JP5497226B1 - Method and apparatus for treating desalted dust containing cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and efficiently remove cesium contained in desalted dust generated when industrial waste and disaster waste containing cesium are incinerated using a cement facility, and safe recovery is possible. It is providing the processing method and processing apparatus of the desalination dust containing cesium which become.
SOLUTION: A step of adding water to a desalted dust containing cesium to form a slurry; a step of filtering the slurry to separate into solid and liquid; and a salt of a hexacyanoferrate (II) acid complex to the obtained cesium-containing filtrate. An iron salt is added and mixed to form a Prussian blue-type metal complex in the filtrate, and the pH in the filtrate is adjusted to reduce the solubility of the Prussian blue-type metal complex to form a cesium-containing precipitate. A demineralized dust treatment method and treatment apparatus containing cesium, comprising a step of separating a precipitate containing the step and the cesium-containing precipitate.
[Selection] Figure 1

Description

  The present invention provides a cesium-containing waste liquid from desalted dust containing cesium produced by an alkali bypass facility or a chlorine bypass facility in a cement production facility when cesium is produced using industrial waste or disaster waste. In addition, the present invention relates to a processing method and a processing apparatus for desalted dust containing cesium using an existing cement manufacturing facility that adsorbs and reduces cesium by preparing a Prussian blue-type metal complex in the cesium-containing waste liquid. .

In recent years, in cement manufacturing facilities, volatile components such as chlorine contained in industrial waste have increased in kilns as the amount of industrial waste processed has increased, which has led to cement quality and cement kiln operations. There is a risk of adverse effects. Therefore, as a countermeasure, a chlorine bypass device is installed to remove chlorine from the cement manufacturing facility.
This chlorine bypass device extracts chlorine from the bottom of the kiln kiln and cools it to remove volatile components such as chlorine that have been repeatedly evaporated and condensed between the cement kiln and the preheater. This is an apparatus for removing chlorine from the cement kiln by generating chlorine bypass dust in which volatile components mainly composed of compounds are solidified and discharging the chlorine bypass dust out of the system.

In particular, the desalted dust produced using waste containing cesium contains high levels of cesium and also includes nuclides such as strontium elements.
Cesium contained in desalted dust has a longer half-life than iodine, so desalted dust cannot be discharged as it is, and cesium needs to be recovered.

As means for separating and recovering cesium, various methods for separating and removing cesium from wastewater containing cesium have been proposed.
For example, in JP-A-9-173732 (Patent Document 1), a quaternary ammonium salt that is soluble in a low-boiling organic solvent and hardly soluble in water is supported on a porous resin, and hexacyanoiron (II ) After treatment with an aqueous solution containing an acid salt, this treated product is brought into contact with an aqueous solution containing a copper salt to deposit copper hexacyanoferrate (II) in the pores of the resin, and then the quaternary ammonium salt in the resin is removed. A hexacyanoiron (II) copper-supported porous resin obtained by extraction with a low-boiling organic solvent is prepared in advance, and the hexacyanoferrate (II) copper-supported porous resin is mixed with a cesium-containing solution to adsorb cesium. There is a proposed method.

In addition, various ion exchange materials such as polymer materials having a sulfo group and inorganic materials such as zeolite have been proposed for removing cesium from a cesium-containing solution.
In recent years, a resin called an ion exchange resin that has been used in particular is exemplified by a resin having a large number of sulfo groups and the like. The resin is packed in a column and the waste water is passed through the column. Thus, adsorption and exchange of ions are realized.

For example, studies have been made on zeolites, crown ethers, and metal complexes.
Prussian blue (bitumen), which is a kind of metal complex, has cation adsorption performance, and a method of adsorbing and removing cesium using bitumen has been proposed.
In Japanese Patent Laid-Open No. 2011-200856 (Patent Document 2), a composite material in which a Prussian blue-type metal complex is disposed on a conductor is mixed with a solution containing a cation such as cesium and brought into contact with the predetermined material. A method for adsorbing cations on the Prussian blue-type metal complex is described.

However, the above conventional method is a method for separating and removing cesium from a waste liquid containing cesium, but a hexacyano iron (II) copper-supported porous resin or Prussian blue type metal complex is previously disposed on a conductor. The prepared composite material must be prepared in advance, which is costly and not a simple processing method.
In addition, development of a safe and simple method for separating cesium from desalted dust containing cesium is desired.

Japanese Patent Laid-Open No. 9-173832 JP 2011-200856 A

The object of the present invention has been made in view of the above problems, and specifically, it is included in desalted dust generated from cement facilities when industrial waste and disaster waste containing cesium are used. It is an object of the present invention to provide a treatment method and a treatment apparatus for desalted dust containing cesium that can remove cesium simply and efficiently and can be safely recovered.
That is, cesium is contained in the desalted dust generated from cement facilities when using waste containing cesium, etc., and cesium is efficiently removed from the desalted dust containing cesium, and as a result, cesium It is an object of the present invention to provide a treatment method and a treatment apparatus for desalted dust containing cesium, which can efficiently and safely recover and remove contained radioactive cesium.

In addition, demineralized dust contains not only cesium but also heavy metals, which can remove cesium and remove harmful heavy metals. A processing method and a processing apparatus are provided.
In particular, in a desalted dust containing selenium as a heavy metal, it is an object of the present invention to provide a method and an apparatus for treating desalted dust containing cesium that can efficiently remove selenium together with cesium.

  In the present invention, Prussian blue (bitumen) is produced in the cesium-containing filtrate, rather than adding pre-produced Prussian blue (bituminous) to the cesium-containing filtrate in the filtrate from the slurry of desalted dust containing cesium. As described above, it was found that cesium contained in the filtrate can be efficiently and easily removed and recovered by adding and blending the raw material of bitumen into the filtrate obtained by treating the slurry of desalted dust containing cesium. Is.

The method for treating desalted dust containing cesium according to claim 1 of the present invention includes a step of adding water to desalted dust containing cesium to form a slurry, a step of filtering the slurry and performing solid-liquid separation, and A cesium-containing filtrate having a pH of 9 to 13 and containing no selenium was added to a salt of hexacyanoferrate (II) complex which is potassium hexacyanoferrate (II) and / or sodium hexacyanoferrate (II) and a second chloride. Adding a ferric salt selected from the group consisting of iron, ferric sulfate, and ferric nitrate to form a Prussian blue-type metal complex according to the reaction formula shown in the following formula in the filtrate: Adjusting the pH of the Prussian blue-type metal complex so that the solubility of the Prussian blue-type metal complex is reduced to form a cesium-containing precipitate, and separating the precipitate containing the cesium-containing precipitate. Characterized in that a desalination dust treatment method including cesium.

