JP6909661B2 - Purification device - Google Patents

Description

The present invention relates to a purification apparatus.

Excavated soil generated by carrying out construction work on ground contaminated with heavy metals (for example, arsenic, cadmium, hexavalent chromium, mercury, selenium, lead, fluorine, boron) will be reclaimed from the sea surface as construction-generated soil. In some cases, it may be dealt with by using it as a raw material for cement as construction sludge, or carrying it out to a disposal site. In addition, the sea surface landfill is "a ministerial ordinance that establishes the criteria for waste containing metals, etc. to be discharged to the landfill site, etc. prescribed in Article 5, Paragraph 1 of the Law Enforcement Ordinance on Prevention of Marine Pollution, etc. and Maritime Disasters". It will be implemented based on the standards stipulated in (February 17, 1973, General Ordinance No. 6, Final Amendment: May 30, 2014, Ministry of the Environment Ordinance No. 19). However, the conventional treatment method has a limit in the disposal place and the disposal capacity.

On the other hand, based on the knowledge that a magnetic material such as iron powder adsorbs a heavy metal, a method of recovering the magnetic material by a superconducting magnet separator after adsorbing the heavy metal on the magnetic material, or a method of collecting muddy water containing the heavy metal and the magnetic material is used. A method has been proposed in which heavy metals are adsorbed on the magnetic material by mixing and then the magnetic material is recovered by a centrifuge. However, superconducting magnet separators and centrifuges cannot be used at construction sites where installation space cannot be secured due to the large scale of the equipment. Moreover, since the device itself is expensive, the cost is high.

The applicant applies to a mixing tank that mixes muddy water containing heavy metal and a magnetic material to adsorb the heavy metal to the magnetic material, a magnetic force separating device that separates the magnetic material from the mixture obtained in the mixing tank by magnetic force, and magnetic force. A purification device including a return line for returning the magnetic material separated by the separation device to the mixing tank and a purification treatment method are disclosed (see Patent Document 1). According to this purification device, by repeatedly using a magnetic material and recovering the adsorption ability of the magnetic material to heavy metals as needed, muddy water containing heavy metals can be efficiently used even in a narrow space by using a small amount of magnetic material. Can be purified.

In a purification treatment method for adsorbing heavy metals such as arsenic in muddy water to a magnetic material, it is known that the concentration of heavy metals in muddy water can be reduced in a short time when the pH of muddy water is close to neutral. This is because when the pH is close to neutral, the rate of ionization on the surface of the magnetic material increases, and the formation of ferrihydrate (amorphous ferric hydroxide) that reacts with heavy metals is promoted. It is presumed. Another reason is that the distribution of the heavy metal itself between the solid phase and the liquid phase is also considered to shift to the solid phase side when the pH is close to neutral, and the effect of suppressing the amount of the heavy metal eluted is also obtained. Presumed to be one. On the other hand, muddy water is often weakly alkaline to alkaline. Therefore, in order to purify heavy metals in muddy water, it is desirable to lower (neutralize) the pH of muddy water.
Since it is a method for purifying the discharged soil by removing heavy metals from the discharged soil containing heavy metals such as low-concentration arsenic discharged from mountain tunnel construction and underground tunnel construction, the discharged soil is large and its treatment equipment. Various devices such as mixing tanks and contaminated water tanks have a large capacity. Although the amount of heavy metal to be recovered is very small, the amount of soil to be treated is large, the mixing tank which is the treatment tank has a large capacity, and a large amount of acid neutralizer used for pH adjustment is required.

