JP6358519B1 - Soil purification system - Google Patents

Abstract

Provided is a simple and low-cost soil purification system capable of wet classification of soil into gravel, sand, and fine particles while removing harmful metals and the like adsorbed on the fine particles. A soil purification system (S) is classified into gravel, sand and fine particles while washing soil with washing water by a mill breaker (3), a trommel (4), a hydrocyclone (5) and a thickener (8). The iron content removing device 12 adsorbs and removes iron-based fine particles from the sludge discharged from the thickener 8 by magnetic force, and reduces the content of harmful metals and the like in the sludge. The fine particle cleaning device 13 cleans sludge discharged from the iron content removing device 12 with a chelate cleaning liquid to remove harmful metals and the like from the fine particle content. The filtering device 14 filters the sludge discharged from the iron content removing device 12. The reverse osmosis membrane separation device 16 separates the filtrate of the filtration device 14 into permeated water and concentrated water. The chelating agent regenerator 17 removes harmful metals and the like from the concentrated water and supplies the fine particle cleaning device 13 as a chelate cleaning solution. [Selection] Figure 1

Description

  The present invention relates to a soil purification system for purifying soil containing gravel, sand and fine particles and contaminated with harmful metals and / or compounds thereof.

  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 In Japan, or soil pollution due to illegal dumping of industrial waste containing hazardous metals. Then, soil contaminated with toxic metals (hereinafter referred to as “toxic metal contaminated soil”) is present at the existing location (hereinafter referred to as “original location”), for example, insolubilization, containment or electrical restoration of toxic metals, etc. It is quite difficult to purify more effectively. For this reason, the toxic metal-contaminated soil is generally removed from the original position by excavation and purified at an external soil purification facility.

  As a method for purifying toxic metal-contaminated soil at such off-site soil purification facilities, conventionally, a cleaning method that removes toxic metal by washing toxic metal-contaminated soil with washing water or the like has been widely used. . When the toxic metal-contaminated soil is washed with washing water, most of the toxic metals once released from the soil into the water are adsorbed or adhered to the surface of the fine particles having a relatively small particle size. It is known that they are aggregated on the surface of the film (for example, see Non-Patent Document 1).

  Therefore, after washing the toxic metal contaminated soil with washing water and classifying it into gravel, sand and fine particles, by applying chemical treatment to remove toxic metals etc. on the fine particles, Gravel, sand, and fine particles that contain almost no harmful metals can be obtained. Thus, the applicant of the present application has already washed the hazardous metal-contaminated soil with washing water, classified it into gravel, sand and fine particles, and then washed the fine particles with a chelate washing liquid containing a chelating agent. Various soil purification facilities (contaminated soil purification devices) that remove harmful metals and the like from fine particles have been proposed (for example, see Patent Documents 1 and 2).

Japanese Patent No. 5723054 Japanese Patent No. 5723055 Japanese Patent No. 4755159 Japanese Patent No. 6007144

Issued by the Ministry of the Environment, Water and Air Environment Bureau, Soil Environment Division, “Technical Considerations for Permitted Examination of Contaminated Soil Treatment Industry”, page 21, August 2013 Tetsuo Katsura “Wastewater 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 treatment company, usually a large amount of contaminated soil is purified (for example, 2000 tons per day), so a large amount of fine particles are produced (for example, , 500 to 600 tons per day on a dry basis). Therefore, when washing such a large amount of fine particles with, for example, a chelate washing solution, a large amount of a relatively expensive chelating agent is required, so that there is a problem that the cost for treating contaminated soil increases. The required amount or amount of chelating agent used in such soil purification facilities increases as the content of harmful metals and the like in the fine particles increases. The same problem occurs when the fine particles are washed with chemicals other than the chelating agent to remove harmful metals and the like.

  The present invention was made in order to solve the above-mentioned conventional problems, and washes gravel and sand while washing soil containing gravel, sand and fine particles and contaminated with harmful metals with washing water. To provide a simple and low treatment cost soil purification system that can be classified into fine particles and that can remove harmful metals adsorbed or adhered to the separated fine particles. It is a problem to be solved.

  A soil purification system for purifying soil containing gravels, sand and fine particles and contaminated with harmful metals or the like (toxic metals and / or compounds thereof) according to the present invention made to solve the above problems , Wet crusher, trommel, hydrocyclone, thickener, iron content removal device, fine particle washing device, filtration device, reverse osmosis membrane separation device, chelating agent regeneration device, and permeate transfer Means.

  Here, the mixer mixes the wash water and the soil introduced into the soil purification system. The wet crusher crushes gravel and / or sand in a mixture containing soil discharged from the mixer and washing water, thereby causing iron and / or scattered unevenly in the gravel and / or sand. Or iron oxides (hereinafter collectively referred to as “iron etc.”) produce iron-based fine particles exposed on the surface, and adsorb toxic metals etc. on the iron exposed on the surface of iron-based fine particles ( Attach). Trommel separates gravel from a mixture of gravel, sand, fines and wash water discharged from a wet crusher. The hydrocyclone separates sand from a mixture containing sand, fines and wash water discharged from the trommel. The thickener separates a mixture containing fine particles discharged from the hydrocyclone and washing water into supernatant water and sludge containing fine particles and washing water by sedimentation separation.

