KR102273060B1 - Method for removing Mn in solution after SP-HyBRID decontamination and SP-HyBRID decontamination comprising the same - Google Patents

Abstract

The present invention provides a method for efficiently removing manganese from a solution after the SP-HyBRID decontamination process and an SP-HyBRID decontamination process including the same, and more particularly, it includes a solution after the SP-HyBRID decontamination process containing manganese ions. , providing an electrolytic cell having an electrode comprising a porous metal-type anode and a cathode; and applying a voltage to the electrode to electrodeposit the manganese ions in the solution with manganese oxide on the positive electrode to remove the manganese ions from the solution, and a method for removing manganese from the solution after the SP-HyBRID decontamination process, and the method comprising the steps of: It provides a SP-HyBRID decontamination process comprising

Description

Method for removing Mn in solution after SP-HyBRID decontamination and SP-HyBRID decontamination comprising the same

The present invention relates to a method for treating manganese in a solution generated in the SP-HyBRID decontamination process, and to a method for removing manganese from a solution after the SP-HyBRID decontamination process and the SP-HyBRID decontamination process including the same.

In order to maintain and dismantle an aging nuclear power plant in operation, primary system decontamination is essential. In general, for primary system decontamination, chemical decontamination processes including the HP CORD UV process, which is a typical commercial process, are widely used. In Korea, it is difficult to treat the decontamination waste solution in the commercial decontamination process using organic acids and generates a significant amount of waste ion exchange resin. To solve the same problem, SP-HyBRID (Hydrazine Based Reductive metal Ion Decontamination) process technology using inorganic acid is being developed.

At this time, due to the characteristics of the oxide film formed when decontamination of the primary system of a pressurized light water reactor type or a pressurized heavy water reactor type of a domestic nuclear power plant, the SP-HyBRID decontamination process is an oxidation step - an oxidizer decomposition step - a reduction step - a reducing agent decomposition step - The decontamination process should be carried out in steps such as the decontamination solution purification step (see FIG. 1), and in order to increase the decontamination effect, the secondary and tertiary processes are repeated without ending the primary decontamination. However, in the decontamination solution purification step, an ion exchange resin is used, and the more the process is repeated, the more the waste ion exchange resin is accumulated, which increases the amount of waste generated. In particular, since waste ion exchange resins are not currently accepted at domestic radioactive waste disposal sites, there is a big problem in waste treatment and disposal.

On the other hand, as disclosed in Patent Registration No. 10-1883895, a technique for remarkably reducing the amount of waste after decontamination by using the _{BaSO 4 precipitation method without using an ion exchange resin to purify the decontamination waste liquid is being studied, but as described above} In the technology, manganese ions in the decontamination waste solution are continuously accumulated, _{and a precipitate is formed as manganese oxide (MnO 2} ), so that the decontamination effect decreases as the decontamination process proceeds. _{In addition, manganese ions present in the decontamination solution consume KMnO 4} used as an oxidizing decontamination agent according to the reaction formula as shown in Formula (1), so the more the decontamination process is repeated, the more the decontamination agent must be added. After that, the waste will increase.

2KMnO ₄ + 3MnSO ₄ + 2H ₂ O = MnO ₂ + K ₂ SO ₄ + 2H ₂ SO ₄ ... Formula (1)

Furthermore, Patent Registration No. 10-1950193 describes a method of removing manganese ions in water using powdered activated carbon and a coagulation method using powdered activated carbon, but in this case, radioactive waste containing activated carbon is generated, and currently activated carbon or carbon is included. There is a problem that this technology cannot be applied to the continuous SP-HyBRID process because it is impossible to treat and dispose of the radioactive waste. In the membrane filtration process described in Patent Registration No. 10-1494302, manganese ions contained in backwash water are removed. In order to remove manganese ions, it is described how to remove manganese ions from backwash water by passing backwash water through a manganese adsorption tank to adsorb manganese ions to the adsorbent. , this also has a problem of generating waste ion exchange resin.

Therefore, there is a need for a technology capable of efficiently removing manganese ions and reducing the generation of waste such as waste ion exchange resin.

