Niobic acid aqueous solution

Abstract

The present invention provides an aqueous solution of niobium acid having higher dispersibility than ammonium niobate sol and better solubility than niobate complex salt. The present invention proposes an aqueous solution of niobium acid, characterized in that it contains 0.1 to 40% by mass of niobium in terms of Nb2O5, and in a particle size distribution measurement using a dynamic light scattering method, no particles larger than 1.0 nm are detected; and as a production method thereof, the following production method is proposed: adding an aqueous solution of niobium fluoride containing 1 to 100 g / L of niobium in terms of Nb2O5 to an aqueous solution of ammonia having an ammonia concentration of 20 to 30% by mass, reacting the solution, removing fluorine from the resulting reaction solution, and adding at least one selected from amines and ammonia to the resulting solution, reacting the solution.

Description

Technical Field

[0001] The present invention relates to an aqueous solution containing niobium or niobic acid (also referred to as "niobic acid aqueous solution"). Background Art

[0002] Niobium itself is silvery white, but if a passive oxide film is made on the surface, it has the characteristic of shining beautiful seven colors. In addition, it is light and resistant to a variety of chemical substances. In addition, it has a high melting point (468°C), low vapor pressure, high elastic modulus, high thermal stability, low thermal expansion coefficient, and has the highest superconducting transition temperature among all elements. Moreover, it can be easily molded even at low temperatures and has the characteristics of high biocompatibility.

[0003] As mentioned above, niobium and niobium acid have a wide range of uses because niobium has various properties. For example, they are used in coin slots, corrosion-resistant vapor deposition boats for coating, crucibles made of diamond, implant materials, superconducting cables, magnet materials, etc. Recently, single crystals of lithium niobate are used as nonlinear optical materials, potassium niobate is being researched and developed as a candidate for non-lead piezoelectric ceramics, and niobium acid is also being studied as a catalyst because it shows solid acidity.

[0004] If the above-mentioned niobium or niobic acid can be dissolved, the above-mentioned properties can be imparted to various materials by coating, and the application of niobium or niobic acid can be further broadened. However, it is not easy to dissolve niobium or niobic acid using water, acid, etc.

[0005] Conventionally, as a method for producing a niobium solution, niobium powder or niobium oxide is used as a starting material and dissolved with hydrofluoric acid or melted by adding potassium disulfate or the like.

[0006] As an invention related to a solution containing niobium or niobic acid, for example, Patent Document 1 discloses the following method: using niobium chloride as a starting material, refining the niobium chloride by distillation, then obtaining crystals in a chloride-free state, and then dissolving the crystals to make a solution, thereby obtaining a high-purity niobium solution with few impurities. Specifically, a method for producing a high-purity niobium solution is disclosed, characterized in that it comprises the following steps: distilling niobium chloride in the presence of chlorine gas to obtain niobium chloride substantially free of sodium, aluminum, tantalum and iron; mixing the obtained niobium chloride with water to obtain a slurry containing niobic acid; separating a solid component from the obtained slurry, and then washing the solid component with water; drying the washed solid component at a temperature of 0 to 50° C.; and mixing the dried solid component with an aqueous solution containing a complexing agent.

[0007] Patent Document 2 discloses a water-soluble Nb, which is a complex oxalate complex salt that dissolves in 5.2 Nb% (7.4% in terms of Nb2O5) water at room temperature (20°C). That is, as a new type of niobium compound, (dihydrated oxodioxalate) ammonium niobate (NH4) [Nb(O)(C2O4)2(H2O)2] and its hydrate are disclosed, and as a production method thereof, a production method is also disclosed, which has the following steps: dissolving niobium hydroxide and oxalic acid in water; adding ammonia; and cooling the reaction mixture.

[0008] In addition, Patent Document 3 discloses a niobium sol obtained by dispersing a micronized niobate compound in water. Specifically, the patent document discloses an ammonium niobate sol in which the ratio of ammonia to niobate is within the range of NH3 / Nb2O5 (molar ratio) = 0.5 to 1.5 when dried at 100°C for 10 hours and which contains substantially no organic acid, and discloses a production method thereof, which comprises the following steps: dissolving a niobium compound in hydrofluoric acid or a mixed acid of hydrofluoric acid and sulfuric acid to obtain an aqueous solution, mixing and reacting the aqueous solution with an ammonia aqueous solution while maintaining the pH of the aqueous solution at 8 or above to obtain a dispersion containing microparticles of ammonium niobate, and filtering and washing the dispersion.

