JP2017148760A - Detoxification treatment system of heavy metal contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and appropriately treat muddy water in the whole of a series of steps from the generation of muddy water discharged in a shield method to the production of dewatering cake even when a large amount of muddy water as an object to be treated including a heavy metal such as arsenic is generated.SOLUTION: A detoxification treatment system of muddy water comprises: an iron powder addition apparatus 40 for adding iron powder to muddy water including a fine-grained fraction of not more than a predetermined grain size and adsorbing a heavy metal on the iron powder; a gravity separation apparatus 50 for separating the muddy water, by gravity, into muddy water not containing iron powder and muddy water containing the iron powder on which the heavy metal is adsorbed; a drum type magnetic separation apparatus 60 for recovering the iron powder from the muddy water containing the iron powder on which the heavy metal is adsorbed by utilizing a permanent magnet; and a dehydration treatment apparatus 80 for subjecting the muddy water from which the iron powder has been separated to hydration treatment. A part or all of the iron powder has a great number of micropores form the surface to the inside and the micropores have a particle size of not less than 150 μm and not more than 300 μm, an apparent density of not less than 1.3 g/cmand not more than 1.5 g/cm, and a specific surface area of not less than 0.12 and not more than 0.36 m/g.SELECTED DRAWING: Figure 1

Description

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

  When a tunnel is constructed with a shield method on the ground where heavy metal contamination by natural arsenic or the like is a concern, a dehydrated cake that exceeds environmental standards may occur. Therefore, extraction and separation of heavy metals such as arsenic can be easily carried out by making the excavated soil muddy, and measures to extract and separate heavy metals such as arsenic from the excavated soil in the shield method where the excavated soil exhibits a muddy water state. Is considered.

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

  Furthermore, in the mud pressure shield method, a method of insolubilizing heavy metals while excavating by supplying iron powder or insolubilizing material to the face is also considered.

  Thus, conventionally, various techniques have been proposed for a method and a treatment facility for contaminated soil (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). The technique described in Patent Document 1 is a method for separating heavy metals from various heavy metal-containing aqueous solutions such as industrial wastewater and aqueous nickel sulfate solutions that are intermediate raw materials for nickel chemical products that are electronic materials. That is, the technique described in Patent Document 1 adds the metal iron powder to the heavy metal-containing aqueous solution and mixes by stirring, or passes the heavy metal-containing aqueous solution through a column or the like filled with the metal iron powder, In this technique, after reacting heavy metal on the surface, metal iron powder in which heavy metal is adsorbed as an iron compound by solid-liquid separation is recovered. Here, the particle diameter of the metal iron powder is preferably 1 mm or less and is preferably adjusted to 10 μm to 1 mm.

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

  The technique described in Patent Document 3 is a technique for insolubilizing heavy metal-contaminated soil excavated and discharged at a current position when processing heavy metal-contaminated soil generated in the construction of a sealed shield tunnel. The insolubilized material is injected into the heavy metal contaminated soil at the position from the front face of the excavation face of the sealed shield tunnel, and the mixture is stirred and mixed on the cutter face. Furthermore, it is said that the standard of insolubilization can be secured by promoting remixing and insolubilization treatment reaction in the exhaust pipe.

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

  However, for the above-described first method, it is necessary to comprehensively examine the entire system from generation of shield wastewater to generation of a dewatered cake. In addition, there are many examples of equipment that collects iron powder that has adsorbed heavy metals such as arsenic using equipment that has a small processing capacity relative to the equipment scale, and a large amount of waste mud generated from large-diameter shields. There are various problems such as the need to introduce a large amount of iron powder recovery equipment at an unrealistic level.

  Moreover, about the 2nd method mentioned above, since the added extraction material remains in a dewatering cake, not only the future safety | security of a dewatering cake is not ensured, but since an extraction material is expensive, processing cost is expensive. There are various problems such as.