As a method for neutralizing muddy water, it is conceivable to add a neutralizing agent to the mixing tank to lower the pH in the mixing tank. However, if an acidic neutralizing agent is added directly to the mixing tank, the surface of the magnetic material may be melted and the function of the magnetic material may be deteriorated. If the surface of the magnetic material melts, the purification function deteriorates, and heavy metals adsorbed on the surface of the magnetic material may re-elute.
On the other hand, Patent Document 2 discloses a detoxification treatment system for contaminated soil focusing on pH adjustment. This detoxification treatment system includes a pH adjuster that adjusts the pH of arsenic-containing muddy water to alkaline, an iron powder addition device that adds iron powder to the pH-adjusted muddy water to adsorb arsenic to the iron powder, and iron. It is equipped with a specific gravity separating device that separates specific gravity into muddy water that does not contain powder and muddy water that contains iron powder, and a magnetic separating device that collects iron powder using a permanent magnet.
Even if a pH meter is installed in the pH adjuster and the pH of the muddy water in the pH adjuster is lowered based on the measured value of this pH meter, the pH in the pH adjuster is not stable. When measured, neutralization may be insufficient even if a neutralizing agent is added based on the measured value of the pH meter. Increasing the residence time (mixing time of the neutralizing agent) in the pH adjuster stabilizes the pH of the muddy water in the pH adjuster, but in order to increase the residence time in the pH adjuster, the pH adjuster should be used. It needs to be large.

Japanese Unexamined Patent Publication No. 2016-068013 Japanese Unexamined Patent Publication No. 2016-144783

An object of the present invention is to adjust the pH environment in the mixing tank to be weakly acidic. In particular, it is an object to propose a compact purification apparatus for mixing an acidic neutralizing agent in a mixing tank for mixing the mud and the magnetic material containing heavy metals.

According to the present invention, the pH environment in the mixing tank is adjusted to be weakly acidic by supplying the muddy water during transportation in a state of being mixed with an acidic neutralizing agent before injecting the muddy water into the mixing tank. ..
The main configurations of the present invention are as follows.
In order to solve the above problems, the purification device of the present invention mixes a muddy water storage tank for storing muddy water containing heavy metals with the muddy water supplied from the muddy water storage tank and a magnetic material to obtain heavy metals. A magnetic separator that separates a mixture of the muddy water and the magnetic material that has adsorbed heavy metals into the magnetic material and the treated muddy water by magnetic force, and a magnetic material that supplies the magnetic material to the mixing tank. It is provided with a supply device and a magnetic material supply control device, and a merging stirring device for mixing a neutralizing agent into the muddy water supplied to the mixing tank is provided between the muddy water storage tank and the mixing tank. The magnetic material supply control device is interposed, and is characterized in that the magnetic material to be added to the mixing tank is controlled based on the specific gravity of the mixture in the mixing tank and the specific gravity of the treated muddy water or the muddy water containing the heavy metal. And.

According to the purification apparatus of the present invention, without supplying directly a neutralizing agent to the mixing tank was added in mud supply path such as a pipe, since supplying muddy water mixed with neutralizing agent to the mixing tank, neutralization The concentration gradient of the agent can be made small. The neutralizing agent can be sufficiently mixed by stirring in the mixing tank. Therefore, a large-scale pH adjusting device for sufficiently stirring the neutralizing agent is not required, and as a result, the device can be made compact. Further, since the neutralizing agent is not directly charged into the mixing tank but is charged into the mixing tank in a state of being mixed with muddy water, the neutralizing agent does not concentrate in a part of the mixing tank. Therefore, it is unlikely that the function of the magnetic material is deteriorated by the strongly acidic neutralizing agent, and the possibility that the adsorbed heavy metal is re-eluted is also low.
Further, since the pH of the mixture can be stabilized in an appropriate range in the mixing tank, the adsorption of heavy metals by the magnetic material is promoted. In particular, the appropriate pH value is weakly acidic, in the range of 5.0 to 7.0, preferably in the range of 5.5 to 6.5.
If the mixing tank is provided with a pH meter and further has a control means for controlling the supply of the neutralizing agent to the merging agitator according to the measured value of the pH meter, the inside of the mixing tank is provided. The pH of the mixture can be controlled to an appropriate value.
As the merging agitator, a agitator and a merging pipe connected to the agitator are suitable. The muddy water storage tank and the neutralizing agent storage tank for storing the neutralizing agent are connected to the combined pipe, the neutralizing agent is added to the muddy water in the confluence pipe, and the muddy water is combined with the muddy water by a stirring device. Stir with the neutralizer.
Further, by measuring the specific gravity, the magnetic substance concentration in the mixing tank can be controlled to maintain an appropriate magnetic substance concentration, and the purification function can be maintained.

