JP2019103997A - Soil remediation system - Google Patents

Abstract

To provide a simple and low-cost soil remediation system allowing wet classification of soil into gravel, sand and fine-grained fractions, while removing toxic metal and the like adsorbed to the fine-grained fraction.SOLUTION: A soil remediation system S allows soil to be washed with wash water and classified into gravel, sand and fine-grained fractions by a mill breaker 3, a trommel 4, a liquid cyclone 5 and a thickener 8. An iron removal device 12 causes a ferrous fine-grained fraction to be removed, by adsorption by magnetic force, from sludge discharged from the thickener 8, thereby reducing the content of toxic metal and the like in the sludge. A fine-grained fraction washing device 13 washes the sludge discharged from the iron removal device 12 with a chelating wash liquid to remove toxic metal and the like from the fine-grained fraction. A filter device 14 filters the sludge discharged from the iron removal device 12. A reverse osmosis membrane separation device 16 separates the filtrate of the filter device 14 into a permeate and a concentrate. A chelating agent recycle device 17 removes the toxic metal and the like from the concentrate and supplies it to the fine-grained fraction washing device 13 as the chelating wash liquid.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a soil remediation system that purifies soil that contains straw, sand, and fine particles and that is contaminated with harmful metals and / or compounds thereof.

  In recent years, for example, harmful metals such as chromium, lead, cadmium, selenium, mercury and / or compounds thereof (hereinafter, these are collectively referred to as "harmful metals etc.") In the country, soil pollution occurs frequently due to soil pollution or illegal dumping of industrial waste containing harmful metals. Then, soil contaminated with harmful metals (hereinafter referred to as “toxic metal-contaminated soil”) is present at a position (hereinafter referred to as “in-situ position”), for example, insolubilization of harmful metals or the like, containment or electrical repair It is rather difficult to clean up more effectively. For this reason, harmful metal-contaminated soil is generally removed from the in-situ site by drilling and purified at an external soil purification facility.

  As a method of purifying harmful metal-contaminated soil at such a soil purification facility outside the in-situ site, conventionally, a washing method of washing harmful metal-contaminated soil with washing water etc. to remove harmful metals etc. is widely used . Then, when the harmful metal-contaminated soil is washed with washing water, most of the harmful metals and the like that have been temporarily removed from the soil are adsorbed or adhered to the surface of the relatively small particle size fine particles, and the fine particles It is known to be concentrated on the surface of (see, for example, Non-Patent Document 1).

  Therefore, by classifying the harmful metal contaminated soil with washing water while classifying it into sand, sand and fine particles, the fine particles are subjected to a chemical treatment to remove harmful metals and the like. It is possible to obtain straw, sand and fine particles containing almost no harmful metals. Thus, the applicant has already classified the harmful metal-contaminated soil with washing water, classified it into gravel, sand and fine particles, and then wash the fine particles with a chelating washing solution containing a chelating agent. Various soil purification facilities (contaminated soil purification devices) have been proposed which are designed to remove harmful metals and the like from fine grains (see Patent Documents 1 and 2, for example).

Patent No. 5723054 gazette Patent No. 5723055 gazette Patent No. 4755159 gazette Patent No. 60071144 gazette

Ministry of the Environment Water and Atmosphere Environment Bureau Soil Environment Division "Technical notes on permission assessment etc. of contaminated soil treatment industry" page 21, published in August 2013 Tetsuo Katsura "Drainage treatment by iron powder method" flotation, vol. 23 (1976), no. 3, P190-198 (https://www.jstage.jst.go.jp/article/rpsj1954/23/3/23_3_190/_pdf)

  By the way, in this kind of soil remediation facility by a contaminated soil processor, a large amount of contaminated soil is usually cleaned (for example, 2000 tons per day), so a large amount of fine particles is generated (for example, , 500-600 tons per day on a dry basis). Therefore, when such a large amount of fine particles is washed with, for example, a chelate washing solution, a large amount of a relatively expensive chelating agent is required, resulting in a problem that the cost of treating contaminated soil increases. In addition, the required amount or use amount of the chelating agent in such a soil remediation facility increases as the content of the fine particles of harmful metals and the like increases. In addition, the same problem occurs when the fine particles are washed with a chemical other than the chelating agent to remove harmful metals and the like.

  The present invention has been made to solve the above-mentioned conventional problems, and comprises washing with soil and containing soil, sand and fine particles and contaminated with harmful metals and the like while washing the soil with washing water. It is an object of the present invention to provide a simple and low-cost soil remediation system which can be classified into fine particles and capable of removing harmful metals and the like adsorbed or attached to separated fine particles. It is an issue to be solved.

  A soil remediation system according to the present invention, which has been made to solve the above problems, contains soil, sand and fine particles to purify soil contaminated with harmful metals and the like (hazardous metals and / or compounds thereof). , Wet crusher, trommel, hydrocyclone, thickener, iron content removal device, fine particle content cleaning device, filtration device, reverse osmosis membrane separation device, chelating agent regeneration device, permeated water transfer And means.

  Here, the mixer mixes the wash water with the soil introduced into the soil purification system. The wet crusher is iron and / or unevenly distributed or scattered within the gravel and / or sand by crushing the gravel and / or sand in the mixture containing the soil and the washing water discharged from the mixer. Alternatively, iron oxide (hereinafter referred to as “iron etc.”) forms iron-based fine particles exposed on the surface, and harmful metals etc. are adsorbed on iron etc. exposed on the surface of iron-based fine particles ( Attach it. The trommel separates the straw from the mixture discharged from the wet crusher, which contains straw, sand, fines and wash water. A hydrocyclone separates sand from a mixture comprising sand, fines and wash water discharged from the trommel. The thickener separates the mixture containing the fines and the wash water discharged from the hydrocyclone into the supernatant water and the sludge containing the fines and the wash water by sedimentation.

  The iron content removing device reduces the content of harmful metals and the like of the sludge by magnetically removing the iron-based fine particles from the sludge discharged from the thickener by magnetic adsorption. The iron-based fine particles contain iron and the like to such an extent that they can be adsorbed by magnetic force. The fine particle washing apparatus mixes the sludge discharged from the iron removing apparatus with a chelating washing solution containing a chelating agent and water to form a fine particle slurry, and the fine particle slurry has a preset residence time. The chelating agent is allowed to trap harmful metals or the like or these ions attached (adsorbed) to the fine particle content by flowing so as to ensure. The filtration device filters the fine particle slurry discharged from the fine particle washing device to produce a filtrate and a filter cake.

