JP6411909B2 - Detoxification system for arsenic contaminated soil - Google Patents

Description

  The present invention relates to a detoxification treatment system for arsenic-contaminated soil, and particularly to a technique suitably applied for detoxification treatment of soil containing natural arsenic generated in a muddy water shield method at a construction site. It is.

  When a tunnel is constructed with a shield method on the ground where natural arsenic contamination is a concern, dehydrated cake that exceeds environmental standards may occur. For this reason, arsenic can be easily extracted and separated by making the excavated soil muddy, so a measure to extract and separate arsenic from the excavated soil using a shield method in which the excavated soil exhibits a muddy water shape is considered. It has been.

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

  Furthermore, a method of insolubilizing arsenic while excavating by using a mud pressure shield method and supplying iron powder and an 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 arsenic from various arsenic-containing aqueous solutions such as industrial wastewater and an aqueous nickel sulfate solution that is an intermediate raw material for nickel chemical products that are electronic materials. That is, the technique described in Patent Document 1 adds metal iron powder to an arsenic-containing aqueous solution and stirs or mixes, or passes the arsenic-containing aqueous solution through a column or the like filled with metal iron powder, In this technique, after reacting arsenic on the surface, metal iron powder in which arsenic 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 cases where equipment that collects iron powder that has adsorbed arsenic is being studied using equipment that has a small processing capacity relative to the equipment scale, and a large amount of waste mud generated from a large-diameter shield is treated. Therefore, 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 arsenic-contaminated soil is insolubilized, and since the treated soil contains arsenic, it must be managed permanently.

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

  The arsenic-contaminated soil detoxification treatment system of the present invention has the following features in order to achieve the above-described object. That is, the arsenic-contaminated soil detoxification system of the present invention is a device for detoxifying arsenic-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. In addition, as a group of devices in the arsenic removal step, there are a pH adjusting device, an iron powder adding device, a specific gravity separating device, a drum type magnetic separating device, and a filter type electromagnet separating device. 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 arsenic-contaminated soil. The sieving device is a device for sieving arsenic-contaminated soil and taking out muddy water containing fine particles having a predetermined particle size (for example, 2 mm) or less.

The pH adjusting device is a device for adjusting the pH of the muddy water containing fine particles passed through the sieving device to be alkaline . The iron powder adding device is a device for adding iron powder while neutralizing the pH of mud containing fine particles whose pH is adjusted, and adsorbing arsenic to the iron powder. The specific gravity separation device is a device for separating the specific gravity into muddy water containing no iron powder and muddy water containing iron powder adsorbed with arsenic using a cyclone. The drum type magnetic separation device is a device for recovering iron powder from muddy water containing iron powder adsorbed with arsenic using a permanent magnet. The filter type electromagnet separation device 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. That is, in the filter type electromagnet separator, a small amount of iron powder adsorbed by arsenic remaining in the muddy water and muddy water which is a non-magnetic substance are separated and recovered.

Furthermore, between the drum-type magnetic separator and the filter-type electromagnet separator, an agitator that stirs muddy water containing iron powder that could not be recovered by the drum-type magnetic separator and peels off the clay adhering to the iron powder. It is arranged.

In addition, a muddy water specific gravity measuring device that measures the specific gravity of the muddy water supplied to the specific gravity separation device, and a supply mud water amount adjusting device that adjusts the amount of muddy water supplied to the specific gravity separation device according to the measured specific gravity of the mud water are provided. Also good.

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 adsorbed with arsenic in the previous stage of the specific gravity separator.

Further, in addition to the above-described configuration, the drum-type magnetic separation device recovers an iron powder concentrate containing iron powder and surplus water from muddy water containing iron powder adsorbed with arsenic. It is preferable to provide a surplus water discharge device that separates surplus water and discharges only the surplus water.

  According to the detoxification treatment system for arsenic-contaminated soil according to the present invention, for example, when soil containing natural arsenic generated in muddy water shield construction is detoxified at the construction site, dehydration from generation of shield waste mud water is performed. Even when a large amount of waste mud containing arsenic is generated in the entire series of steps until the cake is generated, it can be efficiently and appropriately treated.

Explanatory drawing which shows the whole structure of the detoxification processing system of the arsenic contaminated 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 processing system for arsenic-contaminated soil according to the present invention will be described with reference to the drawings. 1 to 3 illustrate an arsenic-contaminated soil detoxification system 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>
An arsenic-contaminated soil detoxification system according to an embodiment of the present invention is an apparatus for detoxifying arsenic-contaminated mud generated in, for example, a muddy 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 separating device 50, the drum-type magnetic separating device 60, the filter-type electromagnet separating device 70, and the dehydration processing device 80 I have. 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.

