Process And Mechanisms Of Western Hubei's Oolitic Hematite Ore Dressed By Reduction Roasting-magnetic Separation

Oolitic hematite is a typical refractory iron ore resource in western Hubei province of China. This paper carried out its mineralogy studies, especially focused on the disseminated form of hematite, limonite and the main gangue minerals. Then chose the flow of magnetic roasting-magnetic separation to process this coarse grained ores. Proper conditions were as fallows, roasting temperature of800℃, roasting time of45min, reductant to ore ratio of8%, magnetic field strength0.14T. The iron concentrate grade was57.28%, and iron recovery rate was85.79%, with P content of0.69%.In the magnetic roasting process of raw ores, it was been found that fine grain of iron minerals might grow up. In order to study this phenomena, ground the coarse raw ores to-0.074mm for92.03%, and then began roasting. The results showed that, under the condition of roasting at800℃for60min, reductant to ore ratio of8%, rough magnetic field strength0.14T, concentration magnetic field strength0.08T, the final concentrate grade was57.32%for iron grade,82.60%for iron recovery rate and0.43%of P content. Put the ground ores and the roasted ores to produce polished-section, and made microscope mineral analysis. By ccounting the size of iron ores, it was found that, in large particle levels, such as+37μm, the iron ores' cumulative productivity of the roasted ores was12.46%, while the ground ores's was6.12%. Thus, the magnetite particles will grow when hematite is reduction roasted to magnetite. The Fe-element area scanned images of EPMA also support this opinion.Took red iron oxide powder as pure hematite to reduction roast under the condition of roasting temperature750℃for45min, reductant ratio of10%. With XRD analysis, it was confirmed that the product had been completely reduced to Fe3O4. By screening the product, got about+0.074mm account for57.00%. The microscope mineralogical analysis also confirmed the Fe3O4particles grew significantly.This paper, on thee basis of reduction roasting-magnetic separation, studied the phase-trasiton of iron ores, and innovatively put forward and proved the magnetite's grain-growth in the process of hematite's reduction roasting. For the-3mm raw iron ore's reduction roasting, magnetite grain's growth is not so obvious, as the completed oolitic structure stops its growth. Besides, oolitic band structure also prevents the reduction reaction from fully reaction. By pre-grinding to destroy the oolitic structure, the iron minerals and reducing gas can fully touch and react, Thus, the magnetite grain's growth is more obvious in this condition. Concerning the reaction of reduction roasting from hematite to magnetite, the mechanism of magnetite grain's growth can be explained as follow: First, the lattice changes will lead to grain expansion of about11%from the hexagonal system of hematite to the cubic system of magnetite; Second, secondary grain growth (secondary recrystallization), which means, after primary recrystallization, in order to reduce the system surface energy, small magnetite particles continue to combine nearby small magnetite particles.