JP6643141B2 - Detoxification system for heavy metal contaminated soil - Google Patents

Description

  The present invention relates to a detoxification processing system for heavy metal-contaminated soil, and is suitably applied to, for example, detoxification of soil containing heavy metals such as arsenic derived from nature generated by a muddy water shield method at a construction site. Technology.

  When a tunnel is constructed on the ground where there is concern about heavy metal contamination by naturally occurring arsenic or the like, a dewatered cake exceeding environmental standards may be generated. For this reason, it is easy to extract and separate heavy metals such as arsenic by making the excavated soil muddy, and measures to extract and separate heavy metals such as arsenic from excavated soil in the shield method where the excavated soil has muddy state Is considered.

  Here, in the muddy water shield method, there are the following two methods for extracting and separating heavy metals from waste muddy water. The first method is a method in which iron powder is added to waste mud and a soluble heavy metal is adsorbed, and then the iron powder to which the heavy metal is adsorbed is collected. The second method is a method of adding a chemical that promotes the extraction of heavy metals to waste mud, and then dewatering the waste mud to recover water in which the heavy metals are dissolved.

  Furthermore, in the mud pressure shield construction method, a method of insolubilizing heavy metals while excavating by supplying iron powder and insolubilizing material to the face has been considered.

  As described above, conventionally, various techniques have been proposed for a method and a facility for treating contaminated soil (for example, see Patent Literature 1, Patent Literature 2, and Patent Literature 3). The technique described in Patent Literature 1 is a method for separating heavy metals from various heavy metal-containing aqueous solutions such as an industrial wastewater and an aqueous solution of nickel sulfate which is an intermediate raw material of a nickel chemical product as an electronic material. That is, the technology described in Patent Document 1 is to add a metal iron powder to a heavy metal-containing aqueous solution and stir and mix the solution, or to pass a heavy metal-containing aqueous solution through a column or the like filled with the metal iron powder to thereby remove the metal iron powder. This is a technique for recovering metallic iron powder in which heavy metals are adsorbed as iron compounds by solid-liquid separation after reacting heavy metals on the surface. Here, the particle size of the metal iron powder is set to 1 mm or less, and is preferably adjusted to 10 μm to 1 mm.

  The technique described in Patent Document 2 is a technique relating to a purification material for purifying contaminated soil containing heavy metals such as fluorine, boron, arsenic, chromium, lead, and selenium. That is, the purifying material used in the technique described in Patent Document 2 attaches a hydroxide or oxide of a rare earth element to the surface of metallic iron powder, so that the same amount of the hydroxide or oxide of the rare earth element is removed. It is stated that the ability to adsorb a heavy metal of a hydroxide or oxide of a rare earth element can be improved as compared with the case of using it alone.

  The technology described in Patent Literature 3 is a technology for insolubilizing heavy metal-contaminated soil excavated and discharged at the current position when treating heavy metal-contaminated soil generated due to the construction of a closed shield tunnel. The insolubilizing material is injected into the heavy metal-contaminated soil at the location from the front face of the excavation face of the closed shield tunnel, and is stirred and mixed on the cutter face. Furthermore, it is stated that the standard of insolubilization can be secured by promoting the remixing and insolubilization treatment reaction in the discharge pipe.

JP 2008-155105 A JP 2012-51967 A JP 2006-316599 A

  However, the first method described above requires a comprehensive study of the entire system from the generation of shield mud to the formation of a dewatered cake. In many cases, studies are being conducted on equipment that collects iron powder that has absorbed heavy metals such as arsenic, using equipment that has a small processing capacity with respect to the equipment scale. There are various problems, such as the need to introduce a large amount of iron powder recovery equipment at an unrealistic level in order to treat the wastewater.

  In the second method described above, the added extraction material remains in the dewatered cake, so that not only the safety of the future dewatered cake is not ensured, but also the processing cost is high because the extraction material is expensive. And various other problems.

  Further, when the mud pressure shield method is adopted, the soil contaminated with heavy metals is insolubilized. Since the treated soil contains heavy metals such as arsenic, it must be permanently managed.

  The present invention has been proposed in view of the above-described circumstances.For example, a large amount of mud to be treated including heavy metals such as arsenic was generated in a series of processes from generation of shielded muddy water to generation of a dewatered cake. Even in this case, it is an object of the present invention to provide a detoxification system for heavy metal contaminated soil that can efficiently and appropriately treat the soil.

