JP2018030114A - Recovery method of chelating agent in soil cleaning facility which uses chelating agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, in a soil cleaning facility which cleans soil contaminated with poisonous metals and the like with wash water containing a chelating agent, a means for preventing the chelating agent from being carried away by a filter cake.SOLUTION: A soil cleaning facility S, which cleans soil contaminated with poisonous metals and the like with wash water containing a chelating agent, is provided with: a vacuum filter which filters sludge containing fine-grained soil and, on the other hand, washes away the chelating agent contained in the filter cake by spraying rinse water on the filter cake; and a chelating agent recovery part 7 which recovers the chelating agent from rinse water discharged from the vacuum filter. In the recovery method of chelating agent according to the present invention, rinse water is sprayed from a rinse water spraying device 93 on sand in a sand storage part 85 and, on the other hand, rinse water adhered to the sand is removed by evaporation. Then, the sand which has the chelating agent accumulated in the sand storage part 85 is introduced in a classification part of the soil cleaning facility S to recover the chelating agent. Further, the sand discharged from the classification part is used as sand to be stored in the sand storage part 85.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a method for recovering a chelating agent 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, soil contaminated with toxic metals (hereinafter referred to as “toxic metal-contaminated soil”) is insolubilized, for example, with toxic metals at the location where the toxic metal-contaminated soil actually exists (hereinafter referred to as “original location”). 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. It should be noted that the site where the toxic metal-contaminated soil has been removed is usually backfilled with the original soil purified by a soil purification facility or another clean soil.

  As a method for purifying toxic metal-contaminated soil at such off-site soil purification facilities, conventionally, a soil clarification method has been widely used in which toxic metal-contaminated soil is washed with a cleaning solution to remove toxic metals. ing. Thus, the applicants of the present application wash the contaminated soil contaminated with harmful metals with washing water containing a chelating agent to remove the harmful metals, etc. Various closed system type soil remediation facilities that regenerate and reuse wash water or chelating agents by removing them and do not discharge the 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

  In the soil purification facilities disclosed in Patent Documents 1 to 4 related to the applicants of the present application, the soil containing stones, gravel, sand, and fine-grained soil and contaminated with harmful metals is received and mixed in the soil. And crushing the stones and gravel, and then mixing the soil and washing water containing a chelating agent, separating harmful metals adhering to the soil from the soil and capturing the chelating agent, The soil is classified or separated to produce coarse aggregate, sand, and soil (fine-grained soil).

  By the way, although the washing water containing a chelating agent adheres to the soil which is the filter cake produced in this way, there is a problem that the soil containing the chelating agent is not preferable for, for example, agricultural soil. In addition, the chelating agent in the soil purification facility is reduced by the amount taken away by the soil that is the filter cake. 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 taken away by the soil that is the filter cake. 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 there is a problem that the cost of soil treatment in the soil remediation facility is high .

  For example, in a soil remediation facility that purifies 1000 tons of soil per day, about 250 tons of filter cake or soil (dry basis) is generated per day. The water content of such a filter cake is about 40%. It is predicted that Therefore, for example, when washing water containing 0.3% by mass of a chelating agent is used for washing contaminated soil, 0.30 tons (250 × 0.4 × 0.003 = 0.30) per day, that is, If the annual working days are 300 days, 90 tons of chelating agent per year will be lost from the soil purification facility. In addition, when washing water containing 1.0% by mass of a chelating agent is used, 1.0 ton per day (250 × 0.4 × 0.01 = 1.0), that is, the annual operating days is 300 days If so, 300 tons of chelating agent per year will be lost from the soil remediation facility.

  The present invention has been made to solve the above-described conventional problems, and purifies soil contaminated with toxic metals and the like with washing water containing a circulating chelating agent. To provide a means that makes it possible to prevent the chelating agent from being taken away by soil (filter cake) in a soil purification facility that separates and reuses sand and soil (fine-grained soil). It is a problem to be solved.

