JP2012035161A - Soil purification apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil purification apparatus capable of efficiently purifying soil.SOLUTION: The purification apparatus 10 includes a cathode electrode tank 12A, an anode electrode tank 12B and a voltage application device 14. The cathode electrode tank 12A includes: a first container 16A storing weak acid solution 20A; and a cathode electrode 18A arranged within the first container 16A and immersed in the weak acid solution 20A. The anode electrode tank 12B includes: a second container 16B storing electrolyte solution 20B; and an anode electrode 18B arranged within the second container 16B and immersed in the electrolyte solution 20B. The first container 16A and the second container 16B are constituted of porous ceramic in which a rate of gas cavities having 2 μm or less of diameter with respect to all gas cavities is 40% or more and a water permeability coefficient is ≥10cm/sec and ≤10cm/sec.

Description

  The present invention relates to a soil purification apparatus.

  If soil contaminated with heavy metals such as cadmium, copper, arsenic, and pollutants such as organic compounds is left as it is, the pollutants contained in the soil may be diffused by groundwater, biological chains, or the like. In particular, contamination by heavy metals such as cadmium in paddy fields is serious, and countermeasures are required.

As a method of purifying soil contaminated with such pollutants, excavating the soil to be purified, filling the electrolyte solution there and inserting a pair of electrodes, and applying a voltage between the electrodes, Methods for recovering contaminants are known (see, for example, Patent Documents 1 to 4).

In Patent Document 1, an electrode tank having water permeability is provided around an electrode to be inserted into soil, the pH in the electrode tank is measured, and the pH in the electrolytic tank is maintained within a certain range. A purification device that supplies a neutralizing agent according to the pH in the electrode tank has been proposed.
In Patent Document 2, an electrode is placed in an electrolytic cell composed of water-permeable filter paper or woven fabric, and a voltage is applied to the electrolytic cell to elute contaminants in the soil into water. An apparatus has been proposed in which the contaminants in the aqueous solution from which the contaminants are eluted are adsorbed and removed by an adsorbent and then returned to the electrolytic cell container.

Further, in Patent Document 3, an electrolytic cell having water permeability is provided around the cathode electrode, a pH high buffering capacity material is filled in the electrolytic cell, and a voltage is applied between the anode electrode and the soil. An apparatus for purifying the water has been proposed.
In Patent Document 4, a complexing agent is mixed in soil contaminated with heavy metal to complex the heavy metal, and a pair of electrodes covered with an adsorbent is formed in the soil containing the complexed heavy metal. An apparatus has been proposed in which a complex heavy metal is adsorbed on an adsorbent by arranging and applying a voltage between electrodes.

JP 2003-260458 A JP 2004-25149 A JP 2000-84366 A JP 2000-218261 A

However, even if a pair of electrodes covered with an adsorbent or a water-permeable container is inserted into the soil to be purified and a voltage is applied to these electrodes, such as clay contained in the soil is not subject to removal. In some cases, the contamination of the soil is not sufficiently performed due to the movement of the pollutant to be removed to the electrode.
This invention is made | formed in view of the above, and makes it a subject to achieve the following objectives.
That is, an object of the present invention is to provide a purification device that can efficiently purify soil.

As a result of intensive studies, the present inventors have found that the soil is efficiently purified by using the unique porous ceramic according to the present invention as the first container and the second container, and have completed the present invention.
That is, specific means for solving the above-described problems are as follows.
<1> a cathode electrolytic cell comprising a first container containing a weakly acidic solution therein, and a cathode electrode disposed in the first container and immersed in the weakly acidic solution;
An anode electrode tank comprising: a second container containing an electrolyte solution therein; and an anode electrode disposed in the second container and immersed in the electrolyte solution;
Voltage application means for applying a DC voltage between the cathode electrode and the electrode of the anode electrode;
With
The first container and the second container are porous ceramics in which the ratio of pores having a diameter of 2 μm or less to the total pores is 40% or more and the water permeability is 10 ⁻⁴ cm / sec or more and 10 ⁻⁷ cm / sec or less. A soil purification device consisting of
<2> The soil purification apparatus according to <1>, wherein the weakly acidic solution is acetic acid.

