JP2006051440A - Purification method of heavy metal contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a purification method of heavy metal contaminated soil that purifies heavy metal contaminated soil inexpensively. <P>SOLUTION: The purification method of the heavy metal contaminated soil comprises cracking the heavy metal contaminated soil to form a plurality of particle groups classified by particle size, then firstly conducting the pickling of the heavy metal contaminated soil of the smallest particle size group, adding the residual classified heavy metal contaminated soil to a slurry comprised of the heavy metal contaminated soil of the smallest particle size group and the acid solution after the pickling and conducting the mixed washing upon every addition when adding and washing the heavy metal contaminated soil of the smallest particle size group to the largest particle size group in order, lastly adding the heavy metal contaminated soil of the largest particle size and subjecting the slurry obtained from the mixed washing to a solid-liquid separator to separate the soil and the acid solution, wherein the rinsing of the soil is conducted preferably at an area of pH 2 or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a purification method for washing soil contaminated with heavy metals such as lead with an acidic solution, and relates to a method capable of purification at a low cost.

  As techniques for purifying soil contaminated with heavy metals such as lead, a washing classification method, b heat treatment method, and c electrophoresis method are known.

  The water washing classification method is a method for separating, concentrating, and capturing fine particles containing a large amount of contaminants or contaminants from the surface of coarse soil particles by washing, lump or physical soil polishing.

  In the case of the water washing classification method, if the soil grinding is insufficient, contaminants from coarse soil particles or fine particles containing a large amount of contaminants may not be completely removed, and it may not be possible to reduce the contaminants to below the specified soil standard value. There is sex.

  In addition, the removal rate of fine particles containing a large amount of contaminants or contaminants from coarse soil particles is improved by extending the soil grinding time or applying an advanced grinding device that completely polishes the surface of coarse soil particles. However, even in this case, in soil contaminated at a high concentration, it is not always possible to reliably reduce the pollutant to a soil designated reference value or less. Furthermore, in this case, it is pointed out that the former increases the running cost and the latter increases the initial cost of the apparatus. In addition, the amount of fine particles by grinding increases and the yield of the purified soil decreases.

  The heat treatment method is a method of containing heavy metals such as lead as a pollutant in a very stable state by heating and sintering or vitrifying the soil with a rotary kiln or an electric resistance furnace.

  In the case of the heat treatment method, in the case of soil contaminated with heavy metals such as lead, heat sintering: 800 to 1200 ° C., vitrification: 1600 to 2000 ° C. are carried out in order to obtain heat sintering or vitrification. This requires a large amount of heat source, which increases running costs.

  Furthermore, additional equipment for appropriately treating exhaust gas generated during heating is required, leading to an increase in initial cost. In addition, it is pointed out that if heavy metals such as lead, which is a contaminant, are not volatilized and removed, the contaminant may re-elute if the heat-sintered or vitrified state is not completely formed. .

  Electrophoresis is a method of collecting and removing contaminants in the vicinity of an electrode by providing an anode and a cathode for contaminated soil, and applying a direct current after adding an electrolyte or the like.

  In the case of electrophoresis, when it is carried out at a low voltage and a low current, the purification speed becomes very slow, and it takes a very long time to complete the purification. In addition, when it is carried out at a high voltage and a high current, the purification speed is considered to be high, but a large amount of power is required and the running cost becomes very high. In addition, if the electrode surface is covered with contaminants and the like, the removal efficiency deteriorates. Therefore, the contaminants concentrated near the electrode must be removed from time to time. It has been pointed out that a pollutant recovery device is required.

  As described above, all of the water washing classification method, heat treatment method and electrophoresis method have drawbacks, so in recent years, with the aim of shortening the purification time and improving the removal efficiency of lead contaminants, Drug extraction and cleaning with solutions have been proposed.

  For example, Patent Document 1 describes a method of removing heavy metal contaminants by applying strong attrition at the time of addition of an acidic solution or after the addition. Patent Document 2 describes a method in which a heavy metal contaminant is extracted with an acidic solution, a surfactant is added to the extract, and heavy metal is recovered by bubbles. Patent Document 3 also describes a soil extraction and washing method using an acidic solution.

  In the case of the purification methods disclosed in Patent Documents 1 to 3, since there are many parameters such as soil properties, chemical types, chemical concentrations, cleaning times, solid-liquid weight ratios, etc., the optimum conditions are selected from these parameters. It is very difficult to find and various disadvantages arise when the technology is embodied and applied locally.

  For example, when cleaning is performed with excessive chemical concentration, cleaning time, and solid-liquid weight ratio, the equipment becomes large and the running cost increases. Yield is also reduced. In addition, when washing is performed under conditions where the chemical concentration, washing time, and solid-liquid weight ratio are insufficient, there is a risk that the soil after washing cannot be reduced below the soil specification standard value.

  In order to solve these problems, the present inventors have developed a soil purification technology with excellent cost performance in Japanese Patent Application No. 2004-099599.

