JP6053325B2 - Sintered product, metal ion adsorbent, metal ion removal method, and metal ion removal equipment - Google Patents

Description

  The present invention relates to a fired product, a metal ion adsorbent containing the fired product, a metal ion removal method and a metal ion removal facility using the metal ion adsorbent.

  Waste liquids from nuclear reactor facilities, nuclear fuel reprocessing plants, and the like contain various radionuclides, and various adsorbents have been proposed to remove them.

Patent Document 1 discloses titania hydrate TiO ₂ · mH ₂ O (m = 0) obtained by extracting a K ₂ O component from potassium titanate K ₂ OnTiO ₂ (where n = 2 to 4). To 3), strontium in the aqueous solution is adsorbed and ion-exchanged, and the strontium adsorbent Sr _x O.nTiO ₂ .mH ₂ O (x = 0.5 to 1, n = 2 to 8, m = 2 to 2) 8), and a method for immobilizing strontium, characterized in that the strontium adsorbent is heated to 900 to 1300 ° C. to form a mixture of strontium titanate SrTiO ₃ and titanium dioxide.

Patent Document 2 includes a general formula: Ce (HPO ₄ ) _x · yH ₂ O (wherein x is a number in the range of 1.8 to 2.1 and y is a number in the range of 1 to 4). A strontium ion fixative comprising a water-containing composite oxide is disclosed.

  Patent Document 3 discloses that a sodium / titanium molar ratio is 0.6 or less, a selectivity coefficient for substituting Na with Sr is 50,000 or more, an ion exchange capacity is 4.5 meq / g or more, and a pH of 2.0M. Disclosed is a sodium titanate ion exchanger composed of granules having a partition coefficient of radioactive strontium measured in an aqueous solution of NaCl of 40,000 ml / g or more and a particle size of 0.1 to 2 mm.

JP 61-256922 A Japanese Patent No. 2535783 Japanese Patent No. 4428541

  The adsorbent for removing the radionuclide is used by being packed in an adsorption tower, for example. By passing the waste liquid through the adsorption tower filled with the adsorbent and bringing the waste liquid into contact with the adsorbent, the radionuclide in the waste liquid is adsorbed by the adsorbent.

  When the adsorbent is used on an industrial scale, it is desired to have a granule shape suitable for use in an adsorption tower, and the granule is required to have an appropriate mechanical strength. If the mechanical strength is insufficient, the adsorbent may be pulverized to generate fine powder during liquid flow, and the fine powder may leak to the subsequent stage of the adsorption tower. Since the leaked fine powder is a radioactive waste adsorbing the radionuclide, it must be removed by a process such as filtering, leading to a reduction in work efficiency. In addition, in applications where radioactive nuclides are removed, transportation using a water stream may be carried out to remove the used adsorbent from the adsorption tower, but if the adsorbent is brittle, it will be pulverized by water pressure to produce fine powder. The fine powder may clog the piping.

  Alkali titanate is known as an adsorbent for the purpose of removing strontium, but considering its use on an industrial scale for the purpose of removing radioactive strontium, it has sufficient radiation resistance and is suitable for column packing. It is difficult to obtain what can be adjusted to a suitable particle shape. Only Patent Document 3 discloses a granular ion exchanger of titanate. In this patent, titanium oxide and an alkali agent are reacted, and the reaction solution is washed, dried, and pulverized to obtain ion exchanger granules. However, since the granules are aggregates due to spontaneous aggregation by drying, when the granules are dispersed in water, fine powder is generated and the supernatant liquid becomes a colloidal solution. Therefore, even if this granule is packed in a column or an adsorption tower, fine powder continues to be generated, and there is a risk that the fine powder adsorbing radioactive strontium will be washed away later. Further, since the strength of the granule is weak, when it is transported using a water stream in a pipe, a part of the granule may be crushed by water pressure, and as a result, the crushed granule may be clogged in the pipe.

  One aspect of the present invention relates to a fired product of a mixture containing hydrous titanium oxide and an alkali metal compound.

