JP2007187464A - Method for treating uranium waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the generation of secondary waste and decrease the cost of its treatment, in the treatment of uranium waste. <P>SOLUTION: The treatment method for separating and recovering uranium from decontamination waste liquid, generated by decontaminating a waste to which uranium has adhered with acid and a solution obtained, by dissolving uranium waste containing fluoride with acid includes a masking agent addition process 1 for adding a masking agent to prevent impurities from mixing into the deposit to be purified; a main uranium removal process 2 for separating the uranium in the solution after the process 1 through precipitation and the like; a residual uranium removal process 3 for removing the uranium remaining in the solution, after the process 2 by ion exchange resin and an adsorbent; and a neutralization process 4 for giving a neutralization treatment to the solution, after the process 3 and a masking agent separation process 5 for separating the masking agent from the neutralized salt generated in the process 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for treating uranium waste contaminated with radioactive substances such as uranium.

  Conventionally, regarding decontamination methods of metal waste to which uranium or uranium compounds are attached, a method of decontamination with sulfuric acid (see Patent Document 1), a method of decontamination with an organic acid (see Patent Document 2), and decontamination with oxalic acid A method (see Patent Document 3) has been proposed.

  However, in the methods shown in Patent Documents 1 to 3, no useful treatment method has been proposed for secondary waste generated by decontamination of metal waste to which uranium adheres.

  For example, Patent Document 1 does not mention secondary waste, but since neutralization is usually required when treating sulfuric acid, a large amount of neutralized salt containing uranium is used as secondary waste. It is assumed that it will occur.

  Further, in Patent Document 2, an organic acid is used for decontamination of radioactive metal waste, and the metal component eluted in the decontamination waste liquid is recovered with an ion exchange resin. The recovered ion exchange resin is regenerated with sulfuric acid. Therefore, it is necessary to treat sulfuric acid, and it is assumed that neutralized salts are generated as secondary waste by the neutralization treatment.

  Furthermore, Patent Document 3 uses a decontamination liquid in which hydrogen peroxide and oxalic acid are mixed. Uranyl oxalate and oxalic acid, which are separated into water by distillation to recover secondary waste, are recovered. Secondary waste is expected.

  A technique for separating uranium from radioactive liquid waste has also been proposed, and Patent Document 4 describes a method of adding uranium to acidic liquid waste and separating uranium by a solvent extraction method using tributyl phosphoric acid (TBP).

  In the nitric acid-based solvent extraction method, the separation performance of uranium is excellent, but the waste liquid treatment is difficult. Nitrate-based nitrogen has strict effluent standard values by the water pollution method, and even if neutralization is performed, it is impossible to store a large amount of nitrate under the Fire Service Law. For this reason, in order to recover nitric acid from the waste liquid at a very high recovery rate, a large-scale nitric acid recovery device is required, which increases the cost of the processing apparatus.

  In addition, tributyl phosphate generated as a waste solvent has a boiling point as high as 289 ° C. and is difficult to recover by evaporation, and a decomposition treatment is required for disposal. Since decomposition products such as calcium phosphate are generated by the decomposition treatment, these become a large amount of secondary waste.

  As a method for removing uranium, a method using both uranium precipitation and removal with a chelate resin is used. When carrying out this uranium precipitation, a masking agent is added, but this masking agent eventually becomes a large amount of secondary waste.

Furthermore, the chelating resin is difficult to elute and regenerate, and if the resin is repeatedly reused to reduce the amount of waste resin, a large amount of reclaimed waste liquid containing uranium is generated, which in turn increases the amount of uranium waste. Accordingly, the resin cannot be repeatedly used, and a large amount of waste resin is generated. In addition, since treatment with a hydrochloric acid system is performed, the final wastewater needs to be neutralized and a large amount of neutralized salt is generated.
JP 2000-199800 A Japanese Patent Laid-Open No. 9-113690 JP-A-10-132999 Japanese Patent Laid-Open No. 5-80195

  In the uranium waste processing method by a known technique, there is a problem that a large amount of secondary waste such as neutralized salt, waste ion exchange resin, and waste solvent is generated, and the processing cost of these secondary wastes is increased. .

