High-purity hafnium oxide and preparation method thereof

Abstract

The invention discloses high-purity hafnium oxide and a preparation method thereof, and relates to the technical field of hydrometallurgy. The preparation method of the high-purity hafnium oxide comprises the following steps: crushing a hafnium oxide raw material to obtain hafnium oxide powder; sequentially carrying out alkali fusion, water immersion and filtration treatment on the hafnium oxide powder to obtain a hafnium hydroxide filter cake; dissolving the hafnium hydroxide filter cake in a sulfuric acid solution to obtain a hafnium sulfate solution; adding sodium sulfate into the hafnium sulfate solution to obtain hafnium-containing double salt; dissolving the hafnium-containing double salt in a sulfuric acid solution, heating, evaporating, cooling and crystallizing to obtain hafnium sulfate crystals; dissolving the hafnium sulfate crystal in concentrated hydrochloric acid to obtain a hafnium oxychloride solution, heating, evaporating, cooling and crystallizing to obtain a hafnium oxychloride crystal; dissolving the hafnium oxychloride crystal in pure water, adding an oxalic acid solution, and precipitating to obtain hafnium oxalate; and calcining hafnium oxalate to obtain high-purity hafnium oxide. The preparation method of the high-purity hafnium oxide is green, environment-friendly, simple and efficient.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to high-purity hafnium oxide and a preparation method thereof. Background Art

[0002] Hafnium oxide has the characteristics of high hardness, high wear resistance, high thermal stability and high optical refractive index, and is widely used in ceramics, coatings, electronic materials, optical materials, refractory materials and other fields. High-purity hafnium oxide has broad market prospects. In the field of ceramics, it can be used as a ceramic sintering agent to improve the properties of ceramics and enhance their high temperature resistance, acid and alkali resistance and mechanical strength; in the field of aerospace, hafnium oxide is widely used in rocket nozzle materials, gas turbine blades, and aviation engine combustion chamber liners; hafnium oxide is also an important electronic device material due to its excellent insulation properties, and is widely used in transistor devices, capacitor materials, high-frequency microwave devices, microprocessors and other electronic devices; in addition, high-purity hafnium oxide can also be used as a high-quality raw material for the preparation of high-purity hafnium tetrachloride, sponge hafnium and other products.

[0003] At present, the main processes for purifying hafnium oxide impurities are solvent extraction and sublimation. These methods have long cycles, low yields and high costs. Among them, the sublimation method has high equipment costs, long operation time, and large product losses. It is not suitable for the purification of large quantities of products and requires high-temperature chlorine treatment, which poses a greater safety risk. The organic solvents used in the solvent extraction method are volatile, flammable, and explosive, and pose a greater potential risk to the environment and human health, requiring strict safety measures. Therefore, it is of great significance to develop an efficient, low-consumption, green and environmentally friendly hafnium oxide purification process. Summary of the invention

[0004] The invention provides a green, environmentally friendly, simple and efficient method for preparing high-purity hafnium oxide.

[0005] The method for preparing high-purity hafnium oxide provided by the present invention comprises the following steps:

[0006] S1, crushing hafnium oxide raw materials to obtain hafnium oxide powder;

[0007] S2, treating the hafnium oxide powder by alkali melting, water immersion and filtration in sequence to obtain a hafnium hydroxide filter cake;

[0008] S3, dissolving the hafnium hydroxide filter cake in a sulfuric acid solution to obtain a hafnium sulfate solution; adding sodium sulfate to the hafnium sulfate solution to obtain a hafnium-containing double salt;

[0009] S4, dissolving the hafnium-containing complex salt in a sulfuric acid solution, heating to evaporate, and cooling to crystallize to obtain hafnium sulfate crystals;

[0010] S5, dissolving the hafnium sulfate crystals in concentrated hydrochloric acid to obtain a hafnium oxychloride solution, heating to evaporate, cooling to crystallize, and obtaining hafnium oxychloride crystals;

[0011] S6, dissolving the hafnium oxychloride crystals in pure water, filtering, adding oxalic acid solution, and precipitating to obtain hafnium oxalate;

[0012] S7, calcining the hafnium oxalate to obtain high-purity hafnium oxide.