  This fired product has an excellent ability to adsorb metal ions and has sufficient mechanical strength, and generation of fine powder is sufficiently suppressed in applications as an adsorbent. The reason why such an effect is exerted is considered that the alkali metal compound works as a binder during firing to improve the mechanical strength of the fired product.

  In one embodiment, the alkali metal compound may include an alkali metal nitrate. When the alkali metal compound contains an alkali metal nitrate, the pore density of the fired product is improved, and the metal ion adsorption ability of the fired product is further improved. The reason why such an effect is exhibited is considered to be that a gas generated as a decomposition product of nitrate ions during firing causes pores to be generated in the fired product.

In one embodiment, the molar ratio C ₁ / C ₂ of the content C ₁ of titanium element to the content C ₂ of alkali metal element in the mixture may be 0.5 to 5.0. When the molar ratio C ₁ / C ₂ is within this range, a fired product having further excellent metal ion adsorption ability can be obtained.

  In one embodiment, the fired product may be obtained by firing the mixture at 100 ° C. or higher, preferably 200 to 600 ° C. When the firing temperature is less than 100 ° C., the binding effect of the alkali metal compound may not be sufficiently obtained. When the firing temperature exceeds 600 ° C., a part of the fired product is crystallized and the metal ion adsorption ability decreases. There is. That is, by setting the firing temperature within the above range, the effect as a binder of the alkali metal compound can be more effectively obtained while suppressing the crystallization of the fired product, and both the metal ion adsorption ability and the mechanical strength can be obtained. Can be further improved.

  In one embodiment, the fired product may be porous, and the average pore diameter may be 0.1 to 10 μm. Such a baked product is further excellent in metal ion adsorption ability.

In one embodiment, the fired product is a particle containing an alkali titanate compound represented by A ₂ Ti _n O _{2n + 1} (A represents an alkali metal and n represents 0.5 to 5.0) (hereinafter, In some cases, it may be composed of an aggregate of “alkali titanate particles”).

  A fired product of a mixture containing hydrous titanium oxide and an alkali metal compound can be an aggregate of alkali titanate particles. In addition, although the conventional adsorbent may take the form which the inorganic particle aggregated, conventionally, it was difficult to suppress generation | occurrence | production of the fine powder by dispersion | distribution of the said inorganic particle. On the other hand, the fired product of the present embodiment has a strong cohesive force between particles, and generation of fine powder is sufficiently suppressed even when used as an adsorbent.

  In one embodiment, the average particle diameter of the alkali titanate particles may be 0.1 to 10 μm. When the average particle diameter is within the above range, the metal ion adsorption ability of the fired product is further improved.

  Another aspect of the present invention relates to a metal ion adsorbent containing the fired product described above.

  Since this metal ion adsorbent contains the above-mentioned fired product, it has excellent metal ion adsorption ability. Moreover, according to this metal ion adsorbent, the leakage of fine powder to the outside of the adsorption tower is suppressed, and the processing burden such as filtering in the latter stage of the adsorption tower is reduced, so that the work efficiency can be improved.

  Another aspect of the present invention includes a step of bringing a treatment liquid containing metal ions into contact with the metal ion adsorbent to remove at least a part of the metal ions from the treatment liquid. It relates to a removal method.

  Furthermore, the other side surface of this invention is related with the metal ion removal equipment provided with the packed tower filled with the said metal ion adsorption material.

  According to the present invention, there are provided a fired product having an excellent ability to adsorb metal ions and capable of sufficiently suppressing the generation of fine powder in the use as an adsorbent, and a metal ion adsorbent containing the same. Can do. Moreover, according to this invention, the removal method of a metal ion using the said metal ion adsorption material, and a metal ion removal equipment can be provided.

It is a mimetic diagram showing one embodiment of the metal ion removal equipment concerning the present invention. FIG. 4 is a diagram showing the SEM observation result of the fired product of Example 1. It is a figure which shows the SEM observation result of the baking products of Example 2. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments.

