Method for forming heavy metal adsorbent

Abstract

To provide a heavy metal adsorption body for adsorbing heavy metal by a simple method and efficiently, in soil.SOLUTION: There is provided a formation method of a heavy metal adsorption body in which, a first solution and a second solution are caused to contact in processing object soil, for forming a heavy metal adsorption body at an original position, the method comprises: a first step for supplying the first solution to the processing object soil from a preset supply point, for permeating the first solution in the processing object soil; a second step for supplying the second solution to the processing object soil from the supply point, for permeating the second solution in the processing object soil for bringing the same into contact with the first solution. In the method, any one of the first and second solutions includes a calcium compound, the other thereof includes a phosphate compound.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for forming a heavy metal adsorbent in the ground, the method being for forming a heavy metal adsorbent that adsorbs heavy metals. [Background technology]

[0002] When soil containing heavy metals is present in the unsaturated zone of the ground, rainwater that seeps into the unsaturated zone from the ground surface washes out the heavy metals before reaching the saturated zone, which can cause the heavy metals to move with the groundwater and spread to the surrounding ground.

[0003] For this reason, soil purification measures have been implemented, such as excavating and washing soil containing heavy metals, or scattering iron powder, which absorbs heavy metals, on soil containing heavy metals. Both of these methods are effective when the soil containing heavy metals is shallow near the surface. However, when the soil contains heavy metals over a wide depth range, the construction costs become enormous, and when scattering the iron powder, it is filtered out near the surface, so it is not necessarily an appropriate method.

[0004] In this context, for example, Patent Document 1 discloses a method in which a calcium compound and a phosphate compound are added to fluorine-contaminated soil, mixed and stirred, and reacted with fluoride ions in the soil to form fluoroapatite, thereby suppressing the elution of fluorine. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-305387 A Summary of the Invention [Problem to be solved by the invention]

[0006] According to Patent Document 1, elution of fluorine can be efficiently suppressed. However, the work tends to be large-scale, as heavy machinery for ground improvement is required to mix and stir the ground. Therefore, problems arise in terms of workability, such as difficulty in carrying out the work when the target area is narrow or in an environment where sufficient working space cannot be secured. In addition, when the target area is wide, the amounts of calcium compounds and phosphate compounds to be added to the soil also increase, which tends to be economically disadvantageous.

[0007] The present invention has been made in view of the above problems, and a main object of the present invention is to form a heavy metal adsorbent in the ground that efficiently adsorbs heavy metals by a simple method. [Means for solving the problem]

[0008] In order to achieve the above object, the method for forming a heavy metal adsorbent of the present invention is a method for forming a heavy metal adsorbent in situ by contacting a first aqueous solution with a second aqueous solution in the ground to be treated, the first aqueous solution being supplied to the ground to be treated from a supply point set in advance, It penetrates into the gaps between soil particles. a first step of permeating the first aqueous solution into the After the first step, The second aqueous solution is supplied from the supply point to the ground to be treated, and It penetrates into the gaps between soil particles. and a second step of permeating the second aqueous solution into the first aqueous solution to contact the first aqueous solution, wherein one of the first aqueous solution and the second aqueous solution contains a calcium compound and the other contains a phosphate compound, The amount of the first aqueous solution to be infiltrated is an amount that fills the gaps in the treatment target area. It is characterized by:

[0009] Method for forming the heavy metal adsorbent of the present invention the ground to be treated is in an unsaturated zone, the supply point is set at a predetermined position on or above the ground surface of the unsaturated zone, the first aqueous solution is dripped at a flow rate set based on a predetermined rainfall intensity in the first step, and the second aqueous solution is dripped within a range not exceeding the flow rate set in the first step in the second step. . In the second step, the second aqueous solution is dropped while the flow rate is increased stepwise.

[0010] The method for forming a heavy metal adsorbent of the present invention is characterized in that the ground to be treated is a saturated zone, the supply point is set at a predetermined position inside the saturated zone, and in the first step and the second step, the first aqueous solution and the second aqueous solution are respectively injected from the supply point.

