JPH035560B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a decontamination agent waste liquid treatment method. PRIOR ART Numerous proposals have been made for the decontamination (hereinafter referred to as "decontamination") of equipment, piping, and valves in conventional nuclear reactor primary cooling systems, purification systems, fuel handling and storage systems, radioactive waste processing systems, etc. Single Step for chemical decontamination
It can be divided into method, Multi Step method, and Dilute Solvent method. As such Multi Step method, AP-Citrox
Law is a typical example. This is caused by CRUD (mainly composed of oxides of iron, nickel, chromium, manganese and cobalt) attached to the stainless steel surface by the alkaline oxidizing agent AP liquid (mainly composed of alkaline potassium permanganate). After rinsing, Citrox liquid (mainly composed of citric acid and oxalic acid or their organic acid salts) is an acidic chemical solution used in the second stage after rinsing. ) to dissolve and remove iron oxides, nickel oxides, etc. However, two methods have been conventionally proposed as waste liquid treatment methods in the AP-Citrox method. AP waste liquid is solidified into concrete as it is,
On the other hand, Citrox waste liquid is directly solidified into concrete after being neutralized. Mix the AP waste liquid and the first washing liquid. Mix the Citrox waste liquid and the first washing liquid. After neutralization, potassium permanganate is reduced with formalin, and then calcium salt is added, and the insoluble citrate is , produces oxalate. Supernatant water and second AP solution and
The volume of the Citrox washing solution is reduced in an evaporator, while the sludge is solidified with cement or asphalt. However, in the waste liquid treatment methods of ) and ), the oxalic acid and citric acid components in the Citrox liquid remain without being decomposed, so the volume of solidified waste is large and a large storage space must be secured. This method has disadvantages in that harmful substances such as chromium ions do not precipitate and can damage the evaporator, leading to corrosion of the can body. Purpose of the Invention The present invention was made against the background of the above-mentioned technical problem, and by decomposing or precipitating the main component of the decontamination agent and precipitating the metal ions constituting the cladding, the present invention reduces the generation of sludge. Furthermore, harmful substances such as chromium remaining in the processing solution are greatly reduced, and the processing process can be easily carried out.
The purpose of this paper is to provide a method for treating waste liquid from AP-based decontamination agents and Citrox-based decontamination agents. Components of the Invention That is, the present invention provides waste liquid of an AP decontamination agent whose main component is alkaline permanganate and a Citrox decontamination agent whose main components are oxalic acid and citric acid or their organic acid salts. When processing waste liquid,
This is a decontamination agent waste liquid treatment method characterized by combining the following steps (a) to (d). (b) The first step of mixing and neutralizing the waste liquid of AP-based decontamination agent and the waste liquid of Citrox-based decontamination agent. (b) A second step in which permanganate, oxalic acid, citric acid, or their organic acid salts are decomposed by adding acid to make the pH 7 or lower. (c) At least one metal ion from the group such as manganese, iron, nickel, cobalt, uranium, and ruthenium contained in the waste liquid is converted into a hydroxide, oxide, or salt by adding an alkali to make the pH 7 or higher. The third step is precipitation. (d) A fourth step (A) in which chromium ions contained in the waste liquid are precipitated as a salt by adding a metal salt. Further, the present invention is a decontamination agent waste liquid treatment method characterized by combining the steps (a) to (c) above and the steps (d)' below. (d) Add acid to the filtered solution to remove the precipitate.
