WO2019045205A1 - Method for treating chemical decontamination process waste of nuclear facility by using oxidation-reduction and precipitation reactions - Google Patents

Abstract

The present invention relates to a method for treating the chemical decontamination process waste of a nuclear facility by using oxidation-reduction and precipitation reactions, the method: being readily applicable to a primary cooling system-based chemical decontamination process of a nuclear facility, particularly, a pressurized water reactor nuclear power plant; using oxidation-reduction and precipitation reactions so as to precipitate the metal oxide of process waste into a precipitate and remove the same, thereby minimizing the generation of waste; and enabling the acceptance of waste disposal to increase.

Description

Decomposition process of nuclear facility using oxidation-reduction and precipitation reaction

The present invention relates to a method for treating chemical decontamination wastes in a nuclear facility using oxidation-reduction and precipitation reactions, and more particularly to a chemical decontamination process for a nuclear power plant, particularly a primary system of a pressurized light water reactor type nuclear power plant To a waste treatment method capable of minimizing the amount of waste generated by precipitating and removing metal oxides of process wastes into sediments using oxidation-reduction and precipitation reactions, and increasing the water-solubility of waste.

Oxidation and reduction multi - stage chemical decontamination technology of the primary system of nuclear power plant has been developed since 1970 for reduction of radiation exposure of workers, reduction of waste disposal and low level, and it is widely used worldwide now. In Korea, research and development has been carried out at Korea Atomic Energy Research Institute, KHNP, KEPCO KPS, Kyungpook National University, and some parts (RCP) decontamination technology in the first line has been industrialized from KEPCO 10 years ago.

The primary system of the nuclear power plant is a system that circulates water at high temperature (over 300 ℃), high pressure (over 150 atmospheres) and high speed. Therefore, even if using internal materials such as SUS and INCONEL, Fe _(3-xy) Ni _x Cr _y O ₄ ) is generated and the radioactive material is deposited, causing radiation exposure of the worker. Chemical decontamination is a process in which the corrosion oxide film is chemically dissolved and removed. The corrosion oxide film is mainly removed by the reduction decontamination process. However, the pressurized light water reactor type nuclear power plant which has a large amount of chromium oxide film needs to be repeatedly applied repeatedly with the oxidizing salt process and the reduction decontamination process. Korea's nuclear power plants are mostly PWR-type power plants.

Oxidation and reduction multistage chemical decontamination process Waste is divided into primary wastes which are metal oxide (Fe, Ni, Co, Cr, Sr, Cs, etc.) corrosion oxide film wastes and secondary wastes which are chemical decontamination (oxidizing agent and reducing agent) wastes. . The early chemical decontamination technology focused on decontamination performance and generated a lot of secondary chemical waste. However, due to the social acceptability of radioactive waste disposal, the disposal cost has risen sharply (domestic radioactive waste disposal ratio is 60 million Yuan / m ³ or more, industrial waste is mostly 20-30 million yuan / m ³ or less) .

Currently, the world's most used primary chemical chemical decontamination technology is HP_CORD_UV (Hydrgen Permanganate_Chemical Oxidation and Reduction Decontamination_Ultra Violate) technology which is repeatedly applied the oxidation / reduction decontamination process sequentially.

In addition to HP_CORD technology, different decontamination agents are used in currently commercialized decontamination technologies. For example, NP (Nitric Acid Permanganate), an oxidant salt technique, uses HNO ₃ to control acidity and AP (Alkaline Permanganate) is a method to decontaminate in an alkaline environment using NaOH. AP is intended to prevent electrostatic adhesion to the system due to the zeta potential of MnO ₂ , which is an intermediate product in the Cr oxide oxidation process. However, the reduction decontamination must be an acidic atmosphere, .

Reduction and decontamination technologies include Citrox decontamination technology, which uses Oxalic Acid and Citric Acid together, and technologies that add inorganic acids that can not be decomposed or removed. Therefore, HP_CORD decontamination technology is a technology developed to reduce the amount of waste generated by using Oxalic Acid, which has the smallest pKa of organic acids and can be adjusted to a low concentration, while it is the easiest to decompose the reducing agent.

Most of the decontamination technology is caustic oxide metal ion and chemical decontamination agent mainly collecting as ion exchange resin, and the main final waste is ion exchange resin waste. That is, since it is possible to collect 1.9 equivalents of metal ion per liter of ion exchange resin, it is necessary to use about 2,000 ml of ion exchange resin in order to remove 20 ml of metal ion, so that the amount of radioactive waste is excessively There is a problem that a lot occurs.

In addition, most of the ion exchange resin waste is occupied by the ion exchange resin, and since the ion exchange resin waste is an organic matter, there is a limitation in the disposal, and the disposal water solubility is poor.

The resin in the ion exchange resin waste is composed of organic styrene and divinyl benzene copolymer. When it is heated or comes into contact with a strong oxidizing agent such as MnO ₄ ^- or HCrO ₄ ^- , CO ₂ , H ₂ O, N ₂ And disadvantages the long-term safety of the disposal site. Therefore, the disposal of cement is prohibited at the domestic disposal sites, and disposal methods such as HIC containers (High Integrated Containers: thickness of 1m or more) are currently being carried out by KORAD (Korea Atomic Energy Authority) As a result, there is a need for a technique for treating radioactive waste that can improve disposal stability.

