KR102448891B1 - Method for remediation of contaminated soil with radioactive nuclide - Google Patents

Abstract

The present invention relates to a method for restoring radionuclide-contaminated soil. The restoration method according to the present invention includes: an aggregation dissolution step of dissolving, in an aqueous solution, carbonate, organic matter, iron oxide, and manganese oxide, which are aggregate forming agents that agglomerate soil particles in soil contaminated with radionuclides, and separating the contaminated soil and the aqueous solution into solid and liquid; separating the contaminated soil from which soil aggregates are disintegrated into a plurality of groups according to particle size; analyzing the concentration of nuclides for each particle size group, and classifying the same into a first group requiring subsequent processing and a second group requiring no subsequent processing; and selecting only soil particles contaminated with nuclides by applying physical screening technology to the first group. The present invention is the most economical and effective technique.

Description

METHOD FOR REMEDIATION OF CONTAMINATED SOIL WITH RADIOACTIVE NUCLIDE

The present invention relates to a technology for restoring contaminated soil, and more particularly, to a technology for purifying soil contaminated with radionuclides such as uranium and cesium.

A radioactive nuclide is a substance that emits radiation energy and is used in various fields such as nuclear power generation, nuclear weapons, and medical devices, and is introduced into the environment by nuclear tests, nuclear accidents, and waste spills.

During radioactive decay of radionuclides, ionizing radiation such as alpha (α) particles, beta (β) particles, gamma (γ) rays or neutrons are emitted, which act as environmental hazards. The degree of risk is determined by the concentration of the nuclide, the energy of the emitted radiation, the type of radiation, and how close the nuclide is to the human body. When the human body is excessively exposed to alpha particles, beta particles, gamma rays, and X-rays emitted from radionuclides, tissue may be damaged or altered. The most severe damage occurs to tissues or organs with active cell division. In particular, it can cause genetic modification because it affects the germ cells. Therefore, excessive exposure to radionuclides increases the risk of birth defects and cancer.

Soil contaminated with radionuclides is complexly contaminated with various nuclides such as ¹³⁷ Cs, ⁶⁰ Co, ⁹⁰ Sr, ¹²⁹ I, ³ H, ¹⁴ C, and ⁹⁹ Tc. Radionuclide-contaminated soil is treated by applying technologies such as soil washing, electrokinetic extraction, and particle size separation. Rather than complete decontamination, the goal is to minimize the volume of soil contaminated with environmental standards. Soil contaminated with more than the environmental standard is stored in a safe place (radioactive waste disposal site).

However, it is very difficult to secure a site because the radioactive waste repository is recognized as a socially hateful facility regardless of whether it is a real risk. Therefore, in the treatment of radionuclide-contaminated soil, it is very important how much soil exceeds the environmental standard to be stored in the radioactive waste repository after the treatment of radionuclide-contaminated soil is completed. In other words, the treatment efficiency of radionuclides-contaminated soil purification technology is determined by the volume reduction of the contaminated soil to be stored in the radioactive waste repository.

It is necessary to develop high-efficiency radionuclide-contaminated soil volume reduction technology for the reduction of risks caused by radionuclide-contaminated soil and the efficient operation of a radioactive waste repository.

An object of the present invention is to solve the above problems, and it is an object of the present invention to provide a method for determining an application technique that can most economically and effectively treat radionuclide-contaminated soil among various contaminated soil restoration technologies.

On the other hand, other objects not specified in the present invention will be further considered within the range that can be easily inferred from the following detailed description and effects thereof.

In the method for restoring radionuclide-contaminated soil according to the present invention for achieving the above object, (a) by injecting the soil contaminated with radionuclides into a treatment aqueous solution, the agglomeration agent for agglomeration of soil particles in the contaminated soil is dissolved in the aqueous solution, , aggregation resolution step of mutually solid-liquid separation of contaminated soil and aqueous solution; (b) separating the contaminated soil from which the soil aggregate is dismantled into a plurality of groups according to the particle size; (c) analyzing the concentration of nuclides for each particle size group and classifying them into a first group requiring subsequent treatment and a second group that does not require subsequent treatment; (d) selecting only soil particles contaminated with nuclides by applying a physical screening technique to the first group;

According to the present invention, the step of dissolving the aggregation is the step of dissolving the carbonate in the contaminated soil and the nuclide bound to the carbonate by putting the contaminated soil into an acid solution, then solid-liquid separation, and the contaminated soil is put into an aqueous solution containing an oxidizing agent. Dissolving the organic matter in the contaminated soil and the nuclides bound to the organic material together, and then solid-liquid separation, and the contaminated soil is added to an aqueous solution containing a reducing agent and a chelating agent to form iron oxide and manganese oxide in the contaminated soil, and the iron oxide and manganese oxide Dissolving the bound nuclides together and then solid-liquid separation.