A method for treating desalted dust containing cesium according to claim 2 of the present invention includes a step of adding water to a desalted dust containing cesium to form a slurry, a step of filtering the slurry and performing solid-liquid separation, and A cesium-containing filtrate having a pH of 9 to 13 and containing selenium , a salt of hexacyanoferrate (II) complex which is potassium hexacyanoferrate (II) and / or sodium hexacyanoferrate (II) and ferrous chloride A ferrous salt selected from the group consisting of ferrous sulfate and ferrous nitrate and a pH adjuster are added and mixed to adjust the pH of the filtrate to 3 to 6, and the filtrate Selenium and ferrous salt react to precipitate selenium, and the reaction between the ferric ion produced by oxidation of part of the ferrous salt by selenium and excess ferrous salt The reaction formula represented by the above formula in the filtrate by Forming a Prussian blue-type metal complex and adjusting the pH in the filtrate so as to reduce the solubility of the Prussian blue-type metal complex to form a cesium-containing precipitate, a precipitate containing the cesium-containing precipitate It is the desalinization dust processing method containing cesium characterized by including the process of isolate | separating.

Preferably, the method for treating demineralized dust containing cesium according to claim 3 is the method for treating demineralized dust containing cesium according to claim 1 or 2 , wherein the precipitate containing cesium-containing precipitate is dehydrated. It is characterized in that the precipitate is separated in a step of solid-liquid separation by filtering the slurry and adding the water to salt dust to form a slurry.

More preferably, in the method for treating desalted dust containing cesium according to any one of claims 1 to 3 , in the step of adding water to the desalted dust containing cesium to form a slurry, hexacyano iron ( II) A salt of an acid complex and an iron salt are added and mixed to form a Prussian blue-type metal complex in the slurry, a cesium-containing precipitate is formed in the slurry, and the slurry is filtered to obtain a solid-liquid solution. It isolate | separates as a precipitate in the process to isolate | separate.

The processing apparatus for desalinized dust containing cesium according to claim 5 of the present invention is a dissolution tank in which desalted dust containing cesium is mixed with water to form a slurry, and the slurry is filtered and solid-liquid separated to contain cesium. Filtration device for obtaining a filtrate , cesium-containing filtrate of pH 9 to 13 obtained, and hexafluoroiron (II) which is potassium hexacyanoferrate (II) and / or sodium hexacyanoferrate (II) in the filtrate without selenium An acid complex salt and a ferric salt selected from the group consisting of ferric chloride, ferric sulfate, and ferric nitrate are added and blended, and Prussian blue according to the reaction formula represented by the above formula in the filtrate. A reaction vessel for forming a metal complex, adding a pH adjusting agent and a polymer flocculant to produce a precipitate containing a cesium-containing precipitate, and a precipitation vessel for separating a precipitate containing a cesium-containing precipitate Characterized in that it comprises a processing device desalination dust containing cesium.
Moreover, the processing apparatus of the desalination dust containing the cesium of Claim 6 of this invention is a dissolution tank which mixes the desalination dust containing a cesium with water, and makes it a slurry, This slurry is filtered and solid-liquid-separated. A filtration device for obtaining a cesium-containing filtrate , a cesium-containing filtrate obtained at pH 9 to 13, and containing selenium in the filtrate , potassium hexacyanoferrate (II) and / or hexacyanoferrate (II) hexacyanoferrate (II) ) Add salt of acid complex and ferrous salt selected from the group consisting of ferrous chloride, ferrous sulfate and ferrous nitrate and pH adjuster, and adjust pH of the filtrate to 3-6 The selenium in the filtrate is reacted with the ferrous salt to precipitate selenium, and the ferric ion produced by oxidizing a part of the ferrous salt with selenium and the excess first ferrous ion. In the filtrate by reaction with iron salts A reaction vessel for forming a Prussian blue-type metal complex according to the reaction formula shown below, adding a pH adjuster and a polymer flocculant to produce a precipitate containing a cesium-containing precipitate, and a cesium-containing precipitate. characterized in that it comprises a sedimentation tank to separate the precipitate containing, Ru processor der desalination dust containing cesium.

  Preferably, the desalinized dust processing apparatus containing cesium according to the present invention is characterized by comprising a transport facility for circulating the cesium-containing precipitate recovered from the settling tank to the dissolution tank.

The processing method and processing apparatus for desalinated dust containing cesium according to the present invention includes heavy metals and cesium contained in desalted dust generated from cement equipment when using waste containing cesium and the like. Cesium can be effectively removed from desalted dust containing cesium.
In particular, by adding and blending raw materials that generate Prussian blue-type metal complexes of zinc hexacyanoferrate and hexacyanoferrate (II) and iron (III) to generate Prussian blue-type metal complexes in the waste liquid, It is possible to remove and separate cesium from the waste liquid more efficiently and more easily than a treatment method in which the cesium-containing waste liquid is added and blended in advance.
As a result, cesium can be well removed from waste liquid containing cesium, and as a result, radioactive cesium contained as a part of cesium can be efficiently removed. It is presumed that the standard can be satisfied by No. 5 (the number of isotopes that emit radiation, etc.).

  Also, by circulating the cesium precipitate, mixing it with the slurry of desalted dust, and filtering it, there is no need to handle extremely high concentration cesium-containing precipitates, and it is safe for humans and the environment. It becomes possible.

  In particular, when selenium is contained in the desalted dust, selenium can be effectively removed together with the precipitation of iron hydroxide.

It is a figure which shows the outline of the suitable example of the processing method and processing apparatus of the desalination dust (a selenium is not included) containing the cesium of this invention. It is a figure which shows the outline | summary of the suitable example of the processing method and processing apparatus of the desalinated dust (including selenium) containing the cesium of this invention. It is a figure which shows the outline of the processing method and processing apparatus for finally discharging the processing liquid from the processing method and processing apparatus of the desalination dust containing the cesium of FIG.1 and FIG.2.

