A method for improving the solidification rate of V element in a ball containing waste SCR catalyst and the obtained ball

Abstract

This invention discloses a method for improving the solidification rate of V element in pellets containing waste SCR catalyst and the resulting pellets, belonging to the field of pellet preparation. The invention involves crushing the waste SCR catalyst (after removing blockages) into powder, and uniformly mixing it with magnetite and bentonite to form green pellets. After drying the pellets, they are first subjected to low-temperature oxidation preheating to oxidize Fe3O4 to Fe2O3. Fe2O3 reacts with V2O5 to generate FeVO4, achieving initial solidification of V element. Then, under an inert atmosphere such as N2 protection, high-temperature calcination is performed, converting FeVO4 to FeV2O4. FeV2O4 has a high melting point and strong stability, and V element exists stably in the pellets in the form of FeV2O4, ultimately achieving efficient solidification of V element. This invention achieves a V element solidification rate of over 98.5%, ensuring both harmlessness and resource utilization of waste SCR catalyst, which is of great significance.

Description

Technical Field

[0001] This invention relates to the field of pellet preparation technology, and more specifically, to a method for improving the solidification rate of V element in pellets containing waste SCR catalyst and the resulting pellets. Background Technology

[0002] With increasing environmental pressures year by year, enterprises are investing more and more in the research and development of flue gas pollutant treatment. Among these efforts, the NH3-SCR process is the most widely used in industrial denitrification, and the V2O5-WO3 / TiO2 denitrification catalyst is used extensively in this process. In practical applications, sintering, chemical poisoning, and particulate matter blockage can cause catalyst deactivation, resulting in a large amount of waste SCR catalyst. Waste SCR catalyst is classified as HW50 hazardous waste and must be disposed of in a harmless manner.

[0003] Currently, catalyst disposal mainly includes recovering valuable elements and solidification treatment. Recovering and extracting valuable elements requires large amounts of acids and alkalis, resulting in waste liquid that requires further treatment, leading to high costs and environmental pollution. Solidification treatment often relies on adding a small amount of waste catalyst to existing raw material production and processing processes to disperse and reduce its toxicity. Compared to cement and lime, which still pose a risk of secondary pollution after simple solidification, pelletizing processes are more adaptable to raw materials and operate at higher temperatures, effectively utilizing denitrification waste catalysts and transforming them into ironmaking raw materials for blast furnaces.

[0004] The applicant has conducted research on the disposal and application of waste SCR catalysts for many years. For example, the prior patent application No. 2021102143353 disclosed a pelletizing process, its preparation method, and molten iron. The proposed method involves using iron-containing raw materials, waste SCR catalyst powder, and bentonite as pelletizing raw materials, mixing them, and then pelletizing them to form green pellets. These green pellets are then dried, preheated, and calcined to form finished pellets containing waste SCR catalyst, which can effectively utilize the waste SCR catalyst. The applicant has continued to deepen its research and found that, compared with green pellets, the waste SCR catalyst pellets prepared according to the above scheme have a significantly lower V content. This means that a considerable amount of V still volatilizes during preheating and calcination, and the V is not completely solidified. In fact, even when the waste SCR catalyst content is 10%, the V volatilization rate is as high as 8.80%. V, which volatilizes into the air, is highly toxic. At the same time, the volatilized V cannot be used in subsequent steelmaking processes to improve steel quality, and the waste SCR catalyst cannot be effectively disposed of in a harmless and resource-efficient manner, leaving room for further optimization. Summary of the Invention

[0005] 1. The technical problem that the invention aims to solve To address the problem of low V element solidification rate in existing SCR catalyst pellets, this invention aims to provide a method for improving the V element solidification rate in SCR catalyst pellets and the resulting pellets. Using this method, V element can be stably present in the pellets, achieving a high V element solidification rate.

