JP2005279454A - Washing method of contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a washing method of contaminated soil which requires less amount of water consumption, can reduce the water treatment cost and the water charges, enhances the classification and washing efficiency and is capable of reduces the equipment cost. <P>SOLUTION: The washing method of contaminated soil comprises a step of supplying the contaminated soil 12 on the topmost sieve 28 among multi-step sieves 28, 30 and 32 of which the meshes gradually becomes finer from the upper step through the lower step, a step of washing the contaminated soil 12 on the topmost sieve 28 by jetting the hyperbaric pressure water 46 thereto and dropping the soil of which the particle size is finer than the sieve 28 to classify them, a step of conducting the washing and the classification of the soil dropped on the next-step sieve 30 by jetting the hyperbaric pressure water 46 and a step of repeating the washing and the classification by the hyperbaric pressure water 46 to the lowest step sieve 32 successively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for cleaning contaminated soil for cleaning and classifying soil contaminated with heavy metals, oil, dioxins and the like.

  When redeveloping factory sites, disposal of contaminated soil has become a major social problem.

  As one of the purification methods for contaminated soil, a soil washing method has attracted attention.

  This soil washing method is a method for washing soil contaminated with heavy metals or oil using water or chemicals and classifying coarse and fine particles.

  In general, harmful substances condense into fine particles, so coarse particles can be washed to harmless concentrations and reused for backfilling, while fine particles are usually disposed of as industrial waste. Yes.

  In general, the boundary between fine particles and coarse particles is about 75 μm.

  As this soil washing | cleaning method, what is shown to patent document 1 is known, for example.

In this soil washing method, sodium hydroxide is added immediately before the clay slurry is introduced into the line mixer by a slurry pump and the pH of the contaminated soil slurry is adjusted to 9 to 11 while mixing with the line mixer. It is sent to a sonic wave generator and further introduced into a hydrocyclone so that clean soil and fine particles or heavy metal ions containing a large amount of heavy metals are taken out separately.
JP 2000-325936 A

  Such a soil washing method as shown in Patent Document 1 uses a large amount of water to make contaminated soil into a slurry, which increases water treatment costs and water charges.

  In addition, since cleaning is performed with an ultrasonic generator and classification is performed with a liquid cyclone, classification and cleaning steps are separated, so that there is a problem that time efficiency is low and the cost of the apparatus is high.

  An object of the present invention is to provide a method for cleaning contaminated soil, which can use less water, reduce water treatment costs and water charges, improve classification and cleaning efficiency, and reduce apparatus costs.

In order to achieve the above object, the contaminated soil cleaning method of the present invention is a contamination contaminated with heavy metals, oils, dioxins, etc. on the uppermost sieve of the multistage sieve that gradually becomes finer from the upper stage to the lower stage. Supplying the soil;
Washing by spraying high-pressure water onto the contaminated soil on the uppermost sieve, dropping and classifying the soil with a particle size finer than the sieve eyes, and classification,
Washing and classification by spraying high-pressure water onto the soil that has fallen on the next-stage sieve, and sequentially repeating washing and classification by jetting high-pressure water up to the bottom sieve;
It is characterized by including.

  According to the present invention, while washing by spraying high-pressure water directly onto contaminated soil on a multi-stage sieve, sieving with the sieve, classification and washing are performed simultaneously, and classification efficiency and washing efficiency are improved by high-pressure water. By reducing the amount of water used, water treatment costs and water charges can be reduced.

  In the present invention, a vibration sieve can be used as the sieve.

  By setting it as such a structure, classification efficiency can be improved further by a vibration sieve.

  In the present invention, high-temperature water, steam, mixed jet or superheated steam can be used as the high-pressure water sprayed onto the contaminated soil.

  By adopting such a configuration, the cleaning efficiency can be further enhanced.

  In the present invention, the inclination angle of the sieve can be made variable.

  With such a configuration, the processing speed can be adjusted by changing the inclination of the sieve according to the degree of contamination.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  1-3 is a figure which shows the washing | cleaning method of the contaminated soil which concerns on one embodiment of this invention.

  FIG. 1 is a schematic explanatory view showing a contaminated soil cleaning system used in the method for cleaning contaminated soil of the present invention. This contaminated soil cleaning system 10 supplies contaminated soil 12 to a soil cleaning device 14, and this soil cleaning device. 14, while washing the contaminated soil through the water tank 16, the washing water 18 is sprayed as high-pressure water onto the contaminated soil 12 in the soil washing apparatus 14 and washed, and the soil washing apparatus 14 has a particle size of, for example, 75 μm or more. They are classified into coarse particles and fine particles having a particle size of less than 75 μm.

