A method for preparing high-purity zirconium oxide

Abstract

This invention discloses a method for preparing high-purity zirconium oxide, belonging to the field of compound preparation technology. The method provides a breakthrough adjustment of the final concentration state and the cooling process after concentration and evaporation of an acidic zirconium oxychloride solution under the action of an oxidant. Simultaneously, crystallization is achieved through a two-stage concentration and evaporation process, followed by calcination to obtain hafnium-free zirconium oxide. The resulting zirconium oxide not only has a high yield but also high purity. Furthermore, the technical solution of this invention avoids the generation of ammonia nitrogen wastewater as in existing technologies, thus not only avoiding environmental impact but also significantly reducing production costs through the recycling of hydrochloric acid condensation, achieving a green and environmentally friendly effect.

Description

Technical Field

[0001] This invention belongs to the field of compound preparation technology, and particularly relates to a method for preparing high-purity zirconium oxide. Background Technology

[0002] Zirconium oxychloride is an inorganic chemical product, currently mainly produced by the hydrochloric acid method. The process involves melting zircon with caustic soda, rinsing and removing silicon, then reacting with sulfuric acid, followed by the addition of ammonia to obtain zirconium hydroxide precipitate. This precipitate is then dissolved in hydrochloric acid to obtain zirconium oxychloride. Finally, through evaporation, concentration, cooling, crystallization, and crystal crushing, the finished zirconium oxychloride is obtained. Zirconium oxychloride is primarily used as a stabilizer for oilfield formations, a rubber additive, a paint drying agent, a refractory material, and a treatment agent for ceramics, glazes, and fibers. It can also be used in the manufacture of zirconium dioxide and as a coagulant for wastewater treatment in the paper industry.

[0003] Currently, in common preparation processes, zirconium oxychloride dissolves in water and is usually accompanied by hafnium. Therefore, it is necessary to extract zirconium and hafnium using an extractant in a hydrochloric acid system. After the hafnium is extracted, a low-hafnium zirconium oxychloride solution is obtained. Currently, because the extractant in the zirconium oxychloride solution is present and has a certain degree of water solubility, normal concentration and crystallization cannot be carried out. Therefore, the commonly used post-treatment process for the low-hafnium zirconium oxychloride solution involves first adding ammonia water for precipitation, followed by multiple water washings, and then drying and calcining to produce low-hafnium zirconium oxide. Although this process can directly produce low-hafnium zirconium oxide, it requires a large amount of ammonia water, and the numerous water washings generate a large amount of ammonia nitrogen wastewater, which not only pollutes the environment but also has high production costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing high-purity zirconium oxide with high yield, high purity, green environmental protection, and high cost-effectiveness.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing high-purity zirconium oxide, comprising the following steps:

[0006] (1) Add the oxidant dropwise into the acidic solution of zirconium oxychloride, and then heat and evaporate it. When the zirconium oxide content in the system is 145-170 g / L, add hydrochloric acid to adjust the zirconium oxide content in the system to 84.1-95.8 g / L and the acidity to 6.2-6.8 N, to obtain mixed system I.

[0007] (2) Cool and filter the mixture I, collect the slurry, add hydrochloric acid to the slurry until the zirconium oxide content in the system is 75-84.2 g / L, to obtain the mixture II;

[0008] (3) Add the oxidant dropwise into the mixed system II, and then heat and evaporate it; when the zirconium oxide content in the system is 135-145 g / L, add hydrochloric acid to adjust the zirconium oxide content in the system to 101-106.4 g / L and the acidity to 6.3-6.6 N, to obtain the mixed system III;

[0009] (4) Cool and filter the mixed system III, collect the high-purity zirconium oxychloride crystals, dry and calcine the high-purity zirconium oxychloride crystals to obtain high-purity zirconium oxide.

