JP2014199187A - Apparatus for processing contaminated fly ash, and processing method of contaminated fly ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for processing contaminated fly ash, in which eluted radioactive cesium is adsorbed with high efficiency after washing radiation contaminated fly ash with a water solvent.SOLUTION: An apparatus 10A for processing contaminated fly ash includes: a contaminated fly ash depositing unit 11 in which contaminated fly ash of radioactive cesium is deposited; a washing water infusion unit 12 into which washing water is infused; an elution unit 13 in which the deposited contaminated fly ash is mixed with the infused washing water to elute cesium; a solid-liquid separation unit 14A in which a suspension liquid containing the fly ash from which cesium is eluted and the water, is separated into a solid phase and a liquid phase; a cesium water solution collecting unit 15 in which a cesium water solution separated as the liquid phase is collected; a neutralizer adding unit 16A which adds a neutralizer into the elution unit 13; and a cesium adsorption unit 17 in which cesium is adsorbed and eliminated from the cesium water solution.

Description

  The present invention relates to a technology for treating contaminated fly ash that removes cesium contained in fly ash.

When radioactive materials are released to the outside as a result of an accident at a nuclear power plant, the pollution diffuses into the environment. Of these diffusing radioactive materials, radioactive cesium is diffused in the form of gas and fine particles, so there is a concern that contaminants will be distributed over a wide range.
Among these radioactive cesiums, ¹³⁷ Cs, which has a half-life of 30 years, emits strong radiation and has the property of staying in the living body and being easily concentrated by the food chain. There are concerns about giving.

On the other hand, waste such as sludge in a sewage treatment plant is incinerated to reduce the discharge amount, but the contained radioactive cesium is concentrated.
In the incineration plant, high-temperature treatment is performed, so the cesium salt with a low melting point / boiling point becomes a gas and moves to the upper part of the incinerator, where it is condensed and deposited at the temperature below the boiling point, and is recovered as fly ash. . Since the cesium salt contained in this fly ash is water-soluble, if it is buried as it is, it will come into contact with rainwater or seawater and be easily released to the environment, and there is a concern about further expansion of pollution.
For this reason, establishment of the processing technique which removes cesium from radioactively contaminated fly ash is required before burying disposal.

Various methods have been proposed in the past for techniques for removing metal ions from a solid phase (for example, Patent Document 1).
On the other hand, radioactively contaminated substances are decontaminated by washing with an aqueous solvent and eluting the radionuclide, and the aqueous solvent eluting the radionuclide is decontaminated by passing through a filter made of an adsorbent such as zeolite. A method has been proposed in which the radionuclide-concentrated adsorbent is stabilized and then discarded.

JP-A-6-23340

However, when trying to decontaminate radioactively contaminated fly ash using the method described in Patent Document 1, the pollutant that adsorbs radioactive cesium contained in this contaminated fly ash is newly discharged. Therefore, there is a problem that radioactive waste increases.
In addition, the method of washing radioactively contaminated fly ash with an aqueous solvent has a problem that the adsorption efficiency in an adsorbent such as zeolite is lowered because the aqueous solvent from which radioactive cesium is eluted becomes a strong alkali.

  The present invention has been made in view of such circumstances, and provides a treatment technology for contaminated fly ash that adsorbs the radioactive cesium eluted with high efficiency after washing the radioactively contaminated fly ash with an aqueous solvent. Objective.

  In the processing apparatus for contaminated fly ash according to the present invention, a contaminated fly ash injection unit for introducing radioactive cesium contaminated fly ash, a cleaning water injection unit for injecting cleaning water, the injected contaminated fly ash and the injected The washing phase was mixed to elute cesium, the fly ash eluted from the cesium and the solid-liquid separation part for separating the suspension of water into a solid phase and a liquid phase, and the liquid phase. A cesium aqueous solution recovery part for recovering a cesium aqueous solution; a neutralizer addition part for adding a neutralizing agent to the elution part or the cesium aqueous solution recovery part; and a cesium adsorption part for adsorbing and removing cesium from the cesium aqueous solution. It is characterized by that.

  INDUSTRIAL APPLICABILITY According to the present invention, there is provided a technology for treating contaminated fly ash that adsorbs radioactive cesium eluted with high efficiency after washing radioactively contaminated fly ash with an aqueous solvent.