  The detoxification system for heavy metal-contaminated soil according to the present invention has the following features in order to achieve the above object. That is, the detoxification system for heavy metal-contaminated soil of the present invention is a device for detoxifying heavy metal-contaminated soil, and includes a group of devices used in each stage of the detoxification process.

As a group of devices in the clay crushing process, there are a clay crushing device and a sieving device. Further, as a group of devices in the heavy metal removing step, there are an iron powder adding device, a specific gravity separating device, a drum type magnetic separating device, and a filter type electromagnet separating device . Further, as a group of devices at a later stage of the detoxification process, there is a dehydration device. Note that another device may be added to each device group.

  The clay crusher is a device for crushing clay lumps contained in heavy metal contaminated soil. The sieving apparatus is an apparatus for sieving heavy metal-contaminated soil to take out muddy water containing fine particles having a predetermined particle size or less.

The iron powder adding device is a device for adding iron powder to muddy water containing fine particles and causing heavy iron to be adsorbed to the iron powder. The specific gravity separation device is a device for separating specific gravity into muddy water containing no iron powder and muddy water containing iron powder to which heavy metals are adsorbed. The drum-type magnetic separation device is a device for recovering iron powder from muddy water containing iron powder to which heavy metals have been adsorbed using a permanent magnet. The filter-type electromagnet separator is a device for further recovering iron powder from muddy water containing iron powder that could not be recovered by the drum-type magnetic separator. The dehydration treatment device is a device for dehydrating the muddy water containing no iron powder separated by the specific gravity separation device and the muddy water from which the iron powder is separated by the drum type magnetic separation device and the filter type electromagnet separation device .

In the above group of devices, some or all of the iron powder to be added has a large number of micropores extending from the surface to the inside, has a particle size of 150 μm or more and 300 μm or less, and an apparent density of 1.3 g / cm ³ or more and 1.5 g. / cm ^3, specific surface area is to equal to or less than 0.12 m ² / g or more 0.36 m ² / g. The specific surface area is a value measured by the BET multipoint method / adsorption side relative pressure (P / P ₀ = 0.001 to 0.30) in accordance with JIS Z 8830: 2013.

  Further, in addition to the above-described configuration, it is preferable to dispose a muddy water supply device that uniformly supplies muddy water containing iron powder to which heavy metals have been adsorbed, in front of the specific gravity separation device.

  Further, in addition to the above-described configuration, a muddy water specific gravity measuring device for measuring the specific gravity of the muddy water supplied to the specific gravity separating device, and a supplied muddy water amount for adjusting the amount of muddy water supplied to the specific gravity separating device according to the measured specific gravity of the muddy water Preferably, an adjusting device is provided.

In addition, in addition to the above-described configuration, the drum-type magnetic separation device recovers iron powder concentrate containing iron powder and excess water from muddy water containing iron powder to which heavy metal has been adsorbed. It is preferable to provide a surplus water discharging device for separating surplus water and discharging only surplus water.

  According to the detoxification system for heavy metal-contaminated soil according to the present invention, for example, when detoxifying soil containing heavy metals such as arsenic of natural origin generated in the muddy water shield construction at the construction site, the shield wastewater By properly managing the properties of iron powder that adsorbs heavy metals such as arsenic in the entire series of processes from generation to dehydration cake generation, a large amount of waste mud containing heavy metals such as arsenic is generated. However, this can be efficiently and appropriately processed.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the whole structure of the detoxification processing system of the heavy metal contaminated soil which concerns on embodiment of this invention. FIG. 1 is an explanatory diagram illustrating a configuration of a specific gravity separation device according to an embodiment of the present invention. FIG. 1 is an explanatory diagram illustrating a configuration of a drum-type magnetic separation device according to an embodiment of the present invention.

  Hereinafter, an embodiment of a system for detoxifying heavy metal-contaminated soil according to the present invention will be described with reference to the drawings. 1 to 3 illustrate a detoxification system for heavy metal-contaminated soil according to an embodiment of the present invention. FIG. 1 is an explanatory diagram showing the entire configuration, and FIG. 2 is an explanatory diagram (cross-sectional view) of a specific gravity separation device. (A) and longitudinal section (b)), FIG. 3 is an explanatory view showing the configuration of a drum type magnetic separation device.

