KR20150079546A - Method for eliminating radioactive cesium and method for producing burned product - Google Patents

Abstract

A method of easily and efficiently removing radioactive cesium from waste contaminated with radioactive cesium is provided. A method for removing radioactive cesium comprising heating a radioactive cesium-contaminated waste and a CaO source and / or an MgO source to 1200 to 1350 ° C to volatilize radioactive cesium in the waste, , MgO and SiO each of the _second mass ((CaO + 1.39 × MgO) / SiO 2) = 1.0 ~ 2.5 ( wherein, CaO, MgO, SiO ₂ are each terms of oxides by mass of calcium oxide in terms of mass of magnesium, silicon Of the waste, the CaO source and the MgO source are determined so as to satisfy the following formula (1).

Description

TECHNICAL FIELD [0001] The present invention relates to a method for removing radioactive cesium and a method for producing the same,

The present invention relates to a method for removing radioactive cesium from wastes contaminated with radioactive cesium and a method for producing a harmless fired product (for example, cement admixture, aggregate, earthwork material) using waste contaminated with radioactive cesium as a raw material .

There is a problem that radioactive cesium emitted to the external environment is contained in waste or soil due to a great accident of a nuclear power plant. Since radioactive cesium (cesium 137) has a half-life of 30 years and can adversely affect the human body over a long period of time, it is often required to remove radioactive cesium from waste or the like.

As a method for removing radioactive cesium, for example, radioactive waste existing in the form of a nitrate is dissolved by electromagnetic induction heating in a cooled vessel having a slit provided with an energizing coil which is turned to the outside, And collecting the solidified product after cooling and solidifying, the method comprising the steps of: providing a metal oxide produced by the method of claim 1, A method of separating / recovering long-lived nuclear species such as cesium vaporized from radioactive waste during heating is described. (Patent Document 1)

However, since the method of Patent Document 1 is directed not to the radioactive cesium emitted to the external environment by accident but to the radioactive waste generated in a limited area such as a nuclear power plant, the treatment of an enormous amount of contaminated soil There is a problem that the apparatus is complicated, expensive, and expensive.

(Patent Document 1) JP-A-1993-157897

 It is an object of the present invention to provide a method for easily and efficiently removing radioactive cesium from radioactive cesium-contaminated wastes.

It is another object of the present invention to provide a method for producing a harmless fired product (for example, cement admixture, aggregate, earthwork material) by using radioactive cesium-contaminated waste as a raw material.

As a result of intensive studies to solve the above problems, the inventors of the present invention found that the above objects can be achieved by heating the waste contaminated with radioactive cesium and the CaO source and / or MgO source at a specific compounding ratio, .

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

[1] A method for removing radioactive cesium comprising heating a radioactive cesium-contaminated waste and a CaO source and / or an MgO source to 1200 to 1350 ° C to volatilize radioactive cesium in the waste, Wherein a kind and a mixing ratio of each of the waste, the CaO source and the MgO source are determined so that the mass of each of CaO, MgO and SiO ₂ satisfies the following formula (1).

((CaO + 1.3 x 9 MgO) / SiO ₂ ) = 1.0 to 2.5 (1)

(Wherein CaO, MgO, and SiO ₂ each represent an oxide-reduced mass of calcium, an oxide-reduced mass of magnesium, and an oxide-reduced mass of silicon, respectively).

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

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

[4] A method for producing a sinter including a heating step of heating radioactive cesium-contaminated waste and a CaO source and / or an MgO source to 1200 to 1350 ° C to volatilize radioactive cesium in the waste to obtain a sintered material, Wherein a kind and a mixing ratio of each of the waste, the CaO source and the MgO source are determined so that the mass of each of CaO, MgO, and SiO ₂ satisfies the following formula (1).

((CaO + 1.39 x MgO) / SiO ₂ ) = 1.0 to 2.5 (1)

(Wherein CaO, MgO, and SiO ₂ each represent an oxide-reduced mass of calcium, an oxide-reduced mass of magnesium, and an oxide-reduced mass of silicon, respectively).

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

[6] The method for producing a fired product as described in [4] or [5] above, 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.

[7] A cement admixture obtained by pulverizing a calcined material obtained by the method for producing a calcined material according to any one of [4] to [6] above.

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

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

According to the method of removing radioactive cesium according to the present invention, radioactive cesium can be easily and efficiently removed from radioactive cesium-contaminated waste, and radioactive waste can be reduced.

Further, according to the method for producing a calcined product of the present invention, a harmless calcined material from which radioactive cesium is removed can be obtained. These sintered materials can be used as cement admixtures and aggregates for revival concrete (such as banks, breakwaters, sofa blocks, etc.), which can be used in large amounts in the future, and can protect natural resources. Also, it can be used for landfill return material of soil from which soil has been removed as earthwork material.

Hereinafter, the present invention will be described in detail.

The method for removing radioactive cesium according to the present invention includes a heating process for heating radioactive cesium-contaminated waste and a CaO source and / or an MgO source to 1200 to 1350 ° C to volatilize radioactive cesium in the waste Wherein the kind and the mixing ratio of each of the waste, the CaO source and the MgO source are determined so that the mass of each of CaO, MgO and SiO ₂ satisfies the following formula (1) in the heating process.

((CaO + 1.39 x MgO) / SiO ₂ ) = 1.0 to 2.5 (1)

(Wherein CaO, MgO, and SiO ₂ each represent an oxide-reduced mass of calcium, an oxide-reduced mass of magnesium, and an oxide-reduced mass of silicon, respectively).

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

The wastes contaminated with radioactive cesium are, for example, general wastes such as soil, sewage sludge, municipal waste incineration ash, melting slag derived from waste, shell, vegetation, sewage mud, sewage slag, Industrial wastes such as tiles, sculptures and stones, and radioactive cesium. These may be used alone or in combination of two or more. The radioactive cesium-enriched material (intermediate treated material), which can be obtained by previously removing a portion that does not substantially contain radioactive cesium (for example, sand or stone in the case of soil) in advance, Waste that has been contaminated with waste ").

