”). Effective purification, such as by containment or electrical repair, is quite difficult. For this reason, the toxic metal-contaminated soil is generally removed from the original position by excavation and purified at an external soil purification facility.

  As a method for purifying toxic metal-contaminated soil at such off-site soil purification facilities, conventionally, a soil clarification method for cleaning toxic metal-contaminated soil with a cleaning solution to remove toxic metals and the like has been widely used. Thus, the present inventor removes harmful metals by washing the contaminated soil contaminated with harmful metals with washing water containing a chelating agent, while using a solid phase adsorbent from the washed water after washing. Various closed system type soil remediation facilities that regenerate and repeatedly use wash water or chelating agents by removing etc. and do not discharge wash water outside the facility have been proposed (see Patent Documents 1 to 4).

Japanese Patent No. 5662111 Japanese Patent No. 576094 Japanese Patent No. 5771342 Japanese Patent No. 5771343

Hideki Kiyosawa “Estimation method of soil surface evaporation based on ground temperature change” Bulletin of Mie University, Mie University Faculty of Agriculture, 1984, 68, 25-40

  By the way, in the soil remediation facilities disclosed in Patent Documents 1 to 4, the soil contaminated with harmful metals and the like and the washing water containing the chelating agent are mixed, and the harmful metals adhering to the soil are removed from the soil. The soil is separated and captured by the chelating agent, and the soil is classified to produce coarse aggregate and sand.

  And the washing | cleaning water containing a chelating agent has adhered to the sand produced | generated in this way, However, Sand containing a chelating agent is not preferable as a civil engineering / building material. In addition, the chelating agent in the soil purification facility is reduced by the amount taken away by the sand. Therefore, even if the chelating agent is regenerated and repeatedly used, it is necessary to replenish the chelating agent in an amount corresponding to the chelating agent carried away by the sand. For this reason, in a soil remediation facility that purifies a large amount of contaminated soil (for example, 1000 tons / day), a large amount of chelating agent must be replenished, and the soil processing cost in the soil remediation facility is very high. There is.

  In addition, soil purification facilities that purify a large amount of contaminated soil are quite large-scale facilities, and their installation area and height are quite large, so they cannot be placed in buildings. Installed on the street. On the other hand, it sometimes rains on the site of the soil remediation facility, but there is a possibility that the contaminated soil has been dissipated or leaked from the soil remediation facility, so the rainwater that falls on the site is contaminated with soil contaminants. May contain.

  Therefore, if the rainwater that falls on the site of a closed system type soil purification facility is discharged to the outside as it is, this soil purification facility is not a true closed system. For this reason, it is necessary to reliably treat rainwater that has fallen on the site of the soil purification facility without discharging harmful metals contained therein to the outside.

  The present invention has been made in order to solve the above-mentioned conventional problems. The soil contaminated with harmful metals or the like is purified with wash water containing a circulating chelating agent, while sand is separated from the soil. In a closed system type soil remediation facility that is reused, the chelating agent is prevented or reduced from being taken away by sand, and rainwater that has fallen to the site of the soil remediation facility is removed from the toxic metals contained in this facility. It is an object to be solved to provide a means for enabling reliable processing without being discharged to the outside without being processed.

  The present invention made in order to solve the above-mentioned problems provides a soil purification method in a soil purification facility that purifies soil contaminated with harmful metals and the like with washing water containing a chelating agent. Here, the soil purification facility includes a mixing section, a classification section, a sedimentation separation section, a chelating agent regeneration section, and a chelating agent supplement section. The mixing section mixes soil containing gravel, sand and fine-grained soil and contaminated with harmful metals, etc., and washing water containing chelating agents, and removes harmful metals attached to the soil from the soil. Separated and captured by chelating agent. The classifying unit receives a mixture of soil and washing water discharged from the mixing unit, and separates coarse aggregate and sand from the mixture. The sedimentation separation unit separates the wash water containing fine-grained soil discharged from the classification unit into supernatant water and sludge containing fine-grained soil by sedimentation separation. The chelating agent regeneration unit receives the supernatant water discharged from the sedimentation separation unit, and removes the harmful metal and the like from the chelating agent capturing the harmful metal and the like in the supernatant water to regenerate the chelating agent. The chelating agent replenishing unit supplies the chelating agent to the cleaning water so as to replenish the reduced amount of the chelating agent and maintain the chelating agent concentration of the cleaning water at a preset value.

  A chelating agent recovery device that recovers the chelating agent contained in or attached to the sand separated by the classification unit is provided outside the site of the soil purification facility. Here, the chelating agent recovery device includes a chelating agent removing unit that removes the chelating agent by washing the sand separated in the classification unit with rinsing water, and rinses rainwater that has fallen on the site of the soil purification facility into the chelating agent removing unit. A rainwater supply unit that supplies water as a water and a chelating agent recovery unit that recovers the chelating agent from the cleaning wastewater discharged from the chelating agent removal unit. The chelating agent removing unit has a sand rinsing device that removes the chelating agent held on the sand by spraying or spraying rinsing water on the sand separated in the classifying unit.

  The chelating agent recovery unit includes a cleaning wastewater storage tank, a sand container, a roof, a cleaning wastewater spraying device, and a cleaning wastewater reflux mechanism. Here, the washing waste water storage tank receives and stores the washing waste water containing the chelating agent discharged from the sand rinsing device. The sand container is a container having an upper side that is disposed on the ground and accommodates water evaporating sand. A roof is arrange | positioned above a sand accommodating part, and prevents the fall of rain water to a sand accommodating part. The cleaning wastewater spraying device sprays the cleaning wastewater stored in the cleaning wastewater storage tank onto the water evaporation sand stored in the sand storage unit. The washing waste water recirculation mechanism recirculates excess washing waste water flowing down through the gaps between the water evaporation sand particles contained in the sand containing portion to the washing waste water storage tank.

  In the soil purification method according to the present invention, the cleaning wastewater is sprayed from the cleaning wastewater spraying device onto the water evaporation sand accommodated in the sand container, while the cleaning wastewater moisture adhering to the water evaporation sand is dispersed. Is removed from the sand container by evaporating it into the air, and the water evaporating sand used in the sand container for a predetermined period and containing the chelating agent is introduced into the classification unit or mixing unit and accumulated in the water evaporating sand. The chelating agent thus collected is recovered and used as water evaporating sand in which a part of the sand discharged from the sand rinsing device is accommodated in the sand accommodating portion.

  In the soil purification method according to the present invention, the water evaporating sand used in the sand container is preferably fine sand (that is, sand having a particle size of 0.075 to 0.25 mm). It is preferable to set the amount of washing wastewater sprayed to the storage unit so that the water content of the water evaporation sand stored in the sand storage unit is maintained at 30 to 35%.

  According to the soil purification method of the present invention, rinsing water is sprayed or sprayed on the sand separated in the classifying unit by the sand rinsing device, and the chelating agent adhering to the sand is washed away. High quality sand (washing sand) can be produced. Further, the water of the cleaning wastewater discharged from the sand rinsing device and stored in the cleaning wastewater storage tank evaporates in the sand container, and the chelating agent contained in this cleaning wastewater is accumulated in the water evaporating sand in the sand container. The And since the water evaporating sand in which the chelating agent is accumulated in this way is introduced into the classification unit or the mixing unit, the chelating agent adhering to the sand discharged from the classification unit is discharged to the outside. Is done. In other words, in a soil purification facility in which sand is separated from the soil and reused while cleaning with cleaning water containing a chelating agent that circulates in soil contaminated with hazardous metals, the chelating agent is exposed to the outside by sand. It can be prevented or reduced from being taken away. Furthermore, since a part of the sand discharged from the sand rinsing device is used as water evaporating sand to be accommodated in the sand accommodating portion, it is not necessary to separately procure water evaporating sand to be used in the sand accommodating portion. Sand can be procured easily.

  In addition, all the rainwater that has fallen to the site of the soil cleaning device is used as rinse water by the sand rinsing device, so the rainwater that has fallen to the site of the soil purification facility is discharged to the outside without any harmful metals contained in it. Can be reliably processed without any problems. Furthermore, since tap water or industrial water is not used in the sand rinsing device and rainwater is used effectively, the running cost of the sand rinsing device can be reduced.

