KR20210026517A - Method and system for contamination of uranium-contaminated particle - Google Patents

Abstract

The present invention relates to a method and a system for decontamination of uranium-contaminated particulate matter. The method for decontamination of uranium-contaminated particulate matter comprises the steps of: (a) mixing uranium-contaminated particulate matter with a carbon source to manufacture a mixture; (b) chlorinating the mixture in a dry state at 400 to 700°C to produce uranium chloride; and (c) condensing the uranium chloride. Therefore, the cost of disposing of radioactive waste can be dramatically reduced.

Description

Method and system for decontamination of particulate matter contaminated with uranium {METHOD AND SYSTEM FOR CONTAMINATION OF URANIUM-CONTAMINATED PARTICLE}

The present invention relates to a method and system for decontamination of particulate matter (soil, concrete, etc.) contaminated with uranium.

In Korea, from the viewpoint of radioactive waste, it is a general concept to remove uranium from the soil contaminated with uranium through decontamination and then dispose of the soil itself. It covers the affected area and manages the area.

The technology to remove uranium from soil contaminated with uranium mainly consists of a washing process using acid or alkali, which is one of the soil restoration technologies, and a representative one of which is the hybrid electrokinetic technology developed by the Korea Atomic Energy Research Institute. Specifically, the hybrid coinage technology applies the concept of converting uranium into a dissolved state through pickling, and disposing of the dissolved uranium after it is recovered using precipitation or ion exchange resin. Among them, when it is impossible to meet the self-disposal criteria of radioactivity concentration only by washing, the electrokinetic technology that uses the phenomenon of movement in an electric field is applied so that the self-disposal criteria can be satisfied.

Combined copper technology has proven to be efficient in decontamination of uranium-contaminated soil and concrete with 80% reduction rate and self-disposal standards. As it can act as a problem in the situation, research on an alternative to this is necessary.

Kim et al., J. Environ. Rad. 164, 239-244, 2016

The present invention is a technology for decontaminating particulate matter (soil, concrete, etc.) contaminated with uranium through a dry process, specifically, a method and system for decontaminating particulate matter contaminated with uranium by introducing a chlorination reaction. I want to provide.

However, the technical problem to be achieved by the present invention is not limited to the problems mentioned above, and other problems that are not mentioned will be clearly understood by those skilled in the art from the following description.

The present invention comprises the steps of: (a) preparing a mixture by mixing particulate matter contaminated with uranium with a carbon source; (b) chlorinating the mixture at 400°C to 700°C in a dry state to produce uranium chloride; And (c) condensing the uranium chloride.

In one embodiment of the present invention, a mixer for mixing particulate matter contaminated with uranium and a carbon source; A chlorination reactor for producing uranium chloride by chlorinating the mixture at 400°C to 700°C in a dry state; And a condenser for condensing the uranium chloride.

The decontamination method and system according to the present invention comprises the steps of: (a) preparing a mixture by mixing particulate matter contaminated with uranium with a carbon source; (b) chlorinating the mixture at 400°C to 700°C in a dry state to produce uranium chloride; And (c) comprising the step of condensing the uranium chloride, the uranium oxide _{can be recovered as uranium chloride (UCl 5} , UCl _6, etc.), it is possible to easily decontaminate particulate matter contaminated with uranium. Has an advantage. At this time, it has the advantage of suppressing the chlorination reaction of silicon oxide or aluminum oxide, which is the main component of the particulate matter.

Therefore, ① it is possible to drastically reduce the cost of disposing of radioactive waste. Specifically, a disposal cost of about 200 billion won is required based on 10,000 drums of radioactive waste. However, since the recovered product (a mixture of condensed uranium chloride and iron chloride) recovered from the condenser of the decontamination system according to the present invention can be separated only uranium through distillation and refining, disposal costs do not occur. Even without such distillation and refining, and solidification treatment, radioactive waste is only about 6% (600 drums, disposal cost of 12 billion won) compared to the prior art. In addition, the reduction of the disposal burden of domestic radioactive waste storage facilities can be evaluated as an additional effect in addition to the economic aspect.

