Mechanism of improved magnetizing roasting of siderite–hematite iron ore using a synergistic CO–H₂ mixture

A fluidized-bed magnetizing roasting–magnetic separation process was selected to treat this type of material. Phase transformations and microstructural changes in the product resulting from magnetizing roasting under different reducing gases (CO, H₂, CO + H₂) were clarified by vibrating sample magnetometry, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicated that the conversion ratio and saturation magnetization of samples roasted in a mixed gas of CO and H₂ were higher than those of samples produced under CO or H₂ alone. This indicated that synergy of the combined CO and H₂ gas had a positive effect on the fluidized-bed magnetizing roasting process. The mechanism and kinetics of the improved magnetizing roasting of a siderite–hematite iron ore mixture under this synergistic CO–H₂ system were investigated under isothermal conditions. The results indicated that the apparent activation energies of the reactions of the iron oxides decreased from 37.7 and 17.9 to 15.9 kJ/mol when the roasting atmosphere was changed from pure H₂ or CO to a gas mixture of CO and H₂, respectively. The mixed CO–H₂ gas promoted the conversion ratio of hematite and siderite to magnetite, thereby improving the conversion ratio in the fluidized-bed magnetizing roasting process.