A method for recovering vanadium from chromium-silicon residue

Abstract

The present application relates to the field of vanadium oxide preparation, and discloses a method for recovering vanadium from chromium-removed silicon residue. The method comprises the following steps: S1, performing alkaline oxidation leaching on the chromium-removed silicon residue to make water-soluble vanadium and water-insoluble vanadium in the chromium-removed silicon residue enter the liquid phase, and performing solid-liquid separation to obtain a leaching solution; S2, adjusting the pH value of the leaching solution to make silicon and aluminum precipitate, and then performing solid-liquid separation to obtain a purified solution; S3, adding an ammonium salt to the purified solution to perform vanadium precipitation, and then performing solid-liquid separation to obtain ammonium metavanadate; and S4, drying and calcining the ammonium metavanadate to obtain vanadium pentoxide. According to the method, vanadium in different occurrence states can enter the liquid phase in the same leaching system, and impurities such as silicon and aluminum can be effectively removed in subsequent treatment, so that the process flow is shortened, the subsequent purification burden is reduced, and vanadium pentoxide products with high purity are obtained.

Description

Technical Field

[0001] This invention relates to the field of vanadium oxide preparation, and more particularly to a method for recovering vanadium from chromium-removed silicon slag. Background Technology

[0002] In vanadium chemical production, sodium vanadate solutions containing hexavalent chromium typically require reduction treatment to remove chromium. The resulting slag from this reduction process contains not only chromium but also vanadium, silicon, sodium, potassium, and other components. When aluminum salts are used simultaneously for silicon removal during this process, aluminum also enters the slag. The solid residue produced by the reduction and aluminum salt silicon removal processes is referred to in this specification as chromium-removing silicon slag.

[0003] Chromium-removing silicon slag typically has a high moisture content, with a certain amount of water-soluble vanadium entrained in the liquid phase. Simultaneously, with deeper reduction, some vanadium transforms from pentavalent to tetravalent and enters the solid phase, resulting in the simultaneous presence of water-soluble and water-insoluble vanadium in the slag. The vanadium content of this type of slag can reach 3%–15%, making it valuable for recovery. However, the two types of vanadium exist in different states, making it difficult to recover water-insoluble vanadium using a single water washing method. Separate water washing and subsequent leaching would prolong the process and increase the number of solid-liquid separation steps. To address this, existing technologies have proposed several improvement schemes, such as: Patent document CN102329964B discloses a method for first washing and recovering water-soluble salts, then subjecting the solid phase to alkaline oxidation leaching and crystallization to obtain sodium orthovanadate. This method requires the segmented recovery of water-soluble and water-insoluble vanadate, resulting in a lengthy process. Furthermore, it is insufficient in removing impurities such as silicon and aluminum, leaving room for improvement in the purity of the obtained sodium orthovanadate.

[0004] Patent document CN104357671B discloses a process for acid leaching of vanadium and chromium followed by alkaline precipitation, oxidation, acidic vanadium precipitation, and calcination, and further treatment of sodium sulfate and chromium-containing solutions. This process involves multiple dissolutions, precipitations, and solution conversions, resulting in a long process flow, significant consumption of acids, alkalis, and oxidants, and the silicon and aluminum impurities in the vanadium solution increase the burden on subsequent purification and vanadium precipitation.

[0005] Patent document CN104178637B uses calcification roasting and acid leaching to recover vanadium, followed by sodium roasting and water leaching to recover chromium. This requires two high-temperature roasting processes, resulting in high energy consumption and operational complexity.

[0006] Patent document CN107055612B separates vanadium and chromium through steps such as reduction and alkali leaching, which involves a large amount of alkali and multiple processing steps.

[0007] While the above methods can achieve the resource-based treatment of vanadium- and chromium-containing materials, for chromium-removing silicon slag that simultaneously contains water-soluble vanadium, water-insoluble vanadium, silicon, and aluminum, it is still necessary to take into account the centralized recovery of vanadium, the control of chromium, silicon, and aluminum impurities, process simplification, and the preparation of high-purity vanadium pentoxide. Summary of the Invention

[0008] In view of this, the present invention proposes a method for recovering vanadium from chromium-removing silicon slag, which enables vanadium in different occurrence states to enter the liquid phase in the same leaching system and effectively remove impurities such as silicon and aluminum in subsequent processing, thereby shortening the process flow, reducing the burden of subsequent purification, and obtaining a vanadium pentoxide product with high purity.

