JP2017111027A - Method for reducing secondary waste chemically decontaminated, apparatus for eluting and collecting secondary waste and chemical decontamination system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a method for reducing secondary waste chemically decontaminated, capable of collecting metal ions and/or radioactive nuclides adsorbed in a cation exchange resin by electrodeposition at a high current utilization rate and improving the collection rate of the metal ions and/or radioactive nuclides by the electrodeposition; an apparatus for eluting and collecting the secondary waste; and a chemical decontamination system.SOLUTION: An elution liquid tank 32 stores a mixed solution of hydrazine and at least one of formic acid, glycolic acid and malonic acid as an elution liquid. The elution liquid obtained by introducing the elution liquid to a cation exchange resin tower 21 having captured metal ions and/or radioactive nuclides to collect the metal ions and/or radioactive nuclides is introduced to the cathode chamber of an electrodeposition collection device isolated by a cation exchange membrane while controlling a pH; an electrolysis solution is introduced to the anode chamber; and the metal ions and/or radioactive nuclides are deposited and collected on the surface of a cathode by energizing an anode and the cathode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for reducing the amount of secondary waste generated when a radionuclide is removed by a chemical from the surface of a metal member contaminated with a radionuclide, such as a nuclear power plant, and a metal member surface of a system including these, a secondary The present invention relates to an apparatus for eluting and recovering waste and a chemical decontamination system.

In a nuclear power plant, equipment contaminated with radionuclides is used to reduce the radiation exposure to workers during periodic inspection work and during plant decommissioning, and to reduce the amount of radioactive waste generated by plant demolition during decommissioning. Then, an operation (hereinafter referred to as chemical decontamination) is performed to remove radionuclides with chemicals from the surfaces of the pipes and the metal members of the system including them.
Patent Document 1 is known regarding such chemical decontamination. In Patent Document 1, a mixed solution of oxalic acid and hydrazine is used as a reductive decontamination agent, a potassium permanganate solution is used as an oxidative decontamination agent, and decontamination using a reductive decontamination agent (hereinafter referred to as reductive decontamination). And decontamination using an oxidative decontamination agent (hereinafter referred to as oxidative decontamination) are alternately repeated a plurality of times to dissolve the metal oxide film containing the radionuclide. The dissolved metal ions and radionuclides are removed by passing water through a cation exchange resin tower packed with a cation exchange resin during the reductive decontamination and adsorbing the cation exchange resin. Potassium permanganate used for oxidative decontamination is mixed with oxalic acid contained in the reducing agent after oxidative decontamination, decomposes into manganese ions and potassium ions, and is removed by passing water through a cation exchange resin tower. Furthermore, oxalic acid and hydrazine are reacted with hydrogen peroxide and a catalyst to decompose into carbon dioxide, water, and nitrogen. The cation exchange resin produced by the above operation is generated as secondary waste for chemical decontamination.
Further, in Patent Document 2, metal ions or radionuclides adsorbed on a cation exchange resin are mixed with a sulfuric acid solution, and an electrode is installed so that the mixture is sandwiched between them so that the metal ions are deposited on the cathode. A method of collecting is disclosed.

JP 2000-105295 A JP 2013-217801 A

However, in patent document 1, the cation exchange resin which is a secondary waste by chemical decontamination is discarded without being regenerated.
Further, in Patent Document 2, metal ions or radionuclides adsorbed on a cation exchange resin are mixed with a sulfuric acid solution, and an electrode is placed so as to sandwich the mixture, and then the metal ions are deposited and collected on the cathode. To do. However, much electricity is expended for the movement of hydrogen ions that are not the target, and the movement of metal ions such as Fe or Co, which should be moved to the cathode, is impaired, and the current utilization rate is reduced. In other words, the electrodeposition efficiency of metal ions and / or radionuclides may be reduced.

  Therefore, the present invention makes it possible to deposit metal ions and / or radionuclides adsorbed on the cation exchange resin at a high current utilization rate and improve the recovery rate by electrodeposition of metal ions and / or radionuclides. Another object is to provide a secondary waste reduction method for chemical decontamination, a secondary waste elution recovery apparatus, and a chemical decontamination system.

  In order to solve the above-described problems, the secondary waste elution recovery apparatus of the present invention includes an eluent tank that contains a mixed liquid of hydrazine and at least one of formic acid, glycolic acid, and malonic acid as an eluent. The eluent is passed through a cation exchange resin tower in which metal ions and / or radionuclides are captured, and the eluent containing the metal ions and / or radionuclides is separated by a cation exchange membrane. And introducing an electrolytic solution into the anode chamber and energizing the anode and the cathode, thereby depositing and collecting the metal ions and / or radionuclides on the cathode surface. The pH of the eluent containing metal ions and / or radionuclides is measured, and the pH of the eluent flowing through the cathode chamber is adjusted according to the pH measurement result.

  The secondary decontamination method for chemical decontamination of the present invention includes a step of passing system water containing a chemical decontaminant to piping or equipment to be subjected to chemical decontamination, and water passing to the chemical decontamination target. The step of passing the system water later to the cation exchange resin tower, and the cation exchange resin tower as an eluent with a mixture of hydrazine and at least one of formic acid, glycolic acid and malonic acid The step of eluting the metal ions or radionuclides trapped in the cation exchange resin tower through the water and the eluent containing the metal ions and / or radionuclides are separated from the inside of the electrolytic cell by a cation exchange membrane. Introducing into the cathode chamber in which the cathode is disposed, introducing an electrolyte into the anode chamber in which the anode is disposed, and adjusting the pH of the eluent containing the metal ions and / or radionuclides introduced into the cathode chamber. Measure the pH A pH adjusting step for adjusting the pH of the eluent flowing through the cathode chamber according to the result, and a collecting step for energizing the cathode and anode to deposit the metal ions and / or radionuclides on the cathode surface; Have.

  Furthermore, in the chemical decontamination system of the present invention, system water containing a chemical decontaminant is passed through piping or equipment to be chemically decontaminated, and metal ions and / or radioactive substances contained in the system water after the water has passed. A chemical decontamination apparatus having a cation exchange resin tower for capturing nuclides, an eluent tank for containing a mixture of hydrazine and at least one of formic acid, glycolic acid and malonic acid as an eluent, and a cation An electrodeposition recovery apparatus having an electrolytic cell separated by a replacement membrane into a cathode chamber in which a cathode is disposed and an anode chamber in which an anode is disposed; and the eluent that captures the metal ions and / or radionuclides. And an elution recovery device having an eluent recovery tank for recovering an eluent containing the metal ions and / or radionuclides flowing out from the cation exchange resin tower and flowing out from the cation exchange resin tower. The recovery device introduces the eluent in the eluent recovery tank into the cathode chamber and introduces an electrolyte into the anode chamber, energizes the anode and the cathode, and applies the metal ions or radionuclides to the cathode surface. The pH of the eluent introduced into the cathode chamber is measured, and the pH of the eluent flowing through the cathode chamber is adjusted according to the pH measurement result.

According to the present invention, metal ions and / or radionuclides adsorbed on a cation exchange resin (cation exchange resin tower) can be electrodeposited and recovered at a high current utilization rate. Alternatively, the recovery rate by radionuclide electrodeposition can be improved.
Moreover, since the cation exchange resin tower is regenerated by electrodepositing and recovering metal ions and / or radionuclides, the cation exchange resin tower can be reused.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is an overall configuration diagram of a chemical decontamination system according to an embodiment of the present invention. FIG. 3 is a relationship diagram between formic acid concentration and iron ion elution rate when iron ions adsorbed on a cation exchange resin are eluted into a mixed solution of formic acid and hydrazine. It is process explanatory drawing for calculating | requiring the Fe ion elution rate shown in FIG. It is a related figure of a hydrazine density | concentration at the time of adding a hydrazine to 1 mol / L formic acid, a cation density | concentration, and pH. FIG. 4 is a relationship diagram between pH of a mixed solution and Fe ion elution rate when Fe ions adsorbed on a cation exchange resin are eluted into a mixed solution of formic acid and hydrazine. It is a schematic block diagram of the electrodeposition collection | recovery apparatus which comprises the elution collection | recovery apparatus shown in FIG. It is a figure which shows the time-dependent change of the iron ion concentration in the eluent collect | recovered by the electrodeposition collection | recovery apparatus shown in FIG. FIG. 6 is a relationship diagram between the pH of the recovered eluent and the iron ion removal rate (recovery rate). It is explanatory drawing which adjusts pH of the collect | recovered eluent, Comprising: It is a figure which shows the time change of pH of the collect | recovered eluent by addition of a pH adjuster. It is operation | movement explanatory drawing of the chemical decontamination system of Example 1 which concerns on one Example of this invention. It is operation | movement explanatory drawing of the chemical decontamination system of Example 1 which concerns on one Example of this invention. It is a whole block diagram of the chemical decontamination system of Example 2 which concerns on the other Example of this invention. It is a whole block diagram of the chemical decontamination system of Example 3 which concerns on the other Example of this invention.

In FIG. 1, the whole block diagram of the chemical decontamination system which concerns on one Embodiment of this invention is shown. The chemical decontamination system 1 includes a chemical decontamination device 2 and an elution recovery device 3. The chemical decontamination apparatus 2 includes a chemical decontamination target 20 including a pipe or a device connected to the pipe or a pump, a valve 17, a pump 4, a heater 27, a cooler 28, a valve 16, a surge tank 24, a pump. 5 and the valve 11 are connected to each other by a pipe 40 so that one closed loop can be formed. The solution flowing in the pipe 40 flows in the order of the heater 27, the cooler 28, the valve 16, and the surge tank 24 by the pump 4, and flows in the order of the valve 11, the chemical decontamination target 20, the valve 17, and the pump 4 by the pump 5. .
The valve 16 is sandwiched, the downstream of the cooler 28 and the upstream of the surge tank 24 are connected by a pipe 42, and the valve 14, the mixed resin tower 22, and the valve 12 are installed in the pipe 42. The mixed resin tower 22 is filled with an ion exchange resin obtained by mixing a cation exchange resin and an anion exchange resin at a ratio of 1: 1 or 1: 2. Further, the downstream of the cooler 28 and the upstream of the surge tank 24 are connected by a pipe 43, and the valve 15, the cation exchange resin tower 21, and the valve 13 are installed in the pipe 43. The cation exchange resin tower 21 is filled with a cation exchange resin. That is, with respect to one closed loop formed by the chemical decontamination object 20, the pipe 40, the valve 17, the heater 27, the cooler 28, the valve 16, the surge tank 24, the pump 5, and the valve 11, the cooler 28 and Between the surge tank 24, the cation exchange resin tower 21 and the mixed resin tower 22 can be connected in parallel via valves 12-15.

