JP2016191691A - Method for processing metal ion-containing acid liquid, and processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress unavailability of electrodeposition and deterioration in the electrodeposition rate that are caused by decrease in the pH of a catholyte attributed to concentration diffusion of an acid in the catholyte, which has entered from an acid liquid of an anode chamber through a cation exchange membrane to the catholyte, in a method in which an anode chamber including an anode and a cathode chamber including a cathode are separated from each other by a cation exchange membrane, an acid liquid containing a metal ion is introduced into the anode chamber, a catholyte is introduced into the cathode chamber, the metal ion in the liquid in the anode chamber is, by electrification between the anode and the cathode, made to permeate the cation exchange membrane to move into the catholyte, thereby depositing a metal onto the cathode.SOLUTION: A salt of an acid contained in an acid liquid introduced into an anode chamber is added to a catholyte introduced into a cathode chamber in advance to suppress concentration diffusion of the acid in the catholyte, which has entered from the acid liquid of the anode chamber through a cation exchange membrane to the catholyte. The addition of the salt to the cathode chamber enables reduction of an applied voltage, reduction in the amount of hydrogen generated at the cathode, and reduction of power consumption.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a processing method and a processing apparatus for a metal ion-containing acid solution, and more specifically, the ions are removed from an acid solution containing metal ions such as iron (Fe), cobalt (Co), and nickel (Ni). It relates to a method and a device. The present invention particularly relates to an acid containing metal ions generated from nuclear power plants such as decontamination waste liquid generated in nuclear power plants and eluents obtained by eluting metal ions from ion exchange resins used in nuclear power plants. It is suitably used for the treatment of waste liquid.

  In a nuclear power plant, a large amount of decontamination waste liquid is generated when the radioactive material is chemically removed from the primary cooling system equipment and piping contaminated with the radioactive material and the metal member surface of the system including these. These decontamination waste liquids contain metal ions such as Fe, Co or Ni, and also contain a lot of radioactive substances such as Co-60 (cobalt 60) and Ni-63 (nickel 63). Usually, the decontamination waste liquid is reused as a decontamination liquid after the ionic components dissolved by the ion exchange resin are removed. For this reason, there exists a problem that the waste of the ion exchange resin containing many radioactive substances generate | occur | produces.

  In nuclear power plants, etc., ion exchange resins used to purify cooling water systems containing radioactive materials by directly touching fuel rods such as the reactor water purification system (CUW) and the fuel storage pool water purification system (FPC) Because it absorbs a lot of radioactive material, it is stored as a high dose rate waste in a resin tank installed at the power plant.

  Waste containing these radioactive substances is finally kneaded with a solidification aid such as cement and stabilized, and then buried. The cost for disposal is different depending on the amount of radioactive material contained, and the higher the concentration of radioactive material, the higher the cost. For this reason, it is economical to reduce the volume of waste with a high dose rate as much as possible and then use it as a solid waste. Specifically, it is desirable in terms of volume reduction if the radioactive substance can be separated from the ion exchange resin as a solid and can be contained in a shielding container. Waste ion exchange resin from which radioactive materials have been removed is a low-dose rate waste with low disposal costs, and if the radioactive materials can be removed to a level where incineration of the waste ion exchange resin can be achieved, incineration will significantly Volume reduction can be achieved.

  As a method for treating such high-dose waste resin, there are methods of decomposing waste resin by wet oxidation such as Fenton method and supercritical water oxidation as proposed in Patent Document 1 and Patent Document 2. In this case, a large amount of waste liquid with a high dose rate is generated. When the waste liquid with a high dose rate is finally disposed of, it is necessary to stabilize it as a solidified body by a method such as evaporating and concentrating and kneading the concentrated liquid with cement. In this case, since a solidification aid such as cement is newly added, there is a problem that the amount of waste at a high dose rate to be finally disposed increases and the amount of waste cannot be reduced.

  Patent Document 3 discloses a technique in which sulfuric acid is passed through waste resin, ionic radioactive substances are eluted, radioactive substances are separated from the eluent by diffusion dialysis, and sulfuric acid is circulated and reused. Patent Document 4 discloses a waste resin treatment method in which waste resin is immersed in an oxalic acid aqueous solution to dissolve the metal clad on the surface, and metal ions adsorbed on the resin are eluted into the oxalic acid aqueous solution. Yes. In these cases as well, waste liquid containing radioactive substances is generated, but the solidification process is not covered.

  On the other hand, as a method for removing radioactive substances from waste liquid containing ionic radioactive substances, Patent Document 5 discloses that a decontamination solution in which radioactive cations are dissolved is energized while passing through an electrodeposition cell, and the radioactive cations are used. Has been disclosed in which a decontamination solution is regenerated and reused by depositing as a radioactive metal particle on a cathode. At that time, the cathode on which radioactive metal particles are deposited is described as pouring catholyte over the entire cathode to desorb the radioactive metal particles.

Japanese Patent Publication No. 61-9599 Japanese Patent No. 3657747 JP 2004-28697 A JP 2013-44588 A Japanese Patent No. 4438898

  In Patent Document 5, the decontamination solution in which the radioactive cation is dissolved is energized while being directly introduced into the cathode side of the electrodeposition cell, and the radioactive cation is deposited on the cathode as radioactive metal particles. Since the catholyte properties change depending on the decontamination solution, the catholyte cannot be adjusted to a liquid property suitable for electrodeposition. When the decontamination solution is an acidic waste solution, the radioactive metal component deposited on the cathode surface is dissolved again in the acidic waste solution, so that no precipitation occurs or the deposition rate is significantly reduced. In addition, when the waste liquid is neutral or alkaline, a hydroxide precipitate is formed in the vicinity of the cathode surface, and it becomes difficult to recover by depositing radioactive metal on the cathode surface. For this reason, in order to efficiently recover radioactive substances from the waste liquid by the electrodeposition method, it is not preferable to introduce the waste liquid directly into the cathode chamber, and it is important to make the catholyte liquid suitable for electrodeposition. Become.

