JP2004261795A - How to remove non-volatile contaminants in soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the recycling rate of treated soil, reduce installation space, reduce processing cost and treat contaminated soil (disposal soil) when treating soil mixed with non-volatile contaminants such as oil and heavy metals. ) To provide a method for removing non-volatile contaminants in soil, which can realize the reduction of the amount of non-volatile contaminants.
SOLUTION: The soil mixed with the non-volatile contaminant is mixed with water to wash the soil, and the soil particles in the obtained muddy water are classified to separate coarse particles having a low contaminant content. A method for removing non-volatile contaminants in soil, comprising separating solid-liquid muddy water containing fine particles containing a high concentration of water and separating soil fine particles containing a large amount of contaminants.
[Selection] Fig. 2

Description

  The present invention relates to a method for removing nonvolatile pollutants in soil.

  BACKGROUND ART Conventionally, various plating materials, insulating oils, pigments, resins, solvents, agricultural chemicals, and the like have been used as materials for the metal industry, electric industry, electronic industry, and chemical industry. Water quality standards and environmental standards related to soil pollution are established for these substances.However, if the above contaminants that have been mixed into the soil in the past are left as they are, they will penetrate deep into the ground over time, and eventually There is a problem of environmental pollution that causes contamination of groundwater by mixing into groundwater.

  From such a background, various methods for removing contaminants such as heavy metals mixed in soil have been studied, and a classification cleaning method has been proposed as one of the methods (Patent Document 1). In this method, a major problem is how to transfer or react the contaminants to the cleaning mediator (water, steam, chemical, etc.). In addition, pollutants tend to be concentrated in small soil particles, and there is a problem that incomplete purification reduces the reuse rate of purified soil. Further, in the conventional washing process, the amount of washing water used is about 10 times as large as that of the soil to be treated, which complicates the treatment equipment in the latter stage of the washing, increases the space for installing the treatment equipment, and increases the equipment cost. It is low practicality.

JP 2000-251995

  Accordingly, an object of the present invention is to increase the recycling rate of treated soil, reduce installation space, and reduce processing and disposal at low cost when treating soil mixed with non-volatile contaminants such as oil and heavy metals. An object of the present invention is to provide a method for removing non-volatile contaminants in soil, which can reduce the amount of residual soil as a target soil.

  The above object is achieved by the present invention described below. That is, the present invention provides a method for mixing soil with non-volatile contaminants, washing the soil with water, classifying the soil particles in the obtained muddy water, separating coarse particles having a small amount of contaminants, and contaminating the soil. Disclosed is a method for removing non-volatile contaminants in soil, which comprises solid-liquid separation of muddy water containing a substance at a high concentration and separating soil fine particles containing a large amount of contaminants.

  In the present invention, the specific gravity of the mud containing a high concentration of pollutants is adjusted to a range of 1.05 to 1.35; a mixture of soil and water mixed with nonvolatile contaminants is washed in a washing tank. Peptization by aeration, mechanical agitation and / or pump circulation in the above; air, steam or chemicals are further mixed with a mixture of soil and water contaminated with nonvolatile contaminants and peptized by a static mixer. Removing impurities in the muddy water before washing the muddy water; and 60% by mass or more of coarse particles having a particle size of 75 μm or more and 40% by mass of fine particles having a particle size of less than 75 μm in the muddy water after peptization. It is preferably less than.

  The method of the present invention is simple in equipment and can be miniaturized, can efficiently purify contaminated soil in a small space, and can remove non-volatile contaminants such as oil and heavy metals in soil in soil. The soil of the coarse particles that can be transferred and concentrated to fine particles and separated as coarse particles can be reused as backfill soil on site. In addition, water is usually added to contaminated soil containing contaminants to form muddy water, and the specific gravity of the muddy water after removing coarse particles in the muddy water is adjusted to a range of 1.05 to 1.35, which is usually required. Eliminates the need for sedimentation separation equipment and slurry concentration equipment. Therefore, in the present invention, it is possible to effectively treat the soil at a low treatment cost.