  A pipe 44 having one end connected to the pipe 40 downstream of the pump 5 and the valve 11 upstream and the other end connected to the pipe 40 via the valve 33, the catalyst tower 26, and the valve 18 is laid. The catalyst tower 26 is packed with a catalyst that promotes a chemical reaction between hydrogen peroxide and an organic acid, for example, 0.5% Ru-supported activated carbon. In addition, it is good also as a structure which replaces with the catalyst tower 26 and installs an ultraviolet irradiation device. A pump 7, a valve 19, and a hydrogen peroxide tank 25 are installed in a pipe 44 downstream of the valve 33 and upstream of the catalyst tower 26. A pipe 41 branched from the pipe 40 is laid in the pipe 40 between the downstream of the pump 5 and the valve 11, and the pump 6, the valve 10, and the chemical decontamination tank 23 are connected by the pipe 41. The chemical decontamination tank 23 stores chemicals used for chemical decontamination. When a plurality of chemicals are used, the pump 6, the valve 10 and the chemical decontamination tank 23 are cleaned and used each time. Note that a plurality of pipes 41, pumps 6, valves 10, and chemical decontamination tanks 23 may be connected in parallel to the pipes 40 according to the number of chemicals to be used. The surge tank 24 is provided with a water supply / drainage pipe 50, and a valve 34 is installed in the water supply / drainage pipe 50.

  The elution recovery apparatus 3 includes a valve 36, a pump 8, a valve 35, and an eluent tank 32 connected by a pipe 46 having one end connected to a pipe 43 between the downstream of the cation exchange resin tower 21 and the valve 13. In addition, the elution recovery device 3 includes a valve 37 and an eluent recovery tank 31 connected by a pipe 45 having one end connected to a pipe 43 between the upstream of the cation exchange resin tower 21 and the valve 15. The pump 9 and the electrodeposition recovery device 30 are installed downstream of the eluent recovery tank 31, and the electrodeposition recovery device 30 is connected to the eluate recovery tank 31 via the pump 9 by a pipe 48. In addition, the downstream side of the electrodeposition recovery apparatus 30 is connected to the eluent recovery tank 31 by a pipe 49. The eluent recovery tank 31 is provided with a drain pipe 51, and a valve 38 is installed in the drain pipe 51.

Next, the eluent supplied to the cation exchange resin 21 from the eluent tank 32 constituting the elution recovery device 3 through the valve 35, the pump 8, and the valve 36 will be described. FIG. 2 is a relationship diagram between the formic acid concentration and the iron ion elution rate when the iron ions adsorbed on the cation exchange resin are eluted into the formic acid hydrazine mixed solution. As test conditions, a cation exchange resin in which an iron sulfate (FeSO ₄ ) aqueous solution was passed through the iron ion so that the iron ion adsorption capacity was about 80% of the total adsorption capacity was used. As an eluent, 400 mL of a mixture of formic acid and hydrazine whose pH was adjusted to 4.7 with hydrazine (hereinafter referred to as a formate hydrazine mixture) was prepared, and water was passed through 200 mL of a cation exchange resin at 400 mL / h. Ions were eluted. Further, 100 mL of pure water was passed through to elute the formic acid hydrazine solution in the cation exchange resin. The temperature is room temperature (25 ° C. ± 5 ° C.).
The results at this time are shown in Table 1. Table 1 shows the Fe ion adsorption amount (g), Fe ion elution amount (g), and Fe ion elution rate (%) for each formic acid concentration M (mol / L).

Here, measurement of Fe ion elution amount (g) and calculation of Fe ion elution rate (%) will be described. FIG. 3 shows a process explanatory diagram for obtaining the iron ion elution rate shown in FIG. As shown in the left diagram of FIG. 3, first, V ₁ mL of a hydrazine formate mixed solution adjusted to pH 4.7 with hydrazine is prepared as an eluent, and water is passed through the pipe 46 to the cation exchange resin tower 21. The eluent in which the Fe ions adsorbed on the cation exchange resin tower 21 are eluted in the eluent is recovered in the eluent recovery tank 31 via the pipe 45. The Fe ion concentration C ₁ in the eluent recovered in the eluent recovery tank 31 is measured, and the Fe ion elution amount is determined by C ₁ · V ₁ from the eluent liquid amount V ₁ .
Next, as shown in the right figure of FIG. 3, V ₂ mL of an aqueous HCl solution (hydrochloric acid) in which water and 3.5 wt% HCl are mixed at a volume ratio of 1: 1 is prepared. Water is passed to the resin tower 21. As a result, Fe ions not previously eluted by the eluent and remaining in the cation exchange resin tower 21 are eluted and recovered in the eluent recovery tank 31 through the pipe 45 together with the aqueous HCl solution. The Fe ion concentration C ₂ in the HCl aqueous solution recovered in the eluent recovery tank 31 is measured, and the residual amount of Fe ions is determined by C ₂ · V ₂ from the liquid amount V ₂ of the HCl aqueous solution.

The adsorption amount of Fe ions in Table 1 is obtained as (C ₁ · V ₁ + C ₂ · V ₂ ), and the elution amount of Fe ions is obtained as C ₁ · V ₁ . Further, the Fe ion elution rate (%) is obtained by the following equation (1).
Fe ion elution rate = (C ₁ · V ₁ ) / (C ₁ · V ₁ + C ₂ · V ₂ ) × 100 (1)
FIG. 2 is a plot of the results shown in Table 1, with the horizontal axis representing the formic acid concentration (M: mol / L) in the formic acid hydrazine mixture and the vertical axis representing the iron ion elution rate (%). From FIG. 2, it was found that 90% or more of iron ions can be eluted when the formic acid concentration is 1 mol / L or more. Furthermore, it was found that the elution rate of iron ions was comparable even when the formic acid concentration was 1 mol / L or more.

When using a hydrazine formate mixture, iron ions are eluted by hydrazine ions (N ₂ H ₅ ⁺ ). The cation adsorbed on the cation exchange resin tower 21 is eluted by replacing with another cation. Dissociation of formic acid (HCOOH) occurs in the following formula (2), and since the equilibrium constant of the following formula (2) is 2.88 × 10 ⁻⁴ , even if formic acid is 1 mol / L, hydrogen ions (H The concentration of ⁺ ) is 0.02 mol / L.
HCOOH = H ⁺ + HCOO ⁻ (2)
On the other hand, dissociation of hydrazine (N ₂ H ₄ ) occurs in the following formula (3), and since the equilibrium constant of the following formula (3) is 1.07 × 10 ^−6, it is a cation with respect to 1 mol / L of hydrazine. The concentration of a certain hydrazine ion (N ₂ H ₅ ⁺ ) is 0.001 mol / L. In order to increase the cation concentration, it is necessary to increase the concentration of formic acid or hydrazine. However, if the concentration is increased, the spent eluent reacts with hydrogen peroxide for detoxification, and nitrogen, dioxide The eluent decomposition process that decomposes into carbon and water takes time. Alternatively, it is not preferable because the equipment scale becomes large.
In order to increase the cation concentration with a small concentration of formic acid and hydrazine, it is only necessary to increase the concentration of hydrazine ions, which are cations, by mixing formic acid and hydrazine and by chemical reaction (the following formula (3)).
HCOOH + N ₂ H ₄ = N ₂ H ₅ ⁺ + HCOO ⁻ (3)
FIG. 4 shows the relationship between the hydrazine concentration, the cation concentration and the pH when hydrazine is added to 1 mol / L formic acid. The calculation result of the cation concentration when the formic acid concentration is constant at 1 mol / L and the hydrazine concentration is increased from 0.0 to 1.5 mol / L is shown. The cation concentration here is the sum of the hydrogen ion (H ⁺ ) concentration and the hydrazine ion (N ₂ H ₅ ⁺ ) concentration. In FIG. 4, the solid line indicates the relationship between the hydrazine concentration and the cation concentration, and the arrow indicates that the vertical axis to be referred to is the cation concentration (mol / L). A dotted line indicates the relationship between hydrazine concentration and pH, and an arrow indicates that the vertical axis to be referred to is pH.
For example, when formic acid and hydrazine are mixed so that formic acid is 1 mol / L and hydrazine concentration is 0.95 mol / L (pH is 4.8), a total of 0.95 mol / L cation is obtained as a sum of hydrogen ions and hydrazine ions. Can be generated. That is, the cation concentration can be 50 times or more than when formic acid and hydrazine are each independently 1 mol / L. Therefore, in order to increase the hydrazine ion (N ₂ H ₅ ⁺ ) concentration used for elution of iron ions, it is necessary to increase the pH. Therefore, the pH is desirably 4 or more. In this test, the pH was adjusted to 4.7, but the pH is preferably adjusted to a range of 4 to 5. From the viewpoint of reducing the hydrogen ion concentration, it is preferable to make the pH near neutral. However, if the pH is higher than 6, the eluted iron ions are precipitated as iron oxide in the cation exchange resin, so that the elution becomes difficult. Further, as shown in FIG. 4, when the pH exceeds 5, the pH greatly changes (raises rapidly) at a low hydrazine concentration, and it is difficult to adjust the pH of the formic acid hydrazine mixed solution. Accordingly, the pH is desirably 5 or less.

FIG. 5 shows the relationship between the pH of the mixed solution and the Fe ion elution rate when Fe ions adsorbed on the cation exchange resin are eluted into the hydrazine formate mixture.
As test conditions, the concentration of formic acid was kept constant at 2 mol / L, and 240 ml of a formic acid hydrazine mixed solution added to hydrazine was used as an eluent. This eluent was passed through 20 mL of cation exchange resin at 40 mL / h. The exchange capacity (adsorption capacity) of the cation exchange resin is 0.46 meq / mL-Resin. Here, meq / mL-Resin is a unit indicating how many milliequivalents of ions can be exchanged with 1 mL of cation exchange resin. The temperature is room temperature (25 ° C. ± 5 ° C.). Further, the pH was changed from 3.7 to 7.8.
The results at this time are shown in Table 2. Table 2 shows the Fe ion adsorption amount (mg), Fe ion elution amount (mg), and Fe ion elution rate (%) for each pH.

Here, the calculation of the Fe ion adsorption amount (mg), the Fe ion elution amount (mg), and the Fe ion elution rate (%) is the same as in FIG.
As shown in FIG. 5, when the pH is changed between 3.7 and 7.8, the Fe ion elution rate is 95% or more in the pH range of 4 to 5, and it is suitable for the elution. confirmed.

