KR102371470B1 - Method and system for contamination of uranium-contaminated particle - Google Patents

Abstract

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

Description

Method and system for decontamination of particulate matter contaminated with uranium

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 through decontamination and then dispose of the soil by itself. It is taking the method of managing the area by covering it with soil in the affected area.

The technology to remove uranium from uranium-contaminated soil mainly consists of a cleaning process using acid or alkali, one of the soil restoration technologies, and a representative one of them is the complex electrokinetic technology developed by the Korea Atomic Energy Research Institute. Specifically, the complex electrokinetic technology applies the concept of converting uranium to a dissolved state through pickling, and disposing of uranium in a dissolved state after recovery using precipitation or ion exchange resin. Among them, if it is impossible to meet the standards for self-disposal of radioactivity concentration by washing alone, electrokinetic technology using the phenomenon of movement in an electric field is applied to treat the standards to meet the standards for self-disposal.

Combined galvanic technology has been proven to be effective in decontamination of uranium-contaminated soil and concrete with a reduction rate of 80% and meeting self-disposal standards. can act as a problem, and research on alternatives is needed.

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

The present invention is a technology for decontamination of particulate matter (soil, concrete, etc.) contaminated with uranium through a dry process. Specifically, a method and system for decontamination of particulate matter contaminated with uranium by introducing a chlorination reaction would like to provide

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

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

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

A decontamination method and system according to the present invention comprises the steps of (a) mixing particulate matter contaminated with uranium with a carbon source to prepare a mixture; (b) chlorinating the mixture in a dry state at 400° C. to 700° C. to produce uranium chloride; and (c) condensing the uranium chloride, so that uranium oxide can be recovered as uranium chloride (UCl ₅ , UCl ₆ , etc.), so that particulate matter contaminated with uranium can be simply decontaminated have an advantage In this case, the chlorination reaction of silicon oxide or aluminum oxide, which is a main component of the particulate material, can be suppressed.

Therefore, ① it is possible to dramatically 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 only uranium can be separated from the recovered product (a mixture of condensed uranium chloride and iron chloride) from the condenser of the decontamination system according to the present invention through distillation and refining, there is no disposal cost. Even if such distillation and refining are not performed and solidification treatment is performed, the amount of 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 other than the economic aspect.

In addition, ② it is possible to build a large-capacity small facility. The conventional hybrid electromotive technology requires about 30 days of processing time, so the equipment becomes bloated. 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 miniaturized large-capacity facility. Therefore, since the process can be modularized and a mobile facility can be built, there is an advantage that it can be moved and operated at a place requiring decontamination. Since the conventional hybrid electrokinetic technology requires 30 days of processing time per 800 L module, if 4 drums of soil can be treated 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 performing a simulation experiment on 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 (tens to thousands of ppm), the present inventors introduced a chlorination reaction under optimized temperature conditions as a dry process rather than a wet process such as conventional combined electromotive technology. As a result, 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 the natural state, three types of isotopes such as U-234, U-235 and U-238 are representatively present, and all of them undergo alpha decay. Since uranium has the same chemical properties of isotopes, the type of isotope present does not affect the applicability of the process. The uranium may be contaminated with particulate matter such as soil and concrete in the form of uranium oxide, in this case, the uranium oxide is 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.

Method for decontamination of particulate matter contaminated with uranium

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

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

The particulate material is a concept including soil and concrete (in the form of crushed material) contaminated by uranium, 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 at least one selected from the group consisting of mixtures thereof, 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 wt% to 90 wt%, but is not limited thereto. The chlorination reaction described later must be suppressed in these silicon oxides and aluminum oxides.

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

specific ingredients Content (wt %) 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 for accelerating the chlorination reaction to be described later by removing oxygen in the uranium oxide contained in the particulate material, and may include both a solid material or a gaseous material, but a gaseous material such as CCl ₄ has its own toxicity Since it is subject to regulation, it is preferable that it is 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, and 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 addition amount of the carbon source with respect to the total weight of the particulate material needs to be optimized in consideration of the iron oxide and potassium oxide contents and the concentration of uranium in the particulate material. Since specific components of the particulate material vary depending on characteristics of soil, concrete, and the like, the amount of the carbon source added to the total weight of the particulate material may also vary. However, based on the case where the particulate material is general soil as shown in Table 1, the amount of the carbon source added to the total weight of the particulate material may be 5 wt% to 20 wt%, and 8 wt% to 15 wt% It is preferred that the weight %, but is not limited thereto.

The mixing of the particulate material and the carbon source may be performed through a mixer, in particular, a homogenizer.