The present invention provides a method for efficiently removing manganese from a solution after the SP-HyBRID decontamination process.

The present invention provides a SP-HyBRID decontamination process comprising the above method.

The present invention comprises the steps of providing an electrolytic cell comprising a solution after the SP-HyBRID decontamination process containing manganese ions, and having an electrode including a porous metal-type anode and a cathode; and applying a voltage to the electrode to electrodeposit the manganese ions in the solution with manganese oxide on the positive electrode to remove the manganese ions from the solution, providing a method of removing manganese from the solution after the SP-HyBRID decontamination process do.

The present invention provides a SP-HyBRID decontamination process comprising a method of removing manganese from a solution after the SP-HyBRID decontamination process of the present invention.

The present invention can be applied immediately after the decomposition of the reducing decontamination agent essential in the SP-HyBRID continuous process, so that the overall process time is not significantly increased and the decontamination process can be continuously performed. Furthermore, since the input of an additional oxidizing agent due to manganese ions in the solution after decontamination is prevented and the used electrode can be regenerated, waste ion exchange resin does not occur, thereby reducing costs and reducing waste. In addition, since it is possible to analyze the electrodeposition process electrochemically in real time, there is an advantage in that it can work according to the optimal operating conditions.

1 shows a schematic diagram of a conventional decontamination process including an oxidation step - an oxidizer decomposition step - a reduction step - a reducing agent decomposition step - a decontamination solution purification step.
2 shows a schematic diagram of the decontamination process of the present invention.
3 shows an exemplary view of the electrolytic cell used in the present invention.
4 shows an image of an electrodeposition layer formed of a current and an anode formed by an applied voltage in the electrolytic cell according to an embodiment of the present invention.
5 shows the electrodeposition efficiency by the applied voltage in the electrolytic cell according to the embodiment of the present invention.
6(A) shows a cyclic voltammetry curve according to the concentration of manganese ions in the solution in the reference electrode of the electrolyzer, FIG. 6(B) shows the peak voltage change according to the manganese ion concentration, and FIG. 6(C) shows the manganese ion concentration. The peak current density change according to the ion concentration is shown.
7 shows an electrodeposition layer peeling image of a current and an anode formed by an applied voltage in wet regeneration during cathode regeneration according to an embodiment of the present invention.
8 shows an electrodeposition layer peeling image when the electrodeposition layer formed positive electrode is dried in dry regeneration during positive electrode regeneration according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiment of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

The primary system of a nuclear power plant refers to a nuclear reactor system or a primary system, and various devices and facilities surrounding the nuclear reactor, for example, a control rod for controlling the output of the reactor, pipes through which coolant is circulated, a pressurizer, a steam generator , containment containers, etc.

At this time, a metal oxide containing a radioactively contaminated metal or alloy is formed at various positions in the primary system, and the metal oxide may be chromium oxide, iron oxide or nickel oxide.

In the case of decontamination of radioactively contaminated metal oxide as described above, in the oxidation process for dissolving chromium oxide, MnO ₄ ⁻ _{ions are generally used as an oxidizing agent, and MnO 2} particles in the decontamination solution are generated in this process. flows with the decontamination solution. Furthermore, to perform the reduction process after the oxidation process is completed, hydrogen peroxide, hydrazine, an acidic solution, etc. are used _{to decompose/dissolve MnO 4} ^- _{ions, which are oxidizing agents, and MnO 2} particles, which are products of the oxidation process, to dissolve manganese ions (Mn) in the decontamination solution. ²⁺ ) form, and in this case, the concentration of manganese ions in the decontamination solution is present at a level of several hundred ppm.

Accordingly, the present invention provides a technique for removing manganese in the decontamination solution.

In detail, the present invention includes the steps of providing an electrolytic cell comprising a solution after the SP-HyBRID decontamination process containing manganese ions, and having an electrode including a porous metal-type anode and a cathode; and applying a voltage to the electrode to electrodeposit the manganese ions in the solution with manganese oxide on the positive electrode to remove the manganese ions from the solution, providing a method of removing manganese from the solution after the SP-HyBRID decontamination process will do

Basically, the solution after the SP-HyBRID decontamination process contains sulfuric acid, so it may be an acidic solution, for example, having a pH of 2.0 to 3.0. Electrodeposition of manganese ions in such an acidic solution can be easily electrodeposited into _{manganese oxide (MnO 2} ) through a reaction such as the following Chemical Formula (2) at the anode.