<Overall configuration>
The detoxification system for heavy metal-contaminated soil according to the embodiment of the present invention is, for example, an apparatus for detoxifying heavy metal-contaminated muddy water generated in a muddy shield construction, and as shown in FIG. , A clay crushing device 10, a sieving device 20, a pH adjusting device 30, an iron powder adding device 40, a specific gravity separating device 50, a drum type magnetic separating device 60, and a dewatering device 80 are provided in this order. The detoxification treatment system according to the present invention can be applied not only to the muddy shield work but also to the residual soil generated in the mud pressure shield work and the normal excavation work by performing appropriate pretreatment. it can.

  In the detoxification system for heavy metal-contaminated soil according to the present invention, the pH adjusting device 30 and the filter-type electromagnet separator 70 are not indispensable devices. It may be provided in the case or when it is necessary to improve the separation accuracy of the iron powder after the treatment. Heavy metals refer to fluorine, boron, arsenic, chromium, lead, selenium, and the like.

<Equipment group in clay dewatering process>
In the clay disintegration process, a clay disintegration device 10, a sieving device 20, and an excess mud tank 120 are arranged. The portion under the sieve in the sieving apparatus 20 is stored in an excess muddy water tank 120, and an amount of muddy water required for shield excavation is sent to the muddy water tank 100 and supplied to the shield machine 110. The excess mud stored in the excess mud tank 120 is sent to the waste mud receiving tank 33 of the pH adjusting device 30 to adjust the pH.

<Clay crusher>
The clay crusher 10 is a device for crushing clay lumps contained in heavy metal contaminated soil. In general shielding work, muddy water discharged from the shielding machine 110 is often sieved with a vibrating sieve into sand having a size of more than 2 mm and fine particles having a size of 2 mm or less, and the remaining portion of the sieve is subjected to residual soil treatment as sand. When excavating a naturally-occurring heavy metal-contaminated soil, the soil to be excavated is likely to be soil, and in that case, the possibility that clay residue solidified by soil is included in the residual sieve Can not. For this reason, in this embodiment, a clay crusher 10 for crushing the sieve residue is provided. As the clay crusher 10, for example, a roller mill, a dent tooth roller, a ball mill, a high-speed melting machine (stirrer) or the like can be used.

<Sieving device>
The sieving apparatus 20 is an apparatus for sieving heavy metal-contaminated soil to take out muddy water containing fine particles having a predetermined particle size or less. The predetermined particle size is, for example, 2 mm based on the sand content. That is, the sand exceeding 2 mm is separated as containing no heavy metal, and treated as the 0th treated soil. On the other hand, muddy water containing fine particles of 2 mm or less is assumed to contain heavy metals, and the heavy metals are separated and made harmless. As the sieving device 20, for example, a vibration sieve can be used.

  In the present embodiment, two vibrating sieves are provided as the sieving device 20. The first vibrating sieve is a device for sieving the gravel and clay lumps contained in the mud discharged from the shield machine 110. The gravel / clay mass sieved by the first vibrating sieve is pulverized by the mud crusher 10 and sent to the mud tub 90, and mixed with a part of the excess mud sent from the excess mud tank 120. And then sieved with a second vibrating sieve. Then, the portion under the sieve sieved by the first vibrating sieve and the second vibrating sieve is stored in the excess muddy water tank 120. The residue sieved by the second vibrating sieve is treated as the 0th treated soil.

<Threshing tank>
The deflocculation tank 90 is a storage tank for storing a portion under the sieve sieved by the sieving device 20 as the first vibrating sieve and a part of the excess mud discharged from the excess mud tank 120, The muddy water is stirred by a stirring blade 92 driven by a stirring motor 91 to make it uniform. The shape and the like of the stirring blade 92 can be appropriately set according to the properties of the portion under the sieve. Further, although not shown, the mud tub 90 is provided with a pump for sending muddy water. The surplus muddy water stored in the deflocculation tank 90 is supplied to a sieving device 20 that is a second vibrating sieve.

<Excess mud tank>
The surplus mud tank 120 stores the surplus mud consisting of a portion under the sieve that has been sieved by the first vibrating sieve and the second vibrating sieve, and stores the muddy tank 90, the mud feed tank 100, and the pH adjusting device 30 (a waste mud receiving tank). This is a storage tank for supplying to 33). Even in the surplus mud tank 120, the muddy water is stirred by the stirring blades 122 driven by the stirring motor 121 so as to be uniform. Although not shown, the excess muddy water tank 120 is provided with a pump for sending out muddy water.

