JP2007050328A - Contaminated soil purification method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soil purification method effective when contaminated soil contains a clay mineral and volatile organic compound. <P>SOLUTION: The contaminated soil purification method comprises the steps of adding a conditioning material containing a far-infrared radiator to the contaminated soil containing the clay mineral and volatile organic compound to agitate or mix. As a conditioning material, an RD material where a nanoparticle comprising the far-infrared radiator is firmly fixed on a substrate consisting of a volcanic glass particle, or an RDW material where the nanoparticle comprising the far-infrared radiator is firmly fixed on a substrate consisting of a calcium mineral powder is used, so that the contaminated soil which contains the clay mineral and makes it hard to remove the volatile organic compound can be cleared of the volatile organic compound up to the environmental standard value or less about a few weeks after a concrete placing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for purifying contaminated soil containing clay minerals and volatile organic compounds.

  Volatile organic compounds such as dichloromethane, carbon tetrachloride, 1,2-dichloromethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, 1,1,1-trichloroethylene, tetrachloroethylene, benzene, 1,2-dichloroethylene Have been used in large quantities for various purposes such as cleaning of IC substrates and electronic parts, pretreatment cleaning of metal parts, and solvents for dry cleaning.

  Except for benzene, volatile organic compounds have a specific gravity greater than that of water, are not easily dissolved in water, and have a high vapor pressure, so that they easily evaporate into the atmosphere.

  For this reason, a hot spot (contamination center) of soil contaminated with volatile organic compounds is formed at the site where volatile organic compounds are used or where volatile organic compounds have moved through the groundwater surface, etc., and measures are taken. There is an urgent need.

  Therefore, the present inventors previously proposed an effective method for treating contaminated soil (Patent Document 1: Japanese Patent No. 3634849).

  By the way, the contaminated soil often contains a lot of clay minerals. Most of the contaminated soil containing clay mineral is negatively charged, and a strongly adsorbed water zone that strongly adsorbs moisture and cations is formed on the surface of the soil particles. On the other hand, since the volatile organic compound has a small soil adsorption coefficient, it is considered that the volatile organic compound exists in the weakly adsorbed water zone to the interstitial water zone formed outside the strong adsorbed water zone.

  Since volatile organic compounds in indoor air or soil such as sand can basically move freely, it is not difficult to remove them. However, when the contaminated soil contains clay minerals and volatile organic compounds, it is very difficult to remove the volatile organic compounds. When the clay is stirred, a thixotropy phenomenon occurs, and once softens, the weakly adsorbed water zone is destroyed, and the volatile organic compound is not bonded to the clay particles. However, shortly thereafter, the clay particles are re-cured to reconstitute the weakly adsorbed water zone. At this time, when the volatile organic compound is recombined with the clay particles, the volatile organic compound can no longer be removed. For this reason, the countermeasure for removing a volatile organic compound from a viscous soil effectively was not known.

In brief, in the prior art, when contaminated soil contains clay minerals and volatile organic compounds, removal of volatile organic compounds was impeded by the thixotropic hardening process and impossible.
Japanese Patent No. 3634849 JP 2002-146335 A

  When the contaminated soil contains clay minerals and volatile organic compounds, the present inventors diligently studied an effective soil purification method, developed a new purification method, and confirmed its effectiveness through experiments.

  That is, an object of the present invention is to provide an effective soil purification method when contaminated soil contains clay minerals and volatile organic compounds.

  In the contaminated soil purification method according to claim 1, an improving material containing a far-infrared radiator is added to the contaminated soil containing a clay mineral and a volatile organic compound, followed by stirring and mixing.

  In this configuration, by adding an improving material containing a far-infrared radiator, the contaminated soil contains clay minerals and volatile organic compounds, and even if it is difficult to remove the volatile organic compounds, an experimental example to be described later As can be seen, the volatile organic compound transitions to a state satisfying the environmental standard value due to the material age for several weeks, and effective soil remediation can be performed.

  In the contaminated soil purification method according to claim 2, the improving material is an RD material in which nanoparticles made of a far-infrared radiator are fixed on a base material made of volcanic glass-based particles.

