JP2004337695A - Purification method for heavy-metal-contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently removing heavy metals from a heavy-metal-containing soil to separate and recover the heavy metals. <P>SOLUTION: The purification method for heavy-metal-containing soil comprises separating and removing heavy metals from a contaminated soil containing the heavy metals. The method comprises (a) a cleaning step for extracting metal components from the contaminated soil with a cleaning solution, (b) a separation step for separating a liquid obtained by the cleaning step and containing soil dispersed therein into the soil and a liquid containing a fine particle component, (c) an agglomeration step for agglomerating the liquid containing the fine particle component and obtained at the separation step, (d) a reseparation step for subjecting a liquid containing agglomerated particles dispersed therein and obtained at the agglomeration step to solid-liquid separation, and (e) a step for separating and recovering heavy metals from a liquid obtained at the reseparation step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD 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 the heavy metals.
[0002]
[Prior art]
In recent years, with the increase in investigations due to redevelopment of urban areas, cases in which heavy metal contamination at factory sites and the like are found are increasing. With the enactment of the Soil Contamination Countermeasures Law of 2002, a legal system for such soil contamination is established, and it is expected that the number of cases of measures such as removal of contamination will increase significantly in the future.
[0003]
The current countermeasures against heavy metal contamination in the soil in Japan are generally methods of isolating the surrounding environment from the source of pollution, such as insolubilization, earth covering, and water shielding. However, these methods leave heavy metals in the field, which may lead to pollution due to re-elution due to changes in the environment, which may damage the property value of the land. It is not a preferable method from the viewpoint of saving heavy metals.
[0004]
As another method different from the above method, there is a method of excavating contaminated soil and replacing it with clean soil, and disposing the contaminated soil as industrial waste. However, the tightness of the final disposal site has become a social problem in recent years, and this method is not preferable.
[0005]
In order to solve such a problem, introduction of a soil purification method for separating and removing contaminants from contaminated soil and returning the soil to clean soil is being studied. For example, (1) classification cleaning of contaminated soil, (2) soil cleaning by foam floating method, (3) heat treatment technology for heavy metal contaminated soil, (4) purification of contaminated soil by steam heating method, (5) chloride volatilization method, (6) Electrophoretic soil repair technology, (7) Purification of heavy metal contaminated soil by electrophoresis, (8) Electroosmotic soil repair technology, and the like are known. (See Non-Patent Document 1)
[0006]
Among these purification methods, the classification and cleaning method for contaminated soil involves dissolving and removing contaminants that are easily soluble in water while classifying the soil, and simultaneously removing microparticles that are mainly adsorbed by metals. It is a method to take out the separated soil. However, this method has a problem that it is necessary to treat the waste of the fine particles having the contaminated heavy metal adsorbed thereon.
[0007]
The soil washing method based on the foam flotation method is a technique also referred to as flotation ore separation method, in which particles having a hydrophobic surface are attached to foam generated by bubbling and floated and separated. This method is effective for heavy metal sulfides having a hydrophobic surface, but cannot be separated by ordinary flotation because heavy metal-containing particles contained in general soil do not necessarily have a hydrophobic surface There is a problem that there are cases. Although a method of converting heavy metals into sulfides and separating them by using a sulphide in combination is also conceivable, there is a problem that the sulphide is expensive or the sulphide may remain in the soil.
[0008]
The heat treatment technique for heavy metal contaminated soil is a method of removing volatile metals from the soil 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 cannot treat heavy metals that are easily melted before volatilizing, it is necessary to treat exhaust gas containing heavy metals, There are problems such as difficulty in backfilling because the properties change considerably from the original soil.
[0009]
The contaminated soil purification method by the steam heating method is a technique for separating a metal from soil by blowing heated steam while heating the soil to volatilize the metal. This method is excellent in metal separation efficiency and has a high possibility that soil can be backfilled.However, it requires a heat source for supplying 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 chloride volatilization method is a method in which a calcium chloride aqueous solution is added to soil to convert heavy metals into chlorides to lower the boiling point, and then the soil is heated to 800 to 1000 ° C. to volatilize and separate heavy metals. This method also requires the treatment of exhaust gas, as well as the heat treatment technology for heavy metal contamination treatment and the method of contaminated soil purification by steam heating, and requires the treatment of water used for exhaust gas treatment, Harmful substances may be generated unintentionally.
