JP2015036137A - Magnetic adsorbent for cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic adsorbent for cesium, which has excellent adsorption of cesium and low leakage of ferrocyanide into treatment water after collection of the magnetic adsorbent, with a high collection ratio of the magnetic adsorbent.SOLUTION: The magnetic adsorbent for cesium includes at least water-insoluble ferrocyanide, a binder, and magnetic material particles with a content ratio of 60 to 97 mass%. Preferably the magnetic adsorbent for cesium further includes an antiblocking agent. Preferably the antiblocking agent is a clay mineral. Preferably the antiblocking agent is montmorillonite.

Description

  The present invention relates to a magnetic adsorbent for cesium.

  Various methods have been studied to separate these from solutions containing harmful components such as heavy metal ions and radioactive cesium. Most simply, a method using an adsorbent such as activated carbon or ion exchange resin is widely used. When these adsorbents are used by adding them to the solution, it is necessary to separate the adsorbent from the treated solution, and this operation has been accompanied with great difficulty. In recent years, as superconducting magnets and high gradient magnetic separation technologies have advanced, the practicality of technologies for separating harmful components in solutions using magnetism has increased and has attracted attention. Furthermore, in the accident at the Fukushima Daiichi nuclear power plant that occurred in 2011, radioactive cesium was scattered over a wide area, and technology for separating radioactive cesium attached to various substances has become necessary.

  It is known that a metal ferrocyanide compound is an adsorbent having high selectivity for radioactive cesium even in the presence of coexisting ions such as sodium, potassium and calcium. As a magnetic adsorbent combining a ferrocyanide metal compound and magnetism, a magnetic adsorbent having a multilayer structure in which a core portion made of magnetic nanoparticles, a coating layer, and a surface layer made of metal ferrocyanide, zeolite, etc. are sequentially laminated. It is disclosed (for example, see Patent Document 1). Further, a magnetic adsorbent containing bitumen, a magnetic substance of at least one of iron and iron oxide, and a polymer compound as essential components is disclosed (for example, see Patent Document 2).

  These magnetic adsorbents can provide the desired radioactive cesium adsorptivity, but are recovered by ferrocyanide ions derived from ferrocyanide compounds and magnetism in the treated water after recovering the magnetic adsorbent. There was a problem of leaking ferrocyanide that was not done. According to the Water Pollution Control Law, cyanide compounds including ferrocyanides are regulated substances, and the wastewater standard is 1 mg / L. When the cyanide concentration exceeds the drainage standard, it is necessary to reduce the cyanide concentration in the treated water by some method, and the work is complicated.

  The present inventors have developed a magnetic adsorbent obtained by binding magnetic particles and a water-insoluble ferrocyanide using a water-soluble resin or an aqueous resin emulsion as a practical magnetic adsorbent having good adsorbability. However, there has been a problem that ferrocyanide leaks into the treated water after recovering the magnetic adsorbent. Such leaked ferrocyanide does not have magnetic particles and is weak in magnetism, so it is difficult to recover by a magnetic recovery device, the recovery rate of magnetic adsorbent is reduced, and the cesium magnetic separation rate from treated water Has led to a decline. Although the process becomes complicated, the leaked solid ferrocyanide can be removed by membrane treatment. On the other hand, those eluted in water and converted to ferrocyanide ions are difficult to remove by membrane treatment and remain in the treated water, and some treatment has been required to meet the wastewater standards.

Japanese Patent No. 4932004 JP 2013-2865 A

  The present invention provides a magnetic adsorbent for cesium that is excellent in cesium adsorptivity, has little leakage of ferrocyanide into treated water after the magnetic adsorbent is recovered, and has a high recovery rate of the magnetic adsorbent.

  The above problems have been studied intensively, and at least the water-insoluble ferrocyanide, the binder, and the magnetic particles are contained, and the magnetic adsorbent for cesium containing 60 to 97% by mass of the magnetic particles makes the cesium adsorptive. The present inventors have found that the present invention is excellent and that leakage of ferrocyanide into treated water after recovering the magnetic adsorbent can be reduced.

