A method for preparing white cloud bo iron ore fluxed pellets with low reduction expansion and high reduction degree

Abstract

The application relates to a preparation method of white cloud ore smelting pellets with low reduction expansion and high reduction degree, and belongs to the technical field of iron ore pellet production. By adjusting the SiO2 and CaO contents in the mixture, the binary basicity R2 is 0.6-0.9, and the liquid phase content in the pellets after oxidation roasting is controlled to be 12%-15%; under the liquid phase content condition, the MgO mass fraction in the pellets is controlled to be 1.8%-2.5%, the MgO is preferentially provided by the iron ore raw material, and MgO powder is supplemented when the content is insufficient; the MgO reacts with the iron oxide to form Mg x Fe 3‑x O4, the excessive growth of hematite grains under the high liquid phase condition is limited, the reduction degree caused by the increase of the liquid phase is compensated, and the loss of the solidification strength caused by the excess MgO is avoided. The obtained pellets have a compression strength of not less than 2500 N / piece, a reduction expansion index of not higher than 15%, and a reduction degree of not less than 65%.

Description

Technical Field

[0001] This invention belongs to the field of iron ore pellet production technology, and specifically relates to a preparation method that improves the reducibility of pellets by regulating iron oxide grain size, based on suppressing abnormal reduction expansion of flux-induced pellets from Bayan Obo iron ore. Background Technology

[0002] As blast furnace burden structures trend towards higher pellet ratios, flux-modified pellets have significant application value due to their ability to partially fulfill slag-forming functions and improve burden structure. Bayan Obo iron ore is a typical complex and refractory iron ore, containing various impurities such as K, Na, F, and S in addition to iron oxides. When preparing oxide pellets from this type of iron ore, it is necessary not only to meet compressive strength requirements but also to control metallurgical properties such as reduction expansion, degree of reduction, and reduction pulverization.

[0003] The Bayan Obo iron ore deposit has relatively high contents of alkali metals such as K and Na, which can easily have an adverse effect on the phase evolution and reduction behavior of pellets during oxidative roasting and reduction processes. Existing technologies have proposed that by introducing components rich in SiO2 and CaO to increase the amount of liquid phase generated during the oxidative roasting stage, it is possible to promote the enrichment of alkali metals in the liquid phase and reduce their migration into iron oxides, thereby inhibiting the abnormal reduction expansion of high-alkali metal pellets.

[0004] However, for Bayan Obo flux pellets with a binary basicity of 0.6–0.9, simply increasing the liquid phase content to reduce reduction expansion has significant limitations. As the amount of liquid phase generated increases, while promoting pellet consolidation, the liquid phase also accelerates hematite grain growth and fills the pores between iron oxide particles, making the pellet structure more compact. This increases the resistance to the diffusion of reducing gas into the pellet interior, leading to a decrease in the pellet's reducibility. Therefore, there is a mutually restrictive relationship between low reduction expansion and high reducibility.

[0005] Current technologies primarily focus on improving the reducing expansion and compressive strength of high-alkali metal pellets by increasing the liquid phase, but lack further compensatory and control measures to address the decrease in reducibility caused by high liquid phase conditions. Therefore, how to control the iron oxide grain structure and reduce the reduction loss caused by high liquid phase while maintaining the inhibitory effect of the liquid phase on abnormal reducing expansion is a technical problem that needs to be further solved in the preparation of flux-dependent pellets from Bayan Obo iron ore. Summary of the Invention

[0006] To address the problem that existing liquid phase control methods can reduce abnormal reduction expansion in Bayan Obo flux-treated pellets, but high liquid phase content leads to coarsening of hematite grains, denser pellet structure, and decreased reducibility, this invention provides a method for preparing Bayan Obo iron ore flux-treated pellets that balances low reduction expansion and high reducibility. This invention controls the liquid phase of the pellets after oxidative roasting within a range that effectively suppresses abnormal reduction expansion, and further regulates the MgO content within the pellets under these liquid phase conditions, allowing MgO to react with iron oxides to form MgO. x Fe 3-x O4 limits the excessive growth of hematite grains to compensate for the loss of reduction caused by the high liquid phase; at the same time, by limiting the upper limit of MgO content in the pellets, the excessive inhibition of hematite recrystallization is avoided, which would cause a decrease in the compressive strength of the pellets, thereby achieving synergistic control of reduction expansion, reduction degree and compressive strength.