[0011] The method for forming a heavy metal adsorbent of the present invention is a method for forming a heavy metal adsorbent in situ by contacting a first aqueous solution with a second aqueous solution in ground to be treated, the method comprising: a first step of supplying the first aqueous solution to the ground to be treated from a predetermined supply point and allowing the first aqueous solution to permeate into the ground to be treated; and a second step of supplying the second aqueous solution to the ground to be treated from the supply point and allowing the second aqueous solution to permeate into the ground to be contacted with the first aqueous solution, wherein one of the first aqueous solution and the second aqueous solution contains a calcium compound and the other contains a phosphate compound, the ground to be treated is in an unsaturated zone, the supply point is set at a predetermined position on or above the ground surface of the unsaturated zone, the first aqueous solution is dripped at a flow rate set based on a predetermined rainfall intensity in the first step, and the second aqueous solution is dripped in a range not exceeding the flow rate set in the first step. . In the second step, the second aqueous solution is dropped while the flow rate is increased stepwise.

[0012] Method for forming the heavy metal adsorbent of the present inventionAccording to the method, a heavy metal adsorbent capable of adsorbing fluorine in situ is formed by successively infiltrating and contacting a first aqueous solution and a second aqueous solution containing a calcium compound or a phosphate compound into the ground to be treated. This eliminates the need for extensive work such as excavating and cleaning the ground to be treated for the purpose of removing heavy metals, or mixing and stirring chemicals into the ground to be treated for the purpose of insolubilization. . Therefore, even if the ground to be treated is narrow or in an environment where sufficient working space cannot be secured, it is possible to efficiently form heavy metal adsorbents in situ without any restrictions, and it is possible to adsorb fluorine washed out by rainwater that permeates the ground to be treated onto the heavy metal adsorbents without it being washed out. . In addition, since this method involves infiltrating the first and second aqueous solutions into the ground to be treated, the amount of each solution to be infiltrated can be at least enough to fill the gaps between soil particles in the ground to be treated, and preferably about twice that amount. This, combined with the elimination of the need for large-scale work, makes it possible to economically form a heavy metal adsorbent in situ.

[0013] According to the method for forming a heavy metal adsorbent of the present invention, the first aqueous solution is dripped at a flow rate set based on a predetermined rainfall intensity, so that the first aqueous solution permeates into the ground to be treated with a behavior similar to that of rainwater permeating during rainfall. After dripping the first aqueous solution, the second aqueous solution is dripped at a flow rate not exceeding this flow rate. This allows the second aqueous solution to come into contact with the first aqueous solution while suppressing the phenomenon of the first aqueous solution being pushed out and washed away.

[0014] This allows many of the heavy metal adsorbents to be formed in positions that correspond to the behavior of rainwater infiltration in the unsaturated zone. Therefore, when rain falls, the rainwater permeates and flows down the unsaturated zone while washing out the fluorine and reliably contacting the heavy metal adsorbents. Therefore, the fluorine washed out by the rainwater can be efficiently adsorbed by the heavy metal adsorbents, and the amount of fluorine that flows out from the unsaturated zone can be significantly reduced.

[0016] According to the method for forming a heavy metal adsorbent of the present invention, the flow rate of the second aqueous solution is increased stepwise within a range that does not exceed the flow rate set when the first aqueous solution is dropped. This prevents the first aqueous solution from being washed away, and allows the second aqueous solution to penetrate into the areas where the suction acting between soil particles is large (areas with small gaps) first in the first drop, and also penetrates in the depth direction, forming a heavy metal adsorbent.

[0017] After this, the second aqueous solution can be gradually permeated into the areas with smaller suction or in the planar direction to form heavy metal adsorbents in these areas. This makes it possible to more reliably form heavy metal adsorbents in the positions corresponding to the behavior of rainwater permeation, where the first aqueous solution was permeated in the first step.