(Fired product)
The fired product according to the present embodiment is a fired product of a mixture containing hydrous titanium oxide and an alkali metal compound, and has excellent metal ion adsorption ability. In addition, the fired product has sufficient mechanical strength and can sufficiently suppress the generation of fine powder in the application as an adsorbent. The reason why such an effect is exerted is considered that the alkali metal compound works as a binder during firing to improve the mechanical strength of the fired product.

  Firing generally refers to a phenomenon in which an aggregate of solid powders is solidified by heating to a temperature below the melting point or a temperature at which a partial liquid phase is formed, and becomes a dense solid with a large strength called a sintered body. . The driving force for sintering is the force that tries to minimize the surface energy of the diameter composed of particle aggregates. When energy is applied, mass transfer occurs between particles due to solid diffusion or melting, and bonding occurs. .

  The fired product according to the present embodiment is obtained by sintering the alkali metal compound in the mixture by melting or solid diffusion. Moreover, in the baked product according to the present embodiment, it is considered that the alkali metal is transferred to the hydrous titanium oxide to produce an alkali titanate compound. Further, when the alkali metal compound contains an alkali metal nitrate, nitric acid gas is further generated by thermal decomposition of the nitrate, and the fired product becomes porous.

Hydrous titanium oxide is a compound represented by TiO ₂ · nH ₂ O, and can also be referred to as a hydrate of titanium dioxide. The method for obtaining hydrous titanium oxide is not particularly limited, and can be obtained, for example, by hydrolysis of titanium tetrachloride.

  Examples of the alkali metal include lithium, sodium, potassium, rubidium and cesium, and among these, lithium, sodium and potassium are preferable.

  Examples of the alkali metal compound include alkali metal hydroxides and alkali metal salts, and examples of the alkali metal salt include alkali metal nitrates.

  Moreover, as an alkali metal compound, what has melting | fusing point is the range of 200-600 degreeC is preferable. Such an alkali metal compound can be melted at a suitable firing temperature, which will be described later, and more effectively exhibit the effect as a binder. For example, the melting point of sodium nitrate is 306 ° C., the melting point of potassium nitrate is 339 ° C., the melting point of sodium hydroxide is 328 ° C., and the melting point of potassium hydroxide is 360 ° C., and these alkali metal compounds can be suitably used.

  More preferably, the alkali metal compound contains an alkali metal nitrate. When the alkali metal compound contains an alkali metal nitrate, the pore density of the fired product is increased, and the metal ion adsorption ability of the fired product tends to be further improved. The reason why such an effect is exhibited is considered to be that pores are generated in the fired product due to the gas generated as a decomposition product of nitrate ions during firing.

Mixing amount of hydrous titanium oxide and alkali metal compounds are, for example, the molar ratio C _{1 /} C ₂ content C ₁ of the titanium element to the content C ₂ of the alkali metal element in the mixture with 0.5 to 5.0 It is preferable to adjust so that it becomes.

In the present embodiment, the fired product is a particle containing an alkali titanate compound represented by A ₂ Ti _n O _{2n + 1} (A represents an alkali metal and n represents 0.5 to 5.0) (hereinafter, (Sometimes referred to as “alkali titanate particles”).

N of an alkali titanate compound can be adjusted by changing the above-mentioned molar ratio C ₁ / C ₂ . A is derived from an alkali metal compound, and the alkali metal represented by A may be one kind or plural kinds.

  In addition, although the conventional adsorbent may take the form which the inorganic particle aggregated, conventionally, it was difficult to suppress generation | occurrence | production of the fine powder by dispersion | distribution of the said inorganic particle. On the other hand, in this embodiment, the cohesive force between the particles in the aggregate is strong, and even when used as an adsorbent, the generation of fine powder is sufficiently suppressed.

  The average particle diameter of the alkali titanate particles is preferably 0.1 to 10 μm, and more preferably 0.5 to 5 μm. When the average particle diameter of the alkali titanate particles is in the above range, the metal ion adsorption ability of the fired product tends to be further improved.