  The iron content removing device reduces the content of harmful metals and the like in the sludge by adsorbing and removing the iron-based fine particles from the sludge discharged from the thickener by magnetic force. The iron-based fine particles contain iron or the like to such an extent that they can be adsorbed by magnetic force. The fine particle cleaning device mixes the sludge discharged from the iron content removal device with a chelate cleaning solution containing a chelating agent and water to generate a fine particle slurry, and the fine particle slurry is set in a preset residence time. In order to ensure that the toxic metal or the like adhering (adsorbing) to the fine particles is captured by the chelating agent. 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 concentrated water in which the chelating agent is concentrated and permeated water not containing the chelating agent by the reverse osmosis membrane. The chelating agent regeneration device accepts the concentrated water discharged from the reverse osmosis membrane separation device, and adsorbs harmful metals or the like ions in the concentrated water when it has a higher complexing power than the chelating agent and comes into contact with the concentrated water. Using a solid phase adsorbent, harmful metals and the like are removed from the chelating agent in the concentrated water, and the concentrated solution is supplied as a chelate cleaning solution to the fine particle cleaning device. The permeated water transfer means transfers (returns) the permeated water discharged from the reverse osmosis membrane separation device to the thickener.

  The iron removing device includes a sludge tank, a magnet mounting drum, and a drum rotating mechanism. Here, the sludge tank holds sludge discharged from the thickener. The magnet mounting drum is formed in a drum shape, and is arranged such that the drum center axis faces the horizontal direction and the lower part of the drum is immersed in the sludge in the sludge tank. A plurality of permanent magnets are mounted (arranged) side by side in the drum circumferential direction so that the magnetic poles face outward in the drum radial direction inside the drum circumferential surface of the magnet mounting drum. The drum rotating mechanism rotates the magnet-equipped drum around the drum central axis.

  The soil purification system according to the present invention preferably includes a clarification filter that performs clarification filtration on the filtrate discharged from the filtration device. Further, the iron content removing device has a pH adjusting device for adjusting the hydrogen index of sludge retained in the sludge tank within a pH range of 4 to 6, and a neutralizing device for neutralizing sludge discharged from the sludge tank. It is preferable.

  In general, in the process of cleaning and classification of contaminated soil using washing water, toxic metals and the like are hardly adsorbed (attached) to gravel and sand, but are aggregated and adsorbed (attached) to fine particles (for example, non-adhesive) Patent Document 1). The fine particles are divided into a relatively small amount of iron-based fine particles containing iron or the like that can be adsorbed by a magnetic force, and a relatively large amount of fine particles that cannot be adsorbed by a magnetic force other than the iron-based fine particles (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 adsorption of harmful metals and the like of iron-based fine particles including iron exposed on the surface (adhesion amount) ) Is considerably larger than the adsorption amount (adhesion amount) of toxic metals and the like for non-ferrous fine particles.

  And according to the soil purification system which concerns on this invention, although a gravel and / or sand are crushed with a wet crusher and a fine particle part is produced | generated, among these fine particle parts, it is unevenly distributed in a gravel or sand. The fine particles containing a large amount of fine particles such as iron that are scattered are iron-based fine particles, and the iron that is exposed on the surface of these iron-based fine particles is transferred from the wet crusher to the iron removal device. Adsorbs a relatively large amount of toxic metals in a series of distribution processes. Therefore, iron-based fine particles that existed before crushing and iron-based fine particles generated by crushing are introduced into the iron removal device, and both of these iron-based fine particles are considerably large (non-ferrous). (Compared with fine particles of the system)) Adsorbs harmful metals.

  Thus, in the iron removing device, the iron-based fine particles having a large amount of adsorption of these harmful metals and the like are removed from the sludge by the magnet mounting drum, so that the content or holding ratio of the harmful metals and the like in the sludge is greatly reduced. be able to. Therefore, the load of harmful metals, etc. on the fine particle washing device that purifies sludge discharged from the iron removal device with the chelate washing liquid, and the load of harmful metals, etc. on the chelating agent regenerator that removes the harmful metals, etc. from the chelating agent. It is possible to reduce the necessary amount or use amount of the chelating agent and the solid-phase adsorbent, and the soil treatment cost can be reduced. In addition, since the wet crusher and the iron content removal apparatus have a simple mechanical structure for performing physical treatment and do not use any special chemicals, the operation cost is very low.

It is a block diagram which shows schematic structure of the soil purification system which concerns on this invention. (A) is typical sectional drawing of the iron content removal apparatus which is a component of a soil purification system, (b) is a typical top view of the iron content removal apparatus shown to (a). (A) is typical sectional drawing of another iron content removal apparatus, (b) is a typical top view of the iron content removal apparatus shown to (a). (A) is a schematic plan view of the fine particle cleaning device, (b) is a cross-sectional view taken along line AA of the fine particle cleaning device shown in (a), and (c) is a fine particle cleaning device. FIG. 3 is an elevational cross-sectional view of one slurry passage of the apparatus. It is a typical elevation view of a chelating agent reproduction device.

