JP4418884B2 - Cobalt ion adsorbent - Google Patents

Description

The present invention relates to a cobalt ion adsorbent comprising potassium niobate having a large cobalt ion exchange capacity, and more specifically, for example, 0.1 g, 0.00 g of the cobalt ion adsorbent of the present invention in high-temperature water at 200 ° C. from 05M cobalt ions aqueous 10 cm ^3, the cobalt ion adsorption performance is high potassium niobate ion adsorbent showing the cobalt ion exchange capacity of at least 1 mmol / g, in which about the how to efficiently produce the ion adsorbent. The present invention has a large cobalt ion exchange capacity, for example, a new cobalt ion adsorbent that can be suitably used for a purification device for removing radionuclides in the primary cooling water of a reactor with high efficiency, and the production thereof. And new technologies and products related to applied technologies.

Conventionally, in nuclear power generation, a small amount of metal is eluted from reactor materials such as pipes in the primary cooling water of a nuclear reactor and activated in the core, and radionuclides such as ⁵⁴ Mn, ⁵⁹ Fe, ⁵⁸ Co, and ⁶⁰ Co are produced. It is known to generate. For the purpose of removing this radionuclide, a reactor water purification apparatus using an ion exchange resin is attached.

  However, since the ion exchange resin is inferior in heat resistance, a part of the high-temperature reactor water is taken out, cooled to about 40 ° C., then sent to the reactor water purification device, and the purified water is heated again to react with the reactor water. An operation to return to is performed. Since such a method involves heat loss, development of an ion exchange material excellent in heat resistance that can be used in high-temperature water at 50 ° C. or higher is desired instead of an ion exchange resin. In particular, cobalt ions in the radionuclide have a high activation energy, which causes a problem of exposure to workers during periodic inspection of the reactor.

  As an attempt to adsorb and remove cobalt ions from high-temperature water, for example, an example using crystalline titanate fibers that are inorganic ion exchangers has been reported (Non-patent Document 1). However, this crystalline titanic acid fiber is not suitable for use in high-temperature water because the cobalt ion adsorption ability decreases with a change in crystal phase at 100 ° C. or higher.

  In addition, an adsorbent in which hydrous titanium oxide is supported on porous titanium metal has been studied, and it has been reported that this adsorbent has a chemisorption ability to produce a compound in which cobalt ions are incorporated into crystals in high-temperature water. (Non-Patent Document 2). However, this adsorbent has a defect that the cobalt ion exchange capacity is as small as 0.1 mmol / g and is not suitable for practical use.

  Potassium niobate has a layered structure, and has attracted attention as one of heat-resistant inorganic ion exchangers because potassium ions existing between layers can be exchanged with other cations. Normally, potassium niobate is synthesized by solid phase reaction using potassium carbonate and niobium oxide powder as raw materials (Non-patent Document 3). At this time, heat treatment at a high temperature of 1000 ° C. or higher is required, and a large amount of heat energy is required. Therefore, development of a synthesis process under mild conditions to replace solid-phase synthesis operation is desired. In addition, the solid phase synthesized product has a particle size of micron order or more and has a problem that the specific surface area is remarkably reduced.

  Hydrothermal synthesis has advantages such as those produced by solid-phase synthesis exceeding 1000 ° C can be synthesized under milder temperature conditions, and the product can be obtained as homogeneous and fine particles. ,Attention has been paid. However, no hydrothermal synthesis example has been reported for potassium niobate ion exchangers.

Bull. Chem. Soc. Jpn. 59, 49 (1986) Ceramicskus, Volume 20, No. 3, p. 203 (1985) J. et al. Catalysis, 102, pp. 92-98 (1986)

Under such circumstances, the present inventors have conducted intensive research with the goal of developing a new inorganic ion exchanger useful as a cobalt ion adsorbent in view of the above-described prior art. It was found that potassium niobate excellent in cobalt ion exchange ability was obtained by heat-treating with potassium hydroxide aqueous solution under hydrothermal conditions, and the present invention was completed based on this finding. The present invention overcomes the drawbacks of the conventional cobalt ion exchanger as described above, has an excellent cobalt exchange capacity, and is technically and economically advantageous potassium niobate ion adsorption that can be easily produced by a simple operation. The object is to provide materials , their manufacture and applied technology.