DISCLOSURE OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a nuclear power plant using a redox and a precipitation reaction capable of collecting metal ions, It is an object of the present invention to provide a method for treating chemical decontamination waste.

In addition, it can be applied to the nuclear waste disposal system of the nuclear facility using the oxidation and reduction and precipitation reaction which can be easily applied to the existing nuclear power plant by forming the primary and secondary wastes in the form of hydroxide or oxide. The purpose is to provide.

In order to accomplish the above object, the present invention provides a method for treating a chemical decontamination process using an oxidation-reduction reaction and a precipitation reaction, comprising the steps of: (a) mixing a metal waste having a radionuclide-containing metal oxide film (Fe _n Ni _m Cr ₁ O ₄ ) A first step of adding permanganic acid as a salt to oxidize the chromium ions from the metal oxide film and dissolving the chromium ions on the decontamination waste solution; A second step of introducing a first reducing agent salt into the decontamination waste solution in which permanganic acid and chromium ions are dissolved, and reducing and precipitating manganese ions and chromium ions into a first precipitate; And oxalic acid as an organic acid second reducing agent salt is added to the decontamination wastewater that has undergone the second step to reduce metal ions including iron ion and nickel ion and unreacted residual manganese ions from the metal oxide film to dissolve A third step; A fourth step of decomposing oxalic acid in the decontamination waste liquid; And a carbonic acid ion precursor which is a precipitant in the decontamination waste solution to adjust the pH of the decontamination waste solution in real time to form a carbonic acid ion precursor which is a decomposition product of oxalic acid, And a fifth step of precipitating the precipitate.

According to the solution of the above problems, the method of treating chemical decontamination wastes of nuclear facilities using oxidation-reduction and precipitation reaction of the present invention is characterized in that manganese ions (MnO ₄ ^- ) and chromium ions (HCrO ₄ ^- ) Is precipitated using a first reducing agent salt, and the metal ions are precipitated in the form of a carbonate by using carbon dioxide, which is a decomposition product of the second reducing agent salt, which is an organic acid, and a precipitant, and the metal ion of the metal oxide and the residual oxidizing agent (Mn ²⁺ ) Can be removed in the form of hydroxides or oxides, so that the amount of waste generated can be significantly reduced as compared with the conventional waste disposal method using an ion exchange resin process.

As a result, metal ions and metal oxide ions, which are dissolved in a metal oxide film, and Mn ^{2 +} ions, which are oxidant-based waste wastes, are removed by filtration with oxides, hydroxide precipitates and MnO ₂ precipitates, . In particular, the cost of low-grade solid wastes is over KRW 12 million per 200L drums, and ion exchange resin wastes are not accepted due to long-term (hundreds to thousands of years) stability problems due to the decomposition of resin organic materials. Therefore, expensive HIC containers (High Integrated Container: 1 m or more in thickness) can be reduced.

In addition, the disposal safety can be greatly improved as compared with the ion exchange resin waste by filtering out the metal ions as the metal oxide lysate and the Mn ^{2 +} ions as the oxidizer salt waste with the oxides, hydroxide precipitates and MnO ₂ precipitates . This is because styrene and divinyl benzene copolymers, organic constituents of the resin in the waste ion exchange resin, are heated and contacted with a strong oxidizing agent such as MnO ₄ ^- or HCrO ₄ ^- to form CO ₂ , H ₂ O or N ₂ Decomposition and deteriorate the long-term safety of the repository.

FIG. 1 is a schematic view showing a method of treating a waste chemical decontamination process using a redox reaction and a precipitation reaction of the present invention.

2 is a graph showing the content of carbonic acid ions according to the pH of the decontamination waste solution of the present invention.

FIG. 3 is a graph comparing the volumes of wastes according to the treatment method of the present invention and the wastes according to a conventional treatment method using the ion exchange resin method.

4 is a photograph showing a simulated metal waste in which metal ions have been removed according to the first reduction decontamination reaction of the present invention.

FIG. 5 is a graph showing the results of the simulated metal waste performed only with the oxidant salt reaction of the present invention and the first reduced decontamination reaction.

FIG. 6 is a photograph showing reduction characteristics and precipitation filtration results of the first reducing agent salt after addition of the oxidizing agent salt of the present invention. FIG.

FIG. 7 is a graph showing the results of analyzing the particle size of the first precipitate generated after adding the first reducing agent salt to the decontamination waste solution through the oxidant salt of the present invention. FIG.

8 is a photograph showing the decontamination waste solution and the separated iron precipitate in which the iron (III) precipitate of the present invention is formed.

