TWI559329B - A method for removing radioactive cesium, and a method for producing a calcined product - Google Patents

Description

Method for removing radioactive cesium and method for producing the same

The present invention relates to a method for removing radioactive cesium from waste contaminated with radioactive cesium and using waste contaminated with radioactive cesium as a raw material for producing a harmless burned product (for example, cement mixed materials, aggregate materials, soil materials) ) method.

Because major accidents in nuclear power plants cause problems with the inclusion of radioactive cesium in the external environment in waste or soil. Radioactive cesium (铯137) has a half-life of 30 years. Because it has been adversely affected by human body for a long time, it is often required to remove radioactive cesium from waste.

As a method of removing radioactive cesium, for example, it is described that radioactive waste in the form of a nitrate is dissolved by electromagnetic induction in a cooled container having a slit around an externally applied coil to decompose nitrate. The generated metal oxide is around the container, so that the reduced white metal element is concentrated in the central part of the container by electromagnetic pressing force, and secondly, cooling. After coagulation, the radioactive waste formed by the recovery of the solidified body is treated by electromagnetic induction heating. A method of recovering long-lived nuclear species such as cesium which is volatilized from radioactive waste (Patent Document 1).

However, the method of Patent Document 1 does not target radioactive cesium released in the external environment due to an accident, and it is not suitable for a large amount of radioactive waste that occurs in an area defined by a nuclear power plant or the like. Treatment of contaminated soil, etc., and the device is complicated and high Price, there is a problem of high cost.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 5-157897

[Summary of the Invention]

The present invention aims to provide a method for easily and efficiently removing radioactive cesium from waste contaminated with radioactive cesium. It is also an object of the present invention to provide a method for producing a harmless burned product (for example, a cement mixed material, an aggregate material, a soil wage material) by using a waste contaminated with radioactive cesium as a raw material.

As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be attained by heating a waste contaminated with radioactive cesium, and a source of CaO and/or a source of MgO at a specific blending ratio. The present invention has been completed.

That is, the present invention provides the following [1] to [9].

[1] A method for removing radioactive cesium, which comprises heating a radioactive cesium-contaminated waste, and heating a CaO source and/or a MgO source at 1200 to 1350 ° C to volatilize the radioactive cesium in the waste. The method for removing radioactive cesium is characterized in that, in the heating step, each of the waste, the CaO source, and the MgO source is defined so that the mass of each of CaO, MgO, and SiO ₂ satisfies the following formula (1). Type and blending ratio: ((CaO+1.39×MgO)/SiO ₂ )=1.0~2.5‧‧‧(1) (In the formula, each of CaO, MgO, and SiO ₂ represents the mass of calcium in terms of oxide, The mass of magnesium in terms of oxide, and the mass of oxide in terms of oxide.

[2] The method for removing radioactive cesium according to the above [1], wherein the chloride is further used in the above heating step.

[3] The method for removing radioactive cesium according to [1] or [2] above, wherein in the heating step, heating is performed in a reducing atmosphere.

[4] A method for producing a fired product, comprising: a waste contaminated with radioactive cesium, and a CaO source and/or a MgO source heated at 1200 to 1350 ° C to volatilize radioactive cesium in the waste; The method for producing a fired product in the heating step of the fired product is characterized in that the waste is provided in a manner that the mass of each of CaO, MgO, and SiO ₂ satisfies the following formula (1) in the heating step. Types and blending ratios of CaO source and MgO source: ((CaO+1.39×MgO)/SiO ₂ )=1.0~2.5‧‧‧(1) (In the formula, CaO, MgO, and SiO ₂ each represent calcium The mass in terms of oxide, the mass of magnesium in terms of oxide, and the mass in terms of oxide.

[5] The method for producing a fired product according to the above [4], wherein in the heating step, heating is performed in a reducing atmosphere.

[6] The method for producing a fired product according to the above [4] or [5], which comprises mixing at least one of the fired product obtained by the heating step and a group selected from the group consisting of a reducing agent and an adsorbent. The mixing step.

[7] A cement-mixed material obtained by pulverizing the fired product obtained by the method for producing a fired product according to any one of the above [4] to [6].

[8] An aggregate obtained by the method of producing a fired product according to any one of the above [4] to [6].

[9] A burned material obtained by the method for producing a fired product according to any one of the above [4] to [6].

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 amount of radioactive waste can be reduced in volume.

Moreover, according to the method for producing a fired product of the present invention, a harmless fired product obtained by removing radioactive cesium can be obtained. This burned material can be used as a cement mixed material or aggregate, and can be used for a large amount of concrete (dikes, breakwaters, wave eliminators, etc.) that must be rebuilt in the future, and can protect natural resources. In addition, as a soil wage material, it can be used for land backfill materials such as soil removal.

Hereinafter, the present invention will be described in detail.

The method for removing radioactive cesium according to the present invention is characterized in that it comprises a heating step of heating the radioactive cesium-contaminated waste and the CaO source and/or the MgO source at 1200 to 1350 ° C to volatilize the radioactive cesium in the waste. In the heating step, in the heating step, the respective types of the waste, the CaO source, and the MgO source are defined so that the mass of each of CaO, MgO, and SiO ₂ satisfies the following formula (1). Blending ratio:

((CaO+1.39×MgO)/SiO ₂ )=1.0~2.5‧‧‧(1) (In the formula, CaO, MgO, and SiO ₂ each represent the mass in terms of calcium oxide, converted in magnesium oxide The quality, the quality converted by bismuth oxide).

The object to be treated according to the present invention is waste contaminated with radioactive cesium.

Here, the so-called radioactive cesium-contaminated waste is, for example, soil or sewage sludge dry powder, municipal waste incineration ash, general waste from molten slag, shells, grass, etc., or sewage sludge, sewage slag, net Industrial waste such as water sludge and construction sludge, or disaster waste such as rubble, contains radioactive cesium. These may be used alone or in combination of two or more. Further, the concentrated radioactive cesium (intermediate treatment) obtained by removing a portion containing almost no radioactive cesium (for example, sand or stone in the case of soil) is also included in the "radiation contaminated with radioactive cesium" in the present invention. The concept.

