Titanium-containing pellet and preparation method thereof

Abstract

The invention discloses a titanium-containing pellet and a preparation method thereof, and belongs to the technical field of pellets. Green pellet raw materials of the titanium-containing pellet comprise iron-containing ore powder, an adhesive and a modified titanium-containing waste catalyst, and the modified titanium-containing waste catalyst is obtained by performing roasting modification treatment on the titanium-containing waste catalyst in an inert atmosphere by taking a calcium additive and metallurgical iron-containing dust as modifiers. According to the method, the titanium-containing waste catalyst is modified in advance and then used for pellet manufacturing, so that the compressive strength of the pellets can be effectively improved, the yield of green pellets is increased, the curing rate of V can be increased, and the adverse effect caused by introduction of the waste catalyst is eliminated.

Description

Technical Field

[0001] This invention belongs to the field of pellet technology, and more specifically relates to a titanium-containing pellet and its preparation method. Background Technology

[0002] The main principle behind using titanium-containing pellets in blast furnaces is that during the blast furnace smelting process, TiO2 in the titanium-containing materials undergoes a reduction reaction with C and N at high temperatures, producing TiC and TiN. These substances dissolve in the molten iron, increasing its viscosity and reducing its fluidity, thus forming a precipitation layer in the hearth erosion zone, achieving the purpose of protecting the hearth. There are many types of titanium-containing pellets, but most typically maintain a titanium content between 6% and 10%. This enhances cooling intensity while facilitating the precipitation of TiC and TiN, thus protecting the furnace. The use of titanium-containing pellets can also improve the desulfurization performance of slag and enhance its fluidity, which is beneficial for blast furnace production.

[0003] Waste SCR denitrification catalysts are hazardous waste; improper storage or disposal can cause serious harm to the natural environment and people's lives. With the increasing use of SCR denitrification catalysts year by year, the treatment of large quantities of waste SCR catalysts has become a severe challenge. In recent years, researchers have made some progress in the resource utilization of waste SCR catalysts. Researchers in the steel industry have proposed utilizing metallurgical processes to recycle waste catalysts and produce waste catalyst pellets. However, existing research generally suffers from problems such as low compressive strength of roasted pellets, low green pellet qualification rate, and low solidification rate of harmful element V, which significantly affects blast furnace smelting efficiency. Poor pellet strength reduces the permeability of the blast furnace charge and furnace stability, leading to increased energy consumption and decreased product quality. Furthermore, insufficient V solidification in the pellets, resulting in volatilization, negatively impacts worker health and the atmospheric environment, affecting the economic benefits and market competitiveness of enterprises. Therefore, ensuring that waste catalyst-containing pellets have sufficient compressive strength, a high green pellet qualification rate, and the ability to solidify harmful elements is crucial for improving smelting efficiency, reducing costs, and protecting the environment.

[0004] A search revealed that, to improve the solidification rate of V, application number 202311061935.6 discloses a method for co-processing waste vanadium-tungsten-titanium catalysts from denitrification using a rotary hearth furnace. This method utilizes the rotary hearth furnace process to recycle the waste catalyst. Under a reducing atmosphere, the highly toxic, low-melting-point V₂O₅ in the waste catalyst is reduced to a high-melting-point V₂O₃, which is then solidified and fed into the blast furnace. Finally, it is solidified in glassy slag, achieving harmless treatment. While this application avoids the volatilization problem of V₂O₅ through the reducing atmosphere of the rotary hearth furnace, in practice, it faces the problem of reduced strength of carbon-containing pellets and low green pellet yield due to the introduction of TiO₂. Furthermore, its main application is in the preparation of carbon-containing pellets.

[0005] In order to solve the above-mentioned problems of spent catalyst pellets, the research group of the inventors of this application has also conducted a series of studies and achieved certain research results.

[0006] For example, in order to improve the strength of pellets, application CN202110214158.9 discloses a blast furnace pellet and its preparation method that can be used to treat the failed SCR denitrification catalyst. It prepares low-melting-point materials by roasting the blockage material and iron-containing materials, thereby generating a low-melting-point liquid phase during the pellet roasting process. These liquid phases can act as a buffer between the stress-generating α-F2O3 phase and rutile titanium dioxide, and can also fill the spaces between the oxidized magnetite grains to connect the grains, thereby improving the strength of the pellets.

[0007] Application CN202110214419.7 discloses a method for treating waste catalysts to enhance the cohesiveness of pellets. The method involves preparing a low-melting-point liquid phase additive by roasting sintered return ore and waste incineration fly ash. This low-melting-point liquid phase is generated during the pellet roasting process. The liquid phase solidifies during the condensation process, binding the pellets together and thus improving the pellet strength.

[0008] The aforementioned patent applications all involve preparing low-melting-point materials and then mixing them with spent catalysts to form pellets, utilizing the solidification and consolidation effect of the low-melting-point liquid phase to improve pellet strength. However, in actual operation, it was found that because the proportion of low-melting-point materials in the pelletizing material is relatively small, there are few opportunities for contact and bonding with the spent catalyst, making it difficult to eliminate the void shrinkage problem caused by TiO2, and the problem of low V solidification rate remains unsolved.

[0009] For example, to improve the solidification rate of V, application CN 202410517575.4 discloses a method for improving the solidification rate of V element in pellets containing waste SCR catalyst and the resulting pellets. This method involves first subjecting the pellets to low-temperature oxidation preheating, oxidizing Fe3O4 to Fe2O3. Fe2O3 reacts with V2O5 to generate FeVO4, thus achieving initial solidification of V element. Then, under inert atmosphere protection, high-temperature calcination converts FeVO4 into FeV2O4. FeV2O4 has a high melting point and strong stability, allowing V element to exist stably in the pellets in the form of FeV2O4, ultimately achieving efficient solidification of V element. However, the inert atmosphere calcination in this application significantly reduces the pellet strength.