  In the method for recovering a chelating agent according to the present invention made to solve the above-mentioned problems, in a soil purification facility for purifying soil contaminated with harmful metals with washing water containing a chelating agent, rinsing is discharged from a filtration unit. Recover chelating agent from water. The soil purification facility in which the chelating agent recovery method according to the present invention is used includes a crushing section, a classification section, a sedimentation separation section, a chelating agent regeneration section, a filtration section, and a chelating agent recovery section.

  Here, the crushing unit accepts soil containing stones, gravel, sand, and fine-grained soil and contaminated with harmful metals or the like, and crushes stones and gravel mixed in the soil. The classification unit mixes the soil discharged from the crushing unit and washing water containing a chelating agent, separates harmful gold adhering to the soil from the soil, and captures the chelating agent. Separating coarse aggregate and sand. 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, regenerates the chelating agent by removing the harmful metals from the chelating agent capturing the harmful metals and the like in the supernatant water. The filtration unit is configured to filter the sludge discharged from the sedimentation separation unit, and to rinse or spray rinse water on the filter cake to wash away the chelating agent contained in the filter cake. The chelating agent recovery unit recovers the chelating agent from the rinse water discharged from the filtration unit.

  The chelating agent recovery unit includes a rinse water storage tank, a sand storage unit, a roof, a rinse water spray device, and a rinse water reflux mechanism. Here, the rinse water storage tank receives and stores the rinse water containing the chelating agent discharged from the filtration unit. 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 rinse water spraying device sprays the rinse water stored in the rinse water storage tank onto the water evaporating sand accommodated in the sand accommodating portion. The rinsing water reflux mechanism causes excess rinsing water flowing down through the gaps between the particles of water evaporating sand accommodated in the sand accommodating portion to recirculate to the rinsing water storage tank.

  In the chelating agent recovery method according to the present invention, the rinsing water is sprayed from the rinsing water spraying device on the water evaporation sand accommodated in the sand container, while the rinse water adhering to the water evaporation sand is removed. The chelating agent accumulated in the water evaporating sand by evaporating it into the air and removing it from the sand accommodating portion and introducing the water evaporating sand in which the chelating agent is accumulated in the sand accommodating portion for a predetermined period into the classification portion And a part of the sand discharged from the classification part is used as water evaporating sand which is accommodated in the sand accommodating part.

  In the chelating agent recovery method according to the present invention, the water evaporation sand used in the sand container is preferably fine sand (that is, sand having a particle size of 0.075 to 0.25 mm). The amount of rinsing water sprayed onto the sand container is preferably set so that the water content of the water evaporating sand stored in the sand container is maintained at 30 to 35%.

  According to the chelating agent recovery method of the present invention, the rinsing water is sprayed or sprayed on the filter cake and the chelating agent contained in the filter cake is washed away in the filter section. High-quality soil (improved soil) that can be reused as cultivated soil can be generated. The rinse water discharged from the filtration unit and stored in the rinse water storage tank evaporates in the sand container, and the chelating agent contained in the rinse water is accumulated in the water evaporating sand in the sand container. And since the water evaporating sand in which the chelating agent is accumulated in this way is introduced into the classifying unit, the chelating agent contained in the rinse water discharged from the filtering unit is not discharged to the outside. To be recovered. In other words, while purifying with washing water containing a chelating agent that circulates in soil contaminated with toxic metals, coarse aggregate, sand and soil (fine-grained soil) are separated and reused. In the soil purification facility, the chelating agent can be reliably prevented from being taken away by the soil (filter cake). Further, since a part of the sand discharged from the classification unit is used as water evaporating sand accommodated in the sand accommodating unit, it is not necessary to separately procure the water evaporating sand used in the sand accommodating unit. Can be easily procured.