Here, the oxidizing agent for removing the organic material is sodium hypochlorite (NaOCl), and the aqueous solution containing the oxidizing agent is preferably in a pH range of 8 to 10.

And the reducing agent for dissolving and removing the iron oxide and manganese oxide is sodium dithionite (Na ₂ S ₂ O ₄ ), and the chelating agent is sodium citrate (Na ₃ C ₆ H ₅ O ₇ ).

In an embodiment of the present invention, the physical screening technology may apply magnetic separation technology and electrostatic screening technology, and flotation screening may be applied to fine particles.

In one embodiment of the present invention, it is preferable to further include the step of confirming the dispersion of soil particles after removing carbonate, organic matter, iron oxide and manganese oxide from the contaminated soil and then washing the contaminated soil with a washing solution.

In one example of the present invention, after performing particle size separation into a plurality of groups by sampling a portion of the contaminated soil as a representative sample, and dividing the group into a group that requires post-treatment and a group that does not require post-treatment through nuclide contamination concentration analysis, , it is preferable to perform particle size separation on the entire contaminated soil by dividing the particle size groups into smaller numbers than the number of particle size separation groups for the representative sample based on the analysis results for the representative sample.

In one example of the present invention, after separating the contaminated soil by particle size, it is analyzed whether the particle size group contaminated with nuclide is composed of a composite mineral in which heterogeneous minerals are combined, and when a nuclide is bound to a specific mineral, the particle size group It may further include the step of group separation so that the different minerals are separated from each other by pulverizing the contaminated soil.

In one embodiment of the present invention, the second group includes fine particles contaminated with nuclides, and the fine particles have a particle size of 10 μm or less. On the other hand, the second group includes gravel of 2 mm or more.

Through the method for restoring soil contaminated with radionuclides according to the present invention, nuclides weakly bound to soil particles can be removed by dissolving them by chemical treatment. The contaminated soil is purified by sorting and disposing of it.

While removing nuclides by chemical treatment, the efficiency of physical treatment is improved by separating soil aggregates into individual soil particles.

In physical treatment, a specific particle size group contaminated with nuclides is first selected through particle size separation and group separation, and then magnetic and electrostatic sorting is applied to a specific particle size group to select only soil particles contaminated with nuclides. Soil volume can be reduced as much as possible.

On the other hand, even if it is an effect not explicitly mentioned herein, it is added that the effects described in the following specification expected by the technical features of the present invention and their potential effects are treated as described in the specification of the present invention.

1 is a schematic flowchart of a method for restoring radionuclide-contaminated soil according to an embodiment of the present invention.
2 is for explaining a 2:1 layered silicate mineral.
The table of FIG. 3 is an example of the particle size separation criteria of the representative sample.
The table of FIG. 4 is an example of the particle size separation criteria.
※ It is revealed that the accompanying drawings are exemplified as a reference for understanding the technical idea of the present invention, and the scope of the present invention is not limited thereby.

In the description of the present invention, if it is determined that the subject matter of the present invention may be unnecessarily obscured as it is obvious to those skilled in the art with respect to related known functions, the detailed description will be omitted.

The present invention is a technique for restoring soil contaminated with radionuclides. Radionuclides to be treated in the present invention are mainly ¹³⁷ Cs, ⁹⁰ Sr, ⁶⁰ Co, ¹²⁹ I, ⁹⁹ Tc, U, and the like, and in addition, it can be applied to soil contaminated with various radionuclides.

The present invention provides the most effective decontamination method based on a study on the form and binding form of radionuclides in the soil. In the present invention, the removal of contamination means two things. One is to separate and dispose of soil particles contaminated with radionuclides. This is a case where it is difficult to remove the nuclide itself because the radionuclide is strongly bound to the soil particles. The other is the case of melting and removing nuclides. If it is weakly bound or adsorbed to the soil particles, it can be removed by dissolving the nuclides in an acid solution or the like.