[0010] Application CN 202410517588.1 discloses a method for suppressing vanadium volatilization during the preparation of pellets containing waste SCR catalyst. This method involves double-layer pelletizing, with a layer of CaO powder coated around the inner pellet. V₂O₅ volatilizes at around 700℃ and reacts with the CaO powder on the outer layer to form CaV₂O₆. The outer pellet effectively encapsulates and prevents the volatilization of vanadium from the inner pellet. However, because this application requires separate double-layer pelletizing and uses different raw materials for the inner and outer layers, it easily leads to uneven pellet composition and stratification during pellet calcination, affecting pellet strength.

[0011] In summary, introducing liquid-phase additives dispersed throughout the pellets reduces contact and bonding opportunities with spent catalysts. While this can improve pellet strength to some extent, it cannot prevent V volatilization or increase the green pellet yield. Modifications to traditional pelletizing processes, such as reducing atmosphere roasting and double-layer pelletizing, can effectively solidify V but neglect pellet consolidation strength. Therefore, effectively coordinating these two aspects—ensuring pellet strength, preventing V volatilization, and maintaining a high green pellet yield—is crucial for the resource utilization of titanium-containing spent catalysts in the pelletizing field. Furthermore, the surface of spent catalysts, deactivated by sulfur dioxide poisoning in flue gas, is covered with ammonium bisulfate, a strongly hydrophobic substance. This disrupts the capillary forces formed between pelletizing particles by water molecules, resulting in poor pelletizing properties and a low green pellet yield. Summary of the Invention

[0012] To address the issues of lower compressive strength or lower V solidification rate when using vanadium-containing waste catalysts in pelletizing processes compared to ordinary pellets, this invention provides a titanium-containing pellet prepared from waste catalysts and its preparation method. This invention pre-modifies the vanadium-containing waste catalyst before using it in pelletizing, thereby effectively improving the compressive strength and V solidification rate of the pellets, increasing the green pellet yield, and eliminating the adverse effects of introducing waste catalysts.

[0013] To achieve the above objectives, the technical solution provided by the present invention is as follows: The first aspect of the present invention provides a titanium-containing pellet, wherein the raw pellet raw material mixture comprises iron ore powder, binder and modified titanium-containing waste catalyst, wherein the modified titanium-containing waste catalyst is obtained by calcining and modifying the titanium-containing waste catalyst under an inert atmosphere using calcium additives and metallurgical iron dust as modifiers.

[0014] The mechanism by which pellets solidify and achieve a certain strength is the interconnection of hematite crystals. The applicant conducted multiple tests at different stages on the spent catalyst pellets and summarized the reasons for the decrease in pellet strength and low V solidification rate. On one hand, some TiO2 in the spent catalyst added to the pellets forms ilmenite during high-temperature roasting. The formation of ilmenite inhibits the recrystallization and polycrystalline growth of hematite grains in the pellets, resulting in hematite grains existing mainly in granular form rather than interconnected into plates. On the other hand, the presence of unreacted TiO2 in the pores causes some pores to shrink during roasting, thus affecting the size and morphology of the hematite grains, resulting in poor strength of the pellets after roasting. Furthermore, the melting point of V2O5 in the spent catalyst is 690℃, while the roasting temperature of the pellets reaches as high as 1250℃, causing some V to volatilize, resulting in poor V solidification. Ammonium bisulfate on the surface of the waste catalyst is a strongly hydrophobic substance, which disrupts the capillary force formed between the pelletizing particles by water molecules, resulting in poor pelleting and a low qualified pellet rate.

[0015] Based on the above, this invention creatively employs a combination of calcium-based additives and metallurgical iron-containing dust to pre-calcine and modify titanium-containing waste catalysts. On one hand, the ammonium bisulfate on the surface of the waste catalyst is solidified by the alkaline oxides in the calcium-based additives and metallurgical iron-containing dust, significantly reducing its hydrophobicity. On the other hand, the CaO provided by the calcium-based additives, the FeO provided by the metallurgical iron-containing dust, and the SiO2 contained in the waste catalyst can form a CaO-SiO2-FeO low-melting-point liquid phase. When the modified catalyst is mixed with iron ore powder and bentonite to form pellets, the CaO-SiO2-FeO low-melting-point liquid phase is formed again during the pellet calcination process. This low-melting-point liquid phase, on the one hand, causes hematite grains to agglomerate and bond together, thereby improving the strength of the roasted pellets; on the other hand, it also melts and encapsulates components in the waste catalyst, such as TiO2 and titanium hematite, which are detrimental to the growth of iron crystals in the pellets, within the low-melting-point liquid phase, which further promotes the agglomeration of hematite grains. At the same time, the CaO-SiO2-FeO low-melting-point liquid phase also encapsulates and dissolves V2O5 in the waste catalyst powder, efficiently solidifying V in the pellets, thereby effectively reducing the volatilization of V in the waste catalyst and promoting the harmless utilization of waste catalysts by enterprises.

[0016] It should be noted that the control of the roasting environment during the modification treatment of the waste catalyst in this application is crucial. If the roasting treatment is carried out in an oxidizing environment, the high-temperature oxidizing roasting will make FeO easily oxidized to Fe2O3, resulting in a small amount of CaO-SiO2-FeO low-melting-point liquid phase formed, and thus the above-mentioned effect cannot be achieved.

[0017] According to any of the technical solutions described in the first aspect of the present invention, the compressive strength of the titanium-containing pellet product is 3600~3800 N·P. -1 The solidification rate of V element is over 98%.

[0018] According to any of the technical solutions described in the first aspect of the present invention, the amount of the modified titanium-containing waste catalyst added accounts for 8 to 20% of the total dry weight of the titanium-containing pellet raw material mixture.

