Reduction Of Magnetite Research Articles

Remagnetization under hydrothermal alteration of Paleocene South Tibetan lavas: maghematization, hematization, and grain size reduction of (titano)magnetite

Remagnetization under hydrothermal alteration of Paleocene South Tibetan lavas: maghematization, hematization, and grain size reduction of (titano)magnetite

Remagnetization under hydrothermal alteration of Paleocene South Tibetan lavas: maghematization, hematization, and grain size reduction of (titano)magnetite

Remagnetization under hydrothermal alteration of Paleocene South Tibetan lavas: maghematization, hematization, and grain size reduction of (titano)magnetite

Kinetics and microstructural changes during fluidized reduction of magnetite with hydrogen at low temperatures

Hydrogen reduction has received much attention in reducing carbon dioxide emissions and becoming carbon neutral in the iron and steel industry. In this study, the low-temperature hydrogen reduction (H2: N2 = 80%: 20%) process of natural magnetite in a fluidized bed was investigated. The reduction kinetics, phase transformation, and microstructure changes were characterized using chemical analyses, X-ray diffraction, Brunauer–Emmett–Teller method, and scanning electron microscopy. The results revealed that the magnetite was reduced to metallic iron in one step in the temperature range of 495 °C to 570 °C, and the reaction rate increased with increasing temperature. The one-step reduction of magnetite was controlled by the phase boundary reaction, and the apparent activation energy was 29.76 kJ/mol. Microstructural analysis indicated that as the reduction reaction progressed, micropores and cracks on the surface of the solid particles gradually developed. The dense magnetite core was wrapped by the porous metallic iron, which promoted the penetration of hydrogen into the particles and continued the reaction.

Розрахунок температур перебігу хімічних реакцій процесу ступінчастого відновлення заліза з гематиту газом СО і газифікації твердого вуглецю за мірами хімічної спорідненості речовин до кисню

This article presents the results of a theoretical analysis that made it possible to evaluate the thermodynamic conditions for the flow of chemical reactions of the stepwise reduction of iron from hematite with a reducing gas CO and the Bell–Boudoir chemical reaction (gasification of solid carbon). Taking into account the degrees of chemical affinity for oxygen of the reduced substance and the reducing agent, it is confirmed that for each of the indicated reduction reactions, there is a certain (called the “boundary” temperature by the author), up to (for the processes of reduction of magnetite from hematite and wustite from magnetite) or above (for the process of reducing iron from wuestite) which the reducing gas CO can not thermodynamically be a reducing agent for iron or its lower oxides, and also up to which the gasification of solid carbon by the Bell–Boudoir reaction is thermodynamically impossible. Using the expressions available in the literature and derived by the author of the work, graphical dependences of the numerical values of the Gibbs free energy on temperature were obtained for oxidative reactions of obtaining (due to oxidation with gaseous oxygen) iron oxides (FeO from Fe, Fe3O4 from FeO, Fe2O3 from Fe3O4 and carbon oxides (CO from C, СО2 from C and from CO), which made it possible to estimate the degree of chemical affinity of the reduced substance and the reducing agent for oxygen in these oxidative reactions; based on which all possible numerical values of the boundary temperatures and the temperature range of their thermodynamically possible occurrence were found for the reduction reactions of the stepwise production of iron from hematite with CO gas and gasification of solid carbon, the most probable of them were substantiated.

Temperature programmed reduction of a core-shell synthetic magnetite: Dependence on the heating rate of the reduction mechanism

Temperature programmed reduction studies of a core-shell synthetic nano-magnetite showed that its reduction mechanism is influenced by the heating rate. According to magnetic measurements 30% of synthetic magnetite sample consists in a paramagnetic thin layer composed of γ-Fe2O3 and a superficial layer of FeOOH. Wüstite disproportionation determines, at temperatures below 843 K (570 °C), the apparent reduction of magnetite directly to metallic iron. The static reduction of this synthetic magnetite at various temperatures revealed details of the reduction mechanism. The kinetic parameters of all the reduction processes were evaluated by TPR thermogram simulations.

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

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.