[0013] Optionally, in step S2, the alkali fusion treatment specifically includes:

[0014] The hafnium oxide powder is mixed with solid alkali and potassium nitrate in a mass ratio of 1:2-5:0.1-0.2, and then put into a crucible of an alkali melting furnace, heated to 500-800° C. for reaction for 2-8 hours, cooled to 400° C., and then the reaction material is poured out;

[0015] Alternatively, the hafnium oxide powder is mixed with solid alkali and sodium peroxide in a mass ratio of 1:2-5:0.1-0.2 and then loaded into a crucible of an alkali melting furnace, heated to 500-800° C. for reaction for 2-8 hours, cooled to 400° C. and then the reaction material is poured out.

[0016] Optionally, in step S2, the water immersion and filtration process specifically includes:

[0017] The cooled reaction material is dissolved in pure water at a liquid-to-solid ratio of 3-5:1, reacted at 75° C.-85° C. for 1-4 hours, and filtered to obtain the hafnium hydroxide filter cake.

[0018] Optionally, the step S3 specifically includes:

[0019] The hafnium hydroxide filter cake is dissolved in 100-200 g / L sulfuric acid solution, reacted at 55-85° C. for 1-2 hours, and completely dissolved to obtain the hafnium sulfate solution; sodium sulfate is added to the hafnium sulfate solution, the amount of sodium sulfate added is 100-300 g / L, and the mixture is kept warm for reaction at 50-70° C. for 3-8 hours, and then filtered to obtain the hafnium-containing complex salt.

[0020] Optionally, the step S4 specifically includes:

[0021] The hafnium-containing complex salt is dissolved in 300-400 g / L sulfuric acid solution, heated to 100-120° C. and kept warm for 2-6 hours, cooled and crystallized when crystals are precipitated, and centrifuged to obtain the hafnium sulfate crystals.

[0022] Optionally, in step S5, the hafnium content in the hafnium oxychloride solution is 150-200 g / L, and the step of cooling and crystallizing to obtain hafnium oxychloride crystals specifically includes:

[0023] The hafnium oxychloride solution is heated to 100-150° C. and kept warm for 2-5 hours. When crystals are precipitated, the solution is cooled and crystallized, and centrifuged to obtain the hafnium oxychloride crystals.

[0024] Optionally, the step S6 specifically includes:

[0025] The hafnium oxychloride crystals are completely dissolved in pure water at a solid-liquid ratio of 1:1-2, filtered and added into a 70-85 g / L oxalic acid solution, heated to 60°C-80°C for reaction for 2-4 hours, filtered and precipitated to obtain hafnium oxalate; wherein the amount of oxalic acid added is 1.3-1.6 times the total amount of hafnium.

[0026] Optionally, the step S7 specifically includes:

[0027] The hafnium oxalate washed with pure water is placed in a crucible, and the temperature is raised to 700° C. to 900° C. for reaction for 2 to 6 hours to obtain the high-purity hafnium oxide.

[0028] Optionally, in the step S1, the 200 mesh pass rate of the hafnium oxide powder is greater than 99%.

[0029] The present invention has the following beneficial effects:

[0030] The high-purity hafnium oxide preparation method provided by the present invention crushes the hafnium oxide raw material, and then adopts the process flow of alkali melting-water immersion-dissolution-sodium sulfate impurity removal-evaporation crystallization-oxalic acid precipitation-washing-calcination to efficiently recover the valuable hafnium metal therein to prepare high-purity hafnium oxide. The process flow is simple and has the following advantages:

[0031] 1. The material is treated by alkali fusion, which effectively avoids the danger of high temperature chlorine gas in the traditional chlorination process;

[0032] 2. Alkali fusion can remove alkali-soluble impurities directly through water leaching, and sodium sulfate impurity removal further effectively improves the purity of hafnium and has a higher hafnium recovery rate;

[0033] 3. The evaporation crystallization of sulfuric acid system and hydrochloric acid system avoids the use of extraction process, improves the purity of hafnium, does not involve the use of extraction agent, has a short recovery cycle, is environmentally friendly, and is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0035] Figure 1 It is a flowchart of some embodiments of the method for preparing high-purity hafnium oxide of the present invention;

[0036] Figure 2The figure is a process flow chart of some embodiments of the method for preparing high-purity hafnium oxide of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The embodiment of the present invention provides a green, environmentally friendly, simple and efficient method for preparing high-purity hafnium oxide.

