Method for recovering tungsten by molten salt electrolysis

Abstract

This application belongs to the field of metallurgical technology and provides a method for recovering tungsten by molten salt electrolysis. The method includes: adding molten tungstate salt to a metallic electrolytic cell; heating the molten tungstate salt to a first temperature using a heater placed inside the electrolytic cell; activating a cooling system located outside the electrolytic cell; while maintaining the cooling system on, continuing to heat the molten tungstate salt to a second temperature using the heater, causing the molten tungstate salt on the inner wall surface of the electrolytic cell to solidify and form a solid protective shell layer; inserting the cathode and anode into the molten tungstate salt for electrolysis, while maintaining the heater on to compensate for heat loss; and removing the cathode and collecting the electrolysis products after electrolysis. This ensures the protective layer is in place before the molten salt becomes corrosive, preventing corrosion of the cell and the introduction of metallic impurities; simultaneously, the independent internal heater decouples heating from electrolysis, reducing energy consumption.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, and in particular to a method for recovering tungsten by molten salt electrolysis. Background Technology

[0002] Tungstate molten salt electrolysis is one of the important technical approaches for recycling waste tungsten resources. This method uses molten tungstate salt as the electrolyte and usually uses waste tungsten material as the anode. Tungsten is deposited on the cathode through high-temperature electrochemical reduction, thereby achieving selective recycling of waste tungsten material.

[0003] Currently, this technology is only applied in small-scale experimental settings, and the electrolysis process generally employs external heating, with alumina crucibles being the primary electrolytic vessels. The heat source for external heating is located outside the electrolytic cell, requiring heat to penetrate the cell wall and be conducted into the molten salt. This inherently results in slow heating rates and low thermal efficiency. Long-term high-temperature operation exacerbates the risk of chemical corrosion and thermal shock cracking of the alumina crucible, leading to frequent crucible replacements. Limited by the manufacturing process and mechanical properties of alumina crucibles, the diameter of alumina electrolytic vessels cannot be significantly increased to over 350 mm, failing to meet the demands of large-scale production and hindering the industrial scaling-up of this technology.

[0004] In external heating mode, heat is conducted into the molten salt from the outside of the tank wall, resulting in a long heat transfer path and significant heat loss. When a lower electrolysis current is used, the Joule heat generated by the current is limited. Coupled with the insufficient heating capacity of external heating, the overall heat cannot maintain a constant electrolysis temperature in the molten salt system, leading to instability in the electrolysis process and large fluctuations in product quality. If the current is increased to raise the temperature, the electrolysis conditions deviate from the suitable process window, resulting in decreased current efficiency and increased energy consumption.

[0005] Therefore, it is necessary to develop new methods for recovering tungsten by electrolysis of tungstate molten salts on a ton-scale basis. Summary of the Invention

[0006] This application provides a method for recovering tungsten by molten salt electrolysis, the method comprising: Electrolytic cells made of metal are available; Add molten tungstate salt to the electrolytic cell; The molten tungstate salt is heated to a first temperature and held at that temperature using a heater placed inside the electrolytic cell, in order to dry and preheat the molten tungstate salt. The cooling system located outside the electrolytic cell is activated to lower the temperature of the inner wall of the electrolytic cell below the melting point of the tungstate molten salt. While keeping the cooling system on, the heater continues to heat the molten tungstate salt to a second temperature and perform a second heat preservation, so that the molten tungstate salt melts to obtain molten tungstate electrolyte, and the molten tungstate electrolyte on the inner wall surface of the electrolytic cell solidifies to form a solid shell protective layer. At least one set of cathodes and anodes are inserted into the molten tungstate salt for electrolysis, and the heater is kept on to maintain the molten tungstate salt at the electrolysis temperature. Through the electrolysis, tungsten-containing electrolytic products are formed on the cathode surface.

[0007] In some embodiments of this application, the tungstate molten salt comprises tungstate and tungsten oxide.

[0008] In some embodiments of this application, the tungstate is sodium tungstate, the tungsten oxide is tungsten trioxide, and the mass ratio of sodium tungstate to tungsten trioxide is 100:(6-9).

[0009] In some embodiments of this application, the first temperature is 100°C to 200°C lower than the melting point of the tungstate molten salt, and the second temperature is 0°C to 200°C higher than the melting point of the tungstate molten salt.

[0010] In some embodiments of this application, the first temperature is 400℃~500℃, and the first heat preservation time is 4 hours~6 hours.

[0011] In some embodiments of this application, the second temperature is 600°C to 800°C, and the second heat preservation time is 2 hours to 4 hours.

[0012] In some embodiments of this application, the diameter of the electrolytic cell is 800mm to 1200mm, the depth of the electrolytic cell is 1000mm to 1200mm, and the salt content of the electrolytic cell is 800kg to 3000kg.

[0013] In some embodiments of this application, the thickness of the solid shell protective layer is 15mm to 100mm. If the protective layer thickness is too low, it may cause localized overheating, melting, and penetration, damaging the tank wall; if the protective layer thickness is too high, it may reduce the effective volume of the electrolytic cell and decrease the actual amount of material used per batch.

[0014] Furthermore, the thickness of the solid crust protective layer on the inner wall of the electrolytic cell is 15mm to 30mm, and the thickness of the solid crust protective layer at the bottom of the electrolytic cell is 70mm to 100mm.

[0015] In some embodiments of this application, the electrolysis is performed using a constant current electrolysis method, with an electrolysis current of 30A to 200A, an electrolysis voltage of 20V to 35V, an electrolysis temperature of 700℃ to 800℃, and an electrolysis time of 3 hours to 12 hours.

[0016] If the electrolysis time is too short, insufficient electrolysis will be achieved, resulting in low electrolysis efficiency. If the electrolysis time is too long, the anode electrolysis will be exhausted or the cathode will reach saturation, interrupting the electrolysis process. Excessive electrolysis time wastes time and equipment capacity, reducing production efficiency. If the electrolysis current is too low, the electrolytic product powder particle size will be small, but the electrolysis efficiency will be low. If the electrolysis current is too high, the electrolysis efficiency will be high, but the electrolytic product powder will agglomerate with excessively large particle sizes.

[0017] In some embodiments of this application, during the heating to the first temperature, the second temperature, and the first and second heat preservation processes, the heating power of the heater is 25 kW to 35 kW, and during the electrolysis process, the heating power of the heater is 2 kW to 5 kW.

[0018] In some embodiments of this application, the cathode is a tungsten rod with a diameter of 20 mm to 35 mm.

[0019] In some embodiments of this application, the anode is waste tungsten material, and the tungsten content in the waste tungsten material is 95 wt% or more.

[0020] In some embodiments of this application, during the electrolysis process, the length of the cathode submerged below the surface of the molten tungstate electrolyte is 100 mm to 200 mm, and the length of the anode submerged below the surface of the molten tungstate electrolyte is 80 mm to 120 mm.

[0021] In some embodiments of this application, the anode and cathode are in one, two, or three groups, and each group of anodes and cathodes is simultaneously energized for electrolysis.

[0022] In some embodiments of this application, the number of cathodes and anodes is N, where N≥2; and the method further includes: Once the cathode in operation has achieved enrichment of electrolytic products, it is raised and removed from the electrolytic cell, and another cathode is placed in the molten tungstate electrolyte to continue electrolysis; and / or Once the anode used in the operation is consumed, it is removed from the electrolytic cell, and another anode is placed in the molten tungstate electrolyte to continue electrolysis.