[0009] Patent Document 4 discloses a method for producing a niobate sol, which includes the steps of heating an ammonium niobate sol in the presence of an amine compound to remove ammonia, or washing an ammonium niobate sol mixed with an inorganic acid to remove ammonia, and then heating the sol in the presence of an amine compound.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Publication No. 2012-87085

[0013] Patent Document 2: Japanese Patent Publication No. 2009-509985 (Japanese Patent No. 5222143)

[0014] Patent Document 3: Japanese Patent Application Publication No. 2011-190115 (Japanese Patent No. 5441264)

[0015] Patent Document 4: Japanese Patent Application Publication No. 2015-81220 Summary of the invention

[0016] Problems to be solved by the invention

[0017] If niobium or niobic acid can be dissolved in water to form an aqueous solution, it will be useful in industry. Conventionally, even the sol-state substance disclosed in Patent Document 3 or the aqueous solution of niobium or niobic acid is obtained by complexing niobium or niobic acid with oxalic acid or the like as disclosed in Patent Document 2. However, there is a problem that the oxalic acid or the like used for complexing reduces the purity of niobium.

[0018] An object of the present invention is to provide an aqueous solution of niobium acid having high dispersibility in water and good solubility in water and a method for producing the same.

[0019] Means used to solve problems

[0020] The present invention provides an aqueous solution of niobic acid, characterized in that it contains 0.1 to 40% by mass of niobium in terms of Nb2O5, and in that no particles larger than 1.0 nm are detected in a particle size distribution measurement using a dynamic light scattering method.

[0021] The present invention also proposes a method for producing an aqueous solution of niobium acid, characterized in that the method comprises the following three steps:

[0022] (1) a step of adding an aqueous solution of niobium fluoride containing 1 to 100 g / L of niobium in terms of Nb2O5 to an aqueous solution of ammonia having an ammonia concentration of 10 to 30% by mass to react and obtain a niobium-containing precipitate;

[0023] (2) a step of removing fluorine from the niobium-containing precipitate obtained in the above step;

[0024] (3) A step of preparing a niobium-containing precipitate obtained by removing fluorine into a slurry, adding at least one selected from amines and ammonia, and reacting the slurry.

[0025] Effects of the Invention

[0026] The niobic acid aqueous solution proposed in the present invention is an aqueous solution in which no particles larger than 1.0 nm are detected in particle size distribution measurement using a dynamic light scattering method, and therefore has high dispersibility in water and good solubility in water.

[0027] Furthermore, as described above, the niobium acid aqueous solution proposed in the present invention is an aqueous solution in which niobium acid is dissolved in water and niobium or niobium acid does not exist as particles. Therefore, it not only has less reflection or scattering of light and high optical properties, but also can improve the reactivity as niobium or niobium acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an XRD pattern of a precipitate obtained by using the aqueous niobic acid solution obtained in Example 4 to conduct a reactivity test with NaOH.

[0029] Figure 2This is an XRD pattern of a precipitate obtained by conducting a reactivity test with NaOH using the aqueous niobic acid solution obtained in Comparative Example 3. DETAILED DESCRIPTION

[0030] Next, the present invention will be described based on an example of an embodiment. However, the present invention is not limited to the embodiment described below.

[0031] <Main niobate aqueous solution>

[0032] The niobic acid aqueous solution (“primary niobic acid aqueous solution”) according to one example of an embodiment of the present invention contains niobium or niobic acid and contains no particles of 1.0 nm or more detected in particle size distribution measurement using a dynamic light scattering method.

[0033] Although it has been confirmed that the aqueous solution of primary niobic acid contains niobium or niobic acid, the state in which it exists is still under investigation. However, although it has not been technically proven, it can be inferred that in the aqueous solution of primary niobic acid, niobic acid exists in water as ions in a state of forming ionic bonds with amines or ammonia.

[0034] In the aqueous solution of primary niobate, considering that hydroxide ions exist as anions, halide ions such as fluoride ions and chloride ions are almost absent, and amines or ammonia exist as cations, it can be considered that niobium is present as NbO - Such anions exist.

[0035] In addition, niobium or niobic acid in the aqueous solution of main niobic acid does not necessarily exist in the state of Nb2O5. The content of niobium or niobic acid expressed in terms of Nb2O5 is based on the convention when expressing Nb concentration.

[0036] The aqueous solution of the main niobate preferably contains 0.1 to 40% by mass of niobium in terms of Nb2O5, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. On the other hand, it is preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0037] The aqueous solution of primary niobic acid preferably contains a component derived from at least one selected from amines and ammonia.

[0038] Although it has not been technically proven, it can be speculated that the solubility in water can be improved by forming an ionic bond between amines or ammonia and niobic acid.

[0039] The main niobate aqueous solution is a solution in which no particles larger than 1.0 nm are detected when the particle size distribution is measured by dynamic light scattering, and preferably a solution in which no particles larger than 0.6 nm are detected. In other words, it is a solution in a completely dissolved state. Therefore, the niobate in the solution is completely water-soluble, which is significantly different from a sol.