The block diagram which shows 1st Embodiment of the processing apparatus of the contaminated fly ash which concerns on this invention. The flowchart which shows 1st Embodiment of the processing method of the pollution fly ash which concerns on this invention. The graph which shows the relationship between the liquid-solid ratio of washing water and contaminated fly ash, and the elution rate of radioactive cesium. The graph which shows the relationship between the temperature of washing water, and the elution rate of radioactive cesium. The graph which shows the distribution coefficient of a cesium adsorption agent (mordenite) with respect to the hydrogen ion concentration (pH) of a cesium aqueous solution. The graph which shows the measured value of the radioactivity of the liquid in the inlet_port | entrance and exit of an adsorption | suction part, when letting radioactive cesium aqueous solution pass through the adsorption | suction part filled with mordenite. The block diagram which shows 2nd Embodiment of the processing apparatus of the contaminated fly ash which concerns on this invention. The flowchart which shows 2nd Embodiment of the processing method of the contaminated fly ash which concerns on this invention. The graph which shows the separation rate at the time of processing the suspension of fly ash and water in the solid-liquid separation part applied to 2nd Embodiment.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the contaminated fly ash treatment apparatus 10A according to the first embodiment includes a contaminated fly ash injection unit 11 that injects radioactive cesium contamination fly ash, a cleaning water injection unit 12 that injects cleaning water, The elution part 13 for mixing the injected contaminated fly ash and the injected washing water to elute cesium, and the solid-liquid separation part for separating the suspension of fly ash and water eluted by cesium into a solid phase and a liquid phase 14A, a cesium aqueous solution recovery unit 15 that recovers a cesium aqueous solution separated as a liquid phase, a neutralizer addition unit 16A that adds a neutralizer to the elution unit 13, and a cesium adsorption unit that adsorbs and removes cesium from the cesium aqueous solution 17.

  Radioactive cesium-contaminated fly ash is, for example, general waste because the radioactive concentration of cesium (Bq; becquerel) exceeds the standard value among the fly ash generated by incineration of sludge generated at sewage treatment plants. It refers to fly ash that is impossible to do.

  Incineration ash generated by incineration of sludge, etc., is solid particulate matter floating in the incineration exhaust gas, and fly ash (fly ash) collected in a dust collector, boiler, gas cooling chamber, recombustion chamber, etc. The main ash (bottom ash) recovered from the bottom of the incinerator is roughly classified.

And incineration ash (fly ash and main ash) is enriched with elements derived from minerals such as Na, K, Mg, Ca, Fe, Zn, Al, Si, Pb, P, S, etc. Yes.
Radiocesium diffused in the environment due to a nuclear accident and contained in sludge, etc. in water treatment plants is also concentrated in the same way, and after cooling the cesium salt during vaporization, it is cooled and condensed and deposited. There is a tendency to further concentrate in the ash.

Washing water can be easily obtained such as pure water, tap water, rain water, ground water, river water, etc., and the water source is not particularly limited.
Further, the cleaning water recovered by the cleaning water recovery unit 23 can be transferred to the cleaning water injection unit 12 and repeatedly used.

  The elution unit 13 mixes the introduced contaminated fly ash and the injected wash water while stirring with the stirrer 21 to elute the cesium contained in the contaminated fly ash into the wash water. Moreover, you may install a baffle plate (not shown) in the elution part 13 so that fly ash and washing water may be mixed well.

The graph of FIG. 3 shows the relationship between the liquid-solid ratio of the washing water and the contaminated fly ash and the elution rate of radioactive cesium after the stirring treatment.
The elution rate is expressed by the following formula (1).
Elution rate (%) = (1− (contamination amount of fly ash before washing [Bq / kg] / contamination amount of fly ash after washing [Bq / kg])) × 100 (1)

  As experimental conditions, the liquid-solid ratio, which is the mixing ratio of the wash water and contaminated fly ash contained in the elution unit 13, is set to 4, 10, 20, 50 mL / g, the temperature is set to room temperature, and the elution (stirring) time is set. Set to 10 minutes.

The amount of contamination of fly ash after washing was measured at each liquid-solid ratio, and the elution rate was derived based on the formula (1). When the liquid-solid ratio was 4 mL / g, the elution rate was 84% and the liquid-solid ratio was 10 mL. An elution rate of 90% was obtained at / g, an elution rate of 82% at a liquid / solid ratio of 20 ml / g, and an elution rate of 88% at a liquid / solid ratio of 50 mL / g.
From the above results, it was confirmed that an elution rate of 80% or more was obtained at a liquid-solid ratio of 4 mL / g or more.

The graph of FIG. 4 shows the relationship between the temperature of the washing water injected into the elution part 13 and the elution rate of radioactive cesium.
As experimental conditions, the temperature of washing water was set to room temperature (20 ° C.) and 50 ° C., the liquid-solid ratio of washing water and contaminated fly ash was set to 20 mL / g, and the elution (stirring) time was set to 10 minutes. .