  Furthermore, when the mud pressure shield method is adopted, the heavy metal contaminated soil is insolubilized, and the treated soil contains heavy metals such as arsenic, and thus must be managed permanently.

  The present invention has been proposed in view of the above-described circumstances. For example, a large amount of muddy water to be treated containing heavy metals such as arsenic was generated in the entire series of processes from generation of shield mud water to generation of a dewatered cake. Even if it is a case, it aims at providing the detoxification processing system of the heavy metal contaminated soil which can process this efficiently and appropriately.

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

  As a group of apparatuses in the clay demolition process, there are a clay crushing apparatus and a sieving apparatus. Moreover, as an apparatus group in a heavy metal removal process, there are an iron powder addition apparatus, a specific gravity separation apparatus, and a drum type magnetic separation apparatus. Moreover, there is a dehydration processing apparatus as a group of apparatuses at a later stage of the detoxification process. In addition, another device may be added to each device group.

  The clay crushing device is a device for crushing clay lumps contained in heavy metal contaminated soil. The sieving device is a device for sieving heavy metal-contaminated soil and taking 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 mud containing fine particles and adsorbing heavy metals on the iron powder. The specific gravity separation device is a device for performing specific gravity separation into muddy water not containing iron powder and muddy water containing iron powder adsorbed with heavy metals. The drum-type magnetic separation device is a device for recovering iron powder from muddy water containing iron powder adsorbed with heavy metals using a permanent magnet. The dehydration apparatus is an apparatus for dehydrating muddy water after separating iron powder.

In the apparatus group described above, part or all of the iron powder to be added has a large number of fine holes extending from the surface to the inside, the particle size is 150 μm or more and 300 μm or less, and the apparent density is 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.

  In addition to the above-described configuration, it is preferable to include a filter type electromagnet separation device that further collects iron powder from muddy water containing iron powder that could not be collected by the drum type magnetic separation device.

  Further, in addition to the above-described configuration, it is preferable to arrange a muddy water supply device that uniformly supplies muddy water containing iron powder that has adsorbed heavy metals, in the preceding stage of the specific gravity separator.

  In addition to the above-described configuration, a mud specific gravity measuring device that measures the specific gravity of the mud supplied to the specific gravity separator, and a supplied mud water amount that adjusts the amount of mud supplied to the specific gravity separator according to the measured specific gravity of the mud. It is preferable to provide an adjustment device.

  Moreover, in addition to the structure mentioned above, it is preferable to provide the surplus water discharge apparatus which isolate | separates the iron powder collect | recovered with the drum-type magnetic separation apparatus, and the surplus water collect | recovered simultaneously, and discharges | emits only the surplus water.

  According to the detoxification system for heavy metal contaminated soil according to the present invention, for example, when soil containing heavy metals such as arsenic derived from nature generated in muddy water shield construction is detoxified at the construction site, the shield mud water This is the case where a large amount of waste mud containing heavy metals such as arsenic is generated by appropriately managing the properties of iron powder that adsorbs heavy metals such as arsenic throughout the entire series of processes from generation to generation of dehydrated cake. However, this can be processed efficiently and appropriately.

Explanatory drawing which shows the whole structure of the detoxification processing system of the heavy metal contamination soil which concerns on embodiment of this invention. Explanatory drawing which shows the structure of the specific gravity separation apparatus which concerns on embodiment of this invention. Explanatory drawing which shows the structure of the drum-type magnetic separation apparatus which concerns on embodiment of this invention.

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

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

  Moreover, in the detoxification treatment system for heavy metal-contaminated soil according to the present invention, the pH adjusting device 30 and the filter-type electromagnet separating device 70 are not essential devices, and pH adjustment is necessary to promote adsorption of heavy metals to iron powder. It may be arranged in the case or when it is necessary to improve the separation accuracy of the iron powder after processing. Moreover, heavy metal means fluorine, boron, arsenic, chromium, lead, selenium, and the like.