[0007] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing flux-dependent pellets of Bayan Obo iron ore that balances low reducing expansion and high reducing power, comprising the following steps: Iron ore raw materials containing Bayan Obo iron ore are mixed with limestone and bentonite, and MgO powder is selectively added according to the MgO content of each raw material to obtain a mixture. The SiO2 and CaO content in the mixture is controlled by adjusting the amount of limestone and bentonite added, so that the binary basicity R2 of the mixture (CaO / SiO2) is 0.6 to 0.9. The mixture is pelletized to obtain green pellets, wherein the preferred particle size of the green pellets is 10-13 mm. The green pellets are preheated, preferably at a temperature of 900–950°C and for a time of 8–10 min, ensuring that the FeO mass fraction of the preheated pellets is not higher than 8%. The preheated pellets are subjected to oxidative roasting. The preferred oxidative roasting temperature is 1250–1280℃ and the preferred roasting time is 15–20 min, so that the liquid phase content in the pellets after oxidative roasting is controlled at 12%–15%. This liquid phase range is used to suppress abnormal reduction expansion. On this basis, the MgO mass fraction in the pellets after oxidative roasting is controlled at 1.8%–2.5% to compensate for the reduction loss under high liquid phase conditions. The MgO is preferentially provided by the MgO contained in the raw material itself. When its content is insufficient, MgO powder is added to suppress the excessive growth of hematite grains under high liquid phase conditions.

[0008] This invention regulates the grain structure of iron oxides by controlling the MgO content within the pellets; the MgO within the pellets is preferentially provided by the raw materials themselves, and MgO powder is added when insufficient, but the added MgO powder is not used solely to promote the formation of the liquid phase.

[0009] In a preferred embodiment of the present invention, the mass fraction of SiO2 in the mixture is not less than 4.5%, and the mass fraction of CaO is not less than 3.4%.

[0010] In a preferred embodiment of the present invention, the mass percentages of SiO2, CaO and Fe2O3 in the liquid phase are 30%–35%, 25%–35% and 25%–30%, respectively.

[0011] In a preferred embodiment of the present invention, the binary basicity R2=CaO / SiO2 of the mixture is 0.6 to 0.9.

[0012] This invention regulates the SiO2 and CaO content by adjusting the amount of limestone and bentonite added, thereby ensuring flux alkalinity while providing the component conditions for forming a suitable liquid phase of 12% to 15%.

[0013] In a preferred embodiment of the present invention, the particle size of the green pellets is 10-13 mm.

[0014] In a preferred embodiment of the present invention, the preheating temperature is 900-950°C, the preheating time is 8-10 min, and the FeO mass fraction of the pellets after preheating is not higher than 8%.

[0015] In a preferred embodiment of the present invention, the oxidation calcination temperature is 1250–1280°C, and the oxidation calcination time is 15–20 min.

[0016] During oxidative roasting, MgO reacts with iron oxides to form Mg. x Fe 3-x O4 can inhibit excessive recrystallization and growth of hematite grains, thus refining the iron oxide particles. During reduction, this structure can reduce the volume expansion caused by the phase transformation of hematite to magnetite, and improve the degree of pellet reduction by refining the particles and increasing the reduction reaction interface. Excessive MgO content in the pellets will significantly inhibit hematite recrystallization and reduce the compressive strength of the pellets, therefore it should not exceed the above-mentioned limits.

[0017] This invention does not simply combine liquid phase regulation and MgO addition. Instead, it further utilizes MgO to compensate for the decrease in reduction degree caused by high liquid phase content, based on the premise that an appropriate liquid phase has already suppressed abnormal reducing expansion. Insufficient liquid phase leads to excessive reducing expansion, while excessive liquid phase reduces the reduction degree. Excessive MgO content within the pellets decreases compressive strength. Therefore, by matching the liquid phase content with the MgO content within the pellets, the reducing expansion index, reduction degree, and compressive strength are synergistically controlled.

[0018] The second technical solution of the present invention is a flux-sensitive pellet of Bayan Obo iron ore prepared by the above-mentioned preparation method.

[0019] The flux-type pellets of Bayan Obo iron ore prepared by the method of the present invention have a compressive strength of not less than 2500 N / pellet, a reduction expansion index of not more than 15%, and a reduction degree of not less than 65%.

[0020] The third technical solution of the present invention is the application of the above-mentioned Bayan Obo iron ore flux pellets in blast furnace ironmaking, wherein the Bayan Obo iron ore flux pellets are used as flux oxide pellets in blast furnace charge.

[0021] The fourth technical solution of the present invention is a method for compensating for the loss of high liquid phase reduction in flux pellets of Bayan Obo iron ore, using the above-mentioned preparation method.