According to the purification apparatus of the present invention, by using a compact apparatus stably neutralizing agent can be added and mixed into the mud, it can be performed detoxification treatment against mud containing heavy metals It becomes. In particular, it is practically effective processing apparatus for purification treatment of the low concentration of heavy metals-containing exhaust sediment generated from underground excavation, such as a tunnel.

It is the schematic of the purification apparatus which concerns on 1st Embodiment of this invention. It is a schematic diagram of a stirrer. It is a schematic diagram of a magnet separator. (A) shows the relationship between the stirring time of muddy water and iron powder having different pH and the liquid phase arsenic concentration, and (b) shows the relationship between the stirring time of muddy water and iron powder having different pH and the solid phase arsenic concentration. It is a graph. It is the schematic which shows the collection place of muddy water in an Example. It is a graph which shows the behavior of the pH of muddy water with respect to the pH setting value in a mixing tank. It is the schematic of the purification apparatus which concerns on 2nd Embodiment of this invention.

<First Embodiment>
Hereinafter, the case of purifying mud W _D generated by mud Shielded construction in ground that contains natural origin of arsenic (heavy metals). In the first embodiment, the purification device 1 shown in FIG. 1 is used. The heavy metal to be purified is not limited to arsenic, and may be, for example, cadmium, hexavalent chromium, mercury, selenium, lead, fluorine, boron and the like.
The purification device 1 of the present embodiment includes a muddy water storage tank 2, a merging stirring device 3, a mixing tank 4, a neutralizing agent storage tank 5, a magnetic force separation device 6, and a treated water storage tank 7. ..

Mud storage tank 2 is a tank for storing the mud W _D. The muddy water storage tank 2 is connected to the merging agitator 3 via the first transport pipe 81. First transport tube 81 is a conduit for transporting the mud W _D, the liquid feed pump P1 is provided. Mud W _D pooled in mud reservoir 2, the liquid feed pump P1, after being pumped to the merging stirring device 3 via a first transport tube 81, is supplied to the mixing tank 4.
The liquid feed pump P1 may be automatically controlled. That is, according to the change of the mixture W _DFN amount of mixing tank 4, automatically may be feeding a mud W _D to the mixing tank 4 from the mud storage tank 2, the preset flow rate it may be continuously feeding a mud W _D to the mixing tank 4 from the mud storage tank 2. Further, feeding the mud W _D from mud storage tank 2 to the mixing tank 4 may be performed periodically.

Merging stirrer 3 is intended to incorporate a neutralizing agent N in mud W _D supplied to the mixing tank 4. The combined stirring device 3 of the present embodiment is arranged between the muddy water storage tank 2 and the mixing tank 4, and includes a stirring device 31 and a joining pipe 32 connected to the stirring device 31. The first transport pipe 81 extending from the muddy water storage tank 2 and the second transport pipe 82 extending from the neutralizer storage tank 5 are connected to the combined pipe 32.
The neutralizing agent storage tank 5 is a tank for storing the neutralizing agent N. In this embodiment, liquid dilute sulfuric acid is used as the neutralizing agent N. The neutralizing agent N is pumped from the neutralizing agent storage tank 5 to the merging stirring device 3 via the second transport pipe 82 by the liquid feeding pump P2. The agent constituting the neutralizing agent N is not limited, and may be, for example, sulfuric acid.

And mud W _D that is pumped from the mud storage tank 2, a neutralizing agent N pumped from the neutralization agent reservoir 5, after merge at junction pipe 32, is supplied to the stirring device 31. As shown in FIG. 2, the stirring device 31 of the present embodiment is a so-called line mixer including a pipe body 33 and a stirring blade 34 arranged inside the pipe body 33. The liquid that has flowed into the stirring device 31 is stirred by flowing between the inner surface of the tubular body 33 and the stirring blade 34. The stirring device 31 is not limited to the line mixer (static mixer). Further, the merging stirring device 3 may have a power for rotating the stirring blade 34.