[0023] The beneficial effects of the technical solutions provided in this application include at least the following: The method described in this application involves electrolyzing molten tungstate salt using an electrolytic cell made of metal and equipped with an internal heater. Specifically, the molten tungstate salt is first heated to a first temperature by the heater inside the electrolytic cell and then kept at that temperature for a first time to dry and preheat it. The cooling system outside the electrolytic cell is then activated to keep the temperature of the inner wall of the electrolytic cell below the melting point of the molten tungstate salt. While maintaining the cooling system, the molten tungstate salt is further heated to a second temperature by the heater and kept at that temperature for a second time to melt it, resulting in a molten tungstate electrolyte. The molten tungstate electrolyte on the surface of the inner wall of the electrolytic cell solidifies to form a solid protective shell layer. The cathode and anode are then inserted into the molten tungstate electrolyte for electrolysis, and the heater is kept on to maintain the molten tungstate electrolyte at the electrolysis temperature. Through this electrolysis, tungsten-containing electrolytic products are formed on the cathode surface. This method combines a metal electrolytic cell with a solid protective shell formed by molten tungstate salt, which can solve the problems of impurities introduced by corrosion of alumina crucibles, size limitations preventing scale-up, and thermal shock cracking. Heating through an internal heater decouples heating from electrolysis, resolving the contradiction between insufficient heat at low currents and the shift in the electrochemical window at high currents, thus balancing stable electrolysis with sufficient heat supply. Active adjustment of the cooling system ensures the stable existence of the protective layer throughout the electrolysis process, thereby protecting the metal electrolytic cell from chemical corrosion by high-temperature molten tungstate salt, guaranteeing product purity, extending equipment lifespan, and improving operational safety, meeting the requirements of industrial production. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of an electrolysis device provided in an embodiment of this application; Figure 2 This is a schematic diagram of a cooling system provided in an embodiment of this application; Figure 3 This is a schematic diagram of an electrode layout provided in an embodiment of this application; Figure 4 This is the X-ray diffraction pattern of the tungsten powder prepared in Example 1; Figure 5 This is the X-ray diffraction pattern of the tungsten powder prepared in Example 2; Figure 6 This is the X-ray diffraction pattern of the powder prepared in Example 3; Figure 7 This is a schematic diagram of another electrode layout provided in an embodiment of this application; Figure 8 The X-ray diffraction pattern of the powder prepared in Example 4; Figure 9 The X-ray diffraction pattern of the tungsten powder prepared in Example 5 is shown.

[0026] Figure 10 The X-ray diffraction pattern of the powder prepared in Example 6 is shown.

[0027] Figure 11 The X-ray diffraction pattern of the powder prepared in Example 10 is shown.

[0028] Explanation of reference numerals in the attached figures: 11. Electrolytic cell; 12. Heater; 13. Cooling system; 14. Cathode; 15. Anode; 16. Tungstate molten salt; 17. Solid crust protective layer. Detailed Implementation

[0029] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0030] The "scope" disclosed in this application is defined in the form of a lower limit and / or an upper limit, whereby a given scope is defined by selecting a lower limit and / or an upper limit. This type of scope may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined scope, and any lower limit can be combined with other lower limits to form an undefined scope, similarly, any upper limit can be combined with any other upper limit to form an undefined scope. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value, or with other lower or upper limits, to form an undefined scope.

[0031] It should be noted that in this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0032] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0033] In related technologies, alumina crucibles react with alkaline oxides in a high-temperature alkaline molten salt environment to form aluminates. The released trivalent aluminum ions are co-deposited on the cathode during electrolysis, causing excessive aluminum impurities in the tungsten product. Furthermore, the crucible is limited by ceramic processing technology, making large-scale production difficult. It also exhibits poor thermal shock resistance, is prone to cracking, has a short high-temperature service life, and requires frequent replacement. In addition, traditional external heating suffers from inherent defects such as long heat transfer paths, high heat loss, and slow heating, resulting in insufficient Joule heating and difficulty in molten salt temperature control during low-current electrolysis, leading to large fluctuations in product quality. Forcibly increasing the current for supplemental heating deviates from the optimal electrochemical window, reducing current efficiency and deteriorating product quality. Simultaneously, increasing the current for supplemental heating raises the temperature of the molten liquid near the protective shell, reducing the thickness of the protective shell. Specifically, when the current density is too high, the cathode potential shifts significantly negatively (overpotential increases). When the cathode potential shifts negatively to the precipitation potential of other metal ions in the molten salt, impurity ions that should not have deposited (such as Fe, Co, Ni, etc.) will also be reduced and co-deposited. At the same time, the intense precipitation reaction deteriorates the deposition layer structure (porosity, dendrites, molten salt inclusions), resulting in decreased current efficiency, poorer product quality, and a thinner protective shell leading to the risk of corrosion of the electrolytic cell. Accordingly, this application provides a method for recovering tungsten by molten salt electrolysis, which can solve some or all of the technical problems in related technologies.

[0034] The method for recovering tungsten by molten salt electrolysis provided in this application embodiment can be implemented in an electrolysis device. Please refer to [link / reference]. Figure 1 , Figure 1 This is a schematic diagram of the structure of an electrolysis device provided in an embodiment of this application. The electrolysis device may include an electrolysis cell 11 made of metal, a heater 12 and a cooling system 13. The method may include the following steps 101 to 105.

[0035] Step 101: Provide an electrolytic cell 11 made of metal. Due to the good ductility of metal, the size of this electrolytic cell is significantly larger than that of the alumina crucible in related technologies.

[0036] Step 102: Add tungstate molten salt 16 to electrolytic cell 11; Step 103: The tungstate molten salt 16 is heated to a first temperature and kept warm for the first time using a heater 12 placed inside the electrolytic cell 11 to dry and preheat the tungstate molten salt 16.

[0037] Step 103 further includes: activating a cooling system 13 located outside the electrolytic cell 11 to lower the temperature of the inner wall of the electrolytic cell below the melting point of the tungstate salt. For example, the cooling system 13 may be activated immediately upon reaching the first temperature, or the cooling system 13 may be activated during the first heat preservation period.

[0038] Step 104: While keeping the cooling system 13 on, continue to use the heater 12 to heat the molten tungstate salt 16 to a second temperature and perform a second heat preservation, so that the molten tungstate salt 16 melts to obtain molten tungstate electrolyte, and the molten tungstate electrolyte on the inner wall surface of the electrolytic cell solidifies to form a solid shell protective layer.

[0039] Here, since a protective layer has been formed, the fully molten tungstate salt 16 (i.e., electrolyte) no longer directly contacts the metal wall of the electrolytic cell 11, but is isolated by the solid shell layer, and the electrolytic cell 11 itself is not corroded.

[0040] Step 105: At least one set of cathodes 14 and anodes 15 are inserted into a molten tungstate electrolyte (molten tungstate salt 16) for electrolysis, and the heater 12 is kept on to heat the molten tungstate electrolyte at the electrolysis temperature. Through electrolysis, tungsten-containing electrolysis products are formed on the surface of the cathode 14.

[0041] Specifically, the cathode 14 ("-") and anode 15 ("+") are inserted into the molten tungstate salt 16 and a low current is passed through for electrolysis. At this time, the Joule heat generated by the electrolysis current is insufficient to maintain the temperature required for the electrolysis of the molten tungstate salt 16, so the heater 12 continues to be turned on at a certain power to heat the molten tungstate salt to compensate for the heat loss caused by the cooling system, etc., and to ensure that the molten tungstate salt 16 is always kept within the temperature range required for electrolysis.

