Preparation method of high-purity spherical bismuth hydroxide

Abstract

The application discloses a preparation method of high-purity spherical bismuth hydroxide. The method comprises the following steps: dissolving bismuth oxide in excessive concentrated nitric acid and evaporating to remove excessive nitric acid to obtain a bismuth nitrate solution; cooling and crystallizing the bismuth nitrate solution, and performing solid-liquid separation to obtain solid bismuth nitrate; slowly adding the solid bismuth nitrate into ammonia water containing citric acid under stirring to perform reaction; and after the reaction reaches an end point, performing filtration, washing and drying in sequence. The method can obtain bismuth hydroxide with a purity of 5N or above, uniform particle size and approximate spherical morphology, and has a higher application prospect compared with conventional bismuth hydroxide.

Description

Technical Field

[0001] This invention relates to a method for preparing bismuth hydroxide, and particularly to a method for preparing high-purity spherical bismuth hydroxide, belonging to the field of bismuth hydroxide preparation technology. Background Technology

[0002] Currently, bismuth hydroxide is mainly used for doping and modifying paints and for producing bismuth salts, and there is relatively little research on bismuth hydroxide in existing technologies.

[0003] The existing traditional method for producing bismuth hydroxide involves dissolving metallic bismuth or bismuth oxide with acid, neutralizing it with alkali, and then filtering, drying, and pulverizing the material to obtain bismuth hydroxide. The prepared bismuth hydroxide contains many impurity compounds, such as bismuth oxynitrate, bismuth oxychloride, and other bismuth compounds. Furthermore, the resulting bismuth hydroxide is in block form, requiring further pulverization to obtain irregular particles, leading to poor application performance. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing high-purity spherical bismuth hydroxide. This method can obtain bismuth hydroxide with a purity of 5N or higher, uniform particle size, and approximately spherical morphology, which has higher application prospects than conventional bismuth hydroxide.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing high-purity spherical bismuth hydroxide, the method comprising the following steps:

[0006] 1) Dissolve bismuth oxide in excess concentrated nitric acid and evaporate to remove excess nitric acid to obtain bismuth nitrate solution;

[0007] 2) The bismuth nitrate solution is cooled and crystallized, and solid-liquid separation is performed to obtain solid bismuth nitrate;

[0008] 3) Solid bismuth nitrate was slowly added to ammonia water containing citric acid under stirring to carry out the reaction. After the reaction reached the endpoint, the mixture was filtered, washed and dried in sequence.

[0009] In the preparation of high-purity spherical bismuth hydroxide, this invention involves two key aspects. First, the bismuth oxide raw material undergoes acid hydrolysis and crystallization to further remove impurities, yielding 99.999% high-purity bismuth nitrate raw material, which is beneficial for subsequent production of bismuth hydroxide of grade 5N or higher. Second, and crucially, using solid bismuth nitrate as the raw material and ammonia water containing citric acid as the neutralizing agent, this process produces bismuth hydroxide with uniform particles and a near-spherical morphology. Citric acid plays a crucial role in generating uniformly shaped, near-spherical bismuth hydroxide. In ammonia water, citric acid exists as ammonium citrate, which can capture bismuth ions generated from the slow hydrolysis of solid bismuth nitrate through ammonium ion exchange, forming highly dispersed chelated molecules. This facilitates the uniform nucleation of bismuth hydroxide. The chelated bismuth ions are then converted into bismuth hydroxide under the action of ammonia water, while citric acid induces the growth of bismuth hydroxide crystals to form spherical particles, ultimately resulting in uniformly shaped, near-spherical bismuth hydroxide.

[0010] As a preferred embodiment, the bismuth oxide is of the 3N to 4N grade. 3N or 4N grade bismuth oxide is a readily available raw material in the prior art, and using it as a raw material for preparing bismuth nitrate makes it easier to obtain 5N grade bismuth nitrate.

[0011] As a preferred embodiment, the mass ratio of bismuth oxide to concentrated nitric acid is 1:(3-5). Excess nitric acid promotes the complete conversion of bismuth oxide to bismuth nitrate. Concentrated nitric acid is a common analytical grade raw material.