Further, examples of the CaO source include calcium carbonate, limestone, quicklime, slaked lime, limestone, dolomite, and blast furnace slag. Examples of the MgO source include magnesium carbonate, magnesium hydroxide, dolomite, serpentine, and nickel-iron alloy slag. These examples may be used alone or in combination of two or more.

In the present invention, both of the CaO source and the MgO source may be used, or only one of them may be used, but it is preferable to mix only the CaO source from the viewpoint of the volatility of the radioactive cesium.

Further, it is preferred that the CaO source and the MgO source use a pulverized powder.

In the present invention, the term "radioactive cesium" means that the radioactive isotopes of strontium are 铯134 and 铯137. These radioactive cesiums are released from radioactive materials in the external environment due to accidents in nuclear power plants, and the half-lives are each about 2 years and about 30 years.

In the present invention, in order to remove the radioactive cesium of the object, the nuclear power plant causing the accident is released into the external environment simultaneously with radioactive iodine in the form of cesium iodide or the like, and is dropped from the sky to the surface. Barium iodide has a boiling point of 1200 ° C or higher and has a property of being less volatile than a simple substance having a boiling point of about 700 ° C. In addition, the radioactive cesium that has landed on the surface of the earth is enclosed in clay minerals contained in the soil, and it is difficult to separate from the soil, or there are variations. Further, the disaster waste attached to the rubble or the like, or the radioactive raft which has landed on the surface of the ground flows out by the rain, and is concentrated by the sewage treatment process to produce sewage sludge containing a high concentration of radioactive cesium. Further, by absorbing the radioactive cesium contained in the soil, the vegetation is contaminated by the radioactive energy, and when the incineration ash generated by the vegetation contaminated with the radioactive energy is incinerated, the radioactive cesium may be blocked in the glass or the like. It is an object of the present invention to separate and recover such radioactive cesium compounds which become difficult to handle.

The radioactive cesium-contaminated waste and the CaO source and/or the MgO source satisfy the respective masses of calcium oxide (CaO), magnesium oxide (MgO), and cerium oxide (SiO ₂ ) in the obtained mixture. In the embodiment of the above formula (1), the waste and the CaO source and/or the MgO source are mixed and mixed.

((CaO+1.39×MgO)/SiO ₂ )=1.0~2.5‧‧‧(1) (In the formula, CaO, MgO, and SiO ₂ each represent the mass in terms of calcium oxide, converted in magnesium oxide The quality, the quality converted by bismuth oxide).

The mass of each of CaO, MgO, and SiO ₂ and the lower limit of the numerical value derived from the above formula (1) are preferably 1.2 or more, and more preferably 1.4 or more from the viewpoint of increasing the amount of volatilization of radioactive cesium. More preferably, it is 1.7 or more, still more preferably 1.8 or more, and particularly preferably a value of more than 1.9.

Further, the upper limit of the numerical value derived from the above formula (1) is such that the radioactive cesium in the mixture is volatilized, and from the viewpoint of reducing the amount of volatilization of potassium or sodium in the mixture, it is preferably 2.4 or less, more preferably 2.3 or less, more preferably 2.2 or less, still more preferably 1.9 or less, and particularly preferably 1.8 or less.

Further, since the mass of CaO 1 molar is equivalent to the mass of MgO 1.39 mole, in the above formula (1), the mass of MgO is multiplied by 1.39.

When the mass ratio is less than 1.0, the firing temperature becomes high and the liquid phase is likely to be generated, and the amount of volatilization of the radioactive cesium is reduced. When the mass ratio exceeds 2.5, the total amount of volatilization of potassium or sodium in the mixture of the radioactive cesium-contaminated waste and the CaO source and/or the MgO source increases, and is obtained by cooling the exhaust gas. The amount of waste containing radioactive material in the body content is increased.

The material of the mixture is intended to promote the chlorination of the radioactive cesium, and to reduce the volume of the volatile recovery, and further, calcium chloride (CaCl ₂ ), potassium chloride (KCl), sodium chloride (NaCl) or the like can be used. chloride. Among them, calcium chloride is preferred from the viewpoint of promoting chlorination and volatilization.

The amount of chloride, the molar ratio of chlorine, bismuth and potassium (Cl/(Cs+K)) is preferably 1.00 or less, more preferably 0.010 to 0.60, still more preferably 0.015 to 0.40, and particularly preferably 0.03 to 0.30. The amount. When the molar ratio is 1.0 or less, since potassium or sodium cannot be volatilized, most of the radioactive cesium is volatilized, and the volume of the waste containing the radioactive substance can be reduced.

Further, the amount of chlorine in the above mixture is preferably 1,500 mg/kg or less. When the amount of chlorine is 1500 mg/kg or less, it is difficult to generate a liquid phase even at a high temperature, and most of the radioactive cesium is volatilized.

The above molar ratio (Cl/(Cs+K)) is preferably 1.0 or less, and the amount of chlorine in the above mixture is 1500 mg/kg or less, and the above molar ratio is more preferably 0.5 or less, and chlorine in the above mixture When the amount is 1250 mg/kg or less, the volatilized ruthenium is in the form of ruthenium chloride, and in addition to volatilization, the volume of the recovered product described later can be reduced.

When the above waste is mixed with the CaO source and/or the MgO source, if necessary, mixing, crushing, pulverization, or the like, or a crusher or a pulverizer may be combined with the mixer to perform a two-stage treatment. When the rotary kiln described later is used for firing, the CaO source, the MgO source, and the waste can be directly supplied to the kiln opening by rotating the materials in the rotary kiln. Further, the above mixture is preferably a granular material having a degree of less than 5 mm. Also It is possible to remove the stone or the like which is not more than 5 mm in size without being washed with water.

The heating temperature of the mixture of the radioactive cesium-contaminated waste and the CaO source and/or the MgO source is 1200 to 1350 ° C, preferably 1200 to 1300 ° C.

