Preparation method of low-oxygen niobium powder

Abstract

The invention relates to a preparation method of low-oxygen niobium powder. According to the method, by optimizing key experimental links such as raw material pretreatment, dehydrogenation and oxygen reduction and wastewater treatment, unification of high performance of niobium powder preparation and green production is achieved. The specific process comprises the following steps: taking an electron beam melting niobium ingot as a raw material, and removing oil through supercritical CO2; then carrying out primary hydrogenation, crushing, screening, secondary hydrogenation, crushing, airflow milling, acid pickling, dehydrogenation and oxygen reduction and secondary acid pickling; wherein in the dehydrogenation and oxygen reduction link, calcium powder and niobium powder are subpackaged, and dehydrated CaCl2 is introduced to consume a reaction byproduct CaO, so that impurities are reduced, and the oxygen reduction efficiency is remarkably improved; after acid washing, ultrasonic wave is utilized to strengthen water washing to reduce water consumption; finally, the wastewater is treated by a column reactor crystallization and fluidized bed induced crystallization coupling technology, so that deep removal of fluoride and recovery of high-purity calcium fluoride are realized. The niobium powder prepared by the method has the characteristics of low oxygen content (less than or equal to 400ppm), low magnesium content (less than or equal to 3ppm), uniform particle size distribution (D50 is 10-75mu m) and the like.

Description

Technical Field

[0001] This invention relates to the field of niobium powder technology, and specifically to a method for preparing low-oxygen niobium powder. Background Technology

[0002] Niobium is a grayish-white metal with a melting point of 2468℃, a boiling point of 4742℃, and a density of 8.57 g / cm³. 3 Niobium is a grayish-white metal with a melting point of 2468℃, a boiling point of 4742℃, and a density of 8.57 g / cm³. Niobium powder is a lustrous gray metallic powder with paramagnetic properties. It has high ductility but hardens with increasing impurity content. The outermost electron configuration of niobium is significantly different from other Group 5 elements. Niobium powder is relatively stable in air at room temperature and is not completely oxidized when heated to red-hot in oxygen. At high temperatures, it can directly combine with sulfur, nitrogen, and carbon, and it can also form alloys with metals such as titanium, zirconium, hafnium, and tungsten. Niobium does not react with inorganic acids or bases, is insoluble in aqua regia, but is soluble in hydrofluoric acid.

[0003] Niobium powder is often used in 3D printing technology, sputtering targets, metal injection molding, laser rapid prototyping and other fields. These fields require niobium powder with low oxygen content, high purity and narrow particle size distribution. Such applications have extremely high requirements for the oxygen content, purity and particle size distribution of niobium powder, and need to achieve low oxygen (≤400ppm), high purity and narrow particle size distribution (D50). At the same time, the requirements for energy saving, emission reduction and environmental protection in the production process are increasing.

[0004] The existing process for producing niobium powder typically includes: hydrogenation of niobium ingots, crushing, acid washing, dehydrogenation and deoxygenation, acid washing again, drying, and sieving. Niobium powder produced by this process has large particle size, high oxygen content, and high magnesium content. Furthermore, some processes have high equipment requirements or expensive raw material costs, which are not conducive to large-scale production and make it difficult to meet the demand for low-oxygen, high-purity niobium powder in high-end applications. In addition to the above problems, we also face significant energy consumption and environmental protection bottlenecks in some stages. In the pretreatment stage of raw materials, traditional degreasing processes use a single high-concentration alkaline solution, which requires high temperature maintenance and generally has high energy consumption; or organic solvents such as toluene are used, which have high recycling costs and are prone to environmental pollution, making it difficult to achieve the dual effects of degreasing and energy saving and emission reduction. After acid washing and activation, to remove residual acid and oxidation products from the surface, traditional processes require multiple rinsing with running water. The water consumption of a single rinsing can be 10 to 15 times the powder mass, resulting in serious water waste. Incomplete rinsing can easily lead to secondary oxidation of niobium powder in the subsequent process. In the treatment of acid washing wastewater, the neutralization step often requires repeated pH adjustment due to the imbalance of acid-base ratio, which not only increases the consumption of alkaline agents such as sodium hydroxide and sodium carbonate, but also prolongs the adjustment treatment cycle, resulting in high environmental protection costs. In addition, while some improved processes can enhance the purity of niobium powder, they rely on high-cost equipment (such as special high-pressure hydrogenation furnaces) or long-term high-temperature processes (such as dehydrogenation at temperatures above 1000°C), further increasing energy consumption and production difficulty. This makes it difficult to adapt to the needs of large-scale, low-energy production and fails to meet the dual demands of high-end fields for niobium powder performance and green production. Summary of the Invention

