JP7320469B2 - Method for removing radioactive cesium and apparatus for removing radioactive cesium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a processing method and a processing apparatus that contribute to volume reduction of radioactive contaminants.

Due to the nuclear power plant accident caused by the Great East Japan Earthquake, for example, there are 22 million ^cubic meters of radioactive contaminated soil that need to be treated in Fukushima Prefecture alone. Development of volume reduction technology for contaminated waste (hereinafter referred to as "decontaminated soil, etc.") is underway. In particular, a processing technology based on the so-called chloride volatilization method, in which radioactive cesium is recovered as dust by heating decontaminated soil and the like and a chlorine source at the same time, is one of the effective volume reduction technologies (see Patent Documents 1 to 3). ).

On the other hand, for example, in Patent Document 4, radioactive cesium recovered as dust such as incineration ash by incineration treatment or the like is eluted into the liquid phase by washing the dust with water, and heavy metals are removed using an appropriate chelating agent. It is described that the waste water can be discharged outside the system after recovery treatment or the like is performed.

JP 2013-122440 A JP 2017-062143 A JP 2017-150955 A JP 2014-117684 A

However, for example, when decontaminated soil, etc. accompanying the Great East Japan Earthquake is treated by the chloride volatilization method, the radiation dose of the collected dust exceeds 1,000,000 Bq/kg, and the radiation dose of the washing residue generated by washing the dust is also high. In some cases, it showed a value as high as 200,000 Bq/kg or more. Therefore, landfill disposal of such washing residues has been difficult because the landfill standard value of 8000 Bq/kg or less cannot be satisfied.

Therefore, an object of the present invention is to provide a processing method and a processing apparatus that can solve the above-mentioned problem of difficulty in landfill disposal of the washing residue of dust generated in the volume reduction processing of decontaminated soil and the like. to do.

In order to achieve the above object, the present invention, in its first aspect,
A method for removing radioactive cesium from radioactive cesium contaminants, comprising:
a heating step for heating the radioactive cesium contaminant, the calcium source, the magnesium source, and the chlorine source together to volatilize the radioactive cesium;
A solid-gas separation step for recovering dust containing radioactive cesium by solid-gas separation after cooling the combustion exhaust gas generated in the heating step;
A water washing step for adding water to the dust to make a slurry and eluting radioactive cesium in the slurry liquid phase;
a solid-liquid separation step for solid-liquid separation of the slurry that has undergone the water washing step to separate the washing residue and waste water;
and a circulation step for circulating the washing residue as the radioactive cesium contaminant in the heating step.

According to the method for removing radioactive cesium of the present invention, the calcium source, magnesium source and chlorine source are heated together to volatilize the radioactive cesium. However, the sintered material remaining after the heating process has a radiation dose of 100 Bq/kg or less, and can be utilized without special consideration. In addition, since the dust containing radioactive cesium is recovered by solid-gas separation after cooling the combustion exhaust gas generated in the heating process, gas containing radioactive substances is not discharged outside the system. In addition, since the collected dust is washed with water and separated into washing residue and waste water, the waste water can be subjected to conventional radioactive cesium recovery treatment. On the other hand, although a considerable amount of radioactive cesium may remain in the washing residue, it is not discharged outside the system by circulating it in the heating process.

In the method for removing radioactive cesium of the present invention, the mass represented by the following formula in the preparation containing the radioactive cesium contaminant, the calcium source, the magnesium source, and the chlorine source, which is subjected to the heating step It is preferred that the ratio R1 is between 1.0 and 1.9.
R1 = (CaO (mass%) + 1.39 x MgO (mass%))/( _SiO2 (mass%))

The MgO coefficient of 1.39 in the mass ratio R1 is for converting MgO (mass %) into CaO (mass %) equivalent.

According to this, it is possible to effectively suppress the amount of liquid phase (melt phase) generated by melting of the object to be heated in the heating step, and to create an environment in which radioactive cesium chloride volatilization is likely to occur.

Further, in the method for removing radioactive cesium of the present invention, it is preferable that the water content of the washing residue circulated in the circulating step is 25% by mass or more.

