JP5684102B2 - Method and apparatus for treating radioactive cesium-containing material - Google Patents

Description

  The present invention relates to a technique for treating a radioactive cesium-containing substance that recovers cesium by solvent extraction.

In a nuclear power plant, if a severe accident occurs in which radioactive materials are scattered outside the building, it is assumed that the environment is radioactively contaminated over a wide area. The effects of such radioactive contamination extend to the treatment process of sludge generated at soil and sewage treatment plants, sludge ash obtained by incineration of this sludge, and incineration ash and fly ash generated at municipal waste incineration sites in various places. .
In preparation for such a situation where radioactive materials are widely scattered in the environment, it is desired to develop a method for treating materials containing radionuclides.

Most of the radionuclides contained in radioactive contaminants derived from severe accidents at nuclear power plants are 134Cs and 137Cs. Of these, 137Cs has a half-life of 30.2 years, and there is a concern that relatively high-intensity radiation may be released to the environment over a long period of time. For this reason, it is desired to remove cesium from radioactive contaminants such as sludge ash, sludge, and soil.
Several proposals have been made so far regarding techniques for removing radionuclides from such radioactive contaminants (for example, Patent Document 1).

JP-A-6-23340

A method is conceivable in which a radioactive cesium-containing substance is introduced into a good cesium solvent and the cesium extracted in this good solvent is recovered using an adsorbent such as zeolite.
However, the above-described sludge ash and incineration ash basically have a high adsorbability for cesium and contain a large amount of mineral components other than cesium.
For this reason, when sludge ash or incineration ash is added to the solvent, the elution of these mineral components hinders the extraction of cesium, and the extraction rate of cesium in one solvent treatment deteriorates and the efficiency of the decontamination treatment decreases. There was a problem.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a processing technique for a radioactive cesium-containing material that efficiently and effectively removes the contained cesium.

  In the method for treating a radioactive cesium-containing substance, a step of eluting a mineral component other than cesium from a substance containing radioactive cesium into a first solvent, a step of extracting cesium from a substance treated with the first solvent into a second solvent, A step of adsorbing and recovering cesium extracted by the second solvent on an adsorbent; and a step of mixing and stabilizing the cesium recovered by the adsorbent with an immobilization material. .

  The present invention provides a technique for treating a radioactive cesium-containing material that efficiently and effectively removes cesium contained therein.

The flowchart which shows embodiment of the processing method of the radioactive cesium containing substance of this invention. Explanatory drawing of the process of the radioactive cesium containing substance which concerns on 1st Embodiment. Explanatory drawing of the process of the radioactive cesium containing substance which concerns on 1st Embodiment. Explanatory drawing of the process of the radioactive cesium containing substance which concerns on 1st Embodiment. Explanatory drawing of the process of the radioactive cesium containing substance which concerns on 1st Embodiment. Explanatory drawing of the process of the radioactive cesium containing substance which concerns on 2nd Embodiment. Explanatory drawing of the process of the radioactive cesium containing substance which concerns on 2nd Embodiment. The block diagram which shows embodiment of the processing apparatus of the radioactive cesium containing substance of this invention. The graph which shows the abundance of the cesium which moved to the solid phase and the water phase when the sludge ash containing radioactive cesium was immersed in the water solvent. The table | surface which shows the mass of the mineral component contained per unit weight of immersion water, when the sludge ash containing radioactive cesium is immersed in a water solvent. The table | surface which shows the extraction rate of cesium when the sludge ash containing radioactive cesium is immersed in various solvents other than water.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
In the method for treating a radioactive cesium-containing substance according to the first embodiment, as shown in FIG. 2, a step of eluting the first solvent 11 from mineral substances 13 other than cesium from the substance 17 containing radioactive cesium (FIG. 1; S11); 3, the step of extracting cesium from the substance 17 treated with the first solvent into the second solvent 12 as shown in FIG. 3 (FIG. 1; S12), and the second solvent 12 as shown in FIGS. A step of adsorbing the recovered cesium by the adsorbent 14 (FIG. 1; S13), and a step of mixing the cesium recovered by the adsorbent with the immobilization material and performing a stabilization process (FIG. 1; S14) Including.

