JP3115200B2 - How to capture pollutants - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to environmental protection, in particular, to the construction of a barrier around an area that is polluted or at risk of contamination by preventing the transfer of pollutants from that area to the surroundings. The present invention relates to a method for trapping pollutants when preserving the environment while preventing the impact on the environment.

[0002]

2. Description of the Related Art With the development of industry and the diversification of urban life, the problems of industrial waste and municipal waste have been greatly highlighted. In particular, in addition to an increase in the amount of waste treated, harmful substances contained in the waste, such as heavy metals such as mercury, cadmium, and chromium, flow out to living areas, for example, through groundwater.

[0003] For this purpose, it is a suitable solution to construct a blocking wall around a contaminated or at risk of contaminant to prevent the transfer of contaminants from that region to the surroundings. Indeed, it has been conventional to build concrete walls around the area, or even concrete impermeable walls at the bottom.

However, concrete walls have a high possibility of permeating heavy metals, and when cracks occur, they will intensively flow out therefrom.

[0005] In contrast, in JP-A-61-105500, Bentona wells - cement as the basic material, clays therein, siliceous material, sodium carbonate, alkali metal pyrophosphates or tartrate salt of It is proposed to construct a barrier having high barrier properties for heavy metals by including the above.

[0006]

However, as a material constituting the barrier wall, a barrier wall mainly composed of bentonite and cement shows excellent barrier properties against contaminants, but still has a sufficiently low water permeability. It does not indicate.

[0007] As a countermeasure, it is conceivable to block the flow of groundwater by combining with a blocking sheet made of rubber or plastic material.
Or damaged Ri by <br/> deterioration or breakage by external force or prolonged exposure unexpectedly hard to say that appropriate means.

Accordingly, in the present situation, an optimal approach to achieve blocking only blocking wall consisting mainly of bay Tonanto and cement. However, while this barrier provides excellent barrier properties for most contaminants, it is exceptionally 6
The barrier properties of valent chromium (Cr ⁶⁺ ) are not sufficient.

Therefore, an object of the present invention is to reduce the water permeability of the barrier wall and to provide an excellent hexavalent chromium (Cr)
⁶⁺ ).

[0010]

SUMMARY OF THE INVENTION The above object is outside the contaminated or against contamination Target area of risk is contaminated, the blocking wall to build a cutoff wall composed mainly of cement and bentonite On the other hand, in a method for preventing the outflow of pollutants, the problem can be solved by including magnesium chloride in the inside of the barrier wall or in the region to be contaminated.

On the other hand, in this case, it is desirable that magnesium chloride be present at a concentration of 250 to 1000 mg per liter of groundwater around the wall surface of the blocking wall.

[0012]

According to the present invention, since the barrier wall mainly composed of cement and bentonite (more preferably, sodium bentonite) -based solidifying material is constituted by fine calcium silicate hydrates entangled with each other, the water blocking property is improved. It is rich. In addition, the hydration reaction proceeds with time, and the crystals of the hydrate become tighter (strengthen), indicating a decrease in the water permeability.

However, as described above, there is a limit to the reduction in the water permeability of the blocking wall. Thus, the present inventors
As a result of the following experiment, the inventors have found that it is effective to contain magnesium chloride inside the barrier wall or in the region to be contaminated, and have completed the present invention.

The outline of this experiment is as follows.
A 10 cm high columnar specimen was prepared, and distilled water (control), groundwater from Noda City, Chiba Prefecture (hereinafter referred to as pure groundwater for convenience), and groundwater containing hexavalent chromium and magnesium chloride dissolved therein. (Pseudo-improved groundwater), and the permeability of the test specimen, the pH, and the amount of hexavalent chromium flowing out were examined over time. The results shown in FIGS. 2 to 5 were obtained.