According to this, since the atmosphere in the heating process can be made to be rich in water vapor, radioactive cesium can be preferentially chlorinated and volatilized while suppressing chlorinated volatilization of sodium and potassium.

In the method for washing chlorine-containing powder of the present invention, the pH of the slurry in the washing step is preferably 8-11.

According to this, the dissolution of heavy metals in the waste water in which radioactive cesium is separated and recovered in the solid-liquid separation step is suppressed, so that it is possible to avoid the trouble caused by the disposal of heavy metals in the waste water.

In order to achieve the above object, the present invention, in its second aspect,
A radioactive cesium removal device for removing radioactive cesium from radioactive cesium contaminants,
a heating device for heating the radioactive cesium contaminant, the calcium source, the magnesium source, and the chlorine source together to volatilize the radioactive cesium;
a solid-gas separation device for recovering dust containing radioactive cesium by solid-gas separation after cooling the combustion exhaust gas from the heating device;
a water washing device for adding water to the dust collected by the solid-gas separation device to form a slurry, and eluting radioactive cesium into the liquid phase of the slurry;
a solid-liquid separation device for solid-liquid separating the slurry discharged from the water washing device into washing residue and waste water;
and a circulation device for circulating the washing residue separated by the solid-liquid separation device as the radioactive cesium contaminant to be heated by the heating device. It is.

According to the configuration of the removal apparatus provided by the present invention, the above-described method for removing radioactive cesium can be preferably carried out.

Preferably, the apparatus for removing radioactive cesium of the present invention further comprises an air pipe for sending the exhaust gas separated by the solid-gas separator to the water washing apparatus.

According to this, the CO ₂ contained in the exhaust gas generated from the heating device can be effectively used to change the slurry to the acidic side. Alternatively, the heat of the exhaust gas can be effectively used to heat the slurry, or the heat quantity of the exhaust gas can be effectively used to agitate the slurry. These purposes may serve as multiple purposes.

In the apparatus for removing radioactive cesium of the present invention, the washing apparatus includes a pH meter for measuring the pH of the slurry washed by the apparatus, and a pH adjuster added to the slurry washed by the apparatus. and a control device for automatically controlling the amount of the pH adjuster added by the pH adjuster addition device based on the measurement result of the pH meter. Further, it is preferable to have.

According to this, pH adjustment of slurry can be performed more stably.

In the apparatus for removing radioactive cesium of the present invention, the washing apparatus includes a pH meter for measuring the pH of the slurry washed by the apparatus, and a pH adjuster added to the slurry washed by the apparatus. A pH adjuster addition device for adding is attached, a flow rate adjustment valve is attached to the air pipe, and the amount of the pH adjuster added by the pH adjuster addition device based on the measurement result of the pH meter and/or a control device for automatically controlling the amount of the exhaust gas supplied by the flow control valve.

According to this, pH adjustment of slurry can be performed more stably.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart explaining one Embodiment of the removal method of the radioactive cesium which concerns on this invention. 1 is a configuration diagram of one embodiment of a processing apparatus for carrying out the method for removing radioactive cesium shown in FIG. 1. FIG.

Hereinafter, the method for removing radioactive cesium according to the present invention will be described with reference to the drawings. In the figures used for this explanation, the solid arrows indicate the flow of solid or liquid such as washing residue, the dotted arrows indicate the flow of gas such as combustion exhaust gas, and the dashed-dotted lines indicate the path of signals such as control signals. ing. Further, in the following description, the calcium source and the magnesium source may be collectively referred to as "Kalmag source".

The method for removing radioactive cesium of the present invention includes a heating step for heating the decontaminated soil or the like M2, the Calmag source CM1, and the chlorine source Cl1 together to chloride volatilize the radioactive cesium contained in the decontaminated soil or the like M2. a solid-gas separation step for recovering radioactive cesium-containing dust M3 by solid-gas separation after cooling the combustion exhaust gas G1 generated in the heating step; and washing with water the radioactive cesium-containing dust M3 recovered in the solid-gas separation step. In addition, a water washing step for obtaining the slurry S1, a solid-liquid separation step for separating the slurry S1 obtained in the water washing step into a washing residue M4 and waste water W3 in which radioactive cesium is dissolved, and a solid-liquid separation step A circulation step is provided for sending the separated and collected water washing residue M4 to the heating step, and circulating the supplied decontaminated soil and the like M1 together with the decontaminated soil and the like M2 so as to be heated. In the water washing step, the slurry may be washed with water while adjusting the pH of the slurry by optionally adding a pH adjuster A1 as necessary.

