Method for preparing ultra-high purity molybdenum powder by segmental speed-controlled peroxide dissolution and selective complexation impurity removal

Abstract

This invention provides a method for preparing ultra-high purity molybdenum powder. The method first employs segmented, rate-controlled hydrogen peroxide dissolution, allowing the molybdenum powder to dissolve safely and controllably in a hydrogen peroxide system into a molybdenum peroxide complex solution. Second, selective complexation is used for stepwise impurity removal, first decomposing residual hydrogen peroxide and then removing refractory metal impurities such as tungsten through complexation adsorption. Subsequently, alkali metal and transition metal impurities are removed through ion exchange, and high-purity ammonium molybdate crystals are obtained through recrystallization purification. Next, controlled calcination is used to decompose the ammonium molybdate into high-purity molybdenum trioxide under an oxidizing atmosphere. Then, multi-stage gas-phase hydrogen reduction is performed, combining segmented pre-reduction with high-temperature deep reduction to ensure the depth and uniformity of reduction, yielding metallic molybdenum powder. Finally, cooling and grading under an inert atmosphere yield ultra-high purity molybdenum powder with a purity of 4N–5N and controllable particle size distribution, meeting the application requirements of high-end electronic fields such as semiconductor integrated circuits and flat panel displays.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy and high-purity metal material preparation technology, specifically relating to a method for preparing ultra-high purity molybdenum powder with a purity of 4N to 5N (99.99% to 99.999%), and particularly relating to a deep impurity removal process that utilizes segmented controllable oxidation dissolution combined with complexation separation and multi-stage gas phase reduction. Background Technology

[0002] With the rapid development of electronic fields such as semiconductor integrated circuits, thin-film transistor liquid crystal displays (TFT-LCDs), and thin-film solar cells, the market demand for high-purity molybdenum powder continues to grow. Specifically, the flat panel display industry requires molybdenum powder purity of 4N (99.99%) or higher, while the integrated circuit industry requires 5N (99.999%) or higher. However, the purity of existing industrially produced molybdenum powder is generally only 99.95%, which is insufficient to meet the application requirements of high-end electronics industries.

[0003] Impurities in molybdenum powder significantly affect its application performance. Refractory metal impurities (such as tungsten, rhenium, tantalum, and niobium) are high-melting-point metals like molybdenum, with similar physicochemical properties, making deep separation difficult using traditional metallurgical methods. In particular, tungsten, affected by the lanthanide contraction effect, has an ionic radius extremely close to that of molybdenum, making tungsten-molybdenum separation a recognized technical challenge in the field of powder metallurgy. In addition, alkali metals (such as Na and K), radioactive elements (such as U and Th), transition metals (such as Fe, Ni, and Cu), and gaseous impurities (such as O, C, and N) all severely affect the conductivity, stress state, and high-temperature stability of molybdenum films.

[0004] In the prior art, CN117604276A discloses a high-purity molybdenum purification method based on liquid phase metallurgy. This method removes silicides and sulfides through hydrogen peroxide oxidation and then removes rhenium by water washing, increasing the molybdenum powder purity from 99.9% to 99.996%. However, this method has limited effectiveness in removing refractory metal impurities such as tungsten, and single-stage reduction is difficult to consistently achieve a purity of 5N. CN115178749B discloses a reduction method for preparing high-purity molybdenum powder, using anion exchange resin to purify ammonium molybdate solution. However, this process introduces organic reagents such as sodium alkyl sulfonate, posing a risk of carbon pollution.

[0005] Therefore, there is an urgent need in this field to develop a method for preparing ultra-high purity molybdenum powder that can deeply remove refractory metal impurities (especially achieve efficient separation of tungsten and molybdenum) while effectively removing alkali metals, transition metals and gaseous impurities. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing ultra-high purity molybdenum powder through segmented rate-controlled oxygen dissolution and selective complexation impurity removal, thereby solving the technical problems of difficulty in deep separation of tungsten and molybdenum and limited removal of refractory metal impurities in existing technologies. This invention employs a process of segmented rate-controlled oxidation dissolution, catalytic decomposition of residual hydrogen peroxide, and pH adjustment followed by complexation adsorption to deeply remove refractory metal impurities, including tungsten, as well as alkali metals and transition metal impurities, yielding ultra-high purity molybdenum powder suitable for the integrated circuit field.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention first provides a method for preparing ultra-high purity molybdenum powder by segmented rate-controlled oxygen dissolution and selective complexation impurity removal, comprising the following steps: S10, first add 10wt% to 15wt% of the total molybdenum powder raw material to the hydrogen peroxide solution. After the oxidation reaction starts, add the remaining molybdenum powder raw material at a constant rate over 2 to 4 hours, controlling the liquid-solid mass ratio to be (10 to 20): 1. After solid-liquid separation, a molybdenum peroxide complex solution is obtained. S20, after removing residual hydrogen peroxide from the molybdenum peroxide complex solution, a complexing agent is added to complex the tungsten element, and the tungsten impurities are removed by adsorption with a tungsten selective chelating resin; then the solution is concentrated and the pH is adjusted, impurities are removed by ion exchange, and finally ammonium molybdate crystals are obtained by recrystallization. S30, ammonium molybdate crystals are placed in a high-temperature resistant inert crucible and heated to 450-550℃ under an oxidizing atmosphere and held for 2-4 hours to obtain molybdenum trioxide powder; S40, under a hydrogen atmosphere, molybdenum trioxide powder is first kept at 400-500℃ for 1-2 hours, and then kept at 500-650℃ for 2-4 hours to obtain molybdenum dioxide powder. After being ball-milled and passed through a 100-200 mesh sieve, it is reduced at 850-1050℃ for 6-12 hours to obtain metallic molybdenum powder. S50 involves cooling metallic molybdenum powder to room temperature under an inert atmosphere, followed by air classification or ultrasonic sieving to obtain 4N or 5N grade molybdenum powder products with a particle size distribution D50 of 2–10 μm.

