JP2012198103A - Processing method for radioactive waste liquid containing phosphate ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method capable of efficiently decomposing a radioactive waste liquid containing phosphate ester under a relaxed condition.SOLUTION: The processing method for the radioactive waste liquid containing phosphate ester includes an oxidative decomposition processing process of adding a solution containing copper salt capable of producing copper ions or copper ions produced from copper salt and hydrogen peroxide to the radioactive waste liquid, and oxidatively decomposing the phosphate ester within a temperature range of 20-60°C in the presence of the copper ions produced from the copper salt.

Description

  The present invention relates to a method for treating a radioactive liquid waste containing a phosphate ester.

  In Japan, nuclear power generation contributes to global warming and stable energy supply. The national policy is to steadily promote this as a core power source, and plutonium recovered by reprocessing spent fuel, The basic policy is to make effective use of uranium. In a domestic reprocessing plant, spent fuel is dissolved in nitric acid, and uranium and plutonium are extracted and recovered by bringing the tributyl phosphate (TBP) into contact with an organic solvent diluted with n-dodecane (n-D). The so-called Purex method is adopted. The organic solvent deteriorates due to radiolysis or acid hydrolysis during use, and contains deterioration products such as dibutyl phosphate (DBP), monobutyl phosphate (MBP), and phosphoric acid. . These degradation products form complexes with uranium, plutonium and fission products, and have a negative impact on extraction and back-extraction, such as reduced decontamination factors, loss of uranium and plutonium, and formation of interfacial precipitates (cladding). Effect. In particular, DBP must be removed sufficiently to form a stable complex with uranium, plutonium, zirconium, etc., remain in the organic solvent, and significantly reduce the extraction performance.

  For this reason, a solvent washing step is provided for the purpose of recovering the performance of the organic solvent and recycling and using the organic solvent. Here, the solvent washing step is a step of removing the degradation products using an alkali solution of sodium hydroxide and sodium carbonate and nitric acid. In this process, a waste product (alkaline waste solution) containing degradation products such as DBP and radioactivity is generated. The alkaline waste liquid is concentrated and then mixed with the high-level concentrated waste liquid and vitrified in a high-level vitrification facility (solidification step). In this process, there is a concern that DBP forms an insoluble complex with metals and deposits in the storage tank and affects the temperature management of the melting furnace.

Japanese Patent Publication No. 7-23920

Among the treatment techniques for waste liquids containing organic substances, the wet oxidation method is promising in that the waste liquid can be treated under mild conditions as compared with other methods, and the treatment process can be simplified. However, when the most common iron ion catalyst in the wet oxidation method is used, it is feared that an insoluble complex such as Fe (DBP) ₃ is formed with DBP to precipitate (W. Davis, Jr. and D.O. Rester, J. Inorg.Nucl.Chem., 1968, 30, 3317-3324), the use of iron ion catalysts is considered difficult. As a similar processing technique, Patent Document 1 proposes a method using a metal copper powder catalyst instead of iron ions. However, in this case, since the copper metal powder and the like added to the reaction tank remain as precipitates, it is necessary to treat the precipitates separately. Furthermore, Patent Document 1 does not disclose a treatment method focusing on the production of an insoluble complex by DBP.

From the above situation, it is desired to develop a treatment method that efficiently decomposes radioactive waste liquid containing degradation products such as DBP and MBP under mild conditions and does not require separation of precipitates.
In addition, in the treatment of radioactive waste liquids other than TBP and its degradation products, in other words, in the treatment of radioactive waste liquids containing other phosphate esters, it is desirable to develop a treatment method that can be performed efficiently under mild conditions as described above. ing.

  Therefore, the objective of this invention is providing the processing method which can decompose | disassemble the radioactive waste liquid containing a phosphate ester efficiently on mild conditions.

  The present invention is, for example, a method for treating a radioactive waste liquid containing a phosphate ester, wherein the radioactive waste liquid contains a copper salt capable of generating copper ions or a copper ion generated from a copper salt, hydrogen peroxide, The present invention relates to a method for treating a radioactive liquid waste comprising a step of oxidizing and decomposing the phosphate ester in the temperature range of 20 to 60 ° C. in the presence of copper ions generated from the copper salt. .

  According to the treatment method of the present invention, a radioactive liquid waste containing a phosphate ester can be safely and efficiently decomposed under mild conditions.

FIG. 1 is a diagram for explaining a method for treating a radioactive liquid waste containing a phosphate ester according to the present invention.