  The reverse osmosis membrane separation device separates the filtrate discharged from the filtration device into the concentrated water in which the chelating agent is concentrated and the permeated water which does not contain the chelating agent by the reverse osmosis membrane. The chelating agent regenerator receives concentrated water discharged from the reverse osmosis membrane separation device, and has a higher complexing power than the chelating agent, and adsorbs harmful metals and the like in the concentrated water when contacted with the concentrated water. The solid phase adsorbent removes harmful metals and the like from the chelating agent in the concentrated water, and the concentrate is supplied to the fine particle size washing apparatus as a chelating washing solution. The permeated water transfer means transfers (returns) the permeated water discharged from the reverse osmosis membrane separation device to the thickener.

  The iron content removing device has a sludge tank, a magnet mounting drum, and a drum rotation mechanism. Here, the sludge tank holds the sludge discharged from the thickener. The magnet mounting drum is formed in a drum shape, and is disposed such that the central axis of the drum is directed in the horizontal direction and the lower portion of the drum is immersed in the sludge in the sludge tank. A plurality of permanent magnets are mounted (arranged) in the circumferential direction of the drum such that the magnetic poles are directed outward in the radial direction of the drum, inside the circumferential surface of the drum. The drum rotation mechanism rotates the magnet mounting drum about the drum center axis.

  The soil purification system according to the present invention preferably comprises a clear filter for performing clear filtration on the filtrate discharged from the filtering device. In addition, the iron content removing device has a pH adjusting device for adjusting the hydrogen index of the sludge retained in the sludge tank within the range of pH 4 to 6, and a neutralizing device for neutralizing the sludge discharged from the sludge tank. Is preferred.

  Generally, in the process of washing and classification of contaminated soil using washing water, harmful metals and the like are hardly adsorbed (adhered) on the gravel and sand, but collected in fine particles and adsorbed (adhered) (for example, non-adhesion) Patent Document 1). The fine particle content is a relatively small amount of iron-based fine particle content containing iron etc. to an extent that can be adsorbed by magnetic force, and a relatively large amount of fine particle content that can not be adsorbed by magnetic force other than iron-based fine particle content (hereinafter Non-ferrous fine particles). On the other hand, since iron and the like have the property of adsorbing harmful metals and the like (see, for example, Non-patent Document 2), the amount of adsorbed harmful metals and the like of iron-based fine particles including iron and the like exposed on the surface (adhesion amount ) Is considerably larger than the adsorption amount (adhesion amount) of harmful metals and the like of non-ferrous fine particles.

  And, according to the soil remediation system according to the present invention, the gravel and / or sand are crushed by the wet crusher to generate fine particles, and among these fine particles, uneven distribution or in sand or sand Fine particles containing a large amount of small agglomerates such as iron scattered are iron-based fine particles, and iron etc. exposed on the surface of these iron-based fine particles are transferred from a wet crusher to an iron removal device Adsorbs relatively large amounts of harmful metals etc. in a series of distribution processes. Therefore, iron-based fine particles existing before crushing and iron-based fine particles generated by crushing are introduced into the iron-removing apparatus, and all of these iron-based fine particles are considerably large (non-ferrous It adsorbs harmful metals, etc.) compared to the system fines.

  Thus, in the iron removing apparatus, since the iron-based fine particles having a large adsorption amount of these harmful metals and the like are removed from the sludge by the magnet mounting drum, the content or retention of harmful metals and the like of the sludge is significantly reduced. be able to. Therefore, the load of harmful metals and the like on the fine particle washing apparatus for purifying the sludge discharged from the iron removing apparatus with the chelate washing solution, and the load of the harmful metals and the like on the chelating agent regenerating apparatus for removing harmful metals and the like from the chelating agent. It is possible to reduce the required amount of chelating agent and solid phase adsorbent, or to reduce the amount used and to reduce the cost of treating the soil. In addition, the wet crusher and the iron removing device are of a simple machine structure which physically processes and do not use special chemicals, so the operation cost is very low.

It is a block diagram showing a schematic structure of a soil purification system concerning the present invention. (A) is typical side surface sectional drawing of the iron content removal apparatus which is a component of a soil purification system, (b) is a schematic plan view of the iron content removal apparatus shown to (a). (A) is typical side surface sectional drawing of another iron content removal apparatus, (b) is a schematic plan view of the iron content removal apparatus shown to (a). (A) is a schematic plan view of the fine particle washing apparatus, (b) is a sectional view taken along line A-A of the fine particle washing apparatus shown in (a), (c) is the fine particle washing FIG. 5 is an elevational cross-sectional view of one slurry passage of the device. It is a typical elevation view of a chelating agent regeneration device.

  As shown in FIG. 1, in the soil purification system S according to the embodiment of the present invention, soil collected by excavating ground contaminated with harmful metals etc. (hazardous metals and / or compounds thereof) or these ions The (contaminated soil) is received in the input hopper 1. Examples of the harmful metals include chromium, lead, cadmium, selenium, mercury, metal arsenic and the like. Then, the soil in the charging hopper 1 is continuously or intermittently charged into the mixer 2 and mixed with the washing water continuously supplied to the mixer 2. Here, the soil includes a weir (for example, a particle size of 2 to 75 mm), sand (for example, a particle size of 0.075 to 2 mm), and a fine particle fraction (for example, a particle size of 0.075 mm or less) Some contain stones (eg, 75 mm or more in particle size).

  A mixture containing soil and wash water generated by the mixer 2 (hereinafter referred to as "soil / water mixture") is transferred to a mill breaker 3 which is a wet crusher. For example, a rod mill can be used as the mill breaker 3. Although not shown in detail, the rod mill is a crushing apparatus in which a plurality of rods (for example, 10 75 mmφ × 2 m steel rods) are disposed in a drum, and the rods rotate parallel to one another by rotation of the drum. Can move into line contact and break up gravel and sand (in some cases even stones) by their impact force, shear force, frictional force etc. to produce small diameter soil particles such as fines . A ball mill or the like can be used as the mill breaker 3 in addition to the rod mill. In addition, a part of the gravel and the sand become fine particles, and not all the fine particles.

