Effect of Slag Basicity on Phase Equilibria and Selenium and Tellurium Distribution in Magnesia-Saturated Calcium Iron Silicate Slags

New measurements have been made on the phase equilibria of magnesia-saturated CaO-FeOx-SiO2 slags at 1573 K (1300 °C) and an oxygen partial pressure of 10−9 atm. The thermodynamic behavior of selenium (Se) and tellurium (Te) in the slag and the stability of oxide mineral phases within the slag were examined as a function of slag composition. The measured equilibrium distribution of Se and Te between the slag and the copper showed nonlinear dependence on the slag basicity, reaching maxima at CaO/(CaO + SiO2) ratios of about 0.2 and 1 and a minimum at a ratio of about 0.5. The solubility of the copper oxide in the bulk slag also passed through a minimum value at a ratio of about 0.5. Results from drop-quench experiments confirmed the stability of various oxide solid solution phases at 1573 K (1300 °C) that had virtually no solubility for Se and Te. The deduced capacity of the liquid slag for Se was found to be independent of basicity in relatively basic slags, and decreased sharply as SiO2 replaced CaO in relatively acidic slags.