JP3689094B2 - 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 contaminated with heavy metals such as lead, cadmium and mercury in factories and shooting ranges.
[0002]
[Prior art]
Patent Documents 1 to 4 and the like have been provided as methods for purifying local soil contaminated with heavy metals, and these use a chelating agent as a treatment material for removing heavy metals from heavy metal-contaminated soil, and muddy the chelating agent. It teaches how to contact heavy metal contaminated soil to bind the heavy metal in the mud to the chelating agent and then remove the aqueous chelating agent solution bound to the heavy metal with a solid-liquid separator.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-282836
[Patent Document 2]
JP-A-6-218355
[Patent Document 3]
JP-A-4-263874
[Patent Document 4]
JP-A-11-156338
[Problems to be solved by the invention]
As in the above patent document, the present invention employs a method of binding heavy metal in mud water to a chelating agent, and can dehydrate and remove (solid-liquid separation) an aqueous solution of heavy metal binding chelating agent from mud water efficiently. Provide a purification method.
[0008]
In addition, the present invention circulates and uses the washing solution of soil obtained by solid-liquid separation, particularly heavy metal-containing soil exceeding the reference value, and circulates and uses the aqueous chelating agent solution after removing heavy metals from the aqueous heavy metal binding chelating agent solution, Provide a method for purifying heavy metal-contaminated soil that contributes to environmental conservation by controlling the discharge of harmful treatment liquids to the outside.
[0014]
[Means for Solving the Problems]
The present invention provides a method for purifying heavy metal-contaminated soil including the following steps A to F.
A: The process of making heavy metal contaminated soil mud and bringing it into contact with a chelating agent to bind the heavy metal in the mud to the chelating agent,
B: a step of dewatering the mud that has been brought into contact with the chelating agent and separating it into soil and an aqueous heavy metal binding chelating agent solution;
C: a step of separating the soil into a soil whose heavy metal content is within the reference value and a soil that is outside the reference value;
D: washing the soil outside the reference value to remove residual chelating agent bound or not bound to heavy metal, and circulating washing water containing the remaining chelating agent to step A;
E: a step of separating the heavy metal-bonded chelating agent aqueous solution obtained by the dehydration into a heavy metal and a chelating agent aqueous solution;
F: a step of circulating the chelating agent aqueous solution from which the heavy metal has been separated into the step A,
It is a purification method of heavy metal contaminated soil containing.
[0015]
The cleaning water containing the chelating agent discharged from the cleaning step and the aqueous chelating agent solution obtained by removing heavy metals from the heavy metal binding chelating agent discharged from the dehydration step are circulated and reused in the system. Contributes to environmental conservation by suppressing discharge of the processing solution to the outside, and enables efficient use of chelating agents.
[0016]
As the dehydrating means, a filter press or a centrifugal separator is suitable.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS.
[0018]
As shown in FIGS. 1 and 2, a heavy metal contaminated soil 1 of a factory or shooting range (hereinafter referred to as a local site) contaminated with heavy metals is collected using a heavy machine such as a shovel car, and the collected heavy metal contaminated soil 1 1 It puts in the muddy water tank 2 and adds water 3 and stirs it to make muddy water. That is, a soil slurry is formed. For example, a soil slurry is obtained by kneading at a ratio of soil: water = 1: 3.
[0019]
Before putting heavy metal contaminated soil 1 collected by heavy machinery such as the above-mentioned excavator into the first mud tank 2, a process of removing coarse foreign matters and grass is provided, and after passing through the process, the first mud tank 2 is contaminated with heavy metal. Soil 1 is added.
[0020]
Next, the muddy water 4 in the first muddy tank 2 is supplied to the classifier 6 by the submersible pump 5 installed in the first muddy tank 2, and the classifier 6 is used to remove lead balls, iron pieces, pebbles, etc. in the contaminated soil 1. The heavy foreign matter 7 is removed and collected in the pit 9.
[0021]
FIG. 3 shows a specific example of the classifier 6, and the classifier 6 has a plurality of vibrating screens 8 having different mesh degrees, and the muddy water 4 is allowed to flow through the vibrating screens 8. 7 is removed, and the muddy water 4 that has passed through the sieve 8 is stored in the storage tank 10.