As shown in FIG. 1, a confluence pipe 32 is connected to one end (upstream side end) of the stirring device 31, and a third leading to the mixing tank 4 is connected to the other end (downstream side end) of the stirring device 31. The transport pipe 83 is connected. Mud W _D and neutralizer N supplied to the stirring device 31 passes through the stirring device 31 by the pressure of the liquid feed pump P1, P2. At this time, mud W _D with a neutralizing agent N and is agitated (mud W _D neutralizer into N by surrounding the flowing mud W _D and neutralizer N of stirring vanes 34 in the stirrer 31 It will be in a mixed state). A mixture of mud W _D which was stirred at a stirring device within 31 and neutralizer N (first mixture W _DN) is supplied to the mixing tank 4 through the third transport tube 83.

Mixing tank 4 is a tank for stirring and mixing the first mixture W _DN and iron powder (magnetic) P _F and a fixed residence time. By mixing the first mixture _{W DN} and iron powder _{P F,} arsenic contained in the first mixture _{W DN} (mud _{W D)} is adsorbed to the iron powder _{P F.} Iron powder P _F of this embodiment is the ability to adsorb the arsenic has been granted. Incidentally, the magnetic body to be used for the adsorption of arsenic (heavy metals) are not limited to iron powder P _F. In the mixing tank 4, pH control is performed, and a neutralizing agent is added based on the measured value of the pH meter 42.
Mixing tank 4 of this embodiment has a stirrer 41, the first mixture W _DN charged into the mixing tank 4 _(mud W _D) stirring the iron powder P _F. A fourth transport pipe 84 (transport pipe) leading to the magnetic force separation device 6 is connected to the mixing tank 4. The configuration of the stirrer 41 is not limited. For example, the number of agitators 41 provided in the mixing tank 4 is not limited, and may be appropriately determined.

Fourth transport tube 84 is a conduit for transporting the second mixture W _DFN obtained by mixing the first mixture W _DN and iron powder P _F. The second mixture W _DFN is pressure-fed to the magnetic force separator 6 via the fourth transport pipe 84 by the liquid feed pump P4 provided in the fourth transport pipe 84.
The mixing tank 4 of the present embodiment is provided with a pH meter 42. The pH meter 42 is connected to the control means 9 for controlling the neutralizing agent to be added, and outputs the measured value of the pH of _{the second mixture WDFN in the mixing tank 4 to the control means 9.} The control means 9 controls ON / OFF and the discharge amount of the liquid feed pump P2 according to the measured value of the pH meter 42, and adjusts the supply amount of the neutralizing agent N to the merging agitator 3.

Magnetic separator 6, the iron powder P _F from the second mixture W _DFN supplied from the mixing tank 4 is separated by a magnetic force. In the present embodiment, a general-purpose simple magnet separator is used as the magnetic force separating device 6. As shown in FIG. 3, for example, the magnet separator includes a magnet core 61, an outer cylinder 62 that covers the outer circumference of the magnet core 61, a roller 63 that squeezes water from _{the second mixture WDFN adhering to the outer cylinder 62, and the like.} and a scraper 64 peeling off the iron powder P _F where moisture is squeezed by the rollers 63 from the outer cylinder 62. The configuration of the magnetic force separating device 6 is not limited, and the magnetic separator 6 does not necessarily have to be a magnet separator.

As shown in FIG. 1, the magnetic field separation device 6 of the present embodiment is connected to the mixing tank 4 via the return means 65. Iron powder P _F taken peeled by the scraper 64 is returned to the mixing tank 4 through a return means 65. The return means 65 of the present embodiment includes a so-called screw feeder. The configuration of the return means 65 is not limited, and may be, for example, a belt conveyor. Further, by disposing the magnetic separator 6 above the mixing tank 4, when configured as an iron powder P _F taken peeled by the scraper 64 falls directly into the mixing tank 4, returning means 65 is omitted You may.
A fifth transport pipe 85 is connected to the magnetic force separating device 6. Fifth transport tube 85 is a pipe line for transporting the treated water W _S separated by magnetic separator 6 into treated water reservoir 7.

