JP5677610B1 - Radiocesium separation promoter - Google Patents

Abstract

Disclosed is a separation accelerator capable of sufficiently lowering the temperature of heat treatment for separating radioactive cesium from waste and achieving a sufficiently high removal rate of radioactive cesium with a sufficiently small addition amount. A mixture or a double salt prepared using two or more kinds of chlorides and having a melting point of 700 ° C. or lower is included. [Selection] Figure 15

Description

  The present invention relates to a separation accelerator for removing radioactive cesium from waste contaminated with radioactive cesium.

  The radioactive materials released by the accident at the nuclear power plant are concentrated in soil, sewage sludge, waste incineration ash, etc., and it is difficult to dispose of waste contaminated with these. In general, it is necessary to put pollutants with radioactive materials exceeding 8000 Bq / kg into a controlled disposal site. Since the capacity of this disposal site is limited, it is desirable to reduce the volume of such waste as much as possible. .

  Radioactive cesium occupies most of the radioactive material, and removing and concentrating it leads to volume reduction of waste. As a method for removing and reducing the volume of radioactive cesium in waste, a method of volatilizing radioactive cesium in waste by heat treatment and collecting it with a bag filter or the like can be mentioned. Moreover, the method of eluting the radioactive cesium in a waste by a water-washing process and collecting the eluted radioactive cesium with an adsorbent is mentioned.

Patent Document 1 discloses a method for removing radioactive cesium from waste. This method includes a heating step in which waste contaminated with radioactive cesium is heated at 1200 to 1350 ° C. to volatilize radioactive cesium in the waste. In this heating step, the types and mixing ratios of the waste, the CaO source, and the MgO source are determined so that the masses of CaO, MgO, and SiO ₂ satisfy specific conditions.

  Patent Document 2 discloses a method for removing radioactive cesium from soil. This method includes an addition step of adding to the soil contaminated with radioactive cesium an inorganic calcium compound content of 3% by mass to 30% by mass and sodium chloride in an amount of more than 0.5% by mass to 5% by mass; And a heating step of volatilizing radioactive cesium from the soil after the addition step by performing a heat treatment at a temperature of from ℃ to 1200 ℃ for a period of from 30 minutes to 120 minutes.

Japanese Patent No. 5159971 Japanese Patent No. 5175959

However, although the method described in Patent Document 1 has a high removal rate of cesium, (1) a very large amount of heat is required for high-temperature treatment at 1200 to 1350 ° C., and (2) for waste to be treated Many CaO sources and MgO sources need to be added, and there is room for improvement in that the volume of waste after treatment cannot be sufficiently reduced. Regarding the improvement (2), for example, when the waste to be treated is soil containing a large amount of SiO ₂ , the amount of calcium carbonate added as a CaO source is very large, and the amount of waste after the treatment is greatly increased. There was an increasing problem.

  Patent Document 1 discloses that in order to efficiently remove radioactive cesium contained in waste by volatilization, a liquid phase of other components should be avoided as much as possible. That is, paragraph [0010] of Patent Document 1 relates to the lower limit value of the mass ratio range (1.0 to 1.9) of CaO, MgO, and SiO calculated by the specific formula: “The mass ratio is 1. If it is less than 0, a liquid phase is likely to occur as the firing temperature becomes higher, and the volatilization amount of radioactive cesium is reduced. ”Paragraph [0012] states that“ when the heating temperature is less than 1200 ° C., radioactive cesium. If the temperature exceeds 1350 ° C., the formation of a liquid phase is not preferable because radioactive cesium is taken in and hardly volatilizes. ” In addition, paragraph [0011] of Patent Document 1 describes that a chloride such as calcium chloride may be used for the purpose of “accelerating the chlorination of radioactive cesium and reducing the volume of the volatile recovery product” Furthermore, it is described that “if the amount of chlorine in the mixture is 1500 mg / kg or less, a liquid phase is less likely to be generated even at a high temperature, and a large amount of radioactive cesium is volatilized”.

  On the other hand, although it is recognized that the heating process of the method described in Patent Document 2 has a merit in that it is a low temperature (900 ° C. or more and 1200 ° C. or less) compared to the heating process of the method described in Patent Document 1, There is room for improvement in terms of the removal rate of radioactive cesium. That is, depending on the chemical composition of the soil, the removal rate of radioactive cesium may not be sufficiently increased only by adjusting the addition amount of the inorganic calcium compound and sodium chloride to the above range. In addition, paragraph [0020] of Patent Document 2 describes that sodium chloride is “cheaper than calcium chloride that has been used as a conventional cesium removal accelerator” as a reason for using sodium chloride together with inorganic calcium. Yes.

  The present invention has been made in view of the above circumstances, and can sufficiently reduce the temperature of heat treatment for separating radioactive cesium from waste, and can provide a sufficiently high removal rate of radioactive cesium with a sufficiently small addition amount. The object is to provide a separation promoter that can be achieved.

  The inventors focused on the fact that it is easy to remove radioactive cesium contained in the waste depending on the form of the radioactive cesium in the waste, and proceeded with the study. For example, incineration ash (main ash and fly ash) containing radioactive cesium, cesium contained in the main ash is mainly present in the state of cesium aluminosilicate, while cesium contained in the fly ash is in the state of cesium chloride. Mainly exists. Cesium aluminosilicate is hardly volatile and insoluble, whereas cesium chloride is easily volatile and water soluble. Therefore, it can be said that among these, cesium chloride is an embodiment that is easier to remove. In the soil contaminated with radioactive cesium, the radioactive cesium is adsorbed on the clay mineral as ions, and even if the soil is washed with water, it is difficult to dissolve. Since the soil contains silica and aluminum, when the soil contaminated with radioactive cesium is heated, the above-mentioned cesium aluminosilicate (hardly volatile and insoluble) is likely to occur.

  From the above examination results, in order to efficiently remove radioactive cesium from waste, the present inventors (1) promote the chlorination of radioactive cesium and (2) suppress the production of cesium aluminosilicate. It was found that is effective. Based on these findings, the present inventors conducted evaluation tests and simulations on various compounds, and as a result, the melting point was lower than the melting point of a single chloride. It has been found that the use of the mixture or double salt obtained is effective in solving the above problems, and the present invention has been completed.

  That is, the separation accelerator according to the present invention is for removing radioactive cesium from waste contaminated with radioactive cesium, and is prepared using two or more kinds of chlorides and has a melting point of 700 ° C. or less. Contains mixtures or double salts.

  According to the separation accelerator of the present invention, it is possible to achieve both a high removal rate of radioactive cesium and a low processing temperature at a sufficiently high level with a sufficiently small addition amount. The reason why such an effect is obtained is not necessarily clear, but the present inventors speculate as follows. That is, by using a plurality of chlorides and lowering the melting point thereof, radioactive cesium can be taken into the molten salt partially generated in the object to be treated at a relatively low temperature. Thereby, while being able to accelerate | stimulate the production | generation of the easily volatile and water-soluble cesium chloride (the said knowledge (1)), the production | generation of the hardly volatile and insoluble cesium aluminosilicate can be suppressed (the said knowledge ( 2)).