  In view of this, the inventors of the prior application (Japanese Patent Application No. 2013-221322) separated the anode chamber provided with the anode and the cathode chamber provided with the cathode with a cation exchange membrane, and the metal ion-containing acid in the anode chamber. The liquid is introduced, the catholyte is introduced into the cathode chamber, and energization is performed between the anode and the cathode, so that the metal ions in the liquid in the anode chamber pass through the cation exchange membrane and move into the liquid in the cathode chamber. A method of depositing metal on top was proposed. In the present invention, since the anode chamber for introducing the metal ion-containing acid solution and the cathode chamber for depositing the metal are separated by a cation exchange membrane, it depends on the liquid properties of the metal ion-containing acid solution. Therefore, it is possible to efficiently deposit metal. In particular, when the metal ion-containing acid solution is an acid waste solution, the metal electrodeposited on the cathode is dissolved in the conventional method such as Patent Document 5, or the electrodeposition rate of the metal is significantly reduced. Even if the acid waste liquid is introduced into the anode chamber, the cathode chamber can be in a condition suitable for electrodeposition.

However, according to the study of the present inventors, in the method of the prior invention, although the degree varies depending on the type and current density of the cation exchange membrane, the acid in the acid waste liquid in the anode chamber permeates the cation exchange membrane by concentration diffusion. Thus, there has been found a problem that a phenomenon occurs in which the metal electrode is not electrodeposited on the cathode or the electrodeposition speed is lowered by moving to the cathode chamber side and lowering the pH of the catholyte.
This is considered to be because the rate at which the metal electrodeposited on the cathode is redissolved increases as the pH of the catholyte decreases.

  In the electrodeposition bath in which the anode chamber and the cathode chamber are separated from each other by a cation exchange membrane, the present invention allows the acid in the anode chamber to permeate through the cation exchange membrane by concentration diffusion, It aims at providing the processing method and processing apparatus of a metal ion containing acid solution which can suppress moving to a cathode chamber.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention applied an acid salt contained in an acid solution containing metal ions introduced into the anode chamber in the cathode chamber. It was found that the inclusion in the catholyte introduced in advance can suppress the acid in the anode chamber from passing through the cation exchange membrane due to concentration diffusion and shifting to the cathode chamber, thereby completing the present invention. .

  That is, the gist of the present invention is as follows.

[1] An anode chamber having an anode and a cathode chamber having a cathode are separated by a cation exchange membrane, an acid solution containing metal ions is introduced into the anode chamber, and a cathode containing the acid salt in the cathode chamber By introducing a liquid and energizing between the anode and the cathode, metal ions in the liquid in the anode chamber are allowed to pass through the cation exchange membrane and move into the catholyte, and the metal is placed on the cathode. A method for treating a metal ion-containing acid solution, characterized by causing precipitation.

[2] Between the anode chamber provided with the anode and the cathode chamber provided with the cathode, the anode chamber side and one or more intermediate chambers separated from the cathode chamber side through an ion exchange membrane are provided, and the cathode chamber And an intermediate chamber adjacent to the cathode chamber are separated by a cation exchange membrane, an acid solution containing metal ions is introduced into the intermediate chamber adjacent to the cathode chamber, and a cathode including the acid salt in the cathode chamber Introducing a liquid and passing a current between the anode and the cathode to cause metal ions in the liquid in the intermediate chamber adjacent to the cathode chamber to pass through the cation exchange membrane and move into the catholyte, A method for treating a metal ion-containing acid solution, comprising depositing the metal on a cathode.

[3] The method for treating a metal ion-containing acid solution according to [1] or [2], wherein the acid solution contains sulfuric acid, and the catholyte contains a sulfate.

[4] The concentration of the salt in the cathode chamber is 0.5 to 2 times the acid in the acid solution as a molar concentration, according to any one of [1] to [3] A method for treating a metal ion-containing acid solution.

[5] The metal ion according to any one of [1] to [4], wherein the catholyte contains one or more additives selected from dicarboxylic acids and salts thereof and tricarboxylic acids and salts thereof. A method for treating the acid solution.

[6] An electrodeposition chamber having an anode chamber having an anode, a cathode chamber having a cathode, a cation exchange membrane separating the anode chamber and the cathode chamber, and energization means for energizing between the anode and the cathode And a liquid passing means for passing an acid solution containing metal ions into the anode chamber, and a liquid passing means for passing a catholyte containing the acid salt into the cathode chamber, the anode and the cathode A metal ion containing the metal ion, wherein the metal ions in the liquid in the anode chamber are moved through the cation exchange membrane and moved into the catholyte by being energized between them, and the metal is deposited on the cathode Acid solution processing equipment.

[7] An anode chamber having an anode, a cathode chamber having a cathode, and at least one intermediate provided between the anode chamber and the cathode chamber and separated by the ion chamber and the anode chamber. An electrodeposition tank having a chamber; an energizing means for energizing between the anode and the cathode; a liquid passing means for passing an acid solution containing metal ions into the intermediate chamber adjacent to the cathode chamber; and An ion exchange membrane that separates the cathode chamber and the intermediate chamber adjacent to the cathode chamber is a cation exchange membrane. By energizing between the cathodes, the metal ions in the liquid in the intermediate chamber adjacent to the cathode chamber are moved through the cation exchange membrane and moved into the catholyte to deposit the metal on the cathode. An apparatus for treating a metal ion-containing acid solution.

