A method for recovering tungsten-molybdenum waste

Abstract

The application belongs to the technical field of metallurgy, and particularly relates to a tungsten-molybdenum waste recovery method. The method places waste tungsten material or waste molybdenum material in an electrolysis system with sodium hydroxide or ammonia water as an electrolyte, and electrolyzes the waste tungsten material or waste molybdenum material as an anode to efficiently dissolve tungsten and molybdenum in the form of ions, so as to obtain an alkaline electrolyte rich in tungstate and molybdate; and then the electrolyte is subjected to subsequent treatment to recover corresponding products, thereby realizing the unity of process shortening, environmental friendliness and efficient resource recovery.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for recycling tungsten and molybdenum waste. Background Technology

[0002] Tungsten and molybdenum are both rare refractory metals with high strength, high melting point, excellent thermal and electrical conductivity, and good corrosion resistance and high-temperature resistance. Both metals and their alloys occupy an important position in the national economy and high-tech sectors, and are widely used in key areas such as steel metallurgy, aerospace, electronics, defense, chemical catalysis, and new energy, making them an important component of the nation's strategic resources.

[0003] Long-term, large-scale mining has led to increasingly strained primary mineral resources, putting growing pressure on ensuring resource supply security. Simultaneously, industrial production and manufacturing processes generate a large amount of secondary resources containing tungsten and molybdenum, such as waste cemented carbide, waste tungsten / molybdenum alloy scrap, waste catalysts, waste electrodes, waste targets, and various offcuts. The tungsten and molybdenum grades in these wastes are often far higher than in the original ore, making them valuable renewable resources. Therefore, developing efficient and clean technologies for recycling secondary tungsten and molybdenum resources is of profound significance for reducing dependence on primary minerals, ensuring national strategic resource security, promoting the development of a circular economy, and achieving the green and low-carbon transformation of the non-ferrous metals industry.

[0004] Currently, the technical approaches adopted by industry and research in the recycling and processing of waste tungsten and waste molybdenum materials can be mainly summarized into three categories, but all of them have significant limitations.

[0005] Pyrometallurgical processes: This method mainly includes high-temperature processes such as oxidative roasting, sintering, or smelting. For example, oxidative roasting converts tungsten and molybdenum into volatile oxides (such as WO3 and MoO3), which are then collected by condensation. Although this process can achieve preliminary enrichment of metals, it consumes extremely high amounts of energy and easily generates large amounts of metal-containing dust and harmful gases (such as SO2) during the high-temperature process, resulting in serious environmental pollution and high costs for subsequent tail gas treatment. Furthermore, metal volatilization losses may lead to low direct recovery rates and poor adaptability to complex mixed waste materials. In tungsten recovery, oxidative roasting also easily leads to kiln scaling, resulting in high tungsten content in the waste residue and making it difficult to improve the recovery rate.

[0006] Hydrometallurgical process: This is currently the most widely used method. It involves leaching waste materials with acid (such as a mixture of nitric and hydrochloric acid) or alkali (such as sodium hydroxide or sodium carbonate) solutions, allowing tungsten and molybdenum to enter the solution in ionic form. After multiple complex separation and purification steps (such as solvent extraction, ion exchange, and chemical precipitation), the ions are ultimately converted into intermediate products such as ammonium paratungstate, ammonium molybdate, or their corresponding oxides. Although the reaction conditions are relatively mild, this process suffers from problems such as lengthy procedures, complex operations, and high consumption of chemical reagents. It also generates large amounts of wastewater and waste residue containing salt, nitrogen, or organic matter, placing significant pressure on environmental treatment. Furthermore, to obtain metallic tungsten and molybdenum, further processing of the intermediate products, such as hydrogen reduction, is required, resulting in relatively high overall energy and material consumption.

