A method for inhibiting the volatilization of vanadium during the preparation of spent SCR catalyst-containing pellets

Abstract

The application discloses a method for inhibiting vanadium element volatilization in a preparation process of waste SCR catalyst-containing pellet, and belongs to the field of blast furnace pellet preparation. The method comprises the following steps: uniformly mixing magnetite, bentonite and waste SCR catalyst according to a proportion to obtain an inner layer pelletizing material; mixing the magnetite and the bentonite according to a proportion to obtain an outer layer pelletizing material; preparing the inner layer pelletizing material into an inner layer pellet through a disc pelletizer, wrapping the inner layer pellet with a layer of CaO powder, adding the outer layer pelletizing material into the disc pelletizer to obtain a double-layer pellet, and drying, preheating and roasting the double-layer pellet in an air atmosphere. The double-layer pellet produced by the application can meet various metallurgical performance indexes required by the pellet into a blast furnace, can solve the problem of vanadium element volatilization of the waste SCR catalyst-containing pellet in a preheating and roasting stage, and can expand the application prospect of the waste SCR catalyst in a pellet process.

Description

Technical Field

[0001] This invention relates to the field of blast furnace pellet preparation technology, and more specifically, to a method for suppressing the volatilization of vanadium during the preparation of pellets containing waste SCR catalyst. Background Technology

[0002] Currently, NH3-SCR denitrification technology, with VWTi catalysts as its core, is widely used in coal-fired power generation, cement, and steel industries. SCR catalysts are prone to deactivation in flue gas environments. Due to their high content of heavy metals, spent SCR catalysts are classified as hazardous waste, requiring effective treatment measures to avoid environmental hazards. Blast furnaces are one of the main reaction vessels in steel production. The interior of blast furnaces is corroded by the scouring action of molten iron, necessitating the use of furnace lining materials for repair. Titanium ions in titanium-containing pellets transform into high-melting-point TiC and TiN in the blast furnace, adhering to damaged areas and thus repairing the furnace. Spent SCR catalysts, with a TiO2 content as high as 75-85%, are a high-quality titanium-containing raw material that can be added to blast furnace feedstock.

[0003] The applicant has been diligently researching the effective utilization of waste SCR catalysts for many years. For example, the prior patent application (application number 2021102142702) disclosed a titanium-containing pellet with waste SCR catalyst and its preparation method. This method uses iron-containing raw materials, waste SCR catalyst powder, and liquid-phase additives to prepare titanium-containing pellets. The pelletizing process in the metallurgical process is used to solidify the waste SCR catalyst. Furthermore, the binding effect produced by the addition of waste SCR catalyst powder gives the pellets excellent metallurgical properties. The applicant has prepared this type of titanium-containing pellet with waste SCR catalyst in the laboratory and found that compared with green pellets, the vanadium volatilization rate in the preheated and roasted pellets reached 7.23%. Another example is the prior patent application (application number 202110214335.3), which disclosed a pellet, its preparation method, and molten iron. This method involves crushing and grinding waste SCR catalyst to remove impurities, then adding the waste SCR catalyst powder to the pelletizing raw materials to prepare titanium-containing pellets, effectively utilizing the blast furnace pelletizing process to decompose the waste SCR catalyst. Based on this, the applicant continued with numerous repeated experiments and discovered that even after adding spent SCR catalyst to the raw materials for pellet preparation and undergoing preheating and calcination, the vanadium volatilization rate in the pellets remained high. In fact, even with only 10% spent SCR catalyst added, the vanadium volatilization rate reached as high as 8.80%. Vanadium volatilizes into the air as V₂O₅, which is highly toxic and poses a significant environmental pollution risk. This necessitates additional treatment of the pellet production waste gas, increasing production costs and indicating considerable room for technological improvement in practical production. Therefore, improving the vanadium solidification rate in pellets containing spent SCR catalyst and reducing V₂O₅ volatilization into the air is of great significance for the application of spent SCR catalyst in pellet production. Summary of the Invention

[0004] 1. The technical problem that the invention aims to solve

[0005] This invention aims to provide a method for suppressing the volatilization of vanadium during the preparation of pellets containing waste SCR catalyst, thereby alleviating the problem of easy volatilization of vanadium in the application of waste SCR catalyst in pellets in the prior art and reducing the risk of environmental pollution caused by the volatilization of toxic V2O5 into the air.