  Thus, the mill breaker 3 crushes sand and sand (in some cases, stones) in the soil-water mixture discharged from the mixer 2 to generate small-diameter soil particles such as fine particles. As a result, harmful metals and the like adsorbed (adhered) or contained in the straw and sand are released into the water. At this time, basically (except for adsorption by iron and the like described later), harmful metals and the like released in water are hardly adsorbed or not attached to straw and sand, and collected into fine particles and adsorbed. Or attach (see, for example, Non-Patent Document 1).

  In addition, a large number of iron-based fine particles are generated in which micro-mass of iron or the like (iron and / or iron oxide) unevenly distributed or scattered in the straw and sand is exposed to the surface. On the other hand, iron and the like generally have the property of adsorbing harmful metals and the like. For this reason, some of the harmful metals and the like or these ions present in the wash water are adsorbed or attached to the exposed surface of the iron-based fine particles such as iron. As a result, the adsorption amount (adhesion amount) of harmful metals and the like of iron-based fine particles is considerably larger than the adsorption amount (adhesion amount) of harmful metals and the like of non-ferrous fine particles. That is, the fine particles discharged from the mill breaker 3 are iron-based fine particles having a large amount of adsorption (adhesion) of harmful metals etc. and non-ferrous fine particles having a small amount of adsorption (adhesion) of harmful metals etc. And consists of In addition, it is needless to say that iron-based fine particles existing before crushing also adsorb considerably more harmful metals and the like than non-ferrous-based fine particles.

  The iron-based fine particles that adsorb the harmful metals and the like in this manner are removed by the iron removing device 12 as described later. On the other hand, it is generally known that iron and the like (iron and / or iron oxide) have the property of adsorbing harmful metals and the like, and utilizing this property, iron powder or iron oxide is contained in sludge containing harmful metals and the like. Various "iron powder methods" have been proposed in which harmful metals and the like are removed from sludge by adding powder (see, for example, Patent Documents 3 to 4 and Non-Patent Document 2). However, as in the present invention, crushing iron and sand forms iron-based fine particles in which fine lumps such as fresh iron (which has not adsorbed harmful metals and the like yet) are exposed on the surface. There is no proposal for a method for treating harmful metals and the like in which harmful metals and the like are adsorbed on the exposed micro-mass (iron-based fine particles) such as iron.

  The soil / water mixture discharged from the mill breaker 3 is introduced into the trommel 4. Although not shown in detail, the trommel 4 is a sieving device having a receiving tank capable of storing water, and a substantially cylindrical drum screen disposed to be inclined with respect to a horizontal surface, and the drum screen Is rotatable about its central axis (the central axis of the cylinder) by a motor. In addition, the washing water can be sprayed in the form of a spray into the drum screen.

  As the soil-water mixture flows inside the rotating drum screen of Trommel 4, soil particles finer than the mesh of the drum screen pass through the mesh of the drum screen together with the washing water and go out of the drum screen to the inside of the receiving tank to go into. On the other hand, since soil particles coarser than the mesh of the drum screen can not pass through the mesh of the drum screen, they are discharged out of the drum screen via the lower open end of the drum screen.

  In the trommel 4, the classification diameter (opening) of the mesh of the drum screen is set so that soil particles having a particle size of less than 2 mm, that is, sand and fine particles pass through the mesh of the drum screen. Therefore, in this trommel 4, a weir, which is a soil particle having a particle size of 2 mm or more (sometimes also a stone), is separated from the soil-water mixture. As mentioned above, since harmful metals and the like released in water are hardly adsorbed or attached to straw and sand, the straw separated by the trommel 4 is clean, and is used, for example, as an aggregate for concrete be able to. The mesh size (opening) of the drum screen of the trommel 4 is not limited to the above, and of course it can be set arbitrarily according to the particle size of the soil particles to be obtained. It is.

  Soil particles contained in the receiving tank of the trommel 4 and having a particle diameter of less than 2 mm, that is, a soil / water mixture containing sand and fine particles and washing water, are introduced into the cyclone 5 (hydrocyclone). Although not shown in detail, the cyclone 5 pumps the soil-water mixture into a generally conical cylinder that narrows downward to generate a swirling flow, and the centrifugal force generated thereby is used to A mixture of soil and water, a mixture of fine particles having a relatively small particle size (for example, particle size less than 0.075 mm) and water, sand having a relatively large particle size (for example, a particle size of 0.075 mm or more) and water Separated into a mixture of

  Then, a mixture of fine particles and water (hereinafter referred to as “fine-grain-containing water”) is discharged from the upper end of the cyclone 5, and a mixture of sand and water having a relatively large particle diameter is discharged from the lower end of the cyclone 5. Be done. Here, since the sand discharged from the lower end portion of the cyclone 5 hardly contains harmful metals and the like as described above, it is drained or dried and used as regenerated sand. On the other hand, the fine particle-containing water is transferred to the PH adjustment tank 6.

  In the PH adjustment tank 6, the pH of the fine particle-containing water is adjusted to be substantially neutral using an acid solution (for example, sulfuric acid, hydrochloric acid) and an alkali solution (for example, sodium hydroxide aqueous solution). Although not shown, in the pH adjustment tank 6, the pH of the fine particle-containing water is automatically adjusted by a pH automatic control device equipped with a pH meter or the like.

  The fine particle-containing water whose pH has been adjusted in the PH adjustment tank 6 is introduced into the aggregation tank 7. In the coagulation tank 7, an aqueous solution of polyaluminum chloride (PAC), a polymer flocculant, and a pH adjuster (acidic solution or alkaline solution) are added to the fine particle-containing water. As a result, a large number of flocs in which the water-insoluble metal hydroxide and the fine particles are mixed are generated in the aggregation tank 7.

  Fine-grain-containing water (including floc) in the coagulation tank 7 is introduced into the thickener 8. The chicna 8 is not shown in detail, but the non-water-soluble floc or fines are caused to settle by gravity while the fines-containing water is almost stationary, and the sludge layer located at the lower part (for example, solid) (5 to 10%) and a supernatant (wash water) which is located on the top and contains almost no floc or fines. When floated oil floats on the surface of the supernatant water, the floated oil is removed by overflowing a small amount of supernatant water from the top of the thickener 8.

  Supernatant water in the chicna 8 is introduced into the washing water tank 10 and temporarily stored. When the washing water tank 10 is full, the spare water tank 11 is used. The washing water stored in the washing water layer 10 or the reserve water tank 11 is supplied to the mixer 2 and the trommel 4 as circulating water. In addition, when the wash water stored by the wash water tank 10 reduces by evaporation etc., tap water is replenished suitably. On the other hand, the sludge which has been deposited or accumulated in the lower part of the thickener 8 is transferred to the intermediate tank 9 and temporarily stored. Then, the sludge in the intermediate tank 9 is continuously transferred to the iron removal device 12 (12A, 12B).