From the viewpoint of achieving a higher removal rate of radioactive cesium, the separation enhancing agent including a calcium source. When the total mass of the separation accelerator is 100 parts by mass, the total content of the mixture and the double salt may be 1 to 65 parts by mass, and the content of the calcium source may be 35 to 99 parts by mass. When calcium is added, calcium produces aluminosilicate preferentially over cesium, and the production of cesium aluminosilicate can be suppressed more efficiently than when only chloride is added. It is also possible to promote the decomposition of cesium aluminosilicate contained in radioactive waste.

In the present invention, the two or more types of chlorides can be selected from the group consisting of alkaline earth metal chlorides, alkali metal chlorides and iron chlorides, and more specifically, CaCl ₂ , MgCl ₂ , NaCl, It can be selected from the group consisting of KCl, LiCl, FeCl ₃ and FeCl ₂ .

In the present invention, the mixture or double salt may be prepared using any of the following combinations 1 to 6 of the first chloride and the second chloride, and the first chloride in the mixture or double salt: The ratio (M ₁ / M ₂ ) between the number of moles M ₁ of the product and the number of moles M ₂ of the second chloride may be in the following range.
Combination 1: first chloride CaCl ₂ and second chloride NaCl, 3/7 ≦ M ₁ / M ₂ ≦ 7/3
Combination 2: first chloride KCl and second chloride CaCl ₂ , 2/8 ≦ M ₁ / M ₂ ≦ 3/7 or 65/35 ≦ M ₁ / M ₂ ≦ 85/15
Combination 3: first chloride MgCl ₂ and second chloride NaCl, 2/8 ≦ M ₁ / M ₂ ≦ 8/2
Combination 4: first chloride MgCl ₂ and second chloride KCl, 2/8 ≦ M ₁ / M ₂ ≦ 85/15
Combination 5: first chloride NaCl and second chloride FeCl ₃ , 15/85 ≦ M ₁ / M ₂ ≦ 35/65
Combination 6: first chloride NaCl and second chloride FeCl ₂ , 4/6 ≦ M ₁ / M ₂ ≦ 8/2

  According to the present invention, a separation accelerator for heating waste contaminated with radioactive cesium to remove the radioactive cesium from the waste, the temperature of the heat treatment can be sufficiently lowered, and the addition amount is sufficiently small Provides a separation promoter that can achieve a sufficiently high removal rate of radioactive cesium.

It is a phase diagram of a NaCl-CaCl _2. It is a phase diagram of a CaCl ₂ -KCl. It is a phase diagram of a NaCl-MgCl _2. It is a phase equilibrium diagram of KCl—MgCl ₂ . It is a graph which shows the relationship between the amount of calcium contained in the process target used for a volatilization process, the amount of low melting-point chloride, and the removal rate of radioactive cesium. It is a graph which shows the relationship between the amount of calcium contained in the process target used for a series of processes of a volatilization process and a water washing process, the amount of low melting-point chloride, and the removal rate of radioactive cesium. 2 is an X-ray diffraction profile of cesium aluminosilicate synthesized in Example. It is a graph which shows the relationship between the heating temperature in a cesium removal process (volatilization), and a cesium removal rate (addition conditions No. 1-6). It is a graph which shows the relationship between the heating temperature and cesium removal rate in a cesium removal process (volatilization + water washing process) (addition conditions No. 1-6). It is a graph which shows the relationship between the heating temperature in a cesium removal process (volatilization), and a cesium removal rate (addition conditions No. 7-11). It is a graph which shows the relationship between the heating temperature in a cesium removal process (volatilization + water washing process) and a cesium removal rate (addition conditions No. 7-11). It is a graph which shows the ratio of the cesium volatilized and removed by heating temperature 700 degreeC, and the cesium removed by subsequent water washing, 1 to 6 are shown, and (b) Addition Condition No. The result of 7-11 is shown. It is a graph which shows the ratio of the cesium volatilized and removed by heating temperature 900 degreeC, and the cesium removed by subsequent water washing, 1 to 6 are shown, and (b) Addition Condition No. The result of 7-11 is shown. It is a graph which shows the ratio of the cesium volatilized and removed by heating temperature 1100 degreeC, and the cesium removed by subsequent water washing, 1 to 6 are shown, and (b) Addition Condition No. The result of 7-11 is shown. It is a graph which shows results, such as Example 14 and Example 15.

  Hereinafter, embodiments of the present invention will be described in detail. The separation promoter according to this embodiment is for removing radioactive cesium from waste contaminated with radioactive cesium. The separation accelerator includes a mixture or a double salt prepared using two or more kinds of chlorides and having a melting point of 700 ° C. or less. First, the separation accelerator containing a mixture of two types of chloride will be described.

<Radiocesium separation promoter>
The separation accelerator according to this embodiment is for removing radioactive cesium from waste contaminated with radioactive cesium, and is a first chloride and a different type of chloride from the first chloride. And a second chloride that forms a double salt having a melting point of 700 ° C. or lower (hereinafter referred to as “low melting point chloride”) together with the first chloride. The melting point of the low melting point chloride is preferably lower than both the melting point of the first chloride and the melting point of the second chloride. It is preferable that all of the first chloride, the second chloride and the low melting point chloride are powdery or granular (average particle size of about 1 μm to 10 mm).

  The melting point of the low melting point chloride produced by heating the mixture of the first chloride and the second chloride is adjusted to 700 ° C. or lower. In order to set the melting point of the low melting point chloride to 700 ° C. or lower, the specific first and second chlorides are used, and the blending ratio (molar ratio) of these two types of chlorides may be adjusted. The melting point of the low melting point chloride is lower than the heating temperature for treating the waste. The melting point of the low melting point chloride is preferably 150 ° C. or higher and 700 ° C. or lower, more preferably 150 ° C. or higher and 600 ° C. or lower, and further preferably 300 ° C. or higher and 600 ° C. or lower. If the melting point of the low melting point chloride is 700 ° C. or less, the temperature of the heat treatment for separating the radioactive cesium from the waste can be sufficiently lowered, and a sufficiently high removal rate of the radioactive cesium can be achieved with a sufficiently small addition amount. it can. If the melting point of the low melting point chloride is 150 ° C. or higher, the adhesion of the chloride to the heating apparatus for treating the waste can be sufficiently suppressed.

The first chloride and the second chloride can be selected from the group consisting of alkaline earth metal chloride, alkali metal chloride, and iron chloride, respectively, and more specifically, CaCl ₂ , MgCl ₂ , NaCl, KCl, LiCl, FeCl ₃ and FeCl _2, respectively.