The pH is adjusted to 1 to 4, then a reducing agent is added to reduce the chromium ions contained in the waste liquid, and an alkali is added to adjust the pH to 7 to 11.The reduced chromium ions are converted into hydroxide or oxide. The fourth step (B) is precipitation. The present invention will be explained in detail below step by step. (b) First step AP-based decontamination agents are usually alkaline aqueous solutions containing permanganates such as potassium permanganate and alkali metal hydroxides such as sodium hydroxide, while Citrox-based decontamination agents is an acidic aqueous solution containing oxalic acid and citric acid or their organic acid salts as main components. Therefore, each waste liquid of AP type decontamination agent and Citrox type decontamination agent (hereinafter referred to as “AP type waste liquid” or “Citrox type waste liquid”)
) mixes and neutralizes these two types of waste liquids. The preferred means in this case is:
Mix the AP waste liquid and the first washing water, and
It is recommended to mix the Citrox waste liquid and the first washing water, and then mix and neutralize the two. Further, the temperature of the mixing/neutralization treatment may be from room temperature to 100°C. By mixing and neutralizing AP-based waste liquid and Citrox-based waste liquid, permanganate, oxalic acid, citric acid, or their organic acid salts partially react, and permanganate is reduced. One part becomes manganese dioxide, and one part of oxalic acid, citric acid, etc. is oxidized and decomposed into carbon dioxide. (b) 2nd step The treated solution (including sediment) after mixing and neutralization in the 1st step has not been completely neutralized yet because the AP waste solution itself is strongly alkaline in composition. It is alkaline. Therefore, in the second step, an acid such as nitric acid, sulfuric acid, hydrochloric acid, or acetic acid, preferably nitric acid, is added to the treatment liquid obtained in the first step to adjust the pH to 7 or less, preferably 3 to 7, more preferably Must be 5.5 or less. Thus, the remaining permanganate, oxalic acid, citric acid, or their organic acid salts are decomposed to generate carbon dioxide, and the chromium component contained in the waste liquid is oxidized to become hexavalent chromium ions. The decomposition reaction by addition of acid in the second step is an exothermic reaction accompanied by foaming, but the reaction temperature is room temperature to 100°C and the reaction time is 5 minutes or more, preferably 5 to 120°C.
It is best to do this in about a minute. A typical reaction example in the second step is as follows, using nitric acid as the acid to be added. 5H ₂ C ₂ O ₄ +2KMnO ₄ +6HNO ₃ →10CO ₂ +2Mn(NO ₃ ) ₂ +2KNO ₃ +8H ₂ O 5C ₆ H ₈ O ₇ +18KMnO ₄ +54HNO ₃ →30CO ₂ +18Mn(NO ₃ ) ₂ +18KNO ₃ +47H ₂ O 5( NH ₄ ) ₂ C ₂ O ₄ +2KMnO ₄ +6HNO ₃ →10CO ₂ +2Mn(NO ₃ ) ₂ +2KNO ₃ +10NH ₃ +
8H ₂ O (c) Third step Since the second step is a decomposition reaction accompanied by the generation of carbon dioxide, the completion of foaming is a measure of the end of the decomposition reaction. Therefore, after the completion of foaming, an alkali such as sodium hydroxide, potassium hydroxide, or aqueous ammonia is added to the treated liquid (including the precipitate) obtained in the second step.
By making the pH pH 7 or higher, preferably 7 to 13, and more preferably 9.5 or higher, the manganese (including AP decontamination agent components), iron, nickel, cobalt, At least one metal ion from the group such as uranium and ruthenium is precipitated as a hydroxide, oxide or salt. Typical reaction examples in the third step are as follows. Mn ²⁺ +2OH ^- →Mn(OH) ₂ (white precipitate) Fe ³⁺ +3OH ^- →Fe(OH) ₃ (red and colored precipitate) Co ²⁺ +NO ₃ ^- +OH ^- →Co(OH)NO ₃ (blue precipitate) ) Co ²⁺ +2OH ^- →Co(OH) ₂ (pink precipitate) UO ₂ (NO ₃ ) +2NH ₄ OH→(NH ₄ ) ₂ U ₂ O ₇ (yellow precipitate) 2UO ₂ ²⁺ +6OH ^- +2Na ⁺ →Na ₂ U ₂ O ₇・3H ₂ O (yellow precipitate) Ru ³⁺ +3OH ^- →Ru(OH) ₃ (black precipitate) (d), (d)′ 4th step In the 3rd step, precipitation reaction occurs under alkaline conditions Therefore, the chromium ions contained in the waste liquid do not dissolve and precipitate by forming chromite ions. Therefore, in the fourth step, chromium ions are precipitated by employing the step (A) or (B). <Fourth step (A)> Add lead to the treatment solution containing the precipitate obtained in the third step.