<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 arsenic-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 natural arsenic-contaminated ground, there is a high possibility that the soil to be excavated will become soil, and in that case, the screen residue may contain clay lumps solidified with soil. 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 arsenic-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 not containing arsenic and treated as zero-order treated soil. On the other hand, the muddy water containing fine particles of 2 mm or less is assumed to contain arsenic, and arsenic is separated and detoxified. 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 arsenic removal process>
In the arsenic 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 is adjusted by the pH adjusting device 30 is added with iron powder by the iron powder adding device 40 to adsorb arsenic, and is sent to the specific gravity separation device 50. In the present embodiment, in front of the gravity separator 50, muddy water supply unit uniformly supplying muddy water containing iron powder arsenic is adsorbed (not shown) is disposed. 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. Meanwhile, mud arsenic separated by gravity separation device 50 is adsorbed is sent to a 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. Further, since the non-magnetic material separated by the drum-type magnetic separation device 60 includes magnetic material (iron powder for arsenic adsorption separation) that cannot be separated, after stirring by the stirring device 150, the filter-type electromagnet separation device The magnetic material (arsenic-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, a non-magnetic material and a magnetic material. The magnetic material is separated and recovered as iron powder for arsenic adsorption by the drum type magnetic separation device 60 and the filter type electromagnet separation device 70. In this step, arsenic 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 arsenic. 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 (the muddy water from which arsenic has 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 into the magnetic material (arsenic-containing material) side by the filter type electromagnet separator 70 is sent to the iron powder receiving tank 140.

<PH adjuster>
The pH adjusting device 30 is a device for adjusting the pH of the mud containing fine particles that have passed through the sieving device 20, and is a waste mud receiving tank 33, and a charging device for charging the pH adjusting material and the extracting material ( And a stirring blade 32 driven by a stirring motor 31. Since arsenic contained in the excess mud water is likely to be arsenic derived from iron hydroxide, 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 arsenic is preferably secured for about 1 hour, for example.

<Iron powder adding device>
The iron powder adding device 40 is a device for neutralizing the pH by adding a pH adjuster to the muddy water containing fine particles whose pH is adjusted, and adding iron powder to adsorb arsenic to the iron powder. And an arsenic adsorption tank 41, a charging device (not shown) for charging iron powder, and a stirring blade 43 driven by a stirring motor 42. Adsorption of arsenic by iron powder is maximized when the pH is near neutral, so iron powder is added 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 should be porous (sponge-like) iron powder with a particle size of about 6 times larger than the iron powder used in the prior art. Is preferred. When iron powder having a large particle size is used, the specific surface area of the iron powder is reduced, and the arsenic adsorption capacity is expected to decrease.However, the iron powder used in this embodiment is porous (sponge-like). Therefore, even if the particle size is large, the specific surface area of the iron powder itself does not decrease, and the arsenic adsorption efficiency does not decrease.

<Specific gravity separator>
As shown in FIG. 2, the specific gravity separation device 50 is a device for separating the specific gravity into mud containing no iron powder and mud containing iron powder adsorbed with arsenic 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 drawings, the facility (for example, a quantitative feeder) that supplies the under-sieving portion of the specific gravity separator (cyclone) 80 to the drum-type magnetic separator 60 is a facility that can supply a workpiece quantitatively. While supplying the muddy water discharged to the magnetic material side to the quantitative feeder, it is preferable 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.

<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. And 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 the cyclone treatment (specific gravity separation process by the specific gravity separation device 50), the muddy water to which iron powder having a specific gravity of about 1.25 is added is almost free of iron powder remaining on the sieve by applying centrifugal force of about 100G. Although it becomes zero, 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 muddy water supplied to the specific gravity separation device 50 and adjusting the discharge amount of the pump that supplies the muddy water to the cyclone according to the specific gravity of the muddy water, operation management is performed so that iron powder does not remain on the sieve. Is possible. 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 arsenic using a permanent magnet. That is, since the cyclone processed 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 clay particles are adhered around the iron powder and the apparent magnetism is lowered 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 arsenic has 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 arsenic. However, iron powder only adsorbs a small amount of arsenic eluted from the soil into the water, and the arsenic content is negligible. On the other hand, the main processed materials separated as non-magnetic materials are sand, silt, clay, and water. Since the amount of iron powder mixed in is small, arsenic is hardly 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 arsenic decreases. Therefore, the arsenic adsorption capacity can be restored by treating the iron powder reused a predetermined number of times with either 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 apparatus 80 is an apparatus for reducing the volume by dehydrating the waste mud from which the arsenic stored in the waste mud tank 130 has been 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. Further, by using a vacuum pressure dehydrator that performs dehydration processing by adding cement as the dehydration processing apparatus 80, a dehydration cake having self-hardening is generated, and the risk of future arsenic elution 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 treatment system for arsenic-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.