FIG. 1 is a block diagram showing a schematic configuration of a soil purification facility. FIG. 2 is a block diagram showing a specific configuration of the soil purification facility shown in FIG. FIG. 3 is a schematic diagram showing a specific configuration of the chelating agent regeneration unit of the soil purification facility shown in FIG. FIG. 4 is a schematic side cross-sectional view of a vacuum filter (filter unit). FIG. 5 is a schematic cross-sectional side view of the separation mechanism of filtrate and rinse water in a vacuum filter. FIG. 6 is a plan view schematically showing an arrangement form of the chelating agent recovery unit of the soil purification facility. FIG. 7 is a schematic partial sectional elevational view of the sand container, the rinse water 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 the main part of the sand container and the rinse water spraying device 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 provided with a chelating agent recovery unit using the chelating agent recovery method according to the present invention will be described with reference to FIG. As shown in FIG. 1, the soil purification facility S includes a crushing unit 1, a classifying unit 2, a sedimentation separating unit 3, a filtering unit 4, a chelating agent regeneration unit 5, a chelating agent supplementing unit 6, and a chelating agent. And a recovery unit 7.

  Here, the crushing part 1 accepts soil containing stone and / or gravel, sand and fine-grained soil (silt and / or clay) and contaminated with harmful metals or the like (toxic metals and / or compounds thereof). The stone and / or gravel mixed in the soil is crushed. The classifying unit 2 mixes the soil discharged from the crushing unit 1 and washing water containing a chelating agent, separates harmful metals attached to the soil from the soil, and captures the chelating agent. Coarse aggregate (gravel) and sand are separated from the soil. 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 is configured to filter the sludge discharged from the sedimentation separation unit 3, and to spray or spray rinse water on the filter cake generated by the filtration to wash away the chelating agent contained in the filter cake. Has been. 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. The chelating agent recovery unit 7 recovers the chelating agent from the rinse water discharged from the filtering unit 4 and returns it to the classification unit 2.

  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.

  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 and mixed with the cleaning 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), stones, gravel, sand and the like.

  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 and / or gravel having a relatively large particle size by applying impact force, shearing force, frictional force and the like to the stones and / or gravel. 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. The mixing device 12 may not be provided, and the soil in the charging hopper 11 may be supplied to the mill breaker 13 while the cleaning water containing the chelating agent may be supplied to the mill breaker 13.

  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 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 the trommel 14, soil particles (pebbles, stones) having a particle size of 2 mm or more are separated or recovered from the soil / water mixture. Soil particles (pebbles, stones) having a particle size of 2 mm or more contain almost no contaminants. For this reason, soil particles (pebbles, stones) having a particle diameter of 2 mm or more separated by the trommel 14 can be used as aggregates or coarse aggregates for concrete, for example. 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. Since this sand contains almost no pollutants, it is used as recycled sand (washed sand) or sold. 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 continuously transferred by a sludge pump or the like to a drum rotary vacuum filter 24 having a filter cake rinsing mechanism. The vacuum filter 24 continuously performs vacuum filtration (vacuum filtration) on the sludge received from the intermediate tank 23, and rinses or sprays rinsing water on the filter cake to wash away the chelating agent contained in the filter cake. In addition, the specific structure and function of the vacuum filter 24 provided with the filter cake rinsing mechanism will be described in detail later. Thus, from the vacuum filter 24, the filter cake (soil) containing almost no chelating agent, the filtrate containing the chelating agent, and the rinse water containing the chelating agent washed away from the filter cake are discharged. Filter cake (soil) contains almost no toxic metals or other pollutants, and contains almost no chelating agent. Therefore, it can be reused as, for example, agricultural soil after drying if necessary. Or can be sold. The filtrate is returned to the thickener 22. Moreover, the rinse water containing a chelating agent is sent to the chelating agent collection | recovery part 7 (refer FIG. 6) demonstrated later, and a chelating agent is collect | recovered.

  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 supernatant water (washing water) stored in the washing water layer 25 or the reserve 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.

  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 or other contaminants are released into the wash water containing the chelating agent, but these contaminants released into the wash water are concentrated on the surface of the fine soil having a relatively small particle size. Therefore, 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.

  As described above, toxic metals and other pollutants separated into the washing water during the flow from the mixing device 12 to the sand clean 17 are collected on the surface of the fine soil having a relatively small particle size. The 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 course of distribution 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 vacuum filter 24 contains almost no harmful metals or other contaminants, and hardly contains a chelating agent as described above. Therefore, it can be dried and reused. it can.