  The blending ratio of the two types of chlorides can be determined based on the phase equilibrium diagram. The phase equilibrium diagram can be created by commercially available thermodynamic equilibrium calculation software (for example, FactSage Ver. 6.4 (trade name, manufactured by Computational Mechanics Research Center Co., Ltd.) Here, a combination of two types of chlorides 1 -6 will be described as an example.

(Combination 1)
FIG. 1 is a phase equilibrium diagram of NaCl—CaCl ₂ . The melting point of NaCl alone is 802 ° C. and the melting point of CaCl ₂ alone is 775 ° C., whereas the melting point of the double salt (49NaCl · 50CaCl ₂ ) having a molar ratio of CaCl ₂ : NaCl = 50: 49 is 502.degree. 5 ° C. The melting point to obtain a sufficiently low double salt (low melting point chlorides), the ratio of the number of moles _{M 2} number of moles _{M 1} and NaCl of CaCl ₂ (first chloride) in a mixture (second chloride) ( M ₁ / _{M 2)} is preferably 3/7 to 7/3, more preferably 4 / 6-6 / 4, more preferably from 45 / 55-55 / 45.

(Combination 2)
FIG. 2 is a phase equilibrium diagram of CaCl ₂ -KCl. The melting point of CaCl ₂ alone is 775 ° C. and the melting point of KCl alone is 772 ° C., whereas the double salt (25CaCl ₂ · 75 KCl) has a KCl content of 75 mol% and a CaCl ₂ content of 25 mol%. The melting point of is 599 ° C. The melting point to obtain a sufficiently low double salt (low melting point chlorides), the ratio of the number of moles _{M 2} of KCl in a mixture moles _{M 1} and CaCl ₂ (second chloride) (first chloride) ( M ₁ / _{M 2)} is preferably 65 / 35-85 / 15, more preferably from 7 / 3-8 / 2, more preferably from 72 / 28-78 / 22.

(Combination 3)
FIG. 3 is a phase equilibrium diagram of NaCl—MgCl ₂ . The melting point of NaCl alone is 802 ° C. and the melting point of MgCl ₂ alone is 714 ° C., whereas the double salt (57NaCl · 43MgCl ₂ ) has an MgCl ₂ content of 43 mol% and an NaCl content of 57 mol%. The melting point of is 458 ° C. In order to obtain a double salt (low melting point chloride) having a sufficiently low melting point, the ratio of the number of moles M ₁ of MgCl ₂ (first chloride) to the number of moles M ₂ of NaCl (second chloride) in the mixture ( M ₁ / M ₂ ) is preferably 2/8 to 8/2, more preferably 25/75 to 7/3, still more preferably 3/7 to 6/4, and most preferably 35/65. 48/52.

(Combination 4)
FIG. 4 is a phase equilibrium diagram of KCl—MgCl ₂ . KCl alone has a melting point of 770 ° C. and MgCl ₂ alone has a melting point of 714 ° C., whereas MgCl ₂ content is 30 mol% and KCl content is 70 mol% (3MgCl ₂ · 7 KCl) Has a melting point of 421.7 ° C. In order to obtain a double salt having a sufficiently low melting point (low melting point chloride), the ratio of the number of moles M ₁ of MgCl ₂ (first chloride) to the number of moles M ₂ of KCl (second chloride) in the mixture ( M ₁ / M ₂ ) is preferably 2/8 to 85/15, more preferably 25/75 to 65/35, still more preferably 25/75 to 6/4, and most preferably 25/75. ~ 4/6.

(Combination 5)
The melting point of FeCl ₃ alone is 306 ° C. and the melting point of NaCl alone is 802 ° C., whereas the double salt (25NaCl · 75FeCl ₃ ) has an NaCl content of 25 mol% and an FeCl ₃ content of 75 mol%. Has a melting point of 156 ° C. The melting point to obtain a sufficiently low double salt (low melting point chlorides), the ratio of the number of moles _{M 2} of NaCl in the mixture moles _{M 1} and FeCl ₃ (first chloride) (second chloride) ( M ₁ / M ₂ ) is preferably 15/85 to 35/65, and more preferably 20/80 to 30/70.

(Combination 6)
The melting point of FeCl ₂ alone is 677 ° C. and the melting point of NaCl alone is 802 ° C., whereas the double salt (58NaCl · 42FeCl 2) has an NaCl content of 58 mol% and an FeCl ₂ content of 42 mol%. The melting point is 370 ° C. The melting point to obtain a sufficiently low double salt (low melting point chlorides), the ratio of the number of moles _{M 2} of NaCl in the mixture moles _{M 1} and FeCl ₂ (second chloride) (first chloride) ( M ₁ / _{M 2)} is preferably 4 / 6-8 / 2, more preferably 5 / 5-65 / 35, more preferably from 55 / 45-60 / 40.

(Other combinations)
In addition to the above combinations, low melting point chlorides prepared from two types of chlorides include 37PbCl ₂ -63FeCl ₃ (melting point 175 ° C.), 60SnCl ₂ -40KCl (melting point 176 ° C.), 70SnCl ₂ -30NaCl (melting point 183 ° C. ), 60KCl-40FeCl ₂ (melting point 355 ° C.), 70PbCl ₂ -30NaCl (melting point 410 ° C.), 52PbCl ₂ -48KCl (melting point 411 ° C.), 80PbCl 2-20CaCl ₂ (melting point 475 ° C.), and the like. These chlorides may be appropriately prepared by selecting materials that can be procured.

The separation accelerator according to this embodiment may be composed of a mixture of the first chloride and the second chloride, and may further include other components. Other ingredients include calcium sources. In addition, when calcium chloride is used as the chloride constituting the low melting point chloride, this calcium chloride shall not fall under the “calcium source” here. Examples of the raw material containing a calcium source include limestone (calcium carbonate), quick lime (calcium oxide), slaked lime (calcium hydroxide), and dolomite (CaMg (CO ₃ ) ₂ ). The component added to the separation accelerator is preferably one having as little silicon and aluminum content as possible from the viewpoint of not producing cesium aluminosilicate as much as possible. From the viewpoint of achieving a higher removal rate of radioactive cesium, when the total mass of the separation accelerator is 100 parts by mass, the content of the calcium source in the separation accelerator is preferably 35 to 99 parts by mass, and more preferably 54 It is -91 mass parts, More preferably, it is 57-88 mass parts, Most preferably, it is 70-88 mass parts.

  Further, from the viewpoint of achieving a higher removal rate of radioactive cesium, the content of the mixture of the first chloride and the second chloride is preferably 1 to 65 parts by mass, more preferably 9 to 46 parts by mass, More preferably, it is 12-43 mass parts, Most preferably, it is 12-30 mass parts.