  This invention is made | formed in view of the said subject, and when processing uranium waste, it aims at reducing the processing cost of secondary waste while reducing generation | occurrence | production of secondary waste.

  In order to solve the above-mentioned problems, the uranium waste treatment method according to the present invention includes a decontamination waste liquid obtained by decontaminating waste with uranium attached thereto with an acid, as described in claim 1, and a fluoride. In a treatment method for separating and recovering uranium from a solution obtained by dissolving uranium waste with an acid, a mask agent addition step for adding a mask agent for preventing impurities from being mixed into the generated precipitate in the solution; and , A main uranium removal step for separating uranium in the solution after the mask agent addition step by precipitation, and a residual uranium removal step for removing uranium remaining in the solution after the main uranium removal step with an ion exchange resin or an adsorbent And a neutralization step for neutralizing the solution after the residual uranium removal step, and a mask agent separation step for separating the mask agent from the neutralized salt produced in the neutralization step. That.

  According to the method for processing uranium waste according to the present invention, when processing uranium waste, the generation of secondary waste is reduced and the processing cost of secondary waste can be reduced.

  An embodiment of a method for treating uranium waste according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a flowchart showing a procedure of a method for treating uranium waste according to the present invention.

  This procedure is a masking agent that adds a masking agent to a decontamination waste liquid when decontaminating waste contaminated with radioactive materials containing uranium with an acid or a solution of fluoride-containing uranium waste dissolved in an acid. An addition step 1, a main uranium removal step 2 for separating and removing the uranium precipitate from the solution obtained in the masking agent addition step 1, and a solution after removing the uranium precipitate in the main uranium removal step 2 In the residual uranium removal process 3 for removing uranium remaining in the substrate by an ion exchange resin or an adsorbent, the neutralization process 4 for neutralizing the solution after the residual uranium removal in the residual uranium removal process 3, and the neutralization process 4 A mask agent separation step 5 for separating and recovering the mask agent from the produced neutralized salt.

  Further, if necessary, uranium is eluted from the ion exchange resin or adsorbent after uranium adsorption used in the residual uranium removal step 3 to regenerate the resin or adsorbent, uranium elution / resin regeneration step 6, and uranium elution / Uranium immobilization step 7 for immobilizing uranium in a stable form from the uranium elution solution after elution of uranium in the resin regeneration step 6, and a final waste solution for enabling drainage of the solution such as removal of residual fluorine after the neutralization step 4 Processing step 8 is added.

  An organic acid such as formic acid or oxalic acid is used alone or in combination as a decontamination solution for waste contaminated with uranium or a solution for fluorinated uranium waste used in the masking agent addition step 1.

This decontamination waste liquid or fluoride solution contains uranium, metal components, fluorine, and the like. From this solution, uranium is precipitated and separated as uranium peroxide by adding H ₂ O ₂ while controlling the pH in the main uranium removal step 2.

  At this time, a masking agent that prevents co-precipitation of other impurities in the solution acts on the uranium precipitate, so that the recovered uranium precipitate has a high purity and an effect of reducing the amount of uranium waste.

  The uranium remaining in the solution after the uranium precipitation removal in the main uranium removal step 2 is adsorbed and removed by an ion exchange resin, an adsorbent or the like in the residual uranium removal step 3.

  FIG. 2 shows the uranium concentration in the solution due to uranium peroxide precipitation. According to FIG. 2, uranium precipitation is performed and the uranium concentration in the solution is reduced to about 1/20, thereby reducing the amount of ion exchange resin used in the residual uranium removal step 3 to about 1/20. Can do.

  That is, by using uranium adsorption (residual uranium removal step 3) with ion exchange resin after performing uranium precipitation (main uranium removal step 2), the amount of ion exchange resin used compared to when uranium precipitation is not performed. Can be greatly reduced.

  And the ion exchange resin which adsorb | sucked uranium can further reduce resin usage-amount by carrying out elution, reproduction | regeneration, and reuse.