[0012] As a preferred embodiment, the bismuth ion concentration in the bismuth nitrate solution is controlled within the range of 200–350 g / L. Concentrating the bismuth nitrate solution to an appropriate range is more conducive to the cooling and crystallization of bismuth nitrate. If the bismuth ion concentration is too high, impurities are easily carried over and precipitated; if the bismuth ion concentration is too low, the amount of bismuth nitrate precipitated will be low.

[0013] As a preferred embodiment, the cooling crystallization temperature is -5℃ to 0℃. Within the preferred temperature range, the precipitation of bismuth nitrate is favorable. If the temperature is too low, the precipitation rate of bismuth nitrate is too fast, which easily leads to the precipitation of impurities. If the temperature is too high, the precipitation rate of bismuth nitrate is slow.

[0014] As a preferred embodiment, the solid-liquid separation employs low-temperature refrigerated centrifugation, with a freezing temperature of -5°C to 0°C. Low-temperature centrifugation can reduce the amount of bismuth nitrate dissolving back into the crystallization mother liquor.

[0015] As a preferred embodiment, the ammonia concentration in the ammonia solution containing citric acid is 5wt%–25wt%, and the citric acid concentration is 0.1–0.5 g / L. The concentration of citric acid affects the growth process of bismuth hydroxide crystals, thereby affecting the crystal morphology. Within the preferred concentration range, the uniformity of bismuth hydroxide particle size and spherical morphology can be ensured. As a preferred embodiment, the endpoint pH of the reaction is 7–9. Bismuth nitrate hydrolyzes to a weakly acidic state; by controlling the endpoint pH to be slightly alkaline, bismuth nitrate can be completely converted into bismuth hydroxide.

[0016] As a preferred embodiment, the drying is performed at a temperature of 85–95°C.

[0017] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0018] The bismuth hydroxide prepared by this invention can achieve a purity of over 99.999%, with uniform particles and a spherical morphology.

[0019] The preparation method of the present invention is simple to operate, low in energy consumption, highly efficient, and environmentally friendly. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the bismuth hydroxide product prepared in Example 2.

[0021] Figure 2 Scanning electron microscope image of the bismuth hydroxide product prepared in Comparative Example 1. Detailed Implementation

[0022] The following specific embodiments are intended to further illustrate the content of the present invention, rather than to limit the scope of protection of the claims.

[0023] Unless otherwise specified, all reagents used in the following specific examples are of analytical grade, and the water used is deionized water.

[0024] Example 1

[0025] Bismuth oxide with a purity of 3N (99.9%) was added to a glass reactor at a weight ratio of 1:3 with concentrated nitric acid. The reactor was heated at 100°C with stirring until the bismuth oxide was completely dissolved. The reactor temperature was then adjusted to 105°C, and the solution was heated and concentrated until the bismuth ion content was 200 g / L. The solution was then transferred to a polytetrafluoroethylene beaker, sealed, and placed at -5°C for 2 hours. After crystallization, the material was added to a refrigerated centrifuge for solid-liquid separation at -5°C. The separated solid bismuth nitrate was then slowly added to ammonia water with a concentration of 0.1 g / L citric acid and 5% ammonia concentration under stirring. The pH was adjusted to 7 to end the reaction. The resulting material was vacuum filtered, washed with deionized water, and then dried at 85°C until the weight no longer changed.

[0026] The bismuth hydroxide prepared in this embodiment has a purity of 99.999%, and also has uniform particle size, a particle size of about 1 micrometer, and a spherical morphology.

[0027] Example 2

[0028] Bismuth oxide with a purity of 4N (99.9%) was added to a glass reactor at a weight ratio of 1:5 with concentrated nitric acid. The reactor was heated at 100°C with stirring until the bismuth oxide was completely dissolved. The reactor temperature was then adjusted to 105°C, and the solution was heated and concentrated until the bismuth ion content was 350 g / L. The solution was then transferred to a polytetrafluoroethylene beaker, sealed, and placed at 0°C for 4 hours. After crystallization, the material was added to a refrigerated centrifuge for solid-liquid separation. The separated solid bismuth nitrate was slowly added to ammonia water with a citric acid concentration of 0.5 g / L and an ammonia concentration of 25% under stirring. The pH was adjusted to 9 to end the reaction. The resulting material was vacuum filtered, washed with deionized water, and then dried at 95°C until the weight no longer changed.