  In the present specification, the average particle diameter of the alkali titanate particles is measured by the following method. From the image obtained by surface observation with a scanning electron microscope (hereinafter referred to as “SEM observation” in some cases), the maximum diameter in the fixed direction of 100 arbitrary alkali titanate particles was measured, and the arithmetic average was It is set as the average particle diameter of alkali titanate particles.

  In the present embodiment, the fired product is porous, and the average pore diameter is preferably 0.5 to 5 μm. Such a fired product is further excellent in metal ion adsorption ability. The pores of the fired product are not necessarily in the form of closed cells so that the average pore diameter can be measured. For example, the fired product has a form in which many fine gaps exist between alkali titanate particles ( Open-cell porous) may be used.

  In the present specification, the average pore diameter of the fired product is measured by the following method. From the image obtained by SEM observation of the fired product, the maximum diameter in the fixed direction of 100 arbitrary pores is measured, and the arithmetic average thereof is defined as the average pore diameter.

  From the result of X-ray diffraction, the form of the primary particles constituting the alkali titanate particles is amorphous particles, nano-sized crystalline particles, nano-sized crystalline particles and amorphous particles. It is considered to be either semi-crystalline or mixed with particles.

  The fired product can be prepared, for example, by the following method.

  First, an alkali metal compound is added to a slurry in which hydrous titanium oxide is suspended in a solvent (for example, water). Next, the solvent is dried and removed from the slurry to obtain a solid content that is a mixture of hydrous titanium oxide and an alkali metal compound. By baking this solid content at 200 to 600 ° C., a fired product is obtained.

  In addition, solid content which is a mixture of hydrous titanium oxide and an alkali metal compound is agglomerated by pressure bonding with each other when the solvent is removed by drying. In the present embodiment, the agglomerated solid content may be directly subjected to firing, or may be subjected to firing after compression molding.

  The solvent can be removed by drying, for example, by heating at 60 to 95 ° C. Further, the solvent can be removed by drying under normal pressure or under reduced pressure.

  The firing time is not particularly limited, but can be, for example, 1 to 10 hours.

  The average particle diameter of the alkali titanate particles can be adjusted by changing the particle diameter of the hydrous titanium oxide in the slurry. For example, alkali titanate particles having a small average particle size can be obtained by reducing the particle size of the hydrous titanium oxide in the slurry.

  The fired product may be used as it is as a metal ion adsorbent, or may be used after being crushed to a size according to the application. For example, in the use of the adsorbent filled in the adsorption tower, the fired product is preferably used in the form of granules, and the particle diameter of the granules is preferably 0.1 to 5 mm, more preferably 0.2 to 2 mm. is there.

(Metal ion adsorbent)
The metal ion adsorbent according to the present embodiment contains the fired product. Since the metal ion adsorbent according to the present embodiment contains the fired product, the metal ion adsorbent has excellent metal ion adsorption ability.

  Moreover, according to this metal ion adsorbent, the leakage of fine powder to the outside of the adsorption tower is sufficiently suppressed, and the processing burden such as filtering in the latter stage of the adsorption tower is reduced, so that the work efficiency can be improved. .

  In particular, when adsorbents are used to remove radionuclides (eg, cesium, strontium, etc.) from waste liquids at nuclear reactor facilities, nuclear fuel reprocessing plants, etc., because the leakage of fine powder is the leakage of radioactive waste, The processing involves an excessive work burden and corresponding risks. According to the metal ion adsorbent according to the present embodiment, the leakage of the fine powder can be sufficiently suppressed. Therefore, the metal ion adsorbent according to the present embodiment is preferably used as an adsorbent for removing radionuclides. Can do.

  Moreover, in the use which removes a radionuclide, a used adsorbent may be transported using a water flow. However, if the adsorbent is brittle and easily generates fine powder, the fine powder may clog the pipe. In this regard, according to the metal ion adsorbent according to the present embodiment, the generation of fine powder is sufficiently suppressed, and therefore, the occurrence of clogging of piping during transportation by a water flow can be sufficiently prevented.