  ADVANTAGE OF THE INVENTION According to this invention, the purification apparatus which can purify | clean soil efficiently can be provided compared with the case where the 1st container and 2nd container in this invention are not used.

It is a mimetic diagram showing roughly the purification device concerning this embodiment. It is a schematic diagram which shows roughly the experimental apparatus to which the purification apparatus in this Embodiment is applied. It is a diagram which shows the cadmium content in dry soil with respect to the voltage application days in an Example.

  Hereinafter, an embodiment of the soil purification apparatus of the present invention will be described in detail.

In FIG. 1, the schematic diagram which shows one embodiment of the soil purification apparatus 10 (henceforth a "purification apparatus" only) of this Embodiment was shown.
In addition, although the case where the contaminated soil 30 to be purified in the purification apparatus 10 of the present embodiment is a contaminated soil containing cadmium as a contaminant is described, it is not limited thereto.
For example, the contaminated soil 30 to be purified by the purification apparatus 10 of the present embodiment includes, as a contaminant, other heavy metals such as copper, lead, and chromium, and contaminants such as arsenic and selenium, in addition to cadmium. It may be soil.

  As shown in FIG. 1, the purification device 10 according to the present embodiment includes a cathode electrode tank 12A, an anode electrode tank 12B, and a voltage application device 14.

  The cathode electrode tank 12A includes a cylindrical first container 16A and a long cathode electrode 18A disposed inside the first container 16A. The first container 16A and the second container 16B, which will be described later, are composed of a porous ceramic having a plurality of pores at least partially communicating with each other (details will be described later).

In the present embodiment, the bottom of the cylindrical first container 16A is closed by the bottom member 24A, and the weakly acidic solution 20A is accommodated inside the first container 16A. A lid member 22A is provided on the opening side of the cylindrical first container 16A facing the bottom member 24A.

In the present embodiment, “weakly acidic” indicates that the pH is 4 or less. Examples of the weakly acidic solution 20A accommodated in the cathode electrode tank 12A (first container 16A) include acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, and the like. Among these, anionic components contained in the contaminated soil 30 From the viewpoint of improving the purification efficiency, acetic acid is preferably used.

  On the other hand, the anode electrode tank 12B includes a cylindrical second container 16B and a long anode electrode 18B disposed inside the second container 16B. The bottom of the cylindrical second container 16B is closed by a lid member 22B, and the electrolyte solution 20B is accommodated in the second container 16B. Further, a lid member 22B is provided on the opening side of the cylindrical second container 16B facing the bottom member 24B.

  Examples of the electrolyte solution 20B accommodated in the second container 16B include known electrolyte solutions, and specific examples include a sulfuric acid solution, an oxalic acid solution, sodium hydroxide (NaOH), and the like. Among these, as the electrolyte solution accommodated in the anode electrode tank 12B (second container 16B), the purification efficiency of the cation component contained in the contaminated soil 30 is improved in the purification of the contaminated soil 30 described later in detail. From the viewpoint, it is preferable to use an alkaline solution.

  In the present embodiment, the case where the first container 16A and the second container 16B are cylindrical will be described. However, an electrode (cathode electrode 18A or anode electrode 18B) is disposed inside and a liquid (weak) is formed inside. A hollow configuration in which the acidic solution 20A or the electrolyte solution 20B) is accommodated may be used, and the configuration is not limited to a cylindrical shape. Further, in the present embodiment, the first container 16A and the second container 16B are formed in a cylindrical shape, and the openings at both ends in the longitudinal direction are provided with a lid member (lid member 22A, lid member 22B) and a bottom member (bottom member). 24A, the bottom member 24B) has been described as being sealed, but the lid member (the lid member 22A, the lid member 22B) is not provided, and is one end in the longitudinal direction (the insertion direction into the contaminated soil 30) The structure which the other side) opened may be sufficient. Moreover, each of the 2nd container 16B, the bottom member 24B, and the 1st container 16A and the bottom member 24A may be comprised integrally.