As shown in FIG. 2, a substance 17 containing radioactive cesium is filled in a predetermined container 16, water (first solvent 11) is added to the substance 17, and the mixture is stirred and mixed as necessary. Then, the mineral components 13 other than cesium contained in the substance 17 are preferentially eluted in water (first solvent 11). In addition, the 1st solvent 11 is not limited to the illustrated water, If it suppresses the elution of cesium and the other mineral component 13 elutes preferentially, it will be employ | adopted suitably.
In FIG. 1, the substance 17 and water (first solvent 11) are illustrated separately, but in reality, the above-described stirring and mixing operation and the aspect (form, size, etc.) of the substance 17 are described. Concomitantly, substance 17 is dispersed in water.

The container 16 may be a glass container such as a beaker at a laboratory level, but is preferably a container made of a material such as SUS having high corrosion resistance at a practical level. The capacity of the container 16 can be appropriately selected according to the amount of the substance 17 to be processed.
In the first embodiment, a batch type processing method is shown to clarify the features of the present invention, but the processing method of the present invention is not limited to such a batch type processing method. Alternatively, a continuous processing method can be used as necessary.

Examples of the substance 17 include all substances that may contain radioactive cesium. For example, incinerated ash generated after incineration of soil, sludge, sand, rock, clay, concrete, asphalt, and flammable waste And sludge ash and fly ash.
Among these, incineration ash and sludge ash are rich in mineral-derived elements (mineral component 13) such as Na, K, Mg, Ca, Fe, Zn, Al, Si, Pb, P, and S. .

Some of these mineral components 13 are preferentially eluted in water (first solvent 11) in order to exhibit higher solubility in water (first solvent 11) than cesium (Cs), and cesium ( Suppression of Cs) is suppressed.
Therefore, as shown in FIG. 2, in the container 16, a liquid phase containing the mineral component 13 other than cesium (first solvent 11) and the remainder of the substance 17 insoluble in the first solvent 11 ( And a solid phase on which cesium is precipitated) are separated from each other.
Although the 1st solvent 11 which eluted the mineral component 13 will be discharged | emitted from the container 16, since the solubility of radioactive cesium is low, the subsequent process can be simplified.

  As shown in FIG. 3, the second solvent 12 is newly charged into the container 16 from which the first solvent 11 has been discharged. This second solvent 12 dissolves the cesium compound in the substance 17 and extracts cesium. Therefore, in the container 16, a liquid phase containing cesium (second solvent 12) and a solid phase in which the remainder of the substance 17 that is insoluble in the second solvent 12 is precipitated are separated. Will exist.

The second solvent 12 is an acid solution such as formic acid solution, oxalic acid solution, acetic acid solution, sodium hydroxide solution, calcium hydroxide solution, ammonia solution, citric acid solution, tartaric acid solution, sodium hydrogen carbonate solution, hydrochloric acid solution, sulfuric acid solution, etc. Alternatively, an alkaline solution can be used.
Since oxalic acid can be decomposed, the use of the oxalic acid can eliminate the operation of treating it as an acid secondary waste. In the case of sodium hydroxide, the amount of secondary waste generated can be reduced by adding a neutralization operation.

By the way, although these compounds have a high elution effect of cesium strongly bonded to the substance 17, they also have a high elution effect of mineral components 13 other than cesium.
For example, when oxalic acid is used for the second solvent 12, the extraction effect of cesium may be reduced by the following reaction.
(COOH) ₂ + Ca ²⁺ → Ca (COO) ₂ ↓ + 2H ⁺
However, in each embodiment, since the mineral component 13 other than cesium is previously removed from the substance 17 by the first solvent 11, the extraction effect of cesium by the second solvent 12 does not decrease.

  The acid concentration or alkali concentration in the second solvent 12 is appropriately set according to the type of the substance 17. For example, when oxalic acid and sodium hydroxide are used, the concentration of oxalic acid and sodium hydroxide in the solution Is preferably set to 0.05 to 2.5 M (mol / L).

  The mixing ratio of the first solvent 11 and the substance 17 in FIG. 2 and the second solvent 12 and the substance 17 in FIG. 3 is preferably in the range of 5: 1 to 200: 1, respectively. If it deviates from the 5: 1 limit, the ion elution ability of the solvent will reach saturation in a short time, and if it deviates from the 200: 1 limit, the processing efficiency of cesium recovery will decrease in the next step.

