JPH05323095A - Processing method for decontamination waste liquid - Google Patents

Abstract

PURPOSE:To reduce the radioactive secondary waste generation by oxidizing the trivallent Ce in decontamination waste liquid to quadrivallent Ce with electrolytic oxidation, separating the quadrivallent Ce and acid from the processed decontamination waste liquid and reusing it. CONSTITUTION:Decontamination waste liquid 11 is oxidized by electrolysis 12 to raise the concentration of Ce<4+> in the decontamination waste liquid and the waste liquid and dialysis liquid 14 are passed by water through a negative ion exchanger film 15. Then, the acid in the waste liquid 11 and Ce<4+> having formed complex negative ion move through the exchanger film to the dialysis liquid and are recovered as recovery solution 16. The recovery solution after controlling 17 concentration is reused as decontamination liquid. On the other hand, a little Ce<4+> remains in the processed waste liquid 19 eliminated of acid and Ce<4+> and therefore, by adding hydrogen peroxide to reduce in process 20 to be chemically stable Ce<4+>. The reduction processed 18 process waste liquid 19 is neutralized in process 21 with sodiumhydrate solution and dried and solidified 22 sludge and sodium salt are stored as radioactive waste.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a decontamination waste liquid for regenerating a used acidic decontamination liquid generated after decontaminating radioactive metal waste.

[0002]

2. Description of the Related Art For example, radioactive waste-contaminated metal waste generated by the abolition and dismantling of nuclear power generation facilities is disposed of after being removed and stored and reused. ..

Here, as means for decontaminating radioactively contaminated metal waste, cerium trivalent ions (Ce ³⁺ )
And using cerium tetravalent ions (Ce ⁴⁺⁾ and decontamination liquid acidic containing (hereinafter referred redox decontamination liquid), produces a Ce ⁴⁺ from Ce ³⁺ by electrolytic oxidation reaction of the Ce ⁴⁺ A decontamination method is known in which radioactive substances are removed from the surface of metal waste by utilizing the oxidizing power.

The treatment with the redox decontamination solution is carried out using a redox decontamination apparatus as shown in FIG. 3, for example. In FIG. 3, reference numeral 1 is an electrolytic tank, reference numeral 2 is a decontamination tank, and a decontaminating agent C is present in the electrolytic tank 1 and the decontamination tank 2.
An acidic redox decontamination solution 3 in which e ³⁺ and Ce ⁴⁺ are dissolved is stored. Further, an anode 4 and a cathode 5 made of an inert metal are immersed in the electrolytic cell 1.

The metal waste 6 contaminated with radioactivity is immersed in the decontamination solution 3 in the decontamination tank 2, and the radioactivity is removed from the metal waste 6 by the following dissolution reaction in which the metal waste 6 is M. To be done.

Ce ⁴⁺ + M → Ce ³⁺ + M ⁺ (1) The decontamination tank 2 and the electrolytic cell 1 are connected by a circulation pipe 7 and an overflow pipe 8, and the decontamination liquid 3 is collected by a circulation pump 9. The electrolytic bath 1 and the decontamination bath 2 are circulated.

For this reason, the Ce ⁴⁺ consumed by the dissolution of the metal waste 6 causes the following reaction because the direct current voltage is applied between the anode 4 and the cathode 5 in the electrolytic cell 2. Will be played.

Ce ³⁺ → Ce ⁴⁺ + e (2) When a large amount of metal waste is decontaminated in this way, the concentration of the eluted metal (Fe, Cr, Ni, etc.) ions in the decontamination solution increases, and radiation is emitted. Since the concentration of Noh (Co, Mn, etc.) increases and the amount of workers exposed to radiation increases, the decontamination liquid must be discarded as decontamination waste liquid.

[0009] Conventionally, in the disposal treatment of this decontamination waste liquid, if the decontamination waste liquid containing elution metal ions and Ce ⁴⁺ having an oxidizing power is directly stored in the drum can and the drum can is corroded, a reducing agent is added. It has been used to reduce and reduce it, transfer it to a waste liquid treatment facility, neutralize it, and then dry and solidify it.

[0010]

However, the above-mentioned method for treating the decontamination waste liquid has the following problems.

(1) When all the decontamination waste liquid is discarded,
A large amount of radioactive secondary waste is generated.