  It is preferable that the magnetic adsorbent for cesium further contains an antiblocking agent.

  The antiblocking agent is preferably a clay mineral.

  The antiblocking agent is preferably montmorillonite.

  The magnetic adsorbent for cesium of the present invention contains at least a water-insoluble ferrocyanide, a binder, and magnetic particles, and the content of the magnetic particles is 60 to 97% by mass. By doing so, it is possible to reduce the leakage of ferrocyanide into the treated water during the treatment with the magnetic adsorbent because of excellent cesium adsorptivity.

Hereinafter, the magnetic adsorbent for cesium of the present invention will be described in detail.
The present inventors have already confirmed that a magnetic adsorbent containing at least a water-insoluble ferrocyanide, a binder, and magnetic particles is excellent in cesium adsorption ability, but the treated water after collecting the magnetic adsorbent is confirmed. The inventors of the present invention have made extensive studies on the leakage of ferrocyanide, and found that the content of magnetic particles has an influence on the leakage of ferrocyanide, leading to the present invention.

  In the magnetic adsorbent for cesium of the present invention, the content of the magnetic particles is 60 to 97 mass% of the total solid content of the magnetic adsorbent for cesium. The water-insoluble ferrocyanide that is a cesium-adsorbing compound has magnetism, and is considered to interact with and attract the magnetic particles in the magnetic adsorbent. By making the content of the magnetic particles 60 to 97% by mass, the attractive force between the water-insoluble ferrocyanide and the magnetic particles becomes stronger, and when the magnetic adsorbent is stirred and recovered in water, the ferrocyanide It is speculated that the leakage of water will be suppressed. When the content of the magnetic particles is less than 60% by mass, the effect of suppressing leakage of ferrocyanide is small. If it is more than 97% by mass, the amount of water-insoluble ferrocyanide and binder is reduced, leading to a decrease in cesium adsorptivity and a decrease in physical strength of the magnetic adsorbent for cesium. The content is more preferably 70 to 96% by mass, particularly preferably 80 to 96% by mass.

  The magnetic particles according to the present invention are not particularly limited, and any material exhibiting magnetism can be used. For example, powders of metals such as iron, nickel and cobalt, or powders of magnetic alloys based on these, iron oxide trioxide, iron sesquioxide, cobalt-added iron oxide, barium ferrite, strontium ferrite, etc. A powder is mentioned. In addition, the particle diameter of the magnetic particles is preferably 0.1 to 100 μm from the viewpoint of handleability and mixing uniformity.

The water-insoluble ferrocyanide according to the present invention has high selectivity for cesium among cesium-adsorbing compounds, and exhibits good adsorption ability. Specific examples of the water-insoluble ferrocyanide include, for example, the general formula [M] _a [Fe (CN) ₆ ] _b (where M is a transition metal such as Cu, Co, Ni, Zn, Cd, Mn, Fe, or A ferrocyanide represented by an alkaline earth metal such as Ca, Sr, Ba, and Ra, and a and b are integers satisfying the valence of M × a = 4 × b, or a part of M A ferrocyanide substituted with a monovalent cation or a ferrocyanide in which a transition metal is replaced by an oxide such as Mo, Ti, or W, and insoluble in water can be exemplified. Among these, ferric ferrocyanide is preferable because it is inexpensive, high in safety, and excellent in cesium adsorption.

  As the water-insoluble ferrocyanide, a magnetic adsorbent can be obtained by granulating, drying, and pulverizing a water-insoluble ferrocyanide synthesized in advance and optionally dried together with a binder and magnetic particles. Alternatively, a method may be employed in which a water-insoluble ferrocyanide is synthesized in an aqueous liquid, and then granulated, dried and pulverized with a binder and magnetic particles. According to the latter method, the water-insoluble ferrocyanide is stably present in the form of fine particles, and since its specific surface area is large, it exhibits a high cesium adsorption ability, so it is advantageous as a magnetic adsorbent for cesium. Water removal at the time of synthesis of the insoluble ferrocyanide is not necessary, and the water derived from the binder can be used when mixing with the binder or the like.