Mn ²⁺ + 2H ₂ O = MnO ₂ + 4H ⁺ + 2e ^- ... Formula (2)

E ₁ = 1.228 - 0.1182 pH - 0.0203 log[Mn ²⁺ ]

Therefore, in the method of removing manganese from the solution after the SP-HyBRID decontamination process of the present invention, the reaction of formula (2) may be performed at the positive electrode.

However, when the voltage of the electrode is applied to E ₁ or more, MnO ₂ is formed, but if too high voltage is applied, a reaction such as the following Chemical Formula (3) may occur to form permanganate ions.

MnO ₂ + 2H ₂ O = MnO ₄ ^- + 4H ⁺ + 3e ^- ... formula (3)

E ₂ = 1.692 - 0.788 pH + 0.0197 log[MnO ₄ ^- ]

Therefore, theoretically, _{a voltage of E 1} or more and E ₂ or less should be applied to electrodeposit _{MnO 2 .} However, an overvoltage is always applied in an electrode reaction, and these values depend on the reaction characteristics, the concentration of ions, the characteristics of the electrode material, etc.

Therefore, the present invention confirmed a voltage with particularly excellent electrodeposition efficiency when applied to the electrolytic cell, and as a result, the voltage applied to the electrode in the method for removing manganese from the solution after the SP-HyBRID decontamination process of the present invention is 1.1 to 1.65 V , preferably 1.1 to 1.4V. When the voltage is less than 1.1V, there is a problem that electrodeposition does not occur because current does not flow in the anode, and when it exceeds 1.65V, the current efficiency of the anode is reduced due to a reaction as shown in the following formula (4) to increase the electrodeposition efficiency. reduction problems may arise.

2H ₂ O = O ₂ + 4H ⁺ + 4e ^- ... formula (4)

E ₃ = 1.228 - 0.0591 pH

Furthermore, a reaction such as the following Reaction Formula (5) occurs in the cathode of the electrolyzer to facilitate the flow of current in the electrolyzer.

2H ⁺ + 2e ^- = H ₂ ... formula (5)

On the other hand, the porous metal-type positive electrode and the negative electrode of the present invention can provide an effect of filtering suspended matter present in the solution after the SP-HyBRID decontamination process through a porous structure, respectively. Furthermore, the electrodeposition efficiency of manganese ions in the solution can be increased by increasing the surface area that the solution can contact through the porous structure as described above.

Therefore, a metallic filter material or a porous metal material may be used for the anode and the cathode, and the metal may be platinum, stainless steel, Inconel steel, or nickel, but is not limited thereto.

In this case, the porous metal-type positive electrode and the negative electrode may each have a porosity of 20 to 95%, preferably 50 to 60%. If the porosity is less than 20%, the flow of process water may not be smooth, and if it exceeds 95%, there may be a problem in the soundness of the material.

Furthermore, two or more anodes may be used to increase electrodeposition efficiency, but in this case, a porous metal-type anode having finer pores may be used as the electrode is located on the side from which the manganese-removed solution is discharged in order to enhance the filtering effect.

The porous metal-type positive electrode and the negative electrode may have a pore size of 0.1 to 500 μm in diameter, and preferably a pore size of 0.1 to 10 μm. In this case, when the pore size is less than 0.1 μm, there is a risk of clogging immediately during electrodeposition, and when the pore size exceeds 500 μm, there may be a problem in filtration of particulate matter in the process water.

Furthermore, the electrolyzer may include a reference electrode (RE) to measure the manganese ion concentration in the solution in real time, and the reference electrode is an Oxidation-Reduction Potentail (ORP) electrode to be used. can In this case, as a method of measuring the voltage or current applied to the electrode, a cyclic voltammetry method, a potentiostatic method, a constant current method, etc. may be used, but the present invention is not limited thereto. It can measure voltage or current.

