JP2005279531A - Method for cleaning lead polluted soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method of lead polluted soil by washing the same with an acidic solution. <P>SOLUTION: The printing method of lead polluted soil includes the first process (a) for disintegrating lead polluted soil, the second process (b) for classifying the soil disintegrated in the first process at least into two particle groups, the third process (c) for mixing the soils classified in the second process with soil by a classification means selected from magnetic force sorting, specific gravity sorting and floating sorting to remove foreign matter, the fourth process (d) for washing the soils from which the foreign matter is removed in the third process, with the acidic solution at every particle group to separate the same into soil and the acidic solution by a solid-liquid separator and using a part or the whole of the recovered acidic solution in the washing of the soil or recirculation and the fifth process (e) for washing the soil, which is washed with the acidic solution in the fourth process, with a rinsing solution at every particle group. The washing with the acidic solution in the fourth process is performed under an environment with a pH of 0.5 or below and a hydrochloric acid solution is used as the acidic solution of the fourth process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a purification method for washing lead-contaminated soil with an acidic solution, and particularly relates to an excellent cost performance.

  Known techniques for purifying soil contaminated with lead include the water washing classification method, the b heat treatment method, and the c electrophoresis method.

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 soil polishing is insufficient, there is a possibility that contaminants from coarse soil particles or fine particles containing a large amount of contaminants may not be completely removed, and the contaminants may not be reduced to the soil specified standard value or less. There is.

  In addition, it is possible to improve the removal rate of contaminants or large amounts of contaminants from coarse soil particles by extending the soil polishing time or applying an advanced device that completely polishes the surface of coarse soil particles. Although it is possible, in this case as well, 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. Further, it has been pointed out that the former increases the running cost and the latter increases the initial cost of the apparatus. Furthermore, the amount of fine particles by grinding increases and the yield of the purified soil decreases.

The heat treatment method is a method for containing lead, which is a pollutant, in a very stable state by heat-sintering or vitrifying the soil with a rotary kiln or an electric resistance furnace.
In the case of heat treatment method, in the case of soil contaminated with lead, it is necessary to heat up to 800-1200 ° C, vitrification: 1600-2000 ° C in order to heat-sinter or vitrify the soil. A large amount of heat source is required, resulting in an increase in running cost.

  Furthermore, additional equipment for appropriately treating exhaust gas generated during heating is required, leading to an increase in initial cost. In addition, it has been pointed out that when lead, which is a contaminant, has not been volatilized and removed, the contaminant may be re-eluted 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.

JP 11-197643 A JP 2002-371324 A Japanese Patent Laid-Open No. 2001-149913

  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, if washing is performed with excessive drug concentration, washing time, and solid-liquid weight ratio, the equipment becomes larger and the running cost increases, which not only increases the purification cost but also due to dissolution of soil particles. The yield of purified soil is also reduced. In addition, when washing is performed under conditions where the chemical concentration, washing time, and solid-liquid weight ratio (acid capacity) are insufficient, there is a risk that the soil after washing cannot be reduced below the designated soil value.

  Therefore, since the acid concentration, washing time and solid-liquid weight ratio (acid capacity) required for washing greatly depend on the soil soil, especially the particle size, it is acidic to the soil particle group composed of each particle size. Cost performance by optimizing conditions such as drug type, concentration, and washing time of the solution, minimizing the amount of acidic drug used, and reducing initial costs and running costs with less burden on subsequent processes It is possible to establish an excellent soil purification technology.

  An object of the present invention is to provide a soil purification technology excellent in cost performance in which the particle size of the target soil is limited to sandy when washing with an acidic solution.

  The present inventors have intensively studied a method for purifying soil contaminated with lead using an acidic solution, and that the concentration of contamination due to lead depends on the particle size of the soil, and the cleaning efficiency with an acidic solution depends on the particle size. We noticed that there is a big difference.

  First, the soil to be purified is crushed and separated into single particles such as silty, clayey and sandy particles. After that, only soil with a particle size of 0.075 mm or larger was washed with an acidic solution by classification, thereby minimizing running costs and completing a soil purification technology with extremely high washing efficiency and excellent cost performance.

  Fig. 2 shows the results of an investigation of the lead content for each soil particle size for soil contaminated with lead (hereinafter, lead-contaminated soil). The lead content varies depending on the soil particle size. As the particle size increases, the lead content decreases.

  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, in the present invention, the soil particles are crushed in advance to simple particles, and sandy soil with a loose lead binding state is washed by classification, so that the acid concentration of the acidic solution used for washing is lowered and the amount of acidic solution is reduced. Can be reduced.

