JP2006194621A - Radioactive waste liquid treating method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress an increase of secondary waste, to avoid clogging of a circulation system of an electrodialysis vessel generated by sediment caused by metal ions, and to improve a recovery rate of an acid in decontamination waste liquid. <P>SOLUTION: Radioactive waste liquid including a radioactive material, metal ions and an acid is supplied to a treated waste liquid chamber 3b of the electrodialysis vessel 3 having the treated waste liquid chamber 3b and a recovery liquid chamber 3c separated by a dialysis membrane 12, and the acid dialyzed into the other chamber through the dialysis membrane is recovered, and a suspended matter in the radioactive waste liquid discharged from the treated waste liquid chamber is removed by a suspended matter removal means 4, and then, the radioactive waste liquid is circulated and supplied into the treated waste liquid chamber. Hereby, since sedimentation of the metal ions can be prevented from being accumulated in the circulation system of the treated waste liquid, even if pH in the treated waste liquid chamber of the electrodialysis vessel becomes high, the recovery rate of sulfuric acid can be heightened. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radioactive liquid waste treatment method and a processing apparatus, and more specifically, a radioactive liquid waste generated by decontaminating a metal waste to which a radioactive substance is attached with an acid such as sulfuric acid, particularly a metal contaminated with uranium. The present invention relates to a technique for separating sulfuric acid from an acid waste liquid obtained by decontaminating waste with sulfuric acid.

  Metal waste with nuclear fuel materials and radioactive materials such as uranium attached can be decontaminated with a decontamination solution containing sulfuric acid, and the decontamination waste solution is finally disposed of after being solidified with cement or the like. When the sulfuric acid in the decontamination waste liquid is solidified with cement, the sulfate ions react with the components of the cement and cause cracks. Therefore, it is necessary to neutralize the acid in the waste liquid. It is effective to use barium hydroxide as the neutralizing reagent and to fix sulfate ions to barium sulfate having low solubility. In this case, the waste liquid containing the barium sulfate precipitate and the cement are mixed. However, if the amount of barium sulfate precipitate increases, the workability of the kneading deteriorates. Therefore, there is an upper limit to the precipitation concentration of barium sulfate, and on the contrary, the amount of decontamination waste liquid after neutralization increases, which may increase the number of solidified bodies that are secondary waste.

  On the other hand, in Patent Document 1, a decontamination waste liquid generated by decontaminating radioactive metal waste using a mixed acid such as nitric acid, hydrochloric acid, and hydrofluoric acid is neutralized with alkali, and metal ions contained in the decontamination waste liquid In addition, it has been proposed to precipitate and remove most of the radioactive material, and then separate and recover it into warm acid, alkali, and demineralized water by electrodialysis using a bipolar membrane.

  In addition, although it is not a technique for removing acid in a radioactive substance decontamination liquid, as a technique for removing acid in waste liquid, for example, Patent Document 2 discloses an electrodialysis treatment of a nitric hydrofluoric acid washing waste liquid containing iron ions. A technique for efficiently recovering nitric hydrofluoric acid is described.

JP-A-8-240695 JP-A-8-24586

  By the way, when radioactive waste liquid containing radioactive substances, metal ions and acids such as sulfuric acid is treated by electrodialysis, the pH of the radioactive waste liquid rises as the acid is separated and removed, and metal ions such as iron dissolved in the waste liquid. Is hydrolyzed to form a precipitate. Usually, in the electrodialysis treatment, the acid recovery rate is increased by circulating the radioactive waste liquid in the electrodialysis tank and repeatedly performing dialysis treatment. Therefore, the precipitate generated by hydrolysis of metal ions may circulate in the circulation system of the electrodialysis tank, causing the precipitate to accumulate locally and causing problems such as blockage.

