JP2005028290A - Treatment method for soil polluted with heavy metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method for heavy metal-polluted soil which is capable of efficiently separating and removing particles containing heavy metals in a high concentration in the soil and recovering a large amount of cleaned soil. <P>SOLUTION: Soil polluted with heavy metals is sieved and soil with a particle size in a prescribed range is introduced into an attrition tank 5 and mixed with an insolubilization agent. Particles are abraded one another to separate pollutants adhering to the surface. After that, the particles are sent to a liquid cyclone 7 to take out particles from which the pollutants are separated as clean soil and the remaining fine particles are led to a centrifugal jig type specific-gravity separator 8. The centrifugal jig type specific-gravity separator 8 has a layer of particles with a prescribed diameter and separates the particles into a high specific gravity fraction containing a much amount of heavy metals passing through the layer by the centrifugal force and a low specific gravity fraction containing a little amount of heavy metals, and the high specific gravity fraction and particles with 30 μm or smaller are discarded after dewatering with a dewatering means 10. The low specific gravity fraction is treated by a detoxification means 9 and turned back or discarded. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for selecting heavy metal-contaminated soil, removing a portion with a high heavy metal content, and collecting clean soil that can be backfilled to the original ground.
[0002]
[Prior art]
There are an increasing number of cases where heavy metal contamination, such as factory sites, has been found in surveys associated with urban redevelopment. On the other hand, in the soil pollution countermeasure guidelines for heavy metals, etc. of the Environment Agency, the standard for setting the countermeasure range as of 1996 for lead contamination is an elution amount of 0.01 mg / l and a content reference value of 600 mg / kg. Yes. Moreover, according to the Tokyo standard for countermeasures against contaminated soil, the lead elution amount is 0.01 mg / l, and the content reference value is 300 mg / kg. Furthermore, the “Soil Contamination Countermeasures Law” enforced on February 15, 2003 stipulates that lead elution is 0.01 mg / l or less and the content is 150 mg / kg or less.
[0003]
The countermeasures against soil contamination currently taken in Japan against heavy metal contamination are generally methods of shielding from surrounding environment, such as insolubilization treatment of pollutants, water shielding work, and soil covering work. However, in this method, heavy metal itself remains on the site, and there is a limit to land use even after the treatment by the construction. Therefore, recently, the soil contaminated at a high concentration is discarded and the soil at the contaminated site is replaced. However, since it is clear that there will be a shortage of industrial waste final disposal sites in the near future, introduction of soil cleaning methods that have been put to practical use in Europe and the United States is beginning to be considered.
[0004]
The soil washing method is a method of physically and chemically extracting and separating contaminants from the soil using water or an appropriate solvent in order to remove the contaminants. For example, by washing contaminated soil, particles containing a high concentration of heavy metals are removed, and the soil thus cleaned is used for backfilling the contaminated site. As a result, it is possible to reduce the volume of contaminated soil that becomes waste, that is, the contaminated soil that is discarded in a disposal site that is provided with strict facilities so that leakage and diffusion of the contaminant do not occur. In this case, the higher the ratio of the amount of the obtained clean matter (cleaned soil) to the amount of the supplied contaminant (contaminated soil), the more effective the treatment method.
[0005]
Conventionally, the following has been proposed as a method for selecting a portion containing a high concentration of contaminants or a clean portion containing almost no contaminants from soil contaminated with heavy metals.
In the purification method described in Patent Document 1, firstly, contaminated soil with heavy metals is classified to separate small and medium-sized particles having a high ability to adsorb contaminating elements, and clean large particles that are not contaminated. Take it out as a thing. Next, the separated and removed particles are classified according to particle size by concentration and removal of heavy metal-rich particles by specific gravity sorting, heavy metal leaching with a solvent such as an acid solution or a chelating agent solution, or electroosmosis or iontophoresis. Perform electrolytic treatment to accumulate heavy metal ions.