Treated water reservoir 7 is a tank for temporarily storing the treated water W _S discharged from the magnetic separator 6. In the present embodiment, the treated water storage tank 7 is arranged at a position lower than the magnetic force separator 6. Treated water W _S discharged from the magnetic separator 6 is sent to the treated water storage tank 7 by gravity flow through the fifth transport tube 85. In the case where the treated water reservoir 7 is not disposed at a position lower than the magnetic separator 6, by using the liquid feed pump or the like, it may be pumped treated water W _S.

Cleaning method using the cleaning device 1, first, the iron powder arsenic contained in mud W _D mud W _D in the mixing tank 4 _(the first mixture W _DN) and iron powder P _F by stirring thoroughly mixed adsorbed onto P _F (adsorption step). Note that the mud W _D to be supplied to the mixing tank 4 _(the first mixture W _DN), neutralizer N is mixed in the confluent stirrer 3. The amount of neutralizing agent N mixed into mud W _D is appropriately determined according to the magnitude of the pH value of the pH meter 42 mixing vessel 4 which is measured by. In the present embodiment, the neutralizing agent N is supplied so that the pH value in the mixing tank 4 is in the range of 5.0 to 7.0, preferably in the range of 5.5 to 6.5. The control means 9 supplies the neutralizing agent N when the pH value in the mixing tank 4 is large, and stops the supply of the neutralizing agent N when the pH value is small. Here, there is a risk that the value of pH in the mixing tank 4 is dissolved iron powder P _F falls below 5.0. If the value of pH in the mixing tank 4 exceeds 7.0, the rate of ionization in the surface of the iron powder P _F is decreased, the adsorption performance of the arsenic with iron powder may be lowered.

Next, a second mixture W _DFN from the mixing tank 4 is a mixture of the first mixture W _DN and iron powder P _F to the magnetic separator 6, for feeding through the fourth transport tube 84. _{The liquid transfer of the second mixture WDFN} from the mixing tank 4 to the magnetic force separating device 6 may be performed periodically at predetermined time intervals, or may be continuously performed according to the processing capacity of the magnetic force separating device 6. .. _{Further, the liquid feeding of the second mixture WDFN} from the mixing tank 4 to the magnetic force separating device 6 may be automatically controlled according to the processing capacity of the magnetic force separating device 6 or the like, or may be performed manually.
In magnetic separator 6 to separate the iron powder _{P F} from the second mixture _{W DFN} by the magnetic force of the magnet core 61 (separation step). Treated water W _S of detoxification is made by separating the iron powder P _F from the second mixture W _DFN flows down to the treated water reservoir 7 through the fifth transport tube 85. On the other hand, iron powder P _F which is separated from the second mixture W _DFN is returned to the mixing tank 4 through a return means 65.

According to the purification apparatus 1 of the present invention, in the mixing tank 4 it can be mixed thoroughly neutralizer N, mixing chamber can be reliably neutralized. Therefore, a large-scale pH adjusting device for sufficiently stirring the neutralizing agent N is not required, and as a result, the entire purification device 1 can be made compact. Moreover, since it is possible to stabilize the pH of the second mixture W _DFN in the mixing tank 4 with a suitable range, the adsorption of arsenic with iron powder P _F is promoted. Further, the neutralizing agent N is mixing tank 4 instead of directly injected in order to put into the mixing vessel 4 in a state mixed in the mud W _D, neutralizer N is concentrated on a part of the mixing vessel 4 Never. Therefore, the possibility that function is reduced iron powder P _{F (magnetic)} strongly acidic neutralizer N is low, less likely to adsorbed arsenic is re-dissolution.
_{Further, a pH meter 42 is provided in the mixing tank 4, and the pH of the second mixture WDFN} in the mixing tank 4 is set in order to set the supply amount of the neutralizing agent N according to the pH value in the mixing tank 4. Can be managed to be an appropriate value.