The present invention will be described with reference to the following preferred examples, but is not limited thereto.
The method for treating desalted dust containing cesium of the present invention includes a step of adding water to a desalted dust containing cesium to form a slurry, a step of filtering the slurry to separate into solid and liquid, and an obtained cesium-containing filtrate. A salt of hexacyanoferrate (II) complex and an iron salt are added and mixed to form a Prussian blue type metal complex in the filtrate, and the pH in the filtrate is adjusted so that the solubility of the Prussian blue type metal complex is reduced. A demineralized dust treatment method containing cesium, comprising a step of adjusting to form a cesium-containing precipitate and a step of separating a precipitate containing the cesium-containing precipitate.

  The processing apparatus for desalted dust containing cesium according to the present invention is a dissolution tank that mixes desalted dust containing cesium with water to form a slurry, and the slurry is filtered to obtain a cesium-containing filtrate by solid-liquid separation. A filtration device, a hexacyanoferrate (II) complex salt and an iron salt are added to the cesium-containing filtrate, and a Prussian blue-type metal complex is formed in the filtrate. A processing apparatus for desalted dust containing cesium, comprising: a reaction tank that generates a precipitate containing a cesium-containing precipitate by addition and mixing; and a precipitation tank that separates a precipitate containing a cesium-containing precipitate.

  The suitable example of this invention is divided into the case where selenium is included as a heavy metal in desalted dust, and the case where it is not included, and is demonstrated below with reference to FIGS.

A. The case where selenium is not included: A description will be given with reference to FIG.
(1) Dissolution Step First, cesium-containing desalted dust is charged into the dissolution tank 1, and water W to such an extent that the desalted dust is fluidized is, for example, 2 to 10 times the amount of the desalted dust. In addition to stirring and slurrying, soluble components such as chlorine compounds and cesium contained in the desalted dust are eluted in water and repulped.
As the water W, industrial water, secondary drainage discharged from a manufacturing process or the like, water supply, or the like is used.

The reason why the preferred amount of water is the above amount is that if the amount of water is less than 2 times the mass of the desalted dust, the elution of soluble components in the desalted dust is not sufficient, and the latter filter It is because the soluble component which remains in each desalted cake solid content obtained by filtering with the filter 2 such as a press increases. Moreover, it is because the viscosity of the obtained slurry becomes high and it becomes difficult to transport the pump to the subsequent process.
In addition, when the amount of water added exceeds 10 mass times that of the desalted dust, the elution of other components such as heavy metals increases, and therefore, the amount of drug used to remove these components in the subsequent steps. Because there will be more.

  In said repulp, the temperature in the dissolution tank 1 is 20-40 degreeC, for example, Preferably, in order to raise the melt | dissolution rate of a soluble component, you may raise the temperature in the dissolution tank 1 to 40 degreeC or more. In addition, the solubilized component can be sufficiently dissolved within 10 hours of stirring time. Moreover, you may adjust pH as needed.

  In the dissolution tank 1, the cesium-containing precipitate obtained in the precipitation tank 6 in a later step or a heavy metal-containing precipitate other than cesium is returned and mixed with water W together with desalted dust to be slurried.

(2) Filtration process (precipitate collection process)
Slurry S1 produced | generated by this repulp is thrown into the filter 2, is squeezed, and solid-liquid separation is performed, and it isolate | separates into dehydrated cake solid content and filtrate F1.
As the filter 2, filter means such as a filter press, a belt filter, pressure filtration, suction filtration, and centrifugal separation can be applied.

Moreover, if necessary, water W may be introduced into the filter 2 and water containing soluble components remaining in the solid content may be washed with the water W. Washing with water W can be performed efficiently with a small amount of water by pumping the water W from one direction to the solid content while the filter 2 is pressurized.
The water W used for this washing is preferably 0.5 to 2.0 times the solid content.

The obtained dehydrated cake solid content includes desalted dust solid content, cesium-containing precipitate returned to the dissolution tank 1 from the precipitation tank 6, and heavy metal precipitates other than cesium. Therefore, the concentration of cesium contained in the obtained dehydrated cake does not become high, and as a result, the concentration of radioactive cesium contained does not become high, handling becomes easy, and environmentally It is safe for the human body.
The obtained dehydrated cake solids contain cesium, and thus radioactive cesium, and these dehydrated cake solids are stored and managed in a dedicated storage container.

(3) Cesium-containing precipitate / heavy metal-containing precipitate generation step In the filtrate F1 discharged from the filter 2, components such as heavy metals such as chlorine, cesium, lead, etc. contained in the desalted dust are dissolved. Yes.
The filtrate F1 discharged from the filter 2 is sent to the reaction tanks 4 and 5. Before being transferred to the reaction tank 4, it may be once sent into the buffer tank 3 and then into the reaction tank 4.

In the filtrate from the filtration process, cesium and other heavy metals such as lead (but not containing selenium) are dissolved, and the pH of the filtrate F1 is 9 to 13.
The cesium-containing filtrate is transported to the reaction tank 4 and a salt of hexacyanoferrate (II) complex and a ferric salt are added and blended, and the Prussian blue-type metal complex is added to the filtrate in the reaction tank 4. Let it form.
Next, preferably, the pH of the filtrate is adjusted in the reaction tank 5 so that the solubility of the Prussian blue-type metal complex is reduced, and the precipitate generated in the waste liquid is precipitated in the precipitation tank 6. Separated into a precipitate and a treatment liquid.

The obtained precipitate includes a cesium-containing precipitate obtained by reacting cesium contained in the filtrate F1 with a Prussian blue-type metal complex formed in the filtrate.
By passing through this process, it becomes possible to effectively remove cesium contained in the filtrate as a precipitate, while reducing the content of cesium in the obtained treatment liquid, as well as cyanide and iron It is also possible to make the residual concentration below the wastewater standard by the Ordinance of the Ministry of the Environment (Ordinance No. 15 of the Ministry of the Environment on May 23, 2012).

Specifically, in the present invention, a salt of a hexacyanoferrate (II) acid complex and a ferric salt are added to the reaction vessel 4 to form a Prussian blue-type metal complex in the cesium-containing filtrate, Cesium in the filtrate is adsorbed on the formed Prussian blue type metal complex.
The Prussian blue-type metal complex has a property of adsorbing cations such as cesium. However, in the present invention, the Prussian blue-type metal complex prepared in advance is not added to the cesium-containing filtrate, but cesium. By forming a Prussian blue-type metal complex in a filtrate containing cesium, it is possible to remove cesium as a precipitate more effectively than a method of adding and blending a pre-generated Prussian blue-type metal complex into a cesium filtrate. is there.