The radioactive cesium contained in the waste can be efficiently volatilized by heating in the above temperature range. The heating temperature is less than 1200 ° C to reduce the amount of radioactive cesium volatilization. When it exceeds 1350 ° C, it is not preferable to form a liquid phase because it is difficult to volatilize because it is incorporated into radioactive cesium.

The heating time of the mixture is preferably 15 minutes or longer, more preferably 30 minutes or longer, from the viewpoint of obtaining a sufficient amount of radioactive cesium to be volatilized. The upper limit of the heating time is not particularly limited, but is preferably 180 minutes or shorter, more preferably 120 minutes or shorter. When the heating time exceeds 180 minutes, the radioactive cesium in the mixture is increased to increase the amount of potassium or sodium volatilized.

In the rotary kiln or the like, when the raw material is rotated, since the contact ratio between the gas and the radioactive cesium is increased and the thermal conductivity is also improved, a high evaporation rate can be obtained with a shorter firing time than the static standing condition.

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 and the like.

Examples of the batch heating means include an incinerator, an electric furnace, a microwave heating device, and the like.

Among them, the continuous heating means is suitable for use in the present invention from the viewpoint of improving the processing efficiency. In particular, the rotary kiln is easy to give the heating temperature and the residence time of the waste because it is suitable for the volatilization of the radioactive cesium. good.

As the environment for heating, if it is heated under air containing water vapor, the amount of volatilization of alkali metal (potassium and sodium) can be reduced, and the amount of volatilization of radioactive cesium is increased, which is preferable.

On the other hand, when heated under air (pure air) without water vapor, the amount of volatilization of alkali metals (potassium and sodium) is also increased, and more radioactive cesium can be volatilized.

By adjusting the amount of the above-mentioned chloride, the heating temperature, the time, and the amount of water vapor during heating, the amount of volatilization of the alkali metal (potassium and sodium) is reduced, and the amount of volatilization of the radioactive cesium is increased.

Further, when the waste contaminated with radioactive cesium contains chromium, the obtained fired product may contain hexavalent chromium (Cr ⁶⁺ ).

When such a fired product is used as a cement admixture, a bone material, a soil material, etc. (especially when used as a soil wage material), hexavalent chromium contained in the burned material is melted, causing water pollution and soil pollution. The possibility of waiting.

Therefore, in the above heating step, heating can be carried out in a reducing environment. By heating in a reducing environment, even if chromium is contained in the waste, it is possible to prevent the formation of hexavalent chromium in an oxidizing environment, and in the step of heating the waste, the waste is temporarily heated in an oxidizing environment. Even if hexavalent chromium is formed, it is safe to use the obtained fired product as a soil wage material or the like because it is reduced to trivalent chromium (Cr ³⁺ ). Further, the method of heating in the air containing the above-described steam and the method of heating in a reducing environment may be carried out in combination. Hereinafter, the method of heating in a reducing environment is an internal combustion type apparatus (internal combustion type rotary kiln, etc.), but an example of a device using a countercurrent type (combustion on the raw material outlet side) is explained, but the present invention It is not limited to these forms.

An example of a method of heating waste contaminated with radioactive cesium in a reducing environment is a method of burning a combustible substance when the waste is heated. By burning flammable substances, the periphery of the waste can be kept in a reducing environment. Further, even if chromium is contained in the waste, generation of hexavalent chromium can be prevented, and in the step of heating the waste, even if hexavalent chromium is formed, hexavalent chromium is reduced to trivalent chromium.

Here, examples of the flammable substance include a solid waste block which compresses and/or solidifies waste such as charcoal, coke, activated carbon, waste wood, waste plastics, heavy oil sludge, and municipal waste.

As a method of supplying a flammable substance, waste contaminated with radioactive cesium can be mixed in advance as a device for heating, and when a rotary kiln is used, a flammable substance can be supplied from the inlet side, the outlet side, or the rotary kiln of the waste. Supply on the way.

When the flammable substance is mixed in advance as a raw material, the fired material obtained by heating may be in a range in which the flammable substance in an unburned state is not left, and the flammable substance is preferably mixed in a large amount, and the flammable substance is preferably a flammable substance. The particle size is also preferably large.

Here, a case where the combustible substance is supplied to the waste inlet side of the rotary kiln or the middle of the rotary kiln will be described.

In this case, the flammable substance is preferably maintained in a reducing environment for a long period of time. Specifically, for example, the burning speed can be cited as compared with the main fuel of the rotary kiln. Slower, or a flammable substance that has the same burning rate as the main fuel and is coarser than the main fuel. Specifically, petroleum coke, charcoal coke, anthracite, etc. are mentioned. The slower the burning rate, the better the flammable substance can be refined.

The average particle diameter of the combustible material is preferably from 0.5 to 20 mm, more preferably from 1 to 5 mm. When the average particle diameter is less than 0.5 mm, it is completely burned out at the very early stage of combustion, and the reducing environment may not be maintained for a long period of time. When the average particle diameter exceeds 20 mm, the flammable substance in an unburned state remains in a large amount in the obtained fired product, so that the supplied flammable substance becomes wasteful, and the burned material is used as a cement mixed material or concrete bone. In the case of the material, the AE agent is adsorbed by the remaining unburned carbon, which may cause deterioration of the air entrainment property of the mortar concrete or the occurrence of unburned carbon on the surface in the case of compaction, which may deteriorate the appearance of the mortar concrete.

The amount of the combustible substance is preferably from 5 to 40 kg, more preferably from 10 to 40 kg, particularly preferably from 12 to 40 kg, per 1000 kg of the calcined product obtained by heating. When the amount is less than 5 kg, it is less effective in a reducing environment. When the amount exceeds 40 kg, a large amount of unburnable flammable substance remains in the obtained fired product, and when the fired product is used as a cement mixed material or a concrete aggregate, the air entrainment property or appearance of the mortar concrete deteriorates. .

Further, when the flammable substance is supplied on the way to the rotary kiln, it is preferably supplied from the highest temperature in the rotary kiln to the inlet side of the waste.

When the flammable substance is burned, the concentration of oxygen (O ₂ ) in the furnace is preferably 5% by mass or less, and more preferably 3% by mass or less from the viewpoint that the flammable substance cannot be immediately disappeared.