[0040] In the present invention, a liquid containing niobic acid in which particles of 1.0 nm or more are not detected when measured by a dynamic light scattering method is referred to as a "niobic acid aqueous solution".

[0041] Dynamic light scattering refers to the following method: a solution such as a suspension is irradiated with light such as a laser, the light scattering intensity from a group of particles in Brownian motion is measured, and the particle size and distribution are obtained from the time variation of the intensity. At this time, the measurement is carried out according to JIS Z 8828:2019 "Particle size analysis-dynamic light scattering method".

[0042] In the present invention, "when the particle size distribution is measured, particles larger than 1.0 nm are detected" means a situation where a reliable value of the particle size can be measured when the particle size is measured by a dynamic light scattering method, and "no particles larger than 1.0 nm are detected" means a situation where a reliable value of the particle size cannot be measured, such as a particle size smaller than 1.0 nm as a reliable measured value, or an unreliable value is displayed when the particle size is measured by a dynamic light scattering method.

[0043] For example, in the case of a sol containing niobic acid, colloidal particles are dispersed in a liquid, and the particle size of the colloidal particles is 1.0 nm or more, so when the particle size distribution is measured, particles with a size of 1.0 nm or more are detected. In contrast, when a substance derived from niobic acid is dissolved in water as ions, particles with a size of 1.0 nm or more cannot be detected when the particle size is measured using a dynamic light scattering method.

[0044] In addition, regarding the measurement conditions of the above-mentioned dynamic light scattering method, the higher the concentration of niobium, the higher the possibility of containing measurable particles. Therefore, it is preferable to adjust the state in which niobium is contained at a concentration of 10 mass%, 15 mass% or 20 mass% in terms of Nb2O5 for measurement.

[0045] (Other ingredients)

[0046] The aqueous solution of main niobic acid may contain components other than niobium or niobic acid as long as it does not hinder the characteristic that particles with a size of 1.0 nm or more are not detected when the particle size distribution is measured by a dynamic light scattering method.

[0047] (Reactivity with aqueous sodium hydroxide solution)

[0048] The main niobium acid aqueous solution is characterized in that, when 20 g of a 3 mass % concentration sodium hydroxide aqueous solution (25° C.) is added to 20 g of a niobium acid aqueous solution (25° C.) adjusted to contain 1 g of niobium per 10 g of Nb2O5 while stirring for 1 minute, and then the solution is left to stand at 5° C. for 20 hours, Na8Nb6O 19 ·Precipitation of 13H2O.

[0049] Therefore, it can be said that the reactivity of the aqueous solution of niobic acid with the alkali metal salt is high, and when it reacts with the aqueous solution of sodium hydroxide as described above, Na8Nb6O is generated. 19 ·Precipitation of 13H2O.

[0050] Usually, in order to obtain niobate hydrate (Na8Nb6O 19 ·13H2O), it is difficult to simply make it by mixing Nb hydroxide with an aqueous sodium hydroxide solution and heating it to above 80°C to react. However, since aqueous niobate solution has high reactivity with alkali metal salts, niobate acid hydrate (Na8Nb6O) can be obtained by simply mixing it with an aqueous sodium hydroxide solution, reacting it, and cooling it. 19 ·13H2O).

[0051] In addition, the precipitate generated is Na8Nb6O 19 The precipitation of 13H2O can be confirmed by, for example, identification using the following X-ray diffraction measurement (XRD). However, the present invention is not limited to this method.

[0052] That is, the generated precipitate can be measured by X-ray diffraction under the following conditions and compared with the XRD pattern of ICDD card No. 00-014-0370 to identify whether it is Na8Nb6O 19 ·13H2O.

[0053] The X-ray diffraction measurement conditions at this time may be as follows.

[0054] Device: MiniFlexII (made by Rigaku Co., Ltd.)

[0055] Measuring range (2θ): 5 to 90°

[0056] Sampling width: 0.02°

[0057] Scanning speed: 2.0° / min

[0058] X-ray: CuKα ray

[0059] Voltage: 30kV

[0060] Current: 15mA

[0061] Divergence slit: 1.25°

[0062] Scattering slit: 1.25°

[0063] Light receiving slit: 0.3mm

[0064] <Main manufacturing method>

[0065] Next, a preferred method for producing the main niobic acid aqueous solution (referred to as "main production method") will be described.

[0066] As an example of the main production method, the following production method can be cited: adding a niobium fluoride aqueous solution to an ammonia aqueous solution of a predetermined concentration to obtain a niobium-containing precipitate (referred to as a "reverse neutralization step"); removing fluorine from the niobium-containing precipitate (referred to as an "F cleaning step"); making a slurry of the niobium-containing precipitate obtained by removing fluorine, adding at least one selected from amines and ammonia, and reacting them to obtain a main niobium acid aqueous solution (referred to as a "water dissolution step"). However, the production method of the main niobium acid aqueous solution is not limited to the above production method.

