Kinetics of hydrogen reduction of magnetite ore fines

The current work deals with the production of iron by the hydrogen reduction of magnetite ore fines in a thermogravimetric analyzer (TGA). The variables studied were time (0-30 min), temperature (973-1273 K), hydrogen flow rate (0.1-0.5 L min−1), hydrogen partial pressure (0.25-1 atm), sample bed height (0.25-0.75 cm) and particle size (75-180 μm). Phase identification, chemical analysis and elemental analysis were carried out by X-ray diffraction (XRD), X-ray fluorescence (XRF) analysis and energy-dispersive X-ray spectroscopy (EDS) of the scanning electron microscopic (SEM) images, respectively. The governing rate equations for the gas-solid reaction in a cylindrical/rectangular powder bed system with reacting gas flowing over the solid were used. Consistent with the thermodynamic prediction, the experimental results showed that the reduction of magnetite fines took place in two stages: Fe3O4 to FeO and FeO to Fe. Each stage was controlled by pore diffusion kinetics. The activation energies in the two stages were found to be 42 kJ mol−1 and 55 kJ mol−1, respectively. The fractional reduction of magnetite in the ore went up to 1.0. In addition to the kinetic study, the thermodynamics of the hydrogen reduction of magnetite (Fe3O4) is discussed briefly, giving the theoretical efficiency of hydrogen utilization in the reduction.