  In addition, cesium among radionuclides can be removed relatively easily by a coprecipitation method or the like, but a method for removing strontium from the waste liquid has not been well established. The metal ion adsorbent according to the present embodiment has excellent adsorbability for strontium ions, and can be suitably used as a strontium adsorbent.

  Note that the metal ion adsorbent according to the present embodiment does not necessarily need to be used by being packed in an adsorption tower, and can be used for various known uses as an adsorbent. Moreover, the metal species to be adsorbed are not limited to radionuclides, and can be used for applications that adsorb various metal species.

  The metal ion adsorbent may be composed of the fired product, and may contain components other than the fired product. For example, the metal ion adsorbent may be a mixture of the fired product and another material known as an adsorbent (zeolite, phosphate, antimonic acid, chelate resin, etc.).

(Metal ion removal method)
In the method for removing metal ions according to the present embodiment, a treatment liquid containing metal ions is brought into contact with the metal ion adsorbent to remove at least a part of the metal ions from the treatment liquid (hereinafter referred to as a case). (Referred to as “removal step”).

  The removal step can be performed, for example, by passing the treatment liquid through an adsorption tower filled with a metal ion adsorbent and bringing the treatment liquid and the metal ion adsorbent into contact with each other.

  The removal method according to the present embodiment may include steps other than the removal step. For example, the removal method may include a pretreatment step of removing a part of the metal ions from the treatment liquid before the removal step.

  The removal step can be performed, for example, by circulating the treatment liquid through the adsorption tower at a space velocity of 10 to 200 (1 / hr). In addition, space velocity shows the value which remove | divided the amount of processing liquids per hour passing through the inside of the adsorption tower by the adsorbent capacity in the adsorption tower.

  As a pretreatment process, iron coprecipitation treatment removes part of the metal ions in the treatment liquid as sludge, and carbonate coprecipitation treatment removes part of the metal ions in the treatment liquid as sludge. Carbonate coprecipitation treatment step, and the like. The removal method may include one process as a pretreatment process or may include two or more processes.

  Moreover, the removal method may be provided with the post-processing process which removes a metal ion further from the process liquid which passed the said removal process. Examples of the post-treatment step include a step of circulating the treatment liquid through a column packed tower packed with a filler. The removal method may include one step as a post-processing step or may include two or more steps.

  Since the metal ion removal method according to the present embodiment uses the above-described metal ion adsorbent, it is suitable as a method for removing at least a part of the radionuclide from the treatment liquid containing the radionuclide, and strontium. As a method for removing at least a part of the strontium ions from the treatment liquid having ions, it is more preferable.

(Metal ion removal equipment)
FIG. 1 is a schematic view showing an embodiment of a metal ion removing facility according to the present invention. The metal ion removal equipment 100 includes an iron coprecipitation treatment equipment 10, a carbonate coprecipitation treatment equipment 20, a multistage adsorption tower 30, and a column type multistage packed tower 40.

  A treatment liquid containing metal ions (for example, wastewater containing a radionuclide) is supplied to the iron coprecipitation treatment facility 10. In the iron coprecipitation treatment facility 10, a part of metal ions in the treatment liquid is removed as sludge by the iron coprecipitation treatment. The sludge taken out from the iron coprecipitation treatment facility 10 is stored in the storage container 11.

  The treatment liquid that has undergone the iron coprecipitation treatment is supplied to the carbonate coprecipitation treatment facility 20. In the carbonate coprecipitation treatment facility 20, a part of metal ions in the treatment liquid is removed as sludge by the carbonate coprecipitation treatment. The sludge taken out from the carbonate coprecipitation treatment facility 20 is stored in the storage container 21.

  The treatment liquid that has undergone the carbonate coprecipitation treatment is supplied to the multistage adsorption tower 30. In the multistage adsorption tower 30, a plurality of adsorption towers 31 filled with a metal ion adsorbent are connected. In the metal ion removal equipment 100, the multistage adsorption tower 30 has a structure in which eight adsorption towers 31 are connected in series. In the metal ion removal equipment of this embodiment, the number of adsorption towers in the multistage adsorption tower is as follows. There is no particular limitation.

