JP2016064323A - Muddy water treatment system and muddy water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system and a method capable of decontaminating muddy water containing sand contaminated with heavy metals without using a special device.SOLUTION: A muddy water treatment system is provided that treats muddy water containing sand contaminated with heavy metals and includes separation means for separating sand particles having a predetermined size or larger contained in the muddy water, water washing means for washing the separated particles, extracting means for adding an agent to the muddy water containing particles having a size smaller than the predetermined size after separating the larger particles and extracting the heavy metals sticking to the particles having a size smaller than the predetermined size into the muddy water, and dehydration means for dehydrating the muddy water.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a system and method for treating mud containing sediments contaminated with heavy metals.

  As a technique for constructing a tunnel, a shield method that uses a shield machine to perform excavation and lining while preventing the collapse of the ground is known, and many are actually used. In this shield construction method, a muddy water type shield construction method in which muddy water is used for excavation is becoming mainstream.

  The muddy water type shield method is a method in which excavation is carried out while filling the pressurized muddy water between the face at the front of excavation and the partition wall provided behind the cutter head of the shield machine, and stabilizing the face. In this method, excavated earth and sand are discharged as mud together with a part of the mud supplied, and the mud is treated in a mud treatment plant.

  Here, the configuration of a conventional muddy water treatment plant will be briefly described with reference to FIG. The discharged mud discharged from the shield machine 10 is sent to the primary treatment facility by the discharged mud pump 11. The waste mud is sent to the pretreatment machine 12 of the primary treatment facility, and large gravel and solid soil in the waste mud are separated and removed. The remaining waste mud is collected in the muddy water receiving tank 13, and coarse particles such as sand and gravel having a particle diameter of 75 μm or more are separated and removed by the cyclone 14 and the primary classifier 15.

  The coarse particles separated by the pretreatment machine 12 and the primary classifier 15 are placed on the belt conveyor 16 and carried to the earth and sand pit. The muddy water containing fine particles having a particle size of less than 75 μm is sent to the adjusting tank 17, and water, muddy water, viscosity adjusting agent and the like are added as appropriate, and the concentration, specific gravity and viscosity of the muddy water are adjusted. The adjusted muddy water is pressurized by the supply pump, sent to the shield machine 10 again, and reused.

  A part of the muddy water in the adjustment tank 17 is sent to the secondary treatment facility as surplus muddy water. The surplus muddy water is sent to the surplus muddy water tank 18 of the secondary treatment facility, and after adding the inorganic flocculant from the inorganic flocculant tank 19, the fine particles are aggregated in the slurry tank 20. The muddy water (slurry) containing the agglomerated fine particles is dehydrated by pressure filtration with the filter press 21 and discharged as a dehydrated cake to the dehydrated cake pit.

  The waste water discharged from the filter press 21 is appropriately sent from a fresh water tank 22 to a dilution water tank 23 where fresh water is added and diluted. The dilution water is used as water to be added to the adjustment tank 17, water for dissolving the thickener in the thickener dissolving tank 24, and water for dissolving the clay in the clay dissolving tank 25. The solutions prepared in the thickener dissolution tank 24 and the clay dissolution tank 25 are collected in the mud storage tank 26 and used to adjust the concentration, specific gravity, and viscosity in the adjustment tank 17 together with the muddy water from the excess mud tank 18. Is done.

The diluted water is also sent to the water quality adjustment processing facility. The raw water tank 28 of the water quality adjusting treatment facility receives the diluted water and sends it to the muddy water treatment facility 27 by a submersible pump (not shown). On the way, the pH is adjusted by the carbon dioxide gas generated by the CO ₂ vaporizer 29, and the inorganic flocculant and the polymer flocculant are added from the inorganic flocculant tank 19 and the polymer flocculant tank 30. In the turbid water treatment equipment 27, the fine particles remaining in the diluted water are agglomerated and precipitated by these flocculants and separated into a supernatant and sludge. The supernatant liquid is sent to the discharge water tank 31 and discharged to the sewer, etc., and the sludge is sent to the slurry tank 20 to be discharged as a dehydrated cake.

  In such a conventional muddy water treatment plant, when the waste mud is contaminated with heavy metals, the primary treatment soil such as sand, gravel and consolidated soil collected by the primary treatment equipment is in accordance with the environmental standards for heavy metals. It is assumed that it will be nonconforming, and may not be recycled as healthy soil. A dehydrated cake enriched with heavy metals is sure to exceed environmental standards, and must be properly treated and disposed of as a dehydrated cake containing heavy metals. As a result, these processing costs become enormous in large-scale shield construction.