Examples of Prussian blue-type metal complex raw materials that are added and blended so that Prussian blue-type metal complexes are produced in a cesium-containing filtrate used in the treatment of the above-mentioned cesium-containing filtrate include, for example, salts of hexacyanoiron (II) acid complexes And ferric salts and the like.
The salt of hexacyanoferrate (II) complex is potassium hexacyanoferrate (II) and / or sodium hexacyanoferrate (II), and the salt of iron is ferric chloride, ferric sulfate and nitrate. It is preferable that at least one selected from the group consisting of diiron is selected.

The Prussian blue-type metal complex produced in these cesium-containing liquids can adsorb and remove cesium from the cesium-containing filtrate very efficiently.
Further, for example, hexacyanoferrate (II) acid as a Prussian blue-type metal complex raw material so that the amount of Prussian blue-type metal complex produced in the cesium-containing filtrate can sufficiently adsorb the contained cesium. The salt of the complex and the salt of iron are mixed thoroughly.

Furthermore, it is desirable to add the iron salt to the hexacyanoiron (II) acid complex salt in an amount greater than the stoichiometric amount by which the Prussian blue-type metal complex is produced.
Examples of the generation of the Prussian blue type metal complex include the following reaction formulas.

Thereby, the hexacyanoferrate (II) acid complex added and blended can be sufficiently formed in the cesium-containing filtrate into the Prussian blue-type metal complex used for removing cesium, and from the cesium-containing filtrate, 6, when separated into a cesium-containing precipitate and the treatment liquid, the amount of cyan remaining in the treatment liquid can be sufficiently reduced.
In addition, surplus iron ions after the Prussian blue-type metal complex is formed also precipitates as hydroxide when adjusted to an appropriate pH, for example, pH 8 to 9, in the reaction vessel 5, so that the final treatment liquid The remaining amount of cyanide and the amount of iron ions remaining in the environment also meet the wastewater standards according to the Ministry of the Environment Ordinance (final revision: Ministry of the Environment Ordinance No. 15 on May 23, 2012, Ministry Ordinance that sets wastewater standards: Water Pollution Control Law) It will be.
Therefore, no further treatment for removing cyan and iron from the treatment liquid is required, and the wastewater can be discharged as it is.

  After adding and blending each raw material of the Prussian blue type metal complex to the cesium-containing filtrate reaction tank 4, the pH of the Prussian blue type metal complex produced in the cesium-containing filtrate in the reaction tank 4 is preferably reduced, preferably the lowest. The pH of the liquid in the reaction vessel 5 is adjusted to a pH that results in Suitable pH is pH 4-11. Such pH can be determined depending on the composition of the resulting Prussian blue-type metal complex.

For adjusting the pH of the solution in the reaction vessel 5, an appropriate alkaline solution such as sodium hydroxide, potassium hydroxide, calcium hydroxide, or an inorganic acid solution such as hydrochloric acid, carbonic acid, nitric acid, sulfuric acid, or the like can be used. .
By adjusting the pH of the liquid in this way, the cesium adsorbed on the generated Prussian blue-type metal complex can be precipitated in the liquid.

  Since some precipitates generated in the liquid settle or float in a suspended state in the liquid, it is preferable to use a polymer in the reaction vessel 5 in order to efficiently separate them. A flocculant is added to aggregate the precipitate, and then the precipitate is separated into the precipitate and the treatment liquid in the precipitation tank 6.

  The polymer flocculant is not particularly limited as long as it can coagulate and precipitate the Prussian blue type metal complex, and any known polymer flocculant can be used.

  Moreover, the heavy metals such as lead dissolved in the filtrate F1 are adjusted to adjust the pH of the reaction tank 5 to the above range, so that the solubility of the dissolved heavy metals is lowered and the heavy metal hydroxide is precipitated. By adding the polymer flocculant, the suspended heavy metal, finely divided heavy metal or hydroxide heavy metal can be aggregated. Thereby, in the sedimentation tank 6, a heavy metal containing deposit is isolate | separated as a deposit with the said cesium containing deposit.

  In addition, the reaction tank 4 and the reaction tank 5 may be used as one reaction tank, and the above processing may be performed sequentially or as separate reaction tanks.

The slurry is put into the settling tank 6 and allowed to stand for a predetermined time to settle and separate the slurry, and separated into a solid content (slurry) containing a precipitate and a supernatant.
If necessary, the precipitate may be subjected to solid-liquid separation and dehydration using a filter (for example, a filter press).
Further, if necessary, water W may be introduced into the filter, and water containing soluble components remaining in the precipitate may be washed with water W. This washing with water W can be performed efficiently with a small amount of water by pumping the water W from one direction to the precipitate in a state where the filter is pressurized.

  The means for separating the precipitate and the treatment liquid in the precipitation tank 6 is not particularly limited, and for example, filtration means such as pressure filtration, suction filtration, and centrifugal separation can be applied. Next, the treatment liquid is fed into the buffer tank 8, acid or alkali is added for discharge, the pH is adjusted, and the liquid is discharged.

  The cesium-containing precipitate obtained in the sedimentation tank 6 contains cesium at a high concentration. The cesium-containing sediment is returned to the dissolution tank 1 by the transport device 7 and mixed with the desalted dust solids. By being collected as a dehydrated cake, the cesium concentration and the resulting radioactive cesium concentration are lowered to facilitate handling and collection.

  In addition, in the slurrying step in the dissolution tank 1 when the cesium-containing precipitate is fed into the dissolution tank 1, as necessary, a salt of a hexacyanoiron (II) acid complex, an iron salt, and Is added to the dissolution tank 1 to form a Prussian blue-type metal complex in the slurry, and the remaining cesium is converted into a cesium precipitate. The slurry is filtered and solid-liquid separated in the next filtration step, and then precipitated. Can also be separated.

(4) Discharge treatment step In the treatment liquid separated in the settling tank 6, cyanide and iron derived from the salt of hexacyanoiron (II) acid complex added and blended to form the Prussian blue type metal complex. The remaining amount sufficiently satisfies the wastewater standard of the Ministry of the Environment Ordinance (Ministry of the Environment Ordinance No. 15 on May 23, 2012), and can be discharged safely and environmentally.
Therefore, it is not particularly necessary to perform further processing for removing cyan from the processing liquid, that is, processing for satisfying the above drainage standard for discharge.