The present invention relates to a method for treating a radioactive liquid waste containing a phosphate ester.
The radioactive liquid waste treated in the present invention is generated from a solvent washing step.
In the process of extracting uranium and plutonium by the Purex method, generally, first, spent fuel is dissolved in nitric acid, and this nitric acid solution, tributyl phosphate (TBP), and an organic containing n-dodecane as a diluent are used. Contact with the solvent extracts uranium and plutonium to the organic solvent side. Next, this organic solvent is brought into contact with dilute nitric acid to extract uranium and plutonium to the dilute nitric acid side. In addition to TBP, organic solvents used in this extraction process include degradation products such as dibutyl phosphate (DBP), monobutyl phosphate (MBP), and phosphoric acid that have deteriorated TBP due to radiolysis or acid hydrolysis. Will be included. In the solvent washing step, the degradation products are removed using an alkali solution of sodium hydroxide and sodium carbonate and nitric acid, and the organic solvent is regenerated and recycled. Therefore, alkaline waste liquid containing degradation products such as DBP and radioactivity is generated from this process. In the present invention, alkaline waste liquid can be treated as radioactive waste liquid.

  For this reason, the phosphate in the radioactive liquid waste to be treated in the present invention usually includes at least one of the group consisting of tributyl phosphate, dibutyl phosphate and monobutyl phosphate.

In the radioactive liquid waste treated in the present invention, the phosphate ester is usually contained at a concentration of 1 to 1000 mmol / L.
In the present invention, a copper salt capable of generating copper ions or a solution containing copper ions generated from a copper salt and hydrogen peroxide are added to the radioactive liquid waste, and the copper ions generated from the copper salt as a catalyst are added. An oxidative decomposition treatment step of oxidatively decomposing (wet oxidative decomposition) the phosphate ester in the temperature range of 20 to 60 ° C. in the presence is included.

  Examples of the copper salt include copper salts capable of generating monovalent or divalent copper ions, for example, inorganic copper salts such as copper chloride, copper sulfate, copper nitrate, and basic copper carbonate. These may be anhydrous or hydrated. These may be used alone or in combination of two or more. When nitric acid is contained in the radioactive liquid waste, copper nitrate is preferably used.

  The copper salt may be added to the radioactive liquid waste as it is, or may be added to the radioactive liquid waste as a solution (copper ion-containing solution) containing copper ions previously generated from the copper salt. Examples of the solution include an aqueous solution obtained by adding a copper salt to water. In general, the copper salt is dissociated and copper ions are generated in the aqueous solution.

  From the viewpoint of promptly performing the decomposition reaction, the copper salt or copper ion-containing solution is preferably used in the following amounts. That is, in the total of copper salt and waste liquid or in the total of copper ion-containing solution and waste liquid, the copper salt and / or so that the copper ion concentration is 1 to 100 mmol / L, more preferably 5 to 50 mmol / L. It is preferable to use a copper ion-containing solution.

  Hydrogen peroxide may be added in a preferable amount as appropriate depending on the amount of radioactive liquid waste to be treated, but it is preferably added as 2 to 70 w / v% hydrogen peroxide solution, and 30 to 70 w / v% excess. More preferably, it is added as hydrogen oxide water.

  From the viewpoint of promptly performing the decomposition reaction, hydrogen peroxide may be added to the radioactive liquid waste so that the hydrogen peroxide is in a ratio of 10 to 500 mol, more preferably 50 to 300 mol, per 1 mol of the phosphate ester. preferable.

When the copper salt or the copper ion-containing solution and hydrogen peroxide are added to the radioactive liquid waste, the copper produced from the copper salt by the reaction shown in the following formulas (1) and (2) in the obtained reaction solution The ion or the copper ion contained in the copper ion-containing solution reacts with the hydrogen peroxide solution to generate a hydroxy radical (for example, AC Melo-Filho and R. Meneghini, Mutation Res., 1991, 251). 109-113). This hydroxy radical can be decomposed until the phosphate ester becomes carbon dioxide (CO ₂ ). Thus, in the oxidative decomposition treatment step, the phosphate ester is oxidatively decomposed in the presence of copper ions generated from the copper salt.

Cu ²⁺ + H ₂ O ₂ → Cu ⁺ + O ₂ ⁻ + 2H ⁺ (1)
Cu ⁺ + H ₂ O ₂ → Cu ²⁺ + HO ⁻ + HO. (2)
In the oxidative decomposition treatment step, the temperature of the radioactive waste liquid (reaction liquid) to which the copper salt or copper ion-containing solution and hydrogen peroxide are added is set to 20 to 60 ° C, preferably 40 to 60 ° C. In the present invention, since the copper salt is used, the phosphate ester can be oxidatively decomposed under relatively low temperature and mild conditions.