Hereinafter, as an example, the test results confirmed for the method of adjusting the pH of muddy water are shown.
First, a laboratory test was conducted for the purpose of clarifying the effect of high and low pH values of muddy water on the arsenic purification effect. In the laboratory test, the purification test (Examples 1 and 2) was carried out by adjusting the pH of the test muddy water prepared using naturally-derived arsenic-contaminated soil to 7.0 and 6.5. Further, as a comparative example, a purification test was also conducted on a sample in which the pH was not adjusted (Comparative Example 1) and a sample in which the pH was adjusted to 8.0 (Comparative Example 2).
The test muddy water was prepared by sieving the arsenic-contaminated soil with a 250 μm sieve, adding distilled water to the sieved portion and stirring well to adjust the specific density to 1.3. Dilute sulfuric acid was added to 250 mL of the prepared test muddy water to adjust the pH to a predetermined pH (8.0, 7.0, 6.5), and then iron powder having a weight of 5% of the weight of the muddy water was added and stirred. .. At this time, three pH-adjusted test muddy waters were prepared, and the stirring times were set to 5 minutes, 10 minutes, and 30 minutes, respectively. After stirring, iron powder (magnetic deposit) in the slurry of each test mud was recovered. The test muddy water from which iron powder had been removed was separated into solid and liquid by centrifugation, and the liquid phase was filtered through a 0.45 μm filter before analysis (liquid phase arsenic concentration). In addition, the solid phase was subjected to an elution test in which arsenic was eluted after air drying in a draft, and the eluate was used for analysis (solid phase arsenic elution amount). The test results are shown in FIGS. 4 (a) and 4 (b). The data of the stirring time of 0 minutes on the graphs shown in FIGS. 4 (a) and 4 (b) showed the analytical value (arsenic concentration) of the initial muddy water before the addition of dilute sulfuric acid.

As shown in FIGS. 4 (a) and 4 (b), 5% of iron powder was added to arsenic-contaminated muddy water whose pH was not adjusted, and after stirring for 30 minutes, both the liquid phase arsenic concentration and the solid phase arsenic elution amount were the reference values ( Purification to the soil environmental standard: 0.01 mg / L) could not be achieved (Comparative Example 1). Further, in Comparative Example 2 in which the pH was adjusted to 8.0, neither the liquid phase arsenic concentration nor the solid phase arsenic elution amount reached the reference values after stirring for 30 minutes. Further, in Example 1 in which the pH was adjusted to 7.0, the solid phase arsenic elution amount did not fall below the reference value even after stirring for 30 minutes, but the liquid phase arsenic concentration was the reference value (0) after 5 minutes of stirring the iron powder. It decreased to 0.01 mg / L) or less. On the other hand, in Example 2 in which the pH was adjusted to 6.5, both the liquid phase arsenic concentration and the solid phase arsenic elution amount were below the reference values by stirring the iron powder within 10 minutes. Therefore, it was confirmed that the purification of arsenic was promoted by lowering the pH to 7.0 or less, preferably 6.5 or less.

Next, the pH adjustment test of muddy water was conducted by the purification device 1 of the present embodiment.
^{First, 4 m 3 of} muddy water having a pH adjusted to 7 is stored in the mixing tank 4, and 5% of iron powder with respect to the weight of the muddy water is mixed therein, and the inflow amount from the muddy water storage tank 2 to the mixing tank 4 and the mixing tank 4 The muddy water was purified by setting the amount of outflow from the iron to the magnetic force separator 6 to 400 L / min. At the same time as the operation of the liquid feed pump P1, the liquid feed pump P2 was operated, and dilute sulfuric acid (neutralizing agent) was added to the muddy water in the confluence pipe 32 immediately before the stirring device 31. The amount of liquid to be fed was fixed to the amount required to bring the pH of the muddy water to 6.5. 8 m ³ of muddy water is continuously treated (20 minutes), and 10 minutes and 20 minutes after the start of the test, muddy water is collected at multiple points in the mixing tank 4 to measure the pH and arsenic concentration of the liquid phase. did. The muddy water was collected at five points: the upper right portion G1, the upper center G2, the upper left portion G3, the middle right portion G4, and the lower right portion G5 of the mixing tank 4 (see FIG. 5).
The test results are shown in Table 1.