[0008] Specifically, step S10 employs a batch feeding method, starting the reaction with a small initial proportion and then uniformly adding the remaining molybdenum powder. This achieves safe and controllable oxidation and dissolution in the hydrogen peroxide system. Controlling the liquid-to-solid mass ratio helps ensure complete dissolution. After solid-liquid separation to remove insoluble matter, a molybdenum peroxide complex solution is obtained. Step S20 uses a step-by-step impurity removal route: first, decomposing the residual hydrogen peroxide to prevent subsequent oxidation of the complexing agent; then, separating tungsten and molybdenum through adsorption with tungsten selective chelating resin; followed by ion exchange to remove alkali metal and transition metal impurities; and finally, recrystallization purification. This approach can specifically reduce the content of various impurities. The process involves several steps: First, high-purity ammonium molybdate crystals are obtained. In step S30, the ammonium molybdate is placed in a high-temperature resistant inert crucible and calcined and decomposed in a controlled atmosphere, reducing external contamination and producing high-purity molybdenum trioxide powder. In step S40, a multi-stage hydrogen reduction process—first reducing to molybdenum dioxide at low temperature and then ball-milling followed by high-temperature deep reduction—improves reduction uniformity and depth, yielding metallic molybdenum powder. In step S50, cooling under an inert atmosphere prevents oxidation of the molybdenum powder, and particle size distribution is controlled by airflow classification or ultrasonic sieving to obtain 4N or 5N grade ultra-high-purity molybdenum powder. In summary, the entire process route does not use strong acids, strong alkalis, or toxic organic extractants, poses no additional carbon pollution risk, is safe and environmentally friendly, and has value for large-scale production.

[0009] Preferably, the purity of the molybdenum powder raw material is 99.5% to 99.9%; before step S10, a surface activation treatment is also included: the molybdenum powder raw material is ball-milled at room temperature under an inert atmosphere at a speed of 100 to 200 r / min for 30 to 60 min; or, the molybdenum powder raw material is soaked and activated at room temperature for 10 to 20 min using dilute nitric acid with a mass fraction of 0.5 wt% to 2 wt%.

[0010] Specifically, industrial molybdenum powder with a purity of 99.5%–99.9% is selected as raw material. This ensures that the raw material cost is controllable while providing a reasonable impurity basis for subsequent purification processes. Before oxidation and dissolution, the molybdenum powder is subjected to surface activation treatment. Ball milling at room temperature under an inert atmosphere can mechanically destroy any possible oxide passivation layer on the surface of the molybdenum powder and homogenize the surface activity state. Immersion in dilute nitric acid can remove the surface oxide layer and attached impurities through weak acid etching. Both activation methods help improve the uniformity and controllability of the subsequent hydrogen peroxide oxidation and dissolution, and reduce the phenomenon of violent local reactions caused by uneven surface activity.

[0011] Preferably, in step S10, the concentration of the hydrogen peroxide solution is 15wt% to 25wt%, wherein a stabilizer of 0.01wt% to 0.05wt% by mass is added beforehand, the stabilizer being phosphoric acid or hydroxyethylidene diphosphonic acid; and / or, the oxidation reaction temperature is 10 to 20°C, and the reaction stirring rate is 200 to 400 r / min; and / or, the solid-liquid separation is as follows: first passing through a 100 to 200 mesh standard sieve, and then filtering through a 0.5 to 1.0 μm polytetrafluoroethylene or polypropylene microporous membrane to obtain a molybdenum peroxide complex solution.