  As shown in FIGS. 2A and 2B, the iron content removing device 12A according to one embodiment includes a sludge tank 21 and a magnet mounting drum 22A. Here, the sludge tank 21 receives sludge consisting of fine particles (ferrous fine particles and non-ferrous fine particles) transferred from the intermediate tank 9 through the pipeline 23 and water, and temporarily Hold. Then, after the iron-based fine particles are removed as described later, the sludge in the sludge tank 21 is transferred to the fine particle washing device 13 (see FIG. 1) through the pipe line 24. In addition, in the sludge tank 21, in order to prevent the precipitation to the bottom part of a fine particle, the stirrer 25 is provided.

  The magnet mounting drum 22A includes the rotary shaft 26, the cylindrical drum main body 27 coaxially attached to the rotary shaft 26, and the drum circumference inside (for example, by fitting) the circumferential portion (outer edge portion) of the drum main body 27. A plurality of permanent magnets 28 annularly mounted or arranged adjacent to each other in the direction and a cylindrical cover 29 covering the outer peripheral surface of the annularly arranged permanent magnet group are provided. Here, the magnet mounting drum 22A or the drum main body 27 is disposed such that its central axis of rotation is directed in the horizontal direction and the lower part of the drum is immersed in the sludge in the sludge tank 21.

  The plurality of permanent magnets 28 are disposed such that the magnetic poles face outward in the radial direction of the drum (outwardly). The permanent magnet 28 may be disposed such that all N poles or S poles face outward, or may be disposed such that N poles and S poles alternately face outward. The cylindrical cover 29 is preferably formed of a soft magnetic metal material (e.g. iron or iron alloy) having a relatively thin thickness (e.g. 5 to 10 mm), but a diamagnetic metal material (e.g. copper or aluminum or You may form with these alloys.

  The rotary shaft 26 and thus the drum body 27 are rotationally driven by the motor 30 (electric motor) via the reduction gear 31 and are slowed in the clockwise direction (e.g. 0.5 to 2...) In the positional relationship in FIG. Rotate at 0r.p.m.). When the magnet mounting drum 22A or the drum main body 27 is immersed in the sludge in the sludge tank 21, the iron-based fine particles in the sludge are attracted to the outer peripheral surface of the cylindrical cover 29 by the magnetic force of the permanent magnet 28. It is absorbed. Thus, when the magnet mounting drum 22A or the drum main body 27 comes out of the sludge, an iron-based fine particle separation layer is formed on the outer peripheral surface of the cylindrical cover 29. The iron-based fine particle separation layer formed on the outer peripheral surface of the cylindrical cover 29 is scraped off by the scraper 32 and removed from the magnet mounting drum 22A. The removed iron-based fine particles can be used, for example, as an iron-making material.

  The iron-based fine particles are those produced by crushing straw and sand with the mill breaker 3 (see FIG. 1), which is a wet crusher, or those which exist before crushing of the straw and sand, both of which Micro-mass such as iron is exposed on the surface, and a considerable amount of harmful metals and the like are adsorbed on the micro-mass such as iron which is exposed. In general, small pieces of iron or the like are unevenly distributed or scattered in a gutter and sand, and the proportion of such small pieces is about 2 to 5% by mass. For this reason, a part of the fine particles generated by crushing of the straw and sand becomes an iron-based fine particle in which fresh iron and the like are exposed on the surface.

Iron is a ferromagnetic material (soft magnetic material) and is adsorbed to a magnet. In addition, iron oxides present in the soil substantially include triiron tetraoxide (Fe ₃ O ₄ ), γ-type diiron trioxide (γ-Fe ₂ O ₃ ), and α-type diiron trioxide ( Triiron tetraoxide and γ-type diiron trioxide, which are made of α-Fe ₂ O ₃ ), are ferromagnetic substances (soft magnetic substances) and are adsorbed to a magnet. The α-type diiron trioxide is not magnetized and is not adsorbed to the magnet. For this reason, the iron-based fine particle fraction in which the micromass such as iron is exposed on the surface is attracted to the permanent magnet 28 by the ferromagnetism (soft magnetism) of iron, triiron tetraoxide or γ type ferric trioxide It is adsorbed to the outer peripheral surface of the cylindrical cover 29.

In addition, the inventor of the present invention crushes gravel and sand with a mill breaker a plurality of times (ten times) in July 2017 at the contaminated soil treatment site of Yamazaki Co., Ltd., a gravel shop along the way in Otsu City, Shiga Prefecture. Of sludge (fine particle content 1 to 3% by mass), which is a mixture of fine particles and water produced, using a magnet-equipped drum with a diameter of about 1 m (using neodymium magnet as a permanent magnet) It was carried out adsorption experiment, the average ferrous fine fraction of 3.4kg per sludge 10 m ³ was taken.

  Micro-mass such as iron exposed on the surface of iron-based fine particles generated by crushing gravel and sand with mill breaker 3 (see FIG. 1) is unevenly distributed or scattered in the gravel or sand It is produced from small pieces of fresh iron or the like that does not adsorb harmful metals and the like, and is exposed to the surface after crushing and adsorbs harmful metals and the like from washing water around them. Thus, the fine particles discharged from the mill breaker 3 (see FIG. 1) and introduced into the iron removing device 12A are iron-based fine particles having a relatively large (or considerable) adsorption amount of harmful metals and the like, harmful metals and the like And the non-ferrous fine particles having a relatively (or considerably) low adsorption amount.

  And, as described above, since the iron-based fine particles are removed from the sludge in the iron-removing device 12A, the fine particles contained in the sludge discharged from the iron-removing device 12A have a relatively high adsorption amount of harmful metals and the like. Most (or rather) non-ferrous fine particles are small. Therefore, the iron removal device 12A removes a part or a substantial part of harmful metals and the like contained in the contaminated soil introduced into the soil purification system S. In addition, if the hydrogen index of the sludge in the sludge tank 21 is adjusted within the range of pH 4 to 6, the adsorption amount of harmful metals and the like of the iron-based fine particles slightly increases. In this case, it is preferable to neutralize the sludge discharged from the sludge tank 21.