[8] The processing apparatus for a metal ion-containing acid solution according to [6] or [7], wherein the acid solution contains sulfuric acid, and the catholyte contains a sulfate.

[9] The concentration of the salt in the cathode chamber is 0.5 to 2 times the acid in the acid solution as a molar concentration, according to any one of [6] to [8] Metal ion containing acid solution processing equipment.

[10] The metal ion according to any one of [6] to [9], wherein the catholyte contains one or more additives selected from dicarboxylic acids and salts thereof and tricarboxylic acids and salts thereof. Processing equipment for acid solution.

  According to the present invention, the anode chamber provided with the anode and the cathode chamber provided with the cathode are separated by the cation exchange membrane, the acid solution containing metal ions is introduced into the anode chamber, the catholyte is introduced into the cathode chamber, When the metal ions in the liquid in the anode chamber are moved through the cation exchange membrane and moved into the catholyte by depositing a metal between the anode and the cathode, the acid is previously added to the catholyte. By adding a salt, it is possible to suppress acid concentration diffusion from the acid solution in the anode chamber to the catholyte through the cation exchange membrane, and the pH of the catholyte decreases due to acid diffusion from the anode chamber. By doing so, it is possible to suppress the phenomenon that the electrodeposition of the metal does not occur on the cathode or the electrodeposition rate of the metal decreases, and a stable treatment can be performed. In addition, the presence of an acid salt in the cathode chamber makes it possible to reduce the applied voltage, reduce the amount of hydrogen generated at the cathode, and reduce the amount of electric power.

It is a systematic diagram of the processing apparatus which shows an example of embodiment of this invention. It is a systematic diagram of the processing apparatus which shows the other example of embodiment of this invention. It is a systematic diagram of the processing apparatus which shows the other example of embodiment of this invention. It is a graph which shows the time-dependent change of pH of the catholyte of Examples 1-3. It is a graph which shows a time-dependent change of Co density | concentration of the simulated acid waste liquid of Examples 1-3. It is a graph which shows the time-dependent change of Fe density | concentration of the simulated acid waste liquid of Examples 1-3. 6 is a graph showing the change over time in the pH of the catholyte of Comparative Example 1.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a system diagram showing an example of an embodiment of a processing apparatus for a metal ion-containing acid solution of the present invention.
In the electrodeposition apparatus of FIG. 1, an anode chamber 2A provided with an anode 2 in an electrodeposition tank 1 and a cathode chamber 3A provided with a cathode 3 are separated by a cation exchange membrane 5, and an acid containing metal ions is contained in the anode chamber 2A. The liquid is passed through, the catholyte is passed through the cathode chamber 3A, and the anode 2 and the cathode 3 are energized by a power source (not shown), so that the metal ions in the liquid in the anode chamber 2A pass through the cation exchange membrane 5. The metal is deposited on the cathode 3 by being moved into the liquid in the cathode chamber 3A.

In FIG. 1, reference numeral 10 denotes a metal ion-containing acid solution storage tank. The metal ion-containing acid solution is introduced into the anode chamber 2 </ b> A through the pipe 11 by the pump P ₁ , and the discharged liquid is fed through the pipe 12 to the metal ion-containing acid solution. A circulation system for returning to the storage tank 10 is formed. Further, 20 is a catholyte tank, a pump P ₂ via the pipe 21 by introducing a catholyte to the cathode compartment 3A, the circulatory system back to the catholyte reservoir 20 to discharge fluid through the pipe 22 is formed.

  If an acidic metal ion-containing acid solution (acid waste solution) is directly introduced into a bath in which the cathode is immersed without providing a cation exchange membrane, the metal electrodeposited on the cathode unless the pH is appropriately adjusted with alkali. This causes problems such as redissolving or electrodeposition itself. On the other hand, in the apparatus provided with a cation exchange membrane as shown in FIG. 1, if the catholyte on the cathode side is in a condition suitable for electrodeposition, the waste liquid is strongly acidic with a pH of less than 2, particularly less than pH 1. Even in this case, the metal can be electrodeposited and removed satisfactorily.

  In addition, when removing the metal ions from the strongly acidic waste liquid and reusing the liquid, if the pH of the waste liquid is adjusted with an alkali, it becomes difficult to reuse it as a strongly acidic liquid. Without reducing the acidity of the waste liquid, it is possible to remove the metal ions from the waste liquid through the cation exchange membrane and reuse the treatment liquid.

  The liquid to be treated in the present invention, that is, the liquid introduced into the anode chamber 2A is an acidic metal ion-containing liquid, and together with metal ions, inorganic acids such as sulfuric acid, hydrochloric acid and nitric acid, formic acid, acetic acid and oxalic acid In the present invention, as shown in FIG. 1, the metal ions are transferred to the catholyte through the cation exchange membrane, so that the metal ion concentration is 0.1 to 10,000 mg. / L, particularly even a low concentration waste liquid of about 1 to 1000 mg / L can be treated efficiently.

  In the treatment of such a metal ion-containing acid solution, in the present invention, the same acid salt as the acid in the metal ion-containing acid solution introduced into the anode chamber 2A is added to the catholyte. For example, when the metal ion-containing acid solution contains sulfuric acid, sulfate is added to the catholyte, and when the metal ion-containing acid solution contains oxalic acid, oxalate is added to the catholyte.

  The acid salt added to the catholyte is the same acid salt as the acid in the metal ion-containing acid solution, and any salt can be used as long as it is water-soluble. Sodium salt, potassium salt, magnesium salt, calcium salt, iron Examples thereof include salts, cobalt salts, nickel salts and the like. Only 1 type may be used for the salt of an acid, and 2 or more types may be mixed and used for it.