  As shown in FIG. 1, in the soil purification system S according to the embodiment of the present invention, soil collected by excavation of ground contaminated with harmful metals or the like (harmful metals and / or their compounds) or these ions. (Contaminated soil) is received by the input hopper 1. Examples of harmful metals include chromium, lead, cadmium, selenium, mercury, and metal arsenic. 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 gravel (for example, particle size 2 to 75 mm), sand (for example, particle size 0.075 to 2 mm), and fine particles (for example, particle size 0.075 mm or less). Some contain stones (for example, a particle size of 75 mm or more).

  A mixture (hereinafter referred to as “soil / water mixture”) containing soil and washing water generated by the mixer 2 is transferred to a mill breaker 3 which is a wet crusher. As the mill breaker 3, for example, a rod mill can be used. Although not shown in detail, the rod mill is a crushing device in which a plurality of rods (for example, ten 75 mmφ × 2 m steel rods) are arranged in a drum, and the rods rotate parallel to each other by the rotation of the drum. Moves and makes line contact, and can crush gravel and sand (and stone in some cases) by the impact force, shear force, friction force, etc. to generate small-diameter soil particles such as fine particles. . As the mill breaker 3, a ball mill or the like can be used in addition to the rod mill. The gravel and sand are partly fine and not all fine.

  Thus, the mill breaker 3 crushes the gravel and sand (and possibly stones) in the soil / water mixture discharged from the mixer 2 to generate small-sized soil particles such as fine particles. As a result, harmful metals adsorbed (attached) or contained in gravel and sand are released into the water. At this time, basically (aside from adsorption by iron, etc., which will be described later), harmful metals etc. released into the water are hardly adsorbed to gravel and sand, or do not adhere to them and are aggregated and adsorbed into fine particles. Or adhere (see, for example, Non-Patent Document 1).

  Furthermore, a large number of fine iron-based fine particles are produced in which minute masses of iron or the like (iron and / or iron oxide) that are unevenly distributed or scattered in the gravel and sand are exposed on the surface. On the other hand, iron and the like generally have a property of adsorbing harmful metals and the like. For this reason, noxious metals, etc. present in the washing water or a part of these ions are adsorbed or adhered to the exposed surface of the iron-based fine particles such as iron. As a result, the amount of adsorption (adhesion amount) of harmful metals and the like for iron-based fine particles is considerably larger than the amount of adsorption (adhesion amount) of harmful metals and the like for non-ferrous fine particles. In other words, the fine particles discharged from the mill breaker 3 are iron-based fine particles with a large amount of adsorption (adhesion amount) of toxic metals and non-ferrous fine particles with a small amount of adsorption (adhesion amount) of toxic metals. It consists of. Needless to say, iron-based fine particles existing before crushing also adsorb considerably more harmful metals and the like than non-ferrous fine particles.

  As described later, the iron-based fine particles adsorbing harmful metals and the like are removed by the iron content removing device 12. On the other hand, it is generally known that iron or the like (iron and / or iron oxide) has a property of adsorbing harmful metals and the like, and using this property, iron powder or iron oxide is added to 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, by crushing gravel and sand, fine iron-based fine particles with exposed fine lumps of iron (not yet adsorbing harmful metals, etc.) are generated on the surface. There has been no proposal of a method for treating harmful metals or the like in which harmful metals or the like are adsorbed on a fine lump (iron-based fine particles) of exposed iron or the like.

  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 arranged to be inclined with respect to a horizontal plane. Can be rotated around its central axis (cylindrical central axis) by a motor. Further, the washing water can be sprayed into the drum screen.

  When the soil / water mixture flows through the rotating drum screen of the trommel 4, the 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 and into the receiving tank. to go into. On the other hand, the soil particles coarser than the mesh of the drum screen cannot pass through the mesh of the drum screen, and 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 diameter of less than 2 mm, that is, sand and fine particles, pass through the mesh of the drum screen. Therefore, in this trommel 4, gravel (soil in some cases) which is a soil particle having a particle size of 2 mm or more is separated from the soil / water mixture. As described above, toxic metals and the like that have separated into the water are hardly adsorbed or adhered to the gravel and sand, so the gravel separated by Trommel 4 is clean and used, for example, as an aggregate for concrete be able to. The mesh size (opening) of the drum screen of Trommel 4 is not limited to that described above, and can be arbitrarily set according to the particle size of the soil particles to be obtained. It is.

  Soil particles having a particle diameter of less than 2 mm, that is, a soil / water mixture containing sand and fine particles and washing water, contained in the trombone 4 receiving tank is introduced into a cyclone 5 (liquid cyclone). Although not shown in detail, the cyclone 5 pumps the soil / water mixture in a substantially conical cylinder that narrows downward to generate a swirling flow, and utilizes the centrifugal force generated thereby, A mixture of soil and water, a mixture of fine particles having a relatively small particle size (for example, a particle size of 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

  A mixture of fine particles and water (hereinafter referred to as “fine particle-containing water”) is discharged from the upper end of the cyclone 5, and a mixture of sand and water having a relatively large particle size is discharged from the lower end of the cyclone 5. Is done. Here, since the sand discharged from the lower end of the cyclone 5 does not contain any harmful metals or the like as described above, it is drained or dried and used as reclaimed sand. On the other hand, the water containing fine particles is transferred to the PH adjustment tank 6.