<Group of equipment in clay demolition process>
A clay crushing device 10, a sieving device 20, and an excess mud water tank 120 are arranged in the clay thawing process. The portion under the sieve in the sieving device 20 is stored in the surplus muddy water tank 120, and an amount of muddy water necessary for shield excavation is sent to the muddy water tank 100 and supplied to the shield machine 110. Moreover, the excess muddy water stored in the excess muddy water tank 120 is sent to the waste muddy water receiving tank 33 of the pH adjusting device 30 to adjust the pH.

<Clay crusher>
The clay crushing apparatus 10 is an apparatus for crushing clay lumps contained in heavy metal contaminated soil. In general shield construction, the muddy water discharged from the shield machine 110 is often sieved with a vibrating sieve into sand of more than 2 mm and fine particles of 2 mm or less, and the residual residue is treated as residual sand as sand. When excavating naturally-derived heavy metal contaminated ground, it is highly possible that the soil to be excavated will become soil, and in this case, the possibility that clay residue with solidified soil will be included in the sieve residue is eliminated. Can not. For this reason, in this embodiment, the clay crushing apparatus 10 for crushing a sieve residue is provided. As the clay crusher 10, for example, a roller mill, a demon roller, a ball mill, a high-speed dissolver (stirrer), or the like can be used.

<Sieving device>
The sieving device 20 is a device for sieving heavy metal-contaminated soil and taking out muddy water containing fine particles having a predetermined particle size or less. The predetermined particle size is, for example, 2 mm on the basis of sand content. That is, sand exceeding 2 mm is separated as containing no heavy metal and treated as zero-order treated soil. On the other hand, the muddy water containing fine particles of 2 mm or less is treated as detoxified by separating the heavy metal, assuming that it contains heavy metal. As the sieving device 20, for example, a vibrating sieve can be used.

  In the present embodiment, two sieving sieves are provided as the sieving device 20. The first vibrating screen is a device for screening gravel and clay contained in the muddy water discharged from the shield machine 110. The gravel / clay lump screened by the first vibrating screen is pulverized by the mud crushing apparatus 10 and sent to the thawing tank 90, and mixed with a part of the excess mud water sent from the excess mud tank 120. After making muddy water, it is sieved with a second vibrating sieve. Then, the under-sieving portion screened by the first vibrating sieve and the second vibrating sieve is stored in the excess mud tank 120. Moreover, the residual part screened with the 2nd vibration sieve is processed as 0th-order treated soil.

<Through tank>
The sludge tank 90 is a storage tank for storing a part of the excess mud water sent out from the excess muddy water tank 120 and the under-sieving part sieved by the sieving device 20 that is the first vibration sieve, The muddy water is stirred and uniformed by a stirring blade 92 driven by a stirring motor 91. The shape and the like of the stirring blade 92 can be appropriately set according to the properties of the undersieving part. Moreover, although not shown in figure, the thaw tank 90 is equipped with the pump for sending out muddy water. The surplus muddy water stored in the thawing tank 90 is supplied to a sieving device 20 that is a second vibrating sieve.

<Excess mud tank>
The surplus muddy water tank 120 stores surplus muddy water consisting of the under-sieved portion screened by the first vibrating sieve and the second vibrating sieve, and the demud tank 90, the muddy water tank 100, the pH adjusting device 30 (the waste muddy water receiving tank). It is a storage tank for supplying to 33). Also in the excess muddy water tank 120, the muddy water is agitated by the agitating blade 122 driven by the agitating motor 121 and is made uniform. Moreover, although not shown in figure, the excess muddy water tank 120 is equipped with the pump for sending out muddy water.

<Muddy water tank>
The muddy water tank 100 is a storage tank for storing muddy water received from the excess muddy water tank 120 and supplying the muddy water to the shield machine 110 again. Also in the muddy water tank 100, the muddy water is agitated and made uniform by the agitating blade 102 driven by the agitating motor 101. Moreover, although not shown in figure, the muddy water tank 100 is equipped with the pump for sending muddy water, and the hydration apparatus for muddy water specific gravity adjustment.