[0007] Traditional electrochemical processes: Electrolysis theoretically allows for the direct extraction of metals from waste, with a relatively simple process. Existing research largely focuses on high-temperature molten salt electrolysis (such as fluoride systems) or strongly acidic electrolyte systems. However, these methods face significant challenges: molten salt electrolysis requires temperatures of several hundred degrees Celsius, placing stringent demands on the electrolytic cell material, resulting in high equipment investment and energy consumption, and significant operational risks; while in acidic aqueous solution electrolysis, the molybdenum anode is prone to passivation, forming a dense oxide film, leading to a sharp decline in electrolysis efficiency or even interruption, making the process extremely unstable. For tungsten electrolytic recovery, similar challenges exist in acidic media, including severe equipment corrosion, the need to improve current efficiency, and insufficient adaptability to waste with different compositions (such as high cobalt content).

[0008] Therefore, developing a new, efficient, clean, and short-process technology that can overcome the above-mentioned defects and is suitable for the recycling of tungsten and molybdenum secondary resources is of urgent need and has important application value for realizing the recycling of strategic rare metal resources and the sustainable development of the industry. Summary of the Invention

[0009] To address the problems in existing technologies, this invention provides a method for recycling tungsten and molybdenum waste. This method involves placing waste tungsten or molybdenum material in an electrolytic system using sodium hydroxide or ammonia as the electrolyte, and electrolyzing the waste tungsten or molybdenum material as the anode. This allows tungsten and molybdenum to be efficiently dissolved in ionic form, resulting in an alkaline electrolyte rich in tungstate and molybdate. The electrolyte is then further processed to recover the corresponding products, achieving a unified approach of shortened process, environmental friendliness, and efficient resource recovery.

[0010] The technical solution of this invention is: A method for recycling tungsten and molybdenum waste includes the following steps: Waste tungsten or waste molybdenum is pretreated, and then the pretreated waste tungsten or waste molybdenum is placed in an electrolyte for constant current electrolysis, so that tungsten or molybdenum is dissolved in ionic form, resulting in an electrolyte rich in tungstate or molybdate. The electrolyte is an aqueous solution of sodium hydroxide or an aqueous solution of ammonia. The electrolysis temperature is 25-90℃, the concentration of the sodium hydroxide aqueous solution is 10-300 g / L, the mass fraction of the ammonia aqueous solution is 2%-28%, and the anolyte current density ranges from 0.05-0.5 A / cm². The electrolyte rich in tungstate or molybdate is post-treated to obtain tungsten or molybdenum products.

[0011] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, the pretreatment includes: chemically degreasing the waste tungsten or molybdenum material at 25°C, followed by sequential alcohol washing, water washing, ultrasonic washing, and drying; the degreasing agent used in the chemical degreasing includes: NaOH: 20-40 g / L, Na2CO3: 20-40 g / L, Na2SiO3: 5-10 g / L, Na3PO4·12H2O: 5-10 g / L, and OP-emulsifier: 1-3 g / L; the drying condition is low-temperature drying (<80°C) in a vacuum drying oven.

[0012] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, determining the end point of electrolysis during the electrolysis process refers to real-time monitoring of the cell voltage during electrolysis. When the cell voltage tends to stabilize and there is no significant fluctuation within 1 hour, it indicates that there is no effective reaction on the electrode surface.

[0013] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, when the electrolyte is an aqueous sodium hydroxide solution, the post-treatment method includes: direct evaporation crystallization, chemical precipitation, solvent extraction, or ion exchange.

[0014] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, the direct evaporation crystallization refers to evaporating and crystallizing an electrolyte rich in tungstate or molybdate to obtain sodium tungstate or sodium molybdate crystals. Specifically, the method is as follows: using the salting-out crystallization method, the electrolyte containing sodium hydroxide is directly evaporated. When the sodium tungstate or sodium molybdate reaches a saturation concentration, its crystals precipitate out. The crystals are separated by hot filtration at a temperature above 70°C. The separated high-alkali mother liquor is then returned to the electrolysis process for recycling after filtration and adsorption to remove impurities; or using the saturation crystallization method, the liquid is directly evaporated to saturation at a temperature above 90°C, then cooled to below 50°C to crystallize, and then filtered at a temperature below 60°C to obtain the crystals.