FIG. 1 is a block diagram showing a schematic configuration of a soil purification facility and a chelating agent recovery device. FIG. 2 is a block diagram showing a specific configuration of the soil purification facility shown in FIG. FIG. 3 is a schematic elevation view showing a specific configuration of the chelating agent regeneration unit of the soil purification facility shown in FIG. 2. FIG. 4 is a schematic side view of the sand rinsing apparatus. FIG. 5 is a schematic side view of the coarse aggregate rinsing apparatus. FIG. 6 is a plan view schematically showing the arrangement of the chelating agent recovery device. FIG. 7 is a schematic partial cross-sectional elevation view of the sand container, the washing wastewater spray device, and the roof, cut along a plane perpendicular to the longitudinal direction (front-rear direction) of the sand container. FIG. 8 is a schematic plan view of a main part of the sand container and the washing wastewater spraying apparatus in a state where the roof and the frame structure are removed. FIG. 9 is a block diagram showing the flow rates of soil, water, and chelating agent in a predetermined part of the soil purification facility.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
First, a schematic configuration of a soil purification facility using the soil purification method according to the present invention will be described with reference to FIG. As shown in FIG. 1, the soil purification facility S installed on the site R includes a mixing unit 1, a classifying unit 2, a sedimentation separating unit 3, a filtering unit 4, a chelating agent regeneration unit 5, and a chelating agent supplement. Part 6. A chelating agent recovery device T for the soil purification facility S is provided outside the site R.

  The mixing unit 1 includes soil containing gravel, sand and fine-grained soil (silt and / or clay) and contaminated with harmful metals or the like (toxic metals and / or compounds thereof), washing water containing a chelating agent, Are mixed, and harmful metals adhering to the soil are separated from the soil and captured by the chelating agent. The classifying unit 2 receives the mixture of soil and washing water discharged from the mixing unit 1 and separates coarse aggregate (pebbles) and sand from the mixture. The sedimentation separation unit 3 separates the wash water containing fine-grained soil discharged from the classification unit 2 into supernatant water and sludge containing fine-grained soil by sedimentation separation. The filtration unit 4 filters the sludge discharged from the sedimentation separation unit 3 to generate a filter cake. The chelating agent regeneration unit 5 receives the supernatant water (washing water) discharged from the sedimentation separation unit 3 and captures harmful metals, etc. in the supernatant water (washing water) from the chelating agent or ions thereof. To regenerate the chelating agent. The chelating agent replenishing unit 6 supplies the chelating agent to the cleaning water so as to supplement the reduced amount of the chelating agent and maintain the chelating agent concentration of the cleaning water at a preset value.

  As will be described in detail later, the chelating agent regeneration unit 5 has a solid-phase adsorbing material that has a higher complexing power than the chelating agent and adsorbs toxic metals or these ions when contacted with the supernatant water. Harmful metals and / or these ions are removed from the chelating agent in the water to regenerate the supernatant water as washing water and to regenerate the chelating agent. The solid-phase adsorbent has a multipoint interaction by coordinating bonds and hydrogen bonds in which a cyclic molecule is supported on a carrier and a chelate ligand is modified on the cyclic molecule, and harmful metals, etc. or these ions are selectively selected. It is something to capture. The harmful metal adsorbed on the solid-phase adsorbent or these ions can be removed with an acid solution, so that the solid-phase adsorbent can be easily regenerated.

  The chelating agent recovery device T recovers the chelating agent contained in or attached to the sand and / or coarse aggregate separated in the classification unit 2 and returns it to the classification unit 2 or the mixing unit 1. Specifically, the chelating agent recovery device T stores the sand separated in the classification unit 2 with rinsing water and removes the chelating agent, and stores rainwater that has fallen to the site R. A rainwater supply unit 7 for supplying the chelating agent removing unit 8 as rinse water and a chelating agent collecting unit 9 for recovering the chelating agent from the washing wastewater discharged from the chelating agent removing unit 8 are provided.

  As will be described in detail later, the chelating agent removing unit 8 sprays or jets rinsing water on the sand separated by the classifying unit 2 to remove the chelating agent held in the sand 61 ( 4). Moreover, the chelating agent collection | recovery part 9 has the washing | cleaning wastewater storage tank 84, the sand accommodating part 85, the roof 92, the washing | cleaning wastewater spraying apparatus 93, and the washing | cleaning wastewater recirculation | reflux mechanism 94 (refer FIGS. 6-7). The cleaning wastewater storage tank 84 receives and stores the cleaning wastewater containing the chelating agent discharged from the sand rinsing device 61 (see FIG. 6). The sand accommodating part 85 is a container-like thing opened on the upper side which accommodates the water evaporation sand arrange | positioned on the ground (refer FIG. 6). The roof 92 is disposed above the sand container 85 and prevents rain water from dropping to the sand container 85 (see FIG. 7). The cleaning wastewater spraying device 93 sprays the cleaning wastewater stored in the cleaning wastewater storage tank 84 onto the water evaporation sand stored in the sand storage unit 85 (see FIG. 6). The cleaning wastewater recirculation mechanism 94 recirculates excess cleaning wastewater flowing down through the gaps between the water evaporation sand particles accommodated in the sand accommodating portion 85 to the cleaning wastewater storage tank 84 (see FIG. 6).

  Next, a specific configuration of the soil purification facility S will be described with reference to FIG. As shown in FIG. 2, in the soil remediation facility S, first, it is contaminated with harmful metals or the like (toxic metals and / or compounds thereof), and in some cases other contaminants (for example, fluorine, boron, cyan, etc.) The soil (contaminated soil) collected by excavation of the ground contaminated with the two kinds of specific harmful substances) is received by the input hopper 11. Then, the soil in the charging hopper 11 is first introduced into the mixing device 12 (mixing unit) and mixed with the washing water containing the chelating agent in the mixing device 12. Here, the soil includes fine-grained soil (silt or clay having a particle size of 0.075 mm or less), gravel and sand, and in some cases includes stone. In the mixing device 12, harmful metals and the like adhering to the soil are separated from the soil and captured by the chelating agent.

  The soil in the input hopper 11 is contaminated with harmful metals or the like, and in some cases, is further contaminated with other contaminants. Examples of harmful metals include chromium, lead, cadmium, selenium, mercury, metal arsenic, and compounds thereof. Examples of other contaminants include fluorine or a compound thereof, boron or a compound thereof, and second-type specific harmful substances such as a cyanide compound.

  A mixture of soil and washing water generated by the mixing device 12 (hereinafter referred to as “soil / water mixture”) is transferred to a wet mill breaker 13. As the mill breaker 13, for example, a rod mill can be used. The mill breaker 13 crushes stones or gravel by applying impact force, shear force, friction force, or the like. At that time, toxic metals or other contaminants adhering to or contained in stones, gravel, etc. or other pollutants are peeled off or removed and separated into the washing water. Harmful metals and other contaminants or ions of these released from the soil surface are captured by the chelating agent in the wash water. Depending on the state of the soil (for example, when the soil does not include stones), the mill breaker 13 may be omitted.

  Examples of the chelating agent include EDTA (ethylenediaminetetraacetic acid), HIDS (3-hydroxy-2,2′-iminodisuccinic acid), IDS (2,2′-iminodisuccinic acid), MGDA (methylglycine diacetic acid), EDDS ( Ethylenediaminediacetic acid) or sodium salt of GLDA (L-glutamic acid diacetic acid) can be used. The chelating agent captures (chelates) toxic metals or the like ions adhering to the soil. When treating the soil, a chelating agent suitable for the treatment is selected according to the type of harmful metal or the like contained in the soil. The higher the concentration of the chelating agent in the washing water, the higher the trapping amount of harmful metals and the like or these ions, but practically the range of 0.005 to 0.1 mol / liter, preferably 0.01 to 0. .05 mol / liter is set.

  The soil / water mixture discharged from the mill breaker 13 (in the case where the mill blue breaker 13 is not provided, the soil / water mixture discharged from the mixing device 12) is introduced into the trommel 14. The trommel 14 is a wet sieving device having a receiving tank capable of storing cleaning water and a substantially cylindrical drum screen arranged to be inclined with respect to a horizontal plane. The drum screen is driven by a motor. Can rotate around the central axis. Further, the cleaning water can be sprayed into the drum screen.