Rate-enhancement effect of CO in magnetite concentrate particle reduction by H2+CO mixtures

ABSTRACT The kinetics of the reduction of magnetite concentrate particles by H2+CO mixtures have been investigated in drop-tube reactors (DTRs) to obtain rate expressions for the design of novel flash ironmaking reactors. The experimental temperature varied from 1423 K (1150°C) to 1873 K (1600°C). The H2/CO ratio was varied from 0.5 to 2, which is the typical composition range of the product gas from the partial oxidation of natural gas. The experimental data were analysed separately in two temperature ranges 1423 K (1150°C)–1623 K (1350°C) and 1623 K (1350°C)–1873 K (1600°C), as the magnetite concentrate particles tend to fuse and melt at temperatures above 1623 K (1350°C) changing the reduction mechanism. CFD (Computational Fluid Dynamics) simulations were used to more accurately account for temperature and concentration variations. Synergistic effects were observed in the reduction by H2+CO mixtures compared with the simple summation of contributions of the individual component gases.

The kinetics of carbon monoxide reduction of magnetite concentrate particles through CFD modelling

ABSTRACT The kinetics of CO reduction of magnetite concentrate particles was investigated in drop-tube reactors (DTR) to obtain a rate equation for the design and analysis of a flash ironmaking reactor. The effect of CO partial pressure was determined and temperature was varied from 1473 K to 1873 K in few seconds of residence time similar to that in a typical flash reactor. The experimental data were divided into two temperature ranges, below 1623 K and above where the magnetite concentrate melts. The reduction degrees achieved at temperatures below 1623 K were under 50%, while significant reduction degrees (higher than 85%) were achieved at higher temperatures. Computational fluid dynamics (CFD) analysis was employed to improve the accuracy of the rate expressions. It was determined that the nucleation and growth kinetics best describes the investigated reaction. The activation energy was 451 and 88 kJ mol−1, respectively, below and above 1623 K.

The influence of an external magnetic field on the dynamics of magnetite reduction with hydrogen.

The kinetics of hydrogen reduction of magnetite was investigated in different magnetic fields. The magnetic moment measurements in situ were used for the control of the reaction. A strong difference in the magnetic properties of the reaction results was obtained for applied strong and weak magnetic fields. The X-ray diffraction and Mössbauer spectra of the reduced samples confirmed their different composition. The mechanism of the magnetic field effect is discussed.

Reduction of Magnetite from Copper Smelting Slag in the Presence of a Graphite Rod

Through the reduction reaction of Fe3O4 and graphite rod, the viscosity of slag was reduced and the settlement of matte in slag was promoted. The reduction of Fe3O4 in copper slag by a graphite rod was studied and the kinetics of the reduction process analyzed. The results show that the content of Fe3O4 decreased with increase in reduction temperature and reduction time. The slag samples after reduction were examined and found to consist of three layers: a slag foam layer, a fayalite layer, and a matte layer. A substantial number of large-sized matte particles were found in the slag foam layer. Also, a layer of Fe3O4 was attached to the upper surface of the matte layer. The reduction of Fe3O4 was concluded to be a second-order reaction, the apparent activation energy was 610 kJ/mol, and the limiting step was the Boudouard reaction.

Kinetics of hydrogen reduction of magnetite concentrate particles at 1623–1873 K relevant to flash ironmaking

ABSTRACT The reduction of magnetite concentrate particles by H2 has been investigated in drop-tube reactor (DTR) to obtain a rate equation that can be applied to the design and analysis of an ironmaking flash reactor. The temperature range in this work is 1623 to 1873 K, where the magnetite concentrate particles become molten droplets. Full reduction of the magnetite concentrate is achieved at a residence time greater than 4 s and H2 partial pressure of 0.15 atm within the temperature range investigated. Computational fluid dynamics analysis is used to improve the accuracy of the obtained rate expressions where the variation of particle temperature is taken into consideration. The reduction of magnetite concentrate particles in this temperature range is best described by the nucleation and growth model with an Avrami parameter n = 1 and a first-order dependence on the partial pressure of H2. The activation energy of reaction is 180 kJ mol−1.