[0019] According to any of the technical solutions described in the first aspect of the present invention, the amount of calcium additive and metallurgical iron-containing dust added is calculated based on the amount of CaO, SiO2, and FeO in the mixture composed of the modifier and titanium-containing waste catalyst. After the calculation, the mass ratio of CaO, SiO2, and FeO is (3~4):1:(10~11), and the mass of CaO is 22~30% of the mass of the titanium-containing waste catalyst.

[0020] By further optimizing and controlling the ratio of the modifier to the titanium-containing waste catalyst, especially controlling the mass ratio of CaO, SiO2, and FeO in the modified mixture, the melting point of the low-melting-point liquid phase can be lowered, allowing the liquid phase to form at a lower temperature. More preferably, the mass ratio of CaO, SiO2, and FeO in the green pellet raw material mixture is 1:(3~3.5):(12~13). It should be noted that when converting the mass of CaO, SiO2, and FeO, for example, CaO can originate not only from calcium additives but also from waste catalysts and metallurgical iron-containing dust; therefore, a unified conversion should be performed.

[0021] According to any of the technical solutions described in the first aspect of the present invention, the calcium additive is a substance or combination thereof containing CaO, Ca(OH)2 or CaCO3.

[0022] According to any of the technical solutions described in the first aspect of the present invention, the calcium additive is calcium carbonate sludge, the metallurgical iron-containing dust is OG coarse particles, the binder is bentonite, and the amount of binder added accounts for 1.5 to 2.5% of the total dry weight of the mixture of raw materials for titanium-containing pellets.

[0023] Calcium carbonate sludge mainly originates from industrial production and contains a high proportion of calcium carbonate and silicate minerals. OG coarse particles primarily originate from dust and sludge generated during steel smelting and contain a high proportion of FeO. Currently, China's sludge treatment and disposal technology has made some progress, but it still faces challenges such as large sludge production, poor matching between treatment technologies and sludge characteristics, and insufficient resource utilization. This invention, by using calcium carbonate sludge and OG coarse particles as modifiers, also facilitates the full utilization of solid waste generated by enterprises, achieving solid waste utilization, saving production costs, and demonstrating good economic benefits.

[0024] Furthermore, the TiO2 content (mass percentage) in the waste catalyst is preferably ≥80%; the TFe content (mass percentage) in the iron ore powder is preferably ≥50%.

[0025] According to any of the technical solutions described in the first aspect of the present invention, the moisture content of the titanium-containing pellet green pellets is 8.0~8.5%, and the particle size of the green pellets is 12~15.0 mm.

[0026] A second aspect of the present invention also provides a method for preparing titanium-containing pellets, comprising: Modifiers containing calcium additives and iron-containing metallurgical dust are roasted together with titanium-containing waste catalyst under an inert atmosphere to obtain modified titanium-containing waste catalyst. The pelletizing process involves mixing a modified titanium-containing waste catalyst with iron ore powder to obtain titanium-containing green pellets.

[0027] According to any of the technical solutions described in the second aspect of the present invention, the amount of modified titanium-containing waste catalyst added accounts for 8 to 20% of the total dry weight of the titanium-containing pellet raw material.

[0028] According to any of the technical solutions described in the second aspect of the present invention, the amount of calcium additive and metallurgical iron-containing dust added is calculated based on the amount of CaO, SiO2, and FeO in the mixture composed of modifier and titanium-containing waste catalyst. After the calculation, the mass ratio of CaO, SiO2, and FeO is (3~4):1:(10~11), and the mass of CaO is 22~30% of the mass of titanium-containing waste catalyst. More preferably, the mass ratio of CaO, SiO2, and FeO in the raw pellet mixture is 1:(3~3.5):(12~13).

[0029] According to any of the technical solutions described in the second aspect of the present invention, the calcium additive is a substance or combination thereof containing CaO, Ca(OH)2 or CaCO3.

[0030] According to any of the technical solutions described in the second aspect of the present invention, the calcium additive is calcium carbonate sludge, the metallurgical iron-containing dust is OG coarse particles, the binder is bentonite, and the amount of binder added accounts for 1.5 to 2.5% of the total dry weight of the titanium-containing pellet raw material.

[0031] According to any of the technical solutions described in the second aspect of the present invention, the modifier comprising calcium additives and metallurgical iron-containing dust is calcined together with titanium-containing waste catalyst under an inert atmosphere, wherein the calcination temperature is 1400~1500℃ and the calcination time is 15~30min. If the calcination temperature is too low, it is difficult to form a liquid phase, which will result in difficulty in encapsulating the waste catalyst TiO2, etc.; if the calcination temperature is too high, energy will be wasted.

[0032] According to any of the technical solutions described in the second aspect of the present invention, the pelletizing process of the mixture of modified titanium-containing waste catalyst and iron ore powder is performed, and the pelletizing process parameters include: disc rotation speed of 25~30 r / min and inclination angle of 45°±1°; furthermore, the moisture content of the titanium-containing green pellets obtained after pelletizing is 8.0~8.5%, the green pellet particle size is 12~15.0 mm, and the green pellet qualification rate reaches more than 92%.

[0033] According to any of the technical solutions described in the second aspect of the present invention, the method further includes: drying and oxidizing the obtained titanium-containing green pellets to obtain titanium-containing finished pellets, wherein during calcination, the temperature is first increased at 8~10℃ / min, preheated at 920~980℃ for 10~15min, and after preheating, the temperature is continued to rise until it reaches 1200~1300℃, at which point the temperature is stopped, and calcination is carried out for 15~25min to complete the oxidative calcination.

[0034] Furthermore, the compressive strength of the titanium-containing pellets obtained after oxidative calcination is 3600~3800 N·P. -1 The solidification rate of V element is over 98%.