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 rock, ferronickel alloy slug, and the like. These examples may be used singly or in combination of two or more.

In the present invention, both CaO and MgO sources can be used or only one of them can be used, but it is preferable to mix only CaO source in view of the volatility of radioactive cesium.

The CaO source and the MgO source are preferably pulverized powders.

In the present invention, radioactive cesium means cesium 134 and cesium 137, which are radioactive isotopes of cesium. These radioactive cesium is a radioactive substance released into the external environment by the accident of a nuclear power plant and has a half-life of about 2 years and about 30 years, respectively.

In the present invention, the radioactive cesium to be removed is emitted from an accidental nuclear power plant in the form of cesium iodide or the like, together with radioactive iodine, to the external environment and dropped from the air to the earth's surface. Cesium iodide has a boiling point of 1200 ° C or higher and is less volatile than a cesium compound having a boiling point of about 700 ° C. In addition, radioactive cesium that has fallen on the surface of the earth is trapped in the clay minerals contained in the soil, so that it does not fall off from the soil well, and sometimes its shape changes. In addition, radioactive cesium deposited on disaster wastes such as tiles and sculptures and stones, or radioactive cesium that has fallen on the surface of the ground, is flowed by rain and is concentrated in the sewage treatment process, resulting in sewage mud containing radioactive cesium at a high concentration. In addition, the vegetation is contaminated with radioactivity by absorbing the radioactive cesium contained in the soil. In the incineration ash containing the vegetation contaminated with these radioactivity, radioactive cesium is trapped in the glass. In the present invention, the radioactive cesium compound which is in a state difficult to treat is separated and recovered.

The waste contaminated with radioactive cesium and the CaO source and / or the MgO source are mixed so that the mass of each of calcium oxide (CaO), magnesium oxide (MgO) and silicon dioxide (SiO ₂ ) in the obtained mixture satisfies the following formula (1) The waste and the CaO source and / or the MgO source are mixed in a predetermined condition.

((CaO + 1.39 x MgO) / SiO ₂ ) = 1.0 to 2.5 (1)

(Wherein CaO, MgO, and SiO ₂ each represent an oxide-reduced mass of calcium, an oxide-reduced mass of magnesium, and an oxide-reduced mass of silicon, respectively).

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

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

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

When the mass ratio is less than 1.0, the liquid phase is easily generated as the firing temperature becomes high, and the volatilization amount of radioactive cesium is reduced. When the mass ratio is more than 2.5, the amount of potassium or sodium in the mixture of the radioactive cesium-contaminated waste and the CaO source and / or MgO source is increased, and the amount of radioactive material- .

Further, as a material of the mixture, a chloride such as calcium chloride (CaCl 2), potassium chloride (KCl) or sodium chloride (NaCl) may be used for the purpose of accelerating the chlorination and volatilization of the radioactive cesium and for reducing the volatilized recovered product. Among them, calcium chloride is preferable from the viewpoint of promoting chlorination and volatilization.

The amount of chloride is preferably such that 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, still more preferably 0.015 to 0.40, particularly preferably 0.03 to 0.30 Is the amount that becomes. When the molar ratio is 1.0 or less, potassium or sodium is not volatilized and radioactive cesium is volatilized to a great extent, so that waste containing radioactive materials can be reduced.

Further, the amount of chlorine in the mixture is preferably 1500 mg / kg or less. If the chlorine content is less than 1500 mg / kg, the liquid is not easily generated even at a high temperature, and a lot of radioactive cesium is volatilized.

Preferably, when the molar ratio (Cl / (Cs + K)) is 1.0 or lower and the chlorine content in the mixture is 1500 mg / kg or lower, more preferably the molar ratio is 0.5 or lower and the chlorine content in the mixture is 1250 mg / kg or lower, Cesium can easily be volatilized in the form of cesium chloride while simultaneously reducing the amount of recovered material as described later.

When the waste is mixed with the CaO source and / or the MgO source, the mixture may be subjected to a two-step treatment by mixing or crushing, crushing or the like, or by combining a crusher or a crusher and a mixer have. In the case of firing at a high temperature using a rotary kiln to be described later, since the respective materials are rotationally mixed in the rotary kiln, the above-mentioned CaO source, MgO source, and waste can be partially introduced into the kiln. It is also preferable that the mixture is smaller than granular material of about 5 mm. It is also possible to remove a stone or the like having a diameter of 5 mm or more, which does not contain much cesium in advance, while performing cleaning.

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

By heating within the temperature range, the radioactive cesium contained in the waste can be efficiently volatilized. When the heating temperature is less than 1200 ° C, the volatilization amount of radioactive cesium is reduced. When the temperature exceeds 1350 占 폚, a liquid phase is formed, which is not preferable because radioactive cesium is blown and does not volatilize well.

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, and more preferably 120 minutes or less. When the heating time exceeds 180 minutes, the volatilization amount of potassium or sodium increases together with radioactive cesium in the mixture.

When the raw materials such as the rotary kiln are driven, the contact ratio between the gas and the radioactive cesium is increased, and the thermal conductivity is also improved, so that a high volatilization rate can be obtained in a short firing time than the stationary condition.

Both the continuous type and the batch type can be used as the heating means.

Examples of the continuous heating means include a rotary kiln and the like.

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

Among them, the continuous heating means is preferably used in the present invention from the viewpoint of enhancing treatment efficiency. In particular, the rotary kiln is preferable because it can easily reduce the heating temperature and the residence time of the waste suitable for the volatilization of radioactive cesium.

The heating atmosphere is preferable because it can reduce the volatilization amount of the alkali metal (potassium and sodium) and increase the volatilization amount of the radioactive cesium when heated in air containing water vapor.

