JP2017166849A - Method for processing cesium adsorption prussian blue - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing cesium adsorption Prussian blue which conducts an oxidation treatment on a slurry after adsorption of radioactive cesium and separates a cesium compound by elution, whereby significantly reducing the amount of the remaining cesium compound after the cesium compound is separated by combustion.SOLUTION: The method for processing cesium adsorption Prussian blue includes: a heating oxidation decomposition step of generating a decomposition product by performing drying and heating oxidation decomposition processing on a slurry of Prussian blue adsorbing cesium ions; a step of eluting a cesium product from the decomposition product; and a step of sublimating and combusting a combustion residue for extremely reducing the amount of the remaining cesium compound of the combustion residue with the cesium compound separated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating Prussian blue adsorbed with cesium. One embodiment of the present invention relates to a treatment method for reducing residual cesium in a residue obtained by performing high-elution separation of a cesium compound after the slurry is oxidized and separating the cesium compound.

  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 studied as adsorbents, and some are used in actual decontamination sites. It is desirable that the adsorbent has a high adsorbing ability capable of adsorbing a large amount of cesium so that the amount of waste after decontamination is small. In addition, in the environment, a much larger amount of other metal ions than radioactive cesium is present, so the adsorbent is required to have a highly selective adsorption ability for adsorbing only cesium.

  Patent Documents 1, 2, and 3 describe a method for separating radioactive cesium using Prussian blue. The reason why Prussian blue has cesium selective adsorption characteristics is that the hydration radius of cesium ions matches the size of the internal pores of Prussian blue. That is, Prussian blue has a cubic lattice shape, and the lattice constant is about 0.5 nm. Since the hydrated cesium ion has a size that almost completely enters this lattice, Prussian blue selectively adsorbs cesium.

  In Patent Document 4, as a treatment of a slurry after decontamination of radioactive cesium, a cesium-adsorbed Prussian blue slurry is oxidized and decomposed to efficiently dispose of and dispose of cesium from the decomposition product. Although a method of further evaporating water from the aqueous cesium solution and precipitating it as a cesium compound has been proposed, the recovery rate of cesium and the residual cesium of decomposition products are not described.

  In Non-Patent Document 1, it is possible to recover combustion residue water, cesium elution rate with 0.5N nitric acid water by 80% or more with water, and 95% or more with water + 0.5N nitric acid water. Although it is described that about 5% of Cs remains in the combustion residue (iron oxide) after the elution treatment, a specific method has not been proposed for recovering the combustion residue (iron oxide) residual Cs.

  A Prussian blue nanoparticle dispersion is mixed with sodium alginate to form a slurry, and this slurry is dropped into an aqueous calcium chloride solution to form a granulated body (capsule-like structure) in which a gel-like surface layer enriched with calcium is formed. (Patent Document 5) describes a method for producing a body.

JP 2011-200856 A JP 2014-109461 A JP 2014-20806 A JP, 2015-141082, A JP 2014-77720 A

4th Annual Meeting of Environmental Radioactivity Decontamination Society S5-3 Abstract July 8, 2015

  The first object of the present invention is to highly reduce the volume of the cesium compound by performing high-elution separation of the cesium compound after oxidizing Prussian blue after the adsorption of radioactive cesium.

  The second object of the present invention is to propose a reasonable method for recovering cesium by combining a Prussian blue dispersion and granulation in the method for recovering radioactive cesium.

  In the method of treating cesium-adsorbed Prussian blue of the present invention, a metal pot containing Prussian blue granules adsorbing cesium ions is induction-heated and air or low oxygen gas is introduced into the pot to produce a slurry. A method of treating cesium-adsorbed Prussian blue, which is dried and then further heated to raise the oxidation temperature to oxidatively decompose Prussian blue, wherein the amount of air or low oxygen gas introduced so that the temperature in the pot is 150 to 400 ° C. It is characterized in that Prussian blue is heated and decomposed by controlling at least one of induction heating.

  In one embodiment of the present invention, Prussian blue is subjected to thermal oxidative decomposition by controlling at least one of air or low oxygen gas introduction amount and induction heating so that the temperature in the pot becomes 150 to 400 ° C.

In one embodiment of the present invention, the oxygen content of the air introduced into the pot is limited to 1 to 10%, and the form of the heated oxidative decomposition product is a suppressed crystalline oxide as shown in FIG. 4 (XRD analysis), Fe ₃ O. ₄ is used as a combustion method.

  In one embodiment of the present invention, the Prussian blue granule is an alginic acid / calcium film inclusion.

  In one embodiment of the present invention, a pot filled with Prussian blue is a combined container system in which a pot is attached to a heating oxidative decomposition apparatus and heated after cesium adsorption.