FIG. 9 is a photograph showing the decontamination waste solution and separated iron and manganese precipitate in which iron (III), manganese (II) precipitates of the present invention are formed.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below, but may be embodied in various different forms, and these embodiments are not intended to be exhaustive or to limit the scope of the present invention to the precise form disclosed, It is provided to inform the person completely of the scope of the invention. And the terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. The singular forms herein include plural forms unless the context clearly dictates otherwise.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Brief Description of Drawings FIG. 1 is a block diagram of a computer system according to an embodiment of the present invention; FIG. 2 is a block diagram of a computer system according to an embodiment of the present invention; FIG.

FIG. 1 is a schematic view showing a method of treating a waste chemical decontamination process using a redox reaction and a precipitation reaction of the present invention.

Referring to FIG. 1, the method of treating the chemical decontamination waste in the nuclear facility using the redox reaction and the precipitation reaction according to the present invention includes a first step of an oxidant salt process, a second step of an oxidant salt waste treatment process, A fourth step of a second reducing agent-based cracking process, and a fifth step of a waste precipitation treatment process.

Prior to describing the first step in detail, the step of pre-treating the inside of the system in which the metal oxide film containing the radionuclide is generated may be further included. In the pretreatment, the system in which the metal oxide film is formed is supported on ultrapure water and is washed with ultrasonic waves to remove impurities in the system to prevent side reactions caused by impurities in the second to fifth steps to be described later.

In the first step, permanganic acid or permanganate, which is an oxidizer salt, is added to the metal oxide film formed in the system containing the radionuclide, and the chromium oxide is oxidized to chromium ions from the metal oxide film and dissolved in the decontamination waste solution.

The system in the present invention means a primary system and a secondary system of a nuclear power plant. The primary system is the reactor system or the primary system. It is used to control various devices and facilities surrounding the reactor, ie, control rods for controlling the output of the reactor, piping for circulating coolant, pressurizer, steam generator, . The secondary system is a secondary system, which includes the turbines, generators, and condensers necessary for electricity production, and various facilities that supply water to the steam generator.

Also, the system of the present invention may be made of SUS 304 (steel use stainless) alloy, the metal oxide film is formed of metallic components dissolved from the SUS 304 alloy, and the spinel structure of Fe _(3-xy) Ni _x Cr _y O ₄ Lt; / RTI >

On the other hand, the oxidizer salts of permanganic acid or permanganate is a strong oxidizing agent, and a chromium oxide in the metal oxide _{(Cr 2 O 3) HCrO 4} - or CrO ₄ ^- in other words, by the oxidation of Cr ^{3 +} to Cr ^{6 +} the decontamination peaek Since Cr ^{6 +} can be reduced in acidic conditions, it can be dissolved in Cr ^{3 +} state. Although potassium permanganate (KMnO ₄ ) can be used as the permanganate salt, inorganic acid can be used as an acidity controlling agent instead of an oxidizing agent.

In the first step of the present invention, a solution of 1 to 10 mmol / L can be used as an oxidizing agent. If the concentration is outside the above range, the efficiency of chromium ion dissolution decreases due to excessive accumulation of MnO ₂ particles.

In addition, the time for oxidizing and decontaminating the chromium oxide after the oxidizing agent is added may be 60 minutes to 600 minutes, and more preferably 120 minutes to 300 minutes.

For example, in the first step, permanganic acid, which is an oxidant salt, oxidizes chromium oxide and, as shown in Reaction Scheme 1 below, can be reduced to produce MnO ₂ .

[Reaction Scheme 1]

4H ⁺ + MnO ₄ ^- + 3e ^- ? MnO ₂ (s) + 2H ₂ O

Next, in the second step, the first reducing agent salt is added to the decontamination waste solution in which the chromium ions are dissolved, and the unreacted oxidant salt and the chromium ions are reduced to precipitate and remove the first precipitate.

At this time, the reducing power of the first reducing agent salt is preferably smaller than the reducing power of oxalic acid as the second reducing agent salt in the third step described later.

Specifically, the decontamination solution after the first step may contain CrO ^{3 +} , MnO ₂ produced by reduction of permanganic acid, and residual MnO ₄ ^- . When oxalic acid with strong reducing power is added to the decontamination waste solution without using the first reducing agent salt, Mn ^{4 +} of MnO ₂ is reduced to Mn ^{2 +} and dissolved in the decontamination waste solution. In order to remove Mn ^{2 +} There is a problem to use the law.

On the other hand, the first reducing agent salts in the second step may be conveniently removed by solid-liquid separation method capable of holding an Mn ⁴⁺ of reducing power smaller than oxalic MnO ₂ MnO ₂ in the precipitate was difficult to form the reduction in Mn ^{+ 2} have. Accordingly, it is preferable to carry out a second step of introducing a first reducing agent salt having a reducing power lower than that of oxalic acid between the first step and the third step of adding oxalic acid.

In addition, the first reducing agent salt causes the pH of the decontamination waste liquid to rise so that the Cr ^{3 +} dissolved in the decontamination waste liquid is precipitated as Cr (OH) ₃ , and the zeta potential of the MnO ₂ precipitate is It is preferable to use a strong alkaline substance. For example, since the pH of the isoelectric point of MnO ₂ is 4 to 5, it has a negative zeta potential on the strongly alkaline decontamination waste liquid. At this time, SUS304 because the system also be strong alkaline conditions have a negative zeta potential of MnO ₂ and the repulsive force from the alloys will occur, it is possible to separate the precipitate from the more stable metallic waste.

