Abstract
Electron-microscope data show that the magnetite crystals in iron ore have different microstructure, depending on the temperature and time of ore formation. Thus, in sedimentary–metamorphic iron quartzites and magmatic skarns, the structure of the magnetite crystals is homogeneous and the composition is close to stoichiometric. In Kovdor ore, the magnetite crystals are heterogeneous. The matrix contains isomorphic Al, Mg, Ti, and other impurities as individual spinel microphases. The reduction of magnetite crystals in conditions that resemble sintering indicates that heterogeneous crystals disintegrate on sintering, with the formation of two ore phases: solid solutions of magnetite and wustite that are not involved in liquid-phase strengthening of the sinter. In the final stage of fluxed-sinter production, calcium–silicon silicate binders of melilite composition are formed in the product in place of the melt; these binders are not strong. On the basis of the research findings, it is important, in assessing iron-ore fields, to pay attention not only to the content of iron and silicon oxides in the ore but also to the structure of the magnetite crystals, since the iron in the magnetite determines the direction of melt formation in processing.
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