(2) When the decontamination waste liquid is disposed of, a reducing agent and a neutralizing agent are added to replace the eluted metal ions with hydroxides, and the solids are dried and solidified. The amount increases.

(3) When Ce ⁴⁺ is not completely reduced,
Corrosion of waste liquid treatment facility.

The present invention has been made in order to solve the above-mentioned problems, and has radioactive metal ions (for example, Co and M).
n)) and metal ions (eg, iron ions, nickel ions, chromium ions) eluted from the metal waste are dissolved, it can be reused as a decontamination liquid and can be further treated as waste liquid. It is an object of the present invention to provide a method for treating decontamination waste liquid, which can reduce the amount of radioactive secondary waste generated due to the above.

[0015]

Means for Solving the Problems That is, the present invention relates to a method for treating a radioactive decontamination waste liquid generated by decontaminating a metal waste contaminated with a radioactive substance using an acidic decontamination liquid containing Ce, An electrolytic oxidation treatment step of electrolytically oxidizing the decontamination waste liquid to oxidize trivalent Ce in the waste liquid to tetravalent Ce, and tetravalent Ce and acid existing as complex anions from the electrolytic deoxidization-treated decontamination waste liquid Diffusion dialysis step for separating the acid and Ce through an anion exchange membrane, a concentration adjustment step for adjusting the concentration of the acid and Ce separated in the diffusion dialysis step for reuse as a decontamination solution, and a Ce after the diffusion dialysis step. A reduction treatment step to reduce and chemically stabilize the treated waste liquid from which the acid and acid have been separated and removed, a neutralization treatment step to neutralize the reduced treatment waste liquid, and a drying process to store the neutralized treated waste liquid.・ Drying / solidifying to solidify Characterized by comprising the a.

[0016]

In the method for treating decontamination waste liquid having the above structure, Ce ³⁺ in the decontamination waste liquid is oxidized to Ce ⁴⁺ in the electrolytic oxidation treatment step. This is decontaminant Ce ^3+, since Ce ⁴⁺ of Ce ⁴⁺ is to form a complex anions passing through the anion exchange membrane in an acidic solution, the Ce ⁴⁺ prior to the diffusion dialysis step This is done to improve the recovery rate. In the diffusion dialysis step, the waste liquid after the electrolytic oxidation treatment is passed through the anion exchange membrane in a counter flow with dialyzed water. During this passage, Ce ^4+, which forms a complex anion with the acid in the decontamination waste liquid due to the difference in concentration with the dialysis water, moves to the dialysis water side through the anion exchange membrane. Therefore, the acid and Ce ⁴⁺ can be easily recovered from the decontamination waste liquid. Acid recovery by diffusion dialysis treatment using an anion exchange membrane is used in general chemical industry such as recovery of acid from various plating waste liquids, but in the present invention, it is removed along with the acid in the decontamination waste liquid. Ce, which is a dyeing agent, is also collected so that it can be reused as a decontamination solution.

Acid and Ce separated and recovered in the diffusion dialysis step
⁴⁺ is adjusted to a predetermined concentration in the concentration adjustment process and reused as a decontamination solution. On the other hand, the waste liquid after the Ce ⁴⁺ and the acid have been separated and removed contains a slight amount of the decontaminating agent acid and Ce ^4+, so it is chemically stabilized in the reduction treatment step, and then neutralized-dried-solidified. And store as radioactive waste.

Therefore, according to this treatment method, the active ingredient in the decontamination waste liquid can be separated and recovered and reused, and the amount of radioactive waste generated can be reduced.

[0019]

Embodiments of the present invention will be described below with reference to the drawings, using a redox decontamination waste liquid as an example. FIG. 1 is a block flow chart showing an embodiment of the method for treating decontamination waste liquid according to the present invention. As shown in this figure, as the disposal procedure, the decontamination waste liquid 11 is electrolyzed in the electrolytic oxidation treatment step 12, and the Ce ⁴⁺ concentration in the decontamination waste liquid is increased by the oxidation reaction shown in the formula (2). The electrolytic oxidation treatment is performed in the electrolytic cell 2 shown in FIG.