Therefore, as the first reducing agent salt of the present invention, it is preferable to use a substance having a stronger reducing power and stronger alkali than the second reducing agent salt. For example, hydrazine (N ₂ H ₄ ) may be used.

In the second step, unreacted residual oxidizing agents HMnO ₄ and HCrO ₄ ^- using hydrazine as the first reducing agent salt may be reacted as shown in the following reaction formula 2.

[Reaction Scheme 2]

3N ₂ H ₅ ⁺ + 4MnO ₄ ^- + H ⁺ ? 3N ₂ + 4MnO ₂ + 8H ₂ O

3N ₂ H ₅ ⁺ + 4HCrO ₄ ^- + 13H ^{+ -} > 4Cr ³⁺ + 3N ₂ + 16H ₂ O

As shown in Reaction Scheme 2, hydrazine is oxidized to harmless N ₂ to produce a harmless reaction product, the hydrogen ion is consumed, the pH of the decontamination waste solution is raised, and Cr ³⁺ can easily precipitate as a hydroxide because of no complexing agent.

The first reducing agent salt may be added in an appropriate amount for the oxidation-reduction reaction, for example, 5-15 mmol / L, preferably 6-12 mmol / L. Further, it is preferable that the time for reduction decontamination of manganese ion and chromium ion after the first reducing agent salt is added is 1 to 60 minutes. When the addition amount of the first reducing agent salt is less than 5 mmol / L or when the reduction decontamination time is less than 1 minute, the reduction reaction of manganese ions and chromium ions can not be sufficiently induced, and the addition amount is preferably 15 mmol / Minute, it is undesirable from the viewpoint that energy is unnecessarily consumed after forming a complete reduction product.

Next, in the third step, an organic acid including oxalic acid, which is a second reducing agent salt, is added to the decontamination waste solution that has undergone the second step, and a metal oxide containing iron ion and nickel ion is removed from the metal oxide film, Ions are reduced and dissolved on the decontamination waste solution.

Organic acids including oxalic acid oxidize iron oxides (Fe ₂ O ₃ , Fe ₃ O ₄ ) and nickel oxides (NiO) from metal oxide films of metal waste to produce iron ions (Fe ^{2 +} , Fe ^{3 +} ) and nickel ions ²⁺ ) is a decontamination process. For example, iron ions of Fe ₂ O ₃ can be reduced as shown in Reaction Scheme 3 below.

[Reaction Scheme 3]

Fe ₂ O ₃ + H ₂ C ₂ O ₄ + 4H ⁺ → Fe ²⁺ + 3H ₂ O + 2CO ₂

In addition, even after the second step, unreacted MnO ₂ and HMnO _{4 as a} residual oxidizing agent can be reduced to Mn ^{2 +} in the reduction decontamination step, so that MnO ₂ does not remain in the system.

When oxalic acid is directly added to the reducing chemical decontamination process without using the first reducing agent salt as in the present invention, Cr ^{3 +} of the residual metal ions forms an anionic complex with oxalic acid, It is necessary to use a separate anion exchange resin because oxalic acid is present as HC ₂ O ₄ ^- anion and it is necessary to remove even the reducing agent salt, so that anion exchange treatment is difficult. On the other hand, in the present invention, since Cr ^{3 +} does not form an anion complex with oxalic acid, it can be easily precipitated as a hydroxide and removed by filtration together with MnO ₂ . In addition, although the ion exchange resin method may be additionally used to remove a trace amount of metal ions in the third step of the present invention, the amount of waste can be significantly reduced rather than the conventional ion exchange resin processing method.

Next, the fourth step decomposes the second reducing agent salt in the decontamination waste liquid. For example, oxalic acid is decomposed into water and carbon dioxide, water is dissolved in a liquid state on decontamination waste liquid, and carbon dioxide is dissolved in carbonic acid.

The second reducing agent on the decontamination waste liquid may be an ordinary oxidation process for decomposing a salt of a reducing agent, such as chlorine or ozone, but it is preferable to use an advanced oxidation process (AOP).

The advanced oxidation process is collectively referred to as a water treatment technique in which a hydroxide radical having an oxidizing power stronger than an oxidizing agent used in an ordinary oxidation process is produced as an intermediate product to decompose the substance in the water. For example, a method of adding ozone and controlling the pH or a method of treating with hydrogen peroxide and ultraviolet rays can be used. Preferably, the ultraviolet ray can be decomposed by UV-AOP using hydrogen peroxide and ultraviolet rays.

Finally, in the fifth step, a carbonic acid ion precursor, which is a precipitant, is added to the decontamination waste solution to control the pH of the decontamination waste solution in real time, and carbon dioxide and the carbonate ion precursor, which are decomposition products of the second reducing agent salt, And the precipitated second precipitate is formed.