  In this regard, as described in Patent Document 1, if the metal ion is precipitated and removed by neutralizing the decontamination waste liquid with alkali before electrodialysis treatment, the precipitate accumulates in the circulation system of the electrodialysis tank. Can be prevented. However, according to this method, not only pretreatment with alkali is required, but also most of radioactive materials are precipitated in addition to metal ions by alkali treatment, so secondary waste that must be solidified. There is a problem that increases.

On the other hand, according to Patent Document 2, iron ions are once recovered from a waste liquid chamber into another intermediate chamber by dialysis, and the pH of the liquid in the intermediate chamber is appropriately set to generate and remove iron precipitates. Therefore, there is a problem that the configuration and processing of the electrodialysis tank becomes complicated.
Even if metal ions are hydrolyzed and precipitates are generated, sulfuric acid is recovered while circulating the electrodialysis tank together with the decontamination waste liquid, and when the recovery of sulfuric acid is completed, the system is washed to obtain precipitates. It is conceivable to remove. However, since the cleaning waste liquid becomes secondary waste, there is a problem in that the amount of waste solidified material is increased.

  The present invention can suppress the increase in secondary waste, can prevent clogging of the circulation system of the electrodialysis tank due to precipitates caused by metal ions, and improve the recovery rate of acid in the decontamination waste liquid. Let it be an issue.

  In order to solve the above problems, the radioactive waste liquid treatment method or treatment apparatus of the present invention supplies a radioactive waste liquid containing a radioactive substance, metal ions and an acid to one chamber of an electrodialysis tank having two chambers separated by a dialysis membrane. And recovering the acid-containing liquid dialyzed into the other chamber through the dialysis membrane and removing the suspended matter in the radioactive liquid waste discharged from the one chamber. The one chamber is circulated and supplied.

  According to this, even when the pH of the radioactive liquid waste circulating in one chamber of the electrodialysis tank rises and the dissolved metal ions are hydrolyzed and precipitated, Since the suspended matter is removed and then returned to the chamber, it is possible to prevent the sediment in the circulating radioactive liquid waste from accumulating in the circulating system and clogging. As a result, the radioactive liquid waste can be repeatedly and sufficiently circulated in the electrodialysis tank, so that the acid recovery rate can be improved. In addition, since no neutralization or cleaning is performed, an increase in secondary waste can be suppressed.

  In this case, in order to remove the suspension, the treatment waste liquid discharged from the electrodialysis tank is guided to the precipitation tank, and after the precipitate formed by hydrolysis of metal ions is removed, for example, the treatment waste liquid is circulated. It can return to an electrodialysis tank by a circulation pump through a supply tank. Further, instead of the sedimentation tank for removing the suspended solids, the treatment is performed by a sedimentation chamber formed by a weir plate provided between the treatment liquid waste inlet of the circulation supply tank and the outlet connected to the circulation pump. It can also be made to precipitate in a circulating supply tank of waste liquid.

  Moreover, an anion exchange membrane is used for the dialysis membrane, and one chamber in which the radioactive waste liquid is circulated can be formed by a hydrogen ion selective permeable membrane provided between the cathode and the ion exchange membrane. The other chamber for collecting the acid can be formed by a hydrogen ion selective permeable membrane provided between the anode and the ion exchange membrane.

  Moreover, in said case, a metal ion contains an iron ion and an acid can use a sulfuric acid.

Hereinafter, the present invention will be described based on embodiments.
(Embodiment 1)
FIG. 1 shows a system configuration diagram of a radioactive waste liquid treatment apparatus to which an embodiment of the radioactive waste liquid treatment method of the present invention is applied, and FIG. 2 shows a detailed configuration diagram of an electrodialysis tank.

  FIG. 1 is a system configuration diagram of an embodiment in which a metal waste contaminated with uranium is applied to a decontamination waste liquid generated by decontamination with sulfuric acid. As shown in FIG. 1, the radioactive waste liquid treatment apparatus includes a decontamination waste liquid receiving tank 1, a treatment waste liquid circulation supply tank 2, an electrodialysis tank 3, a suspension removal means 4, and a recovered liquid circulation supply tank 5. The polar liquid recovery tank 6, the circulation pumps 7a, 7b and 7c, and the uranium adsorption tower 8 are configured.