  In the neutralization step 4, fluorine, metal components, and mask agent components in the solution are precipitated as hydroxides and separated and removed. At this time, by adding a calcium component to the solution, it is possible to produce calcium fluoride that is hardly soluble with calcium and fluorine, and to remove fluorine from the solution.

  In the mask agent separation step 5, the amount of the neutralized salt generated in the neutralization step 4 is greatly increased by separating, collecting and reusing the mask agent component from the neutralized salt generated in the neutralization step 4. Can be reduced.

  Here, if organic acid is used as waste decontamination solution or fluoride-containing uranium waste solution, residual organic acid can be decomposed by oxidizing agents such as hydrogen peroxide and ozone, so neutralization treatment is unnecessary It becomes. According to this method using an organic acid, the amount of neutralized salt generated by waste liquid treatment can be greatly reduced as compared with the case where an inorganic acid is used for decontamination or waste solution.

  Since the organic acid ions are coordinated to uranyl ions in the solution to form an anion complex, in the residual uranium removal step 3, it is possible to adsorb and remove uranium using an anion exchange resin.

  Therefore, it is possible to separate uranium from other metal cations. In addition, since uranium adsorbed on the anion exchange resin can be eluted with water, the elution waste liquid does not require neutralization if the organic acid component contained in a small amount is decomposed, and no neutralized salt is generated.

  FIG. 3 shows the relationship between the water flow rate and the concentration of uranium in the eluent and the relationship between the water charge and the elution rate when uranium adsorbed on the anion exchange resin in the formic acid system is passed through pure water. FIG. 3 shows that uranium is eluted from the anion exchange resin by passing pure water.

  Since uranium elutes by passing pure water, neutralization of the anion exchange resin elution regeneration solution is not necessary, and no neutralized salt containing uranium is generated. In addition, the anion exchange resin can be used repeatedly. is there.

  FIG. 4 shows the relationship between the number of repetitions and the amount of uranium adsorbed when the anion exchange resin is repeatedly used. According to FIG. 4, it is considered that the repeated use of about 20 times shows no effect on the uranium adsorption amount and can be repeated more times.

  Using an anion exchange resin in the residual uranium removal step 3 after roughing the uranium in the solution in the main uranium removal step 2 from the organic acid-based decontamination waste liquid or waste solution, and the anion exchange resin By repeatedly reusing the above, the amount of waste ion exchange resin required for removing residual uranium is greatly reduced.

  Since the organic acid can be decomposed and the elution regeneration of the anion exchange resin can be performed with pure water, the amount of neutralized salt generated in the final waste liquid and the elution waste liquid of the anion exchange resin is greatly reduced. In addition, the chemical cost of the masking agent can be reduced by separating and reusing the masking agent.

FIG. 5 shows the disposal costs of the waste ion exchange resin and the neutralized salt when the mask agent is used and when it is not used. In the calculation of the disposal cost, it is assumed that CaF ₂ is treated as fluoride-based uranium waste, and in the main uranium removal step 2, the uranium concentration in the solution is reduced to 1/20, and the ion exchange resin is 20 times. It was assumed that after repeated reuse, the volume was reduced to 1/20 by incineration. Also, it was assumed that 80% of the masking agent was reused. It was assumed that the disposal unit price of the ion exchange resin to be uranium waste is 100 times the disposal unit price of the neutralized salt that is non-uranium waste.

  In the case of (1) in FIG. 5, when uranium precipitation is not performed (and therefore no masking agent is added) and all uranium in the solution is removed with an anion exchange resin, the case of (2) adds a masking agent. This is a case where uranium remaining in the solution is removed with an anion exchange resin after the uranium precipitation treatment (in the case of the present invention).

  As shown in FIG. 5, according to the method for treating uranium waste according to the present invention (case (2)), the disposal cost of resin is about 1/20 compared to (1), and the disposal of neutralized salt. The cost was about ½, and the total disposal cost could be greatly reduced to 1/10.

  Next, a first embodiment of the method for treating uranium waste according to the present invention will be described with reference to FIGS.