  When Prussian blue is added to the liquid to be treated containing cesium ions, the cesium ions are quickly adsorbed by Prussian blue. A slurry (including a dehydrated cake) generated by solid-liquid separation of the liquid containing Prussian blue adsorbing cesium ions is heated in a pot, and the slurry is dried in an air or low-oxygen atmosphere. Prussian blue is oxidatively decomposed by heating in a low oxygen atmosphere.

  In the present invention, the solid-liquid separation is simplified by using Prussian blue as a granulated material, and the cesium recovery system is simplified by heating the pot as it is. The Prussian blue granule has a cesium adsorption / accumulation performance comparable to that of Prussian blue nanoparticles, but the decontamination factor is considerably inferior, so the granule is used for the recovery of circulating cesium in the treated water, and the treated water discharge system is nano. It is preferable to use a particle body.

  In the present invention, preferably, air or a low oxygen gas is introduced from the Prussian blue drying step, and is gradually oxidized to carry out the oxidation treatment while maintaining the pot internal temperature at 400 ° C. or lower. The cesium compound is eluted and separated from the oxidative decomposition product with water, and the eluate is concentrated and recovered as a cesium compound. However, several percent of cesium compounds remain in the elution separation residue even after acid elution. The oxidative decomposition product contains a high concentration of radioactive cesium, and even if the remaining amount is several%, it becomes a high concentration radioactive waste. In the present invention, by oxidizing in a low oxygen atmosphere, the oxidation form of the oxidative decomposition product can be changed, and the water elution rate and the acid elution rate can be greatly improved. Furthermore, low concentration radioactive waste can be obtained by further subliming and removing cesium from the elution separation residue.

  In general, Prussian blue granulates are produced by adding Prussian blue to other inorganic and organic carriers, but avoiding the inclusion of residuals that affect the vitrification of the next step in the oxidative decomposition products. There is a need to. In one embodiment of the present invention, a granulated body encapsulated with calcium alginate gel is used as the Prussian blue granulated body. Alginate is burned during the oxidative decomposition process of the granulated material, and only the calcium content remains. Since this calcium oxidation product is insoluble in water, the resulting cesium compound does not affect vitrification.

It is a flowchart explaining the cesium adsorption | suction process which collect | recovers the cesium of the to-be-processed water which generate | occur | produces from an ash washing process with an adsorption pot (granulation body filling). It is a flowchart explaining a cesium collection | recovery system. It is a flowchart explaining a cesium collection | recovery system. It is an X-ray diffraction chart of an oxidation product. It is an X-ray diffraction chart of an oxidation product.

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

  Prussian blue to be treated by the method of the present invention adsorbs cesium, particularly radioactive cesium. This cesium-adsorbed Prussian blue includes facility water contaminated with radioactive materials, lake water in contaminated areas, river water, groundwater, pooled water such as pools, decontamination wastewater, and radioactive material contamination. Examples include cesium-adsorbed Prussian blue that adsorbs acid-extracted water from soil, washing wastewater from waste incineration ash, and the like. These liquids to be treated contain various metal ions and solids in addition to cesium. The cesium concentration of the liquid to be treated is not particularly limited, and it can be processed from a low concentration contaminated water of about 100 Bq / L to a high concentration contaminated water of about 100,000 Bq / L.

  The present invention particularly reduces the volume by dripping the radioactive cesium-containing water obtained by incineration of the radioactive cesium deposits with water and bringing the radioactive cesium-containing water into contact with Prussian blue to adsorb the radioactive cesium to Prussian blue, and oxidizing the Prussian blue. It is suitably applied to the process of making it.

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

[Cesium adsorption treatment with Prussian blue]
Thus, it is preferable to circulate the to-be-processed liquid which carried out the solid substance removal process as needed in the pot filled with the Prussian blue granulation body, and to adsorb cesium.

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 at least part of iron ions may be other metals such as vanadium, chromium, manganese, ruthenium, cobalt, rhodium, nickel, palladium, platinum, copper, It may be substituted with one or more metals selected from the group consisting of silver, zinc, lanthanum, europium, gadolinium, lutetium, barium, strontium, and calcium. Such a Prussian blue-type metal complex is represented by the following formula, for example.

_{A x M A [M B (} CN) 6] y · zH 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 is Fe (III), and M _B is Fe (II).

  For Prussian Blue, nanoparticles with a primary particle size (average particle size) of 50 nm or less and secondary particle size (aggregation size) (average particle size) of about 5 nm to 1 mm are cesium adsorption performance and deposit layer formation. From the viewpoint of performance, a pigment having a large primary particle size and a secondary particle size of about 10 to 100 μm, so-called “bitumen” or the like can also be used. (Measurement method (primary particle size): measured with an X-ray diffractometer, calculated by calculating the crystal lattice diameter from the peak. Measurement method (secondary particle size): measured with a laser diffraction / scattering particle size distribution analyzer Value.)