  Therefore, after mixing iron powder and adsorbing heavy metals to the iron powder, technology to collect the iron powder (see, for example, Patent Documents 1 and 2) and technology using special drugs and high-performance classifiers (For example, refer nonpatent literature 1) etc. are proposed.

JP 2011-56482 A JP 2014-73464 A

Kazuhiko Tsujimi and two others, “Development of purification technology for naturally-derived arsenic-contaminated soil generated by muddy water shield construction”, 20th Annual Conference on Groundwater and Soil Contamination and Prevention Measures, General Soil Environment Center, June 2014, p. 231-236

  However, in the conventional technology, it is necessary to use a special device, and when such a special device is used, it takes a huge amount of money in consideration of maintenance management. Therefore, it is desired to provide a system and method capable of purifying muddy water containing earth and sand contaminated with heavy metals without using a special device.

  In view of the above problems, the present invention is a muddy water treatment system for treating muddy water containing earth and sand contaminated with heavy metals, separation means for separating particles of earth and sand having a predetermined particle size or more contained in muddy water, and separation A water washing means for washing the particles separated by the means, and a drug is added to the muddy water containing particles having a particle size less than a predetermined value discharged from the separation means, and the heavy metal adhering to the particles is added to the muddy water. There is provided a muddy water treatment system including an extracting means for extracting and a dehydrating means for dewatering muddy water.

  Further, a muddy water treatment method for treating muddy water containing earth and sand contaminated with heavy metals, a step of separating particles of earth and sand having a particle size of a predetermined size or more contained in muddy water, and a step of washing the separated particles with water In addition, a method for treating muddy water is provided, which includes a step of adding a chemical to muddy water containing particles having a particle size less than a predetermined value, extracting heavy metal adhering to the particles into muddy water, and a step of dehydrating muddy water. The

  ADVANTAGE OF THE INVENTION According to this invention, the muddy water containing the earth and sand contaminated with the heavy metal can be purified without using a special apparatus.

The figure which showed the structural example of the conventional muddy water processing system. The figure which showed the structural example of the muddy water processing system of this invention. The figure which showed the other structural example of the secondary treatment equipment of the muddy water processing system shown in FIG. The flowchart which showed the flow of the process which the muddy water processing system shown in FIG. 2 performs.

  FIG. 2 is a diagram showing a configuration example of the muddy water treatment system of the present invention. This muddy water treatment system 40 is not limited to this, but is used in the muddy water type shield construction described above. Hereinafter, the muddy water treatment system 40 will be described as being used for muddy water type shield construction. In the muddy water type shield construction, soil is excavated by a cutter head provided on one circular surface (front surface) facing the face of the cylindrical shield machine 10, and the shield machine 10 is set so that the face does not collapse at that time. The pressurized muddy water is filled between the provided partition wall and the face.

  The muddy water treatment system 40 supplies pressurized muddy water between the partition wall and the face, and collects and processes together with part of the muddy water supplied with the excavated soil generated by excavation. The muddy water treatment system 40 includes a primary treatment facility, a secondary treatment facility, and a water quality adjustment treatment facility, similarly to the conventional muddy water treatment system described above. Similar to the conventional system, the primary processing equipment includes a pretreatment device 41, a muddy water receiving tank 42, a cyclone 43, a primary classifier 44, a belt conveyor 45, and an adjustment tank 46.

  The mud containing the excavated sediment from the shield machine 10 is sent to the pretreatment machine 41 by the mud pump 47 as muddy water. This muddy water contains fine fine particles such as silt and clay and coarse particles such as pebbles, gravel and sand. In addition, it includes wood chips and garbage. The pretreatment machine 41 and the primary classifier 44 are, for example, vibrating sieve machines, and the pretreatment machine 41 has an arbitrary mesh size that can remove gravel, consolidated soil, wood chips, dust, etc. having a relatively large particle size. In the primary classifier 44, a mesh-size sieve is used which is finer than the pretreatment machine 41 and can separate earth and sand particles having a particle size of a predetermined size or more, for example, a particle size of 75 μm or more. Is done. The primary classifier 44 is used together with the cyclone 43 to separate the coarse particles.

  The adjustment tank 46 is provided with a stirring device, and dilution water, muddy water, or the like is appropriately added to adjust the concentration, specific gravity, and viscosity of the muddy water in the tank to predetermined values. The supply pump 48 pressurizes the adjusted mud water to a predetermined pressure, and then supplies it to the shield machine 10. Surplus muddy water is supplied to the secondary treatment facility by the supply pump 49.