[0019] According to the method for forming a heavy metal adsorbent of the present invention, it is possible to form a heavy metal adsorbent in a wide area in the saturated zone, centering on the supply point. As a result, even if fluorine flows out from the unsaturated zone into the saturated zone, most of it is adsorbed by the heavy metal adsorbent while flowing down through the saturated zone together with groundwater. Therefore, it is possible to prevent the phenomenon that fluorine moves together with groundwater and diffuses into the surrounding ground. Effect of the Invention

[0020] According to the present invention, it is possible to efficiently form a heavy metal adsorbent that adsorbs fluorine in the ground to be treated by a simple method of successively permeating a first aqueous solution and a second aqueous solution containing a calcium compound or a phosphate compound into the ground to be treated. [Brief description of the drawings]

[0021] [Figure 1] FIG. 2 is a diagram showing a state in which a heavy metal adsorbent is formed in the ground to be treated in an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a procedure for forming a heavy metal adsorbent in an unsaturated zone in an embodiment of the present invention. [Diagram 3] FIG. 13 is a diagram showing a state of verifying the effect of a heavy metal adsorbent formed in an unsaturated zone in an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing a procedure for forming a heavy metal adsorbent in a saturated zone in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention is a method for forming a heavy metal adsorbent capable of adsorbing fluorine in situ in the ground to be treated. The details of the method will be described below with reference to Figs. 1 to 4, taking as examples a case where the ground to be treated is an unsaturated zone where soil containing fluorine-containing slag exists, and a case where the ground is a saturated zone located below the unsaturated zone.

[0023] As shown in Fig. 1, a heavy metal adsorbent 3 is formed in each of the unsaturated zone 1 and the saturated zone 2. In this embodiment, calcium phosphate is used as the heavy metal adsorbent 3, and is formed by contacting a first aqueous solution 4 containing a calcium compound with a second aqueous solution 5 containing a phosphate compound. Calcium phosphate is a substance that is widely known as a chemical substance that can insolubilize fluorine as fluoroapatite.

[0024] The calcium compound contained in the first aqueous solution 4 is preferably calcium chloride, and the phosphate compound contained in the second aqueous solution 5 is preferably sodium dihydrogen phosphate or sodium hydrogen phosphate. However, the calcium compound and the phosphate compound are not limited thereto, and any compound that can form calcium phosphate upon contact with each other may be used.

[0025] The first aqueous solution 4 and the second aqueous solution 5 are each infiltrated into and brought into contact with the unsaturated zone 1 in separate steps, thereby forming the heavy metal adsorbent 3 in situ. This makes it possible to form the heavy metal adsorbent 3 in situ efficiently and without any constraints, even when the unsaturated zone 1 to be treated is in a narrow environment or when a sufficient working space cannot be secured.

[0026] The process of infiltrating the first aqueous solution 4 and the second aqueous solution 5 in separate steps is similar to that for forming the heavy metal adsorbent 3 in the saturated zone 2. Details of the method for forming the heavy metal adsorbent 3 in situ will be described below for each of the unsaturated zone 1 and the saturated zone 2.

[0027] <<Method for forming heavy metal adsorbent 3 in unsaturated zone 1>> In this embodiment, the procedure for forming a heavy metal adsorbent 3 will be described using as an example a case in which a first aqueous solution 4 and a second aqueous solution 5 are infiltrated into an unsaturated zone 1 using a perforated pipe 6 as shown in Figure 1.

[0028] As shown in Fig. 1, the perforated pipe 6 is arranged in a horizontal position on or above the ground surface of the unsaturated zone 1, and a plurality of pores 62 communicating with the hollow portion 61 are provided at predetermined intervals in the axial direction of the perforated pipe 6 at a position in the pipe wall facing the ground surface. The pores 62 may be formed in any size or shape as long as they are formed so that the liquid supplied to the hollow portion 61 can be dripped. In Fig. 1, three perforated pipes 6 having such a shape are arranged in parallel at a predetermined interval, but the number and arrangement interval are not limited in any way.