  In addition, you may add acids, such as a sulfuric acid, and alkalis, such as sodium hydroxide, to a reaction liquid as needed in order to adjust pH. The addition of the acid or alkali may be performed at any time from before the start of the oxidative decomposition treatment process to after the end of the process.

  In the oxidative decomposition treatment step of the present invention, the pH of the reaction solution is usually 1 to 3. Moreover, in this invention, a change of pH is hardly seen as the oxidative decomposition process of phosphate ester advances, and pH is 1-3 normally. By the way, the pH at which the oxidative decomposition treatment proceeds is usually 1 to 5, and the pH at which the oxidative decomposition treatment proceeds most efficiently is usually 1 to 3. Therefore, it is often unnecessary to adjust the pH in the oxidative decomposition treatment step of the present invention.

  Furthermore, in the oxidative decomposition treatment step of the present invention, since the decomposition of the phosphate ester proceeds gently, foaming during the decomposition reaction is hardly observed, and it is often unnecessary to add an antifoaming agent. This is particularly preferable in the treatment of radioactive liquid waste where safety in operation is important. However, this does not prevent the addition of the antifoaming agent in the present invention.

  Whether or not the decomposition of the phosphate ester in the radioactive liquid waste has been completed can be confirmed by measuring the TOC (total organic carbon). In the treatment of radioactive liquid waste, when the decomposition rate of TOC is 70% or more, more preferably 75% or more, it can be considered that the decomposition of the phosphate ester is completed.

  After the decomposition of the phosphate ester is completed, the treated radioactive liquid waste (reaction liquid in which the decomposition of the phosphate ester is completed) is usually sent to the next step such as a solidification step. When sending to the next step, alkali may be supplied as necessary to neutralize the treated radioactive liquid waste. In the oxidative decomposition treatment step of the present invention, a precipitate such as copper hydroxide is not generated, so that the next step can be performed as it is without separating the treated radioactive liquid waste and the precipitate.

More specifically, in the present invention, for example, the processing apparatus shown in FIG. 1 is used.
The processing apparatus of FIG. 1 is connected to a reaction tank 1 for wet oxidative decomposition of a phosphate ester, and a reaction tank 1, and a radioactive waste liquid supply tank 2 for supplying radioactive waste liquid to the reaction tank 1. A hydrogen peroxide supply tank 3 for supplying hydrogen peroxide, and a catalyst supply tank 4 for supplying a catalyst (specifically, a copper salt or a solution containing copper ions generated from the copper salt); It is connected to the reaction tank 1 and comprises an acid supply tank 5 for supplying acid to the reaction tank 1 as needed, and an alkali supply tank 6 for supplying alkali as needed. Is done. In addition, the reaction tank 1 is provided with a stirrer M for stirring the radioactive liquid waste during oxidative decomposition and a thermometer T for monitoring the temperature of the radioactive liquid waste during the oxidative decomposition. Furthermore, if necessary, a gas analyzer A that analyzes the exhaust gas generated by the decomposition treatment of the radioactive liquid waste can be provided.

  The processing method of the present invention is performed as follows using the processing apparatus of FIG. 1 in an embodiment using a copper ion-containing solution prepared from a copper salt, for example. First, radioactive waste liquid is supplied to the reaction tank 1 from the radioactive waste liquid supply tank 2. Next, a copper ion-containing solution is supplied to the reaction tank 1 from the catalyst supply tank 4, and hydrogen peroxide solution is supplied from the hydrogen peroxide supply tank 3. In addition, the supply order of radioactive waste liquid, hydrogen peroxide, and a copper ion containing solution is not limited to the above, You may supply in arbitrary orders. Here, the amount of the copper ion-containing solution to be added to the radioactive liquid waste and the ratio of the phosphate ester and hydrogen peroxide in the radioactive liquid waste are within the preferred range described above, the radioactive liquid waste, the copper ion-containing solution and the peroxide. It is desirable to supply hydrogen water.

  The pH of a radioactive waste liquid (also referred to as a reaction liquid in the present specification) to which a hydrogen peroxide solution and a copper ion-containing solution are added is usually 1 to 3. If the pH is within this range, the oxidative decomposition of the phosphate ester proceeds promptly. In this case, it is not necessary to supply acid from the acid supply tank 5. However, when the pH of the radioactive liquid waste exceeds 3, it is preferable to supply the acid from the acid supply tank 5 in order to adjust the pH to 1 to 3.