[0012] Specifically, a moderate concentration of hydrogen peroxide oxidant ensures the oxidative solubility of molybdenum powder while avoiding excessive concentration that could trigger a violent reaction. Stabilizers help inhibit the ineffective decomposition of hydrogen peroxide and improve the utilization rate of oxidant. Controlling the reaction temperature at 10–20°C and using a stirring rate of 200–400 r / min helps to slow down the exothermic reaction rate and enhance mass transfer, making the oxidation and dissolution process stable and controllable. A two-stage solid-liquid separation method, first using a 100–200 mesh sieve and then using a 0.5–1.0 μm polytetrafluoroethylene or polypropylene microporous membrane for precision filtration, can remove insoluble particles step by step, helping to obtain a molybdenum peroxide complex solution with high clarity.

[0013] Preferably, the stabilizer is hydroxyethylidene diphosphonic acid, and its addition amount is 0.02wt% to 0.03wt% of the mass of the hydrogen peroxide solution.

[0014] Specifically, the phosphonic acid group contained in hydroxyethylidene diphosphonic acid has a good stabilizing effect on hydrogen peroxide. Within this dosage range, it helps to inhibit the ineffective decomposition of hydrogen peroxide and slow down the exothermic reaction rate. At the same time, hydroxyethylidene diphosphonic acid has a certain complexing ability for metal ions, which can reduce the catalytic effect of trace metal ions in the solution on the decomposition of hydrogen peroxide to a certain extent. In addition, the addition amount is relatively low, which helps to avoid the introduction of foreign impurities that are difficult to remove due to excessive stabilizer.

[0015] Preferably, step S20 specifically includes: S201, the molybdenum peroxide complex solution was heated to 80-95°C, catalyzed with a platinum mesh and stirred for 30-60 min to decompose the residual hydrogen peroxide, and then confirmed with starch-potassium iodide test paper that there was no residual oxidizing property. S202, adjust the pH of the molybdenum peroxide complex solution to 4.0-5.5 with ammonia water, add ammonium citrate to a concentration of 0.05-0.3 mol / L, then adjust the pH to 3.0-4.0 with dilute nitric acid, and react at 60-80°C for 1-3 h; subsequently, separate by adsorption with tungsten-specific aminophosphonic acid chelating resin, with a resin column height-to-diameter ratio of (6-10):1 and a solution flow rate of 6-12 m / h; S203: The solution obtained in step S202 is heated to 90-110°C for evaporation and concentration, cooled to 40-60°C, and then ammonia is added to adjust the pH to 8.5-10.5. Subsequently, cationic impurities are removed by passing the solution through an H-type strong acid cation exchange resin column at a flow rate of 5-12 m / h, and anionic impurities are removed by passing the solution through an OH-type strong base anion exchange resin column to obtain an ammonium molybdate solution. S204, ammonium molybdate solution is evaporated and concentrated at a vacuum degree ≤ -0.08MPa and a temperature of 70-85°C, with a concentration ratio of (3-5):1; then cooled to 5-15°C at a cooling rate of 1-3°C / min for crystallization, with a crystallization time ≥12h, and ammonium molybdate crystals are obtained after separation and washing.

[0016] Specifically, step S201, by heating to 80–95°C and using platinum mesh for catalytic stirring, effectively decomposes residual hydrogen peroxide, preventing it from oxidizing the subsequently added ammonium citrate complexing agent. Starch-potassium iodide test paper detection helps confirm complete decomposition, providing a stable solution basis for subsequent impurity removal. Step S202, by adjusting the pH stepwise and adding ammonium citrate, allows tungsten to form a complex anion while molybdenum exists as a molybdate ion. Selective adsorption by a tungsten-specific aminophosphonic acid chelating resin facilitates deep separation of tungsten and molybdenum, allowing for control of the resin column height-to-diameter ratio and solution flow rate. This helps ensure the adsorption effect; in step S203, molybdenum is converted into ammonium molybdate by evaporation and concentration and pH adjustment. The molybdenum is then passed through an H-type strong acid cation exchange resin column and an OH-type strong base anion exchange resin to remove alkali metal, transition metal cations and anions, respectively, which helps to further reduce the impurity content in the solution; in step S204, vacuum low-temperature evaporation and concentration and slow crystallization by controlling the cooling rate are used to facilitate the removal of impurities during crystallization. After separation and washing, high-purity ammonium molybdate crystals are obtained, providing high-quality raw materials for subsequent calcination and reduction.

[0017] Preferably, the separation and washing in step S204 is as follows: after centrifugation, the ammonium molybdate crystals are washed 2 to 3 times with deionized water with a resistivity ≥18.2 MΩ·cm.

[0018] Specifically, centrifugation can quickly separate the crystals from the mother liquor. The impurity ion content in high resistivity deionized water is extremely low, and it is not easy to introduce new impurities during the washing process. Multiple washings help to remove the mother liquor and adsorbed trace impurity ions carried on the crystal surface, thereby improving the purity of ammonium molybdate crystals to a certain extent.