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

  Prussian blue nanoparticles have a high cesium adsorption rate. In addition, since the distance that cesium ions entering the lattice gap of Prussian blue nanoparticles diffuse and move to the core of the particles is short, almost all of the Prussian blue nanoparticles are used for adsorption of cesium, and quickly become almost saturated. Cesium can be adsorbed until

  Since the granulation body has a lower decontamination factor than the nanoparticle body, several pots (for example, 4 to 8) filled with Prussian blue granulation body are connected in series, and the water to be treated is passed in series. Is preferred. Since the cesium adsorption / accumulation performance of the granulated material is almost the same as that of the nanoparticle, about 6 of them are installed in series, and the liquid to be treated is distributed first, starting from the most upstream pot where the concentration of cesium adsorption has increased. The cesium in the liquid to be treated can be efficiently adsorbed by exchanging and sequentially raising the distribution sequence and installing a pot filled with the granulated material not adsorbed with cesium on the most downstream side.

  When the radioactive cesium-containing liquid to be treated eluted by ash washing is treated by the method of the present invention, the liquid having a reduced cesium concentration is used again as an ash washing liquid through a pot attached in series.

  A certain amount of the ash washing circulating fluid needs to be extracted and desalted to suppress an increase in salt concentration. The extracted liquid obtains treated water from which radioactive cesium has been adsorbed and separated by adsorption with a nanoparticle body having a high decontamination coefficient, and discharges a salt not containing cesium. The nanoparticle body-containing liquid is filtered to obtain a treatment liquid.

The filter medium is preferably made of a porous cloth, sheet or film, among which a woven cloth of synthetic resin fibers having a thickness of about 0.5 to 1.2 mm, particularly about 0.9 to 1 mm is suitable. is there. As the synthetic resin, polypropylene, polyphenylene sulfide (PPS), polyester, polytetrafluoroethylene, or the like can be used, but is not limited thereto. Examples of the woven fabric include plain weave, satin weave and twill weave, but are not limited thereto. 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 adhering deposit layer is formed on the filter medium, and most of the Prussian blue nanoparticles in the liquid pass through the filter medium in a straight line, but some of the relatively large particle sizes are relatively small. The secondary particles are trapped by the filter medium, and the trapped amount gradually increases. As a result, particles having a relatively small particle size are also trapped, and finally, an adhered deposit layer is formed. When the deposited deposit layer is formed, Prussian blue nanoparticles having a small particle size are also captured by the deposited deposit layer, and the thickness of the deposited deposit layer increases.

  When the thickness of the adhering deposit layer adhering to the filter medium exceeds a predetermined value, the supply of the liquid to the filter medium is stopped, and the filter medium is back-washed with a gas such as water or air. When water or air or the like is supplied to the filter medium in the opposite direction to that during filtration, the adhered deposit layer adhering to the filter medium is peeled off and falls in the filter device. When the discharge valve at the bottom of the filtration device is opened, the slurry flows out. When the residual adsorption capacity of Prussian blue in this slurry is large, this slurry is returned to the cesium adsorption step. If the amount of Prussian blue cesium adsorbed is close to saturated adsorption, it is accommodated in a pot.

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

[Prussian blue granule filled in pot]
The Prussian blue granule preferably contains 70 wt% or more of Prussian blue nanoparticles and has a diameter of 0.5 to 1.5 mm. The granulated material is preferably granulated with alginic acid / calcium gel. As a granulation method, Prussian blue nanoparticles are dispersed in a sodium alginate sol aqueous solution and dropped into a calcium chloride solution with a nozzle having a diameter of 1 to 2 mm to form a granulated body encapsulated in an alginate / calcium gel film. (Method of Patent Document 5) is preferable. It is preferable to make the granulated body porous by washing the granulated body with water and drying (room temperature to 50 ° C. or the like) or freeze-drying.

  As this Prussian blue granulated body, what is marketed as Prussian Blue MC by Kanto Chemical Co., Inc. can be used.

  As described above, it is preferable that this Prussian blue granule is accommodated in a pot, and the liquid to be treated is passed through this pot to adsorb radioactive cesium to Prussian blue.

[Drying and oxidative decomposition of cesium adsorption slurry]
In the present invention, the Prussian blue slurry adsorbing cesium as described above is dried and then oxidized. In order to perform this drying and oxidation treatment, it is preferable to inductively heat a pot containing cesium-adsorbed Prussian blue to dry the slurry, and then further raise the temperature in an oxidizing atmosphere to oxidize the dried product.

  In addition, whether or not almost all of the attached water has evaporated from Prussian blue is measured by measuring the weight of the pot over time, and if this weight reaches a substantially constant weight, it is judged that almost all of the attached water has evaporated. Can do. Further, when the evaporation amount from the pot is observed and the evaporation of water almost disappears, it can be determined that substantially the entire amount of attached water has evaporated.