  Specifically, at the time of discharge, as shown in FIG. 3, the processing liquid from the buffer tank 8 may be discharged as it is (FIG. 3 (a)), and further passed through the MF membrane device 9 for discharge. (FIG. 3B). Furthermore, the concentrated solution may be discharged by passing through the RO membrane or the ion exchange membrane device 10, and the permeate may be sent to the buffer tank 11 and circulated through the dissolution tank 1 to be reused (FIG. 3 ( c)).

B. The case where selenium is included will be described with reference to FIG.
(1) Dissolution Step The dissolution step is performed according to the A. above. The same treatment as in the dissolution step when selenium is not included is performed.
However, the dissolution tank 1 is returned with the cesium-containing precipitate obtained in the subsequent precipitation tank 6 and the heavy metal-containing precipitate other than cesium, and is mixed with water W together with desalted dust to be slurried. However, the selenium-containing precipitate is included in the heavy metal-containing precipitate.

(2) Filtration process (precipitate collection process)
The filtration treatment step is performed according to the above A.1. The same treatment as in the dissolution step when selenium is not included is performed.
However, the obtained dehydrated cake solid content includes desalted dust solid content, cesium-containing precipitate returned to the dissolution tank 1 from the precipitation tank 6, selenium-containing precipitate, and other heavy metal precipitates. Will be.

(3) Cesium-containing precipitates, selenium-containing precipitates, and other heavy metal-containing precipitate generation steps The filtrate F1 discharged from the filter 2 contains chlorine, cesium, selenium, lead, etc. contained in the desalted dust Ingredients such as heavy metals are dissolved.
The filtrate F1 discharged from the filter 2 is fed into the reaction tank 4. Before being transferred to the reaction tank 4, it may be once sent into the buffer tank 3 and then into the reaction tank 4.

Other heavy metals such as cesium, selenium, and lead are dissolved in the filtrate from the filtration step, and the pH of the filtrate F1 is 9-13.
The cesium-containing filtrate is conveyed to the reaction vessel 4 and a pH adjuster, a ferrous salt and a hexacyanoferrate (II) acid complex salt are added and blended. A pH adjuster is added to the reaction vessel 4 and the pH of the reaction vessel 4 is adjusted to 3-6.
An inorganic acid solution such as carbonic acid, hydrochloric acid, nitric acid or sulfuric acid can be used to adjust the pH of the filtrate in the reaction tank 4.

In the reaction tank 4, selenium dissolved in the filtrate reacts with the ferrous salt by the action of ferrous iron, which is a reducing agent, to deposit selenium.
In this reaction, selenium is reduced and precipitated by ferrous salt, while part of the ferrous salt is oxidized by selenium to become ferric ions.
Although the specific mechanism of selenium precipitation is not clear, reduced selenium precipitates as fine-grained metal selenium and precipitates, and reduced selenium precipitates as poorly water-soluble hydroxide or reduced selenium. May be adsorbed on iron salts and precipitated.
The ferrous salt is preferably selected from the group consisting of ferrous chloride, ferrous sulfate and ferrous nitrate.

In the reduction reaction of selenium and ferrous salt, ferric ions produced by oxidation of a part of the ferrous salt by selenium and surplus ferrous ions are produced in the reaction tank 4. A Prussian blue-type metal complex is formed with the salt of the hexacyanoferrate (II) acid complex added to.
The Prussian blue-type metal complex formed in the filtrate adsorbs cesium contained in the filtrate.

That is, in the present invention, a pH adjusting agent is added to the reaction vessel 4 to adjust the pH to 3 to 6, and the salt of hexacyanoferrate (II) acid complex and ferrous salt are added to the reaction vessel. 4 Prussian blue-type metal complex is formed in the cesium-containing filtrate from ferric ions generated by oxidation with selenium added and mixed with excess ferrous ions, and the resulting Prussian blue The cesium in the filtrate is adsorbed on the type metal complex.
The Prussian blue-type metal complex has a property of adsorbing cations such as cesium. However, in the present invention, the Prussian blue-type metal complex prepared in advance is not added to the cesium-containing filtrate, but cesium. By forming a Prussian blue-type metal complex in a filtrate containing cesium, it is possible to remove cesium as a precipitate more effectively than a method of adding and blending a pre-generated Prussian blue-type metal complex into a cesium filtrate. is there.

  A salt of a hexacyanoferrate (II) acid complex used as a Prussian blue-type metal complex raw material, which is added and blended so that a Prussian blue-type metal complex is produced in a cesium-containing filtrate, is used for the treatment of the filtrate containing cesium. Examples include potassium hexacyanoferrate (II) and / or sodium hexacyanoferrate (II).

The Prussian blue-type metal complex produced in these cesium-containing liquids can adsorb and remove cesium from the cesium-containing filtrate very efficiently.
Further, for example, hexacyanoferrate (II) acid as a Prussian blue-type metal complex raw material so that the amount of Prussian blue-type metal complex produced in the cesium-containing filtrate can sufficiently adsorb the contained cesium. The salt of the complex and the ferrous salt used for the reduction reaction of selenium are sufficiently mixed.

In addition to an amount sufficient to reduce dissolved selenium, the ferrous salt is composed of the Prussian blue-type metal by the salt of the hexacyanoiron (II) acid complex and the generated ferric ion. It is desirable to add in an amount greater than the stoichiometric amount by which the complex is formed by reaction.
Examples of the generation of the Prussian blue type metal complex include the following reaction formulas.

  Thereby, the hexacyanoferrate (II) acid complex added and blended can be sufficiently formed in the cesium-containing filtrate into the Prussian blue-type metal complex used for removing cesium, and from the cesium-containing filtrate, 6, when separated into a cesium-containing precipitate and the treatment liquid, the amount of cyan remaining in the treatment liquid can be sufficiently reduced.

Further, surplus iron ions after the Prussian blue-type metal complex is formed also precipitates as hydroxide when adjusted to an appropriate pH in the reaction tank 5, so that cyan cyan remaining in the final treatment liquid remains. The remaining amount of iron and the amount of iron ions will also meet the wastewater standards according to the Ordinance of the Ministry of Environment (final revision: Ordinance of the Ministry of the Environment No. 15 on May 23, 2012, the Ordinance for Establishing Wastewater Standards: Water Pollution Control Law)
Therefore, no further treatment for removing cyan and iron from the treatment liquid is required, and the wastewater can be discharged as it is.

