JP6296269B1 - Soil purification method - Google Patents

Abstract

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 or the like, and rainwater that has fallen to the site of the soil purification facility is untreated. A means is provided that enables processing without discharging to the outside. A soil purification facility S that purifies toxic metal-contaminated soil with washing water containing a chelating agent. 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. The chelating agent recovery unit 9 includes a cleaning wastewater storage tank 84, a sand storage unit 85, a side groove 91, and a water level holding device 94. In this soil purification method, the water level in the side groove 91 is held at the upper end position of the sand immersion by the water level holding device 94, a capillary water zone is formed in the sand layer, and the washing waste water adhering to the water evaporating sand in the capillary water zone Is removed by evaporation. Then, the water evaporating sand in which the chelating agent is accumulated is introduced into the classification unit or the mixing unit to recover the chelating agent. [Selection] Figure 6

Description

  The present invention relates to a soil purification method in a soil purification facility in which soil contaminated with a toxic metal or a compound thereof is purified with wash 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 removed contaminated soil contaminated with harmful metals with washing water containing a chelating agent to remove the harmful metals and the like, while removing the harmful metals with the 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

Tokyo University of Science, Geotechnical Laboratory, Soil Mechanics I / II Lecture Materials, Chapter 2, “Saturated Properties of Unsaturated Soil”, p. 1-18 http: // www. rs. noda. tus. ac. jp / soil / lecture / SoilMechanics / 02_Unsaturated / H23unsaturated. pdf Development Ichiro “Experiment on Water Behavior and Groundwater Runoff in Capillary Zone” 11, 1987, 79-83 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 storage unit, a roof, a side groove, a cleaning wastewater supply device, a cleaning wastewater recirculation path, and a water level holding device. The cleaning wastewater storage tank receives and stores cleaning wastewater containing a chelating agent discharged from the sand rinsing device. The sand container is disposed on the ground, and is disposed in a space formed by the peripheral wall, a bottom wall coupled to the lower end of the peripheral wall, and the peripheral wall and the bottom wall, and allows cleaning wastewater to pass but not sand. A container having a perforated plate and containing water evaporating sand on the perforated plate in its internal space. A roof is arrange | positioned above a sand accommodating part, and prevents the fall of rain water to a sand accommodating part. The side groove is disposed adjacent to the outer surface of the peripheral wall of the sand container, and its internal space communicates with the internal space of the sand container via a communication hole formed in the peripheral wall below the perforated plate. The cleaning wastewater supply device supplies the cleaning wastewater stored in the cleaning wastewater storage tank to the side groove. The cleaning waste water return path returns the cleaning waste water in the side groove to the cleaning waste water storage tank. The water level holding device holds the level of the cleaning wastewater in the groove at a preset sand immersion upper end position. Note that the sand soaking upper end position is formed by the water evaporating sand located between the sand soaking upper end position and the position of the upper surface of the water evaporating sand accommodated in the internal space of the sand accommodating portion. Is set as follows.

  In this soil purification method, the water level holding device holds the level of the washing waste water in the gutter at the sand immersion upper end position, and forms a capillary water zone in the sand layer above the sand immersion upper end position. And the water | moisture content of the washing waste water adhering to the water evaporation sand in a capillary water zone is evaporated in air, and is removed from a sand accommodating part. On the other hand, the water evaporating sand that has been used in the sand container for a predetermined period and accumulated the chelating agent is introduced into the classifying unit or the mixing unit, and the chelating agent accumulated in the water evaporating sand is recovered. A part of the sand discharged from the sand rinsing device is used as water evaporating sand accommodated in the sand accommodating portion.

  In the soil purification method according to the present invention, it is preferable to separate fine sand from sand discharged from the sand rinsing apparatus and use the fine sand (part or all) as water evaporation sand that is accommodated in the sand accommodating portion. . In this case, it is preferable to separate the fine sand by drying and sieving the sand discharged from the sand rinsing apparatus.

  According to the soil purification method according to the present invention, the water level holding device holds the water level of the ditch at the sand soaking upper end position, and is adhered to the water evaporation sand in the capillary water zone above the sand soaking upper end position. Waste water can be evaporated from the sand and removed from the sand reservoir. At this time, since the chelating agent contained in the washing wastewater does not evaporate and remains in the sand container, it is possible to prevent the chelating agent from being lost to the outside. Moreover, since the water evaporation sand used for a predetermined period in the sand container is introduced into the soil purification facility, the chelating agent adhering to the sand separated from the classification unit can be returned to the soil purification facility. Moreover, since a part of sand which does not contain the chelating agent which comes out of the sand rinsing device is used as water evaporating sand accommodated in the sand accommodating portion, the water evaporating sand used in the sand accommodating portion can be easily procured.

