High Basicity Sinter Research Articles

The Effects of MgO and Al2O3 Content in Sinter on the Softening-Melting Properties of Mixed Ferrous Burden.

The softening-melting properties of mixed ferrous burden made from high-basicity sinter with increased MgO and Al2O3 content and acid pellets was investigated for optimization. The influences of MgO and Al2O3 are discussed with the aid of phase analysis. The results showed that, with decreasing MgO mass%/Al2O3 mass% in mixed burden, all the softening-melting characteristic temperatures decreased, which can be attributed to the low melting temperature and viscosity of the slag caused by MgO and Al2O3. The permeability of the melting zone deteriorated again when MgO mass%/Al2O3 mass% decreased to a certain content. The softening interval widened slightly at first and then narrowed, while the melting interval first increased slightly and then increased greatly later. It can be deduced that the softening properties were improved, but the melting properties were worsened. Under comprehensive consideration of its softening-melting properties, permeability, iron ore reduction and the thermal state of the blast furnace hearth, the optimal softening-melting properties of a mixed ferrous burden with MgO mass%/Al2O3 mass% of 0.82 is optimal.

A Review of Calcium Ferrite in Sintering of Iron Ore and The Effect of Gangue Composition on Its Formation

In this paper, published studies on the bonding phase of calcium ferrite are reviewed. As the main bonding phase of high-basicity sinter, calcium ferrite has the advantages of high strength, good reducibility and easy formation of liquid phase. In particular, we emphasize the formation process of calcium ferrite phases, especially Silico-Ferrite of Calcium and Aluminum(‘SFCA’), and the influence of common gangue components (Al2O3, SiO2, MgO) on its formation. Based on the critical analysis of the current data, some deficiencies in this field are put forward and the research directions we think will be key in this field in the future are attached, so as to improve the theories related to calcium ferrite in iron ore sintering. The relevant results provide theoretical basis for understanding the formation process of calcium ferrite and producing high quality sinter.

A Study of the Crystallization Properties of CaO-SiO2-Al2O3 Glass Phase in Sinter

The glass phase is one of the binding phases in high-basicity sinter, which is mainly formed during a high-temperature cooling process while cannot crystallize in time. The phase still involves the “structure” information of the binding phase’s liquid phase in the sinter. In addition, the generation of glassy phases can seriously deteriorate the metallurgical properties of sintered ore. However, the formation mechanism and crystallization process of glass phases are still unclear. In this work, the glass phase and the crystallized samples of the CaO-SiO2-Al2O3 system were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy and Raman spectroscopy. The effect of alkalinity (R) and Al2O3 on crystallization and the relationship between crystallization and structure are discussed. The results showed that the chemical composition significantly influences the crystallization of the CaO-SiO2-Al2O3 glass. Decreasing basicity (R = 0.8–1.2, the mass ratio of CaO and SiO2) favors the crystallization of the glass phase, while increasing the content of Al2O3 (9–12%) can inhibit the crystallization of the glass phase. In addition, the crystallization order of the 45mass%CaO-45mass%SiO2-10mass%Al2O3 sample is CaSiO3 → CaAl2O4. Raman spectroscopic analysis showed that increase of slag basicity promoted the aggregation degree (Q3/Q2), resulting in deterioration of the glass phase crystallization. and that the glass phase crystallization deteriorated as the aggregation degree increased. However, increasing the Al2O3 content has little effect on the agglomeration degree but does promote the formation of SiO4 tetrahedra (Q0), which results in the deterioration of glass-phase crystallization.

Study on Sintering Characteristics of Ultra-Poor Vanadium-Titanium Magnetite

Artificial rich ore for blast furnace use can be produced by sintering ultra-poor vanadium-titanium magnetite (PVTM) with a high-grade iron concentrate. Here, acid (R = 0.33, 0.50), self-fluxing (R = 1.10), and high-basicity (R = 2.60) PVTM sinters were produced in a sinter pot. Their performances were determined using the comprehensive index. The microstructures of the PVTM sinter were observed by metallographic microscope and scanning electron microscopy equipped with an energy dispersion spectrum (SEM-EDS). The results suggest that the acid PVTM sinter had a low flame front speed, low productivity, an uneven size distribution, and poor softening properties. It did have a high tumble index (TI) and low-temperature reduction disintegration index (RDI). The self-fluxing PVTM sinter had the worst performance (TI, RDI, reducibility index (RI)), while the high-basicity PVTM sinter had the highest flame front speed, highest productivity, a reasonable size distribution, excellent softening properties, and satisfactory TI and RDI values. The main consolidation form of the acid sinter was crystal stock, the main bonding phase of the self-fluxing sinter was silicate, and the main bonding phase of the high-basicity sinter was silico-ferrite of calcium and aluminum (SFCA). The comprehensive index values (from high to low) were the high-basicity (R = 2.60), acid (R = 0.50), natural acid (R = 0.33), and self-fluxing (R = 1.10) PVTM sinters. When the production capacity of the acid pellet was in shortage, the acid PVTM sinter (R = 0.50) could be produced by the surplus from the sinter plant. This replaced a part of the acid pellet and the burden structural model of the blast furnace smelting vanadium so the titanium burden could adopt a ‘high-basicity PVTM sinter + acid V-Ti pellet + acid (R = 0.50) PVTM sinter’.

