KR20210041658A - Method for removing Mn in solution after SP-HyBRID decontamination and SP-HyBRID decontamination comprising the same - Google Patents

Abstract

Provided are a method for efficiently removing manganese from a solution after an SP-HyBRID decontamination process and the SP-HyBRID decontamination process including the same. More specifically, the method comprises: providing an electrolytic cell including a solution after the SP-HyBRID decontamination process containing manganese ions and having an electrode including a porous metal-type anode and cathode; and removing manganese ions in the solution by applying a voltage to the electrode to electrodeposit the manganese ions in the solution with manganese oxide on the anode.

Description

Method for removing Mn in solution after SP-HyBRID decontamination process and SP-HyBRID decontamination process including the same {Method for removing Mn in solution after SP-HyBRID decontamination and SP-HyBRID decontamination comprising the same}

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

Primary system decontamination must be preceded in order to maintain and repair a nuclear power plant in operation and to dismantle an aging nuclear power plant. In general, primary system decontamination is a chemical decontamination process including the HP CORD UV process, which is a representative commercial process, and in Korea, it is difficult to treat decontamination waste liquid in a commercial decontamination process using organic acids and the generation of a considerable amount of waste ion exchange resin. In order 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 decontaminating the pressurized light water reactor type or pressurized heavy water reactor type primary system of a domestic nuclear power plant, the SP-HyBRID decontamination process is an oxidation step-an oxidant 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 the second and third processes are repeated without finishing at the first decontamination in order to increase the decontamination effect. However, in the decontamination solution purification step, an ion exchange resin is used, and as the process is repeated, the waste ion exchange resin accumulates, which increases the amount of waste generated. In particular, since waste ion exchange resins are not currently accepted at domestic radioactive waste disposal sites, a big problem occurs in waste treatment and disposal.

On the other hand, as disclosed in Registration Patent No. 10-1883895, a technique for remarkably reducing the amount of waste after decontamination by using a _{BaSO 4 precipitation method without using an ion exchange resin for purification of the decontamination waste solution has been studied.} In the technology, manganese ions in the decontamination waste solution continue to accumulate, _{and a precipitate is formed as manganese oxide (MnO 2} ), so that the decontamination effect decreases as the decontamination process proceeds. In addition, since the manganese ion present in the decontamination solution _{consumes KMnO 4} used as an oxidizing decontamination agent according to the reaction formula (1), the more the decontamination process is repeated, the more decontamination agent needs to 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 No. 10-1950193 describes a method of removing manganese ions in water using powdered activated carbon and a method of coagulation using powdered activated carbon, but in this case, radioactive waste containing activated carbon is generated, and currently activated carbon or carbon is included. Since the treated radioactive waste cannot be treated and disposed of, there is a problem that this technology cannot be applied to the continuous SP-HyBRID process. In the membrane filtration process described in Registration Patent No. 10-1494302, manganese ions contained in backwash water are removed. In order to remove manganese, manganese ions are removed from backwashed water by passing backwash water through the manganese adsorption tank to adsorb manganese ions, but the adsorbent used at this time is a magnetite-based adsorbent or ion exchange resin, which is a functional adsorbent. Also, there is a problem that waste ion exchange resin is generated.

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 resins.

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

The present invention is to provide an SP-HyBRID decontamination process comprising the above method.

The present invention includes a solution after the SP-HyBRID decontamination process containing manganese ions, and provides an electrolytic cell provided with an electrode including a porous metal anode and a cathode; And applying a voltage to the electrode to electrodeposit manganese ions in the solution as manganese oxide to the anode, thereby removing manganese ions in the solution, and removing manganese from the solution after the SP-HyBRID decontamination process. do.

The present invention provides an SP-HyBRID decontamination process including 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 step of the reducing decontamination agent essential in the continuous SP-HyBRID process, so that the total process time is not significantly increased, and the decontamination process can be continuously performed. Furthermore, since the addition 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 is not generated, thereby reducing cost and reducing waste. In addition, since it is possible to analyze the electrodeposition process in real time electrochemically, there is an advantage of being able to work according to optimal operating conditions.