Therefore, in the heating step, the decontaminated soil M2 consisting of the provided decontaminated soil M1 and the circulated washing residue M4, the Calmag source CM1, and the chlorine source Cl1 are heated together to obtain the decontaminated soil M1. and the step of causing chloride volatilization to the radioactive cesium contained in the washing residue M4.

In the present invention, the radioactive cesium to be removed is cesium-134 with a half-life of about 2 years and cesium-137 with a half-life of about 30 years, which are radioactive isotopes of cesium. For example, due to the accident at the nuclear power plant caused by the Great East Japan Earthquake, cesium iodide and other forms of cesium iodide are released into the external environment together with radioactive iodine, and are radioactive substances that descend from the sky to the ground surface.

Cesium iodide has the property of being difficult to volatilize, and radioactive cesium that has fallen to the ground surface easily intercalates into clay minerals contained in the soil. become difficult.

Specifically, the decontaminated soil M1 is radioactive contaminated soil, radioactive contaminated waste, etc. For example, soil, sewage sludge, sewage sludge dry powder, sewage slag, purified water sludge, municipal waste incineration ash, garbage Molten slag, shells, vegetation, construction sludge, rubble, etc. that contain radioactive cesium. These may be used alone or in combination of two or more.

The treatment amount of the decontaminated soil M1 contained in the decontaminated soil M2 and subjected to the heating process is based on the premise that the entire amount of the washing residue M4 contained in the decontaminated soil M2 is heated. Within the range of processing capacity, as described later, the mass ratio R1 of (calcium oxide and magnesium oxide) and silicon dioxide is adjusted to be within a predetermined range, or chlorine and (cesium and potassium ) may be adjusted so that the molar ratio R2 is within a predetermined range, and the addition amounts of the chlorine source and Calmag source may be adjusted. On the other hand, the decontaminated soil or the like M1 and the washing residue M4 have a side as a Calmag source. Therefore, the above mass ratio and molar ratio are values that take into account the components brought in from the decontaminated soil M1 and the washing residue M4.

The chlorine source Cl1 is used for the purpose of causing chloride volatilization of radioactive cesium, and chlorides such as calcium chloride (CaCl ₂ ), potassium chloride (KCl) and sodium chloride (NaCl) are preferably used. Among them, calcium chloride is preferable from the viewpoint of promoting chloride volatilization of radioactive cesium.

The amount of chlorine source Cl1 added is determined by the chlorine (Cl) content, (cesium (Cs) and potassium (K) ) and the molar ratio R2 ((Cl (mol)) / (Cs (mol) + K (mol))) is preferably 0.5 to 1.3, more preferably 0.5 to 1.1 is the amount. If the molar ratio R2 is 1.3 or less, chlorination volatilization of radioactive cesium occurs preferentially over potassium and sodium.

Calmag source CM1 is used for the purpose of preferentially causing chloride volatilization of radioactive cesium, such as calcium carbonate, limestone, quicklime, slaked lime, limestone, dolomite, blast furnace slag, magnesium carbonate, magnesium hydroxide, and serpentinite. , ferronickel alloy slag, and the like.

The mixed amount of the Calmag source CM1 is the amount of (calcium oxide (CaO) and magnesium oxide (MgO)) and silicon dioxide in the total amount of the decontaminated soil M2, the Calmag source CM1, and the chlorine source Cl1 subjected to the heating step. The mass ratio R1 ((CaO (mass%) + 1.39 × MgO (mass%)) / (SiO ₂ (mass%))) to (SiO ₂ ) is preferably 1.0 to 1.9, more preferably The amount is 1.2 to 1.9. If the mass ratio R1 is less than 1.0, a liquid phase tends to occur as the firing temperature rises, and the amount of radioactive cesium volatilized by chloride decreases. Further, when the mass ratio R1 exceeds 1.9, the amount of chlorinated volatilization of potassium and sodium increases, and the amount of radioactive cesium-containing dust M3 separated and recovered in the solid-gas separation step, which will be described later, increases.