  As a method of synthesizing a water-insoluble ferrocyanide in an aqueous liquid, a soluble ferrocyanide is dissolved in water, and a transition metal ion solution and / or an alkaline earth metal ion solution or the like is added thereto while stirring. Alternatively, conversely, a transition metal ion solution and / or an alkaline earth metal ion solution or the like is dissolved in water, and the soluble ferrocyanide solution may be added thereto while stirring. A binder may be mixed in water in advance. When transition metal ions or alkaline earth metal ions are dissolved in the binder, gel-like substances may be separated. Therefore, after synthesizing a water-insoluble ferrocyanide in water, a binder solution is added, or a soluble ferrocyan is soluble in water. A method of adding a transition metal ion solution, an alkaline earth metal ion solution or the like after mixing the chemical compound and the binder liquid is preferable.

Examples of the soluble ferrocyanide include sodium ferrocyanide and potassium ferrocyanide. When the water-insoluble ferrocyanide is represented by the general formula [M] _a [Fe (CN) ₆ ] _b , the number of moles of ferrocyanide ions in the soluble ferrocyanide, transition metal ion solution, alkaline earth metal When the ratio of the product of the valence and the number of moles of each metal ion in the ion solution is 1: 4, the reaction is performed without excess or deficiency. In the case of a water-insoluble ferrocyanide in which a part of M in the general formula [M] _a [Fe (CN) ₆ ] _b is a trivalent ion and the rest is replaced by one monovalent cation, When the ratio between the number of moles of ferrocyanide ions in the fluoride and the product of the valence and the number of moles of each metal ion in the transition metal ion solution and alkaline earth metal ion solution is 1: 3, there is no excess or deficiency. Reaction takes place. In addition, in the case of a water-insoluble ferrocyanide in which a part of M in the general formula [M] _a [Fe (CN) ₆ ] _b is a divalent ion and the rest is replaced by two monovalent cations, When the ratio between the number of moles of ferrocyanide ions in the ferrocyanide and the product of the valence and the number of moles of each metal ion in the transition metal ion solution and alkaline earth metal ion solution is 1: 2, The reaction takes place without shortage. It is preferable to adjust the ratio of both so that all the ferrocyanide ions in the soluble ferrocyanide react. Specifically, 1: 2 to 1: 8 is preferable, 1: 3 to 1: 6 is more preferable, and 1: 4 to 1: 5 is particularly preferable.

  The content of the water-insoluble ferrocyanide according to the present invention is preferably 1.5 to 20% by mass, more preferably 2 to 10% by mass, and particularly preferably 2 to 8% by mass based on the total solid content of the magnetic adsorbent for cesium. . If the content of the water-insoluble ferrocyanide is less than 1.5% by mass, the adsorption efficiency of cesium cannot be denied. On the other hand, even if the content of water-insoluble ferrocyanide exceeds 20% by mass, improvement in cesium adsorption efficiency can not be expected, but the mechanical stirring at the time of cesium adsorption or the like brings the ferrocyanide into the cesium-containing liquid. Leakage is likely to occur. In addition, when using a dispersion of water-insoluble ferrocyanide synthesized in an aqueous liquid, the amount of water used during synthesis increases, so the mixture or granulated product of each component is dried to obtain a magnetic adsorbent for cesium. In some cases, the amount of water to be evaporated increases, and the production efficiency may decrease.

  A cesium-adsorbing compound other than the water-insoluble ferrocyanide can be used as long as the object of the present invention is not impaired. Examples thereof include crystalline tetratitanic acid, ammonium phosphomolybdate, ammonium phosphotungstate, and silicotitanate.