By adjusting the above conditions, residence time, and the like, generation of hexavalent chromium is prevented, and flammable substances are not left. Further, when the obtained fired product is used as the cement mixed material or the concrete aggregate, the above conditions and residence time are adjusted so as not to impart air interferability or appearance adverse effects to the mortar concrete.

Next, the case where the combustible substance is supplied from the outlet side of the waste will be described.

The flammable substance can be easily pumped from the side of the waste outlet using air to the furnace. Further, a dedicated input port can be provided on the exit side of the rotary kiln. Further, a coarse flammable substance (having an average particle diameter of about 1 to 10 mm) can be partially dropped as a part of the main furnace fuel.

The flammable substance is preferably a more reductive state than when it is supplied on the inlet side of the waste or on the way to the rotary kiln. Specifically, for example, a combustible substance having a faster burning speed than the main fuel of the rotary kiln can be cited. Examples of the flammable substance having a high burning rate include waste compacts such as compressed and/or solidified waste wood, waste plastics, heavy oil sludge, and municipal waste.

The average particle diameter of the flammable substance is preferably from 0.1 to 10 mm, more preferably from 1 to 5 mm. When the average particle diameter is less than 0.1 mm, it is completely burned out at the very early stage of combustion, and the reducing environment may not be maintained for a long period of time. When the average particle diameter exceeds 10 mm, the flammable substance in an unburned state remains in a large amount in the obtained fired product, and the supplied flammable substance becomes a wave. In addition, when the fired product is used as a cement mixed material or a concrete aggregate, the air entrainment property or appearance of the mortar concrete deteriorates. Furthermore, the time during which the reducing environment can be maintained can be adjusted by the average particle size of the flammable substance. For example, a flammable substance that burns at a high speed can maintain a reducing environment for a longer period of time by increasing the average particle size (coarse).

The heat of the combustible material can be used for 2 to 40% of the heat of the fuel used in the main furnace. When the heat of the combustible substance is less than 2%, it is less effective in a reducing environment. When the amount of heat of the combustible substance exceeds 40%, a large amount of unburnable flammable substance remains in the obtained fired product, and the supplied combustible substance becomes wasteful, and the burned material is used as a cement admixture or In the case of concrete aggregates, there is a case where the air entrainment or appearance of the mortar concrete deteriorates.

When the above-mentioned flammable substance is supplied from the outlet side of the waste or the rotary kiln, when it is supplied from the outlet side of the waste, since a part of the inside of the furnace becomes a reducing environment in the rotary kiln, it is maintained for a long time. At the same time as the reduction environment, the high temperature zone with a high reduction rate is used as the reducing environment, and the supply position (drop position) of the combustible material is adjusted to be higher than the position of the highest temperature in the rotary kiln. The supply position is preferably such that the inner diameter of the kiln is generally D, and the depth from the outlet of the kiln 4D is preferably deep. Further, when the setting conditions of the main furnace or the like are closer to the outlet side than the position of the highest temperature in the kiln, it is preferable to be the inner side from the position of the outlet 3D of the kiln. The supply position (drop position), the input port angle of the flammable substance, the position of the input port, the tempering substance, the adjustment speed, the particle size of the flammable substance, and the density of the flammable substance are preferred.

When the flammable substance is added, the oxygen (O ₂ ) concentration in the furnace is preferably 5% by mass or less, and more preferably 3% by mass or less from the viewpoint that the flammable substance does not disappear immediately.

By adjusting the above conditions, the formation of hexavalent chromium is prevented, and it is preferable that no flammable substance remains.

As another method of heating the waste contaminated with radioactive cesium in a reducing environment, a method of directly contacting the flame with the above waste may be mentioned.

Specifically, in an internal combustion type device (internal heating type rotary kiln, etc.), the radioactive cesium-contaminated waste during heating (during firing) is directly contacted with the flame of the furnace and fired (hereinafter, also referred to as " Flame film firing"). As a method of firing a flame film using an internal heat type rotary kiln, (a) heating (sintering) the main furnace for heating at the bottom, the flame tip touching the waste, and (b) adjusting the amount of fuel or The air velocity causes the flame to diverge, the flame tip is heated (sintered) like a waste, and (c) the flame is grown by facing the angle of the main furnace, and the flame tip is heated (sintered) like a waste. . Further, a supplemental fire furnace for firing a flame film can be provided in addition to the main furnace for heating. By adjusting the conditions, the longer the contact time of the waste with the flame, the more the reduction effect is. Further, even if chromium is contained in the waste, generation of hexavalent chromium can be prevented, and in the step of heating the waste, even if hexavalent chromium is formed, hexavalent chromium is reduced to trivalent chromium.

The oxygen concentration at the time of firing the flame film is preferably 5% by mass or less, and more preferably 3% by mass or less from the viewpoint of producing a more flame film.

By adjusting the above conditions, the hexavalent chromium melting prevention effect can be further increased. Further, the combustion of the above flammable substance and the firing of the flame film may be used in combination.

Moreover, by adjusting the environment during heating, it can also be carried out in a reducing environment.

For example, in a reducing environment, as another method of heating the waste contaminated with radioactive cesium, a method of burning the fuel for heating at a smaller amount of air than the theoretical amount of air may be mentioned.

Specifically, it is an internal combustion type apparatus (internal heating type rotary kiln, etc.), and the air ratio in the furnace (the ratio of the amount of air supplied to the theoretical air amount) is maintained at 0.8 to 1.0, or in the furnace. The method of burning the fuel while the oxygen concentration is as low as 1% by mass or less, or burning the fuel while maintaining the concentration of one of the carbon oxides in the furnace at 0.1 to 1.0% by mass.

When the air in the furnace is less than 0.8 or the concentration of carbon monoxide is more than 1.0% by mass, the combustion necessary for heating becomes difficult. When the air ratio in the furnace exceeds 1.0, when the oxygen concentration exceeds 1% by mass, or when the concentration of carbon monoxide in the furnace is maintained at less than 0.1% by mass, the reduction effect is small.