On the other hand, the water washing residue M4 separated and recovered in the water washing step to be described later is circulated to the heating step in order to remove the radioactive cesium remaining in the residue. On the other hand, the washing residue M4 also has aspects as a Calmag source and a water source.

The aspect of the washing residue M4 as a Calmag source is derived from the fact that the amount of silicon dioxide contained in the radioactive cesium-containing dust M3 separated and recovered in the solid-gas separation step described later is small. is 5.0 or more.

The aspect of the water washing residue M4 as a water source is that the higher the water vapor partial pressure in the atmosphere in the heating process, the less the amount of potassium and sodium chlorinated volatilized, and the more the chlorinated volatilized amount of radioactive cesium. and the water content of the washing residue M4 is usually 25% by mass or more.

The size of the decontaminated soil M2, Calmag source CM1, and chlorine source Cl1 to be subjected to the heating step is preferably 5 mm or less. Here, the size of objects subjected to these heating steps refers to the minimum size of the sieve mesh through which they pass.

The heating temperature in the heating step is preferably 1200°C to 1350°C, more preferably 1200°C to 1300°C. By heating within this temperature range, radioactive cesium contained in M2 such as decontaminated soil can be efficiently chlorinated and volatilized. If the heating temperature is less than 1200°C, the amount of chlorinated cesium decreases, and if it exceeds 1350°C, the amount of chlorinated volatiles of potassium and sodium increases, and the radioactive cesium-containing dust M3 separated and recovered in the solid-gas separation process described later. increases the amount of

The heating time in the heating step is preferably 15 minutes or longer, more preferably 30 minutes or longer. Although the upper limit of the heating time is not particularly limited, it is preferably 180 minutes or less, more preferably 120 minutes or less. When the heating time exceeds 180 minutes, the amount of chloride volatilization of potassium and sodium increases, and the amount of radioactive cesium-containing dust M3 separated and recovered in the solid-gas separation step described later increases.

The atmosphere in the heating step may be either an oxidizing atmosphere or a reducing atmosphere, but preferably contains a moderate amount of moisture. This is because, as described above, the higher the water vapor partial pressure in the atmosphere, the greater the amount of chlorinated volatile radioactive cesium can be increased while the chlorinated volatile amounts of potassium and sodium are reduced. When the partial pressure of water vapor in the atmosphere is low, the amount of radioactive cesium volatilized by chloride is greater than when the water vapor in the atmosphere is high. For the water vapor partial pressure of the atmosphere in the actual heating process, the optimum conditions can be found by adjusting the molar ratio R2 of cesium and potassium, the heating temperature, the heating time, and the water content of the washing residue M4. can.

The sintered product M5 obtained by the heating process has a sufficiently safe radiation dose of 100 Bq / kg or less, and is used for general purposes related to ordinary slag, specifically cement mixtures, aggregates or Can be used as an earthwork material.

The radioactive cesium chlorinated and volatilized in the heating process is contained in the flue gas G1 and sent to the flue gas flow path.

In the subsequent solid-gas separation step, the radioactive cesium in the flue gas G1 is cooled to solid (radioactive cesium chloride), and then combined with other dust to separate and recover as dust containing radioactive cesium M3.

In the subsequent water washing step, the radioactive cesium-containing dust M3 is stirred with water W1 to form slurry S1. The mass ratio (W1/M3) of the radioactive cesium-containing dust M3 and the water W1 in the slurry S1 is preferably 4-10, more preferably 4-8, and particularly preferably 4-6. If the mass ratio (W1/M3) is less than 4, elution of radioactive cesium from the radioactive cesium-containing dust M3 may be insufficient. Moreover, when the mass ratio (W1/M3) is greater than 10, the amount of waste water W3 to be separated and recovered in the subsequent solid-liquid separation step increases.