On the other hand, when heated under air containing no water vapor (pure air), the volatilization amount of the alkali metal (potassium and sodium) increases, but more radioactive cesium can be volatilized.

By adjusting the amount of the chloride, the heating temperature, the time, and the amount of water vapor at the time of heating, the amount of volatilization of the alkali metal (potassium and sodium) can be reduced and the amount of radioactive cesium can be increased.

Further, when chromium is contained in the waste contaminated with radioactive cesium, there is a possibility that hexavalent chromium (Cr6 +) is contained in the obtained fired product.

When such a sintered material is used as a cement admixture, an aggregate, an earthwork material (especially when used as a material for earthworks), the hexavalent chromium contained in the sintered material may be eluted and cause water pollution and soil pollution.

Therefore, in the heating step, heating can be performed in a reducing atmosphere. It is possible to prevent the formation of hexavalent chromium that easily occurs in an oxidizing atmosphere even if chromium is contained in the waste by heating in a reducing atmosphere. In the step of heating the waste, the waste is temporarily heated in an oxidizing atmosphere, Even if it is produced, it is reduced to trivalent chromium (Cr3 +). Therefore, the obtained fired product can be safely used with earthworks or the like. It is also possible to carry out the combination of the above-mentioned method of heating under air containing water vapor and the method of heating in a reducing atmosphere. Hereinafter, a method of performing heating in a reducing atmosphere will be described by taking as an example a case where a countercurrent type (which is combusted at the raw material outlet side) is used in an internal soft compacting device (internal rotary type rotary kiln or the like) Is not limited to this form.

As an example of a method of heating waste contaminated with radioactive cesium in a reducing atmosphere, there is a method of burning a combustible material when the waste is heated. By burning the combustible material, the periphery of the waste can be maintained in the reducing atmosphere. In addition, even if chromium is contained in the waste, the production of hexavalent chromium can be prevented. In the step of heating the waste, hexavalent chromium is reduced to trivalent chromium even if hexavalent chromium is produced.

Here, the combustible material is, for example, a solid waste lump of waste obtained by compressing and / or solidifying waste such as coal, coke, activated carbon, waste wood, waste plastics, heavy oil sludge, municipal waste and the like.

As a method of supplying a combustible material, it is possible to mix the waste material contaminated with radioactive cesium in advance. When a rotary kiln is used as a device for heating, a combustible material can be supplied to the inlet side, the outlet side, or the rotary kiln of the waste have.

In the case where the combustible material is preliminarily mixed with the raw material, the mixing amount of the combustible material is preferably large and the particle size of the combustible material is also preferably large so long as the combustible material is not left in the unburned state in the baked material obtained by heating.

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

In this case, it is preferable that the combustible material can maintain the reducing atmosphere for a long time. Specifically, for example, there is a burning speed lower than that of the main fuel of the rotary kiln, or a combustible material having particles having the same burning speed as that of the main fuel and being less coarse than the main fuel. Specific examples thereof include petroleum coke, coal coke and anthracite coal. As the burning rate is slower, the combustible material can be made finer, which is preferable.

The average particle diameter of the combustible material is preferably 0.5 to 20 mm, more preferably 1 to 5 mm. If the average particle diameter is less than 0.5 mm, the reducing atmosphere may be unable to be maintained for a long time because it burns very early during combustion. When the average particle diameter exceeds 20 mm, a large amount of unburned combustible material remains in the obtained fired body, so that the supplied combustible material is wasted, and when the fired body is used as a cement mixed material or a concrete aggregate, Since the unburned carbon adsorbs the AE agent, when the air entraining property of the mortar concrete deteriorates or compaction occurs, unburnt carbon may appear on the surface and the appearance of the mortar concrete may be deteriorated.

The amount of the combustible material 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 reducing the atmosphere may be small. If the amount exceeds 40 kg, a large amount of unburned combustible material remains in the obtained fired product, and the air entraining property or appearance of the mortar concrete may deteriorate when the fired product is used as a cement mixed material or a concrete aggregate.

Further, when the combustible material is supplied during the rotary kiln, it is preferable to supply the combustible material in the middle from the position where the rotary kiln becomes the highest temperature in the rotary kiln to the inlet side of the waste.

The oxygen (O 2) concentration in the furnace when combusting the combustible material is preferably not more than 5% by mass, more preferably not more than 3% by mass from the viewpoint of not immediately burning off the combustible material.

It is possible to prevent the formation of hexavalent chromium and to prevent the flammable substance from remaining, by adjusting the above-described conditions and the residence time. When the obtained fired product is used as a cement admixture or a concrete aggregate, the above-mentioned conditions and the residence time are adjusted so as not to adversely affect air entraining property and appearance of the mortar concrete.

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

The combustible material can be easily pumped from the outlet side of the waste toward the inside of the furnace using air. A dedicated inlet may be provided at the outlet of the rotary kiln. In addition, it is also possible to drop a solid combustible material (having an average particle diameter of about 1 to 10 mm) as a part of the fuel of the main burner.

It is desirable that the combustible material can be brought into a stronger reducing state than when it is supplied on the inlet side of the waste or on the rotary kiln. Specifically, for example, a combustible material having a higher burning rate than the main fuel of the rotary kiln can be cited. Examples of combustible materials having a high burning rate include waste solid lumps obtained by compressing and / or solidifying waste such as waste wood, waste plastic, heavy oil sludge, and municipal waste.

The average particle diameter of the combustible material is preferably 0.1 to 10 mm, more preferably 1 to 5 mm. If the average particle diameter is less than 0.1 mm, the reducing atmosphere may not be maintained because it burns very early during firing. If the average particle diameter exceeds 10 mm, a large amount of unburned combustible material remains in the obtained fired body, and the supplied combustible material is wasted. When the fired body is used as a cement mixed material or a concrete aggregate, There is a possibility that the appearance or the appearance may deteriorate. The time during which the reducing atmosphere can be maintained can be adjusted by the average particle diameter of the combustible material. For example, a combustible material with a high burning rate can increase the time for maintaining the reducing atmosphere by increasing the average particle size (roughness).

