JP2005138107A - Soil-cleaning agent and soil cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soil cleaning method for directly and efficiently removing organic halogenated compounds or the like from the soil polluted with the organic halogenated compounds or the like, and a soil-cleaning agent advantageously used in the method. <P>SOLUTION: The soil-cleaning agent is an aqueous suspension containing slurry including fine iron particles in which the spherical fine iron particles having an average diameter below 10μm are dispersed in water. The contaminated-soil cleaning method uses this agent. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a soil purification agent containing an iron fine particle slurry used for removing the contaminants from soil contaminated with organic halides, hexavalent chromium, and the like, and a method for purifying the contaminated soil.

  A large amount of organic halides such as trichlorethylene has been used for industrial cleaning such as oil removal of machinery. From the viewpoint of environmental pollution, the use of such organic halides has recently been regulated. However, a large amount of organic halide has already been used, and as a result, soil contamination or water pollution is also progressing. That is, organic halides such as trichlorethylene are stable and difficult to be decomposed by microorganisms, and organic halides discarded in the natural environment not only contaminate the soil, but ultimately pollute rivers and groundwater, which can be used as beverages. It can become raw water, which is a problem. In addition, it is known that such pollution of the natural environment is also caused by hexavalent chromium left in a factory site such as a plating factory.

  Known methods for purifying soil contaminated with volatile organic compounds such as organic halides include a soil gas suction method, a groundwater pumping method, and a soil excavation method. The soil gas suction method forcibly sucks the target substances present in the unsaturated zone. A suction well is installed in the ground by boring, and the inside of the suction well is depressurized by a vacuum pump, and the vaporized organic The compounds are collected in a suction well, guided to the underground, and treated by a method such as adsorption of organic compounds in soil gas onto activated carbon. When the contamination by the organic compound extends to the aquifer, a method is adopted in which a submersible pump is installed in the suction well and the water is pumped and treated simultaneously with the soil gas.

  The underground pumping method is a method of setting up a pumping well in soil and pumping up contaminated groundwater. Furthermore, the soil excavation method is a method in which contaminated soil is excavated, and the excavated soil is subjected to wind drying and heat treatment to remove and collect organic compounds.

  As a method for purifying contaminated water such as collected water or ground water as described above, for example, in Patent Document 1, after removing dissolved oxygen in contaminated water, the contaminated water is brought into contact with a metal surface such as iron. A method for reducing and removing organic halides contained in contaminated water is disclosed. Such a method for purifying contaminated water using the reducing action of iron is also described in Patent Documents 2 to 6 and the like. In any of these methods, the contaminated water is treated by passing it through a certain portion such as a layer containing iron or a filter.

  However, these methods are not methods for directly purifying soil, but are methods for purifying contaminated water collected by the soil gas suction method, groundwater pumping method, etc., or contaminated water such as rivers and groundwater. The amount is extremely large, and the treatment often takes a long time. It is also a drawback that the processing steps are often complicated. For this reason, a method for directly and simply purifying soil that is a source of contamination is required.

  In addition, for the soil contaminated with hexavalent chromium, a method of purifying with a reducing agent such as ferrous sulfate is known. However, when the soil exists in the form of trivalent and hexavalent chromium as in a chromium slag. On the other hand, ferrous sulfate cannot be sufficiently reduced because of the short time during which it exhibits a reducing action. Therefore, the appearance of a purifier that exhibits a reducing action over a long period of time is desired.

Japanese Patent No. 2636171 JP-A-3-106496 JP-A-3-30895 JP-T 6-501521 JP-A-8-257570 Japanese Patent Laid-Open No. 10-263522

  It is an object of the present invention to detoxify iron particles that can be removed from soil contaminated with contaminants such as organic halides, hexavalent chromium, etc. directly or efficiently by detoxification, or removed after detoxification. It is providing the soil purification agent containing a slurry, and the purification method using this soil purification agent.