1 shows a schematic diagram of an existing decontamination process including an oxidation step-an oxidant 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 an electrolytic cell used in the present invention.
4 shows an image of forming an electrodeposition layer of an anode and a current formed by an applied voltage in an electrolytic cell according to an embodiment of the present invention.
5 shows the electrodeposition efficiency according to the applied voltage in the electrolyzer according to the embodiment of the present invention.
6(A) shows a circulating voltage current curve according to the concentration of manganese ions in the solution at the reference electrode of the electrolyzer, FIG. 6(B) shows the peak voltage change according to the concentration of manganese ions, and FIG. 6(C) is It shows the peak current density change according to the ion concentration.
7 shows an image of a current formed by an applied voltage and an electrodeposition layer peeling image of the anode in wet regeneration during anode regeneration according to an embodiment of the present invention.
8 shows an image of peeling off the electrodeposition layer when the positive electrode on which the electrodeposition layer is formed is dried in dry regeneration during positive electrode regeneration according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified into 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 the reactor system or primary system, and various devices and facilities surrounding the reactor, for example, control rods that control the output of the reactor, pipes through which coolant is circulated, pressurizers, and steam generators. , Containment containers, etc. are included.

In this case, a metal oxide including a radioactively contaminated metal or alloy is formed at various locations of the primary system, and the metal oxide may be a chromium oxide, an iron oxide, or a nickel oxide.

_{When decontaminating metal oxides contaminated with radioactivity as described above, MnO 4} ^- ions are generally used as an oxidizing agent in the oxidation process to dissolve chromium oxide, _{and MnO 2} particles in the decontamination solution are generated in the system. It flows with the decontamination solution. Furthermore, hydrogen peroxide, hydrazine, and acidic solutions are used to perform the reduction process after the oxidation process is completed to decompose/dissolve _{MnO 4} ^- _{ions as an oxidizing agent and MnO 2} particles as a product of the oxidation process. ²⁺ ) form, and in this case, the concentration of manganese ions in the decontamination solution is present at a level of several hundred ppm.

Thus, the present invention is to provide a technology for removing manganese in the decontamination solution.

In detail, the present invention includes a solution after an SP-HyBRID decontamination process containing manganese ions, and provides an electrolytic cell provided with an electrode including a porous metal anode and a cathode; And applying a voltage to the electrode to electrodeposit manganese ions in the solution as manganese oxide to the anode, thereby removing manganese ions in the solution, and removing manganese from the solution after the SP-HyBRID decontamination process. It is to 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 to _{manganese oxide (MnO 2} ) through a reaction as shown in Formula (2) below at the positive electrode.

_{^{Mn 2+ + 2H 2 O = MnO}} 2 + 4H + + 2e - ... formula (2)

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

Accordingly, 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 anode.

However, at this time, if the voltage of the electrode is applied to E ₁ or more, MnO ₂ is formed. However, if too high a voltage is applied, a reaction as shown in the following formula (3) may occur and permanganate ions may be formed.

_{MnO 2 + 2H 2 O = MnO} 4 - + 4H + + 3e - ... Chemical Formula (3)

_{E 2 = 1.692 - 0.788pH + 0.0197log} [MnO 4 -]

Therefore, in theory, _{a voltage of E 1} or more and E ₂ or less must be applied to electrodeposit _{MnO 2.} However, an overvoltage is always applied in the electrode reaction, and these values vary depending on the reaction characteristics, the concentration of ions, the characteristics of the electrode material, and so on, so it must be confirmed by experiment.

Therefore, when the present invention is applied to the electrolytic cell, it has been confirmed that the voltage has particularly excellent electrodeposition efficiency.As a result, the voltage applied to the electrode in the method of removing manganese from the solution after the SP-HyBRID decontamination process of the present invention is 1.1 to 1.65V. , Preferably it may be 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 to the anode, and when it exceeds 1.65V, the current efficiency of the anode is reduced due to a reaction as in the following formula (4), thereby reducing the electrodeposition efficiency. Reducing problems can arise.