[0005] To address the technical deficiencies in the background technology, this invention proposes a method for preparing low-oxygen niobium powder. By optimizing raw material selection, improving pretreatment processes, precisely controlling hydrogenation and ball milling parameters, and innovating dehydrogenation and oxygen reduction charging methods, the method solves the problems of oxidation and oxygenation, impurity residues, and uneven particle size in existing processes. The specific technical solution is as follows:

[0006] A method for preparing low-oxygen niobium powder includes the following steps:

[0007] Raw material pretreatment

[0008] Electron beam smelted niobium ingots were selected as raw materials; the electron beam smelted niobium ingots were prepared in a high vacuum environment, and the initial impurity content was much lower than that of ordinary high-purity niobium ingots, which can reduce gaseous impurities from the source and reduce the subsequent oxygen de-oxidation pressure.

[0009] S1: Degreasing treatment: Supercritical CO2 circulation technology is used in the degreasing process.

[0010] S2: Pickling and Activation: Removes residual impurities from the surface, followed by ultrasonic-enhanced water washing after acidification.

[0011] S3 Vacuum Drying: Drys niobium ingots to prevent secondary oxidation.

[0012] Specifically, in step S1, the recycled polyester yarn is loaded into a high-pressure treatment container. The system is heated to 60°C and pressurized to 20MPa, and supercritical CO2 is circulated at a flow rate of 415kg / h for 1 hour to allow CO2 molecules to penetrate the fiber pores and dissolve the oil by weakening hydrogen bonds and van der Waals forces. The experimental setup for this process includes a CO2 storage tank, a condenser, a high-pressure pump, and a separator. The CO2 fluid flows from the inside of the reactor to the outside to ensure uniform contact.

[0013] Specifically, in step S2, the degreased niobium ingot is immersed in a 40% hydrofluoric acid solution for 48 hours to dissolve the dense oxide film on the surface. Then, it is ultrasonically cleaned with deionized water to thoroughly remove residual acid and oxidation products from the surface. The niobium powder after acid washing and activation is then subjected to ultrasonic-enhanced water washing.

[0014] Specifically, in step S3, the cleaned niobium ingots are placed in a vacuum drying oven (drying method) and dried at 80°C for 24 hours. After drying, they are cut into 5mm thick blocks for later use.

[0015] The specific technical solution is as follows:

[0016] S1 First hydrogenation: Niobium ingots are hydrogenated to obtain hydrogenated niobium ingots;

[0017] S2 primary crushing: The niobium hydride ingot is crushed to obtain niobium hydride powder;

[0018] S3 screening: Use a 100~500 mesh standard sieve to sieve to obtain niobium hydrogenation powder that can pass through a 100~500 mesh standard sieve;

[0019] S4 Secondary Hydrogenation: The unsieved hydrogenated niobium powder undergoes secondary hydrogenation treatment;

[0020] S5 Secondary Crushing: The hydrogenated niobium powder that has undergone secondary hydrogenation is crushed to obtain hydrogenated niobium powder.

[0021] S6 Airflow milling: The niobium hydride powder obtained in steps S3 and S5 is loaded into an airflow mill for high-pressure airflow milling to obtain fine niobium hydride powder with uniform particle size.

[0022] S7 pickling: Pickling fine niobium niobium powder;

[0023] S8 Dehydrogenation and Oxygen Reduction: Dehydrogenation and oxygen reduction of fine-particle hydrogenated niobium powder;

[0024] S9 Acid Washing and Impurity Removal: Niobium powder that has undergone dehydrogenation and oxygen reduction is acid washed and dried to obtain low-oxygen niobium powder that can pass through a 200-500 mesh standard sieve;

[0025] S10 wastewater treatment: Wastewater is neutralized and recycled using a dual-technology approach of column reactor crystallization and fluidized bed induced crystallization.

[0026] Specifically, in step S1, the pretreated niobium ingot is placed in a hydrogenation furnace, and the heating rate is controlled at 7.5℃ / min. First, 0.1MPa of hydrogen gas is introduced into the hydrogenation furnace, and the temperature is maintained at 500℃ for 1 hour. Then, the temperature is kept constant and the holding time is continued for another hour. During the holding process, the hydrogenation furnace is slowly rotated to increase the degree of hydrogenation of the niobium ingot. After cooling, hydrogenated niobium ingot is obtained.

[0027] Specifically, in steps S2 and S5, a horizontal planetary ball mill is used for grinding. High-purity argon gas is continuously introduced during the crushing process to isolate the powder from air and prevent oxidation.