[0042] In the method provided in this application embodiment, a metal electrolytic cell 11 is used. Before heating to the melting point of the tungstate molten salt 16, the cooling system is turned on and maintained in advance. The temperature of the inner wall of the electrolytic cell 11 is kept below the melting point of the tungstate molten salt, so that the solid shell protective layer 17 is formed on the inner wall of the electrolytic cell 11 before the tungstate molten salt 16 is completely melted, thereby physically isolating the molten tungstate electrolyte from the metal tank. In this way, on the one hand, direct contact between the high-temperature molten salt and the metal tank wall can be avoided, eliminating the pathway for tank corrosion and the introduction of metal impurities into the molten salt, and ensuring product purity; on the other hand, by utilizing the characteristic of metal materials to manufacture large-size tanks through processes such as welding and rolling, the size limitation of alumina crucibles can be overcome, making the electrolytic cell 11 suitable for ton-scale industrial electrolytic molten salt recovery of tungsten, thereby improving recovery efficiency.

[0043] Meanwhile, the heater 12, placed inside the molten salt, is directly immersed in the tungstate molten salt 16 to generate heat. The heat is directly transferred to the molten salt system, resulting in a short heat transfer path and high thermal utilization, which can overcome the thermal efficiency defects of the external heating mode. In the electrolysis stage of step 105, the heater 12 is continuously turned on to compensate for the heat loss caused by the cooling system 13 and the insufficient Joule heating due to low current, so that heating and electrolysis can be controlled separately. The heater mainly undertakes the task of maintaining thermal balance, and the electrolysis current can be independently maintained at a low level without being forced to increase for supplemental heating. This avoids excessively high cathode potential, co-deposition of impurity ions, and deterioration of the deposition layer structure caused by excessive current density, so that the electrolysis process is always within a stable electrochemical window, ensuring current efficiency and product quality.

[0044] In summary, this application, through the combination of the metal electrolytic cell 11 and the solid shell protective layer 17, can solve the problems of impurities introduced by corrosion of alumina crucibles, size limitations preventing scale-up, and thermal shock cracking. The heating by the internal heater 12 decouples heating from electrolysis, resolving the contradiction between insufficient heat at low currents and the shift in the electrochemical window at high currents, thus balancing stable electrolysis with sufficient heat supply. The active adjustment by the cooling system 13 ensures the stable existence of the protective layer throughout the electrolysis process, preventing the electrolytic cell 11 from being chemically corroded by the high-temperature molten tungstate salt 16, guaranteeing product purity, extending equipment lifespan, improving operational safety, and meeting the requirements of industrial production.

[0045] Optionally, after a certain period of operation (e.g., one quarter), the molten salt system can be shut down and the material discharged. Specifically, the electrolytic cell 11 is first cooled down and shut down. After the molten salt cools, the product and residue deposited at the bottom of the cell are collected and incorporated into the next process for product separation and purification. At the same time, the remaining waste molten salt in the cell is cleaned, and new tungstate molten salt 16 is added before continuing the next stage of molten salt electrolysis production. Regular slag removal and salt replacement help maintain the stability of the molten salt composition and prevent impurities from accumulating in the molten salt and affecting the quality of the electrolytic products.

[0046] In this application, the metal material of the electrolytic cell 11 may specifically include stainless steel (e.g., 304, 310S), nickel-based alloys, heat-resistant steel, etc. The size of the electrolytic cell 11 can be customized according to actual needs. In particular, the method of this application can achieve industrial-scale molten salt recovery of tungsten, so the size of the electrolytic cell 11 can be increased accordingly.

[0047] In some exemplary embodiments, the diameter of the electrolytic cell 11 is 800mm to 1200mm, such as 800mm, 900mm, 950mm, 1000mm, 1050mm, 1100mm, 1200mm, etc., and the depth of the electrolytic cell is 1000mm to 1200mm, such as 1000mm, 1050mm, 1100mm, 1150mm, 1200mm, etc. In the embodiments of this application, the electrolytic cell 11 can be cylindrical or frustum-shaped, and the diameter refers to the inner diameter of the top of the electrolytic cell 11.

[0048] In some exemplary embodiments, the salt content of the electrolytic cell 11 is 800kg to 3000kg, such as 800kg, 1000kg, 1200kg, 1500kg, 2000kg, 3000kg, etc.

[0049] The tungstate molten salt 16 of this application comprises sodium tungstate and tungsten trioxide in a mass ratio of 100:(6-9), such as 100:6, 100:7, 100:8, 100:9, etc. This application does not restrict the source of sodium tungstate; for example, it can be industrial sodium tungstate or crude sodium tungstate obtained from recycled waste tungsten. After heating and melting, sodium tungstate constitutes the electrolyte matrix of the tungstate molten salt 16, and tungsten trioxide dissolves therein to provide an additional tungsten ion source to compensate for the consumption of tungsten ions during electrolysis. Simultaneously, the anode 15 (usually various waste tungsten materials) dissolves during electrolysis to generate tungsten ions that enter the molten salt. These tungsten ions, together with those provided by tungsten trioxide, maintain the concentration of tungsten ions in the molten salt, ensuring that the deposition process of the cathode 14 is not solely limited by the dissolution rate of the anode 15, thereby increasing the deposition rate.

[0050] In step 103, the first temperature is lower than the melting point of the tungstate molten salt. Optionally, the first temperature is 100°C to 200°C lower than the melting point of the tungstate molten salt. For example, the difference between the melting point of the tungstate molten salt and the first temperature is 100°C, 110°C, 130°C, 150°C, 180°C, 200°C, etc.

[0051] In one exemplary embodiment, the first temperature is 400℃ to 500℃, for example, 400℃, 410℃, 420℃, 430℃, 460℃, 480℃, 500℃, etc., and the first holding time is 4 hours to 6 hours, for example, 4 hours, 4.5 hours, 5 hours, 6 hours, etc. The first temperature is sufficient to fully remove the water of crystallization from the tungstate molten salt 16 (the water of crystallization of tungstate molten salt begins to be removed at 100℃ to 150℃, and can be fully dried above 400℃), avoiding the decomposition of water during electrolysis and the resulting gas production, which could affect the electrode reaction and product quality.

[0052] In step 103, the cooling system 13 is activated to lower the temperature of the inner wall of the electrolytic cell 11 below the melting point of the tungstate molten salt.

[0053] In step 104, the second temperature is greater than or equal to the melting point of the tungstate molten salt. Optionally, the second temperature is 0°C to 200°C higher than the melting point of the tungstate molten salt. For example, the difference between the second temperature and the melting point of the tungstate molten salt is 0°C, 10°C, 20°C, 50°C, 100°C, 110°C, 130°C, 150°C, 180°C, 200°C, etc.

[0054] In one exemplary embodiment, the second temperature is 600°C to 800°C, for example, 600°C, 650°C, 680°C, 700°C, 720°C, 750°C, 790°C, 800°C, etc., and the second holding time is 2 hours to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 4 hours, etc. The temperature difference between the second temperature and the melting point of the tungstate molten salt is sufficient to ensure that the tungstate molten salt 16 is completely melted and has good ionic conductivity; and, the second temperature is avoided from being too high to avoid excessively long heating process leading to increased energy consumption and decreased production efficiency. Since the temperature of the inner wall of the electrolytic cell 11 is kept below the melting point of the tungstate molten salt, when heated to a second temperature greater than or equal to the melting point of the tungstate molten salt, a solid shell protective layer 17 is formed on the inner wall of the electrolytic cell 11 before the tungstate molten salt 16 is completely melted, thereby physically isolating the molten tungstate electrolyte from the metal tank.

[0055] In one exemplary embodiment, the thickness of the solid crust protective layer 17 is 15 mm to 100 mm. As an example, the thickness of the solid crust protective layer 17 formed on the sidewall of the electrolytic cell 11 is 15 mm to 30 mm, and the thickness of the bottom protective layer is 70 mm to 100 mm.