  In addition, all rainwater that has fallen to the site of the soil purification 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. It is a typical sectional elevation view of a sand storage part, a roof, and a gutter cut by a plane perpendicular to the longitudinal direction (front-rear direction) of the sand storage part. It is a typical top view of the principal part of a sand storage part and a side groove in the state where a perforated panel and a sand layer were removed. It is a block diagram which shows the flow volume of the soil, water, and a chelating agent in the predetermined site | part of a 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. In addition, 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). Further, the chelating agent removing unit 8 sprays or jets rinsing water on the coarse aggregate separated by the classifying unit 2 and removes the chelating agent held by the coarse aggregate 62 ( (See FIG. 5).

  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 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 the fine-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 the chelating agent recovery method 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 unit 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 accommodated in each of the cleaning wastewater receiving tanks 67 and 77 (see FIGS. 4 and 5) of the sand rinsing device 61 and the coarse aggregate rinsing device 62 is sent to the chelating agent recovery unit 9 to be chelated. The agent is recovered. 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. In this way, the chelating agent is recovered from the cleaning wastewater by the cleaning wastewater evaporator 63, and this chelating agent is returned 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 wastewater evaporator 63 is provided with cleaning wastewater containing a chelating agent discharged from the cleaning wastewater receiving tanks 67 and 77 (see FIGS. 4 and 5) and a cleaning wastewater discharge passage 83. A cleaning waste water storage tank 84 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, the cleaning wastewater storage tank 84 and the cleaning wastewater discharge passage 83 are aligned in FIG. 6 in order to clearly show the positional relationship between the facility or the apparatus in the chelating agent recovery unit 9 or the cleaning wastewater evaporator 63 (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 accommodating portion 85 for accommodating water evaporating sand, which is appropriately separated from the cleaning waste water storage tank 84 in a direction perpendicular to the left-right direction. Yes. In this embodiment, fine sand (sand having a particle size of 0.075 to 0.25 mm) is used as such water evaporation sand. In the following, the cleaning wastewater storage tank 84 and the sand container 85 are arranged side by side (a direction perpendicular to the left-right direction) in order to clearly show the positional relationship between the facility or the apparatus in the chelating agent recovery unit 9 or the cleaning wastewater evaporator 63. , The side where the cleaning waste water storage tank 84 is located is referred to as “front”, and the side where 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 container that has a rectangular planar shape and has a depth that can accommodate an appropriate amount of water evaporating sand and is installed on the ground or buried in the ground. A side groove 91 is provided on the left side of the sand container 85, and the side groove 91 is disposed adjacent to the outer surface (left surface) of the left wall 88 of the sand container 85. The side groove 91 is made of concrete and is integrally formed with the sand accommodating portion 85.

  Further, in the cleaning waste water evaporation device 63, the cleaning waste water supply device 92 that supplies the cleaning waste water stored in the cleaning waste water storage tank 84 to the side groove 91, and the excess cleaning waste water in the side groove 91 is returned to the cleaning waste water storage tank 84. The cleaning wastewater recirculation path 93 and a water level holding device 94 that holds the level of the cleaning wastewater in the side groove 91 at a preset position of the sand immersion in the sand container 85 are provided. Here, the sand soaking upper end position means that the water evaporating sand located between the sand soaking upper end position and the position of the upper surface of the water evaporating sand accommodated in the internal space of the sand accommodating portion 85 is a capillary water zone ( Saturated moisture state sand layer) is formed.

  Hereinafter, a specific configuration and function of the cleaning wastewater evaporator 63 will be described. The sand accommodating portion 85 for accommodating water evaporating sand is made of concrete, and is embedded in the ground 100 so that the vicinity of the upper end portion 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, 30 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. Is configured to accommodate a suitable amount of water evaporating sand (for example, 0.8 to 1.0 m), the front end wall 86, the rear end wall 87, the left side wall 88, the right side wall 89, and the bottom wall 90, Is a box-shaped container. The lengths of the sand container 85 in the left-right direction and the front-rear direction are preferably set according to the amount of water evaporated in the sand container 85. Further, as the water evaporating sand accommodated in the sand accommodating portion 85, it is preferable to use fine sand generated in the soil treatment facility S. The fine sand can be generated, for example, by drying and sieving the sand discharged from the sand rinsing device 61.

