JP2006255515A - Method for decontaminating soil contaminated with heavy metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for decontaminating the soil contaminated with a heavy metal, in which sorting work and the work of treating waste water are done efficiently and even a contaminated soil particle, which is discarded in the conventional method, can be decontaminated. <P>SOLUTION: A heavy metal collecting fibrous material produced by a radiation graft polymerization method is mixed with the soil contaminated with the heavy metal and an aqueous medium and then recovered. The heavy metal adsorbed on the heavy metal collecting fibrous material is eluted and cleaned by using a dilute acid, for example, dilute hydrochloric acid to regenerate the heavy metal collecting fibrous material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for purifying heavy metal-contaminated soil that can more efficiently purify soil contaminated with heavy metals.

  There are an increasing number of cases where soil contamination has been identified following the enforcement of the Soil Contamination Countermeasures Law. According to the survey results of the Ministry of the Environment, there are the most cases of heavy metal contamination.

  Japan's cleanup measures against heavy metal-contaminated soil include methods such as insolubilizing contaminated soil, methods of containment of contaminated soil, water-impervious construction methods, and methods of covering soil, but these measures can also remove contaminants. This is not to say that land use is restricted even after measures are taken, and it is often a negative factor in real estate transactions. Measures are also taken to remove contaminated soil and replace it with uncontaminated soil, but it is clear that there will be a shortage of final disposal sites that accept contaminated soil. Therefore, the soil cleaning method with a track record mainly in Europe attracts attention and has been introduced in Japan.

  The soil washing method is a method of washing soil with water or an appropriate solvent, dissolving contaminants in the liquid, and separating them. A typical example is that the soil is separated by a predetermined particle size by adding water to the contaminated soil, fine soil particles rich in heavy metals are discarded, and coarse soil particles are washed to remove contaminants and buried. It is a method of reusing it by returning it to reduce the volume of contaminated soil. In this construction method, the more fine soil particles containing a lot of heavy metals, the more effective the purification method.

  The soil cleaning method consists of a process for cleaning and classifying heavy metal contaminated soil and a wastewater treatment process for purifying the soil-washed water and water containing heavy metals after dehydration of the soil. For example, a large amount of water is required for cleaning with a small particle size such as 0.075 mm, so that a large amount of water containing heavy metals is generated. In the soil washing method, this water is generally purified and reused, but in order to purify it, a chemical and a chelating material corresponding to the adjustment of pH and the type of heavy metal are required. Therefore, in addition to the equipment for cleaning and classification, the equipment for the treatment associated with the purification of the washing water becomes very large, and the cost of materials such as chemicals and chelating materials is increased, resulting in an increase in the unit price of the purification. In particular, the more soil particles that are likely to contain a lot of heavy metals, the more soil that is discarded, and the higher the cost for disposal. In Japan, there are many areas where fine soil particles such as volcanic ash are deposited, and there is a problem that they are not practical.

  An object of the present invention is to solve the above-mentioned problems, and in particular, it is possible to improve the efficiency of classification and wastewater treatment, and further to the heavy metal-contaminated soil that can purify soil particles that were discarded in the conventional method. It is to provide a purification method.

  The present invention relates to a polymer chain (eg, polyacrylonitrile) bonded to a base material (eg, polyethylene nonwoven fabric) known as an adsorbent for collecting uranium resources dissolved in seawater by, for example, a radioactive graft polymerization method. Adsorbent formed by amidoximation of the chain, polyacrylonitrile-methacrylic chain portion (see “Journal of the Seawater Society of Japan” 53, p. 180-184 (1999)) quickly and rapidly removes metals such as cadmium in aqueous media. It is based on the knowledge that it adsorbs effectively and that the adsorbed metal is easily desorbed and released by washing with dilute acid.

  Therefore, the present invention brings a slurry-like mixture obtained by mixing heavy metal-contaminated soil and an aqueous medium into contact with a fibrous heavy metal collecting material prepared by a radiation graft polymerization method, and harmful metals eluted from the heavy metal-contaminated soil. The slurry mixture is dehydrated to separate the soil and the aqueous medium; the heavy metal adsorbed by the collection material is recovered by eluting with a dilute acid; A method for removing heavy metals from soil contaminated with heavy metals including various processes is provided.

  In the method of the present invention, a solution containing an acid such as hydrochloric acid or an organic acid aqueous solution may be used as an aqueous medium in order to promote elution of heavy metals from heavy metal contaminated soil.

  In the method of the present invention, in the method of simultaneously mixing heavy metal-contaminated soil, an aqueous medium and a fibrous heavy metal collector, a fibrous heavy metal collector prepared by radiation graft polymerization of heavy metal eluted from the heavy metal-contaminated soil into the aqueous medium is used. Since it is adsorbed quickly, the concentration of heavy metals eluted from the contaminated soil into the aqueous medium is kept low, so that the elution efficiency is good.

  In the method of the present invention, in the contact operation of the fibrous heavy metal collector prepared by mixing the heavy metal and the aqueous medium and the radiation graft polymerization method, the soil content test conducted by the heavy metal contaminated soil according to Ministry of the Environment Notification No. 19 Is carried out over a period of time that is reduced until the content of heavy metal-contaminated soil measured in accordance with is reduced below the content standard stipulated in the Soil Contamination Countermeasures Law.