[0056] In steps 103 and 104, the internal heater 12 first raises the tungstate molten salt 16 from room temperature to a first temperature (e.g., 500°C) and performs a first heat preservation. When the first temperature is reached, the cooling system 13 is started. Then, the temperature is raised to a second temperature (e.g., 750°C) to completely melt the molten salt and reach the appropriate electrolysis operating temperature. Before the tungstate molten salt 16 is completely melted, a solid crust protective layer 17 is formed on the inner wall of the electrolytic cell 11.

[0057] In one optional embodiment, the heater 12 placed inside the electrolytic cell 11 adopts an armored heater structure. The heater 12 contains a nickel-chromium alloy heating wire, surrounded by high-purity magnesium oxide powder as an insulating medium. The outer layer is covered by a nickel-based alloy sheath, which provides electrical insulation between the sheath and the heating wire through the magnesium oxide powder. The sheath is grounded during use to avoid interference with the electrolytic current. This heater 12 is high-temperature resistant, corrosion-resistant, and can support heating temperatures above 1000°C, with a heating rate of 5°C / min to 10°C / min. A mounting beam is provided at the top of the electrolytic cell 11, and the heater 12 is fixed to the beam via an insulating mounting flange, vertically inserted into the electrolytic cell 11, with its heating section completely submerged below the molten salt surface. Furthermore, when multiple electrodes are used, the heater 12 is located within the enclosed area formed by multiple cathodes 14 and anodes 15, maintaining a distance of 60mm to 150mm from the nearest electrode to avoid electric field interference and localized overheating. The wiring terminals of heater 12 are located outside the electrolytic cell 11 and are connected to the power control cabinet via high-temperature resistant wires; the cover of the electrolytic cell 11 and heater 12 are sealed with a sealing element. Preferably, the lower end of heater 12 is suspended 100mm to 200mm above the bottom of the electrolytic cell 11 to avoid short circuit caused by contact with the bottom.

[0058] In one alternative implementation, please refer to Figure 2 The cooling system 13 includes a cooling medium channel disposed on the outer wall of the electrolytic cell 11. After the cooling system 13 is started, the thickness of the solid shell protective layer 17 can be adjusted by regulating the flow rate or temperature of the cooling medium in the cooling medium channel. During the start-up of the cooling system 13, the cooling system 13 can actively control the temperature of the cell wall to ensure that the wall temperature is always lower than the freezing point of the tungstate molten salt 16, thus ensuring that the solid shell protective layer 17 exists stably throughout the electrolysis process. Furthermore, the thickness of the protective layer can be actively adjusted by regulating the flow rate or temperature of the cooling medium, achieving a balance between protecting the cell body and maintaining the effective volume within the cell.

[0059] In one alternative embodiment, the cooling system 13 can be an air-cooled system or a water-cooled system. Cool air or cooling water carries away heat through the cooling medium channel on the outer wall of the electrolytic cell 11, causing the temperature of the molten tungstate salt 16 in contact with the inner wall of the metal cell to drop below the freezing point and solidify to form a solid shell protective layer 17. This solid shell protective layer 17 can physically isolate the molten tungstate electrolyte from the metal electrolytic cell 11.

[0060] In step 105, the required electrolysis temperature is achieved by heating with heater 12 installed inside the tank. For example, the electrolysis temperature can be 700°C to 800°C.

[0061] In one exemplary embodiment, the electrolysis employs a constant current electrolysis method, with an electrolysis current of 30A to 200A, such as 30A, 35A, 40A, 60A, 65A, 80A, 100A, 150A, or 200A; and an electrolysis voltage of 20V to 35V, such as 20V, 22V, 23V, 25V, 28V, 30V, 32V, 33V, or 35V. Using a constant current electrolysis method avoids the interference of resistance fluctuations in the tungstate molten salt 16 on the current, ensuring a constant tungsten deposition rate, thereby obtaining a uniformly sized and densely structured deposition layer. Controlling the current density within a low range not only helps suppress dendrite growth and pulverization, making the cathode 14 product easier to collect and of high purity, but also reduces electrode polarization and suppresses side reactions (such as co-deposition of impurity metals), further improving product purity. Furthermore, the operating voltage of 20V to 35V is within a safe low-voltage range, enhancing the safety of equipment operation.

[0062] As an example, the electrolysis time can be from 3 hours to 12 hours, such as 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 8 hours, 8.2 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 12 hours, etc. To obtain high-purity elemental tungsten powder while increasing its yield, an electrolysis time of 5 hours to 9 hours is preferred.

[0063] In step 105, exemplarily, after inserting the cathode 14 and anode 15 into the molten tungstate 16, a DC power supply is turned on, and a constant current value (e.g., 35A or 65A) is set. The current flows through the electrolyte in the molten tungstate 16, forming a closed loop between the cathode and anode 15. In constant current mode, as electrolysis proceeds, or as the composition of the molten tungstate 16 changes slightly or the electrode area changes, the power supply automatically adjusts the output voltage (within the range of 20V to 35V) to maintain a constant current. Tungsten ions are reduced and deposited on the surface of the cathode 14, and the waste tungsten material from the anode 15 gradually dissolves to replenish the tungsten ions in the molten tungstate 16. Because the electrolysis current is low, the generated Joule heat is insufficient to maintain the temperature of the molten tungstate 16; therefore, heat needs to be continuously replenished through the heater 12.

[0064] In step 105, the cathode 14 used can be a tungsten rod, such as a pure tungsten rod. Optionally, the diameter of the cathode 14 is 20mm to 35mm, such as 20mm, 25mm, 30mm, 35mm, etc. The anode 15 can be made from various waste tungsten materials, with a tungsten content of 95wt% or more, such as, but not limited to, waste tungsten rods, waste tungsten wires, waste tungsten cutting materials, waste tungsten contacts, waste tungsten catalysts, etc., and its raw materials have a wide range of applications. For example, the anode 15 is a waste tungsten rod with a diameter of 20mm to 35mm, such as 20mm, 25mm, 32mm, 35mm, etc.

[0065] In step 105, the length of the cathode 14 submerged below the surface of the molten tungstate electrolyte can be adaptively adjusted according to the size of the electrolytic cell 11, the amount of material loaded, and the electrolytic current. For example, the length of the cathode submerged below the surface of the molten tungstate electrolyte is 100mm to 200mm, such as 100mm, 130mm, 170mm, or 200mm. Further, the depth of the anode 15 inserted below the molten salt surface is 80mm to 120mm, such as 80mm, 85mm, 90mm, 100mm, 110mm, or 120mm, and the insertion depth of the cathode 14 is greater than that of the anode 15. This helps ensure that the cathode 14 remains in a stable molten salt environment during electrolysis, preventing partial exposure of the cathode 14 above the surface due to fluctuations in the molten salt surface, which could affect the deposition effect.

[0066] In one exemplary embodiment, during electrolysis, the liquid level of molten tungstate salt 16 in the electrolytic cell 11 is maintained at 350 mm to 400 mm. This liquid level range ensures the effective immersion depth of the cathode 14 and anode 15, while reserving sufficient space for the gradual consumption of the anode 15 and the deposition and growth of the cathode 14 during electrolysis, preventing molten salt overflow due to excessive liquid level or electrode exposure due to excessive liquid level. The liquid level of molten tungstate salt 16 in the electrolytic cell 11 is maintained at 350 mm, 360 mm, 370 mm, 380 mm, 400 mm, etc.

