JP6628282B2 - Method for removing radioactive cesium and method for producing fired product - Google Patents

Description

  The present invention relates to a method for removing radioactive cesium from radioactive cesium-contaminated waste, and a harmless calcined material (for example, cement mixture, bone) using radioactive cesium-contaminated waste as a raw material. Materials, earthwork materials).

The problem has arisen that radioactive cesium released into the external environment by a major nuclear power plant accident may be contained in waste or soil. Since radioactive cesium (cesium 137) has a half-life of 30 years and can have an adverse effect on the human body over a long period of time, it is often required to remove radioactive cesium from waste and the like.
As a method for removing radioactive cesium, for example, radioactive waste present in the form of nitrate is dissolved by electromagnetic induction heating in a cooled container having a slit with an energizing coil circulating outside, and the nitrate is decomposed. Of the radioactive waste, consisting of accumulating the metal oxide produced around the container and the reduced white metal element in the center of the container by the electromagnetic pinch force, and then collecting the solidified product after cooling and condensing. As a treatment method, there is described a method of separating and recovering long-lived nuclides such as cesium volatilized from radioactive waste during electromagnetic induction heating (Patent Document 1).
However, the method of Patent Document 1 is not intended for radioactive cesium released into the external environment due to an accident, but for radioactive waste generated in a limited area such as a nuclear power plant. Therefore, it is not suitable for treating an enormous amount of contaminated soil and the like, and the apparatus is complicated, expensive, and expensive.

JP-A-5-157897

  An object of the present invention is to provide a method capable of easily and efficiently removing radioactive cesium from waste contaminated with radioactive cesium. Another object of the present invention is to provide a method for producing harmless calcined products (eg, cement mixture, aggregate, earthwork material) by using waste contaminated with radioactive cesium as a raw material. I do.

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, heating the waste contaminated with radioactive cesium and the CaO source and / or the MgO source at a specific blending ratio, thereby achieving the above object. Have been achieved, and the present invention has been completed.
That is, the present invention provides the following [1] to [9].
[1] A method for removing radioactive cesium including a heating step of heating a waste contaminated with radioactive cesium and a CaO source and / or a MgO source at 1200 to 1350 ° C. to volatilize radioactive cesium in the waste. In the heating step, the mass of each of CaO, MgO, and SiO ₂ is adjusted so that the numerical value derived from the following equation (1) is larger than 1.9 and equal to or smaller than 2.5. A method for removing radioactive cesium, wherein the types and mixing ratios of waste, CaO source and MgO source are determined.
((CaO + 1.39 × MgO) / SiO ₂ ) (1)
(In the formula, CaO, MgO, and SiO ₂ represent a mass in terms of calcium oxide, a mass in terms of magnesium oxide, and a mass in terms of silicon oxide, respectively.)
[2] The method for removing radioactive cesium according to [1], wherein a chloride is further used in the heating step.
[3] The method for removing radioactive cesium according to [1] or [2], wherein in the heating step, heating is performed in a reducing atmosphere.
[4] Includes a heating step of heating a waste contaminated with radioactive cesium and a CaO source and / or a MgO source at 1200 to 1350 ° C. to volatilize radioactive cesium in the waste and obtain a fired product. A method for producing a fired product, wherein in the heating step, the mass of each of CaO, MgO, and SiO ₂ is greater than 1.9 derived from the following formula (1) and is 2.5 or less. so that, the waste, defining the types and blending ratio of each of the CaO source and MgO source (provided that the baked product comprises _{C 2} S and _C 2 _aS, and _C 2 aS per C 2 S100 parts by A method for producing a fired product, characterized in that the waste, the CaO source, and the MgO source are determined in the respective types and mixing ratios so that the total amount of C ₄ AF is 10 to 100 parts by mass.) .
((CaO + 1.39 × MgO) / SiO ₂ ) (1)
(In the formula, CaO, MgO, and SiO ₂ represent a mass in terms of calcium oxide, a mass in terms of magnesium oxide, and a mass in terms of silicon oxide, respectively.)
[5] The method for producing a fired product according to [4], wherein in the heating step, heating is performed in a reducing atmosphere.
[6] The production of the fired product according to the above [4] or [5], including a mixing step of mixing at least one selected from the group consisting of a reducing agent and an adsorbent with the fired product obtained by the heating step. Method.
[7] A method for producing a cement mixture, comprising obtaining a calcined product by the method for producing a calcined product according to any one of [4] to [6], and then pulverizing the calcined product to obtain a cement mixture. .
[8] A method for manufacturing an aggregate, comprising obtaining a fired product by the method for manufacturing a fired product according to any one of [4] to [6], and then pulverizing or classifying the fired product to obtain an aggregate. .
[9] A method for manufacturing an earthwork material, wherein a fired material is obtained by the method for manufacturing a fired material according to any of [4] to [6], and the fired material is pulverized or classified to obtain an earthwork material. .

According to the method for removing radioactive cesium of the present invention, radioactive cesium can be easily and efficiently removed from waste contaminated with radioactive cesium, and the volume of radioactive waste can be reduced.
Further, according to the method for producing a fired product of the present invention, a harmless fired product from which radioactive cesium has been removed can be obtained. This calcined product can be used as a cement mixture or aggregate for reconstruction concrete (dikes, breakwaters, breakwater blocks, etc.), which will be required in large quantities in the future, and can protect natural resources. . In addition, as an earthwork material, it can be used as a backfill material for land from which soil has been removed.

Hereinafter, the present invention will be described in detail.
The method for removing radioactive cesium according to the present invention comprises a heating step of heating a radioactive cesium-contaminated waste and a CaO source and / or a MgO source at 1200 to 1350 ° C. to volatilize radioactive cesium in the waste. In the above heating step, the mass of each of CaO, MgO, and SiO ₂ is larger than 1.9 derived from the following equation (1), and 2.5. It is characterized in that the types and the mixing ratios of the waste, the CaO source and the MgO source are determined as follows.
((CaO + 1.39 × MgO) / SiO ₂ ) (1)
(In the formula, CaO, MgO, and SiO ₂ represent a mass in terms of calcium oxide, a mass in terms of magnesium oxide, and a mass in terms of silicon oxide, respectively.)