  The fibrous heavy metal scavenger prepared by the radiation graft polymerization method in the method of the present invention introduces a polymerizable monomer (acrylic acid, acrylonitrile, glycidyl methacrylate, etc.) as a graft side chain into the fiber substrate by the radiation graft polymerization method, It is obtained by introducing a chelate-forming group and an ion exchange group corresponding to the type of heavy metal into the side chain. As chelate-forming groups and ion-exchange groups, heavy metal ion-adsorptive functional groups such as iminodiacetic acid, dimethylamine, trimethylamine, ethanolamine, diethanolamine, triethanolamine, ethanoldiamine, amidoxime, phosphone, sulfone, and carboxyl are used alone or in combination. What has been introduced.

  In the method of the present invention, the fibrous heavy metal collection material prepared by the radiation graft polymerization method is recovered after mixing the heavy metal and the aqueous medium, and regenerated by washing the elution of heavy metal adsorbed on the heavy metal collection agent with a dilute acid such as dilute hydrochloric acid. can do.

  According to the present invention, soil contaminated with heavy metals can be more efficiently purified.

  According to the present invention, it is not necessary to classify contaminated soil smaller than a predetermined particle size to a particle size smaller than that, and the aqueous medium after purification and washing of the soil by a fibrous heavy metal collector prepared by a radiation graft polymerization method. Since purification can be performed, classification and wastewater treatment can be made more efficient. Moreover, since the fine soil which was thrown away by the conventional soil washing method can be purified, it can be effectively used as a backfill material, and the cost can be reduced.

  FIG. 1 shows an example of a conventional soil cleaning method, and FIG. 2 shows an example of the method of the present invention. In the purification method of FIG. 1, for example, water is added to the contaminated soil from which large lumps and burrs having a particle diameter of 40 mm or more have been removed, washed by the cleaning device 1, and sorted by the sorting device A to obtain clean soil larger than the particle size A. Next, classification is performed with a particle size B smaller than the particle size A to obtain clean soil larger than the particle size B. Sediment that has been concentrated by heavy metals that has passed through the sorting device B is divided into contaminated soil that has been concentrated by heavy metals and contaminated water that contains heavy metals. The heavy metal concentrated contaminated soil is treated as waste, and the contaminated water is treated with water. Reuse. This method is an example, and there are various particle sizes and methods employed in the washing process and classification, but generally the final selection particle size often corresponds to a silt content of 0.075 mm, Since soil with such a fine particle size contains a large amount of heavy metals, it is discarded as contaminated soil. Therefore, in order to reduce waste soil, precise classification is required, and the number of cleaning / classification devices increases. In addition, washing water containing heavy metals generally requires pH adjustment according to the heavy metals, chemicals according to the type of heavy metals, chelating materials, reaction tanks, and treatment tanks, which greatly increases the equipment.

  FIG. 2 shows an example of the present invention. First, large lumps and glass such as 40 mm or more are removed. Next, an aqueous medium is added to an extraction cleaning / classifying apparatus C loaded with a fibrous heavy metal collection material prepared by a graft polymerization method that can be recovered, and the heavy metal is collected in a slurry-like mixture of heavy metal contaminated soil and aqueous medium. While contacting the material, sorting by particle size C is performed to obtain clean soil larger than particle size C. About the earth and sand smaller than the particle size C, dehydration is performed to obtain clean soil. The said heavy metal collection material which heavy metal adsorb | sucked is wash | cleaned with dilute hydrochloric acid after collection | recovery, and is reused. In addition, when using an acid solution as an aqueous medium for these clean soils, the pH of the soil is low, so there are cases where heavy metals are likely to elute, but in this case, rinsing with clean water or a small amount of quicklime is possible. In order to prevent the elution of heavy metals, it is also possible to promote the drying of earth and sand and raise the pH to a neutral range.

  In the present invention, unlike the conventional soil cleaning method, it is not necessary to perform precise classification in order to reduce waste soil, so that the apparatus required for cleaning and classification is simplified. Furthermore, soil with a fine particle size that was discarded in the conventional technology can be washed, and can be reused as a high-quality backfill soil by mixing with soil with a coarse particle size after washing, thereby reducing waste. In addition, the cost can be reduced. In addition, by bringing the heavy metal contaminated soil and the aqueous medium into contact with the heavy metal collector, it is possible to purify both the soil and the aqueous medium, thereby reducing the size of equipment necessary for the purification of the aqueous medium. Cost reduction is possible.

  The heavy metal collector is a commercially available dehydration sheet for civil engineering (polypropylene nonwoven fabric having a fiber diameter of 40 μm), grafted with acrylonitrile using a radiation graft polymerization method, reacted with hydroxylamine to form an amidoxime group of 3.5 mmol / g. Introduced and produced. This amidoxime-type chelate resin was placed in a 2.5% aqueous potassium hydroxide solution and alkali-treated at 80 ° C. for 1 hour. After the alkali treatment, the sample was washed with water until the washing solution became neutral to obtain a collection material that adsorbs heavy metals.