As a specific experimental facility, as shown in FIG. 1, a material having a composition of 250 kg of cement and 60 kg of Na bentonite was cured in water at a water temperature of 20 ° C. for 7 days.
The specimen was finished in the above dimensions, placed in a mold for permeability test, and adjusted using potassium dichromate reagent so that the hexavalent chromium concentration was 5 mg / 1 liter and the magnesium chloride was 2705 mg / 1 liter. The pseudo-improved groundwater was passed through the specimen at a pressure of 0.5 kgf / cm ² . Further, in consideration of the pressure in the groundwater, the lateral pressure of 1.0 kgf / cm ² was applied to the specimen. After passing the water, the water was collected by a plastic bag, and each water was tested for the above-mentioned measurement items. The experiment was performed for each condition for 28 days.

Looking at the results, as shown in FIG.
Although the permeability decreases with time, the rate of decline is slower in the case of distilled water and groundwater, whereas in the case of pseudo-improved groundwater in which hexavalent chromium and magnesium chloride are dissolved, the permeability decreases in about 7 days. However, it can be seen that it shows a lower permeability than distilled water and groundwater.

As shown in FIG. 3, in the case of pseudo-improved groundwater, there is a slight tendency to decrease depending on the number of days elapsed, but practically there is almost no change. Shows a tendency to decrease. Also,
For a pseudo-contaminated water without magnesium chloride and pseudo improved groundwater, Cr for the leachate amount by changing the leaching water by varying the passing water against the specimen
^From the results shown in FIGS. 4 and 5 showing the results of examining the ⁶⁺ concentration, it is understood that the leaching of hexavalent chromium can be significantly reduced by adding magnesium chloride. FIG. 5 shows the theoretical value of the amount of Cr ⁶⁺ associated with water flow. In addition, when considering an actual barrier, it was found that the one having the above-mentioned low permeability can be constructed. Therefore, the amount of leached water is considered to be 5 liters or less in FIG. It can be inferred that the amount of leached hexavalent chromium is as close to zero as possible. Even if it is assumed that a water passage is formed in the blocking wall due to an unexpected accident, according to the results shown in the figure, even if the amount of leachate is larger,
In the case of pseudo-improved groundwater, the amount of hexavalent chromium leached is lower than that of pseudo-polluted water, so that leaching of hexavalent chromium can be suppressed to a low level.

On the other hand, separately, 5 mg / 1 liter of Cr ⁺⁶ was added to distilled water and magnesium chloride solution.
Was immersed in a solution in a beaker containing, and visually observed 18 days later, there was no white turbidity at the bottom of the beaker and there was no color change of the specimen. On the other hand, when it was immersed in the groundwater in the same manner, cloudiness occurred at the bottom of the beaker, and the specimen turned pale green. In addition, about 10
It contains mg / l of Mg ⁶⁺ .

From these facts, it is inferred that the following reaction is caused by adding magnesium chloride to groundwater according to the present invention.

Potassium dichromate K ₂ Cr ₂ O ₇ is subjected to alkali treatment under the following conditions: Cr ₂ O ₇ ²⁻ + 2OH ⁻ → 2CrO ₄ ²⁻ + 2H ₂ O (1) Further, sulfur (CaS) in slag cement and the like Works, and Cr is reduced to trivalent as described below. 2CrO ₄ ²⁻ + 4H ₂ O + 3e ⁻ → Cr (OH) ₃ + 5OH ⁻ (2) Cr (OH) ₃ → Cr ₂ O ₄ .nH ₂ O (3) Moreover, when becoming alkaline, Cr ₂ O _4. nH ₂ O → spinel double oxide (chromite) M ^II (CrO ₂ ) ₂ : sparingly soluble in water ... (4) Cr ₂ O ₄ .nH ₂ O → other than spinel type MgO.2CrO ₃ … ( 5) Thus, as shown in equations (4) and (5), chromite is formed, causing clogging in the barrier, and C
r ⁶⁺ is ^retained in the barrier.

[0021]

EXAMPLES The present invention will be further described based on the results of another experiment. When the change due to the pH of pseudo-improved groundwater was examined, the results shown in FIGS. 6 and 7 were obtained. In other words, it was found that a pH of about 9 was particularly excellent in lowering the water permeability and in blocking chromium. Therefore, in consideration of practical use and alkali pollution, the pH is preferably 7.0 to 9.5.