The calorific value of the combustible material can be used so that it is usually 2 to 40% with respect to the calorific value of the whole fuel used in the main burner. If the calorific value of the combustible material is less than 2%, the effect of reducing the atmosphere may be small. If the calorific value of the combustible material exceeds 40%, a large amount of unburned combustible material remains in the obtained burned material, thereby wasting the supplied combustible material. When the burned material is used as a cement admixture or a concrete aggregate, The air entraining property and the appearance may be deteriorated.

Compared to the case where the above-mentioned combustible material is supplied from the outlet side of the waste or from the outlet side of the rotary kiln, the reducing atmosphere in the rotary kiln is a part of the furnace, so the reducing atmosphere is maintained for a long time (Fall position) of the combustible material is adjusted to the inlet side of the waste rather than the position where the highest temperature is reached in the rotary kiln so that the reducing atmosphere becomes the reducing atmosphere at a high temperature at which the reduction rate is high. Preferably, the supply position is preferably inward of the point of 4D from the exit of the kiln with the inner diameter of the kiln as D in general. Further, when the position at which the maximum temperature in the kiln becomes the outlet side due to the setting condition of the main burner or the like, the inside of the 3D point from the outlet of the kiln is preferable. The supply position (falling position) is preferably adjusted by the angle of the inlet of the combustible material, the position of the inlet, the rate of input of the combustible material, the particle size of the combustible material, and the density of the combustible material.

In the case of adding a combustible material, the oxygen (O2) concentration in the furnace is preferably 5 mass% or less, more preferably 3 mass% or less, from the viewpoint of not immediately burning off the combustible material.

It is preferable to prevent the formation of hexavalent chromium and to prevent the flammable substance from remaining by adjusting the above-mentioned conditions.

Another method of heating waste contaminated with radioactive cesium under a reducing atmosphere is to bring the waste into direct contact with the flame.

Specifically, in an internal soft device (heat-resistant rotary kiln or the like), firing is performed at a high temperature so that the flame of the burner comes into direct contact with the waste contaminated with radioactive cesium which is being heated (under firing). (Hereinafter, also referred to as [membrane firing]). A method of performing a salt film firing using a heat resistant rotary kiln is as follows. (A) A main burner for heating is installed at the bottom, (B) heating (firing) the flame by emitting a flame by adjusting the amount of fuel or the air speed so that the flame burns the waste, etc., (c) the flame is made longer by turning the angle of the main burner downward, (Firing) so as to burn out the light-emitting layer and the like. In addition to the main burner for heating, an auxiliary burner for firing a salt film may also be provided. The longer the contact time between the waste or the like and the flame is, by the adjustment of each condition, the more the reduction effect is improved. Also, even if chromium is contained in the waste, it is possible to prevent the formation of hexavalent chromium, and hexavalent chromium is reduced to trivalent chromium even if hexavalent chromium is produced in the process of heating the waste.

The oxygen concentration at the time of performing the salt film firing is preferably 5 mass% or less, more preferably 3 mass% or less, from the viewpoint of generating more salt film.

By adjusting the above-mentioned conditions, the hexavalent chrome leaching prevention effect can be further increased. In addition, combustion of the above-described combustible material and salt film firing may be used in combination.

It is also possible to make a reducing atmosphere by adjusting the atmosphere at the time of heating.

For example, another method of heating the waste contaminated with radioactive cesium in a reducing atmosphere is a method of burning the fuel used for heating at an air amount less than the theoretical air amount.

Specifically, it is preferable that 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 1 mass% or less, A method of burning fuel, or a method of burning fuel while maintaining the concentration of carbon monoxide in the furnace at 0.1 to 1.0 mass%.

When the air ratio in the furnace is less than 0.8 or the carbon monoxide concentration is more than 1.0% by mass, the combustion required for heating may become difficult. When the air ratio in the furnace exceeds 1.0, the oxygen concentration exceeds 1% by mass, or when the fuel is burned while maintaining the carbon monoxide concentration in the furnace at less than 0.1% by mass, the reducing effect is reduced.

Examples of the fuel used for heating include heavy oil, pulverized coal, regenerated oil, LPG, NPG, combustible waste, and the like as the main fuel (fuel for the burner), and the particle size is adjusted so as to burn in the space.

It may also be used in combination with combustion and / or salt film firing of the above-mentioned combustible material.

In addition, a method of replacing or circulating an inert gas such as nitrogen gas in an apparatus (such as an exothermic rotary kiln or an electric furnace) used for heating may be mentioned. A mixture of the inert gas and a reducing gas such as a carbon monoxide gas may be substituted or distributed.

The volatilized radioactive cesium in the exhaust gas produced according to the above-described heating method can be cooled and solidified, and then recovered by a dust collector, a scrubber, or the like. Further, when the kiln is equipped with a preheater, a portion of the exhaust gas containing the volatilized radioactive cesium at a high concentration can be extracted and cooled to recover the solidified radioactive cesium. The recovered radioactive cesium can be stored in a closed container such as a concrete container after further treatment by washing, adsorption, etc., if necessary. As a result, the waste containing the radioactive material can be retained and stored without leaking to the outside.

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

The fired product obtained after heating can be used as a cement admixture, aggregate (aggregate for concrete, aggregate for asphalt), earthwork material (backfill material, embankment material, roadbed material, etc.)

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

The amount of free lime (free lime) of the above-mentioned calcined product is preferably 1.0 mass% or less, more preferably 0.5 mass% or less, still more preferably 0.2 mass% or less. If the amount of free lime exceeds 1.0% by mass, there is a possibility that when the fired product is used as concrete aggregate or earthworks, the concrete may be expanded or broken, or the fired product itself may collapse.

