JP2873902B2 - How to treat pollutant barriers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating a pollutant barrier wall for use in applications such as constructing a barrier wall around a hazardous waste dumping area and preventing the pollutant from flowing out of the area. About.

[0002]

2. Description of the Related Art A variety of wastes are generated in large quantities as the industry becomes active. This waste also contains harmful substances,
It may be left unexposed without detoxifying it or only detoxifying a part of it.

In this case, if there is rain at the dumping site,
The infiltration of the rainwater into the ground eventually contaminates the groundwater and becomes a serious social problem when drinking water is used.

Accordingly, the applicant of the present application has disclosed Japanese Patent Publication No. Hei 3-1550.
No. 9 and Japanese Patent Application Laid-Open No. 3-2088853 have been improved with the applicant.

[0005]

The low water permeability of this type of barrier shows excellent barrier properties against contaminants, but the present invention does not provide a sufficiently low water permeability. They considered combining it with, for example, a blocking sheet. In fact, the idea of preventing the diffusion of contaminants by using only the shielding sheet is known in Japanese Patent Publication No. 5-15847.

However, in the case of a shielding sheet made of plastic or the like, there is a risk that the sheet may be broken or a hole may be formed due to external force or long-term aging. Therefore, it has been desired to reduce the water permeability of the barrier wall itself.

[0007] Accordingly, an object of the present invention is to remarkably reduce the water permeability of the barrier wall itself and to simplify the means.

[0008]

The above object can be attained by applying carbonic acid from the outside to a barrier wall for contaminants mainly composed of bentonite and cement-based solidified material.

In this case, carbon dioxide can be applied by blowing carbon dioxide gas or air containing carbon dioxide gas in a region where groundwater flows near the blocking wall to dissolve the carbon dioxide gas component in the groundwater. Further, carbonated water can be directly injected. In addition, an inorganic substance serving as a hardness component of the groundwater, such as a silicate, can be added to the vicinity of the blocking wall to dissolve the groundwater.

[0010]

The barrier against contaminants mainly composed of bentonite and cement-based solidified material is made of fine hydrated silicate hydrate crystals in which bentonite and cement are entangled, and thus has a high water-blocking property. In particular, the hydration reaction proceeds with time, the structure of the hydrate is densified, and the water permeability decreases.

[0011] However, there is a limit to the decrease in the permeability. Therefore, the present inventors prepared a sample having a diameter of 5 cm and a length of 10 cm from the material of the blocking wall, and dissolved distilled water, groundwater collected in Noda City, Chiba Prefecture, and dissolved carbon dioxide gas in the groundwater. When the carbonated water was circulated and the water permeability and the pH were lowered over time, the results shown in FIGS. 1 and 2 were obtained.

According to this result, the permeability and pH decrease in distilled water are only slight, whereas in the case of groundwater, the permeability is 10 ^-1 order in 10 days, 25 days. in may experience slow ^10-2 order decrease in pH is small. However, when the carbonated water was allowed to flow, the drop in pH was large and the water permeability dropped rapidly on the 15th, making it impossible to pass the liquid.

According to the experimental results, it is considered that when carbonic acid is applied to the barrier according to the present invention, the water permeability decreases due to the following reaction.

That is, as shown in FIG. 3, in a state in which cement bentonite particles, in which cement hydrate and bentonite particles are physically bonded, are interlocked with each other, The SiO ₂ therein reacts with free lime Ca (OH) ₂ ,
Generating a cement hydrates, also, CO ₂ gas blown in by that carbonated (HCO ₃ ^-) and free lime Ca (OH)
₂ reacts to form calcium carbonate (insoluble) C
aCO ₃ is produced, leading to a decrease in pH. In particular, the sedimentable calcium carbonate particles settle between the microstructures of the cement bentonite particles and act as fillers, resulting in a decrease in water permeability.

On the other hand, according to the theory, carbon dioxide dissolves calcium carbonate as in the following formula. CO ₂ + CaCO ₃ → Ca (OH) ₂ + HCO ₃ ^- If this reaction occurs, CO ₂ should react with the cement hydrate before reacting with calcium carbonate as follows: . _{CO 2 + XCaO · YSiO 2 ·} ZH 2 O → X'CaO
· Y'SiO by ^{_{2 · Z'H 2 O + Ca 2+}} + SiO 2 which is believed to be the production of cement hydrate increases.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The present invention can be implemented, for example, in the modes shown in FIGS. That is, after or while excavating by appropriate means, the barrier wall 1 for pollutants mainly composed of bentonite and cement-based solidified material is formed. When the blocking wall 1 is formed, an underground continuous wall forming method, a soil cement column wall method, a mechanical stirring method, a jet stirring method, an injection method, and the like can be adopted.

Preferably, an insertion hole 2 is drilled in the blocking wall 1 on the side of the contaminated area, and a discharge pipe 3, for example, a strainer pipe, is inserted into the insertion hole 2. The space between the insertion hole 2 and the pouring pipe 3 can be filled with, for example, gravel 4.