In addition, ② it is possible to build a large-capacity small facility. Conventional hybrid electric technology requires a processing time of about 30 days, resulting in an enlarged facility. However, in the case of the chlorination reaction of the decontamination method according to the present invention, since the reaction time is short, it is possible to construct a compact and large-capacity facility. Therefore, since the process can be modularized to construct a mobile facility, there is an advantage of being able to move and operate in a place where decontamination is required. Conventional hybrid electric technology requires a treatment time of 30 days per 800 L module, so if it can treat 4 drums of soil per month, in the case of the chlorination reaction of the decontamination method according to the present invention, 200 L according to the process design. The scale unit process can treat 30 drums of soil per month. It is expected that the processing capacity can be increased if process optimization is carried out.

1 is a schematic diagram showing a decontamination system according to an embodiment of the present invention.
FIG. 2 is a photograph showing the recovered material recovered from the condenser as a result of a simulation experiment on the very low level general soil (0.2 Bq U/g) according to Example 1. FIG.

In order to decontaminate particulate matter such as soil and concrete contaminated with uranium (at the level of several tens to several thousand ppm), the present inventors introduced a chlorination reaction under optimized temperature conditions as a dry process rather than a wet process such as the conventional composite electrokinetic technology. It was confirmed that, while suppressing the chlorination reaction of silicon oxide or aluminum oxide _{, it was confirmed that uranium oxide can be recovered as uranium chloride (UCl 5} , UCl _6, etc.), and the present invention was completed.

In the present specification, "uranium" is a radioactive metal, and in its natural state, three types of isotopes such as U-234, U-235, and U-238 are representative, and all of them undergo alpha decay. Uranium has the same chemical properties of the isotopes, so the type of isotope present does not affect the applicability of the process. The uranium may be contaminated in the form of uranium oxide in particulate matter such as soil and concrete, at this time, the uranium oxide from the group consisting of UO, UO ₂ , U ₂ O ₅ , U ₃ O ₈ , UO ₃ and mixtures thereof. It may be one or more selected.

Hereinafter, the present invention will be described in detail.

Decontamination method of particulate matter contaminated with uranium

The present invention comprises the steps of: (a) preparing a mixture by mixing particulate matter contaminated with uranium with a carbon source; (b) chlorinating the mixture at 400°C to 700°C in a dry state to produce uranium chloride; And (c) condensing the uranium chloride.

First, the decontamination method according to the present invention includes a step [step (a)] of preparing a mixture by mixing particulate matter contaminated with uranium with a carbon source.

The particulate material is a concept including soil contaminated by uranium, concrete (in the form of crushed material), and the like, and the particulate material is silicon oxide, aluminum oxide, potassium oxide, iron oxide, phosphorus oxide, calcium oxide, in addition to uranium oxide. , Sodium oxide, magnesium oxide, and a mixture thereof, may include at least one selected from the group consisting of, wherein the particulate material may include silicon oxide and aluminum oxide as main components, the total weight of the particulate material With respect to, the content of the silicon oxide and the aluminum oxide is more preferably 80% by weight to 90% by weight, but is not limited thereto. Such silicon oxide and aluminum oxide must suppress the chlorination reaction described later.

Examples of specific components for the particulate matter (general soil) are shown in Table 1 below. Of course, the specific components of the particulate matter may vary according to characteristics of soil, concrete, and the like.

Concrete ingredients Content (% by weight) SiO ₂ 68.1 Al ₂ O ₃ 16.7 K ₂ O 8.27 Fe ₂ O ₃ 2.2 P ₂ O ₂ 1.63 CaO 1.51 Na ₂ O 0.97 MgO 0.21

The carbon source is to promote the chlorination reaction described later by removing oxygen in the uranium oxide contained in the particulate material, _{and may include both solid materials or gaseous materials, but gaseous materials such as CCl 4} have their own toxicity. Therefore, it is preferably a solid material such as activated carbon or graphite. The carbon source may be included as an organic material in the particulate material itself.