  The voltage application device 14 is electrically connected to the cathode electrode 18A and the anode electrode 18B, and applies a DC voltage so that the cathode electrode 18A side becomes a cathode and the anode electrode 18B side becomes an anode. Therefore, the cathode electrode 18A functions as a cathode electrode when a voltage is applied from the voltage application device 14. On the other hand, the anode electrode 18B functions as an anode electrode when a voltage is applied from the voltage application device 14.

  The cathode electrode 18A and the anode electrode 18B may be housed in each of the cathode electrode tank 12A and the anode electrode tank 12B, and may be configured to be able to apply a voltage from the voltage applying device 14. From the viewpoint of purifying the contaminated soil 30 more efficiently, the cathode electrode 18A preferably has a length that extends from the lid member 22A side of the cathode electrode tank 12A to a position that reaches the bottom member 24B. Similarly, the anode electrode 18B preferably has a length that extends from the lid member 22B side of the anode electrode tank 12B to a position that reaches the bottom member 24A.

  The cathode electrode 18A and the anode electrode 18B may be made of any material that can be used as an electrode, but it is particularly preferable to use a noble metal having a low ionization tendency such as platinum.

When the contaminated soil 30 is purified by the purification apparatus 10 of the present embodiment, first, the cathode electrode tank 12A and the anode electrode tank 12B are inserted into the contaminated soil 30 to which an electrolyte solution such as water is added, and these cathode electrodes are inserted. It arrange | positions at intervals so that the tank 12A and the anode electrode tank 12B may oppose. In addition, what is necessary is just to adjust suitably the insertion depth to the contaminated soil 30 of this cathode electrode tank 12A and the anode electrode tank 12B according to the use of the contaminated soil 30 of the object to be purified. For example, when the contaminated soil 30 to be purified by the purification apparatus 10 of the present embodiment is soil for cultivating crops such as paddy fields, the depth exceeds at least the root depth of the crop to be cultivated. It is preferable to insert up to. Moreover, when the contaminated soil 30 to be purified by the purification apparatus 10 is soil for cultivating crops such as paddy fields, the depth of the root of the crop to be cultivated is significantly exceeded (for example, the depth of the roots). It is considered that it is not necessary to insert the cathode electrode tank 12A and the anode electrode tank 12B to a depth of at least twice the depth), and it is considered that the cathode electrode tank 12A and the anode electrode tank 12B can be downsized.
Specific examples of the insertion depth of the cathode electrode tank 12A and the anode electrode tank 12B into the contaminated soil 30 include a depth of 12 cm to 15 cm.

Further, the length of the cathode electrode tank 12A and the anode electrode tank 12B in the direction of insertion into the contaminated soil 30 (in the present embodiment, in the direction intersecting the circumferential direction of the cylindrical first container 16A and the second container 16B). The length) only needs to be adjusted in advance so as to be longer than the depth of insertion into the contaminated soil 30. Specifically, when the soil for cultivating crops such as the above-mentioned paddy field is the contaminated soil 30 to be purified, and the purification apparatus 10 has a depth of 15 cm or less to be inserted into the contaminated soil 30, The lengths of the first container 16A and the second container 16B may be adjusted so that the length in the insertion direction into the contaminated soil 30 exceeds 15 cm.

  When the contaminated soil 30 is purified, the cathode electrode 18A becomes the cathode and the cathode electrode 18A and the anode electrode 18B in the cathode electrode tank 12A and the anode electrode tank 12B inserted into the contaminated soil 30 to be purified, and the anode electrode A DC voltage is applied from the voltage application device 14 so that 18B becomes an anode. The voltage value of the DC voltage applied from the voltage application device 14 to the cathode electrode 18A and the anode electrode 18B is electrolyzed in the contaminated soil 30 between the cathode electrode tank 12A and the anode electrode tank 12B. A voltage that is generated and an electroosmotic flow is generated between these electrodes (between the cathode electrode 18A and the anode electrode 18B), and ionized contamination components contained in the contaminated soil 30 can be electrophoresed between the electrodes. Any value may be used, and it may be appropriately adjusted according to the distance between the electrodes in the cathode electrode tank 12A and the anode electrode tank 12B inserted into the contaminated soil 30, the diameter of the cathode electrode 18A and the anode electrode 18B, and the like.