  The acid salt added to the catholyte is preferably 0.5 to 2 times, more preferably 0.8 to 1.5 times the acid in the metal ion-containing acid solution, as a molar concentration. More preferably, it is 1.0 to 1.2 times. If the amount of acid salt added to the catholyte is too small, the acid in the metal ion-containing acid solution cannot be sufficiently prevented from passing through the cation exchange membrane and transferred to the catholyte. There is a possibility that the salt of the acid in the catholyte permeates the cation exchange membrane and moves to the metal ion-containing acid solution.

  The pH of the catholyte containing the same acid salt as the acid in the metal ion-containing acid solution used in the present invention is preferably 1.5 to 10, more preferably 2 to 9, and 3 to 8 More preferably. When the pH of the catholyte is too low, re-dissolution of the electrodeposited metal occurs on the cathode, which may reduce the electrodeposition rate. On the other hand, when the pH of the catholyte is too high, metal hydroxide is likely to be generated as a suspended substance in the liquid. For this reason, when the pH of the catholyte is outside the above range, it is preferable to adjust the pH appropriately with an alkali or an acid. However, in the present invention, the acid in the metal ion-containing acid solution permeates the cation exchange membrane. Therefore, it is possible to prevent the pH of the catholyte from being lowered and the pH of the catholyte to be lowered, so that an alkali as a pH adjusting agent is not necessary or the amount thereof can be reduced.

  In the present invention, a complexing agent suitable for electrodeposition of metal ions (hereinafter sometimes referred to as “additive of the present invention”) is preferably added to the catholyte.

The additive of the present invention includes a dicarboxylic acid having two carboxyl groups in the molecule and a salt thereof (hereinafter sometimes referred to as “dicarboxylic acid (salt)”), and having three carboxyl groups in the molecule. Those selected from tricarboxylic acids and salts thereof (hereinafter sometimes referred to as “tricarboxylic acids (salts)”) are preferred. These may use only 1 type and may mix and use 2 or more types. Dicarboxylic acids (salts) and tricarboxylic acids (salts) suppress the generation of suspended substances during electrodeposition due to their chelating effects, and have an excellent effect in improving the electrodeposition effect.
In contrast, a monocarboxylic acid having one carboxyl group in the molecule has a weak binding force with metal ions, and a suspended substance composed of a metal hydroxide is generated in the liquid. Problems such as not wearing. Further, when a carboxylic acid having four or more carboxyl groups in the molecule is used, there is a problem that the binding force with metal ions is too strong, the metal is retained in the liquid, and the electrodeposition rate is significantly reduced. .

  As the dicarboxylic acid (salt) and tricarboxylic acid (salt), those represented by the following formula (1) are particularly preferable in that suspended substances are hardly generated and electrodeposition proceeds rapidly. The dicarboxylic acid (salt) or tricarboxylic acid (salt) represented by the following formula (1) has 1 to 3 carbon atoms between the carboxyl groups in the molecule, and is derived from its shape. Thus, it is estimated that an appropriate binding force can be obtained with the metal ion.

^{_{M 1 OOC- (CHX 1) a}} - (NH) b - (CX 2 X 4) c -CX 3 X 5 -COOM 2
... (1)
(In the formula (1), X ¹ , X ² and X ³ each independently represent H or OH, X ⁴ and X ⁵ each independently represent H, OH or COOM ³ , M ¹ , M ² , M ³ each independently represent H, monovalent alkali metal or ammonium ion, and a, b, and c each independently represent an integer of 0 or 1. However, in Formula (1), X ⁴ and X ⁵ are simultaneously COOM ³ will never be reached.)

Suitable dicarboxylic acids in the present invention, for example, oxalic acid (ethanedioic acid, HOOC-COOH), malonic acid (propanedioic acid, _HOOC-CH 2 -COOH), succinic acid (butanedioic acid, HOOC-CH ₂ -CH ₂ -COOH), glutaric acid (pentanedioic _{acid, HOOC-CH 2 -CH 2 -CH} 2 -COOH), malic acid (2-hydroxybutanedioic _{acid, HOOC-CH 2 -CH (OH} ) -COOH) , Tartaric acid (2,3-dihydroxybutanedioic acid, HOOC—CH (OH) —CH (OH) —COOH), iminodiacetic acid (HOOC—CH ₂ —NH—CH ₂ —COOH), etc. Acid, succinic acid, malic acid, tartaric acid and iminodiacetic acid are particularly preferred. Examples of the tricarboxylic acid include citric acid (HOOC—CH ₂ —COH (COOH) —CH ₂ —COOH), 1,2,3-propanetricarboxylic acid, and citric acid is particularly preferable. In addition, examples of salts of these dicarboxylic acids and tricarboxylic acids include alkali metal salts such as sodium salts and potassium salts, and ammonium salts.

  In the present invention, when the metal ion-containing acid solution contains a plurality of types of metal ions, it is preferable that an ammonium salt coexists with a dicarboxylic acid (salt) and / or a tricarboxylic acid (salt). For example, when a metal ion-containing acid solution containing Co and Fe is treated according to the present invention, when no ammonium salt is added, Co is usually faster in electrodeposition than Fe, and the top of the Co electrodeposition layer In this case, an electrodeposited layer of Fe is formed, but by adding an ammonium salt, the electrodeposition rates of Co and Fe become substantially equal, and Co and Fe are electrodeposited in an alloy form. When the electrodeposition rates of Co and Fe are different and electrodeposition is performed by separating the Co layer and the Fe layer, the electrodeposition tends to float or peel off due to the difference in the physical properties of Co and Fe, and continuous electrodeposition processing is performed. There is a risk that it will not be possible.

