Experimental simulations of primary slag formation in blast furnace

Primary slag formation of the blast furnace ferrous burden was experimentally simulated using synthetic MgO-Al₂O₃-CaO-SiO₂ slags with FeO, Na₂O, or FeS additions. The combined effect of FeO and Na₂O or FeS was also examined. The melting behaviour and viscosity of five different base slags (sinter, pellet, or lump ore) were investigated using optical dilatometry, thermogravimetric-differential thermal analysis (TGA-DTA), and viscometric analysis. The results indicate the importance of FeO (wüstite) in the formation and nature of liquid primary slags. Solidus temperature, fusion temperature, solidus-fusion interval, and viscosity were all significantly affected by FeO. A clear, but not simple or linear, tendency showed a lowering of the solidus and fusion temperatures and a concomitant decrease of the viscosity with increased FeO addition. The presence of Na₂O or FeS in the slag system, alone or combined with the FeO addition, created an initial melting at lower temperatures, but the liquid volume produced was limited. The effect of the added components was distinctly different on different base slag systems. It is proposed that the effect is fundamentally dependent on the chemical or, more exactly, on the mineralogical composition of the base slag systems at the initial stage of the melting. The results of the experiments are considered to represent reasonable simulations of the melting behaviour of the corresponding primary slags of the blast furnace ferrous burden in the cohesive zone.