JP4097562B2 - Purification method for heavy metal contaminated soil - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying soil containing heavy metals. More specifically, the present invention relates to a soil purification method for efficiently removing heavy metals from soil containing heavy metals and separating and recovering heavy metals.
[0002]
[Prior art]
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 of measures such as removal of contamination will increase significantly in the future.
[0003]
In general, domestic pollution countermeasures against soil heavy metal contamination include methods such as insolubilization treatment, soil covering work, and water shielding work to block the surrounding environment from pollution sources. However, these methods leave heavy metals on-site, which may damage the asset value of the land due to the risk of re-elution due to environmental changes and causing pollution, and scarce resources. From the viewpoint of saving heavy metals, it is not a preferable method.
[0004]
As another method different from the above method, there is a method in which the contaminated soil is excavated and replaced with clean soil, and the contaminated soil is disposed as industrial waste. However, in recent years, the final disposal site has become a social problem, and this method is not preferable.
[0005]
In order to solve such problems, introduction of a soil remediation method that separates and removes contaminants from contaminated soil and returns them to clean soil is being considered. For example, (1) classified washing of contaminated soil, (2) soil washing by foam flotation method, (3) heat treatment technology of heavy metal contaminated soil, (4) contaminated soil purification by steam heating method, (5) chloride volatilization method, (6) Electrophoretic soil remediation technology, (7) Heavy metal contaminated soil purification by electrophoresis, (8) Electroosmotic soil remediation technology, etc. are known. (See Non-Patent Document 1)
[0006]
Among these purification methods, the classification cleaning method for contaminated soil dissolves and removes pollutants that are easily dissolved in water while classifying the soil, and simultaneously removes fine particles that are mainly adsorbed by metals, thereby removing contaminated metals. This is a method of taking out the separated soil. However, this method has a problem that it is necessary to dispose of a waste of minute particles on which contaminated heavy metals are adsorbed.
[0007]
The soil washing method by the foam flotation method is a technique called a flotation method, and is a method in which particles having a hydrophobic surface are attached to the foam generated by bubbling and floated and separated. This method is effective for heavy metal sulfides having a hydrophobic surface, but the heavy metal-containing particles contained in general soils do not necessarily have a hydrophobic surface and cannot be separated by ordinary flotation. There is a problem that there are cases. A method of separating heavy metals by converting them into sulfides in combination with a sulfiding agent is also conceivable, but there is a problem that the sulfiding agent may be expensive or the sulfiding agent may remain in the soil.
[0008]
The heat treatment technology for heavy metal-contaminated soil is a method for removing metals that are likely to volatilize by heating to about 1000 ° C. while passing air through the heavy metal-containing soil. This method is effective as a soil treatment technology for complex-contaminated soil with organic matter, but it cannot treat heavy metals that are easy to melt before volatilizing, it must treat exhaust gas containing heavy metals, heated soil Has a problem that it is difficult to backfill because its properties change considerably from the original soil.
[0009]
The contaminated soil purification method by the water vapor heating method is a technique for separating metal from soil by blowing heated steam and volatilizing the metal while heating the soil. This method has the advantage of excellent metal separation efficiency and high possibility of being able to backfill the soil, but requires a heat source that supplies heated steam, requires treatment of exhaust gas and condensed water, There is a problem that metals that are difficult to volatilize cannot be separated.
[0010]
The chlorinated volatilization method is a method in which an aqueous calcium chloride solution is added to soil, the heavy metal is converted into chloride to lower the boiling point, and then the soil is heated to 800 to 1000 ° C. to volatilize and separate the heavy metal. This method also requires the treatment of exhaust gas, like the heat treatment technology for heavy metal contamination treatment and the method of remediation of contaminated soil by the steam heating method. There is a problem that unintentionally harmful substances may be generated.
[0011]
The electrophoretic soil remediation technique is a method in which anionic metal is moved to an anode by filling a gap in the soil with water and a direct current is applied, and the metal concentrated in the anode portion is recovered. According to this method, extraction can be performed at the original position, but there is a problem that it takes time because the removal speed is not fast. In addition, when the soil contains a large amount of chlorine ions, there is a problem that generation of chlorine gas is expected.
