Phase Equilibria in the System CaO-SiO2-Al2O3-MgO-15 and 20 wt% “FeO” with CaO/SiO2 Ratio of 1.3

The “FeO”-containing slags in the low part of blast furnace (BF) are of great importance to the operation of BF, particularly the primary and bosh slags. To optimise the slag components for the smooth operation of BF, the phase equilibria studies have been carried out in the system “FeO”-CaO-SiO2-Al2O3-MgO in equilibrium with metallic iron. High temperature equilibrations followed by quenching were conducted in experiments and electron probe X-ray microanalysis were employed to analyse the samples. For better interpretation and easy implementation of experimental results, the data obtained from measurements were symmetrically analysed and then plotted in the pseudo-ternary phase diagrams of (CaO+SiO2)-Al2O3-MgO with fixed CaO/SiO2 weight ratio of 1.3 and “FeO” of 15 and 20 wt%, respectively. The primary phases such as melilite, Ca2SiO4, merwinite, spinel and (Mg, Fe2+)O were observed with liquid phases and metallic iron in the composition range. The liquidus temperatures increase in melilite and spinel primary phase fields, but decrease in dicalcium silicate and merwinite primary phase fields with increasing Al2O3/(CaO+SiO2) ratio. In addition, the liquidus temperatures firstly increase then decrease with increasing MgO/(CaO+SiO2) ratio in dicalcium silicate and melilite primary phase fields, while they have an increasing trend in merwinite and monoxide primary phase fields. The data resulted from this study provide accurate experimental information that can be used for optimisation of the computed thermodynamic models.