  In addition, when iron powder is repeatedly used, the arsenic adsorption capacity decreases. However, in the processing method in which the iron powder is always returned to the iron powder mixing tank, the arsenic adsorption capacity decreases 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, in the arsenic-contaminated soil detoxification treatment system according to the present invention, the treatment capacity is high and not only can the equipment be made compact, but also a system for reusing iron powder has been established. 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 regard, in the arsenic-contaminated soil detoxification system 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 thrown into the muddy water mixed with arsenic, 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 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 arsenic-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 Arsenic adsorption tank 42 Stirring motor 43 Stirring blade 50 Specific gravity separation apparatus (cyclone)
DESCRIPTION OF SYMBOLS 60 Drum type magnetic separation apparatus 61 Permanent magnet 62 Rotating drum 63 Baffle plate 64 Air nozzle 65 Scraper 66 Flowing drop 70 Filter type electromagnet separation apparatus 80 Dehydration processing apparatus 90 Demolition tank 91 Stirring motor 92 Stirring blade 100 Mud water tank 101 Stirring motor DESCRIPTION OF SYMBOLS 102 Stirring blade 110 Shield machine 120 Surplus muddy water tank 121 Stirring motor 122 Stirring blade 130 Waste muddy water tank 131 Stirring motor 132 Stirring blade 140 Iron powder receiving tank 141 Overflow weir 150 Stirring device 151 Stirring tank 152 Stirring motor 153 Stirring blade

Claims (4)

An apparatus for detoxifying arsenic-contaminated soil,
A clay crushing device for crushing clay lumps contained in the arsenic-contaminated soil;
Sieving the arsenic-contaminated soil, and a sieving device for taking out muddy water containing fine particles having a predetermined particle size or less;
A pH adjusting device that adjusts the pH of the mud containing the fine particles that have passed through the sieving device to be alkaline ;
An iron powder adding device for adsorbing arsenic to the iron powder by adding iron powder while neutralizing the pH of the muddy water containing the fine particles whose pH has been adjusted;
Using a cyclone, a specific gravity separation device that separates specific gravity into muddy water not containing iron powder and muddy water containing iron powder adsorbed with arsenic,
A drum-type magnetic separation device that recovers iron powder from muddy water containing iron powder adsorbed by arsenic using a permanent magnet;
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;
A dehydrating apparatus for dehydrating muddy water after separating the iron powder;
The equipped Rutotomoni,
Stirring between the drum-type magnetic separation device and the filter-type electromagnet separation device to stir mud containing iron powder that could not be recovered by the drum-type magnetic separation device and to tear off the clay adhering to the iron powder A detoxification treatment system for arsenic-contaminated soil, characterized in that a device is arranged . An apparatus for detoxifying arsenic-contaminated soil,
A clay crushing device for crushing clay lumps contained in the arsenic-contaminated soil;
Sieving the arsenic-contaminated soil, and a sieving device for taking out muddy water containing fine particles having a predetermined particle size or less;
A pH adjusting device that adjusts the pH of the mud containing the fine particles that have passed through the sieving device to be alkaline ;
An iron powder adding device for adsorbing arsenic to the iron powder by adding iron powder while neutralizing the pH of the muddy water containing the fine particles whose pH has been adjusted;
Using a cyclone, a specific gravity separation device that separates specific gravity into muddy water not containing iron powder and muddy water containing iron powder adsorbed with arsenic,
A drum-type magnetic separation device that recovers iron powder from muddy water containing iron powder adsorbed by arsenic using a permanent magnet;
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;
A dehydrating apparatus for dehydrating muddy water after separating the iron powder;
The equipped Rutotomoni,
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;
A detoxification treatment system for arsenic-contaminated soil. 3. The arsenic-contaminated soil detoxification system according to claim 1, wherein a muddy water supply device that uniformly supplies muddy water containing iron powder adsorbed with arsenic is disposed in a stage preceding the specific gravity separation device. . The drum-type magnetic separation device recovers an iron powder concentrate containing iron powder and surplus water from muddy water containing iron powder adsorbed by the arsenic, separating the iron powder and the surplus water, The arsenic-contaminated soil detoxification system according to any one of claims 1 to 3, further comprising a surplus water discharge device that discharges only the surplus water.

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