Full-Scale Experimental Test Production of High-Basicity Sinter in the Enakievo Metallurgical Plant Sinter Shop

We describe the results for full-scale experimental test production of high-basicity sinter (basicity 2.0–5.0) at the Enakievo Metallurgical Plant Sinter Shop. As sinter basicity increased from 2.0 to 5.0, the iron content of the sinter decreased from 53.05% to 32.24%, and the ferrous oxide concentration decreased from 17.55% to 9.29%. However, the strength specifications of the sinter were improved: The concentration of 0–5-mm fines decreased from 19.32% to 15.89%, and the yield of +5 mm size class in a drum test increased from 65.9% to 72.3% through optimization of the sintering process parameters. The use of high basicity sinter in blast-furnace smelting reduced the specific consumption of lime in the blast-furnace charge from 233.9 kg/metric ton of cast iron (at sinter basicity 2.0) to 103.5 kg/metric ton (at basicity 4.5) and, correspondingly, the specific feed rate for coke during castiron production decreased from 538.1 kg/metric ton to 476.6 kg/metric ton.

Effect of aluminum content on reduction of silico-ferrite of calcium and aluminum (SFCA)

Silico-ferrite of calcium and aluminum (SFCA) is a key bonding phase in high basicity sinter and its reducibility affects the reducibility of sinter. In this work, the reduction process of the Ca5Si2(Fe18−xAlx)O36 with change of aluminum content had been investigated using the thermogravimetric method at 1073 K, 1173 K and 1273 K in reducing atmosphere respectively. X-ray diffraction was used to characterize the mineral composition of the samples. Jade software was used to calculate the grain size of minerals and micro stain in samples. The results show that the reduction process of the SFCA to FeO could be divided into two steps, SFCA to Fe3O4 and Fe3O4 to FeO. Ca2Al2SiO7 as a by-product appeared in the stage of SFCA to Fe3O4. The increase of aluminum content in SFCA decreased the formation of Ca2Fe2O5 to promote the reducibility of SFCA at 1273 K. By calculation it was also found that the addition of aluminum resulted in more micro strain in the SFCA, which could deduced that the release of stress in the reduction process is also conducive to promote the reduction of SFCA.

Effect of Alumina on Liquid Phase Formation in Sintering Process of Iron Ore Fines

The formation of liquid phase is of great significance for improving the quality of high basicity sinter which is widely used as raw materials in blast furnace ironmaking. As an important component of gangue in iron ore, alumina affects the amount of liquid phase by influencing the formation of calcium ferrites‐bonding phase. In this work, the hematite solid solution with aluminum (Hss) was prepared and sintered with CaO to investigate the effect of alumina on liquid phase formation in sintering process of iron ore fines. Three homogeneous phases of CaFe2O4 (CF), Ca2Fe15.57O25.56 (CF3.9), and Ca3.18Fe15.48Al1.34O28 (CFA) are prepared to determine the melting temperature by using DSC method. XRD, SEM‐EDS, and optical microscope are used to characterize the change of mineral and microstructure of sintered samples. The results show that an Fe‐rich calcium ferrite CF3.9 is produced above 1200 °C in Fe2O3‐CaO binary system. The liquid phase formation temperature can be reduced to 1206 °C when CF3.9 and CF coexist. The ternary calcium ferrite CFA, which has a eutectic temperature of 1201 °C with CF, is generated above 990 °C in Fe2O3‐CaO‐Al2O3 ternary system. The formation of liquid phase is promoted by adding alumina in moderation through changing the mass ratio of CF to CFA, and the largest amount of liquid phase is produced when the ratio is 8:2.

