Contaminated soil washing equipment and contaminated soil washing method

Abstract

To provide compactified equipment for cleaning contaminated soil contaminated with heavy metals using iron powder and to speed up the cleaning process.SOLUTION: Contaminated soil cleaning equipment stirs and mixes contaminated slurry containing viscous soil contaminated with heavy metals and iron powder, and cleans the heavy metals in the viscous soil by making the iron powder adsorb the heavy metals to prepare cleaned slurry, and comprises an iron powder addition tank for adding the iron powder to the contaminated slurry, a continuous rapid agitation system for preparing iron powder-mixed slurry by allowing the iron powder-added contaminated slurry to pass through the system, and an iron powder separation system for separating the iron powder-mixed slurry into iron powder having adsorbed heavy metals and cleaned slurry. The continuous rapid agitation system is provided with a pipe for connecting the iron powder addition tank and the iron powder separation system and a rapid stirrer for continuous treatment which is connected to the pipe in line and stirs and mixes the contaminated slurry to which the passed iron powder has been added.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a contaminated soil washing facility that uses iron powder to wash contaminated soil contaminated with heavy metals, and a contaminated soil washing method using the contaminated soil washing facility. [Background technology]

[0002] For example, naturally occurring heavy metal-contaminated soil generated during shield or tunnel construction, etc., is often clayey soil containing a large amount of fine particles. Therefore, the inventors developed a method for washing heavy metal-contaminated soil using iron powder and heavy metal-contaminated soil washing equipment for use in the washing method, as a method for efficiently removing heavy metals such as arsenic contained in clayey soil, as shown in Patent Document 1.

[0003] The heavy metal-contaminated soil washing facility in Patent Document 1 is equipped with three or more heavy metal removal devices, each consisting of a heavy metal adsorption tank and a centrifuge, as a means for purifying contaminated soil by stirring and mixing contaminated muddy water and iron powder. Each heavy metal removal device performs the following tasks: stirring and mixing the contaminated muddy water and iron powder, recovering the iron powder by centrifuging the muddy water containing iron powder, recovering the iron powder that has been centrifuged, and supplying new contaminated muddy water. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6458635 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the contaminated soil washing equipment of Patent Document 1, contaminated muddy water can be effectively purified using a heavy metal removal device. However, the work of purifying contaminated muddy water using a heavy metal removal device takes several tens of minutes to several hours, so three or more heavy metal removal devices with the same capacity are needed to handle the amount of contaminated muddy water generated per hour by the construction work, which requires a large installation space.

[0006] Furthermore, if the heavy metal adsorption tank used to stir and mix the polluted muddy water with iron powder is enlarged in order to purify large amounts of polluted muddy water, the degree of mixing of the two is likely to vary, creating problems with purification performance.

[0007] The present invention has been made in consideration of such problems, and its main purpose is to make the equipment for washing contaminated soil contaminated with heavy metals using iron powder more compact and to speed up the washing process. [Means for solving the problem]

[0008] In order to achieve this object, the contaminated soil washing equipment of the present invention is a contaminated soil washing equipment that stirs and mixes contaminated muddy water containing clayey soil contaminated with heavy metals with iron powder, washing the clayey soil by having the heavy metals adsorb to the iron powder, and produces washing muddy water.The equipment comprises an iron powder addition tank that adds the iron powder to the contaminated muddy water, a continuous rapid stirring system that produces iron powder-mixed muddy water by passing the contaminated muddy water with the iron powder added, and an iron powder separation system that separates the iron powder-mixed muddy water into the iron powder with the heavy metals adsorbed and the washing muddy water, and the continuous rapid stirring system is characterized by comprising a pipe that connects the iron powder addition tank and the iron powder separation system, and a rapid mixer for continuous treatment that is connected in-line to the pipe and stirs and mixes the contaminated muddy water with the iron powder added that has passed through.

[0009] The contaminated soil washing facility of the present invention is characterized in that the continuous rapid mixing system is provided with a plurality of the rapid mixers. In addition, the contaminated soil washing equipment of the present invention is characterized in that the iron powder separation system comprises a disposal centrifuge to which the iron powder mixed muddy water containing the iron powder that has been used repeatedly the number of times until it loses its ability to adsorb the heavy metals is supplied, and a circulation centrifuge to which the iron powder mixed muddy water containing the iron powder in a state that can be reused is supplied, and the circulation centrifuge is arranged so that the iron powder that has been separated by specific gravity can be supplied to the iron powder addition tank.

[0010] The contaminated soil washing equipment of the present invention comprises: The system includes a first electromagnetic valve provided upstream of the circulation centrifuge, a second electromagnetic valve provided upstream of the disposal centrifuge, and a control device for controlling the opening and closing of the first electromagnetic valve and the second electromagnetic valve, wherein the control device supplies the iron powder mixed muddy water containing the iron powder in a reusable state to the circulation centrifuge by opening the first electromagnetic valve and closing the second electromagnetic valve, and supplies the iron powder mixed muddy water containing the iron powder that has been repeatedly used the number of times until the disposal centrifuge loses its ability to adsorb heavy metals by closing the first electromagnetic valve and opening the second electromagnetic valve. The system further comprises a flow meter connected upstream of the first solenoid valve and the second solenoid valve to acquire an instantaneous flow rate of the iron powder mixed muddy water, and a sequence control unit that calculates an integrated flow rate based on the instantaneous flow rate acquired by the flow meter and sets the integrated flow rate at the point when the iron powder has been used repeatedly the number of times until it loses its ability to adsorb and immobilize the heavy metals as an upper flow rate limit value, and when the sequence control unit detects that the integrated flow rate has exceeded the upper flow rate limit value, the control device closes the first solenoid valve and opens the second solenoid valve, thereby supplying the iron powder mixed muddy water containing the iron powder that has been used repeatedly the number of times until it loses its ability to adsorb the heavy metals to the disposal centrifuge. The system further includes a cyclone pump connected upstream of the first electromagnetic valve and the second electromagnetic valve for pressure-feeding the iron powder mixed muddy water to the circulation centrifuge or the disposal centrifuge, and a sequence control unit that acquires the operating time of the cyclone pump and sets the operating time of the cyclone pump at the point in time when the cyclone pump has been used repeatedly the number of times until the iron powder loses its ability to adsorb and immobilize the heavy metals as an upper time limit, and when the sequence control unit detects that the operating time has exceeded the upper time limit, the control device closes the first electromagnetic valve and opens the second electromagnetic valve, thereby supplying the iron powder mixed muddy water containing the iron powder that has been used repeatedly the number of times until the iron powder loses its ability to adsorb the heavy metals to the disposal centrifuge.

