Liquidus relationships of calcium ferrite and ferrous calcium silicate slag in continuous copper converting

While calcium ferrite slags have been successfully used in continuous copper converting for the past 30 years, ferrous calcium silicate slag was proposed similar to 8 years ago as an additional alternative for copper smelting. Although these slags are normal extensions of each other, their phase relations have not been completely clarified. In this paper, liquidus relations for both slags have been quantified in some regions of common composition. Existing experimental data are reviewed and discussed in relation to the solidification procedure. An original physical model is then used to predict diagrams of the liquidus surface of both slags. It is shown that the ternary liquidus diagrams normally used for FeOx-SiO2-CaO system are not suitable for industrial slags. The new model diagrams of Fe/CaO versus SiO2 and Fe/SiO2 versus CaO, as well as Fe/CaO versus temperature and Fe/SiO2 versus temperature are proven much more convenient for ferrite and ferrous calcium silicate slags. Based on these diagrams, the effect of SiO2 and CaO on the melting temperature is quantified. The effect of Cu2O is also quantified through the model. Fe/CaO versus Cu2O and Fe/SiO2 versus CaO relationships at various copper contents are predicted. The results show good agreement with the experimental data. It is also shown that, in the presence of liquid copper, Cu2O is dissolved in the slag to an extent depending on the oxidation degree of the system, which may lower the liquidus temperature. Discussions are presented taking into account plant observations, and important conclusions are drawn for copper smelting and converting.