The amount of contamination of fly ash after washing was measured at each liquid-solid ratio, and when the elution rate was derived based on the above formula (1), the elution rate was 82% at room temperature (20 ° C.), When the temperature of the washing water was 50 ° C., an elution rate of 89% was obtained.
From the result of FIG. 4, it was confirmed that the elution rate of 80% or more can be obtained for the washing water by setting the temperature to 20 ° C. or higher. Therefore, the washing water may be injected into the elution unit 13 while maintaining the room temperature.

By treating the contaminated fly ash in this way, 80% or more of radioactive cesium is eluted in the wash water, but mineral-derived Na, K, Mg, Ca, Fe, Zn, Al, Si, Pb, P, Elements such as S are also eluted at a predetermined ratio.
For this reason, the suspension of fly ash and water after being stirred in the elution part 13 exhibits strong alkalinity.

Therefore, the neutralizing agent is added from the neutralizing agent addition unit 16 to the fly ash and water suspension of the elution unit 13. The neutralizing agent can be appropriately used as long as it exhibits acidity, but it is desirable that the neutralizing agent be a strong acid in order to reduce the addition amount.
When an acid is added to the suspension of fly ash and water as a neutralizing agent, the above-described mineral-derived elements precipitate as salts.

The solid-liquid separation unit 14A receives the supply of the suspension after adding the neutralizing agent and reacting it with the pump power from the elution unit 13, and separates it into a solid phase and a liquid phase. Fly ash and salt deposits are separated from the solid phase, and an aqueous solution of radioactive cesium is separated from the liquid phase.
The solid-liquid separation unit 14A is exemplified by a filter press, filtration, sedimentation separation, a centrifugal dehydrator, and the like, but may be appropriately employed as long as the liquid phase and the solid phase are separated without remaining.

In the solid content collection tank 22A, a solid phase composed of decontaminated fly ash and salt precipitate (mineral component) is collected. This solid phase can be disposed of as it is because the radioactive concentration of radioactive cesium (Bq; becquerel) is below the reference value.
The cesium aqueous solution recovery unit 15 recovers the cesium aqueous solution separated as a liquid phase.
In the first embodiment, the cesium aqueous solution recovered by the cesium aqueous solution recovery unit 15 is already prepared to be neutral.

The cesium adsorption unit 17 is filled with an adsorbent (zeolite or the like) that can adsorb and remove cesium from a cesium aqueous solution. The adsorbent is not particularly limited as long as it can adsorb cesium from an aqueous solution.
Examples of the zeolite include mordenite-type zeolite, chabazite-type zeolite, clinoptilolite-type zeolite, A-type zeolite, Y-type zeolite, and X-type zeolite. Among these, mordenite-type is preferably used.

FIG. 5 shows the distribution coefficient of the cesium adsorbent (mordenite) with respect to the hydrogen ion concentration (pH) of the cesium aqueous solution.
The partition coefficient is represented by a ratio between the radioactive cesium concentration of the cesium aqueous solution and the cesium concentration of the adsorbent. The higher the distribution coefficient, the more radioactive cesium in the cesium aqueous solution is removed and the adsorbent is adsorbed.

As experimental conditions, the hydrogen ion concentration pH of the cesium aqueous solution = 11.9 (comparative example: when neutralization treatment is not performed) and the hydrogen ion concentration pH = 7 (example: when neutralization treatment is performed) are set. did.
From the results of FIG. 5, it can be said that when the aqueous cesium solution shows strong alkali (comparative example), the removal efficiency of radioactive cesium in the adsorbing part 17 is lower than when neutral (example).
Thereby, it was demonstrated that the removal efficiency of radioactive cesium is improved by preparing the cesium aqueous solution neutral and then sending the solution from the recovery unit 15 to the adsorption unit 17 with pump power.

The graph of FIG. 6 has shown the measured value of the radioactivity of the liquid in the entrance and exit of an adsorption part, when letting radioactive cesium aqueous solution pass through the adsorption part 17 filled with mordenite.
In other words, the radioactivity measurement value of the liquid at the inlet of the adsorption unit is the radioactivity measurement value in the cesium aqueous solution recovery unit 15, and the radioactivity measurement value of the liquid in the outlet is in the cleaning water recovery unit 23 after removal of radioactive cesium. Radioactivity measurement.
From the result of FIG. 6, it was confirmed that almost 100% of the radioactive cesium in the cesium aqueous solution was removed by the adsorption part 17 filled with mordenite.