The object to be treated according to the present invention is waste contaminated with radioactive cesium.
Here, the waste contaminated with radioactive cesium is, for example, soil and general waste such as sewage sludge dry powder, municipal waste incineration ash, refuse-derived molten slag, shells and plants, sewage sludge, sewage slag, Industrial waste such as purified water sludge and construction sludge, and disaster waste such as debris, which contain radioactive cesium. These may be used alone or in combination of two or more. In addition, the radioactive cesium-enriched (intermediately treated product) obtained by previously removing a portion containing almost no radioactive cesium (for example, in the case of soil, sand and stone) is also referred to as “contaminated with radioactive cesium” in the present invention. Waste ”.
Examples of the CaO source include calcium carbonate, limestone, quicklime, slaked lime, limestone, dolomite, blast furnace slag, and the like. Examples of the MgO source include magnesium carbonate, magnesium hydroxide, dolomite, serpentine, ferronickel alloy slag, and the like. One of these examples may be used alone, or two or more may be used in combination.
In the present invention, both the CaO source and the MgO source may be used, or only one of them may be used. However, it is preferable to mix only the CaO source from the viewpoint of the volatility of radioactive cesium.
Further, it is preferable to use a pulverized powder as the CaO source and the MgO source.

In the present invention, radioactive cesium means cesium-134 and cesium-137, which are radioisotopes of cesium. These radioactive cesiums are radioactive substances that are released into the external environment due to a nuclear power plant accident, and have a half-life of about 2 years and about 30 years, respectively.
In the present invention, the radioactive cesium to be removed is released from the nuclear power plant where the accident occurred into the external environment together with radioactive iodine in the form of cesium iodide and the like, and falls from the sky to the ground surface. . Cesium iodide has a boiling point of 1200 ° C. or higher, and has a property of being less likely to volatilize than cesium alone having a boiling point of about 700 ° C. In addition, the radioactive cesium that has fallen to the ground surface is trapped in the clay minerals contained in the soil, making it difficult for the radioactive cesium to separate from the soil, and may change its form. In addition, radioactive cesium that has adhered to disaster waste such as debris or has fallen on the ground surface is washed away by rain and is concentrated in the course of sewage treatment, thereby producing sewage sludge containing radioactive cesium at a high concentration. Furthermore, plants absorb radioactive cesium contained in the soil, causing the plants to become radioactively contaminated.Incinerated ash produced by incineration of plants containing these radioactively contaminated plants, the radioactive cesium is confined in glass, etc. Sometimes. In the present invention, these radioactive cesium compounds in a state that is difficult to treat are separated and recovered.

The radioactive cesium-contaminated waste and the CaO source and / or the MgO source have the following masses: calcium oxide (CaO), magnesium oxide (MgO), and silicon dioxide (SiO ₂ ). The waste, the CaO source and the MgO source are mixed and determined in such a manner that the value derived from the equation (1) is larger than 1.9 and 2.5 or less. .
((CaO + 1.39 × MgO) / SiO ₂ ) (1)
(In the formula, CaO, MgO, and SiO ₂ represent a mass in terms of calcium oxide, a mass in terms of magnesium oxide, and a mass in terms of silicon oxide, respectively.)
The lower limit of the mass of each of the above CaO, MgO and SiO ₂ and the numerical value derived from the above formula (1) is a value larger than 1.9 from the viewpoint of increasing the volatilization amount of radioactive cesium.
The upper limit of the numerical value derived from the above formula (1) is preferably 2.4 or less, from the viewpoint of volatilizing radioactive cesium in the mixture and reducing the volatilization amount of potassium and sodium in the mixture. It is more preferably not more than 2.3, and further preferably not more than 2.2.
In addition, since the mass of 1 mol of CaO corresponds to the mass of 1.39 mol of MgO, in the above formula (1), the mass of MgO is multiplied by 1.39.
When the mass ratio is less than 1.0, a liquid phase is likely to be generated as the firing temperature increases, and the volatilization amount of radioactive cesium decreases. If the mass ratio exceeds 2.5, the total volatilization of potassium and sodium in the mixture of the radioactive cesium-contaminated waste and the CaO source and / or MgO source increases, and the exhaust gas is cooled. The amount of radioactive waste containing solids is increased.

For the purpose of accelerating the chloride volatilization of radioactive cesium and reducing the volume of the volatilized recovered material, chlorides such as calcium chloride (CaCl ₂ ), potassium chloride (KCl), sodium chloride (NaCl), etc. May be used. Among them, calcium chloride is preferred from the viewpoint of promoting volatilization of chloride.
As for the amount of chloride, the molar ratio of chlorine to cesium and potassium (Cl / (Cs + K)) is preferably 1.00 or less, more preferably 0.010 to 0.60, and still more preferably 0.015 to 0. .40, particularly preferably 0.03 to 0.30. When the molar ratio is 1.0 or less, the radioactive cesium volatilizes in a large amount without volatilizing potassium or sodium, so that the volume of radioactive substance-containing waste can be reduced.
Further, the amount of chlorine in the mixture is preferably 1500 mg / kg or less. When the amount of chlorine is 1500 mg / kg or less, a liquid phase hardly occurs even at a high temperature, and a large amount of radioactive cesium is volatilized.
Preferably, the molar ratio (Cl / (Cs + K)) is 1.0 or less, and the amount of chlorine in the mixture is 1500 mg / kg or less, more preferably, the molar ratio is 0.5 or less; If the amount of chlorine in the mixture is 1250 mg / kg or less, the volatilized cesium can be easily volatilized in the form of cesium chloride, and the volume of the collected material described below can be reduced.
When mixing the above-mentioned waste with the CaO source and / or the MgO source, if necessary, crushing and pulverizing also serving as mixing, or combining a crusher or crusher with a mixer, Two-stage processing may be performed. In the case of firing using a rotary kiln described later, since each material is rotationally mixed in the rotary kiln, a part of the above-described CaO source, MgO source, waste, and the like may be directly introduced into the kiln kiln butt. The mixture is preferably smaller than a granular material of about 5 mm. Alternatively, stones of 5 mm or more that do not contain much cesium may be removed while washing with water.