In addition, the average particle size of the carbon source needs to be optimized in consideration of the reaction surface area. The average particle size of the carbon source may be 100 µm to 400 µm, preferably 200 µm to 350 µm, but is not limited thereto.

In addition, the amount of the carbon source added to the total weight of the particulate material needs to be optimized in consideration of the content of iron oxide and potassium oxide and the concentration of uranium in the particulate material. Since the specific components of the particulate matter vary according to the properties of soil, concrete, etc., the amount of the carbon source added to the total weight of the particulate matter may also vary. However, based on the case where the particulate matter is a general soil as shown in Table 1, the amount of the carbon source added to the total weight of the particulate matter may be 5% by weight to 20% by weight, and 8% to 15% by weight. It is preferable that it is% by weight, but is not limited thereto.

The mixing of the particulate matter and the carbon source can be carried out through a mixer, in particular, a homogenizing device.

Next, the decontamination method according to the present invention includes the step of producing uranium chloride by chlorinating the mixture at 400°C to 700°C in a dry state [Step (b)].

The chlorination reaction corresponds to a dry process without using water, and may be performed at 400°C to 700°C, preferably at 400°C to 600°C, and more preferably at 450°C to 550°C. However, it is not limited thereto. At this time, when the temperature of the chlorination reaction is too low, there _{is a problem in that uranium chloride (UCl 5} , UCl _6, etc.) cannot be generated from the uranium oxide, and when the temperature of the chlorination reaction is too high, the chlorination of silicon oxide or aluminum oxide The reactions come together and cause process failure.

The chlorination reaction may be performed using a chlorination reactor, and the chlorination reactor may be a column or a stirred-type complete mixing reactor, but is preferably a column in order to minimize weathering of the particulate matter, but is not limited thereto. In addition, the chlorination reaction may be changed to an upward flow type or a downward flow type, if necessary.

For the chlorination reaction, chlorine gas is supplied. When the chlorination reaction is performed for 5 hours based on 1 kg of the particulate matter, the flow rate of the chlorine gas may be 100 ml/min to 500 ml/min, and the gas circulation system The use of chlorine will be reduced if the system is optimized by applying.

The uranium chloride may be released from the particulate matter in a gaseous form vaporized by chlorine gas, and the uranium chloride may include uranium contaminant, uranium hexachloride, or a mixture thereof. Considering that uranium hexachloride with a boiling point of about 75°C is evaporated immediately after formation, uranium contaminated with a boiling point of about 527°C may be a major product. Meanwhile, among uranium chlorides, uranium tetrachloride has a high boiling point of about 791°C, so volatilization is not easy. Therefore, if the process temperature is set high to recover uranium tetrachloride, the chlorination reaction of silicon oxide or aluminum oxide occurs together, which causes process failure.

Based on the uranium oxide U ₃ O ₈ contained in the particulate material, the chlorination reaction equation is shown in Equation 1 below, and the Gibbs free energy (ΔG) at 500° C. is -212.5 kcal.

U ₃ O ₈ + 4C + 7.5Cl ₂ (g) = 3UCl ₅ (g) + 4CO ₂ (g) (Equation 1)

On the other hand, based on each of the specific components included in the particulate matter, the expected chlorination reaction equation and Gibbs free energy (ΔG) at 500 ℃ are shown in Table 2.

Expected reaction formula Gibbs free energy at 500℃ (ΔG)(kcal) SiO ₂ + C + 2Cl ₂ (g) = SiCl ₄ (g) + CO ₂ (g) (Equation 2) -44.3 Al ₂ O ₃ + 1.5C + 3Cl ₂ (g) = 2AlCl ₃ + 1.5CO ₂ (g) (Equation 3) -57.4 2K ₂ O + C + 2Cl ₂ (g) = 4KCl + CO ₂ (g) (Equation 4) -320.4 Fe ₂ O ₃ + 1.5C + 3Cl ₂ (g) = 2FeCl ₃ (g) + 1.5CO ₂ (g) (Equation 5) -107.7 P ₂ O ₂ + C + 2Cl ₂ (g) = 2PCl ₂ + CO ₂ (g) (Equation 6) No data 2CaO + C + 2Cl ₂ (g) = 2CaCl ₂ + CO ₂ (g) (Equation 7) -153.8 2Na ₂ O + C + 2Cl ₂ (g) = 4NaCl + CO ₂ (g) (Equation 8) -269.9 MgO + C + 2Cl ₂ (g) = 2MgCl ₂ + CO ₂ (g) (Equation 9) -95.2