[0067] As long as the main manufacturing method includes the above-mentioned steps, other steps or other treatments may be appropriately added.

[0068] (Reverse neutralization process)

[0069] In the reverse neutralization step, it is preferred that the niobium fluoride aqueous solution is added to an ammonia aqueous solution of a predetermined concentration to obtain a niobium-containing precipitate. That is, reverse neutralization is preferably performed.

[0070] It is preferred to perform reverse neutralization in which an aqueous niobium fluoride solution is added to an aqueous ammonia solution for neutralization rather than direct neutralization in which an aqueous ammonia solution is added to an aqueous niobium fluoride solution for neutralization.

[0071] It is speculated that the structure of niobic acid will become a structure that is easily soluble in water through reverse neutralization.

[0072] The niobium fluoride aqueous solution can be prepared as follows: niobium or niobium oxide is reacted with hydrofluoric acid (HF) to produce niobium fluoride (H2NbF7), and the niobium fluoride (H2NbF7) is dissolved in water.

[0073] In addition, the aqueous niobium fluoride solution is preferably prepared by adding water (e.g., pure water) to contain 1 to 100 g / L of niobium in terms of Nb2O5. At this time, if the niobium concentration is 1 g / L or more, a niobium acid compound hydrate that is easily soluble in water is obtained, so the niobium concentration of the aqueous niobium fluoride solution is more preferably 1 g / L or more in terms of Nb2O5, and in consideration of productivity, it is more preferably 10 g / L or more, and more preferably 20 g / L or more. On the other hand, if the niobium concentration is 100 g / L or less, a niobium acid compound hydrate that is easily soluble in water is obtained, and in order to more reliably synthesize a niobium acid compound hydrate that is easily soluble in water, it is more preferably 90 g / L or less, and more preferably 80 g / L or less, and more preferably 70 g / L.

[0074] From the viewpoint of completely dissolving niobium or niobium oxide, the pH of the niobium fluoride aqueous solution is preferably 2 or less, more preferably 1 or less.

[0075] On the other hand, the aqueous ammonia solution preferably has an ammonia concentration of 10 to 30% by mass.

[0076] By setting the ammonia concentration of the ammonia solution used for reverse neutralization to 10 mass % or more, it is possible to prevent the dissolution of Nb and allow niobium or niobic acid to be completely dissolved in water. On the other hand, if the ammonia concentration of the ammonia solution is 30 mass % or less, it is near the saturated aqueous solution of ammonia, so it is preferred.

[0077] From the above viewpoint, the ammonia concentration of the aqueous ammonia solution is preferably 10% by mass or more, more preferably 15% by mass or more, more preferably 20% by mass or more, and more preferably 25% by mass or more. On the other hand, it is preferably 30% by mass or less, more preferably 29% by mass or less, and more preferably 28% by mass or less.

[0078] In the reverse neutralization step, the addition amount of the niobium fluoride aqueous solution relative to the ammonia aqueous solution (NH3 / Nb2O5 molar ratio) is preferably set to 95-500, more preferably to 100 or more or 450 or less, and even more preferably to 110 or more or 400 or less.

[0079] In addition, the amount of niobium fluoride aqueous solution added to ammonia aqueous solution (NH3 / HF molar ratio) is preferably 3.0 or more, more preferably 4.0 or more, and even more preferably 5.0 or more from the viewpoint of generating a niobium acid compound dissolved in amine or dilute ammonia water. On the other hand, from the viewpoint of reducing costs, it is preferably 100 or less, more preferably 50 or less, and even more preferably 40 or less.

[0080] In addition, the niobium fluoride aqueous solution and the ammonia aqueous solution may both be at room temperature.

[0081] In the reverse neutralization step, when the niobium fluoride aqueous solution is added to the ammonia aqueous solution, it is preferred that the neutralization reaction be caused within 1 minute. That is, it is preferred that the niobium fluoride aqueous solution be added within 1 minute, for example, all at once, rather than slowly adding the niobium fluoride aqueous solution over time.

[0082] At this time, the addition time of the niobium fluoride aqueous solution is preferably within 1 minute, more preferably within 30 seconds, and even more preferably within 10 seconds.

[0083] (F cleaning process)

[0084] Since the niobium-containing precipitate, which is the liquid obtained in the neutralization reaction, contains fluorine compounds such as ammonium fluoride as impurities, it is preferable to remove them.

[0085] The fluorine compound can be removed by any method, and for example, in addition to a method using ammonia water or pure water, reverse osmosis filtration, ultrafiltration, microfiltration, or other filtration methods using a membrane, centrifugal separation or other known methods can be used.