The present invention for solving the above-described problems comprises the following technical means.
(1) The basic structure is a general formula:
Nb ₂ O ₅ xK ₂ O
(X in the formula is a number of 0.6 to 1) Ri Do potassium hydrothermal synthesis niobate represented by the crystal structure of potassium the niobate, potassium six niobate _{(K 4} Nb _{6 O 17} Or a mixed phase of potassium hexaniobate and potassium niobate (KNbO ₃ ).
(2) a specific surface area of at least 20 m ² g ^- Oh Ru ^1, wherein (1) Symbol placement refractory cobalt ions adsorbent.
( 3 ) The heat-resistant cobalt ion adsorbent according to (1) or (2), which has hot water resistance even in high-temperature water at 200 ° C.
( 4 ) The reaction product obtained by mixing niobium oxide with potassium hydroxide aqueous solution and treating under hydrothermal conditions is filtered, washed with water, and dried, so that the basic structure has the general formula:
Nb ₂ O ₅ xK ₂ O
(X in the formula is a number of 0.6 to 1) Ri Do potassium hydrothermal synthesis niobate represented by the crystal structure of potassium the niobate, potassium six niobate _{(K 4} Nb _{6 O 17} Or a heat-resistant cobalt ion adsorbent that is a mixed phase of potassium hexaniobate and potassium niobate (KNbO ₃ ).
( 5 ) The method for producing a heat-resistant cobalt ion adsorbent according to ( 4 ), wherein the hydrothermal treatment temperature is 300 ° C or higher and 450 ° C or lower.
( 6 ) The method for producing a heat-resistant cobalt ion adsorbent as described in ( 4 ) above, wherein the calcining is performed in the air or in an oxidizing atmosphere after drying.

Next, the present invention will be described in more detail.
In the present invention, the basic structure has the general formula:
Nb ₂ O ₅ xK ₂ O
Points (x is 0.6 to 1 number a is of the formula) hydrothermal synthesis niobate potassium represented by either Ranaru high heat resistance cobalt ions adsorbent, the niobium oxide is mixed with aqueous potassium hydroxide The reaction product obtained by treatment under hydrothermal conditions is characterized by the production method of a cobalt ion adsorbent whose basic structure is represented by the above general formula, which is filtered, washed with water, and dried. It is what has.

That is, in the present invention, the basic structure is represented by the general formula Nb ₂ O ₅ · xK ₂ O.
(Wherein x is a number from 0.6 to 1), and provides a potassium niobate ion adsorbent . The present invention also provides a method for producing the above potassium niobate ion adsorbent and its application, wherein the niobium oxide powder is hydrothermally treated with an aqueous potassium hydroxide solution, and the resulting slurry is filtered, washed with water and dried. Provide products.

The cobalt ion adsorbent of the present invention has a general formula:
Nb ₂ O ₅ xK ₂ O
(Wherein x is a number from 0.6 to 1), the composite oxide having such a basic structure has a good cobalt ion exchange capacity. It can be used suitably as a cobalt ion adsorbent . In the above general formula, x is preferably in the range of 0.6 to 1, and if the value of x is smaller than 0.6, the ratio of unreacted niobium oxide increases, and hexaniobic acid having a high ion exchange capacity. The proportion of potassium decreases. On the other hand, if the value of x is larger than 1, the product becomes a single phase of potassium niobate that does not show ion exchange ability, and does not show ion exchange characteristics.

Such a cobalt ion adsorbent can be produced by a production process of potassium niobate. In the production step of potassium niobate, potassium niobate can be produced by subjecting niobium oxide to hydrothermal treatment in an aqueous potassium hydroxide solution. The conditions for the hydrothermal treatment include a temperature range of 200 ° C. to 500 ° C., preferably 300 ° C. to 450 ° C. The reaction time is from 2 hours to 24 hours. However, when the reaction temperature is low, it is preferably about 8 hours to 24 hours, and when the reaction temperature is high, it is preferably about 2 hours to 8 hours. The amount of potassium added is more than the stoichiometric amount necessary for potassium niobate.