Before describing the present invention, the binding form of major radionuclides in soil will be described.

Strontium ( ⁹⁰ Sr) exists as a free ion, adsorbed, and solid in soil. ⁹⁰ Sr is adsorbed to the mineral surface and organic matter by ion exchange reaction. The adsorption of ⁹⁰ Sr in soil is determined by the cation exchange capacity (CEC) of the soil. The adsorbed ⁹⁰ Sr is easily exchanged with cations such as Ca ²⁺ , Mg ²⁺ and becomes a free ion state. Sr is produced in the soil from sulfates such as celestite (SrSO ₄ ), carbonates such as strontianite (SrCO ₃ ), or CaSO ₄ , CaSO ₄ ·2H ₂ O, and CaCO ₃ obtained by isomorphic substitution of Ca. It is known that the ⁹⁰ Sr introduced into the soil accounts for 60-100% of the ⁹⁰ Sr in the soil in an ion-exchangeable form and in a form combined with organic matter. Since they are weakly bound to soil particles, they can be removed by dissolving the nuclides themselves by chemical treatment.

Cobalt ( ⁶⁰ Co) is more stable than +2-valent Co and +3-valent Co in the surface environment. Co forms a complex with organic ligands and tends to adsorb to clay minerals. Above pH 7, Co together with Ni and Al form low solubility and stable layered double hydroxides. It is known to be adsorbed or co-precipitated on the surface of iron oxide and manganese oxide. Forms adsorbed on the surface of iron oxide and manganese oxide are weakly bound to soil particles, so they can be removed by dissolving the nuclides themselves by chemical treatment.

Iodo ( ¹²⁹ I) has oxidation states of -1, 0, +1, +3, and +5. Iodide (I ^- ) and iodate (IO ₃ ^- ) are important inorganic iodine in the surface environment, and methyl iodide is an organic iodine. In soil, iodine is adsorbed by organic matter and Fe- and Al- oxides. At pH > 6, I is mainly adsorbed by soil organic matter, and at pH < 6, I is mainly adsorbed by Fe- and Al- oxides. As before, iodine adsorbed on organic matter and iron oxide can be removed by chemical treatment.

Technetium ( ⁹⁹ Tc) has an oxidation state of -1 to +7, and Tc(VII) and Tc(IV) are the most common oxidation states in the surface environment. Pertechnetate[Tc(VII)O ₄ ^- ] is the most common chemical form in the surface environment and has low reactivity and high mobility. Pertechnetate solubility is about 11 mol/L in an oxidizing environment, and Tc(IV) in the form of co-precipitation with TcO ₂ ·nH ₂ O, TcS ₂ , and Fe-(oxy)hydroxide has a relatively low solubility of 3.08*10 ^-9 mol/L to be. The mobility of Tc in a reducing environment is determined by the solubility of Tc(IV)O ₂ ·nH ₂ O species and is dissolved by acid in an oxidizing environment. The mineral surface of Tc(VII) is very weakly adsorbed, and the adsorbed Tc(VII) is easily desorbed. On the other hand, Tc(IV) is strongly adsorbed and precipitated on the mineral surface. Fe(II)-containing minerals and rocks (magnetite, siderite, granite, gabbro), Fe(III) (oxyhydr)oxide (ferrihydrite, goethite, hematite), Fe sulfide (mackinawite, pyrite, yrrhotite, greigite) adsorb Tc, Reduction and sedimentation to fix Tc in the soil. Phyllosilicates (clay minerals) and organic matter have low adsorption capacity for Tc(IV).