  The conventional method of purifying soil contaminated with organic halides is to collect contaminated water from the contaminated soil and purify it, or collect the soil itself and purify it. It is not a way to purify.

  The present inventors have paid attention to iron that exhibits an action of reducing and decomposing organic halides (so-called dehalogenation action), and have made extensive studies to develop a simple purification method using the iron. However, the iron fine particles that have been used in the conventional purification method have a relatively large average particle size of several tens of μm, and the shape thereof is also indefinite, so even if the aqueous dispersion is directly applied to the soil, for example. I found that there was a problem that it was difficult to penetrate. Based on such knowledge, further research was conducted, and it was found that iron fine particles having a large iron surface area and a spherical shape were effective in solving the above-mentioned problems. Is. Thus, by finely pulverizing iron particles, the surface area of iron is increased to increase the processing capacity of pollutants, and in addition to atomization, the shape of the particles is made spherical so that iron can quickly enter the soil. Permeation can be made possible. As described above, the iron fine particles conventionally used for purification have an average particle diameter of several tens of μm, whereas the iron fine particles of the present invention are less than 10 μm, which is 2 times or more (in some cases, 10 times or more). ) And a spherical shape, which is far superior in permeability to soil compared to conventional amorphous ones.

  It has also been found that the reducing action of such iron fine particles is effective against contaminants that can be reduced, particularly hexavalent chromium.

  Therefore, the object can be solved by a soil purifier containing an iron fine particle slurry in which spherical iron fine particles having an average particle size of less than 10 μm (preferably 0.1 to 6 μm) are dispersed in water. By making such a very small particle size, it is possible to greatly improve the cleaning power. Further, the slurry preferably contains an antioxidant. Thereby, it can maintain so that iron may not be oxidized. The solid content of the slurry is preferably 20 to 70% by mass (particularly 30 to 50% by mass).

  In addition, the object is to detoxify pollutants (eg, organic halides, hexavalent chromium, etc., especially organic halides) from contaminated soil, which comprises infiltrating the soil purification agent into the contaminated soil, or This can be achieved by detoxification and removal methods. Preferably, the method of performing the penetration of the soil purification agent by spraying the soil purification agent over substantially the entire surface of the soil; inserting an injection pipe for supplying the soil purification agent to the contaminated soil; Mention may be made of a method comprising injecting a soil purification agent into the injection tube.

  The iron fine particle slurry used in the present invention is characterized by containing iron fine particles having an average particle diameter of less than 10 μm and a spherical shape. The soil purification agent of the present invention comprising an aqueous suspension containing this slurry is useful for decontaminating contaminants from contaminated soil, such as by reduction, or after detoxification.

  Examples of the contamination source to be purified according to the present invention include organic halides, hexavalent chromium, and cyanide. Organic halides and hexavalent chromium are suitable, and organic halides are particularly suitable. Examples of organic halides include 1,1-dichloroethylene, 1,2-dichloroethylene, trichloroethylene, tetrachloroethylene, dichloromethane, carbon tetrachloride, 1,2-dichloromethane, 1,1,1-trichloroethane, 1,1,2- Examples include trichloroethane, 1,1,2,2-tetrachloroethane, dichlorodifluoroethane, and the like. These organic halides are considered to be removed from the soil by losing halogen to the corresponding hydrocarbons due to the dehalogenation action (reduction action) of iron. The organic halide is particularly effective for organic chlorides (organic chlorine-substituted compounds). Hexavalent chromium can be efficiently reduced to trivalent chromium by an effective iron reducing action over a long period of time, and then removed from the soil as necessary. Furthermore, cyanide (cyanide ions) is detoxified by forming a complex with iron ions.

  The iron fine particles contained in the slurry used in the soil purification agent of the present invention are extremely fine particles. For this reason, when directly applied to contaminated soil, they rapidly penetrate into the soil. The average particle size of the iron fine particles is less than 10 μm, preferably 0.1 to 6 μm, particularly preferably 0.1 to 3 μm. By using such ultrafine iron powder, the detergency can be greatly improved. Further, since the iron fine particles are ultrafine particles as described above and the shape thereof is a sphere, when applied to the contaminated soil, the iron fine particles penetrate into the soil very quickly and exhibit a purification action.