[0028] Specifically, in step S3, the hydrogenated niobium powder after primary crushing is sieved using a 100-500 mesh standard sieve. The hydrogenated niobium powder that can pass through the 100-500 mesh standard sieve is collected, while the coarse hydrogenated niobium powder that does not pass through the sieve is transferred to the secondary hydrogenation process to improve the utilization rate of raw materials.

[0029] Specifically, in step S4, the unsieved coarse niobium hydrogenation powder is placed in a hydrogenation furnace, hydrogen gas at 0.25 MPa is introduced, the heating rate is controlled at 7.5 °C / min, and the temperature is maintained at 850~950 °C to prepare for subsequent secondary crushing and cooling to obtain secondary niobium hydrogenation powder.

[0030] Specifically, in step S6, the niobium hydrogenation powder obtained in steps S3 and S5 is fed into an air jet mill for high-pressure air jet pulverization. A mixture of argon and hydrogen is used as the high-pressure air jet (the volume ratio of argon to hydrogen is 100~500:1), and the gas pressure is controlled at 5~7 kPa. Finally, fine niobium hydrogenation powder with uniform particle size is obtained.

[0031] Specifically, in step S7, the fine niobium hydrogenation powder obtained by air jet milling is soaked in a 10-18% hydrochloric acid solution for 8-10 hours to dissolve trace metal impurities on the powder surface caused by ball milling and air jet milling. After acid washing, the powder is repeatedly washed with deionized water until the washing solution is neutral. Then, it is placed in a vacuum drying oven and dried at 120°C for 12 hours to ensure that the powder is dry.

[0032] Specifically, in step S8, the dried fine-particle hydrogenated niobium powder undergoes dehydrogenation and deoxygenation treatment, as follows:

[0033] 1. Select metallic calcium powder as a reducing agent. The amount of reducing agent added is 3-6% of the mass of fine niobium hydrogenation powder. Use a separate loading method: put metallic calcium powder into a crucible separately and place it in the lower layer of the dehydrogenation and deoxygenation furnace. Put fine niobium hydrogenation powder into another crucible and place it in the upper layer of the furnace. Place a porous calcium chloride partition between the two crucibles.

[0034] 2. High-purity argon gas is introduced into the dehydrogenation and oxygen reduction furnace to isolate air. The heating rate is controlled at 5~8℃ / min. The temperature is raised to 900~950℃ and held for 4~10h to initially remove hydrogen and oxygen from niobium powder. During this period, calcium powder vapor reacts with niobium powder through a porous partition to generate CaO.

[0035] 3. Add dehydrated CaCl2 powder into the furnace, wherein the mass ratio of niobium powder to CaCl2 is 1:3. Continue heating until the temperature reaches 1200K and hold for 3 hours. Utilize the high solubility of molten CaCl2 for CaO to fully dissolve the product impurity CaO.

[0036] 4. After the heat preservation is completed, the heating system is turned off and the furnace is allowed to cool down naturally to about 30°C. Then, a small amount of oxygen is introduced for passivation treatment. After passivation is completed, the niobium powder is removed from the furnace and dehydrogenated.

[0037] Specifically, in step S9, the niobium powder after dehydrogenation and deoxygenation is subjected to a second acid wash. The acid wash solution is a mixture of 30% hydrochloric acid solution and 40% hydrofluoric acid solution at a volume ratio of 4:1, which is then diluted with water at a volume ratio of 4:1:30. After preparing the solution, the niobium powder is immersed in the solution for 3 hours to thoroughly remove residual calcium chloride and other impurities. After the acid wash is completed, the powder is repeatedly filtered with pure water until the washing solution is neutral. Then, the niobium powder is placed in a vacuum drying oven and dried at 120°C for 14 hours. Finally, it is passed through a 200-500 mesh standard sieve again.

[0038] Specifically, in step S10, a dual-technology approach based on column reactor crystallization and fluidized bed induced crystallization is adopted. Through a dissolution-precipitation-recrystallization mechanism, deep removal of fluorides and recovery of high-purity calcium fluoride are achieved. In the column reactor system, calcium sulfate dihydrate is used as the reaction medium. Synthesized calcium sulfate dihydrate packing material is loaded into the reaction column. Wastewater is pumped in from the bottom, flows through the packing layer, and overflows from the top. During this process, the packing material gradually dissolves, releasing Ca²⁺ ions, which react with F⁻ ions in the wastewater to form a precipitation reaction. The fluoride removal rate exceeds 99%, and the effluent fluoride concentration is below 10 mg / L. The fluidized bed crystallization process focuses on treating wastewater with high fluoride concentrations, using silica sand with a particle size of (0.5-1 mm) as seed crystals. Wastewater and calcium chloride solution are pumped into the bottom of the fluidized bed reactor. The seed crystals provide a large specific surface area in the fluidized state, inducing fluoride ions and calcium ions to nucleate heterogeneously on their surface and grow into CaF₂ crystals. The fluoride recovery rate is as high as approximately 90%.