[0015] Furthermore, the above-mentioned high-alkali mother liquor recycling treatment method refers to the separation of high-alkali mother liquor first being filtered through a filter membrane to remove solid suspended residues. The filtered mother liquor is then passed through a chelating resin to adsorb and remove impurities and heavy metal ions. It can be recycled 10-15 times. Long-term recycling will lead to the continuous accumulation of impurities, reduce the conductivity of the electrolyte, increase energy consumption, and reduce product quality.

[0016] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, the chemical precipitation method refers to the following post-treatment method when the electrolyte is an aqueous sodium hydroxide solution: adding acid to the electrolyte rich in tungstate or molybdate to adjust the pH to 2-4 to generate tungstic acid or molybdate precipitate, and sequentially filtering, washing, drying and calcining the precipitate to obtain tungsten trioxide or molybdenum trioxide.

[0017] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, the acid is hydrochloric acid or sulfuric acid, wherein the concentration of hydrochloric acid is 5%-40% and the concentration of sulfuric acid is 5%-30%; the drying temperature is 100-300℃ and the calcination temperature is 500-800℃.

[0018] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, the solvent extraction or ion exchange method refers to the following post-treatment method when the electrolyte is an aqueous sodium hydroxide solution: adsorbing tungstate or molybdate from the electrolyte using an extractant or ion exchange resin, then desorbing with an NH4Cl-NH4OH mixture to obtain an ammonium salt solution, and finally obtaining the corresponding oxide product, i.e., tungsten trioxide or molybdenum trioxide, through evaporation, crystallization, and calcination.

[0019] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, the extractant is selected from at least one of N235, Alamine-336, N263, and TOMAC; the ion exchange resin is a strongly basic anion exchange resin, including one of D201×7, WA, Amberlite IRA-400, and AB-17Π.

[0020] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, when the electrolyte is an ammonia solution, the post-processing includes: filtering and evaporating the electrolyte rich in tungstate or molybdate to obtain ammonium tungstate or ammonium molybdate crystals.

[0021] Furthermore, the selection of the ammonia solution concentration mentioned above takes into account that too low a concentration results in insufficient conductivity, low electrolysis efficiency, and slow tungsten and molybdenum dissolution rates, while too high a concentration of ammonia solution leads to severe volatilization, causing equipment corrosion and environmental problems.

[0022] Furthermore, in the above-mentioned method for recycling tungsten and molybdenum waste, the cathode for electrolysis is graphite.

[0023] In this invention, when electrolysis is performed using sodium hydroxide solution as the electrolyte, the anodic reaction involves the oxidation of tungsten and molybdenum in the anode to sodium tungstate, which then dissolves in the electrolyte. The cathode reaction involves the reduction of water molecules in the solution, producing hydrogen gas, and continuous bubble formation on the cathode surface. The reaction mechanism during electrolysis is shown in Equations 1-3. When electrolysis is performed using ammonia solution as the electrolyte, the anodic reaction involves the oxidation of tungsten and molybdenum in the anode to ammonium tungstate, which then dissolves in the electrolyte. The cathode reaction is the same as when sodium hydroxide is used as the electrolyte, with water molecules in the solution being reduced to produce hydrogen gas. The reaction mechanism at the anode in this case is shown in Equations 4 and 5.

[0024] During electrolysis, as tungsten and molybdenum dissolve, their ion concentration continuously increases, causing changes in solution viscosity and conductivity, and gradually decreasing the overall pH value of the electrolyte.

