A method for removing impurities and recovering vanadium resources from a bayer process of alumina production

Abstract

The application discloses a method for removing impurities and recycling vanadium resources from a Bayer process of alumina production, and belongs to the technical field of non-ferrous metallurgy and resource comprehensive utilization. In view of the problem that vanadium impurities in the circulating mother liquor in the Bayer process of alumina production continuously accumulate and affect the production stability and product quality, the application introduces an adsorbent into the alkaline solution of the system, and the impurities in the solution are precipitated by accurately controlling the reaction temperature, alkali concentration and adsorption time, so that the purified solution is obtained after solid-liquid separation; the solution is crystallized by adjusting the temperature to precipitate the crude product, and the liquid is returned to the main process of alumina production by heat exchange; the crude product is melted by hot water, and sulfuric acid is added to adjust the PH and temperature; after the impurities are removed by adding aluminum salt and magnesium salt, the ammonium salt is introduced into the solution of the system. The application has the advantages of simple process, effective connection with the existing alumina production line, impurity purification and valuable element extraction of the alumina system, and environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy and comprehensive resource utilization technology, specifically to a method for removing vanadium impurities and recovering resources during alumina production. In particular, it relates to a method for purifying the system and recovering valuable elements by introducing an adsorbent to remove impurities from an alkaline aluminate solution in the Bayer process alumina system, crystallizing and separating impurities such as sodium vanadate with high vanadium content. Background Technology

[0002] Vanadium, as a by-product impurity in bauxite, enters the circulating mother liquor system during the Bayer process of alumina production. As the process continues, vanadium accumulates in the mother liquor, leading to a decline in alumina product quality, reduced decomposition efficiency, and increased energy consumption and production costs. Therefore, effectively controlling and removing vanadium impurities from the Bayer process system while simultaneously achieving its resource recovery has become a key technological requirement for clean production in the alumina industry.

[0003] Currently, the industry commonly uses a "single-stage vanadium precipitation" process to treat vanadium-containing mother liquor, which involves precipitating vanadium through a single cooling process. However, this method suffers from problems such as low vanadium recovery rate, low grade of the resulting vanadium cake, complex subsequent purification processes, and high overall processing costs, making it difficult to simultaneously achieve the dual goals of efficient impurity removal and high-value utilization of resources.

[0004] While there are various methods for recovering vanadium-containing materials (such as vanadium slag, vanadium-containing wastewater, and metallurgical slag) in existing patented technologies, their process conditions, raw material properties, and system environment differ significantly from the Bayer process for alumina, resulting in insufficient adaptability when directly applied to this system.

[0005] Among them, patent CN115571913B discloses a method for recovering vanadium resources from silicon slag in vanadium liquid, which involves reducing vanadium with oxalic acid. 5+ For V 4+ Vanadium pentoxide is then prepared through pH adjustment, oxidation, and vanadium precipitation. While this method achieves a high vanadium recovery rate and harmless treatment of byproducts, it is only suitable for treating silica-removing slag systems with relatively well-defined compositions and limited impurity types, and it relies on organic reducing agents such as oxalic acid and multi-step pH control. When applied to Bayer process circulating mother liquor with complex compositions, high alkalinity, and high ionic strength, it may lead to decreased reduction efficiency and increased reagent consumption due to system interference, and the introduced organic matter may affect the stability of the main process.

[0006] Another related technology is patent CN113337715B, which proposes a method for the resource-based recovery of vanadium and chromium from vanadium- and chromium-containing wastewater. This method uses hydrogen to directly reduce and precipitate vanadium trioxide under the action of a catalyst. This method avoids the use of ammonium salts, simplifies the process, and yields high-value-added products. However, this process is suitable for low-concentration, near-neutral, or weakly acidic wastewater systems. The Bayer process mother liquor, on the other hand, is strongly alkaline (pH>13) and contains high concentrations of sodium aluminate and other coexisting ions. This not only inhibits the hydrogen reduction reaction but may also lead to catalyst deactivation or the formation of non-target precipitates, thus affecting the selective recovery efficiency of vanadium and the purity of the product.