  When the soil / water mixture flows through the rotating drum screen of the trommel 14, the soil particles finer than the mesh of the drum screen pass through the mesh of the drum screen together with the wash water, and go out of the drum screen and into the receiving tank. to go into. On the other hand, soil particles coarser than the mesh of the drum screen are discharged out of the drum screen via the opening end on the lower side of the drum screen. In the trommel 14, the soil particles in the soil / water mixture rub against each other, so that toxic metals and other contaminants remaining on or attached to the surface of the soil particles or other contaminants are peeled off and separated into the wash water. Harmful metals and the like or other contaminants or these ions released in the washing water are trapped by the chelating agent in the washing water.

  In this embodiment, the classification diameter (opening) of the drum screen of the trommel 14 is set so that soil particles having a particle diameter of less than 2 mm pass through the mesh of the drum screen. Therefore, in this trommel 14, soil particles (pebbles) having a particle size of 2 mm or more are separated or recovered from the soil / water mixture. Soil particles (pebbles) having a particle size of 2 mm or more contain almost no contaminants. For this reason, soil particles (gravels) having a particle size of 2 mm or more separated by the trommel 14 can be used as aggregates or coarse aggregates for concrete, for example. These coarse aggregates are transferred to the chelating agent recovery unit 9. Note that the mesh size (opening) of the drum screen of the trommel 14 is not limited to that described above, and is arbitrarily set according to the particle size of the relatively large soil particles to be obtained. be able to.

  A soil / water mixture containing soil particles having a particle size of less than 2 mm and wash water contained in a receiving tank of the trommel 14 is introduced into the cyclone 15. The cyclone 15 divides the soil / water mixture into a mixture of fine soil having a relatively small particle size (for example, less than 0.075 mm) and washing water, and soil particles having a relatively large particle size (for example, 0.075 mm or more). To separate. A mixture of fine-grained soil and washing water (hereinafter referred to as “fine-grained soil-containing water”) is discharged from the upper end portion of the cyclone 15, and soil particles having a relatively large particle size are discharged from the lower end portion of the cyclone 15. . Here, the fine-grained soil-containing water is temporarily stored in the seal tank 16 (intermediate storage tank). The fine-grained soil contained in the fine-grained soil-containing water is, for example, silt or clay having a particle diameter of less than 0.075 mm.

  On the other hand, soil particles having a relatively large particle size discharged from the lower end of the cyclone 15 are introduced into the sand clean 17. The soil particle having a relatively large particle size is, for example, sand having a particle size of 0.075 to 2 mm. The sand clean 17 causes the washing water to flow at a predetermined pressure and an amount of water to perform a rinsing washing process on soil particles having a relatively large particle size, that is, sand, and removes remaining suspended matters or foreign matters. Soil particles, that is, sand having a relatively large particle size that has been subjected to the rinsing process, are transferred to the chelating agent removing unit 8 of the chelating agent recovery device T. Since these sands contain little contaminants, they are used or sold as recycled sand. The washing water discharged from the sand clean 17 is temporarily stored in the feed tank 18 (intermediate storage tank).

The fine soil-containing water stored in the seal tank 16 is introduced into the PH adjustment tank 19. Moreover, the wash water temporarily stored in the feed tank 18 is also introduced into the PH adjustment tank 19 and added to the fine-grained soil-containing water. In the pH adjustment tank 19, the pH (hydrogen index) of the fine-grained soil-containing water uses a pH adjuster such as an acidic liquid (for example, sulfuric acid or hydrochloric acid) and an alkaline liquid (for example, an aqueous sodium hydroxide solution). Thus, the pH is adjusted to be almost neutral or a predetermined pH (for example, pH 7 to 8).

  The fine-soil-containing water whose pH has been adjusted in the pH adjustment tank 19 is introduced into the agglomeration tank 20. In the agglomeration tank 20, a polyaluminum chloride liquid (PAC), a polymer flocculant, and a pH adjuster (an acidic liquid or an alkaline liquid) are added to fine-grained soil-containing water. As a result, a large number of flocs in which water-insoluble metal hydroxide and fine-grained soil are mixed are generated in the aggregation tank 20. At that time, water-polluting substances in the washing water are adsorbed on or attached to the floc. The polyaluminum chloride liquid and the polymer flocculant may be added to the fine-grained soil-containing water in the pH adjustment tank 19 instead of the aggregation tank 20.

  The fine-soil-containing water in the coagulation tank 20 is introduced into the thickener 22 after the suspended matter is removed by the suspended matter collection device 21. The thickener 22 sinks water-insoluble flock or fine-grained soil by gravity in a state where the fine-grained soil-containing water is almost stationary, and a sludge layer (solid content ratio: 5 to 10%) located at the bottom. It forms a supernatant water (wash water) which is located in the upper part and hardly contains flock or fine-grained soil. The floating oil floating on the surface of the supernatant water is removed by overflowing a small amount of the supernatant water from the upper part of the thickener 22.

  Sludge staying or accumulating in the lower portion of the thickener 22 is extracted by a sludge pump or the like, transferred to the intermediate tank 23, and temporarily stored in the intermediate tank 23. The sludge in the intermediate tank 23 is transferred to the filter press 24 intermittently or continuously. The filter press 24 pressure-filters the sludge received from the intermediate tank 23, and produces | generates a filter cake and a filtrate. The filtration pressure of the filter press 24 is set so that the water content of the filter cake is 30 to 40%, for example. The filtrate of the filter press 24 is returned to the thickener 22. Since the filter cake discharged from the filter press 24 does not contain harmful metals or the like or other pollutants, it can be reused or sold after being dried as necessary.

  On the other hand, the supernatant water (wash water) in the thickener 22 is introduced into the wash water tank 25 and stored. When the washing water tank 25 becomes full, the spare water tank 26 is used. The treated water (washing water) stored in the washing water layer 25 or the preliminary water tank 26 is introduced into the chelating agent regeneration unit 5. When the cleaning water (circulated water) stored in the cleaning water tank 25 decreases due to evaporation or the like, the cleaning water tank 25 is appropriately replenished with tap water, industrial water, or the like.

  In the soil remediation facility S, when the soil contaminated with harmful metals or the like is sequentially treated with the mixing device 12, the mill breaker 13, the trommel 14, the cyclone 15, and the sand clean 17, the harmful adhering to the soil. Metals and other contaminants are released into the wash water containing the chelating agent. Accordingly, the coarse aggregate recovered by the trommel 14 or the sand recovered by the sand clean 17 contains almost no harmful metals and can be reused as a material for civil engineering and construction.

  Further, the fine-grained soil is in contact with the cleaning water containing the chelating agent for a sufficiently long time (for example, 1 to 4 hours) in the flow process from the seal tank 16 or the feed tank 18 to the thickener 22. For this reason, most of the harmful metals and other contaminants adhering to the fine-grained soil are released into the washing water. Then, harmful metals and the like or other contaminants or these ions released in the washing water are captured by the chelating agent. Therefore, the filter cake (soil) produced by the filter press 24 contains almost no harmful metals or other contaminants and can be dried and reused.

  Hereinafter, a specific configuration and function of the chelating agent regeneration unit 5 of the soil purification facility S will be described with reference to FIG. As shown in FIG. 3, the chelating agent regeneration unit 5 is provided with a liquid fluidized bed device 30 as a cleaning agent regeneration device. The liquid fluidized bed apparatus 30 accommodates particles of a solid-phase adsorbent or small pieces or granular materials to which the solid-phase adsorbent is fixed (hereinafter collectively referred to as “solid-phase adsorbent particles”). Wash water to be regenerated (hereinafter simply referred to as “wash water”) stored in the wash water tank 25 flows from the lower side to the upper side, and the solid-phase adsorbent particles are fluidized by the upward flow of the wash water. It has become so. The liquid fluidized bed apparatus 30 is provided with a substantially cylindrical mantle 30a (shell), in which an upper porous plate 30b is disposed at the upper portion and a lower porous plate 30c is disposed at the lower portion. . A rectifying member 30d that rectifies the cleaning water is disposed below the lower porous plate 30c.