[0029] <Step of penetrating first aqueous solution 4 (first step)> After the perforated pipe 6 having the above-mentioned configuration is placed at a supply point P set in advance in the unsaturated zone 1, the first aqueous solution 4 is supplied to the perforated pipe 6. Then, the first aqueous solution 4 continuously drips from the pores 62 toward the unsaturated zone 1, and as shown in Fig. 2(a), it adheres to the surfaces of the soil particles or enters the gaps between the soil particles, and permeates in the depth direction due to gravity while spreading in the horizontal direction.

[0030] At this time, the first aqueous solution 4 is controlled to drip from the pores 62 toward the unsaturated zone 1 at a flow rate set based on a predetermined rainfall intensity. This is intended to cause the first aqueous solution 4 to permeate into the unsaturated zone 1 in a manner similar to the rainwater permeation that occurs when continuous rainfall occurs. Note that rainfall intensity refers to the amount of rainfall (mm / h) converted per unit time (for example, per hour).

[0031] The rainfall intensity used to set the flow rate is preferably 18 to 19 (mm / h), which corresponds to the maximum rainfall intensity expected in Japan, excluding unforeseen events such as torrential rain. This allows the first aqueous solution 4 to infiltrate into the unsaturated zone 1 in the manner expected for the infiltration behavior of rainwater when rainfall of the maximum intensity occurs.

[0032] The amount of the first aqueous solution 4 to be dripped into the unsaturated zone 1 should be at least an amount sufficient to fill the gaps in the treatment target area of ​​the unsaturated zone 1 (the product of the volume of the entire target area and the porosity), but it is preferable to prepare about twice that amount.

[0033] <Step of penetrating the second aqueous solution 5 (second step)> After the first aqueous solution 4 thus prepared is dripped at the above flow rate, the perforated pipe 6 is washed and the second aqueous solution 5 is supplied and continuously dripped into the unsaturated zone 1 through the pores 62 of the perforated pipe 6 in the same manner as the first aqueous solution 4, as shown in Fig. 2(b). At this time, the second aqueous solution 5 should be dripped at a flow rate not exceeding the flow rate set when the first aqueous solution 4 was dripped.

[0034] This makes it possible to suppress the phenomenon in which the first aqueous solution 4 that has permeated into the unsaturated zone 1 is pushed out and washed away by the second aqueous solution 5. Furthermore, since the second aqueous solution 5 comes into contact with the first aqueous solution 4 that has permeated into the unsaturated zone 1 in a manner similar to the permeation of rainwater, it becomes possible to reliably form most of the heavy metal adsorbents 3 at positions in the unsaturated zone 1 that correspond to the permeation behavior of rainwater.

[0035] Therefore, as shown in Figure 2(c), when rain falls in the unsaturated zone 1 after the heavy metal adsorbent 3 has been formed, the rainwater washes out the fluorine present in the unsaturated zone 1 and permeates and flows down through the unsaturated zone 1 while coming into contact with the heavy metal adsorbent 3. As a result, most of the rainwater R2 with a high fluorine concentration has fluorine adsorbed by the heavy metal adsorbent 3, becoming rainwater R1 with a low fluorine concentration, which flows down into the saturated zone 2. Therefore, it is possible to significantly reduce the amount of fluorine that flows down into the saturated zone 2 by the rainwater permeating the unsaturated zone 1.

[0036] <Step of Permeating the Second Aqueous Solution 5 (Other Examples)> Incidentally, the second step of dripping the second aqueous solution 5 and permeating it into the unsaturated zone 1 may be carried out in multiple batches. In this case, the second aqueous solution 5 is dripped while increasing the flow rate stepwise within a range that does not exceed the flow rate set when dripping the first aqueous solution 4.