[0006]
Further, in the purification method described in Patent Document 2, contaminated soil containing carbonaceous organic compounds such as heavy metals and organic halogen compounds and volatile organic compounds is crushed and classified, and is floated from a slurry containing soil particles of 150 μm or less. The carbonaceous organic matter is lifted and removed together with bubbles by means. Next, the slurry from which the carbonaceous organic substances have been removed is subjected to sulfidation treatment to convert the heavy metal into sulfide, and the heavy metal is separated and recovered by flotation means.
[0007]
[Patent Document 1]
JP-A-10-296230
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-248459
[0008]
[Problems to be solved by the invention]
However, the following problems remain in the conventional techniques as described above.
In the purification method described in Patent Literature 1, heavy metals are recovered by performing leaching treatment or electrolytic treatment on classified soil particles of 450 μm or less. However, chemicals and treatment time to be added depending on the form of heavy metals contained in the soil, etc. Unlikely, it is difficult to take out a clean part efficiently. A considerable amount of soil is discarded as contaminated soil. Further, in the purification method described in Patent Document 2, heavy metals are recovered by flotation means for soil particles classified to 150 μm or less. However, since pH adjustment and sulfidation treatment are required, the treatment becomes complicated and efficient cleaning is achieved. It is difficult to take out the correct part.
[0009]
In addition, there is a specific gravity sorting method as a method for separating soil particles containing a lot of heavy metals. In this method, for example, a vibrating jig sorting method in which particles are separated into layers by specific gravity discrimination by applying vibration to soil particles in a natural gravity field, or particles having different specific gravity are sorted by the action of water flowing on a gently inclined surface. There is a thin flow sorting method. Such a specific gravity sorting method can efficiently separate a portion containing a lot of heavy metals from the contaminated soil, but it is difficult to effectively sort a soil particle having a small particle size, particularly 150 μm or less. For this reason, the leaching process, the electrolytic process, the flotation process, etc. are performed like the said prior art in the range with a small soil particle. However, these methods cannot efficiently select clean soil, and a large amount of contaminated soil that must be discarded at a disposal site is generated in a range where the particle size of the soil is small. In particular, many Japanese soils are being crushed and contain a large amount of small soil particles, making it difficult to select clean soil that can be backfilled. That is, the soil to be subjected to the purification treatment contains many 70 μm to 30 μm soil particles, which may occupy about 30%. The specific gravity sorting method cannot be applied to these soil particles, and the amount of soil that must be discarded increases.
[0010]
On the other hand, in the case of soil particles having a slightly large particle size, for example, soil particles of about 100 μm to 5 mm, the treatment of contaminants adhering to a part of the surface may be a problem. When the entire soil particles to which such heavy metals are attached are disposed of in a disposal site, the amount of waste increases and efficient treatment cannot be performed. In addition, soil particles having heavy metals attached to a part thereof are not significantly different from specific soil particles in terms of specific gravity, and are difficult to sort by specific gravity sorting. Therefore, there is a need for an efficient treatment method in the case where contaminants such as heavy metals adhere to the surface of soil particles having a slightly larger particle size.
[0011]
The invention according to the present application has been made in view of the circumstances as described above, and its purpose is to efficiently separate soil having a low content of pollutants from soil contaminated with heavy metals as clean soil. To get more soil that can be handled.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that a granular material having a diameter larger than the diameter of the small hole is accommodated in a centrifuge tank having a cylindrical wall body in which a large number of small holes are formed. And rotating the centrifuge tank around the axis of the cylindrical wall body to form a layer of the granular body along the inner surface of the wall body, adding water to the soil contaminated with heavy metal, and classifying it. The soil having a maximum particle size equal to or smaller than the diameter of the small hole is introduced into the centrifugal separation tank, and passes through the granular layer and the small hole in the wall body when the centrifugal separation tank is driven to rotate. Is separated as soil particles containing a large amount of heavy metals, and a method for treating heavy metal-contaminated soil is provided.