[0006] 2. Technical Solution

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0008] This invention discloses a method for suppressing vanadium volatilization during the preparation of pellets containing waste SCR catalyst. This method utilizes pelletizing technology to treat waste SCR catalyst, reducing the vanadium volatilization rate during the preheating and roasting stage of the pellets, thus effectively addressing the resource utilization problem of waste SCR catalysts. The double-layer pellets produced by this method meet the various metallurgical performance indicators required for pellet ore input into the furnace, solve the problem of vanadium volatilization during the preheating and roasting stage of pellets containing waste SCR catalyst, and expand the application prospects of waste SCR catalysts in the pelletizing process.

[0009] The method of this invention is as follows: magnetite, bentonite and waste SCR catalyst are uniformly mixed in proportion to obtain inner layer pelletizing material; magnetite and bentonite are mixed in proportion to obtain outer layer pelletizing material; the inner layer pelletizing material is prepared into inner layer pellets by a disc pelletizer; a layer of CaO powder is coated on the surface of the inner layer pellets; the outer layer pelletizing material is added into the disc pelletizer to obtain double layer pellets; and the pellets are dried, preheated and calcined in an air atmosphere.

[0010] Furthermore, the specific steps are as follows:

[0011] Step 1: Prepare the ingredients:

[0012] After separating the spent SCR catalyst from the blockage, the spent SCR catalyst was crushed and dried; the spent SCR catalyst was then finely ground and sieved to obtain spent SCR catalyst powder.

[0013] Magnetite, bentonite, and spent SCR catalyst are mixed uniformly in a certain proportion to obtain the inner layer pelletizing material; magnetite and bentonite are mixed in a certain proportion to obtain the outer layer pelletizing material.

[0014] Step 2: Preparing pellets:

[0015] The inner layer pelletizing material is prepared into inner layer pellets using a disc pelletizer. Once the inner layer pellets reach a certain size, a layer of CaO powder is coated on the surface of the inner layer pellets. Then, the outer layer pelletizing material is added to the disc pelletizer to obtain double-layer pellets.

[0016] Step 3: Pellet drying, preheating, and calcination:

[0017] The raw pellets from step two are first dried, and then the unroasted pellets are preheated and roasted at a certain temperature to obtain roasted pellets.

[0018] In practice, the following operations can be performed to test the quality of roasted pellets:

[0019] Step 4: Testing the compressive strength of the calcined double-layer pellets:

[0020] According to the standard GB / T 14201-2018 "Determination of compressive strength of iron pellets for blast furnace and direct reduction", the compressive strength of 20 roasted double-layer pellets was measured using a pellet compressive strength tester, and the average value was taken.

[0021] Step 5: Elemental content detection of pellets:

[0022] The pellets were crushed into powder using an electromagnetic crusher and passed through a 200-mesh sieve. The powder passing through the sieve was used to determine the vanadium content using a dissolution and ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) method. 0.25g of powder was added to a mixed solution of 10ml HNO3 and 5ml HClO4 and heated continuously until completely dissolved. The determination was performed according to the national standard GB / T 6730.76-2017. A portion of the unbaked pellets was crushed, and the vanadium content of the unbaked pellets was determined. Because the raw materials were completely and uniformly mixed, the vanadium content of each pellet was the same, so this vanadium content represents the vanadium content of each unbaked pellet. Fifteen unbaked pellets were weighed, preheated, and then weighed to determine the vanadium content of the roasted double-layer pellets. The vanadium content was determined according to the formula... Calculate the vanadium solidification rate of the pellets. M0 and M1 refer to the mass of the pellets containing waste SCR catalyst before and after calcination, respectively; ρ0 and ρ1 refer to the vanadium content of the waste SCR catalyst in the pellets before and after calcination, respectively.

[0023] Preferably, the content of magnetite, spent SCR catalyst, bentonite, and CaO powder particles should all reach ≥98% by mass in the -0.074mm particle size range.

[0024] Preferably, the amount of waste SCR catalyst added to the inner layer pelletizing material is 5-10%, and in practice, 5%, 6%, 6.5%, 7%, 8%, 10%, etc. can be used; the amount of bentonite added to the inner layer pelletizing material is 1-2%, and in practice, 1%, 1.2%, 1.5%, 1.8%, 2%, etc. can be used; the remainder is magnetite.