<Sludge tank>
The mud feed tank 100 is a storage tank for storing the mud received from the surplus mud tank 120 and supplying it to the shield machine 110 again. The muddy water tank 100 is also configured such that the muddy water is stirred by the stirring blades 102 driven by the stirring motor 101 to make the muddy water uniform. Although not shown, the mud feed tank 100 is provided with a pump for sending mud and a water adding device for adjusting the specific gravity of mud.

<Equipment group in heavy metal removal process>
In the heavy metal removing step, a pH adjusting device 30, an iron powder adding device 40, a specific gravity separating device 50, a drum type magnetic separating device 60, and a filter type electromagnet separating device 70 are arranged. The excess muddy water whose pH has been adjusted by the pH adjusting device 30 is added with iron powder by the iron powder adding device 40 to adsorb heavy metals, and is sent to the specific gravity separation device 50. In the present embodiment, a muddy water supply device (not shown) for uniformly supplying muddy water containing iron powder to which heavy metals have been adsorbed is disposed in front of the specific gravity separation device 50. Further, the muddy water supplied to the specific gravity separator 50 is measured for its specific gravity by a muddy water specific gravity measuring device (not shown), and is supplied to the specific gravity separating device 50 by a supplied muddy water amount adjusting device (not shown) in accordance with the specific gravity of the muddy water. The amount of mud to be supplied is adjusted.

  The mud containing no iron powder separated by the specific gravity separator 50 is temporarily stored in a waste mud tank 130 and then sent out to the dehydration treatment device 80. On the other hand, the muddy water that has absorbed the heavy metals separated by the specific gravity separator 50 is sent to the drum type magnetic separator 60. The waste mud tank 130 is provided with a stirring blade 132 driven by a stirring motor 131.

  The iron powder collected by the drum type magnetic separation device 60 is temporarily stored in an iron powder receiving tank 140 functioning as a surplus water discharging device, and then sent out to the iron powder adding device 40. Since the non-magnetic material separated by the drum-type magnetic separation device 60 contains a magnetic material (iron powder for heavy metal adsorption separation) that cannot be completely separated, the non-magnetic material is stirred by the stirrer 150 and then filtered by the filter-type electromagnet separator. The magnetic material (heavy metal-containing material) is sent out to 70.

  That is, in the drum-type magnetic separation device 60 and the filter-type electromagnet separation device 70, the excess muddy water is separated into two types, a non-magnetic substance and a magnetic substance. Then, the magnetic substance is separated and collected by the drum-type magnetic separation device 60 and the filter-type electromagnet separation device 70 as iron powder for heavy metal adsorption. In this step, the heavy metal is included in the magnetic substance. The non-magnetic substance is a component that is separated by not being attracted by a magnetic force, and basically contains neither iron powder (magnetic substance) nor heavy metals. However, the drum-type magnetic separation device 60 is capable of processing a large amount of muddy water with a high mixing ratio of the magnetic substance, although the separation accuracy of the magnetic substance and the non-magnetic substance is slightly inferior. On the other hand, the filter-type electromagnet separator 70 has high accuracy in separating magnetic and non-magnetic substances, but when the mixing ratio of magnetic substances is large, frequent clogging occurs, so that the time required for the cleaning process is increased, and the processing amount is reduced. May decrease. Therefore, in this embodiment, the waste mud is separated into a non-magnetic substance and a magnetic substance by using both the drum type magnetic separator 60 and the filter type electromagnet separator 70.

  The non-magnetic substance (mud water from which heavy metals have been removed) separated by the filter-type electromagnet separator 70 is temporarily stored in a waste mud tank 130 and then sent to the dehydration processing apparatus 80. The processed material separated by the filter-type electromagnet separator 70 toward the magnetic substance (heavy metal-containing substance) is sent to the iron powder receiving tank 140.

<PH adjustment device>
The pH adjusting device 30 is a device that is installed when pH adjustment is necessary, and adjusts the pH of muddy water containing fine particles that have passed through the sieving device 20. The pH adjusting device 30 includes a waste muddy water receiving tank 33, a charging device (not shown) for charging a pH adjusting material and an extracting material, and a stirring blade 32 driven by a stirring motor 31. That is, when the heavy metal contained in the surplus mud is arsenic, the arsenic is likely to be a heavy metal derived from iron hydroxide, and thus the elution is promoted by making the pH alkaline. For this reason, after making the excess muddy water alkaline, the excess muddy water is stirred by the stirring blade 32 to adjust the pH. The elution time of the heavy metal (arsenic) is preferably, for example, about 1 hour.

