Phase Equilibria Studies in the CaO-MgO-Al₂O₃-SiO₂ System with Al₂O₃/SiO₂ Weight Ratio of 0.4

Abstract

With the raw materials for ironmaking becoming increasingly complex, more accurate phase equilibrium information on the slag is needed to refine the blast furnace operation to reduce the energy cost and CO2 emissions. CaO-SiO2-Al2O3-MgO is a basic system of ironmaking slag in which CaO and MgO mainly come from the flux, SiO2 and Al2O3 are mainly from raw materials. The effect of flux additions on the phase equilibrium of the slag can be described by a pseudo-ternary system CaO-MgO-(Al2O3+SiO2) at a fixed Al2O3/SiO2 ratio of 0.4. Liquidus temperatures and solid solutions in the CaO-MgO-Al2O3-SiO2 system with Al2O3/SiO2 weight ratio of 0.4 have been experimentally determined using high temperature equilibration and quenching techniques followed by electron probe microanalysis. Dicalcium silicate (Ca2SiO4), cordierite (2MgO·2Al2O3·5SiO2), spinel (MgO·Al2O3), merwinite (3CaO·MgO·2SiO2), anorthite (CaO·Al2O3·2SiO2), mullite (Al2O3·SiO2), periclase (MgO), melilite (2CaO·MgO·2SiO2-2CaO·Al2O3·SiO2) and forsterite (Mg2SiO4) are the major primary phases in the composition range investigated. A series of pseudo-binary phase diagrams have been constructed to demonstrate the application of the phase diagrams on blast furnace operation. Composition of the solid solutions corresponding to the liquidus have been accurately measured and will be used for the development of the thermodynamic database.

Keywords

• phase equilibria
• liquidus temperature
• CaO-MgO-Al₂O₃-SiO₂ system
• blast furnace slag
• basicity