[0011] The method for washing contaminated soil of the present invention comprises the steps of: In the iron powder addition tank, an iron powder addition process for adding iron powder to the contaminated muddy water containing clayey soil contaminated with heavy metals after adjusting the pH; From the iron powder addition tank The contaminated muddy water to which the iron powder has been added is A rapid mixer connected inline to the pipinga continuous purification step in which the heavy metals are continuously passed through the iron powder, agitated and mixed, to produce iron powder-mixed muddy water in which the heavy metals are adsorbed onto the iron powder; Passed through the rapid mixer The iron powder mixed mud water Feed into the iron powder separation system an iron powder separation step of separating the iron powder to which the heavy metals have been adsorbed and the washing muddy water by gravity; The present invention is characterized by comprising:

[0012] The method for washing contaminated soil of the present invention is the same as that of the method for separating iron particles from soil. The iron powder to which the heavy metals have been adsorbed is supplied to the iron powder adding tank, and in the iron powder adding step, The iron powder to which the heavy metals have been adsorbed and adding the contaminated muddy water after adjusting the pH.

[0013] According to the contaminated soil washing equipment and contaminated soil washing method of the present invention, a continuous rapid mixing system uses a rapid mixer for continuous processing connected to a piping inline. This allows the installation area of ​​the contaminated soil washing equipment to be significantly reduced and made more compact than when a batch mixer, which requires a mixing tank, is used to mix the contaminated muddy water and iron powder. This makes it possible to install the contaminated soil washing equipment even in narrow construction sites, easing construction requirements imposed by the site area.

[0014] Furthermore, the contaminated muddy water to which iron powder has been added is continuously passed through a rapid agitator for continuous treatment, agitating and mixing the water to produce iron powder-mixed muddy water in which heavy metals are adsorbed onto the iron powder. This makes it possible to clean large amounts of contaminated muddy water while significantly reducing the time required for purification compared to using a batch mixer.

[0015] Furthermore, rapid stirring of contaminated muddy water with added iron powder using an inline continuous treatment rapid mixer promotes the elution of heavy metals from contaminated soil contained in the contaminated muddy water into the gaps between soil particles. At the same time, the iron powder added to the contaminated muddy water can be dispersed homogeneously, improving the contact efficiency between the eluted heavy metals and the iron powder. This allows for the rapid production of iron powder-mixed muddy water in which the eluted heavy metals are adsorbed and fixed on the iron powder, making it possible to efficiently carry out the entire process of washing heavy metal-contaminated soil using iron powder in a short amount of time.

[0016] Furthermore, if multiple rapid agitators for continuous processing are installed in the continuous rapid agitation system, the contaminated muddy water with added iron powder can be agitated and mixed for a long period of time while it passes through the pipes, which further promotes the elution of heavy metals and makes it possible for the eluted heavy metals to be efficiently adsorbed and fixed onto the iron powder.

[0017] In addition, the iron powder separation system is provided with a disposal centrifuge and a circulation centrifuge, and the iron powder that has been repeatedly used the number of times until it loses its ability to adsorb heavy metals is discarded via the disposal centrifuge, and the iron powder in a reusable state is supplied to the iron powder addition tank via the circulation centrifuge. This makes it possible to continuously use the reusable iron powder without letting it sit dormant. [Effects of the Invention]

[0018] According to the present invention, by passing contaminated muddy water to which iron powder has been added through a continuous rapid mixing system using a rapid mixer for continuous treatment connected inline to a pipe, and mixing the water, the elution of heavy metals in the soil can be promoted while improving the contact efficiency between the eluted heavy metals and the iron powder, thereby enabling the rapid washing of soil contaminated with heavy metals using iron powder and the compactness of the equipment. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a diagram showing a contaminated soil washing facility according to the present embodiment. [Figure 2] FIG. 10 is a diagram showing another example of a continuous rapid stirring system installed in the contaminated soil washing facility in this embodiment. [Figure 3] FIG. 10 is a diagram showing another example of a control system provided in the contaminated soil washing facility according to the present embodiment. [Figure 4] FIG. 1 is a diagram showing a method for washing contaminated soil using the contaminated soil washing equipment in this embodiment (part 1). [Figure 5]FIG. 2 is a diagram showing a method for washing contaminated soil using the contaminated soil washing equipment in this embodiment (part 2). [Figure 6] FIG. 1 is a diagram showing the verification results of the effects obtained by rapidly stirring contaminated muddy water using the rapid stirrer for continuous treatment in this embodiment (part 1). [Figure 7] FIG. 2 is a diagram showing the verification results of the effect obtained by rapidly stirring contaminated muddy water using the rapid stirrer for continuous treatment in this embodiment (part 2). DETAILED DESCRIPTION OF THE INVENTION

[0020] This invention provides an apparatus and method for cleaning clayey soil contaminated with heavy metals contained in contaminated muddy water by repeatedly using iron powder, which has the ability to adsorb and fix heavy metals, until it loses this ability.By adopting an in-line mixing method in the process of stirring and mixing the iron powder and contaminated muddy water, the efficiency of the cleaning process is improved and the process is made faster.

[0021] The contaminated soil washing equipment of the present invention and the contaminated soil washing method using the contaminated soil washing equipment will be explained below with reference to Figures 1 to 7, taking as an example the case of treating heavy metals in clay soil contained in excess muddy water generated by a muddy water shield method with iron powder.

[0022] <<Contaminated soil cleaning equipment>> As shown in Figure 1, contaminated soil washing equipment 10 is an apparatus that uses iron powder F to wash clayey soil contaminated with heavy metals contained in contaminated mud, and is equipped with a mud storage tank 20, a pH adjustment tank 30, a heavy metal removal device 40, and a washing mud tank 80. In the following explanation of contaminated soil washing equipment 10, the upstream and downstream sides are defined based on the direction of movement of the iron powder F.