[0009] To achieve the above objectives, one aspect of the present invention provides a method for recovering vanadium from chromium-removing silicon slag, specifically comprising the following steps: S1, alkaline oxidation leaching of chromium-removing silicon slag, so that water-soluble vanadium and water-insoluble vanadium in the chromium-removing silicon slag enter the liquid phase, and solid-liquid separation is performed to obtain leachate; S2, adjust the pH value of the leachate to precipitate silicon and aluminum, and then separate the solid and liquid to obtain the purified solution; S3, after adding ammonium salt to the purification liquid to precipitate vanadium, solid-liquid separation is performed to obtain ammonium metavanadate. S4, after drying and calcining ammonium metavanadate, yields vanadium pentoxide.

[0010] In some embodiments, in step S1, the vanadium content of the chromium-free silicon slag is 3% to 15% by mass percentage, and the moisture content is 30% to 80%; in the chromium-free silicon slag, pentavalent vanadium accounts for no less than 60% of the vanadium component, the remaining vanadium is present in the form of tetravalent vanadium, and chromium is present in the form of trivalent chromium.

[0011] In some embodiments, in step S1, sodium hydroxide is used to adjust the pH value of the leaching system, and sodium chlorate is used as an oxidant. The sodium hydroxide is solid sodium hydroxide or a sodium hydroxide solution with a mass fraction of 30% to 50%, and the amount of sodium chlorate added is 2% to 9% of the mass of the chromium-removing silicon slag.

[0012] In some embodiments, in step S1, the liquid-to-solid mass ratio of the leaching system is 2-5:1, the pH value is 12-13.5, the leaching temperature is 20℃-100℃, and the leaching time is 30-120 min.

[0013] In some embodiments, the solid-liquid separation in step S1 also yields leaching residue, which is washed with room temperature water at a liquid-to-solid mass ratio of 0.2 to 0.5:1, and the resulting washing liquid is incorporated into the leaching liquid.

[0014] In some embodiments, in step S2, the pH value of the leachate is adjusted to 7.5-8.5 using sulfuric acid with a mass fraction of 50%-98%, reacted for 30-90 minutes, and then allowed to stand for 12-48 hours before solid-liquid separation is performed.

[0015] In some embodiments, the solid-liquid separation in step S2 also yields a filter residue with impurities removed. The filter residue is washed with room temperature water at a liquid-to-solid mass ratio of 0.1 to 0.5:1, and the resulting washing liquid is incorporated into the purification liquid.

[0016] In some embodiments, in step S3, the ammonium salt is ammonium sulfate, the ratio of the added mass of ammonium sulfate to the total mass of vanadium in the purification liquid is 2~4:1, the vanadium precipitation temperature is 20℃~35℃, and the vanadium precipitation time is 2~5h. The obtained ammonium metavanadate was washed with an ammonium bicarbonate solution with a mass fraction of 1% to 2% at a washing temperature of 10℃ to 30℃ and a washing solution-to-solid mass ratio of 0.5 to 2:1.

[0017] In some embodiments, in step S4, the ammonium metavanadate is dried at a temperature of 40°C to 80°C until the moisture content is no more than 1%.

[0018] In some embodiments, in step S4, the dried ammonium metavanadate is calcined in air at a temperature of 580°C to 630°C for 2 to 5 hours.

[0019] This invention offers at least the following beneficial technical effects: It treats the chromium- and silicon-removing slag generated during the reduction of chromium and aluminum salts for silicon removal. Through alkaline oxidation leaching, the water-soluble vanadium in the slag directly enters the liquid phase, while the water-insoluble low-valence vanadium is oxidized and converted into a soluble form before simultaneously entering the liquid phase. This concentrates both types of vanadium in the same leaching solution, reducing the need for separate washing and re-leaching. Subsequently, the pH is adjusted according to the solution chemistry of silicon and aluminum impurities in the leaching solution, causing silicon and aluminum to precipitate and be removed through solid-liquid separation. The resulting purified solution can be directly used for ammonium salt precipitation of vanadium. The ammonium metavanadate obtained from vanadium precipitation is dried and calcined to convert into vanadium pentoxide. This invention balances vanadium recovery rate and impurity control, helping to reduce the impact of chromium, silicon, and aluminum impurities on subsequent vanadium precipitation and product purity. It also produces high-purity vanadium pentoxide without requiring two high-temperature roastings or multiple acid-base conversions. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart of an embodiment of the method for recovering vanadium from chromium-removed silicon slag provided by the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0023] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0024] Based on the above objectives, a first aspect of the present invention provides a method for recovering vanadium from chromium-removed silicon slag, such as... Figure 1 As shown, it includes the following steps: S1, alkaline oxidation leaching of chromium-removing silicon slag, so that water-soluble vanadium and water-insoluble vanadium in the chromium-removing silicon slag enter the liquid phase, and solid-liquid separation is performed to obtain leachate; S2, adjust the pH value of the leachate to precipitate silicon and aluminum, and then separate the solid and liquid to obtain the purified solution; S3, after adding ammonium salt to the purification solution to precipitate vanadium, solid-liquid separation is performed to obtain ammonium metavanadate (AMV). S4, after drying and calcining ammonium metavanadate, yields vanadium pentoxide.