As shown in Table 1, the pH of the muddy water in the mixing tank 4 shows a substantially constant value regardless of the location and time, and it is shown that the pH of the muddy water can be adjusted evenly by using the merging agitator 3. Was done. On the other hand, the pH of the mixing tank 4 was about 7 on average, which was slightly higher than the set value of 6.5. This is because the supply amount of the neutralizing agent is fixed, and the water on the surface of the iron powder comes into contact with a certain amount (equivalent to 5%) of iron powder existing in the muddy water in the mixing tank 4 and the neutralizing agent. It is considered that the cause is that ferrous oxide and the like were partially dissolved to ^{supply OH −. The OH −} supply rate (neutralization rate) from the iron powder, the supply of the neutralizing agent, and the residence time in the mixing tank 4 were balanced, and the pH was substantially constant. From these, it was found that it is important to control the pH value in a state where iron powder and muddy water are mixed.

Subsequently, a pH meter 42 was installed in the mixing tank 4, and when the pH of the mixing tank 4 was higher than the set value, a neutralizing agent was supplied (liquid feeding rate: 3.5 to 4.5 mL / L). The inflow amount from the muddy water storage tank 2 to the mixing tank 4 and the outflow amount from the mixing tank 4 to the magnetic force separator 6 were set to 150 L / min, respectively, and the test was continuously performed. FIG. 6 shows the relationship between the amount of muddy water treated in the muddy water storage tank 2, the mixing tank 4, and the merging agitator 3 and the pH in the muddy water.
As shown in FIG. 6, the pH error in the mixing tank 4 is kept within an error range of about 0.3 for a long period of time, and the pH of muddy water can be adjusted within a range that does not affect the purification treatment with iron powder. It could be confirmed. Therefore, by using the merging stirring device 3 composed of a line mixer or the like, the pH in the mixing tank 4 can be appropriately controlled without requiring a large-scale pH adjusting device, and by extension, the purification device 1 is compact. It is possible to make it.

Next, when the pH value is adjusted to 5.5 to 7.0, Table 2 shows the change in the arsenic concentration of the muddy water due to the pH adjustment.
As shown in Table 2, even when the initial concentration (arsenic concentration of inflowing muddy water) is 5 to 11 times the environmental standard value (= 0.01 mg / L), the pH is 5.5 to 7.0. It was confirmed that it is possible to surely purify the liquid phase arsenic concentration of muddy water to below the environmental standard value by adjusting it in the meantime.

<Second embodiment>
A second embodiment of the present invention is shown in FIG. In this embodiment, a device for controlling the amount of magnetic material newly added to the mixing tank 4 is added to the purification device 1 shown in FIG. 1 based on the specific gravity measurement.
The purification device 100 of the second embodiment includes a muddy water storage tank 2, a merging stirring device 3, a mixing tank 4, a neutralizing agent storage tank 5, a magnetic force separation device 6, a treated water storage tank 7, and a magnetic material supply. The device 10 and sampling holes 86 and 87 are provided.
The magnetic material content of the mixing tank 4 is within an appropriate range, or the specific gravity of the mixing tank 4 and the specific gravity of the muddy water (first mixture _WDN ) to which the neutralizing agent N is added before entering the mixing tank 4 or the treated water. specific gravity of W _S, to estimate the magnetic abundance present in the mixing tank 4, is to add-on magnetic if there is shortage (iron powder P _F).
In the present invention, a magnetic material is appropriately replenished to secure an appropriate amount in the mixing tank 4.
Formula to estimate the iron powder of mixing tank 4 in the case of using the iron powder P _F as a magnetic body may be as follows.
Amount of iron powder = (1 / Relative density of mixing tank-1 / Relative density of treated water) / (1 / Relative density of iron-1 / Relative density of treated water) x 100
When the specific gravity of the neutralizing agent-mixed muddy water (first mixture _WDN ) is used, the specific gravity of the treated water is replaced.