The pH of the decontamination waste solution is preferably adjusted to 5 to 12 due to the introduction of the carbonate ion precursor. At this time, while the pH of the decontamination waste liquid is controlled, carbonate ions (CO ₃ ^2- ) are formed from carbon dioxide and carbonate ion precursors, and the carbonate ion reacts with metal ions on the decontamination waste solution to form carbonates or metal hydroxides 2 Form a precipitate.

Specifically, the carbonate ion precursor may be any one selected from the group consisting of sodium carbonate, sodium hydrogencarbonate, and mixtures thereof.

2 is a graph showing the content of carbonic acid ions according to the pH of the decontamination waste solution of the present invention.

Referring to FIG. 2, it is more preferable that the pH of the decontamination waste solution is adjusted to 8 to 12 since sodium carbonate, sodium hydrogencarbonate, and carbonic acid are mostly decomposed to carbonate ion at pH 8 or higher.

For example, divalent metal radionuclides such as iron ions (Fe ^{2 +} ) and nickel ions (Ni ²⁺ ) and residual manganese ions (Mn ²⁺ ) dissolved in decontamination effluent by oxalic acid, chromium ions (Cr ^{+ 3)} and iron ion (Fe ³⁺⁾ and trivalent metal radionuclides are the same, through a carbonate ion is a pH adjustment formed of decontamination waste liquid can be precipitated to form a carbonate. A second precipitate in the carbonate form can be formed according to the following Reaction Scheme 4.

[Reaction Scheme 4]

Fe ²⁺ + CO ₃ ^2- ? FeCO ₃ (s)

Ni ²⁺ + CO ₃ ^2- ? NiCO ₃ (s)

Mn ²⁺ + CO ₃ ^2- ? MnCO ₃ (s)

2Fe ³⁺ + 3CO ₃ ^2- ? Fe ₂ (CO ₃ ) ₃ (s)

2Cr ³⁺ + 3CO ₃ ^2- ? Cr ₂ (CO ₃ ) ₃ (s)

FIG. 3 is a graph comparing the volumes of wastes according to the treatment method of the present invention and the wastes according to the conventional treatment methods using the ion exchange resin method, wherein (a) shows the wastes according to the conventional treatment method using ion exchange resin , (b) are diagrams schematically showing the amount of waste according to the treatment method of the present invention.

As shown in FIG. 3, since the conventional ion exchange resin processing method uses an ion exchange resin, the amount of radioactive waste is excessively larger than that of the radioactive metal material to be removed. On the other hand, The metal ions which are metal oxide films dissolved in the metal oxide film and the Mn ^{2 +} ions which are the oxidizer salt waste are filtered out by the precipitates of oxides, hydroxide precipitates and MnO ₂ , .

For example, 1.05 L of ion exchange resin waste is generated in order to remove 1 moles of manganese ions (Mn ^{2 +} ) through the conventional treatment method using the ion exchange resin method, and through the treatment method of the present invention, And the mass of 1 mol of MnO ₂ to be removed is 86.9 g and the specific gravity is 5 g / cm 3, the volume of 1 mol of MnO ₂ is 0.01738 L. That is, according to the prior art, 1.05 L of waste was generated in order to remove 1 mol of manganese ions, and the volume of 1 mol of MnO ₂ removed according to the present invention was 0.01738 L, When used, the volume of waste can be reduced by about 1/64.

The method of treating the chemical decontamination process waste using the oxidation reduction and precipitation reaction according to the present invention can be called HC CORD (Hydrazine Carbonate Chemical Oxidation Reduction Decontamination).

Hereinafter, the present invention will be described in more detail by way of examples, but the scope of the present invention is not limited by the examples.

<Experimental Example>

1. Removal of Mn and Cr from decontamination waste liquid

Pellet-shaped SUS304 having a metal oxide film (Fe _n Ni _m Cr ₁ O ₄ ) as a simulated metal waste was prepared and ₃ mol / L of HMnO ₄ solution was added to the SUS304 pellet to prepare Cr ^{3 +} of Cr ₂ O ₃ as HCrO ₄ ^{- &lt}; / RTI &gt; of Cr ^&lt; ^{6 +} &gt; to dissolve on the decontamination waste solution. Oxidation reactions were carried out for a total of 3 hours and the pH and concentration of metal ions in the decontamination wastewater were measured and recorded at 1 hour intervals.

After completion of the oxidation reaction, N ₂ H ₄ solution was added to reduce unreacted MnO ₄ ^- and HCrO ₄ ^- into MnO ₂ and Cr ^{3 +} , respectively, and then precipitated with MnO ₂ and Cr (OH) ₃ . The reduction reaction was carried out for a total of 15 minutes. After addition of N ₂ H ₄ solution every 5 minutes, the pH and the concentration of metal ions in the decontamination waste solution were measured and recorded. Specifically, 3.73 mmol / L of N ₂ H ₄ solution was added and reacted for 5 minutes. Then, 3.73 mmol / L of N ₂ H ₄ solution was further added for 5 minutes, and 3.73 mmol / L of N ₂ H ₄ solution Was further added thereto and reacted for 5 minutes.