  Both the porous plates 30b and 30c are discs in which a large number of through-holes penetrating them in the thickness direction are formed. The diameter of the through hole is set to a preferable value within a range in which the solid-phase adsorbent particles can be prevented from passing through. And the solid-phase adsorbent particle | grains are accommodated in the hollow part between both the porous plates 30b and 30c. Here, the particle size of the solid-phase adsorbent particles can form a fluidized bed by dynamically suspending the solid-phase adsorbent particles according to the flow rate of the washing water flowing in the liquid fluidized bed apparatus 30. It is set to a preferable value in the range. In addition, when the cleaning water (chelating agent) is regenerated, the chelating agent regeneration unit 5 transfers the cleaning water stored in the cleaning water tank 25 to the liquid fluidized bed device 30. A pump 33 and a plurality of pipes 34 to 37 for transferring the regenerated cleaning water to the cleaning water tank 27 are provided. The regenerated cleaning water in the cleaning water tank 27 is supplied (refluxed) to the mixing device 12, the trommel 14, and the sand clean 17 by the pump 31 and the pipe line 32.

  Further, when the solid phase adsorbent particles are regenerated, the chelating agent regeneration unit 5 transfers the acid liquid stored in the acid liquid tank 28 to the liquid fluidized bed apparatus 30, while from the liquid fluidized bed apparatus 30. A pump 38 and a plurality of pipes 39 and 40 for returning the discharged acid solution to the acid solution tank 28 are provided. Further, when the solid phase adsorbent particles regenerated with the acid solution are washed with water, the chelating agent regeneration unit 5 transfers the water stored in the water tank 29 to the liquid fluidized bed device 30 while the liquid fluid flow. A pump 41 and a plurality of pipes 42 and 43 for returning water discharged from the layer apparatus 30 to the water tank 29 are provided.

  The inlet-side pipelines 34, 35, 39, and 42 for transferring the washing water, the acid solution, or the water to the liquid fluidized bed apparatus 30 have valves 44, 45, 46, which open and close the corresponding pipelines, respectively. 47 is interposed. On the other hand, the outlet side pipes 36, 37, 40, 43 for discharging the washing water, the acid liquid or the water from the liquid fluidized bed apparatus 30 are valves 48, 49, which open and close the corresponding pipe lines, respectively. 50 and 51 are provided. By switching the open / closed state of these valves 44 to 51, either the washing water, the acid solution, or the water can be supplied to and discharged from the liquid fluidized bed apparatus 30. The opening and closing of these valves 44 to 51 is automatically controlled by a controller (not shown).

  Hereinafter, an example of the operation method of the chelating agent regeneration unit 5 shown in FIG. 3 will be described. When regenerating the cleaning water (chelating agent), the valves 44, 45, 48, 49 provided in the pipes 34 to 37 are opened, while the other valves 46, 47, 50, 51 are closed, The pump 33 is operated. Thus, the cleaning water in the cleaning water tank 25 is transferred to the cleaning water tank 27 after being cleaned through the liquid fluidized bed apparatus 30.

  In the liquid fluidized bed apparatus 30, washing water containing a chelating agent capturing toxic metals and the like is brought into contact with a solid phase adsorbent (solid phase adsorbent particles) having a higher complexing power than the chelating agent. The solid-phase adsorbent has a multipoint interaction by coordinating bonds and hydrogen bonds in which a cyclic molecule is supported on a carrier and a chelate ligand is modified on the cyclic molecule, and selectively incorporates ions such as harmful metals. is there. As a result, harmful metals or the like captured by the chelating agent or these ions are released from the chelating agent and are adsorbed or extracted by the solid phase adsorbent (solid phase adsorbent particles). As a result, harmful metals and the like are removed and collected from the cleaning water, while the chelating agent is again in a state where it can capture the harmful metals and the cleaning water is regenerated.

  The cleaning water regenerated in this manner is temporarily stored in the cleaning water tank 27 and then refluxed to the mixing device 12, the trommel 14, and the sand clean 17 by the pump 31 and the pipe line 32. That is, the wash water containing the chelating agent circulates in the soil purification facility S while repeating the purification of the soil and the regeneration of the chelating agent. That is, the washing water circulation mechanism in the soil purification facility S is a closed system and basically does not discharge the waste water to the outside. Thus, since the chelating agent is recycled and used, basically it is not necessary to supply the chelating agent, and it is only necessary to replenish the reduced amount appropriately.

  A solid-phase adsorbent having a higher complexing power than a chelating agent is a solid material such as a gel, and is generally coordinated with a chelating agent when contacted with an aqueous solution containing a chelating agent capturing a metal. It has a strong binding force other than a covalent bond to such an extent that the metal ions can be detached from the chelating agent and transferred to the solid phase adsorbent. Examples of such a solid-phase adsorbent include a material in which a cyclic molecule is densely supported on a carrier such as silica gel or a resin and a chelate ligand is modified on the cyclic molecule. When such a solid-phase adsorbent is used, a plurality of various bonds and interactions such as coordination bonds and hydrogen bonds occur due to adjacent cyclic molecules and chelate ligands, resulting in multipoint interactions, and metal ions In contrast to this, a chemical bond stronger than that of a chelating agent is generated, and metal ions can be selectively taken in by the properties of the cyclic molecule.

  Accompanying such regeneration of the washing water, the amount of adsorption of harmful metals and the like in the solid phase adsorbent increases with time, but there is an upper limit on the adsorption capacity of the solid phase adsorbent. For this reason, when the amount of adsorption of toxic metals or the like in the solid phase adsorbent reaches a saturated state or in the vicinity thereof, the solid phase adsorbent is converted into a solid phase adsorbent regeneration mechanism (acid solution tank 28, pump 38, pipe 39, 35, 36, 40, etc.). That is, the solid-phase adsorbent regeneration mechanism allows an acid solution to flow through the liquid fluidized bed apparatus 30 with the washing water removed, and removes harmful metals adsorbed on the solid-phase adsorbent material with the acid solution. Regenerate the adsorbent. Thus, while the toxic metal and the like are recovered by the acid solution, the solid phase adsorbent is regenerated and becomes capable of adsorbing or extracting the toxic metal and the like or these ions again. The solid-phase adsorbent is regenerated with an acid solution and then washed with a water washing mechanism (water tank 29, pump 41, pipes 42, 35, 36, 43, etc.) and adhered to the solid-phase adsorbent. A small amount of acid solution is removed.

  As described above, when the adsorption amount of the harmful metal or the like of the solid phase adsorbent in the liquid fluidized bed apparatus 30 reaches the saturated state or the vicinity thereof and the solid phase adsorbent is regenerated with the acid solution, the pipe line 39, The valves 46, 45, 48, 50 interposed in 35, 36, 40 are opened, while the other valves 44, 47, 49, 51 are closed, and the pump 38 is operated. Thus, the acid solution in the acid solution tank 28 flows through the liquid fluidized bed apparatus 30 and returns to the acid solution tank 28. Before starting the regeneration operation of the solid-phase adsorbent, the washing water in the liquid fluidized bed apparatus 30 is removed. If a plurality of liquid fluidized bed devices 30 are arranged in parallel, the wash water can be regenerated continuously even when the supply of the wash water to some liquid fluidized bed devices 30 is stopped. Can do. Whether or not the amount of adsorption of toxic metals, etc. on the solid phase adsorbent has reached or has reached its saturation state is determined by detecting the content of toxic metals, etc. in the wash water discharged from the liquid fluidized bed apparatus 30. can do.

  The time during which the acid solution is allowed to flow through the liquid fluidized bed apparatus 30 is preferably set according to the size or shape of the liquid fluidized bed apparatus 30, the dimensions of the solid-phase adsorbent particles, and the like. The acid solution circulates through the acid solution tank 28 and the liquid fluidized bed device 30. At that time, the solid phase adsorbent in the liquid fluidized bed apparatus 30 comes into contact with the acid solution, and harmful metals and the like adsorbed on the solid phase adsorbent are separated into the acid solution. That is, harmful metals and the like are recovered by the acid solution, while the solid-phase adsorbent is regenerated and becomes capable of adsorbing the harmful metals and the like or these ions again.