  In the magnetic adsorbent for cesium of the present invention, the binder for binding the water-insoluble ferrocyanide and magnetic particles is not particularly limited, and binders known in the granulation and molding fields can be used. Specifically, for example, polyacrylate resin, polyamide resin, polyvinyl acetate resin, urea resin, epoxy resin, polyurethane resin, polyvinyl chloride resin, poly (styrene / butadiene) resin, poly (acrylonitrile / butadiene) Organic systems such as resins, poly (ethylene / vinyl acetate) resins, silicone resins, and water-insoluble resins obtained by copolymerizing one or more monomers constituting these resins and one or more other monomers Aqueous resin emulsion, starch, gelatin, chitosan, polyvinyl alcohol resin (polyvinyl alcohol, cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, ethylene-polyvinyl alcohol copolymer, polyvinyl acetal, etc.), cellulose-based Organic water-soluble resins such as fat (methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, etc.), polyacrylic acid resins, polyacrylamide, polyvinylpyrrolidone, polyethylene oxide, polypropylene oxide, etc. And organic non-aqueous resins such as urea resin, epoxy resin, polyurethane resin and nitrile rubber, and inorganic binders such as colloidal silica and cement.

  The content of the binder according to the present invention is preferably 1.5 to 20% by mass, more preferably 2 to 15% by mass, and particularly preferably 2 to 10% by mass based on the total solid content of the magnetic adsorbent for cesium. If the binder content is less than 1.5% by mass, the constituent components of the magnetic adsorbent for cesium can no longer be bound, or even if bound, the physical strength can be reduced and it can collapse due to mechanical stirring during cesium adsorption. Increases nature. Conversely, if the content exceeds 20% by mass, the binding properties and mechanical strength are satisfactory, but the adsorption efficiency of cesium tends to decrease.

  The magnetic adsorbent for cesium of the present invention preferably contains an antiblocking agent. The anti-blocking agent according to the present invention is a mixture obtained by stirring and mixing each component of the magnetic adsorbent for cesium when producing the magnetic adsorbent for cesium by a granulation method having an appropriate water absorption. It is a material that can reduce the apparent moisture in the inside, has the effect of suppressing the mixture from becoming a large bowl-like lump, and can produce a granulated product having a uniform diameter and stability. . Anti-blocking agents include montmorillonite, kaolins, talc, zeolite, clay minerals such as natural or synthetic swelling or non-swelling mica, synthetic or natural silica, alumina, calcium silicate, calcium carbonate, barium sulfate, magnesium oxide Inorganic fine particles such as beryllium oxide and diatomaceous earth, and organic fine particles such as cross-linked polymethylmethacrylic acid.

  Among these antiblocking agents, inorganic particles are preferably used from the standpoint of durability during repeated use as a magnetic adsorbent for cesium, which has a large effect of suppressing the formation of large cocoon-like lumps. Furthermore, clay minerals are preferably used in that there is little leakage of ferrocyanide ions into the treated water after using and recovering the magnetic adsorbent. It is speculated that clay minerals have a great effect of incorporating ferrocyanide ions eluted in water, and that leakage of ferrocyanide ions into treated water is reduced. Clay minerals include smectites such as montmorillonite, beidellite, nontronite, saponite, and hectorite, kaolins such as kaolinite, nacrite, dickite, and halloysite, and antigolite such as antigolite, amiteite, and cronsteadite. , Pyrophyllites such as pyrophyllite and talc, mica such as illite, sea green stone, ceradonite, sericite and muscovite, zeolite, vermiculite and chlorite. In particular, montmorillonite is preferable. An example of a clay mineral containing montmorillonite as a main component is bentonite. Commercial products of bentonite include Kunigel V1, Kunigel V2, Kunibond (made by Kunimine Industry Co., Ltd.), Bentonite Myogi, Bentonite Fuji, Bentonite Asama, Bentonite Akagi, Bentonite Haruna (made by Hojun Co., Ltd.), Shimane Bentonite, Izumo Bentonite, Kansai Bentonite (manufactured by Kasanen Kogyo Co., Ltd.), Mizuka Ace, Benclay (manufactured by Mizusawa Chemical Co., Ltd.), Detersoft A, Detersoft C, Detersoft DGA (manufactured by LAVIOSA CHIMICA MINARIA), Landrosil PR414, Landrosil PRW414 (manufactured by Sud Chemie) Etc.

  1-30 mass% is preferable, as for the content rate of the antiblocking agent which concerns on this invention, More preferably, it is 2-25 mass%, Most preferably, it is 2-12 mass%. When the content is less than 1% by mass, it is difficult to obtain the added effect. If it exceeds 30% by mass, the anti-blocking agent according to the present invention does not exhibit cesium adsorptivity, so that the cesium adsorbing ability is lowered, or the anti-blocking agent itself must be bound by a binder. It tends to cause a decrease in physical strength as an adsorbent.