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

The chlorination reaction corresponds to a dry process that does not use 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, the present invention 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 uranium oxide, and when the temperature of the chlorination reaction is too high, chlorination of silicon oxide or aluminum oxide Reactions co-exist 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 complete mixing reactor, but preferably a column in order to minimize weathering of the particulate material, but is not limited thereto. In addition, the chlorination reaction may be changed to an up-flow type or a down-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 material, the flow rate of the chlorine gas may be 100 ml/min to 500 ml/min, and the gas circulation system Chlorine consumption will be reduced if the system is optimized by applying

The uranium chloride may be separated from the particulate material in a gaseous form vaporized with chlorine gas, and the uranium chloride may include uranium contamination, uranium hexachloride, or a mixture thereof. Considering that uranium hexachloride having a boiling point of about 75° C. is vaporized immediately after formation, a uranium pentachloride having a boiling point of about 527° C. can be the main product. On the other hand, 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, causing 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) (Formula 1)

On the other hand, based on each specific component included in the particulate material, the expected chlorination reaction equation and Gibbs free energy (ΔG) at 500 °C are shown in Table 2.

expected reaction equation Gibbs free energy (ΔG) (kcal) at 500 °C 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) (Formula 5) -107.7 P ₂ O ₂ + C + 2Cl ₂ (g) = 2PCl ₂ + CO ₂ (g) (Equation 6) Absence of 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) at 500°C is different for each specific component included in the particulate material, the chlorination reaction cannot necessarily occur at 500°C. When the particulate material contains silicon oxide or aluminum oxide as a main component, it is preferable that the silicon chloride or aluminum chloride is not produced. According to prior reports, it is confirmed that a temperature of 700 ° C or higher is required for the chlorination reaction as in Equations 2 and 3, but in the present invention, since the chlorination reaction is performed at 400 ° C to 700 ° C, chlorination as in Equations 2 and 3 reaction may be inhibited.

Meanwhile, when the particulate material includes 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 below.

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

The uranium chloride and optionally the iron chloride may 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 if necessary. 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 comprise washing and neutralizing the decontaminated particulate matter by the generation and condensation of the uranium chloride [step (d)].

The neutralization is for the neutralization of the particulate material or the removal of the solid chloride generated according to Table 2, in which case 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 complete mixing reactor, but preferably a column in order to minimize weathering of the particulate material, but is not limited thereto.

In addition, the neutralization may be performed using a Na ₂ CO ₃ and NaHCO ₃ mixed solution or NaHCO ₃ solution, thereby minimizing the use of chemicals to exclude an impact on the environment.

Optionally, the decontamination method according to the present invention may further comprise 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 only uranium can be separated through the chloride distillation and uranium refining, so that the cost of disposing of radioactive waste may not occur. At this time, for distillation and refining, a known technique may be applied.

On the other hand, such distillation and refining may not be possible because there are many legal considerations due to the nature of uranium handling. Accordingly, even with solidification treatment, the amount of 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 provides a mixer for mixing uranium-contaminated particulate matter and a carbon source; a chlorination reactor for chlorinating the mixture in a dry state at 400° C. to 700° C. to produce uranium chloride; 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 chlorinating the mixture at 400° C. to 700° C. in a dry state to produce uranium chloride; and a condenser 30 for condensing the uranium chloride.

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

First, the mixer is for mixing the uranium-contaminated particulate matter and the carbon source, and specifically, may be a homogenizer.

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 stirred complete mixing reactor, but the weathering of the particulate material is minimized In order to do so, it is preferable that it is a column, but it is not limited thereto. In addition, the chlorination reaction may be changed to an up-flow type or a down-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 may operate a cooling device if necessary.

In addition, the decontamination system according to the present invention may be configured to 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) mixing uranium-contaminated particulate matter with a carbon source to prepare a mixture; (b) chlorinating the mixture in a dry state at 400° C. to 700° C. to produce uranium chloride; and (c) condensing the uranium chloride, so that uranium oxide can be recovered as uranium chloride (UCl ₅ , UCl ₆ , etc.), so that particulate matter contaminated with uranium can be simply decontaminated have an advantage In this case, the chlorination reaction of silicon oxide or aluminum oxide, which is a main component of the particulate material, can be suppressed.

Therefore, ① it is possible to dramatically 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 only uranium can be separated from the recovered product (a mixture of condensed uranium chloride and iron chloride) from the condenser of the decontamination system according to the present invention through distillation and refining, there is no disposal cost. Even if such distillation and refining are not performed and solidification treatment is performed, the amount of 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 other than the economic aspect.