[0025] In some embodiments, in step S1, the vanadium content of the chromium-removing silicon slag is 3% to 15%, and the water content is 30% to 80%. In the chromium-removing silicon slag, pentavalent vanadium accounts for no less than 60% of the vanadium composition, the remaining vanadium is present in the form of tetravalent vanadium, and chromium is present in the form of trivalent chromium. This composition includes both water-soluble pentavalent vanadium carried in the liquid phase of the slag and water-insoluble tetravalent vanadium that enters the solid phase after reduction. Typical compositional ranges of chromium-removing silicon slag are shown in Table 1.

[0026] Table 1

[0027] In some embodiments, step S1 is used to centrally transfer vanadium in different occurrence states in the chromium-removing silicon slag to the same liquid phase. In practice, the chromium-removing silicon slag and the leaching liquid phase are mixed at a liquid-to-solid mass ratio of 2-5:1, sodium hydroxide is added to establish an alkaline leaching system, and sodium chlorate is added as an oxidant. Sodium hydroxide can be added in solid form or as a 30%-50% sodium hydroxide solution, adjusting the pH of the system to 12-13.5. The amount of sodium chlorate added is 2%-9% of the dry weight of the chromium-removing silicon slag. Under alkaline conditions, the water-soluble pentavalent vanadium originally present in the chromium-removing silicon slag enters the liquid phase. Sodium chlorate oxidizes the water-insoluble tetravalent vanadium to pentavalent vanadium, and the oxidized vanadium enters the liquid phase in the form of soluble vanadate. The leaching temperature is 20-100°C, and the leaching time is 30-120 min. Temperature, time, pH, and oxidant dosage are used in combination to complete the oxidative leaching of tetravalent vanadium, while controlling the amount of trivalent chromium, silicon, and aluminum entering the liquid phase.

[0028] In this alkaline oxidative leaching process, sodium chlorate is chosen instead of peroxides such as hydrogen peroxide, persulfates, or potassium chlorate. This is because peroxides cause chromium to form soluble chromium-containing peroxide complexes that enter the liquid phase; persulfates increase the oxidative leaching of chromium; and potassium chlorate introduces potassium ions that are difficult to remove subsequently. Using a combination of sodium chlorate and sodium hydroxide achieves the oxidation of low-valent vanadium while avoiding the introduction of additional potassium ions and reducing the burden of chromium impurities entering the leaching solution.

[0029] After alkaline oxidation leaching, solid-liquid separation is performed. The liquid phase is the initial leachate, and the solid phase is the leaching residue. In some embodiments, the leaching residue is washed twice with room temperature water, with a liquid-to-solid mass ratio of 0.2-0.5:1 for each wash. All the resulting washing liquid is added to the initial leachate and used together as the leaching solution. The washing water is used to displace the vanadium-containing liquid phase entrained in the pores of the leaching residue.

[0030] In step S1, water-soluble vanadium and water-insoluble vanadium enter the same leaching solution in a single alkaline oxidation leaching treatment. The vanadium carried by the leaching residue is returned to the leaching solution by washing, thereby reducing segmented recovery and repeated solid-liquid separation, and providing a liquid phase material with a well-defined composition for subsequent centralized impurity removal.