  The particle size of the antiblocking agent according to the present invention is preferably 50 μm or less. When the particle diameter is larger than 50 μm, the effect of stably obtaining a granulated product during production by the granulation method tends to be small. However, if the particle size is too small, handling tends to be complicated, so the particle size of the antiblocking agent is more preferably 0.05 to 30 μm, particularly preferably 0.1 to 20 μm. In the present invention, the antiblocking agent may be a single type or a combination of two or more types. Moreover, when using 2 or more types together, the mixing ratio and each particle size can be selected suitably.

  Examples of the method for producing a magnetic adsorbent for cesium of the present invention include, for example, agitation granulation method, fluidized bed granulation method, extrusion granulation method, rolling granulation method, rolling fluidization granulation method, compression granulation method, Examples thereof include a crushing granulation method and a spray granulation method.

  The particle size of the magnetic adsorbent for cesium of the present invention is adjusted as appropriate by mixing and drying the components and then mechanically pulverizing. When the magnetic adsorbent for cesium is produced by the granulation method, the granulated product may be pulverized and the particle diameter may be adjusted, followed by drying. The particle diameter of the magnetic adsorbent for cesium is preferably 20 mm or less from the viewpoint of workability such as charging into the cesium eluate, stirring, and recovery. More preferably, it is 0.5-10 mm, Most preferably, it is 1-7 mm.

  The magnetic adsorbent for cesium of the present invention is intended to remove cesium from water containing at least radioactive cesium. The water containing at least radioactive cesium includes cesium-eluting water in which a solid substance containing at least radioactive cesium is charged and stirred in water to elute the radioactive cesium. The elution water may contain a cesium eluent or heat the water in order to enhance the elution of cesium from the solid matter.

  Methods for removing solids from water after elution of cesium in water include screw press, filter press, roller press, vacuum dehydrator, centrifugal concentrating dehydrator, belt press, belt screen, vibrating screen, multi-plate wave filter And a method of dehydrating with a dehydrating device such as a multiple disk dehydrator.

  Regarding the introduction of the magnetic adsorbent for cesium, the solid adsorbent for cesium may be added after removing the solid matter from the cesium-containing solution, or the magnetic adsorbent for cesium may be added without removing the solid matter. However, the former method is preferable in terms of increasing the removal rate of cesium. The contact method between the cesium eluate and the magnetic adsorbent for cesium includes batch processing in which the magnetic adsorbent for cesium is added to and stirred in the cesium eluate, and the magnetic adsorbent for cesium is introduced into a water tank equipped with a stirrer. Any of the continuous treatments in which the cesium-containing solution is continuously charged and discharged can be used.

  There is no limit to the amount of the magnetic adsorbent for cesium of the present invention added to the cesium-containing solution, and the amount of cesium to be removed to the target level may be determined experimentally according to the concentration of cesium. Specifically, it is preferable to add so that the total adsorption capacity of the magnetic adsorbent for cesium is 2 to 100 times the amount of cesium present in the liquid to be treated. If the amount of magnetic adsorbent for cesium is less than twice the amount of cesium, removal of cesium may be insufficient. Moreover, even if it is added 100 times or more, the cesium removal level does not change and is uneconomical, and in some cases, it may hinder stirring and magnetic separation operations.

  Examples of the method for stirring the magnetic adsorbent for cesium in the cesium-containing solution include a method of stirring with a stirring blade, a method of aeration such as aeration, and a method of stirring the magnetic adsorbent by electromagnet control. The time for stirring the magnetic adsorbent for cesium in the cesium eluate is preferably 10 minutes to 5 hours. When the contact time is shorter than 10 minutes, the adsorption of cesium may be insufficient. Even if the contact is made for longer than 5 hours, the adsorption has already reached equilibrium, which is not preferable in terms of work efficiency, and long-time stirring may adversely affect the mechanical strength of the magnetic adsorbent for cesium.