  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 soil purification in the case where the soil purification facility S shown in FIG. 2 purifies 100 tons (mass including water) of soil with washing water containing 0.3% by mass of a chelating agent, for example. The specific example of the flow volume of the soil in the important point of the facility S, water, and a chelating agent is shown. In the example shown in FIG. 9, 100 tons of soil contain 25 tons of gravel (stones and gravel), 30 tons of sand, 25 tons of fine particles, and 20 tons of water, and their water content ratio Is 25%. The filter cake or soil discharged from the vacuum filter 24 is 25 tons (dry basis), and its water content is 40%. Since this filter cake is rinsed by the filter cake rinse mechanism of the vacuum filter 24, it does not contain a chelating agent. However, before the rinsing treatment, the washing water contained in the filter cake contains 0.3% by mass of a chelating agent, so that 0.03 (25 ton × 0.4 × 0.003 = 0.03) is included in the filter cake. Tons) contains tons of chelating agents. This chelating agent is washed away by the rinsing water and introduced into the chelating agent recovery section 7 or the rinsing water evaporator 81 (see FIG. 6). In addition, when using the wash water containing 1.0 mass% chelating agent in the soil purification facility S, the flow rate of the chelating agent in each table in FIG. 9 is about 3.3 times these. In this case, 0.1 ton of chelating agent per hour is introduced into the chelating agent recovery unit 7 (see FIG. 6).

Hereinafter, a specific configuration and function of the vacuum filter 24 including the filter cake rinsing mechanism will be described with reference to FIGS. 4 and 5.
As shown in FIG. 4, the vacuum filter 24 is basically a drum rotary vacuum filter, and includes a sludge tank 60 for storing sludge supplied from the intermediate tank 23 (see FIG. 2), and a lower part thereof. Is provided with a vacuum drum 61 immersed in the sludge in the sludge tank 60. Sludge is continuously supplied to the sludge tank 60 through the sludge inlet 62, while the sludge overflowing the weir plate 63 having a predetermined height passes through the intermediate tank 23 (see FIG. 2)). Therefore, a certain amount of sludge corresponding to the height of the weir plate 63 is held in the sludge tank 60, whereby the immersion depth of the vacuum drum 61 becomes substantially constant. The sludge tank 60 is provided with a stirrer (not shown) for preventing sedimentation or uneven distribution of fine-grained soil in the sludge.

  The vacuum drum 61 has a rotation shaft 65 that is rotated by a rotation drive mechanism (not shown) provided with a motor at the center thereof, whereby the vacuum drum 61 is in the direction indicated by the arrow P (counterclockwise direction). It is designed to rotate at a constant speed. A filter medium 66 (or filter cloth) is disposed on the outer peripheral surface of the vacuum drum 61. A plurality of filtration chambers 68 that are partitioned from each other in the circumferential direction by a plurality of partition plates 67 are provided inside the outer peripheral portion of the vacuum drum 61. In FIG. 4, eight filtration chambers 68 are provided, but it goes without saying that the number of filtration chambers 68 may be larger (for example, 16 to 32 chambers) (rather, it is better. ). The filtration chamber 68 is connected to a suction passage 70 provided in the rotary shaft 65 corresponding to each filtration chamber 68 via a suction pipe 69 corresponding to each filtration chamber 68. Further, on the upper side of the horizontal plane H passing through the center of the vacuum drum 61, in the vicinity of the vacuum drum 61 (above or obliquely above), rinsing water (industrial water) is attached to the filter cake on the filter medium 66 attached to the outer peripheral surface of the vacuum drum 61. A plurality of watering nozzles 71 that spray or spray water) are provided.

  As shown in FIG. 5, a hollow connecting member that is fixedly arranged (does not rotate) has an end face that abuts or slides on the end face on one end face in the central axis direction of the rotating shaft 65 that rotates at a constant speed. 72 is provided. The hollow portion of the connection member 72 is divided into upper and lower parts (divided into two equal parts) by a partition wall 73, and an upper suction chamber 74 and a lower suction chamber 75 are formed in the connection member 72. In addition, a sealing mechanism (that maintains a vacuum state) prevents air from entering from the outside to the contact portion or the sliding contact portion between the end surface of the rotating shaft 65 that rotates and the end surface of the connection member 72 that does not rotate. (Not shown) is provided.