[0007] In summary, existing vanadium recovery technologies are mostly designed for metallurgical solid waste or specific wastewater systems. Their process parameters and reagent systems are difficult to directly adapt to the highly alkaline, high-salinity, and multi-component complex environment of Bayer process alumina production. There is still a lack of an integrated clean method that can simultaneously achieve efficient removal of vanadium impurities and high-value resource recovery without affecting the stable operation of the main process. Summary of the Invention

[0008] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a method for removing impurities and recovering vanadium resources from the Bayer process alumina production. By introducing a specific adsorbent into a strongly alkaline, high-salinity circulating mother liquor system, combined with gradient cooling-induced crystallization, multi-stage impurity removal, and ammonium salt precipitation of vanadium, the method achieves efficient removal and high-value recovery of vanadium impurities while ensuring the stable operation of the main process.

[0009] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: a method for removing impurities and recovering vanadium resources from the Bayer process alumina production, comprising the following steps: S1: Obtain vanadium-containing evaporation mother liquor from the alumina production system; the evaporation mother liquor is an alkaline solution enriched with vanadium after multiple cycles in the Bayer process; S2: Introduce an adsorbent into the mother liquor of the evaporation, wherein the adsorbent is one or more of activated alumina, diatomaceous earth or modified zeolite; S3: Use the clarified filtrate obtained in step S2 as the subsequent crystallization reaction system; S4: Control the crystallization conditions of the reaction system to crystallize vanadium ions, sodium ions, etc. in the solution to precipitate sodium vanadate and other salts; S5: The solid-liquid mixture obtained in step S4 is subjected to solid-liquid separation to obtain crude sodium vanadate filter cake and purified mother liquor; the purified mother liquor is returned to the decomposition or evaporation process of the alumina main process after heat exchange with the mother liquor in step S2. S6: Dissolve the crude sodium vanadate filter cake obtained in step S5 in hot water to prepare a vanadium-containing solution. Then add sulfuric acid to adjust the pH, introduce aluminum salt, let it stand to remove impurities, and then discharge the impurities. S7: Adjust the pH of the high-purity vanadium-containing solution obtained in step S6, and introduce an ammonium salt, wherein the ammonium salt is one of ammonium sulfate, ammonium chloride or ammonium nitrate, to precipitate ammonium metavanadate crystals; S8: Perform solid-liquid separation on the solid-liquid mixture obtained in step S7 to obtain crude ammonium metavanadate product and vanadium precipitation mother liquor. S9: The vanadium precipitate mother liquor obtained in step S8 is transported to the front end of the impurity removal process in step S6 and mixed with the crude sodium vanadate solution. S10: Add the crude ammonium metavanadate product obtained in step S8 to deionized water, heat it with steam to completely dissolve it, filter it while hot, and recrystallize it; after solid-liquid separation, the obtained crystals are dried by indirect heating with steam to obtain the ammonium metavanadate product.

[0010] Preferably, the concentration of caustic alkali Na2O in the mother liquor of evaporation in step S1 is 200-250 g / L, and the concentration of elemental vanadium can fluctuate around 400 mg / L.

[0011] Preferably, in step S2, the amount of adsorbent introduced is 5-15 g / L, the temperature is 40-70℃, the residence time is 2-4 h, and the adsorbent is γ-alumina microspheres with a specific surface area of ​​150 to 300 square meters per gram and a pore size distribution of 5 to 20 nanometers. Before use, the microspheres are dried at 100 to 120 degrees Celsius for 2 hours.

[0012] Preferably, the crystallization conditions in step S4 are 20-40 °C, and 0.5% to 2% of crude vanadium slag by volume is added as seed crystals in step S4.

[0013] Preferably, in step S6, the pH is controlled at 7-8, the volume ratio of the introduced aluminum salt is 1:200, the reaction time is 1-2 hours, and the aluminum salt solution is a 10% to 20% aluminum sulfate aqueous solution. The solution is added slowly dropwise under stirring for 30 to 60 minutes.