[0013]
The slurry-like soil after classification is introduced into the centrifuge tank, and centrifugal force is generated by rotationally driving the centrifuge tank. This centrifugal force causes the centrifuge tank to have a large specific gravity and a large specific gravity. The driving force toward the wall acts. And the soil particle containing many heavy metals contacts the layer of the granular material formed along the wall. Particles having a specific gravity greater than that of the granular material are gradually taken into the granular material layer, pass through the small holes in the granular material layer and the wall, and are recovered as contaminated soil. On the other hand, soil with a low content of heavy metals is transported above the centrifuge tank together with water and discharged from the centrifuge tank due to a difference in specific gravity with soil particles containing a lot of heavy metals. In this treatment method, by limiting the particle size of the soil particles and applying a centrifugal force to the soil particles, small-diameter soil particles that are difficult to sort in a natural gravitational field, a heavy metal content portion and a heavy metal content Can be efficiently separated into a portion having a small amount. In addition, by appropriately selecting the specific gravity of the granular material put in the centrifuge tank in advance, it becomes possible to sort according to the type of pollutant and the content of the pollutant.
[0014]
The invention according to claim 2 is the method for treating heavy metal-contaminated soil according to claim 1, wherein the soil introduced into the centrifuge tank is determined in a range from 1/10 to 1/4 of the diameter of the granular material. It is assumed that part or most of soil particles having a diameter smaller than the obtained value are removed by classification.
[0015]
Soil particles having a particle size smaller than about ¼ of the diameter of the granular material accommodated in the centrifugal separation tank can easily pass through the granular material layer in the centrifugal separation tank regardless of the specific gravity. In other words, there are gaps between the granular materials, and the soil particles having a small particle diameter easily pass through the gaps. For this reason, when a large amount of soil particles having a particle size smaller than a predetermined ratio compared with the diameter of the granular material is put into the centrifuge tank, the selection based on the size of the specific gravity is not performed on these. The efficiency of will decrease. Therefore, the efficiency of specific gravity sorting can be improved by previously removing particles having a small particle diameter from the soil put into the centrifuge tank. At this time, the particle size of the soil particles to be excluded can be determined based on the particle size distribution of the soil, but by setting the particle size to be equal to or less than the value determined in the range of 1/4 to 1/10 of the particle size of the granular material. , Sorting efficiency is good.
[0016]
According to a third aspect of the present invention, in the method for treating heavy metal-contaminated soil according to the first aspect, the diameter of the small holes is 100 μm to 600 μm.
[0017]
By setting the diameter of the small holes provided in the wall of the centrifuge tank to a value determined in the range of 100 μm to 600 μm, it is possible to perform specific gravity sorting for soil particles having a particle size less than this value. Soil particles containing high concentrations of heavy metals can be efficiently separated from the soil.
[0018]
The invention according to claim 4 is the method for treating heavy metal-contaminated soil according to claim 1, wherein the granular material charged into the centrifugal separation tank has a specific gravity higher than that of soil particles containing a heavy metal content in the heavy metal-contaminated soil. It is made of a substance having a small specific gravity and a larger specific gravity than soil particles having a small content of heavy metals.
[0019]
When soil is introduced into the centrifuge tank and the centrifuge tank is rotationally driven, soil particles larger than the specific gravity of the granule and containing a large amount of heavy metals are reduced in the size of the granule layer and the wall of the centrifuge tank. It passes through the hole and is discharged out of the centrifuge tank. On the other hand, soil particles that are smaller than the specific gravity of the granular material and have a small amount of heavy metal are not transported through the granular layer, but are transported upward together with water inside the layer, separated from the heavy metal-rich portion, and cleaned. It is collected as soil. In this treatment method, by selecting a granular material having an appropriate specific gravity, it is possible to satisfactorily separate into soil particles containing a large amount of heavy metal and soil particles containing a small amount of heavy metal.