  Further, when almost the entire amount of adhering water evaporates from Prussian blue, the temperature of the exhaust from the pot becomes higher than 100 ° C., so that when the exhaust temperature from the pot becomes higher than 100 ° C., for example, 100 to 105 ° C. It can be determined that substantially the entire amount of Prussian blue adhering water has evaporated.

  In the present invention, it is preferable to introduce air into the pot from the start of evaporation of Prussian blue adhering water. However, air is introduced into the pot in the course of drying after a predetermined time has elapsed since the induction heating of the pot has started. It may be.

  In the present invention, in particular, in the step of evaporating Prussian blue adhering water, it is preferable to introduce air into the pot and suck the inside of the pot with an ejector to discharge the generated water vapor. The ejector is preferably supplied with water as a working fluid. Water vapor sucked and discharged from the pot and scattered matter accompanying the water vapor are absorbed or collected by this water.

  After drying of Prussian blue under inflow of air, specifically, when the exhaust temperature from the pot reaches 110 ° C. or higher, preferably 110 to 150 ° C., for example, 120 ° C. Decomposes oxidatively. In this oxidative decomposition treatment, air or a low oxygen concentration gas (for example, a mixed gas of air and nitrogen) is circulated in the pot to oxidatively decompose cesium-adsorbed Prussian blue. The heating temperature is 150 ° C. or higher, preferably 200 ° C. or higher and 400 ° C. or lower, preferably 370 ° C. or lower, for example, 150 ° C. to 400 ° C., particularly about 200 ° C. to 370 ° C. is desirable. By performing the oxidative decomposition treatment at a low temperature in this way, Prussian blue is decomposed below the melting temperature of the cesium compound, and iron oxide, a cesium compound, and the like are generated. The evaporative distillation of cesium compounds is considerably suppressed.

  Prussian blue contains a small amount of salt that is a by-product of Prussian blue production. This salt varies depending on the Prussian blue process, and is chloride, nitrate, or sulfate. In the thermal oxidative decomposition process, nitrate ions and cesium ions cause a binding reaction due to the decomposition of the CN group of Prussian blue. As a result of the inventor's research, it has been found that this conjugation reaction occurs by thermal oxidative decomposition of the CN group. When cesium chloride and cesium carbonate are used as simulated cesium and Prussian blue adsorbed on cesium is subjected to thermal oxidative decomposition, cesium nitrate is bound and formed. Even when iron chloride is used instead of iron nitrate as the raw material for Prussian blue, Prussian blue by-product is not sodium nitrate but sodium chloride. Cesium forms a bond. Since the melting point of cesium nitrate is about 409 ° C., it is important to control the oxidative decomposition treatment so that the heat oxidative decomposition treatment temperature is 400 ° C. or lower.

The oxygen concentration of the low oxygen gas is preferably set to a low oxygen concentration in which XRD analysis of the thermal oxidative decomposition product is mainly composed of a suppressed crystal oxide as shown in FIG. ₄ and generates a small amount of Fe ₃ O ₄ . As a guide, when Prussian blue is a granulated body, the oxygen concentration is preferably 10% or less, and when it is a nanoparticle body, it is preferably 1 to 5%. The granulated body is covered with a calcium alginate film of Prussian blue, and the oxygen supply rate is suppressed, resulting in extremely low oxygen air combustion. Since there is no nanoparticle body that suppresses the oxygen supply rate, the supply oxygen concentration is set lower than that. The thermal oxidative decomposition product composed of the XRD analysis-suppressing crystal oxide and a small amount of Fe ₃ O ₄ is remarkably quick to elute the cesium compound into water and an acid solution. The amount of low oxygen gas introduced is preferably such that the temperature inside the pot is 400 ° C. or lower and the generation of accompanying scattered matter is suppressed. Also in this oxidative decomposition treatment step, it is preferable that the inside of the pot is sucked with an ejector using water as a working fluid, and the generated gas components and the associated scattered matters are absorbed or collected in water.

  FIG. 2 is a configuration diagram of a system for performing the above-described Prussian blue drying / oxidation treatment. The induction heating unit 2 includes an induction coil and is installed on the seat 5 of the base 15. The base 15 is provided with a weight sensor 16. The pot 1 is a pot body 3 with a lid.

  A pipe 17 is connected to the upper end of the inlet 4 a of the pot 1. The pipe 17 is provided with a flow meter 18 and a flow rate adjusting valve 19. Air or low oxygen gas can be supplied to the pot 1 through the pipe 17. The outlet 4 b of the pot 1 is connected to the suction part of the ejector 23 via a pipe 22 provided with a flow rate adjusting 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 circulating water cooling cooler (heat exchanger) 27.

  A liquid level sensor 28 is provided in the tank 24. A gas discharge pipe 29 is connected to the upper portion of the tank 24, and a gas sensor 30 is provided in the pipe 29.

  Next, procedures for drying and oxidizing the Prussian blue using this processing system will be described.