  The magnetic adsorbent for cesium that adsorbs cesium is collected in a short time by a permanent magnet, an electromagnet, or a superconducting magnet, and separated from the liquid to be treated.

  EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples. In addition, the percentage in an Example is a mass reference | standard.

Example 1
90 g of potassium ferrocyanide trihydrate was dissolved in 360 g of water. In a separate container, 120 g of a 40% iron (III) chloride aqueous solution was prepared, and the whole amount of the potassium ferrocyanide aqueous solution was slowly added while stirring, followed by stirring for 10 minutes. Furthermore, 300 g of polyvinyl chloride emulsion (Nissin Chemical Industry Co., Ltd .; VINYBRAN 985; 37%) as a binder was added and stirred for 10 minutes to prepare an aqueous liquid A containing water-insoluble ferrocyanide and a binder. . In a Henschel agitation granulator with a vessel capacity of 10 L, 750 g of iron trioxide with an average particle diameter of 5 μm, which is a magnetic particle, is added, and the aqueous liquid A is added while stirring. After the addition, the mixture is stirred for 10 minutes. Produced. The obtained granulated material was pulverized with a cutter mill, passed through a 2 mm sieve, and then dried at 105 ° C. for 24 hours to obtain a magnetic adsorbent for cesium. The magnetic particle content of this magnetic adsorbent for cesium is 81.3%.

Example 2
45 g of potassium ferrocyanide trihydrate was dissolved in 180 g of water. In a separate container, 60 g of a 40% aqueous solution of iron (III) chloride was prepared, and the entire amount of potassium ferrocyanide aqueous solution was slowly added while stirring, followed by stirring for 10 minutes. Furthermore, 100 g of a polyvinyl chloride emulsion (Nisshin Chemical Industry Co., Ltd .; VINYBRAN 985; 37%) as a binder was added and stirred for 10 minutes to prepare an aqueous liquid B containing water-insoluble ferrocyanide and a binder. . In a Henschel agitation granulator with a vessel capacity of 10 L, 1.4 kg of iron trioxide with an average particle diameter of 5 μm, which is a magnetic particle, is added, and aqueous liquid B is added while stirring, and the mixture is stirred for 10 minutes after the addition. A product was made. The obtained granulated material was pulverized with a cutter mill, passed through a 2 mm sieve, and then dried at 105 ° C. for 24 hours to obtain a magnetic adsorbent for cesium. The magnetic particle content of this magnetic adsorbent for cesium is 95.4%.

Example 3
In Example 2, a magnetic adsorbent for cesium was obtained in the same manner as in Example 2 except that the amount of iron trioxide was changed to 1.8 kg. The magnetic particle content of this magnetic adsorbent for cesium is 96.4%.

Example 4
In Example 1, a magnetic adsorbent for cesium was obtained in the same manner as in Example 1 except that the amount of iron trioxide was changed to 300 g. The magnetic particle content of this magnetic adsorbent for cesium is 63.6%.

Example 5
An aqueous liquid A was produced in the same manner as in Example 1. In a Henschel agitation granulator with a vessel capacity of 10 L, 560 g of iron trioxide having an average particle diameter of 5 μm and 190 g of bentonite (montmorillonite content: 84%) having an average particle diameter of 20 μm, which are magnetic particles, were added and stirred while stirring. Liquid A was added and stirred for 10 minutes after the addition to produce a granulated product. The obtained granulated material was pulverized with a cutter mill, passed through a 2 mm sieve, and then dried at 105 ° C. for 24 hours to obtain a magnetic adsorbent for cesium. This magnetic adsorbent for cesium has a magnetic particle content of 60.7% and an antiblocking agent content of 20.6%.

Example 6
An aqueous liquid A was produced in the same manner as in Example 1. In a Henschel stirring granulator with a vessel capacity of 10 L, 650 g of iron trioxide having an average particle diameter of 5 μm and 100 g of bentonite (montmorillonite content: 84%) having an average particle diameter of 20 μm, which are magnetic particles, are added and stirred while stirring. Liquid A was added and stirred for 10 minutes after the addition to produce a granulated product. The obtained granulated material was pulverized with a cutter mill, passed through a 2 mm sieve, and then dried at 105 ° C. for 24 hours to obtain a magnetic adsorbent for cesium. This magnetic adsorbent for cesium has a magnetic particle content of 70.5% and an antiblocking agent content of 10.8%.