The heating temperature of the mixture of the radioactive cesium-contaminated waste and the CaO source and / or MgO source is from 1200 to 1350C, preferably from 1200 to 1300C.
By heating within the above temperature range, radioactive cesium contained in waste can be efficiently volatilized. If the heating temperature is lower than 1200 ° C., the volatilization amount of radioactive cesium decreases. When the temperature exceeds 1350 ° C., a radioactive cesium is taken in due to the formation of a liquid phase, which makes it difficult to volatilize, which is not preferable.
The heating time of the mixture is preferably 15 minutes or more, more preferably 30 minutes or more, from the viewpoint of obtaining a sufficient volatilization amount of radioactive cesium. The upper limit of the heating time is not particularly limited, but is preferably 180 minutes or less, more preferably 120 minutes or less. If the heating time exceeds 180 minutes, the volatilization amount of potassium and sodium increases together with the radioactive cesium in the mixture.
When the raw material rolls, such as in a rotary kiln, the contact ratio between the gas and the radioactive cesium increases, and the thermal conductivity also increases. it can.
As the heating means, either a continuous type or a batch type can be used.
Examples of the continuous heating means include a rotary kiln.
Examples of the batch-type heating means include an incinerator, an electric furnace, and a microwave heating device.
Above all, a continuous heating means is preferably used in the present invention from the viewpoint of increasing the efficiency of the treatment. In particular, a rotary kiln is preferable because it can easily provide a heating temperature and a waste residence time suitable for volatilizing radioactive cesium.

As an atmosphere at the time of heating, it is preferable to perform heating under air containing water vapor because the amount of volatilization of alkali metals (potassium and sodium) can be reduced and the amount of volatilization of radioactive cesium can be increased.
On the other hand, when heating is performed under air (pure air) that does not contain water vapor, the amount of volatilization of alkali metals (potassium and sodium) increases, but more radioactive cesium can be volatilized.
By adjusting the amount of chloride, the heating temperature, the time, and the amount of water vapor during heating, it is possible to reduce the volatilization amount of alkali metals (potassium and sodium) and increase the volatilization amount of radioactive cesium. .

When chromium is contained in waste contaminated with radioactive cesium, hexavalent chromium (Cr ⁶⁺ ) may be contained in the obtained fired product.
When such a calcined product is used as a cement mixture, an aggregate, an earthwork material, etc. (particularly when used as an earthwork material), hexavalent chromium contained in the calcined material elutes, and water pollution, soil contamination, etc. Can cause
Therefore, in the heating step, heating may be performed in a reducing atmosphere. By heating in a reducing atmosphere, even if the waste contains chromium, it is possible to prevent the generation of hexavalent chromium, which is likely to occur in an oxidizing atmosphere, and in the step of heating the waste, Even if the waste is temporarily heated in an oxidizing atmosphere to generate hexavalent chromium, it is reduced to trivalent chromium (Cr ³⁺ ), so the obtained fired material can be safely used as earthwork material, etc. Can be used. Note that the above-described method of heating under steam-containing air and the method of heating under a reducing atmosphere may be performed in combination. Hereinafter, a method of heating under a reducing atmosphere will be described by taking as an example a case where an internal combustion type device (such as an internal combustion rotary kiln) and a countercurrent type device (combustion at the raw material outlet side) is used. However, the present invention is not limited to these modes.

As an example of a method of heating waste contaminated with radioactive cesium under a reducing atmosphere, a method of burning a combustible substance when heating the waste is mentioned. By burning the combustible material, the surroundings of the waste can be kept in a reducing atmosphere. Further, even if the waste contains chromium, the generation of hexavalent chromium can be prevented, and even if hexavalent chromium is generated in the step of heating the waste, hexavalent chromium can be prevented. Is reduced to trivalent chromium.
Here, examples of the flammable substance include a solid waste such as coal, coke, activated carbon, waste wood, waste plastic, heavy oil sludge, and compressed and / or solidified waste such as municipal waste.
As a method of supplying a combustible substance, it may be mixed in advance with waste contaminated with radioactive cesium, and when a rotary kiln is used as a device used for heating, the combustible substance is supplied to a waste inlet side, It may be supplied from the outlet side or from the middle of the rotary kiln.
When the flammable substance is preliminarily mixed with the raw material, as long as the flammable substance does not remain in an unburned state in the fired product obtained by heating, the mixing amount of the flammable substance is preferably larger, and The larger the particle size, the better.

Here, a case where the combustible material is supplied on the inlet side of the waste of the rotary kiln or in the middle of the rotary kiln will be described.
In this case, it is preferable that the flammable substance can maintain the reducing atmosphere for a long time. Specifically, for example, a fuel having a lower combustion rate than the main fuel of the rotary kiln, or a combustible substance having a combustion rate similar to that of the main fuel and having coarser particles than the main fuel may be used. Specific examples include petroleum coke, coal coke, and anthracite. The lower the burning rate, the more preferable the combustible substance can be.
The average particle size of the combustible material is preferably 0.5 to 20 mm, more preferably 1 to 5 mm. If the average particle size is less than 0.5 mm, the burning will occur at the very beginning of the combustion, so that the reducing atmosphere may not be maintained for a long time. When the average particle size exceeds 20 mm, a large amount of unburned combustible material remains in the obtained fired material, so that the supplied combustible material is wasted. When used as a concrete aggregate, the remaining unburned carbon adsorbs the AE agent, thereby deteriorating the air entrainment of the mortar concrete, or when compacted, unburned carbon appears on the surface and the mortar concrete Problems such as deterioration of appearance may occur.
The amount of the combustible substance is preferably 5 to 40 kg, more preferably 10 to 40 kg, particularly preferably 12 to 40 kg per 1000 kg of the fired product obtained by heating. If the amount is less than 5 kg, the effect of the reducing atmosphere may be small. If the amount exceeds 40 kg, a large amount of unburned combustible material remains in the obtained fired material, and when the fired material is used as a cement mixture or concrete aggregate, the air entrainment and appearance of mortar concrete are reduced. May worsen.
When the flammable substance is supplied in the middle of the rotary kiln, it is preferable to supply the flammable substance in the middle from the hottest position in the rotary kiln to the waste inlet side.
The oxygen (O ₂ ) concentration in the furnace when the combustible material is burned is preferably 5% by mass or less, more preferably 3% by mass or less, from the viewpoint of not immediately eliminating the combustible material.
By adjusting the above-mentioned conditions, the residence time, and the like, it is possible to prevent hexavalent chromium from being generated and prevent the combustible substance from remaining. When the obtained fired product is used as a cement mixture or a concrete aggregate, the above-mentioned conditions, residence time, and the like are adjusted so as not to adversely affect the air entrainment and appearance of the mortar concrete.