After the oxidation treatment in the electrolytic oxidation treatment step 12, when the decontamination waste liquid 11 and the dialysate water 14 are passed from the opposite sides through the anion exchange membrane 15 in the diffusion dialysis step 13, the decontamination waste liquid 11 contains Acid and C forming complex anions
e ⁴⁺ passes through the anion exchange membrane 15 and moves to dialysis water,
It is recovered as the recovery solution 16. The recovered solution 16 is reused as a decontamination solution after the Ce ⁴⁺ , Ce ³⁺ concentration and the acid concentration are adjusted in the concentration adjusting step 17.

The principle of diffusion dialysis in the diffusion dialysis step 13 is shown in FIG. As the dialysis operation, the oxidation treatment waste liquid 11a is introduced from the lower part of the one side chamber A of the dialysis device 13a which is vertically isolated by the anion exchange membrane 15, and the dialysis water 14 is introduced from the upper part of the other side chamber B to flow in a downward flow. .. The concentration of the acid and Ce ⁴⁺ in the oxidation treatment waste liquid 11a is lowered toward the upper part while diffusing to the dialyzed water 14 side. The dialysis water 14 is gradually converted into acid and Ce ⁴⁺ by the diffused acid and Ce ^4+.
The concentration increases and reaches the bottom. In this way, by flowing in a counter flow through the anion exchange membrane 15, both chambers A, B
In both sides, a stable specific gravity gradient layer is formed in which the upper part has a smaller specific gravity in the vertical direction and the lower part has a larger specific gravity. Therefore, acid and Ce in each part of the oxidation treatment waste liquid 11a and the dialyzed water 14 contacting each other through the anion exchange membrane 15 ^{The 4+} concentration difference is almost constant. Therefore, the acid and C in the oxidation treatment waste liquid 11a are
Almost the entire amount of e ⁴⁺ is transferred to the dialyzed water 14 side and is recovered as a recovery solution 16.

On the other hand, the oxidation treatment waste liquid 11a is used as a dialysis device 13
Since the difference in acid concentration with the dialyzed water 14 is kept small at the upper outlet of a, it is recovered as the treatment waste liquid 19 from which most of the acid and Ce ⁴⁺ have been removed.

Since a small amount of Ce ⁴⁺ remains in this treatment waste liquid 19, hydrogen peroxide is added in the reduction treatment step 20 to reduce it to chemically stable Ce ³⁺ , as shown in FIG. ..
The treated waste liquid after the reduction treatment is neutralized with a sodium hydroxide aqueous solution in the neutralization treatment step 21, and then dried / solidified step 22.
The sludge and Na salt generated by the neutralization process in 1. are dried and solidified and stored as radioactive waste.

Next, the concrete examples will be given to calculate the amount of waste generated when treated according to the method for treating decontamination waste liquid according to the present invention, and to compare with the conventional example.

As a first example, a nitric acid redox decontamination waste liquid is selected, and the amount of waste generated when 1000 liters of this decontamination waste liquid is treated is determined. In the nitric acid-based redox waste liquid, in addition to nitric acid, Ce ⁴⁺ and Ce ³⁺ which are decontaminating agents, Fe is dissolved as an elution metal, and Ce ⁴⁺ is a complex anion [Ce (NO ₃ ) ₆ ] ^{2 -Exists} as. The concentration of each component in the decontamination waste liquid was 2 mol / l of nitric acid, Ce (Ce ⁴⁺
+ Ce ³⁺ ) is 0.8 mol / l and Fe is 1 mol / l.

When this decontamination waste liquid is subjected to electrolytic oxidation treatment, the Ce ⁴⁺ / Ce concentration ratio in the decontamination waste liquid rises to 0.85, and then this is subjected to diffusion dialysis treatment to obtain Ce ⁴⁺ of 8%.
0% and 80% of nitric acid are recovered. The treated waste liquid subjected to the diffusion dialysis treatment is subjected to neutralization-evaporation-drying treatment after hydrogen peroxide is added to reduce Ce ⁴⁺ remaining in the treated waste liquid to chemically stable Ce ³⁺ . By this treatment, the hydroxide and Na salt shown below are generated as waste.