_{2H 2 O = O 2 + 4H} + + 4e - ... Chemical Formula (4)

E ₃ = 1.228-0.0591pH

Further, in the cathode of the electrolyzer, a reaction as shown in the following reaction formula (5) may occur, thereby facilitating the flow of current in the electrolyzer.

_{^{2H + + 2e - = H 2}} ... chemical formula (5)

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

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

In this case, the porous metal-type positive and negative electrodes 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 integrity of the material.

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

The porous metal anode and cathode may have a pore size of 0.1 to 500 μm in diameter, and preferably may have a pore size of 0.1 to 10 μm. At this time, if the pore size is less than 0.1 μm, there is a risk of clogging immediately during electrodeposition, and if it exceeds 500 μm, there may be a problem in filtering particulate matter in the process water.

Further, the electrolyzer may include a reference electrode (RE) to measure the concentration of manganese ions in the solution in real time, and the reference electrode uses an ORP (Oxidation-Reduction Potentail, Pt-Ag/AgCl) electrode. I can. In this case, a method of measuring the voltage or current applied to the electrode may use a cyclic voltammetry method, a static potential method, etc., but is not limited thereto. For example, a cyclic voltammetry method is used to measure the voltage or current applied to the electrode. You can measure voltage or current.

Meanwhile, since iron ions may be additionally included in the solution after the SP-HyBRID decontamination process, at this time, when an electrode voltage of E ₁ ^{or more is applied to the positive electrode, Fe 2+} present in the SP-HyBRID decontamination solution as shown in Formula (6) below. Ions can be electrodeposited into _{Fe 2} O _3.

_{^{2Fe 2+ + 3H 2 O = Fe}} 2 O 3 + 6H + + 2e - ... chemical formula (6)

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

At this time, the calculation of the comparison of the E ₄ values of E ₁ and the formula 6 of the formula (2), SP-HyBRID decontamination solution of E ₁ and in E ₄ pH is a value equal to E ₁ and E ₄ In the last term, the influence of the difference in concentration of each ion is insignificant, so the relationship of _{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 on the anode. have.

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

The wet regeneration may be performed by applying a cathode voltage to the anode electrodeposited with manganese oxide to reduce, for example, immersing the anode electrodeposited with manganese oxide in a sulfuric acid solution and applying a voltage of -0.4 to -0.7V to the manganese oxide. It may be carried out through the step of regenerating the anode by removing, and 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 due to no current flowing through the cathode, and if the voltage exceeds -0.7V, the manganese oxide no longer exists. There is no need to apply excess voltage. In addition, the concentration of the sulfuric acid solution is irrelevant as long as the current can flow smoothly through the anode electrodeposited with manganese oxide, and for example, a 40 mM sulfuric acid solution may be used.

Further, dry regeneration may be performed by drying the anode electrodeposited with manganese oxide 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 manganese oxide is peeled off, for example, manganese Drying the anode electrodeposited with oxide at 50 to 100° C. for 8 to 12 hours; And regenerating the anode by removing the dried manganese oxide. In addition, the drying may be performed in an oven, 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 by any one of, for example, hot air drying, oven drying, and evaporation concentration.

Meanwhile, the present invention provides an SP-HyBRID decontamination process including 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, and may be performed, for example, in a flow as shown in FIG. 2.

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

Manufacturing Example 1

For the evaluation of a simulation test to remove the manganese components present in the decontamination solution after the oxidation process during the primary system chemical decontamination process of a nuclear power plant, a simulated decontamination solution for the solution after SP-HyBRID decontamination 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 bath provided with an electrode including a porous positive electrode and a negative electrode. Both the positive and negative electrodes were made of platinum, and an ORP electrode (reference electrode), which is a Pt-Ag/AgCl electrode, was installed in the electrolyzer to measure the concentration of remaining manganese ions. An exemplary diagram of the electrolyzer is shown in FIG. 3, and this was referred to as Manufacturing Example 1.

Experimental Example 1: Measurement of the voltage of the electrode on electrodeposition

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

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

Further, it was confirmed that 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, large and small air bubbles were formed on the surface. This is because water decomposition is performed when a voltage is applied, and oxygen is generated violently, and the current efficiency of the electrodeposition reaction is reduced due to the generation of oxygen as described above. The oxygen evolution reaction takes place in the same manner as in the formula (4).