JP-A-11-197643 JP 2002-371324 A JP 2001-149913 A

  In Japanese Patent Application No. 2004-099599, an acidic solution obtained by washing highly contaminated soil such as fine soil made of silt or clay is solid-liquid separated, and the recovered acidic solution is used for coarse soil made of sand. It is used to wash soil contaminated with low concentrations such as.

  However, in the method described in Japanese Patent Application No. 2004-099599, the acidic solution adheres to the soil after the solid-liquid separation, so that the acidic solution cannot be completely recovered by the solid-liquid separation device and can be reused. The amount decreases.

  In addition, when rinsing the soil washed with an acidic solution for each particle group, a large number of rinse tanks are required, and the space for installing these rinse tanks also increases.

  An object of the present invention is to provide a soil purification technology that solves these problems and is further excellent in cost performance.

  The present inventors have intensively studied a method for purifying soil contaminated with heavy metals (hereinafter, heavy metal-contaminated soil) using an acidic solution, and finely contaminated soil such as silt and clay (hereinafter, finely contaminated soil). In a slurry obtained by washing contaminated soil contaminated with high concentration (hereinafter referred to as “highly contaminated soil”), it is contaminated with coarsely contaminated soil such as sand (hereinafter referred to as “polluted contaminated soil”) or at a lower concentration. We have completed a soil purification technology with excellent cost performance that mixes and cleans fresh soil (hereinafter, low-contaminated soil). In the present invention, the slurry includes contaminated soil purified by an acidic solution and an acidic solution after washing the contaminated soil.

  Fig. 9 shows the results of an investigation of the lead content for each soil particle size for soil contaminated with lead, one of the heavy metals (hereinafter lead-contaminated soil), and contains lead depending on the soil particle size. The rate changes, and the lead content decreases as the soil particle size increases.

  In addition, in the case of fine-grained soil such as silt and clay, it is easy to bind firmly to contaminants such as heavy metals due to permanent charge action by soil fine particles, especially clay minerals, and mutation charge action such as allophane. Fine-grained soil is more active than coarse-grained soil and tends to form heavy metals, sparingly soluble compounds and minerals. On the other hand, in the case of coarse-grained soil such as sandy material, it is often bonded relatively gently due to physical adsorption or adhesion to the surface of the soil particles.

  Therefore, the present invention classifies heavy metal-contaminated soil for each soil particle size, and when purifying soil with a small soil particle size, a low pH region, that is, a high acid capacity (high acid concentration and / or a small amount of acidic solution), When the soil particle size is large, the pH is higher than that when the soil particle size is small, that is, a low acid capacity (low acid concentration and / or a large amount of acidic solution).

  Lead-contaminated soil has the highest removal efficiency when washed with hydrochloric acid. FIGS. 10 and 11 show the lead content after washing when the lead-contaminated soil is washed with various acidic solutions (washing using a stirring washing device with a stirring blade rotating at 300 rpm for 15 minutes, hydrochloric acid concentration: FIG. 11 1 mol / L, FIG. 10 is 3 mol / L, hydrochloric acid amount: FIG. 10 is a solid-liquid weight ratio of 1: 1, FIG. 11 is a test result at 1: 2, and FIG. 10 is a coarse soil particle (sandy) FIG. 11 shows a case where the soil particles are fine (silt / clay).

 In the present invention, it is preferable to use hydrochloric acid as the acidic solution from the viewpoint of availability and the ability to remove lead.

