Recycling method for fluorine in vanadium-containing salt-removed filter cake in aluminum oxide process

Abstract

The invention provides a method for recycling fluorine in a vanadium-containing salt-removed filter cake in an aluminum oxide process, and belongs to the field of solid waste recycling. The method comprises the following steps: dissolving the vanadium-containing salt-removed filter cake in the aluminum oxide process into water at a set temperature to obtain first slurry; carrying out dephosphorization treatment on the dissolved slurry to obtain second slurry; adding a defluorinating agent into the second slurry for defluorination treatment to obtain third slurry; filtering the third slurry to obtain a first filtrate and a fluorine-containing product; adding an impurity removal agent into the first filtrate to remove impurities in the first filtrate so as to obtain fourth slurry; filtering the fourth slurry to obtain a second filtrate and tailings; adjusting the pH value of the second filtrate, and adding ammonium salt to precipitate vanadium to obtain an ammonium metavanadate product. Through the multi-step collaborative process design, fluorine and vanadium dual-valuable resources in the filter cake are converted into available products respectively, resource waste is reduced, and the overall resource utilization rate is remarkably increased.

Description

Technical Field

[0001] This application relates to the field of solid waste recycling technology, and in particular to a method for recovering and utilizing fluorine from vanadium-containing salt discharge filter cake in an alumina process. Background Technology

[0002] During the use of Guinean bauxite, vanadium accumulates in the system and is removed through cooling crystallization, forming vanadium-containing desalination filter cake, which can serve as an important source for vanadium recovery. However, the vanadium-containing desalination filter cake precipitated during the process contains impurities such as phosphorus, fluorine, arsenic, oxalate, and alkali. These impurities need to be removed during vanadium recovery, generating a large amount of waste residue and causing serious environmental impact.

[0003] Current research on the recovery of impurities from vanadium-containing desalination filter cakes is limited. Fluorine recovery often involves preparing cryolite to recover fluorine from the solution. While cryolite preparation can recover a certain amount of fluorine, the reaction conditions are quite demanding, resulting in only about 50% fluorine recovery from the vanadium-containing desalination filter cake, leading to a low fluorine recovery rate. Therefore, improving the resource utilization rate of vanadium-containing desalination filter cakes in alumina processes is a pressing technical problem that needs to be addressed. Summary of the Invention

[0004] This application provides a method for recovering and utilizing fluorine in vanadium-containing salt discharge filter cake from an alumina process, in order to solve the following technical problem: how to improve the resource utilization rate of vanadium-containing salt discharge filter cake in an alumina process.

[0005] This application provides a method for recovering and utilizing fluorine from vanadium-containing salt discharge filter cake in an alumina process, the method comprising: The vanadium-containing salt discharge filter cake from the alumina process is dissolved in water at a set temperature to obtain the first slurry; The dissolved slurry is then subjected to dephosphorization treatment to obtain a second slurry; A defluorinating agent is added to the second slurry to perform defluorination treatment, resulting in a third slurry; The third slurry is filtered to obtain the first filtrate and a fluorine-containing product; Add a purifying agent to the first filtrate to remove impurities and obtain a fourth slurry; The fourth slurry is filtered to obtain a second filtrate and tailings; and The pH of the second filtrate was adjusted, and ammonium salt was added to precipitate vanadium, yielding ammonium metavanadate product.

[0006] Optionally, the set temperature is 40℃~90℃.

[0007] Optionally, the liquid-to-solid ratio of the first slurry is 4 to 10.

[0008] Optionally, the defluorinating agent is calcium oxalate.

[0009] Optionally, the molar ratio of calcium in the calcium oxalate to fluorine in the vanadium-containing desalination filter cake is (1-1.1):1.

[0010] Optionally, the reaction time for the defluorination treatment is 0.5 h to 1 h.

[0011] Optionally, the fluorine-containing product is calcium fluoride, wherein the purity of the calcium fluoride is ≥90% and the arsenic content of the calcium fluoride is ≤0.5%.

[0012] Optionally, the impurity remover includes one or more of aluminum chloride, aluminum nitrate, and aluminum sulfate.

[0013] Optionally, in the fourth slurry, the arsenic concentration is ≤0.2g / L and the oxalate concentration is 2g / L~3g / L.

