Research

14 pages, 7220 KiB

Open AccessArticle

Microstructure and Minerals Evolution of Iron Ore Sinter: Influence of SiO₂ and Al₂O₃

by Zhiyun Ji, Yuanjie Zhao, Min Gan, Xiaohui Fan, Xuling Chen and Lin Hu

Minerals 2019, 9(7), 449; https://doi.org/10.3390/min9070449 - 19 Jul 2019

Cited by 15 | Viewed by 3517

SiO₂ and Al₂O₃ are two important minerals that can affect the mechanical and metallurgical properties of sinter. This investigation systematically studied the influences of these minerals and revealed their functional mechanisms on sinter quality. Results showed that with an [...] Read more.

SiO₂ and Al₂O₃ are two important minerals that can affect the mechanical and metallurgical properties of sinter. This investigation systematically studied the influences of these minerals and revealed their functional mechanisms on sinter quality. Results showed that with an increasing Al₂O₃ content in sinter, the sintering indexes presented an improvement before the content exceeded 1.80%, while the quality decreased obviously after the content exceeded 1.80%. With an increasing SiO₂ content, the sinter quality presented a decreasing tendency, especially when the content exceeded 4.80%. Consequently, the optimal content of Al₂O₃ was ≤1.80% and that of SiO₂ was ≤4.80%. The evolution of the microstructure and minerals in sinter showed that enhancing the Al₂O₃ content increased the proportion of SFCA generated, which improved the sinter’s mechanical strength, while excessive Al₂O₃ led to the formation of sheet-like SFCA with weak mechanical strength. Increasing the content of SiO₂ strained the formation of SFCA and promoted the formation of calcium silicate, the mechanical strength of which is lower than that of SFCA. The research findings will be useful in guiding practical sintering processes. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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28 pages, 17292 KiB

Open AccessArticle

Measurement of Process Conditions Present in Pilot Scale Iron Ore Sintering

by Stuart Nicol, Jiang Chen, Wei Qi, Xiaoming Mao, Evgueni Jak and Peter C. Hayes

Minerals 2019, 9(6), 374; https://doi.org/10.3390/min9060374 - 22 Jun 2019

Cited by 9 | Viewed by 5741

Abstract

An improved experimental technique has been developed to measure, concurrently, the oxygen partial pressures and temperatures within a pilot scale iron ore sinter pot as a function of time. The measurements and thermodynamic calculations have demonstrated that the oxygen partial pressure at peak [...] Read more.

An improved experimental technique has been developed to measure, concurrently, the oxygen partial pressures and temperatures within a pilot scale iron ore sinter pot as a function of time. The measurements and thermodynamic calculations have demonstrated that the oxygen partial pressure at peak bed temperature and during cooling can be oxidising or reducing relative to hematite. Examples of typical microstructures and phase assemblages observed in product sinters are presented. Potential mechanisms of hematite and magnetite formation at sub-liquidus and sub-solidus conditions are demonstrated. The relative impacts of changes to coke rate and draft pressure drop on the process conditions and proportions of the phases formed in the sinter have been measured. Increasing coke rate was shown to result in a faster sinter heating rates, higher peak bed temperatures and times at peak temperature. Higher draft pressures across the sinter bed resulted in faster sinter heating rates and shorter times at peak temperature. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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13 pages, 3523 KiB

Open AccessArticle

Thermodynamic Modelling of Iron Ore Sintering Reactions

by Chunlin Chen, Liming Lu and Kexin Jiao

Minerals 2019, 9(6), 361; https://doi.org/10.3390/min9060361 - 13 Jun 2019

Cited by 19 | Viewed by 4029

Abstract

Silico-ferrite of calcium and aluminum (SFCA) is one of the most commonly-produced phases in fluxed iron-ore sintering, and has long been regarded as an important bonding phase in industrial sinters. It is thus considered to have a significant effect on sinter quality. In [...] Read more.