  In the muddy water treatment system 40, the primary treatment equipment is provided with water washing means for washing the coarse particles separated by the pretreatment machine 41 and the primary classifier 44. In FIG. 2, the water injection apparatus 50 provided with the shower nozzle is provided as a washing means. The water injection device 50 injects water toward the coarse particles separated on the sieves of the pretreatment machine 41 and the primary classifier 44, and rinses the particles. The water injection device 50 may spray water in the form of a mist.

  It is known that heavy metals that contaminate earth and sand are unevenly distributed in particles having a particle size less than a predetermined value, that is, fine particles such as silt and clay. For this reason, it hardly adheres to coarse particles such as gravel and sand. However, although the heavy metals themselves are hardly adhered to the coarse particles, fine particles to which the heavy metals are adhered are adhered. In the water washing by the water injection device 50, the fine particles attached to the coarse particles are washed away. Thereby, the primary treated soil composed of the coarse particles separated by the pretreatment machine 41 and the primary classifier 44 can be surely adapted to the environmental standards for heavy metals. The primary treated soil is transported to the sediment pit 51 by the belt conveyor 45 and can be reused as healthy soil. Here, it is separated into a coarse particle having a particle size of 75 μm or more and a fine particle having a particle size of less than 75 μm, but is not limited thereto, and is separated at other particle sizes depending on the concentration of heavy metals. Also good.

  Examples of heavy metals that are unevenly distributed in fine particles include mercury, lead, copper, chromium, manganese, cobalt, nickel, cadmium, selenium, zinc, bismuth, and arsenic.

  Similarly to the conventional system, the secondary treatment equipment is also a surplus muddy water tank 60, a flocculant tank 61, a slurry tank 62, a filter press 63, a fresh water tank 64, a dilution water tank 65, and a thickener dissolving tank 66. And a clay dissolution tank 67 and a mud storage tank 68. Each of these devices can be the same as the conventional system and will not be described in detail here.

  In the muddy water treatment system 40 shown in FIG. 2, the flocculant tank 61 is filled with an inorganic flocculant and a polymer flocculant. As the inorganic flocculant, sulfate band (aluminum sulfate), aluminum chloride, polyaluminum chloride (PAC), ferric chloride, polyferric sulfate, polysilica iron, etc. well known as inorganic flocculants are used. . As the polymer flocculant, polyacrylamide flocculants well known as polymer flocculants are used. The flocculants exemplified here are only examples, and other substances can be used as long as they have an aggregating effect.

  These flocculants agglomerate fine particles in the muddy water to form lumps. This is to make a lump of a certain size so that it can be appropriately filtered under pressure by the filter press 63.

  In the muddy water treatment system 40, an extraction / removal tank 69 and a chemical are added as extraction means for adding a chemical to the muddy water containing fine particles and extracting heavy metals adhering to the fine particles to the muddy water in the secondary treatment equipment. A tank 70 is provided. The extraction / removal tank 69 receives the muddy water from the surplus muddy water tank 60 and the drug from the chemical tank 70, and stirs and mixes with a stirrer to extract heavy metals adhering to fine particles into the muddy water. .

  As the drug, for example, a chelating agent can be used. The chelating agent reacts with heavy metal ions to generate a chelate compound and extract heavy metals into the mud liquid. Examples of chelating agents that can be used include ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), and metal salts thereof. In addition, as long as it is a chemical | medical agent which can extract the heavy metals adhering to a fine particle part in muddy water, it will not be restricted to a chelating agent.

  The muddy water treatment system 40 can send the slurry from which heavy metals have been extracted from the extraction / removal tank 69 to the filter press 63 via the slurry tank 62, and dehydrate the slurry with the filter press 63 as a dehydrating means. The reason why the extraction / removal tank 69 is arranged on the upstream side of the slurry tank 62 is to extract the heavy metal before the fine particles are aggregated and it is difficult to extract the heavy metal. Since the above-mentioned chelate compound is present in the liquid, it is contained in the waste water discharged by this dehydration and sent to the water quality adjusting treatment facility. On the other hand, the dehydrated cake that is a solid obtained by dehydrating with the filter press 63 is discharged to the dehydrated cake pit 71 in a state that conforms to environmental standards for heavy metals. Therefore, this dehydrated cake can also be reformed at an intermediate treatment facility and reused as healthy soil.