[0010] In the method for preparing zirconium oxide provided by this invention, by selecting a suitable endpoint state for heating and evaporation and the process state after heating, evaporation and cooling, and simultaneously achieving crystallization and calcination through two-stage heating and evaporation, zirconium oxide is obtained. The obtained zirconium oxide has a high yield and high purity, and does not contain hafnium, making it nuclear-grade zirconium oxide. In addition, in the preparation method of this invention, zirconium oxychloride is concentrated and crystallized through two-stage heating and evaporation, which not only breaks through the bottleneck of existing concentration and crystallization technology, but also does not generate a large amount of wastewater. Furthermore, in steps (1) and (3) of this invention, hydrochloric acid can be recovered and reused by condensing the hydrochloric acid that has been heated and evaporated. Therefore, the preparation method provided by this invention does not generate wastewater, that is, the preparation method of this invention also achieves the purpose of being green, environmentally friendly, efficient and economical.

[0011] As a preferred embodiment of the preparation method of the present invention, in step (1), when the zirconium oxide content in the system is heated and evaporated to 160 g / L, hydrochloric acid is added to adjust the zirconium oxide content in the system to 90.75 g / L and the acidity to 6.5 N.

[0012] As a preferred embodiment of the preparation method of the present invention, in step (3), when the zirconium oxide content in the system is heated and evaporated to 140 g / L, hydrochloric acid is added to adjust the zirconium oxide content in the system to 103.7 g / L and the acidity to 6.5 N.

[0013] When the zirconium oxide content in the system after final heating and evaporation in the preferred steps (1) and (3) is the above value, and the zirconium oxide content and acidity in the adjusted system are the above values, the yield and purity of the obtained product are optimal; and the problem of energy waste caused by excessive heating and evaporation (at which time the zirconium content in the system will exceed the preferred range of the present invention) can be avoided, thus achieving the purpose of green energy saving.

[0014] As a preferred embodiment of the preparation method of the present invention, in step (1), the acidic solution of zirconium oxychloride includes zirconium oxychloride extract obtained by extracting and separating zirconium and hafnium using a hydrochloric acid system.

[0015] In a preferred embodiment of the preparation method described in this invention, in step (1), the zirconium oxide content in the acidic solution of zirconium oxychloride is 60-170 g / L, and the acidity is 7.9-8.1 N; preferably, the acidity is 8.0 N. This invention uses the zirconium oxychloride extract solution obtained after extracting and separating zirconium and hafnium using a hydrochloric acid system as the acidic solution for zirconium oxychloride, thereby solving the problems of difficult subsequent treatment of the zirconium oxychloride extract solution and excessive ammonia nitrogen wastewater during treatment in the prior art; thus achieving green and environmentally friendly treatment of the zirconium oxychloride extract solution and obtaining hafnium-free zirconium oxide.

[0016] In a preferred embodiment of the preparation method described in this invention, the oxidant comprises hydrogen peroxide with a mass percentage concentration of 2-5%.

[0017] In a preferred embodiment of the preparation method described in this invention, the oxidant comprises hydrogen peroxide with a mass percentage concentration of 3%.

[0018] In a preferred embodiment of the preparation method described in this invention, the dropping rate of the oxidant is 0.8-1.2 L / min.

[0019] In a preferred embodiment of the preparation method described in this invention, the dropping rate of the oxidant is 1 L / min.

[0020] Hydrogen peroxide is preferred as the oxidant for two reasons: firstly, a 2-5% (w / w) concentration of hydrogen peroxide possesses suitable oxidizing properties; secondly, hydrogen peroxide is environmentally friendly, as its reduction product is water, which does not generate additional impurities or pollution to the reaction system or the environment. Furthermore, controlling the dropping rate of the oxidant to 0.8-1.2 L / min, especially 1 L / min, is crucial. This ensures the uniformity of the reaction during heating and evaporation, guaranteeing product purity, and avoids safety issues caused by excessively rapid addition or excessively vigorous reaction, or low reaction efficiency due to excessively slow addition. Hydrogen peroxide oxidizes organic impurities in the zirconium oxychloride aqueous solution, reducing the negative impact on zirconium oxychloride crystallization. Although some hydrogen peroxide reacts with zirconium oxychloride to form zirconium oxide, zirconium oxide is poorly soluble in water and does not negatively affect the crystallization of zirconium oxychloride. In a preferred embodiment of the preparation method of the present invention, the acidity of the hydrochloric acid is 4.9-5.1N; preferably, the acidity of the hydrochloric acid is 5N; further, dilute hydrochloric acid with an acidity of 5N is used for dissolution, taking into account the solubility of zirconium oxychloride, which has excellent solubility in hydrochloric acid solution at the above acidity.