  Moreover, in this invention, it is preferable to use hydrochloric acid as an acidic solution from a viewpoint of an acquisition price or the performance which removes lead. As shown in FIG. 8, hydrochloric acid is the most apparent from the results of washing for 15 minutes with various 1 (mol / L) acidic solutions on lead-contaminated soil under a solid-liquid weight ratio of 1: 1. It turns out to be effective.

That is, the present invention
1 A method for purifying lead-contaminated soil, comprising the following steps.
a First step of crushing lead-contaminated soil.
b A second step of classifying the soil crushed in the first step into at least two particle groups with a specific particle diameter as a boundary.
c A third step of removing the foreign matter mixed in the soil by the sorting means selected from magnetic sorting, specific gravity sorting, and floating sorting of the soil classified in the second step.
d After the soil from which foreign matters have been removed in the third step is washed with an acidic solution for each particle group, the solid solution is separated into soil and acidic solution by a solid-liquid separator, and the collected acidic solution is partly used for washing the soil. Or the 4th process that recycles all.
e Fifth step of washing the soil washed with the acidic solution in the fourth step with a rinsing liquid for each particle size.
2. The method for purifying lead-contaminated soil according to claim 1, wherein washing with an acidic solution in the fourth step is performed in an environment having a pH of 0.5 or less.
3. The method for purifying lead-contaminated soil according to 1 or 2, wherein the lead-contaminated soil in the fourth step is mainly soil having a particle diameter of 0.075 mm or more.
4 The method for purifying lead-contaminated soil according to any one of 1 to 3, wherein the acidic solution in the second step is a hydrochloric acid solution.

  According to the present invention, after pulverizing lead-contaminated soil into simple particles, it is not necessary to use high-concentration hydrochloric acid by applying an acidic solution to wash sandy soil in which the lead binding state is mild by classification. It is very useful industrially because it can purify large amounts of lead-contaminated soil at low cost, with little load and burden on equipment, post-process, soil.

  In the method of purifying soil contaminated with lead (hereinafter referred to as lead-contaminated soil) using an acidic solution, the present invention has the highest cleaning efficiency and cost performance after disintegrating the contaminated soil into single particles. Sandy soil is classified, and the soil is washed with an acidic solution.

  FIG. 1 is a process diagram of an embodiment of a soil purification method according to the present invention. In the figure, 1 is a process of crushing lead-contaminated soil into single particles (hereinafter referred to as a first process), and 2 is a first process. The step of classifying the heavy metal contaminated soil crushed by the process into a soil particle group using a classifier (hereinafter referred to as the second step), 3 is magnetic sorting, specific gravity sorting, floating sorting of the soil classified by the second step The step of removing foreign matters mixed in the soil by a more selective separation means (hereinafter, third step), 4 uses an acidic solution for the sandy particles of the lead-contaminated soil from which foreign matters have been removed by the third step And a step (hereinafter referred to as a fourth step) and 5 indicate a step (hereinafter referred to as a fifth step) of rinsing (rinsing) the soil washed in the fourth step.

[First step]
The purpose is to loosen the excavated lead-contaminated soil from the aggregated and lump-like state to single particles 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. The soil crusher uses existing equipment such as a drum washer, paddle mixer, lot mill, attritor, and ball mill.

[Second step]
The purpose of the second step is to classify the soil that has been loosened into single particles in the first step into silt, clay, and sand.

  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, a particle size of 0.075 mm or less is silt / clay, and a soil having a particle size of more than 0.075 mm is sandy.

[Third step]
The purpose of the third process is to remove foreign matter such as paint pieces containing lead, lead dust and lead pollutants, and carbon particles and metal pieces that are easily adsorbed and adsorbed by specific gravity sorters, magnetic sorters, and floating sorters. And
In the presence of these foreign substances, particularly metal pieces, paint pieces, and lead shots, the dissolution reaction of these foreign substances occurs in parallel in the soil washing with the acidic solution in the subsequent stage, so that the consumption amount of the acidic solution increases. Therefore, it is preferable to remove these foreign substances before soil washing with an acidic solution.

  Moreover, this process should just be before soil washing | cleaning by an acidic solution, and may be implemented before the soil crushing of a 1st process and the soil classification of a 2nd process. Furthermore, this step may be omitted when the amount of foreign matter is small.

[Fourth process]
The purpose of the fourth step is to wash the sandy soil with an acidic solution among the lead-contaminated soils classified and removed by the third step, and collect the washed acidic solution with a solid-liquid separator. And In addition, silt and clayey soil shall be treated separately, such as reuse for cement raw materials and delivery to managed facilities in consideration of their contamination.

  In the present invention, the washing conditions with the acidic solution are defined so that the sandy soil has a predetermined washing ability. The concentration, pH, washing time, etc. of the acidic solution are adjusted as washing conditions.