The following Table 1 and Table 2 show the metal ion removal efficiency in the decontamination waste solution according to the first reduction decontamination reaction and the second reduction decontamination reaction of the present invention. Is a photograph showing the removed simulated metal waste. FIG. 5 is a photograph showing the effect of the first reduction decontamination reaction of the present invention, wherein FIG. 5 (a) is a photograph showing a simulated metal waste subjected to only the oxidant salt reaction of the present invention, Which is a graph showing the results obtained when the reduction decontamination reaction is not performed.

division		HMnO 4 (mmol / L)	N 2 H 4 (mmol / L)	Time (minutes)	pH	H + (mmol / L)	MnO 4 - (mmol / L)	MnO 2 (mmol / L)	HClO 4 - (mg / L)	Cr 3 + (mg / L)	Cr 3 + (mmol / L)
Oxidant salt	Early	-	-	0	2.64	2.29	3.00	0	0	-	-
	1-1	3	-	60	2.72	1.91	2.46	0.54	5.35	-	-
	1-2	3	-	120	2.7	2.00	2.46	0.54	8.7	-	-
	1-3	3	-	180	2.68	2.09	2.08	0.92	11.85	-	-
1st reduction decontamination	1-3a	-	3.73	5	3.28	0.52	0.38	2.62	0	15	0.29
	1-3b	-	7.46	10	7.53	0	0.02	2.98	0	0	0
	1-3c	-	11.19	15	9.25	0	0.02	2.98	0	0	0

Referring to Table 1 above, the concentration of HCrO ₄ ^- was the highest in the group 1-3 which was subjected to the oxidant salt reaction for 180 minutes, followed by the group 1-2 which was the oxidant salt reaction for 120 minutes. That is, it is preferable to use 3 mM / L of HMnO ₄ solution for oxidative salt reaction for 120 minutes or more in order to efficiently conduct the oxidative salt reaction of Cr ^{6 +} of Cr ₂ O ₃ with Cr ^{3 +} of HCrO ₄ ^- have.

After 1-3 oxidizer salt reactions, the Cr ^{3 +} ions were precipitated as Cr (OH) ₃ in 1-3b and 1-3c of 1-3a to 1-3c where the first reduction decontamination reaction proceeded to form Cr ^{3 +} concentration was 0 mmol / L, and the concentration of MnO ₄ ^- was 0.02 mmol / L. However, it can be considered that MnO ₄ ^- was completely precipitated with MnO ₂ by the experimental error.

This is because with reference to Figure 4 looking simulated waste metal of SUS304 pellet can be seen that as the pH of the simulated decontamination waste liquid rising from 1-3c out MnO ₂ particle that was accumulated in the surface of the SUS304 pellets are turned away from the color of the pellets SUS304 , And the difference can be more evident when compared with the photograph of FIG. 5 (a).

division	Oxidant salt	HMnO 4	1st reduction decontamination	N 2 H 4	2nd reduction decontamination	C 2 H 2 O 4	Solid-liquid separation	IX
2-1	○	3 mmol / L	×	-	×	-	-	-
2-2	×	-	×	-	○	30 mmol / L	-	○

Referring to Table 2 and FIG. 5 (a), in 2-1, only 3 mmol / L of 3M HMnO ₄ solution was added to perform the oxidant salt reaction. SUS304 pellets treated with oxidizing agent according to 2-1, It can be seen that MnO ₂ is integrated on the surface and is completely black.

In 2-2, after the oxidant salt reaction, 30 mmol / L of C ₂ H ₂ O ₄ solution was added to perform the second reduction decontamination reaction. In order to remove the radioactive nuclide metal ions, an ion exchange resin (IX, ion exchange) Respectively. At this time, oxalic acid reacts with Cr ^{3 +} to form a complex, which is not completely removed by cation exchange over time (see FIG. 5 (b)). In order to remove complex oxalic acid and Cr ^{3 +} , anion exchange resin should be used. In this case, the amount of waste increases very much.

FIG. 6 is a photograph showing the reduction reaction characteristics and precipitate filtration results according to addition of the first reducing agent salt after the oxidizing agent salt of the present invention, and FIG. 6 7 is a graph showing the result of analyzing the particle size of the first precipitate generated after adding the first reducing agent dye to the decontamination waste solution passing through the oxidant salt of the present invention.

division	Amount of N 2 H 4 added (mmol / L)	pH	H + (mmol / L)	MnO 4 - (mmol / L)	HCrO 4 - (mmol / L)
3-1	0	2.62	2.40	2.57	0.007
3-2	2.7975	2.83	1.48	1.94	0.008
3-3	5.595	3.06	0.87	1.09	0.007
3-4	8.3925	4.01	0.10	0.22	0.007
3-5	11.19	9	0.00001	0.01	0.002

Referring to Table 3, as the addition amount of N ₂ H ₄ was increased, the concentration of H ⁺ was decreased and the pH was increased. The concentration of MnO ₄ ^- and HCrO ₄ ^- was decreased by N ₂ H ₄ , ₂ and Cr (OH) ₃ .

