High-purity anhydrous scandium fluoride and a method for preparing the same

Abstract

The application discloses high-purity anhydrous scandium fluoride and a preparation method thereof, and belongs to the field of rare earth fluoride preparation. The preparation method comprises the following steps: mixing scandium oxide and zinc fluoride by a mechanical activation treatment method to obtain mixed raw materials, using mechanical activation to induce crystal lattice defects, significantly improving the kinetic conditions of the solid-solid reaction process of scandium oxide and zinc fluoride, and making fluorination more sufficient; roasting the mixed raw materials under an inert atmosphere to obtain roasted materials; putting the roasted materials into a mixed leaching system containing ammonia and ammonium salt for selective leaching, and then filtering and separating to obtain a solid crude product; using an ammonia-ammonium salt complex system, using the high stability of Zn(NH3)4] 2+ complex ions to realize accurate separation of by-products Zn and main products ScF3; and washing and drying the solid crude product to obtain anhydrous scandium fluoride, with a content of 400 ppm or less and a fluorination rate of 99.99%.

Description

Technical Field

[0001] This invention belongs to the field of rare earth fluoride preparation, specifically relating to a high-purity anhydrous scandium fluoride and its preparation method. Background Technology

[0002] Scandium fluoride (ScF3) is a core precursor for the preparation of metallic scandium and its alloys (such as aluminum-scandium alloys). With the increasing demand for high-performance scandium-based materials in 5G communications, particularly for AlScN thin-film-based RF filters, and in the aerospace field, higher requirements are being placed on the large-scale production of high-purity, anhydrous scandium fluoride. Scandium fluoride preparation technologies include three types: wet fluorination, gas-phase fluorination, and solid-phase fluorination. Among these, the presence of large amounts of water vapor in wet fluorination technology easily leads to high oxygen impurity content in the scandium fluoride, reducing the purity of the final scandium. While gas-phase fluorination technology has advantages such as a short production process and simple operation, the HF gas it uses is highly toxic and corrosive, easily endangering the health of operators, polluting the environment, and severely damaging equipment. In contrast, ammonium bifluoride solid-phase fluorination technology, with its simple production process, convenient product collection, and safe operation, has become the mainstream technology for producing scandium fluoride and other rare earth fluorinated metals.

[0003] For example, invention patent CN102153128A discloses a method for preparing scandium fluoride. Using scandium oxide as a raw material, it is dissolved in excess hydrochloric acid at a concentration of 6-10 mol / L, the pH is adjusted to 4-5, ammonium fluoride salt is added to generate a fluorinated precipitate, and then solid-liquid separation is performed to obtain a double salt precipitate. The double salt precipitate is dried to constant weight, dehydrated, and deammoniated until no smoke is generated, yielding the scandium fluoride product. However, the scandium fluoride product obtained by this method contains trace amounts of Sc2O3 and a small amount of impurities.

[0004] For example, invention patent CN118343823A discloses a method for preparing scandium fluoride using a low-temperature, high-efficiency solid-phase method, comprising the following steps: mixing excess ammonium bifluoride and scandium oxide, followed by fluorination and deammoniation to obtain the scandium fluoride; the fluorination temperature is 120℃~180℃, and the holding time is 2~4 h; the deammoniation temperature is 350℃~500℃, and the holding time is 2~4 h. This invention, by controlling the fluorination temperature at 120℃~180℃, ensures that the fluorination reaction is complete within 2~4 h, generating an intermediate compound, thus reducing energy consumption; by controlling the deammoniation temperature at 350℃~500℃, it ensures that the deammoniation reaction is complete within 2~4 h, yielding scandium fluoride. However, the scandium fluoride prepared by the above method has an oxygen content of 0.476~0.556 wt.%, indicating low purity. Summary of the Invention

[0005] To improve the purity of scandium fluoride preparation, this invention provides a high-purity anhydrous scandium fluoride and its preparation method. This method has the advantages of a short process flow, extremely low oxygen content in the anhydrous scandium fluoride, environmental friendliness, and recyclable byproducts.

[0006] This invention provides a method for preparing high-purity anhydrous scandium fluoride, comprising the following steps: (1) Scandium oxide and zinc fluoride are mixed by mechanical activation treatment to obtain a mixed raw material; (2) The mixed raw materials are roasted under an inert atmosphere to obtain roasted material; (3) The roasted material is put into a mixed leaching system containing ammonia and ammonium salt to selectively leach zinc, and then filtered and separated to obtain a solid crude product; (4) The solid crude product is washed and dried to obtain anhydrous scandium fluoride.