Next, a case where the combustible material is supplied from the waste outlet will be described.
The combustible material can be easily pumped into the furnace from the waste outlet using air. Further, a dedicated inlet may be provided on the outlet side of the rotary kiln. Further, a coarse combustible substance (having an average particle size of about 1 to 10 mm) may be dropped as a part of the fuel of the main burner.
The flammable substance is preferably one that can be brought into a stronger reduced state than when supplied at the inlet side of waste or in the middle of a rotary kiln. Specifically, for example, a combustible substance whose combustion speed is higher than that of the main fuel of the rotary kiln is exemplified. Examples of the combustible substance having a high burning rate include a solid waste mass obtained by compressing and / or solidifying waste such as waste wood, waste plastic, heavy oil sludge, and municipal waste.
The average particle size of the combustible material is preferably 0.1 to 10 mm, more preferably 1 to 5 mm. If the average particle size is less than 0.1 mm, the burning may occur at the very beginning during the firing, so that the reducing atmosphere may not be maintained. If the average particle size exceeds 10 mm, a large amount of unburned combustible material remains in the obtained fired material, so that the supplied combustible material is wasted. When used as a material, the air entrainment and appearance of mortar concrete may deteriorate. The time during which the reducing atmosphere can be maintained can be adjusted by the average particle size of the combustible substance. For example, for a combustible substance having a fast burning rate, the time during which the reducing atmosphere can be maintained can be lengthened by increasing (roughly) the average particle size.
The calorific value of the combustible substance can be used so that it is usually 2 to 40% based on the total calorific value of the fuel used for the main burner. If the calorific value of the combustible substance is less than 2%, the effect of the reducing atmosphere may be small. If the calorific value of the combustible substance exceeds 40%, a large amount of the unburned combustible substance remains in the obtained fired material, and the supplied combustible material becomes useless. When used as an aggregate, the mortar concrete may have poor air entrainment and appearance.
Compared with the case where the combustible material is supplied from the waste inlet side or the middle of the rotary kiln as described above, when the waste is supplied from the outlet side, the reducing atmosphere in the rotary kiln is a part of the furnace. In order to maintain the reducing atmosphere for a long time and reduce the atmosphere in a high temperature zone where the reduction rate is high, the supply position (drop position) of the combustible material is set at the entrance of waste more than the position where the maximum temperature is reached in the rotary kiln. It is preferable to adjust to the side. Preferably, the supply position is usually deeper than a point 4D from the kiln outlet, where D is the inner diameter of the kiln. Further, when the position of the highest temperature in the kiln is closer to the outlet side due to the setting conditions of the main burner or the like, the depth is more preferable than the point 3D from the outlet of the kiln. The supply position (fall position) is preferably adjusted by the angle of the flammable substance inlet, the position of the flammable substance, the speed of charging the flammable substance, the particle size of the flammable substance, and the density of the flammable substance.
When adding a combustible substance, the oxygen (O ₂ ) concentration in the furnace is preferably 5% by mass or less, more preferably 3% by mass or less, from the viewpoint that the combustible substance is not immediately lost.
By adjusting the above-described conditions, it is preferable to prevent the generation of hexavalent chromium and prevent the combustible substance from remaining.

Another method of heating the waste contaminated with radioactive cesium under a reducing atmosphere includes a method in which a flame is brought into direct contact with the waste.
Specifically, in an internal combustion type device (internally heated rotary kiln, etc.), baking is performed so that the waste of the radioactive cesium contaminated with radioactive cesium being heated (during firing) is directly in contact with the burner flame (hereinafter, referred to as Also called "flame film firing.") As a method of performing flame film baking using an internal heating rotary kiln, (a) a main heating burner is installed at a lower portion, and heating (firing) is performed so that the flame licks wastes, etc., (b) fuel amount Or by adjusting the air velocity to radiate the flame and heat (fire) so that the flame licks the waste, etc. (c) The flame is lengthened by lowering the angle of the main burner, A method of heating (firing) so as to lick waste and the like can be given. In addition, an auxiliary burner for firing the flame film may be provided in addition to the main burner for heating. By adjusting each condition, the longer the contact time between the waste and the like and the flame is, the more the reduction effect is improved. Further, even if the waste contains chromium, the generation of hexavalent chromium can be prevented, and even if hexavalent chromium is generated in the step of heating the waste, hexavalent chromium can be prevented. Is reduced to trivalent chromium.
The oxygen concentration at the time of performing the flame film firing is preferably 5% by mass or less, more preferably 3% by mass or less, from the viewpoint of generating more flame films.
By adjusting the above conditions, the effect of preventing hexavalent chromium elution can be further increased. In addition, you may use together the combustion of the above-mentioned combustible substance, and the flame film baking.

Further, by adjusting the atmosphere at the time of heating, the atmosphere can be reduced.
For example, as another method of heating waste contaminated with radioactive cesium under a reducing atmosphere, a method of burning a fuel used for heating with an air amount smaller than a stoichiometric air amount may be mentioned.
Specifically, in an internal combustion type device (internally heated rotary kiln, etc.), the air ratio in the furnace (the ratio of the supply air amount to the theoretical air amount) is 0.8 to 1.0, or the oxygen concentration in the furnace is And burning the fuel while keeping the concentration of carbon monoxide in the furnace at 0.1 to 1.0% by mass.
If the air ratio in the furnace is less than 0.8 or the concentration of carbon monoxide exceeds 1.0% by mass, the combustion required for heating may be difficult. When the air ratio in the furnace exceeds 1.0, when the oxygen concentration exceeds 1% by mass, or when burning fuel while keeping the carbon monoxide concentration in the furnace below 0.1% by mass, the reduction effect is obtained. Becomes smaller.
The fuel used for heating includes heavy oil, pulverized coal, regenerated oil, LPG, NPG, and combustible waste as main fuel (burner fuel), and the particle size is adjusted to burn in space. Is used.
Further, it can be used in combination with the above-described burning of combustible substances and / or sintering.
In addition, there is a method in which the inside of a device used for heating (externally heated rotary kiln, electric furnace, etc.) is replaced or circulated with an inert gas such as nitrogen gas. Further, a mixture of the inert gas and a reducing gas such as a carbon monoxide gas may be replaced or distributed.

Volatile radioactive cesium in the exhaust gas generated by the above-described heating method can be collected by a dust collector or a scrubber after being cooled to a solid. When a preheater is attached to the kiln, a part of the exhaust gas containing a high concentration of volatile radioactive cesium may be extracted and cooled to recover solid radioactive cesium. The recovered radioactive cesium can be further sealed and stored in a concrete container or the like after being subjected to further volume reduction treatment by washing or adsorption as necessary. Thereby, the volume of the waste containing the radioactive material can be reduced and stored without leaking to the outside.
When chloride is added to a mixture of waste and a CaO source and / or MgO source, radioactive cesium can be recovered in the form of radioactive cesium chloride. The radioactive cesium chloride can be easily dissolved in water and can be recovered as an aqueous solution.
The fired material obtained after heating is pulverized as necessary and used as cement mixture, aggregate (aggregate for concrete, aggregate for asphalt), earthwork material (backfill material, embankment material, roadbed material, etc.) can do.