[0035] Beneficial effects Compared with the prior art, the present invention can achieve the following technical effects: (1) The present invention pre-modifies the titanium-containing waste catalyst and then pelletizes it together with iron ore powder and other pelletizing raw materials to prepare titanium-containing pellets. Through the modification treatment of the titanium-containing waste catalyst, a CaO-SiO2-FeO low-melting-point liquid phase can be formed in advance, so that the modifier and the waste catalyst can be fully combined. Then, in the subsequent pelletizing process, a low-melting-point liquid phase will be formed again, which can not only promote the connection of hematite grains into plates during the oxidative roasting of the pellets, but also encapsulate or dissolve the components in the waste catalyst such as TiO2 and titanium hematite that are not conducive to the growth of iron crystals in the pellets, as well as V2O5 in the waste catalyst. Therefore, it is beneficial to improve the compressive strength of the pellets and greatly reduce the volatilization of V. In particular, it solves the technical problem in the prior art that it is difficult to simultaneously ensure the compressive strength of the waste catalyst pellets and the solidification rate of V.

[0036] (2) The present invention further optimizes the addition of calcium additives and metallurgical iron dust to control the mass ratio of CaO, SiO2 and FeO in the raw material mixture of green pellets, so that the pellets can start to form a low melting point liquid phase of CaO-SiO2-FeO at a lower temperature (around 1100℃), which is beneficial to further promote the bonding of hematite grains.

[0037] (3) The present invention uses calcium carbonate sludge and OG coarse particles as modifiers to modify the waste catalyst, thereby effectively improving the utilization rate of waste catalysts and solid waste such as calcium carbonate sludge and OG coarse particles by enterprises.

[0038] (4) This invention weakens the hydrophobicity of the modified waste catalyst surface by pre-calcining, thereby enhancing the hydrophilicity of the material surface and allowing for more uniform moisture distribution. This is beneficial for the subsequent process of bentonite absorbing water, expanding, and bonding to form pellets. At the same time, the high-temperature treatment homogenizes the particle characteristics of the modified waste catalyst, creating conditions for the close packing of particles during pelleting. This increases the contact points between particles, thereby enhancing the van der Waals forces between the pelletizing materials. This can enhance the mechanical interaction between particles and significantly improve the yield of green pellets, solving the problem of low yield in the prior art. Attached Figure Description

[0039] Figure 1 This is a schematic flowchart of a method for preparing titanium-containing pellets according to an embodiment of the present invention; Figure 2 Phase diagram calculation for the melting point of the CaO-SiO2-FeO mixture in this embodiment of the invention; Figure 3 This is a scanning electron microscope image of rutile TiO2 particles in the waste catalyst of this invention embodiment; Figure 4 This is a diagram illustrating the consolidation mechanism of the spent catalyst pellets in this embodiment of the invention. Figure 5 This is a scanning electron microscope image of the liquid phase bonding effect of CaO-SiO2-FeO in an embodiment of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0041] It should be noted that concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to about 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0042] Next, this embodiment of the invention will be illustrated using calcium carbonate sludge and OG coarse particles as modifiers. The components of calcium carbonate sludge, OG coarse particles, waste catalyst, iron ore powder, and bentonite are shown in Tables 1-5 below. However, the specific composition of each component, as well as the selection of the types of calcium additives and metallurgical iron-containing dust, are not limited by the embodiments. For example, quicklime can also be used as the calcium additive, and iron-containing dust can also be used as rolled iron oxide scale.

[0043] Table 1. Main chemical components of calcium carbonate sludge, wt.%

[0044] Table 2. Main chemical components of OG coarse particles, wt.%

[0045] Table 3. Main chemical components of spent catalyst, wt.%

[0046] Table 4. Main chemical components of iron ore powder (Zhangzhuang Mine), wt.%

[0047] Table 5. Main chemical components of bentonite, wt.%

[0048] Example 1 The preparation method of titanium-containing pellets in this embodiment, combined with Figure 1 As shown, the specific implementation steps are as follows: Step 1: Modification and treatment of spent catalysts (1) Take the waste catalyst, remove the blockage fly ash from the waste catalyst, and crush the separated waste catalyst body into powder; take calcium carbonate sludge and OG coarse particles, dry and crush them into powder, and then mix the waste catalyst, calcium carbonate sludge and OG coarse particle powder through a 100-mesh sieve according to the mass ratio to obtain a modified waste catalyst mixture, wherein the mass percentage of particles with a particle size of 0.074 mm after sieving is ≥98%. Weigh the mass of the mixture M1 and detect the mass fraction of V C1 in the mixture.

[0049] (2) The modified waste catalyst mixture was roasted at 1400℃ under an inert atmosphere for 20 minutes to obtain the modified titanium-containing waste catalyst.

[0050] The inert atmosphere helps prevent the oxidation of FeO in the modifier, facilitating the better formation of the CaO-SiO2-FeO low-melting-point liquid phase in the pellets. Pre-mixing the waste catalyst and modifier helps ensure that the waste catalyst and modifier are always tightly bound during the later pelletizing and roasting process. This better prevents the waste catalyst from generating ilmenite and volatilizing V2O5 in the pellets when the liquid phase is formed during roasting, thereby reducing the impact of the addition of waste catalyst on the pellet strength and V solidification rate.

[0051] Step 2: Ball Formation Processing Zhangzhuang ore, bentonite and modified titanium-containing waste catalyst were weighed and mixed in proportion, with the moisture content controlled at 7.5%. The mixture was added to a three-dimensional mixer and mixed for 6 minutes to obtain green pellet mixture. Its mass was weighed and recorded as Q1.