The pH of the slurry S1 in the water washing step is preferably 8-11, more preferably 8-10.5, particularly preferably 8.5-10.5. By setting the pH of the slurry S1 to 8 to 11, the concentration of heavy metals other than radioactive cesium dissolved in the liquid phase of the slurry S1 can be reduced, so that they are separated and recovered in the subsequent solid-liquid separation step. It is possible to reduce the processing steps related to heavy metals in the waste water W3.

If the pH of the slurry S1 without pH adjustment is on the acidic side, an alkalinizing agent such as an aqueous solution of sodium hydroxide (NaOH) may be used as the pH adjuster A1 added to the slurry S1 in the water washing step. .

Further, when an acidifying agent is required for adjusting the pH of the slurry S1, in addition to a general-purpose acidifying agent such as dilute sulfuric acid or hydrochloric acid, the exhaust gas G2 released to the atmosphere in the solid-gas separation step can also be used. This is because when limestone (calcium carbonate) or dolomite (CaMg(CO ₃ ) ₂ ) is used as the Calmag source CM1 in the heating process, the flue gas G1 and the flue gas G2 contain a large amount of carbon dioxide. That is, by diffusing the exhaust gas G2 into the slurry S1, the carbon dioxide in the exhaust gas G2 can be dissolved and the slurry S1 can be changed to the acidic side.

The stirring time of the slurry S1 is preferably 15 minutes or longer, more preferably 20 minutes or longer, from the viewpoint of sufficiently eluting the radioactive cesium from the radioactive cesium-containing dust M3.

The higher the temperature of the slurry S1 in the water washing step, the greater the amount of radioactive cesium eluted from the radioactive cesium-containing dust M3. °C to 50 °C is more preferred. In that case, as a method of heating the slurry S1, there is a method of diffusing the exhaust gas G2 into the slurry S1 and using the sensible heat of the exhaust gas G2.

Next, in the solid-liquid separation step, the slurry S1 supplied from the water washing step is separated into a washing residue M4 (solid phase) and waste water W3 (liquid phase).

The water content of the washing residue M4 separated and recovered in the solid-liquid separation step is preferably 25% by mass to 80% by mass. If the water content is too high, the radioactive cesium eluted into the liquid phase tends to remain in the washing residue M4 together with the liquid phase. On the other hand, by containing a moderate amount of water, it is possible to supply water to the heating step so as to provide the above-described appropriate water vapor partial pressure. On the other hand, in order to ensure the separation and recovery of radioactive cesium, the washing residue M4 separated and recovered in the solid-liquid separation step may be further washed with water W2.

All of the washing residue M4 separated and recovered in the solid-liquid separation step is sent to the heating step through the circulation step. In addition, depending on the case, the washing residue M4 may be extracted out of the system as needed.

Next, the apparatus for removing radioactive cesium of the present invention will be described. FIG. 2 shows an overall configuration diagram representing one embodiment of a processing apparatus when performing the embodiment of the method for removing radioactive cesium shown in FIG.

The radioactive cesium processing apparatus 1 according to this embodiment includes a heating device 2 for heating the decontaminated soil M2, the Calmag source CM1, and the chlorine source Cl1 to volatilize the radioactive cesium by chloride, and combustion from the heating device 2 A solid-gas separator 3 for recovering radioactive cesium-containing dust M3 by solid-gas separation of the exhaust gas G1, and a device for eluting radioactive cesium in the radioactive cesium-containing dust M3 recovered by the solid-gas separator 3 into a liquid phase. a water washing device 4; a solid-liquid separation device 5 for solid-liquid separating the slurry S1 discharged from the water washing device 4; A transport device 6 is provided. In the processing apparatus 1 according to this embodiment, the transportation apparatus 6 circulates the washing residue M4 to the heating apparatus 2 and heats it again, which constitutes the circulation apparatus of the present invention.

Therefore, in the heating device 2, the decontaminated soil M2, the Calmag source CM1, and the chlorine source Cl1, which are composed of the supplied decontaminated soil M1 and the circulated washing residue M4, are heated together to decontaminate. Chloride volatilization is caused in the radioactive cesium contained in the soil M1 and the washing residue M4.