<Device 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 mud 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) that uniformly supplies muddy water containing iron powder that has adsorbed heavy metals is disposed in the previous stage of the specific gravity separation device 50. Furthermore, the specific gravity of the mud supplied to the specific gravity separator 50 is measured by a mud specific gravity measuring device (not shown), and the specific gravity separator 50 is supplied to the specific gravity separator 50 according to the specific gravity of the mud by a supplied mud water amount adjusting device (not shown). The amount of mud supplied is adjusted.

  The muddy water containing no iron powder separated by the specific gravity separation device 50 is temporarily stored in the waste muddy water tank 130 and then sent to the dehydration processing device 80. On the other hand, the muddy water adsorbing the heavy metal separated by the specific gravity separator 50 is sent to the drum type magnetic separator 60. The waste muddy 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 that functions as a surplus water discharging device, and then sent to the iron powder adding device 40. In addition, since the non-magnetic material separated by the drum-type magnetic separation device 60 includes a magnetic material that cannot be completely separated (iron powder for heavy metal adsorption separation), after stirring by the stirring device 150, the filter-type electromagnet separation device The magnetic material (the heavy metal-containing material) is separated by being sent 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: non-magnetic material and magnetic material. The magnetic substance is separated and recovered as iron powder for heavy metal adsorption by the drum type magnetic separation device 60 and the filter type electromagnet separation device 70. In this step, the heavy metal is included in the magnetic material. Further, non-magnetic materials are components that are separated by being not attracted by magnetic force, and basically contain neither iron powder (magnetic material) nor heavy metals. However, although the drum-type magnetic separation device 60 is slightly inferior in the separation accuracy between the magnetic material and the non-magnetic material, it is possible to process a large amount of muddy water with a high mixing ratio of the magnetic material. On the other hand, the filter-type electromagnet separator 70 has a high separation accuracy between the magnetic material and the non-magnetic material. However, if the mixing ratio of the magnetic material is large, the filter type electromagnet separation device 70 is frequently clogged. May decrease. Therefore, in the present embodiment, the drum-type magnetic separation device 60 and the filter-type electromagnet separation device 70 are used in combination to separate the waste muddy water into a non-magnetic material and a magnetic material.

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

<PH adjuster>
The pH adjusting device 30 is a device that is installed when pH adjustment is necessary, and adjusts the pH of the mud containing fine particles that have passed through the sieving device 20. The pH adjusting device 30 includes a waste mud receiving tank 33, a charging device (not shown) for charging the pH adjusting material and the extracting material, and a stirring blade 32 driven by the stirring motor 31. That is, when the heavy metal contained in the excess mud is arsenic, there is a high possibility that the arsenic is a heavy metal derived from iron hydroxide, so that 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 heavy metal (arsenic) is preferably secured for about 1 hour, for example.

<Iron powder adding device>
The iron powder adding device 40 is a device for adding iron powder to adsorb heavy metal to the iron powder, a heavy metal adsorption tank 41, a charging device (not shown) for charging iron powder, and stirring. A stirring blade 43 driven by a motor 42 is provided. In addition, in the iron powder addition apparatus 40, you may neutralize pH by adding a pH adjuster to the muddy water containing a fine grain part. For example, arsenic adsorption by iron powder is most effective when the pH is near neutral. Therefore, it is preferable to add iron powder while neutralizing mud water. The 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 all of a large number of fine pores extending from the surface to the inside, a particle size of 150 μm to 300 μm, and an apparent density of 1.3 g / cm ^{3 to} 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 1.3 g / cm ³ or more and 2.0 g / cm ³ or less. In addition, the value of a specific surface area is based on JIS Z 8830: 2013, and is measured by the BET multipoint method / adsorption side relative pressure (P / P ₀ = 0.001 to 0.30). The critical significance of the properties of such iron powder will be described.