[0067] In step 105, the number of cathodes 14 and anodes 15 inserted into the molten tungstate electrolyte can be one set or multiple sets. Please refer to [reference needed]. Figure 3 , Figure 3 This is a schematic diagram of an electrode layout provided in an embodiment of this application, where multiple sets of electrodes can be distributed circumferentially. Furthermore, the multiple sets of electrodes (each set including a cathode 14 and a cathode 15) can be symmetrically arranged within the electrolytic cell 11, ensuring uniform current distribution throughout the entire volume of the tungstate molten salt 16. This avoids localized current concentrations and helps maintain the uniformity of the molten salt electric field and the consistency of the electrolytic product quality. For example, one to three sets of electrodes are arranged along the axial direction of the electrolytic cell; after current is applied, the multiple sets of electrodes are simultaneously energized and participate in the electrolytic reaction.

[0068] In one exemplary embodiment, there are two or three sets of anodes 15 and cathodes 14 inserted into the molten tungstate electrolyte, and each set of anodes 15 and cathodes 14 is simultaneously energized for electrolysis.

[0069] In one exemplary embodiment, the cathode current density is 0.3 A / cm². 2 ~0.8A / cm 2 For example, 0.3A / cm 20.4A / cm 2 0.6A / cm 2 0.8A / cm 2 The electrolysis temperature is 700℃~800℃, for example, 700℃, 720℃, 750℃, 780℃ or 800℃. Since heater 12 performs the heating function, the electrolysis current does not need to be increased for supplemental heating. In step 105, a lower cathode current density (0.3A / cm²~0.8A / cm²) can be used for electrolysis to avoid excessively high cathode potential and dendrite growth caused by excessive current density. This results in a denser and more uniform cathode deposition layer, reduces molten salt entrainment, lowers the risk of impurity co-deposition, and thus improves product purity. The electrolysis temperature of 700℃~800℃ ensures that the tungstate molten salt has sufficient ionic conductivity and reactivity, and also facilitates control of the phase composition of the product. High-purity tungsten powder can be obtained within this temperature range. The synergistic effect of the lower current density and suitable electrolysis temperature allows the electrolysis process to operate within a stable electrochemical window, ensuring current efficiency and stable product quality.

[0070] In one exemplary embodiment, the number of cathodes 14 and anodes 15 is N, where N≥2; and the method of this application embodiment (specifically step 105) further includes: Once the cathode 14 in operation has achieved enrichment of electrolytic products, it is raised and removed from the electrolytic cell, and another cathode 14 is placed in the molten tungstate electrolyte to continue electrolysis; and / or Once the working anode 15 is consumed, it is removed from the electrolytic cell, and another anode 15 is placed in the molten tungstate electrolyte to continue electrolysis.

[0071] Exemplarily, the heater 12 in this embodiment adopts a two-stage power control strategy, balancing heating efficiency and electrolysis stability. In the heating stages of steps 103 and 104, the heater 12 operates at a high power of 25 kW to 35 kW, rapidly raising the ton-sized amount of molten tungstate salt 16 from room temperature to 400°C to 500°C. After activating the cooling device, the temperature continues to rise to 700°C to 800°C. During this stage, the molten tungstate salt 16 has not yet been electrolyzed; all heat is provided by the internal heater 12. High-power operation shortens the heating time and improves production efficiency. Simultaneously, it allows the molten tungstate salt 16 to quickly pass through the highly corrosive 600°C to 800°C temperature range, rapidly forming a protective layer and reducing the erosion time of the molten tungstate salt 16 on the tank wall, thus extending the service life of the electrolytic cell 11. In the electrolysis maintenance stage of step 105, after electrolysis begins, the heater 12 can automatically switch or manually adjust to a low power operation of 2 kW to 5 kW. At this point, the temperature of the tungstate molten salt 16 has reached 700℃~800℃. The Joule heat generated by the electrolysis current itself can supplement some of the heat. The heater 12 only needs to compensate for the heat loss caused by radiation from the surface of the tungstate molten salt 16 and heat dissipation from the tank wall to maintain the thermal balance of the system, without the need for continuous high-power heating. In this way, on the one hand, it can avoid the accelerated volatilization of the tungstate molten salt 16 and the deterioration of product quality caused by overheating; on the other hand, since the electrolysis stage accounts for most of the production cycle, the power difference between low-power maintenance and high-power heating can reduce the overall energy consumption during equipment operation.

[0072] The method of this application can be implemented by operating an electrolysis device equipped with a control component (e.g., a PLC or industrial computer), a power supply, and a cooling system 13. The cooling system 13 includes a cooling medium supply component (e.g., a fan or water pump), a cooling medium delivery pipe, an annular cooling pipe, a flow regulating valve, and temperature sensors. The annular cooling pipe is attached to the outer wall of the electrolysis cell 11 in a spiral or ring manner. Its inlet end is connected to the outlet of the cooling medium supply component via a pipe, and its outlet end is connected to a discharge or circulation loop. The flow regulating valve is installed on the pipe between the cooling medium supply component and the annular cooling pipe to regulate the flow rate of the cooling medium. Temperature sensors are respectively installed on the outer wall surface of the electrolysis cell 11 and in the cooling medium outlet pipe to monitor the wall temperature and medium temperature rise in real time. The control component is electrically connected to the temperature sensors, the flow regulating valve, the drive motor (or frequency converter) of the cooling medium supply component, and the power control module of the heater 12 to achieve coordinated control of cooling intensity and heating power.

[0073] When the temperature of the molten tungstate 16 rises to a first temperature, the control component sends a start signal to drive the cooling medium supply component to operate, causing the cooling medium to flow continuously within the annular cooling pipe. As it flows past the outer wall of the electrolytic cell 11, it carries away heat, ensuring that the temperature of the metal cell wall remains below the melting point of the molten tungstate 16. The molten tungstate 16 in contact with the cell wall solidifies as its temperature drops below its melting point, gradually forming a solid protective shell layer. After the protective layer is formed, the thickness of the protective layer is maintained relatively stable by controlling the cooling system 13. For example, when the temperature of the molten tungstate 16 is 700°C to 800°C, controlling the temperature of the cooling medium flowing out of the cooling system 13 to be between 100°C and 130°C allows the thickness of the solid protective shell layer 17 to be between 15mm and 100mm. The operator can set the target protective layer thickness through the control component. The control component calculates the wall temperature and medium temperature rise data fed back by the temperature sensor and outputs the adjustment signal to the flow regulating valve or frequency converter. When it is necessary to thicken the protective layer, the cooling medium flow rate is increased (such as increasing the fan speed or water pump frequency) or the cooling medium temperature is reduced (by adjusting through the cooling tower or heat exchanger) to enhance heat exchange, reduce the wall temperature, and promote the solidification of more tungstate molten salt 16. Conversely, reducing the flow rate or increasing the temperature will thin the protective layer.

[0074] Through the aforementioned control mechanism, the thickness of the protective layer can be actively adjusted. Operators can flexibly adjust the thickness based on the actual temperature of the tungstate molten salt 16, the amount of material loaded, and heat dissipation conditions to ensure effective protection under different operating conditions. Simultaneously, precise adjustment of the cooling intensity can maintain the sidewall protective layer within a preset thickness range. This avoids damage to the tank wall caused by localized overheating and melting due to an excessively thin protective layer, while also preventing the protective layer from encroaching on the effective volume and reducing the actual material usage per batch due to an excessively thick protective layer. This achieves a balance between protection reliability and the space utilization of the electrolytic cell 11. Furthermore, the melting point of the tungstate molten salt 16, which contains industrial sodium tungstate and tungsten trioxide from different sources and compositions, typically fluctuates between 600℃ and 700℃. The adjustability of the cooling intensity allows this system to flexibly match the solidification characteristics of different tungstate molten salt 16 systems, broadening the applicability of the process. The annular cooling pipes are arranged on the outer wall of the electrolytic cell 11, without contacting the tungstate molten salt 16, eliminating the risk of corrosion. The pipe connections are simple, maintenance is convenient, and it is suitable for long-term stable industrial operation.