  In the pH adjusting tank 6, the pH of the fine particle-containing water is adjusted to be almost neutral using an acid solution (for example, sulfuric acid and hydrochloric acid) and an alkali solution (for example, an aqueous sodium hydroxide solution). Although not shown, in the pH adjustment tank 6, the pH of the water containing fine particles 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 adjusting tank 6 is introduced into the coagulating tank 7. In the agglomeration tank 7, a polyaluminum chloride aqueous solution (PAC), a polymer flocculant, and a pH adjuster (an acidic liquid or an alkaline liquid) are added to the water containing fine particles. As a result, a large number of flocs in which the water-insoluble metal hydroxide and fine particles are mixed are generated in the aggregation tank 7.

  Water containing fine particles (including floc) in the coagulation tank 7 is introduced into the thickener 8. Although the thickener 8 is not shown in detail, the water-insoluble floc or fine particle is settled by gravity in a state where the fine particle-containing water is almost stationary, and a sludge layer (for example, solid And 5% to 10%), and supernatant water (wash water) which is located in the upper part and hardly contains flocs or fine particles. When the floating oil is floating on the surface of the supernatant water, the floating oil is removed by overflowing a small amount of the supernatant water from the upper part of the thickener 8.

  The supernatant water in the thickener 8 is introduced into the washing water tank 10 and temporarily stored. When the washing water tank 10 is full, the auxiliary water tank 11 is used. The washing water stored in the washing water layer 10 or the auxiliary water tank 11 is supplied to the mixer 2 and the trommel 4 as circulating water. In addition, when the wash water stored in the wash water tank 10 decreases due to evaporation or the like, tap water is appropriately replenished. On the other hand, the sludge that has settled or stayed in the lower part of the thickener 8 is transferred to the intermediate tank 9 and temporarily stored. The sludge in the intermediate tank 9 is continuously transferred to the iron content removing 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 the sludge composed of fine particles (iron-based fine particles and non-ferrous fine particles) and water transferred from the intermediate tank 9 via the pipe line 23 and temporarily receives them. Hold. And the sludge in the sludge tank 21 is transferred to the fine particle washing apparatus 13 (refer FIG. 1) via the pipe line 24, after an iron-type fine particle content is removed so that it may demonstrate later. In addition, in the sludge tank 21, a stirrer 25 is provided in order to prevent precipitation at the bottom of the fine particles.

  The magnet mounting drum 22A includes a rotating shaft 26, a cylindrical drum body 27 coaxially attached to the rotating shaft 26, and a drum circumference (for example, by fitting) inside a circumferential portion (outer edge portion) of the drum body 27. A plurality of permanent magnets 28 that are mounted or arranged in an annular shape adjacent to each other in the direction are provided, and a cylindrical cover 29 that covers the outer peripheral surface of the group of permanent magnets arranged in an annular shape. Here, the magnet mounting drum 22 </ b> A or the drum main body 27 is arranged so that the rotation center axis thereof is oriented in the horizontal direction and the lower part of the drum is immersed in the sludge in the sludge tank 21.

  Each of the plurality of permanent magnets 28 is disposed (outward) such that the magnetic poles face outward in the drum radial direction. The permanent magnet 28 may be arranged so that all the N poles or S poles are outward, or may be arranged so that the N poles and S poles are alternately outward. The cylindrical cover 29 is preferably formed of a soft magnetic metal material (for example, iron or iron alloy) having a relatively small thickness (for example, 5 to 10 mm), but a diamagnetic metal material (for example, copper or aluminum or These alloys may be used.

  The rotating shaft 26 and the drum main body 27 are rotationally driven by a motor 30 (electric motor) via a speed reducer 31 and are slow in the clockwise direction in the positional relationship in FIG. Rotate at 0 rpm). When the magnet mounting drum 22 </ b> A 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. Adsorbed. Thus, when the magnet-equipped drum 22A or the drum body 27 comes out of the sludge, an iron-based fine particle layer is formed on the outer peripheral surface of the cylindrical cover 29. The iron-based fine particle 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 a raw material for iron making.

  The iron-based fine particles are produced by crushing gravel and sand with a mill breaker 3 (see FIG. 1), which is a wet crusher, or existing before the crushing of gravel and sand. On the surface, a fine lump of iron or the like is exposed, and a considerably large amount of harmful metal or the like is adsorbed on the exposed fine lump of iron or the like. In general, small blocks such as iron are unevenly distributed or scattered in gravel and sand, and the ratio of such small blocks is about 2 to 5% by mass. For this reason, a part of the fine particles produced by crushing of gravel and sand becomes an iron-based fine particles in which fresh iron or the like is exposed on the surface.

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

In addition, the inventor of the present application crushed gravel and sand with a mill breaker several times (10 times) in July 2017 at a contaminated soil treatment plant at a factory in Yamazaki, Otsu City, Shiga Prefecture. The sludge (1-3% by mass of fine particles), which is a mixture of fine particles and water produced in this way, is magnetized using a magnet mounting drum (using a neodymium magnet as a permanent magnet) with a diameter of about 1 m. As a result of an adsorption experiment, an average of 3.4 kg of iron-based fine particles was collected per 10 m ³ of sludge.

