JP2001163621A - Method for crystallizing niobium and/or tantalum and oxide production process using the same method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce niobium oxide and/or tantalum oxide, each having a low fluoride ion content. SOLUTION: This crystallization method comprises mixing a niobium and/or tantalum aqueous solution containing fluoride ion, with boric acid to crystallize out niobium and/or tantalum from the resulting solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for crystallizing niobium and / or tantalum and a method for producing niobium oxide and / or tantalum oxide using the method.

[0002]

2. Description of the Related Art Niobium oxide and tantalum oxide are widely used in the fields of electronics and optics. In these fields, high-purity products are required. In particular, niobium oxide and tantalum oxide having a low impurity content have been demanded for use as raw materials for producing lithium niobate and lithium tantalate single crystals.

For this reason, methods for purifying niobium oxide and tantalum oxide have been proposed, for example, methods such as a solvent extraction method and an ion exchange resin method. For example, in U.S. Pat.No. 2,962,327, an ore containing niobium and tantalum is pulverized and treated with a mixed acid of hydrofluoric acid and a mineral acid such as sulfuric acid to convert niobium and tantalum into iron, manganese,
Dissolve with calcium, rare earth elements and other metal impurities, contact this solution with organic solvents such as lower aliphatic ketones, esters or ethers, especially methyl isobutyl ketone, and extract and separate niobium and tantalum into organic solvent phase A method is described, and in JP-A-58-176128, the solution is passed through an F-type anion-exchange resin layer, and niobium and tantalum are once adsorbed on the anion-exchange resin, and other impurity metals are removed. And a method of eluting and recovering with hydrofluoric acid and an aqueous solution of ammonium chloride after separation.

[0004] In these purification methods, niobium and / or tantalum after removal of the impurity metals is, NbF ₇ ^2-, NbOF ₅
^2, have been dissolved as fluorinated complexes such as TaF ₇ ^2-, in order to recover a high-purity niobium and / or tantalum from an aqueous solution, an alkali is added to niobium hydroxide and / or hydroxide such as ammonia water After crystallizing the tantalum, the tantalum oxide is separated by filtration, and the niobium hydroxide and / or tantalum hydroxide is calcined at 500 to 1000 ° C. to obtain high-purity niobium oxide and / or high-purity tantalum oxide.

[0005] However, in the above method, a large amount of fluorine ions is contained in niobium hydroxide and / or tantalum hydroxide obtained by filtration, and the temperature is 500 to 1000 ° C.
When calcined, the obtained niobium oxide and / or tantalum oxide has a disadvantage that fluorine ions are contained.

Therefore, a method has been proposed in which the crystals of niobium hydroxide and / or tantalum hydroxide obtained by crystallization are washed with a large amount of an aqueous alkali solution such as aqueous ammonia or pure water to reduce the concentration of fluorine ions. It has been. For example, in JP-A-7-101726, by washing niobium hydroxide or tantalum hydroxide until the fluorine ions in the cleaning water fall within a predetermined range, the fluorine ions contained in the niobium oxide or tantalum oxide after firing are reduced. Methods for reducing the concentration have been proposed. However, since niobium hydroxide or tantalum hydroxide crystallized by ammonia has a very small particle size, it is difficult to filter and separate washing water and crystals, and it takes a long time to repeat the washing operation, There was a problem that the filtration area had to be increased.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present inventors
In order to obtain niobium oxide and / or niobium oxide having a small fluorine ion content by a simple processing means, various studies were carried out on a crystallization method of niobium hydroxide and / or tantalum hydroxide, and the present invention was completed.

[0008]

SUMMARY OF THE INVENTION The present invention is a method for crystallizing niobium and / or tantalum, comprising mixing an aqueous solution of niobium and / or tantalum containing fluorine ions with boric acid.

Further, the present invention is characterized in that boric acid is mixed with an aqueous solution of niobium and / or tantalum containing fluorine ions to crystallize niobium and / or tantalum, and the crystallized product is fired. A method for producing niobium oxide and / or tantalum oxide is also provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The raw material aqueous solution targeted in the present invention may be any aqueous solution in which fluorine ions, fluorine-containing complex ions and niobium and / or tantalum ions (including complex ions) coexist in the system. However, an aqueous solution of niobium and / or tantalum that can be preferably used is niobium and / or tantalum.
Alternatively, it is an aqueous solution in which raw materials such as industrial products and minerals containing tantalum are dissolved in hydrofluoric acid or a mixed acid of hydrofluoric acid and a mineral acid such as sulfuric acid, or a salt containing fluorine ions and a mineral acid such as sulfuric acid.