[0023] ≪≪Mud storage tank 20 and pH adjustment tank 30≫≫ The mud storage tank 20 is a tank that also serves as an excess mud tank in the mud treatment facility used in the mud shield construction method, and stores the contaminated mud W1 to be treated. The contaminated mud W1 is excess mud containing clayey soil containing heavy metals and soil particles smaller than 75 μm that are generated during the construction of the mud shield.

[0024] The sludge storage tank 20 is equipped with a specific gravity detector 21 that detects the specific gravity of the contaminated muddy water W1 stored therein. Also provided are a submersible pump 22 and a mud transport pipe 23 for supplying the contaminated muddy water W1 to the pH adjustment tank 30. As a result, the contaminated muddy water W1 stored in the sludge storage tank 20 is supplied to the pH adjustment tank 30 with its specific gravity always stably controlled and adjusted.

[0025] The pH adjustment tank 30 is a tank for adjusting the pH of the contaminated muddy water W1 supplied from the mud storage tank 20 via the mud transport pipe 23, and is provided with an adjuster reservoir 31 in which a pH adjuster R is stored, an agitator 32 for agitating the contaminated muddy water W1, a pH meter 33, and a water level gauge 34. The pH adjuster R may be any commonly used chemical, such as dilute sulfuric acid. A pump 35 and a supply pipe 36 are connected to the pH adjustment tank 30, and the contaminated muddy water W1, whose pH has been adjusted to neutral, is supplied to the heavy metal removal device 40 via the supply pipe 36.

[0026] ≪≪Heavy metal removal equipment 40≫ The heavy metal removal device 40 is a device that adds iron powder F to the pH-adjusted contaminated muddy water W1 and then performs continuous high-speed in-line stirring to adsorb the heavy metals onto the iron powder F, and is equipped with an iron powder addition tank 50, a continuous rapid stirring system 60, and an iron powder separation system 70. The contaminated soil washing facility 1 is significantly characterized by the inclusion of this continuous rapid stirring system 60.

[0027] <Iron powder addition tank 50> The iron powder addition tank 50 is a tank for adding iron powder F to the contaminated muddy water W1 supplied from the pH adjustment tank 30, and is provided with at least an iron powder tank 51, a precipitation suppression device 52, and a water level gauge 53.

[0028] The iron powder tank 51 is a tank that stores iron powder F and is positioned so that the iron powder F can be dropped into the iron powder addition tank 50. The iron powder F is used to adsorb and immobilize heavy metals that have eluted from the contaminated soil contained in the contaminated muddy water W1, and examples of heavy metals that can be adsorbed include arsenic, fluorine, boron, selenium, hexavalent chromium, cadmium, lead, and cyanide.

[0029] It is known that iron powder F has the ability to efficiently adsorb and fix heavy metals, but there is a limit to the amount of heavy metals it can absorb and fix, and it can be reused until that ability is exhausted. For this reason, the contaminated soil washing equipment 10 is designed to allow the iron powder F initially added to be reused. Details of this will be described later.

[0030] The precipitation suppression device 52 is a device for suppressing the precipitation of iron powder F so that the iron powder F added to the contaminated muddy water W1 stored in the iron powder addition tank 50 flows smoothly together with the contaminated muddy water W1 into the continuous rapid stirring system 60. Therefore, any device may be used as long as it can suppress the precipitation of iron powder F, and Figure 1 shows an example in which a stirring device is used.

[0031] <Continuous Rapid Mixing System 60> The continuous rapid stirring system 60 continuously stirs the contaminated muddy water W1 to which iron powder F has been added in the iron powder addition tank 50 at high speed in-line, uniformly dispersing the iron powder F in the contaminated muddy water W1. At the same time, the system is a device that dissolves heavy metals from the contaminated soil contained in the contaminated muddy water W1 into the gaps between soil particles, thereby efficiently bringing the eluted heavy metals into contact with the iron powder F and causing them to be adsorbed and fixed.

[0032] The system is structured to include a first pipe 61, a relay tank 62, and a second pipe 63. A rapid agitator 611 for continuous processing is connected in-line to the first pipe 61, which is provided between the iron powder addition tank 50 and the relay tank 62. A cyclone pump 631 is provided to the second pipe 63, which is provided between the relay tank 62 and the iron powder separation system 70.

[0033] Any agitator for continuous processing that can be connected in-line with the first pipe 61 may be used as the rapid agitator for continuous processing 611. For example, a high-speed rotary shear agitator 611a as shown in FIG. 1 or a line mixer 611b as shown in FIG. 2 may be used.

[0034] The high-speed rotation shearing type agitator 611a is a device that can efficiently disperse powder added to the fluid to be treated by forcibly passing the fluid through a high-speed rotation rotor and a fixed stator that meshes with it, thereby applying shearing force. For example, a device equipped with a high-speed rotation rotor having a slit shape with a groove width of about 2 to 8 mm is preferred, and a representative example is the Cavitron (registered trademark: manufactured by Pacific Machinery Works Co., Ltd.) with a built-in pump. Furthermore, a representative example of the line mixer 611b is the static mixer (manufactured by Noritake Co., Ltd.).

[0035] 1 illustrates a case where the high-speed rotational shear type agitator 611a is used alone, while FIG. 2 illustrates a case where the high-speed rotational shear type agitator 611a and the line mixer 611b are used in combination. However, this is not limited to this, and the line mixer 611b may be used alone, or multiple high-speed rotational shear type agitators 611a and multiple line mixers 611b may be provided. When the line mixer 611b is used, it is recommended to also install a pump for pressure-feeding the contaminated muddy water W1.

[0036] When these rapid agitators 611 for continuous processing are adopted, the high-speed rotary shear agitator 611a can ensure a great agitation and dispersion effect by the shear force generated between the rotor rotating at a peripheral speed of about 20 to 40 m / s and the fixed stator that meshes with it. Also, the line mixer 611b can ensure a great agitation and mixing effect by the division, conversion, and inversion actions of the fluid to be treated as it passes through various elements (partition plates) inside the device.

[0037] The relay tank 62 is a tank that relays the first pipe 61 and the second pipe 63, and temporarily stores the iron powder mixed muddy water W2 that flows down from the continuous treatment rapid mixer 611. The iron powder mixed muddy water W2 is muddy water in which most of the heavy metals eluted from the contaminated soil contained in the contaminated muddy water W1 are adsorbed by iron powder F. The iron powder mixed muddy water W2 temporarily stored in the relay tank 62 is then sucked into the cyclone pump 631 and pressure-fed to the iron powder separation system 70 via the second pipe 63. Note that the iron powder mixed muddy water W2 may be pressure-fed directly from the rapid mixer 611 to the iron powder separation system 70 without passing through the relay tank 62.