[0020]
The invention according to claim 5 is the method for treating heavy metal-contaminated soil according to claim 1, wherein the contaminated soil introduced into the centrifugal separation tank is a soil whose particle size is included in a range from a predetermined upper limit value to a lower limit value. A first classification step of removing particles by classification, a friction step of stirring the extracted soil particles and rubbing them between the soil particles to separate heavy metal contaminants adhering to the surface of the soil particles; Performing a second classifying step of separating the fine particles containing a large amount of contaminants separated in the friction step and the coarse particles containing a large amount of soil particles after the contaminants are separated; The fine particles separated in the classification step are included.
[0021]
Soil particles having a particle size in a predetermined value range are separated from the contaminated soil by classification, and these are stirred and rubbed together. By appropriately selecting the range of the particle size at this time, a portion containing a lot of heavy metal that is a contaminant adhering to the surface of the soil particle is peeled off. Particles separated in such a friction process have a considerably smaller particle size than the original soil particles, and can be further classified and separated. This small particle size contains a lot of heavy metals. By introducing this into the centrifuge tank and performing specific gravity sorting, a portion containing a lot of heavy metals adhering to the surface of the soil particles is obtained. It can be separated and recovered efficiently.
[0022]
The invention according to claim 6 is a first classification step for classifying, by classification, soil particles whose particle size is in a range from a predetermined upper limit value to a lower limit value from soil contaminated with heavy metals, and the extracted soil particles And rubbing between the soil particles to separate the heavy metal contaminants adhering to the surface of the soil particles, and a fine fraction containing a large amount of contaminants separated in the friction step, A second classification step of separating the coarse particles containing a large amount of soil particles after the pollutants are peeled off, and the soil particles of the coarse particles separated in the second classification step are buried in the ground There is provided a method for treating heavy metal-contaminated soil, characterized in that after that, the fine particles are treated as contaminated soil containing a large amount of contaminants.
[0023]
In this treatment method, by removing the soil particles whose particle size is within the range from the predetermined upper limit value to the lower limit value by classification, the soil particles are agitated and adhered to the surface by rubbing between the particles. Strip heavy metal contaminants. After that, when the coarse particles containing a lot of soil particles after the pollutants are peeled off by the second classification process are taken out, the content of the pollutants is reduced and refilled in the ground as it is or after a simple treatment. be able to. On the other hand, the fine particles containing a large amount of the polluted substances can be removed by selecting the subsequent treatment according to the contamination concentration and the elution amount of heavy metal.
[0024]
The invention according to claim 7 is the heavy metal pollutant which is ionized by adding a pollutant insolubilizing agent before or during the friction process in the heavy metal contaminated soil treatment method according to claim 6. Is included in the solidification step.
[0025]
By adding a pollutant insolubilizer before or during the friction process to solidify the ionized heavy metal contaminant, the amount of heavy metal eluted into the water during this process is suppressed. For this reason, it can be avoided that a large amount of heavy metal eluted in water remains in the coarse particles containing a large amount of soil particles separated in the second classification step and after the pollutants are separated. Also, by stirring the soil particles during the friction process and rubbing them between the particles, the solidified heavy metal is peeled off from the surface of the particles, and in the second classification step, the portion containing a lot of heavy metals is efficiently recovered. can do.
[0026]
The invention according to claim 8 is the method for treating heavy metal-contaminated soil according to claim 6, wherein the upper limit value is 1 mm to 5 mm, and the lower limit value is 100 μm to 600 μm.
[0027]
By limiting the diameter of the soil particles to be rubbed by stirring to the range of the above values, heavy metals attached to the surface can be efficiently peeled off. If the particle size of the soil particles is too small, the volume ratio with the attached heavy metal component becomes small, and the heavy metal component becomes difficult to peel off. On the other hand, if the particle size becomes too large, the surface areas that come into contact with each other when stirring are reduced, and efficient peeling does not occur.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a flowchart showing a method for treating heavy metal-contaminated soil, which is an embodiment of the present invention.