[0039] Specifically, in step S8, the dehydrated CaCl2 powder needs to be vacuum dried at 120℃ for 12 hours in advance to remove internal moisture and prevent moisture from reacting with niobium powder at high temperature and introducing oxygen; the heating rate is controlled at 5~8℃ / min to avoid excessive local temperature causing niobium powder sintering, which would affect the subsequent particle size and dispersibility.

[0040] Specifically, the low-oxygen niobium powder is expected to have an oxygen content ≤400ppm, a magnesium content ≤3ppm, a D50 of 10~75μm, and a purity ≥99.9%. Attached Figure Description

[0041] Figure 1 This is a diagram of the raw material pretreatment process;

[0042] Figure 2 It is a flowchart of the specific technical solution;

[0043] Figure 3 This is a cross-sectional view of a hydrogenation furnace;

[0044] Figure 4 This is an exterior view of the hydrogenation furnace;

[0045] Figure 5 This refers to the temperature change in traditional degreasing methods;

[0046] Figure 6 This is a top view of the polyester fibers during the degreasing process;

[0047] Figure 7 This is a flow chart for crystallization wastewater treatment based on a column reactor.

[0048] Figure 8 This is a diagram illustrating the treatment of fluidized bed induced crystallization wastewater under high fluoride concentrations.

[0049] Figure 9 Schematic diagram of a ball mill. Detailed Implementation

[0050] The embodiments of the present invention will be described below with reference to relevant examples. The embodiments of the present invention are not limited to the following examples, and the present invention relates to relevant necessary components in this technical field, which should be regarded as well-known technology in this technical field and can be known and mastered by those skilled in this technical field.

[0051] Example 1: Electron beam smelted niobium ingots were prepared, and after degreasing with supercritical CO2, activation by soaking in 40% hydrofluoric acid solution for 48 hours, ultrasonic-enhanced water washing, and vacuum drying at 80℃ for 24 hours, they were cut into 5mm thick blocks for later use. The pretreated niobium ingots were placed in a hydrogenation furnace. Hydrogen gas at 0.5MPa was first introduced into the furnace, and the furnace was held at 900℃ for 1.5 hours. Then, the hydrogen pressure was reduced to 0.25MPa, and the furnace was held at 900℃ for 0.5 hours. After cooling, hydrogenated niobium ingots were obtained. The hydrogenated niobium ingots were then fed into a horizontal planetary ball mill for crushing. During the crushing process, high-temperature argon gas was continuously introduced to isolate oxygen, resulting in hydrogenated niobium powder. The powder was sieved through a 100-mesh standard sieve to obtain hydrogenated niobium powder that could pass through the 100-mesh standard sieve. The unsieved hydrogenated niobium powder was placed back into the hydrogenation furnace, and hydrogen gas at 0.25MPa was introduced into the furnace. The furnace was then heated at 900℃. The niobium powder was kept at a temperature of ℃ for 2.5 hours, followed by cooling. The resulting niobium hydrogenate powder was then fed into an air jet mill for further crushing. Specifically, a high-pressure gas mixture of argon and hydrogen was used, with a volume ratio of argon to hydrogen of 300:1 and a pressure of 6 kPa. This process simultaneously performed secondary hydrogenation, further increasing the degree of hydrogenation of the niobium ingot and thus reducing the oxygen content, ultimately yielding niobium hydrogenate powder. The fine niobium hydrogenate powder was then soaked in a 15% hydrochloric acid solution for 9 hours, followed by ultrasonic-enhanced water washing until neutral. Finally, it was dried in a vacuum drying oven. The dried niobium hydrogenate powder was then further processed... The dehydrogenation and deoxygenation treatment was carried out as follows: Calcium metal powder was selected as the reducing agent, with an addition amount of 4% of the niobium powder mass. A separate loading method was used: the calcium metal powder was placed in a separate crucible on the lower layer of the dehydrogenation and deoxygenation furnace, and the treated niobium powder was placed in another crucible on the upper layer, separated by a porous calcium chloride partition. High-purity argon gas was introduced into the dehydrogenation and deoxygenation furnace to isolate it from air, and the heating rate was controlled at 5℃ / min to reach 920℃ and held for 6 hours. Subsequently, dehydrated CaCl2 powder was added to the dehydrogenation and deoxygenation furnace, with the ratio of niobium powder to calcium chloride being 1:3, and the temperature was further increased to 1200K and held. After 4 hours of heat preservation, the heating system was turned off, and the furnace was allowed to cool naturally to 30°C in an argon atmosphere. Then, a small amount of oxygen was introduced and the furnace was removed after passivation was completed, yielding niobium powder after dehydrogenation and deoxygenation. The obtained niobium powder was soaked in an acid washing solution for 2-3 hours to completely remove residual impurities. After being washed with pure water until neutral, it was placed in a vacuum drying oven and dried at 120°C for 14 hours. After passing through a 200-mesh standard sieve, low-oxygen niobium powder was obtained. Finally, we adopted a dual technical approach based on column reactor crystallization and fluidized bed induced crystallization for wastewater treatment. The wastewater was tested after treatment, and the content and particle size distribution of the main impurities are shown in Table 1.

