Reduction Behavior and Structural Evolution of Iron Ores in Fluidized Bed Technologies—Part 2: Characterization and Evaluation of Worldwide Traded Fine Iron Ore Brands

Pichler, Anton; Mali, Heinrich; Plaul, Friedemann; Schenk, Johannes; Skorianz, Michael; Weiss, Brandon

doi:10.1002/srin.201500176

Cited by 8 publications

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“…Denser areas appears brighter under the optical microscope, which indicates oxidized magnetite. [29][30][31][32][33][34][35] The raw magnetite appears to be dense iron ore, as given in Figure 1(a). The conversion due to the oxidation of the magnetite ultra-fines follows a plate-like growth from the outer surface towards the core, as illustrated with the white areas in Figures 1(b) and (c) for the 53 and 90 pct oxidized magnetite.…”

Section: A Materialsmentioning

confidence: 99%

Influence of a Prior Oxidation on the Reduction Behavior of Magnetite Iron Ore Ultra-Fines Using Hydrogen

Wolfinger

Spreitzer

Zheng

et al. 2021

Metall Mater Trans B

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The reduction behavior of raw and prior-oxidized magnetite iron ore ultra-fines with hydrogen was investigated. Reduction tests were conducted with a thermogravimetric analyzer in a temperature range from 873 K to 1098 K at 1.1 bar absolute, using hydrogen as reducing gas. The experimental results show that a prior oxidation of the magnetite has a positive effect on the reduction behavior because of changing morphology. The apparent activation energies show a turnaround to negative values, depending on the prior oxidation and degree of reduction. A multi-step kinetic analysis based on the model developed by Johnson–Mehl–Avrami was used to reveal the limiting mechanism during reduction. At 873 K and 948 K, the reduction at the initial stage is controlled by nucleation and chemical reaction and in the final stage by nucleation only, for both raw and pre-oxidized magnetites. At higher temperatures, 1023 K and 1098 K, the reduction of raw magnetite is mainly controlled by diffusion. This changes for pre-oxidized magnetite to a mixed controlled mechanism at the initial stage. Processing magnetite iron ore ultra-fines with a hydrogen-based direct reduction technology, lower reduction temperatures and a prior oxidation are recommended, whereby a high degree of oxidation is not necessary.

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Section: A Materialsmentioning

confidence: 99%

Influence of a Prior Oxidation on the Reduction Behavior of Magnetite Iron Ore Ultra-Fines Using Hydrogen

Wolfinger

Spreitzer

Zheng

et al. 2021

Metall Mater Trans B

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“…It is well established that hematite iron ores show better reducibility than that of magnetite iron ores. [ 59,60 ] It is of great of interest to know the difference of reduction behavior between oxidized magnetite and hematite in particle scale. Edström [ 61 ] oxidized natural single crystals of magnetite (Fe 3 O 4 ) and compared the reduction rate with that of hematite (Fe 2 O 3 ) in CO atmosphere at 1000 °C.…”

Section: The Influence Of Oxidation Of Magnetite On Its Subsequent Reductionmentioning

confidence: 99%

Review on the Oxidation Behaviors and Kinetics of Magnetite in Particle Scale

Zheng

Schenk

Spreitzer

et al. 2021

steel research int.

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One possible route for ironmaking process is using a hydrogen‐gas‐based fluidized bed to produce direct reduced iron (DRI), which allows to use the natural magnetite directly in particle scale. The magnetite particles are oxidized during the preheating stage before being charged into the reduction unit. The exothermic effect, the crystal transformation, and the structural evolution during the oxidation of magnetite are introduced. The oxidation of magnetite is summarized in both thermodynamics and kinetics aspects. Furthermore, the influence of the oxidation of magnetite on its subsequent reduction behavior is examined.

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“…The gaseous reduction of solid iron oxide particles usually proceeds in a topochemical manner (occurring at the interface between phases), with the reaction starting from the particle surface (Ross, 1980;Kaushik and Fruehan, 2006;Weiss et al, 2010Weiss et al, , 2011Spreitzer and Schenk, 2019b). Figure 2.2 shows example of cross-section images of two types of partially reduced iron oxide particles: (a) dense particles, and (b) porous particles (from Pichler et al, 2016). Partially reduced dense iron oxide particles typically show a central unreacted region of iron oxide surrounded by metallic iron on the outer surface.…”

Section: Fundamentals In Iron Ore Reduction By H2 Gasmentioning

confidence: 99%

“…However, for porous iron oxide particles, the reaction can nucleate from pores within the particle, and the microstructure of the partially reduced porous particle does not show a topochemical type boundary (Pichler et al, 2016).…”