  Coarse particles having a particle size of 75 μm or more are rendered harmless and are reused for backfilling. Fine particles having a particle size of less than 75 μm are subjected to press treatment by the filter press 20. It is separated into dewatered cake and filtered water, the dewatered cake is treated as industrial waste, drained water is discharged into the sewer after being drained, and it is circulated in the water tank 16 as circulating water and again as washing water. It has come to be used.

  Further, a precipitation tank may be installed in the previous stage of the filter press 20, and the supernatant water may be reused as the initial washing water.

  In this way, the water charge can be reduced by circulating the washing water.

  As shown in FIG. 2, the soil cleaning device 14 includes a vibration sieving device 22 and a high-pressure water jetting device 24.

  The vibration sieving device 22 has a plurality of stages, for example, three stages of screens 28, 30, and 32, which are disposed below the earth and sand hopper 26 that supplies the contaminated soil, and supports these screens 28, 30, and 32 with springs 34. The vibration generator 36 applies vibration.

  The three-stage sieves 28, 30 and 32 are arranged so that the meshes become finer in order from the upper stage to the lower stage. The screen is a 2 mm mesh screen, and the lowermost screen 32 is a 75 μm mesh screen.

  Further, the sieves 28, 30, and 32 of each stage are inclined so that the earth and sand hopper 26 side is high and the opposite side to the earth and sand hopper 26 is low, and the inclination angles of the sieves 28, 30, and 32 are variable. The processing speed can be adjusted by changing the inclination of the sieves 28, 30, and 32 in accordance with the degree of contamination of the contaminated soil.

  Note that the periphery of the sieves 28, 30, and 32 is covered with a diffusion prevention plate 48.

  The high-pressure water injection device 24 branches a plurality of, for example, three high-pressure water injection tubes 40, 42, 44 from the high-pressure water supply pipe 38, and the high-pressure water injection tubes 40, 42, 44 are connected to the sieves 28, 30, 32, and a plurality of injection nozzles are provided at positions corresponding to the sieves 28, 30, 32 of the high-pressure water injection pipes 40, 42, 44 so that the high-pressure water is directed toward the sieves 28, 30, 32. It can be jetted.

The pressure of the high pressure water can be, for example, ^{0.3N / mm 2 ~10N / mm 2} .

  The high-pressure water jetted from the high-pressure water jet pipes 40, 42, 44 can be high-temperature water of about 90 ° C., for example.

  And in the washing | cleaning method of the contaminated soil using such a soil washing | cleaning apparatus 14, the state of the sieve hopper 26 is made into the uppermost stage sieve in the state which act | operated the vibration generator 36 first and vibrated the sieves 28, 30, and 32 first. 28 is supplied with contaminated soil.

  Next, high-pressure high-pressure water 46 is jetted from the uppermost high-pressure water jet tube 40 to the contaminated soil of the uppermost sieve 28 to remove soil having a particle size smaller than the eyes of the sieve 28, for example, less than 40 mm, as the middle-stage sieve 30. It is dropped down and soil (large gravel or foreign matter) having a particle size larger than 40 mm is taken out of the sieve 28.

  Next, high temperature high-pressure water 46 is jetted from the middle-stage high-pressure water jet pipe 40 onto the soil that has fallen on the middle-stage sieve 30 to perform washing and classification.

  In this case, for example, soil (pebbles) having a particle diameter of 2 mm or more is taken out of the sieve 30, and soil having a particle diameter of less than 2 mm falls on the lowermost sieve 32.

  Further, high-pressure high-pressure water is sprayed from the high-pressure water injection pipe 44 onto the soil that has fallen on the lowermost screen 32, and washing and classification are performed. For example, coarse particles having a particle size of 75 μm or more are taken out of the screen 32. The fine particles having a particle diameter of less than 75 μm and the muddy water are dropped below the sieve 32 and taken out to the filter press 20 side.

  In this way, cleaning and classification are performed simultaneously by jetting high-temperature high-pressure water 46 sequentially from the uppermost sieve 28 to the lowermost sieve 32, and further, the classification efficiency and washing efficiency are improved by the high-temperature high-pressure water. The amount of water used can be reduced to reduce water treatment costs and the amount of water.

  Moreover, since the filtered water separated by the filter press 20 is circulated to the water tank 16 and reused, the amount of water used such as fluidized water can be further reduced to reduce water charges.