Next, FIG. 6 shows a schematic configuration diagram of the electrodeposition recovery device constituting the elution recovery device shown in FIG. 1, and FIG. 7 shows iron ions in the eluent recovered by the electrodeposition recovery device shown in FIG. The change with time of concentration is shown. As shown in FIG. 6, the electrodeposition collection apparatus 30 for collecting the eluted iron ions on the electrode surface is divided (isolated) by the electrolytic cell 300 by a cation exchange membrane 301, and each of the separated (isolated) electrolytic cells 300 is separated. The cathode 302 is installed in the region, that is, the cathode chamber 304, and the anode 303 is installed in the anode chamber 305. The cathode 302 is connected to a DC power source 310 via a conducting wire 308, and the anode 303 is connected to a DC power source 310 via a conducting wire 309.
A pipe 48 is connected to the cathode chamber 304 in which the cathode 302 is installed, and the eluent recovery tank 31 and the pump 9 are connected to the pipe 48. The eluent recovered after passing through the cation exchange resin tower 21 in the eluent recovery tank 31 is passed from the lower part of the electrolytic cell 300 to the cathode chamber 304 by the pump 9 and extracted from the upper part of the cathode chamber 304. Then, it returns to the eluent recovery tank 31 through the pipe 49 again. On the other hand, a pipe 311 is connected to the anode chamber 305 where the anode 303 is installed, and an electrolyte tank 306 and a pump 307 are connected to the pipe 311. The electrolytic solution in the electrolytic solution tank 306 is passed through the anode chamber 305 from the lower portion of the electrolytic cell 300 by the pump 307, extracted from the upper portion of the anode chamber 305, and refluxed again to the electrolytic solution tank 306. The eluent recovery tank 31 and the electrolyte tank 306 are each provided with a gas discharge port (not shown) at the upper part of the tank.
Further, as shown in FIG. 6, the pump 313 and the pH adjuster tank 314 are connected to the eluent recovery tank 31 by a pipe 312. The eluent recovery tank 31 is provided with a pH meter 315 so that the electrode section is immersed in the eluent recovered after passing through the cation exchange resin tower 21. Based on the measured pH value of the recovered eluent measured by the pH meter 315, the control unit 316 controls the discharge pressure of the pump 313 and the like, and adjusts the pH adjusting agent stored in the pH adjusting agent tank 314 to the piping. The pH of the recovered eluent added to the eluent recovery tank 31 via 312 is adjusted. Here, hydrazine is used as the pH adjuster stored in the pH adjuster tank 314. The addition of the pH adjusting agent by the pump 313 to the eluent recovery tank 31 will be described later.

  In FIG. 6, a drain pipe 51 connected to the eluent recovery tank 31 shown in FIG. 1 via a valve 38 and a pipe 45 connected to the eluent recovery tank 31 via a valve 37 are shown. Is omitted. FIG. 6 shows a case where the pH meter 315 is installed in the eluent recovery tank 31, but the present invention is not limited to this. For example, the pH meter 315 is installed between the eluent recovery tank 31 and the pump 9 in the pipe 48 that connects the eluent recovery tank 31 and the cathode chamber 304 of the electrolytic cell 300 via the pump 9. Also good. Further, the pH meter 315 may be installed between the pump 9 and the cathode chamber 304 in the pipe 48.

As test conditions, the eluent recovery tank 31 of the electrodeposition recovery apparatus 30 shown in FIG. 6 was filled with 1 L of an eluent (Fe ion concentration: 7.3 g / L) from which iron ions were eluted, and the electrolyte tank 306 was formic acid. 1 L of 1 mol / L was charged. A stainless steel plate electrode (10 cm × 10 cm) was used as the cathode 302, and a titanium steel plate electrode (10 cm × 10 cm) on which platinum was deposited was used as the anode 303. A constant current (9 A) was supplied from the DC power source 310, and the eluent from which the iron ions were eluted was appropriately collected, and the change over time in the iron ion concentration in the eluent from which the iron ions were eluted was analyzed. The volumes of the cathode chamber 304 and the anode chamber 305 were 250 mL, and 170 mL / min eluent was passed through the cathode chamber 304 and 170 mL / min electrolyte was passed through the anode chamber 305. Further, the pH adjuster (hydrazine) was not added from the pH adjuster tank 314 to the eluent recovery tank 31 by the pump 313.
The results at this time are shown in Table 3. In Table 3, the Fe ion concentration in the eluent for each energization time (h) is shown as the iron concentration (g / L) in the eluent. The energization time was set to 0.0 to 5.9 h, and when the energization time was 2.7 h, the electrodeposition collection apparatus 30 was once stopped and the cathode 302 was replaced with another new stainless steel electrode.

  As shown in Table 3 and FIG. 7, the iron ion concentration decreased to 0.57 g / L with 5.9 hours of energization. That is, 90% or more of iron ions could be recovered.

The current utilization rate is defined as a percentage of a value obtained by dividing the amount of recovered iron by the amount of iron when all the amount of electricity is used for iron recovery. The current utilization rate at energization time 5.9h is calculated as 12%. Here, the recovered iron amount is obtained by the following equation (4), and the iron amount calculated from the energization amount is obtained by the following equation (5).
(Recovered iron amount: mol) = {(initial value: 7.3 g / L) − (end value: 0.57 g / L)} × (eluent amount: 1 L) ÷ 55.847 g / mol × 1 L = 0 .12 mol (4)
(The amount of iron when the amount of electricity is all used for iron recovery: mol) = (current value: 9 C / s) × (energization time: 6 h) × (unit conversion: 3600 s / h) ÷ (valence of iron: 2) ÷ (Faraday constant: 96500 C / mol) = 1.0 mol (5)
Here, 55.847 g / mol in the formula (4) is the atomic weight of Fe, and in the formula (5), the energization time of 5.9 h was calculated as 6 h.

  When the current utilization factor is calculated using data from an energization time of 4.6 h to 5.9 h when the iron ion concentration is 0.96 g / L or less, it is calculated to be 3.1%. Since the iron ion concentration in the decontamination liquid during chemical decontamination is about 0.01 to 0.1 g / L, compared to the conventional method of directly recovering iron ions from the decontamination liquid during chemical decontamination, According to the present embodiment, the current efficiency can be improved several times. That is, in the conventional method, since the Fe ion concentration is low, it is necessary to lengthen the energization time, and the current utilization rate decreases.

In the present embodiment, as shown in FIG. 6, the electrolytic cell 300 is separated into the cathode chamber 304 and the anode chamber 305 by the cation exchange membrane 301. For comparison, the anode and the cathode were installed and energized without installing the cation exchange membrane 301 in the electrolytic cell 300. In this case, the eluent from which the iron ions were eluted changed from brown to black and the recovery of the iron ions at the electrode was hindered. This is presumed to be because, as shown in the following formulas (6) and (7), divalent iron ions were oxidized to trivalent on the surface of the anode, and iron oxide was generated by reaction with the divalent iron ions. Is done.
Fe ²⁺ = Fe ³⁺ + e ⁻ (6)
_{^{Fe 2+ + 2Fe 3+ + 4H 2}} O = Fe 3 O 4 + 8H + ··· (7)
Therefore, it is important to install the cation exchange membrane 301 so that the eluent from which iron ions are eluted does not come into contact with the anode 303.

Next, a third experimental result in the present embodiment will be described below with reference to FIG. Similar to the second experiment described with reference to Table 3 and FIG. 7, the electrodeposition collection apparatus 30 shown in FIG. 6 was used. In an eluent recovery tank 31 of the electrodeposition recovery apparatus 30 shown in FIG. 6, an iron ion solution (iron ion concentration: 10 g / L) adjusted to pH 0.1 to 3.5 with iron sulfate containing 5 g of iron and sulfuric acid. ) 0.5 L was charged, and 1 L / L of formic acid 1 mol / L was charged in the electrolyte tank 306. A stainless steel plate electrode (10 cm × 10 cm) was used as the cathode 302, and a titanium steel plate electrode (10 cm × 10 cm) on which platinum was deposited was used as the anode 303. A constant current (6 A) was applied for 1 hour by the DC power source 310, and the iron ion concentration in the iron ion solution after the application was analyzed. As in the second experiment, the pH adjuster (hydrazine) was not added from the pH adjuster tank 314 to the eluent recovery tank 31 by the pump 313. The result at this time is shown in FIG. In FIG. 8, the vertical axis represents the iron ion removal rate (%), and the horizontal axis represents the pH of the iron ion solution, showing the relationship. The iron ion removal rate (%) on the vertical axis was calculated by the following equation (8).
R = (A ₀ −A ₁ ) / A ₀ × 100 (8)
Here, R is the iron ion removal rate, A ₀ is the initial iron ion concentration in the iron ion solution, and A ₁ is the iron ion concentration in the iron ion solution after electrodeposition.

As shown in FIG. 8, it can be seen that iron ions cannot be attached to the electrode (cathode 302) when the pH is 0.26. It can be seen that when the pH is set to 1, iron ions can be attached to the electrode (cathode 302), although the speed is small. Furthermore, it can be seen that when the pH is controlled to 2 or more, the deposition rate of iron ions to the electrode (cathode 302) is greatly increased. This is considered to be because when the pH is lowered, the precipitated iron comes into contact with the acidic liquid and is dissolved as iron ions by the following formula (9).
Fe + 2H ⁺ = Fe ²⁺ + H ₂ ↑ (9)
As in the second experiment described above in this embodiment, when the iron ions are attached to the cathode 302, the pH of the eluent from which the iron ions are eluted is lowered. On the surface of the cathode 302, iron ions are deposited as iron by the reaction shown in the following formula (10).
Fe ²⁺ + 2e ⁻ = Fe (10)
When iron ions are deposited, H ⁺ ions permeate from the anode 303 through the cation exchange membrane 301 at a rate of 2 mol with respect to 1 mol of Fe ²⁺ ions so that the liquid flowing through the cathode 302 is electrically balanced. Move to. Accordingly, the H ⁺ concentration on the cathode 302 side increases, and the pH decreases.