  In Example 1, in the main uranium removal step 2, as a masking agent added to prevent the fluorine in the solution from being mixed into the uranium precipitate, Zr, Th, Ti, Sc, Al, B, Be, A single element or compound of any element of Fe (hereinafter referred to as a mask agent element) is used alone or in combination.

  Consider the case of generating uranium peroxide precipitate in the main uranium removal step 2. It is considered that uranium in the solution exists in a hexavalent state having a high oxidation number by the addition of hydrogen peroxide. The stability of the fluoride of the mask agent element is greater than that of hexavalent uranium fluoride. Therefore, when a mask agent element is present in the solution, fluorine generates a stable fluoride with these elements and remains in the solution, so that mixing of fluorine into the uranium precipitate is suppressed.

  FIG. 6 shows the precipitation rate of fluorine when the mask agent (aluminum) is added and when it is not added. When the masking agent is not added, 90% or more of the fluorine in the solution is precipitated simultaneously with the operation for generating the uranium peroxide precipitate, and a large amount of fluorine is mixed in the uranium precipitate. On the other hand, when aluminum is added as a masking agent, the fluorine precipitation rate is 0.1%, the fluorine precipitation rate is greatly reduced, and coprecipitation into uranium precipitation is suppressed.

FIG. 7 shows the weight ratio of uranium waste when the masking agent is added and when it is not added. When a waste containing calcium fluoride as the main component and containing 10% of uranium is treated, the concentration of uranium in the uranium precipitate is calculated from the molecular weight ratio of uranium / uranium peroxide (U / UO ₄ ) if a masking agent is added. About 80%.

  Thus, when almost all of the uranium in the waste has migrated to uranium precipitation, uranium is recovered in about 13% of the initial waste weight. When no masking agent is added, 90% or more of the fluorine in the waste is mixed in the uranium precipitate, so the uranium precipitate contains fluorine and weighs about 70% of the initial waste.

  That is, the weight of the radioactive waste is reduced to only 70% of the initial waste weight when the mask agent is not added, but is greatly reduced to about 10% when the mask agent is added. Therefore, the disposal cost of radioactive waste can be significantly reduced by adding a mask agent element to the solution.

  Next, a second embodiment of the uranium waste processing method of the present invention will be described with reference to FIG.

  In Example 2, as a masking agent, a solution obtained by dissolving the simple substance of the masking agent element shown in Example 1 in an acid is used.

  When a simple substance such as a metal as a mask agent element is immersed in an acid, those elements are dissolved in the acid solution. If the simple substance is dissolved using the same acid as that used for decontamination or waste dissolution, liquidity adjustment when added as a masking agent becomes easier.

  FIG. 8 shows the relationship between the dissolution concentration and the dissolution rate when aluminum metal, which is one of the mask agent elements, is dissolved in formic acid or oxalic acid. The effect of an element that becomes a mask agent does not appear unless it is dissolved in a solution. However, as shown in FIG. 8, aluminum is dissolved by formic acid or an organic acid of oxalic acid, and can be used as a mask agent. It becomes a form.

  When the organic acid solution is heated to about 50 ° C. or more, the dissolution reaction is promoted. For example, when foil-like metallic aluminum is immersed in 2N formic acid at 50 ° C., a high-concentration aluminum solution on the order of% is obtained in about 1 hour.

  According to Example 2, it was possible to prepare a solution that functions as a masking agent with a simple apparatus configuration and method in which a simple substance of the masking agent element was immersed in an acid solution.

  Moreover, when the mask agent element alone is dissolved in an acid, the amount of salt contained in the solution is reduced as compared with the case where inorganic salts such as chloride of the mask agent element are dissolved. Thereby, the amount of neutral salt to be finally discharged can be reduced, and the processing cost of the neutralized salt can be reduced.

  Moreover, when discharging wastewater to the environment, the load on the environment is also reduced.