The treatment system used in this method includes a drum-type stirrer 1 that hydrolyzes and agitates and mixes the soil contaminated with heavy metals to break up the soil mass, and a first wet vibrating sieve 2 having a mesh size of 5 to 10 mm. The second wet vibrating sieve 3 having a mesh size of 2 mm, the first spiral classifier 4 for classifying the soil that has passed through the first and second wet vibrating sieves, and the first spiral classifier 4 An insolubilizing agent was added to the coarse particles (particle size of 150 μm or more) to cause an insolubilization reaction, and stirring and mixing were performed in the attrition tank 5 in which soil particles were rubbed against each other by stirring and mixing. A second spiral classifier 6 for classifying the later soil, and a finer particle size (particle size of 150 μm or less) classified by the first and second spiral classifiers, a portion having a smaller diameter (particle size of 30 μm or less) Separation And a centrifugal jig specific gravity separator 8 for separating a slurry containing coarse particles classified by the liquid cyclone 7 (particle size 150 μm or less, 30 μm or more) into a high specific gravity component and a low specific gravity component, Detoxification processing means 9 for processing the slurry containing fine particles classified by the hydrocyclone 7 (particle size of 30 μm or less) and the low specific gravity separated by the centrifugal jig specific gravity separator 8 according to the contamination concentration; A dehydrating means 10 comprising a settling tank, a filter press, etc. for dehydrating a high specific gravity separated by the centrifugal jig type specific gravity separator 8 or a slurry containing a high concentration of contaminants separated by the detoxifying means 9 And dehydrating means 11 for dehydrating the slurry separated by the detoxifying means 9 and containing a small amount of contaminants.
[0029]
In addition, the diameter used as the reference | standard of the classification | category by the said wet vibration sieves 2 and 3, the spiral classifiers 4 and 6, and the liquid cyclone 7 is not restricted to the said value, It can set suitably. In particular, the classification by the first spiral classifier 4 and the second spiral classifier 6 is based on a particle size determined in a range of about 100 μm to 600 μm as a standard, and the particle size or larger can be separated as a coarse particle fraction. it can. In addition, it is desirable to determine the standard particle size in the range of about 100 μm to 300 μm. The second spiral classifier 6 is preferably classified based on the same diameter as the first spiral classifier 4, but the standard diameter of the second spiral classifier 6 is the first spiral classifier. You may set smaller than the diameter used as the standard of the vessel 4.
[0030]
In the treatment method using the above system, first, the ground contaminated with heavy metal is excavated, and the collected soil is put into the drum stirrer 1 from the hopper, and is added to the soil, and the stirrer is driven to rotate. And crush the clod contained in the soil. Then, a slurry in which soil and water are mixed is applied to the first wet vibrating sieve 2 and the second wet vibrating sieve 3 to separate coarse particles having a particle diameter of 2 mm or more. The heavy metal that is a contaminant hardly adheres to the coarse particles, and the separated coarse particles can be refilled into the raw ground as a clean component. On the other hand, the slurry containing fine particles having a particle size of 2 mm or less separated from the coarse particles is classified by the first spiral classifier 4 and separated into a portion having a particle size of approximately 150 μm or more and a portion having a particle size of 150 μm or less. To do. The coarse particles (particle size of 150 μm or more) separated as described above are fed into the attrition tank 5. The fine particles (particle size of 150 μm or less) are further classified and processed, and this processing will be described later.
[0031]
The attrition tank 5 has a stirring blade, and a slurry containing coarse particles (particle size of 150 μm or more and 2 mm or less) charged in the tank is stirred and mixed by the stirring blade to rub the soil particles together. . As a result, the contaminants adhering to the surface of the soil particles are peeled off, and in order to remove the pollutants efficiently, a particle having a particle size of the soil particles of about 2 mm to 150 μm is added. Yes.
[0032]
Before injecting the slurry into the attrition tank 5 or while stirring and mixing the slurry in the attrition tank 5, an insolubilizing agent is added to the slurry to solidify the contaminants dissolved in water. For example, when the contaminant is lead, when a solution of sodium hydrogen sulfide NaHS is added as an insolubilizing agent, the water-soluble sodium hydrogen sulfide NaHS reacts with lead to produce insoluble PbS.