  In the potassium niobate production step, niobium oxide powder is added to the potassium hydroxide aqueous solution to prepare a suspension solution. Alternatively, the potassium hydroxide aqueous solution is dropped into the niobium oxide suspension solution to prepare the suspension solution. You can also The potassium to be mixed is used in an amount of 3 times or less, preferably 2 times or less as a molar ratio to niobium oxide. The obtained suspension solution can be subjected to hydrothermal treatment using a sealed container such as a Teflon (registered trademark) inner tube reaction container, a glass ampule, or an autoclave. The by-product solute is removed by filtering and washing the hydrothermally treated product.

The product after the reaction is filtered, washed with water and dried. Drying is performed at room temperature to 50 ° C. using a general dryer or a desiccator containing a desiccant. Moreover, although it can dry also by a spray-drying system or a freeze-drying system, after shaping | molding in arbitrary shapes before drying, it can also dry. The product obtained shows a fine powder form. The crystal structure of the obtained potassium niobate is a mixed phase of potassium hexaniobate (K ₄ Nb ₆ O ₁₇ ) or potassium hexaniobate and potassium niobate (KNbO ₃ ).

The potassium niobate ion adsorbent thus obtained can be confirmed by measurements such as chemical analysis, X-ray diffraction, thermal analysis, infrared spectroscopy, and scanning electron microscope. For example, the x value can be obtained by chemical analysis. The cobalt ion exchange capacity can be evaluated, for example, by examining the change in the concentration of cobalt ions under high-temperature hot water conditions in the presence of an ion adsorbent . In potassium hexaniobate, there are two types of layers, and cobalt ions are intercalated by ion exchange with potassium ions and trapped between the layers.

The production of the cobalt ion adsorbent of the present invention can be easily confirmed by, for example, X-ray diffraction measurement. When measured using a copper tube and a nickel filter, the precipitates obtained in the above steps are 2θ = 4.5 °, 9.4 °, 27.8 °, 31.6 ° and 45.0. (020), (040), (231), (0, 12, 1) and (0, 18, 1) of potassium hexaniobate (K ₄ Nb ₆ O ₁₇ 3H ₂ O: JCPDS21-1297) 1) A peak corresponding to the diffraction line is observed.

Depending on the synthesis conditions such as the processing temperature and time, (110), 2θ = 22.1 °, 50.8 °, 56.2 ° and 65.9 ° of potassium niobate (KNbO ₃ : JCPDS32-0822), Peaks corresponding to (221), (311) and (222) diffraction lines are also observed. The size of the crystallite can be estimated from the half width of the (040) diffraction line. The form of the potassium niobate ion adsorbent of the present invention can be observed as fine particle aggregates by a scanning electron microscope.

Conventionally, examples of using an ion exchange resin, an inorganic ion exchanger such as crystalline titanate fiber, hydrous titanium oxide, etc. as a means for purifying the primary cooling water of a nuclear reactor have been reported. Due to problems such as low exchange capacity, the development of new ion exchangers to replace them has been strongly requested. On the other hand, the hydrothermally synthesized potassium niobate ion adsorbent of the present invention has a large specific surface area (20 m ² g ⁻¹ or more), a large cobalt ion exchange capacity, and a relatively moderate temperature of 300 to 400 ° C. Under the conditions, it can be synthesized as homogeneous fine particles in a short time, and is useful as a new cobalt ion adsorbent that can replace conventional organic and inorganic ion exchangers. The cobalt ion adsorbent of the present invention is a submicron-sized fine powder having the characteristics that the cobalt ion exchange capacity is 1.5 mmol / g or more and the specific surface area is 20 m ² g ⁻¹ or more, and uses the cobalt ion adsorbent. to, build high heat resistance cobalt ions adsorbent made of the cobalt ion-adsorbing material can be realized be provided. In the present specification, the cobalt ion exchange capacity and the cobalt ion exchange capacity of the cobalt ion adsorbent of the present invention are described, but this is to allow comparison with the performance of the conventional cobalt ion exchanger. These performances are shown as comparative standards.