The particle size of the calcined material may be adjusted by a sieve or the like in consideration of necessary particle size, compactibility, and the like to be used for a cement admixture or the like.

Further, in the case where chrome is contained in the waste, besides the heating in the heating step described above in a reducing atmosphere, the hexavalent chromium can be prevented from being eluted from the baked product by subjecting the obtained calcined product to the following treatments. Particularly, in the case of using the fired material as the earthwork material, it is preferable to take measures against the release of hexavalent chrome from the viewpoint of preventing water pollution and soil contamination. Hereinafter, a specific method of measures for dissolving hexavalent chrome will be described.

When the obtained fired product contains hexavalent chrome, a method of mixing the high-temperature fired product obtained by the heating step with a combustible substance as a countermeasure for dissolving hexavalent chromium. The hexavalent chromium in the sintered product is reduced to trivalent chromium by mixing the hot sintered product after the heating step with a combustible material and cooling the same, so that hexavalent chromium in the sintered product can be reduced.

Specifically, there is a method in which a sintered body after the heating step is mixed with a combustible material while maintaining the temperature of the sintered body at a high temperature in a hot air furnace, or a method in which a sintered body of high temperature and a combustible material after the heating step are filled, Is maintained at a high temperature.

In addition, a high-temperature sintered material and a combustible material may be mixed in a cooling process using an air quenching cooler, a rotary cooler, or the like, which is performed after the heating process. Among them, it is preferable to use a rotary cooler which is less in contact with oxygen and has a high degree of mixing of combustible materials.

When the combustible material is mixed during the cooling process, the mixing method of the combustible material is not particularly limited, but from the viewpoint of maintaining the high temperature condition and the reducing atmosphere for a long time, it is preferable to mix the combustible material immediately after the heating process. For example, when heating is carried out using a rotary kiln, it is preferable to drop the combustible material into the outlet of the rotary kiln and mix them.

The higher the temperature of the baked material when mixing the combustible material, the greater the reduction effect of hexavalent chromium, preferably 800 DEG C or more, and more preferably 1000 DEG C or more. In addition, when heating is performed using a rotary kiln, the temperature at which the firing temperature in the rotary kiln becomes maximum can be made close to the discharge port side, thereby increasing the temperature of the fired product in mixing in the rotary cooler.

The longer the time until the fired product is cooled after mixing the combustible material, the greater the effect of reducing the hexavalent chromium. However, the time until the temperature of the fired product becomes 600 ° C or less after mixing is preferably 1 minute or more , More preferably not less than 3 minutes.

The combustible material is preferably mixed with an amount corresponding to a calorific value of 2 to 20% of the total calorific value of the mixture of the calcined material and the combustible material. When the amount corresponds to a calorie of less than 2%, the effect of reducing hexavalent chromium is reduced. When the amount corresponds to a heat quantity exceeding 20%, a large amount of unburned combustible material remains in the sintered product after cooling.

Examples of the combustible material include waste solid lumps obtained by compressing and / or solidifying waste such as coal, coke, activated carbon, waste wood, waste plastics, heavy oil sludge, municipal waste, and the like. Among them, it is preferable that a stronger reduction state can be obtained. Specifically, a combustible material having a high burning rate can be mentioned. Examples of combustible materials having a high burning rate include waste solid lumps obtained by compressing and / or solidifying waste such as waste wood, waste plastics, heavy oil sludge, and municipal waste.

The average particle diameter of the combustible material is preferably 0.1 to 10 mm, more preferably 1 to 5 mm. If the thickness exceeds 10 mm, a large amount of combustible material remains in the sinter after the cooling. If it is less than 0.1 mm, the effect of reducing the hexavalent chromium becomes small, and the amount of mixing with the sintered body is reduced by scattering due to the air velocity of the cooling air at the time of input.

The above-mentioned combustible material having a high burning rate can make the average particle diameter large (rough). By increasing the average particle diameter, the time for maintaining the reducing atmosphere can be prolonged, and at the same time, the combustible material can be prevented from scattering due to the wind speed of the cooling air or the like.

The oxygen concentration at the time of mixing the combustible material is not particularly limited. In addition, the exhaust gas may be used from the viewpoint of reducing contact with oxygen and reducing the amount of the combustible material added, if possible.

It is preferable to adjust the above condition so that the effect of reducing hexavalent chromium is large and the combustible remains. Further, when the fired product is used as a cement admixture, it is preferable that the reducing atmosphere is made too strong so that the color of the cement using the fired product is not changed.

As a countermeasure for dissolution of hexavalent chromium, there is a method of further dissolving the fired product obtained by the heating step.

When the hexavalent chromium contained in the calcined material is dissolved in the glass and the earthworks material is used, the elution amount of hexavalent chromium is less than the environmental standard value.

After the fired product is further heated and dissolved, the melt is cooled to form a granular product. The resulting granular liquor has a low water absorption rate and high strength, so it can be used as a concrete aggregate. Cooling of the melt can also be quenched or slowly cooled.

In addition, it is preferable from the viewpoint of energy cost to directly dissolve the fired product at a high temperature obtained by the heating process (for example, the fired product immediately after the fired product from the kiln).

Further, as a countermeasure against hexavalent chrome leaching, a mixing step of mixing at least one selected from the group consisting of a calcined material obtained by a heating step and a reducing agent and an adsorbent can be carried out.

For example, hexavalent chromium contained in the sintered product or hexavalent chromium eluted from the sintered product can be reduced to trivalent chromium by mixing the calcined 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, iron and the like.

Further, by mixing the fired product and the adsorbent, the hexavalent chromium eluted from the fired product can be adsorbed to suppress the insolubilization or elution of the hexavalent chromium.