When a DC voltage is applied from the voltage application device 14 to the cathode electrode 18A and the anode electrode 18B in the cathode electrode tank 12A and the anode electrode tank 12B inserted into the contaminated soil 30 to be purified, on the anode electrode tank 12B side, Then, hydrogen ions (H ⁺ ) are generated by electrolysis of water, and the contaminated soil 30 around the anode electrode tank 12B is denatured into acid. On the other hand, hydroxide ions (OH ⁻ ) are generated on the cathode electrode tank 12A side, and the contaminated soil 30 around the cathode electrode tank 12A is denatured to be alkaline. And the cation component (cationized heavy metal component) which is a contaminating component contained in the contaminated soil 30 between the cathode electrode tank 12A and the anode electrode tank 12B is electrophoresed to the cathode electrode tank 12A side, and the anion The component (anionized heavy metal component) is electrophoresed to the anode electrode tank 12B side. For example, cation components such as Cd ²⁺ , Cu ²⁺ , and Pb ²⁺ in the contaminated soil 30 are electrophoresed to the cathode electrode tank 12 </ _b > A side, and CrO ₄ ²⁻ and Cr ₂ O ₇ exist as anion components in the contaminated soil 30. ²⁻ , AsO ₄ ³⁻ , SeO ₃ ^{2− and the} like are electrophoresed to the anode electrode tank 12B side.

The cationic component that has reached the cathode electrode tank 12A passes through the pores of the first container 16A of the cathode electrode tank 12A and reaches the first container 16A. The cation component that has reached the first container 16A reacts with the hydroxide ions and precipitates at the bottom of the first container 16A.
Here, since the contaminated soil 30 around the cathode electrode tank 12A is denatured by application of the DC voltage from the voltage application device 14, the weakly acidic solution 20A is contained in the first container 16A as described above. It is considered that the cation component contained in the contaminated soil 30 is promoted by being contained.

  On the other hand, the anion component reaching the anode electrode tank 12B passes through the pores of the second container 16B of the anode electrode tank 12B and reaches the second container 16B. The anion component that has reached the second container 16B reacts with the hydrogen ions and precipitates at the bottom of the second container 16B.

  As described above, the contamination component in the contaminated soil 30 is accommodated in the first container 16A and the second container 16B by applying a DC voltage from the voltage application device 14 to the cathode electrode 18A and the anode electrode 18B. It becomes.

  Here, since the contaminated soil 30 includes components that are not to be removed such as clay components, the application of the voltage to the cathode electrode 18A and the anode electrode 18B causes the first container 16A and the second container 16B. In some cases, components that are not subject to removal, such as clay components, may enter the container, and purification of the contaminated soil 30 may be impeded.

Therefore, in the purification device 10 of the present embodiment, the first container 16A and the second container 16B used in each of the cathode electrode tank 12A and the anode electrode tank 12B have a diameter of 2 μm or less with respect to all pores included in the porous ceramic. A specific porous ceramic having a porosity of 40% or more and a water permeability of 10 ⁻⁴ cm / sec or more and 10 ⁻⁷ cm / sec or less (hereinafter, the first container 16A and the second container of the present embodiment) The porous ceramic used for the container 16B is referred to as “specific porous ceramic”).

In the present embodiment, a specific porous ceramic in which the ratio of pores having a diameter of 2 μm or less to the total pores is 40% or more and the water permeability is 10 ⁻⁴ cm / sec or more and 10 ⁻⁷ cm / sec or less is used. By using as the first container 16A and the second container 16B, components that are not to be removed, such as clay components, contained in the contaminated soil 30 pass through the pores of the porous ceramic and pass through the first container 16A and the second container 16B. It is considered that the contamination component to be removed contained in the contaminated soil 30 selectively enters the first container 16A and the second container 16B.
For this reason, it is considered that the contaminated soil 30 can be efficiently purified by the purification device 10 of the present embodiment by configuring the first container 16A and the second container 16B with the above-described unique porous ceramic.