  In addition, if organic acids are all used for the decontamination solution, waste solution, and mask agent element solution, the effect of reducing the amount of neutralized salt is further increased. In addition, when a high-concentration masking agent solution is used, the amount of the masking agent addition solution is small, so that the apparatus scale of the entire process can be reduced and the apparatus cost can be reduced.

  Next, a third embodiment of the method for treating uranium waste according to the present invention will be described.

  In Example 3, as a masking agent, a solution obtained by electrolytic dissolution of the masking agent element shown in Example 1 in an acid solution is used.

  The anode component is dissolved in the electrolytic solution by electrolyzing a simple substance such as a metal of the mask agent element as an anode and an acid solution as an electrolytic solution. If electrolysis is performed using the same acid as that used for decontamination and waste dissolution, liquidity adjustment when added as a masking agent becomes easier.

  An element used as a masking agent does not show its effect unless it is dissolved in a solution. In Example 3, it is possible to prepare a solution that functions as a mask agent by electrolytically dissolving a simple substance such as a metal of the mask agent element.

  When the mask agent element alone is used after being electrolytically dissolved, the amount of salt contained in the solution is reduced as compared with the case where inorganic salts such as chloride of the mask agent element are used. For this reason, it becomes possible to reduce the amount of neutralized salt to be finally discharged, and to reduce the processing cost of the neutralized salt.

  Moreover, when discharging wastewater to the environment, the load on the environment can be reduced. If organic acids are all used for the decontamination solution, the waste solution, and the masking element electrolysis solution, the effect of reducing the neutralized salt content is further improved. In addition, since the electrolytic method can increase the dissolution rate as compared with the case of simple immersion dissolution, it is possible to shorten the time for preparing the masking agent.

  Next, Embodiment 4 of the uranium waste processing method of the present invention will be described with reference to FIGS.

  In Example 4, a solution obtained by dissolving the hydroxide of the mask agent element shown in Example 1 in an acid is used as the mask agent.

  When the hydroxide of the masking agent element is immersed in an acid, the masking agent element dissolves in the acid solution, so that it functions as a masking agent in the solution. If the hydroxide is dissolved using the same acid as that used for decontamination or dissolution of waste, liquidity adjustment at the time of addition becomes easier.

  FIG. 9 shows the relationship between the formic acid concentration and the aluminum concentration in a solution obtained by immersing an aluminum hydroxide, which is one of the mask agent elements, in a formic acid solution at room temperature for 40 hours. According to FIG. 9, the aluminum concentration dissolved becomes higher as the formic acid concentration is higher up to the vicinity of 10M (molar concentration). However, when the formic acid concentration becomes 20M, the aluminum concentration tends to decrease. It was found that the solubility of aluminum is high at a formic acid concentration of 5 to 15M, and it is low at 5M or less and 15M or more.

  FIG. 10 shows the relationship between the temperature and the aluminum concentration in a solution obtained by immersing aluminum hydroxide in 10 M formic acid for 2 hours. According to FIG. 10, the dissolved aluminum concentration tended to increase rapidly at 50 ° C. or higher.

  Therefore, when aluminum hydroxide is dissolved in formic acid, it is possible to obtain a masking agent solution having a high aluminum concentration in a shorter time if dissolution is performed in a formic acid concentration range of 5 to 15 M and a temperature condition of 50 ° C. or higher. It is.

  An element used as a masking agent does not show its effect unless it is dissolved in a solution. In Example 4, it is possible to prepare a solution that functions as a masking agent by dissolving the hydroxide of this element.

  According to Example 4, the amount of salt contained in the solution is reduced as compared with the case where the mask agent element chloride and other salts are dissolved and used. Thereby, the amount of neutral salt discharged | emitted finally decreases, and the processing cost of neutral salt can be reduced.

  Moreover, when discharging wastewater to the environment, the burden on the environment is reduced.

  In addition, the neutralized salt content can be further reduced by using an organic acid for the decontamination solution, the waste solution, and the mask agent element hydroxide solution.