[0021] In a preferred embodiment of the preparation method of the present invention, in step (1), the heating and evaporation process is to slowly heat and evaporate to a temperature of 118-122℃.

[0022] In a preferred embodiment of the preparation method of the present invention, the heating and evaporation temperature in step (3) is 120-170°C.

[0023] In a preferred embodiment of the preparation method described in this invention, the cooling process is as follows: when the temperature of the mixed system I or the mixed system III is reduced to 80-90°C, the system temperature is reduced to 50-60°C at a cooling rate of 3-5°C / h, and then the system temperature is reduced to 38-42°C at a cooling rate of 4.8-5.2°C / h, and finally cooled to room temperature.

[0024] Controlling the cooling process after heating and evaporation can effectively achieve crystallization, resulting in crystals of appropriate size. This avoids situations where the cooling rate is too fast, preventing the crystals from growing quickly enough, or the cooling rate is too slow, causing the crystals to grow too large.

[0025] In a preferred embodiment of the preparation method of the present invention, in step (4), the calcination temperature is 500-800℃ and the calcination time is 2-4h; preferably, the calcination temperature is 600℃.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] In the preparation method provided by this invention, the concentration endpoint of the acidic zirconium oxychloride solution is adjusted under the action of an oxidant, as well as the cooling process after concentration and evaporation. At the same time, crystallization is achieved through a two-stage concentration and evaporation method, and finally, hafnium-free zirconium oxide is obtained by calcination. The obtained zirconium oxide not only has a good yield but also high purity. Furthermore, the technical solution of this invention can eliminate the generation of ammonia nitrogen wastewater in the prior art, which not only does not affect the environment, but also greatly reduces production costs through the recycling of hydrochloric acid condensation, achieving a green and environmentally friendly effect. Detailed Implementation

[0028] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0029] Example 1

[0030] This invention provides a zirconium oxide, the preparation method of which is as follows:

[0031] (1) After extracting and separating zirconium and hafnium using hydrochloric acid, 5000L of zirconium oxychloride extraction solution was obtained (zirconia content of 80g / L, acidity of 8.0N). A 3% hydrogen peroxide solution was added dropwise to the zirconium oxychloride extraction solution at a dropping rate of 1L / min. When 200L of hydrogen peroxide was consumed, it was added to an evaporator for slow heating and evaporation to a temperature of 120℃. During the heating and evaporation process, the zirconium oxide content and acidity in the solution were monitored, and the gas evaporated was condensed. When the zirconium oxide content in the system reached 145g / L, 2000L of hydrochloric acid was added to adjust the zirconium oxide content in the system to 84.1g / L and the acidity to 6.2N, resulting in mixed system I.

[0032] (2) Cool the mixed system I. When the temperature of mixed system I drops to 80℃, the system temperature is reduced to 60℃ at a cooling rate of 3℃ / h. Then the system temperature is reduced to 40℃ at a cooling rate of 5℃ / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, add dilute hydrochloric acid with an acidity of 5N to adjust the zirconium oxide content in the system to 75g / L, and obtain mixed system II.

[0033] (3) A 2% hydrogen peroxide solution was added dropwise to mixture II at a rate of 1 L / min. Mixture II was heated and evaporated to a temperature of 145°C. During the heating and evaporation process, the concentration of the liquid was measured, and the gas evaporated was condensed. When the zirconium oxide content in the system was 135 g / L, 1000 L of hydrochloric acid was added to adjust the zirconium oxide content in the system to 101 g / L and the acidity to 6.6 N, thus obtaining mixture III.

[0034] (4) Cool the mixed system Ⅲ. When the temperature of mixed system Ⅰ drops to 80℃, the system temperature is reduced to 60℃ at a cooling rate of 3℃ / h. Then the system temperature is reduced to 40℃ at a cooling rate of 5℃ / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, centrifuge them to dry, and then calcine them at 600℃ for 2.5h to obtain zirconium oxide.