  The ratio of the pores having a diameter of 2 μm or less to the total pores contained in the specific porous ceramic is essential to be 40% or more, but the components such as clay that are not to be removed such as clay are the first. From the viewpoint of suppressing entry into the container 16A and the second container 16B, the ratio is preferably 45% or more.

The “ratio of pores having a diameter of 2 μm or less with respect to the total pores” included in this specific porous ceramic is the ratio of the volume of pores with a diameter of 2 μm to the volume (volume) of all the pores included in the porous ceramic. Is shown.
The proportion of pores having a diameter of 2 μm or less in all pores contained in this specific porous ceramic is measured by a pore distribution measuring device.
Specifically, this “ratio of pores having a diameter of 2 μm or less with respect to the total pores” is determined by the mercury intrusion method proposed by Washburn (“Surface”, Vol. 13, No. 10, p. Measured by the theory, apparatus and problem of the pore distribution measurement method of the material (Part 1) ”). Specifically, a pore distribution measuring device (trade name: Autopore IV9500) manufactured by Shimadzu Corporation is used as the measuring device. The ratio of pores other than the diameter of 2 μm is also measured by the same method.

  Further, the ratio of the ratio of pores having a diameter of 2 μm or less to the ratio of pores having a diameter exceeding 2 μm in the specific porous ceramic may be a ratio in which the water permeability coefficient of the specific porous ceramic satisfies the above range. Specifically, the ratio of the pores having a diameter of 2 μm or less (the ratio of the pores having a diameter of 2 μm or less / the ratio of the pores having a diameter exceeding 2 μm) to the ratio of the pores having a diameter exceeding 2 μm is preferably 1/2 or less.

As described above, the water permeability of the porous ceramic constituting the first container 16A and the second container 16B is in the range of 10 ⁻⁴ cm / sec or more and 10 ⁻⁷ cm / sec or less. of contaminants, from the viewpoint to reach more selectively to the inside of the first container 16A and the second container ^16B, preferably 10 -4 cm / sec or more ¹⁰ -5 cm / sec or less in the ^{range, 10} -4 cm / sec is particularly preferred.

The “water permeability” of the porous ceramic is measured by the following test.
Specifically, the permeability coefficient k of this porous ceramic is obtained by measuring according to JIS_A — 1218 (soil permeability test method). The unit of the water permeability coefficient k is cm / sec. Here, there are two types of soil permeability test methods of JIS_A — 1218, namely, a constant water level permeability test and a variable water level permeability test, but in this embodiment, a water level permeability test was used.

  The constant water level permeability test is the amount of water that permeates within a certain time under a certain water level difference in a specimen (specific porous ceramic in the present embodiment) having a certain cross section and length. It is a test to measure. Specifically, a permeable cylinder is arranged inside the overflow tank, a specimen (specific porous ceramic) is arranged in the permeable cylinder, and a metal mesh, a filter, and a perforated plate are used above and below the specimen. Insert the water into the permeable cylinder so that the difference between the water level in the overflow tank and the water level in the permeable cylinder is constant (however, the water level in the overflow tank <the water level in the permeable cylinder) and measure the time. In this test, the amount of water overflowing from the overflow tank was measured with a graduated cylinder.

  Further, the water level permeation test is a drop in water level when penetrating a specimen having a certain cross section and length (in this embodiment, a specific porous ceramic) with a certain water level difference as an initial state. It is a test to measure the quantity and its elapsed time. Specifically, a permeable cylinder is arranged inside the overflow tank, a specimen (specific porous ceramic) is arranged in the permeable cylinder, and a metal mesh, a filter, and a perforated plate are used above and below the specimen. The difference h1 between the water level in the overflow tank and the water level in the standpipe at time t1 when the standpipe is placed straight above the permeable cylinder and water is supplied from the standpipe to the permeable cylinder. This is a test in which the difference h2 between the water level in the overflow tank and the water level in the standpipe at time t2 is measured while measuring and supplying water.

