JP6515437B2 - Processing method of cesium adsorption slurry - Google Patents

Description

  The present invention relates to a method of treating a slurry of Prussian blue having adsorbed cesium, and more particularly to a method of treating a cesium-adsorbed slurry for reducing the volume of the slurry.

  As a method of recovering radioactive cesium dissolved in water, a method of recovering with an adsorbent can be mentioned. At present, various materials including zeolite are considered as adsorbents, and some are used in actual decontamination sites. The adsorbent desirably has a high adsorption capacity capable of adsorbing a large amount of cesium so that the amount of waste after decontamination becomes small. In addition, since other metal ions are much more abundant than radioactive cesium in the environment, the adsorbent is required to have a highly selective adsorptive ability to adsorb only cesium.

  It is reported that cesium is easily eluted from water from municipal solid waste incineration fly ash. The cesium adsorption capacity of bentonite from incinerated ash wash water, which is known to adsorb radioactive cesium ions in pure water well, is much lower than that for pure water and is about 1/100 (MOE 5th Disaster waste safety evaluation study meeting materials). One of the reasons for this is that bentonite adsorbs not only cesium but also other ions in incineration ash cleaning water.

  Prussian blue is a candidate for a highly selective cesium adsorbent capable of highly efficient recovery of cesium. Prussian blue was administered to livestock during the Chernobyl nuclear power plant accident to reduce cesium in milk.

  The reason why Prussian blue has a cesium selective adsorption property is because the hydration radius of cesium ions matches the size of the internal pore of Prussian blue. That is, Prussian blue has a cubic lattice shape, and the lattice constant is about 0.5 nm. Prussian blue selectively adsorbs cesium because the hydrated cesium ions are sized so as to fit almost all the way into this lattice.

  Patent Document 1 describes a radioactive cesium adsorbent composed of Prussian blue nanoparticles and a method of separating radioactive cesium using the same.

JP, 2011-200856, A

  As described above, the nanoparticles of Prussian blue have a large adsorption amount of cesium and are also excellent in the selective adsorption of cesium. When these Prussian blue nanoparticles are supplied into cesium-containing water, the cesium ions are selectively And, it is rapidly adsorbed to Prussian blue nanoparticles. Therefore, the radioactive cesium contaminated water can be decontaminated by separating the radioactive cesium ion-adsorbed Prussian blue nanoparticles from the water. Thus, there is a need for a technique for further reducing the volume of Prussian blue nanoparticles having adsorbed radioactive cesium ions.

  As a volume reduction treatment of liquid waste, evaporation is generally used, and in the case of a solid-liquid slurry, a thin film evaporator and a dryer are useful. Cesium decontamination waste is high concentration radioactive waste, and equipment used for volume reduction treatment itself is also high concentration radioactive waste. Therefore, there is a need for a volume reduction treatment technology that does not make volume reduction treatment equipment high concentration radioactive waste.

  The present invention provides a method of treating a cesium-adsorbed slurry which efficiently treats the slurry after decontamination of radioactive cesium, and the amount of waste is extremely small, and the treated material can be stored as it is in a vessel. The purpose is

  In the method for treating cesium adsorption slurry according to the present invention, a slurry of Prussian blue to which cesium ions are adsorbed is contained in a metal vessel, the vessel is inductively heated to dry the slurry, and then the heating temperature is further raised to Disassemble blue.

  In one aspect of the present invention, the vessel containing the decomposition product is stored as it is.

  As the vessel, one having an inner surface made of a corrosion resistant metal material such as stainless steel is preferable.

  When the Prussian blue nanoparticles are added to a liquid to be treated containing cesium ions, the cesium ions are rapidly adsorbed to the Prussian blue nanoparticles. A slurry (including a dewatered cake) formed by solid-liquid separation of a solution containing Prussian blue nanoparticles adsorbed with cesium ions is contained in a vessel, induction heating of the vessel is performed, the slurry is dried, and further oxidation is performed. Heat in an atmosphere to decompose Prussian blue. This significantly reduces the volume of the slurry. Since the decomposed matter remains in the vessel, the vessel can be transported and stored as it is to a storage location.