By adding an excessive amount of metal salts such as nitrates, sulfates, hydrochlorides, and acetates such as calcium, barium, strontium, or magnesium, preferably barium nitrate, dissolved chromium ions such as hexavalent ions can be removed. Precipitate as chromate, filter, and separate into total precipitate and liquid. Typical reaction examples are as follows. K ₂ CrO ₄ +Ba(NO ₃ ) ₂ →BaCrO ₄ +2KNO ₃ K ₂ CrO ₄ +Pb(CH ₃ COO) ₂ →PbCrO ₄ +2CH ₃ COOK Note that the liquid obtained in the fourth step (A) contains the added metal. Since some salt ions (lead, calcium, barium, strontium, magnesium, etc.) are dissolved as surplus, nitric acid, sulfuric acid, hydrochloric acid, acetic acid, etc. are further added to the solution to convert the ions into insoluble salts. A clear liquid may be obtained by precipitating and removing the precipitate again, and this liquid may be neutralized to obtain the final treatment liquid. <Fourth step (B)> The treatment solution containing the precipitate obtained in the third step is filtered to separate the precipitate and the liquid. Next, an acid such as nitric acid, sulfuric acid, hydrochloric acid, or acetic acid, preferably nitric acid, is added to this liquid to adjust the pH to 1-4, preferably 2-3.
and pear, followed by sodium sulfite, sodium bisulfite,
By adding reducing agents such as hydrogen peroxide, ferrous sulfate, and sulfur dioxide gas, chromium ions such as hexavalent ions dissolved in the waste liquid are reduced, and then sodium hydroxide,
Add an alkali such as potassium hydroxide or aqueous ammonia to adjust the pH to 7 to 11, precipitate the reduced chromium ion as a hydroxide or oxide, and separate it into a precipitate and a liquid. A typical reaction example in the fourth step (B) is as follows. Cr ₂ O ₇ ^2- +3SO ₃ ^2- +8H ⁺ → _2Cr ³⁺ +3SO ₄ ^2- +4H ₂ O Cr ₂ O 7 ^2- +6Fe ²⁺ +14H ⁺ →2Cr ³⁺ +6Fe ³⁺ +7H ₂ O Cr ³⁺ +3OH ^- → Cr(OH) ₃ (dark green precipitate) The liquid obtained in the fourth step (B) may be further neutralized to obtain the final treatment liquid. In this way, in the present invention, AP system waste liquid and
Citrox waste liquid can be separated into a precipitate and a clear final treated liquid, and the latter can be greatly reduced in volume by using evaporation means such as an ordinary evaporator. Although the present invention has mainly been described with respect to the decontamination of radioactive equipment, it is not limited thereto, and is not limited to decontamination of equipment contaminated with radioactivity. It goes without saying that it can also be applied to waste liquid. EXAMPLES The present invention will be explained in more detail with reference to Examples below. Example 1 AP-based decontamination agent (composition: sodium hydroxide 105g/
, potassium permanganate 32g/) and Citrox decontamination agent (composition: oxalic acid 25g/, diammonium citrate 50g/, ferric nitrate 2g/, diethylthiourea 1g/) each at 130g/, 80
g/dissolved aqueous solution was prepared one by one, and 2 g of eluted chromium from the object to be decontaminated was added as potassium chromate (4 g in total), and these were used as pseudo waste liquids (hereinafter referred to as "AP waste liquid", "Citrox waste liquid"). system waste liquid”
). The AP waste liquid and the Citrox waste liquid were mixed and neutralized (first step), then concentrated nitric acid was added to the mixed liquid to adjust the pH to 5.5, and a decomposition reaction was carried out at a temperature of 50° C. for 60 minutes (second step). After confirming that the carbon dioxide foaming associated with the decomposition reaction has been completed, the liquid is
When a 10N aqueous sodium hydroxide solution was added to adjust the pH to 9.5, precipitates of manganese ions and iron ions dissolved in the waste liquid were formed (third step).
500 ml of an 8 g/100 ml barium nitrate aqueous solution was added to the treatment solution containing the obtained precipitate to precipitate the chromium ions dissolved in the treatment solution as barium chromate [4th step (A)]. After filtering the obtained treatment solution containing the precipitate and separating it into the precipitate and the liquid, 12 ml of concentrated sulfuric acid was added to this solution to precipitate excess barium ions, and then a 10N aqueous sodium hydroxide solution was added to adjust the pH to 8. Adjust to .0,
The treated solution was further filtered to separate the precipitate and the solution. This solution is the final treatment solution, and the analysis results of this treatment solution are shown in Table 1.