[0038] <Iron powder separation system 70 and cleaning mud tank 80> The iron powder separation system 70 comprises a first outflow pipe 71 whose base end is connected to the second pipe 63 and which has a branching section that branches in two directions along the way, a circulation centrifuge 72 provided at the tip of one of the branches, a disposal centrifuge 73 provided at the other tip, and a disposal sludge tank 74.

[0039] The first outflow pipe 71 is located downstream of the branching portion, and an electromagnetic valve V1 is provided between the first outflow pipe 71 and the circulation centrifuge 72, and an electromagnetic valve V2 is provided between the first outflow pipe 71 and the disposal centrifuge 73. As a result, the iron powder mixed muddy water W2 pumped through the second pipe 63 is supplied to either the circulation centrifuge 72 or the disposal centrifuge 73. The opening and closing operations of the electromagnetic valves V1 and V2 will be described later in connection with the control system 100.

[0040] Both the circulation centrifuge 72 and the disposal centrifuge 73 are devices that separate the iron powder mixed muddy water W2 supplied from the continuous rapid stirring system 60 based on specific gravity, and in this embodiment, a cyclone is used. A cyclone has the function of pouring a liquid containing solids or the like into a cylindrical container from the circumferential direction in a vortex pattern, causing the iron powder F, which has a high specific gravity, to collide with the inner wall of the cylindrical container through centrifugal force and separate downward, while discharging the remaining muddy water upward from the center of the cylinder.

[0041] As a result, the iron powder mixed muddy water W2 is gravity separated into an iron powder-containing separated matter containing iron powder F and unseparated soil particles, and cleaning muddy water W3 from which heavy metals have been removed. The iron powder-containing separated matter containing iron powder F and unseparated soil particles discharged by the disposal centrifuge 73 is stored in the disposal sludge tank 74.

[0042] Meanwhile, the iron powder F discharged from the circulation centrifuge 72 and the iron powder-containing separated matter, including soil particles that were not completely separated, are dropped into the iron powder addition tank 50. In other words, the iron powder F used to wash the contaminated muddy water W1 is added to the iron powder addition tank 50 from the circulation centrifuge 72. Therefore, the iron powder F in its initial state dropped from the iron powder tank 51 circulates through the iron powder addition tank 50, the continuous rapid stirring system 60, and the iron powder separation system 70, and can be used continuously without being left dormant.

[0043] The cleaning muddy water W3 discharged from the circulation centrifuge 72 and the disposal centrifuge 73 is both discharged into the cleaning muddy water tank 80. The cleaning muddy water tank 80 is a tank in which the cleaning muddy water W3 is stored, and is connected to the circulation centrifuge 72 and the disposal centrifuge 73 via a second outlet pipe 81.

[0044] Control System The contaminated soil washing facility 10 is also provided with a control system 100 as shown in Fig. 3. The control system 100 includes a first control device 110 that adjusts the flow rate of the cyclone pump 631, and a second control device 120 that monitors the number of times the iron powder F is used. It also includes a management device 130 that manages the performance of the rapid agitator 611 for continuous treatment and the cyclone pump 631.

[0045] <First control device> The first control device 110 is a device that controls the instantaneous flow rate of the iron powder mixed muddy water W2 that is pumped from the cyclone pump 631 to the circulation centrifuge 72, and is equipped with an inverter control unit 111 and a sequence control unit 112. The instantaneous flow rate of the cyclone pump 631 is controlled based on the instantaneous flow rate acquired by a flow meter F1 provided in the first outflow pipe 71 located downstream of the cyclone pump 631.

[0046] Therefore, the instantaneous flow rate that is desired to be set in the cyclone pump 631 is set in advance as a flow rate setting value in the sequence control unit 112. Then, while the contaminated soil washing equipment 10 is in operation, the instantaneous flow rate obtained by the flow meter F1 is converted into an appropriate signal and sent to the sequence control unit 112. Upon receiving this signal, the sequence control unit 112 constantly outputs a command signal to the inverter control unit 111 based on the observed value of the instantaneous flow rate and the preset flow rate setting value.

[0047] Based on this command signal, the inverter control unit 111 changes the rotation speed of the motor provided in the cyclone pump 631 and adjusts the flow rate so that the instantaneous flow rate becomes a preset flow rate value. As a result, the iron powder mixed muddy water W2 temporarily stored in the relay tank 62 is pumped by the inverter-controlled cyclone pump 631 to the circulation centrifuge 72 at a constant instantaneous flow rate.

[0048] <<Second control device>> The second control device 120 monitors the number of times the iron powder F has been repeatedly used. The number of times the iron powder F has been repeatedly used is determined based on the integrated flow rate based on the instantaneous flow rate obtained by the flow meter F1 provided in the first outflow pipe 71 located downstream of the cyclone pump 631, or based on the operating time of the cyclone pump 631.

[0049] Furthermore, the opening and closing operations of the electromagnetic valves V1 and V2 are controlled based on the monitoring results, and iron powder F that has been used repeatedly enough to lose its ability to adsorb and immobilize heavy metals is guided to the disposal centrifuge 73. The second control device 120 includes an inverter control unit 121 and a sequence control unit 122.

[0050] <When using flow meter F1 to measure the number of times iron powder F is used repeatedly> The accumulated flow rate at the point when the iron powder F has been used repeatedly the number of times (for example, 20 times) until it loses its ability to adsorb and immobilize heavy metals is set in advance as the upper flow rate limit in the sequence control unit 122. Then, while the contaminated soil washing equipment 10 is in operation, the instantaneous flow rate obtained by the flow meter F1 is converted into a signal as appropriate and sent to the sequence control unit 122.

[0051] Upon receiving this signal, the sequence control unit 122 calculates the integrated flow rate based on the received instantaneous flow rate, and outputs a command signal based on this integrated flow rate and a preset upper flow rate limit to the inverter control unit 121. Then, when the integrated flow rate exceeds the upper flow rate limit (when the iron powder F has been used repeatedly enough times to lose its ability to adsorb and immobilize heavy metals), the sequence control unit 122 outputs a command signal to the inverter control unit 121 to close the solenoid valve V1 and open the solenoid valve V2. The inverter control unit 121 controls the solenoid valves V1 and V2 based on this command signal.