  As described later, the sludge or fine particles discharged from the iron removing device 12A are subjected to a chelate washing treatment with a chelating agent by the fine particle washing device 13 (see FIG. 1), and the chelating agent regeneration In the apparatus 17 (see FIG. 1), the chelating agent is regenerated by the solid phase adsorbent, but as described above, since the harmful metals and the like in the sludge are reduced by the iron removing apparatus 12A, fine particles (sludge) The burden of harmful metals and the like on the chelate washing treatment and the regeneration treatment of the chelating agent is reduced. For this reason, the required amount or use amount of the chelating agent and solid phase adsorbent in the soil purification system S can be reduced, and the processing cost of the soil can be reduced. That is, the iron removing device 12A functions as a pretreatment device or pretreatment device for reducing the load of harmful metals and the like on the fine particle content washing device 13 or the chelating agent regeneration device 17.

  Hereinafter, the configuration and function of another iron removal device 12B having a different configuration from the iron removal device 12A shown in FIGS. 2 (a) and 2 (b) will be described with reference to FIGS. 3 (a) and 3 (b). . However, most of the components of the iron removal device 12B shown in FIGS. 3 (a) and 3 (b) are the same as the components of the iron removal device 12A shown in FIGS. 2 (a) and 2 (b). In the following, differences from the iron removal device 12A will be mainly described in order to avoid duplication of In addition, in the component of iron content removal apparatus 12B shown to FIG. 3 (a), (b), the same reference is carried out to what is common in the component of iron content removal apparatus 12 A shown to FIG. 2 (a), (b). It is numbered.

  In the iron content removing device 12B shown in FIGS. 3A and 3B, a cylindrical drive roller 41 is provided above the sludge tank 21 separately from the magnet mounting drum 22B or the drum main body 27. It is coaxially attached to the drive shaft 42. The drive roller 41 and the drive shaft 42 are disposed such that their central axes of rotation are parallel to the central axis of rotation of the drum body 27, and are rotationally driven by the motor 30 via the reduction gear 31. The driving roller 41 has a smaller diameter (e.g., 1/5 to 1/10) than the drum main body 27.

  A plurality of permanent magnets 28 are mounted or disposed on the drum body 27 in the same specification as the iron content removing device 12A shown in FIG. 2A. The rotating shaft 26 of the magnet mounting drum 22B is rotatably supported by a bearing fixed to the sludge tank 21. In addition, you may provide the cylindrical cover similar to 12 A of iron content removal apparatuses. An endless belt 43 (e.g., iron or iron alloy) made of a soft magnetic metal material (e.g., iron or iron alloy) extends over the drum body 27 and the drive roller 41 in which a plurality of permanent magnets 28 are annularly attached or arranged inside the circumferential portion. , A steel belt) is wound. The endless belt 43 may be formed of a diamagnetic metal material (for example, copper or aluminum or an alloy thereof).

  When the drive roller 41 is rotationally driven clockwise in the positional relationship in FIG. 3A by the motor 30 via the reduction gear 31, the drum main body 27 or the magnet mounting drum 22B is rotationally driven in the clockwise direction. The endless belt 43 travels in the clockwise direction between the driving roller 41 and the drum main body 27. The rotational speed of the motor 30 or the drive roller 41 is set so that the drum body 27 rotates at a slow speed (e.g., 0.5 to 2.0 rpm).

  An endless belt 43 traveling in a clockwise direction in a positional relationship in FIG. 3A between the drive roller 41 and the drum main body 27 is annularly arranged on the inner side of the circumferential surface of the drum main body 27. The iron-based fine particles in the sludge are attracted to the outer surface of the endless belt 43 by the magnetic force of the permanent magnet 28 when being in contact with the outer peripheral surface of the magnet group and immersed in the sludge in the sludge tank 21. . Thus, when the endless belt 43 comes out of the sludge, an iron-based fine particle separation layer is formed on the outer surface of the zero endless belt 43. The iron-based fine particle separation layer formed on the outer surface of the endless belt 43 is scraped off by the scraper 32 in the vicinity of the driving roller 41 and removed from the endless belt 43.

  Also in the iron content removing device 12B shown in FIGS. 3 (a) and 3 (b), as in the iron content removing device 12A shown in FIGS. 2 (a) and 2 (b), the iron-based fine particles are removed from the sludge. The fine particle fraction contained in the sludge discharged from the iron content removing device 12B is mostly a non-ferrous fine particle fraction having a relatively (or considerably) small adsorption amount of harmful metals and the like. Therefore, the iron removal device 12B removes a part or a considerable part of harmful metals and the like contained in the contaminated soil introduced into the soil purification system S.

  The sludge discharged from the iron content removing device 12 (12A, 12B) is introduced into the fine particle content cleaning device 13 (see FIG. 1). The fine particle content washing device 13 receives sludge from the nonferrous fine particles discharged from the iron content removing device 12 (12A, 12B) and washing water, and a chelating agent regenerating device 17 (see FIG. 1) described later. Accept the supplied chelating agent and the chelate washing solution containing water, mix and stir them to form a fine particle slurry, and secure a preset residence time (for example, 0.5 to 2 hours) As described above, by flowing continuously in a plug flow (plug flow), harmful metals and the like attached to (adsorbed) fine particles or these ions are captured by the chelating agent. Thereby, harmful metals and the like adsorbed (adhered) on the surface of the fine particles in the fine particle slurry are removed. The ratio of the flow rate of the sludge supplied to the fine particle size washing device 13 to the flow rate of the chelate washing solution is set to, for example, 1: 1.

  As a chelating agent used for the chelate washing solution, for example, EDTA (ethylenediaminetetraacetic acid), or HIDS (3-hydroxy-2,2'-iminodisuccinic acid), IDS (2,2'-iminodisuccinic acid), MGDA (methylglycine) And sodium salts of EDDS (ethylenediaminediacetic acid) or GLDA (L-glutamic acid diacetic acid). Any of these chelating agents can effectively capture (chelate) harmful metals and the like contained in the fine particle slurry or fine particle fraction. Of course, a chelating agent suitable for the treatment is selected or plural kinds of chelating agents are used according to the type of harmful metal and the like contained in the fine particle fraction.