Section: Fundamentals In Iron Ore Reduction By H2 Gasmentioning

confidence: 99%

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Reduction of New Zealand Titanomagnetite Ironsand by Hydrogen Gas in a Fluidised Bed System

Prabowo¹

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<p>Titanomagnetite (TTM) ironsand has been used to produce steel in New Zealand (NZ) for about 40 years. However, the current steelmaking process in NZ produces high emissions of CO2 because it uses coal as a primary reducing agent. The fluidised bed (FB) process allows the use of pure hydrogen gas to reduce ironsand, and as a result, does not produce CO2 gas. However, for conventional hematite ores, reduction in a FB system is usually limited by the onset of particle sticking at temperatures ≳ 800°C. This thesis investigates the reduction of NZ TTM ironsand by hydrogen gas in the FB system with a key focus on ore sticking behaviour. Initially, this thesis reports preliminary fluidisation tests by nitrogen and helium gases at room temperature, carried out to determine key fluidisation parameters for ironsand powder. From these results, a laboratory-scale experimental FB reactor has been designed and built for the hydrogen reduction study at high temperatures. A key feature of the reactor is a novel in-situ sampling system, which enables extraction of multiple samples during a single experimental run without interrupting operation of the FB. Quantitative X-ray diffraction (q-XRD) has been used to determine the metallisation degree of partially reduced samples. Phase evolution during the reaction has also been analysed using q-XRD alongside scanning electron microscopy/energy dispersed spectroscopy (SEM/EDS). Additionally, the water vapour compositions in the exhaust gas were calculated from the q-XRD data and also measured in real-time using a high-temperature humidity sensor. The effect of various parameters has been investigated within the FB reduction experiments: hydrogen gas concentrations, hydrogen gas flow rate, bed mass, particle size, and temperature. The results indicate that across the entire range of controlled studied, the FB reduction rate of TTM ironsand is simply controlled by the rate of hydrogen gas supply. Interestingly, there were no occurrences of the sticking phenomenon at any point during the reduction by hydrogen gas at high temperatures of up to 1000°C. Sticking appears to be prevented by the formation of a protective titanium-rich oxide shell around each particle during the initial reduction stage. Importantly, this shell remains present throughout the reduction process, and as a result, the reduction reaction proceeds rapidly to completion with a metallisation degree of ~93%. The influence of temperature on the reaction progress has also been investigated. The reduction pathway appears to vary within different temperature regimes. At low temperatures (750°C-800°C), TTM is directly reduced to metallic iron and ilmenite without any evidence of wüstite phase. At ‘intermediate temperatures’ (850°C-900°C) small amount of short-lived wüstite is observed. Some of the amount of TTM appears to be reduced to wüstite, and some is directly reduced to metallic iron. At high temperatures (≥ 950°C), approximately half of the initial TTM phase is quickly reduced to wüstite. After that point, wüstite is then reduced to metallic iron whilst the reduction of TTM stops. This is due to the enrichment of Ti species in TTM phase, which stabilises TTM crystal. Once wüstite has been fully reduced, the reduction of TTM then resumes. Throughout the entire experimental program for this thesis, particle sticking was observed to occur only under two specific sets of experimental conditions. These were: reduction by 100% H2 gas at 1050°C (case A) and reduction by 7.5 mol.% H2O – 92.5 mol.% H2 at 950°C (case B). In both cases, sticking occurred as a sinter which nucleated at the reactor wall surface, while most particles remained fluidised as loose powder. The mechanism of these sticking cases has been analysed by XRD and SEM. The results suggest that silica from the quartz reactor wall reacted and bonded with Fe from particles to nucleate the initial sinter. In summary, the findings in this thesis show that the hydrogen-FB process is highly effective in reducing NZ ironsand to a direct reduced iron (DRI) product. These findings open up the possibility of developing a new industrial FB technology for the direct reduction of NZ TTM ironsand, with extremely low CO2 emissions.</p>

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Reduction Behavior and Structural Evolution of Iron Ores in Fluidized Bed Technologies—Part 2: Characterization and Evaluation of Worldwide Traded Fine Iron Ore Brands

Cited by 8 publications

References 14 publications

Influence of a Prior Oxidation on the Reduction Behavior of Magnetite Iron Ore Ultra-Fines Using Hydrogen

Influence of a Prior Oxidation on the Reduction Behavior of Magnetite Iron Ore Ultra-Fines Using Hydrogen

Review on the Oxidation Behaviors and Kinetics of Magnetite in Particle Scale

Reduction of New Zealand Titanomagnetite Ironsand by Hydrogen Gas in a Fluidised Bed System

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