[0006] 2. Technical Solution The applicant conducted various follow-up studies on the prior patent application technology (application number 2021102143353), preparing green pellets containing waste SCR catalyst. After drying the pellets, they were calcined at temperatures of 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, and 1300℃, and the V content was then measured. It was found that the V content in the pellets calcined at 500℃ and 600℃ did not change. From 700℃ onwards, V in the calcined pellets would volatilize and be lost, and the volatilization rate increased with increasing temperature. Analysis of the pellet composition at different calcination temperatures revealed that above 700℃, V mainly existed in the form of FeVO4, and above 1200℃, V mainly existed in the form of FeV2O4. Physicochemical reaction analysis using Factsage revealed that V₂O₅ can combine with Fe₂O₃ to form FeVO₄ above 300℃. However, as the temperature increases, FeVO₄ transforms into FeV₂O₄ above 1150℃ in the lower oxygen partial pressure pellet interior, while FeVO₄ decomposes into Fe₂O₃ and V₂O₅ above 950℃ in the higher oxygen partial pressure outer layer of the pellets. V₂O₅ further volatilizes from the pellet surface into the gas phase.

[0007] Since Fe₂O₃ recrystallization and consolidation at high temperatures are necessary to ensure the pellets have sufficient strength, the pellet calcination temperature must be above 1200℃. Therefore, the thermodynamic state of 8FeVO₄ = 4FeV₂O₄ + 2Fe₂O₃ + 5O₂ at 1250℃ is analyzed. The standard Gibbs free energy ΔG for this reaction at 1250℃ is given by Factsage. θ 401914.4 J·mol -1 Then ΔG = ΔG θ +RT ln =401914.4+RT ln

[0008] In the formula, ΔG is the Gibbs free energy of the reaction, J·mol⁻¹ -1 ;ΔG θ The standard Gibbs free energy of the reaction is given in J·mol⁻¹. -1 R is the gas constant, with a value of 8314 J·mol⁻¹. -1 ·K -1 T is the reaction temperature, in K; P is the temperature at which the reaction occurs. O2O2 pressure, atm; P θ The pressure is standard atmosphere, with a value of 1 atm; the Gibbs free energy ΔG of this reaction is only related to the oxygen partial pressure P. O2 related, Figure 1 ΔG and P are given O2 The relationship diagram. Calculations revealed that only in P... O2 Only when ΔG is less than 0 atm (<0.00175 atm) can the reaction proceed in the forward direction and FeVO4 be converted to FeV2O4.

[0009] Therefore, to improve the solidification efficiency of V2O5 in pellets containing waste SCR catalyst, it is necessary to start from the pellet preheating and calcination process, and adopt low-temperature oxidation preheating and low-oxygen partial pressure calcination crystallization technology to achieve green and efficient utilization of waste SCR catalyst in pellets.

[0010] In summary, V₂O₅ has a melting point of 670℃. During preheating and calcination, V₂O₅ that does not react with Fe₂O₃ to form FeVO₄ will volatilize above 700℃; or it may combine with Fe₂O₃ to form FeVO₄, but then decompose back into V₂O₅ above 950℃ on the outer layer of the pellets, and will still volatilize. Therefore, reducing V₂O₅ volatilization requires blocking both of these pathways. By changing the preheating and calcination regime, V₂O₅ is first allowed to fully react with Fe₂O₃ to form FeVO₄, and then FeVO₄ is converted to FeV₂O₄. FeV₂O₄ has a high melting point and stable properties, allowing it to exist stably within the pellets, thus achieving a high solidification rate of V.

[0011] To achieve the above objectives, the technical solution provided by the present invention is as follows: This invention discloses a method for improving the solidification rate of V element in pellets containing waste SCR catalyst. The method involves crushing the waste SCR catalyst (after removing blockages) into powder, uniformly mixing it with magnetite and bentonite to form green pellets. After drying the pellets, a low-temperature oxidation preheating process is performed to oxidize Fe3O4 to Fe2O3. Fe2O3 reacts with V2O5 to generate FeVO4, achieving initial solidification of V element. Then, high-temperature calcination is carried out under an inert atmosphere, such as N2 protection, converting FeVO4 to FeV2O4. FeV2O4 has a high melting point and strong stability, allowing V element to stably exist in the pellets in the form of FeV2O4, ultimately achieving efficient solidification of V element. Using this invention to prepare pellets containing waste SCR catalyst can significantly improve the solidification rate of V element in the pellets and reduce V element volatilization.