  Hereinafter, a case where hydrochloric acid having the most purification effect and economical economical acid solution is used for the lead-contaminated soil will be described.

  The concentration or amount of hydrochloric acid used for washing considers the effect of washing, the soil yield after washing, etc. In the case of sandy soil with a particle diameter exceeding 0.075 mm, the pH of the soil after mixing hydrochloric acid is 0.5 or less Preferably, it may be adjusted to 0 or more and 0.5 or less.

  That is, as shown in FIG. 3, it can be seen that the lead dissolution and extraction effects are excellent when the pH is 0.5 or less. However, when the pH is lower than 0, lead is dissolved and extracted, the main minerals and substances constituting the soil are dissolved, the extraction ratio is increased, the yield of the purified soil is reduced, and the liquid after washing is rinsed and rinsed. Cost performance decreases significantly, such as an increase in the amount of water used.

  FIG. 4 explains cost performance (cleaning efficiency = lead removal rate / cleaning cost) when sandy lead-contaminated soil having a soil particle diameter of 0.075 mm and 2.0 mm or less is washed by changing the concentration of hydrochloric acid. A schematic diagram is shown.

  In this figure, the lead content reduction rate, the purification cost, and the purification efficiency are set to 1 at a hydrochloric acid concentration of 1.0 mol / L corresponding to the conventional purification method. Although the concentration of hydrochloric acid to be used is not particularly specified, it is preferable to use hydrochloric acid having a hydrochloric acid concentration of 0.4 to 1.0 mol / L in consideration of the figure, the scale, burden and workability of the apparatus. .

  When the sandy soil is washed under the above-mentioned optimum pH condition (pH = 0.5 or less), the lead content after washing becomes constant in 5 to 30 minutes as shown in FIG. Therefore, the cleaning time may be 30 minutes or less, and preferably 15 minutes or less from the viewpoint of further suppressing the initial cost of the cleaning device.

  The weight ratio between the lead-contaminated soil and the hydrochloric acid solution is preferably 1: 1 to 1: 2 in consideration of cleaning efficiency, effect, load on equipment, scale, and the like.

[Fifth process]
The purpose of the fifth step is to remove the remaining lead and hydrochloric acid by rinsing the lead-contaminated soil washed with the acidic solution in the fourth step with water. In the present invention, water refers to tap water and the like.

  The soil that has undergone the third step has a low pH, and chemical components such as lead and chlorine remain. Rinse with water to cause the steel foundation corrosion of the building foundation when reused by backfilling.

  Fig. 6 shows the relationship between the number of rinses and the amount of residual chlorine when lead-contaminated soil was washed with 0.5 and 1 (mol / L) hydrochloric acid and then rinsed with a weight ratio of water to purified soil of 1: 1. Indicates. FIG. 7 shows the relationship between the weight ratio of rinsing water and purified soil and the amount of residual chlorine when lead-contaminated soil is washed with 1 (mol / L) hydrochloric acid.

  6 and 7, when the amount of water used is the same, reducing the water ratio and increasing the number of times of rinsing reduces the amount of residual chlorine. The number of washings is preferably 2 or more.

  In addition, after rinsing, it is preferable to use an alkaline agent such as calcium hydroxide, calcium oxide, calcium carbonate, etc. to make the purified soil a neutral region.

  15% of water is added to each of the three types of solid lead-contaminated soils with different contamination backgrounds and soils, and after crushing at 100 rpm for 10 minutes with a paddle mixer, the water becomes a solid-liquid weight ratio of 1: 1. Were added. The soil 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 1.0 mol / L hydrochloric acid solution at a solid-liquid weight ratio of 1: 1 was added to the sieved soil after classification, and the mixture was 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 immediately after the start of cleaning and 0.3 before the end.

  The obtained purified soil was rinsed with water having a solid / liquid weight ratio of 1: 1, then dehydrated with a classifier, and this rinsing operation was repeated twice. Thereafter, slaked lime was added and mixed to neutralize the soil (pH = 7-9) 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 soil slurry was washed with water for 10 minutes at a rotation speed of a stirring blade of 300 rpm, and then divided into a magnetized material and a non-magnetized material using a 1500 gauss wet drum magnetic separator.

  Non-magnetized material is classified with a 0.075 mm vibrating sieve, and a 1.0 mol / L hydrochloric acid solution at a solid-liquid weight ratio of 1: 1 is added to the soil on the sieve and stirred for 10 minutes (stirring conditions: stirring blades) Of 300 rpm). The pH of the hydrochloric acid cleaning solution at this time was 0.05 immediately after the start of cleaning and 0.25 before the end.

  The obtained purified soil was rinsed with water having a solid / liquid weight ratio of 1: 1, then dehydrated with a classifier, and this rinsing operation was repeated twice. Thereafter, slaked lime was added and mixed to neutralize the soil (pH = 7-9) 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.