The concentration of magnesium chloride is preferably from 250 to 1000 mg per liter of groundwater. Mg ²⁺ ion concentration in groundwater is 50-30
0 mg / 1 liter (usually 50 to 200 mg). Therefore, in order to reduce the water permeability and prevent the leaching of hexavalent chromium, it is necessary to increase the Mg ²⁺ ion concentration at least higher than that of general groundwater. On the other hand, when magnesium chloride is excessively contained, as shown in FIG.
When added in excess of 1000 mg, the water permeability increases, and especially when it is about 5000 mg, the cement-bentonite wall is softened tattered.

Next, when a shielding wall is actually constructed to capture a contaminant, the following method can be employed, for example.

FIG. 9 and FIG. 10 are conceptual views showing the construction target area of the present invention, in which a blocking wall 2 is constructed so as to surround the area where the waste 1 is dumped. Around the area A that is contaminated by waste or is likely to be contaminated, the blocking wall 2 that prevents the transfer of contaminants from the area A to the periphery is preferably provided with an impermeable layer 3 at the bottom. , It reaches the water-impermeable layer 3 and is constructed. Moreover, it does not have the water-impermeable layer 3,
Alternatively, when there is a risk of infiltration by riding on groundwater downward, a bottom wall similar to the blocking wall 2 can be constructed below the contaminated area by appropriate means. In this case, the bottom wall is desirably continuous with the blocking wall 2.

The material for constructing the barrier 2 is as follows.
Use is made mainly of cement-bentonite. In the blocking wall 2, a trapping core material composed of particles for adsorbing and holding the contaminants in the waste 1 or pellets obtained by granulating the particles, or a coating on the surface thereof for preventing direct contact with the contaminants Containing a trapping material that forms
Can.

When the continuous underground wall is used for the construction method when constructing the blocking wall 2, a guide wall is formed,
After excavating the excavation trench while filling with the bentonite stabilizing solution, and excavating, a solidifying material such as cement and the above-mentioned trapping material are added to the bentonite stabilizing solution and agitated or replaced and agitated to solidify.

In general, the formed barrier wall 2 has a large water permeability at the beginning, and therefore, the rate at which the liquid containing contaminants permeates the inside of the barrier wall 2 is large. At this time, the trapping material is partially or entirely dissolved by contact with the liquid, and the trapping core material is exposed. Contaminants are adsorbed and held on the exposed trapping core material. Eventually, with the passage of time after the formation of the barrier wall 2, the water permeability decreases, and the liquid barrier property is exhibited. Even in this case, the core material captures and holds the contaminant with respect to the liquid entering the blocking wall 2 through cracks or the like. As a result, it is possible to prevent the outflow of pollutants around the blocking wall 2. In addition, by selecting the material or the thickness of the film, it is possible to control the film to be dissolved by the time the solidification is completed.

In the case where the excavation groove 12 is not filled with the stabilizing liquid, for example, the trapping material can be mixed in advance with the constituent material of the blocking wall 2 and can be poured into the excavation groove.

In the above example, the trapping material is one that adsorbs or retains contaminants, such as activated carbon, coal, charcoal, zeolite, vermiculite, kaolin,
In addition to sodium bentonite, silica, blast furnace slag,
Other clay minerals can be used singly or in a mixed state. This type has an ion exchange capability, an adsorption capability, or a porous retention capability in pores, and can be used.

Further, as the coating for covering the surface of the core material for capturing, a material soluble in water or a slurry constituting the barrier wall may be used, and for example, gelatin, cellulose material, vinyl acetate material can be used. .

As a specific composition, 20 to 250 kg, particularly 40 to 80 kg, of Na bentonite per 250 kg of cement (more preferably, blast furnace cement), and if necessary, an expanding agent such as "Denka CSA" 15 to 4 manufactured by Denki Kagaku Kogyo KK
0 kg, water reducing agents such as Pozzolith Bussan Co. necessary "Pozzolith series" 1-5 kg, if necessary, a suitable amount of the contaminant capturing materials, this water, for example 10
00 kg can be blended and used.