  In the multistage packed tower 30, the treatment liquid is brought into contact with the metal ion adsorbent in the packed tower 31 to adsorb the metal ions in the treatment liquid onto the metal ion adsorbent. Note that the metal ion adsorbent can be appropriately replaced according to the metal ion adsorption capacity, the metal ion concentration in the treatment liquid, and the flow rate of the treatment liquid.

  The treatment liquid that has passed through the multistage packed tower 30 is supplied to the column-type multistage packed tower 40. The column-type multistage packed tower 40 is connected to a plurality of column-type packed towers 41. In the metal ion removal equipment 100, the column-type multistage packed tower 40 has a structure in which two column-type packed towers 41 are connected, but the column-type multistage packed tower has a structure in which three or more column-type packed towers are connected. You may have.

  In the column-type multistage packed tower 40, metal ions remaining in the processing liquid are removed. The column-type multi-stage packed tower 40 can also function as a trap when metal ion adsorbent fine powder leaks from the multi-stage adsorption tower 30.

  The treatment liquid that has passed through the column-type multistage packed tower 41 is collected in the storage container 50.

  The metal ion removal equipment 100 includes an adsorption tower 31 filled with the metal ion adsorbent described above in the multistage adsorption tower 30. Therefore, in the metal ion removal equipment 100, excellent metal ion removal performance is achieved, and leakage of adsorbent fine powder from the multistage adsorption tower 30 can be sufficiently prevented.

  Moreover, since the metal ion removal equipment 100 includes the adsorption tower 31 filled with the above-described metal ion adsorbent, it is suitable as a radionuclide removal equipment for treating a treatment liquid containing a radionuclide, and strontium. It is also suitable as a strontium removal facility for treating a treatment liquid having ions.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to an Example.

Example 1
15 g of titanium tetrachloride aqueous solution (TC-36, 36 mass% titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Co., Ltd.) and 114 g of 1N sodium hydroxide aqueous solution were mixed, and the deposited precipitate was collected by filtration. The precipitate was washed with water to remove by-produced sodium chloride, thereby obtaining a white solid hydrous titanium oxide.

The obtained hydrous titanium oxide was dispersed in water to prepare a slurry. To this slurry, 2.0 g of sodium nitrate (the molar ratio C ₁ / C ₂ of the titanium element content C ₁ to the sodium element content C ₂ in the mixture was 1.21) was added. Next, the slurry was heated to 80 ° C. and dried, and the obtained solid was fired at 400 ° C. for 5 hours to obtain a white aggregate (baked product).

  The fired product obtained in Example 1 was subjected to surface observation with a scanning electron microscope (hereinafter referred to as “SEM”). The observation results are shown in FIG. From the SEM observation results, it was confirmed that the fired product was an aggregate of particles and was porous. Moreover, the average particle diameter computed by the following method from the SEM observation result was 1.6 micrometers. Moreover, the average pore diameter computed by the following method from the SEM observation result was 2.1 micrometers.

<Calculation of average particle size>
From the image obtained by SEM observation, the maximum diameter in the fixed direction of 100 arbitrary particles was measured, and the arithmetic average thereof was obtained, which was defined as the average particle diameter of the particles.

<Calculation of average pore diameter>
From the image obtained by SEM observation, the maximum diameter in the fixed direction of 100 arbitrary pores was measured, and the arithmetic average thereof was obtained, and this was taken as the average pore diameter.

<Adsorbent evaluation>
The fired body obtained in Example 1 was pulverized and classified to a size of 0.25 to 1.0 mm. Using this as an adsorbent sample, strontium adsorption ability was evaluated by the following method.

1.5 ml of the adsorbent sample and 150 ml of simulated contaminated water (NaCl content: 10000 ppm, Ca ²⁺ content: 16 ppm, Mg ²⁺ content: 10 ppm, Sr ²⁺ content: 10 ppm) are placed in a 200 ml sealed container, The mixture was stirred with a shaker at 110 rpm, a swinging width of 3.7 cm, and 0.5 hours. After stirring, the mixture was centrifuged (3000 rpm, 5 minutes), and the supernatant was filtered through a 0.45 μm filter to obtain a measurement solution.