  With this configuration, the volcanic glass-based particles that are the base material of the RD material have almost no hydrogen occlusion and can perform effective soil purification in a state where alkalinization does not proceed.

  In the contaminated soil purification method according to claim 3, the improvement material is an RDW material in which nanoparticles made of a far-infrared radiator are fixed on a substrate made of calcium mineral powder.

  With this configuration, the volatile organic compound transitions to a state satisfying the environmental standard value with less material age than the RD material, and more rapid soil purification can be performed.

  In the contaminated soil purification method according to claim 4, at least before stirring and mixing, reduced water is further added, and the reduced water is made by mixing water and a far-infrared radiator and allowing to stand, and consisting of the supernatant water.

  In this configuration, reduced water is added, and the reduced water has a high electronegativity. Therefore, the reduced water promotes the detachment of the volatile organic compound from the adsorbed water zone and can effectively perform soil purification.

  According to the present invention, as is apparent from the experimental examples, even if the contaminated soil contains clay minerals and volatile organic compounds, the volatile organic compounds are reduced to an environmental standard value or less by a material age of about several weeks. Can be removed.

  Embodiments of the present invention will be described below with reference to the drawings. First, important elements in the present invention will be described.

  In this embodiment, the improvement material uses at least one of the following RD material and RDW material.

  The RD material is obtained by fixing nanoparticles made of a far-infrared radiator on a base material made of volcanic glass-based particles.

  The RDW material is obtained by fixing nanoparticles made of a far-infrared radiator on a base made of calcium mineral powder.

  In any improvement material, the technique described in Patent Document 2 (Japanese Patent Laid-Open No. 2002-146335) may be used for the “fixing” method.

  These nanoparticles have a diameter of about 5 to 50 nanometers. When they come into contact with water molecules, they promote electrolysis of water by a weak discharge, and are always far infrared (wavelength: 6 to 14 μm) at room temperature. ).

  Reduced water is a supernatant taken from a mixture of water and a far-infrared radiator (preferably RDW material) in a suitable container and left to stand for about one night.

  Next, experimental examples will be described. An RD material, an RDW material, and reduced water that meet the above definitions were prepared, and the inventors conducted experiments as follows. First, Kanto Loam was selected as a soil rich in clay minerals, and trichlorethylene was selected as a pseudo pollutant (volatile organic compound). It is assumed that the same result is obtained for other volatile organic compounds.

(Sample preparation)
1. 60 g of dried Kanto loam was put in a plastic bag, 24 ml of tap water (equivalent to 40% soil water content) was added, and thoroughly mixed by hand in the plastic bag.

  2. To 6 ml of tap water, 20 μl of trichlorethylene (manufactured by Kanto Chemical Co., Ltd., special grade) was added, mixed well, then added to a plastic bag, and thoroughly mixed by hand.

  3. 1) Blank (reduced water only), 2) RD material (reduced water and RD material), 3) RDW material (reduced water and RDW material), so that the soil moisture content is equivalent to 60% respectively. Was added to the inside of the plastic bag and thoroughly mixed (mixed and stirred). In 1) to 3), 4 samples were prepared and 12 samples in total were prepared. Further, it is desirable to add about 6% of the reduced water with respect to the total weight of the sample.

1) Blank Reduced water: 6ml
2) RD material Reduced water: 6 ml, RD material: 4.5 g
3) RDW material Reduced water: 6 ml, RDW material: 4.5 g
4). After mixing, the sample in the plastic bag was immediately transferred to a brown glass storage bottle (capacity: 50 ml) and stored.

(Test and results)
The test which measures the time-dependent change by material age was done.

  1. When the soil moisture content% (water weight / dry soil weight × 100) was measured for the sample immediately after mixing, the following results were obtained.

1) Blank 59.0%
2) RD material 59.7%
3) RDW material 62.3%
The soil water content was a predetermined value of about 60%.