[0022] For flux-induced pellets from Bayan Obo, a suitable liquid phase can reduce abnormal reduction expansion, but excessive liquid phase will promote coarsening and densification of hematite grains, leading to a decrease in the degree of reduction. This invention, based on a liquid phase content controlled at 12%–15%, utilizes the reaction of MgO with iron oxides to form Mg... x Fe 3-x O4 limits excessive grain growth to compensate for the loss of reduction degree; at the same time, it limits the MgO content in the pellets to avoid excessive inhibition of hematite recrystallization and reduction of compressive strength, thus taking into account the reduction expansion index, reduction degree and compressive strength.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention addresses the problem of reduced reducibility when liquid-phase controlled flux pellets of Bayan Obo. While maintaining the inhibitory effect of liquid phase on abnormal reduction expansion, it reduces the adverse effect of hematite grain coarsening on reduction performance by controlling the iron oxide grain structure with MgO.

[0024] (2) In this invention, MgO is formed by the reaction of MgO with iron oxides. x Fe 3-x O4 limits excessive recrystallization and grain growth of hematite, increases the effective reduction reaction interface, and enables the pellets to improve the degree of reduction while maintaining a low reduction expansion index.

[0025] (3) The present invention simultaneously limits the suitable range of liquid phase and MgO in pellets. When the MgO content in pellets is insufficient, it is difficult to fully compensate for the reduction loss caused by the high liquid phase, while the MgO content in pellets is too high, which will inhibit the consolidation of iron oxide crystals and reduce the compressive strength. Therefore, it is possible to achieve comprehensive performance of compressive strength not less than 2500 N / pellet, RSI not more than 15% and RI not less than 65% by matching two parameters.

[0026] (4) The present invention can be achieved through conventional pelleting, pelletizing, preheating and roasting processes without the need for additional complex production equipment, and has good industrial adaptability. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The graph shows the changes in reduction expansion index (RSI), reduction degree (RI), and reduction pulverization index (RDI) of Baiyun Obo flux pellets under different liquid phase contents in Experiment 1.

[0029] Figure 2 The graph shows the changes in RSI, RI, and RDI of pellets in Comparative Examples 1-2 and Examples 2-4 as a function of MgO content.

[0030] Figure 3 The graphs show the microstructure and grain size of iron oxide pellets in Comparative Examples 1-2 and Examples 2-4 as a function of MgO content; where (a) is Comparative Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, (e) is Comparative Example 2, and (f) is the curve showing the average grain size of hematite in the pellets of Comparative Examples 1, Examples 2-4 and Comparative Example 2 as a function of MgO content in the pellets. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0034] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0035] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0036] In this invention, the percentages of raw material composition, pellet chemical composition, and MgO content within the pellets, unless otherwise specified, all refer to mass percentages; the percentage of liquid phase content refers to the area ratio of the solidified liquid phase region of the calcined pellets after cooling in a SEM two-dimensional image.

[0037] The MgO content in the pellets described in this invention refers to the MgO mass fraction of the finished pellets on a dry basis after oxidative roasting, contributed by the MgO contained in each raw material and, if necessary, selectively added MgO powder. Priority is given to utilizing the MgO inherent in the iron ore raw material; if insufficient, MgO powder is added according to the chemical composition and proportion of the raw materials, and verified by the chemical analysis results of the finished pellets.

[0038] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0039] This invention establishes a method for controlling the flux-induced pelletizing of tungsten obo using MgO to compensate for the loss of reduction degree in a high liquid phase, based on a suitable liquid phase. The suitable liquid phase is used to suppress abnormal reducing expansion, while MgO alleviates the decrease in reduction degree caused by the increase of liquid phase by limiting the excessive growth of iron oxide grains.

[0040] It should be noted that MgO itself is not used to promote liquid phase formation. For the Baiyun Obo flux pellets, the SiO2-CaO composition adjustment is mainly used to increase the appropriate amount of liquid phase formation and regulate the distribution of alkaline components; under the premise of ensuring appropriate liquid phase formation, controlling MgO within the pellets within a suitable range can be achieved by forming Mg x Fe 3-x O4 inhibits excessive growth of hematite grains, while excessively high MgO content within the pellets significantly inhibits hematite recrystallization and reduces pellet consolidation strength. Therefore, liquid-phase regulation and MgO regulation target the distribution of alkaline components and the grain structure of iron oxides, respectively. Since they act on different targets, they require synergistic control.