The fired product obtained after the heating is a fired material having an absolute dry density of preferably 1.5 to 3.0 g / cm ³ , more preferably 2.0 to 3.0 g / cm ³ .
Further, the amount of free lime (free lime) of the fired product is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, further preferably 0.2% by mass or less. If the amount of free lime exceeds 1.0% by mass, when the fired product is used as an aggregate for concrete or an earthwork material, the concrete may be expanded and destroyed, or the fired product itself may collapse.
The particle size of the fired product may be adjusted by sieving or the like in consideration of the required particle size, compaction property, and the like, and used as a cement mixture or the like.
In the case where chromium is contained in the waste, in addition to the method of performing heating in a reducing atmosphere in the above-described heating step, by performing the following treatment on the obtained fired product, hexavalent chromium can be removed from the fired material. Can be prevented from being eluted. In particular, when the fired material is used as an earthwork material, it is preferable to take measures to dissolve hexavalent chromium from the viewpoint of preventing water pollution and soil pollution. Hereinafter, a specific method for preventing the elution of hexavalent chromium will be described.

When hexavalent chromium is contained in the obtained calcined product, a method of mixing a combustible substance with the high-temperature calcined product obtained in the heating step may be used as a measure for elution of hexavalent chromium. By mixing and cooling the high-temperature fired material and the combustible substance after the heating step, hexavalent chromium in the fired material is reduced to trivalent chromium, and hexavalent chromium in the fired material can be reduced. .
Specifically, a method of mixing the fired material after the heating step with a combustible substance while maintaining the temperature of the fired substance at a high temperature in a hot blast stove, or a method of mixing the high temperature fired substance and the combustible substance after the heating step in a container A method in which the mixture is put and filled, and the mixture of the fired material and the combustible substance is allowed to stand while maintaining the temperature of the mixture at a high temperature.

In the cooling step using an air quenching cooler, a rotary cooler, or the like, which is performed after the heating step, a high-temperature fired material and a combustible substance may be mixed. Above all, it is preferable to use a rotary cooler that is less in contact with oxygen and has a high degree of mixing of combustible substances.
When the combustible substance is mixed in the cooling step, the method of mixing the combustible substance is not particularly limited, but it is preferable to mix the combustible substance immediately after the heating step from the viewpoint of maintaining the high-temperature condition and the reducing atmosphere for a long time. For example, when heating is performed using a rotary kiln, a method in which a combustible substance is dropped at the outlet of the rotary kiln and mixed is preferable.
As for the temperature of the calcined product at the time of mixing the combustible substance, the higher the temperature, the greater the effect of reducing hexavalent chromium. In addition, when heating is performed using a rotary kiln, the temperature of the fired product when mixing in the rotary cooler can be increased by bringing the position where the firing temperature in the rotary kiln becomes maximum closer to the outlet side.
After mixing the combustible substance, the longer the time until the fired material is cooled, the greater the effect of reducing hexavalent chromium. However, the time from mixing to the temperature of the fired material being 600 ° C. or lower is preferably 1 hour. Minutes or more, more preferably 3 minutes or more.
The combustible substance is preferably mixed in an amount corresponding to 2 to 20% of the calorific value of the entire mixture of the fired material and the combustible substance. When the amount corresponds to a calorific value of less than 2%, the effect of reducing hexavalent chromium is reduced. If the amount corresponds to a heat amount exceeding 20%, a large amount of unburned combustible material remains in the fired product after cooling.
Examples of the flammable substance include solid wastes obtained by compressing and / or solidifying waste such as coal, coke, activated carbon, waste wood, waste plastic, heavy oil sludge, and municipal waste. Among them, those which can be brought into a stronger reduced state are preferable. Specifically, a combustible substance having a high burning rate is used. Examples of the combustible substance having a high burning rate include a solid waste mass obtained by compressing and / or solidifying waste such as waste wood, waste plastic, heavy oil sludge, and municipal waste.
The average particle size of the combustible material is preferably 0.1 to 10 mm, more preferably 1 to 5 mm. If it exceeds 10 mm, a large amount of combustible substances will remain in the fired product after cooling. If it is less than 0.1 mm, the effect of reducing hexavalent chromium is reduced, and at the time of introduction, the hexavalent chromium is scattered by the wind speed of cooling air and the like, and the amount mixed with the fired material is reduced.
The above-described combustible material having a high burning rate can have a large (coarse) average particle size. By increasing the average particle size, the time during which the reducing atmosphere can be maintained can be prolonged, and the flammable substance can be prevented from being scattered due to the wind speed of the cooling air at the time of introduction.
The oxygen concentration when mixing the combustible substance is not particularly limited. If possible, the exhaust gas may be used from the viewpoint of reducing the contact with oxygen or the amount of the combustible substance added.
It is preferable to adjust the above conditions so that the effect of reducing hexavalent chromium is large and no combustible material remains. When the fired product is used as a cement mixture, it is preferable that the color of the cement using the fired product does not change by setting the reducing atmosphere too strong.

Further, as a countermeasure for elution of hexavalent chromium, there is a method of further heating and melting the fired product obtained in the heating step.
By melting the fired product, hexavalent chromium contained in the fired product is sealed in the glass, and when used as an earthwork material, the elution amount of hexavalent chromium becomes equal to or less than the environmental standard value.
After further heating and melting the fired product, the melt is cooled to be granular. The obtained granular melt has a low water absorption and a high strength, so that it can be used as an aggregate for concrete. The cooling of the melt may be rapid cooling or slow cooling.
In addition, it is preferable from the viewpoint of energy cost to directly melt a high-temperature fired product obtained in the heating step (for example, a fired product immediately after coming out of the kiln).