  Any ammonium salt may be used as long as it produces ammonium ions in the liquid. For example, ammonium chloride, ammonium sulfate, ammonium oxalate, and ammonium citrate are preferable. These ammonium salts may be used alone or in combination of two or more. In particular, if ammonium dicarboxylate such as ammonium oxalate or ammonium tricarboxylate such as ammonium citrate is used, the ammonium salt and the additive of the present invention can be used, and the suspended substance due to the chelating effect of dicarboxylic acid or tricarboxylic acid It is possible to obtain the effect of suppressing the generation of carbon and the effect of adjusting the electrodeposition rate of Co and Fe with one agent.

  The concentration of the above-mentioned additive of the present invention in the catholyte used in the present invention is not particularly limited, but the cathode chamber is based on the total molar concentration of metal ions in the metal ion-containing acid solution introduced into the anode chamber. The molar concentration of the additive of the present invention in the catholyte introduced into the catalyst is preferably 0.1 to 50 times, particularly preferably 0.5 to 10 times. As the catholyte, for example, the additive of the present invention is used. An aqueous solution having a pH of 1.5 to 10, preferably pH 2 to 9, containing 0.01 to 20% by weight, preferably 0.1 to 5% by weight and containing the aforementioned acid salt in the aforementioned preferred content is used. . If the amount of the additive of the present invention in the catholyte is too small, the effect of inhibiting suspended solids by using the additive of the present invention cannot be sufficiently obtained, and if too large, the chelate effect becomes too large. As a result, the electrodeposition rate decreases.

  The additive of the present invention is oxidatively decomposed when it comes into contact with the anode of the electrodeposition tank, but the electrodeposition tank of the present invention is added because the anode chamber and the cathode chamber are separated by a cation exchange membrane. Since the electrodeposition liquid containing the agent does not come into direct contact with the anode, the additive is not oxidized and consumed wastefully. Therefore, in the present invention, the amount of additive to be replenished to the catholyte may be very small, and the amount of chemicals used can be reduced.

  When an ammonium salt is used, the ammonium salt is preferably used in an amount such that the concentration in the catholyte is 0.01 to 20% by weight, preferably 0.1 to 5% by weight. If the concentration of the ammonium salt is too low, the above effect due to the use of the ammonium salt cannot be sufficiently obtained, and if it is too high, the effect is not improved and the amount of chemicals used increases.

The electrodeposition conditions (current value, current density, temperature, etc.) are not particularly limited, but the current density is preferably 5 to 600 mA / cm ² with respect to the cathode area in terms of electrodeposition efficiency.

  The metal ion-containing acid solution in the present invention is usually an acid solution containing one or more of iron, manganese, cobalt, and nickel, particularly one or more of iron group metal ions of iron, cobalt, and nickel. Although it is preferable, there is no problem even if a metal other than the iron group metal is contained. In particular, the present invention is a waste liquid containing radioactive metal ions generated from a nuclear power plant, such as a decontamination waste liquid generated in a nuclear power plant, or an eluent obtained by eluting metal ions from an ion exchange resin used in a nuclear power plant, In particular, it is suitable for the treatment of acid waste liquids having a pH of less than 2. From these waste liquids, metal ions can be efficiently removed and the treatment liquid can be reused.

  Below, the example which applied this invention to the decontamination process of the waste ion exchange resin used in the nuclear power plant is demonstrated with reference to FIG. In FIG. 2, members having the same functions as those shown in FIG.

  The apparatus shown in FIG. 2 includes an eluent storage tank 30 that stores an eluent obtained by eluting metal ions from a waste ion exchange resin, an elution tank 8 that is a packed tower filled with a waste ion exchange resin 40, and an elution tank 8. A metal ion-containing acid solution storage tank 10 which is an acid waste solution storage tank for storing the discharged acid waste solution, an electrodeposition tank 1 into which the acid waste solution from the metal ion-containing acid solution storage tank (acid waste solution storage tank) 10 is introduced, and electrodeposition A catholyte storage tank 20 for storing the catholyte supplied to the tank 1. The electrodeposition tank 1 has a structure in which an anode chamber 2A having an anode 2 and a cathode chamber 3A having a cathode 3 are separated by a cation exchange membrane 5, and from a metal ion-containing acid solution storage tank (acid waste liquid storage tank) 10. The acid waste liquid is passed through the anode chamber 2A, and the catholyte is passed through the cathode chamber 3A. 9A and 9B are heat exchangers.

Eluent of the eluent storage tank 30 is a heat exchanger 9A 60 ° C. or higher in the process of being delivered to the elution tank 8 through the pipe 31 by the pump _{P 3,} preferably 70 to 120 ° C., more preferably 80 to 100 After being heated to ° C., the elution tank 8 is passed upwardly, and the effluent (acid waste liquid) passes through the pipe 32, and the cation exchange membrane 8 in the electrodeposition tank 4 is deteriorated by the heat exchanger 9B. After cooling to a small temperature of less than 60 ° C., for example, 10 ° C. or more and less than 60 ° C., the metal ion-containing acid solution storage tank (acid waste liquid storage tank) 10 is fed. Acid waste liquid metal ion-containing acid solution storage tank (acid waste liquid storage tank) 10 is pumped P ₁ is introduced into the anode chamber 2A of the through pipe 11 electrodeposition tank 1, electrodeposition processing liquid eluent tank 30 from line 34 And recycled as eluent.

On the other hand, the catholyte in the catholyte storage tank 20 is introduced into the cathode chamber 3A of the electrodeposition tank ₁ through the pipe 21 by the pump P2, and returned to the catholyte storage tank 20 through the pipe 22.
The eluent storage tank 30 is appropriately replenished with acid through a pipe 33, and the catholyte storage tank 20 is replenished with a catholyte through a pipe 23.