For example, commercially available industrial niobium oxide having a purity of about 98%, industrial tantalum oxide, metal niobium, metal tantalum, ferroniob, ferrotantalum, columbite, niocalite, tantalite, stroberite, tin slag, etc. An aqueous solution dissolved with a mixed acid of hydrofluoric acid and mineral acid is used. From the viewpoint of easy availability, an aqueous solution in which industrial products such as industrial niobium oxide, industrial tantalum oxide, metal niobium, metal tantalum, ferroniob, and ferrotantalum having a purity of about 98% are dissolved is more preferable.

When a raw material such as an industrial product or a mineral containing niobium and / or tantalum is dissolved in hydrofluoric acid or a mixed acid of hydrofluoric acid and sulfuric acid, or a mineral acid of a salt containing fluorine ions and sulfuric acid or the like. It is preferable to use hydrofluoric acid containing a sufficient amount of fluorine ions or a salt containing fluorine ions to dissolve the niobium and / or tantalum raw material. Since niobium and tantalum dissolve according to the following formula, the amount of hydrofluoric acid and the salt containing fluorine ions is preferably 5 to 14 moles per 1 mole of niobium and / or tantalum element, and smooth dissolution is performed and excess fluorine ions are used. To avoid this, a 7- to 10-fold molar amount is more preferred.

In the case of oxide 1 / 2M ₂ O ₅ + 5HF →
1 / 2H ₂ MOF ₅ + 2H ₂ O or 1 / 2M ₂ O ₅ + 7HF → H ₂ MF ₇ +
In the case of 5 / 2H ₂ O metal, M + 7HF → H ₂ MF ₇ + 5 / 2H ₂ (M represents niobium or tantalum) When dissolving niobium and / or tantalum with a salt containing fluorine ion and sulfuric acid, for example, And alkali fluoride salts such as ammonium fluoride, ammonium acid fluoride, sodium fluoride and potassium fluoride. Since they do not contain metals such as sodium and potassium, ammonium salts such as ammonium fluoride and ammonium acid fluoride are more preferred.

The aqueous solution of niobium and / or tantalum used in the present invention is preferably an aqueous solution from which metal impurities have been removed by a known purification means such as a solvent extraction method or an ion exchange resin method. By once extracting niobium and / or tantalum into an organic solvent such as methyl isobutyl ketone or tributyl phosphate, it is separated from metals such as iron and titanium,
An aqueous solution of niobium and / or tantalum re-extracted with pure water, hydrofluoric acid aqueous solution, ammonium fluoride aqueous solution or the like, or niobium and / or tantalum is adsorbed on an anion exchange resin to elute an ammonium fluoride aqueous solution or ammonium chloride aqueous solution It is preferable to use an aqueous solution or the like eluted with the liquid. When higher purity niobium and / or tantalum is required, two or more known purification methods may be combined as necessary.

When boric acid is added to the above aqueous solution of niobium and / or tantalum containing fluorine ions, precipitation of niobium and / or tantalum occurs. As already described, niobium and / or tantalum are dissolved in aqueous solution as stable ions having fluorine bonded thereto, and surprisingly, the affinity between boron and fluorine is reduced to niobium and fluorine and / or tantalum.
Alternatively, the boron deprives the niobium and / or tantalum of fluorine because the affinity between tantalum and fluorine is exceeded, and niobium and / or tantalum crystallizes. This crystallized product is considered to be mainly a hydroxide.