[0019] Preferably, in step S30, the high-temperature resistant inert crucible is a platinum crucible or a high-purity alumina crucible that has undergone high-temperature calcination passivation treatment at temperatures above 1200°C, and the heating rate is 2–5°C / min; and / or, the oxidizing atmosphere is dry air or oxygen with a purity of not less than 99.999%, and the gas flow rate is 5–15 L / min.

[0020] Specifically, platinum crucibles are chemically stable and do not readily react with reactants at high temperatures, while passivated alumina crucibles are less expensive and help reduce the release of impurities at high temperatures. Both can reduce the contamination of molybdenum trioxide by the crucible material. A programmed heating rate of 2–5°C / min is beneficial for the stable decomposition of ammonium molybdate and avoids powder splashing or incomplete decomposition caused by excessively rapid heating. The introduction of dry air or oxygen with a purity of not less than 99.999% and a controlled flow rate of 5–15 L / min provides a clean oxidizing atmosphere for calcination and decomposition, while also helping to remove ammonia and water vapor generated during decomposition in a timely manner, thus ensuring complete decomposition and obtaining molybdenum trioxide powder with high purity to a certain extent.

[0021] Preferably, in step S40, molybdenum trioxide powder is spread in a pure molybdenum or tantalum boat-shaped dish with a layer thickness of 10–25 mm; and / or, the purity of hydrogen is not less than 99.999%, and the dew point is not higher than -60°C; and / or, during the heat preservation stages at 400–500°C and 500–650°C, the hydrogen flow rate is 8–20 m³ / h. 3 / h; and / or, during the reduction phase at 850–1050℃, the hydrogen flow rate is 15–30 m³ / h. 3 / h, the boat pushing speed is 15~30mm / min.

[0022] Specifically, pure molybdenum or tantalum boats are chemically stable under high-temperature reducing atmospheres, making them less likely to react with molybdenum powder or introduce foreign impurities. A thinner material layer facilitates hydrogen permeation and the removal of water vapor generated during reduction, improving the uniformity of reduction. The aforementioned high-purity hydrogen helps ensure the cleanliness of the reducing atmosphere, reducing the impact of oxygen and trace impurities on the product. Matching the hydrogen requirements of the reduction reaction in stages helps ensure sufficient and uniform reduction, and to a certain extent reduces the oxygen content in the product.

[0023] Preferably, when preparing 4N grade molybdenum powder, the ammonium molybdate crystals obtained in step S204 are recrystallized at least twice; when preparing 5N grade molybdenum powder, the ammonium molybdate crystals obtained in step S204 are recrystallized at least three times.

[0024] Specifically, multiple recrystallizations can utilize the difference in solubility between ammonium molybdate and impurities to gradually enrich and remove trace impurities in the mother liquor that are similar in properties to ammonium molybdate, so that the crystal purity gradually increases with the number of recrystallizations. Setting the number of recrystallizations in stages helps to meet the requirements of different purity levels while avoiding the increased costs and decreased product yield caused by over-purification.

[0025] Preferably, after step S40 and before step S50, the process further includes: when preparing 5N grade molybdenum powder, keeping the metallic molybdenum powder at 1100–1300°C for 2–4 hours under hydrogen protection.

[0026] Specifically, the hydrogen reducing atmosphere at high temperature helps to further remove residual oxygen in the molybdenum powder, while also causing some trace impurities with relatively high vapor pressure to volatilize, thereby reducing the oxygen and impurity content in the product to a certain extent. This step is only set for 5N grade products with higher purity requirements, which helps to meet the ultra-high purity requirements while avoiding unnecessary high-temperature treatment of 4N grade products, thus balancing product quality and production costs.

[0027] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a method for preparing ultra-high purity molybdenum powder using segmented, rate-controlled hydrogen peroxide dissolution and selective complexation for impurity removal. The method first employs segmented, rate-controlled hydrogen peroxide dissolution, allowing the molybdenum powder to dissolve safely and controllably in a hydrogen peroxide system into a molybdenum peroxide complex solution. Secondly, selective complexation is used for stepwise impurity removal, first decomposing residual hydrogen peroxide and then removing refractory metal impurities such as tungsten through complexation adsorption. Subsequently, alkali metal and transition metal impurities are removed through ion exchange, and high-purity ammonium molybdate crystals are obtained through recrystallization purification. Then, controlled calcination is used to decompose ammonium molybdate into high-purity molybdenum trioxide under an oxidizing atmosphere. Next, multi-stage gas-phase hydrogen reduction is performed, combining segmented pre-reduction with high-temperature deep reduction to ensure the depth and uniformity of reduction, yielding metallic molybdenum powder. Finally, cooling and grading under an inert atmosphere yield ultra-high purity molybdenum powder with a purity of 4N–5N and controllable particle size distribution, meeting the application requirements of high-end electronic fields such as semiconductor integrated circuits and flat panel displays. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process for preparing ultra-high purity molybdenum powder by segmented rate-controlled peroxy dissolution and selective complexation impurity removal provided in an embodiment of the present invention.