[0007] This invention first utilizes mechanical activation to induce lattice defects, significantly improving the kinetic conditions of the solid-solid reaction process between scandium oxide and zinc fluoride, thus ensuring more complete fluorination; then, it employs an ammonia-ammonium salt complexation system, utilizing Zn(NH3)4... 2+ The high stability of the complex ion enables precise separation of the byproduct Zn from the main product scandium fluoride (ScF3), thereby significantly improving the purity of anhydrous scandium fluoride.

[0008] Preferably, the molar ratio of scandium oxide to zinc fluoride in step (1) is 1:(3~3.6).

[0009] More preferably, the molar ratio of scandium oxide to zinc fluoride in step (1) is 1:(3.1~3.3).

[0010] Preferably, the mechanical activation treatment in step (1) is performed by dry ball milling, and the ratio of the mass of the ball milling beads to the total mass of scandium oxide and zinc fluoride is 5:1 to 15:1. The ball mill speed is 200~500 rpm, and the ball milling time is 1~4 h.

[0011] Inducing lattice defects through mechanical activation can reduce diffusion resistance in the early stages of the reaction, and using ball milling parameters within the aforementioned range allows for more complete fluorination.

[0012] More preferably, the ratio of the mass of the grinding beads to the total mass of scandium oxide and zinc fluoride is 10:1 to 12:1; The ball mill speed is 350~450 rpm, and the ball milling time is 2~3 hours.

[0013] Preferably, the inert atmosphere in step (2) is argon or nitrogen.

[0014] Preferably, the roasting temperature in step (2) is 750℃~1000℃ and the roasting time is 1~4 h.

[0015] By setting the reaction temperature and reaction time within the above parameter range, the thermodynamic requirements of the fluorination reaction are met while improving the efficiency of Sc. 3+ With F - The diffusion coefficient promotes the diffusion of ions in the lattice during solid-phase reactions; and within this temperature range, zinc fluoride will partially or completely melt into a liquid phase. The liquid zinc fluoride can better wet and encapsulate scandium oxide particles, greatly increasing the solid-liquid reaction interface, thereby improving reaction efficiency; avoiding the decomposition / volatilization of ScF3, ensuring that Sc is completely converted into ScF3 and ZnO can be leached.

[0016] More preferably, the calcination temperature is 850℃~950℃, and the calcination time is 2~4 h.

[0017] More preferably, the roasting temperature is 900℃ and the roasting time is 3 h.

[0018] Preferably, the total ammonia concentration in the mixed leaching system in step (3) is 4~10 mol / L.

[0019] The total ammonia concentration is expressed as free ammonia (molecular state NH3(aq)) and ammonium ions (NH4+). + The total concentration of ).

[0020] More preferably, the total ammonia concentration in the mixed leaching system is 6-8 mol / L.

[0021] More preferably, the concentration of ammonia in the mixed leaching system in step (3) is 2.5~6 mol / L, and the concentration of ammonium salt is 2~5.5 mol / L.

[0022] Ammonia and ammonium salts are chosen to form an alkaline buffer solution, which has a strong complexing and dissolving ability for zinc compounds. ScF3 has extremely low solubility in water and weak acids / weak bases, and is almost insoluble in the ammonia-ammonium salt system. Therefore, it is filtered and separated in solid form, thus achieving selective leaching.

[0023] More preferably, the ammonia concentration in the mixed leaching system is 3~3.5 mol / L, and the ammonium salt concentration is 4~5.5 mol / L.

[0024] Preferably, in step (3), the leaching temperature for selective leaching is 30℃~80℃, and the leaching time is 60~120min.

[0025] Selective leaching within the above temperature range can significantly increase the reaction rate of zinc-ammonia complex formation, maintain the high selectivity of ScF3, and avoid violent volatilization of ammonia. Selective leaching within the above time range can ensure that zinc is fully leached out, resulting in extremely low zinc residue.

[0026] More preferably, the leaching temperature for selective leaching is 45°C to 60°C.

[0027] Preferably, the washing in step (4) includes: first, using ammonia water with a mass concentration of 2% to 3% to replace and wash the solid crude product, and then using deionized water to wash until neutral.