[0029] The bismuth hydroxide prepared in this example has a purity of 99.999%, and the main impurities and their contents are shown in Table 1. The specific morphology of the bismuth hydroxide is as follows: Figure 1 As shown, it can be seen that it has a spherical morphology and uniform particle size, with a particle size of about 800 nm.

[0030] Table 1. Detection results of bismuth hydroxide (impurity content / ppm):

[0031] 0.3 0.1 0.2 0.1 0.1 0.1 0.1 0.2 0.1 0.1 0.2 Mn Sb Cr Co Zr Na Ca Si Ag Cl Ti 0.1 / / / / 0.1 0.2 0.1 0.1 / /

[0032] Comparative Example 1

[0033] Bismuth oxide with a purity of 4N (99.9%) was added to a glass reactor at a weight ratio of 1:5 with concentrated nitric acid. The reactor was heated to 100°C with stirring until the bismuth oxide was completely dissolved. The reactor temperature was then adjusted to 105°C, and the solution was heated and concentrated until the bismuth ion content was 350 g / L. The solution was then slowly added to ammonia water with a concentration of 25% with stirring. The pH was adjusted to 9 to end the reaction. The resulting material was vacuum filtered, washed with deionized water, and then dried at 95°C until the weight no longer changed. The bismuth hydroxide obtained was shown to be in an amorphous state under an electron microscope.

[0034] Table 2. Detection results of bismuth hydroxide (impurity content / ppm):

[0035] 0.5 0.2 3.1 0.5 0.8 0.5 0.2 0.2 0.6 0.2 0.5 Mn Sb Cr Co Zr Na Ca Si Ag Cl Ti 0.1 / / / / 5.4 2.1 0.5 1.8 / /

[0036] For the reader's convenience, the above description focuses on representative examples of all possible embodiments, which illustrate the principles of the invention and demonstrate the best mode for carrying out the invention. This description does not attempt to exhaustively list all possible variations. Other variations or modifications not described may also be possible.

Claims

1. A method for preparing high-purity spherical bismuth hydroxide, characterized in that: Includes the following steps: 1) Dissolve bismuth oxide in excess concentrated nitric acid and evaporate to remove excess nitric acid to obtain bismuth nitrate solution; 2) The bismuth nitrate solution is cooled and crystallized, and solid-liquid separation is performed to obtain solid bismuth nitrate; 3) Solid bismuth nitrate was slowly added to ammonia water containing citric acid under stirring to carry out the reaction. After the reaction reached the endpoint, the mixture was filtered, washed and dried in sequence. The concentration of citric acid in the ammonia water containing citric acid is 0.1~0.5g / L.

2. The method for preparing high-purity spherical bismuth hydroxide according to claim 1, characterized in that: The bismuth oxide is of the 3N to 4N grade.

3. The method for preparing high-purity spherical bismuth hydroxide according to claim 1 or 2, characterized in that: The mass ratio of bismuth oxide to concentrated nitric acid is 1:(3~5).

4. The method for preparing high-purity spherical bismuth hydroxide according to claim 1, characterized in that: The concentration of bismuth ions in the bismuth nitrate solution is controlled within the range of 200~350 g / L.

5. The method for preparing high-purity spherical bismuth hydroxide according to claim 1, characterized in that: The cooling crystallization temperature is -5℃ to 0℃.

6. The method for preparing high-purity spherical bismuth hydroxide according to claim 1, characterized in that: The solid-liquid separation is performed using low-temperature refrigerated centrifugation, with a freezing temperature of -5℃ to 0℃.

7. The method for preparing high-purity spherical bismuth hydroxide according to claim 1, characterized in that: The ammonia concentration in the ammonia water containing citric acid is 5wt% to 25wt%.

8. The method for preparing high-purity spherical bismuth hydroxide according to claim 1, characterized in that: The final pH of the reaction is 7-9.

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