[0031] In some embodiments, in step S2, sulfuric acid with a mass concentration of 50% to 98% is added to the leachate to adjust the pH of the leachate to 7.5 to 8.5. The reaction is carried out at this pH for 30 to 90 minutes, followed by standing for 12 to 48 hours. The leachate is stirred during the addition of sulfuric acid to homogenize the local acidity in a timely manner. After reaching the target pH, the reaction continues to allow the silicon and aluminum components in the solution to fully precipitate. When the pH of the leachate is adjusted from strongly alkaline to 7.5 to 8.5, silicon and aluminum form a silicon-aluminum composite precipitate and an aluminum hydroxide precipitate, while vanadium remains in the liquid phase. The standing process after the reaction is used to promote the aggregation and sedimentation of fine precipitates, facilitating subsequent solid-liquid separation. After solid-liquid separation, the liquid phase is the purified liquid, and the solid phase is the impurity-removed filter residue.

[0032] In some embodiments, the impurity-removing filter residue is washed once with room temperature water at a solid-to-wash mass ratio of 0.1 to 0.5:1, and the resulting wash solution is incorporated into the purification solution. This washing step displaces the vanadium-containing mother liquor entrained in the impurity-removing filter residue, allowing the physically entrained vanadium to return to the purification solution.

[0033] In step S2, silicon and aluminum in the leaching solution are transformed from a dissolved state into a separable solid phase. The vanadium-containing liquid phase carried by the impurity removal filter residue is washed and returned to the purification solution, thereby reducing the impact of silicon and aluminum on ammonium salt precipitation of vanadium and product purity, and maintaining the continuous transfer of vanadium in the purification solution.

[0034] In some embodiments, in step S3, ammonium sulfate is added to the purification solution. The amount of ammonium sulfate added is determined according to an ammonium salt coefficient of 2-4:1, that is, the ratio of the mass of ammonium sulfate to the total mass of vanadium in the purification solution is 2-4:1. The vanadium precipitation reaction is carried out at 20-35°C for 2-5 hours. Ammonium sulfate provides ammonium ions, and the soluble vanadium in the purification solution reacts with the ammonium ions to form ammonium metavanadate crystals. The reaction temperature and time are used to control crystal formation and growth. After the reaction is completed, solid-liquid separation is performed, and the obtained solid phase is ammonium metavanadate, and the liquid phase is the vanadium precipitation mother liquor.

[0035] In some embodiments, ammonium metavanadate is washed once with an ammonium bicarbonate solution with a mass concentration of 1% to 2%, at a washing temperature of 10 to 30°C, and with a washing solution-to-solid mass ratio of 0.5 to 2:1. The ammonium bicarbonate washing solution is used to replace the vanadium precipitate mother liquor trapped on the surface and between particles of ammonium metavanadate, remove soluble sodium salts, potassium salts and other impurities, and at the same time maintain the washing environment of ammonium metavanadate with an ammonium-containing washing solution.

[0036] In step S3, vanadium in the purification solution is concentrated and precipitated in the form of ammonium metavanadate solid. The soluble impurities carried by the ammonium metavanadate are removed by washing with ammonium bicarbonate solution, so that the vanadium precipitation product can directly enter the drying and calcination steps, and the impact of the mother liquor entrainment on the purity of vanadium pentoxide is reduced.

[0037] In some embodiments, in step S4, ammonium metavanadate is first dried at 40-80°C until its moisture content is no higher than 1%. The dried ammonium metavanadate is then placed in an air atmosphere and calcined at 580-630°C for 2-5 hours to obtain vanadium pentoxide. The drying step removes moisture between ammonium metavanadate particles and on the surface, providing a feed with stable moisture content for subsequent calcination. Calcination in an air atmosphere allows for the thermal decomposition of ammonium metavanadate and ensures that the resulting vanadium oxide remains vanadium pentoxide, corresponding to pentavalent vanadium. The calcination temperature and holding time are used in combination within the stated range to complete the conversion of ammonium metavanadate to vanadium pentoxide.

[0038] In step S4, the washed ammonium metavanadate is dried with controlled moisture content and then stably enters the calcination stage, where it is converted into vanadium pentoxide in an air atmosphere.

[0039] The present invention will be further explained below with reference to specific embodiments.

[0040] Example 1 100g of chromium-removing silicon slag was used as raw material. The vanadium content of the chromium-removing silicon slag was 10%, and the moisture content was 50%. A leaching system was prepared at a liquid-to-solid mass ratio of 3:1. A 50% sodium hydroxide solution was added to adjust the pH of the system to 13. Sodium chlorate was added at 4% of the dry weight of the chromium-removing silicon slag, and alkaline oxidation leaching was carried out at 50℃ for 60 min.