[0052] Comparative Example 1: Prepare niobium ingots and place them in a hydrogenation furnace. First, introduce hydrogen gas at 0.5 MPa into the furnace and hold at 900°C for 1.5 hours. Then, reduce the hydrogen pressure to 0.25 MPa and hold at 900°C for 0.5 hours. After cooling, obtain hydrogenated niobium ingots. Place the hydrogenated niobium ingots into a ball mill for crushing. During crushing, continuously introduce high-temperature argon gas to isolate oxygen, obtaining hydrogenated niobium powder. Sieve the powder through a 100-mesh standard sieve to obtain hydrogenated niobium powder that can pass through the 100-mesh standard sieve. Place the unsieved hydrogenated niobium powder back into the hydrogenation furnace and introduce hydrogen gas... Hydrogen gas at 0.25 MPa was introduced into the hydrogenation furnace, and the furnace was held at 900℃ for 2.5 hours, followed by cooling. The resulting niobium hydrogenation powder was then fed into an air jet mill for further crushing. Specifically, a high-pressure gas flow was used, consisting of a mixture of argon and hydrogen at a volume ratio of 300:1 and a pressure controlled at 6 kPa. This secondary hydrogenation process, while producing the powder, further increased the degree of hydrogenation of the niobium ingot, thereby reducing the oxygen content and ultimately yielding niobium hydrogenation powder. The fine niobium hydrogenation powder was then soaked in a 15% hydrochloric acid solution for a specified soaking time. After 9 hours of washing with deionized water until neutral, the niobium powder is dried in a vacuum drying oven. The dried niobium powder then undergoes dehydrogenation and deoxygenation treatment. Calcium powder is used as a reducing agent, added at 2-4% of the niobium powder mass. A mixed loading method is employed: calcium and niobium powders are mechanically mixed and directly placed into a single crucible; the crucible is then placed in a dehydrogenation and deoxygenation furnace, and high-purity argon gas is introduced into the furnace. The temperature is increased to 920℃ at 5℃ / min and held for 6 hours. During this process, no calcium chloride powder is added, and no high-temperature holding at 1200K is performed. The process involves naturally cooling the furnace to 30°C under an argon atmosphere, introducing a small amount of oxygen, and allowing it to passivate before removing it from the furnace to obtain niobium powder after dehydrogenation and deoxygenation. The obtained niobium powder is then soaked in an acid washing solution for 2-3 hours to thoroughly remove residual impurities. After being washed with pure water until neutral, it is placed in a vacuum drying oven and dried at 120°C for 14 hours. After passing through a 200-mesh standard sieve, low-oxygen niobium powder is obtained. Finally, the wastewater is treated using conventional neutralization and precipitation methods, without achieving deep reuse. The content of substances in the treated wastewater is tested, and the content and particle size distribution of the main impurities are shown in Table 1.