6 (a) is a photograph showing the result of filtration of the first precipitate in the simulated decontamination waste liquid according to 3-1, (b), 3-2, (c) . Referring to FIG. 6, as the amount of N ₂ H ₄ increases, the color of the decontamination waste solution gradually decreases from black, and the amount of N ₂ H ₄ is the highest (d), the filtration result of the first precipitate was the best. That is, N ₂ H ₄ is preferably added in an amount of 10 mmol / L or more for reduction of manganese ion and chromium ion and removal of the first precipitate. And, simulated decontamination waste liquid. Referring to Fig hydrazine 11.19mmol / L For a 3-5 was added and the pH of the waste solution is raised sufficiently MnO ₄ ^- and HCrO ₄ ^- is sufficiently reduced MnO _{2 3} and Cr (OH) Since the precipitate forms, most of it can be removed with 0.45um filter.

2. Removal of Fe ²⁺ from decontamination waste solution using carbonate ion

500 ml of 1 mM Fe (NH ₄ ) ₂ (SO ₄ ) ₂ solution was used as a simulated decontamination waste solution. Na ₂ CO ₃ was added to the simulated decontamination waste solution to raise the pH. In the simulated decontamination waste solution, Fe ^{2 +} Concentration were measured and recorded as shown in Table 4 below.

division	pH	Na 2 CO 3 (g)	CO 3 2- (mmol / L)	? CO 3 2- (mmol / L)	Fe 2+ (mmol / L)
Early	2.87	-	-	-	0.773
4-1	4.12	0.0717	1.380	2.220	0.360
4-2	5.03	0.0034	1.447	0.066	0
4-3	6.01	0.0086	1.616	0.169	0
4-4	6.96	-	1.616	0.000	0
4-5	9	0.0937	3.476	1.860	0
4-6	10.95	2.3803	51.233	47.757	0

Referring to Table 4, in the case of the 4-1 pH adjusted to 4.12 eoteuna Fe ^{2 +} concentration is reduced from the beginning of 0.773mmol / L in 0.360mmol / L was found that is not completely removed. On the other hand, 4-1 through 4-6, as the pH increased to over 5 for the increase of the concentration of the CO ₃ ^2-, CO ₃ ^2- and the Fe ^{2 +} is coupled to a FeCO ₃ Fe ^{2 +} is completely removed . At this time, Na ₂ CO ₃ was not added to the simulated decontamination waste solution of 4-3 which reached pH 6, and the pH reached 6.96 as a result of stirring for 90 minutes at a constant speed or more.

Therefore, by controlling the pH of the decontamination waste liquid containing Fe ^{2 +} to 5 or more, it is possible to efficiently remove Fe ^{2 +} .

3. Removal of Fe ³⁺ from decontamination waste solution using carbonate ion

500 ml of 1 mM FeCl ₃ solution was used as a simulated decontamination waste solution and the pH was raised by adding Na ₂ CO ₃ to the simulated decontamination waste solution. The Fe ³⁺ concentration in the simulated decontamination waste liquid was measured according to the pH change, I recorded it together. And FIG. 8 is a photograph showing a decontamination waste liquid in which (a) iron (III) precipitate is formed and (b) iron (III) precipitate separated from the decontamination waste solution in the method for treating decontamination waste liquid of the present invention.

division	pH	Na 2 CO 3 (g)	CO 3 2- (mmol / L)	? CO 3 2- (mmol / L)	Fe 3+ (mmol / L)
Early	2.96	-	-	-	0.992
5-1	4.1	0.0737	1.419	1.419	0.664
5-2	5.11	0.0032	1.481	0.062	0.112
5-3	6.05	0.0029	1.538	0.057	0
5-4	7	-	1.538	0	0
5-5	9.01	0.0049	1.635	0.097	0
5-6	11.01	0.8164	18.015	16.38	0

Referring to Table 5 and 8, the case of the 5-1 pH adjusted to 4.1 Fe ^{3 +} concentration is reduced to negligible at the beginning of 0.992mmol / L in 0.664mmol / L not suitable for efficient removal of the Fe ^{3 +} . On the other hand, in the case of the 5-2 adjusted to pH 5.11 as Fe ^{3 +} concentration 0.112mmol / L indicated by the sharp drop was compared to the initial concentration, in particular 5-3 ~ 5-6 pH is increased to more than 6 for CO ₃ ^2- increased, and it was confirmed that this CO ₃ ^2- and Fe ^{3 +} were combined with Fe ₂ (CO ₃ ) ₃ to completely remove Fe ^{3 +} . At this time, Na ₂ CO ₃ was not added to the simulated decontamination waste solution of pH 5-6, and pH 7 was reached by stirring for 90 minutes at a constant stirring rate or more.

Therefore, by controlling the pH of the decontamination waste liquid containing Fe ^{3 +} to 5 or more, it is possible to efficiently remove Fe ^{3 +} .