[0014] Optionally, the method can meet the following requirements: fluoride removal rate ≥ 97%, vanadium loss rate in solution ≤ 1%.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for recovering fluorine from vanadium-containing desalination filter cake in an alumina process. The method includes: dissolving the vanadium-containing desalination filter cake in water at a set temperature to obtain a first slurry; subjecting the dissolved slurry to dephosphorization treatment to obtain a second slurry; adding a defluorinating agent to the second slurry to defluorinate it to obtain a third slurry; filtering the third slurry to obtain a first filtrate and a fluorine-containing product; adding a purification agent to the first filtrate to remove impurities from the first filtrate to obtain a fourth slurry; filtering the fourth slurry to obtain a second filtrate and tailings; and adjusting the pH of the second filtrate and adding ammonium salt to precipitate vanadium to obtain ammonium metavanadate. This application effectively improves the resource utilization rate of vanadium-containing filter cake in an alumina process through a multi-step synergistic process design: First, the filter cake is dissolved to convert fluorine, vanadium, and impurities into soluble ions, laying the foundation for subsequent separation; then, phosphorus pretreatment is performed to remove phosphorus impurities, preventing them from interfering with the purification of fluorine and vanadium; subsequently, a defluorinating agent is added to convert fluoride ions into solid fluorine-containing products, which are then recovered through filtration, allowing potentially wasteful fluorine resources to be utilized; next, a purification agent is added to the vanadium-containing filtrate to remove residual impurities, ensuring the purity of vanadium; finally, the pH is adjusted and ammonium salt is added to precipitate vanadium, obtaining ammonium metavanadate, achieving high-value recovery of vanadium resources. Thus, the valuable resources of fluorine and vanadium in the filter cake are converted into usable products, reducing resource waste and significantly improving the overall resource utilization rate. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic flowchart illustrating a method for recovering fluorine from vanadium-containing salt discharge filter cake in an alumina process, provided as an embodiment of this application. Figure 2 This is a schematic diagram of the actual process for recovering and utilizing fluorine in vanadium-containing salt discharge filter cake from an alumina process, as provided in an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0021] Figure 1 A schematic flowchart illustrating a method for recovering fluorine from vanadium-containing salt discharge filter cake in an alumina process, provided as an embodiment of this application. Figure 2This is a schematic diagram of the actual process for recovering and utilizing fluorine in vanadium-containing salt discharge filter cake from an alumina process, as provided in an embodiment of this application.

[0022] like Figure 1 and Figure 2 As shown in the embodiment of this application, a method for recovering and utilizing fluorine in vanadium-containing salt discharge filter cake from an alumina process is provided. The method includes: S1. Dissolve the vanadium-containing salt discharge filter cake from the alumina process in water at a set temperature to obtain the first slurry; S2. The dissolved slurry is subjected to dephosphorization treatment to obtain a second slurry; S3. Add a defluorinating agent to the second slurry to perform defluorination treatment and obtain a third slurry; S4. Filter the third slurry to obtain the first filtrate and the fluorine-containing product; S5. Add a purifying agent to the first filtrate to remove impurities from the first filtrate and obtain the fourth slurry; S6. Filter the fourth slurry to obtain a second filtrate and tailings; and S7. Adjust the pH of the second filtrate and add ammonium salt to precipitate vanadium to obtain ammonium metavanadate product.

[0023] It should be noted that step S1 converts the solid fluorine, vanadium and other impurities (such as phosphorus and arsenic) in the filter cake into soluble ionic forms, creating conditions for subsequent separation and purification.

[0024] The dephosphorization process in step S2 is a crucial pretreatment step to ensure the purity of subsequent fluorine recovery and the quality of vanadium products. Vanadium-containing desalination filter cake typically contains a certain amount of phosphorus impurities (mostly in the form of phosphate ions). If not removed beforehand, during the subsequent S3 defluorination process, phosphorus will react with the defluorinating agent (such as calcium oxalate) or other ions in the system (such as calcium ions) to form solid precipitates such as calcium phosphate. These precipitates will mix with the defluorination product (calcium fluoride), leading to a decrease in the purity of the final fluorine-containing product (calcium fluoride), failing to meet the quality standard of ≥90%. Simultaneously, if phosphorus impurities enter the subsequent vanadium recovery stage, they will combine with vanadium in the vanadium precipitation step to form impurity phases, affecting the purity and performance of the ammonium metavanadate product, and may even cause the product to fail to meet industry standards. Therefore, targeted dephosphorization in step S2 can remove phosphorus impurities in advance, avoiding "cross-interference" with the fluorine and vanadium separation and purification process, and providing a pure reaction system for precise separation in subsequent processes.