[0028] The above-mentioned washing strategy can completely remove soluble zinc-containing impurities and ammonium salts adsorbed on the surface and encapsulated within the main product ScF3 without losing the main product. Specifically, by utilizing the common ion effect, ammonia water with the above-mentioned specifications is used to maintain a high concentration of ammonia environment to prevent the decomposition of zinc ammonia complex ions, thereby removing zinc ammonia complex ions and residual free ammonia while retaining the main product ScF3. Then, it is repeatedly washed with deionized water until the pH of the washing solution is close to 7, indicating that ammonia and ammonium salts have been completely removed, and finally, residual ammonia water, ammonium salts, and a small amount of residual zinc ammonia ions are completely washed away.

[0029] Preferably, the drying in step (4) is carried out by vacuum drying, with a temperature of 120℃~180℃ and a drying time of 4~6 h; The vacuum level is better than -0.09 MPa.

[0030] More preferably, the vacuum drying temperature is 160℃~170℃.

[0031] On the other hand, the present invention also provides high-purity anhydrous scandium fluoride prepared by the preparation method described above.

[0032] Preferably, the oxygen content of the high-purity anhydrous scandium fluoride is less than 400 ppm.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) Unlike the traditional solid-phase fluorination technology of ammonium bifluoride to prepare scandium fluoride, the preparation method provided by this invention first utilizes mechanical activation to induce lattice defects, which significantly improves the kinetic conditions of the solid-solid reaction process between scandium oxide and zinc fluoride, making the fluorination more complete; then, an ammonia-ammonium salt complexation system is used to utilize Zn(NH3)4] 2+ The high stability of the complex ion enables precise separation of the byproduct Zn from the main product ScF3, thereby significantly improving the purity of scandium fluoride.

[0034] (2) The preparation method provided by the present invention is simple and does not use or generate toxic gases such as HF in the entire preparation process. It is highly safe and the zinc liquid after leaching can be recycled into metallic zinc through subsequent processes, which meets the environmental protection requirements of closed-loop resource recycling.

[0035] (3) The oxygen content of the scandium fluoride product prepared by the preparation method provided by the present invention is stably controlled below 400 ppm, and the fluorination rate reaches 99.99%. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] To make the above-mentioned objectives, features and advantages of the present invention clearer and easier to understand, the following detailed description will be provided in conjunction with specific embodiments.

[0038] All raw materials used in the examples were purchased from the market.

[0039] Example 1 This embodiment provides a method for preparing high-purity anhydrous scandium fluoride, including the following steps: 1. Weigh 13.89 kg of scandium oxide with a purity of 99.9% and 32.58 kg of zinc fluoride powder, place them in a ball mill, set the ratio of ball mass to total mass of scandium oxide and zinc fluoride to 10:1, rotate at 350 rpm, and mechanically activate for 2 hours to obtain mixed raw materials; 2. The mixed raw materials are loaded into a graphite crucible and placed in a fluorination furnace. Under the continuous introduction of argon gas with a purity of 99.999%, the temperature is increased to 900℃ at 10℃ / min and the reaction is kept at a constant temperature for 3 hours. After cooling, the material is taken out and ground to below 100 mesh to obtain the calcined material. 3. Add the roasted material to the prepared mixed leaching system (ammonia concentration 5 mol / L, ammonium chloride concentration 4 mol / L), stir and leach at 50℃ for 90 minutes, and then filter to obtain solid crude product; 4. The crude solid product was washed three times each with 3% ammonia and deionized water, and then placed in a vacuum drying oven and dried at 160℃ and -0.095 MPa for 4 hours to obtain high-purity anhydrous scandium fluoride.

[0040] The high-purity anhydrous scandium fluoride prepared was tested and found to have an oxygen content of 0.0385 wt.% (oxygen content of 385 ppm) and a zinc residue of 28 ppm, with a product purity of 99.99%.

[0041] Example 2 The preparation process of Example 2 is the same as that of Example 1, except that: 1. The raw material ratio and activation process are the same as in Example 1; 2. Heat the reaction apparatus to 800°C, introduce high-purity nitrogen into the furnace for protection, maintain the temperature for 4 hours, and remove it after cooling to room temperature; 3. The leaching process is the same as in Example 1, but the leaching temperature is set to 60°C; 4. The drying process is the same as in Example 1.