[0035] Example 2

[0036] This invention provides a zirconium oxide, the preparation method of which is as follows:

[0037] (1) After extracting and separating zirconium and hafnium using hydrochloric acid, 5000L of zirconium oxychloride extraction solution was obtained (zirconia content was 80g / L, acidity was 8.0N). A 3% (w / w) hydrogen peroxide solution was added dropwise to the 5000L zirconium oxychloride extraction solution at a dropping rate of 1L / min. When 200L of hydrogen peroxide was consumed, it was added to an evaporator for slow heating and evaporation to 120℃. During the heating and evaporation process, the concentration of the solution was monitored, and the gas evaporated was condensed. When the zirconium content in the system reached 160g / L, 1907.7L of hydrochloric acid was added to adjust the zirconium content to 90.75g / L and the acidity to 6.5N, resulting in mixed system I.

[0038] (2) Cool the mixed system I. When the temperature of mixed system I drops to 90℃, the system temperature is reduced to 55℃ at a cooling rate of 4℃ / h. Then the system temperature is reduced to 40℃ at a cooling rate of 5℃ / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, add dilute hydrochloric acid with an acidity of 5N to adjust the zirconium oxide content in the system to 80.3g / L, and obtain mixed system II.

[0039] (3) A 4% hydrogen peroxide solution was added dropwise to mixture II at a rate of 1 L / min. Mixture II was heated and evaporated to a temperature of 170 °C. During the heating and evaporation process, the concentration of the liquid was measured, and the gas evaporated was condensed. When the zirconium oxide content in the system was 140 g / L, 1000 L of hydrochloric acid was added to adjust the zirconium oxide content in the system to 103.7 g / L and the acidity to 6.5 N, thus obtaining mixture III.

[0040] (4) Cool the mixed system Ⅲ. When the temperature of mixed system Ⅰ drops to 90℃, the system temperature is reduced to 55℃ at a cooling rate of 4℃ / h. Then the system temperature is reduced to 40℃ at a cooling rate of 5℃ / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, centrifuge them to dry, and then calcine them at 500℃ for 4h to obtain zirconium oxide.

[0041] Example 3

[0042] This invention provides a zirconium oxide, the preparation method of which is as follows:

[0043] (1) After extracting and separating zirconium and hafnium using hydrochloric acid, 5000L of zirconium oxychloride extraction solution was obtained (zirconia content of 80g / L, acidity of 8.0N). A 3% (w / w) hydrogen peroxide solution was added dropwise to the 5000L zirconium oxychloride extraction solution at a dropping rate of 1L / min. When 200L of hydrogen peroxide was consumed, it was added to an evaporator for slow heating and evaporation to a temperature of 120℃. During the heating and evaporation process, the zirconium oxide content and acidity in the solution were monitored, and the gas evaporated was condensed. When the zirconium oxide content in the system reached 170g / L, 1823.5L of hydrochloric acid was added to adjust the zirconium oxide content to 95.8g / L and the acidity to 6.8N, resulting in mixed system I.

[0044] (2) Cool the mixed system I. When the temperature of mixed system I drops to 85°C, the system temperature is reduced to 50°C at a cooling rate of 5°C / h. Then the system temperature is reduced to 40°C at a cooling rate of 5°C / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, add dilute hydrochloric acid with an acidity of 5N to adjust the zirconium oxide content in the system to 84.2 g / L, and obtain mixed system II.

[0045] (3) A 5% hydrogen peroxide solution was added dropwise to mixture II at a rate of 1 L / min. Mixture II was heated and evaporated to a temperature of 120°C. During the heating and evaporation process, the zirconium oxide content and acidity in the solution were measured, and the gas evaporated was condensed. When the zirconium oxide content in the system was 145 g / L, 1000 L of hydrochloric acid was added to adjust the zirconium oxide content in the system to 106.4 g / L and the acidity to 6.3 N, thus obtaining mixture III.

[0046] (4) Cool the mixed system Ⅲ. When the temperature of mixed system Ⅰ drops to 85℃, the system temperature is reduced to 50℃ at a cooling rate of 5℃ / h. Then the system temperature is reduced to 40℃ at a cooling rate of 5℃ / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, centrifuge them to dry, and then calcine them at 800℃ for 2h to obtain zirconium oxide.