[0025] W+8OH - →WO4 2- +4H2O+6e - (1) Mo + 8OH - →MoO4 2- +4H2O+6e - (2) 2H2O+2e - →H2↑+2OH- (3) W + 4H₂O + 2NH₃ → (NH₄)₂WO₄ + 6H₂O + +6e - (4) Mo + 4H₂O + 2NH₃ → (NH₄)₂MoO₄ + 6H₂O + +6e - (5) Advantages and beneficial effects of the present invention: (1) The process flow is significantly simplified, resulting in higher recycling efficiency and economy. This invention adopts alkaline electrolysis, simplifying the lengthy processes required in traditional recycling processes, such as high-temperature oxidation roasting, multi-step acid-base leaching, and complex solid-liquid separation, into a single electrochemical dissolution core step. This process uses waste tungsten and molybdenum materials as raw materials and directly produces a relatively pure electrolyte under mild conditions. It can be directly connected to subsequent mature processes such as crystallization or ion exchange, thereby significantly shortening the production cycle, reducing energy and material consumption, and achieving higher overall recycling efficiency and economy.

[0026] (2) Flexible process control, stable product, and strong adaptability. The alkaline electrolysis system of the present invention can effectively control the dissolution rate of tungsten and molybdenum and the concentration of the target metal in the electrolyte by flexibly adjusting parameters such as current density, electrolyte concentration, and temperature, providing a reliable guarantee for obtaining intermediate products with stable quality. At the same time, the system has a wide range of adaptability to raw materials and can handle complex wastes with different compositions and forms, improving the universality of the process.

[0027] (3) It is environmentally friendly, has high production safety, and low overall cost. The entire process is carried out in a closed, mild alkaline aqueous solution, which fundamentally avoids the high energy consumption and harmful fumes of pyrometallurgical processes, as well as the pollution problems of acidic wastewater and organic waste liquid caused by the use of large amounts of strong acids and organic extractants in traditional wet processes. The main media used, such as sodium hydroxide and ammonia, are inexpensive and readily available with low corrosivity, and the electrolyte can be recycled, reducing the discharge of waste gas, wastewater, and solid waste from the source, reducing the difficulty of environmental protection and end-of-pipe treatment costs, and improving production safety. Attached Figure Description

[0028] Figure 1 This is a process flow diagram for Example 1; Figure 2 This is a process flow diagram for Example 2; Figure 3 This is a process flow diagram for Example 4; Figure 4 Here is a structural diagram of the electrolytic cell used in this invention: In the diagram, 1-waste tungsten or molybdenum material, 2-graphite crucible, 3-sodium hydroxide or ammonia electrolyte. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. The following examples are for illustrative purposes only and should not be used to limit the scope of the present invention.

[0030] In the following specific embodiments, the electrolytic cell structure used is as follows: Figure 4 As shown, the electrolysis uses a DC power supply, with waste tungsten or molybdenum material 1 as the anode and a graphite crucible 2 as the cathode. The crucible is filled with sodium hydroxide or ammonia electrolyte 3.

[0031] Because tungsten and molybdenum have similar chemical properties and the same specific processing procedures, the following examples only mention the recycling of tungsten waste.

[0032] Example 1 This embodiment describes a method for recycling tungsten waste, the process flow diagram of which is shown below. Figure 1 As shown, the specific steps include: Waste tungsten rods were used as raw materials, and a chemical degreasing solution was prepared: NaOH: 30 g / L, Na₂CO₃: 30 g / L, Na₂SiO₃: 8 g / L, Na₃PO₄·12H₂O: 8 g / L, and OP-emulsifier: 2 g / L. The solution was soaked at 25°C for 30 minutes until the surface oil was completely removed. The degreased waste tungsten material was then ultrasonically washed sequentially in anhydrous ethanol and deionized water for 10 minutes each. After washing, it was placed in a vacuum drying oven and dried at 60°C for later use.

[0033] Pretreated waste tungsten was used as the anode and a high-purity graphite plate as the cathode. A sodium hydroxide solution with a concentration of 100 g / L was prepared, the electrolysis temperature was controlled at 50℃, and the anode current density was 0.08 A / cm². 2 A constant current electrolysis process was initiated by turning on a DC power supply. Bubbles continuously precipitated on the cathode surface. Electrolysis lasted approximately 24 hours, during which electrolyte was replenished periodically to maintain the liquid level. After electrolysis, an alkaline electrolyte rich in sodium tungstate was obtained.