  The muddy water treatment system 40 does not send the slurry from the extraction / removal tank 69 to the filter press 63 via the slurry tank 62 but, as shown in FIG. 3, a centrifugal dehydrator 72 as a dewatering means and a water washing means as It can also be sent through the rinsing tank 73. The centrifugal dehydrator 72 has a spiral blade around a shaft body that extends in one direction, and moves a slurry from one side to the other by rotation of the shaft body, and a screw decanter that removes moisture by the centrifugal force. Can be used. Here, the centrifugal dehydrator 72 is used. However, the present invention is not limited to this, and other dewatering devices such as a filter press can also be used.

  The rinsing tank 73 is used in place of the slurry tank 62 or together with the slurry tank 62, and is composed of a container having a predetermined shape and capacity, and a stirring device, and fresh water is placed in the container. The rinsing tank 73 is charged with the solid matter dehydrated by the centrifugal dehydrator 72 or the slurry after the flocculant is added in the slurry tank 62 and washed with water by a stirrer. Thereby, the chelate compound adhering to the solid can be washed away and removed from the solid. The slurry containing the solid matter can be sent to the filter press 63, dehydrated, and discharged as a dehydrated cake to the dehydrated cake pit 71. Here, although the example using the rinse tank 73 containing fresh water was shown, it is not restricted to this, You may wash with water using said water injection apparatus 50 grade | etc.,.

  Similarly to the filter press 63, since the waste water is discharged from the centrifugal dehydrator 72, the waste water can be processed by being sent to a water quality adjustment processing facility. In this way, rather than being sent from the extraction / removal tank 69 to the filter press 63 via the slurry tank 62 and dehydrated, it is dehydrated once by the centrifugal dehydrator 72, washed with water in the rinse tank 73, and then dehydrated by the filter press 63. Thus, the dehydrated cake can be discharged to the dehydrated cake pit 71 in a state that more reliably meets the environmental standards for heavy metals.

Referring to FIG. 2 again, the water quality adjustment treatment facility is configured to include a muddy water treatment facility 80, a raw water tank 81, a CO ₂ vaporizer 82, and a discharge water tank 83, as in the conventional system. In addition, since the polymer dissolution tank can share the flocculant tank 61 in a secondary processing equipment, it is abbreviate | omitting here. When using the waste water discharged from the filter press 63 and the centrifugal dehydrator 72, the mud treatment system 40 receives the waste water discharged from the centrifugal dehydrator 72 in the raw water tank 81.

  Drainage is supplied from the raw water tank 81 to the turbid water treatment facility 80 using an underwater pump, and an acidic or alkaline gas or solution is added as a pH adjuster during the process. Here, the wastewater is made alkaline, and carbon dioxide, which is an acidic gas, is supplied. Also, a flocculant is added to agglomerate the particles in the waste water. Further, an adsorbent tank 84 containing an adsorbent that adsorbs heavy metals is provided, and the adsorbent is added thereto.

  As an adsorbent that adsorbs heavy metals, for example, diatomaceous earth, silica, alumina, activated carbon, zeolite, iron, iron oxide, a mixture thereof, at least one of them as a main component, and other components are added thereto. A mixture or the like can be used.

  In the muddy water treatment facility 80, particles such as clay and silt in the wastewater are aggregated by a flocculant to form a floc, and are deposited on the bottom together with the adsorbent on which heavy metals are adsorbed. This precipitate is sludge having a high concentration of heavy metals, and is called heavy metal concentrated sludge. The heavy metal concentrated sludge is collected from the bottom of the muddy water treatment facility 80 by a pump, transported to an industrial waste disposal site, and processed. Since the heavy metal concentrated sludge is less than the amount of dehydrated cake, the disposal cost can be reduced.

  In the turbid water treatment facility 80, the heavy metal concentrate sludge that precipitates at the bottom and the supernatant liquid thereon are separated. Since the supernatant liquid contains almost no particles such as clay and silt and heavy metals, it can be sent to the dilution water tank 65 as fresh water and circulated and used in the mud treatment system 40. At that time, surplus water can be discharged into sewers or the like as discharged water.

  The muddy water treatment using this muddy water treatment system 40 will be described with reference to the flowchart shown in FIG. Muddy water is prepared in the adjustment tank 46 of the muddy water treatment system 40, and the flocculant tank 61 and the like are filled with the flocculant and the like. The excavation is started by the shield machine 10, and in step 400, the supply pump 48 is activated to start supplying muddy water between the face and the partition wall. When excavation is started, excavated earth and sand are generated, so that the mud pump 47 is activated to discharge the excavated sediment, and discharge is started together with part of the mud water.

