A method for extracting vanadium pentoxide from molten vanadium slag

Abstract

This invention relates to a method for extracting vanadium pentoxide from molten vanadium slag, comprising: (1) molten calcification transformation: while the vanadium slag remains in a molten state, calcium oxide is added and reacted under an oxidizing atmosphere; (2) cooling calcification roasting: the molten slag is cooled to 700-900℃, a composite calcification agent is added and roasted to obtain porous calcified slag; (3) ammonium salt leaching: the calcified slag is leached using an ammonium salt gradient; (4) vanadium precipitation and calcination: vanadium is precipitated from the leaching liquid to obtain ammonium polyvanadate, which is then calcined to obtain vanadium pentoxide. This invention utilizes the residual heat of molten vanadium slag to complete the calcification transformation, avoiding secondary heating energy consumption; the filtration performance of the calcified slag is improved by in-situ pore formation using organic calcium salts; gradient leaching effectively inhibits the co-leaching of impurities such as phosphorus and silicon, achieving a vanadium leaching rate of up to 95% and a product purity of 99.5%. This invention does not produce harmful gases throughout the entire process, and the ammonia in the vanadium precipitation wastewater can be recycled, making it a clean production process with good prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgy and comprehensive resource utilization technology, specifically relating to a method for extracting vanadium pentoxide from converter vanadium slag or molten vanadium slag. Background Technology

[0002] Vanadium is an important strategic metal, widely used in steel, aerospace, chemical, and energy storage industries. The traditional vanadium extraction process from vanadium slag is a "sodium roasting-water leaching-vanadium precipitation" process. Specifically, vanadium slag containing V₂O₅ is cooled, ground, mixed with sodium salts, and subjected to high-temperature sodium roasting to convert vanadium into soluble sodium vanadate. This is followed by water leaching to obtain a vanadium-containing solution, then ammonium salts are added to the solution to precipitate vanadium polyvanadate, which is finally calcined to obtain V₂O₅. This traditional process has the following problems: 1) Long process, numerous equipment, high investment and operating costs. 2) High energy consumption, requiring continuous high-temperature heating during roasting. 3) Heavy pollution, producing harmful gases such as HCl, Cl₂, and SO₂ during roasting, and generating large amounts of high-concentration sodium and ammonium salt wastewater after vanadium precipitation, resulting in high treatment costs. 4) The tailings contain sodium salts and hexavalent chromium, which are difficult to utilize effectively.

[0003] In recent years, the vanadium extraction route through calcification has attracted attention. The principle involves replacing sodium salts with calcium salts to convert vanadium into calcium vanadate, which is then leached using carbonates or acids. However, existing calcification processes have several problems: First, calcification roasting requires cooling the vanadium slag before reheating, resulting in secondary heating energy consumption. Second, existing molten calcification technologies all involve adding the calcifying agent (usually calcium oxide) at high temperatures (1300-1500℃) in a single step, which has the following drawbacks: CaO preferentially reacts with oxides such as silicon and phosphorus in the slag, limiting the vanadium calcification efficiency; simultaneously, the resulting calcified slag has a dense structure, which is not conducive to subsequent leaching, with the vanadium leaching rate only reaching approximately 92%. CN102560086B discloses a method for leaching calcified roasted vanadium slag with ammonium carbonate, but its calcification method involves roasting after mixing raw materials, using only CaO as the calcifying agent, resulting in a dense slag structure, and employing constant-temperature leaching, which still does not solve the problems of dense slag structure and demanding leaching conditions. Summary of the Invention

[0004] To address the problems in existing vanadium extraction processes involving molten vanadium slag calcification, such as the formation of impurity phases due to high temperatures, dense calcified slag structure, and stringent subsequent leaching conditions, this invention provides a clean vanadium extraction method that utilizes the residual heat of molten vanadium slag for segmented calcification. Through a two-stage design of molten calcification transformation and cooling calcification roasting, the instantaneous decomposition of organic calcium salts enables in-situ pore formation and secondary calcification of the calcified slag, thereby achieving efficient vanadium extraction under mild conditions in the subsequent ammonium carbonate leaching stage.

[0005] This invention provides a method for extracting vanadium pentoxide from molten vanadium slag, comprising the following steps:

[0006] (1) Molten calcification transformation: When the vanadium slag is kept in a molten state after being discharged from the furnace, calcium oxide is added and reacted under an oxidizing atmosphere to obtain transformed slag; so that the vanadium oxide in the vanadium slag is converted into calcium vanadate.