In this apparatus, by passing the heated eluent through the elution tank 8 filled with the waste ion exchange resin 40, the ionic radionuclide adsorbed on the waste ion exchange resin 40 is eluted and removed. Then, the clad mixed in the waste ion exchange resin 40 or entering the resin particles is dissolved and removed. In contact with the waste ion exchange resin 40, the eluent (acid waste liquid) containing ionic radionuclides and clad dissolved material passes through the metal ion-containing acid liquid storage tank (acid waste liquid storage tank) 10 and the anode chamber of the electrodeposition tank 1. 2A. By energizing the anode 2 and the cathode 3 of the electrodeposition tank 1, metal ions such as radioactive metal ions in the acid waste liquid and iron ions derived from the cladding permeate the cation exchange membrane 5 and move to the cathode chamber 3A. Electrodeposited on the cathode 3. The acid waste liquid treatment liquid from which metal ions have been removed in the electrodeposition tank 1 is returned to the eluent storage tank 30 and recycled.
The catholyte in the cathode chamber 3 </ _b > A is circulated between the catholyte storage tank 20 by the pump P < _b > _2, and the reduced amount of the catholyte is circulated and reused while being added to the catholyte storage tank 20.

In the apparatus of FIG. 2, it is preferable to use an acid eluent heated to 60 ° C. or higher as the eluent used for decontamination of the waste ion exchange resin. The radioactive metal ions adsorbed on the cation exchange resin of the ion exchange resin can be eluted and removed by ion exchange with H ⁺ ions, and the clad mixed in the waste ion exchange resin can be efficiently dissolved and removed. It becomes.

  As the acid eluent, an aqueous solution of an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid, or an organic acid such as formic acid, acetic acid or oxalic acid can be used. These acids may be used alone or as a mixture of two or more, but sulfuric acid and / or oxalic acid that does not easily volatilize when heated and used and does not fall under hazardous materials is used. It is preferable.

The acid concentration in the eluent has a suitable concentration depending on the acid used. For example, the sulfuric acid concentration is preferably 5 to 40% by weight, more preferably 10 to 30% by weight. The oxalic acid concentration is preferably 0.1 to 40% by weight, more preferably 1 to 20% by weight. When the acid concentration is lower than the above range, the dissolution efficiency of hematite (α-Fe ₂ O ₃ ), which is the main component of the cladding, is lowered. That is, the clad is present in a form mixed in or entering the waste ion exchange resin, the main component of which is hardly soluble hematite, and it is difficult to dissolve with a low concentration of acid. If the acid concentration in the eluent is high, the amount of hydrogen generated in the subsequent electrodeposition tank becomes excessive, and the electrodeposition efficiency decreases.

  In the apparatus of FIG. 2, the radioactive substance is highly concentrated by electrodepositing what becomes a metal cation upon dissolution, such as cobalt-60 and nickel-63 contained in the radioactive waste ion exchange resin. can do. On the other hand, it is possible to obtain a waste ion exchange resin whose radiation dose is reduced to an extremely low level, and the treated waste ion exchange resin can be incinerated. Then, the amount of waste can be reduced to a capacity of 1/100 to 1/200 by incinerating the waste ion exchange resin into incineration ash.

  FIG. 3 shows another embodiment of the electrodeposition tank 1 in the apparatus of FIGS. 1 and 2. 3, members having the same functions as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.

  The electrodeposition tank 1A of FIG. 3 includes an anode chamber 2A including an anode 2, a cathode chamber 3A including a cathode 3, and one or more intermediate chambers 4 between the anode chamber 2A and the cathode chamber 3A. In the present embodiment, the intermediate chamber 4 is composed of four chambers, the anode chamber 2A, the first intermediate chamber 4A, the second intermediate chamber 4B, the third intermediate chamber 4C, the fourth intermediate chamber 4D, and the cathode chamber 3A, respectively. Is separated by an ion exchange membrane.

  The cation exchange membrane 5 is used as the ion exchange membrane between the anode chamber 2A and the first intermediate chamber 4A, the second intermediate chamber 4B and the third intermediate chamber 4C, and the fourth intermediate chamber 4D and the cathode chamber 3A. Further, the bipolar membrane 6 is used as the ion exchange membrane between the first intermediate chamber 4A and the second intermediate chamber 4B and between the third intermediate chamber 4C and the fourth intermediate chamber 4D. The bipolar membrane 6 is an ion exchange membrane having a surface having a cation exchange group and a surface having an anion exchange group, with the surface having a cation exchange group facing the cathode chamber 3A and the surface having an anion exchange group facing the anode chamber 2A. Arranged. Although it is possible to replace the bipolar membrane 6 with an anion exchange membrane, when the anion exchange membrane is used, the acid in the acid waste liquid passes through the anion exchange membrane and moves to the catholyte, and the pH of the catholyte decreases. This may cause a problem that the acidity of the acid waste solution is lowered and the acid waste solution is difficult to be reused as an acid solution.

  The metal ion-containing acid solution (acid waste solution) is passed through the pipe 11 in parallel to the anode chamber 2A, the second intermediate chamber 4B, and the fourth intermediate chamber 4D, and then discharged through the pipe 12 to obtain a metal ion concentration. Is reused as a reduced acid solution. The catholyte is introduced into the first intermediate chamber 4A from the catholyte storage tank (catholyte storage tank 20 in FIGS. 1 and 2) via the pipe 21 and discharged from the first intermediate chamber 4A via the pipe 23. A circulation system that is introduced into the third intermediate chamber 4C, the discharged liquid from the third intermediate chamber 4C is introduced into the cathode chamber 3A through the pipe 24, and the discharged liquid from the cathode chamber 3A is returned to the catholyte storage tank through the pipe 22. Is formed.