Further, as a measure against elution of hexavalent chromium, a mixing step of mixing at least one or more selected from the group consisting of a reducing agent and an adsorbent with the fired product obtained in the heating step may be performed.
For example, hexavalent chromium contained in the fired product or hexavalent chromium eluted from the fired product can be reduced to trivalent chromium by mixing the fired product and the reducing agent.
Examples of the reducing agent include sulfites such as sodium sulfite, iron (II) salts such as iron (II) sulfate and iron (II) chloride, sodium thiosulfate, and iron powder.
Further, by mixing the calcined product and the adsorbent, hexavalent chromium eluted from the calcined product can be adsorbed, and the insolubilization of hexavalent chromium or the elution can be suppressed.
Examples of the adsorbent include zeolites, clay minerals, layered double hydroxides such as hydrotalcite compounds such as Mg-Al and Mg-Fe, Ca-Al-based hydroxides, ettringite and monosulfate. Ca-Al based compounds, hydrated oxides such as iron oxide (hematite) and bismuth oxide, magnesium compounds such as magnesium hydroxide, lightly burned magnesium, calcined dolomite and magnesium oxide, iron sulfide, iron powder, schwermanite, FeOOH, etc. Or a mixture or a baked product of one or more of silicon oxide, aluminum oxide, iron oxide, and the like, and a compound containing cerium and a rare earth element.
The reducing agent and the adsorbent may be used alone or in a combination of two or more.
As a method of mixing the calcined product and the drug (reducing agent and / or adsorbent), the calcined product and a powdered drug may be mixed, and the drug is mixed with water in advance to form a slurry or an aqueous solution (hereinafter, referred to as “ Also referred to as "slurry etc."), a method of mixing the fired product with the slurry, spraying the slurry or the like on the fired product, or immersing the fired product in the slurry or the like can be used.
The amount of the above agent used is such that the amount of the metal salt per 100 kg of the fired product is preferably 0.01 to 10 kg, more preferably 0.1 to 7 kg, and particularly preferably 0.2 to 5 kg. The amount of the chemical, the concentration of the slurry and the like, the spray amount of the slurry and the like, and the amount of the burned material to the slurry and the like are adjusted. When the amount of the metal salt per 100 kg of the fired product is less than 0.01 kg, the effect of reducing the elution amount of hexavalent chromium is reduced. If the amount exceeds 10 kg, the effect of reducing the elution amount of hexavalent chromium saturates, which is not economical.
The temperature of the calcined product at the time of mixing is preferably 100 to 800C, more preferably 125 to 600C, and particularly preferably 150 to 400C. If the temperature of the fired product exceeds 800 ° C., cracks or the like are generated in the fired material, or the fired product is atomized, whereby the strength is reduced, which is not preferable. If the temperature is lower than 100 ° C., it is not preferable because the drug hardly adheres to the surface of the fired product.
A method of spraying a slurry or the like containing a drug onto a high-temperature fired product is preferable because the drug adheres to the surface of the fired product and hardly comes off. When the fired product has pores, a method of immersing the fired product in a slurry or the like is preferable because the drug penetrates well into the inside and adheres to the surface.

Furthermore, as a measure against elution of hexavalent chromium, there is a method of washing the fired product obtained in the heating step with water.
As the water washing method, (i) a method in which a cleaning liquid is sprayed on a fired material in a container or on a belt conveyor by using a sprinkler or the like to wash the fired material, and (ii) the fired material and the cleaning liquid are put into a container, and the fired material is washed for a predetermined time. After washing, the washing liquid after draining is discharged and a new washing liquid is supplied repeatedly to perform washing. (Iii) Using a trommel or the like, the fired articles are sequentially replaced while the fired articles are immersed in the washing liquid. A washing method and the like can be mentioned.
The washing liquid may be ordinary tap water, or an aqueous solution of the above-described drug (reducing agent or adsorbent) may be used. The washing liquid after the water washing may be reused as the washing liquid, or may be treated and then discarded.
The washing time, the number of washings, and the amount of the washing solution used for washing are not particularly limited, and washing may be performed until the elution amount of hexavalent chromium satisfies the environmental standard value (notified by the Environment Agency No. 46).
These methods may be performed in combination with the above-described heating step in which heating is performed in a reducing atmosphere.

  Since the fired product obtained by the heating step of the present invention has an excellent ability to fix heavy metals (lead, arsenic, etc.) other than hexavalent chromium inside, the above-described treatment for preventing elution of hexavalent chromium is performed. If performed, it can be suitably used as an earthwork material (backfill material, embankment material, roadbed material, etc.).

The fired product obtained by the heating step can be pulverized and used as a cement mixture. In addition, gypsum can be contained in an amount of 1 to 6 parts by mass in terms of SO ₃ with respect to 100 parts by mass of the pulverized product of the calcined product.
The pulverization method is not particularly limited, and may be, for example, pulverization by a normal method using a ball mill or the like.
It is preferable that the ground material of the fired product has a Blaine specific surface area of 2500 to 5000 cm ² / g from the viewpoint of reducing bleeding of mortar or concrete, fluidity and strength.
The pulverization may be performed simultaneously on the calcined product, cement clinker and gypsum. When the pulverization is performed at the same time, the cement preferably has a Blaine specific surface area of 2500 to 4500 cm ² / g from the viewpoint of reducing bleeding of mortar and concrete, fluidity, and strength.
When the cement mixture is mixed with cement to obtain a cement composition, the cement composition can have low heat of hydration and good fluidity.

The fired product obtained by the heating step can be pulverized or classified as necessary, and used as an aggregate (aggregate for concrete or aggregate for asphalt) or an earthwork material.
When a fired product containing hexavalent chromium is used as aggregate, hexavalent chromium is taken into the cement hardened material. Therefore, prevent elution of hexavalent chromium by preventing rainwater during transportation and storage of the aggregate. Can be. Further, the above-described treatment for preventing the elution of hexavalent chromium may be performed.
The obtained fired product can be used for both fine aggregate and coarse aggregate. When used as coarse aggregate, the particle size is adjusted to 5 mm or more by sieving or the like.
When used as an earthwork material, the thickness is adjusted to 0.1 to 100 mm in consideration of compaction properties and the like.
When used as an aggregate, the calcined product preferably has an absolute dry density of 2.0 to 3.0 g / cm ³ . When the absolute dry density is less than 2.0 g / cm ³ , there is a possibility that the strength of the concrete is reduced. Further, the water absorption of the fired product is preferably 15% or less. If the water absorption is more than 15%, the strength of concrete may be reduced.
In particular, when used as an aggregate for concrete, it is preferable that the calcined product has an absolute dry density of 2.5 to 3.0 g / cm ³ and a water absorption of 3% or less.
The amount of free lime is preferably 1.0% by mass or less, more preferably 0.5% by mass or less. If the amount exceeds 1.0% by mass, the concrete may expand and break.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.
[Synthesis Example 1: Preparation of Cesium-Adsorbed Clay A]
After 500 g of bentonite was immersed in 2 liters of an aqueous solution containing cesium at a concentration of 250 mg / liter for 1 day, the solid content was recovered by centrifugation, the solid content was washed with water, and centrifuged again. As a result, cesium-adsorbed clay A containing cesium at a concentration of 1060 mg / kg was obtained.
[Synthesis Example 2: Preparation of Cesium-Adsorbed Clay B]
After 500 g of bentonite was immersed in 2 liters of an aqueous solution containing cesium at a concentration of 500 mg / liter for 1 day, the solid content was collected by centrifugation, the solid content was washed with water, and centrifuged again. As a result, cesium-adsorbed clay B containing cesium at a concentration of 2200 mg / kg was obtained.