[0047] Example 4

[0048] This invention provides a zirconium oxide, the preparation method of which is as follows:

[0049] (1) After extracting and separating zirconium and hafnium using hydrochloric acid, 5000L of zirconium oxychloride extraction solution was obtained (zirconia content of 80g / L, acidity of 8.0N). A 3% (w / w) hydrogen peroxide solution was added dropwise to the 5000L zirconium oxychloride extraction solution at a dropping rate of 1L / min. When 200L of hydrogen peroxide was consumed, it was added to an evaporator for slow heating and evaporation to 120℃. During the heating and evaporation process, the zirconium oxide content and acidity in the solution were monitored, and the gas evaporated was condensed. When the zirconium oxide content in the system reached 160g / L, 1907.7L of hydrochloric acid was added to adjust the zirconium oxide content to 90.75g / L and the acidity to 6.5N, resulting in mixed system I.

[0050] (2) Cool the mixed system I. When the temperature of mixed system I drops to 85℃, the system temperature is reduced to 50℃ at a cooling rate of 5℃ / h. Then the system temperature is reduced to 40℃ at a cooling rate of 5℃ / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, add dilute hydrochloric acid with an acidity of 5N to adjust the zirconium oxide content in the system to 80.3g / L, and obtain mixed system II.

[0051] (3) A 5% hydrogen peroxide solution was added dropwise to mixture II at a rate of 1 L / min. Mixture II was heated and evaporated to a temperature of 145 °C. During the heating and evaporation process, the zirconium oxide content and acidity in the solution were measured, and the gas evaporated was condensed. When the zirconium oxide content in the system was 140 g / L, 1000 L of hydrochloric acid was added to adjust the zirconium oxide content in the system to 103.7 g / L and the acidity to 6.5 N, thus obtaining mixture III.

[0052] (4) Cool the mixed system Ⅲ. When the temperature of mixed system Ⅰ drops to 85℃, reduce the system temperature to 50℃ at a cooling rate of 5℃ / h. Then reduce the system temperature to 40℃ at a cooling rate of 5℃ / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, centrifuge them to dry, and then calcine them at 600℃ for 2h to obtain zirconium oxide.

[0053] Comparative Example 1

[0054] The present invention provides a zirconium oxide comparative example, the only difference from Example 1 is that in step (2), dilute hydrochloric acid with an acidity of 8N is added to adjust the zirconium oxide content in the system to 75g / L.

[0055] Comparative Example 2

[0056] The present invention provides a zirconium oxide comparative example, the only difference from Example 1 is that in step (1), the zirconium oxide content in the system is heated and evaporated to reach 200 g / L.

[0057] Comparative Example 3

[0058] The present invention provides a comparative example of zirconium oxide, the only difference from Example 1 being that in step (1), hydrochloric acid is added to adjust the zirconium oxide content in the system to 170 g / L and the acidity to 6.8 N.

[0059] Comparative Example 4

[0060] The present invention provides a zirconium oxide comparative example, the only difference from Example 1 is that in step (1), hydrochloric acid is added to adjust the zirconium oxide content in the system to 125 g / L and the acidity to 8 N.

[0061] Comparative Example 5

[0062] This invention provides a comparative example of zirconium oxide, the preparation method of which is as follows:

[0063] (1) After extracting and separating zirconium and hafnium using hydrochloric acid, 5000L of zirconium oxychloride extraction solution was obtained (zirconia content was 80g / L, acidity was 8.0N). A 3% hydrogen peroxide solution was added dropwise to the 5000L zirconium oxychloride extraction solution at a dropping rate of 1L / min. When 200L of hydrogen peroxide was consumed, it was added to an evaporator for slow heating and evaporation to a temperature of 120℃. During the heating and evaporation process, the zirconium oxide content and acidity in the solution were monitored, and the gas evaporated was condensed. When the zirconium oxide content in the system reached 145g / L, 2000L of hydrochloric acid was added to adjust the zirconium oxide content in the system to 84.1g / L and the acidity to 6.2N, resulting in mixed system I.