[0014] Preferably, in step S7, the pH is controlled at 8-9, the amount of ammonium salt introduced is in a molar ratio of 1:2, the temperature is controlled at 25-30℃, and the reaction time is more than 6 hours.

[0015] Preferably, in step S10, the mass ratio of deionized water to crude ammonium metavanadate used for recrystallization is 3:1 to 5:1, and the dissolution temperature is maintained at 95 degrees Celsius or above for at least 30 minutes.

[0016] Preferably, in step S9, a small amount of ammonium ions are mixed with those in step S6 to recover vanadium and ammonia from the solution, thereby achieving the purpose of solution recycling.

[0017] According to the present invention, by introducing an adsorbent into the original strongly alkaline mother liquor, some colloidal and organic complexed impurities are preferentially adsorbed, reducing interference in the subsequent crystallization process and improving the purity and precipitation rate of sodium vanadate crystals. This adsorption step is carried out in the range of 40 to 70 degrees Celsius, utilizing the heat energy of the mother liquor itself while avoiding adsorbent deactivation or vanadium species transformation caused by high temperatures. The clarified liquid after adsorption is directly used for low-temperature induced crystallization without additional alkalinity adjustment or dilution, maintaining the material balance of the system.

[0018] During the crystallization stage, by precisely controlling the temperature within the range of 20 to 40 degrees Celsius, sodium vanadate (NaVO3) is selectively precipitated due to its reduced solubility, while simultaneously inhibiting the co-precipitation of main components such as sodium aluminate. This temperature range is significantly higher than the 0 to 10 degrees Celsius commonly used in traditional "primary vanadium precipitation" processes, significantly reducing refrigeration energy consumption and avoiding filtration difficulties caused by increased viscosity at low temperatures. Adding coarse vanadium slag as seed crystals effectively controls the crystal nucleation rate, resulting in crystalline products with uniform particle size that are easy to filter.

[0019] After the crude sodium vanadate is dissolved in hot water, it enters an acidic impurity removal stage. By precisely controlling the pH to a weakly acidic range of 7 to 8, impurities such as aluminum, silicon, phosphorus, and arsenic precipitate as hydroxides or phosphates, while vanadium remains in the solution as soluble vanadate ions. The addition of aluminum salts not only provides Al... 3+ It is used to precipitate phosphate and arsenate ions, and can also capture colloidal silica through co-precipitation. This impurity removal step is carried out at near-boiling temperatures, which improves the reaction kinetics and precipitate density, facilitating subsequent solid-liquid separation.

[0020] During the vanadium precipitation stage, ammonium salts are reacted under weakly alkaline conditions (pH 8 to 9) and at room temperature (25 to 30 degrees Celsius) to selectively precipitate ammonium metavanadate (NH4VO3). These conditions avoid corrosion of the equipment by strong acid or alkali environments and also prevent the reduction or excessive polymerization of pentavalent vanadium. A reaction time of over 6 hours ensures the integrity of crystal growth, resulting in a high-purity, highly crystalline product.

[0021] The vanadium precipitation mother liquor is not discarded, but returned to the upstream of the impurity removal process. Because the impurity removal solution has a pH of 7 to 8, making it weakly acidic, it can remove NH4+ from the mother liquor. + The ammonia ions exist stably and promote the re-co-precipitation of trace amounts of unprecipitated vanadate ions under the action of aluminum salts, thereby achieving dual recovery of vanadium and ammonia. This design eliminates the discharge of ammonia-containing wastewater and constructs an internal material circulation loop.

[0022] The final product is purified through recrystallization. Steam heating ensures complete dissolution of ammonium metavanadate, hot filtration removes mechanical impurities, and slow cooling promotes the formation of large crystal particles. Indirect steam drying avoids contact between the product and open flames or high-temperature fumes, preventing decomposition caused by localized overheating and ensuring the product's color and purity.