[0039] See also Figure 1 The method for preparing high-purity hafnium oxide provided by the embodiment of the present invention comprises the following steps:

[0040] S1, crushing and fine grinding: crushing the hafnium oxide raw material to obtain hafnium oxide powder.

[0041] In some embodiments, the hafnium oxide raw material may be waste hafnium oxide target materials, so as to achieve the recycling of waste hafnium oxide target materials.

[0042] In some embodiments, the hafnium oxide raw material is crushed and ground to obtain hafnium oxide powder with a 200 mesh pass rate greater than 99%.

[0043] S2, alkali melting and water immersion: the hafnium oxide powder is sequentially subjected to alkali melting, water immersion and filtration to obtain a hafnium hydroxide filter cake.

[0044] In this step, the material is treated by alkali fusion, which effectively avoids the high safety risk of treating hafnium oxide under high-temperature chlorine gas in traditional purification methods.

[0045] In this step, alkali fusion can remove the impurities dissolved in alkali directly through water leaching, thereby improving the purity of the prepared hafnium oxide.

[0046] In some embodiments, the alkali fusion treatment specifically includes:

[0047] Mix hafnium oxide powder, solid alkali and potassium nitrate in a mass ratio of 1:2~5:0.1~0.2 and put them into the nickel crucible of the alkali melting furnace, heat to 500-800℃ and react for 2~8h, cool to 400℃ and pour out the reaction materials to cool.

[0048] In some other embodiments, the alkali fusion treatment specifically includes:

[0049] Mix hafnium oxide powder, solid alkali and sodium peroxide in a mass ratio of 1:2~5:0.1~0.2 and put them into the crucible of the alkali melting furnace, heat to 500-800℃ and react for 2~8h, cool to 400℃ and pour out the reaction materials to cool.

[0050] In some embodiments, the water immersion and filtration process specifically includes:

[0051] The cooled reaction mass is dissolved in pure water at a liquid-to-solid ratio of 3-5:1, reacted at 75°C-85°C for 1-4 hours, and filtered to obtain a hafnium hydroxide filter cake.

[0052] S3, acid leaching-impurity removal: dissolving the hafnium hydroxide filter cake in a sulfuric acid solution to obtain a hafnium sulfate solution; adding sodium sulfate to the hafnium sulfate solution to obtain a hafnium-containing complex salt.

[0053] In this step, hafnium sulfate and sodium sulfate form a hafnium-containing complex salt. Impurities in the hafnium sulfate solution that do not form a complex salt with sodium sulfate can be removed by filtration, thereby effectively improving the purity of the prepared hafnium oxide, and the recovery rate can reach more than 98%, reducing the loss of hafnium.

[0054] In some embodiments, the step specifically includes:

[0055] The hafnium hydroxide filter cake is dissolved in 100-200 g / L sulfuric acid solution, reacted at 55-85°C for 1-2 hours, and completely dissolved to obtain a hafnium sulfate solution; sodium sulfate is added to the hafnium sulfate solution, the amount of sodium sulfate added is 100-300 g / L, and after keeping the temperature at 50-70°C for 3-8 hours, filter-pressing is performed to obtain a hafnium-containing complex salt.

[0056] S4, primary evaporation crystallization: dissolving the hafnium-containing complex salt in a sulfuric acid solution, heating for evaporation and cooling for crystallization to obtain hafnium sulfate crystals.

[0057] In some embodiments, the step specifically includes:

[0058] Dissolve the hafnium-containing complex salt in 300-400 g / L sulfuric acid solution, heat to 100-120°C and keep warm for 2-6 hours, cool and crystallize when crystals precipitate, and centrifuge to obtain hafnium sulfate crystals.

[0059] S5, secondary evaporation crystallization: dissolving hafnium sulfate crystals in concentrated hydrochloric acid to obtain hafnium oxychloride solution, heating to evaporate and cooling to crystallize to obtain hafnium oxychloride crystals.