2. Immediately after mixing, the elution test of trichlorethylene by the Environmental Agency Notification No. 46 method was conducted for the 1st, 3rd, and 6th weeks of the material age, and the test solution was measured according to JIS K0125 5.4.1, and the following results were obtained. . In addition, the soil environmental standard value of trichlorethylene elution amount is 0.03 mg / l.
<Concentration of trichlorethylene (mg / l)>
Sample Material 1 day Material 7 days Material 21 days Material 42 days
1) Blank 2.8 3.1 1.4 1
2) RD material 2.7 0.90 1.3 0.001
3) RDW material 2.6 6.9 0.005 Not measured Moreover, when the pH of each sample was also measured, the following result was obtained.
<PH>
Sample Material 1 day Material 7 days Material 21 days Material 42 days
1) Blank Not measured 5.90 6.10 6.51
2) RD material Not measured 6.14 6.81 6.50
3) RDW material Not measured 10.74 10.75 Not measured Concerning trichlorethylene concentration, 1) In the blank, the concentration decay is observed at every age. This indicates that the monomolecular water molecular ion in the reduced water promotes the decomposition of trichlorethylene. However, on the 42nd day (6 weeks), the environmental standard value is not satisfied. In addition, it is thought that such clear concentration attenuation | damping cannot be obtained only with a simple soil sample which does not add reduced water.

  2) The RD material satisfies the environmental standard value on the 42nd day (6 weeks) of the material age. By combining the reduced water and the RD material, adding to the soil, mixing and stirring, the soil can be effectively purified. I understand that. Concentration decay is faster than 1) blank.

  3) RDW material temporarily detected 1) more than double the concentration of blank on 7th day (1 week), but it was below the environmental standard value on 21st day (3 weeks). 2) Concentration decay more rapid than that of the RD material was obtained.

  From the measurement results of pH, it can be seen that 3) RDW material is alkalized. This can be considered as follows.

  First, the base material of the RDW material is a calcium mineral powder, which itself does not dissolve in water and become alkaline. As described above, the nanoparticle promotes the electrolysis of water by a weak discharge when it comes into contact with water molecules, and emits far infrared rays (wavelength: 6 to 14 μm) at normal temperature. Play.

  These combined actions produce water molecules ions that are unimolecularized (hydroxyl negative ions), which have high surface activity, hydrolytic power, osmotic power, and reducing power, and contribute to the decomposition of trichlorethylene. .

  Further, when water is electrolyzed, it is divided into hydrogen ions and hydroxide ions. Here, since the calcium-based mineral of the RDW material has a property of occluding hydrogen ions, the hydrogen ions in the solution are reduced, and the concentration of hydroxide ions is relatively increased. That is, alkalinization is promoted.

  As described above, trichlorethylene is considered to be bound to the weakly adsorbed water zone because the surface of the clay particles is negatively charged. However, when alkalization with the RDW material proceeds, the solution itself becomes negatively charged. It is thought that it can counter the negative charge on the clay particle surface. Therefore, it is considered that the binding force of trichlorethylene in the weakly adsorbed water zone can be relatively weakened and the release and decomposition thereof can be promoted. In addition, the liberation and decomposition are considered to proceed from the outside to the inside sequentially from the clay particles.

  In addition, when using RDW material, the addition of reducing water can be omitted. This is because if the RDW material comes into contact with water in the sample and is allowed to stand for a while, water similar to reduced water is considered to be generated in the sample.

  In addition, by adding the RDW material, mixing and stirring, alkalization proceeds, but this is not a problem in terms of safety. This is because it is not a change in pH due to a solute such as sodium hydroxide, but a change in the pH of the solvent water itself, and a stimulating reaction does not occur even when the pH is increased.

  When contaminated soil contains clay minerals and volatile organic compounds, in the prior art, removal of volatile organic compounds was impeded by the thixotropic hardening process and was given up as impossible. Thus, according to the present invention, effective soil purification can be realized.

  Next, based on the above knowledge, a specific soil purification method using the above-described improving material will be described.