  A plurality of bottom grooves 101 extending in parallel in the left-right direction with a predetermined interval in the front-rear direction and having a predetermined depth (for example, 10 to 15 cm) are provided on the upper surface of the bottom wall 90. Each of these bottom grooves 101 communicates with the internal space of the side groove 91 via a communication hole 102 formed in the left side wall 88. That is, the internal space (lower space) of the side groove 91 and the internal space (lower space) of the sand accommodating portion 85 are in communication with each other via the communication hole 102 and the bottom groove 101 in the vicinity of these bottom portions.

  A porous plate 104 that allows cleaning wastewater to pass through but does not allow water evaporation sand to pass therethrough is disposed on the plurality of convex portions 103 positioned between the bottom grooves 101 in the front-rear 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, 50 to 80 cm) is provided on the porous plate 104. Further, a roof 117 supported by the frame structure 116 is provided above the sand accommodating portion 85 to prevent rain water from dropping to the water evaporating sand in the sand accommodating portion 85.

  Thus, when the cleaning wastewater is introduced into the side groove 91, the cleaning wastewater flows into the sand accommodating portion 85 through the communication hole 102 and the bottom groove 101, and enters the sand particle gap. As a result, the sand layer 105 is completely immersed in the cleaning wastewater up to a position L that is substantially the same height as the level of the cleaning wastewater in the side groove 91, and there is no air in the gaps between the sand particles. Filled with waste water, the buoyancy due to washing waste water is in a sand soak state where each sand particle acts. Hereinafter, the upper end position of the sand layer 105 completely immersed in such washing waste water is referred to as “sand immersion upper end position L”.

  Above the sand soaking upper end position L, washing wastewater is sucked into the sand layer 105 by capillary action, and most of the gaps between the sand particles are filled with washing wastewater, but there is a capillary water zone in which some air exists ( Or a saturated capillary water zone), that is, a sand layer 105 in a substantially saturated water state. In such a capillary water zone, the amount of evaporation of washing wastewater from the sand particles to the atmosphere becomes very large, for example, compared to the amount of evaporation from the water surface of the pond (0.5 to 1.0 m3 / m2 / year). Thus, it is estimated to be 3 to 5 times.

  The height or thickness of the capillary water zone or saturated capillary water zone increases as the particle size of the water evaporation sand decreases. For example, in Non-Patent Document 1, the height of a sand capillary water zone having a particle size of 0.02 mm is 180 cm, and the height of a sand capillary water zone having a particle size of 0.2 mm is 21 cm. There is a description. Non-Patent Document 2 describes that the height of the capillary water zone of glass beads having a particle size of 0.1 mm is about 55 cm.

  In view of such facts, in the present embodiment in which fine sand (particle size: 0.075 to 0.25 mm) is used as water evaporating sand accommodated in the sand accommodating portion 85, the height of the capillary water zone is It is estimated to be about 0.2 to 0.4 m. Therefore, the sand immersion upper end position L is preferably set to a position in the range of 20 to 40 cm downward from the upper surface of the sand layer 105, for example. Note that, in a portion near the upper surface of the sand layer 105 in the sand container 85 (for example, 2 to 3 cm downward from the upper surface of the sand layer), a large amount of air exists in the gap between the sand particles, while the surface of the sand particles is washed. It is presumed that a film water zone (unsaturated water state sand layer) covered with a waste water film is formed.

  In the present invention, the water evaporating sand used in the sand container 85 is not limited to fine sand, and it is needless to say that sand having a particle size different from that of fine sand may be used. In this case, the height of the capillary water zone corresponding to the particle size is estimated, and the sand soaking upper end position L may be set based on this. For example, when medium sand (particle size: 0.25 to 0.85 mm) is used, the sand immersion upper end position L may be set to a position in the range of 10 to 20 cm downward from the upper surface of the sand layer 105, for example.

  The side groove 91 is a concrete water channel formed integrally with the sand container 85, and the bottom wall of the side groove 91 is at the same height as the bottom wall 90 of the sand container 85 (the bottom of the bottom groove 101). . Further, the upper end portion of the side groove 91 is at the same height as the upper end portion of the left side wall 88 of the sand accommodating portion 85. The width (lateral dimension) of the side groove 91 is preferably about 0.5 to 1 m, for example.