On the other hand, since iron ions may be additionally included in the solution after the SP-HyBRID decontamination process, when an electrode voltage of E ₁ ^{or more is applied to the anode, Fe 2+} present in the SP-HyBRID decontamination solution as shown in Formula (6) below. Ions may be electrodeposited as _{Fe 2} O _{3 .}

2Fe ²⁺ + 3H ₂ O = Fe ₂ O ₃ + 6H ⁺ + 2e ^- ... Formula (6)

E ₄ = 0.728 -0.1773 pH -0.0591 log[Fe ²⁺ ]

_{At this time, comparing the values of E 1} of Formula (2) _{and E 4} of Formula (6), the pH is the same in _{E 1} and E ₄ of the SP-HyBRID decontamination solution, and the formulas of _{E 1} and E _{4 are} In the last term, the effect of the concentration difference of each ion is insignificant, so that the relationship _{E 4} < E _{1 is always established.}

Therefore, in the method of removing manganese from the solution after the SP-HyBRID decontamination process of the present invention, iron ions are additionally included in the solution after the SP-HyBRID decontamination process, so that the reaction of formula (6) can be additionally performed at the positive electrode. have.

Meanwhile, in the present invention, wet regeneration and dry regeneration may be used to regenerate the anode on which manganese oxide is electrodeposited in the electrolytic cell.

The wet regeneration may be performed by applying a cathode voltage to the electrodeposited anode of manganese oxide to reduce the cathode voltage. For example, the manganese oxide is immersed in a sulfuric acid solution by applying a voltage of -0.4 to -0.7V. may be carried out through the step of regenerating the anode by removing the , preferably a voltage of -0.45 to -0.7V may be applied.

If the voltage is less than -0.4V, there may be a problem that the manganese oxide is not peeled off because no current flows to the cathode, and when it exceeds -0.7V, the manganese oxide is no longer peeled off, so -0.7V is applied. There is no need to apply excess voltage. In addition, the concentration of the sulfuric acid solution does not matter as long as the current can smoothly flow through the cathode on which the manganese oxide is electrodeposited, for example, 40 mM sulfuric acid solution may be used.

Furthermore, dry regeneration may be performed by drying the anode on which the manganese oxide is electrodeposited at a high temperature to peel the manganese oxide, and the drying may be performed without limitation as long as the manganese oxide is dried to the extent that the manganese oxide is peeled off, for example, manganese drying the electrodeposited anode at 50 to 100° C. for 8 to 12 hours; and removing the dried manganese oxide to regenerate the positive electrode. In addition, the drying may be performed in an oven, etc., but is not limited thereto.

For example, preferably, the drying step may be performed at 50 to 70° C. for 8 to 10 hours, and the drying method may be performed, for example, by any one of hot air drying, oven drying, and evaporation.

Meanwhile, the present invention provides a SP-HyBRID decontamination process comprising a method of removing manganese from a solution after the SP-HyBRID decontamination process of the present invention. The method of removing manganese from the solution after the SP-HyBRID decontamination process may be performed after the reducing agent decomposition step during the SP-HyBRID decontamination process, for example, it may be performed in the same flow as in FIG. 2 .

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are merely examples to help the understanding of the present invention, and the scope of the present invention is not limited thereto.

Preparation Example 1

In order to evaluate the simulation test for removing manganese components in the decontamination solution after the oxidation process during the primary chemical decontamination process of a nuclear power plant, a simulated decontamination solution for the solution after decontamination of SP-HyBRID was prepared. The simulated decontamination solution was _{prepared by injecting 40 mM H 2} SO ₄ and 6.33 mM manganese ions into deionized water.

The simulated decontamination solution was injected into an electrolytic cell equipped with an electrode including a porous anode and a cathode. Both the anode and the cathode were made of platinum, and an ORP electrode (reference electrode) as a Pt-Ag/AgCl electrode was installed in the electrolytic cell to measure the concentration of the remaining manganese ions. An exemplary view of the electrolytic cell is shown in FIG. 3 , which was referred to as Preparation Example 1.