[0052] The green pellet mixture was fed in batches into a disc pelletizer for pelletizing. The main parameters of the disc pelletizer were: diameter Φ = 1000 mm, disc rotation speed 25 r / min, and inclination angle 45° (±1°). Each batch of green pellet mixture (pelletizing material) was 2 kg (±0.1 kg), and the pelletizing time was approximately 20 minutes. Specifically, the processed pelletizing material (green pellet mixture) was added to the disc pelletizer to replenish moisture and create a core of suitable particle size. Then, pelletizing material was continuously added to the disc pelletizer to replenish moisture and allow the core to grow into pellets. The moisture content of the green pellets was controlled at 8%, resulting in titanium-containing green pellets (particle size approximately 12 mm). The total mass of qualified green pellets was measured as Q2.

[0053] Step 3: Drying and roasting the pellets. Titanium-containing green pellets were placed in a 200°C forced-air drying oven at a flow rate of 0.4 m / s for 8 minutes. The dried pellets were then placed in a muffle furnace for calcination using a furnace-based heating regime. The temperature was increased at a rate of 10°C / min, and stabilized at 950°C for 15 minutes for preheating. After preheating, the temperature was further increased to 1250°C and held for 20 minutes to complete the calcination, yielding the finished titanium-containing pellets. The mass of the finished pellets was weighed and recorded as M2, and the mass percentage of vitamin V in the finished pellets was determined and recorded as C2.

[0054] Performance testing: Take a batch of green pellets (Q1) and pelletize it. Screen out green pellets in the range of 9-16mm, weigh them to obtain Q2, and calculate the percentage of Q2 in the total mass of the mixture as the green pellet pass rate. η ,Right now: η =Q2 / Q1×100%.

[0055] The compressive strength of the calcined titanium-containing pellets was tested according to ISO 4700-1996 standard using a pellet compressive strength tester (WDW-QT-10). Twelve calcined pellets of similar size were selected, and one pellet was tested at a time. The average value was calculated as the pellet compressive strength.

[0056] The vanadium content was determined according to the national standard GB / T6730.76-2017. The vanadium content was determined using a dissolution and ICP-OES (inductively coupled plasma optical emission spectrometry) method. 0.25g of crushed pellet powder was added to a mixed solution of 10ml of 65% HNO3 and 5ml of 70% HClO4, and heated continuously until completely dissolved. The mixing, pelletizing, and drying processes are physical deformation processes and do not cause vanadium volatilization. The pellets are oxidized during preheating and calcination, resulting in an increase in mass. Therefore, the pelletizing process... .

[0057] In this embodiment, the titanium-containing pellet raw material made from waste catalyst consists of Zhangzhuang mineral powder, waste catalyst (SRC catalyst), bentonite, calcium carbonate sludge and OG coarse particles. The dry material mass ratio of the pelletizing material is shown in Table 6.

[0058] Table 6. Pelletizing raw material ratio in Example 1, g

[0059] Comparative Example 1 This comparative example serves as a baseline experiment for preparing ordinary pellets. The pellet preparation process in this comparative example is the same as in Example 1, except that no modified waste catalyst is added to the pellets. In this comparative example, the dry material of the pellet mixture contains: 1760g of Zhangzhuang magnetite and 40g of bentonite. The mixture is then added to a disc pelletizer to replenish moisture and produce pellets. After pelletizing, the green pellet qualification rate is calculated, and the compressive strength of the roasted pellets is tested. The experimental results are recorded in Table 7.

[0060] Comparative Example 2 The pellet preparation process in this comparative example is the same as in Example 1, except that waste catalyst is added to the pellets, but it is not modified. The mass of each component in the pellet mixture of this comparative example is as follows: Zhangzhuang magnetite: 1760g, waste catalyst: 200g, bentonite: 40g. Then, it is added to a disc pelletizer to replenish water and produce pellets. After pelletizing, the green pellet qualification rate is calculated, and the compressive strength and vanadium solidification rate of the roasted pellets are tested. The experimental results are recorded in Table 7.

[0061] Comparative Example 3 The pellet preparation process in this comparative example is the same as in Example 1, except that: after simply mixing calcium carbonate sludge, OG coarse particles and waste catalyst, no roasting pretreatment is performed. Instead, after being proportioned with magnetite and bentonite, the mixture is directly added to a disc pelletizer to supplement water and produce pellets. After pelletizing, the green pellet qualification rate is calculated, and the compressive strength and vanadium solidification rate of the roasted pellets are tested. The experimental results are recorded in Table 7.

[0062] Comparative Example 4 The pellet preparation process of this comparative example is the same as that of Example 1, except that: no inert atmosphere protection is introduced during the roasting pretreatment stage after the waste catalyst and modifier are fully mixed. After pretreatment, the pellets are mixed with magnetite and bentonite raw materials and then pelletized. After pelletizing, the qualified rate of green pellets is calculated and then roasted. After roasting, the compressive strength and vanadium solidification rate of the pellets are tested. The experimental results are recorded in Table 7.

[0063] Table 7. Green pellet pass rate, pellet strength, and V-curing rate in Example 1 and Comparative Examples 1-4

[0064] The following conclusions can be drawn from the data in Table 7: (1) Through the experiments of Comparative Example 1 and Example 1, it can be found that mixing calcium carbonate sludge, OG coarse particles and waste catalyst, and then calcining and modifying them under inert gas, and then mixing them with magnetite and bentonite for pellet production, can ensure the green pellet qualification rate and the pellet strength is almost unaffected, which meets the requirements for blast furnace feeding. This shows that the modified waste catalyst in this invention can be used in the pellet production process, which is beneficial to saving pelletizing materials and will not have a negative impact on the pellet due to the introduction of waste catalyst.