[0041] After leaching, solid-liquid separation is performed to obtain the initial leachate and leaching residue. The leaching residue is washed twice with room temperature water, with a liquid-to-solid mass ratio of 0.5:1 for each wash. Both wash solutions are combined with the initial leachate, and the combined solution is used as the leachate. This operation allows the vanadium-containing liquid phase entrained in the pores of the leaching residue to return to the leachate.

[0042] 98% sulfuric acid was added to the leachate to adjust the pH to 8.0. After reacting for 60 minutes, the solution was allowed to stand for 24 hours to allow silicon and aluminum to precipitate. Solid-liquid separation was then performed to obtain a purified solution and a filtered residue. The filtered residue was washed once with room temperature water at a solid-to-wash volume ratio of 0.2:1, and the resulting washing solution was added to the purified solution. This process removes the silicon and aluminum solid phases while allowing the vanadium-containing liquid phase entrained in the filtered residue to return to the purified solution.

[0043] Ammonium sulfate was added at a mass ratio of 3:1 to the total vanadium mass in the purified solution, and the reaction was carried out at 30°C for 3 hours to precipitate vanadium. After the reaction, solid and liquid were separated to obtain ammonium metavanadate. The ammonium metavanadate was washed once at 20°C with a 1.5% ammonium bicarbonate solution at a solid-to-wash mass ratio of 1:1. This operation caused vanadium to precipitate as ammonium metavanadate and washed away any entrained soluble impurities.

[0044] The washed ammonium metavanadate was dried at 60℃ to a moisture content of 0.8%, and then calcined in air at 600℃ for 3 hours to obtain vanadium pentoxide. This operation completes the drying and thermal decomposition of ammonium metavanadate, achieving the final conversion of vanadium to vanadium pentoxide. The product test results are shown in Table 2.

[0045] Table 2

[0046] Example 2 50g of chromium-removing silicon slag was used as raw material. The vanadium content of the chromium-removing silicon slag was 15%, and the moisture content was 60%. A leaching system was prepared at a liquid-to-solid mass ratio of 5:1. Solid sodium hydroxide was added to adjust the pH of the system to 13.5. Sodium chlorate was added at 9% of the dry weight of the chromium-removing silicon slag, and alkaline oxidation leaching was carried out at 100℃ for 120min.

[0047] After leaching, solid-liquid separation is performed to obtain initial leachate and leaching residue. The leaching residue is washed twice with room temperature water, with a liquid-to-solid mass ratio of 0.5:1 for each wash. Both wash solutions are combined with the initial leachate, and the combined solution is used as the leachate. This operation is used to recover the vanadium-containing liquid phase entrained in the leaching residue.

[0048] 98% sulfuric acid was added to the leachate to adjust the pH to 8.5. After reacting for 90 minutes, the solution was allowed to stand for 48 hours to allow silicon and aluminum to precipitate. Solid-liquid separation was then performed to obtain a purified solution and a filtered residue. The filtered residue was washed once with room temperature water at a solid-to-wash mass ratio of 0.5:1, and the resulting washing solution was added to the purified solution. This process effectively separates the silicon and aluminum precipitates from the vanadium-containing purified solution.

[0049] Ammonium sulfate was added at a mass ratio of 4:1 to the total vanadium mass in the purified solution, and the reaction was carried out at 35°C for 5 hours to precipitate vanadium. After the reaction, the solid and liquid were separated to obtain ammonium metavanadate. The ammonium metavanadate was washed once with a 2% ammonium bicarbonate solution at 30°C, with a solid-to-wash mass ratio of 2:1. This operation caused the vanadium in the purified solution to form ammonium metavanadate and removed soluble impurities carried by the ammonium metavanadate.

[0050] The washed ammonium metavanadate was dried at 80℃ to a moisture content of 1%, and then calcined in air at 630℃ for 5 hours to obtain vanadium pentoxide. This operation completes the conversion of ammonium metavanadate to vanadium pentoxide. The product test results are shown in Table 3.

[0051] Table 3

[0052] Example 3 100g of chromium-removing silicon slag was used as raw material. The dry basis vanadium content of the chromium-removing silicon slag was 3%, and the wet basis moisture content was 30%. A leaching system was prepared at a liquid-to-solid mass ratio of 2:1. A 30% sodium hydroxide solution was added to adjust the pH of the system to 12. Sodium chlorate was added at 2% of the dry basis mass of the chromium-removing silicon slag, and alkaline oxidation leaching was carried out at 20℃ for 30 minutes.