  The solid content of the slurry is preferably 20 to 70% by mass (particularly 30 to 50% by mass). Further, the slurry preferably contains an antioxidant. Thereby, it can maintain so that iron may not be oxidized. In the solid content, 90% by mass or more is metallic iron and an iron-containing compound. In solid content, metal iron accounts for 30 mass% or more.

  Such a slurry is generally obtained by collecting steelmaking dust in an exhaust gas generated during refining (preferably wet dusting) from an oxygen blow furnace for steelmaking and removing a gas such as carbon dioxide. A slurry made of steelmaking dust can be advantageously used. Usually, after dust collection, the steelmaking dust is made into a slurry of iron powder sludge by a thickener. If desired, a high-grade iron powder for a specific application (eg, for toner) can be further added to the obtained steelmaking dust to form a slurry.

  An example of a method for producing the iron fine particle slurry will be described with reference to FIG.

  In an oxygen blowing furnace for steelmaking, pig iron containing impurities such as C, Si, and P is charged and oxygen is rapidly blown from above while stirring. In this state, a reaction occurs between the impurity-containing pig iron and oxygen, C, Si, P, etc. become oxides, and pig iron becomes a rope. During this time, the exhaust gas containing fine iron powder generated by blowing oxygen is collected by wet dust collection through a gas recovery hood. In wet dust collection, a gas such as CO is sent to a gas recovery tank. Steelmaking dust obtained by collecting exhaust gas is in the form of a slurry. This slurry is coarsely divided (at 60 μm), the coarse is collected as coarse iron powder, and the fine is concentrated by a thickener. Finally, only fine particles are selected by a filter press, and fine iron powder (that is, iron fine particle slurry) can be obtained.

  The iron fine particles obtained in this way contain iron oxides in various oxidation stages, but such iron oxides are also in a reduced state in the dust trapped in the gas combustion state, and are considered to exhibit a reducing action that leads to a purification action. It is done. Therefore, even if metallic iron does not occupy 30% by mass or more, the iron fine particles can often exhibit a high reducing action.

  Examples of the particle size of 97% by mass Fe in the coarse iron powder are as follows.

  A composition example of the fine-grained iron powder is as follows.

  The range of the components of the fine iron powder is as follows.

  As described above, the iron fine particles of the present invention can be obtained by using a by-product during iron refining without using a special method and apparatus for producing the iron fine particles, and are simple and economical. . Moreover, since it is obtained in the form of a slurry, oxidation of the iron particle surface can be prevented, and therefore oxidation during transportation can be prevented. During transportation, it is preferable to stir so that the iron particles do not precipitate and solidify. Moreover, in order to prevent the oxidation of the iron particle surface, it is preferable to add an antioxidant to the slurry. Examples of the antioxidant include organic acids (eg, ascorbic acid (vitamin C), citric acid, malic acid, particularly ascorbic acid) and salts thereof. 01-10 mass% is common, and 0.1-3 mass% is preferable. Furthermore, since it is a slurry form, when manufacturing a soil purification agent, there exists an advantage that mixing with another material is easy.

  The soil purification agent of the present invention containing the iron fine particle slurry can be used in combination with metals other than iron, such as Mn, Mg, Zn, Al, and Ti, which have a reducing action. These metals too. The average particle size is preferably as small as possible.

  Since the fine iron powder has a large surface area and is easily oxidized (passivated) on the surface, it is preferable to use a hydrophilic binder and / or a metal halide together in the present invention to prevent this.

Examples of the metal halide include NaCl, KCl, MgCl ₂ and CaCl ₂ , and NaCl is particularly preferable. Metal halides have the function of reducing iron hydroxide and oxide to metallic iron. The amount used is generally 0.5 to 200% by mass, preferably 0.5 to 50% by mass, based on the iron fine particles.

