JP2007090301A - Method for purifying heavy metal contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for separating/removing a harmful metal in soil in situ and remedying contaminated soil to obtain purified soil. <P>SOLUTION: A method for purifying contaminated soil employs a method for purifying heavy metal contaminated soil in the ground under a ground structure, and includes the following steps of (a)-(e) for washing/removing the heavy metals in the contaminated soil in situ. The method includes: (a) the step of setting a cut-off wall in the soil for encircling the contaminated soil containing the heavy metals; (b) the step of setting a well for supplying a detergent solution and a pumping well in the contaminated soil containing the heavy metals in the cut-off wall; (c) the step of injecting the detergent solution into the well for supplying a detergent solution and immersing the whole of the contaminated soil containing the heavy metals in the cut-off wall in the detergent solution; (d) the step of pumping the detergent solution from the pumping well simultaneously with an additional injection of the detergent solution; and (e) the step of pumping the detergent solution from the pumping well simultaneously with injection of water to remove the detergent solution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for purifying soil containing heavy metals existing in the underground of a ground structure, and more particularly to a method for efficiently removing heavy metals from soil containing heavy metals.

In recent years, with the increase in surveys due to urban redevelopment, there have been an increase in cases where heavy metal contamination is found in factory sites and the like. With the establishment of the Soil Contamination Countermeasures Law in 2002, a legal system for such soil contamination is established, and it is predicted that cases such as decontamination procedures will increase significantly in the future.
On the other hand, ground structures (buildings, public facilities, general houses, etc.) constructed on the site of the factory are not subject to the presence of soil contamination in the basement of the structure, and are not subject to sufficient contamination investigations. In many cases, a structure has been constructed, and after the construction of the structure, soil contamination has been detected, which has become a major social problem in recent years.

  The current domestic pollution control measures against heavy metal contamination of soil include methods such as insolubilization, soil covering work, water shielding work, etc., which are isolated from the source of contamination from the surrounding environment. Since heavy metals are left on site, there remains a risk of re-elution due to environmental changes and causing pollution, and it is not a preferable method from the viewpoint of saving scarce resources. There is potential for damage.

  In recent years, there are many methods of excavating contaminated soil, replacing it with clean soil, and disposing of contaminated soil as industrial waste. When a structure has already been built on the land, it is necessary to dismantle the structure and then carry out the contaminated soil, which requires enormous costs and is not a preferable method. In addition, when a ground structure has already been constructed, heavy metals cannot be efficiently and completely insolubilized. Under such a background, a method for purifying soil contaminated in situ without dismantling the ground structure is strongly desired. Nevertheless, regarding the method of remediating soil contaminated in-situ, organic solvents that are burdensome to the environment are used, or extraction is incomplete due to the use of a water level gradient. It has not reached the technique which can be solved (for example, refer patent documents 1-3).

JP 2003-164844 A JP 2004-074158 A JP-A-6-023340

  The present invention has been made against the background of the problems of the prior art as described above, and its purpose is to separate and remove harmful metals in the soil from the soil and restore the contaminated soil as purified soil. It is to provide a method.

As a result of intensive studies in view of the above-described conventional technology, the present inventors are a method for purifying heavy metal-containing contaminated soil existing underground in a ground structure, and the contaminated soil is represented by the following (a) to ( e) Remove and remove hazardous metals from contaminated soil and remove by-products using a contaminated soil remediation method, characterized in that heavy metals are washed and removed with an aqueous cleaning agent solution in situ. It came to complete the method of repairing the contaminated soil as a purified soil without putting out anything.
(A) A step of installing a water blocking wall surrounding the heavy metal-containing contaminated soil in the soil (b) A step of installing a cleaning solution supply well and a pumping well on the heavy metal-containing contaminated soil in the water blocking wall (c) Injecting the cleaning solution into the cleaning solution supply well and immersing the entire heavy metal-containing contaminated soil in the water blocking wall in the cleaning solution (d) Pumping the cleaning solution from the pumping well and simultaneously cleaning the cleaning solution Step of additionally injecting aqueous solution (e) Step of removing the aqueous cleaning solution by simultaneously injecting water from the well for pumping and injecting water

  According to the present invention described above, it is extremely useful as a method for efficiently removing harmful metals in soil and repairing contaminated soil to purified soil without dismantling the above ground structure.