In order to efficiently cause chloride volatilization of radioactive cesium in the heating device 2, it is desirable that the decontaminated soil M2, the Calmag source CM1, and the chlorine source Cl1 be heated in a sufficiently mixed state. 1, an internal combustion rotary kiln is used as the heating device 2 . If the firing chamber is a rotary kiln that rotates, the heat treatment can be performed while physically and continuously mixing the decontaminated soil M2, Calmag source CM1, and chlorine source Cl1.

The heating device 2 is not particularly limited as long as it can heat the decontaminated soil M2, Calmag source CM1, and chlorine source Cl1 at 1200 ° C. to 1350 ° C. Fixed furnace, stoker furnace, rotary kiln, fluidized bed furnace. , a vertical furnace, a multi-stage furnace, and the like can be used. Among them, a rotary kiln is preferable from the viewpoint that the above physical stirring can be performed.

Further, an internal combustion rotary kiln is more preferable from the viewpoint that even if dioxins or the like derived from the chlorine source Cl1 are generated, they can be rendered harmless by being directly combusted by the flame of the burner.

From the heating device 2, volatilized radioactive cesium is contained in the combustion exhaust gas G1 and sent to the solid-gas separation device 3. For example, when the solid-gas separation device 3 is a bag filter, radioactive cesium chloride derived from the radioactive cesium component and chlorine component contained in the flue gas G1 is generated on the surface of the filter cloth, and is combined with dust to generate radioactive A cesium-containing dust M3 (solid) is formed.

In the solid-gas separation device 3, the exhaust gas G2 after the radioactive cesium is recovered is discharged outside the system, and the radioactive cesium-containing dust M3 is separated from the surrounding environment so that dust of the radioactive cesium-containing dust M3 is not generated into the surrounding environment. It is transported to the washing device 4 by an enclosed dust transport device (not shown) such as a belt conveyor, a chain conveyor, a pipe conveyor, or the like.

Here, the exhaust gas G2 can be used for pH adjustment and heating in the water washing process as described above. In the embodiment of FIG. 2, a branch pipe 7 is provided in the middle of the air supply pipe for the exhaust gas G2 so that the exhaust gas G2 can be sent into the tank of the water washing device 4 and diffused. Further, the branch pipe 7 is provided with a gas flow rate adjusting device 71 so that the amount of gas in the exhaust gas G2 sent to the washing device 4 can be controlled.

In the water washing device 4, a process of mixing and agitating the radioactive cesium-containing dust M3 and water W1 to generate a slurry S1, and a process of eluting radioactive cesium from the radioactive cesium-containing dust M3 in the slurry S1 into the liquid phase are performed. will be

The water washing device 4 includes a powder supply device 41 for supplying radioactive cesium-containing dust M3 to the water washing device 4, a liquid supply device 42 for supplying water W1 to the water washing device 4, and a pH adjuster A1 to the water washing device. 4 is provided with a liquid supply device 43 for supplying. Furthermore, a slurry agitating device 44 is provided for mixing the radioactive cesium-containing dust M3 and the water W1 and for agitating the slurry S1 generated by the mixing. In the embodiment of FIG. 2, a stirring impeller is used as the slurry stirring device 44 .

Further, the washing device 4 is provided with a pH meter 45 for continuously measuring the pH of the slurry S1. The measurement result of the pH meter 45 is transmitted to the control device 10 as needed.

In this embodiment, the control device 10 automatically controls the supply amount of the pH adjuster A1 and/or the air supply amount of the exhaust gas G2 based on the measurement result of the pH meter 45 . Specifically, based on a signal from the control device 10, the opening degree of the discharge valve of the liquid supply device 43 and the gas flow rate adjustment device 71 of the branch pipe 7 are automatically controlled.

As the pH meter 45, a known measuring device may be used, and it is particularly preferable to use a measuring device for high-concentration suspension.

Slurry S1 discharged from the water washing device 4 is transported to the solid-liquid separator 5 by a normal slurry liquid transport device (not shown) such as a slurry centrifugal pump, a piston pump, and a mono pump. As the solid-liquid separation device 5, an ordinary filtering device such as a filter press, a pressurized leaf-shaped filtering device, a screw press or a belt press may be used.