  The volume of Prussian blue in the pot 1 is preferably about 85 to 95% by volume of the pot volume. The water content of the Prussian blue to be treated is preferably about 50 to 95% by weight. The pot 1 is mounted on the induction heating unit 2 as shown in FIG. 2, and the pipes 17 and 22 are connected.

The valves 19 and 20 are opened, the pump 26 is operated to pass water through the ejector 23, the gas is sucked from the pot 1, the induction coil is energized, the secondary current is induced in the pot 1, and the resistance loss Heat pot 1 with exotherm. Inductive detection temperature _{T 2} of the temperature sensor 13 provided to the heating unit 2 is 100 to 150 ° C. preferably controls the energization of the induction coil such that 100 to 120 ° C.. To the temperature T ₂ and 0.99 ° C. or less is because the ion elution suppression from Prussian blue. The Prussian blue in the pot 1 is heated and the water evaporates. In order to suppress scattering of nanoparticles adsorbed with radioactive cesium during the evaporation of water, it is desirable that the vapor linear velocity in the pipe 22 is 100 mm / sec or less, particularly 50 mm / sec or less. The detected temperature _{T 2} of the temperature sensor 21 during the evaporation is about 96-100 ° C.. When the water evaporates, the valve 19 is opened and air is supplied as carrier gas to the pot 1 to prevent condensation in the pot 1 and the pipe 22.

The evaporated vapor is condensed by an ejector 23 having both a condensing function and a droplet nanoparticle collecting function, and accumulates in a tank 24. Water circulating in the pipe 25 is cooled by a cooler 27 and is set to 40 ° C. or lower. The amount of dehydration is roughly detected by the detected weight W ₁ of the weight sensor 16 of the induction heating device and the liquid level rise amount of the tank 24 (the detected liquid level L _{1 of the} level sensor 28). When the water content of the slurry in the pot 1 decreases, the amount of dewatering decreases. Therefore, when almost the entire amount of water adhering to Prussian blue evaporates, no change is observed in the detected weight W ₁ of the weight sensor 16 or the detected liquid level L ₁ of the level sensor 28.

No change is observed in the detected weight W ₁ of the weight sensor 16 or the detected liquid level L ₁ of the level sensor 28, evaporation of adhering moisture from the dehydrated cake is completed, and the detected temperature T ₃ of the temperature sensor 14 is 150 ° C. Even after the temperature exceeds or the detected temperature T ₂ of the temperature sensor 13 exceeds 150 ° C., water (H ₂ O) exists in the pot 1. This water is a hydrate contained in Prussian blue. If condensed water is present in the pot 1 when the temperature in the pot 1 is raised above 150 ° C., Prussian blue may be partially oxidized and cyanide may be generated. By setting the atmosphere in the pot to a dew point or higher, it is possible to suppress the generation of cyanide due to partial oxidation of Prussian blue in the drying process.

The detected temperature _{T 1} of the sensor 21 is 110 ° C. or higher, if preferably became 110 to 150 ° C. For example 120 ° C., and ends the drying process proceeds to oxidative decomposition treatment process of the Prussian blue. At this time, air or low oxygen gas is continuously supplied into the pot 1. In this step, the detection of the sensor 14 the temperature _{T 3} is a Atsushi Nobori rate 0.3 to 2 ° C. / min preferably 150 to 400 ° C. at 0.5 to 1 ° C. / min, the coil preferably such that the 200-370 ° C. Energize to. Further, the amount of air or low oxygen gas introduced into the pot 1 is adjusted by adjusting the valve 19 so that the detected temperature difference T ₂ −T ₁ between the temperature sensors 13 and 21 is 50 ° C. or less, particularly 20 ° C. or less. Prussian blue is oxidatively decomposed into iron oxide, CO ₂ , N ₂ , cyanide, and a small amount of unburned matter by this oxidative decomposition treatment. Residual cyanide is 1/1000 or less.

A measure of completion of the oxidative decomposition treatment is determined by the amount of change in the weight W ₁ detected by the weight sensor 16 or the amount of CO ₂ change detected by the gas sensor 30. If organic matter remains as an unburned component in the oxidative decomposition treatment, it will affect the vitrification treatment, so it must be burned sufficiently. The oxidative decomposition treatment is preferably completed within 48 hours. After the oxidative decomposition treatment is completed, the atmosphere in the pot 1 is replaced with air, the pipes 17 and 22 are removed, and the inlet 4a and outlet 4b are sealed. Next, the pot 1 is preferably cooled by cooling.

The oxidation product preferably contains 40% by weight or more of cesium salt, for example, 40 to 80% by weight. Moreover, it is preferable to contain 15 weight% or more of sodium salt, for example, 15 to 50 weight%.
In the case of a granule encapsulated in an alginic acid / calcium gel film, it is preferable to contain 15% by weight or more, for example, 15 to 50% by weight of calcium salt.