Examples of the adsorbent include zeolites, clay minerals, layered multi-oxides such as hydrotalcite compounds such as Mg-Al and Mg-Fe, CaAl-based hydroxides, ettringite, monosulphate ), Calcium oxide such as iron oxide (hematite) and bismuth oxide, magnesium compounds such as magnesium hydroxide, light magnesium, fired dolomite and magnesium oxide, iron compounds such as iron powder, iron powder, schwermannite, FeOOH , A mixture of at least one of silicon oxide, aluminum oxide and iron oxide, or a mixture thereof, and a compound containing cerium and a rare earth element.

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

As the method of mixing the fired product with the agent (reducing agent and / or adsorbent), the fired product and the powdered agent may be mixed, and the agent may be previously mixed with water to prepare a slurry or an aqueous solution (hereinafter also referred to as [slurry] A method of mixing a fired product with a slurry or the like, a method of spraying a slurry or the like to a fired product, or a method of immersing a fired product in a slurry or the like.

The amount of the above-mentioned medicament to be used is such that the amount of the metal salt per 100 kg of the baked product, preferably 0.01 to 10 kg, more preferably 0.1 to 7 kg, particularly preferably 0.2 to 5 kg, The amount of spraying, and the amount of fired material to slurry or the like are adjusted. If 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 becomes small. If the amount exceeds 10 kg, the effect of reducing the elution amount of hexavalent chromium is saturated, which is not economical.

The temperature of the baked material at the time of mixing is preferably 100 to 800 DEG C, more preferably 125 to 600 DEG C, and particularly preferably 150 to 400 DEG C. When the temperature of the baked product exceeds 800 ° C, cracks are generated in the baked product or the baked product is atomized and the strength is lowered, which is not preferable. If it is less than 100 ° C, it is not preferable because the medicament becomes difficult to adhere to the surface of the baked product.

A method of spraying a slurry containing a chemical agent to a high-temperature sintered material is very suitable because the medicament is not easily peeled off due to adhesion to the surface of the sintered material. Further, in the case where pores are present in the fired product, the method of immersing the fired product in a slurry or the like is very suitable because the agent penetrates well into the interior and adheres to the surface.

Further, as a countermeasure for dissolution of hexavalent chrome, there is a method of washing the fired product obtained by the heating process.

As a cleaning method, there are (i) a method of spraying a cleaning liquid onto a sintered object in a container or on a belt conveyor by sprinkling with a sprinkler or the like, (ii) a method in which a sintered material and a cleaning liquid are placed in a vessel, (Iii) a cleaning method in which the sintered material is sequentially changed while dipping the sintered material in a cleaning liquid by using Tronmel or the like, and the like.

The washing liquid may be a conventional tap water or an aqueous solution of the above-mentioned medicament (reducing agent or adsorbent) may be used. The cleaning liquid after cleaning may be reused as a cleaning liquid or may be disposed of after being treated.

The cleaning time, the number of times of cleaning, and the amount of the cleaning liquid to be used for cleaning are not particularly limited, and the cleaning may be performed until the elution amount of hexavalent chrome satisfies the environmental standard value (Environmental Agency Notice No. 46).

Such a method may be carried out in combination with a method of heating in a reducing atmosphere in the heating step described above.

Further, since the fired product obtained by the heating process of the present invention is excellent in the ability to fix a heavy metal (lead, arsenic, etc.) other than hexavalent chrome in the interior thereof, if the above-mentioned treatment for preventing elution of hexavalent chrome is performed, (Backfill material, embankment material, roadbed material, etc.).

The calcined material obtained by the heating process can be used as a cement admixture by pulverization. Further, 1 to 6 parts by mass of gypsum in terms of SO 3 may be contained in 100 parts by mass of the pulverized product of the fired product.

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

The pulverized product of the fired product preferably has a brain specific surface area of 2500 to 5000 cm2 / g from the viewpoints of reducing the bleeding of the mortar or concrete, and exhibiting fluidity and strength.

Grinding can simultaneously crush fired material, cement clinker and gypsum. When crushing is carried out at the same time, the brains specific surface area of the cement is preferably 2500 to 4500 cm 2 / g from the viewpoints of reduction in bleeding of the mortar or concrete, fluidity and strength development.

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

The fired product obtained by the heating process can be used as aggregate (aggregate for concrete, aggregate for asphalt) and earthworks material by pulverizing or classifying as necessary.

When a sintered material containing hexavalent chromium is used as an aggregate, since hexavalent chromium is blown into the cement cured product, the release of hexavalent chrome can be prevented by preventing rainwater from being transported or stored during storage. Further, a treatment for preventing elution of the hexavalent chrome described above may be performed.

Both the fine aggregate and the coarse aggregate can be used as the obtained fired product. When used as a coarse aggregate, adjust the particle size to 5 mm or more by using a sieve or the like.

When used as earth-boring materials, it is adjusted to 0.1 to 100 mm in consideration of compactibility and the like.

When used as an aggregate, the absolute density of the calcined product is preferably 2.0 to 3.0 g / cm 3. If the required solid density is less than 2.0 g / cm 3, the strength of the concrete may be lowered. The water absorption rate of the baked product is preferably 15% or less. If the water absorption rate is larger than 15%, the strength of the concrete may be lowered.

Particularly, when used as a concrete aggregate, it is preferable that the calcined product has a solid density of 2.5 to 3.0 g / cm 3 and an absorption rate of 3% or less.

The amount of free limes is preferably 1.0 mass% or less, more preferably 0.5 mass% or less. If the amount exceeds 1.0% by mass, the concrete may be expanded and broken.

(Example)

Hereinafter, the present invention will be described concretely with reference to Examples, but the present invention is not limited by these Examples.