  Add 50 g of aqueous medium and 1.2 g of the above collection material in the shape of a square with a side of 1 cm to 20 g of coarse sand having a particle diameter of 2 mm or less containing 200 mg / kg of cadmium and lead, respectively, and shake with a shaker for 1 hour. did. As the aqueous medium, a solution in which 1 mol of malic acid and 1 mol of sodium hydroxide were mixed at a ratio of 1: 1 was used. The pH of this mixed solution was 3.9. Cadmium and lead adsorbed on the collecting material were eluted using 1 molar nitric acid.

Table 1 shows the cadmium and lead contents of the soil after shaking, the cadmium adsorbed on the above collection material, the amount of lead adsorbed, the cadmium eluted in the aqueous medium, and the lead concentration. In addition, the value in a table | surface is represented by the absolute value of the amount of heavy metals per 1 kg of soil.

  The cadmium and lead contents before the treatment exceeded 200 mg / kg and the soil content standard of 150 mg / kg, but mixing with an aqueous medium reduced cadmium to 40 mg / kg and lead to 60 mg / kg, The soil content was reduced to 150 mg / kg or less. The cadmium adsorbed by the heavy metal collector adsorbed 153 mg / kg and lead adsorbed 110 mg / kg. The adsorbed amount of the trapping material is about 77% for cadmium and 55% for lead, and the concentration of the aqueous medium is as low as 12 mg / kg for cadmium and 13 mg / kg for lead. As a result, it is not necessary to wash the aqueous medium every time, which leads to downsizing of the apparatus and cost reduction.

  Add 20 g of viscous soil containing 333 and 367 mg / kg of cadmium and lead to a particle size of 0.075 mm or less and 50 g of aqueous medium and 1.2 g of the above collecting material in the shape of a square of 1 cm on a side. Shake for 1 hour. As the aqueous medium, a solution in which 1 mol of malic acid and 1 mol of sodium hydroxide were mixed at a ratio of 1: 1 was used. Soil content after infiltration is reduced to 47 mg / kg for cadmium and 133 mg / kg for lead. Cadmium and lead are reduced to below the soil environmental standard even in fine-grained soil of 0.075 mm or less, enabling effective use. Become.

  A polyethylene long fiber having a fiber diameter of 25 μm was placed in a deoxygenation vessel, and irradiated with cobalt-60γ rays at 10 kGy to carry out impregnation graft polymerization of deoxygenated glycidyl methacrylate (GMA). Iminodiacetic acid was reacted with the glycidyl group of the GMA graft fiber to introduce 4.0 mmol / g of iminodiacetic acid group and hydrophilic hydroxyl group. A collection container filled with 1.5 g of polyethylene long fiber introduced with iminodiacetic acid groups in a 1 cm square triangular triangle pack made of saran net contains particles of 200 mg / kg each of lead, zinc and nickel 0.075 mm or less The mixture was added to 20 g of the viscous soil together with 50 g of the aqueous medium and shaken for 1 hour with a shaker. As the aqueous medium, a solution in which 1 mol of malic acid and 1 mol of sodium hydroxide were mixed at a ratio of 1: 1 was used. Soil content after infiltration is 30 mg / kg for lead, 33 mg / kg for zinc, 35 mg / kg for nickel, and even for fine-grained soil of 0.075 mm or less, heavy metals are reduced to below the soil environmental standard. The removal effect of heavy metals was confirmed.

It is a figure which shows one Example of the conventional soil washing | cleaning method. It is a figure which shows one Example of the soil washing | cleaning method of this invention.

Claims (7)

  A slurry-like mixture obtained by mixing heavy metal-contaminated soil and an aqueous medium is brought into contact with a fibrous heavy metal collector prepared by radiation graft polymerization, and the heavy metal eluted from the heavy metal-contaminated soil is adsorbed to the collector. Separating the slurry mixture into soil and an aqueous medium; recovering the heavy metal adsorbed by the trapping material by eluting with dilute acid; and taking out the separated purified soil out of the system; A method of removing heavy metals from heavy metal contaminated soil, including a process.   The method according to claim 1, wherein the fibrous heavy metal collecting material produced by the radiation graft polymerization method is a heavy metal collecting material in which a chelate-forming group corresponding to the type of harmful metal is introduced into the fiber.   The fibrous heavy metal collector after removing the adsorbed heavy metal by eluting with dilute acid is washed with alkali, neutralized, regenerated, and then reused for heavy metal adsorption. The method described.   4. The method according to claim 1, wherein the heavy metal collecting material has a shape separable from the slurry mixture.   The method according to any one of claims 1 to 4, wherein a mineral acid such as hydrochloric acid, nitric acid or phosphoric acid is used alone or in a mixture as a dilute acid for eluting heavy metals.   The method according to any one of claims 1 to 5, further comprising a step of neutralizing by adding basic soil and / or quicklime to the clean soil after separation of heavy metals.   The method according to any one of claims 1 to 6, wherein the aqueous medium to be mixed with the heavy metal contaminated soil is an inorganic acid or an organic acid aqueous solution alone or as a mixture.

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