Optimisation of MgO addition in low and high silica iron ore sinter to improve sinter reducibility at JSW Steel Limited

Abstract

The quality of iron ore sinter mainly depends on sinter mineralogy, which in turn depends on the chemical composition of the sinter mix. The reduction properties of the mineral phases formed in the sinter influences the sinter reducibility. MgO has a varying effect on sinter reducibility at different silica contents. A recent trend in blast furnace operation shows that there is a considerable increase in usage of dolomite as a basic flux either directly or through sinter. Recently the silica levels in the sinter product of Sinter plant 1(SP1) of JSW Steel Limited have been fluctuating in the range of 5·5–9·6% due to variation in silica content of iron ore fines. At the same time, as per blast furnace requirement, the addition of dolomite has been changed from 2·4 to greater than 3·0% at SP1, and the reducibility of the sinter decreased (<60·0%). Laboratory pot grate sintering experiments have been carried out to determine the influence of MgO addition on microstructure and reducibility of low and high silica sinter. MgO additions have been varied from 1·4 to 3·2% for low silica (4·5%), and high silica (6·3%) iron ore fines.From the studies it was found that the reducibility of both sinters decreased with increase in MgO addition due to an increase in magnetite/magnesio spinel phase and silicate/slag phase. Reducibility of low silica sinter was greater with high silica sinter. High silica with high MgO sinter had lower reducibility compared to low silica with low MgO/high MgO and high silica with low MgO sinter.