  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. The soil slurry was washed with water for 10 minutes at a rotation speed of a stirring blade of 300 rpm, and then the soil having a particle size of 0.5 mm to 4.75 mm was classified with a vibration sieve.

  This soil was subjected to a two-stage specific gravity sorting of upper and lower layers using a jig specific gravity sorter. A 1.0 mol / L hydrochloric acid solution at a solid-liquid weight ratio of 1: 1 was added to the upper soil layer, and the mixture was stirred for 5 minutes (stirring conditions: the number of revolutions of a stirring blade was 300 rpm).

  The pH of the hydrochloric acid cleaning solution at this time was 0.02 immediately after the start of cleaning and 0.2 before the end. The obtained purified soil was rinsed with water having a solid / liquid weight ratio of 1: 1, then dehydrated with a classifier, and this rinsing operation was repeated twice. Thereafter, slaked lime was added and mixed to neutralize the soil (pH = 7-9) 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 3.

  As Comparative Example 1, 15% of water was added to each of the three kinds of solid lead-contaminated soils having different contamination backgrounds and soils used in Example 1, and then crushed at 100 rpm for 10 minutes using a paddle mixer. Was added at a solid-liquid weight ratio of 1: 1. The soil 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.

  Water was added to the sieved soil after classification at a solid-liquid weight cost ratio of 1: 1, and the mixture was stirred for 10 minutes (stirring conditions: rotation speed of stirring blade 300 rpm). Then, after dehydrating with a classifier and air-drying, the lead content was measured in accordance with the method of Ministry of the Environment Notification No. 19. The results are shown in Table 4.

  As Comparative Example 2, 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 liquid-solid weight ratio of 1: 1 was added.

This soil slurry was washed with water for 10 minutes at a rotation speed of a stirring blade of 300 rpm, and then divided into a magnetized material and a non-magnetized material using a 1500 gauss wet drum magnetic separator. Each of the magnetized material and the non-magnetized material was classified with a vibration sieve of 0.075 mm, and the soil on the sieve was 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 5.

  As Comparative Example 3, 15% of water was added to the lead-contaminated soil collected from the factory site used in Example 3, 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.

  The soil slurry was washed with water for 10 minutes at a rotation speed of a stirring blade of 300 rpm, and then the soil having a particle size of 0.5 mm to 4.75 mm was classified with a vibration sieve. This soil was subjected to a two-stage specific gravity sorting of upper and lower layers using a jig specific gravity sorter.

  The upper and lower soils were classified with a 0.5 mm vibrating sieve, the sieved soil was air-dried, and the 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 6.

The process drawing of the lead pollution soil purification method concerning one embodiment of the present invention. The figure which shows the relationship between a lead contamination density | concentration and a soil particle diameter. The figure which shows the influence of pH after soil / hydrochloric acid solution mixing on the lead content in the soil after purification | cleaning. The characteristic view which shows the influence of the hydrochloric acid concentration on the purification characteristic of lead. The figure which shows the influence of the soil washing | cleaning time in an acidic solution on the lead content after purification | cleaning. The figure which shows the influence of the number of times of rinsing on the quantity of the residue in the soil after purification | cleaning. The figure which shows the influence of the water quantity ratio of the rinse washing on the quantity of the residue in the soil after purification | cleaning. The figure which shows the relationship between the kind of acidic solution and soil content: Lead content after purification | cleaning of 0.075-2mm sandy soil.

Claims (4)

A method for purifying lead-contaminated soil, comprising the following steps.
a First step of crushing lead-contaminated soil.
b A second step of classifying the soil crushed in the first step into at least two particle groups with a specific particle diameter as a boundary.
c A third step of removing the foreign matter mixed in the soil by the sorting means selected from magnetic sorting, specific gravity sorting, and floating sorting of the soil classified in the second step.
d After the soil from which foreign matters have been removed in the third step is washed with an acidic solution for each particle group, the solid solution is separated into soil and acidic solution by a solid-liquid separator, and the collected acidic solution is partly used for washing the soil. Or the 4th process that recycles all.
e Fifth step of washing the soil washed with the acidic solution in the fourth step with a rinsing liquid for each particle group.   The method for purifying lead-contaminated soil according to claim 1, wherein washing with an acidic solution in the fourth step is performed in an environment having a pH of 0.5 or less.   The lead-contaminated soil purification method according to claim 1 or 2, wherein the lead-contaminated soil in the fourth step is mainly soil having a particle diameter of 0.075 mm or more.   The method for purifying lead-contaminated soil according to any one of claims 1 to 3, wherein the acidic solution in the second step is a hydrochloric acid solution.

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