Fundamental Studies in Ironmaking Slags to Lower Operating Temperatures and to Recover Titania From Slag

The eutectic temperature between iron and carbon is 1150 degrees C. This is the lowest temperature in which Fe-C solution can be tapped from a blast furnace. Current operating temperatures of iron blast furnace are much higher than 1150 degrees C and limited by melting temperature of the slag. There is room to lower the operating temperature of the iron blast furnace. As a result, coke consumption and CO, gas emissions can be reduced and campaign length of the furnace can be increased. A key factor in achieving the low operating temperature of the blast furnace is to use an optimum slag composition that can be tapped at low temperature. Phase equilibria studies have been undertaken in the system "TiO2"-CaO-MgO-Al2O3-SiO2 at carbon saturation. Extensive experimental data are presented in the form of pseudo-ternary "TiO2"-(CaO+MgO)-(Al2O3+SiO2) at fixed MgO/CaO and Al2O3/SiO2 ratios. Melting temperatures of complex slag are described as functions of basicity weight ratio (CaO+MgO)/(SiO2+Al2O3) and TiOx concentration. The phase diagrams determined in this study explain the behaviour of titanium-containing slag such as Panzhihua ironmaking slag. These diagrams will be used for selection of optimum slag composition with low liquidus temperature for both Ti-free and Ti-containing slag. The possibility of lowering ironmaking temperature by adding titania has been discussed based on the experimental data determined in this study. A large amount of iron blast furnace slag containing 20-25 wt% "TiO2" are produced in Panzhihua Iron & Steel. "TiO2" has to be concentrated before it can be efficiently extracted from the slag. It was found in this study that titanium is present in the blast furnace slag mainly in two minerals, perovskite CaTiO3 and pseudobrookite (Mg2+, Al3+, Ti3+, Ti4+)(3)O-5. Electron probe X-ray microanalysis (EPMA) has been used to determine phase assemblage of the slag quenched from high temperature and the compositions of the phases. It was found that "TiO2" is 58 wt% in perovskite and 80-90 wt% in pseudobrookite. The particle size of the pseudobrookite is much larger than that of the perovskite. It was found that the composition of the current Panzhihua ironmaking slag is located in the perovskite primary phase field. The maximum "TiO2" concentration in the recovered materials is only 58 wt% if the crystal phase is perovskite. With the information provided in this study it may be possible to recover "TiO2" from the Panzhihua slag in the form of pseudobrookite so that recovered materials contains 80-90 wt% "TiO2" and can be used directly for production Of pure TiO2