The present invention
1 In a method of pickling and cleaning heavy metal contaminated soil with an acid solution,
After pulverizing the heavy metal contaminated soil into a plurality of particle groups classified according to particle size, first pickle the heavy metal contaminated soil of the particle group having the smallest particle size, In slurry consisting of heavy metal contaminated soil and acidic solution of small particles,
When the remaining heavy metal contaminated soil of classified particles is washed by sequentially adding heavy metal contaminated soil of large particle size to heavy metal contaminated soil of small particle size, mixed washing each time it is added And
Finally, the heavy metal-contaminated soil of the particle group having the largest particle size is added, and the slurry obtained by mixing and washing is separated from the soil and the acidic solution with a solid-liquid separator, and the soil is rinsed. Purification method for heavy metal contaminated soil.
2. Adding a particle group having the largest particle diameter, separating the slurry obtained by mixing and washing into soil and acidic solution using a solid-liquid separator, and washing the soil with a rinse solution in a pH of 2 or less. 2. The method for purifying heavy metal-contaminated soil according to 1.
3. The method for purifying heavy metal-contaminated soil according to 1 or 2, wherein the soil obtained after rinsing is adjusted to the same pH as the heavy metal-contaminated soil before pulverization.
4. The soil obtained after rinsing is adjusted to the same pH as the heavy metal-contaminated soil before crushing, and then mixed with non-contaminated soil and / or humus soil at or near the site where the heavy metal-contaminated soil is collected. Purification method for heavy metal contaminated soil.
5. The method for purifying heavy metal-contaminated soil according to any one of 1 to 4, wherein in rinsing the soil separated by the solid-liquid separator, the number of times of rinsing N satisfies the following formula.
However, solid-liquid weight ratio between soil and rinsing liquid: A, moisture content of soil after solid-liquid separation: B, soil content of target pollutant before washing with acidic solution: C0, soil content designation Standard: α.
N ≧ 2.2 × ln [1.3 × (α / C0)] / ln [B / {A × (1−B)}] − 1
6 The heavy metal-contaminated soil is crushed, the particle group having the smallest particle size is made less than 0.075 mm, the particle group having the largest particle size is made 0.075 mm to 2.0 mm, A particle group having a particle diameter of less than 075 mm was washed with an acidic solution having a pH of -0.3 or less after mixing with the particle group having a particle diameter of less than 0.075 mm, and then a slurry was obtained. 6. The method for purifying heavy metal-contaminated soil according to 5, wherein soil of a particle group classified to 0 mm or less is added to the slurry and washed with an acidic solution having a pH of 0.5 or less after mixing.
7 In the method of pickling and cleaning heavy metal contaminated soil with an acid solution,
After the heavy metal contaminated soil is divided into a plurality of groups sorted according to the contamination concentration, the heavy metal contaminated soil of the group with the highest contamination concentration is first pickled, and after pickling, the heavy metal contamination of the group with the highest contamination concentration To slurry consisting of soil and acidic solution,
When the remaining heavy metal-contaminated soils are added and washed sequentially from the group of heavy metal-contaminated soils with high contamination concentration to the group of heavy metal-contaminated soils with low contamination concentration, mixed washing is performed each time they are added,
Finally, the heavy metal-contaminated soil having the lowest contamination concentration is added, and the slurry obtained by mixing and washing is separated from the soil and the acidic solution by a solid-liquid separator, and the soil is rinsed, and the soil is rinsed with heavy metal Purification method.
8. The method for purifying heavy metal-contaminated soil according to any one of 1 to 7, wherein the heavy metal is lead and the acidic solution is hydrochloric acid.
9. Washing heavy metal contaminated soil with an acidic solution, and rinsing the soil with a rinsing liquid after washing with an acidic solution, wherein the washing with the rinsing liquid is performed in a region having a pH of 2 or less. .
10. A method for purifying heavy metal-contaminated soil, characterized in that when rinsing heavy metal contaminated soil with an acidic solution, the number of times of rinsing N satisfies the following formula in rinsing the soil with a rinsing liquid after washing with an acidic solution.
However, solid-liquid weight ratio between soil and rinsing liquid: A, moisture content of soil after solid-liquid separation: B, soil content of target pollutant before washing with acidic solution: C0, soil content designation Standard: α.
N ≧ 2.2 × ln [1.3 × (α / C0)] / ln [B / {A × (1−B)}] − 1

  According to the present invention, in washing heavy metal-contaminated soil using an acidic solution, the acidic solution obtained by washing fine-grained contaminated soil and highly-concentrated contaminated soil can be reused for washing coarse-grained contaminated soil and low-concentrated contaminated soil. Therefore, a large amount of heavy metal-contaminated soil can be purified at a low cost, which is extremely useful in the industry.

  The present invention is a method for purifying soil contaminated with heavy metals using an acidic solution, and comprises a particle group having a small particle size with respect to a plurality of particle groups of contaminated soil classified with a specific particle size as a boundary. The particle group is washed with an acidic solution, and a particle group having a larger particle diameter is sequentially added to a slurry formed by mixing the soil after washing with an acidic solution, and mixed and washed. Compared to the case of using a new acidic solution, the amount of the acidic solution used is greatly reduced. Hereinafter, the present invention will be described in detail using specific steps.

  FIG. 1 is a process diagram showing an embodiment of a soil purification method according to the present invention, and shows a case where heavy metal contaminated soil is classified into two large and small particle size groups. In the figure, 1 is a step of crushing heavy metal-contaminated soil into single particles (hereinafter referred to as the first step), 2 is a heavy metal-contaminated soil crushed in the first step, and a specific particle size is determined by a classifier. The step of classifying the boundary (hereinafter referred to as the second step), 3 is a step of washing the particle group consisting of particles having a small particle diameter classified in the second step with an acidic solution (hereinafter referred to as the third step) ) 4 is a step of adding a particle group consisting of a particle having a large particle size to a slurry in which an acid solution is mixed with a particle group consisting of a particle having a small particle size generated in the third step and washing the mixture. (Hereinafter referred to as the fourth step) 5 is a step (hereinafter referred to as the fifth step) of separating the acidic solution from the soil washed in the fourth step using a solid-liquid separation device, and 6 is according to the fifth step. A step of washing soil washed with an acidic solution with a rinsing solution (hereinafter referred to as sixth step) It is.

[First step]
The first step aims to loosen the excavated heavy metal-contaminated soil from a state in which the soil particles are aggregated into a single particle by crushing means.

  In the first step, the soil that has been loosened into single particles can be classified according to the size of the soil particles. Further, in the cleaning with the acidic solution, the contact area between the soil particles and the acidic solution is increased, the cleaning time is shortened, and the efficiency of removing contaminants is improved. The soil crusher uses existing equipment such as a drum washer, paddle mixer, lot mill, attritor, and ball mill.