PbS ²⁺ + S ^2- → PbS ↓
Then, when the soil particles are rubbed together in the attrition tank, the contaminants insolubilized by the above treatment are also peeled off from the surface of the soil particles and become very small particles and included in the slurry.
[0033]
Further, by adding an insolubilizing agent to the slurry to solidify the ionized heavy metal contaminant, the amount of heavy metal eluted in water is suppressed. For this reason, a large amount of heavy metal eluted in water remains in the coarse particles separated by the second spiral classifier 6 or the soil separated as a low content of contaminants in the subsequent process. Can be avoided. Further, heavy metals eluted from the soil particles are prevented from adhering again to the cleaned soil particles, and can be efficiently separated into a portion having a high heavy metal content and a portion having a low heavy metal content.
[0034]
The soil particles that have been sufficiently stirred in the attrition tank 5 and rubbed together to remove the contaminants adhering to the surface are then classified by the second spiral classifier 6 and again have a particle size of 150 μm. It separates into the above part and the part below 150 micrometers.
[0035]
When the particle size is 150 μm or more, the contaminants adhering to the surface are removed, the content of the contaminants is reduced, and the soil is recovered as soil that can be backfilled to the original ground. On the other hand, the fine particle fraction of 150 μm or less contains contaminants peeled off from the surface of the soil particles, the concentration of the contaminants is high, and the particle size of 150 μm or less separated by the first spiral classifier 4 The following treatment is performed along with the fine particles.
[0036]
The slurry containing soil particles having a particle size of 150 μm or less separated by the first spiral classifier 4 and the second spiral classifier 6 is sent to the hydrocyclone 7 to further separate fine particles (particle size of 30 μm or less). Classify as you do. The coarse particles separated by the hydrocyclone 7, that is, the slurry containing soil particles having a particle size of approximately 150 μm or less and 30 μm or more, are introduced into a centrifugal jig type specific gravity separator 8 which will be described in detail later and subjected to specific gravity selection.
[0037]
On the other hand, the slurry containing a fine particle having a particle size of 30 μm or less has a high content of contaminants, and from here it is difficult to separate the soil that can be backfilled into the ground. Therefore, this slurry is dehydrated by a dehydrating means 11 equipped with a sedimentation tank, a filter press device, and the like, and discarded. In addition, although the insolubilizing agent is added to the slurry in the attrition tank, insolubilization treatment may be performed again before dehydration. By carrying out sufficient insolubilization treatment in this way, the separated water hardly contains contaminants and can be discharged or reused by simple treatment.
[0038]
The slurry containing soil particles having a particle size of 150 μm to 30 μm classified by the hydrocyclone 7 is introduced into a centrifugal jig type specific gravity separator 8 into a high specific gravity containing a lot of heavy metals and a low specific gravity containing little heavy metals. To separate. Then, the high specific gravity is dehydrated by the dehydrating means 10 and discarded in a disposal site managed so as not to cause leakage and diffusion of pollutants. Further, the low specific gravity is further processed by the detoxification processing means 9. And the soil in which the content and elution amount of pollutants became below a predetermined value by the leaching process or the electrolytic process is backfilled to the original ground. On the other hand, soil whose content and elution amount of pollutants cannot be reduced below the predetermined value is subjected to insolubilization treatment and the like and then discarded to a disposal site.
[0039]
As shown in FIG. 2, the centrifugal jig type specific gravity sorter includes a cylindrical outer tub 21 fixedly supported by a support member 28, and a centrifuge tank 22 is supported in the inside so as to be rotatable in the horizontal direction. Yes. The centrifuge tank 22 is rotated by driving a rotary drive shaft 27 a supported in the vertical direction by a drive device 27. Further, a water supply pipe 23 for supplying water from above is provided at the center of the centrifugal separation tank 22, and a slurry supply pipe 24 for supplying slurry into the centrifugal separation tank is connected to the outer tank 21 on the outside thereof. It is supported. On the other hand, the inside of the outer tank 21 passed through the first discharge path 25 for collecting the slurry containing the low specific gravity overflowed from the centrifugal separation tank 22 and the small hole 31a of the wall 31 of the centrifugal separation tank 22. A second discharge path 26 is provided for collecting slurry containing a high specific gravity.