[0012] Specifically, the steps include: Step 1: Separate the waste SCR catalyst powder; Clean the waste SCR catalyst, remove the blockages on the catalyst surface, and crush the remaining catalyst into waste SCR catalyst powder. Step 2: Prepare green pellets containing waste SCR catalyst; Magnetite, bentonite and SCR catalyst powder are mixed evenly and rolled into pellets to obtain green pellets containing waste SCR catalyst. Step 3: Drying and preheating the pellets containing waste SCR catalyst; The waste SCR catalyst pellets from step two are first dried, and then transferred to a high-temperature furnace for preheating to allow the pellets to be fully oxidized. Step 4: Calcination of pellets containing waste SCR catalyst; The preheated SCR catalyst pellets containing waste were calcined at high temperature to obtain finished SCR catalyst pellets containing waste.

[0013] Furthermore, the mass fraction of V2O5 in the waste SCR catalyst powder is 5-10%; the TFe content of magnetite is ≥60.00%.

[0014] Furthermore, the bentonite content in the pelletizing mixture is 0.5-3%, and in practice, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. can be used; the content of waste SCR catalyst powder is 5-10%, and in practice, 5%, 6%, 8%, 9%, 10%, etc. can be used; the remainder is magnetite.

[0015] Furthermore, the content of magnetite, bentonite, and waste SCR catalyst powder particles must all reach ≥98% by mass in the 0.074mm particle size range.

[0016] Furthermore, the mixture is rolled on a disc pelletizer to form pellets, and the resulting pellets have a diameter between 10-12 mm.

[0017] Furthermore, the pellets are dried by forced air at a temperature of 200-300℃, with 200℃, 220℃, 250℃, 280℃, 300℃, etc. used in practice; the drying time is 10-20 min, with 10 min, 12 min, 15 min, 20 min, etc. used in practice.

[0018] Furthermore, the preheating temperature for pellet oxidation is 650-660℃. In practice, 650℃, 652℃, 655℃, 658℃, 660℃, etc. can be used, with 650℃ being preferred. Preheating is carried out in an air atmosphere for a time of not less than 40 minutes. To avoid affecting production efficiency and preheating costs due to excessive time, 40-60 minutes is preferred. In practice, 40 min, 45 min, 50 min, 60 min, etc., as well as 65 min and 70 min, can also be used, and can be set according to specific needs.

[0019] Furthermore, the pellets are roasted under N2 protection conditions with an oxygen partial pressure of <0.00175 atm and a roasting temperature of 1250-1300℃. In practice, 1250℃, 1255℃, 1260℃, 1280℃, 1300℃, etc. can be used, with 1250℃ being preferred. The roasting time is 15-20 min, and in practice, 15 min, 16 min, 18 min, 20 min, etc. can be used.

[0020] The present invention also provides a pellet containing waste SCR catalyst, which is prepared by the above method.

[0021] 3. Beneficial effects Compared with the prior art, the technical solution provided by this invention has the following advantages: The present invention provides a method for improving the solidification rate of V element in pellets containing waste SCR catalyst. Before V2O5 volatilizes, the pellets are oxidized and preheated under low-temperature conditions to ensure that Fe3O4 is fully oxidized to Fe2O3. Fe2O3 and V2O5 combine to form FeVO4, achieving the first step of V element solidification. Then, the preheated pellets are calcined under N2 protection conditions. Under extremely low oxygen partial pressure, FeVO4 is converted to FeV2O4. FeV2O4 has a high melting point and strong stability, achieving stable solidification of V element. Simultaneously, Fe2O3 undergoes recrystallization, achieving pellet solidification and obtaining qualified finished pellets that can be used as raw materials for ironmaking in blast furnaces.