[0086] The F cleaning process may be performed at room temperature, and there is no particular need to adjust the temperature.

[0087] (Water dissolution process)

[0088] Next, the niobium-containing precipitate obtained by removing fluorine in the above step is made into a slurry, and at least one selected from amines and ammonia water is added to the slurry to react, thereby obtaining a primary niobic acid aqueous solution.

[0089] In order to prepare the niobium-containing precipitate into a slurry, it is only necessary to add the niobium-containing precipitate into a dispersion medium such as pure water and disperse it.

[0090] The water dissolution step may be performed at room temperature, and there is no particular need to adjust the temperature.

[0091] Preferred examples of the amine to be added include alkylamine, choline ([(CH3)3NCH2CH2OH] + ), choline hydroxide ([(CH3)3NCH2CH2OH] + OH - )wait.

[0092] As the above-mentioned alkylamine, a substance having 1 to 4 alkyl groups can be used. In the case of having 2 to 4 alkyl groups, the 2 to 4 alkyl groups may all be the same or may include different alkyl groups. As the alkyl group of the alkylamine, from the viewpoint of solubility, an alkyl group having 1 to 6 carbon atoms is preferred, with 4 or less being more preferred, 3 or less being further preferred, and 2 or less being further preferred.

[0093] Specific examples of the above-mentioned alkylamines include methylamine, dimethylamine, trimethylamine, tetramethylammonium hydroxide, ethylamine, methylethylamine, diethylamine, triethylamine, methyldiethylamine, dimethylethylamine, tetraethylammonium hydroxide, n-propylamine, di-n-propylamine, tri-n-propylamine, isopropylamine, diisopropylamine, triisopropylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, isobutylamine, diisobutylamine, triisobutylamine, tert-butylamine, n-pentylamine, n-hexylamine and the like.

[0094] Among them, from the viewpoint of solubility, methylamine, dimethylamine, trimethylamine, tetramethylammonium hydroxide, ethylamine, methylethylamine, diethylamine, triethylamine, methyldiethylamine, dimethylethylamine and tetraethylammonium hydroxide are preferred, and methylamine, dimethylamine, trimethylamine and tetramethylammonium hydroxide are more preferred. Methylamine is most preferred.

[0095] When aqueous ammonia is used, from the viewpoint of solubility, it is preferably added so that the concentration of NH3 in the niobium-containing precipitate slurry becomes 7% by mass or less, more preferably added so that the concentration becomes 6% by mass or less, and particularly preferably added so that the concentration becomes 5% by mass or less. From the same viewpoint, it is preferably added so that the concentration of NH3 in the niobium-containing precipitate slurry becomes 0.2% by mass or more, more preferably added so that the concentration becomes 0.5% by mass or more, and particularly preferably added so that the concentration becomes 1% by mass or more.

[0096] When an amine is used, from the viewpoint of solubility, it is preferably added so that the amine concentration in the niobium-containing precipitate slurry becomes 15 mass % or less, more preferably added so that the amine concentration becomes 12 mass % or less, and particularly preferably added so that the amine concentration becomes 10 mass % or less. From the same viewpoint, it is preferably added so that the amine concentration in the niobium-containing precipitate slurry becomes 0.5 mass % or more, more preferably added so that the amine concentration becomes 1.0 mass % or more, and particularly preferably added so that the amine concentration becomes 1.5 mass % or more.

[0097] After the amine is added, stirring is preferably performed as necessary to promote the reaction.

[0098] <Application>

[0099] The aqueous solution of niobic acid can be used as, for example, various coating liquids.

[0100] <Explanation of terms>

[0101] In the present specification, when expressed as "X to Y" (X, Y are arbitrary numbers), unless otherwise specified, it means "X or more and Y or less", and means "preferably greater than X" or "preferably less than Y".

[0102] In addition, when expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the meaning of "preferably greater than X" or "preferably less than Y".

[0103] Example

[0104] The present invention is further described by the following examples. However, the following examples do not limit the present invention.

[0105] (Example 1)

[0106] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0107] The 200 mL niobium fluoride aqueous solution was added to 1 L ammonia water (NH3 concentration of 25 mass%) (NH3 / Nb2O5 molar ratio = 177.9, NH3 / HF molar ratio = 12.2) in less than 1 minute to obtain a reaction solution (pH 11). The reaction solution is a slurry of a niobium acid compound hydrate, in other words, a slurry containing a niobium precipitate.

[0108] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0109] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 50% dimethylamine aqueous solution was added in such a way that the dimethylamine concentration became 7.2% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 24.0% by mass.

[0110] The slurry was stirred for 48 hours to obtain a niobic acid aqueous solution (sample).

[0111] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0112] (Example 2)

[0113] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 1830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 50 g / L of niobium (Nb2O5=4.69 mass%) in terms of Nb2O5.