The separation accelerator according to this embodiment can be applied to the following two types of separation processes. Two types of separation processing will be described later.
(1) A method of volatilizing radioactive cesium by heat treatment (800 ° C. or higher and lower than 1200 ° C.).
(2) A method in which radioactive cesium is volatilized by heat treatment (600 ° C. or more and 900 ° C. or less), and then the radioactive cesium is eluted by washing with water.

  When preparing a separation accelerator containing a calcium source in advance, the blending amount of the calcium source may be adjusted depending on which of the above two types of separation treatment is applied.

  FIG. 5 shows the amount of calcium (CaO equivalent, based on the total mass of the object to be treated) and the amount of low melting point chloride (treatment) in the method (1) (volatilization treatment) described above, after the separation accelerator is added. It is a graph which shows the relationship with a target object total mass reference | standard. The amount of calcium (calculated in terms of CaO) and the amount of low-melting-point chloride of the object to be subjected to volatilization is preferably adjusted to the region surrounded by the dotted line in FIG. 5 and adjusted to the region surrounded by the solid line. More preferred.

In FIG. 5, “estimated values by FactSage” indicated by ◯ and X are FactSage Ver., Which is thermodynamic equilibrium calculation software manufactured by Computational Mechanics Research Center. The ratio of cesium chloride existing as a gas is estimated using 6.4. The thermodynamic equilibrium calculation is not limited to a single substance database such as NaCl, CaCl ₂ and CsCl, which is usually used in the thermodynamic database, but a double salt (solution) of NaCl—CaCl ₂ —CsCl, cesium alumino In addition to the thermodynamic data of the silicate, the gas conditions in the electric furnace were set and tuned to match the experimental data. In FIG. 5, “Experimental values” indicated by ● are plotted based on data based on the examples shown in Tables 2 and 4.

  Point A in FIG. 5 is a point that shows the composition of the waste before addition of the separation accelerator, which does not contain calcium and chlorine, and is one of the most difficult to separate radioactive cesium. . By adding both a calcium source and a low-melting-point chloride to the waste, thereby adjusting the composition of the object to be treated to points B to E in FIG. 5, for example, radioactive cesium contained in the waste Can be separated relatively easily. In consideration of suppressing the amount of the separation accelerator used and keeping the amount of chloride contained in the processing object as low as possible, the composition of the processing object may be adjusted to, for example, point D or point E in FIG. preferable. Points B and C are the upper limit (point B) and lower limit (point C) of the amount of low melting point chloride that can achieve a cesium removal rate of 50% when radioactive contaminants are heated at 1100 ° C. D and point E are the upper limit (point D) and lower limit (point E) of the low melting point chloride amount that can achieve a cesium removal rate of 70% when the radioactive contaminant is heated at 1100 ° C.

In order to obtain an object to be processed having the composition of points B to E in FIG. 5 by adding a separation accelerator to the waste having the composition of point A, CaCO ₃ (calcium source) and low melting point chloride A separation promoter having a ratio (mass ratio) as described below may be used. Wherein the amount of CaCO ₃ is obtained by calculating the terms of CaCO ₃ content of CaO amount in FIG.
Point B CaCO ₃ : low melting point chloride = 35: 65
Point C CaCO ₃ : low melting point chloride = 99: 1
Point D CaCO ₃ : low melting point chloride = 54: 46
Point E CaCO ₃ : low melting point chloride = 88: 12

Assuming that the mixing ratio of the separation accelerator CaCO ₃ (calcium source) is x mass% and the mixing ratio of the low melting point chloride of the separation accelerator is y mass%, from the examination result based on FIG. It is preferable that the separation accelerator used satisfies all of the following conditions.
(conditions)
35 ≦ x ≦ 99 (more preferably 54 ≦ x ≦ 88)
1 ≦ y ≦ 65 (more preferably 12 ≦ y ≦ 46)

  FIG. 6 shows the amount of calcium (calculated in terms of CaO, based on the total mass of the object to be processed) and the amount of low melting point chloride in the object to be treated after the addition of the separation accelerator in the method (2) (volatilization + water washing treatment). It is a graph which shows the relationship with (process target object total mass reference | standard). It is preferable to adjust the calcium amount (CaO conversion) and the low-melting-point chloride amount of the processing object to be subjected to the volatilization treatment prior to the water washing treatment to the region surrounded by the solid line in FIG.

  In FIG. 6, the estimation results by FactSage indicated by ◯ and X are FactSage Ver., Which is thermodynamic equilibrium calculation software manufactured by Computational Mechanics Research Center. The ratio of cesium chloride existing as gas and water-soluble chloride is estimated using 6.4. The conditions for the thermodynamic equilibrium calculation were the same as the conditions in FIG. In FIG. 6, the experimental value indicated by ● is a plot of data based on Example 3 shown in Table 4.

  Point A in FIG. 6 is a point that shows the composition of the waste that does not contain calcium and does not contain chlorine and before the addition of the separation accelerator, and that waste is one of the most difficult to separate radioactive cesium. . By adding both a calcium source and a low-melting-point chloride to the waste, thereby adjusting the composition of the object to be treated to points B to E in FIG. 6, for example, radioactive cesium contained in the waste Can be separated relatively easily. Considering that the amount of the separation accelerator (calcium source and low melting point chloride) used is suppressed and the amount of chloride contained in the object to be treated is kept as low as possible, the composition of the object to be treated is, for example, point D in FIG. Or it is more preferable to adjust to the point E. In addition, the point B and the point C are the upper limit (point B) and lower limit (point C) of the amount of low melting point chloride which can achieve a cesium removal rate of 50% when the object to be treated is heated at 700 ° C. and then washed with water. Points D and E are the upper limit (point D) and lower limit (point E) of the low melting point chloride amount that can achieve a cesium removal rate of 70% when radioactive contaminants are heated at 1100 ° C.

In order to obtain a treatment object having the composition of points B to E in FIG. 6 by adding a separation accelerator to the waste having the composition of point A, the ratio (mass ratio) of CaCO ₃ and low melting point chloride is obtained. ) May be used as follows. Wherein the amount of CaCO ₃ is obtained by calculating the terms of CaCO ₃ content of CaO content in FIG.
Point B CaCO ₃ : low melting point chloride = 57: 43
Point C CaCO ₃ : low melting point chloride = 93: 7
Point D CaCO ₃ : low melting point chloride = 70: 30
Point E CaCO ₃ : low melting point chloride = 91: 9

Assuming that the mixing ratio of the separation accelerator CaCO ₃ (calcium source) is x mass% and the mixing ratio of the low melting point chloride of the separation accelerator is y mass%, from the examination result based on FIG. It is preferable that the separation accelerator used satisfies all of the following conditions.
(conditions)
57 ≦ x ≦ 93 (more preferably 70 ≦ x ≦ 91)
7 ≦ y ≦ 43 (more preferably 9 ≦ y ≦ 30)

  In the above embodiment, the low melting point chloride (melting point: 700 ° C. or lower) is exemplified by a mixture of two types of chlorides. However, the low melting point chloride is composed of a mixture of three or more types of chlorides. May be.