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

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

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

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

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

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

As shown in Figure 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 it was efficient to perform electrodeposition 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 performing the electrodeposition process as in Experimental Example 1, the end point of the electrodeposition process can be determined only when the concentration of manganese ions remaining in the solution is analyzed in real time.

However, since it is very tedious to directly analyze the concentration of manganese ions by collecting a solution in which the electrodeposition process has been performed, and the process can be delayed, a technique of 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 method in the ORP electrode of Preparation Example 1 is shown in FIG. 6(A).

In FIG. 6(A), (a) shows the case where the manganese ion concentration is 0, (b) shows the case where the manganese ion concentration is 4 mM, and (c) shows the case where the manganese ion concentration 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 the curve as shown in (a) was formed, the concentration of manganese ions in the solution As can be seen that is 0, at this time, the electrodeposition process can be terminated.

Further, 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 positive electrode and the negative electrode is minimal. When, as shown in FIG. 6(C), when the difference between the peak currents between the anode and the cathode is 0, the concentration of manganese ions in the solution is 0, and thus the electrodeposition process can be terminated.

Preparation Example 2: Regeneration of anode electrodeposited with manganese oxide

(1) wet regeneration

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

As shown in FIG. 7, it was confirmed that a rapid reduction current flows from -0.3V or less, and after that, it was confirmed that the reduction current constantly increases in proportion to the voltage.

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

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

(2) dry regeneration

Fig. 8 shows an image of each electrodeposition layer taken with an optical microscope and an electron microscope after drying the electrodeposition layer for each voltage of the five sections obtained in Experimental Example 2 in an oven at 50° C. for 10 hours.

As shown in FIG. 8, it was confirmed that the electrodeposition layer was split into pieces while drying, so that it could be easily peeled off.

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 without departing from the technical spirit of the present invention described in the claims. It will be obvious to those of ordinary skill in the field.

Claims (10)

Providing an electrolytic cell including a solution after the SP-HyBRID decontamination process containing manganese ions and having an electrode including a porous metal anode and a cathode; And
Applying a voltage to the electrode to electrodeposit manganese ions in the solution as manganese oxide to the anode to remove manganese ions in the solution;
Containing, a method of removing manganese from the solution after the SP-HyBRID decontamination process.
The method of claim 1,
A 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.
The method of claim 1,
The reaction occurring at the anode is a method of removing manganese from the solution after the SP-HyBRID decontamination process, as shown in the following formula (2).
_{^{Mn 2+ + 2H 2 O = MnO}} 2 + 4H + + 2e - ... formula (2)
The method of claim 1,
The voltage applied to the electrode is 1.1 to 1.65V, the method of removing manganese from the solution after the SP-HyBRID decontamination process.
The method of claim 1,
The porous metal-type positive electrode and the negative electrode each have a porosity of 50 to 90%, a method of removing manganese from a solution after the SP-HyBRID decontamination process.
The method of claim 1,
The method of removing manganese from a solution after the SP-HyBRID decontamination process, wherein the porous metallic anode and the cathode each have a pore size of 5 to 500 μm in diameter.
The method of 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 the following formula (6) is performed at the anode.
_{^{2Fe 2+ + 3H 2 O = Fe}} 2 O 3 + 6H + + 2e - ... chemical formula (6)
The method of claim 1,
Removing manganese from the solution after the SP-HyBRID decontamination process, further comprising the step of regenerating the anode by immersing the anode with manganese oxide electrodeposited in a sulfuric acid solution and applying a cathode voltage of -0.4 to -0.7V to remove the manganese oxide How to.
The method of claim 1,
Drying the anode electrodeposited with manganese oxide at 50 to 100° C. for 8 to 12 hours; And
Regenerating the anode by removing the dried manganese oxide
A method for removing manganese from the solution after the SP-HyBRID decontamination process, which further comprises.
An SP-HyBRID decontamination process comprising a method of removing manganese from a solution after the SP-HyBRID decontamination process of any one of claims 1 to 9.

Images