[0060] In some embodiments, the step specifically includes:

[0061] Take the hafnium sulfate crystals obtained in the previous step, add concentrated hydrochloric acid to dissolve, and obtain a hafnium oxychloride solution with a hafnium content of 150-200 g / L. Heat the dissolved hafnium oxychloride solution to 100-150° C. and keep it warm for 2-5 hours. When crystals precipitate, cool and crystallize them, and centrifuge to obtain hafnium oxychloride crystals.

[0062] S6, dissolving hafnium oxychloride crystals in pure water, adding oxalic acid solution, and precipitating to obtain hafnium oxalate.

[0063] In some embodiments, the step specifically includes:

[0064] The hafnium oxychloride crystals are completely dissolved in pure water at a solid-liquid ratio of 1:1~2, filtered and added to a 70~85g / L oxalic acid solution, the amount of oxalic acid added being 1.3~1.6 times the total amount of hafnium, heated to 60℃~80℃ for reaction for 2~4h, filtered and precipitated to obtain hafnium oxalate.

[0065] S7, calcining hafnium oxalate to obtain high-purity hafnium oxide.

[0066] In some embodiments, the step specifically includes:

[0067] The hafnium oxalate is washed with pure water, and the hafnium oxalate washed with pure water is put into a quartz crucible, and the temperature is raised to 700°C~900°C for reaction for 2~6 hours to obtain high-purity hafnium oxide.

[0068] The embodiment combining the above steps can prepare hafnium oxide with a purity of more than 99.95%. The impurity content in the product except Zr is less than 1 ppm as detected by ICP-OES.

[0069] The method for preparing high-purity hafnium oxide proposed in the embodiment of the present invention, compared with the prior art, treats the material by alkali fusion, effectively avoiding the danger of chlorine in the chlorination process; alkali fusion can directly remove impurities dissolved in alkali by water leaching, and sodium sulfate impurity removal effectively improves the purity of hafnium, and the recovery rate of hafnium can reach more than 98%, reducing the loss of hafnium; the evaporation crystallization of sulfuric acid system and hydrochloric acid system avoids the use of extraction process, greatly improves the purity of hafnium solution, and the purity of hafnium oxide prepared is higher than 99.95%. The whole process is simple to operate, can be processed in large quantities, does not involve the use of high-temperature chlorine and extractant, has a short recovery period, and has the advantages of being green, environmentally friendly, simple and efficient.

[0070] The present invention is further described below in conjunction with specific embodiments.

[0071] It should be noted that the following are preferred specific embodiments of the present invention, which are not limitations of the present invention. Those skilled in the art may adjust specific parameters based on these embodiments to obtain more embodiments, but these embodiments do not depart from the spirit and scope of the technical solution of the present invention.

[0072] Example 1

[0073] Crushing and fine grinding: The waste hafnium oxide target material is crushed and ground to obtain a 200-mesh powder with a pass rate of 99.3%.

[0074] Alkali dissolution: Mix hafnium oxide powder, solid alkali, potassium nitrate or sodium peroxide in a mass ratio of 1:2:0.1~0.2 and put it into the nickel crucible of the alkali melting furnace, heat it to 500℃, react for 2h, cool it to 400℃, turn the alkali melting furnace to pour out the reacted materials and cool them down.

[0075] Water leaching: dissolve the cooled material in pure water at a liquid-to-solid ratio of 3:1, react at 75°C for 1 hour, and filter to obtain the water leaching liquid and hafnium hydroxide filter cake.

[0076] Acid leaching-impurity removal: Add the hafnium hydroxide filter cake after water leaching into sulfuric acid solution for acid leaching. The sulfuric acid concentration is 100g / L. React at 55℃ for 1h. After complete dissolution, obtain hafnium sulfate solution. Add analytical pure sodium sulfate at 100-300g / L to the hafnium sulfate solution. Heat to 50℃, keep warm for 3h, and filter to obtain hafnium-containing complex salt and impurity-removed liquid.

[0077] Primary evaporation crystallization: Take a hafnium-containing complex salt, add sulfuric acid solution to dissolve it, obtain hafnium sulfate solution, control the sulfuric acid concentration to 300g / L, raise the temperature to 100°C, keep warm for 2h, cool and crystallize when crystals precipitate, and centrifuge to obtain hafnium sulfate crystals and mother liquor.