[0012]
Purification of heavy metal-contaminated soils by electrophoresis is performed by flowing a direct current through soil that contains water, so that anions move to the anode and cations move to the cathode, so heavy metals are collected near the electrodes inserted in the soil. A technique for collecting heavy metals by covering an electrode with a semipermeable membrane and circulating an EDTA solution injected into the membrane has been reported. This method also has a problem that, like the method of electrophoretic soil repair technology, the treatment tends to take time, and when chlorine ions are contained in large quantities, attention must be paid to generation of chlorine gas. .
[0013]
Electroosmotic soil remediation technology is a method in which a direct current is passed through the ground to create an electromagnetic field, and soil water is moved from the anode to the cathode, and along with this flow, water-soluble metal is moved from the anode to the cathode and recovered. . This method also requires a long treatment time, like the electrophoretic soil remediation technology and the purification method of heavy metal contaminated soil by electrophoresis, and it is necessary to pay attention to the generation of chlorine gas when chlorine ions are contained in the soil. In addition, when it is necessary to supply water, there is a problem that post-treatment of this water is also required.
[0014]
[Non-Patent Document 1]
“Survey and Countermeasure Guidelines Operational Standards for Soil and Groundwater” edited by the Environment Agency Water Quality Conservation Bureau, 1999, p. 51-53
[0015]
[Problems to be solved by the invention]
The present invention has been made against the background of the problems of the prior art described above, and its purpose is to efficiently separate and remove harmful heavy metals in the soil without producing by-product waste, It is to provide a purification method for repairing soil.
[0016]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above problems, the present inventors have
In the method for purifying contaminated soil containing heavy metals, it has been found that this method can be achieved by a method for purifying contaminated soil characterized by the following steps (a) to (e).
(A) Washing step for extracting metal components in contaminated soil using a washing solution (b) A solution in which soil obtained in the washing step is dispersed contains fine particles with a soil particle size of 100 μm or less. (C) agglomeration step for aggregating the separation liquid containing fine particles having a particle size of 100 μm or less obtained in the separation step (d) agglomerated particles obtained in the agglomeration step The liquid in which the liquid is dispersed is subjected to solid-liquid separation, and the agglomerated fine particles, which are the agglomerated particles subjected to solid-liquid separation, are returned to the separation process of (b) (e) The separation obtained in the re-separation process Step of separating and recovering heavy metals from the liquid
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
Examples of the heavy metals contained in the contaminated soil to be purified by the present invention include cadmium, copper, lead, arsenic, calcium, iron, aluminum and the like. Although the existence 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.
[0018]
In the present invention, first, the heavy metal component in the contaminated soil is extracted into the cleaning liquid using the cleaning liquid. At that time, the contaminated soil may be pulverized in advance by a pulverizer or the like to form fine particles, or may be used as it is. An existing pulverizer may be used as the pulverizer, and examples thereof include a high-speed rotary impact pulverizer, an autogenous pulverizer, and a ball mill. On the other hand, the cleaning liquid is not particularly limited as long as it can dissolve and extract heavy metal components, and any cleaning liquid such as an acid aqueous solution, an alkali aqueous solution, a chelating agent solution, and the like can be used. Among these, an aqueous acid solution is preferable, and an aqueous hydrochloric acid solution is particularly preferable.
[0019]
In the washing step, heavy metal components in the contaminated soil are extracted into the washing liquid, and the liquid in which the soil obtained by this step is dispersed is separated into the liquid containing the soil and fine particles. As a separation apparatus used here, arbitrary separation apparatuses, such as a normal centrifugal filter, a drum filter, a Young filter, a filter press, a belt press, and a liquid cyclone, can be used. The separated solid content may be repeatedly subjected to, for example, re-washing with a new washing liquid and solid-liquid separation in order to further recover heavy metal components such as heavy metal ions in the washing liquid remaining in the solid content. Thus, the soil in which the content of heavy metals is reduced can be discharged as purified soil.
[0020]
In the above separation step, in order to increase the processing capacity of the step, it is necessary to entrain fine particles of soil, preferably fine particles having a particle size of 100 μm or less, on the liquid side. Here, the method of bringing the fine particles into the liquid side is arbitrary, but examples thereof include, for example, increasing the opening of the filter cloth of the separation device.