Experimental Example 1: Measurement of electrode voltage on electrodeposition

FIG. 4 shows a voltage-current curve measured by applying a voltage of 0 to 2.0V to the electrode of Preparation Example 1 and an image obtained by photographing the electrodeposition layer formed in each section.

As shown in FIG. 4 , it could be confirmed that the oxidation current started to flow when a voltage of 1.1V or higher was applied, and it was confirmed that the oxidation current rapidly increased at 1.65V or higher.

Furthermore, the electrodeposition layer formed at 1.65V or less was formed as a relatively homogeneous film, but in the electrodeposition layer formed near 1.85V, it was confirmed that large and small bubbles were formed on the surface. This is because water decomposition is performed when a voltage is applied, and oxygen generation is vigorously performed, and the current efficiency of the electrodeposition reaction is reduced due to the oxygen generation as described above. The oxygen evolution reaction occurs in the same manner as in Chemical Formula (4).

According to Formula (4), water decomposition should start at 1.2V, but in the actual experiment, water decomposition started to occur at 1.65V or higher, so it was confirmed that the overvoltage was about 0.45V.

Therefore, it was confirmed that it is effective to remove the manganese ions by applying a voltage between 1.1 and 1.65V, which is a range in which the oxygen evolution reaction is suppressed.

Experimental Example 2: Measurement of electrodeposition efficiency according to the voltage applied to the electrode

When a voltage of 1.1 to 2.0V is applied to the electrode of Preparation Example 1, the total amount of current flowing (measured by cyclic voltammetry) and the weight of the electrodeposition layer were measured, 1.1-1.2V, 1.4-1.5V, 1.6-1.7 V, the electrodeposition efficiency obtained in the sections of 1.8-1.9V and 1.9-2.0V is shown in FIG. 5 .

At this time, since MnO ₂ electrodeposition proceeds according to Chemical Formula (2), the electrodeposition efficiency was calculated from the _{total amount of charge flowing and the weight of the generated MnO 2 according to Faraday's law.} Since the weight increase of the electrode is the amount of generated MnO ₂ , it was calculated by the following general formula (1).

Electrodeposition efficiency = ( _{weight of MnO 2} produced)/(weight of MnO ₂ calculated by Faraday's law) x 100

As shown in FIG. 5, since the electrodeposition efficiency was significantly reduced at 1.6-1.7V, 1.8-1.9V and 1.9-2.0V, it was confirmed that the electrodeposition was effective at 1.1 to 1.65V as measured in Experimental Example 1. could

Experimental Example 3: Real-time analysis of manganese ion concentration in solution

When the electrodeposition process as in Experimental Example 1 is performed, the concentration of manganese ions remaining in the solution must be analyzed in real time to determine the end time of the electrodeposition process.

However, since it is very tedious to collect the solution in which the electrodeposition process has been performed and directly analyze the concentration of manganese ions, and the process may be delayed, a technique for analyzing the concentration of manganese ions in the solution in real time during the electrodeposition process is required.

Accordingly, the voltage-current curve according to the concentration of manganese ions remaining in the solution using the cyclic voltammetry in the ORP electrode of Preparation Example 1 is shown in FIG. 6(A).

In FIG. 6(A), (a) shows a case where the concentration of manganese ions is 0, (b) shows a case where the concentration of manganese ions is 4 mM, and (c) shows a case where the concentration of manganese ions is 12.6 mM.

As shown in FIG. 6(A), it was confirmed that the density of the current flowing according to the voltage decreased as the concentration of manganese ions in the solution decreased. When a curve as shown in (a) is formed, the concentration of manganese ions in the solution It can be seen that is 0, at this time, the electrodeposition process can be terminated.

Furthermore, the peak voltage and current according to the concentration of manganese ions in the solution are shown in FIGS. 6(B) and 6(C), and as shown in FIG. 6(B), the difference between the peak voltages of the anode and the cathode is minimal. , and further, when the difference between the peak currents of the anode and the cathode is 0, as shown in FIG. 6(C), the concentration of manganese ions in the solution is 0, so the electrodeposition process can be terminated at this time.