  The decontamination waste liquid receiving tank 1 is adapted to receive a radioactive decontamination waste liquid obtained by decontaminating metal waste with uranium attached thereto with sulfuric acid from a decontamination apparatus (not shown). The decontamination waste liquid in the decontamination waste liquid receiving tank 1 is configured to be supplied to the circulation supply tank 2 by a batch process. Although not shown, when insoluble components are suspended in the decontamination waste liquid, the waste liquid in the decontamination waste liquid receiving tank 1 is transferred to the sedimentation tank and subjected to sedimentation treatment, and then the supernatant liquid is circulated and supplied. 2 can be configured to be transported. In this case, the suspended matter settled in the settling tank can be extracted from the lower part of the settling tank and sent to a cement solidifying device to be solidified. When the decontamination waste liquid does not contain a suspended matter, as shown in FIG. 1, the sedimentation process can be omitted and the decontamination waste liquid can be directly sent from the decontamination waste liquid receiving tank 1 to the circulation supply tank 2.

  Here, unreacted sulfuric acid, components such as iron eluted from metal waste, and decontaminated uranium are dissolved in an ionic form in the decontamination waste liquid. As an example of the composition of the decontamination waste liquid, it is assumed that approximately 0.5 wt% sulfuric acid and several thousand ppm of transition metal ions are included. As a transition metal, iron is a typical example, but in summary, a suspension is likely to be generated as the decontamination waste liquid moves from acidic to neutral. Furthermore, it is assumed that several tens ppm of uranium is contained.

  As shown in FIG. 2, the electrodialysis tank 3 is provided with hydrogen ion selective permeable membranes 11 a and 11 b on both sides of the anion exchange membrane 12. A cathode 9 is disposed on the opposite side of the anion exchange membrane 12 with the hydrogen ion selective permeable membrane 11a interposed therebetween, and a cathode chamber 3a is formed. In addition, an anode 10 is disposed on the opposite side of the anion exchange membrane 12 across the hydrogen ion selective permeable membrane 11b, thereby forming an anode chamber 3d. Further, a treatment waste liquid chamber 3b partitioned by the anion exchange membrane 12 and the hydrogen ion selective permeable membrane 11a and a recovery liquid chamber 3c partitioned by the anion exchange membrane 12 and the hydrogen ion selective permeable membrane 11b are formed. As shown in FIG. 1, polar liquid (for example, 0.1% to 5% sulfuric acid) is circulated and supplied from the polar liquid recovery tank 6 to the cathode chamber 3a and the anode chamber 3d by the circulation pump 7a. It has become. This polar liquid is supplied to balance the charges in the cathode chamber 3a and the anode chamber 3d.

The operation of the decontamination waste liquid treatment of the embodiment configured as described above will be described. The treatment waste liquid that is the decontamination waste liquid stored in the circulation supply tank 2 is supplied to the treatment waste liquid chamber 3b of the electrodialysis tank 3 by the circulation pump 7b. In the decontamination waste liquid, sulfuric acid (H ₂ SO ₄ ) is dissociated into hydrogen ions (H ⁺ ) and sulfate ions (SO ₄ ²⁻ ). When an electric current is passed between the cathode 9 and the anode 10, hydrogen ions (H +) in the treatment waste liquid are attracted to the cathode, and hydrogen ions (H +) that permeate the hydrogen ion selective permeable membrane 11a are allowed to flow into the cathode chamber 3a. Take in the polar liquid flowing down. In addition, sulfate ions (SO4−) in the treatment waste liquid are sucked into the anode 10, and sulfate ions (SO4−) that permeate the anion exchange membrane 12 are taken into the recovery liquid flowing down in the recovery liquid chamber 3c. . In this way, the sulfuric acid in the processing liquid supplied to the processing waste liquid chamber 3b is transferred to the recovered liquid. Further, since most of transition metals and uranium dissolved in the treatment waste liquid exist as cations, the transition metal and uranium try to move to the recovery liquid chamber 3c on the cathode side. Since it is separated by the exchange membrane 12 (corrected, please confirm), the transfer to the recovered liquid is suppressed.