  In addition, the temperature of the radioactive liquid waste to which the hydrogen peroxide solution and the copper ion-containing solution are added is usually 20 to 60 ° C., preferably 20 to 40 ° C. The temperature of the reaction solution is usually adjusted to 20 to 60 ° C, preferably 40 to 60 ° C.

  In the radioactive waste liquid to which the hydrogen peroxide solution and the copper ion-containing solution are added, the reactions of the above formulas (1) and (2) occur to generate hydroxy radicals, thereby starting the oxidative decomposition of the phosphate ester. It is preferable to oxidatively decompose the phosphate ester while stirring the reaction solution with the stirrer M. The gas generated by the oxidative decomposition is exhausted from the reaction tank 1. At this time, it is preferable to monitor the exhaust gas with a gas analyzer A and measure the concentration and generation amount of carbon dioxide in the exhaust gas.

Further, during the oxidative decomposition treatment process of the phosphate ester, whether the temperature is maintained within the above range is monitored by a thermometer T, and if it is out of the above range, the heating temperature is adjusted.
In the treatment method of the present invention, since the pH hardly changes during the oxidative decomposition treatment step of the phosphate ester, it is not usually necessary to adjust the pH. Further, since almost no foaming is observed during the oxidative decomposition treatment step of the phosphate ester, it is usually unnecessary to add an antifoaming agent to the reaction tank 1. Moreover, in the said decomposition process process, since precipitates, such as copper oxide and copper hydroxide, are not produced | generated, the next process can be performed as it is, without isolate | separating a processed reaction liquid and a precipitate.

  After confirming that the decomposition of the phosphate ester is complete by measuring TOC (total organic carbon), if necessary, alkali may be supplied from the alkali supply tank 6 to neutralize the treated reaction solution. Good. The treated reaction liquid is usually sent to the next step such as a solidification step.

  In the embodiment in which the copper salt is used as it is, when the processing apparatus of FIG. 1 is used, instead of supplying the copper ion-containing solution from the catalyst supply tank 4 to the reaction tank 1 in the above description, the copper salt is directly supplied. do it.

  As described above, according to the treatment method of the present invention, the phosphate ester can be oxidatively decomposed at a relatively low temperature such as 20 to 60 ° C. Moreover, almost no foaming is observed during oxidative decomposition, and the waste liquid can be treated gently and safely. This is very advantageous in the treatment of radioactive liquid waste where safety is paramount.

  Moreover, in this invention, when a decomposition reaction advances, deposits, such as copper oxide and copper hydroxide, do not produce | generate. This is because the increase in pH during oxidative decomposition is suppressed by using a copper salt as a supply source of copper ions. Thereby, it is not necessary to provide a precipitate separation step after the oxidative decomposition treatment step, and a solidification step or the like can be immediately performed on the radioactive waste liquid that has been subjected to the oxidative decomposition treatment.

In addition, even when the concentration of the phosphate ester in the waste liquid is high, no precipitate is generated and the decomposition reaction proceeds.
Thus, according to the treatment method of the present invention, radioactive waste liquid can be decomposed gently, safely and efficiently.

On the other hand, as will be described later in the examples, in the method for treating radioactive waste liquid of the present invention, when iron salt is used instead of copper salt as a catalyst, foaming occurs violently during oxidative decomposition, so that waste liquid treatment can be safely performed I can't. In addition, precipitates are formed during oxidative decomposition. This is considered to be because iron ions generated from the iron salt form insoluble complexes such as DBP and Fe (DBP) ₃ in the waste liquid. Thus, when using an iron salt, the decomposition | disassembly of DBP itself is inhibited. Moreover, the process of isolate | separating the said deposit is needed.

  In addition, if the concentration of phosphate ester in the waste liquid is high, iron ions form a large amount of an insoluble complex and precipitate, so the iron ion catalyst is exhausted significantly and the phosphate ester is decomposed during the decomposition process. It may be impossible to progress. In this case, in order to proceed the oxidative decomposition of the phosphate ester, a large amount of iron salt must be added. Further, if the reaction is carried out at a high temperature in order to accelerate the decomposition treatment, foaming may become intense.

  Furthermore, in the method for treating radioactive liquid waste according to the present invention, even when copper powder is used instead of copper salt as a catalyst, foaming occurs during oxidative decomposition, so that the liquid waste treatment cannot be performed safely. Further, the pH of the solution rises during oxidative decomposition, and precipitation of hydroxides and the like may occur. As will be described later in Comparative Example 2, after the oxidative decomposition treatment step, the decomposed solution contains copper powder remaining not used for decomposition, and copper oxide and copper hydroxide precipitates. And a process for separating them is required.