[0007] Furthermore, the vanadium slag contains 10-16 wt% vanadium and 1-5 wt% CaO.

[0008] Furthermore, the temperature of the molten state is 1300-1500℃.

[0009] Furthermore, the amount of calcium oxide added is 45-80 wt% of the mass of vanadium slag V2O5.

[0010] Furthermore, the oxidizing atmosphere is air or oxygen; the reaction time is 8-15 minutes.

[0011] Furthermore, the flow rate of the oxidizing atmosphere is adjusted proportionally according to the amount of vanadium slag being processed, so that the surface of the melt is slightly agitated. For example, the flow rate of the oxidizing atmosphere is 0.2-0.6 L / min or 0.001-0.003 m³ / kg of vanadium slag. 3 / min.

[0012] Furthermore, the molten state can be formed naturally in the oxidizing atmosphere of oxygen blowing to remove vanadium in a converter, or it can be maintained in the molten state by utilizing the residual heat of the vanadium slag after it is discharged from the furnace.

[0013] In step (1), the high-temperature thermal energy of the molten vanadium slag is used to oxidize the low-valence vanadium oxide in the vanadium slag into vanadium pentoxide, and react with CaO to generate calcium vanadate (Ca2V2O7 and CaV2O5), thus completing the initial calcification transformation of vanadium.

[0014] (2) Cooling and calcining: Cool the transformation slag obtained in step (1) to 700-900℃, add composite calcining agent, calcinate for 20-40 minutes, and then cool to room temperature to obtain calcined vanadium slag.

[0015] Furthermore, the composite calcifying agent comprises an organic calcium salt and calcium oxide, wherein the organic calcium salt is selected from at least one of calcium citrate and calcium oxalate.

[0016] During the cooling calcination roasting stage, in the composite calcining agent composed of calcium oxide and organic calcium salts, calcium oxide ensures sufficient reaction with residual vanadium compounds to generate calcium vanadate, preventing a decrease in vanadium leaching rate; while organic calcium salts participate in pore formation and replenishment of active calcium. In this invention, the cooling roasting temperature is 700-900℃. The gases released from the decomposition of organic calcium salts are difficult to escape rapidly from the solid or semi-solid vanadium slag, forming a porous structure inside the material, which is beneficial for the penetration of the leaching agent during subsequent leaching. Simultaneously, the active CaO generated from the decomposition of organic calcium salts, together with the added calcium oxide, replenishes the calcium source, promoting the full conversion of vanadium into calcium vanadate. This simultaneous achievement of in-situ pore formation and active calcium replenishment synergistically significantly improves the vanadium leaching rate.

[0017] Furthermore, the amount of organic calcium salt added is 15-30 wt% of the mass of V2O5 in the vanadium slag, and the amount of calcium oxide added is 20-30 wt% of the mass of V2O5 in the vanadium slag.

[0018] If the amount of organic calcium salt added is too low, the pore-forming effect will be insignificant, the calcified slag structure will be too dense, making it difficult for the leaching agent to penetrate, and the amount of active calcium produced by decomposition will be insufficient, preventing some vanadium from being converted into calcium vanadate, thus reducing the leaching rate. If the amount of organic calcium salt added is too high, excessive gas release will cause the pore walls of the calcified slag to become too thin and the strength to decrease, making it easy to generate fine powder during ball milling and clogging the filter pores during filtration, which will actually reduce the leaching rate.

[0019] (3) Ammonium salt leaching: Calcified vanadium slag is ground and then mixed with leaching agent to carry out leaching reaction. Solid-liquid separation is carried out to obtain vanadium-containing leaching solution and calcified leaching slag; so that vanadium enters the solution in the form of soluble ammonium vanadate, thereby realizing the separation of vanadium from the slag phase.

[0020] Furthermore, the grinding particle size is 100-200 mesh.

[0021] Furthermore, the leaching agent is selected from an aqueous solution of ammonium carbonate or ammonium bicarbonate.

[0022] Furthermore, the concentration of the leaching agent is 100-200 g / L, and the liquid-to-solid ratio is (3-6):1.

[0023] Furthermore, the leaching reaction is first carried out at 70-90°C for 20-40 minutes, and then the temperature is lowered to 40-60°C for another 20-40 minutes.