  Further, when the solid adsorbent is washed with water after the regeneration of the solid adsorbent with the acid solution is completed, the valves 47, 45, 48, 51 provided in the pipes 42, 35, 36, 43 are opened. On the other hand, the other valves 44, 46, 49, 50 are closed and the pump 41 is operated. As a result, the water in the water tank 29 flows through the liquid fluidized bed apparatus 30 and returns to the water tank 29. Before the washing operation of such solid phase adsorbent (solid phase adsorbent particles) is started, the acid solution in the liquid fluidized bed apparatus 30 is removed. Water circulates between the water tank 29 and the liquid fluidized bed apparatus 30 and flows. At that time, the solid-phase adsorbent particles in the liquid fluidized bed apparatus 30 come into contact with water, and the acid solution adhering to the solid-phase adsorbent particles is removed. Thereafter, the regeneration of the washing water is resumed.

  FIG. 9 shows the essential points of the soil purification facility S when the soil purification facility S shown in FIG. 2 is used to purify 100 tons of soil per hour with, for example, cleaning water containing 0.3% by mass of a chelating agent. The specific example of the flow volume of soil, water, and a chelating agent is shown. In the example shown in FIG. 9, 100 tons of soil includes 25 tons of gravel, 30 tons of sand, 25 tons of fine particles, and 20 tons of water, and the water content is 25%. . The moisture content of the coarse aggregate discharged from the trommel 14 is 5%, and the moisture content of the sand discharged from the sand clean 17 is 20%. As is clear from FIG. 9, in this example, 0.024 tons of chelating agent per hour is taken away from the soil purification facility S by coarse aggregate and sand. In addition, when using the wash water containing 1.0 mass% chelating agent in the soil purification plant S shown in FIG. 2, the flow rate of the chelating agent in each table in FIG. 9 is about 3.3 times these. . In this case, about 0.08 tons of chelating agent per hour is taken away from the soil purification facility S.

  Hereinafter, the soil purification method or chelating agent recovery apparatus T according to the present invention will be described in detail with reference to FIGS.

  As shown in FIG. 4, the sand rinsing device 61 constituting the chelating agent removing unit 8 includes a belt conveyor 64, a sand supply device 65, a rinse water spraying device 66, and a washing waste water receiving tank 67. Here, the belt conveyor 64 is coaxially attached to a substantially cylindrical drive roller 68 that is coaxially attached to a shaft 68a that is rotationally driven by an electric motor (not shown), and a shaft 69a that is not connected to a drive source. A substantially cylindrical driven roller 69, a ring-shaped or endless conveying belt 70 wound around the driving roller 68 and the driven roller 69, and a plurality of supporting rollers 71 that support or guide the conveying belt 70. , And a guide plate 72 for guiding sand discharged from the belt conveyor 64. The sand rinsing device 61 sprays or sprays rinsing water on the sand discharged from the sand clean 17 (see FIGS. 1 and 2) forming a part of the classifying unit 2, and is held or adhered to the sand. Wash away the chelating agent.

  The driving roller 68 and the driven roller 69 have the same diameter and are disposed at the same height. The conveyor belt 70 is made of a porous material, mesh material, fibrous material, or cloth material that can be curved in a ring shape that allows rinsing water to pass but not sand particles. The rinse water spraying device 66 sprays rinse water on the sand transported by the transport belt 70 in an area having a predetermined length (for example, 1 to 2 m) with respect to the moving direction of the transport belt 70. Note that the amount of rinse water sprayed from the rinse water spray device 66 is preferably set so that almost all of the wash water adhering to the sand can be washed away. For example, an amount of rinse water of 1.0 to 2.0 times (preferably 1.2 to 1.5 times) the amount of cleaning water adhering to the sand is sprayed. As a specific example, for example, when sand having a moisture content of 20% is transported at 5 tons per hour (dry basis), 1.0 to 2.0 tons of rinse water is sprinkled per hour.

  The sand supply device 65 supplies the sand discharged from the sand clean 17 onto the conveying belt 70 in the vicinity of the driven roller 69 at a predetermined flow rate. The sand thus supplied is conveyed by the conveying belt 70, falls downward via the guide plate 72 at a position corresponding to the driving roller 68, and is stored in a sand storage (not shown). Rinsing water is sprayed from the rinsing water spraying device 66 onto the sand transported by the transport belt 70, and the rinsing water moves downward through the gaps between the sand particles and passes through the transport belt 70 to be washed waste water receiving tank. It flows down to 67. At that time, the washing water containing the chelating agent adhering to the sand is washed downward by the rinse water and falls to the washing waste water receiving tank 67, but a part of the rinse water is held in the gap between the sand particles. That is, the washing water containing the chelating agent held or adhered to the sand is replaced with rinsing water not containing the chelating agent. That is, the chelating agent contained in or adhering to the sand is washed away by the rinsing water and accommodated in the washing waste water receiving tank 67 together with a part of the rinsing water. Thus, a sand reservoir (not shown) stores clean sand that is substantially free of chelating agents and contaminants.

  As shown in FIG. 5, the coarse aggregate rinsing device 62 includes a belt conveyor 74, a coarse aggregate supply device 75, a rinse water spraying device 76, and a washing waste water receiving tank 77. Here, the belt conveyor 74 is coaxially attached to a substantially cylindrical drive roller 78 coaxially attached to a shaft 78a that is rotationally driven by an electric motor (not shown), and a shaft 79a that is not connected to a drive source. A substantially cylindrical driven roller 79, a ring-shaped or endless conveying belt 80 wound around the driving roller 78 and the driven roller 79, and a number of supporting rollers 81 for supporting or guiding the conveying belt 80. , A guide plate 82 for guiding the coarse aggregate discharged from the belt conveyor 74, and a coarse aggregate storage (not shown). The coarse aggregate rinsing device 62 sprays or jets rinsing water on the coarse aggregate discharged from the trommel 14 (see FIGS. 1 and 2) forming a part of the classifying unit 2. The retained or attached chelating agent is washed away and removed.

  The structure and function of the coarse aggregate rinsing device 62 is substantially the same as the sand rinsing device 61 shown in FIG. 4 except that the object to be cleaned with the rinsing water is not coarse sand but coarse aggregate. Therefore, in order to avoid duplication of explanation, detailed explanation of the coarse aggregate rinsing device 62 is omitted.

  As shown in FIG. 6, the rainwater supply device 7 receives and stores all rainwater that has fallen to the site R via a rainwater discharge passage (not shown), and rainwater stored in the rainwater storage tank 55. Is supplied as a rinsing water to the sand rinsing device 61 and the coarse aggregate rinsing device 62 of the chelating agent removing unit 8. The rainwater storage tank 55 is a concrete reservoir buried in the ground and having a rectangular planar shape.

For example, the area of the site R is 2000 m ² (for example, a rectangular land of 40 m left and right and 50 m before and after in plan view), and the soil treatment capacity of the soil purification facility S is 500 m ³ / day (about 850 tons / day). In this case, the specification of the rainwater storage tank 55 may be set as follows, for example.
<Example of specifications of rainwater storage tank 55>
・ Cuboid storage tank (right and left dimensions: 15m, front and rear dimensions: 30m, depth: 3m)
・ Top surface area 450m ²
・ Maximum water storage capacity: about 1300m ³

  Thus, the cleaning wastewater containing the chelating agent stored in the cleaning wastewater receiving tanks 67 and 77 of the sand rinsing device 61 and the coarse aggregate rinsing device 62 is sent to the chelating agent recovery unit 9 to recover the chelating agent. Specifically, the cleaning wastewater is introduced into the cleaning wastewater evaporator 63 of the chelating agent recovery unit 9. The cleaning waste water evaporation device 63 recovers the chelating agent by evaporating (vaporizing) the moisture of the cleaning waste water containing the chelating agent discharged from the sand rinsing device 61 and / or the coarse aggregate rinsing device 62. Thus, the cleaning wastewater evaporator 63 collects the chelating agent from the cleaning wastewater and returns it to the classification unit 2 (Trommel 14 or Sandclean 17).