  Moreover, when the concentration of the phosphate ester in the waste liquid is high, precipitation of copper hydroxide may be promoted due to an increase in pH accompanying oxidative decomposition. Therefore, in order to advance oxidative decomposition efficiently, it is necessary to add a large amount of copper powder catalyst to supplement the copper powder catalyst exhausted by precipitation, and it is necessary to carry out a reaction at a high temperature, and foaming may be intense. There is also. Further, there is a concern that if the pH further increases with oxidative decomposition, it becomes a region where oxidative decomposition does not proceed.

On the other hand, according to the treatment method of the present invention, the problem when using an iron salt catalyst or a copper powder catalyst as described above can be solved.
In the above description, the treatment of radioactive waste liquid containing TBP and its degradation product as a phosphate ester has been described. However, in the present invention, the treatment of radioactive waste liquid containing phosphate ester other than TBP and its degradation product is also described. Similarly, it can be performed efficiently under mild conditions. The treatment method of the present invention can also be applied to the treatment of domestic wastewater and industrial wastewater containing a phosphate ester.

From the above, the present invention relates to the following (1) to (3), for example.
(1) A method for treating a radioactive liquid waste containing a phosphate ester, wherein a copper salt capable of producing copper ions or a solution containing copper ions produced from a copper salt and hydrogen peroxide are added to the radioactive liquid waste. A method for treating a radioactive liquid waste comprising an oxidative decomposition treatment step of oxidatively decomposing the phosphate ester in a temperature range of 20 to 60 ° C. in the presence of copper ions generated from the copper salt.
According to the treatment method of the present invention, a radioactive liquid waste containing a phosphate ester can be safely and efficiently decomposed under mild conditions.

(2) The method for treating a radioactive liquid waste according to (1), wherein the phosphate ester contains at least one member selected from the group consisting of tributyl phosphate, dibutyl phosphate and monobutyl phosphate.
As described above, the treatment method of the present invention is suitably used for the treatment of radioactive waste liquid discharged in the process of extracting uranium and plutonium for reuse from spent fuel.

(3) The method for treating a radioactive liquid waste according to (1) or (2), wherein the oxidative decomposition treatment step is performed in a temperature range of 40 to 60 ° C.
According to the treatment method of the present invention, the radioactive liquid waste can be decomposed even under mild conditions such as 40 to 60 ° C.

[Example 1]
A wet oxidation test is performed on the nitrate waste liquid containing DBP (concentration 22 mmol / L) and MBP (concentration 18 mmol / L) as degradation products of TBP under the following conditions using the processing apparatus of FIG. It was. That is, 0.2 L of nitric acid waste liquid was supplied from the radioactive waste liquid supply tank 2 and 0.2 L of an aqueous solution of copper nitrate trihydrate (concentration 40 mmol / L) was supplied from the catalyst supply tank 4 to the reaction tank 1. Thereafter, 0.14 L of 35 wt% hydrogen peroxide solution was supplied from the hydrogen peroxide supply tank 3 to start the oxidative decomposition treatment step of the reaction solution. Here, the temperature of the reaction solution in the reaction vessel 1 was maintained at 60 ° C. with a heater, and the phosphoric acid ester was oxidatively decomposed while stirring with the stirrer M. In the oxidative decomposition treatment step, the pH of the reaction solution in the reaction vessel 1 changed between pH = 1 and 2.

  In order to evaluate the decomposition rate of DBP and MBP, TOC (total organic carbon) was measured. Specifically, the measurement was carried out on the nitric acid waste liquid (before the test) immediately after supplying the catalyst and the reaction liquid (after the test) two days after the start of the oxidative decomposition treatment step.

  Moreover, in order to evaluate the precipitation of a copper ion catalyst, the change of the copper ion concentration in a waste liquid was measured. Specifically, the measurement was carried out on the nitric acid waste liquid (before the test) immediately after supplying the catalyst and the reaction liquid (after the test) two days after the start of the oxidative decomposition treatment step.

  In addition, TOC was measured by Shimadzu Corporation total organic carbon meter TOC-VCSN. The copper ion concentration was measured with an ICP emission spectroscopic analyzer SPS5520 manufactured by SII Nano Technology. In the present specification, “immediately after supplying the catalyst” means immediately after supplying the catalyst to the reaction tank 1 and before supplying hydrogen peroxide.