  The step of extracting cesium into the second solvent 12 can be performed in an open state (under atmospheric pressure) by setting the temperature in a range from room temperature to 95 ° C. Further, by heating the second solvent 12 to 80 ° C. or higher, the dissolution rate of cesium can be improved, and the operation can be speeded up.

  As shown in FIG. 4, cesium is recovered from the second solvent 12 by dispersing a cesium adsorbent 14 in the second solvent 12. As this adsorbent 14, ferrocyanide, silicotitanate, and zeolite can be applied.

Examples of the ferrocyanide include potassium ferrocyanide, sodium ferrocyanide, calcium ferrocyanide, iron ferrocyanide, nickel ferrocyanide, and copper ferrocyanide.
Examples of silicic titanate include barium silicotitanate, potassium titanate, and sodium titanate.
Examples of the zeolite include mordenite type zeolite, chabazite type zeolite, clinoptilolite type zeolite, A type zeolite, Y type zeolite, X type zeolite and the like.

It is desirable that the amount of the adsorbent 14 used is such that the distribution coefficient Kd represented by the following formula is 1000 ml / g or more.
Kd = (Ci−Cf) / Ci × V / m
(Kd: partition coefficient (ml / g), Ci: initial concentration of cesium in solution (Bq / g), Cf: concentration after equilibrium of cesium in solution (Bq / g), V: volume of solution (ml), m: adsorbent Weight (g)

  The higher the distribution coefficient Kd, the better. However, the upper limit value in the present situation is about 10,000. If the distribution coefficient Kd is less than this limit value, the effect of removing radioactive cesium in the substance 17 becomes insufficient.

  In addition, in 1st Embodiment, as shown in FIG. 5, although the example which sediments the adsorbent 14 which adsorb | sucked cesium and isolate | separates into a liquid phase and a solid phase is shown, filtration, centrifugation, etc. are shown in addition. The solid-liquid separation can be performed by a general-purpose solid-liquid separation operation. Further, a method in which the adsorbent 14 is packed in a column suitable for exchange efficiency, the second solvent 12 containing radioactive cesium is passed therethrough, and cesium is adsorbed can also be applied.

Thus, the solid phase which concentrated cesium is collect | recovered from the container 16, and a stabilization process (FIG. 1; S14) is implemented. In this stabilization process, a general low-level radioactive waste disposal method, for example, a concrete pit disposal enclosed in a drum can is performed.
As the fixing material, Portland cement, blast furnace cement, fly ash cement, alumina cement, or the like is used.

(Second Embodiment)
In the processing method for a radioactive cesium-containing substance according to the second embodiment, in step S13 shown in FIG. 1, the adsorbent 14 supporting the magnetic material is dispersed in the second solvent 12, and the adsorbent 14 adsorbs cesium. As shown in FIG. 6 and FIG. The other steps (S11, S12, S14) are the same as those in the first embodiment.

The adsorbent 14 applied to the second embodiment generates the adsorbent 14 carrying the magnetic material by adding the adsorbent simple substance and the magnetic substance simple substance (or its precursor) to the second solvent 12. At the same time, cesium is adsorbed.
The process of supporting the magnetic material on the adsorbent 14 and further adsorbing cesium can be optimized by adjusting the pH and temperature of the solvent.
A general method can be applied to support the magnetic material on the adsorbent, and a pressure bonding method or a sol-gel method can be employed.

(Treatment equipment for radioactive cesium-containing substances)
As shown in FIG. 8, the embodiment of the radioactive cesium-containing substance processing apparatus 20 is charged with a radioactive cesium-containing substance storage tank 23, a first solvent storage tank 24, a radioactive cesium-containing substance and a first solvent. An elution tank 21 for eluting mineral components other than cesium, a storage tank 26 for the second solvent, a substance (solid phase) treated in the elution tank 21 and an extraction tank 22 for extracting cesium by introducing the second solvent, and adsorption An adsorption tank 29 for recovering the liquid phase (second solvent from which cesium has been extracted) of the agent storage tank 28 and the extraction tank 22 and adsorbing cesium to the adsorbent; and cesium adsorbed on the adsorbent by centrifugation or the like A recovery tank 30 to be separated and recovered, a storage tank 31 for cement (an immobilization material), and a solid phase (cesium adsorbed on an adsorbent) recovered from the recovery tank 30 are mixed with an immobilization material and stabilized. A mixing tank 32, and a.