A plurality of discharge pipes 3 are preferably installed parallel to the blocking wall 1 at appropriate intervals from each other. Further, a carbon dioxide gas cylinder 5 is connected to each of the discharge pipes 3, 3,..., And a compressor 6 is connected as necessary.

Thus, after the formation of the barrier wall 1, desirably, each reaction from the carbon dioxide gas cylinder 5 is performed in a state where the reaction and hardening of the bentonite and the wall forming material mainly composed of the cement-based solidified material are stable, for example, after 7 days. Tubes 3,3 ...
And supply carbon dioxide to the outlets of the outlet pipes 3, 3 ...
Pour into the ground. By the discharge of the carbon dioxide gas, the carbon dioxide gas comes into contact with the groundwater, becomes carbonated water, and permeates through the blocking wall 1. In the permeation process, the above-mentioned reaction causes the formation of cement hydrate crystals and the formation of sedimentary calcium carbonate, which causes a sharp drop in pH and the sedimentation of calcium carbonate particles between the microstructure of cement bentonite particles. Due to sedimentation, this acts as a filler, leading to a reduction in hydraulic conductivity.

(Other Examples) In the present invention, when the barrier wall 1 is constructed, it is preferable that the barrier wall 1 is constructed so as to surround the entire contaminated area. However, when the groundwater flows in one direction, for example, when the groundwater flows on a slope. Alternatively, it may be formed only on the downstream side.

Further, in the above embodiment, in addition to the carbon dioxide gas alone, air from the compressor 6 can be mixed therein. Instead of carbon dioxide gas, carbonated water may be produced in advance, and this may be poured out from the discharge pipe 3. As an embodiment of the discharge pipe 3, in addition to the strainer pipe, a double pipe structure is used.
The spout of the outer tube has covered with sleeves, such as rubber, to insert the inner tube having a packer at both ends, by supplying carbon dioxide gas into the inner tube,
The so-called double pipe double packer system, in which carbon dioxide gas is discharged from between the packers and the sleeve is pushed out from the spout at the corresponding position while pressing the sleeve, can be poured out while appropriately selecting the pouring position. it can. Of course, other outlet pipes could be employed.

On the other hand, a carbon dioxide gas or carbonated water may be discharged by inserting the discharge pipe 3 into the blocking wall 1.

As a material for forming the barrier wall, any material mainly composed of (Na-) bentonite and a cement-based solidification material may be used, and a fine silica powder as a water-stopping material is added to the material at 10 to 30 kg / m ^3. Charcoal, silica gel,
100 kg / m ³ of clay minerals such as calcium bentonite, activated clay, zeolite and attapulgite to which a porous material such as activated carbon is added in a range of 60 kg / m ³ or less.
The addition of carbonates in the range of 30 kg / m ³ or less, which is added in the following range, is effective for enhancing the trapping property of the pollutant in view of the type of the pollutant.

Further, an inorganic substance serving as a hardness component of groundwater, for example, a silicate, can be added to the vicinity of the blocking wall to dissolve the groundwater. When adding this inorganic substance,
Preferably, it can be carried out by injecting into the ground a substance dissolved or dispersed in groundwater, in addition to a substance in which an inorganic substance is dissolved in water.

[0025]

As described above, according to the present invention, the water permeability of the barrier wall itself can be significantly reduced, and the outflow of pollutants to the outside can be prevented, and the means can be simplified.

[Brief description of the drawings]

FIG. 1 is a graph showing a change with time in water permeability.

FIG. 2 is a graph showing a change in pH over time.

FIG. 3 is an explanatory diagram of a reaction mechanism according to the present invention.

FIG. 4 is a schematic longitudinal sectional view of an embodiment of the present invention.

FIG. 5 is a horizontal sectional view of a main part thereof.

[Explanation of symbols]

 1 ... cut-off wall, 3 ... outlet pipe, 5 ... carbon dioxide gas cylinder.

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Masatoshi Iio 4-35, Kudankita, Chiyoda-ku, Tokyo Light Industry Co., Ltd. (56) References JP-A-50-127417 (JP, A) JP-A Sho 51-61119 (JP, A) JP-A-59-27021 (JP, A) JP-A-4-155008 (JP, A) JP-A-2-221510 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) E02D 3/12 101

Claims (4)

(57) [Claims] 1. A method for treating a pollutant barrier, comprising applying carbonic acid from the outside to the pollutant barrier mainly composed of bentonite and cement-based solidified material. 2. The blocking of pollutants according to claim 1, wherein, when the carbon dioxide is applied, carbon dioxide or air containing the carbon dioxide is blown into the groundwater in a region where the groundwater flows near the blocking wall to dissolve the carbon dioxide in the groundwater. Wall treatment method. 3. The method for treating a pollutant barrier according to claim 1, wherein the carbonated water is injected into or near the barrier. 4. The method for treating a pollutant barrier according to claim 1, wherein an inorganic substance serving as a hardness component of the groundwater is added near the barrier to dissolve the groundwater.