[0022]
The muddy water 4 in the storage tank 10 is introduced into the second muddy water tank 12 by the submersible pump 11.
[0023]
A chelating agent aqueous solution 13 is added to the mud water 4 in the second mud water tank 12, and mineral particles 14 having a multi-pore structure composed of one or more of diatomaceous earth, calcined vermiculite, calcined zeolite, and calcined bentonite are added.
[0024]
Alternatively, as shown by a broken line in FIG. 1, the mineral particles 14 can be added to the mud water 4 taken out from the second mud tank 12. That is, the muddy water 4 is taken out from the second muddy water tank 12 into the third muddy water tank 19, and the mineral substance particles 14 are added to the muddy water 4 in the third muddy water tank 19 and stirred.
[0025]
As the chelating agent, EDTA ₂ Na-2H ₂ O in EDTA (ethylenediaminetetraacetic acid) is used, and the chelating agent powder is dissolved in water and added to the mud water 4 in the second mud tank 12.
[0026]
The mixing ratio of the chelating agent to the mud water 4 in the second mud tank 12 is selected in the range of 0.1 to 9% (weight ratio) depending on the degree of heavy metal contamination.
[0027]
The blending ratio of the mineral substance particles 14 to the mud water 4 in the second mud tank 12 is selected in the range of 3 to 10% (weight ratio).
[0028]
While stirring the mud water 4 in which the chelating agent aqueous solution 13 and the mineral substance particles 14 in the second mud water layer 12 are mixed, the binding between the chelating agent and the heavy metal is promoted.
[0029]
Next, the muddy water 4 in the second muddy water tank 12 is introduced into a dehydrator 15, that is, a solid-liquid separator, and the muddy water 4 is dehydrated and separated into the soil 1 a and the heavy metal binding chelating agent aqueous solution 13 a.
[0030]
As the dehydrating means, for example, a filter press 18 or a centrifugal separator is used. As shown in FIGS. 4A, B, and C, the filter press 18 has a plurality of filter chambers 20 arranged in parallel, and the muddy water 4 is injected into the filter chamber 20 at a high pressure, and the heavy metal-bonded chelating agent is passed through the filter wall 21. The aqueous solution 13 a is dehydrated to produce cake-like soil 1 a in the filter chamber 20. The cake-like soil 1a is taken out by opening the filter chamber 20.
[0031]
Therefore, the muddy water 4 is separated into the soil 1a and the heavy metal binding chelating agent aqueous solution 13a. The moisture content of this soil is about 50 to 80%.
[0032]
The diatomaceous earth is a fossilized soil of algae plankton deposited on the seabed and lake bottom for many years, and has numerous fine pores on the surface. That is, it has a high void structure.
[0033]
Natural vermiculite is a natural ore similar to mica, chlorite, and talc, and its component is a monoclinic system of approximately (Mg, Fe) ₃ [(Si, Al) ₄ O ₁₀ ] (OH) ₂ 4H ₂ O. is there.
[0034]
This natural vermiculite expands rapidly when heated at a high temperature of 400 ° C. or higher, that is, it boils and becomes enormous, and has the high porosity and cation exchange performance.
[0035]
For example, calcined vermiculite having a particle size of 0.5 to 3 millimeters is added to the muddy water 4.
[0036]
Zeolite (natural zeolite) contains alkali and alkaline earth hydrated aluminum silicate as a component. When this natural zeolite is heated at a high temperature, it boils and becomes enormous, has a porous structure with high porosity, and has cation exchange performance. To have.
[0037]
The zeolite (zeolite) includes orthorhombic zeolite (clinoptilolite) and cubic zeolite (mordelite). In particular, orthorhombic zeolite has high cation exchange performance.
[0038]
For example, calcined zeolite having a particle size of 0.5 to 3 millimeters is added to the mud water 4.
[0039]
Bentonite is a kind of clay, mainly composed of montmorillonite (mineral component), has a very strong affinity with water, and absorbs water. Here, the bentonite (natural mineral) heat-treated at 200 ° C. to 300 ° C. is used.