[0022] Using the method of this invention, the solidification rate of V element is above 98.5%, which greatly reduces the environmental harm caused by V element volatilization. At the same time, the V element retained in the pellets can be used as a beneficial element to improve the quality of steel in subsequent steelmaking processes. It is of great significance to achieve both harmlessness and resource utilization of waste SCR catalyst. Attached Figure Description

[0023] Figure 1 The Gibbs free energy ΔG and oxygen partial pressure P of the reaction 8FeVO4=4FeV2O4+2Fe2O3+5O2 at 1250℃. O2 The relationship diagram.

[0024] Figure 2 This is a schematic diagram of the process flow of the method of the present invention. Detailed Implementation

[0025] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings.

[0026] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0027] The present invention will be further described below with reference to embodiments.

[0028] Example 1 The waste SCR catalyst is cleaned to remove blockages, leaving the catalyst body for crushing. The crushed waste SCR catalyst powder is then mixed evenly with magnetite powder and bentonite to prepare pelletizing material, wherein the mass fraction of waste SCR catalyst powder is 10% and the mass fraction of bentonite is 2%. The mixed pelletizing material is rolled with water in a pelletizer to form pellets, controlling the diameter of the pellets to be 10-12 mm.

[0029] Green pellets containing waste SCR catalyst were dried in a forced-air dryer at 300℃ for 10 min. The content of V in the dried pellets was then determined and recorded as follows: Weigh the dried pellets and record the mass as follows: The results are shown in Table 1.

[0030] The dried pellets were transferred to a high-temperature furnace and preheated at 650℃ in air atmosphere for 50 min. The FeO content in the preheated pellets was measured, and the results are shown in Table 1.

[0031] The preheated pellets were placed under N2 protection, with an oxygen partial pressure of 0.00160 atm and a temperature of 1250℃, and calcined for 20 minutes. The content of vitamin V in the finished pellets was measured and recorded as follows: Weigh the finished pellets and record the mass as follows: The results are shown in Table 1.

[0032] Pelletizing and drying are physical deformation processes that do not cause volatilization of vitamin V. The dried pellets undergo oxidation during preheating and calcination, resulting in increased mass. Therefore, the pelletizing process... The results are shown in Table 1.

[0033] Comparative Example 1 This comparative example serves as a baseline experiment. Pellets containing waste SCR catalyst were prepared using a conventional pellet preheating and calcination method. The basic process is the same as in Example 1, except that the dried pellets were preheated at a conventional temperature of 950℃ for 15 min; the preheated pellets were then calcined at 1250℃ under a conventional air atmosphere. The V element content and pellet mass in the dried pellets and the finished pellets were measured to determine the V element solidification rate. The FeO content in the preheated pellets was also measured. The results are shown in Table 1.

[0034] Comparative Example 2 The pellet preparation method of this comparative example adopts a conventional pellet preheating regime, and its preparation process is basically the same as that of Example 1. The difference is that the dried pellets are oxidatively preheated at a conventional temperature of 950℃ for 15 min. The content of V element in the dried pellets and the mass of the finished pellets were measured respectively, and the solidification rate of V element was obtained. The FeO content of the preheated pellets was detected, and the results are shown in Table 1.

[0035] Comparative Example 3 The pellet preparation method of this comparative example adopts a conventional pellet calcination regime, and its preparation process is basically the same as that of Example 1. The difference is that the preheated pellets are subjected to conventional heating and calcination, that is, the pellets are heated to 1250°C in an air atmosphere to achieve pellet calcination. The content of V element in the dried pellets and the mass of the pellets were measured respectively, and the solidification rate of V element was obtained. The FeO content of the preheated pellets was detected, and the results are shown in Table 1.

[0036] Comparative Example 4 The pellet preparation method in this comparative example uses the conventional pellet preheating time, and its preparation process is basically the same as in Example 1. The difference is that the dried pellets are only preheated at 650℃ for 15 min. The content of V element and the mass of the pellets in the dried pellets and the finished pellets were measured respectively, and the solidification rate of V element was obtained. The content of FeO in the preheated pellets was detected, and the results are shown in Table 1.