[0025] Step S3 is the core step in achieving fluorine recovery and utilization. Its function is to remove free fluoride ions (F ions) from the solution through a chemical reaction. -This process converts fluoride into a solid fluorine-containing product, achieving efficient separation of fluorine and vanadium. Choosing calcium oxalate as the defluorinating agent is one of the key improvements in this process, offering significant advantages: While traditional defluorinating agents (such as calcium chloride) can react with fluoride ions to form calcium fluoride, the calcium ions provided by calcium chloride may react with vanadate ions in the solution during the reaction, forming calcium vanadate precipitate, leading to increased vanadium loss. Simultaneously, calcium oxalate essentially does not react with arsenic in the solution, maintaining the purity of the produced calcium fluoride product. Adding traditional defluorinating agents such as calcium chloride easily reacts with arsenic in the solution, resulting in a decrease in the purity of the generated calcium fluoride, rendering it unusable. In contrast, the oxalate ions (C2O4) in calcium oxalate... 2- The reactivity of calcium oxalate with vanadate ions is extremely low, which can minimize the combination of vanadium and calcium ions, thereby reducing vanadium loss. At the same time, the calcium fluoride precipitate formed by the reaction of calcium oxalate with fluoride ions has good crystallinity, is easy to separate by subsequent filtration, and the oxalate ions can be removed in subsequent impurity removal steps without introducing new stubborn impurities into the system.

[0026] The S4 step filtration completely separates the solid fluorine-containing product (calcium fluoride) generated from the defluorination reaction from the first filtrate containing vanadium ions, completing the recovery of fluorine and the initial enrichment of vanadium. After the S3 defluorination treatment, the third slurry contains calcium fluoride precipitate, a small amount of unreacted defluorinating agent, and other trace solid impurities. The purpose of step S5 is to remove trace impurities (mainly arsenic ions and excess oxalate ions) remaining in the first filtrate, providing a high-purity vanadium solution for the subsequent vanadium precipitation step and ensuring the quality of the ammonium metavanadate product. After filtration in S4, the main component of the first filtrate is vanadate ions, but a small amount of arsenic ions (from the original filter cake) and excess oxalate ions (from the calcium oxalate defluorinating agent in S3) still remain. If arsenic ions enter the vanadium precipitation step, they will react with ammonium salts to form arsenate impurities, which will be mixed into the ammonium metavanadate product, causing the heavy metal content of the product to exceed the standard and lose its industrial application value. Excess oxalate ions may react with ammonium ions or other metal ions in the vanadium precipitation process to form ammonium oxalate or metal oxalate salt precipitates, which will also affect the purity and crystallization performance of ammonium metavanadate.

[0027] The core function of step S6 is to separate the solid impurities (aluminum hydroxide-arsenic complex, aluminum oxalate, etc.) generated during the purification process in S5 from the vanadium-containing second filtrate, thereby completely removing impurities from the system and obtaining a pure vanadium solution.

[0028] Step S7 is the core step in vanadium recovery. Its function is to convert vanadate ions in solution into solid ammonium metavanadate through chemical regulation, thus completing the resource utilization of vanadium. Ammonium metavanadate is an important industrial raw material (used in the production of vanadium pentoxide, vanadium alloys, etc.), therefore, the key to this step is to ensure efficient precipitation of vanadium and product purity.

[0029] In some embodiments, the set temperature is 40°C to 90°C.

[0030] Low temperatures (e.g., below 40°C) significantly reduce the dissolution rate of salts in the filter cake, prolonging dissolution time, reducing production efficiency, and potentially causing incomplete dissolution of some fluorine and vanadium compounds, directly impacting subsequent recovery rates. While high temperatures (e.g., above 90°C) can further increase the dissolution rate, they also significantly increase energy costs. Examples of temperature settings include 40°C, 48°C, 55°C, 62°C, 70°C, 78°C, 85°C, and 90°C.

[0031] In some embodiments, the liquid-to-solid ratio of the first slurry is 4 to 10.

[0032] The liquid-to-solid ratio refers to the mass ratio of water to filter cake during the dissolution process. If the liquid-to-solid ratio is too low (e.g., less than 4), the concentration of solid particles in the slurry will be too high, leading to increased system viscosity, difficulty in stirring, and hindered ion diffusion during dissolution, thus affecting the uniformity and completeness of dissolution. If the liquid-to-solid ratio is too high (e.g., greater than 10), although it can ensure complete dissolution, it will result in an excessively large volume of slurry for subsequent processing. This not only increases the volumetric load on the reaction equipment but also consumes more energy and reagents (such as defluorinating agents and vanadium precipitating agents) in subsequent filtration, evaporation, and other steps, increasing process costs. For example, the liquid-to-solid ratio of the first slurry can be 4, 5, 6, 7, 8, 9, 9.5, 10, etc.

[0033] In some embodiments, the defluorinating agent is calcium oxalate.