The present invention has the following effects.
(1) The hydrothermally synthesized potassium niobate ion adsorbent of the present invention has a higher cobalt ion exchange capacity than a potassium niobate ion exchanger obtained by a conventional solid phase reaction.
(2) The hydrothermal composite can be synthesized using a relatively low concentration (1M or less) potassium hydroxide solution.
(3) Compared with solid phase synthesis, the product can be obtained by a simple process under hydrothermal conditions at a low synthesis temperature.
(4) The obtained hydrothermal synthesis product is in the form of submicron fine particles and has a characteristic of being easily dispersed in an aqueous solution.
(5) A cobalt ion adsorbent having a large specific surface area with a crystallite diameter as small as 1/4 to 1/3 and a specific surface area exceeding 20 m ² g ⁻¹ can be obtained as compared with a solid phase synthetic product.
(6) A potassium niobate ion adsorbent that has a high cobalt ion exchange capacity and can be suitably used to remove radionuclides in the primary reactor cooling water can be provided.
(7) Since no decrease in cobalt ion exchange capacity is observed even in high-temperature water at 200 ° C., it has high hot water resistance, and a treatment temperature for taking out and purifying a part of the reactor cooling water is 100 ° C. Since there is no need to lower it below, heat loss in the purification process can be reduced.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited at all by the following examples and comparative examples.

  10 g of niobium oxide was added to 200 ml of 0.5 M aqueous potassium hydroxide solution and shaken for 1 hour. The sample was transferred to a Ni inner cylinder container together with the mother liquor and kept at 300 ° C. for 8 hours in a pressure-resistant autoclave. After standing to cool, the inner cylinder container was taken out from the autoclave, and the precipitate was filtered, washed with water and dried. The obtained hydrothermally synthesized potassium niobate was recovered by solid-liquid separation and dried at 60 ° C. for 24 hours to obtain Product 1 of the present invention.

The X-ray diffraction result of the product of the present invention is shown in FIG. In this X-ray analysis result, 2θ = 4.5 ° considered to correspond to (020), (040), (231), (0, 12, 1) and (0, 18, 1) of potassium hexaniobate. , 9.4 °, 27.8 °, 31.6 °, 45.0 °, and the like. The crystallite diameter determined from the half width of the (020) diffraction line was 9.7 nm. The value of x obtained from chemical analysis was 0.62. The specific surface area was 20.9 m ² g ⁻¹ .

The product 2 of the present invention was obtained according to Example 1 except that the hydrothermal reaction temperature was 400 ° C. and the hydrothermal reaction time was 2 hours. The X-ray diffraction result of the obtained product of the present invention is shown in FIG. In this X-ray diffraction result, 2θ = 4.5 °, 9.4 °, 27.27 which is considered to correspond to (020), (040), (231) and (0, 12, 1) of potassium hexaniobate. Peaks were observed at 8 ° and 31.6 °. In addition, peaks considered to correspond to (110), (111), (220), (221), (311) and (222) of KNbO ₃ are 2θ = 22.1, 31.6, 45. Observed at 0, 50.8, 56.2 and 65.9 °. The crystallite diameter determined from the half width of the (020) diffraction line of potassium hexaniobate was 7.0 nm. The value of x obtained from the chemical analysis value was 0.63. The specific surface area was 65.6 m ² g ⁻¹ .

Comparative Example 1
A solid phase synthesis product of potassium hexaniobate was prepared by solid phase reaction. Niobium oxide and potassium carbonate powder were mixed at a K: Ti molar ratio of 2.2: 6, placed in a platinum crucible, and heated at 1100 ° C. for 10 hours using an electric furnace to obtain Comparative Product 1. The X-ray diffraction result of the comparative product 1 obtained is shown in FIG. In this X-ray diffraction result, 2θ = considered to correspond to (020), (040), (151), (231), (0, 12, 1) and (0, 17, 1) of potassium hexaniobate. Sharp peaks were observed at 4.5 °, 9.4 °, 22.1 °, 27.8 °, 31.6 °, 45.0 °, and the like. The crystallite diameter determined from the half width of the (020) diffraction line was 38.9 nm. The value of x obtained from chemical analysis was 0.65. The specific surface area was 12.9 m ² g ⁻¹ .