Therefore, it is preferable to measure the pH of the eluent from which iron ions have been eluted (recovered eluent) and to control the pH of the recovered eluent so that the pH becomes 1 or more. It is desirable to control the pH of the eluent so that is 2 or more. Further, the pH is the same as the solution used for elution of iron ions from the cation exchange resin tower 21, that is, the mixture of formic acid and hydrazine, which is the eluent stored in the eluent tank 32 (FIG. 1). Specifically, the pH is set to 5 or less. This is because, when the pH of the recovered eluent becomes higher than 6, as described above, iron ions in the recovered eluent are precipitated as iron oxides, and the adhesion of iron ions to the cathode 302 is inhibited and the electric charge is prevented. This is because the recovery rate due to the analysis decreases. In addition, adjusting the pH of the recovered eluent in this way means that the eluent used for elution of iron ions, that is, the hydrazine contained in the eluent contained in the eluent tank 32 is excessive after use. It is also desirable from the viewpoint of detoxification with hydrogen oxide or the like. Specifically, hydrazine (N ₂ H ₄ ) is rendered harmless by the reaction represented by the following formula (11).
N ₂ H ₄ + 2H ₂ O ₂ = N ₂ + 4H ₂ O (11)
As in the case of the iron ion solution described above, in the case of the cobalt ion solution, the reactions shown in the above formulas (9) and (10) are expressed by the following formulas (9 ′) and (10 ′), respectively. It becomes the reaction shown.
Co + 2H ⁺ = Co ²⁺ + H ₂ ↑ (9 ′)
Co ²⁺ + 2e ⁻ = Co (10 ′)
Next, returning to FIG. 6, the pH adjustment of the eluent containing the recovered iron ions will be described. The control unit 316 illustrated in FIG. 6 includes a processor such as a CPU (not shown), a ROM that stores various programs, a RAM that temporarily stores calculation results, and a storage device such as an HDD.

First, the eluent containing iron ions after passing through the cation exchange resin tower 21 flows into the eluent recovery tank 31 via the valve 37 and the pipe 45 (FIG. 1). At the stage of flowing into the eluent recovery tank 31 and at the time when it flows into the cathode chamber 304 of the electrolytic cell 300 via the pump 9 (before energization), the pH of the eluent containing iron ions is the eluent. It is the same as the pH of the eluent when water is passed from the tank 32 to the cation exchange resin tower 21. Thereafter, when the cathode 302 and the anode 303 are energized by the DC power supply 301 and the electrodeposition is started, the cation exchange membrane 301 is transmitted through the anode chamber 305 in which the formic acid as the electrolyte circulates according to the electrodeposition time (energization time). Then, H ⁺ ions move to the cathode chamber 304 side. In order to deposit Fe ²⁺ on the cathode 302, H ^{+ in} an amount twice as large as Fe ²⁺ is consumed as described above, and an eluent containing iron ions refluxed in the cathode chamber 304 and the eluent recovery tank 31 (recovered). The pH of the eluent decreases with the electrodeposition time.

Therefore, the control unit 316 takes in the pH measurement value of the eluent containing iron ions after the start of electrodeposition measured by the pH meter 315 in a predetermined cycle, and the pH of the eluent containing iron ions is in the range of pH 1 to pH 5. Then, a start command is transmitted to the pump 313, and hydrazine (N ₂ H ₄ ) as a pH adjuster is added (injected) from the pH adjuster tank 314 to the eluent recovery tank 31 via the pipe 312. Here, based on the result of the second experiment described above, the pH is adjusted under the condition that the deposition rate of iron ions in the eluent to the cathode 302 is constant even if the pH of the eluent containing iron ions is changed. FIG. 9 shows the results of determining the change in pH of the eluent containing iron ions with the addition of hydrazine (N ₂ H ₄ ) as a regulator. Here, the eluent recovery tank 31 of the elution recovery apparatus 3 is filled with 1 L of an eluent from which iron ions have been eluted (Fe ion concentration: 7.3 g / L), and the electrolyte tank 306 is charged with 1 L of formic acid 1 mol / L. did. A stainless steel plate electrode (10 cm × 10 cm) was used as the cathode 302, and a titanium steel plate electrode (10 cm × 10 cm) on which platinum was deposited was used as the anode 303. In FIG. 9, the vertical axis represents the pH of the eluent containing iron ions, the horizontal axis represents the electrodeposition time (energization time) (h) as the test time, and hydrazine (N ₂ H ₄ ) as the pH adjuster is used. The time change when adding intermittently is shown. As shown in FIG. 9, the pH of the eluent containing iron ions decreases with time after the start of electrodeposition. When 0.1 mol / L hydrazine (N ₂ H ₄ ) is added at the time before the pH of the eluent containing iron ions reaches pH 1, for example, when the pH reaches 1.20, after elapse of a predetermined time (pH The pH of the eluent containing iron ions rapidly increases and exceeds pH 4.5. From there, the pH once suddenly drops to around pH 2.5 before it reaches pH 5 (pH 4.7), and then gradually drops. When 0.1 mol / L hydrazine (N ₂ H ₄ ) was added before reaching pH 1, for example, when the pH reached 1.20, the same change as described above was obtained.
Accordingly, the control unit 316 stores a preset lower limit value (for example, pH 1.20) in a storage device (not shown), and a pH measurement value of the eluent containing iron ions obtained from the pH meter 315 at a predetermined cycle. The preset lower limit value is compared. As a result of the comparison, when the pH is equal to or less than the pH measurement value of the eluent containing iron ions, the control unit 316 transmits an activation command to the pump 313 and pH from the pH adjuster tank 314 to the eluent recovery tank 31 via the pipe 312. Hydrazine (N ₂ H ₄ ), which is a regulator, is added, and the pH is adjusted so that the pH of the eluent containing iron ions during the electrodeposition period is in the range of pH 1 to pH 5. In addition, what is necessary is just to use the value calculated | required beforehand by experiment for the setting of the said lower limit. As described above, the control unit 316 acquires the pH measurement value of the eluent containing iron ions obtained from the pH meter 315 at a predetermined period, and performs feedback control based on the acquired pH measurement value.

Next, the control unit 316 replaces the above-described feedback control with hydrazine (N ₂₎ necessary for controlling to a desired pH every energization time (deposition time) stored in a storage device (not shown) in advance. A configuration for adjusting the pH of the eluent containing iron ions using the relationship with the amount of addition of H ₄ ) will be described. Table 4 shows the hydrazine (N ₂ H) required for controlling the iron ion concentration, pH 1, pH 2, pH 3, pH 4, and pH 4.7 in the eluent for each energization time (deposition time (h)). ₄ ) The relationship with the added amount is shown. The relationship shown in Table 4 is the same as that of the above-mentioned second experimental condition in advance, and the amount of hydrazine (N ₂ H ₄ ) that is a pH adjuster is changed, and iron current is increased for each energization time (deposition time). The pH of the eluent containing ions was measured with a pH meter 315, and the amount of hydrazine (N ₂ H ₄ ) added when the measured pH was pH 1, pH 2, pH 3, pH 4, and pH 4.7, respectively. It is obtained by storing in a storage device (not shown). Here, the above-described second experimental condition is that 1 L of an eluent (Fe ion concentration: 7.3 g / L) eluted from iron ions is filled in the eluent recovery tank 31 of the elution recovery apparatus 3 to obtain an electrolyte solution. A tank 306 is filled with 1 L of formic acid 1 mol / L, a stainless steel plate electrode (10 cm × 10 cm) is used as the cathode 302, and a titanium steel plate electrode (10 cm × 10 cm) on which platinum is deposited is used as the anode 303. It is used.

The control unit 316 stores the relationship shown in Table 4 in a storage device (not shown), for example, as a table. After the start of electrodeposition, the control unit 316 acquires pH measurement values of the eluent containing iron ions obtained from the pH meter 315 at a predetermined cycle, and refers to a table stored in a storage device (not shown). Thereafter, the control unit 316 determines the measurement time of the obtained pH measurement value, that is, the amount of hydrazine (N ₂ H ₄ ) added to control the desired pH during the energization time (h) in Table 4. Extract. The control unit 316 outputs an operation amount such as a start command and a discharge pressure to the pump 313 so that the extracted amount of hydrazine (N ₂ H ₄ ) is added, and from the pH adjuster tank 314, hydrazine which is a pH adjuster (N ₂ H ₄ ) is added to the eluent recovery tank 315 via the pipe 312.

In the present embodiment shown in FIG. 6, the pH adjusting agent is added to the eluent recovery tank 31 via the pipe 312. However, the present invention is not limited to this. One end of the pipe 312 (the end opposite to the end connected to the pH adjuster tank 314) is the elution of the pipe 48 connecting the eluent recovery tank 31 and the cathode chamber 304 of the electrolytic cell 300. It is good also as a structure merged between the liquid collection | recovery tank 31 and the pump 9. FIG. Further, one end of the pipe 312 may be configured to merge between the pump 9 and the cathode chamber 304 in the pipe 48. Furthermore, although the pH adjustment effect of the recovered eluent is somewhat reduced, one end of the pipe 312 may be connected to the cathode chamber 304 of the electrolytic cell 300 from below.
In the above-described embodiment, the control unit 316 controls the addition of the pH adjusting agent to the eluent containing iron ions (recovered eluent). However, the present invention is not limited to this. In some cases, the pH measurement value of the recovered eluent obtained by the pH meter 315 is displayed on a display unit (not shown), the operator determines the displayed pH measurement value, and starts the pump 313 to adjust the pH. The pH adjusting agent may be added from the agent tank 314 to the eluent recovery tank 31 via the pipe 312.
Further, in addition to the measured pH value of the recovered eluent obtained by the pH meter 315, the iron ion concentration in the eluent, pH 1 shown in Table 4 above, for each energization time (deposition time (h)). , PH 2, pH 3, pH 4, and the relationship with the addition amount of the pH adjusting agent necessary for controlling to pH 4.7 may be displayed on a display unit (not shown). In this case, in addition to the displayed pH measurement value, the operator can refer to the addition amount of the pH adjusting agent for adjusting to the desired pH, and can start the pump 313 more appropriately. .

In addition, although the case where a stainless steel plate was used as the cathode 302 was described, a stainless steel mesh electrode may be used instead.
In the present embodiment, a mixed solution of formic acid and hydrazine is used as the eluent. However, the present invention is not limited to this, and a mixed solution of glycolic acid and hydrazine or a mixed solution of malonic acid and hydrazine may be used. Further, it may be a mixed liquid of at least one of formic acid, glycolic acid and malonic acid and hydrazine. That is, for example, formic acid and glycolic acid may be mixed at a predetermined concentration and hydrazine may be added to form a mixed solution. Alternatively, after mixing formic acid and malonic acid at a predetermined concentration, hydrazine may be added to form a mixed solution.
Moreover, although Fe ion was demonstrated to the example as a metal ion eluted from the cation exchange resin tower 21, it is not restricted to this. For example, the cation may be Co, Ni or the like.
According to this embodiment, as described above, the metal ions and / or radionuclides adsorbed on the cation exchange resin (cation exchange resin tower) can be recovered at a high current utilization rate, and the metal The recovery rate by ion deposition of ions and / or radionuclides can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. In the following examples, the case where Fe ions are used as an example of metal ions eluted from the cation exchange resin tower 21 and a mixed solution of formic acid and hydrazine is used as an eluent will be described as an example.

