T. Ya. Malysheva

Sinter at Cherepovets Metallurgical Works (basicity 1.0–3.0)

The strength and mineral composition of sinter (basicity 1.0–3.0) is studied for Cherepovets Metallurgical Works (OAO Severstal’).

Influence of the mineralogical composition of binders on the strength of sinter

The formation of ferrosilicate melt in hightemper� ature sintering zones is responsible for the strengthen� ing of the ironore batch and its conversion to pellets or briquets. The melt is formed from the silicon and calcium components of the batch, the solidphase reaction products in the heating zone, and, to some extent, from the small ore fraction of the concentrate. When the solidand liquidphase reactions are com� plete, the cooled sinter is converted to a twophase mineral system consisting of ore phases (magnetite Fe3O4 and hematite Fe2O3) and silicate-ferrite bind� ers. Their composition is determined by the batch basicity (CaO/SiO2), while their microstructure depends on the sintering parameters and the cooling of the product. The mineralogical composition of the sinters and the thermal properties of the oregrain binders deter� mine the strength of the final product and its behavior on reduction in the blast furnace (1-5). Several researchers have studied the influence of the sinters mineral composition on its strength. In comparing the strength of ironore sinter of the same basicity produced from ore concentrates of different origin, we find, for example, that the strength of the sinter is lowest at low basicity (0.7-1.5). As the basic� ity rises 2.0, the strength gradually rises (6). Decrease in sinter strength is may be attributed to the multiphase structure of the silicate binders with different physico� mechanical properties, while increase in strength is associated with the appearance of ferrite phase in highbasicity sinters, according to (6). However, we still do not know why the direction of mineral formation of the sinter binders changes with increase in flux content of the ironore batch over a broad range of sinter basicity, even with increase in the fuel content. The binder composition for magnetite grains varies from ironsilicate form, when the melt� forming component is divalent iron CaFeSiO

Influence of ore formation on the mineral composition and strength of fluxed iron-ore sinter

The natural formation of iron ores has the determining influence on the sintering process and the strength of fluxed sinter. Homogeneous magnetite crystals are actively converted to melt, forming silicate binder for the ore grains in low-basicity sinter. With increase in basicity, the conversion from silicate binder to ferrite binder is determined by the quantity of iron in the melt and the high oxidative potential of the gas phase. The participation of heterogeneous magnetite in melting is limited. In sintering, low iron content in the melt expands the region where silicate binder is formed, shifting the onset of ferrite formation toward higher-basicity sinter.

Sintering with Kovdor magnetite concentrates in the batch

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.

Effects of adding low-alkali red mud to the sintering batch at OAO Ural’skaya Stal’

The influence of low-alkali red mud on the mineral composition and physicomechanical properties of the sinter produced from OAO Ural’skaya Stal’ iron-quartzite ore is established. At the granulation stage, adding finely disperse low-alkali red mud increases the proportion of large fractions in the batch. The replacement of silicate binder by ferrite binder increases the strength of the sinter and reduces its abrasion.

Influence of low-alkali red mud on the composition and structure of sintering batch consisting of heterogeneous iron-ore concentrates

The influence of low-alkali red mud on the composition and structure of pelletized sintering batch at OAO Severstal’ consisting of ferruginous-quartzite ore from the Olenegorsk and Yakovlevsk deposits and magmatic ore from the Kovdor deposit is analyzed. In pelletization, the addition of low-alkali red mud improves the granulation, with increase in the mean granule diameter. The distribution of the main meltforming elements among the batch fractions is established.

Crust formed in the reduction of concentrate pellets from iron quartzite ore

219 In Russia today, most of the iron ore supplied for steel production consists of iron quartzites. Ore con centrates of iron quartzites are predominantly used for the production of oxidized pellets. In Russia, the purchase and sale of iron ore is based on two main characteristics, the Fe and SiO2 content, without attention to the mineral form of the SiO2. In iron ore of different genetic types, the SiO2 content may reflect a whole group of minerals. Each silicate has specific physicomechanical and thermal proper ties, which determine the required pelletization tem perature and time [1]. In concentrates of ferrous quartzite ore at all enrichment enterprises, the silicon dioxide consists of silicates of different composition and properties. At present, in the oxidative roasting of the pellets, the composition and thermal properties of alkaline sili cates are disregarded. Most such silicates are present in the concentrate in tiny quantities relative to refrac tory quartz. The influence of small quantities of sili con bearing minerals is underestimated, as shown in [2]. For the example of a particular enterprise, the influence of alkaline silica minerals on industrial pellet hardening and quality was established in [2]. It was shown that the industrial production of weak zonal pellets may be attributed to inadequate roasting of the pellets, without taking account of the content of low temperature alkaline silicates in the concentrate. The pellets used for reduction in a shaft furnace must be characterized by high strength, with mini mum alkali content [3, 4]. In the present work, since the industrial pellets previously studied are character ized by low strength, and there is no information regarding the influence of pellets in studies of pellet production and the composition of reduced bri quettes, we consider the behavior of zonal pellets from concentrates of iron quartzite ore in a shaft furnace.