  Thus, while passing through the treatment waste liquid chamber 3b of the electrodialysis tank 3, the sulfuric acid in the treatment waste liquid moves to the recovered liquid side. The treatment waste liquid that has passed through the treatment waste liquid chamber 3 b is returned to the circulation supply tank 2 via the suspension removal means 4. The treatment waste liquid returned to the circulation supply tank 2 is supplied again to the treatment waste liquid chamber 3b by the circulation pump 7b, and is circulated between the circulation supply tank 2 and the treatment waste liquid chamber 3b, thereby recovering a predetermined ratio of sulfuric acid. Is done. As the sulfuric acid is recovered and the sulfuric acid concentration in the treatment waste liquid is lowered, the pH becomes neutral, so the dissolved metal ions are hydrolyzed to produce insoluble hydroxides. This hydroxide is suspended in the treatment waste liquid, and the amount of suspension increases as the recovery of sulfuric acid proceeds. For example, when the sulfuric acid is recovered from the decontamination waste liquid containing 0.5% sulfuric acid and 3000ppm Fe (III), the result of the trial calculation of how the dissolved Fe (III) concentration decreases is shown in the figure. 3 shows. In FIG. 3, the horizontal axis indicates the recovery rate (wt%) of sulfuric acid, and the vertical axis indicates the precipitation rate (wt%) in Fe. As shown in the figure, it can be seen that when 95 wt% sulfuric acid is recovered, most of the Fe (III) ions become insoluble hydroxides during that time.

  If the treatment waste liquid is circulated in a state where the hydroxide is suspended, precipitation may locally accumulate between the membranes or in the pipes, which may cause clogging. Therefore, in the present embodiment, the processing waste liquid exiting the processing waste liquid chamber 3b of the electrodialysis tank 3 is removed through the suspension removing means 4 and then returned to the circulation supply tank 2. Here, as the suspension removal means 4, for example, a precipitate removal tank is applied, the suspension is separated by sedimentation, and the supernatant liquid is sent to the circulation supply tank 2, thereby being generated in the treatment waste liquid chamber 3 b. The precipitate is removed and circulated to the electrodialysis tank 3. Thereby, sulfuric acid can be removed from the decontamination waste liquid with high efficiency without accumulation of suspension in the circulation system of the treatment liquid.

On the other hand, when removing sulfuric acid from sulfuric acid-based decontamination waste liquid containing uranium by electrodialysis, in addition to the precipitation of transition metals, part of uranium is accompanied by the sulfuric acid recovery liquid. Uranium needs to be removed. In the uranium in this sulfuric acid aqueous solution, a part of uranyl ion exists as an anion complex. The proportion existing as an anion complex can be predicted from the stability constant of the uranyl ion sulfate complex as shown in FIG. In FIG. 4, the horizontal axis represents SO ₄ ²⁻ concentration (mol / L), and the vertical axis represents the ratio (%) of each ion complex. As shown, approximately 20% is present as an anion complex in a 5% sulfuric acid aqueous solution. This uranium moves to the collection liquid on the anode side through the anion exchange membrane 12. According to the test results of the inventors, when 90% sulfuric acid was recovered from the decontamination waste liquid containing 5% sulfuric acid, about 20% of uranium was transferred to the recovery liquid side along with the sulfuric acid.
When uranium migrates to the recovered liquid side, there is a high possibility of causing cross contamination when decontaminating waste with uranium attached using recovered sulfuric acid. In this case, it is necessary to perform a sufficient cleaning process after the decontamination process. Therefore, the volume of decontamination waste liquid increases. In order to avoid this, it is necessary to lower the uranium concentration in the recovered liquid. Therefore, in the embodiment of FIG. 1, uranium is adsorbed and separated by providing a uranium adsorption tower 8 in the middle of a pipe for circulating the recovered sulfuric acid. Here, an adsorption method using an anion exchange resin is effective as a method for efficiently separating uranium in sulfuric acid.