High-Temperature Reduction and Melting Mechanism of Sinter with Different MgO Content

Adding MgO to sinter is considered to be a popular counter measure to cope with the use of high Al2O3 ores. The purpose of this paper is to investigate the effect of the MgO content on the reduction melting behavior in order to clarify the main mechanism of melting and dripping under simulated blast furnace (BF) conditions. It was found that reduction behavior was inhibited with an increased MgO content; the reduction mechanism was further investigated by means of XRD, SEM, and kinetic analysis. The influence of MgO on the melting mechanism of high basicity sinter was also studied. The softening start temperature and softening temperature increased, and the softening zone increased as a whole with the increased MgO contents from 1.3 to 2.0 wt%. The melting temperature was similar, because the MgO remained in an unslagged state and existed in wustite as FeO-MgO solid solution. The dripping temperature was increased; the main reason for this was that high melting-point slags appeared, and that it was more difficult for carburization to occur with increased MgO content. The most appropriate MgO content in the sinter was 1.3 wt% according to principal component analysis (PCA).

Effect of Mineral Elements Migration on Softening–melting Properties of Ti–bearing High Basicity Sinter

Effect of Mineral Elements Migration on Softening–melting Properties of Ti–bearing High Basicity Sinter

The Effects of Al2O3 and SiO2 on the Formation Process of Silico-Ferrite of Calcium and Aluminum (SFCA) by Solid-State Reactions

The silico-ferrite of calcium and aluminum (SFCA) is a significant crystalline phase that bonds in high basicity sinter. Al2O3 and SiO2 play an important role in the formation of SFCA in the Fe2O3–CaO–SiO2–Al2O3 system, but the effect mechanism of Al2O3 and SiO2 on the formation of SFCA is unclear. To investigate this effect, sintering experiments were carried out with different temperatures and different times. It was found that the reaction of Al2O3 with CaFe2O4 (CF) as an initial product was easier to form during the calcium iron aluminum oxide (CFA) than that of SiO2 with CF to form SFC. This was due to the former directly forming to CFA while the latter initially formed Ca2SiO4 (C2S) and Ca2.5Fe15.5O25, and then SFC. It was also observed that when Al2O3 and SiO2 existed simultaneously, the Al2O3 initially reacted with CF to form CFA at 1100 °C, while the SiO2 participated in the formation of SFCA at 1150 °C without the formation of SFC. Moreover, it was understood that these were different effects in that the Al2O3 promoted the transformation from the orthorhombic crystal system to the triclinic crystal system, while the SiO2 dissolved into CFA to form the SFCA phase when Al2O3 existed.

An experience of high-fluxed sinter production at Enakievo steel-works sintering plant

Industrial experience of high-basicity sinter production in different raw materials conditions, in particular, at sintering of fine concentrates and hardly utilized wastes is a matter of an interest for sinter production specialists. At Enakievo sinter plant in 2014–2018 under very complicated conditions of non-regular supplies of iron ore raw materials, forced utilization of a big amount of metallurgical wastes, non-satisfactory equipment technical state, a production of solid enough high-basicity sinter was provided. High-basicity sinter indices and sintering parameters for the period mentioned quoted. An analytical estimation of main stages of sinter production state and some kinds of technological equipment made. Peculiarities of the technology and production parameters of high-fluxed sinter at utilization of different iron ore concentrates, wastes and special additives to sinter burden considered. Scientific and practical recommendations for technology improving and modernization of technological equipment, used for the sinter burden preparation, elaborated. Based on these studies and authors practical experience, methods of sintering non-uniformity along the sintering machine width overcoming proposed: rational burden layer forming in the charging hopper and burden layer profile along the pallets width; compaction of the burden layer in peripheral pallets zones. Measures proposed for modernization of the drum-pelletizer and of the charging hopper. Description of the facility for rational burden preparation for sintering quoted.

Development of technologies with a purpose of increasing of metallurgical properties of Kachkanar pellets

A blast furnace technology developed, using equally basicity Kachkanar iron ore raw materials. Research work carried out to study gas media content and pellets basicity influence on their structure and metallurgical properties, as well as basicity and fuel content in the burden influence on metallurgical properties and structure of sinter. It was determined, that usage of low basicity pellets and high basicity sinter with weak rupture during reduction, provide a high gas penetrability in the upper horizons of blast furnace.It was shown, that presence of amphoteric titanium oxides and aluminum in Kachkanar sinter and pellets, as well as decrease of slope angle of the shaft in blast furnace prevents the early sticking of burden materials in the lower horizons of the furnace, that provides smooth burden lowering, high degree of gas reduction potential usage and thus the increase of the furnace productivity as well as coke rate decrease.An analysis of the work to optimize the technology of pellets production of Kachkanar concentrates made. It was determined, that an increase of the pellets quality can be reached as a result of implementation of a technology of their roasting with a partial dissociation of hematite. A complex estimation of metallurgical properties of partially dissociated pellets carried out. It was shown, that the pellets with hematite-magnetite structure, being a result of partial dissociation of hematite, are reduced at higher temperatures, when their intensive swell and rupture at the stage of hematite-into-magnetite transfer do not happen.