[0065] (2) Through the experiments of Comparative Examples 1 and 2, it can be found that when the waste catalyst is directly mixed with magnetite and bentonite for pellet production, the hydrophobicity of the waste catalyst surface causes the green pellet qualification rate to decrease from 90.13% to 81.52%, and the strength of the resulting pellets is significantly reduced, from 3701 N / P of ordinary pellets to 2212 N / P. At the same time, only 90.81% of the V element in the added waste catalyst is solidified in the pellets, that is, 9.19% volatilizes away from the pellets. This is because, on the one hand, TiO2 in the waste catalyst added to the pellets partially forms ilmenite during high-temperature roasting. The formation of ilmenite inhibits the recrystallization and polycrystalline growth of hematite grains in the pellet ore, resulting in hematite grains mainly existing in the form of particles and not connected into plates; on the other hand, the presence of unreacted TiO2 in the pores causes some pores to shrink during roasting, thereby affecting the size and morphology of hematite grains, resulting in poor strength of the pellets after roasting. Meanwhile, V2O5 will volatilize and leave the pellets during the roasting process.

[0066] (3) Through the experiments of Comparative Examples 2 and 3, it can be found that after adding calcium carbonate sludge, OG coarse particles and waste catalyst, the green pellet qualification rate increased from 81.52% to 84.31%, the strength of waste catalyst pellets increased from 2212 N / P to 3227 N / P, and the V solidification rate increased from 90.81% to 92.76%. This is because calcium carbonate sludge and OG coarse particles are mainly composed of CaO and FeO. The addition of these components weakens the hydrophobicity of ammonium bisulfate on the surface of some catalysts, slightly improving the green pellet qualification rate. At the same time, the high-temperature calcination process will form a certain amount of CaO-SiO2-FeO low-melting-point liquid phase, which makes the crystals bond together, thereby improving the strength of the calcined pellets, encapsulating and dissolving V2O5 in the waste catalyst powder, and improving the V solidification rate.

[0067] However, since the modifier and spent catalyst are mixed at room temperature, the solidification effect of the alkaline oxides in the modifier with ammonium bisulfate is weak, resulting in limited improvement in hydrophilicity and a limited increase in the green pellet yield. Because the amounts of calcium carbonate sludge, OG coarse particles, and spent catalyst are relatively small, their contact opportunities within the pellets are low. Furthermore, high-temperature oxidative roasting causes FeO to be predominantly oxidized to Fe2O3, resulting in a smaller amount of the CaO-SiO2-FeO low-melting-point liquid phase formed. Therefore, the CaO-SiO2-FeO low-melting-point liquid phase has fewer opportunities to dissolve and encapsulate components such as TiO2 and ilmenite (which are detrimental to iron crystal growth) and V2O5 in the subsequent pellets, leading to a relatively poor improvement in pellet strength and V solidification rate.

[0068] (4) Through the experiments of Comparative Examples 3 and 4, it can be found that the mixture of calcium carbonate sludge, OG coarse particles and waste catalyst, followed by roasting and pelletizing with magnetite and bentonite, has a certain effect on improving the qualified rate of green pellets, pellet strength and V solidification effect. This is because during the pre-roasting process of waste catalyst mixed with modifier, the alkaline oxide in the modifier is highly active, effectively solidifying the ammonium bisulfate on the surface of the waste catalyst and improving hydrophilicity; at the same time as the formation of the CaO-SiO2-FeO low-melting-point liquid phase, it encapsulates and dissolves components such as TiO2 and timolite, which are not conducive to the growth of iron crystals in the pellets, as well as V2O5. Compared with the simultaneous mixing and roasting of waste catalyst, modifier, magnetite and bentonite, the pre-roasted waste catalyst has more opportunities to come into contact with the CaO-SiO2-FeO low-melting-point liquid phase. During the subsequent pellet roasting process, the components such as TiO2 and timolite in the waste catalyst, which are not conducive to the growth of iron crystals in the pellets, as well as V2O5, are still in a certain encapsulated and dissolved state.

[0069] (5) Through the experiments of Comparative Example 4 and Example 1, it can be found that if air is directly introduced during the roasting pretreatment, the FeO component in the OG coarse particles will be oxidized by the air in advance, the amount of alkaline oxides will be reduced, and the formation of the CaO-SiO2-FeO low-melting-point liquid phase in the pellet roasting will be affected, thereby reducing the effect of the modifier. However, the introduction of inert gas during the roasting pretreatment can effectively avoid the premature oxidation of FeO, thereby giving full play to the effect of the modifier, promoting the consolidation of ammonium bisulfate and the formation of more CaO-SiO2-FeO low-melting-point liquid phase, increasing the chance of encapsulation and dissolution of components such as TiO2 and ilmenite that are not conducive to the growth of iron crystals in the pellets and V2O5, and improving the green pellet qualification rate, pellet strength and V solidification rate.

[0070] Combination Figure 3 As shown, when spent catalyst is directly introduced into the pellets, the strength of the pellets decreases due to the formation of ilmenite and the transformation of TiO2 crystal form. Specifically, as... Figure 3As indicated by the orange markings, on the one hand, the formation of ilmenite inhibits the recrystallization and polycrystalline growth of hematite grains in the pellets, resulting in hematite grains existing mainly in granular form and not connected into plates. On the other hand, as... Figure 3 As indicated by the red markings, the presence of unreacted TiO2 in the pores causes some pores to shrink during roasting, thus affecting the size and morphology of hematite grains and resulting in decreased strength of the pellets after roasting. This invention, by pre-modifying the spent catalyst, not only solves the problems of reduced green pellet yield and pellet strength caused by directly introducing spent catalyst into the pellets, but also addresses the issue of low V-curing rate.