[0023] Compared with the prior art, the present invention provides a method for removing impurities and recovering vanadium resources from the Bayer process alumina production, which has the following beneficial effects: (1) Source control and purification process: This invention directly treats the impurity solution inside the alumina production system. Harmful vanadium and organic impurities are removed from the system in solid form by crystallization, which fundamentally solves the problem of impurity accumulation, improves production efficiency, reduces the risk of equipment scaling, improves product quality, and stabilizes the main process operation.

[0024] (2) Resource recycling, turning waste into treasure: The "waste" that traditionally needs to be discharged and treated is transformed into ammonium metavanadate products with market value. This product can be used as a raw material for the production of vanadium pentoxide, realizing the transformation from "pollution negative benefits" to "resource positive benefits".

[0025] (3) Strong process adaptability: The process steps of this invention are simple, the operating conditions are mild (within the temperature range of the alumina production system itself), and it is easy to integrate with the existing Bayer process production line. There is no need to make large-scale modifications to the main process, and the investment and operating costs are low.

[0026] (4) Environmentally friendly: It achieves "zero discharge" or "reduction" of waste liquid, avoids pollution of the environment by alkaline and saline wastewater, and conforms to the development direction of green production and circular economy. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the operation process of the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] First, vanadium-containing evaporation mother liquor is obtained from the evaporation and desalination system of the Bayer process alumina production line. This mother liquor is an alkaline solution enriched with vanadium after multiple cycles, with a caustic alkali Na₂O concentration of 200 to 250 g / L and an elemental vanadium concentration of 350 to 450 mg / L. This mother liquor is then pumped into the adsorption reaction tank via an alkali-resistant pump.

[0030] In the adsorption reaction tank, an adsorbent, consisting of γ-alumina microspheres with a specific surface area of ​​150 to 300 square meters per gram and a pore size distribution of 5 to 20 nanometers, is added to the aforementioned evaporation mother liquor. The adsorbent is dried at 100 to 120 degrees Celsius for 2 hours before use. The amount of adsorbent added is 5 to 15 grams per liter, and the system temperature is controlled at 40 to 70 degrees Celsius. The reaction is carried out by stirring at 60 to 100 rpm for 2 to 4 hours. After the reaction, the mixture is subjected to solid-liquid separation. Solid-liquid separation can be performed using a plate and frame filter press with a filter cloth pore size of 5 to 10 micrometers and an operating pressure of 0.3 to 0.5 MPa. The resulting filter residue is waste adsorbent containing colloidal and organic complexed impurities, which can be treated as hazardous waste or further recovered for trace metals. The clarified filtrate proceeds to the subsequent crystallization process.

[0031] The clarified filtrate is fed into a crystallization tank, which is a jacketed cylindrical reactor. Circulating cooling water flows through the jacket, and the temperature is gradually reduced from the initial temperature (approximately 60 degrees Celsius) to 20-40 degrees Celsius at a rate of 5-10 degrees Celsius per hour. Before cooling begins, 0.5% to 2% of the system volume of coarse vanadate slag is added to the crystallization tank 2 through the seed inlet as seed crystals. The coarse vanadate slag is a byproduct of sodium vanadate crystals accumulated in previous processes, with a particle size ranging from 50 to 200 micrometers. After standing at a constant temperature for 2-4 hours, vanadate ions and sodium ions in the solution co-crystallize, precipitating a mixed salt crystal dominated by sodium vanadate. After crystallization, the solid-liquid mixture is separated to obtain a coarse sodium vanadate filter cake and a purified mother liquor. The purified mother liquor undergoes heat exchange with the mother liquor from step S1 via a heat exchanger. After recovering residual heat, it is returned to the decomposition or evaporation process in the main alumina flow, achieving dual recovery of heat and materials.