  After the predetermined sulfuric acid is collected, the processing waste liquid in the circulation supply tank 2 is sent to a cement solidifying device (not shown) and solidified. Further, the transition metal hydroxide precipitated in, for example, the sediment removal tank of the suspension removing means 4 is also extracted and sent to a cement solidifying apparatus for solidification. Further, since a small amount of sulfuric acid remains in the treatment waste liquid, it is neutralized with barium hydroxide or the like and then kneaded with cement together with a transition metal hydroxide to be solidified. On the other hand, the collected sulfuric acid is reused in the decontamination apparatus after the concentration is adjusted.

As described above, according to the radioactive liquid waste treatment apparatus of this embodiment, the precipitation of the metal ions does not accumulate in the circulation system of the liquid treatment waste, so that the pH of the liquid treatment chamber 3b of the electrodialysis tank 3 is increased. Therefore, the sulfuric acid recovery rate can be increased. As a result, since the sulfuric acid in the treatment waste liquid can be reduced, it is possible to eliminate a problem when the treatment waste liquid and the transition metal hydroxide are solidified with cement, and to increase the filling rate.
(Embodiment 2)
5 and 6 show system configuration diagrams of another embodiment of the radioactive liquid waste treatment apparatus of the present invention. The present embodiment differs from the embodiment of FIG. 1 in that instead of providing the suspension removal means 4 between the electrodialysis tank 3 and the treatment waste liquid circulation supply tank 2, the treatment waste liquid circulation supply tank 13 is provided. Is provided with a suspension removing means. As shown in FIG. 6, the circulation supply tank 13 of the present embodiment is partitioned into a chamber A and a chamber B by a dam plate 14 provided upright from the bottom. In addition, a baffle plate 15 is provided at an upper end position of the weir plate 14 in the upper part of the B chamber with an interval. At the bottom of the A chamber, there is provided an inlet nozzle 16 to which processing waste liquid is supplied from the processing waste liquid chamber 3b of the decontamination waste liquid receiving tank 1 or the electrodialysis tank 3. Further, an outlet nozzle 17 connected to the circulation pump 7b is provided at the upper part C of the baffle plate 15 of the B chamber. A sediment discharge nozzle 18 is provided at the bottom of the A chamber.

  Since it is configured in this way, the hydroxide which is a suspension in the processing waste liquid supplied to the A chamber of the circulation supply tank 13 settles in the A chamber, and the supernatant liquid passes over the weir plate 14 and the B chamber. to go into. The processing waste liquid entering the B chamber rises toward the outlet nozzle 17, but the flow to the C section is suppressed by the baffle plate 15. As a result, since the supernatant of the treatment waste liquid with little hydroxide precipitation is obtained in the vicinity of the outlet nozzle 17, precipitation in the treatment waste liquid returned to the electrodialysis tank 3 by the circulation pump 7b can be reduced.

  On the other hand, the sediment accumulated in the A chamber is appropriately extracted from the discharge nozzle 18 and sent to a cement solidifying device, and is solidified after neutralization.

  According to the present embodiment, metal ion hydroxide precipitates generated in the electrodialysis tank 3 can be removed by a simple suspension removal means than in the embodiment of FIG. It is possible to recover the acid component of the decontamination waste liquid by solving problems such as blockage of the supply system.

  Moreover, although the example which removes by suspension sedimentation was demonstrated as embodiment of FIG.1 and FIG.6 as a suspension removal means, this invention is not limited to this, Metal filtration of a metal ion is carried out by the filtration apparatus using a filter. Hydroxide precipitation can be removed.