(1) Shallow layer treatment method The surface layer or shallow layer volatile organic compound contaminated soil is purified. The following three processing methods can be listed depending on the processing method. Both are suitable for soil contamination of shallow unsaturated ground, and are intended to demonstrate the purification function of far-infrared radiators through underground moisture and voids. If natural rainfall, especially light rain, is desired, the permeated water will serve as a medium for the purification function of the far-infrared emitter (ie, carry the action of the far-infrared emitter far) The effect can be expected.

1. In-situ shallow layer mixing method Using a machine such as a backhoe or a stabilizer, the improved material and the local surface soil are mixed and stirred uniformly in-situ.

2. Plant mixing and laying method A plant is set up on the site, and the local soil is dug once and mixed with the improved material in the plant on the ground, or mixed with the liquid to which the improved material is added and dried and fixed.

3. In-situ spraying method Disperse the improved material or the liquid to which it is added evenly on the ground surface and purify it. This is the simplest method, but if there are local soil conditions, weather conditions such as a sunny day or dry season, it is more effective to spray the added liquid.

(2) Deep-layer mixing treatment method Contaminated soil and improvement material are mixed while injecting the improved material using a deep ground improvement machine or chain conveyor cutter excavator, etc. Stir to form improved pillars and purify contaminated soil in and around the improved pillars.

  Depending on the degree of contamination, distribution, scale, etc., it is desirable to use the following three treatment methods.

1. Fixed interval arrangement method As shown in the plan view of FIG. 1 (a) and the underground elevation view of FIG. 1 (b), the improved pillars 1 are constructed at a constant arrangement interval. It is also possible to change the arrangement interval (that is, the density) between the improved columns according to the level of contamination at the site. This is effective when the contamination is widely dispersed. Further, as shown by the hatched portion in FIG. 1B, it is desirable that the above-mentioned shallow layer processing method is additionally applied to the surface portion in order to reinforce the purification action.

2. Lattice arrangement method As shown in FIG. 2, improved columns are continuously formed to form a continuous wall, and the contaminated soil is surrounded by the continuous wall. Compared to the fixed spacing method, the construction cost increases as the amount of improved pillars increases, but the purification function improves as the improved pillars continue. This is especially effective at sites where there are large variations in the strength and distribution of contaminated soil.

  As in the case of the fixed interval arrangement method, it is desirable to additionally perform the above-described shallow layer processing method on the ground surface portion.

3. Whole Cross-Section Method When a contaminant is concentrated locally, such as a so-called hot spot, the entire cross-section is covered with an improved column as shown in FIG. The construction cost per unit volume is higher than that of the lattice arrangement method, but it is effective because it can provide the root of the diffusion of pollutants. In addition, from this root, the water affected by the far-infrared radiator flows on the diffusion route of the pollutant and plays a role as a medium for the purification function. A purification effect can be expected.

(A) Plane explanatory diagram of the regular interval arrangement method in one embodiment of the present invention (b) Elevation explanatory diagram of the regular interval arrangement method in one embodiment of the present invention Explanatory drawing of the grid | lattice arrangement | positioning method in one embodiment of this invention Explanatory drawing of the whole cross-section method in one embodiment of this invention

Explanation of symbols

1 Improvement pillar

Claims (5)

A method for purifying contaminated soil, comprising adding an improving material containing a far-infrared radiator to a contaminated soil containing a clay mineral and a volatile organic compound, followed by stirring and mixing. The contaminated soil purification method according to claim 1, wherein the improving material is an RD material in which nanoparticles made of a far-infrared emitter are fixed on a base material made of volcanic glass-based particles. The contaminated soil purification method according to claim 1, wherein the improvement material is an RDW material in which nanoparticles made of a far-infrared emitter are fixed on a base material made of calcium-based mineral powder. 4. The method for purifying contaminated soil according to claim 1, wherein reduced water is further added at least before stirring and mixing, and the reduced water is made by mixing water and a far-infrared radiator and allowing to stand, and consisting of the supernatant water. The diameter of the said nanoparticle is 5 nanometers or more and 50 nanometers or less, The contaminated soil purification method of Claim 2 or 3.

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