[0078] Secondary evaporation crystallization: Take hafnium sulfate crystals, add concentrated hydrochloric acid solution to dissolve, and obtain hafnium oxychloride solution with a hafnium content of 150 g / L. Heat the dissolved solution to 100°C and keep it warm for 2 hours. When crystals precipitate, cool and crystallize, and centrifuge to obtain hafnium oxychloride crystals and mother liquor.

[0079] Crystal dissolution: Add pure water at a solid-liquid ratio of 1:1 to dissolve the hafnium oxychloride crystals, stir until completely dissolved, and filter to obtain the hafnium oxychloride solution.

[0080] Precipitation-washing-calcination: add hafnium oxychloride solution to 70g / L oxalic acid solution, the amount of oxalic acid added is 1.3 times the total amount of hafnium metal, heat to 60℃ and react for 2h, filter to obtain hafnium oxalate; wash the hafnium oxalate with pure water and put it into a quartz crucible, heat to 700℃ and react for 2h to obtain hafnium oxide with a purity of 99.96%. ICP-OES test shows that the impurity content of the product except Zr is less than 1ppm.

[0081] Example 2

[0082] Crushing and fine grinding: The waste hafnium oxide target material is crushed and ground to obtain a 200 mesh powder with a pass rate of 99.9%.

[0083] Alkali dissolution: Mix hafnium oxide powder, solid alkali, potassium nitrate or sodium peroxide in a mass ratio of 1:5:0.2 and put it into the nickel crucible of the alkali melting furnace, heat it to 800℃, react for 8h, cool it to 400℃, turn the alkali melting furnace to pour out the reacted material and cool it down.

[0084] Water leaching: dissolve the cooled material in pure water at a liquid-to-solid ratio of 5:1, react at 85°C for 4 hours, and filter to obtain the water leaching liquid and hafnium hydroxide filter cake.

[0085] Acid leaching-impurity removal: The hafnium hydroxide filter cake after water leaching is added to a sulfuric acid solution for acid leaching. The sulfuric acid concentration is 200 g / L. The reaction is carried out at 85°C for 2 hours. After complete dissolution, a hafnium sulfate solution is obtained. Analytical pure sodium sulfate is added to the hafnium sulfate solution at a rate of 300 g / L. The temperature is raised to 70°C. The reaction is kept warm for 8 hours. The hafnium-containing complex salt and the impurity-removed liquid are obtained by filter pressing.

[0086] Primary evaporation crystallization: Take a hafnium-containing complex salt, add sulfuric acid solution to dissolve it, obtain hafnium sulfate solution, control the sulfuric acid concentration to 400g / L, raise the temperature to 120°C, keep warm for 6h, stop heating and stirring when crystals precipitate, cool and crystallize, and centrifuge to obtain hafnium sulfate crystals and mother liquor.

[0087] Secondary evaporation crystallization: Take hafnium sulfate crystals, add concentrated hydrochloric acid solution to dissolve, and obtain hafnium oxychloride solution with a hafnium content of 200 g / L. Heat the dissolved solution to 150°C and keep it warm for 5 hours. When crystals precipitate, stop heating and stirring, cool and crystallize, and centrifuge to obtain hafnium oxychloride crystals and mother liquor.

[0088] Crystal dissolution: Add pure water at a solid-liquid ratio of 1:2 to dissolve the hafnium oxychloride crystals, stir until completely dissolved, and filter to obtain the hafnium oxychloride solution.

[0089] Precipitation-washing-calcination: add hafnium oxychloride solution to 85g / L oxalic acid solution, the amount of oxalic acid added is 1.6 times the total amount of hafnium metal, heat to 80℃ and react for 4h, filter to obtain hafnium oxalate; wash the hafnium oxalate with pure water and put it into a quartz crucible, heat to 900℃ and react for 6h to obtain hafnium oxide with a purity of more than 99.95%. ICP-OES test shows that the impurity content of the product except Zr is less than 1ppm.

[0090] Example 3

[0091] Crushing and fine grinding: The waste hafnium oxide target material is crushed and ground to obtain a 200-mesh powder with a pass rate of 99.5%.