In addition, ② it is possible to build a large-capacity small facility. The conventional hybrid electromotive technology requires about 30 days of processing time, so the equipment becomes bloated. 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 miniaturized large-capacity facility. Therefore, since the process can be modularized and a mobile facility can be built, there is an advantage that it can be moved and operated at a place requiring decontamination. Since the conventional hybrid electrokinetic technology requires 30 days of processing time per 800 L module, if 4 drums of soil can be treated 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, preferred examples are presented to help the understanding of the present invention. However, the following examples are only 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 standard (1.0 Bq U/g or less). A simulation was conducted on very low level general soil (0.2 Bq U/g), not uranium-contaminated soil, and if the radioactivity concentration of uranium can be reduced in very low level general soil, it is guaranteed to meet the self-disposal standard even in 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, a chlorination reaction is performed at 500° C. for 5 hours in a dry state under an Ar atmosphere and about 300 ml Cl ₂ gas supply using a chlorination column to generate gaseous uranium chloride and impurities, and then a condenser (condensator) ) was used to condense gaseous uranium chloride and impurities, and then washed to reduce the radioactivity 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 465.0 7.75x10 ^-2 3.62x10 ^-3 7.98x10 ^-2 1.61x10 ^-1 After condensing and washing 463.5 7.34x10 ^-2 3.42x10 ^-3 7.56x10 ^-2 1.52x10 ^-1

As shown in Table 3, it is confirmed that uranium is removed through the chlorination reaction. Specifically, the radioactive 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 only 0.2 Bq U/g of uranium-contaminated soil can be treated by chlorination alone.

On the other hand, if impurities such as silicon chloride or aluminum chloride are produced, silicon chloride (boiling point 57.65 ℃) and aluminum chloride (boiling point 180) ℃) is volatilized to cause a weight loss. According to Table 3, the weight loss after the chlorination reaction was about 5.8%, which is due to Fe 2 O 3 accounting for 2.2% of Fe ₂ O ₃ and carbon consumption and loss during handling. It may have been, but it is difficult to view it as a weight loss due to volatilization of SiO ₂ and Al ₂ O ₃ . In addition, it was confirmed that there was almost no weight loss after washing the soil sample after chlorination, which means that chlorination of other elements such as K ₂ O, which accounts for about 8%, hardly progressed. If it is present as chloride, a clear weight loss should be confirmed due to high solubility during washing, but this is because it was not. In conclusion, the reaction conditions applied in the present invention mean that the effect of side reactions except for 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 relative radioactivity concentrations of K-40 and Cs-137 tend to increase because the weight loss occurs due to the components removed through the chlorination reaction. This is because K-40 and Cs-137 remain in the soil without being vaporized even after being chlorinated.

2 is a photograph showing a recovered product recovered from a condenser as a result of performing 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 is confirmed that the main component of the recovered material recovered from the condenser is 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 recovery of Fe ₂ O ₃ after the chlorination reaction was vaporized and condensed.

The description of the present invention described above is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms 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 in all respects and not restrictive.

Claims (8)

(a) preparing a mixture by mixing particulate matter contaminated with uranium with a carbon source having an average particle size of 100 μm to 400 μm;
(b) chlorinating the mixture in a dry state at 400° C. to 700° C. to produce uranium chloride; and
(c) condensing the uranium chloride;
When the particulate material in step (a) contains silicon oxide, silicon chloride is not produced in step (b),
When the particulate material in step (a) contains aluminum oxide, aluminum chloride is not generated in step (b), a method for decontamination of particulate matter contaminated with uranium.
The method of claim 1,
In step (a), the particulate material further comprises at least one selected from the group consisting of potassium oxide, iron oxide, phosphorus oxide, calcium oxide, sodium oxide, magnesium oxide, and mixtures thereof, particulate matter contaminated with uranium decontamination method.
delete According to claim 1,
When the particulate material in step (a) contains iron oxide, the method for decontamination of particulate matter contaminated with uranium, in which iron chloride is produced and condensed together with uranium chloride in steps (b) and (b) .
delete According to claim 1,
In step (b), the uranium chloride includes uranium contamination, uranium hexachloride, or a mixture thereof, a method for decontamination of particulate matter contaminated with uranium.
According to claim 1,
(d) washing and neutralizing the decontaminated particulate material by generation and condensation of the uranium chloride.
a mixer for mixing particulate matter contaminated with uranium and a carbon source having an average particle size of 100 μm to 400 μm;
a chlorination reactor for chlorinating the mixture in a dry state at 400° C. to 700° C. to produce uranium chloride; and
a condenser for condensing the uranium chloride;
When the particulate matter contaminated with uranium includes silicon oxide, silicon chloride is not produced in the chlorination reactor,
Wherein, when the particulate matter contaminated with uranium includes aluminum oxide, aluminum chloride is not generated in the chlorination reactor.

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