Uranium (U) has various oxidation states (+3, +4, +5, +6), and the oxidation state is determined by the redox potential of the surrounding environment. +4 and +6 are known to be common in the surface environment. U(IV), which is stable in a reducing environment (Eh < 200 mV), exists in the form of uranyl oxide (UO ₂ ) with low solubility and forms a strong complex with organic matter. In a pH < 3 environment, when sufficient amounts of F ^- , Cl ^- , PO ₄ ^3- , and SO ₄ ^2- are present, UF ₂ ²⁺ becomes the dominant species. In the pH > 8 environment, hydrolytic species such as U(OH ^{) 3+} _become dominant regardless of the concentration of F ^- , Cl ^- , PO ₄ ^3- , and SO ₄ ^2- . U(VI), which is stable in an oxidizing environment, exists as uranyl(UO ₂ ²⁺ ) and has high mobility. In an acidic environment, when uranyl ions (UO ₂ ²⁺ ) dominate and pH increases without complexing ions, hydrolysed species [UO ₂ OH ⁺ , UO ₂ (OH) ₂ , (UO ₂ ) ₂ (OH) ₂ ²⁺ ] is created It forms a complex with CO ₃ ^2- , HPO ₄ ^2- , SO ₄ ^2- , organic ligands, and increases the mobility of U. Forms stable complexes with acid biphosphate, bicarbonate, and tricarbonate in neutral-alkaline environments. U(VI) forms a relatively weak complex with organic matter compared to U(IV). Soil adsorption of U shows an increase in the adsorption amount with increasing pH in an acidic environment, and the maximum adsorption amount when pH 5 - 7 is reached. On the other hand, when the pH increases in an alkaline environment, the amount of U adsorption decreases. Organic matter and clay minerals provide a U adsorption site, and organic matter increases the adsorption amount by ion exchange reaction and increases mobility in the soil through complex formation. Iron oxide not only provides a U adsorption site but also coprecipitates with U.

For reference, since cesium (Cs) is an important subject, it will be described in detail later.

In the present invention, the most reasonable method for purifying contaminated soil was developed based on the study on the form and behavior of radionuclides in the soil.

With reference to the accompanying drawings, a method for restoring soil contaminated with radionuclides according to an embodiment of the present invention will be described in more detail.

1 is a schematic flowchart of a method for restoring radionuclide-contaminated soil according to an embodiment of the present invention.

Referring to FIG. 1 , the present invention performs physical treatment after chemical treatment on contaminated soil.

Chemical treatment has two purposes.

In contaminated soil, various soil particles are agglomerated to form soil aggregates, and chemical treatment is carried out for the purpose of dispersing the soil aggregates into individual particles. Dispersing the agglomerates into individual particles through chemical treatment can improve the efficiency when treating individual particles containing radionuclides using a physical method. This is because it is difficult to separate only particles contaminated with nuclides when the soil is aggregated in the form of aggregates. If it is difficult to separate and remove nuclides from particles contaminated with nuclides, the contaminated soil particles themselves should be disposed of. Therefore, reducing the volume of soil to be disposed of by selecting only contaminated soil particles is the most important in the restoration of radioactively contaminated soil. Therefore, it is very important that the soil particles are individually separated and not agglomerated.

Another purpose is to elute and remove radionuclides ( ¹³⁷ Cs, ⁹⁰ Sr, ⁶⁰ Co, ⁹⁹ Tc, ¹²⁹ I, U, etc.) from soil particles during chemical treatment.

In order to disperse soil aggregates into individual soil particles, it is necessary to remove carbonate, organic matter, and iron oxide, which are binding agents that bind soil particles together, and to control the surface charge of soil particles. In the process of dispersing the soil aggregates, various nuclides are eluted. In the chemical treatment, carbonate, organic matter, and iron oxide/manganese oxide, which are aggregate forming agents, are sequentially removed. The process sequence will be described in detail.

First, the carbonate is removed using an acid solution.

Contaminated soil and acid solution are mixed and stirred to form a suspension. In this example, an aqueous solution of hydrochloric acid having a concentration of 0.05 to 0.5 M may be used as the acid solution, and it is determined according to the pH of the soil. The lower the soil pH, the lower the concentration of the aqueous HCl solution, and the higher the soil pH, the higher the concentration of the aqueous HCl solution. The mixing ratio (weight ratio) of the soil and the acid solution is about 1:4-10, and the contaminated soil and the acid solution are reacted for several hours. When the contaminated soil reacts with an acid solution, the carbonate in the soil dissolves. As the carbonate melts, the soil particles that have been aggregated through the carbonate are dispersed. In addition, radionuclides that have formed carbonates such as strontium are dissolved in an acid solution in an ionic state.

Although optional according to the embodiment, in this example, the ultrasonic wave is irradiated so that the soil particles can be better dispersed in the acid solution. For example, ultrasound can be irradiated three times at 450 to 500 J/ml.