[0092] Alkali dissolution: Mix hafnium oxide powder, solid alkali, potassium nitrate or sodium peroxide in a mass ratio of 1:4:0.15 and put it into the nickel crucible of the alkali melting furnace, heat it to 700℃, react for 6h, cool it to 400℃, turn the alkali melting furnace to pour out the reacted materials and cool them down.

[0093] Water leaching: dissolve the cooled material in pure water at a liquid-to-solid ratio of 4:1, react at 80°C for 3 hours, and filter to obtain the water leaching liquid and hafnium hydroxide filter cake.

[0094] Acid leaching-impurity removal: Add the hafnium hydroxide filter cake after water leaching into sulfuric acid solution for acid leaching. The sulfuric acid concentration is 150g / L. React at 80℃ for 1.5h. After complete dissolution, obtain hafnium sulfate solution. Add analytical pure sodium sulfate at 100-300g / L to the hafnium sulfate solution. Heat to 65℃, keep warm for 6h, and filter to obtain hafnium-containing complex salt and impurity-removed liquid.

[0095] Primary evaporation crystallization: Take a hafnium-containing complex salt, add sulfuric acid solution to dissolve it, obtain hafnium sulfate solution, control the sulfuric acid concentration to 350g / L, heat to 110°C, keep warm for 5h, stop heating and stirring when crystals precipitate, cool and crystallize, and centrifuge to obtain hafnium sulfate crystals and mother liquor.

[0096] Secondary evaporation crystallization: Take hafnium sulfate crystals, add concentrated hydrochloric acid solution to dissolve, and obtain hafnium oxychloride solution with a hafnium content of 170 g / L. Heat the dissolved solution to 120°C and keep it warm for 4 hours. When crystals precipitate, stop heating and stirring, cool and crystallize, and centrifuge to obtain hafnium oxychloride crystals and mother liquor.

[0097] Crystal dissolution: Add pure water at a solid-liquid ratio of 1:1.5 to dissolve the hafnium oxychloride crystals, stir until completely dissolved, and filter to obtain the hafnium oxychloride solution.

[0098] Precipitation-washing-calcination: add hafnium oxychloride solution to 80g / L oxalic acid solution, the amount of oxalic acid added is 1.5 times the total amount of hafnium metal, heat to 75℃ and react for 3h, filter to obtain hafnium oxalate; wash the hafnium oxalate with pure water and put it into a quartz crucible, heat to 850℃ and react for 4h to obtain hafnium oxide with a purity of 99.99%. ICP-OES test shows that the impurity content of the product except Zr is less than 1ppm.

[0099] As can be seen from the above, the method for preparing high-purity hafnium oxide provided by the embodiment of the present invention can efficiently and quickly recover hafnium metal in waste hafnium oxide target materials, avoiding the problems of treating hafnium oxide under high-temperature chlorine gas in traditional methods, high cost, and difficult treatment of organic wastewater. It does not need to undergo a long period of extraction process with complex control engineering to remove impurities. High-purity hafnium oxychloride can be obtained through simple chemical dissolution and evaporation purification process. A small amount of pure water is directly added to dissolve hafnium oxychloride crystals, which reduces acid and alkali consumption and the introduction of new impurities. After that, a high-purity hafnium oxide product with a single impurity content of less than 1ppm can be obtained by adding oxalic acid precipitation, washing, and calcination processes. The evaporation crystallization purification process used has the advantages of easy equipment, simple operation, short process route, short reaction cycle, low energy consumption, environmental friendliness, high hafnium yield and high product purity, and is suitable for industrial production. The prepared high-purity hafnium oxide can be directly used for the preparation of target materials and the manufacture of electronic devices, energy materials, etc., and can also be directly chlorinated to prepare IC-grade hafnium tetrachloride with high market value.