Silico-ferrite of calcium and aluminum (SFCA) is one of the most commonly-produced phases in fluxed iron-ore sintering, and has long been regarded as an important bonding phase in industrial sinters. It is thus considered to have a significant effect on sinter quality. In this study, a solid solution model and database has been developed for the SFCA phase, and has been incorporated into the thermodynamic software, Multi-Phase Equilibrium (MPE). MPE calculations were compared with the in situ X-ray powder diffraction (XRD) observations of the formation of SFCA phase during sintering. The effects of the raw material composition, temperature and the oxygen partial pressure on the formation of mineral phases in the sinter, as well as the viscosity of the melt formed during sintering under equilibrium conditions, were modelled using MPE. The results show that the formation of SFCA phase can be promoted by increasing oxygen partial pressure and basicity of the raw material. Increases of Al₂O₃ and MgO content have no significant effect on the SFCA formation under equilibrium condition. The increase of oxygen partial pressure (10⁻³ atm or above) and basicity also leads to a decrease in melt viscosity, which enhances the fluidity of the melt, and hence, the assimilation of the sinter. However, increases of Al₂O₃ and MgO result in the increase of melt viscosity. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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17 pages, 7072 KiB

Open AccessArticle

Comparison of the Mineralogy of Iron Ore Sinters Using a Range of Techniques

by T. Honeyands, J. Manuel, L. Matthews, D. O’Dea, D. Pinson, J. Leedham, G. Zhang, H. Li, B. Monaghan, X. Liu, E. Donskoi, N. A. S. Webster and M. I. Pownceby

Minerals 2019, 9(6), 333; https://doi.org/10.3390/min9060333 - 28 May 2019

Cited by 31 | Viewed by 5495

Abstract

Many different approaches have been used in the past to characterise iron ore sinter mineralogy to predict sinter quality and elucidate the impacts of iron ore characteristics and process variables on the mechanisms of sintering. This paper compares the mineralogy of three sinter [...] Read more.

Many different approaches have been used in the past to characterise iron ore sinter mineralogy to predict sinter quality and elucidate the impacts of iron ore characteristics and process variables on the mechanisms of sintering. This paper compares the mineralogy of three sinter samples with binary basicities (mass ratio of CaO/SiO₂) between 1.7 and 2.0. The measurement techniques used were optical image analysis and point counting (PC), quantitative X-ray diffraction (QXRD) and two different scanning electron microscopy systems, namely, Quantitative Evaluation of Materials by Scanning Electron Microscopy (QEMSCAN) and TESCAN Integrated Mineral Analyser (TIMA). Each technique has its advantages and disadvantages depending on the objectives of the measurement, with the quantification of crystalline phases, textural relationships between minerals and chemical compositions of the phases covered by the combined results. Some key differences were found between QXRD and the microscopy techniques. QXRD results imply that not all of the silico-ferrite of calcium and aluminium (SFCA types) are being identified on the basis of morphology in the microscopy results. The amorphous concentration determined by QXRD was higher than the glass content identified in the microscopy results, whereas the magnetite and total SFCA concentration was lower. The scanning electron microscopy techniques were able to provide chemical analysis of the phases; however, exact correspondence with textural types was not always possible and future work is required in this area, particularly for differentiation of SFCA and SFCA-I phases. The results from the various techniques are compared and the relationships between the measurement results are discussed. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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14 pages, 4153 KiB

Open AccessArticle

Investigations of MgO on Sintering Performance and Metallurgical Property of High-Chromium Vanadium-Titanium Magnetite

by Liheng Zhang, Songtao Yang, Weidong Tang and Xiangxin Xue

Minerals 2019, 9(5), 324; https://doi.org/10.3390/min9050324 - 27 May 2019

Cited by 14 | Viewed by 2828

Abstract

High-chromium vanadium-titanium magnetite (HCVTM) in the Hongge region has been used as an essential mineral resource in ironmaking. The effects of MgO on sintering performance and metallurgical properties were investigated by sintering pot tests, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy [...] Read more.