[0025] Preferably, the amount of CaO powder added is 1-1.5% of the total mass of the double-layer pellets. In practice, 1%, 1.1%, 1.2%, 1.3%, 1.5%, etc. can be used.

[0026] Preferably, the amount of bentonite added to the outer pelletizing material is 1-2%, and in practice, 1%, 1.3%, 1.6%, 1.8%, 2%, etc. can be used, with the remainder being magnetite.

[0027] Preferably, the inner layer pellet has a diameter of 10-11 mm, and the sum of the thicknesses on both sides of the outer layer pellet is 1-2 mm, so that the overall diameter of the double-layer pellet is 11-13 mm.

[0028] Preferably, the double-layer pellets are dried by forced air, with a forced air velocity of 0.5-0.8 m / s, and in practice, 0.5 m / s, 0.6 m / s, 0.7 m / s, 0.8 m / s, etc. can be used; the drying temperature is 250-300℃, and in practice, 250℃, 280℃, 300℃, etc. can be used; the forced air time is 5-15 min, and in practice, 5 min, 10 min, 12 min, 15 min, etc. can be used.

[0029] Preferably, the preheating temperature of the pellets is 925-975℃, and in practice, 925℃, 940℃, 950℃, 960℃, 970℃, 975℃, etc. can be used; the preheating time is 20-25min, and in practice, 20min, 22min, 25min, etc. can be used.

[0030] Preferably, the roasting temperature is 1225-1275℃, and in practice, 1225℃, 1240℃, 1250℃, 1260℃, 1270℃, 1275℃, etc. can be used; the roasting time is 20-25min, and in practice, 20min, 22min, 25min, etc. can be used.

[0031] The applicant discovered through years of research that vanadium significantly volatilizes from spent catalyst pellets. Fe3O4 and V2O5 do not react between 300-500℃; V2O5 does not transform and is almost non-volatile. However, above 700℃, V2O5 volatilizes significantly. V2O5 melts into a liquid phase at around 670℃, and further rapid heating causes violent volatilization. In previous research, the applicant uniformly mixed Fe3O4 powder and V2O5 powder in a 4:1 ratio, which more significantly revealed the reaction of Fe2O3 solidifying V2O5. After pressing the mixture into cylindrical samples and calcining them, scanning electron microscopy was used to observe the pellet radius profile. This revealed that at a distance of 625 μm from the surface of the cylindrical sample (e.g., ... Figure 2As shown in the figure, the vanadium content in the outer layer of the pellets decreases significantly, and the vanadium content decreases further closer to the pellet surface. The vanadium content inside the pellets also decreases, and V₂O₅ volatilization occurs, but in the outer layer of the pellets, the vanadium content decreases further closer to the pellet surface, and V₂O₅ volatilization is more significant. Therefore, it was found that preparing a 1-2 mm outer layer pellet based on the inner layer pellets, the double-layer pellet structure can effectively block V₂O₅ volatilization.

[0032] This invention adds CaO powder to the pellets to allow CaO to react with V₂O₅ to form calcium metavanadate (CaV₂O₆), thus solidifying the V element. If CaO powder is directly added to the inner pellets, CaO can react with Fe₂O₃, TiO₂, and V₂O₅, with V₂O₅ being the least abundant and far lower than Fe₂O₃ and TiO₂. Therefore, the actual amount of CaO reacting with V₂O₅ is extremely small. By coating the inner pellets with a layer of CaO powder, V₂O₅ volatilizes at around 700°C and reacts with the CaO powder on the outer layer to form CaV₂O₆. The remaining CaO reacts with Fe₂O₃ to form CaFe₂O₄, which has a melting point of 1216°C. During calcination, CaFe₂O₄ produces a liquid phase, causing the pellets to stick together. In actual production, this exacerbates ring formation in the pellet calcination equipment, affecting normal production. Preparing the outer pellets avoids this problem.

[0033] Preparing an outer layer of pellets effectively prevents the volatilization of vanadium from the inner layer pellets and simultaneously encapsulates the liquid phase generated during roasting. If the outer layer pellets are too thin, they cannot achieve the above effects; if the outer layer pellets are too thick, although they can prevent vanadium volatilization and encapsulate the liquid phase, the pellets will exhibit significant stratification, affecting pellet strength. This invention prepares an outer layer pellet of 1-2 mm based on the inner layer pellets, thus alleviating the above problems.