The Mechanical Alloying of Magnetite Concentrate with Biochar

Aim:In this work, the effect of milling time on the mechanical alloying of the mixture containing the magnetite concentrate and biomass waste was investigated.Materials and Methods:The ore’s grade consisting of hematite and magnetite minerals was increased from 49.87% Fe to 67.29% Fe using the low intensity wet magnetic separator. Biomass waste which was supplied from ÇAYKUR black tea facilities, used as a carbon source was subjected to carbonization processes at 800°C for 1440 min. After the carbonization process, the carbon and sulphur contents of the biomass were measured as 94.68% and 0.03%, respectively. For the mechanical alloying process, a mixture consisting of magnetite concentrate with a grain size of -45 μm and biomass which was added two times the amount of carbon required for the reduction of magnetite to metallic iron was used.Result:After the mechanical alloying process which was carried out at different times, it was observed in the particle size analysis that the particle size of 90% of the mixture was reduced to about 4 μm. In SEM (Scanning Electron Microscopy) images, cube-like particles along with the spherical particles were observed depending on the mechanical alloying times. After 45 minutes of alloying, it was observed that the carbonized product milled together with magnetite concentrate was partially integrated into the crystal structure.Conclusion:The carbonized tea plant waste milled together with magnetite concentrate was partially integrated into the crystal structure. And the mechanical alloying provide to increase in the specific surface area in parallel with the grain size decrease in the study. Thus, in the later stage of the study, the milled powder acquired more ability to react.

Experimental Investigation and Computational Fluid Dynamics Simulation of the Magnetite Concentrate Reduction Using Methane-Oxygen Flame in a Laboratory Flash Reactor

An experimental investigation of the reduction of magnetite concentrate particles was conducted in a laboratory-scale flash reactor representing a novel flash ironmaking process. In this reactor, methane was partially oxidized by oxygen to form a reducing H2 + CO gas mixtures. The test variables in this work included the particle residence time, the extent of excess reducing gases, particle feeding mode, and flame configuration. The experimental results obtained from this reactor proved that the concentrate particles can be reduced directly in a flash reactor utilizing natural gas. More than 80 pct reduction was achieved in this reactor despite its low operating temperature (1170 °C). In addition, a three-dimensional computational fluid dynamics model was developed to describe the reduction of concentrate particles in this reactor. The model was used to simulate the fluid flow, heat transfer, and chemical reactions involved. The gas phase was simulated in the Eulerian frame of reference, while the particles were tracked in the Lagrangian framework. The partial combustion of methane by oxygen was also simulated in this study. The temperature profile obtained from the simulations satisfactorily agreed with the experimental measurements, while the calculated reduction degrees consistently over predicted the experimental values. This was attributed to the soot formation as a consequence of methane cracking due to large metal surface of the reactor. The soot formation led to a high-water vapor generation in the partial combustion, which lowered the excess of hydrogen.

Influence of an external magnetic field on the dynamics of magnetite reduction by hydrogen

Influence of an external magnetic field on the dynamics of magnetite reduction by hydrogen

Contribution to the Examination of the Mechanisms of Copper Loss with the Slag in the Process of Sulfide Concentrates Smelting

This paper presents the results of an experimental investigation into the distribution of copper in the slag of an industrial reverberatory furnace sulfide concentrates smelting process in the copper smelter RTB Bor (Serbia). The influence of copper content in the matte, the temperature and the height of the slag on the content of copper in the slag was determined as Cuoxide, Cusulfide and Cutotal and was based on possible mechanisms for the loss of copper in a silicate slag from the smelting of sulfide copper concentrates. The greatest quantity of copper in the silicate slag was found in the form of matte particles, which were captured in the slag as a result of the “flotation” of SO2 gas which was formed by magnetite reduction with FeS at the slag–matte interphase boundary.

Thermal Upgrading of Nickeliferous Pyrrhotite Tailings for the Recovery of Nickel in the Form of Ferronickel Alloy

Production of ferronickel alloy by thermal treatment of nickeliferous pyrrhotite (Pyrr) tailings was studied by both thermodynamic assessment and experimentation. It was demonstrated that Ni can be extracted from Pyrr by increasing the Fe/S ratio of the material, which was achieved by either partial oxidation of Pyrr followed by H2 reduction or in situ generation of metallic Fe from the reduction of magnetite by petroleum coke pre-mixed with Pyrr. Examination of the samples produced from thermal treatment at 1173 K demonstrated that both approaches were effective in generating ferronickel, although the size of the particles was suboptimal for subsequent separation. Increasing the ferronickel particle size could be achieved by a smelting step at 1473 K, forming a sulfur-deficient molten matte. Slow cooling of the molten matte resulted in precipitation, settling, and growth of ferronickel alloy particles.