[0029] Figure 2 This is a process flow diagram of the preparation of ultra-high purity molybdenum powder provided in Example 1. Detailed Implementation

[0030] 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.

[0031] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and are not intended to limit the scope of protection of the present invention to the parameter ranges of the following embodiments. Unless otherwise specified, the reagents or instruments used in the present invention are all conventional products that can be purchased through commercial channels.

[0032] Example 1 (4N grade ultra-high purity molybdenum powder): Please see Figure 1 and Figure 2 This embodiment 1 provides a method for preparing 4N grade ultra-high purity molybdenum powder, the specific steps of which are as follows: Step (1), segmented rate-controlled oxidation dissolution and solid-liquid separation: Step (1.1), surface activation pretreatment: Take 1 kg of industrial molybdenum powder raw material with a purity of 99.5%, and ball mill it at room temperature under a nitrogen atmosphere at a speed of 200 r / min for 20 min to homogenize the surface activity of the molybdenum powder for later use. Step (1.2), reverse feeding and controlled-rate dissolution: 15 kg of 20 wt% hydrogen peroxide solution was placed in a reactor, and 0.025 wt% hydroxyethylidene diphosphonic acid was added as a stabilizer beforehand. The reaction temperature was maintained at 20 °C and the stirring rate was 300 r / min under stirring and external cooling conditions. The activated molybdenum powder was added to the hydrogen peroxide solution in batches. The initial addition was 120 g (12 wt% of the total molybdenum powder). After the reaction started, the remaining 880 g of molybdenum powder was added at a uniform rate over 3 hours, controlling the liquid-solid mass ratio at 15:1, so that the molybdenum powder was oxidized and dissolved to form a molybdenum peroxide complex solution. Step (1.3), residual solids separation: The dissolved slurry is first passed through a 200-mesh standard sieve, and then precisely filtered using a 0.8μm polytetrafluoroethylene microporous membrane to obtain a clear molybdenum peroxide complex solution.

[0033] Step (2), selective complexation and stepwise impurity removal: Step (2.1), catalytic decomposition of residual hydrogen peroxide: The molybdenum peroxide complex solution obtained in step (1.3) is heated to 90°C, and a platinum mesh is used for catalysis. The mixture is stirred for 40 min to decompose the residual hydrogen peroxide. The presence of residual oxidizing properties is confirmed by testing with starch-potassium iodide test paper. After decomposition, high-purity ammonia is added immediately to adjust the pH of the system to 8.5 to avoid molybdenum loss caused by the precipitation of molybdenum acid under acidic conditions.

[0034] Step (2.2), deep tungsten removal: The solution obtained in step (2.1) was kept at a temperature of 55–60°C with high-purity ammonia water. Ammonium citrate was added to a concentration of 0.1 mol / L, and the mixture was stirred for 30 min, utilizing the selective complexation and masking effect of ammonium citrate on molybdate. The system pH was maintained at 8.2–9.0. The solution was then passed through a tungsten-specific aminophosphonic acid chelating resin (D403) that had transformed to the OH form for adsorption and separation. The resin column height-to-diameter ratio was 9:1, and the empty column flow rate was 1.5 m / h. Under weakly alkaline conditions, tungsten was selectively adsorbed by the resin in the form of monomeric tungstate anions, while molybdenum… Ammonium citrate soluble complexes flow out of the resin column with the solution, achieving deep separation of the molybdenum matrix from trace tungsten impurities; Step (2.3), deep removal of alkali and transition metals: The solution obtained in step (2.2) is heated to 100℃ for evaporation and concentration, while simultaneously decomposing any remaining organic matter; then cooled to 40℃, and high-purity ammonia is added to adjust the pH to 9, converting molybdenum to ammonium molybdate; this solution is then passed through an H-type strong acid cation exchange resin column at a flow rate of 10 m / h to remove Na. + K + Fe 3+ Ni 2+ Cu 2+ Cation impurities are then passed through an OH-type strong basic anion exchange resin column to remove Cl. - SO4 2- NO3 - Anionic impurities.

[0035] Step (2.4), precise crystallization purification: The ammonium molybdate solution after ion exchange was concentrated and evaporated under a vacuum of -0.1 MPa and a temperature of 80 °C, with the concentration ratio controlled at 4:1; then cooled to 10 °C at a cooling rate of 3 °C / min for crystallization, and the crystallization time was 14 h; after centrifugation, the crystals were washed twice with deionized water with a resistivity of 18.2 MΩ·cm to obtain ammonium molybdate crystals.

[0036] Step (2.5), multiple recrystallization: The ammonium molybdate crystals obtained in step (2.4) are recrystallized twice under the above crystallization conditions to obtain high-purity ammonium molybdate crystals.