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

<Grain 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 when performing 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 treated mud water decreases in the process of adsorbing the heavy metal to the iron powder, and the adsorption efficiency of heavy metals decreases.

<Apparent density of iron powder>
When the apparent density of the iron powder is less than 1.3 g / cm ³ , the number of fine holes increases and the strength of the iron powder decreases. If 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 heavy metal adsorption efficiency 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 a device for separating the specific gravity into, for example, a mud containing no iron powder and a mud containing iron powder adsorbed with heavy metal using a cyclone. In this embodiment, since iron powder having a large particle size is used, it is possible to easily recover iron powder from muddy water only by gravity sedimentation. Specific gravity separation is made between muddy water containing no iron and muddy water enriched with iron powder. Thereby, it becomes possible to reduce the amount of muddy water used as iron powder collection object to about 20-30% of the prior art.

  Although not shown in the drawing, the equipment (for example, a quantitative feeder) for supplying the residual portion separated by the specific gravity separator (cyclone) 50 as having a large weight (high specific gravity) to the drum type magnetic separator 60 is quantitative. It is preferable to supply the muddy water discharged to the magnetic material side to the quantitative feeder and to arrange a plurality of protrusions having an L-shaped cross section on the quantitative feeder. By setting it as such a structure, the muddy water which is a to-be-processed object can be uniformly expanded and supplied at the muddy water supply outlet. In the present embodiment, a cyclone is preferably used as the specific gravity separation device 50 in that the effect of separating iron powder 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 measuring device>
In this embodiment, although not shown, a mud specific gravity measuring device that measures the specific gravity of the mud supplied to the specific gravity separator 50 and a supply that adjusts the amount of mud supplied to the specific gravity separator 50 according to the measured specific gravity of the mud. It is preferable to provide a muddy water amount adjusting device. The mud specific gravity supplied to the specific gravity separator 50 varies within a range of about 1.00 to 1.50 depending on the 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 about 1.25 is added is caused to act by applying a centrifugal force of about 100G. The amount of iron powder remaining on the sieve becomes almost zero, but when the mud specific gravity exceeds about 1.25, the amount of iron powder remaining on the sieve increases.

  In this case, it is possible to reduce the amount of residual iron powder to almost zero by increasing the centrifugal force to about 200 G (optimally 180 G). Therefore, by measuring the specific gravity of the mud supplied to the cyclone and adjusting the discharge rate of the pump that supplies the mud to the cyclone according to the specific gravity of the mud, it is possible to manage the operation so that iron powder does not remain on the sieve. Become. In addition, since the abrasion inside a cyclone becomes so severe that the centrifugal force made to act on a cyclone becomes large, the one where the centrifugal force made to act is smaller is preferable from a viewpoint of maintenance property improvement.

  As the mud specific gravity measuring device, for example, a device that estimates the specific gravity of the mud supplied to the specific gravity separator 50 based on the water level of the waste mud receiving tank 33 and the output value of the pressure gauge installed in the lower part of the waste mud receiving tank 33 is used. That's fine. As the supply mud amount adjusting device, for example, by adjusting the current value to be applied to the mud supply pump using an inverter or the like according to the specific gravity of the mud supplied to the specific gravity separation device 50 estimated by the above-described method, In other words, a device that adjusts the centrifugal force that acts on the muddy water in the specific gravity separator 50 may be used.

<Drum type magnetic separator>
The drum-type magnetic separation device 60 is a device for recovering iron powder from muddy water containing iron powder adsorbed with heavy metals 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 collect only the iron powder therefrom. For this reason, in this embodiment, the iron powder recovery process is performed by the drum-type magnetic separation device 60 using the permanent magnet 61. At this time, the processing weight per unit time can be increased by adopting a facility for supplying muddy water containing iron powder from the upper part of the drum magnetic separator (for example, an apparatus including the downflow basin 66 (see FIG. 3)). It becomes possible.