[0040]
The centrifuge tank 22 has a cylindrical wall body 31 in which a large number of small holes 31 a are formed. The diameter of the small holes 31 a is greater than that of soil particles contained in the slurry supplied into the centrifuge tank 22. It has a large diameter and is determined in a range of about 100 μm to 600 μm depending on the particle size of the soil. A granular body 32 having a diameter larger than that of the small hole 31a is placed inside the wall body 31, and a layer is formed along the inner peripheral surface of the wall body 31 by a centrifugal force generated by the rotation of the centrifugal separation tank 22. It is to be formed.
[0041]
In the apparatus of this embodiment, the diameter of the small hole 31a is 180 μm, and the diameter of the granular material is 200 μm. And the diameter of the soil particle selected is classified into 150 micrometers or less, and can pass the said small hole 31a. Further, fine particles having a particle size of 30 μm or less are excluded by classification, and the fine particles are prevented from passing through the granular material layer regardless of the specific gravity and causing a decrease in efficiency. On the other hand, it is desirable that the granular material 32 has a specific gravity smaller than that of soil particles containing a large amount of heavy metals and larger than that of soil particles having a low content of heavy metals, and particles of ores such as magnetite and garnet are used. A suitable one can be selected according to the specific gravity and particle size of the soil particles.
[0042]
In this centrifugal jig type specific gravity sorter 8, first, the granular material 32 is accommodated in the centrifugal separation tank 22, the centrifugal separation tank 22 is rotationally driven, and the granular material 32 is moved along the inner surface of the wall body 31 by centrifugal force. Form a layer. Next, a slurry containing coarse particles (particle size of 30 μm or more) separated by the hydrocyclone 7 is introduced into the centrifugal separation tank 22 from the slurry supply pipe 24, and is added with water from the water supply pipe 23. Is driven to rotate. As a result, the high specific gravity containing a large amount of heavy metal contacts the layered granular material 32 by centrifugal force, and is taken into and passed through the layer of the granular material 32 by the swinging of the granular material due to the water flow. Then, it passes through the small hole 31a, is sent to the second discharge path 26, and is discharged to the outside from the second discharge port 26a provided in the second discharge path 26. On the other hand, the soil particles having a small amount of heavy metal are sent to the first discharge path 25 from above along with the flow of water inside the layer 32 without passing through the layer of the granular material 32, and enter the first discharge path 25. It is discharged to the outside from the provided second discharge port 25a.
[0043]
In this centrifugal jig type specific gravity sorter 8, the particle size of the soil particles is limited to a range of 150 μm to 30 μm, and the centrifugal separation tank is driven to rotate under conditions such as a rotation speed according to the particle size, so that the natural gravity Small-sized soil particles that are difficult to sort on site can be efficiently separated into a portion containing a large amount of heavy metal and a portion containing a small amount of heavy metal. Moreover, since the heavy metals contained in the slurry are present as insoluble solids by the insolubilization treatment, a large portion containing heavy metals can be recovered.
[0044]
【The invention's effect】
As described above, in the method for treating heavy metal-contaminated soil according to the present invention, by introducing the slurry-like soil after classification into the centrifugal separation tank and rotating the centrifugal separation tank, the specific gravity containing a large amount of heavy metals. Centrifugal force acts on large soil particles, and the soil particles pass through the granular layer formed in advance along the wall and the small holes in the wall, and are collected as contaminated soil. By limiting the particle size of the soil particles in this way and applying a centrifugal force to the soil particles, small-sized soil particles that are difficult to sort in a natural gravitational field, a portion containing a large amount of heavy metals and a low content of heavy metals. It can be separated efficiently into parts.
