| Recent years, with the development of China’s iron and steel industry, the demand for iron ore is increasing, however, China cannot become self-sufficient and needs to import large quantities of iron ore every year. High degree of external dependence is up to 60% for years, which poses a serious threat to national resources security. Strengthening of domestic complex refractory iron ore efficient development and utilization of research and enhancing iron ore self-sufficiency rate have an important strategic significance.The mineralogy characteristics of high phosphorus oolitic hematite ores from hubei province were systematically investigated in this dissertation. On this basis, according to Gibbs free energy minimum principle, the possibility and the priority of reactions were calculated and analysis. The phase composition and microstructure before and after the reduction of materials were also studied.The research of process mineralogy showed that the total iron grade was 42.21% in raw ore, which mainly existed in the hematite, and the occupancy was 69.22%. The harmful element phosphorus grade was 1.31%, which mainly existed in cellophane, and the content of collophane was 4.26%. The gangue minerals were mainly quartz and chamosite.The amount and mineral particle of hematite crystal and aggregate had a certain effect on the grade of concentrate of theory. Hematite and chamosite, partial collophane tightly embeded into oolitic, which could not be choosen in monomer dissociation. The qualified index was difficult to obtain with traditional processing methods.Thermodynamic calculation results showed that aluminum, silicon, magnesium, calcium element could not be restored for elemental in the reduction process. The generation order of iron complex compounds was 2CaOFe2O3>CaO·Fe2O3>FeO·Al2O3>FeSiO3>2FeOSiO2. The reaction order of iron complex compounds with carbon was CaO·Fe2O3>2CaO·Fe2O3> 2FeOSiO2>FeSi03>FeOAl2O3. CaO decreased the minimum reduction temperature of iron complex compounds. FeO·AlO2O3 and 2FeO·SiO2 could not react with CO, which made it possible.In the system of Fe2O3-SiO2-CaO-Al2O3-P2O5-C, phosphorus migration process was mainly Ca3(PO4)2â†'Ca2P2O7â†'Fe3P. And a few phosphorus element process was Ca3(PO4)2â†'Ca2P2O7->Fe2P/FeP. The main process of the iron was Fe2O3â†'Fe3O4â†'FeOâ†'Fe. And a few iron element process was Fe2O3â†'Fe3O4â†'FeOâ†'iron complex compoundsâ†'Fe.The results were evaluated by metallization rate of reduced materials and grade of iron powder.In this thesis, systemic experiments were carried out to investigate the effects of reducing temperature, reducing time, carbon additive on reduction.The results showed that metallization rate and particle size of metallic iron were determined by reducing temperature, reducing time and carbon additive.The optimum conditions for reduction determined by experiments were that reducing temperature was 1200℃, reducing time was 60 min, carbon additive was 2.0. Reduced materials with metallization rate 90.84%, iron grade 90.56%, content of metallic iron 92.03% were obtained under this condition.Adding calcium carbonate in the ore changed the binary basicity, which improved the index of reduced materials. The calcium oxide decomposed from calcium carbonate reacted with SiO2 and Al2O3, which generated larnite, Al2Ca2SiO7 and CaAl2(SiO)4 etc. Then that effectively reduced the amount of iron complex compounds resulting from FeO reacted with gangue.Optical microscope, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used to analyse the mineralogical properties of the materials both before and after reduction, including mineral composition. The results showed that the reduction process of high phosphorus oolitic hematite were two paths; one path was Fe2O3â†'Fe3O4â†'FeOâ†'Fe, and the other one path was Fe2O3â†'Fe3O4â†'FeOâ†'2FeO·SiO2, FeO·Al2O3, etcâ†'Fe. Temperature was one important effect on the growth of metallic iron grain. The increasing temperature promoted the diffusion of iron phase, and it was good for the growth of metallic iron grain. At a relatively low reduction temperature, the reactions were occurred in some parts of the ore, and the reduction of metal iron was difficult. At the same time, the iron oxide and gangue minerals reacted to form fayalite and hercynite, etc. When the temperature was risen, the metallic iron phase gradually formed and began to form at the location of fayalite and hercynite, etc. The generation, gathering of Fe and FeO destroyed the oolitic structure.The results of this study make a theoretical basis for high efficient utilizing of high phosphorus oolitic hematite ore. |
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