  For example, as shown in FIG. 3, the drum magnetic separator makes a surface of the rotating drum 62 a magnetic surface by attaching a permanent magnet 61 inside the rotating drum 62. Then, the rotating drum 62 is rotated to attract the magnetic material to the attracting surface, and the magnetic material attracted by the scraper 65 is scraped off. Further, in the present embodiment, the baffle plate 63 is installed in the vicinity of the vertically lower portion of the boundary between the permanent magnet installation unit and the non-installation unit located on the lower side of the rotary drum 62, and the separation unit between the non-magnetic material and the magnetic material. By blowing air from the air nozzle 64 toward the head, the non-magnetic material and the magnetic material can be distinguished and dropped.

<Agitator>
Furthermore, the iron magnetic powder in which the apparent magnetic properties are reduced due to 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 made of a mixer or the like to peel the clay adhered 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 that is separated and discharged to the magnetic material side by the drum magnetic separator may contain a lot of moisture. Therefore, as shown in FIGS. 1 and 3, the overflow weir 141 is provided in the iron powder receiving tank 140 for storing the iron powder discharged to the magnetic material side, and the iron powder is upstream of the overflow weir 141. To discharge. And the moisture discharged to the magnetic material side together with the iron powder is configured to flow over the overflow weir 141, so that when the amount of water discharged to the magnetic material side increases, only the moisture is discharged. can do. As above-mentioned, the iron powder receiving tank 140 and the apparatus incidental to this function as a surplus water discharging apparatus.

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

  That is, since the main body of the processed material separated as a magnetic material is iron powder, it contains heavy metals. However, iron powder only adsorbs a slight amount of heavy metal eluted from the soil into water, and the content of heavy metal is negligible. On the other hand, the main processed materials separated as non-magnetic materials are sand, silt, clay, and water, and the amount of iron powder mixed therein is small, so that hardly any heavy metals are contained. Further, the content of iron powder in the non-magnetic material is smaller in the filter type electromagnet separation device 70 than in the drum type magnetic separation device 60. Thus, in this embodiment, a trace amount of iron powder that could not be separated by the drum-type magnetic separation device 60 is removed by the filter-type electromagnet separation device 70.

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

<Device group in the post-treatment stage (dehydration processing device)>
A dehydration processing apparatus 80 is disposed at a later stage of the detoxification process. The dehydration processing device 80 is a device that reduces the volume by dehydrating the waste mud from which the heavy metal stored in the waste mud tank 130 is separated and removed, and includes, for example, a filter press. That is, the amount of waste mud can be reduced by dehydrating the muddy water from which all the iron powder has been collected with a filter press or the like. In addition, by using a vacuum pressure dehydrator that performs dehydration processing by adding cement as the dehydration processing device 80, a dehydration cake with self-hardening is generated, and the risk of elution of heavy metals in the future is further reduced. be able to. Moreover, the filtrate discharged | emitted from the dehydration processing apparatus 80 can recycle the obtained fresh water by processing muddy water with a muddy water processing apparatus (not shown).

<Advantageous Effects of the Present Invention>
Hereinafter, the point that the detoxification processing system for heavy metal-contaminated soil according to the present invention has an advantageous effect as compared with a conventionally considered system will be described. It is difficult to recover iron powder from waste muddy water exceeding about 700 m ³ with an apparatus configuration that pumps up the waste mud mixed with iron powder from the iron powder mixing tank to the magnetic separator and collects purified muddy water. This is because in the method of pumping up the waste mud mixed with iron powder from the iron powder mixing tank to the magnetic separator and recovering the purified mud, it is necessary to treat the waste mud 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 devices are required.