  The specific porous ceramic that satisfies the above conditions and that constitutes the first container 16A and the second container 16B of the present embodiment is made using metal oxide ceramic powder and non-oxide ceramic powder. Is mentioned. Examples of the metal oxide ceramic include alumina, cordierite, mullite, zirconia, silica, magnesia, and a mixture thereof. Non-oxide ceramics include silicon carbide and silicon nitride.

As the composition of the specific porous ceramic that satisfies the above-described conditions and that constitutes the first container 16A and the second container 16B of the present embodiment, specifically, a composition containing SiO ₂ and Al ₂ O ₃ is given. It is done.

  As a method for producing the above-mentioned specific porous ceramic used in the present embodiment, for example, the above-mentioned materials listed as constituent materials of the specific porous ceramic used in the present embodiment are made muddy water, and this is starch. And a method of manufacturing by impregnating with a pore agent such as, and sintering at a high temperature (about 1500 ° C.).

  The ratio of pores having a diameter of 2 μm to the total pores of this specific porous ceramic and the water permeability adjust the diameter of the material particles constituting the porous ceramic, the amount of pore agent added at the time of production, and the like. It will be adjusted.

As described above, in the purification device 10 of the present embodiment, the ratio of pores having a diameter of 2 μm or less to the total pores is 40% or more, and the water permeability is 10 ⁻⁴ cm / sec or more and 10 ⁻⁷ cm / sec. Since the following specific porous ceramics are used as the first container 16A and the second container 16B, it is considered that the contaminated soil 30 to be purified can be efficiently purified.

  In addition, if the purification apparatus 10 of this Embodiment demonstrated above is the purification target object which has electroconductivity, it can purify not only in soil, For example, it can purify also the contaminated liquid. Needless to say.

  Moreover, the purification apparatus 10 of this Embodiment is not restricted to the contaminated soil 30 of a specific place, It is applied to purification of the contaminated soil of various places. In addition, the shape and size of the cathode electrode tank 12A and the anode electrode tank 12B in the purification apparatus 10 may be adjusted as appropriate according to the state of the object to be purified, the size of the area to be purified, and the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof.

[Example 1]
In FIG. 2, the schematic diagram of the experimental apparatus 50 for implementing purification | cleaning of the contaminated soil 30 using the purification apparatus 10 demonstrated above was shown.

-Adjustment of experimental tank-
First, a plastic container 40 having a volume of about 24 L (length 380 mm, width 260 mm, height 235 mm) was prepared (see FIG. 2). Then, the container 40 is filled with the contaminated soil 30 to be purified until the depth (height from the bottom surface of the container 40) reaches 12 cm, and 4 L of water (tap water, see reference numeral 32 in FIG. 2). Was added to make the water level (height from the bottom surface) 15 cm, and the experimental tank 42 was obtained. In addition, during the period of the purification process by the purification apparatus 10 to be described later, the water level was adjusted by appropriately adding water so that the water level was maintained.

-Adjustment of first container 16A and second container 16B-
Next, as the first container 16A and the second container 16B, containers made of the following specific porous ceramics were prepared.

(First container 16A and second container 16B made of unique porous ceramic)
・ Shape: Cylindrical (outer diameter 30mm, inner diameter 27mm, length 180mm)
Composition: SiO ₂ 23% by mass, Al ₂ O ₃ 76% by mass
・ Porosity distribution:
Ratio of pores with a diameter of less than 1 μm to all pores 33%
Ratio of pores with a diameter of 1 μm or more and less than 2 μm to the total pores 12%
Ratio of pores with a diameter of 2 μm or more and less than 5 μm to all pores 16%
Ratio of pores with a diameter of 5μ or more and less than 10μm to all pores 16%
Ratio of pores with a diameter of 10 μm or more and less than 20 μm to all pores 17%
Percentage of pores exceeding 20 μm in diameter with respect to all pores 6%
・ Water permeability coefficient: 10 ⁻⁴ cm / sec cm / sec
The pore distribution was measured with a pore distribution measuring apparatus (trade name: Autopore IV9500) manufactured by Shimadzu Corporation.
・ Pressure resistance: 100 kPa

  The pore distribution, water permeability coefficient, and porosity were measured by the methods described above.