[0040]
Like the calcined vermiculite and calcined zeolite, the bentonite expands by this heat treatment, has a porous structure with a high porosity, and similarly has cation exchange performance.
[0041]
The diatomaceous earth, calcined vermiculite, calcined zeolite, and calcined bentonite all have a high void structure and impart water permeability to the soil. For example, water permeability is imparted to heavy metal contaminated soil with poor water permeability, and the contact effect with the heavy metal by the chelating agent is enhanced.
[0042]
In addition, the efficiency of dehydration in the dehydration process will be improved, and the soil after the local restoration will be given water permeability and oxygen uptake to provide a healthy soil suitable for plant growth.
[0043]
As shown in FIG. 1, the soil 1a separated by the dehydrator 15 typified by the filter press 18 measures the heavy metal content (content and elution amount) for each batch by the batch method, and the content is the standard. The soil 1b within the value and the soil 1c outside the reference value are separated.
[0044]
The soil improving material 22 is added to the above-mentioned reference value soil 1b, kneaded and then restored to the site. On the other hand, the soil 1c outside the reference value is circulated to the second mud tank 12 through the first bypass R1, that is, circulated to the step of bringing the chelating agent into contact with the mud 4 and again treated with the chelating agent.
[0045]
The soil improvement material 22 is mainly composed of fly ash, that is, a heavy metal absorbent material having a multi-cavity structure typified by coal incineration ash. For example, a soil conditioner containing 50-60% fly ash, 25-40% blast furnace cement, 6-15% anhydrous gypsum, and 4-8% inorganic flocculant is used.
[0046]
The fly ash absorbs heavy metal remaining in the soil 1b within the reference value due to its multi-void structure, surrounds the surface with a flocculant, and suppresses elution of heavy metal.
[0047]
Anhydrite promotes initial solidification of the soil by its ettling guide action, and blast furnace cement continuously maintains the solidification of the soil.
[0048]
The fly ash can be replaced with the above-described diatomaceous earth, calcined vermiculite, calcined zeolite, and calcined bentonite. Moreover, the soil improvement material 22 which does not contain the said anhydrous gypsum can be used.
[0049]
These soil improvement materials 22 cooperate with the above-described mineral substance particles 14 to provide a favorable environment for the growth of living organisms in the above-mentioned reference value soil 1b.
[0050]
On the other hand, as shown in FIG. 1 and FIG. 2, the heavy metal binding chelating agent aqueous solution 13a separated by the dehydrating device 15 represented by the filter press 18 is introduced into the heavy metal separating device 23 represented by the electrolysis device, and the heavy metal binding is performed. The chelating agent aqueous solution 13a is separated into the heavy metal 17 and the chelating agent aqueous solution 13b. The heavy metal separator 23 includes devices using electroosmosis, electrophoresis, and biological / chemical treatment.
[0051]
The separated chelating agent aqueous solution 13b is circulated to the second mud tank 12 through the second bypass R2, that is, circulated in the step of bringing the chelating agent into contact with the mud 4 and reused.
[0052]
In FIG. 2, the heavy metal content (content and elution amount) is measured for each batch of the soil 1a obtained from the dehydrator 15 by the batch method, and the content of the soil 1b within the standard value and the standard value. This shows a case where the soil is separated into the outside soil 1c, and further subjected to the step of washing the outside soil 1c outside the reference value, and the soil 1b within the reference value based on the above measurement is restored to the site.
[0053]
That is, the soil 1c outside the reference value is passed through the cleaning device 24, the residual chelating agent bound to or not bound to the heavy metal in the soil 1c outside the reference value is removed, and the cleaning water 25 containing the residual chelating agent is added to the second mud. It circulates in the water tank 12 through the third bypass R3. That is, it recirculates to the step of bringing the chelating agent into contact with the muddy water 4 and reuses it.
[0054]
On the other hand, the heavy metal content of the washed soil 1d obtained from the cleaning device 24 is measured, the soil 1b whose heavy metal content is within the reference value is restored to the site, and the soil 1c outside the reference value is passed through the first bypass R1. Through the second mud tank 12. That is, it recirculates to the process which makes a mud 4 contact a chelating agent, and makes the non-standard-value soil 1c contact again with a chelating agent.