[0064] (2) Cool the mixed system I. When the temperature of mixed system I drops to 80°C, reduce the system temperature to 60°C at a cooling rate of 3°C / h, then reduce the system temperature to 40°C at a cooling rate of 5°C / h. Finally, cool to room temperature, filter, collect zirconium oxychloride crystals, centrifuge them to dry, and then calcine them at 600°C for 2.5h to obtain zirconium oxide.

[0065] Comparative Example 6

[0066] The present invention provides a zirconium oxide comparative example, the only difference from Example 1 is that in step (3), hydrochloric acid is added to adjust the zirconium oxide content in the system to 100 g / L.

[0067] Example of effect

[0068] This effect example records the purity, yield, and impurity element content of the zirconium oxide prepared in Examples 1-4 and Comparative Examples 1-6. The specific statistics are shown in Table 1.

[0069] Table 1

[0070]

[0071]

[0072] As can be seen from Table 1, when the technical solution of the present invention is adopted, the purity of the obtained product is above 99.76%, the yield is above 75.23%, and the content of other impurity elements is below 67 ppm.

[0073] As can be seen from Example 1 and Comparative Example 1, when dilute hydrochloric acid is added for dissolution, if the acidity of the added dilute hydrochloric acid is too high, the yield of zirconium oxide will be reduced, and the purity of zirconium oxide will also show a downward trend to some extent.

[0074] As can be seen from Example 1 and Comparative Examples 2-4, changing the endpoint state after the first heating and evaporation or changing the adjusted state after heating and evaporation will have a significant impact on the yield or purity of the product.

[0075] As can be seen from Example 1 and Comparative Example 5, when only one heating evaporation and cooling is used, the purity of the product decreases significantly, and the content of other elements in zirconium oxide increases significantly.

[0076] As can be seen from Example 1 and Comparative Example 6, when the adjusted state after the second heating and evaporation is changed, the yield shows a significant decrease.

[0077] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing high-purity zirconium oxide, characterized in that, Includes the following steps: (1) Add the oxidant dropwise into the acidic solution of zirconium oxychloride, and then heat and evaporate it; when the zirconium oxide content in the system is 145-170 g / L, add hydrochloric acid to adjust the zirconium oxide content in the system to 84.1-95.8 g / L and the acidity to 6.2-6.8 N, to obtain mixed system I; (2) Cool and filter the mixed system I, collect the zirconium oxychloride crystals, add hydrochloric acid to the zirconium oxychloride crystals until the zirconium oxide content concentration in the system is 75-84.2 g / L, to obtain the mixed system II; (3) Add the oxidant dropwise into the mixed system II, and then heat and evaporate it; when the zirconium oxide content in the system is 135-145 g / L, add hydrochloric acid to adjust the zirconium oxide content in the system to 101-106.4 g / L and the acidity to 6.3-6.6 N, to obtain the mixed system III; (4) Cool, filter, and collect the high-purity zirconium oxychloride crystals from the mixed system III, and dry and calcine the high-purity zirconium oxychloride crystals to obtain high-purity zirconium oxide; In step (1), the acidic solution of zirconium oxychloride includes zirconium oxychloride extract obtained by extracting and separating zirconium and hafnium using a hydrochloric acid system. The hydrochloric acid has an acidity of 4.9-5.1 N.

2. The preparation method according to claim 1, characterized in that, The oxidant includes hydrogen peroxide with a mass percentage concentration of 2-5%.

3. The preparation method according to claim 1, characterized in that, The oxidant is added at a rate of 0.8-1.2 L / min.

4. The preparation method according to claim 1, characterized in that, In step (1), the heating and evaporation process involves slowly heating and evaporating to a temperature of 118-122℃.

5. The preparation method according to claim 1, characterized in that, In step (3), the heating and evaporation temperature is 120-170℃.

6. The preparation method according to claim 1, characterized in that, The cooling process is as follows: when the temperature of mixture system I or mixture system III is reduced to 80-90℃, the system temperature is reduced to 50-60℃ at a cooling rate of 3-5℃ / h, then the system temperature is reduced to 38-42℃ at a cooling rate of 4.8-5.2℃ / h, and finally cooled to room temperature.

7. The preparation method according to claim 1, characterized in that, In step (4), the burning temperature is 500-800℃ and the burning time is 2-4h.

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