[0053] Comparative Example 2: Prepare niobium ingots and place them in a hydrogenation furnace. First, introduce hydrogen gas at 0.5 MPa into the furnace and hold at 900°C for 1.5 hours. Then, reduce the hydrogen pressure to 0.25 MPa and hold at 900°C for another 0.5 hours. After cooling, obtain hydrogenated niobium ingots. Place the hydrogenated niobium ingots into a ball mill for crushing. During crushing, continuously introduce high-temperature argon gas to isolate oxygen, obtaining hydrogenated niobium powder. Sieve the powder through a 100-mesh standard sieve to obtain powder that can pass through a 100-mesh sieve. The standard sieve-sieved niobium powder was used. The unsieved niobium powder was placed again in a hydrogenation furnace, and hydrogen gas at 0.25 MPa was introduced. The furnace was held at 900℃ for 2.5 hours, followed by cooling. The treated niobium powder was then directly acid-washed and soaked in a 15% hydrochloric acid solution for 9 hours. After washing with deionized water until neutral, it was dried in a vacuum drying oven. The dried niobium powder underwent dehydrogenation and deoxygenation treatment, for which calcium was selected. The powder was added as a reducing agent at a rate of 2-4% of the niobium powder mass. A mixed loading method was used: calcium powder and niobium powder were mechanically mixed and directly placed into a single crucible; the crucible was placed in a dehydrogenation and deoxygenation furnace, and high-purity argon gas was introduced into the furnace, heating to 920℃ at 5℃ / min and holding for 6 hours; during this process, no calcium chloride powder was added, and the high-temperature holding at 1200K was not performed. The furnace was allowed to cool naturally to 30℃ in an argon atmosphere, and a trace amount of oxygen was introduced until passivation was complete before removing the niobium powder after dehydrogenation and deoxygenation. The obtained niobium powder was soaked in an acid washing solution for 2-3 hours to thoroughly remove residual impurities. After being washed with pure water until neutral, it was placed in a vacuum drying oven and dried at 120℃ for 14 hours. After passing through a 200-mesh standard sieve, low-oxygen niobium powder was obtained. Finally, the wastewater was treated using conventional neutralization and precipitation methods, without achieving deep reuse. The content of substances in the treated wastewater was tested, and the content and particle size distribution of the main impurities are shown in Table 1.

[0054] Comparative Example 3: Prepare niobium ingots and place them in a hydrogenation furnace. First, introduce hydrogen gas at 0.5 MPa into the furnace and maintain the temperature at 900℃ for 2 hours. After cooling, obtain hydrogenated niobium ingots. Place the hydrogenated niobium ingots into a ball mill for crushing to obtain hydrogenated niobium powder. Sieve the powder through a 100-mesh standard sieve to obtain hydrogenated niobium powder that can pass through the 100-mesh standard sieve. Soak the hydrogenated niobium powder in a 15% hydrochloric acid solution for 8 hours, then wash it thoroughly with clean water and dry it. Mix the hydrogenated niobium powder with 3% magnesium powder. After mixing, the niobium powder was added to a dehydrogenation and deoxygenation furnace, heated to 900℃ and held for 5 hours, then the furnace pressure was released, and the powder was held at 900℃ for 4 hours. Finally, it was cooled to 25℃, passivated, and then removed from the furnace to obtain dehydrogenated and deoxygenated niobium powder. The obtained niobium powder was acid-washed with a 30% hydrochloric acid solution and water in a volume ratio of 2:15 to remove impurities such as magnesium oxide. After being filtered with pure water, it was dried in a vacuum drying oven at 120℃ for 14 hours and then passed through a 200-mesh standard sieve to obtain niobium powder. The content of its main impurities and particle size distribution are shown in Table 1.

[0055] Table 1 Performance Comparison

[0056] project O content (ppm) Impurity content (ppm) Particle size D50 (μm) Total water consumption (L / kg) Niobium ingots ﹤400 ﹤3 -- -- Example 1 290 2.81 11.9 90 Comparative Example 1 301 2.87 12.6 150 Comparative Example 2 293 2.95 16.6 160 Comparative Example 3 310 4.71 20.3 220

[0057] Comparative Example 1 involved the following steps: raw material pretreatment, primary hydrogenation, primary crushing, screening, secondary hydrogenation, secondary crushing, airflow milling, acid washing, dehydrogenation and oxygen reduction, and acid washing for impurity removal. Compared to Example 1, Comparative Example 1 used a mixed loading method and did not add calcium chloride for high-temperature heat preservation, resulting in niobium powder with a higher oxygen content. Traditional deionized water was used for rinsing until neutral, but this method consumed a significant amount of water.

[0058] Comparative Example 2 underwent a process of one hydrogenation, one crushing, screening, secondary hydrogenation, secondary crushing, acid washing, dehydrogenation and oxygen reduction, and acid washing to remove impurities. Compared to Example 1, airflow milling was not used, and a mixed loading method was employed. No calcium chloride was added for high-temperature insulation. The washing method was more traditional, resulting in higher water consumption. The niobium powder obtained in Comparative Example 2 had a higher oxygen content, a higher particle size D50, and a larger particle size compared to the low-oxygen niobium powder obtained in Example 1.

[0059] Comparative Example 3 illustrates the existing process for producing niobium powder, including: niobium ingot hydrogenation, crushing, acid washing, dehydrogenation and oxygen reduction, acid washing, drying, and sieving. The entire process utilizes high-water-consumption flowing rinsing and simple wastewater treatment. Compared to the low-oxygen niobium powder obtained in Example 1, the resulting niobium powder has higher oxygen content, higher magnesium content, a higher particle size D50, and a larger particle size.