  In the drying process and the oxidative decomposition process, cyanide is dissolved in the water in the tank 24. Therefore, after the oxidative decomposition process is completed, the water in the tank 24 is detoxified using sodium hydroxide, sodium hypochlorite, or the like. After performing, it is preferable to send to an adsorption process. Further, it is more preferable that sodium hydroxide is dissolved in water in the tank 24 in advance to fix the cyanide generated in the oxidative decomposition treatment step with alkali.

[Elution and separation of salts]
The decomposition product in the pot 1 after the oxidative decomposition treatment is composed of iron oxide, a cesium compound mainly composed of cesium nitrate and cesium chloride, and a small amount of other salts. Therefore, by adding water to this decomposition treatment product, a cesium compound and other soluble salts can be eluted, and an aqueous solution containing these can be separated from a hardly soluble decomposition product solid such as iron oxide.

  When taking out the oxidation product from the pot 1, it is preferable to supply water into the pot 1, to stir, and to collect the product as a slurry in an elution separation container. Although illustration is omitted, a pipe extending to the bottom of the pot 1 is connected to the lower end of the inflow port 4a. When the water from this pipe flows into the pot 1, the oxidation product in the pot is stirred with running water and flows out from the outlet 4b.

  In elution separation of cesium compounds and the like from oxidative decomposition products, the oxidative decomposition products are pulverized to 100 μm or less, and 95% or more of the cesium contained in the product is obtained at a water temperature of 50 to 90 ° C., preferably 60 to 80 ° C. It is preferable to elute. Thereafter, unextracted residual cesium in the product is preferably further eluted with an aqueous nitric acid solution of about 0.2 to 1 N, and a high elution rate of 99.5% or more is preferably obtained. Separation between an aqueous solution of a cesium compound or the like and a hardly soluble oxidative decomposition product solid can be performed by filtration, centrifugation, or the like. The separated solution of cesium compound and salts is concentrated and dried to obtain a solid (precipitate) containing a cesium salt as a main component.

  About 0.5% of the cesium compound still remains in the separated oxidatively decomposed solids. In order to further remove this contained cesium compound and obtain a solid content of oxidative decomposition product that can be safely discarded, a sublimation heat treatment is performed at 1000 ° C. or higher, for example, 1000 to 1100 ° C. The heating and holding time is about 1 hour or longer, for example, 1 to 3 hours. Thereby, the oxidative decomposition product solid content in which the cesium compound is reduced to 0.05% by weight or less is obtained.

[Example 1]
<Preparation of Prussian blue nanoparticle granulated dispersion>
Kanto Chemical Co. Prussian blue nanoparticle granules _{MC-B (Fe 4 [Fe} (CN) 6] 3 · 15H 2 O, granulated particle size about 1mm) by dispersing 10g to 2.4L purified water A dispersion was prepared.

<Simulation treatment liquid adsorption treatment>
A simulated liquid to be treated consisting of an aqueous solution prepared by dissolving 0.6 g of cesium chloride manufactured by Wako Pure Chemical Industries, Ltd. in 0.1 L of pure water was divided into four portions, and the above 2.4 L Prussian blue nanoparticle granules (hereinafter referred to as MC-B). The mixture was charged and dispersed and stirred to adsorb cesium.

  A small amount of the liquid after the above adsorption treatment was collected, and cesium adsorption MC-B was separated by filtration, and quantitative analysis of iron and cesium in the filtrate was performed. As a result, 0.475 g of 0.6 g of cesium chloride input was adsorbed. It was recognized that When the amount of cesium adsorbed on MC-B was estimated from the results, 35.5 g of cesium was adsorbed per 1 kg of MC-B.

<Drying and heat oxidative decomposition>
4.5 g of the cesium-adsorbed MC-B was collected in a combustion boat, and this combustion boat was inserted into a tube of a small tube furnace. It was dried at 220 ° C. for 3 hours under a flow of air (0.5 L / min), further heated to 350 ° C. (1 ° C./min), maintained at 350 ° C. for 3 hours, and oxidized. As a result, 2,44 g of an oxidation treatment product was obtained. The outflow gas from the tube furnace was collected by a water trap (200 mL × 2). CN and NH ⁺ were analyzed from the trap water.

<Water elution treatment>
The oxidized product was ground in a mortar and used as sample 1. A small sample was taken, dissolved in acid, and diluted with distilled water. When the concentration of cesium contained in the eluate was quantified by ICP-MS, the amount of cesium contained in Sample 1 was Cs-73000 mg / sample-kg.

  1 g of sample 1 was collected, mixed with 10 mL of distilled water, and stirred in a water bath (80 ° C.) for 6 hours to elute soluble salts into distilled water. The eluate was sample 2 by centrifuging (3000 rpm, 20 minutes), washing the separation residue with pure water, and drying. A small amount of Sample 2 was collected, dissolved in the entire acid, and diluted with distilled water. When the concentration of cesium contained in the eluate was quantified by ICP-MS, the amount of cesium contained in Sample 2 was Cs-2700 mg / sample-kg.