  In the apparatus of FIG. 3, when the anode 2 and the cathode 3 are energized, the metal ions in the acid waste liquid permeate the cation exchange membrane 5 and move to the catholyte side, and are electrodeposited on the cathode 3.

  In the electrodeposition tank 1 of FIG. 3, the acid waste liquid is introduced into the anode chamber 2A. However, the acid waste liquid is not introduced into the anode chamber 2A, and a separate anolyte tank is provided. It is preferable that the anolyte be circulated between them. In that case, it is preferable to add to the anolyte an electrolyte that is not easily consumed by the anodic reaction, such as sulfuric acid or sodium sulfate. In addition, when the additive of the present invention is added to the catholyte, if the catholyte is introduced into the anode chamber 2A, the additive is decomposed by the anodic reaction, so that the catholyte is not introduced into the anode chamber 2A. Is preferred.

  In FIG. 3, the acid waste liquid is passed through the anode chamber 2A, the second intermediate chamber 4B, and the fourth intermediate chamber 4D in parallel, but the anode chamber 2A, the second intermediate chamber 4B, and the fourth intermediate chamber 4D. It is also possible to adopt a form in which liquid is passed in series in order.

1 to 3 show an example of a processing apparatus suitable for carrying out the present invention, and the processing apparatus of the present invention is not limited to the illustrated one.
Although the electrodeposition tank 1 is a closed system in the apparatus of FIGS. 1-3, since hydrogen gas is generated from a cathode, it is preferable to set it as the open system which opened the upper part. In addition, when replacing the cathode electrodeposited with metal, the replacement is easier if the upper part of the electrodeposition tank is open. In FIG. 2, the eluent is passed through the elution tank 8 in an upward flow, but may be a downward flow. However, when the waste ion exchange resin is in the form of a powder, it is preferable to make the flow upward because the differential pressure is likely to increase during liquid flow. In the electrodeposition tank 1, the acid waste liquid and the catholyte may be passed through the cation exchange membrane 5 in the opposite directions. Furthermore, it is possible to exchange heat between the eluent introduced into the elution tank 8 and the discharged acid waste liquid.

In FIG. 3, four intermediate chambers 4 are provided between the anode chamber 2 </ b> A and the cathode chamber 3 </ b> A in a stacked manner. However, the intermediate chamber is not limited to four chambers and may be a single chamber. Two, three, or five or more rooms may be used. However, the anode chamber and the adjacent intermediate chamber are separated by a cation exchange membrane, the cathode chamber and the adjacent intermediate chamber are separated by a cation exchange membrane, and between the other intermediate chambers The cation exchange membrane and the bipolar membrane are preferably provided alternately.
Thus, in the configuration in which the intermediate chamber is provided between the anode chamber and the cathode chamber, the moving speed of the metal ions from the acid waste liquid to the catholyte per electrodeposition tank can be improved without increasing the current density. It is preferable in terms.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Examples 1-3>
Using a simulated acid waste solution having the properties shown in Table 1 as the metal ion-containing acid solution, a simulated electrodeposition solution (catholyte) to which sodium sulfate has been added was prepared, and using the apparatus shown in FIG. A test was conducted. The sodium sulfate in the catholyte was added so as to have an equimolar concentration with the sulfuric acid concentration in the simulated acid waste solution. The electrodeposition conditions are as shown in Table 1. The anode 2 was a Pt-plated Ti plate, and the cathode 3 was a Cu plate. The energization time was 8 hours, and the pH of the catholyte in the catholyte storage tank 20 and the Co and Fe concentrations of the simulated acid waste liquid in the metal ion-containing acid solution storage tank 10 were continuously measured.

As a result, as shown in FIG. 4, it was found that by adding sodium sulfate to the catholyte, a decrease in the pH of the catholyte can be suppressed. It was also found that the pH of the catholyte increases because the rate at which Co and Fe permeate the cation exchange membrane increases as the current density increases, and the pH can be maintained high.
5 and 6 show the changes over time in the Co and Fe concentrations in the simulated acid waste liquid, respectively. It can be seen that Co and Fe can be removed from the simulated acid waste solution with the energization time.

<Comparative Example 1>
Simulated waste ion exchange resin (a mixture of 10 g of powdered cation exchange resin and 10 g of powdered anion exchange resin added with Co and Fe) is stirred in 5% sulfuric acid at 90 ° C., and Co and Fe are simulated waste ions. The simulated acid waste solution was eluted from the exchange resin.
Using the apparatus shown in FIG. 2, the elution tank 8 is filled with the simulated waste ion exchange resin after the elution treatment, the simulated acid waste liquid is filled into the eluent storage tank 30, and the Co and Fe electrodeposition tests are performed under the conditions shown in Table 2. Went. The anode 2 in the electrodeposition tank 1 was a Pt-plated Ti plate, and the cathode 3 was a Cu plate. The circulation amounts of the simulated acid waste liquid and the electrodeposition liquid (catholyte) (flow rates of the pumps P _{1 to} P ₃ ) were both 1 L / hr.
The treatment time (energization time) was 24 hr, and the pH of the catholyte in the catholyte storage tank 20 was continuously measured. Moreover, the electrodeposit after the test was dissolved by mixing hydrochloric acid (1: 1 mixture of 35% hydrochloric acid and pure water) and nitric acid (1: 1 mixture of 60% nitric acid and pure water) in a ratio of 2: 3. The solution was completely dissolved in the solution, and the amount of electrodeposition was measured with an atomic absorption photometer.