[0052] <When determining the number of times Iron Powder F has been used repeatedly based on the operating hours of Cyclone Pump 631> The operating time of the cyclone pump 631 at the point when the iron powder F has been used repeatedly the number of times (for example, 20 times) until it loses its ability to adsorb and immobilize heavy metals is set in advance as an upper time limit in the sequence control unit 122. Then, while the contaminated soil washing equipment 10 is in operation, the operating time obtained from the cyclone pump 631 is converted into a signal as appropriate and sent to the sequence control unit 122.

[0053] Upon receiving this signal, the sequence control unit 122 outputs a command signal based on the received operating time and a preset upper time limit to the inverter control unit 121. Then, when the operating time exceeds the upper time limit (when the number of times the iron powder F has been repeatedly used reaches the point where it loses its ability to adsorb and immobilize heavy metals), the sequence control unit 122 outputs a command signal to the inverter control unit 121 to close the solenoid valve V1 and open the solenoid valve V2. The inverter control unit 121 controls the solenoid valves V1 and V2 based on this command signal.

[0054] As a result, the iron powder mixed muddy water W2 containing iron powder F that has lost its ability to adsorb and immobilize heavy metals is supplied from the continuous rapid stirring system 60 to the disposal centrifuge 73. In the initial state, the electromagnetic valve V1 is open and the electromagnetic valve V2 is closed, so that the iron powder mixed muddy water W flows into the circulation centrifuge 72.

[0055] ≪Management device≫ The management device 130 is a device that grasps the health of the rapid agitator 611 and cyclone pump 631 for continuous processing, and the cumulative processing flow rate of the contaminated mud water W1 supplied from the mud storage tank 20 to the pH adjustment tank 30, and is equipped with an output unit 131 and a sequence control unit 132.

[0056] The integrity of the continuous treatment rapid mixer 611 and cyclone pump 631 is evaluated based on the minimum required differential pressure. For this reason, the contaminated soil washing facility 10 is provided with pressure gauges P1 and P2 on the upstream and downstream sides of the continuous treatment rapid mixer 611 in the first piping 61. In addition, pressure gauges P3 and P4 are provided on the upstream and downstream sides of the cyclone pump 631 in the second piping 63. The cumulative treatment flow rate of the contaminated muddy water W1 is managed based on the instantaneous flow rate obtained by a flow meter F2 installed in the mud transport pipe 23.

[0057] <<Integrity of the rapid agitator 611 and cyclone pump 631 for continuous processing>> The minimum required differential pressures for the rapid agitator 611 and the cyclone pump 631 for continuous treatment are set in advance in the sequence control unit 132. Then, while the contaminated soil washing equipment 10 is in operation, the pressure values ​​acquired by the pressure gauges P1 to P4 are converted into appropriate signals and sent to the sequence control unit 132.

[0058] Upon receiving this signal, the sequence control unit 132 constantly calculates the differential pressure of the rapid mixer 611 for continuous processing using pressure gauges P1 and P2 and monitors the differential pressure fluctuations. Similarly, the sequence control unit 132 calculates the differential pressure of the cyclone pump 631 using pressure gauges P3 and P4 and monitors the differential pressure fluctuations. If these differential pressure fluctuations do not satisfy a preset minimum required differential pressure, a command signal is output to the output unit 131, and warning information, for example, is output via the output unit 131 to the administrator terminal 200 or the like.

[0059] <<Cumulative treatment flow rate of contaminated muddy water W1>> While the contaminated soil washing equipment 10 is in operation, the instantaneous flow rate acquired by the flow meter F2 is converted into an appropriate signal and sent to the sequence control unit 132. Upon receiving this signal, the sequence control unit 132 constantly calculates the cumulative flow rate based on the received instantaneous flow rate and outputs a command signal to the output unit 131, which outputs the cumulative flow rate as the treatment cumulative flow rate of the contaminated muddy water W1 to the administrator terminal 200 or the like via the output unit 131.

[0060] <<Contaminated soil cleaning method using contaminated soil cleaning equipment 10>> The procedure for washing contaminated soil contained in contaminated muddy water W1 using the contaminated soil washing equipment 10 having the above configuration will be described below with reference to Figures 4 and 5. Note that the number of times the iron powder F is repeatedly used is determined by the operating time of the cyclone pump 631, and an example is given in which a high-speed rotary shear type agitator 611a with a built-in pump is used as the rapid agitator 611 for continuous treatment connected in-line to the first pipe 61.

[0061] <Pretreatment process> Prior to washing the contaminated soil contained in the contaminated muddy water W1, the specific gravity is adjusted by adding water to the contaminated muddy water W1 stored in the mud storage tank 20, and the amount of iron powder F to be used is set according to the specific gravity.

[0062] Furthermore, when the first control device 110 performs inverter control of the instantaneous flow rate of the cyclone pump 631, the flow rate setting value of the instantaneous flow rate is set in the sequence control unit 112. Furthermore, when the second control device 120 manages the number of repetitions of the iron powder F, the operating time of the cyclone pump 631 at the point when the iron powder F has been used the number of times until it loses its ability to adsorb and immobilize heavy metals is set in the sequence control unit 122 as an upper time limit.

[0063] ≪pH adjustment process≫ As shown in Figure 4(a), contaminated muddy water W1 is supplied to the pH adjustment tank 30 via the mud transport pipe 23, and a pH adjuster stored in the adjuster storage section 31 is added. These are stirred with the stirring device 32, and the pH of the contaminated muddy water W1 is adjusted to neutral. At this time, the management device 130 described in Figure 2 is used to constantly monitor the cumulative treatment flow rate based on the instantaneous flow rate of the contaminated muddy water W1 supplied from the mud storage tank 20 to the pH adjustment tank 30.

[0064] <Iron powder addition process> The contaminated muddy water W1 whose pH has been adjusted in the pH adjustment tank 30 is supplied to the iron powder addition tank 50 via the supply pipe 36. Furthermore, the initial iron powder F stored in the iron powder tank 51 is dropped into the iron powder addition tank 50, and the iron powder F is added to the contaminated muddy water W1. At this time, the precipitation suppression device 52 is operated to suppress the precipitation of the iron powder F in the iron powder addition tank 50 while the addition work is being carried out.