[Table] Corrosion tests were carried out using the obtained final treated liquid according to conventional methods under normal pressure and boiling point conditions, which are the same as the operating conditions of the evaporator, and the results showed that the corrosion was only general corrosion.
It was confirmed that it was 0.1 mm/g or less, which was within the normally acceptable range. Example 2 The treated solution containing the precipitate obtained in the third step of Example 1 was filtered and separated into the precipitate and the liquid. Concentrated nitric acid was added to this solution to adjust the pH to 3, and then sodium sulfite was added to the solution. Add 100ml of 200g/water solution and pH with nitric acid.
3 and reduce the chromium ion from hexavalent to trivalent,
Furthermore, add 10N aqueous sodium hydroxide solution.
When the pH was set to 9.5, a precipitate of chromium hydroxide was formed [4th step (B)]. The resulting treatment liquid containing the precipitate was filtered to separate the precipitate and liquid, and the liquid was neutralized to pH 8 with concentrated sulfuric acid to obtain a final treatment liquid. The analysis results of this final treatment solution are shown in Table 2.

[Table] Effects of the Invention As described above, according to the present invention, oxalic acid, citric acid, and their organic acid salts, which constitute the Citrox decontamination agent, can be decomposed into carbon dioxide. Volume reduction can be achieved, and the waste liquid can be separated into a precipitate and a clear final treated liquid, so radioactive substances can be concentrated in the former (precipitate) and radioactive substances can be concentrated in the latter (final treated liquid). The treatment of the present invention can greatly reduce contamination, and since the final treatment liquid does not substantially contain harmful metal ions, the volume of the liquid can be reduced in an evaporator without causing damage to the can. The process itself has many advantages, such as being extremely simple and easy to operate, and the amount of sludge (precipitate) generated during waste liquid treatment is extremely small, and its industrial significance is extremely large.

Claims (1)

[Claims] 1. Main component is alkaline permanganate
When treating the waste liquid of AP-based decontamination agent and the waste liquid of Citrox-based decontamination agent whose main components are citric acid and oxalic acid or their organic acid salts, the following steps (a) to (d) are combined. A decontamination agent waste liquid treatment method characterized by the following. (b) The first step of mixing and neutralizing the waste liquid of AP-based decontamination agent and the waste liquid of Citrox-based decontamination agent. (b) A second step in which permanganate and citric acid and oxalic acid or their organic acid salts are decomposed by adding acid to make the pH 7 or lower. (c) At least one metal ion from the group such as manganese, iron, nickel, cobalt, uranium, and ruthenium contained in the waste liquid is converted into a hydroxide, oxide, or salt by adding an alkali to make the pH 7 or higher. The third step is precipitation. (d) A fourth step (A) in which chromium ions contained in the waste liquid are precipitated as a salt by adding a metal salt. 2 Main ingredient is alkaline permanganate
When treating waste liquid from AP decontamination agents and waste liquid from Citrox decontamination agents whose main components are citric acid and oxalic acid or their organic acid salts, the following (a) to (d)'
A decontamination agent waste liquid treatment method characterized by combining the following steps. (b) The first step of mixing and neutralizing the waste liquid of AP-based decontamination agent and the waste liquid of Citrox-based decontamination agent. (b) A second step in which permanganate and citric acid and oxalic acid or their organic acid salts are decomposed by adding acid to make the pH 7 or lower. (c) At least one metal ion from the group such as manganese, iron, nickel, cobalt, uranium, and ruthenium contained in the waste liquid is converted into a hydroxide, oxide, or salt by adding an alkali to make the pH 7 or higher. The third step is precipitation. (d)′ Add acid to the filtrate that has been filtered to remove precipitates.
Adjust the pH to 1 to 4, then add a reducing agent to reduce the chromium ions contained in the waste liquid, and then add an alkali to adjust the pH to 7 to 11. The fourth step (B) is to precipitate the product as a solid.