Next, the present invention will be described in more detail with reference to preferred embodiments.
Non-volatile contaminants mixed into the soil targeted by the present invention include, for example, heavy metal compounds such as cadmium, cyanide, organic phosphorus, lead, hexavalent chromium, arsenic, mercury, copper and their compounds, and PCBs. , Heavy oil, tar, pitch and so on.

  Embodiments of the present invention will be described more specifically with reference to the drawings. FIG. 1 is a diagram showing a basic configuration of the method of the present invention. As shown in FIG. 1, first, muddy water to be treated obtained by adding an appropriate amount of water to contaminated soil to be treated is uniformly mixed and washed in a washing tank 1 and coarse particle sedimentation is prevented. At this time, the specific gravity of the muddy water is desirably controlled at about 1.20 (range of 1.05 to 1.35).

  Peptization and washing of the mud to be treated can be performed by any means. For example, suitable means include mechanical stirring by the stirrer 2, blowing of air by the air distributor 4 or circulation of muddy water by the circulation pump P 1, and action of air supplied from the pollutant separator 5 and the air compressor 6. Alternatively, supply of chemicals, steam, and the like to the contaminant separator 5 can be mentioned, and these means can be used in combination of plural kinds. The muddy water thus pulverized to homogenize the mixture and to remove the fine particles from the coarse particles contains coarse particles having a particle size of 75 μm or more in a range of 60% by mass or more and fine particles having a particle size of less than 75 μm in a range of less than 40% by mass. Is preferred. The muddy water is transferred to the classifier 9 by the circulation pump P1, and the coarse particles 10 are separated in the classifier. The treated mud from which the coarse particles 10 have been separated is preferably adjusted to have a specific gravity in the range of 1.05 to 1.35 and sent to the solid-liquid separation device 12 (FIG. 2) to be separated into solid and liquid.

  The concentration of the contaminants in the coarse particles (for example, a particle diameter of 75 μm or more) separated above is equal to or less than a specified reference value, and the contaminants are fine particles (for example, particles) of the soil separated above. (Diameter less than 75 μm). Accordingly, the coarse particles can be reused as they are as ordinary residual soil. Further, the fine particles in which the contaminants are concentrated are treated as soil for disposal. If the contaminants in the water are below the reference value, the solid-liquid separated water is discharged as it is. If the contaminants exceed the reference value, the water is treated and discharged according to a conventional method.

  Next, a practical method for removing contaminants using the principle of the present invention will be described with reference to FIG. In the method shown in FIG. 2, volatile organic compounds can be removed simultaneously with nonvolatile contaminants. As the volatile organic compound to which the present invention is applied, for example, trichloroethylene, tetrachloroethylene, dichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene, 1,1,1-trichloroethane, 1,1,1 Examples thereof include organic chlorine compounds such as 2-trichloroethane and 1,3-dichloropropene, aromatic compounds such as benzene, toluene and xylene, ketones such as acetone, simazine, and thiobencarb.

  As shown in FIG. 2, first, soil and water to be treated are peptized and washed in a peptizer. The amount of water used at this time is the same as described above. The fluidized muddy water often contains concrete fragments, pebbles, crushed stones, metal fragments, glass fragments, and other contaminants.

  If these contaminants are mixed, problems will occur in the subsequent pumping of the muddy water, etc., so that these contaminants are removed by passing the muddy water through an appropriate mesh sieve-1 (for example, a 4 mm vibrating sieve). It is desirable to do. Spray water with sieve-1 as needed. These contaminants hardly contain contaminants. The mud from which contaminants have been removed is preferably collected in a mud receiving tank and stirred in the mud receiving tank by a suitable stirring device.