[0071] This embodiment utilizes a mixture of calcium carbonate sludge and OG coarse-grained waste catalyst, and optimizes the mass ratio of CaO, SiO2, and FeO in the modified mixture, thereby resulting in a modifier with a lower melting point (e.g., Figure 2 As shown). Figure 5 As shown, after CaO, SiO2, and FeO begin to react, the low-melting-point CaO-SiO2-FeO liquid phase formed quickly melts, generating a liquid phase with good mass transfer that flows between the grains. Components in the pellets that are detrimental to iron crystal growth, such as TiO2 and ilmenite, dissolve in this liquid phase and precipitate upon cooling. This reduces the impact of spent catalyst on the strength of the roasted pellets. Hematite grains can also bond together in sheets during roasting, thereby improving the strength of the roasted pellets and eliminating the negative impact of spent catalyst on the roasting strength of the pellets. Simultaneously, when dissolving the spent catalyst, the CaO-SiO2-FeO liquid phase encapsulates and dissolves V2O5 in the spent catalyst, efficiently solidifying V within the pellets and effectively reducing the volatilization of V from the spent catalyst. Furthermore, the addition of coarse OG particles improves the particle size distribution and surface properties of the raw materials, enhances the mechanical interaction between the mixed particles, and thus significantly improves the yield of green pellets.

[0072] Specifically, in combination Figure 4As shown, during the oxidative roasting process, the pellets shrink, forming pores. CaO reacts with TiO2 to form CaTiO3, and TiO2 undergoes a crystal transformation from anatase to rutile. When the temperature reaches 902℃, TiO2 reacts with Fe2O3 to form Fe2TiO5 around the Fe2O3 grains. When the temperature is further increased to 1094℃, CaO, SiO2, and FeO form a Ca-Fe-Si-O liquid phase. This liquid phase melts CaTiO3, Fe2TiO5, and TiO2 to form a Ca-Fe-Si-Ti-O liquid phase, which fills the pellet pores. After roasting, Ti in the Ca-Fe-Si-Ti-O liquid phase precipitates as secondary FeTiO5. The addition of the modifier forms a low-melting-point liquid phase that fills the pores created by the shrinkage of iron oxides and the transformation of TiO2 crystals in the pellets. It also dissolves TiO2 and FeTiO5, which inhibits the recrystallization and growth of iron oxides, eliminating inclusions between iron oxide grains. Secondary FeTiO5 is formed after the iron oxide recrystallization is complete. Through this process, the adverse effects of spent catalyst on the pellets are largely eliminated, thereby significantly improving the compressive strength of the pellets.

[0073] Example 2 The specific steps of the preparation method of titanium-containing pellets in this embodiment are as follows: Step 1: Modification and treatment of spent catalysts (1) Take the waste catalyst, remove the blockage fly ash from the waste catalyst, and crush the separated waste catalyst body into powder; take calcium carbonate sludge and OG coarse particles, dry and crush them into powder; after passing the waste catalyst, calcium carbonate sludge and OG coarse particle powder through a 100-mesh sieve, mix them evenly according to the mass ratio to obtain a modified waste catalyst mixture. In this embodiment, the mass ratio of waste catalyst, calcium carbonate sludge and OG coarse particles is 9:2:8.

[0074] (2) The modified waste catalyst mixture was roasted at 1500℃ under an inert atmosphere for 15 minutes to obtain the modified titanium-containing waste catalyst.

[0075] Step 2: Ball Formation Processing Zhangzhuang ore, bentonite, and modified titanium-containing waste catalyst were weighed and mixed in a certain proportion, with the moisture content controlled at 9%. The mixture was then added to a three-dimensional mixer and mixed for 8 minutes to obtain a green pellet mixture. The mass percentages of Zhangzhuang ore, bentonite, and modified titanium-containing waste catalyst in the dry green pellet mixture were 81.5%, 2.5%, and 16%, respectively.

[0076] The green pellet mixture was fed in batches into a disc pelletizer for pelletizing. The main parameters of the disc pelletizer were: diameter Φ = 1000 mm, disc rotation speed 30 r / min, inclination angle 45° (±1°), and pelletizing time approximately 25 min. Specifically, the processed pelletizing material was added to the disc pelletizer to replenish moisture and create a core of suitable particle size. More pelletizing material was then added to the disc pelletizer, and moisture was replenished to allow the core to grow into pellets. The moisture content of the green pellets was controlled at 8.5%, resulting in titanium-containing pellets with a particle size of 15.0 mm and a green pellet qualification rate of 92.14%.

[0077] Step 3: Drying and roasting the pellets. The titanium-containing green pellets were placed in a 180°C forced-air drying oven for 15 minutes, with a forced-air flow rate of 0.6 m / s. The dried pellets were then calcined in a muffle furnace using a furnace-based heating regime. The temperature was increased at 8°C / min, and stabilized at 920°C for 10 minutes for preheating. After preheating, the temperature was further increased to 1200°C and held for 25 minutes to complete the calcination, yielding the finished titanium-containing pellets. The compressive strength of the titanium-containing pellets obtained in this embodiment is 3598 N·P. -1 The solidification rate of V element was 98.27%.

[0078] Example 3 The specific steps of the preparation method of titanium-containing pellets in this embodiment are as follows: Step 1: Modification and treatment of spent catalysts (1) Take the waste catalyst, remove the blockage fly ash from the waste catalyst, and crush the separated waste catalyst body into powder; take calcium carbonate sludge and OG coarse particles, dry and crush them into powder; after passing the waste catalyst, calcium carbonate sludge and OG coarse particle powder through a 100-mesh sieve, mix them evenly according to the mass ratio to obtain a modified waste catalyst mixture. In this embodiment, the mass ratio of waste catalyst, calcium carbonate sludge and OG coarse particles is 11:3:11.

[0079] (2) The modified waste catalyst mixture was roasted at 1450℃ under an inert atmosphere for 30 minutes to obtain the modified titanium-containing waste catalyst.