[0034] In some embodiments, the molar ratio of calcium in the calcium oxalate to fluorine in the vanadium-containing desalination filter cake is (1-1.1):1.

[0035] A controlled calcium-to-fluorine molar ratio of 1–1.1:1 ensures a fluoride removal rate of ≥97% by allowing a slight excess of calcium ions to promote a full reaction between fluoride and calcium ions to form calcium fluoride, thus avoiding calcium vanadate precipitation due to excess calcium ions. This prevents vanadium loss in the solution from exceeding 1%, balancing defluorination efficiency with vanadium resource conservation, and avoiding waste of defluorinating agent while controlling raw material costs. For example, the molar ratio of calcium in calcium oxalate to fluorine in the vanadium-containing desalination filter cake can be 1:1, 1.01:1, 1.03:1, 1.05:1, 1.06:1, 1.08:1, 1.09:1, 1.1:1, etc.

[0036] In some embodiments, the reaction time for the defluorination treatment is 0.5 h to 1 h.

[0037] Limiting the defluorination reaction time to 0.5h to 1h allows for matching the reaction kinetics of calcium oxalate and fluoride ions. This ensures complete conversion of fluoride ions into calcium fluoride precipitate, preventing residual fluoride from affecting subsequent processes, while also preventing excessively long reaction times that lead to high equipment occupancy and low production efficiency, thus achieving highly efficient defluorination. For example, the defluorination reaction time can be 0.5h, 0.6h, 0.65h, 0.7h, 0.75h, 0.8h, 0.9h, or 1h.

[0038] In some embodiments, the fluorine-containing product is calcium fluoride, the purity of the calcium fluoride is ≥90%, and the arsenic content of the calcium fluoride is ≤0.5%.

[0039] Calcium fluoride with a purity of ≥90% meets industrial application standards and can be used in glass, ceramics, and other fields, realizing the resource utilization of fluorine. An arsenic content of ≤0.5% ensures product safety and environmental friendliness, meeting industry requirements and enhancing the economic value and market acceptance of fluorine products. For example, the purity of calcium fluoride can be 90%, 92%, 93%, 94%, 95%, 96%, 98%, 99%, etc.; the arsenic content can be 0.1%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0040] In some embodiments, the impurity remover includes one or more of aluminum chloride, aluminum nitrate, and aluminum sulfate.

[0041] Aluminum salts can hydrolyze to form aluminum hydroxide colloids, which efficiently adsorb arsenic ions. At the same time, they react with excess oxalate to form aluminum oxalate precipitate, which precisely removes impurities. Furthermore, they have weak adsorption of vanadate, which avoids vanadium loss and ensures the purity of subsequent vanadium-precipitated products.

[0042] In some embodiments, the fourth slurry has an arsenic concentration ≤0.2g / L and an oxalate concentration of 2g / L to 3g / L.

[0043] An arsenic concentration ≤0.2 g / L prevents arsenic from entering the subsequent vanadium precipitation process, ensuring that the arsenic content of the ammonium metavanadate product meets the standard. Controlling the oxalate concentration within this range avoids its reaction with ammonium salts to form impurities that affect vanadium precipitation, while also eliminating the need for excessive addition of impurity removal agents, thus balancing the impurity removal effect and cost. For example, the arsenic concentration in the fourth slurry can be 0.05 g / L, 0.08 g / L, 0.1 g / L, 0.12 g / L, 0.15 g / L, 0.17 g / L, 0.19 g / L, 0.2 g / L, etc.; the oxalate concentration in the fourth slurry can be 2 g / L, 2.2 g / L, 2.3 g / L, 2.4 g / L, 2.5 g / L, 2.7 g / L, 2.9 g / L, 3 g / L, etc.

[0044] In some embodiments, the method can meet the following requirements: fluoride removal rate ≥97%, vanadium loss rate in solution ≤1%.

[0045] High fluorine removal rates can significantly reduce the fluorine content in tailings, alleviating environmental disposal pressure, and the recovered fluorine can generate economic benefits; low vanadium loss rates maximize vanadium resource retention, increasing ammonium metavanadate production and overall process economic efficiency, achieving efficient resource utilization. For example, fluorine removal rates can be 97%, 97.5%, 98%, 98.2%, 98.5%, 99%, 99.3%, 99.5%, etc.; vanadium loss rates in the solution can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, etc.

[0046] In some embodiments, the pH of the second filtrate is adjusted to 8-9.