  As a result, as shown in FIG. 7, the pH of the catholyte decreased with the treatment time, and the pH decreased from 4.4 to about 1 (the hydrogen ion concentration increased by about 0.1 mol / L). This is because the sulfuric acid in the simulated acid waste liquid permeates the cation exchange membrane by concentration diffusion and moves to the catholyte. The electrodeposition amount on the cathode is 0.52 mg for Co and 12.8 mg for Fe, and the electrodeposition rate is 14% for Co and 1.8% for Fe in the simulated acid waste solution. It was low.

<Example 4>
A simulated waste ion exchange resin (a mixture of 2 g of powdered cation exchange resin and 2 g of powdered anion exchange resin with Co and Fe added) was stirred in 90 wt. The simulated acid waste solution was eluted from the exchange resin.
Using the apparatus of FIG. 2, the elution tank 8 is filled with the simulated waste ion exchange resin after the elution treatment, the simulated acid waste liquid is filled into the eluent storage tank 30, and the treatment time (energization time) is 48 hours under the conditions shown in Table 3. Co and Fe electrodeposition tests were performed. Other conditions were the same as in Comparative Example 1 and the test was performed.
As a result, although the pH of the catholyte was decreased, it was suppressed by a decrease from pH 8.4 to pH 4.6 (an increase of about 2.5 × 10 ⁻⁵ mol / L as the hydrogen ion concentration) by energization for 48 hours. The amount of electrodeposition on the cathode was 1.1 mg for Co and 165 mg for Fe, and the electrodeposition rates were 98% for Co and 87% for Fe in the simulated acid waste solution, and high electrodeposition efficiency was obtained.

1, 1A Electrodeposition bath 2 Anode 2A Anode chamber 3 Cathode 3A Cathode chamber 4 Intermediate chamber 4A First intermediate chamber 4B Second intermediate chamber 4C Third intermediate chamber 4D Fourth intermediate chamber 5 Cation exchange membrane 6 Bipolar membrane 8 Elution tank 9A , 9B Heat exchanger 10 Metal ion-containing acid storage tank (acid waste liquid storage tank)
20 Catholyte storage tank 30 Eluent storage tank 40 Waste ion exchange resin

Claims (10)

  An anode chamber with an anode and a cathode chamber with a cathode are separated by a cation exchange membrane, an acid solution containing metal ions is introduced into the anode chamber, and a catholyte containing a salt of the acid is introduced into the cathode chamber The metal ions in the liquid in the anode chamber are transferred through the cation exchange membrane and moved into the catholyte by depositing the metal between the anode and the cathode, and the metal is deposited on the cathode. A method for treating a metal ion-containing acid solution.   Between the anode chamber provided with the anode and the cathode chamber provided with the cathode, there are provided one or more intermediate chambers separated from the anode chamber side and the cathode chamber side through an ion exchange membrane, the cathode chamber and the cathode The intermediate chamber adjacent to the chamber is separated by a cation exchange membrane, an acid solution containing metal ions is introduced into the intermediate chamber adjacent to the cathode chamber, and a catholyte containing the acid salt is introduced into the cathode chamber The metal ions in the liquid in the intermediate chamber adjacent to the cathode chamber are moved through the cation exchange membrane and moved into the catholyte by passing an electric current between the anode and the cathode. A method for treating a metal ion-containing acid solution, wherein the metal is precipitated.   The method for treating a metal ion-containing acid solution according to claim 1 or 2, wherein the acid solution contains sulfuric acid, and the catholyte contains a sulfate.   4. The metal ion-containing acid solution according to claim 1, wherein a concentration of the salt in the cathode chamber is 0.5 to 2 times as much as an acid in the acid solution as a molar concentration. Processing method.   The treatment of a metal ion-containing acid solution according to any one of claims 1 to 4, wherein the catholyte contains one or more additives selected from dicarboxylic acids and salts thereof and tricarboxylic acids and salts thereof. Method.   An anode chamber having an anode; a cathode chamber having a cathode; a cation exchange membrane that separates the anode chamber from the cathode chamber; an energizing means for energizing between the anode and the cathode; A liquid passing means for passing an acid solution containing metal ions into the anode chamber; and a liquid passing means for passing a catholyte containing the acid salt into the cathode chamber, and a current is passed between the anode and the cathode. The metal ion-containing acid solution is characterized in that metal ions in the liquid in the anode chamber permeate the cation exchange membrane and move into the catholyte, and deposit the metal on the cathode. Processing equipment.   An anode chamber provided with an anode, a cathode chamber provided with a cathode, and at least one intermediate chamber provided between the anode chamber and the cathode chamber and separated by the ion exchange membrane. An electrodeposition tank having electricity, an energizing means for energizing between the anode and the cathode, a liquid passing means for passing an acid solution containing metal ions into the intermediate chamber adjacent to the cathode chamber, and a solution of the acid in the cathode chamber. An ion exchange membrane that separates the cathode chamber and the intermediate chamber adjacent to the cathode chamber is a cation exchange membrane, and has a liquid passage means for passing a catholyte containing salt. The metal ions in the liquid in the intermediate chamber adjacent to the cathode chamber are moved through the cation exchange membrane and moved into the catholyte, and the metal is deposited on the cathode. An apparatus for treating a metal ion-containing acid solution.   The apparatus for treating a metal ion-containing acid solution according to claim 6 or 7, wherein the acid solution contains sulfuric acid, and the catholyte contains a sulfate.   The metal ion-containing acid solution according to any one of claims 6 to 8, wherein the concentration of the salt in the cathode chamber is 0.5 to 2 times as much as the acid in the acid solution as a molar concentration. Processing equipment.   The treatment of a metal ion-containing acid solution according to any one of claims 6 to 9, wherein the catholyte contains one or more additives selected from dicarboxylic acids and salts thereof and tricarboxylic acids and salts thereof. apparatus.

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