[0032] The crude sodium vanadate filter cake is fed into a dissolving tank, where deionized water at 80-95°C is added at a solid-liquid mass ratio of 1:3 to 1:5. The solution is heated and dissolved for 30-60 minutes with stirring to obtain a vanadium-containing solution. This solution is then pumped into a purification reaction tank. In the purification reaction tank, sulfuric acid with a mass concentration of 30%-50% is slowly added dropwise using an automatic dosing pump to adjust the pH of the system to 7-8 over a period of 30-60 minutes. Subsequently, an aqueous solution of 10%-20% aluminum sulfate is added at a volume ratio of 1:200, also slowly, with the addition time controlled within 30 minutes. The system temperature is maintained at 85-95°C, and the reaction is stirred for 1-2 hours. Under these conditions, impurities such as aluminum, silicon, phosphorus, and arsenic in the solution form insoluble precipitates such as aluminum hydroxide, silicic acid, aluminum phosphate, and aluminum arsenate, respectively. After the reaction is complete, the mixed slurry is conveyed to a plate and frame filter press pre-coated with a filter aid, diatomaceous earth, at a dosage of 0.1% to 0.5% of the filtrate volume, and the filter cloth has a pore size of 5 micrometers. The separated filter residue is redissolved in a 10% sodium hydroxide solution and returned to the red mud system to recover vanadium and aluminum; the resulting filtrate is a high-purity vanadium-containing solution, which enters the vanadium precipitation process.

[0033] A high-purity vanadium-containing solution is fed into a vanadium precipitation reaction tank. In the tank, ammonia or ammonium bicarbonate solution is first added via an automatic dosing pump to adjust the pH to 8-9. Then, solid ammonium sulfate, pre-ground to below 80 mesh, is added at a vanadium to ammonium molar ratio of 1:2. The reaction temperature is controlled at 25-30 degrees Celsius, the stirring speed is 60-100 rpm, and the reaction is continued for 6-8 hours. During the reaction, ammonium metavanadate crystals gradually precipitate. After the reaction, the solid-liquid mixture is transferred to a vacuum filtration device with a filter cloth pore size of 5-10 micrometers and a filtration pressure of -0.06 to -0.08 MPa. The crude ammonium metavanadate product obtained from the separation enters the recrystallization process; the residual vanadium concentration in the obtained vanadium precipitation mother liquor is less than 1 g / L, and it is transported to the feed end of the impurity removal reaction tank 5 to be mixed with the crude sodium vanadate solution. The weakly acidic environment (pH 7 to 8) is used to promote the conversion of residual ammonia into ammonium ions, and trace amounts of vanadium are precipitated in synergistic way under the action of aluminum salt, so as to achieve the synergistic recovery of ammonia and vanadium.

[0034] The crude ammonium metavanadate product is fed into a recrystallization tank, where deionized water is added at a solid-liquid mass ratio of 1:3 to 1:5. Steam is introduced to heat the solution to 90 to 98 degrees Celsius, maintaining this temperature for at least 30 minutes to ensure complete dissolution of the ammonium metavanadate. While still hot, the solution is filtered through a 1-micron pore size filter to remove insoluble mechanical impurities. The filtrate is allowed to cool naturally to 25 to 30 degrees Celsius and allowed to stand for 3 to 6 hours for recrystallization. After recrystallization, the crystal slurry is fed into a plate and frame filter press for solid-liquid separation. The resulting wet crystals are then sent to a drying unit. The drying unit is an oven equipped with a steam coil, with a material layer thickness not exceeding 5 cm. Indirect steam heating is used, and the drying temperature is controlled at 60 to 80 degrees Celsius for 4 to 6 hours, until the product moisture content is below 0.5%. The dried product is then cooled and packaged to obtain the high-purity ammonium metavanadate finished product.

[0035] The following describes embodiments of the present invention. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0036] Example 1 500 liters of Bayer process circulating mother liquor, with a Na₂O concentration of 220 g / L and a vanadium concentration of 400 mg / L, was pumped into an adsorption reaction tank. 7.5 kg of γ-alumina microspheres (specific surface area 200 m² / g, pore size 10 nm), dried at 110°C for 2 hours, were added. The tank temperature was controlled at 60°C, the stirring speed at 80 rpm, and the reaction was carried out for 3 hours. The slurry after the reaction was filtered through a plate and frame filter press (filter cloth pore size 8 μm) to obtain 485 liters of clear filtrate.