[0041] The liquid phase content referred to in this invention refers to the area ratio of the solidified phase region formed by the liquid phase after the calcined pellets are cooled in a two-dimensional SEM image. After pellet sample preparation, SEM observation was performed, and representative area images were acquired at a 100 μm scale. The ImageJ Trainable Weka Segmentation plugin was used to segment the iron oxide, pore, and solidified liquid phase regions, and the liquid phase content was calculated based on the image area ratio. Fifty SEM images were collected for each pellet, and the average value was used as the liquid phase content.

[0042] The liquid phase composition described in this invention is analyzed by SEM-EDS of the solidified liquid phase region after the calcined pellets are cooled. Several representative solidified liquid phase regions are selected for testing, and the average value of the test results is used to characterize the content ratio of SiO2, CaO and Fe2O3 in the liquid phase.

[0043] The following examples are intended to further illustrate the present invention, but not to limit the scope of protection of the claims. The compressive strength of the pellets was tested according to ISO 4700; the reduction expansion index (RSI) was tested according to GB / T 13240-2018; the degree of reduction (RI) was tested according to GB / T 13241-2017; and the reduction pulverization index (RDI) was... +3.15 mm was tested according to GB / T13242-2017.

[0044] The Bayan Obo iron ore used in the following examples of this invention is an iron concentrate containing alkaline components such as K and Na, with the following main chemical composition: TFe 64.54%, FeO 27.69%, SiO2 1.69%, CaO 2.05%, MgO 1.64%, Al2O3 0.49%, S 0.65%, F 0.29%, K2O 0.12%, and Na2O 0.11%. During batching, SiO2 and CaO are adjusted using bentonite and limestone; MgO in the pellets is preferentially provided by the iron ore raw material itself, and MgO powder is added to the target range if insufficient. Unless otherwise specified, the binary basicity of the flux-treated pellets is controlled within the range of 0.6 to 0.9.

[0045] The MT-1 used in Example 1 is ordinary high-magnesium magnetite, whose main chemical composition is: TFe 65.94%, FeO 27.23%, SiO 23.18%, CaO 1.59%, MgO 1.39%, Al2O3 1.62%, S 0.46%, K2O 0.10%, Na2O 0.06%; the main components of the limestone used are CaO 53.58%, SiO 21.72%, MgO 0.41%, Al2O3 1.45%, and the purity of the MgO powder used is not less than 98%.

[0046] In this invention, TFe refers to the total mass fraction of iron in the iron ore raw material; FeO refers to the mass fraction of divalent iron oxides in the sample, calculated as FeO. TFe is an elemental analysis index and does not have a direct summation relationship with the contents of FeO and other oxides to 100%.

[0047] Binary basicity R2 = mass of CaO / mass of SiO2.

[0048] Comparative Experiment 1: Effect of Liquid Phase Content on the Reduction Performance of Flux-Based Pelletizing The liquid phase content of the pellets was adjusted within the range of flux basicity, and the reduction expansion index (RSI), degree of reduction (RI), and reduction pulverization index (RDI) of the pellets under different liquid phase contents were tested. The results are as follows: Figure 1 As shown, when the liquid phase content is approximately 8%, the RSI of the pellets is 100.67%, and the RI is 74.12%. With increasing liquid phase content, the RSI decreases significantly. When the liquid phase content reaches approximately 14%, the RSI decreases to 16.35%, but the RI decreases simultaneously to 64.35%. When the liquid phase content further increases to approximately 15%, the RSI decreases to 12.16%, and the RI further decreases to 59.17%. The results indicate that increasing the liquid phase content can significantly suppress abnormal reducing expansion, but it reduces the pellet reducibility. Relying solely on liquid phase control is insufficient to simultaneously control both RSI and RI.

[0049] Example 1: Flux-induced pellets of Bayan Obo iron ore with suitable liquid-phase-MgO matching control Based on 100% iron ore raw materials (Bayan Obo iron ore + MT-1 iron ore), Bayan Obo iron ore and MT-1 iron ore were blended at a mass ratio of 75:25, with the addition of limestone (2.50% by mass of the iron ore raw materials) and bentonite (4.00% by mass) to adjust the mixture composition. A necessary amount of MgO powder was added according to the MgO content of the raw materials, so that the MgO mass fraction in the pellets after oxidative roasting was 2.03%. The resulting mixture contained 60.64% TFe, 4.53% SiO2, a binary basicity R2 of 0.75, and approximately 3.4% CaO. The mixture was then pelletized (pelletizing is a conventional technique in this field and is not the focus of this patent protection; therefore, it will not be described in detail here). The particle size of the green pellets was controlled to be 10–13 mm. The pellets were preheated at 950℃ for 10 min and then roasted at 1250℃ for 20 min to obtain Bayan Obo iron ore fluxing pellets.