It is sectional drawing of a vessel and an induction heating unit. It is explanatory drawing of this invention method. It is a flowchart explaining the cesium adsorption process by Prussian blue. It is explanatory drawing of the drying and oxidation decomposition processing apparatus used in the Example of this invention.

  Hereinafter, the present invention will be described in detail. In the following description, nanoparticles of Prussian blue may be simply referred to as nanoparticles.

  The liquid to be treated in the method of the present invention contains cesium, particularly radioactive cesium. The liquid to be treated includes nuclear power plant equipment water contaminated with radioactive materials, lake water in the contaminated area, river water, groundwater, reservoir water of tanks such as pools, decontamination drainage, radioactive substance contaminated soil Acid-extracted water, and waste water from waste incineration ash. These liquids to be treated contain various metal ions and solid contents in addition to cesium. There is no restriction | limiting in particular about the cesium density | concentration of to-be-processed liquid, It can process from 100 Bq / L low concentration contaminated water to about 100,000 Bq / L high concentration contaminated water.

  Prior to the cesium adsorption treatment by the addition of Prussian blue nanoparticles, it is desirable to remove solids from the liquid to be treated by filtration treatment, centrifugation treatment or the like. The radioactive cesium is ionized and dissolved, and the amount of attached radioactive cesium of the removed solid is very small.

  As described above, Prussian blue nanoparticles are added to the liquid to be treated which has been subjected to the solid matter removal treatment as needed, and cesium is adsorbed (the adsorption step in FIG. 3). As the Prussian blue nanoparticles, those having a primary particle diameter (average particle diameter) of 50 nm or less and a secondary particle diameter (aggregation diameter) (average particle diameter) of about 5 nm to 1 mm, cesium adsorption performance, deposited deposit layer Although preferred from the viewpoint of formation ability, pigments having a large primary particle diameter and a secondary particle diameter of about 10 to 100 μm, so-called "bitumen" and the like can also be used. (Measuring method (primary particle size): Measured with an X-ray diffractometer, the value determined by calculating the crystal lattice diameter from the diffraction peak Measurement method (secondary particle size): Measured with a laser diffraction / scattering particle size distribution analyzer Value))

The specific surface area measured by the BET method using nanoparticles of N ₂ gas is preferably about 150 to 2500 m ² / g in terms of adsorption capacity and handling.

  By using Prussian blue as nanoparticles, the adsorption rate of cesium is increased. In addition, since the distance of diffusion of cesium ions in the interstitial space of Prussian blue nanoparticles to the core of the particles is short, almost the entire Prussian blue nanoparticles are used for cesium adsorption, and the saturated adsorption state is rapidly reached. Cesium can be adsorbed until

Although the chemical formula of Prussian blue is represented by Fe (III) ₄ [Fe (II) (CN) ₆ ] ₃ , Prussian blue used in the present invention may contain water of crystallization, and some iron ions may be contained. Is selected from the group consisting of other metals such as vanadium, chromium, manganese, ruthenium, cobalt, rhodium, palladium, platinum, copper, silver, zinc, lanthanum, europium, gadolinium, lutetium, barium, strontium, and calcium It may be a Prussian blue-type metal complex represented by the following formula, which is substituted by one or more metals.
A _x M _A [M _B (CN) ₆ ] _y · _z H ₂ O
A is an atom derived from a cation. x is 0 to 2, y is 1 to 0.3, and z is 0 to 20. M _A and M _B are metal atoms.

Amount of Prussian blue nanoparticles into the liquid to be treated, 0.2~10kg / ^{m 3,} especially 1-5 kg / ^m of about ³ is preferred. As the cesium concentration in the liquid to be treated is higher, it is preferable to increase the addition amount of Prussian blue nanoparticles within the above range.

  Since the cesium adsorption rate of Prussian blue nanoparticles is extremely large, the adsorption is completed within about 0.1 to 1 hour after the Prussian blue nanoparticles are added to the liquid to be treated. Therefore, the nanoparticle-added water is preferably centrifuged using a decanter or the like to separate it into a sediment and a supernatant. When sufficient adsorption capacity remains in Prussian blue nanoparticles in the sediment, it is preferable to return to the adsorption step and reuse (add to the liquid to be treated). If the Prussian blue nanoparticles are in a state close to saturated adsorption, the sediment may be sent to a centrifugal dehydration step described later.