The boric acid may be in the form of a powder or an aqueous solution and added to the aqueous solution of niobium and / or tantalum containing fluorine ions. Since the amount of boric acid varies depending on the amount of fluorine ions, niobium, and / or tantalum contained in the aqueous solution, it is preferable to determine the amount by performing a small-scale experiment in advance. Usually, 0.05 to the amount of fluorine contained in the aqueous solution
Boric acid having a molar amount of 0.1 to 1 times the molar amount of fluorine in the aqueous solution is more preferable because the recovery of niobium and / or tantalum can be increased and the amount of boric acid used can be reduced. More preferably, it is used in an amount of 0.25 times or more that is a chemical equivalent. As for the abundance of fluorine, as shown in the reaction formula described above, the amount of fluorine bonded to niobium and / or tantalum is 5 to 7 times the molar amount of niobium and / or tantalum, The amount of fluorine in the aqueous solution is 7 times the amount of niobium and / or tantalum in the aqueous solution.
What is necessary is just to use the total value of the double molar amount and the amount of fluorine previously contained in the aqueous solution.

The method of adding boric acid to an aqueous solution of niobium and / or tantalum containing fluorine ions is not particularly limited, and boric acid may be added as a powder or an aqueous solution.
The concentration of each component when boric acid is added is not particularly limited. However, when niobium and / or tantalum are too high in concentration, impurities tend to accompany crystallization, and a dilute solution should be used. Is not preferable because it leads to an increase in equipment and energy. Generally, the concentration of niobium and / or tantalum is about 10 to 200 g / L.

After adding boric acid, it is preferable to take a crystallization time in order to sufficiently precipitate niobium and / or tantalum. The deposition time is generally 1 to 48 hours, more preferably 2 to 8 hours. Precipitation proceeds even in a stationary state, but mixing such as stirring may be performed as necessary to make the concentration in the liquid uniform.

The crystallization of niobium and / or tantalum can be carried out even at room temperature, but heating may be carried out if necessary in order to shorten the crystallization time. Heating at from 20 ° C to 70 ° C is preferred in order to shorten the boiling point of the aqueous solution and the precipitation time.

The niobium and / or tantalum crystals obtained by crystallization are separated from the crystals and the aqueous phase by a known method.
Solid-liquid separation techniques such as sedimentation, filtration, and centrifugation may be used.

The niobium and / or tantalum crystallized with boric acid is calcined at 500 to 1000 ° C.
It can be niobium oxide and / or tantalum oxide.

Therefore, niobium containing fluorine ions and / or
Alternatively, boric acid is mixed with an aqueous solution of tantalum in an amount of 0.05 to 4 times the molar amount of fluorine ions in the aqueous solution to crystallize a hydroxide of niobium and / or tantalum. By baking at a temperature of about 1000 ° C., niobium oxide and / or tantalum oxide can be produced.

[0023]

The crystallized niobium and / or tantalum obtained according to the present invention can be prepared without any particular washing operation.
By firing as it is, niobium oxide and / or tantalum oxide containing almost no fluorine ions can be obtained. Further, the obtained niobium oxide and / or tantalum oxide can be easily filtered, and hardly any boron remains.

[0024]

EXAMPLE 1 In a 1 L container made of FEP resin (tetrafluoroethylene-hexafluoropropylene copolymer), 140 g of industrial niobium oxide (purity: 98%) and a magnetic stirrer were put, and anhydrous hydrofluoric acid was added.
150 g (7.0 times the mol of niobium) was added, and the mixture was stirred using a magnetic stirrer to dissolve niobium oxide. After 100 mL of pure water was added and the insolubles were separated by filtration, 400 g of concentrated sulfuric acid was added to the filtrate, and the whole was diluted with pure water to 1.4 L.

The niobium oxide aqueous solution 50 prepared by the above method
0 mL and 500 mL of tributyl phosphate (TBP) are placed in a separatory funnel and mixed for 30 minutes to remove niobium in the aqueous solution from TB.
Extracted into P. After separating the TBP layer, the TBP layer was washed with 100 mL of a mixed acid containing 1 mol / L hydrofluoric acid and 3 mol / L sulfuric acid. 1 L of pure water was added to the washed TBP and mixed for 30 minutes to re-extract niobium in the TBP to the aqueous phase. Analysis of niobium content in re-extracted water by inductively coupled plasma emission spectrometry (ICP-AES) 5
It contained 6 g / L of niobium.