[0050] Under the above conditions, a suitable SiO2-CaO composition promotes the formation of a liquid phase in the flux-induced pellets. The liquid phase content of the calcined pellets, as determined by the aforementioned liquid phase characterization method, is approximately 14%, falling within the control range of 12% to 15%. Simultaneously, a suitable MgO content within the pellets inhibits excessive growth of iron oxide grains. Pilot-scale testing results show that the compressive strength of the flux-induced pellets reaches 2915 N / pellet, the reduction expansion index is 14.2%, and the degree of reduction is 65.5%, all meeting the performance requirements of this invention. This example demonstrates that by controlling the MgO mass fraction within the pellets to 2.03% based on a suitable liquid phase, high compressive strength, low reduction expansion, and good degree of reduction can be simultaneously obtained.

[0051] Comparative Example 1 Based on 100% iron ore raw materials (Bayan Obo iron ore + MT-1 iron ore), the Bayan Obo iron ore and MT-1 iron ore were blended at a mass ratio of 75:25, with the addition of limestone (2.50% by mass of iron ore raw materials) and bentonite (4.00% by mass) as conditioning agents. No MgO powder was added in this comparative example; the MgO in the pellets was provided by the MgO contained in each raw material itself, resulting in a MgO mass fraction of 1.60% in the pellets after oxidative roasting. The resulting mixture contained approximately 60.64% TFe, 4.53% SiO2, 3.40% CaO, and a binary basicity R2 of approximately 0.75.

[0052] After the above mixture was thoroughly mixed, it was pelletized. The particle size of the green pellets was controlled to be 10-13 mm. The pellets were preheated at 950℃ for 10 min, and then oxidatively roasted at 1250℃ for 20 min to obtain flux-forming pellets of Bayan Obo iron ore. Liquid phase characterization showed that the liquid phase content in the pellets after oxidative roasting was approximately 14%.

[0053] Performance testing revealed that the resulting pellets had a reduction expansion index (RSI) of 16.35%, a reduction ratio (RI) of 64.35%, and a reduction pulverization index (RDI) of 97.13%. The MgO mass fraction within the pellets was below the 1.8%–2.5% range specified in this invention. Although a suitable liquid phase can effectively reduce pellet reduction expansion, the RI remained below 65%, indicating that under suitable liquid phase conditions, insufficient MgO content within the pellets cannot adequately compensate for the reduction loss caused by increased liquid phase concentration.

[0054] Example 2 Except for controlling the MgO mass fraction in the pellets to 1.8%, the other conditions were the same as those in Comparative Example 1, and the resulting pellets had RSI, RI and RDI of 14.16%, 65.52% and 97.51%, respectively.

[0055] Example 3 Except for controlling the MgO mass fraction in the pellets to 2.0%, the other conditions were the same as those in Comparative Example 1, and the resulting pellets had RSI, RI and RDI of 13.25%, 67.31% and 97.96%, respectively.

[0056] Example 4 Except for controlling the MgO mass fraction in the pellets to 2.5%, the other conditions were the same as in Comparative Example 1, and the resulting pellets had RSI, RI, and RDI of 10.82%, 68.15%, and 98.08%, respectively. The RSI and RI of Examples 2-4 all met the performance control targets of this invention.

[0057] Comparative Example 2 Except for increasing the MgO mass fraction in the pellets to 3.0%, the other conditions were the same as in Comparative Example 1. The resulting pellets had RSI, RI, and RDI of 8.37%, 70.32%, and 98.35%, respectively, but the compressive strength decreased to 2416 N / pellet. The reduction performance and changes in the microstructure and grain size of iron oxides under different MgO contents are shown in the figures below. Figure 2 and Figure 3 As shown, with increasing MgO content, Mg... x Fe 3-x As O4 production increases, hematite grains gradually become finer, RSI continuously decreases while RI continuously increases; excessive MgO inhibits hematite recrystallization and crystallization consolidation, therefore MgO in pellets needs to be controlled within a reasonable range.