[0047] It should be noted that the dosage of ammonium salt can be controlled by "adding ammonium salt while monitoring pH". When a stable white precipitate of ammonium metavanadate begins to appear in the solution, and the amount of precipitate no longer increases significantly after adding more ammonium salt, and the pH value stabilizes at 7.5-8.5, the addition of ammonium salt (commonly ammonium chloride, ammonium sulfate, etc.) is stopped.

[0048] In summary, this application possesses significant advantages in multiple dimensions in the field of resource recovery and treatment of vanadium-containing brine filter cake. These advantages are primarily reflected in five key aspects: resource utilization, product quality, process design, cost control, and environmental benefits, as detailed below: From a resource utilization perspective, this application achieves efficient recovery and high-value utilization of core valuable resources in filter cake. On the one hand, it breaks through the limitation of traditional processes that discard fluorine as an impurity, and through targeted process design, converts fluorine into industrially applicable fluorine-containing products, giving economic value to previously idle fluorine resources. On the other hand, it emphasizes the protection of vanadium resources throughout the entire process, avoiding vanadium loss in dissolution, defluorination, and impurity removal stages, maximizing the retention of vanadium resources and converting them into high-value ammonium metavanadate products, achieving efficient utilization of both fluorine and vanadium resources, and significantly improving the overall resource utilization rate of filter cake.

[0049] Regarding product quality assurance, this application ensures that the quality of the two core products meets standards through multi-stage impurity control. Pre-emptive dephosphorization avoids interference from phosphorus impurities on the purity of the fluorine product, and precise removal of arsenic ions and excess oxalate ensures that the purity and safety of the fluorine-containing product meet industrial standards while preventing impurities from affecting the performance of the vanadium product. This allows the ammonium metavanadate product to meet industry requirements, and both products possess stable market application value.

[0050] In terms of process design, this application demonstrates significant innovation and rationality. The selection of calcium oxalate as the defluorinating agent effectively solves the problem of vanadium loss caused by traditional defluorinating agents. Furthermore, its reaction products are easily separated and readily processed. Each step is tightly integrated, forming a complete "separation-purification-recovery" chain from dissolution pretreatment to final vanadium precipitation. Parameter control is used to match the reaction kinetics, ensuring efficient progress at each step, avoiding ineffective operations, and improving overall production efficiency.

[0051] In terms of cost control, this application achieves cost savings through precise parameter setting and process optimization. Reasonable limitation of dissolution temperature and liquid-solid ratio balances dissolution effect with energy and reagent consumption; precise control of defluorinating agent dosage avoids raw material waste; and impurity removal agents are added as needed in the impurity removal process, avoiding over-treatment. These measures reduce production costs from multiple aspects, including energy consumption, raw materials, and equipment usage, thereby improving the economic feasibility of the process.

[0052] From an environmental benefit perspective, this application significantly reduces solid waste pollution and disposal pressure. High fluoride removal rates reduce the fluoride content in tailings, and low vanadium loss rates reduce the likelihood of valuable resources being discarded with the tailings, resulting in a substantial reduction in the pollution of the final tailings, classifying them as low-pollution solid waste and alleviating the burden of environmental disposal. Simultaneously, heavy metal impurities such as arsenic are effectively controlled through targeted impurity removal, preventing them from entering products or the environment and causing pollution, thus aligning with the concept of green production.

[0053] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0054] Example 1 This embodiment provides a method for recovering and utilizing fluorine from vanadium-containing salt discharge filter cake in an alumina process, the method comprising: S11. The vanadium-containing desalination filter cake (taken from an alumina plant, with a vanadium content of 6% and a fluorine content of 4.6%) in the alumina process is dissolved in hot water at a temperature of 90°C to obtain the first slurry; wherein, the liquid-to-solid ratio of the first slurry is 4, and the mass of the desalination filter cake used is 60g. S21. The first slurry is subjected to dephosphorization treatment to obtain a second slurry; wherein the dephosphorization treatment adopts the method disclosed in Chinese Patent CN202510865822.4, a method for recovering phosphorus and vanadium from vanadium-containing desalination filter cake; S31. Add a defluorinating agent to the second slurry to perform defluorination treatment and obtain a third slurry; wherein the defluorinating agent is calcium oxalate, the molar ratio of calcium in calcium oxalate to fluorine in vanadium-containing salt discharge filter cake is 1.0:1, and the reaction time for defluorination treatment is 0.5h; S41. The third slurry is filtered to obtain the first filtrate and the fluorine-containing product; after filtration, the fluorine-containing product (filter residue) is washed, and the test results show that: the fluorine removal rate in the solution is 97.4%, the calcium fluoride content in the fluorine-containing product (filter residue) is 95.4%, the arsenic content in the fluorine-containing product (filter residue) is 0.24%, and the vanadium loss rate in the solution is 0.14%; S51. Add a purifying agent to the first filtrate to remove impurities (mainly arsenic) from the first filtrate to obtain a fourth slurry; wherein the purifying agent is aluminum sulfate, and the arsenic concentration in the fourth slurry after purifying is less than 0.2 g / L; S61. Filter the fourth slurry to obtain the second filtrate and tailings; S71. Adjust the pH of the second filtrate to 9, and add ammonium salt to precipitate vanadium. Then filter and wash to obtain ammonium metavanadate product. The ammonium salt is ammonium chloride. The final ammonium metavanadate product has a purity of 99%.