Effect of Aluminum Dissolved in Hematite on Formation of Calcium Ferrites at 1473 K

Silico-ferrite of calcium and aluminum (SFCA) is a primary bonding phase, which determines the quality of high basicity sinter used widely as raw materials in blast furnace ironmaking. Calcium ferrite containing aluminum (CFA) is a key precursor during the formation process of SFCA and is influenced by Al2O3 content in iron ore fines. In this work, the experiment was conducted to investigate the effect of the aluminum occurrence state on the formation of calcium ferrite by the simulating sintering process of different types of aluminum-bearing hematite at 1473 K. X-ray diffraction, optical microscope, scanning electron microscopy, and energy-dispersive spectroscopy were used to characterize the mineral change in sintered samples. The result shows that the formation of CFA was promoted by both granular Al2O3 wrapped in Fe2O3 and aluminum dissolved in Fe2O3 solid solution, especially for the latter, due to the formation of the CFA directly from the reaction between Fe2O3-Al2O3 solid solution and CaO, and the aluminum content in CFA formed was influenced obviously by the solid solution amount of alumina into Fe2O3 as raw materials.

The effects of MgO and Al2O3 behaviours on softening–melting properties of high basicity sinter

ABSTRACTBecause the behaviours of MgO and Al2O3 during slag formation of high basicity sinter are not clearly understood, the effects of MgO and Al2O3 on softening-melting properties are always arguable. In this paper, four kinds of sinter containing different MgO and Al2O3 content are investigated. Some observations are obtained. The mechanism of the influence of MgO and Al2O3 on softening properties of sinter are different. Al2O3 has priority over MgO to enter into slag phase and forms low-melting point phase while MgO remains unslagged state and mainly exists in wustite as FeO–MgO solid solution. When sinter melts, the viscosity of the slag generated from sinter containing high MgO and Al2O3 content is low, which could result in low pressure drop. As MgO and Al2O3 content increase, the main minerals of residual slag change from 2CaO•SiO2 to merwinte and melilite. The changes of the minerals in slag phase can well explain the trend of softening-melting characteristic temperatures.

The Dissolution Kinetics of MgO into CaO-MgO-Fe2O3 Slag

Calcium ferrite is the main binding phase for high-basicity sinter. The production and structure of calcium ferrite greatly influence the quality of the sinter. With the change in gangue composition, MgO becomes an important factor in the generation of calcium ferrite. In this study, the rotating cylinder method was used to study the dissolution kinetics of MgO into CaO-MgO-Fe2O3 melt. The experimental variables included the temperature, the initial composition of the melt, the Fe2O3/CaO mass ratio, the rotation time, and the rotation speed. The results indicate that the dissolution rate increases with increasing dissolution time, temperature, and rotation speed but decreases with increasing MgO content and Fe2O3/CaO mass ratio in the initial slag. The dissolution rate was observed to increase and then decrease with the addition of SiO2 in the initial slag. The activation energy and diffusion coefficient for MgO dissolution were found to range from 117.31 to 234.24 kJ mol−1 and from 1.03 × 10−6 to 1.18 × 10−5 cm2 s−1, respectively. The concentration difference between the solid and liquid phases is the main driving force for dissolution, but the viscosity and magnesium ion diffusivity of the melt also affect the process.

Optimisation of the blast furnace burden based on its primary slag formation behaviour

The iron ore consumption doubled several times due to the rapid development of ironmaking industry in China, resulting in the worse quality of iron ores in the past decade. Therefore, the efficient utilisation of poor quality iron ore resources is of great importance for the sustainable development of ironmaking industry. In this work, a new method for optimisation of blast furnace burdens was studied based on the primary slag formation behaviour because it has significant influence on the formation of the cohesive zone. The results showed that there was obvious interaction between sinter and acid iron ores at high temperature, and the primary slag formation behaviour was clearly improved by the high temperature interaction. The poor quality lump ore could be utilised together with high basicity sinter and self-fluxed pellet to enhance the high temperature interaction. Besides, increasing CaO and MgO content in blast furnace burdens would further improve their primary slag formation behaviour and the performance of cohesive zone.