[0037] For example, when the operation of dripping the second aqueous solution 5 is divided into three times, the flow rate for the first drip is set to about 30% of the flow rate when the first aqueous solution 4 was dripped, the flow rate for the second drip is set to about 50%, and the flow rate for the third drip is set to about 70%, and 1 / 3 of the amount of the second aqueous solution 5 prepared in advance is dripped each time.

[0038] Then, in the first drip, the second aqueous solution 5 penetrates first into the areas where suction between soil particles is large (areas with small gaps), and flows down in the depth direction due to gravity. After this, in the second and third drips, as the flow rate increases, the second aqueous solution 5 penetrates into the areas where suction between soil particles is small (areas with large gaps) and in the horizontal direction. This allows the second aqueous solution 5 to efficiently come into contact with the entire first aqueous solution 4 that has penetrated into the unsaturated zone 1, making it possible to reliably form the heavy metal adsorbent 3 in the area where the first aqueous solution 4 has penetrated.

[0039] <<Verification of the effectiveness of heavy metal adsorbent 3>> The effect of the heavy metal adsorbent 3 formed in the unsaturated zone 1 through the above-mentioned first and second steps was verified in the following procedure.

[0040] The experiment was carried out at an experimental site separated by a water barrier 8 as shown in Fig. 3(a). The heavy metal adsorbent 3 was formed by adopting the above-mentioned method (other examples) in which the first aqueous solution 4 was dripped and allowed to permeate into the unsaturated zone 1, where soil containing fluorine-containing slag exists, and then the second aqueous solution 5 was dripped and allowed to permeate in three separate portions.

[0041] The volume of unsaturated zone 1 to be treated is 24 m 3 (length 4m × width 1m × depth 6m), and the first aqueous solution 4 was an aqueous solution containing calcium chloride (concentration: 3.6 wt%), and the second aqueous solution 5 was an aqueous solution containing disodium hydrogen phosphate (concentration: 2.0 wt%).

[0042] The amount of dripping was the amount that filled the gaps in the experimental area of ​​the unsaturated zone 1 (the above volume of 24 m 3The amount of calcium in the groundwater was set to twice the product of the amount of calcium and the porosity. This was because, when the calcium concentration in the groundwater was observed over time in an observation well 9 installed in the experimental site while dripping the first aqueous solution 4, it was confirmed that the calcium concentration had reached a steady state when the amount of calcium dripping reached the above amount. The porosity was set to 0.3.

[0043] For the dropping of the first aqueous solution 4 and the second aqueous solution 5, three rows of perforated pipes 6, each 4 m long and 25 mm in diameter, were arranged at 50 cm intervals. The perforated pipes 6 had 16 mm fine holes 62 equipped with pressure valves arranged at 300 mm intervals.

[0044] Water was sprayed 10 onto the unsaturated zone 1 in which the heavy metal adsorbent 3 was formed under the above conditions using the perforated pipe 6 used in the formation of the heavy metal adsorbent 3, at a flow rate equivalent to a rainfall intensity of 18 (mm / h), and groundwater was sampled from an observation well 9. The groundwater was sampled for five days starting immediately after the water spraying 10, and the fluorine concentration in the groundwater was monitored over time.

[0045] As a comparative example, water was sprayed 10 under similar conditions on the unsaturated zone 1 before the heavy metal adsorbent 3 was formed at the experimental site, and the fluorine concentration in the groundwater was observed over time. Figure 3(b) shows the results of the experiment.

[0046] Figure 3(b) shows that in the unsaturated zone 1 before the formation of the heavy metal adsorbent 3, the fluorine concentration in the groundwater was below the environmental standard at about 0.6 mg / L immediately after watering 10. However, it can be seen that two days after watering 10, the fluorine concentration rose to about 1.4 mg / L, and continued to exceed the environmental standard until the fourth day. This can be assumed to be because the watering 10 washed out the fluorine present in the unsaturated zone 1 and caused it to flow into the saturated zone 2.