[0114] 400 mL of the niobium fluoride aqueous solution was added to 1 L of ammonia water (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 177.9, NH3 / HF molar ratio = 12.2) in less than 1 minute to obtain a reaction solution (pH 12). The reaction solution is a slurry of niobium acid compound hydrate, in other words, a slurry containing niobium precipitate.

[0115] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0116] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 50% dimethylamine aqueous solution was added in such a way that the dimethylamine concentration became 2.0% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0117] The slurry was stirred for 48 hours to obtain a niobic acid aqueous solution (sample).

[0118] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0119] (Example 3)

[0120] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0121] The 200 mL niobium fluoride aqueous solution was added to 2 L ammonia water (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 355.7, NH3 / HF molar ratio = 24.3) in less than 1 minute to obtain a reaction solution (pH 11). The reaction solution is a slurry of a niobium acid compound hydrate, in other words, a slurry containing a niobium precipitate.

[0122] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0123] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 50% dimethylamine aqueous solution was added in such a way that the dimethylamine concentration became 2.0% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0124] The slurry was stirred for 48 hours to obtain a niobic acid aqueous solution (sample).

[0125] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0126] (Example 4)

[0127] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 9800 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 10.3 / L niobium (Nb2O5=1 mass%) in terms of Nb2O5.

[0128] 2L of the niobium fluoride aqueous solution was added to 2L of ammonia water (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 345.4, NH3 / HF molar ratio = 23.6) in less than 1 minute to obtain a reaction solution (pH 12). The reaction solution is a slurry of niobium acid compound hydrate, in other words, a slurry containing niobium precipitate.

[0129] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0130] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 40% methylamine aqueous solution was added in such a way that the methylamine concentration became 1.0% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0131] The slurry was stirred for 48 hours to obtain a niobic acid aqueous solution (sample).

[0132] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0133] (Example 5)

[0134] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0135] The 200 mL niobium fluoride aqueous solution was added to 2 L ammonia water (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 355.7, NH3 / HF molar ratio = 24.3) in less than 1 minute to obtain a reaction solution (pH 11). The reaction solution is a slurry of a niobium acid compound hydrate, in other words, a slurry containing a niobium precipitate.

[0136] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0137] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a triethylamine aqueous solution of more than 99% was added in such a manner that the triethylamine concentration became 3.0% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0138] The slurry was stirred for 20 days to obtain a niobic acid aqueous solution (sample).

[0139] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0140] (Example 6)

[0141] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0142] The 200 mL niobium fluoride aqueous solution was added to 2 L ammonia water (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 355.7, NH3 / HF molar ratio = 24.3) in less than 1 minute to obtain a reaction solution (pH 11). The reaction solution is a slurry of a niobium acid compound hydrate, in other words, a slurry containing a niobium precipitate.

[0143] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0144] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. 25% ammonia water and pure water were added to the slurry to prepare a slurry with a Nb2O5 solid content concentration of 1.5% by mass and an ammonia concentration of 2.5% by mass.

[0145] The slurry was stirred for 48 hours to obtain a niobic acid aqueous solution (sample).

[0146] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0147] (Example 7)

[0148] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0149] The 200 mL niobium fluoride aqueous solution was added to 2 L ammonia water (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 355.7, NH3 / HF molar ratio = 24.3) in less than 1 minute to obtain a reaction solution (pH 11). The reaction solution is a slurry of a niobium acid compound hydrate, in other words, a slurry containing a niobium precipitate.

[0150] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0151] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 25% TMAH (tetramethylammonium hydroxide) aqueous solution was added in such a way that the TMAH concentration became 10.0% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0152] The slurry was stirred for 5 days to obtain a niobic acid aqueous solution (sample).

[0153] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0154] (Example 8)

[0155] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0156] The 200 mL niobium fluoride aqueous solution was added to 2 L ammonia water (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 355.7, NH3 / HF molar ratio = 24.3) in less than 1 minute to obtain a reaction solution (pH 11). The reaction solution is a slurry of a niobium acid compound hydrate, in other words, a slurry containing a niobium precipitate.

[0157] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0158] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 50% choline aqueous solution was added in such a way that the choline concentration became 10.0% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0159] The slurry was stirred for 5 days to obtain a niobic acid aqueous solution (sample).

[0160] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0161] (Example 9)

[0162] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0163] The 200 mL niobium fluoride aqueous solution was added to 2 L ammonia water (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 355.7, NH3 / HF molar ratio = 24.3) in less than 1 minute to obtain a reaction solution (pH 11). The reaction solution is a slurry of a niobium acid compound hydrate, in other words, a slurry containing a niobium precipitate.

[0164] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0165] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 27% trimethylamine aqueous solution was added in such a way that the trimethylamine concentration became 10.0% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0166] The slurry was stirred for 5 days to obtain a niobic acid aqueous solution (sample).