  In addition, foreign matter such as charcoal dust, metal fragments, etc., to which heavy metal contaminants are likely to adhere, are removed from the soil before pulverization or after pulverization with a specific gravity sorter, magnetic sorter, floating sorter, or large soil particles. It is desirable to remove with a vibrating screen.

[Second step]
The purpose of the second step is to classify the soil loosened into single particles in the first step for each particle group with a specific particle diameter as a boundary.

  Classification is performed by using a vibrating screen, a classifier, a spiral classifier, a centrifuge, a cyclone, a filter press or the like alone or in combination.

  When classifying, the particle size of 0.075 mm or less is silt / clayy, the particle size of 0.075 mm to 2.0 mm or less is sandy, soil properties are different, and the washing conditions with the acidic solution are greatly different. It is preferable to classify the particles into at least two kinds of particles having a particle diameter of 0.075 mm or less and a particle diameter of 0.075 mm to 2.0 mm. You may further classify each with a particle diameter of 0.075 mm or less and a particle diameter of 0.075 mm to 2.0 mm.

  FIG. 2 shows the influence of pH on the lead content after hydrochloric acid cleaning when the solid-liquid weight ratio of the soil and hydrochloric acid solution is 1: 1 to 1: 2 in a lead-contaminated soil. In the case of silt or clay less than 075 mm, pH = −0.3 or less, preferably −0.5 or more and −0.3 or less, and in the case of sandy particles having a particle diameter of 0.075 mm or more and 2.0 mm or less. When the pH is 0.5 or less, preferably 0 or more and 0.5 or less, an excellent cleaning effect can be obtained.

  That is, as shown in FIG. 2, in the case of silt / clay having a particle diameter of less than 0.075 mm, pH = −0.3 or less, and in the case of sand having a particle diameter of 0.075 mm or more and 2.0 mm or less, the pH is It can be seen that the lead dissolution and extraction effects are excellent at 0.5 or less.

 However, the lower the pH, the more the lead is dissolved and extracted, as well as the dissolution of the main minerals and substances that make up the soil, the extraction ratio increases, the yield of purified soil decreases, and it is used to treat and rinse the liquid after washing. Since the cost performance is remarkably lowered, for example, the amount of water to be increased, the pH is preferably -0.5 or more for silt and clay, and the pH is preferably 0 or more for sand.

  In addition, FIG. 2 is a test result in a washing condition: once × 15 minutes using a stirring washing device (rotation speed of stirring blade: 300 rpm), and pH is measured in a state where hydrochloric acid is added to and mixed with soil. is there.

[Third step]
The third step is intended to wash a particle group consisting of particles having a smaller particle diameter from the two particle groups classified in the second step with an acidic solution. In this washing | cleaning, what is necessary is just an apparatus which can fully mix soil and acidic solution, such as mixing washing | cleaning by a stirring blade.

[Fourth process]
The fourth step is a particle group consisting of particles having a larger particle size and a slurry in which an acid solution is mixed with a particle group consisting of particles having a small particle size after pickling produced in the third step. Is added and mixed and washed.

  That is, as described above, when washing soil contaminated with lead with hydrochloric acid, when washing soil with a small particle size, high concentration hydrochloric acid is required to lower the pH after adding hydrochloric acid to the soil and mixing it. However, as the particle size increases, low-concentration hydrochloric acid can be used, so the hydrochloric acid solution after washing the soil with a small particle size can be used for washing soil with a larger particle size, thereby reducing purification costs. It is.

  Therefore, by cleaning soil with a small particle size with a high-concentration acidic solution, and further adding soil with a large particle size to this slurry and cleaning with residual acid contained in this slurry, the purification cost is greatly reduced. be able to.

  In addition, when soil contaminated with lead is classified and washed with silt and clay in the third step, and sand is washed with hydrochloric acid in the fourth step, as described above, in the case of silt and clay in the third step, hydrochloric acid It is preferable that the pH of the soil after mixing is set to -0.3 or less, and in the case of the sand in the fourth step, the pH of the soil after additional mixing of the sand is set to 0.5 or less.

  If the pH after mixing in the fourth step exceeds 0.5, new hydrochloric acid may be added separately. In addition, the solid-liquid weight ratio between the heavy metal-contaminated soil and the acidic solution is preferably 1: 1 to 1: 2 in consideration of washing efficiency, effect, load on equipment, scale, and the like.

  Also in this washing | cleaning, what is necessary is just an apparatus which can fully mix soil and acidic solutions, such as mixing washing | cleaning by a stirring blade.

  As shown in FIG. 3, when washing is performed under the above-mentioned optimum pH conditions (pH = -0.3 or less in the case of silt or clay, pH = 0.5 or less in the case of sand), The cleaning time does not depend on the particle size of the soil, and the lead content after cleaning becomes constant in 5 to 30 minutes. Therefore, the cleaning time for the third and fourth steps is 30 minutes or less, and the initial cost of the cleaning device is reduced. Further, from the viewpoint of suppression, it may be preferably 15 minutes or less.