[Reference Example 1]
6.6 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 13.2 g of limestone powder were mixed. The obtained mixture was heated at 1300 ° C. for 60 minutes in a tube-free electric furnace under steam-free air (pure air) to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results.
[Reference Example 2]
6.6 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 13.2 g of limestone powder were mixed. Using a tubular electric furnace, the obtained mixture was heated at 1300 ° C. for 60 minutes under air (7% moisture) obtained by bubbling through water at 60 ° C. using a tubular electric furnace to obtain a fired product. . The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results.
The heating in the air having a moisture content of 7% is performed for the purpose of simulating heating in an actual internal heat kiln.
[Reference Example 3]
8 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 12 g of limestone powder were mixed. The resulting mixture was passed through water at 60 ° C. using a tubular electric furnace and heated at 1300 ° C. for 60 minutes under air (water content 7%) obtained by bubbling to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results.
[Reference Example 4]
9 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 11 g of limestone powder were mixed. The resulting mixture was passed through water at 60 ° C. using a tubular electric furnace and heated at 1300 ° C. for 60 minutes under air (water content 7%) obtained by bubbling to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results.
[Reference Example 5]
10 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 10 g of limestone powder were mixed. The resulting mixture was passed through water at 60 ° C. using a tubular electric furnace and heated at 1300 ° C. for 60 minutes under air (water content 7%) obtained by bubbling to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results.
[Reference Example 6]
6.6 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 13.2 g of limestone powder were mixed. The obtained mixture was heated at 1200 ° C. for 60 minutes under pure air using a tubular electric furnace to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results.
[Reference Example 7]
11 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 9 g of limestone powder were mixed. The obtained mixture was heated at 1200 ° C for 60 minutes under air (water content 7%) bubbled with water at 60 ° C using a tubular electric furnace to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results.

[Comparative Example 1]
Cesium-adsorbed clay A obtained in Synthesis Example 1 was heated at 1000 ° C. for 60 minutes in a tubular electric furnace under pure air to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results. When the cesium-adsorbed clay was calcined at 1200 ° C., the sample was melted and stuck to the container, so that it could not be recovered.
[Comparative Example 2]
6.6 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 13.2 g of limestone powder were mixed. The obtained mixture was heated at 1000 ° C. for 60 minutes under pure air using a tubular electric furnace to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 1 shows the results.

From Reference Examples 1 to 7 in Table 1, the mass of each of calcium oxide (CaO), magnesium oxide (MgO), and silicon dioxide (SiO ₂ ) in the mixture, and ((CaO + 1.39 × MgO) / SiO ₂ ) It is understood that the numerical value derived from the equation is about 1.0 to 1.8, and that cesium can be volatilized by heating at about 1200 to 1300 ° C.
Further, when the reference example 1 is compared with the reference examples 2 to 5 (particularly, the reference example 1 and the reference example 2), the volatility of potassium and sodium is reduced by heating under air containing steam, and the volatility of cesium is reduced. It can be seen that can be raised.

[Reference Example 8]
30 g of the cesium-adsorbed clay B obtained in Synthesis Example 2, 60 g of limestone powder, and 0.0246 g of calcium chloride were pulverized and mixed. 20 g of the obtained mixture was heated at 1300 ° C. for 60 minutes under air (water content 7%) bubbled with water at 60 ° C. using a tubular electric furnace to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 2 shows the results.
[Reference Example 9]
30 g of the cesium-adsorbed clay B obtained in Synthesis Example 2, 60 g of limestone powder, and 0.0492 g of calcium chloride were pulverized and mixed. 20 g of the obtained mixture was heated at 1300 ° C. for 60 minutes under air (water content 7%) bubbled with water at 60 ° C. using a tubular electric furnace to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 2 shows the results.
[Reference Example 10]
30 g of the cesium-adsorbed clay B obtained in Synthesis Example 2, 60 g of limestone powder, and 0.0492 g of calcium chloride were pulverized and mixed. 20 g of the obtained mixture was heated at 1300 ° C. for 120 minutes under air (water content 7%) bubbling with water at 60 ° C. using a tubular electric furnace to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 2 shows the results.
[Reference Example 11]
30 g of the cesium-adsorbed clay B obtained in Synthesis Example 2, 60 g of limestone powder, and 0.0984 g of calcium chloride were pulverized and mixed. 20 g of the obtained mixture was heated at 1300 ° C. for 60 minutes under air (water content 7%) bubbled with water at 60 ° C. using a tubular electric furnace to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 2 shows the results.
[Reference Example 12]
30 g of the cesium-adsorbed clay B obtained in Synthesis Example 2, 60 g of limestone powder, and 0.246 g of calcium chloride were mixed. Using a tubular electric furnace, 20 g of the obtained mixture was heated at 1300 ° C. for 60 minutes under air (water content 7%) bubbled with water at 60 ° C. to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 2 shows the results.
[Reference Example 13]
10 g of the cesium-adsorbed clay B obtained in Synthesis Example 2, 10 g of limestone powder, and 0.49 g of calcium chloride were mixed. The obtained mixture was heated at 1200 ° C. for 60 minutes under pure air using a tubular electric furnace to obtain a fired product. The Cs and Cl contents of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (% by mass) of Cs. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 2 shows the results.

  From Reference Examples 8 to 13 in Table 2, it can be seen that cesium is volatilized even when chloride is added. In particular, from Reference Examples 8, 9 and 11, the molar ratio of chlorine to cesium and potassium (Cl / (Cs + K)) is about 0.09 to 0.26, and the amount of chlorine is about 410 to 1210 mg / kg. When the heating time is about 60 minutes, the volatility of cesium is high while the volatility of sodium and potassium is low.