[0034] 3. Beneficial effects

[0035] This invention discloses a method for suppressing vanadium volatilization during the preparation of SCR catalyst pellets containing waste. The method employs a double-layer pellet structure, with the inner pellet coated with a layer of CaO powder. CaO readily reacts with V₂O₅ to form CaV₂O₆, thus solidifying the vanadium in the pellets. Secondly, the outer pellet can encapsulate CaFe₂O₄ generated from the reaction of CaO and Fe₂O₃ in the inner pellet, effectively preventing pellet agglomeration during roasting and avoiding the exacerbation of ring formation in the pellet roasting equipment and disruption of normal production. Thirdly, Fe₃O₄ in the pellets oxidizes to Fe₂O₃, which reacts with V₂O₅ to form FeVO₄, further generating FeV₂O₄, thereby further solidifying the vanadium in the pellets.

[0036] The processing method of this invention achieves a vanadium solidification rate of over 98.5%, thereby reducing V2O5 volatilization, increasing the vanadium solidification rate, and improving the environmental benefits of using pelletizing processes to treat waste SCR catalysts. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0038] Figure 2 This is a schematic diagram showing the thickness of the vanadium volatilization boundary layer in a single-layer calcined pellet after grinding and calcination of a mixture of Fe3O4 and V2O5 powders, observed by electron microscopy. Figure 2 As shown, SEM analysis was performed on the vanadium content in the edge region of the monolayer roasted pellets containing spent catalyst, revealing the boundary layer for vanadium volatilization. Five edge regions of the monolayer roasted pellets containing spent catalyst were selected and labeled 1-5. Within each labeled region, 14 smaller rectangular regions with a width of 62.5 μm were divided inward from the boundary. The mass fraction of vanadium in different rectangular regions was measured using scanning electron microscopy. The vanadium mass fraction data of rectangles at the same distance from the boundary were averaged to obtain the relationship between vanadium content and boundary distance. The results show that the vanadium content is lower closer to the boundary, with an average vanadium content of only 7.14 wt.% in the boundary rectangles. At a distance of 625 μm from the boundary, the average vanadium content is 9.95 wt.%, and when the distance exceeds 625 μm, the vanadium content remains at 10.9 wt.%, indicating that vanadium in the monolayer roasted pellets containing spent catalyst volatilizes within a 625 μm range from the boundary; this provides a reference for controlling vanadium volatilization. Detailed Implementation

[0039] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings.

[0040] 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.

[0041] The present invention will be further described below with reference to embodiments.

[0042] Example 1

[0043] This embodiment provides a method for suppressing vanadium volatilization during the preparation of pellets containing spent SCR catalyst, comprising the following steps:

[0044] Step 1: Prepare raw materials

[0045] After separating the spent SCR catalyst from the blockage, the spent SCR catalyst was crushed and dried; the spent SCR catalyst was then finely ground and sieved to obtain spent SCR catalyst powder.

[0046] Magnetite, bentonite, and spent SCR catalyst are mixed uniformly in a certain proportion to obtain the inner layer pelletizing material; magnetite and bentonite are mixed in a certain proportion to obtain the outer layer pelletizing material; the mass percentage content of magnetite, spent SCR catalyst powder, bentonite, and CaO powder must all reach ≥98% for the -0.074mm particle size.

[0047] Specifically, the inner layer pelletizing material contains 88% magnetite by mass, 2% bentonite by mass, and 10% spent SCR catalyst by mass. The outer layer pelletizing material contains 98% magnetite by mass and 2% bentonite by mass.

[0048] Step 2: Preparation of pellets

[0049] The inner layer pelletizing material is prepared into inner layer pellets using a disc pelletizer. A layer of CaO powder is then coated onto the surface of the inner layer pellets, with the CaO powder accounting for 1% of the total mass of the double-layer pellets. The outer layer pelletizing material is then added to the disc pelletizer to obtain the double-layer pellets. The inner layer pellets have a diameter of 10 mm, the combined thickness of the outer layer pellets on both sides is 2 mm, and the overall diameter of the double-layer pellets is 12 mm.