A method for treating contaminated fly ash according to the first embodiment will be described based on the flowchart of FIG.
Radioactive cesium-contaminated fly ash is added, and washing water is further injected, and both are stirred and mixed to form a suspension in which cesium is eluted (S11).
After the cesium is eluted, a neutralizing agent is added to the suspension, and the dissolved mineral-derived elemental component is precipitated as a salt (S12).

  And this suspension is isolate | separated into the solid phase which consists of decontaminated fly ash and a salt deposit, and the liquid phase which consists of radioactive cesium aqueous solution (S13). Here, the separated solid phase has a sufficiently low radioactivity level and can be generally discarded.

On the other hand, the aqueous cesium solution separated as the liquid phase is recovered (S14), and the cesium contained by passing through the adsorbent is removed (S15). At this time, since the aqueous cesium solution is adjusted to be neutral, cesium is removed with high efficiency.
Since the radioactive cesium is concentrated and the radioactivity level is high, the adsorbent is buried in the final disposal site after being stabilized by concrete solidification or the like.

Then, the washing water that has passed through the adsorbent is collected and is disposed of in general because the radioactivity level is sufficiently lowered, or reused for washing contaminated fly ash (S16).
As described above, fly ash contaminated with radioactive cesium can be decontaminated with water, and radioactive cesium can also be removed from the washed water after decontamination.

(Second Embodiment)
A contaminated fly ash treatment apparatus 10B according to the second embodiment will be described with reference to FIG.
7 that have the same configuration or function as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.
In the processing apparatus 10B for contaminated fly ash according to the second embodiment, a neutralizing agent addition unit 16B for adding a neutralizing agent is provided in the cesium aqueous solution recovery unit 15.
Further, a solid-liquid separation unit 14B that separates the suspension of the cesium aqueous solution and the mineral-derived precipitated salt into a liquid phase and a solid phase is provided after the cesium aqueous solution recovery unit 15, respectively.

That is, depending on the composition or liquid-solid ratio of the contaminated fly ash to be decontaminated, the suspension in which the precipitated salt of the mineral-derived component and fly ash coexist is processed in the solid-liquid separation unit 14A as in the first embodiment. Then, the solid-liquid separation performance may deteriorate.
In such a case, the neutralization process is not performed in the elution unit 13 and the solid-liquid separation unit 14A provided in the subsequent stage of the elution unit 13 uses the decontaminated fly ash as a solid phase to liquidate the radioactive cesium aqueous solution. Separate as phases.

The graph of FIG. 9 shows the solid-liquid separation rate when the suspension of fly ash and water is processed in the solid-liquid separation unit 14A.
The solid-liquid separation rate is expressed by the following formula (2).
Solid-liquid separation rate (%) = (1- (solid content concentration in separated liquid phase [mg / mL] / solid content concentration in suspension [mg / mL])) × 100 (2)

  As experimental conditions, the liquid-solid ratio of the washing water and the contaminated fly ash in the suspension was set to 4, 10, 20 mL / g, the temperature was set to room temperature, and the elution (stirring) time was set to 10 minutes.

Each liquid-solid ratio suspension was separated with a filter press, and the solid content concentration of the liquid phase was measured.
When the solid-liquid separation rate was derived based on the formula (2), the separation rate was 99.96% at a liquid-solid ratio of 4 mL / g, the separation rate was 99.95% at a liquid-solid ratio of 10 mL / g, and the liquid-solid ratio was 20 ml / g. For g, the elution rate was 99.92%.

In addition, as a comparative example (not shown), when the suspension in which the precipitated salt of the mineral-derived component and fly ash coexist is processed in the solid-liquid separation unit 14A, the solid-liquid separation performance is reduced as compared with the example. Was recognized.
From the above results, it can be said that the solid-liquid separation performance between the decontaminated fly ash and the cesium aqueous solution is improved by treating the suspension with the solid-liquid separation unit 14A before the neutralization treatment.
In the solid content collection tank 22A, a solid phase made of decontaminated fly ash is collected. In this solid phase, the radioactive concentration of radioactive cesium (Bq; becquerel) is further suppressed.

The cesium aqueous solution recovery unit 15 in the second embodiment recovers the strong alkaline cesium aqueous solution separated as the liquid phase.
And an acidic chemical | medical agent is added to the cesium aqueous solution collection | recovery part 15 from the neutralizer addition part 16B, and a cesium aqueous solution is prepared neutrally.
Then, the mineral-derived element contained in the cesium aqueous solution becomes a salt and becomes a suspended suspension.