  In the reaction tank 5, the pH of the liquid in the reaction tank 5 is adjusted to a pH at which the solubility of the Prussian blue-type metal complex produced in the cesium-containing filtrate in the reaction tank 4 is reduced, preferably to the lowest pH. Suitable pH is pH 4-11. Such pH can be determined depending on the composition of the resulting Prussian blue-type metal complex.

For adjusting the pH of the solution in the reaction vessel 5, an appropriate alkaline solution such as sodium hydroxide, potassium hydroxide, calcium hydroxide, or an inorganic acid solution such as hydrochloric acid, carbonic acid, nitric acid, sulfuric acid, or the like can be used. .
By adjusting the pH of the liquid in this manner, the cesium adsorbed on the generated Prussian blue-type metal complex can be precipitated in the liquid, and excess iron or the like is removed as iron hydroxide. be able to.

  Since some precipitates generated in the liquid settle or float in a suspended state in the liquid, it is preferable to use a polymer in the reaction vessel 5 in order to efficiently separate them. A flocculant is added to aggregate the precipitate, and then the precipitate is separated into the precipitate and the treatment liquid in the precipitation tank 6.

  The polymer flocculant is not particularly limited as long as it can coagulate and precipitate a Prussian blue type metal complex, selenium or the like, and any known polymer flocculant can be used.

  Furthermore, heavy metals such as lead are dissolved in the filtrate F1. By adjusting the pH of the reaction vessel 5 to the above range, these heavy metals such as lead decrease the solubility of the dissolved heavy metal, precipitate heavy metal hydroxide, and add the polymer flocculant. Thus, suspended heavy metal, finely divided heavy metal and hydroxide heavy metal can be aggregated. Thus, the heavy metal-containing precipitate is separated as a precipitate together with the cesium-containing precipitate and the selenium-containing precipitate in the precipitation tank 6.

  In addition, the reaction tank 4 and the reaction tank 5 may be used as one reaction tank, and the above processing may be performed sequentially or as separate reaction tanks.

The slurry is put into the settling tank 6 and allowed to stand for a predetermined time to settle and separate the slurry, and separated into a solid content (slurry) containing a precipitate and a supernatant.
If necessary, the precipitate may be subjected to solid-liquid separation and dehydration using a filter (for example, a filter press).
Further, if necessary, water W may be introduced into the filter, and water containing soluble components remaining in the precipitate may be washed with water W. This washing with water W can be performed efficiently with a small amount of water by pumping the water W from one direction to the precipitate in a state where the filter is pressurized.

  The means for separating the precipitate and the treatment liquid in the precipitation tank 6 is not particularly limited, and for example, filtration means such as pressure filtration, suction filtration, and centrifugal separation can be applied. Next, the treatment liquid is fed into the buffer tank 8, acid or alkali is added for discharge, the pH is adjusted, and the liquid is discharged.

  The cesium-containing precipitate contained in the precipitate obtained in the sedimentation tank 6 contains cesium at a high concentration, and is returned to the dissolution tank 1 by the transport device 7 and mixed with the desalted dust solids. Then, the cesium concentration and the resulting radioactive cesium concentration are lowered by being collected as a dehydrated cake by the filtration device 2 to facilitate handling and collection.

  In addition, in the slurrying step in the dissolution tank 1 when the cesium-containing precipitate is fed into the dissolution tank 1, if necessary, a ferrous salt and a hexacyanoferrate (II) acid complex To form a Prussian blue-type metal complex in the slurry, and the remaining cesium is converted into a cesium precipitate, and the slurry is filtered and solid-liquid separated and separated as a precipitate in the next filtration process step. You can also.

(Discharge treatment process)
The discharge treatment step is performed according to the above A.1. The same treatment as in the dissolution step when selenium is not included is performed.

  Thus, in the present invention, cesium can be efficiently removed, and as a result, it is possible to sufficiently infer that radioactive cesium contained as a part of cesium is also efficiently removed, and radioactive It becomes possible to remove radioactive cesium from desalted dust containing cesium extremely effectively, simply and safely.

The present invention is illustrated by the following examples and test examples, but is not limited thereto.
[Raw materials]
(1) Demineralized dust and demineralized dust containing cesium (including selenium) were used. The radioactive concentrations of cesium Cs-134 and Cs-137 contained in the desalted dust were 1925 Bq / kg and 3417 Bq / kg, respectively.
・ Desalted dust containing cesium (not containing selenium) was used. The radioactive concentrations of cesium Cs-134 and Cs-137 contained in the desalted dust were 1780 Bq / kg and 2825 Bq / kg, respectively.
(2) Water Ion exchange water was used.
(3) Hydrochloric acid Special grade hydrochloric acid (35%) manufactured by Wako Pure Chemical Industries, Ltd. was used.
(4) Ferrous chloride solution FeCl ₂ .4H ₂ O (molecular weight 179, manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in pure water to prepare a 32 wt% solution.
(5) Hexacyanoferrate (II) potassium solution K ₄ [Fe (CN) ₆ ] · 3H ₂ O (molecular weight 422.39, manufactured by Kishida Chemical Co., Ltd.) dissolved in pure water to give a 0.5 mol / L solution Adjusted to use.
(6) Polymer flocculant Acofloc A150 (manufactured by MT Aqua Polymer Co., Ltd.) was used.
(7) Sodium hydroxide Reagent grade 1 (made by Yoneyama Pharmaceutical Co., Ltd.) was used.
(7) Ferric sulfate solution Fe ₂ (SO ₄ ) ₃ · 7H ₂ O (molecular weight 526, manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in pure water to prepare a 1 mol / L solution.

(8) Sodium hydroxide solution Special grade 1N solution (manufactured by Wako Pure Chemical Industries, Ltd.) was used.
(9) Zeolite Natural zeolite Zeophil 1424 # (manufactured by Shinto Chemical Co., Ltd.) was used.
(10) Bentonite Kunigel 1 (Kunimine Kogyo Co., Ltd.) was used.

