JP6914166B2 - Embankment structure, method of maintaining the performance of the adsorption layer, and method of suppressing leakage of heavy metals - Google Patents

Description

The present invention relates to an embankment structure, a method for maintaining the performance of an adsorption layer, and a method for suppressing leakage of heavy metals.

Spring water and soil generated during excavation of the ground may contain heavy metals, etc. that exceed the standard value. In recent years, there has been a demand for countermeasures against pollution of the surrounding environment by heavy metals contained in such spring water and infiltration water generated by infiltration of rainwater into soil.
When soil containing heavy metals is treated as industrial waste, there is a concern that there will be a shortage of treatment plants. Therefore, it is recommended that soil containing heavy metals be purified and then reused as treated soil, or contained and then used. Such soil is used for embankment of roads and the like, for example.

At the time of containment, measures are taken to prevent rainwater from permeating the soil and heavy metals eluted by the water permeating the soil from leaking into the environment. As a measure against the infiltration of rainwater, for example, there is a method of covering the soil with bentonite or an impermeable sheet. As a countermeasure against leakage of heavy metals, for example, there is an adsorption layer construction method. In the adsorption layer construction method, an adsorption layer containing a heavy metal adsorbent is provided below the embankment layer formed from soil containing heavy metals. Since the water leached from the embankment layer passes through the adsorption layer, heavy metals in the water are adsorbed by the heavy metal adsorbent and insolubilized when passing through the adsorption layer (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2012-110852

The adsorption performance of heavy metal adsorbents may deteriorate when exposed to an alkaline environment for a long period of time. Therefore, when the containment is performed under the roadbed, there is a concern that the adsorption layer is alkalized due to concrete and the performance of the heavy metal adsorbent is deteriorated accordingly. When the soil is coated with bentonite, there is a concern that the adsorption layer is alkalized due to bentonite and the performance of the heavy metal adsorbent is deteriorated accordingly.
The adsorption layer is provided so as to contain a sufficient amount of heavy metal adsorbent to adsorb heavy metals in soil. However, if the performance of the heavy metal adsorbent deteriorates, the heavy metal allowance of the adsorption layer decreases, and the long-term Containment safety is compromised.

The present invention has been made in view of the above circumstances, and is an embankment structure capable of suppressing deterioration of the performance of the adsorption layer over time when confining soil containing heavy metals by the adsorption layer method, and a method for maintaining the performance of the adsorption layer. , And a method for suppressing leakage of heavy metals.

The present invention has the following aspects.
[1] An embankment layer formed from soil containing heavy metals,
An adsorption layer containing a heavy metal adsorbent provided below the embankment layer and
An alkalinization prevention layer provided between the embankment layer and the adsorption layer to prevent alkalinization of the adsorption layer,
The embankment structure is equipped with.
[2] A water-impervious layer containing an alkaline water-shielding agent that covers the embankment layer, the adsorption layer, and the alkalinization prevention layer.
A water-impervious sheet provided between the adsorption layer, the alkalinization prevention layer, and the water-impervious layer,
The embankment structure of [1] further equipped with.
[3] An anti-alkali layer for preventing alkalization of the adsorption layer between an embankment layer formed from soil containing a heavy metal and an adsorption layer containing a heavy metal adsorbent provided below the embankment layer. A method of maintaining the performance of the adsorption layer.
[4] The embankment layer, the adsorption layer, and the alkalinization prevention layer are covered with a water-impervious layer containing an alkaline water-shielding agent.
The method for maintaining the performance of the adsorption layer according to [3], wherein a water-impervious sheet is provided between the adsorption layer, the alkalinization prevention layer, and the water-impervious layer.
[5] In a method for suppressing leakage of heavy metals, in which an adsorption layer containing a heavy metal adsorbent is provided below the embankment layer formed from soil containing heavy metals, and the heavy metals eluted from the embedding layer are adsorbed by the heavy metal adsorbent.
A method for suppressing leakage of heavy metals, in which an alkalinization prevention layer for preventing alkalization of the adsorption layer is provided between the embankment layer and the adsorption layer.
[6] The embankment layer, the adsorption layer, and the alkalinization prevention layer are covered with a water-impervious layer containing an alkaline water-shielding agent.
The method for suppressing leakage of heavy metals according to [5], wherein a water-impervious sheet is provided between the adsorption layer, the alkalinization prevention layer, and the water-impervious layer.