[0055] Example 2 This embodiment provides a method for recovering and utilizing fluorine from vanadium-containing salt discharge filter cake in an alumina process, the method comprising: S12. The vanadium-containing desalination filter cake (taken from an alumina plant, with a vanadium content of 6% and a fluorine content of 4.6%) in the alumina process is dissolved in water at a temperature of 40°C to obtain the first slurry; wherein the liquid-to-solid ratio of the first slurry is 10, and the mass of the desalination filter cake used is 60g. S22. The first slurry is subjected to dephosphorization treatment to obtain the second slurry; S32. Add a defluorinating agent to the second slurry to perform defluorination treatment and obtain a third slurry; wherein the defluorinating agent is calcium oxalate, the molar ratio of calcium in calcium oxalate to fluorine in vanadium-containing salt discharge filter cake is 1.1:1, and the reaction time for defluorination treatment is 1 hour; S42. The third slurry is filtered to obtain the first filtrate and the fluorine-containing product; after filtration, the fluorine-containing product (filter residue) is washed, and the test results show that: the fluorine removal rate in the solution is 97.8%, the calcium fluoride content in the fluorine-containing product (filter residue) is 90.2%, the arsenic content in the fluorine-containing product (filter residue) is 0.12%, and the vanadium loss rate in the solution is 0.23%; S52. Add a purifying agent to the first filtrate to remove impurities (mainly arsenic) from the first filtrate to obtain a fourth slurry; wherein the purifying agent is aluminum chloride, and the arsenic concentration in the fourth slurry after purifying is less than 0.2 g / L; S62. Filter the fourth slurry to obtain the second filtrate and tailings; S72. Adjust the pH of the second filtrate to 9, and add ammonium salt to precipitate vanadium. Then filter and wash to obtain ammonium metavanadate product. The ammonium salt is ammonium chloride. The final ammonium metavanadate product has a purity of 99%.

[0056] Example 3 This embodiment provides a method for recovering and utilizing fluorine from vanadium-containing salt discharge filter cake in an alumina process, the method comprising: S13. The vanadium-containing desalination filter cake (taken from an alumina plant, with a vanadium content of 7% and a fluorine content of 3.2%) in the alumina process is dissolved in water at a temperature of 70°C to obtain the first slurry; wherein the liquid-to-solid ratio of the first slurry is 6, and the mass of the desalination filter cake used is 60g. S23. The first slurry is subjected to dephosphorization treatment to obtain the second slurry; S33. Add a defluorinating agent to the second slurry to perform defluorination treatment and obtain a third slurry; wherein the defluorinating agent is calcium oxalate, the molar ratio of calcium in calcium oxalate to fluorine in vanadium-containing salt discharge filter cake is 1.05:1, and the reaction time for defluorination treatment is 1 hour; S43. The third slurry is filtered to obtain the first filtrate and the fluorine-containing product; after filtration, the fluorine-containing product (filter residue) is washed, and the test results show that: the fluorine removal rate in the solution is 97.1%, the calcium fluoride content in the fluorine-containing product (filter residue) is 93.3%, the arsenic content in the fluorine-containing product (filter residue) is 0.22%, and the vanadium loss rate in the solution is 0.43%; S53. Add a purifying agent to the first filtrate to remove impurities (mainly arsenic) from the first filtrate to obtain a fourth slurry; wherein the purifying agent is aluminum sulfate, and the arsenic concentration in the fourth slurry after purifying is less than 0.2 g / L; S63. Filter the fourth slurry to obtain the second filtrate and tailings; S73. Adjust the pH of the second filtrate to 9, and add ammonium salt to precipitate vanadium. Then filter and wash to obtain ammonium metavanadate product. The ammonium salt is ammonium sulfate, and the final ammonium metavanadate product has a purity of 99%.