  The supernatant obtained by this centrifugation may be subjected to a filtration step as shown in FIG. In this filtration step, the supernatant is passed through the filter medium for permeation. Preferably, the supernatant is circulated and filtered. In addition, said centrifugation is not essential, You may use for the filtration process the addition liquid of Prussian blue nanoparticles as it is.

The filter medium is preferably a porous cloth, sheet or film, and among them, a woven fabric of synthetic resin fibers having a thickness of about 0.5 to 1.2 mm, particularly about 0.9 to 1 mm is preferable. is there. As a synthetic resin, although polypropylene, polyphenylene sulfide (PPS), polyester, polytetrafluoroethylene, etc. can be used, it is not limited to this. Examples of the woven fabric include, but are not limited to, plain weave, satin weave, twill weave and the like. The air permeability of the woven fabric is preferably about 0.1 to ⁵ cm ³ / cm ² · sec, particularly about 0.3 to 1.3 cm ³ / cm ² · sec.

  At the beginning of the filtration operation, no deposit layer is formed on the filter medium, and most of the Prussian blue nanoparticles in the solution pass through the filter medium, but some relatively large particle sizes The next particles are trapped in the filter medium, the amount of trapping gradually increases, and accordingly, particles of relatively small particle size are also trapped, and finally a deposit layer is formed. As the deposited deposit layer is formed, small particle size Prussian blue nanoparticles are also trapped in the deposited deposit layer, and the thickness of the deposited deposit layer increases. When the solution from the filtration step is centrifuged and then filtered, it is preferable to use a filter material having a small opening as compared with the case of direct filtration without centrifugation.

  When the thickness of the deposit layer adhering to the filter medium becomes a predetermined thickness or more, the supply of the liquid to the filter medium is stopped, and the filter medium is backwashed with a gas such as water or air. When water, air or the like is supplied to the filter medium in the opposite direction to that at the time of filtration, the deposited deposit layer adhering to the filter medium is peeled off and falls within the filtration device. When the discharge valve at the bottom of the filter is opened, the slurry flows out. When the residual adsorption capacity of Prussian blue nanoparticles in the slurry is large, the slurry is returned to the cesium adsorption step. When the cesium adsorption amount of Prussian blue nanoparticles is close to saturation adsorption, or when reducing volume even if Prussian blue with small cesium adsorption amount is stored, etc., the slurry is dewatered by a centrifugal dehydrator and dehydrated. Make a cake and put it in a vessel.

  After the backwashing of the filter medium is completed, the solution is circulated through the filter medium. Also in this case, when the liquid permeation is started, the secondary particles having a large particle size are first captured by the filter medium to form a deposit layer, and then the small particle size Prussian blue nanoparticles are also captured, and Layer thickness increases. In the present invention, a filter aid may be used. The filter aid is preferably one that does not become a flame retardant in the combustion oxidation step.

  In the present invention, a slurry of Prussian blue (including a dehydrated cake) having cesium adsorbed thereon as described above is contained in a vessel, and then the vessel is induction heated to dry the slurry and then further heated to obtain Prussian blue. Disassemble. At the time of this decomposition treatment, it is preferable to circulate air in the vessel to oxidatively decompose cesium-adsorbed Prussian blue.

  FIG. 1 is a cross-sectional view of a metallic vessel 1 for performing volume reduction processing of the Prussian blue, and an induction heating unit 2 for inductively heating the vessel 1. The vessel 1 comprises a vessel body 3 in the form of an upper open vessel and a lid 4 for covering the vessel body 3. A flange 3a protrudes from the upper edge of the vessel body 3, and a first current-carrying terminal 3b is provided on the lower surface of the flange 3a. The bottom of the vessel body 3 is provided with a second current-carrying terminal 3c. A plurality (four in this embodiment) of the current-carrying terminals 3b and 3c are provided at equal intervals in the circumferential direction of the vessel body 3.

  The lid 4 is provided with an inlet 4a for air and the like, and an outlet 4b for water vapor and the like. The lid 4 is fixed at its peripheral portion to the flange 3 a by a bolt (not shown).