  In addition, by optimizing the acid concentration condition and the temperature condition, it is possible to obtain a high concentration mask solution in a short time. For example, when aluminum hydroxide is dissolved in formic acid, it is possible to obtain a masking agent solution having a high aluminum concentration by dissolving it in a formic acid concentration range of 5 to 15 M and a temperature condition of 50 ° C. or higher.

  When a high-concentration masking agent solution is used, the amount of the masking agent addition solution is small, so that the apparatus scale of the entire process can be reduced and the apparatus cost can be reduced.

  Next, a fifth embodiment of the method for treating uranium waste according to the present invention will be described.

  In Example 5, the organic acid salt of the mask agent element shown in Example 1 is used as the mask agent. This organic acid salt is produced by reacting a mask agent element sulfate with a barium organic acid salt.

  The organic acid salt of the mask agent element is added to the decontamination waste liquid or waste solution, and the dissolved element acts as a mask agent. The organic acid ion, which is a counter ion of the mask agent element, can be decomposed into carbon dioxide and water by an oxidizing agent such as hydrogen peroxide or ozone at a later stage, and therefore does not become a secondary waste source.

  In addition, some organic acid salts of this element are not commercially available, so they need to be produced. The organic acid salt of the masking agent is produced by reacting the organic acid salt of barium with the sulfate of the masking agent element. For example, when producing aluminum formate, aluminum sulfate and barium formate are reacted in water as in the following formula (1).

[Chemical 1]
Al ₂ (SO ₄ ) 3 + 3Ba (HCOO) ₂ → 2Al (HCOO) ₃ + 3BaSO ₄ ↓
...... (1)

  Since barium sulfate, which is a reaction product other than aluminum formate, has very low solubility, it precipitates as soon as it is formed and is removed from the solution. A saturated barium formate solution is added dropwise to the aluminum sulfate solution little by little, and the end point can be determined when the supernatant liquid no longer becomes cloudy. The filtrate obtained by filtering off barium sulfate can be used as it is as a mask agent.

  By using an organic acid salt as a masking agent, the organic acid ion, which is the counter ion of the masking agent element, is decomposed, so the amount of salt in the waste liquid is reduced compared to the case of using an inorganic acid salt, Processing costs can be reduced.

  Moreover, when discharging wastewater to the environment, the load on the environment is reduced. In addition, when organic acids are used for decontamination and waste solution, the effect of reducing the neutralized salt content is even greater.

  Next, a sixth embodiment of the method for treating uranium waste according to the present invention will be described with reference to FIGS.

  In Example 6, while using an aluminum compound as a masking agent, in the masking agent separation step 5, the neutralized salt produced in the neutralization step 4 is dissolved and separated with an acid solution or an alkaline solution and reused.

  When aluminum is used as the mask agent element, the mask agent element is precipitated together with calcium fluoride as aluminum hydroxide in the neutralization step 4. Here, FIG. 11 shows the dissolution concentration of aluminum at each pH. Aluminum is an amphoteric element and dissolves in both acid and alkali as shown in FIG.

  On the other hand, calcium fluoride is a salt that is less soluble than aluminum. Therefore, by dipping in a solution having a pH condition in which aluminum is dissolved but calcium fluoride is difficult to dissolve, only aluminum can be dissolved and only aluminum can be recovered.

  However, since calcium fluoride dissolves under strong acidic conditions, it is necessary to optimize pH conditions when dissolving under acidic conditions.

  FIG. 12 shows the calcium precipitation rate and aluminum dissolution rate for each pH when calcium fluoride and aluminum chloride are added to the acidic solution. The added concentration of calcium and aluminum is 0.5M.

  According to FIG. 12, calcium has a low precipitation rate in the region where the solution pH is 4 or less, and is easily dissolved. Aluminum has a very low dissolution rate and precipitates at pH 4 and above. The optimum pH point at which calcium fluoride is difficult to dissolve and aluminum is easily dissolved is around pH 3.5, which is the intersection of the curves in the figure.

  Since the pH of this intersection varies depending on the total concentration of aluminum, it is considered that pH around 3 to 4 is an appropriate pH range for separation of aluminum in consideration of the variation range. In the vicinity of the optimum pH of 3.5 in FIG. 12, 80% or more of aluminum is dissolved, and 80% or more can be recovered and reused using this aluminum as a mask agent.