[0024] For the calcified slag with a porous structure of the present invention, step (3) is first leached at a higher temperature. The leaching agent enters the interior of the calcified slag through the pores and dissolves calcium vanadate. During the cooling process, the negative pressure generated by the thermal shrinkage effect promotes the discharge of the residual vanadium-containing solution. At the same time, the solubility of impurities such as silicon and phosphorus decreases at low temperature, which is beneficial to improving the leaching selectivity.

[0025] Furthermore, the cooling rate is 1-4℃ / min.

[0026] (4) Vanadium precipitation and calcination: Vanadium-containing leachate obtained in step (3) is precipitated to obtain ammonium polyvanadate, and then calcined to obtain vanadium pentoxide.

[0027] Further, the pH of the vanadium-containing leachate is adjusted to 2.5-3.5 to precipitate ammonium polyvanadate; the ammonium polyvanadate is then calcined at 500-600℃ for 1-2 hours to obtain vanadium pentoxide.

[0028] Furthermore, the pH value is adjusted using acidic solutions, such as hydrochloric acid, sulfuric acid, phosphoric acid, etc.

[0029] Furthermore, the ammonia gas released during the calcination process in step (4) is collected and absorbed, and can be returned to step (3) for the preparation or replenishment of the leaching agent, thereby realizing a closed-loop circulation of ammonia.

[0030] Furthermore, the ammonia gas released during the calcination process is collected under negative pressure and then passed into an absorption tower for countercurrent absorption with water or dilute ammonium carbonate solution to obtain ammonia water with a concentration of 10-20%, which can be used to prepare the ammonium carbonate leaching agent in step (3), thereby realizing a closed-loop circulation of ammonia and reducing ammonium salt consumption and ammonia nitrogen emissions.

[0031] The leaching tailings of this invention are found to contain mainly calcium carbonate and do not contain harmful elements such as sodium and chlorine. They can be used as an additive in cement production or as a desulfurizing agent for power plant flue gas, thus realizing the resource utilization of solid waste.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1. This invention utilizes the residual heat of molten vanadium slag to complete the calcification transformation, avoiding the process of reheating and roasting the vanadium slag after cooling. This not only saves energy and reduces emissions, but also shortens the process and increases efficiency.

[0034] 2. This invention employs a two-stage calcification process. First, vanadium undergoes initial transformation through melting and calcification at a high temperature of 1300-1500℃. Then, the temperature is lowered to 700-900℃, utilizing the gas generated by the decomposition of organic calcium salts to create pores in situ, and supplementing with active calcium to achieve secondary calcification. This design optimizes the pore structure of the calcified slag, significantly improving leaching kinetics and filtration performance. Simultaneously, the supplementation of active calcium promotes the full conversion of vanadium into calcium vanadate, laying a structural foundation for subsequent efficient leaching.

[0035] 3. This invention designs a cooling gradient leaching process for porous calcified slag. First, efficient leaching is achieved at a higher temperature, and then cooling is used to further dissolve the residual vanadium components in the slag pores. At the same time, the solubility of impurities such as silicon and phosphorus is reduced at low temperatures, effectively inhibiting the co-leaching of impurities. Thus, a high vanadium leaching rate and product purity are obtained under relatively low leaching agent concentration (100-200g / L) and milder temperature conditions.

[0036] 4. This invention does not produce harmful gases such as hydrogen chloride, chlorine, or sulfur dioxide throughout the entire process. The ammonia in the vanadium precipitation wastewater can be recovered and recycled, and the leaching tailings are mainly calcium carbonate, which can be utilized as a resource. This invention belongs to a clean production process and is conducive to industrialization and promotion. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the process flow for extracting vanadium pentoxide from molten vanadium slag according to the present invention. Detailed Implementation

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] The detection method in this embodiment includes:

[0040] V2O5 content: determined by ferrous ammonium sulfate titration (refer to YB / T 547.1-2014);

[0041] The contents of Si, Ca, and P elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0042] Vanadium pentoxide purity: calculated using the difference method.

[0043] Example 1 (Laboratory)

[0044] Vanadium slag cooled from a steel plant converter was crushed to 5-10 mm as experimental material and then ground to 100 mesh. The vanadium content, calculated as V₂O₅, was 15.2 wt%, SiO₂ 13.8 wt%, CaO 2.9 wt%, and P 0.09 wt%.