  The upper suction chamber 74 and the lower suction chamber 75 are in the vicinity of the upper end portion of the end surface opposite to the rotary shaft 65 side via vacuum passages 76 and 77 (not shown) (for example, a vacuum pump, Connected to a steam ejector). The upper suction chamber 74 is connected to the rinse water discharge pipe 78 in the vicinity of the lower end portion thereof, and the lower suction chamber 75 is connected to the filtrate discharge pipe 79 in the vicinity of the lower end portion thereof. The rinse water discharge pipe 78 and the filtrate discharge pipe 79 are configured so that the air does not flow backward even when the upper suction chamber 74 and the lower suction chamber 75 are in a vacuum state, and the rinse water and the filtrate are discharged downward without any trouble. As shown, it extends downwards by 10 m or longer. The bottom ends of the rinse water discharge pipe 78 and the filtrate discharge pipe 79 are rinse water storage tanks (so that air does not flow in) so that the upper suction chamber 74 and the lower suction chamber 75 can maintain a vacuum state. (Not shown) and a filtrate storage tank (not shown).

  Hereinafter, the function of the vacuum filter 24 will be described. When the vacuum drum 61 in which each filtration chamber 68 is in a vacuum state or a reduced pressure state rotates in the direction indicated by the arrow P (counterclockwise direction), the filter cake is applied to the filter medium 66 adjacent to the filtration chamber 68 immersed in the sludge tank 60. Is formed. At that time, moisture in the sludge is sucked into the corresponding filtration chamber 68 through the filter medium 66 and the filter cake itself. When these filtration chambers 68 are located below the horizontal plane H after leaving the sludge in the sludge tank, the filtration cake above the filtration chamber 68 is dewatered by vacuuming. The water or filtrate sucked into the filtration chamber 68, that is, the cleaning liquid, enters the lower suction chamber 75 through the corresponding suction pipe 69 and the suction passage 70. The filtrate in the lower suction chamber 75 is discharged to a filtrate storage tank (not shown) through a filtrate discharge pipe 79, and then refluxed to the thickener 22 (see FIG. 2). That is, when each filtration chamber 68 is located below the horizontal plane H, the filtrate sucked into the filtration chamber 68, that is, the washing liquid, corresponds to the corresponding suction pipe 69 and suction passage 70, the lower suction chamber 75, and the filtrate discharge. It is returned to the thickener 22 via the tube 79.

  Thereafter, when these filtration chambers 68 rotate upward from the horizontal plane H, rinse water is sprinkled or sprayed from the watering nozzle 71 onto the filtration cake on the filtration chamber 68. The amount of rinse water to be spread is set to 1.2 to 2.0 times the amount of moisture (cleaning liquid) contained in the filter cake before rinsing, for example. Thereby, the cleaning liquid containing the chelating agent contained in or attached to the filter cake is removed from the filter cake. That is, the chelating agent contained or adhering to the filter cake is transferred to the rinse water.

  When the filtration chamber 68 is positioned above the horizontal plane H, the filter cake above the filtration chamber 68 is dewatered by evacuation. Moisture, ie, rinse water, sucked into the filtration chamber 68 enters the upper suction chamber 74 via the corresponding suction pipe 69 and the suction passage 70. The rinsing water in the upper suction chamber 74 is discharged to a rinsing water storage tank (not shown) via a rinsing water discharge pipe 78, and thereafter, a rinsing water discharge passage 83 (see FIG. 6) described later. It is introduced into the rinse water storage tank 84 (see FIG. 6). That is, when each filtration chamber 68 is positioned above the horizontal plane H, the water sucked into the filtration chamber 68, that is, rinse water, is discharged from the corresponding suction pipe 69 and suction passage 70, the upper suction chamber 74, and the rinse water. It is introduced into the rinse water storage tank 84 through the pipe 78. Thus, the chelating agent initially contained or adhering to the filter cake is recovered in the rinse water storage tank 84 by the rinse water.