Dissolution Kinetics of SiO2 into CaO-Fe2O3-SiO2 Slag

High-basicity sinter is the predominant Fe-bearing material used in blast furnace process in East Asia. The dissolution of SiO2 into molten calcium ferrite influences the assimilation process. In this study, a rotating cylinder method was used to explore the dissolution kinetics of SiO2 into CaO-Fe2O3-SiO2 slag. The influencing factors, including temperature, rotating time and speed, and initial composition of the slag, were considered. Results showed that the dissolution rate increased with increasing rotation speed and temperature, whereas the increase in ω(SiO2) or ω(Fe2O3)/ω(CaO) ratio in the initial slag composition decreased the dissolution rate. The diffusion coefficient and activation energy of SiO2 during the dissolution process ranged from 2.09 × 10−6 to 6.40 × 10−6 cm2 s−1 and 106.62 to 248.20 kJ mol−1, respectively. Concentration difference between the boundary layer and bulk phase was the primary driving force of the dissolution process; however, this process was also influenced by the slag viscosity and ion diffusivity.

Softening and melting properties of different burden structures containing high chromic vanadium titano-magnetite

The present work studied the softening and melting properties of different burden structures including pellet, sinter and mixed burden (pellet mixed with sinter) with a pellet ratio of 33.65%. The content of high chromic vanadium titano-magnetite in sinter and pellet was different. The experimental results indicated that the compositions of the burden have an important effect on the softening and melting properties. The softening and melting properties of pellet burden structure were improved when the high basicity sinter was added into the acid pellet forming mixed burden. The softening and melting properties of mixed burden with a pellet ratio of 33.65% were better than other burden structures. The initial softening temperature, the temperature interval of softening, the starting melting temperature, the temperature interval of melting, and maximum differential pressure were 1100°C, 130°C, 1250°C, 130°C and 15.7kPa, respectively. By comparing the contents of Ti, V and Cr of iron that had dripped through the different burden structures, the content of valuable components (Ti 0.349%, V 0.244% and Cr 0.094%) was highest of the pig iron collected from the mixed burden.

The Sintering Characteristics of Mixing SiO2 with Calcium Ferrite at 1473 K (1200 °C)

The liquid-generating capability in high basicity sinter was investigated by adding SiO2 to CaO·Fe2O3 (CF) at 1473 K (1200 °C) in air for 4 hours. X-ray diffraction, electron-probe microanalysis, and optical microscopy combining with etching test were used to characterize the phase change of sintered samples. The results show that the minor SiO2 additions from 0.14 wt pct to 6.49 wt pct to CF depressed the melting temperature of CF. New phases of formation included from SFC (silico-ferrite of calcium), SFC + Hem (Fe2O3) + CS (CaO·SiO2) to Hem + CS in samples with SiO2 additions from 0.05 wt pct to 21.74 wt pct. With the maximum SFC produced in sample, the amount of SiO2 addition was 10.64 wt pct. To understand the depressing mechanism of CF melting temperature, the experiments of differential scanning calorimetry for samples of CF, SFC, CF-SiO2 (3.0 wt pct), and CF-SFC (50.0 wt pct) had been carried out. The result shows that mixing of SiO2 or SFC with CF decreased the melting temperature of CF by 35 K and 34 K (35 °C and 34 °C), respectively, resulted in melting temperature approaching the eutectic temperature between CF and SFC. The phase relations between CF and SFC, as well as the intermediate products in depressing the melting temperature, will be an important guide to improve the sintering characteristics of iron ores.

Wetting Behavior of Al<sub>2</sub>O<sub>3</sub> Substrate by Calcium Ferrite Series Melts

Calcium ferrite (CF) is the adhesive phase formed in high-basicity sinter. The wettability of CF with other solid phases plays an important role in assimilation process. In this study, an improved sessile drop technique was used to explore the wettability of a CF series slag, in which constant contents of Al2O3, MgO, SiO2, and TiO2 were added, with solid Al2O3 substrate at 1250°C. The interfacial structure and spreading mechanisms were also discussed. The dissolution of Al2O3 into the slag was found to be the driving force of the wetting process. The CF series slag could rapidly spread after melting until a low apparent contact angle of approximately 10°–20° was attained. The spreading time positively correlated with the dissolution amount. The addition of MgO, SiO2, and TiO2 improved the wettability of CF on Al2O3 and decreased the surface tension of CF melt. After cooling, a three-layer structure was formed in the slag phase.