  The low melting point chloride may be composed of a double salt of two or more kinds of chlorides. Two or more types of double salts of chloride can be prepared as follows. First, a predetermined amount of chloride is mixed to obtain a mixture. The mixture is melted by heating and then cooled to obtain a double salt. By pulverizing this, a powdery double salt (low melting point chloride) can be obtained.

  According to the separation accelerator containing the low melting point chloride, the temperature of the heat treatment for separating the radioactive cesium from the waste can be sufficiently lowered. Specifically, the temperature of the heat treatment can be set to 600 ° C. or higher and lower than 1200 ° C. When the separation accelerator is used in a process for removing radioactive cesium from waste by volatilizing by heating, the temperature of the heat treatment is preferably 800 ° C. or higher and lower than 1200 ° C., more preferably 900 ° C. or higher. It is 1100 degrees C or less, More preferably, it is 900 degrees C or more and 1000 degrees C or less. When the separation accelerator is used in the process of removing radioactive cesium from waste by volatilization by heating and subsequent washing treatment, the temperature of the heat treatment is preferably 600 ° C. or higher and 900 ° C. or lower, more preferably Is 700 ° C. or higher and 850 ° C. or lower, more preferably 700 ° C. or higher and 800 ° C. or lower.

  Moreover, according to the said separation promoter, a sufficiently high removal rate of radioactive cesium can be achieved with a smaller amount of addition than known separation promoters.

<Radiocesium removal method>
Next, a method for removing radioactive cesium from waste contaminated with radioactive cesium will be described. Wastes to be treated include industrial waste such as soil, sewage sludge dry powder, municipal waste incineration ash, waste slag, shells, vegetation and other general waste, sewage sludge, sewage slag, purified sludge, construction sludge, etc. Wastes such as waste and debris, which contain radioactive cesium. Only one of these wastes may be treated, or a combination of two or more may be treated.

  In addition, the “waste contaminated with radioactive cesium” mentioned here is a concentrated radioactive cesium obtained by removing in advance a portion that does not substantially contain radioactive cesium (for example, sand and stone in the case of soil). It is a concept that includes intermediate processed products. The “radioactive cesium” here means cesium 134 and cesium 137, which are radioisotopes of cesium. When these radioactive cesiums are dissipated by accidents such as nuclear power plants, they exist in the form of cesium aluminosilicate in the waste or adsorb on clay minerals, both of which are conventional heat treatment ( It is an aspect that is difficult to remove by volatilization) or water washing treatment.

  With removal treatment using the above low melting point chloride (mixture or double salt) or separation accelerator, even with waste to be treated, especially soil with low removal efficiency of radioactive cesium and sewage sludge, etc. with high removal rate Radiocesium can be removed.

  Hereinafter, a method for removing radioactive cesium from waste will be specifically described.

(1) Removal method by heat treatment (heat treatment)
The removal method by heat treatment volatilizes and removes radioactive cesium by heating waste to be treated. This removal method includes the following steps.
A mixing step for obtaining a mixture of the waste to be treated and the low melting point chloride.
-The heating process which volatilizes radioactive cesium by heating the said mixture.

  In the above mixing step, a separation accelerator prepared in advance may be added to the waste, or two or more types of chlorides that produce low-melting chloride and a calcium source as needed are prepared, each of which has a predetermined amount. May be added to the waste. For example, a container rotating mixer such as a ribbon mixer, a screw mixer, or a rocking mixer can be used as the equipment for performing the mixing step, and a stoker furnace, a kiln furnace, or the like can be used as the equipment for performing the heating process. The mixing step and the heating step may be performed with the same equipment (for example, heating while mixing in a kiln furnace or a stoker furnace).

When adding the calcium source to the waste, as described above, the addition amount of the calcium source (CaCO ₃ conversion, x mass%) and the addition amount of two or more chlorides (y mass%) are as follows: It is preferable to satisfy all the conditions (see FIG. 5).
(conditions)
35 ≦ x ≦ 99 (more preferably 54 ≦ x ≦ 88)
1 ≦ y ≦ 65 (more preferably 12 ≦ y ≦ 46)

  When the total mass of the object to be treated (base excluding combustible substances and moisture) is 100 parts by mass, the amount of calcium in terms of CaO contained in the object to be treated is 5.0 parts by mass or more (more preferably 5.0 to 40). The amount of Cl contained in the object to be treated is 1.0 to 15.0 parts by mass (more preferably 3.0 to 10.0 parts by mass, most preferably 10.0 to 35 parts by mass). It is preferably 4.0 to 8.0 parts by mass). In addition, when processing things that contain a lot of water, such as sewage sludge, or things that contain a lot of combustible materials such as plants and wood chips, the amount of calcium and Cl in the mixture of these ash after heating and the separation accelerator May be adjusted so that is within the above range.

  The amount of the above separation accelerator added depends on the type of waste to be treated, but the total amount of waste and separation accelerator (two or more chlorides and calcium sources) (base excluding combustible substances and moisture) ) As an addition amount (ratio) of 5 to 80% by mass (more preferably 10 to 75% by mass, still more preferably 15 to 70% by mass, most preferably 20 to 50% by mass) of radioactive cesium. A sufficiently high removal rate can be achieved. If the total amount of the two or more chlorides and the calcium source is less than 5% by mass, the removal rate of radioactive cesium tends to be insufficient, while if it exceeds 80% by mass, the waste containing radioactive cesium obtained after treatment It is easy to reduce the amount of water.

  The equipment used for the heating process may be a continuous type or a batch type, and specific examples include an incinerator, an electric furnace, and a rotary kiln. In order to prevent radiation of radioactive material, a seal may be provided in the heating facility.

  The treatment temperature in the heating step is preferably 800 ° C. or higher and lower than 1200 ° C., more preferably 900 ° C. or higher and 1100 ° C. or lower, and further preferably 900 ° C. or higher and 1000 ° C. or lower. 1150 degreeC may be sufficient as the upper limit of the process temperature in a heating process. If the treatment temperature is 700 ° C. or lower, the removal rate of radioactive cesium tends to be insufficient. On the other hand, if it is 1200 ° C. or higher, the cost of fuel, etc. required for the heat treatment is likely to increase and higher heat resistance is used. There is a need to. In addition to this, troubles such as melting of the waste and excessive adhesion to the heating equipment are likely to occur.