[Synthesis Example 1 Preparation of cesium adsorbent clay A]

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 and then centrifuged to recover the solid content. The solid content was again washed and centrifuged again. Whereby cesium adsorbed clay A containing cesium at a concentration of 1060 mg / kg was obtained.

[Synthesis Example 2 Preparation of Cesium Adsorption Clay B]

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 and then centrifuged to recover the solid content. The solid content was again washed and centrifuged again. Whereby cesium adsorbed clay B containing cesium at a concentration of 2200 mg / kg was obtained.

[Example 1]

6.6 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 13.2 g of limestone powder were mixed. The resulting mixture was heated at 1300 占 폚 for 60 minutes in air containing no steam (pure air) using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1.

[Example 2]

6.6 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 13.2 g of limestone powder were mixed. The obtained mixture was bubbled through 60 ° C water using a tubular electric furnace, and heated at 1300 ° C for 60 minutes under air (moisture content 7%) to obtain a sintered product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1.

The reason why the heating is carried out under the air having the moisture content of 7% is for simulating the heating in the actual heat-resistant kiln.

[Example 3]

8 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 12 g of limestone powder were mixed. The resultant mixture was bubbled through 60 ° C water using a tubular electric furnace, and heated at 1300 ° C for 60 minutes under air (water content 7%) to obtain a baked product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1.

[Example 4]

9 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 11 g of limestone powder were mixed. The resultant mixture was bubbled through 60 ° C water using a tubular electric furnace, and heated at 1300 ° C for 60 minutes under air (water content 7%) to obtain a baked product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1.

[Example 5]

10 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 10 g of limestone powder were mixed. The resultant mixture was bubbled through 60 ° C water using a tubular electric furnace, and heated at 1300 ° C for 60 minutes under air (water content 7%) to obtain a baked product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1.

[Example 6]

6.6 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 13.2 g of limestone powder were mixed. The obtained mixture was heated at 1200 DEG C for 60 minutes in a tubular electric furnace under a pure air to obtain a baked product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1.

[Example 7]

11 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 9 g of limestone powder were mixed. The resulting mixture was heated at 1200 DEG C for 60 minutes in air (moisture content 7%) bubbled with water at 60 DEG C using a tubular electric furnace to obtain a sintered material. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1.

[Comparative Example 1]

The cesium-adsorbed clay A obtained in Synthesis Example 1 was heated at 1000 占 폚 for 60 minutes in a tubular electric furnace under a pure air to obtain a fired product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1. Further, although the cesium adsorbent clay was calcined at a high temperature of 1200 캜, the sample was dissolved and adhered to the vessel and could not be recovered.

[Comparative Example 2]

6.6 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 13.2 g of limestone powder were mixed. The obtained mixture was heated in a tubular electric furnace under pure air at 1000 캜 for 60 minutes to obtain a baked product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 1.

(CaO + 1.39 x MgO) / SiO ₂ ) of each of calcium oxide (CaO), magnesium oxide (MgO) and silicon dioxide (SiO ₂ ) Is about 1.0 to 1.8, and it can be seen that cesium can be volatilized by heating to about 1200 to 1300 ° C.

Further, by comparing Example 1 with Examples 2 to 5 (particularly, Examples 1 and 2), it is possible to lower the volatilization rate of potassium or sodium and increase the volatilization rate of cesium by heating under air containing steam .

[Example 8]

30 g of the cesium-adsorbing 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 占 폚 for 60 minutes in air (moisture content: 7%) bubbled with water at 60 占 폚 using a tubular electric furnace to obtain a sintered product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 2.

[Example 9]

30 g of the cesium-adsorbing clay B obtained in Synthesis Example 2, 60 g of limestone powder and 0.0492 g of calcium chloride were mixed and pulverized. 20 g of the obtained mixture was heated at 1300 占 폚 for 60 minutes in air (moisture content: 7%) bubbled with water at 60 占 폚 using a tubular electric furnace to obtain a sintered product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 2.

[Example 10]

30 g of the cesium adsorbent clay B obtained in Synthetic 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 占 폚 for 120 minutes under air (water content: 7%) bubbled with water at 60 占 폚 using a tubular electric furnace to obtain a baked product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 2.

[Example 11]

30 g of the cesium adsorbing 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 to 60 minutes in air (moisture content: 7%) bubbled with 60 water using a tubular electric furnace to obtain a baked product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 2.

[Example 12]

30 g of the cesium adsorbent 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 at 1300 占 폚 for 60 minutes in air (moisture content: 7%) bubbled with water at 60 占 폚 using a tubular electric furnace to obtain a sintered product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 2.

[Example 13]

10 g of the cesium adsorbent 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 DEG C for 60 minutes in a tubular electric furnace under a pure air to obtain a baked product. The content of Cs and Cl in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 2.

From Examples 8 to 13 of Table 2, it can be seen that cesium is volatilized even when chlorides are added. Particularly, it was confirmed that the molar ratio of chlorine to cesium and potassium (Cl / (CsK)) was about 0.09 to 0.26, the amount of chlorine was about 410 to 1210 mg / kg from Example 8, Example 9 and Example 11, When the time is about 60 minutes, it can be seen that the volatilization rate of cesium is high when the volatilization rate of sodium and potassium is low.

[Example 14]

A fired product was obtained in the same manner as in Example 1 except that it was heated at 1300 캜 for 120 minutes under air containing no steam (pure air). The respective contents of cesium (Cs), chlorine (Cl), Na ₂ O and K ₂ O in each of the mixture before heating and the baked product obtained by heating were measured in the same manner as in Example 1 to determine the volatilization rates of Cs, Na and K Mass%) was obtained. The results are shown in Table 3.

[Example 15]

A fired product was obtained in the same manner as in Example 1 except that it was heated at 1300 캜 for 30 minutes under air containing no steam (pure air). The respective contents of cesium (Cs), chlorine (Cl), Na ₂ O and K ₂ O in each of the mixture before heating and the baked product obtained by heating were measured in the same manner as in Example 1 to determine the volatilization rates of Cs, Na and K %). The results are shown in Table 3.