The fuel used for heating, as the main fuel (fuel for the furnace), may be heavy oil, fine carbon, reclaimed oil, LPG, NPG, or combustible waste, and the like, which is used to adjust the combustion particle size in space.

Further, it may be used in combination with the combustion of the above combustible material and/or the firing of the flame film.

Moreover, the apparatus used for heating (external heating type rotary kiln, electric In a furnace or the like, a method in which an inert gas such as nitrogen is substituted or circulated. Further, in the inert gas, a reducing gas such as a mixed carbon monoxide gas may be replaced or circulated.

The radioactive cesium volatilized in the exhaust gas is generated by the above-described heating method, and after cooling to form a solid, it can be recovered by a dust collector, a dust collector or the like. Further, when the preheater is taken out of the kiln, the volatilized radioactive cesium is evacuated at a portion of the exhaust gas contained in the high concentration, and by cooling, the radioactive cesium which becomes a solid can be recovered. The recovered radioactive cesium may be sealed in a concrete container or the like after being washed by water, adsorbed, or the like, and then subjected to volume reduction treatment. Therefore, the waste containing the radioactive substance is not leaked to the outside, but the volume can be lowered and stored.

When a mixture of waste and a CaO source and/or a MgO source is added to the chloride, the radioactive cesium can be recovered in the form of radioactive cesium chloride. The radioactive cesium chloride can be easily dissolved in water, so it can also be recovered as an aqueous solution.

The fired product obtained after heating can be pulverized if necessary, and can be used as a cement mixed material, an aggregate (a concrete aggregate, an asphalt aggregate), a soil wage material (backfill material, a filling material, a road base material, etc.). Use it.

The fired product obtained after heating is preferably a fired product having an absolute dry density of from 1.5 to 3.0 g/cm ³ , more preferably from 2.0 to 3.0 g/cm ³ .

Moreover, the amount of free lime of the fired product is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.2% by mass or less. When the amount of the free lime exceeds 1.0% by mass, when the fired product is used as the aggregate material for concrete or the soil material, there is a possibility that the concrete is swelled and destroyed, or the fired product itself is disintegrated.

The particle size of the fired product may be adjusted by screening or the like in consideration of the necessary particle size, compactness, etc., and may be used in a cement mixed material or the like.

Further, when the waste contains chromium, in the heating step described above, in addition to the heating method in the reducing environment, the obtained fired product can be prevented from melting the hexavalent chromium from the fired product by the following treatment. . In particular, when a burnt material is used as a soil-based material, it is preferable to carry out a countermeasure for melting hexavalent chromium from the viewpoint of preventing water pollution and soil pollution. Hereinafter, a specific method of the hexavalent chromium melting countermeasure will be described.

When the obtained fired product contains hexavalent chromium, a method of melting the hexavalent chromium may be a method of mixing the high-temperature fired product and the combustible material obtained by the heating step. By mixing the high-temperature fired product and the combustible material after the heating step, by cooling, the hexavalent chromium in the fired product can be reduced to trivalent chromium, and the hexavalent chromium in the fired product can be lowered.

Specifically, the calcined product after the heating step is mixed with the combustible material while maintaining the temperature of the calcined product at a high temperature in the hot air oven, or the high temperature is burned after the heating step is added to the vessel. A method in which a product and a combustible substance are filled, and the temperature of the mixture of the fired material and the combustible substance is maintained at a high temperature.

Further, in the cooling step such as an air quenching cooler or a rotating cold air which is performed after the heating step, a high-temperature fired product and a combustible substance may be mixed. Among them, it is preferable to use a rotating cold air which is less in contact with oxygen and which has a high mixing sensitivity of a combustible substance.

When the flammable substance is mixed in the cooling step, the mixing method of the flammable substance is not particularly limited, and the high temperature condition and the reducing environment are maintained from a long period of time. From the point of view, it is preferred to mix immediately after the heating step. For example, when heating is performed using a rotary kiln, it is preferred to mix the flammable substance and mix it at the falling port of the rotary kiln.

The temperature of the fired product when the combustible material is mixed is higher as the effect of lowering the hexavalent chromium is higher, and is preferably 800 ° C or higher, more preferably 1000 ° C or higher. In addition, when the heating is performed in the rotary kiln, the temperature at which the firing temperature in the rotary kiln is maximized is close to the drop port side, and the temperature of the fired product can be increased when mixing in the rotary cooling air.

After mixing the combustible material, the longer the time for cooling the calcined product, the greater the effect of reducing the hexavalent chromium, and the time from the mixing to the temperature at which the calcined product is lowered to 600 ° C or lower is preferably 1 minute or longer. Good for more than 3 minutes.

The combustible material is preferably mixed in an amount equivalent to 2 to 20% of the heat of the entire mixture of the fired material and the combustible material. When the amount is less than 2%, the effect of reducing the hexavalent chromium becomes small. When the amount exceeds 20% of the amount of heat, a large amount of the combustible material in the unburned state remains in the fired product after cooling.

Examples of the flammable substance include waste solid blocks which are compressed and/or solidified by wastes such as charcoal, coke, activated carbon, waste wood, waste plastics, heavy oil sludge, and municipal waste. Among them, it is preferable to be a stronger reduction state. Specifically, a combustible substance having a high burning rate can be cited. Examples of the flammable substance having a high burning rate include waste solid blocks which are compressed and/or solidified by waste materials such as waste wood, waste plastics, heavy oil sludge, and municipal garbage.

The average particle diameter of the flammable substance is preferably from 0.1 to 10 mm, more preferably from 1 to 5 mm. When it exceeds 10 mm, the flammable substance in an unburned state remains in a large amount in the burned material after cooling. When the thickness is less than 0.1 mm, the effect of reducing the hexavalent chromium is small, and it is scattered by the wind speed of the cooling air or the like at the time of the input, and the amount of the mixed with the burned material is small.

The above-mentioned flammable substance having a high burning speed can increase the average particle diameter (thickness). By increasing the average particle diameter, it is possible to increase the time during which the reducing environment is maintained, and it is possible to prevent the flammable substance from being scattered by the wind speed of the cooling air or the like at the time of input.