[0045] Experimental group 1

[0046] 200g of converter-cooled vanadium slag is placed in a muffle furnace and heated to 1400℃ under a protective atmosphere until it is completely melted.

[0047] (1) Melting and calcification transformation: Add 16g of calcium oxide (accounting for 52.6% of V2O5 in vanadium slag), and react for 10 minutes by introducing air at 0.4L / min.

[0048] (2) Cooling and calcining: When the temperature drops to 850℃, add 6g of calcium citrate (accounting for 19.7% of V2O5 in vanadium slag) and 8g of calcium oxide (accounting for 26.3% of V2O5 in vanadium slag), keep warm for 20 minutes, take it out, and let it cool naturally to room temperature to obtain calcified vanadium slag.

[0049] (3) Ammonium salt leaching: Grind the calcified slag to 200 mesh. Take 100g of the ground slag and add 400mL of ammonium carbonate solution with a concentration of 180g / L (liquid-solid ratio 4:1). Heat to 80℃ and stir for leaching for 30 minutes. Then cool down to 50℃ at a rate of 2℃ / min and continue stirring for leaching for 30 minutes. Filter to obtain vanadium-containing leachate and calcified leaching slag. Record the filtration time as approximately 3.5 minutes and the moisture content of the filter cake as 18%.

[0050] (4) Vanadium precipitation and calcination: Dilute sulfuric acid was slowly added to the leachate to adjust the pH to 3, and ammonium polyvanadate was precipitated. The precipitate was then calcined at 550°C for 1.5 hours to obtain vanadium pentoxide. The vanadium leaching rate was 96.2%, the phosphorus content of the leachate was 0.08 g / L, the silicon content was 0.35 g / L, and the purity of vanadium pentoxide was 99.7%.

[0051] Control group 1

[0052] Take 200g of cooled vanadium slag from the same batch, heat it to 1400℃ to melt it, add 24g of calcium oxide and 6g of calcium citrate, and react with air at 0.4L / min for 30 minutes, then let it cool naturally to room temperature. Grind it to 200 mesh, take 100g of the ground residue, add 400mL of ammonium carbonate solution with a concentration of 180g / L, heat to 80℃ and stir to leach for 30 minutes, then cool to 50℃ at a rate of 2℃ / min, and continue stirring to leach for 30 minutes. Filter to obtain vanadium-containing leachate and calcified leachate residue; the filtration time is 6.5 minutes, and the moisture content of the filter cake is 29%.

[0053] Dilute sulfuric acid was slowly added to the leachate to adjust the pH to 3, and ammonium polyvanadate was precipitated. This precipitate was then calcined at 550℃ for 1.5 hours to obtain vanadium pentoxide. The vanadium leaching rate was 91.4%, the phosphorus content of the leachate was 0.22 g / L, the silicon content was 0.78 g / L, and the purity of vanadium pentoxide was 98.5%.

[0054] Control group 2

[0055] Steps (1)-(2) and (4) are the same as in experimental group 1.

[0056] (3) Ammonium salt leaching: The calcified slag was ground to 200 mesh. 100g of the ground slag was added to 400mL of ammonium carbonate solution with a concentration of 180g / L, heated to 80℃ and stirred for leaching for 60 minutes; the filtration time was recorded as approximately 3.8 minutes, and the moisture content of the filter cake was 19%. The final vanadium leaching rate was 93.0%, the phosphorus content of the leachate was 0.15g / L, the silicon content was 0.52g / L, and the vanadium pentoxide purity was 99.1%.

[0057] Control group 3

[0058] Take 200g of cooled vanadium slag from the same batch, heat it to 1400℃ to melt it, add 16g of calcium oxide, and react with air at 0.4L / min for 10 minutes. When the temperature drops to 850℃, add only 14g of calcium citrate, keep it at that temperature for 20 minutes, then remove it and let it cool naturally to room temperature to obtain calcified vanadium slag.

[0059] The subsequent steps (3) ammonium salt leaching and (4) vanadium precipitation and calcination are the same as those in experimental group 1.

[0060] Testing revealed that the calcified slag had a relatively loose structure but low strength, and ball milling produced a certain amount of fine powder. The filtration time was approximately 5.2 minutes, and the filter cake moisture content was approximately 23%. The vanadium leaching rate was 89.2%, the phosphorus content of the leachate was approximately 0.17 g / L, the silicon content was approximately 0.62 g / L, and the vanadium pentoxide purity was approximately 98.6%.