[0167] The pH of the niobic acid aqueous solution (sample) was 11. The particle size of the niobic acid aqueous solution (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). As a result, the particle size could not be measured. That is, no particles with a particle size of 1.0 nm or more were detected.

[0168] (Comparative Example 1)

[0169] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0170] To the 200 mL niobium fluoride aqueous solution, 200 mL of aqueous ammonia (NH3 concentration 25 mass%) (NH3 / Nb2O5 molar ratio = 355.7, NH3 / HF molar ratio = 24.3) was added over 60 minutes to obtain a reaction solution (pH 11) (neutralized). The reaction solution is a slurry of a niobium acid compound hydrate, in other words, a slurry containing a niobium precipitate.

[0171] Next, the reaction solution was filtered by suction using 5C filter paper and washed until the free fluorine content was 100 ppm or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0172] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 50% dimethylamine aqueous solution was added in such a way that the dimethylamine concentration became 2.0% by mass, thereby preparing a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0173] The slurry was stirred for 48 hours, but the obtained liquid had no transparency and was a white turbid slurry.

[0174] The pH of the slurry was 11. The solution was diluted 100 times with pure water, and the particle size of the niobium-containing liquid (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). The volume average particle size was 282 nm.

[0175] (Comparative Example 2)

[0176] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 830 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 100 g / L niobium (Nb2O5=8.84 mass%) in terms of Nb2O5.

[0177] 80 mL of the niobium fluoride aqueous solution was added to 390 mL of ammonia water (NH3 concentration 5 mass%) (NH3 / Nb2O5 molar ratio = 34.7, NH3 / HF molar ratio = 2.4) in less than 1 minute to obtain a reaction solution (pH 9). The reaction solution is a slurry of niobium acid compound hydrate, in other words, a slurry containing niobium precipitate.

[0178] Next, the reaction solution was decanted using a centrifugal separator and washed until the amount of free fluorine became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed. Ammonia water was used as the washing solution.

[0179] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry to prepare a slurry having a Nb2O5 solid content concentration of 10.0% by mass.

[0180] A 50% aqueous dimethylamine solution was added to the slurry so that the concentration of dimethylamine became 2.0% by mass, and the mixture was stirred for 48 hours. The obtained liquid was a white turbid slurry without transparency.

[0181] The pH of the slurry was 11. The solution was diluted 100 times with pure water, and the particle size of the niobium-containing liquid (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). The volume average particle size was 290 nm.

[0182] (Comparative Example 3)

[0183] 100 g of niobium pentoxide was dissolved in 200 g of a 55% hydrofluoric acid aqueous solution, and 19600 mL of ion-exchanged water was added to obtain an aqueous niobium fluoride solution containing 5.1 g / L niobium (Nb2O5=0.5 mass%) in terms of Nb2O5.

[0184] 9L of the niobium fluoride aqueous solution was added to 5L of ammonia water (NH3 concentration 1 mass%) (NH3 / Nb2O5 molar ratio = 15.5, NH3 / HF molar ratio = 1.1) over 60 minutes to obtain a reaction solution (pH 8) (reverse neutralization). The reaction solution is a slurry of niobium acid compound hydrate, in other words, a slurry containing niobium precipitate.

[0185] Next, the slurry was washed using a filtration device (Microza UF: Model ACP-0013D; manufactured by Asahi Kasei Corporation) until the amount of free fluorine in the slurry became 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluorine had been removed.

[0186] Next, the niobium-containing precipitate from which fluorine had been removed was diluted with pure water to obtain a slurry. A portion of the slurry was dried at 110°C for 24 hours and then calcined at 1000°C for 4 hours to generate Nb2O5, and the Nb2O5 concentration contained in the slurry was calculated from its weight. Pure water was added to the slurry, and then a 50% dimethylamine aqueous solution was added in such a way that the concentration of dimethylamine became 2.0% by mass. A slurry having a Nb2O5 solid content concentration of 10.0% by mass was prepared.

[0187] The slurry was stirred for 48 hours. The obtained liquid was a white turbid slurry without transparency.

[0188] The pH of the slurry was 11. The solution was diluted 100 times with pure water, and the particle size of the niobium-containing liquid (sample) was measured by a dynamic scattering method (ELSZ-2000S, manufactured by Otsuka Electronics). The volume average particle size was 293 nm.

[0189] <Dynamic light scattering measurement>

[0190] The particle sizes of the niobic acid aqueous solutions (samples) obtained in Examples and Comparative Examples were measured using a dynamic light scattering particle size distribution analyzer ELSZ-2000S (manufactured by Otsuka Electronics).

[0191] The detection limit of the dynamic light scattering particle size distribution analyzer used was 0.6 nm, and therefore, in the case where measurement was not possible, it was indicated as "<0.6 nm" in the table.