[0047] On the other hand, in the unsaturated zone 1 after the heavy metal adsorbent 3 was formed, the fluorine concentration in the groundwater remained at about 0.4 mg / L and did not exceed the environmental standard even five days after the watering 10. This can be assumed to be because the water that flowed into the unsaturated zone 1 by the watering 10 efficiently came into contact with and permeated the heavy metal adsorbent 3, causing the washed-out fluorine to be reliably adsorbed by the heavy metal adsorbent 3.

[0048] <<Method for forming heavy metal adsorbent 3 in saturated zone 2>> Next, when the ground to be treated is in the saturated zone 2, the procedure for forming a heavy metal adsorbent 3 as shown in FIG. 1 in the saturated zone 2 will be explained below with reference to FIGS. 1 and 4, taking the example of using a chemical injection pipe 7.

[0049] 1, any type of chemical injection pipe 7 may be used as long as it is disposed or inserted into a drilled hole provided so as to reach the saturated zone 2 from the unsaturated zone 1, and is capable of injecting the first aqueous solution 4 and the second aqueous solution 5 into the saturated zone 2. For example, in this embodiment, a pipe material is used in which a strainer 72 communicating with a hollow portion 71 is provided on the peripheral wall in the height range in contact with the saturated zone 2. The chemical injection pipe 7 having such a shape is placed at a supply point P set in advance in the saturated zone 2.

[0050] <Step of penetrating first aqueous solution 4 (first step)> As shown in Figure 4(a), the first aqueous solution 4 is supplied to the chemical injection pipe 7 placed at the supply point P, and the first aqueous solution 4 is injected into the saturated zone 2 at a predetermined injection pressure. Then, the first aqueous solution 4 pushes out the groundwater from the gaps between the soil particles in the saturated zone 2, and penetrates in the depth direction while spreading in the horizontal direction.

[0051] At this time, the injection pressure of the first aqueous solution 4 is set to a level that can push groundwater out of the gaps between the soil particles in the saturated zone 2, but does not significantly disturb the saturated zone 2. The injection amount is prepared to fill the gaps in the treatment target range of the saturated zone 2, but it is also advisable to take into account the amount that may be washed away due to the influence of groundwater.

[0052] <Step of penetrating the second aqueous solution 5 (second step)> After the first aqueous solution 4 thus prepared is injected at the above-mentioned injection pressure, as shown in Fig. 4(b), the chemical injection pipe 7 is cleaned and then the second aqueous solution 5 is supplied and injected into the saturated zone 2 at the same injection pressure and amount as the first aqueous solution 4. As a result, the second aqueous solution 5 comes into contact with the first aqueous solution 4 that has spread in the horizontal direction and penetrated in the depth direction in the saturated zone 2 centered on the supply point P, and the heavy metal adsorbent 3 is formed.

[0053] Therefore, as shown in Figure 4(c), when fluorine-containing groundwater W2 flowing out from the unsaturated zone 1 flows down through the saturated zone 2 in which the heavy metal adsorbent 3 is formed and permeates into this heavy metal adsorbent 3, much of the fluorine is adsorbed by the heavy metal adsorbent 3 and becomes harmless groundwater W1, which is then discharged into the saturated zone 2. Therefore, even if fluorine flows out from the unsaturated zone 1 into the saturated zone 2, it is possible to suppress the phenomenon of fluorine moving together with the groundwater and diffusing into the surrounding ground.

[0054] The method for forming a heavy metal adsorbent of the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit and scope of the present invention.

[0055] For example, in this embodiment, the first aqueous solution 4 is set to an aqueous solution containing a calcium compound, and the second aqueous solution 5 is set to an aqueous solution containing a phosphate compound. However, this is not limited to this, and the aqueous solution containing a phosphate compound may be set to the first aqueous solution 4 and permeated first.

[0056] In the present embodiment, the perforated pipe 6 is used as a device for dripping the first aqueous solution 4 and the second aqueous solution 5 into the unsaturated zone 1, but the present invention is not limited to this. Any device may be used as long as it can drip the first aqueous solution 4 and the second aqueous solution 5 at a desired rainfall intensity without disturbing the ground surface of the unsaturated zone 1.