  The induction heating unit 2 includes a bottom plate 5, a seat 6 provided on the upper surface of the central portion of the bottom plate 5, a heat insulating wall 7 surrounding a vessel mounted on the seat 6, and a lower portion of the heat insulating wall 7. An induction heating coil 8 surrounding the outer periphery, a casing 9 surrounding the heat insulating wall 7 and the induction heating coil 8, connectors 10 and 11 engaged with the current-carrying terminals 3b and 3c, and a conductive material 12 for conducting the connectors 10 and 11; And a temperature sensor 13 for detecting the temperature of the vessel 3.

  The induction heating coil 8 is obtained by winding a copper wire around a ring-shaped iron core which circulates the heat insulating wall 7. The temperature sensor 13 is provided through the casing 9 and the heat insulating wall 7 so as to measure the temperature of the vessel 1 disposed inside the heat insulating wall 7.

  When the vessel 1 is placed on the inside of the heat insulating wall 7 from above and placed on the receiving seat 6, the current-carrying terminals 3 b and 3 c engage with the connectors 10 and 11. In this state, when the induction heating coil 8 is energized, an induction current flows through the circuit composed of the vessel body 3 and the conductive material 12, the vessel body 3 is heated, and the slurry in the vessel 1 or its dried matter is heated.

  FIG. 2 is a configuration diagram of a slurry processing system using the vessel 1 and the induction heating unit 2. The induction heating unit 2 is installed on the base 15. The base 15 is provided with a weight sensor 16.

  An air pipe 17 is connected to the inlet 4 a of the vessel 1. The air pipe 17 is provided with a flow meter 18 and a flow control valve 19. The outlet 4 b of the vessel 1 is connected to the suction portion of the ejector 23 through a pipe 22 provided with a flow control valve 20 and a temperature sensor 21. The ejector 23 is installed in the tank 24. The water in the tank 24 is supplied from the bottom of the tank 24 to the working fluid inlet of the ejector 23 through the pipe 25, the pump 26 and the cooler (heat exchanger) 27 for circulating water cooling.

  The tank 24 is provided with a liquid level sensor 28. Further, a pipe 29 for discharging gas is connected to an upper portion of the tank 24, and the gas sensor 30 is provided on the pipe 29.

  Next, a slurry processing method using this slurry processing system will be described.

  A cake in which the slurry is dehydrated to a water content of about 50 to 95% by weight is placed in a vessel 1. In this case, it is preferable to store the cake in the vessel 1 at about 85 to 95% by volume of the volume of the vessel. The vessel 1 is attached to the induction heating unit 2 as shown in FIG. 2, and the pipes 17 and 22 are connected.

The pump 26 is operated to supply water to the ejector 23, a gas is sucked from the vessel 1, and the coil 8 is energized to induce a secondary current in the vessel 1, thereby heating the vessel 1 by heat generation due to resistance loss. The detected temperature _{T 2} of the temperature sensor 13 provided in the induction heating unit 2 is 100 to 150 ° C. preferably controls the energization of the coil 8 so that 100 to 120 ° C.. To the temperature T ₂ and 0.99 ° C. or less, because ferrocyanide ion elution suppression. The pressure _{P 1} in the vessel 1 is to adjust the opening of the valve 20 so that about 50～90KPa. The cake in the vessel 1 is heated under reduced pressure to evaporate the water. At the time of evaporation of the water, it is desirable to set the vapor linear velocity to 100 mm / sec or less, particularly 50 mm / sec or less, in order to suppress scattering of the nanoparticles to which radioactive cesium is adsorbed. The detected temperature _{T 2} of the temperature sensor 21 during the evaporation is about 96-100 ° C..