[Fifth process]
The purpose of the fifth step is to collect the washed acidic solution from the heavy metal contaminated soil washed through the fourth step by a solid-liquid separator. The solid-liquid separator is an existing apparatus such as a vibrating screen, a classifier, a spiral classifier, a centrifuge, a cyclone, a filter press, a membrane / hollow fiber membrane apparatus or the like.

  In addition, when recirculating the acidic solution collected by the solid-liquid separator for washing the soil, the mixing ratio with the new solution is adjusted appropriately so that the acidic solution for pickling the soil can secure the predetermined washing ability. To do.

  FIG. 4 shows an example of equipment embodying the fifth step. In the figure, 7 is a detector for detecting the concentration and / or pH of the acidic solution, 8 is the concentration of the acidic solution detected by the detector 7 and / or Or a control device that adjusts the amount of new liquid used in the acid cleaning tank according to pH, 9 is a flow control valve that adjusts the amount of new liquid that is a new acidic solution, and 10 is an acidic solution recovered from the solid-liquid separation device. The piping (recirculation path) joined to the piping system which supplies the acidic solution used for the said soil is shown. FIG. 4 is an example in which the mixing ratio with the new solution is adjusted as appropriate so that the acidic solution for pickling the soil can ensure a predetermined cleaning ability.

[Sixth step]
The purpose of the sixth step is to rinse the soil from which the acidic solution has been removed by the solid-liquid separator in the fifth step. In order to reuse soil washed with an acidic solution as purified soil, contaminants and chemical components remaining in the soil are removed.

  Figure 6 shows that in lead-contaminated soil, the silt / clay is washed under a condition where the pH after mixing the soil and hydrochloric acid is -0.3 or less, and the sand is washed under a condition where the pH after mixing the soil and hydrochloric acid is 0.5 or less. This indicates the effect of pH in rinsing on the rinsing effect (lead content in the soil after rinsing) for each soil after solid-liquid separation. A rinsing effect is obtained.

When soil is washed with an acidic solution, it dissolves and extracts lead, as well as iron, aluminum, and other components of the soil. In general, when iron and aluminum reach a certain pH or higher (Fe ²⁺ : pH 5.2 or higher, Fe ³⁺ : pH 2.8 or higher, Al ³⁺ : precipitation starts at pH 4.3), heavy metal ions such as lead are statically removed. Although the coprecipitation phenomenon which adsorb | sucks electrically is produced, as shown in FIG. 6, when the pH after soil / rinsing liquid mixing is 2 or more, the phenomenon of redeposition occurs and the lead content in the soil is large.

  The pH ranges lower than the pH at which coprecipitation occurs, due to the presence of organic components, calcium, etc. generated by dissolution of the soil and the adsorptivity of the soil (iron: pH 2 to 2.8, aluminum: pH 2 to 4) It is considered that reattachment to the soil extracted in .8) occurs and remains in the soil.

  Therefore, by adjusting the pH after mixing the soil and the rinsing liquid to 2 or less for both silt, clay, and sand, reattachment of soil contaminants can be prevented and an excellent rinsing effect can be obtained. . Note that this effect is not limited as long as the soil to be rinsed can be obtained by a solid-liquid separator after washing heavy metal-contaminated soil with an acidic solution. Water or a weak acid is preferred as the rinsing liquid.

  In addition, if the number of times of rinsing the soil is insufficient, the rinsing liquid containing a large amount of contaminants remains and adheres to the soil again, so that the cleaning effect by the acidic solution is impaired.

  In order to prevent the re-deposition of the contaminants caused by the remaining of the rinsing liquid to the soil, it is sufficient that the rinsing liquid can be completely separated from the soil. However, there are limitations in the existing solid-liquid separator. A certain amount of rinsing liquid remains in the soil.

  Therefore, by performing solid-liquid separation and soil rinsing multiple times, these effects on the soil after purification can be made extremely small. In this case, the optimal number of rinsing, solid-liquid ratio, etc. If it is not carried out under conditions, the amount of rinsing liquid used and the cost of equipment such as solid-liquid separators and rinsing tanks will increase.

  Therefore, the present inventors set the solid-liquid weight ratio between the soil and the rinsing liquid: A, the moisture content of the soil after solid-liquid separation: B, and the object before washing with an acidic solution, based on various rinsing tests. The relationship of the following formula (1) was found between the soil content of the pollutant: C0, the soil content designation standard: α and the number of times of rinsing: N (an integer of 0 or more).

  The number of times of rinsing is defined as the number of repetitions of the step of solid-liquid separation again after rinsing the soil after solid-liquid separation after washing with an acidic solution.

      N ≧ 2.2 × ln [1.3 × (α / C0)] / ln [B / {A × (1−B)}] − 1 −−−−− (1)

  FIG. 7 shows the results of a rinsing test for various lead-contaminated soil samples with the pH after mixing the soil and the rinsing liquid being 2 or less.

  Regardless of the grain size of the soil, if the relationship of the above formula (1) is satisfied, the lead content of the soil after purification is below the content specification standard set by the Ministry of the Environment (open symbol), but if not, The lead content of the soil after purification exceeded the content specification standard set by the Ministry of the Environment (solid symbol).