[Comparative Example 1]
A wet oxidation test is performed on the nitrate waste liquid containing DBP (concentration 22 mmol / L) and MBP (concentration 18 mmol / L) as degradation products of TBP under the following conditions using the processing apparatus of FIG. It was. That is, after supplying 0.2 L of nitric acid waste liquid from the radioactive waste liquid supply tank 2 to the reaction tank 1, an aqueous solution of ferrous sulfate heptahydrate salt (concentration 20 mmol / L) 0. 2 L and 0.14 L of 35 wt% hydrogen peroxide water were supplied from the hydrogen peroxide supply tank 3 to start the oxidative decomposition treatment step of the reaction solution. Here, the temperature of the reaction solution in the reaction vessel 1 was maintained at 60 ° C. with a heater, and the phosphoric acid ester was oxidatively decomposed while stirring with the stirrer M. In the oxidative decomposition treatment step, the pH of the reaction solution in the reaction vessel 1 changed between pH = 1 and 2.

  In order to evaluate the decomposition rate of DBP and MBP, TOC was measured. Specifically, the measurement was performed on the nitric acid waste liquid immediately after supplying the catalyst (before the test) and the reaction liquid 0.5 hours after the start of the oxidative decomposition treatment process (after the test).

  Moreover, in order to evaluate the precipitation of an iron ion catalyst, the change of the iron ion concentration in a waste liquid was measured. Specifically, the measurement was performed on the nitric acid waste liquid immediately after supplying the catalyst (before the test) and the reaction liquid 0.5 hours after the start of the oxidative decomposition treatment process (after the test).

  In addition, TOC was measured by Shimadzu Corporation total organic carbon meter TOC-VCSN. The iron ion concentration was measured with an ICP emission spectroscopic analyzer SPS5520 manufactured by SII Nano Technology.

  Table 1 shows the measurement results of the TOC concentration and the copper or iron ion concentration of the waste liquid in Example 1 and Comparative Example 1 obtained as described above. Table 1 also shows the observation results regarding the foaming of the waste liquid during the oxidative decomposition treatment process.

  As shown in Table 1, in Example 1, the TOC concentration was reduced by 80% or more by the oxidative decomposition test, suggesting that DBP and MBP were efficiently decomposed. Moreover, since the copper ion concentration in the waste liquid before and after the test was not changed, it was suggested that the copper ion catalyst did not precipitate and kept in a dissolved state. Further, during the decomposition test, almost no foaming of the waste liquid was observed, and it was confirmed that the oxidative decomposition reaction proceeded gently.

On the other hand, in the method of Comparative Example 1, the TOC concentration decreased by 95% or more, but at the same time, the iron ion concentration decreased by 80% or more, and a large amount of precipitate was observed. Since the precipitate is considered to be an insoluble complex such as Fe (DBP) ₃ , the decrease in the TOC concentration is considered to be substantially due to the formation of the insoluble complex. Therefore, in Comparative Example 1, it is difficult to achieve the decomposition treatment of phosphate ester, which is the object of the present invention. Further, it was observed that the waste liquid foamed vigorously due to the formation of the complex and the reaction between the iron ion catalyst and hydrogen peroxide. Foaming as described above is inappropriate in the treatment of radioactive liquid waste where safety is of utmost importance, resulting in practical disadvantages.

[Example 2]
A wet oxidation test is performed on the nitrate waste liquid containing DBP (concentration 11 mmol / L) and MBP (concentration 9 mmol / L) as degradation products of TBP under the following conditions using the processing apparatus of FIG. It was. That is, after supplying 0.4 L of nitrate waste liquid and 8 mmol of copper nitrate trihydrate salt from the radioactive waste liquid supply tank 2 to the reaction tank 1, 35 wt% hydrogen peroxide from the hydrogen peroxide supply tank 3. 0.14 L of water was supplied to start the oxidative decomposition treatment process of the reaction solution. Here, the temperature of the reaction solution in the reaction vessel 1 was kept at 40 ° C. by a heater, and the phosphoric acid ester was subjected to oxidative decomposition treatment with stirring by the stirrer M. In the oxidative decomposition treatment step, the pH of the nitrate waste liquid in the reaction tank 1 changed between pH = 1 and 2.

  In order to evaluate the decomposition rate of DBP and MBP, TOC was measured. Specifically, the measurement was performed on the nitrate waste liquid immediately after supplying the catalyst (before the test) and the nitrate waste liquid 14 days after the start of the oxidative decomposition treatment process (after the test).

  Moreover, in order to evaluate the precipitation of a copper ion catalyst, the change of the copper ion concentration in a waste liquid was measured. Specifically, the measurement was performed on the nitric acid waste liquid immediately after supplying the catalyst (before the test) and the reaction liquid 14 days after the start of the oxidative decomposition treatment process (after the test).