[0050] Step 3: Pellet drying, preheating and calcination

[0051] The qualified green pellets were placed in a forced-air drying oven for drying. The forced-air flow rate was 0.5 m / s, the temperature was 250℃, and the forced-air time was 15 min.

[0052] Unbaked pellets were placed in a horizontal tube furnace, preheated at 950°C in air for 20 minutes, and calcined at 1250°C in air for 20 minutes to obtain calcined double-layer pellets.

[0053] Step 4: Test the compressive strength of the calcined pellets

[0054] The compressive strength of 20 calcined double-layer pellets was measured using a pellet compressive strength tester, and the average value was taken.

[0055] Step 5: Detect the vanadium content in the double-layer pellets.

[0056] The pellets were crushed into powder using an electromagnetic crusher, then ground in a mortar and pestle, and finally passed through a 200-mesh sieve. The powder passing through the sieve was collected, and the content of the heavy metal vanadium was determined using a dissolution and ICP-OES (inductively coupled plasma optical emission spectrometry) method. 0.25g of powder was added to a mixed solution of 10ml HNO3 and 5ml HClO4, and heated continuously until completely dissolved. The determination was performed according to the national standard GB / T 6730.76-2017. A portion of the unbaked pellets was crushed, and the vanadium content ρ0 of the unbaked pellets was determined. Because the raw materials were completely and uniformly mixed, the vanadium content of each pellet was the same, so this vanadium content is the vanadium content ρ0 of each unbaked pellet. Fifteen unbaked pellets were weighed (M0), and after preheating and calcining, their mass (M1) was measured to determine the vanadium content ρ1 of the calcined double-layer pellets. The determination was performed according to the formula... Calculate the vanadium solidification rate of the pellets. Record the experimental results in Table 1.

[0057] Comparative Example 1

[0058] The experimental procedure for this comparative example is the same as in Example 1, except that magnetite, spent SCR catalyst, and bentonite were uniformly mixed to prepare monolayer pellets with a diameter of 12 mm. The composition of the pellets was 88% magnetite, 2% bentonite, and 10% spent SCR catalyst. The experimental results are recorded in Table 1.

[0059] Comparative Example 2

[0060] The experimental procedure for this comparative example is the same as in Example 1, except that CaO powder was added to the inner layer pelletizing material to prepare single-layer pellets with a diameter of 12 mm. The mass percentage of magnetite was 87%, the mass percentage of spent SCR catalyst powder was 10%, the mass percentage of bentonite was 2%, and the mass percentage of CaO powder was 1%. The experimental results are recorded in Table 1.

[0061] Comparative Example 3

[0062] The experimental procedure for this comparative example is the same as that in Example 1, except that CaO powder was not added to the pellets, and a double-layer pellet was prepared. The inner pellet had a diameter of 10 mm, the outer pellet had a thickness of 2 mm, and the overall double-layer pellet had a diameter of 12 mm. The experimental results are recorded in Table 1.

[0063] Comparative Example 4

[0064] The experimental procedure for this comparative example is the same as that in Example 1, except that the inner layer pellet diameter is 9 mm, the outer layer pellet thickness is 3 mm, and the overall double-layer pellet diameter is 12 mm. The experimental results are recorded in Table 1.

[0065] Example 2

[0066] This embodiment provides a method for suppressing vanadium volatilization during the preparation of pellets containing waste SCR catalyst. It is basically the same as in Embodiment 1, except that the mass percentage of waste SCR catalyst in the inner layer pelletizing material of this embodiment is 5%, the mass percentage of magnetite is 93%, and the mass percentage of bentonite is 2%.

[0067] The experimental results are recorded in Table 1.

[0068] Example 3

[0069] This embodiment describes a method for suppressing vanadium volatilization during the preparation of spent SCR catalyst pellets. It is essentially the same as in Example 1, except that the inner pellet diameter is 11 mm and the outer pellet thickness is 1 mm. Experimental results are recorded in Table 1.

[0070] Table 1. Pellet Performance Testing Information

[0071]

[0072] By analyzing the data in Table 1, we can conclude that:

[0073] (1) Compared with Comparative Example 1, the waste SCR catalyst was simply mixed with magnetite and bentonite to prepare single-layer pellets. The vanadium solidification rate in the roasted pellets was significantly reduced, from 98.57% to 91.81%. The compressive strength of the double-layer pellets after roasting was reduced from 2370.52 N / piece to 2178.23 N / piece.