As shown in Table 2, since the Gibbs free energy (ΔG) is different at 500° C. for each specific component contained in the particulate material, it cannot be said that the chlorination reaction always occurs at 500° C. When the particulate matter contains silicon oxide or aluminum oxide as a main component, the silicon chloride or aluminum chloride is preferably not produced. According to a conventional report, it is confirmed that a temperature of 700° C. or higher is required for the chlorination reaction such as Equations 2 and 3, but since the chlorination reaction is performed at 400° C. to 700° C. in the present invention, chlorination such as Equations 2 and 3 It can inhibit the reaction.

Meanwhile, when the particulate material contains iron oxide, iron chloride having a boiling point of about 316° C. may be produced as an impurity together with the uranium chloride, which may be condensed as described later.

Next, the decontamination method according to the present invention further includes the step of condensing the uranium chloride [step (c)].

The uranium chloride and, optionally, the iron chloride can be recovered in solid form through condensation. The condensation may be performed using a condenser operated at room temperature, and a cooling device may be operated as needed. The recovered product recovered from the condenser may include the condensed uranium chloride and, optionally, the condensed iron chloride.

Optionally, the decontamination method according to the present invention may further include washing and neutralizing the particulate matter decontaminated by generation and condensation of the uranium chloride [step (d)].

The neutralization is for neutralization of the particulate matter or for the removal of solid chlorides generated according to Table 2. At this time, the generated waste liquid is treated as a general waste liquid, not a radioactive waste liquid, and can be regenerated using an ion exchange resin. .

The neutralization may be performed using a neutralization tank, and the neutralization tank may be a column or a stirred-type complete mixing reactor, but it is preferably a column in order to minimize weathering of the particulate matter, but is not limited thereto.

In addition, the neutralization may be _{performed using a Na 2} CO ₃ and NaHCO ₃ mixed solution or a NaHCO ₃ solution, thereby minimizing the use of chemicals and excluding the effect on the environment.

Optionally, the decontamination method according to the present invention may further include distilling and refining the condensed uranium chloride [step (e)].

The condensed uranium chloride and, optionally, the condensed iron chloride, can be distilled and refined, and since only uranium can be separated through the chloride distillation and uranium refining, the disposal cost of disposing of radioactive waste may not be incurred. At this time, a known technique may be applied for distillation and refining.

On the other hand, since there are many legal considerations due to the nature of uranium handling, such distillation and refining may be impossible. Accordingly, even if the solidification treatment is performed, radioactive waste is only about 6% (600 drums, disposal cost of 12 billion won) compared to the prior art.

Decontamination system for particulate matter contaminated with uranium

The present invention is a mixer for mixing the particulate matter and carbon source contaminated with uranium; A chlorination reactor for producing uranium chloride by chlorinating the mixture at 400°C to 700°C in a dry state; And a condenser for condensing the uranium chloride.

1 is a schematic diagram showing a decontamination system according to an embodiment of the present invention. As shown in FIG. 1, the decontamination system according to an embodiment of the present invention is a mixer for mixing particulate matter contaminated with uranium and a carbon source. (10); A chlorination reactor 20 for producing uranium chloride by chlorinating the mixture at 400°C to 700°C in a dry state; And a condenser 30 for condensing the uranium chloride.

The decontamination system according to the invention comprises a mixer, a chlorination reactor and a condenser.

First, the mixer is for mixing particulate matter and carbon source contaminated with uranium, and specifically, may be a homogenization device.