  The muddy water homogenized in the muddy water receiving tank is transferred to the washing tank 1 by the pump P0, and is washed in the washing tank 1 in the same manner as shown in FIG. At this time, when fine sand is mixed in the muddy water, it is desirable to remove the sand through sieve-2 (for example, a 0.8 mm vibrating sieve) or the like. In cleaning the mud, air, steam or chemical is injected into the contaminant separator 5 by the air compressor 6, the steam generator 7 or the chemical injecting device 8, and adheres to the particles in the mud in the contaminant separator 5. Removes contaminants and migrates into solution.

Examples of the washing tank 1 include a diffuser for retaining muddy water and blowing air into the muddy water, and a device for circulating muddy water in an air flow opposed to the muddy water flow for aeration. it can. These devices include the following devices (1) to (3).
(1) A diffuser that blows air into muddy water in a tank for aeration in the form of bubbles, or a device that drops muddy water in a tank and makes it contact an opposing air flow.
(2) A device that mechanically stirs muddy water so as not to redissolve the scum-like suspended matter or settle the soil at the bottom of the tank (an air diffuser may also have a stirring function). Also, the bottom of the tank may be cone-shaped or inclined to facilitate the discharge of muddy water.
(3) A lid that covers the tank so that air containing volatile organic compound gas does not scatter. This lid is connected to a suction device.

  The cleaning tank 1 shown in FIG. 2 is of a type that blows the above-mentioned air, and air from a blower 3 for cleaning and settling prevention is blown into muddy water from an air distributor 4 (aeration tube) provided at the bottom of the cleaning tank. The volatile organic compounds contained in the mud are volatilized in the washing tank by vigorously agitating the mud with air, and are sucked through an exhaust pipe provided at the top of the washing tank. The volatile organic compound is removed or made harmless through an adsorption tower filled with activated carbon, a decomposition device filled with a catalyst, a combustion device, and the like, and the air from which the volatile organic compound is removed or made harmless can be released into the atmosphere.

  The aeration treatment varies depending on the concentration of mud, the content of volatile organic compounds, the size of the apparatus, and the like. In general, the amount of air diffused per liter of mud is about 1 to 3 liter / min. The higher the temperature at the time of aeration, the more the separation and removal of the volatile organic compound is promoted. However, since the heating of the muddy water is expensive, it is usually performed at room temperature. The aeration time also varies depending on the temperature and the content of organic substances, but is generally about 0.5 to 3 hours.

  The mud after the aeration treatment is directly transferred to the water classifier 9 by the pump P1, and the coarse particles 10 having a small content of the non-volatile contaminants are separated by the above-described treatment, thereby increasing the amount of the contaminants. The muddy water containing fine particles 11 is separated into solid and liquid in the same manner as shown in FIG. At this time, preferably, a muddy pollutant separator 5 is further provided between the pump P1 and the water classifier 9, and the muddy water is transferred to the water classifier 9 via the pollutant separator 5. Is preferred. Thus, the muddy water is further washed. Many known mixing devices can be used for the pollutant separator 5, and for example, a static mixer (manufactured by Seika Sangyo Co., Ltd.) OHR mixer is preferably used. In addition, uniform mixing of muddy water and separation of contaminants from soil particles can also be performed by air blowing, steam blowing, mixing by chemical injection, and circulation to the cleaning tank 1 by the pump P1. In the muddy water sent to the water classifier 9 via the pollutant separator 5, coarse particles 10 of the soil are separated in the same manner as described above. Examples of the water classifier used here include a hydrocyclone and a centrifuge.

  The treated mud from which the coarse particles 10 have been separated may be immediately sent to the solid-liquid separator 12, but in order to facilitate the treatment, the treated mud is stored in a mud storage tank, and a centrifugal separator is used by a pump P2. Is sent to a solid-liquid separator 12 such as a filter press or the like to separate soil fine particles containing a large amount of contaminants. The separated high concentration contaminated soil is about 40% by mass or less of the contaminated soil initially charged. The high concentration contaminated soil is regarded as a soil to be disposed.