Hereinafter, the configuration and function of the cleaning wastewater evaporator 63 will be described in detail.
As shown in FIGS. 6 to 8, the cleaning waste water evaporator 63 includes chelate discharged from the cleaning waste water receiving tanks 67 and 77 (see FIGS. 4 to 5) of the sand rinsing device 61 and the coarse aggregate rinsing device 62. A cleaning waste water storage tank 84 for receiving cleaning waste water containing the agent via the cleaning waste water discharge passage 83 is provided. The washing waste water storage tank 84 is a concrete storage tank embedded in the ground and having a rectangular planar shape. In the following, in order to briefly show the positional relationship between the facility or apparatus in the chelating agent recovery apparatus T or the cleaning waste water evaporation apparatus 63, the cleaning waste water storage tank 84 and the cleaning waste water discharge passage 83 are aligned in FIG. 6 (in FIG. 6). (The left-right direction in this positional relationship), the side where the cleaning waste water storage tank 84 is located is referred to as “left”, and the side where the cleaning waste water discharge passage 83 is located is referred to as “right”.

  Further, the cleaning waste water evaporation device 63 is provided with a container-shaped sand storage portion 85 for storing sand, which is appropriately separated from the cleaning waste water storage tank 84 in a direction perpendicular to the left-right direction. In this embodiment, fine sand (sand having a particle size of 0.075 to 0.25 mm) is used as such sand. In the following, in order to briefly show the positional relationship between the facility or the apparatus in the chelating agent recovery unit 9 or the cleaning waste water evaporator 63, the direction in which the cleaning waste water storage tank 84 and the sand container 85 are aligned (a direction perpendicular to the left-right direction) , The side on which the cleaning wastewater storage tank 84 is located is referred to as “front”, and the side on which the sand container 85 is located is referred to as “rear”.

  The sand accommodating portion 85 includes a front end wall 86, a rear end wall 87, a left side wall 88, a right side wall 89, and a bottom wall 90, and has a relatively short length in the left-right direction and a relatively long length in the front-rear direction. It is a concrete box-shaped container that has a rectangular planar shape and has a depth that can accommodate an appropriate amount of sand (water evaporating sand) and is installed on the ground or buried in the ground. Further, the cleaning wastewater evaporator 63 includes a roof 92 disposed above the sand container 85 to prevent rainwater from dropping into the sand container 85 and a cleaning agent containing a chelating agent stored in the cleaning wastewater storage tank 84. A cleaning wastewater spraying device 93 that sprays wastewater onto the sand stored in the sand storage unit 85 and a cleaning wastewater recirculation mechanism 94 that returns the cleaning wastewater at the bottom of the sand storage unit 85 to the cleaning wastewater storage tank 84 are provided.

  The sand container 85 is made of concrete, and is embedded in the ground 100 so that the vicinity of the upper end of the sand container 85 is exposed to the atmosphere. The sand container 85 has a rectangular shape with a relatively short length in the left-right direction (for example, 20 to 50 m) and a relatively long length in the front-rear direction (for example, 100 to 300 m) in plan view, and its depth. Are configured so as to accommodate a suitable amount of sand (for example, 0.4 to 0.8 m), and integrally formed front end wall 86, rear end wall 87, left side wall 88, right side wall 89, and bottom wall 90 A box-like (shallow pool-like) container having Note that the lengths of the sand container 85 in the left-right direction and the front-rear direction are appropriately set according to the amount of cleaning waste water evaporated in the sand container 85.

  On the upper surface of the bottom wall 90, a plurality of drainage grooves 101 extending in parallel in the front-rear direction at a predetermined interval and having a predetermined depth (for example, 5 to 10 cm) are provided. These drainage grooves 101 are connected to a collective drainage groove 102 provided in the vicinity of the front end portion of the sand accommodating portion 85. The front end of the collective drainage groove 102 is connected to the cleaning wastewater storage tank 84. The drainage groove 101 and the collective drainage groove 102 are components of the cleaning wastewater recirculation mechanism 94.

  Thus, the cleaning wastewater that has flowed down through the gaps between the sands and has flowed into the drainage grooves 101 (that is, the excess cleaning wastewater that has not evaporated) naturally returns to the cleaning wastewater storage tank 84 through the collective drainage grooves 102 by gravity. To do. A perforated plate 104 that allows cleaning wastewater to pass but does not allow sand to pass therethrough is disposed on the plurality of convex portions 103 positioned between the drain grooves 101 in the left-right direction. Here, the perforated plate 104 is not a single plate-like member, but a large number of perforated plates having dimensions suitable for production and transportation (for example, a perforated plate having 1 to 2 m on the left and right, 2 to 5 m on the front and back, and 5 to 10 mm in thickness). It consists of A sand layer 105 having a predetermined thickness (for example, 30 to 60 cm) is formed on the porous plate 104.

  A plurality of left vertical frames 107 are disposed on the left side wall 88 of the sand container 85 with an appropriate interval (for example, 5 to 10 m) in the front-rear direction. A plurality of right vertical frames 108 are arranged at appropriate intervals (for example, 5 to 10 m). Note that the left vertical frame 107 and the right vertical frame 108 are disposed at the same position in the front-rear direction. Then, the vicinity of the upper end of the left vertical frame 107 and the vicinity of the upper end of the right vertical frame 108 that are disposed at the same position in the front-rear direction are connected by a horizontal frame 109 that extends horizontally in the left-right direction. Further, the vicinity of the upper end of the left vertical frame 107 adjacent in the front-rear direction is connected by a vertical frame (not shown) extending in the front-rear direction, and the vicinity of the upper end of the right vertical frame 108 adjacent in the front-rear direction is in the front-rear direction. They are connected by an extending vertical frame (not shown).

  As described above, the roof 92 is mounted on the bowl-shaped frame structure constituted by the left vertical frame 107, the right vertical frame 108, the horizontal frame 109, and the vertical frame (not shown). The roof 92 has a slightly larger planar shape than the sand accommodating portion 85 so that rainwater can be prevented from falling to the sand accommodating portion 85 during normal rainfall. Although not shown, the rain that has fallen on the roof 92 is discharged out of the sand container 85 by a rainwater discharger such as a kite and does not flow into the washing wastewater storage tank 84.

  The cleaning wastewater spraying device 93 includes a plurality of water supply pipes 111 disposed below the roof 92 above the sand containing portion 85 and extending in the front-rear direction. Although not shown in detail, each water supply pipe 111 is supported by the horizontal frame 109 using a fixture. These water supply pipes 111 are arranged in parallel with an appropriate interval (for example, 1 to 2 m) in the left-right direction. Each water supply pipe 111 is provided with a plurality of water discharge nozzles 112 that open downward with an appropriate interval (for example, 1 to 2 m) in the front-rear direction.

  The front end portion of each water supply pipe 111 extending in the front-rear direction is connected to the rear end portion of the cleaning wastewater supply pipe 114 via an intermediate pipe 113 extending in the left-right direction. In addition, the rear end part of each water supply pipe 111 is closed. The front end portion of the cleaning wastewater supply pipe 114 is immersed in the cleaning wastewater in the cleaning wastewater storage tank 84. A cleaning wastewater supply pump 115 is interposed in the cleaning wastewater supply pipe 114 in the vicinity of the cleaning wastewater storage tank 84. Here, the cleaning wastewater supply pump 115 sucks and pressurizes the cleaning wastewater in the cleaning wastewater storage tank 84 through the cleaning wastewater supply pipe 114 (the part on the cleaning wastewater storage tank side from the cleaning wastewater supply pump 115), and pressurizes the cleaning wastewater supply pipe. 114 is supplied to each water supply pipe 111 via 114 (the part on the sand accommodating part side from the washing wastewater supply pump 115) and the intermediate pipe 113. Thus, cleaning wastewater can be discharged from each water discharge nozzle 112 toward the upper surface of the sand layer 105 (sand) in the sand container 85.

  Hereinafter, a method for recovering the chelating agent by treating the cleaning wastewater containing the chelating agent with the chelating agent recovery unit 9 or the cleaning waste water evaporator 63 will be described in detail. The cleaning wastewater containing the chelating agent discharged from the cleaning wastewater receiving tanks 67 and 77 (see FIGS. 5 to 6) is removed through the cleaning wastewater discharge passage 83 except for the moisture that naturally evaporates (vaporizes) in the atmosphere. It flows into the washing wastewater storage tank 84 and is stored. In addition, when the roof is not attached to the washing | cleaning wastewater storage tank 84, the rainwater which fell to the washing | cleaning wastewater storage tank 84 itself will also be stored in the washing | cleaning wastewater storage tank 84. FIG.