[0037] Comparative Example 5 In this comparative example, the oxygen partial pressure during pellet calcination exceeds 0.00175 atm. The preparation process is basically the same as in Example 1, except that the oxygen partial pressure during preheated pellet calcination is 0.00200 atm. The content of V element and the mass of the pellets in the dried pellets and finished pellets were measured respectively to obtain the solidification rate of V element. The FeO content of the preheated pellets was measured, and the results are shown in Table 1.

[0038] Example 2 First, the separated and crushed waste SCR catalyst powder was uniformly mixed with magnetite powder and bentonite, wherein the mass fraction of waste SCR catalyst powder was 10% and the mass fraction of bentonite was 2%. The mixture was then rolled into pellets using a pelletizing machine with water added, controlling the pellet diameter to be 10-12 mm. The green pellets containing waste SCR catalyst were dried at 300 ℃ for 10 min, then transferred to an air atmosphere at 650 ℃ for oxidative preheating for 60 min. The preheated pellets were then placed under N2 protection conditions, with an oxygen partial pressure of 0.0016 atm and a temperature of 1250 ℃, and held for 20 min. The content of V element and the mass of the pellets in the dried pellets and the finished pellets were measured respectively, and the solidification rate of V element was obtained. The FeO content of the preheated pellets was also measured. The results are shown in Table 1.

[0039] Example 3 First, the separated and crushed waste SCR catalyst powder was uniformly mixed with magnetite powder and bentonite, wherein the mass fraction of waste SCR catalyst powder was 10% and the mass fraction of bentonite was 2%. The mixture was rolled into pellets with water in a pelletizing machine, controlling the pellet diameter to be 10-12 mm. The waste SCR catalyst green pellets were dried at 300 ℃ for 10 min. The dried pellets were then transferred to an air atmosphere at 650 ℃ for oxidative preheating for 40 min. The preheated pellets were placed under N2 protection conditions, with an oxygen partial pressure of 0.00160 atm and a temperature of 1250 ℃, and held for 20 min. The content of V element and the mass of the pellets in the dried pellets and finished pellets were measured respectively, and the solidification rate of V element was obtained. The FeO content of the preheated pellets was measured, and the results are shown in Table 1.

[0040] Example 4 First, the separated and crushed waste SCR catalyst powder was uniformly mixed with magnetite powder and bentonite, wherein the mass fraction of waste SCR catalyst powder was 10% and the mass fraction of bentonite was 2%. The mixture was then rolled into pellets using a pelletizing machine with water added, controlling the pellet diameter to 10-12 mm. The green waste SCR catalyst pellets were dried at 300 ℃ for 10 min. The dried pellets were then transferred to an air atmosphere at 650 ℃ for oxidative preheating for 70 min. The preheated pellets were placed under N2 protection conditions, with an oxygen partial pressure of 0.00160 atm and a temperature of 1250 ℃, and held for 20 min. The content of V element and the mass of the pellets in the dried pellets and the finished pellets were measured respectively, and the solidification rate of V element was obtained. The FeO content of the preheated pellets was also measured. The results are shown in Table 1.

[0041] Table 1. Information on FeO content and solidification rate of V element in preheated pellets.

[0042] Analysis of the indicators in Table 1 leads to the following conclusions: (1) Compared with Example 1, the preheating temperature of the dried pellets was raised to 950°C, the FeO content in the preheated pellets decreased to 2.32%, and the V element solidification rate decreased to 91.2%. Due to the increased preheating temperature, the pellets were oxidized more fully, and FeO was oxidized to Fe2O3, so the FeO content in the preheated pellets would decrease. Under the preheating temperature of 950°C, V2O5 volatilized significantly, so some V2O5 in the pellets did not combine with Fe2O3 to form FeVO4, but volatilized away from the pellets; when the preheated pellets were calcined in an air atmosphere at 1250°C, the FeVO4 on the outer layer of the pellets with higher oxygen partial pressure could not be converted to FeV2O4, but decomposed into V2O5 and Fe2O3, and V2O5 volatilized away from the pellets, resulting in a decrease in the V element solidification rate.