[0057] Furthermore, in the method for forming the heavy metal adsorbent 3, the operation of carrying out the above-mentioned first step and second step is regarded as one cycle, and this operation may be repeated a number of times.

[0058] In this embodiment, the heavy metal adsorbent 3 is formed in both the unsaturated zone 1 and the saturated zone 2, but it may be formed in either one of them. [Explanation of symbols]

[0059] 1 Unsaturated Zone 2. Saturation Zone 3 Heavy metal adsorbent 4 1st aqueous solution 5 Second aqueous solution 6 Perforated pipe 61 Hollow part 62 Pore 7. Chemical injection pipe 71 Hollow part 72 Strainer 8. Water-impermeable walls 9. Observation Well 10 Watering R1 Rainwater with low fluoride concentration R2 Rainwater with high fluoride concentration W1 Decontaminated groundwater W2 Fluorine-containing groundwater

Claims

1. A method for forming a heavy metal adsorbent in situ by contacting a first aqueous solution with a second aqueous solution in ground to be treated, comprising the steps of: a first step of supplying the first aqueous solution to the ground to be treated from a predetermined supply point and allowing the first aqueous solution to permeate into gaps between soil particles in the ground to be treated; a second step of supplying the second aqueous solution from the supply point to the ground to be treated after the first step, and allowing the second aqueous solution to penetrate into gaps between soil particles in the ground to be treated and contact the second aqueous solution with the first aqueous solution; one of the first aqueous solution and the second aqueous solution contains a calcium compound and the other contains a phosphate compound; A method for forming a heavy metal adsorbent, wherein the amount of the first aqueous solution to be permeated is an amount that fills gaps in the treatment target area.

2. 2. The method for forming a heavy metal adsorbent according to claim 1 , The ground to be treated is an unsaturated zone, and the supply point is set at a predetermined position on or above the ground surface of the unsaturated zone; In the first step, the first aqueous solution is dropped at a flow rate set based on a predetermined rainfall intensity, A method for forming a heavy metal adsorbent, wherein in the second step, the second aqueous solution is dropped at a flow rate not exceeding the flow rate set in the first step.

3. 3. The method for forming a heavy metal adsorbent according to claim 2, A method for forming a heavy metal adsorbent, wherein in the second step, the second aqueous solution is dropped while a flow rate is increased stepwise.

4. 2. The method for forming a heavy metal adsorbent according to claim 1 , The ground to be treated is a saturated zone, The supply point is set at a predetermined position inside the saturated zone, A method for forming a heavy metal adsorbent, characterized in that in the first step and the second step, the first aqueous solution and the second aqueous solution are respectively injected from the supply point.

5. A method for forming a heavy metal adsorbent in situ by contacting a first aqueous solution with a second aqueous solution in ground to be treated, comprising: A first step of supplying the first aqueous solution to the ground to be treated from a predetermined supply point and allowing the first aqueous solution to permeate the ground to be treated; A second step of supplying the second aqueous solution from the supply point to the ground to be treated and allowing the second aqueous solution to permeate into the ground to be treated and contact with the first aqueous solution, one of the first aqueous solution and the second aqueous solution contains a calcium compound and the other contains a phosphate compound; The ground to be treated is an unsaturated zone, and the supply point is set at a predetermined position on or above the ground surface of the unsaturated zone, and in the first step, the first aqueous solution is dripped at a flow rate set based on a predetermined rainfall intensity, A method for forming a heavy metal adsorbent, wherein in the second step, the second aqueous solution is dropped at a flow rate not exceeding the flow rate set in the first step.

6. A method for forming a heavy metal adsorbent according to claim 5, A method for forming a heavy metal adsorbent, wherein in the second step, the second aqueous solution is dropped while a flow rate is increased stepwise.

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