[0057] Example 4 This embodiment provides a method for recovering and utilizing fluorine from vanadium-containing salt discharge filter cake in an alumina process, the method comprising: S14. The vanadium-containing desalination filter cake (taken from an alumina plant, with a vanadium content of 7% and a fluorine content of 3.2%) in the alumina process is dissolved in water at a temperature of 80°C to obtain the first slurry; wherein the liquid-to-solid ratio of the first slurry is 6, and the mass of the desalination filter cake used is 60g. S24. The first slurry is subjected to dephosphorization treatment to obtain the second slurry; S34. Add a defluorinating agent to the second slurry to perform defluorination treatment and obtain a third slurry; wherein the defluorinating agent is calcium oxalate, the molar ratio of calcium in calcium oxalate to fluorine in vanadium-containing salt discharge filter cake is 1.0:1, and the reaction time for defluorination treatment is 1 hour; S44. The third slurry is filtered to obtain a first filtrate and a fluorine-containing product. After filtration, the fluorine-containing product (filter residue) is washed. The test results show that the fluorine removal rate corresponding to the fluorine content in the filtrate is 97.0%, the calcium fluoride content in the fluorine-containing product (filter residue) is 96.4%, the arsenic content in the fluorine-containing product (filter residue) is 0.14%, and the vanadium loss rate in the solution is 0.33%. S54. Add a purifying agent to the first filtrate to remove impurities (mainly arsenic) from the first filtrate to obtain a fourth slurry; wherein the purifying agent is aluminum sulfate, and the arsenic concentration in the fourth slurry after purifying is less than 0.2 g / L; S64. Filter the fourth slurry to obtain the second filtrate and tailings; S74. Adjust the pH of the second filtrate to 9, and add ammonium salt to precipitate vanadium. Then filter and wash to obtain ammonium metavanadate product. The ammonium salt is ammonium sulfate, and the final ammonium metavanadate product has a purity of 99%.

[0058] Comparative Example 1 This comparative example provides a method for treating vanadium-containing desalination filter cake in an alumina process, the method comprising: S1a. The vanadium-containing desalination filter cake (taken from an alumina plant, with a vanadium content of 6% and a fluorine content of 4.6%) in the alumina process is dissolved in water at a temperature of 90°C to obtain a slurry; wherein the liquid-to-solid ratio of the slurry is 6 and the mass of the desalination filter cake used is 60g. S2a. Sulfuric acid is added to the slurry to adjust the pH to 9, resulting in the formation of cryolite precipitate in the solution. The mixture is then filtered to obtain filtrate and filter residue. The test results show that the fluoride concentration in the filtrate is 3.4 g / L, the fluoride removal rate is 47%, and the cryolite content in the filter residue is 42%. S3a. Add calcium sulfate to the filtrate to remove impurities such as phosphorus, arsenic, and fluorine from the solution, and obtain a purified solution. S4a. Add ammonium sulfate to the purified solution to precipitate vanadium, then filter and wash to obtain ammonium metavanadate product; wherein, the purity of the ammonium metavanadate product is 98%.

[0059] Comparative Example 2 This comparative example provides a method for treating vanadium-containing desalination filter cake in an alumina process, the method comprising: S1b. The vanadium-containing desalination filter cake (taken from an alumina plant, with a vanadium content of 6% and a fluorine content of 4.6%) in the alumina process is dissolved in water at a temperature of 90°C to obtain a slurry; wherein the liquid-to-solid ratio of the slurry is 6, and the mass of the desalination filter cake used is 60g. S2b. The slurry is subjected to dephosphorization treatment to obtain dephosphorized slurry; S3b. Add a defluorinating agent (calcium chloride) to the dephosphorized slurry to carry out defluorination treatment. The reaction time for defluorination treatment is 1 hour. The molar ratio of calcium in calcium chloride to fluorine in vanadium-containing desalination filter cake is 1.0:1. S4b. The defluorinated mixture was filtered to obtain filtrate and filter residue. After filtration, the filter residue was washed. The test results showed that the fluoride content in the filtrate was 1.2 g / L, the fluoride removal rate was 75%, the calcium fluoride content in the filter residue was 71.3%, the arsenic content in the filter residue was 4.3%, and the vanadium loss rate in the solution was 3.5%. S5b. Add a purifying agent (aluminum chloride) to the filtrate to remove arsenic from the solution, and obtain a purified solution; wherein the arsenic concentration in the purified solution is less than 0.2 g / L; S6b. Adjust the pH of the purified solution to 9, add ammonium sulfate to precipitate vanadium, and then filter and wash to obtain ammonium metavanadate product.

[0060] The fluoride removal rate, calcium fluoride content in the fluoride-containing product (filter residue), arsenic content in the fluoride-containing product (filter residue), vanadium loss rate in the solution, and purity of ammonium metavanadate product in Examples 1-4 and Comparative Examples 1-2 are summarized, and the results are shown in Table 1.