4. Removal of Fe ³⁺ and Mn ²⁺ from decontamination waste solution using carbonate ion

A simulated decontamination waste liquid was used to 1mM FeCl ₃ and 1mM MnCl mixed liquid 500ml mixed with the _second solution, was to raise the pH brought by the addition of Na ₂ CO ₃ to the simulated decontamination waste liquid, Fe in the simulated decontamination waste liquid according to the pH change ³⁺ and to measure the Mn ^{+ 2} concentration was recorded as shown in Table 6. And FIG. 9 is a photograph showing a decontamination waste liquid in which (a) iron (III) and manganese (II) precipitates are formed in the method of treating the decontamination waste liquid of the present invention, and (B) iron (III), manganese ) &Lt; / RTI &gt;

division	pH	Na 2 CO 3 (g)	CO 3 2- (mmol / L)	? CO 3 2- (mmol / L)	Fe 3+ (mmol / L)	Mn 2+ (mmol / L)
Early	2.87	-	-	-	0.773	1.21
6-1	4.12	0.071	1.380	2.220	0.360	1.16
6-2	5.03	0.0034	1.447	0.066	0	1.17
6-3	6.01	0.0086	1.616	0.169	0	1.16
6-4	6.96	-	1.616	0	0	1.12
6-5	9	0.0937	3.476	1.860	0	0.12
6-6	10.95	2.3803	51.233	47.757	0	0

Referring to Table 6 and 9, the case of 6-1, adjusted to pH 4.12 Fe ^{3 +} concentration that is not suitable for efficient removal of the Fe ^{+ 3} is reduced to insignificant compared to the initial concentration of 0.360 mmol / L appear. On the other hand, in the case of 6-2 ~ 6-6, the concentration of CO ₃ ^2- increased as the pH increased to 5 or higher, and this CO ₃ ^2- and Fe ^{3 +} were combined with Fe ₂ (CO ₃ ) ₃ It can be confirmed that Fe ³⁺ is completely removed.

In addition, the concentration of Mn ^{2 +} was decreased to 1.12 mmol / L in the case of 6-4, which was adjusted to pH 6.96, so that it was not suitable for the efficient removal of Mn ^{2 +} . On the other hand, the concentration of Mn ^{2 +} was decreased to 0.12 mmol / L in the case of 6 - 5, which was adjusted to pH 9. Especially, in case of 6-6, the concentration of CO ₃ ^2- , And it was confirmed that Mn ^{2 +} was completely removed by binding of CO ₃ ^2- and Mn ^{2 +} to MnCO ₃ . At this time, Na ₂ CO ₃ was not added to the simulated decontamination waste solution of pH 6, which reached 6, and the pH reached 6.96 as a result of stirring for 90 minutes at a constant rate or more.

Therefore, by controlling the pH of the decontamination waste solution containing Fe ^{3 +} and Mn ^{2 +} together to 9 or more, Fe ³⁺ and Mn ²⁺ can be efficiently removed at the same time.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the claims of the invention to be described below may be better understood. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing detailed description, and all changes or modifications derived from the appended claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (6)

1. A first step of introducing permanganic acid or permanganate, which is an oxidant salt, into the metal oxide film formed inside the system containing the radionuclide to oxidize the chromium oxide from the metal oxide film to chromium ions and dissolve the decomposed waste solution on the decontamination waste solution;

   A second step of introducing a first reducing agent salt into the decontamination waste solution in which the chromium ions are dissolved and reducing and precipitating the unreacted oxidant salt and chromium ions into a first precipitate;

   An organic acid including oxalic acid which is an organic acid second reducing agent salt is added to the decontamination waste solution that has undergone the second step to reduce iron oxide and nickel ion-containing metal oxide and unreacted residual manganese ion from the metal oxide film, A third step of dissolving in a waste solution;

   A fourth step of decomposing the second reducing agent salt in the decontamination waste solution; And

   The pH of the decontamination waste liquid is adjusted in real time by injecting a carbonate ion precursor as a precipitating agent into the decontamination waste liquid, and carbon dioxide and the carbonate ion precursor, which are decomposition products of the second reducing agent salt, and metal ions on the decontamination waste liquid are reacted And a fifth step of depositing a second precipitate on the surface of the waste water.
2. The method according to claim 1,

   Wherein the pH of the decontamination waste solution is adjusted to 5 to 12 in the fifth step. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt;
3. 3. The method of claim 2,

   In the fifth step, carbonate ion (CO ₃ ^2- ) is formed from the carbon dioxide and the carbonate ion precursor while the pH of the decontamination waste liquid is controlled, and the carbonate ion reacts with the metal ions on the decontamination waste liquid, And the second precipitate in the form of hydroxide is formed. The method for treating chemical waste decontamination waste in a nuclear facility using a redox and precipitation reaction.
4. The method according to claim 1,

   Wherein the carbonate ion precursor is any one selected from the group consisting of sodium carbonate, sodium bicarbonate, and mixtures thereof, and a method for treating the chemical decontamination waste of a nuclear power plant using the oxidation-reduction and precipitation reaction.
5. The method according to claim 1,

   Wherein the reducing power of the first reducing agent salt is less than the reducing power of the second reducing agent salt.
6. 6. The method of claim 5,

   Wherein the first reducing agent salt is added in an amount of 5 to 15 mmol / L, and the method of treating the chemical decontamination waste in a nuclear facility using the redox reaction and the precipitation reaction.

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