  Hereinafter, the specific configuration and function of the fine particle content washing device 13 will be described with reference to FIGS. 4 (a) to 4 (c). The fine particle content washing apparatus 13 has a storage tank 50 provided with five elongated rectangular parallelepiped or prismatic slurry passages 55 to 59 extending in parallel with each other and formed by dividing by four flat plate-like partition walls 51 to 54. doing. The storage tank 50 may be, for example, an iron rectangular parallelepiped tank installed on the ground, or a concrete rectangular pit. The partition walls 51 to 54 may be formed, for example, by connecting a plurality of iron plates or plastic plates in the extending direction of the slurry passage.

  The two slurry channels adjacent in the slurry channel 55 to 59 have four curves in the communicating portion (FIG. 4A) at one end of the slurry channel longitudinal direction (lateral direction in the positional relationship in FIGS. 4A and 4B). Communicate with each other at the portions shown by That is, the partition walls 51 to 54 do not exist in these communicating portions, and the adjacent slurry passages communicate with each other.

  At the bottom of each of the slurry passages 55 to 59, air release pipes 61 to 65 for releasing air into the fine particle slurry and stirring the fine particle slurry are disposed. Each air discharge pipe 61 to 65 extends in the longitudinal direction of the slurry passage, and is a porous pipe in which a plurality of air discharge holes are formed in the bottom of the peripheral wall (lower side) aligned in the longitudinal direction of the slurry passage. Although not shown, it is connected to a compressor or blower that supplies compressed air. When pressurized air is supplied to the air release pipes 61 to 65, the air becomes air bubbles from the air release holes, is released into the fine particle slurry and floats up, and the air bubbles agitate the fine particle slurry by the air bubbles. Be done.

  FIG. 4C shows a cross section of the most upstream slurry passage 55 as viewed in the flow direction of the fine particle slurry (the direction indicated by the curved arrow and the straight arrow in FIG. 4A). . As is clear from FIG. 4 (c), the air discharge pipe 61 is disposed in the vicinity of the slurry passage bottom in the vicinity of one side surface of the slurry passage 55. Therefore, the air bubbles discharged from the air discharge pipe 61 rise in the vicinity of this side surface. As a result, a circulating flow is formed in the slurry passage 55 in the direction indicated by the arrow P in a plane perpendicular to the longitudinal direction of the slurry passage, and the fine particle slurry is agitated. The shape, size, volume and the like of the storage tank 50 and the respective slurry passages 55 to 59, and the supply amount of the pressurized air to the air release pipes 61 to 65, etc. The water content is preferably set corresponding to the water content, flow rate, residence time, flow rate, turbulent flow rate (eg, Reynolds number), and the like.

  As shown in FIG. 1 again, the fine particle slurry discharged from the fine particle washing device 13 is transferred to the filtering device 14. The filtration unit 14 filters the fines slurry to produce a filter cake with a moisture content of 30 to 40 percent and a filtrate. In addition, as the filtration apparatus 14, a filter press, a vacuum filter, etc. can be used. The filter cake (fine particle content) discharged from the filter device 14 contains almost no harmful metals and the like, and therefore, is used as a culture soil for agriculture, for example, or disposed of in landfills or the like.

  The filtrate or chelate washing solution discharged from the filtration device 14 is transferred to the reverse osmosis membrane separation device 16 after suspended matter or suspended matter (SS) is removed by a clear filter 15 (for example, sand filter). . Although not shown in detail, the reverse osmosis membrane separation device 16 receives the chelate washing solution discharged from the clear filter 15, is pressurized by a high-pressure pump, and is concentrated by the reverse osmosis membrane by which the chelating agent is concentrated. Separate into water and permeate free of chelating agent.

  The reverse osmosis membrane of the reverse osmosis membrane separation device 16 has, for example, a three-layer structure in which a polysulfone supporting layer and a crosslinked aromatic polyamide dense layer are laminated on the surface of a polyester non-woven fabric (100 to 120 μm thick). It can be used. The cross-linked aromatic polyamide dense layer has a large number of pores with a pore diameter of approximately 0.5 to 1.5 nm, and is permeable to water but impermeable to the chelating agent (eg, 0.2 to 0.2 nm) 0.25 μm) semipermeable membrane. Also, the polysulfone support layer is a relatively thick (e.g., 40 to 50 [mu] m) porous membrane to support or protect a very thin crosslinked aromatic polyamide dense layer to prevent its failure.

The reverse osmosis membrane separation device 16 is a spiral type, and includes a plurality of reverse osmosis membrane elements in which a spirally wound reverse osmosis membrane is accommodated in a cylindrical container. For example, it is practical that each reverse osmosis membrane element has a total length of about 1 to 2 m and an outer diameter of about 0.2 to 0.4 m. For example, the effective membrane area of the reverse osmosis membrane in a commercially available reverse osmosis membrane element of this type having a total length of about 1 m and an outer diameter of about 0.2 m (for example, manufactured by Austentec Co., Ltd., Nakatsugawa City, Gifu Prefecture) is It is about 40 m ² . In the case of this reverse osmosis membrane element, when the chelating agent concentration of about 1% by mass is supplied at a pressure of about 1 MPa, the processing amount of the chelating agent is estimated to be about 1.5 m ³ / hr. Therefore, for example, in the case of processing a chelate washing solution at 60 m ^{3 /} h, 40 reverse osmosis membrane elements may be connected in parallel.

  The reverse osmosis membrane separation device 16 is a continuous type, and the operating conditions such as the supply amount and supply pressure (operating pressure) of the chelate cleaning liquid, the discharge amount of concentrated water and permeated water, and the chelating agent concentration ratio of concentrated water It is appropriately set in accordance with the amount of chelating cleaning fluid to be supplied to the cleaning device 13 and the concentration of the chelating agent. For example, the ratio of the flow rate of the sludge supplied to the fine particle washing apparatus 13 to the flow rate of the chelate washing solution is set to 1: 1, and the chelating agent concentration of the fine particle slurry in the fine particle washing apparatus 13 is set to 1% by mass If so, the reverse osmosis membrane separation device 16 generates about 50% of permeate water (chelating agent concentration 0) and about 50% concentrated water (chelating agent concentration about 2% by mass) of the supply amount of the chelate washing solution. Set to Therefore, in the fine particle content washing device 13, the sludge containing no chelating agent and the chelate washing solution having a chelating agent concentration of about 2% by mass are mixed 1: 1, and the chelating agent concentration in the fine particle content washing device 13 is 1 mass. It is maintained at about%.