The solid-liquid separation device 5 divides the transported slurry S1 into waste water W3 (liquid phase) containing eluted radioactive cesium and washing residue M4 (solid phase) containing dust M3 containing radioactive cesium after eluting radioactive cesium. ) and In the embodiment of FIG. 2, in order to ensure the recovery of the eluted radioactive cesium, the solid-liquid separation device 5 is provided with a water washing device 51 for washing the washing residue M4, and the washing residue is washed with water W2. M4 can be washed.

In this washing, the mass ratio (W2/M4) of the washing residue M4 and water W2 is preferably 4 to 10, more preferably 4 to 7, and particularly preferably 4 to 5, from the viewpoint of suppressing the amount of washing wastewater generated. . Note that the generated washing waste water becomes part of the waste water W3 and is subjected to necessary treatment.

The waste water W3 separated and recovered by the solid-liquid separator 5 may be subjected to concentration treatment of dissolved radioactive cesium by a conventional method.

In most cases, the washing residue M4 separated and recovered by the solid-liquid separator 5 contains residual radioactive cesium that cannot be landfilled.

Therefore, the transport device 6 transports the entire amount of the washing residue M4 separated and recovered by the solid-liquid separation device 5 to the heating device 2 . In addition, as described above, the water washing residue M4 may be extracted out of the system depending on the situation. As the transporting device 6, for example, a cake transporting device such as a belt conveyor, a screw conveyor, a pipe conveyor, etc. with an enclosed periphery may be used so as not to cause radiation contamination by the washing residue M4 to the surrounding environment.

The washing residue M4 transported to the heating device 2 is combined with the decontaminated soil and the like M1 to form the decontaminated soil and the like M2, and then heat-treated together with the Calmag source CM1 and the chlorine source Cl1.

Finally, the test of the method for removing radioactive cesium of the present invention will be explained. In the test, instead of radioactive cesium-containing dust M3, cement kiln dust obtained by bleeding the combustion exhaust gas of the cement kiln from the bottom of the kiln was used, and the behavior of cesium in the water washing process and solid-liquid separation process and The concentration of heavy metals in the waste water W3 separated in the solid-liquid separation step was evaluated.

Table 1 shows the chemical composition of cement kiln dust as a substitute for radioactive cesium-containing dust M3. The chemical composition of the cement kiln dust was measured according to JIS R 5204 "Method for fluorescent X-ray analysis of cement". For cesium, ICP mass spectrometry (apparatus used: Agilent 7900 ICP-MS (trade name) manufactured by Agilent Technologies) of a sample completely dissolved in acid was used.

Cement kiln dust (M3) is mixed with water (W1) at 20°C to prepare a slurry having a mass ratio of M3:W1 = 1:6, and then stirred for 30 minutes in an environment of 20°C to obtain slurry S1. It was created. The slurry S1 had a pH of 6.5.

In addition, cement kiln dust (M3), 20°C water (W1) and 20°C aqueous sodium hydroxide solution (A1) were mixed at M3: (W1 + A1) = 1:6, and 30 A slurry S2 having a pH of 9.5 was prepared by stirring for a minute.

Both slurries after stirring were solid-liquid separated with a Buchner funnel (suction filter) to obtain washing residue (M4) and waste water (W3). Both slurries had almost the same chemical composition of the residue obtained after washing with water. As a representative, Table 2 shows the chemical composition of the washing residue (M4) obtained from the slurry S2 having a pH of 9.5. The method of analyzing the chemical composition of the washing residue is the same as the method of analyzing the chemical composition of cement kiln dust.

As seen in the comparison between Tables 1 and 2, the residual rate of cesium in the water-washed residue (M4) was about 6% by mass (=1-(16.0-1.0)/16.0). . Therefore, most of the cesium contained in the cement kiln dust used in this test is removed in the waste water (W3), and it can be recovered by subjecting it to conventional heavy metal recovery means. On the other hand, with regard to the washing residue containing cesium that was not washed away, even if it is returned to the heating process and newly treated together with the decontaminated soil, etc., there is no problem if this amount is brought in. , it can be seen that it is possible to prevent the discharge from the system.