[0034] The electrolyte was initially filtered using filter paper to remove any trace suspended residues, resulting in a clear solution of sodium tungstate and sodium hydroxide. The filtered electrolyte was then transferred to an evaporator and heated to above 85°C for evaporation and concentration. As water evaporated, the concentration of sodium tungstate in the solution continuously increased. Evaporation was stopped when the solution reached supersaturation and a large amount of sodium tungstate crystals precipitated. The solution was then vacuum-filtered while hot at a temperature >70°C to separate the sodium tungstate crystals. The mother liquor adhering to the crystal surface was washed with a small amount of hot, dilute sodium hydroxide solution, and then dried at 100°C to obtain industrial-grade sodium tungstate crystals. The highly alkaline mother liquor after crystal separation was filtered and adsorbed for impurity removal before being returned to the electrolytic cell. After adding an appropriate amount of solid NaOH to adjust the concentration, it could be used for the next batch of electrolysis.

[0035] Example 2 This embodiment describes a method for recycling molybdenum waste, and its process flow diagram is as follows: Figure 2 As shown, the specific steps include: Waste molybdenum wire was used as raw material, and a chemical degreasing solution was prepared: NaOH: 30 g / L, Na₂CO₃: 30 g / L, Na₂SiO₃: 8 g / L, Na₃PO₄·12H₂O: 8 g / L, and OP-emulsifier: 2 g / L. The solution was soaked at 25°C for 30 minutes until the surface oil was completely removed. The degreased waste tungsten material was then ultrasonically washed sequentially in anhydrous ethanol and deionized water for 10 minutes each. After washing, it was placed in a vacuum drying oven and dried at 60°C for later use.

[0036] Pretreated waste molybdenum wire was used as the anode, and a high-purity graphite plate as the cathode. A sodium hydroxide solution with a concentration of 150 g / L was prepared, and the electrolysis temperature was controlled at 70℃, with an anode current density of 0.1 A / cm². 2Constant current electrolysis for about 36 hours yields an alkaline electrolyte rich in sodium molybdate.

[0037] Electrolyte filtration removes residue, yielding a clear sodium molybdate solution. The filtrate is placed in a beaker equipped with stirring and heating, and heated to 60°C. Under vigorous stirring, a 20% sulfuric acid solution is slowly added dropwise, monitored with a pH meter, until the pH stabilizes at approximately 3.0. At this point, molybdate ions in the solution are converted into a yellow molybdate precipitate. This precipitate is then collected by vacuum filtration. The precipitate is washed repeatedly with deionized water at 60°C until no sulfate ions are detected in the filtrate using BaCl2 solution, thus removing any entrained sodium salts. The washed molybdate filter cake is dried in an oven at 120°C for 12 hours to obtain a yellow dried molybdate. The dried molybdate is then placed in a muffle furnace and calcined at 600°C for 2 hours. During this process, the molybdate dehydrates and decomposes, changing its color from yellow to white or pale yellow, yielding a high-purity molybdenum trioxide powder product.

[0038] Example 3 This embodiment describes a method for recycling tungsten waste, which specifically includes the following steps: Take waste high-density tungsten alloy and prepare a chemical degreasing solution: NaOH: 30 g / L, Na₂CO₃: 30 g / L, Na₂SiO₃: 8 g / L, Na₃PO₄·12H₂O: 8 g / L, OP-emulsifier: 2 g / L. Immerse the solution at 25°C for 30 minutes until the surface oil is completely removed. Then, ultrasonically wash the degreased tungsten material sequentially in anhydrous ethanol and deionized water for 10 minutes each. After washing, place the material in a vacuum drying oven and dry it at 60°C for later use.