  In addition, the soil sample uses a hydrochloric acid solution as an acidic solution before rinsing, and in the case of fine-grained soil composed of silt / clay of 0.075 mm or less, the pH after mixing the hydrochloric acid solution is -0.5 to- In the case of coarse-grained soil made of sand having a size of 0.3, 0.075 to 2.0 mm, the pH after mixing with the hydrochloric acid solution was set to 0 to 0.5 and washed for 15 minutes.

  When rinsing is performed a plurality of times and the conditions such as solid-liquid ratio: A, water content: B, etc. are different in each rinsing, N under each condition is calculated by the above equation (1) An arithmetic average or harmonic average of numerical values may be used. The effect of the above formula (1) in rinsing is not limited as long as the soil to be rinsed can be obtained by a solid-liquid separator after washing heavy metal contaminated soil with an acidic solution.

  The present invention can purify heavy metal contaminated soil at a low cost by the first to sixth steps described above. In addition, although FIG. 1 used for description of each process showed the case where each process was implemented once, this invention implements any process in multiple times as needed until the desired cleaning effect is acquired. It is possible.

[Soil restoration process]
When the purified soil is backfilled after the sixth step, the pH may be readjusted to the same value as the soil before excavation. In addition, the same value here should just be a grade which the ecosystem of a surrounding environment can recover rapidly, and does not mean that it is the same.

  As a means of readjusting the pH, soil washing with 1 water is performed several times. 2 Add alkaline chemicals such as calcium hydroxide, calcium oxide, calcium carbonate. 3 Add alkaline soil and / or coal ash that is confirmed to be non-polluted. One or more of the above may be implemented.

  In addition, if the soil at the site where backfilling has been performed is adapted to the surrounding environment at an early stage, after the readjustment of the soil pH is completed, uncontaminated soil and / or humus soil near the site where the contaminated soil was collected or mixed. That's fine.

  Although the above description has described the case where the soil is classified into two large and small particle sizes after crushing, the present invention does not limit the number of particle groups to be classified after crushing, as shown in FIG. In addition, after pulverization, the soil may be classified into three or more particle size groups, and washed with an acidic solution in order from the smallest particle size.

  In addition, the acidic solution concentration required for washing with an acidic solution depends on the soil contamination concentration in addition to the particle size. When the particle size composition is constant, washing with a low acidic solution concentration is possible when the soil contamination concentration is low. It becomes. The following describes the case of washing heavy metal contaminated soil with different contamination concentrations.

  FIG. 8 is a process diagram. In the figure, 1 is a process for washing heavy metal highly contaminated soil (H) (high concentration contaminated soil of heavy metal contaminated soil), which is known in advance, with an acidic solution (hereinafter referred to as process A), 2 Is a process in which heavy metal low-contaminated soil (L) (low-contaminated soil of heavy metal-contaminated soil) is added to the slurry in which the high-concentrated contaminated soil and acidic solution produced in step A are mixed and washed (hereinafter referred to as B). 3), 3 is a step of separating the acidic solution from the soil washed by the step B using a solid-liquid separator (hereinafter referred to as step C), and 4 is a soil washed by the acidic solution by the step C. A step of washing with a rinsing liquid (hereinafter, step D) is shown. The rinsing process and the soil recovery process after washing and solid-liquid separation are based on the classification for each particle size.

  This is effective when there is a high or low pollution concentration in the plane and / or depth direction due to the influence of the type of pollutant, pollutant runoff process, diffusion situation, etc. in the land with the same soil particle size distribution.

  High-concentration lead-contaminated soil (A) and low-concentration lead-contaminated soil (B) as sandy soil were collected from the same factory site.

  A 3.0 mol / l hydrochloric acid solution at a solid-liquid weight ratio of 1: 2 was added to the high-concentration lead-contaminated soil (A), and the mixture was stirred for 15 minutes (stirring conditions: rotation speed of stirring blade 300 rpm). The pH of the hydrochloric acid cleaning solution at this time was −0.3 or less immediately after the start of cleaning, and 0 before the end.

  Next, to the slurry of high-concentration lead-contaminated soil (A) and hydrochloric acid cleaning solution, add low-concentration lead-contaminated soil (B) at the same weight as the high-concentration lead-contaminated soil (A) and stir for 15 minutes (stirring conditions) : Stirring blade rotation speed 300 rpm). The pH of the hydrochloric acid cleaning solution at this time was 0.2 before the completion.

  This slurry soil is dewatered with a centrifuge (3000 rpm, 10 minutes), and the resulting purified soil is rinsed with water having a solid-liquid weight ratio of 1: 2, and dewatered with a centrifuge (3000 rpm, 10 minutes). The rinsing operation was repeated three times.

  At this time, the pH of the rinse liquid was 0.6, 1.2, and 1.7. Furthermore, slaked lime was added and mixed to bring the soil to the same pH 8.5 as the original soil and air-dried. This purified soil was measured for lead content according to the method of Ministry of the Environment Notification No. 19. The results are shown in Table 1.