  The longer the treatment time in the heating step, the higher the removal rate of radioactive cesium, but from the viewpoint of waste treatment efficiency, it is preferably 30 minutes to 6 hours, more preferably 1 to 4 hours. Note that the radioactivity level in the waste after the heat treatment may be monitored, and the treatment time and treatment temperature of the heating step, the addition amount of various components in the mixing step, and the like may be adjusted according to this value.

  The removal method according to the present embodiment further includes a pulverization step of pulverizing the mixture after the mixing step from the viewpoint of increasing the degree of mixing of waste and additives such as separation accelerators or increasing the removal efficiency of radioactive cesium. You may prepare. Moreover, you may further provide the collection | recovery process which collect | recovers the radioactive cesium volatilized by heat processing with a dust collector (for example, bag filter) with other chlorides and dust components.

(2) Removal method by heat treatment and water washing treatment (heat treatment + water washing treatment)
The removal method by heat treatment and water washing treatment is to further remove the remaining radioactive cesium by volatilizing radioactive cesium by heating the waste to be treated and then washing the waste with water. This removal method includes the following steps.
A mixing step for obtaining a mixture of the waste to be treated and the low melting point chloride.
-The heating process which volatilizes radioactive cesium by heating the said mixture.
-A water washing step for leaching radioactive cesium by washing the waste after the heating step with water.
Hereinafter, differences from the above-described (1) removal method by heat treatment will be mainly described.

When adding the calcium source to the waste, as described above, the addition amount of the calcium source (CaCO ₃ conversion, x mass%) and the addition amount of two or more chlorides (y mass%) are as follows: It is preferable to satisfy all the conditions (see FIG. 6).
(conditions)
57 ≦ x ≦ 93 (more preferably 70 ≦ x ≦ 91)
7 ≦ y ≦ 43 (more preferably 9 ≦ y ≦ 30)

  When the total mass of the object to be treated (base excluding combustible substances and moisture) is 100 parts by mass, the amount of calcium in terms of CaO contained in the object to be treated is 20.0 parts by mass or more (more preferably 20.0 to 40). The amount of Cl contained in the object to be processed is 4.0 to 25.0 parts by mass (more preferably 4.0 to 20.0 parts by mass, most preferably 5.0.0 to 15.0). Part by mass). In addition, when processing things that contain a lot of water, such as sewage sludge, or things that contain a lot of combustible materials such as plants and wood chips, the amount of calcium and Cl in the mixture of these ash after heating and the separation accelerator May be adjusted so that is within the above range.

  The amount of the above separation accelerator added depends on the type of waste to be treated, but the total amount of waste and separation accelerator (two or more chlorides and calcium sources) (base excluding combustible substances and moisture) ) As an addition amount (ratio) of 5 to 80% by mass (more preferably 10 to 75% by mass, still more preferably 15 to 70% by mass, most preferably 20 to 50% by mass) of radioactive cesium. A sufficiently high removal rate can be achieved. If the total amount of the two or more chlorides and the calcium source is less than 5% by mass, the removal rate of radioactive cesium tends to be insufficient, while if it exceeds 80% by mass, the waste containing radioactive cesium obtained after treatment It is easy to reduce the amount of water.

  The treatment temperature in the heating step is preferably 600 ° C. or higher and 900 ° C. or lower, more preferably 700 ° C. or higher and 850 ° C. or lower, and still more preferably 700 ° C. or higher and 800 ° C. or lower. If the treatment temperature is less than 600 ° C., the removal rate of radioactive cesium tends to be insufficient. On the other hand, if it is 900 ° C. or more, a sufficiently high removal rate of radioactive cesium may be achieved only by the heating step. The need to carry out the process is reduced.

  The equipment used for the water washing step may be a continuous type or a batch type. For example, an object may be put into a water tank and stirred for a certain period of time, and this operation may be performed in one stage or in multiple stages. In order to prevent the radioactive material from being diffused, a seal may be provided in the washing facility. The final radioactive contamination level may be confirmed, and if necessary, the washing time may be extended, the treatment time and treatment temperature of the heating step, and the addition amount of various components in the mixing step may be adjusted. Radiocesium eluted in water by the water washing process is collected by an adsorbent such as zeolite, and then transported to a final disposal site through a concentration process and the like.

  As for the separation accelerator of this embodiment, the lower the amount of calcium or chlorine in the waste to be treated, the higher the cesium separation effect can be obtained than the conventional separation accelerator. The calcium content (CaO equivalent) of the waste to be treated is 0 to 30% by weight (preferably 0 to 20% by weight, more preferably 0 to 10% by weight, most preferably 0) based on the total weight of the waste to be treated. ˜5% by mass), and the chlorine content is 0 to 10% by mass (preferably 0 to 7%, more preferably 0 to 5%, most preferably 0 to 1%). The effect is remarkable.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Preparation of cesium adsorption clay]
Assuming that radioactive cesium and stable cesium behave in the same manner, experiments were conducted using cesium carbonate, which is stable cesium, instead of radioactive cesium. In addition, as a result of past studies, it has been clarified that radioactive cesium is adsorbed by clay minerals in soil and is not easily dissolved in water. Therefore, stable cesium was adsorbed on clay minerals by the following method for testing. Provided. The method for preparing the cesium-adsorbed clay sample is as follows. Cesium carbonate (250 to 300 mg / kg in terms of Cs) was added to 1000 g of the clay, water was added at 40 mass% with respect to the clay, and the mixture was kneaded with a Hobart mixer. Then, it was allowed to stand for about a week to sufficiently adsorb cesium on the clay mineral. And the clay soil which adsorb | sucked cesium was dried at 100 degreeC, the excess water | moisture content was removed, and it was set as the cesium adsorption clay sample.

[Production of cesium-containing incineration ash]
Previous studies have revealed that radioactive cesium in incineration ash exists in the form of aluminosilicate, so the reagents cesium carbonate, Al ₂ O ₃ and SiO ₂ are formulated to be chemical components of CsAlSiO _4. Then, the cesium aluminosilicate synthesized by heating at 900 ° C. for 1 hour was added to the waste incineration ash so as to be 250 to 300 mg / kg in terms of cesium to produce a cesium-containing incineration ash. FIG. 7 is an X-ray diffraction profile of the synthesized cesium aluminosilicate. This profile shows that most is produced as CsAlSiO ₄ , contains a small amount of CsAlSi ₂ O ₆ , and some unreacted SiO ₂ and CsO remain.

  Table 1 shows the chemical composition of the clay soil (cesium adsorption clay) and incineration ash (cesium-containing incineration ash) to which cesium was added.

[Preparation of cesium separation promoter]
As the cesium separation accelerator, calcium carbonate, calcium chloride, and sodium chloride were used and prepared according to the formulation shown in Table 2. When both CaCl ₂ and NaCl are added, the melting point indicated by the line A → B → C shown in FIG. The conditions of Examples 1 to 3 and Reference Example 4 in Table 2 are such that the melting point of the chloride is 504 ° C. (molar ratio CaCl ₂ : NaCl = 50: 49).