  Therefore, the recovery rate of leaching cesium from the oxidation treatment residue by water extraction was (73000-2700) /73000=96.3%.

<0.5N nitric acid elution treatment>
1 g of the sample 2 was collected, mixed with 10 mL of 0.5N nitric acid solution, and stirred in a water bath (80 ° C.) for 6 hours to elute soluble salts in distilled water. The eluate was sample 3 by centrifuging (3000 rpm, 20 minutes), washing the separation residue with pure water, and drying. A small amount of sample 3 was collected, dissolved in acid, diluted with distilled water, and the concentration of cesium was quantified by ICP-MS. The amount of cesium contained in sample 3 was Cs-62 mg / sample-kg. The cesium recovery rate from the oxidation treatment residue was 99.91% by extracting the oxidation treatment product with water and with 0.5N nitric acid solution.

<Sublimation removal treatment>
0.93 g of the sample 3 was collected, collected in a combustion boat, and inserted into the tube of the small tube furnace. It was held and dried at 150 ° C. for 15 minutes, heated to 1000 ° C. with 0.5 L / min air, and held for 1 hour. After natural cooling, this was used as sample 4. Similarly, the sample was collected, dissolved in acid, diluted with distilled water, and the concentration of cesium was determined by ICP-MS. The amount of cesium contained in sample 4 was Cs-24 mg / sample. -Kg. The oxidation treatment product was extracted with water, extracted with 0.5N nitric acid solution, and further subjected to sublimation removal treatment, whereby the cesium removal rate from the oxidation treatment residue was 99.97%.

[Comparative Example 1]
<Preparation and adsorption of simulated treatment liquid>
Kanto Chemical Co. Prussian Blue _{L-purified (Fe 4 [Fe} (CN) 6] 3 · 15H 2 O, particle size 16 nm) and cesium chloride charged to a dispersion of, adsorbed, dehydrated, Prussian blue 1kg per Then, a sample in which 47.72 g of cesium (60.47 g in terms of cesium chloride) was adsorbed was obtained. The water content of the sample was about 73.8% by weight.

<Drying and heat oxidative decomposition treatment>
The dehydrated cake was dried and oxidatively decomposed by a drying and oxidative decomposition apparatus shown in FIG. This apparatus includes a pot 1 and an induction heating unit 2 having the same configuration as that shown in FIG. In FIG. 3, the illustration of the valve is omitted.

  3.09 kg of the dehydrated cake (moisture content: 73.8% by weight) was charged into the pot 1 and incorporated in the induction heating unit 2, and the outlet 4 b was connected to the receiver 44 through the steam exhaust pipe 42 and the cooler 43. .

While air from the inlet 4a is supplied at 5L / min, detection temperature _{T 2} of the temperature sensor 13 is energized to introduce the coil such that the 120 ° C.. When the amount of condensed water in the receiver 44 reached 2.0 L, the amount of air from the inlet 4a was increased to 10 L / min. After 420 minutes, the exhaust temperature stabilized at 200-210 ° C. Thereafter, the temperature was raised and when 150 minutes passed, the exhaust temperature reached 220 ° C., and the amount of condensed water in the receiver 44 was 2.2 L. The condensed water was transparent. Therefore, the energization amount to the introduction coil was increased, and the temperature was increased at 2 ° C./min until the detected temperature T ₂ of the temperature sensor 13 reached 350 ° C. In the detected temperature T ₃ of the temperature sensor 14 indicative of the temperature of the internal pot 380 ° C. or less, (detected temperature T ₁ of the temperature sensor ₂₁₎ pot outlet combustion gas temperature air was supplied so that the 300 ° C.. The difference between the temperature _{T 2} and the temperature _{T 1} of were 50 ° C. or less. NaOH was added to the receiver 44 so that the pH was 13.5. The exhaust gas was collected by the receiver 44 and then released. Hydrogen cyanide was not detected from the collected exhaust gas, and the exhaust gas components were CO ₂ , NH ₃ , N ₂ , and O ₂ , but cyanide was detected from the water in the receiver 44.

After 300 minutes, heating was stopped, and after cooling, the pot 1 was opened, and the contents (hereinafter referred to as oxidation treatment product A) were analyzed. As a result, iron oxide such as Fe ₂ O ₃ was mainly used. Cesium was 8.33 wt% in terms of oxide (Cs ₂ O). The weight of the residue in the pot 1 was 420 g, which was 1/7 or less of the weight of the slurry charged into the pot. FIG. 5 shows an XRD analysis of this oxidized product A. The peaks of Fe ₂ O ₃ and CsNO ₃ can be remarkably read.

