Characterization of Precipitated Carbon by XPS and Its Prevention Mechanism of Sticking during Reduction of Fe2O3 Particles in the Fluidized Bed

Abstract

The Fe2O3 particles with the diameter between 74 and 150 μ m were pre-reduced with CO at 923 K to precipitate the carbon on the surface. Then the particles were reduced by CO at 1 173 K in the fluidized bed for examining the efficiency of the precipitated carbon for preventing the sticking. The result showed that the sticking of particles with high metallization ratio could be retarded or prevented by the precipitated carbon. For clarifying the prevention mechanism of the sticking, the carbon in different states was characterized by X-ray Photoelectron Spectroscopy (XPS) and its effects on sticking were discussed. The carbon on the surface was divided into two states, the graphitic carbon and the carbon in Fe3C. On account of the sticking of Fe3C at approximately 1 054 K and the sticking of the sponge iron at the micron scale, the structural change of the precipitated iron by the carburization and the formation of Fe3C only retard the sticking. Therefore, the prevention of the sticking at 1 173 K was attributed to the graphitic carbon. Due to the formation of metallic iron layer avoiding the consumption of the carbon and the formation of Fe3C restraining the dissolution of the graphitic carbon, the graphitic carbon accumulated on the surface of the particles, resulted in nC/nFe above 1.0, so that Fe3C and the metallic iron was coated by the graphitic carbon to block their contact among the particles.

The Effect of Carbon Dissection of Waste Plastics on Inhibiting the Adhesion of Fine Iron Ore Particles during Hydrogen Reduction

“…Thus, the direct contact between iron and iron is avoided, the diffusion of iron atoms is hindered, and the formation of solid bridges between particles is prevented. Therefore, the carbon precipitation reaction attaches a layer of graphite to the surface of particles, and the formation of the graphite is the main reason that sticking is avoided, which is consistent with the reported opinion [28], that is, carbon in Fe 3 C slows down the sticking of iron ore powder, but graphite inhibits sticking. Figure 8, a layer of metal forms on the particle surface and the dissolved carbon on the iron layer becomes saturated and forms a layer of Fe3C between the graphite and metal iron, thereby hindering the graphite solid solution.…”

“…Fe, Fe 3 C, and graphite were identified by XRD, shown in Figure 6. The main reactions are as follows [28]. The thermodynamics analysis of the above-mentioned reactions was performed using Factsage thermodynamics software (7.2, ThermFact LTD, Mont-Royal, QC, Canada), and the Gibbs free energy change is shown in Figure 7.…”

A Review on Prevention of Sticking during Fluidized Bed Reduction of Fine Iron Ore

“…[88][89][90] Due to the presence of the boudouard reaction (2CO = CO 2 + C), the CO in the reducing gas causes carbon deposition on the surface of the ore fines under certain conditions. The carbon produced is in two states, such as the graphitic carbon and the carbon in Fe 3 C. 91) It is generally considered that the carbon deposited on the surface of the ore fines has a physical separation effect and can suppress the sticking problem. However, it has also been considered that carburization will cause a decrease in the melting point of metallic iron, which leads to more serious sticking.…”

“…131) However, in general, the amount of carbon coating that achieves the suppression of sticking problem is over 5% by weight, 111,132,133) and even more than 10% by weight. 91) Excessive carbon deposition is likely to cause an increase in the amount of dust in production, and is not conducive to the subsequent treatment of DRI products. Appropriately increasing the hydrogen content in the carbon pre-reduction gas can increase the metallization ratio of pre-reduction and reduce the carbon content, and make the deposited carbon unstable, 133) but can obtain a better final reduction to prevent the sticking problem.…”

Flash Suspension Reduction of Ultra-fine Fe₂O₃ Powders and the Kinetic Analyzing

“…Except for the large reduction rate, it can avoid the solid-solid contact during reduction thus solve the sticking problem existed in the fluidized bed or other direct reduction processes of iron ore concentrate. [2][3][4] Themelis and Gauvin 5) derived a rate equation for reduction of iron oxide particles by hydrogen with particle sizes ranging from 70 to 42 000 μm in diameter and indicated that the measured rates might contain mass transfer effects. F. Tsukihashi 6) investigated the kinetics and mechanism of reduction of molten iron oxide (wustite) with CO gas at high temperatures of 1 723 K and 1 873 K with a gas conveyed system, and he found that the oxide particles were melted and became spherical with reduced iron surrounded by liquid FeO during reduction.…”