<Iron powder addition device>
The iron powder adding device 40 is a device for adding iron powder to make the iron powder adsorb heavy metals, and includes a heavy metal adsorption tank 41, a charging device (not shown) for charging iron powder, and a stirring device. And a stirring blade 43 driven by a motor 42. In the iron powder addition device 40, a pH adjuster may be added to muddy water containing fine particles to neutralize the pH. For example, the effect of arsenic adsorption by iron powder is maximized when the pH is near neutrality, so it is preferable to add iron powder while neutralizing muddy water. The appropriate amount of iron powder added is, for example, about 3 to 5% per dry soil weight.

The iron powder to be used has a part or the whole having a large number of micropores extending from the surface to the inside, a particle size of 150 μm or more and 300 μm or less, and an apparent density of 1.3 g / cm ³ or more and 1.5 g / cm. ³ or less and a specific surface area and not more than 0.12 m ² / g or more 0.36 m ² / g. Here, it is desirable that the iron powder having a particle size of 150 μm or more is 90%. Further, the apparent density can be set to 1.3 g / cm ³ or more and 2.0 g / cm ³ or less. The value of the specific surface area is measured by the BET multipoint method / adsorption side relative pressure (P / P ₀ = 0.001 to 0.30) according to JIS Z 8830: 2013. The critical significance of the properties of such iron powder will be described.

<Iron powder is porous>
By using a property having a large number of micropores extending from the surface to the inside, that is, a porous (sponge-like) iron powder, the surface area of the iron powder itself is increased, and the adsorption efficiency of heavy metals is improved.

<Size of iron powder>
If the particle size of the iron powder is less than 150 μm, the muddy water and the iron powder may not be reliably separated during the specific gravity separation. On the other hand, when the particle size of the iron powder exceeds 300 μm, the dispersibility of the iron powder in the mud to be treated decreases in the process of adsorbing heavy metals to the iron powder, and the adsorption efficiency of heavy metals decreases.

<Apparent density of iron powder>
If the apparent density of the iron powder is less than 1.3 g / cm ³ , the number of micropores increases and the strength of the iron powder decreases. When there is no problem in strength, the apparent density of the iron powder can be allowed up to 1.0 g / cm ³ . On the other hand, when the apparent density of the iron powder exceeds 1.5 g / cm ³ , the number of micropores decreases, and the adsorption efficiency of heavy metals decreases.

<Specific surface area of iron powder>
If the specific surface area of the iron powder deviates from the 0.12 m ² / g or more 0.36 m ² / g or less in the range, it becomes impossible to adsorb heavy metals effectively, the amount of removable heavy metals is reduced.

<Specific gravity separator>
As shown in FIG. 2, the specific gravity separation device 50 is, for example, a device that uses a cyclone to separate specific gravity into muddy water containing no iron powder and muddy water containing iron powder to which heavy metals are adsorbed. In the present embodiment, since iron powder having a large particle diameter is used, it is possible to easily recover iron powder from muddy water only by gravity sedimentation. Specific gravity is separated into muddy water containing no iron and muddy water in which iron powder is concentrated. This makes it possible to reduce the amount of muddy water to be collected as iron powder to about 20 to 30% of the related art.

  Although not shown, a facility (for example, a fixed-quantity feeder) that supplies the residue separated by the specific gravity separation device (cyclone) 50 as having a large weight (high specific gravity) to the drum-type magnetic separation device 60 is quantitative. It is preferable to supply muddy water discharged to the magnetic material side to a fixed-quantity feeder and to arrange a plurality of L-shaped projections on the fixed-quantity feeder in order to provide a facility capable of supplying an object to be treated. With such a structure, the muddy water to be treated can be uniformly spread and supplied at the muddy water supply outlet. Further, in the present embodiment, it is preferable to use a cyclone as the specific gravity separation device 50 from the viewpoint that the iron powder separation effect from the muddy water is high. However, depending on the state of the muddy water, a specific gravity separation device 50 having another configuration may be used. Good.