[0039] Pretreated waste tungsten was used as the anode and graphite as the cathode. A sodium hydroxide solution with a concentration of 200 g / L was prepared. The electrolysis temperature was controlled at 50℃, and the anode current density was 0.2 A / cm³. 2 Constant current electrolysis for about 24 hours yields an alkaline electrolyte rich in sodium molybdate.

[0040] The electrolyte was filtered, and N235 was used as the extractant. The organic phase and aqueous phase were mixed at a volume ratio of 1:1, and extracted by shaking at room temperature for 10 minutes. After standing and phase separation, tungstate ions were extracted into the organic phase. The tungsten-loaded organic phase was washed with deionized water to remove entrained sodium ions. Then, a 5 mol / L mixed solution of NH4Cl and NH4OH was used as the back-extraction agent, and back-extraction was performed at the specified ratio, shaking for 10 minutes. After standing and phase separation, tungsten entered the aqueous phase as ammonium tungstate, yielding a pure ammonium tungstate solution. The back-extracted ammonium tungstate solution was evaporated and concentrated at 80°C until a large amount of crystals precipitated, and then cooled to room temperature. Ammonium paratungstate crystals were obtained by filtration and washed with a small amount of cold water. The ammonium paratungstate crystals were placed in a muffle furnace and the temperature was programmed: first, the temperature was maintained at 250°C for 1 hour to remove water of crystallization and some ammonia, and then calcined at 550°C for 2 hours to completely decompose it, yielding a high-purity yellow tungsten trioxide powder product.

[0041] Example 4 This embodiment describes a method for recycling tungsten waste, the process flow diagram of which is shown below. Figure 3 As shown, the specific steps include: Waste tungsten rods were used as raw materials, and a chemical degreasing solution was prepared: NaOH: 30 g / L, Na₂CO₃: 30 g / L, Na₂SiO₃: 8 g / L, Na₃PO₄·12H₂O: 8 g / L, and OP-emulsifier: 2 g / L. The solution was soaked at 25°C for 30 minutes until the surface oil was completely removed. The degreased waste tungsten material was then ultrasonically washed sequentially in anhydrous ethanol and deionized water for 10 minutes each. After washing, it was placed in a vacuum drying oven and dried at 60°C for later use.

[0042] Pretreated waste tungsten was used as the anode, and a high-purity graphite plate as the cathode. A 10% ammonia solution was used, the electrolysis temperature was controlled at 25℃, and the anode current density was 0.1 A / cm³. 2 A constant current electrolysis process was initiated by turning on a DC power supply. Bubbles continuously precipitated on the cathode surface. Electrolysis lasted approximately 24 hours, during which electrolyte was periodically replenished to maintain the liquid level. Upon completion of electrolysis, an alkaline electrolyte rich in ammonium tungstate was obtained.

[0043] The electrolyte was initially filtered through filter paper to remove any trace suspended residues, resulting in a clear ammonium tungstate solution. The filtered electrolyte was then transferred to an evaporator and heated to above 85°C for evaporation and concentration. As water evaporated, the concentration of ammonium tungstate in the solution continuously increased. Evaporation was stopped when the solution reached supersaturation and a large amount of ammonium tungstate crystals precipitated. The solution was then vacuum-filtered while hot at a high temperature (>70°C) to separate the ammonium tungstate crystals. The crystal surface was washed with a small amount of dilute ammonia and then dried at 100°C to obtain industrial-grade ammonium paratungstate crystals.

Claims

1. A method for recycling tungsten and molybdenum waste, characterized in that, Includes the following steps: Waste tungsten or waste molybdenum is pretreated, and then the pretreated waste tungsten or waste molybdenum is placed in an electrolyte for constant current electrolysis, so that tungsten or molybdenum is dissolved in ionic form, resulting in an electrolyte rich in tungstate or molybdate. The electrolyte is an aqueous solution of sodium hydroxide or an aqueous solution of ammonia. The electrolysis temperature is 25-90℃, the concentration of the sodium hydroxide aqueous solution is 10-300 g / L, the mass fraction of the ammonia aqueous solution is 2%-28%, and the anolyte current density ranges from 0.05-0.5 A / cm². The electrolyte rich in tungstate or molybdate is post-treated to obtain tungsten or molybdenum products.