When the treatment with the acid solution and ultrasonic irradiation are completed, the soil particles and the acid solution are separated from each other in solid-liquid using a centrifuge or the like. The separated acid solution can be recycled or disposed of as it is or through a separate treatment according to the concentration of nuclides contaminants.

After solid-liquid separation, organic matter is removed from the contaminated soil. Organic matter, like carbonate, acts as an aggregate former in the soil. In order to remove organic matter, in the present invention, a suspension is formed by mixing an aqueous solution containing an oxidizing agent and contaminated soil. The mixing ratio (weight ratio) of the contaminated soil and the oxidizing agent aqueous solution is about 1:4 to 10, and the contaminated soil and the oxidizing agent aqueous solution are reacted for several hours (12 hours in this example). Organic matter in contaminated soil is oxidized and ionized by an oxidizing agent. In this example, the oxidizing agent aqueous solution uses a 6% concentration of sodium hypochlorite (NaOCl) aqueous solution (alkaline pH 8 to 10).

Of course, other materials such as hydrogen peroxide may be used as the oxidizing agent. As organic matter melts, soil aggregation is released, and radionuclides weakly adsorbed to organic matter, such as cesium, or radionuclides that have formed a complex with organic matter, such as cobalt, are dissolved in aqueous solution. When the reaction between the contaminated soil and the oxidizing agent solution is completed, the contaminated soil from which organic matter has been removed through solid-liquid separation is separated as before. The separated oxidizing agent aqueous solution can be recycled again in this process after analyzing the concentration of contaminants as before.

Iron oxide and manganese oxide are removed from contaminated soil from which carbonates and organic matter have been removed. Iron oxide and manganese oxide also act as binders forming soil aggregates. In addition, various radionuclides are adsorbed to iron oxide and manganese oxide. Oxide forms such as iron oxide and manganese oxide do not dissolve well in acid solutions, so a reducing agent is added to dissolve them. That is, an aqueous solution containing a reducing agent and the contaminated soil are mixed and reacted to dissolve iron oxide and manganese oxide in the contaminated soil. In addition, a chelating agent is supplied together to maintain solubility after iron and manganese are melted. In this example, sodium dithionite is used as the reducing agent, sodium citrate is used as the chelating agent, and an aqueous solution is prepared by mixing them with water. In the aqueous solution, sodium dithionite is at a concentration of 1% (mass %), and sodium citrate is at a concentration of 10% (mass %).

The mixing ratio (weight ratio) of the contaminated soil and the aqueous solution is about 1:4 to 10, and the contaminated soil and the reducing agent aqueous solution are reacted for a certain period of time (16 hours in this example). As iron oxide and manganese oxide are melted through the reaction of the contaminated soil with the reducing agent, the radionuclides adsorbed to them are also dissolved in the aqueous solution. In addition, as iron oxide and manganese oxide, which act as binders, are removed, the soil agglomerates are also dismantled. After the reaction is complete, solid-liquid separation is performed. The reducing agent solution can be recycled again as a reducing agent solution after a certain treatment.

As described above, the contaminated soil can be dispersed into individual soil particles by sequentially removing carbonate, organic matter, iron oxide, and manganese oxide, which act as binders forming soil aggregates in the contaminated soil. In addition, in the above-described chemical treatment process, radionuclides bound to or adsorbed to each material are dissolved in an aqueous solution and removed.

In the last stage of chemical treatment, the contaminated soil from which the aggregate forming agent has been removed is washed 2-3 times in a sodium carbonate (Na ₂ CO ₃ ) solution (pH10), and finally, the degree of soil dispersion is checked.

As described above, after the aggregate form is removed from the contaminated soil through chemical treatment and dispersed in the state of individual soil particles, physical treatment is performed. In physical treatment, it is a process of sorting out soil particles containing a lot of radionuclides among soil particles. In the previous chemical treatment, radionuclides were dissolved in an aqueous solution and removed in the process of dispersing the soil. That is, nuclides bound to and adsorbed between carbonate, organic matter, iron oxide, and manganese oxide can be easily removed through a chemical method. However, it is not easy to remove the nuclide in the form that remains in the contaminated soil even after the above chemical treatment methods. This is mainly a radionuclide bound to a 2:1 layered silicate mineral.

The 2:1 layered silicate mineral has a particle size of sand or silt, mainly mica, partially weathered mica: edge weathered mica, mica-vermiculite mixture, mica-kaolonite mixture, vermiculite, vermiculite, There is hydroxy interlayered vermiculite (HIV). And a form having a particle size of clay is mainly composed of smectite.