[0192] In addition, when particles of 1.0 nm or more are detected, it is determined that colloidal particles are “present”, and when particles of 1.0 nm or more are not detected, it is determined that colloidal particles are “absent”.

[0193] Table 1

[0194]

[0195] ※The detection limit of the dynamic scattered light device is 0.6nm. Since there are no particles larger than 0.6nm, it cannot be measured.

[0196] (Research)

[0197] When the particle size of the aqueous niobate solutions (samples) obtained in Examples 1 to 9 was measured by dynamic light scattering, at least no particles larger than 1.0 nm were detected. That is, they were completely dissolved and at least did not contain colloidal particles or particles larger than colloidal particles. Therefore, the dispersibility of the aqueous niobate solutions (samples) obtained in Examples 1 to 9 was higher than that of ammonium niobate sol, and the solubility was better than that of niobate complex salt.

[0198] <Reactivity test with NaOH>

[0199] In the case where the niobium concentration of each of the niobic acid aqueous solutions (samples) obtained in Examples 1 to 9 was higher than 10% by mass in terms of Nb2O5, pure water was added to dilute the niobium concentration to 10% by mass in terms of Nb2O5, and the diluted niobic acid aqueous solutions were used as test samples for the reactivity test. On the other hand, in the case where the niobium concentration of the niobic acid aqueous solutions (samples) was less than 10% by mass in terms of Nb2O5, the solutions were used as test samples for the reactivity test without dilution with pure water.

[0200] While slowly adding 20 g of 3 mass % NaOH aqueous solution (25°C) to 20 g of aqueous niobate solution (2 g in terms of Nb2O5) as a test sample of the reactivity test over 1 minute, 20 g of the solution was stirred with a magnetic stirrer, resulting in a slightly turbid liquid (25°C). The turbid liquid (25°C) was placed in a cooler to maintain the liquid temperature at 5°C for 20 hours, resulting in the formation of a precipitate. The generated precipitate was suction filtered with 5C filter paper, washed with pure water, and then heated to 60°C (set temperature) in a vacuum drying furnace and vacuum dried for 15 hours. The dried precipitate was crushed with an agate mortar, and the obtained powder was subjected to X-ray diffraction measurement.

[0201] For the aqueous solution of niobic acid (sample) obtained in any one of Examples 1 to 9, the precipitate was identified as Na8Nb6O4 by ICDD card No. 00-014-0370 from the X-ray diffraction measurement results (XRD pattern). 19 ·13H2O. In addition, Figure 1 , the XRD pattern of Example 4 is shown as a representative figure.

[0202] On the other hand, the same test was carried out on the niobium-containing liquids (samples) of Comparative Examples 1 to 3, but the precipitates were amorphous and were not identified as Na8Nb6O of ICDD card No. 00-014-0370. 19 ·13H2O. In addition, Figure 2 , the XRD pattern of Comparative Example 3 is shown as a representative diagram.

Claims

1. A niobic acid aqueous solution, characterized in that: It contains 0.1 to 40% by mass of niobium calculated as Nb2O5, and the amount of free fluorine is 100 mg / L or less. In the particle size distribution measurement using the dynamic light scattering method, no particles larger than 1.0 nm were detected. The aqueous solution of niobic acid as a test sample was adjusted to a concentration of 1 g of niobium in terms of Nb2O5 per 10 g of the aqueous solution, and 20 g of a 3 mass % aqueous solution of sodium hydroxide at 25°C was added to 20 g of the aqueous solution of niobic acid at 25°C while stirring for 1 minute, and then the solution was left to stand at 5°C for 20 hours. The generated Na8Nb6O 19 ·Precipitation of 13H2O.

2. The niobic acid aqueous solution according to claim 1, wherein the pH value is 11. 3 . The niobic acid aqueous solution according to claim 1 , comprising a component derived from at least one selected from amines and ammonia.

4. The method for producing an aqueous solution of niobic acid according to claim 1 or 2, characterized in that: The manufacturing method has the following three steps: (1) a step of adding an aqueous solution of niobium fluoride containing 1 to 100 g / L of niobium in terms of Nb2O5 to an aqueous solution of ammonia having an ammonia concentration of 10 to 30% by mass to react and obtain a niobium-containing precipitate; (2) a step of removing fluorine from the niobium-containing precipitate obtained in the above step; (3) A step of preparing a niobium-containing precipitate obtained by removing fluorine into a slurry, adding at least one selected from amines and ammonia, and reacting the slurry.

5. The method for producing an aqueous solution of niobic acid according to claim 4, characterized in that: In the step (1), the niobium fluoride aqueous solution is added to the ammonia aqueous solution to allow a neutralization reaction to proceed within 1 minute.

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