[0037] The clarified filtrate was pumped into a crystallization tank, and 1.5 liters of coarse vanadium slag (particle size 100 micrometers) were added. The jacket cooling system was activated, and the temperature was lowered to 30 degrees Celsius at a rate of 8 degrees Celsius per hour, then held at this temperature for 3 hours. After crystal precipitation, the precipitated crystals were separated by centrifugation to obtain 28.5 kg of crude sodium vanadate filter cake and 450 liters of purified mother liquor. The purified mother liquor was returned to the main process after heat exchange.

[0038] The crude sodium vanadate filter cake was added to a dissolving tank, followed by 120 liters of deionized water at 90°C, and stirred for 45 minutes to dissolve. The solution was then transferred to a purification reaction tank, and 40% sulfuric acid was added dropwise to adjust the pH to 7.5 over 45 minutes. Subsequently, 1.5 liters of 15% aluminum sulfate solution (at a volume ratio of 1:200) was added dropwise over 30 minutes, and the temperature was raised to 90°C for 1.5 hours. The reaction slurry was filtered through a plate and frame filter press pre-coated with diatomaceous earth (0.3%) to obtain 115 liters of high-purity vanadium-containing filtrate. The filter residue was treated with NaOH solution and then returned to the red mud system.

[0039] The high-purity vanadium-containing filtrate was introduced into a vanadium precipitation reaction tank, and ammonia water was added to adjust the pH to 8.5. Then, 12.8 kg of ammonium sulfate (V:NH4) ground to 100 mesh was added. + The mixture was stirred at a molar ratio of 1:2 for 8 hours at a controlled temperature of 28 degrees Celsius. The slurry was then vacuum filtered (-0.07 MPa) to obtain 22.1 kg of crude ammonium metavanadate and 95 liters of vanadium precipitation mother liquor. The vanadium precipitation mother liquor was returned to the front end of the impurity removal reaction tank.

[0040] The crude product was added to a recrystallization tank, along with 88 liters of deionized water. The mixture was heated with steam to 95 degrees Celsius for 40 minutes to dissolve the crystals. After hot filtration, the solution was cooled to 28 degrees Celsius and allowed to stand for 4 hours. The crystals were then pressure filtered and dried with steam at 60 degrees Celsius for 5 hours to obtain 19.8 kg of the final product.

[0041] Example 2 Take 600 liters of Bayer process desalination mother liquor, with a Na₂O concentration of 240 g / L and a vanadium concentration of 420 mg / L. Add 9 kg of modified zeolite (specific surface area 250 m² / g) and adsorb at 50°C for 4 hours. The subsequent crystallization temperature is controlled at 25°C, and the seed crystal amount is 1.2%. Aluminum chloride solution is used for impurity removal, and the pH is controlled at 7.2. For vanadium precipitation, the pH is adjusted to 8.2 using ammonium bicarbonate, and the ammonium salt is ammonium chloride. Other conditions are the same as in Example 1.