  10 and 11 are diagrams for explaining the operation of the chemical decontamination system according to the first embodiment of the present invention. The chemical decontamination system 1 including the chemical decontamination device 2 and the elution recovery device 3 in this embodiment is the same as the configuration shown in FIG. 1 described above, and the electrodeposition recovery device 30 constituting the elution recovery device 3. The configurations of the pH adjusting agent tank, pH meter, and pump, which are mechanisms for adjusting the pH of the recovered eluent, are the same as those shown in FIG.

  Below, the chemical decontamination process by the chemical decontamination system 1 of a present Example in case the piping and apparatus which are the chemical decontamination object 20 are stainless steel or a nickel base alloy is demonstrated. In FIGS. 10 and 11, a valve represented by white represents an open state, and a valve filled with black represents a closed state. First, a preparation process for making the chemical decontamination system 1 operable will be described.

(1) Preparation process
First, as shown in the upper diagram of FIG. 10, the valves 10, 19, 36, and 37 are closed. All other valves are open. In this state, ion exchange water is introduced from the water supply / drain pipe 50 connected to the surge tank 24. After introducing the necessary amount of ion-exchanged water, the valve 34 installed in the water supply / drainage pipe 50 is closed and the valves 12, 13, 14, 15, 18 and 33 are closed as shown in the lower diagram of FIG. To. Thereby, the chemical decontamination object 20, the valve 17, the pump 4, the heater 27, the cooler 28, the valve 16, the surge tank 24, the pump 5 and the valve 11 form one closed loop by the pipe 40 connecting them. The
With the closed loop formed, the pumps 4 and 5 are started, and water (hereinafter referred to as system water) filled in the chemical decontamination apparatus 2 and the piping or equipment that is the chemical decontamination target 20 is called in the closed loop. Circulate. In addition, system | strain water here means the water which exists in the chemical decontamination apparatus 2 including the water after the chemical | medical agent supplied from the chemical decontamination agent tank 23 is added, for example.
The system water circulating in the closed loop is heated to a predetermined temperature by the heater 27 and then controlled to maintain the predetermined temperature. Here, the predetermined temperature is desirably 90 ± 5 ° C. After completion of the preparation process, the process proceeds to the oxidative decontamination process.

(2) Oxidative decontamination process
In the oxidative decontamination step, the chemical decontamination agent tank 23 is filled with a chemical decontamination agent (oxidation decontamination agent) in the open / closed state of each valve shown in the lower diagram of FIG. After filling with the oxidative decontamination agent, the valve 10 is opened and the pump 6 is started. The open / closed state of each valve at this time is as shown in FIG. When the pump 6 is started, the oxidative decontamination agent filled in the chemical decontamination agent tank 23 is injected into the pipe 40 that forms the closed loop through the pipe 41. Here, potassium permanganate or permanganate is suitable as the oxidative decontamination agent. Potassium permanganate and permanganate are injected into the pipe 40 from the chemical decontamination tank 23 through the pump 6 so that the permanganate ion concentration in the system water circulating in the closed loop is 200 to 500 mg / L.
After the injection of the oxidative decontamination agent is completed, the pump 6 is stopped and the valve 10 is closed. At this time, the open / closed state of each valve returns to the state shown in the lower diagram of FIG. 10, and the pump 4 and the pump 5 remove the oxidative decontamination agent for 2 to 6 hours (hours). For example, it is circulated through a valve or a pump. Next, the process proceeds to the oxidative decontamination agent decomposition step.

(3) Oxidative decontamination process
In the oxidative decontamination agent decomposition step, the chemical decontamination tank 23 is filled with a chemical that reduces permanganate ions to manganese ions in the open / closed state of each valve shown in the lower diagram of FIG. For example, oxalic acid is suitable as a chemical that reduces permanganate ions to manganese ions. Oxalic acid and permanganate ions cause the reaction shown in the following formula (12).
2MnO ₄ ⁻ +5 (COOH) ₂
^{= 2Mn 2+ + 6OH - + 10CO} 2 + 2H 2 O ··· (12)
Therefore, oxalic acid having a molar ratio of 2.5 or more permanganate ions is prepared.

The valve 10 is opened and the pump 6 is started. At this time, the open / closed state of each valve is as shown in FIG. When the pump 6 is started, a chemical that reduces permanganate ions filled in the chemical decontamination agent tank 23 to manganese ions is injected into the pipe 40 via the pipe 41.
After the injection of chemicals for reducing permanganate ions into manganese ions into the pipe 40 is completed, the pump 6 is stopped and the valve 10 is closed. Thereby, the open / closed state of each valve becomes the state shown in the lower diagram of FIG. Thereafter, the water in the surge tank 24 is visually confirmed by an operator to confirm that the purple color of permanganate ions has become transparent, and then the oxidative decontamination agent decomposition step is completed. After completion of the oxidative decontamination agent decomposition step, the process proceeds to a reduction decontamination step.

(4) Reduction decontamination process
In the reduction decontamination step, the valves 13 and 15 are opened from the open / closed state of the valves shown in the lower diagram of FIG. 10, and the system water is circulated through the cation exchange resin tower 21. Further, the chemical decontamination tank 23 is filled with a reductive decontamination agent. After completion of filling with the reducing decontaminating agent, the valve 10 is opened and the pump 6 is started. When the pump 6 is started, the reductive decontamination agent filled in the chemical decontamination agent tank 23 is injected into the pipe 40 via the pipe 41. Here, as the reducing decontaminating agent, for example, oxalic acid or a mixed solution of oxalic acid and hydrazine is suitable. Oxalic acid is supplied from the chemical decontamination tank 23 by the pump 6 so that the concentration of oxalic acid in the system water circulating through the chemical decontamination target 20 and the cation exchange resin tower 21 by the pipe 40 and the pipe 43 is 2000 to 3000 mg / L. Is injected into the pipe 40. Similarly, hydrazine is injected into the pipe 40 so that the hydrazine concentration in the system water is 400 to 600 mg / L.
After the injection of the reductive decontamination agent into the pipe 40 is completed, the pump 6 is stopped and the valve 10 is closed. Then, the reducing decontaminating agent is circulated by the pump 4 and the pump 5 to the pipe or the equipment which is the chemical decontamination target 20 for 6 to 12 hours. Thereafter, the process proceeds to a reductive decontamination decomposition process.
(5) Reductive decontamination process
In the reduction decontaminating agent decomposition step, the hydrogen peroxide tank 25 is filled with hydrogen peroxide. At this time, the valve 19 is in a closed state. Further, the valve 18 and the valve 33 are opened, and the system water is circulated through the catalyst tower 26.
Subsequently, the valve 19 is opened and the pump 7 is started. By the activation of the pump 7, the hydrogen peroxide filled in the hydrogen peroxide tank 25 flows through the pipe 44 through the valve 33 in an open state and is injected into the pipe 40. The injection concentration of hydrogen peroxide is preferably 1 to 2 times the reaction equivalent with the reducing decontamination reagent. When the reductive decontaminating agent is oxalic acid or hydrazine, it reacts with hydrogen peroxide as shown in the following formulas (13) and (14), respectively.
(COOH) ₂ + H ₂ O ₂ = 2CO ₂ + 2H ₂ O (13)
N ₂ H ₄ + 2H ₂ O ₂ = N ₂ + 4H ₂ O (14)
When the oxalic acid concentration is 3000 ppm, the reaction equivalent of hydrogen peroxide is 1133 ppm, and when the hydrazine concentration is 600 ppm, the reaction equivalent of hydrogen peroxide is 1275 ppm. Note that the hydrogen peroxide injection concentration may be changed with the decomposition of the reductive decontaminating agent, or the hydrogen peroxide concentration calculated by the initial concentration of the reducing decontaminating agent may be kept constant.
When the oxalic acid concentration and the hydrazine concentration reach the detection limit (10 mg / L) by the reaction of the equations (13) and (14), the pump 7 is stopped and the valves 10, 18 and 33 are closed. And Thus, the injection of hydrogen peroxide filled in the hydrogen peroxide tank 25 into the pipe 40 is completed. After the reduction decontaminant decomposition step, the process proceeds to the necessity determination step for additional decontamination.

(6) Additional decontamination necessity determination process
In the additional decontamination necessity determination process, the purification process is performed when the radiation dose of the piping or equipment that is the target of chemical decontamination 20 is less than the target value or when additional decontamination cannot be performed due to economic or time demands. Migrate to In cases other than the above, the valves 13 and 15 are closed, that is, the open / closed state of each valve is set to the state shown in the lower part of FIG. 10, and the process returns to (2) the oxidative decontamination step and the subsequent steps are repeated.

(7) Purification process
In the purification process, heating by the heater 27 is stopped, and cooling by the cooler 28 is started. System that circulates in a closed loop formed by the chemical decontamination object 20, valve 17, pump 4, heater 27, cooler 28, valve 16, surge tank 24, pump 5, valve 11, and piping 40 connecting them. When the temperature of the water becomes 60 ° C. or lower, the valves 12 and 14 are opened. Thereby, the system water flows into the mixed resin tower 22 through the pipe 40 and the pipe 42, and then flows and circulates to the chemical decontamination target 20. The electrical conductivity of system water is appropriately measured with the surge tank 24. Purification (circulation of the system water) is continued until the electrical conductivity of the system water in the surge tank 24 becomes 1 mS / m or less. When the electrical conductivity of the system water in the surge tank 24 becomes 1 mS / m or less, the pump 4 and the pump 5 are stopped, the valves 18, 33, 34 are opened, and the chemical decontamination from the water supply / drainage pipe 50 is performed. The system water in the apparatus 2 is drained. Thereby, a chemical decontamination process is complete | finished.

  Next, the chemical decontamination process by the chemical decontamination system 1 of the present embodiment in the case where the pipe or device that is the chemical decontamination target 20 is carbon steel or low alloy steel will be described.

(1 ') Preparation process
First, as shown in the upper diagram of FIG. 10, the valves 10, 19, 36, and 37 are closed. All other valves are open. In this state, ion exchange water is introduced from the water supply / drain pipe 50 connected to the surge tank 24. After introducing the necessary amount of ion-exchanged water, the valve 34 installed in the water supply / drainage pipe 50 is closed and the valves 12, 13, 14, 15, 18 and 33 are closed as shown in the lower diagram of FIG. To. Thereby, the chemical decontamination object 20, the valve 17, the pump 4, the heater 27, the cooler 28, the valve 16, the surge tank 24, the pump 5 and the valve 11 form one closed loop by the pipe 40 connecting them. The
In a state where the closed loop is formed, the pumps 4 and 5 are started, and the system water filled in the chemical decontamination apparatus 2 and the piping or equipment that is the chemical decontamination target 20 is circulated in the closed loop. The system water circulating in the closed loop is heated to a predetermined temperature by the heater 27 and then controlled to maintain the predetermined temperature. Here, the predetermined temperature is desirably 90 ± 5 ° C. After completion of the preparation process, the process proceeds to the organic acid decontamination process.