According to the present invention, it is possible to provide an embankment structure capable of suppressing deterioration of the performance of the adsorption layer over time when confining soil containing heavy metals by the adsorption layer method, a method of maintaining the performance of the adsorption layer, and a method of suppressing leakage of heavy metals. ..

It is a schematic cross-sectional view which shows the embankment structure which concerns on embodiment. It is a schematic cross-sectional view which shows the modification of the embankment structure which concerns on embodiment. It is a schematic cross-sectional view which shows the modification of the embankment structure which concerns on embodiment. It is a graph which shows the relationship between the dissolved selenium concentration after the adsorption treatment of selenate ion by acaganate, and pH.

Hereinafter, the present invention will be described with reference to the accompanying drawings with reference to embodiments.
In addition, in this specification, "~" indicating a numerical range means that the numerical values described before and after it are included as the lower limit value and the upper limit value.

FIG. 1 is a schematic cross-sectional view showing an embankment structure according to an embodiment of the present invention.
The embankment structure 10 of the present embodiment includes an embankment layer 1, an adsorption layer 2, an alkalinization prevention layer 3, an impermeable layer 4, an impermeable sheet 5, a soil covering layer 6, and a pavement 7.

The adsorption layer 2 is provided below the embankment layer 1 in contact with the ground G. The alkalinization prevention layer 3 is provided between the embankment layer 1 and the adsorption layer 2. That is, the adsorption layer 2, the alkalizing prevention layer 3, and the embankment layer 1 are laminated in this order from the lower side (ground G side) of the embankment structure 10.
The cross section in the width direction of each of the adsorption layer 2, the alkalizing prevention layer 3, and the embankment layer 1 is trapezoidal in width as it goes downward. The upper surface of the adsorption layer 2 and the lower surface of the anti-alkali layer 3 are in contact with each other, and the width of the upper surface of the adsorption layer 2 and the width of the lower end of the anti-alkali layer 3 are the same. Further, the upper surface of the anti-alkali layer 3 and the lower surface of the embankment layer 1 are in contact with each other, and the width of the upper surface of the anti-alkali layer 3 and the width of the lower surface of the embankment layer 1 are the same. The entire cross section of the adsorption layer 2, the alkalinization prevention layer 3 and the embankment layer 1 is also trapezoidal.

The impermeable layer 4 covers the upper surface and the side surface of the embankment layer 1, the side surface of the adsorption layer 2, and the side surface of the alkalizing prevention layer 3.
The water-impervious sheet 5 is arranged between the adsorption layer 2 and the alkalizing prevention layer 3 and the water-impervious layer 4, and covers the entire side surface of each of the anti-alkali layer 3 and the adsorption layer 2. Further, the water-impervious sheet 5 bends toward the water-impervious layer 4 at the position of the upper edge of the side surface of the alkalizing prevention layer 3 and enters the water-impervious layer 4. Further, the geomembrane sheet bends toward the center of the adsorption layer 2 at the position of the lower edge of the side surface of the adsorption layer 2 and covers the outer edge portion of the lower surface of the adsorption layer 2. Further, the water-impervious sheet 5 bends toward the adsorption layer 2 at a position closer to the center than the outer edge of the lower surface of the adsorption layer 2 and enters the adsorption layer 2.

The soil covering layer 6 covers the upper surface and the side surface of the impermeable layer 4. As a result, the impermeable layer 4 can be protected and the surface can be greened.
The pavement 7 is provided on the upper surface of the soil covering layer 6.

The embankment layer 1 is formed from soil containing heavy metals.
Examples of heavy metals include selenium, arsenic, lead and the like. The heavy metal contained in the soil may be one kind or two or more kinds. Heavy metals in soil may exist as simple substances or as compounds.
Examples of soil containing heavy metals include excavated soil generated during ground excavation and mountain excavation.
The content of heavy metals in the soil may be the same as the content of heavy metals in the soil (soil requiring countermeasures) that has been conventionally contained by the adsorption layer method.

The adsorption layer 2 contains a heavy metal adsorbent.
The heavy metal adsorbent adsorbs heavy metals (ions containing heavy metals) eluted from the embankment layer 1 and insolubilizes them. As the heavy metal adsorbent, one corresponding to the heavy metal contained in the soil forming the embankment layer 1 is used. The heavy metal adsorbent contained in the adsorption layer 2 may be one kind or two or more kinds.