[0042] Example 3 400 liters of mother liquor from the Bayer process was used, containing 210 g / L Na₂O and 380 mg / L vanadium. The adsorbent was a 1:1 mixture of activated alumina and diatomaceous earth, added at 12 g / L, and reacted at 70°C for 2 hours. During the crystallization stage, the cooling rate was 5°C per hour, with a final temperature of 40°C. During the impurity removal stage, 20% aluminum sulfate was added dropwise over 60 minutes. Ammonium nitrate was used for vanadium precipitation, with a reaction temperature of 30°C and a reaction time of 6 hours. The recrystallization water ratio was 1:5, and the drying temperature was 80°C. All other conditions were the same as in Example 1.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for removing impurities and recovering vanadium resources from the Bayer process alumina production, characterized in that, Includes the following steps: S1: Obtain vanadium-containing evaporation mother liquor from the alumina production system; the evaporation mother liquor is an alkaline solution enriched with vanadium after multiple cycles in the Bayer process; S2: Introduce an adsorbent into the mother liquor of the evaporation, wherein the adsorbent is one or more of activated alumina, diatomaceous earth or modified zeolite; S3: Use the clarified filtrate obtained in step S2 as the subsequent crystallization reaction system; S4: Control the crystallization conditions of the reaction system to crystallize vanadium ions, sodium ions, etc. in the solution to precipitate sodium vanadate and other salts; S5: The solid-liquid mixture obtained in step S4 is subjected to solid-liquid separation to obtain crude sodium vanadate filter cake and purified mother liquor; the purified mother liquor is returned to the decomposition or evaporation process of the alumina main process after heat exchange with the mother liquor in step S2. S6: Dissolve the crude sodium vanadate filter cake obtained in step S5 in hot water to prepare a vanadium-containing solution. Then add sulfuric acid to adjust the pH, introduce aluminum salt, let it stand to remove impurities, and then discharge the impurities. S7: Adjust the pH of the high-purity vanadium-containing solution obtained in step S6, and introduce an ammonium salt, wherein the ammonium salt is one of ammonium sulfate, ammonium chloride or ammonium nitrate, to precipitate ammonium metavanadate crystals; S8: Perform solid-liquid separation on the solid-liquid mixture obtained in step S7 to obtain crude ammonium metavanadate product and vanadium precipitation mother liquor. S9: The vanadium precipitate mother liquor obtained in step S8 is transported to the front end of the impurity removal process in step S6 and mixed with the crude sodium vanadate solution. S10: Add the crude ammonium metavanadate product obtained in step S8 to deionized water, heat it with steam to completely dissolve it, filter it while hot, and recrystallize it; after solid-liquid separation, the obtained crystals are dried by indirect heating with steam to obtain the ammonium metavanadate product.

2. The method for removing impurities and recovering vanadium resources from the Bayer process alumina production according to claim 1, characterized in that, In step S1, the concentration of caustic alkali Na2O in the evaporation mother liquor is 200-250 g / L, and the concentration of elemental vanadium can fluctuate around 400 mg / L.

3. The method for removing impurities and recovering vanadium resources from the Bayer process alumina production according to claim 1, characterized in that, In step S2, the amount of adsorbent introduced is 5-15 g / L, the temperature is 40-70℃, the residence time is 2-4 h, and the adsorbent is γ-alumina microspheres with a specific surface area of ​​150 to 300 square meters per gram and a pore size distribution of 5 to 20 nanometers. Before use, it is dried at 100 to 120 degrees Celsius for 2 hours.

4. The method for removing impurities and recovering vanadium resources from the Bayer process alumina production process according to claim 1, characterized in that, The crystallization conditions in step S4 are 20-40 °C, and 0.5% to 2% of crude vanadium slag by volume is added as seed crystals in step S4.

5. The method for removing impurities and recovering vanadium resources from the Bayer process alumina production according to claim 1, characterized in that, In step S6, the pH is controlled at 7-8, the volume ratio of the introduced aluminum salt is 1:200, the reaction time is 1-2 hours, and the aluminum salt solution is a 10% to 20% aluminum sulfate aqueous solution. The solution is added slowly dropwise under stirring for 30 to 60 minutes.

6. The method for removing impurities and recovering vanadium resources from the Bayer process alumina production according to claim 1, characterized in that, In step S7, the pH is controlled at 8-9, the amount of ammonium salt introduced is 1:2 in molar ratio, the temperature is controlled at 25-30℃, and the reaction time is more than 6 hours.

7. The method for removing impurities and recovering vanadium resources from the Bayer process alumina production according to claim 1, characterized in that, In step S10, the mass ratio of deionized water to crude ammonium metavanadate used for recrystallization is 3:1 to 5:1, and the dissolution temperature is maintained at 95 degrees Celsius or above for at least 30 minutes.

8. The method for removing impurities and recovering vanadium resources from the Bayer process alumina production according to claim 1, characterized in that, In step S9, a small amount of ammonium ions are mixed with those in step S6 to recover vanadium and ammonia from the solution, thus achieving the purpose of solution recycling.

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