  The primary treatment facility is activated, and the muddy water is supplied to the pretreatment machine 41 by the mud discharge pump 47, and in step 405, gravel, consolidated soil and the like having a large particle size are separated and removed. Then, the muddy water passing through it is collected in the muddy water receiving tank 42 and supplied to the primary classifier 44. The primary classifier 44 separates and removes coarse particles by sieving and the cyclone 43 uses centrifugal force. Incidentally, the coarse particles recovered by the cyclone 43 are sent to the primary classifier 44.

  In step 410, the water injection apparatus 50 injects water with respect to the coarse particle part isolate | separated on the sieve which the pre-processing machine 41 and the primary classifier 44 have, and wash | cleans the particle | grains. As long as the adhering fine particles can be washed away, the water pressure and the time for washing may be any pressure and time.

  The particles on the sieve washed with water are placed on the belt conveyor 45 and carried to the earth and sand pit 51. The muddy water that has passed through the sieve contains fine particles and is sent to the adjustment tank 46. In step 415, the concentration, specific gravity, viscosity, etc. of the muddy water are adjusted in the adjustment tank 46, supplied to the shield machine 10 and reused, and the surplus is sent to the secondary processing equipment.

  In the secondary treatment facility, the surplus muddy water tank 60 receives the surplus muddy water. In step 420, the chemical is added to the surplus mud water, and heavy metals are extracted into the mud liquid in the extraction / removal tank 69. In step 425, the flocculant is added from the flocculant tank 61 and sent to the slurry tank 62, and the fine particles in the muddy water are aggregated by the flocculant in the slurry tank 62. The slurry containing the agglomerated fine particles is sent to the filter press 63. In step 430, pressure filtration is performed by the filter press 63 to dehydrate, and the solid content is discharged to the dewatered cake pit 71 as a dehydrated cake. Wastewater discharged by dehydration includes heavy metals.

In step 435, the waste water discharged from the filter press 63 is received by the raw water tank 81, carbon dioxide is added from the CO ₂ vaporizer 82, and the pH is adjusted by the carbon dioxide. Further, a flocculant is added from the flocculant tank 61 to aggregate the particles in the waste water. In step 440, an adsorbent is added from the adsorbent tank 84 to adsorb heavy metals in the waste water. The adsorbent on which the agglomerated particles and heavy metals are adsorbed is precipitated at the bottom of the muddy water treatment facility 80.

  In step 445, the heavy metal concentrated sludge precipitated on the bottom of the muddy water treatment facility 80 is collected, and the supernatant liquid is sent to the discharge water tank 83 as fresh water, and is sent from the discharge water tank 83 to the dilution water tank 65 for reuse. Excess water can be discharged into sewers and the like. The sludge can be collected when a certain amount of sludge is accumulated. This process is repeatedly performed until excavation by the shield machine 10 is completed. When the excavation is completed and there is no more muddy water to be processed, the muddy water treatment system 40 is stopped, and this processing is terminated in step 450.

  As described above, since only the water injection device 50 equipped with a general-purpose shower nozzle, a generally used chemical such as a chelating agent, and a heavy metal adsorbent are used, without using a special device, Heavy metals can be removed on site, and not only coarse particles but also fine particles can be reused as healthy soil. The turbid water treatment facility 80 discharges heavy metal-concentrated sludge, but it is a small amount compared to the amount of dehydrated cake, which can reduce the amount to be disposed as industrial waste, and reduce the disposal cost. Can be reduced.

  So far, the muddy water treatment system and the muddy water treatment method of the present invention have been described in detail with reference to the embodiments shown in the drawings. However, the present invention is not limited to the above-described embodiments, and other embodiments are described. It can be modified within the range that can be conceived by those skilled in the art, such as addition, change, deletion, etc., and any embodiment is included in the scope of the present invention as long as the operation and effect of the present invention are exhibited. is there.