[0043] (2) Compared with Example 1, when the preheating temperature of the pellets was increased to 950°C, the FeO content in the preheated pellets decreased to 2.33%, and the V element solidification rate decreased to 93.24%. This is because with the increased preheating temperature, the pellets are oxidized more fully, and FeO is oxidized to Fe2O3, thus reducing the FeO content in the preheated pellets. At the same time, V2O5 volatilizes significantly at 950°C, so some V2O5 does not combine with Fe2O3 to form FeVO4, but volatilizes away from the pellets, resulting in a decrease in the V element solidification rate.

[0044] (3) Compared with Example 1, the preheated pellets were calcined in an atmosphere with high oxygen partial pressure. The FeO content in the preheated pellets remained almost unchanged, and the V element solidification rate decreased to 92.05%. This is because when calcined in an air atmosphere, the oxygen partial pressure on the outer layer of the pellets is high. The FeVO4 generated in the preheating stage cannot be converted into FeV2O4 during high-temperature calcination. Instead, it decomposes into V2O5 and Fe2O3, causing V2O5 to volatilize and leave the pellets, resulting in a decrease in the V element solidification rate.

[0045] (4) Compared with Example 1, Comparative Example 4 showed that the preheating time of the pellets was shortened to 15 min, the oxidized FeO in the preheated pellets increased to 8.52%, and the solidification rate of V element decreased to 95.38%. This is because the preheating time was shortened, the pellets were not fully oxidized, and the FeO was not sufficiently oxidized to Fe2O3. As a result, the FeO content in the preheated pellets increased. At the same time, V2O5 was not fully combined with Fe2O3 to form FeVO4. This part of V2O5 that was not combined with Fe2O3 volatilized away from the pellets in the next high-temperature calcination stage, resulting in a decrease in the solidification rate of V element.

[0046] (5) Compared with Example 1, the oxygen partial pressure of preheated pellets exceeded 0.00175 atm during calcination. The FeO content in the preheated pellets remained almost unchanged, and the solidification rate of V element decreased to 94.75%. This is because, according to the thermodynamic equation, at 1250℃ and oxygen partial pressure of 0.00200 atm, the Gibbs free energy ΔG of the reaction FeVO4→FeV2O4+Fe2O3+O2>0, that is, FeVO4 generated in the preheating stage cannot be converted into FeV2O4 during high-temperature calcination, but decomposes into V2O5 and Fe2O3, causing V2O5 to volatilize and leave the pellets, resulting in a decrease in the solidification rate of V element.

[0047] Examples 1-4 all involved pelletizing pellets containing waste SCR catalyst according to this technical solution. The preheated pellets had low FeO content, indicating sufficient oxidation. The final pellets showed a V element solidification rate of over 98.5%, demonstrating that improving the preheating and calcination process allowed for the transformation of V element from V₂O₅ to FeVO₄ to FeV₂O₄ within the pellets, significantly improving the V element solidification rate in pellets containing waste SCR catalyst. In Example 4, the preheating time was 70 min, the FeO content of the pellets was 2.40%, and the V solidification rate reached 98.81%. This indicates that excessively extended preheating time had almost no impact on pellet oxidation and the improvement of V element solidification rate. Considering energy and time costs, a preheating time of 40-60 min is more in line with practical production needs.