[0037] Step (3), high-purity molybdenum trioxide is prepared by controlled calcination: the high-purity ammonium molybdate crystals obtained in step (2) are placed in a platinum crucible and heated to 500°C at a heating rate of 3°C / min in an ultra-clean environment with a cleanliness level better than Class 1000. The temperature is held for 3 hours for calcination and decomposition. High-purity oxygen with a purity of 99.999% is introduced during the calcination process at a gas flow rate of 10L / min to obtain high-purity molybdenum trioxide powder; Step (4), multi-stage gas-phase hydrogen reduction: Step (4.1), a low-temperature pre-reduction: The high-purity molybdenum trioxide powder obtained in step (3) is evenly spread in a pure molybdenum boat with a material layer thickness of 20 mm, and placed in a reduction furnace; high-purity hydrogen gas with a purity of 99.999% and a dew point of -60℃ is introduced at a flow rate of 10 m³ / h. 3 / h; The temperature is controlled by a program, with the first temperature zone at 450℃ for 2 hours and the second temperature zone at 600℃ for 3 hours, so that molybdenum trioxide is converted into molybdenum dioxide.

[0038] Step (4.2), Second-stage high-temperature deep reduction: The molybdenum dioxide powder obtained from the first-stage reduction in step (4.1) is ball-milled, passed through a 200-mesh sieve, and then reloaded into a pure molybdenum boat; the reduction temperature is controlled at 900℃ and the hydrogen flow rate is 20m³ / h. 3 The boat speed is 20 mm / min, and the reduction time is 10 h, so that molybdenum dioxide is deeply reduced to metallic molybdenum powder.

[0039] Step (5), post-processing and packaging: The molybdenum powder obtained from the reduction in step (4.2) is cooled to room temperature in an ultra-clean glove box, and air classification is performed under the protection of high-purity argon to obtain a molybdenum powder product with a particle size distribution D50 of 5μm, and then vacuum-sealed.

[0040] According to Glow Discharge Mass Spectrometry (GDMS) analysis, the molybdenum powder obtained in Example 1 has a purity of 99.99%, meeting the 4N grade requirement.

[0041] Example 2 (Preparation of 5N grade ultra-high purity molybdenum powder): This embodiment 2 provides a method for preparing 5N grade ultra-high purity molybdenum powder. The specific preparation steps are roughly the same as those in embodiment 1, except that step (2.5) is different, and step (4.3) is performed after step (4.2): Step (2.5), multiple recrystallization: The ammonium molybdate crystals obtained in step (2.4) are recrystallized three times under the above crystallization conditions to obtain high-purity ammonium molybdate crystals.

[0042] Step (4.3), three-stage ultra-high temperature crystallization degassing: The molybdenum powder obtained from the two-stage reduction in step (4.2) is subjected to ultra-high temperature treatment at 1200℃ for 4 hours under hydrogen protection. This process is used to remove gaseous impurities adsorbed inside the powder, promote the volatilization of low-boiling-point alkali metal impurities, and achieve homogenization of molybdenum powder grains. High-boiling-point refractory metal impurities such as tungsten, tantalum, and niobium cannot be volatilized and removed in this step, and their removal requires the previous wet deep impurity removal process.

[0043] According to glow discharge mass spectrometry, the total content of metallic impurities in the molybdenum powder obtained in Example 2 is ≤10ppm, and the purity of metallic impurities is 99.999%, which meets the 5N grade requirement; interstitial gas impurities are detected separately, and the oxygen content of the product is ≤80ppm.

[0044] Comparative Example 1 (Preparation of conventional molybdenum powder): Comparative Example 1 provides a conventional method for preparing molybdenum powder. The specific preparation steps are roughly the same as those in Example 1, except for steps (1.2) and (4). Step (2.2) is omitted, and the solution obtained in step (2.1) is directly sent to step (2.3) for processing. Specifically, steps (1.2) and (4) are as follows: Step (1.2), Oxidation and Dissolution: 15 kg of a 20 wt% hydrogen peroxide solution was placed in a reactor, and 0.025 wt% hydroxyethylidene diphosphonic acid was added as a stabilizer beforehand. The reaction temperature was maintained at 20°C under stirring and external cooling conditions, and the stirring rate was 300 r / min. Then, without using a segmented, controlled-rate feeding method, 1 kg of activated molybdenum powder was added all at once to the above hydrogen peroxide solution, controlling the liquid-to-solid mass ratio at 15:1. During the addition process, the reaction was violently exothermic, and the temperature inside the reactor rapidly rose to 45°C, accompanied by the generation of a large number of bubbles.

[0045] Step (4), hydrogen reduction: without staged heating reduction, the molybdenum trioxide powder was directly reduced with hydrogen at 950℃ for 10 hours, with a hydrogen flow rate of 20 m³ / h. 3 The boat is pushed at a speed of 20 mm / min per hour, which directly reduces molybdenum trioxide to metallic molybdenum powder.