[0065] <Continuous purification process> In the continuous purification process, contaminated muddy water W1 to which iron powder F has been added in an iron powder addition tank 50 is supplied to a continuous rapid stirring system 60, and heavy metals in the contaminated soil contained in the contaminated muddy water W1 are adsorbed by the iron powder F to produce iron powder-mixed muddy water W2.

[0066] 4(b), the contaminated muddy water W1 to which iron powder F has been added and stored in the iron powder addition tank 50 is sucked by a pump (not shown) of the high-speed rotary shear type agitator 611a connected in-line to the first pipe 61. In this way, the contaminated muddy water W1 is forced to pass between the high-speed rotary rotor and the fixed stator meshing with it in the high-speed rotary shear type agitator 611a, and a strong shear force is applied to the contaminated muddy water W1.

[0067] As described above, this promotes the elution of heavy metals in the contaminated soil contained in the contaminated muddy water W1 into the gaps between the soil particles, while the iron powder F added to the contaminated muddy water W1 is uniformly dispersed. This allows the eluted heavy metals and the iron powder F to come into efficient contact with each other, producing iron powder-mixed muddy water W2 containing iron powder F with the heavy metals adsorbed and fixed thereon, which is then discharged from the high-speed rotary shear-type agitator 611a.

[0068] The iron powder mixed muddy water W2 discharged from the high-speed rotary shear type agitator 611a passes through the relay tank 62, is sucked into the cyclone pump 631 provided in the second pipe 63, and is pressure-fed to the iron powder separation system 70. These processes are performed while constantly monitoring the health of the high-speed rotary shear type agitator 611a and the cyclone pump 631 using the management device 130 described in FIG.

[0069] <Iron powder separation process> In the iron powder separation process, iron powder F is separated from the iron powder mixed muddy water W2 pumped into the first outflow pipe 71 of the iron powder separation system 70, and the iron powder F that has been used repeatedly the number of times until it loses its ability to adsorb and fix heavy metals is discarded, while the reusable iron powder F is dropped into the iron powder addition tank 50 for reuse.

[0070] As described above, the iron powder F contained in the iron powder mixed muddy water W2 is reused repeatedly, so in the initial state, the electromagnetic valve V1 provided in the first outlet pipe 71 is open and the electromagnetic valve V2 is closed. Therefore, the iron powder mixed muddy water W2 that flows into the first outlet pipe 71 first passes through the electromagnetic valve V1 and flows into the circulation centrifuge 72. In the circulation centrifuge 72, the iron powder mixed muddy water W2 is gravity-separated into an iron powder-containing separated matter that includes the iron powder F and soil particles that were not completely separated, and washing muddy water W3 from which heavy metals have been removed.

[0071] The cleaning muddy water W3 is stored in the cleaning muddy water tank 80 via the second outflow pipe 81. Meanwhile, the iron powder-containing separated matter, which includes iron powder F and soil particles that were not completely separated, is dropped into the iron powder addition tank 50. Since new contaminated muddy water W1 is supplied to the iron powder addition tank 50 from the pH adjustment tank 30, the iron powder F dropped from the circulation centrifuge 72 is added to this new contaminated muddy water W1 and is reused. At this time, the iron powder tank 51 is closed, and no new iron powder F is dropped into the iron powder addition tank 50.

[0072] The above procedure is carried out continuously as long as the contaminated muddy water W1 is supplied from the mud storage tank 20 to the pH adjustment tank 30. These processes are carried out using the first control device 110 described in Figure 3, while inverter control is used to ensure that the instantaneous flow rate of the iron powder mixed muddy water W2 flowing from the cyclone pump 631 into the circulation centrifuge 72 is equal to a preset flow rate setting value. In addition, the second control device 120 is used to monitor the number of times the iron powder F is repeatedly used, and the opening and closing operations of the electromagnetic valves V1 and V2 provided in the first outflow pipe 71 are carried out under inverter control.

[0073] <Iron powder disposal process> When the second control device 120 detects that the iron powder F has been used repeatedly enough times to lose its ability to adsorb and immobilize heavy metals, the solenoid valve V1 closes and the solenoid valve V2 opens. As a result, as shown in Figure 5(a), the iron powder-mixed muddy water W2 that has flowed into the first outlet pipe 71 passes through the disposal centrifuge 73 and is gravity-separated into an iron powder-containing separated matter that includes the iron powder F and any soil particles that have not been separated, and washing muddy water W3 from which the heavy metals have been removed.

[0074] Therefore, the cleaning muddy water W3 is stored in the cleaning muddy water tank 80 via the second outflow pipe 81, and the iron powder-containing separated matter, which includes iron powder F and soil particles that were not completely separated, is disposed of in the disposal sludge tank 74. Even during this disposal process of the iron powder F, the contaminated muddy water W1 is being supplied from the storage tank 20 to the iron powder addition tank 50 via the pH adjustment tank 30, so that initial iron powder F is dropped in and added from the iron powder tank 51. Thereafter, as shown in Figure 5(b), the above procedure is repeated to continuously purify the contaminated muddy water W1 and obtain cleaning muddy water W3.

[0075] The contaminated soil washing facility 10 having the above configuration employs a high-speed rotary shear mixer 611a connected inline to the first pipe 61 in the continuous rapid mixing system 60. This allows the installation area of ​​the contaminated soil washing facility 10 to be significantly reduced and made more compact than when a batch mixer requiring a tank is used to mix the contaminated muddy water W1 and iron powder F. This makes it possible to install the contaminated soil washing facility 10 even in a narrow construction site, easing construction conditions imposed by the site area.

[0076] Furthermore, the contaminated muddy water W1 with added iron powder F is continuously passed through the high-speed rotary shear type agitator 611a to mix and stir, thereby producing iron powder mixed muddy water W2 in which heavy metals are adsorbed onto the iron powder F. Therefore, compared to using a batch type mixer, it is possible to clean a large amount of contaminated muddy water W1 while significantly reducing the time required for purification.

[0077] Furthermore, rapid stirring of the contaminated muddy water W1 to which iron powder F has been added using the high-speed rotary shear-type mixer 611a promotes the elution of heavy metals in the contaminated soil contained in the contaminated muddy water W1 into the gaps between the soil particles. At the same time, the iron powder F added to the contaminated muddy water W1 can be uniformly dispersed, improving the contact efficiency between the eluted heavy metals and the iron powder F. This makes it possible to quickly produce iron powder-mixed muddy water W2 in which the eluted heavy metals are adsorbed and fixed by the iron powder F, and enables the entire process of washing soil contaminated with heavy metals using iron powder F to be carried out efficiently in a short amount of time.