Example 7
An aqueous liquid A was produced in the same manner as in Example 1. In a Henschel stirring granulator with a vessel capacity of 10 L, 740 g of iron trioxide having an average particle diameter of 5 μm and 10 g of bentonite (montmorillonite content: 84%) having an average particle diameter of 20 μm, which are magnetic particles, are added and stirred with water. Liquid A was added and stirred for 10 minutes after the addition to produce a granulated product. The obtained granulated material was pulverized with a cutter mill, passed through a 2 mm sieve, and then dried at 105 ° C. for 24 hours to obtain a magnetic adsorbent for cesium. This magnetic adsorbent for cesium has a magnetic particle content of 80.3% and an antiblocking agent content of 1.1%.

Example 8
An aqueous liquid B was produced in the same manner as in Example 2. A Henschel agitation granulator with a vessel capacity of 10 L was charged with 1.38 kg of iron trioxide having an average particle diameter of 5 μm and 20 g of bentonite (montmorillonite content: 84%) having an average particle diameter of 20 μm. Then, the aqueous liquid B was added and stirred for 10 minutes after the addition to produce a granulated product. The obtained granulated material was pulverized with a cutter mill, passed through a 2 mm sieve, and then dried at 105 ° C. for 24 hours to obtain a magnetic adsorbent for cesium. This magnetic adsorbent for cesium has a magnetic particle content of 94.0% and an antiblocking agent content of 1.4%.

Example 9
In Example 6, the anti-blocking agent was changed to zeolite having an average particle size of 10 μm to obtain a magnetic adsorbent for cesium. This magnetic adsorbent for cesium has a magnetic particle content of 70.5% and an antiblocking agent content of 10.8%.

Example 10
In Example 6, the anti-blocking agent was changed to synthetic silica having an average particle diameter of 10 μm to obtain a magnetic adsorbent for cesium. This magnetic adsorbent for cesium has a magnetic particle content of 70.5% and an antiblocking agent content of 10.8%.

Comparative Example 1
In Example 2, a magnetic adsorbent for cesium was obtained in the same manner as in Example 2 except that the amount of iron trioxide was changed to 2.4 kg. The magnetic particle content of this magnetic adsorbent for cesium is 97.3%.

Comparative Example 2
In Example 1, a magnetic adsorbent for cesium was obtained in the same manner as in Example 1 except that the amount of iron trioxide was changed to 250 g. The magnetic particle content of this magnetic adsorbent for cesium is 59.2%.

Comparative Example 3
An aqueous liquid A was produced in the same manner as in Example 1. In a Henschel stirring granulator with a vessel capacity of 10 L, 530 g of iron trioxide having an average particle diameter of 5 μm and 220 g of bentonite (montmorillonite content: 84%) having an average particle diameter of 10 μm, which are magnetic particles, are added and stirred while stirring. Liquid A was added and stirred for 10 minutes after the addition to produce a granulated product. The obtained granulated material was pulverized with a cutter mill, passed through a 2 mm sieve, and then dried at 105 ° C. for 24 hours to obtain a magnetic adsorbent for cesium. This magnetic adsorbent for cesium has a magnetic particle content of 57.5% and an antiblocking agent content of 23.9%.

<Evaluation of adsorption performance of radioactive cesium>
10g of magnetic adsorbent for cesium was added to 500mL of elution water (A) with a radioactive concentration of 385Bq / kg, which was obtained by washing the incinerated fly ash containing radioactive cesium with 5 mass water and filtering it. For 30 minutes. Thereafter, a magnet was applied to collect the magnetic adsorbent for cesium to obtain a treatment liquid. The radioactivity concentration of this treatment solution was measured.

