Effects of Basicity and FeO Content on the Softening and Melting Temperatures of the CaO-SiO₂-MgO-Al₂O₃ Slag System

Abstract

The effects of basicity (the ratio between CaO and SiO₂) and FeO content on softening and melting temperatures of direct reduced iron (DRI) residual, otherwise known as slag, were investigated.
Sample slag pellets were prepared for two target compositions, CaO-SiO₂-10%MgO-5%Al₂O₃ and CaO-SiO₂-5%MgO-10%Al₂O₃. Two sets of experiments were conducted on the pellets: one varied basicity values between 1.83 and 0.55, and the other varied the FeO contents between 10% and 50% at constant basicity. The softening and melting process under elevated temperature was recorded using an optical softening-melting temperature measuring device and the temperature points were recorded at the four distinct shape changes of the sample pellets: initial deformation, sphere and hemisphere formation, and complete melting.
The lowest softening and melting temperatures of the CaO-SiO₂-5%MgO-10%Al₂O₃ samples occurred at a basicity of 0.55 while for the CaO-SiO2-10%MgO-5%Al₂O₃ samples it occurred at 0.70. This corresponds to the liquidus temperatures on the CaO-SiO₂-MgO-Al₂O₃ quaternary phase diagram. At constant basicity, the deformation temperature of CaO-SiO₂-10%MgO-5%Al₂O₃ samples was found to be higher than that of CaO-SiO₂-5%MgO-10%Al₂O₃ samples. Lastly, the addition of FeO below 20% to the CaO-SiO₂-MgO-Al₂O₃ system significantly decreased the softening and melting temperatures of the slag samples. However, further addition of FeO beyond 20% produced inconclusive results.