[0061] Table 1. Data of experimental group 1 and each control group in Example 1

[0062]

[0063] The experimental data above show that Experiment 1 uses a two-stage calcification combined with gradient leaching process, with a vanadium leaching rate of up to 96.2%, a vanadium pentoxide purity of 99.7%, and phosphorus and silicon contents in the leachate of only 0.08 g / L and 0.35 g / L, respectively. Moreover, the calcified slag has a loose and porous structure, the filtration time is only 3.5 minutes, and the moisture content of the filter cake is only 18%.

[0064] In control group 1, calcium oxide and calcium citrate were added in a single, molten state at 1400℃. Upon contact with the molten slag, the calcium citrate decomposed violently, causing gases to rapidly escape from the surface, thus failing to create pores in the slag. Therefore, organic calcium salts must be added at an appropriate calcification stage to exert their pore-forming and synergistic calcification effects. Consequently, the slag structure in control group 1 was dense, the filtration time was as long as 6.5 minutes, and the leaching rate was only 91.4% with a purity of only 98.5%.

[0065] Control group 2 used a constant-temperature leaching process, which lacked the thermal shrinkage and discharge effect of the cooling process, resulting in insufficient dissolution of vanadium remaining in the pores. Simultaneously, phosphorus and silicon had higher solubility at high temperatures, leading to increased co-leaching of impurities. Therefore, the leaching rate of control group 2 decreased to 93.0%, the phosphorus and silicon contents increased to 0.15 g / L and 0.52 g / L respectively, and the purity decreased to 99.1%.

[0066] In control group 3, only organic calcium salt (without added calcium oxide) was added during the cooling stage. Although gradient leaching was used, some CaO reacted with SiO2 and P2O5 in the slag during the melting and calcification process, limiting the vanadium calcification effect. If calcium oxide was not added during the cooling stage, the total amount of active calcium was insufficient, and some vanadium could not be converted into calcium vanadate, resulting in a decrease in the leaching rate. If an attempt was made to supplement calcium by increasing the amount of organic calcium salt, excessive gas would lead to over-pore formation, a decrease in the strength of the calcified slag, and the generation of fine powder that would clog the filter pores, thus reducing the leaching efficiency. Therefore, organic calcium salt alone cannot simultaneously meet the dual requirements of appropriate pore formation and sufficient calcification.

[0067] Experimental group 2

[0068] All other steps were the same as in Experimental Group 1, except for (2) cooling and calcination: when the temperature dropped to 850℃, 3g of calcium citrate (accounting for 10% of V2O5 in the vanadium slag) and 8g of calcium oxide were added. After keeping warm for 20 minutes, the slag was taken out and allowed to cool naturally to room temperature to obtain calcified slag. According to the test, the vanadium leaching rate was about 91.6%, the filtration time was about 5.8 minutes (the slag structure was relatively dense, and the pore-forming effect was limited), the filter cake moisture content was about 23%, and the vanadium pentoxide purity was about 99.0%. This was because the amount of organic calcium added was too low, the amount of CO2 gas was insufficient, the pore-forming effect was limited, the calcified slag was still relatively dense, and the filterability was poor; at the same time, the amount of active CaO produced by decomposition was insufficient, so the leaching rate was lower than that of Experimental Group 1.

[0069] Experimental group 3

[0070] All other steps were the same as in Experimental Group 1, except for (2) cooling and calcination roasting: when the temperature dropped to 850℃, 10g of calcium citrate (accounting for 33% of V2O5 in the vanadium slag) and 8g of calcium oxide were added. After keeping warm for 20 minutes, the slag was taken out and allowed to cool naturally to room temperature to obtain calcified slag. According to the test, the vanadium leaching rate was about 92.8%, the filtration time was about 5.0 minutes (the slag structure was loose but not strong, and it was easy to generate micro powder blockage), the moisture content of the filter cake was about 22.0%, and the purity of vanadium pentoxide was about 98.9%. This was because the amount of organic calcium added was too high, and the excessive gas caused the pore walls to be too thin and the slag strength to decrease. The ball milling produced micro powder that blocked the filter pores. At the same time, the excessive gas escape may cause uneven local composition, affecting the full conversion of calcium vanadate. Therefore, the leaching rate and purity were lower than those of Experimental Group 1.