Preparation Example 2: Regeneration of a cathode electrodeposited with manganese oxide

(1) Wet regeneration

The voltage-current curve obtained by applying a cathode voltage from 0V to -0.7V by immersing the electrodeposition layer obtained after applying the anode voltage up to 2.0V in Experimental Example 1 in 40mM aqueous sulfuric acid solution and the shape of the electrodeposition layer in each section The photographed image is shown in FIG. 7 .

As shown in FIG. 7, it can be confirmed that a rapid reduction current flows from below -0.3V, and thereafter, it can be confirmed that the reduction current is constantly increased in proportion to the voltage.

However, it was confirmed that the actual electrodeposition layer was peeled off at -0.45V or less, and it was confirmed that the electrodeposition layer was completely peeled off from the electrode when it reached -0.7V.

Therefore, it was confirmed that the electrode can be regenerated by applying a negative voltage of -0.4 to -0.7 V after immersing the positive electrode in 40 mM sulfuric acid solution for regeneration of the positive electrode having the electrodeposition layer formed thereon.

(2) dry regeneration

After drying the electrodeposition layers for each voltage of the five sections obtained in Experimental Example 2 in an oven at 50° C. for 10 hours, images of each electrodeposition layer were photographed with an optical microscope and an electron microscope, as shown in FIG. 8 .

As shown in FIG. 8 , it was confirmed that the electrodeposition layer was easily peeled off as it dried.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations are possible within the scope without departing from the technical spirit of the present invention described in the claims. It will be apparent to those of ordinary skill in the art.

Claims (10)

providing an electrolytic cell comprising a solution after the SP-HyBRID decontamination process containing manganese ions and having an electrode including a porous metal-type anode and a cathode; and
A voltage having a potential of 1.1 to 1.65 V with respect to the Pt-Ag/AgCl reference electrode is applied to the electrode to electrodeposit the manganese ions in the solution as manganese oxide on the positive electrode, and on the negative electrode by the reaction of the following formula (5) removing manganese ions in the solution to prevent this from occurring;
A method for removing manganese from a solution after the SP-HyBRID decontamination process, comprising a.
2H ⁺ + 2e ^- = H ₂ ... Equation (5)
According to claim 1,
The method of removing manganese from the solution after the SP-HyBRID decontamination process, wherein the solution after the SP-HyBRID decontamination process is an acidic solution.
According to claim 1,
The reaction occurring at the anode is as shown in Equation (2) below, a method of removing manganese from the solution after the SP-HyBRID decontamination process.
Mn ²⁺ + 2H ₂ O = MnO ₂ + 4H ⁺ + 2e ^- ... Equation (2)
delete According to claim 1,
The method for removing manganese from the solution after the SP-HyBRID decontamination process, wherein the porous metal-type positive electrode and the negative electrode each have a porosity of 50 to 90%.
According to claim 1,
The method for removing manganese from the solution after the SP-HyBRID decontamination process, wherein the porous metal-type positive electrode and the negative electrode each have a pore size of 5 to 500 μm in diameter.
According to claim 1,
A method of removing manganese from the solution after the SP-HyBRID decontamination process, in which iron ions are additionally included in the solution after the SP-HyBRID decontamination process, and the reaction of Equation (6) is performed at the positive electrode.
2Fe ²⁺ + 3H ₂ O = Fe ₂ O ₃ + 6H ⁺ + 2e ^- ... Equation (6)
According to claim 1,
Removing manganese from the solution after the SP-HyBRID decontamination process, further comprising the step of immersing the electrodeposited anode with manganese oxide in a sulfuric acid solution and applying a cathode voltage of -0.4 to -0.7V to remove the manganese oxide to regenerate the cathode How to.
According to claim 1,
drying the cathode on which manganese oxide is electrodeposited at 50 to 100° C. for 8 to 12 hours; and
Regenerating the positive electrode by removing the dried manganese oxide
A method for removing manganese from the solution after the SP-HyBRID decontamination process, further comprising a.
The SP-HyBRID decontamination process comprising a method of removing manganese from the solution after the SP-HyBRID decontamination process according to any one of claims 1 to 3 and 5 to 9.

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