The system configuration | structure figure of one Embodiment of the radioactive waste liquid processing apparatus of this invention is shown. 1 is a structural diagram of an electrodialysis tank according to an embodiment applied to the present invention. It is a figure explaining the reduction | decrease of an iron (III) ion concentration accompanying the fall of a sulfuric acid concentration. It is a figure explaining the existence form of uranium in sulfuric acid. The system block diagram of other embodiment of the radioactive waste liquid processing apparatus of this invention is shown. It is a figure which shows the detailed structure of the circulation supply tank of the process waste liquid of embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Decontamination waste liquid receiving tank 2 Circulation supply tank 3 Electrodialysis tank 4 Suspension removal means 5 Circulation supply tank 6 Polar liquid collection tank 7a, 7b, 7c Circulation pump 8 Uranium adsorption tower

Claims (9)

  A radioactive waste solution containing radioactive substances, metal ions and acid is supplied to one chamber of an electrodialysis tank having two chambers separated by a dialysis membrane, and the acid dialyzed into the other chamber is recovered through the dialysis membrane. At the same time, the radioactive waste liquid treatment method comprising removing the suspended matter in the radioactive waste liquid discharged from the one chamber and then circulatingly supplying the radioactive waste liquid to the one chamber. The dialysis membrane is an anion exchange membrane,
The one chamber is formed by a hydrogen ion selective permeable membrane provided between a cathode and the ion exchange membrane,
2. The radioactive waste liquid treatment method according to claim 1, wherein the other chamber is formed by a hydrogen ion selective permeation membrane provided between an anode and the ion exchange membrane.   The radioactive liquid waste treatment method according to claim 1 or 2, wherein the metal ions include iron ions, and the acid is sulfuric acid.   The radioactive waste liquid treatment method according to any one of claims 1 to 3, wherein the radioactive substance in the recovered liquid discharged from the other chamber is adsorbed and removed and then circulated and supplied to the other chamber. .   An electrodialysis tank having two chambers separated by a dialysis membrane, to which a radioactive waste liquid containing a radioactive substance, metal ions and an acid is supplied in one chamber, and the dialysis discharged from the other chamber of the electrodialysis tank A recovery liquid tank for receiving a recovery liquid containing an acid dialyzed by a membrane; waste liquid circulation means for circulating and supplying the treatment waste liquid treated by the electrodialysis tank discharged from the one chamber to the one chamber; A radioactive waste liquid treatment apparatus comprising: a suspension removal means for removing a suspension in the radioactive waste liquid circulated by the waste liquid circulation means. The dialysis membrane is an anion exchange membrane,
The one chamber is formed by a hydrogen ion selective permeable membrane provided between a cathode and the ion exchange membrane,
6. The radioactive waste liquid treatment apparatus according to claim 5, wherein the other chamber is formed by a hydrogen ion selective permeable membrane provided between an anode and the ion exchange membrane. The waste liquid circulation means comprises a circulation supply tank of treatment waste liquid that receives the treatment waste liquid treated by the electrodialysis tank, and a circulation pump that supplies the treatment waste liquid of the circulation supply tank to the one chamber,
The radioactive waste liquid treatment apparatus according to claim 5 or 6, wherein the suspension removing means is a sedimentation tank provided between the electrodialysis tank and the circulation supply tank. The waste liquid circulation means comprises a circulation supply tank of treatment waste liquid that receives the treatment waste liquid treated by the electrodialysis tank, and a circulation pump that supplies the treatment waste liquid of the circulation supply tank to the one chamber,
The suspension removing means is a sedimentation chamber formed by a weir plate provided between an inlet of the treatment waste liquid in the circulation supply tank and an outlet connected to the circulation pump. The radioactive liquid waste processing apparatus of Claim 5 or 6.   9. The recovery liquid circulating means for adsorbing and removing the radioactive substance in the recovery liquid from the recovery liquid tank and circulatingly supplying the recovered liquid to the other chamber is provided. The radioactive waste liquid processing apparatus as described in the paragraph.

Images