The solid-liquid separation unit 14B receives supply of the neutralized suspension from the cesium aqueous solution recovery unit 15 by pump power and separates it into a solid phase and a liquid phase. A salt precipitate is separated from the solid phase, and an aqueous solution of radioactive cesium is separated from the liquid phase.
In the solid content collection tank 22B, a solid phase composed of a salt precipitate (mineral component) is collected. This solid phase can be disposed of as it is because the radioactive concentration of radioactive cesium (Bq; becquerel) is below the reference value.

Based on the flowchart of FIG. 8, the processing method of the contaminated fly ash which concerns on 2nd Embodiment is demonstrated.
Radioactive cesium-contaminated fly ash is added, and washing water is injected, and both are stirred and mixed to obtain a suspension in which cesium is eluted (S21).
Then, the suspension is separated into a solid phase composed of decontaminated fly ash and a liquid phase composed of a radioactive cesium aqueous solution (S22). Here, the separated solid phase has a sufficiently low radioactivity level and can be generally discarded.

On the other hand, the aqueous cesium solution separated as a liquid phase exhibits strong alkalinity, and after recovery (S23), a neutralizing agent is added (S24), and dissolved mineral-derived elemental components are precipitated as salts, To.
Then, the suspension is separated into a solid phase composed of a salt precipitate and a liquid phase composed of a radioactive cesium aqueous solution.

Here, since the separated solid phase has a sufficiently low radioactivity level, it can be generally discarded, and the separated liquid phase is passed through an adsorbent to remove cesium contained (S25). . Since the separated liquid phase (cesium aqueous solution) is adjusted to be neutral, cesium is removed with high efficiency.
Since the radioactive cesium is concentrated and the radioactivity level is high, the adsorbent is buried in the final disposal site after being stabilized by concrete solidification or the like.

Then, the washing water that has passed through the adsorbent is collected and is disposed of in general because the radioactivity level is sufficiently lowered, or reused for washing contaminated fly ash (S26).
As described above, fly ash contaminated with radioactive cesium can be decontaminated with water, and radioactive cesium can also be removed from the washed water after decontamination.

  According to the contaminated fly ash treatment apparatus of at least one embodiment described above, the radioactive cesium contained in the fly ash is eluted into the wash water, and further, the wash solution is neutralized, thereby using the adsorbent to make the wash solution. The contained radioactive cesium can be removed with high efficiency.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 (10A, 10B) ... Contamination fly ash processing apparatus, 11 ... Contamination fly ash injection part, 12 ... Washing water injection | pouring part, 13 ... Elution part, 14 (14A, 14B) ... Solid-liquid separation part, 15 ... Cesium aqueous solution Recovery part (recovery part), 16 (16A, 16B) ... neutralization agent addition part, 17 ... cesium adsorption part (adsorption part), 21 ... stirrer, 22 (22A, 22B) ... solid content recovery tank, 23 ... washing Water recovery department.

Claims (5)

A contaminated fly ash input unit for introducing radioactive cesium contaminated fly ash,
A cleaning water injection part for injecting cleaning water;
An elution part for mixing the introduced contaminated fly ash and the injected washing water to elute cesium;
A solid-liquid separation unit that separates the suspension of fly ash and water eluted from the cesium into a solid phase and a liquid phase;
A cesium aqueous solution recovery unit for recovering the cesium aqueous solution separated as the liquid phase;
A neutralizing agent addition unit for adding a neutralizing agent to the elution unit or the cesium aqueous solution recovery unit;
And a cesium adsorption part for adsorbing and removing cesium from the cesium aqueous solution.   2. The processing apparatus for contaminated fly ash according to claim 1, wherein a ratio of the washing water mixed in the elution unit and the contaminated fly ash is 4 mL / g or more.   The apparatus for treating contaminated fly ash according to claim 1 or 2, wherein a filter press is used for the solid-liquid separator.   The processing apparatus for contaminated fly ash according to any one of claims 1 to 3, wherein the cesium adsorption part is filled with zeolite. A step of introducing radioactive cesium contaminated fly ash;
Injecting wash water;
Mixing the injected contaminated fly ash and the injected washing water to elute cesium;
Separating the suspension of fly ash and water eluted from the cesium into a solid phase and a liquid phase;
Recovering the aqueous cesium solution separated as the liquid phase;
A method for treating contaminated fly ash, comprising: a step of adding a neutralizing agent after the cesium elution step or the step of recovering the cesium aqueous solution; and a step of adsorbing and removing cesium from the cesium aqueous solution.

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