Isothermal Reduction Kinetics of Powdered Hematite and Calcium Ferrite with CO–N₂ Gas Mixtures

Abstract

CF is regarded as the best bonding phase with superior strength and reducibility in sintering. The comparison of hematite and CF reduction process was made in this study. Isothermal reduction experiments of powdered hematite and CF in a continuous stream of 30% CO and 70% N 2 at 1 123 K, 1 173 K and 1 223 K were conducted through thermo-gravimetric analysis (TGA). Reduction rate analysis revealed that the reduction of hematite comprises three independent steps (H→M→W→I), whereas that of CF mainly comprises two steps (H→M→I). The reduction of powdered hematite and CF can be described by shrinking layer model, not shrinking core model completely. Results of the ln-ln and Sharp analysis methods indicated that the reduction of hematite included two kinetics stages, namely, plane-like mechanism and then spherulitic-type mechanism. The reduction of CF only included the plane-like mechanism stage. The model free method revealed that the activation energy of hematite and CF reduction were 5.81 kJ·mol − 1 and 46.89 kJ·mol − 1 , respectively.

Carbothermal reduction of fayalite: Thermodynamic and non-isothermal kinetic analysis

“…At the beginning of the carbothermal reduction of fayalite, there is not enough CO to be provided to make the reduction reaction proceed sharply. Therefore, the chemical reaction of gasification of graphite is the controlling step of the carbothermal reduction of fayalite, which is consistent with the results reported by other researchers [29]. In other words, the kinetics of the carbothermal of fayalite can be improved by increasing the reaction rate constant of the gasification of graphite and the special surface area of the graphite in the low reduction rate [38].…”

“…Meanwhile, the immersion of reducing agent can compensate for the decrease of reaction temperature, and the reduction rate is about four times faster than the one when the reductant is dispersed on the surface of liquid copper slag [26]. With a floating graphite disk or immersed graphite rod at the temperature from 1250℃ to 1450℃, the carbothermal reaction of synthetic fayalite slag is controlled by the Boudouard reaction, which is same to the carbothermal reduction of the other iron oxides [27][28][29], and the activation energy was 246±29 kJ/mol. According to the results of Zhang et al [30], the coal-based isothermal reduction mechanisms of fayalite with some impurities of magnetite and quartz can be described as two stages: firstly, the phase boundary chemical reaction is the limited step, and the second stage is controlled by diffusion and boundary chemical reaction.…”

Study on Reduction of Partially Oxidized Cauliflower-like Copper Powder by Hydrogen

“…Reduction by hydrogen does not introduce additional impurities. Moreover, it does not produce greenhouse gases and is more environment-friendly compared with CO [9,10].…”

Surface Structures of CaFe₂O₄ (001), (100), (110) and (111): A Density Functional Theory Study

“…Moreover, the reduction behavior of calcium ferrite minerals under CO and H 2 were also investigated. [7][8][9][10][11][12] In addition, in recent research, it has been widely applied including as a thermal catalyst for decreasing the NOx emission in the sintering process, [13][14][15] as a photocatalytic for degradation of the organic wastewater 16,17) and volatile organic compounds, [18][19][20] as a photocathode for producing hydrogen in water splitting, [21][22][23] as a oxygen carrier for chemical looping gasification applications, [24][25][26][27][28] as a anode material for lithiumion batteries 29) and as a visible light activated gas sensor. 30) The surface structure of calcium ferrite affects the strength of sinter and reduction reaction of it with CO and H 2 in the blast furnace.…”