In addition, the chlorination reactor is for producing uranium chloride by chlorinating the mixture at 400°C to 700°C in a dry state. Specifically, it may be a column or a stirred type complete mixing reactor, but the weathering of the particulate matter is minimized. In order to do so, it is preferably a column, but is not limited thereto. In addition, the chlorination reaction may be changed to an upward flow type or a downward flow type, if necessary.

In addition, the condenser is for condensing the uranium chloride and, optionally, the iron chloride, and may be operated at room temperature, and a cooling device may be operated if necessary.

In addition, the decontamination system according to the present invention may further include a neutralization tank and a distillation and refining device.

As described above, the decontamination method and system according to the present invention comprises the steps of: (a) preparing a mixture by mixing particulate matter contaminated with uranium with a carbon source; (b) chlorinating the mixture at 400°C to 700°C in a dry state to produce uranium chloride; And (c) comprising the step of condensing the uranium chloride, the uranium oxide _{can be recovered as uranium chloride (UCl 5} , UCl _6, etc.), it is possible to easily decontaminate particulate matter contaminated with uranium. Has an advantage. At this time, it has the advantage of suppressing the chlorination reaction of silicon oxide or aluminum oxide, which is the main component of the particulate material.

Therefore, ① it is possible to drastically reduce the cost of disposing of radioactive waste. Specifically, a disposal cost of about 200 billion won is required based on 10,000 drums of radioactive waste. However, since the recovered product (a mixture of condensed uranium chloride and iron chloride) recovered from the condenser of the decontamination system according to the present invention can be separated only uranium through distillation and refining, disposal costs do not occur. Even without such distillation and refining, and solidification treatment, radioactive waste is only about 6% (600 drums, disposal cost of 12 billion won) compared to the prior art. In addition, the reduction of the disposal burden of domestic radioactive waste storage facilities can be evaluated as an additional effect in addition to the economic aspect.

In addition, ② it is possible to build a large-capacity small facility. Conventional hybrid electric technology requires a processing time of about 30 days, resulting in an enlarged facility. However, in the case of the chlorination reaction of the decontamination method according to the present invention, since the reaction time is short, it is possible to construct a compact and large-capacity facility. Therefore, since the process can be modularized to construct a mobile facility, there is an advantage of being able to move and operate in a place where decontamination is required. Conventional hybrid electric technology requires a treatment time of 30 days per 800 L module, so if it can treat 4 drums of soil per month, in the case of the chlorination reaction of the decontamination method according to the present invention, 200 L according to the process design. The scale unit process can treat 30 drums of soil per month. It is expected that the processing capacity can be increased if process optimization is carried out.

Hereinafter, a preferred embodiment is presented to aid the understanding of the present invention. However, the following examples are provided for easier understanding of the present invention, and the contents of the present invention are not limited by the following examples.

[Example]

The decontamination technology of uranium-contaminated soil must be able to meet the self-disposal criteria (1.0 Bq U/g or less). A simulation was conducted on ultra-low-level general soil (0.2 Bq U/g), not uranium-contaminated soil. can do.

Specifically, about 1 kg of ultra-low level general soil (0.2 Bq U/g) and about 100 g of activated carbon were mixed using a homogenizing vessel. Then, by performing a chlorination reaction for 5 hours at 500°C in _{an Ar atmosphere and a supply of about 300 ml Cl 2} gas in an Ar atmosphere using a chlorination column to generate gaseous uranium chloride and impurities, a condensator (condensator) ) To condense gaseous uranium chloride and impurities, and then wash to reduce the radioactive concentration of uranium. The results are shown in Table 3.

division Weight(g) U-238 (Bq/g) U-235 (Bq/g) U-234 (Bq/g) Total U (Bq/g) Early 493.8 9.34x10 ^-2 4.36x10 ^-3 9.62x10 ^-2 1.94x10 ^-1 After chlorination reaction 465.0 7.75x10 ^-2 3.62x10 ^-3 7.98x10 ^-2 1.61x10 ^-1 After condensation and washing 463.5 7.34x10 ^-2 3.42x10 ^-3 7.56x10 ^-2 1.52x10 ^-1

As shown in Table 3, it was confirmed that uranium was removed through a chlorination reaction. Specifically, the radioactivity concentration of uranium decreased by about 17% ^{from 1.94 x 10 -1} Bq/g to 1.61 x 10 ^{-1 Bq/g.} This means that uranium-contaminated soil can be treated with 0.2 Bq U/g or less only by the chlorination reaction.