[0048] The applicant's experimental research, combined with prior studies, revealed that V₂O₅ significantly volatilizes above 700℃. Analysis of the components of pellets containing waste SCR catalyst showed that V ultimately exists in the inner layer of the pellets as FeV₂O₄. Thermodynamic analysis indicated that the main reactions occurring in the pellet components included: Fe3O4 + O2 → Fe2O3, temperature > 300℃; V₂O₅ + Fe₂O₃ → FeVO₄, temperature < 950℃; The compact structure of the pellets hinders air diffusion into the inner layers, resulting in a lower oxygen partial pressure in the inner layers and a higher oxygen partial pressure in the outer layers. The following reactions occur in the inner layers of the pellets: FeVO4→FeV2O4+Fe2O3+O2, temperature>1150℃; It can be seen that V2O5 that has not reacted with Fe2O3 to form FeVO4 will volatilize when preheated above 700℃; or it may combine with Fe2O3 to form FeVO4, but decompose back into V2O5 when the outer layer of the pellets is calcined above 950℃, and will still volatilize. Therefore, the current industry practice of conventional preheating (950℃) and calcination (1250℃, in air atmosphere) inevitably causes V2O5 to volatilize into the air.

[0049] Based on the reaction characteristics of the internal components of the pellets, this invention proposes low-temperature preheating to convert V2O5 into FeVO4 before it volatilizes, thus achieving the first step of simple consolidation. It also proposes calcination under an inert atmosphere, where the oxygen partial pressure in both the inner and outer layers of the pellets is low at 1250℃, ensuring that FeVO4 is converted into FeV2O4 smoothly and rapidly. FeV2O4 has a high melting point and stable properties, thus achieving the second step of stable consolidation.

[0050] The present invention and its embodiments have been described above illustratively. This description is not restrictive and is merely one embodiment of the present invention, and is not actually limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for improving the solidification rate of V element in pellets containing waste SCR catalyst, characterized in that: The waste SCR catalyst, after removing the blockage, is crushed into powder and mixed evenly with magnetite and bentonite to form green pellets. After drying the green pellets, they are first subjected to low-temperature oxidation preheating to oxidize Fe3O4 in the pellets to Fe2O3. Fe2O3 and V2O5 react to generate FeVO4, achieving the initial solidification of V element. Then, under the protection of an inert atmosphere, they are calcined at high temperature to convert FeVO4 into FeV2O4, and V element exists stably in the pellets in the form of FeV2O4. The oxidation preheating temperature of green pellets is 650-660℃, preheating in air atmosphere, and the preheating time is not less than 40 minutes. The green pellets are roasted under a protective atmosphere with an oxygen partial pressure of <0.00175 atm and a roasting temperature of 1250-1300℃ for 15-20 min. The pelletizing mixture contains 0.5-3% bentonite, 5-10% waste SCR catalyst powder, and the remainder is magnetite; The mass fraction of V2O5 in the waste SCR catalyst powder is 5-10%; the TFe content of magnetite is ≥60.00%.

2. The method for improving the solidification rate of V element in pellets containing waste SCR catalyst according to claim 1, characterized in that: The raw pellets are dried by forced air at a temperature of 200-300℃ for 10-20 minutes.

3. The method for improving the solidification rate of V element in pellets containing waste SCR catalyst according to claim 1, characterized in that: The mixture is rolled on a disc pelletizer to form pellets, and the resulting pellets have a diameter between 10-12 mm.

4. A method for improving the solidification rate of V element in pellets containing waste SCR catalyst according to any one of claims 1-3, characterized in that, The specific process is as follows: Step 1: Separate the waste SCR catalyst powder; Clean the waste SCR catalyst, remove the blockages on the catalyst surface, and crush the remaining catalyst into waste SCR catalyst powder. Step 2: Prepare green pellets containing waste SCR catalyst; Magnetite, bentonite and SCR catalyst powder are mixed evenly and rolled into pellets to obtain green pellets containing waste SCR catalyst. Step 3: Drying and preheating the pellets containing waste SCR catalyst; The green pellets containing waste SCR catalyst are first dried, and then transferred to a high-temperature furnace for preheating to allow the pellets to be fully oxidized; Step 4: Calcination of pellets containing waste SCR catalyst; The preheated SCR catalyst pellets containing waste were calcined at high temperature to obtain finished SCR catalyst pellets containing waste.

5. A pellet containing waste SCR catalyst, characterized in that: It is prepared by the method described in any one of claims 1-4.

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