Three-dimensional structure and micro-mechanical properties of iron ore sinter

A new analysis method based on serial sectioning and three-dimensional (3D) reconstruction was developed to characterize the mineral microstructure of iron ore sinter. Through the 3D reconstruction of two types of iron ore sinters, the morphology and distribution of minerals in three-dimensional space were analyzed, and the volume fraction of minerals in a 3D image was calculated based on their pixel points. In addition, the microhardness of minerals was measured with a Vickers hardness tester. Notably, different mineral compositions and distributions are obtained in these two sinters. The calcium ferrite in Sinter 1 is dendritic with many interconnected pores, and these grains are crisscrossed and interwoven; the calcium ferrite in Sinter 2 is strip shaped and interweaves with magnetite, silicate and columnar pores. The calculated mineral contents based on a two-dimensional region are clearly different among various layers. Quantitative analysis shows that Sinter 1 contains a greater amount of calcium ferrite and hematite, whereas Sinter 2 contains more magnetite and silicate. The microhardness of minerals from highest to lowest is hematite, calcium ferrite, magnetite and silicate. Thus, Sinter 1 has a greater tumbler strength than Sinter 2.     

Mineralogical properties and co-sintering characteristics of fluxed iron ore with magnetite concentrates

To investigate the feasibility of co-sintering of fluxed iron ore with magnetite concentrates,the mineralogical properties of a novel fluxed iron ore were studied using particle size analysis,microscopic morphology characterization,and X-ray diffraction Rietveld analysis.Following that,the experiments for granulation performance and basic sintering characteristics were designed under seven different fluxed iron ore ratios,and the integrated ranking of different fluxed iron ore ratios was determined using gray relation analysis.Finally,the results of the industrial trails were combined with the feasibility analysis.Test and experimental results show that the fraction of the fluxed iron ore particles larger than 0.5 mm can account for more than 48％,and the particles have two morphologies:spherical-rough and flaky-smooth.Ca elements are found in the form of calcite(CaCO3)and dolomite(CaMg(CO3)2).The average particle size of granules and powder removal rate can be improved from 2.50 to 3.16 mm and 39.60％to 24.20％,respectively,with the increase in the fluxed iron ore ratio.Furthermore,the fluxed iron ore can improve assimilability and liquid fluidity of magnetite concentrates.In terms of overall granulation performance and sintering characteristics,the fluxed iron ore ratios are graded from best to worst as follows:12％,15％,9％,18％,21％,6％and 3％.The industrial trails show that when the fluxed iron ore ratio is increased,the beneficial effect of the superior sintering characteristics of the fluxed iron ore itself is ideally balanced with the negative effect of the lower amount of additional CaO at 12％ratio,and thus,it is feasible to bring the fluxed iron ore into production at a level of roughly 12％.     

Influence of nature and particle size distribution on granulation of iron ore mixtures used in a sinter strand

Abstract

The ore mixture granulation process is described and the granulation fitness of a series of iron ores forming part of the mixture is studied. Good granulation and control of the maximum sintering temperature makes it possible to achieve the optimum sinter structure, formed by a hematite nucleus surrounded by a lattice of acicular ferrites. The granulation fitness of ore mixtures used to manufacture a series of sinters in a pilot plant are also determined. It is verified that sinters with an optimum structure have been obtained. A series of iron ores are classified using the granulation index (G index). The evolution of the G index of ore mixtures used in ACERALIA during recent years is considered and it is verified how improvement of the G index increases productivity and decreases coke consumption in the sinter strand.     

Influence of charcoal replacing coke on microstructure and reduction properties of iron ore sinter

This study was carried out to determine the influence of using charcoal as a supplementary fuel on the microstructure and reduction properties of sinter. The primary fuel was coke breeze with 0, 20, 30 and 40% replacement of weight input with charcoal to produce sinter. Experimental results indicate that when the replacement percentage of charcoal to coke breeze increased from 0 to 40%, the porosity and FeO content of sinter also rose. These changes result in an enhancement from 79.8 to 84.3% for the reducibility index due to the increased reducing surface area. In addition, the reduction degradation of sinter also improves since degradation during crystalline transformation is restricted. Therefore, replacing coke breeze with charcoal is able to improve the reducing properties of sinter, which is beneficial to small and large blast furnace operation.     