A 2:1 layered silicate mineral may contain various nuclides, but mainly contains a large amount of cesium. The form in which cesium is bonded to the layered silicate mineral will be described in more detail with reference to FIG. 2 .

¹³⁷ Cs is a nuclear fission product of U-reactor and Pu-reactor, and has a half-life of 30.2 years. It emits β particles and is converted to stable ¹³⁷ Ba, or after passing through ^137m Ba, a daughter nuclide with a short half-life (about 2 minutes) that emits β particles and emits γ-rays, it is changed to ¹³⁷ Ba. It has geochemical behavior similar to that of K in soil and is weakly adsorbed to kaolinite, iron oxide, smectite, and organic matter. On the other hand, it is strongly adsorbed to edge weathered (fred edge) muscovite, biotite, illite, vermiculite, and hydroxy interlayered vermiculite (HIV).

The ¹³⁷ Cs adsorption sites for 2:1 clay minerals, which are known to adsorb a lot of ¹³⁷ Cs in soil, can be divided into five as shown in Fig. 2: 1) basal surface (exchangeable), 2) edge sites (exchangeable) 3) hydrated interlayer sites (exchangeable and nonexchangeable), 4) frayed edge sites (nonexchangeable), 5) interlayer sites (nonexchangeable).

The ¹³⁷ Cs adsorbed to the basal surface and edge sites are capable of ion exchange. On the other hand, ¹³⁷ Cs adsorbed to frayed edge sites and interlayer sites are difficult to ion exchange due to layer collapse and are nonexchangeable. For ^{137 Cs adsorbed to hydrated interlayer sites, the ion exchange potential of adsorbed 137 Cs} is determined by the interlayer charge of the mineral. ¹³⁷ Cs adsorbed to the hydrated interlayer with a large interlayer charge is difficult to ion exchange due to layer collapse and is nonexchangeable. On the other hand, ¹³⁷ Cs adsorbed to the hydrated interlayer with a small interlayer charge is ion-exchangeable. Among the 2:1 clay minerals, illite, edge weathered muscovite (muscovite) and biotite (biotite), and HIV (hydroxide interlayer vermiculite) have frayed edge sites. Vermiculite has hydrated interlayer sites with high interlayer charge, and areas with low weathering progress have frayed edge sites and interlayer sites. Smectite has a hydrated interlayer site with a small interlayer charge.

In summary, ^{137 Cs adsorbed to illite, edge weathered muscovite and biotite, vermiculite, and HIV is difficult to desorb by ion exchange, and 137 Cs} adsorbed to smectite is capable of ion exchange desorption using K ⁺ , NH ₄ ⁺ , etc. Among cesium, most of the forms bound and adsorbed to carbonate, organic matter, iron oxide, manganese oxide and smectite are removed through the previous chemical treatment. However, as described above, the forms that are adsorbed to illite, mica, etc. and are difficult to desorb by ion exchange are difficult to remove by chemical treatment.

However, illite, mica, and the like have a particle size similar to sand or silt, and are concentrated in a specific particle size section. Therefore, in the physical treatment process, the presence of nuclides contamination by soil particle size is first analyzed through particle size separation.

Particle size separation uses a vibrating screen, wet cyclone, etc., and the particle size standard can be set in various ways. It is advantageous in terms of the efficiency of restoration of contaminated soil to subdivide the particle size criteria, but it is disadvantageous in terms of economic feasibility. Therefore, in the present invention, only a part (representative sample) is sampled from the contaminated soil and granular particle size separation is performed to identify the state and condition of the contaminated soil. The table of FIG. 3 is a particle size separation standard for a representative sample.

After particle size separation of the representative sample, the concentration of nuclides, mineral composition, and mineral composition of particles (single mineral particles vs. multi-mineral particles) are identified by group divided by particle size through XRD analysis, microscopic observation, and nuclide concentration analysis. Then, the granularity groups that require post-processing (group 1) and those that do not require post-processing (group 2) are divided. For example, in the table of Fig. 4, the 'selection technology not applicable' areas on the left and the 'within environmental standards' areas on the right are the second group that does not require post-processing, and the middle area is the first group that requires post-processing. can

Through this analysis of the representative samples, when it is determined which treatment is necessary for each particle size group and what is not, then the particle size separation of the entire contaminated soil is carried out. For example, if the analysis result for the representative sample is the same as in the table of FIG. 4 , the particle size separation is performed on the basis of 2 μm or less, 2 μm to 2 mm, or 2 mm or more for the entire contaminated soil.