  The cleaning wastewater stored in the cleaning wastewater storage tank 84 is supplied to each water supply pipe 111 by the cleaning wastewater supply pump 115 via the cleaning wastewater supply pipe 114 and the intermediate pipe 113, and from each water discharge nozzle 112 to the sand container. 85 is discharged in a drop-like or mist-like manner toward the upper surface of the sand layer 105 in 85 and is uniformly distributed on the sand layer 105. In this way, the washing waste water is sprayed on the sand layer 105 in the sand container 85 by the water discharge nozzle 112, and the washing waste water is always held between the sand particles in the sand layer 105, or the sand particles are thin films of the washing waste water. Is maintained in a saturated moisture state (for example, a water content ratio of 30 to 35%) covered with.

  Then, the cleaning wastewater retained in the sand layer 105 is evaporated (vaporized) into the atmosphere. Thus, all of the cleaning wastewater flowing into the cleaning wastewater storage tank 84 (including rainwater falling to the cleaning wastewater storage tank 84 when no roof is attached) is evaporated (vaporized) from the sand layer 105 into the atmosphere. At that time, the chelating agent contained in the cleaning wastewater remains in the sand layer 105. Therefore, the chelating agent contained in the cleaning wastewater is reliably recovered without being discharged to the outside. The area or size of the sand container 85 required for evaporating the cleaning wastewater from the sand layer 105 will be described later.

  The amount of cleaning wastewater sprayed from the cleaning wastewater spraying device 93 (water discharge nozzle 112) to the sand layer 105 is preferably set to be larger than the amount of cleaning wastewater evaporated from the sand layer 105 (for example, 1. 2 to 2.0 times). Thereby, the sand which comprises the sand layer 105 is maintained in a saturated moisture state (for example, water content ratio 30-35%). Here, excess cleaning wastewater flows down the gaps between the sand particles in the sand layer 105, passes through the perforated plate 104, and flows into the drain grooves 101. Then, excess cleaning wastewater in the drainage groove 101 is returned to the cleaning wastewater storage tank 84 via the collective drainage groove 102.

When such a cleaning wastewater evaporation process is repeatedly performed, the chelating agent is gradually accumulated in the sand layer 105 in the sand container 85. Therefore, every time a predetermined period elapses (for example, every 2 to 6 months), sand in a predetermined area or section (for example, an area of 100 to 200 m ² ) in the sand container 85 is removed to purify the soil. It introduce | transduces into the classification part 2 (Trommel 14 or Sandclean 17) of the facility S, and collect | recovers chelating agents. Then, fine sand obtained by sieving from the sand obtained by the sand rinsing device 61 is introduced into the section or region where the sand is removed from the sand container 85. That is, the sand containing the chelating agent in a predetermined section or region in the sand container 85 is exchanged with fine sand obtained by sieving from the sand. Therefore, the loss of the chelating agent from the soil purification facility S to the outside can be prevented or reduced. Moreover, since a part of sand which does not contain the chelating agent which comes out from the sand rinsing device 61 is used as sand to be accommodated in the sand accommodating portion 85, the sand used in the sand accommodating portion 85 can be easily procured.

  Hereinafter, an example of the specifications (surface area, dimensions, etc.) of the cleaning wastewater storage tank 84 and the sand container 85 required for evaporating the cleaning wastewater from the sand layer 105 will be described. For example, as shown in FIG. 9, a soil purification facility S that purifies 100 tons of contaminated soil (including water) per hour with washing water containing 0.3% by mass of a chelating agent is used for 8 hours a day. When operating for 250 days a year, the specifications of the washing waste water storage tank 84 and the sand container 85 may be set as follows, for example. The cleaning wastewater storage tank 84 is provided with a roof, and rainwater does not fall or flow into the cleaning wastewater storage tank 84.

  As shown in FIG. 9, 100 tons of soil (including moisture) is composed of 25 tons of gravel (dry basis), 30 tons of sand (dry basis), and 25 tons of fine particles (dry basis). , 20 tons of water, and its water content is 25%. Further, the moisture content of the aggregates discharged from the trommel 14 is 5%, and the moisture content of the sand discharged from the sand clean 17 is 20%. In addition, the specification demonstrated here is an example to the last, and even when the soil treatment amount of the soil remediation facility S, or operation time or operation days differ from these, the washing | cleaning wastewater storage tank 84 and the sand accommodating part 85 of the same method are used. Of course, specifications or dimensions can be set.

<Specifications of washing wastewater storage tank>
The specification of the washing waste water storage tank 84 is set as follows, for example.
・ Cuboid storage tank (right and left dimensions: 15m, front and rear dimensions: 30m, depth: 3m)
・ Surface area 450m ²
・ Maximum water storage capacity: about 1300 tons

<Specifications of sand container>
The specification of the sand accommodating part 85 is set as follows, for example.
・ Cuboid (left and right dimensions: 40m, front and rear dimensions: 200m, depth: 0.8m)
・ Top surface area 8000m ²
・ Sand capacity approximately 4000m ³

<Discharge of washing wastewater from sand rinsing equipment>
The discharge amount of the cleaning wastewater containing the chelating agent from the sand rinsing device 61 is 16800 tons / year if the amount of the rinsing water is 1.2 times that of the cleaning water contained in or adhering to the sand. .
7 tons / hr x 8 hr x 250 days x 1.2 = 16800 tons / year

<Discharge of washing wastewater from coarse aggregate rinsing device>
The discharge amount of the washing waste water containing the chelating agent from the coarse aggregate rinsing device 62 is 2400 tons if the amount of the rinse water used is 1.2 times the washing water contained in or attached to the coarse aggregate. / Year.
1 ton / hr x 8 hr x 250 days x 1.2 = 2400 ton / year

<Water evaporation in washing wastewater storage tank>
In general, it is known that the evaporation amount of water from the water surface in lakes and reservoirs is 0.5 to 1.0 ton per 1 m ^{2 of} water surface. Therefore, it is estimated that at least 225 tons of rainwater evaporates annually from the washing wastewater storage tank 84 (surface area 450 m ² ).
0.5 tons / m ² · year × 450 m ² = 225 tons / year As described above, the maximum water storage capacity of the washing waste water storage tank 84 is about 1300 tons, which is the sand rinsing device 61 and the coarse aggregate rinsing device 62. This is equivalent to about 17 days of discharge amount of washing waste water (19200 tons / year, that is, about 77 tons / day). On the other hand, since the cleaning wastewater stored in the cleaning wastewater storage tank 84 is processed in the sand container 85 every day, the cleaning wastewater storage tank 84 can store the cleaning wastewater with sufficient margin without overflowing the cleaning wastewater. it can.

<Water evaporation in sand layer>
For example, in view of the disclosure (research results) of Non-Patent Document 1, the amount of water evaporation in the sand layer 105 in the sand container 85 is 3.15 ton / m ² · year as described below. Estimated. That is, in Non-Patent Document 1, the water content ratio is 32.1% (saturated moisture state) when the temperature is 14.2 ° C., the relative humidity is 59%, and the air flow rate is 250 cm / second. The evaporation rate of water from the soil is disclosed as 11.3 × 10 ⁻⁶ g / cm ² · sec. In addition, when the temperature is 14.8 ° C., the relative humidity is 57%, and the air flow rate is 170 cm / sec, the water content is evaporated from the soil having a water content ratio of 32.9% (saturated moisture state). The speed is disclosed to be 7.9 × 10 ⁻⁶ g / cm ² · sec.