[0053] After leaching, solid-liquid separation was performed to obtain the initial leachate and leaching residue. The leaching residue was washed twice with room temperature water, with a liquid-to-solid mass ratio of 0.2:1 for each wash. The two wash solutions were combined with the initial leachate, and the combined solution was used as the leachate.

[0054] 50% sulfuric acid was added to the leachate to adjust the pH to 7.5. After reacting for 30 minutes, the solution was allowed to stand for 12 hours to allow silicon and aluminum to precipitate. Solid-liquid separation was then performed to obtain a purified solution and a filtered residue. The filtered residue was washed once with room temperature water at a solid-to-wash mass ratio of 0.1:1, and the resulting washing solution was added to the purified solution.

[0055] Ammonium sulfate was added at a mass ratio of 2:1 to the total vanadium mass in the purified solution, and the reaction was carried out at 20°C for 2 hours to precipitate vanadium. After the reaction, the solid and liquid were separated to obtain ammonium metavanadate. The ammonium metavanadate was washed once with a 1% ammonium bicarbonate solution at 10°C, with a solid-to-wash mass ratio of 0.5:1.

[0056] The washed ammonium metavanadate was dried at 40°C until the moisture content was no more than 1%, and then calcined in air at 580°C for 2 hours to obtain vanadium pentoxide. The product test results are shown in Table 4.

[0057] Table 4

[0058] Example 4 100g of chromium-removing silicon slag was used as raw material. The dry basis vanadium content of the chromium-removing silicon slag was 15%, and the wet basis moisture content was 80%. A leaching system was prepared at a liquid-to-solid mass ratio of 5:1. A 50% sodium hydroxide solution was added to adjust the pH of the system to 13.5. Sodium chlorate was added at 9% of the dry basis mass of the chromium-removing silicon slag, and alkaline oxidation leaching was carried out at 100℃ for 120min.

[0059] After leaching, solid-liquid separation was performed to obtain the initial leachate and leaching residue. The leaching residue was washed twice with room temperature water, with a liquid-to-solid mass ratio of 0.5:1 for each wash. The two wash solutions were combined with the initial leachate, and the combined solution was used as the leachate.

[0060] 98% sulfuric acid was added to the leachate to adjust the pH to 8.5. After reacting for 90 minutes, the solution was allowed to stand for 48 hours to allow silicon and aluminum to precipitate. Solid-liquid separation was then performed to obtain a purified solution and a filtered residue. The filtered residue was washed once with room temperature water at a solid-to-wash mass ratio of 0.5:1, and the resulting wash solution was added to the purified solution.

[0061] Ammonium sulfate was added at a mass ratio of 4:1 to the total vanadium mass in the purified solution, and the reaction was carried out at 35°C for 5 hours to precipitate vanadium. After the reaction, the solid and liquid were separated to obtain ammonium metavanadate. The ammonium metavanadate was washed once with a 2% ammonium bicarbonate solution at 30°C, with a solid-to-wash mass ratio of 2:1.

[0062] The washed ammonium metavanadate was dried at 80℃ until the moisture content was no more than 1%, and then calcined in air at 630℃ for 5 hours to obtain vanadium pentoxide. The product test results are shown in Table 5.

[0063] Table 5

[0064] In summary, the dry-basis vanadium content and wet-basis moisture content of the raw materials determine the vanadium load and liquid-phase entrainment degree in the unit wet slag. The leaching liquid-to-solid ratio, pH, sodium chlorate dosage, leaching temperature, and time jointly determine the equilibrium of tetravalent vanadium conversion to soluble pentavalent vanadium and the co-leaching of impurities. Sulfuric acid concentration, purification pH, reaction time, and settling time affect the formation and separation of silica-alumina precipitates. Ammonium salt coefficient, vanadium precipitation temperature, and time affect the precipitation of ammonium metavanadate. Washing conditions, drying conditions, and calcination conditions affect the removal of entrained substances from the mother liquor and the conversion of ammonium metavanadate to vanadium pentoxide. The product testing results of Examples 1-4 demonstrate that parameter combinations within the two-endpoint numerical range can yield vanadium pentoxide products with a purity higher than 99.5%.