Now, according to the present invention, as a specific means for containing magnesium chloride inside the barrier wall 2 or in the area to be contaminated, a discharge pipe 10 is provided on the barrier wall 2. As shown in FIG. 12, a plurality of injection ports 11 are formed on the wall surface of the outer tube 10A in a high direction, and the inner tube 10B is inserted and installed concentrically inside the wall of the outer tube 10A.
, A magnesium chloride aqueous solution 12 is discharged, and a flexible short tubular sleeve 15
Can be injected into the blocking wall 2 and the area to be contaminated while expanding.

In this case, since the permeation of the magnesium chloride aqueous solution 12 into the wide range is not so expected particularly with respect to the blocking wall 2, it expands and contracts by the fluid pressure of air or water across the inlet 13 of the inner tube 10 B. Packer 14,1
4, the magnesium chloride aqueous solution 12 is injected in a state where the respective packers 14, 14 are inflated from the ground and are brought into contact with the inner wall surface of the outer tube 10A. In this stage, it is preferable to repeat the same injection.

The time of this injection is the time when the hardening of the blocking wall 2 is started, more specifically, 24 hours after the formation of the blocking wall.
It is preferred to inject after ~ 48 hours. Thereby, a water path can be formed in the direction of the contamination target area of the blocking wall 2,
This is because hexavalent chromium can be captured later when contaminated groundwater tries to pass through the water channel and pass through the blocking wall 2.

For the injection, in addition to injection at a low pressure by an injection pump, as shown in FIG. 11, an aqueous magnesium chloride solution 12 is stored in an elevated tank 16 and can be gradually injected using a head head. .

If necessary, magnesium chloride can be present in the area to be contaminated by an appropriate means such as a simple pouring or the like in addition to the above-described injection form.
To present a is configured to require a large amount of magnesium chloride, in reality or final, the because is achieved capture in blocking wall, the inside of the barrier walls 2, close to the particular contamination target region side position Is preferably set as the injection position.

[0037]

As described above, according to the present invention, the water permeability of the blocking wall can be reduced, and the excellent
Those exhibiting a barrier property of valent chromium (Cr ⁶⁺ ) can be constructed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an experimental facility on which the present invention is based.

FIG. 2 is a graph showing experimental results.

FIG. 3 is a graph showing experimental results.

FIG. 4 is a graph showing experimental results.

FIG. 5 is a graph showing experimental results.

FIG. 6 is a graph showing experimental results.

FIG. 7 is a graph showing experimental results.

FIG. 8 is a graph showing experimental results.

FIG. 9 is a schematic sectional view of a construction example of the present invention.

FIG. 10 is a plan view of a construction example.

FIG. 11 is a schematic sectional view of an installation example of an injection tube.

FIG. 12 is a schematic sectional view of an example of an injection tube.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Waste, 2 ... Blocking wall, 3 ... Impervious layer, 10 ... Outlet pipe, 10A ... Outer pipe, 10B ... Inner pipe, A ... Contaminated area.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masatoshi Iio 4-35, Kudankita, Chiyoda-ku, Tokyo Light Industry Co., Ltd. (56) References JP-A-5-115861 (JP, A) JP-A Heisei 5-115862 (JP, A) JP-A-6-166556 (JP, A) JP-A-7-112171 (JP, A) JP-A-5-263420 (JP, A) JP-A-61-1722 (JP, A) A) JP-A-51-69057 (JP, A) JP-A-5-309354 (JP, A) JP-A-8-150381 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) B09B 1/00 A62D 3/00 B09C 1/02 B09C 1/08 B09B 3/00

Claims (2)

(57) [Claims] 1. A contaminated or threatened contaminant.
Against elephant area, building a cutoff wall composed mainly of cement and bentonite in a method for preventing the outflow of contaminants to the outside of the barrier wall, the magnesium chloride into or contamination target region of the blocking wall A method for trapping contaminants, characterized in that they are contained. 2. Magnesium chloride of 250 to 1000 m per liter of groundwater around the wall of the barrier wall.
2. The method according to claim 1, wherein said contaminants are present at a concentration of g.