In view of such disclosure of Non-Patent Document 1, when the average climatic state in Japan is assumed to be a temperature of 15 ° C., a relative humidity of 60%, and a wind speed of about 2 m / second, saturated moisture in the sand container 85 is assumed. The average amount of water evaporated from the sand layer 105 in the state is estimated to be approximately 10.0 × 10 ⁻⁶ g / cm ² · sec. The amount of evaporation is 3.15 ton / m ² · year when converted to a practical unit.
10.0 × 10 ⁻⁶ g / cm ² · sec = 10.0 × 10 ⁻⁶ × 10 ⁻⁶ × 10 ⁴ tons / m ² · sec = 1.0 × 10 ⁻⁷ tons / m ² · sec = 1 0.0 × 10 ⁻⁷ × 3600 × 24 × 365 tons / m ² · year = 3.15 tons / m ² · year Accordingly, 25200 tons of water evaporates from the sand layer 105 in the sand container 85 annually.
3.15 tons / m ² · year x 8000 m ² = 25200 tons / year

<Balance of water in washing waste water evaporator>
As described above, the amount of cleaning wastewater discharged from the sand rinsing device 61 and the coarse aggregate rinsing device 62 is estimated to be 19,200 tons per year. On the other hand, at least 225 tons of water evaporates annually in the washing wastewater storage tank 84, and 25200 tons of water evaporates annually in the sand container 85. Accordingly, it is estimated that 25425 tons of water evaporates annually in the cleaning wastewater evaporator 63. Thus, in the cleaning wastewater evaporation device 63, the total amount of cleaning wastewater discharged from the sand rinsing device 61 and the coarse aggregate rinsing device 62 (19,200 tons per year) is about 1.3 times (1 year). 25425/19200 = 1.31) of the amount of water can be evaporated, so that basically all of the cleaning waste water can be evaporated and treated. However, since the amount of water evaporation decreases during, for example, the winter season or the rainy season, it is preferable to lengthen the dimension (200 m) in the front-rear direction of the sand accommodating portion 85 in the specific example by about 10 to 20%.

  As described above, according to the soil purification method or the chelating agent recovery apparatus T according to the embodiment of the present invention, it is possible to prevent or reduce the chelating agent from being taken away by sand and coarse aggregate, which is contaminated with harmful metals. The replenishment amount of the chelating agent in the soil purification facility S that purifies the soil with the washing water containing the chelating agent can be greatly reduced, and the treatment cost of the contaminated soil can be reduced. Moreover, since all the rainwater which fell to the site | part R of the soil washing | cleaning apparatus S is used as rinse water with the sand rinse apparatus 61 and the coarse aggregate rinse apparatus 62, the rainwater which fell to the site | part R of the soil purification facility S is used for this. The hazardous metals contained can be treated reliably without being discharged to the outside without being treated. Further, since tap water or industrial water is not used in the chelating agent removing unit 8 (sand rinsing device 61 and coarse aggregate rinsing device 62), rainwater is effectively used as rinsing water. Can be reduced.

  R site, S soil purification facility, T chelating agent recovery device, 1 mixing section, 2 classification section, 3 sedimentation separation section, 4 filtration section, 5 chelating agent regeneration section, 6 chelating agent replenishment section, 7 rainwater supply section, 8 chelation Agent removal unit, 9 Chelating agent recovery unit, 11 Input hopper, 12 Mixing device, 13 Mill breaker, 14 Trommel, 15 Cyclone, 16 Seal tank, 17 Sand clean, 18 Feed tank, 19 PH adjustment tank, 20 Coagulation tank, 21 Floating material recovery equipment, 22 thickener, 23 intermediate tank, 24 filter press, 25 wash water tank, 26 spare water tank, 27 wash water tank, 28 acid liquid tank, 29 water tank, 30 liquid fluidized bed apparatus, 31 pump, 32 pipe Line, 33 Pump, 34-37 Pipeline, 38 Pump, 39-40 Pipeline, 41 Pump, 42-4 Pipe line, 44 to 51 valve, 55 rainwater storage tank, 56 rainwater supply device, 61 sand rinse device, 62 coarse aggregate rinse device, 63 washing waste water evaporation device, 64 belt conveyor, 65 sand supply device, 66 rinse water spray device, 67 Cleaning waste water receiving tank, 68 Drive roller, 68a shaft, 69 Driven roller, 69a shaft, 70 Conveyor belt, 71 Support roller, 72 Guide plate, 74 Belt conveyor, 75 Coarse aggregate supply device, 76 Rinsing water spray device, 77 Cleaning Waste water receiving tank, 78 driving roller, 78a shaft, 79 driven roller, 79a shaft, 80 conveyor belt, 81 support roller, 82 guide plate, 83 cleaning waste water discharge passage, 84 cleaning waste water storage tank, 85 sand container, 86 front end wall, 87 Rear end wall, 88 Left side wall, 89 Right side wall, 90 Bottom wall, 92 Roof, 9 Washing wastewater spraying device, 94 Washing wastewater recirculation mechanism, 100 ground, 101 drainage groove, 102 collecting drainage groove, 103 convex portion, 104 perforated plate, 105 sand layer, 107 left vertical frame, 108 right vertical frame, 109 horizontal frame, 111 water supply Pipe, 112 Water discharge nozzle, 113 Intermediate pipe, 114 Washing wastewater supply pipe, 115 Washing wastewater supply pump.

Claims (3)

A soil purification method in a soil purification facility that purifies soil contaminated with a toxic metal or a compound thereof with wash water containing a chelating agent,
The soil purification facility is
A soil containing gravel, sand and fine soil and contaminated with a harmful metal or a compound thereof is mixed with washing water containing a chelating agent to remove the harmful metal or the compound adhering to the soil from the soil. A mixing part to be separated and captured by the chelating agent;
Receiving a mixture of soil and washing water discharged from the mixing unit, and separating the coarse aggregate and sand from the mixture;
A settling separation unit that separates wash water containing fine-grained soil discharged from the classification unit into supernatant water and sludge containing fine-grained soil by settling separation;
Receiving the supernatant water discharged from the sedimentation separation unit, removing the harmful metal or its compound from the chelating agent capturing the harmful metal or its compound in the supernatant water, regenerating the chelating agent, A chelating agent regenerating part that is refluxed to the mixing part as washing water,
Washing is performed so that the wash water containing the regenerated chelating agent from the chelating agent regeneration unit is supplemented with the reduced amount of the chelating agent so that the chelating agent concentration in the washing water is maintained at a preset value. A chelating agent replenishment unit for supplying a chelating agent to water,
Outside the site of the soil purification facility, a chelating agent recovery device that recovers the chelating agent contained in or attached to the sand and coarse aggregate separated by the classification unit is provided,
The chelating agent recovery device includes a chelating agent removing unit that removes the chelating agent by washing the sand and coarse aggregate separated in the classification unit with rinse water, and the rainwater that has fallen on the site of the soil purification facility. A rainwater supply unit that supplies the agent removal unit as rinse water, and a chelating agent recovery unit that recovers the chelating agent from the cleaning wastewater discharged from the chelating agent removal unit,
The chelating agent removing unit is
A sand rinsing device that removes a chelating agent held in the sand by spraying or spraying rinsing water on the sand separated in the classification unit;
A coarse aggregate rinsing device that sprays or sprays rinsing water on the coarse aggregate separated in the classifying unit to remove the chelating agent held in the coarse aggregate;
The chelating agent recovery unit
A cleaning wastewater storage tank for receiving and storing cleaning wastewater containing a chelating agent discharged from the sand rinsing device and the coarse aggregate rinsing device;
A container-shaped sand container that is disposed on the ground and accommodates water evaporating sand, the upper side being opened;
A roof disposed above the sand container and preventing rain water from dropping into the sand container;
A cleaning wastewater spraying device for spraying the cleaning wastewater stored in the cleaning wastewater storage tank to the water evaporation sand stored in the sand storage unit,
A washing waste water recirculation mechanism that recirculates excess washing waste water flowing down through the gaps between the particles of water evaporating sand contained in the sand containing portion to the washing waste water storage tank;
The soil purification method includes:
While spraying cleaning wastewater from the cleaning wastewater spraying device on the water evaporation sand accommodated in the sand container, the water of the cleaning wastewater adhering to the water evaporation sand is evaporated into the air to Remove it from the sandbox,
Introducing the water evaporating sand in which the chelating agent is accumulated for a predetermined period in the sand accommodating unit into the classification unit or the mixing unit, and recovering the chelating agent accumulated in the water evaporating sand,
A method for soil purification, wherein a part of sand discharged from the sand rinsing device is used as water evaporating sand stored in the sand storage unit.   The water evaporating sand is fine sand, and the water content of the water evaporating sand accommodated in the sand accommodating portion is set to 30 to 35 in terms of the amount of washing waste water sprayed from the washing waste water dispersing device to the sand accommodating portion. The soil purification method according to claim 1, wherein the soil purification method is set so as to be maintained at%.   The soil purification method according to claim 2, wherein a particle size of the fine sand is in a range of 0.075 to 0.25 mm.

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