[Reference Example 14]
A fired product was obtained in the same manner as in Reference Example 1, except that heating was performed at 1300 ° C. for 120 minutes under air (pure air) containing no steam. Each content of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of each of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Reference Example 1. , Cs, Na, and K were determined for volatility (% by mass). Table 3 shows the results.
[Reference Example 15]
A fired product was obtained in the same manner as in Reference Example 1, except that heating was performed at 1300 ° C. for 30 minutes under air (pure air) containing no steam. Each content of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of each of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Reference Example 1. , Cs, Na, and K were determined for volatility (% by mass). Table 3 shows the results.
[Reference Example 16]
A fired product was obtained in the same manner as in Reference Example 1, except that heating was performed at 1250 ° C. for 60 minutes under air (pure air) containing no steam. Each content of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of each of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Reference Example 1. , Cs, Na, and K were determined for volatility (% by mass). Table 3 shows the results.
[Reference Example 17]
A fired product was obtained in the same manner as in Reference Example 1, except that heating was performed at 1250 ° C. for 120 minutes under air (pure air) containing no steam. Each content of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of each of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Reference Example 1. , Cs, Na, and K were determined for volatility (% by mass). Table 3 shows the results.
[Reference Example 18]
A fired product was obtained in the same manner as in Reference Example 1, except that heating was performed at 1350 ° C. for 30 minutes under air (pure air) containing no steam. Each content of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of each of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Reference Example 1. , Cs, Na, and K were determined for volatility (% by mass). Table 3 shows the results.

[Example 1]
30 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 68 g of limestone powder were mixed. The obtained mixture was heated at 1300 ° C. for 60 minutes using a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 4 shows the results.
[Example 2]
30 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 77 g of limestone powder were mixed. The obtained mixture was heated at 1300 ° C. for 60 minutes using a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 4 shows the results.
[Example 3]
30 g of the cesium-adsorbed clay A obtained in Synthesis Example 1, 77 g of limestone powder, and 0.122 g of calcium chloride were mixed. The obtained mixture was heated at 1300 ° C. for 60 minutes using a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 4 shows the results.
[Example 4]
30 g of the cesium-adsorbed clay A obtained in Synthesis Example 1, 77 g of limestone powder, and 0.122 g of calcium chloride were mixed. The obtained mixture was heated at 1250 ° C. for 60 minutes in a tube-free electric furnace under steam-free air (pure air) to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 4 shows the results.
[Example 5]
30 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 90 g of limestone powder were mixed. The obtained mixture was heated at 1300 ° C. for 60 minutes using a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 4 shows the results.
[Example 6]
30 g of the cesium-adsorbed clay A obtained in Synthesis Example 1 and 90 g of limestone powder were mixed. The obtained mixture was heated at 1250 ° C. for 60 minutes in a tube-free electric furnace under steam-free air (pure air) to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 4 shows the results.
[Example 7]
30 g of the cesium-adsorbed clay A obtained in Synthesis Example 1, 90 g of limestone powder, and 0.039 g of calcium chloride were mixed. The obtained mixture was heated at 1300 ° C. for 60 minutes using a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 4 shows the results.
Example 8
30 g of the cesium-adsorbed clay A obtained in Synthesis Example 1, 90 g of limestone powder, and 0.039 g of calcium chloride were mixed. The obtained mixture was heated at 1250 ° C. for 60 minutes in a tube-free electric furnace under steam-free air (pure air) to obtain a fired product. The cesium (Cs) and chlorine (Cl) contents of each of the mixture before heating and the fired product obtained by heating were measured by a wet method to determine the volatility (mass%) of Cs. Was. In addition, the respective amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectroscopy (XRF) to determine the volatility (% by mass) of Na and K. Table 4 shows the results.

Claims (7)

The radioactive cesium-contaminated waste and the mixture of the CaO and / or MgO sources are mixed with each other in a heated atmosphere consisting of air containing water vapor or air containing no water vapor without adding chloride at 1250 to 1350. A method for removing radioactive cesium comprising a heating step of heating at ℃ and evaporating radioactive cesium in the waste,
The waste contains, as a SiO ₂ source, soil, sewage sludge dry powder, or municipal waste incineration ash,
The CaO source and / or MgO source, which contains only limestone powder,
In the heating step, the types and types of the waste and the CaO source and / or the MgO source are set so that the value derived from the following equation (1) is larger than 1.9 and equal to or smaller than 2.5. A method for removing radioactive cesium, comprising determining a mixing ratio.
((CaO + 1.39 × MgO) / SiO ₂ ) (1)
(In the formula, CaO, MgO, and SiO ₂ represent a mass in terms of calcium oxide, a mass in terms of magnesium oxide, and a mass in terms of silicon oxide, respectively.)   The method for removing radioactive cesium according to claim 1, wherein the heating atmosphere is air containing water vapor. The radioactive cesium-contaminated waste and the mixture of the CaO and / or MgO sources are mixed with each other in a heated atmosphere consisting of air containing water vapor or air containing no water vapor without adding chloride at 1250 to 1350. Heating at ℃, volatilizing radioactive cesium in the waste, a method for producing a fired product including a heating step of obtaining a fired product,
The waste contains, as a SiO ₂ source, soil, sewage sludge dry powder, or municipal waste incineration ash,
The CaO source and / or MgO source, which contains only limestone powder,
In the heating step, the types and types of the waste and the CaO source and / or the MgO source are set so that the value derived from the following equation (1) is larger than 1.9 and equal to or smaller than 2.5. The mixing ratio is determined (however, the above-mentioned fired product contains C ₂ S and C ₂ AS, and the above-mentioned composition is so set that the total amount of C ₂ AS and C ₄ AF per 100 parts by mass of C ₂ S is 10 to 100 parts by mass. Excluding the case where the types and the mixing ratios of the waste and the CaO source and / or the MgO source are determined.)
((CaO + 1.39 × MgO) / SiO ₂ ) (1)
(In the formula, CaO, MgO, and SiO ₂ represent a mass in terms of calcium oxide, a mass in terms of magnesium oxide, and a mass in terms of silicon oxide, respectively.)   The method for producing a fired product according to claim 3, further comprising a mixing step of mixing at least one selected from the group consisting of a reducing agent and an adsorbent with the fired product obtained by the heating step.   A method for producing a cement mixture, comprising: obtaining a calcined product by the method for producing a calcined product according to claim 3 or 4; and crushing the calcined product to obtain a cement mixture.   A method for manufacturing an aggregate, comprising obtaining a fired product by the method for manufacturing a fired product according to claim 3, and then crushing or classifying the fired product to obtain an aggregate.   A method for manufacturing an earthwork material, comprising obtaining a fired material by the method for manufacturing a fired material according to claim 3, and then pulverizing or classifying the fired material to obtain an earthwork material.