  At this time, if the same acid solution as the decontamination solution or the waste solution is used as the acid solution for dissolving aluminum, the filtrate obtained by filtering off the remaining calcium fluoride may be added as it is as a mask agent. It is possible and work becomes easy.

  On the alkali side, the solubility of calcium fluoride is very low, so only the pH conditions under which aluminum dissolves need be considered. Since an aluminum concentration of 0.5 M or higher, which is considered appropriate for use as a masking agent, dissolves at pH 11 or higher, pH 11 to 14 is an appropriate condition on the alkali side.

  However, when aluminum is dissolved with an alkali, the filtrate obtained by filtering the remaining calcium fluoride cannot be used as it is as a mask agent. Therefore, when aluminum is dissolved with an alkali, the pH of the filtrate is readjusted to the acid side to obtain a mask agent solution, or the filtrate is neutralized and aluminum is precipitated again as a hydroxide and recovered. Need to be used as.

  According to Example 6, it becomes possible to dissolve and recover only the mask agent component from the neutralized salt generated in the neutralization step 4 and reuse it, and to reduce the amount of secondary waste originating from the mask agent. .

  In aluminum separation under acidic conditions, more than 80% of the masking agent can be reused, and the secondary waste originating from the masking agent can be reduced to 1/5 or less of the case without reuse. .

  Next, a seventh embodiment of the uranium waste processing method of the present invention will be described with reference to FIG.

  In Example 7, in the neutralization step 4, fluorine contained in the solution is precipitated as calcium fluoride by adding an organic acid salt of calcium.

  In the neutralization step 4, the fluorine contained in the process solution is precipitated and removed as hardly soluble calcium fluoride by addition and neutralization of calcium. When organic acid calcium is used as a calcium additive, the organic acid ion, which is a counter ion of calcium, can be subsequently decomposed into carbon dioxide and water by an oxidizing agent such as hydrogen peroxide. Must not.

  FIG. 13 shows the fluorine concentration in the solution when calcium formate, which is an organic acid salt of calcium, is added to the fluorine-containing solution for neutralization. 99% or more of the fluorine was precipitated by the addition and neutralization of calcium formate, and it was confirmed that the fluorine removal method of Example 7 was effective.

  According to Example 7, since the organic acid ion which is a counter ion of calcium can be decomposed, the amount of salt in the waste liquid can be reduced compared to the case of using an inorganic acid salt, and the salt processing cost can be reduced. It becomes.

  Moreover, when discharging wastewater to the environment, it is possible to reduce the load on the environment.

  In addition, when an organic acid is used in the decontamination solution or waste solution together with the neutralizing agent, the effect of reducing the salt content is even greater.

The flowchart which shows the procedure of the processing method of the uranium waste which concerns on this invention. The figure which shows the uranium density | concentration in the solution by uranium peroxide precipitation production | generation. The figure which shows the relationship between the amount of water flow and the concentration of uranium in the eluent, and the relationship between the water flow rate and the elution rate when pure water is passed through uranium adsorbed on an anion exchange resin in a formic acid system. The figure which shows the relationship between the number of repetitions and the amount of uranium adsorption | suction at the time of the repeated utilization of an anion exchange resin. The figure which shows the disposal expense of the waste ion exchange resin and the neutralization salt in the case where the mask agent is used and the case where it is not used. The figure which shows the fluorine precipitation rate in the case where a mask agent (aluminum) is added, and the case where it does not add. The figure which shows the uranium waste weight ratio with the case where a mask agent is added and the case where it does not add. The figure which shows the relationship between the melt | dissolution density | concentration at the time of melt | dissolving the metal of the aluminum which is one of the mask agent elements in formic acid or oxalic acid. The figure which shows the relationship between the formic acid density | concentration and the aluminum density | concentration in the solution which immersed the hydroxide of aluminum which is one of the mask agent elements in the formic acid solution at room temperature for 40 hours. The figure which shows the relationship between the temperature in the solution which immersed aluminum hydroxide in 10M formic acid for 2 hours, and aluminum concentration. The figure which shows the melt | dissolution density | concentration in each pH of aluminum. The figure which shows the calcium precipitation rate and aluminum dissolution rate with respect to each pH at the time of adding calcium fluoride and aluminum chloride to an acidic solution. The figure which shows the fluorine density | concentration in a solution at the time of adding and neutralizing calcium formate which is an organic acid salt of calcium to the solution containing fluorine.