The vapor evaporated from the dewatered cake is condensed by an ejector 23 having a condensing function and a collecting function of droplet nanoparticles, and is accumulated in a tank 24. The water circulating through the pipe 25 is cooled by the cooler 27 to 40 ° C. or less. Amount of dehydration is schematically detected by the liquid level rising amount of detected weight W ₁ and the tank 24 of the weight sensor 16 of the induction heating device (detecting liquid level L ₁ of the level sensor _28). As the water content of the cake in the vessel 1 decreases, the amount of dehydration decreases. Therefore, when no longer observed detects the weight W ₁ decreases, and the change of the detection liquid level L ₁ increase in the level sensor 28 of the weight sensor 16, the valve 19 is opened to supply air to the vessel 1. It is preferable that the air flow rate be 50 mm / sec or less for the vapor linear velocity. If the detected temperature T ₁ of the sensor 21 is turned 120 ° C., to exit the cake drying step, it proceeds to the combustion oxidation process of Prussian blue. In this step, the detected temperature _{T 2} of the sensor 13 is energized to the coil 8 so that 280 to 300 ° C.. The valve 19 is adjusted to adjust the amount of air introduced into the vessel 1 so that the temperature differential pressure T ₂ -T ₁ detected by the temperature sensors 13 and 20 is 50 ° C. or less, particularly 20 ° C. or less. By this combustion oxidation treatment, Prussian blue Fe (III) ₄ [Fe (II) (CN) ₆ ] ₃ is oxidized and decomposed to iron oxide, CO ₂ , N ₂ , cyanide and a small amount of unburned matter. The residual cyanide of Vessel 1 is less than 1/1000.

The indication of the completion of the combustion oxidation treatment is judged by the decrease change of the detected weight W ₁ of the weight sensor 16 and the CO ₂ change amount detected by the gas sensor 30. The combustion oxidation treatment is preferably completed within 4 hours. After completion of the combustion and oxidation treatment, the inside of the vessel 1 is replaced with air, and then the pipes 17 and 22 are removed, and the inlet 4a and the outlet 4b are sealed. Next, the vessel 1 is cooled by leaving it to cool and then transferred to a storage place for storage.

  The content of the vessel 1 is reduced to about 1/10 to 1/20, and by consolidating the content, it is possible to further reduce and reduce the volume of the container itself.

  All the water in the tank 24 is sent to the adsorption process which is a front facility. In the case where cyanide is eluted in the water in the tank 24, it is preferable to carry out detoxification treatment using sodium hydroxide, sodium hypochlorite or the like, and then send it to the adsorption step.

Example 1
<Preparation of Prussian Blue Nanoparticles>
An aqueous solution of 14.5 g of sodium ferrocyanide 10-hydrate dissolved in 60 mL of water was mixed with 30 mL of an aqueous solution of 16.2 g of iron nitrate 9-hydrate dissolved in water, and stirred for 5 minutes. The precipitated blue Prussian blue precipitate was centrifuged and washed three times with water followed by one time with methanol and dried under reduced pressure. The yield at this time was 11.0 g, and the yield was 97.4% as Fe ₄ [Fe (CN) ₆ ] ₃ · 15H ₂ O.

As a result of analyzing the produced Prussian blue with a powder X-ray diffractometer, it was consistent with Prussian blue (Fe ₄ [Fe (CN) ₆ ] ₃ ) retrieved from a standard sample database. Moreover, also in FT-IR measurement, the peak resulting from Fe-CN stretching vibration appeared in 2080 cm < ^-1 > vicinity, It showed that this solid substance is Prussian blue. The BET specific surface area of this Prussian blue was 300 m ² / g, the average particle size of the primary particles was 16 nm, and the average particle size of the secondary particles was 55 μm.

<Preparation of simulated liquid to be treated>
Cesium carbonate was dissolved in pure water and hydrochloric acid was added to prepare a cesium solution with a pH of 6 and a cesium concentration of 100 ppb, which was used as a liquid to be treated.

<Suction process>
400 g of the Prussian blue was added to 2000 L of the liquid to be treated, and the mixture was stirred for 10 minutes to adsorb cesium.

<Dehydration treatment>
The slurry with a Prussian blue nanoparticle concentration of 2000 ppm was dewatered by a centrifuge and separated into a slurry supernatant of 50 ppm and a dewatered cake with a water content of 87.5% by weight.

<Drying treatment>
The Prussian blue nanodehydrated cake was subjected to a drying treatment by the drying and oxidative decomposition treatment apparatus shown in FIG. This apparatus comprises a vessel 1 and an induction heating unit 2 of the same configuration as that shown in FIG. In addition, illustration of a valve etc. is abbreviate | omitted in FIG.
2 kg of this Prussian blue nanoparticle dewatered cake is introduced into an iron vessel 1 with an inner diameter of 200 mm, a length of 200 mm, an inner volume of 6 L, and a thickness of 6 mm, and incorporated into an induction heating unit 2. It was connected to the receiver 44 via the tube 42 and the cooler 43.