配加贾家堡铁矿对烧结矿性能的影响

为降低烧结矿成本,对烧结原料中配加一定比例的贾家堡铁矿进行了研究。烧结杯试验结果表明,随着烧结铁料中贾家堡铁矿配比增加,烧结矿成品率呈现逐渐降低趋势,转鼓指数也逐渐降低。贾家堡铁矿配比由0增加到4.48%时,烧结矿低温还原粉化率由76.7%降低到71.9%,而当贾家堡铁矿配比继续增加时,低温还原粉化率却有所上升。     

Influence of magnesia on iron ore sinter properties and productivity

Abstract

Dolomite and other MgO bearing materials are being increasingly used as basic flux constituents for production of fluxed sinters. Addition of flux materials in sinter influences the resultant sinter microstructure and chemical properties. The physical and metallurgical properties of sinter mainly depend on mineralogy of the sinter. Dolomite is the source of double carbonate of calcium and magnesium. Recent studies reveal that, apart from the additional fuel needed, the addition of dolomite and MgO bearing material greatly influences the magnetite content and the properties of the sinter produced. The increasing use of MgO bearing fluxes in the blast furnace burden, and the trend to incorporate a major part of fluxes in the sinter mix led to an investigation of the influence of MgO on sinter properties and productivity. In this study, the systematic investigation has been made on the influence of MgO% (1·4 to 2·6) on sinter mineralogy and sinter properties with dolomite. Microstructural examination of dolomite sinter revealed that hematite and calcium ferrite phases decreased whereas magnetite phase increased with increase in MgO percentage in sinter. From the laboratory pot grate sintering results it was found that sinter reduction degradation index improved whereas tumbler index and reducibility decreased with increase in MgO%.     

Optimising method for improving granulation effectiveness of iron ore sintering mixture

Abstract

The structure of granules has been investigated and a model of granulation determined. The results show that a granule consists of an adhesive layer and a nucleus. Particles with diameter under 0.5 mm act as adhesive fines, while the remainders act as nuclei. By studying the influencing factors of granulation, two significant particle characteristics assessing granulation performance were determined. One is the relative proportion of adhesive fines and nucleus particles, and the other is the specific surface area of adhesive fines. The method of optimising granulation of sinter mixtures is proposed as follows: the proportion of adhesive fines should be 40–50% and the specific surface area should exceed 1000 cm² g^?1, which contributes to achieving a better bed permeability, a faster sintering speed and higher productivity.     

浅谈烧结矿的强度与成品率

由于烧结用原燃产的不均一性,使得烧结工艺过程是一个不平衡的工艺过程,影响着烧结矿的成品率和强度。通过对烧结工艺中诸多技术要素的探讨,寻求均匀烧结的途径,从而改善烧结矿的成品率和强度。     

Optimisation model of fuel distribution in materials bed of iron ore sintering process

In this study, the optimisation model of fuel distribution base on numerical simulation was proposed to reduce the fuel consumption of sintering process. The simulation model of sintering process was carried out according to the heat and mass transfer, and the physical and chemical reactions of sintering. Then the heat income and expenditure of solid mixture in different materials unit was analysed via the simulation model. And the fuel proportion was adjusted on the basis of the difference between total heat quantity and heat quantity that the materials unit required to reach setting temperature. This model was validated by sintering pot test, the simulation results of bed temperature at different depth were very close to the detection results. The sintering pot test shows that the sinter yield and quality indices had little change after the optimisation of fuel distribution, while the solid fuel consumption was decreased by 3.83?kg?t^?1.     

Influence of sinter grate suction pressure (flame front speed) on microstructure,productivity and quality of iron ore sinter

Abstract

From a sinter production point of view, it is important to optimise the sintering process with regard to both sinter quality and production rate. In sintering, airflow rate within the sinter bed decides the production rate and its physical and metallurgical properties. To study the influence of airflow rate (flame front speed) on sinter production and sinter quality, pot grate sintering experiments were conducted at sinter grate suction pressures ranging from 900 to 1700 mm water column over the sinter bed. During sintering, time–temperature data were recorded, and mineralogical studies were carried out. This study reveals that increase in sinter grate suction pressure through the sinter bed from 900 to 1700 mm water column significantly improved the sinter productivity from 34·37 to 48·90 t/m²/day; however, the physical and metallurgical properties of the sinter at higher suction pressure were not optimum with respect to blast furnace requirements. The maximum sinter productivity with desired physical and metallurgical properties was obtained at suction pressure 1300 mm water column. At this pressure, improvement in sinter quality was due to optimum firing temperature and enough retention time available for formation of mineral phases. At an airflow rate 1300 mm water column, sinter productivity was 41·0 t/m²/day, sinter strength (TI) was 73·10%, reduction degradation index was 25·0 and reducibility was 71·50%.     