Some heavy metal adsorbents have reduced adsorption performance in an alkaline environment. The alkaline environment is, for example, an environment in which water having a pH of 8 or more is present.
For example, when the pavement 7 is a concrete pavement, the water that has permeated the embankment layer 1 due to the concrete is alkaline. When the impermeable layer 4 contains clay such as bentonite, the water that has permeated into the embankment layer 1 due to the clay is alkaline. When such alkaline water flows down from the embankment layer 1 and permeates into the adsorption layer 2, the adsorption layer 2 becomes an alkaline environment (alkaline).
Since the embankment structure 10 includes an alkalinization prevention layer 3 between the embankment layer 1 and the adsorption layer 2, even if the water flowing down from the embankment layer 1 is alkaline, the adsorption layer 2 does not alkalize and adsorbs heavy metals. The adsorption performance of the agent is maintained. Therefore, the present invention is highly useful when a heavy metal adsorbent whose adsorption performance is deteriorated in an alkaline environment is used.

Examples of heavy metal adsorbents whose adsorption performance deteriorates in an alkaline environment include adsorbents that adsorb ions containing heavy metals using ionic bonds. In the case of such an adsorbent, the higher the alkaline environment, the lower the adsorption performance of ions containing heavy metals.

Acaganate is an example of a heavy metal adsorbent whose adsorption performance deteriorates in an alkaline environment. Akaganeite is an iron oxide mineral represented by the chemical composition β-Fe ³⁺ (O (OH, Cl)). The crystal system is a monoclinic system, and the crystallographic data of space group I2 / m, unit cell: a = 10.600, b = 3.0339, c = 10.513, β = 90.24 ° is academic. It is described in the paper "Post JE, Buchwald VF, American Mineralogist, 76 (1991) p.272-277, Crystal structure refinement of akaganeite". It is also described that the crystal structure of acaganate revealed in this paper has a tunnel structure that retains chloride ions, and a hydroxyl group is projected from the wall of the tunnel toward the center.
Akaganate adsorbs anions of inorganic compounds. Examples of the inorganic compound include inorganic compounds containing inorganic elements such as selenium, arsenic, chromium, fluorine, sulfur and phosphorus. Specific examples thereof include oxo acids of selenium, arsenic and chromium, hydrofluoric acid (hydrofluoric acid), sulfuric acid, phosphoric acid and the like.
When water containing anions of an inorganic compound comes into contact with acaganate, it is considered that the anions contained in the water are trapped in the tunnel structure of the acaganate and adsorbed. By this adsorption, the chloride ion pre-existing in the tunnel structure is replaced with the anion and desorbed.
Akaganate exhibits a strong adsorptive power to the oxo acid of selenium. Therefore, when the heavy metal contains selenium, it is preferable that the heavy metal adsorbent contains acaganate.

The content of the heavy metal adsorbent in the adsorption layer 2 may be equal to or greater than the amount required to adsorb all the heavy metals eluted from the embankment layer 1. The required amount varies depending on the type of heavy metal adsorbent and the concentration of the target substance, and is usually determined after conducting an elution test and estimating the amount of heavy metal elution from the degree of heavy metal content.
For example, the amount of selenium adsorbed by the heavy metal adsorbent is 2 g / kg, the amount of selenium eluted from the soil of the filling layer 1 is 0.5 mg / kg, and the amount of soil per unit area of the filling layer 1 is 15 t / m ² . In some cases, the required amount of adsorbent per unit area is 3,750 g / m ² . When the thickness of the adsorption layer 2 is 0.3 m and the safety factor is 1.2 times, the content of the heavy metal adsorbent is 1.5 kg / m3.

The adsorption layer 2 may be made of only a heavy metal adsorbent, or may further contain a material other than the heavy metal adsorbent. Examples of other materials include soils that do not correspond to soils requiring countermeasures.

The alkalinization prevention layer 3 is a layer that prevents the adsorption layer 2 from being alkalized (becoming an alkaline environment).
By providing the alkalizing prevention layer 3, it is possible to suppress the deterioration of the performance of the heavy metal adsorbent due to the alkalinization of the adsorption layer 2 as described above. Further, since the alkalinization prevention layer 3 also has the effect of insolubilizing the heavy metal eluted from the embankment layer 1 as in the adsorption layer 2, it is possible to reduce the contact amount of the heavy metal with the adsorption layer 2 and delay the saturation. can. As a result, the performance of the adsorption layer 2 can be maintained for a long time.