High-chromium vanadium-titanium magnetite (HCVTM) in the Hongge region has been used as an essential mineral resource in ironmaking. The effects of MgO on sintering performance and metallurgical properties were investigated by sintering pot tests, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). HCVTM sinters with varying MgO contents (2.7–3.5%), which was achieved by adding dolomite, were tested for yield, strength, reduction degradation index (RDI), reduction index (RI), and softening-melting properties. The productivity and the comprehensive index were evaluated. The results show that yield and productivity increased, while the vertical sintering speed and the tumbler index (TI) initially increased then decreased with the increase of MgO content. The mineral structure of HCVTM sinter changed from a non-uniform state to a uniform state with increased MgO content. Most of the Mg²⁺ entered the magnetite lattice, while a small amount entered the perovskite and the calcium silicate. The increase of MgO content improved RDI and softening-melting properties while reducing RI. The best recommended amount of MgO was 3.3% from the comprehensive index. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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11 pages, 4778 KiB

Open AccessArticle

Influence of MgO on Low Temperature Reduction and Mineralogical Changes of Sinter in Simulated COREX Shaft Furnace Reducing Conditions

by Deqing Zhu, Jianlei Chou, Benjing Shi and Jian Pan

Minerals 2019, 9(5), 272; https://doi.org/10.3390/min9050272 - 01 May 2019

Cited by 16 | Viewed by 2598

Abstract

COREX (Coal-Reduction-Extreme) smelting reduction process provides a sustainable developing way for ironmaking industry, but the sources of iron ore materials restrict its development in China. Meanwhile, the application of sinter, which is marked by low manufacture cost and overcapacity in China, to COREX [...] Read more.

COREX (Coal-Reduction-Extreme) smelting reduction process provides a sustainable developing way for ironmaking industry, but the sources of iron ore materials restrict its development in China. Meanwhile, the application of sinter, which is marked by low manufacture cost and overcapacity in China, to COREX furnace faced proportion limitation due to its worse low temperature reduction degradation performance. This work explored the influence of MgO content on the low-temperature (550 °C) reduction of sinter in reducing conditions simulating COREX shaft furnace. The mineralogical change of sinter containing different content of MgO before and after reduction was analyzed by X-ray diffraction (XRD), optical microscopy, and scanning electron microscopy for revealing the action mechanism of MgO on the low-temperature-reduction of sinter. The results show that increasing MgO (1.36–3.10%) improved the low temperature reduction degradation performance of sinter, and decreased its reduction degree and reduction rate at low temperature. More MgO the sinter contained, less Fe₂O₃ and SFCA was observed in sinter. Meantime, less Fe₂O₃ was reduced and the generation of innerstress was restrained during reduction process. The improved RDI (reduction degradation index) in COREX process of sinter by increasing MgO content is a comprehensive result of lowering strength and inhibiting probable reduction of sinter. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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25 pages, 12392 KiB

Open AccessArticle

Ore Assimilation and Secondary Phases by Sintering of Rich and High-Gangue Iron Ores

by Roland Mežibrický, Mária Fröhlichová, Róbert Findorák and Valerie Sue Goettgens

Minerals 2019, 9(2), 128; https://doi.org/10.3390/min9020128 - 22 Feb 2019

Cited by 14 | Viewed by 4954

Abstract

During the iron ore sintering process, two types of particles are present in the sinter bed: (1) fines, which are actively taking part in melting and the formation of secondary phases, and (2) coarse ores, which are partially interacting with the surrounding melt. [...] Read more.

During the iron ore sintering process, two types of particles are present in the sinter bed: (1) fines, which are actively taking part in melting and the formation of secondary phases, and (2) coarse ores, which are partially interacting with the surrounding melt. The quality of the final sinter is particularly determined by the secondary phases and their bonding ability. Due to chemical differences between the fines and coarse particles, knowing the overall chemical composition of the sintering blend is not sufficient to estimate the final sinter microstructure. In this study, different ore types were used to prepare iron-rich, high-alumina, and high-silica blends, which were sintered in a laboratory sinter pot to investigate the behavior of fine as well as coarse particles. As a result, very different sinter matrices formed depending on the useful basicity in each sinter. The density, mineral nature, and the gangue of the ore affected coarse ore assimilation. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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12 pages, 8034 KiB

Open AccessArticle

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

by Fei Liao and Xing-Min Guo

Minerals 2019, 9(2), 101; https://doi.org/10.3390/min9020101 - 10 Feb 2019

Cited by 12 | Viewed by 4519

Abstract

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–Al [...] Read more.

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 Ca_2.5Fe_15.5O₂₅, 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. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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