-Production of cathode electrode tank 12A and anode electrode tank 12B-
Next, as the cathode electrode 18A and the anode electrode 18B, copper electrodes having a diameter of 10 mm and a length of 270 mm were prepared one by one (two in total).
And this copper electrode was installed one each in each of the 1st container 16A and the 2nd container 16B which consist of the characteristic porous ceramics adjusted above. And the bottom member 24A and the bottom member 24B were provided in the bottom part of each of these containers (1st container 16A and 2nd container 16B), and the bottom part of these containers was sealed.

  And after filling the 0.14 mol / L acetic acid solution in the container (the 1st container 16A and the 2nd container 16B) in which these copper electrodes (cathode electrode 18A and anode electrode 18B) were installed, these containers Each of the openings was closed with a lid member 22A and a lid member 22B. Note that acetic acid was added as appropriate so that the concentration of acetic acid and the amount of acetic acid solution in the acetic acid solution were maintained during the purification process by the purification device 10 described later.

  The acetic acid was added using the plastic tube 44A and the plastic tube 44B shown in FIG. Specifically, holes (not shown) are formed in the lid member 22A and the lid member 22B provided in each of the first container 16A of the cathode electrode tank 12A and the second container 16B of the anode electrode tank 12B, and the holes are passed through the holes. Insert plastic tubes (see plastic tube 44A and plastic tube 44B in FIG. 2) to collect the liquid in first container 16A and second container 16B, and to add acetic acid into these containers. It was.

  Thus, two electrode tanks corresponding to the cathode electrode tank 12A and the anode electrode tank 12B were produced.

―Evaluation of whether or not components that are not subject to removal pass through the pores of porous ceramic―
Each of the first container 16A and the second container 16B made of a specific porous ceramic adjusted as described above and sealed at the bottom of the container by the bottom member 24A and the bottom member 24B is immersed in distilled water to a depth of 12 cm. Then, the insides of the first container 16A and the second container 16B were depressurized to −40 kPa to −60 kPa, and the liquid accumulated in the containers was collected. And about the extract | collected liquid, when the light absorbency with respect to the light of a wavelength of 665 nm was measured, it was 0.0000.

Next, each of the first container 16A and the second container 16B made of a specific porous ceramic and having the bottom member 24A and the bottom member 24B sealed with the bottom member 24A adjusted as described above was adjusted as described above. Insert into the contaminated soil 30 of the tank 42 to a depth of 12 cm from the surface of the contaminated soil 30, depressurize the inside of the first container 16A and the second container 16B to −40 kPa to −60 kPa, and collect the liquid accumulated in the container did. And about the extract | collected liquid, when the light absorbency with respect to the light of a wavelength of 665 nm was measured, it was 0.0022.
From this result, in the first container 16A and the second container 16B made of a specific porous ceramic produced in this example, the components other than the removal target such as clay are the first container 16A produced in this example and It can be said that contaminants to be removed such as heavy metal ions that have not passed through the pores of the second container 16B (porous ceramic) have passed through the pores of the first container 16A and the second container 16B (porous ceramic).

-Production of experimental device 50 (purification device 10)-
The cathode electrode tank 12A and the anode electrode tank 12B produced above are placed in the contaminated soil 30 filled in the container 40 of the experimental tank 42 prepared above (the distance between the electrodes of the cathode electrode 18A and the anode electrode 18B (cathode electrode). It was inserted until it abutted against the bottom surface of the container 40 so that the minimum distance between the facing surfaces of 18A and anode electrode 18B was 30 cm. For this reason, the insertion depth to the contaminated soil 30 of these cathode electrode tank 12A and anode electrode tank 12B was 12 cm.