[0065] This invention offers at least the following beneficial technical effects: It treats the chromium- and silicon-removing slag generated during the reduction of chromium and aluminum salts for silicon removal. Through alkaline oxidation leaching, the water-soluble vanadium in the slag directly enters the liquid phase, while the water-insoluble low-valence vanadium is oxidized and converted into a soluble form before simultaneously entering the liquid phase. This concentrates both types of vanadium in the same leaching solution, reducing the need for separate washing and re-leaching. Subsequently, the pH is adjusted according to the solution chemistry of silicon and aluminum impurities in the leaching solution, causing silicon and aluminum to precipitate and be removed through solid-liquid separation. The resulting purified solution can be directly used for ammonium salt precipitation of vanadium. The ammonium metavanadate obtained from vanadium precipitation is dried and calcined to convert into vanadium pentoxide. This invention balances vanadium recovery rate and impurity control, helping to reduce the impact of chromium, silicon, and aluminum impurities on subsequent vanadium precipitation and product purity. It also produces high-purity vanadium pentoxide without requiring two high-temperature roastings or multiple acid-base conversions.

[0066] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for recovering vanadium from chromium-removing silicon slag, characterized in that, Includes the following steps: S1, alkaline oxidation leaching of chromium-removing silicon slag, so that water-soluble vanadium and water-insoluble vanadium in the chromium-removing silicon slag enter the liquid phase, and solid-liquid separation is performed to obtain leachate; S2, adjust the pH value of the leachate to precipitate silicon and aluminum, and then separate the solid and liquid to obtain the purified solution; S3, after adding ammonium salt to the purification liquid to precipitate vanadium, solid-liquid separation is performed to obtain ammonium metavanadate. S4, after drying and calcining ammonium metavanadate, yields vanadium pentoxide.

2. The method according to claim 1, characterized in that, In step S1, the vanadium content of the chromium-free silicon slag is 3% to 15% by mass percentage, and the moisture content is 30% to 80%. In the chromium-free silicon slag, pentavalent vanadium accounts for no less than 60% of the vanadium composition, the remaining vanadium is present in the form of tetravalent vanadium, and chromium is present in the form of trivalent chromium.

3. The method according to claim 1, characterized in that, In step S1, sodium hydroxide is used to adjust the pH value of the leaching system, and sodium chlorate is used as an oxidant. The sodium hydroxide is solid sodium hydroxide or a sodium hydroxide solution with a mass fraction of 30% to 50%, and the amount of sodium chlorate added is 2% to 9% of the mass of the chromium-removing silicon slag.

4. The method according to claim 3, characterized in that, In step S1, the liquid-solid mass ratio of the leaching system is 2~5:1, the pH value is 12~13.5, the leaching temperature is 20℃~100℃, and the leaching time is 30~120min.

5. The method according to claim 1, characterized in that, The solid-liquid separation in step S1 also yields leaching residue. The leaching residue is washed with room temperature water at a liquid-to-solid mass ratio of 0.2 to 0.5:1, and the resulting washing liquid is incorporated into the leaching liquid.

6. The method according to claim 1, characterized in that, In step S2, the pH of the leachate is adjusted to 7.5-8.5 using sulfuric acid with a mass fraction of 50%-98%. After reacting for 30-90 minutes and standing for 12-48 hours, solid-liquid separation is performed.

7. The method according to claim 1, characterized in that, In step S2, the solid-liquid separation also yields a filter residue with impurities removed. The filter residue is washed with room temperature water at a liquid-to-solid mass ratio of 0.1 to 0.5:1, and the resulting washing liquid is incorporated into the purification liquid.

8. The method according to claim 1, characterized in that, In step S3, the ammonium salt is ammonium sulfate, the ratio of the added mass of ammonium sulfate to the total mass of vanadium in the purification solution is 2~4:1, the vanadium precipitation temperature is 20℃~35℃, and the vanadium precipitation time is 2~5h; The obtained ammonium metavanadate was washed with an ammonium bicarbonate solution with a mass fraction of 1% to 2% at a washing temperature of 10℃ to 30℃ and a washing solution-to-solid mass ratio of 0.5 to 2:

1.

9. The method according to claim 1, characterized in that, In step S4, the drying temperature of ammonium metavanadate is 40℃~80℃, and it is dried until the moisture content is no more than 1%.

10. The method according to claim 1, characterized in that, In step S4, the dried ammonium metavanadate is calcined in air at a temperature of 580℃~630℃ for 2h~5h.

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