Hereinafter, the configuration and function of the chelating agent recovery method according to the present invention or the chelating agent recovery unit 7 using the same will be described with reference to FIGS.
As shown in FIG. 6, the chelating agent recovery unit 7 includes a rinse water evaporation device 81 that evaporates rinse water discharged from the vacuum filter 24 (see FIG. 2) of the soil purification facility S. The rinse water evaporator 81 is provided with a rinse water storage tank 84 that receives the rinse water containing the chelating agent discharged from the vacuum filter 24 (see FIG. 2) via the rinse water discharge passage 83. The rinse 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 simply show the positional relationship between the facility or apparatus in the chelating agent recovery unit 7 or the rinse water evaporator 81, the direction in which the rinse water storage tank 84 and the rinse water discharge passage 83 are aligned in FIG. 6 (in FIG. 6). With respect to the left-right direction), the side where the rinse water storage tank 84 is located is referred to as “left”, and the side where the rinse water discharge passage 83 is located is referred to as “right”.

  Further, the rinse water evaporation device 81 is provided with a container-shaped sand accommodating portion 85 that accommodates sand (sand for water evaporation) at an appropriate distance from the rinse water storage tank 84 in a direction perpendicular to the left-right direction. It is installed. 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, the direction in which the rinse water storage tank 84 and the sand container 85 are lined up (in 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 7 or the rinse water evaporator 81. , The side on which the rinse water 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 rinse water evaporation device 81 includes a roof 92 that is disposed above the sand container 85 and prevents rainwater from dropping into the sand container 85, and a rinsing agent that is stored in the rinse water storage tank 84. A rinsing water spraying device 93 for spraying water onto the sand accommodated in the sand accommodating portion 85 and a rinsing water reflux mechanism 94 for causing the rinsing water at the bottom of the sand accommodating portion 85 to return to the rinsing water 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 The length of the sand container 85 in the left-right direction and the front-rear direction is appropriately set according to the amount of rinsing 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 rinse water storage tank 84. The drainage groove 101 and the collective drainage groove 102 are components of the rinse water reflux mechanism 94.

  Thus, the rinsing water that has flowed down through the gaps between the sands and has flowed into each drainage groove 101 (that is, excess rinsing water that has not evaporated) naturally returns to the rinse water storage tank 84 through the collective drainage groove 102 by gravity. To do. A porous plate 104 that allows rinsing water to pass but does not allow sand to pass 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 rinse water storage tank 84.

  The rinse water spraying device 93 includes a plurality of water supply pipes 111 disposed below the roof 92 above the sand container 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 rinse water 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 rinse water supply pipe 114 is immersed in the rinse water in the rinse water storage tank 84. A rinsing water supply pump 115 is interposed in the rinsing water supply pipe 114 in the vicinity of the rinsing water storage tank 84. Here, the rinsing water supply pump 115 sucks and pressurizes the rinsing water in the rinsing water storage tank 84 through the rinsing water supply pipe 114 (the portion on the rinsing water storage tank side from the rinsing water supply pump 115), and pressurizes the rinsing water supply pipe. 114 is supplied to each water supply pipe 111 via 114 (a portion closer to the sand container than the rinse water supply pump 115) and the intermediate pipe 113. Thus, rinse water 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 rinsing water containing the chelating agent with the chelating agent recovery unit 7 or the rinsing water evaporator 81 will be described in detail. The rinse water containing the chelating agent discharged from the vacuum filter 24 (see FIG. 2) of the soil purification facility S is rinsed through the rinse water discharge passage 83 except for water that naturally evaporates (vaporizes) into the atmosphere. It flows into the water storage tank 84 and is stored. In addition, when the roof is not attached to the rinse water storage tank 84, the rain water which fell to the rinse water storage tank 84 itself is also stored by the rinse water storage tank 4. FIG.