  The water separated by the solid-liquid separator 12 can be discharged as it is if the water contains other contaminants below a reference value. If further treatment is required, the water is treated in a water treatment facility by a coagulation sedimentation method or the like, and then stored in a water tank and discharged as needed. The separated water can be circulated through a peptizer and used as water for pulverizing and washing the first soil by a pump P3 or the like. In this case, it is not always necessary to pass through the water treatment equipment, and after repeated use, the contaminants in the water after solid-liquid separation are concentrated and then treated in the water treatment equipment by the coagulation sedimentation method, etc. It is efficient to do.

  Although the contaminated soil is processed by the above-described processing, when only the volatile organic compound is contained in the contaminated soil, the contaminated soil need not be passed through the contaminant separator 5 shown in FIG. However, in the case of soil containing nonvolatile contaminants, volatile organic compounds are often contained at the same time. Therefore, as shown in FIG. It is desirable to integrate the equipment for performing the method shown in FIG.

  According to the method of the present invention as described above, the removal of non-volatile contaminants in soil is performed mainly by water, and in some cases, by injecting air, steam, chemicals, etc. into the contaminant separator 5. Can be processed efficiently. Also, the amount of water used may be relatively small. In particular, by treating the muddy water with a specific gravity of about 1.20 (range of 1.05 to 1.35), the sedimentation separation equipment and the slurry concentration equipment which are usually required can be eliminated. An increase in installation area can be avoided. Since each device shown in FIG. 2 can be carried to the site by a truck or the like and treat the soil there, there is no need to transport contaminated soil having a large mass over a long distance. Therefore, in the present invention, it is possible to effectively treat the soil at a low treatment cost.

Next, the present invention will be described more specifically with reference to examples.
Example 1
As the contaminated soil, 40 kg of soil collected at a site contaminated with arsenic was used. Forty kg of the contaminated soil was mixed with 40 liters of water and stirred vigorously to produce muddy water, which was passed through a 1.18 mm mesh wire mesh. The mud from which contaminants have been removed is put into the washing tank 1 (50 liters) shown in FIG. 1, and the washing agitator 2, washing and settling prevention blower 3 and air distributor 4 shown in FIG. The pump P1 and the air compressor 6 for separating contaminants are operated to treat muddy water. After 15 minutes and 30 minutes, the circulation by the pump P1 is stopped, and the muddy water is dehydrated. Was measured.

  In the present embodiment, the cleaning tank 1 is provided with an exhaust port. On the other hand, an air distributor 4 is provided at the bottom, and is blown into the tank bottom by the blower 3 for cleaning and settling prevention and the air distributor 4. Further, the washing tank 1 is provided with a washing stirrer 2 for generating a shearing force in the muddy water. In order to realize a more powerful cleaning effect, a contaminant separator 5, a circulation pump P1 for circulating muddy water, and a contaminant separation air compressor 6 for sending air to the contaminant separator 5 are arranged near the cleaning tank 1. The pipes were joined together.

The muddy water treatment was performed under the following conditions.
Mud temperature: 15 ° C
Aeration speed; 100 liter / min
Stirrer: 295 rpm x 2 stages x 3 propellers Mud circulation: 30 l / min
Pressure air volume: 30 liter / min
Processing time: 30 min

  The removal rate of arsenic by the above treatment was determined by collecting 2,000 ml of the treated mud as a sample every 15 minutes and measuring the degree of contamination for each particle size. The measurement results are as shown in FIGS. FIG. 3 shows the particle size accumulation curve of the degree of contamination, FIG. 4 shows the degree of contamination for each particle size before cleaning, and FIG. 5 shows the degree of contamination for each particle size after cleaning. According to FIG. 3, the particle size distribution of the soil particles in the treated muddy water is found. Most of the particles have a particle size of 75 μm or more, and the mass ratio of the soil particles having a particle size of less than 75 μm is small. According to FIGS. 4 and 5, most of the soil particles contain arsenic irrespective of the particle size, but after 15 minutes and 30 minutes treatment by the method of the present invention, the arsenic elution value of the soil particles of 106 μm or more becomes , The arsenic elution value is high for soil particles smaller than 75 μm. Therefore, in the present invention, it is clear that arsenic is sufficiently removed from the soil of coarse particles after washing and classification.