返矿对烧结过程和烧结矿质量影响的研究

混匀矿中返矿的比率约为25%～50%。如此大比例的返矿会对烧结过程和烧结矿质量产生很大影响。研究旨在揭示返矿量和焦粉量变化的影响。研究采用了因子设计方法,研究表明返矿的产生主要取决于烧结混合料中的固体燃料和返矿比例,增加混合料中的返矿配入量会减少烧结过程中的返矿发生量。烧结过程效率随着混合料中返矿比例的增加而提高(最适宜的混合碱度为1.6)。研究表明,要确保返矿平衡率在90%～110%的范围内,混合料中返矿配比最高不能超过35%,最小不能<25%。     

氧化铝对铁矿石烧结质量和生产率的影响(英文)

烧结矿是现代高炉生产的主要含铁原料。合理控制入炉烧结矿的理化性能与冶金性能对高炉生产和稳定操作是很必要的。铁矿粉是烧结矿的主要原料,其化学成分和烧结料层内的热量条件在烧结过程中起着重要的作用。化学成分等参数也决定着烧结矿矿相结构和质量。由于含氧化铝原料的低反应性及其液相的高粘性,因此在人们的预料中高铝矿石对烧结矿结构组成的影响并不好。烧结混合料中的氧化铝在同化过程中需要消耗大量热量,延迟烧结过程。在确保高炉渣的流动性方面,氧化铝也需要消耗较大热量。不论是烧结还是高炉的生产实绩均表明,氧化铝是有害的。一般而言,高含铁量与低脉石的印度矿与其他矿石的不同特点就是氧化铝含量高。由于高品味铁矿石的消耗殆尽,使用可利用的烧结原料成为生产必需。因此,必须要掌握氧化铝的作用及其对烧结矿质量和生产过程的影响。实验室完成了不同氧化铝含量水平(2.00%～5.46%)的实验,可从中了解氧化铝在烧结矿矿物学、生产率、物理性能和冶金性能方面的影响。随着烧结矿中氧化铝含量的增加,残存赤铁矿、复合铁酸钙(SFCA)和孔隙率增加,而磁铁矿和硅酸盐比例下降。烧结生产率和烧结矿转鼓强度(TI)随着氧化铝含量上升而下降,反映烧结矿冶金性能的诸如低温还原粉化率(RDI)和还原率(RI)提高。     

Optimal proportioning of iron ore in sintering process based on improved multi-objective beluga whale optimisation algorithm

Proportioning is an important part of sintering,as it affects the cost of sintering and the quality of sintered ore.To address the problems posed by the complex raw material information and numerous constraints in the sintering process,a multi-objective optimisation model for sintering proportioning was established,which takes the proportioning cost and TFe as the optimisation objectives.Additionally,an improved multi-objective beluga whale optimisation(IMOBWO)algorithm was proposed to solve the nonlinear,multi-constrained multi-objective optimisation problems.The algorithm uses the con-strained non-dominance criterion to deal with the constraint problem in the model.Moreover,the algorithm employs an opposite learning strategy and a population guidance mechanism based on angular competition and two-population competition strategy to enhance convergence and population diversity.The actual proportioning of a steel plant indicates that the IMOBWO algorithm applied to the ore proportioning process has good convergence and obtains the uniformly distributed Pareto front.Meanwhile,compared with the actual proportioning scheme,the proportioning cost is reduced by 4.3361 ¥/t,and the TFe content in the mixture is increased by 0.0367％in the optimal compromise solution.Therefore,the proposed method effectively balances the cost and total iron,facilitating the comprehensive utilisation of sintered iron ore resources while ensuring quality assurance.     