  The concentrated water, that is, the chelate washing solution discharged from the reverse osmosis membrane separation device 16 is introduced into the chelating agent regeneration device 17 and regenerated. The chelating agent regenerating apparatus 17 has a complexing power higher than that of the chelating agent, and when it comes in contact with a chelating washing solution, it adsorbs or extracts harmful metals and the like in the chelating washing solution, or a small piece on which the solid adsorption material is immobilized. Or having particulate matter, and removing harmful metals and the like from the chelating agent in the chelating washing solution to regenerate the chelating washing solution.

  The solid phase adsorbent is a carrier having a cyclic molecule supported on the carrier, a coordination with a chelate ligand modified to the cyclic molecule and multipoint interaction by hydrogen bond and selectively incorporating ions such as harmful metals. is there. Thereby, harmful metals and the like captured by the chelating agent are released from the chelating agent and adsorbed or extracted by the solid phase adsorbent. As a result, harmful metals and the like are removed and recovered from the chelate washing liquid (chelating agent), and the chelate washing liquid (chelating agent) is in a state capable of capturing harmful metals and the like again.

  Solid phase adsorbents having higher complexing power than chelating agents are in solid form such as, for example, a gel, and generally, when contacted with an aqueous solution containing a chelating agent capturing a metal, coordination bond with the chelating agent The metal ion has a strong avidity other than the degree of covalent bonding that can release the metal ion from the chelating agent and transfer it to the solid phase adsorbent. Such a solid phase adsorbent, for example, when using EDTA (ethylenediaminetetraacetic acid) as a chelating agent, has a strong binding ability to recover almost 100% of metal ions from an aqueous solution of EDTA having a concentration of 10 mM / l. It is possessed.

  As such a solid phase adsorbent, for example, a solid support of a cyclic molecule on a carrier such as silica gel or resin, and a modification of a chelate ligand to this cyclic molecule, and the like can be mentioned. When such a solid phase adsorbent is used, a plurality of various bonds and interactions such as coordination bonds and hydrogen bonds are caused by adjacent cyclic molecules and chelate ligands, resulting in multipoint interaction and metal ion On the other hand, stronger chemical bonds occur than chelating agents, and metal ions can be selectively incorporated by the nature of cyclic molecules.

  Hereinafter, the specific configuration and function of the chelating agent regenerating apparatus 17 will be described with reference to FIG. The chelating agent regenerating apparatus 17 is provided with a packed tower 70 in which solid adsorbent particles or a packing (solid packing) to which the solid adsorbent is fixed is packed. In addition, the chelating agent regenerating apparatus 17 includes an intermediate storage tank 71 for storing the chelate cleaning liquid (concentrated water) to be regenerated, a cleaning liquid storage tank 72 for storing the regenerated chelate cleaning liquid, and an acid liquid storage tank 73 for storing the acid liquid. , And a water storage tank 74 for storing water.

  In the intermediate storage tank 71, the concentrated water discharged from the reverse osmosis membrane separation device 16, that is, the chelate washing liquid is temporarily stored. Then, when the chelate washing liquid is regenerated, the pump 76 for transferring the chelate washing liquid stored in the intermediate storage tank 71 to the washing liquid storage tank 72 while transferring the chelate washing liquid stored in the intermediate storage tank 71 to the packing tower 70 Pipelines 77-80 are provided. Further, a pump 81 and a pipeline 82 are provided for supplying the chelate washing solution stored in the washing solution storage tank 72 to the fine particle content washing device 13 (see FIG. 1).

  Further, when the solid phase adsorbent is regenerated to the chelating agent regenerating apparatus 17, the acid solution stored in the acid solution storage tank 73 is transferred to the packing tower 70, while the acid liquid discharged from the packing tower 70 is acid. A pump 83 and a plurality of pipelines 84, 85 for returning to the liquid storage tank 73 are provided. In the chelating agent regenerating apparatus 17, when the solid phase adsorbent regenerated with the acid solution is washed with water, the water stored in the water storage tank 74 is transferred to the packing tower 70, and the water is discharged from the packing tower 70. A pump 86 and a plurality of lines 87, 88 are provided for returning water to the water reservoir 74.

  Pipes 77, 78, 84, 87 for transferring the chelate washing solution, acid solution or water to the packed column 70 are provided with valves 91, 92, 93, 94 for opening and closing the corresponding pipes, respectively. There is. On the other hand, in the conduits 79, 80, 85, 88 for discharging the chelate washing solution, the acid solution or the water from the packed column 70, valves 95, 96, 97, 98 for opening and closing the corresponding conduits are interposed, respectively. It is done. By switching the open / close states of these valves 91 to 98, it is possible to supply or discharge the chelate washing solution, the acid solution or the water to the packed tower 70. The opening and closing of these valves 91 to 98 are automatically controlled by a controller (not shown).

  Hereinafter, an example of the operation method of the chelating agent regenerating apparatus 17 will be described. When the chelating cleaning solution (chelating agent) is regenerated, the valves 91, 92, 95, 96 provided in the conduits 77-80 are opened while the other valves 93, 94, 97, 98 are closed, The pump 76 is operated. Thereby, the chelate cleaning liquid in the intermediate storage tank 72 flows through the inside of the cleaning liquid regenerating apparatus 35 and is transferred to the cleaning liquid storage tank 36.

  In the packed tower 70, a chelating cleaning solution containing a chelating agent capturing harmful metals and the like is brought into contact with the solid phase adsorbent (solid phase adsorbent particles). As a result, harmful metals and the like trapped in the chelating agent are released from the chelating agent and adsorbed or extracted by the solid phase adsorbent. As a result, harmful metals and the like are removed and recovered from the chelate washing solution, and the chelating agent becomes able to capture the harmful metals and the like again, and the chelate washing solution is regenerated.

  While the amount of adsorption of harmful metals and the like in the solid phase adsorbent increases with the regeneration of the chelate washing solution, the adsorption capacity of the solid phase adsorbent has an upper limit. For this reason, when the adsorption amount of harmful metals and the like in the solid phase adsorbent reaches a saturated state or in the vicinity thereof, the solid phase adsorbent is regenerated. That is, the acid solution is flowed into the packed column 70 in a state where the chelate washing solution has been removed, and harmful metals and the like adsorbed on the solid phase adsorbent are removed by the acid solution to regenerate the solid phase adsorbent. Thus, while harmful metals and the like are recovered by the acid solution, the solid phase adsorbent is regenerated to be in a state capable of adsorbing or extracting harmful metals or these ions again.