<Muddy water specific gravity measurement device>
In the present embodiment, although not shown, a muddy water specific gravity measuring device for measuring the specific gravity of the muddy water supplied to the specific gravity separating device 50, and a supply for adjusting the amount of muddy water supplied to the specific gravity separating device 50 according to the measured specific gravity of the muddy water It is preferable to provide a muddy water amount adjusting device. The specific gravity of the muddy water supplied to the specific gravity separation device 50 fluctuates in a range of about 1.00 to 1.50 depending on construction conditions. In particular, when a cyclone is used as the specific gravity separation device 50, in the cyclone treatment (specific gravity separation treatment) step, the muddy water to which iron powder having a specific gravity of up to about 1.25 is applied is subjected to a centrifugal force of about 100G. The iron powder remaining on the sieve is almost zero, but when the specific gravity of the mud exceeds about 1.25, the amount of iron powder remaining on the sieve increases.

  In this case, by increasing the centrifugal force to about 200 G (optimally 180 G), the amount of residual iron powder can be reduced to almost zero. Therefore, by measuring the specific gravity of the muddy water supplied to the cyclone and adjusting the discharge rate of the pump for supplying the muddy water to the cyclone according to the specific gravity of the muddy water, it is possible to manage the operation so that iron powder does not remain on the sieve. Become. The greater the centrifugal force applied to the cyclone, the greater the abrasion inside the cyclone. Therefore, the smaller the centrifugal force applied is preferable from the viewpoint of improvement in maintenance.

  As the muddy water specific gravity measuring device, for example, a device for estimating the specific gravity of the muddy water to be supplied to the specific gravity separating device 50 based on the water level of the waste muddy water receiving tank 33 and the output value of a pressure gauge installed at the lower part of the waste muddy water receiving tank 33 is used. I just need. As the supplied muddy water amount adjusting device, for example, by adjusting the current value applied to the muddy water supply pump using an inverter or the like in accordance with the specific gravity of the muddy water supplied to the specific gravity separation device 50 estimated by the method described above, It is sufficient to use a device that adjusts the supply amount, that is, the centrifugal force that acts on the muddy water in the specific gravity separation device 50.

<Drum type magnetic separation device>
The drum-type magnetic separation device 60 is a device for recovering iron powder from muddy water containing iron powder to which heavy metals have been adsorbed using a permanent magnet. That is, since the specific gravity separated product (cyclone treated product) in which the iron powder is concentrated contains sand and the like in addition to the iron powder, it is necessary to further collect only the iron powder therefrom. For this reason, in the present embodiment, the iron powder recovery processing is performed by the drum type magnetic separation device 60 using the permanent magnet 61. At this time, by employing equipment for supplying muddy water containing iron powder from the upper part of the drum magnetic separator (for example, a device including the downflow gutter 66 (see FIG. 3)), the processing weight per unit time can be increased. It becomes possible.

  In the drum magnetic separator, for example, as shown in FIG. 3, a permanent magnet 61 is mounted inside the rotary drum 62, so that the surface of the rotary drum 62 is used as a magnetic material adsorption surface. Then, the rotating drum 62 is rotated to adsorb the magnetic substance on the adsorption surface, and the magnetic substance adsorbed by the scraper 65 is scraped off. Further, in the present embodiment, the baffle plate 63 is installed in the vicinity of vertically below the boundary between the permanent magnet installation portion and the non-installation portion located below the rotary drum 62, and the separation portion between the non-magnetic material and the magnetic material is provided. The non-magnetic material and the magnetic material can be dropped separately by blowing air from the air nozzle 64 toward.

<Stirring device>
Furthermore, the iron powder whose apparent magnetism has decreased due to the adhesion of clay particles around the iron powder may not be collected by the drum magnetic separator. Therefore, as shown in FIG. 3, the non-magnetic material separated by the drum magnetic separator is stored in the stirring tank 151 and stirred by the stirring device 150 such as a mixer to peel off the clay attached to the iron powder. Is preferred. The stirring device 150 includes a stirring tank 151 and a stirring blade 153 driven by a stirring motor 152.

<Excess water discharge device>
Further, the iron powder concentrate separated and discharged to the magnetic substance side by the drum magnetic separator may contain a large amount of water. Therefore, as shown in FIGS. 1 and 3, an overflow weir 141 is provided in an iron powder receiving tank 140 for storing the iron powder discharged to the magnetic material side, and the iron powder is supplied to the upstream side of the overflow weir 141. To be discharged. The water discharged to the magnetic material side together with the iron powder flows over the overflow weir 141, so that when the amount of water discharged to the magnetic material side increases, only the water is discharged. can do. As described above, the iron powder receiving tank 140 and the devices attached thereto function as a surplus water discharging device.