The liquid phase treated in the elution tank 21 (the first solvent in which the mineral components other than cesium are dissolved) is treated in the removal tank 25 that removes the dissolved mineral components, and then the storage tank 24 for the first solvent. Returned to
The solid phase (substance from which cesium has been removed) in the extraction tank 22 is processed by the processing mechanism 27 for the decontaminated substance.
The liquid phase (second solvent) recovered from the recovery tank 30 is transferred to the surge tank 34, adjusted in concentration, and returned to the storage tank 26. When the second solvent is, for example, an oxalic acid solution, it can be decomposed into water and carbon dioxide by performing UV (ultraviolet) irradiation from the UV (ultraviolet) irradiation device 33 after adding hydrogen peroxide.

  Targets sludge ash as a radioactive cesium-containing substance. The composition of this sludge ash is as follows: Si: 23.3 wt%, P: 21.5 wt%, Ca: 15.5 wt%, Fe: 14.0 wt%, Al: 12.7 wt%, Mg: 2.5 wt%, Ba : 2.0 wt%, Ti: 1.3 wt%, S: 0.8 wt% and the balance (including Cs). In the sludge ash, the element is present as an oxide or a predetermined salt.

FIG. 9 is a graph showing the abundance of cesium transferred to a solid phase and an aqueous phase when two types of sludge ash A and B having the same composition of main elements are immersed in an aqueous solvent.
In the experiment, water was added to sludge ash to a liquid-solid ratio of 10 to 14 ml / g, and shaking immersion was performed for 18 hours. Then, the abundance of cesium in the aqueous phase and the solid phase was calculated by measuring the radiation dose of Cs-137 in the aqueous phase and the solid phase.

FIG. 10 is a table showing the mass of mineral components per unit weight contained in the aqueous phase shown in FIG.
Concentration analysis was performed on Na, K, Mg, Ca, Fe, Zn, Al, Si, Pb, P, and S among the soluble elements in the aqueous phase. For cesium (Cs), this analysis method was below the detection limit and could not be detected.

  From the results of FIGS. 9 and 10, it is clear that cesium in the sludge ash is difficult to elute into water, and the reason is that a large amount of alkaline earth metal elements such as Na and K and sludge in the sludge ash are eluted. It can be said that. From these results, it can be said that it is possible to efficiently remove the mineral components that interfere with the decontamination of cesium without eluting cesium by carrying out the pretreatment with water for the sludge ash. Moreover, in the pretreatment of washing with water, an effect of removing such mineral components can be improved by adding a treatment step by ultrasonic irradiation or reduced pressure.

FIG. 11 is a table showing the extraction rate of cesium when sludge ash is immersed in various solvents (acid and alkali) other than water.
Experiments were conducted on 1M formic acid solution, 0.5M oxalic acid solution, 1M acetic acid solution, 1M sodium hydroxide solution, 1M ammonia solution, 1M citric acid solution, 1M tartaric acid solution, 1M sodium bicarbonate solution and 2.5M hydrochloric acid solution. The immersion test was conducted for 1 hour without stirring under conditions of a temperature of 95 ° C., a normal temperature, and a liquid-solid ratio of 10 ml / g.
Further, the 0.5M oxalic acid solution or 1M sodium hydroxide solution was subjected to 1 to 6 repeated stirring immersion tests for 1 hour under the conditions of a temperature of 95 ° C. and a liquid-solid ratio of 10 ml / g or 50 ml / g.

And under various stirring immersion conditions, the liquid phase containing radioactive cesium was separated from sludge ash (solid phase) by solid-liquid separation by filtration. Here, the number of repetitions is the number of times that the same solvent was added again to the solid phase separated in the previous solid-liquid separation operation and the solid-liquid separation operation was performed under the same conditions.
Moreover, the extraction rate calculated the extraction amount of radioactive cesium by measuring the radiation dose of the isolate | separated liquid phase or solid phase.

  From FIG. 11, it is clear that the cesium extraction rate of sludge ash by various solvents (second solvent) is improved by increasing the liquid-solid ratio or the number of repetitions. Furthermore, although accurate quantitative values cannot be shown, it has been found that the extraction rate of cesium with various solvents (second solvent) is improved by performing pretreatment of washing sludge ash with water (first solvent). ing.

  According to the processing technique of the radioactive cesium-containing substance of at least one embodiment described above, decontamination of the substance by previously removing other mineral components contained in the radioactive cesium-containing substance and then extracting the cesium with a solvent. The effect can be improved.