  Moreover, when iron powder is repeatedly used, the heavy metal adsorption capacity is reduced. However, in the processing method in which the iron powder is always returned to the iron powder mixing tank, the heavy metal adsorption capacity is reduced every time the iron powder is repeatedly used. For this reason, it is necessary to collect | recover the iron powder exceeding a use limit, and to add fresh iron powder to an iron powder mixing tank, and a lot of iron powder must be used.

  In this regard, the heavy metal-contaminated soil detoxification treatment system according to the present invention has a high treatment capacity and can not only make equipment compact, but also establish a system for reusing iron powder. The amount of use can be greatly reduced.

  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, if the muddy water having a large amount of sand is to be treated, the water channel on the lower side of the rotating drum is clogged with earth and sand, resulting in a processing failure. Since there is a risk of causing it, there is a concern about making the treatment equipment suitable for the site.

  In this respect, in the detoxification processing system for heavy metal-contaminated soil according to the present invention, since the muddy water to be treated is supplied from the upper side of the rotating drum, the above-described problems do not occur.

  In addition, when only a centrifuge 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 introduced into the muddy water mixed with heavy metal, the sand added together with the iron powder is collected again with the iron powder by the centrifugal separator, and the sand contained in the iron powder every time the process is repeated. There is a risk that the amount of iron will increase and the amount of iron powder added cannot be managed.

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

DESCRIPTION OF SYMBOLS 10 Clay crushing apparatus 20 Sieving apparatus 30 pH adjustment apparatus 31 Stirring motor 32 Stirring blade 33 Waste muddy water receiving tank 40 Iron powder addition apparatus 41 Heavy metal adsorption tank 42 Stirring motor 43 Stirring blade 50 Specific gravity separation apparatus 60 Drum type magnetic separation apparatus 61 Permanent Magnet 62 Rotating drum 63 Baffle plate 64 Air nozzle 65 Scraper 66 Flowing soot 70 Filter type electromagnet separator 80 Dewatering device 90 Thawing tank 91 Stirring motor 92 Stirring blade 100 Feeding mud water tank 101 Stirring motor 102 Stirring blade 110 Shield machine 120 Surplus Muddy water tank 121 Stirrer motor 122 Stirrer blade 130 Waste muddy water 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 (5)

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 device for taking out muddy water containing fine particles having a predetermined particle size or less;
An iron powder adding device for adding iron powder to the muddy water containing the fine particles, and adsorbing heavy metals to the iron powder;
A specific gravity separation device that separates specific gravity into muddy water not containing iron powder and muddy water containing iron powder adsorbed with heavy metals;
A drum-type magnetic separation device that recovers iron powder from muddy water containing iron powder adsorbed by the heavy metal using a permanent magnet;
A dehydrating apparatus for dehydrating muddy water after separating the iron powder;
With
Part or all of the iron powder has a large number of fine pores extending from the surface to the inside, 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 a detoxification treatment system for heavy metal-contaminated soil, characterized in that it is 0.12 m ² / g or more and 0.36 m ² / g or less. A filter-type electromagnet separator that further collects iron powder from muddy water containing iron powder that could not be recovered by the drum-type magnetic separator,
The detoxification treatment system for heavy metal-contaminated soil according to claim 1.   3. A detoxification treatment system for heavy metal-contaminated soil according to claim 1 or 2, wherein a muddy water supply device for uniformly supplying muddy water containing iron powder adsorbing heavy metals is disposed upstream of the specific gravity separator. . A mud specific gravity measuring device for measuring the specific gravity of the mud supplied to the specific gravity separator;
According to the measured specific gravity of the muddy water, a supplied muddy water amount adjusting device that adjusts the amount of muddy water supplied to the specific gravity separation device;
The detoxification treatment system for heavy metal-contaminated soil according to any one of claims 1 to 3, wherein   The surplus water discharge device for separating the iron powder recovered by the drum type magnetic separation device and the surplus water recovered at the same time and discharging only the surplus water is provided. The detoxification treatment system for heavy metal-contaminated soil according to any one of the above items.

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