Examples of the alkalinization prevention layer 3 include a layer containing an alkalinization inhibitor.
As the alkalinization inhibitor, among those that promote the acidification of soil, those that do not contain sulfate or phosphate that preferentially binds to the adsorbent as the main component are preferable. Examples of such an alkalinization inhibitor include acidic soil such as volcanic ash soil, iron chloride, aluminum chloride, and peat moss. The alkalizing inhibitor contained in the alkalizing prevention layer 3 may be one kind or two or more kinds.

The layer containing the alkalinization inhibitor may be composed of only the alkalinization inhibitor, or may further contain a material other than the alkalization inhibitor. Examples of other materials include soils that do not correspond to soils requiring countermeasures.
The alkalinization prevention layer 3 is preferably formed from a material in which an alkalinization inhibitor and soil are mixed at a constant ratio. The constant ratio here is a ratio in consideration of the optimum pH of the adsorption layer 2.
The optimum pH of the adsorption layer 2 is determined by the type of heavy metal adsorbent. For example, when the heavy metal adsorbent has a reduced adsorption performance in an alkaline environment, the optimum pH of the adsorption layer 2 is 4 to 7. The pH of the adsorption layer 2 is the pH of the water flowing down from the alkalinization prevention layer 3.

The impermeable layer 4 contains an alkaline impermeable agent clay.
Examples of the alkaline water-shielding agent include clay and cement-based water-shielding agents. ^{As the clay, cohesive soil having a hydraulic conductivity of 1 × 10-8} cm / s or less when formed into a layer having a thickness of 0.5 m is used, and examples thereof include bentonite. The alkalizing inhibitor contained in the impermeable layer 4 may be one kind or two or more kinds.
The impermeable layer 4 may be made of only an alkaline impermeable agent, or may contain a material other than the alkaline impermeable agent.
The impermeable performance of the impermeable layer 4 may be the same as the impermeable performance of the impermeable layer in the conventional adsorption layer construction method.

Examples of the water-impervious sheet 5 include a synthetic rubber type (synthetic resin type), an asphalt type, and a bentonite type.
The thickness of the water-impervious sheet 5 may be, for example, 1.5 mm or more.
The water-impervious performance of the water-impervious sheet 5 ^{is preferably 1 × 10 -9} cm / s or less as the value of the hydraulic conductivity.

The soil covering layer 6 may be the same as the soil covering layer used in the conventional adsorption layer construction method. For example, the soil covering layer 6 can be formed by soil or the like that does not correspond to the soil requiring countermeasures.

Examples of the pavement 7 include asphalt pavement and concrete pavement.

The embankment structure 10 can be constructed, for example, by the following procedure.
A water-impervious sheet 5 is arranged on the ground G so as to straddle the position of the outer edge of the adsorption layer 2, and a material containing a heavy metal adsorbent is arranged therein to form the adsorption layer 2. Next, a material containing an alkalinization inhibitor is placed on the adsorption layer 2 to form the alkalinization prevention layer 3. At this time, the material constituting the alkalizing prevention layer 3 and the material constituting the adsorption layer 2 may be partially mixed. Next, the soil containing heavy metals is filled on the alkalizing prevention layer 3 to form the embankment layer 1. Next, the side surfaces of the adsorption layer 2 and the alkalinization prevention layer 3 are covered with a portion of the water-impervious sheet 5 that protrudes outside the adsorption layer 2, and in that state, the embankment layer 1, the adsorption layer 2 and the alkalinization prevention layer 3 are covered. Is covered with a material containing clay to form a water-impervious layer 4. Next, the impermeable layer 4 is covered with soil that does not correspond to the soil requiring countermeasures to form the soil covering layer 6. After that, the pavement 7 is formed on the soil covering layer 6.

The operation of the embankment structure 10 will be described.
When rainwater permeates the embankment layer 1, heavy metals are eluted from the soil, and water containing heavy metals flows down from the embankment layer 1 and reaches the adsorption layer 2 via the alkalizing prevention layer 3. Water containing a heavy metal is acidified as it passes through the alkalizing prevention layer 3, which insolubilizes a part of the heavy metal. The insolubilized heavy metal remains in the alkalizing prevention layer 3 as it is. Heavy metals that have passed through the alkalinization prevention layer 3 while being dissolved in acidified water without being insolubilized are adsorbed by the adsorption layer 2 and insolubilized. As a result, heavy metals are prevented from leaking to the outside of the embankment structure 10.