[0011]
The electrophoretic soil restoration technique is a method in which a gap in the soil is filled with water and a direct current is applied to move an anion metal to the anode and collect the metal concentrated in the anode. 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 high. In addition, when the soil contains a large amount of chloride ions, there is a problem that generation of chlorine gas is expected.
[0012]
Purification of heavy metal-contaminated soil by electrophoresis is performed by passing a direct current through water-containing soil, where anions move to the anode and cations move to the cathode, so heavy metals are collected near the electrode inserted into the soil. A method of 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, like the method of the electrophoretic soil remediation technique, tends to take a long time for the treatment, and also has a problem that when a large amount of chloride ions is contained, attention must be paid to the generation of chlorine gas. .
[0013]
Electro-osmosis soil restoration technology is a method in which a direct current is passed through the ground to create an electromagnetic field, soil water is moved from the anode to the cathode, and with this flow, water-soluble metals are moved from the anode to the cathode to collect them. . This method also requires a long treatment time, similar to the method for remediation of heavy metal contaminated soil by electrophoretic soil remediation technology or 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 water needs to be supplied, there is a problem that post-treatment of the water is also required.
[0014]
[Non-patent document 1]
"Operation Standards for Surveys and Countermeasures for Soil and Groundwater," edited by Water Quality Bureau, Environment Agency, 1999, p. 51-53
[0015]
[Problems to be solved by the invention]
The present invention has been made in the background of the above-mentioned problems of the prior art, and its object is to efficiently separate and remove harmful heavy metals in soil without producing by-product waste, thereby contaminating the soil. It is to provide a purification method for repairing soil.
[0016]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to achieve the above object,
It has been found that a method for purifying contaminated soil containing heavy metals can be achieved by a method for purifying contaminated soil characterized by including the following steps (a) to (e).
(A) a washing step of extracting metal components in contaminated soil using a washing liquid; and (b) a separating step of separating a liquid in which the soil obtained in the washing step is dispersed into a soil and a liquid containing fine particles. (C) an aggregating step of aggregating the separated liquid containing fine particles obtained in the separating step; (d) a re-separating step of solid-liquid separating the liquid in which the agglomerated particles obtained in the aggregating step are dispersed (e) A) separating and recovering heavy metals from the separated liquid obtained in the re-separation step;
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
The heavy metals contained in the contaminated soil to be purified by the present invention include, for example, cadmium, copper, lead, arsenic, calcium, iron, aluminum and the like. The form in which these heavy metals are present in the soil is not particularly limited, but is usually contained in the form of ions, oxides, hydroxides, and the like.
[0018]
In the present invention, first, heavy metal components in the above-mentioned contaminated soil are extracted into the washing liquid using the washing liquid. At this time, the contaminated soil may be pulverized by a pulverizer or the like in advance to obtain 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 washing liquid is not particularly limited as long as it can dissolve and extract heavy metal components. For example, an arbitrary washing liquid such as an aqueous acid solution, an aqueous alkali solution, and a chelating agent solution can be used. Among them, an aqueous acid solution is preferable, and an aqueous hydrochloric acid solution is particularly preferable.
[0019]
In the above-mentioned washing step, heavy metal components in the contaminated soil are extracted into the washing liquid. The liquid in which the soil obtained in this step is dispersed is separated into a soil and a liquid containing fine particles. As the separation device used here, any separation device such as a usual centrifugal filter, a drum filter, a young filter, a filter press, a belt press, and a liquid cyclone can be used. In order to further recover heavy metal components such as heavy metal ions in the washing liquid remaining in the separated solid matter, for example, re-washing with a new washing liquid and solid-liquid separation may be repeatedly performed. The soil in which the content of heavy metals has been reduced in this way can be discharged as purified soil.