[0080] Step 2: Ball Formation Processing Zhangzhuang ore, bentonite, and modified titanium-containing waste catalyst were weighed and mixed in a certain proportion, with the moisture content controlled at 8%. The mixture was then added to a three-dimensional mixer and mixed for 7 minutes to obtain a green pellet mixture. The mass percentages of Zhangzhuang ore, bentonite, and modified titanium-containing waste catalyst in the dry green pellet mixture were 90.5%, 1.5%, and 8%, respectively.

[0081] The green pellet mixture was fed in batches into a disc pelletizer for pelletizing. The main parameters of the disc pelletizer were: diameter Φ = 1000 mm, disc rotation speed 28 r / min, inclination angle 45° (±1°), and pelletizing time approximately 25 min. Specifically, the processed pelletizing material was added to the disc pelletizer to replenish moisture and create a core of suitable particle size. More pelletizing material was then added to the disc pelletizer, and moisture was replenished to allow the core to grow into pellets. The moisture content of the green pellets was controlled at 8.3%, resulting in titanium-containing pellets with a particle size of 13.0 mm and a green pellet qualification rate of 92.47%.

[0082] Step 3: Drying and roasting the pellets. The titanium-containing green pellets were placed in a 210°C forced-air drying oven for 5 minutes, with a forced-air flow rate of 0.5 m / s. The dried pellets were then calcined in a muffle furnace using a furnace-based heating regime. The temperature was increased at 9°C / min, and stabilized at 980°C for 12 minutes for preheating. After preheating, the temperature was further increased to 1300°C and held for 15 minutes to complete the calcination, yielding the finished titanium-containing pellets. The compressive strength of the titanium-containing pellets obtained in this example is 3643 N·P. -1 The V element curing rate was 98.31%.

[0083] Example 4 The preparation method of titanium-containing pellets in this embodiment is basically the same as in Example 3, with the main difference being that only calcium carbonate sludge is added during the modification treatment of the waste catalyst in this embodiment, without the addition of OG coarse particles. The results show that when only calcium carbonate sludge is added to modify the waste catalyst, the compressive strength and V element solidification rate of the resulting pellets are effectively improved compared to existing technologies, but the effect is slightly worse than in Example 3, especially the green pellet qualification rate, which is only 87.22% lower than in Example 3.

[0084] The scope of protection of this invention is defined only by the claims. Thanks to the teachings of this invention, those skilled in the art will readily recognize that alternative structures to the structures disclosed herein can be used as feasible alternative implementations, and that the implementations disclosed herein can be combined to produce new implementations, which also fall within the scope of the appended claims.

Claims

1. A titanium-containing pellet, characterized in that, The raw material mixture for the pellets contains iron ore powder, binder and modified titanium-containing waste catalyst. The modified titanium-containing waste catalyst is obtained by roasting and modifying the titanium-containing waste catalyst under an inert atmosphere using calcium additives and metallurgical iron dust as modifiers.

2. The titanium-containing pellets according to claim 1, characterized in that, The compressive strength of the finished titanium-containing pellets is 3600~3800 N·P. -1 The solidification rate of V element is over 98%.

3. The titanium-containing pellets according to claim 1 or 2, characterized in that, The amount of the modified titanium-containing waste catalyst added accounts for 8-20% of the total dry weight of the titanium-containing pellet raw material mixture; The amount of calcium additive and metallurgical iron dust added is calculated based on the amount of CaO, SiO2 and FeO in the mixture of modifier and titanium-containing waste catalyst. After the calculation, the mass ratio of CaO, SiO2 and FeO is (3~4):1:(10~11), and the mass of CaO is 22~30% of the mass of titanium-containing waste catalyst.

4. The titanium-containing pellets according to claim 3, characterized in that, The calcium additive is a substance or combination thereof containing CaO, Ca(OH)2 or CaCO3.

5. The titanium-containing pellets according to claim 4, characterized in that, The calcium additive is calcium carbonate sludge, the metallurgical iron dust is OG coarse particles, the binder is bentonite, and the amount of binder added accounts for 1.5~2.5% of the total dry weight of the raw material mixture of titanium-containing pellets.

6. The titanium-containing pellets according to claim 5, characterized in that, The moisture content of the titanium-containing pellets is 8.0~8.5%, the particle size is 12~15.0 mm, and the qualified rate of the pellets reaches over 92%.

7. A method for preparing titanium-containing pellets as described in any one of claims 1-6, characterized in that, include: Modifiers containing calcium additives and iron-containing metallurgical dust are roasted together with titanium-containing waste catalyst under an inert atmosphere to obtain modified titanium-containing waste catalyst. The pelletizing process involves mixing a modified titanium-containing waste catalyst with iron ore powder to obtain titanium-containing green pellets.

8. The method for preparing titanium-containing pellets according to claim 7, characterized in that, The modifier containing calcium additives and metallurgical iron dust is roasted together with titanium-containing waste catalyst under an inert atmosphere, wherein the roasting temperature is 1400~1500℃ and the roasting time is 15~30min.

9. The method for preparing titanium-containing pellets according to claim 7 or 8, characterized in that, Also includes: The obtained titanium-containing green pellets are dried and oxidized to obtain titanium-containing finished pellets. During calcination, the temperature is first increased at 8~10℃ / min, and then preheated at 920~980℃ for 10~15min. After preheating, the temperature is increased again until it reaches 1200~1300℃, then the temperature is stopped and calcined for 15~25min to complete the oxidative calcination.

10. The method for preparing titanium-containing pellets according to claim 7 or 8, characterized in that, The pelletizing process involves a mixture of modified titanium-containing waste catalyst and iron ore powder. The pelletizing process parameters include: a disc rotation speed of 25~30 r / min and an inclination angle of 45°±1°.

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