After particle size separation of the entire contaminated soil, if the nuclide concentration is below the standard (group 2), it can be recycled immediately without special measures. Here, the concentration of the nuclide may be based on the radiation dose. Mostly, gravel with a particle size of 2 mm or more does not contain nuclides. On the other hand, soil fine particles of 2 μm or less are more likely to contain nuclides, but belong to group 2 that does not require treatment. In the case of fine particles, it is difficult to separate particles containing and not containing radionuclides from each other using physical screening technology. Therefore, if a nuclide is included in the fine particle group through analysis and the concentration of nuclide exceeds the standard value, it is disposed of immediately without further purification treatment. Here, the criterion of 2 mm or more or 2 μm or less may be changed. Fine particles can be determined on the order of 1 to 10 μm. If the particle size separation is subdivided, it is possible to more precisely determine the particle size of the group of fine particles to be disposed of immediately without physical treatment. Likewise, a more precise crystallization is possible even in a coarse-grained region that is not contaminated with nuclides.

However, one problem is that as a result of analyzing the mineral composition using XRD and a microscope at the particle size of coarse or gravel, the soil particles take the form of a complex mineral in which multiple minerals are combined, and only certain minerals may be contaminated with nuclides. have. That is, the above-mentioned mica or vermiculite forms a complex mineral together with other minerals, and the nuclide is mainly bound only to mica and vermiculite. Since nuclides are mainly adsorbed to mica and vermiculite, many of these forms may appear in practice. In the present invention, 'unit separation' is performed through a crushing operation for a particle size group corresponding to this case. That is, the complex minerals in which different minerals are combined are pulverized so that the different minerals are separated from each other. Group separation is not performed for fine particles (ex 2μm or less). Since fine particles are difficult to process further, there is no meaning of group separation. Applies only to coarse particles and gravel. However, group separation does not apply to all particle size groups over a certain size, but applies to groups formed of complex minerals.

As described above, when the chemically treated contaminated soil is subjected to particle size separation and group separation, a group requiring subsequent purification treatment and a group not required are determined.

The group that requires post-treatment (group 1) is a group with nuclides having a concentration above the standard value and having a larger particle size than fine particles. As described above, these are mainly 2:1 lamellar silicate minerals such as mica and vermiculite. The nuclide contained in the 2:1 layered silicate mineral is mainly cesium. This is because cesium is adsorbed to 2:1 lamellar silicate minerals and is fixed by adsorption and interlayers, especially slightly weathered biotite, muscovite, vermiculite, and HIV with high layer charge. It is difficult to separate nuclides such as cesium adsorbed in 2:1 layered silicate minerals from soil particles. Therefore, the soil particles themselves including cesium must be sorted and disposed of. This reduces the volume of soil that has to be disposed of.

In the present invention, soil particles contaminated with cesium are selected through magnetic selection and electrostatic selection. In particular, biotite and vermiculite can be separated through magnetic separation, and muscovite and HIV can be separated through electrostatic screening. Therefore, it is possible to separate the lamellar silicate minerals from the contaminated soil by sequentially applying magnetic separation and electrostatic screening. Since nuclides are contained in stratified silicate minerals, contaminated soil can be purified by disposing of them. Magnetic selection and electrostatic selection are well-known techniques, and detailed descriptions thereof will be omitted.

As described above, in the present invention, soil aggregates are disassembled through chemical treatment and dispersed into individual soil particles, and in this process, nuclides weakly bound to soil particles are dissolved and removed. In the case of nuclides that have not been removed by chemical treatment, it is difficult to remove the nuclides itself, so soil particles containing nuclides are separately selected to reduce the volume of soil to be disposed of. That is, after separating the particle size group including the nuclide-contaminated soil particles through soil particle size selection and group separation, only the individual soil particles contaminated with nuclides are separated from the nuclides-contaminated particle size group through magnetic and electrostatic screening. . In this way, the amount of soil to be disposed of can be reduced to a maximum.

