Srinivas Dwarapudi

Effect of alumina on slag–metal separation during iron nugget formation from high alumina Indian iron ore fines

Abstract Iron nuggets can be obtained from ore–coal composite pellets by high temperature reduction. Alumina in the ore plays a vital role in slag–metal separation during nugget formation, as it increases the liquidus temperature of the slag. In this study, the effect of carbon content, reduction temperature and lime addition on slag–metal separation and nugget formation of varying alumina iron ore fines were studied by means of thermodynamic modelling. The results were validated by conducting experiments using iron ore fines with alumina levels ranging from 1·85 to 6·15%. Results showed that increase in reduction temperature enhances slag metal separation, whereas increasing alumina and carbon content beyond the optimum level adversely affects separation. Carbon below the required amount decreases the metal recovery, and carbon above the required amount reduces the silica and alters the slag chemistry. Optimum conditions were established to produce iron nuggets with complete slag–metal separation using iron ore–coal composite pellets made from high alumina iron ore fines. These were reduction temperature of 1400°C, reduction time minimum of 15 min, carbon input of 80% of theoretical requirement and CaO input of 2·3, 3·0 and 4·2 wt-% for 1·85, 4·0 and 6·15 wt-% alumina ores respectively.

Effect of fluxing agents on reduction degradation behaviour of hematite pellets

During induration at a high temperature, a considerable amount of slag/melt phase forms inside the iron ore pellets, comprising SiO2, Al2O3, CaO, MgO and FeO. After cooling, the slag phase solidifies and acts as an important bonding phase in the finished pellets and influences their room temperature as well as high temperature properties, especially reduction degradation. Fluxing agents play an important role in forming these bonding phases depending on the type and amount of flux. In the present study, the effect of different fluxing agents, namely, limestone, dolomite, magnesite and pyroxenite, on melt formation and microstructure during induration and on reduction degradation behaviour during reduction was examined. From the results, it was understood that to reduce the disintegration during reduction it is essential to increase the amount and distribution of bonding phases like silicates, which are more stable as compared to oxide phases like hematite. Acid pellets exhibited highest reduction degradation due to the presence of more hematite bonds and less silicate bonds. In limestone fluxed pellets, reduction degradation index dropped considerably with increasing CaO content due to the formation of more amount of bonding phase. Dolomite–pyroxenite pellets, on the other hand, showed lower reduction degradation index up to 0.4 basicity, and beyond that, higher degradation was observed due to the increased pore size, which resulted in poor strength of the reduced pellet matrix and hence more degradation. Low reduction degradation observed in pyroxenite and magnesite fluxed pellets could be due to the formation of magnesioferrite and silicate melt, which are more stable phases compared to hematite.

Application of artificial neural network model to predict reduction degradation index of iron oxide pellets

Abstract The reduction degradation index (RDI) is an important metallurgical property of iron ore pellets used for the production of RDI from shaft furnace or for use in blast furnaces. In order to develop a control strategy, a neural network model has been developed to predict the RDI of pellets from 13 input variables, namely feedrate of green pellets, bed height, burn through temperature, firing temperature, specific corex gas consumption, bentonite, moisture and carbon content in green pellets and Al2O3, SiO2, CaO, MgO and FeO in fired pellets. The RDI of pellets was more sensitive to variation in MgO, CaO, bentonite and green pellet carbon content. The predicted results were in good agreement with the actual data.