2. The method for recycling tungsten and molybdenum waste according to claim 1, characterized in that, The pretreatment includes: chemically degreasing the waste tungsten or waste molybdenum material at 25°C, followed by sequential alcohol washing, water washing, ultrasonic washing, and drying; the degreasing agent used in the chemical degreasing includes: NaOH: 20-40 g / L, Na2CO3: 20-40 g / L, Na2SiO3: 5-10 g / L, Na3PO4·12H2O: 5-10 g / L, and OP-emulsifier: 1-3 g / L.

3. The method for recycling tungsten and molybdenum waste according to claim 1, characterized in that, When the electrolyte is an aqueous sodium hydroxide solution, the post-treatment method includes: direct evaporation crystallization, chemical precipitation, solvent extraction, or ion exchange.

4. The method for recycling tungsten and molybdenum waste according to claim 3, characterized in that, The direct evaporation crystallization refers to the evaporation and crystallization of an electrolyte rich in tungstate or molybdate to obtain sodium tungstate or sodium molybdate crystals. The specific methods are as follows: using the salting-out crystallization method, the electrolyte containing sodium hydroxide is directly evaporated. When the sodium tungstate or sodium molybdate reaches a saturation concentration, its crystals precipitate out. The crystals are separated by hot filtration at a temperature above 70°C. The high-alkali mother liquor after separation can be returned to the electrolysis process for recycling after filtration and adsorption to remove impurities. Alternatively, the saturation crystallization method is used, where the electrolyte is directly evaporated to saturation at a temperature above 90°C, then cooled to a temperature below 50°C to crystallize, and then filtered at a temperature below 60°C to obtain the crystals.

5. The method for recycling tungsten and molybdenum waste according to claim 3, characterized in that, The chemical precipitation method refers to the following post-treatment process when the electrolyte is an aqueous sodium hydroxide solution: adding acid to the electrolyte rich in tungstate or molybdate to adjust the pH to 2-4 to generate tungstic acid or molybdate precipitate, and then sequentially filtering, washing, drying and calcining the precipitate to obtain tungsten trioxide or molybdenum trioxide.

6. The method for recycling tungsten and molybdenum waste according to claim 5, characterized in that, The acid is hydrochloric acid or sulfuric acid, wherein the concentration of hydrochloric acid is 5%-40% and the concentration of sulfuric acid is 5%-30%; the drying temperature is 100-300℃ and the calcination temperature is 500-800℃.

7. The method for recycling tungsten and molybdenum waste according to claim 1, characterized in that, The solvent extraction or ion exchange method refers to the following post-treatment process when the electrolyte is an aqueous sodium hydroxide solution: adsorbing tungstate or molybdate from the electrolyte using an extractant or ion exchange resin, then desorbing it with an NH4Cl-NH4OH mixture to obtain an ammonium salt solution, and finally obtaining the corresponding oxide product, i.e., tungsten trioxide or molybdenum trioxide, through evaporation, crystallization, and calcination.

8. The method for recycling tungsten and molybdenum waste according to claim 7, characterized in that, The extractant is selected from at least one of N235, Alamine-336, N263, and TOMAC; the ion exchange resin is a strongly basic anion exchange resin, including one of D201×7, WA, Amberlite IRA-400, and AB-17Π.

9. The method for recycling tungsten and molybdenum waste according to claim 1, characterized in that, When the electrolyte is an ammonia solution, the post-processing includes: filtering and evaporating the electrolyte rich in tungstate or molybdate to obtain ammonium tungstate or ammonium molybdate crystals.

10. The method for recycling tungsten and molybdenum waste according to claim 1, characterized in that, The cathode of the electrolysis is graphite.

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