[0021]
Next, for example, an aggregating agent (PAC or the like) is added to the separation liquid containing heavy metal and soil fine particles separated in the separation step, and the fine particles are aggregated. The obtained dispersion liquid in which the agglomerated particles are dispersed is re-separated by, for example, sending it to a sedimentation device and allowing it to stand for a predetermined time. The agglomerated fine particles separated here are, for example, returned to the separation step (b), separated as solids by the separation device in the step, and discharged as purified soil.
[0022]
On the other hand, the separation liquid containing heavy metals separated from the agglomerated fine particles in the re-separation step is separated and removed from the separation liquid using a known processing apparatus and sent to a disposal facility. It can be circulated and used as a cleaning liquid for the cleaning process or a cleaning liquid for re-cleaning the separated solid content.
[0023]
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, first, soil containing heavy metals is converted into fine particles as it is or using a pulverizer or the like, and sent to an extraction device (1 in the figure). In this extraction apparatus, after adding a washing | cleaning liquid to contaminated soil, a heavy metal component is extracted from a soil particle by stirring or shaking.
[0024]
Subsequently, solid content is isolate | separated with a solid-liquid separator (2 in a figure). At that time, for example, the opening of the filter is adjusted to bring the fine particles into the liquid side.
[0025]
The separated solid content is preferably repeatedly washed and solid-liquid separated by a solid-liquid separation device (3 in the figure) in order to further recover heavy metal ions in the residual liquid remaining in the solid content. The cleaning liquid from the solid-liquid separator (3 in the figure) is sent to the drainage processing apparatus (6 in the figure), where heavy metals are removed and reused as a circulating cleaning liquid. The rewashed soil in which heavy metals are reduced to the desired content is discharged as purified soil.
[0026]
The cleaning liquid containing heavy metals and fine particles separated by the solid-liquid separator (2 in the figure) is sent to the aggregating apparatus (4 in the figure). In the aggregating apparatus, an aggregating agent (PAC or the like) is added to agglomerate the fine particles, which are sent to a sedimentation apparatus (5 in the figure). Therefore, the agglomerated fine particles that have been allowed to stand for a predetermined time and have settled are returned to the solid-liquid separator (2 in the figure).
[0027]
On the other hand, the cleaning liquid containing heavy metal separated by the sedimentation device (5 in the figure) is separated and removed by the heavy metal component by the drainage treatment apparatus (6 in the figure), and the recovered cleaning liquid is separated into the solid-liquid separation device (3 in the figure). ) Is used as a cleaning solution.
[0028]
【The invention's effect】
According to the present invention described above, harmful heavy metals in the soil can be efficiently separated and removed without producing by-product waste, which is extremely useful as a method for restoring contaminated soil to purified soil. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a process illustrating one embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Extraction device 2 Solid-liquid separation device 3 Solid-liquid separation device 4 Coagulation device 5 Sedimentation device 6 Drainage processing device

Claims (3)

In the method for purifying contaminated soil containing heavy metals, the method includes the following steps (a) to (e):
(A) Washing step for extracting metal components in contaminated soil using a washing solution (b) A solution in which soil obtained in the washing step is dispersed contains fine particles with a soil particle size of 100 μm or less. (C) agglomeration step for aggregating the separation liquid containing fine particles having a particle size of 100 μm or less obtained in the separation step (d) agglomerated particles obtained in the agglomeration step The liquid in which the liquid is dispersed is subjected to solid-liquid separation, and the agglomerated fine particles, which are the agglomerated particles subjected to solid-liquid separation, are returned to the separation process of (b) (e) The separation obtained in the re-separation process Process for separating and recovering heavy metals from liquid   The method for purifying contaminated soil according to claim 1, wherein the cleaning liquid used in the step (a) is a hydrochloric acid aqueous solution. The method for purifying contaminated soil according to claim 1 , wherein the agglomerated fine particles, which are the agglomerated particles separated in the step (d), are mixed with the dispersion liquid in the step (b) and solid-liquid separated.

Images