[0055]
The soil after the washing step is passed through a dehydrating device to remove the chelating agent aqueous solution, the chelating agent aqueous solution is circulated to the second mud tank, and the soil within the reference value obtained from the dehydrating device is restored to the site, Circulate soil outside the standard value into the second mud tank.
[0056]
The washing device 24 includes a coagulation sedimentation device that sediments the soil and takes out the liquid containing the chelating agent as a supernatant, measures the heavy metal content of the sedimented soil, and is outside the standard value soil 1b. The soil is separated into soil 1c, the former is restored to the site, and the latter is circulated as described above.
[0057]
【The invention's effect】
The present invention provides a specific method capable of appropriately performing a series of treatments for removing heavy metals by using a chelating agent from collection of soil contaminated with heavy metals and restoring the soil from which heavy metals have been removed.
[0058]
The mineral particles improve the dewatering performance in the solid-liquid separation and significantly promote the separation of the aqueous solution of the heavy metal binding chelating agent. In addition, it will provide water permeability and water retention to the soil after local rehabilitation, take up oxygen into the soil, and improve the growth environment of plants and the like.
[0059]
In addition, the soil after the dehydration process in the above treatment step is classified into soil within the reference value range and soil outside the reference value, and the purpose of purifying heavy metal contaminated soil by feeding back the soil outside the reference value and bringing it back into contact with the chelating agent Can be achieved properly.
[0060]
In addition, the cleaning water containing the chelating agent discharged from the cleaning step and the chelating agent aqueous solution in which the heavy metal is removed from the heavy metal binding chelating agent are circulated in the system and reused. Contributes to environmental conservation by suppressing the emission of methane, and enables efficient use of chelating agents.
[Brief description of the drawings]
FIG. 1 is a flow diagram of a purification method for heavy metal contaminated soil.
FIG. 2 is a flowchart showing another example of a method for purifying heavy metal-contaminated soil.
FIG. 3 is a diagram showing a schematic structure of a classifier.
FIGS. 4A, 4B, and 4C are diagrams showing a schematic structure of a filter press in an operation order;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Heavy metal contaminated soil, 1a ... Solid-liquid separated soil, 1b ... Soil within standard value, 1c ... Non-standard value soil, 2 ... First mud tank, 3 ... Water, 4 ... Mud water, 5 ... Submersible pump, 6 ... Classifier, 7 ... heavy foreign matter, 8 ... sieve, 9 ... pit, 10 ... storage tank, 11 ... submersible pump, 12 ... second mud tank, 13 ... chelating agent aqueous solution, 13a ... heavy metal binding chelating agent aqueous solution, 13b ... chelating agent Aqueous solution, 14 ... mineral particles, 15 ... dehydrator, 16a, 16b ... measuring device, 17 ... heavy metal, 18 ... filter press, 19 ... third mud layer, 20 ... filter chamber, 21 ... filter wall, 22 ... soil improvement 23, heavy metal separator, 24 ... cleaning device, 25 ... cleaning water, R1, R2, R3 ... bypass path

Claims (2)

A method for purifying heavy metal-contaminated soil comprising the following steps A to F.
A: The process of making heavy metal contaminated soil mud and bringing it into contact with a chelating agent to bind the heavy metal in the mud to the chelating agent,
B: a step of dewatering the mud that has been brought into contact with the chelating agent and separating it into soil and an aqueous heavy metal binding chelating agent solution;
C: a step of separating the soil into a soil whose heavy metal content is within the reference value and a soil that is outside the reference value;
D: washing the soil outside the reference value to remove residual chelating agent bound or not bound to heavy metal, and circulating washing water containing the remaining chelating agent to step A;
E: a step of separating the heavy metal-bonded chelating agent aqueous solution obtained by the dehydration into a heavy metal and a chelating agent aqueous solution;
F: A step of circulating the chelating agent aqueous solution from which the heavy metal has been separated into the step A. 2. The method for purifying heavy metal-contaminated soil according to claim 1, wherein a filter press or a centrifugal separator is used as the dehydrating means.

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