The oxygen concentration at the time of mixing the combustible substance is not particularly limited. Further, if possible, exhaust gas can be used from the viewpoint of reducing contact with oxygen or reducing the amount of addition of combustible substances.

Under the above conditions, the effect of reducing the hexavalent chromium is increased, and it is preferable to adjust the non-remaining combustibles. Further, when a fired product is used as the cement mixed material, it is preferable to adjust the thickness of the cement to be used in the fired product by setting the reducing environment too much.

In addition, as a countermeasure against melting of hexavalent chromium, a method of further heating and melting the fired product obtained by the heating step is exemplified.

When the hexavalent chromium contained in the fired product is sealed in the glass and used for the soil wage material or the like, the amount of the hexavalent chromium melted is equal to or less than the environmental reference value.

After further heating the calcined product and melting, the melt is cooled to form a pellet. Since the obtained granular melt has low water absorption and high strength, it can be used as a concrete aggregate. Still, the cooling of the melt can be quenched It can also get cold.

Further, it is preferable to directly melt the fired product in a high temperature state obtained by the heating step (for example, the fired product immediately after being taken out from the kiln) from the viewpoint of energy cost.

In addition, as a measure for melting the hexavalent chromium, a mixing step of at least one selected from the group consisting of the fired product obtained by the heating step and the reducing agent and the adsorbent may be mixed.

For example, by chaotic burned material and a reducing agent, hexavalent chromium contained in the fired product or hexavalent chromium melted from the fired product can be reduced to trivalent chromium.

Examples of the reducing agent include sulfites such as sodium sulfite, iron (II) sulfates, iron (II) salts such as iron (II), sodium thiosulfate, and iron powder.

Further, by mixing the calcined product and the adsorbent, hexavalent chromium which is melted from the calcined product can be adsorbed, and insolubilization or melting of the hexavalent chromium can be suppressed.

Examples of the adsorbent include zeolite, clay minerals, layered rehydrated oxides of hydrotalcite compounds such as Mg-Al or Mg-Fe, Ca-Al-based water oxides or ettringite or monosulfate. a Ca-Al compound, an iron oxide such as iron oxide (hematite) or cerium oxide, a magnesium compound such as magnesium hydroxide or light burnt magnesium or fired dolomite or magnesia, iron sulfide or iron powder or One or a mixture of two or more kinds of iron compounds such as schwertmannite or FeOOH, cerium oxide or aluminum oxide or iron oxide, or a fired product, a cerium, a compound containing a rare earth element, or the like.

The reducing agent and the adsorbent may be used alone or in combination of two or more.

As a method of mixing the fired product with a chemical (reducing agent and/or adsorbent), the fired product and the powdered drug are mixed, and the drug may be mixed with water in advance and placed in a slurry or an aqueous solution (hereinafter also referred to as " The slurry or the like is a method in which a fired product, a slurry, or the like is mixed, and the spray slurry is equal to the fired product or the fired product is immersed in a slurry or the like.

The amount of the above-mentioned agent used is preferably 0.01 to 10 kg, more preferably 0.1 to 7 kg, and particularly preferably 0.2 to 5 kg, to adjust the amount of the powdered medicament, the concentration of the slurry, etc. per 100 kg of the metal salt. The amount of the slurry, the amount of the slurry, and the amount of the slurry to be poured into the slurry. When the amount of the burned product per 100 kg of the metal salt is less than 0.01 kg, the effect of reducing the amount of hexavalent chromium melted is small. When the amount exceeds 10 kg, since the effect of reducing the amount of hexavalent chromium melted is saturated, it is uneconomical.

The temperature of the fired product at the time of mixing is preferably from 100 to 800 ° C, more preferably from 125 to 600 ° C, and particularly preferably from 150 to 400 ° C. When the temperature of the fired product exceeds 800 ° C, cracks or the like are formed in the fired product, or the sintered body is microparticulated, which is disadvantageous because the strength is lowered. When it is less than 100 ° C, it is not preferable because the drug is hard to adhere to the surface of the fired product.

In the high-temperature fired product, a method of spraying a slurry containing a drug or the like is applied, and the drug adheres to the surface of the fired product, and it is difficult to peel off. Further, when the fired product has pores, the fired product is immersed in a slurry or the like, and the chemical is sufficiently permeated into the inside, and it is also suitable because the surface is also adhered.

Further, as a measure for melting the hexavalent chromium, a method of washing the fired product obtained by the heating step by water can be mentioned.

As a washing method, (i) in a container or in a belt The fired product on the machine is washed by a sprayer or the like, and (ii) the fired product and the washing liquid are added to the container, and the fired product is immersed in the washing liquid for a fixed period of time, and then discharged. The washing liquid after the immersion is repeatedly supplied with a new washing liquid to be washed, and (iii) the immersed product is immersed in the washing liquid, and the burned material is sequentially washed. Method, etc.

The washing liquid may be ordinary tap water, and an aqueous solution of the above-mentioned agent (reducing agent or adsorbent) may be used. The washing liquid after washing can be reused as a washing liquid, and can be discarded after the treatment.

The amount of the washing liquid used for the washing time, the number of times of washing, and the washing liquid is not particularly limited, and the amount of melting of the hexavalent chromium can be washed up to the environmental reference value (Japan Environmental Agency Notice No. 46).

These methods may also be carried out in combination with heating in a reducing environment in the above heating step.

In addition, the fired product obtained by the heating step of the present invention has excellent ability to fix heavy metals (lead, arsenic, etc.) other than hexavalent chromium, and can prevent the above-mentioned hexavalent chromium from being melted. It can be used as a soil material (backfill material, filling material, roadbed material, etc.).

The fired product obtained by the heating step can be used as a cement mixed material by pulverization. In addition, it may contain 1 to 6 parts by mass of gypsum in terms of SO ₃ with respect to 100 parts by mass of the ground product of the fired product.

The pulverization method is not particularly limited, and for example, it may be pulverized by a usual method using a ball mill or the like.