Continuous cleaning process of molten copper slags in a channel reactor under the external electric field

Continuous cleaning process of the molten copper slags in a channel reactor under a vertical electric field is proposed. The copper-matte settling velocity under the vertical electric field is much faster than that only under the gravity in the molten slags, and the electric field can also accelerate the magnetite reduction. Cu content in the slag can fall below 0.35 wt. % during the continuous cleaning process, which exceeds much more existing slag treatment process. In addition, the behaviours of some other heavy metal elements in the molten slags during the continuous process are also discussed.

Magnetite reduction in copper converter slag using biodiesel produced from waste cooking oil

ABSTRACTIn copper smelting process, oxygen-enriched smelting leads to the enrichment of magnetite and increase of slag viscosity, which is not conducive to the sedimentation and separation of copper. Therefore, it is necessary to reduce magnetite in order to improve the recovery rate of copper. In this work, biodiesel produced from waste cooking oil was used to replace carbon and diesel, which should be more economical and environment-friendly. Effects of temperature and reaction time on biodiesel pyrolysis, magnetite reduction and slag viscosity were studied. It was found that the main products of biodiesel pyrolysis were carbon monoxide, hydrogen, methane, and carbon. Because methane will decompose to carbon and hydrogen at 823 K, the main reducing agents during magnetite reduction were hydrogen and carbon. With increasing reduction time and temperature, the magnetite phase in the copper slag gradually decreased, while the fayalite phase gradually increased. After injecting biodiesel into molten copper slag at 1523 K for 4 minutes, magnetite was reduced from 31.6% to less than 0.6% and the viscosity decreased from 1.43 poise to 0.68 poise. This low viscosity is beneficial for separation and recovery of copper from the molten slag.

Effect of the Ratio of Magnetite Particle Size to Microwave Penetration Depth on Reduction Reaction Behaviour by H2

In this study, we investigated reduction of magnetite by H2 during microwave irradiation. This process combines the advantages of microwave irradiation and using H2 as a reducing agent to mitigate CO2 emissions during the ironmaking process. Weight change measurements showed that a reduction of 75% was achieved after treatment under H2 for 60 min. For better understanding of the effective parameters in microwave chemistry, scanning electron microscopy, combined with energy-dispersive X-ray spectroscopy (SEM-EDX), was performed, which demonstrated a greater reduction of large particles (>40 μm) than small particles. This behaviour could be attributed to the higher microwave absorption capability of large particles with a higher ratio of particle size to penetration depth (d/δ). Small particles behave as transparent material and are heated via conduction and/or convection; thus, there is no contribution from the catalytic effect of microwaves to the reduction reaction. Moreover, the reduction of Fe3O4 to Fe0.94O, followed by transformation to Fe, seems to proceed from the surface toward the centre of the particle despite the volumetric microwave heating. This could be due to the higher gas accessibility of iron oxide on the particle surface than in the particle centre.

Reduction behavior of vanadium-titanium magnetite carbon composite hot briquette in blast furnace process

The reduction behavior of a new type of blast furnace burden named vanadium‑titanium magnetite carbon composite hot briquette (hereinafter abbreviated as VTM-CCB), including fraction of reaction (f), reduction shrinking, crushing strength after reduction, phase transformation of valuable elements, and softening-melting-dripping behavior, were investigated with simulating blast furnace conditions in laboratory in this article. The reduction process of VTM-CCB could be divided into four stages. The devolatilization of the coal and the reduction of magnetite to wustite mainly occur successively in the first two stages. In the third stage, the reduction rate is much higher than that in the second stage due to the high carbon gasification rate. The reduction of Ti-bearing iron oxides occurs in the final stage. The shrinking of VTM-CCB samples is caused by the removal of carbon and oxygen and the suppression of the growth of iron whiskers during the reduction of wustite to metallic iron. The crushing strength of VTM-CCB after reduction is found to decrease from 1800 N to 600 N correspondingly with increasing temperature from 600 °C to 1100 °C. The loss of the crushing strength correlates to the pyrolysis of the coal, the carbon gasification, and the reduction of iron oxides. The phase transformation of valuable elements during reduction could be described as follows: Fe3O4 → FeO → Fe; Fe2.75Ti0.25O4 → Fe2.5Ti0.5O4 → (Fe2TiO4) → FeTiO3 → (FeTi2O5) → TiO2. The softening-melting-dripping behavior and permeability of mixed burden is improved obviously with charging a certain amount of VTM-CCB. However, the precipitation of Ti(C,N) would deteriorate the dripping behavior of packed bed when VTM-CCB charging ratio exceeds 20%.