In the embankment structure 10, since the alkalizing prevention layer 3 is provided between the embankment layer 1 and the adsorption layer 2, the performance of the adsorption layer 2 can be maintained for a long period of time.
That is, even if the water flowing down from the embankment layer 1 is alkaline, it is acidified by the alkalizing prevention layer 3, so that when this water permeates the adsorption layer 2, the adsorption layer 2 is not alkalized. Therefore, it is possible to suppress the deterioration of the performance of the heavy metal adsorbent due to the exposure of the heavy metal adsorbent to the alkaline environment.
Further, the alkalinization prevention layer 3 has the effect of insolubilizing the heavy metal eluted from the embankment layer 1 as in the adsorption layer 2. Therefore, the amount of heavy metal contacting the adsorption layer 2 can be reduced and saturation can be delayed.
Since the performance of the adsorption layer 2 can be maintained for a long period of time, leakage of the heavy metal embankment structure 10 to the outside can be prevented for a long period of time.

Further, in the embankment structure 10, since the embankment layer 1, the adsorption layer 2 and the alkalizing prevention layer 3 are covered with the impermeable layer 4, the permeation of rainwater into the embankment layer 1 is suppressed and heavy metals are contained. It is suppressed that a large amount of water flows into the adsorption layer 2, and further, the water that has permeated into the embankment layer 1 is suppressed from flowing out from the side surface of the embankment layer 1, the side surface of the alkalizing prevention layer 3, and the side surface of the adsorption layer 2. ing. Therefore, the water that has permeated the embankment layer 1 always passes through the alkalizing prevention layer 3 and the adsorption layer 2.

Further, in the embankment structure 10, the water-impervious sheet 5 prevents the adsorption layer 2, the alkalizing prevention layer 3, and the water-impervious layer 4 from coming into contact with each other. As a result, it is suppressed that the adsorption layer 2 becomes an alkaline environment due to the clay of the impermeable layer 4 and that the impermeable performance of the impermeable layer 4 deteriorates. When the alkalinization prevention layer 3 comes into contact with the impermeable layer 4, there is a concern that the impermeable performance may deteriorate due to neutralization.

In particular, the impermeable sheet 5 bends toward the center of the adsorption layer 2 at the position of the lower edge of the side surface of the adsorption layer 2, covers the outer edge of the lower surface of the adsorption layer 2, and is more centered than the outer edge of the lower surface of the adsorption layer 2. By bending toward the adsorption layer 2 at the position on the side and entering the adsorption layer 2, the water that has permeated the filling layer 1 enters the ground G through the gap between the impermeable sheet 5, the adsorption layer 2, and the alkalinization prevention layer 3. The effect of suppressing the outflow to the water and surely passing through the alkalizing prevention layer 3 can be obtained.
The water-impervious sheet 5 bends toward the impermeable layer 4 at the position of the upper edge of the side surface of the alkalizing prevention layer 3 and enters the impermeable layer 4, so that the water permeating the embankment layer 1 is impermeable. The effect of suppressing the outflow from the gap between the sheet 5 and the impermeable layer 4 can be obtained.

Subsequently, a modified example of the above-described embodiment will be described.
2 and 3 are schematic cross-sectional views of the embankment structure according to the modified example of the above embodiment, respectively. In the following description, the same components as those in the above-described embodiment will be designated by the same reference numerals, and the description thereof will be omitted as appropriate.
The embankment structure 20 shown in FIG. 2 is provided not in a flat place but in a valley-like place (it is a valley-filled embankment structure), and a drainage channel 8 is provided in the ground below the adsorption layer 2. It differs from the above-described embodiment in that the drainage ditch 9 is provided along the outer edge of the embankment layer 1. The drainage flow path 8 is provided near the boundary between the inclined surface and the flat surface forming the valley-shaped ground G.
The embankment structure 20 shown in FIG. 3 is provided not on a flat place but on an inclined place (natural inclined surface, slope, etc.), and a drainage channel 8 is provided in the ground below the adsorption layer 2. It differs from the above-described embodiment in that the drainage ditch 9 is provided along the outer edge of the embankment layer 1 on the upper side of the inclined surface.

Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments. Each configuration in the above embodiment and a combination thereof are examples, and the configuration can be added, omitted, replaced, and other changes can be made without departing from the spirit of the present invention.

(Synthesis of Akaganate)
To 1 L of a 0.2 mol / L iron (III) chloride aqueous solution, 1 L of 0.4 mol / L sodium hydroxide was added, and while gently stirring for 5 minutes, an aqueous solution of about pH 2 (Fe ³⁺ : OH ⁻ = about). In 1: 2), caustic was produced. Then, sodium hydroxide was further added to the suspension containing the produced acaganate, the pH was adjusted to 4 to 5, and the acaganates were agglomerated with each other while gently stirring for 5 minutes. The agglomerated akaganate was collected by filtration to obtain a dry clay-like lump of akaganate. Acaganate, which was obtained by crushing this mass in a mortar into powder, was used in the following experiment.
Assuming that the yield when all the iron ions charged as iron (III) chloride became acaganate was 100% on a molar basis, the acaganate was recovered at a yield of 95%.
When the synthesized acagnate was analyzed by an X-ray diffractometer (XRD), a peak indicating accadate was confirmed.

(Test Example 1)
An aqueous solution (about pH 7) containing sodium selenite at 1.152 mg / L was prepared. The following experimental procedure was carried out using the acaganate obtained in the above synthesis.
The prepared aqueous solution of sodium selenite was divided into a plurality of parts, and the acaganate synthesized above was added to each aqueous solution at 0.2 (w / w)%. Subsequently, the pH of each aqueous solution was adjusted to 2 to 10 using sodium hydroxide or hydrochloric acid, and selenate ion was adsorbed on acaganate. After gently stirring at about 20 ° C. for several minutes, the dissolved selenium concentration in the supernatant of each aqueous solution was measured by JIS K0102: 2013 “67. ICP Emission Spectrometry of Hydrogen Compound Generation of Selenium”.
The results of the above experiment are shown in the graph of FIG. In FIG. 4, the broken line represents the initial concentration of dissolved selenium in the aqueous solution (1.152 mg / L), the vertical axis represents the concentration of dissolved selenium in the aqueous solution, and the horizontal axis represents the pH of each aqueous solution after pH adjustment.
From the results of FIG. 4, it is clear that the adsorption of selenate ion by acaganate is excellent in the range of less than p8, particularly in the range of pH 4 to 7, and that the adsorption amount decreases when the pH is 8 or more.

1 Embankment layer 2 Adsorption layer 3 Alkaliification prevention layer 4 Impermeable layer 5 Impermeable sheet 6 Soil covering layer 7 Pavement 10 Embankment structure G Ground

Claims (3)

An embankment layer formed from soil containing heavy metals,
An adsorption layer containing a heavy metal adsorbent provided below the embankment layer and
An alkalinization prevention layer provided between the embankment layer and the adsorption layer to prevent alkalinization of the adsorption layer,
An impermeable layer containing an alkaline impermeable agent that covers the embankment layer, the adsorption layer, and the anti-alkali layer.
A water-impervious sheet provided between the adsorption layer, the alkalinization prevention layer, and the water-impervious layer,
The embankment structure is equipped with. An alkalinization prevention layer for preventing alkalization of the adsorption layer is provided between the embankment layer formed from the soil containing heavy metals and the adsorption layer containing a heavy metal adsorbent provided below the embankment layer .
The embankment layer, the adsorption layer, and the alkalinization prevention layer are covered with a water-impervious layer containing an alkaline water-shielding agent.
The water-barrier sheet Ru provided between the water shield layer and the adsorption layer and the alkali prevention layer, the performance maintenance method of the adsorption layer. In a method for suppressing leakage of heavy metals, in which an adsorption layer containing a heavy metal adsorbent is provided below the embankment layer formed from soil containing heavy metals, and the heavy metals eluted from the embankment layer are adsorbed by the heavy metal adsorbent.
An alkalinization prevention layer for preventing alkalinization of the adsorption layer is provided between the embankment layer and the adsorption layer .
The embankment layer, the adsorption layer, and the alkalinization prevention layer are covered with a water-impervious layer containing an alkaline water-shielding agent.
Water shield sheet Ru and provided, heavy metals method suppressing leakage between the adsorption layer and the alkali prevention layer and the water shield layer.

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