* "Addition amount" in Table 2 is the ratio of the mass of the separation accelerator to the total amount (mass) of the cesium adsorption clay and the separation accelerator.

[Heat treatment]
For cesium-containing soil and incineration ash, after adding a predetermined amount of cesium separation accelerator, weigh 10 g of sample, place it on an alumina boat so that the depth of the sample is about 1 cm, and heat-treat in an electric furnace. went. The heating temperature was 700 ° C., 900 ° C., and 1100 ° C., and the heating time was 2 hours.

[Measurement of cesium content and cesium removal rate]
The removal rate of cesium was defined as the ratio of the amount of volatile cesium and the amount of water-soluble cesium contained in the clay after heat treatment to the amount of cesium in the untreated clay in consideration of removal by volatilization and washing with water. The measuring method of volatile cesium and water-soluble cesium is as follows.
(1) Total cesium amount The total cesium amount contained in the sample was quantified by ICP after the sample was completely melted by alkali melting or the like. Based on the total amount of cesium contained in the sample with no separation accelerator added and unheated, the amount of cesium contained in the sample after heating is more concentrated than the amount of cesium at the time of non-heating when part of the sample is volatilized. Therefore, it was converted into the amount of cesium at the time of non-heating by the following formula, and the amount of additive was further corrected to obtain the amount of residual cesium after heating. The amount of mass reduction upon heating includes decarboxylation of CaCO ₃ used as a calcium source in addition to volatilization of cesium and chloride.
Residual cesium content (total cesium content after heat treatment (untreated base)) =
Total amount of cesium in the heat-treated sample × {100 / (100−mass loss% upon heating%)}
X {100 / (100-Amount of separation accelerator%)}

(2) Volatile cesium amount Volatile cesium was determined by subtracting the total amount of cesium in the sample after heat treatment from the total amount of cesium in untreated cesium-containing viscous soil or incinerated ash. The total amount of cesium after the heat treatment, that is, the amount of residual cesium was determined by the above formula.
Volatile cesium amount = total cesium amount of untreated sample-residual cesium amount after heating (untreated base)

(3) Amount of water-soluble cesium The amount of water-soluble cesium was measured as follows. First, 1 g of a sample was placed in 10 g of water and stirred for 10 minutes to elute cesium. Thereafter, the solution was filtered, and the amount of cesium in the filtrate was defined as the amount of water-soluble cesium. Similar to Equation 1, the amount of water-soluble cesium was corrected by the following equation as the amount for the untreated base.
Water-soluble cesium amount (untreated base) =
Amount of water-soluble cesium in the heat-treated sample × {100 / (100−mass decrease in heating%)}
X {100 / (100-Amount of separation accelerator%)}

(4) Slightly soluble cesium amount The hardly soluble cesium amount was determined by subtracting the amount of water soluble cesium from the total amount of cesium after heat treatment (untreated base).
(5) Cesium removal rate The cesium removal rate was determined as follows.
Cesium removal rate% =
(Volume of cesium + amount of water-soluble cesium ^* ) ÷ total amount of cesium when not treated x 100%
* For both volatile cesium and water-soluble cesium, the conversion value based on untreated is used.

1. Confirmation of the effect of radioactive cesium separation accelerator (experiment with cesium adsorption clay)
Table 3 shows the results of cesium removal after heat treatment when various separation accelerators were added and the removal rate of cesium that can be removed by volatilization and water washing. As for the amount of cesium, the amount based on an untreated sample is described.
[Untreated sample]
The amount of cesium in the untreated sample (cesium-adsorbed clay) is 240 mg / kg.

[Comparative Example 1 (no additive)]
No. No separation accelerator added. 1 (Comparative Examples 1-1 to 1-3 in Table 3), even if the heating temperature is increased to 1100 ° C., the amount of volatile cesium is small and the cesium removal rate is as low as 12.5 to 25.0%. Even if water-soluble cesium is included, the cesium removal rate is low and separation by heating is difficult.

[Addition Condition No. in Table 3 2-4]
When CaCO ₃ is used as a separation accelerator (Nos. 2 to 4 in Table 2), the addition amount is 20 to 60%, and even if the heating temperature is increased to 1100 ° C., the volatile cesium does not increase so much, and the cesium is separated. The promoting effect was not obtained (Comparative Examples 2-1 to 4-3 in Table 3). Moreover, water-soluble cesium did not increase so much.

[Addition Condition No. in Table 3 5-6]
Separation promoters composed of CaCl ₂ and CaCO ₃ (Nos. 5 to 6 in Table 2) were added to 50% and except for Reference Example 6-3 heated to 1100 ° C., volatile cesium and water-soluble cesium were It did not increase and the effect of promoting the separation of cesium was not obtained (Comparative Examples 5-1 to 6-3). In the case of this separation accelerator, it is necessary to increase the amount of addition and to heat at a high temperature of 1100 ° C. or higher, which is not economically preferable.

[Addition condition No. in Table 4 7-9]
Addition condition No. 1 in which appropriate amounts of CaCl ₂ and NaCl were mixed (molar ratio 50:49) so that chloride melts at a low temperature of 700 ° C. or less in CaCO ₃ When 7 to 10 were heated at temperatures exceeding 700 ° C. (900 ° C. and 1100 ° C.), the cesium removal rate was 50% or more, and a high cesium separation promoting effect was obtained.

[Addition condition No. in Table 4 10]
Separation accelerators containing appropriate amounts of CaCl ₂ and NaCl (molar ratio 50:49) so that the chloride melts at a low temperature of 700 ° C. or less can also be removed at a rate of 50% or more when heated at 900 ° C. and 1100 ° C. Thus, a high cesium separation promoting effect was obtained.

[Addition condition No. in Table 4 11]
Even when the separation accelerator containing NaCl and CaCO ₃ was heated to 1100 ° C., the cesium removal rate was 50% or less, and the effect of promoting cesium separation was not high.

  Tables 3 and 4 show the cesium (Cs) existence form and the removal rate when a mixture obtained by adding a separation accelerator to viscous soil adsorbed with cesium is heated for 2 hours. A Cs removal rate of 50% or more is indicated by “◯” and less than 50% is indicated by “x”. 8 to 11 are graphs of the results shown in Tables 3 and 4. FIG.

2. Confirmation of effect of radioactive cesium separation accelerator (experiment with incinerated ash containing cesium)
The cesium-containing incinerated ash was also tested in the same manner as the cesium-adsorbed clay. Table 5 shows the type and amount of separation accelerator when cesium-containing incineration ash is used. Table 6 shows the composition and addition amount of the cesium separation accelerator. Table 7 shows the cesium (Cs) existence form and removal rate when heat-treated with incinerated ash for 2 hours. A Cs removal rate of 50% or more is indicated by “◯” and less than 50% is indicated by “x”. As shown in Table 7, the cesium removal efficiency was 50% or more at 900 ° C. and 1100 ° C., and an effect of promoting cesium separation was observed not only on soil (cesium adsorbed clay) but also on incinerated ash.