  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 11 ... 1st solvent, 12 ... 2nd solvent, 13 ... Mineral component, 14 ... Adsorbent, 15 ... Magnetic force generation part, 16 ... Container, 17 ... Substance, 20 ... Treatment apparatus of radioactive cesium containing substance, 21 ... Other than cesium 22 ... Extraction tank of cesium, 23 ... Storage tank for substance containing radioactive cesium, 24 ... Storage tank for first solvent, 25 ... Removal tank for mineral component, 26 ... Storage tank for second solvent 27 ... Processing mechanism for decontaminated substances, 28 ... Storage tank for adsorbent, 29 ... Adsorption tank for cesium and adsorbent, 30 ... Recovery tank for cesium adsorbed on the adsorbent, 31 ... Cement (immobilization material) Storage tank, 32 ... mixing tank of cesium adsorbed on the adsorbent and cement (fixing material), 33 ... UV irradiation device, 34 ... surge tank.

Claims (10)

Eluting mineral components other than cesium into a first solvent from a substance containing radioactive cesium;
Extracting cesium from a material treated with the first solvent into a second solvent;
Adsorbing and recovering cesium extracted in the second solvent on an adsorbent;
Mixing the cesium recovered by the adsorbent with an immobilization material and stabilizing the cesium, and a method for treating a radioactive cesium-containing substance. In the processing method of the radioactive cesium containing substance of Claim 1,
The second solvent is selected from the group consisting of formic acid solution, oxalic acid solution, acetic acid solution, sodium hydroxide solution, calcium hydroxide solution, ammonia solution, citric acid solution, tartaric acid solution, sodium bicarbonate solution, hydrochloric acid solution and sulfuric acid solution. processing method to that radioactive cesium-containing material, characterized in that at least one element. In the processing method of the radioactive cesium containing substance of Claim 1 or Claim 2,
Wherein the first solvent and the substance, and the mixture ratio of the second solvent and the substance, respectively 5: 1 to 200: processing method radioactive cesium-containing material you characterized in that the first range. In the processing method of the radioactive cesium containing substance of any one of Claims 1-3,
Method of processing radioactive cesium-containing material you and extracting the cesium set in a range of 95 ° C. The second solvent from room temperature. In the processing method of the radioactive cesium containing substance of any one of Claims 1-4,
The method for treating a radioactive cesium-containing material is characterized in that the recovery of cesium from the second solvent uses at least one adsorbent selected from the group of ferrocyanide, silicotitanate, and zeolite. In the processing method of the radioactive cesium containing substance of any one of Claims 1-5,
The method for treating a radioactive cesium-containing substance is characterized in that the amount of the adsorbent used is such that a distribution coefficient Kd represented by the following formula is 1000 ml / g or more.
[Formula] Kd = (Ci−Cf) / Ci × V / m
(Kd: partition coefficient (ml / g), Ci: initial concentration of cesium in solution (Bq / g), Cf: concentration after equilibrium of cesium in solution (Bq / g), V: volume of solution (ml), m: adsorbent Weight (g) In the processing method of the radioactive cesium containing substance of any one of Claims 1-6,
A method for treating a radioactive cesium-containing substance, characterized in that an adsorbent carrying a magnetic material is dispersed in the second solvent, cesium is adsorbed on the adsorbent and recovered by magnetic force. In the processing method of the radioactive cesium containing substance of Claim 7,
A radioactive cesium-containing material characterized in that the adsorbent and the magnetic substance (or a precursor thereof) are added to the second solvent so that the adsorbent supports the magnetic substance and adsorbs cesium. How to treat the substance. In the processing method of the radioactive cesium containing substance of any one of Claims 1-8,
The method for treating a radioactive cesium-containing substance, wherein the fixing material is at least one selected from the group consisting of Portland cement, blast furnace cement, fly ash cement, and alumina cement. An elution tank for eluting mineral components other than cesium from a substance containing radioactive cesium into a first solvent;
An extraction tank for extracting cesium into a second solvent from the substance treated with the first solvent;
A collection tank for adsorbing and recovering the cesium extracted in the second solvent;
A treatment apparatus for a radioactive cesium-containing substance, comprising: a mixing tank for mixing and stabilizing cesium recovered by the adsorbent with an immobilizing material.

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