CaO solubility in the FeOt-SiO2-CaO-Al2O3-(ZnO, Cr2O3) system at 1200 and 1250°C under pO2 of 10−10 atm

Abstract

CaO solubility in the FeOt-SiO2-CaO-Al2O3-(ZnO, Cr2O3) system has been experimentally investigated at 1200 and 1250 °C under pO2 of 10−10 atm. Synthetic slags rich in CaO were equilibrated at desired temperatures, followed by water quenching, and analyzed using electron probe X-ray microanalysis (EPMA). In the quaternary FeOt-SiO2-CaO-(6 to 10 wt%) Al2O3 system, CaO solubility exhibits a linear increase from 27.5 to 36.9 wt% with decreasing the FeO/SiO2 (F/S) ratio from 1.66 to 0.62 at 1250 °C. Similarly, at 1200 °C, the CaO solubility increases from 24.9 to 30.8 wt% as the F/S ratio drops from 1.25 to 0.56. Excessive CaO addition to the slags results in the precipitation of melilite phase. Wustite is observed in the F/S ratio range of 1.66 to 1.0, and the size of wustite particles decreases as the F/S ratio decreases. At both 1200 and 1250 °C, the liquid phase with an F/S ratio below 0.42 is in equilibrium with wollastonite (CaSiO3) in the FeOt-SiO2-CaO-Al2O3 system. The addition of a small amount of ZnO (0.4–1.1 wt%) in the slags leads to a slight decrease in CaO solubility by 1–3 wt%, while the presence of 3.3–8.1 wt% of ZnO in the slags results in a decrease of 5–11 wt% in CaO solubility. Similar to the FeOt-SiO2-CaO-Al2O3 system, the equilibrated CaO-containing solid phase is also melilite in the FeOt-SiO2-CaO-Al2O3-ZnO system. With the addition of a small amount of Cr2O3 (1.0 wt%) to the FeOt-SiO2-CaO-Al2O3-ZnO system, spinel and dicalcium silicate (Ca2SiO4) precipitate from the liquid slag, and the dissolved CaO concentration in liquid slag increases by 1–3.6 wt% in the F/S ratio range of 1.58 to 0.84, compared to the Cr2O3-free system.