[0046] According to glow discharge mass spectrometry analysis, the molybdenum powder obtained in Comparative Example 1 has a purity of 99.9%, with a tungsten content of 30 ppm and an oxygen content of 1000 ppm, which does not meet the 4N grade requirements.

[0047] A comparison of Examples 1-2 and Comparative Example 1 shows that the segmented rate-controlled oxidation dissolution and the use of ammonium citrate in a weakly alkaline system are effective. Example 1, using the selective complexation stepwise impurity removal and multi-stage gas-phase hydrogen reduction process with D403 resin, yielded molybdenum powder with a purity of 99.99%, meeting the 4N grade requirement. Example 2, based on Example 1, increased the number of recrystallization steps and added an ultra-high temperature crystallization degassing step, further improving the purity to 99.999%, meeting the 5N grade requirement. However, Comparative Example 1, which omitted the above three core processes, yielded molybdenum powder with a purity of only 99.90%, a tungsten content as high as 30 ppm, and an oxygen content of 1000 ppm, failing to meet the 4N grade requirement.

[0048] The above results indicate that segmented rate-controlled oxidation dissolution can suppress the runaway boiling of the hydrogen peroxide system, ensuring the full and stable dissolution of molybdenum powder; under weakly alkaline conditions, ammonium citrate complexation and masking of molybdenum, combined with D403 chelating resin, can achieve deep selective separation of tungsten impurities; multi-stage gas-phase hydrogen reduction can effectively reduce interstitial oxygen impurities in molybdenum powder, ensuring uniform reduction; the synergistic effect of the above process units enables the indicators of metallic and gaseous impurities in molybdenum powder to meet the application requirements of high-end electronic fields such as semiconductor integrated circuits and flat panel displays. Ammonium paramolybdate recrystallization is mainly used to remove ionic anionic and cation-acid impurities, but its ability to separate high-boiling-point refractory metal impurities such as tungsten is limited; ultra-high temperature hydrogen treatment at 1200℃ can only remove alkali metals and gaseous impurities, but cannot remove tungsten impurities; refractory metal impurities must be pre-removed by a wet resin adsorption unit.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention first employs segmented, rate-controlled hydrogen peroxide oxidation for dissolution, ensuring stable and controllable dissolution of molybdenum powder in the hydrogen peroxide system. Then, a process sequence of first decomposing residual hydrogen peroxide, followed by pH adjustment and complexation, and finally adsorption via tungsten selective chelating resin avoids oxidation of complexing agents such as ammonium citrate, facilitating deep separation of tungsten and molybdenum without introducing additional organic carbon pollution. Finally, combining precise crystallization purification with multi-stage gas-phase hydrogen reduction, ultra-high purity molybdenum powder with a purity of 99.99%–99.999% and a particle size distribution D50 of 2–10 μm can be obtained, meeting the application requirements of high-end electronic fields such as semiconductor integrated circuits and flat panel displays. The entire preparation process does not use strong acids, strong alkalis, or toxic organic extractants, making it safe and environmentally friendly, and possessing value for large-scale production.

[0050] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0051] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing ultra-high purity molybdenum powder by segmented rate-controlled oxygen dissolution and selective complexation impurity removal, characterized in that, Includes the following steps: S10, first add 10wt% to 15wt% of the total molybdenum powder raw material to the hydrogen peroxide solution. After the oxidation reaction starts, add the remaining molybdenum powder raw material at a constant rate within 2 to 4 hours, and control the liquid-solid mass ratio to be (10 to 20):

1. After solid-liquid separation, a molybdenum peroxide complex solution is obtained. S20, after removing residual hydrogen peroxide from the molybdenum peroxide complex solution, a complexing agent is added to complex the tungsten element therein, and the tungsten impurities are removed by adsorption with a tungsten selective chelating resin. The solution was then concentrated and the pH was adjusted. Impurities were removed by ion exchange, and finally purified by recrystallization to obtain ammonium molybdate crystals. S30, the ammonium molybdate crystals are placed in a high-temperature resistant inert crucible and heated to 450-550°C under an oxidizing atmosphere and held for 2-4 hours to obtain molybdenum trioxide powder; S40, under a hydrogen atmosphere, the molybdenum trioxide powder is first kept at 400-500℃ for 1-2 hours, and then kept at 500-650℃ for 2-4 hours to obtain molybdenum dioxide powder. After being ball-milled and passed through a 100-200 mesh sieve, it is reduced at 850-1050℃ for 6-12 hours to obtain metallic molybdenum powder. S50, the metallic molybdenum powder is cooled to room temperature under an inert atmosphere, and then obtained as 4N or 5N grade molybdenum powder with a particle size distribution D50 of 2 to 10 μm by air classification or ultrasonic sieving.