[0060] Example 1 describes a process involving primary hydrogenation, primary crushing, screening, secondary hydrogenation, secondary crushing, airflow milling, acid washing, dehydrogenation and oxygen reduction, acid washing for impurity removal, and wastewater treatment. The resulting low-oxygen niobium powder meets the following conditions: oxygen content ≤400ppm, magnesium content ≤3ppm, D50 of 10~75μm, and minimal water consumption, achieving a balance between high product performance and green production.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing low-oxygen niobium powder, characterized in that, Includes the following steps: Raw material pretreatment: S1: Degreasing treatment: using supercritical CO2 circulation technology S2: Pickling and Activation: Acidification with hydrofluoric acid followed by ultrasonic-enhanced water washing. S3: Vacuum drying: Drying niobium ingots to reduce the degree of re-oxidation. Specific technical solution: S1 First hydrogenation: Niobium ingots are hydrogenated to obtain hydrogenated niobium ingots; S2 primary crushing: The niobium hydride ingot is crushed to obtain niobium hydride powder; S3 screening: Use a 100~500 mesh standard sieve to sieve to obtain niobium hydrogenation powder that can pass through a 100~500 mesh standard sieve; S4 Secondary Hydrogenation: The unsieved hydrogenated niobium powder undergoes secondary hydrogenation treatment; S5 Secondary Crushing: The hydrogenated niobium powder that has undergone secondary hydrogenation is crushed to obtain hydrogenated niobium powder. S6 Airflow milling: The niobium hydride powder obtained in steps S3 and S5 is loaded into an airflow mill for high-pressure airflow milling to obtain fine niobium hydride powder with uniform particle size. S7 pickling: Pickling fine niobium niobium powder; S8 Dehydrogenation and Oxygen Reduction: Dehydrogenation and oxygen reduction of fine-particle hydrogenated niobium powder; S9 Acid Washing and Impurity Removal: Niobium powder that has undergone dehydrogenation and oxygen reduction is acid washed and dried to obtain low-oxygen niobium powder that can pass through a 200-500 mesh standard sieve; S10 wastewater treatment: Wastewater is neutralized and recycled using a dual-technology approach of column reactor crystallization and fluidized bed induced crystallization.

2. In the raw material pretreatment according to claim 1, the characteristic is that, In step S1, the recycled polyester yarn is loaded into a high-pressure treatment container. The system is heated to 60°C and pressurized to 20MPa. Supercritical CO2 is circulated at a flow rate of 415kg / h for 1 hour to allow CO2 molecules to penetrate the fiber pores and dissolve the oil by weakening hydrogen bonds and van der Waals forces. The experimental setup for this process includes a CO2 storage tank, a condenser, a high-pressure pump, and a separator. The CO2 fluid flows from the inside of the reactor to the outside to ensure uniform contact.

3. In the raw material pretreatment according to claim 1, the characteristic is that, In step S2, the degreased niobium ingots are immersed in a 40% hydrofluoric acid solution for 48 hours to dissolve the dense oxide film on the surface. Then, they are ultrasonically cleaned with deionized water to thoroughly remove residual acid and oxidation products from the surface. The niobium powder after acid washing and activation is then subjected to ultrasonic-enhanced water washing.

4. In the raw material pretreatment according to claim 1, the characteristic is that, In step S3, the cleaned niobium ingots are placed in a vacuum drying oven for drying.

5. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, In step S1, the pretreated niobium ingot is placed in a hydrogenation furnace, and the heating rate is controlled at 7.5℃ / min. First, hydrogen gas at 0.1MPa is introduced into the hydrogenation furnace, and the temperature is maintained at 500℃ for 1 hour. Then, the temperature is kept constant and the holding time is continued for another hour. During the holding time, the hydrogenation furnace is slowly rotated to increase the degree of hydrogenation of the niobium ingot. After cooling, hydrogenated niobium ingot is obtained.

6. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, In steps S2 and S5, a horizontal planetary ball mill is used for grinding. High-purity argon gas is continuously introduced during the crushing process to isolate the powder from air and prevent oxidation.

7. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, In step S3, the hydrogenated niobium powder after primary crushing is sieved using a 100-500 mesh standard sieve. The hydrogenated niobium powder that can pass through the 100-500 mesh standard sieve is collected, while the coarse hydrogenated niobium powder that does not pass through the sieve is transferred to the secondary hydrogenation process.

8. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, In step S4, the unsieved coarse niobium hydrogenation powder is placed in a hydrogenation furnace, hydrogen gas at 0.25 MPa is introduced, the heating rate is controlled at 7.5 °C / min, and the temperature is maintained at 850~950 °C to prepare for subsequent secondary crushing and cooling to obtain secondary niobium hydrogenation powder.

9. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, In step S6, the niobium hydrogenation powder obtained in steps S3 and S5 is fed into an air jet mill for high-pressure air jet pulverization. A mixture of argon and hydrogen is used as the high-pressure air jet, and the pressure is controlled at 5~7 kPa. Finally, fine-particle niobium hydrogenation powder with uniform particle size is obtained.

10. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, In step S7, the fine niobium hydrogenation powder obtained by air jet milling is soaked in a 10-18% hydrochloric acid solution for 8-10 hours to dissolve trace metal impurities on the powder surface caused by ball milling and air jet milling. After acid washing, the powder is repeatedly washed with deionized water until the washing solution is neutral. Then, it is placed in a vacuum drying oven and dried at 120°C for 12 hours to ensure that the powder is dry.

11. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, In step S8, the dried fine-particle hydrogenated niobium powder is subjected to dehydrogenation and deoxygenation treatment. Calcium powder is selected as the reducing agent, and the amount added is 3-6% of the mass of the fine-particle hydrogenated niobium powder. The furnace is loaded separately, with calcium powder loaded into a crucible and placed in the lower layer of the dehydrogenation and deoxygenation furnace, and the fine-particle hydrogenated niobium powder loaded into another crucible and placed in the upper layer of the dehydrogenation and deoxygenation furnace. A porous calcium chloride partition is placed between the two crucibles. Then, high-purity argon gas is introduced into the dehydrogenation and deoxygenation furnace to isolate air, and the heating rate is controlled at 5-8℃ / min. The temperature is raised to 900-950℃ and held for 4-10 hours. Next, dehydrated CaCl2 powder is added into the furnace, with the mass ratio of niobium powder to CaCl2 being 1:

3. The temperature is further raised to 1200K and held for 3 hours. After the holding period, the heating system is turned off, and the furnace is allowed to cool naturally to 10-40℃. Then, passivation treatment is performed by introducing a trace amount of oxygen. After passivation, the niobium powder is removed from the furnace to obtain dehydrogenated and deoxygenated niobium powder.

12. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, In step S9, the niobium powder after dehydrogenation and oxygen reduction is subjected to a second acid wash. The acid wash solution is a mixture of 30% hydrochloric acid solution and 40% hydrofluoric acid solution at a volume ratio of 4:1, and then diluted with water at a volume ratio of 4:1:

30. The niobium powder is immersed in this acid wash solution for 3 hours to thoroughly remove residual impurities such as magnesium oxide and calcium chloride. After acid washing, the powder is repeatedly filtered with pure water until the washing solution is neutral. Then, the niobium powder is placed in a vacuum drying oven and dried at 120°C for 14 hours. Finally, it is passed through a 200-500 mesh standard sieve to obtain low-oxygen niobium powder that can pass through a 200-500 mesh standard sieve.

13. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, Specifically, in step S10, a dual-technology approach based on column reactor crystallization and fluidized bed induced crystallization is adopted. Through a dissolution-precipitation-recrystallization mechanism, deep removal of fluorides and recovery of high-purity calcium fluoride are achieved. The column reactor system uses calcium sulfate dihydrate as the reaction medium. The synthesized calcium sulfate dihydrate packing material is loaded into the reaction column. Wastewater is pumped in from the bottom, flows through the packing layer, and overflows from the top. During this process, the packing material gradually dissolves and releases Ca. 2+ Ions and F in wastewater - The ions undergo a precipitation reaction, achieving a fluoride removal rate exceeding 99%, with effluent fluoride concentrations below 10 mg / L. The fluidized bed crystallization process focuses on treating high-fluoride-concentration wastewater, using silica sand with a particle size of 0.5-1 mm as seed crystals. Wastewater and calcium chloride solution are pumped into the bottom of the fluidized bed reactor. The seed crystals, under fluidized conditions, provide a large specific surface area, inducing heterogeneous nucleation of fluoride and calcium ions on their surface, resulting in the growth of CaF2 crystals. Fluoride recovery rates are as high as approximately 90%.

14. The method for preparing low-oxygen niobium powder according to claim 1, characterized in that, The aforementioned low-oxygen niobium powder is expected to have an oxygen content ≤400ppm, a magnesium content ≤3ppm, a D50 of 10~75μm, and a purity ≥99.9%.

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