  15% of water was added to the lead-contaminated soil collected from the factory site, and after crushing at 100 rpm for 10 minutes with a paddle mixer, water was added at a solid-liquid weight ratio of 1: 1. This slurry was washed with water for 10 minutes at a rotation speed of a stirring blade of 300 rpm, and classified with a vibration sieve of 0.075 mm.

  A 3.0 mol / l hydrochloric acid solution with a solid-liquid weight ratio of 1: 2 was added to the sieved soil after classification, and the mixture was stirred for 15 minutes (stirring conditions: rotation speed of stirring blade 300 rpm). The pH of the hydrochloric acid cleaning solution at this time was −0.3 or less both immediately after the start of cleaning and before the end.

  Next, after sieving soil and hydrochloric acid cleaning liquid slurry, the sieving soil after classification is added in 1.5 times the weight of the sieving soil, and stirred for 10 minutes (stirring condition: rotation speed of stirring blade) 300 rpm). The pH of the hydrochloric acid cleaning solution at this time was 0 before the completion. The slurry was dehydrated with a centrifuge (3000 rpm, 10 minutes, soil moisture content after dehydration: 40%), and the resulting purified soil was rinsed with water having a solid-liquid weight ratio of 1: 2, and the centrifuge ( The dehydration and rinsing operations were repeated twice at 3000 rpm for 10 minutes and the soil water content after dehydration: 40%. Furthermore, slaked lime was added and mixed to bring the soil to the same pH 6.8 as the original soil and air-dried. This purified soil was measured for lead content according to the method of Ministry of the Environment Notification No. 19. The results are shown in Table 2.

  As Comparative Example 1, 15% of water was added to the lead-contaminated soil collected from the factory site used in Example 2, and after crushing at 100 rpm for 10 minutes with a paddle mixer, the water was in a solid-liquid weight ratio of 1: 1 was added. This slurry was washed with water for 10 minutes at a rotation speed of a stirring blade of 300 rpm, and classified with a 0.075 mm vibrating sieve.

  A 3.0 mol / l hydrochloric acid solution with a solid-liquid weight ratio of 1: 2 was added to the sieved soil after classification, and the mixture was stirred for 15 minutes (stirring conditions: rotation speed of stirring blade 300 rpm). The pH of the hydrochloric acid cleaning solution at this time was −0.3 or less both immediately after the start of cleaning and before the end.

  Next, after sieving soil and hydrochloric acid cleaning liquid slurry, the sieving soil after classification is added in 1.5 times the weight of the sieving soil, and stirred for 10 minutes (stirring condition: rotation speed of stirring blade) 300 rpm). The pH of the hydrochloric acid cleaning solution at this time was 0 before the completion. This slurry is dehydrated with a centrifuge (3000 rpm, 10 minutes), and the resulting purified soil is added with water at a solid-liquid weight ratio of 1: 2, and then adjusted to pH 3.0 by adding slaked lime, and rinsed. And dehydrated in a centrifuge (3000 rpm, 10 minutes).

  Thereafter, water having a solid / liquid weight ratio of 1: 2 was added and rinsed again, followed by dehydration with a centrifugal separator (3000 rpm, 10 minutes). Furthermore, slaked lime was added and mixed to bring the soil to the same pH 6.8 as the original soil and air-dried. This purified soil was measured for lead content according to the method of Ministry of the Environment Notification No. 19. The results are shown in Table 2 above as Comparative Example 1.

  Further, as another comparative example, the result of assuming that the rinsing operation in Example 2 is performed once and the other conditions are the same as those in Example 2 is also shown as Comparative Example 2 in Table 2 described above.

  As shown in Tables 1 and 2, according to the present invention, it was possible to confirm an excellent purification effect on heavy metal contaminated soil. Further, as shown in the results of Table 2, an excellent rinsing effect was obtained by rinsing under conditions of pH 2 or lower after washing with an acidic solution. In addition, by defining the optimal number of times of soil rinsing, the amount of rinsing liquid (water) used in rinsing could be reduced.

The figure which shows the purification process of the heavy metal contamination soil which concerns on one Embodiment of this invention. The figure which shows the influence of pH after soil / acid solution (hydrochloric acid solution) mixing on the heavy metal (lead) content in the soil after purification | cleaning. The figure which shows the influence of the soil washing | cleaning time by the acidic solution (hydrochloric acid solution) on the heavy metal (lead) content after purification | cleaning. The figure which shows the process of the acidic solution collect | recovered from the solid-liquid separator. The figure which shows the purification process of the heavy metal contaminated soil which concerns on other embodiment of one Embodiment of this invention. The figure which shows the influence of pH after soil / rinsing liquid mixing on the heavy metal (lead) content in the soil after purification | cleaning. The figure which shows the relation of the number of times of rinsing which influences the heavy metal (lead) content to the soil after washing with the acidic solution The figure which shows the process of purifying the heavy metal pollution soil from which the pollution density | concentration which concerns on other embodiment of this invention differs. The figure which shows the relationship between a heavy metal (lead) contamination density | concentration and a soil particle diameter. The figure which shows the relationship between the kind of acidic solution, and heavy metal (lead) content after purification | cleaning of soil (soil particle: 0.075-2.0 mm). The figure which shows the relationship between the kind of acidic solution, and heavy metal (lead) content after purification | cleaning of soil (soil particle: less than 0.075 mm).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st process 2 2nd process 3 3rd process 4 4th process 5 5th process 6 6th process 7 Detector 8 which detects the density | concentration and / or pH of an acidic solution 8 Control apparatus 9 New liquid Flow control valve to adjust the amount of recirculation 10 Recirculation flow path