Table 3 shows the analysis results of heavy metals in waste water (W3) obtained by solid-liquid separation. ICP mass spectrometry (same as above) was used to measure heavy metals in the wastewater.

As can be seen from the results in Table 3, in the case of the cement kiln dust used in this test, adjusting the pH of the slurry to be washed with water in the water washing process suppressed the amount of heavy metals eluted compared to not adjusting the pH. I understand.

1: Radioactive cesium processing device 2: Heating device 3: Solid-gas separator 4: Water washing device 41: Powder supply device 42, 43: Liquid supply device 44: Slurry stirring device 45: pH meter 5: Solid-liquid separation device 51 : Water cleaning device 6 : Transport device 7 : Branch pipe 71 : Gas flow rate adjusting device 10 : Controller A1 : pH adjusting agent Cl1 : Chlorine source CM1 : Calcium source and magnesium source (abbreviation: Karmag source)
G1: Combustion exhaust gas G2: Exhaust gas M1: Provided decontaminated soil, etc. M2: Decontaminated soil, etc. consisting of M1 and M4 M3: Dust containing radioactive cesium M4: Washing residue M5: Sintered product S1: Slurry W1, W2: Water W3: Drainage

Claims (5)

A method for removing radioactive cesium from radioactive cesium contaminants, comprising:
a heating step for heating the radioactive cesium contaminant, the calcium source, the magnesium source, and the chlorine source together to volatilize the radioactive cesium;
A solid-gas separation step for recovering dust containing radioactive cesium by solid-gas separation after cooling the combustion exhaust gas generated in the heating step;
A water washing step for adding water to the dust to make a slurry and eluting radioactive cesium in the slurry liquid phase;
a solid-liquid separation step for solid-liquid separation of the slurry that has undergone the water washing step to separate the washing residue and waste water;
a circulation step for circulating the washing residue as the radioactive cesium contaminant in the heating step ;
A method for removing radioactive cesium, wherein the pH of the slurry is adjusted to 8 to 11 while the exhaust gas generated in the solid-gas separation step is diffused into the slurry in the water washing step. In the preparation containing the radioactive cesium contaminant, the calcium source, the magnesium source, and the chlorine source, which is subjected to the heating step, the mass ratio R1 represented by the following formula is 1.0 to 1.9 The method for removing radioactive cesium according to claim 1.
R1 = (CaO (mass%) + 1.39 x MgO (mass%))/( _SiO2 (mass%)) 3. The method for removing radioactive cesium according to claim 1, wherein the water content of the water-washed residue circulated in the circulating step is 25% by mass or more. A radioactive cesium removal device for removing radioactive cesium from radioactive cesium contaminants,
a heating device for heating the radioactive cesium contaminant, the calcium source, the magnesium source, and the chlorine source together to volatilize the radioactive cesium;
a solid-gas separation device for recovering dust containing radioactive cesium by solid-gas separation after cooling the combustion exhaust gas from the heating device;
a water washing device for adding water to the dust collected by the solid-gas separation device to form a slurry, and eluting radioactive cesium into the liquid phase of the slurry;
a solid-liquid separation device for solid-liquid separating the slurry discharged from the water washing device into washing residue and waste water;
a circulation device for circulating the washing residue separated by the solid-liquid separation device as the radioactive cesium contaminant to be heated by the heating device ;
an air pipe for sending the exhaust gas generated in the solid-gas separation device to the water washing device ,
The washing device is equipped with a pH meter for measuring the pH of the slurry washed by the device, and a pH adjuster addition device for adding a pH adjuster to the slurry washed by the device. and a control device for automatically controlling the amount of the pH adjuster added by the pH adjuster addition device based on the measurement result of the pH meter. Device. The air supply pipe is provided with a flow control valve, and the control device further automatically controls the amount of the exhaust gas supplied by the flow control valve based on the measurement result of the pH meter. 5. The device for removing radioactive cesium according to 4 .