  Next, FIG. 3 shows the result of conducting a cleaning experiment for contaminated soil using such a method for cleaning contaminated soil with high-temperature and high-pressure water in comparison with the results of cleaning by existing soil cleaning methods.

In this experiment, C fuel oil, arsenic, lead and dioxin as harmful substances were used at a water temperature of 90 ° C., an injection pressure of 0.5 N / mm ² , and a treated soil amount of 200 kg. Contaminated soil of 10 g / kg, arsenic pretreatment concentration of 0.4 mg / l, lead pretreatment concentration of 1.1 mg / l, and dioxin pretreatment concentration of 2000 pg-TEQ / g was used.

  As a result, in the case of C heavy oil, with the existing soil cleaning method, the treatment time is 90 seconds, the amount of water used is 600 l, the concentration after treatment is 1.94 g / kg, and the harmful substance removal rate is 93.33%. On the other hand, when the high temperature and high pressure water injection method is used, the treatment time is as short as 60 seconds, the amount of water used is as small as 300 l, the concentration after treatment is as small as 0.52 g / kg, and the harmful substance removal rate is low. A high result of 98.20% was obtained.

  In the case of arsenic, the existing soil washing method has a treatment time of 90 seconds, the amount of water used is 600 l, the concentration after treatment is 0.05 mg / l, and the harmful substance removal rate is 87.5%. On the other hand, in the high temperature and high pressure water injection method, the treatment time is as short as 60 seconds, the amount of water used is as small as 300 l, the concentration after treatment is as small as 0.005 mg / l, and the harmful substance removal rate is as high as 98.75%. Obtained.

  Furthermore, in the case of lead, in the existing soil cleaning method, the treatment time is 90 seconds, the amount of water used is 600 l, the concentration after treatment is 0.071 mg / l, and the harmful substance removal rate is 93.64%. On the other hand, in the high temperature and high pressure water injection method, the treatment time is as short as 60 seconds, the amount of water used is as small as 300 l, the concentration after treatment is as small as 0.0051 mg / l, and the harmful substance removal rate is as high as 99.55%. was gotten.

  Thus, it was found that the treatment time and the amount of water used were both reduced and the removal rate of harmful substances was improved as compared with existing soil cleaning methods.

  The present invention is not limited to the above-described embodiment, and can be modified into various forms within the scope of the gist of the present invention.

  For example, in the embodiment described above, the vibration sieve device is provided with three upper and lower sieves. However, the present invention is not limited to this example, and the number of sieves may be two or four or more.

  Moreover, in the said embodiment, although the vibration sieve apparatus was used for the soil washing | cleaning apparatus, it is also possible to screen the contaminated soil on a sieve with high pressure water, without vibrating a sieve.

  Furthermore, in the above-described embodiment, high-temperature water is used as high-pressure water. However, the present invention is not limited to this example. For example, steam, mixed jet or superheated steam, and room temperature water can be used.

  The size of each sieve can be changed according to the target soil, the concentration of contamination, the injection pressure, and the like.

It is a schematic explanatory drawing which shows the contaminated soil cleaning system used for the cleaning method of the contaminated soil which concerns on one embodiment of this invention. It is an enlarged view which shows the soil washing | cleaning apparatus of FIG. It is explanatory drawing which compared the experimental result of the washing | cleaning method of the contaminated soil of this invention with the existing soil washing | cleaning method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Contaminated soil washing | cleaning system 12 Contaminated soil 14 Soil washing | cleaning apparatus 16 Water tank 18 Washing water 22 Vibrating sieve apparatus 24 High pressure water injection apparatus 28, 30, 32 Sieve 40, 42, 44 High pressure water injection pipe 46 High pressure water

Claims (4)

Supplying the contaminated soil contaminated with heavy metals, oil, dioxins, etc. on the uppermost sieve among the multistage sieves that gradually become finer from the upper stage to the lower stage;
Washing by spraying high-pressure water onto the contaminated soil on the uppermost sieve, dropping and classifying the soil with a particle size finer than the sieve eyes, and classification,
Washing and classification by spraying high-pressure water onto the soil that has fallen on the next-stage sieve, and sequentially repeating washing and classification by jetting high-pressure water up to the bottom sieve;
A method for cleaning contaminated soil, comprising: In claim 1,
A method for cleaning contaminated soil, wherein a vibrating sieve is used as the sieve. In claim 1 or 2,
A high temperature water, steam, mixed gas jet or superheated steam is used as the high-pressure water sprayed on the contaminated soil. In any one of Claim 1 to 3,
The method for cleaning contaminated soil, wherein the sieve has a variable inclination angle.

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