The obtained measurement liquid was subjected to ICP emission analysis, the Sr ²⁺ content in the measurement liquid was quantified, and the removal rate (%) was determined by the following formula.
Removal rate (%) = ((Sr ²⁺ content in simulated contaminated water) − (Sr ²⁺ content in measurement liquid)) × 100 / (Sr ²⁺ content in simulated contaminated water)

Subsequently, the removal rate (%) when stirring time was changed into 1.0 hour, 2.0 hours, 4.0 hours, and 24 hours by the same method was calculated | required. The obtained results are shown in Table 1. In Table 1, “> 99.9” indicates that the measurement limit is exceeded (the Sr ²⁺ content in the measurement solution is less than the measurement limit).

  Moreover, in the said evaluation, the external appearance of the supernatant liquid when it left still for 1 minute after stirring was observed. The case where the supernatant was transparent was designated as A, and the case where it was clouded by fine powder was designated as B, and the degree of generation of adsorbent fine powder was evaluated. The evaluation results are shown in Table 1. In the examples, no sample with an evaluation of B was observed.

  Subsequently, about the several aspect (Examples 2-4) of the baked product which concerns on this invention, the strontium adsorption ability was contrasted with crystalline strontium titanate.

(Example 2)
15 g of titanium tetrachloride aqueous solution (TC-36, 36 mass% titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Co., Ltd.) and 114 g of 1N potassium hydroxide aqueous solution were mixed, and the deposited precipitate was collected by filtration. This precipitate was washed with water to remove by-produced potassium chloride, thereby obtaining a white solid hydrous titanium oxide.

The obtained hydrous titanium oxide was dispersed in water to prepare a slurry, and 1.0 g of potassium nitrate (the molar ratio C ₁ / C ₂ of the titanium element content C ₁ to the potassium element content C ₂ in the mixture was 2) .88) was added. Next, the slurry was heated to 80 ° C. and dried, and the obtained solid was fired at 400 ° C. for 2 hours to obtain a white aggregate (fired product).

  The fired product obtained in Example 2 was subjected to surface observation by SEM. The observation results are shown in FIG. From the SEM observation results, it was confirmed that the fired product was an aggregate of particles and was porous. Moreover, the average particle diameter calculated by the above method from the SEM observation result was 0.81 μm. In the fired product obtained in Example 2, many pores were observed between the aggregated particles, but the average pore diameter could not be measured because the pores were not in the form of closed cells.

Example 3
15 g of titanium tetrachloride aqueous solution (TC-36, 36 mass% titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Co., Ltd.) and 171 g of 1N sodium hydroxide aqueous solution were mixed, and the deposited precipitate was collected by filtration. The precipitate was washed with water to remove by-produced sodium chloride, thereby obtaining a white solid hydrous titanium oxide.

The obtained hydrous titanium oxide was dispersed in water to prepare a slurry. To this slurry, 1.0 g of sodium nitrate (the molar ratio C ₁ / C ₂ of the titanium element content C ₁ to the sodium element content C ₂ in the mixture was 2.42) was added. Next, the slurry was heated to 80 ° C. and dried, and the obtained solid was fired at 400 ° C. for 2 hours to obtain a white aggregate (fired product).

  The fired product obtained in Example 3 was subjected to surface observation by SEM. From the SEM observation results, it was confirmed that the fired product was an aggregate of particles and was porous. Moreover, the average particle diameter calculated by the above method from the SEM observation result was 0.81 μm. Moreover, the average pore diameter calculated by the above method from the SEM observation result was 0.92 μm.

Example 4
15 g of titanium tetrachloride aqueous solution (TC-36, 36 mass% titanium tetrachloride aqueous solution, manufactured by Ishihara Sangyo Co., Ltd.) and 114 g of 1N sodium hydroxide aqueous solution were mixed, and the deposited precipitate was collected by filtration. The precipitate was washed with water to remove by-produced sodium chloride, thereby obtaining a white solid hydrous titanium oxide.