Claims (10)

In a method of pickling and cleaning heavy metal contaminated soil with an acid solution,
After pulverizing the heavy metal contaminated soil into a plurality of particle groups classified according to particle size, first pickle the heavy metal contaminated soil of the particle group having the smallest particle size, In slurry consisting of heavy metal contaminated soil and acidic solution of small particles,
When the remaining heavy metal contaminated soil of classified particles is washed by sequentially adding heavy metal contaminated soil of large particle size to heavy metal contaminated soil of small particle size, mixed washing each time it is added And
Finally, the heavy metal-contaminated soil of the particle group having the largest particle size is added, and the slurry obtained by mixing and washing is separated from the soil and the acidic solution with a solid-liquid separator, and the soil is rinsed. Purification method for heavy metal contaminated soil.   A slurry obtained by adding a particle group having the largest particle diameter, mixing and washing is separated into soil and an acidic solution by a solid-liquid separator, and washing with the soil rinsing liquid is performed in a pH 2 or lower region. The method for purifying heavy metal-contaminated soil according to claim 1.   The method for purifying heavy metal-contaminated soil according to claim 1 or 2, wherein the soil obtained after rinsing is adjusted to the same pH as that of the heavy metal-contaminated soil before pulverization.   4. The soil obtained after rinsing is adjusted to the same pH as the heavy metal-contaminated soil before crushing, and then the uncontaminated soil and / or humus soil at or near the point where the heavy metal-contaminated soil is collected is mixed. To remediate heavy metal contaminated soil. The method for purifying heavy metal-contaminated soil according to any one of claims 1 to 4, wherein in rinsing the soil separated by the solid-liquid separator, the number of times of rinsing N satisfies the following formula.
However, solid-liquid weight ratio between soil and rinsing liquid: A, moisture content of soil after solid-liquid separation: B, soil content of target pollutant before washing with acidic solution: C0, soil content designation Standard: α.
N ≧ 2.2 × ln [1.3 × (α / C0)] / ln [B / {A × (1−B)}] − 1   The heavy metal contaminated soil is crushed, the particle group having the smallest particle diameter is made less than 0.075 mm, the particle group having the largest particle diameter is made 0.075 mm or more and 2.0 mm or less, and the particle diameter is 0.075 mm. After the particle group having a particle size of less than 0.075 mm was mixed with the particle group having a particle size of less than 0.075 mm and washed with an acidic solution having a pH of -0.3 or less to obtain a slurry, the particle size was 0.075 mm to 2.0 mm. 6. The method for purifying heavy metal-contaminated soil according to claim 5, wherein the soil of the particle group classified below is added to the slurry and washed with an acidic solution having a pH of 0.5 or less after mixing. In a method of pickling and cleaning heavy metal contaminated soil with an acid solution,
After the heavy metal contaminated soil is divided into a plurality of groups sorted according to the contamination concentration, the heavy metal contaminated soil of the group with the highest contamination concentration is first pickled, and after pickling, the heavy metal contamination of the group with the highest contamination concentration To slurry consisting of soil and acidic solution,
When the remaining heavy metal-contaminated soils are added and washed sequentially from the group of heavy metal-contaminated soils with high contamination concentration to the group of heavy metal-contaminated soils with low contamination concentration, mixed washing is performed each time they are added,
Finally, the heavy metal-contaminated soil having the lowest contamination concentration is added, and the slurry obtained by mixing and washing is separated from the soil and the acidic solution by a solid-liquid separator, and the soil is rinsed, and the soil is rinsed with heavy metal Purification method.   The method for purifying heavy metal-contaminated soil according to any one of claims 1 to 7, wherein the heavy metal is lead and the acidic solution is hydrochloric acid.   A method for purifying heavy metal-contaminated soil, characterized in that, when washing heavy metal contaminated soil with an acidic solution, the soil is rinsed with a rinsing solution after being washed with an acidic solution, and the washing with the rinsing solution is performed in an area of pH 2 or lower. A method for purifying heavy metal-contaminated soil, characterized in that, when washing heavy metal-contaminated soil with an acidic solution, the number of times of rinsing N satisfies the following formula in rinsing the soil with a rinsing liquid after washing with an acidic solution.
However, solid-liquid weight ratio between soil and rinsing liquid: A, moisture content of soil after solid-liquid separation: B, soil content of target pollutant before washing with acidic solution: C0, soil content designation Standard: α.
N ≧ 2.2 × ln [1.3 × (α / C0)] / ln [B / {A × (1−B)}] − 1

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