Explanation of symbols

1 Mask agent addition process 2 Main uranium removal process 3 Residual uranium removal process 4 Neutralization process 5 Mask agent separation process 6 Uranium elution / resin regeneration process 7 Uranium immobilization process 8 Final waste liquid treatment process

Claims (15)

In a treatment method for separating and recovering uranium from a decontamination waste liquid obtained by decontaminating waste containing uranium with an acid or a solution obtained by dissolving a uranium waste containing fluoride with an acid,
A mask agent addition step of adding a mask agent for preventing impurities from being mixed into the generated precipitate in the solution;
A main uranium removal step of separating uranium in the solution after the mask agent addition step by precipitation;
A residual uranium removal step of removing uranium remaining in the solution after the main uranium removal step by an ion exchange resin or an adsorbent;
A neutralization step of neutralizing the solution after the residual uranium removal step,
A uranium waste treatment method comprising: a mask agent separation step of separating the mask agent from a neutralized salt produced in the neutralization step. 2. The method for treating uranium waste according to claim 1, wherein an organic acid is used alone or in combination as an acid for decontaminating the waste to which the uranium adheres or an acid for dissolving the uranium waste. 2. The mask agent according to claim 1, wherein a single element or a compound of any one of Zr, Th, Ti, Sc, Al, B, Be, and Fe serving as a mask agent element is used alone or in combination. The processing method of uranium waste as described. 4. The method for treating uranium waste according to claim 3, wherein a solution obtained by dissolving a simple substance of the mask agent element in an acid is used alone or in combination as the mask agent. 4. The method for treating uranium waste according to claim 3, wherein a solution obtained by electrolytic dissolution of a simple substance of the mask agent element in an acid solution is used alone or as a mixture. 4. The method for treating uranium waste according to claim 3, wherein a solution obtained by dissolving the hydroxide of the mask agent element with an acid is used alone or in combination as the mask agent. The method for treating uranium waste according to any one of claims 4 to 6, wherein the same acid as that used for decontamination and dissolution of uranium waste is used for dissolving the mask agent element. The hydroxide of the mask agent element is aluminum hydroxide, and a solution obtained by dissolving the aluminum hydroxide with 5 to 15 molar formic acid heated to 50 ° C or higher is used. The processing method of the uranium waste described. 4. The method for treating uranium waste according to claim 3, wherein an organic acid salt of the mask agent element is used as the mask agent. 10. The method for treating uranium waste according to claim 9, wherein the organic acid salt of the mask agent element is generated by reacting a sulfate of the mask agent element and an organic acid salt of barium. The masking agent is an aluminum compound, and in the masking agent separation step, the neutralized salt produced in the neutralization step is separated by dissolving the aluminum component with an acid solution or an alkali solution and reused. Item 3. A method for treating uranium waste according to item 1. 12. The method for treating uranium waste according to claim 11, wherein the acid solution for dissolving the aluminum component of the aluminum compound is a pH 3-4 acid solution. 12. The method for treating uranium waste according to claim 11, wherein the alkaline solution for dissolving the aluminum component of the aluminum compound is an alkaline solution having a pH of 11 to 14. 12. The method for treating uranium waste according to claim 11, wherein the acid solution for dissolving the aluminum component of the aluminum compound is the same acid as that used for decontamination and dissolution of uranium waste. 2. The uranium according to claim 1, wherein in the neutralization step, fluorine contained in the solution is precipitated as calcium fluoride by adding an organic acid salt of calcium to the solution after the residual uranium removal step. Waste disposal method.

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