The pulverized material of the fired product preferably has a specific surface area of 2,500 to 5,000 cm ² /g from the viewpoint of bleed out of mortar or concrete, or fluidity and strength expression.

The pulverization can be carried out simultaneously with the burned material, the cement frit and the gypsum. From the viewpoint of bleed out of mortar or concrete, or fluidity and strength expression, the Bran by surface area of cement is preferably 2500 to 4500 cm ² /g at the same time.

When the cement admixture is mixed with cement to obtain a cement composition, the hydration heat of the cement composition can be lowered, and the fluidity can be improved.

The fired product obtained by the heating step is pulverized or classified as necessary, and can be used as an aggregate (a concrete aggregate, an aggregate for asphalt) or a soil material.

When a burned material containing hexavalent chromium is used as the aggregate, since the hexavalent chromium is poured into the cement cured product, the hexavalent chromium can be prevented from being melted by preventing rainwater during transportation or storage of the aggregate. Further, a treatment for preventing the hexavalent chromium from being melted may be performed.

The obtained fired product can be used for fine aggregates and coarse aggregates. When it is used as a coarse aggregate, the particle size is adjusted to 5 mm or more by screening or the like.

In addition, when it is used as a soil material, it is adjusted to 0.1 to 100 mm in consideration of compactness.

When used as an aggregate, the absolute dry density of the fired product is preferably 2.0 to 3.0 g/cm ³ . When the absolute dry density is less than 2.0 g/cm ³ , there is a fear that the concrete strength is lowered. Further, the water absorption rate of the fired product is preferably 15% or less. When the water absorption rate is more than 15%, there is a fear that the concrete strength is lowered.

In particular, when used as a concrete aggregate, the absolute dry density of the fired product is 2.5 to 3.0 g/cm ³ , and the water absorption is preferably 3% or less.

The amount of free lime is preferably 1.0% by mass or less, more preferably 0.5% by mass or less. When the amount exceeds 1.0% by mass, there is a possibility that the concrete is swelled and destroyed.

[Examples]

Hereinafter, the present invention is specifically described by way of examples, but the present invention is not limited to the examples.

[Synthesis Example 1; Manufacturing of yttrium-adsorbed clay A]

After 500 g of bentonite was immersed for 1 day in a 2 liter aqueous solution containing cerium of 250 mg/liter, the solid content was recovered by centrifugation, and the solid content was further washed with water and centrifuged again. Thus, a ruthenium-adsorbing clay A containing ruthenium at a concentration of 1060 mg/kg was obtained.

[Synthesis Example 2; Manufacturing of yttrium-adsorbed clay B]

After 500 g of bentonite was immersed for 1 day in a 2 liter aqueous solution containing a concentration of 铯500 mg/liter, the solid content was recovered by centrifugation, and the solid content was further washed with water and centrifuged again. Thus, a ruthenium-adsorbing clay B containing ruthenium at a concentration of 2200 mg/kg was obtained.

[Example 1]

6.6 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 13.2 g of limestone powder. The obtained mixture was heated at 1300 ° C for 60 minutes in a tubular electric furnace under air (pure air) without water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

[Embodiment 2]

6.6 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 13.2 g of limestone powder. The obtained mixture was heated in a tubular electric furnace under air (water content: 7%) obtained by foaming in 60 ° C water for 60 minutes at 1300 ° C to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

Furthermore, heating is carried out under air of 7% of water, in order to simulate the actual heating in the internal heat kiln.

[Example 3]

8 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 12 g of limestone powder. The obtained mixture was heated in a tubular electric furnace under air (water content: 7%) obtained by foaming in 60 ° C water for 60 minutes at 1300 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

[Example 4]

9 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 11 g of limestone powder. The obtained mixture was heated in a tubular electric furnace under air (water content: 7%) obtained by foaming in 60 ° C water for 60 minutes at 1300 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

[Example 5]

10 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 10 g of limestone powder. The obtained mixture was heated in a tubular electric furnace under air (water content: 7%) obtained by foaming in 60 ° C water for 60 minutes at 1300 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

[Embodiment 6]

6.6 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 13.2 g of limestone powder. The obtained mixture was heated at 1200 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

[Embodiment 7]

11 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 9 g of limestone powder. The obtained mixture was heated at 1200 ° C for 60 minutes in a tubular electric furnace using air obtained by foaming in 60 ° C water (7% by weight) 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

[Comparative Example 1]

The smear-adsorbed clay A obtained in Synthesis Example 1 was heated in a tubular electric furnace at 1000 ° C for 60 minutes in 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

Further, when the yttrium-adsorbed clay was fired at 1200 ° C, the molten sample was attached to the container, so that it could not be recovered.

[Comparative Example 2]

6.6 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 13.2 g of limestone powder. The obtained mixture was heated in a tubular electric furnace at 1000 ° C for 60 minutes 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 1.

From Examples 1 to 7 of Table 1, the respective masses of calcium oxide (CaO), magnesium oxide (MgO), and cerium oxide (SiO ₂ ) in the mixture, and from ((CaO+1.39×MgO)/SiO ₂ The value derived from the formula is about 1.0 to 1.8, and the volatile enthalpy is understood by heating at about 1200 to 1300 °C.

Further, when Example 1 is compared with Examples 2 to 5 (especially Example 1 and Example 2), it is understood that the evaporation rate of potassium or sodium can be lowered by heating under air containing water vapor, thereby improving the enthalpy Evaporation rate.

[Embodiment 8]

30 g of the 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 in a bubble electric air (water content: 7%) in a tubular electric furnace at 60 ° C for 60 minutes at 1300 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 2.

[Embodiment 9]

The 铯 adsorbed clay B30g 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 in a bubble electric air (water content: 7%) in a tubular electric furnace 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 2.

[Embodiment 10]

The 铯 adsorbed clay B30g 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 in a bubble electric air (water content: 7%) in a tubular electric furnace at 60 ° C for 120 minutes at 1300 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 2.

[Example 11]

The adsorbed clay B30g 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 in a bubble electric air (water content: 7%) in a tubular electric furnace at 60 ° C for 60 minutes at 1300 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 2.