[0045]
Moreover, in this heavy metal contaminated soil treatment method, by removing the soil particles whose particle size is included in the range from the predetermined upper limit value to the lower limit value by classification, stirring the soil particles, rubbing between the particles, Remove heavy metal contaminants adhering to the surface. After that, when the coarse particles containing a lot of soil particles after the pollutants are peeled off by the second classification process are taken out, the content of the pollutants is reduced and refilled in the ground as it is or after a simple treatment. be able to.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method for treating heavy metal-contaminated soil according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a centrifugal jig type specific gravity sorter used in the method for treating heavy metal contaminated soil shown in FIG.
[Explanation of symbols]
1 Drum type stirrer
2 First wet vibrating sieve
3 Second wet vibrating sieve
4 First spiral classifier
5 Attrition tank
6 Second spiral classifier
7 Hydrocyclone
8 Centrifugal jig type gravity separator
9 Detoxification means
10, 11 Dehydration means
21 Outer tank
22 Centrifuge tank
23 Water supply pipe
24 Slurry supply pipe
25 First discharge channel
26 Second discharge channel
27 Drive unit
28 Support members
31 wall
32 Granules

Claims (8)

In a centrifuge tank having a cylindrical wall having a large number of small holes, a granular material having a diameter larger than the diameter of the small holes is accommodated,
The centrifuge tank is driven to rotate about the axis of a cylindrical wall body, and the granular body layer is formed along the inner surface of the wall body,
Water is added to the soil contaminated with heavy metal, classified and introduced into the centrifuge tank with a maximum particle size equal to or less than the diameter of the small pores.
A method for treating heavy metal-contaminated soil, characterized in that, when the centrifugal separation tank is driven to rotate, the soil passing through the granular layer and the small holes in the wall is separated as soil particles containing a large amount of heavy metal. The soil introduced into the centrifuge tank is obtained by classifying a part or most of soil particles having a smaller diameter than a value determined in a range of 1/10 to 1/4 of the diameter of the granular material. The method for treating heavy metal-contaminated soil according to claim 1. The method for treating heavy metal-contaminated soil according to claim 1, wherein the small holes have a diameter of 100 µm to 600 µm. The granular material thrown into the centrifuge tank is made of a substance having a specific gravity smaller than that of soil particles containing a large amount of heavy metals and having a larger specific gravity than soil particles containing less heavy metals. The method for treating heavy metal-contaminated soil according to claim 1. The contaminated soil introduced into the centrifuge tank is
A first classification step in which soil particles whose particle size is included in a range from a predetermined upper limit value to a lower limit value are extracted by classification;
A friction process of stirring the removed soil particles and rubbing them between the soil particles to separate heavy metal contaminants adhering to the surface of the soil particles;
Performing a second classification step of separating fine particles containing a large amount of contaminants separated in the friction step and coarse particles containing a lot of soil particles after the contaminants are separated;
The method for treating heavy metal-contaminated soil according to claim 1, comprising the fine particles separated in the second classification step. A first classification step in which soil particles contained in a range from a predetermined upper limit value to a lower limit value are extracted by classification from soil contaminated with heavy metals;
A friction process of stirring the removed soil particles and rubbing them between the soil particles to separate heavy metal contaminants adhering to the surface of the soil particles;
A second classification step for separating fine particles containing a large amount of contaminants separated in the friction step and coarse particles containing a lot of soil particles after the contaminants have been separated;
Treatment of heavy metal-contaminated soil, wherein the soil particles separated in the second classification step are backfilled in the ground, and the subsequent treatment is performed with the fine particles as contaminated soil containing a large amount of contaminants. Method. The heavy metal-contaminated soil according to claim 6, further comprising a step of solidifying ionized heavy metal contaminants by adding a pollutant insolubilizing agent before or during the friction step. Processing method. The said upper limit is 1 mm-5 mm, and the said lower limit is 100 micrometers-600 micrometers, The processing method of the heavy metal contaminated soil of Claim 6 characterized by the above-mentioned.

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