[0078] The following experiment was conducted to verify the effect of promoting the leaching of heavy metals and improving the adsorption efficiency of iron powder obtained by rapidly stirring the contaminated muddy water W1 using a rapid mixer 611 for continuous processing, including the above-mentioned high-speed rotary shear type mixer 611a.

[0079] <Experiment 1: Comparison of soil elution reduction rates> In Experiment 1, contaminated muddy water W1 with added iron powder F was stirred and mixed, and the muddy water was collected after treatment. The amount of soil leaching (the amount of specific hazardous substances leached when water is added to soil) was analyzed to verify the purification effect.

[0080] The equipment used for the agitation and mixing process included three types of rapid agitators 611 for continuous processing: a high-speed rotary shear agitator 611a (two types: large and small gap) and a line mixer 611b. The test method for collecting treated muddy water involved adding 0.52 kg of iron powder to 40 L of contaminated muddy water W1 and passing it through the rapid agitator 611 for continuous processing at a specified flow rate. This process of collecting treated muddy water after the flow rate stabilized was then repeated three times. The flow rate was set to 28.3 L / min for the high-speed rotary shear agitator 611a and 16.6 L / min for the line mixer 611b using a Mohno pump. The above process was repeated three times (three cases) with the contaminated muddy water W1 replaced.

[0081] As a comparative example, the treated muddy water was also obtained by pumping the above-mentioned iron powder-added muddy water with a slurry pump without stirring and mixing, using the same procedure. The flow rate during the test was set to 16.6 L / min. As a comparative example, treated muddy water was also obtained by stirring and mixing using a batch mixer with a stirring tank, in addition to the case of pumping with a slurry pump. The test method for obtaining treated muddy water was to add 300 L of contaminated muddy water W1 and 3.85 kg of iron powder to the stirring tank of the batch mixer, and stir for 120 minutes using the stirring device attached to the stirring tank. Treated muddy water was sampled every 30 minutes during stirring.

[0082] The results of calculating the reduction rate of soil leaching from the test muddy water obtained in the above test [(initial soil leaching rate - post-treatment soil leaching rate) ÷ initial soil leaching rate] are shown in Figures 6(a) and 6(b). Figure 6(a) shows the results for a comparative example in which a batch mixer using a mixing tank was used for agitation and mixing. Figure 6(b) shows the results for a comparative example in which the soil was pumped using a slurry pump, and for agitation and mixing using the rapid mixer 611 for continuous treatment employed in the contaminated soil washing facility 10. Note that in Figure 6(b), the reduction rate for each treatment cycle is the average value for three cases in which the contaminated muddy water W1 was replaced.

[0083] Looking at the case where a batch mixer was used in Figure 6(a), the reduction rate was low at around 10-20% 30 minutes after treatment, and it can be seen that the reduction rate increases as time goes on. Also, looking at the comparative example in Figure 6(b), where the slurry was pumped (without stirring and mixing) the reduction rate remained at around 30-40% for all three passes. Although this is higher than the reduction rate 30 minutes after treatment when a batch mixer was used, it cannot necessarily be said that high purification performance was obtained.

[0084] On the other hand, when the rapid agitator 611 for continuous processing shown in Figure 6(b) is used, it can be seen that all three types achieve a reduction rate of over 60% in the first run, demonstrating significantly higher purification performance than the comparative examples. In particular, when the high-speed rotation shear type agitator 611a (large gap) is used, the soil elution reduction rate is 70-80% in a single rapid agitation run, demonstrating even higher purification performance. Therefore, it is preferable to use the high-speed rotation shear type agitator 611a (large gap) as the rapid agitator 611 for continuous processing.

[0085] 6(b), it can be seen that the reduction rate tends to improve as the number of treatments increases. Therefore, as explained with reference to FIG. 2, by appropriately combining multiple high-speed rotary shear mixers 611a and line mixers 611b to use multiple mixers as rapid mixers 611 for continuous treatment, and by stirring and mixing these for a long period of time while the contaminated muddy water to which iron powder has been added passes through the first pipe 61, it is possible to further promote the elution of heavy metals.

[0086] Furthermore, since the number of rapid mixers 611 can be increased or decreased without affecting the installation area of ​​the contaminated soil washing equipment 10, the number can be determined appropriately according to various conditions, such as the state of contamination of the clayey soil by heavy metals, and the mixing time can be easily adjusted to suit the state of contamination.

[0087] <Experiment 2: Comparison of changes in filtrate concentration and soil elution amount> In Experiment 2, arsenic-contaminated water was used as the contaminated muddy water W1, and was stirred with the rapid mixer 611 in two patterns, with and without the addition of iron powder F. The filtrate was then extracted and the changes in arsenic concentration and the changes in the amount of soil elution were observed. As a comparative example, a similar test was conducted using slow shaking and stirring.

[0088] Looking at the transition of the filtrate concentration in Figure 7(a), when compared to slow shaking and stirring, when rapid stirring is performed using the rapid stirrer 611, the arsenic concentration in the filtrate increases when iron powder F is not added, and when iron powder F is added, the filtrate concentration decreases in a short time. Figure 7(b)When examining the trends in soil elution, similar to the arsenic concentration in the filtrate, the amount of soil elution increases when iron powder F is not added, but decreases in a short period of time when iron powder F is added.

[0089] In other words, when rapid mixing is performed with the rapid mixer 611, the addition of energy promotes the elution of arsenic, while the eluted arsenic comes into efficient contact with the iron powder F, allowing the arsenic to be adsorbed and removed. Therefore, it was confirmed that when rapid mixing is performed using the rapid mixer 611, arsenic-contaminated soil can be purified in a shorter time than with slow shaking and mixing.

[0090] The contaminated soil washing facility 10 and the contaminated soil washing method of the present invention are not limited to the above-described embodiment, and various modifications are possible within the scope of the present invention.

