Studies on the Reduction Behavior of Iron Oxide Pellet Fines with Hydrogen Gas: Mechanism and Kinetic Analysis

Abstract

The present study contributes to the current worldwide activities aiming to replace fossil carbon in steel making processes with hydrogen causing considerable reduction of greenhouse gas emissions. Compacts prepared from iron oxide pellets fines were isothermally reduced in pure hydrogen gas and a mixture of hydrogen and argon in the temperatures range from 700 to 1100 °C. The total weight loss produced during the reduction process was continuously recorded using thermogravimetric analysis (TG) technique. The findings demonstrated that the temperature has a considerable impact on the conversion and reduction rates. At a given temperature, the reduction rate was accelerated as the amount of H2 increased in the reducing gas. The results indicated that H2 content does not have an effect on reduction behavior, when it is higher than 80%. The reduction reaction of samples was shown to takes place in a step wise manner from hematite to metallic iron. The reduction kinetic and mechanism were deduced from the application of mathematical models and the morphological structure of the reduced samples and correlated with the apparent activation energy (Ea) values. The Ea values at the early, intermediate and final stages were 16.36, 29.24 and 49.35 kJ/mole, respectively. The early stage of the reduction process was controlled by chemical reaction, whereas the gaseous diffusion was controlled the latter stage. At the intermediate stage, the reduction process was controlled by mixed mechanism of gaseous diffusion and chemical reaction. Graphical Abstract

Effect of reduction behavior from Fe2O3 to FeO on the formation of metallic Fe in multi-stage reduction

“…Heidari et al 8 mentioned that chemical reaction has been mentioned as kinetic controller in most studies, while a few studies have shown the importance of diffusion through ash in reduction of wustite. Wolfinger et al 11 and Hammam et al 13 investigated that diffusion is rate-determining step in the reduction from wustite to metallic iron, explaining it as a consequence of the dense structure of iron oxide. In this study, the iron ore is composed of hematite and goethite, which forms the porous structure during reduction.…”

“…The previous studies 5,6,8,9,13,22,23 investigated the kinetic analysis of iron oxide reduction by hydrogen. However, the rate-controlling step varies depending on factors such as the ore phase of hematite and magnetite, amount of pores, temperature and condition of reducing gas atmosphere.…”

“…Several papers showed different kinetic controllers according to experimental conditions such as temperature, gas composition and iron ore type. Hammam et al 13 mentioned that reduction reaction was controlled by a mixed mechanism of diffusion and chemical reaction at an intermediate stage. In this study, reduction in magnetite to wustite was controlled by diffusion and chemical reaction, which showed similar results to those reported by the previous studies.…”

“…The steel industry accounts for a large portion of CO 2 emissions, most of which are generated from the reduction of iron oxides in ore by coal and coke. [1][2][3][4][5][6][7][8][9][10][11][12][13] It is necessary to study the reduction processes with hydrogen gas rather than coal and coke, and one of them is to employ a multistage fluidized bed. 5,6,10,11,[14][15][16][17][18][19] Multi-stage fluidized bed offers some advantages such as no feed agglomeration, uniform temperature distribution in the reactor, and great heat and mass transport.…”

An Overview Analysis of Current Research Status in Iron Oxides Reduction by Hydrogen

“…This interaction is a critical step in the reduction process, facilitating the transformation of iron oxide into iron. The reduction potential of hydrogen (H 2 ) has been extensively analyzed across various studies, with the general consensus indicating that reduction with H 2 occurs more intensively and faster than with carbon monoxide (CO) or in an H 2 /CO mixture [33,47,51,60,[72][73][74]. Tao Zhang et al observed a reduction in fine-grained iron ore using both H 2 and CO in their study.…”