[0075] In one optional embodiment, multiple sets of electrodes are configured for parallel electrolysis or sequential electrolysis. Each set of electrodes may include a cathode 14 and an anode 15, and each electrode may be equipped with an independent lifting mechanism for independently controlling its insertion into or removal from the molten salt surface. The top of the electrolytic cell 11 has multiple electrode windows, each corresponding to a cathode 14 or an anode 15. These electrode windows also function as feeding ports, facilitating the flexible arrangement of multiple sets of cathodes and anodes 15 on a large-scale platform for large-scale synchronous electrolysis. During electrolysis, each set of cathodes 14 and anodes 15 is simultaneously in operation, and their respective required electrolysis currents can be supplied by independent power sources or distributed from the same power source through parallel connection.

[0076] For example, with a charge of 1000-1100 kg of tungstate molten salt 16, an electrolysis temperature of 700-800 °C, and a constant current of 65 A, the two sets of electrodes work simultaneously for 11-12 hours, producing a total of 2200-2500 g of tungsten powder.

[0077] The independent lifting and lowering mechanisms of each electrode group provide a basis for continuous operation. For example, when the tungsten powder deposited on the surface of a cathode 14 reaches its enrichment limit (e.g., an excessively thick deposition layer affecting current distribution or posing a risk of detachment), the lifting mechanism raises the cathode 14 away from the molten salt surface, cools it, and collects the product. Simultaneously, another pre-prepared new cathode 14 (or a cleaned cathode 14) is lowered into the molten salt through another window to continue electrolysis, achieving online replacement of the cathode 14. Regarding the anode 15, the waste tungsten rod gradually shortens as electrolysis progresses. When it is completely consumed, the lifting mechanism raises it and removes it, while a new waste tungsten rod anode 15 is lowered into the molten salt to continue operation. The lifting and replacement operations of each group are independent and do not affect each other, allowing the discharge of cathode 14 and the replacement of anode 15 to be completed without shutting down the furnace or interrupting electrolysis. This avoids the time and energy waste caused by the need to shut down the furnace and reheat in traditional single-electrode configurations, achieving continuous production. The simultaneous operation of multiple electrode groups increases the total electrolysis current and total yield by multiple times with the number of electrode groups, thereby improving production efficiency. At the same time, when one electrode group is replaced, the other groups continue to operate normally, so the electrolytic cell 11 has almost no idle time, thus improving equipment utilization.

[0078] For example, the method of this application includes the following process flow: Industrial sodium tungstate and tungsten trioxide are mixed evenly at a mass ratio of 100:(6-9), and dried in an oven at 100℃-150℃ for 36-48 hours to remove crystal water, and then put into electrolytic cell 11. Heater 12 heats the molten salt to 400℃~500℃ and holds it at that temperature for 4 to 6 hours, allowing residual crystal water, adsorbed water, and volatile impurities to fully evaporate, ensuring the molten salt is converted into a dry, anhydrous state. Simultaneously, cooling system 13 is activated when the molten salt reaches its initial temperature, keeping the temperature of the electrolytic cell wall below the melting point of the tungstate molten salt. If crystal water or adsorbed water is not completely removed before electrolysis, the hydrogen produced by water decomposition at high temperatures may cause hydrogen embrittlement at the cathode 14 or affect the quality of the deposited layer, while oxygen may oxidize the anode 15 or consume carbonaceous materials. Therefore, adequate heat preservation is a prerequisite for ensuring product purity and deposition quality.

[0079] Subsequently, while keeping the cooling system 13 on, the heater 12 continues to heat the molten salt to 700℃~800℃ and holds it at that temperature for 2 to 4 hours, allowing the molten salt to completely melt and the molten tungstate electrolyte on the inner wall surface of the electrolytic cell to solidify into a solid crust protective layer. Internally, convection achieves thorough homogenization of temperature and composition, stabilizing density and viscosity, thus providing a uniform medium environment for electrolysis. The combination of a large-size electrolytic cell with a large salt capacity and a suitable molten salt ratio can increase the output per batch, improve production efficiency, and simultaneously reduce energy consumption and labor costs per unit product.

[0080] Preferably, the tungstate molten salt 16 comprises industrial sodium tungstate and tungsten trioxide. After heating and melting, sodium tungstate forms the electrolyte matrix of the tungstate molten salt 16, and tungsten trioxide dissolves therein to provide an additional tungsten ion source to compensate for the consumption of tungsten ions during electrolysis. At the same time, the waste tungsten rod anode 15 dissolves during electrolysis to generate tungsten ions that enter the molten salt. Together with the tungsten ions provided by tungsten trioxide, they maintain the concentration of tungsten ions in the molten salt, so that the deposition process of the cathode 14 is not solely limited by the dissolution rate of the anode 15, thereby improving the deposition rate and current efficiency.

[0081] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0082] In the following examples and comparative examples, unless otherwise stated, The electrolytic cell (cylindrical) used is made of 310S stainless steel, with a diameter of 1000mm and a depth of 1200mm. The anode is made from waste tungsten rods (diameter D20~D35mm, length 150~180mm). Before use, all rods are polished to remove surface impurities and oxide layers. In this embodiment, the anode is made from tungsten rod scraps or leftover material from other processing steps (such as tungsten material cutting, forging, machining, etc.) or tungsten wire rods pressed from waste tungsten wires. The tungsten content of the waste tungsten rods is 99wt%. The cathodes are all made of pure tungsten rods with a specification of D27mm×200mm.

[0083] Example 1 (1) Molten salt preparation and feeding: Mix 1000kg sodium tungstate and 75kg tungsten trioxide evenly, dry in an oven at 120℃ for 48h to remove crystal water, and add to the electrolytic cell through the feeding port.

[0084] (2) Molten Salt Melting and Shell Formation: The heater placed inside the electrolytic cell is activated to heat the molten tungstate salt to a first temperature of 450°C and hold it at that temperature for 5 hours (first holding). The cooling system located outside the electrolytic cell is activated to lower the temperature of the inner wall of the electrolytic cell below the melting point of the molten tungstate salt. While maintaining the cooling system on, the molten tungstate salt is heated to a second temperature of 750°C using the internal heater and held for 3 hours (second holding) to completely melt the molten tungstate salt and solidify the molten tungstate salt on the surface of the inner wall of the electrolytic cell to form a solid shell protective layer. The molten salt level is maintained at 370 mm to 390 mm. During the holding period, the temperature of the cooling medium is controlled to maintain the thickness of the solid shell protective layer on the side wall at 16 mm to 20 mm and the thickness of the bottom protective layer at 78 mm to 82 mm.

[0085] (3) Constant current electrolysis: The anode (diameter D20mm, length 180mm) and cathode are lowered into the molten salt from the feeding port respectively. The anode is inserted 100mm into the molten salt liquid surface and the cathode is inserted 110mm into the molten salt liquid surface. After fixing, the DC regulated power supply is connected and electrolysis is carried out at a constant current of 35A until the electrolysis is interrupted. The electrolysis time is 8h. During the electrolysis operation, the thickness of the solid protective shell on the side wall remains unchanged at 16mm~20mm.

[0086] (4) Product collection: After electrolysis, the cathode and anode are raised above the molten salt surface, cooled, and the cathode is removed to collect the deposited products.

[0087] In this embodiment, 550g of tungsten powder was obtained with a purity of 96.28% (based on the W content measured by GDMS), a Fisher particle size of 1.70μm, and an electrolysis efficiency of 550÷8=68.75g / h.