  The hydrophilic binder has a function of covering the surface of the iron fine particles and protecting the organic halide from being oxidized before exhibiting a reducing action. Examples of hydrophilic binders include disaccharides such as sucrose, sucrose derivatives (eg, sucrose higher fatty acid esters), monosaccharides such as glucose, alginic acid; pullulan, PVA (polyvinyl alcohol), CMC (carboxyl methylcellulose), polyacrylamide, Mention may be made of water-soluble resins such as guar gum, methylcellulose and hydroxyethylcellulose. Pullulan (particularly preferred because of its low viscosity when made into an aqueous solution), hydroxyethyl cellulose, sucrose, glucose, and PVA are preferred. The use of a biodegradable polymer as the hydrophilic binder is particularly effective against secondary environmental pollution. The amount used is generally 0.01 to 200% by mass, preferably 0.01 to 100% by mass, based on the iron fine particles.

  The soil purification agent of the present invention is obtained by adding an antioxidant, a metal halide or a water-soluble polymer, or a metal halide and a hydrophilic binder to the above iron fine particle slurry, if desired, and suspending or dispersing it. Is. Further, water can be appropriately added to obtain a desired concentration. If necessary, a surfactant can be used at the time of dispersion. The use of a biodegradable polymer (eg, biodegradable polycaprolactone) instead of the hydrophilic binder is particularly effective against secondary environmental pollution.

  It is preferable that the soil purification agent of the aqueous suspension further contains a metal sulfate (particularly ferrous sulfate) as a reducing agent. Since this reacts with oxygen in the air, it is possible to prevent the surface of the metal iron fine particles from being oxidized.

  The aqueous suspension preferably further contains an inorganic carbonate or carbonate-based mineral. Examples of these include calcium carbonate, precipitated calcium carbonate, magnesium carbonate, fossil limestone, limestone, and dolomite, and precipitated calcium carbonate is particularly preferable. Since the soil purification agent of the present invention uses fine particle iron, it can be injected into the gap between soil particles in the soil. However, since the possibility of leaching into groundwater and the like is increased by using fine particles, it is preferable in the present invention to fix the eluted iron ions and prevent this by using the carbonate.

  As described above, the soil-cleaning agent of the aqueous suspension of the present invention is suspended by adding the iron fine particle slurry, and optionally a water-soluble polymer, metal halide or metal halide and a hydrophilic binder, or It is obtained by dispersing. In this case, it is preferable to use reducing electrolyzed water (preferably pH = 7 to 12) from the viewpoint of suppressing iron oxidation as much as possible. A surfactant such as naphthalene sulfonic acid may be used as the dispersant. The amount of the dispersant used is generally 0.01 to 10% by mass and preferably 0.1 to 5% by mass with respect to the iron fine particles. Moreover, you may further use the above-mentioned antioxidant within the said range.

  The method for purifying contaminated soil of the present invention using a soil purification agent is performed by applying the soil purification agent so as to penetrate into the soil (ground) contaminated with an organic halide. Preferably, the soil purification agent is permeated by spraying the soil purification agent (1); or an injection pipe for supplying the soil purification agent is inserted into the soil contaminated with the organic halide. And a method (2) comprising injecting the soil purification agent into the injection tube.

  The said method (2) can be performed as follows, for example.

  An injection pipe for supplying soil cleaner by boring is provided on the surface contaminated with organic halides. If necessary, a plurality of injection tubes can be provided at intervals. Inject the soil cleaner into the supply tube. As a result, iron fine particles or the like penetrate into the contaminated soil and gradually come into contact with the organic halide to decompose and remove the organic halide. Before injecting with an injection pipe, ground water may be discharged from the injection pipe and then a soil purification agent may be injected. The soil surface may be covered with a water-impermeable sheet (eg, bentonite sheet) so that the injected solution does not overflow from the soil surface. Alternatively, a sheet may be embedded in the soil.