  Iron or other fine mass exposed on the surface of fine iron particles produced by crushing gravel and sand with a mill breaker 3 (see FIG. 1) is unevenly distributed or scattered in the gravel or sand. It originates from a small lump of fresh iron or the like that has not adsorbed the toxic metals that have been adsorbed, and is exposed to the surface after crushing and adsorbs toxic metals and / or these ions from the surrounding wash water. 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 considerably) amount of adsorption of harmful metals, harmful metals, etc. Is composed of non-ferrous fine particles with a relatively small (or considerably) adsorption amount.

  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 large amount of adsorption of harmful metals and the like. Most (or quite) non-ferrous fines are the majority. Therefore, a part or a substantial part of harmful metals and the like contained in the contaminated soil introduced into the soil purification system S is removed by the iron content removing device 12A. In addition, if the hydrogen index of the sludge in the sludge tank 21 is adjusted within the range of pH 4-6, the amount of adsorption of harmful metals and the like for the iron-based fine particles slightly increases. In this case, it is preferable to neutralize the sludge discharged from the sludge tank 21.

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

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

  In the iron 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 body 27. The drive shaft 42 is attached coaxially. The drive roller 41 and the drive shaft 42 are arranged so that their rotation center axes are parallel to the rotation center axis of the drum body 27, and are driven to rotate by the motor 30 via the speed reducer 31. The drive roller 41 has a smaller diameter (for example, 1/5 to 1/10) than the drum body 27.

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

  When the driving roller 41 is rotated by the motor 30 via the speed reducer 31 in the clockwise direction in the positional relationship in FIG. 3A, the drum body 27 or the magnet mounting drum 22B is driven to rotate in the clockwise direction. The endless belt 43 runs around the drive roller 41 and the drum body 27 in the clockwise direction. 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 (for example, 0.5 to 2.0 rpm).

  An endless belt 43 that circulates clockwise between the drive roller 41 and the drum body 27 in the clockwise direction in the positional relationship in FIG. 3A is arranged in an annular shape inside the circumferential surface of the drum body 27. When the magnet group is in contact with the outer peripheral surface of the magnet group and immersed in the sludge in the sludge tank 21, the iron 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. . Thus, when the endless belt 43 goes out of the sludge, an iron-based fine particle layer is formed on the outer surface of the 0 endless belt 43. The iron-based fine particle layer formed on the outer surface of the endless belt 43 is scraped off by the scraper 32 in the vicinity of the drive roller 41 and removed from the endless belt 43.

  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 particles contained in the sludge discharged from the iron removing device 12B are mostly non-ferrous fine particles with a relatively small (or considerably) adsorption amount of harmful metals and the like. Therefore, a part or substantial part of the toxic metal contained in the contaminated soil introduced into the soil purification system S is removed by the iron removing device 12B.

  The sludge discharged from the iron content removing device 12 (12A, 12B) is introduced into the fine particle cleaning device 13 (see FIG. 1). The fine particle cleaning device 13 is a sludge containing non-ferrous fine particles discharged from the iron content removing device 12 (12A, 12B) and cleaning water, and a chelating agent regeneration device 17 (see FIG. 1) described later. Accept the chelating agent supplied and the chelating cleaning solution containing water, mix and stir these to produce a fine-grained slurry, and ensure a preset residence time (for example, 0.5-2 hours) In general, by continuously flowing with a plug flow (plug flow), a toxic agent or the like adhering (adsorbing) fine particles is captured by a chelating agent. Thereby, the harmful metal adsorbed (attached) on the surface of the fine particles in the fine particle slurry is removed. The ratio of the flow rate of the sludge supplied to the fine particle cleaning device 13 and the flow rate of the chelate cleaning solution is set to 1: 1, for example.

  Examples of the chelating agent used in the chelate cleaning solution 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). Any of these chelating agents can effectively capture (chelate) the fine metal slurry or the harmful metals contained in the fine particle. Of course, a chelating agent suitable for the treatment is selected or a plurality of chelating agents are used depending on the type of harmful metal contained in the fine particles.

  Hereinafter, a specific configuration and function of the fine particle cleaning device 13 will be described with reference to FIGS. The fine grain cleaning device 13 has a storage tank 50 having five elongated rectangular parallelepiped or prismatic slurry passages 55 to 59 formed by partitioning with four flat partition walls 51 to 54 and extending in parallel to each other. doing. The storage tank 50 may be, for example, an iron rectangular parallelepiped square tank installed on the ground, or may be a concrete rectangular parallelepiped pit. Moreover, the partition walls 51-54 may be formed, for example, by connecting a plurality of iron plates or plastic plates in the direction in which the slurry passage extends.

  Two adjacent slurry passages in the slurry passages 55 to 59 are connected to one end of the slurry passage in the longitudinal direction of the slurry passage (left and right in the positional relationship in FIGS. 4A and 4B) (four curves in FIG. 4A). Are communicated with each other at the site indicated by the arrows. That is, partition walls 51 to 54 do not exist in these communicating portions, and adjacent slurry passages communicate with each other.