The water level holding device 94 is disposed between the water tank 110 that is in communication with the side groove 91 and connected to the cleaning wastewater recirculation path 93, and between the water tank 110 and the cleaning wastewater recirculation path 93. It has a weir 111 that overflows the reflux path 93 and maintains the water level of the water tank 110 and the side groove 91 at a constant value. Here, the water tank 110 is a concrete container that is installed on the ground 100 and is opened at the top, and the upper end thereof is at the same height as the upper end of the side groove 91. And the bottom part of the water tank 110 exists in the position moderately lower than the bottom part of the side groove | channel 91 (for example, 0.5-1.5 m lower position). The water tank 110 and the side groove 91 are connected to and communicate with each other, and the water levels of the cleaning wastewater stored in these are equal to each other. In addition, it is preferable that the planar shape of the water tank 110 is a rectangle, and it is preferable that the water area is about 20-50 m < ² >, for example.

  The weir 111 is for maintaining the water level of the washing waste water in the water tank 110 and the side groove 91 constant, but this water level can be freely changed by changing the overflow height of the weir 111. The overflow height of the weir 111 is preferably set so that the water level of the water tank 110 and the side groove 91 coincides with the predetermined sand immersion upper end position L. The cleaning wastewater overflowing from the water tank 110 to the cleaning wastewater recirculation path 93 through the weir 111 is returned to the cleaning wastewater storage tank 84.

  The cleaning waste water supply device 92 includes a cleaning waste water supply pump 112 and a cleaning waste water supply pipe 113 for continuously supplying the cleaning waste water in the cleaning waste water storage tank 84 to the water tank 110. Here, the cleaning wastewater supply pump 112 transfers the cleaning wastewater stored in the cleaning wastewater storage tank 84 to the water tank 110 at a flow rate (for example, 10 to 20 times) sufficiently larger than the evaporation amount of water in the sand container 85. Supply. Therefore, the water level of the water tank 110 and the side groove 91 is always maintained at the preset sand immersion upper end position L.

  Hereinafter, a method for treating cleaning wastewater containing a chelating agent with the chelating agent recovery unit 9 or the cleaning wastewater evaporation device 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. 4 and 5) is cleaned through the cleaning wastewater discharge passage 83 except for water that naturally evaporates (vaporizes) in the atmosphere. It flows into the wastewater storage tank 84 and is stored. In addition, when the roof is not attached to the washing | cleaning wastewater storage tank 84, the rain water which fell to the washing | cleaning wastewater storage tank 84 itself is also stored by the washing | cleaning wastewater storage tank 84. FIG.

  The cleaning wastewater stored in the cleaning wastewater storage tank 84 is continuously supplied to the water tank 110 by the cleaning wastewater supply pump 112 through the cleaning wastewater supply pipe 113. As described above, the cleaning wastewater supply pump 112 supplies the cleaning wastewater to the side groove 91 at a flow rate sufficiently larger than the evaporation amount of the water in the sand layer 105 in the sand container 85, so that the water level of the water tank 110 and the side groove 91 is the weir. A predetermined position corresponding to the overflow height of 111, that is, a preset sand immersion upper end position L is maintained. The excess cleaning wastewater overflows the weir 111 and returns to the cleaning wastewater storage tank 84 via the cleaning wastewater recirculation path 93.

  Thus, since the water level of the side groove 91 is maintained at the sand immersion upper end position L, the water level of the internal space of the sand accommodating portion 85 communicating with the internal space of the side groove 91 is also maintained at the sand immersion upper end position L. Along with this, a capillary water zone (saturated moisture state sand layer) is formed in the sand layer 105 on the upper side of the sand immersion upper end position L. As described above, while fine sand is used in the present embodiment, the sand immersion upper end position L is set to a position in the range of 20 to 40 cm downward from the upper surface of the sand layer 105, and thus it is estimated that a coating water zone is formed. Except for the vicinity of the upper surface of the sand layer 105 (a sand layer of 2 to 3 cm downward from the upper surface of the sand layer), a capillary water zone above the sand immersion upper end position L, that is, a saturated moisture state (for example, a water content ratio of 30 to 35%) The sand layer 105 is formed.