In a 500 mL FEP resin container, 200 mL of the above re-extracted water (niobium content 0.12 mol, amount of fluorine bonded to niobium 0.84 mol), boric acid 16 g (0.26 mol, 0.31 times the amount of fluorine) and a magnet A stirrer was inserted, and the mixture was heated and stirred at 85 ° C. in an oil bath. After 4 hours, the heating was stopped and the mixture was allowed to cool to room temperature, and the precipitated crystals were filtered through a membrane filter made of tetrafluoroethylene resin (PTFE).

The crystals obtained by filtration were calcined at a temperature of 800 ° C. for 12 hours to obtain 15.9 g of niobium oxide. Identification and quantification of niobium oxide were performed by X-ray diffraction analysis, X-ray fluorescence analysis, and ICP-AES analysis.

The amount of fluorine ions contained in the obtained niobium oxide was measured by ion chromatography.
pm and boron was less than 2 ppm by ICP-AES analysis.

COMPARATIVE EXAMPLE 1 The re-extraction water containing niobium prepared in Example 1
% -Ammonia water (70 mL) was added to crystallize niobium. After firing in the same manner as in Example 1, the amount of fluorine ions contained in the niobium oxide was measured and found to be 150 ppm.

Example 2 A re-extracted water containing niobium was prepared in the same manner as in Example 1. 100 ml of this re-extracted water (niobium 0.06 mol, fluorine amount 0.42 m
ol) was added with boric acid under the conditions shown in Table 1 to obtain crystals. After the obtained crystal was fired in the same manner as in Example 1, the amount of fluorine ions contained in the niobium oxide was measured, and the results shown in Table 1 were obtained.

[0031]

[Table 1] Example 3 Tantalum oxide 10 was placed in a 1-L container made of FEP resin (tetrafluoroethylene-hexafluoropropylene copolymer).
0 g and a magnetic stirrer were put therein, 90 g of hydrofluoric anhydride was put therein, and the mixture was stirred using a magnetic stirrer to dissolve tantalum oxide. After adding 100 mL of pure water and filtering and separating the insoluble matter, 360 g of concentrated sulfuric acid was added to the filtrate, and the whole was diluted with pure water to 1.3 L.

Tantalum oxide aqueous solution prepared by the above method
200 mL of tributyl phosphate (TBP) and 200 mL were placed in a separating funnel and mixed for 30 minutes to extract tantalum in the aqueous solution into TBP. After separating the TBP layer, the TBP layer is
And washed with 100 mL of a mixed acid containing hydrofluoric acid and 3 mol / L sulfuric acid.
400mL of 2mol / L-ammonium fluoride aqueous solution in TBP after washing
, And mixed for 30 minutes to re-extract tantalum in TBP into the aqueous phase. When the amount of tantalum in the re-extracted water was analyzed by inductively coupled plasma emission spectrometry (ICP-AES), it contained 26.8 g / L of tantalum.

In a container made of FEP resin having a capacity of 500 mL, 200 mL of the above-mentioned re-extraction water (a tantalum content of 0.030 mol) and a magnetic stirrer were placed. The amount of boric acid was calculated based on the amount of fluorine (0.21 mol) bound to the tantalum bonds contained in the re-extraction water and the ammonium fluoride (0.40 mol) used in the re-extraction water, and the amount of boric acid was calculated as 14 g (0.23 mol). , 0.38 times the amount of fluorine) and heated and stirred at 85 ° C in an oil bath. After 4 hours, stop heating,
After cooling to room temperature, the precipitated crystals were filtered through a membrane filter made of tetrafluoroethylene resin (PTFE).

The crystals obtained by filtration were calcined in the same manner as in Example 1 to obtain 6.5 g of tantalum oxide. When the amount of fluorine ions was measured, it was less than 1 ppm.

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Claims (2)

[Claims] 1. A method for crystallizing niobium and / or tantalum, comprising mixing an aqueous solution of niobium and / or tantalum containing fluorine ions with boric acid. 2. An aqueous solution of niobium and / or tantalum containing fluorine ions is mixed with boric acid in an amount of 0.05 to 4 moles per mole of fluorine ions in the aqueous solution to obtain niobium and / or tantalum.
Alternatively, the hydroxide of tantalum is crystallized, and the hydroxide is
A method for producing niobium oxide and / or tantalum oxide, wherein the method is calcined at a temperature of about 1000 ° C.