  When the solid phase adsorbent in the packed column 70 is regenerated with the acid solution, the valves 93, 92, 95, 97 provided in the pipelines 84, 78, 79, 85 are opened, while the other valve 91 is , 94, 96, 98 are closed and the pump 83 is operated. As a result, the acid liquid in the acid liquid storage tank 73 flows through the inside of the packed tower 70 and is refluxed to the acid liquid storage tank 73. Whether or not the harmful metal adsorption amount of the solid phase adsorbent has reached a saturated state or in the vicinity thereof can be determined by detecting the content of the harmful metal or the like in the chelate washing solution discharged from the packed column 70 .

  When the solid phase adsorbent is washed with water after the regeneration of the solid phase adsorbent by the acid solution is finished, the valves 94, 92, 95, 98 interposed in the conduits 87, 78, 79, 88 are opened. , The other valves 91, 93, 96, 97 are closed and the pump 86 is operated. Thus, the water in the water storage tank 74 circulates in the packed tower 70 and returns to the water storage tank 74. Water circulates between the water reservoir 74 and the packed tower 70. At this time, the solid phase adsorbent in the packed column 70 comes in contact with water, and the acid solution adhering to the solid phase adsorbent is washed. After this, regeneration of the chelate washing solution is resumed.

  The chelate washing solution thus regenerated is temporarily stored in the washing solution storage tank 72 and then supplied to the fine particle size washing device 13. That is, the chelate washing solution circulates while repeating purification of fine particles and regeneration of the chelating agent. In addition, the loss of the chelating agent is replenished appropriately.

  As described above, according to the soil remediation system S according to the present invention, clean and reusable straw, sand and fines can be obtained. Moreover, since the content rate of harmful metals and the like of the sludge discharged from the iron content removing device 12 (12A, 12B) can be reduced, the load of the harmful metals and the like on the fine particle washing device 13 and the chelating agent regenerating device 17 It is possible to reduce the load of harmful metals and the like to the above, reduce the necessary amount or use amount of the chelating agent and solid phase adsorbent, and reduce the processing cost of the soil. The iron removal device 12 (12A, 12B) has a simple mechanical structure that performs physical processing, and does not use special chemicals, so its operating cost is very low.

  S Soil remediation system, 1 input hopper, 2 mixer, 3 mill breaker (wet crusher), 4 trommel, 5 cyclone, 6 PH adjustment tank, 7 aggregation tank, 8 chicna, 9 intermediate tank, 10 washing water tank, 11 spare Water tank, 12 iron removing device, 12A iron removing device, 12B iron removing device, 13 fine particle washing device, 14 filtration device, 15 clarifying filter, 16 reverse osmosis membrane separation device, 17 chelating agent regeneration device, 21 sludge tank, 22A magnet mounting drum, 22B magnet mounting drum, 23 pipelines, 24 pipelines, 25 stirrers, 26 rotary shafts, 27 drum bodies, 28 permanent magnets, 29 cylindrical covers, 30 motors, 31 speed reducers, 32 scrapers, 41 drives Rollers, 42 drive shafts, 43 endless belts, 50 reservoirs, 51 to 54 partition walls, 55 -59 slurry passage, 61-65 air discharge pipe, 70 packed tower, 71 intermediate storage tank, 72 washing water tank, 73 acid liquid storage tank, 74 water storage tank, 76 pump, 77-80 pipeline, 81 pump, 82 pipeline, 83 Pump, 84 lines, 85 lines, 86 pumps, 87 lines, 88 lines, 91-98 valves.

Claims (3)

What is claimed is: 1. A soil remediation system for remediation of soil contaminated with harmful metals or their compounds, comprising gravel, sand and fine particles,
A mixer for mixing the soil introduced into the soil remediation system with washing water;
Iron or iron oxide that is unevenly distributed or scattered inside the gravel and sand by crushing the gravel and sand in the mixture containing the soil and the washing water discharged from the mixer A wet crusher that produces a fine particulate component and adsorbs a harmful metal or its compound to iron or iron oxide exposed on the surface of the fine particulate iron component;
A trommel that separates the straw from the mixture containing the straw, sand, fine particles and washing water, which is discharged from the wet crusher;
A hydrocyclone separating sand from a mixture comprising sand, fines and wash water discharged from the trommel;
A thickener which separates a mixture containing fine particles and wash water discharged from the hydrocyclone into supernatant water and sludge containing fine particles and wash water by sedimentation separation;
An iron removing device for reducing the content of harmful metals or compounds thereof by removing magnetic fine particles from the sludge discharged from the thickener by magnetic attraction;
The sludge discharged from the iron removing device is mixed with a chelate washing solution containing a chelating agent and water to form a fine particle slurry, and the fine particle slurry is flowed to secure a preset residence time. A fine particle washing apparatus for causing a chelating agent to trap harmful metals or compounds thereof adhering to fine particles by
A filtering device for filtering the fine particle slurry discharged from the fine particle washing device to form a filtrate and a filter cake;
A reverse osmosis membrane separation device that separates the filtrate discharged from the filtration device into concentrated water concentrated with a chelating agent and permeated water containing no chelating agent by a reverse osmosis membrane;
A solid phase adsorbent that receives concentrated water discharged from the reverse osmosis membrane separation device and has a higher complexing power than a chelating agent and adsorbs harmful metals or compounds thereof in the concentrated water when contacted with the concentrated water A chelating agent regenerating apparatus for removing harmful metals or compounds thereof from a chelating agent in water and supplying the concentrate as the chelating washing solution to the fine particle size washing apparatus;
A permeated water transfer means for transferring the permeated water discharged from the reverse osmosis membrane separation device to the thickener;
The iron removal device is
A sludge tank for retaining sludge discharged from the thickener;
The drum is formed in a drum shape, the drum central axis is directed in the horizontal direction, and the lower portion of the drum is disposed so as to be immersed in the sludge in the sludge tank, and a plurality of permanent magnets are radially outward in the drum circumferential surface. Magnet mounted drums, which are mounted side by side in the circumferential direction of the drum, with the magnetic poles facing
And a drum rotation mechanism for rotating the magnet mounting drum around a drum center axis.   The soil purification system according to claim 1, further comprising a clear filter for performing clear filtration on the filtrate discharged from the filtering device.   The iron content removing device comprises a pH adjusting device for adjusting the hydrogen index of the sludge retained in the sludge tank within the range of pH 4 to 6, and a neutralizing device for neutralizing the sludge discharged from the sludge tank The soil purification system according to claim 1 or 2, characterized by comprising.

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