<Water elution treatment>
The above oxidation-treated product A was ground in a mortar to obtain sample A1, a small amount was taken, dissolved in acid, and diluted with distilled water. When the concentration of cesium contained in this eluate was quantified by ICP-MS, the amount of cesium contained in sample A1 was Cs-73000 mg / sample-kg. Further, 1 g of sample A1 was collected, mixed with 10 mL of distilled water, and stirred for 6 hours in a water bath (80 ° C.) to elute soluble salts in distilled water. The eluate was centrifuged (3000 rpm, 20 minutes), and the separation residue was washed with pure water and dried to obtain sample A2. A small amount of sample A2 was collected, dissolved in acid, and diluted with distilled water. When the concentration of cesium contained in the eluate was quantified by ICP-MS, the amount of cesium contained in sample A2 was Cs-13000 mg / sample-kg. Therefore, the water-eluting cesium recovery rate from the oxidized product A by water extraction was 82.2%.

<0.5N nitric acid elution treatment>
1 g of the sample A2 was collected, mixed with 10 mL of a 0.5N nitric acid solution, and stirred in a water bath (80 ° C.) for 6 hours to elute soluble salts into distilled water. The eluate was centrifuged (3000 rpm, 20 minutes), and the separation residue was washed with pure water and dried to obtain sample A3. A small amount of sample A3 was collected, and the total acid dissolution, dilution with distilled water, and the concentration of cesium were quantified by ICP-MS. The amount of cesium contained in sample A3 was Cs-4400 mg / sample-kg. The cesium recovery rate by extracting the oxidized product A with water and further extracting with a 0.5N nitric acid solution was 93.97%.

<Sublimation removal treatment>
5 g of the sample A3 was taken, collected in a combustion boat, and inserted into the tube of the small tube furnace. It was held and dried at 150 ° C. for 15 minutes, heated to 1000 ° C. with 0.5 L / min air, and held for 1 hour. After natural cooling, this was designated as Sample A4. Sample A4 was sampled, and the total acid dissolution, dilution with distilled water, and the concentration of cesium were quantified by ICP-MS. The amount of cesium contained in sample A4 was Cs-480 mg / sample-kg. The cesium removal rate obtained by subjecting the oxidized product to water extraction, extraction with 0.5N nitric acid solution, and further sublimation removal treatment was 99.34%.

[Discussion]
From Example 1 and Comparative Example 1, the maximum temperature in the drying and oxidation treatment steps of cesium-adsorbed Prussian blue was controlled to be equal to or lower than the melting point of cesium nitrate, and a product in which crystallization of the oxide form was suppressed was obtained. It was observed that the extraction rate into water and 0.5N nitric acid solution was dramatically increased. Furthermore, by improving the removal rate of cesium from the oxidation residue in the sublimation removal treatment, the prospect of achieving waste residue below the regulation value was obtained.

1 Pot 2 Induction Heating Unit 3 Pot Body 12, 13, 14 Temperature Sensor 23 Ejector 24 Tank 27 Cooler 42 Steam Exhaust Pipe 43 Cooler 44 Receiver

Claims (7)

A metal pot containing Prussian blue granules adsorbing cesium ions is induction-heated and air or low oxygen gas is introduced into the pot to dry the slurry, and then the heating temperature is further raised to increase Prussian. A method for treating cesium-adsorbed Prussian blue that oxidatively decomposes blue,
A method for treating a cesium adsorption slurry, characterized in that Prussian blue is subjected to thermal oxidative decomposition by controlling at least one of air or low oxygen gas introduction amount and induction heating so that the temperature in the pot becomes 150 to 400 ° C. .   2. The method for treating cesium-adsorbed Prussian blue according to claim 1, wherein the oxygen concentration in the pot is reduced and adjusted by heating and oxidative decomposition so as to obtain a combustion residue containing an oxide in the form of a suppressed crystal structure. .   The method for treating cesium-adsorbed Prussian blue according to claim 1 or 2, wherein the Prussian blue granule is encapsulated with a calcium-enriched film.   4. The cesium adsorption method according to claim 1, wherein in the Prussian blue drying and oxidative decomposition step, the inside of the pot is sucked with an ejector, and water is supplied to the ejector as a working fluid. Prussian blue processing method.   5. The oxidative decomposition treatment of Prussian blue according to any one of claims 1 to 4, wherein water is added to the oxidative decomposition product to elute the cesium compound, and the water is evaporated from the aqueous solution of the eluted cesium compound to form the cesium compound. A method for treating a cesium-adsorbed Prussian blue, characterized by comprising deposits.   6. The elution and separation of a cesium compound according to claim 5, wherein the decomposition product is pulverized to 100 μm or less, eluted with water at a temperature of 50 to 90 ° C., and further eluted with an aqueous nitric acid solution. Processing method of cesium adsorption Prussian blue.   7. The method of treating cesium-adsorbed Prussian blue according to claim 6, wherein the elution residue is heated to 1000 ° C. or higher after further elution with a nitric acid aqueous solution, and the residual cesium compound is sublimated.

Images