[0088] Please refer to Figure 4 , Figure 4 The figure shows the X-ray diffraction (XRD) pattern of the tungsten powder prepared in Example 1. As can be seen from the figure, all diffraction peaks are consistent with the standard card (PDF#04-0806) of body-centered cubic elemental tungsten. The strong peaks at 2θ=40.3°, 58.3° and 73.2° correspond to its (110), (200) and (211) crystal planes, respectively. No other impurity phase diffraction peaks were observed. The sharp peaks indicate that the product is a high-purity tungsten powder with complete crystallization.

[0089] Example 2 (1) Constant current electrolysis: Using the molten sodium tungstate-tungsten trioxide molten salt and the established solid shell protective layer in Example 1, the anode (diameter D20mm, length 180mm) and cathode are lowered into the molten salt from the feeding port respectively. The anode is inserted 100mm into the molten salt liquid surface and the cathode is inserted 110mm into the molten salt liquid surface. After fixing, the DC regulated power supply is connected and electrolysis is performed at a constant current of 65A until the electrolysis is interrupted. The electrolysis time is 5h. During the electrolysis operation, the thickness of the solid protective shell on the side wall is slightly thin, which is 13mm to 15mm.

[0090] (2) Product collection: After electrolysis, the cathode and anode are raised above the molten salt surface, cooled, and the cathode is removed to collect the deposited products.

[0091] In this embodiment, 600g of tungsten powder was obtained with a purity of 99.02% and a Fisher particle size of 1.86μm. The electrolysis efficiency was 600÷5=120g / h.

[0092] Please refer to Figure 5 , Figure 5 The image shows the X-ray diffraction pattern of the tungsten powder prepared in Example 2. The vertical axis represents diffraction intensity (in AU), and the horizontal axis represents the diffraction angle 2θ. The test scanning range is 10° to 90°. All diffraction peaks in the spectrum can be identified as standard characteristic diffraction peaks of elemental tungsten (W) (40.3°, 58.3°, 73.2°, etc.), and there are no impurity diffraction peaks from other phases. The sharp peak shapes indicate that the tungsten powder obtained in Example 2 has complete crystal structure and high phase purity.

[0093] Example 3 (1) Constant current electrolysis: Using the molten sodium tungstate-tungsten trioxide molten salt and the established solid shell protective layer in Example 2, the anode (diameter D20mm, length 180mm) and cathode are lowered into the molten salt from the feeding port respectively. The anode is inserted 100mm into the molten salt liquid surface and the cathode is inserted 110mm into the molten salt liquid surface. After fixing, the DC regulated power supply is connected and electrolysis is performed at a constant current of 130A until the electrolysis is interrupted. The electrolysis time is 3h. During the electrolysis operation, the thickness of the solid protective shell on the side wall is 8mm to 12mm.

[0094] (2) Product collection: After electrolysis, the anode and cathode are raised above the molten salt surface, cooled, and the cathode is removed to collect the deposited product. In this example, 650g of tungsten powder was obtained with a purity of 99.56% and a Fisher particle size of 3.11μm. The electrolysis efficiency was 650÷3=216.7g / h.

[0095] Please refer to Figure 6 , Figure 6This is the X-ray diffraction (XRD) pattern of the powder prepared in Example 3. The vertical axis of the pattern represents diffraction intensity (in AU), and the horizontal axis represents the diffraction angle 2θ. The test scanning range is 10° to 90°. All diffraction peaks in the pattern can be identified as standard characteristic diffraction peaks of elemental tungsten (W) (40.3°, 58.3°, 73.2°, etc.). There are no impurity diffraction peaks from other phases, indicating that the obtained tungsten powder has complete crystal structure and high phase purity.

[0096] Example 4 (1) Electrode installation: Fix two pretreated waste tungsten rods (diameter D32mm, length 180mm) onto two anode rods respectively, and fix two pure tungsten rods (D27mm×200mm) onto two cathode rods respectively.

[0097] (2) Multiple sets of constant current electrolysis: Using the molten sodium tungstate-tungsten trioxide molten salt system and the established solid shell protective layer from Example 3, two anodes and two cathodes were lowered into the molten salt from the feeding port. The anodes were inserted 100 mm into the molten salt surface, and the cathodes were inserted 110 mm into the molten salt surface. Two DC regulated power supplies were connected to the corresponding set of anodes and cathodes. Each set was electrolyzed at a constant current of 65 A until the electrolysis was interrupted. The electrolysis time was 11.5 h. During the electrolysis operation, the thickness of the solid protective shell on the side wall was slightly thinner, by 13 mm to 15 mm. Please refer to Figure 7 , Figure 7 This is a schematic diagram of another electrode layout provided in an embodiment of this application.

[0098] (3) Product collection: After electrolysis, the cathodes of each group are raised above the molten salt surface, cooled, and the cathodes are removed to collect the deposited products. In this example, 2350g of tungsten powder was obtained with a purity of 99.31% and a Fisher particle size of 2.12μm. The electrolysis efficiency was 2350÷2÷11.5=102.2g / h.

[0099] Figure 8 The XRD pattern of the powder prepared in Example 4 is shown in the figure. As can be seen from the figure, all the diffraction peaks in the spectrum can be identified as the standard characteristic diffraction peaks of elemental tungsten (W) (40.3°, 58.3°, 73.2°, etc.), and there are no impurity diffraction peaks of other phases, indicating that the obtained tungsten powder has complete crystal structure and high phase purity.

[0100] Example 5 (1) Electrode installation: Fix two pretreated waste tungsten rods (diameter D32mm, length 180mm) onto two anode rods respectively, and fix two pure tungsten rods onto two cathode rods respectively.

[0101] (2) Multiple sets of constant current electrolysis: Using the molten sodium tungstate-tungsten trioxide molten salt system and the established solid shell protective layer from Example 4, two anodes and two cathodes were lowered into the molten salt from the feeding port. The anodes were inserted 100 mm into the molten salt surface, and the cathodes were inserted 110 mm into the molten salt surface. Two DC regulated power supplies were connected to the corresponding set of anodes and cathodes. Each set was electrolyzed at a constant current of 130 A until the electrolysis was interrupted. The electrolysis time was 7 hours. During the electrolysis, the thickness of the solid protective shell on the side wall decreased by 8 mm to 12 mm. The electrode layout is as follows. Figure 7 As shown.

[0102] (3) Product collection: After electrolysis, the cathodes of each group are raised above the molten salt surface, cooled, and the cathodes are removed to collect the deposited products. In this example, 2400g of tungsten powder with a purity of 99.55% and a Fisher particle size of 2.70μm were obtained, and the electrolysis efficiency was 2400÷2÷7=171.4g / h.

[0103] Figure 9 The XRD pattern of the powder prepared in Example 5 is shown in the figure. As can be seen from the figure, all the diffraction peaks in the spectrum can be identified as the standard characteristic diffraction peaks of elemental tungsten (W) (40.3°, 58.3°, 73.2°, etc.), and there are no impurity diffraction peaks of other phases, indicating that the obtained tungsten powder has complete crystal structure and high phase purity.

[0104] Example 6 Tungsten was recovered using the method described in Example 1, except that the amount of sodium tungstate and tungsten trioxide fed was 1000 kg and 50 kg, respectively, and the tungsten content of the waste tungsten rod at the anode was 95 wt%. The remaining operating conditions were the same as in Example 1.

[0105] This example yielded 300g of tungsten powder with a purity of 86.5% (based on W content measured by GDMS), and an electrolysis efficiency of 300 ÷ 8.5 = 35.3 g / h. Due to a shortage of tungsten oxide, the sodium carbonate impurities in industrial sodium tungstate were not completely removed, resulting in reduced product yield, decreased product purity, and the presence of WC. (Refer to...) Figure 10 .