<Filter type electromagnet separator>
The filter-type electromagnet separator 70 is a device for further recovering iron powder from muddy water containing iron powder that could not be recovered by the drum-type magnetic separator 60. That is, the nonmagnetic material (such as clay from which heavy metals have been removed) is separated by the filter-type electromagnet separator 70, and a small amount of iron powder that cannot be recovered by the drum-type magnetic separator 60 is further recovered. Although not shown, the filter-type electromagnet separator 70 of the present embodiment is configured by a device that generates a magnetic force by applying a magnetic field to an iron ball or the like, separates iron powder from non-magnetic substances, and collects iron powder. . In this way, by treating the non-magnetic material again by the filter-type electromagnet separator 70, almost all of the iron powder can be recovered from the waste mud.

  That is, since the main component of the processed material separated as a magnetic material is iron powder, it contains a heavy metal. However, iron powder only adsorbs a small amount of heavy metal eluted from soil into water, and the content of heavy metal is extremely small. On the other hand, the main components of the processed material separated as a non-magnetic material are sand, silt, clay, and water. Since the amount of iron powder mixed therein is small, it hardly contains heavy metals. Further, the content of iron powder in the non-magnetic material is smaller in the filter type electromagnet separator 70 than in the drum type magnetic separator 60. As described above, in this embodiment, the trace amount of iron powder that cannot be completely separated by the drum type magnetic separation device 60 is removed by the filter type electromagnet separation device 70.

<Reuse of iron powder>
In the present embodiment, the collected iron powder is reused. However, as the frequency of iron powder reuse increases, the ability to adsorb heavy metals decreases. Therefore, the heavy metal adsorption ability can be restored by treating the iron powder reused a predetermined number of times with any one of acid, alkali, and ascorbic acid, or a combination thereof.

<Equipment group at post-treatment stage (dehydration treatment equipment)>
At a later stage of the detoxification treatment, a dehydration treatment device 80 is disposed. The dewatering treatment device 80 is a device for reducing the volume by dewatering waste mud from which heavy metals stored in the waste mud tank 130 have been separated and removed, and is, for example, a filter press or the like. That is, the muddy water from which all the iron powder has been collected can be dewatered by a filter press or the like, thereby reducing the amount of waste mud. In addition, by using a vacuum pressure dehydrator that performs dehydration treatment by adding cement as the dehydration treatment device 80, a self-hardened dehydration cake is generated, and the risk of heavy metal elution in the future is further reduced. be able to. Further, the filtrate discharged from the dehydration treatment device 80 is subjected to turbid water treatment by a turbid water treatment device (not shown), and the obtained fresh water can be reused.

<Advantageous effects of the present invention>
Hereinafter, the point that the detoxification processing system for heavy metal-contaminated soil according to the present invention exerts advantageous effects as compared with conventionally considered systems will be described. It is difficult to recover iron powder from waste mud exceeding about 700 m ³ with an apparatus configuration for pumping up muddy water mixed with iron powder from an iron powder mixing tank to a magnetic separator and collecting purified muddy water. Because, in the method of pumping up the wastewater mixed with iron powder from the iron powder mixing tank to the magnetic separator and recovering the purified slurry, it is necessary to treat the waste slurry exceeding about 700 m ³ within 2 to 3 hours. Therefore, a processing capacity of about 230 to 350 m ³ / h is required, and a plurality of equipment (for example, 5 to 8) processing apparatuses are required.

  In addition, heavy iron adsorption capacity decreases when iron powder is repeatedly used. However, in the processing method in which iron powder is constantly returned to the iron powder mixing tank, heavy metal adsorption capacity decreases each time iron powder is repeatedly used. For this reason, it is necessary to collect the iron powder exceeding the usage limit and add fresh iron powder to the iron powder mixing tank, so that a large amount of iron powder must be used.

  In this regard, the detoxification system for heavy metal-contaminated soil according to the present invention has a high treatment capacity and can not only reduce the size of the equipment, but also has a system for recycling iron powder. Can be greatly reduced.