3. Confirmation of effect of low melting point chloride other than CaCl ₂ -NaCl system (experiment with cesium adsorption clay)
Using cesium adsorbed clay, the effect of low melting point chloride other than CaCl ₂ -NaCl system was confirmed.

(Example 14)
In this example, 25CaCl ₂ · 75 KCl (melting point: 599 ° C.) was used as the low melting point chloride with respect to “Combination 2” described above. In this example, in order to obtain a low melting point chloride, CaCl ₂ and KCl are mixed at a molar ratio of 25:75, and calcium carbonate (CaCO ₃ ) and the low melting point chloride are mixed with each other at a mixing ratio of each other. The following two different types of separation accelerators were prepared.

The separation accelerator according to Example 14-1 is CaCO ₃ : low melting point chloride (mass ratio) of 60:10. The object to be treated was prepared by adding 70% by mass of the separation accelerator to the total amount of the separation accelerator and cesium-adsorbed clay. The object to be treated was heated to 700 ° C. to obtain a heat-treated object. Further, this heat-treated product was washed with water. Table 8 shows the results of the cesium volatilization removal rate by the heat treatment and the water removal rate of cesium by the water washing treatment.

The separation accelerator according to Example 14-2 is CaCO ₃ : low melting point chloride (mass ratio) of 40:10. The heating object was prepared by adding 50 mass% of the separation accelerator to the total amount of the separation accelerator and cesium adsorption clay. The object to be treated was heated to 900 ° C. to obtain a heat-treated object. Further, this heat-treated product was washed with water. Table 8 shows the results of the cesium volatilization removal rate by the heat treatment and the water removal rate of cesium by the water washing treatment.

(Example 15)
In this example, 35 MgCl ₂ · 65 KCl (melting point: 423 ° C.) was used as the low melting point chloride for “Combination 4” described above. In this example, in order to obtain a low melting point chloride, MgCl ₂ and KCl are mixed at a molar ratio of 35:65, and calcium carbonate (CaCO ₃ ) and the low melting point chloride are mixed with each other at a mixing ratio of each other. The following two different types of separation accelerators were prepared.

The separation accelerator according to Example 15-1 is CaCO ₃ : low melting point chloride (mass ratio) of 60:10. The object to be treated was prepared by adding 70% by mass of the separation accelerator to the total amount of the separation accelerator and cesium-adsorbed clay. The object to be treated was heated to 700 ° C. to obtain a heat-treated object. Further, this heat-treated product was washed with water. Table 8 shows the results of the cesium volatilization removal rate by the heat treatment and the water removal rate of cesium by the water washing treatment.

The separation accelerator according to Example 15-2 is CaCO ₃ : low melting point chloride (mass ratio) of 40:10. The heating object was prepared by adding 50 mass% of the separation accelerator to the total amount of the separation accelerator and cesium adsorption clay. The object to be treated was heated to 900 ° C. to obtain a heat-treated object. Further, this heat-treated product was washed with water. Table 8 shows the results of the cesium volatilization removal rate by the heat treatment and the water removal rate of cesium by the water washing treatment.

FIG. 15 is a graph summarizing the results of adding CaCl ₂ alone or NaCl alone, the results of adding 49 NaCl · 50 CaCl ₂ , and the results of Examples 14 and 15. It has been confirmed that by blending the low melting point chloride with the separation accelerator, the effect of promoting cesium separation becomes very high as compared with the case where a single chloride (CaCl ₂ or NaCl) is blended.

  As shown in Tables 3 and 4 and FIG. 15, the separation accelerator used in the above examples has a sufficient effect of removing radioactive cesium in a heating temperature range of 700 to 1200 ° C. that is possible in an incinerator or a rotary kiln. 12 to 14 are graphs of the results shown in Tables 3 and 4, and show the ratio of cesium that is volatilized and removed from the waste and the cesium that is removed by the water washing process that is performed as necessary thereafter. It is a graph. By combining the heat treatment (volatilization removal) and the water washing treatment (water washing removal), the temperature of the heat treatment for volatilization removal can be further lowered. The separation accelerator according to the present invention is useful for decontamination of soil contaminated with radioactive cesium released in an accident at a nuclear power plant, incineration ash, wastewater such as sewage sludge, and volume reduction of radioactive waste. .

Claims (6)

A separation accelerator for removing radioactive cesium from waste contaminated with radioactive cesium,
And the melting point is prepared by using two or more types of chloride further comprises a mixture or unrealized and calcium source double salt is 700 ° C. or less, separation accelerator.   The separation promoter according to claim 1, wherein the two or more types of chlorides are selected from the group consisting of alkaline earth metal chlorides, alkali metal chlorides, and iron chloride. Wherein two or more chlorides _are those selected from CaCl _2, MgCl 2, NaCl, KCl, LiCl, the group consisting of FeCl ₃ and FeCl _2, separation enhancer of claim 1. The mixture or the double salt is prepared using any of the following combinations 1 to 6 of the first chloride and the second chloride, and the mole of the first chloride in the mixture or the double salt: The separation promoter according to any one of claims 1 to 3, wherein the ratio (M ₁ / M ₂ ) of the number M ₁ and the number of moles M ₂ of the second chloride is in the following range.
Combination 1: first chloride CaCl ₂ and second chloride NaCl, 3/7 ≦ M ₁ / M ₂ ≦ 7/3
Combination 2: first chloride KCl and second chloride CaCl ₂ , 2/8 ≦ M ₁ / M ₂ ≦ 3/7 or 65/35 ≦ M ₁ / M ₂ ≦ 85/15
Combination 3: first chloride MgCl ₂ and second chloride NaCl, 2/8 ≦ M ₁ / M ₂ ≦ 8/2
Combination 4: first chloride MgCl ₂ and second chloride KCl, 2/8 ≦ M ₁ / M ₂ ≦ 85/15
Combination 5: first chloride NaCl and second chloride FeCl ₃ , 15/85 ≦ M ₁ / M ₂ ≦ 35/65
Combination 6: first chloride NaCl and second chloride FeCl ₂ , 4/6 ≦ M ₁ / M ₂ ≦ 8/2 When the total mass of the separation accelerator is 100 parts by mass, the total content of the mixture and the double salt is 1 to 65 parts by mass, and the content of the calcium source is 35 to 99 parts by mass. Item 5. The separation promoter according to any one of Items 1 to 4 . The separation promoter according to any one of claims 1 to 5, wherein the calcium source is at least one selected from the group consisting of limestone, quicklime, slaked lime, and dolomite.