[0091] For example, in this embodiment, the contaminated muddy water W1 is exemplified as excess muddy water generated during a muddy water shield construction method, but the present invention is not limited to this. The present invention can also be applied to muddy water generated during construction of a muddy water construction method such as a continuous underground wall construction method, or muddy water generated from a classification and washing facility for purifying excavated contaminated soil. [Explanation of symbols]

[0092] 10. Contaminated soil washing equipment 20 Sludge tank 21 Specific gravity detector 22 Submersible pump 23 Sludge pipe 30 pH adjustment tank 31 Adjustment agent storage section 32 Stirring device 33 pH meter 34 Water level gauge 35 Pump 36 Supply pipe 40 Heavy metal removal equipment 50 Iron powder addition tank 51 Iron powder tank 52 Sedimentation suppression device 53 Water level gauge 60 Continuous Rapid Mixing System 61 First Pipe 611 Rapid Stirrer 611a High-speed rotary shear mixer 611b Line Mixer 62 Relay tank 63 Second Pipe 631 Cyclone Pump 70 Iron powder separation system 71 First Outlet Pipe 72 Circulating Centrifuge 73 Disposal Centrifuge 74 Sludge disposal tank 80 Cleaning mud tank 81 Second Outlet Pipe 100 Control System 110 First control device 111 Inverter control unit 112 Sequence control section 120 Second control device 121 Inverter control unit 122 Sequence control section 130 Management device 131 Output section 132 Sequence control section 200 Administrator terminal F Iron powder W1 Contaminated muddy water W2 Iron powder mixed muddy water W3 cleaning muddy water

Claims

1. A contaminated soil washing facility that mixes contaminated muddy water containing clayey soil contaminated with heavy metals with iron powder to wash the clayey soil by adsorbing the heavy metals in the clayey soil to the iron powder, and produces washing muddy water. an iron powder addition tank for adding the iron powder to the contaminated muddy water; a continuous rapid stirring system for generating iron-powder-mixed mud by passing the contaminated mud with the iron powder added thereto; an iron powder separation system that separates the iron powder-mixed muddy water into the iron powder to which the heavy metals have been adsorbed and the cleaning muddy water, The continuous rapid stirring system comprises: a pipe connecting the iron powder addition tank and the iron powder separation system; a rapid agitator for continuous treatment that is connected in-line to the piping and that agitates and mixes the contaminated muddy water to which the iron powder has been added that has passed through the piping; A contaminated soil washing facility comprising:

2. The contaminated soil washing facility according to claim 1, A contaminated soil washing facility characterized in that the continuous rapid mixing system is provided with a plurality of the rapid mixers.

3. The contaminated soil washing equipment according to claim 1 or 2, The iron powder separation system comprises: a waste centrifuge to which the iron powder mixed muddy water containing the iron powder that has been repeatedly used the number of times until it loses its ability to adsorb the heavy metals is supplied; a circulation centrifuge to which the iron powder mixed muddy water containing the iron powder in a reusable state is supplied, The contaminated soil washing facility is characterized in that the circulation centrifuge is arranged so as to be able to supply the iron powder separated by specific gravity to the iron powder addition tank.

4. In the contaminated soil washing equipment described in claim 3, a first electromagnetic valve provided upstream of the circulation centrifuge; a second electromagnetic valve provided upstream of the waste centrifuge; a control device for controlling opening and closing operations of the first electromagnetic valve and the second electromagnetic valve, The control device By opening the first electromagnetic valve and closing the second electromagnetic valve, the iron powder mixed muddy water containing the iron powder in a reusable state is supplied to the circulation centrifuge; This contaminated soil washing facility is characterized in that by closing the first electromagnetic valve and opening the second electromagnetic valve, the waste centrifuge is supplied with the iron powder mixed muddy water containing the iron powder that has been used repeatedly the number of times until it loses its ability to adsorb the heavy metals.

5. In the contaminated soil washing equipment described in claim 4, a flow meter connected to the upstream side of the first electromagnetic valve and the second electromagnetic valve, for measuring an instantaneous flow rate of the iron powder mixed muddy water; a sequence control unit that calculates an integrated flow rate based on the instantaneous flow rate acquired by the flow meter, and sets the integrated flow rate at the point when the iron powder has been used repeatedly the number of times until it loses its ability to adsorb and immobilize the heavy metals as a flow rate upper limit value; The control device When the sequence control unit detects that the integrated flow rate has exceeded the upper flow rate limit, the first electromagnetic valve is closed and the second electromagnetic valve is opened, thereby supplying the waste centrifuge with the iron powder mixed muddy water containing the iron powder that has been used repeatedly the number of times until the iron powder loses its ability to adsorb the heavy metals.

6. In the contaminated soil washing equipment described in claim 4, a cyclone pump connected to the upstream side of the first electromagnetic valve and the second electromagnetic valve, for pressure-feeding the iron powder mixed muddy water to the circulation centrifuge or the disposal centrifuge; a sequence control unit that acquires an operation time of the cyclone pump and sets the operation time of the cyclone pump at a time when the cyclone pump has been repeatedly used a number of times until the iron powder loses its ability to adsorb and immobilize the heavy metals as an upper time limit value; The control device When the sequence control unit detects that the operating time has exceeded the upper time limit, the first electromagnetic valve is closed and the second electromagnetic valve is opened, thereby supplying the waste centrifuge with the iron powder mixed muddy water containing the iron powder that has been used repeatedly the number of times until the waste centrifuge loses its ability to adsorb the heavy metals.

7. An iron powder addition step of adding iron powder to contaminated muddy water containing clayey soil contaminated with heavy metals after pH adjustment in an iron powder addition tank; a continuous purification process in which the contaminated muddy water to which the iron powder has been added from the iron powder addition tank is continuously passed through a rapid mixer connected in-line to a pipe to mix and stir the contaminated muddy water, thereby producing iron powder-mixed muddy water in which the heavy metals have been adsorbed onto the iron powder; an iron powder separation step in which the iron powder-mixed muddy water that has passed through the rapid agitator is supplied to an iron powder separation system and gravity-separated into the iron powder with the heavy metals adsorbed thereon and the washing muddy water; A method for washing contaminated soil, comprising:

8. In the method for washing contaminated soil described in claim 7, In the iron powder separation step, the iron powder to which the gravity-separated heavy metals are adsorbed is supplied to the iron powder addition tank; A method for washing contaminated soil, characterized in that in the iron powder addition step, the iron powder to which the heavy metals have been adsorbed and the contaminated muddy water after pH adjustment are added.

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