(2 ') Organic acid decontamination process
In the organic acid decontamination step, the valves 13 and 15 are opened from the open / closed state of each valve shown in the lower diagram of FIG. 10, and the system water is circulated through the cation exchange resin tower 21. Next, the organic acid decontamination agent is filled in the chemical decontamination tank 23. After filling with the organic acid decontaminating agent, the valve 10 is opened and the pump 6 is started. By starting the pump 6, the organic acid decontamination agent filled in the chemical decontamination agent tank 23 is injected into the pipe 40 via the pipe 41. Here, malonic acid or a mixed solution of malonic acid and oxalic acid is suitable as the organic acid decontaminant. Malonic acid is injected into the pipe 40 from the chemical decontamination tank 23 by the pump 6 so that the malonic acid concentration in the system water is 2000 to 6000 mg / L. Similarly, oxalic acid is injected into the pipe 40 so that the oxalic acid concentration in the system water is 50 to 400 mg / L.
After the injection of the organic acid decontaminant into the pipe 40 is completed, the pump 6 is stopped and the valve 10 is closed. Then, the organic acid decontaminant is circulated by the pump 4 and the pump 5 to the pipe or the equipment which is the chemical decontamination target 20 for 6 to 12 hours. Thereafter, the process proceeds to an organic acid decontaminant decomposition step.

(3 ') Organic acid decontaminant decomposition process
In the organic acid decontaminant decomposition step, the hydrogen peroxide tank 25 is filled with hydrogen peroxide. At this time, the valve 19 is in a closed state. Further, the valve 18 and the valve 33 are opened, and the system water is circulated through the catalyst tower 26.
Subsequently, the valve 19 is opened and the pump 7 is started. By the activation of the pump 7, the hydrogen peroxide filled in the hydrogen peroxide tank 25 flows through the pipe 44 through the valve 33 in an open state and is injected into the pipe 40. The injection concentration of hydrogen peroxide is preferably 1 to 2 times the reaction equivalent with the organic acid decontaminant. When the organic acid decontaminating agent is oxalic acid or malonic acid, it reacts with hydrogen peroxide as shown in the following formulas (15) and (16), respectively.
(COOH) ₂ + H ₂ O ₂ = 2CO ₂ + 2H ₂ O (15)
_{C 3 H 4 O 4 + 4H} 2 O 2 = 3CO 2 + 6H 2 O ··· (16)
When the oxalic acid concentration is 400 ppm, the reaction equivalent of hydrogen peroxide is 151 ppm, and when the malonic acid concentration is 6000 ppm, the reaction equivalent of hydrogen peroxide is 2794 ppm. The hydrogen peroxide injection concentration may be changed with the decomposition of the organic acid decontaminating agent, or the hydrogen peroxide concentration calculated by the initial concentration of the organic acid decontaminating agent may be kept constant.
When the oxalic acid concentration and malonic acid concentration reach the detection limit (10 mg / L) by the reaction of the equations (15) and (16), the pump 19 is stopped and the valves 10, 18 and 33 are closed. State. Thus, the injection of hydrogen peroxide filled in the hydrogen peroxide tank 25 into the pipe 40 is completed. After the organic acid decontaminant decomposition step is completed, the process proceeds to the necessity determination of additional decontamination.

(4 ') Additional decontamination determination process
In the additional decontamination necessity determination process, the purification process is performed when the radiation dose of the piping or equipment that is the target of chemical decontamination 20 is less than the target value or when additional decontamination cannot be performed due to economic or time demands. Migrate to In cases other than the above, (2 ′) return to the organic acid decontamination step and repeat the subsequent steps.

(5 ') Purification process
In the purification process, heating by the heater 27 is stopped, and cooling by the cooler 28 is started. The temperature of the system water circulating through the chemical decontamination object 20, the valve 17, the pump 4, the heater 27, the cooler 28, the valve 16, the surge tank 24, the pump 5, the valve 11, and the pipe 40 connecting them is 60. When the temperature becomes equal to or lower than ° C., the valves 12 and 14 are opened. Thereby, the system water flows into the mixed resin tower 22 through the pipe 40 and the pipe 42, and then flows and circulates to the chemical decontamination target 20. The electrical conductivity of system water is appropriately measured with the surge tank 24. Purification (circulation of the system water) is continued until the electrical conductivity of the system water in the surge tank 24 becomes 1 mS / m or less. When the electrical conductivity of the system water in the surge tank 24 becomes 1 mS / m or less, the pump 4 and the pump 5 are stopped, and the valves 18, 33 and 34 are opened. System water in the chemical decontamination apparatus 2 is drained from the water supply / drainage pipe 50 by opening the valve 34. Thereby, a chemical decontamination process is complete | finished.

  Next, using the elution recovery apparatus 3 of the present embodiment, metal ions and radionuclides are eluted from the cation exchange resin tower 21 and deposited on the electrode surface as metal or metal oxide to recover metal ions and radionuclides. The elution recovery process will be described.

(1) Metal ion elution process
In the metal ion elution step, the valve 35 is closed and the eluent tank 32 is filled with the eluent. Here, in this example, a formic acid hydrazine mixed solution having a formic acid concentration of 1 to 2 mol / L and a pH adjusted to 4 to 5 with hydrazine is used as an eluent. The eluent is not limited to the formic hydrazine mixed liquid, and for example, a glycolic hydrazine mixed liquid or a malonic hydrazine mixed liquid may be used as the eluent.
After filling the eluent tank 32 with the eluent, the valves 13, 15, 36 and 37 are opened, and the valve 38 installed in the drain pipe 51 is closed. Thereafter, the valve 35 is opened and the pump 8 is started. When the pump 8 is started, the eluent flows through the pipe 46 and flows into the cation exchange resin tower 21. The eluent after flowing through the cation exchange resin tower 21 flows through the pipe 45 and flows into the eluent recovery tank 31 to be recovered. Here, SV 1-2 [l / h] water flow rate by pump 8 so that the same amount of eluent as the amount of cation exchange resin packed in cation exchange resin column 21 can be passed in 0.5 to 1 hour. Adjust. After passing the eluent twice the amount of the cation exchange resin through the cation exchange resin tower 21, the pump 8 is stopped and the valve 35 is closed.

  Next, the eluent tank 32 is filled with ion exchange water. After the filling of the ion exchange water into the eluent tank 32 is completed, the valve 35 is opened again and the pump 8 is started. When the pump 8 is activated, the ion exchange water flows through the pipe 46 and flows into the cation exchange resin tower 21. The ion exchange water after flowing through the cation exchange resin tower 21 flows through the pipe 45 and flows into the eluent collection tank 31 and is collected. Here, SV 1-2 [l / h] is passed by the pump 8 so that ion exchange water of the same amount as that of the cation exchange resin packed in the cation exchange resin tower 21 can be passed in 0.5 to 1 hour. Adjust the amount of water. After 0.5 to 1 times the amount of cation exchange resin is passed through the cation exchange resin tower 21, the pump 8 is stopped and the valves 35 and 37 are closed. Thus, the metal ion elution step is completed, and then the process proceeds to the metal ion recovery step.

(2) Metal ion recovery process
In the metal ion recovery step, the electrolyte tank 306 in the electrodeposition recovery apparatus 30 shown in FIG. 6 is filled with 1-2 mol / L formic acid as the electrolyte. In this embodiment, the case where formic acid is used as the electrolytic solution will be described as an example, but the present invention is not limited thereto. Any other electroconductive solution may be used as the electrolytic solution. After filling the electrolyte tank 306 with the electrolyte, the pump 9 and the pump 307 are started. By starting the pump 9, the eluent in the eluent recovery tank 31 is passed from the lower part of the electrolytic cell 300 to the cathode chamber 304 through the pipe 49. Further, the eluent that has passed through the cathode chamber 304 is extracted from the upper portion of the cathode chamber 304, flows again through the pipe 49, and is refluxed to the eluent recovery tank 31. On the other hand, when the pump 307 is activated, the electrolytic solution filled in the electrolytic solution tank 306 is passed through the pipe 312 from the lower part of the electrolytic cell 300 to the anode chamber 305. Further, the electrolytic solution passed through the anode chamber 305 is extracted from the upper portion of the anode chamber 305, flows again through the pipe 312 and returns to the electrolytic solution tank 306.
The DC power supply 310 is activated and the cathode 302 and the anode 303 are energized. Here, the energization amount is preferable to be 1 to 10 A / dm ^2. By energizing the cathode 302 and the anode 303, metal ions (positive ions) such as Fe ions are deposited on the surface of the cathode 302 and collected.
The radioactivity concentration and metal ion concentration of the eluent in the eluent recovery tank 31 are analyzed as appropriate, and energization is continued until it becomes 1/10 or less of the initial concentration. When the concentration becomes 1/10 or less of the initial concentration, the process proceeds to an eluent reuse process.

(3) Eluent reuse process
In the eluent recycling process, the valve 38 is opened, and the eluent in the eluent recovery tank 31 is discharged from the drain pipe 51. The discharged eluent is introduced into the eluent tank 32, and hydrazine is added so that the pH is 4-5. As a result, the eluent after the metal ions have been recovered can be used again in the (1) metal ion elution step.

(4) Eluent decomposition process
In the eluent decomposition step, the eluent (formic acid hydrazine mixed solution) is chemically reacted with hydrogen peroxide, and formic acid is decomposed by the reaction represented by the following formula (17). Similarly, hydrazine is decomposed by a chemical reaction with hydrogen peroxide.
HCOOH + H ₂ O ₂ = CO ₂ + 2H ₂ O (17)
According to this example, it is possible to recover the metal ions and / or radionuclides adsorbed on the cation exchange resin (cation exchange resin tower) at a high current utilization rate, and the metal ions and / or The recovery rate by radionuclide electrodeposition can be improved.
In addition, according to the present embodiment, since the cation exchange resin filled in the cation exchange resin tower 21 eluting metal ions and radionuclides can be used again for chemical decontamination, the amount of secondary waste due to chemical decontamination Can be reduced.
In addition, according to the present example, metal ions and radionuclides are collected from the solution having a high concentration of metal ions and radionuclides and a low hydrogen ion concentration on the electrode surface. It can be recovered on the electrode surface as metal or metal oxide.
In addition, the mixed solution of hydrazine formate used for elution can be detoxified by decomposing it into carbon dioxide, nitrogen, and water, so secondary waste can be reduced compared to the case of using an inorganic acid such as sulfuric acid for elution. .
Further, according to the present embodiment, the pH of the eluent is adjusted in the range of pH 1 to pH 5 based on the measurement result of the pH of the eluent eluting the metal ions and radionuclides flowing on the cathode side of the electrodeposition recovery apparatus. Therefore, metal ions and / or radionuclides can be efficiently recovered on the cathode side of the electrodeposition recovery apparatus.