  Dewatering performance was measured when the specific gravity of the muddy water after removing the coarse particles after the above-mentioned muddy water treatment was 1.02, 1.05, 1.07, 1.20, 1.35, 1.40. As the muddy water dewatering, the muddy water specific gravity of the muddy water dewatering machine for the muddy pressure shield construction is 1.07 to 1.40. In that case, the muddy water driving time per batch is longer as the specific gravity of the muddy water is lower, and is shorter as the specific gravity is higher. Usually, the time per batch in this case is about 100 minutes as a standard. Further, when the driving pump is a centrifugal pump, the specific gravity of the muddy water is set to 1.4 or less due to problems of pump characteristics and clogging of the piping.

The muddy water dehydration treatment was performed under the following conditions.
Mud temperature: 15 ° C
Mud density: 1.02, 1.05, 1.07, 1.20, 1.35, 1.40
Dehydrator; filter press tester φ150 mm (0.0177 m ² ) × thickness 30 mm
Filtration chamber volume: 0.000531 m ³
Muddy water injection; nitrogen gas injection pressure; 0.5 MPa
SS true specific gravity; 2.6

  Although the dehydration time varies greatly depending on the true specific gravity of the soil particles, the mineral composition, and the particle size distribution, the dehydration time is up to 2.5 hours in consideration of the entire treatment time. Therefore, the specific gravity of the muddy water is desirably 1.05 to 1.35.

  According to the method of the present invention as described above, non-volatile contaminants such as oil and heavy metals in soil can be transferred and concentrated into fine particles in soil, and the separated coarse-grained soil can be used as backfill soil in the field. Can be reused. Further, water is added to the contaminated soil containing the contaminant to produce muddy water, and the specific gravity of the muddy water after removing coarse particles in the muddy water is adjusted to about 1.20 (range of 1.05 to 1.35). This eliminates the necessity of a sedimentation separation device and a slurry concentration device that are usually required. Therefore, in the present invention, it is possible to effectively treat the soil at a low treatment cost.

The figure which shows the basic structure of this invention schematically. FIG. 2 is a diagram showing a practical configuration of the present invention. The figure which shows the particle size accumulation curve of contaminated soil. The figure which shows the pollution degree for every particle size of the contaminated soil before a washing process. The figure which shows the degree of contamination for every particle size after a washing process.

Explanation of reference numerals

1: Washing tank 2: Stirrer 3: Blower for washing and preventing sedimentation 4: Air distributor 5: Contaminant separator 6: Air compressor 7 for contaminant separation 7: Steam generator 8: Chemical injector 9: Classification for water Vessel 10: coarse particles 11: fine particles 12: solid-liquid separator

Claims (6)

  Water is mixed with soil contaminated with nonvolatile contaminants to wash the soil, the resulting soil particles in the muddy water are classified, coarse particles containing less contaminants are separated, and contaminants are contained at a high concentration. A method for removing non-volatile contaminants in soil, comprising separating solid and liquid muddy water and separating fine soil particles containing a large amount of contaminants.   The removal method according to claim 1, wherein the specific gravity of the mud containing the pollutant in a high concentration is adjusted to a range of 1.05 to 1.35.   The removal method according to claim 1, wherein the mixture of soil and water mixed with the non-volatile contaminants is peptized in the washing tank by aeration, mechanical stirring, and / or pump circulation.   The removal method according to claim 3, wherein air, steam or a chemical is further mixed with the mixture of soil and water mixed with the non-volatile contaminants, and the mixture is peptized by a static mixer.   The removal method according to claim 1, wherein contaminants in the muddy water are removed before the muddy water is washed. The removal method according to claim 1, wherein coarse particles having a particle size of 75 µm or more in the muddy water after peptization are 60% by mass or more, and fine particles having a particle size of less than 75µm are less than 40% by mass.

Images