Ce (OH) ³ = (1-0.85 × 0.8) × 0.8 mol / l × 1000 l × 191 g /
mol = 48.9kg Fe (OH) ³ = 1 mol / l × 1000 l × 107 g / mol = 107kg NaNO ³ = [{(1-0.85 × 0.8) × 0.8 mol / l + 1 mol / l} × 3 + 2
mol / l × 0.2] × 1000 l × 85 g / mol = 354 kg Total = 510 kg Next, calculate the amount of waste generated when the nitric acid redox decontamination waste liquid is discarded according to the conventional treatment method. In the conventional example, Ce ⁴⁺ in the decontamination waste liquid is reduced to chemically stable Ce ³⁺ by adding hydrogen peroxide, and neutralization-evaporation-drying treatment is performed.
By this treatment, the hydroxide and Na salt shown below are generated as waste.

Ce (OH) ³ = 0.8 mol / l × 1000 l × 191 g / mol = 153 kg Fe (OH) ³ = 1 mol / l × 1000 l × 107 g / mol = 107 kg NaNO ³ = {(0.8 mol / l + 1 mol / l) × 3 + 2 mol / l} × 1000 l
× 85 g / mol = 629 kg Total = 889 kg Table 1 shows a comparison of the results of examining the amount of waste generated according to the waste liquid treatment method when discarding the decontamination waste liquid of the first example and the conventional example.

[0029]

[Table 1] As is clear from Table 1, the amount of waste generated when 1000 liters of decontamination waste liquid is disposed of is the first amount according to the present invention.
In the case of the above example, it was confirmed to be 510 kg, and in the case of discarding the decontamination waste liquid of the conventional example as it is without processing, it was recognized to be 889 kg.

As described above, according to the first embodiment, in order to recover Ce and nitric acid, the nitric acid redox decontamination waste liquid in which Ce, nitric acid and Fe are dissolved is subjected to diffusion dialysis using an anion exchange membrane. The amount of waste generated can be reduced compared to the conventional waste liquid treatment method, and the recovered C
e, nitric acid can be reused for nitric acid redox decontamination.

In the above embodiment, the nitric acid concentration is 2 mol / l,
Ce (Ce ⁴⁺ + Ce ³⁺ ) concentration 0.8 mol / l, Fe concentration 1
The case of treating mol / l nitric acid redox decontamination waste liquid was explained, but the nitric acid concentration was 0.01 to 10 mol / l, respectively.
l, Ce (Ce ⁴⁺ + Ce ³⁺ ) concentration 0.01 to 2 mol / l,
A decontamination waste liquid having an Fe concentration of 0.01 to 2 mol / l can be treated in the same manner. In addition, as elution metals,
Even if is dissolved, the treatment method of the present invention can be applied.

Next, as a second embodiment, a case where a sulfuric acid redox decontamination waste liquid is selected and 1000 liters of the decontamination waste liquid is treated will be described. In the sulfuric acid redox waste liquid, Fe is dissolved as a metal to be eluted in addition to sulfuric acid, Ce ⁴⁺ and Ce ³⁺ which are decontaminating agents, and Ce ⁴⁺ is [Ce (S
O ₄ ) ₄ ] ⁴⁻ exists. Concentration of each component of decontamination waste liquid is 1 mol / l of sulfuric acid, Ce (Ce ⁴⁺ + Ce ³⁺ )
Is 0.2 mol / l and Fe is 1 mol / l.

By subjecting this decontamination waste liquid to electrolytic oxidation treatment, the Ce ⁴⁺ / Ce concentration ratio in the decontamination waste liquid is raised to 0.85, and then this is subjected to diffusion dialysis treatment to obtain C
Recover 80% of e ⁴⁺ and 80% of sulfuric acid. The treated waste liquid subjected to the diffusion dialysis treatment is subjected to neutralization-evaporation-drying treatment after hydrogen peroxide is added to reduce Ce ⁴⁺ remaining in the treated waste liquid to chemically stable Ce ³⁺ . As a result, the hydroxides and Na salts shown below are generated as waste.

Ce (OH) ₃ = (1-0.85 × 0.8) × 0.2 mol / l × 1000 l × 191 g /
mol = 12.2kg Fe (OH) ₃ = 1 mol / l × 1000 l × 107 g / mol = 107kg Na ₂ SO ₄ = [{(1-0.85 × 0.8) × 0.2 mol / l + 1 mol / l} × 1.5+
1 mol / l × 0.2] × 1000 l × 142 g / mol = 255 kg Total = 374 kg Next, calculate the amount of waste generated when the above sulfuric acid redox decontamination waste liquid is discarded according to the conventional treatment method. Ce ^{4+ in} decontamination waste liquid is chemically stable by adding hydrogen peroxide.
It is reduced to e ³⁺ and neutralized-evaporated-dried. This treatment produces hydroxides and Na salts as waste.