  Then, the cathode electrode 18A in the cathode electrode tank 12A and the anode electrode 18B in the anode electrode tank 12B are electrically connected to a DC power source (manufactured by GS Yuasa Battery Co., Ltd .: trade name PXL 12050) as the voltage application device 14. Thus, the experimental device 50 to which the purification device 10 was applied was obtained.

<Evaluation>
-Evaluation of purification of contaminated soil-
Cadmium content in the contaminated soil 30 when a DC voltage of 12 V is applied to the cathode electrode 18A and the anode electrode 18B from the DC power source (voltage application device 14) of the purification device 10 in the experimental device 50 produced in this example. The transition of was measured.

  Specifically, first, the region between the cathode electrode tank 12A and the anode electrode tank 12B inserted into the contaminated soil 30 of the experimental tank 42 is divided into three areas (from the cathode electrode tank 12A side toward the anode electrode tank 12B ( The same area). These three regions were defined as a region Ar3, a region Ar2, and a region Ar1 in order from the anode electrode tank 12B side to the cathode electrode tank 12A side (see FIG. 2).

--Measurement of cadmium content in contaminated soil--
Using the cathode electrode 18A as a cathode and the anode electrode 18B as an anode, a constant voltage of DC 12V (potential gradient 2V / cm) is continuously applied for 6 days from the voltage application device 14, and the above-mentioned area Ar1 with respect to the applied days of the voltage The cadmium content in each of the regions Ar2 and Ar3 was measured. The measurement results are shown in FIG.

Note that the cadmium content in each of the region Ar1, the region Ar2, and the region Ar3 was measured by the following method.
Specifically, before the start of the application of the constant voltage and every 2 days (every 48 hours) from the voltage application, from each of the regions Ar3, Ar2 and Ar1 in the contaminated soil 30 in the experimental tank 42. 10 g of soil was collected. Then, 10 g of soil collected from each region (region Ar3, region Ar2, and region Ar1) was dried in an oven at 105 ° C. for 2 days, and the weight after drying was measured. Then, 20 ml of a 0.14M hydrochloric acid solution is added to each of the dried soils in each region, and the mixture is stirred for 1 hour using a soil aggregate analyzer (DIK-2012 manufactured by Dairika Kogyo Co., Ltd.). , A mixed solution of each of the regions Ar2 and Ar3 was obtained.

Next, the mixed solution of these soils is filtered using a filter paper (Whatman Co .: No. 5C), and the cadmium content in the filtrate is Z-5010 polarized Zeeman atomic absorption spectrophotometer manufactured by Hitachi, Ltd. Quantified using a meter.
And the content (mg) of cadmium per 1 kg of dry soil in each of the above-mentioned region Ar1, region Ar2, and region Ar3 was determined, and the results are shown in FIG.

  As shown in FIG. 3, in any of the regions Ar1, Ar2, and Ar3, a decrease in the cadmium content per kg of dried soil was observed as the voltage application time increased.

DESCRIPTION OF SYMBOLS 10 Purification apparatus, 12A Anode electrode tank, 12B Anode electrode tank, 14 Voltage application apparatus, 16A 1st container, 16B 2nd container, 18A Cathode electrode, 18B Anode electrode, 20A Weak acidic solution, 20B Electrolyte solution

Claims (2)

A cathode electrolytic cell comprising a first container containing therein a weak acid solution, and a cathode electrode disposed in the first container and immersed in the weak acid solution;
An anode electrode tank comprising: a second container containing an electrolyte solution therein; and an anode electrode disposed in the second container and immersed in the electrolyte solution;
Voltage application means for applying a DC voltage between the cathode electrode and the electrode of the anode electrode;
With
The first container and the second container are porous ceramics in which the ratio of pores having a diameter of 2 μm or less to the total pores is 40% or more and the water permeability is 10 ⁻⁴ cm / sec or more and 10 ⁻⁷ cm / sec or less. A soil purification device consisting of   The soil purification apparatus according to claim 1, wherein the weakly acidic solution is acetic acid.