  The rinsing water stored in the rinsing water storage tank 84 is supplied to each water supply pipe 111 by the rinsing water supply pump 115 via the rinsing water 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 manner, the water discharge nozzle 112 sprays rinsing water on the sand layer 105 in the sand container 85, and the rinsing water is always held between the sand particles in the sand layer 105, or the sand particles are a thin film of rinsing water. Is maintained in a saturated moisture state (for example, a water content ratio of 30 to 35%) covered with.

  The rinse water retained in the sand layer 105 evaporates (vaporizes) into the atmosphere. Thus, all of the rinsing water flowing into the rinsing water storage tank 84 (including rainwater falling to the rinsing water storage tank 84 when no roof is attached) evaporates (vaporizes) from the sand layer 105 into the atmosphere. At that time, the chelating agent contained in the rinse water remains in the sand layer 105. Therefore, the chelating agent contained in the rinse water is reliably recovered without being discharged to the outside. In addition, the area or dimension of the sand accommodating part 85 required in order to evaporate rinse water from the sand layer 105 is demonstrated later.

  The amount of rinse water sprayed from the rinse water spray device 93 (water discharge nozzle 112) to the sand layer 105 is preferably set to be larger than the amount of rinse water 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, the excess rinsing water flows down the gap between the sand particles in the sand layer 105, passes through the porous plate 104, and flows into the drainage groove 101. Then, the excess rinse water in the drainage groove 101 is returned to the rinse water storage tank 84 through the collective drainage groove 102.

When the rinsing water 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 (washed sand) obtained by the sand clean 17 of the soil purification facility S is introduced into the section or region where the sand of the sand containing portion 85 is removed. 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. Further, since a part of the sand coming out of the sand clean 17 is used as sand (water evaporating sand) 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 rinse water storage tank 84 and the sand container 85 required for evaporating the rinse water 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. For example, the specification of the rinse water storage tank 84 and the sand container 85 may be set as follows, for example. The rinsing water storage tank 84 is provided with a roof, and rainwater does not fall or flow into the rinsing water 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%. Here, the water content of the filter cake produced by the vacuum filter 24 is 40%. In addition, the specification demonstrated here is an example to the last, and even if the amount of soil treatment of the soil treatment facility S, or the operation time or operation days differ from these, it is the same method, and the rinse water storage tank 84 and the sand accommodating part 85 are the same. Of course, specifications or dimensions can be set.

<Specifications of rinse water storage tank>
The specification of the rinse 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

<Rinse water discharge from vacuum filter>
If the amount of rinse water containing a chelating agent from the vacuum filter 24 of the soil purification facility S is 1.2 times the amount of rinse water contained in or attached to the filter cake, 24,000 tons / year.
10 tons / hr × 8hr × 250 days × 1.2 = 24,000 tons / year

<Water evaporation in the rinse water 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 rinse 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 rinse water storage tank 84 is about 1300 tons, but the discharge amount of rinse water from the vacuum filter 24 (24000 tons / year This corresponds to about 13 days of year (ie, about 100 tons / day). On the other hand, since the rinsing water stored in the rinsing water storage tank 84 is processed in the sand container 85 every day, the rinsing water storage tank 84 can be stored with sufficient margin without overflowing the rinsing water. 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 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 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 from the soil is 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 (research results) 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, the sand container 85 The average water evaporation from the sand layer 105 in the saturated moisture state is estimated to be approximately 10.0 × 10 ⁻⁶ g / cm ² · sec. This evaporation amount is 3.15 ton / m ² · year when converted into 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 × 10 ^-7 × 3600 × 24 × 365 tons / m ² · year = 3.15 tons / m ² · year Therefore, 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

<Water balance in rinse water evaporator>
As described above, the amount of rinse water discharged from the vacuum filter 24 of the soil purification facility S is estimated to be 24,000 tons per year. On the other hand, at least 225 tons of water evaporates annually in the rinse water storage tank 84, and 25200 tons of rainwater evaporates annually in the sand container 85. Therefore, in the rinse water evaporator 81, 25425 tons of water evaporates per year. As described above, the rinse water evaporation device 81 can evaporate more rinse water than the amount of rinse water discharged from the vacuum filter 24 (24,000 tons per year) overall in one year. Specifically, all of the rinse water can be evaporated and processed. However, since the amount of evaporation of the rinse water decreases, for example, in the winter season or the rainy season, it is preferable to lengthen the size (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 chelating agent recovery method or the chelating agent recovery unit 7 according to the present invention, it is possible to prevent or reduce the chelating agent from being taken away by the filter cake or the soil, and the 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.

