Reduction Behavior of Hematite to Magnetite under Fluidized Bed Conditions

Abstract

Reduction kinetic tests of Mt. Newman hematite ore from Western Australia were carried out in a laboratory-scale fluidized bed reactor at temperatures from 623 to 873 K and an absolute pressure of 10 bar. The reducing gas mixture was thermodynamically in equilibrium with magnetite and consisted of a mixture of H 2 , H 2 O, CO, CO 2 and CH 4 . The effect of temperature and residence time was studied. The original ore and its mineralogical and petrographical changes with increasing reduction time were analyzed. A reflected-light microscope technique with CCD-camera was used to determine the progress and the mechanism of reduction. According to the mineralogy and texture the ore could be classified in four types (coarse hematite, microplaty hematite, limonite and martite) with different reduction characteristics. Limonite and martite showed better reducibility than coarse and fine hematite.At all ore types the growth of dense magnetite rims was observed. The thickness of these layers was found to be linear proportional to reduction time. After analyzing the single steps of the reduction process the phase interface reaction turned out to be rate controlling between 673 and 773 K. Its activation energy is 91 kJ/mol. KEY WORDS: iron ore reduction; fluidized bed; hematite; magnetite; elevated pressure; rate controlling step.

Experimental Study on Hydrogen Direct Reduction of Hematite in a Lab Scale Fluidized Bed Reactor by Estimating the Gas Consumption Rate

“…Reduction of hematite in fluidized bed reactor was demonstrated also by authors in Feilmayr et al [7]. The authors have reported the effect of the temperature and residence time on the reduction rate.…”

“…Newman (Feilmayr et al [7]) was used as the ore sample and hydrogen as reducing agent. Argon was used for the initial phase of heating of the test unit.…”

“…A detail review of the DR processes available can be found in Schenk [7]. At the early stage of research on DR authors in Turkdogan and Vinters [2], Turkdogan et al [3] and Turkdogan and Vinters [4] have studied detail aspects of the gaseous reduction of iron oxides with focus on the iron ore pore structure and its effects on the reduction rate.…”

Mechanism and Kinetics of the Reduction of Hematite to Magnetite with CO–CO2 in a Micro-Fluidized Bed

“…The reducing gas CO diffused through the boundary layer, reaching the external surface of the hematite particles and continuing further into the micropores to the internal surface of the hematite grains. The phase-interface reaction described by Equation (1) occurred at this surface, where the reducing gas picked up oxygen and freed two electrons [9,11,29]:…”

“…Fluidized reduction roasting has been proven to bean industrially economical and efficient method for the chemical synthesis of magnetite, with hematite as the raw material [9,10]. The reaction in fluidized bed reactors offers the advantages of a uniform temperature in the reactor, and of fast heat and mass transfer [11].…”