(Examples 1 to 3, Comparative Example 1)
The desalted dust (including selenium) and ion-exchanged water were mixed at a mass ratio of 1: 5 and stirred to obtain 4300 g of a desalted dust slurry (stock solution) (corresponding to the dissolution tank 1).
Next, the desalted dust slurry was filtered with a Buchner funnel (φ150 mm) to obtain a desalted dust filtrate F1 (corresponding to the filtration device 2).
The following processes were performed using 0.5 L in 2.9 L of the obtained filtrate.
The concentration of selenium contained in the filtrate was 1.5 ppm.

Next, the hydrochloric acid solution was added to 0.5 L of the filtrate to adjust the pH to 3.
5 mL of the ferrous chloride solution (32 wt%) was added to the pH 3 filtrate, and the potassium hexacyanoferrate (II) solution was added with 0 ml (Comparative Example 1), 2 ml (Example 1), 4 ml ( Example 2), 8 ml (Example 3) was added and mixed, and the mixture was stirred for 30 minutes to react (corresponding to reaction tank 4).

Next, sodium hydroxide is added to adjust the pH to about 9.5, and 5 to 10 ppm of Aflock A150, which is a polymer flocculant (corresponding to the reaction tank 5), is left to stand to precipitate or float. The product was allowed to settle (corresponding to reaction vessel 6).
Subsequently, it filtered with a 0.45 micrometer membrane membrane, and measured the cesium radioactivity density | concentration, cyan density | concentration, and selenium density | concentration in each obtained filtrate (processing liquid). The results are shown in Table 1.

The cesium radioactivity concentration was measured using the following method.
・ Analytical equipment: Germanium semiconductor nuclide analyzer manufactured by Canberra Japan ・ Detection unit: HPGe semiconductor detector (GC4020)
・ Analysis method: Radioactivity measurement method series 7 “Gamma-ray spectrometry using germanium semiconductor detector” (Ministry of Education, Culture, Sports, Science and Technology)
・ Conditions: Measurement with U-8 container, measurement time 30 seconds

The cyan density was measured using the following method.
・ Analytical instrument: ICP mass spectrometer (manufacturer: Perkin Elmer),
Model: ELAN DRC-e
・ Performance: Mass range 1-270amu
-Detection part: Two-stage discrete type-Analysis method: ICP mass spectrometry-Conforms to JIS K 0102-38.8

The selenium concentration was measured using the following method.
・ Analyzer: Z-2010 manufactured by Hitachi High-Technology Corporation
・ Hydrogen compound generation atomic absorption method (according to JIS K0102 67.2)

(Examples 4-7, Comparative Example 2)
The desalted dust (including selenium) and ion-exchanged water were mixed at a mass ratio of 1: 5 and stirred to obtain 4300 g of desalted dust slurry (corresponding to dissolution tank 1).
Next, the desalted dust slurry was filtered with a Buchner funnel (φ150 mm) to obtain a desalted dust filtrate F1 (corresponding to the filtration device 2).
The following processes were performed using 0.5 L in 2.9 L of the obtained filtrate.
The concentration of selenium contained in the filtrate was 1.5 ppm.

Next, the hydrochloric acid solution was added to 0.5 L of the filtrate to adjust the pH to 3.
5 mL of the ferrous chloride solution (32 wt%) was added to the pH 3 filtrate, and the potassium hexacyanoferrate (II) solution was added with 0 ml (Comparative Example 2), 10 ml (Example 4), 20 ml ( Example 5), 30 ml (Example 6), 40 ml (Example 7) were added and mixed, and the mixture was stirred for 30 minutes to react (corresponding to the reaction tank 4).

Next, sodium hydroxide is added to adjust the pH to about 9.5, and 5 to 10 ppm of Aflock A150, which is a polymer flocculant (corresponding to the reaction tank 5), is left to stand to precipitate or float. The product was allowed to settle (corresponding to reaction vessel 6).
Subsequently, it filtered with a 0.45 micrometer membrane membrane, and measured the cesium density | concentration, cyan density | concentration, and selenium density | concentration in each obtained filtrate (processing liquid). The results are shown in Table 2.
The concentrations of cesium, cyan and selenium were measured using the same method as in Example 1.

(Examples 8 to 10, Comparative Example 3)
The desalted dust (not containing selenium) and ion-exchanged water were mixed at a mass ratio of 1: 5 and stirred to obtain 4300 g of desalted dust slurry (corresponding to the dissolution tank 1).
Next, the desalted dust slurry was filtered with a Buchner funnel (φ150 mm) to obtain a desalted dust filtrate F1 (corresponding to the filtration device 2).
The following processes were performed using 0.5 L in 2.9 L of the obtained filtrate.

Next, the hydrochloric acid solution was added to 0.5 L of the filtrate to adjust the pH to 9.5.
To the filtrate of pH 9.5, 0 ml (Comparative Example 3), 20 ml (Example 8), 30 ml (Example 9) of the potassium hexacyanoferrate (II) solution and the ferric sulfate solution (1 mol / L), respectively. ), 40 ml (Example 10) were added and mixed, and the mixture was stirred for 30 minutes to react (corresponding to the reaction tank 4).

Next, sodium hydroxide is added to adjust the pH to about 9.5, and 5 to 10 ppm of Aflock A150, which is a polymer flocculant (corresponding to the reaction tank 5), is left to stand to precipitate or float. The product was allowed to settle (corresponding to reaction vessel 6).
Subsequently, it filtered with a 0.45 micrometer membrane membrane, and measured the cesium density | concentration and the selenium density | concentration in each obtained filtrate (processing liquid). The results are shown in Table 3.
The concentrations of cesium and cyan were measured using the same method as in Example 1.

(Comparative Examples 4-7)
The desalted dust (including selenium) and ion-exchanged water were mixed at a mass ratio of 1: 5 and stirred to obtain 4300 g of desalted dust slurry (corresponding to dissolution tank 1).
Next, the desalted dust slurry was filtered with a Buchner funnel (φ150 mm) to obtain a desalted dust filtrate F1 (corresponding to the filtration device 2).
The following processes were performed using 0.5 L in 2.9 L of the obtained filtrate.
The concentration of selenium contained in the filtrate was 1.5 ppm.

  Next, the pH of the filtrate was adjusted to 9.5 using the above sodium hydroxide solution in 0.5 L of the filtrate, and the zeolite was adjusted to 2.5 g / L (Comparative Example 4), 5 g / L (Comparative Example 5), 10 g / L. (Comparative Example 6), 15 g / L (Comparative Example 7) was added and mixed, and stirred for 30 minutes (corresponding to a reaction vessel).