  Air discharge pipes 61 to 65 for discharging air into the fine particle slurry and stirring the fine particle slurry are arranged at the bottoms of the respective slurry passages 55 to 59. Each of the air discharge pipes 61 to 65 is a porous pipe extending in the slurry passage longitudinal direction and having a plurality of air discharge holes arranged in the slurry passage longitudinal direction at the bottom (lower side) of the peripheral wall. Although not shown, it is connected to a compressor or a blower that supplies compressed air. When pressurized air is supplied to the air discharge pipes 61 to 65, the air is bubbled from the air discharge holes and released into the fine particle slurry, and the fine particle slurry is stirred by the bubbles. Is done.

  FIG. 4C shows a cross section of the slurry passage 55 on the most upstream side 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. 4C, the air discharge pipe 61 is disposed near the bottom of the slurry passage in the vicinity of one side surface of the slurry passage 55. For this reason, the bubbles discharged from the air discharge pipe 61 rise in the vicinity of this side surface. As a result, a circulating flow that flows in the direction indicated by the arrow P in a plane perpendicular to the longitudinal direction of the slurry passage is formed in the slurry passage 55, and the fine particle slurry is stirred. The shape, size, capacity, and the like of the storage tank 50 and each of the slurry passages 55 to 59 and the amount of pressurized air supplied to the air discharge pipes 61 to 65 are set in advance in the fine particle washing device 13. The water content, flow rate, residence time, flow velocity, turbulence degree of flow (for example, Reynolds number) and the like are preferably set.

  As shown in FIG. 1 again, the fine particle slurry discharged from the fine particle washing device 13 is transferred to the filtration device 14. The filtration device 14 filters the fine particle slurry to produce a filter cake and filtrate having a water content of 30 to 40 percent. In addition, as the filtration apparatus 14, a filter press, a vacuum filter, etc. can be used. Since the filter cake (fine particles) discharged from the filter device 14 does not contain any harmful metals or the like, it is used as, for example, agricultural soil or disposed of by landfill.

  The filtrate discharged from the filtration device 14, that is, the chelate washing solution is transferred to the reverse osmosis membrane separation device 16 after the suspended matter or suspended matter (SS) is removed by the clarification filter 15 (for example, sand filter). . Although not shown in detail, the reverse osmosis membrane separation device 16 receives the chelate washing liquid discharged from the clarification filter 15, pressurizes it with a high-pressure pump, and then concentrates the chelating agent concentrated by the reverse osmosis membrane. Separation into water and permeate without chelating agent.

  The reverse osmosis membrane of the reverse osmosis membrane separation device 16 is, for example, a three-layer structure in which a polysulfone support layer and a dense cross-linked aromatic polyamide layer are laminated on the surface of a polyester nonwoven fabric (thickness 100 to 120 μm). Can be used. The dense cross-linked aromatic polyamide layer has a large number of pores having a pore diameter of about 0.5 to 1.5 nm, and is very thin (for example, 0.2 to 0.25 μm) a semipermeable membrane. The polysulfone support layer is a relatively thick (for example, 40 to 50 μm) porous membrane for supporting or protecting a very thin crosslinked aromatic polyamide dense layer to prevent breakage thereof.

The reverse osmosis membrane separation device 16 is of a spiral type and has a plurality of reverse osmosis membrane elements in which a reverse osmosis membrane wound in a spiral shape is accommodated in a cylindrical container. It is practical that each reverse osmosis membrane element has, for example, 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 a 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 Authentec Co., Ltd., Nakatsugawa, Gifu Prefecture) is About 40 m ² . In the case of this reverse osmosis membrane element, when the chelate cleaning solution having a chelating agent concentration of about 1% by mass is supplied at a pressure of about 1 MPa, the treatment amount of the chelate cleaning solution is estimated to be about 1.5 m ³ / hr. Therefore, for example, when processing a chelate washing solution of 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 (operation pressure) of the chelate washing liquid, the discharge amount of concentrated water and permeate, the chelating agent concentration ratio of concentrated water are as follows. It is set appropriately according to the amount of chelate cleaning liquid to be supplied to the cleaning device 13 and the chelating agent concentration. For example, the ratio of the flow rate of the sludge supplied to the fine particle cleaning device 13 and the flow rate of the chelate cleaning solution is set to 1: 1, and the chelating agent concentration of the fine particle slurry in the fine particle cleaning device 13 is set to 1% by mass. In this case, the reverse osmosis membrane separation device 16 generates permeated water (chelating agent concentration 0) of about 50% of the supply amount of the chelate washing liquid and concentrated water (chelating agent concentration of about 2 mass%) of about 50%. Set to Therefore, in the fine particle cleaning device 13, the sludge not containing the chelating agent and the chelating cleaning solution having a chelating agent concentration of about 2% by mass are mixed at a ratio of 1: 1, and the chelating agent concentration in the fine particle cleaning device 13 is 1 mass. % Is maintained.

  The concentrated water, that is, the chelate washing liquid 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 complex forming power higher than that of the chelating agent, and a solid phase adsorbing material that adsorbs or extracts a harmful metal or the like in the chelating cleaning solution when it comes into contact with the chelating cleaning solution or a small piece on which the solid adsorbing material is fixed. Or it has a granular material, removes a harmful metal etc. from the chelating agent in the chelating cleaning solution, and regenerates the chelating cleaning solution.