Ce (OH) ₃ = 0.2 mol / l × 1000 l × 191 g / mol = 38.2 kg Fe (OH) ₃ = 1 mol / l × 1000 l × 107 g / mol = 107 kg Na ₂ SO ₄ = {( 0.2 mol / l + 1 mol / l) × 1.5 + 1 mol / l} × 1000
l × 142 g / mol = 398 kg Total = 543 kg Table 2 shows a comparison of the results of examining the amount of waste generated according to the waste liquid treatment method when discarding the decontamination waste liquids of the second example and the conventional example.

[0036]

[Table 2] As is clear from Table 2, the amount of waste generated when 1000 liters of decontamination waste liquid is disposed of is the second amount according to the present invention.
It was confirmed that in the case of the above example, 374 kg was obtained, and when the decontamination waste liquid of the conventional example was discarded as it was without treatment, it was 543 kg.

As described above, in the second embodiment, C
e, sulfuric acid, Fe dissolved sulfuric acid redox decontamination waste liquid by diffusion dialysis treatment using an anion exchange membrane, it is possible to recover Ce, sulfuric acid, compared to the conventional waste liquid treatment method, the amount of waste generated Can be reduced. The recovered Ce and sulfuric acid can be reused as a sulfuric acid redox decontamination solution.

In the above embodiment, the concentration of the components in the sulfuric acid redox decontamination waste liquid was 1 mol / l of sulfuric acid and Ce (Ce
⁴⁺ + Ce) 1 mol / l, Fe 1 mol / l, sulfuric acid concentration 0.01-0.5 mol / l, Ce concentration 0.01-5 mol / l
, A sulfuric acid redox decontamination waste liquid having an Fe concentration of 0.01 to 2 mol / l can also be used. In addition, as elution metal Cr,
It can be used even if Ni is dissolved.

[0039]

As described above, according to the present invention,
It has the following effects.

(1) Since the acid (nitric acid or sulfuric acid) and Ce can be separated and recovered by diffusion dialysis from the redox decontamination waste liquid and reused, the amount of the decontamination waste liquid generated can be reduced.

(2) In addition, the amount of secondary waste generated can be reduced as compared with the conventional method in which the decontamination waste liquid is neutralized as it is and then evaporated, dried and solidified.

[Brief description of drawings]

FIG. 1 is a block flowchart showing a decontamination waste liquid treatment method according to the present invention.

FIG. 2 is a cross-sectional view showing the principle of a diffusion dialysis treatment process.

FIG. 3 is a sectional view schematically showing an example of a redox decontamination device.

[Explanation of symbols]

 11 ………… Decontamination waste liquid 11a …… Oxidation treatment waste liquid 12 ………… Electrolytic oxidation treatment process 13 ………… Diffusion dialysis process 13a …… Dialyzer 14 ………… Dialysis water 15 ………… Anion exchange membrane 16 …… … Recovered solution 17 ………… Concentration adjustment process 18 ………… Reuse 19 ………… Treatment waste liquid 20 ………… Reduction treatment process 21 ………… Neutralization treatment process 22 ………… Drying / solidification process

Claims (1)

[Claims] 1. A metal waste contaminated with radioactive substances is treated as C
In a method of treating radioactive decontamination waste liquid generated by decontaminating using an acid-containing decontamination liquid containing e, the decontamination waste liquid is subjected to electrolytic oxidation treatment to remove trivalent Ce in the waste liquid to 4
Electrolytic oxidation process to oxidize valent Ce and forming complex anion from decontamination waste liquid subjected to electrolytic oxidation process 4
A diffusion dialysis step of separating a high-valent Ce and an acid through an anion exchange membrane, a concentration adjustment step of performing a concentration adjustment to reuse the acid and Ce separated in the diffusion dialysis step as a decontamination solution, A reduction treatment step of reducing and chemically stabilizing the treatment waste fluid after separation and removal of Ce and acid after the diffusion dialysis step, a neutralization treatment step of neutralizing the reduction treatment waste fluid, and a neutralized treatment waste fluid A method for treating decontamination waste liquid, comprising: a drying / solidifying step of drying / solidifying for storing.