[0042] The prepared high-purity anhydrous scandium fluoride had an oxygen content of 0.0392 wt.% (oxygen content of 392 ppm). The results indicate that deep fluorination conversion can also be achieved by appropriately extending the reaction time at a lower temperature.

[0043] Example 3 The preparation process of Example 3 is the same as that of Example 1, except that: 1. The raw material ratio is the same as in Example 1, the ball mill speed is set to 450 rpm, and the time is 1.5 hours; 2. The reaction apparatus is heated to 950℃ and the reaction is maintained at this temperature for 2 hours; 3. The leaching system uses a mixed solution of ammonia and ammonium sulfate (total ammonia concentration 8 mol / L), and leaching is carried out at 45℃ for 120 minutes; 4. The drying process is the same as in Example 1.

[0044] The prepared high-purity anhydrous scandium fluoride had an oxygen content of 0.0355 wt.% (oxygen content of 355 ppm). This demonstrates that the method has good universality for different ammonium salt systems.

[0045] Comparative Example 1 Weigh 1 kg of scandium oxide with a purity of 99.9% and 3.48 kg of ammonium bifluoride powder, place them in a ball mill, set the ratio of ball mass to total mass of scandium oxide and ammonium bifluoride to 10:1, rotate at 350 rpm, and mix for 2 hours to obtain a mixed raw material; The above mixed raw materials were transferred into a graphite crucible and placed in a fluorination furnace. Under the continuous introduction of argon gas with a purity of 99.999%, the temperature was raised to 170°C and held for fluorination at a constant temperature for 2 hours. The above mixture was heated to 500°C in a graphite crucible under a vacuum of 5 Pa at a heating rate of 15 °C / min for 2 hours to remove ammonia, yielding the product. The prepared scandium fluoride was found to have an oxygen content of 0.5642 wt.% (oxygen content of 5642 ppm).

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing high-purity anhydrous scandium fluoride, characterized in that, Includes the following steps: (1) Scandium oxide and zinc fluoride are mixed by mechanical activation treatment to obtain a mixed raw material; (2) The mixed raw materials are roasted under an inert atmosphere to obtain roasted material; (3) The roasted material is put into a mixed leaching system containing ammonia and ammonium salt to selectively leach zinc, and then filtered and separated to obtain a solid crude product; (4) The solid crude product is washed and dried to obtain anhydrous scandium fluoride.

2. The method for preparing high-purity anhydrous scandium fluoride according to claim 1, characterized in that, In step (1), the molar ratio of scandium oxide to zinc fluoride is 1:(3~3.6).

3. The method for preparing high-purity anhydrous scandium fluoride according to claim 1, characterized in that, In step (1), the mechanical activation treatment is carried out by dry ball milling, and the ratio of the mass of the ball milling beads to the total mass of scandium oxide and zinc fluoride is 5:1 to 15:

1. The ball mill speed is 200~500 rpm, and the ball milling time is 1~4 h.

4. The method for preparing high-purity anhydrous scandium fluoride according to claim 1, characterized in that, In step (2), the roasting temperature is 750℃~1000℃ and the roasting time is 1~4 h.

5. The method for preparing high-purity anhydrous scandium fluoride according to claim 1, characterized in that, The total ammonia concentration in the mixed leaching system in step (3) is 4~10 mol / L.

6. The method for preparing high-purity anhydrous scandium fluoride according to claim 5, characterized in that, In step (3), the concentration of ammonia in the mixed leaching system is 2.5~6 mol / L, and the concentration of ammonium salt is 2~5.5 mol / L.

7. The method for preparing high-purity anhydrous scandium fluoride according to claim 1, characterized in that, In step (3), the leaching temperature for selective leaching is 30℃~80℃, and the leaching time is 60~120 min.

8. The method for preparing high-purity anhydrous scandium fluoride according to claim 1, characterized in that, The washing in step (4) includes: first, using ammonia water with a mass concentration of 2% to 3% to replace and wash the solid crude product, and then using deionized water to wash until neutral.

9. High-purity anhydrous scandium fluoride prepared by the preparation method according to any one of claims 1 to 8.

10. The high-purity anhydrous scandium fluoride according to claim 9, characterized in that, The high-purity anhydrous scandium fluoride has an oxygen content of less than 400 ppm.