  Hereinafter, embodiments of the present invention will be described in detail. Examples of heavy metals contained in the contaminated soil to be purified by the present invention include cadmium, copper, lead, arsenic, chromium, selenium, mercury, calcium, iron, and aluminum. Although the presence form in the soil of these heavy metals is not specifically limited, Usually, it contains in the state of an ion, an oxide, a hydroxide, etc. in many cases.

(A) About the process of installing a water blocking wall surrounding the heavy metal-containing contaminated soil in the soil In the present invention, first, the contaminated soil present in the ground of a ground structure such as a building, condominium, hall, auditorium, meeting place, etc. Install a water barrier in the soil that surrounds It is preferable to install the water blocking wall so as to contain the contaminated soil with a length reaching the impermeable ground. The water stop wall in that case should just be a thing which does not permeate | transmit a cleaning agent aqueous solution, For example, a steel sheet pile, a soil cement continuous wall, etc. can be mentioned. Further, it is preferable that the cleaning agent aqueous solution has a sufficient thickness such that water does not pass through, the strength is sufficient, and the installation process does not become very difficult. If the water blocking wall is not installed in this way, it is not preferable because a large amount of the aqueous cleaning solution injected in the subsequent process flows into the soil that is more likely to diffuse than the soil to be purified. For example, when a steel sheet pile is used, the steel sheet pile can be installed in the soil almost vertically. When soil cement is used, a sheet is inserted vertically into the fluidized soil cement wall, a roll-off sheet wall is inserted into the fluidized soil cement wall and pulled horizontally. Navi Wall Construction Method) can be used. Other methods that are usually used in the civil engineering field may also be used.

(B) About the process of installing a cleaning solution supply well and a pumping well in heavy metal-containing contaminated soil in the water blocking wall Next, cleaning to supply the cleaning solution by boring into the contaminated contaminated soil A well for supplying an aqueous solution and a well for pumping up a cleaning solution will be installed. As a more specific method of excavating a well, it can be installed by a commonly used technique such as a press-in method, a no-drainage wall method, a Nakabori pile method, a steel pipe soil cement pile method. Subsequently, a cleaning solution is supplied into the contaminated soil from the cleaning solution supply well, and heavy metal components are extracted from the contaminated soil. The number of each well is not limited and is preferably selected according to the amount of contaminated soil. The distance between each of the cleaning solution supply well and the pumping well is not particularly limited, but it is preferable that the wells are installed with an appropriate distance that can be taken into consideration from the surrounded soil region.

(C) About the process of injecting the detergent aqueous solution into the well for supplying the detergent aqueous solution and immersing the entire heavy metal-containing contaminated soil in the water blocking wall in the detergent aqueous solution As the detergent to be used, the above heavy metal components are extracted. It is not particularly limited as long as it can be used. For example, inorganic acids such as hydrochloric acid and nitric acid, acetic acid, citric acid, tartaric acid, organic acid components represented by ethylenediaminetetraacetic acid (EDTA), alkalis such as caustic soda, etc. A cleaning agent can be used. However, most ground structures have structures using cement underground, and it is preferable to adjust the pH of the aqueous solution of the cleaning agent to 4 or more from the viewpoint of protecting the cement. The adjusting agent used for adjusting the pH is not particularly limited, and caustic soda, acetic acid, hydrochloric acid and the like can be used. In order to further adjust the pH to a certain value, it is described in, for example, “Chemical Handbook Basic Edition”, revised edition, Volume II, page 354 (edited by the Chemical Society of Japan, published by Maruzen Co., Ltd., published on June 25, 1984). It is also possible to use such a buffer solution.

  It is known that heavy metals in contaminated soil are generally low in the deep part of the soil and are likely to exist in the upper part of the soil. However, in order to wash the contaminated soil efficiently at the time of washing, the detergent aqueous solution is filled to the surface position of the contaminated soil, and the contaminated soil is immersed in the detergent aqueous solution. Further, the method of supplying the cleaning agent aqueous solution is not particularly limited. In order to efficiently extract heavy metals from the contaminated soil, it is preferable to maintain a state in which the soil is immersed in the cleaning agent aqueous solution for a predetermined time or more, and the retention time varies depending on the soil, but is usually preferably maintained for several hours to 7 days. Specifically, it is preferably 1 hour to 7 days, more preferably 2 hours to 7 days. The above steps (a) to (c) are preferably performed sequentially.