[0058] Industrial Application Example 1: Verification of Industrial Cage Loading of 100% Bayan Obo Iron Ore under Liquid Phase Control Industrial pelletizing tests were conducted using 100% Bayan Obo iron ore. Before optimization, the main components of the mixture were 63.62% TFe, 2.80% SiO2, 2.15% CaO, and 1.54% MgO, with a binary basicity R² of 0.76. The resulting pellets had a compressive strength of 2057 N / pellet, an FeO content of 1.18%, a reduction expansion index of 98.64%, a reduction degree of 74.35%, and a reduction pulverization index of 86.31%. After optimization, the SiO2 and CaO content in the mixture was increased by adding bentonite and limestone. The resulting mixture composition was 60.69% TFe, 5.15% SiO2, 3.91% CaO, and 1.84% MgO, while the binary basicity R² remained at 0.76. Compared to before optimization, increasing the SiO2 and CaO content at the same flux basicity facilitated the formation of more low-melting-point composite silicate liquid phases. This industrial test did not use the MgO content in the pellets after oxidative roasting as an independent control parameter, nor was it matched and controlled according to the target range of 1.8% to 2.5% MgO in the pellets of this invention. It was mainly used to verify the effect of liquid phase control on reduction expansion.

[0059] Industrial pelleting results showed that the optimized pellets exhibited increased compressive strength from 2057 N / pellet to 2685 N / pellet, decreased FeO content from 1.18% to 0.50%, significantly reduced reduction expansion index from 98.64% to 12.15%, and increased reduction pulverization index from 86.31% to 96.43%, but the degree of reduction remained at 64.35%. These results indicate that liquid phase regulation can significantly suppress the catastrophic reduction expansion of the Baiyun Obo flux-dependent pellets, but the degree of reduction is still lower than the synergistic optimization target of this invention. Examples 1-4 and Comparative Examples 1-2 further demonstrate that controlling the MgO content within the pellets within a suitable range based on a suitable liquid phase can compensate for the reduction loss and achieve synergistic optimization of overall performance.

[0060] In summary, this invention controls the liquid phase content of flux pellets to 12%–15% and the MgO mass fraction in the pellets after oxidative roasting to 1.8%–2.5%. It utilizes the liquid phase to suppress abnormal reduction expansion and further compensates for the reduction loss caused by the high liquid phase through MgO regulation. At the same time, it avoids the decrease in consolidation strength caused by excessive MgO, thereby achieving synergistic control of reduction expansion index, reduction degree and compressive strength.

[0061] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing flux-dependent pellets of Bayan Obo iron ore that balances low reducing expansion and high reducing power, characterized in that, Includes the following steps: Iron ore raw materials containing Bayan Obo iron ore are mixed with bentonite and limestone, and MgO powder is selectively added according to the MgO content of each raw material to obtain a mixture. The mixture is then pelletized to obtain green pellets. The SiO2 and CaO contents in the mixture are adjusted so that the binary basicity R2 = CaO / SiO2 of the mixture is 0.6 to 0.9; The green pellets are preheated and oxidized to achieve a liquid phase content of 12%–15% in the pellets after oxidative roasting. Under the condition that the liquid phase content is 12% to 15%, the MgO mass fraction in the pellets after oxidative roasting is 1.8% to 2.5% to limit the excessive growth of iron oxide grains under high liquid phase conditions; the MgO in the pellets is provided by the MgO contained in each raw material and selectively added MgO powder.

2. The preparation method according to claim 1, characterized in that, The mass fraction of SiO2 in the mixture is not less than 4.5%, and the mass fraction of CaO is not less than 3.4%.

3. The preparation method according to claim 1, characterized in that, The mass percentages of SiO2, CaO, and Fe2O3 in the liquid phase are 30%–35%, 25%–35%, and 25%–30%, respectively.

4. The preparation method according to claim 1, characterized in that, The preheating temperature is 900-950℃, the preheating time is 8-10 min, and the FeO mass fraction of the pellets after preheating is not higher than 8%.

5. The preparation method according to claim 1, characterized in that, The oxidation calcination temperature is 1250–1280℃, and the oxidation calcination time is 15–20 min.

6. The preparation method according to claim 1, characterized in that, The green pellets have a diameter of 10–13 mm.

7. A fluxing pellet of Bayan Obo iron ore prepared by the preparation method according to any one of claims 1 to 6.

8. The application of Bayan Obo iron ore fluxing pellets as described in claim 7 in blast furnace ironmaking, characterized in that, The Bayan Obo iron ore flux pellets are used as flux oxide pellets in blast furnace charge.

9. A method for compensating for the loss of high liquid phase reduction in flux-induced pellets of Bayan Obo iron ore, characterized in that, The preparation method described in any one of claims 1 to 6 is used.

Images