  In FIG. 12, the whole structure of the chemical decontamination system of Example 2 which concerns on the other Example of this invention is shown. In the first embodiment, the chemical decontamination target 20 such as a pipe or equipment is installed in the chemical decontamination apparatus 2, whereas in this embodiment, the chemical decontamination tank 60 is installed in the chemical decontamination apparatus 2. The difference is that a chemical decontamination tank 60 is immersed in a pipe or equipment (valve or pump, etc.) to be chemically decontaminated to perform chemical decontamination. In FIG. 12, the same components as those shown in FIGS. 1, 10, and 11 are denoted by the same reference numerals.

As shown in FIG. 12, the chemical decontamination system 1 a according to this embodiment includes a chemical decontamination apparatus 2 a and an elution recovery apparatus 3. The chemical decontamination apparatus 2a includes a chemical decontamination tank 60, a valve 17, a pump 4, a heater 27, a cooler 28, and a valve for immersing a chemical decontamination object including piping or a valve connected to the piping or a device such as a pump. 16 and the valve 11 are connected to each other by a pipe 40 so that one closed loop can be formed. The solution flowing through the pipe 40 flows in the order of the heater 27, the cooler 28, the valve 16, the valve 11, and the chemical decontamination tank 60 by the pump 4.
Further, the valve 16 is sandwiched, the downstream of the cooler 28 and the upstream of the chemical decontamination tank 60 are connected by a pipe 42, and the valve 14, the mixed resin tower 22, and the valve 12 are installed in the pipe 42. The mixed resin tower 22 is filled with an ion exchange resin obtained by mixing a cation exchange resin and an anion exchange resin at a ratio of 1: 1 or 1: 2. Further, the downstream of the cooler 28 and the upstream of the chemical decontamination tank 60 are connected by a pipe 43, and the valve 15, the cation exchange resin tower 21, and the valve 13 are installed in the pipe 43. The cation exchange resin tower 21 is filled with a cation exchange resin.

  A pipe 44 having one end connected to the pipe 40 downstream of the valve 16 and the upstream of the valve 11 and having the other end connected to the pipe 40 via the valve 33, the catalyst tower 26, and the valve 18 is laid. The catalyst tower 26 is packed with a catalyst that promotes a chemical reaction between hydrogen peroxide and an organic acid, for example, 0.5% Ru-supported activated carbon. In addition, it is good also as a structure which replaces with the catalyst tower 26 and installs an ultraviolet irradiation device. A pump 7, a valve 19, and a hydrogen peroxide tank 25 are installed in a pipe 44 downstream of the valve 33 and upstream of the catalyst tower 26. A pipe 41 branched from the pipe 40 is laid in the pipe 40 between the downstream of the pump 5 and the valve 11, and the pump 6, the valve 10, and the chemical decontamination tank 23 are connected by the pipe 41. The chemical decontamination tank 23 stores chemicals used for chemical decontamination. When a plurality of chemicals are used, the pump 6, the valve 10 and the chemical decontamination tank 23 are cleaned and used each time.

  Since the elution recovery device 3 is the same as that of the first embodiment, the description thereof is omitted here. In the chemical decontamination apparatus 2 a of this embodiment, a water supply / drain pipe 62 is connected to the chemical decontamination tank 60, and a valve 61 is installed in the water supply / drain pipe 62. In the chemical decontamination preparation process, the valves 10, 19, 36 and 37 are closed, and the other valves are all opened. In this state, ion exchange water is introduced from the water supply / drainage pipe 62 connected to the chemical decontamination tank 60. After introducing the necessary amount of ion-exchanged water, the valve 61 is closed, and the valves 12, 13, 14 and 15 are closed and the pump 4 is started to circulate the system water in the closed loop. A pipe or device to be chemically decontaminated in the chemical decontamination tank 60 is immersed in system water. Thereafter, the (2) oxidative decontamination step to (7) purification step or (2 ′) organic acid decontamination step to (5 ′) cleaning step described in Example 1 is executed, and the chemical decontamination step is completed. To do. After completion of the chemical decontamination process, (1) metal ion elution process to (4) eluent decomposition process described in Example 1 are executed, and the elution recovery process is completed.

  According to the present embodiment, in addition to the effects of the first embodiment, since the surge tank 24 and the pump 5 can be eliminated, the number of parts of the chemical decontamination apparatus 2a constituting the chemical decontamination system 1a can be reduced. Become.

  In FIG. 13, the whole structure of the chemical decontamination system of Example 3 which concerns on the other Example of this invention is shown. In Example 2, the chemical decontamination device 2a and the elution recovery device 3 are respectively connected to the inflow side (upstream side) and the outflow side (downstream side) of the cation exchange resin tower 21 installed in the chemical decontamination device 2a. It was set as the structure connected by the piping 45 and the piping 46 to which one end is connected. In contrast, the present embodiment is different from the second embodiment in that the chemical decontamination apparatus 2 and the elution recovery apparatus 3 are installed independently without being connected by piping. In FIG. 13, the same components as those shown in FIGS. 1, 10, 11 and 12 are denoted by the same reference numerals.

As shown in FIG. 13, the chemical decontamination system of the present embodiment is configured by a chemical decontamination device 2 and an elution recovery device 3, and the chemical decontamination device 2 and the elution recovery device 3 are not connected by piping or the like. These are installed separately from each other.
The chemical decontamination apparatus 2 includes a chemical decontamination tank 60, a valve 17, a pump 4, a heater 27, a cooler 28, a valve for immersing a chemical decontamination target including piping or a valve connected to the piping or a pump. 16 and the valve 11 are connected by a pipe 40 and are configured to be able to form one closed loop. The solution flowing through the pipe 40 flows in the order of the heater 27, the cooler 28, the valve 16, the valve 11, and the chemical decontamination tank 60 by the pump 4.
Further, the valve 16 is sandwiched, the downstream of the cooler 28 and the upstream of the chemical decontamination tank 60 are connected by a pipe 42, and the valve 14, the mixed resin tower 22, and the valve 12 are installed in the pipe 42. Similar to Example 1 or Example 2, the mixed resin tower 22 is filled with an ion exchange resin obtained by mixing a cation exchange resin and an anion exchange resin in a ratio of 1: 1 or 2: 1. Further, the downstream of the cooler 28 and the upstream of the chemical decontamination tank 60 are connected by a pipe 43, and the cation exchange is detachable between the upstream valve 15 and the downstream valve 13 installed in the pipe 43. A resin tower 21a is installed. FIG. 13 shows a state in which the cation exchange resin tower 21b is installed. This will be described later by replacing the cation exchange resin tower 21a after metal ion adsorption with another new cation having similar characteristics. This is because the state after the exchange to the exchange resin tower 21b is shown. These cation exchange resin towers 21a and 21b are filled with a cation exchange resin.

  Similarly to the second embodiment, one end is connected to the pipe 40 downstream of the valve 16 and upstream of the valve 11, and the other end is connected to the pipe 40 via the valve 33, the catalyst tower 26, and the valve 18. Is laid. The catalyst tower 26 is packed with a catalyst that promotes a chemical reaction between hydrogen peroxide and an organic acid, for example, 0.5% Ru-supported activated carbon. In addition, it is good also as a structure which replaces with the catalyst tower 26 and installs an ultraviolet irradiation device. A pump 7, a valve 19, and a hydrogen peroxide tank 25 are installed in a pipe 44 downstream of the valve 33 and upstream of the catalyst tower 26. A pipe 41 branched from the pipe 40 is laid in the pipe 40 between the downstream of the pump 5 and the valve 11, and the pump 6, the valve 10, and the chemical decontamination tank 23 are connected by the pipe 41. The chemical decontamination tank 23 stores chemicals used for chemical decontamination. When a plurality of chemicals are used, the pump 6, the valve 10 and the chemical decontamination tank 23 are cleaned and used each time.

  The eluent recovery device 3 is configured to be capable of mounting the cation exchange resin tower 21a after the metal ion adsorption. In the cation exchange resin tower 21a, on the basis of the flow direction of the eluent, a valve 36 is installed on the upstream side and a valve 37 on the downstream side is installed in the pipe 46 and the pipe 45, respectively. On the upstream side of the valve 36, the pump 8, the valve 35, and the eluent tank 32 are sequentially connected to the pipe 46, one end of which is connected to the cation exchange resin 21a, with reference to the flow direction of the eluent. In addition, an eluent recovery tank 31 is connected and installed on the downstream side of the valve 37 in the pipe 45 whose one end is connected to the cation exchange resin tower 21a. A pump 9 and an electrodeposition recovery device 30 are installed downstream of the eluent recovery tank 31. In addition, the configuration of the eluent recovery device 3 is the same as that of the first and second embodiments. The electrodeposition recovery device 30, a pH adjuster tank and a pH meter, which are mechanisms for adjusting the pH of the recovered eluent, and The configuration of the pump is the same as the configuration shown in FIG.

  In the chemical decontamination apparatus 2 of the present embodiment, a water supply / drain pipe 62 is connected to the chemical decontamination tank 60, and a valve 61 is installed in the water supply / drain pipe 62. It is assumed that the cation exchange resin tower 21a is installed between the valve 13 and the valve 15 installed in the pipe 43 in the initial stage. In the chemical decontamination preparation process, the valves 10 and 19 are closed, and the other valves installed in the chemical decontamination apparatus 2 are opened. In this state, ion exchange water is introduced from the water supply / drainage pipe 62 connected to the chemical decontamination tank 60. After introducing the necessary amount of ion-exchanged water, the valve 61 is closed, the valves 12, 13, 14 and 15 are closed, and the pump 4 is started. Thereby, system water circulates in order of pump 4, heater 27, cooler 28, valve 16, valve 11, and chemical decontamination tank 60. Thereby, the piping or apparatus which is the object of chemical decontamination in the chemical decontamination tank 60 is immersed in system water. Thereafter, the (2) oxidative decontamination step to (7) purification step or (2 ′) organic acid decontamination step to (5 ′) cleaning step described in Example 1 is executed, and the chemical decontamination step is completed. .

