Experimental and mechanism research of the effects of alkali on the reduction reaction of hematite during roasting reduction reaction

Abstract

Red mud as one of the major waste materials, the recycling of it is very important for environmental security and resource recovery. However, the alkali in the red mud strongly affects the concentrating of iron. In order to make the reduction process more controllable and enhance the efficiency, this paper studied the roasting reduction reaction behavior of hematite and artificially mixed red mud in different alkaline environments. X-ray diffraction (XRD), vibrating Sample Magnetometer (VSM) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) were used to reveal the phase transformation, magnetic transformation and microstructure variation of the roasting products. The results revealed that the optimum reduction temperature and time of hematite in alkaline environment were 560 °C and 15 min respectively. With the increase of NaOH and Na2SiO3, the phase transformation from Fe2O3 to Fe3O4 of hematite was hindered. The depression effect of NaOH was stronger than that of Na2SiO3. However, with the increase of CaO, Na2SiO3/CaO and NaOH/CaO, the phase transformation from Fe2O3 to Fe3O4 in hematite was enhanced first, and then depressed. The gangue minerals in artificially mixed red mud involved in the reaction and consumed part of alkali. The morphology evolution of hematite was similar under different condition that reduction reaction in cracked region was more sufficient.