[0061] Table 1

[0062] As shown in Table 1, the fluorine-containing products in Examples 1 to 4 are calcium fluoride, with a purity of ≥90%, an arsenic content of ≤0.5%, a fluorine removal rate of ≥97%, and a vanadium loss rate of ≤1% in the solution (first filtrate).

[0063] In Comparative Example 1, no pre-treatment for dephosphorization was performed. Phosphorus impurities in the original filter cake co-precipitated with cryolite, resulting in a cryolite purity of only 42% in the filter residue. Furthermore, phosphorus formed a heterogeneous phase with vanadium during vanadium precipitation, reducing the ammonium metavanadate purity to 98%. Simultaneously, defluorination was achieved by adjusting the pH to generate cryolite, a method that relies on limited Na+ in the system. + Al 3+ With F - The reaction cannot achieve deep removal of fluorine, with a fluorine removal rate of only 47%, which not only wastes fluorine resources but also increases the burden of subsequent impurity removal.

[0064] Comparative Example 2 used calcium chloride as the defluorinating agent, which provided Ca... 2+It readily reacts with vanadate ions in solution to form calcium vanadate precipitate, resulting in a vanadium loss rate as high as 3.5%, far exceeding the level of the example; simultaneously, calcium chloride has poor defluorination selectivity, causing arsenic ions to co-precipitate with calcium fluoride, resulting in an arsenic content of 4.3% in the filter residue, and the generated calcium fluoride easily adsorbs impurities, with a purity of only 71.3%; furthermore, calcium chloride reacts with F - The reaction efficiency was low, with a final fluorine removal rate of only 75%, failing to achieve the goal of deep defluorination.

[0065] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: In this embodiment, calcium fluoride product is formed by independently removing fluoride from the vanadium-containing salt discharge filter cake. The fluoride removal rate can reach 97%, the product purity is over 90%, the arsenic content is less than 0.5%, and the vanadium loss rate in the solution is less than 1%.

[0066] In this embodiment, phosphorus and fluorine are removed independently to form recyclable fluorine products, reducing the amount of waste residue discharged during the vanadium recovery process. This increases the profit of vanadium extraction while reducing the environmental impact of waste residue.

[0067] The method provided in this application embodiment can realize the recovery and utilization of fluorine in vanadium-containing salt discharge filter cake, further reduce the amount of vanadium extraction tailings, improve resource utilization, and promote the efficient and economical utilization of vanadium-containing salt discharge filter cake in the alumina process.

[0068] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for recovering and utilizing fluorine from vanadium-containing salt discharge filter cake in an alumina process, characterized in that, The method includes: The vanadium-containing salt discharge filter cake from the alumina process is dissolved in water at a set temperature to obtain the first slurry; The dissolved slurry is then subjected to dephosphorization treatment to obtain a second slurry; A defluorinating agent is added to the second slurry to perform defluorination treatment, resulting in a third slurry; The third slurry is filtered to obtain the first filtrate and a fluorine-containing product; Add a purifying agent to the first filtrate to remove impurities and obtain a fourth slurry; The fourth slurry is filtered to obtain a second filtrate and tailings; and The pH of the second filtrate was adjusted, and ammonium salt was added to precipitate vanadium, yielding ammonium metavanadate product.

2. The method according to claim 1, characterized in that, The set temperature is 40℃~90℃.

3. The method according to claim 1, characterized in that, The liquid-to-solid ratio of the first slurry is 4 to 10.

4. The method according to claim 1, characterized in that, The defluorinating agent is calcium oxalate.

5. The method according to claim 4, characterized in that, The molar ratio of calcium in the calcium oxalate to fluorine in the vanadium-containing salt discharge filter cake is (1-1.1):

1.

6. The method according to claim 1, characterized in that, The reaction time for the defluorination treatment is 0.5 h to 1 h.

7. The method according to claim 1, characterized in that, The fluorine-containing product is calcium fluoride, the purity of the calcium fluoride is ≥90%, and the arsenic content of the calcium fluoride is ≤0.5%.

8. The method according to claim 1, characterized in that, The impurity removal agent includes one or more of aluminum chloride, aluminum nitrate, and aluminum sulfate.

9. The method according to claim 1, characterized in that, In the fourth slurry, the arsenic concentration is ≤0.2g / L and the oxalate concentration is 2g / L~3g / L.

10. The method according to claim 1, characterized in that, The method can meet the following requirements: fluoride removal rate ≥ 97%, vanadium loss rate in solution ≤ 1%.

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