The detected temperature T ₂ of the temperature sensor 13 is energized to the coil 8 so that the 120 ° C.. When the amount of condensed water in the receiver 44 became 1.6 L, the inlet 4a was connected to the air pump, and the supply of air was started at 2 L / min. After 40 minutes, the steam exhaust temperature stabilized at 110 to 120 ° C. Then, heating was stopped when 30 minutes passed. The amount of condensed water in the receiver 44 at this time was 1.7 L. The condensed water was transparent, and the amount of ferrocyanide-derived iron ion was as small as 0.08 ppm and cesium as 0.003 ppm. After the vessel 1 was allowed to cool, the lid 4 was opened, and the inner Prussian blue nanoparticles were taken out and weighed 240 g.

<Drying and oxidative decomposition treatment>
Drying and oxidative decomposition treatment of Prussian blue nanodehydrated cake were performed by the drying and oxidative decomposition treatment apparatus shown in FIG. That is, 2 kg of the cesium-adsorbed Prussian blue nanodehydrated cake (water content 89.7% by weight) is introduced into the same vessel 1 as the drying process, and incorporated into the induction heating unit 2 as shown in FIG. And the outlet 4 b was connected to the receiver 44 via the steam exhaust pipe 42 and the cooler 43.

The detected temperature T ₂ of the temperature sensor 13 is energized to the coil 8 so that the 120 ° C.. When the amount of condensed water in the receiver 44 reached 1.65 L, the inlet 4a was connected to the air pump to start supplying air at 2 L / min. After 35 minutes, the steam exhaust temperature stabilized at 110 to 120 ° C. Thereafter, the amount of condensed water in the receiver 44 was 30 minutes after the lapse of 30 minutes. The condensed water was clear. Therefore, increasing the amount of current supplied to the coil 8, the detected temperature _{T 2} of the temperature sensor 13 is allowed to warm at 20 ° C. / min until 300 ° C.. Combustion air (oxygen) was supplied such that the temperature at the vessel outlet combustion gas was 300.degree. The difference between the temperature T ₂ and the combustion gas temperature was 20 ° C. or less. The exhaust gas was collected by the receiver 44 and released. Cyan gas was not detected from the collected exhaust gas, and was CO ₂ , N ₂ or O ₂ . Iron ions derived from ferrocyanide detected from the condensed water in the receiver 44 were as small as 0.15 ppm and cesium as 0.007 ppm. In addition, cyanide was detected from the condensed water.

After 20 minutes, the heating was stopped, and after cooling, the lid 4 of the vessel 1 was opened, and the contents were analyzed. Iron oxide such as Fe ₂ O ₃ was mainly contained, and cesium oxide was indistinguishable due to its small amount The The weight of the residue in the vessel 1 was 195 g, which was less than 1/10 of the weight of the slurry charged into the vessel.

Reference Signs List 1 vessel 2 induction heating unit 3 vessel body 3a, 3b conductive terminal 4 lid 5 bottom plate 6 seat 7 insulation 7 induction coil 9 casing 10, 11 connector 23 ejector 24 tank 27 cooler 42 steam exhaust pipe 43 cooler 44 receiver

Claims (4)

A method of drying a slurry containing Prussian blue adsorbed with cesium ions and water, and decomposing the Prussian blue,
The slurry is contained in a metal vessel,
The vessel is inductively heated to evaporate water from the slurry, and the slurry is dried by letting steam flow out of the vessel, and then the heating temperature is raised to 280 ° C. or higher and air is introduced into the vessel. A method of treating a cesium-adsorbed slurry, comprising the steps of: decomposition of Prussian blue by combustion oxidation treatment.   The method for treating a cesium adsorption slurry according to claim 1, wherein the gas in the vessel is sucked by an ejector in the drying and decomposing steps of the slurry.   The processing method of a cesium adsorption slurry according to claim 2, wherein water is supplied as a working fluid to the ejector, and steam and generated gas are brought into contact with and dissolved in the water.   The method for treating a cesium adsorption slurry according to any one of claims 1 to 3, wherein the vessel containing the decomposition product is stored after the decomposition treatment of Prussian blue.

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