Deep understanding of reduction and degradation behavior of iron ore sinter at low temperatures

Low-temperature reduction degradation (LTRD) has long been regarded as a key metallurgical property of iron ore sinter, which exhibits a significant infiuence on the stability and efficiency of blast furnace operation. However, the reduction behavior of sinter under low-temperature conditions is not yet fully understood. The low-temperature reduction behavior of sinter was investigated. The reduction mechanism of sinter under low-temperature conditions was clarified through characterization methods, including X-ray diffraction, microstructural analysis and energy-dispersive X-ray spectroscopy. An interesting phenomenon was found that the reduction degradation index RDI_+3.15 of sinter sharply decreased from 86.05% after reducing for 30 min and to 58.6% for 45 min. The reduction behavior of sinter was further investigated using a thermogravimetric furnace. The results showed that the reduction rate initially reached a peak, followed by a sharp decline to a minimum at approximately 10 min. This decrease occurred as a result of the formation of a reaction product layer, which hindered the diffusion of the reducing gas into the interior of the sinter. Subsequently, the reduction rate increased again, reaching a second peak at approximately 40 min. The increase in reduction rate was attributed to the formation of cracks rather than gas diffusion. It was further determined that the primary cause of LTRD is the volumetric expansion induced by the reduction of surface hematite. Moreover, the low-temperature reduction of sinter involved only the transformation of hematite to magnetite, with the overall reduction degree remaining low at only 6.31%.