  S soil purification facility, 1 crushing section, 2 classification section, 3 sedimentation separation section, 4 filtration section, 5 chelating agent regeneration section, 6 chelating agent replenishment section, 7 chelating agent recovery section, 11 charging hopper, 12 mixing device, 13 mil 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 device, 22 Thickener, 23 Intermediate tank, 24 Vacuum filter machine, 25 Washing water tank , 26 Preliminary water tank, 27 Washing water tank, 28 Acid liquid tank, 29 Water tank, 30 Liquid fluidized bed apparatus, 31 pump, 32 pipe, 33 pump, 34-37 pipe, 38 pump, 39-40 pipe , 41 pump, 42-43 pipe, 44-51 valve, 60 sludge tank, 61 vacuum drum, 62 slurry Inlet, 63 weir plate, 64 sludge outlet, 65 rotating shaft, 66 filter medium (filter cloth), 67 partition plate, 68 filtration chamber, 69 suction pipe, 70 suction passage, 71 sprinkling nozzle, 72 connecting member, 73 partition Wall, 74 upper suction chamber, 75 lower suction chamber, 76 vacuum passage, 77 vacuum passage, 78 rinse water discharge pipe, 79 filtrate discharge pipe, 81 rinse water evaporator, 83 rinse water discharge passage, 84 rinse 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, 93 Rinsing water spraying device, 94 Rinsing water return mechanism, 100 Ground, 101 Drain, 102 Collective 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 pie 112, water discharge nozzle, 113 intermediate pipe, 114 rinse water supply pipe, 115 rinse water supply pump.

Claims (2)

A chelating agent recovery 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 crushing section for receiving soil containing stones, gravel, sand and fine-grained soil and contaminated with harmful metals or compounds thereof, and crushing stones and gravel mixed in the soil;
The soil discharged from the crushing part is mixed with washing water containing a chelating agent, and harmful metals or compounds thereof adhering to the soil are separated from the soil and captured by the chelating agent. A classification part for separating coarse aggregate and sand;
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,
A filtration unit configured to filter sludge discharged from the sedimentation separation unit, and to spray or spray rinse water on the filter cake to wash away the chelating agent contained in the filter cake;
A chelating agent recovery unit that recovers the chelating agent from the rinse water discharged from the filtration unit;
The chelating agent recovery unit
A rinse water storage tank for receiving and storing rinse water containing a chelating agent discharged from the filtration unit;
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;
Rinsing water spraying device for spraying the rinsing water stored in the rinsing water storage tank to the water evaporating sand accommodated in the sand accommodating portion;
A rinsing water recirculation mechanism that recirculates excess rinsing water flowing down through the gaps between the particles of water evaporating sand accommodated in the sand accommodating portion to the rinsing water storage tank;
The chelating agent recovery method includes:
While rinsing water is sprayed from the rinsing water spraying device onto the water evaporation sand stored in the sand storage part, the rinsing water adhering to the water evaporation sand is evaporated into the air to store the sand. Remove from the
Introducing the water evaporating sand in which the chelating agent is accumulated for a predetermined period of time in the sand containing unit into the classifying unit, and recovering the chelating agent accumulated in the water evaporating sand,
A method for recovering a chelating agent, wherein a part of the sand discharged from the classification unit is used as water evaporation 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 determined to be the amount of rinsing water sprayed from the rinse water dispersing device to the sand accommodating portion. The chelating agent recovery method according to claim 1, wherein the chelating agent recovery method is set so as to be maintained at%.

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