  In addition, TOC was measured by Shimadzu Corporation total organic carbon meter TOC-VCSN. The copper ion concentration was measured with an ICP emission spectroscopic analyzer SPS5520 manufactured by SII Nano Technology.

[Comparative Example 2]
A wet oxidation test is performed on the nitrate waste liquid containing DBP (concentration 11 mmol / L) and MBP (concentration 9 mmol / L) as degradation products of TBP under the following conditions using the processing apparatus of FIG. It was. That is, after supplying 0.4 L of nitric acid waste liquid from the radioactive liquid waste supply tank 2 to the reaction tank 1, 8 mm of copper powder and 35 wt% hydrogen peroxide water 0.14 L from the hydrogen peroxide supply tank 3 were added. The reaction solution was oxidatively decomposed and started. Here, the temperature of the nitric acid waste liquid in the reaction tank 1 was maintained at 40 ° C. with a heater, and the phosphoric acid ester was oxidatively decomposed while stirring with the stirrer M. In the oxidative decomposition treatment step, the pH of the reaction solution in the reaction vessel 1 changed between pH = 1.5 and 3.

  In order to evaluate the decomposition rate of DBP and MBP, TOC was measured. Specifically, the measurement was carried out on the nitric acid waste liquid immediately after supplying the catalyst (before the test) and the reaction liquid 5 days after the start of the oxidative decomposition treatment process (after the test).

  Moreover, in order to evaluate the residual amount of a copper powder catalyst, the change of the copper ion concentration in a waste liquid was measured. Specifically, the measurement was carried out on the nitric acid waste liquid immediately after supplying the catalyst (before the test) and the reaction liquid 5 days after the start of the oxidative decomposition treatment process (after the test).

Furthermore, in order to investigate the precipitate generated in the waste liquid, the waste liquid after the oxidative decomposition treatment was filtered, and the filter cake was washed with water and dried, and then analyzed by powder X-ray diffraction.
In addition, TOC was measured by Shimadzu Corporation total organic carbon meter TOC-VCSN. The copper ion concentration was measured with an ICP emission spectroscopic analyzer SPS5520 manufactured by SII Nano Technology. Powder X-ray diffraction was performed using a Rigaku powder X-ray diffractometer RINT-2000.

  Table 2 shows the measurement results of the TOC concentration and the copper ion concentration of the waste liquid in Example 2 and Comparative Example 2 obtained as described above. Table 2 also shows the observation results regarding the foaming of the waste liquid during the oxidative decomposition treatment process.

  As shown in Table 2, in Example 2 and Comparative Example 2, the TOC concentration was reduced by 75% or more by the oxidative decomposition test, suggesting that DBP and MBP were efficiently decomposed. In Example 2, the copper ion concentration in the waste liquid did not change before and after the test. However, in Comparative Example 2, the catalyst was added as a copper powder, so the copper ion concentration before the test was zero. Thereafter, a soluble copper compound (for example, copper phosphate) is generated along with the decomposition of DBP and the like, and it is considered that the copper ion concentration in the waste liquid increased. However, when the waste liquid after the test was investigated, it was confirmed that a light blue powder was produced. According to powder X-ray diffraction, the powder was a compound mainly composed of copper, copper oxide and copper hydroxide. This suggests that in Comparative Example 2, in addition to the copper powder catalyst remaining unreacted, insoluble copper oxide and copper hydroxide are formed. In Comparative Example 2, the pH of the reaction solution increased from 1.5 (initial value) to 3.0 due to decomposition of DBP and the like. This increase in pH increases as the amount of decomposition of DBP and the like increases, so that when a large amount of waste liquid or waste liquid with a high concentration of DBP or the like is decomposed, insoluble copper hydroxide may be generated in a larger amount. . In such a case, there is a concern that the decomposition reaction of DBP or the like does not proceed because the copper powder catalyst added to the waste liquid is exhausted.

  In Comparative Example 2, when all of the copper powder added to the waste liquid is in a dissolved state, the copper ion concentration is estimated to be 1300 mg / L. However, as shown in Table 2, in the waste liquid detected after the test The copper ion concentration of was 700 mg / L. This indicates that about 45% of the initially added copper powder is precipitated in the waste liquid as copper, copper oxide or copper hydroxide.