[0020]
In the above-mentioned separation step, in order to increase the treatment capacity of the step, it is necessary to bring fine particles of soil, preferably fine particles having a particle size of 100 μm or less, into the liquid side. Here, the method of entraining the fine particles into the liquid side is arbitrary, and examples thereof include means for increasing the aperture of the filter cloth of the separation device.
[0021]
Next, for example, an aggregating agent (PAC or the like) is added to the separated liquid containing the heavy metal and the soil fine particles separated in the above separation step to aggregate the fine particles. The dispersion liquid in which the obtained aggregated particles are dispersed is sent again to, for example, a sedimentation device and left for a predetermined time to be separated again. The separated aggregated fine particles are returned to the separation step (b), for example, to be separated as solids by the separation device in this step, and are discharged as purified soil.
[0022]
On the other hand, the separation liquid containing the heavy metal separated from the aggregated 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, and the collected cleaning liquid is, for example, It can be circulated and used as a washing solution in the washing step or a washing solution for rewashing the separated solids.
[0023]
Hereinafter, one embodiment of the present invention will be specifically described with reference to FIG. 1 schematically illustrating the present invention, but the present invention is not limited thereto. In the present invention, first, soil containing heavy metals is sent to an extraction device (1 in the figure) as it is or as fine particles using a crusher or the like. The extractor extracts a heavy metal component from soil particles by stirring or shaking after adding a washing liquid to contaminated soil.
[0024]
Next, the solid content is separated by a solid-liquid separation device (2 in the figure). At this time, for example, the aperture of the filter is adjusted so that the fine particles are entrained on the liquid side.
[0025]
The separated solid is preferably subjected to repeated washing and solid-liquid separation in a solid-liquid separator (3 in the figure) in order to further recover heavy metal ions in the residual liquid remaining in the solid. The cleaning liquid from the solid-liquid separator (3 in the figure) is sent to a drainage treatment apparatus (6 in the figure) to remove heavy metals and reused as a circulating cleaning liquid. The rewashed soil with the reduced heavy metal content is discharged as purified soil.
[0026]
The washing 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 device, a coagulant (PAC or the like) is added to agglomerate the fine particles, and sent to a sedimentation device (5 in the figure). Then, the aggregated fine particles settled for a predetermined time are returned to the solid-liquid separator (2 in the figure).
[0027]
On the other hand, the cleaning liquid containing heavy metals separated by the sedimentation apparatus (5 in the figure) is separated and removed in a wastewater treatment apparatus (6 in the figure), and the recovered cleaning liquid is separated into a solid-liquid separation apparatus (3 in the figure). It is circulated and used as a cleaning solution.
[0028]
【The invention's effect】
According to the present invention described above, harmful heavy metals in soil can be efficiently separated and removed without producing by-product waste, so that they are 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 apparatus 2 Solid-liquid separation apparatus 3 Solid-liquid separation apparatus 4 Agglomeration apparatus 5 Sedimentation apparatus 6 Drainage treatment apparatus

Claims (4)

A method for purifying contaminated soil containing heavy metals, the method comprising the following steps (a) to (e):
(A) a washing step of extracting metal components in contaminated soil using a washing liquid; and (b) a separating step of separating a liquid in which the soil obtained in the washing step is dispersed into a soil and a liquid containing fine particles. (C) an aggregating step of aggregating the separated liquid containing fine particles obtained in the separating step; (d) a re-separating step of solid-liquid separating the liquid in which the agglomerated particles obtained in the aggregating step are dispersed (e) ) Step of separating and recovering heavy metals from the separated liquid obtained in the re-separation step The method for purifying contaminated soil according to claim 1, wherein the washing liquid used in the step (a) is an aqueous hydrochloric acid solution. The method for purifying contaminated soil according to claim 1, wherein the particle diameter of the fine particles contained in the liquid obtained in the step (b) is 100 µm or less. The method for purifying contaminated soil according to claim 1, wherein the solids separated in the step (d) are mixed with the dispersion liquid in the step (b) to perform solid-liquid separation.

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