[0106] Example 7 Tungsten was recovered using the method described in Example 1, except that the amount of sodium tungstate and tungsten trioxide fed was 1000 kg and 60 kg respectively, while the other operating conditions were the same as in Example 1.

[0107] In this embodiment, 530g of tungsten powder with a purity of 95.6% was obtained, and the electrolysis efficiency was 530÷8.5=62.35g / h. No WC was present.

[0108] Example 8 Tungsten was recovered using the method described in Example 1, except that the amount of sodium tungstate and tungsten trioxide fed was 1000 kg and 90 kg respectively, while the other operating conditions were the same as in Example 1.

[0109] In this embodiment, 500g of tungsten powder with a purity of 97.2% was obtained, and the electrolysis efficiency was 500÷9=55.56g / h. No WC was present.

[0110] Example 9 Tungsten was recovered using the method described in Example 1, except that the amount of sodium tungstate and tungsten trioxide fed was 1000 kg, while the other operating conditions were the same as in Example 1.

[0111] In this embodiment, 320g of tungsten powder with a purity of 97.6% was obtained, and the electrolysis efficiency was 320÷9=35.56g / h. Because of the excess tungsten oxide, Na2W2O7 will be generated, which will inhibit the yield of electrolytic products, leading to a decrease in the amount of electrolytic products.

[0112] Example 10 Tungsten was recovered using the method described in Example 1, except that 1000 kg of sodium tungstate was used as feed, and no tungsten trioxide was added. The other operating conditions were the same as in Example 1.

[0113] In this embodiment, 160g of tungsten powder with a purity of 79.78% was obtained, and the electrolysis efficiency was 160 ÷ 9 = 17.78 g / h. Because sodium tungstate has a high sodium carbonate impurity content, the electrolysis product W reacts with sodium carbonate, resulting in a decrease in product yield and purity. The presence of WC (refer to...) Figure 11 .

[0114] Comparative Example 1 Tungsten was recovered using the method described in Example 1, except that the cooling system was not activated and no solid protective crust was formed on the inner wall of the electrolytic cell. All other operating conditions were the same as in Example 1.

[0115] As a result, the inner wall of the electrolytic cell lacked a protective crust, and the interior turned noticeably black and corroded by oxidation; the molten salt near the inner wall turned yellowish-green; the purity of the electrolytic products decreased by about 3%; the oxide layer on the inner wall of the electrolytic cell needed to be completely removed before it could be used; and the equipment could not be used continuously.

[0116] Comparative Example 2 Tungsten was recovered using the method described in Example 1, except that the heater was not activated for heating; instead, the electrolysis current was increased to 1000A to generate sufficient Joule heat to maintain the molten salt temperature. The heater was not turned on during electrolysis. All other operating conditions were the same as in Example 1.

[0117] As a result, the excessive electrolytic current density caused dendritic agglomeration of the product, resulting in larger product particles with a diameter of 10 μm. Because the diameter of the electrodes relative to the inner heater was relatively small, it was insufficient to provide the heat required for the molten salt to be kept warm inside the electrolytic cell. The molten salt formed a shell and cooled from the inner wall heater position outwards and from the bottom to the top. The solidified molten salt was non-conductive, and the electrolysis was prematurely interrupted in less than 2 hours.

[0118] Comparative Example 3 Tungsten was recovered using the method described in Example 1, except that the heating treatment step at the first temperature was omitted. The remaining operating conditions were the same as in Example 1.

[0119] The result was that by omitting the initial heating temperature, a small amount of water of crystallization in the molten salt was introduced into the electrolytic molten salt system, resulting in oxide impurities in the electrolytic products. In this comparative example, electrolysis was performed at a constant current of 35A until the electrolysis was interrupted. The electrolysis time was 8.5 hours, yielding 410g of tungsten powder with a purity of 83.73%. The electrolysis efficiency was 410 ÷ 8.5 = 48.24 g / h.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for recovering tungsten by molten salt electrolysis, characterized in that, The method includes: Electrolytic cells made of metal are available; Pre-dried tungstate molten salt is added to the electrolytic cell; The molten tungstate salt is heated to a first temperature and held at that temperature using a heater placed inside the electrolytic cell, in order to dry and preheat the molten tungstate salt. The cooling system located outside the electrolytic cell is activated to lower the temperature of the inner wall of the electrolytic cell below the melting point of the tungstate molten salt. While keeping the cooling system on, the heater continues to heat the molten tungstate salt to a second temperature and perform a second heat preservation, so that the molten tungstate salt melts to obtain molten tungstate electrolyte, and the molten tungstate electrolyte on the inner wall surface of the electrolytic cell solidifies to form a solid shell protective layer. At least one set of cathodes and anodes are inserted into the molten tungstate electrolyte for electrolysis, and the heater is kept on to maintain the molten tungstate electrolyte at the electrolysis temperature. Through the electrolysis, tungsten-containing electrolysis products are formed on the cathode surface.

2. The method according to claim 1, characterized in that, The tungstate molten salt comprises sodium tungstate and tungsten trioxide, with a mass ratio of sodium tungstate to tungsten trioxide of 100:(6-9).

3. The method according to any one of claims 1 to 2, characterized in that, The first temperature is 100°C to 200°C lower than the melting point of the tungstate molten salt, and the second temperature is 0°C to 200°C higher than the melting point of the tungstate molten salt.

4. The method according to claim 3, characterized in that, The first temperature is 400℃~500℃, and the first heat preservation time is 4 hours~6 hours; and / or The second temperature is 600℃~800℃, and the second heat preservation time is 2 hours~4 hours.

5. The method according to claim 1, characterized in that, The thickness of the solid shell protective layer is 15mm to 100mm; and / or The thickness of the solid crust protective layer on the inner wall of the electrolytic cell is 15mm to 30mm, and the thickness of the solid crust protective layer at the bottom of the electrolytic cell is 70mm to 100mm.

6. The method according to claim 1, characterized in that, The diameter of the electrolytic cell is 800mm to 1200mm, the depth of the electrolytic cell is 1000mm to 1200mm, and the salt content of the electrolytic cell is 800kg to 3000kg.

7. The method according to claim 1, characterized in that, The electrolysis is performed using a constant current electrolysis method, with an electrolysis current of 30A to 200A, an electrolysis voltage of 20V to 35V, an electrolysis temperature of 700℃ to 800℃, and an electrolysis time of 3 hours to 12 hours.

8. The method according to claim 1, characterized in that, During the heating to the first temperature, the second temperature, and the first and second heat preservation processes, the heating power of the heater is 25kW to 35kW. During the electrolysis process, the heating power of the heater is 2kW to 5kW.

9. The method according to claim 6, characterized in that, The cathode is a tungsten rod, and the anode is waste tungsten material, wherein the tungsten content in the waste tungsten material is above 95 wt%. Optionally, the diameter of the tungsten rod is 20mm to 35mm; Optionally, during the electrolysis process, the length of the cathode submerged below the surface of the molten tungstate electrolyte is 100 mm to 200 mm, and the length of the anode submerged below the surface of the molten tungstate electrolyte is 80 mm to 120 mm.

10. The method according to claim 1, characterized in that, The number of cathodes and anodes is N, where N≥2; and the method further includes: Once the cathode in operation has achieved enrichment of electrolytic products, it is raised and removed from the electrolytic cell, and another cathode is placed in the molten tungstate electrolyte to continue electrolysis; and / or Once the anode used in the operation is consumed, it is removed from the electrolytic cell, and another anode is placed in the molten tungstate electrolyte to continue electrolysis.

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