On the other hand, in the above, it was explained that the granular particle size separation was first performed by sampling a representative sample during particle size separation of the contaminated soil, and then the particle size separation standard for the entire contaminated soil was determined based on the analysis result. However, this is only an example, and in another example of the present invention, particle size separation can be performed on the entire contaminated soil according to the particle size standard subdivided from the beginning. Alternatively, the particle size separation may be performed on the entire contaminated soil by reducing the number of groups without subdividing the particle size too much in consideration of economic feasibility from the beginning without analyzing the representative sample. It is added that the case of using a representative sample is an example that considers both accuracy and economic feasibility.

The protection scope of the present invention is not limited to the description and expression of the embodiments explicitly described above. In addition, it is added once again that the protection scope of the present invention cannot be limited due to obvious changes or substitutions in the technical field to which the present invention pertains.

Claims (14)

(a) dissolving the agglomeration forming agent that agglomerates soil particles in the contaminated soil by putting the soil contaminated with radionuclides into the treatment aqueous solution, and dissolving the contaminated soil and the aqueous solution into solid-liquid separation from each other;
(b) separating the contaminated soil from which the soil aggregate is dismantled into a plurality of groups according to the particle size;
(c) analyzing the concentration of nuclides for each particle size group and classifying them into a first group requiring subsequent treatment and a second group that does not require subsequent treatment;
(d) selecting only soil particles contaminated with nuclides by applying a physical screening technique to the first group;
The step of dissolving the aggregation includes the step of dissolving the carbonate in the contaminated soil and the nuclides bound to the carbonate by putting the contaminated soil into an acid solution, and then separating the solid and liquid,
The step of resolving the aggregation includes the step of dissolving the organic matter in the contaminated soil and the nuclides bound to the organic matter together by putting the contaminated soil into an aqueous solution containing an oxidizing agent, and then separating the solid and liquid,
The oxidizing agent for removing the organic material is sodium hypochlorite (NaOCl), and the aqueous solution containing the oxidizing agent is in the range of pH 8 to 10,
The step of resolving the aggregation comprises dissolving the contaminated soil into an aqueous solution containing a reducing agent and a chelating agent, dissolving the iron oxide and manganese oxide in the contaminated soil, and the nuclides bound to the iron oxide and the manganese oxide, followed by solid-liquid separation,
After separating the contaminated soil by particle size, it is analyzed whether the particle size group contaminated with the nuclide consists of a complex mineral combined with different minerals. Further comprising the step of group separation so that the minerals are separated from each other,
The physical screening technology is a magnetic separation technology and an electrostatic screening technology, wherein the magnetic separation technology is used to separate biotite and vermiculite, and the electrostatic screening technology is used to separate muscovite and HIV (hydroxy interlayered vermiculite). A method for restoring soil contaminated with radionuclides. delete According to claim 1,
A method of restoring radionuclide-contaminated soil, characterized in that by irradiating ultrasonic waves to the suspension made by adding the contaminated soil to the acid solution. delete delete delete According to claim 1,
The reducing agent for dissolving and removing the iron oxide and manganese oxide is sodium dithionite (Na ₂ S ₂ O ₄ ). According to claim 1,
The chelating agent used to dissolve and remove the iron oxide and manganese oxide is sodium citrate (Na ₃ C ₆ H ₅ O ₇ ) A radionuclide-contaminated soil restoration method, characterized in that it is. delete According to claim 1,
After removing carbonate, organic matter, iron oxide and manganese oxide from the contaminated soil, washing the contaminated soil with a washing solution and checking the dispersion of soil particles. According to claim 1,
After performing particle size separation into a plurality of groups by sampling a part of the contaminated soil as a representative sample, and dividing it into a group requiring follow-up treatment and a group not requiring follow-up treatment through analysis of the concentration of nuclides contamination,
Radionuclide-contaminated soil restoration method, characterized in that the particle size separation is performed on the entire contaminated soil by dividing the particle size groups into smaller numbers than the number of particle size separation groups for the representative sample based on the analysis result of the representative sample . delete According to claim 1,
The second group includes fine particles contaminated with nuclides,
The fine particles are radionuclide-contaminated soil restoration method, characterized in that the particle size is less than or equal to any one of the particle sizes in the range of 1 to 10 μm. According to claim 1,
The second group is a radionuclide-contaminated soil restoration method, characterized in that it contains gravel of 2 mm or more.

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