  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 and the like captured by the chelating agent are separated from the chelating agent and adsorbed or extracted by the solid phase adsorbent. As a result, harmful metals and the like are removed and collected from the chelate cleaning solution (chelating agent), and the chelate cleaning solution (chelating agent) is in a state where it can capture the harmful metals and the like again.

  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. For example, when EDTA (ethylenediaminetetraacetic acid) is used as a chelating agent, such a solid-phase adsorbent has a strong binding force capable of recovering almost 100% of metal ions from an EDTA aqueous solution having a concentration of 10 mM / l. I have it.

  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.

  Hereinafter, the specific configuration and function of the chelating agent regenerator 17 will be described with reference to FIG. The chelating agent regenerator 17 is provided with a packed tower 70 filled with solid phase adsorbent particles or a packing (packing) in which the solid phase adsorbent is fixed. The chelating agent regenerator 17 includes an intermediate storage tank 71 for storing a 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 an acid liquid. A water storage tank 74 for storing water is provided.

  In the intermediate storage tank 71, the concentrated water discharged from the reverse osmosis membrane separation device 16, that is, the chelate cleaning liquid is temporarily stored. When regenerating the chelate cleaning liquid, the chelate cleaning liquid stored in the intermediate storage tank 71 is transferred to the packed tower 70, while the chelate cleaning liquid regenerated in the packed tower 70 is transferred to the cleaning liquid storage tank 72 and a series. The pipe lines 77 to 80 are provided. In addition, a pump 81 and a pipe line 82 are provided for supplying the chelate cleaning liquid stored in the cleaning liquid storage tank 72 to the fine particle cleaning apparatus 13 (see FIG. 1).

  Further, when the solid phase adsorbent is regenerated, the chelating agent regenerator 17 transfers the acid solution stored in the acid solution storage tank 73 to the packed tower 70, while the acid solution discharged from the packed tower 70 is converted into an acid. A pump 83 and a plurality of pipes 84 and 85 for returning to the liquid storage tank 73 are provided. Further, when the solid phase adsorbent regenerated with the acid solution is washed with water, the chelating agent regenerator 17 transfers the water stored in the water storage tank 74 to the packed tower 70 while being discharged from the packed tower 70. A pump 86 and a plurality of pipes 87 and 88 for returning water to the water storage tank 74 are provided.

  Valves 91, 92, 93, 94 for opening and closing the corresponding pipe lines are interposed in the pipe lines 77, 78, 84, 87 for transferring the chelate cleaning solution, the acid solution or the water to the packed tower 70, respectively. Yes. On the other hand, valves 79, 80, 85, and 88 for discharging the chelate cleaning solution, acid solution, and water from the packed tower 70 are provided with valves 95, 96, 97, and 98 for opening and closing the corresponding channels, respectively. Has been. By switching the open / closed state of these valves 91 to 98, either the chelate cleaning liquid, the acid liquid or the water can be supplied to and discharged from the packed tower 70. Note that 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 regeneration device 17 will be described. When regenerating the chelate cleaning liquid (chelating agent), the valves 91, 92, 95, 96 interposed in the pipe lines 77-80 are opened, while the other valves 93, 94, 97, 98 are closed, The pump 76 is operated. As a result, the chelate cleaning liquid in the intermediate storage tank 72 flows through the cleaning liquid regenerator 35 and is transferred to the cleaning liquid storage tank 36.

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

  As the chelate cleaning solution is regenerated, the amount of adsorption of harmful metals and the like on 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 harmful metals or the like in the solid phase adsorbent reaches a saturated state or the vicinity thereof, the solid phase adsorbent is regenerated. That is, the acid solution is flowed into the packed tower 70 with the chelate cleaning solution removed, and harmful metals adsorbed on the solid phase adsorbent are removed by the acid solution to regenerate the solid phase adsorbent. Thus, while toxic metals and the like are recovered by the acid solution, the solid-phase adsorbent is regenerated so that the toxic metals and / or these ions can be adsorbed or extracted again.

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

  When the solid-phase adsorbent is washed with water after the regeneration of the solid-phase adsorbent with the acid solution is completed, the valves 94, 92, 95, 98 provided in the pipes 87, 78, 79, 88 are opened. The other valves 91, 93, 96, 97 are closed and the pump 86 is operated. Thereby, the water in the water storage tank 74 flows through the packed tower 70 and returns to the water storage tank 74. Water circulates between the water storage tank 74 and the packed tower 70. At that time, the solid phase adsorbent in the packed tower 70 comes into contact with water, and the acid solution adhering to the solid phase adsorbent is washed. Thereafter, regeneration of the chelate cleaning solution is resumed.

  The chelate cleaning liquid regenerated in this way is temporarily stored in the cleaning liquid storage tank 72 and then supplied to the fine particle cleaning apparatus 13. That is, the chelate cleaning liquid circulates while repeating purification of the fine particles and regeneration of the chelating agent. Note that the reduced amount of the chelating agent is appropriately supplemented.