[0074] (2) In comparison with Example 1, CaO powder was added to the inner layer pelletizing material to prepare single-layer pellets. The vanadium solidification rate in the calcined pellets decreased from 98.57% to 92.37%, and the compressive strength of the double-layer pellets after calcination decreased from 2370.52 N / pellet to 1957.67 N / pellet.

[0075] (3) Comparing Comparative Example 3 and Example 1, double-layer pellets were prepared, but without the addition of CaO powder. The vanadium solidification rate in the calcined pellets decreased from 98.57% to 94.25%, and the compressive strength of the double-layer pellets after calcination decreased from 2370.52 N / pellet to 2073.17 N / pellet.

[0076] (4) Compared with Example 1, the outer layer of pellets was thicker, while the overall diameter of the pellets remained unchanged. The vanadium solidification rate in the roasted pellets increased slightly to 98.91%, but the compressive strength of the double-layer pellets after roasting decreased from 2370.52 N / piece to 1993.29 N / piece, which did not meet the standard for pellets entering the furnace (>2000 N / piece).

[0077] 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 suppressing vanadium volatilization during the preparation of spent SCR catalyst pellets, characterized in that: Magnetite, bentonite and waste SCR catalyst are mixed evenly to obtain inner layer pelletizing material. Magnetite and bentonite are mixed evenly to obtain outer layer pelletizing material. The inner layer pellets are first formed using the inner layer pelletizing material. CaO powder is coated on the surface of the inner layer pellets. Then, the outer layer pelletizing material is added to continue pelletizing to obtain double layer pellets. The pellets are dried, preheated and calcined in an air atmosphere. The amount of waste SCR catalyst added to the inner layer pelletizing material is 5-10%, the amount of bentonite is 1-2%, and the remainder is magnetite. The amount of CaO powder added is 1-1.5% of the mass of the double-layer pellets; The amount of bentonite added to the outer pelletizing material is 1-2%, and the remainder is magnetite; The inner layer pellets have a diameter of 10-11 mm, and the overall diameter of the double-layer pellets is 11-13 mm.

2. The method for suppressing vanadium volatilization during the preparation of spent SCR catalyst pellets according to claim 1, characterized in that: Magnetite, spent SCR catalyst, bentonite, and CaO powder particles must all have a mass percentage content of ≥98% in the -0.074mm particle size range.

3. The method for suppressing vanadium volatilization during the preparation of spent SCR catalyst pellets according to claim 1, characterized in that: The double-layer pellets are dried by forced air, with a forced air flow rate of 0.5-0.8 m / s, a drying temperature of 250-300℃, and a forced air time of 5-15 min.

4. The method for suppressing vanadium volatilization during the preparation of spent SCR catalyst pellets according to claim 3, characterized in that: The preheating temperature for the double-layer pellets is 925-975℃, and the preheating time is 20-25 min.

5. The method for suppressing vanadium volatilization during the preparation of spent SCR catalyst pellets according to claim 4, characterized in that: The calcination temperature of the double-layer pellets is 1225-1275℃, and the calcination time is 20-25 minutes.

6. A method for suppressing vanadium volatilization during the preparation of spent SCR catalyst pellets according to any one of claims 1-5, characterized in that, The specific process is as follows: Step 1: Prepare the ingredients: Remove the blockages on the spent SCR catalyst, crush the spent SCR catalyst into powder and dry it, and then grind and sieve it to obtain spent SCR catalyst powder. Magnetite, bentonite, and spent SCR catalyst are mixed evenly in a certain proportion to obtain the inner layer pelletizing material; magnetite and bentonite are mixed in a certain proportion to obtain the outer layer pelletizing material. Step 2: Preparing pellets: The inner layer pelletizing material is prepared into inner layer pellets using a disc pelletizer. Once the inner layer pellets reach a certain size, CaO powder is coated on the surface of the inner layer pellets. Then, the outer layer pelletizing material is added to the disc pelletizer to obtain double-layer pellets. Step 3: Pellet drying, preheating, and calcination: The raw pellets from step two are first dried, and then the unroasted pellets are preheated and roasted to obtain roasted pellets.

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