Crystallization behavior of blast furnace slag modified by adding iron ore tailing

Blast furnace(BF)slag is a by-product of the ironmaking process and could be utilized to manufacture slag fiber by adding iron ore tailing.The crystallization behavior of the modified BF slag is significant to the fibrosis process.To investigate the influence of basicity on the crystallization behavior,BF slag was modified by adding iron ore tailing at room temperature and melted at 1 500°C.FactSage simulation,X-ray diffraction,scanning electron microscopy backscattered electron imaging coupled to an energy dispersive spectrometer,and hot thermocouple technique analysis were performed to explore the crystallization behavior of the modified BF slag during the cooling process.It was found that the initial crystallization temperature increased with the increase in basicity.Melilite,anorthite,clinopyroxene,and wollastonite could be generated during the cooling process as basicity ranged from 0.7 to 0.9.Spinel could be found as one of the phases;however,wollastonite disappeared under a basicity of 1.0.The initial crystallization temperature was controlled by the crystallization of melilite during the cooling process when the basicity of the modified BF slag ranged from 0.7 to 1.0.Moreover,the cooling rate could also influence the crystallization of the modified BF slag.     

提高包钢烧结矿还原透气性的研究

采用配矿和调整烧结矿碱度的方法,研究提高包钢烧结矿还原透气性的途径。试验结果指出,在混合料中配入３０－４０％的河北精矿,将烧结矿碱度由现在的１．８降至１．４ 钢烧结矿的还原透气性。     

Thermodynamic and experimental study of high-temperature roasting of blast furnace gas ash for recovery of metallic zinc and iron

A high-temperature reduction roasting method was used to achieve metallic iron and zinc recovery from blast furnace gas ash(BFA).The reduction processes for Zn-containing and Fe-containing oxides were analyzed in detail by using ther-modynamic equilibrium calculation and the principle of minimum free energy.The results showed that the main reaction in the system is the reduction of ZnFe2O4 and iron oxides.Over the full temperature range,iron oxides were more easily reduced than zinc oxides.Regardless of the amount of CO contained in the system,the reduction of ZnO to Zn was difficult to proceed below the boiling point(906 ℃)of Zn.When the reduction temperature is below 906 ℃,the reduction process of zinc ferrate was ZnFe2O4 → ZnO;when the reduction temperature is above 906 ℃,its reduction process becomed ZnFe2O4 → ZnO → Zn(g).The metallization and dezincification rates of the BFA gradually increased with increasing reaction temperature.As the C/O ratio increased,the metallization and dezincification rates first increased and then decreased.The effect of reduction time on BFA reduction was similar to that of reaction temperature.     

Characterisation of structure of iron ore sinter and its behaviour during reduction at low temperatures

Abstract

Various sinter microstructures were produced in the laboratory using the same iron ore blend, varying only the sinter basicity and the carbon content of the blend via limestone and coke additions, respectively. The sinter cakes were subjected to low temperature, size degradation tests and their structural composition was determined. A relationship has been established between sinter structural composition and its size degradation under low temperature reducing conditions. Also, varying the gas composition led to development of a new reduction test procedure, which is more sensitive to microstructural variations than the conventional standard test (reduction degradation index, RDI).     

A study of reduction and magnetic separation of iron from high iron bauxite ore

Abstract

The removal of iron as magnetite from a high iron bauxite ore was investigated by carbothermal reduction and magnetic separation. Thermodynamic calculations using HSC Chemistry 6·1 were utilised to determine the equilibrium compositions of the reaction products as a function of temperature and carbon additions. Under equilibrium conditions, the formation of hercynite (FeAl₂O₄) restricted the conversion of haematite to magnetite and the equilibrium calculations were adjusted so that the amount of hercynite was limited. Also, thermogravometric analysis and differential thermal analysis with evolved gas analysis tests were performed in order to elucidate the reduction reactions. Furthermore, high temperature reduction experiments were carried out in order to quantify the effects of processing time, temperature and carbon additions on the amount of the magnetic fraction. The degree of removal of the iron and the alumina recovery were determined. For a given set of conditions, the maximum iron removal as magnetite could only be achieved by quenching the reacted samples. The results demonstrated that at a reduction temperature of ～1073 K, ～58% of the iron could be removed in the magnetic fraction with an alumina recovery of ～85% in the non-magnetic fraction.