  You may perform the said purification | cleaning method as follows, for example. That is, as shown in FIG. 2, the periphery of the contaminated soil is blocked by an air-impermeable layer 12 that reaches the underground impermeable ground 11, and the injection tube 9 and, if necessary, the air-permeable columnar portion 2 and The horizontal ventilation layer 4 is installed, covered with an air-impermeable sheet 6 on these, and the periphery thereof is blocked by an air-impermeable layer 7 made of backfill earth and sand mixed with paste material outside the gas-impermeable layer. Can do. In the horizontal ventilation layer 4, an intake pipe 5, which is a porous pipe composed of a large number of holes having a size that does not transmit the air-permeable material 3, is embedded.

  And the purification treatment is, for example, draining through the water injection pipe, injecting the cleaning agent of the present invention from the injection pipe, and reducing the pressure if necessary to remove substances generated by the diffusion of the cleaning agent and the reducing action by iron. Can do.

  As in the above method, it is preferable to cover the surface of soil contaminated with organic halides with a non-breathable sheet (generally, the cover of the sheet is installed after the injection of the cleaning agent), and if necessary, a breathable columnar shape. Part (useful for removal of the generated substance) can be provided.

  Soil contaminated with contaminants other than organic halides can be performed in the same manner as described above. In addition, contaminated soil (especially soil contaminated with hexavalent chromium) can be treated with the soil purification agent of the present invention by introducing the excavated soil into a reaction tank or the like by the soil excavation method. It may be advantageous to remove chromium compounds and the like.

Generally the density | concentration of the iron fine particle in the soil purifier inject | poured into soil is 0.1-50 mass%, and 1-30 mass% is preferable. Further, the injection amount is generally 1 to 400 kg of iron fine particles per 1 m ³ of soil, and preferably 10 to 200 kg.

  Further, the injection of the soil purification agent may be carried out separately by injection of an aqueous suspension of iron fine particles and injection of an aqueous suspension containing a hydrophilic binder or the like used as desired.

[Example 1]
(A) Iron fine particle slurry-containing aqueous suspension (soil purification agent)
Using the method shown in FIG. 1, an iron fine particle slurry was obtained under the following production conditions.

Production conditions: Manufactured in a top-bottom blown converter equipped with OG (oxygen gas) gas treatment system
(T: amount corresponding to the mass of steel in the converter, indicated by capacity)
Input pig iron: Hot metal ratio 70-96%
Oxygen blowing rate: Blowing time of about 20 minutes Slurry production rate: 250 t / D (day)

  The following fine iron powder slurry was obtained by the above method. Its composition is as follows.

  The components of the fine iron powder are as follows.

  The iron fine particles contained in the slurry after the filter press were confirmed to be spherical by observation with an electron microscope (20,000 times). The particle size distribution was as shown in FIG. The average particle size was 1.3 μm.

  The particle size distribution of the iron fine particles was measured under the following conditions.

Measuring instrument: SK Laser Micron Sizer 7000S
Dispersion medium: 0.2% NaHMP
Dispersion condition: Ultrasound (US WAVE) 5 minutes

  Tables 1 and 2 show the volume fraction and the composition of each particle size in FIG.

  The slurry after the filter press (solid content: 65% by mass) is made 30% by adding reducing electrolyzed water in a stirring tank, and further 0.1% by mass of ascorbic acid is added, and the soil of the iron fine particle slurry is stirred. A purifier was obtained.

  Next, the soil cleaner (a) is continuously introduced into a bead mill (dispersing device), and after dispersion, HCl is added to a pH meter of 4 to be described later, mixed with a line mixer, and mixed and then the pH meter is mixed. PH is adjusted with this (by adjusting the amount of HCl added), and then NaOH is added to pH 7 with a pH meter to be described later, and 20 mass% of ferrous nitrate and ascorbic acid 0.1 are added. An aqueous dispersion containing mass% (in the same amount as the soil purification agent (a)) was added, mixed with a line mixer, and after mixing, the pH was measured with a pH meter to obtain a dispersion. This dispersion was continuously produced, and the obtained dispersion was continuously poured into soil contaminated with trichlorethylene.