The obtained hydrous titanium oxide was dispersed in water to prepare a slurry. To this slurry, 0.5 g of sodium nitrate (the molar ratio C ₁ / C ₂ of the titanium element content C ₁ to the sodium element content C ₂ in the mixture was 4. Amount of 4.84) was added. Next, the slurry was heated to 80 ° C. and dried, and the obtained solid was fired at 400 ° C. for 2 hours to obtain a white aggregate (fired product).

(Comparative Example 1)
As an adsorbent of Comparative Example 1, sodium titanate (Na ₂ Ti ₃ O ₇ ) crystal powder (manufactured by Strem Chemicals Inc.) was prepared.

<Evaluation of strontium adsorption capacity>
The fired bodies obtained in the examples were pulverized and classified into sizes of 0.25 to 1.0 mm. Using this as an adsorbent sample, strontium adsorption ability was evaluated by the following method.

An adsorbent sample (1.0 g) and 300 ml of simulated contaminated water (NaCl content: 10000 ppm, Ca ²⁺ content: 16 ppm, Mg ²⁺ content: 10 ppm, Sr ²⁺ content: 10 ppm) are placed in a beaker and mixed with a stirrer. Stir for minutes. After stirring, the mixture was centrifuged (3000 rpm, 5 minutes), and the supernatant was filtered through a 0.45 μm filter to obtain a measurement solution.

The obtained measurement liquid was subjected to ICP emission analysis, and the Sr ²⁺ content (ppm) of the measurement liquid was quantified, and the removal rate (%) was determined by the following formula.
Removal rate (%) = ((Sr ²⁺ content in simulated contaminated water) − (Sr ²⁺ content in measurement liquid)) × 100 / (Sr ²⁺ content in simulated contaminated water)

  Next, the removal rate (%) was determined in the same manner except that the stirring time was changed to 60 minutes. Further, the removal rate (%) was determined in the same manner using the adsorbent of Comparative Example 1 instead of the adsorbent sample. The obtained results are shown in Table 2.

  The fired product of the present invention has an excellent ability to adsorb metal ions, and can sufficiently suppress the generation of fine powder in applications as an adsorbent. For example, from a nuclear facility, a nuclear fuel reprocessing plant, etc. It is useful as an adsorbent for removing radionuclides from waste liquid.

  DESCRIPTION OF SYMBOLS 10 ... Iron coprecipitation processing equipment, 20 ... Carbonate coprecipitation processing equipment, 30 ... Multistage adsorption tower, 31 ... Adsorption tower, 40 ... Column type multistage packed tower, 41 ... Column type packed tower, 11, 21, 50 ... Storage Container, 100 ... Metal ion removal equipment.

Claims (7)

Obtaining hydrous titanium oxide by reaction of titanium tetrachloride with potassium hydroxide or sodium hydroxide;
  Firing a mixture containing the hydrous titanium oxide and potassium nitrate or sodium nitrate to obtain a fired product;
A method for producing a metal ion adsorbent containing the fired product. Molar ratio _C 1 / _{C 2} content _{C 1} of the titanium element to the content _{C 2} of the alkali metal element in the mixture is 0.5 to 5.0 The method according to claim 1. The manufacturing method according to claim 1 or 2 , wherein the mixture is fired at 200 to 600 ° C to obtain the fired product . The fired product is porous,
The manufacturing method as described in any one of Claims 1-3 whose average pore diameter of the said baked product is 0.1-10 micrometers. The fired product is composed of an aggregate of particles containing an alkali titanate compound represented by A ₂ Ti _n O _{2n + 1} (A represents an alkali metal and n represents 0.5 to 5.0). The manufacturing method as described in any one of Claims 1-4 . The manufacturing method of Claim 5 whose average particle diameter of the said particle | grain is 0.1-10 micrometers. A step of producing a metal ion adsorbent by the production method according to claim 1;
A treatment liquid containing metal ions, in contact with the metal ion adsorbent, and removing at least a portion of the metal ions from the processing solution,
A method for removing metal ions.