On the other hand, if impurities such as silicon chloride or aluminum chloride are generated, silicon chloride (boiling point 57.65 ℃) and aluminum chloride (boiling point 180) ℃) volatilizes to cause weight loss.According to Table 3, the weight loss after the chlorination reaction was about 5.8%, which _{is due to the consumption of Fe 2} O ₃ and carbon, which accounts for 2.2%, and loss during handling, which contributes to a very small extent. It may have been, but it is difficult to see it as a weight loss due to volatilization of _{SiO 2} and Al ₂ O _3. In addition, it was confirmed that there was little reduction in weight after washing the soil sample after chlorination, which means that chlorination of other elements such as _{K 2 O, which accounts for about 8%, did not proceed.} If it is present as chloride, a significant weight loss should be observed due to high solubility during washing, but this is not the case. In conclusion, the reaction conditions applied in the present invention mean that the influence of side reactions excluding _{Fe 2} O _{3 in uranium chlorination is very small.}

On the other hand, although not shown in Table 3, it is confirmed that the radioactive concentrations of K-40 and Cs-137 relatively increase because the weight decreases due to the components removed through the chlorination reaction. This is because K-40 and Cs-137 do not vaporize even when chlorinated and remain in the soil.

FIG. 2 is a photograph showing the recovered material recovered from the condenser as a result of a simulation experiment on ultra-low level general soil (0.2 Bq U/g) according to Example 1. FIG.

As shown in FIG. 2, it was confirmed that the main component of the recovered product recovered from the condenser was FeCl ₃ ·6H _{2 O (yellow).} This can be seen as a result of the chlorination reaction of uranium oxide contained in the soil, as well as the result of vaporization and condensation of _{Fe 2} O _{3 after the chlorination reaction.}

The above description of the present invention is for illustrative purposes only, and those of ordinary skill in the art to which the present invention pertains will be able to understand that other specific forms can be easily modified without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative and non-limiting in all respects.

Claims (8)

(a) preparing a mixture by mixing particulate matter contaminated with uranium with a carbon source;
(b) chlorinating the mixture at 400°C to 700°C in a dry state to produce uranium chloride; And
(c) condensing the uranium chloride.
Decontamination method of particulate matter contaminated with uranium.
The method of claim 1,
In the step (a), the particulate material is uranium, comprising at least one selected from the group consisting of silicon oxide, aluminum oxide, potassium oxide, iron oxide, phosphorus oxide, calcium oxide, sodium oxide, magnesium oxide, and mixtures thereof. Decontamination method of contaminated particulate matter.
The method of claim 1,
When the particulate material includes silicon oxide or aluminum oxide in the step (a), silicon chloride or aluminum chloride is not produced in the step (b), a method for decontaminating particulate matter contaminated with uranium.
The method of claim 1,
When the particulate material contains iron oxide in the step (a), the decontamination method of the particulate material contaminated with uranium by generating and condensing iron chloride together with uranium chloride in steps (b) and (b) .
The method of claim 1,
In the step (a), the average particle size of the carbon source is 100 ㎛ to 400 ㎛, the method for decontamination of particulate matter contaminated with uranium.
The method of claim 1,
In the step (b), the uranium chloride is a method for decontaminating particulate matter contaminated with uranium, including uranium contaminated product, uranium hexachloride, or a mixture thereof.
The method of claim 1,
(d) a method of decontaminating particulate matter contaminated with uranium, further comprising washing and neutralizing the particulate matter decontaminated by generation and condensation of the uranium chloride.
A mixer for mixing particulate matter contaminated with uranium and a carbon source;
A chlorination reactor for producing uranium chloride by chlorinating the mixture at 400°C to 700°C in a dry state; And
Containing a condenser for condensing the uranium chloride
A system for decontamination of particulate matter contaminated with uranium.

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