Studies on High Alumina Blast Furnace Slags

Abstract: In the present work, viscosities and sulphide capacities of high alumina blast furnace slags were investigated. The systems investigated were four component CaO-SiO2-MgO-Al2O3 quaternary system, CaO-SiO2-MgO-Al2O3-TiO2 and CaO-SiO2-MgO-Al2O3-CaF2 quinary systems.Viscosities of high alumina blast furnace slags were experimentally determined by the rotating cylinder method using Brookfield digital viscometer model LVDV-II+ pro. Experiments were conducted in the temperature range of 1573- 1873 K. The effects of temperature, basicity, TiO2, CaF2 and silica activity of slags on viscosity were studied. Viscosity decreases with basicity for high alumina blast furnace slags with increase in basicity and CaF2. At higher basicity (~0.8), slag viscosity decreases even with small amount of TiO2 (~2%) addition in the slag. With increase in silica activity in the range of 0.1 to 0.4,viscosity of slag increases and the increase is steeper below liquidus temperature.Sulphide capacity of the slag was measured using gas-slag equlibria. The liquid slag was equilibrated with Ar-CO-CO2-SO2 gas mixture. The slag systems studied were the same as in the case of viscosity measurements. Experiments were conducted in the temperature range of 1773 to 1873 K. Effect of temperature, basicity, MgO,TiO2 and CaF2 contents of slags on sulphide capacity were studied. As expected, sulphide capacity was found to increase with increase in temperature and basicity. At higher experimental temperature (~ 1873 K) TiO2 was found to decrease the sulphide capacity of slags. But, at lower temperature, there was no significant effect of TiO2 on the sulphide capacity. Sulphide capacity increases with increase in MgO content of slag if MgO content is more than 5%.Based on above experimental data, models were developed for estimation of viscosity and sulphide capacity of blast furnace slags. These models were later on applied for designing the slags for achieving the optimum slag characteristics so that slag volume can be reduced. With the help of these models slag volume was reduced to the extent of 5-10 kg per ton hot metal and also silicon content of the hot metal was reduced by around 10% with some improvement in slag viscosity and sulphide capacity of the slag.