[0100] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing high-purity hafnium oxide, characterized in that: The following steps are involved: S1, crushing hafnium oxide raw materials to obtain hafnium oxide powder; S2, sequentially subjecting the hafnium oxide powder to alkali melting, water immersion and filtering to obtain a hafnium hydroxide filter cake; S3, dissolving the hafnium hydroxide filter cake in a sulfuric acid solution to obtain a hafnium sulfate solution; adding sodium sulfate to the hafnium sulfate solution to obtain a hafnium-containing double salt; S4, dissolving the hafnium-containing complex salt in a sulfuric acid solution, heating to evaporate, and cooling to crystallize to obtain hafnium sulfate crystals; S5, dissolving the hafnium sulfate crystals in concentrated hydrochloric acid to obtain a hafnium oxychloride solution, heating to evaporate, cooling to crystallize, and obtaining hafnium oxychloride crystals; S6, dissolving the hafnium oxychloride crystals in pure water, filtering, adding oxalic acid solution, and precipitating to obtain hafnium oxalate; S7, calcining the hafnium oxalate to obtain high-purity hafnium oxide.

2. The method for preparing high-purity hafnium oxide according to claim 1, characterized in that: In step S2, the alkali fusion treatment specifically includes: The hafnium oxide powder is mixed with solid alkali and potassium nitrate in a mass ratio of 1:2-5:0.1-0.2, and then put into a crucible of an alkali melting furnace, heated to 500-800° C. for reaction for 2-8 hours, cooled to 400° C., and then the reaction material is poured out; Alternatively, the hafnium oxide powder is mixed with solid alkali and sodium peroxide in a mass ratio of 1:2-5:0.1-0.2 and then loaded into a crucible of an alkali melting furnace, heated to 500-800° C. for reaction for 2-8 hours, cooled to 400° C. and then the reaction material is poured out.

3. The method for preparing high-purity hafnium oxide according to claim 2, characterized in that: In step S2, the water immersion and filtration process specifically includes: The cooled reaction material is dissolved in pure water at a liquid-to-solid ratio of 3-5:1, reacted at 75° C.-85° C. for 1-4 hours, and filtered to obtain the hafnium hydroxide filter cake.

4. The method for preparing high-purity hafnium oxide according to claim 1, characterized in that: The step S3 specifically includes: The hafnium hydroxide filter cake is dissolved in 100-200 g / L sulfuric acid solution, reacted at 55-85° C. for 1-2 hours, and completely dissolved to obtain the hafnium sulfate solution; sodium sulfate is added to the hafnium sulfate solution, the amount of sodium sulfate added is 100-300 g / L, and the mixture is kept warm for reaction at 50-70° C. for 3-8 hours, and then filtered to obtain the hafnium-containing complex salt.

5. The method for preparing high-purity hafnium oxide according to claim 1, characterized in that: The step S4 specifically includes: The hafnium-containing complex salt is dissolved in 300-400 g / L sulfuric acid solution, heated to 100-120° C. and kept warm for 2-6 hours, cooled and crystallized when crystals are precipitated, and centrifuged to obtain the hafnium sulfate crystals.

6. The method for preparing high-purity hafnium oxide according to claim 1, characterized in that: In step S5, the hafnium content in the hafnium oxychloride solution is 150-200 g / L, and the step of cooling and crystallizing to obtain hafnium oxychloride crystals specifically includes: The hafnium oxychloride solution is heated to 100-150° C. and kept warm for 2-5 hours. When crystals are precipitated, the solution is cooled and crystallized, and centrifuged to obtain the hafnium oxychloride crystals.

7. The method for preparing high-purity hafnium oxide according to claim 1, characterized in that: The step S6 specifically includes: The hafnium oxychloride crystals are completely dissolved in pure water at a solid-liquid ratio of 1:1-2, filtered and added into a 70-85 g / L oxalic acid solution, heated to 60°C-80°C for reaction for 2-4 hours, filtered and precipitated to obtain hafnium oxalate; wherein the amount of oxalic acid added is 1.3-1.6 times the total amount of hafnium.

8. The method for preparing high-purity hafnium oxide according to claim 7, characterized in that: The step S7 specifically includes: The hafnium oxalate washed with pure water is placed in a crucible, and the temperature is raised to 700° C. to 900° C. for reaction for 2 to 6 hours to obtain the high-purity hafnium oxide.

9. The method for preparing high-purity hafnium oxide according to claim 1, characterized in that: In the step S1, the 200 mesh pass rate of the hafnium oxide powder is greater than 99%.

10. High-purity hafnium oxide prepared by the method for preparing high-purity hafnium oxide according to any one of claims 1 to 9.

Images