2. The preparation method according to claim 1, characterized in that, The purity of the molybdenum powder raw material is 99.5% to 99.9%; before step S10, a surface activation treatment is also included: the molybdenum powder raw material is ball-milled at room temperature under an inert atmosphere at a speed of 100 to 200 r / min for 30 to 60 min; or, the molybdenum powder raw material is soaked and activated at room temperature for 10 to 20 min using dilute nitric acid with a mass fraction of 0.5 wt% to 2 wt% for 10 to 20 min.

3. The method according to claim 1, characterized in that, In step S10, the concentration of the hydrogen peroxide solution is 15wt% to 25wt%, wherein a stabilizer of 0.01wt% to 0.05wt% by mass is added beforehand, the stabilizer being phosphoric acid or hydroxyethylidene diphosphonic acid; and / or, the oxidation reaction temperature is 10 to 20°C, and the reaction stirring rate is 200 to 400 r / min; and / or, the solid-liquid separation is as follows: first passing through a 100 to 200 mesh standard sieve, and then filtering through a 0.5 to 1.0 μm polytetrafluoroethylene or polypropylene microporous membrane to obtain the molybdenum peroxide complex solution.

4. The method according to claim 3, characterized in that, The stabilizer is hydroxyethylidene diphosphonic acid, and its addition amount is 0.02wt% to 0.03wt% of the mass of the hydrogen peroxide solution.

5. The method according to claim 1, characterized in that, The S20 step specifically includes: S201, the molybdenum peroxide complex solution is heated to 80-95°C, catalyzed with a platinum mesh and stirred for 30-60 minutes to decompose the residual hydrogen peroxide. Then, the residual oxidizing property is confirmed by starch-potassium iodide test paper. After decomposition, high-purity ammonia water is added immediately to adjust the pH of the system to 8.5 to avoid molybdenum loss caused by the precipitation of molybdenum acid under acidic conditions. S202, maintaining the molybdenum peroxide complex solution at a temperature of 55°C. At 60°C, ammonium citrate was added to a concentration of 0.05–0.3 mol / L. Taking advantage of the selective complexation and masking effect of ammonium citrate on molybdate, the reaction was carried out at 60–80°C for 1–3 h. Subsequently, the mixture was separated by adsorption using a tungsten-specific aminophosphonic acid chelating resin with a column height-to-diameter ratio of (6–10):1 and a solution flow rate of 6–12 m / h. S203, the solution obtained in step S202 is heated to 90-110°C for evaporation and concentration, cooled to 40-60°C, and then ammonia is added to adjust the pH to 8.5-10.5; subsequently, it is passed through H at a flow rate of 5-12 m / h. The cationic impurities are removed by passing the strong acid cation exchange resin column of type OH, and the anionic impurities are removed by passing the strong base anion exchange resin column of type OH, to obtain an ammonium molybdate solution. S204, the ammonium molybdate solution is evaporated and concentrated under vacuum ≤ -0.08 MPa and temperature 70-85°C, with a concentration ratio of (3-5):1; then cooled to 5-15°C at a cooling rate of 1-3°C / min for crystallization, with a crystallization time ≥12h, and the ammonium molybdate crystals are obtained after separation and washing.

6. The method according to claim 5, characterized in that, The separation and washing process in step S204 is as follows: after centrifugation, the ammonium molybdate crystals are washed 2 to 3 times with deionized water with a resistivity ≥18.2 MΩ·cm.

7. The method according to claim 1, characterized in that, In step S30, the high-temperature resistant inert crucible is a platinum crucible or a high-purity alumina crucible that has undergone high-temperature calcination and passivation treatment at temperatures above 1200°C, with a heating rate of 2–5°C / min; and / or, the oxidizing atmosphere is dry air or oxygen with a purity of not less than 99.999%, with a gas flow rate of 5–15 L / min.

8. The method according to claim 1, characterized in that, In step S40, the molybdenum trioxide powder is spread in a pure molybdenum or tantalum boat-shaped dish with a layer thickness of 10–25 mm; and / or, the purity of the hydrogen gas is not less than 99.999%, and the dew point is not higher than -60°C; and / or, during the heat preservation stages at 400–500°C and 500–650°C, the hydrogen flow rate is 8–20 m³ / h. 3 / h; and / or, during the reduction phase at 850–1050℃, the hydrogen flow rate is 15–30 m³ / h. 3 / h, the boat pushing speed is 15~30mm / min.

9. The method according to claim 5, characterized in that, When preparing 4N grade molybdenum powder, the ammonium molybdate crystals obtained in step S204 are recrystallized at least twice; when preparing 5N grade molybdenum powder, the ammonium molybdate crystals obtained in step S204 are recrystallized at least three times.

10. The method according to claim 1, characterized in that, After step S40 is completed and before step S50, the process further includes: when preparing 5N grade molybdenum powder, the metallic molybdenum powder is kept at 1100-1300°C for 2-4 hours under hydrogen protection.

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