(D) A step of pumping a cleaning agent aqueous solution from a well for pumping and simultaneously injecting a cleaning agent aqueous solution at the same time. (E) A step of pumping a cleaning agent aqueous solution from a pumping well and simultaneously injecting water to remove the cleaning solution. The cleaning agent aqueous solution from which the heavy metal component has been extracted is pumped from the pumping well by a pump and collected from the soil. At this time, in order to prevent problems such as land subsidence due to local moisture changes in the soil, it is preferable to pump water from another well at the same time as the amount of pumped water. The soaking rate and pumping rate of the cleaning agent aqueous solution do not differ in the heavy metal cleaning efficiency by soaking, but the hydraulic conductivity varies depending on the soil properties. Therefore, it is preferable to investigate and determine the soil properties. In order to further collect heavy metal components in the soil, for example, instead of the above-described water injection, injection and re-washing of a new detergent aqueous solution may be repeated. The order of this operation is not particularly limited, and the same amount of water as that of the pumped water may be injected at the same time as the water is pumped. . Preferably, it is preferable to inject the water after injecting the cleaning agent additional injection a sufficient number of times and in a sufficient amount.

After achieving the purification level set before construction due to changes in the concentration of heavy metals in the pumped detergent aqueous solution, the remaining detergent is removed by repeatedly injecting and pumping water after changing the detergent aqueous solution to water. .
Thus, the soil in which the content of heavy metals is reduced is obtained as purified soil. On the other hand, wastewater such as detergent aqueous solution containing pumped heavy metal is removed by heavy metal processing equipment such as activated carbon adsorption treatment, chelate adsorption treatment, alkaline precipitation treatment, etc., and then organic matter removal treatment is performed as necessary. And then released into public waters.

  Hereinafter, although it demonstrates concretely using FIG. 1 which represented typically the one aspect | mode of this invention, this invention does not receive any limitation by this. In the present invention, a water blocking wall (2 in the figure) that first reaches the impervious ground (9 in the figure) around the contaminated soil (1 in the figure) containing heavy metals existing underground in the ground structure (10 in the figure). Enclose and contain. A water injection well (3 in the figure) was installed in the soil containing heavy metals contained (1 in the figure), and an aqueous cleaning solution (5 in the figure) was injected from the water injection well using a water injection pump (6 in the figure). To do. Water is pumped from a pumping well (4 in the figure) by a pump (7 in the figure). The heavy metal-containing cleaning solution that has been pumped is discharged after the heavy metal is removed by the waste water treatment device (8 in the figure).

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and the design details can be appropriately changed for the details of the process and the devices to be used without departing from the gist of the present invention. Is natural.

  The method of the present invention efficiently removes harmful metals in the soil without dismantling the ground structure and transporting the contaminated soil to another place even if the ground structure is built. It is extremely useful as a method for restoring contaminated soil to purified soil. It can be efficiently applied to the purification of soil in contaminated places such as landfills for chemical wastes where contamination by heavy metals is a concern.

It is the schematic of the process which showed the one aspect | mode of this invention.

Explanation of symbols

1 Contaminated soil containing heavy metals 2 Water barrier 3 Water injection well (cleaning water supply well)
4 Well for pumping 5 Detergent solution 6 Injection pump
7 Pumping pump 8 Wastewater treatment device 9 Impervious ground 10 Ground structure

Claims (3)

A method for purifying heavy metal-containing contaminated soil existing underground, wherein the contaminated soil is subjected to the following steps (a) to (e) so that heavy metals can be washed with an aqueous solution of a cleaning agent in situ. A method for purifying contaminated soil, comprising washing and removing.
(A) A step of installing a water blocking wall surrounding the heavy metal-containing contaminated soil in the soil (b) A step of installing a cleaning solution supply well and a pumping well on the heavy metal-containing contaminated soil in the water blocking wall (c) Injecting the cleaning solution into the cleaning solution supply well and immersing the entire heavy metal-containing contaminated soil in the water blocking wall in the cleaning solution (d) Pumping the cleaning solution from the pumping well and simultaneously cleaning the cleaning solution Step of additionally injecting aqueous solution (e) Step of removing the aqueous cleaning solution by simultaneously injecting water from the well for pumping and injecting water   The method for purifying contaminated soil according to claim 1, wherein the aqueous cleaning solution used in step (c) uses acid or alkali as the cleaning agent and the pH of the aqueous solution is adjusted to 4 or more.   The method for purifying contaminated soil according to claim 1 or 2, wherein the entire heavy metal-contaminated soil in the water blocking wall is immersed in an aqueous cleaning agent solution and then maintained in an immersed state for a predetermined time or more.

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