  After completion of the chemical decontamination process, the valve 13 and the valve 15 in the chemical decontamination apparatus 2 are closed, and the cation exchange resin tower 21a adsorbing metal ions and / or radionuclides is disconnected from the pipe 43. And is mounted on a carriage 400 for transportation and transported to the elution recovery apparatus 3 spaced from the chemical decontamination apparatus 2. In addition, after removing the cation exchange resin tower 21a, the cation exchange resin tower 21b is newly installed in the pipe 43. The cation exchange resin tower 21 a that adsorbs metal ions or radionuclides is installed in a pipe connection portion between a valve 36 installed in the pipe 46 and a valve 37 installed in the pipe 45 in the elution recovery apparatus 3. As a result, the eluent filled in the eluent tank 32 can be passed through the cation exchange resin tower 21a by the pump 8. Thereafter, (1) metal ion elution step to (4) eluent decomposition step described in the first embodiment are performed.

In addition, although the present Example demonstrated the procedure which removes the cation exchange resin tower 21a which adsorb | sucked the metal ion or the radionuclide from the chemical decontamination apparatus 2 after completion | finish of a chemical decontamination process, ie, the completion | finish of a washing process, However, the present invention is not limited to this, and when the pipe or device to be chemically decontaminated is stainless steel or a nickel-based alloy, (4) the cation exchange resin tower 21a may be removed after the reduction decontamination step.
In addition, in the case where the pipe or the equipment to be chemically decontaminated is carbon steel or low alloy steel, (2 ′) after the organic acid decontamination process is completed. It is good also as a procedure which removes the cation exchange resin tower | column 21a.

  According to the present embodiment, in addition to the effects of the second embodiment, a cation exchange resin tower that adsorbs metal ions or radionuclides between the chemical decontamination apparatus 2 and the elution recovery apparatus 3 that are spaced apart from each other is used as a chemical decontamination apparatus. Since it is a structure which removes from 2, attaches a new cation exchange resin tower, and attaches the removed cation exchange resin tower to an elution collection | recovery apparatus, it implements a chemical decontamination process and an elution collection process in parallel. It becomes possible. This makes it possible to execute a series of steps from chemical decontamination to elution collection in a short time.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace the configurations of other embodiments with respect to a part of the configurations of the embodiments.

DESCRIPTION OF SYMBOLS 1, 1a ... Chemical decontamination system 2, 2a ... Chemical decontamination apparatus 3 ... Elution collection | recovery apparatus 20 ... Chemical decontamination object 21, 21a, 21b ... Cation exchange resin tower 22 .... Mixed resin tower 23 ... Chemical decontamination tank 24 ... Surge tank 25 ... Hydrogen peroxide tank 26 ... Catalyst tower 27 ... Heater 28 ... Cooler 30 ... Electrodeposition recovery device 31 ... eluent recovery tank 32 ... eluent tank,
10-19, 33-38, 61 ... Valves 4-9, 60, 307, 313 ... Pumps 40-46, 48, 49, 311, 312 ... Piping 50, 62 ... Water supply / drainage pipe 51 ... Drain pipe 60 ... Chemical decontamination tank 300 ... Electrolysis tank 301 ... Cation exchange membrane 302 ... Cathode 303 ... Anode 304 ... Cathode chamber 305 ... Anode chamber 306 ... Electrolyte tanks 308, 309 ... Conducting wire 310 ... DC power supply 314 ... pH adjuster tank 315 ... pH meter 316 ... Control unit 400 ... Dolly

Claims (16)

An eluent tank that contains a mixed liquid of hydrazine and at least one of formic acid, glycolic acid, and malonic acid as an eluent;
The eluent is passed through a cation exchange resin tower in which metal ions and / or radionuclides are captured, and the eluent containing the metal ions and / or radionuclides is separated by a cation exchange membrane. And introducing an electrolytic solution into the anode chamber and energizing the anode and the cathode, thereby depositing and recovering the metal ions and / or radionuclides on the surface of the cathode, and
The pH of the eluent containing the metal ions and / or the radionuclide is measured, and the pH of the eluent flowing through the cathode chamber is adjusted according to the pH measurement result. Elution collection device. In the secondary waste elution recovery apparatus according to claim 1,
An eluent recovery tank for recovering an eluent containing the metal ions and / or radionuclide;
A first pipe connecting the eluent recovery tank and the cathode chamber of the electrodeposition recovery apparatus;
A pH meter installed in the eluent recovery tank or the first pipe and measuring the pH of the eluent containing the metal ions and / or radionuclides;
A secondary waste elution recovery apparatus, comprising: a pH adjuster tank that contains a pH adjuster added to the eluent containing the metal ions and / or the radionuclide. In the secondary waste elution recovery apparatus according to claim 2,
The eluent stored in the eluent tank is a mixed solution of formic acid and hydrazine, and has a formic acid concentration of 1 mol / L or more and 2 mol / L or less. In the secondary waste elution recovery apparatus according to claim 3,
The pH adjusting agent is hydrazine, and the pH of the mixed solution containing metal ions and / or radionuclides flowing through the cathode chamber is adjusted to 1 or more and 5 or less. Elution recovery device. The secondary waste elution recovery apparatus according to claim 4,
2. The secondary waste elution recovery apparatus according to claim 1, wherein the electrolytic solution introduced into the anode chamber is formic acid of 1 mol / L to 2 mol / L. The secondary waste elution recovery apparatus according to claim 5,
A second pipe connecting the eluent recovery tank or the first pipe and the pH adjuster tank;
A pump that is installed in the second pipe and allows the hydrazine contained in the pH adjuster tank to flow through the second pipe;
If the pH measurement value of the eluent containing the metal ions and / or the radionuclide obtained from the pH meter is less than or equal to the lower limit value, a predetermined amount of hydrazine is stored in the second pipe. And a controller for controlling the pump so as to flow therethrough. The secondary waste elution recovery apparatus according to claim 5,
A second pipe connecting the eluent recovery tank or the first pipe and the pH adjuster tank;
A pump that is installed in the second pipe and allows the hydrazine contained in the pH adjuster tank to flow through the second pipe;
Maintaining the relationship between pH and hydrazine addition amount every energization time in advance, obtaining pH measurement value of eluent containing the metal ions and / or radionuclide from the pH meter, and adding hydrazine corresponding to the pH measurement value And a controller for controlling the pump so that the amount of hydrazine added is extracted, and a secondary waste elution recovery device. A process of passing system water containing a chemical decontaminant to piping or equipment to be chemically decontaminated;
Passing the system water after passing the chemical decontamination target to a cation exchange resin tower;
The cation exchange resin tower is passed with hydrazine and at least one of formic acid, glycolic acid and malonic acid as an eluent, and the metal ions or radioactive ions captured by the cation exchange resin tower are passed through. Eluting nuclides; and
The eluent containing the metal ions and / or the radionuclide is introduced into the cathode chamber in which the inside of the electrolytic cell is separated by a cation exchange membrane and the cathode is arranged, and the electrolyte is introduced into the anode chamber in which the anode is arranged. Process,
PH adjustment step of measuring the pH of the eluent containing the metal ions and / or radionuclides introduced into the cathode chamber and adjusting the pH of the eluent flowing through the cathode chamber according to the pH measurement result When,
A method of reducing the secondary waste of chemical decontamination, comprising: a collecting step of energizing the cathode and the anode to deposit the metal ions and / or radionuclides on the cathode surface. The secondary waste reduction method for chemical decontamination according to claim 8,
The eluent passed through the cation exchange resin tower is a mixed solution of formic acid and hydrazine and has a formic acid concentration of 1 mol / L or more and 2 mol / L or less. Reduction method. In the secondary waste reduction method of chemical decontamination according to claim 9,
In the pH adjustment step, hydrazine as a pH adjuster is added to the mixed solution containing the metal ions and / or radionuclide, and the pH is adjusted to be within a range of 1 to 5, the chemical removal is characterized in that Secondary waste reduction method for dyeing. The secondary waste reduction method for chemical decontamination according to claim 10,
The pH adjustment step includes adding a predetermined amount of hydrazine to the mixed solution containing the metal ions and / or the radionuclide when the pH measurement result is equal to or lower than a preset lower limit value of the pH. Secondary waste reduction method for decontamination. The secondary waste reduction method for chemical decontamination according to claim 10,
In the pH adjustment step, based on the relationship between the pH and the amount of hydrazine added for each energization time stored in advance, the amount of hydrazine added corresponding to the pH measurement result is added to the liquid mixture containing the metal ions and / or the radionuclide. A method for reducing secondary waste by chemical decontamination, characterized by comprising: Chemistry with a cation exchange resin tower that passes system water containing a chemical decontamination agent to piping or equipment that is subject to chemical decontamination, and captures metal ions and / or radionuclides contained in the system water after passing water A decontamination device,
An eluent tank that contains a mixed liquid of hydrazine and at least one of formic acid, glycolic acid, and malonic acid as an eluent, and a cathode chamber and an anode are arranged by a cation exchange membrane. Electrodeposition recovery apparatus having an electrolytic cell isolated from the anode chamber, and the eluent is passed through the cation exchange resin tower capturing the metal ions and / or radionuclides, and flows out of the cation exchange resin tower. An elution recovery device having an eluent recovery tank for recovering an eluent containing the metal ions and / or the radionuclide.
The elution recovery device introduces the eluent in the eluent recovery tank into the cathode chamber and introduces an electrolyte into the anode chamber, energizes the anode and cathode, and the metal ions or A radionuclide is deposited, the pH of the eluent introduced into the cathode chamber is measured, and the pH of the eluent flowing through the cathode chamber is adjusted according to the pH measurement result. And chemical decontamination system. The chemical decontamination system according to claim 13,
The elution recovery device comprises:
A first pipe connecting the eluent recovery tank and the cathode chamber of the electrodeposition recovery apparatus;
A pH meter installed in the eluent recovery tank or the first pipe and measuring the pH of the eluent containing the metal ions and / or radionuclides;
A chemical decontamination system comprising: a pH adjuster tank that contains a pH adjuster added to the eluent containing the metal ions and / or the radionuclide. The chemical decontamination system according to claim 14,
The eluent contained in the eluent tank is a mixed solution of formic acid and hydrazine and has a formic acid concentration of 1 mol / L or more and 2 mol / L or less. The chemical decontamination system according to claim 15,
The pH adjusting agent is hydrazine, and the pH of the mixed solution containing metal ions and / or radionuclides flowing through the cathode chamber is adjusted to 1 or more and 5 or less. .

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