[Example 3]
A wet oxidation test was performed on the nitrate waste liquid containing DBP (concentration: 100 mmol / L) as a degradation product of TBP under the following conditions using the processing apparatus of FIG. That is, 0.1 L of nitric acid waste liquid from the radioactive liquid supply tank 2 and 0.1 L of an aqueous solution of copper nitrate trihydrate salt (concentration 40 mmol / L) were supplied from the radioactive liquid supply tank 2 to the reaction tank 1. Thereafter, 0.2 L of 35 wt% hydrogen peroxide water was supplied from the hydrogen peroxide supply tank 3 to start the oxidative decomposition treatment step of the reaction solution. Here, the temperature of the reaction solution in the reaction vessel 1 was maintained at 60 ° C. with a heater, and the phosphoric acid ester was oxidatively decomposed while stirring with the stirrer M. In the oxidative decomposition treatment step, the pH of the reaction solution in the reaction vessel 1 changed between pH = 1 and 2.

  In order to evaluate the decomposition rate of DBP and MBP, TOC (total organic carbon) was measured. Specifically, the measurement was carried out on the nitric acid waste liquid immediately after the catalyst was supplied (before the test) and the reaction liquid 6 days after the start of the oxidative decomposition treatment process (after the test).

  Moreover, in order to evaluate the precipitation of a copper ion catalyst, the change of the copper ion concentration in a waste liquid was measured. Specifically, the measurement was carried out on the nitric acid waste liquid immediately after the catalyst was supplied (before the test) and the reaction liquid 6 days after the start of the oxidative decomposition treatment process (after the test).

  In addition, TOC was measured by Shimadzu Corporation total organic carbon meter TOC-VCSN. The copper ion concentration was measured with an ICP emission spectroscopic analyzer SPS5520 manufactured by SII Nano Technology.

  Table 3 shows the measurement results of the TOC concentration and the copper ion concentration of the waste liquid in Example 3 obtained as described above. Table 3 also shows the observation results regarding the foaming of the waste liquid during the oxidative decomposition treatment process.

  As shown in Table 3, in Example 3, the TOC concentration was reduced by 80% or more by the oxidative decomposition test, suggesting that DBP was efficiently decomposed. Moreover, since the copper ion concentration in the waste liquid before and after the test was not changed, it was suggested that the copper ion catalyst did not precipitate and kept in a dissolved state. Further, during the decomposition test, almost no foaming of the waste liquid was observed, and it was confirmed that the oxidative decomposition reaction proceeded gently.

  Moreover, in Example 3, pH of the reaction liquid always changed between 1-2. This is because even when the waste liquid containing a high concentration of phosphate ester is decomposed compared to Example 1, the fluctuation of the pH of the waste liquid is effectively suppressed by the effect of the copper ion catalyst, and a stable decomposition process is possible. It is shown that.

  As is clear from the results of the examples, the present invention can efficiently oxidatively decompose radioactive waste liquid such as nitrate waste liquid containing DBP and MBP even under a temperature condition of 60 ° C. or less. In particular, the ability to undergo oxidative decomposition under mild conditions in which waste liquid foaming hardly occurs is very advantageous for the treatment of radioactive waste liquid in which safety is paramount.

  In addition, the present invention suggests that the copper ion concentration does not decrease even after wet oxidation of the waste liquid, and the copper ion catalyst does not precipitate. Therefore, it is possible to dramatically reduce the load related to the generation of precipitates and the treatment thereof, which has been a problem of the conventional wet oxidation method. This point is advantageous when the treatment method of the present invention is applied not only to the treatment of radioactive waste liquid containing an organic phosphate, but also to the treatment of general domestic wastewater and industrial wastewater.

  As described above, the present invention greatly contributes to the safe treatment of radioactive liquid waste, and can also contribute to the establishment of a spent fuel reprocessing system, which is an important issue in Japan.

1: Reaction tank 2: Waste liquid tank 3: Hydrogen peroxide supply tank 4: Catalyst supply tank 5: Acid supply tank 6: Alkali supply tank M: Stirrer T: Thermometer A: Gas analyzer

Claims (3)

A method for treating radioactive liquid waste containing phosphate ester,
To the radioactive liquid waste, a copper salt capable of producing copper ions or a solution containing copper ions produced from a copper salt and hydrogen peroxide are added, and in the presence of copper ions produced from the copper salt, 20 to 60 ° C. A treatment method for radioactive liquid waste, comprising an oxidative decomposition treatment step of oxidatively decomposing the phosphate ester in a temperature range of   The method for treating a radioactive liquid waste according to claim 1, wherein the phosphate ester includes at least one member selected from the group consisting of tributyl phosphate, dibutyl phosphate and monobutyl phosphate.   The method for treating a radioactive liquid waste according to claim 1 or 2, wherein the oxidative decomposition treatment step is performed in a temperature range of 40 to 60 ° C.

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