Cobalt ion exchange capacity was measured at reaction temperatures of 100 ° C., 150 ° C., and 200 ° C. using the obtained inventive products 1 and 2 and comparative example product 1. 0.1 g of each product and 10 ml of 0.05M cobalt nitrate aqueous solution were added to a Teflon (registered trademark) inner cylindrical pressure vessel and held in a high-temperature thermostatic chamber for 24 hours. After cooling, the solution in the reaction vessel was solid-liquid separated from the ion adsorbent by filtration, the cobalt ion concentration in the filtrate was quantified by ICP emission analysis, and the cobalt ion exchange capacity was calculated from the difference from the initial concentration. The results are shown in Table 1.

  The comparative product 1 synthesized by the solid phase reaction showed a low cobalt ion exchange capacity of 1.0 mmol / g or less at 100 ° C. On the other hand, Example product 1 obtained at a hydrothermal temperature of 300 ° C. and a heating time of 8 hours and the product 2 of the present invention hydrothermally synthesized at a hydrothermal temperature of 400 ° C. and a heating time of 2 hours are 1.5 mmol / g or more. Compared with Comparative Example Product 1, a higher cobalt ion exchange capacity was exhibited.

The cobalt ion adsorbent of the present invention can be synthesized in a relatively short time of 2 hours when the hydrothermal treatment temperature is 300 to 400 ° C. Compared to solid phase synthesis that requires high temperature, it is economically advantageous with low environmental load. Since the hydrothermal compound has a crystallite diameter as small as 1/4 to 1/3 and a large specific surface area compared to the solid-phase compound, the cobalt ions are absorbed into the crystal interlayer in the process of cobalt ion adsorption. It is judged that it is adsorbed .

As described above in detail, the present invention relates to a cobalt ion adsorbent , and according to the present invention, a potassium niobate ion adsorbent excellent in cobalt exchange ability can be produced and provided. The potassium niobate ion adsorbent of the present invention has a large cobalt ion exchange capacity, is in the form of submicron particles that are easily dispersed in an aqueous solution, and has a specific surface area value of 20 m ² g ⁻¹ or more. Further, the present invention, a mild method for the synthesis temperature conditions can synthesize potassium niobate ion adsorbent in new potassium niobate ion adsorbent, potassium said niobate ion or Ranaru cobalt ions adsorbent Can be provided. INDUSTRIAL APPLICABILITY The present invention is useful, for example, as providing a new technology / new product relating to a potassium niobate ion adsorbent that can be used to remove radionuclides in the primary cooling water of a nuclear reactor.

The X-ray diffraction pattern of this invention product 1 is shown. The X-ray diffraction pattern of this invention product 2 is shown. In the figure, black circles represent KNbO ₃ peaks. The X-ray diffraction pattern of the comparative example product 1 is shown.

Claims (6)

The basic structure is a general formula:
Nb ₂ O ₅ xK ₂ O
(X in the formula is a number of 0.6 to 1) Ri Do potassium hydrothermal synthesis niobate represented by the crystal structure of potassium the niobate, potassium six niobate _{(K 4} Nb _{6 O 17} Or a mixed phase of potassium hexaniobate and potassium niobate (KNbO ₃ ). A specific surface area of at least 20 m ² g ^{- 1} Oh Ru in claim 1 Symbol placement refractory cobalt ions adsorbent. The heat-resistant cobalt ion adsorbent according to claim 1 or 2, which has heat-resistant water even in high-temperature water at 200 ° C. The reaction product obtained by mixing niobium oxide with potassium hydroxide aqueous solution and treating under hydrothermal conditions is filtered, washed with water, and dried, so that the basic structure has the general formula:
Nb ₂ O ₅ xK ₂ O
(X in the formula is a number of 0.6 to 1) Ri Do potassium hydrothermal synthesis niobate represented by the crystal structure of potassium the niobate, potassium six niobate _{(K 4} Nb _{6 O 17} Or a heat-resistant cobalt ion adsorbent that is a mixed phase of potassium hexaniobate and potassium niobate (KNbO ₃ ). The manufacturing method of the heat resistant cobalt ion adsorption material of Claim 4 whose hydrothermal treatment temperature is 300 degreeC or more and 450 degrees C or less. The method for producing a heat-resistant cobalt ion adsorbent according to claim 4 , wherein the heat-resistant cobalt ion adsorbent is calcined in the air or in an oxidizing atmosphere after drying.