Next, 5 to 10 ppm of Aflock A150, which is a polymer flocculant, was added (corresponding to the reaction tank 5), and allowed to stand to precipitate sediment and suspended matter (corresponding to the reaction tank 6).
Subsequently, it filtered with a 0.45 micrometer membrane membrane, and measured the cesium density | concentration, cyan density | concentration, and selenium density | concentration in each obtained filtrate (processing liquid). The results are shown in Table 4.
The concentrations of cesium, cyan and selenium were measured using the same method as in Example 1.

(Comparative Examples 8-11)
Except that bentonite was used instead of zeolite, it was carried out in the same manner as Comparative Examples 4 to 7 (Bentonite 2.5 g / L (Comparative Example 8), 5 g / L (Comparative Example 9), 10 g / L (Comparative) Example 10), 15 g / L (Comparative Example 11)).
The cesium concentration, cyan concentration, and selenium concentration in each obtained filtrate (treatment solution) were measured. The results are shown in Table 5.

  INDUSTRIAL APPLICABILITY The present invention can be applied to desalinated dust containing cesium produced by an alkali bypass facility or a chlorine bypass facility in a cement production facility when cement is produced using industrial waste or disaster waste. Therefore, cesium and the like can be easily and efficiently removed, and thus radioactive cesium can also be effectively removed.

DESCRIPTION OF SYMBOLS 1 ... Dissolution tank 2 ... Filtration apparatus 3, 8, 11 ... Buffer tank 4, 5 ... Reaction tank 6 ... Precipitation tank 7 ... Conveyance apparatus 9 ... Microfiltration membrane ( MF) device 10 ... ion exchange membrane or reverse osmosis membrane (RO) device

Claims (7)

A step of adding water to demineralized dust containing cesium to form a slurry, a step of filtering the slurry and separating it into solid and liquid, and a cesium-containing filtrate having a pH of 9 to 13 and containing no selenium, A second salt selected from the group consisting of a salt of hexacyanoferrate (II) that is potassium iron (II) and / or sodium hexacyanoferrate (II) and ferric chloride, ferric sulfate, and ferric nitrate. Add the iron salt and mix in the filtrate

Forming a Prussian blue-type metal complex according to the reaction formula, and adjusting the pH in the filtrate so as to reduce the solubility of the Prussian blue-type metal complex to form a cesium-containing precipitate, the cesium-containing precipitate A method for treating desalted dust containing cesium, comprising a step of separating a precipitate containing a product. A step of adding water to a desalted dust containing cesium to form a slurry, a step of filtering the slurry and performing solid-liquid separation, and a cesium-containing filtrate having a pH of 9 to 13 and containing selenium in the hexacyano iron (II) From the group consisting of a salt of hexacyanoferrate (II) which is potassium acid and / or sodium hexacyanoferrate (II) and ferrous chloride, ferrous sulfate and ferrous nitrate Add and blend the selected ferrous salt and pH adjuster to adjust the pH of the filtrate to 3-6, react selenium and ferrous salt in the filtrate to precipitate selenium, In the filtrate, the following formula is obtained by the reaction of ferric ions produced by oxidation of part of the ferrous salt with selenium and excess ferrous salt.

Forming a Prussian blue-type metal complex according to the reaction formula, and adjusting the pH in the filtrate so as to reduce the solubility of the Prussian blue-type metal complex to form a cesium-containing precipitate, the cesium-containing precipitate A method for treating desalted dust containing cesium, comprising a step of separating a precipitate containing a product.   The method for treating desalted dust containing cesium according to claim 1 or 2, wherein the precipitate containing the cesium-containing precipitate is circulated back into the step of adding water to the desalted dust to form a slurry. A method for treating desalted dust containing cesium, wherein the precipitate is separated in a step of filtration and solid-liquid separation.   The method for treating desalted dust containing cesium according to any one of claims 1 to 3, wherein in the step of adding water to the desalted dust containing cesium to form a slurry, the hexacyanoferrate (II) acid complex In the step of adding a salt and an iron salt to form a Prussian blue-type metal complex in the slurry, forming a cesium-containing precipitate in the slurry, and filtering the slurry for solid-liquid separation A method for treating desalted dust containing cesium, characterized by separating as a precipitate. Dissolution tank for a slurry desalted dust containing cesium is mixed with water, filtration device, a cesium-containing filtrate obtained pH9~13 to obtain cesium containing filtrate the slurry to solid-liquid separation filtration hexacyanoferrate to the filtrate containing no selenium (II) potassium and / or hexacyanoferrate (II) hexacyanoferrate (II) salt and the ferric chloride acid complex is sodium, ferric sulfate, ferric nitrate The ferric salt selected from the group consisting of:

A reaction vessel for forming a Prussian blue-type metal complex according to the reaction formula shown below, adding a pH adjuster and a polymer flocculant to form a precipitate containing a cesium-containing precipitate, and a precipitate containing a cesium-containing precipitate An apparatus for treating desalted dust containing cesium, comprising: a sedimentation tank for separating a product. Dissolution tank for a slurry desalted dust containing cesium is mixed with water, filtration device, a cesium-containing filtrate obtained pH9~13 to obtain cesium containing filtrate the slurry to solid-liquid separation filtration From the salt of hexacyanoferrate (II) that is potassium hexacyanoferrate (II) and / or sodium hexacyanoferrate (II) and ferrous chloride, ferrous sulfate, ferrous nitrate to the filtrate containing selenium A ferrous salt selected from the group and a pH adjuster are added and blended, the pH of the filtrate is adjusted to 3-6, and the selenium and ferrous salt in the filtrate are reacted to form selenium. In the filtrate, the following formula is obtained by the reaction of ferric ions formed by oxidizing part of the ferrous salt with selenium and the excess ferrous salt.

A reaction vessel for forming a Prussian blue-type metal complex according to the reaction formula shown below, adding a pH adjuster and a polymer flocculant to form a precipitate containing a cesium-containing precipitate, and a precipitate containing a cesium-containing precipitate An apparatus for treating desalted dust containing cesium, comprising: a sedimentation tank for separating a product.   The apparatus for treating desalted dust containing cesium according to claim 5 or 6, further comprising a transport facility for circulating the cesium-containing precipitate recovered from the sedimentation tank to the dissolution tank. Desalination dust processing equipment.

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