Contaminated soil is a soil with a crushed stone layer 30 cm deep from the ground, a silt layer up to a depth of 2 m, and a clay layer up to 30 m from there. Laid a slab. A total of 25 holes (diameter 10 cm) were made in the floor slab, 5 pieces every 3 m on the left and right, and the dispersion liquid was injected therefrom. The injection amount was 4 m ³ / hour and was performed for 48 hours.

  As a result, the concentration of trichlorethylene at 5 locations (randomly set) in the soil changed as follows one month after the injection.

Silt layer (before injection → 1 month later (unit: ppm)):
1) 1.85 to less than 0.0005, 2) 0.01 to less than 0.0005,
3) 3.22 → less than 0.0005, 4) 1.97 → less than 0.0005,
5) 0.08 → less than 0.0005.

Clay layer (before injection → 1 month later (unit: ppm)):
1) 5.06 to less than 0.0005, 2) 1.03 to less than 0.0005,
3) 3.08 to less than 0.0005, 4) 1.53 to less than 0.0005,
5) 2.93 → less than 0.0005.

  Moreover, since the position farthest from the injection port among the five locations in the soil is a horizontal distance of 5 m and a depth of 2 m, the purifying agent was effectively acting even at this position. It can be seen that it has good permeability.

FIG. 1 is a flowchart showing an example of an embodiment of a method for producing an iron fine particle slurry of the present invention. FIG. 2 is a cross-sectional view showing an example of an embodiment of the purification method of the present invention. FIG. 3 is a graph showing the particle size distribution of the iron fine particle slurry obtained in Example 1.

Explanation of symbols

2 Breathable column 3 3 Breathable material 3
4 Horizontal ventilation layer 5 Intake pipe 6 Impervious sheet 9 Injection pipe 11 Underwater impermeable ground 12 Impervious layer

Claims (16)

  A soil purification agent for purifying contaminated soil, comprising an aqueous suspension containing an iron fine particle slurry in which spherical iron fine particles having an average particle size of less than 10 μm are dispersed in water.   The soil purification agent according to claim 1, wherein the average particle size is 0.1 to 6 µm.   Furthermore, the soil purification agent of Claim 1 or 2 containing antioxidant.   The soil purifier according to any one of claims 1 to 3, wherein the solid content is 20 to 80% by mass.   The soil purifier according to any one of claims 1 to 4, wherein the aqueous suspension further contains a hydrophilic binder.   The soil purification agent according to any one of claims 1 to 5, wherein the aqueous suspension further contains a metal halide.   The soil purification agent according to any one of claims 1 to 6, wherein the aqueous suspension further contains a metal sulfate as a reducing agent.   The soil purification agent according to any one of claims 1 to 7, wherein the aqueous suspension further contains an inorganic carbonate or a carbonate-based mineral.   The soil purification agent according to any one of claims 1 to 8, wherein the pollutant in the contaminated soil is an organic halide and / or hexavalent chromium.   The soil purification agent according to any one of claims 1 to 8, wherein the pollutant in the contaminated soil is an organic halide.   A soil purification method comprising infiltrating the soil purification agent according to any one of claims 1 to 10 into contaminated soil.   The soil purification method according to claim 11, wherein the soil purification agent is permeated by spraying the soil purification agent over substantially the entire surface of the soil.   A soil purification method comprising inserting an injection pipe for supplying the soil purification agent according to any one of claims 1 to 10 and injecting the soil purification agent into the injection pipe.   The soil purification method according to claim 13, wherein the surface of the contaminated soil is further covered with a sheet.   The soil purification method according to any one of claims 11 to 14, wherein the pollutant in the contaminated soil is an organic halide and / or hexavalent chromium.   The soil purification method according to any one of claims 11 to 15, wherein the pollutant in the contaminated soil is an organic halide.

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