On a examiné l’enlèvement du fer sous forme de magnétite d’un minerai de bauxite à haute teneur en fer, au moyen de la réduction carbothermique et séparation magnétique. On a utilisé des calculs de thermodynamique avec ″HSC Chemistry 6·1″ pour déterminer les compositions d’équilibre des produits de la réaction en fonction de la température et des additions de carbone. Sous les conditions d’équilibre, la formation d’hercynite (FeAl₂O₄) restreignait la conversion d’hématite en magnétite et l’on a ajusté les calculs d’équilibre afin de limiter la quantité d’hercynite. On a également effectué des essais de TGA-DTA avec EGA afin d’élucider les réactions de réduction. De plus, on a exécuté des expériences de réduction à haute température afin de quantifier l’effet de la durée de traitement, de la température et des additions de carbone sur la quantité de fraction magnétique. On a déterminé le degré d’enlèvement du fer et de la récupération d’oxyde d’aluminium. Pour un ensemble donné de conditions, on peut obtenir l’enlèvement maximal de fer sous forme de magnétite seulement par trempe de refroidissement des échantillons réagis. Les résultats ont démontré qu’à une température de réduction d’environ 1073 K, on pouvait enlever environ 58% du fer dans la fraction magnétique, avec une récupération de l’oxyde d’aluminium d’environ 85% dans la fraction non magnétique.     

Proposing a machine learning approach to analyze and predict basic high-temperature properties of iron ore fines and its factors

The basic high-temperature properties of iron ore play a crucial role in optimizing sintering and ore blending,but the testing process for these properties is complex and has significant lag time,which cannot meet the actual needs of ore blending.A prediction model for the basic high-temperature properties of iron ore fines was thus proposed based on a combination of machine learning algorithms and genetic algorithms.First,the prediction accuracy of different machine learning models for the basic high-temperature properties of iron ore fines was compared.Then,a random forest model optimized by genetic algorithms was built,further improving the prediction accuracy of the model.The test results show that the random forest model optimized by genetic algorithms has the highest prediction accuracy for the lowest assim-ilation temperature and liquid phase fluidity of iron ore,with a determination coefficient of 0.903 for the lowest assimi-lation temperature and 0.927 for the liquid phase fluidity after optimization.The trained model meets the fluctuation requirements of on-site testing and has been successfully applied to actual production on site.     

利用人工神经网络模型预测球团矿还原粉化指数

印度JSW钢铁公司是一家年产钢700万t的联合钢铁企业,其炼铁单元由2座COREX和3座高炉组成。COREX和高炉用球团由一个年产420万t的带式焙烧机球团厂供给。作为一项重要的冶金性能指标,球团的还原粉化指数(RDI)要求满足COREX和高炉冶炼的要求。通过建立神经元网络模型和敏感度分析,研究了给料率、料层高度、焙烧温度、干透点温度、COREX煤气单耗、膨润土的添加量、生球水分、生球碳含量、以及成品球的MgO、Al2O3含量和碱度等12个因素对球团RDI指标的影响,并对焙烧机生产球团的RDI(-6.3mm)和RDI(-0.5mm)进行了预测。结果表明,球团中MgO、CaO/SiO2,生球碳含量和Al2O3含量对球团RDI指标影响较大。预测结果与实际的数据误差低于4%。研究得出:①生球的MgO、氧化铝和碳含量以及二元碱度对球团RDI有重要影响。②随着球团MgO含量和球团二元碱度的升高,球团RDI(-6.3mm)和RDI(-0.5mm)得到改善。③随着生球中氧化铝含量的增加,球团RDI升高,因此应尽量使用低氧化铝含量的铁矿粉来降低球团中的氧化铝。随着生球中氧化铝和碳含量的增加,球团RDI(-6.3mm)和RDI(-0.5mm)有所降低。④提高球团二元碱度和MgO含量的同时,降低生球碳含量可以改善球团的RDI。因此需要对它们的配比进行优化。⑤二元碱度0.50～0.55,MgO质量分数0.35%～0.45%,生球碳质量分数1.15%～1.20%,焙烧球氧化铝质量分数低于2.5%,FeO质量分数低于0.60%时,可望得到较低的RDI。⑥相对于球团中的碳和CaO含量,最优的焙烧温度可以改善球团的RDI(-6.3mm)和RDI(-0.5mm)。⑦高给料率和较高的料层高度会使球团的RDI(-6.3mm)和RDI(-0.5mm)升高。