DESCRIPTION OF SYMBOLS 10 ... Shield machine, 11 ... Waste mud pump, 12 ... Pre-processing machine, 13 ... Muddy water receiving tank, 14 ... Cyclone, 15 ... Primary classifier, 16 ... Belt conveyor, 17 ... Adjustment tank, 18 ... Surplus muddy water tank, 19 ... Coagulant tank, 20 ... Slurry tank, 21 ... Filter press, 22 ... Fresh water tank, 23 ... Dilution water tank, 24 ... Thickener dissolution tank, 25 ... Clay dissolution tank, 26 ... Mud storage tank, 27 ... Turbid water treatment equipment, 28 ... raw water tank, 29 ... CO ₂ vaporizer, 30 ... polymer dissolution tank, 31 ... discharged water tank, 40 ... mud processing system, 41 ... preconditioner, 42 ... mud receiving tank, 43 ... cyclone, 44 ... primary classifier 45 ... belt conveyor, 46 ... adjustment tank, 47 ... mud pump, 48, 49 ... supply pump, 50 ... water injection device, 51 ... earth and sand pit, 60 ... surplus mud tank, 61 ... flocculant tank, 62 ... slurry Tank, 63 ... filter 64, fresh water tank, 65 ... dilution water tank, 66 ... thickener dissolution tank, 67 ... clay dissolution tank, 68 ... mud storage tank, 69 ... extraction / removal tank, 70 ... chemical tank, 71 ... dehydrated cake pit, 72 ... centrifugal dehydrator, 73 ... rinsing tank, 80 ... turbid water treatment facility, 81 ... raw water tank, 82 ... CO ₂ vaporizer, 83 ... discharged water tank, 84 ... adsorbent tank

Claims (10)

A muddy water treatment system for treating muddy water containing earth and sand contaminated by heavy metals,
Separating means for separating particles of the earth and sand having a particle size of a predetermined size or more contained in the muddy water;
Water washing means for washing the separated particles,
An extraction means for adding a chemical to muddy water containing particles having a particle size less than a predetermined value after the particles have been separated, and extracting heavy metal adhering to the particles having a particle size less than the predetermined value in the muddy water;
A muddy water treatment system, comprising: dehydrating means for dewatering the muddy water.   The muddy water according to claim 1, further comprising: a second water washing means for washing the solid content obtained by dehydration; and a second dewatering means for dewatering the slurry containing the solid content formed by water washing. Processing system.   The muddy water treatment according to claim 2, further comprising heavy metal removal means for adsorbing the heavy metal contained in the waste water discharged from the dehydration means and the second dehydration means to an adsorbent and removing the heavy metal from the waste water. system.   The separating means is a vibration sieve, and the water washing means sprays water onto the particles having a particle size of the predetermined size or more separated on the sieve provided in the vibration sieve, thereby washing the particles. Item 4. The muddy water treatment system according to any one of Items 1 to 3.   A flocculant is added to the muddy water containing particles having a particle size less than the predetermined value on the downstream side of the extraction means, and the particles are discharged from the aggregating means, the dehydrating means, and the second dehydrating means. PH adjusting means for adjusting the pH of the waste water by adding an acid or alkaline gas or liquid to the waste water, and a second aggregating means for adding a flocculant to the waste water and aggregating particles contained in the waste water The mud treatment system according to claim 2 or 3, further comprising: A muddy water treatment method for treating muddy water containing earth and sand contaminated by heavy metals,
Separating the earth and sand particles having a particle size greater than or equal to a predetermined value contained in the muddy water;
Washing the separated particles with water;
Adding a chemical to muddy water containing particles having a particle size less than a predetermined value after the particles have been separated, and extracting heavy metal adhering to the particles having a particle size less than the predetermined value into a muddy water solution;
And a step of dewatering the muddy water.   The muddy water treatment method according to claim 6, further comprising a step of washing the solid content obtained by dehydration and a step of dehydrating a slurry containing the solid content formed by water washing.   The muddy water according to claim 7, further comprising a step of adsorbing the heavy metal contained in the wastewater discharged in the step of dehydrating the muddy water and the step of dehydrating the slurry to an adsorbent and removing the heavy metal from the wastewater. Processing method.   In the step of separating, a sieve is used, and in the step of washing with water, water is sprayed onto the particles having a particle diameter of the predetermined size or more separated on the sieve to wash the particles with water. The muddy water treatment method according to any one of the above.   Waste water discharged in the step of adding a flocculant to the muddy water containing particles having a particle size less than the predetermined after the extracting step, aggregating the particles, the step of dehydrating the muddy water, and the step of dehydrating the slurry The method further comprises a step of adding an acid or alkaline gas or liquid to the wastewater to adjust the pH of the wastewater, and a step of adding a flocculant to the wastewater to agglomerate particles contained in the wastewater. Or the muddy water treatment method of 8.