[0071] Example 2

[0072] Take 200g of the same batch of converter-cooled vanadium slag, place it in a muffle furnace and heat it to 1400℃ until it is completely melted.

[0073] (1) Melting and calcification transformation: Add 14g of calcium oxide (accounting for 46.1% of V2O5 in vanadium slag), and react for 12 minutes by introducing air at 0.4L / min.

[0074] (2) Cooling and calcining: Turn off the heating power and when the temperature drops to 800℃, add 5g of calcium oxalate (accounting for 16.4% of V2O5 in vanadium slag) and 8g of calcium oxide (accounting for 26.3% of V2O5 in vanadium slag), keep warm for 25 minutes, take it out, and let it cool naturally to room temperature to obtain calcified slag.

[0075] (3) Ammonium salt leaching: Grind the calcified slag to 200 mesh. Take 100g of the ground slag, add 400mL of ammonium carbonate solution with a concentration of 150g / L, heat to 70℃ and stir for leaching for 35 minutes, then cool down to 40℃ at a rate of 1.5℃ / min, continue stirring for leaching for 35 minutes, and filter to obtain vanadium-containing leachate.

[0076] (4) Vanadium precipitation and calcination: Dilute sulfuric acid was slowly added to the leachate to adjust the pH to 2.5, and ammonium polyvanadate was precipitated. The precipitate was then calcined at 600℃ for 1.5 hours to obtain vanadium pentoxide. The vanadium leaching rate was 95.8%, the phosphorus content of the leachate was 0.10 g / L, the silicon content was 0.42 g / L, and the purity of vanadium pentoxide was 99.6%.

[0077] Example 3

[0078] Take 200g of the same batch of converter cooled vanadium slag, place it in a muffle furnace and heat it to 1300℃ until it is completely melted.

[0079] (1) Melting and calcification transformation: Add 20g of calcium oxide (accounting for 65.8% of V2O5 in vanadium slag), and react for 15 minutes by introducing air at 0.3L / min.

[0080] (2) Cooling and calcining: Turn off the heating power and lower the temperature to 900℃. Add 8g of calcium citrate (accounting for 26.3% of V2O5 in vanadium slag) and 8g of calcium oxide (accounting for 26.3% of V2O5 in vanadium slag). Keep warm for 40 minutes and then take it out and let it cool naturally to room temperature to obtain calcified slag.

[0081] (3) Ammonium salt leaching: Grind the calcified slag to 200 mesh. Take 100g of the ground slag, add 500mL of ammonium carbonate solution with a concentration of 200g / L (liquid-solid ratio 5:1), heat to 90℃ and stir for leaching for 20 minutes, then cool to 50℃ at a rate of 4℃ / min, continue stirring for leaching for 20 minutes, and filter to obtain vanadium-containing leachate.

[0082] (4) Vanadium precipitation and calcination: Same as in Example 1. According to the test and calculation, the vanadium leaching rate was 95.2%, the phosphorus content of the leachate was 0.14 g / L, the silicon content was 0.55 g / L, and the vanadium pentoxide purity was 99.5%.

[0083] Example 4

[0084] Take 10 kg of the same batch of converter cooled vanadium slag, place it in a medium-frequency induction furnace, and heat it to 1450℃ to completely melt it.

[0085] (1) Melting calcification transformation

[0086] Add 0.8 kg of calcium oxide (accounting for 76.2% of V2O5 in the vanadium slag) to the molten vanadium slag, and introduce air through a spray gun at a flow rate of 15 L / min. React for 10 minutes to convert the vanadium oxide in the vanadium slag into calcium vanadate.

[0087] (2) Cooling and calcining

[0088] Stop heating and allow the molten slag to cool naturally. When the temperature drops to approximately 850°C, add 0.3 kg of calcium citrate (28.6% of the V₂O₅ in the vanadium slag) and 0.25 kg of calcium oxide (23.8% of the V₂O₅ in the vanadium slag), and hold at 850°C for 30 minutes. Then cool with the furnace to room temperature to obtain calcified slag.