<Measurement of recovery rate of magnetic adsorbent>
10 g of magnetic adsorbent was added to 500 mL of tap water, and stirred for one day with a three-one motor. Thereafter, decant treatment was performed while applying a magnet to separate the treatment liquid from the magnetic adsorbent for cesium. The magnetic adsorbent for cesium was dried, and the recovery rate of the magnetic adsorbent for cesium by a magnet was measured from the mass before and after the test. If the recovery rate is 98% or more, it is good, and if it is 95% or more, there is no practical problem.

<Calculation of theoretical leakage rate of ferrocyanide into water>
Using the measured value of the recovery rate of the magnetic adsorbent for cesium and the blending ratio of each component in the magnetic adsorbent for cesium, the theoretical leakage rate of ferrocyanide into water was calculated according to the following formula.

Theoretical leakage rate of ferrocyanide = (100-cesium magnetic adsorbent recovery rate) × ferrocyanide content / (ferrocyanide content + binder content + blocking agent content)

<Measurement of ferrocyanide ion concentration in processing solution>
About the process liquid obtained by the recovery rate measurement of the magnetic adsorbent for cesium, the filtrate was obtained through the 450 micrometer syringe filter. For this filtrate, the ferrocyanide ion concentration was measured according to “Attachment test method in the notice of the food health department manager dated July 12, 2002”.

  Table 1 shows the results of the magnetic adsorbents for cesium obtained in the examples and comparative examples.

  As shown in the examples, it contains at least a water-insoluble ferrocyanide, a binder, and magnetic particles, and the content of the magnetic particles is 60 to 97% by mass, so that the adsorptivity of cesium is excellent and the magnetic adsorption It is possible to obtain a magnetic adsorbent for cesium with less leakage of ferrocyanide into the treated water after the agent is recovered and a high recovery rate of the magnetic adsorbent. From comparison of Examples 1 to 4, Examples 1 and 2 in which the content of the magnetic particles is 80 to 96% by mass are preferable because the radioactive concentration of the treatment liquid is low. Further, it can be seen that as the content of magnetic particles increases, the recovery rate of the magnetic adsorbent increases, and the theoretical leakage rate of ferrocyanide and the ferrocyanide ion concentration of the treatment liquid tend to decrease.

  As shown in Examples 5 to 10, when the magnetic adsorbent further contains an anti-blocking agent, the ferrocyanide ion concentration of the treatment liquid can be lowered to 1.0 mg / L or less, and the drainage standard for cyanide is set. Satisfies. From the comparison of Examples 6, 9, and 10, Examples 6 and 9 using clay minerals are preferable because the recovery rate of the magnetic adsorbent and the ferrocyanide ion concentration of the treatment liquid are low. Furthermore, Example 6 using bentonite is particularly preferable because these characteristics are much better.

  On the other hand, Comparative Example 1 in which the content of the magnetic particles exceeds 97% by mass has a high radioactivity concentration of the treatment liquid and insufficient cesium adsorption performance. In Comparative Examples 2 and 3 in which the content of the magnetic particles is less than 60% by mass, the radioactive concentration of the treatment liquid is high and the recovery rate of the magnetic adsorbent is also low.

  The magnetic adsorbent for cesium of the present invention contains at least a water-insoluble ferrocyanide, a binder, and magnetic particles, the content of magnetic particles is 60 to 97% by mass, has excellent cesium adsorptivity, and is magnetic. It is possible to provide a magnetic adsorbent for cesium with less leakage of ferrocyanide into the treated water after the adsorbent is recovered and a high recovery rate of the magnetic adsorbent. The present invention is considered effective for decontamination of water contaminated with radioactive cesium, as well as sludge, soil, and incinerated ash.

Claims (4)

  A magnetic adsorbent for cesium containing at least a water-insoluble ferrocyanide, a binder, and magnetic particles, wherein the content of the magnetic particles is 60 to 97% by mass.   The magnetic adsorbent for cesium according to claim 1, wherein the magnetic adsorbent for cesium further contains an antiblocking agent.   The magnetic adsorbent for cesium according to claim 2, wherein the antiblocking agent is a clay mineral.   The magnetic adsorbent for cesium according to claim 2 or 3, wherein the antiblocking agent is montmorillonite.