  And the water | moisture content in the washing waste water hold | maintained in the sand layer 105 of the upper side of the sand immersion upper end position L evaporates (vaporizes) in air | atmosphere. Thus, all of the water in 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) evaporates from the sand layer 105 to 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.

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), the water evaporating sand in a predetermined area or section (for example, an area of 100 to 200 m ² ) in the sand container 85 is removed. Then, it is introduced into the soil purification facility S, and the chelating agent is returned to the soil purification facility S. Then, fine sand obtained by sieving from the sand obtained by purifying the contaminated soil in the soil purification facility 2 is introduced into the section or region where the water evaporating sand is removed from the sand accommodating portion 85. That is, the water evaporating sand containing the chelating agent in a predetermined section or region in the sand container 85 is replaced with fine sand obtained by sieving from the sand discharged from the sand rinsing device 61. Therefore, the loss of the chelating agent from the soil purification facility S to the outside can be prevented or reduced. Further, since a part of the sand that does not contain the chelating agent exiting from the soil purification facility S or the sand rinsing device 61 is used as the water evaporating sand to be accommodated in the sand accommodating portion 85, the water evaporating sand used in the sand accommodating portion 85 is used. Can be procured easily.

  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 water in 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%. 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%. In addition, the specification demonstrated here is an example to the last, and even when the soil processing amount of the soil treatment facility S, or operation time or operation days differ from these, the washing waste water 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 water evaporates from the washing waste water 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>
The amount of water evaporation in the sand layer 105 in the sand container 85 is estimated to be 3.15 ton / m ² · year as described below. That is, first, in Non-Patent Document 3, 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 / sec. 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 the disclosed matters of Non-Patent Document 3, 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 method 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, and soil contaminated with harmful metals or the like. The amount of replenishment of the chelating agent in the soil purification facility S that purifies the soil with the cleaning 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, 91 side groove, 9 Washing wastewater supply device, 93 Washing wastewater return path, 94 Water level holding device, 100 Ground, 101 Bottom groove, 102 Communication hole, 103 Convex part, 104 Perforated plate, 105 Sand layer, 110 Water tank, 111 Weir, 112 Washing wastewater supply pump, 113 Washing waste water supply pipe, 116 frame structure, 117 roof.

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;
A chelating agent regeneration unit that receives the supernatant water discharged from the sedimentation separation unit, removes the harmful metal or the compound from the chelating agent capturing the harmful metal or the compound in the supernatant water, and regenerates the chelating agent. When,
The washing water from the chelating agent regeneration unit is replenished with the reduced amount of the chelating agent, and the washing water containing the regenerated chelating agent is maintained to maintain the chelating agent concentration in the washing water at a preset value. A chelating agent replenishment unit for supplying the chelating agent to
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 perforated plate disposed in the ground, disposed in a space formed by a peripheral wall, a bottom wall coupled to the lower end of the peripheral wall, and the peripheral wall and the bottom wall, and allows cleaning wastewater to pass but not sand A container-shaped sand containing portion opened on the upper side, containing water evaporating sand on the porous plate in its internal space,
A roof disposed above the sand container and preventing rain water from dropping into the sand container;
It is disposed adjacent to the outer surface of the peripheral wall of the sand container, and its internal space communicates with the internal space of the sand container via a communication hole formed in the peripheral wall below the perforated plate. Gutters,
A cleaning wastewater supply device that supplies the cleaning wastewater stored in the cleaning wastewater storage tank to the side groove;
A cleaning wastewater return path for returning the cleaning wastewater in the side groove to the cleaning wastewater storage tank;
A water level holding device for holding the water level of the cleaning wastewater in the side groove at a preset sand immersion upper end position;
The sand soaking upper end position is such that the water evaporating sand located between the sand soaking upper end position and the position of the upper surface of the water evaporating sand accommodated in the internal space of the sand accommodating portion forms a capillary water zone. Is set to
The soil purification method includes:
The water level holding device holds the water level of the washing waste water in the gutter at the upper end position of the sand immersion, forms a capillary water zone in the sand layer above the upper end position of the sand immersion, and evaporates water in the capillary water zone The water of the cleaning wastewater adhering to the sand is removed from the sand container by evaporating it into the air,
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.   2. The soil purification method according to claim 1, wherein fine sand is separated from sand discharged from the sand rinsing device, and the fine sand is used as water evaporating sand stored in the sand storage unit.   The soil purification method according to claim 2, wherein the fine sand is separated by drying and sieving the sand discharged from the sand rinsing device.

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