[0089] (3) Ammonium salt leaching

[0090] The calcified slag was crushed and ground to 200 mesh. 4 kg of the ground calcified slag was added to 16 L of ammonium carbonate solution with a concentration of 180 g / L (liquid-to-solid ratio 4:1), and placed in a leaching reactor. The solution was heated to 80°C and leached with stirring for 30 minutes. Then, the temperature was lowered to 50°C at a rate of 2°C / min, and leaching with stirring continued for another 30 minutes. The solution was filtered to obtain a vanadium-containing leachate.

[0091] (4) Vanadium precipitation and calcination

[0092] Dilute sulfuric acid was slowly added to the leachate to adjust the pH to 3.0, resulting in the precipitation of ammonium polyvanadate. The ammonium polyvanadate was then placed in a muffle furnace and calcined at 550°C for 2 hours to obtain vanadium pentoxide. The calculated vanadium recovery rate was 95.0%, and the purity of vanadium pentoxide was 99.5%. The experimental results of Examples 2-4 are shown in Table 2.

[0093] Table 2 Experimental Results of Examples 2-4

[0094]

[0095] Table 2 shows that the methods in Examples 2-4 all achieved good vanadium extraction results. Specifically, Example 2 achieved a vanadium leaching rate of 95.8% and a purity of 99.6%; Example 3 achieved a vanadium leaching rate of 95.2% and a purity of 99.5%; and Example 4 (10kg scale-up) achieved a vanadium leaching rate of 95.0% and a purity of 99.5%, which are consistent with the results of the small-scale test (96.2% and 99.7% in Experimental Group 1), verifying that the process of the present invention has good scale-up repeatability.

Claims

1. A method for extracting vanadium pentoxide from molten vanadium slag, characterized in that, Includes the following steps: (1) Molten calcification transformation: When the vanadium slag is kept in a molten state after being discharged from the furnace, calcium oxide is added and reacted under an oxidizing atmosphere to obtain transformed slag; (2) Cooling and calcining: Cool the transformation slag to 700-900℃, add a composite calcining agent containing organic calcium salt and calcium oxide, and calcinate to obtain vanadium calcification slag; (3) Ammonium salt leaching: Calcified vanadium slag is ground and then mixed with leaching agent to carry out leaching reaction. Solid-liquid separation is performed to obtain vanadium-containing leaching solution and calcified leaching slag. The leaching reaction is first carried out at 70-90℃ for 20-40 minutes, then the temperature is lowered to 40-60℃ and leaching continues for another 20-40 minutes; (4) Vanadium precipitation and calcination: Vanadium is precipitated from the vanadium-containing leachate to obtain ammonium polyvanadate, and calcination yields vanadium pentoxide.

2. The method according to claim 1, characterized in that, The vanadium content in the vanadium slag in step (1) is 10-16wt%, the CaO content is 1-5wt%, and the temperature of the molten state is 1300-1500℃.

3. The method according to claim 1, characterized in that, In step (1), the amount of calcium oxide added is 45-80 wt% of the mass of V2O5 in the vanadium slag; the oxidizing atmosphere is air or oxygen; and the reaction time is 8-15 minutes.

4. The method according to claim 1, characterized in that, In step (2), the organic calcium salt is selected from at least one of calcium citrate and calcium oxalate; the roasting time is 20-40 minutes.

5. The method according to claim 4, characterized in that, In step (2), the amount of organic calcium salt added is 15-30 wt% of the mass of V2O5 in the vanadium slag, and the amount of calcium oxide added is 20-30 wt% of the mass of V2O5 in the vanadium slag.

6. The method according to claim 1, characterized in that, In step (3), the grinding particle size is 100-200 mesh; the leaching agent is selected from an aqueous solution of ammonium carbonate or ammonium bicarbonate.

7. The method according to claim 6, characterized in that, The concentration of the leaching agent is 100-200 g / L, and the liquid-to-solid ratio is (3-6):

1.

8. The method according to claim 1, characterized in that, In step (3), the cooling rate is 1-4℃ / min.

9. The method according to claim 1, characterized in that, In step (4), the pH of the vanadium-containing leachate is adjusted to 2.5-3.5 to precipitate ammonium polyvanadate; the ammonium polyvanadate is calcined at 500-600℃ for 1-2 hours to obtain vanadium pentoxide.

10. The method according to claim 9, characterized in that, In step (4), the ammonia gas released during the calcination process is collected, absorbed, and returned to step (3) for the preparation or replenishment of the leaching agent.

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