[Embodiment 12]

30 g of the adsorbed clay B obtained in Synthesis Example 2, 60 g of limestone powder, and 0.246 g of calcium chloride were mixed. 20 g of the obtained mixture was heated in a bubble electric air (water content: 7%) in a tubular electric furnace at 60 ° C for 60 minutes at 1300 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 2.

[Example 13]

10 g of adsorbed clay B, 10 g of limestone powder, and 0.49 g of calcium chloride obtained in Synthesis Example 2 were mixed. The obtained mixture was heated at 1200 ° 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 evaporation rate (% by mass) of Cs. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 2.

From Examples 8 to 13 of Table 2, it is understood that even if a chloride hydrazine is added, it volatilizes. In particular, from Examples 8, 9, and 11, it is understood that the molar ratio of chlorine to lanthanum and potassium (Cl/(Cs+K)) is about 0.09 to 0.26, the amount of chlorine is about 410 to 1210 mg/kg, and heating is performed. When the time is about 60 minutes, the evaporation rate of sodium and potassium is low and the evaporation rate of hydrazine is high.

[Embodiment 14]

The fired product was obtained in the same manner as in Example 1 except that it was heated at 1300 ° C for 120 minutes in air (pure air) containing no water vapor. The content of each of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Example 1 to obtain Cs. , Na, and K evaporation rate (% by mass). The results are shown in Table 3.

[Example 15]

The fired product was obtained in the same manner as in Example 1 except that it was heated at 1300 ° C for 30 minutes in air (pure air) containing no water vapor. The content of each of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Example 1 to obtain Cs. , Na, and K evaporation rate (% by mass). The results are shown in Table 3.

[Example 16]

The fired product was obtained in the same manner as in Example 1 except that it was heated at 1250 ° C for 60 minutes in air (pure air) containing no water vapor. The content of each of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Example 1 to obtain Cs. , Na, and K evaporation rate (% by mass). The results are shown in Table 3.

[Example 17]

The fired product was obtained in the same manner as in Example 1 except that it was heated at 1,250 ° C for 120 minutes in air (pure air) containing no water vapor. The content of each of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Example 1 to obtain Cs. , Na, and K evaporation rate (% by mass). The results are shown in Table 3.

[Embodiment 18]

The fired product was obtained in the same manner as in Example 1 except that it was heated at 1,350 ° C for 30 minutes in air (pure air) containing no water vapor. The content of each of cesium (Cs), chlorine (Cl), Na ₂ O, and K ₂ O of the mixture before heating and the fired product obtained by heating was measured in the same manner as in Example 1 to obtain Cs. , Na, and K evaporation rate (% by mass). The results are shown in Table 3.

[Embodiment 19]

30 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 68 g of limestone powder. The obtained mixture was heated at 1300 ° C for 60 minutes in a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 4.

[Example 20]

30 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 77 g of limestone powder. The obtained mixture was heated at 1300 ° C for 60 minutes in a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 4.

[Example 21]

30 g of the 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 in a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 4.

[Example 22]

30 g of the 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 tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 4.

[Example 23]

30 g of the adsorbed clay A obtained in Synthesis Example 1 was mixed with 90 g of limestone powder. The obtained mixture was heated at 1300 ° C for 60 minutes in a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 4.

[Example 24]

The yttrium adsorption clay A30g obtained in Synthesis Example 1 was mixed with 90 g of limestone powder. The obtained mixture was heated at 1250 ° C for 60 minutes in a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 4.

[Example 25]

30 g of the 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 in a tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 4.

[Example 26]

30 g of the 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 tubular electric furnace under air (pure air) containing no water vapor to obtain a fired product. The content of each cesium (Cs) and chlorine (Cl) of the mixture before heating and the fired product obtained by heating was measured by a wet method, and the evaporation rate (% by mass) of Cs was determined. Further, the respective amounts of Na ₂ O and K ₂ O were measured by a fluorescent X-ray analysis method (XRF) to determine the evaporation rates (% by mass) of Na and K. The results are shown in Table 4.

Claims (9)

A method for removing radioactive cesium, which comprises a radioactive cesium of 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 heating step, the respective types of the waste, the CaO source, and the MgO source are defined in such a manner that the mass of each of CaO, MgO, and SiO ₂ satisfies the following formula (1). And blending ratio: ((CaO+1.39×MgO)/SiO ₂ )=1.0~2.5‧‧‧(1) (wherein CaO, MgO, and SiO ₂ each represent the mass of calcium in terms of oxide, magnesium The mass in terms of oxide and the mass in terms of oxide. A method of removing radioactive cesium according to claim 1, wherein the chloride is further used in the heating step. A method of removing radioactive cesium according to claim 1 or 2, wherein in the heating step, heating is carried out in a reducing environment. A method for producing a fired product comprising heating a waste contaminated with radioactive cesium, and heating a CaO source and/or a MgO source at 1200 to 1350 ° C to volatilize radioactive cesium in the waste to obtain a fired product In the heating step, the waste material and the CaO are defined in such a manner that the mass of each of CaO, MgO, and SiO ₂ satisfies the following formula (1). Types and blending ratios of source and MgO source: ((CaO+1.39×MgO)/SiO ₂ )=1.0~2.5‧‧‧(1) (In the formula, CaO, MgO, and SiO ₂ each represent calcium The mass in terms of oxide, the mass of magnesium in terms of oxide, and the mass in terms of oxide. The method for producing a fired product according to claim 4, wherein in the heating step, heating is performed in a reducing atmosphere. The method for producing a fired product according to the fourth or fifth aspect of the invention, comprising the step of mixing a mixture of the fired product obtained by the heating step and at least one selected from the group consisting of a reducing agent and an adsorbent. . A cement-mixed material obtained by pulverizing a fired product obtained by the method for producing a fired product according to any one of claims 4 to 6. An aggregate obtained by the method of producing a fired product according to any one of claims 4 to 6 of the invention. A soil-based material, which is obtained by the method of producing a fired product according to any one of claims 4 to 6.