[Example 16]

A fired product was obtained in the same manner as in Example 1 except that it was heated at 1250 占 폚 for 60 minutes under air containing no steam (pure air). The respective contents of cesium (Cs), chlorine (Cl), Na ₂ O and K ₂ O in each of the mixture before heating and the baked product obtained by heating were measured in the same manner as in Example 1 to determine the volatilization rates of Cs, Na and K %). The results are shown in Table 3.

[Example 17]

A fired product was obtained in the same manner as in Example 1 except that it was heated at 1250 DEG C for 120 minutes under air containing no water vapor (pure air). The respective contents of cesium (Cs), chlorine (Cl), Na ₂ O and K ₂ O in each of the mixture before heating and the baked product obtained by heating were measured in the same manner as in Example 1 to determine the volatilization rates of Cs, Na and K %). The results are shown in Table 3.

[Example 18]

A fired product was obtained in the same manner as in Example 1 except that it was heated at 1350 占 폚 for 30 minutes under air containing no steam (pure air). The respective contents of cesium (Cs), chlorine (Cl), Na ₂ O and K ₂ O in each of the mixture before heating and the baked product obtained by heating were measured in the same manner as in Example 1 to determine the volatilization rates of Cs, Na and K Mass%) was obtained. The results are shown in Table 3.

[Example 19]

30 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 68 g of limestone powder were mixed. The resulting mixture was heated at 1300 占 폚 for 60 minutes in air containing no steam (pure air) using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 4.

[Example 20]

30 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 77 g of limestone powder were mixed. The resulting mixture was heated at 1300 占 폚 for 60 minutes in air containing no steam (pure air) using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 4.

[Example 21]

30 g of the cesium adsorbent clay A obtained in Synthesis Example 1, 77 g of limestone powder and 0.122 g of calcium chloride were mixed. The resulting mixture was heated at 1300 占 폚 for 60 minutes in air containing no steam (pure air) using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 4.

[Example 22]

30 g of the cesium adsorbent clay A obtained in Synthesis Example 1, 77 g of limestone powder and 0.122 g of calcium chloride were mixed. The resulting mixture was heated at 1250 DEG C for 60 minutes in air (normal air) containing no water vapor using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 4.

[Example 23]

30 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 90 g of limestone powder were mixed. The resulting mixture was heated at 1300 占 폚 for 60 minutes in air containing no steam (pure air) using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 4.

[Example 24]

30 g of the cesium adsorbent clay A obtained in Synthesis Example 1 and 90 g of limestone powder were mixed. The resulting mixture was heated at 1250 DEG C for 60 minutes in air (normal air) containing no water vapor using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 4.

[Example 25]

30 g of the cesium adsorbent clay A obtained in Synthesis Example 1, 90 g of limestone powder and 0.039 g of calcium chloride were mixed. The resulting mixture was heated at 1300 占 폚 for 60 minutes in air containing no steam (pure air) using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 4.

[Example 26]

30 g of the cesium adsorbent clay A obtained in Synthesis Example 1, 90 g of limestone powder and 0.039 g of calcium chloride were mixed. The resulting mixture was heated at 1250 DEG C for 60 minutes in air (normal air) containing no water vapor using a tubular electric furnace to obtain a sintered product. The content of cesium (Cs) and chlorine (Cl) in each of the mixture before heating and the fired product obtained by heating was measured by a wet method to determine the volatilization rate (mass%) of Cs. Further, the amounts of Na ₂ O and K ₂ O were measured by X-ray fluorescence spectrometry (XRF) to determine the volatility (% by mass) of Na and K. The results are shown in Table 4

Claims (9)

A method of removing radioactive cesium comprising heating a radioactive cesium-contaminated waste and a CaO source and / or an MgO source to 1200 to 1350 ° C to volatilize radioactive cesium in the waste,
Wherein a kind and a mixing ratio of each of the waste, the CaO source and the MgO source are determined so that the mass of each of CaO, MgO and SiO ₂ satisfies the following formula (1).
((CaO + 1.39 x MgO) / SiO ₂ ) = 1.0 to 2.5 (1)
(Wherein CaO, MgO, and SiO ₂ each represent an oxide-reduced mass of calcium, an oxide-reduced mass of magnesium, and an oxide-reduced mass of silicon, respectively). The method according to claim 1,
A method for removing radioactive cesium, characterized by further using a chloride in the heating step. 3. The method according to claim 1 or 2,
Wherein the heating is carried out in a reducing atmosphere in the heating step. Heating a waste material contaminated with radioactive cesium and a CaO source and / or an MgO source to 1200 to 1350 ° C to volatilize radioactive cesium in the waste to obtain a sintered material,
Wherein a kind and a mixing ratio of each of the waste, CaO source and MgO source are determined so that the mass of each of CaO, MgO and SiO ₂ satisfies the following formula (1).
((CaO + 1.39 x MgO) / SiO ₂ ) = 1.0 to 2.5 (1)
(Wherein CaO, MgO, and SiO ₂ each represent an oxide-reduced mass of calcium, an oxide-reduced mass of magnesium, and an oxide-reduced mass of silicon, respectively). 5. The method of claim 4,
Wherein the heating is carried out in a reducing atmosphere in the heating step. The method according to claim 4 or 5,
And a mixing step of mixing at least one selected from the group consisting of a reducing agent and an adsorbent with the calcined material obtained by the heating step. A cement admixture obtainable by pulverizing a calcined material obtained by the method for producing a calcined material according to any one of claims 4 to 6. An aggregate comprising a calcined material obtained by the method for producing a calcined body according to any one of claims 4 to 6. A soil-borne material comprising a calcined material obtained by the method for producing a calcined material according to any one of claims 4 to 6.