The specific gravity measurement is determined by volume and weight. There is also a floating type hydrometer for the specific gravity of the liquid, but since the iron powder mixed solution is a suspension, it is suitable to obtain it by volume and weight.
The specific gravity can be measured using the sampling hole 86 provided in the muddy water supply system, the sampling hole 87 provided in the treated water system, and the sample sampled from the mixing tank 4, and this measurement can be automated periodically. Based on this measured value, the amount of iron powder added from the magnetic material supply device 10 can be controlled.

Incidentally, the specific gravity of the mud W _D containing heavy metals-containing soil, such as arsenic is about 1.3, the heavy metal concentration is 0.1% or less iron powder P _F is a magnetic material to be mixed is mixed tank 4 It has a concentration of about 5%. Soil is basically discharged into the treatment liquid, and arsenic and the like adsorbed on the magnetic material are reintroduced together with the magnetic material, but the effect on the specific gravity is negligible. Further, when the magnetic material is recovered by a magnet separator or the like, some soil adheres, but the influence of the amount on the specific gravity can be ignored. Therefore, the significant effect on the specific gravity is the concentration of iron powder. In this respect, it is confirmed that the amount of iron powder in the mixing tank 4 matches the estimated amount by the specific gravity measurement and the actually measured amount.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and each of the above-mentioned components can be appropriately modified without departing from the spirit of the present invention.
In the above embodiment, the case where the muddy water generated in the muddy water type shield work is purified is described, but the present invention is not limited to the shield work.
A plurality of merging and stirring devices 3 may be installed.
A plurality of pH meters 42 may be arranged. By using a plurality of pH meters 42, it is possible to carry out periodic calibration and cross-check without stopping the purification process of muddy water.

1 Purification device 2 Muddy water storage tank 3 Confluence stirrer 31 Stirrer 32 Confluence pipe 4 Mixing tank 42 pH meter 5 Neutralizer storage tank 6 Magnetic separation device 7 Treated water storage tank 81-85 Transport pipe 86,87 Sampling hole 9 Control Means 10 Magnetic material supply device N Neutralizer _PF Iron powder (magnetic material)
W _D Muddy water _WDN first mixture (muddy water)
W _DFN second mixture (muddy water)
W _S Treated water

Claims (3)

A muddy water storage tank for storing muddy water containing heavy metals,
A mixing tank that mixes the muddy water supplied from the muddy water storage tank with a magnetic material and adsorbs a heavy metal to the magnetic material.
A magnetic separation device that separates the mixture of the muddy water and the magnetic material that has adsorbed heavy metals into the magnetic material and the treated muddy water by magnetic force.
A magnetic material supply device and a magnetic material supply control device that supply a magnetic material to the mixing tank ,
It is a purification device equipped with
A merging agitator for mixing the neutralizing agent into the muddy water supplied to the mixing tank is interposed between the muddy water storage tank and the mixing tank.
The magnetic material supply control device is a purification device, characterized in that it controls a magnetic material to be added to a mixing tank based on the specific gravity of a mixture in the mixing tank and the specific gravity of the treated muddy water or muddy water containing the heavy metal. A pH meter is provided in the mixing tank, and the mixing tank is provided with a pH meter.
Characterized in that it comprises a control means for controlling the supply of neutralizing agent to the merging stirring device in accordance with the measured value of the pH meter purifying apparatus according to claim 1. The merging agitator includes a agitator and a merging pipe connected to the agitating means.
The purification device according to claim 1 or 2 , wherein the muddy water storage tank and a neutralizing agent storage tank for storing the neutralizing agent are connected to the combined pipe. ..

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