  Further, in the drum type magnetic separation device, in the method of supplying the muddy water to be treated from the lower side of the rotating drum, when the muddy water having a large amount of sand is to be treated, the water passage below the rotating drum is blocked by earth and sand, and the processing failure is caused. There is a concern about using a treatment facility that is suitable for the site because of the possibility of causing such a problem.

  In this regard, in the detoxification system for heavy metal contaminated soil according to the present invention, since the muddy water to be treated is supplied from above the rotating drum, the above-described problem does not occur.

  In addition, if only a centrifugal separator such as a screw decanter is used as a device for centrifuging iron powder, the collected iron powder contains sand, and the iron powder containing sand is reused. Become. For this reason, when iron powder is put into muddy water mixed with heavy metal, the sand added together with the iron powder is again collected together with the iron powder by the centrifugal separator, and the sand contained in the iron powder every time the processing is repeated. This may increase the amount of iron powder, making it impossible to control the amount of iron powder added.

  In this regard, the detoxification system for heavy metal-contaminated soil according to the present invention can reliably separate iron powder and sand, so that the above-described inconvenience does not occur.

REFERENCE SIGNS LIST 10 clay crushing device 20 sieving device 30 pH adjusting device 31 stirring motor 32 stirring blade 33 waste muddy water receiving tank 40 iron powder addition device 41 heavy metal adsorption tank 42 stirring motor 43 stirring blade 50 specific gravity separation device 60 drum type magnetic separation device 61 permanent Magnet 62 Rotary drum 63 Baffle plate 64 Air nozzle 65 Scraper 66 Downspout gutter 70 Filter type electromagnet separator 80 Dehydration treatment device 90 Mud crushing tank 91 Stirring motor 92 Stirrer 100 Stirring water tank 101 Stirring motor 102 Stirrer 110 Shield machine 120 Extra Mud tank 121 Stirrer motor 122 Stirrer blade 130 Waste mud tank 131 Stirrer motor 132 Stirrer blade 140 Iron powder receiving tank 141 Overflow weir 150 Stirrer 151 Stirrer tank 152 Stirrer motor 153 Stirrer blade

Claims (4)

An apparatus for detoxifying heavy metal contaminated soil,
A clay crushing device for crushing clay lumps contained in the heavy metal contaminated soil,
Sieving the heavy metal-contaminated soil, and a sieving apparatus for extracting mud containing fine particles having a predetermined particle size or less,
An iron powder addition device for adding iron powder to the muddy water containing the fine particles, and for adsorbing heavy metals to the iron powder;
A specific gravity separation device that separates specific gravity into muddy water containing no iron powder and muddy water containing iron powder in which heavy metals are adsorbed,
Using a permanent magnet, a drum-type magnetic separation device that recovers iron powder from muddy water containing the iron powder in which the heavy metal is adsorbed,
A filter-type electromagnet separator for further collecting iron powder from muddy water containing iron powder that could not be completely recovered by the drum-type magnetic separator,
A dewatering treatment device that dewaters the muddy water that does not contain the iron powder separated by the specific gravity separation device and the muddy water from which the iron powder is separated by the drum-type magnetic separation device and the filter-type electromagnet separation device ,
With
Part or all of the iron powder has a large number of micropores extending from the surface to the inside, has a particle size of 150 μm to 300 μm, an apparent density of 1.3 g / cm ^{3 to} 1.5 g / cm ³ , and a specific surface area. Is 0.12 m ² / g or more and 0.36 m ² / g or less. 2. The detoxification system for heavy metal-contaminated soil according to claim 1, wherein a muddy water supply device that uniformly supplies muddy water containing the iron powder on which the heavy metal is adsorbed is disposed at a stage preceding the specific gravity separation device. 3. A muddy water specific gravity measurement device that measures the specific gravity of the muddy water supplied to the specific gravity separation device,
The harmless heavy metal-contaminated soil according to claim 1 or 2 , further comprising: a supply mud amount adjusting device that adjusts an amount of mud supplied to the specific gravity separation device according to the measured specific gravity of the mud. Processing system. The drum-type magnetic separation device is for recovering iron powder concentrate containing iron powder and excess water from muddy water containing iron powder in which the heavy metal is adsorbed,
The harmless heavy metal-contaminated soil according to any one of claims 1 to 3 , further comprising a surplus water discharging device that separates the iron powder and the surplus water and discharges only the surplus water. Processing system.

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