  As described above, according to the soil purification system S according to the present invention, clean and reusable gravel, sand and fine particles can be obtained. Moreover, since the content rate of the harmful metal etc. of the sludge discharged | emitted from the iron content removal apparatus 12 (12A, 12B) can be reduced, the load of the harmful metal etc. with respect to the fine grain washing | cleaning apparatus 13, and the chelating agent reproduction | regeneration apparatus 17 It is possible to reduce the load of harmful metals and the like on the soil, to reduce the necessary amount or use amount of the chelating agent and the solid-phase adsorbent, and to reduce the soil treatment cost. In addition, since the iron content removal apparatus 12 (12A, 12B) has a simple mechanical structure that performs physical processing and does not use any special chemical, its operating cost is very low.

  S soil purification system, 1 input hopper, 2 mixer, 3 mil breaker (wet crusher), 4 trommel, 5 cyclone, 6 PH adjustment tank, 7 coagulation tank, 8 thickener, 9 intermediate tank, 10 washing water tank, 11 spare Water tank, 12 Iron content removal device, 12A Iron content removal device, 12B Iron content removal device, 13 Fine-grain content washing device, 14 Filtration device, 15 Clarification filter, 16 Reverse osmosis membrane separation device, 17 Chelating agent regeneration device, 21 Sludge tank, 22A magnet mounting drum, 22B magnet mounting drum, 23 pipe, 24 pipe, 25 stirrer, 26 rotating shaft, 27 drum body, 28 permanent magnet, 29 cylindrical cover, 30 motor, 31 speed reducer, 32 scraper, 41 drive Roller, 42 Drive shaft, 43 Endless belt, 50 Storage tank, 51-54 Partition wall, 55 -59 slurry passage, 61-65 air discharge pipe, 70 packed tower, 71 intermediate storage tank, 72 washing water tank, 73 acid solution storage tank, 74 water storage tank, 76 pump, 77-80 pipe, 81 pump, 82 pipe, 83 Pump, 84 pipelines, 85 pipelines, 86 pumps, 87 pipelines, 88 pipelines, 91-98 valves.

Claims (3)

A soil purification system for purifying soil containing gravel, sand and fine particles and contaminated with harmful metals or compounds thereof,
A mixer for mixing the soil introduced into the soil purification system and washing water;
Iron or iron oxide that is unevenly distributed or scattered in the gravel and sand is exposed to the surface by crushing gravel and sand in the mixture containing soil and washing water discharged from the mixer. A wet crusher that generates a system fine particle and adsorbs a harmful metal or a compound thereof to iron or iron oxide exposed on the surface of the iron system fine particle;
Trommel for separating gravel from a mixture containing gravel, sand, fine particles and washing water discharged from the wet crusher;
A liquid cyclone for separating sand from a mixture containing sand, fine particles and washing water discharged from the trommel;
A thickener that separates the mixture containing fine particles discharged from the hydrocyclone and washing water into supernatant water and sludge containing fine particles and washing water by sedimentation separation,
From the sludge discharged from the thickener, by removing the iron-based fine particles by magnetically adsorbing, an iron content removing device that reduces the content of harmful metals or compounds thereof in the sludge,
The sludge discharged from the iron removal device is mixed with a chelate cleaning liquid containing a chelating agent and water to produce a fine particle slurry, and the fine particle slurry is flowed to ensure a preset residence time. A fine particle cleaning device that captures a toxic metal or a compound thereof adhering to the fine particle by a chelating agent,
A filtration device for filtering the fine particle slurry discharged from the fine particle washing device to produce a filtrate and a filter cake;
A reverse osmosis membrane separation device for separating the filtrate discharged from the filtration device into a concentrated water in which a chelating agent is concentrated and a permeated water not containing the chelating agent by a reverse osmosis membrane;
The concentrated water discharged from the reverse osmosis membrane separator is received and concentrated by a solid-phase adsorbent that adsorbs harmful metals or compounds thereof in the concentrated water when it has higher complexing power than a chelating agent and comes into contact with the concentrated water. A chelating agent regenerator that removes harmful metals or their compounds from the chelating agent in water and supplies the concentrated solution as the chelate cleaning solution to the fine particle cleaning device;
A permeated water transfer means for transferring the permeated water discharged from the reverse osmosis membrane separation device to the thickener,
The iron removing device is
A sludge tank for retaining sludge discharged from the thickener;
It is formed in a drum shape, arranged so that the drum center axis faces in the horizontal direction and the lower part of the drum is immersed in the sludge in the sludge tank, and a plurality of permanent magnets are arranged on the inner side of the drum circumferential surface. A magnet mounting drum mounted side by side in the drum circumferential direction so that the magnetic pole faces
A soil purification system, comprising: a drum rotating mechanism that rotates the magnet mounting drum about a drum central axis.   The soil purification system according to claim 1, further comprising a clarification filter that performs clarification filtration on the filtrate discharged from the filtration device.   The iron removing device includes a pH adjusting device that adjusts a hydrogen index of sludge retained in the sludge tank within a pH range of 4 to 6, and a neutralizing device that neutralizes sludge discharged from the sludge tank. It has, The soil purification system of Claim 1 or 2 characterized by the above-mentioned.

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