Volatility and Thermodynamic Activity of Sb₂O₃ in Sb₂O₃-SiO₂, Sb₂O₃-FeO-SiO₂, and Sb₂O₃-FeO-SiO₂-CaO-Al₂O ₃ Systems at 1473 K

The volatility and thermodynamic activity of Sb2O3 in Sb2O3-SiO2, Sb2O3-FeO-SiO2, and Sb2O3-FeO-SiO2-CaO-Al2O3 systems have been measured at 1473 K by using a transpiration method with purified Ar as a carrier gas. Thermodynamic models for calculating the activities of Sb2O3 and SiO2 in the binary system are established based on the experimental data. The molar Gibbs free energy of mixing of the binary melts is obtained. It is found that the Sb2O3 activity and volatility at 1473 K decreases significantly with increasing SiO2 content. Activity of Sb2O3 in Sb2O3-FeO-SiO2 slags is measured for the slag compositions of 40 and 50 wt pct Sb2O3 at different FeO/SiO2 ratios. The FeO addition into the Sb2O3-SiO2 melts increases the volatility and activity of Sb2O3. At last, the Sb2O3 activity in the Sb2O3-FeO-SiO2-CaO-Al2O3 slags is measured with the compositions of 30 to 50 wt pct Sb2O3 at different CaO/SiO2 ratios to study the effect of CaO addition. The addition of CaO slightly increases the volatility and activity of Sb2O3 when slags contain less than 40 wt pct Sb2O3.